Academic literature on the topic 'Polygonal space vector structures'
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Journal articles on the topic "Polygonal space vector structures"
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Yan, Shiyao, Zequn Zhang, Xian Sun, Guangluan Xu, Shuchao Li, Qing Liu, Nayu Liu, and Shensi Wang. "PolygonE: Modeling N-ary Relational Data as Gyro-Polygons in Hyperbolic Space." Proceedings of the AAAI Conference on Artificial Intelligence 36, no. 4 (June 28, 2022): 4308–17. http://dx.doi.org/10.1609/aaai.v36i4.20351.
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N-ary relational knowledge base (KBs) embedding aims to map binary and beyond-binary facts into low-dimensional vector space simultaneously. Existing approaches typically decompose n-ary relational facts into subtuples (entity pairs, triples or quintuples, etc.), and they generally model n-ary relational KBs in Euclidean space. However, n-ary relational facts are semantically and structurally intact, decomposition leads to the loss of global information and undermines the semantical and structural integrity. Moreover, compared to the binary relational KBs, n-ary ones are characterized by more abundant and complicated hierarchy structures, which could not be well expressed in Euclidean space. To address the issues, we propose a gyro-polygon embedding approach to realize n-ary fact integrity keeping and hierarchy capturing, termed as PolygonE. Specifically, n-ary relational facts are modeled as gyro-polygons in the hyperbolic space, where we denote entities in facts as vertexes of gyro-polygons and relations as entity translocation operations. Importantly, we design a fact plausibility measuring strategy based on the vertex-gyrocentroid geodesic to optimize the relation-adjusted gyro-polygon. Extensive experiments demonstrate that PolygonE shows SOTA performance on all benchmark datasets, generalizability to binary data, and applicability to arbitrary arity fact. Finally, we also visualize the embedding to help comprehend PolygonE's awareness of hierarchies.
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Szczygieł, Jacek, and Maciej J. Mendecki. "Preliminary results of fractal analysis of the poligonal survey from cave: case study of Małołączniak area (Tatra Mts.)." Contemporary Trends in Geoscience 2, no. 1 (September 1, 2013): 95–100. http://dx.doi.org/10.2478/ctg-2014-0014.
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Abstract Traverses (polygons) from two caves have been tested: Wielka Śnieżna Cave System (2858 vectors) and Śnieżna Studnia cave (742). The box counting technique was applied to evaluate the fractal analysis of spatial orientation of traverses. The polygonal survey of Wielka Śnieżna Cave, Śnieżna Studnia and both caves merged together have a fractal geometry. It may be concluded that these caves are close to the full recognition of passages forming by a hydrological system and they could have close relation with geological structures. The usual explanation of fractal dimension D higher than 1 indicates that caves with such dimension fill more space than those with ideal dimension of 1.00 (for example a straight line), and the geological constraints limit the dimension to be lower than 2 (Verbovsek 2007). It may suggest that systems can be developped into more complicated passages in future. The fact that both caves merged together also have showed fractal geometry indicates that they are belonging to the same hydrological system. It was noticed that D-value of merged caves is slightly larger than individual cave. It can be explained by “occupying” more space in rock mass.
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CHETVERIKOV, B., O. KHINTSITSKY, and I. KALYNYCH. "Methodology of mapping of historical and cultural heritage objects by GIS technologies using archival cartographic and aerial materials." Modern achievements of geodesic science and industry 41, no. I (April 1, 2021): 97–103. http://dx.doi.org/10.33841/1819-1339-1-41-97-103.
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Aim. The purpose of the work is to process archival cartographic materials and remote sensing data for the interpretation of objects of historical and cultural heritage (OHCH) of Cherkasy, including those that have not been preserved. Method. One of the possible technological schemes for research is offered. According to her, the first step was to analyze the input data of the study, among which were: a map of Cherkasy in 1895 at a scale of 1:42000; German aerial image of 1944; a fragment of a space image of Cherkasy obtained from the GeoEye-1 satellite in 2018. Geometric correction of the input materials was performed in the Mercator projection and the WGS84 coordinate system, in which the transformed image was obtained. The next step was to vectorize the objects of historical and cultural heritage of Cherkasy, according to the list obtained on the city’s website. There are two types of objects: point and polygonal. When vectorizing polygonal objects, the historical boundaries were specified with the help of archival maps and aerial images. Special symbols have been developed for each of the types of historical and cultural heritage sites, according to the proposed classification. In addition, an attributive database of these objects was created, which had the following structure: number of the passport of object, the name of the object, the address of the OHCH, the number of the decision to take under protection, information about the OHCH. Also, the obtained vector data was exported to the exchange format with the extension kmz and an online version of the thematic map was created on the basis of the free GISFile resource. Results. As a result of the conducted researches, the thematic GIS of the objects of historical and cultural heritage of Cherkasy was created, which are plotted on the space image of high spatial resolution, obtained in 2018. An on-line version of the GIS of Cherkasy historical and cultural heritage sites has been created on the basis of the free GISFile cartographic service, with the possibility of analyzing the location of these objects and building optimal tourist routes. Scientific novelty. Possible algorithms for creating offline and on-line versions of thematic GIS are proposed. Practical value. The obtained results of mapping the objects of historical and cultural heritage of Cherkasy can be used by the structures of protection of objects of historical and cultural heritage of Cherkasy at the Ministry of Culture.
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Nagae, Sadahiko, and Chiaki Ohta. "Algorithm for Automatic Generation of Boundary Lines." Journal of Robotics and Mechatronics 2, no. 1 (February 20, 1990): 59–65. http://dx.doi.org/10.20965/jrm.1990.p0059.
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It may be supposed that the development of an algorithm capable of automatically generating boundary lines among parts for designing IC diagrams and automatic recognition of intervals among parts as well as mapping is widely desired in different industrial sectors. The most basic, effective solution conceivable will be image analysis using an ITV camera. The authors, however, tried to develop an algorithm capable of automatically generating boundary lines which would not interfere with one another using a great number of profiles comprising, in principle, polygons based on vector input data. It is not that this enables every boundary line between graphics to be automatically generated with good precision, but a result has been obtained which can appropriately be applied to roughly calculating the living space in a floor plan, and dividing structures for land use status drawing on a scale of about 1 to 2500. It can also be used for designing wiring drawings among parts. It is conceivable that the utilization of the results of this research will enable the algorithm to be used for graphic recognition by image processing. The following are the proposed problem, definitions, and a detailed description of the algorithm leading to a solution.
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Watson, Layne T., and C. Y. Wang. "Large deformations of rotating polygonal space structures." Computers & Mathematics with Applications 22, no. 9 (1991): 51–59. http://dx.doi.org/10.1016/0898-1221(91)90206-j.
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MILLETT, KENNETH C., MICHAEL PIATEK, and ERIC J. RAWDON. "POLYGONAL KNOT SPACE NEAR ROPELENGTH-MINIMIZED KNOTS." Journal of Knot Theory and Its Ramifications 17, no. 05 (May 2008): 601–31. http://dx.doi.org/10.1142/s0218216508006282.
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For a polygonal knot K, it is shown that a tube of radius R(K), the polygonal thickness radius, is an embedded torus. Given a thick configuration K, perturbations of size r < R(K) define satellite structures, or local knotting. We explore knotting within these tubes both theoretically and numerically. We provide bounds on perturbation radii for which one can obtain small trefoil and figure-eight summands and use Monte Carlo simulations to estimate the relative probabilities of these structures as a function of the number of edges.
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Kuang, Wenhui, Shu Zhang, Xiaoyong Li, and Dengsheng Lu. "A 30 m resolution dataset of China's urban impervious surface area and green space, 2000–2018." Earth System Science Data 13, no. 1 (January 14, 2021): 63–82. http://dx.doi.org/10.5194/essd-13-63-2021.
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Abstract. Accurate and timely maps of urban underlying land properties at the national scale are of significance in improving habitat environment and achieving sustainable development goals. Urban impervious surface (UIS) and urban green space (UGS) are two core components for characterizing urban underlying environments. However, the UIS and UGS are often mosaicked in the urban landscape with complex structures and composites. The “hard classification” or binary single type cannot be used effectively to delineate spatially explicit urban land surface property. Although six mainstream datasets on global or national urban land use and land cover products with a 30 m spatial resolution have been developed, they only provide the binary pattern or dynamic of a single urban land type, which cannot effectively delineate the quantitative components or structure of intra-urban land cover. Here we propose a new mapping strategy to acquire the multitemporal and fractional information of the essential urban land cover types at a national scale through synergizing the advantage of both big data processing and human interpretation with the aid of geoknowledge. Firstly, the vector polygons of urban boundaries in 2000, 2005, 2010, 2015 and 2018 were extracted from China's Land Use/cover Dataset (CLUD) derived from Landsat images. Secondly, the national settlement and vegetation percentages were retrieved using a sub-pixel decomposition method through a random forest algorithm using the Google Earth Engine (GEE) platform. Finally, the products of China's UIS and UGS fractions (CLUD-Urban) at a 30 m resolution were developed in 2000, 2005, 2010, 2015 and 2018. We also compared our products with six existing mainstream datasets in terms of quality and accuracy. The assessment results showed that the CLUD-Urban product has higher accuracies in urban-boundary and urban-expansion detection than other products and in addition that the accurate UIS and UGS fractions were developed in each period. The overall accuracy of urban boundaries in 2000–2018 are over 92.65 %; and the correlation coefficient (R) and root mean square errors (RMSEs) of UIS and UGS fractions are 0.91 and 0.10 (UIS) and 0.89 and 0.11 (UGS), respectively. Our result indicates that 71 % of pixels of urban land were mosaicked by the UIS and UGS within cities in 2018; a single UIS classification may highly increase the mapping uncertainty. The high spatial heterogeneity of urban underlying covers was exhibited with average fractions of 68.21 % for UIS and 22.30 % for UGS in 2018 at a national scale. The UIS and UGS increased unprecedentedly with annual rates of 1605.56 and 627.78 km2 yr−1 in 2000–2018, driven by fast urbanization. The CLUD-Urban mapping can fill the knowledge gap in understanding impacts of the UIS and UGS patterns on ecosystem services and habitat environments and is valuable for detecting the hotspots of waterlogging and improving urban greening for planning and management practices. The datasets can be downloaded from https://doi.org/10.5281/zenodo.4034161 (Kuang et al., 2020a).
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Smith, Philip, and Eleni Panagiotou. "The second Vassiliev measure of uniform random walks and polygons in confined space." Journal of Physics A: Mathematical and Theoretical 55, no. 9 (February 3, 2022): 095601. http://dx.doi.org/10.1088/1751-8121/ac4abf.
