Method Of Synchronized Pulsewidth Modulation Research Articles

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.

Global Synchronous Pulse Width Modulation of Distributed Inverters

Traditionally, the parallel-connected multileg inverter could assume the interleaved pulse width modulation (PWM) to attenuate the high-frequency harmonics by using a single controller to generate the corresponding interleaved switching sequences. However, the interleaved PWM cannot be employed in multiple distributed independent inverters installed at different locations with their own controllers because the multiple independent controllers cannot work synchronously and the operational conditions are different among the distributed inverters. The summed current harmonics of multiple distributed inverters could vary at the point of common coupling (PCC) and worsen the power quality of consumers. This paper, therefore, proposes a global synchronous PWM method for the distributed inverters to attenuate the high-frequency current harmonics at PCC. The optimal interleaved switching angles among the distributed inverters are calculated by fully considering line impedances, modulation indexes, switching frequencies, the number of distributed inverters, etc. Particle swarm optimization method is assumed to find the optimal solution. Then, the low-frequency synchronization operation will synchronize the multiple PWM switching sequences in the wanted variation range. Experimental results are presented to prove the validity of this method.