Three-level PWM for grid-connected PV inverter considering switching loss and common-mode voltage

Abstract

Photovoltaic (PV) power generation has attracted many attentions for a decade. Both two-level and three-level inverters are commonly used topologies to feed the power into the three-phase electric grid system. Further, the three-level neutral point clamped inverter is always applied to the transformerless photovoltaic grid-connected system because of its low leakage current and the low voltage stress comparing with the two-level inverters. In the transformerless grid-connected PV inverter system, both reliability and the efficiency are important factors. Because of no isolation, the common-mode voltage of the inverter must be low to prevent adverse effects from the leakage current. Further, the switching loss must be low to have high efficiency. In this paper, a low switching loss PWM strategy with low common-mode voltage applied to three-level grid-tied inverter is shown. Comparing with the conventional carrier-based phase disposition PWM, both common-mode voltage and the switching loss are improved.