New high frequency switching method of cascaded multilevel inverters in PV application

Abstract

In recent years, interest of using multilevel inverters have been increased. Among different types of multilevel inverters cascaded one is a good choice of power conditioning in renewable energy application, because of their simplicity, modularity, low switches voltage stress and less number of components. Different switching techniques have been proposed for equal power sharing between cells of multilevel inverter. Low order harmonics and inter harmonics in output voltage of multilevel inverter are problems caused by voltage ripple in dc link capacitors. For solving these problems, a large DC capacitor is needed which increases cost and size of the system and reduces lifetime and reliability. Among multilevel switching techniques, In Phase Disposition pulse width modulation (IDPPWM) have the lowest amount of harmonics. In this method power delivery of the inverter cells are not equal. In this paper a method that improves power sharing in IDPPWM is proposed for photovoltaic (PV) application. This method is compared with similar switching patterns in aspects of dc link voltage ripple and amount of DC link capacitor. The switching pattern is applied to a 7 level inverter in which each H-bridge or cell is connected to a PV array operated at maximum power point (MPP). The 7 level inverter supplies a standalone AC inductive load. Simulations are implemented using MATLAB/SIMULINK software and the results confirm effectiveness of the proposed method in balancing power sharing among different inverter cells and requiring smaller DC link capacitors.