I. INTRODUCTION
1.1 What is Electric Drives
1.2 Application of Electric Drives
1.3 Some Driven Units
1.4 Electric Drive quadrant Operation Concepts
1.5 Content of the course
I. INTRODUCTION
1.1 What is Electric Drives
Electric Drives Refers to system which converts electrical power
to Mechanical power in a Controlled Manner. Such systems
consists of:In Traditional Drives:
In Modern Electric Drives
• Electric motors,
• Coupling between the
motor and the driven unit
like gears, belt and chains,
• Electric power supply
control systems like
Magnetic Contactors, pole
changing mechanisms, etc
• Electric motors and the
• Power Electronics (As
Power Processors) and
• Control systems.
I. INTRODUCTION
1.1 What is Electric Drives
The following is a typical block diagram of Modern Electric Drives. There is
Electric Motor from which information like motor speed, rotor position, current
etc are fed back to controller. The controller based on the command (reference
variable) and the feedback variables generate control signal to power electronics
systems like (inverter or converter) to control the electric power flow to the the
electric motor.
I. INTRODUCTION
1.1 What is Electric Drives
As indicated in the block diagram, the knowledge and skills
required for electric drive design and analysis includes, but not
limited to, the following:•
Electric Machinery
•
Power Electronics
•
Control Theory
•
Computer including microprocessors and algorithms
•
Mechanical Systems understanding and modeling
•
Sensors (instrumentations)
•
Electric Utility interaction, etc.
I. INTRODUCTION
1.1 What is Electric Drives
Electric Drives can be DC drives or AC drives. DC drives are
equipped with DC motors and AC/DC or DC/DC converters. On
the other hand AC drives are equipped with either synchronous
motors or induction motors being supplied from inverters.
Typical structure of DC motors
Typical structure of Induction motors
I. INTRODUCTION
1.1 What is Electric Drives
In Modern Electric Drives AC drives are encouraged against DC derives. This is
due to the following reasons.
(1) DC motors require maintenance, are heavy, are expensive, speed limited by
mechanical construction
(2) AC motors require less maintenance, relatively light, are cheaper, are robust,
can run at high speed (esp. squirrel–cage type)
With respect to Control unit:
For DC drives: Simple control – decoupling torque and flux by mechanical
commentator –brush action, the controller can be implemented using simple
analog circuit even for high performance torque control –cheaper.
For AC drives: The types of controllers to be used depend on the required drive
performance –cost increases with performance. Scalar control drives technique
does not require fast processor/DSP whereas in Field Oriented Control or Direct
Torque Control drives, DSPs or fast processors are normally employed.
I. INTRODUCTION
1.2 Application of Electric Drives
Today, electric drives application is everywhere; in residential and
commercial buildings, in our offices, in various industries
including manufacturing, agricultural, transport, etc industries.
•
Heating, Ventilating and Air Conditioning:- blowers, fans, and compressors
•
Moving and Mixing process components:- Agitators, pumps, fans, and
compressors
•
As propellers in Transportation:- elevators, trains, and automobiles
•
Paper and Steel Industry:- hoisting and roller machine derives, winches,
chippers, drill presses, sanders, saws, extruders, feeders, mills, and press
machining
•
Oil, Gas, and Mining:- Conveyers, compressors, pumps, cranes, and shovels
•
Textile:- looms, E.t.c.
I. INTRODUCTION
1.3 Some Driven Units
Electric drives are basically to derive some mechanical driven units. The driven
units can be simple machines to complex systems. Based on their torque-speed
characteristics, simple driven units can be categorized in to four.
Basic torque-speed characteristics of simple Driven Units can be expressed by
the following equation.