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Abstract Biopolymers, like chromatin, are often confined in small volumes. Confinement has a great effect on polymer conformations, including polymer entanglement. Polymer chains and other filamentous structures can be represented by polygonal curves in three-space. In this manuscript, we examine the topological complexity of polygonal chains in three-space and in confinement as a function of their length. We model polygonal chains by equilateral random walks in three-space and by uniform random walks (URWs) in confinement. For the topological characterization, we use the second Vassiliev measure. This is an integer topological invariant for polygons and a continuous functions over the real numbers, as a function of the chain coordinates for open polygonal chains. For URWs in confined space, we prove that the average value of the Vassiliev measure in the space of configurations increases as O(n 2) with the length of the walks or polygons. We verify this result numerically and our numerical results also show that the mean value of the second Vassiliev measure of equilateral random walks in three-space increases as O(n). These results reveal the rate at which knotting of open curves and not simply entanglement are affected by confinement.
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Lakshminarayanan, Sanjay, R. S. Kanchan, P. N. Tekwani, and K. Gopakumar. "Multilevel inverter with 12-sided polygonal voltage space vector locations for induction motor drive." IEE Proceedings - Electric Power Applications 153, no. 3 (2006): 411. http://dx.doi.org/10.1049/ip-epa:20050444.
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Lakshminarayanan, S., G. Mondal, K. Gopakumar, N. S. Dinesh, and S. Figarado. "Eighteen-sided polygonal voltage space-vector-based PWM control for an induction motor drive." IET Electric Power Applications 2, no. 1 (January 1, 2008): 56–63. http://dx.doi.org/10.1049/iet-epa:20070269.
Full textDissertations / Theses on the topic "Polygonal space vector structures"
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Capocci, Michael Sean. "Conformal structures and symmetries." Thesis, University of Aberdeen, 1994. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU070087.
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The purpose of this thesis is to study methods by which conformal vector fields on pseudo-Riemannian manifolds can be simplified. A vector field on a manifold M with metric g is conformal if its local flows preserve the metric g up to a scaling and unlike Killing vector fields, which preserve g exactly, it cannot in general be linearised in a neighbourhood of any given point. The difference is that a Killing vector field is affine, that is it preserves a connection on the manifold. In this case the connection is the canonical (Levi-Civita) connection associated with g, but affine vector fields with respect to any connection are linearisable. The task is to find new connections with respect to which the set of conformal vector fields, or some subset of them, are affine. Suppose that we have a manifold M with a pseudo-Riemannian conformal structure and an orthogonal splitting of the tangent bundle. We construct, for a natural choice of torsion, a unique connection in the principal bundle of frames adapted to the splitting. Moreover this connection is preserved by any transformations which preserve the splitting of the tangent bundle. Thus any conformal vector field which preserves the splitting is affine. The splitting can be chosen to reflect the tangent to the orbits of a subalgebra of conformal vector fields, the principal null directions of the Weyl tensor or the flow of a perfect fluid. We also give a study of conformal vector fields in three-dimensional Lorentzian manifolds. An equivalent of the Cotton-York tensor is used to investigate the behaviour of these vector fields at their fixed points in the same spirit as the Weyl tensor is used in four dimensions.
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Das, Anandarup. "Investigations On Dodecagonal Space Vector Generation For Induction Motor Drives." Thesis, 2009. http://hdl.handle.net/2005/1034.
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Multilevel converters are finding increased attention in industry and academia as the preferred choice of electronic power conversion for high power applications. They have a wide application area in a variety of industries involving transportation and energy management, a significant portion of which comprises of multilevel inverter fed induction motor drives. Multilevel inverters are ideally suitable for high power drives, since the switching frequency of the devices is limited for high power applications. In low power drives, the switching frequency is often in the range of tens of kHz, so that switching frequency harmonics are pushed higher in the frequency spectrum thereby the size and cost of the filter are reduced. But higher switching frequency has its own drawbacks, in particular for high voltage, high power applications. They cause large dv/dt stress on the motor and the devices, increased EMI problems and higher switching losses. An engineering trade-o is thus needed to select the minimum switching frequency without compromising on the output voltage quality. The present work is an alternate approach in this direction. Here, new inverter topologies and PWM strategies are developed that can eliminate a set of harmonics in the phase voltage using 12-sided polygonal space vector diagrams, also called dodecagonal space vector diagrams.
A dodecagonal space vector diagram has many advantages over a hexagonal one. Switching space vectors on a dodecagon will not produce any harmonics of the order 6n 1, (n=odd) in the phase voltage. The next set of harmonics thus reside at 12n 1, (n=integer). By increasing the number of samples in a sector, it is also possible to suppress the lower order harmonics and a nearly sinusoidal voltage can be obtained. This is possible to achieve at a low switching frequency of the inverters. At the same time, a dodecagon is closer to a circle than a hexagon; so the linear modulation range is extended by about 6.6% compared to the hexagonal case. For a 50 Hz rated frequency operation, under constant V/f ratio, the linear modulation can be achieved upto a frequency of 48.3 Hz. Also, the harmonics of the order 6n 1, (n=odd) are absent in the over-modulation region. Maximum fundamental voltage is obtained from this inverter at the end of over-modulation region, where the phase voltage becomes a 12-step waveform.
The present work is developed on dodecagonal space vector diagrams. The entire work can be summarized and explained through Fig. 1. This figure shows the development of hexagonal and dodecagonal space vector diagrams. It is known that, 3-level and 5-level space vector diagrams have been developed as an improvement over 2-level ones. They
Figure 1: Development of hexagonal and dodecagonal space vector diagrams
have better harmonic performance, reduced dv/dt stress on the motor and devices, better electromagnetic compatibility and improvement of efficiency over 2-level space vector diagrams. This happens because the instantaneous error between the reference vector and the switching vectors reduces, as the space vector density increases in the diagram. This is shown at the top of the figure. In the bottom part, the development of the dodecagonal space vector diagram is shown, which is the contribution of this thesis work. This is explained in brief in the following lines.
Initially, a space vector diagram is proposed which switches on hexagonal space vectors in lower-modulation region and dodecagonal space vectors in the higher modulation region. As the reference vector length increases, voltage vectors at the vertices of the outer dodecagon and the vertices from the outer most hexagon is used for PWM control. This results in highly suppressed 5th and 7th order harmonics thereby improving the harmonic profile of the motor current. This leads to the 12-step operation at rated voltage where all the 5th and 7th order harmonics are completely eliminated. At the same time, the linear range of modulation extends upto 96.6% of base speed. Because of this, and the high degree of suppression of lower order harmonics, smooth acceleration of the motor upto rated speed is possible. The presence of multilevel space vector structure also limits the switching frequency of the inverters.
In the next work, the single dodecagonal space vector diagram is improved upon to form two concentric dodecagons spanning the space vector plane (Fig. 1). The radius of the outer dodecagon is double the inner one. It reduces the device rating and the dv/dt stress on the devices to half compared to existing 12-sided schemes. The entire space vector diagram is divided into smaller sized isosceles triangles. PWM switching on these smaller triangles reduces the inverter switching frequency without compromising on the output voltage quality.
The space vector diagram is further refined to accommodate six concentric dodecagons in the space vector plane (Fig. 1). Here the space vector diagram is characterized by alternately placed dodecagons which become closer to each other at higher radii. As such the harmonics in the phase voltage are reduced, in particular at higher modulation indices. At the same time, because of the dodecagonal space vector structure, all the 6n ± 1, (n=odd) harmonics are eliminated from the phase voltage. A nearly sinusoidal phase voltage can be generated without resorting to high frequency switching of the inverters.
The above space vector diagrams are developed using different inverter circuits. The first work is developed from cascaded combination of three 2-level inverters, while the second and third works use 3-level NPC inverters feeding an open end induction motor drive. The circuit topologies are explained in detail in the respective chapters. Apart from this, PWM switching schemes and detailed analysis on duty cycle calculations using the concept of volt-second balance are also presented. They show that with proper switching schemes, the proposed configurations can substantially reduce the overall loss of the inverter. Other operational issues like capacitor voltage balancing of 3-level NPC inverters and improvement of input current drawn from the grid are also covered. All the above propositions are first simulated by MATLAB and subsequently verified by an experimental laboratory prototype. Motor current waveforms both at steady state and transient conditions during motor acceleration show that the induction motor can be fed from nearly sinusoidal voltage at all operating conditions. Simplified comparative studies are also made with the proposed converters and higher level inverters in terms of output voltage quality and losses. These are some of the constituents for chapters 2, 3 and 4 in this thesis. Additionally, the first chapter also covers a brief survey on some of the recent progresses made in the field of multilevel inverter. The thesis concludes with some interesting ideas for further thought and exploration.
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HUANG, CHUNG-TING, and 黃仲廷. "Dilation and Packing of Polygonal Objects in Vector Space." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/828wpr.
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碩士南臺科技大學
資訊工程系
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Aiming on shoe material cutting with dense object packing for die-cutting machine tools, we have developed a polygonal object packing system in vector space. To compute accurate gaps among packed objects to prevent over-cutting, a vector object dilation solution is also proposed in this study. For the optimal packing problem, which has long been proven to be NP-Hard, the objective is to pack as many as possible object to cut in a pre-specified material area, such as paper, leather and metal. Although there is much literature concerning bin packing in 2D or 3D space, relatively fewer studies put emphasis on polygonal object packing in vector space due to intensive computational complexities. To this end, we have developed an automatic, dense object packing method based on the closest alignment of two polygonal objects. We also explore the computational scheme of local optimal object group search for the derivation of denser object packs in global. Additionally, prior to the pack computation, a vector object dilation algorithm is proposed and applied to accurate estimation of required gaps among packed objects, which is a key process to prevent overlapped cutting of object boundaries. Our packing system and pack results with high density and accuracy have not been only verified by experiments, but also approved by field tests in shoe manufacturing factories with industrial partners.
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Ramubhai, Patel Chintanbhai. "Investigations On Sensorless Vector Control Using Current Error Space Phasor And Direct Torque Control Of Induction Motor Drive Based On Hexagonal And 12-Sided Polygonal Voltage Space Vectors." Thesis, 2011. http://etd.iisc.ernet.in/handle/2005/2180.
