# Performance Analysis of Permanent Magnet Motors for Electric Vehicles (EV) Traction Considering Driving Cycles

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## Abstract

**:**

## 1. Introduction

## 2. Target Traction Motors and EV

- (a)
- output power: greater or equal to 10 kW (this makes a total power of 20 kW for the EVs. Explained later);
- (b)
- torque density: greater or equal to 30 Nm/L;
- (c)
- maximum current density: 16–17 A
_{rms}/mm^{2}; - (d)
- outer stator diameter: 160 mm;
- (e)
- air gap: 0.5 mm;
- (f)
- number of slots: 36;
- (g)
- winding configuration: distributed winding; and,
- (h)
- efficiency: greater or equal to 95%.

_{r}) and coercive force (H

_{c}) of 1.2 T and 915 kA/m, respectively.

## 3. Theoretical Background

_{s}and I

_{s_max}are armature current and the maximum current provided by the inverter, respectively; I

_{d}and I

_{q}are d- and q-axis currents, respectively; L

_{d}and L

_{q}are d- and q-axis inductances, respectively; p is number of pole pair; λ

_{m}is PM flux linkage; ω

_{s}is rotor speed; V

_{s_max}is maximum phase voltage; and, V

_{DC}is battery voltage applied to the inverter.

_{s_max}is maximum rotor speed.

_{m}), and this indicates an increase of d-axis inductance and reluctance torque referring to Equation (4) for IPMSMs [22]. For the two types of motors, the output torque can be calculated by [6]:

_{d}and λ

_{q}are, respectively, d- and q-axis flux linkage, p is number of pole pair, I

_{d}and I

_{q}are, respectively, d- and q-axis currents excitations.

_{m}is preferred for low induced BEMF at high speed. In contrast, a large value is desirable for high torque and high efficiency. Therefore, the PMa-SynRMs may require higher total electric loading than that for IPMSMs to achieve the same torque that is required.

## 4. Performance Evaluation of Traction Motors

_{rms}/mm

^{2}), for the cases beyond which a wide speed range can be reached with the voltage limit. Beyond the base speed, the armature current is maintained and the current phase angle is increased for flux weakening until the maximum speed. Note that the base speed depends on the voltage or the power limit. High armature current would also lead to a low base speed. Figure 10 shows that the IPMSM hits the voltage limit at a base speed of 2500 rpm (achievable base speed), an armature current of 54.8 A, and a current density of 9.7 A

_{rms}/mm

^{2}without force cooling. Nevertheless, the speed range of the IPMSM can be enhanced if better cooling is used so that more current can be input to improve the torque at high speed.

## 5. Driving Cycle Applications

_{cycle}is the time period of the entire driving cycle and T(t) is the instantaneous torque.

## 6. Comparison of Motor Performance in Driving Cycles

## 7. Thermal Analysis with Driving Cycle

_{rms}/mm

^{2}for peak torque). This is because the phase resistance of the PMa-SynRM is double that of the IPMSMs. Therefore, the PMa-SynRM can only operate about 4 min at the peak condition and about 26 min at the rated condition, while the IPMSM can achieve 8 and 40 min, respectively. Also, the high winding temperature of the PMa-SynRM leads to the high magnet temperature, as shown in Figure 18. The above analysis can also be verified by the simulation results with the driving cycles, as shown in Figure 20, where the winding temperature of the PMa-SynRM is higher than that of IPMSM, and therefore, the IPMSMs can operate more safely than the PMa-SynRM for the driving cycles.

## 8. Discussions

- -
- The IPMSMs possess the benefit of high PM flux linkage, low armature current, and current angle to reach the maximum torque. Meanwhile, the torque of PMa-SynRM is almost derived from the armature current. Therefore, a higher armature current and current angle are applied in order to generate the maximum torque for PMa-SynRM.
- -
- The PMa-SynRM can achieve very high speed at low armature current because the reluctance torque and saliency ratio are higher than that of IPMSMs. In addition, the PMa-SynRM has a higher efficiency at high speed than that of IPMSMs. This is the advantage of PMa-SynRM for high speed application.
- -
- To produce the same power as the IPMSMs, the PMa-SynRM should be designed with a higher motor volume than that of the IPMSM. Moreover, higher electrical loading is needed for the PMa-SynRM, and this can lead to temperature rise that limits the operating range.
- -
- The IPMSMs are more advantageous in urban driving because of their higher performance and efficiency at lower speed.
- -
- The PMa-SynRM is more suitable than the IPMSM in the highway driving cycle in terms of efficiency. However, the design should be improved by slightly increasing the PM amount so that the winding temperature can be brought down and the torque at high speed can be enhanced. This indicates a better design would lie between the two types of motors that are presented in this paper in terms of PM amount that is employed or sharing between the PM and reluctance torques. Moreover, better cooling may be necessary.

