Control of three-phase cascaded voltage source inverter for grid-connected photovoltaic systems

A three-phase cascaded voltage source inverter (VSI) for a grid-connected photovoltaic (PV) system is proposed in this paper. The topology consists of three traditional two-level six-switch VSIs interconnected through inductors. Each VSI unit is fed by a string of PV panels. To realize the central control of the proposed system, the equivalent model and average model of the three-phase cascaded VSI are established. To harvest more solar energy, a control scheme with maximum power point tracking (MPPT) control is proposed. Phase-shifted discontinuous PWM (PS-DPWM) is applied to control the switching devices of each VSI unit. Simulation and experimental results are presented to validate the proposed ideas.