Akiya Power Tech Training

Centre and Car Importer

EVs Maintenance & Servicing Training

Lecture Handout

Prepared by:

Yared Habtemariam - Automotive Engineer

Marsilas Darsema- Electrical Engineer

September 2024
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1.1. Table of Contents

1.1. Table of Contents ............................................................................................................... i

1. Introduction to Electric Vehicles (EVs) ................................................................................2
1.2. Electric Vehicle (EV) Architecture ....................................................................................2
1.3. Safety Protocols and High-Voltage Systems .....................................................................3
1.4. Classification of Electric Vehicles .....................................................................................5
1.4.1. Battery Electric Vehicles (BEVs) ...................................................................................5
1.4.1.1. Basics operation of Battery Electric Vehicles ............................................................6
1.5. Hybrid Electric Vehicles (HEVs) .......................................................................................7
1.5.1. Basics of Operation Hybrid Electric Vehicles ................................................................8
1.5.2. Hybrid Electric Vehicle (HEV) Configurations: Series and Parallel .............................9
1.6. Plug-in Hybrid Electric Vehicles (PHEVs) ......................................................................12
1.6.1. Basics of Operation: Plug-in Hybrid Electric Vehicles (PHEVs) ................................13
1.7. Mild Hybrid Electric Vehicles (MHEVs): .......................................................................15
1.7.1. Basics of Operation of Mild Hybrid Electric Vehicles (MHEVs)................................16
1.8. Range-Extended Electric Vehicles (REEVs) ...................................................................18
1.8.1. Basic Operation of Range-Extended Electric Vehicles (REEVs) ................................19
1.9. Fuel Cell Electric Vehicles (FCEVs) ...............................................................................19
2. Components of Electric Vehicles: Power Electronics.........................................................23
2.1 Auxiliary Battery ..............................................................................................................23
2.2 Controller Area Network (CAN Bus) ..............................................................................25
2.3 Converters in Electric Vehicles (EVs) .............................................................................27
2.4 Traction Inverters .............................................................................................................29
2.5 On-Board Charger (OBC) / Converter .............................................................................32
2.6 Electric Traction Motor in Electric Vehicles (EVs) .........................................................33
2.7 Electric Vehicle Battery Basics ........................................................................................34
2.7.1 Battery Cell ...................................................................................................................34
2.7.2 Battery Module .............................................................................................................36
2.7.3 Battery Pack ..................................................................................................................38
2.7.4 Lithium-Ion Battery Chemistry ....................................................................................39

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2.7.5 Battery Management System (BMS) ............................................................................42

2.7.5.1 The main functions of BMS ......................................................................................44
2.7.5.2 Battery Balancing......................................................................................................45
2.8 Thermal Management in Electric Vehicles ......................................................................48
2.9 Types of Electric Vehicle Chargers .................................................................................49
2.10 Differential Systems in Electric Vehicles (EVs) ..............................................................51

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History of Electric Vehicles

The history of electric vehicles (EVs) dates back to the early 19th century, when inventors in
Europe and the United States began experimenting with battery-powered vehicles. The first
known electric car was developed in 1828 by Hungarian engineer Ányos Jedlik, who created a
small-scale model powered by a simple electric motor. In the 1830s, Robert Anderson, a Scottish
inventor, built a crude electric carriage using non-rechargeable batteries.

By the late 19th century, electric vehicles had gained popularity, particularly in urban areas, due
to their quiet operation and ease of use compared to steam-powered and gasoline vehicles. In
1891, William Morrison of Iowa created one of the first successful electric automobiles in the
U.S. This period saw significant advancements in battery technology, with French chemist
Gaston Planté inventing the rechargeable lead-acid battery in 1859 and Thomas Edison
developing the nickel-iron battery in the early 1900s.

During the early 20th century, electric vehicles competed with gasoline-powered cars, with many
early automakers offering electric models. However, as internal combustion engine (ICE)
technology improved, gasoline vehicles became more affordable and capable of longer ranges,
leading to a decline in the popularity of EVs. By the 1920s, gasoline vehicles had largely taken
over the automotive market, and electric cars were relegated to niche uses.

The modern era of electric vehicles began in the late 20th century, driven by concerns over air
pollution, oil dependency, and climate change. The development of more efficient batteries,
particularly lithium-ion technology, spurred renewed interest in EVs. In the 1990s, General
Motors introduced the EV1, one of the first mass-produced electric vehicles, although it was
discontinued due to high costs and limited demand.

In the 21st century, electric vehicles have seen a resurgence, led by companies like Tesla, Nissan,
and Chevrolet. Government incentives, advances in battery technology, and growing awareness
of environmental issues have contributed to the rapid growth of the EV market. Today, electric
vehicles are considered a crucial part of the global transition to sustainable transportation, with
many automakers committing to electrify their fleets in the coming decades.

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1. Introduction to Electric Vehicles (EVs)

Electric Vehicles (EVs) are automobiles that are powered by electric motors rather than
conventional internal combustion engines (ICEs). These vehicles rely on electricity as their
primary energy source, which is stored in rechargeable batteries. EVs offer a cleaner and more
efficient alternative to traditional gasoline-powered vehicles, reducing greenhouse gas emissions
and reliance on fossil fuels.

The history of electric vehicles dates back to the 19th century when electric carriages were
introduced. However, with the advent of internal combustion engines, electric vehicles took a
backseat until the 21st century, when environmental concerns and advancements in battery
technology revitalized interest in them.

Today, electric vehicles are gaining significant traction globally due to their efficiency, lower
running costs, and environmental benefits. Tesla, Nissan, and Chevrolet are some leading
manufacturers in the electric vehicle space, offering models like the Tesla Model S, Nissan Leaf,
and Chevrolet Bolt.
1.2. Electric Vehicle (EV) Architecture

The architecture of electric vehicles (EVs) consists of three main sections: the energy source,
power conversion, and the drive system (electro-mechanical actuator). These components are
interconnected by a central vehicle controller.
The energy source includes the battery pack, battery management system, on-board charger
(OBC), and thermal management system. The power conversion section consists of the main
traction drive inverter and a bidirectional DC/DC converter. Lastly, the drive system comprises
the traction motor and mechanical transmission. This architecture enables efficient operation and
performance of electric vehicles.

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Figure 1: The basic architecture of an EV drivetrain

1.3. Safety Protocols and High-Voltage Systems

Electric vehicles (EVs) differ from traditional internal combustion engine (ICE) vehicles in terms
of energy storage, powertrain, and control systems. This necessitates strict safety protocols,
especially due to the presence of high-voltage systems. These protocols aim to protect both the
operator and the technician handling the vehicle, ensuring the safe functioning of its components.

Key Safety Considerations in Electric Vehicles

Personal Protective Equipment (PPE)

 When working with EVs, especially during maintenance or repair, specialized PPE such
as insulated gloves, safety goggles, and protective clothing must be worn.
 Insulated tools are used to prevent accidental electrical conduction.

Electrical Isolation

 The high-voltage systems in EVs must be isolated when performing service or

maintenance to avoid accidental electrical discharge.
 Isolation devices, such as high-voltage disconnect switches, are designed to safely cut off
power when required.

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Fire and Emergency Response

 EV batteries, particularly lithium-ion, pose unique fire risks due to their chemical
makeup. In case of a battery fire, specialized extinguishers (Class D) or water are used,
depending on the severity.
 Emergency responders need to be trained in handling EV-specific hazards such as thermal
runaway, which is a situation where the battery overheats and catches fire.

High Voltage Warning Labels and Training

 EVs are equipped with warning labels in high-voltage areas to prevent accidental contact.
 Vehicle manufacturers and service centers often provide specialized training to
technicians, covering the risks associated with high-voltage systems.

High-Voltage Systems in Electric Vehicles

 Electric vehicles operate with high-voltage (HV) systems, typically ranging from 200 to
800 volts. These systems are crucial for the vehicle’s propulsion and performance,
enabling the efficient transmission of electrical energy to drive the electric motor.

Components of High-Voltage Systems

The components of high-voltage systems in electric vehicles (EVs) include the battery pack,
which stores energy and typically operates between 400 to 800 volts, powering the vehicle’s
motor. The electric motor converts this electrical energy into mechanical energy for propulsion.
An inverter transforms the direct current (DC) from the battery into alternating current (AC)
required by the motor. The charging system enables recharging of the battery through various
types of chargers, including high-voltage fast chargers. Lastly, the thermal management system
regulates the temperature of these components, preventing overheating and ensuring optimal
performance.

