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Volume 46,Issue 10,2019 Table of Contents
2019, 46(10):1-5, 13.
Abstract:
An analytical calculation method of air gap magnetic field in axially magnetized tubular permanent magnet linear synchronous motor (TPMLSM) based on Schwarz Christoffel (S C) transformation method was introduced. Firstly, the air gap magnetic field distribution of the slotless motor was analytically calculated based on S C transformation method. Then, the air gap relative ratio permeance function of slotted motor was obtained based on S C transformation to consider the effect of stator core slots. Finally, the air gap magnetic field distribution of the slotted motor was obtained by the basic air gap magnetic field of the slotless motor and the air gap relative ratio permeance function. The analytical formulas of the air gap magnetic field distribution were derived for the axially magnetized TPMLSM. Experiment was carried out using a 36 slot 12 pole axially magnetized TPMLSM. The predicted air gap magnetic field distribution matched the corresponding finite element result, and the measured no load electromotive force (EMF) of the prototype was also consistent with the analytical and the finite element value, so the validity of the proposed method was proved.
An analytical calculation method of air gap magnetic field in axially magnetized tubular permanent magnet linear synchronous motor (TPMLSM) based on Schwarz Christoffel (S C) transformation method was introduced. Firstly, the air gap magnetic field distribution of the slotless motor was analytically calculated based on S C transformation method. Then, the air gap relative ratio permeance function of slotted motor was obtained based on S C transformation to consider the effect of stator core slots. Finally, the air gap magnetic field distribution of the slotted motor was obtained by the basic air gap magnetic field of the slotless motor and the air gap relative ratio permeance function. The analytical formulas of the air gap magnetic field distribution were derived for the axially magnetized TPMLSM. Experiment was carried out using a 36 slot 12 pole axially magnetized TPMLSM. The predicted air gap magnetic field distribution matched the corresponding finite element result, and the measured no load electromotive force (EMF) of the prototype was also consistent with the analytical and the finite element value, so the validity of the proposed method was proved.
2019, 46(10):6-13.
Abstract:
In view of the analysis of rotor strength of surface mounted permanent magnet motor in high speed and high temperature condition, a rotor model considering magnetic steel with block structure was proposed. Based on the theory of thick walled cylinder, the analytical solution was derived. The tangential and radial stresses of carbon fiber sleeve and magnetic steel were respectively calculated. Based on finite element method, the rotor strength under various working conditions was analyzed. The stress on the rotor would increase under both high speed and high temperature conditions. Compared with the analytical analysis results, it showed that the finite element method and the analytical method could accurately calculate the stress of the carbon fiber sleeve, while the magnetic steel stress would be affected by the edge effect, so that the analytical analysis could not perform accurate calculations. The interference amount between the sheath and the magnetic steel was analyzed by the finite element method, based on which the rotor structure was optimized and the optimal range of the interference amount was given.
In view of the analysis of rotor strength of surface mounted permanent magnet motor in high speed and high temperature condition, a rotor model considering magnetic steel with block structure was proposed. Based on the theory of thick walled cylinder, the analytical solution was derived. The tangential and radial stresses of carbon fiber sleeve and magnetic steel were respectively calculated. Based on finite element method, the rotor strength under various working conditions was analyzed. The stress on the rotor would increase under both high speed and high temperature conditions. Compared with the analytical analysis results, it showed that the finite element method and the analytical method could accurately calculate the stress of the carbon fiber sleeve, while the magnetic steel stress would be affected by the edge effect, so that the analytical analysis could not perform accurate calculations. The interference amount between the sheath and the magnetic steel was analyzed by the finite element method, based on which the rotor structure was optimized and the optimal range of the interference amount was given.
2019, 46(10):14-18, 65.
Abstract:
Permanent magnet synchronous motor (PMSM) was a highly nonlinear dynamic system, which played an important role in industrial driving applications. Real time identification of moment of inertia was of great significance to the control and stability monitoring of high precision PMSM systems. However, traditional identification methods lacked accuracy. Based on the traditional discrete model reference adaptive theory, the Cauchy mutation particle swarm optimization (CMPSO) algorithm was used to replace the adaptive law design of parameters to be identified to realize the identification of PMSM moment of inertia. This method made full use of the fast and efficient convergence of CMPSO algorithm. The simulation and experimental results proved the feasibility, correctness and accuracy of the method.
