It is noted that rotor position information is essential for the operation of the switched reluctance motor (SRM) drive for generating the phase current switching signals. The accuracy of this position information dictates the efficiency and smoothness of the drive. The authors present the results of an accuracy analysis of a novel indirect SRM position sensing scheme, the FM (frequency modulated) encoder. The technique can be used to detect the rotor position with an error of 1 degrees electrical. The analysis breaks down the position error to its fundamental sources in the position sensing system. The same basic approach can be used to evaluate other SRM rotor position sensing schemes. The results are helpful in comparing the various sensing schemes as well as focusing improvement efforts on the right component in the system.
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