# Comparative Study of Permanent Magnet, Conventional, and Advanced Induction Machines for Traction Applications

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## Abstract

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## 1. Introduction

_{2}emissions [1]. Making the transition of the global vehicle fleet to zero-emission vehicle technology is critical for decarbonizing road transportation and fulfilling the environmental and climate targets. Therefore, worldwide electric vehicle (EV) sales, including passenger cars, light trucks, and light commercial vehicles, reached 6.75 million units in 2021, corresponding to a 108% increase over 2020 [2]. It is very critical to choose the right electrical machine topology for EV applications in order to maximize efficiency, transient electromagnetic performance characteristics, flux-weakening capability, and cost. The worldwide five best-selling models in 2021 [3] and their electrical machine technologies are listed in Table 1. In addition, permanent magnet synchronous machines (PMSMs), particularly interior-permanent magnet (IPM) machines, are used in the world’s top commercial EVs and hybrid electric vehicles (HEVs), including Toyota/Prius, Nissan/Leaf, BMW/i3, and numerous other vehicles. Other cars, on the other hand, including the BMW/X5, Renault/Kangoo, GM/EV1, Chrysler/Durango, and a few others, employ induction machines (IMs) [4,5,6,7,8,9,10,11]. Moreover, Tesla Motors Inc., one of the world’s leading plug-in EV manufacturers, utilizes both IM (front) and IPM (rear) machines in its best-selling models, as seen in Table 1 [3]. In addition, Audi also utilizes the same traction topology in e-Tron models.

## 2. Research Method

#### 2.1. Concept

#### 2.2. Description of the Tool

#### 2.3. Analysis Scheme

#### 2.4. Research Results

## 3. Design Specifications

## 4. Performance and Active Material Cost Comparison

#### 4.1. Winding Factor and MMF Harmonics

#### 4.2. Induced Voltage and Back-EMF

#### 4.3. Flux Density and Flux Line Distributions

#### 4.4. Torque and Torque Ripple

#### 4.5. Flux-Weakening Characteristics

#### 4.6. Efficiency Maps

- The IPM machine and CIM shows similar characteristics in terms of efficiency: lower efficiency at the lowest and highest speed regions;
- The efficiency of AIM at a lower speed is lower than those of the IPM machine and CIM. However, its efficiency at a higher speed is higher than those of the IPM machine and CIM.

#### 4.7. Torque Production Capability

#### 4.8. Influence of Stack Lenght

#### 4.9. Comparison of Copper Losses

#### 4.10. Overall Comparison

- Copper: 7.354 £/kg—mass density: 7400 (kg/m
^{3}); - Steel: 0.44 £/kg—mass density: 8933 (kg/m
^{3}); - NdFeB35: 42.28 £/kg—mass density: 7520 (kg/m
^{3}).

## 5. Conclusions

- The overall flux-weakening characteristic of IMs are comparable to that of IPM machines;
- The flux-weakening characteristic of AIM are poorer than that of CIM;
- The overall efficiency of the IPM machine is higher than the CIM, and the difference between the maximum efficiency regions is 1.041% only;
- The efficiency of AIM is higher than CIM in deep flux-weakening regions;
- The torque ripple of the AIM is nearly 57% and 50% higher than that of the IPM machine and CIM, respectively, in the constant torque region;
- By extending the stack length without surpassing the total axial length of an IPM machine or CIM, it is feasible to significantly improve the output power and efficiency of AIM;
- It is also possible to reduce both the stator and rotor current densities simultaneously by extending the stack length;

- The much faster the torque increases for IMs machines, the higher the torque levels become for the electric loading levels higher than the rated current (250Apeak), whilst it is vice-versa for the electric loading levels lower than the 250Apeak;
- The lower the torque ripple for the CIM, whilst it is higher for the IPM machine and the AIM;
- The higher the slip percentage for IMs;
- The higher the risk of demagnetization for the IPM machine.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## Abbreviations

