Fast Response DVR Control Strategy Design to Compensate Unbalanced Voltage Sags and Swells in Distribution Systems

The Synchronous Reference Frame (SRF) has been known as one of the most common methods of voltage sag compensation. Despite suitable performance in 3-phase voltage sags mitigation, the application of the SRF does not work that well in unbalanced situations. This paper addresses this problem, through the use of a novel control strategy based on the pre-fault compensation theory. In this strategy, not only the control system is capable of restoring the amplitude of the voltage to its pre-fault value, but it also can remove phase angle jumps. Furthermore, the compensator's response has been remarkably improved with the application of a Least Squares (LS) algorithm in the estimation part of the control module. The response and accuracy of the proposed LS estimation algorithm is compared with other conventional methods such as SRF, Adaptive Linear Combiner (ADALINE), and Fast Fourier Transform (FFT). Finally, the proposed and SRF control algorithms are simulated in PSCAD/EMTDC,and their performance is assessed in voltage sag/swell mitigation of a distribution system during asymmetrical faults.