Dissertations / Theses on the topic 'Variable frequency drive schemes'

This paper discusses a permanent magnet synchronous motor (PMSM) variable frequency drive (VFD) system developed for an all-terrain Wifi-HaLow connected (802.11ah, 900 MHz) modular electric vehicle that competed in the Mars University Rover Challenge (URC). The quadrature axis flux linkage for each motor was estimated using on-board voltage and current measurements. A synchronous control algorithm tracked the electromagnetic operating parameters, which are highly dependent on variations in motor construction and load conditions. A feed-forward model-driven observer solution calculated flux linkage angles by direct-quadrature-zero transformation of three-phase shunt currents using DSP processors.

There are various methods for speed control of induction motors. This paper specifically describes one of the methods: speed control using variable frequency. The proposed system is a MATLAB simulink model, which is a closed loop model designed to achieve desired speed control of a three-phase induction motor by varying its frequency. The simulink model has four main blocks, namely the inverter, synchronous machine, proportional integral control and current hysteresis control. For accuracy of output results and simplicity, we have used dq to abc transformation block and sin function block. The inverter is comprised of six integrated gate bipolar transistors (IGBTs), which are fired by gate pulses generated by current hysteresis control block. The inverter generates variable frequency and variable voltage output, which is given to motor terminals. The project presents the working principle of variable frequency drive (VFD), its performance, and the use of Pulse Width Modulation (PWM) in a three-phase inverter to control the frequency and thus the speed. The proposed method conformed to performance predictions and delivered the desired outputs.

Radio frequency radiated emission from a variable speed drive must be limited below defined limits to avoid interference with electronic equipment. It is possible to comply with the international standards however, the current state of the art methods such as large gate drive resistance and output filters significantly reduce the efficiency or increase the cost of the products. It is known that the main source of emissions emanate from the switching transients associated with the output power semiconductors, however the exact mechanisms and specific sources are unknown. This thesis examines the interaction of power devices during the switching transient identifying features which can be controlled by a sophisticated gate drive design. Analysis of the frequency content of the signals is presented together with methods to minimise power losses while maintaining compliance with radiated emission standards. A research program has been undertaken to identify the sources responsible for radiated emissions and predict a figure of merit as an indication of compliance. Measuring radio frequency content on high voltage and current signals is difficult and several techniques to accurately achieve this are presented. Simple passive gate drive solutions which can be easily implemented are examined along with a discussion on more complicated optimised solutions.

This study examined the Lake of Egypt Power Plant operated by Southern Illinois Power Cooperative located on the Lake of Egypt south of Marion, IL. The facility has a 173 MW rated turbine operating on a pulverized coal cyclone boiler and three 33 MW rated turbines operating on an oversized circulating fluidized bed boiler with 120 MW capacity. The first area examined was reduction of auxiliary power consumption possible with the addition of variable frequency drives to the forced draft fan and booster fan motors. Included in this examination was an analysis of the economic and environmental impact of such a reduction. From the analysis an annual savings of 24.4 GWh of electricity is possible. The second area examined was the generation capacity lost due to condenser fouling and the possible reduction in facility emissions with altered condenser treatment. From the analysis an additional 3.0 MW of capacity facility wide is possible or a reduction steam production of 1.5% for each boiler.

The use of variable frequency drives in centrifugal pump applications has raised the question of how to select a drive. Clogging obstacles in waste water applications create unknown transient loads for the pump system. A sudden load increase occurrence can clog the pump if the drive cannot supply enough current to reach the motor’s torque demand. In order to select a suitable drive, an empirical approach has been implemented, investigating three different drives. Results have shown that selecting a drive with the highest possible overload capabilities, even if for a short time is most suitable. Operation in vector speed control gives the most reliable operation if an automatic parameter tuning is performed by the drive.
Användningen av frekvensomriktare i centrifugalpumpar har väckt fr ågan om hur en omriktare skall väljas. Igensättande objekt i avloppsvatten kan ge upphov till transienta laster i pumpsystemen. En oförutsedd lastökning kan sätta igen pumpen om frekvensomriktaren inte kan förse motorn tillräckligt med ström för att möta momentbehovet. För att välja en lämplig omriktare har ett empiriskt tillvägag ångssätt valts i en undersökning av tre olika omriktare. Resultat har visat att det är lämpligast att välja en omriktare med högst överbelastningskapacitet, även om under en kort tid. Vektor hastighetskontroll är metoden som ger stabil körning om omriktaren f ått automatiskt ställa in motorparametrarna.

