A constrained orthogonal state estimator for external system modeling

Attention is focussed on the application of constrained orthogonal state estimation to external system modeling. Inequality constraints enforce realistic limits on the estimates of External System (ES) variables that otherwise can become off bounds due to the limited ES monitoring capabilities at the Internal System control center. Equality constraints are used to model known zero bus injections in both systems. The use of orthogonal methods is advocated to ensure numerical stability, since the estimator has to handle a larger range of measurement weights than in conventional applications of state estimation. Tests to evaluate the performance of the proposed constrained estimator using three power networks of different sizes are also reported in the paper.