Research On Fault-tolerant Control For Six-phase Permanent Magnet Synchronous Motor Drives Under Open-Phase Faults

With the development of permanent magnet rare earth in China,the maturity of power electronic technology,the advantages of multi-phase motor drive system itself such as high reliability,safety,and high power density have attracted wide attention from scholars.This subject relies on the National Natural Science Foundation project "Research on Fault Diagnosis and Fault Tolerant Control of Multi-phase Motor Drive Control System for Electric Vehicles(61603263)" to conduct fault tolerant control research on one-phase open and two-phase open faults of six-phase permanent magnet synchronous motor.This thesis takes the neutral point isolated dual Y displacement 30° six-phase permanent magnet synchronous motor as the research object,Based on their working principles and mathematical models,a simulation model is established in MATLAB / Simulink.According to the space vector decoupling coordinate transformation,the fundamental wave space and the harmonic space are respectively subjected to the rotation transformation feedback control and the simulation research analysis are carried out.In this thesis,the six-phase permanent magnet synchronous motor is fault-tolerant after one-phase open,considering the impact of its fifth harmonic,a six-phase static coordinate transformation matrix corrected after the fault is established,according to the matrix and the rotation coordinate transformation matrix,the mathematical model of voltage and torque in fundamental space is established,at the same time,the quadratic rotating coordinate transformation matrix which eliminates the decoupling of d-q axis voltage coupling is adopted.Considering the influence of the fifth harmonic flux linkage and inductance on the voltage and torque of the six-phase permanent magnet synchronous motor in fault-tolerant mode.For the fifth harmonic disturbance in voltage and torque,the feed-forward voltage compensation expression is derived.The feed-forward compensation method effectively reduces the harmonic current content.A closed-loop control strategy based on the minimum constraint of stator copper loss is established,and simulation verification analysis is performed.Considering the influence of the fifth harmonic flux linkage and inductance on the voltage and torque in the fault-tolerant mode of the six-phase permanent magnet synchronous motor,a control method of injecting fifth harmonic current to eliminate thetorque ripple with quadruple and sixfold angular frequency.After adopting fault-tolerant control,different stationary coordinate transformation matrix and rotation transformation matrix are established respectively according to fundamental space and 5th harmonic space.According to different space characteristics,the flux linkage,voltage and torque equations in the fundamental wave space and the 5th harmonic space are obtained.Finally,by calculating the injection ratio of the fundamental current and the 5th harmonic current,the four-fold angle can be eliminated.Torque ripple at frequency and six times the angular frequency.At the same time,according to the minimum constraint condition of the stator copper loss,the torque ripple with one-fold angular frequency and five-fold angular frequency is eliminated.Simulation results prove that this fault-tolerant control method not only eliminates a lot of torque ripple,but also improves the torque output capability.Based on the analysis of magneto-motive force of six-phase permanent magnet synchronous motor under two-phase open condition,a mathematical model of fault-tolerant control under orthogonal two-phase open condition was established and simulated.