THREE PHASE INVERTER

dehisceforkΗλεκτρονική - Συσκευές

2 Νοε 2013 (πριν από 4 χρόνια και 8 μέρες)

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THREE PHASE

INVERTER

AIM

To simulate Three phase inverter using MATLAB Simulink model

SOFTWARE USED

MATLAB 2010

SIMULINK LIBRARY BROWSER

Item

Path

Icon

Opening Simulink


1.

Click on the
Simulink
icon on Matlab taskbar

2.

Type Simulink on
Matlab Command
Window


Selecting New File

File
-
> New
-
> Model


Selecting
DC Source

Libraries
-
>SimpowerSystems

-
> electrical sources


Selecting IGBT

Libraries
-
>SimPowerSystems
-
>
PowerElectronics
-
>Thyristor


Selecting Series RLC branch

Libraries
-
>SimpowerSystems

-
> Elements


Selecting Pulse
Generater(Triggering)

Libraries
-
> Sources


Mux


Libraries
-
> Simulink


-
>
Commonly used blocks



Voltage Measurement

Libraries
-
>SimpowerSystems

-
> Measurement


Scope

Libraries
-
> Sink



THEORY


Device that converts dc input voltage to ac
output voltage of desired magnitude and
frequency is called an inverter.
Inverters can be classified into single phase inverters and three phase
inverters . Switching devices used in inverters uses PWM control signals for producing an ac output
voltage.
If

the input voltage remains constant the inverter is called a Voltage
sourc
e inverter and if the input current
remains constant it is known as a Current source inverter.
Three phase inverters are normally used for high
power
applications. A

Three phase inver
ter can be obta
ined

from a configuration of six transistors and six
diodes as
shown. Two

types control signals can be applied to the transistors 180˚ conduction or 120˚
conduction.180 ˚conduction conduction has better utilisation of switches and is
preferr
ed
method. In

180˚conduction mode each transistor conducts for 180˚ and in 120˚conduction mode each transistor
conducts for 120˚




CIRCUIT


180
o

CONDUCTION

In 180
0

conduction scheme,each device conducts for 180
0
. They are turned ON at regular interval of 60
0

in
the sequence
Q
1,
Q
2
,Q
3,
Q
4,
Q
5,
Q
6
.The output terminals A B and C of this bridge are connected to the terminals
of a 3
-
phase star or delta connected load.

For a star connected balanced load, the operation is explained below.During the period 0
0

to 60
0
, s
1
s
5

and s
6

are conducting. Load terminals A and C are connected to positive terminal of the source and load terminal B
is connected to negative terminal of the source. Equivalent circuit is shown below. Resistance between
positive terminal and neutral is R/
2 and between negative terminal and neutral is R.


Hence,
load voltages are

V
AN
=V/3,

V
BN
=
-
2V/3,

V
CN
=V/3

Line volages are

V
AB
=V
AN
-
V
BN
=V
,

V
BC
=V
BN
-
V
CN
=
-
V

,

V
CA=
V
CN
-
V
AN
=0




Similarly other equivalent circuits and voltages can be
found.