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Variable-speed Induction motor drives are nowadays used for various kinds of industrial processes, transportation systems, wind turbines and household appliances in the world. The majority of drives are for general purpose speed control applications where accurate speed control is not required for entire speed range. But for high dynamic drive application, very precise and fast control of induction motor drive is essential. For such applications, sophisticated and well-performing control design is a key issue. Precise and accurate torque control of the Induction Motor (IM) can only be accomplished by vector control and direct torque control.
In terms of space vector theory, vector control implies that the instantaneous torque is controlled by way of the stator current vector that is orthogonal to the rotor flux vector. Precise knowledge of the rotor flux angle is therefore essential for a vector controlled IM. IMs do not allow the flux position to be easily measured, so most modern vector controlled IM drives rely on flux estimation. This means that the flux angle is derived from a flux estimator, using the dynamic model of the IM. Given that the rotor speed of the IM is measured by a mechanical shaft sensor. Flux estimation is a fairly easy task. However, vector control of IM without mechanical shaft speed sensor is of current interest in industrial environment. The driving motivations behind the development in sensorless control are lower cost, improved reliability and operating environment.
In this thesis, a sensorless vector control scheme for rotor flux estimation using current error space phasor based hysteresis controller is proposed including the method for estimation of leakage inductance, Ls. For frequencies of operation less than 25 Hz, the rotor voltage and hence the rotor flux position is computed during the inverter zero voltage space vector using steady state model of IM. For above 25 Hz, active vector period and steady state model of IM is used. The whole rotor flux estimation scheme is dependent on current error space phasor and the steady state motor model, with rotor flux as a reference vector. Since no terminal voltage sensing is involved, dead time effects will not create problem in rotor flux sensing at low frequencies of operation. But appropriate device on-state drop are compensated at low frequencies (below 5 Hz) of operation to achieve a steady state operation up to less than 1 Hz. A constant switching frequency hysteresis current controller is used in inner current control loop for the PWM regulation, with smooth transition of operation to six-step mode operation. A simple Ls estimation based on current error space phasor is also proposed to nullify the deteriorating effect on rotor flux estimation. The parameter sensitivity of the control scheme to changes in the stator resistance Rs is also investigated. The drive scheme is tested up to a low frequency operation less than 1 Hz. The extensive simulation and experiment results are presented to show the proposed scheme’s good dynamic performance extending up to six-step operation.
In contrast to vector control, direct torque control (DTC) method requires the knowledge of stator resistance only and thereby decreasing the associated sensitivity to parameters variation and the elimination of speed information. DTC as compared to vector control does not require co-ordinate transformation and PI controller. DTC is easy to implement because it needs only two hysteresis comparators and a lookup table for both flux and torque control. This thesis also investigates the possibilities in improvement of direct torque control scheme for high performance induction motor drive applications. Here, two schemes are proposed based on the direct torque control scheme for IM drive using 12-sided polygonal voltage space vectors for fast torque control.
The torque control scheme based on DTC algorithm is proposed using 12-sided polygonal voltage space vector. The basic DTC scheme is used to control the torque. But the IM drive is open-end type. For torque control, the voltage space vectors orthogonal to stator flux vector in 12-sided polygonal space vector structure are used as hexagonal space vector based DTC scheme. The advantages achieved due to 12-sided polygonal space vector are mainly fast torque control and small torque ripple. The fast transient of torque with precise control is achieved using voltage space vector placed with a resolution of ±15. The torque ripple will be less as 6n±1 (n=odd) harmonic torque is totally eliminated from the whole range of PWM modulation. The comparative analysis of proposed 12-sided polygonal voltage space vector based DTC and conventional hexagonal space vector based DTC is also presented. Extensive simulation and experiment results are also presented to show the fast torque control at speeds of operation ranging from 5 Hz to the rated speed.
The concept of 12-sided polygonal space vector based DTC is further extended for a variable speed control scheme using estimated fundamental stator voltage for sector identification. The conventional DTC scheme uses stator flux vector for identification of the sector and the switching vector are selected based on this sector information to control stator flux and torque. However, the proposed DTC scheme selects switching vectors based on the sector information of the estimated fundamental stator voltage vector and its relative position with respect to the stator flux vector. The fundamental stator voltage estimation is based on the steady state model of IM and information of synchronous frequency which is derived from computed stator flux using a low pass filter technique. The proposed DTC scheme utilizes the exact position of fundamental stator voltage vector and stator flux vector position to select optimal switching vector for fast control of torque with small variation of stator flux within hysteresis band. The present DTC scheme allows the full load torque control with fast transient response to very low speeds of operation below 5 Hz. The extensive simulation and experiment results are presented to show the fast torque control for speed of operation from zero speed to rated speed. However, the present scheme will have all the advantages of DTC scheme using stator flux vector for sector identification.
All the above propositions are first simulated by MATLAB/Simulink and subsequently verified by an experimental laboratory prototype. The proposed control schemes are experimentally verified on a 3.7 kW IM drive. The control algorithms of the sensorless vector control using current error space phasor as well as DTC using 12-sided polygonal voltage space vector are completely implemented on a TI TMS320LF2812 DSP controller platform. These are some of the constituents for chapters 2, 3 and 4 in this thesis. Additionally, the first chapter also covers a brief survey on some of the recent progresses made in the field of sensorless vector control, direct torque control and current hysteresis controller. The thesis concludes with suggestion for further exploration.
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Lakshminarayanan, Sanjay. "Generation Of 12-Sided And 18-Sided Polygonal Voltage Space Vectors For Inverter Fed Induction Motor Drives By Cascading Conventional Two-Level Inverters." Thesis, 2007. http://hdl.handle.net/2005/693.
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Multi-level inverters play a significant role in high power drive systems for induction motors. Interest in multi-level inverters started with the three-level, neutral point clamped (NPC) inverter. Now there are many topologies for higher number of levels such as the, flying capacitor and cascaded H-bridge etc. The advantage of multi-level inverters is the reduced voltage stress on the switching devices, lower dv/dt and lower harmonic content. The voltage space vector structure in a multi-level inverter has a hexagonal periphery similar to that in a two-level inverter. In the over-modulation region in multi-level inverters, there is the presence of lower order harmonics such as 5th and 7th in the output voltage, and this can be avoided by using a voltage space vector scheme with more than six polygonal voltage space vectors such as 12, 18, 24 etc. These polygonal voltage space vectors can be generated by using multi-level inverter topologies, by cascading two-level inverter structures with asymmetric DC-links. This thesis deals with the development of 12-sided and 18-sided polygonal voltage space vector schemes for induction motor drives. With the 12-sided polygonal structure, all the 5th and 7th harmonic orders and 6n±1, n=1, 3, 5.. are absent throughout the modulation range, and in the 18-sided voltage space vector scheme, 5th, 7th, 11th and 13th harmonics are absent throughout the modulation range. With the absence of the low order frequencies in the proposed polygonal space vector structures, high frequency PWM schemes are not needed for voltage control. This is an advantage over conventional schemes. Also, due to the absence of lower order harmonics throughout the modulation range, special compensated synchronous reference frame PI controllers are not needed in current controlled vector control schemes in over-modulation.
In this thesis a method is proposed for generating 12-sided polygonal voltage space vectors for an induction motor fed from one side. A cascaded combination of three two-level inverters is used with asymmetrical DC-links. A simple space vector PWM scheme based only on the sampled reference phase amplitudes are used for the inverter output voltage control. The reference space vector is sampled at different sampling rates depending on the frequency of operation. The number of samples in a sector is chosen to keep the overall switching frequency around 1kHz, in order to minimize switching losses. The voltage space vectors that make up the two sides of the sector in which the reference vector lies, are time averaged using volt-sec balance, to result in the reference vector. In the proposed 12-sided PWM scheme all the harmonics of the order 6n±1, n=1, 3, 5... are eliminated from the phase voltage, throughout the modulation range.
In multi-level inverters steps are taken to eliminate common-mode voltage. Common-mode voltage is defined as one third of the sum of the three pole voltages of the inverter for a three phase system. Bearings are found to fail prematurely in drives with fast rising voltage pulses and high frequency switching. The alternating common-mode voltage generated by the PWM inverter contributes to capacitive couplings from stator body to rotor body. This generates motor shaft voltages causing bearing currents to flow from rotor to stator body and then to the ground. There can be a flashover between the bearing races. Also a phenomenon termed EDM (Electro-discharge machining) effect occurs and may damage the bearings. Common-mode voltage has to be eliminated in order to overcome these effects. In multi-level inverters redundancy of space vector locations is used to eliminate common-mode voltages. In the present thesis a 12-sided polygonal voltage space vector based inverter with an open-end winding induction motor is proposed, in which the common-mode voltage variation at the poles of the inverter is eliminated. In this scheme, there is a three-level inverter on each side of the open-end winding of the induction motor. The three-level inverter is made by cascading two, two-level inverters with unequal DC-link voltages. Appropriate space vectors are selected from opposite sides such that the sum of the pole voltages on each side is a constant. Also during the PWM operation when the zero vector is applied, identical voltage levels are used on both sides of the open-end windings, in order to make the phase voltages zero, while the common-mode voltage is kept constant. This way, common-mode voltage variations are eliminated throughout the modulation range by appropriately selecting the voltage vectors from opposite ends. In this method all the harmonics of 6n±1, n=1, 3, 5.. and triplen orders are eliminated.
In the 12-sided polygonal voltage space vector methods, the 11th and 13th harmonics though attenuated are not eliminated. In the 18-sided polygonal voltage space vector method the 11th and 13th harmonics are eliminated along with the 5th and 7th harmonics. This scheme consists of an open-end winding induction motor fed from one side by a two-level inverter and the other side by a three-level inverter comprising of two cascaded two-level inverters. Asymmetric DC-links of a particular ratio are present.
The 12-sided and 18-sided polygonal voltage space vector methods have been first simulated using SIMULINK and then verified experimentally on a 1.5kW induction motor drive. In the simulation as well as the experimental setup the starting point is the generation of the three reference voltages v, vB and vC . A method for determining the sector in which the reference vector lies by comparing the values of the scaled sampled instantaneous reference voltages is proposed. For the reference vector lying in a sector between the two active vectors, the first vector is to be kept on for T1 duration and the second vector for T2 duration. These timing durations can be found from the derived formula, using the sampled instantaneous values of the reference voltages and the sector information. From the pulse widths and the sector number, the voltage level at which a phase in the inverter has to be maintained is uniquely determined from look-up tables. Thus, once the pole voltages are determined the phase voltages can be easily determined for simulation studies. By using a suitable induction motor model in the simulation, the effect of the PWM scheme on the motor current can be easily obtained. The simulation studies are experimentally verified on a 1.5kW open-end winding induction motor drive. A V/f control scheme is used for the study of the drive scheme for different speeds of operation. A DSP (TMS320LF2407A) is used for generating the PWM signals for variable speed operation.
