International Journal of Scientific Engineering and Technology www.ijset.com, Volume No.1, Issue No.4, pg : 61-70
(ISSN : 2277-1581) 01 Oct. 2012
Multi pulse AC-DC Converter Analysis for RL Load D. Singh, Prof. H. Mahala, Prof. P. Kaur Department of Electrical & Electronics Engineering, N.R.I.-I.I.S.T., Bhopal deependra_2001in@yahoo.com, hemantmahala@yahoo.co.in, paramjeet_12@yahoo.com Abstract — This paper presents the analysis of AC current wave shaping AC-DC converters for effective harmonic mitigation under similar loads. The proposed converters consist of a star-connected phase shifting transformer based multipulse AC-DC converters. The proposed AC-DC converters eliminate the most dominant adjacent harmonics and also reduce the higher order harmonics; thereby, resulting in an improved power quality at AC main supply. To validate the approach, same machine indices are presented under all loads. Experimental results obtained are given to validate the model and design of the multipulse converter. Index Terms — Multipulse, Total Harmonic Distortion, THD, Form factor, Ripple Content.
I. INTRODUCTION In the past few years a lot of work has been done for the reduction of Total Harmonic Distortion using different concepts and applications. This thesis work deals with the reduction of Total Harmonic Distortion using Multi-pulse AC to DC Conversion scheme. The results are obtained for both uncontrolled and controlled converters for RL Load. The three-phase multi-pulse AC to DC conversion system employs a phase-shifting transformer and a three-phase converter between the supply and load side of the system. Every such converter provides 6-pulse AC to DC conversion, so in order to produce more sets of 6-pulse systems, a uniform phase-shift is required and hence with proper phase-shifting angle, 12, 18, 24, 30, and higher pulse systems can be produced[1]. Different rectifiers are used for conversion of AC supply into DC supply. For uncontrolled conversion, diodes have been preferred, while for the controlled conversion, thyristors have been implemented. The performance improvement of multi-pulse converter is achieved for total harmonics distortion (THD) in supply current, DC voltage ripples and form factor. All the simulations have been done for similar ratings of RL Load, for all the multi-pulse converters configurations, so as to represent a fair comparison among controlled and uncontrolled continuations of multi-pulse converters. The presented simulation results show the reduced THD at supply side. These results agree with the IEEE Standards 519-1992[2]. Effect of increase in number of pulses in converter circuits for uncontrolled and controlled multipulse converter on input supply current and DC side voltage and current has been presented in this paper.
61
II. OBJECTIVE OF PRESENT STUDY The present work is an effort towards analyzing the different multi-pulse AC to DC converters in solving the harmonic problem in a three-phase converter system. The effect of increasing the number of pulses on the performance of AC to DC converters has been analyzed. For performance comparison the major factors considered are the ripple percentage, form factor and the total harmonic distortion (THD). The effects of load variation on multi-pulse AC to DC converters have also been investigated[2]. III. MULTI-PULSE METHODS Multi-pulse methods involve multiple converters connected so that the harmonics generated by one converter are cancelled by harmonics produced by other converters. By this means, certain harmonics related to number of converters are eliminated from the power source. In multipulse converters, reduction of AC input line current harmonics is important as regards to the impact the converter has on the power system[3]. Multi-pulse methods are characterized by the use of multiple converters or multiple semiconductor devices with a common load. Fig. 1 & Fig. 2 given below depict the various techniques used widely for the reduction of harmonics[4].
Fig. 1. Various Harmonic Reduction Techniques
International Journal of Scientific Engineering and Technology www.ijset.com, Volume No.1, Issue No.4, pg : 61-70
(ISSN : 2277-1581) 01 Oct. 2012
A+ B+
+ -i
a3
A
b3
B
c3
C
C+ ABC-
i + +
-
+ v -
Zigzag Phase Shifting Transformer (+15 deg)
Continuous A+ B+
a3
A
b3
B
c3
C
C+ ABC-
powe rgui +
-
Zigzag Phase Shifting Transformer (-15 deg)
Fig. 5. Uncontrolled twelve pulse converter Fig. 2. Multi-Pulse Converter Configurations FFT window: 1 of 50 cycles of selected signal 50
IV. SIMULATION OF UNCONTROLLED MULTI-PULSE CONVERTERS
0 -50 0.15
+ i i + -
A+ B+
a3
A
b3
B
c3
C
C+ ABC-
+ - v +
-
Continuous
Zigzag Phase Shifting Transformer (0 deg)
powe rgui
0.152
0.154
0.156
0.158
0.16 Time (s)
0.162
0.164
0.166
0.168
Fundamental (50Hz) = 76.73 , THD= 0.63% 0.45 0.4 Mag (% of Fundamental)
A. Six-Pulse Converter The six pulse converter bridge shown in Fig 3. as the basic converter unit of HVDC transmission is used for rectification, where electrical power flows from the AC side to the DC side and inversion where the power flow is from the DC side to the AC side. Thyristor valves operate as switches which turn on and conduct current when fired on receiving a gate pulse and are forward biased. The characteristic AC side current harmonics generated by 6-pulse converters are 6nÂą1, Characteristic DC side voltage harmonics generated by a 6-pulse converter are of the order 6nÂą1.
