Study On Dynamic Voltage Restorer Applied To Distribution System

With the development of science and technology and social civilization, especially the coming of knowledge economy precursed by information technology, more and more automation production assemblies which have the computers and microprocessors as the core and are sensitive to power quality are used, higher requirements are put forward to power quality. Moreover, owing to rapid use of large numbers of nonlinear or impactive loads in power system, many power quality problems will be caused, such as voltage sag, swell, unsymmetry, flicker, fluctuation, harmonic and so on. Therefore, the betterment of power quality is utterly urgent.The application of Custom Power is quite promising in distributed systems. It becomes one of the research emphases in recent years. Its objective is to reconstruct distribution system into real time controlled and flexible one, which has no flickers, no asymmetry, and no harmonics. Dynamic Voltage Restorer (DVR) is an important member of Custom Power family. It can compensate voltage harmonic, fliker, sag, swell, unbalance, and has the advantage of high performance/price, so it is necessary to investigate the theory and operation of DVR.Firstly the main circuit of DVR is discussed in this paper, on the basis of which voltage detecting method, voltage compensation strategy and controlmode are studiedBased on the analysis of several compensation strategies, optimal compensation strategy is proposed which considers both voltage compensation capacity and energy compensation capacity of DVR, so it is more practical. The detecting method of DVR is different from harmonic and reactive current detecting methods. It need detect not only total harmonic distortion but also the difference between fundamental wave component and reference value. An DVR voltage detecting method is brought forward, which is improved from harmonic voltage instantaneous detecting method based on general instantaneous reactive power theory. Arming at the shortages of traditional control mode, voltage loop control strategy is analyzedThe simulation conclusion indicates that voltage compensation strategy, detecting method and control mode are correct and effective. Along with the mature of the technology and the decrease of the cost, DVR will have broad application in distribution system.