Introduction : Separately excited dc motor drive systems are operated with torque control. Closed loop drives may be employed for speed control which requires the feedback speed signal from tacho generators or pulse encoders.

The use of transducer may adversely affect the stable performance of the motor, increases the hardware complexity and costs.

Consequently there has been intense research on the development of speed estimation by using the knowledge of motor parameters, input voltage and current to the motor, the speed estimation can be computed.

However the closed loop estimator is more accurate than open loop estimator[3]. This project consists of a speed sensorless separately excited dc motor drive with an adaptive observer to estimate the rotor speed (closed loop estimator).

The stability of speed estimation was analyzed by using Routh Hurwitz criterion. The modified feed forward control is integrated with the adaptive observer to simplify the implementation.

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