# Advanced Electrical Machines and Machine-Based Systems for Electric and Hybrid Vehicles

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## Abstract

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## 1. Introduction

**Figure 1.**EV classification. ICEV, internal combustion engine vehicle; HEV, hybrid electric vehicle; BEV, battery-powered electric vehicle; FEV, fuel cell electric vehicle.

## 2. Electric Vehicle Drive System

- (1)
- High torque density and power density.
- (2)
- Very wide speed range, for example the speed range of the constant power region should be 3–4-times that of the constant torque region, as shown in Figure 2.
- (3)
- Extended area of high efficiency; it should cover most of the operating regions.
- (4)
- Large torque output at low speeds in order to dispose of enough torque when the vehicle starts or is climbing.
- (5)
- Strong overload capability, for instance the motor can output two-times the rated torque during a short time.
- (6)
- Security and reliability, for instance fault-tolerant configurations should be arranged.
- (7)
- Motor noise and torque ripple should be suppressed.
- (8)
- Reasonable costs.

Items | EV motors | Traditional industrial motors |
---|---|---|

Ambient temperate | −40~140 °C | 20~40 °C |

Operation environment | Adverse | Indoor |

Coolant temperate | 75~150 °C | <40 °C |

Winding temperate | 160~200 °C | 75~130 °C |

Speed range | 0~15,000 rpm | <3000 rpm |

Noise level | Very low | Low |

Speed demand | Frequent changes | Keep uniform |

Installation space | Very limited | Loose |

System voltage | Independent/Variable | Static grid |

Efficiency | Efficient | Determined by application |

**Figure 2.**Torque and power requirements for the electric drive systems [4].

**Figure 3.**Three popular motors in EV: Induction machines (IM), switched reluctance machines (SRM) and permanent magnet synchronous machines (PMSM).

Motor type | Torque (Nm) | Armature current density (A/mm^{2}) | Efficiency (%) |
---|---|---|---|

1500 r/min | |||

PMSM(Prius) | 303 | 15.7 | 91.3 |

SRM | 297 | 15.8/12.1 | 83.1 |

IM | 294 | 20.1 | 85.2 |

6000 r/min | |||

PMSM(Prius) | 45.6 | 3.75 | 96.1 |

SRM | 50.8 | 4.51/3.72 | 95.2 |

IM | 52.1 | 4.02 | 88.2 |

## 3. Advanced Motor Topologies

#### 3.1. Stator Permanent Magnet Motor

**Figure 4.**Two representative stator-permanent magnet (PM) motor topologies. (

**a**) Doubly-salient PM motor (DSPM); (

**b**) Flux switching PM motor (FSPM).

#### 3.1.1. Doubly-Salient PM Motor (DSPM)

#### 3.1.2. Flux Switching PM Motor (FSPM)

#### 3.2. Hybrid-Excitation Motor

#### 3.3. Flux Memory Motor

**Figure 10.**Stator-PM memory motor. (

**a**) DSPM memory motor; (

**b**) DSPM memory motor with NdFeB and AlNiCo; (

**c**) No-load back-EMF at different PM flux levels.

#### 3.4. Redundant Structure and Fault-Tolerance Control

Motor topology | Stator-PM motors | Hybrid-excitation motor | Flux memory motor | ||
---|---|---|---|---|---|

DSPM | FSPM | FRPM | |||

Stator | Salient poles with both PM and armature windings | ||||

Rotor | Salient poles with neither magnets nor windings | ||||

Magnet location | Stator | ||||

Magnet volume | Low | Medium | High | Lower than PM counterpart | Similar to PM counterpart |

Magnet material | NdFeB | NdFeB | NdFeB | NdFeB | AlNiCo |

Field winding | - | - | - | Stator | Stator |

Field coil loss | - | - | - | High | Negligible |

Flux controllability | Low | Low | Low | High | High |

Speed range | Limited | Limited | Limited | Wide | Wide |

Torque Density | Low | Low | High | Medium | Medium |

## 4. Advanced Electric Drive System

#### 4.1. Magnetic-Geared In-Wheel Drive System

_{in}and n

_{in}are the pole pair number and rotation speed of the inner rotor, respectively, and p

_{out}and n

_{out}are the pole pair number and rotation speed of the outer rotor, respectively. Complementing Equation (1) with the equation that states the power invariance, the relationship between the inner and outer rotor torques is readily obtained.

#### 4.2. ISG System Based on the PM Motor

**Figure 18.**DC field regulation of the ISG (hybrid-excitation stator-PM motors). (

**a**) Voltage versus speed; (

**b**) Voltage versus load current.

## 5. Power Distribution System for an HEV

_{sun}, n

_{ring}and n

_{carrier}are the rotation speeds of the sun gear, ring gear and the planets carrier, respectively, and p is a characteristic parameter, which can be considered as the transmission ratio. According to Equation (2), by adjusting the speed of the sun gear connected to the generator shaft, the transmission ratio between ICE speed and wheel speed can vary continuously. Hence, it is called the electric continuously-variable transmission (ECVT).

#### 5.1. Dual-Rotor PM ECVT

#### 5.2. Dual-Stator PM Brushless ECVT

#### 5.3. Dual-Rotor Magnetic-Geared Brushless ECVT

_{ir}and p

_{ir}are the speed and pole pair number of the inner rotor (PM rotor), respectively; n

_{or}and p

_{or}are the speed and pole pair number of the outer rotor (field modulation ring), respectively; and n

_{w}and p

_{w}are the speed and pole pair number of the armature field, respectively. This relationship is very similar to Equation (2), which means that the MGDRM might be a potential replacement for the THS [70,71].

ECVT topology | Dual-rotor PM | Dual-stator PM | Magnetic-geared |
---|---|---|---|

Stator number | 1 | 2 | 1 |

Rotor number | 2 | 1 | 2 |

Winding number | 2 | 2 | 1 |

Brush | Yes | No | No |

Converter number | 2 | 4 | 2 |

Magnet amount | Low | High | Low |

Copper amount | High | High | Low |

Torque density | Medium | Medium | High |

## 6. Conclusions and Developing Trends

- (i)
- Motor level: various novel motor topologies and control algorithm may be proposed to satisfy the specific requirements of EV motors.
- (ii)
- Drive system level: a novel electric drive system with advanced performance should be developed to replace the mechanical gear and transmission axle by electric technology and to achieve the full electrification of the powertrain.
- (iii)
- Powertrain level: the optimized design of the operation patterns for the electrified powertrain, especially for HEVs and plug-in HEVs with ECVT, should be pursued to enhance the energy economy of the vehicles.
- (iv)
- Whole vehicle level: to minimize the overall cost and weight of the vehicle, the motor drive system may be integrated with other electric devices. A motor drive system integrated with a charger for a plug-in HEV is just an example.

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**MDPI and ACS Style**

Cheng, M.; Sun, L.; Buja, G.; Song, L. Advanced Electrical Machines and Machine-Based Systems for Electric and Hybrid Vehicles. *Energies* **2015**, *8*, 9541-9564.
https://doi.org/10.3390/en8099541

**AMA Style**

Cheng M, Sun L, Buja G, Song L. Advanced Electrical Machines and Machine-Based Systems for Electric and Hybrid Vehicles. *Energies*. 2015; 8(9):9541-9564.
https://doi.org/10.3390/en8099541

**Chicago/Turabian Style**

Cheng, Ming, Le Sun, Giuseppe Buja, and Lihua Song. 2015. "Advanced Electrical Machines and Machine-Based Systems for Electric and Hybrid Vehicles" *Energies* 8, no. 9: 9541-9564.
https://doi.org/10.3390/en8099541