Electric Drives

Prof. Adel A. El-Samahy

Dr. Abdalla Abdelmouty Sayed
Advanced DC Drives
 INTRODUCTION

Motion control is required in large number of industrial and

domestic applications like transportation systems, rolling mills,
paper machines, textile mills, machine tools, fans, pumps,
robots, washing machines etc.

Systems employed for motion control or speed control are

called drives and may employ any of the prime movers such as,
diesel or petrol engines, gas or steam turbines, steam engines,
hydraulic motors and electric motors, for supplying mechanical
energy for motion control

Drives employing electric motors are known as electrical

drives.
 Merits of Electric Drives
???

Components of electric Drives

???
 Power Converters
• Rectifiers: convert AC (fixed mag. & freq.,) to DC (fixed output voltage)
Main Switching Device (Diode)

• Controlled Rectifiers: convert AC (fixed mag. & freq.,) to controlled DC

voltage
Main Switching Device (SCR)
• DC Choppers: convert DC (fixed mag) to controlled DC Main
Switching Device (Power transistor, MOSFET, IGBT, etc)
• AC voltage Controllers: convert AC (fixed mag. & freq.,) to controlled
AC voltage Main Switching Device (SCR)
• Inverters: convert DC (fixed mag)to controlled AC voltage and/or
frequency Main Switching Device (Power transistor, MOSFET, IGBT, etc)
• Cycloconverters: convert AC (fixed mag. & freq.,) to controlled AC
voltage and frequency. Main Switching Device (SCR, MOSFET, IGBT, etc)
 Power Converters

• Advantages and disadvantages of each type???

• Applications?
 Electric Motors
TYPES OF DC MOTORS
DC MOTORS

SELF- SEPARATELY- PERMANENT

EXCITED EXCITED MAGNET

SHUNT SERIES COMPOUND

WOUND WOUND WOUND

In our study we are going to concentrate on both separately excited

and series types
 Electric Motors

TYPES OF AC MOTORS

AC MOTORS

Induction Synchronous
Motor Motor

In our study we are going to focus on both types

8
 Electric Motors

Other TYPES OF MOTORS

Brushless
Stepper Reluctance
Motors
Motors Motors

……..

9
 Electric Drive System
It is electromechanical system that converts the electric energy into mechanical
energy and supply this energy to different parts of the system with electric control.
Importance of power modulator

?
Modes of Operation
 Separately Excited DC Motor
Advantages:???????

Speed Control
1. Field Current Control : This is achieved by adding power converter in the
field circuit (Advantages & disadvantages)
2. Armature voltage Control by adopting power converter in the armature
circuit (Advantages & disadvantages)

Example
 Variable Armature Voltage
Vt R T
= − a e2
k T  (k T )
Varying Vt

Vt
Varying TL
kT TL

Vt ↓

Te

Requires variable DC supply

 Variable Armature Voltage
R a Te
Vt = (k T ) +
(k T )
Varying Vt

TL Constant TL

Te

Requires variable DC supply

 R a Te
Vt = (k T ) +
(k T )
Vt = (k T ) + Ia R a Varying Vt
Vt
Vt,rate d Constant TL

Ia R a
base 
 Varying Ra
Vt R T
= − a e2
k T  (k T )
Varying Ra


Vt TL
kT

Ra ↑

Te

Simple control
Losses in external resistor
 Varying 
Vt R T
= − a e2
k T  (k T )

Varying 

Vt TL
kT

↓

Te

Not possible for PM motor

Maximum torque capability reduces
Armature voltage control : retain maximum torque capability
Field flux control (i.e. flux reduced) : reduce maximum torque capability
For wide range of speed control
0 to base → armature voltage, above base → field flux reduction

Armature voltage control

Field flux control
Te

Maximum
Torque capability

base 
Introduction

P Te Constant torque Constant power

Pmax

base 

0 to base → armature voltage, above base → field flux reduction

P = EaIa,max = kaIa,max Pmax = EaIa,max = kabaseIa,max

→   1/
MODELING OF CONVERTERS AND DC MOTOR

POWER ELECTRONICS CONVERTERS

Used to obtain variable armature voltage

• Efficient
Ideal : lossless

• Phase-controlled rectifiers (AC → DC)

• DC-DC switch-mode converters(DC → DC)

Modeling of Converters and DC motor

Phase-controlled rectifier (AC–DC)

ia

+ 
3-phase
Vt Q2 Q1
supply

− Q3 Q4 T
Modeling of Converters and DC motor

Phase-controlled rectifier

+
3-
phase 3-phase
Vt supply
supply
−

Q2 Q1

Q3 Q4
T
Modeling of Converters and DC motor

Phase-controlled rectifier

F1 R1

3-phase
supply
+ Va -
R2 F2

Q2 Q1

Q3 Q4
T
 Controlled Rectifier Drives

1. Single Phase Half Wave Converter Drives

Discontinuous
Operation
Without Free Wheeling Diode

 is the firing angle, the conduction angle , where the thyristor blocks at angle .
. extinction angle
 Controlled Rectifier Drives

1. Single Phase Half Wave Converter Drives

With Free Wheeling Diode

the thyristor blocks at angle p , the conduction angle  = p−

Discontinuous
Operation
 Controlled Rectifier Drives
1. Single Phase Half Wave Converter Drives (one quadrant operation?)

Converters Equations

Va =
Vm
(1 + Cos a )
2p

Vf =
Vm
(1 + Cos )
p
f

Motor Equations

Va = Eb + IaRa

Eb = Kv  If = K 
𝑉𝑓
= K I Very large inductance
Td = Kv I If If =
𝑅𝑓
Continuous operation
Advantages & Disadvantages
 Controlled Rectifier Drives
1. Single Phase Half Wave Converter Drives
Disadvantages
• Producing of highly pulsating current which increases the motor Ia Ra and core
2

losses.
• The AC supply has a large harmonic current content and it has to provide a DC
component.
• Pulsating torque

These draw backs can be tolerated for low motor rating in which the armature
current may discontinuous, and this would increase the losses in the motor, Lm is
normally connected in series with the armature circuit to reduce the ripple current to
an acceptable value (magnitude).

Therefore this arrangement is usually used for hand – tools, small

domestic machines, etc

.
 Controlled Rectifier Drives
1. Single Phase Half Wave Converter Drives With Free Wheeling Diode (one
quadrant operation?)

Very large inductance

Continuous operation