Uncontrolled Generation Analysis and System Optimization of Permanent Magnet Synchronous Motor for Electric Vehicle

电动汽车永磁同步电机不可控发电分析与系统优化

School of Automation, Northwestern Polytechnical University, Xi’an 710129, China

Received: 14 May 2018

Abstract

When a permanent magnet synchronous motor(PMSM) which is controlled by flux-weakening strategy rotates in high speed, the controller would send the turning-off signals to switch off all the transistors quickly if faults(e.g. overvoltage and overcurrent) occur. At this moment, the equivalent electromotive force is higher than battery voltage due to the high speed of motor, so the current flows into the battery through the uncontrolled rectifier bridge composed of six freewheeling diodes, resulting in the drive system works at the status of uncontrolled generation(UCG). Firstly, the mathematical model of the system is established. Then, according to the theoretical analysis, the UCG process is divided into three stages: transistors turning-off stage, diodes freewheeling and turning-on stage and steady-state UCG stage. It is found that the steady-state UCG process has the shortcomings of large current and long time. Therefore, an optimal protection scheme based on fuzzy control is proposed, which can reduce danger damage of UCG. Finally, simulation and experiment are adopted to study the process of UCG, and the effectiveness of the optimization strategy is verified.

摘要

采用弱磁控制方法使电动汽车永磁同步电机高速运行时，若过压、过流等故障发生，控制器迅速发出关断晶体管的控制信号，此时，由于电机高转速产生的等效电动势高于电池电压，电流通过逆变器中的6个续流二极管所构成的不可控整流桥流入电池，导致电机驱动系统处于不可控发电运行状态。首先，建立了系统的数学模型；然后，通过理论分析将不可控发电过程分为晶体管关断、二极管续流以及导通、稳态不可控发电3个阶段，并得到了晶体管与二极管在不可控发电瞬间的开通关断规律；分析中发现，稳态不可控发电过程具有电流大、时间较长的缺点，故提出了基于模糊控制的系统优化保护策略，从而减小该过程造成的危害；最后，通过仿真和实验深入研究了不可控发电过程，验证了优化策略的有效性。