UNIT – III

SPECIAL MACHINES FOR EV AND HEVS

Characteristics of Traction Drive

Requirement of Electric Motors For EV/HEVS
Induction Motor Drives Their Control and Applications In EV/HEVS
Permanent Magnet Synchronous Motor Configuration Control and
Applications In EV/HEVS
Brushless DC Motors Advantages
Control of Application In EV/HEVS. Switch Reluctance Motors Merits
Limitations
Converter Configuration
Control of SRM For EV/HEVS

SPECIAL MACHINES FOR EV AND HEVS

Electric Motors: Electric motors are responsible for converting electrical
energy from the vehicle's battery into mechanical energy to drive the
wheels. There are several types of electric motors used in EVs and HEVs,
each with its own advantages and disadvantages:
Permanent Magnet Synchronous Motors (PMSMs): PMSMs use
permanent magnets to create a magnetic field, and they offer high efficiency
and power density. They are commonly used in EVs due to their compact
size and excellent efficiency.
Brushless DC Motors (BLDC): BLDC motors use electronic commutation to
control the motor's operation, eliminating the need for brushes. They are
efficient, reliable, and have a simple design.
Induction Motors: Induction motors do not require permanent magnets
and are known for their robustness and simplicity. They are often used in
cost-effective EV models.
Generators: Generators in EVs and HEVs serve the purpose of converting
mechanical energy, usually from the vehicle's internal combustion engine or
regenerative braking, into electrical energy to charge the battery or power
auxiliary systems. Generators help improve the overall efficiency of the
vehicle by capturing energy that would otherwise be wasted.
Integrated Starter-Generator (ISG): An ISG combines the functions of a
starter motor and a generator. It starts the engine and can also provide
electrical power during acceleration or assist with regenerative braking.
Wound Field Synchronous Generators: These generators have a wound
field that can be controlled, allowing for efficient power generation across
different operating conditions.
Three-Phase AC Generators: Similar to induction motors, three-phase AC
generators can be used to produce alternating current (AC) electricity for
recharging the battery or powering vehicle systems.
Dual Motors and Motor-Generators: Some EVs and HEVs use multiple
electric machines that can function both as motors and generators. This
setup allows for better energy management, improved performance, and
enhanced regenerative braking.

Characteristics of Traction Drive:

A traction drive is a mechanism used to transmit force or torque between a
power source and a driven component, typically in machinery or
transportation systems. Traction drives are commonly found in various
applications such as vehicles, industrial machinery, and even in some
renewable energy systems. Here are some of the key characteristics of
traction drives:
High Torque Transmission: Traction drives are designed to efficiently
transmit high levels of torque between the power source and the driven
component. This is crucial for applications where a significant amount of
force needs to be transferred, such as in automotive drivetrains or heavy
machinery.
Friction-Based Operation: Traction drives often rely on frictional forces to
achieve torque transmission. Friction between the contacting surfaces of the
drive elements (e.g., wheels, belts, discs) enables the transfer of force from
the power source to the load.
Positive and Non-Positive Engagement: Traction drives can be
categorized into positive engagement and non-positive engagement
systems. Positive engagement systems provide a direct mechanical link
between the power source and the driven component, ensuring a reliable
transfer of torque. Non-positive engagement systems rely on friction to
transmit torque and may slip under certain conditions.
Efficiency and Slip: The efficiency of a traction drive depends on
minimizing energy losses due to friction, wear, and slip. Slip occurs when the
friction forces are not sufficient to prevent relative motion between the drive
elements, leading to a loss of energy. Engineers strive to optimize traction
drive designs to minimize slip and maximize efficiency.
Adjustable Torque Transmission: In some applications, it's desirable to
have the ability to adjust the amount of torque transmitted. Traction drives
can offer this feature through mechanisms that control the pressure or force
applied to the friction surfaces. This adjustability can be particularly useful in
variable load conditions.
Maintenance Considerations: Traction drives that rely on friction for
torque transmission may experience wear over time. This wear can affect
the efficiency and performance of the drive. Regular maintenance and
monitoring are essential to ensure the drive operates optimally and to
identify and address any issues early.
Application Variety: Traction drives are used in a wide range of
applications, from automotive differentials and transmissions to conveyor
systems, elevators, and even in some renewable energy systems like wind
turbines.
Design Complexity: The design of a traction drive involves considerations
of material selection, surface properties, lubrication, cooling, and other
factors that can impact the efficiency, reliability, and lifespan of the drive.
Noise and Vibration: Traction drives, especially those operating with high
friction, can generate noise and vibration during operation. Engineers often
work to minimize these effects through design optimization and the use of
damping mechanisms.
Environmental Impact: The choice of materials and lubricants for traction
drives can impact their environmental footprint. Efforts are being made to
develop more sustainable and environmentally friendly solutions.
It's important to note that the specific characteristics of a traction drive can
vary significantly depending on the application and the design approach
chosen by engineers. As technology evolves, new innovations and
improvements may continue to shape the characteristics of traction drives.

