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A double-source alternate backup type unified power quality conditioner (DS-UPQC) is proposed in this paper, which consists of two shunt inverters and two series inverters, the shunt inverters are connected alternately to the series inverters through the dc links, and a simple effective control scheme is also proposed. DS-UPQC can compensate harmonic voltage, voltage sag and swell, voltage interruption, three-phase voltage unbalance, harmonic current and reactive power current. The proposed system can realize the desired power alternate backup among different sources, and provide uninterrupted power supplythereby improve power system reliability effectively. Simulation results based on MATLAB/SIMULINK are presented to verify the good performance