Electric Vehicle Drive Systems

North Bay Electric Auto Association
Summer 2009 Technical Series
Electric Vehicle Drive Systems
www.nbeaa.org
Presented June 13, 2009
Corrected June 15, 2009
This presentation is posted at:
http://www.nbeaa.org/presentations/drive_systems.pdf
NBEAA Summer Technical Series
TODAY>>
1. EV Drive Systems
2. EV Batteries and Management Systems
3. EV Charging Systems
4. EV Donor Vehicles
Agenda
What is an EV Drive System?
EV Drive System History
EV Drive System Requirements
Types of EV Drive Systems
EV Drive System Cooling
EV Drive System Management
EV Drive System Comparison
Future EV Drive Systems
EV Drive System Testimonials, Show
and Tells and Test Drives
What is an EV Drive System?
From
Battery
Motor
controller
Motor
FlyMotor wheel
Adapter and
Clutch
To Wheel
CV
Joint
Half
Shaft
From
Driver
CV
Joint
Transmission
U
Joint
Drive Shaft
U
Joint
Differential
CV
Joint
Half
Shaft
All or a subset of the components between the batteries
and the wheels shown above.
CV
Joint
To Wheel
What is an EV Drive System?
Demonstration of electric motor principles:
• Two permanent magnets attracting and repelling each other
• An electromagnet attracting and repelling a permanent magnet
with a DC source, reversed with polarity
• A small brushed permanent magnet DC motor, speed increased
with varying voltage through variable resistor, and reversed with
polarity
EV Drive System History
First electric motor, for demonstration only
1821
England
Michael Faraday
First DC motor that could turn machinery
1832
England
William Sturgeon
First electric carriage, 4 MPH with nonrechargeable batteries
1839
Scotland
Robert Anderson
First DC motor that was commercially successful
1873
Belgium
Zenobe Gramme
First AC motor
1888
US
Nikola Tesla
First mass produced electric vehicle, with variable
resistor DC motor control
1914
US
Thomas Edison
and Henry Ford
First high efficiency small air gap motors
1950s
US
First SCR controllers
1960s
US
First MOSFET PWM controllers
1970s
US
First IGBT PWM controllers
1980s
US
First digital configuration PWM controllers
1990s
US
First digital control PWM controllers
2000s
US
EV Drive System Requirements
Safe
High Power
High Efficiency
Durable
EV Drive System Requirements: Safe
Examples of EV drive system safety issues:
Short Circuit
common DC motor controller failure mode, exacerbated by
high currents and hence high heat
probability reduced with improved efficiency
response enhanced with a clutch, circuit breaker and
automatic contactor controller
Low power
some more efficient or lower cost setups with low power
could expose vehicle to oncoming traffic
overheating undersized or poorly controlled systems could
induce thermal cutback that can exacerbate this
EV Drive System Requirements: High Power
Power = Watts = Volts x Amps
Power out = power in x efficiency of portion of system being evaluated
at the output “shaft” or at the “brake” pads
1 Horsepower = 746 Watts
Motor controller efficiency = >90%
Motor efficiency = 85-95%
Rest of drive train efficiency = 85-90%
Overall efficiency 65-75%
25-35% lost due to heat
EV Drive System Requirements: High Power
Example
Accelerating or driving up a short steep hill
Peak Motor Shaft Power = ~50 HP or ~37,000 W
Peak Motor Current
~500A for 144V nominal pack with DC drive
~200A RMS for 288V nominal pack with AC drive
Driving steady state on flat ground at high speed
Continuous Motor Shaft Power = ~20 HP or ~15,000 W
Continuous Motor Current
~200A for 144V nominal pack with DC drive
~75A RMS for 288V nominal pack with AC drive
Regenerative Braking
Depends on battery type
Example: 3C max charge Thunder Sky LFP series LiFePO4
180A for 60 Ah cells
270A for 90 Ah cells
EV Drive System Requirements: High Efficiency
Power losses due to heat cause power and range reduction.
Switching Transistor,
freewheel diode heat
Motor
controller
Bearing
heat
Copper,
bearing heat
Motor
FlyMotor wheel
Adapter and
Clutch
Transmission
Bearing
heat
U
Joint
Drive Shaft
Bearing
heat
U
Joint
Bearing
heat x5
CV
Joint
Half
Shaft
CV
Joint
Differential
CV
Joint
Half
Shaft
CV
Joint
The more current, the more load, and hence the more heat is lost throughout.
EV Drive System Requirements: Durable
Wide range of driving requirements combined with downwards pressure on
size and weight for performance and cost reasons can put excess stress
on drive system components
Harsh automotive environment much worse than indoor environment:
temperature: -40C to 50C
humidity: 5% to condensing
shock: potholes
vibration: gravel roads
Make sure to use a motor for and EV that was intended for on-road use.
Types of EV Drive Systems:
Which Type is Best?
