Design methodology for low-speed variable reluctance motors

Lowering the gear reduction in actuators by utilizing high-torque low-speed motors enables the use of less expensive and simpler gear systems and decreases the overall system inertia. Variable reluctance machines can produce high torque at low speeds. Their static torque, a critical quantity for determination of low speed operation, is compared for three variable reluctance motor design variations using linear analysis. Saturation effects, which are crucial to the accurate determination of static torque, are modeled using a dual energy technique first proposed by Lord Rayleigh. Dual energy techniques utilizing flux tubes and magnetomotive force slices are developed into a numerical method for predicting nonlinear three-dimensional magnetostatic field parameters. The dual energy method offers a compromise between the accurate but laborious finite element method and the speed of simplified lumped parameter magnetic circuit calculations. A two-dimensional dual energy model of a variable reluctance motor is developed. Results of calculations on a 4 kW Oulton machine are compared to measurements and other calculation methods. Finally, as a demonstration, the model is used to evaluate two competing variable reluctance motors for use as replacements for a DC windshield wiper motor