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?

Motor

Fly- wheel and

Clutch

Trans-mission

Drive Shaft Differ-ential

Motor Adapter

All or a subset of the components between the batteries and the wheels shown above.

Motor controller

From Battery

U Joint

U Joint

CV Joint

CV Joint

Half Shaft

CV Joint

CV Joint

Half Shaft

To Wheel

To Wheel

From Driver

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 non-rechargeable 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 Circuitcommon DC motor controller failure mode, exacerbated

by high currents and hence high heat

probability reduced with improved efficiencyresponse enhanced with a clutch, circuit breaker and

automatic contactor controller

Low powersome 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 PowerExample

Accelerating or driving up a short steep hillPeak Motor Shaft Power = ~50 HP or ~37,000 WPeak 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 speedContinuous Motor Shaft Power = ~20 HP or ~15,000 WContinuous Motor Current

~200A for 144V nominal pack with DC drive ~75A RMS for 288V nominal pack with AC drive

Regenerative BrakingDepends on battery typeExample: 3C max charge Thunder Sky LFP series LiFePO4

180A for 60 Ah cells270A for 90 Ah cells

Motor

Fly- wheel and

Clutch

Trans-mission

Drive Shaft Differ-ential

Motor Adapter

Motor controller

U Joint

U Joint

CV Joint

CV Joint

Half Shaft

CV Joint

CV Joint

Half Shaft

Switching Transistor, freewheel diode heat

Copper, bearing heat

EV Drive System Requirements: High Efficiency

Power losses due to heat cause power and range reduction.

Bearing heat

Bearing heat

Bearing heat

Bearing heat x5

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 50Chumidity: 5% to condensingshock: potholesvibration: 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. DCAC is more efficient, less maintenance and more robust

DC is less expensive, but mainly due to higher volumefork lift industry trend is moving from DC to AClate model OEM EVs have mostly been AC; conversions mostly DC

Transmission or fixed gearTransmission is more efficientFixed gear is lighter and less complex

Clutch or no clutchClutch 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 SystemsCategory

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

AC Synchronous Siemens2 Siemens2

Induction AC Propulsion

Azure Dynamics

Brusa

Curtis

MES

Siemens2

AC Propulsion

Azure Dynamics

Brusa

Curtis

MES

Siemens2

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? Picture

Smooth Keyed Yes

Splined No

Involuted Spline Heck No

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

From batteries

Motor Armature (and field for DC series;

separate circuit for DC shunt and AC synchronous)

Power switching transistors (MOSFETs

or IGBTs)

From PWM control circuit

Freewheel diodes

Filter capacitors

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

delta wye

Coil voltage = line voltage

RPM varies with voltage

Used at lower voltages to maximize speed

Coil current = line current

Torque varies with current

Used at higher voltages to maximize torque

A AB

C

B

C

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

May corrode due to humidity, or overheat due to dust accumulation

External fan, open Takes up more volume; Needs debris and splash shield; low slung motor can not be submerged

Types of EV Drive Systems: Management Systems

Voltage (speed) or current (torque) regulation vs. pedal (potbox or hall effect) input

Motor current limitingBattery current limitingLow pack voltage cutoffLow cell voltage cutoff

Motor controller thermal cutbackMotor 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

Controller Curtis 1231C-8601

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 smooth keyed smooth keyed smooth keyed smooth keyed smooth keyed involuted spline, but 8.64:1 Carraro gearbox with differential available

Sealed Controller? yes no yes no yes yes yes

Brushes? 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

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

Example – to be updated

EV Drive System Comparison

EV Drive System ComparisonAdvanced DC 9” Series DC at 120V

EV Drive System ComparisonD&D Shunt “SepEx” DC at 72V

EV Drive System ComparisonD&D Shunt “SepEx” DC at 72V

EV Drive System ComparisonPMG 132 Brushed Permanent Magnet DC at 72V

EV Drive System ComparisonEt-RT Brushed Permanent Magnet DC at 48V

EV Drive System ComparisonAzure Dynamics AC24LS/DMOC445 delta at 156V

EV Drive System ComparisonAzure Dynamics AC24LS/DMOC445 delta at 156V

EV Drive System ComparisonAzure Dynamics AC24LS/DMOC445 wye at 312V

EV Drive System ComparisonAzure 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?

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)

EV Drive System Testimonials, Show and Tells and Test Drives

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