2D | Two-Dimensional |

AIM | Advanced Non-overlapping winding Induction Machine |

ANW | Advanced Non-overlapping Winding |

CIM | Conventional Induction Machine |

CO_{2} | Carbon Dioxide |

DC | Direct Current |

EMF | Electromotive Force |

EV | Electric Vehicle |

HEV | Hybrid Electric Vehicle |

IM | Induction Machine |

IPM | Interior-Permanent Magnet |

ISDW | Integer Slot Distributed Winding |

M | Magnet Number |

MMF | Magnetomotive Force |

NdFeB | Neodymium Iron Boron |

P | Pole Number |

PM | Permanent Magnet |

PMSM | Permanent Magnet Synchronous Machine |

R | Rotor Slot Number |

S | Stator Slot Number |

THD | Total Harmonic Distortion |

## Nomenclature

${A}_{S}{}_{coil}$ | Surface Area of Stator Slot |

${D}_{Cu}{}_{R}$ | Mass Density of Rotor Bar Copper Material |

${D}_{Cu}{}_{S}$ | Mass Density of Stator Copper Material |

${\ell}_{Ring}$ | Ring Axial Length |

${\ell}_{a}$ | Total Axial Length |

${A}_{Bar}$ | Surface Area of Rotor Slot |

${A}_{PM}$ | Surface Area of Magnet |

${A}_{Rcore}$ | Surface Area of Rotor Core Lamination |

${A}_{Ring}$ | Surface Area of Rotor Ring |

${A}_{Score}$ | Surface Area of Stator Core Lamination |

${D}_{PM}$ | Mass Density of Magnet |

${D}_{W330}$ | Mass Density of Core Material (W330) |

${H}_{R}$ | Surface Integrations of Rotor Flux Intensity |

${H}_{S}$ | Surface Integrations of Stator Flux Intensity |

${H}_{g}$ | Surface Integrations of Airgap Flux Intensity |

${I}_{NL}$ | No Load Current Amplitude |

${I}_{d}$ | D-axis Current |

${I}_{n}$ | Rated Current Amplitude |

${I}_{q}$ | Q-axis Current |

${I}_{q}^{es}$ | D-Axis Current in Synchronous Reference Frame Oriented to Stator Flux |

${J}_{r}$ | Rotor Bar Current Density |

${J}_{s}$ | Stator Current Density |

${L}_{d}$ | D-axis Inductance |

${L}_{q}$ | Q-axis Inductance |

${M}_{To{t}_{IM}}$ | Total Weight of IM |

${M}_{To{t}_{PM}}$ | Total Weight of IPM Machine |

$MM{F}_{R}$ | Rotor Magnetomotive Force |

$MM{F}_{S}$ | Stator Magnetomotive Force |

$MM{F}_{g}$ | Airgap Magnetomotive Force |

${M}_{T}$ | Total Weight |

${N}_{PM}$ | Number of Magnets |

${N}_{c}$ | Number of Coil |

${P}_{ou{t}_{1}}$ | Working Output Power |

${P}_{add}$ | Additional Power Loss |

${P}_{mech}$ | Mechanical Power Loss |

${P}_{out}$ | Rated Output Power |

${R}_{ph}$ | Phase Resistance |

${T}_{em}$ | Electromagnetic Torque |

${b}_{sw}$ | Stator Slot Width |

${f}_{0}$ | Fundamental Frequency |

${f}_{1}$ | Working Frequency |

${f}_{n}$ | Rated Frequency |

${k}_{m1,2}$ | Mechanical Loss Coefficients |

${k}_{sat}$ | Saturation Factor |

${n}_{s}$ | Serial Turn Number |

${\tau}_{s}$ | Average Coil Pitch |

${\psi}_{PM}$ | Magnet Flux |

${\psi}_{d}$ | D-axis Flux |

${\psi}_{d}^{es}$ | D-Axis Flux in Synchronous Reference Frame Oriented to The Stator Flux |

${\psi}_{q}$ | Q-axis Flux |

$\Delta T$ | Torque Ripple |

$\ell $ | Stack Length |

$P$ | Pole Number |

$R$ | Rotor Slot Number |

$m$ | Number of Phases |

$s$ | Slip |

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**Figure 1.**Two-dimensional views of the compared machines: (

