This document discusses the design and characteristics of electric car propulsion systems, focusing on various types of electric motors such as DC and AC motors, along with their efficiencies, torque-speed relationships, and braking methods. It highlights the advantages and disadvantages of different motor types, including brushless DC motors and switch reluctance motors, as well as the significance of battery technologies for powering electric vehicles, particularly emphasizing lithium iron phosphate batteries. The analysis culminates in evaluating motor specifications and performance to determine the best options for electric vehicle applications.

1. By
Ir. Raymond Wong
Building Service and Electrical Engineering Unit
Industrial Centre
Master of Science
in
Automotive Engineering Design
Electrical Car Propulsion
System

2.  A general term apply to all kind of electrical
appliances work with magnetic field
o Generator --- Mechanical - Electrical energy
conversion, rotary action
o Motor----------- Electrical – Mechanical energy
conversion, rotary action
o Transformer- Electrical – Electrical energy
conversion, no mechanical action
o Solenoid Electrical – Mechanical energy
conversion, linear action
Electric Machine-1

3. Motor is the most popular driving device
used in all kind of industry. In car industry we
only consider the small to medium power
driving (traction) motor.
Category of motor:
o DC motor--Shunt; Series; Separately excited;
Permanent magnet; Brushless
o AC Motor-- Induction; Permanent magnet
Synchronous; Switch Reluctance
Electric Machine-2

4. Essential parameters for a driving motor
are:
 Torque (Nm)
 Speed (RPM; rev/min)
 “Mechanical” Power (KW/HP) – function of Torque and
Speed
 “Electrical” Power
 Electrical rating: Voltage, Current, Frequency(AC)
o At 100% conversion efficiency, mechanical
power = Electrical power
Motor Characteristics

5. Constant Torque, to maintain the output
torque constant through out the entire speed
range, or to keep the torque curve as flat as
possible.
Sufficient large torque to reduce shift
requirement and transmission lost.
Wide speed range, reduce shift requirement
and provide large reserve power.
Fast response with the driving command
Low M.I. and gross weight.
Ideal Requirements of
a Car driving source

6.  It is difficult to
achieve constant
torque from a
internal combustion
engine.
 Engine output can
be roughly divided
into two region:
increasing and
decreasing torque
region.
Real Situation of
Car driving source - 1

7. As the torque is not constant,
transmission (speed change) become
necessary.
Both torque and power can be divided
into two region, but torque is more
important than power as it determines
the car driving behavior.
Engine torque curve can be more even
by using supercharge or turbo charge.
Real Situation of
Car driving source - 2

8. 
Real Situation of
Car driving source - 3

9.  Theoretically speaking, the output curve of an electric motor
is more linear than a combustion engine.
 Mechanical force to rotate the motor is generated by the
interaction of TWO magnetic fields
 At least one magnetic field will be generated by the supply
current. the other one may be generated by the supply
current, the induce current or a permanent magnet.
 Motor always consists of two parts: the rotor and stator. For
certain type of motor they may called as Field and Armature.
 In electrical engineering, an armature is classified as the
part of an alternator, motor or generator that produces
power, or the rotating part of a motor that emits electric
energy into a magnetic field.
Car Driving by a motor

10. DC MOTOR
N
S
·
·
·
·
·
·
N
S
DC Motor can be divided into
three major parts, the stator,
rotor and base.

11. DC motor Characteristics
It is a theoretical envelop, not
the actual output of a
particular motor
 DC motor torque speed relationship. However,
it is linear but not constant. Why?

12. DC Motor Output Curves-1
 From above diagram,
we can derive a
typical DC motor
characteristic
Field
Weakening
region

13. DC Motor Output Curves-2
Essential parameters:
1. V = E + IR (motor)
2. E = V – IR (generator)
Where
V = supply voltage
E = Back emf of winding
R = resistance of winding
Ia = armature current
R
V
Vr
E
 Motor speed and Torque:
Where N = speed (rpm)
Φ = flux (weber)
K = proportional constant
T = Motor Torque
T=KT Ia
I

14. DC Motor Types-1
1. Shunt motor: the field is
connected in parallel
with the armature.
2. Series motor: the field
is connect in series with
armature.