Currently, the Southern Illinois University Carbondale (SIUC) power plant produces steam at high pressure to drive a high pressure (HP) turbine to make a portion of the electrical power needed by campus, then using 969 kPa (125 psig) steam to provide hot water all year, heat buildings, and to operate a low pressure (LP) turbine that powers the compressor of the central air conditioning (A/C) system. In the proposed system, the HP turbine is replaced by a much higher efficiency, multi-level turbine, the LP turbine is replaced with a motor and Variable Frequency Drive (VFD), and a cooling tower is added to condense more possible steam. This thesis has provided computer models to evaluate the economical feasibility of the proposed system, which are written by using Engineering Equation Solver (EES) software. The results of the study are presented in two cases. Case 1 examines the same amount of coal use between current and proposed systems, while Case 2 exames operating the high pressure boiler at the maximum rate. The results are a cost savings of $1,921,000 and $3,604,000 with payback periods of 4 and 2.2 years for Case 1 and Case 2, respectively. The annual primary energy saved and CO2 reduction from this modification was 200,000 GJ and 564,814 moles, respectively.

As power electronic based controllers and loads become more prevalent in power systems, there is a growing concern about how the harmonics generated by these controllers and loads affect the power quality of the system. One widely used power electronic based load is the Variable Frequency Drive (VFDs) used to vary the speed of an induction motor; whereas a common example of a power electronic based controller used in power systems is the Static VAR Compensator (SVC) for improving a system’s power factor. In this thesis, the harmonic content and overall performance of a system including both a VFD and a SVC will be studied and analyzed. Specifically, the cases of no compensation, static capacitor compensation, and power electronic based static VAR compensation are examined. A small-scale model of a system for study was constructed in lab. Several cases were then performed and tested to simulate a system which contained both fixed and power electronic based harmonic generating loads. The performance of each case was determined by total harmonic current and voltage distortions, true power factor, and RMS current levels at different points in the system.

System characteristics of automated pumping systems may change due to wear, aging of piping, and accumulation of deposits in the system and/or due to configuration changes. Such changes might result in conflicts between the controlling algorithms and the actual system requirements for each particular case. The said mismatch between the actual physical system and the software controlling it, may result in inefficient operation of the pump which may even lead to total system failures (overpressurization of instrumentation and sensing elements etc.) due to temporary malfunctioning of the system components or permanent damages incurred by them during operating under unsuitable conditions. It is intended in this study to design and construct an experimental automated pump bench with operational components (mechanical, electronical and instrumentation etc.), serving in a system introducing multiple geometric heads and its controlling and monitoring software in order to visualize effects of the above-mentioned cases for education and training purposes. System characteristics data acquisition module (system test module) provides the means of recognizing new pump and system characteristics, provided that they were changed due to some reason (throttled valve, changed pump speed, changed flowrate or elevation of discharge etc.). Then the pump operation module enables users to make comparative judgments by observing the effects of the abovementioned changes. Above-mentioned testing sequence and monitoring of changing physical quantities were achieved by employing four pressure transducers, a custom made DC motor operated -throttling valve with position feedback which was designed and constructed specifically for this study and a variable frequency drive (VFD) which were all connected to a custom made Main Control Circuit (MCC) Board.

In this study, an innovative solution is examined for transmission problems and frequency control for wind Turbines. Power electronics and the gear boxes are the parts which are responsible of a significant amount of failures and they are increasing the operation and maintenance cost of wind turbines. Continuously transmission (CVT) systems are investigated as an alternative for conventional gear box technologies for wind turbines in terms of frequency control and power production efficiency. Even though, it has being used in the car industry and is proven to be efficient, there are very limited amount of studies on the CVT implementation on wind turbines. Therefore, this study has also an assertion on being a useful mechanical analyse on that topic. After observing several different types of possibly suitable CVT systems for wind turbines; a blade element momentum code is written in order to calculate the torque, rotational speed and power production values of a wind turbine by using aerodynamic blade properties. Following to this, a dynamic model is created by using the values founded by the help of the blade element momentum theory code, for the wind turbine drive train both including and excluding the CVT system. Comparison of these two dynamic models is done, and possible advantages and disadvantages of using CVT systems for wind turbines are highlighted. The wind speed values, which are simulated according to measured wind speed data, are used in order to create the dynamic models, and Matlab is chosen as the software environment for modelling and calculation processes. Promising results are taken out of the simulations for both in terms of energy efficiency and frequency control. The wind turbine model, which is using the CVT system, is observed to have slightly higher energy production and more importantly, no need for power electronics for frequency control. As an outcome of this study, it is possible to say that the CVT system is a candidate of being a research topic for future developments of the wind turbine technology.