Requirement of Electric Motors For EV/HEVS :

The requirements for electric motors in Electric Vehicles (EVs) and Hybrid
Electric Vehicles (HEVs) are determined by a combination of factors that
include performance, efficiency, reliability, and cost considerations. Here are
some key requirements for electric motors used in EVs and HEVs:
Power and Torque Output: Electric motors must provide sufficient power
and torque output to meet the vehicle's performance requirements. This
includes acceleration, top speed, and overall driving dynamics. The motor's
power rating is a critical factor in determining the vehicle's performance
capabilities.
Efficiency: Electric motors in EVs and HEVs should be highly efficient to
maximize the energy conversion from the battery to the wheels. Higher
efficiency leads to longer driving ranges and improved overall energy
consumption.
Compact Size and Weight: Electric motors should have a compact and
lightweight design to optimize space utilization within the vehicle's chassis.
This is particularly important for EVs, where battery space is limited and
weight reduction is crucial for maximizing range.
Regenerative Braking Capability: Electric motors should be capable of
functioning as generators during regenerative braking. This capability allows
the motor to capture and convert kinetic energy back into electrical energy,
which can be stored in the battery and reused.
Thermal Management: Efficient thermal management is necessary to
prevent the electric motor from overheating during operation. Proper cooling
systems are required to maintain optimal motor performance and longevity.
Durability and Reliability: Electric motors need to be durable and reliable
to withstand the demands of everyday driving. They should be able to
operate smoothly and consistently over the vehicle's lifespan.
Cost-effectiveness: The cost of the electric motor is a significant factor in
the overall cost of the vehicle. Balancing performance and efficiency with
cost considerations is crucial for making EVs and HEVs more accessible to a
broader range of consumers.
Integration with Power Electronics: Electric motors need to be compatible
with the power electronics systems that control their operation. This includes
motor controllers, inverters, and other components that manage the flow of
electricity to and from the motor.
Noise and Vibration Control: Electric motors should operate quietly and
minimize vibrations to enhance the driving experience and reduce cabin
noise.
Manufacturability and Scalability: The design and manufacturing of electric
motors should be scalable and adaptable to different vehicle models and
production volumes.
Environmental Impact: Motors should be designed with consideration for
environmental impact, including the materials used in their construction and
the energy efficiency of their operation.

Induction Motor Drives:

