Articles de revues : « MRAS TECHNIQUE »

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Ghany, M. A. Abdel, et Mohamed A. Shamseldin. « Model reference self-tuning fractional order PID control based on for a power system stabilizer ». International Journal of Power Electronics and Drive Systems (IJPEDS) 11, n^o 3 (1 septembre 2020) : 1333. http://dx.doi.org/10.11591/ijpeds.v11.i3.pp1333-1343.

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This paper presents a novel approach of self-tuning for a Modified Fractional Order PID (MFOPID) depends on the Model Reference Adaptive System (MRAS). The proposed self-tuning controller is applied to Power System Stabilizer (PSS). Takaji-Sugeno (TS) fuzzy logic technique is used to construct the MFOPID controller. The objective of MRAS is to update the five parameters of Takaji-Sugeno Modified FOPID (TSMFOPID) controller online. For different operating points of PSS, MRAS is applied to investigate the effectiveness of proposed controllers. The harmony optimization technique used to obtain the optimal parameters of TSMFOPID controllers and MRAS parameters. For different operating points with different disturbance under parameters variations the simulation results are obtained. This is to show that Self-Tuning of TSMFOPID based on (MRAS) have better performance than the fixed parameters TSMOFOPID controller.

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Qu, Zhi Yong, et Zheng Mao Ye. « Speed Regulation of a Permanent Magnet Synchronous Motor via Model Reference Adaptive Control ». Advanced Materials Research 268-270 (juillet 2011) : 513–16. http://dx.doi.org/10.4028/www.scientific.net/amr.268-270.513.

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A speed estimation technique for the permanent magnet synchronous motor drive is presented in this paper A Model Reference Adaptive System (MRAS) has been formed using the voltage and current to estimate the speed. It has been shown that such unique MRAS offers several desirable features. The proposed technique is completely independent of stator resistance and is less parameter sensitive, as the estimation-algorithm is only dependent on q-axis stator inductance. Also, the method requires less computational effort as the simplified expressions are used in the MRAS. The stability of the proposed system is achieved through Popov’s Hyperstability criteria. Matlab simulation results are presented to validate the proposed technique.

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R, Mini, Shabana Backer P., B. Hariram Satheesh et Dinesh M. N. « Low Speed Estimation of Sensorless DTC Induction Motor Drive Using MRAS with Neuro Fuzzy Adaptive Controller ». International Journal of Electrical and Computer Engineering (IJECE) 8, n^o 5 (1 octobre 2018) : 2691. http://dx.doi.org/10.11591/ijece.v8i5.pp2691-2702.

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This paper presents a closed loop Model Reference Adaptive system (MRAS) observer with artificial intelligent Nuero fuzzy controller (NFC) as the adaptation technique to mitigate the low speed estimation issues and to improvise the performance of the Sensorless Direct Torque Controlled (DTC) Induction Motor Drives (IMD). Rotor flux MRAS and reactive power MRAS with NFC is explored and detailed analysis is carried out for low speed estimation. Comparative analysis between rotor flux MRAS and reactive power MRAS with PI as well as NFC as adaptive controller is performed and results are presented in this paper. The comparative analysis among these four speed estimation methods shows that reactive power MRAS with NFC as adaptation mechanism shows reduced speed estimation error and actual speed error at steady state operating conditions when the drive is subjected to low speed operation. Simulation carried out using MATLAB-Simulink software to validate the performance of the drive especially at low speeds with rated and variable load conditions.

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Yang, Li Yong, et Liu Shuo. « Parameter Tuning for Sensorless Induction-Motor Drive Use Stator-Current-Based MRAS Estimator ». Advanced Materials Research 383-390 (novembre 2011) : 352–57. http://dx.doi.org/10.4028/www.scientific.net/amr.383-390.352.

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This paper proposes an analysis of the vector-controlled induction-motor (IM) drive with a novel modelreference adaptive system (MRAS)-type rotor speed estimator .In this scheme which stator-current-error-based MRAS is used instead of the rotor-ﬂux-error-based MRAS scheme,an stator-current-error-based MRAS is used for estimate the IM rotor speed ,and this is used as feedback signals for the indirect field oriented control technique (IFOC),which is a widely used control method for Induction Motor drive (IM). For improving the dynamic characteristic of the system, it is very improtant for vector control to proceed parameter tuning.Some experimental results based on TMS 320F2812 DSP are provided to verify the proposed system performance in a low speed at no-load and load conditions.

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Asfu, Workagegn Tatek. « Stator Current-Based Model Reference Adaptive Control for Sensorless Speed Control of the Induction Motor ». Journal of Control Science and Engineering 2020 (14 octobre 2020) : 1–17. http://dx.doi.org/10.1155/2020/8954704.

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This paper described that the stator current-based model reference adaptive system (MRAS) speed estimator is used for the induction motor (IM) indirect vector speed control without a mechanical speed sensor. Due to high sensitivity of motor parameters variation at low speed including zero, stability analysis of MRAS design is performed to correct any mismatch parameters value in the MRAS performed to estimate the motor speed at these values. As a result, the IM sensorless control can operate over a wide range including zero speed. The performance of the stator current-based MRAS speed estimator was analyzed in terms of speed tracking capability, torque response quickness, low speed behavior, step response of drive with speed reversal, sensitivity to motor parameter uncertainty, and speed tracking ability in the regenerative mode. The system gives a good performance at no-load and loaded conditions with parameter variation. The stator current-based MRAS estimator sensorless speed control technique can make the hardware simple and improve the reliability of the motor without introducing a feedback sensor, and it becomes more important in the modern AC IM. The sensorless vector control operation has been verified by simulation on Matlab and experimentally using Texas Instruments HVMTRPFCKIT with TMS320 F28035 DSP card and 0.18 kw AC IM.

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Ho, Sang Dang, Petr Palacky, Martin Kuchar, Pavel Brandstetter et Cuong Dinh Tran. « Particle swarm optimization-based stator resistance observer for speed sensorless induction motor drive ». International Journal of Electrical and Computer Engineering (IJECE) 11, n^o 1 (1 février 2021) : 815. http://dx.doi.org/10.11591/ijece.v11i1.pp815-826.

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This paper presents a different technique for the online stator resistance estimation using a particle swarm optimization (PSO) based algorithm for rotor flux oriented control schemes of induction motor drives without a rotor speed sensor. First, a conventional proportional-integral controller-based stator resistance estimation technique is used for a speed sensorless control scheme with two different model reference adaptive system (MRAS) concepts. Finally, a novel method for the stator resistance estimation based on the PSO algorithm is presented for the two MRAS-type observers. Simulation results in the Matlab/Simulink environment show good adaptability of the proposed estimation model while the stator resistance is varied to 200% of the nominal value. The results also confirm more accurate stator resistance and rotor speed estimation in comparison with the conventional technique.

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Kumar Samal, Sidhartha, Smrutisikha Jena, Bibhu Prasad Ganthia, S. Kaliappan, M. Sudhakar et S. K. Sriram Kalyan. « Sensorless Speed Contorl of Doubly-Fed Induction Machine Using Reactive Power Based MRAS ». Journal of Physics : Conference Series 2161, n^o 1 (1 janvier 2022) : 012069. http://dx.doi.org/10.1088/1742-6596/2161/1/012069.

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Abstract A sensorless speed control method for doubly-fed induction machine (DFIM) operating with constant frequency but in variable speed mode is presented in this project work. The control method is based on rotor speed estimation technique by a reactive power model reference adaptive system (MRAS) observer. The presented technique does not depend on any kind of flux evaluation and also independent to the resistance variation of either stator or rotor. The MRAS observer has a capacity for speed catching operation. PI controller is designed and also optimized using algorithm for better dynamic behaviour of the machine. MATLAB Simulink model and the simulation results are shown to check the effectiveness of the observer and also of the controller.

