Nonlinear multi-input multi-output control of DC motor in field weakening region

Speed control of a separately excited DC motor has been implemented in field weakening region where the motor dynamics are considerably nonlinear. Based on nonlinear motor system dynamics, a multi-input multi-output speed tracking controller is developed using input-output linearization technique. Owing to decoupling and linearization, we carry out perfect speed tracking while achieving constant power field weakening. In view of the controller requiring measurement of the motor speed and complete knowledge of load torque, the control scheme combining this controller with a nonlinear speed/load torque observer is proposed. This scheme uses only current measurements and thus eliminates the need for a costly mechanical speed sensor system. Simulation results presented show high speed tracking performance of the proposed sensorless control scheme under unknown and constant load torque disturbance.