This master thesis deals with the mechanical and electrical design of the drive of the inclined construction lift. Individual components are selected in the design. Furthermore, a theoretical research is carried out regarding wireless modules and logic controllers. The selection of sensors is made and the method of retrieving signals from sensors and converting them into iputs the control circuits is also outlined. A program is written in Arduino IDE that wirelessly controls the motion of a motor via variable frequency drive.

Orientador: Walmir de Freitas Filho
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
Made available in DSpace on 2018-08-27T18:46:05Z (GMT). No. of bitstreams: 1 Ricciardi_TiagoRodarte_D.pdf: 6633244 bytes, checksum: bcb56f82b62350db77ed247ac2913cc9 (MD5) Previous issue date: 2015
Resumo: Modelos matemáticos e computacionais precisos dos diversos componentes de um sistema de energia elétrica são importantes para estudos e simulações em um cenário de planejamento e operação da rede elétrica. Dentre os elementos de um sistema de geração, transmissão e distribuição de energia elétrica, as cargas são as que apresentam maiores dificuldades em serem adequadamente representadas. Embora esse tema de pesquisa tenha sido exaustivamente explorado, a modelagem de carga tem recebido renovada atenção do setor produtivo e da academia por uma série de fatores, dentre os quais podemos destacar a proliferação de medidores eletrônicos, o interesse por modelos de novos equipamentos e a necessidade da representação mais fiel do comportamento de diferentes cargas frente a distúrbios no sistema. Esta tese de doutoramento propõe duas contribuições na linha de pesquisa sobre modelagem de carga em sistemas de energia elétrica. A primeira delas trata-se de um método de modelagem de carga baseado em medições e na detecção de distúrbios naturais de tensão. O procedimento proposto emprega medidores eletrônicos simples, que são instalados junto a instalações em sistemas de distribuição com motivo outro que não o de modelagem de carga. A ideia principal é a de utilizar tais medidores para, paralelamente a função que desempenham, fornecer para a concessionária informações sobre modelos de carga, como um subproduto da função principal que desempenham. A segunda contribuição proposta é na linha da modelagem de carga baseada em templates, uma técnica recentemente proposta na literatura para modelagem dinâmica de cargas industriais de grande porte. Nesta tese é proposto um modelo dinâmico simplificado de motores de velocidade variável controlados via conversores eletrônicos (Variable Frequency Drives ¿ VFDs), o qual é baseado em um modelo modificado de um motor de indução. O modelo proposto é adequado ao contexto da estrutura de modelagem de cargas industriais proposta pela técnica de modelagem baseada em templates e pode ser facilmente agregado e analisado em programas de simulação por parte de usuários sem necessidades de alterações do código fonte
Abstract: Accurate mathematical and computational models from various electric power systems components are important in a scenario of power systems studies and simulations for grid planning and operation. Among the elements in the electricity generation, transmission and distribution systems, the loads are probably the most difficult ones to be accordingly represented. Though this research topic has been exhaustively explored, there is a renewed interest in industry and academia for power systems load modeling, due to several reasons, including the proliferation of smart meters, the appearance of non-conventional types of load and the continuing need for even more confident representation of different load response for system disturbances. This Ph.D. thesis proposes two contributions to power systems load modeling research field. The first one deals with a load modeling method based on measurements and the detection of natural voltage disturbances. The proposed scheme uses simple smart meters, installed close to customers with a main goal other than load modeling. The main idea is to use data provided by those meters to, in parallel to the main function performed by this device, provide to the utility information regarding load models, as a byproduct capable to add value to the investment in this meters. The second contribution is in the template based load modeling, a recently methodology proposed for dynamic modeling of large industrial facilities. In this thesis, a simplified Variable Frequency Drive (VFD) dynamic model is proposed, which one is based on a modified induction machine model. The proposed model is suitable to the dynamic load model structure proposed by the template based methodology and can be easily aggregated and analyzed in simulation software by basic users without the need of programming a complex model
Doutorado
Energia Eletrica
Doutor em Engenharia Elétrica