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Sedhuraman, K., S. Himavathi et A. Muthuramalingam. « Neural learning adaptive system using simplified reactive power reference model based speed estimation in sensorless indirect vector controlled induction motor drives ». Archives of Electrical Engineering 62, n^o 1 (1 mars 2013) : 25–41. http://dx.doi.org/10.2478/aee-2013-0003.

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Abstract This paper presents a novel speed estimator using Reactive Power based Model Reference Neural Learning Adaptive System (RP-MRNLAS) for sensorless indirect vector controlled induction motor drives. The Model Reference Adaptive System (MRAS) based speed estimator using simplified reactive power equations is one of the speed estimation method used for sensor-less indirect vector controlled induction motor drives. The conventional MRAS speed estimator uses PI controller for adaptation mechanism. The nonlinear mapping capability of Neural Network (NN) and the powerful learning algorithms have increased the applications of NN in power electronics and drives. This paper proposes the use of neural learning algorithm for adaptation in a reactive power technique based MRAS for speed estimation. The proposed scheme combines the advantages of simplified reactive power technique and the capability of neural learning algorithm to form a scheme named “Reactive Power based Model Reference Neural Learning Adaptive System” (RP-MRNLAS) for speed estimator in Sensorless Indirect Vector Controlled Induction Motor Drives. The proposed RP-MRNLAS is compared in terms of accuracy, integrator drift problems and stator resistance versions with the commonly used Rotor Flux based MRNLAS (RF-MRNLAS) for the same system and validated through Matlab/Simulink. The superiority of the RP-MRNLAS technique is demonstrated.

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SAIHI, Lakhdar, Youcef Bakou, Fateh Ferroudji, Abdelkader Hadidi et Ibrahim Oulimar. « A Hybrid H∞-MRAS Observer of Wind Turbines Conversion Systems based on DFIG ». Algerian Journal of Renewable Energy and Sustainable Development 4, n^o 01 (15 juin 2022) : 101–10. http://dx.doi.org/10.46657/ajresd.2022.4.1.10.

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This study proposes the robust sensor-less advanced frequency control (robust H∞ control) of the system of wind turbine based on a doubly fed induction generator (DFIG), the power exchange between the machine stator and the network is achieved by applying the rotor of DFIG via a bidirectional converter. The purpose of the control is to regulate the stator active and reactive power produced by the DFIG using a robust H∞ controller. The Model reference and adaptive system (MRAS-Observer) uses the error between the actual and estimated values (voltage/current) to construct the observed mechanical parameters (speed and position) value, this technique uses two separate models: the first is the reference model, the second is the adjustable mode. The error between these models is used by the adaptive mechanism. The adjustment mechanism is mostly a PI controller, to improve the performance and robustness of the classical MRAS observer, we replace the classical PI controller with a robust H∞ controller. The results simulations confirm the robustness of the sensorless robust H∞ control using the H∞-MRAS observer compared to conventional MRAS, which improves the quality and quantity of generated power.

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Fnaiech, Mohamed Amine, Jaroslaw Guzinski, Mohamed Trabelsi, Abdellah Kouzou, Mohamed Benbouzid et Krzysztof Luksza. « MRAS-Based Switching Linear Feedback Strategy for Sensorless Speed Control of Induction Motor Drives ». Energies 14, n^o 11 (26 mai 2021) : 3083. http://dx.doi.org/10.3390/en14113083.

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This paper presents a newly designed switching linear feedback structure of sliding mode control (SLF-SMC) plugged with an model reference adaptive system (MRAS) based sensorless field-oriented control (SFOC) for induction motor (IM). Indeed, the performance of the MRAS depends mainly on the operating point and the parametric variation of the IM. Hence, the sliding mode control (SMC) could be considered a good control alternative due to its easy implementation and robustness. Simulation and experimentation results are presented to show the superiority of the proposed SLF-SMC technique in comparison with the classical PI controller under different speed ranges and inertia conditions.

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A. Mossa, Mahmoud, Hamdi Echeikh et Alfian Ma’arif. « Dynamic Performance Analysis of a Five-Phase PMSM Drive Using Model Reference Adaptive System and Enhanced Sliding Mode Observer ». Journal of Robotics and Control (JRC) 3, n^o 3 (1 mai 2022) : 289–308. http://dx.doi.org/10.18196/jrc.v3i3.14632.

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This paper aims to evaluate the dynamic performance of a five-phase PMSM drive using two different observers: sliding mode (SMO) and model reference adaptive system (MRAS). The design of the vector control for the drive is firstly introduced in details to visualize the proper selection of speed and current controllers’ gains, then the construction of the two observers are presented. The stability check for the two observers are also presented and analyzed, and finally the evaluation results are presented to visualize the features of each sensorless technique and identify the advantages and shortages as well. The obtained results reveal that the de-signed SMO exhibits better performance and enhanced robustness compared with the MRAS under different operating conditions. This fact is approved through the obtained results considering a mismatch in the values of stator resistance and stator inductance as well. Large deviation in the values of estimated speed and rotor position are observed under MRAS, and this is also accompanied with high speed and torque oscillations.

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Irie, Ryusuke, Shiori Amemiya, Tsuyoshi Ueyama, Yuichi Suzuki, Kouhei Kamiya, Hidemasa Takao, Harushi Mori et Osamu Abe. « Accelerated acquisition of carotid MR angiography using 3D gradient-echo imaging with two-point Dixon ». Neuroradiology 62, n^o 10 (18 mai 2020) : 1345–49. http://dx.doi.org/10.1007/s00234-020-02452-6.

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Abstract This pilot study tests the feasibility of rapid carotid MR angiography using the liver acquisition with volume acceleration-flex technique (LAVA MRA). Seven healthy volunteers and 21 consecutive patients suspected of carotid stenosis underwent LAVA and conventional time-of-flight (cTOF) MRAs. Artery-to-fat and artery-to-muscle signal intensity ratios were manually measured. LAVA MRA exhibited a significantly larger artery-to-fat signal intensity ratio compared with cTOF MRA in all slices (P < 0.001) and exhibited a larger (P < 0.001) or equivalent (P = 1.0) artery-to-muscle signal intensity ratio in the extracranial carotid arteries. The image quality of the cervical carotid bifurcation and the signal change on each MRA were visually assessed and compared among the MRAs. There was no significant difference between the two MRAs in visual assessment. LAVA MRA can provide visualization similar to cTOF MRA in the evaluation of the cervical carotid bifurcation while reducing scan time by one-fifth.

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Xu, Kai, et Shanchao Liu. « Speed-Sensorless Vector Control Based on ANN MRAS for Induction Motor Drives ». Journal of Advanced Computational Intelligence and Intelligent Informatics 19, n^o 1 (20 janvier 2015) : 127–33. http://dx.doi.org/10.20965/jaciii.2015.p0127.

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In the speed-sensorless induction motor drives system, Model Reference Adaptive System (MRAS) is the most common strategy. However, speed estimation using reactive power based MRAS has the problem of instability in the regenerating mode of operation. Such estimation technique is simple and has several notable advantages, but is not suitable for induction motor drives. To overcome these problems, a suitable Artificial Neural Networks (ANN) is presented to replace the adjustable model to make the system stable when working at low speed and zero crossing. Simultaneously, in order to enhance the ANN convergence speed and avoid the trap of local minimum value of algorithm, we used themodified Particle Swarm Optimization (PSO) to optimize the weights and threshold values of neural networks. Then the ANN-based MRAS was used to identify the speed of motor in the indirect vector control system. The results of the simulation show that, by this method, the speed of motor can be identified accurately in different situations, and the result is reliable.

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Stando, Dariusz, et Marian P. Kazmierkowski. « Simple Technique of Initial Speed Identification for Speed-Sensorless Predictive Controlled Induction Motor Drive ». Power Electronics and Drives 5, n^o 1 (1 janvier 2020) : 189–98. http://dx.doi.org/10.2478/pead-2020-0014.