15. DC Motor Types-2
Separately Excited DC
Motor
Shunt motor can be
modified by connecting the
field circuit to a
independent power source.
Therefore, the field circuit
is allowed to have different
parameters to the
armature circuit. Such as
the different source voltage.

16. DC Motor Torque Balance-1
1. Shunt Motor and Separately
Excited DC Motor
If the load torque is increased, the
armature rotation will be slow
down momentarily. Hence the
back emf E will be decreased.
According to the motor eqt.
V=E+IR, V is a constant(power
source), if E is reduced the IR
part must be increased, that is,
I must be increased. The
torque is then increase for
compensation. The motor
speed will not change
significantly. This is very
important for constant speed
application.

17. DC Motor Torque Balance-2
The torque balance sequence
T2  n
Φ n
K
E E

E
a
a
a
R
E
U
I


Ia 
T  a
ΦI
K
T T


18. Shunt Motor Characteristics
Shunt Motor and Separately
Excited DC Motor
Family of the doted lines
represent the torque-speed
characteristics for a motor
driven by different voltages,
that is, the variable speed
control

19. Series Motor Characteristics
Series DC Motor
Similar to shunt motor
1. the increased load torque
causes the armature current
increase.
As the field winding is connected in
series with the armature, then
2. the field current hence the
magnetic field will be increased
also.

20. Selection priority of motor characteristics:
Speed? Torque? Power? Voltage? AC/DC?
Which one is better?

21. DC motor speed is significantly
affected by the field strength,
The speed is inversely
proportional to the field.
Therefore, series motor is the
optimum choice for various
speed application. Like vehicle
drive. With series motor, vehicle
can eliminate the most bulky
driving device: the gear box!
For Car Driving

22. Vehicle Drive in the Past
 In early years, electric car mainly uses DC
series motor as the main propulsion device.
 - the disadvantage: they need commutation.
 >>>commutator and carbon bushes need
frequent and “heavy” maintenance
 >>> cause high operation and maintenance
cost
 >>> system reliability is also reduced.

23. Commutator and Carbon Brushes

24. Commutator and Carbon Brushes
The rear end view of
1800Hp Separately excited
DC motor.
The motor is used as the
main drive power for a
aluminium hot rolling mill.
The typical commutator and
carbon brushes
arrangement
Thanks to Meyer Aluminum Ltd Co

33. What Motor Shall We Use?
What kind of motor is working without carbon
brushes? We have many choices. For example
we use AC induction motor, Switch reluctance
motor, Brushless DC Motor etc.
Is their characteristics better than DC series?
No, but not too bad if we can use certain
technologies to improve their performance: the
Power Electronic devices and switching control
systems.

34. AC induction Motor
Modern Design of AC Induction Motor, Totally Enclosed Fan Cool
(TEFC)

35. AC induction Motor
3-phase TEFC induction motors are the most popular
driving devises used in various engineering areas.
1. Induction motors have almost the lowest
manufacturing and operating cost.
2. In technical point of view, they are robust and easy
to use.
The disadvantages:
Low Starting torque as the rotor (armature) current
(the torque) is only “induced” from the magnetic field.
It is not directly connected to the power source.

36. AC induction Motor-1
The rotational
magnetic field
created by 3-
phase voltage
A 4-pole
construction
The squirrel
cage rotor

37.  Magnetic field is generated first in the stator of the
motor. As the AC field is varying from phase to phase
in a fix frequency. This will induce EMF in rotor winding
(coil) hence produces currents.
 To increase motor efficiency we need to make use of
the current to produce sufficient torque. There are 2
methods:
 (1)- Small current but a large turn nos. of winding
 (2). Large current but a small turn nos. winding
 (1) is called Wound Rotor motor (less popular)
 (2) is called Squirrel Cage motor (more popular)
AC induction Motor-2

38.  Torque –speed curve
could not be a straight
line because of the
induction process.
 How about the motor
speed?
 Motor speed is only
affect by the
rotational speed of
the magnetic field!
Not Voltage nor
Current
AC induction Motor-3

