Two-degree-of-freedom Quasi-PIR Controller for Smooth Speed Control of Permanent Magnet Vernier Machine

In the direct-drive applications, the low-frequency torque ripples produced by some nonideal factors of the system deteriorates the control performance. The proportional-integral-resonant (PIR) controller is generally employed to suppress the torque ripple and smooth the speed. Generally, the PIR controller is designed based on the internal model principle, and quasi-PIR controller is usually employed instead of the classical PIR controller due to its less sensitivity to the resonant frequency. However, the disturbance rejection ability of the quasi-PIR controller is restricted by the measurement noise. Moreover, undesired dynamics will be caused by the rapid change in speed reference and multiple resonant controllers are required for suppressing multiple torque harmonics. In this paper, a new design method of the PIR controller is introduced to show the essence of the resonant controller. Instantaneous speed observer is employed to suppress the measurement noise so that better disturbance rejection ability of quasi-PIR controller can be achieved with higher gain. To avoid the undesired dynamics, two-degree-of-freedom quasi-PIR controller is proposed by employing a tracking differentiator as the prefilter for speed reference. With the proposed TDOF quasi-PIR controller, multiple torque harmonics can be suppressed by only one resonant controller. Experimental results are shown to verify the proposed method.