0.35 0.3 0.25 0.2 0.15 0.1 0.05 0
0
2
4
6
8
10 Harmonic order
12
14
16
18
Fig. 6. THD for input current
C. Eighteen Pulse Converter In this 18-pulse topology, the magnetic circuit involved is same as that of a 6-pulse converter. Therefore this topology is comparatively a preferred one. The simulated results are in close agreement with any result obtained from an 18 pulse converters. A phase shift of 200 has been provided between all three phase shift transformers with star connected secondary.
Fig. 3. Uncontrolled Six-Pulse Converter +
A+ B+
a3
A
b3
B
c3
C
C+ A-
i
+
BC-
-
i -
+
-
Zigzag Phase Shifting Transformer (0 deg)
FFT window: 1 of 50 cycles of selected signal 50
A+
0
B+
a3
A
b3
B
c3
C
C+ A-
-50
B-
0.15
0.152
0.154
0.156
0.158
0.16 Time (s)
0.162
0.164
0.166
C-
0.168
+
+ -
v
-
Zigzag Phase Shifting Transformer (+20 deg)
Continuous powe rgui
Fundamental (50Hz) = 68.5 , THD= 1.07%
A+
0.8
B+
a3
A
b3
B
c3
C
C+
Mag (% of Fundamental)
0.7
AB-
0.6
C-
+
-
Zigzag Phase Shifting Transformer (-20 deg)
0.5 0.4
Fig. 7. Uncontrolled eighteen pulse converter
0.3 0.2 0.1 0
0
2
4
6
8
10 Harmonic order
12
14
16
18
20
FFT window: 1 of 50 cycles of selected signal 50
Fig. 4. THD for input current
0 -50 0.15
0.152
0.154
0.156
0.158
0.16 Time (s)
0.164
0.166
0.168
Fundamental (50Hz) = 80.63 , THD= 0.41%
0.2 0.15 0.1 0.05
0
0
5
10
15 Harmonic order
Fig. 8. THD for input current
62
0.162
0.25
Mag (% of Fundamental)
B. Twelve Pulse Converter Twelve-pulse converter is a series connection of two fully controlled six pulse converter bridges and requires two 3phase systems which are spaced apart from each other by 30 electrical degrees. The phase difference effected to cancel out the 6-pulse harmonics on the AC and DC side.
20
20
25
International Journal of Scientific Engineering and Technology www.ijset.com, Volume No.1, Issue No.4, pg : 61-70
(ISSN : 2277-1581) 01 Oct. 2012 FFT window: 1 of 50 cycles of selected signal
A+ B+
a3
A
b3
B
c3
C
C+ ABC-
i -
+
+
B+
a3
A
b3
B
c3
C
C+ ABC-
A
b3
B
c3
C
C+ ABC-
-
v
+
-
Continuous
Zigzag Phase Shifting Transformer (-15 deg)
powe rgui
A+ B+
a3
A
b3
B
c3
C
C+ ABC-
0.154
0.156
0.158
0.16 Time (s)
0.162
0.164
0.166
0.168
Fundamental (50Hz) = 83.43 , THD= 0.36% 0.25
0.2
0.15
0.1
0.05
0
0
5
10
15
20 Harmonic order
25
30
35
40
Fig. 12. THD for input current
F. Thirty-Six Pulse Converter The connection for 36-pulse converter and the corresponding connections are shown in fig. 13 Five sixpulse converters phase shifted by 10from each other, can provide thirty-six pulse conversion, and obviously with much lower harmonics on AC and DC side. Its AC output voltage would have 30n±1order harmonics
+
+
a3
0.152
-
-
B+
0.15
i -
Zigzag Phase Shifting Transformer (+15 deg)
A+
0 -50
+
Zigzag Phase Shifting Transformer (0 deg)
A+
50
Mag (% of Fundamental)
D. Twenty-Four Pulse Converter The connection for 24-pulse converter and the corresponding connections are shown in fig. 9. Four six pulse converters phase shifted by 15 degrees from each other, can provide twenty four pulse rectification, obviously with much lower harmonics on AC and DC side. Its AC output voltage would have 24n±1 order harmonics i.e., 23 rd, 25th, 47th , 49th harmonics with magnitudes of 1/23rd , 1/25th , 1/47th ,1/49th ,… respectively, of the phase shift.