The 12-sided polygonal voltage space vector scheme with the motor fed from a single side has a simple power bus structure and it is also observed that the pole voltage is clamped to zero for 30% of the time duration of one cycle of operation. This will increase the overall efficiency. The proposed scheme eliminates all harmonics of the order 6n±1, n=1, 3, 5…for the complete modulation range. The 12-sided polygonal voltage space vector scheme with common-mode elimination requires the open-end winding configuration of the induction motor. Two asymmetrical DC-links are required which are common to both sides. The leg of the high voltage inverter is seen to be switched only for 50% duration in a cycle of operation. This will also reduce switching losses considerably. The proposed scheme not only eliminates all harmonics of the order 6n±1, n=1, 3, 5…for the complete modulation range, but also maintains the common-mode voltage on both sides constant. The common-mode voltage variation is eliminated. This eliminates bearing currents and shaft voltages which can damage the motor bearings.
In the 18-sided polygonal voltage space vector based inverter, the 11th and 13th harmonics are eliminated along with the 5th and 7th. Here also an open-end winding induction motor is used, with a two-level inverter on one side and a three-level inverter on the other side. A pole of the two-level inverter is at clamped to zero voltage for 50% of the time and a pole of the three-level inverter is clamped to zero for 30% of the time for one cycle of operation. The 18-sided polygonal voltage space vectors show the highest maximum peak fundamental voltage in the 18-step mode of 0.663Vdc compared to 0.658Vdc in the 12-step mode of the 12-sided polygonal voltage space vector scheme and 0.637Vdc in the six-step mode of a two-level inverter or conventional multi-level inverter (where Vdc is the radius of the space vector polygon).
Though the schemes proposed are verified on a low power laboratory prototype, the principle and the control algorithm development are general in nature and can be easily extended to induction motor drives for high power applications.
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Kaarthik, R. Sudharshan. "Multilevel Dodecagonal Space Vector Structures and Modulation Schemes with Hybrid Topologies for Variable Speed AC Drives." Thesis, 2015. http://etd.iisc.ernet.in/handle/2005/2765.
Full textAbstract:
MULTILEVEL inverters are the preferred choice of converters for electronic power conversion for high power applications. They are gaining popularity in variety of industrial applications including electric motor drives, transportation, energy management, transmission and distribution of power. A large portion of energy conversion systems comprises of multilevel inverter fed induction motor drives. The multilevel inverters are ideal for such applications, since the switching frequency of the devices can be kept low. In conventional two level inverters, to get nearly sinusoidal phase current waveform, the switching frequency of the inverter is increased and the harmonics in the currents are pushed higher in the frequency spectrum to reduce the size and cost of the filters. But higher switching frequency has its own drawbacks – in particular for medium voltage, high power applications. They cause large dv_/ dt stresses on the motor terminals and the switching devices, leading to increased electromagnetic interference (EMI) problems and higher switching losses.
Harmonics in the motor currents can further be minimized by adopting dodecagonal voltage space vector (SV) switching (12-sided polygon). In case of dodecagonal SV switching, the fifth and seventh order (6n , 1, n = odd) harmonics are completely eliminated for the full modulation range including over modulation and twelve step operation in the motor phase voltages and currents. In addition to low order harmonic current suppression, the linear modulation range for dodecagonal SV switching is also more by 6% when compared to that of the conventional hexagonal SV switching. The dodecagonal voltage SV structure is made possible by connecting two inverters with DC-link voltages Vd and 0:366Vd on either side of an open-end winding induction motor. The dodecagonal space vector switching can be used to produce better quality phase voltage and current waveforms and overcome the problem of low order fifth and seventh harmonic currents and to improve the range for linear modulation while reducing the switching frequency of the inverters when compared to that of the conventional hexagonal space vector based inverters.
This thesis focuses on three aspects of multilevel dodecagonal space vector structures
(i) Two new power circuit topologies that generate a multilevel dodecagonal voltage space vector structure with symmetric triangles, (ii) A multilevel dodecagonal SV structure with nineteen concentric dodecagons, (iii) Pulse width modulation (PWM) timing calculation methods for a general N-level dodecagonal SV structure.
(i) Two new power circuit topologies capable of generating multilevel dodecagonal voltage space vector structure with symmetric triangles with minimum number of DC link power supplies and floating capacitor H-bridges are proposed. The first power topology is composed of two hybrid cascaded five level inverters connected to either side of an open end winding induction machine. Each inverter consists of a three level neutral point clamped (NPC) inverter, cascaded with an isolated capacitor fed H-bridge making it a five level inverter. The second topology is a hybrid topology for a normal induction motor (star or delta connected), where the power is fed to the motor only from one side. The proposed scheme retains all the advantages of multilevel topologies as well the advantages of the dodecagonal voltage space vector structure. Both topologies have inherent capacitor balancing for floating H-bridges for all modulation indices including transient operations. The proposed topologies do not require any pre-charging circuitry for startup. PWM timing calculation method for space vector modulation is also explored in this chapter. Due to the symmetric arrangement of congruent triangles within the voltage space vector structure, the timing computation requires only the sampled reference values and does not require any iterative searching, off-line computation, look-up tables or angle estimation. Experimental results for steady state operation and transient operation are also presented to validate the proposed concept.
(ii) A multilevel dodecagonal voltage space vector structure with nineteen concentric do-decagons is proposed for the first time. This space vector structure is achieved by connecting two sets of asymmetric hybrid five level inverters on either side of an open-end winding induction motor. The dodecagonal structure is made possible by proper selection of DC-link voltages and switching states of the inverters. In addition to that, a generic and simple method for calculation of PWM timings using only sampled reference values (v and v ) is proposed. This enables the scheme to be used for any closed loop application like vector control. Also, a new switching technique is proposed which ensures minimum switching while eliminating the fifth and seventh order harmonics and suppressing the eleventh and thirteenth harmonics, eliminating the need for bulky filters. The motor phase voltage is a 24-stepped waveform for the entire modulation range thereby reducing the number of switchings of the individual inverter modules. Experimental results for steady state operation, transient operation including start-up have been presented and the results of Fast Fourier Transform (FFT) analysis is also presented for validating the proposed concept.
(iii) A method to obtain PWM timings for a general N-level dodecagonal voltage space vector structure using only sampled reference values is proposed. Typical methods that are used to find PWM timings for dodecagonal SV structures use modulation index and the reference vector angle, to get the timings T1 and T2 using trigonometric calculations. This method requires look-up tables and is difficult to implement in closed loop systems. The proposed method requires only two additions to compute these timings. For multilevel case, typical iterative methods need timing calculations (matrix multiplications) to be performed for each triangle. The proposed method is generic and can be extended to any number of levels with symmetric structures and does not require any iterative searching for locating the triangle in which the tip of the reference vector lies. The algorithm outputs the triangle number and the PWM timing values of T0, T1 and T2 which can be set as the compare values for any carrier based PWM module to obtain space vector PWM like switching sequences. Simulation and experimental results for steady state and transient conditions have been presented to validate the proposed method.
A 3.7 kW, 415 V, 50 Hz, 4-pole open-end winding induction motor was used for the experimental studies. The semiconductor switches that were used to realize the power circuit for the experiment were 75 A, 1200 V insulated-gate bipolar transistor (IGBT) half-bridge modules (SKM75GB12T4). Opto-isolated gate drivers with desaturation protection (M57962L) were used to drive the IGBTs. For the speed control and PWM timing computation a digital signal processor (DSP-TMS320F28335) with a clock frequency of 150 MHz was used. For modulation frequencies 10 Hz and below, a constant sampling frequency of 1 kHz was used as the frequency modulation ratio is high. For modulation frequencies above 10 Hz, synchronous PWM strategy was used. The time duration Ts is the sampling interval for which the timings T1 , T2 and T0 are calculated. As in the case of any synchronous PWM method, the duration of sampling time (Ts) is a function of the fundamental frequency of the modulating signal. In this case, Ts = 1_.fm • 12n) sec. where fm is fundamental frequency in Hertz and ‘n’ is the number of samples per 30ý dodecagonal sector. The PWM timings and the triangle data (from the DSP) is fed to field programmable gate array (FPGA) (SPARTAN XC3S200) clocked at 50 MHz where the actual gating pulses are generated. The capacitor balancing algorithm and the dead-time modules were implemented within FPGA. No external hardware was used for generation of dead-time. The dead-time block generates a constant dead-time of 2 s for all the switches. Extensive testing was done for steady state operations and transient operations including quick acceleration and start-up to validate the proposed concepts.
With the advantages like extension of linear modulation range, elimination of fifth and seventh harmonics in phase voltages and currents for the full modulation range, suppression of eleventh and thirteenth harmonics in phase voltages and currents, reduced device voltage ratings, lesser dv_dt stresses on devices and motor phase windings, lower switching frequency, inherent cascaded H-bridge (CHB) capacitor balancing, the proposed space vector structures, the inverter power circuit topologies, the switching techniques and the PWM timing calculation methods can be considered as viable schemes for medium voltage, high power motor drive applications.
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Boby, Mathews. "Multilevel Dodecagonal and Octadecagonal Voltage Space Vector Structures with a Single DC Supply Using Basic Inverter Cells." Thesis, 2017. http://etd.iisc.ernet.in/2005/3712.
Full textAbstract:
Multilevel converters have become the direct accepted solution for high power converter applications. They are used in wide variety of power electronic applications like power transmission and distribution, electric motor drives, battery management and renewable energy management to name a few. For medium and high voltage motor drives, especially induction motor drives, the use of multilevel voltage source inverters have become indispensible. A high voltage multilevel inverter could be realized using low voltage switching devices which are easily available and are of low cost. A multilevel inverter generates voltage waveforms of very low harmonic distortion by switching between voltage levels of reasonably small amplitude differences. Thus the dv/dt of the output voltage waveform is small and hence the electromagnetic interference generated is less. Because of better quality output generation, the switching frequency of the multilevel inverters could be reduced to control the losses. Thus, a multilevel converter stands definitely a class apart in terms of performance from a conventional two-level inverter. Many multilevel inverter topologies for induction motor drives are available in the literature. The basic multilevel topologies are the neutral point clamped (NPC) inverter, flying capacitor (FC) inverter and the cascaded H-bridge (CHB) inverter. Various other hybrid multilevel topologies have been proposed by using the basic multilevel inverter topologies. It is also possible to obtain multilevel output by using conventional two-level inverters feeding an open-end winding induction motor from both sides.
