Coordinated Switching Controllers for Transient Stability of Multi-Machine Power Systems

This paper proposes two switching controllers working in a coordinated manner to enhance the transient stability of multi-machine power systems. One is switching excitation controller (SEC) and the other is switching governor (SG). The SEC switches between a bang-bang excitation controller (BEC) and a conventional excitation controller (CEC) and the SG switches between a bang-bang governor (BG) and a conventional governor (CG), via a state-dependent switching strategy. The BEC and the BG are designed as bang-bang constant funnel controllers (BCFC), which are able to provide fast switching of excitation voltage and valve position between their upper and lower limits. A detailed steam turbine model including boiler pressure effect is considered in the controller design process. Simulation studies are undertaken in the IEEE 16-generator 68-bus power system to evaluate the control performance of the switching controllers, which include the cases that three-phase-to-ground fault and transmission line outage occur in the system, respectively. Coordination between the excitation loop and speed governing loop is studied. Two system resilience indexes are introduced, and the short-term resilience is investigated for the power systems with and without switching controllers installed, respectively.