A dual topology of Unified Power Quality Conditioner: The iUPQC

Configurations of combined series and shunt active filters, also known as unified power quality conditioners (UPQCs), are designed for simultaneous compensation of voltage and current harmonics and imbalances. Sometimes, compensation of voltage sag/swell is also included as additional functionality of the UPQC. Traditionally, the shunt active filter of the UPQC behaves as a controlled current source that compensates the load current, whereas the series active filter behaves as a controlled voltage source that compensates the supply voltage. Here, a dual configuration of UPQC, hereafter called as iUPQC, is presented. In contrast to the conventional approach of UPQC, the shunt active filter of the new iUPQC behaves as an ac voltage source and the series one as an ac current source. An advantage of the iUPQC over traditional UPQCs is the fact of having fundamental positive-sequence currents and voltages references for the series and shunt active filters, respectively. Contrarily, conventional approaches of UPQC must deal with nonsinusoidal compensating voltage and current references, with aleatoric frequency spectra. In this case, it is impossible to practically unsure zero steady-state errors in all frequency components. Beside all those compensation characteristics of the UPQC, the iUPQC can also keep the voltage at load terminal tracking its referential values, according to the desired specifications. In other words, the iUPQC has voltage sag/swell compensation capability, with fast response, comparable to that of a dynamic voltage restorer (DVR). The basic control strategy and an improved version are presented and the system performance is compared through simulations. Finally, experimental results are presented to validate the proposed iUPQC controller.