A Constant Common Mode Voltage Single-Phase Five-Level Transformerless PV Inverter Considering the Effect of Switch Device Junction Capacitance

Abstract

Constant common mode voltage (CCMV) is critical in Solar Photovoltaic (SPV) systems. Maintaining CCMV further eliminates the voltage transitions across the parasitic capacitance of the PV panel, making it a low-frequency output voltage wave-form. This further reduces the CMC and leakage current in the SPV systems. This paper presents a CCMV switched capacitor PV inverter configuration that maintains a low-frequency terminal voltage while considering the effect of switch device junction capacitance (SDJC). Thus, the proposed configuration eliminates the transitions in the common mode and terminal voltage due to the SDJC. The two switched capacitors employed in the proposed configuration are charged and discharged within each switching period, supporting the self-charge balance feature apart from low voltage and RMS current rating, reducing its size and value. Further, the proposed system effectively utilizes the PV source as switch capacitors and the DC-bus buffer capacitor across the PV source comes in parallel in each switching period. The proposed configuration can also operate at lower modulation indices, generating three levels with CCMV. A new mathematical analysis considering SDJC is given for the derivation of expression for CMV and terminal voltage, which is further verified using simulation and experimental results.