The diploma thesis describes design of bladeless machine known as a Tesla turbine. The work is divided into theoretical part, practical part involving the design and experimental measurements of made bladeless turbine and a final assessment of thesis. The theoretical part deals with the basic design features of bladeless machines and their design modifications and flow in the nozzles. Furthermore there is a dedicated part of the dynamics of working fluid in the rotor of bladeless turbine represented by CFD modeling. The practical part includes the design and construction of parts of the turbine on a preliminary calculation using an analytical model of the flow in the turbine. The designed turbine components were checked for operational safety with structural calculations of shaft and disk impeller. The thesis was also performed experimental measuring of parameters of designed bladeless turbine. Measured values were compared with the analytical model which predicted turbine efficiency. In conclusion, besides to assessment, thesis also outlines possible proposals for further improvements of constructed bladeless turbine.

The development of a numeric simulation for predicting the performance of an Ocean Current Energy Conversion System is presented in this thesis along with a control system development using a PID controller for the achievement of specified rotational velocity set-points. In the beginning, this numeric model is implemented in MATLAB/Simulink® and it is used to predict the performance of a three phase squirrel single-cage type induction motor/generator in two different cases. The first case is a small 3 meter rotor diameter, 20 kW ocean current turbine with fixed pitch blades, and the second case a 20 meter, 720 kW ocean current turbine with variable pitch blades. Furthermore, the second case is also used for the development of a Voltage Source Variable Frequency Drive for the induction motor/generator. Comparison among the Variable Frequency Drive and a simplified model is applied. Finally, the simulation is also used to estimate the average electric power generation from the 720 kW Ocean Current Energy Conversion System which consists of an induction generator and an ocean current turbine connected with a shaft which modeled as a mechanical vibration system.

