Modelling and Control of Four Leg Inverter with Utilization in Power Quality Improvement in Grid Connected System

In standalone power supply system, three phase inverter with an additional neutral leg is used to deal with load unbalance. The goal of the three phase four leg inverter is to maintain the desired sinusoidal output voltage waveform over all loading conditions and transients. It is ideal for applications like data communication, industrial automation, military equipment, which require high performance uninterruptible power supply. The three phase four leg inverter can be utilized in grid connected system as power converter to inject power generated from photovoltaic cell to the grid and also as shunt APF to compensate current unbalance, load current harmonics, load reactive power demand and load neutral current. All these functions may be achieved either individually or simultaneously. In this paper the topology of three phase four leg inverter is shown along with its control. The MATLAB/Simulink based simulations are provided which support the functionality of the four leg inverter.