A SiC-based Neutral Leg for the Three-phase Four-wire Inverter

SiC-based inverters can operate at high switching frequency with high efficiency, which can reduce the size of passive components and heat sinks to achieve high power density. However, in three-phase four-wire inverters supplying unblanced loads, the second-order ripples in the DC bus need to be mitigated by large DC capacitance, which increases the size of the converter. The conventional neutral leg is widely used in three-phase four-wire inverters to provide neutral currents for the unbalanced loads. In this paper, an improved neutral leg is proposed, which can provide neutral currents and reduce the second-order ripples in the DC bus simultaneously. The DC bus ripples can be reduced without adding any hardware components. Furthermore, the proposed neutral leg can save 50% DC capacitance comparing to the conventional neutral leg. The proposed neutral leg was built with SiC MOSFETs and tested with a three-phase four-wire inverter in the laboratory. The experimental results verified the effectiveness of the proposed neutral leg.