All the conventional multilevel voltage source inverters generate hexagonal (6 sided polygons) voltage space vector structures. When an inverter with hexagonal space vector structure is operated in the over modulation range, significant low order harmonics are generated in the phase voltage output. Over modulation operation is required for the full utilization of the available DC-link voltage and hence maximum power generation. Among the harmonics generated, the fifth and seventh harmonics are of significant magnitudes. These harmonics generate torque ripple in the motor output and are undesirable in high performance motor drive applications. The presence of these harmonics further creates problems in the closed loop current control of a motor, affecting the dynamic performance. Again, the harmonic currents generate losses in the stator windings. Therefore, in short, the presence of harmonic voltages in the inverter output is undesirable.
Many methods have been proposed to eliminate or mitigate the effect of the harmonics. One solution is to operate the inverter at high switching frequency and thereby push the harmonics generated to high frequencies. The stator leakage inductance offers high impedance to the high frequency harmonics and thus the harmonic currents generated are negligible. But, high switching frequency brings switching losses and high electromagnetic interference generation in the drive system. And also, high switching frequency operation is effective only in the linear modulation range. Another solution is to use passive harmonic filters at the inverter output. For low order harmonics, the filter components would be bulky and costly. The loss created by the filters degrades the efficiency of the drive system as well. The presence of a filter also affects the dynamic performance of the drive system during closed loop operation. Special pulse width modulation (PWM) techniques like selective harmonic elimination (SHE) PWM can prevent the generation of a particular harmonic from the phase voltage output. The disadvantages of such schemes are limited modulation index, poor dynamic performance and extensive offline computations. An elegant harmonic elimination method is to generate a voltage space vector structure having more number of sides like a dodecagon (12 sided polygons) or an octadecagon (18 sided polygons) rather than a hexagon.
Inverter topologies generating dodecagonal voltage space vector structure eliminate fifth and seventh order harmonics, represented as 6n 1; n = odd harmonics, from the phase voltages and hence from the motor phase currents, throughout the entire modulation range. The first harmonics appearing the phase voltage are the 11th and 13th harmonics. Another advantage is the increased linear modulation range of operation for a given DC-link voltage, because geometrically dodecagon is closer to circle than a hexagon. An octadecagonal structure eliminates the 11th and 13th harmonics as well from the phase voltage output. The harmonics present in the phase voltage are of the order 18n 1; n = 1; 2; 3; :::. Thus the total harmonics distortion (THD) of the phase voltage is further improved. The linear modulation range also gets enhanced compared to hexagonal and dodecagonal structures. Multilevel dodecagonal and octadecagonal space vector structures combines the advantages of both multilevel structure and dodecagonal and octadecagonal structure and hence are very attractive solutions for high performance induction motor drive schemes. Chapter 1 of this thesis introduces the multilevel in-verter topologies generating hexagonal, dodecagonal and octadecagonal voltage space vector structures. Inverter topologies generating multilevel dodecagonal and octadecago-nal voltage space vector structures have been proposed before but using multiple DC sources delivering active power. The presence of more than one DC source in the inverter topology makes the back to back operation (four-quadrant operation) of the drive system difficult. And also the drive system becomes more costly and bulky. This thesis proposes induction motor drive schemes generating multilevel dodecagonal and octadecagonal volt-age space vector structures using a single DC source.
In Chapter 2, an induction motor drive scheme generating a six-concentric multilevel dodecagonal voltage space vector structure using a single DC source is proposed for an open-end winding induction motor. In the topology, two three-level inverters drive an open-end winding IM, one inverter from each side. DC-link of primary inverter is from a DC source (Vdc) which delivers the entire active power, whereas the secondary inverter DC-link is maintained by a capacitor at a voltage of 0:289Vdc, which is self-balanced during the inverter operation. The PWM scheme implemented ensures low switching frequency for primary inverter. Secondary inverter operates at a small DC-link voltage. Hence, switching losses are small for both primary and secondary inverters. An open-loop V/f scheme was used to test the topology and modulation scheme.
In the work proposed in Chapter 3, the topology and modulation scheme used in the first work is modified for a star connected induction motor. Again, the scheme uses only a single DC source and generates a six-concentric multilevel space vector struc-ture. The power circuit topology is realized using a three-level flying capacitor (FC) inverter cascaded with an H-bridge (CHB). The capacitors in the CHB inverter are maintained at a voltage level of 0:1445Vdc. The FC inverter switches between volt-age levels of [Vdc; 0:5Vdc; 0] and the CHB inverter switches between voltage levels of [+01445Vdc; 0; 0:1445Vdc]. The PWM scheme generates a quasi-square waveform output from the FC inverter. This results in very few switchings of the FC inverter in a funda-mental cycle and hence the switching losses are controlled. The CHB inverter switches Ch. 0: at high frequency compared to the FC inverter and cancels the low order harmonics (6n 1; n = odd) generated by the FC inverter. Even though the CHB operates at higher switching frequency, the switchings are at low voltage thereby controlling the losses. The linear modulation range of operation is extended to 48:8Hz for a base frequency of 50Hz. An open-loop V/f scheme was used to test the topology and modulation scheme.
In Chapter 4, a nine-concentric multilevel octadecagonal space vector structure is proposed for the first time, again using a single DC source. The circuit topology remains same as the work in Chapter 3, except that the CHB capacitor voltage is maintained at 0:1895Vdc. The 5th; 7th; 11th and 13th harmonics are eliminated from the phase voltage output. The linear modulation range is enhanced to 49:5Hz for a base speed of 50Hz. An open-loop V/f scheme and rotor field oriented control scheme were used to test the proposed drive system.
All the proposed drive schemes have been extensively simulated and tested in hard-ware. Simulation was performed in MATLAB-SIMULINK environment. For implement-ing the inverter topology, SKM75GB12T4 IGBT modules were used. The control al-gorithms were implemented using a DSP (TI’s TMS320F28334) and an FPGA (Xilinx Spartan XC3S200). A 1kW , 415V , 4-pole induction motor was used for the experiment purpose.
The above mentioned induction motor drive schemes generate phase voltage outputs in which the low order harmonics are absent. The linear modulation range is extended near to the base frequency of operation compared to hexagonal space vector structure. In the inverter topologies, the secondary inverters or the CHB inverters functions as harmonic filters and delivers zero active power. The primary inverter in the topologies switches at low frequency, reducing the power loss. Single DC source requirement brings down the cost of the system as well as permitting easy four-quadrant operation. This is also advantageous in battery operated systems like EV applications. With these features and advantages, the proposed drive schemes are suitable for high performance, medium voltage induction motor drive applications.
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Mathew, Jaison. "Investigation On Dodecagonal Multilevel Voltage Space Vector Structures By Cascading Flying Capacitor And Floating H-Bridge Cells For Medium Voltage IM Drives." Thesis, 2013. http://hdl.handle.net/2005/2600.
Full textAbstract:
In high-power electric drives, multilevel inverters are generally deployed to address issues such as electromagnetic interference, switch voltage stress and harmonic distortion. The switching frequency of the inverter is always kept low, of the order of 1KHz or even less to reduce switching losses and synchronous pulse width modulation (PWM) is used to avoid the problem of sub-harmonics and beat frequencies. This is particularly important if the switching frequency is very low. The synchronous PWM is getting popularity as its realization is very easy with digital controllers compared to analog controllers. Neutral-point-clamped (NPC) inverters, cascaded H-bridge, and flying-capacitor multilevel inverters are some of the popular schemes used for high-power applications. Hybrids of these multilevel inverters have also been proposed recently to take advantage of the basic configurations. Multilevel inverters can also be realized by feeding the induction motor from both ends (open-end winding) using conventional inverter structures. For controlling the output voltage of these inverters, various PWM techniques are used. Chapter-1 of this thesis provides an over view of the various multilevel inverter schemes preceded by a discussion on basic two-level VSI topology.
The inverters used in motor drive applications have to be operated in over-modulation range in order to extract the maximum fundamental output voltage that is possible from the dc-link. Operation in this high modulation range is required to meet temporary overloads or to have maximum power operation in the high speed range (flux weakened region). This, however, introduces a substantial amount of low order harmonics in the Motor phase voltages. Due to these low-order harmonic frequencies, the dynamic performance of the drive is lost and the current control schemes are severely affected especially due to 5th and 7th harmonic components. Further, due to these low-order harmonics and non-linear PWM operation in over-modulation region, frequent over-current fault conditions occur and reliability of the drive is jeopardized. The twelve sided-polygonal space vector diagram (dodecagonal space vectors) can be used to overcome the problem of low order 5th and 7th harmonics and to give more range for linear modulation while keeping the switching frequency at a minimum compared to conventional hexagonal space vector based inverters. Thus, the dodecagonal space-vector switching can be viewed as an engineering compromise between low switching frequency and quality load current waveform.
Most of the previous works of dodecagonal space-vector generation schemes are based on NPC inverters. However, sophisticated charge control schemes are required in NPC inverters to deal with the neutral-point voltage fluctuation and the neutral-point voltage shifting issues. The losses in the clamping diodes are another major concern. In the second chapter, a multilevel dodecagonal space-vector generation scheme based on flying capacitor topology, utilizing an open end winding induction motor is presented. The neutral point charge-balancing problem reported in the previous works is not present in this scheme, the clamping diodes are eliminated and the number of power supplies required has been reduced. The capacitors have inherent charge balancing capability, and the charge control is done once in every switching cycle, which gives tight voltage control for the capacitors.
For the speed control of induction motors, the space-vector PWM scheme is more advantageous than the sine-triangle PWM as it gives a more linear range of operation and improved harmonic performance. One major disadvantage with the conventional space-vector PWM is that the trigonometric operations demand formidable computational efforts and look-up tables. Carrier based, common-mode injected PWM schemes have been proposed to simplify the PWM process. However, the freedom of selecting the PWM switching sequences is limited here. Another way of obtaining SVPWM is using the reference voltage samples and the nearest vector information to switch appropriate devices for proper time intervals, realizing the reference vector in an average sense. In-formation regarding the sector and nearest vectors can be easily obtained by comparing the instantaneous amplitudes of the reference voltages. This PWM approach is pro-posed for the speed control of the motor in this thesis. The trigonometric operations and the requirement of large look-up tables in the conventional SVPWM are avoided in this method. It has the additional advantage that the switching sequences can be decided at will, which is helpful in reducing further, the harmonic distortion in certain frequency ranges. In this way, this method tries to combine the advantages of vector based methods (conventional SVPWM) and scalar methods (carrier-based methods).