Permanent magnet synchronous motor (PMSM) was a highly nonlinear dynamic system, which played an important role in industrial driving applications. Real time identification of moment of inertia was of great significance to the control and stability monitoring of high precision PMSM systems. However, traditional identification methods lacked accuracy. Based on the traditional discrete model reference adaptive theory, the Cauchy mutation particle swarm optimization (CMPSO) algorithm was used to replace the adaptive law design of parameters to be identified to realize the identification of PMSM moment of inertia. This method made full use of the fast and efficient convergence of CMPSO algorithm. The simulation and experimental results proved the feasibility, correctness and accuracy of the method.
2019, 46(10):19-24.
Abstract:
The model of a 60 kW permanent magnet synchronous motor for electric vehicles was established. The optimal number of flow channels and the range of flow channel parameters were acquired by theoretical analysis. The cooling channel width aand height bwere taken as design variables, and the motor temperature rise and the inlet outlet pressure difference were the objective functions. Through the Isight integrated mesh deformation software Sculptor and CFD calculation software Fluent, the sample points were created by using the Latin hypercube design method, and the data were automatically submitted for simulation calculation. Based on the obtained data, a response surface model was established, and the multi island genetic algorithm was used to optimize the approximate model. After optimization, the motor temperature rise and inlet outlet pressure difference were decreased by 6.01% and 6.81%, respectively. The performance and safe operation of the motor were guaranteed.
The model of a 60 kW permanent magnet synchronous motor for electric vehicles was established. The optimal number of flow channels and the range of flow channel parameters were acquired by theoretical analysis. The cooling channel width aand height bwere taken as design variables, and the motor temperature rise and the inlet outlet pressure difference were the objective functions. Through the Isight integrated mesh deformation software Sculptor and CFD calculation software Fluent, the sample points were created by using the Latin hypercube design method, and the data were automatically submitted for simulation calculation. Based on the obtained data, a response surface model was established, and the multi island genetic algorithm was used to optimize the approximate model. After optimization, the motor temperature rise and inlet outlet pressure difference were decreased by 6.01% and 6.81%, respectively. The performance and safe operation of the motor were guaranteed.
2019, 46(10):25-34, 45.
Abstract:
Large scale access to wind farms would have a significant impact on the static voltage stability of power grid. Taking the extended single machine infinite bus system with direct drive wind turbines as an example, the equivalent model of the system with direct drive wind turbines was analyzed by two static power flow calculation methods, and the analytical formula of bus voltage at the grid connected point of the system was derived after wind power was connected. The simulation models of the extended single machine infinite bus system with direct drive wind turbines and the actual power grid system were established in BPA. The theoretical calculation results and simulation results were compared. The permeability of wind power, the grid connected position of wind turbines, the load access ratio and the load access position of the bus voltage at the grid connected point were analyzed under different control modes. The influences of the factors on the static voltage stability of the system were discussed.
Large scale access to wind farms would have a significant impact on the static voltage stability of power grid. Taking the extended single machine infinite bus system with direct drive wind turbines as an example, the equivalent model of the system with direct drive wind turbines was analyzed by two static power flow calculation methods, and the analytical formula of bus voltage at the grid connected point of the system was derived after wind power was connected. The simulation models of the extended single machine infinite bus system with direct drive wind turbines and the actual power grid system were established in BPA. The theoretical calculation results and simulation results were compared. The permeability of wind power, the grid connected position of wind turbines, the load access ratio and the load access position of the bus voltage at the grid connected point were analyzed under different control modes. The influences of the factors on the static voltage stability of the system were discussed.
2019, 46(10):35-39.
Abstract:
When the light intensity and temperature change in photovoltaic system, the conventional maximum power point tracking (MPPT) algorithm was difficult to track the maximum power point quickly and accurately. Aiming at this problem, a fuzzy controller based on improved particle swarm optimization (PSO) was designed. Firstly, according to the characteristics of conventional MPPT algorithm, a fuzzy control algorithm with adjusting factor was designed to rapidly converge to the maximum power point. Then, parameters adaptive PSO was used to dynamically optimize the adjusting factors of the designed fuzzy controller. The simulation results showed that the designed parameters adaptive PSO optimized fuzzy controller could track the maximum power point quickly and accurately, which ensured the dynamic response speed and steady state accuracy of MPPT and improved the work efficiency of photovoltaic system.
