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The theory and experiments have demonstrated that the unified constant-frequency integration (UCI) controller features excellent performance, simple circuitry, and low cost for the control of three-phase APF connected to either symmetrical or asymmetrical three-phase power systems. In reality, three-phase grid voltages and/or three-phase nonlinear loads may not be balanced all the time, therefore it is vital for an APF to be able to handle unbalanced source or load. Studies have shown that the UCI controlled APF performs satisfactorily in unbalanced systems. In continuation, the performance of a three-phase APF working in unbalanced load with a UCI controller is evaluated in this paper. Simulation and experiment results indicate that with UCI control, sinusoid input current can be realized, whether the loads are balanced or unbalanced.