Induction motor drives are a type of electric motor drive system that utilizes
induction motors as the prime movers. Induction motors, also known as
asynchronous motors, are widely used due to their ruggedness, reliability,
and relatively simple construction. They are commonly employed in various
industrial, commercial, and residential applications, including Electric
Vehicles (EVs) and Hybrid Electric Vehicles (HEVs). Here's an overview of
induction motor drives:
Induction Motor Basics: An induction motor operates based on
electromagnetic induction. It consists of a stator and a rotor. The stator
contains the stationary winding, typically connected to a three-phase AC
power supply. The rotor, which is often squirrel-cage shaped, is free to
rotate within the stator's magnetic field.
Working Principle: When AC voltage is applied to the stator windings, it
creates a rotating magnetic field. This rotating field induces currents in the
rotor bars through electromagnetic induction. The interaction between the
stator's rotating magnetic field and the induced currents in the rotor
generates torque, causing the rotor to rotate.
Advantages of Induction Motor Drives:
Simplicity: Induction motors have a simple and rugged construction,
requiring minimal maintenance.
Reliability: The absence of brushes and commutators reduces wear and
tear, making induction motors highly reliable.
Low Cost: Compared to other motor types like permanent magnet motors,
induction motors tend to be more cost-effective.
Robustness: They can withstand high overloads and adverse operating
conditions.
Regenerative Braking: Induction motors can function as generators during
regenerative braking, converting kinetic energy back into electrical energy.
Challenges and Considerations:
Lower Efficiency: Induction motors can have slightly lower efficiency
compared to permanent magnet motors under certain operating conditions.
Control Complexity: Precise speed and torque control of induction motors
require more complex control strategies compared to some other motor
types.
Starting Torque: While induction motors have good starting torque, they
may require additional methods like soft starters or variable frequency
drives for controlled and smooth starting.
Speed Control: Achieving precise and wide-range speed control can be
challenging, especially at low speeds.
Induction Motor Drives in EVs and HEVs: Induction motors are used in
some EVs and HEVs, particularly in vehicles where cost-effectiveness and
simplicity are priorities. Their robustness and ability to handle high overloads
can be advantageous in certain applications. However, in more performance-
oriented or high-efficiency vehicles, permanent magnet motors like
Permanent Magnet Synchronous Motors (PMSMs) are often preferred due to
their higher efficiency and better controllability.

Induction Motor Drives Their Control and Applications In EV/HEVS:

Induction Motor Characteristics:

Simplicity and Durability: Induction motors have a simple construction with
no brushes or commutators, leading to lower maintenance requirements and
increased durability.
High Starting Torque: Induction motors provide high starting torque without
the need for additional components, making them suitable for applications
requiring frequent starts and stops.
Self-Cooling: The rotor design of induction motors allows for natural air
circulation, aiding in cooling without the need for additional cooling systems.
Wide Speed Range: While induction motors have a base speed, they can
operate at variable speeds through the use of frequency converters, making
them suitable for various applications.
Control of Induction Motor Drives:
Variable Frequency Drives (VFDs): To control the speed of an induction
motor, VFDs are commonly used. VFDs adjust the frequency and voltage
supplied to the motor, allowing for precise control of speed and torque.
Vector Control: Field-Oriented Control (FOC) or Vector Control is a
sophisticated control strategy that enables precise control of both the torque
and speed of the induction motor by independently controlling the
magnetizing and torque-producing currents.
Direct Torque Control (DTC): DTC is another advanced control technique
that directly regulates the torque and flux of the motor, providing rapid and
accurate torque response with reduced complexity compared to FOC.
Regenerative Braking: Induction motor drives in EVs and HEVs can also
facilitate regenerative braking, where the motor acts as a generator during
braking to recover energy and store it in the vehicle's battery.
Applications in EVs and HEVs:
Electric Propulsion: Induction motor drives are used in electric propulsion
systems in EVs and HEVs, providing the necessary torque and power for
vehicle movement.
Regenerative Braking: The regenerative braking capability of induction
motor drives helps extend the range of EVs and improve overall energy
efficiency by converting kinetic energy back into electrical energy.
Cost-Effectiveness: Induction motor drives are generally less expensive to
manufacture compared to some other motor types, making them attractive
for cost-sensitive applications like EVs and HEVs.
Robustness: The inherent durability and simplicity of induction motors make
them suitable for the demanding operating conditions of EVs and HEVs.
Traction Control: Precise control over the motor's torque and speed allows
for effective traction control, enhancing vehicle stability and safety.
Power-to-Weight Ratio: Induction motors offer a good balance between
power output and weight, making them suitable for achieving desired
performance characteristics in EVs and HEVs.