Analysis and control of single-phase transformerless dual-frequency grid-connected inverter

To simplify the inverter topology and suppress the leakage current more effectively, a novel transformerless dual-frequency grid-connected inverter with a common direct current (DC) bus is proposed. The proposed inverter retains the advantages of the traditional dual-frequency inverter such as high efficiency and absence of resonance. In the novel topology, the power unit adopts the highly efficient reliable inverter concept (HERIC) topology with a unipolar modulation strategy, and the auxiliary unit adopts the H-bridge topology with a bipolar modulation strategy. It is verified that the circulating current between the two units can be eliminated in the proposed inverter. The sensitivity of the circulating current is discussed by considering the tolerance of the filter inductances. In the leakage current equivalent circuit, the DC bus of the power unit is connected to the grid through a low-impedance branch in parallel with the parasitic capacitance. Therefore, the leakage current is effectively suppressed. Finally, the experimental results are provided to verify the performance of the inverter. A novel transformerless dual-frequency grid-connected inverter with a common DC bus is called CDB-DFI; the CDB-DFI that is composed of two units can not only eliminate the circulating current between two common DC units but also suppress the leakage current more effectively.image