AC vs. DC
AC is more efficient, less maintenance and more robust
DC is less expensive, but mainly due to higher volume
fork lift industry trend is moving from DC to AC
late model OEM EVs have mostly been AC; conversions mostly DC
Transmission or fixed gear
Transmission is more efficient
Fixed gear is lighter and less complex
Clutch or no clutch
Clutch is more efficient
No clutch is lighter and less complex
The debate rages on, but the highest performance is AC with transmission
and clutch.
Types of EV Drive Systems:
Motor Terminology
Rotor:
rotating part of motor
Stator:
stationary part of motor
Field:
produces magnetic field to be acted upon by armature;
can be electromagnet or permanent magnet
Armature:
carries current normal to field to
generate torque
Rotor or stator can be either field or armature.
Types of EV Drive Systems:
Motor Comparison
type
brushes
Stator
Rotor
DC Series
Yes
Field windings
Armature windings, commutated
through brushes and split rings, in
series with field
DC Shunt
Yes
Field windings
Armature windings, commutated
through brushes, separately
excited from field
DC Brushed
Permanent Magnet
Yes
Field permanent magnet
Armature windings, commutated
through brushes
DC Brushless
Permanent Magnet
No
Armature windings, PWM’d
via rotor position sensor
Field permanent magnet
AC Synchronous
Yes
Armature windings, PWM’d
via rotor position sensor
Field windings, DC energized
through brushes and slip rings
AC Induction
No
Armature windings, PWM’d
via rotor position sensor
Opposing magnetic field induced
via eddy currents caused by slip
between stator and rotor in copper
or aluminum “squirrel cage” frame
Types of EV Drive Systems
Categ
ory
Type
Example Motors
Example Controllers
DC
Series
Advanced DC
Kostov2
Netgain
Alltrax
Auburn3
Café Electric1
Curtis
Raptor1
Shunt
D&D
Alltrax
Sevcon
Brushed Permanent Magnet
Perm PMG
Et-R, RT
Alltrax
Brushless Permanent Magnet
Mars
Toyota RAV4 EV3
Sevcon
Toyota RAV4 EV3
Synchronous
Siemens2
Siemens2
Induction
AC Propulsion
Azure Dynamics
Brusa
Curtis
MES
Siemens2
AC Propulsion
Azure Dynamics
Brusa
Curtis
MES
Siemens2
AC
Notes: 1 Requires special order, 2 are no longer readily available in the US, 3 are obsolete.
Types of EV Drive Systems:
Drivelines
Shaft Type
Fit for flywheel and clutch?
Smooth Keyed
Yes
Splined
No
Involuted Spline
Heck No
Picture
Types of EV Drive Systems:
Motor Control via Pulse Width Modulation
100%
duty cycle
75%
50%
25%
0%
Types of EV Drive Systems:
Switch Mode Power Supply Buck Regulator
Filter
capacitors
From
batteries
Freewheel
diodes
From
PWM
control
circuit
Motor Armature (and
field for DC series;
separate circuit for DC
shunt and AC
synchronous)
Power switching
transistors (MOSFETs
or IGBTs)
When power is applied to input, capacitors are charged up. When transistors are
switched on, current flows from the batteries and capacitors to the motor. When the
transistors are off, the capacitors are recharged by the batteries while current flows
from the motor to the freewheel diodes while the motor’s magnetic field collapses to
keep from increasing the voltage across the transistor to the point of failure.
Types of EV Drive Systems:
3 Phase AC Configurations
wye
delta
A
B
A
B
C
C
Coil voltage = line voltage
Coil current = line current
RPM varies with voltage
Torque varies with current
Used at lower voltages to maximize
speed
Used at higher voltages to
maximize torque
Types of EV Drive Systems:
PWM control circuit types
Analog
Digital configuration
Digital control
Types of EV Drive Systems:
Cooling Systems
Type
Motor
Motor Controller
Sealed, no fan
Center may overheat
Needs large area heat
sink; can be flat plate
Sealed, external fan
on heat sink
Takes up a single large
fixed volume
Sealed, liquid
Requires small cooling system Requires small cooling
system
Internal fan, open
Needs debris and splash
shield; low slung motor can
not be submerged
External fan, open
Takes up more volume;
Needs debris and splash
shield; low slung motor can
not be submerged
May corrode due to
humidity, or overheat
due to dust accumulation
Types of EV Drive Systems:
Management Systems
Voltage (speed) or current (torque) regulation vs. pedal (potbox
or hall effect) input
Motor current limiting
Battery current limiting
Low pack voltage cutoff
Low cell voltage cutoff
Motor controller thermal cutback
Motor thermal cutback
Battery thermal cutback
EV Drive System Comparison
Type
Safety
Efficiency
Torque
Regen
DC Series
~
~
+
~
DC Shunt
~
~
~
~
DC Brushed PM
~
~
~
~
DC Brushless PM
+
+
~
+
AC Synchronous
+
+
~
+
AC Induction
+
+
~
+
EV Drive System Comparison
Curtis 1231C8601
Raptor 600
Cafe Electric
Zilla 1K-LV
Raptor 1200
Cafe Electric
Zilla 2K-LV
Solectria DMOC445
MES-DEA TIM600
Motor
Advanced DC
9" FB1-4001
Advanced DC
9" FB1-4001
Advanced DC
9" FB1-4001
Advanced DC
9" FB1-4001
Advanced DC
9" FB1-4001
Solectria AC24
w/smooth keyed output
shaft
MES 200-150
Peak HP at 144V
72
86
144
172
288
58
73
Continuous HP
28
28
28
28
28
24
19
Peak Torque at 144V, ft-lb
110
132
220
264
440
55
118
Regenerative Braking
no
no
no
no
no
yes
yes
Efficiency
75%
75%
75%
75%
75%
85%
85%
Output Shaft
smooth keyed
Sealed Controller?