Maintenance and Diagnostics

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Only trained professionals should work on high-voltage components. Before any service is
conducted, the high-voltage system is powered down, and checks are performed to ensure no
residual charge remains.

Diagnostic tools are used to monitor the voltage, current, and thermal state of high-voltage
components to ensure they are within safe operating limits.

1.4. Classification of Electric Vehicles

There are several classifications of EVs based on their propulsion systems and energy sources:

1.4.1. Battery Electric Vehicles (BEVs)

Battery Electric Vehicles (BEVs) are fully electric vehicles powered entirely by electricity. They
have no internal combustion engine or fuel tank and rely solely on rechargeable batteries to power
the electric motor. Key characteristics include:

 Zero Emissions: BEVs produce no tailpipe emissions since they don't burn fuel.
 High-capacity Battery Pack: The main power source, typically lithium-ion batteries,
which store energy for the vehicle.
 Electric Motor: Powers the vehicle's movement using the stored electricity from the
battery.
 Charging: BEVs are charged via external electric sources, including home chargers or
public charging stations.

Examples of BEVs include Tesla Model 3, Nissan Leaf, and Chevrolet Bolt. Would you like to
dive deeper into any specific aspects of BEVs?

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Figure 2: Components OF BEVs

1.4.1.1. Basics operation of Battery Electric Vehicles

A Battery Electric Vehicle operates primarily on electricity stored in its batteries, eliminating the
need for conventional fuels. The process begins with charging the vehicle's battery using an
electric power source, which can be done at home, public charging stations, or through fast-
charging networks. Once charged, the vehicle draws energy from the battery to power an electric
motor, which drives the wheels and propels the vehicle. The electric motor converts electrical
energy into mechanical energy, providing instantaneous torque for smooth acceleration.
Regenerative braking is a key feature, allowing the vehicle to recover energy during braking and
feed it back into the battery, enhancing overall efficiency. The vehicle's management system
monitors battery health, energy consumption, and performance, ensuring optimal operation. This
combination of components allows BEVs to operate quietly, produce zero tailpipe emissions,
and offer a more sustainable alternative to traditional internal combustion engine vehicles.

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1.5. Hybrid Electric Vehicles (HEVs)

Hybrid Electric Vehicles (HEVs) combine the use of both an internal combustion engine (ICE)
and an electric motor to power the vehicle. The ICE typically runs on gasoline or diesel, while
the electric motor is powered by a smaller battery pack compared to fully electric vehicles. HEVs
do not require external charging because their batteries are recharged through regenerative
braking and the internal combustion engine. This dual-power system allows HEVs to offer a
balance between fuel efficiency and performance. Key characteristics of HEVs include:
 Dual Power Sources: HEVs use a combination of gasoline or diesel engines and electric
motors, allowing for greater flexibility in power delivery.
 Regenerative Braking: This system recovers energy during braking, which is then stored
in the battery for later use, improving overall efficiency.
 Improved Fuel Economy: By utilizing both the electric motor and internal combustion
engine, HEVs can achieve better fuel economy compared to conventional vehicles.
 Charging: Unlike Battery Electric Vehicles, HEVs do not require external charging; they
recharge their batteries through the internal combustion engine and regenerative braking.

Examples of popular HEVs include the Toyota Prius, Honda Insight, and Ford Fusion Hybrid.

Figure 3: Components OF HEVs

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1.5.1. Basics of Operation Hybrid Electric Vehicles

The operation of a Hybrid Electric Vehicle involves a seamless integration between its internal
combustion engine and electric motor.
Low-Speed Operation: When the vehicle is first started or driven at low speeds, the electric
motor is typically the primary power source. This reduces fuel consumption and emissions.
Acceleration and High-Speed Operation: As the vehicle accelerates or when more power is
needed, the internal combustion engine takes over or works in combination with the electric
motor. This ensures optimal performance without excessive fuel consumption.
Regenerative Braking: During braking, the vehicle’s regenerative braking system recaptures
kinetic energy that would otherwise be lost as heat. This energy is then stored in the battery and
used to power the electric motor later, improving the vehicle's overall efficiency.

Intelligent Control System: A sophisticated control system manages the interaction between
the electric motor and the internal combustion engine, ensuring that the vehicle uses the most
efficient power source at any given moment. This system helps optimize fuel economy,
performance, and emission levels.

Figure 4: Series hybrid vehicle propulsion system.

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1.5.2. Hybrid Electric Vehicle (HEV) Configurations: Series and Parallel

Hybrid Electric Vehicles (HEVs) utilize various powertrain configurations to integrate the
electric motor(s) and internal combustion engine (ICE). The two primary configurations are
Series and Parallel HEV setups. These configurations determine how power is delivered to the
wheels and how the engine and electric motor interact.

1. Series HEV Configuration

In a Series HEV, only the electric motor directly drives the wheels, while the internal combustion
engine functions as a generator to recharge the battery or provide electricity to the motor. This
means that the engine is not mechanically connected to the wheels. Instead, the engine operates
solely to generate electrical power for the motor and/or battery.

Characteristics of Series HEVs:

Electric-Only Drive: The electric motor is the sole source of propulsion, providing power to the
wheels at all times.

Engine as Generator: The internal combustion engine powers a generator, which produces
electricity for the electric motor and/or charges the battery.

Energy Path: The power from the engine does not reach the wheels directly; it first goes through
the generator and then to the electric motor.

Efficiency at Low Speeds: Series HEVs are particularly efficient at lower speeds since the
electric motor can operate independently without relying on the engine.

Operation:

Start and Low-Speed Driving: The electric motor drives the vehicle using power from the
battery.

Normal Operation: As battery levels drop or more power is needed, the internal combustion
engine starts, generating electricity for the motor and charging the battery.

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Regenerative Braking: Energy is recovered during braking and stored in the battery.

Figure 5: Series HEV Configuration

2. Parallel HEV Configuration

In a Parallel HEV, both the internal combustion engine and the electric motor can drive the
wheels, either independently or in combination. The engine and motor are mechanically
connected to the drivetrain, meaning that power can be delivered directly from either the electric
motor, the engine, or both.

Figure 6: Parallel HEV Configuration

Characteristics of Parallel HEVs:

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Dual Power Delivery: Both the engine and the electric motor are mechanically connected to the
wheels, enabling them to work together or separately to propel the vehicle.

Battery and Fuel Engine Synergy: The electric motor assists the engine during acceleration,
and at higher speeds, the engine often takes the lead while the electric motor provides
supplementary power.

Engine and Motor Interaction: The vehicle’s control system decides the most efficient mode
of operation (engine-only, motor-only, or combined).

Operation:

Start and Low-Speed Driving: The vehicle often uses the electric motor for driving at low
speeds, with the engine turned off to save fuel.

High-Speed Driving: The internal combustion engine takes over at higher speeds when
efficiency improves.

Acceleration: Both the engine and the motor can work together to deliver maximum power
during heavy acceleration or steep climbs.

Regenerative Braking: Energy recovered during braking is stored in the battery to be reused by
the electric motor.

Example:

 Toyota Prius is a well-known example of a parallel hybrid, where both the electric motor
and internal combustion engine can drive the vehicle depending on driving conditions.

3. Series-Parallel HEV Configuration (Combined Hybrid)

Some modern hybrids use a Series-Parallel (Combined) configuration, which combines

elements of both series and parallel systems. This allows for greater flexibility, as the vehicle can
operate as a series hybrid at low speeds and a parallel hybrid at higher speeds, optimizing fuel
efficiency.

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Example:

 Toyota Prius (latest generations), Chevrolet Volt, and Ford Fusion Hybrid use series-
parallel systems.

