# Electromagnetic Field Analysis and Design of an Efficient Outer Rotor Inductor in the Low-Speed Section for Driving Electric Vehicles

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## Abstract

**:**

## 1. Introduction

_{2}emissions and the particulate matter generation from internal combustion engine vehicles, such as gasoline- and diesel-fueled cars. As a result, electric vehicles are gaining acceptance in most countries, such as in Europe and the United States of America. Furthermore, limited vehicle types, such as passenger cars, are being converted into electric vehicles; moreover, various small electric vehicles, including smart mobility vehicles, are under development [1].

## 2. Outer Rotor Induction Motor

## 3. Outer Rotor Induction Motor Design Outer Rotor Induction Motor

#### 3.1. Basic Design Specification Selection

#### 3.2. Electrical Steel Selection

^{3}, a maximum iron loss of 2.3 W/kg, a minimum magnetic flux density of 1.62 T, and a space factor exceeding 95%.

#### 3.3. Number of Poles and Slot Combination

#### 3.4. Motor Dimensions

## 4. Analysis of Induction Motor Characteristics via Electromagnetic Field Analysis

#### 4.1. Slot Combination

#### 4.2. Stator Slot Shape

#### 4.3. Rotor Bar Shape

#### 4.4. Lamination

#### 4.5. Wire Diameter and Turn Count

#### 4.6. End Ring Design

#### 4.7. Summary of Trend Analysis

## 5. Fabrication of Outer Rotor Induction Motor Prototype and Performance Evaluation Device

#### 5.1. Fabrication of Outer Rotor Inductor

#### 5.2. Outer Rotor Inductor Performance Evaluation Device

## 6. Inductor Performance Evaluation

#### 6.1. 6-Pole Model Performance Evaluation

#### 6.2. 10-pole Model Performance Evaluation

#### 6.3. 16-pole Model Performance Evaluation

## 7. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 2.**Graphs of motor characteristics according to stator slot shape: (

**a**) Stator slot shape; graphs of output and efficiency according to (

**b**) slot opening, (

**c**) tooth thickness and (

**d**) slot height.

**Figure 3.**Graphs of motor characteristics according to rotor bar shape: (

**a**) Rotor bar shape; graphs of power output and efficiency according to (

**b**) rotor bar thickness, (

**c**) rotor bar height and (

**d**) rotor slot opening.

**Figure 8.**Three-dimensional (3D) modeling images and photographs of actual fabricated components of the outer rotor (induction motor and assembled device: 3D drawing of (

**a**) stator and (

**b**) rotor; (

**c**) two-dimensional (2D) drawing of winding; produced (

**d**) stator, (

**e**) rotor, (

**f**) winding and (

**g**) assembled outer rotor inductor.

**Figure 9.**Inductor test equipment and test device configuration: (

**a**) Induction motor test equipment, (

**b**) test device configuration.

**Figure 10.**Graphs of motor characteristics according to voltage and frequency for the outer rotor inductor with 6 poles: Voltage_frequency of (

**a**–

**o**): 41.7 V_55 Hz, 51.9 V_65 Hz, 25.3 V_80 Hz, 47.2 V_80 Hz, 51.9 V_80 Hz, 31.3 V_100 Hz, 34.4 V_100 Hz, 43.2 V_100 Hz, 46.7 V_100 Hz, 51.9 V_100 Hz, 54.1 V_100 Hz, 62.3 V_100 Hz, 69.2 V_100 Hz and 36.6 V_120 Hz, respectively.

**Figure 11.**Graphs of motor characteristics according to voltage and frequency for outer rotor inductor with 10 poles: Voltage_frequency of (

**a**–

**h**): 36.7 V_90 Hz, 46.7 V_90 Hz, 52.7 V_90 Hz, 34.6 V_100 Hz, 46.7 V_100 Hz, 46.3 V_110 Hz, 49.6 V_110 Hz and 52.7 V_110 Hz, respectively.

