Robust Speed Servo Control Scheme for Varying Loads

The problem being taken up is, the speed servo control of a PMDC motor. The reference input is continuously changing and also the load torque on the motor shaft is continuously varying. A control law based on the load torque is proposed. The Computed Torque Control scheme is used. The load torque, being of unknown kind, cannot be sensed and hence it has to be estimated. The load torque is estimated using a minimum order state observer. The estimated load is fed to the control law. The performance of the control law is tested using simulations. A comparison of closed loop PID, and Computed Torque Control schemes with and without load torque observer, is provided, thus giving a clear picture of the proposed control strategy.