Control of grid connected photovoltaic system using dual three-level stage conversion

This paper presents the control of a photovoltaic distributed generation system based on dual-stage topology of three level DC-DC boost converter (3LBC) and three-level neutral-point-clamped (NPC) voltage source inverter (VSI). Decoupling control strategy of three-level VSI is proposed to control the current injected into the grid, reactive power compensation, and DC-link voltage. The resulting system is able to extract the maximum power from photovoltaic generator, to achieve sinusoidal grid currents, and to ensure reactive power compensation. The design and the selection of 3LBC are based not only on boosting up the photovoltaic generator (PVG) voltage but also to ensure equal balancing of the DC-link voltage capacitors. Moreover, they do not change the conventional three-level space vector modulation witch required heavy computational capability to implement the neutral point balance control algorithm. The proposed system performance is investigated at different operating conditions.