Three-Phase Four-Wire Unified Power Quality Conditioner Structure With Independent Grid Current Control And Reduced Dc-Bus Voltage Operating With Inverted/Dual Compensating Strategy

This work proposes a 3-phase 4-wire unified power quality conditioner (UPQC) structure, which has ability to operate with per-phase independent grid current control, reduced dc-bus voltage and inverted/dual compensation strategy. Since the grid currents are controlled by the series converter, two distinct strategies, namely, independent current compensation strategy (ICCS) and load unbalance compensation strategy (LUnCS) can be employed. Using the ICCS, the controls of the grid currents are performed independently per-phase, such that the UPQC can operate even when grid voltage outage occurs in one or two phases of the power source. Furthermore, to guarantee the proper parallel converter operation, the dc-bus voltage amplitude must be higher than the grid voltage peak amplitude. Thus, since the parallel converter operation is assured, the functioning of the series converter is also guaranteed because it needs lower dc-bus amplitude to operate. However, depending on the converter topology adopted in the parallel converter, the series converter could be subjected to operate with dc-bus voltage higher than necessary. Thus, to minimize this aspect, this paper proposes a UPQC scheme composed of 3-Leg split-capacitor (3-Leg-SC) and 4-Leg topologies, operating as series and parallel converters, respectively. Thus, besides the use of the ICCS, lower dc-bus voltage is allowed when compared to the UPQC composed of two 3-Leg-SC converters, as well as reduced power switches number is achieved when the propose scheme is compared to UPQC composed of two 4-Leg converters. Extended experimental results based on digital signal controller are presented to evaluate the effectiveness and performance of the proposed UPQC.