Control problem of eld weakening for a separately excited DC motor system, modeled in nonlinear diOE erential equations, is tackled in this paper. A novel constant power eld weakening controller, based on nonlinear load-adaptive multi-input multi-output (MIMO) linearization technique, is developed to achieve high-performance speed tracking through rejecting load disturbance. The eOE ects of decoupling and linearization permit the controller to be implemented and operated at desired eld weakening point of operation. Computer simulations are presented to demonstrate the eOE ectiveness of the proposed controller for a speci c motor. It has been shown that the proposed controller provides higher dynamic performance in comparison with traditional PI controllers, whereas the motor system is run over wide dynamic eld weakening regimes.Implementation of eld weakening is combined with armature voltage control to give a very wide speed range in separately excited DC motor (SEDCM) drive applications. Typical examples of these applications are extensively found in rolling mills, paper mills, robotics, and machine tools. An SEDCM system is modeled by three nonlinear diOE erential equations in eld-weakening region (! ! N ). Therefore, it is di cult to apply the linear control techniques, based on the linearized model about a nominal set point, to the nonlinear system [1,2]. For example, it is clear that the motor speed response becomes worse when it is operated by the traditional linear PI implemented control scheme shown in [2-4] over wide dynamic eld-weakening regimes (Fig. 1). For drive applications requiring high dynamic control performance, it is necessary to take the full-order electromechanical motor system with nonlinearities into account in the closed-loop control design.There has been recent interest in the study of advanced approaches for dealing with the SEDCM drive with eld weakening by adaptive gain scheduling and neural network controllers [5,6]. These approaches appear to be valuable in the situation

This paper addresses speed control of a separately excited DC motor (SEDCM) in nonlinear eld weakening region. Input output linearization (IOL) technique is used to deal with the motor system with considerable nonlinearity, and a nonlinear multi-input multi-output (MIMO) speed tracking controller is developed for constant power eld weakening. The eOE ects of decoupling and linearization permit the controller to be implemented and operated at any desired eldweakening point of operation. The control scheme combining this controller with nonlinear speed/load torque observer is, in particular, proposed for speed sensorless operation. Computer simulations are presented to show speed tracking performance of the proposed overall scheme.