Summary Table: Series vs. Parallel HEV Configuration

Characteristic Series HEV Parallel HEV

Primary Propulsion Electric motor only Both engine and electric
motor
Engine Role Generates electricity, does Drives wheels directly, can
not drive wheels work with electric motor
Efficiency More efficient at low More efficient at high
speeds speeds
Transmission Complexity Simpler (no mechanical More complex (mechanical
link between engine and link required)
wheels)
Examples BMW i3 (range extender), Toyota Prius, Honda
Nissan e-Power Insight, Ford Fusion Hybrid
1.6. Plug-in Hybrid Electric Vehicles (PHEVs)

Plug-in Hybrid Electric Vehicles (PHEVs) represent a hybrid system that combines an internal
combustion engine (ICE) and an electric motor with a larger battery that can be charged
externally. Unlike conventional Hybrid Electric Vehicles (HEVs), PHEVs offer the ability to
charge their batteries by plugging into an external power source (e.g., a home charger or public
charging station). This feature allows them to operate on electric power alone for longer distances
before the internal combustion engine is needed, enhancing efficiency and reducing emissions.

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Figure 7: Components OF PHEVs

1.6.1. Basics of Operation: Plug-in Hybrid Electric Vehicles (PHEVs)

Plug-in Hybrid Electric Vehicles (PHEVs) operate using a combination of an internal combustion
engine (ICE) and an electric motor, supported by a larger battery that can be externally charged.
The basic operation of PHEVs revolves around two primary modes: electric-only mode and
hybrid mode.

Electric-Only Mode: In this mode, the vehicle runs purely on electric power, drawing energy
from its battery. Depending on the model, PHEVs can travel between 20 to 60 miles in this mode
before the battery requires recharging. This mode is ideal for short trips and urban driving, where
fuel consumption and emissions can be minimized.

Hybrid Mode: Once the battery's charge is depleted, the PHEV automatically switches to hybrid
mode. In this mode, both the internal combustion engine and the electric motor work together to
power the vehicle. The electric motor assists the engine during acceleration or when extra power
is needed, improving fuel efficiency and performance.

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Charging: PHEVs can be recharged through external power sources, such as home charging
stations or public chargers. Additionally, the battery is recharged during driving through
regenerative braking, which captures energy when the brakes are applied and stores it in the
battery. In some models, the internal combustion engine can also recharge the battery.

By utilizing both electric and fuel power, PHEVs offer flexibility, reduced fuel consumption, and
lower emissions compared to conventional vehicles. The dual-source powertrain allows PHEVs
to cover longer distances while benefiting from the efficiency of electric propulsion for shorter
commutes.

Figure 8: Plug-in hybrid electric vehicle (parallel configuration).

Advantages and Disadvantages

Plug-in Hybrid Electric Vehicles (PHEVs) offer several advantages and disadvantages. One of
the key advantages is fuel savings, especially for short commutes where the vehicle can run
entirely on electric power. This can significantly reduce fuel consumption and save on costs.
Additionally, PHEVs produce lower emissions compared to traditional internal combustion
engine (ICE) vehicles and even some hybrid electric vehicles (HEVs), particularly when driven
in electric-only mode. Another advantage is the increased range flexibility; with both electric

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and gasoline power, PHEVs provide the convenience of extended driving ranges without the
concern of depleting the battery entirely.

However, there are also some disadvantages to PHEVs. One of the main challenges is the need
for charging infrastructure. To fully benefit from the electric driving capabilities of a PHEV,
access to home or public charging stations is essential, which may not always be convenient.
Furthermore, PHEVs typically have a higher initial cost compared to conventional hybrids due
to their larger battery and additional electric components, which can make them more expensive
to purchase upfront.

Examples of PHEVs:

 Chevrolet Volt: A PHEV with a significant all-electric range before switching to

gasoline power.
 Toyota Prius Prime: A plug-in version of the popular hybrid Prius, offering an all-
electric range of up to 25 miles.
 Mitsubishi Outlander PHEV: A plug-in hybrid SUV with a combination of electric and
gasoline power, known for its versatility.

1.7. Mild Hybrid Electric Vehicles (MHEVs):

Mild Hybrid Electric Vehicles (MHEVs) are a type of hybrid vehicle that use an internal
combustion engine (ICE) assisted by a small electric motor and battery. Unlike full hybrids
(HEVs) and plug-in hybrids (PHEVs), MHEVs cannot operate solely on electric power. Instead,
the electric motor is used to support the engine by providing additional power during
acceleration, powering auxiliary systems, and enabling smoother start-stop functionality. This
leads to improved fuel efficiency and reduced emissions.

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1.7.1. Basics of Operation of Mild Hybrid Electric Vehicles (MHEVs)

Mild Hybrid Electric Vehicles (MHEVs) are designed to assist the internal combustion engine
(ICE) rather than fully power the vehicle on their own. One of the key characteristics is that the
electric motor in MHEVs provides electric assist, but it does not have the capability to drive
the vehicle independently. The electric motor mainly helps during acceleration and deceleration,
improving fuel efficiency. MHEVs also feature a smaller battery compared to full hybrids or
plug-in hybrids, typically operating at 48V. This smaller battery powers the electric motor and
stores energy captured through regenerative braking, where energy generated during
deceleration is stored and later used to assist the engine or power the vehicle’s electrical systems.

Additionally, MHEVs incorporate start-stop technology, which automatically shuts off the
engine when the vehicle is at a stop (such as at traffic lights) and restarts it when needed. This
reduces fuel consumption and emissions during idling.

The operation of MHEVs includes three primary functions:

1. Start-Stop Functionality: The engine shuts off when idling to conserve fuel, and the
electric motor ensures a smooth and quick restart when the driver accelerates.

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2. Acceleration Assist: The electric motor provides extra power during acceleration,
reducing the load on the internal combustion engine and improving fuel economy.
3. Regenerative Braking: The energy generated during braking or deceleration is captured
and stored in the battery, which is then used to assist the engine or to power the vehicle’s
auxiliary systems.

This combination of features makes MHEVs more fuel-efficient and environmentally friendly
without the need for full electric drive capability.

Advantages of MHEVs: Mild Hybrid Electric Vehicles (MHEVs) offer several benefits,
primarily focusing on improved fuel efficiency by reducing the engine's workload and utilizing
regenerative braking. This helps them achieve better fuel economy compared to traditional
internal combustion engine (ICE) vehicles. Additionally, MHEVs produce lower emissions due
to less idling and more efficient fuel use, making them environmentally friendlier than
conventional vehicles. Another key advantage is that MHEVs are a cost-effective hybrid
solution—they are less expensive than full hybrids or plug-in hybrids because they use smaller
batteries and less complex systems.

Disadvantages of MHEVs: Despite their benefits, MHEVs also have some limitations. One
major drawback is that they lack an electric-only driving mode, meaning they cannot run solely
on electric power like full hybrids or plug-in hybrids (PHEVs). This limits their potential for
greater fuel savings. Additionally, the electric assistance provided by the motor is modest, so
while MHEVs do improve fuel economy and reduce emissions, the overall impact is less
significant than in more advanced hybrid systems.

Examples of MHEVs:

 Audi A6 TFSI MHEV: A luxury sedan using mild hybrid technology for improved
efficiency and performance.
 Ford F-150 PowerBoost MHEV: A pickup truck that uses mild hybrid technology to
offer better fuel economy and enhanced towing capacity.

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 Suzuki Swift SHVS: A compact car that features mild hybrid technology to improve fuel
economy without the need for charging infrastructure.
1.8. Range-Extended Electric Vehicles (REEVs)

Range-Extended Electric Vehicles (REEVs) are a type of hybrid electric vehicle designed to
overcome one of the major challenges of fully electric vehicles: limited driving range. REEVs
primarily operate as electric vehicles, using an onboard battery to power an electric motor for
propulsion. However, unlike traditional electric vehicles (EVs), REEVs are equipped with a
small internal combustion engine (ICE) or generator that acts as a "range extender." This
generator is not connected to the wheels but is used to recharge the battery or provide additional
power when the battery is depleted, allowing the vehicle to travel further without needing to stop
for external charging.
The main advantage of REEVs is that they combine the benefits of electric driving—such as
reduced emissions, lower fuel costs, and quieter operation—with the flexibility of an extended
driving range. This makes REEVs an attractive option for drivers who want the environmental
and economic benefits of electric driving but still need the assurance of longer-range capabilities
for longer trips or areas with limited charging infrastructure.

