Estimation of speed and armature temperature in a brushed DC drive using the extended Kalman filter

Abstract

Closed-loop speed control of a DC drive requires a rotor-speed feedback signal which can be obtained using a speed measuring device. However this device adds to the cost of the drive and the number of electrical connections to the motor. The paper describes a method of speed estimation using armature voltage and current measurements that eliminates the speed measuring device. By including thermal effects in the estimation process the effect of temperature variations on the speed estimte are minimised and an estimate of average armature temperature is produced. An extended Kalman filter observer for real-time estimation of speed and armature temperature is formulated using electrical, mechanical and thermal models of the motor. The observer is implemented using a TMS 320C30 digital signal processor system. A range of experimental results demonstrating the observer's steady-state and transient performance is presented for the particular case of a 3 kW machine with constant field current supplied from a phase-controlled rectifier, although the estimation method is applicable to DC drives of any power rating and configuration.