Effect of Pole Placement of a Full Order State Observer in Sensorless Speed Estimation of Brushed DC Motor

Usually for controlling the speed of DC motor we use mechanical sensors like tachometers, encoders and Hall effect sensors which need to be coupled with the shaft of the DC motor for estimating the speed of the motor. But for small motors where miniaturization is required, these sensors will increase cost, mounting place and maintenance problems. In this work, a 'full-ordered state observer' based sensorless speed estimation of DC motor has been used. Since we take 'the speed of the DC motor' as a state variable, we will estimate it using the proposed observer. The effect of variations in load torque and input voltage on speed estimation are discussed. The observer works well in all dynamic variations on motor, for estimating the speed. The effect of placement of poles of observer on error of the estimated speed for the given variation on the motor are also been discussed. All these results are simulated in MATLAB.