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Suppression of line voltage related distortion in current controlled grid connected inverters

By T. Abeyasekera, C.M. Johnson, D.J. Atkinson and M. Armstrong


The influence of selected control strategies on the level\ud of low-order current harmonic distortion generated by an inverter\ud connected to a distorted grid is investigated through a combination\ud of theoretical and experimental studies. A detailed theoretical\ud analysis, based on the concept of harmonic impedance, establishes\ud the suitability of inductor current feedback versus output\ud current feedback with respect to inverter power quality. Experimental\ud results, obtained from a purpose-built 500-W, three-level,\ud half-bridge inverter with an L-C-L output filter, verify the efficacy of inductor current as the feedback variable, yielding an\ud output current total harmonic distortion (THD) some 29% lower\ud than that achieved using output current feedback. A feed-forward\ud grid voltage disturbance rejection scheme is proposed as a means to\ud further reduce the level of low-order current harmonic distortion.\ud Results obtained from an inverter with inductor current feedback\ud and optimized feed-forward disturbance rejection show a THD of\ud just 3% at full-load, representing an improvement of some 53% on\ud the same inverter with output current feedback and no feed-forward\ud compensation. Significant improvements in THD were also\ud achieved across the entire load range. It is concluded that the use\ud of inductor current feedback and feed-forward voltage disturbance\ud rejection represent cost–effect mechanisms for achieving improved\ud output current quality

Year: 2005
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