yes
Brushes?
Controller
smooth keyed
smooth keyed
smooth keyed
smooth keyed
smooth keyed
involuted spline, but 8.64:1 Carraro
gearbox with differential available
no
yes
no
yes
yes
yes
yes
yes
yes
yes
yes
no
no
Cooling
air
air with
internal fan
water,
controller only
air with
internal fan
water,
controller only
air
water, motor and controller
adjustable battery minimum
voltage (and maximum if regen)
no
?
yes
?
yes
yes
yes
independent main contactor safety
control
no
?
yes
?
yes
yes
yes
accelerator modulation
speed
?
torque
?
torque
torque
torque
Motor and Controller Weight, lbs
170
170
170
190
190
117
121
System Price
$3,000
$3,000
$3,500
$3,500
$4,000
$6,500
$12,000
Example – to be updated
Other Drive Systems Not Considered:
- Solectria AC55: too heavy at 234 lbs, aand splined shaft with no matching gearbox, requiring custom differential gear machining or non-standard flywheel coupling.
- MES 200-175 28 HP: exceeds rating of Carraro gearbox, leaving an involuted spline, not good for a flywheel.
- Siemens AC: also splined shafts only with no matching gearbox. And they are surplus, so they might be hard to get support for, but they do carry a 10 year warranty.
- Brusa AC: also splined shaft with no matching gearbox.
- AC Propulsion: cost prohibitive at $25KK for 150 kW system (although it includes high power charging).
- Kostov series wound DC motors: not readily available.
- Auburn series DC controllers: company no longer in business.
- Curtis 1244 Sep-Ex shunt DC regen controller: complex with marginal performance.
- Zapi Sep-Ex shunt DC regen controller: same as above.
- Customized series wound DC motor with variable mechanical brush timing to improve forward and regen efficiency: too many parts
- Dual DC with no transmission: too inefficient. 60% efficiency estimated.
The following AC drive systems are under development or are currently not available to hobbyists: Enova, UQM, TM4, Reliance, AC Electric Vehicles
EV Drive System Comparison
EV Drive System Comparison
Advanced DC 9” Series DC at 120V
EV Drive System Comparison
D&D Shunt “SepEx” DC at 72V
EV Drive System Comparison
D&D Shunt “SepEx” DC at 72V
EV Drive System Comparison
PMG 132 Brushed Permanent Magnet DC at 72V
EV Drive System Comparison
Et-RT Brushed Permanent Magnet DC at 48V
EV Drive System Comparison
Azure Dynamics AC24LS/DMOC445 delta at 156V
EV Drive System Comparison
Azure Dynamics AC24LS/DMOC445 delta at 156V
EV Drive System Comparison
Azure Dynamics AC24LS/DMOC445 wye at 312V
EV Drive System Comparison
Azure Dynamics AC24LS/DMOC445 wye at 312V
Future EV Drive Systems
Even more efficient motors and motor controllers?
4 wheel hub motors?
4 inboard wheel motors?
Fully integrated braking systems?
Nano-capacitor driven motor controllers?
Optical pedal input?
EV Drive System Testimonials, Show and Tells and
Test Drives
Peter Oliver: Azure Dynamics AC24 motor and DMOC445
controller in Porsche Speedster conversion
(http://www.evalbum.com/1683) ; AC 55 motor
Brian Hall: Curtis 96V AC drive system in 72V Geo Metro
conversion; 72V Et-RT permanent magnet brushed DC
motor
Chris Jones: 9” Advanced DC motor and Curtis 1231C
motor controller in Ford Mustang conversion
(http://www.evalbum.com/733)
Things to add in future:
0-60 MPH comparison – DC, AC, gasoline
Diagrams and graphs for each motor and controller type
Movies for each motor and controller type
Update table comparing all parameters of all drive systems
Overlays of motor curves
Written descriptions of how to read motor curves
More detailed written descriptions of how motors and motor
controllers work
References