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1. POWER ELECTRONICS AND
APPLICATIONS
(DC Motor Drives)
Rakan Khalil Antar
Department of Power Electrical
Engineering
Technical College / Mosul

2. DC Motors
• Several limitations:
• Advantage: Precise torque and speed
control without sophisticated electronics
• Regular Maintenance • Expensive
• Heavy • Speed limitations
• Sparking

3. Lf Rf
if
a
a
a
a
t e
dt
di
L
i
R
v 


+
ea
_
La
Ra
ia
+
Vt
_
+
Vf
_
dt
di
L
i
R
v f
f
f
f


a
t i
k
Te 
 Electric torque

 E
a k
e Armature back e.m.f.
Equivalent Circuit

4. a
a
a
t E
I
R
V 

In steady state,
 2
T
e
a
T
t
k
T
R
k
V





Therefore speed is given by,
Three possible methods of speed
control:
Field flux
Armature voltage Vt
Armature resistance Ra
a
a
a
a
t e
dt
di
L
i
R
V 


Armature circuit:

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

6. What is power electronics
Branch of electrical engineering
devoted to conversion and control
of electric power using electronic
converter based on semiconductor
power switches

7. Input
DC
AC
Output
DC
AC
Choppers
Cycloconverters or controllers
Types of power conversion and the
corresponding power converters

8. Power Electronics Approach
The main objective of the power electronics is to
produce
Efficient and Controllable systems that process
electric power...

9. Thyristor Family
Thyristors
Uncontrollable Half-controllable Fully-controllable
Diode
Reverse-Blocking
Triode Thyristor
SCR
Bidirectional
Triode Thyristor
Triac
Gate-Turn Off
Thyristor
GTO
MOSFET-
Controlled Thyristor
MCT

10. Power Diodes
IFM
VFM
IRM
VBR
V
A K
i

11. Silicon Controlled Rectifier, SCR
K
V
A
G
I
IG0
IG1
IG2
IG3
IG4
IG4 < IG3 <IG2<IG1<IG0=0
ITH
VTH
VRB
IL
IH
I
V
VFB

12. How the SCR can be turned ON?
2. Through the Gate: If the Anode current (IT) increased to
higher than the device latching current (IL), while the gate
pulse is being applied.
1. If the forward voltage (VAK) acceded the forward
blocking voltage of the device (VFB)

13. How the SCR can be turned OFF?
SCR can be turned-off ,when the forward conduction current
be reduced to a value below the holding current (Ih ) of the
devices for sufficient time.
In AC circuits SCR turns OFF as the currents tends to
change its polarity (natural commutation)
In DC circuits, to turn OFF the SCR an additional
auxiliary circuit is applied to bring the SCR to zero
(forced commutation)

14. MODELING OF CONVERTERS
AND DC MOTOR
Used to obtain variable armature voltage
POWER ELECTRONICS CONVERTERS
• Efficient
Ideal : lossless
• Phase-controlled rectifiers (AC  DC)
• DC-DC switch-mode converters(DC  DC)

15. Modeling of Converters and DC motor
Phase-controlled rectifier (AC–DC)
T
Q1
Q2
Q3 Q4

3-phase
supply
+
Vt

ia

16. Common Applications
AC-to-DC converter applications:
•DC motor supply.
•High voltage DC transmission.
•Supply DC-fed converters (such as inverters).
•Battery chargers.
•Electric Welding.

17. AC-to-DC Converters
Uncontrolled and controlled Rectifiers
1. Three-pulse rectifier
2. Six pulse rectifier

18. Three-Pulse Diode Rectifier
N
VAN
VBN
VCN
DA
DB
DC
Vo
Io

19. 0 p/6 5p/6 3p/2
Van
Vbn
Vcn
DA DB DC

20. vo
p
LN
p
LN
dc
o
V
t
d
t
V
V
,
6
5
6
,
,
2
3
3
)
sin(
2
3
p


p
p
p

 
0 p/6 5p/6 3p/2

21. Six Pulse Diode Rectifier
VAN
VBN
VCN
DA DB DC
DA- DB- DC-
Io
N
Vo
P
N

22. van vbn vcn
DA DB DC
DA- DB-
DC-
DB-
0° 30° 90° 150° 210° 270° 330° 390°

23. Controlled Rectifier
VAN
VBN
VCN
N
Vo
TA TB TC
TA' TB' TC'
a
ap/3
a2p/3
ap
a4p/3
a5p/3
I
o
p
n

24. 0 20 40 60 80 100 120 140 160 180
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Vout,dc verses Alpha
alpha(degree)
Vout,dc/Vll,p
Vo,dc is negative
for a >90°

26. io
vo VAN
VBN
VCN
N
Vo
I
o
VAN
VBN
VCN
N
Vo
TA TB TC
TA' TB' TC'
a
a+p/3
a+2p/
3
a+p
a+4p/3
a+5p/3
I
o
1
2
3 4

27. The output voltage verses, a
The
line-to-line
voltages
a=0
(identical to
uncontrolled
converter)
p/3 a
a>90
(The average of the
output voltage is
negative)
p/3
a
p/3
a<90
(The average of the
output voltage is
positive)