An FPGA based minimum inductance sensor-less technique for Switched Reluctance Motors

This paper proposes a technique to detect the rotor position in a Switched Reluctance Motor(SRM) which only requires knowledge of the phase resistance and the number of stator and rotor poles. Accuracy can be further improved if prior knowledge of the mutual phase inductance is known. The technique operates by sensing the minimum inductance location which allows positional information to be obtained. This is performed using a controlled low level sense current during the un-energised period. A Digital Phase Locked Loop is described to derive rotational positions between minimum inductance locations. Factors affecting the detection of the minimum inductance position are described and proposals to mitigate errors are discussed. The technique is implemented using a Field Programmable Gate Array(FPGA) with results showing good performance over a range of speeds and motor operating conditions.