Figure 9: Examples of Range-Extended Electric Vehicles (REEVs) topology

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1.8.1. Basic Operation of Range-Extended Electric Vehicles (REEVs)

Range-Extended Electric Vehicles (REEVs) operate primarily as electric vehicles, using a large
battery to power an electric motor that drives the vehicle. Here is an overview of their basic
operation:

1. Electric-Only Mode: During normal driving, REEVs rely solely on the energy stored in
the battery to power the electric motor. The vehicle operates like a fully electric vehicle
(EV), providing a quiet, smooth, and efficient driving experience with zero emissions
when running in this mode. The vehicle can travel a certain distance, known as its electric
range, before the battery becomes depleted.
2. Activation of Range Extender: Once the battery charge drops below a certain threshold
and electric-only driving is no longer possible, the range extender (a small internal
combustion engine or generator) kicks in. The range extender does not power the wheels
directly; instead, it generates electricity to recharge the battery or provide supplementary
power to the electric motor. This extends the vehicle’s range, allowing the driver to
continue driving without needing to stop and recharge from an external source.
3. Seamless Transition: The transition from electric-only driving to range-extended mode
is usually seamless and automatic. The driver may not even notice the change as the range
extender works quietly to maintain the vehicle’s power.
4. Regenerative Braking: Like other hybrids and electric vehicles, REEVs use regenerative
braking to capture energy during braking or deceleration. This energy is converted into
electricity and stored in the battery, helping to extend the vehicle’s electric range.
5. External Charging: REEVs can also be plugged into an external power source to
recharge the battery, just like a plug-in hybrid electric vehicle (PHEV) or battery electric
vehicle (BEV). Drivers can use home charging stations or public chargers to replenish
the battery, maximizing the electric-only driving range.

1.9. Fuel Cell Electric Vehicles (FCEVs)

Fuel Cell Electric Vehicles (FCEVs) are a type of electric vehicle that uses a fuel cell to generate
electricity for propulsion. Instead of relying on batteries as the primary energy source, FCEVs

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generate electricity through a chemical reaction between hydrogen (stored in onboard tanks) and
oxygen (from the air). The electricity produced powers an electric motor, which drives the
vehicle. Water vapor and heat are the only by-products of this process, making FCEVs zero-
emission vehicles.

Figure 10: Components OF FCEVs

Key Characteristics of FCEVs:

Hydrogen Fuel Cell: FCEVs use a hydrogen fuel cell to generate electricity through an
electrochemical reaction between hydrogen and oxygen.

Electric Propulsion: The vehicle is powered by an electric motor, similar to Battery Electric
Vehicles (BEVs), but the electricity is generated on-demand by the fuel cell.

Zero Emissions: The only by-products of the fuel cell reaction are water vapor and heat, making
FCEVs emission-free at the tailpipe.

Hydrogen Refueling: FCEVs are refueled at hydrogen refueling stations, which takes only a
few minutes, similar to conventional gasoline or diesel vehicles.

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Fuel Cell Electric Vehicles (FCEVs) topology

Figure 11: Examples of Fuel Cell Electric Vehicles (FCEVs) topology

Operation:

1. Hydrogen Storage: Hydrogen is stored in high-pressure tanks within the vehicle.

2. Power Generation: Inside the fuel cell, hydrogen reacts with oxygen from the air in a
process called reverse electrolysis. This reaction produces electricity, water vapor, and
heat.
3. Electric Motor: The electricity generated powers an electric motor, which drives the
wheels of the vehicle.
4. Battery Assistance: FCEVs often have a small battery to store energy from regenerative
braking or provide additional power when needed, but the primary energy source is the
fuel cell.

Advantages of FCEVs:

 Zero Tailpipe Emissions: FCEVs produce no harmful emissions, only water vapor and
heat, making them environmentally friendly.

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 Quick Refueling: Refueling a hydrogen-powered vehicle takes only a few minutes, much
like refueling a gasoline car, providing a significant advantage over long battery charging
times in BEVs.
 Extended Driving Range: FCEVs typically offer longer driving ranges compared to
most BEVs, with ranges exceeding 300 miles on a full hydrogen tank.

Disadvantages of FCEVs:

 Hydrogen Infrastructure: The main challenge for FCEVs is the lack of widespread
hydrogen refueling stations, limiting their practicality in many regions.
 Hydrogen Production: Hydrogen is primarily produced from natural gas, a process that
emits carbon dioxide. However, hydrogen can also be produced from renewable sources,
which would make the entire process more sustainable.
 Higher Costs: FCEVs and hydrogen fuel infrastructure are currently expensive, though
costs are expected to decrease as technology advances.

Examples of FCEVs:

 Toyota Mirai: One of the most well-known FCEVs, offering a driving range of over 300
miles and quick refueling capabilities.
 Honda Clarity Fuel Cell: Another popular FCEV known for its range, efficiency, and
smooth driving experience.
 Hyundai NEXO: A hydrogen-powered SUV with an extended range and advanced
technology features, making it one of the leaders in the FCEV market.

Summary Table: Types of Electric Vehicles (EVs)

Type of EV Primary Energy Charging/Refueling Electric-Only Examples

Source Driving
Battery Electric Battery (Electric) External Charging Fully Electric Tesla Model 3,
Vehicles (BEVs) Nissan Leaf

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Hybrid Electric Battery & No External Limited (Low Toyota Prius,

Vehicles (HEVs) Gasoline/Diesel Charging (Engine & Speeds Only) Honda Insight
Regenerative
Braking)
Plug-in Hybrid Battery & External Charging & Extended Electric Chevrolet Volt,
Electric Vehicles Gasoline/Diesel Regenerative Range Toyota Prius
(PHEVs) Braking Prime
Mild Hybrid Battery-Assisted No External No Electric-Only Audi A6
Electric Vehicles Gasoline/Diesel Charging (Engine & Mode MHEV, Suzuki
(MHEVs) Regenerative Swift SHVS
Braking)
Range-Extended Battery & External Charging, Extended Electric Chevrolet Volt
Electric Vehicles Gasoline/Diesel Regenerative Range
(REEVs) (for generation) Braking
Fuel Cell Electric Hydrogen Fuel Hydrogen Refueling Fully Electric Toyota Mirai,
Vehicles (FCEVs) Cell Hyundai NEXO

2. Components of Electric Vehicles: Power Electronics

2.1 Auxiliary Battery

The auxiliary battery in an electric vehicle (EV) is a smaller, low-voltage battery (usually 12V)
that powers the vehicle's auxiliary systems and electronics, independent of the high-voltage
traction battery that drives the electric motor. Similar to traditional vehicles, the auxiliary battery
is responsible for ensuring that the vehicle's non-motor functions work, even when the vehicle is
off or in idle mode.

Auxiliary Battery in Electric Vehicles (EVs)

In electric vehicles (EVs), the auxiliary battery is a smaller, low-voltage battery (typically 12V)
that powers various essential systems and electronic components, independent of the main high-
voltage battery used to drive the electric motor. Although EVs rely on a large traction battery for

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propulsion, the auxiliary battery plays a crucial role in maintaining the functionality of auxiliary
systems, much like in conventional internal combustion engine (ICE) vehicles.

Figure 12: Auxiliary Battery Pack in an Electric Vehicle

Charging the Auxiliary Battery:

 DC-DC Converter: EVs use a DC-DC converter to charge the auxiliary battery. This
converter steps down the high voltage from the main traction battery (often hundreds of
volts) to the 12V required for the auxiliary battery. This process occurs while the vehicle
is in operation, ensuring the auxiliary battery remains charged.
 Regenerative Braking: Some EVs use regenerative braking to help recharge the
auxiliary battery, as energy is recovered during braking and redirected into the battery
systems.
 External Charging: When the EV is plugged into an external charging source, the
auxiliary battery is typically charged along with the main high-voltage traction battery,
ensuring that both batteries are fully powered for the next use.

Role of the Auxiliary Battery

In electric vehicles (EVs), the auxiliary battery plays a crucial role during vehicle start-up,
although its function differs from that of a conventional internal combustion engine (ICE)
vehicle. Rather than cranking the engine as in ICE vehicles, the auxiliary battery in EVs powers

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the low-voltage systems and control electronics during the start-up process. First, it provides
power to the vehicle’s electronic control units (ECUs), which manage critical systems such as
the powertrain, braking, and infotainment. It also initiates the computer systems that monitor the
vehicle's components, such as the battery's state of charge and motor condition. Additionally, the
auxiliary battery activates the high-voltage system by powering relays and contactors, which
connect the high-voltage traction battery to the inverter and motor, ensuring a safe flow of power.
This battery also powers essential low-voltage electronics like the dashboard, lighting, HVAC,
and infotainment systems, making them fully operational from the moment the vehicle starts.

