A Single-Phase Five-Level Transformer-less PV Inverter

Abstract

Single-phase five-level transformer-less inverter has been widely used in photovoltaic (PV) applications because of low total harmonic distortion (THD) and excellent output quality. However, a serious problem for transformer-less inverters is the leakage current issue which will lead to safety problems. This paper proposes a single-phase five-level transformer-less inverter to eliminate the leakage current. The circuit consists of eleven active switches and can keep the common mode voltage half of the DC bus voltage. The voltages of flying capacitors are balanced within one switching cycle through selecting the proper switching states. The mechanism of suppressing the leakage current is analyzed in detail with operational modes and modulation strategy. A 1 kW single-phase five-level inverter prototype is built to verify the validity and flexibility of the proposed topology and modulation.