Research On State Estimation Of Transmission Grid And Distribution Grid

With the development of the power system, the modern power system requiresto get the actual operating state of power system accurately、comprehensively andquickly, it makes provision for predict and analysis the operation trend of powersystem as well as solve the problems happened on the actual operating. It poses achallenge to power system state estimation.Transmission state estimation has achieved rich results on theoretical researchafter40years’ research on power system state estimation. Although the SCADAsystem of transmission grid could basically meet state estimation’s observabilityrequirements, but it must contain bad data due to the errors in the data acquisitionstage、digtial to analog conversion conversion process. With the expansion of thescale of the power system as well as the increase of amount of information, theproportion of bad data also increases. And the traditional state estimation has beenunable to meet the real time requirement of large scale systems, we need to developnew algorithms what possess the qualities of high calculation speed and goodnumerical stability. The algorithm for transmission grid proposed in the paper isbased on the concept of normal measuring point and the credibility of measuringpoint, give every measuring point reasonable credibility value, with the objectiveof maximum system credibility (the sum of all measuring points’ credibility value)while satisfying various constraints, propose a novel method of power system stateestimation. Compared with existing state estimation methods, this method takesinto account all types of measuring point, it is more flexible because of settingdifferent credibility value of doubtful measuring point for different strict degree ofgood measuring rate. The rationality and accuracy of the method proposed isproved by test results of the IEEE standard systems, it proves the superiority of themethod compared with other methods.People begin to analysis the characteristics of distribution state estimationwith the apper of distribution management system. As the power network thatdirectly connect to the users, the distribution grid has the properties of lowvoltage level、 multiple branching construction、 three-phase load imbalance、three-phase line imbalance and so on that differ from transmission grid, thereforethe existing achievements of state estimation can’t be copied to distribution stateestimation. The challenges for distribution state estimation are as follows:(1)The situation that the serious shortage of measuring devices as the biggest challengemakes state estimation unable to run;(2)We can’t guarantee all measurement dataare measured and stored in the database synchronously. The paper proposes a loadforecasting model by using single exponential smoothing on the basic of the timeseries forecasting algorithm, this will solve the problem of desynchrony inmeasurement data except the problem of insufficient redunda. For the unobservablepoints, this paper proposes a new concept—average power factor to solove theproblem of insufficient redunda. After getting the network configuration ofdistribution grid firstly, then make ues of forward and backward substitutionmethod to get the actual operating state. Take Jiujiang region distribution as anexample, this algorithm can obtain the operating state quickly and accurately.Meanwhile, the more real time measurement data, the more accurate and reliable ofthe results by state estimation.