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An improved hybrid current control algorithm is presented for active power filter (APF) to compensate the harmonic current in three-phase four-wire asymmetric power system. Based on the analysis of the circuit structure of three-phase four-leg APF, the feasibility of hybrid current control is described in this paper. The method of instantaneous value comparison by timing control based on voltage space vector is put into control main power circuit, while carrier-wave comparison method is used to control the neutral leg. This hybrid method belongs to the fixed-frequency control method and has the advantages such as easy of calculation and realization. The results of simulation are helpful to the optimal design of experimental equipment.