A Novel Bidirectional Transformer-less Gridconnected Inverter with Common-Mode leakage current suppression

Abstract

To suppress the common-mode leakage current, a bipolar modulation on 2-level full bridge usually has to be chosen at the sacrifice of lower efficiency and higher cost compared to unipolar modulation. In this paper, a novel bidirectional transformerless grid-connected inverter topology with the corresponding hybrid PWM modulation is proposed to achieve both low common-mode (CM) leakage current and high efficiency at the same time. In the proposed topology, dv/dt on the CM stray capacitor can be well controlled by adding only a filtering capacitor so that strong attenuation to the high-frequency CM leakage current is achieved. Thus, the unipolar modulation scheme can be employed in current shaping which makes the inverter lower cost and higher efficiency. Additionally, with the introduction of the auxiliary filtering capacitor, conventional L filer can be reconfigured to LCL structure without adding additional inductor. Highfrequency differential mode ripple current filtering performance is also well improved. To illustrate the benefits the proposed inverter topology, a benchmark on efficiency, cost, power density and common-mode current is conducted between several candidate topologies. An inverter prototype is also built up using Silicon Carbide (SiC) MOSFETs. The simulation and experimental results are given to demonstrate the effectiveness and feasibility of this novel topology with hybrid PWM modulation.