hybrid drive systems for vehicles n

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© Mats Alaküla EHS

Hybrid Drive Systems for Vehicles

• L4

– Alternative drive train Components

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Drawback with conventional

drivetrains

• Limited ability to optimize operating point

• No ability to regenerate braking power

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Solutions

• Smaller Engine

+ Reach higher operating points

- Still cannot regenerate

• Store energy in the vehicle mass

- Speed variations

- Still cannot regenerate

• Secondary energy storage

+ Selectable operating point (Pstorage = Pice – Proad)

+ Can regererate

- Expensive

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Smaller Engine – cylinder

deactivation

IC E EM

PE Batt

GEAR Clutch

D

DIFF IC E Clutch

0 200 400 600 0

50

100

150

0 200 400 600 0

50

100

150

0 200 400 600 0

50

100

150

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Combustion On Demand

• Cylinder deactivation via free valve control

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Optimized efficiency

0

200

400

600

0

20

40

60

80

0

0.05

0.1

0.15

0.2

0.25

0.3

Speed [rad/s]Torque [Nm] 0

200

400

600

0

20

40

60

80

0

0.05

0.1

0.15

0.2

0.25

0.3

Speed [rad/s]Torque [Nm] 0

200

400

600

0

20

40

60

80

0

0.5

1

1.5

2

Speed [rad/s]

Number of Cylinders in use

Torque [Nm]

4

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Max efficiency

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 104

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

ICE Power [W]

Optim

al E

ffic

iency

Blue=2-cylinder std, Red=2-cylinder COD

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Secondary Energy Storage

selection

• Why electric?

– Efficient secondary energy converters

(Electrical machines)

– Safe, quiet, flexible installation

– Increasing need for Auxilliary electric power

– High torque density of Electrical Mchines

• Up to 30 Nm/kg

• ICE: <2 Nm/kg

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Secondary energy storage –

Hybridisation

IC E EM

PEBatt

GEARClutch

D

DIFF

IC E EM PE Batt

D

DIFF PE EM

Series

Parallell

Industrial Electrical Engineering and Automation

Lund University, Sweden

Energy Storage Systems

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How does a battery look? In

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Cost

Operation Performance

Vehicle

Design criteria

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ECBECB

Source: Uppsala University

Driving the Hybrid by the Atoms In

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Technologies

NiMH

Li-ion S.C.

Lead

8

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Limiting Factors

NiMH Durability

Weight

Cost

Li-ion Cost

Safety S.C. Energy

Initial Cost

Lead Charge Power

Durability

Weight

Maintenance

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Pb-

Acid

NiMH

Li-ion

Po

we

r D

en

sit

y

Energy Density

S.C

Effpower

Performance

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”Next Generation Need”

Po

we

r

Energy

Cranking

Propulsion

Hybrid Mode

Propulsion

Electric Mode

10 kW

100 kW

Relation to needs In

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Battery Cell Properties

– All parameters are non-linear

– Strong dependance on SOC, temperature, current

rate & direction, and history.

+

-

OCV = f(SOC, T,I…)

R = f(SOC, T,I…)

C = f(SOC, T,I…)

Losses

+

-

Terminal

Voltage

No Steady-State Operation!

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Super Capacitor Cell Properties

– Fewer non-linear elements

– Strong dependance on SOC & temperature only

Rohm = f(T, ω)

C = f(U, T, ω)

Terminal

Voltage

+

-

Rleak = f(T)

L = f(T, ω)

Losses

”Semi” Steady-State Operation!

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Combined Energy Storage System

SuperCaps

En

erg

y D

en

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y

Power Density

Combined System Battery

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Driving Criteria

Power output/regeneration at a specific

time

Charge and Discharge Properties

Cooling Issues

Pure Electric Range

Upcoming energy need (GPS, weather and

traffic info, etc.)

Factors Determined by:

State of Function = State of Charge + State

of Health

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State of Charge

Vo

ltag

e

100% State of Charge 0%

Li-ion

NiMH

S.C.