Voltage source inverter (VSI) fed induction motors are increasingly used in industrial and transportation applications as variable speed drives. However, VSIs generate non-sinusoidal voltages and hence result in harmonic distortion in motor current, motor heating, torque pulsations and increased acoustic noise. Most of these undesirable effects can be reduced by increasing the switching frequency of the inverter. This is not necessarily true for acoustic noise. Acoustic noise does not decrease monotonically with increase in switching frequency since the noise emitted depends on the proximity of harmonic frequencies to the motor resonant frequencies. Also there are practical limitations on the inverter switching frequency on account of device rating and losses. The switching frequency of many inverters often falls in the range 2 kHz - 6 kHz where the human ear is highly sensitive. Hence, the acoustic noise emission from the motor drive is of utmost important. Further, the acoustic noise emitted by the motor drive is known to depend on the waveform quality of the voltage applied. Hence, the acoustic performance varies with the pulse width modulation (PWM) technique used to modulate the inverter, even at the same modulation index. Therefore a comprehensive study on the acoustic noise aspects of induction motor drive is required. The acoustic noise study of the motor drive poses multifaceted challenges. A simple motor model is sufficient for calculation of total harmonic distortion (THD). A more detailed model is required for torque pulsation studies. But the motor acoustic noise is affected by many other factors such as stator winding distribution, space harmonics, geometry of stator and rotor slots, motor irregularities, structural issues controlling the resonant frequency and environmental factors. Hence an accurate model for acoustic noise would have to be very detailed and would span different domains such as electromagnetic fields, structural engineering, vibration and acoustics. Motor designers employ such detailed models along with details of the materials used and geometry to predict the acoustic noise that would be emitted by a motor and also to design a low-noise motor. However such detailed motor model for acoustic noise purposes and the necessary material and constructional details of the motor are usually not available to the user. Also, certain factors influencing the acoustic noise change due to wear and tear during the operational life of the motor. Hence this thesis takes up an experimental approach to study the acoustic noise performance of an inverter-fed induction motor at any stage of its operating life. A 10 kVA insulated gate bipolar transistor (IGBT) based inverter is built to feed the induction motor; a 6 kW and 2.3 kW induction motors are used as experimental motors. A low-cost acoustic noise measurement system is also developed as per relevant standards for measurement and spectral analysis of the acoustic noise emitted. For each PWM scheme, the current and acoustic noise measurements are carried out extensively at different carrier frequencies over a range of fundamental frequencies. The main cause of acoustic noise of electromagnetic origin is the stator core vibration, which is caused by the interaction of air-gap fluxes produced by fundamental current and harmonic currents. In this thesis, an experimental procedure is suggested for the acoustic noise characterization of an induction motor inclusive of determination of resonant frequencies. Further, based on current and acoustic noise measurements, a vibration model is proposed for the stator structure. This model is used to predict the acoustic noise pertaining to time harmonic currents with reasonable accuracy. Literature on motor acoustic noise mainly focuses on sinusoidal PWM (SPWM), conventional space vector PWM (CSVPWM) and random PWM (RPWM). In this thesis, acoustic noise pertaining to two bus-clamping PWM (BCPWM) schemes and an advanced bus-clamping PWM (ABCPWM) scheme is investigated. BCPWM schemes are mainly used to reduce the switching loss of the inverter by clamping any of the three phases to DC rail for 120◦ duration of the fundamental cycle. Experimental results show that these BCPWM schemes reduce the amplitude of the tonal component of noise at the carrier frequency, compared to CSVPWM. Experimental results with ABCPWM show that the overall acoustic noise produced by the motor drive is reduced at low and medium speeds if the switching frequency is above 3 kHz. Certain spread in the frequency spectrum of noise is also seen with both BCPWM and ABCPWM. To spread the acoustic noise spectrum further, many variable-frequency PWM schemes have been suggested by researchers. But these schemes, by and large, increase the current total harmonic distortion (THD) compared to CSVPWM. Thus, a novel variable-frequency PWM (VFPWM) method is proposed, which offers reduced current THD in addition to uniformly spread noise spectrum. Experimental results also show spread in the acoustic noise spectrum and reduction in the dominant noise components with the proposed VFPWM. Also, the current THD is reduced at high speeds of the motor drive with the proposed method.

碩士
國立臺北科技大學
能源與冷凍空調工程系
107
According to the US Department of Energys survey on the use of electricity in buildings, the most power-consuming part in air-conditioning systems is chiller unit, accounting for 60% of all systems. 99% of typical chiller units are partially loaded. Therefore, the use of high-efficiency inverters will make the energy-saving effect very significant. This paper shows that the Exchange efficiency COP（Coefficient of Performance, COP）value of the spiral-type chiller units driven by frequency conversion in Taiwans climatic conditions are much better than that of the general fixed-frequency chiller units. This paper takes the air conditioning system of the teaching hospital in the eastern region as an example. After the air conditioning system is replaced and integrated, the monitoring system is used to calculate the required air-conditioning tonnage of the building, control the frequency converting host and auxiliary equipment to load and off-load, and record the electricity consumption to do analysis in order to understand the actual energy saving situation after the replacement of air conditioning equipment. When the equipment is used, the COP value can reach more than 5.50 when operating at 40%~60%. Because the on-site cooling water temperature conditions cannot be matched, there is no expected efficiency. However, the efficiency of the operational state is better than the national standard after comparing with the energy efficiency standards of the chiller unit of the Bureau of Energy, Ministry of Economic Affairs. After the completion of the replacement, the electricity consumption in 2015 was saved by 14.22%, the savings in 2016 was 17.78%, and the emission of CO2 was reduced by about 284,539 kg.

碩士
中原大學
物理研究所
99
We propose a color reflective dual-frequency (DF) cholesteric liquid crystal display (CLCD) characterized by the short switching time of merely ~ms from the focal conic (FC) texture to the planar (P) state. Because of the existence of the bistable—P and FC—states at zero field, it is not necessary to hold the driving voltage for operation. Three distinct cholesteric pitches are prepared such that the Bragg reflections take place in red, green and blue in order to realize a color pixel. The cholesteric cells can be directly switched from the bright (reflecting) P state to the dark (light-scattering) FC state by a low-frequency voltage pulse and reversibly from the FC to P state by a high-frequency pulse. We present two drive schemes for the passive- and active-matrix DF-CLCDs. Gray levels are achievable by either amplitude tuning or frequency tuning of the applied voltage pulse.

