UNIT-2

Components of Electric Vehicles

Main components of Electric Vehicles
Electric vehicles consist of electric motor that is powered by a battery pack. The main advantage
of electric vehicles is that they emit zero emissions and are eco-friendly. They also do not
consume any fossil fuels and use a sustainable form of energy to power their car. The main
components of electric vehicles are :
1. Traction battery pack
2. DC-DC Converter
3. Electric motor
4. Power inverter
5. Charge Port
6. Onboard charger
7. Controller
8. Auxiliary batteries
9. Thermal system (cooling)
10. Transmission
1. Traction battery pack

A traction battery pack is also known as an Electric vehicle battery (EVB). It powers the electric
motors of an electric vehicle. The battery acts as an electrical storage system. It stores energy in
the form of DC current. The range will be higher with increasing kW of the battery. The life and
operation of the battery depending on its design. The lifetime of a traction battery pack is
estimated to be 200,000 miles.

2. DC-DC Converter

The traction battery pack delivers a constant voltage. But different components of the vehicle
have different requirements. The DC-DC converter distributes the output power that is coming
from the battery to a required level. It also provides the voltage required to charge the auxiliary
battery.

3. Electric motor

The electric traction motor is the main component of an electric vehicle. The motor converts
electrical energy into kinetic energy. This energy rotates the wheels. An electric motor is the
main component that differentiates an electric car from a conventional car. An important feature
of an electric motor is the regenerative braking mechanism. This mechanism slows down the
vehicle by converting its kinetic energy into another form and storing it for future use. There are
basically two types of motors DC and AC motors.

4. Power Inverter
It converts DC power from the batteries to AC power. It also converts the AC current generated
during regenerative braking into a DC current. This is further used to recharge the batteries. The
inverter can change the speed of the

5. Charge Port

The charge port connects the electric vehicle to an external supply. It charges the battery pack.
The charge port is sometimes located in the front or rear part of the vehicle

6. Onboard charger

The onboard charger is used to convert the AC supply received from the charge port to the DC
supply. The onboard charger is located and installed inside the car. It monitors various battery
characteristics and controls the current flowing inside the battery pack.

7. Controller

The power electronics controller determines the working of an electric car. It performs the
regulation of electrical energy from the batteries to the electric motors. The pedal set by the
driver determines the speed of the vehicle and the frequency of variation of voltage that is input
to the motor. It also controls the torque produced.

8. Auxiliary batteries

Auxiliary batteries are the source of electrical energy for the accessories in electric vehicles.
Without the main battery, the auxiliary batteries will continue to charge the car. It prevents the
voltage drop, produced during engine start from affecting the electrical system.

9. Thermal system(cooling)

The thermal management system is responsible for maintaining an operating temperature for the
main components of an electric vehicle such as an electric motor, controller, etc. It functions
during charging as well to obtain maximum performance. It uses a combination of thermoelectric
cooling, forced air cooling, and liquid cooling.

10. Transmission

It is used to transfer the mechanical power from the electric motor to the wheels, through
a gearbox. The advantage of electric cars is that they do not require multi-speed transmissions.
The transmission efficiency should be high to avoid power loss.
Power Converters
With the focus on vehicular technology shifting towards replacing mechanical, hydraulic, or
pneumatic systems with electrical systems, power electronic circuits (PECs) have gained a lot of
importance in the last decade. Increasing vehicular loads such as utility, entertainment, luxury,
and safety loads have increased the demand for compact and efficient PECs. The electric
components inside the vehicle vary in their voltage requirements, with a majority of them
running on lower voltages. This includes the radio, dashboard readouts, air conditioning, and in-
in
built computers and displays.

Types of Power Converters in Electric Vehicles

Commercial electric vehicles may be broadly classified as:
Battery electric vehicles (BEVs),
Hybrid electric vehicles (HEVs) and
Fuel cell vehicles (FCVs).
BEVs are purely electric vehicles (EVs), whereas HEVs combine EVs and internal combustion
engines (ICEs). FCVs use power from both the battery and fuel cell stack.
The different configurations of EV power supply show that at least one DC/DC converter is
necessary to interface the FC, the battery, or the supercapacitors module to the DC-link.
DC