0
-
60
0

: T
1,
T
5,
T
6

V
AB
=V
AN
-
V
BN
=V,

V
BC
=V
BN
-
V
CN
=
-
V ,

V
CA=
V
CN
-
V
AN=
0


V
AN
=V/3,


V
BN
=
-
2V/3,


V
CN
=V/3



60
0
-
120
0
: T
1,
T
2,
T
6

V
AB
=V
AN
-
V
BN
=V,

V
BC
=V
BN
-
V
CN
=
0 ,

V
CA=
V
CN
-
V
AN=
-
V


V
AN
=2V/3,

V
BN
=
-
V/3,


V
CN
=
-
V/3




12
0
0
-
18
0
0
: T
1,
T
2,
T
3

V
AB
=V
AN
-
V
BN
=0,

V
BC
=V
BN
-
V
CN
=
V ,

V
CA=
V
CN
-
V
AN=
-
V


V
AN
=V/3,

V
BN
= V/3,


V
CN
=
-
2V/3



180
0
-
240
0
: T
2
,
T
3,
T
4


V
AB
=V
AN
-
V
BN
=
-
V
,

V
BC
=V
BN
-
V
CN
=
V ,

V
CA=
V
CN
-
V
AN=
0


V
AN
=

-
V/3,

V
BN
=
2

V/3,


V
CN
=


-
V/3



240
0
-
300
0
: T
3,
T
4,
T
5


V
AB
=V
AN
-
V
BN
=
-
V,

V
BC
=V
BN
-
V
CN
=
0

,

V
CA=
V
CN
-
V
AN=
V


V
AN
=
-
2
V/3,

V
BN
= V/3,


V
CN
=

V/3


3
00
0
-
360
0
: T
4,
T
5,
T
6


V
AB
=V
AN
-
V
BN
=
0
,

V
BC
=V
BN
-
V
CN
=
-
V

,

V
CA=
V
CN
-
V
AN=
V


V
AN
=
-
V/3,

V
BN
=
-

V/3,


V
CN
=

2
V/3








Wave forms for 180˚conduction mode


























120
0

CONDUCTION


In 120
0

conduction scheme each device conducts for 120
0
.It is preferable for a delta connected load
because it provides a six step waveform across any phase.As each device conducts for
120
0

, only two
devices are in conduction state at any instant.

During the period 0
0

to 60
0

, Q
1
to Q
6

are conducting. Load terminals A is connected to positive terminal and
load terminal B is connected to negative terminal of the source. Load terminal C is in floating state.

Phase Voltages=Line Voltages

V
AB
= V

V
BC
=
-
V/2


Vca=
-
V/2




Waveform for

120˚conduction










SETTING PULSE DELAY FOR IGBT



1.

The Pulse Generator block generates square wave pulses at regular intervals.
This square wave
pulses are applied to IGBT for triggering.
The block's waveform parameters,
Amplitude
,
Pulse
Width
,
Period
, and
Phase Delay
, determine the sh
ape of the output waveform.

Pulse type

The pulse type for this block: time
-
based or sample
-
based. The default is time
-
based.

Time

Specifies whether to use simulation time or an external signal as the source of values for

the output
pulse's time variable. If you specify an external source, the block displays an input port for
connecting the source. The output pulse differs as follows:

If you select Use simulation time, the block generates an output pulse where the time var
iable equals
the simulation time.




If you select Use external signal, the block generates an output pulse where the time variable equals
the value from the input port, which can differ from the simulation time.

So set pulse type and time as shown in the
figure.

2.

Amplitude

The pulse amplitude. The default is 1.


3.

Period

The pulse period specified in seconds if the pulse type is time
-
based or as number of sample times if
the pulse type is sample
-
based. The default is 10 seconds.


Here the period to be set =20
millisecond because the time period of the ac wave to be
generated = =1/frequency of ac wave =1/50=20ms ,



4.Pulse width

The duty cycle specified as the percentage of the pulse period that the signal is on if time
-
based
or as
number of sample times if sample
-
based. The default is 5 percent

Here time delay is set as 33.33 %


5
.
Phase delay

The delay bef
o
re the pulse is generated specified in seconds if the pulse type is time
-
based or as
number of sample times if the
pulse type is sample
-
based. The default is 0 seconds.


Values for phase delay can be obtained as follows


20ms=360
0

1
0
=20/360

60
0
=(20/360)*60


In the figure shown above the specifications given are for pulse generator 4


PULSE GENERATOR

DELAY IN DEGREE

DELAY IN
MILLISECONDS

Pulse generator 1

0

0

Pulse generator 2

60

3.33ms

Pulse generator 3

120

6.66ms

Pulse generator 4

180

10ms

Pulse generator 5

240

13.33ms

Pulse generator 6

300

16.66ms





6
.

Sample time

The length of the sample time for this block in seconds. This parameter appears only if the block's
pulse type is sample
-
based.

7
.

Interpret vector parameters as 1
-
D

If you select this check box and the other parameters are one
-
row or one
-
column matrices,

after
scalar expansion, the block outputs a 1
-
D signal (vector). Otherwise the output dimensionality is the
same as that of the other parameters.


RESULT:


The simulation of 3
-
phase ac inverter was done using matlab and obtained the output

waveforms .