Effect of Gear Ratio on a Magnetic Gear Integrated Switched Reluctance Motor

Electric motors with high torque density are sought after in applications with constrained equipment footprint. In recent years, torque density enhancement is often being achieved by using magnetic gears with the motors. The gear ratio has a substantial impact on the relative size of the motor and the magnetic gear and eventually on the system volume and performance. This paper investigates the effect of gear ratio on the design and performance parameters of a magnetic gear integrated machine in two different ways. Firstly, five machines are designed for the same output torque and speed ratings but for different gear ratios. In another set of five machines, magnetic gears of different gear ratios are integrated to the same motor to determine the trend and limitation in torque density enhancement. These designs are optimised with finite element analysis for a fair comparison. A magnetic gear integrated segmented rotor switched reluctance motor has been chosen for this study. The optimised designs are compared for material mass, loss, footprint and efficiency. Guidelines are provided towards the choice of gear ratio for magnetic gear integrated electric motors.