Induction motors and Variable Frequency Drives (VFDs) are widely used in industry to drive machinery trains. However, some mechanical trains driven by VFD-motor systems have encountered torsional vibration problems. This vibration can induce large stresses on shafts and couplings, and reduce the lifetime of these mechanical parts. Long before the designed lifetime, the mechanical train may encounter failure. This thesis focuses on VFDs with voltage source rectifiers for squirrel-cage induction motors of open-loop Volts/Hertz and closed-loop Field Oriented Control (FOC). First, the torsional vibration problems induced by VFDs are introduced. Then, the mathematical model for a squirrel-cage induction motor is given. Two common control methods used in VFD are discussed - open-loop Volts/Hertz and closed-loop FOC. SimPowerSystems and SimMechanics are used as the modeling software for electrical systems and mechanical systems respectively. Based on the models and software, two interface methods are provided for modeling the coupled system. A simple system is tested to verify the interface methods. The study of open-loop Volts/Hertz control method is performed. The closed-form of electromagnetic torque sideband frequency due to Pulse Width Modulation is given. A torsional resonance case is illustrated. The effects of non-ideal power switches are studied, which shows little in uence on the system response but which uses little energy consumption. A study of a non-ideal DC bus indicates that a DC bus voltage ripple can also induce a big torsional vibration. Next, the study of the closed-loop FOC control method is presented. Simulation for a complete VFD machinery train is performed. With the recti er and DC bus dynamic braking, the system shows a better performance than the ideal-DC bus case. Lastly, a parametric study of the FOC controller is performed. The effects of primary parameters are discussed. The results indicate that some control parameters (i.e. speed ramps, proportional gain in speed PI controller) are also responsible for the mechanical torsional vibration.

碩士
國立臺北科技大學
冷凍空調工程系所
94
Centrifugal chiller is the single largest electrical load in central air-conditioning system. Energy efficiency of a chiller is critical to energy saving performance for a building. This thesis presents that the COP of a variable frequency drive (VFD) centrifugal chiller at operating conditions here in Taiwan is far better than a constant speed drive (CSD) chiller. An ARI certified computer program is used to simulate operation of two 350 tons centrifugal chillers, one is VFD and the other one is constant speed. Analyzed results show that COP of a VFD chiller operates between 100% and 40% load is up to 70% higher than that of the CSD chiller if ECWT drops to 20 ℃ from 30 ℃. COP can be further improved by resetting leaving chilled water temperature if relative humidity is not a concern. The conclusion of this thesis may provide some guidelines for those professionals when they make a selection of centrifugal chillers. Then VFD chillers may be more popularly applied in air-conditioning system design as an effective measure to achieve energy saving requirements.

碩士
國立臺北科技大學
能源與冷凍空調工程系碩士班
96
As chiller for central air-conditioning system is the largest power equipment in the project, the crucial importance of energy-saving impact. The performance tests of the VSD mode and slide-valve mode are in accordance with the ARI Standard ARI-550.590. The curve fitting data of the testing results are inputted for DOE-2 energy simulation models of the office, hotel and hospital building types to do energy-saving analysis and comparison. This research showed that the part load efficiency of variable speed drive control mode of flooded screw chiller is 17% to 30 percent better than that of the slide-valve control mode. Under the climate conditions of Taiwan , the energy consumption of variable speed drive control mode of flooded screw chiller is much lower than that of the slide-valve control mode. The simple pay back year of the additional cost of VSD is about 1 year.

碩士
國立勤益科技大學
電機工程系
100
The advantages of dc motors are starting easy and speed control convenient, but the dc motors require frequent maintenance because of the presence of commutators and brushes, which make the motor unsuitable for dirty and explosive environments. In this paper, a high- power-factor high-efficiency inverter drive for three-phase outside rotor induction motor of ceiling fan is presented. First, a control board applying dsPIC30F3010 based on voltage-frequency ratio (V/F) to generate PWM signals is established. Second, the power stage using power MOSFETs as power switches and with protection circuit is developed. Third, a power factor correction (PFC) is designed to improve input current waveform and power factor, and a radio frequency (RF) wireless remote device is established for users to control ceiling fan easy. Experimental results confirm the effectiveness of the proposed drive for ceiling fan.

