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.