Moreover, the auxiliary battery enables internal communication between various control units
via systems like the CAN bus and powers diagnostic checks to ensure key components are
functioning correctly before driving. It also ensures safety-critical systems, including airbags,
anti-lock braking (ABS), and electronic stability control (ESC), are ready to operate even before
the high-voltage system is engaged. In some EVs, the auxiliary battery can also start the HVAC
system, allowing for preconditioning of the cabin by heating or cooling it, especially in extreme
climates. This highlights the auxiliary battery's essential role in ensuring seamless start-up and
safe operation of electric vehicles.

2.2 Controller Area Network (CAN Bus)

The Controller Area Network (CAN Bus) is a robust vehicle bus standard designed to allow
microcontrollers and devices to communicate with each other in applications without a host
computer. It was originally developed by Bosch in the 1980s to provide efficient and reliable
communication between various systems in automobiles. Today, CAN Bus is widely used in
automotive, industrial, aerospace, and other embedded systems due to its simplicity, reliability,
and efficiency.

CAN Bus in Electric Vehicles (EVs)

In electric vehicles (EVs), the Controller Area Network (CAN Bus) plays a crucial role in
managing communication between various electronic components and systems. EVs rely heavily
on electronic control systems to monitor and manage everything from the battery and motor to

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the driver assistance systems and infotainment. The CAN Bus allows these systems to
communicate efficiently, ensuring the seamless operation of the vehicle.

CAN networks significantly reduce the amount of wiring in vehicles by allowing multiple
electronic control units (ECUs) to communicate over a single communication bus, instead of
requiring individual, dedicated wires for each connection. This not only simplifies the vehicle's
wiring system but also improves reliability, reduces weight, and lowers manufacturing costs.

Figure 13: Example of CAN and Without CAN in automotive application

Key roles of can bus in electric vehicles

The Controller Area Network (CAN) Bus plays a pivotal role in electric vehicles by enabling
efficient communication between various subsystems. It allows the Battery Management System
(BMS) to share vital data such as the state of charge, voltage, and temperature with the vehicle's
central control unit. The CAN Bus also facilitates motor control by transmitting real-time data
like motor speed and torque between the motor controller and the Vehicle Control Unit (VCU),
optimizing performance. Additionally, it helps regulate the charging system by communicating
between the vehicle and charging stations, ensuring safe and efficient charging. CAN Bus is
essential for other systems as well, such as regenerative braking, infotainment, thermal
management, and safety systems like ABS and electronic stability control. This communication
network ensures seamless coordination of all EV functions, enhancing efficiency, safety, and
performance.

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2.3 Converters in Electric Vehicles (EVs)

A voltage converter is a device designed to change the voltage level of an electrical power
source. It can convert various types of electrical power, including alternating current (AC) to AC,
direct current (DC) to DC, AC to DC, or DC to AC.

There are two main types of voltage converters:

1. Step-Up Converter: Increases the voltage from a lower level to a higher one, typically
used to boost low-voltage sources for high-power applications.
2. Step-Down Converter: Reduces the voltage from a higher level to a lower one, making
it suitable for low-power or light load devices.

Voltage converters are commonly used to step up low-voltage sources for heavy-duty tasks
involving high power consumption, but they can also work in reverse to step down voltage for
light loads.

DC/DC Converter in Electric Vehicles (EVs)

The DC/DC converter in electric vehicles (EVs) is a vital component that steps down high
voltage from the main battery to a lower voltage to power various vehicle systems. Since EVs
have a high-voltage battery pack (typically between 200V to 400V, or even higher), and many
of the vehicle's auxiliary systems (like lighting, infotainment, and control systems) operate on
low voltage (typically 12V or 48V), a DC/DC converter is necessary to provide the correct power
to these systems.

Key Functions of the DC/DC Converter in EVs:

1. Voltage Step-Down:
o The main function of the DC/DC converter is to step down the high voltage from
the main battery to a lower voltage, usually 12V, for systems that need lower
power. This is similar to what a conventional internal combustion engine (ICE)
vehicle's alternator does for the 12V system.
2. Auxiliary Battery Charging:

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o The DC/DC converter also helps in charging the auxiliary 12V battery. This 12V
battery powers the vehicle’s accessories and essential systems like lights, wipers,
infotainment, and safety systems when the vehicle is not running, or the high-
voltage system is turned off.

Figure 14: Basic Circuit configuration of the DC/DC converter

Converter Components

Voltage detection circuit (input side)：Measures an incoming voltage from the lithium ion
battery
Noise filter (input side)：Composed of capacitors and a coil to eliminate noise
Voltage conversion circuit: Converts voltage through an insulation transformer and FETs that
switch on/off
Noise filter (output side)：Composed of capacitors and a coil to eliminate noise
Voltage detection circuit (output side)：Measures an output voltage

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Control circuit: Controls the conversion circuit, etc.

DC/DC converter: Supplies power to the control circuit
Communication circuit: Communicates with external equipment

2.4 Traction Inverters

Traction inverters are essential components in electric vehicles (EVs) and hybrid electric
vehicles (HEVs), responsible for converting direct current (DC) from the vehicle's batteries into
alternating current (AC) to power the electric motor. This conversion is critical for efficient
vehicle prolusion and performance.

Figure 15: schematic of power electronics in EV

A traction inverter plays a vital role in managing the speed and torque of the motor, ensuring
efficient vehicle propulsion. Typically, traction inverters operate at high voltages, ranging from
300V to 800V, which helps to optimize performance and reduce the overall weight of the vehicle.
They use advanced semiconductor technologies like insulated gate bipolar transistors (IGBTs)
or MOSFETs for enhanced efficiency and thermal management. Additionally, traction inverters
utilize sophisticated control algorithms to provide smooth acceleration, deceleration, and
improved vehicle responsiveness, making them essential for efficient and reliable EV
performance.

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Figure 16: Basic Circuit configuration of the inverter

Noise filter: Suppresses internal noise or noise from external equipment

Voltage measuring circuit: Measures voltage for controlling the conversion circuit

Voltage conversion circuit: Converts voltage by switching of FETs, etc.

Current measuring circuit: Measures current for controlling the conversion circuit

Control circuit: Controls the conversion circuit, etc.

DC/DC converter: Supplies power to the control circuit

Communication I/F:A communication circuit that communicates with external equipment

Common terms related to traction inverters

Motor Drive or Motor Controller

The terms "motor drive" or "motor controller" refer to devices used to operate electric motors,
whether they are AC or DC machines. This terminology encompasses a wide range of systems,
from basic brushed DC controllers found in older battery-operated tools to sophisticated

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industrial drives. Any device that can "drive" or "control" a motor qualifies as a motor drive or
controller. While an inverter that operates a motor is classified as a motor drive, not all motor
drives are necessarily inverters. Nevertheless, as the prevalence of brushed DC machines
decreases, "motor drive" is increasingly becoming synonymous with "inverter."

Variable Frequency Drive (VFD)

A "Variable Frequency Drive" (VFD) is a type of motor drive system that controls the
operation of an electric motor by adjusting the frequency of the supplied power. For AC
machines, this frequency is directly linked to the motor's rotational speed. While the term is still
commonly used in industrial settings, it has become somewhat redundant for modern AC motor
drives since all such systems must vary frequency to control motor performance. VFDs are
specifically designed for AC machines and deliver AC power, thus they are generally classified
as inverters.

High and Low Voltage

In discussions surrounding traction inverters, "low voltage" typically refers to voltages below
60-100V, whereas "high voltage" refers to voltages exceeding 100V. However, according to
ANSI and NEC codes, voltage classifications differ significantly. For example, "high voltage" is
defined as anything above 115,000 Vac, while "low voltage" ranges from 240 to 600 Vac
(approximately 850V dc). Consequently, all electric vehicles currently fall under the "low
voltage" classification according to NEC standards. It's important to note that voltage definitions
and classifications can vary among different organizations.

