A Transformer-Less High-Gain Inverter with Step-up/down and Single Energy-Processing Features

Many transformer-less pseudo DC-link inverters with step-up/down feature have been proposed to simplify circuit complexity and improve efficiency. Among them, the traditional boost converter is usually used to step up output voltage. In actuality, however, voltage gain will be limited by both the parasitic resistance of the power components and the reverse-recovery problems exhibited by the power diodes under a high duty ratio. Therefore, in order to develop grid-tied photovoltaic (PV) power systems with 220 Vrms voltage, this paper proposes a transformer-less high-gain step-up/down inverter. The proposed inverter is composed of a high-gain boost converter and a full-bridge unfolder. The input current is equally shared by the two boost inductors, so the conduction losses can be reduced to improve efficiency. A partial sinusoidal pulse-width modulation (P-SPWM) controls the full-bridge unfolder to implement the step-down function. The proposed inverter requires only a single stage of energy processing to generate 220 Vrms sinusoidal output voltage. Finally, a 1kW laboratory prototype is built using careful analysis and design procedures. The experimental results are provided to verify the validity and feasibility of the proposed inverter.¹