A new modulation technique to reduce leakage current without compromising modulation index in PV systems

The transformerless grid-connected PV system suffers from leakage current and neutral voltage imbalance if three-level inverters are utilized. This paper first investigates the common-mode voltage (CM voltage) reduction/elimination methods in three-phase PV inverters, especially three-level inverters. Several mainstream common-mode voltage reduction/elimination methods, including AZSPWM, 2MV1Z, 3MV, 3MV120, are compared in terms of CM voltage reduction/elimination performance, switching losses, modulation index, linear region and neutral point voltage balancing ability. Then a new topology and modulation scheme are proposed, which reduce the frequency of the CM voltage to the order of line frequency and could reach a 100% modulation index. This method is discussed in detail and is verified by simulation.