When the light intensity and temperature change in photovoltaic system, the conventional maximum power point tracking (MPPT) algorithm was difficult to track the maximum power point quickly and accurately. Aiming at this problem, a fuzzy controller based on improved particle swarm optimization (PSO) was designed. Firstly, according to the characteristics of conventional MPPT algorithm, a fuzzy control algorithm with adjusting factor was designed to rapidly converge to the maximum power point. Then, parameters adaptive PSO was used to dynamically optimize the adjusting factors of the designed fuzzy controller. The simulation results showed that the designed parameters adaptive PSO optimized fuzzy controller could track the maximum power point quickly and accurately, which ensured the dynamic response speed and steady state accuracy of MPPT and improved the work efficiency of photovoltaic system.
2019, 46(10):40-45.
Abstract:
Based on a new four phase transverse flux permanent magnet motor, the MATLAB/Simulink software platform and Simpower System toolbox were used to study the closed loop control system. Based on the traditional double closed loop speed regulating control, zero level was introduced into the hysteresis current control loop. The hysteresis loop was divided into upper loop and lower loop. The switching frequency and current THD were considered to determine the appropriate hysteresis loop width. The inverter control signal was obtained according to the comparison results of deviation current value and the hysteresis loop width. The running data of motor under various working conditions were obtained by simulation. The simulation results showed that the control method could effectively control the four phase transverse flux permanent magnet motor.
Based on a new four phase transverse flux permanent magnet motor, the MATLAB/Simulink software platform and Simpower System toolbox were used to study the closed loop control system. Based on the traditional double closed loop speed regulating control, zero level was introduced into the hysteresis current control loop. The hysteresis loop was divided into upper loop and lower loop. The switching frequency and current THD were considered to determine the appropriate hysteresis loop width. The inverter control signal was obtained according to the comparison results of deviation current value and the hysteresis loop width. The running data of motor under various working conditions were obtained by simulation. The simulation results showed that the control method could effectively control the four phase transverse flux permanent magnet motor.
2019, 46(10):46-50, 57.
Abstract:
Aiming at the problem of terminal voltage pulse caused by non conducting phase continuum during commutation of brushless DC motor, based on the principle of back electromotive force (EMF) zero crossing, the causes of terminal voltage pulse and its influence on the detection accuracy of back EMF zero crossing were analyzed. A control strategy for high precision commutation of sensorless brushless DC motor by avoiding terminal voltage pulse using software algorithm was proposed. The conditional statement and program run time difference were used to avoid the terminal voltage pulse. At the same time, in order to improve the fault tolerance rate of run time difference of the designed program under heavy load, a strategy to reduce commutation continuum time was proposed. Finally, a sensorless brushless DC motor experimental platform was built to verify the above strategy. The experimental results showed the effectiveness and accuracy of the proposed strategy under different duty cycles and loads.
Aiming at the problem of terminal voltage pulse caused by non conducting phase continuum during commutation of brushless DC motor, based on the principle of back electromotive force (EMF) zero crossing, the causes of terminal voltage pulse and its influence on the detection accuracy of back EMF zero crossing were analyzed. A control strategy for high precision commutation of sensorless brushless DC motor by avoiding terminal voltage pulse using software algorithm was proposed. The conditional statement and program run time difference were used to avoid the terminal voltage pulse. At the same time, in order to improve the fault tolerance rate of run time difference of the designed program under heavy load, a strategy to reduce commutation continuum time was proposed. Finally, a sensorless brushless DC motor experimental platform was built to verify the above strategy. The experimental results showed the effectiveness and accuracy of the proposed strategy under different duty cycles and loads.
ZHU Mengmei
,
ZHOU Guangxu
,
SONG Ningran
,
MU Yongyun
,
GAO Jia
,
MA Jianhui
,
MA Hongwei
,
LIU Yijun
2019, 46(10):51-57.
