3-level Z-source inverter based PV system with bidirectional buck-boost BESS

This paper presents a three-level ZSI for photovoltaic (PV) application to achieve single stage buck-boost (as per the solar variation). A single LC impedance network is used between DC voltage source (including PV array and a bidirectional buck-boost system) and neutral-point clamped (NPC) inverter. 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. Traditional MPPT technique (like Perturbed and Observed (P&O)) does not allow boosting the Z-network capacitor voltage more than the maximum power point (MPP) voltage of the PV array. This paper 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.