Research On Characterizations Detection Method And Compensation Strategy Of Voltage Sag

Voltage sag causes expensive downtime, which has become one of the most serious problems of power quality. Research on voltage sag detection is an essential part of the voltage sag compensator. The peak detection method needs half of a cycle time to get the information of voltage sags, which can't detect the phase angle jump. The new method based on peak value presented in this paper enhances the detection accuracy and speed, and the phase angle of voltage can be derived rapidly. The results of MATLAB simulation results verify the validity of the methods. In order to eliminate reactive current and improve power factor, Active Power Factor Correction(APFC) circuit is used in Uninterrupted Dynamic Voltage Restorer(UDVR). By controlling the switch of the APFC circuit, the harmonic from rectifier can hardly inject into the power system, and the power factor can be improved to 1. A double close-loop control strategy with incorporating inner current loop and outer voltage loop is used in single-phase APFC circuit and its control circuit is simple and inexpensive. The open-loop control strategy is used in inverter. The same phase compensation is adopted to compensate voltage sag. MATLAB simulation results show that the APFC-Based UDVR can provide the loads with a pure and standard sine voltage wave and can solve the continuous voltage sag. To solve the problem of voltage sag, Dynamic Voltage Restorer(DVR) is used to compensate load voltage instantly with active hybrid energy store system. An equivalent circuit of Dynamic Voltage Restorer powered by active hybrid energy store system is presented. Both the mathematical model of the ultracapacitor/attery hybrid system and the control system of the model are set up. The paper presents a simulation study of this Dynamic Voltage Restorer powered by active hybrid energy store system. The active hybrid energy store system can raise the whole working characteristic and economy of DVR. The results prove that this active hybrid energy store system can effectively maintain the voltage of sensitive load in the conditions of long-time-last power interrupts and frequent voltage sag.