**Figure 12.**Graphs of motor characteristics according to voltage and frequency of outer rotor inductor with 10 poles: Voltage_frequency of (

**a**−

**f**): 32.3 V_126 Hz, 35 V_126 Hz, 33.2 V_137 Hz, 33 V_138 Hz, 23.9 V_140 Hz and 33.2V_140 Hz, respectively.

Number of Poles | Number of Stator Slots | Number of Rotor Slots | Number of Poles Number | Number of Stator Slots | Number of Rotor Slots |
---|---|---|---|---|---|

2 | 24 | 28, 16, 22 | 6 | 36 | 42, 48, 54, 30 |

36 | 24, 28, 48, 16 | 54 | 72, 88, 48 | ||

48 | 40, 52 | 72 | 90, 88, 84, 50 | ||

4 | 36 | 24, 40, 42, 60 | 8 | 36 | 48 |

48 | 60, 84, 56, 44 | 48 | 72, 60 | ||

60 | 72, 48, 84, 44 | 72 | 96 |

8 Poles | 6 Poles |
---|---|

Rotation speed: 1000 rpm $N=\frac{120\times f}{P}=\frac{120\times 66.6}{8}=1000\mathrm{rpm}$ | Rotation speed: 1000 rpm $N=\frac{120\times f}{P}=\frac{120\times 50}{6}=1000\mathrm{rpm}$ |

Torque: 11.4 Nm $T=\frac{974\times Power}{RPM}=kgf\times 9.8=\mathrm{Nm}$ $=\frac{974\times 1.2}{1000}=1.1688\times 9.8=11.4\mathrm{Nm}$ | Torque: 11.4 Nm $T=\frac{974\times Power}{RPM}=kgf\times 9.8=\mathrm{Nm}$ $=\frac{974\times 1.2}{1000}=1.1688\times 9.8=11.4\mathrm{Nm}$ |

Rotor Core | Stator Core | ||
---|---|---|---|

Outer diameter | 216 | Outer diameter | 187.4 |

Inner diameter | 188 | Inner diameter | 146 |

Stack | 20 | Stack | 20 |

Air gap | 0.3 | ||

$\mathrm{w}20,\text{}\mathrm{d}20\ge 0.8\u20131.2(\mathrm{d}20\ge \mathrm{w}20$) | $\mathrm{Slot}\text{}\mathrm{open}=2\u20133\text{}\mathrm{mm}$ | ||

$\mathrm{Slot}\text{}\mathrm{opening}\text{}\mathrm{w}\text{}20=0.8$ | $\Rightarrow \mathrm{Selected}\text{}\mathrm{as}\text{}2\text{}\mathrm{mm}\text{}$ $\text{}\mathrm{considering}\text{}\mathrm{the}\text{}\mathrm{windings}$ | ||

$\mathrm{Slot}\text{}\mathrm{face}\text{}\mathrm{width}\text{}\mathrm{w}\text{}20=0.8$ | $\mathrm{Slot}\text{}\mathrm{face}\text{}\mathrm{width}=0.8\text{}\mathrm{mm}$ | ||

$\mathrm{Tooth}\text{}\mathrm{thickness}=\text{}\frac{0.95\text{}\times \text{}S1\text{}\times {t}_{0}}{S2}$ | $\mathrm{Tooth}\text{}\mathrm{thickness}=3\text{}\mathrm{mm}$ | ||

$=\frac{0.95\times 72\times 3}{88}=2.5$ | $\mathrm{Core}\text{}\mathrm{back}=\frac{1.05\times D}{{k}_{e}\times P}\times \frac{{B}_{0}}{{B}_{CO}}$ | ||

$\mathrm{Core}\text{}\mathrm{back}=0.95\times {h}_{0}$ | $=\frac{1.05\times 146}{0.95\times 6}\times 0.3=8.1$ | ||

$=0.95\times 8.1=7.7$ | $\mathrm{Core}\text{}\mathrm{space}\text{}\mathrm{factor}=0.9\u20130.95$ | ||

