A new low-noise two-phase switched reluctance motor

This paper presents a detailed analysis of a 2-phase switched reluctance motor in which a significant component of the acoustic noise (ovalization) is suppressed or neutralized by means of a flux-switching transition. The flux transforms naturally and smoothly without electronic control from a 2-pole to a 4-pole configuration before the phase current commutates, causing the ovalizing stress to be dispersed before the point of commutation. The unique asymmetrical geometry of the motor also produces low torque ripple, because the rate of change of inductance in each phase remains constant over a wide angle as the rotor rotates. Measurements and finite-element analysis show that this angle can approach 180 electrical degrees, which is exceptional for a 2-phase switched reluctance machine. With only two phases, the motor and drive connections are simplified; the component count is kept to a minimum, and the shaft-position sensing requirements are inexpensive. The paper describes the basic theory of the motor and presents test data together with new finite-element computations and insights