Wide-range reliable stabilization of time-delayed power systems

Steam valve control is usually discarded in power system stability due to belief in its slow response. The present manuscript makes use of it as a backup control in the case of failure of the main fast excitation control. The model describing system dynamics as a function of the two controllers, with wide range loading conditions, is derived in a norm-bounded format. Linear matrix inequalities are derived as a sufficient condition to obtain reliable controllers that provide good oscillation damping when both controllers are sound or even in the case of failure of either one. The design scheme is robust in the sense that it keeps reliable stability against wide load changes as well. A single machine infinite bus system is presented to illustrate the proposed design procedure and exhibit its performance. Results of excitation and governor controller testing show that the desired performance could be fulfilled from light load to heavy load conditions. System performance shows a remarkable improvement of dynamic stability by obtaining a well-damped oscillation time response even in the case of failure of either controller. Extension of the proposed controller to multiarea load-frequency control with time delay is also presented.