In traditional low-speed ac drives, the stability and design of the current closed-loop system are well-studied areas. However, in the case of ultra-high-speed (UHS) motors, the same stability analysis, and current closed-loop design techniques cannot be applied directly. In this work, the stability issues of the current controller of the UHS permanent magnet synchronous motor (PMSM) are analyzed. The three sources of instability are found and explained in detail. Next, a new method of complex feedforward compensation for the current controller of UHS PMSM is proposed. With the proposed method, 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. Finally, its performance is compared with the traditional proportional-integral (PI) controller and highbandwidth deadbeat controller. The comparison is made through extensive simulations using MATLAB/Simulink. 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

Ultra-high-speed motor, high-speed drives, current control, stability of high-speed drives.