A Novel Three Phase Transformerless Inverter with Negative Grounding for PV Application

Three phase transformerless inverters are quite popular due to its high efficiency and compact structure. However, removal of the isolation transformer can lead to varying common mode voltage across the PV parasitic capacitance. This leads to the flow of a large common mode leakage current which compromises the safety of the inverter. One method to tackle this issue is applying only those vectors wherein the common mode voltage remains constant. However, this reduces the inverter modulation index and leads to poor dc link utilization. In this paper, a novel three phase transformerless inverter is presented wherein the leakage current is directly eliminated by grounding the PV negative terminal. Moreover, the proposed topology facilitates the application of all the active vectors thereby improving the dc link utilization. The proposed topology employs stored energy modulation (SEM) thereby reducing the interlinking capacitor size. The proposed topology is analyzed in detail and its control is discussed. Simulations of the proposed inverter confirm the feasibility and good performance of the inverter.