The open-end winding schemes allowed the required phase voltage levels to be generated quite easily by feeding from both ends of the windings. Thus, most of the multilevel inverters based on dodecagonal space-vector structures relied on induction motors with open-end windings. The main disadvantage of open-end winding induction motor is that six wires are to be run from the inverter to the motor, which may be unacceptable in certain applications. Apart from the inconvenience of laying six wires, the voltage reflections in the wires can lead to over voltages at the motor terminals, causing insulation failures. Where as the topology presented in chapter-2 of this thesis uses open-end winding motor with flying-capacitor inverters for the generation of dodecagonal space-vectors, the topology presented in chapter-3 utilizes a cascade connection of flying-capacitors and floating H-bridge cells to generate the same set of voltage space-vectors, thus allowing any standard induction motor as the load.
Of the methods used for the speed control of induction motors, namely sine-triangle PWM and space vector PWM, the latter that provides extra modulation range is naturally preferred. It is a well-understood fact that the way in which the PWM switching sequences are applied has a significant influence on the harmonic performance of the drive. However, this topic has not been addressed properly for dodecagonal voltage space-vector based multilevel inverter drives. In chapter-4 of the thesis, this aspect is taken into ac-count and the notion of “harmonic flux trajectories” and “stator flux ripple” are used to analyze the harmonic performance of the various PWM switching schemes. Although the PWM method used in this study is similar to that in chapter-2, the modification in the PWM switching sequence in the PWM algorithm yields significant improvements in harmonic performance.
The proposed topologies and PWM schemes are extensively simulated and experimentally verified. The control scheme was implemented using a DSP processor running at a clock frequency 150MHz and a four-pole, 3.7kW, 50Hz, 415V three-phase induction motor was used as the load. Since the PWM ports are limited in a DSP, a field-programmable gate array (FPGA) was used to decode the PWM signals from the DSP to generate timing information required for PWM sequencing for all the power devices. The same FPGA was used to generate the dead-time signals for the power devices also.
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Mathew, K. "Induction Motor Drives Based on Multilevel Dodecagonal and Octadecagonal Volatage Space Vectors." Thesis, 2013. http://hdl.handle.net/2005/3290.
Full textAbstract:
For medium and high-voltage drive applications, multilevel inverters are very popular. It is due to their superior performance compared to 2-level inverters such as reduced harmonic content in the output voltage and current, lower common mode voltage and dv=dt, and lesser voltage stress on power switches. The popular circuit topologies for multilevel inverters are neutral point clamped, cascaded H-bridge and flying capacitor based circuits. There exist different combinations of these basic topologies to realize multilevel inverters with modularity, better fault tolerance, and reliability. Due to these advantages,
multilevel converters are getting good acceptance from the industry, and researchers all over the world are continuously trying to improve the performance of these converters. To meet such demands, three multilevel inverter topologies are proposed in this thesis.
These topologies can be used for high-power induction motor drives, and the concepts
presented are also applicable for synchronous motor drives, grid-connected inverters, etc.
To get nearly sinusoidal phase current waveforms, the switching frequency of the
conventional inverter has to be increased. It will lead to higher switching losses and
electromagnetic interference. The problem with lower switching frequency is the intro-
duction of low order harmonics in phase currents and undesirable torque ripple in the motor. The 5th and 7th harmonics are dominant for hexagonal voltage space-vector based low frequency switching, and it is possible to eliminate these harmonics by dodecagonal switching. Further improvement in the waveform quality is possible by octadecagonal voltage space-vectors. In this case, the complete elimination of 11th and 13th harmonic is possible for the entire modulation range. The concepts of dodecagonal and octadecagonal voltage space-vectors are used in the proposed inverter topologies.
The first topology proposed in this thesis consists of cascaded connection of two
H-bridge cells. The two cells are fed from unequal DC voltage sources having a ratio
of 1 : 0:366, and this inverter can produce six concentric dodecagonal voltage space-
vectors. This ratio of voltages can be obtained easily from a combination of star-delta transformers, since 1 : 0:366 = (
p 3 + 1) : 1. The cascaded connection of two H-bridge cells can generate nine asymmetric pole voltage levels, and the combined three-phase inverter can produce 729 voltage space-vectors (9 9 9). From this large number of combinations, only certain voltage space-vectors are selected, which forms dodecagonal pattern. In the case of conventional multilevel inverters, the voltage space-vector diagram consists of equilateral triangles of equal size, but for the proposed inverter, the triangular
regions are isosceles and are having different sizes. By properly placing the voltage space-vectors in a sampling period, it is possible to achieve lower switching frequency for the individual cells, with substantial improvement in the harmonic spectrum of the output voltage. During the experimental veri cation, the motor is operated at di erent speeds using open loop v=f control method. The samples taken are always synchronised with the start of the sector to get synchronised PWM. The number of samples per sector is decreased with increase in the fundamental frequency to limit the switching frequency.
Even though many topologies are available in literature, the most preferred topology for drives application such as traction drives is the 3-level NPC structure. This
implies that the industry is still looking for viable alternatives to construct multilevel inverter topologies based on available power circuits. The second work focuses on the development of a multilevel inverter for variable speed medium-voltage drive application with dodecagonal voltage space-vectors, using lesser number of switches and power sources compared to earlier implementations. It can generate three concentric 12-sided polygonal voltage space-vectors and it is based on commonly available 2-level and 3-level inverters. A simple PWM timing computation method based on the hexagonal space-vector PWM is developed. The sampled values of the three-phase reference voltages are initially converted to the timings of a two-level inverter. These timings are mapped
to the dodecagonal timings using a change of basis transformation. The voltage space-
vector diagram of the proposed drive consists of sixty isosceles triangular regions, and the dodecagonal timings calculated are converted to the timings of the inner triangles. A searching algorithm is used to identify the triangular region in which the reference vector is located. A front-end recti er that may be easily implemented using standard star-delta transformers is also developed, to provide near-unity power factor. To test
the performance of the inverter drive, an open-loop v=f control is used on a three-phase induction motor under no-load condition. The harmonic spectra of the phase voltages were computed in order to analyse the harmonic distortion of the waveforms. The carrier frequency was kept around 1.2 KHz for the entire range of operation.
If the switching frequency is decreased, the conventional hexagonal space-vector
based switching introduce signifi cant 5th, 7th, 11th and 13th harmonics in the phase currents. Out of these dominant harmonics, the 5th and 7th harmonics can be completely
suppressed using dodecagonal voltage space-vector based switching as observed in the first and second work. It is also possible to remove the 11th and the 13th harmonics by using voltage space-vectors with 18 sides. The last topology is based on multilevel octadecagonal (18-sided polygon) voltage space-vectors, and it has better harmonic performance than the previously mentioned topologies. Here, a multilevel inverter system capable of producing three octadecagonal voltage space-vectors is proposed for the fi rst time, along with a simple timing calculation method. The conventional three-level inverters are only
required to construct the proposed drive. Four asymmetric power supply voltages with
0:3054Vdc, 0:3473Vdc, 0:2266Vdc and 0:1207Vdc are required for the operation of the drive, and it is the main drawback of the circuit. Generally front-end isolation transformer is essential for high-power drives and these asymmetric voltages can be easily obtained from the multiple windings of the isolation transformer. The total harmonic distortion of the phase current is improved due to the 18-sided voltage space-vector switching. The ratio of the radius of the largest polygon and its inscribing circle is cos10 = 0:985. This
ratio in the case of hexagonal voltage space-vector modulation is cos30 = 0:866, which means that the range of the linear modulation for the proposed scheme is signifi cantly higher. The drive is designed for open-end winding induction motors and it has better fault tolerance. It any of the inverter fails, it can be easily bypassed and the drive will be still functional with reduced speed. Open loop v=f control and rotor flux oriented vector control schemes were used during the experimental verifi cation.
TMS320F2812 DSP platform was used to execute the control code for the proposed
drive schemes. For the entire range of operation, the carrier was synchronized with the fundamental. For the synchronization, the sampling period is varied dynamically so that the number of samples in a triangular region is fi xed, keeping the switching frequency around 1.2 KHz. The average execution time for the v=f code was found to be 20 S, where as for vector control it took nearly 100 S. The PWM terminals and I/O lines of the DSP is used to output the timings and the triangle number respectively. To convert the triangle number and the timings to IGBT gate drive logic, an FPGA (XC3S200) was used. A constant dead-time of 1.5 S is also implemented inside the FPGA. Opto-isolated gate drivers with desaturation protection (M57962L) were used to drive the IGBTs. Hall-effect sensors were used to measure the phase currents and DC bus voltages. An incremental shaft position encoder with 2500 pulse per revolution is also connected to the motor shaft, to measure the angular velocity. 1200 V, 75 A IGBT half-bridge module is used to realize the switches. The concepts were initially simulated and experimentally verifi ed using laboratory prototypes at low power. While these concepts maybe easily extended to higher power levels by using suitably rated devices, the control techniques presented shall still remain applicable.
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Kshirsagar, Abhijit. "Reduced Switch Count Multilevel Inverter Topologies for Open End Induction Motor Drives." Thesis, 2016. http://etd.iisc.ernet.in/handle/2005/2722.
Full textAbstract:
MU LT I L E V E L inverters are becoming the preferred choice for medium voltage high power applications. Multilevel inverters have a number of inherent advantages over conventional two level inverters. The output voltage has multiple steps or levels, resulting in reduced dV/dt, which leads to lower electromagnetic interference, making it easier to meet electromagnetic compatibility (EMC) regulations. Multilevel inverters have a much lower effective switching frequency, which leads to a reduction in switching losses. The output voltage of multilevel inverters has a much lower harmonic content. In applications such as power conversion or grid-connection, filters need to be much smaller, or can be eliminated. In motor drive applications, the low harmonic content results in smoother, ripple-free shaft torque.
The neutral-point clamped (NPC), cascaded H-bridge (CHB) and flying capacitor (FC) topologies were among the earliest multilevel topologies. NPC topologies require additional clamping diodes to clamp the output to the DC bus midpoint. CHB topologies use a number of isolated DC suplies to generate multilevel output. FC topologies work with a single DC link but use additional floating capacitors. Since then, a number derivatives and improvements to these topologies have been proposed.
Topologies with low switch counts are desirable because of the corresponding reduction in system size and cost. A low total component count is also desirable since it results in better reliability.
