A sensorless drive method for switched reluctance motor based on gradient of phase inductance

This paper describes a simple method for indirect rotor position sensing in switched reluctance motors (SRM´s) using the gradient of phase inductance. Phase inductance of a SRM can be considered as a function of the rotor position and varies with the rotor position regularly. The inductance of the energized phase increases as the rotor approaches the aligned position, and the active phase inductance has a maximum value when the stator and the rotor poles are aligned. After that, the phase inductance decreases. The gradient of the active phase inductance is zero when the stator and the rotor poles are aligned. Therefore, it is basically possible to drive the SRM without a position sensor by changing the energized phase appropriately when the gradient of the phase inductance is equal to zero or less than zero. In this method, the gradient of the phase inductance can be easily computed using basic equations from the applied voltage and the stator current measured. Experimental results with the laboratory drive system are presented in this paper.