Low-torque-ripple switched reluctance motors for direct-drive robotics

A contender for direct-drive application, the switched reluctance motor, is examined. It is first described how the number of teeth on the rotor and stator can be selected to achieve an electromagnetic gearing, with the goal of eliminating the need for a mechanical gearbox. It is also discussed how the tooth arcs of the rotor and stator can be adjusted so as to reduce the torque ripple of the motor during commutation. The treatment of these subjects includes a detailed case study in which the performance of four related motors is compared using finite-element analysis with a commutation algorithm for torque control. It is discovered that, although a tradeoff exists between peak torque and torque ripple, the maximum smooth torque and minimum torque ripple can be achieved by the same direct-drive motor design