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State of Health

Temperature and Temperature Changes

Charge and Discharge Properties

Pure Electric Range

State of Charge 200 - 500 individual cells in a battery

system

-- ALL need to be managed Management unit is needed

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© Mats Alaküla EHS © Mats Alaküla

SAFT data

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© Mats Alaküla EHS © Mats Alaküla

SAFT Lithium teknologi In

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Battery simulation model : 1

b a t t i

b a t t e

b a t t R

e c h P a r g t e r m P

l o s s P

term

ech

batt

losstermech

battbattloss

batt

term

batt

batt

batt

battbatt

battbattbattbattbattbattbattbattterm

P

P

PPP

iRP

R

P

R

e

R

ei

iRieiiReP

arg

arg

2

2

2

22

)(

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Battery Simulation model : 2

-1 -0.5 0 0.5 1

x 105

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2Battery charge efficiency

Battery power [W]

Eff

icie

ncy

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Super Capacitors : 1

• Low voltage -> series connection

2

2

1CC uCW

units unit

system

C

C

#

1

1

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Supe Capacitors : 2

Size

22 liter / 15 kg

Capacitance

145 Farads

Max electric

specs

50 V / 600 A

Power density

2900 W/kg

Energy density

2.3 Wh/kg

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Fly wheel energy storage

• High speed rotating mass 2

2

1wheel

JWmech

16

Industrial Electrical Engineering and Automation

Lund University, Sweden

Electric Motor Drive

Systems

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Torque and Power

• Torque = Force * radius

on the shaft

T = F * r

• Power = Torque*Speed

on the shaft

P = T *

but, also …

• Power = Voltage * Current

on the electrical terminals

P = U * I

r

F

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Stator, Rotor and Airgap

• The stator is static

(not moving)

• The rotor rotates

• The air gap

seperates them

– Usually < 1 mm

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D Diesel

Engine

Hybrid Topologies

El

Ma

ch

El.

mach

El.

mac

h

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Rotor Rotor

Stator

Stator Stator

Stator

Ro

tor

Sta

tor

Sta

tor

Ro

tor

Inner or Outer Rotor, Radial or Axial flux …

Inner rotor

Radial flux

Outer rotor

Radial flux

Axial flux

End winding

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Distributed or Concentrated winding

Axially shorter end

winding

Cheaper assembly

Lower torque quality

Longer end winding

More expensive

assembly

Higher torque quality

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Shear Force & Torque

Current and Flux interact for

tangential force

s = Force/Unit area is a key

figure

A good design accomplish

about s = 10000-30000

[N/m2] in continuous

operation and 2..4 times more

in transient operation

s

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Form Factor

• For the same torque, a

machine can be either short

and wide, or long and slender

…

• Assume 25000 [N/m2], and a

desired torque of 1000 Nm,

AND that the stator outer

radius is 0.15 – 0.5 meter.

– How long will the machine be

to fulfill the torque

requirement?

• The long and slender machine will

accelerate faster

– Torque ~ radius2*length

– Inertia ~ radius4*length

• Acceleration = Torque/Inertia ~

1/radius2 High torque density but

low acceleration

Low torque

density but high

acceleration

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0

0.1

0.2

0.3

0.4

0.5

0.6

Radius

Le

ngth

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Eaton

• ”ISAM”

• ”Short and

Wide”

• Concentrated

winding

• PM motor from

Hitachi

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Voith • ”ExSAM”

• ”Long and slender”

• Induction motor from

??

– Probably very close

to standard

industrial … good

commonality

• 150 kW 520 nm @

motor or input shaft?

Siemens 1FHX

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Volvo/Renault/Mack/Nissan

• ”ISAM”

• ”Short and Wide”

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Some

Cars

”ISAM”

PM Motor

Concentrated

windings”

Complex

PM Machines

Distributed windings

97000 N/m2 !!!

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Generic Force

Force = Flux density * Current * length (twice)

Power = Force * Speed = Voltage * current

Voltage = Force *speed / current =

= Flux density * length * speed

Current

Force Flux density

Lorentz force =

current in magnetic

field

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Linear movement from generic force

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Rotating movement from generic

force In

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Conclusions on force and movement

• The same generic circuit accomplish both linear

and rotating movement.

