LKF based robust control of electrical servodrives

The paper describes a new robust controller for the positioning of a servomotor. The position control system design is based on pole placement by the state feedback method with an additional feedforward compensation term. The state feedback controller gains are tuned on the nominal parameters of the motor and load. To obtain the specified ideal dynamic performance of the drive, the feedforward action has to compensate for the equivalent disturbance, which takes into account the unknown external load torque, nonlinear viscous friction torque terms, and parameter variations occurring in the controlled process. The robustness of the new controller is guaranteed by the recursive algorithm, based on discrete linear Kalman filter (LKF) theory, that the authors have developed to estimate online the nonlinear time varying equivalent disturbance. The desired ideal dynamic performance of the drive is so obtained without adjusting the state feedback controller gains. In particular, negligible steady-state error occurs and good transient responses are attained.