Leakage current analysis of grid connected transformerless solar inverters with zero vector isolation

The leakage current due to parasitic capacitance of the photovoltaic modules of the widely utilized transformerless photovoltaic inverters is confined by the standards to 300 mA-peak for safety reasons. This paper investigates the leakage current of the widely utilized zero vector isolating grid connected transformerless solar inverters (ZVI-GCTSI) by means of analytical modeling and simulations. The paper shows, in contrast to common knowledge, the source of leakage current in these topologies is not the inverter common-mode voltage variation but grid voltage variation during zero vector states, in particular near grid voltage zero crossings. It has been shown that the peak currents can exceed several hundred mA levels of standard limits (especially for large parasitic capacitor cases), thus leakage current suppression is required.