MOSFET

A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a transistor utilized for

amplifying or switching electronic signals. It comprises a metal gate, typically constructed from
polysilicon, an insulating oxide layer, and a semiconductor channel. The channel's conductivity
between the source and drain is controlled by the voltage applied to the gate, allowing the
MOSFET to act as a voltage-controlled resistance device. When no voltage is applied, the
channel shows very high resistance (open circuit or "OFF"). Conversely, when the appropriate

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voltage is applied, the channel becomes a good conductor, with resistance measured in milli-
ohms for power devices (representing "ON"). MOSFETs are extensively used in digital and
analog circuits, power electronics, and microelectronics applications.

2.5 On-Board Charger (OBC) / Converter

An On-Board Charger (OBC) is an essential component in electric vehicles (EVs) and plug-in
hybrid electric vehicles (PHEVs). It serves as the interface between the vehicle's battery and the
external power supply, converting AC power from the grid into DC power for charging the
vehicle's battery. The OBC ensures safe, efficient charging and plays a vital role in the overall
energy management system of the vehicle.

The On-Board Charger (OBC) performs several essential functions in electric vehicles (EVs). Its
primary role is AC to DC conversion, transforming alternating current (AC) from the grid into
direct current (DC) for charging the battery, which primarily operates on DC power. The OBC
also engages in battery management, working with the battery management system (BMS) to
monitor battery health, state of charge, and temperature, adjusting charging current and voltage
to optimize performance.

Figure 17: EV charging system with on-board and off-board chargers.

It controls the charging process to ensure appropriate charging rates and prevent issues like
overcharging or overheating. Many OBCs provide a user interface that displays real-time

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charging information, such as charge level and estimated time to completion. Additionally, the
OBC facilitates communication with the charging station to negotiate charging rates and ensure
compatibility with various standards. Overall, the OBC is crucial for the efficiency and safety of
EV operation.

2.6 Electric Traction Motor in Electric Vehicles (EVs)

The electric traction motor is a crucial component in electric vehicles (EVs), responsible for
converting electrical energy from the battery into mechanical energy to propel the vehicle. Unlike
internal combustion engines, which rely on burning fuel, electric traction motors offer smooth,
instant torque and higher efficiency, making them ideal for EV applications.

Key Characteristics of Electric Traction Motors:

1. Types of Traction Motors:

o Permanent Magnet Synchronous Motors (PMSM): Often used in modern EVs,
PMSMs offer high efficiency, compact size, and strong performance due to their
use of permanent magnets.
o Induction Motors (IM): Used in vehicles like the Tesla Model S, induction
motors provide robustness and high durability without the need for permanent
magnets, though they are slightly less efficient than PMSMs.
o Brushless DC Motors (BLDC): These motors are highly efficient, offering
excellent torque-to-weight ratios and are commonly found in smaller EVs.
2. Instant Torque: Electric traction motors provide instant torque from a standstill, which
enables quick acceleration without the need for traditional gears found in combustion
engines. This feature gives EVs their distinctive rapid acceleration.
3. Efficiency: Traction motors are significantly more efficient than internal combustion
engines, often reaching efficiency levels above 90%. This high efficiency reduces energy
loss and extends the range of EVs, making them more energy-efficient and
environmentally friendly.
4. Regenerative Braking: Many electric traction motors support regenerative braking, a
feature where the motor operates in reverse during deceleration, converting kinetic energy

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back into electrical energy to recharge the battery. This improves the overall efficiency
and extends the vehicle’s range.
5. High Power-to-Weight Ratio: Electric motors are compact and have a high power-to-
weight ratio, which contributes to lighter, more efficient EVs. The compact size allows
flexibility in vehicle design, enabling motors to be placed on individual wheels or axles,
further enhancing performance and stability.

Advantages of Electric Traction Motors:

 Smooth Operation: Electric motors offer quiet and smooth operation, eliminating the
noise and vibration associated with traditional combustion engines.
 Low Maintenance: With fewer moving parts, electric traction motors require less
maintenance compared to traditional engines, which makes them more reliable over the
long term.
 Environmentally Friendly: Since they do not rely on burning fuel, traction motors
contribute to reducing greenhouse gas emissions, making EVs a cleaner transportation
option.
2.7 Electric Vehicle Battery Basics

Electric vehicle (EV) batteries are essential components that store and provide the electrical
energy needed to power the vehicle's electric motor. The performance, range, and efficiency of
an EV largely depend on the type and configuration of its battery. Understanding the basic
structures of EV batteries, including battery cells, modules, and their configurations in series and
parallel, is crucial for grasping how they function.
2.7.1 Battery Cell

A battery cell is the fundamental unit of an electric vehicle battery, comprising the basic
electrochemical components that convert chemical energy into electrical energy. Each cell
typically consists of three main parts: the anode (negative electrode), the cathode (positive
electrode), and an electrolyte that facilitates ion movement between the electrodes during
charging and discharging. The most common battery cell type used in EVs is the lithium-ion cell,
known for its high energy density and efficiency. The performance of individual cells is crucial,
as they dictate the overall characteristics of the battery pack.

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Types of Battery Cells:

The most commonly used types of lithium battery cells are cylindrical, prismatic, pouch, and
the emerging blade cells.

 Cylindrical Cells: These are the most traditional battery format, often used in consumer
electronics and electric vehicles. They are valued for their durability, ease of
manufacturing, and better thermal management due to their shape.
 Prismatic Cells: These cells have a rectangular or square shape, which allows for more
efficient use of space in battery packs. Their compact design is ideal for electric vehicles
where space is at a premium.
 Pouch Cells: These are lightweight and flexible, encased in a thin, polymer material.
Their design makes them highly adaptable for various applications, particularly where
form factor and weight are critical considerations.

Overall, cylindrical cells are the most widely used in electric vehicles, particularly in high-
performance models. Their robust design, ease of manufacturing, and superior thermal
management make them a preferred choice for many EV manufacturers. Cylindrical cells also
offer better structural integrity and can efficiently handle high power demands, making them
ideal for performance-oriented applications in electric vehicles.

Figure 18: Types of battery cells

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2.7.2 Battery Module

A battery module is a collection of multiple battery cells connected together to increase the
overall voltage and capacity of the battery system. Modules provide a balance between
manageability and performance, enabling efficient thermal management and safety features. By
grouping cells into modules, manufacturers can optimize the design for various vehicle
applications, ensuring that the battery can handle the power demands of the electric motor while
maintaining safety and durability. Modules are also designed to simplify the assembly process
and facilitate easier maintenance or replacement.

Figure 19: Battery Module

Series and Parallel Connection

Battery cells and modules can be connected in two primary configurations: series and parallel.

 Series Connection: In a series connection, the positive terminal of one cell is connected
to the negative terminal of the next, effectively increasing the total voltage of the battery
pack while maintaining the same capacity (amp-hours). This configuration is commonly

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used to achieve higher voltage levels necessary for the electric motor's operation,
allowing for efficient power delivery and improved performance.

Figure 20: Batter series connection

 Parallel Connection: In a parallel connection, the positive terminals of multiple cells are
connected together, as are the negative terminals. This configuration maintains the same
voltage as a single cell but increases the overall capacity (amp-hours), allowing the
battery pack to store more energy and extend the vehicle's range. Parallel connections are
essential for providing sufficient power during high-demand situations, such as
acceleration.

Figure 21:Series and Parallel Connection

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2.7.3 Battery Pack

The battery pack is a fundamental component of electric vehicles, integrating multiple battery
cells with advanced management and cooling systems to deliver efficient, reliable, and
sustainable energy storage.

Figure 22: battery packs

Figure 23: Electric-vehicle battery production

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2.7.4 Lithium-Ion Battery Chemistry

Lithium-ion (Li-ion) batteries are the predominant energy storage technology used in electric
vehicles (EVs), portable electronics, and renewable energy systems. Their unique chemistry
allows for high energy density, lightweight construction, and efficient cycling capabilities. Below
is an overview of lithium-ion battery chemistry, including its components, reactions, and
characteristics.

Figure 24: Technical Analysis of the Working Mechanism of Lithium Iron Phosphate Battery

Key Components

1. Anode:
o Typically made of graphite, the anode is the negative electrode where lithium ions
are stored during charging.

