Detecting the rotor position by employing pulse injection technique and digital pulse width modulation decoder in switched reluctance motor

This paper presents a new and novel method which is designed to detect the rotor position at standstill and also low speeds in switched reluctance motor. In this method a small capacitor is connected in series with the motor winding for sampling the voltage rise during the detection period. The supply voltage in conjunction with the drive transistor produces short pulses for this series connection. Since the motor phase inductance varies according to the rotor position, therefore the rise-time for the voltage produced on the capacitor is different. Now this voltage is compared with a pre-set value and a voltage pulse with proper width is then generated. The width of created pulse is proportional to the rotor position. Now, a digital pulse width modulation decoder (DPWM Decoder) employed to convert the produced pulse width to a digital value. This technique is applied to all the phases at stand still to select the proper phase. In the running mode, the same procedure is applied but only to the un-energized phases winding. Finally, experimental results derived from an FPGA based drive are also presented for the motor to confirm the feasibility and practicability of the method.