A modulation scheme for a 3L-NPC converter in transformerless PV applications

This paper presents a modulation strategy for a neutral point clamped multilevel converter (NPC) used as transformerless inverter in a grid-connected applications. The selected topology is used with an output L filter to inject active power to the grid. The proposed modulation strategy is based in the conventional sinusoidal pulse width modulation (SPWM) for the NPC inverter. This SPWM allows to operate the converter with very low leakage currents, which are generated throughout the stray capacitances as well as accomplish with the international standards. To achieve this aim, also a current mode controller is used to guarantee that the inverter output current is in phase to the grid voltage. To assess the performance of the proposed SPWM in the grid-tied applications, simulation and experimental results are presented.