Electrical drive systems incorporating variable reluctance motors

Abstract

In a two-phase salient pole variable reluctance motor in which the number of stator poles is four or a multiple of four, alternate stator poles carry windings of different phases and each stator pole has an elongated pole shoe, so that the pole tips of each adjacent pair of stator poles are closely spaced. Each rotor pole has an iron depletion layer in the vicinity of its poleface surface which defines a saturating zone, across which the greater part of the magnetomotive force produced by stator windings is developed by uniform flux build-up with rotor angle throughout almost the entire duration of pole overlap. A working stroke approximating a stator pole pitch is achieved. The circumferential extent of each rotor pole is matched to that of the stator poles so that when the rotor poles are fully aligned with a pair of stator poles, each rotor poletip is located in the vicinity of a pair of spaced apart stator pole tips, the relative disposition of the pole tips being such that when both phases of the motor are then simultaneously excited, fringing flux passes through the rotor poletips, this flux being relatively strong for one poletip of each rotor pole and relatively weak for the other poletip. When the rotor poles are initially positioned so that there is partial overlap between rotor and stator poles, the motor is started by a conventional reluctance motor phase sequence, but when the rotor poles are initially fully aligned with stator poles, in which position neither phase acting alone is capable of producing torque, both phases are excited simultaneously, so that torque is applied to the rotor by the flux asymmetry to move the rotor into normal phase energization. The motor is bi-directional and self-starting in both senses from any rotor position.