The Design of the Outer-Rotor Brushless DC Motor and an Investigation of Motor Axial-Length-to-Pole-Pitch Ratio

Abstract

In this study, the effects of the ratio of a motor’s axial length to its pole pitch on efficiency, magnetic flux density distribution, torque, torque/weight, and motor volume were investigated in an outer-rotor (hub) brushless direct current motor. The weight and volume of an electrical machine affects the output power, efficiency and output torque, and it is advantageous to design an electric motor at an appropriate power and high efficiency with an appropriate weight and volume. Therefore, the aim of this study was to optimize the motor’s axial length and stator outer diameter, which affects the motor volume. Initially, the axial-length-to-pole-pitch ratio of the hub BLDC motor was taken at 0.75. According to this ratio, the dimensions of the rotor outer diameter, rotor inner diameter, stator outer diameter, stator inner diameter, slot height, motor axial length, and magnet thickness were optimally determined. Then, the axial-length-to-pole-pitch ratio was considered as 1, 1.50, 2, and 3, respectively. The effects of the change in the motor’s axial-length-to-pole-pitch ratio on the efficiency, torque, speed, torque/volume, torque/weight, and cogging torque were examined in a simulation environment. According to the motor’s axial-length-to-pole-pitch ratio, the torque value in the final state was 28.65% higher than the torque value in the initial state. In the last part, the motor axial length and the stator outer diameter were defined as variables in a genetic algorithm procedure and optimized. The number of poles and the number of slots were fixed parameters. Simulation studies were carried out using the finite element method via AN-SYS/Maxwell software.

Design of a HTS 2 MW Electric Motor for Single-Aisle Regional Aircraft

“…For this analysis, different geometric ratios related with the output power and the power-density can be used, such as the L/D factor, defined as the ratio of the stack length and the air gap diameter [67], or the L/τ factor, defined as the ratio of the stack length and the pole-pitch [68]. For this study, the L/D factor is chosen and a value of 1.75 has been set as the upper limit, which is a widespread practice in the manufacturing of electric machines to avoid mechanical issues regarding the shaft, the bearings, and the housing.…”

Optimal Rotor Design and Analysis of Energy-Efficient Brushless DC Motor-Driven Centrifugal Monoset Pump for Agriculture Applications

“…High-power-density motors prioritize lightweight structures and high electromagnetic loads, optimizing power density through strategic rotor and stator configurations. Magnetic circuits design boost efficiency and reduce cogging torque [56,57]. Additionally, enhancements in no-load back EMF and phase current improve motor output power density.…”

The Design, Optimization, and Experimental Study of Hub and Axial Flux BLDC Motor Under Operating Conditions For Light Electric Vehicles

“…Table 6 shows the Axial Flux and Hub BLDC motor's constant parameters. The variable parameters selected in the GA for the axial flux and hub BLDC motors are represented by equations ( 4) to (9). Equation ( 4) describes the electromechanical power of both motors.…”

“…In addition, features such as the winding method, pole type, and magnet type are also examined during the design phase [8]. The rotor design and optimization of the 10 KW BLDC motor with the desired torque and speed have been carried out in [9], considering the effect of rotor design on BLDC motor performance is effective on torque, speed, and efficiency. To optimize the two-wheel electric motor in terms of required torque, speed, size, mass, and cost, the effect of the air gap length on the efficiency was investigated between the determined mere limited values.…”