+
-
Zigzag Phase Shifting Transformer (-30 deg)
A+ B+
a3
A
b3
B
c3
C
C+ AB-
Fig. 9. Uncontrolled twenty four pulse converter
+
C-
i
i +
+
-
-
Zigzag Phase Shifting T ransformer (+05 deg)
-
A+ B+
a3
A
b3
B
c3
C
C+ ABC-
+
-
Zigzag Phase Shifting T ransformer (+15 deg)
FFT window: 1 of 50 cycles of selected signal
A+ B+
a3
A
b3
B
c3
C
C+ A-
50
BC-
0
-
+ -
B+
-50
a3
A
b3
B
C+ AB-
0.15
0.152
0.154
0.156
0.158
0.16 Time (s)
0.162
0.164
0.166
C-
0.168
v
Continuous
A+
C
c3
pow ergui
+
-
Zigzag Phase Shifting T ransformer (-05 deg)
A+ B+
a3
A
b3
B
c3
C
C+ AB-
Fundamental (50Hz) = 82.41 , THD= 0.06%
C-
+
-
Zigzag Phase Shifting T ransformer (-15 deg)
0.025
A+ B+
Mag (% of Fundamental)
+
Zigzag Phase Shifting T ransformer (+25 deg)
a3
A
b3
B
c3
C
C+ A-
0.02
BC-
+
-
Zigzag Phase Shifting T ransformer (-25 deg)
0.015
Fig. 13. Uncontrolled Thirty-Six Pulse Converter
0.01
0.005
0
0
5
10
15
20 Harmonic order
25
30
35
40
FFT window: 1 of 50 cycles of selected signal
Fig. 10. THD for input current
50 0 -50
A+ B+
a3
A
b3
B
c3
C
C+ AB-
+
i
C-
+ +
i -
-
Zigzag Phase Shifting Transformer (+0.01 deg)
-
A+ B+
a3
A
b3
B
c3
C
C+ ABC-
+
-
Zigzag Phase Shifting Transformer (+12 deg) A+ B+
a3
A
b3
B
c3
C
C+ ABC-
+
+ -
v
-
Zigzag Phase Shifting Transformer (-12 deg) A+ B+
a3
A
b3
B
c3
C
C+ ABC-
+ C ontinuous powe rgui
Zigzag Phase Shifting Transformer (+24 deg) A+ B+
a3
A
b3
B
c3
C
C+ ABC-
+
-
Zigzag Phase Shifting Transformer (-24 deg)
Fig. 11. Uncontrolled thirty pulse converter
63
0.15
0.152
0.154
0.156
0.158
0.16 Time (s)
0.162
0.164
0.166
0.168
Fundamental (50Hz) = 84.2 , THD= 0.17% 0.12
Mag (% of Fundamental)
E. Thirty-Pulse Converter The connection for 30-pulse converter and the corresponding connections are shown in fig. 11 six pulse converters phase shifted by 12 degrees from each other, can provide thirty-pulse conversion, and obviously with much lower harmonics on AC and DC side. Its AC output voltage would have 30n±1 order harmonics i.e., 29 th, 31st, 59th , 61st harmonics with magnitudes of 1/29th, 1/31st, 1/59th , 1/61st,…respectively, of the phase shift.
0.1 0.08 0.06 0.04 0.02 0
0
5
10
15
20 Harmonic order
25
30
35
40
Fig. 14. THD for input current
G. Forty-Eight Pulse Converter For high power FACTS controllers, from the point of view of the AC systems even a twenty-four, thirty or thirty-six pulse converter without AC filters could have voltage harmonics, which are higher than the acceptable level. The alternative of course is go to 48 pulse operation with eight six pulse groups with one set of transformers of one 24 pulse converters phase shifted converter from 7.5 degrees all 8 transformer primaries may be connected in series.