he main components of an Electric Vehicle are a DC-AC inverter, a DC-DC DC converter, a battery,
and an electric motor.
There are two major power electronic units in the general configuration
DC-DC converter
DC-AC inverter
Usually, AC motors are used in HEV HEVss or EVs for traction and they are fed by an inverter and it is
fed by a DC-DC converter.
DC-DC Converters
DC-DC converters in an electric vehicle may be classified into unidirectional and bidirectional
converters. Unidirectional DC-DC DC converters cater to various onboard loads such as sensors,
controls, entertainment, utility, and safety equipment. They are also used in DC motor drives and
electric traction. Bidirectional DC
DC-DC converters find applications in places where battery
charging, regenerative braking, and backup power are required. The power flow in a
bidirectional converter is usually from a low voltage end such as a battery or a super capacitor to
a high voltage side and is referred to as boost operation.
During regenerative braking, the power flows back to the low voltage bus to recharge the battery
(buck mode). As a backup power system, the bidirectional DC DC-DC
DC converter facilitates the safe
operation of the vehicle when ICEs or electric drives fail to drive the motor. Due to the
aforementioned reasons, high-po power bidirectional DC-DC
DC converters have gained a lot of
importance in the recent past.
The converter topologies are classified as:
Buck Converter:
The buck converter is a step
step-down
down converter and produces a lower average output voltage
than the dc input voltage.
Boost converter:
In the boost converter, the output voltage is always greater than the input voltage.
Buck-Boost converter:
In a buck-boost
boost converter, the output voltage can be either higher or lower than the input
voltage.
Cuk converter:
The output voltage can be either higher or lower than the input voltage providing some
advantages over buck-boost (likee a continuous current, less current ripple etc.)
SEPIC converter:
The output voltage can be either higher or lower than the input voltage (with no polarity
reversal compared to Buck-boost
boost or Cuk converter).

Isolated DC-DC converter:

In this type, the input and output stages are separated and there is a presence of a
transformer which can further reduce (or increase) the output voltage apart from being done by
the duty cycle. Forward, Flyback, Half bribridge, Full bridge, and Push-pull
pull converters fall under
this category.

The amount of power flow between the input and the output can be controlled by adjusting the
duty cycle (ratio of on/off time of the switch). Usually, this is done to control the output voltage,
the input current, and the output current or to maintain constant power.
The Importance of DC/DC Converters

While DC/DC converters can be based on several different designs, the underlying function
remains the same. A step-up up converter, w
which turns a low-voltage
voltage input into a high-voltage
high
output, or a step-down
down converter, which does the exact opposite.
In electric vehicles that use a DC motor, the running motor can use up to three times the voltage
provided by the battery. With the help of the right converter, we can bridge this gap without
having to use a larger, heavier battery.

DC-AC converters (Inverters)

An inverter is a device that converts DC power from the battery to AC power in an electric
vehicle motor. The inverter can change tthe
he speed at which the motor rotates by adjusting the
frequency of the alternating current.

The Significance of DC/AC Converters

The use of inverters can increase or decrease the power or torque of the motor by adjusting the
amplitude of the signal.
It plays a significant role in capturing energy from regenerative braking and feeding it back to
the battery. The key component is that it has a direct impact on onon-road
road performance, driving
range, and reliability of the vehicle also as a consequence of th
their
eir weight and size.
The output voltage waveform of ideal inverters should be sinusoidal. However, the waveform of
practical inverters is non-sinusoidal
sinusoidal and contains certain harmonics.

Controller and Electric Traction Motor

EV Power Systems (Motors and controllers)
The power system of an electric vehicle consists of just two components: the motor that
provides the power and the controller that controls the application of this power. In
comparison,the power system of gasoline
gasoline-powered
powered vehicles consists of a number of
 components, such as theengine, carburetor, oil pump, water pump, cooling system, starter,
exhaust system, etc.
Motors
Electric motors convert electrical energy into mechanical energy. Two types of electric
motors are used in electric vehicles to provide power to the wheels: the direct current (DC)
motor andthe alternating current (AC) motor.

DC electric motors have three main components:

 A set of coils (field) that creates the magnetic forces which provide torque
 A rotor or armature mounted on bearings that turns inside the field
 Commutating device that reverses the magnetic forces and makes the armature
turn,thereby providing horsepower.
As in the DC motor, an AC motor also has a set of coils (field) and a rotor or armature,
however, since there is a continuous current reversal, a commutating device is not needed.
Both types of electric motors are used in electric vehicles and have advantages and
disadvantages, as shown here.
While the AC motor is less expensive and lighter weight, the DC motor has a simpler
controller,making the DC motor/controller combination less expensive. The main
disadvantage of the AC motor is the cost of the electronics package needed to convert (invert)
the battery‘s direct current to alternating current for the motor.
Past generations of electric vehicles used the DC motor/controller system because they
operateoff the battery current without complex electronics. The DC motor/controller system
is still used today on some electric vehicles to keep the cost down.
However, with the advent of better and less expensive electronics, a large number of today’s
electric vehicles are using AC motor/controller systems because of their improved motor
efficiency and lighter weight.
These AC motors resemble motors commonly used in home appliances and machine tools,
and are relatively inexpensive and robust. These motors are very reliable, and since they have
only one moving part, the shaft, they should last the life of the vehicle with little or no
maintenance.

