Hierarchical State Estimation Using a Fast Rectangular-Coordinate Method

Hierarchical computing methods for large-scale Power System State Estimation (PSSE) has gained considerable interest over the last few years. So far, however, no method has been developed that is both practical and optimizes the total system's cost function. The Newton-Raphson method for PSSE has the drawback that the Jacobian matrix is evaluated at each iteration and, each time, must be sent to all the other computers in the hierarchical system. In this paper a new hierarchical computing scheme is developed by carefully considering mismatches arising from the system decomposition. The proposed method makes use of an extension of a fast second-order load-flow method which allows to employ a fixed Jacobian matrix in the hierarchical algorithm. In the problem formulation the power network is decomposed into two or more subsystems; the interaction among the systems is taken into account through the tie-line bus voltages. The hierarchical structure of the proposed method consists of two levels: the upper level, where the optimal tie-line bus voltages are evaluated; and the lower level, where the optimal states of each subsystem are determined by minimizing a cost function that involves the entire system. Three test cases of the proposed method are reported in the paper;more » the test results are compared with those obtained by another hierarchical PSSE method.« less