# Design Optimization and Analysis of an Outer-Rotor Direct-Drive Permanent-Magnet Motor for Medium-Speed Electric Vehicle

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## Abstract

**:**

## 1. Introduction

## 2. Design of the Outer-Rotor Direct-Drive Brushless DC Motor

#### 2.1. Design Parameters of the Motor

#### 2.1.1. Determination of Motor Power

_{e}, the maximum power of the vehicle achieving the maximum gradient is p

_{a}, and the power of the vehicle achieving the highest acceleration time is p

_{c}.

- Taking the maximum speed as the basis$${p}_{e}=\frac{{u}_{\mathrm{max}}}{3600{\eta}_{T}}\left(mgf+\frac{{C}_{D}A{u}_{\mathrm{max}}^{2}}{21.15}\right)$$
- Taking the climbing capability as the basis$${p}_{a}=\frac{{u}_{i}}{3600{\eta}_{T}}\left(mgf\mathrm{cos}{\alpha}_{\mathrm{max}}+mg\mathrm{sin}{\alpha}_{\mathrm{max}}+\frac{{C}_{D}A{u}_{i}^{2}}{21.15}\right)$$
- Taking the acceleration capability as the basis$${p}_{c}=\frac{1}{3600{t}_{a}{\eta}_{T}}\left(\delta m\frac{{u}_{a}^{2}}{2\sqrt{{t}_{a}}}+mgf\frac{{u}_{a}}{1.5}{t}_{a}+\frac{{C}_{D}A{u}_{a}^{3}}{21.15\times 2.5}{t}_{a}\right)$$
_{a}is the acceleration final velocity(km/h), and δ is the mass conversion coefficient whose value is 1.04.

#### 2.1.2. Determination of the Rated Speed and Peak Speed

_{max}of the motor is deduced as

#### 2.2. Main Dimensions of the Motor and Electromagnetic Load

#### 2.3. Design of the Stator and Rotor of the Motor

#### 2.3.1. Dimensions of the Stator and Rotor

_{a}= 317.86 mm.

#### 2.3.2. Determination of the Armature Winding

#### 2.3.3. Parameter Optimization Based on the Equivalent Magnetic Circuit Method

#### Optimization of the Air-Gap Length

#### Optimization of the Pole-Arc Coefficient

#### 2.3.4. Structural Design of the Motor Stator and Rotor

#### Mechanical Structure of the Stator

#### Mechanical Structure of the Rotor

#### Integral Mechanical Structure of Motor

## 3. Analysis of the Electromagnetic Field of the Outer-Rotor Direct-Drive Brushless DC Motor

#### 3.1. Establishment of the Motor Model

#### 3.2. Analysis of the Static Magnetic Field of the Motor

_{1}, m

_{2}, m

_{3}, and m

_{4}are the vector magnetic potential values of the four points from Figure 15 (Wb/m).

