Transformerless nine-level switched capacitor inverter with common-ground for grid-tied PV system

Abstract

Transformerless multilevel inverters (MLIs) with voltage-boosting capabilities have become an attractive choice for utility grid-connected photovoltaic (PV) systems due to their compactness, high efficiency, and cost-effectiveness. However, leakage current caused by the absence of galvanic isolation remains a major concern, affecting both safety and power quality. To address these challenges, this paper proposes a single-phase nine-level (9 L) common-ground (CG) switched-capacitor (SC) inverter with a voltage gain of four. The main novelty of the proposed topology lies in integrating a CG configuration with a high-gain, self-balanced-SC structure to simultaneously achieve complete leakage current suppression, reduced component count, and low device voltage stress without compromising voltage gain. Comparative analysis with state-of-the-art 9 L topologies demonstrates that the proposed inverter offers reduced component count, low device voltage stress, high efficiency, zero leakage current, and lower implementation cost. Experimental validation using a 1.3 kW laboratory prototype under both stand-alone and grid-connected operating conditions confirms the effectiveness of the proposed topology. Owing to its compact structure and high voltage gain, the proposed topology requires a lower input DC voltage, making it particularly suitable for low-voltage PV systems.