Common Mode Circulation Current Suppression Method for Dual-Frequency Converter based PMSM Drive

In order to improve the efficiency of the permanent magnet synchronous motor (PMSM) and reduce the volume and mass of the motor, the PMSM is developing to the direction of high speed and high power. Using the dual-frequency converter, the high switching frequency characteristics of SiC-MOSFET converter can effectively suppress the motor current harmonics, while making full use of the advantages of low cost and large capacity of Si-IGBT converter. However, there is a serious common mode circulation between the two-frequency converters. In order to suppress the internal common mode circulation of dual-frequency inverter(DFI), the circulation mechanism is analyzed in detail and a new suppression method is proposed. In the proposed method, the common mode voltage of the low frequency inverter(LFI) is extracted and feed forward to the high frequency converter in each high frequency PWM cycle, and a closed-loop feedback control is performed for the output zero sequence current of the high frequency inverter(HFI). With the proposed method, the common mode circulation and the switching loss is effectively reduced. Specially, in order to avoid the saturation of the HFI output voltage caused by the low-frequency common-mode voltage(CMV) feed-forward, an improved SVPWM modulation method based on the zero-sequence voltage time distribution is adopted. Simulation verified the proposed method.