Research On The Detection And Control Of Voltage Sag Of Dynamic Voltage Restorer

Voltage sag is one of the most important parts of electrical index, the electrical companies all around nation pay more attention to the voltage sag than the other power quality events. Especially, with the rapid development of high technology and information economy lately five to ten years, all kinds of electrical equipments based on computer have been applied. These electrical equipments are very sensitivity to the voltage sags. For the above reason, it is essential to lucubrate the voltage sags, especially, focusing on the sag detective and control strategies.At first, following introducing the d-q transformation based on instantaneous reactive power theory, this paper proposed a novel detection method to voltage sags. The proposed method need to generate reference voltage which is always in-phase with the grid. By this method we can get rid of Phase-Locked-Loop (PLL), and the re-synchronization is not necessary. Using the new space vector coordinate, we also can singly define the zero sequence component. Therefore, coordinates transformation is used to pick-up the distorted voltage wave and detect the sags and harmonics.By analyzing the traditional feed-forward control loop, this paper also describes the limits of control system of DVR which singly using feed-forward loop, such as the low level of control system damping, insufficiency of steady abundance, insusceptibility to the harmonics and the poor adaptability to the load voltage. To those issues, this paper proposed a new feed-forward control system including a digital repetitive control loop. Afterward, establishing the entire control system scheme and deduce the transfer function of the system output and input with the disturbing. By appropriately selecting all parts of parameters, the proposed control system is not only compensating the voltage sags, but also preferably compensating the source harmonics and the other voltage disturbing due to non-linearity load, and improving the DVR control system's steady abundance and dynamic response. The both theoretically analyzing and simulation results verified the proposed detection and control voltage sags have good performance.