Induction motors in high power applications are often operated in the open-end configuration. Here, the start terminals of the motor phase windings are connected to one three phase inverter, while the end terminals are connected to a second three-phase inverter. The two inverters are typically powered by isolated supplies to prevent the flow of common mode currents through the motor. The open end configuration has a number of advantages
It can be used with nearly all high power motors with no need for electrical or mechanical modification, since all six winding terminal are available externally. The two inverters driving the open-end motor are effectively cascaded. As a result, two inverters of lower voltage and power rating can replace a single inverter with higher voltage and power rating. In addition, if one of the inverter fails, it can be bypassed and the system can be operated at reduced power. In many applications such as heating, ventilation and air conditioning (HVAC), the load power is proportional to the cube of the shaft speed, so a 50% reduction in power translates to only 20% reduction in speed, thereby improving overall system reliability. The cascading of inverters also enables multilevel operation, which is exploited for the topologies proposed in this thesis. In the open-end configuration it is important to ensure that both the DC supplies deliver power to the load. Otherwise, power can circulate through the motor windings. In addition, if the two inverters are powered by rectifier supplies, the DC bus of one inverter can charge uncontrollably, resulting in distortion of phase voltages and currents. If DC bus overcharging continues unchecked the DC bus voltage can even exceed the system rating, resulting in permanent damage.
This thesis proposes two novel topologies for open-end induction motor drives with low switch counts. Both topologies are powered by two unequal, isolated DC sources having DC voltages in a 3:1 ratio. Multiple levels in the output voltage are obtained using a number of floating capacitors in each phase. Modulation and control schemes are also proposed for both topologies to ensure that DC bus overcharging never occurs, while all the capacitor voltages are kept balanced at their nominal values.
The first of these two topologies is a nine level inverter for open end induction motor drives. It consists of two three-level flying capacitor inverters connected to the induction motor in the open end configuration. The two inverters are powered by DC sources of voltage 6VDC/8 and 2VDC/8, which generates an effective phase voltage having nine levels in steps of VDC/8. This topology has only eight switches and two floating capacitors per phase. The space vector structure for this topology is hexagonal, and has 217 space vector locations. A space-vector based formulation is used to determine the pole voltage of the inverter such that DC bus over charging is prevented. In addition, selection of switching states is used to balance the voltages of all floating capacitors. This scheme allows the floating capacitors to be charged up during system startup, thereby eliminating the need for separate pre-charging circuitry. A level-shifted carrier PWM based modulation scheme has been developed, which can be used with both scalar and vector control schemes.
The gating signal for switches turning on must be delayed by a small amount (to allow the complementary switch to turn of), failing which current shoot through can occur.
This delay is called dead time, during which gate signals to both complementary devices are turned of. Under certain conditions in the flying capacitor topology, the pole voltage can contain large undesirable transients during the dead time which result in phase current distortion, and electromagnetic noise.
A novel scheme to eliminate this problem is proposed using a digital state machine approach. The switching state for each subsequent switching interval is determined based on the present switching state such that the pole voltage does not contain a transient, without affecting the phase voltage of the inverter, and irrespective of the current magnitude or direction. The state machine was implemented using an FPGA, and required an additional computation time of just 20ns, which is much smaller than the inverter dead time duration of typically 2.5µs.
The second novel topology proposed in this thesis is a seventeen level inverter for an open end induction motor drive. Here, one three-level inverter and one seven-level inverter are connected to the two ends of the induction machine. The three-level inverter is a flying capacitor inverter. The seven-level inverter is a hybrid topology – it consists of an H-bridge cascaded to each phase of a three level flying capacitor inverter. This scheme is also powered by two isolated DC sources in 3:1 ratio with magnitudes 12VDC/16 and 4VDC/16. The effective phase voltage has seventeen levels in steps of VDC/16. This topology has a total of twelve switches and three floating capacitors per phase.
The space vector structure for this topology is hexagonal, and has 817 space-vector locations. Space vector analysis was used to determine the pole voltages, and the switching states such that DC bus overcharging is prevented while also balancing the voltages of the floating capacitors. A non-iterative algorithm was developed for determining the switching states, suitable for implementation in digital logic using an FPGA. The scheme is able to charge the all capacitors at startup as well, eliminating the need for separate pre-charging circuits.
Hardware prototypes were built for both the topologies described above for experimental verification, and used to drive a three phase 50Hz, 1.5kW, four pole induction motor in V/f control mode. The inverters topologies were built using 1200V, 75A IGBT half-bridge modules (Semikron SKM75GB12T4) with hybrid opto-isolated gate drivers (Mitsubishi M57962). Three phase rectifiers were used to create the asymmetric DC supplies Hall effect sensors were used to sense the DC link and floating capacitor voltages and phase currents (LEM LV20P voltage sensors and LA55 current sensors). Signal conditioning circuitry was built using discrete components. The PWM signals and V/f controller were implemented using a digital signal processor (Texas Instruments TMS320F28335). Synchronous PWM with was used to eliminate sub-harmonics from the phase voltage, and to ensure three-phase and half-wave symmetry. The internal ADC of the DSP was used for sampling all voltages and currents. The remaining digital logic for switch state selection was implemented on a FPGA (Xilinx Spartan3 XC3S200). Dead time functionality was also implemented within the FPGA, eliminating the need for separate dead time hardware.
Both topologies were first tested for steady state operation over the full modulation range, and the pole voltages, phase voltages and phase currents were recorded. System startup, and the ability of the controllers to balance all the capacitors at startup was tested next. The capacitor voltages were also observed during sudden loading, by quickly accelerating the motor. Finally, the phenomenon of DC bus overcharging was also demonstrated.
These results demonstrate the suitability of the proposed topology for a number of applications, including industrial drives, alternate energy systems, power conversion and electric traction.
Books on the topic "Polygonal space vector structures"
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McDuff, Dusa, and Dietmar Salamon. Linear symplectic geometry. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198794899.003.0003.
Full textAbstract:
The second chapter introduces the basic concepts of symplectic topology in the linear algebra setting, such as symplectic vector spaces, the linear symplectic group, Lagrangian subspaces, and the Maslov index. In the section on linear complex structures particular emphasis is placed on the homotopy equivalence between the space of symplectic forms and the space of linear complex structures. The chapter includes sections on symplectic vector bundles and the first Chern class.
Book chapters on the topic "Polygonal space vector structures"
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Al Khayer, Mohamad, and Haresh Lalvani. "Scissors-Action Deployables Based on Space-Filling of Polygonal Hyperboloids." In IUTAM-IASS Symposium on Deployable Structures: Theory and Applications, 1–10. Dordrecht: Springer Netherlands, 2000. http://dx.doi.org/10.1007/978-94-015-9514-8_1.
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Zhang, Jie, and Futai Zhang. "Information-Theoretical Secure Verifiable Secret Sharing with Vector Space Access Structures over Bilinear Groups." In Information Security Practice and Experience, 318–29. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-06320-1_24.
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Mete, Mutlu, Ye-Lin Ou, and Nikolay Metodiev Sirakov. "Skin Lesion Feature Vector Space with a Metric to Model Geometric Structures of Malignancy for Classification." In Combinatorial Image Analaysis, 285–97. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-34732-0_22.
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Gantes, C. "85. Geometric constraints in assembling polygonal deployable units to form multi-unit structural systems." In Space Structures 4, 1: 793–803. Thomas Telford Publishing, 1993. http://dx.doi.org/10.1680/ss4v1.19683.0085.
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Canarutto, Daniel. "Spinors and Minkowski Space." In Gauge Field Theory in Natural Geometric Language, 37–52. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198861492.003.0003.
Full textAbstract:
A partly original approach to spinor geometry, showing how a 2-dimensional vector space, without any further assumpions, generates by natural constructions the fundamental algebraic structures needed to deal with spacetime geometry and particles with spin. Several related notions are expressed in a concise, intrinsic form.
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Brooks, Christopher. "A Genetic Algorithm to Design Optimal Patch Configurations Using Raster Data Structures." In Spatial Evolutionary Modeling. Oxford University Press, 2001. http://dx.doi.org/10.1093/oso/9780195135688.003.0013.
Full textAbstract:
The design of optimal patch configurations is a generic problem relevant to many spatial planning exercises. Spatial pattern affects processes in the natural and manufacture of environment and should be incorporated as a criterion in planning. Currently, while geographic inormation systems (GISs) are adequate for data storage, analysis, and visualization they do not provide sophisticated spatial decision-making functions. With the help of GISs, pattern can be incorporated into spatial decision-making explicitly, using ad hoc procedures, or implicitly, through visualization of alternative plans. Other computer technologies like remote sensing and decision support systems facilitate decision-making by supplying timely data and techniques for solving multi-criteria evaluation problems. There are now a number of artificial intelligence techniques that can be coupled with GIS to address a variety of hard spatial problems. Genetic algorithms are particularly attractive for optimization problems because they are efficient and effective in complex search spaces. Landscape ecologists use the twin concepts of patch and matrix to describe the spatial structure of the environment (McGarigal & Marks, 1994). The matrix is the dominant landscape element and patches are distributed within it. Patches can be crisp objects with well-defined boundaries, such as administrative areas, or inferred objects with fuzzy boundaries, such as vegetation or habitat patches in natural environments. In the former case, patches can be adequately represented by polygons in a vector GIS. In the second case patches are inferred from a continuous spatial distribution of attribute values. The raster data model is the most common representation of continuous fields within a GIS and is preferred to vector models in environmental applications because it is a better representation of the continuous variation characteristic of natural phenomena. There is a need for decision support tools that use raster GISs when spatial criteria relate to natural phenomena. Patch design involves many complexities: in a raster GIS it is also a complex problem in spatial geometry. This chapter describes a genetic algorithm for designing patch configurations in raster GISs. The genetic algorithm is coupled with GIS and multicriteria evaluation functions to build an autonomous system that explicitly includes pattern as a criterion in the design of patch networks. Conceptually, the problem is to extract from an infinite set of possible spatial patterns a single pattern that is optimal by some criterion.
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Hilorme, Tetiana, and Mykola Dron’. "SUBSTANTIATION OF PROJECTS IN THE SPACE DEBRIS MARKET IN THE AGE OF NEW SPACE." In European vector of development of the modern scientific researches. Publishing House “Baltija Publishing”, 2021. http://dx.doi.org/10.30525/978-9934-26-077-3-23.
