Research On Control Strategy Of Modular Multi-unit Permanent Magnet Synchronous Hub Motor

Modular multi-unit motors usually adopt the spatial structure of circumferentially arranged units.Since there is no potential difference between the units,in order to avoid phase-to-phase circulation,independent power devices are used for control.Compared with traditional three-phase motors,modular multi-unit motors have stronger fault tolerance.At the same time,compared with the multi-phase motor,the control algorithm of the modular multi-unit motor can be realized by using a lower-dimensional control algorithm,and the control algorithm is relatively simple,so the motor has a broad application prospect in the field of low voltage,high current and high reliability such as electric vehicles.The torque distribution algorithm of each module during normal operation and the fault-tolerant control algorithm under single-phase and two-phase open circuit faults are proposed,which lays a theoretical foundation for the further application of modular multi-unit motors.The main research contents and key fruits of this thesis are as follows:1.Combined with the symmetry of the modular multi-unit motor structure,the motor operating mode was formulated;furthermore,the iron and copper loss distribution rules during operation were analyzed,and the q-axis current distribution principle of each module was proposed;based on the power device switching loss and the law of system efficiency change,a method for calculating the number of modules put into operation at light load is proposed.2.According to the principle of magneto-motive force invariance,a fault-tolerant current hysteresis control algorithm is proposed.Based on the analysis of the complexity of control algorithm,copper consumption,power factor and other factors,the structure of fault-tolerant motor control system and the calculation method of healthy phase current are proposed.3.In order to solve the problems of current hysteresis control,such as the varying switching frequency and the high current harmonic content of the healthy phase and the torque ripple,based on the carrier pulse width modulation strategy,a SP-OC-CBPWM and a DP-OC-CBPWM fault-tolerant algorithm suitable for single-and two-phase open circuit faults is proposed,respectively.4.Based on the traditional three-phase space voltage vector modulation algorithm,a SP-OC-SVPWM fault-tolerant algorithm suitable for single-phase open circuit faults is proposed.This algorithm makes up for the shortage of the carrier pulse width modulation algorithm which cannot realize the independent control of each unit motor.5.Based on model predictive control theory,a fault-tolerant control algorithm for two-phase open circuit faults is proposed,and by adding space voltage vector modulation strategy and compensation for vector screening calculation time,the torque ripple and phase current fluctuation are greatly reduced.6.A three-phase 48-slot/52-pole modular four-unit permanent magnet hub motor was developed.The performance of the motor under different operating conditions,such as normal operation,single-phase open circuit and two-phase open circuit,was analyzed by simulation and experimental test,and the effectiveness of the above algorithm was verified.