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Further developments in indirect-rotor position sensing of variable-reluctance motors using waveform-detection technique

Abstract:

The waveform-detection technique detects rotor position in variable-reluctance motors indirectly by monitoring rise or fall times of the chopped phase current waveform. The chop rise and fall times can be either of an active or inactive phase. The drawbacks of monitoring chop current rise and fall times of an active phase have already been analyzed and presented in [2], [3], [4]. In this paper an investigation is made for using chop phase current rise time of an inactive phase for rotor position detection. A digital controller based on the waveform-detection technique which uses the inactive phase chop current rise time is implemented. The analysis together with experimental results obtained by applying the controller to drive a 3-phase VR step motor suggest that: the use of chop current rise-time leads to instability in the drive system and hence is not recommended. On the other hand, chop fall-time provides stable operation and therefore, is recommended. An algorithm implemented to start and run the VR step motor from stand-still position maintaining correct direction of rotation is also presented.