An improved SHE algorithm and filter design method for high power grid-connected converter under unbalanced and harmonic distorted grid

Due to the low switching frequency and excellent harmonic performance, selective harmonic eliminated pulse width modulation (SHEPWM) is very suitable for high power grid-connected converters. However, most of the research on SHEPWM so far is based on an ideal grid, which ignores the influences of the unbalanced and harmonic grid voltages that turn out to be rather significant and have limited the engineering application of SHEPWM. Based on a three-level grid connected converter topology, this paper studies the characteristics of SHEPWM under a non-ideal grid. An improved modulation algorithm and a novel filter design method are proposed to solve the problems caused by the unbalanced grid and harmonically distorted grid conditions, respectively. Simulation results confirmed the effectiveness of the method proposed.