39.  The induction motor speed control can only be
obtained by changing the AC frequency. How do we
change the frequency? There is no short-cut! We
need to re-generate the AC power with frequency we
wanted. Traditional way is using a system that has a
motor mechanically connect to a generator.
Induction Motor Speed Regulation-1

40.  Now we do this easily. There is a kind of devise can
first convert the supplied AC to DC, then “invert” the
DC to AC with the frequency we wanted, which is
called “Frequency inverter”, “Variable Frequency
Drive
Induction Motor Speed Regulation-2

41.  Inverter’s contribution is not only changes the motor
speed but optimize the motor output characteristics.
See diagrams used before
Induction Motor Speed Regulation-3
For the motor directly powered by
50Hz AC, i.e. the red curve, we
can only drives a load at the
torque below 6.5Nm.
As inverters are electronic device,
we can adjust the frequency easy
and smoothly. Try to think if the
frequency is vary from 0Hz to
50Hz gradually, the motor output
will follows the 5 curves from left
to right. Actually we can use the
step in 1Hz to have more curves
and make it smooth. Thus we can
raise the load torque to about
25Nm!

42.  Moreover, with inverter the induction can be
operate at variable torque.
 Recall DC motor curve:
Induction Motor Speed Regulation-4
Constant torque
Variable Power Region
Variable torque
Constant Power Region

43.  Induction motor has a drawback for electric car
application. It takes a part of input power to establish a
magnetic field hence reduces the energy efficiency. The
way to improve this is to use a motor with permanent
magnet. A very strong magnet made by rare earth metals.
Actually it is very similar to a separately excited DC
motor.
Brushless DC Motor
Commutation is still required for the motor but we
can eliminates the needs of commutator and carbon
brushes. But how?
We can mount the magnet on the moving rotor and
the armature on the fixed stator. If there is a sensor
to sense the position of magnetic poles, we can use
switches to change the current direction in the fixed
armature.

44. SRM is theoretically better than induction motor and
brushless motor. The advantages are:
Switch Reluctance Motor-1
1. High robustness as no winging and brushes in rotor
2. High temperature rise as no permanent magnet
3. Current in one direction, simple switching control
4. Small Inertia
5. Large speed range
6. Allow frequent Start/Stop operation
7. Low starting current but high torque
8. High efficiency

45. Switch Reluctance Motor-2
Disadvantages of SRM:
1.Pole alignment cause pulsation torque
2.High noise generate from motor and driver
3.Less power density and less efficiency compare
with permanent magnet motors (BLDC motor)
4.Need position transduce (sensor) hence lower
reliability

46.  A transportation device such as a car, normally
we need to drive it in forward direction and
backward direction. These occupies 2
quadrants of operation. Further, if we need to
stop/brake the car, we need forward braking
Car Driving Requirement
 and reverse braking
operation. Therefore, for a
motor operation there are 4
quadrants of operation in
max.

47.  Simply speaking, 4 quadrant operation for a
driving system means:
 1. Forward motoring
 2. Forward braking
 3. Reverse motoring
 4. Reverse Braking.
 Driving a motor is natural. But how about
braking? Dose it mean a mechanical brake?
Car Driving Requirement - 1

48.  A mechanical brake is necessary for any kind
vehicles. But here the word “brake” means the
electrical methods to brake / stop a car. How?
 To brake a moving vehicle, we need to absorb,
convert or to dissipate the car Kinetic energy.
Since an electric motor can be an electric
generator naturally, the handling of Kinetic
energy is actually the handling of electric
energy generated by the motor.
Car Driving Requirement - 2

49. There are 4 ways to brake a electric motor
Car Driving Requirement - 3
Types of
Braking
Details Advantage Disadvantage
Plugging To reverse the motor rotational
direction at braking
Instantly stops
the motion
Great
mechanical
impact
Dynamic
Braking
Using resistance devices to
dissipate the electric energy
Simple control Less energy
efficiency
DC
injection
Braking
Inject DC into motor winding.
Energy dissipated by eddy
current circulation
Easy to
implement,
less bulky
Poor energy
efficiency
Re-
generation
Braking
Use power electronic devices
to send back the energy to the
power source
Good braking
effect and high
energy
efficiency
Complicate
and high
costs