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o The anode’s structure allows for the intercalation (insertion) of lithium ions,
enabling efficient storage and release during the charge/discharge cycles.
2. Cathode:
o Made from various lithium metal oxides (e.g., lithium cobalt oxide (LiCoO₂),
lithium iron phosphate (LiFePO₄), lithium nickel manganese cobalt oxide
(NMC)).
o The cathode is the positive electrode that provides the lithium ions during the
discharge cycle, generating electrical energy.
3. Electrolyte:
o A lithium salt (e.g., lithium hexafluorophosphate (LiPF₆)) dissolved in a solvent
(such as ethylene carbonate or dimethyl carbonate).
o The electrolyte facilitates the movement of lithium ions between the anode and
cathode while acting as an insulator for electrons.
4. Separator:
o A porous membrane placed between the anode and cathode to prevent short
circuits while allowing the passage of lithium ions.
o The separator is critical for maintaining safety and performance during battery
operation.

Charge and Discharge Mechanism

 Charging:
o When a lithium-ion battery is charged, an external power source (like a charger)
applies voltage to the battery.
o This causes lithium ions to move from the cathode through the electrolyte to the
anode, where they are intercalated into the graphite structure.
o During this process, electrons flow through the external circuit, generating an
electric current.
 Discharging:
o During discharge, the process reverses. Lithium ions move from the anode back
to the cathode through the electrolyte.

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o As the lithium ions return to the cathode, electrons flow from the anode through
the external circuit to the cathode, providing electrical energy to power the device.

Types of Lithium-Ion Batteries

Lithium-ion batteries come in various chemistries, each with distinct properties and applications.
Here’s a brief overview of the most common types:

Lithium Nickel Manganese Cobalt Oxide (NMC)

 Composition: Contains nickel, manganese, and cobalt in varying ratios.

 Advantages: Offers a balanced performance with high energy density, good thermal
stability, and long cycle life.
 Applications: Widely used in electric vehicles (EVs), energy storage systems, and power
tools.

Lithium Nickel Cobalt Aluminum Oxide (NCA)

 Composition: Composed of nickel, cobalt, and aluminum.
 Advantages: Provides high energy density and excellent performance at high voltages,
with good thermal stability.
 Applications: Commonly used in electric vehicles (e.g., Tesla), aerospace, and high-
performance applications.

Lithium Iron Phosphate (LFP)

 Composition: Utilizes iron phosphate as the cathode material.

 Advantages: Known for its excellent thermal stability, safety, and long cycle life,
although it has a lower energy density than other chemistries.
 Applications: Often found in electric buses, stationary energy storage, and low-speed
electric vehicles.

Lithium Cobalt Oxide (LCO)

 Composition: Contains cobalt as the primary material.

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 Advantages: Offers high energy density and good thermal stability, making it suitable
for compact applications.
 Applications: Primarily used in consumer electronics such as smartphones, laptops, and
tablets.

Lithium Manganese Oxide (LMO)

 Composition: Uses manganese oxide for the cathode.

 Advantages: Provides good thermal stability, safety, and moderate energy density. It has
a higher discharge rate, making it suitable for high-power applications.
 Applications: Used in power tools, medical devices, and some electric vehicles.

Lithium Titanate (LTO)

 Composition: Uses lithium titanate for the anode material.

 Advantages: Known for its extremely fast charging capabilities, long cycle life, and
excellent thermal stability. It has a lower energy density compared to other lithium-ion
batteries.
 Applications: Often used in applications requiring rapid charging and discharging, such
as hybrid electric vehicles (HEVs) and grid energy storage systems.

2.7.5 Battery Management System (BMS)

A Battery Management System (BMS) is a crucial electronic control unit in electric vehicles
(EVs) that ensures the safe and efficient operation of the battery pack. The primary role of the
BMS is to monitor and manage various parameters related to the battery's health, performance,
and safety.

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Figure 25: Battery Management System (BMS)

Here’s an overview of the key functions of a BMS:

1. Monitoring Battery Parameters

 Voltage and Current: The BMS continuously monitors the voltage of individual cells
and the total battery pack, as well as the current flowing during charging and discharging.
 Temperature: It tracks the temperature of the battery cells to prevent overheating, which
can lead to thermal runaway or degradation.
 State of Charge (SoC): The BMS calculates the battery’s SoC, which is a measure of
the remaining energy in the battery, similar to a fuel gauge in conventional vehicles.
 State of Health (SoH): It assesses the overall health of the battery, determining its
capacity, lifespan, and any potential degradation.

2. Safety Management

 Overcharge/Over-discharge Protection: The BMS prevents the battery from being

overcharged or over-discharged, which can damage cells or cause safety risks.

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 Thermal Management: If the battery overheats or gets too cold, the BMS activates
cooling or heating mechanisms to maintain an optimal operating temperature.
 Short-Circuit and Overcurrent Protection: It safeguards the battery pack from
excessive currents or short circuits that could lead to malfunction or fire.

3. Balancing Cells

 Cell Balancing: The BMS ensures that all cells in a battery pack are evenly charged and
discharged. This balancing helps to extend the life of the battery and maintain its
efficiency, as imbalances can lead to premature wear or reduced performance.

4. Communication with Vehicle Systems

 Data Transmission: The BMS communicates with other vehicle systems, such as the
powertrain control module, to provide real-time data on the battery's condition and energy
availability.
 Integration with Charging Systems: It communicates with the on-board charger (OBC)
and external charging stations to regulate the charging process, ensuring optimal charging
rates and safety.

5. Energy Management

 The BMS optimizes the energy usage of the battery pack to maximize vehicle range and
performance. It manages the power distribution between the electric motor and other
auxiliary systems, ensuring efficient energy utilization.

2.7.5.1 The main functions of BMS

The Battery Management System (BMS) in electric vehicles is responsible for overseeing the
safe and efficient use of the battery pack. Its primary functions include:

State of Charge (SoC) represents the current charge level of the battery, expressed as a
percentage of the total capacity. It is similar to a fuel gauge for traditional vehicles, showing how

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much energy remains in the battery. The BMS continuously monitors SoC to provide accurate
information on available range and to prevent overcharging or excessive discharge.

State of Health (SoH) indicates the overall condition of the battery compared to its original
capacity when new. It is a measure of battery degradation over time and is usually expressed as
a percentage. SoH reflects how much of the battery’s initial capacity still usable, helping to
predict performance and longevity is. A lower SoH means the battery has degraded and may not
hold as much charge or provide as much power as before.

Depth of Discharge (DoD) refers to how much of the battery's capacity has been used or
discharged. For example, if a battery has a capacity of 100 kWh and 30 kWh have been used, the
DoD is 30%. A higher DoD can accelerate battery wear, so the BMS often aims to minimize deep
discharges to prolong battery life. Managing DoD is critical for optimizing battery performance
and durability.

2.7.5.2 Battery Balancing

To maximize the battery's capacity and prevent localized under-charging or over-charging, the
Battery Management System (BMS) actively ensures that all cells within the battery are
maintained at the same voltage or State of Charge through a process known as balancing. The
BMS can achieve this balancing in several ways:

Energy Dissipation: The BMS can waste energy from the most charged cells by connecting
them to a load, such as through passive regulators. This method reduces the charge of the
overcharged cells.

Energy Redistribution: The system can shuffle energy from the most charged cells to the least
charged ones using balancers, ensuring a more uniform charge across all cells.

Current Limitation: The BMS may reduce the charging current to a level that prevents damage
to fully charged cells while allowing less charged cells to continue charging. However, this
approach does not apply to lithium chemistry cells.

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Figure 26: Battery Management System architecture diagram

Why is Cell Balancing Important?

In any multi-cell battery pack, slight inconsistencies between cells are inevitable. Without
balancing, some cells might become overcharged or over-discharged during operation, leading
to:

1. Reduced Capacity: The weakest cell limits the total capacity of the battery pack. If one
cell is fully discharged, the entire pack is considered discharged, even if other cells still
have energy left.
2. Decreased Lifespan: Repeated overcharging or over-discharging of cells can accelerate
degradation and shorten battery life.
3. Safety Risks: Imbalanced cells can lead to overheating, overvoltage, or undervoltage,
increasing the risk of damage or thermal runaway in extreme cases.

Types of Cell Balancing

There are two primary methods of cell balancing:

Passive Cell Balancing: Passive cell balancing is a commonly used technique in electric vehicle
(EV) battery packs. It leverages the natural voltage differences between individual cells and

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employs passive components, such as resistors or diodes, to dissipate excess charge from higher-
voltage cells. This energy is typically converted into heat. The process mainly occurs during the
charging phase, gradually equalizing the voltage across all cells. While this method is simpler
and cost-effective, it is less energy-efficient since the surplus energy is wasted as heat.

