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

摘要

The influence of selected control strategies on the leveludof low-order current harmonic distortion generated by an inverterudconnected to a distorted grid is investigated through a combinationudof theoretical and experimental studies. A detailed theoreticaludanalysis, based on the concept of harmonic impedance, establishesudthe suitability of inductor current feedback versus outputudcurrent feedback with respect to inverter power quality. Experimentaludresults, obtained from a purpose-built 500-W, three-level,udhalf-bridge inverter with an L-C-L output filter, verify the efficacy of inductor current as the feedback variable, yielding anudoutput current total harmonic distortion (THD) some 29% lowerudthan that achieved using output current feedback. A feed-forwardudgrid voltage disturbance rejection scheme is proposed as a means toudfurther reduce the level of low-order current harmonic distortion.udResults obtained from an inverter with inductor current feedbackudand optimized feed-forward disturbance rejection show a THD ofudjust 3% at full-load, representing an improvement of some 53% onudthe same inverter with output current feedback and no feed-forwardudcompensation. Significant improvements in THD were alsoudachieved across the entire load range. It is concluded that the useudof inductor current feedback and feed-forward voltage disturbanceudrejection represent cost–effect mechanisms for achieving improvedudoutput current quality.