Sensorless control method using differentiation circuit for switched reluctance motor

A method is introduced for estimating the rotor phase of a switched reluctance motor (SRM) accurately. The rotor phase is estimated by substituting a differential current into the motor model. The differential current is measured by sampling the current twice and dividing the difference in the two values by the sampling period. The division error increases in high carrier frequency because the sampling period is short. First-order analog circuit is utilized to reduce the error in the proposed method. The circuit is a stable feedback system which has a first-order integrator element. When current is input to the circuit, the output signal of the integrator is convergence to the current and the input signal of the integrator is measured as a differential current. Therefore, the differential current is directly measured without division. The experimental results confirm the effectiveness of the proposed method at a carrier frequency of 20 kHz.