Modelling and controller design of quasi-Z-source cascaded multilevel inverter-based three-phase grid-tie photovoltaic power system

Quasi-Z source cascaded multilevel inverter (qZS-CMI) is an emerging topology applied to photovoltaic (PV) power system. It can overcome disadvantages of conventional CMI-based PV power system, because of achieving the balanced dc-link voltage through using its boost ability, and saving one-third modules. At present, there was not literature to disclose the modelling and controller design for qZS-CMI-based three-phase grid-tie PV power system. In this study, a control scheme for three-phase qZS-CMI-based grid-tie PV power system is proposed, where distributed maximum power point tracking (MPPT) and constant dc-link peak voltage are achieved for all qZS H-bridge inverter (qZS-HBI)-based PV modules, with grid-injected power in unity power factor. The detailed controller parameter design is demonstrated by using Bode plots and the built models of qZS-HBI-based PV module and whole system. A test bench of 7-level three-phase qZS-CMI-based PV power system is built. Simulation and experimental results validate the proposed control scheme and design method.