Two-stage converter with reduced leakage currents for transformerless photovoltaic systems

Abstract

In this paper the two-stage converter modulated by a proposed pulse-width modulation technique is presented as a low cost and high efficiency solution for reducing the leakage currents in three-phase transformerless photovoltaic systems. Transformerless topologies naturally present lower cost and size and higher efficiency when compared with conventional solutions. As counterpart, these systems present high ground leakage currents, due to the absence of galvanic isolation, and they should have a boost stage to compensate the absence of the step-up transformer. The two-stage converter modulated by the conventional space vector modulation has the dc-dc boost stage necessary to connect the photovoltaic system to the grid, but presents high leakage currents caused by the modulation technique and the dead-time of the voltage source inverter. Therefore, a specific modulation technique that maintain the common-mode voltage of the system constant even during the inverter's dead-time is proposed, in order to reduce the circulating ground leakage currents. Simulation and experimental results are obtained to validate the proposed system.