Switched Reluctance Motor Design for a Mid-Drive E-Bike Application

Abstract

The popularity of electric bicycles (e-bikes) among urban commuters and cyclists is constantly increasing because e-bikes provide an efficient, more powerful, and a low-cost mode of transportation. Since the main issue is to increase the power density of the drive system, a permanent magnet (PM) machine is the preferred choice. In mid-drive systems, higher speed motors are commonly used, which provides the opportunity to use switched reluctance machines (SRM), because they can provide better performance when designed for higher speeds. Moreover, the simple, robust, and low-cost structure of SRM makes it a favorable option for e-bike drive systems. In this paper, an SRM design for an e-bike mid-drive system is investigated. Several 3-phase configurations with higher number of rotor poles than the stator poles are considered: 6/10, 6/14, and 12/16, as well as the conventional 12/8 SRM, for the sake of comparison. Main dimensions and requirements are defined from Shimano Steps mid-drive PM machine, whose characteristics are taken as the design goal. According to the results, the best configuration is selected and further optimized, leading to the final design for which a prototype is built and tested.