Three-phase seven-switch inverter with common mode voltage reduction for transformerless photovoltaic system

Common mode voltage reduction is one of the most important issues for transformerless PV grid-connected inverters. Many interesting single-phase inverter topologies have been reported to reduce the common mode voltage. However, three-phase PV inverter topologies with reduced common mode voltage are not well explored. In this paper, a novel three-phase seven-switch (H7) inverter is proposed to reduce the common mode voltage. It is derived from the conventional three-phase inverter, but has different operation principles. Therefore, a new modulation is presented to achieve the effective common mode voltage reduction. In addition, a simple control strategy is proposed to achieve the fast and accurate grid current regulation. Theoretical analysis and performance evaluation tests are carried out to verify the effectiveness of the proposed H7 topology and control strategy.