19.02.2018 1

Innovative

Winding and Stator Architectures

for

High Torque and Lightweight Electrical Machines

Advanced E-Motor Technology Berlin 2018

Prof. Dr.-Ing. Roland Kasper

Institute of Mobile Systems

Otto-von-Guericke Universität Magdeburg

19.02.2018 2

Content

• Introduction

demands and opportunities

• Architectures and lightweight potential

• Design and manufacturing

• Cooling considerations

• View of new materials for lightweight

electrical machines

• Applications

• Overview and outlook

Advanced E-Motor Technology Berlin 2018

Air-gap windings

Combined windings

U V W

U V W

U V W

19.02.2018 3

Low Weight, High Efficiency E-Machines

Introduction

Lilium ujet

VC200 Volocopter

Toyota i-TRIL

Autonomous

suitcases

Rinspeed

Toyota e-Palette

Yamaha

Honda

19.02.2018 4

State of the Art

Demands from Applications

• Compact

• Low weight

• Low cost

• Efficient

• High power

• Scalable

• Adaptable

Introduction

Available designs

• Permanent magnets for high power

• Bulky coils to lead current and to build

magnetic field copper

• Slotted stator back-iron to carry coils and

lead magnetic field iron

• Sums up to

– weight,

– cost and

– losses

19.02.2018 5

Faulhaber

State of the Art

Basic design

• Totally ironless winding

• Self-sustaining winding

• Number of turns > 1

• Air-cooled winding

Example 3272...CR

• Ø 32 mm, length 72 mm

• 5500 rpm, 120 mNm torque

• 120 Watt, 24 V

• 87% efficiency

• Mechanical time constant < 3 ms

• Weight 312 g

19.02.2018 6

Maxon

State of the Art

Basic design

• Knitted winding

• Number of turns > 1

• Low loss back-iron to limit iron losses

• Back-iron cooled winding

Example EC 4-pole

• Ø 30 mm, length 64 mm

• 16100 rpm, 95.6 mNm torque

• 200 Watt, 24 V

• 90% efficiency

• Weight 300 g

19.02.2018 7

Thin Gap Motors

State of the Art

Basic design

• Air-gap winding fixed by polymer

• Totally iron-free stator

• Double air-gap

• Air-cooled winding

Example TG715X

• Ø 190 mm, length 39 mm

• 10,600 rpm

• 4.8 Nm torque

• 4 kW power

• 91% efficiency

• Weight 1.5 kg

19.02.2018 8

N

SN

SNS N

S

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

x x x· · ·

Features Slotless Air-gap Winding

Basic

• Low weight

• No cogging torque

• Very compact

Additional

• High torque

• Excellent cooling

• High power

• Metal formed winding technology

– High fill factor low losses

– Low cost

State of the Art

State of the Art

PMSM Air-gap winding

Stator

Winding

Rotor

19.02.2018 9

Magnetic Circuit Air-gap Winding

Compact magnetic circuit

• High B field in air-gap + axial wires

high torque by Lorentz force

• Extremely thin stator back-iron without

saturation

low weight

small iron losses

• Low need of copper for winding

low weight

low cost

Air-gap Winding

ANSYS magnetic field simulation for 0.5

mm air-gap

• Single wires in phase to avoid eddy

currents

rotor

stator

U V W

19.02.2018 10

Patented Design Slotless Air-gap Winding

DE 10 2011 111 352 B4, US 9.685.830 B2, RU 2 603 680 C2, CN 103931085 B, EP 2751906 A2, WO 2013029579 A2

Meandering multi wire air-gap winding attached on stator back-iron

• Simple slotless ring geometry

• Flexible adaptable design

• Applicable to all motors and generators with external rotor

automated winding technology available

• Internal rotor machines possible

improved winding technology

under development

Air-gap winding

Eisenrückschluss (Rotor)

Permanentmagnet

Eine Phase

stator back-iron

one phase

rotor back-iron permanent

magnet

19.02.2018 11

Prototype Design Electric Power Wheel EPW I

Integrated into 15‘‘ rim

• app. 300 mm

• Width 100 mm

• Weight 20 kg

• Nominal

– torque 300 Nm

– speed 1350 rpm

– voltage 400 V

– power 40 kW 2 kW/kg

• Max. efficiency ≥ 93 %

• Excellent cooling

Air-gap Winding

CAD

Stator

19.02.2018 12

Prototype EPW I - Test I

General results

• DC Motor behavior

• Constant torque for all speed

• No weakening of B-field

Integrated electrical control unit

• Small phase inductance 10 µH

• Complex 2-stage electronic control

Air-gap Winding

0

100

200

300

0 500 1000 1500

T

[rpm]

[Nm]

19.02.2018 13

bac

k e

mf

[V]

Prototype EPW I - Test II

• EMF 𝑒 = 𝑎𝑘

𝑛𝑘=1 ∙ sin(𝑘 ∙ 𝜔 ∙ 𝑡)