Abstract:
Single phase induction motor was replaced by high efficiency switched reluctance motor (SRM) in direct drive electric bench drill. The drill bit was directly fixed to the output end of the motor rotor. The belt, tower wheel and other mechanical transmission devices of traditional bench drill were omitted,and the direct drive was achieved. In order to realize the stepless speed regulation of the direct drive type electric bench drill in the full speed range, the control strategies were proposed as follows: in the starting phase, chopped current control (CCC) was used to provide high torque; in the low speed phase, a method based on sine and cosine current distribution was proposed to suppress low speed torque ripple; in the middle and high speed stage, the variable angle voltage chopping combination control method of chopped voltage control (CVC) + angle position control (APC) was used to adjust the speed and achieve smooth switching between different control modes. The experimental results showed that the proposed full speed range control strategy had high efficiency and good speed regulation performance, which could effectively improve the performance of the electric bench drill.
Single phase induction motor was replaced by high efficiency switched reluctance motor (SRM) in direct drive electric bench drill. The drill bit was directly fixed to the output end of the motor rotor. The belt, tower wheel and other mechanical transmission devices of traditional bench drill were omitted,and the direct drive was achieved. In order to realize the stepless speed regulation of the direct drive type electric bench drill in the full speed range, the control strategies were proposed as follows: in the starting phase, chopped current control (CCC) was used to provide high torque; in the low speed phase, a method based on sine and cosine current distribution was proposed to suppress low speed torque ripple; in the middle and high speed stage, the variable angle voltage chopping combination control method of chopped voltage control (CVC) + angle position control (APC) was used to adjust the speed and achieve smooth switching between different control modes. The experimental results showed that the proposed full speed range control strategy had high efficiency and good speed regulation performance, which could effectively improve the performance of the electric bench drill.
2019, 46(10):58-65.
Abstract:
In order to improve the reliability of the five phase permanent magnet synchronous motor (PMSM) drive system, the five phase salient pole PMSM with the third order harmonic components in permanent magnet flux was studied. Based on fault free mathematical model, a fault tolerant direct torque control (DTC) strategy was proposed for two phase open circuit situation. The strategy constructed the α1β1 subspace voltage vector map of the five phase motor under two phase open fault, and selected the optimal voltage vector of the inverter output in the next cycle based on the fundamental subspace flux linkage information and torque information in the current cycle. In order to achieve smooth motor torque, the torque ripple caused by the third order harmonic flux linkage coupled to the α1β1 subspace was overcome by adding the torque feed forward compensation. The experiments showed that the proposed method could run smoothly under two phase open circuit and switch fast from normal to fault tolerant operation.
In order to improve the reliability of the five phase permanent magnet synchronous motor (PMSM) drive system, the five phase salient pole PMSM with the third order harmonic components in permanent magnet flux was studied. Based on fault free mathematical model, a fault tolerant direct torque control (DTC) strategy was proposed for two phase open circuit situation. The strategy constructed the α1β1 subspace voltage vector map of the five phase motor under two phase open fault, and selected the optimal voltage vector of the inverter output in the next cycle based on the fundamental subspace flux linkage information and torque information in the current cycle. In order to achieve smooth motor torque, the torque ripple caused by the third order harmonic flux linkage coupled to the α1β1 subspace was overcome by adding the torque feed forward compensation. The experiments showed that the proposed method could run smoothly under two phase open circuit and switch fast from normal to fault tolerant operation.
2019, 46(10):66-71.
Abstract:
Aiming at the problem of high precision synchronous control of the joints of manipulators, a fractional order reaching law which was different from the traditional reaching law was selected. A cross coupling control structure was proposed. A synchronous control strategy of fractional order reaching law based on the variance virtual principal axis was proposed. The stability of the proposed control strategy was proved. Simulation was carried out for a two joint manipulator. The simulation results showed that the proposed control strategy could make the tracking error and synchronization error of the manipulator system converge quickly, and had faster response speed and stronger robustness.
Aiming at the problem of high precision synchronous control of the joints of manipulators, a fractional order reaching law which was different from the traditional reaching law was selected. A cross coupling control structure was proposed. A synchronous control strategy of fractional order reaching law based on the variance virtual principal axis was proposed. The stability of the proposed control strategy was proved. Simulation was carried out for a two joint manipulator. The simulation results showed that the proposed control strategy could make the tracking error and synchronization error of the manipulator system converge quickly, and had faster response speed and stronger robustness.
2019, 46(10):72-76, 110.
