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

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.