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The DC current rejection of a single phase half-bridge grid-connected inverter with a line-frequency isolation transformer is researched in this paper. The impact of the magnetic dc bias of the transformer is given out from the mathematic model of the transformer in current-mode control. For the half-bridge current-mode inverter, the dc current rejection method is presented based on the relationship of dc current component and voltages across the filter capacitors of the dc bus. Simulation and experiment results indicate that the dc component of inverter current saturates the transformer and degrades the quality of current injected into the grid. With voltage balance control of the filter capacitors, the dc current control of half-bridge current-mode grid connected inverter is realized.