A Day and Night Operational Quasi-Z Source Multilevel Grid-Tied PV Power System to Achieve Active and Reactive Power Control

Abstract

A day and night operational single-phase energy stored quasi-Z-source-cascaded H-bridge (ES-qZS-CHB) inverter photovoltaic (PV) power system to achieve the active and reactive power control is proposed in this article. The ES-qZS-CHB inverter PV power system usually employs the unity power factor control method to ensure the output current tracking the desired reference in phase with the grid voltage, combining with distributed maximum power point tracking (MPPT) to determine the values of shoot-through duty ratios Dn. These cannot operate at night because there is no PV power input. Meanwhile, as multiple combinations of Dn and modulation ratio Mn could achieve the same voltage gain at night operation, but which is optimal has not been addressed. This article proposes a solution to address these issues. First, a comprehensive control scheme, which not only has the attractiveness of day and night operation but also shows the advantage of active and reactive power control simultaneously, is proposed; then, an optimization control method is proposed for night operational ES-qZS-CHB inverter to achieve optimal combination of Dn and Mn. Simulation and experimental results validate the day and night operational ES-qZS-CHB inverter and the proposed optimal control technique.