## 9. Experiments

## 10. Conclusions

## Author Contributions

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Traction motors using rare-earth permanent magnet (PM): (

**a**) double-layers interior permanent magnet synchronous machines (IPMSM). Rotor material: 50CS1300. Stator material: 25CS1500HF; (

**b**) V-shaped IPMSM. Rotor material: 35CS550. Stator material: 25CS1500HF; and, (

**c**) PM-assisted synchronous reluctance motors (PMa-SynRM). Rotor material: 50CS1300. Stator material: 25CS1500HF. Permanent magnet: NdFeB-N35H, B

_{r}= 1.2T @ 20 °C, H

_{c}= 915 kA/m. All of the cases are distributed windings.

**Figure 4.**Comparison of PM flux linkage of IPMSM and PMa-SynRM: (

**a**) IPMSM and (

**b**) PMa-SynRM. Reference angle starts from q-axis.

**Figure 8.**Flux linkage variations on (

**a**) d- and (

**b**) q-axis of IPMSM with respect to current and current angle.

**Figure 15.**Efficiency map of IPMSMs and PMa-SynRM over the driving cycles: (

**a**) double layers magnet IPMSM, (

**b**) v-shaped magnets IPMSM, and (

**c**) PMa-SynRM.

**Figure 16.**The temperature distribution profiles for (

**a**) winding and (

**b**) magnet of double-layer IPMSM.

**Figure 19.**The temperature rise for winding and magnet: (

**a**) peak; and, (

**b**) rated/continuous operations.

**Figure 21.**Prototypes of IPMSMs and PMa-SynRM: (

**a**) stator of double-layers IPMSM with winding, (

**b**) stator of V-Shaped IPMSM without winding, (

**c**) stator of PMa-SynRM with winding, (

**d**) rotor of double-layers IPMSM with PM, (

**e**) rotor of V-shaped IPMSM without PM, and (

**f**) rotor of PMa-SynRM without PM.

**Figure 23.**Torque-power vs speed curve at rated condition: (

**a**) double layers IPMSM, (

**b**) V-Shaped IPMSM, and (

**c**) PMa-SynRM.

**Figure 24.**Efficiency vs speed curve at rated condition: (

**a**) double layers IPMSM, (

**b**) V-Shaped IPMSM, and (

**c**) PMa-SynRM.

Parameter (Unit) | Double Layers | V-Shaped | PMa-SynRM |
---|---|---|---|

Max. power (kW) | 10 | 10 | 10 |

Max. torque (Nm) | 56 | 56 | 65 |

Max. speed (rpm) | 7000 | 7000 | 7000 |

Rated power (kW) | 6.6 | 6.6 | 6.6 |

Rated torque (Nm) | 30 | 30 | 30 |

Base speed @ maximum torque (rpm) | ≥1800 | ≥1800 | ≥1500 |

Base speed @ rated torque (rpm) | ≥2100 | ≥2100 | ≥2100 |

No. of slots | 36 | 36 | 36 |

No. of poles | 8 | 8 | 4 |

No. of turns | 4 | 5 | 6 |

Max. current (A) | 110 | 100 | 80 |

Outer rotor diameter (mm) | 94 | 109 | 94 |

Stack length (mm) | 86 | 90 | 120 |

Coil pitch | 4 | 3 | 9 |

PM amount per pole (mm^{3}) | 7740 | 8100 | 5760 |

Current density @ rated torque (A/mm^{2}) | 8.3 | 8.3 | 8.3 |

Parameter (Unit) | Value |
---|---|

Radius of wheels (m) | 0.265 |

Vehicle mass (kg) | 950 |

Mass correction coefficient | 1.04 |

Gravitational acceleration (m/s^{2}) | 9.8 |

Rolling resistance coefficient | 0.011 |

Air mass density (kg/m^{3}) | 1.225 |

Aerodynamic drag coefficient | 0.4 |

Vehicle frontal area (m^{2}) | 2.14 |

Differential gear ratio | 7 |

Battery pack nominal voltage (V) | 310 |

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**MDPI and ACS Style**

Huynh, T.A.; Hsieh, M.-F.
Performance Analysis of Permanent Magnet Motors for Electric Vehicles (EV) Traction Considering Driving Cycles. *Energies* **2018**, *11*, 1385.
https://doi.org/10.3390/en11061385

**AMA Style**

Huynh TA, Hsieh M-F.
Performance Analysis of Permanent Magnet Motors for Electric Vehicles (EV) Traction Considering Driving Cycles. *Energies*. 2018; 11(6):1385.
https://doi.org/10.3390/en11061385

**Chicago/Turabian Style**

Huynh, Thanh Anh, and Min-Fu Hsieh.
2018. "Performance Analysis of Permanent Magnet Motors for Electric Vehicles (EV) Traction Considering Driving Cycles" *Energies* 11, no. 6: 1385.
https://doi.org/10.3390/en11061385