Full textAbstract:
The article highlights research, dedicated to the study of the peculiarities of justification of the projects in the emerging space debris market in the age of New Space. It has been proved that human-induced debris in orbital space has reached catastrophic proportions, which requires making immediate changes for sustainable development of space activity. The research objective resides in the development of theoretical and methodological foundations, scientific and methodological approaches, and a practical toolkit for justifying projects in the emerging space debris market. The methodological platform of the research included the Stakeholder concept as an eco-system of interrelated groups. One built the BCG matrix of growth of the “Access to outer space” sector of the global market of space products and services. Also, there were distinguished four groups of space services for this segment using two factors – “the share of the types of space services” and “the relative share of the service market.” During the research, the authors developed a matrix for analysis of the project stakeholders in the emerging space debris market. It has been identified that there are three groups of stakeholders by the factors’ levels “Influence – Interest”: partners – alpha-stakeholders ( -stakeholders), consultants and support – beta-stakeholders ( -stakeholders). A situational model for the choice of a negotiating strategy for the development of projects in the space debris management market has been developed based on the methodological approach of “decision tree” to determine a rational negotiating strategy for reduction of destructive behaviour and avoidance of organizational conflicts among residential stakeholders. It was proposed to determine the general efficiency of the projects in the emerging space debris market based on the methodology by M. Farrell: as production of technical effectiveness and allocative (distributional) efficiency. All components of general efficiency were analyzed by the authors who also provided analytical calculation formulae: technical, economic, social, and ecological. A method of determining expenditures for a project on emerging space debris on the assumption of an alternative cost of projects and determining the stage of the project’s life cycle has been proposed. Making decisions on the project development requires structural analysis of expenditures of operating activity by the life cycle stages. To do that, the operating activity costs should be structures in the following way: preproduction costs; production costs; off-production costs; postproduction costs. The following main parameters used for making managerial decisions during project development were considered: profitability, the cost of deferred decisions, and deviation from costs. It was discovered that project development is carried out in the risk and uncertainty conditions. The authors formed a system for assessing risks, related to financing of the projects on recycling of space debris, which grounds on risks classification (technical, financial, procedural), which enabled the possibility to develop risk management strategies. The risk groups were analyzed following the requirements of stakeholders.
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Karunaratne, Geethan, Michael Hersche, Giovanni Cherubini, Abu Sebastian, and Abbas Rahimi. "Chapter 24. Few-Shot Continual Learning Based on Vector Symbolic Architectures." In Frontiers in Artificial Intelligence and Applications. IOS Press, 2023. http://dx.doi.org/10.3233/faia230156.
Full textAbstract:
Vector Symbolic Architecture (VSA) is a powerful computing model that is built on a rich algebra in which all representations—from atomic to composite structures—are high-dimensional holographic distributed vectors of the same, fixed dimensionality. VSA is mainly characterized by the following intriguing properties: (i) quasi-orthogonality of a randomly chosen vector to other random vectors with very high probability, aka concentration of measure; (ii) exponential growth of the number of such quasi-orthogonal vectors with the dimensionality, which provides a sufficiently large capacity to accommodate novel concepts over time; (iii) availability of these vectors to be composed, decomposed, probed, and transformed in various ways using a set of well-defined operations. Motivated by these properties, this chapter presents a summary of recently developed methodologies on the integration of VSA with deep neural networks that enabled impactful applications to few-shot [1] and continual [2, 3] learning. Resorting to VSA-based embedding allows deep neural networks to quickly learn from few training samples by storing them in an explicit memory, where many more class categories can be continually expressed in the abstract vector space of VSA with fixed dimensions, without causing interference among the learned classes. Experiments on various image datasets show that the considered neuro-symbolic AI approach outperforms pure deep neural network baselines with remarkable accuracy, scalability, and compute/memory efficiency.
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Scholze, Peter, and Jared Weinstein. "Mixed-characteristic shtukas." In Berkeley Lectures on p-adic Geometry, 90–97. Princeton University Press, 2020. http://dx.doi.org/10.23943/princeton/9780691202082.003.0011.
Full textAbstract:
This chapter looks at mixed-characteristic shtukas. Much of the theory of mixed-characteristic shtukas is motivated by the structures appearing in (integral) p-adic Hodge theory. The chapter assesses Drinfeld's shtukas and local shtukas. In the mixed characteristic setting, X will be replaced with Spa Zp. The test objects S will be drawn from Perf, the category of perfectoid spaces in characteristic p. For an object, a shtuka over S should be a vector bundle over an adic space, together with a Frobenius structure. The product is not meant to be taken literally (if so, one would just recover S), but rather it is to be interpreted as a fiber product over a deeper base. Motivated by this, the chapter then defines an analytic adic space and shows that its associated diamond is the appropriate product of sheaves on Perf.
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Segal, Yoram, Ofer Hadar, and Lenka Lhotska. "Assessing Human Mobility by Constructing a Skeletal Database and Augmenting it Using a Generative Adversarial Network (GAN) Simulator." In Studies in Health Technology and Informatics. IOS Press, 2022. http://dx.doi.org/10.3233/shti220967.
Full textAbstract:
This paper presents a neural network simulator based on anonymized patient motions that measures, categorizes, and infers human gestures based on a library of anonymized patient motions. There is a need for a sufficient training set for deep learning applications (DL). Our proposal is to extend a database that includes a limited number of videos of human physiotherapy activities with synthetic data. As a result of our posture generator, we are able to generate skeletal vectors that depict human movement. A human skeletal model is generated by using OpenPose (OP) from multiple-person videos and photographs. In every video frame, OP represents each human skeletal position as a vector in Euclidean space. The GAN is used to generate new samples and control the parameters of the motion. The joints in our skeletal model have been restructured to emphasize their linkages using depth-first search (DFS), a method for searching tree structures. Additionally, this work explores solutions to common problems associated with the acquisition of human gesture data, such as synchronizing activities and linking them to time and space. A new simulator is proposed that generates a sequence of virtual coordinated human movements based upon a script.
Conference papers on the topic "Polygonal space vector structures"
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Krishna Raj, R., K. Gopakumar, Apurv Kumar Yadav, L. Umanand, Mariusz Malinowski, and Wojciech Jarzyna. "A Thirteen Level Twenty-Four Sided Polygonal Voltage Space Vector Structure for Drives." In IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society. IEEE, 2018. http://dx.doi.org/10.1109/iecon.2018.8591564.
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Das, A., K. Sivakumar, G. Mondal, and K. Gopakumar. "A Multilevel inverter with hexagonal and 12-sided polygonal space vector structure for induction motor drive." In IECON 2008 - 34th Annual Conference of IEEE Industrial Electronics Society. IEEE, 2008. http://dx.doi.org/10.1109/iecon.2008.4758104.
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Surana, Prashant, Rakesh R, K. Gopakumar, and Loganathan Umanand. "A 24-sided Polygonal Voltage Space Vector Structure for IM drive with Open end winding Configuration." In IECON 2021 - 47th Annual Conference of the IEEE Industrial Electronics Society. IEEE, 2021. http://dx.doi.org/10.1109/iecon48115.2021.9589640.
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Gudapati, Tanvi, and P. P. Rajeevan. "20-Sided Polygonal Voltage Space Vector Structure Based Switching Scheme for Five Phase Induction Motor Drives." In 2021 IEEE 2nd International Conference on Smart Technologies for Power, Energy and Control (STPEC). IEEE, 2021. http://dx.doi.org/10.1109/stpec52385.2021.9718710.
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Rakesh, R., Mriganka Ghosh Majumder, K. Gopakumar, Loganathan Umanand, Leopoldo G. Franquelo, and Wojciech Jarzyna. "A Fifteen Concentric 30-sided Polygonal Space Vector Structure Using a Single DC-link for OEIM drive." In 2020 IEEE 29th International Symposium on Industrial Electronics (ISIE). IEEE, 2020. http://dx.doi.org/10.1109/isie45063.2020.9152382.
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Shekhar, Ishank, and P. P. Rajeevan. "Generation of 24-Sided Polygonal Voltage Space Vector Structure with Reduced Hardware Complexity for Induction Motor Drives." In 2022 IEEE International Conference on Power Electronics, Smart Grid, and Renewable Energy (PESGRE). IEEE, 2022. http://dx.doi.org/10.1109/pesgre52268.2022.9715925.
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Dewani, Rahul, K. Gopakumar, L. Umanand, and S. Bhattacharya. "Suppression of lower order harmonics by Switched-Capacitive filtering using Polygonal Space Vector Structures and Capacitor Sizing for Induction Motor Drive Applications." In IECON 2021 - 47th Annual Conference of the IEEE Industrial Electronics Society. IEEE, 2021. http://dx.doi.org/10.1109/iecon48115.2021.9589848.
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Surana, Prashant, Mriganka Ghosh Majumder, K. Gopakumar, Loganathan Umanand, and Leopoldo Garcia Franquelo. "A Dense Multilevel 24-sided Polygonal Voltage Space Vector Structure for IM Drive with Open-end Winding Configuration." In IECON 2022 – 48th Annual Conference of the IEEE Industrial Electronics Society. IEEE, 2022. http://dx.doi.org/10.1109/iecon49645.2022.9968937.
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R., Rakesh, Apurv Kumar Yadav, Krishna Raj R., K. Gopakumar, and L. Umanand. "A 30-sided polygonal space vector structure with modular low voltage capacitor fed cascaded H bridge for IM drive." In 2019 IEEE 28th International Symposium on Industrial Electronics (ISIE). IEEE, 2019. http://dx.doi.org/10.1109/isie.2019.8781446.
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Dewani, Rahul, Mriganka Ghosh Majumder, Rakesh R., K. Gopakumar, L. Umanand, Dariusz Zieliski, and Wojciech Jarzyna. "Generation of 42-sided polygonal Voltage Space Vector Structure for suppression of lower order harmonics in IM Drive Applications." In 2020 IEEE 29th International Symposium on Industrial Electronics (ISIE). IEEE, 2020. http://dx.doi.org/10.1109/isie45063.2020.9152249.
Full textReports on the topic "Polygonal space vector structures"
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Yan, Tak W., and Hector Garcia-Molina. Index Structures for Information Filtering Under the Vector Space Model,. Fort Belvoir, VA: Defense Technical Information Center, November 1993. http://dx.doi.org/10.21236/ada326033.
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Frigo, Nicholas J., Vincent J. Urick, and Frank Bucholtz. Modeling Interferometric Structures with Birefringent Elements: A Linear Vector-Space Formalism. Fort Belvoir, VA: Defense Technical Information Center, November 2013. http://dx.doi.org/10.21236/ada594532.
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