50. Thanks to the technology improvement, present
power electronic technologies are very mature. 4-
quadrant motor controller is almost a standard
equipment for high demand driving control.
In most cases, re-generation braking is the
optimum braking for electric car as it can save a
very critical resource: the battery energy.
Is the regeneration energy easy to store? No, but
we will discuss it later.
Car Driving Requirement - 4

51. Car Driving Requirement - 5
 Understand the essential motor specification,
especially those appeared on the name plate.
 Power: the output mechanical power = input
power x efficiency
 Voltage: Nominated input voltage
 Current: Current at full load
 RPM: Maximum rotational speed
 Cos θ: The power factor
 Duty: S_x, e.g. S1 means continuous operation
 Class: Insulation temperature, e.g. F = 1550C

52. Car Driving Requirement - 6
 What type motor is the best for electric car?
 It depends on the design requirement
Motor
Performance
DC
Series
DC Shunt DC-PM AC Induction SRM PM-
Synchronous
Brushless DC
Starting 5 4 4 2 4 3 4
Low seed characteristic 5 4 4 3 4 3 4
Operation efficiency 3 3 4 3 4 5 5
Average efficiency 3 3 4 4 3 5 5
Power density 2 2 3 4 4 4 5
Overload Characteristic 4 4 4 4 4 4 5
Power regeneration 3 5 4 3 2 5 5
Reliability 2 2 2 5 5 4 4
Motor cost 4 4 4 5 5 4 4
Controller cost 5 5 5 3 3 4 4
Total Score 36 36 38 36 39 41 45

53. The Energy Source - 1
 Most of the electric car are power by batteries. The traditional
type of battery is the rechargeable Lead-Acid battery, which is
very robust and low cost. The other type of batteries are Ni-Cd,
Nickel metal hybrid and Lithium ion rechargeable batteries.
 At present time, LiFeSO4 Lithium Iron Phosphate or LFP(磷酸鐵
鋰電池) is the most appropriate types of battery for electric car
application. The advantages of it are:
1. Long life. 2000 cycle life compare to 200-500 of Long-
life lead-acid battery with standard charge (5 hours
rate) Under same conditions, LPF has 7-8 years life
compare to 1-1.5 years of lead-acid batteries. There
are 4 times improvement of the cost performance.

54. The Energy Source - 2
2. Safe for using. Even in the worst traffic accident it will not
produce an explosion.
3. Can be high current 2C fast charge and discharge, under
the dedicated charger, 1.5C within 40 minutes you can
recharge the battery full, the starting current could up to
2C,
4. Can be used in high temperature, lithium iron phosphate
peak heating up to 350 ℃ -500 ℃ and the lithium
manganese oxide and lithium cobalt only about 200 ℃.
5. High-capacity.
6. No memory effect.
7. Small size and light weight.
8. Green for environmental protection.

55. The Energy Source - 3
Disadvantages of LFP:
1. Poor conductivity, lithium-ion diffusion is slow. High-rate charge and
discharge, the actual specific capacity is low.
2. Tap and lower density. General can only achieve 0.8-1.3, low tap density
LFP can be said that a significant drawback. There is no advantage use as
cell phone batteries but good for power battery.
3. Consistency problem is serious. Single lithium iron phosphate battery life
is currently more than 2,000 times, but the consistency of the battery
produced poor, thereby affecting the use of battery performance and
overall life expectancy.
4. Low-temperature performance of LFP is bad. Under normal conditions
the capacity at 0 ℃ >> 60 ~ 70%, -10 ℃ >> 40 ~ 55%, -20 ℃ ~ 40%.

56. The Energy Source - 4
Disadvantages of LFP:
5, manufacturing costs are high. Lithium iron phosphate has
safety, environmental protection, cycles of higher benefits is not
in doubt, but the current production costs are relatively lead-acid
batteries, lithium manganese batteries is higher, mainly due to:
1)material physical properties, and other lithium battery materials
difference between the larger, its size is small,
2)2), lithium iron phosphate battery is only 3.2V, low power than
other lithium about 20%, single cell to multi-purpose 20%,
resulting in the composition of the increase in the battery
numbers.

