Three-Phase-Four-Wire Three-Level Inverter with Neutral Inductor and Neutral Module for Saving AC-Filter-Inductances and DC-Link-Capacitances

Three-phase-four-wire (3P4W) three-level (3L) inverters are widely used for feeding unbalanced ac loads. Because of the neutral wire, however, the size and volume of the ac filter inductors and dc-link capacitors are much increased, leading to reduced power density. This paper discusses the way of reducing ac filter inductances and dc-link capacitances in the 3P4W 3L inverter. To save the total ac inductances, a neutral inductor is proposed to insert in the neutral wire, and closed-form formulas are derived for guiding the ac filter design. To minimize the dc-link capacitances, a neutral module is employed to bypass part of the midpoint current and neutral wire current. Finally, the proposed works are verified on a 10-kVA 3P4W 3L inverter.