Design of the Neutral Line Inductor for Three phase Four leg Inverters

The three-phase four-leg inverter is one of the advanced solutions to feed unbalanced loads. However, the design of the neutral line hasn’t been well studied yet. This paper presents a mathematical model of the three-phase four-leg inverter with neutral line inductor, which is decoupled in the αβ0 coordinate and illustrates the effects of the neutral line inductor on filter inductor current ripple. Then, several constraints are derived limit the value of the neutral line inductor, including the filter current ripple and the dc-link voltage. In order to determine the value of neutral line inductor, simulation analysis is also conducted. Through comparing the system efficiency and the performance of output voltage, the optimal value of the neutral line inductor is finally obtained.