THREE PHASE INVERTER
AIM
To simulate Three phase inverter using MATLAB Simulink model
SOFTWARE USED
MATLAB 2010
SIMULINK LIBRARY BROWSER
Item
Opening Simulink
Selecting New File
Selecting DC Source
Selecting IGBT
Selecting Series RLC branch
Selecting Pulse
Generater(Triggering)
Mux
Path
1. Click on the Simulink
icon on Matlab taskbar
2. Type Simulink on
Matlab Command
Window
File -> New -> Model
Libraries ->SimpowerSystems
-> electrical sources
Icon
Libraries ->SimPowerSystems >PowerElectronics ->Thyristor
Libraries ->SimpowerSystems
-> Elements
Libraries -> Sources
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 source 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 inverter can be obtained 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 preferredmethod. In
180˚conduction mode each transistor conducts for 180˚ and in 120˚conduction mode each transistor
conducts for 120˚
CIRCUIT
180o CONDUCTION
In 1800 conduction scheme,each device conducts for 1800. They are turned ON at regular interval of 600 in
the sequence Q1,Q2,Q3,Q4,Q5,Q6.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 600, s1 s5 and s6
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
VAN=V/3,
VBN=-2V/3,
VCN=V/3
Line volages are
VAB=VAN-VBN=V,
VBC=VBN-VCN=-V ,
VCA=VCN-VAN=0
Similarly other equivalent circuits and voltages can be found.
0-600 : T1,T5,T6
600-1200: T1,T2,T6
VAB=VAN-VBN=V,
VBC=VBN-VCN=-V ,
VCA=VCN-VAN=0
VAB=VAN-VBN=V,
VBC=VBN-VCN=0 ,
VCA=VCN-VAN= -V
VAN=V/3,
VBN=-2V/3,
VCN=V/3
VAN=2V/3,
VBN= -V/3,
VCN= -V/3
1200-1800: T1,T2,T3
1800-2400: T2,T3,T4
VAB=VAN-VBN=0,
VBC=VBN-VCN=V ,
VCA=VCN-VAN= -V
VAN=V/3,
VBN= V/3,
VCN= -2V/3
VAB=VAN-VBN=-V,
VBC=VBN-VCN=V ,
VCA=VCN-VAN= 0
VAN= -V/3,
VBN=2 V/3,
VCN= -V/3
2400-3000: T3,T4,T5
3000-3600: T4,T5,T6
VAB=VAN-VBN=-V,
VBC=VBN-VCN=0 ,
VCA=VCN-VAN= V
VAB=VAN-VBN=0,
VBC=VBN-VCN=-V ,
VCA=VCN-VAN= V
VAN= -2V/3,
VBN= V/3,
VCN= V/3
VAN= -V/3,
VBN=- V/3,
VCN= 2V/3
Wave forms for 180˚conduction mode
1200 CONDUCTION
In 1200 conduction scheme each device conducts for 1200.It is preferable for a delta connected load
because it provides a six step waveform across any phase.As each device conducts for 1200 , only two
devices are in conduction state at any instant.
During the period 00 to 600 , Q1 to Q6 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
VAB= V
VBC= -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 shape 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 variable 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 before 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=3600
10=20/360
600=(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 .