Electric Motor Comparison

AC Motor DC Motor
Single – speed transmission Multi-speed transmission
Light weight Heavier for same power
Less expensive More expensive
95% efficiency at full load 85-95$ efficiency at full load
More expensive controller Simple controller
Motor/Controller/Inverter more expensive Motor/controller less expensive
Controllers
The electric vehicle controller is the electronics package that operates between the batteries
andthe motor to control the electric vehicle‘s speed and acceleration much like a carburetor
does ina gasoline-powered vehicle. The controller transforms the battery’s direct current into
 alternating current (for AC motors only) and regulates the energy flow from the battery.
Unlikethe carburetor, the controller will also reverse the motor rotation (so the vehicle can go
in reverse), and convert the motor to a generator (so that the kinetic energy of motion can be
used to recharge the battery when the brake is applied).

In the early electric vehicles with

DC motors,a simple variable-
resistor-type controller controlled
the acceleration and speed of the
vehicle. With this type of
controller, full current and power
was drawn from the battery all of
the time. At slow speeds, when full
power was not needed, a high
resistance was used to reduce the
current to the motor. With this type
of system, a large percentage of the
energy from the battery was wasted
as an energy loss in the resistor.
The only time that all of the
available power was used was at
high speeds.

Modern controllers adjust speed and acceleration by an electronic process called pulse width
modulation. Switching devices such as silicone-controlled rectifiers rapidly interrupt (turn on and
turn off) the electricity flow to the motor. High power (high speed and/or acceleration) is
achieved when the intervals (whenthe current is turned off) are short. Low power (low speed
and/or acceleration) occurs when theintervals are longer.

The controllers on most vehicles also have a system for regenerative braking. Regenerative
braking is a process by which the motor is used as a generator to recharge the batteries when
thevehicle is slowing down. During regenerative braking, some of the kinetic energy normally
absorbed by the brakes and turned into heat is converted to electricity by the motor/controller
and is used to re-charge the batteries. Regenerative braking not only increases the range of an
electric vehicle by 5 - 10%, it also decreases brake wear and reduces maintenance cost.
Bi Directional DC-DC Converter

The different configurations of EV power supply show that at least one DC/DC converter is necessary to
interface the FC, the Battery or the Supercapacitors module to the DC-link.

In electric engineering, a DC to DC converter is a category of power converters and it is an electric

circuit which converts a source of direct current (DC) from one voltage level to another, by storing the input
energy temporarily and then releasing that energy to the output at a different voltage. The storage may be in
either magnetic field storage components (inductors, transformers) or electric field storage components
(capacitors).

DC/DC converters can be designed to transfer power in only one direction, from the input to the output.
However, almost all DC/DC converter topologies can be made bi-directional. A bi-directional converter can
move power in either direction, which is useful in applications requiring regenerative braking.

The amount of power flow between the input and the output can be controlled by adjusting the duty
cycle (ratio of on/off time of the switch). Usually, this is done to control the output voltage, the input current,
the output current, or to maintain a constant power. Transformer-based converters may provide isolation
between the input and the output. The main drawbacks of switching converters include complexity, electronic
noise and high cost for some topologies. Many different types of DC/DC power converters are proposed in
literature (Chiu & Lin, 2006), (Fengyan et al., 2006). The most common DC/DC converters can be grouped as
follows:

3.1. Non-isolated converters

The non-isolated converters type is generally used where the voltage needs to be stepped up or down by
a relatively small ratio (less than 4:1). And when there is no problem with the output and input having no
dielectric isolation. There are five main types of converter in this non-isolated group, usually called the buck,
boost, buck-boost, Cuk and charge-pump converters. The buck converter is used for voltage step-down, while
the boost converter is used for voltage step-up. The buck-boost and Cuk converters can be used for either step-
down or step-up. The charge-pump converter is used for either voltage step-up or voltage inversion, but only in
relatively low power applications.

