Implementation of ZVS Concept in Four Wire Inverter for UPS Fed (Unbalanced) Star Connected Load

Abstract

This paper presents a method for controlling the output voltage of a three phase four leg inverter based UPS. The use of a four wire inverter increases the quality of the output whereas the soft switching technique employed helps to increases the overall efficiency of the inverter. Furthermore, in order to improve the system response to load variations, a PI control strategy is proposed. The 4 leg three phase inverters handles the neutral current caused by non-linear loads in a better manner.
The main feature of a 4 leg inverter is its ability to deal with load unbalance in a system. The additional leg maintains a desired sinusoidal output voltage waveform for all loading conditions and transients. The neutral connection is present to handle the ground current due to unbalanced loads. The feasibility of the proposed modulation technique is verified by MATLAB simulation. It also discusses the experimental analysis of the 4 wire inverter.