International Journal of Scientific Engineering and Technology www.ijset.com, Volume No.1, Issue No.4, pg : 61-70 +
A+ B+
a3
A
b3
B
c3
C
C+ AB-
+
C-
i -
06 12 18 24 30 36 48
i -
+
-
Zigzag Phase Shifting Transformer (0 deg) A+ B+
a3
A
b3
B
c3
C
C+ ABC-
+
-
Zigzag Phase Shifting Transformer (+7.5 deg)
+ -
A+ B+
a3
A
b3
B
c3
C
C+ ABC-
v
+
powergui
A+ a3
A
b3
B
c3
C
C+ ABC-
C. Analysis of DC Voltage Form Factor Table 3: Form Factor Observed on Simulation No. of Pulses Form Factor 06 1.001 12 1 18 1 24 1 30 1 36 1 48 1
+
-
Zigzag Phase Shifting Transformer (+22.5 deg) A+ B+
a3
A
b3
B
c3
C
C+ ABC-
+
-
Zigzag Phase Shifting Transformer (-7.5 deg) A+ B+
a3
A
b3
B
c3
C
C+ ABC-
+
-
Zigzag Phase Shifting Transformer (-15 deg) A+ B+
a3
A
b3
B
c3
C
C+ ABC-
4.352 0.9479 0.5821 0.0588 0.313 0.2739 0.2988
Continuous
-
Zigzag Phase Shifting Transformer (+15 deg)
B+
(ISSN : 2277-1581) 01 Oct. 2012
+
-
Zigzag Phase Shifting Transformer (-22.5 deg) A+ B+
a3
A
b3
B
c3
C
C+ ABC-
+
VI. SIMULATION OF CONTROLLED MULTI-PULSE CONVERTERS
-
Zigzag Phase Shifting Transformer (-30 deg)
Fig. 15. Uncontrolled Forty-Eight Pulse Converter
For the simulation of controlled multi pulse converters instead of the diode bridge we use the Thyristor Bridge and the corresponding pulses are given.
FFT window: 1 of 50 cycles of selected signal 50 0 -50 0.15
0.152
0.154
0.156
0.158
0.16 Time (s)
0.162
0.164
0.166
A. Six-Pulse Converter
0.168
+ i Fundamental (50Hz) = 85.12 , THD= 0.11%
75
0.08
Mag (% of Fundamental)
i +-
In1 Conn1 Out1 Conn2
0.07 0.06 0.05
g
Conn3 A+
0.04
B+
0.03
a3
A
b3
B
c3
C
C+ 0.02
A-
0.01 0
-
B0
5
10
15
20
25 Harmonic order
30
35
40
45
C-
50
+ - v
+
Zigzag Phase Shifting Transformer (0 deg)
Continuous powergui
Fig. 16. THD for input current
V. UNCONTROLLED MULTI-PULSE CONVERTERS FOR RL LOAD
Fig. 17. Controlled six-pulse Converter
FFT window: 1 of 50 cycles of selected signal 50
0
-50 0.15
0.152
0.154
0.156
0.158
64
0.162
0.164
0.166
14
16
0.168
Fundamental (50Hz) = 68.58 , THD= 0.44%
0.2 0.15
0.1 0.05
0
0
2
4
6
Fig. 18. THD for input current
B. Analysis of DC Voltage Ripple Content Table 2: % Ripple Content Observed on Simulation No. of Pulses Ripple Content
0.16 Time (s)
0.25 Mag (% of Fundamental)
A. Analysis of Supply Current THD Table 1: Total Harmonic Distortion Observed on Simulation No. of Pulses THD 06 1.07 12 0.63 18 0.41 24 0.06 30 0.36 36 0.17 48 0.11
8
10 Harmonic order
12
18
20
International Journal of Scientific Engineering and Technology www.ijset.com, Volume No.1, Issue No.4, pg : 61-70 B. Twelve Pulse Converter
(ISSN : 2277-1581) 01 Oct. 2012 In1
75
Conn1 Out1
Conn2
