breaking-lecture-notes/39233625

1. Electric
Machines and
their Controllers
for electric
vehicles
Prof Khaled Mahmoud

2. The ‘Brushed’ DC Electric Motor
• Electric vehicles use what can seem a bewildering
range of different types of electric motors.
However, the simplest form of electric motor, at
least to understand, is the ‘brushed’ DC motor. This
type of motor is very widely used in applications
such as portable tools, toys, electrically operated
windows in cars, and small domestic appliances
such as hair dryers, even if they are AC mains
powered. However, it is also still used as a traction
motor, although the other types of motors
considered later in this chapter are becoming more
common for this application. The brushed DC
motor is a good starting point because, as well as
being widely used, most of the important issues in
electric motor control can be more easily explained
with reference to this type of motor.

3. Torque Speed Characteristics
• If a wire in an electric motor has a length l
meters, carries a current I amperes and is in
a magnetic field of strength B Weber per
square meter, then the force on the wire is
F = BIl

7. Torque vs Speed of brushed DC motor

8. Controlling the Brushed DC Motor
• A brushed DC motor is an electrical
machine that converts direct current
electrical energy into mechanical
energy. It consists of a rotor (the
rotating part of the motor) and a stator
(the stationary part of the motor), with
brushes and a commutator that help
transfer electrical power to the rotor.
To control a brushed DC motor, you
need to be able to control the speed
and direction of the rotor.

9. Controlling the Brushed DC Motor
• There are several ways to control the speed of a brushed DC motor, including:
• Voltage Control: The simplest way to control the speed of a brushed DC motor is to control
the voltage applied to it. By increasing or decreasing the voltage, you can increase or
decrease the speed of the motor. However, this method may not be suitable for applications
where precise speed control is required.
• Pulse Width Modulation (PWM): PWM is a technique that involves rapidly switching the
voltage on and off to the motor. By varying the duty cycle (the percentage of time the voltage
is on), you can control the average voltage applied to the motor and hence the speed. This
method provides more precise speed control than voltage control.
• Current Control: You can also control the speed of a brushed DC motor by controlling the
current supplied to it. By increasing or decreasing the current, you can increase or decrease
the torque produced by the motor, and hence the speed. This method is commonly used in
applications where high torque is required, such as in electric vehicles.
• To control the direction of a brushed DC motor, you need to reverse the polarity of the
voltage applied to it. This can be achieved by using a reversing switch or by using an H-bridge
circuit, which allows you to control both the speed and direction of the motor.
• It's important to note that brushed DC motors require regular maintenance, such as replacing
the brushes and cleaning the commutator, to ensure optimal performance and longevity.

10. Controlling the Brushed DC Motor
• In addition to the methods mentioned earlier, there are other techniques for controlling brushed DC motors,
such as:
4. Feedback Control: Feedback control involves measuring the speed or position of the motor and adjusting the
voltage or current accordingly to maintain a desired speed or position. This method provides highly precise
control of the motor and is commonly used in applications such as robotics and automation.
5. Sensorless Control: Sensorless control is a technique that does not require external sensors to measure the
speed or position of the motor. Instead, it uses the back EMF (electromotive force) of the motor to estimate
its speed and position. This method is less expensive and simpler than feedback control but may not provide
as precise control.
6. Microcontroller Control: Microcontroller control involves using a microcontroller (a small computer) to
control the motor. The microcontroller can receive input from sensors, buttons, or other sources and use this
information to adjust the motor's speed and direction. This method provides highly versatile control and is
commonly used in hobbyist and DIY projects.
When selecting a method for controlling a brushed DC motor, it's important to consider the requirements of
the specific application, such as the required speed and torque, the need for precise control, and the available
budget. Additionally, it's important to choose a method that is compatible with the motor and the power
supply being used.

11. A brushless DC motor (BLDC)

12. A brushless DC motor (BLDC)
• A brushless DC motor (BLDC) is an electric motor that operates using direct
current (DC) and employs electronic commutation instead of the traditional
mechanical commutation used in brushed DC motors.
• The brushless design uses a permanent magnet rotor and a stator that contains a
series of coils, which are energized in a particular sequence to generate a rotating
magnetic field that drives the rotor. The sequence of energizing the coils is
controlled by an electronic device called a motor controller, which determines the
speed and direction of the motor.
• BLDC motors are widely used in many applications, including electric vehicles,
drones, and industrial machinery, due to their efficiency, high power density, and
low maintenance requirements. They also have a longer lifespan compared to
brushed DC motors, as there are no brushes that wear out over time. However,
they do require more complex control systems and are generally more expensive
than brushed DC motors.