3.2. Isolated converters

Usually, in this type of converters a high frequency transformer is used. In the applications where the
output needs to be completely isolated from the input, an isolated converter is necessary. There are many types
of converters in this group such as Half-Bridge, Full-Bridge, Fly-back, Forward and Push-Pull DC/DC
converters (Garcia et al., 2005), (Cacciato et al., 2004). All of these converters can be used as bi-directional
converters and the ratio of stepping down or stepping up the voltage is high.
 Block Diagram for Bi Directional DC-DC Converter:

Voltage Source Inverter

1. Two-Level PWM DC-AC Inverters (TLIs) Topologies

The two-level PWM DC-AC inverter (TLI) topologies can be classified as hard-switching and soft-switching
inverters, according to their power switching features.
Hard Switching Topologies
In hard-switching topologies, the power semiconductor devices are connected either to a stiff voltage
source inverter (VSI), as shown in Figure 5 or to a current source inverter (CSI), as shown in Figure 6 , or
impedance source inverter (ISI), as shown in Figure 7 . A VSI is essentially used to invert a constant DC
voltage into an AC
voltage with an adjustable magnitude and frequency. VSIs and CSIs have some restrictions; thus, they are not
appropriate for some types of applications. For example, VSIs cannot boost the voltage level, and CSIs
cannot decrease the voltage level; therefore, they cannot work independently for a variety of applications.
Furthermore, sudden variations in the switch voltages and currents cause severe switching losses and EMI
problems on the switching devices and for the motor supplied from the VSI or CSI.

S S S

C
Vdc B EVM
A

S S S

Figure 5. Three-phase voltage source inverter (VSI) topology.

L D S1 S3 S5

C
Vdc SB C B EVMD
A

S4 S6 S2

Figure 6. Three-phase current source inverter (CSI) topology.

An impedance source inverter is distinguished by the presence of an impedance network constituted by

capacitors and inductors between the input source and the inverter bridge. The ZSI has the specific ability to
use inverter switches to increase the DC-bus voltage. An ISI circuit can turn into a VSI circuit if both
inductances have zero value. However, an ISI can become a CSI if both capacitors have zero capacitance.
Consequently, ISIs have more flexibility in regulating the output AC voltage than VSIs and CSIs. Moreover,
ISIs can overcome the restrictions of VSIs and CSIs by maintaining a smaller size than the DC-DC
patterned PWM inverter. The ISI produces the necessary voltage level for an EV motor by monitoring
the battery state-of-charge (SOC) and regulating the output power all at once. The addition of LC
impedance network increases the cost and volume of the converter. The ISI for electric vehicle
applications is shown in Figure 7 . ISIs have a lower rating of switching devices for a low boost ratio
ranging from 1 to 2.

L1
D S1 S3 S5
C C

C
Vd A
B EVM

L2 S4 S6 S2

Figure 7. Three-phase impedance source inverter (ISI) topology.

Another type of DC-AC inverter is the two-boost inverter (TBI), with Figure 8 demon- strating the circuit
diagram .The DC inputs of two boost DC-DC power converters are connected in parallel with a DC
supply, and the load is connected across the two outputs. Both converters are modulated to generate
unipolar DC-biased sinusoidal outputs that are out-of-phase with the other by 180°. Thus, the output voltage
across the load shapes a pure sinusoidal waveform. Usually, a sliding mode control can be employed to
enhance the dynamic performance of the inverter .
Load

Vo
S1 S3
V1 V2

L1 L2
C1 C2

S4 S2
Vdc
Boost 1 Boost 2

Figure 8. Single-phase two boost inverter (TBI) topology.

The disadvantages of hard-switching VSI, CSI, ISI, and TBI PWM inverters are :
• The switching devices in VSI, CSI, ISI, and TBI PWM inverters are required to be controlled at a
higher switching frequency to achieve low harmonic distortion in the output voltages and currents.
• Switching losses are high owing to the operation at a higher switching frequency. The VSIs and CSIs
are controlled from a small number of kHz up to approximately 100 kHz, while the ISIs and TBIs are
usually switched at 20 kHz and higher to realize lower harmonic distortion at the output.
• The switching at higher frequencies is valuable in the CSI, as a minimized element volume can
be utilized. Consequently, this can result in an increase in the power losses in the switching devices in
both the CSI and VSI, which require a heat sink for cooling. This increases the inverter volume and
destroys the benefit of a high frequency switching.
• The output filter is required at both the VSI and CSI output, resulting in an increase in the system size
and cost.
Table 1 summarizes the topologies and applications of conventional hard switching converters .
Table 1. Summary of the Conventional Hard Switching Topologies and Applications.

