Robust decentralized nonlinear controller design for multimachine power systems

In this paper, a robust decentralized excitation control scheme is proposed for multimachine power system transient stability enhancement. First, a direct feedback linearization (DFL) compensator through the excitation loop is designed to eliminate the nonlinearitles and interconnections of the multl-machine power system. Then, a robust decentralized controller IS proposed to guarantee the asymptotic stability of the DFL compensated system considering the effects of plant parametric uncertainties and remaining nonlinear interconnections. The design procedure for an n-machine power system involves in solving n Riccati equations. In the design of the robust nonlinear decentralized controller, only the bounds of generator parameters need to be known, but not the transmission network parameters, system operating points or the fault locations. Since the proposed robust nonlinear decentralized controller can guarantee the stability of the large scale power system within the whole operating region for all admissible parameters, transient stability of the overall system can be greatly enhanced. The design procedure is tested on a three-machine example power system. Simulation results show that the proposed control scheme can greatly enhance the transient stability of the system regardless of the network parameters, operating points and fault locations. I. Introduction Power systems are increasingly called upon to operate transmission lines at high transmission levels for economic or envlron-mental reasons. This requires the control system to have the ability to suppress potential instability and poorly damped power angle oscillations that might threaten the system stability as the load is expected to increase in the future. In a lot of cases, transient stability transfer limits are more constraining than the steady-state transfer limit under contingency. All these practical demands require the control system to have the ability to regulate the system under diverse operating conditions. Unfortunately , power systems are large scale nonlinear systems; the characteristics of conventional controllers that are designed based on approximately linearized power system models, such as power system stabilizers, vary significantly with respect to the changes in operating conditions. Application of nonlinear feedback to cancel the inherent system nonlinearities have the potential to enhance power system transient stability (see Wang et al.,