Abstract:
According to the warmup process and jacking oil pump system of high power high speed synchronous motor in long distance pipeline, the unit warmup process was tested and analyzed. The warmup process was not highly correlated with the vibration value of the synchronous motor near the critical speed point, and the warmup time could be reduced or cancelled. The synchronous motor jacking oil pump system was tested, and the changes of the synchronous motor vibration, temperature, start stop time, etc. when the jacking pump was cancelled were analyzed. The results showed that the chain stop pump speed of the jacking oil pump could be reduced.
According to the warmup process and jacking oil pump system of high power high speed synchronous motor in long distance pipeline, the unit warmup process was tested and analyzed. The warmup process was not highly correlated with the vibration value of the synchronous motor near the critical speed point, and the warmup time could be reduced or cancelled. The synchronous motor jacking oil pump system was tested, and the changes of the synchronous motor vibration, temperature, start stop time, etc. when the jacking pump was cancelled were analyzed. The results showed that the chain stop pump speed of the jacking oil pump could be reduced.
2019, 46(10):77-83.
Abstract:
Compared with traditional medium frequency power supply, modular medium frequency static power supply had the advantages of flexible selection, high reliability, good redundancy and easy system maintenance. The rectifier of medium frequency static power supply should achieve unit power factor control while controlling bus voltage stability. For this reason, the dual current loop control strategy was analyzed concretely. The principle of separating positive and negative sequences of voltage and current in dual current loop controller and the concrete realization method of double dqphase locked loop were introduced, i.e., delay signal cancellation (DSC) and quasi proportional resonance (PR). Aiming at the problems of high harmonic content and difficulty in tracking the fundamental wave of the output voltage of the inverter, a multiple quasi PR control strategy was adopted to achieve the stable output of the medium frequency voltage. The simulation and experimental results showed that the dual current loop controller could achieve bus voltage stability and unit power factor control simultaneously. The medium frequency inverter with double closed loop multiple quasi PR control strategy could output stable medium frequency AC voltage.
Compared with traditional medium frequency power supply, modular medium frequency static power supply had the advantages of flexible selection, high reliability, good redundancy and easy system maintenance. The rectifier of medium frequency static power supply should achieve unit power factor control while controlling bus voltage stability. For this reason, the dual current loop control strategy was analyzed concretely. The principle of separating positive and negative sequences of voltage and current in dual current loop controller and the concrete realization method of double dqphase locked loop were introduced, i.e., delay signal cancellation (DSC) and quasi proportional resonance (PR). Aiming at the problems of high harmonic content and difficulty in tracking the fundamental wave of the output voltage of the inverter, a multiple quasi PR control strategy was adopted to achieve the stable output of the medium frequency voltage. The simulation and experimental results showed that the dual current loop controller could achieve bus voltage stability and unit power factor control simultaneously. The medium frequency inverter with double closed loop multiple quasi PR control strategy could output stable medium frequency AC voltage.
2019, 46(10):84-91.
Abstract:
Electric vehicles were gradually used in people’s daily transportation, and the requirements of their technical reliability and safety were very high. The motor controller was a device that converted the battery DC power supply to the three phase AC power supply, and then drove the permanent magnet synchronous motor (PMSM) of electric vehicles. A PMSM controller based on Renesas microcontroller was designed. Analysis was carried out from the aspects of component selection, hardware protection structure principle, printed circuit board (PCB) layout, control algorithm, structural strength and thermal analysis. Finally, the prototype controller was produced and the experimental platform was built. The efficiency characteristic test, power generation test and temperature rise test were performed on the PMSM controller. The experimental results verified the rationality of the design.
Electric vehicles were gradually used in people’s daily transportation, and the requirements of their technical reliability and safety were very high. The motor controller was a device that converted the battery DC power supply to the three phase AC power supply, and then drove the permanent magnet synchronous motor (PMSM) of electric vehicles. A PMSM controller based on Renesas microcontroller was designed. Analysis was carried out from the aspects of component selection, hardware protection structure principle, printed circuit board (PCB) layout, control algorithm, structural strength and thermal analysis. Finally, the prototype controller was produced and the experimental platform was built. The efficiency characteristic test, power generation test and temperature rise test were performed on the PMSM controller. The experimental results verified the rationality of the design.
2019, 46(10):92-98, 110.
