Comparative study of topologies for three-phase transformerless photovoltaic systems

This paper introduces a comparative study of three topologies with voltage boost capability for three-phase transformerless photovoltaic systems: two modifications of the original Z-source inverter and the conventional two-stage converter (dc-dc boost converter plus voltage source inverter). First, an overview on pulse-width-modulation possibilities for these converters is given, in order to compare its main characteristics. In special, a study of losses is presented and its methodology is used to compare the three topologies in such a way that the option of best efficiency can be chosen. The loss models of the switches and diodes based on the operating points given by data sheets or based on PSpice models of the devices are used to estimate the converters overall efficiency. As result of the comparative study, the conventional two-stage converter appears as the lowest cost and highest efficiency structure among those studied. Simulation and experimental results of the two-stage converter are obtained to validate its application in three-phase transformerless photovoltaic systems.