A Novel Accurate Active and Reactive Power Calculation Method for Paralleled UPS System

Among the paralleled UPS control strategies, output droop method and average power control method need to calculate UPS output active and reactive powers accurately for control of the phase (frequency) and amplitude of output voltage. In light or no load conditions, active circulation currents may cause high DC voltages which will damage the machine. This paper suggests using the UPS output filter inductor current instead of the output current when calculating the UPS output active and reactive powers. For improving accuracy of the power calculation, the sampling delay of the inductor current needs to be adjusted. Two digital controlled three-phase four-wire 30 KVA paralleled UPS systems are implemented for experimental verification of the theory analysis. The experimental results show that better current-sharing performance is achieved.