#### 3.3. Analysis of the Transient Magnetic Field of the Motor

#### 3.3.1. Analysis of the No-Load Transient Magnetic Field

#### 3.3.2. Analysis of the Load Transient Magnetic Field

#### 3.4. Loss Analysis of the Motor

## 4. Analysis of the Torque Ripple Characteristics of the Outer Rotor Direct-Drive Brushless DC Motor

#### 4.1. Analysis of the Cogging Torque

#### 4.2. Analysis of the Electromagnetic Torque

#### 4.3. Reduction of the Torque Ripple of the Motor

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

- Jinghong, L. Drive System Design and Simulation Analysis for Hybrid Electric Vehicles. J. Shanghai Dianji Univ.
**2007**, 1, 33–35. [Google Scholar] - Ruiqing, D. New energy vehicles development strategy research. J. New Ind.
**2011**, 1, 18–24. [Google Scholar] - Lianqiao, T. The Full Text of China’s 13th Five-Year Plan. Available online: http://www.woc88.com/doc-12659458.html (accessed on 1 March 2018).
- Ningning, T. Finite Element Modeling and Multi-Field Coupling Analysis of BLDC Wheel Motor; Jilin University: Jilin, China, 2014. [Google Scholar]
- Shumei, C.; Junyun, S. The Research of the Direct-driven Wheel Motor Applied in Electric Vehicle. Micromotors Servo Tech.
**2006**, 39, 68–70. [Google Scholar] - Xinmei, L. Design and Research of the High-Power Density Permanent Magnet In-Wheel Motor Based on the Reluctance Torque; Harbin Institute of Technology: Harbin, China, 2008. [Google Scholar]
- Tesla Model S. Automotive Observer
**2018**, 1, 25. - Zhenpo, W.; Fengchun, S.; Peng, L. The Electric Car Principle and Application Technology; Mechanical Industry Press: Beijing, China, 2015. [Google Scholar]
- Ekram, S.; Mahajan, D.; Fazil, M.; Patwardhan, V.; Ravi, N. Design Optimization of Brushless Permanent Magnet Hub Motor Drive Using FEA. In Proceedings of the International Conference on Electrical Machines and Systems, Seoul, Korea, 8–11 October 2007; Volume 8, pp. 8–11. [Google Scholar]
- Gombert, B.; Fischer, R.; Heinrich, W. Wheel-Hub Motors Criteria of Construction and Vehicle Integrtation. ATZelektronik Worldw.
**2010**, 5, 4–10. [Google Scholar] [CrossRef] - Rix, A.J.; Kamper, M.J. Radial-Flux Permanent-Magnet Hub Drives: A Comparison Based on Stator and Rotor Topologies. IEEE Trans. Ind. Electron.
**2012**, 59, 2475–2483. [Google Scholar] [CrossRef] - Xiong, S. Motor drive technology research of the electric car. Silicon Val.
**2014**, 21, 41. [Google Scholar] - Li, G.; Ojeda, J.; Hoang, E.; Gabsi, M.; Lecrivain, M. Thermal-electromag-netic analysis for driving cycles of embedded flux-switching permanent-magnet motors. IEEE Trans. Veh. Technol.
**2012**, 61, 140–151. [Google Scholar] [CrossRef] - Hejra, M.; Mansouri, A. Optimal Design of a Permanent Magnet Synchronous Motor: Application of In-Wheel Motor. In Proceedings of the 15th Intemational Renewable Energy Congress IREC, Hammamet, Tunisia, 25–27 March 2014. [Google Scholar]
- Kock, A.; Groninger, M.; Mertens, A. Fault Tolerant Wheel Hub Drive with Integrated Converter for Electric Vehicle Applications. In Proceedings of the 2012 IEEE Vehicle Power and Propulsion Conference, Seoul, Korea, 9–12 October 2012. [Google Scholar]
- Tashakori, A.; Ektesabi, M. Fault diagnosis of in-wheel BLDC motor drive for electric vehicle application. In Proceedings of the 2013 IEEE Intelligent Vehicles Symposium, Gold Coast, QLD, Australia, 23–26 June 2013. [Google Scholar]
- Li, Y.; Wenjin, D. Theory and Practice of Motor Design; Tsinghua University Press: Beijing, China, 2013. [Google Scholar]
- Sumin, W. The Study on the Optimization for the Structural Parameters of Permanent Magnet Synchronous Motor Based on Ansoft; University of Electronic Science and Technology: Chengdu, China, 2014. [Google Scholar]
- Feng, Y.; Yang, K.; Gu, C. Design and optimization of external-rotor torque motor. In Proceedings of the 12th International Conference on Electrical Machines and Systems, Funabori, Tokyo, 15–18 November 2009; pp. 1–4. [Google Scholar]
- Yuejin, Z.; Chunjiang, L.; Guanzhen, T. Analytical Method for Air-Gap Main Magnetic Field Computation of Surface Mounted Permanent Magnet Torque Motors. Trans. China Electrotech. Soc.
**2011**, 26, 13–17. [Google Scholar] - Lei, L. The Study of Thermal Characteristics in Various Conditions and Cooling System of Permanent Magnet Synchronous Motor in Pure Electric Vehicle; Hefei University of Technology: Chengdu, China, 2015. [Google Scholar]
- Zhu, Z.Q. Influence of Design Parameters on Cogging Torque in Permanent Magnet Machines. IEEE Trans. Energy Convers.
**2000**, 15, 407–412. [Google Scholar] [CrossRef]

A Geely Automobile | Technical Parameters | Value |
---|---|---|

Basic parameters | The entire vehicle mass $m$ (kg) | 800 |

Windward area A (${m}^{2}$) | 2 | |

Coefficient of air resistance ${C}_{D}$ | 0.32 | |

Rolling resistance coefficient $f$ | 0.015 | |

System transmission efficiency ${\eta}_{T}$ | 0.96 | |

The wheel radius $r$ (m) | 0.27 | |

Performance index | The maximum speed ${u}_{\mathrm{max}}$ (km/h) | 80 |

The maximum gradeability $a$ (°) | 11.3 | |

0–60 km/h acceleration time ${t}_{a}$ ($s$) | 9 |

Parameters | Value |
---|---|

Rated power | ${p}_{N}=22kw$ |

Peak power | ${p}_{\mathrm{max}}=55kw$ |

Rated speed | ${n}_{N}=260r/\mathrm{min}$ |

Maximum speed | ${n}_{\mathrm{max}}=780r/\mathrm{min}$ |

Rated torque | ${T}_{\mathrm{N}}=2.02\text{}\mathrm{kN}\cdot \mathrm{m}$ |

Phase number | M = 3 |

Efficiency | $\eta \ge 85\%$ |

Permanent magnet material | N35SH |

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## Share and Cite

**MDPI and ACS Style**

Yuan, Y.; Meng, W.; Sun, X.; Zhang, L.
Design Optimization and Analysis of an Outer-Rotor Direct-Drive Permanent-Magnet Motor for Medium-Speed Electric Vehicle. *World Electr. Veh. J.* **2019**, *10*, 16.
https://doi.org/10.3390/wevj10020016

**AMA Style**

Yuan Y, Meng W, Sun X, Zhang L.
Design Optimization and Analysis of an Outer-Rotor Direct-Drive Permanent-Magnet Motor for Medium-Speed Electric Vehicle. *World Electric Vehicle Journal*. 2019; 10(2):16.
https://doi.org/10.3390/wevj10020016

**Chicago/Turabian Style**

Yuan, Yuan, Wenjun Meng, Xiaoxia Sun, and Liyong Zhang.
2019. "Design Optimization and Analysis of an Outer-Rotor Direct-Drive Permanent-Magnet Motor for Medium-Speed Electric Vehicle" *World Electric Vehicle Journal* 10, no. 2: 16.
https://doi.org/10.3390/wevj10020016