$\mathrm{Slot}\text{}\mathrm{depth}=\mathrm{Rotor}\text{}\mathrm{outer}\text{}\mathrm{radius}-\mathrm{Rotor}\text{}\mathrm{inner}\text{}\mathrm{radius}-\mathrm{Core}\text{}\mathrm{back}$ | $\mathrm{Slot}\text{}\mathrm{depth}=\frac{\left[{D}_{0}-\left(2{h}_{0}+D\right)\right]}{2}$ | ||

$=108-94-7.7=6.3$ | $=\frac{187.4-\left(2\times 8.1+146\right)}{2}=12.6$ |

Output (W) | Efficiency (%) | Torque (Nm) | Weight (kg) | |
---|---|---|---|---|

54/42 | 598 | 70.5 | 4.5 | 9.94 |

54/66 | 722 | 72.2 | 5.5 | 10.17 |

72/54 | 800 | 82.8 | 6.1 | 9.37 |

72/84 | 927 | 82.9 | 7.1 | 9.66 |

72/88 | 939 | 82.9 | 7.2 | 9.7 |

90/124 | 1210 | 81.9 | 9.3 | 9.7 |

108/124 | 1406 | 75 | 10.8 | 9.52 |

Turn Count | Wire Diameter (mm) | Reel Count | Space Factor (%) | Rated Output (W) | Efficiency (%) | Torque (Nm) | Current Density (A/mm^{2}) | |
---|---|---|---|---|---|---|---|---|

1 | 12 | 0.5 | 4 | 42.2 | 1561 | 63.8 | 11.9 | 12.8 |

2 | 13 | 0.55 | 3 | 41.5 | 1447 | 72.9 | 11.11 | 9.62 |

3 | 14 | 0.35 | 7 | 42.2 | 1336 | 79.1 | 10.25 | 7.21 |

4 | 15 | 0.45 | 4 | 42.7 | 1210 | 82 | 9.29 | 5.94 |

5 | 16 | 0.5 | 3 | 42.2 | 1086 | 83 | 8.33 | 5.28 |

Rotor End Ring Thickness (mm) | Rated Output (W) | Efficiency (%) | Weight of the Rotor End Ring (kg) |
---|---|---|---|

10 | 998 | 80.8 | 0.74 |

11 | 1068 | 81.1 | 0.78 |

12 | 1136 | 81.2 | 0.83 |

13 | 1200 | 81.3 | 0.87 |

14 | 1259 | 81.3 | 0.92 |

15 | 1315 | 81.3 | 0.96 |

With Increasing Value of | Output | Efficiency | Weight |
---|---|---|---|

Lamination | ↓ | ↑ | ↑ |

Turn Count | ↓ | ↑ | ↑ |

Wire Diameter | ↓ | ↑ | ↑ |

Throw | ↓ | ↑ | ↑ |

Rotor End Ring Thickness | ↑ | ↑ | ↑ |

Pole Number | ↓ | ↑ | ↑ |

Stator Slot | ↑ | ↑ | ↓ |

Rotor Slot | ↑ | ↑ | ↑ |

Stator Outer Diameter | ↑ | ↑ | ↑ |

Stator Inner Diameter | ↑ | ↑ | ↑ |

Rotor Outer Diameter | ↑ | ↑ | ↑ |

Rotor Inner Diameter | ↓ | ↑ | ↓ |

Stator Slot Opening | ↑ | ↓ | ↓ |

Stator Tooth Thickness | ↑ | ↑ | ↑ |

Stator Slot Height | ↓ | ↓ | ↓ |

Rotor Bar Thickness | ↑ | ↑ | ↑ |

Rotor Bar Height | ↑ | ↑ | ↑ |

Rotor Slot Opening | ↑ | ↓ | ↑ |

**Table 8.**Motor characteristics according to voltage and frequency for the outer rotor inductor with 6 poles.

Voltage (V) | Frequency (Hz) | Maximum Efficiency (%) | Speed at Maximum-Efficiency Point (rpm) | Output at Maximum-Efficiency Point (W) | Torque at Maximum-Efficiency Point (Nm) |
---|---|---|---|---|---|

