Implementation of SHE-PWM Technique for Parallel Voltage Source Inverters Employed in Uninterruptible Power Supplies

This paper proposes a new selective harmonic elimination pulse-width modulation (SHE-PWM) technique with fixed and low switching frequency for paralleled voltage source inverters (VSIs). The proposed SHE-PWM technique involves the use of using different switching patterns for each inverter module instead of using the same switching pattern for each module, which is the standard practice. This allows more harmonics to be eliminated from the output AC waveforms and helps reduce circulating current in inverters, but also increases the complexity and the number of non-linear equations that need to be solved. The proposed new SHE-PWM technique is based on recent advances in genetic algorithm (GA) optimization methods that are well suited to solving multi-objective problems so that the optimum firing angles needed to minimize harmonic content and circulating current in paralleled VSIs modules can be achieved. Simulation and experimental results obtained from a laboratory prototype are presented and analyzed to demonstrate the features of the proposed control strategy, such as its ability to reduce circulating current and output harmonic content.