Theory analysis of harmonic current generation and harmonic current extraction of three-phase grid-connected inverter

Theory of the harmonic current generation of three-phase grid-connected inverter under unbalanced grid conditions is analyzed in detail in this paper. Based on the characteristic of three-phase currents, the structure of three adaptive notch filter(ANF) cells collaborating with fast positive and negative sequence decomposition(FPNSD) cell is proposed, which employs for the extraction of harmonic current. The main function of this harmonic current extraction method is to provide harmonic current for voltage regulation and power control of inverter. Moreover, this method is capable of extracting a selective order of harmonic where elimination of certain harmonic is of concern. The performance and analysis of the proposed structure in this study are verified through experimental cases.