State Observation of Power Systems Equipped With Phasor Measurement Units: The Case of Fourth-Order Flux-Decay Model

The problem of effective use of phasor measurement units (PMUs) to enhance power systems awareness and security is a topic of key interest. The central question to solve is how to use these new measurements to reconstruct the
state
of the system. In this article, we provide the first solution to the problem of (globally convergent) state estimation of multimachine power systems equipped with PMUs and described by the
fourth-order
flux-decay model. This article is a significant extension of our previous result, where this problem was solved for the simpler third-order model, for which it is possible to recover
algebraically
part of the unknown state. Unfortunately, this property is lost in the more accurate fourth-order model, and we are confronted with the problem of estimating the
full
state vector. The design of the observer relies on two recent developments proposed by the authors, a parameter estimation based approach to the problem of state estimation and the use of the dynamic regressor extension and mixing (DREM) technique to estimate these parameters. The use of DREM allows us to overcome the problem of lack of persistent excitation that stymies the application of standard parameter estimation designs. Simulation results illustrate the latter fact and show the improved performance of the proposed observer with respect to a locally stable gradient-descent-based observer.