Delay-Dependent Stability of SMIB with Two Types of Excitation Controllers

Remote signals become available for designing a wide-area controllers in power system which introduces time delays into the control loop from the latency of communication networks. Moreover, fault of measurement sensors for local signals can be converted to delays in the signal measurement loop. This paper examines the stability of power systems with time delay by calculating the delay margin, which represents the maximum delay a system can tolerate before becoming unstable, considering delays from two sources. A stability criterion, utilizing Lyapunov theory and linear matrix inequalities, is proposed to calculate the delay margin for both constant and time-varying delays. Case studies focus on a single-machine infinite-bus (SMIB) power system with various exciters, such as AVR and AVR+PSS exciter controllers. Comparison the impact of time delays for different excitation controllers and relationship between the controller gains and delay margin are addressed. Accuracy of delay margin calculated is demonstrated by simulation studies, which also compare the delay tolerance of different exciters.