An Enhanced Current Control Structure for Ultra-High-Speed Permanent Magnet Synchronous Motor Applications

In traditional low-speed AC drives, the stability and design of the current control system have been extensively studied. However, for ultra-high-speed (UHS) motors, the same stability analysis and current closed-loop design techniques cannot be applied directly. This study focuses on analyzing the stability issues of the current controller of the UHS permanent magnet synchronous motor (PMSM). The three sources of instability are found and explained in detail. To mitigate these issues, a special current controller structure is proposed for UHS PMSM. By using this control structure, the transfer function of a closed-loop current system can be set to have the desired behavior of a low-pass filter even at very high fundamental frequencies. Furthermore, to improve the robustness of the current controller in case of electrical parameters change or electrical parameters uncertainty, a new transient state compensator is included in the proposed control structure. Its performance is verified through a series of experiments. It is found that with the proposed current controller, the motor is able to stably operate at very high rotational speeds and achieves smooth transient performance.