Study On Speed Regulation System Of Permanent Magnet Synchronous Traction Motor At Low Switching Frequency

Compared with traditional asynchronous traction motor,permanent magnet synchronous traction motor has the advantages of high efficiency,stable speed control and simple structure,and it is considered as the development direction of the next generation of rail transit traction motor.The power level of permanent magnet synchronous traction motor in rail transit is as high as several hundred kilowatts.In order to reduce the power loss of switching devices,driving inverter must work at low switching frequency,which will bring a series of problems to the design of motor speed control system.Based on the basic theory of vector control,the speed control system of permanent magnet synchronous traction motor(PMSM)at low switching frequency is studied in this paper,considering the delay of inverter.Firstly,the scalar mathematical model and complex vector mathematical model of PMSM under d-q axis are established,and the design method of double closed-loop PI control system with voltage feed-forward decoupling is introduced.The relevant simulation is established under MATLAB/Simulink software environment,and the performance of current loop control system is analyzed under complex vector mathematical model.It is concluded that this method is not suitable for permanent magnet synchronous motor at low switching frequency.Then,current PWM predictive control(PPC)method is chosen as the studied control method in this paper.Through analysis of traditional current PPC,it is found that it does not consider of inverter delay when establishing the predictive model,which will lead to poor control performance at low switching frequency.In order to consider inverter delay,the integrated complex vector model of inverters and permanent magnet synchronous motors is built in discrete domain.Based on the modified model,an improved current PPC control method is proposed.The simulation model is built in the software environment of MATLAB/Simulink to verify the steady-state and dynamic performance advantages of improved current PPC control system compared with the double closed-loop PI control system and traditional current PPC control system.Based on the simulation results,the static error of current PPC control system is eliminated by introducing current error integral compensation method.The simulation results show that the compensation method in improved current PPC control system can eliminate the static error of current very well,and within a certain range of current error,the system performance has little influence.The performance of improved and traditional current PPC control system are compared and analyzed by using the automatic control theory.The analysis results further verify the advantages of the improved method.At the same time,the parameter sensitivity of the improved method is analyzed,which shows that the improved method has better robustness.Finally,in order to verify the correctness of theoretical research,a permanent magnet synchronous motor experimental platform based on NI cRIO-9033 controller is built.Based on the experimental platform,the experiment of PMSM speed regulation at low switching frequency is completed.The performance of traditional and improved current PPC control methods in PMSM speed regulation system is compared.Finally,the experimental results are analyzed in detail,and the correctness of the theoretical analysis is verified.