碩士
國立成功大學
工程科學系碩博士班
95
The piezoelectric actuators have been applied popularly for servo systems, such as the Rotary Traveling-Wave LUSM and the standing-wave Linear Ultrasonic Motor (LUSM). The standing-wave LUSM attracts special interest as direct drive type actuator in industry, medical science, consumers, robotics and automotive application. The speed and position of the conventional LUSM can be manipulated by controlling the frequency, the difference of phases and the voltage amplitude of the sinusoidal voltage waveforms. However, the two-phase sinusoid output voltages of the conventional LUSM are unbalanced under the same switching frequency. Therefore, a good dynamic performance of the conventional LUSM is difficult to be obtained due to the unbalanced two-phase voltages. Because the standing-wave LUSM could be supplied a single phase sinusoidal wave, there is an outstanding performance in practical application without the demerit of the unbalanced two-phase voltages. The driving circuit for the standing-wave LUSM combines the two control circuits to regulate the frequency and the amplitude of the driving voltage. The driving circuit is composed of four stages: voltage-controlled oscillator circuit, voltage-controlled gain amplifier circuit, power amplifier and transformer. The hardware of experiment system is implemented with a low-cost digital signal processor based microcontroller and the separate-type linear scale system. The experiment system reduces the size and cost of hardware and measures the relative position coordinate by feedback signals. According to the experiment results, the driving circuit for the standing-wave LUSM gives more flexible control range and more variable control condition than the other driving circuits.

碩士
國立成功大學
系統及船舶機電工程學系碩博士班
101
In a ship’s central cooling system, seawater cooling pumps are normally designed to operate for the temperature of in-take seawater at 32°C when the pumps are under full speed to reach the flow nowadays. However, seawater temperatures have ever gone up this high only in limited areas in the seas around the world within certain seasons. Thus, the actual in-take seawater flow rate can be reduced, resulting in a large reduction of the required amount of electrical energy. This thesis investigates energy consumption reduction in seawater cooling pumps using variable frequency drives (VFDs) and throttle valves to supply continuously variable flow rates to a ship’s central cooling system. A pump characteristic curve is determined in this study to calculate the minimum flow rate of seawater cooling pumps for overcoming the friction losses in the pipe and the actual needs of seawater flow is learned by using thermal equilibrium calculation. Then, the seawater flows are substituted into the pump characteristic equation obtained from the simulation in order to calculate the energy consumption for seawater cooling pumps. In addition, the theoretical results obtained from this thesis are validated by an experiment of a small-scale ship cooling system and the energy-saving benefit of an actual voyage for a practical ship is theoretically assessed by applying the developed equations. Hopefully, the results obtained from this study can be used for ship design for future reference.

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.

This dissertation aims at developing techniques to achieve high power density in motor drives under the performance requirements for transportation system. Four main factors influencing the power density are the main objects of the dissertation: devices, passive components, pulse width modulation (PWM) methods and motor control methods. Firstly, the application of SiC devices could improve the power density of the motor drive. This dissertation developed a method of characterizing the SiC device performance in phase-leg with loss estimation, and claimed that with SiC Schottky Barrier Diode the advantage of SiC JFET could benefit the motor drive especially at high temperature. Then the design and improvement of the EMI filter in the active front-end rectifier of the motor drive was introduced in this dissertation. Besides the classical filter design method, the parasitic parameters in the passive filter could also influence the filtering performance. Random PWM could be applied to reduce the EMI noise peak value. The common-mode (CM) noise reduction by PWM methods is also studied in this dissertation. This dissertation compared the different PWM methods’ CM filtering performance. Considering the CM loop, the design of PWM methods and switching frequency should be together with the CM impedance. Variable switching frequency PWM (VSFPWM) methods are introduced in the dissertation for the motor drive’s EMI and loss improvement. The current ripple of the three-phase converter could be predicted. Then the switching frequency could be designed to adapt the current ripple requirements. Two VSFPWM methods are introduced to satisfy the ripple current peak and RMS value requirements. For motor control issue, this dissertation analyzed the principle of the start-up transient and proposed an improved start-up method. The transient was significantly reduced and the motor could push to high speed and high power with speed sensorless control. Next, the hardware development of modular motor drive was introduced. The development and modification of 10kW phase-legs and full power test of a typical 30kW modular converter is realized with modular design method. Finally, the techniques developed in this dissertation for high power density motor drive design and control are summarized and future works are proposed.