Modulation Techniques Mode

Inverter Controlle & of
Type r Control Strategies Operation
VSI PWM Unipolar PWM Buck
VSI PWM Pulse Width Modulation Buck
high carrier frequency
VSI PWM unipolar PWM modulation Buck
VSI SPWM Sinusoidal pulse width modulation Buck
CSI PI Dual Loop Control Boost
CSI SMC Sliding Mode Control Boost
CSI SPWM Sinusoidal pulse width modulation Boost
Buck,
CSI PWM Pulse width modulation
Boost and
Buck-Boost
Boost the Voltage in Shoot Through the State Modified as
CSI PWM
[41] Improved

CSI PWM SBI Microcontroller-based reference-waveform

generation Method

ISI PWM Modified PWM Space Vector Control Boost

—

Shoot-through duty factor control Modified multiple

ISI PWM
[27] source and modulation index control application
Maximum Constant Boost with
ISI PWM Third Harmonic Injection Control —

ISI PWM Maximum Boost Control PWM Technique —

TBI SMC Sliding Mode Control Boost

Boost
TBI PI Dual Loop Control and
Buck-Boost

TBI PID Ziegler-Nichols Tuning Buck-Boost

TBI PWM Dual Loop Control Boost

TBI PWM Unipolar PWM Control Boost

TBI PWM One-Cycle Control Boost

Adaptive Fuzzy Rule-Based

TBI Boost
AFNN Neural Network
C Control
PWM Inverters Used in EV’s

CONCEPT OF PULSE WIDTH MODULATION

Higher order harmonics in the load current could be easily filtered out using a series
Inductor. A selected range of lower order harmonics can be reduced or eliminated
by choosing the number of pulses per half cycle. When number of pulses increases
then the order of harmonics is also increased and that can be easily eliminated by
means of filters. In this method, a fixed AC voltage is given to the converter and
controlled DC output voltage is obtained by adjusting the ON and OFF periods of
the pulses. This is the most popular method of controlling the output voltage and this
method is termed as pulse width modulation control.

ADVANTAGES OF PWM
1) The advantages possessed by PWM technique are as under: The output voltage
control can be obtained without any additional components.
2) Lower order harmonics can be eliminated or minimized along with its output voltage
control. As higher order harmonics can be filtered easily, the filtering requirements are
minimized.
Multiple -Pulse-Width Modulation
The harmonic content can be reduced using several pulses in each half-cycle of
output voltage. The generation of gating signals for turning on and off of transistors
is shown in figure 6.9 by comparing a reference signal with a triangular carrier
wave. The frequency of reference signal sets the output frequency, fo, and the carrier
frequency, fc, determines the number of pulses per half-cycle. The modulation index
controls the output voltage. This type of modulation is also known as uniform pulse-
width modulation (UPWM).
The number of pulses per half-cycle is found from

where mf = f0/fc is defined as the frequency modulation ratio.

Figure 6.9 Multiple Pulse Width Modulation

If δ is the width of each pulse, the RMS output voltage can be found from
 Sinusoidal Pulse Width Modulation
Instead of maintaining the width of all pulses the same as in the case of
multiple-pulse modulation, the width of each pulse is varied in proportion to
the amplitude of a sine wave evaluated at the centre of the same pulse. The
distortion factor and lower-order harmonics are reduced significantly. The
gating signals as shown in figure 6.10 are generated by comparing a sinusoidal
reference signal with a triangular carrier wave of frequency, fc. This type of
modulation is commonly used in industrial applications and abbreviated as
SPWM. The frequency of the reference signal, fr, determines the output
frequency fo, and its peak amplitude, Ar, controls the modulation index m, and
then in turn the RMS output voltage, Vo. The number of pulses per half cycle
depends on the carrier frequency. The RMS output voltage can be varied by
varying the modulation index m. If δm is the width of the pulse, the RMS output
voltage can be found from the waveforms.

The three PWM techniques listed above differ from each other in the harmonic
content in their respective output voltages. Thus the choice of a particular PWM
technique depends upon the permissible harmonic content in the converter
output voltage. The devices are switched on and off several times within each
half cycle to control the output voltage which has low harmonic content.

Bipolar sinusoidal pulse width modulation:

Unipolar sinusoidal pulse width modulation