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Abstract This article presents a simple technique of identifying the initial speed that allows for restarting a sensorless induction motor (IM) drive controlled by a model predictive flux control (MPFC). Initial speed identification is required because, according to the research, the applied current-model reference adaptive system (C-MRAS) can restart the IM after failure only if the error of the initial speed set in the estimator is <25%. The proposed technique is based on short periods of flux generation for the certain initial speed and observation of the estimated torque respond. The direction of the estimated torque determines whether the real speed is higher or lower than the initial one set in the estimator. In two steps, the algorithm identifies the initial speed with an accuracy of 25%. This allows for a quick restart of the IM from any speed, eliminating the disadvantage of the sensorless drive control system with the C-MRAS speed estimator. The experimental results measured on a 50 kW drive which illustrates the operation and performances of the system are presented.

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Lee, Dong-Myung. « On-line parameter identification of SPM motors based on MRAS technique ». International Journal of Electronics 104, n^o 4 (22 août 2016) : 593–607. http://dx.doi.org/10.1080/00207217.2016.1220635.

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Halvaei Niasar, Abolfazl, et Hossein Rahimi Khoei. « Sensorless Direct Power Control of Induction Motor Drive Using Artificial Neural Network ». Advances in Artificial Neural Systems 2015 (30 mars 2015) : 1–9. http://dx.doi.org/10.1155/2015/318589.

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This paper proposes the design of sensorless induction motor drive based on direct power control (DPC) technique. It is shown that DPC technique enjoys all advantages of pervious methods such as fast dynamic and ease of implementation, without having their problems. To reduce the cost of drive and enhance the reliability, an effective sensorless strategy based on artificial neural network (ANN) is developed to estimate rotor’s position and speed of induction motor. Developed sensorless scheme is a new model reference adaptive system (MRAS) speed observer for direct power control induction motor drives. The proposed MRAS speed observer uses the current model as an adaptive model. The neural network has been then designed and trained online by employing a back propagation network (BPN) algorithm. The estimator was designed and simulated in Simulink. Some simulations are carried out for the closed-loop speed control systems under various load conditions to verify the proposed methods. Simulation results confirm the performance of ANN based sensorless DPC induction motor drive in various conditions.

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Xu, Bowen, Jien Ma, Qiyi Wu, Lin Qiu, Xing Liu, Chao Luo et Youtong Fang. « Sensorless Control Strategy of Novel Axially Magnetized Vernier Permanent-Magnet Machine ». Energies 15, n^o 15 (28 juillet 2022) : 5470. http://dx.doi.org/10.3390/en15155470.

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Vernier permanent-magnet machines have been attracted more and more attention because of their high torque density. In this paper, the sensorless control strategy of the novel axially magnetized Vernier permanent-magnet (AMVPM) machine is presented. First, the inductance non-linearity is investigated under different load conditions. Second, the mathematical model is established in cooperation with the finite element method. After that, the back electromotive force based sensorless control strategy is developed according to the state equation of the motor. In the sensorless drive, the model reference adaptive system (MRAS) technique incorporated with the inductance non-linearity is used for the speed estimation. The modified control strategy not only increases the stability but also improves the dynamic response of the system. Finally, the simulation results show that the modified MRAS is of high estimation precision, and the AMVPM machine can be well controlled, and the experimental results validated the theoretical design process.

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Mabrouk, Haddar, et Allaoua Boumediene. « An efficient predictive current controller with adaptive parameter estimation in 3-ϕ inverter ». International Journal of Power Electronics and Drive Systems (IJPEDS) 12, n^o 2 (1 juin 2021) : 858. http://dx.doi.org/10.11591/ijpeds.v12.i2.pp858-869.

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In this paper, a detail design and description of a predictive current control scheme are adopted for three-phase grid-connected two-level inverter and its application in wind energy conversion systems. Despite its advantages, the predictive current controller is very sensitive to parameter variations which could eventually affected on system stability. To solve this problem, an estimation technique proposed to identify the value of harmonic filter parameter based on Model reference adaptive system (MRAS). Lyapunov stability theory is selected to guarantee a robust adaptation and stable response over large system parameter variation. The simulation results shows the efficiency of the proposed techniques to improve the current tracking performance.

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Sedhuraman, K., S. Himavathi et A. Muthuramalingam. « Reactive Power based Model Reference Neural Learning Adaptive System for Speed Estimation in Sensor-less Induction Motor Drives ». Journal of Engineering Research [TJER] 9, n^o 2 (1 décembre 2012) : 17. http://dx.doi.org/10.24200/tjer.vol9iss2pp17-26.

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In this paper, a novel reactive power based model reference neural learning adaptive system (RP-MRNLAS) is proposed. The model reference adaptive system (MRAS) based speed estimation is one of the most popular methods used for sensor-less controlled induction motor drives. In conventional MRAS, the error adaptation is done using a Proportional-integral-(PI). The non-linear mapping capability of a neural network (NN) and the powerful learning algorithms have increased the applications of NN in power electronics and drives. Thus, a neural learning algorithm is used for the adaptation mechanism in MRAS and is often referred to as a model reference neural learning adaptive system (MRNLAS). In MRNLAS, the error between the reference and neural learning adaptive models is back propagated to adjust the weights of the neural network for rotor speed estimation. The two different methods of MRNLAS are flux based (RF-MRNLAS) and reactive power based (RP-MRNLAS). The reactive power- based methods are simple and free from integral equations as compared to flux based methods. The advantage of the reactive power based method and the NN learning algorithms are exploited in this work to yield a RPMRNLAS. The performance of the proposed RP-MRNLAS is analyzed extensively. The proposed RP-MRNLAS is compared in terms of accuracy and integrator drift problems with popular rotor flux-based MRNLAS for the same system and validated through Matlab/Simulink. The superiority of the RP- MRNLAS technique is demonstrated

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Sogawa, Keiji, Yoichi Kikuchi, Toshihiro O'Uchi, Michihiro Tanaka et Tomio Inoue. « Fenestrations of the Basilar Artery Demonstrated on Magnetic Resonance Angiograms : An Analysis of 212 Cases ». Interventional Neuroradiology 19, n^o 4 (décembre 2013) : 461–65. http://dx.doi.org/10.1177/159101991301900409.

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Fenestration of the basilar artery (BA) is a rare variant of the intracranial artery, well demonstrated in autopsy and angiographic studies. Some angiographic series show a high incidence of associated aneurysms at the basilar fenestration site. The purpose of this study is to report the incidence of BA fenestration, its configurations, associated aneurysms, and arterial anomalies in a large series of intracranial MR angiograms (MRAs). A total of 16,416 MRAs were retrospectively reviewed to identify the location, size and associated intracranial arterial anomalies of BA fenestrations. All images were obtained with the time-of-flight (TOF) technique. Of the 16,416 MRAs, 215 fenestrations were found in 212 cases (1.29%). Most fenestrations were located in the proximal BA. The average length of the fenestration was 4.6 mm; the largest was 15.6 mm. No aneurysm was found at the site of the fenestration. Thirteen aneurysms were found in nine cases at locations other than the BA: seven in the middle cerebral artery (MCA), one in the anterior cerebral artery (ACA), one in the anterior communicating artery (Acom), one in the vertebral artery (VA), one at the carotid siphon, and two at the internal carotid-posterior communicating artery (IC-PC). Arterial anomalies in other locations were found in 26 cases. BA fenestrations were found in 1.29% of the 16,416 cases studied. There were no aneurysms at the BA fenestration site. Aneurysms at the BA fenestration site may be an exceedingly rare phenomenon.

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Soni, Sujeet Kumar, Manish Khemariya et Anand Singh. « Sensorless Speed Control of Induction Machine with Adaptive-Neuro Fuzzy Technique Integrated MRAS Module ». International Journal of Engineering Trends and Technology 70, n^o 7 (31 juillet 2022) : 405–13. http://dx.doi.org/10.14445/22315381/ijett-v70i7p242.

