Modeling and Control of Quasi Z-source Cascaded H-bridge Multilevel Inverter for Grid Connected Photovoltaic Systems

This paper presents the modeling and controlling the power of Quasi Z-Source cascaded H-bridge multilevel inverter for grid connected photovoltaic systems. The Quasi Z-Source inverter is an inverter that provides buck / boost output along with DC-AC conversion in a single stage. This topology has numerous advantages which makes it reliable and suitable for PV applications. Due to the impedance network and the cascaded H-bridge structure, it provides high gain, reduced total harmonic distortion (THD) and high reliability in PV systems. In this paper, a five level cascaded H-Bridge Quasi Z-source inverter has been considered for which the impedance network has been designed. Phase Shifted Inverted Sine carrier pulse width modulation has been implemented along with shoot- through control for controlling the switches of the inverter. The closed loop power control scheme has been implemented in two stages. In the PV input side, each string voltage is controlled by adjusting the shoot-through states of the inverter using Independent Maximum Power Point Tracking Control. DC link voltage of each bridge has been balanced by using DC link voltage control. Both of these controlling actions result in the control of grid injected power. A 2kVA PV inverter has been designed and built using MATLAB/SIMULINK and the hardware has been completed for the open loop control. The simulation and open loop hardware results are discussed.