A Common-Mode Voltage Reduction Method Using an Active Power Filter for a Three-Phase Three-Level NPC PWM Converter

This article proposes a common-mode (CM) voltage reduction method using an active power filter (APF) and common-mode transformer (CMT) for a grid-connected three-phase three-level neutral-point-clamped (NPC) AC-DC pulsewidth modulation (PWM) converter. The CM voltage can be caused by switching operations of converters and the CM voltage should be reduced because it is one of the main causes of electromagnetic interference (EMI) noises. In this article, the CM voltage of the three-phase converter with the proposed APF is analyzed to explain the CM voltage reduction using the proposed APF. Based on this analysis, the application of a specific PWM method to the three-phase converter for an optimal reduction of the CM voltage is described. Besides, the APF circuit design and its switching method are proposed considering practical problems such as the self-resonance of inductors and the effect of the dead-time on the CM voltage. To prove the effectiveness of the proposed APF on the CM voltage reduction, experimental results for the CM voltage and current are presented in this article. Furthermore, EMI noise measurement results are shown to verify the performance of the noise reduction capability of the proposed APF.