Torque ripple reduction of PM synchronous motor for wide speed operating ranges

The back emf harmonics of a PM synchronous motor is the main source of the torque ripples. The torque ripples make the mechanical vibration at low speeds and the acoustic noise at high speeds. The feed-forward harmonic currents compensation may reduce the torque ripples at low speeds, but the torque ripples at high speeds can't be reduced due to the limited bandwidth of the current controller. In this paper, the torque ripple reduction algorithm for wide speed operating ranges is proposed. The harmonic currents and the harmonic voltages that cancel the 6th order torque ripples are compensated to the reference currents and reference voltages, respectively. The torque ripples at low speeds are reduced by the compensated harmonic currents, and the torque ripples at high speeds are reduced by the compensated harmonic voltages. It is verified by the analysis and simulation that the proposed compensation reduces the torque ripples for wide speed ranges.