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Gutzeit, Andreas, Boris Eckhardt, Jan Beranek, Klaus U. Wentz, Edwin Willemse, Regula Jenelten, Christoph A. Binkert et Johannes M. Froehlich. « Clinical Experience in Timed Arterial Compression Contrast-enhanced Magnetic Resonance Angiography of the Hand ». Canadian Association of Radiologists Journal 61, n^o 4 (octobre 2010) : 206–16. http://dx.doi.org/10.1016/j.carj.2009.11.005.

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Purpose A retrospective analysis of the diagnostic performance of the timed arterial compression (TAC) technique, which allows freezing of the contrast bolus during first-pass contrast-enhanced (CE) magnetic resonance angiography (MRA) to diagnose vascular pathologies in the hand. Material and Methods A total of 14 consecutive CE-MRAs of the hand were acquired by using the TAC technique. By inflating a blood pressure cuff up to 200 mm Hg triggered to the arterial contrast filling of the hand, prolonged measurement times up to 144 seconds, with a spatial resolution of 0.59 × 0.59 × 0.8 mm3, could be realized. Overall image qualities, arterial signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and vessel conspicuity besides the final diagnosis were evaluated. Results All 14 TAC-CE-MRAs of the hand were successfully accomplished without any adverse events and yielded, in all cases, a final diagnosis with a high total number of vascular pathologies (57). High arterial SNR and CNR values exceeding the soil of 85 and 60, respectively, resulted. Thus, overall vessel visibility (>90%), vessel conspicuity (mean Δ signal intensity [SI]/mm = 1,193) and image quality on a per patient level (>60%) were rated as excellent or good. Conclusions TAC-CE-MRA of the hand offers high diagnostic performance because of its increased spatial resolution while preserving contrast, which allowed detection of tiny stenoses of the digital arteries.

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Mohammed, Inas Jabbar. « The Active Direct Torque Control of an Induction Motor based on an Artificial Neural Network ». NeuroQuantology 20, n^o 4 (30 avril 2022) : 522–30. http://dx.doi.org/10.14704/nq.2022.20.4.nq22333.

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In this paper, a method is developed to control the induction motor IM using direct torque control (DTC), by means of artificial neural networks (ANN), in order to reach the optimum performance .And then using the MRAS technique, the desired and efficient control of the rotor speed could be estimated and achieved. The design uses the individual training technique with the fixed weight and the controlled models to avoid the difficult DTC calculation. A specific comparison analysis was conducted between both the control for direct torque neural networks (DTNNC) and conventional direct torque control (CDTC) applied to select voltage vector switching. The chassis was designed by Matlab / Simul for DTC.

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Utrata, Grzegorz, et Jaroslaw Rolek. « The Induction Motor MRAS-Based Speed Estimator Capable of Modelling the Slip Frequency Dependent Variability of the Rotor Impedance ». Energies 16, n^o 6 (9 mars 2023) : 2591. http://dx.doi.org/10.3390/en16062591.

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Speed feedback is indispensable not only for closed-loop controlled induction motors (IM) but also for the state monitoring systems of open-loop controlled IMs. Replacing speed sensors with speed estimations has many advantages including, e.g., hardware complexity reduction, sensor cabling elimination, and reduction of IM drive costs. From the various methods for IM speed estimation proposed in the literature, the model reference adaptive system (MRAS)-based speed estimator stands out because of its straightforward synthesis technique and lower computational complexity. On the other hand, this estimator is inherently sensitive to mismatching of IM equivalent circuit parameters. During transients, when the slip frequency cannot be temporarily controlled over the assumed operating point, rotor impedance varies with the slip frequency changes. This phenomenon is even more significant for open-loop controlled high-slip IMs (NEMA design D IMs), which operate under the cycling load like in, e.g., oil well pumps. The rate and the range of rotor impedance variability are related to the rate and the range of the slip frequency changes. Therefore, a speed estimator capable of modelling the slip frequency dependent variability of the rotor impedance may be required, particularly for the state monitoring systems of open-loop controlled IMs. This paper presents an MRAS-based speed estimator developed on the IM space vector model with the rotor impedance variability modelled by the parallel connected branches of the series rotor equivalent resistance and leakage inductance. The experimental test results confirm the precise speed estimation of the tested IMs achieved by the devised MRAS-based speed estimator in the considered slip frequency range and indicate its potential industrial application.

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Antar, Rakan Kh, et Ahmed A. Allu. « Sensorless Speed/Torque Control of DC Machine Using Artificial Neural Network Technique ». Tikrit Journal of Engineering Sciences 23, n^o 3 (31 août 2016) : 55–62. http://dx.doi.org/10.25130/tjes.23.3.06.

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In this paper, Artificial Neural Network (ANN) technique is implemented to improve speed and torque control of a separately excited DC machine drive. The speed and torque sensorless scheme based on ANN is estimated adaptively. The proposed controller is designed to estimate rotor speed and mechanical load torque as a Model Reference Adaptive System (MRAS) method for DC machine. The DC drive system consists of four quadrant DC/DC chopper with MOSFET transistors, ANN, logic gates and routing circuits. The DC drive circuit is designed, evaluated and modeled by Matlab/Simulink in the forward and reverse operation modes as a motor and generator, respectively. The DC drive system is simulated at different speed values (±1200 rpm) and mechanical torque (±7 N.m) in steady state and dynamic conditions. The simulation results illustrate the effectiveness of the proposed controller without speed or torque sensors.

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Said, Legrioui, Rezgui Salah Eddine et Benalla Hocine. « Exponential Reaching Law and Sensorless DTC IM Control with Neural Network Online Parameters Estimation based on MRAS ». IAES International Journal of Robotics and Automation (IJRA) 7, n^o 2 (1 juin 2018) : 77. http://dx.doi.org/10.11591/ijra.v7i2.pp77-86.

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The most important problem in the control of induction machine (IM) is the change of its parameters, especially the stator resistance and rotor-time constant. The objective of this paper is to implement a new strategy in sensorless direct torque control (DTC) of an IM drive. The rotor flux based model reference adaptive system (MRAS) is used to estimate conjointly the rotor speed, the stator resistance and the inverse rotor time constant, the process of the estimation is performed on-line by a new MRAS-based artificial neural network (ANN) technique. Furthermore, the drive is complemented with a new exponential reaching law (ERL), based on the sliding mode control (SMC) to significantly improve the performances of the system control compared to the conventional SMC which is known to be susceptible to the annoying chattering phenomenon. An experimental investigation was carried out via the Matlab/Simulink with real time interface (RTI) and dSPACE (DS1104) board where the behavior of the proposed method was tested at different points of IM operation.

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Bouslimani, Samir, Samir Meradi, Said Drid, Larbi Chrifi-Alaoui et Ali Bezziane. « State Estimation MRAS and Identification of Stator Winding Phase Fault Detection of the PMSG in Wind Energy Based on the Sliding Mode Control ». Power Electronics and Drives 8, n^o 1 (1 janvier 2023) : 109–27. http://dx.doi.org/10.2478/pead-2023-0009.

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Abstract This paper proposes a method for the diagnosis of stator inter-turn short-circuit fault for permanent magnet synchronous generators (PMSG). Inter-turn short-circuit currents are among the most critical in PMSG. For safety considerations, a fast detection is required when a fault occurs. This approach uses the parameter estimation of the per-phase stator resistance in closed-loop control of variable speed of wind energy conversion system (WECS). In the presence of an incipient short-circuit fault, the estimation of the resistance of the stator in the d-q reference frame does not make it possible to give the exact information. To solve this problem, a novel fault diagnosis scheme is proposed using parameter estimation of the per-phase stator resistance. The per-phase stator resistance of PMSG is estimated using the MRAS algorithm technique in real time. Based on a faulty PMSG model expressed in Park’s reference frame, the number of short-circuited turns is estimated using MRAS. Fault diagnosis is on line detected by analysing the estimated stator resistance of each phase according to the fault condition. The proposed fault diagnosis scheme is implemented without any extra devices. Moreover, the information on the estimated parameters can be used to improve the control performance. The simulation results demonstrate that the proposed method can estimate the faulty phase.

