Waveform detection technique for indirect rotor-position sensing of switched-reluctance motor drives part 1: analysis

Abstract

Rotor-position detection either directly or indirectly is essential for SR motors operating in variable-speed drive applications. Direct rotor-position sensors provide stable operation of the drive system. However, the use of direct sensors leads to reliability problems in certain industrial environments e.g. high-temperature conditions or where electromagnetic interference is present. Additionally, for fractional horse power drives the cost of the position sensors becomes a significant part of the overall drive system cost. Indirect rotor-position sensing is an attractive alternative in such applications. In this part of the paper the waveform detection technique is analysed using computer simulation with back EMF taken into account. Simulation is carried out to find which parameter, out of the current chop rise and fall-times in the active and inactive phases, is best suited to rotor-position detection under various operating conditions. It is concluded that the current chop falltime in the inactive phase provides reliable position detection under varying operating conditions. The simulation is based on a 4kW-4-phase SR motor.