recent development in electric traction drive technologies · pdf filerecent development in...

The University of SheffieldElectrical Machines & Drives Research Group

Recent Development in Electric Recent Development in Electric

Traction Drive TechnologiesTraction Drive Technologies

J. WangJ. Wang

University of Sheffield, United KingdomUniversity of Sheffield, United Kingdom

Joint EC/EPoSS Workshop on Smart Systems for Full Electric Vehicle


Basic electric traction configurationsBasic electric traction configurations

Electric Traction

Single motor via

Mechanical

transmission

Independently controlled

In-wheel drives

Direct-drive Via reduction gear


Candidate Electric Machine TechnologiesCandidate Electric Machine Technologies

Permanent Magnet Machine High power density & power factor

High efficiency

High cost

Induction Machine Low cost

Robust rotor structure

Low power density

Inferior power factor and efficiency

Switched reluctance machine Robust rotor structure

High torque ripple

Poor power factor


Great operational flexibility and mechanical simplicity

Optimal torque balance for great manoeuvrability and safety

Traction control and anti-skid built into each wheel

Regenerative braking recovers almost all energy

Fast acceleration and high top speed

Independently controlled InIndependently controlled In--wheel Driveswheel Drives

Key features


HubHub--mounted Electric Traction Drivemounted Electric Traction Drive

Traction motor: 60Nm and 75kW, max speed: 20000rpm12kg weight

Epicyclic gear 10:1, 13kg weight

Integrated hub-mounted traction drives are commercially available


Key technology for HubKey technology for Hub--mounted Directmounted Direct--DriveDrive

B/B

B/

B

C/

C

C/

C

A

A

A/

A/

A

A/

A

A/

C/

C

CC/

BB/

B

B/

Phase B

Phase C

Ph

ase A

Phase CPhase B

Phase A

B/

A

A

B/

C

C

A/

A/

B/

B/

C/

C/

Phase A

Phase B

Phase

C

Phase BPhase

A

Phase C

External rotor brushless PM machines with modular windings

All teeth

wound

Alternate

teeth wound

High packing factor High power density High efficiency

Low manufacturing cost Negligible cogging torque Great fault-tolerance


Single motor Single motor vsvs Dual or Quad Electric DriveDual or Quad Electric Drive

Minimum modification to mechanical transmission and braking systems

Use of high speed motor for weight and cost reduction Ease of thermal and safety managements Reliability, noise and vibration of gear box are often of concern

Added weight increases unsprung mass which is not desirable for suspension performance although this may be offset by the removal of brake caliper/pads and drive shaft

More complex control and safety management are required

Hub-mounted or in-wheel traction drive

Single motor traction drive


High performance magnetic gearsHigh performance magnetic gears

Only 3 components

2 are free to rotate, the 3rd is earthed

Prototype 5.75:1 gear

• Torque density: 78kNm/m3 Zero wear and no lubrication

Low maintenance/high reliability

Inherent overload protection/no jamming

Transmitted torque density comparable to mechanical gear


SystemSystem : Electrical machine + Magnetic gear: Electrical machine + Magnetic gear

Torque density of electrical machine

Electrical machine

Magnetic gear

Pseudo directPseudo direct--drive electrical machinesdrive electrical machines

Mechanically coupled electrical machine and magnetic gear


Pseudo directPseudo direct--drive electrical machinesdrive electrical machines

Stationary permanent magnets

High speed rotor with permanent magnets

Low speed rotor with poles-pieces

Mechanically and magnetically coupled electrical machine and magnetic gear


Pseudo direct drive electrical machinesPseudo direct drive electrical machines

•• Torque density in excess of 60kNm/mTorque density in excess of 60kNm/m33

(> transverse flux machines)(> transverse flux machines)

•• Power factor higher than 0.9Power factor higher than 0.9

•• Very low current densityVery low current density

International patent application PCT/GB2007/001456International patent application PCT/GB2007/001456Prototype


Pseudo direct drive electrical machinesPseudo direct drive electrical machines

External rotor topology for hub-mounted traction drive

Stator


24 pole-pair low

speed rotor (Ωl)

Input rotor with 28

ferromagnetic

pole-pieces (Ωs)

4 pole-pair high-

speed rotor (Ωh)

hlhslsl

ssllhh

pppn

npp

Ω−Ω=Ω∴

Ω=Ω+Ω

)/()/(

Magnetic CVTMagnetic CVT

Output speed/torque/power can be controlled by regulating the high speed rotor


(Ωs,Ts) (Ωl,Tl) (Ωd,Td)

Magnetic CVT Based Hybrid Power TrainMagnetic CVT Based Hybrid Power Train

Simpler More efficient Lighter and more compact

An arbitrary traction torque/speed combination can be achieved by independent control of speed of MG1 and torque of MG2 while maintaining the most fuel-efficient operation point of engine


Control of electric traction drivesControl of electric traction drives

Effective flux weakening control for maximum operation

capability with variable battery voltage

Sensorless operation for high reliability and low cost

Traction control/Anti-lock braking by detecting wheel

slippage

Torque vectoring --- improve driving dynamics and

manoeuvrability by controlling drive torque distribution


Future ResearchFuture Research

Novel high power/torque dense electric

traction devices

Drive health monitoring, fault diagnosis and

detection

Fail-safe and fault-tolerant operation

Optimisation, integration and cost reduction

Reliability improvement

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