A Novel High-Efficiency Three-Phase Multilevel PV Inverter With Reduced DC-Link Capacitance

In this article, we present a novel three-phase multilevel inverter (MLI) design for photovoltaic applications which does not require large dc-link capacitors to buffer the 120-Hz power ripple and allows individual inverter module to process trapezoidal power instead of sinusoidal power. This new design features two inverters connected in parallel to each dc source and N inverters connected in series to each grid phase to support the grid voltage. The trapezoidal operation improves the overall system’s efficiency by allowing the inverter module to output peak or zero power for most of the ac cycle. We present the controller design and simulate the proposed MLI system in power electronics simulation software (PLECS). We demonstrate an experimental 110-V dc input, 208 $V_{\text{rms}}$ three-phase ac output, and 1-kW five-level prototype with $>$ 95% efficiency. With the same inverter module, we compare the efficiency of the proposed design to the conventional MLI design, where all modules share phase power evenly. We demonstrate that the proposed design consistently outperforms the conventional design in efficiency, with $>$ 20% loss reduction at light load conditions.