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Prince et Ananda Shankar Hati. « TEMPERATURE AND HUMIDITY DEPENDENT MRAS BASED SPEED ESTIMATION TECHNIQUE FOR INDUCTION MOTOR USED IN MINE VENTILATION DRIVE ». Физико-технические проблемы разработки полезных ископаемых, n^o 5 (2021) : 150–59. http://dx.doi.org/10.15372/ftprpi20210514.

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Prince et Ananda Shankar Hati. « Temperature and Humidity Dependent MRAS Based Speed Estimation Technique for Induction Motor Used in Mine Ventilation Drive ». Journal of Mining Science 57, n^o 5 (septembre 2021) : 842–51. http://dx.doi.org/10.1134/s1062739121050148.

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Reddy, C. Upendra, Kashyap Kumar Prabhakar, Amit Kumar Singh et Praveen Kumar. « Speed Estimation Technique Using Modified Stator Current Error-Based MRAS for Direct Torque Controlled Induction Motor Drives ». IEEE Journal of Emerging and Selected Topics in Power Electronics 8, n^o 2 (juin 2020) : 1223–35. http://dx.doi.org/10.1109/jestpe.2019.2901523.

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Benmohamed, F. E., I. K. Bousserhane, A. Kechich, B. Bessaih et A. Boucheta. « New MRAS secondary time constant tuning for vector control of linear induction motor considering the end-effects ». COMPEL - The international journal for computation and mathematics in electrical and electronic engineering 35, n^o 5 (5 septembre 2016) : 1685–723. http://dx.doi.org/10.1108/compel-07-2015-0263.

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Purpose The end-effects is a well-recognized phenomenon occurring in the linear induction motor (LIM) which makes the analysis and control of the LIM with good performance very difficult and can cause additional significant non-linearities in the model. So, the compensation of parameters uncertainties due to these effects in the control system is very necessary to get a robust speed control. The purpose of this paper is to propose a new technique of LIM end-effects estimation using the inverse rotor time constant tuning in order to compensate the flux orientation error in the indirect field-oriented control (IFOC) control law. Design/methodology/approach First, the dynamic model of the LIM taking into consideration the end-effects based on Duncan model is derived. Then, the IFOC for LIM speed control with end-effects compensation is derived. Finally, a new technique of LIM end-effects estimation is proposed based on the model reference adaptive system (MRAS) theory using the instantaneous active power and the estimated stator currents vector. These estimated currents are obtained through the solution of LIM state equations. Findings Simulations were carried out in MATLAB/SIMULINK to demonstrate the effectiveness and robustness of LIM speed control with the proposed MRAS inverse rotor time constant tuning to estimate end-effects value. The numerical validation results show that the proposed scheme permits the drive to achieve good dynamic performance, satisfactory for the estimated end-effects of the LIM model and robustness to uncertainties. Originality/value The end-effects causes a drop in the magnetizing, primary and the secondary inductance, requiring a more complex LIM control scheme. This paper presents a new approach of LIM end-effect estimation based on the online adaptation and tuning of the LIM inductances. The proposed scheme use the inverse rotor time constant tuning for end-effects correction in LIM vector control block.

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Donga, Kan, Li Jun Diaob, Da Nan Sun, Bai Shui Ruan et Zhi Gang Liu. « MRAS-Based Rotor Time Constant Estimation for Indirect Vector Controlled Induction Motor Drive ». Advanced Materials Research 433-440 (janvier 2012) : 6812–18. http://dx.doi.org/10.4028/www.scientific.net/amr.433-440.6812.

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Decoupling the stator current into magnetizing current and torque current, the vector control technique improves the performance of AC drive system effectively. However, the rotor time constant varies widely with rotor temperature and the flux level of the machine, which decreases the quality of the drive system. By the contrastive analysis of the variable current on-line estimation methods, this paper uses the Model Reference Adaptive System (MRAS) and designs a set of self-adaption estimation arithmetic which has its basis on the Lyapunov theorem of stability. The simulation shows that the estimation arithmetic has the characteristics of fast convergence speed, few stability errors, good track performance and etc. On the basis of simulation of the rotor time constant on-line estimation, this paper designs the system of vector control with the rotor time constant on-line estimation and has the simulation. According to the simulation results, applying the estimation to the vector control system can improve the performance of the system effectively and establish the theoretical basis of the research on the high-performance AC drive system.

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A. Mossa, Mahmoud, Houari Khouidmi et Alfian Ma’arif. « Robust Flux and Speed State Observer Design for Sensorless Control of a Double Star Induction Motor ». Journal of Robotics and Control (JRC) 3, n^o 4 (1 juillet 2022) : 464–75. http://dx.doi.org/10.18196/jrc.v3i4.15667.

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In this paper, a robust flux and speed observer for sensorless control of a double star induction motor is presented. Proper operation of vector control of the double star induction motor requires reliable information from the process to be controlled. This information can come from mechanical sensors (rotational speed, angular position). Furthermore, mechanical flux and speed sensors are generally expensive and fragile and affect the reliability of the system. However, the control without sensors must-have performance that does not deviate too much from that which we would have had with a mechanical sensor. In this framework, this work mainly deals with the estimation of the flux and speed using a robust state observer in view of sensorless vector control of the double star induction motor. The evaluation criteria are the static and dynamic performances of the system as well as the errors between the reference values and those estimated. Extensive simulation results and robustness tests are presented to evaluate the performance of the proposed sensorless control scheme. Furthermore, under the same test conditions, a detailed comparison between the proposed state observer and the sliding mode-MRAS technique is carried out where the results of its evaluation are investigated in terms of their speed and flux tracking capability during load and speed transients and also with parameter variation. It is worth mentioning that the proposed state observer can obtain both high current quality and low torque ripples, which show better performance than that in the MRAS system.

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Singh, Shweta, A. N. Tiwari et Sri N. Singh. « Performance Analysis of Sensor-based and Sensorless Methods for PMSM Drive ». Recent Advances in Electrical & ; Electronic Engineering (Formerly Recent Patents on Electrical & ; Electronic Engineering) 13, n^o 3 (18 mai 2020) : 304–15. http://dx.doi.org/10.2174/2352096512666190311162605.

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Objective: Permanent Magnet Synchronous Motor (PMSM) drives require speed/position information for the efficient performance of industrial applications. Methods: A sensor-based method utilizes sensors for extracting this information which increases weight, size, and cost of the drive system, whereas the sensorless method utilizes model-based estimators which depend on motor parameters. Thus, the performance degrades due to the parameter variations. Model Reference Adaptive System (MRAS), a robust estimation technique has been implemented for speed/position estimation. Conclusion: In this paper, sensor-based and sensorless methods have been studied and the performance has been compared in four operating environments of speed and torque values. The comparative results of both methods have been shown in the MATLAB/Simulink environment.

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Horch, Mohamed, Abdelmadjid Boumediene et Lotfi Baghli. « MRAS-based Sensorless Speed Integral Backstepping Control for Induction Machine, using a Flux Backstepping Observer ». International Journal of Power Electronics and Drive Systems (IJPEDS) 8, n^o 4 (1 décembre 2017) : 1650. http://dx.doi.org/10.11591/ijpeds.v8.i4.pp1650-1662.

