Control and Modulation Method of a Three-phase Eight-switch Inverter for Two-stage Grid-connected Photovoltaic Systems

A novel transformerless two-stage photovoltaic (PV) grid-connected inverter is introduced in this paper. The system is composed of three-level boost (TL-Boost) DC/DC circuit and three-phase T-type eight-switch DC/AC topology. By using the multiloop interleaved control strategy and adjusting the conduction time of power switch phase of the first-stage boost DC/DC part, the inductor current ripple is reduced and the balance of DC bus capacitor voltage could be achieved respectively. Meanwhile, a nine-vector space vector pulse width modulation (SVPWM) algorithm based on optimal five-stage is adopted for eight-switch DC/AC inverter circuit, which could simplify the algebraic operation, reduce the switching loss and improve the utilization of the DC bus voltage. Finally, a 10kW experimental platform is built to verify the validity and effectiveness of the proposed control and modulation method.