57. The Energy Source - 5
Charging the LFP:
1. LFP has a nominal open-circuit voltage of 3.2 V and a
typical charging voltage of 3.6 V. Lithium nickel
manganese cobalt (NMC) oxide cathode with graphite
anodes have a 3.7 V nominal voltage with a 4.2 V max
charge. The charging procedure is performed at constant
voltage with current-limiting circuitry (i.e. charging with
constant current until a voltage of 4.2 V is reached in the
cell and continuing with a constant voltage applied until the
current drops close to zero). Typically, the charge is
terminated at 3% of the initial charge current.

58. The Energy Source - 6
Charging the LFP:
Stage 1: Apply charging current until the voltage limit per cell is
reached. (CC)
Stage 2: Apply maximum voltage per cell limit until the current
declines below 3% of rated charge current (CV)
Stage 3: Periodically apply a top-off charge about once per 500
hours
Charge time>>3-5 hours depend on the charger. But it can be left
indefinitely depending on desired charging time. Some fast chargers
skip stage 2 and claim the battery is ready at 70% charge
Top-off charging is recommended when voltage goes below 4.05
V/cell

59. A single Li-ion cell is charged in 2 stages
(1).CC
(2).CV
A Li-ion battery (a set of Li-ion cells in series) is
charged in 3 stages:
(1).CC
(2).Balance (not required once a battery is balanced)
(3).CV
The Energy Source - 7

60. Stage 1: CC: Apply charging current to the battery, until the
voltage limit per cell is reached.
Stage 2: Balance: Reduce the charging current (or cycle the
charging on and off to reduce the average current) while the
State Of Charge of individual cells is balanced by a balancing
circuit, until the battery is balanced.
Stage 3: CV: Apply a voltage equal to the maximum cell voltage
times the number of cells in series to the battery, as the current
gradually declines asymptotically towards 0, until the current is
below a set threshold
The Energy Source - 8

61. The Energy Source - 9
LFP Charging Curves:

62. Battery Chargers
The battery chargers for a electric car be designed as
inboard or off-board types. Inboard design are more
popular as the charging point will be city main format.
In Hong Kong it will be 220V 13A.
Electric car driving system voltage may higher than
the charging voltage. This implies that the BMS and
charging circuit should able to provide different
connection scheme to match with the voltage.
For the limitation of current, onboard chargers may
only provide CV charging but off-board chargers can
be more powerful.

63. Battery Management
Battery management system (BMS) is not critical to
Lead-acid batteries but very important to LFP. LFPs
are easily be damaged by over-charging and
discharging. Therefore, a management system to
control the charging and discharging process is
necessary.
BMS will monitoring the current, voltage and
temperature for each of the battery cell. Once
abnormal values are detected, BMS will isolate or
bypass the cell to protect the whole system and avoid
vital accidence from happens.

64. A hybrid vehicle is a vehicle that uses two or
more distinct power sources to move the
vehicle.
The term most commonly refers to hybrid
electric vehicles (HEVs), which combine an
internal combustion engine and one or more
electric motors
Hybrid Car

65. Power sources for hybrid vehicles include:
 On-board or out-board rechargeable energy storage system
(RESS)
 Coal, wood or other solid combustibles
 Electricity
 Electromagnetic fields, Radio waves
 Compressed or liquefied natural gas
 Human powered e.g. pedaling or rowing
 Hydrogen
 Petrol or Diesel fuel
 Solar
 Wind
Hybrid Car

66. Hybrid vehicle power train configurations
Parallel hybrid-1
 single electric motor and the internal
combustion engine are installed such that
they can power the vehicle either individually
or together.
 Most commonly the internal combustion
engine, the electric motor and gear box are
coupled by automatically controlled clutches
Hybrid Car

67. Hybrid Car
Parallel hybrid-2
For electric driving the clutch between the
internal combustion engine is open while
the clutch to the gear box is engaged. While
in combustion mode the engine and motor
run at the same speed.

