Design Methodology for Filter Inductors and Neutral Inductor in Three-Phase Four-Leg Three-Level Inverter

The three-phase four-leg four-wire three-level (3P4L4W 3L) inverters are widely used in mediate-to-high power applications for supplying power to unbalanced and/or nonlinear ac loads. To save filter inductance, a neutral inductor is often inserted in the neutral wire for reducing the ripple of the common-mode (CM) current at the high switching frequency. The filter inductance and the neutral inductance are yet not specifically designed for the 3P4L4W 3L inverter. For obtaining the minimum required inductance, a complete design methodology is proposed for calculating the ac filter inductance and neutral inductance. Finally, simulation results are presented to verify the feasibility the proposed optimized design for the filter inductors and the neutral inductor.