Definition of PE

gilamonsterbirdsElectronics - Devices

Nov 24, 2013 (3 years and 6 months ago)

103 views

2013.11.24.

Power Electronics

1

Definition of PE

Topics:

1.











Definition of Power Electronics


Interdisciplinary character of PE


Historical background:


Thyratrons, Mercury
-
Arc


Rectifiers




Saturable Reactors


Relays and Contactors



Mechanical Speed Changers


Economical Significance

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Power Electronics

2

Block diagram of a power
electronic system.

Load
Power
processor
Controller
Power input
Power output
v
i
v
o
i
o
i
i
Reference
Measurements
Control signals
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Power Electronics

3

POWER PROCESSOR BLOCK
DIAGRAM

Power processor
Input
Output
Converter 2
Converter 1
Energy
storage
element
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4

INTERDISCIPLINARY
CHARACTER OF PE


Power
electronics
Electromagnetics
Systems and
control
theory
Electronics
Signal
processing
Circuit
theory
Solid-state
physics
Electric
machines
Power
systems
Simulation
and
computing
Interdisciplinary nature of power electronics.
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HISTORICAL BACKGROUND OF
DEVICES



Thyratron tubes


Controllable rectifier, basically gas
-
discharged tube.


Drawback: limited in current (approx.
50A), limited lifetime ( due to emitting
cathode) and high forward voltage drop.

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MERCURY
-
ARC RECTIFIERS

Current is conducted

by the electric arc between the
anode (graphite) and the cathode (mercury) when
the anode is positive as compared to the cathode.
Conduction is initiated by ignition through a gate
pulse.

Mercury
C
G
A
Vacuum
pump
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FURTHER DEVICES

Saturable Reactors


Use the magnetic properties of the core inside a
coil.


Were replaced by thyristor circuits.

Relays and Contactors

Mechanical Speed Changers

Rheostats



e.g. Electric arc welding and motor starters (wet
resistance)

Constant voltage transformers

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TYPES OF CONVERTER SYSTEMS



AC voltage controllers:


Fixed voltage AC to variable voltage AC


Rectifiers: (uncontrolled)

Fixed voltage AC to fixed voltage
DC


Rectifiers: (controlled)

Fixed voltage AC to variable voltage DC


DC/DC converters

Fixed voltage DC to variable DC
(Choppers):


Reduction:

Buck Converter



Increase:

Boost Converter


Reduce/inc.:

Buck
-
Boost Converter


Inverters (uncontrolled.):

Fixed DC to fixed AC voltage


Inverters (controlled):

Fixed DC to variable AC voltage
(Square/trapezoidal/sine wave output)


Cycloconverters:

Fixed frequency and voltage AC to variable


frequency (and voltage)AC

output (frequency reduction)


Matrix Converters

Fixed frequency and voltage AC to
variable frequency (and voltage) AC

output (frequency
increase/reduction, changing the number of phases)

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9

CONTRIBUTION OF
HUNGARIAN SCIENTISTS



M.
Déry

(1854
-
1938)

-

1 phase comutating repulsion
motor, AC transformer


O.Bláthy

(1860
-
1939)

-

parallel connection of ac
generators, induction current




meter, contribution in development of electric
locomotive,



AC transformer


Zipernowsky

-

AC transformer


K. Kandó

(1869
-
1931)

-

development of the first 3
phase high
-
voltage





locomotive.


I.
Rácz

( )

-

Park vector theory application
in PE, particularly in induction motor


drives


F.
Csáky

(1921
-
1977)

-

control theory, automation,
power electronics

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ECONOMICAL SIGNIFICANCE


Consumption of electric energy in the world
is largely in converted form. Power
Electronic systems has penetrated almost
all fields of technology and our everyday
life.

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Circuits with Switches












The Ideal and Real Switch



(static and mechanical)


Ideal and Real Diode


Role of the Switch in a Network


Switched DC Source, Circuit Equations


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Circuits with Switches and
Diodes


The
role

of a switch in a network:



Apply an energy source


Remove an energy source.


Change the configuration of the network.

V
R
V
SW
_
+
i
v
R
t
1
t
0
i
V/R
t
1
t
0
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RC Load Circuit


Circuit diagram and time functions

V
SW
C
_
_
+
+
i
R

i
C

u
C

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Transient process

In the circuit, when SW is closed at t=0, by
Kirchhoff’s voltage law



V
v
v
C
idt
Ri
V
C
R
t





1
0
1
Solution gives an expression for the time variation of
current I, and hence also for the voltages v
C

and v
R
.
Differentiation of the equation yields
:

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Differentiation of the equation
yields

:

The solution:



di
dt
RC
i
A
s


1
0
/


i
Ae
A
t
RC


/
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Determining initial conditions


For v
C
to change instantaneously, q must change
instantaneously, and this would call for an infinite current.
Thus immediately after the switch is closed at t=0+, v
C
=0,


V= v
R
= Ri [V]


so that at t=0+,


I= V/R [A]
,
substitution of t=0 and


i= V/R in equation yields:


A= V/R [A]


so that
:



i
V
R
e
A
t
RC


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RL Load Circuit


W
hen SW is closed at t=0


R
V
v
L
v
S
v
R
SW
L
_
_
+
+
i


V
v
v
L
di
dt
Ri
V
L
R




or

di
dt
R
L
i
V
L
A
s








(2.4)

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RL Load Circuit

-

cntd


When the steady
-
state has been reached, the
derivative by definition, equals to zero, so that
the forced component of the current is


i
F
= V/R [A]


The natural component is obtained by solution
of the homogeneous equation:




di
dt
R
L
i
A
s
N
N


0
/
of which the solution is
:



i
Ae
A
N
R
L
t


(
/
)
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RL Load Circuit

-

cntd

T
he

complete solution of
E
qu
.
2.4
:



i
i
i
V
R
Ae
A
F
N
R
L
t





(
/
)


i
V
R
e
A
R
L
t



(
)
(
/
)
1


v
L
di
dt
Ve
V
L
R
L
t



(
/
)
and

At t=0, i=0, and substitution in Equ.2.5 yields
,
A=
V/R [A], thus:


(2.5)

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RL Load Circuit



time
functions

Inductor current (upper trace)

Inductor voltage (lower trace)