68. Hybrid Car
Mild parallel hybrid
Usually powered by
compact electric motor
(<20 kW) to provide auto-
stop/start features and
to provide extra power
assist during the
acceleration, and to
generate on the
deceleration phase
(regenerative braking).
The Honda Insight is a Mild Parallel Hybrid

69. Hybrid Car
Power-split or series-parallel
hybrid
Power from electric motor and
combustion engine can be
shared to drive the wheels via a
power splitter, which is a simple
planetary gear set. The ratio can
be from 0–100% between the
combustion engine and the
electric motor. The electric motor
can act as a generator charging
the batteries.
The Toyota Prius is a series-
parallel hybrid

70. Hybrid Car
Series hybrid
Also call Extended Range
Electric Vehicle or Range-
Extended Electric Vehicle
(EREV/REEV).
the electric motor with no
mechanical connection to the
engine. Instead there is an
engine tuned for running a
generator when the battery
pack energy supply isn't
sufficient for demands.
The Chevrolet Volt is a series
plug-in hybrid released at the
end of 2010

71. Car Driving System Design-1
 Car information prior to the design
1. Gross weight
2. Maximum speed
3. Cruise speed
4. Acceleration requirements
5. Types of the car or the car outline
6. Wheel information
7. Drive scheme or the car use pattern
8. Energy supply scheme
9. Types of energy storage devices
10. Capacity of stored energy
11. Energy recovery scheme

72. Car Driving System Design-2
 Design Calculations:
 1. The power/weight ratio:
 (Where Pe is the total engine power and GL is the total car weight in ton)
 2. Driving force F at constant speed:
 F＝mgf十CdAua2／21.15 (1)
 f＝0．014*(1十ua2／19440) (2)
 where m = mass of the car, g = 9.81, Cd = windage coefficient, ua = speed,
A = forward project area of the car.

73. Car Driving System Design-3
 Design Calculations:
The driving force calculated from (1) is the traction force the
wheel exerted on the ground. To convert the force to engine
torque we need to know to wheel diameter. Example of
practical wheel specification for private cars is:
225/45R17
225 = Indicated section width = 225mm
45 = aspect ratio = ratio of section height to
section width = 0.45 x 225 = 101.3mm
R17 = Rim diameter in inches = 17 x 25.4 =
431.8mm
Overall wheel diameter = (101.3 x 2) + 431.8
= 634.4mm

74. Car Driving System Design-4
 Calculation examples: we are going to design an electrical car
with following information:
 weight = 1100kg
 Motor = BLDC, 25KW(*peak 60KW), 288VDC, 4000RPM
 Battery = LFP 60AH, 3.2V x 90 pcs
 wheel diameter = 585mm
 Windage coefficient = 0.32.
 Forward projection area = 1.8 sqm
 Please estimate:
 1. the gear/final reduction ratio at 100 and 70 KM/H
respectively.
 2. Starting traction force for 0-100KM acceleration
 3. The max. mileage/driving time

75. Car Driving System Design-5
 100Km/h:
 Traction force required is about 501N (by (1) and (2))
 The rated motor output torque is 60Nm (at 25KW)
 For 585mm wheel diameter (292.5mm radius) the
traction force at ground is 205N.
 Final reduction ratio = 501 / 205 = 2.45
 For 100km/hr speed the wheel rotation speed is
906rpm. The motor speed is 2.45 x 906 =
2219.7rpm, the corresponding motor output power
will be:
 60 / 9.81 * 2219.7 = 13.58Kw


76. Car Driving System Design-6
 70Km/h:
 Traction force required is about 322.6N (32.88kgf).
 The rated motor output torque is 60Nm.
 For 585mm wheel diameter (292.5mm radius) the traction force at
ground is 205N.
 Final reduction can be reduced to 1.57. But 100Km/h is the
design maximum speed, the final reduction ratio 2.45 has to
be maintained.
 For 70km/h speed the wheel rotation is 635rpm. The motor speed
is 2.45 x 635 = 1556rpm, then
 Driving torque before reduction: 322.6 * 0.2925 / 2.45 =
38.52Nm
 motor output torque will the corresponding motor output
power will be:
 38.52 / 9.81 * 1556 = 6.11Kw

