Efficiency improved and current balanced three-phase modular cascaded H-bridge multilevel PV inverter for grid-connected applications

A three-phase modular cascaded H-bridge multilevel inverter can be applied to grid-connected photovoltaic (PV) systems. The isolated dc buses make the individual maximum power point tracking (MPPT) control of the connected PV string of each H-bridge module possible. However, with the individual MPPT control, the solar power supplied to each phase of the three-phase system may be different, leading to unbalanced injected grid current. To solve this issue, a control scheme is proposed to improve the PV system efficiency and balance the grid current. The limitation of the proposed control scheme is also discussed. A modular cascaded multilevel PV inverter prototype has been built. Experimental results under different test conditions are presented to validate the proposed ideas.