EFFECT OF ROTOR PROFILES ON THE TORQUE OF A SWITCHED-RELUCTANCE MOTOR

The torque produced in a switched-reluctance motor (SRM) may be viewed from the manner in which the radial and tangential flux density components interact. With a common stator and rotor pole geometry, the radial flux component in the overlapping region of the excited stator and rotor poles is loaf shaped; it is, in most situations, the dominant component. The tangential component, on the other hand, is mostly insignificant except around the pole tips of the excited stator and rotor poles. This paper examines effects on the torque that simple variations of the standard rotor pole face profile could have, basically from an elementary viewpoint of how the modified profiles affect the distribution and magnitude of the radial and tangential components of the flux density. It is observed that the average torque is mostly affected by changes that alter the dominant radial component, such as changes in the effective air gap length. The other observation that an increase in the average torque can also be obtained by a favorable shift in the torque versus angle characteristics by relatively, simple changes of the rotor pole profile is, perhaps, not so well known. Such a shift that reduces the slope of the torque angle characteristic, skewing the curve towards the unaligned position, has two advantages: one is that the phase inductance is at its maximum positive slope and, hence, the maximum torque, when the phase is energized; second, the flatter inductance profile near the aligned position when the phase current is to be commutated would allow a faster drop off of the commutated current and, thus, a smaller negative torque.