Work On Improving The Performance Of Power System State Estimation Based On PMU

Although the main theories of power system state estimation have been well developed,but in practice,state estimators,such as these based on weighted least square(WLS) criterion,can't provide with good performance as expected.To a specific state estimator,its performance is determined mainly by the possible occurrence of bad data,the measurement capacity and precision,and the accuracy of the model(measurement function).In this paper,attention is paid mainly to making use of the measurement capacity optimally and improving the accuracy of the model.In chapter 1,the main work of power system state estimation in the recent 30 years is surveyed and analyzed.And the main knowledge points and procedures of WLS state estimation are listed in chapter 2,which will serve the following chapters as a theoreticl base.In chapter 3 and 4,the optimal PMU placement problems are discussed.In chapter 3,under the framework of using the hybrid measurement systems of SCADA and PMU,the multi-objective optimal PMU placement(OPP) problems,which include objects as the observability of the measurement sets,the equipment cost and the performance of the corresponding state estimator,are classified into two types.The typeâ… problem is solved with a standard genetic algorithm(GA) when all the schemes are collated and coded properly.And for the typeâ…¡problem,a strategy of sorting all these obects first and then applying the Pareto rule is proposed,from which a stepwise mutation GA arises.Combined examples support the above methods well.As a continuing part of chapter 3,in chapter 4,a weighted formula of calculating the estimation accuracy is proposed.It is pointed out that the objective function of the typeâ…¡problem is a multi-modal function.The improved clonal algorithm(CLONALG) with recombination and hypermutation operators is introduced to search the optimal and sub-optimal solutions.And an accelerating operator based on memory is proposed and the number of cycle supplement population and the probabilities of hypermutation and recombination are stepwisely adjusted.The modifications can quicken and stabilize the optimizing process and prevent the search from locally optimal traps.The examples based on IEEE 14-bus/57-bus indicate that the proposed algorithm is more applicable than the original CLONALG.The SMGA method is relatively simpler and can reach the globally optimal solution faster than the improved CLONALG,while the latter can provide both the globally and the locally optimal solutions and offer much more options to the designerns.In this sense,the improved CLONALG is better than the SMGA algorithm.The following work is about improving the model accuracy of transmission lines. In chapter 5,a knowledge-based correction term for the objective function of parameter estimation is proposed.The relationship between the function extreme points of state estimatin and parameter estimation is deduced.A strategy of projecting the parameter objective function from the augmented solution space to the parameter space is proposed and proved.Corresponding to the unimodality of the vertical projection,a heuristic algorithm called as staged particle swarm optimization(SPSO) is proposed.The estimation errors are analyzed and the mean values are proposed as unbiased estimators of the parameters.The examples indicate that the unkown line parameters can be estimated faster and more accurately with the proposed objective function and SPSO and the solving procedure relies less on the augmented jacobian matrix.It is also shown that the mean estimated values of the parameters are close to the truth values.In chapter 6,a novel and complete strategy of estimating transmission line parameters based on dynamic filtering is proposed,which includes static linear estimation,pseudo-measurement conversion,measurement error conversion,deducing the dimension of the state vector,parameter dynamic models based on ratio adjustable transformer,and the dynamic filtering based on Kalman filter.The examples simulate two different cases of equiping and not equiping with transformers in a line.The results show that the proposed strategy is much better than the method of taking average over estimates from multiple shots.Further discussions proceed then.In brief,all the proposed motheds above can solve the specific problems efficiently.Futhure work will be focused on how to improve both the configuration of the measurement system and the accuracy of the line parameters at the same time and integrate these methods into practice.