• Torque

𝑇 = 𝑘𝑀 ∙ 𝐵𝑘3𝑘=1 ∙ 𝑖𝑘

Air-gap Winding

time [ms]

y = 2,3x + 3,4

0

25

50

75

100

125

150

175

200

225

250

0 10 20 30 40 50 60 70 80 90 100

RM

S t

orq

ue

[N

m]

Current [A]

MeasurementLinear (Measurement)

y = 2,3x

0

50

100

150

200

250

300

350

400

0 20 40 60 80 100 120 140 160

RM

S b

ac

k-e

mf

[V]

Angular velocity [rad/s]

MeasurementLinear (Measurement)

19.02.2018 14

Electromechanical Design Flow

Air-gap Winding

Matlab/Simulink

• Table based model variable parameters

– System simulation

• Control, Test, …

– Optimization

• e.g. efficiency weight

wM=1500

wM=1000

wM=500

wM=200

wM=100

wM=50

wM=20

wM=10

wM=1500 wM=1000

wM=500

wM=200

wM=100

wM=50

wM=20

wM=10

84

86

88

90

92

94

96

98

100

10 20 30 40 50 60 70

ηM

ax

[%

]

m [kg]

Radial

Halbach

MAXWELL

• 2/3D-model fixed parameters

• Function

– B, EMF, torque, U, I, …

• Losses

– Stator Eddy, Remagnetization

– Air-gap winding Eddy

19.02.2018 15

Prototype EPW I - Test III

Heating-up experiment

• Very good heat transfer

• Uniform temperature distribution

• No hot spots

1 min 3 min

Air-gap Winding

Temperature distribution

• FE simulation

• Experiment

10

15

20

25

30

35

40

45

50

0 25 50 75 100 125 150 175 200 225 250 275 300

tem

pera

ture [ C

]

time [s]

thermal step response

heat losses 2250W

heat losses 2000W

heat losses 1750W

heat losses 1500W

heat losses 1250W

heat losses 1000W

heat losses 750W

heat losses 500W

heat losses 250W

ΔT=2,6 C

ΔT=5,0 C

ΔT=4,7 C

ΔT=2,3 C

ΔT=4,1 C

ΔT=4,9 C

ΔT=3,8 C

ΔT=4,9 C

19.02.2018 16

Competition Wheel-Hub-Motor

Air-gap Winding

Air-gap Winding

General

Motors

Schaeffler

AG

Siemens

AG Fraunhofer

Protean

Electric EPW I

Rim Size [inch] 17 16 17 17 18 15

Weight [kg] 30 53 50 42 34 20

Power [kW] 16 33 63 55 54 40

Power/Weight

[kW/kg] 0.53 0.62 1.26 1.31 1.59 2

19.02.2018 17

Air-gap Winding Applications I

E-Scooter

• Power 4.5 kW

• Speed 500 rpm

• Torque 85 Nm

• Extreme lightweight construction

– Scooter total: 32 kg

– Motor: 2.7 kg

• Driving test successful

(spring 2016)

Air-gap Winding

ePower Wheel-Generator Trailer

• Recuperation power 30 kW

• Speed 350 rpm

• Air-cooled

• IAA commercial vehicles Hannover 2016

(2. award)

• Test stand evaluation successful

(fall 2016)

19.02.2018 18

Air-gap Winding Applications II

E-Motorcycle

• Integration into existing engine

block/gearbox

• Power 12 kW

• Speed 6000 rpm

• Weight app. 8 kg

• Integrated water

cooling system

• Design study (2017)

Air-gap Winding

E-Flyboat

• Low weight

• High efficiency

• Power 2 x 5.5 kW

• Integration into hull

• Speed 600 to 2600 rpm

• Weight app. 8 kg

• Prototype (spring 2018)