firing angle
Conn3
PWM
g +
A+ B+
a3
A
b3
B
c3
C
C+ A-
75
In1 Conn1 Out1 Conn2 Conn3
BC-
+
Zigzag Phase Shifting Transformer (0 deg)
-
i -
+
A
a3
B+
i
+
g
A+
+ -i
B-
Zigzag Phase Shifting Transformer (+15 deg)
g
Conn3
C-
+ - v
B C
+ Out1
PWM2
a3
B
b3
BC-
C
c3
Zigzag Phase Shifting Transformer (-15 deg)
A+ a3
A
b3
B
c3
C
C+ B-
B+
powe rgui Out1
g +
PWM3 a3
A
b3
B
c3
C
C+ A-
powergui
BC-
C ontinuous
Conn1
A+
Continuous
-
In1
Conn3
+
v
A
C+
In1 Conn1 Out1 Conn2
+
Conn2
C-
g
Conn3
A-
-
Conn1 Conn2
B+
g
A-
A
In1
A+
Conn3
B+
+
PWM1
c3
Zigzag Phase Shifting Transformer (+15 deg)
-
C
c3
C-
Out1
Conn2
b3
B-
B
b3
A-
In1
a3
C+ A-
C+
i -
Conn1
A+ B+
+
-
-
Zigzag Phase Shifting Transformer (-30 deg)
-
Fig. 23. Controlled twenty four pulse converter
Zigzag Phase Shifting Transformer (-15 deg)
Fig. 19. Controlled Twelve Pulse Converter FFT window: 1 of 50 cycles of selected signal 50 0
FFT window: 1 of 50 cycles of selected signal
-50
50
0.15
0.152
0.154
0.156
0.158
0.16 Time (s)
0
0.162
0.164
0.166
0.168
-50 0.15
0.152
0.154
0.156
0.158
0.16 Time (s)
0.162
0.164
0.166
Fundamental (50Hz) = 82.43 , THD= 0.13%
0.168 0.09 Mag (% of Fundamental)
0.08
Fundamental (50Hz) = 76.86 , THD= 0.13%
Mag (% of Fundamental)
0.05 0.04
0.07 0.06 0.05 0.04 0.03 0.02 0.01 0
0.03
0
5
10
15
20 Harmonic order
25
30
35
40
0.02
Fig. 24. THD for input current
0.01 0
0
2
4
6
8
10 Harmonic order
12
14
16
18
20
E. Thirty Pulse Converter
Fig. 20. THD for input current
In1
75
Conn1 Out1
Conn2
firing angle1
Conn3
PWM
g +
A+ B+
a3
A
b3
B
c3
C
C+
C. Eighteen-Pulse Converter
ABC-
+
Zigzag Phase Shifting Transformer (+0.01 deg)
i -
+
i -
-
In1 Conn1 Out1
Conn2 Conn3
75
PWM1
In1 Conn1 Out1 Conn2
A
a3
C+ A-
i -
b3
B
c3
C
+
+
i
A-
C-
-
C-
v
g + A
C+
A
b3
B
c3
C
B
b3
AB-
+ + -
C
c3
C-
Zigzag Phase Shifting Transformer (-12 deg)
v
-
powergui Out1
Conn3
g
PWM3
+
A+
Continuous
In1 Conn1 Out1 Conn2
B+
a3
A
b3
B
C+
powe rgui
Conn3
A-
g
A+ a3
A
b3
B
C+
B-
C
c3
C-
+
In1 Conn1
C
c3
-
Zigzag Phase Shifting Transformer (+24 deg)
-
B-
Continuous
-
In1 Conn1 Conn2
Zigzag Phase Shifting Transformer (+20 deg)
C-
Out1
a3
B+
g
a3
B-
A-
+
Conn1
PWM2
Conn3
B+
-
In1
A+
C+
C-
C
Conn2
In1 Conn1 Out1 Conn2
A+
A-
B
c3
Zigzag Phase Shifting Transformer (+12 deg)
Conn3
Zigzag Phase Shifting Transformer (0 deg)
B+
A
b3
B-
-
B-
a3
C+
g
+
+
B+
A+ B+
g
A+
Conn3
Out1
Conn2
g
Conn3
Zigzag Phase Shifting Transformer (-20 deg)
A+
+ PWM4
a3
B+
A
C+ A-
b3
B
c3
C
BC-
Fig. 21. Controlled eighteen pulse converter
-
Zigzag Phase Shifting Transformer (-24 deg)
Fig. 25. Controlled Thirty Pulse Converter
FFT window: 1 of 50 cycles of selected signal 50 0 FFT window: 1 of 50 cycles of selected signal