• One phase is not enough for continuos force

• Qualitative:

– Voltage ~ Speed

– Current ~ Force

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Field Weakening : I

• Remember: – Voltage ~ flux density * speed

– Torque ~ flux density * current

– Power ~ speed*torque = voltage*current

• The required voltage ”hits the roof” at some speed. What to do, to increase speed beyond? – Answer: Reduce flux density’

– Consequences:

• The voltage requirement is kept constant, as desired

• The torque capability drops as the flux density.

• The power is kept constant, since the speed increases in the same rate as the torque drops with increasing speed.

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Field Weakening : II

0

50

100

150

200

250

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

[rp

m]

[Nm]

[kW, V]

Ba

se

sp

ee

d

Const

torque

Constant

power

Field weakening

ratio 1:4

Ma

x s

pe

ed

Max voltage and power

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Example from Toshiba ”Large Torque and High Efficiency Permanent Magnet Reluctance

Motor for A Hybrid Truck” - Masanori Arata et. Al, EVS-22

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Permanent Magnet Synchronous Machines

• Same as the generic machine

• Voltage and frequency

proportional to speed

• Current proportional to torque

• High torque density

– 1...10 Nm/kg

– Compare to ICE 1...2 Nm/kg

• High efficiency

– Up to 97%

• Higher efficiency, higher torque

density and more expensive than

other machines

– Due to the permanent magnets.

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The Induction Machine : I

• Same stator as the PMSM

• The rotor is a short circuited ”cage”

• The rotor current must be induced magnetically – Losses related to magnetization

”competes” with losses due to torque generation.

• Robust construction

• Low cost

• Low/no maintenance

• Heavily standardized for industrial applications

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The Induction Machine : II

• Voltage and frequency proportional to speed, like PMSM

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Comparison – Electric Drives

1.0 2.0

AC (IM)

PM

2.0

4.0

6.0

8.0

Tmax [Nm/kg]

Pcontinuous [kW/kg]

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Electrical machine losses

• Several types:

– Copper losses (Ri2)

– Iron losses (k1*f*B2 + k2*(f*B)2)

– Windage losses (surface speed)

– Other friction losses

• Approximately calculated by – [EtaEM,Tem,Wem] = CreateEMmap(Pem_max,wem_max,Tem_max)

Hysteresis losses

Eddy current losses

0200

400600

800

0

50

100

150

200

0

0.5

1

Speed [rad/s]

Electrical machine efficiency

Torque [Nm]

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The Traction motor efficiency

0200

400600

800

0

50

100

150

200

0

0.5

1

Speed [rad/s]

Electrical machine efficiency

Torque [Nm]

Torque limit

Power limit

Speed limit

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Power Electronics

• Needed to condition the battery voltage to the

different electrical drives

• Use switching technology for high efficiency

– Conventional converters (like loudspeaker amplifiers)

efficiency 25-60 % due to continuous control of the

voltage.

– Switching means “on/off” control of voltage, leading to

efficiency above 95 %.

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1 Phase Pulse Width Modulation

(PWM)

Modulating wave Voltage reference

Output voltage 0 0.005 0.01 0.015

0

20

40

60

80

100

0 0.005 0.01 0.015

0

20

40

60

80

100

sa 0 va

+50

- 50

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Three-phase Converters

id

sa 0 va

+Ud/2

-Ud/2

sb vb sc vc

+ uab - + ubc -

- uca +

+

ua

-

+

ub

-

+

uc

- vo

Traction motor

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Three-phase Pulse Width Modulation

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-500

0

500

uaref & tri

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-500

0

500va

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-500

0

500vo

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02-500

0

500ua

varef

tri

va

v0

u=va-v0 grundton 50 Hz

• The voltages

contain high

harmonics

that cause:

– Audible noise

– Torque ripple

– EMC

problems

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Power Electronics Efficiency

• Several types of losses

– Switching losses

– Conduction losses

I0

+VDC

vS

iS

I0

VDC

vS, iS

von

t

pS

Pcond

ttcondton toff

Tsw

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Power Electronic Efficiency

• Mostly depending on the ratio

• Almost constant over wide operating range

• Can be represented by a constant, e.g. 0.97

Output voltage

DC link voltage

hybrid drive systems for vehicles n

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