19.02.2018 19

Air-gap Winding Applications III

E-Longboard

• Integration into standard axle

• Usable for any kind of rack

• Power 250 W

• Speed 2500 rpm

• Range 12 km

Air-gap Winding

Darrieus Windmill Generator

• Integration into tower

• Power 2.75 kW

• Speed 180 rpm

• Ø 350 mm

• Length 100 mm

19.02.2018 20

COMO Test Vehicle with EPW I

Electrified Smart

• ICE replaced by battery

• Range 150 km

• Voltage 400 V

Air-gap Winding

Integrated Wheel-Hub-Motors

• 2 back wheels

• Re-use wheel-suspension

• Re-use brake

Need for torque

19.02.2018 21

Features Combined Winding

All advantages of air-gap winding + Nearly double power and torque

• Windings share permanent magnet field re-use of magnets

• Windings do not interfere besides adding torque and emf

Combined Winding

State of the Art PMSM Air-gap winding

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

x x x xx x x x

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

· · · ·· · · ·

N

SN

S N

SN

S

x x x· · ·

stator

winding

rotor N

SN

S

x x x· · ·

. . . x x x

OvGU IICombined winding

Additional slot

winding

19.02.2018 22

ANSYS magnetic field simulation for 0.5

mm air-gap

• 1 wire to maximize fill factor

rotor

stator

U V W

U V W

Magnetic Circuit Combined Winding

Compact magnetic circuit

• 2 windings working together

approx. double torque

• Only slightly higher stator back-iron without

saturation

low weight

small iron losses

• Only slightly higher need for copper of slot

winding

low weight

low cost

Combined Winding

19.02.2018 23

Patented Design Combined Winding

DE 10 2016 100 744, WO 2017/125416 A1

Meandering 1 wire slot winding in series to air-gap winding

• Simple weakly slotted ring geometry

• Special slot winding technology

– High fill factor low losses

– Low cost

• Customization of cogging torque

and inductance by slot geometry

• Can use modified existing slot

winding technology

Combined Winding

permanent

magnets

one

phase

rotor back-iron

air-gap

winding

slot

winding stator

back-iron

19.02.2018 24

First Prototype EPW III

Design Parameters

• Extension of air-gap winding with slot

winding using existing 15‘‘ EPW I prototype

• Torque 480 Nm

• Nominal power 62 kW

• Weight 21 kg

• Power/Weight ca. 3 kW/kg

• Max. efficiency ≥ 94 %

• Completion February 2017

Combined Winding

Stator

Winding Heads

19.02.2018 25

Proof of Combined Winding Principle

Experimental Parameters EPW III

• Voltage (EMF) of combined winding sums

up

• Torque of combined winding sums up

• No mutual interference of windings

Proof of principle of combined winding

Combined Winding

0

100

200

300

400

500

0 40 80 120 160

RM

S b

ac

k-e

mf

[V]

Angular velocity [rad/s]

0

50

100

150

200

250

0 20 40 60

RM

S T

orq

ue [

Nm

]

RMS current [A]

Lim

ited

by te

st e

qu

ipm

en

t air-gap slot combined

19.02.2018 26

Regular Prototype EPW II

Exploiting Full Potential of Combined Winding

• Rim size 16 inch

• Width 100 mm

• Nominal

– Torque 600 Nm

– Power 64 kW

• Weight 16 kg

• Power/Weight 4 kW/kg

• Max. efficiency ≥ 95 %

• Larger inductance standard FOC

Combined Winding

19.02.2018 27

Regular Prototype EPW II - Additional Features

• New method of integration of motor into rim

tolerating misuse of 15 kN on rim

• Lightweigth materials

(BMWi project LeiRaMo)

– Al-foams

– Carbon fibers

– Hybrid = Al-foam + carbon

• Lightweight completely integrated power

control unit

Combined Winding

air-gap reduction

19.02.2018 28

Regular Prototype EPW II - Thermal FE Design

Combined Winding

Pump power < 20W

Max ϑ (heads) 112 °C

8 kW lost heat, inflow 65°C

19.02.2018 29

Comparison Wheel-Hub-Motor EPW II

Combined Winding

General

Motors

Schaeffler

AG

Siemens

AG Fraunhofer

Protean

Electric EPW II

Rim Size [Zoll] 17 16 17 17 18 16

Weight [kg] 30 53 50 42 34 16

Power [kW] 16 33 63 55 54 64

Power/Weight

[kW/kg] 0.53 0.62 1.26 1.31 1.59 4

Torque [Nm] 200 350 500 700 650 600

Torque/Weight

[Nm/kg] 6.67 6.60 10 16.67 19.12 37.5

19.02.2018 30

Lightweight sports vehicle

• 4WD wheel hub motors

• Vehicle dynamics control

• Total vehicle weight 700 kg

• Unlimited range with range extender

• New project

(picture similar)

Combined Winding Applications

Hybrid motor

• Power 90 kW

• Speed 7000 rpm

• Integration into gear

• Active weight app. 6 kg

• reduction by 20%

• Simulation study for OEM

(picture

similar)

Combined Winding

19.02.2018 31

Summary

New motor technology

• Lightweight

• High power

• Compact

• Cost efficient

• Scalable

• Design environment

Summary and Outlook

Air-gap winding offers

• Minimum iron/copper

• Small losses iron/copper

• Excellent cooling/overload

• Thin ring motor

• No cogging torque

• Automated winding application

Combined winding adds

• Double torque

• Best power/ and torque/weight

• Compactness

Rim [inch]

13 16 19 21 23

T [Nm] 400 600 850 1000 1200

19.02.2018 32

Outlook

Technology

• Optimization of production

– of air-gap and slot winding

– wound stator back-iron

• Improved architecture for higher power and

torque

+ 50%

Summary and Outlook

Applications

• Automotive

– Hybrid motor

– Electric drive axle

– Non-powertrain e-drives

• Non-automotive

– Wind- and watermill generators

1-250 kW

6-300 rpm

– Pump motors

2-20 kW

2000-3000 rpm

Rim [inch]

13 16 19 21 23

T [Nm] 600 900 1275 1500 1800

19.02.2018 33

Innovative Winding and Stator Architectures for High Torque

and Lightweight Electrical Machines

Thank you

Prof. Dr.-Ing. Roland Kasper

Otto-von-Guericke University Magdeburg

39106 Magdeburg, Germany

Am Universitätsplatz 2

+49 391 675 8606

Roland.Kasper@ovgu.de

Advanced E-Motor Technology Berlin 2018