Transformerless photovoltaic systems using neutral point clamped multilevel inverters

In some photovoltaic applications it is possible to remove the transformer of the system in order to reduce losses, cost and size. In transformerless systems the photovoltaic module parasitic capacitance can introduce leakage currents in which the amplitude depends on the converter topology, on the pulse-width-modulation and on the resonant circuit composed by the system components. In this paper a modulation technique for three-phase neutral point clamped multilevel inverters is proposed to eliminate the leakage current in photovoltaic systems without requiring any modification on the multilevel inverter. The neutral point clamped inverter is studied for systems with function of active filter using the p-q theory. The proposed system presents control of the maximum power point and compensation of current harmonics and reactive power.