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The unitary power factor control for distributed grid-connected power generation systems is considered in this paper, i.e., the fundamental-frequency positive-sequence components are extracted from the utility voltages under unbalanced and distorted conditions and output currents of the grid-connected power inverter are always in phase with the corresponding positive-sequence voltages. The extracted method of α-axis fundamental-frequency positive-sequence component in α -βstationary frame based on the finite impulse response (FIR) filter is presented. The imaginative component with leading 90° phase shift based on an all-pass filter instead of the existing β-axis positive-sequence component is designed in order to reduce the calculating burden of DSP, therefore, the phase-locked loop (PLL) is carried out by the imaginative two-phase transformation. The experimental results verify the proposed method has the better performance such as good PLL control and unitary power factor.