Performance Evaluation of Single Phase Transformerless Inverter for Grid-connected Photovoltaic Application

Abstract

This paper presents the performance evaluation of single-phase grid-connected transformerless inverter according to the level of leakage ground current. The leakage ground current ismeasured through the parasitic capacitance of PV array when the high or line transformer is omitted in the system. To prevent the electric shock, the low amplitude of leakage current is important to be achieved. The factors contribute to the leakage current, which are the PWM techniques used; parasitic capacitance and AC filter are investigated in this paper. From the Matlab Simulink simulation result, Bipolar SPWM achieves zero leakage current due to constant common mode voltage. Meanwhile the Unipolar SPWM has higher leakage current due to changing common mode voltage. However, the leakage current is reduced when the inductor filter magnitude is doubled. Generally, the efficiency of unipolar SPWM is slightly higher compared to bipolar SPWM and further improved when the inductor filter magnitude is doubled. The increase in the parasitic capacitance slightly reduces the efficiency of the inverter as well. From this finding, it is concluded that factors such as parasitic capacitance of the PV array, the PWM switching method used and the filter design must be taking into consideration in the design of the transformerless PV inverter in order to achieve minimum leakage current according to VDE-415 standard and optimum efficiency.