A Hybrid State Estimator For Systems With Limited Number of PMUs

This paper is concerned about effective incorporation of a limited number of phasor measurement unit (PMU) measurements into the state estimation solution in order to enhance the state tracking accuracy and speed. This is particularly important for fast changing system conditions when rapid control action may be necessary based on the onset of voltage instability due to an unexpected event. Under such conditions, SCADA-based state estimators may be too slow in capturing the changes in system state due to the low scan rates of the order of seconds. PMU measurements on the other hand provide refresh rates of milliseconds; however, they may not provide full system observability. In this work, a solution is proposed in order to address the lack of observability by the PMU measurements while maintaining fast tracking capability as well as estimation robustness against pseudo-measurement and PMU errors. Robustness is accomplished via the use of the so-called least absolute value estimator which minimizes L1 norm of the residuals. Simulation results are provided to illustrate the expected benefits of this implementation on test systems.