Night operation, analysis, and control of single-phase quasi-Z-source photovoltaic power system

The existing single-phase, quasi-Z-source inverter (qZSI), photovoltaic (PV) power system with integrated battery energy storage (BES), abbreviated as BES-qZSI-PV power system, has several well-known advantages, but cannot operate at night because there is no PV power input. In this study, a solution to overcome this issue is proposed. First, the power circuit of the conventional BES-qZSI-PV topology is modified to allow its operation at both day and night. Then, the system model for the night-operation mode is built and a qZS network parameters' design method to limit the double-line frequency harmonic at the dc side is developed. A control strategy to ensure the high-performance operation of the system at all times, is proposed. Based on an experimental platform of single-phase BES-qZSI-PV power system, three groups of experimental tests with different qZS network parameters and battery voltages are carried out to verify the model and parameters design method by means of comparing the experimental, circuit-based simulated, and model-based calculated results. The proposed BES-qZSI-PV system performance is experimentally evaluated in steady-state operation and day-to-night transit operation, as well as by the power efficiency curves in day- and night-modes.