Three Level Z source Inverter Based Photovoltaic Power Conversion Systems

A Z-source inverter (ZSI) has a unique ability to achieve single stage voltage buck-boost operation for energy conversion. This paper presents a three level ZSI using a single impedance network for photovoltaic (PV) application. A single LC impedance network is used between DC voltage source and neutral-point-clamped (NPC) inverter to achieve the desired stepped-up and stepped-down output voltage level. Alternative phase opposition and disposition (APOD) modulation technique with proper triplen offset and appropriate addition of time delay/advance is used to achieve the required boost in DC link voltage. A traditional MPPT technique is used to introduce a shoot-through interval in switching waveform to extract the maximum power from the PV panel. Traditional MPPT technique does not allow to boost the Z-network capacitor voltage more than the maximum power point (MPP) voltage of the PV array. This paper also presents a unified voltage control technique to track the MPPT and also maintains the desired Z-source capacitor voltage level. The design, implementation and control of single impedance network based multilevel ZSI for photovoltaic application is discussed and their MATLAB/Simulink simulation and results are presented in the later section of the paper to validate proposed control scheme in PV application.