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Environmentally Friend Factor of Electric Vehicles
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Environmentally Friend Factor of Electric Vehicles

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Electric Vehicles – Are They Environmentally Friendly?

Electric Vehicles – Are They Environmentally Friendly?

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Environmentally Friend Factor of Electric Vehicles Presentation Transcript

  • 1. Wali Memon walimemon.com The Electrix 1988 Homda CRX Restored & converted to electric in 2000 Range 40 km Top speed 130 kphWali Memonwalimemon.com 1
  • 2. Wali Memon walimemon.comEV Fundamentals  Basic Elements of an EV  Basic Electricity  Energy and Power  Batteries, Batteries, Batteries 2
  • 3. Wali Memon walimemon.comBasic Elements of an EV  Motor  Controller  Battery Pack  Battery Charger  Ancillary Electronics 3
  • 4. Wali Memon walimemon.comBasic Elements of an EV Block Diagram Ignition Switch Start + 12 V Battery - Advanced Curtis DC Motor Controller 144 V +ve Main Voltmeter Contactor Battery Pack Ammeter 500 Amp 144 V -ve Current Shunt Accelerator - DC/DC + + Converter - Pot Box 4
  • 5. Wali Memon walimemon.comBasic Elements of an EV Motor AC Motors  Higher efficiency  No brushes  Complex drive electronics  Generally not suitable for amateur EVs Series Wound DC Motor  Stator and rotor in series  Stator and rotor fields add, so torque goes up as square of current  High starting torque  Simple drive electronics – variable current  Not suitable for regenerative braking  Most popular for amateur EVs 5
  • 6. Wali Memon walimemon.comBasic Elements of an EV Motor  Shunt Wound DC Motor  Stator and rotor in parallel  Stator winding has high resistance  Torque increases linearly with current  Can be used for regenerative braking  Compond Wound DC Motor  Combination series and shunt wound  Has advantages of both  Complex drive electronics  Permanent Magnet and Brushless DC Motors  Similar performance to shunt wound motors  High efficiency 6
  • 7. Wali Memon walimemon.comBasic Elements of an EV Series Wound DC Motor Stator and rotor have very low resistance  High current hence high torque at low speeds Motor generates back EMF (voltage) as it speeds up  Higher battery voltage allows more current at higher revs hence increased power Potential motor runaway at low load  Do not apply voltage when not in gear or with clutch disengaged 7
  • 8. Wali Memon walimemon.comBasic Elements of an EV Controller For Series Wound DC Motor  Modern solid-state variable current motor drive  Very High Power  Up to 150 Volts  Up to 500 Amps  75 Kilowatts  Requires large heat sink with good air flow for cooling 8
  • 9. Wali Memon walimemon.comBasic Elements of an EV Battery Pack Practical pack voltage - 96 volts to 144 volts Multiple 6, 8, or 12 volt batteries  16 x 6 volts = 96 volts  16 x 8 volts = 128 volts  12 x 12 volts = 144 volts Higher voltage = more cells (2 volts per cell)  144 volts = 72 cells  Range limited by weakest cell 9
  • 10. Wali Memon walimemon.comBasic Elements of an EV Battery Charger On-board charger Input - 115 or 230 volts AC Single pack charger or individual charger per battery Interlock to prevent starting EV with charger plugged in Battery pack must be vented while charging  explosive hydrogen released 10
  • 11. Wali Memon walimemon.comBasic Elements of an EV Ancillary Electronics  Battery voltage and current meters  Battery monitoring system  Battery venting and cooling  Battery heater  Car heater  Charger for auxiliary 12 volt battery  Vacuum pump for brakes 11
  • 12. Wali Memon walimemon.comBasic Electricity Water Analogy Voltage, Current, Resistance (Ohm’s Law) Serial and Parallel Circuits Electrical Power and Energy 12
  • 13. Wali Memon walimemon.comBasic Electricity Water Analogy Voltage - water pressure Current - water flow Resistance - pipe diameter (smaller diameter equals greater resistance) The higher the water pressure, the greater the water flow The smaller the pipe diameter, the less the water flow 13
  • 14. Wali Memon walimemon.comBasic Electricity Voltage, Current, Resistance Voltage - Volts (V) Current - Amps (I) Resistance - Ohms (R) Ohm’s Law: V I= R 14
  • 15. Wali Memon walimemon.comBasic Electricity Voltage, Current, Resistance Current increases as voltage increases and resistance decreases Voltage sometimes referred to as electro-motive force (EMF)  Back EMF was discussed earlier in relation to DC motors 15
  • 16. Wali Memon walimemon.comBasic Electricity Serial and Parallel Circuits Batteries may be serial or serial/parallel connected Serial connection increases voltage Parallel connection provides more current “Buddy pairs” of batteries are sometimes used with lower capacity batteries to increase range 16
