A 30kW transformer-less PV NPC inverter

Conventional PV power converters are usually based on configurations that include DC-DC boost converter stage, voltage source inverter stage, passive filter stage and grid interface isolation transformer, whose presence implies less efficiency and higher costs, in particular for medium size power PV converters. Thereby, many transformer-less applications have been proposed in the last years and in particular the Neutral Point Clamped inverter is growing as a reference topology. In this paper a transformer-less NPC inverter prototype is described, some discussions on control strategy and phase-locked loop approach are provided; complete experimental results are also given.