Nonlinear Stabilizing Control of Multimachine Systems

It is of great importance to improve stability as well as dynamic performances of power systems for both small and large disturbance. Such issues have received a great deal of attention and many contributions have been made to this objective. However, some of the design methods developed previously are based on second-order synchronous generator model, so excitation systems or/and governor systems could hardly be considered by them, the others based on linear models, which are set up by approximate linearizing at an equilibrium point of the system. Since, in fact, a power system is a nonlinear dynamic one, the controller designed by using the approximate linearized model may cause untolerable errors, while the state point of the system is changed away from the equilibrium point at which the linearization is realized. A new approach to nonlinear decoupled optimal control based on the differential geometric control theory for interconnected power systems is proposed. And it is successfully applied to nonlinear steam valving control of multimachine systems. For an m-machine system the optimal steam valving control law of the ith-machine can be expressed as ui= TS; ii(K1-M& 1+ K2 cw-+ K3; | wdt + TsiPei+ (Pmj-Pmjo) (18) where Mi inertia coefficient (in sec.) Tsi, time constant of servomotor and steam (in sec.) wi, speed (in per unit) Di damping coefficient Pei electrical power (in per unit) Pmi mechanical power (in per unit) and K1j, K2j, and K3j are optimal feedback gain coefficients.