Overmodulation Strategy for Electrolytic Capacitorless PMSM Drives: Voltage Distortion Analysis and Boundary Optimization

Permanent magnet synchronous motor (PMSM) drives equipped with slim film capacitors have many advantages, including longer lifetime, smaller volume, and lower cost. However, improving the dc-link voltage utilization rate by the typical overmodulation strategy will cause the distortion of the stator voltage and current due to the dc-link voltage fluctuation. In this article, the influence of the dual-mode overmodulation strategy used in the small dc-link capacitor PMSM drive, including the stator voltage distortion and uncontrollable time for entering the six-step operation, is analyzed. A novel overmodulation strategy named as the optimized voltage boundary-based overmodulation strategy is proposed to reduce the distortion of the stator voltage and current. By switching between the actual dc-link voltage and the fixed dc-link voltage used for space vector pulse width modulation (SVPWM), the performance can be improved in the overmodulation region if the value of the dc-link voltage for SVPWM is selected appropriately. Experimental results on a PMSM drive platform are provided to verify the effectiveness of the proposed strategy.