Characterization of Distortion Reduction for Single-Phase Multiple Inverter Operation

A technique for reducing the total harmonic distortion in the voltage output of naturally sampled pulse width modulated inverters is investigated. This technique is based on synchronization of parallel-connected inverters and makes use of a phase-shift in transistor gating between these inverters. Often, in practice parallel inverters are operated with no synchronization, resulting in far less than optimal harmonic distortion reduction. The output waveform of a single inverter, two parallel inverters, and three parallel inverters is analyzed and compared in simulation and experimentally. This is done for two and three level pulse width modulation, for several values of modulation index, and different carrier to fundamental frequency ratios. Both simulation and experimental results indicate that a significant reduction in total harmonic distortion occurs using the synchronization technique, and observations are provided on the ability to reduce harmonic distortion in multiple inverter systems.