An electrostatic actuator driven by conventional voltage control and charge control requires high actuation voltage and suffers from the pull-in phenomenon that limits its operation range, much less than its entire gap. To provide effective solutions to these problems, we present complete analytical and numerical models of various electrostatic actuators coupled with resonant drive circuits that are able to drive electrostatic actuators at much lower input voltage than that of conventional actuation methods and to extend their operation range beyond their conventional pull-in points in the presence of high parasitic capacitance. Moreover, in order to validate the analytical and numerical models of various electrostatic actuators coupled with the resonant drive circuits, we perform the experiment on the microplate and the micromirror coupled with the resonant drive circuit. For instance, using a high voltage amplifier, we manage to rotate the micromirror with sidewall electrodes by 6 ° at 180 V. However, using the resonant drive circuit, we are able to rotate the same micromirror by 6 ° at much lower input voltage, 8.5 V. In addition, the presented work also facilitates the stability analysis of electrostatic actuators coupled with the resonant drive circuits and provides how the effect of the parasitic capacitance can be minimized. For example, the resonant drive circuit placed within a positive feedback loop of a variable gain amplifier is able to extend the operation range much further even in the presence of very high parasitic capacitance. The resonant drive circuit with the proposed feedback controllers is also able to minimize the detrimental effects of the parasitic capacitance and to displace a parallel-plate actuator over its entire gap without the saddle-node bifurcation. Finally, we present a new displacement measurement method of electrostatic actuators coupled with the resonant drive circuits by sensing the phase delay of an actuation voltage with respect to an input voltage. This new measurement method allows us to easily implement feedback control into existent systems employing an electrostatic actuator without any modification or alteration to the electrostatic actuator itself. Hence, this research work presents the feasibility of electrostatic actuators coupled with the resonant drive circuit in various industrial and medical applications, in which the advantages of miniaturization, low supply voltage, and low power consumption are greatly appreciated.

Indiana University-Purdue University Indianapolis (IUPUI)
The following thesis looks into modeling a chilled water system equipped with variable speed drives on different piece of equipment and optimization of system setpoints to achieve energy savings. The research was done by collecting data from a case-study and developing a system of component models that could be linked to simulate the overall system operation.

Dissertação de mestrado integrado em Engenharia Eletrónica Industrial e Computadores
Desde a revolução industrial do século XVIII que a rentabilidade depende, em grande parte, do volume de matéria produzido, que permite às empresas baixar preços e ser competitivas. Um equipamento vastamente utilizado na indústria mundial para movimentação de cargas, que atuam como agentes importantes numa linha de produção convencional, são as pontes rolantes e seus homólogos (pórticos, etc). Visto que o transporte de materiais é uma operação diária e não rentável, todo o tempo desperdiçado com esta tarefa é algo a evitar. Esta dissertação de mestrado é direcionada à agilização de processos e modernização destas máquinas. As principais áreas de interesse passam pela interatividade entre a máquina e o utilizador, a soma de cargas entre múltiplos diferenciais e a integração de inversores de frequência. Inerente a estes pontos espera-se um aumento da fiabilidade da máquina e alerta para a responsabilidade que o movimento de grandes materiais implica. Este projeto realizou-se na empresa Norcranes - Equipamentos, Lda [1], fabricante nacional de pontes rolantes, sediada no concelho da Trofa.
Since the industrial revolution that took place in the 18th century profit relies significantly on the amount of matter produced which allows companies to low their prices and get competitive. A widely used equipment in world’s industry to load transportation, that plays as a key element on a traditional production line, are cranes and its counterparts (gantries, etc). Since material transportation is a daily task and a non-profitable one, every second spent doing it is something to avoid. This master’s thesis is oriented to the processes streamlining and cranes renewal. The main fields of interest are the Human-Machine interactivity, load sum between multiple hoists and variable frequency drives integration. Inherent to those topics, it’s expected to increase machine reliability and alert about the responsabilty that movement of big dimensions materials involves. This project was developed in Norcranes - Equipamentos, Lda, national manufacturer of cranes, headquartered in Trofa.