Inductance vector angle based sensorless speed estimation in Switched Reluctance motor drive

Feedbacks signals of rotor speed and motor torque are essential in most of switched reluctance (SR) motor control applications. An SR motor has highly nonlinear characteristics that do not allow to be modeled by simple equations. Hence, the feedback signals can not be mathematically calculated from the model. Instead of calculation, they should be measured or estimated. In direct torque control (DTC) drive, which enables easy control of torque ripple in the SR motor, position sensor is employed to obtain the feedback signals. Position sensor causes DTC drive not only less reliable but also more expensive. Estimation of feedback signals is required in order to eliminate position sensor (or encoder). This paper concerns about sensorless speed estimation under the DTC condition and presents a simple method. The proposed method is based on inductance vector angle. The inductance vector angle is obtained by applying alpha - beta transformation to the phase inductances. A relay triggers a speed calculation circuit according to its band limits and the inductance vector angle. Inside the circuit, triggering time is kept in a memory until the next triggering. Then, rotor pole pitch is divided by the time difference between two consecutive triggerings. Finally, the estimation circuit outputs the rotor speed. Estimation method is simulated and verified experimentally to show its validity.