Electric Vehicle Drive Systems

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Russell Hall
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1 North Bay Electric Auto Association Summer 2009 Technical Series Electric Vehicle Drive Systems Presented June 13, 2009 Corrected June 15, 2009 This presentation is posted at:

2 NBEAA Summer Technical Series TODAY>> 1. EV Drive Systems 2. EV Batteries and Management Systems 3. EV Charging Systems 4. EV Donor Vehicles

3 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

4 What is an EV Drive System? To Wheel From Battery Motor controller From Driver CV Joint Half Shaft Motor Motor Adapter Flywheel and Clutch U Joint Drive Shaft U Joint CV Joint Transmission Differential CV Joint Half Shaft All or a subset of the components between the batteries and the wheels shown above. CV Joint To Wheel

5 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

6 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

7 EV Drive System Requirements Safe High Power High Efficiency Durable

8 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

9 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

10 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

11 EV Drive System Requirements: High Efficiency Power losses due to heat cause power and range reduction. Copper, bearing heat Motor Switching Transistor, freewheel diode heat Motor controller Motor Adapter Flywheel and Clutch Bearing heat U Joint Bearing heat Drive Shaft Bearing heat U Joint Bearing heat x5 CV Joint Half Shaft CV Joint Transmission Differential CV Joint Half Shaft CV Joint The more current, the more load, and hence the more heat is lost throughout.

12 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.

13 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.

14 Types of EV Drive Systems: Motor Terminology Rotor: Stator: rotating part of motor stationary part of motor Field: Armature: produces magnetic field to be acted upon by armature; can be electromagnet or permanent magnet carries current normal to field to generate torque Rotor or stator can be either field or armature.

15 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

16 Types of EV Drive Systems Categ ory Type Example Motors Example Controllers DC Series Advanced DC Alltrax Kostov 2 Auburn 3 Netgain Café Electric 1 Curtis Raptor 1 Shunt D&D Alltrax Sevcon Brushed Permanent Magnet Perm PMG Alltrax Et-R, RT Brushless Permanent Magnet Mars Sevcon Toyota RAV4 EV 3 Toyota RAV4 EV 3 AC Synchronous Siemens 2 Siemens 2 Induction AC Propulsion AC Propulsion Azure Dynamics Brusa Azure Dynamics Brusa Curtis Curtis MES MES Siemens 2 Siemens 2 Notes: 1 Requires special order, 2 are no longer readily available in the US, 3 are obsolete.

17 Types of EV Drive Systems: Drivelines Shaft Type Fit for flywheel and clutch? Picture Smooth Keyed Yes Splined No Involuted Spline Heck No

18 Types of EV Drive Systems: Motor Control via Pulse Width Modulation 100% duty cycle 75% 50% 25% 0%

19 Types of EV Drive Systems: Switch Mode Power Supply Buck Regulator From batteries Filter capacitors From PWM control circuit Freewheel diodes 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.

20 Types of EV Drive Systems: 3 Phase AC Configurations delta wye A B A B C Coil voltage = line voltage RPM varies with voltage Used at lower voltages to maximize speed C Coil current = line current Torque varies with current Used at higher voltages to maximize torque

21 Types of EV Drive Systems: PWM control circuit types Analog Digital configuration Digital control

22 Type Types of EV Drive Systems: Cooling Systems Motor Motor Controller Sealed, no fan Sealed, external fan on heat sink Sealed, liquid Internal fan, open External fan, open Center may overheat Requires small cooling system Needs debris and splash shield; low slung motor can not be submerged Takes up more volume; Needs debris and splash shield; low slung motor can not be submerged Needs large area heat sink; can be flat plate Takes up a single large fixed volume Requires small cooling system May corrode due to humidity, or overheat due to dust accumulation

23 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

24 EV Drive System Comparison Type Safety Efficiency Torque Regen DC Series ~ ~ + ~ DC Shunt ~ ~ ~ ~ DC Brushed PM ~ ~ ~ ~ DC Brushless PM + + ~ + AC Synchronous + + ~ + AC Induction + + ~ +

25 EV Drive System Comparison Controller Curtis 1231C Raptor 600 Cafe Electric Zilla 1K-LV Raptor 1200 Cafe Electric Zilla 2K-LV Solectria DMOC445 MES-DEA TIM600 Motor Advanced DC 9" FB Advanced DC 9" FB Advanced DC 9" FB Advanced DC 9" FB Advanced DC 9" FB Solectria AC24 w/smooth keyed output shaft MES Peak HP at 144V Continuous HP Peak Torque at 144V, ft-lb Regenerative Braking no no no no no Efficiency Output Shaft Sealed Controller? 75% smooth keyed 75% 75% 75% 75% 85% smooth keyed smooth keyed smooth keyed smooth keyed smooth keyed Example to be updated no no 85% involuted spline, but 8.64:1 Carraro gearbox with differential available Brushes? 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?? independent main contactor safety control no?? accelerator modulation speed? torque? torque torque torque Motor and Controller Weight, lbs 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 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

26 EV Drive System Comparison

27 EV Drive System Comparison Advanced DC 9 Series DC at 120V

28 EV Drive System Comparison D&D Shunt SepEx DC at 72V

29 EV Drive System Comparison D&D Shunt SepEx DC at 72V

30 EV Drive System Comparison PMG 132 Brushed Permanent Magnet DC at 72V

31 EV Drive System Comparison Et-RT Brushed Permanent Magnet DC at 48V

32 EV Drive System Comparison Azure Dynamics AC24LS/DMOC445 delta at 156V

33 EV Drive System Comparison Azure Dynamics AC24LS/DMOC445 delta at 156V

34 EV Drive System Comparison Azure Dynamics AC24LS/DMOC445 wye at 312V

35 EV Drive System Comparison Azure Dynamics AC24LS/DMOC445 wye at 312V

36 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?

com/1683) ; AC 55 motor Brian Hall: Curtis 96V AC drive system in 72V Geo Metro conversion; 72V Et-RT

37 EV Drive System Testimonials, Show and Tells and Test Drives Peter Oliver: Azure Dynamics AC24 motor and DMOC445 controller in Porsche Speedster conversion ( ; 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 (

38 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

The Science of Electric Vehicles

The Science of Electric Vehicles Alan Soule and Chris Jones North Bay Electric Auto Association www.nbeaa.org Presentation to Science Buzz Café French Garden Restaurant, Sebastopol July 22, 2010 6:30 PM