Motor-Parameter-Free Solution of Optimal Harmonic Currents for Torque Ripple Reduction of PMSM Drives With Response Surface Method

Torque ripples of permanent magnet synchronous motors (PMSMs) will degrade the torque performance of PMSM drive systems in high-performance applications and are one of the sources of vibration and noise. To reduce torque ripples, one of the solutions is to inject harmonic currents into stator windings, so that extra torque ripples are generated to compensate for the original ones. To obtain the optimal harmonic current solutions, torque ripple model (TRM) and speed harmonics are commonly used in optimization. However, the performance of TRM-based methods in torque ripple reduction is limited due to the accuracy of the PMSM TRM model and motor parameters. Also, the speed harmonic-based methods have speed limitations, since the speed harmonics caused by torque ripples will be filtered out by the inertia of the drive systems when the motor is operated over the cut-off frequency. Therefore, one torque ripple reduction method with no motor parameters involved and with no speed limitations needs to be discussed and proposed. In this article, the response surface TRM for PMSM drives is first established based on the measurements of speed harmonics. Based on the response surface TRM, the motor-parameter-free solution of optimal harmonic currents is analytically derived for torque ripple reduction with minimal motor loss. The proposed method is verified by experimental results, which demonstrate that the proposed method can reduce torque ripples of PMSM drives effectively without prior knowledge of any motor parameters and can also avoid the limitation of speed operations.