Variable reluctance stepper motors are commonly used in applications where incremental motion is desired. Recently, these motors have been used in situations which call for a large stepping rate; so large in fact, that the motor hums continuously. Although the equations which describe the stepper motor in this mode are decoupled, they are not time invariant. In order to eliminate the time varying terms, Park’s transformation is applied to the motor equations. It is found that this transformation does not render the system equations time invariant, so an averaging technique is employed which does provide the desired time invariance. The averaged model is evaluated by comparing its dynamic response with that of a derailed simulation of the motor in a variety of operating modes. It is found that the averaged model does not adequately represent the motor dynamics under most operating conditions.
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