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This paper presents a study concerning a sensorless vector control of an induction machine fed by a voltage source inverter. The aim is to provide a scheme to control the speed and the rotor flux using a sensorless integral backstepping control approach. The rotor speed estimation is done by an observer using the model reference adaptive system (MRAS) technique whereas the nonlinear backstepping observer is used to get the rotor flux. The main objective is to achieve a robust control, adaptive and efficient, which will allow us to test and evaluate the performance of the proposed observer, combined with a sensorless control of the induction machine. Tests and validation are done using numerical simulations with MATLAB/SIMULINK-PSB (Power System Block set) toolbox. The results show good performance in terms of robustness regarding machine parameter variations and show the excellent quality of the control law associated with the observer, despite the observability problems when the machine operates at low speed.

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Imane, Ghlib, Messlem Youcef, Gouichiche Abdelmadjid et Chedjara Zakaria. « Neural Adaptive Kalman Filter for Sensorless Vector Control of Induction Motor ». International Journal of Power Electronics and Drive Systems (IJPEDS) 8, n^o 4 (1 décembre 2017) : 1841. http://dx.doi.org/10.11591/ijpeds.v8.i4.pp1841-1851.

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This paper presents a novel neural adaptive Kalman filter for speed sensorless field oriented vector control of induction motor. The adaptive observer proposed here is based on MRAS (model reference adaptive system) technique, where the linear Kalman filter calculate the stationary components of stator current and the rotor flux and the rotor speed is calculated with an adaptive mechanism. Moreover, to improve the performance of the PI classical controller under different conditions, a novel adaptation scheme based on ADALINE (ADAptive LInear NEuron) neural network is used. It offers a solution to the PI parameters to stabilize automatically about their optimum values and speed estimation to converge quicker to the real. The proposed adaptive Kalman filter represents a good comprise between estimation accuracy and computationally intensive. The simulation results showed the robustness, efficiency, and superiority of the proposed scheme compared to the classical method even in low speed region.

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Hassan, Marwa, Alsnosy Balbaa, Hanady Issa et Noha El-Amary. « Asymptotic Output Tracked Artificial Immunity Controller for Eco-Maximum Power Point Tracking of Wind Turbine Driven by Doubly Fed Induction Generator ». Energies 11, n^o 10 (2 octobre 2018) : 2632. http://dx.doi.org/10.3390/en11102632.

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This paper aims to design a controller for a Doubly Fed Induction Generator (DFIG) targeting the Eco-Maximum Power Point Tracking (EMPPT) for environmental aspects. The proposed controller consists of two clusters, which are the novel Artificial Immunity sensorless Eco-Maximum Power Point Tracking (AI EMPPT) and the asymptotic non-linear control techniques. The main target of the AI EMPPT is to reduce the carbon dioxide emission by generating the maximum possible power from the renewable electrical energy resource, which is wind electrical power generation to replace the fossil-fuel conventional generation. To build the AI EMPPT, an Artificial Immunity System Estimator (AISE) based on artificial immunity technique and a Model Reference Adaptive System (MRAS) are used to estimate the DFIG rotor speed. Then, the AI EMPPT is applied to provide the reference electromagnetic torque signal. Subsequently, the reference electromagnetic torque interacts with the estimated generator speed, determined by the wind mechanical power, to supply the wind electrical power. The second cluster is the asymptotic non-linear control technique which proposes the reference signal tracking of the rotor direct and quadratic current, respectively. Thus, assigning specific zeros through feedback ensures the reproduction of an output that converges asymptotically to a required reference rotor current. For online operation, the Artificial Immunity Technique (AIT) is utilized to deal with the generated control reference signal. A proposal hardware implementation on Field Programmed Gate Array (FPGA) is also presented. The introduced approach was applied to a wind turbine generator driving a 3.7 kW load. MATLAB program was used to simulate and test the performance of the proposed control methods. The results to show the effectiveness of the proposed technique. The reduction in CO2 emission was calculated.

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Sueyoshi, E., I. Sakamoto, Y. Matsuoka, H. Hayashi et K. Hayashi. « Symptomatic peripheral vascular tree stenosis : Comparison of subtracted and nonsubtracted 3D contrast-enhanced MR angiography with fat suppression ». Acta Radiologica 41, n^o 2 (mars 2000) : 133–38. http://dx.doi.org/10.1080/028418500127345136.

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Objective: To determine the clinical feasibility of contrast-enhanced three-dimensional (3D) MR angiography (MRA) with fat suppression spectral inversion at lipids and to compare subtracted and nonsubtracted images. Material and Methods: In 13 patients suspected of having lower extremity ischemia, 3D dynamic contrast-enhanced MRA of the iliac and femoral arteries was performed using the fat suppression technique. The validity of the MRA interpretations of the degree of stenoses was evaluated by comparing with conventional angiography as the gold standard. The contrast-to-noise (C/N) ratios of both subtracted and nonsubtracted maximum-intensity-projection (MIP) images were calculated. Results: In the arteries with stenosis of 50% or greater, the sensitivity and specificity of the subtracted MR angiograms were 100% and 96.5%, respectively, not significantly different from the correponding values in nonsubtracted MRAs (100% and 94.1%, respectively). The C/N ratios of the subtracted images were significantly higher than those of the nonsubtracted images ( p<0.001). Conclusion: With this technique, fat suppression can be performed with only a slight increase in the examination time. A lower dose of contrast material can be used in MRA with fat suppression than without it. Subtracted MRA improves the ease of interpretation compared to nonsubtracted MRA.

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Seo, Yeongkyo, et Kon-Woo Kwon. « Area Optimization Techniques for High-Density Spin-Orbit Torque MRAMs ». Electronics 10, n^o 7 (26 mars 2021) : 792. http://dx.doi.org/10.3390/electronics10070792.

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This paper presents area optimization techniques for high-density spin-orbit torque magnetic random-access memories (SOT-MRAMs). Although SOT-MRAM has many desirable features of nonvolatility, high reliability and low write energy, it poses challenges to high-density memory implementation because of the use of two access transistors per cell. We first analyze the layout of the conventional SOT-MRAM bit-cell that includes two vertical metal lines, a bit-line and a source-line, limiting the horizontal dimension. We further propose two design techniques to reduce the horizontal dimension by decreasing the number of metal lines per cell without any performance overhead. Based on the fact that adjacent columns in a bit-interleaved array are not simultaneously accessed, the proposed techniques share a single source-line between two consecutive bit-cells in the same row. The simulation result shows that proposed techniques can achieve a bit-cell area reduction of 10–25% compared to the conventional SOT-MRAM. The comparison of our proposed designs with the standard spin-transfer torque MRAM shows 45% lower write energy, 84% lower read energy, and 2.3 × higher read-disturb margin.

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Usama, Muhammad, et Jaehong Kim. « Robust adaptive observer-based finite control set model predictive current control for sensorless speed control of surface permanent magnet synchronous motor ». Transactions of the Institute of Measurement and Control 43, n^o 6 (10 janvier 2021) : 1416–29. http://dx.doi.org/10.1177/0142331220979264.

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The objective of the paper is to present the efficient and dynamic sensorless speed control of a surface permanent magnet synchronous motor (SPMSM) drive at a wide speed range. For high-performance speed sensorless control, a finite control set model predictive current control (FCS-MPCC) algorithm based on a model reference adaptive system (MRAS) is proposed. With the FCS-MPCC algorithm, the inner current control loop is eliminated, and the limitations of the cascaded linear controller are overcome. The proposed speed sensorless control algorithm provides an efficient speed control technique for the SPMSM drive owing to its fast dynamic response and simple principle. The adaptive mechanism is adopted to estimate the rotor shaft speed and position used in FCS-MPCC for dynamic sensorless control. FCS-MPCC uses a square cost function to determine the optimal output voltage vector (VV) from the switching states that give the low cost index. A discrete-time model of a system is used to predict future currents across all the feasible VVs produced by the voltage source inverter. The VV that reduced the cost function is adopted and utilized. Simulation results showed the efficacy of the presented scheme and the viability of the proposed sensorless speed control design under various load conditions at a wide speed operation range.

