Transformerless three-phase T-type three-level inverter for medium-power photovoltaic systems

In three-phase PV grid-connected system, the PV panel input voltage can achieve 1000 volt and the power level can reach several kilo-watts. In this paper, a three-phase two-stage three-level transformerless PV system was investigated for the high power and high voltage applications. The multiloop control and the interleaved control method was adopted for the three-level boost DC/DC part, and a carrier modulation method was implemented for T-type three-level inverter. Compared to conversional SVM pulse width modulation method, it has no need of complex computation. All algorithms and controllers were implemented on a single-chip DSP. Experimental results obtained on a 20 KW prototype show high-performance, the power conversion efficiency of the PV system can achieve 98.10%.