A New State Estimation Model of Utilizing PMU Measurements

The PMU can measure voltage phasors of the PMU node and current phasors of the correlative branch, and voltage phasors of the correlative nodes can be calculated by PMU measurements, so the state variable of these nodes are known. Two ways of research on the state estimation(SE) with PMU measurements are: one regards the PMU measurements as normal measurements and uses them together with SCADA measurements in the nonlinear state estimation; the other is linear state estimation with only PMU measurements on the condition that the system is observable fully with PMUs. The former has not considered the PMU's ability of measuring state variables, and the latter is difficult to realize now. Considering the high measurement precision and reliability of the PMU, the paper gives a new model to regard the state variable measured or calculated by PMU as the state variable of nodes in the state estimation. The model can utilize the PMU's ability of measuring state variables, reduce the scale of estimator. The improvement of calculating time- consuming and convergence speed in the new model is analyzed by the simulation. In the new SE model, the weight of PMU measurements is assumed to be infinite, and not equal to the variance reciprocal of measurements error, so the state estimation precision is influenced by the weight departure of the PMU measurements. The paper analyses and expands the new model more deeply, and presents a double state estimation model: at first, the nonlinear SE is done on the condition of taking the state variable measured or calculated by PMU as the state variable of nodes, then the linear SE is done with both nonlinear SE results and PMU measurements. The model adds little calculation time, but improves the SE equations' convergence speed and estimation precision simultaneously. The double state estimation model is validated by the simulation.