Optimal Power Flow Control in a Stand-Alone PV System with a Battery-Assisted Quasi-Z-Source Inverter

This paper presents a photovoltaic (PV) power system with a battery storage unit and the quasi-Z-source inverter (qZSI). This inverter belongs to the group of transformerless single-stage inverters with buck/boost capability. The considered system is designed for autonomous load supply and battery charging in areas isolated from the utility grid. The batteries ensure continuous operation in the case of energy shortage/surplus and compensate for the oscillations of the PV power due to changes in atmospheric conditions. They also enable capturing of the maximum available power from the PV modules. The maximum power point tracking (MPPT) algorithm utilized in this study belongs to the group of perturb-and-observe (P&O) algorithms, which are widely used in commercial PV systems. The state of charge (SOC) of the employed batteries represents an important factor in the context of MPPT operation and is taken into account in the proposed power flow control algorithm. The performance of the proposed system has been tested through simulations in the MATLAB Simulink over wide ranges of solar irradiation, PV module temperatures, and SOC levels.