State Estimation And Optimal Allocation Of Power System Using Hybrid Measurement

Along with the trend that the scale of power system in our country is expanding gradually,the network structure of power system becomes more complicated.The dispatching personnel should understand and grasp the operation of power system faster and more accurate,only in this way can they keep the electric power transmission safe and effective,which makes more and more strict demands on the state estimation of power system.The traditional Supervisory Control And Data Acquisition(SCADA)has been unable to meet the needs of the power system,while the hybrid measurement system by adding phasor measurement unit(PMU)plays a more and more important role in the estimation of power system.The measurement data of the hybrid system is provided by the Supervisory Control And Data Acquisition(SCADA)and phasor measurement unit(PMU).Considering the price and technology,there will be some problems in the installation of PMU in power system.So,for a long period of time,it is necessary to present the state of the coexistence of traditional SCADA system and PMU measurement system,the way to make full use of the information of the mixed measurement to estimate the state of power system is becoming an urgent problem to be solved.Firstly,the background,purpose and significance of state estimation of power system under the trend of mixed measurement are described in this paper.The algorithm of mixed state estimation is introduced,and the performance index of state estimation of hybrid power system is proposed.On the basis of these introductions,the wide area measurement system(WAMS)is introduced,and the measurement characteristics,time delay and data compatibility of the hybrid measurement system are analyzed and studied.Comparing the measurement principle and function of PMU with SCADA system,and analyze the matching problem of angle and time in the fusion process of the hybrid measurement system.Then,two new strategies of state estimation of power system are proposed,which are used for the measurement of SCADA/PMU mixture.The first strategy is used to enhance the ability of data processing by using a prior state information(APSI)and a blocked version of orthogonal Givens rotations in the hybrid state estimation.The second strategy is a three-stage scheme that depends on estimation fusion principles to optimally combine previously determined SCADA-based and PMU-based estimates.Detailed description and discussion of the multilevel strategy is presented in this paper,which is proved that the multilevel strategy can effectively reduce the computation of state estimation,and increase the synchronization and accuracy of measured data.At last,study on the optimal allocation of PMU in hybrid electric power system.First,study on the optimal allocation of PMU by using the method of algorithm iteratively.The method initially considers PMU in all buses of the network.Stage I and Stage II of the algorithm iteratively determine(i)less important bus locations from where PMUs are eliminated and(ii)strategically important bus locations where PMUs are retained.Stage III ofthe algorithm further minimizes the number of PMU using pruning operation.The set of PMUs obtained after Stage III is an optimal set of PMU locations for network observability.Proposed method is further extended for assuring complete observability under single PMU outage cases.Simulation results for IEEE 14,IEEE 24,IEEE 30,IEEE 39,IEEE 57 and IEEE118 test systems are presented and compared with the exist in techniques.Results show that the proposed method is simple to implement and accurate compared to other existing methods.Second,the optimal combination of PMU locations that maximizes the accuracy of the proposed hybrid state estimator is determined by utilizing a binary integer program iteratively and in each iteration a PMU bus is chosen.Each chosen bus is included in the set of the previously chosen PMU buses and for each time,a state estimation is performed taking into consideration the current PMU bus set.The iterative process is stopped when the variance of the hybrid state estimator is smaller than a predefined threshold.The proposed hybrid state estimator along with the optimal PMU placements determined by the proposed methodology,have been tested using the IEEE 14-bus,30-bus,and 57-bus systems.