Active Cell Balancing: Active cell balancing is a more advanced method used in EV battery
packs. It employs active electronic components like switches or integrated circuits to redistribute
charge between cells dynamically. Unlike passive balancing, active balancing can occur during
charging, discharging, or even when the system is idle. This method transfers energy from higher-
voltage cells to lower-voltage ones, improving efficiency by conserving energy that would
otherwise be wasted. Though more complex and expensive, active cell balancing provides greater
flexibility and helps maintain better long-term cell health in the battery pack.

Figure 27: Passive and Active Cell Balancing for Electric Vehicles

a) How Active Cell Balancing Works

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Active cell balancing works by redistributing energy between cells to equalize their voltage
levels. This method transfers excess energy from higher-voltage cells to lower-voltage cells, thus
ensuring an even charge distribution across the pack. This is done using transformers, capacitors,
or inductors that shuttle energy efficiently between cells. Active balancing is more complex and
costly but highly efficient, as it can maintain balance even during both charging and discharging
processes, optimizing the overall performance of the battery pack.

b) How Passive Cell Balancing Works

Passive cell balancing works by dissipating excess energy from the higher-voltage cells as heat.
Resistors are used to drain energy from the overcharged cells, bringing them down to the voltage
level of the lower-voltage cells. This method is simpler and cheaper than active balancing but
less efficient, as energy is wasted in the process. Passive balancing is typically done near the end
of the charging cycle to equalize the cells and prevent overcharging.

Benefits of Cell Balancing

 Maximized Capacity: By keeping all cells at a similar voltage, cell balancing ensures
that the full capacity of the battery pack is available for use.
 Prolonged Battery Life: Preventing individual cells from being overcharged or over-
discharged helps reduce wear and tear, extending the battery's lifespan.
 Improved Safety: Properly balanced cells reduce the risk of thermal issues and ensure
the battery operates within safe limits.

2.8 Thermal Management in Electric Vehicles

The thermal management system in electric vehicles (EVs) is essential for maintaining optimal
operating temperatures for critical components such as the battery, electric motor, and power
electronics. It can be classified into two main categories: passive cooling and active cooling.

Passive Cooling

Passive cooling relies on natural processes to dissipate heat without additional energy input. This
includes the use of heat sinks, which absorb and release heat through increased surface area, and

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thermal insulation materials that minimize heat transfer between components. Natural convection
also plays a role, allowing hot air to rise and cool air to replace it without the need for fans.
Additionally, selecting materials with high thermal conductivity, like aluminum or copper,
enhances heat dissipation. The primary advantages of passive cooling are its energy efficiency
and lower maintenance needs due to fewer moving parts.

Active Cooling

In contrast, active cooling employs mechanical systems and energy input to actively control
temperatures. This can involve liquid cooling systems that circulate coolant through components,
absorbing heat and dissipating it via radiators or heat exchangers. Air cooling systems utilize
fans to increase airflow over components, enhancing heat dissipation. Heat pumps can transfer
heat for both cooling and heating, providing efficiency for cabin climate control. Phase change
materials (PCMs) can also be used to manage temperature fluctuations by absorbing and
releasing thermal energy during phase transitions. Active cooling systems are particularly
effective under high loads or extreme conditions, offering rapid cooling or heating as needed to
enhance performance and comfort.

2.9 Types of Electric Vehicle Chargers

Electric vehicle (EV) chargers are categorized based on charging speed, power output, and the
type of current they supply (AC or DC). There are three primary types of EV chargers: Level 1,
Level 2, and DC Fast Chargers (Level 3). Each type is suited for different use cases and
charging environments.

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Figure 28: Main charging levels of EVs

1. Level 1 Chargers (AC Charging)

 Power Source: Standard household outlet (120V AC).

 Charging Speed: Slow (2 to 5 miles of range per hour).
 Charging Time: It can take between 8 to 20+ hours to fully charge an EV, depending on
the battery size.
 Use Case: Best suited for home charging with light daily driving needs or overnight
charging. It’s the most basic and accessible charging option but also the slowest.

2. Level 2 Chargers (AC Charging)

 Power Source: Requires a 240V AC outlet, similar to what is used for large appliances
like dryers.
 Charging Speed: Medium (10 to 30 miles of range per hour).
 Charging Time: Typically takes 4 to 8 hours to fully charge an EV.
 Use Case: Ideal for home, workplace, and public charging stations. It offers faster
charging than Level 1 and is suitable for daily use.

3. DC Fast Chargers (Level 3 Charging)

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 Power Source: Direct current (DC) supplied at high power levels, usually from a 480V
AC source converted to DC.
 Charging Speed: Fast (60 to 80 miles of range in 20 minutes).
 Charging Time: Can charge most EVs from 20% to 80% in 30 to 60 minutes.
 Use Case: Typically found at public charging stations along highways or in urban areas.
They are ideal for long trips or when fast charging is needed, but not suitable for home
charging due to the high power demand.

2.10 Differential Systems in Electric Vehicles (EVs)

In electric vehicles, the differential system plays a crucial role in distributing power from the
motor(s) to the wheels. EV differential systems can vary depending on whether the vehicle uses
a single motor, dual motor, or more advanced setups that enable torque vectoring. Unlike
traditional internal combustion engine vehicles that rely on mechanical differentials, EVs benefit
from advanced electronic control systems to manage power distribution more precisely.

1. Differential Gear Ratios in EVs

The gear ratio in an EV’s differential system refers to how many times the input gear (connected
to the motor) turns compared to the output gear (connected to the wheels). This ratio determines
how torque and speed are balanced:

 Single Motor Differential: In single motor EVs, a single differential distributes power
to both wheels. The gear ratio is optimized to ensure a balance between acceleration and
top speed. Since the motor delivers a wide torque range at different speeds, fewer gears
are needed compared to traditional vehicles.
 Dual Motor Differential: Dual motor EVs, such as those with motors on the front and
rear axles, can use differentials at both axles. In such systems, the front and rear motors
can have different gear ratios optimized for their respective axles, providing better
handling and performance in various driving conditions.

2. Torque Vectoring and Power Distribution in EVs

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Torque vectoring is a technology that allows for the precise distribution of torque to each wheel.
This enhances handling, traction, and stability. In an EV:

 Torque Vectoring: Uses electronic control systems to distribute different amounts of

torque to individual wheels. For example, in a corner, more torque might be sent to the
outer wheel to improve stability and cornering precision. This is particularly useful in all-
wheel-drive (AWD) EVs with dual or more motors.
 Power Distribution: In EVs with dual motors, power distribution between the front and
rear motors is controlled electronically. This ensures the most efficient use of energy and
maximizes traction. Power can be distributed dynamically based on road conditions,
driver inputs, and vehicle speed.

3. Advantages of Advanced Differential Systems in EVs

Advanced differential systems in electric vehicles offer several key advantages over traditional
mechanical differentials:

 Improved Efficiency: Electronic differentials and torque vectoring reduce mechanical

losses by distributing torque more precisely, resulting in better energy efficiency.
 Enhanced Handling: The ability to independently control torque to each wheel improves
the vehicle’s handling, particularly during cornering or on slippery surfaces.
 Better Traction: EVs with torque vectoring can adapt to changing road conditions in
real-time, improving traction in wet or icy conditions.
 Simplified Drivetrain: Without the need for complex mechanical differentials and
gearboxes, EVs have a simplified drivetrain, which can reduce weight and improve
reliability.

4. Practical Applications

 Single Motor EVs: In single motor electric vehicles, a simplified differential system
distributes power to the front or rear wheels. These are most commonly found in compact
and economical EVs.

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 Dual Motor EVs: More advanced electric vehicles, such as the Tesla Model S and Audi
e-tron, use dual motor systems with torque vectoring to distribute power between front
and rear axles. These systems enable superior performance, especially in all-wheel-drive
(AWD) configurations.
 High-Performance EVs: In high-performance electric vehicles, torque vectoring allows
for precise handling at high speeds. Systems like these are found in vehicles such as the
Porsche Taycan, which delivers exceptional cornering performance by controlling torque
distribution across all four wheels.

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