41.7 | 55 | 53 | 1010 | 1516.8 | 12.8 |

51.9 | 65 | 49.8 | 1076 | 1723.7 | 15.3 |

25.3 | 80 | 88.2 | 1555 | 245.4 | 1.5 |

47.2 | 80 | 62.7 | 1444 | 1711.7 | 11.3 |

51.9 | 80 | 62.2 | 1438 | 1654.2 | 11 |

31.3 | 100 | 81.2 | 1922 | 442.3 | 2.2 |

34.4 | 100 | 79.9 | 1913 | 587.7 | 2.9 |

43.2 | 100 | 74 | 1892 | 1049.9 | 5.3 |

46.7 | 100 | 72.8 | 1898 | 1148 | 5.8 |

51.9 | 100 | 72.2 | 1893 | 1160.1 | 5.9 |

54.1 | 100 | 67.8 | 1871 | 1747.6 | 8.9 |

62.3 | 100 | 66.8 | 1826 | 2165.1 | 11.3 |

69.2 | 100 | 63.7 | 1853 | 2238.3 | 11.5 |

36.3 | 120 | 81.2 | 2300 | 666.5 | 2.8 |

41 | 120 | 80.1 | 2292 | 874.8 | 3.6 |

**Table 9.**Motor characteristics according to voltage and frequency for outer rotor inductor with 10 poles.

Voltage (V) | Frequency (Hz) | Maximum Efficiency (%) | Speed at Maximum-Efficiency Point (rpm) | Output at Maximum-Efficiency Point (W) | Torque at Maximum-Efficiency Point (Nm) |
---|---|---|---|---|---|

36.67 | 90 | 77 | 1027 | 1197.9 | 11.14 |

46.71 | 90 | 76.6 | 1028 | 1182.8 | 11 |

52.76 | 90 | 72.9 | 1011 | 1797.1 | 16.9 |

34.6 | 100 | 80.6 | 1165 | 454 | 3.72 |

46.71 | 100 | 79 | 1153 | 1029 | 8.5 |

46.36 | 110 | 80.7 | 1267 | 1052.8 | 7.9 |

49.65 | 110 | 80.3 | 1265 | 1229.6 | 9.28 |

52.76 | 110 | 79.9 | 1269 | 1286.1 | 9.37 |

**Table 10.**Motor characteristics according to voltage and frequency for outer rotor inductor with 16 poles.

Voltage (V) | Frequency (Hz) | Maximum Efficiency (%) | Speed at Maximum-Efficiency Point (rpm) | Output at Maximum-Efficiency Point (W) | Torque at Maximum-Efficiency Point (Nm) |
---|---|---|---|---|---|

32.35 | 126 | 81.6 | 914 | 1189 | 12.4 |

35.12 | 126 | 79.7 | 912 | 1405 | 14.7 |

33.21 | 137 | 82.9 | 999 | 1090 | 10.4 |

33 | 138 | 83 | 1007 | 1059 | 10 |

23.87 | 140 | 84.8 | 1027 | 452 | 4.2 |

33.2 | 140 | 82.7 | 996 | 1192.6 | 11.4 |

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**MDPI and ACS Style**

Hwang, M.-H.; Lee, H.-S.; Yang, S.-H.; Cha, H.-R.; Park, S.-J.
Electromagnetic Field Analysis and Design of an Efficient Outer Rotor Inductor in the Low-Speed Section for Driving Electric Vehicles. *Energies* **2019**, *12*, 4615.
https://doi.org/10.3390/en12244615

**AMA Style**

Hwang M-H, Lee H-S, Yang S-H, Cha H-R, Park S-J.
Electromagnetic Field Analysis and Design of an Efficient Outer Rotor Inductor in the Low-Speed Section for Driving Electric Vehicles. *Energies*. 2019; 12(24):4615.
https://doi.org/10.3390/en12244615

**Chicago/Turabian Style**

Hwang, Myeong-Hwan, Hae-Sol Lee, Se-Hyeon Yang, Hyun-Rok Cha, and Sung-Jun Park.
2019. "Electromagnetic Field Analysis and Design of an Efficient Outer Rotor Inductor in the Low-Speed Section for Driving Electric Vehicles" *Energies* 12, no. 24: 4615.
https://doi.org/10.3390/en12244615