3-LEVEL Z-SOURCE INVERTER BASED PV SYSTEM WITH BIDIRECTIONAL BUCK-BOOST BESS

Abstract

Z-source inverters (ZSI) have a unique ability to achieve single stage voltage buck-boost operation for energy conversion. This thesis presents a three-level ZSI using a single LC impedance network for photovoltaic (PV) application. The network is used between DC voltage source (including PV array and a bidirectional buck-boost system) and neutral-point-clamped (NPC) inverter to achieve the desired stepped-up and stepped-down output voltage level as per the solar variation. 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 (Perturbed and Observed (P&O) 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 boosting the Z-network capacitor voltage more than the maximum power point (MPP) voltage of the PV array. This thesis 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 with BESS according to generation-demand is discussed. This proposed topology not only tracks MPPT output voltage but also maintained constant output voltage with wide range of variation of insulation (irradiance). To validate the proposed scheme the system is extensively simulated in MATLAB/Simulink.