Global Synchronous Pulse Width Modulation of Distributed Inverters

Traditionally, the parallel-connected multi-leg inverter could assume the interleaved PWM to attenuate the switching frequency harmonics by using a single controller to generate the corresponding interleaved switching sequences. However, the interleaved PWM cannot be employed in multiple distributed inverters installed at different locations with their own controllers because the multiple independent controllers cannot work synchronously and the operational conditions are variable 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 pulse width modulation (GSPWM) method for the distributed inverters to attenuate the high frequency current harmonics at PCC meanwhile improve the PCC voltage quality. The optimal interleaved switching angles among the distributed inverters are calculated by fully considering the line impedances, the modulation indexes, the switching frequencies, the number of distributed systems and etc. Then the low frequency synchronous operation will synchronize the pulse width modulation sequences in the wanted variation range. Experimental results are presented to prove the validity of this method.