A Quasi-Z-Source-Based Space-Vector-Modulated Cascaded Four-Level Inverter for Photovoltaic Applications

Abstract

This article proposes a single-stage buck-boost topology for photovoltaic (PV) applications with a three-phase output. This power converter is constituted by three quasi-Z-source (qZS) networks that are integrated with a four-level cascaded multilevel inverter (FCMI). Compared to the conventional multilevel inverter (MLI) configurations, such as the neutral-point-clamped (NPC) and the cascaded H-bridge (CHB) inverters, the proposed topology is structurally simple with lesser number of components. The proposed power converter and its modulation scheme enhance the boost factor by 50% compared to the aforementioned topologies while alleviating the voltage stress on the switching devices. It is shown that the proposed converter can regulate the output voltage in the stand-alone mode by controlling the shoot-through duty ratio of the qZS networks. Furthermore, it is shown that the proposed converter can be interfaced with the grid by controlling the modulation index along with the shoot-through duty ratio to achieve the twin objectives of maximum power point tracking (MPPT) and the unity power factor (UPF) operation with the grid. The simulation studies and experimentation on a scaled-down laboratory prototype verify the steady-state and dynamic performances of the proposed power circuit configuration and the associated control strategy