Common-Mode Current Reduction at DC and AC Sides in Inverter Systems by Passive Cancellation

It is well known that PWM inverters generate common-mode (CM) voltages, which may cause the CM electromagnetic interference and leakage current in the applications such as photovoltaic or motor drive systems. The CM noise issue becomes more severe with the application of silicon-carbide devices, which have higher dv/dt than silicon devices. In this article, a passive cancellation method is proposed by inserting two CM transformers (CMT) into the input and output side of the inverter, respectively. The selection of the turns ratio for two CMTs is analyzed and revealed to achieve the best CM noise cancellation, and the influence of the parasitics in the CMT is investigated as they limit the bandwidth for CM noise cancellation. Compared to the passive filter, floating filter, and the active cancellation method, the proposed method could reduce the CM noise at both sides simultaneously regardless of the CM impedance of the source or the load. A single-phase inverter is built, and the proposed method achieves 40 dB reduction at both sides, which verifies the effectiveness of the proposed method.