  • 17. Wali Memon walimemon.comBasic Electricity Electrical Power and Energy Power - watts (W) The instantaneous power is equal to the voltage times the current P=VI Transposing Ohm’s law V = I R Therefore P = I2R This shows that wiring losses square with increasing current 17
  • 18. Wali Memon walimemon.comBasic Electricity Electrical Power and Energy Energy - joules (J) Energy is power integrated over time (watt/hours) Energy is used to overcome wind and rolling resistance, to accelerate, and to climb hills Assuming a relatively constant battery voltage, the total energy from the battery pack is proportional to the total current drawn  Important when calculating required battery pack capacity 18
  • 19. Wali Memon walimemon.comEnergy and Power Basic Physics - Mechanical Force, Work, Power Total Energy and Peak Power Relationship to Electrical Energy and Power 19
  • 20. Wali Memon walimemon.comEnergy and Power Force, Work, Power Newtons First Law: Mass and Inertia An object at rest tends to stay at rest, and an object in motion tends to stay in motion in a straight line at a constant speed 20
  • 21. Wali Memon walimemon.comEnergy and Power Force, Work, Power Newtons Second Law: Mass and Acceleration F = ma Where F is force, m is mass, and a is acceleration (F and a are vectors). If m is in kg, and a is in m/s2, then F is in newtons 21
  • 22. Wali Memon walimemon.comEnergy and Power Force, Work, Power Example:What force is required to accelerate a 1200 kg EV from 0 to 100 kph in 30 seconds?Final speed (Vf) 100 kph = 28 m/sTime (t) 30 sMass (m) 1200 kgAcceleration a = v/t = 0.93 m/s2Force F = ma = 1,111 newtons 22
  • 23. Wali Memon walimemon.comEnergy and Power Force, Work, Power Work Work is the product of the net force and the displacement through which that force is exerted W = Fd F is in newtons, and d is in meters The unit of work is the newton.meter or joule Work is an alternative word for energy 23
  • 24. Wali Memon walimemon.comEnergy and Power Force, Work, Power Example (force over a distance): F = 50 N D = 60 m W = 3,000 j 24
  • 25. Wali Memon walimemon.comEnergy and Power Force, Work, Power Example (acceleration over time) m 1,200 kg t 30 s Vf 100 kph = 28 m/s a 0.93 m/s2 F 1,111 N d 417 m W 463 kj 25
  • 26. Wali Memon walimemon.comEnergy and Power Force, Work, Power Power Power is the work done divided by the time used to do the work P = Fd/t The unit of power is the joule/second or watt (1 kW = 1.34 HP, 1 HP = 746 W) 26
  • 27. Wali Memon walimemon.comEnergy and Power Force, Work, Power Example: P = 0.5ma2t m 1200 kg Vf 100 kph t 30 s a 0.93 m/s2 P 15.4 kW 27
  • 28. Wali Memon walimemon.comEnergy and Power Total Energy and Peak Power The total energy (or work) is the sum of the energy required to:  Accelerate and climb hills  Overcome rolling and wind resistance 28
  • 29. Wali Memon walimemon.comEnergy and Power Total Energy and Peak Power Example: Our 1,200 kg EV accelerating to 100 kph up a 5% grade hill. Acceleration Force Fa = ma W 1200 kg Vf 100 kph t 30 s a 0.93 m/s2 Fa 1111 N 29
  • 30. Wali Memon walimemon.comEnergy and Power Total Energy and Peak Power Grade Force Fg = W g G (for typical grades) W = vehicle weight in kg g = gravitational force G = Percent grade g 9.8 m/s2 Grade 5 % Fg 588 N 30
  • 31. Wali Memon walimemon.comEnergy and Power Total Energy and Peak Power Rolling Resistance Force Fr = Cr W g cos f Cr = 0.007(1+ (v/30.5)) W = vehicle weight in kg g = gravitational force f = angle of incline Cr 0.0134 f 2.86 degrees (0.05 radians) Fr 120 N 31
  • 32. Wali Memon walimemon.comEnergy and Power Total Energy and Peak Power Aerodynamic Drag Force Fd = (Cd p A V^2)/2 Fd = drag force in Newtons Cd = coefficient of drag p = air density (1.29 kg/m2 @sea level) A = frontal area in sq m Va = average speed in m/s Cd 0.3 P 1.29 kg/m2 A 1.39 sq m Fd 52 N 32
  • 33. Wali Memon walimemon.comEnergy and Power Total Energy and Peak Power Propulsion Force Propulsion Force = acceleration + grade + rolling resistance + aerodynamic drag Fa 1111 N Acceleration 59% Fg 588 N Grade 31% Fr 120 N Rolling Resistance 6% Fd 52 N Aerodynamic Drag 3% Total Propulsion Force 1871 N 33
  • 34. Wali Memon walimemon.comEnergy and Power Total Energy and Peak Power Total Energy Total Propulsion Force = 1871 N From before, distance = 417 m W = Fd = 779 kj Peak Power P = W/t = 779/30 = 26 kW (35 HP) Note: This would be the power delivered to the wheels! 34
  • 35. Wali Memon walimemon.comEnergy and PowerRelationship to Electrical Energy and Power Assume efficiency is 80% Total Energy W = 779 kj = 217 wh If V = 144 volts Then Ah = 217/(144 x 0.8) = 1.9 Ah Peak Power P = 26 kW A = 26 x 1000/(144 x 0.8) = 226 Amps 35
