Torque Ripple Reduction of PMSMs using a Novel Angle-based Repetitive Observer

The angle-based repetitive controller (RC) has been applied successfully in literature for torque ripple suppression in variable speed permanent magnet synchronous machines (PMSMs). The RC is preferred because of its learning capability which allows the cancellation of all periodic ripple from multiple sources. However, its tuning method has not yet been proposed. Since the structure of the repetitive controller is found similar to the disturbance observer (DOB) which is convenient to tune through pole placement, this paper merges the angle-based RC and DOB into a novel angle-based repetitive observer (ARO) for the first time for the torque ripple reduction in PMSMs. ARO takes advantages of its DOB structure that it can be designed separately and can easily be added into an existing control loop. Taking advantages of its RC nature, ARO can tackle a wide frequency range of torque ripple even in the presence of measurement noise. The experimental test results have confirmed the robust performance of ARO under five conditions, including the ideal integral delay, the fractional delay, the load transient, the speed transient and the detuned mechanical parameters conditions. The execution time of the ARO is less than 10 μs.