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Bard, Edouard, et Timothy J. Heaton. « On the tuning of plateaus in atmospheric and oceanic 14C records to derive calendar chronologies of deep-sea cores and records of 14C marine reservoir age changes ». Climate of the Past 17, n^o 4 (16 août 2021) : 1701–25. http://dx.doi.org/10.5194/cp-17-1701-2021.

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Abstract. We assess the methodology of the so-called 14C plateau tuning (PT) technique used to date marine sediment records and determine 14C marine reservoir ages (MRAs) as recently reviewed by Sarnthein et al. (2020). The main identified problems are linked to the assumption of constant MRA during 14C age plateaus; the lack of consideration of foraminifera abundance changes coupled to bioturbation that can create spurious plateaus in marine sediments; the assumption that plateaus have the same shapes and durations in atmospheric and oceanic records; the implication that atmospheric 14C / 12C peaked instantaneously from one plateau to the next; that the 14C plateaus represent 82 % of the total time spent between 14 000 and 29 000 cal yr BP, whereas during the remaining 18 % of the time, the radiocarbon clock was running almost 5 times faster than the radioactive decay; that the sparsity, combined with the level of analytical uncertainties and additional noise, in both atmospheric and marine data do not currently allow one to reliably or robustly identify plateaus (should they exist) beyond 15 000 cal yr BP; and that the determination and identification of plateaus in the deep-sea cores is reliant upon significant changes in sedimentation rate within those marine sediments which are, a priori, unknown and are not verified with an independent method. The concerns we raise are supported and strengthened with carbon cycle box model experiments and statistical simulations of pseudo-atmospheric and pseudo-marine records, allowing us to question the ability to identify and tune 14C age plateaus in the context of noisy and sparse data.

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Tar, József Kázmér, Imre J. Rudas, János F. Bitó et Krisztián Kósi. « Robust Fixed Point Transformations in the Model Reference Adaptive Control of a Three DoF Aeroelastic Wing ». Applied Mechanics and Materials 300-301 (février 2013) : 1505–12. http://dx.doi.org/10.4028/www.scientific.net/amm.300-301.1505.

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The Model Reference Adaptive Controllers (MRAC) of dynamic systems have the purpose of simulating the dynamics of a reference system for an external control loop while guaranteeing precise tracking of a prescribed nominal trajectory. Such controllers traditionally are designed by the use of some Lyapunov function that can guarantee global and sometimes asymptotic stability but pays only little attention to the primary design intent, has a great number of arbitrary control parameters, and also is a complicated technique. The Robust Fixed Point Transformations (RFPT) were recently introduced as substitutes of Lyapunov’s technique in the design of adaptive controllers including MRACs, too. Though this technique guarantees only stability (neither global nor asymptotic), it works with a very limited number of control parameters, directly concentrates on the details of tracking error relaxation, and it is very easily can be designed. In the present paper this novel technique is applied for the MRAC control of a 3 Degrees-of-Freedom (DoF) aeroelastic wing model that is an underactuated system the model-based control of which attracted much attention in the past decades. To exemplify the efficiency of the method via simulations it is applied for PI and PID-type prescribed error relaxation for a reference model the parameters of which considerably differ from that of the actual system.

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Weon, Young Cheol, Seong Hoon Choi, Jae Cheol Hwang, Shang Hun Shin, Woon-Jung Kwon et Byeong Seong Kang. « Classification of persistent primitive trigeminal artery (PPTA) : a reconsideration based on MRA ». Acta Radiologica 52, n^o 9 (novembre 2011) : 1043–51. http://dx.doi.org/10.1258/ar.2011.110191.

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Background Persistent primitive trigeminal artery (PPTA) is the most common permanent carotid-basilar anastomosis. Magnetic resonance angiography (MRA) has become the primary non-invasive imaging technique for evaluation of cerebral vascular anatomy and can provide detailed 3D imaging of intracranial vessels. Purpose To evaluate the usefulness of MRA for the detection of PPTA and to re-classify its variations based on the embryologic types of PcomA and its relationship with the basilar artery and its branches. Material and Methods Of the total 7329 patients who underwent MRA at our institution from March 2008 through November 2010, we retrospectively analyzed the MRAs of 24 patients with a PPTA. Special attention was given to defining the relationship of the PPTA and the basilar artery with PcomA and to determine the site of origin, size, and course of the PPTA. The PPTA classification included five types based on their anatomic relationship to the neighboring arteries. Clinical features and associated vascular anomalies are also described. Results Twenty-four (17 women and seven men, 34 ∼ 81 years of age, mean age 59.67 years) of the 7329 patients had a PPTA (0.33 %). Eleven cases (45.8%) were classified as type 1, three (12.5%) as type 2, five (20.8%) as type 3, one (4.2%) as type 4, and four (16.7%) as type 5b. Fifteen PPTAs (62.5%) were located on the left side and nine were located (37.5%) on the right side. The basilar artery proximal to the insertion of the PPTA showed severe to moderate hypoplasia in 13 cases (54%). Nine intracranial artery aneurysms were detected in seven (29%) of the 24 study patients. Conclusion This study revealed five types of PPTA and necessitates an adjustment of the previous classification of PPTA on the basis of our MRA examinations. A PPTA should be considered by both the clinician and the radiologist who interpret MR angiography.

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Ishdorj, Bayartulga, Jeongyeon Kim, Jae Hwan Kim et Taehui Na. « A Timing-Based Split-Path Sensing Circuit for STT-MRAM ». Micromachines 13, n^o 7 (26 juin 2022) : 1004. http://dx.doi.org/10.3390/mi13071004.

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Spin-transfer torque magnetoresistive random access memory (STT-MRAM) applications have received considerable attention as a possible alternative for universal memory applications because they offer a cost advantage comparable to that of a dynamic RAM with fast performance comparable to that of a static RAM, while solving the scaling issues faced by conventional MRAMs. However, owing to the decrease in supply voltage (VDD) and increase in process fluctuations, STT-MRAMs require an advanced sensing circuit (SC) to ensure a sufficient read yield in deep submicron technology. In this study, we propose a timing-based split-path SC (TSSC) that can achieve a greater read yield compared to a conventional split-path SC (SPSC) by employing a timing-based dynamic reference voltage technique to minimize the threshold voltage mismatch effects. Monte Carlo simulation results based on industry-compatible 28-nm model parameters reveal that the proposed TSSC method obtains a 42% higher read access pass yield at a nominal VDD of 1.0 V compared to the SPSC in terms of iso-area and -power, trading off 1.75× sensing time.

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Tomic, Aleksandar, Novak Milovic, Ivan Marjanovic, Zoran Bjelanovic, Ivan Lekovic, Sasa Mickovic et Dusica Stamenkovic. « Different techniques of vessel reconstruction during kidney transplantation ». Vojnosanitetski pregled 72, n^o 7 (2015) : 614–18. http://dx.doi.org/10.2298/vsp131210038t.

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Background/Aim. Multiple renal arteries (MRAs) represent a surgical challenge by the difficulty in performing anastomoses, bleeding and stenosis. MRAs should be preserved and special attention should be paid to accessory polar arteries. All renal arteries (RAs) must be reconstructed and prepared for safe anastomosis. The paper decribed the different techniques of vessel reconstruction during kidney transplantation including important steps within recovery of organs, preparation and implantation. Methods. In a 16-year period (1996-2012) of kidney transplantation in the Military Medical Academy, Belgrade, a total of 310 living donors and 44 human cadaver kidney transplantations were performed, of which 28 (8%) kidneys had two or more RAs. Results. All the transplanted kidneys had immediate function. We repaired 20 cases of donor kidneys with 2 arteries, 4 cases with three RAs, one case with 4 RAs, one case with 4 RAs and renal vein reconstruction, one case with 3 arteries and additional polytetrafluoroethylene (PTFE) graft reconstruction, one case with transected renal artery and reconstruction with 5 cm long deceased donor external iliac artery. There were no major complications and graft failure. At a minimum of 1-year follow-up, all the patients showed normal renal function. Conclusion. Donor kidney transplantation on a contralateral side and ?end-to-end? anastomosis of the renal artery to the internal iliac artery (IIA) is our standard procedure with satisfactory results. Renal artery reconstruction and anastomosis with IIA is a safe and highly efficient procedure and kidneys with MRAs are not contraindicated for transplantation. A surgical team should be fully competent to remove cadaveric abdominal organs to avoid accidental injuries of organs vessels.

