A Block Version of Orthogonal Rotations for Improving the Accuracy of Hybrid State Estimators

This paper addresses the problem of hybrid state estimation, which relies on data provided by both conventional SCADA systems and phasor measurement units. A previously proposed cascaded architecture is employed, whose first estimation module processes the asynchronous measurements through a conventional, nonlinear state estimator. The focus, however, is on the second estimation module, where the SCADA-based estimates are combined with synchrophasor data in order to enhance the quality of the state estimates. For the benefit of computational performance, that task must be performed by a non-iterative and numerically robust algorithm. It is equally important to avoid awkward uncorrelatedness assumptions while defining measurement weighting factors, since they may severely compromise the statistical characterization of the final solution. To accomplish both objectives, a generalized 2\times 2 block version of the 3-multiplier Givens rotations has been developed and is introduced in this paper. This leads to numerically stable solutions, whose statistical properties are preserved. The features and advantages of the proposed two-stage hybrid state estimator are illustrated through case studies conducted on the IEEE 14-bus, 30-bus, 57-bus, and 300-bus test systems.