  • 36. Wali Memon walimemon.comEnergy and Power Torque Torque is rotational energy (work) in newton.meters Wheel torque is the applied force in newtons multiplied by the wheel radius Motor torque is the wheel torque divided by the transmission ratio Power is proportional to torque multiplied by RPM P = n.m x 2 π x RPM/60 36
  • 37. Wali Memon walimemon.comBatteries, Batteries, Batteries Brief Introduction (will be covered in more detail later in course) Lead acid batteries are the most practical for amateur conversions Nickel cadmium are available, but are expensive and have other problems Nickel metal hydride are generally low power and expensive, but could provide good performance Lithium ion provide best performance, but at a high price and are not easily available 37
  • 38. Wali Memon walimemon.comBatteries, Batteries, Batteries Lead Acid Batteries Most common type is flooded:  Liquid electrolyte - must be kept horizontal  Can tolerate deeper discharge  Can be over-charged to equalize cells  Require periodic topping up with distilled water Gell Cells:  Gelled starved electrolyte  Sealed - can be mounted on sides if required  Lower capacity, lower tolerance to deep discharge  Mustn’t be overcharged 38
  • 39. Wali Memon walimemon.comBatteries, Batteries, Batteries Lead Acid Batteries Spiral Wound:  A form of absorbent glass mat (AGM) battery where the plates are wound in a spiral  Very rugged and can tolerate high rates of discharge  Not available in very high capacities so sometimes connected as “buddy pairs”  Expensive 39
  • 40. Wali Memon walimemon.comBatteries, Batteries, Batteries Battery Capacity Relationship to Total Energy and Peak Power An earlier example was from an Excel spreadsheet that calculates total energy and peak power required for a typical EV trip scenario From spreadsheet:  For a typical 20 km highway trip in the Electrix:  Total Energy = 3 kwh = 21 Ah  Peak power = 30 kW = 206 A 40
  • 41. Wali Memon walimemon.comBatteries, Batteries, Batteries Battery Limitations Quoted Versus Actual Capacity The nominal capacity of a battery is quoted at the C/20 rate, i.e. the ampere hours delivered if discharged 100% over 20 hours The actual capacity drops exponentially as the discharge rate is increased Peukert’s Law can be used to estimate actual capacity at a given discharge rate 41
  • 42. Wali Memon walimemon.comBatteries, Batteries, Batteries Battery Limitations Peukert’s Law t = H(C/IH)k H is the hour rating that the battery is specified against C is the rated capacity at that discharge rate, in A·h I is the discharge current, in A k is the Peukert constant, (varies between 1.1 and 1.3) t is the discharge time, in hours 42
  • 43. Wali Memon walimemon.comBatteries, Batteries, Batteries Battery Limitations Peukert Calculation Rated battery capacity 130 amp-hours C rate for quoted capacity 20 Hours Discharge rate 75 amps Peukert exponent 1.2 Acceptable depth of discharge (DoD) 60 percent Amp-hours available at discharge rate 48 amp-hours Life at discharge rate to specified DoD 0.64 hours Percentage of rated capacity 37 % 43
  • 44. Wali Memon walimemon.comBatteries, Batteries, Batteries Battery Limitations Operating Temperature Range Batteries are specified at 78O F (26O C) The safe operating range is about 15O to 35O C The optimum operating range is about 20O to 30O C Too low a temperature reduces capacity, increases DoD Too high a temperature decreases life, increases failure rate Batteries are like babies - don’t drop them, don’t let them get too hot or cold, feed and water them, and keep them clean 44
  • 45. Wali Memon walimemon.comBatteries, Batteries, Batteries Battery Limitations The Weakest Link A 144 volt battery pack consists of twelve 12 volt batteries in series This is really seventy-two 2 volt cell in series Which ever cell discharges first determines the capacity of the pack – if you have one weak cell your pack capacity will be reduced Once a cell is fully discharged the other cells are forcing current through it - which can cause futher damage Cell matching must be maintained to prevent premature discharge 45
  • 46. Wali Memon walimemon.comBatteries, Batteries, Batteries Battery Limitations Cell Matching Insist all batteries in a pack are from the same production batch and have not been sitting around in stock for too long Batteries should be kept at the same temperature  Difficult to do, especially with multiple battery boxes Cells within a battery should remain fairly matched if an equalizing charge is performed regularly Series (bulk) charging can cause batteries to get out of balance Charger per battery ensures all batteries are fully charged 46
  • 47. Wali Memon walimemon.com Thank YouWali Memonwalimemon.com 47