Improving DC-Link Voltage Utilization in PMSM Drives with Resistance Asymmetry via Active Harmonic Injection

This paper presents an active harmonic current injection scheme for permanent-magnet synchronous machines (PMSMs) considering resistance asymmetry. Conventional control methods suppress the negative-sequence current caused by the parameter asymmetry to mitigate the undesired torque ripple in PMSM with resistance asymmetry. However, the use of additional harmonic voltages for harmonic current reduction can result in the increased voltage amplitude and decreased dc-link voltage utilization. To address this issue, an active harmonic injection scheme is proposed to suppress voltage fluctuation by injecting appropriate d-axis harmonics. The key principle involves injecting appropriate d-axis harmonics to counteract the fluctuations in stator voltage amplitude caused by q-axis harmonic regulation. A cascade structure of resonant controllers is employed to simultaneously regulate both the harmonic voltage and harmonic current. Comparative simulations and experiments are carried out to verify the correctness of the presented analysis and the effectiveness of the proposed scheme. It is verified that the proposed scheme can effectively reduce the torque ripple while achieving higher dc-link voltage utilization than existing methods. Consequently, the proposed solution is effective even under conditions with limited dc-link voltage margin.