This paper deals with a feedback control using automatic choosing functions and the observer-control design procedure for nonlinear systems with linear measurement. A constant term which arises from linearization of a nonlinear equation is treated as a coefficient of a stable zero dynamics. A given nonlinear system is linearized piecewise so as to be able to design the linear optimal controllers with the linear observers. By the automatic choosing functions, these controllers are smoothly united into a single nonlinear feedback controller, which is called an augmented automatic choosing control of observer type. This controller is applied to a transient stability of power systems, whose simulation results show that the new controller enables to expand the stable region well.

In this paper a novel approach to nonlinear control, called an Augmented Automatic Choosing Control (AACC), is presented. Considering the nonlinearity, a separative function is introduced and its inverse do main associated with the region of the system is divided into some subdomains. On each subdomain, the system equation is linearized by Taylor expansion around a suitable point so that a constant term is included in it. This constant term is treated as a coefficient of a stable zero dynamics proposed here. Thus the given nonlinear system approximately makes up an augmented linear system, to which the optimal linear control theory is applied to get the linear quadratic (LQ) control. These LQ controls are smoothly united into a single nonlinear feedback controller by automatic choosing functions of sigmoid type. Parameters of these functions are suboptimally selected with the aid of a genetic algorithm (GA). This approach is applied to a field excitation control problem of power system to demonstrate the splendidness of the AACC. Simulation results show that the new controller can improve performance remarkably well.

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