Research For Real-time Detection Of Characteristics Of Voltage Sag And Compensation Method Of Dynamic Voltage Restorer

Since recent 5 years to 10 years, with the rapid development of new technology (especially information technology), various sensitive devices such as electronic devices based on computer and micro-processor have been applied in the industry production. Thus voltage sag became one of main problems of power quality. Voltage sag and its most cost-effective compensation device dynamic voltage restorer (DVR) are being paid more and more attention to and turning into the hottest direction of research.Several detection methods of characteristics of voltage sag were proposed. Unfortunately, they have some problems such as complicated algorithm and time-delay. Based on the detection method which uses delayed single-phase signal to construct three-phase signals and calculates the sag characteristics from the formed signal through dq transformation, this paper propose an advanced detection method of sag characteristics. It reduces time delay, and has simpler calculation. The simulation results illustrates its effects.Currently there are pre-sag compensation method, in-phase compensation method and minimum real-power compensation method for DVR. The former two have no control of the power of DVR. Although minimum real-power compensation method minimize real-power of DVR, it brings disadvantages such as phase jump, increase of the injected voltage and apparent-power. Advanced minimum real-powercompensation method of DVR is proposed first to improve the calculation and control of DVR. In addition, the method can mitigate the disturbs caused by phase jump of the compensated voltage of minimum real-power method. In order to overcome the problems of injected voltage and apparentrpower of minimum real-power compensation, a new method named minimum apparent-power compensation is proposed which minimizes apparent-power of DVR, reduces the capacity and injected voltage of DVR. It also limits real and reactive power of DVR to be lower. Detailed theory comparisons of parameters such as injected voltage and power between minimum real-power compensation and minimum apparent-power compensation have been implemented in the paper. Finally circuit simulations of three power factors have been made, the results demonstrate the Tightness of the comparison conclusions. From the results it is also found that minimum apparent-power compensation is decided by condition of voltage sag, it has no business with the loads characteristics. Therefore the control are simple, in other hand it can maintain the compensation continuity, reduce disturbs to loads.In further study, relation between D phasor and positive component of sag voltages has been found. The discovery resolves some problems in former study. It proves that minimum-apparent power compensation and in-phase compensation are same in condition that loads are symmetrical. Thus minimum-apparent power compensation can decrease the injected voltage of DVR. In addition, in-phase compensation has control effects to power of DVR. This paper also proposed that various compensation methods should be studied from voltage components power expression of asymmetrical three phase circuit to make concept clear and analysis simple. After knowing relation of D phasor and positive component of sag voltages, this paper proposes a new detection algorithm of positive and negative of sag voltages which simplifies construction and calculation greatly. In the end, various compensation methods of DVR are studied when loads are asymmetrical.