Where:-




TL  T f  Tn  T f 


n

x
TL is torque the driven unit exerts on the motor driving it in N-m when the
driven unit is running at speed .
Tf is frictional torque of the driven unit in N-m,
Tn torque the driven unit exert on the motor driving it at its rated operating
speed, n, and power. Speed n is rated speed in radians per second.
I. INTRODUCTION
1.3 Some Driven Units
Driven units can be categorized into four depending on the value of
exponent x of the equation.
Category 1: x = 0, torque independent of speed.
Category 2: x = 1, torque proportional to speed.
Category 3: x = 2, torque proportional to speed squared.
Category 4: x = -1, torque inversely proportional to speed.
I. INTRODUCTION
1.3 Some Driven Units
Category 1: x = 0, torque independent of speed.
Examples:‐ Crane lifting load at constant speed, conveyer with
constant rate of material moved.
I. INTRODUCTION
1.3 Some Driven Units
Category 2: x=1, torque proportional to speed.
Examples:‐ Electric generator with resistive load
I. INTRODUCTION
1.3 Some Driven Units
Category 3: x=2, torque proportional to speed squared.
Examples:- Fans and centrifugal pumps
I. INTRODUCTION
1.3 Some Driven Units
Category 4: x=-1, torque inversely proportional to speed.
Examples:- Drilling machines, metal cutting spindle drives
I. INTRODUCTION
1.3 Some Driven Units
Some Driven units have combination of these characteristics.
Example is an electric driven train has force components which is
independent of speed, proportional to speed, proportional to speed
squared, … Accelerating force is constant or independent of speed,
force required to overcame rail gradient is also independent of
speed while, friction and aerodynamic resistance is proportional to
speed and speed squared.
MgC4
TL  rMa  rMg sin   C1  C2v  C3v  r
R
2
Exercise: Explain each of the above components using physical laws.
I. INTRODUCTION
1.4 Electric Drive quadrant Operation Concepts
Some of the driven units require operation of the electric drive in various
quadrants. Four quadrants are possible on speed versus torque plane. The first
quadrant is where the torque and speed are positive and known as forward
motoring operation. The second quadrant is where the torque is positive while
the speed is negative. This is breaking mode of operation and is known as
reverse braking. The third quadrant is where both speed and torque are
negative and is known as reverse motoring. The last, fourth, quadrant is
forward braking mode of operation where speed is positive while torque is
negative.
In the two motoring modes of operation, electric power is converted to
mechanical power while the reverse is true for the braking modes of operation.
Electric drives which can operate in the four quadrants are sometimes known as
Ward Leonard Systems.
I. INTRODUCTION
1.4 Electric Drive quadrant Operation Concepts
Example 1: Crane operation
An example of driven unit requiring operation in multiple quadrants is a
crane. A crane speed and torque can be considered as positive when it is
lifting the load. During this time, electric energy is converted to potential
energy. The motor drive is operating in first quadrant. When the crane is to
put down the load, the speed becomes negative while the torque has to remain
positive in order to prevent the load from acceleration due to gravity. So, the
motor is operating in reverse braking mode as shown below.
I. INTRODUCTION
1.4 Electric Drive quadrant Operation Concepts
Example 2: Electric Vehicle Drive
In an electric vehicle drive, the electric drives are required to operate in four quadrants.
The first quadrant is when the electric vehicle moves forward bring propelled by the
motor. This operation can be considered as first quadrant torque and speed being
positive.
•
If we intend to stop the vehicle, we apply a negative torque decelerating the motor
speed. Then we are operating in the fourth quadrant.
•
The electric vehicle can also move backward with negative speed and torque, that is
•
third quadrant.
Again while the vehicle is moving
backward, we may need to apply
braking which is positive torque
while the speed remains negative.
That is reverse breaking, quadrantII operation.
I. INTRODUCTION
1.5 Content of the Course
In this course we will cover the following main sections
II. Electromechanical Energy Conversion Principles
III. Basic Electric Machine Models
IV. DC motor Drives
V. Reference Frame Theory
VI. Induction Machine Drives
VII. Synchronous Machine Drives