Overmodulation Strategy Based on Dynamic Voltage Boundary Regulation for Electrolytic Capacitorless PMSM Drives

Due to the periodic dc-link voltage and the fluctuation of the reference voltage vector, which is caused by the incomplete voltage compensation, the electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives have obvious harmonics in overmodulation (OVM) regions. To address this issue, a novel OVM strategy based on dynamic voltage boundary (DVB) regulation is proposed. By analyzing the trajectories of output voltage vectors with the consideration of periodic fluctuation, the harmonics of stator voltage caused by switching aliasing in OVM regions are revealed. The OVM regions are divided by a dynamic voltage which contains the characteristics of reference voltage vectors. Then the action time of fundamental vectors can be obtained by using the dc-link voltage and the dynamic voltage. Based on the fluctuating information of dynamic voltage, OVM regions can be smoothly switched with the dc component of the amplitude of reference voltage vectors. The proposed method can reduce the fluctuation of reference modulation index (RMI), thus decreasing the total harmonic distortion (THD) of stator voltage and current. Experimental results on a 2.2 kW electrolytic capacitorless PMSM platform validate the effectiveness of the proposed method.