Two-Layer Global Synchronous Pulse Width Modulation Method for Attenuating Circulating Leakage Current in PV Station

This paper proposes a two-layer global synchronous pulsewidth modulation (GSPWM) method for attenuating the circulating leakage current of a photovoltaic (PV) station with many inverters connected in parallel, and meanwhile allowing the simple two-level string inverters instead of the commonly used three-level string inverters to directly connect in parallel without the transformer isolation in order to save cost and increase efficiency. The first-layer GSPWM could calculate the optimal phase-shift angles of triangular carriers among the parallel-connected two-level inverters to effectively attenuate their circulating leakage current. The second-layer GSPWM collects the equivalent variable per group provided by the first-layer GSPWM and can still significantly attenuate the total current harmonics at the point of common coupling. Experimental results of a small-scale prototype are presented to verify the performance of the proposed two-layer GSPWM.