13. A brushless DC motor (BLDC) efficiency
• The efficiency of a brushless DC motor (BLDC) can vary depending on various factors,
such as the design of the motor, the operating conditions, and the load on the motor.
However, BLDC motors are generally known for their high efficiency compared to other
types of motors.
• The efficiency of a BLDC motor is typically in the range of 80-90%, meaning that a
majority of the electrical energy supplied to the motor is converted into mechanical
energy. This high efficiency is due to the absence of brushes, which reduces friction and
eliminates the need for maintenance.
• However, the efficiency of a BLDC motor can be affected by various factors, such as the
quality of the motor design, the operating temperature, and the load on the motor. For
example, operating the motor at higher temperatures can reduce its efficiency, and
operating the motor at very low speeds can also reduce its efficiency.
• Overall, a well-designed and properly operated BLDC motor can be a highly efficient and
reliable option for various applications, such as in electric vehicles, drones, and industrial
machinery.

14. A brushless DC motor (BLDC) control
• A brushless DC motor (BLDC) control system is a system that manages the operation of a BLDC
motor. The control system typically includes a microcontroller or a specialized BLDC motor
controller, sensors for measuring motor speed and position, and a power supply.
• The main function of the control system is to regulate the power supplied to the motor windings in
a precise and efficient manner, to achieve the desired speed and torque output. This is achieved by
using feedback from the motor sensors to adjust the timing and duration of the power pulses
supplied to the motor windings.
• There are two main types of BLDC motor control systems: sensor-based and sensorless. Sensor-
based control systems use feedback from Hall effect sensors or other position sensors to determine
the rotor position and adjust the power pulses accordingly. Sensorless control systems use
algorithms to estimate the rotor position based on the back electromotive force (EMF) generated by
the motor windings.
• BLDC motor control systems can be implemented in various ways, ranging from simple open-loop
control to complex closed-loop control systems that include advanced features such as current
limiting, fault detection, and automatic tuning. The choice of control system depends on the
application requirements, the motor specifications, and the available resources for implementing
the control system

15. Comparison between brushless and brushed
DC motor
• Brushed DC motors and brushless DC motors (BLDC) are two different types of electric motors that operate
using direct current (DC) power. Here are some key differences between the two:
1. Brushed DC motors have brushes that meet the commutator, while BLDC motors do not have brushes. This
means that BLDC motors do not suffer from brush wear and maintenance issues.
2. Brushed DC motors have a simpler design compared to BLDC motors, which have more complex electronics
and sensor systems for control. This complexity can make BLDC motors more expensive and more difficult
to repair.
3. Brushed DC motors are typically less efficient than BLDC motors due to energy losses in the brushes and
commutator. BLDC motors can be more efficient because they don't have these components, resulting in
lower power consumption and longer battery life.
4. Brushed DC motors are generally better suited for low-speed and low-torque applications, while BLDC
motors are better suited for high-speed and high-torque applications. This is because BLDC motors can
operate at higher speeds without overheating, and they can deliver more torque without the brushes wearing
down.
5. Brushed DC motors are simpler to control and can be easily driven using simple electronic circuits, while
BLDC motors require more complex control electronics, such as microcontrollers and sensors, to achieve
precise speed and torque control.

16. DC Motor efficiency

17. Which is more suitable for electric vehicle
brushless DC motor, brushed DC motor, or AC
induction motor
• All three types of motors have their advantages and disadvantages, and the suitability of
each for an electric vehicle depends on several factors.
• Brushless DC (BLDC) motors are often preferred for electric vehicles due to their higher
efficiency, longer lifespan, and better torque characteristics. They also require less
maintenance than brushed DC motors and have no brushes to wear out. However, BLDC
motors can be more expensive and may require more complex electronic control systems.
• Brushed DC motors are simpler and less expensive than BLDC motors, but they have
lower efficiency and a shorter lifespan due to the brushes wearing out. They also have
limited torque compared to BLDC motors and may require more maintenance.
• AC induction motors are also an option for electric vehicles, and they are known for their
high torque output and low maintenance requirements. However, they are generally less
efficient than BLDC motors and may require more complex control systems.
• Ultimately, the choice of motor depends on the specific requirements of the electric
vehicle, such as its size, weight, power requirements, and budget.