Optimization methods for preventive/corrective control in transmission systems

This chapter discusses a methodology for the assessment of corrective control actions to be implemented in power system after the occurrence of a severe contingency. This pre-calculation can be intended as one of the contingency screening functions to be developed within each Supervisory Control and Data Acquisition (SCADA)/Energy Management Systems (EMS) control cycle and in the framework of online Dynamic Security Assessment (DSA). It is assumed that, based on latest system state information and calculations carried out for a selected number of severe fault events, pre-calculated control actions can be applied on actuators during the power system transient that follows such contingencies. The methodology can be adopted, for example, for the arming of Remedial Actions Schemes based on load shedding, generation shedding, Flexible AC Transmission Systems (FACTS) or any other fast actuator. The goal is preserving power system stability and its integrity even after that a specific severe contingency had occurred. The proposed methodology is based on the conversion of a dynamic optimization problem in the continuous time domain, into a static optimization problem in the discrete time domain. In order to show the key working principle of the proposed approach, a dynamic optimization problem is first formulated in his general form and then solved with the classical method and through discretization. Finally, the methodology is explicitly adapted to the set of equations and constraints that represent the dynamic behaviour of power systems. The same general methodology is then also applied to the solution of a preventive control optimization problem.