**a**) IPM (48S/16M/8P). (

**b**) CIM (48S/52R/8P). (

**c**) AIM (24S/26R/8P).

**Figure 2.**Comparison of winding factors and MMF harmonics of the considered machines. (

**a**) Winding factors of harmonics. (

**b**) MMF harmonics spectra for 1-turn and 1-ampere.

**Figure 3.**Comparison of back-EMF waveforms and their harmonic spectra. (

**a**) Line Back-EMF and induced voltage waveforms. (

**b**) Harmonic spectra of the back-EMF and induced voltage.

**Figure 4.**Flux density and flux line distributions of the machines. (

**a**) IPM machine flux density. (

**b**) IPM machine flux line. (

**c**) CIM flux density. (

**d**) CIM flux line. (

**e**) AIM flux density. (

**f**) AIM flux line.

**Figure 5.**Comparison of the torque waveforms and their spectra. (

**a**) Electromagnetic torque waveforms. (

**b**) Harmonic spectra of torque.

**Figure 6.**Flux-weakening characteristics. (

**a**) Torque-speed characteristics. (

**b**) Power-speed characteristics.

**Figure 7.**Comparison of the efficiency maps of the considered machines. (

**a**) IPM machine. (

**b**) CIM. (

**c**) AIM.

**Figure 8.**Variation of current angle (for IPM machine) and slip percentage (for IMs) with respect to peak current.

**Figure 13.**Comparison of copper losses including stator in-slot winding, stator end-windings, and rotor bars.

**Table 1.**Top selling EV models in 2021 and their machine technology [3].

Top Selling Models | Machine Technology |
---|---|

Tesla/Model 3 | IM + IPM |

Wuling/Hongguang Mini EV | PMSM |

Tesla/Model Y | IM + IPM |

Volkswagen/ID.4 | PMSM |

BYD/Qin Plus PHEV | PMSM |

Parameters | IPM | CIM | AIM |
---|---|---|---|

S/(R or M) */P | 48S/16M/8P | 48S/52R/8P | 24S/26R/8P |

Voltage limit (Vrms) | $650\mathrm{V}\times 85\%\times 2/\pi $ | ||

Rated current (Apeak) | 250 | ||

Number of coils per phase | 8 | 8 | 8 |

Number of turns per coil | 11 | 8 | 11 |

Number of series turn per phase | 88 | 64 | 88 |

Fundamental winding factor | 0.966 | 0.966 | 0.866 |

Number of parallel brunch | 1 | ||

Slot fill factor | 0.6 | ||

Phase resistance at 21 °C | 0.077 | 0.05612 | 0.0577 |

Stack length (mm) | 50.8 | ||

Stator parameters | |||

Outer diameter (mm) | 264 | ||

Inner diameter (mm) | 161.9 | 185.85 | 184.8 |

Tooth width (mm) | 7.55 | 8.45 | 11.52 |

Slot opening (mm) | 1.88 | 1.88 | 5.8 |

Slot height (mm) | 30.9 | 15.4 | 22/11 |

Air-gap length (mm) | 0.73 | 0.4 | 0.4 |

Rotor parameters | |||

Tooth width (mm) | ― | 6.83 | 11.97 |

Slot opening (mm) | ― | 1.88 | 5.6 |

Slot height (mm) | ― | 14 | 20 |

Magnet dimensions | 49.3 × 17.88 × 7.16 | ― | ― |

Cage material | ― | Copper | Copper |

Iron grade | DW310-35 | ||

${k}_{h}$ | 179.038 | ||

${k}_{c}$ | 0.375 | ||

${k}_{e}$ | 0.262 | ||

Magnet grade | NdFeB (N35) | ― | ― |

${\mu}_{r}$ | 1.05 | ― | ― |

${B}_{r}$ | 1.1 | ||

${H}_{c}$(kA/m) | −805.4 | ― | ― |

IPM | CIM | AIM | AIM1 | AIM2 | |
---|---|---|---|---|---|

${n}_{s}$ | 88 | 64 | 84 | 60 | 60 |

$\ell $ (mm) | 50.8 | 50.8 | 50.8 | 72.4 | 76 |

${\ell}_{a}$ (mm) | 97.5 | 101.1 | 76.66 | 97.5 | 101.1 |

${R}_{ph}$ (Ω) | 0.077 | 0.0561 | 0.0577 | 0.0408 | 0.0371 |

${T}_{em}$ (Nm) | 222.38 | 220.75 | 219.15 | 218.38 | 220.45 |

$\Delta T$ (%) | 8.45 | 10.15 | 19.63 | 19.5 | 19.8 |

$s$ (%) | 0 | 3.33 | 4.4 | 3.2 | 3.33 |

${P}_{out}$ (kW) | 34.93 | 33.52 | 32.909 | 33.2 | 33.48 |

$\eta $ (%) | 85.532 | 83.00 | 79.32 | 84.21 | 84.47 |

${M}_{T}$ (kg) | 22.7 | 25.22 | 24.279 | 31.02 | 32.7 |

Cost (£) | 76.7 | 69.71 | 68.55 | 70.77 | 76.97 |

${J}_{s}$ (A/mm^{2}) | 21.77 | 28.52 | 28.76 | 23.92 | 21.6 |

${J}_{r}$ (A/mm^{2}) | ― | 18.17 | 16.69 | 13.35 | 12.65 |

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## Share and Cite

**MDPI and ACS Style**

Gundogdu, T.; Zhu, Z.-Q.; Chan, C.C.
Comparative Study of Permanent Magnet, Conventional, and Advanced Induction Machines for Traction Applications. *World Electr. Veh. J.* **2022**, *13*, 137.
https://doi.org/10.3390/wevj13080137

**AMA Style**

Gundogdu T, Zhu Z-Q, Chan CC.
Comparative Study of Permanent Magnet, Conventional, and Advanced Induction Machines for Traction Applications. *World Electric Vehicle Journal*. 2022; 13(8):137.
https://doi.org/10.3390/wevj13080137

**Chicago/Turabian Style**

Gundogdu, Tayfun, Zi-Qiang Zhu, and Ching Chuen Chan.
2022. "Comparative Study of Permanent Magnet, Conventional, and Advanced Induction Machines for Traction Applications" *World Electric Vehicle Journal* 13, no. 8: 137.
https://doi.org/10.3390/wevj13080137