A Single-Phase Transformer-Less Grid-Tied Inverter Based on Switched Capacitor for PV Application

In this paper, a transformer-less grid-tied single-phase inverter is proposed which is directly connected to the topology. The voltage across the leakage capacitor has the base frequency, which decreases the leakage current under the defined value in the standards. This inverter's active switches are high- and low-frequency types. High-frequency switches control the inductor's current. In addition, the low-frequency switches are synchronous with the grid and operate in the base frequency. Since no power electrolytic decoupled capacitor is utilized between the high- and low-frequency switches, the system's total efficiency and lifespan are improved. The proposed inverter has the capability of stepping up/down the output voltage, making it suitable for operating in a wide range of voltages and also providing large range of powers to the grid. This topology is directly connected to the grid, without any output filter, leading to elimination of the losses caused by the filter and increased efficiency. In the proposed inverter, a digital current controller is employed to control the injected current to the grid. Furthermore, P&O algorithm is adapted to extract the maximum power from the input source. For proving the proposed converter's performance, a 770-W prototype has been implemented and comprehensive experimental results are presented.