77. Car Driving System Design-7
 Calculation of starting traction force (0-100km/h)
 Assume the acceleration a = 0.2
 Since V = u + at
 Therefore acceleration time t = 100kmh / (0.2 x 9.81) =
14.15 sec
 Acceleration force F = ma = 1100 x 0.2 = 220kgf x 9.81 =
2158.2N
 Acceleration friction fs = 0.1 x gross weight = 0.1 x 1100
= 110kgf = 1079N
 Required driving force = 2158.2 + 1079 = 3237N
 Required motor torque = 3237N x 0.2925m = 947Nm

78. Car Driving System Design-8
 Peak battery current is 180A up to 1200A. The motor max. current is 190A. >> the
motor power which is allowed to output max. torque at 130Nm
 Reduction ration required = 947 / 130 = 7.29
 The 1st shift ratio will be 2.98 plus 2.45 final reduction)
 Total energy supply by battery system is 60A x 288V = 17280VAH
 Energy consumption during acceleration is:
 60KW x 14.15sec /3600 = 235.8VAH
 Energy consumption for 0.5 hour drive at constant speed 100km/h is:
 13.5kwh / 2 = 6750VAH
 Energy consumption for 0.5 hour drive at constant speed 70km/h is:
 6.12kwh /2 = 3060VAH
 For driving cycle with 10 accelerations and 1 hour combined constant speed
drive. Assume overall energy loss is 20%
 (235.8 * 10) + 6750 + 3060 = 12168VAH /0.8 = 15210VAH
 Total driving time:
 17280 / 15210 = is 1.136 hours

79. Car Driving System Design-9
 The mileage of electric car can be extended by braking
power recovery. But batteries cannot absorb energy at a
short time. We need the help of supercapacitor.
 The super capacitor, also known as ultracapacitor or double-
layer capacitor, differs from a regular capacitor in that it has
a very high capacitance. There are 3 types of capacitor: the
most basic is the electrostatic capacitor with capacitance
from pf to uF. The next one is electrolytic capacitor rate in
uF. Its capacitance is several thousand times higher than
electrostatic type. The third one is the supercapacitor, rated
in F, which is thousands of times higher than the electrolytic
type capacitor.
 The storage power of supercapacitor is less than battery but
very close. Its advantage is the fast operation speed.

80. Car Driving System Design-10
 For above example, capacity of a supercapacitor system
can be estimated as:
1. K.E. of the car at 100Km/h and 70 Km/h are:
 1/2 * 1100 * 27.782 = 424kj
 1/2 * 1100 * 19.442 = 208kj
1. For a 7 second braking time of 100Km/h, the average braking power is:
 424/7 = 60.57KW ≒ 60KW
1. Capacitance required: (assume 0.8 conversion efficiency)
 424kj * 0.8 = 339.2kj
 339.2kj = 1/2 * C * 1922
 C = 18.4F

81. Car Driving System Design-12
 Notes in determine the specification and driving system
elements:
 1. Voltage should be as high as possible. This will
significantly reduce the current hence the size of the
conductor. Another advantage of this is that the current
switching burden of power electronic element such as
IGBT can be reduce and increase the reliability
 2. Motor power rating can be boost up to 2 times, even
more, of the nominated values especially the BLDC.
The limitation is only the cooling of motor. For car to be
used under severe conditions we even need to consider
water cooling systems.

82. Driving System integration-1
Voltage
Selection Charger
Driver
Driver
Motor
Gear
Motor
Gear
Battery Unit BMU
Drive
Controller
Shaft
Encoder
Accelerator
Brake
Steering
sensor
A system integration design approach for a electric
car driven by dual hub motors

83. Driving System integration-2
 Communication in between different parts of the
integrated system
 Can stands for “Controller–area network”. It is a message-
based protocol, designed specifically for automotive
applications and other areas.
 CAN is a multi-master broadcast serial bus standard for
connecting electronic control units (ECUs).
 Bit rates of CAN up to 1 Mbit/s are possible at network
lengths below 40 m. Decreasing the bit rate allows longer
network distances
 * CAN cannot eliminate the direct connection of essential
control signals such as braking and emergency signals.