Abstract:
Due to the strict requirement of small size and light weight, the motors used in new energy vehicle had the characteristics of high power density, light weight, small volume and compact structure, which inevitably had a significant influence on the heat dissipation of motors. Thus, the motors cooled by water jacket had emerged as a mainstream, but how to set up the efficient heat conduction passage from the internal motor to the shell was still one of the important problems restricting the motor performance. In order to improve the thermal conduction efficiency of windings, the potting gum with relatively higher thermal conductivity was filled into the stator slot winding and the end winding. The fluid field and temperature field of the potting motor and the unpotted motor were studied using the method of fluid simulation. The simulation results were verified by experiment using the existing experimental platform. The results showed that the heat dissipation condition of the end winding and the winding in the slot is improved effectively after the motor was potted, the temperature gradient between the end winding and the slot winding was reduced, and the maximum temperature of the motor winding was reduced by 22 ℃.
Due to the strict requirement of small size and light weight, the motors used in new energy vehicle had the characteristics of high power density, light weight, small volume and compact structure, which inevitably had a significant influence on the heat dissipation of motors. Thus, the motors cooled by water jacket had emerged as a mainstream, but how to set up the efficient heat conduction passage from the internal motor to the shell was still one of the important problems restricting the motor performance. In order to improve the thermal conduction efficiency of windings, the potting gum with relatively higher thermal conductivity was filled into the stator slot winding and the end winding. The fluid field and temperature field of the potting motor and the unpotted motor were studied using the method of fluid simulation. The simulation results were verified by experiment using the existing experimental platform. The results showed that the heat dissipation condition of the end winding and the winding in the slot is improved effectively after the motor was potted, the temperature gradient between the end winding and the slot winding was reduced, and the maximum temperature of the motor winding was reduced by 22 ℃.
2019, 46(10):99-103.
Abstract:
A dual motor controller for dual motor hybrid electric vehicle was developed. The overall design scheme of the controller was described. The structure, hardware and software of the system were analyzed. A design scheme of dual motor controller based on double side water cooling IGBT was proposed. The thermal simulation of double side water cooling radiator was carried out to study its heat dissipation effect on IGBT module. The bench test of the prototype was carried out. The experimental waveform showed that the dual motor controller had a good control effect.
A dual motor controller for dual motor hybrid electric vehicle was developed. The overall design scheme of the controller was described. The structure, hardware and software of the system were analyzed. A design scheme of dual motor controller based on double side water cooling IGBT was proposed. The thermal simulation of double side water cooling radiator was carried out to study its heat dissipation effect on IGBT module. The bench test of the prototype was carried out. The experimental waveform showed that the dual motor controller had a good control effect.
2019, 46(10):104-110.
Abstract:
Aiming at the problem that mechanical sensors of electric vehicle were easy to fail in complex working environment, the speed sensorless technology based on model reference adaptive system (MRAS) was applied to electric vehicle. In order to solve the problem of large phase delay of rotor position estimation and large speed estimation error in traditional MRAS speed sensorless control, the model predictive control algorithm was applied to MRAS. Permanent magnet synchronous motor (PMSM) current flux linkage equation was selected as the reference model, and voltage flux linkage equation was selected as the adjustable model. The cost function was the difference of flux linkage, and the rotor position was selected as the estimated parameters. Compared with the traditional MRAS speed sensorless control algorithm, the proposed algorithm had more accurate speed and rotor position estimation, less estimation error, and excellent dynamic and steady state performance. The feasibility and effectiveness of the algorithm were verified by simulation and experiment.
Aiming at the problem that mechanical sensors of electric vehicle were easy to fail in complex working environment, the speed sensorless technology based on model reference adaptive system (MRAS) was applied to electric vehicle. In order to solve the problem of large phase delay of rotor position estimation and large speed estimation error in traditional MRAS speed sensorless control, the model predictive control algorithm was applied to MRAS. Permanent magnet synchronous motor (PMSM) current flux linkage equation was selected as the reference model, and voltage flux linkage equation was selected as the adjustable model. The cost function was the difference of flux linkage, and the rotor position was selected as the estimated parameters. Compared with the traditional MRAS speed sensorless control algorithm, the proposed algorithm had more accurate speed and rotor position estimation, less estimation error, and excellent dynamic and steady state performance. The feasibility and effectiveness of the algorithm were verified by simulation and experiment.
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Electric Machines & Control Application ® 2025
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Electric Machines & Control Application ® 2025
Supported by:Beijing E-Tiller Technology Development Co., Ltd.
