Performance Investigation and Improvement of a Double-Layer Outer Rotor Consequent-Pole Permanent Magnet Motor

Abstract

Due to the high power density and low loss, Permanent Magnet (PM) motors are widely used in electrical vehicles such as e-bike. However, the price of PM material is a significant challenge in PM machines for cost-sensitive applications. The consequent-pole concept is a promising strategy to overcome unsteady sources and the high price of PM material by removing half of the PMs and replacing them with iron poles, leading to a high PM utilization ratio. So, this paper investigates a new Double-layer Outer Rotor Consequent-Pole Permanent Magnet (DORCPM) motor as an appropriate alternative for use in price-sensitive applications. The proposed motor consists of two rotor layers that the rear layer is rotated by degree compared to the front layer. The rotation of the rear rotor layer causes the cancellation of the corresponding harmonics in the air gap flux density, which result in the reduction of torque harmonics. The operation theory of the DORCPM motor is presented based on the Magneto Motive Force (MMF) -Permeance model, and the main parameters are analyzed to achieve minimum torque ripple and maximum average torque. Furthermore, the electromagnetic performances of the proposed motor are derived and evaluated via finite element analysis, such as the average torque, air gap flux density, and torque ripple to validate the model. The results illustrate that the proposed DORCPM motor can provide low torque ripple and high torque density with reducing PM cost.