Observability and Observer Design for Dynamic Security Assessment in Power Systems

Dynamic Security Assessment (DSA) relies on dynamic simulation which needs a reliable initial point. In case of a major incident or in case of systematic DSA (run in quasi real-time), the initial point is not necessarily an equilibrium (load-flow) one and thus needs to be dynamically estimated. For this task, one can rely on static state estimator data and on real-time grid measures. However, internal states of the dynamic devices (like generators) are not accessible for measure and should thus be estimated. The related observability issue is studied here and a solution to estimate these states is proposed, taking into account the nonlinearities of the regulations of the dynamic devices (mainly related to the saturations of the actuating variables like excitation voltages and mechanical torque of the generators). It is shown that numerical solutions can be obtained despite the weak observability.