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Hassan, Mohamed H., Salah Kamel, Ali Selim, Tahir Khurshaid et José Luis Domínguez-García. « A Modified Rao-2 Algorithm for Optimal Power Flow Incorporating Renewable Energy Sources ». Mathematics 9, n^o 13 (29 juin 2021) : 1532. http://dx.doi.org/10.3390/math9131532.

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In this paper, a modified Rao-2 (MRao-2) algorithm is proposed to solve the problem of optimal power flow (OPF) in a power system incorporating renewable energy sources (RES). Quasi-oppositional and Levy flight methods are used to improve the performance of the Rao algorithm. To demonstrate effectiveness of the MRao-2 technique, it is tested on two standard test systems: an IEEE 30-bus system and an IEEE 118-bus system. The objective function of the OPF is the minimization of fuel cost in five scenarios. The IEEE 30-bus system reflects fuel cost minimization in three scenarios (without RES, with RES, and with RES under contingency state), while the IEEE 118-bus system reflects fuel cost minimization in two scenarios (without RES and with RES). The achieved results of various scenarios using the suggested MRao-2 technique are compared with those obtained using five recent techniques: Atom Search Optimization (ASO), Turbulent Flow of Water-based Optimization (TFWO), Marine Predators Algorithm (MPA), Rao-1, Rao-3 algorithms, as well as the conventional Rao-2 algorithm. Those comparisons confirm the superiority of the MRao-2 technique over those other algorithms in solving the OPF problem.

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Tsiakmakis, Kyriakos, Vasileios Delimaras, Argyrios T. Hatzopoulos et Maria S. Papadopoulou. « Real Time Discrete Optimized Adaptive Control for Ionic Polymer Metal Composites ». WSEAS TRANSACTIONS ON SYSTEMS AND CONTROL 18 (7 mars 2023) : 26–37. http://dx.doi.org/10.37394/23203.2023.18.3.

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This paper describes a proposed method for optimizing the parameters of a Model Reference Adaptive Control (MRAC) system. The MRAC system uses a reference model to control a plant with unknown dynamics and continuously updates its parameters to improve control accuracy. The system requires an adjustment of parameter γ, which participates in the feedback of the system but cannot be adjusted in real time through trial and error. The proposed method uses optimization techniques to adjust the γ parameters in real time, specifically at the start of the control process, when the maximum deviation of the plant from the reference model is observed. The optimization technique varies the parameters and seeks the best solution to quickly reduce the error. Once the optimal solution is found, the optimization is turned off, allowing the MRAC to continue efficiently reducing the error. In the case of sudden changes in the error due to endogenous or exogenous factors, optimization is activated again to redefine the γ parameters. The magnitude of the change depends on the rate of error changes. The response of the IPMC was measured and compared against a reference signal using three different control techniques MRAC, Model Reference Adaptive Control (MRAC), MRAC-Taguchi, and MRAC-Taguchi-DCT, and the results show that the last penalizes frequencies beyond the fundamental frequency through the cost function, resulting in negligible harmonic distortion.

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Pal, A. K., Indrajıt Naskar et Sampa Paul. « Fuzzy-based Gain Adaptive Scheme for Set-Point Modulated Model Reference Adaptive Controller ». International Journal of Natural Computing Research 7, n^o 4 (octobre 2018) : 1–19. http://dx.doi.org/10.4018/ijncr.2018100101.

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In model reference adaptive controller (MRACs), the adaptive gain of the controller is varied according to the process dynamic variation as it is directly related with the system stability. In MRAC, there is no provision of an automatic selection of adaptive gain and adaptation rate. To get rid of this problem and for the automatic selection of adaptive gain, a fuzzy-based scheme is presented in this article. In the proposed fuzzy-based technique, the controller output gain is illustrated as the function of input process parameters, which is continuously amended for any process parameter variations. A set-point modulation scheme is also incorporated to tackle the undesired process parameter variations and to improve performance indices of the process under control. The performance of the proposed set-point modulated fuzzy-based model reference adaptive controller (SFMRAC) is demonstrated on different second order linear, marginally stable and nonlinear models. The scheme is also explored on a real-time twin arm overhead crane for transport of material without pendulation.

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LIAO, AN-CHI, WEI-TOU NI et JOW-TSONG SHY. « PICO-WATT AND FEMTO-WATT WEAK-LIGHT PHASE LOCKING ». International Journal of Modern Physics D 11, n^o 07 (août 2002) : 1075–85. http://dx.doi.org/10.1142/s021827180200258x.

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Advances in laser physics and its applications have triggered the proposition and development of Laser Astrodynamics. In carrying out research projects on Laser Space Programs, it is necessary to process the laser signal sent back from remote spacecraft. After traveling an extremely long distance, the power of this signal is greatly reduced. Weak-light phase-locking is the key technique used for signal amplification in these space projects. After the returning laser beam is collected by telescope, it is used to phase-lock a local laser oscillator. The local laser then carries the phase information of the remote spacecraft laser. we used diode-pumped non-planar ring cavity Nd:YAG lasers to serve as the remote weak-light laser and the local strong-light laser. We then built an optical phase-locked loop to phase-lock them. The weak-light laser signal was simulated using ND (neutral density)-filters to decrease the light intensity. In the phase detection, we used balanced detection to eliminate laser intensity noise and improve the S/N ratio. Combining this with an appropriate loop filter, we were able to control the laser frequency and improve the phase-locking ability. We phase-locked a 2 nW weak-light beam and a 2 mW strong-light beam with a 57 mrads(rms)phase error. The locking duration was very long. Locking of a 200 pW and a 2007thinsp;μW light beam, with phase error of 200 mrad (rms) and duration of over 2 hours was achieved. The phase error for locking a 200 μW to a 20pW light beam was 160 mrad (rms). The locking duration was also longer than 2 hours. the last locking performed was carried out with a 2 pW and a 200 μW light beam. The phase error and the locking duration were 290 mrad(rms) and 1.5 min respectively.

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Singh, Shweta, Amar Nath Tiwari et S. N. Singh. « Performance evaluation of MRAS and SMO based sensorless PMSM drives ». World Journal of Engineering 17, n^o 3 (2 mars 2020) : 347–55. http://dx.doi.org/10.1108/wje-07-2019-0208.

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Purpose For vector control of permanent magnet synchronous motor (PMSM) requires motor speed and rotor position estimation. The precision of the open-loop techniques of the stator flux and speed for vector control PMSM drive drops as mechanical speed decreases. The stator resistance and estimated stator flux values crisscross have a huge effect on the transient and steady-state performance of the drive at lower speed. The framework turns out to be increasingly strong against parameter crisscross and signal noises by using adaptive observers for estimation of speed and flux. Design/methodology/approach This paper presents a comparison of two-speed observers for the vector control PMSM drive: the sliding mode observer (SMO) and the model reference adaptive system (MRAS). A comprehensive analysis of SMO and MRAS respects dynamic, steady-state performance and robustness, affectability, stability and computational complexity has been introduced. The abstract of the advantages and disadvantages of both observer and their comparative analysis have also been discussed. Findings Dynamic performance steady-state performance and robustness, affectability and stability. Originality/value This paper presents a sensorless scheme, namely, MRAS and SMO for control of PMSM drive. These sensorless techniques have been tested for a PMSM motor drive and the motor performance was compared for both techniques. Matlab/Simulink based simulation results conclude that the adaptive methods improve dynamic response, reduces torque ripples and extended speed range.

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