Hybrid Observability Analysis Method For Power System State Estimation

State estimation(SE)is a key part of the power system EMS to ensure the quality of real-time data and the normal operation of other advanced functions of the EMS.A prerequisite for the normal operation of SE is that the power system is observable.Therefore,the observability analysis algorithm will directly affect the performance of SE.With the growing size of the power grid,the dispatching and operation are becoming more and more complicated.When analyzing the observability of large-scale power systems,traditional topological algorithms that directly search the spanning tree in the entire network is prone to the combinatorial explosion problem.For numerical algorithms,the execution time and the numerical instability will increase greatly when the system scale goes large.In order to solve these problems,this paper proposes a topology-numerical hybrid observability analysis method.Initially,the basic theory of topological observability analysis method based on the solvability of power flow under SCAD A measurement is utilized in the topological part,and measurement islands are recursively merged from local parts of the network to simplify the network scale under the combinability principles and rules.After the topological combination process,the simplified network composed of the boundary buses and the inter-island unobservable branches between is a disconnected network,which cannot be directly used in numerical observability analysis.Thus,a minimum number of equivalent branches with power flow pseudo-measurements are added inside the remaining islands to form the connected simplified network.After that,an improved numerical observability analysis method based on the decoupled DC model is used to judge the final observability.Furthermore,this paper proves that the basic idea of the proposed hybrid method is also applicable to the observability analysis under PMU measurements with minor adjustments according to the characteristics of PMU measurements.Moreover,two new combinability rules for PMU measurement island are added in the topological part,and then the overall hybrid observability analysis method for PMU measurements are proposed.Finally,systems of different scales are constructed to test the proposed method and existing methods,thereby verifying the effectiveness and practicability of the proposed method in large-scale power systems.