Advanced Power Electronics and Drives (EGLM02)

12 Pulse AC/DC Converter Fed From 3‐Phase 400V, 50Hz
Supply Using MATLAB/SIMULINK/POWER SYSTEM TOOL
BOX.
Abstract: The paper present the modeling,
simulation of the 12 pulse AC to DC 3-phase
converter using MATLAB.FFT (using powerful)
analysis has been performed and total
harmonic distortion (using spectrum analysis)
(THD ) results obtained .
Introduction: Now a day’s harmonics are
serious problem in the power system due to
highly uses of electronics equipment’s. AC to DC
converters are mainly used in power system.
This problem can be reduced by using the active
filters. These filters are operated at high
switching frequency. Power factor cos(angle)
and harmonic components of input line current
can be improved by the poly-phase AC/DC
Converter. For this an autotransformer is
connected with 12 pulse AC to DC converter to
obtain high power factor and low harmonic
distortion. For this simulations and their results
are given below.
12-Pulse AC to DC Converter:
12 pulse AC to DC converter is shown in figure.
The power factor and harmonic components of
the line current can be improved by shifting the
input voltage from 00 to 300 in delta to star
connected AC to DC converter. An auto-
transformer also used for this purpose. Figure
shows a 12 pulse AC to DC converter fed from
3-phase 400V, 50 Hz supply. A level constant
100 A DC current is flowing through the load.
The transform‐1 has a turn ratio of NY1/
NY2=1:1 and the output voltage Vdc1 and
Vdc2 are equal.
Figure shows the 12 pulse AC to DC converter in
which Ia1, Ib1 and Ic1 is line current and Va1 is
phase voltage of transformer-1.Ia2, Ib2 and Ic2
is line current and Va2 is phase voltage of
transformer-2.
Total load voltage is Vdc=Vdc1+Vdc2
If Vdc1=Vdc2
Than Vdc=2 V
Harmonics in voltage:
The rectifier bridge forming the double bridge
contain 6K–th harmonics, while 6*(2K-1)-th
harmonic generated by bridge-1 and 2 are equal
to the harmonic current but polarity is
opposite.so they cancel out each other.
So h=2*K
Here k=(1, 2, 3......n)
For double pulse inverter harmonics are 12, 24,
36......etc.
Advantage of the 12 pulse AC/DC
converter:
The ripple content of ac voltage superimposing
the mean value of the dc voltage is reducing
greatly.
The ac line voltage has only odd harmonics and
the value of is increase to 0.96, that is

fundamental current is 96 % of the total rms
value of the current.
It also has better power factor.
The harmonics presents are 12K±1, here
K=1,2,3....
Power quality can be improved by using 12
pulse AC to DC converter.
Figure 1: Circuit Diagram of 12 pulse AC to DC
converter
Matlab Simulations:
Discrete,
Ts = 1e-06 s.
powergui
A
B
C
a
b
cD11 Y
Transform er 2
A
B
C
a
b
cY Y
transformer 1
D1 D3
D4 D6
d1
d6
d3
i
+ -
ia
v
+
-
Vdc1
N
A
B
C
400 V/50 HZ
v
+
-
Vdc2
v
+
-
Vdc
D5
D2
d2
d5
+
10.5 ohm & 20 e-3 H
i
+ -
ia1
i +
-ia2
Current in ia, ia1,ia2
Voltage across Vdc1,Vdc2,Vdc
d4
i
+ -
iA1
i
+ -
Id4
i
+ -
id1
current in IA1,ID1,ID4
Spectrum
Analyzer of Ia1
Spectrum
Analyzer1 of Ia
Spectrum
Analyzer2 of Ia2
i
+ -
id2
i
+ -
id3
current in IA1,ID1,ID1
Figure 2: MATLAB circuit of 12 pulse AC/DC
converter
Magnitude across Vdc1 and Vdc2 is equal.
Figure 3: Voltage across Vdc1, Vdc2 and Vdc
Figure 4: Spectrum Analysis of current Ia1
(THD=17.33 %)

Figure 5: Spectrum Analysis of current Ia2
(THD=19.81 %)
Figure 6: Spectrum Analysis of current Ia3
(THD=13.32%)
Figure 7: Current wave forms across Ia,Ia1 and
Ia2
Conclusion: The result obtained by MATLAB
simulink is analyzed and it is proved that as we
increase the number of pulses THD decreases,
settling time decreases and output voltage and
current ripple also decreases. It also improve
the power quality and power factor. Results are
shown above using MATLAB.
References:
1) https://www.researchgate.net/
publication/
3818410_Analysis_of_12_pulse_phase_
control_ACDC_converter
2) https://www.researchgate.net/
publication/
3275498_Harmonic_Mitigation_Using_
12-Pulse_AC DC_Converter_in_Vector-
Controlled_Induction_Motor_Drives