-50
50
0.15
0.152
0.154
0.156
0.158
0.16 Time (s)
0.162
0.164
0.166
0.168
0 -50 0.15
0.152
0.154
0.156
0.158
Fundamental (50Hz) = 80.64 , THD= 0.11%
0.16 Time (s)
0.162
0.164
0.166
0.168
0.08
Fundamental (50Hz) = 83.55 , THD= 0.10%
0.06
0.07
0.05
0.06
Mag (% of Fundamental)
Mag (% of Fundamental)
0.07
0.04 0.03 0.02 0.01 0
0
5
10
15
20
25
0.05 0.04 0.03 0.02 0.01
Harmonic order 0
0
5
10
Fig. 22. THD for input current Fig. 26. THD for input current
D. Twenty-Four Pulse Converter
65
15
20 Harmonic order
25
30
35
40
International Journal of Scientific Engineering and Technology www.ijset.com, Volume No.1, Issue No.4, pg : 61-70
(ISSN : 2277-1581) 01 Oct. 2012
F. Thirty-Six Pulse Converter FFT window: 1 of 50 cycles of selected signal 75
In1
50
Conn1
firing angle1
Out1
Conn2
g
Conn3 A+
+ PWM
a3
A-
b3
B
c3
C
BC-
+
Zigzag Phase Shifting Transformer (+05 deg)
i -
0.15 Out1
Conn2
-
C
c3
Out1
PWM2
a3
A
b3
B
c3
C
B-
Zigzag Phase Shifting Transformer (+25 deg)
+ -
Conn1 Out1
Conn2
RLC Branch
g
Conn3
A
C+
powergui
B
b3
B-
Out1
Conn2
B
b3
B-
10
15
20
25 Harmonic order
30
45
50
In1 Out1
g
Conn3
+ PWM5
a3
A
C+ b3
B
c3
C
B-
-
VII. CONTROLLED MULTI-PULSE CONVERTERS FOR RL LOAD
Zigzag Phase Shifting Transformer (-25 deg)
Fig. 27. Controlled Thirty-Six Pulse Converter
A. Analysis of Supply Current THD Table 4: Total Harmonic Distortion Observed on Simulation No. of Pulses THD 06 0.44 12 0.13 18 0.11 24 0.13 30 0.10 36 0.06 48 0.06
FFT window: 1 of 50 cycles of selected signal 50 0 -50 0.156
0.158
0.16 Time (s)
0.162
0.164
0.166
0.168
Fundamental (50Hz) = 84.23 , THD= 0.06% 0.045 0.04 Mag (% of Fundamental)
5
Conn1
A+
0.154
0
Fig. 30. THD for input current
-
C
c3
Conn2
0.152
0.01
A
C+
0.15
0.02 0.015
+ PWM4
Zigzag Phase Shifting Transformer (-15 deg)
C-
40
0.03 0.025
g
Conn3 a3
0.035
0
In1 Conn1
A+
A-
35
0.168
0.005
-
C
c3
Zigzag Phase Shifting Transformer (-05 deg)
B+
Continuous
+ PWM3
a3
C-
v
-
In1
A+
A-
0.166
Fundamental (50Hz) = 85.16 , THD= 0.06%
+
C+
B+
0.164
0.04
g
Conn3
C-
0.162
Conn1
A+
A-
0.16 Time (s)
0.045
In1 Conn2
B+
0.158
B
b3
B-
C-
0.156
A
C+
A-
0.154
+ PWM1
Zigzag Phase Shifting Transformer (+15 deg)
B+
0.152
g
Conn3
C-
-50
Conn1
a3
A-
i -
+ -
In1
A+ B+
0
A
C+
Mag (% of Fundamental)
B+
0.035 0.03 0.025 0.02 0.015 0.01 0.005 0
0
5
10
15
20 Harmonic order
25
30
35
Fig. 28. THD for input current
G. Forty-Eight Pulse Converter In1
75
Conn1
firing angle1
Out1
Conn2
g
Conn3 A+ B+
+ PWM
a3
A
C+ AB-
+
i -
C-
C
c3
Zigzag Phase Shifting Transformer (0 deg)
Conn1 Out1
Conn2
g
Conn3
+ PWM1
a3
A
C+ A-
b3
B
c3
C
BC-
Zigzag Phase Shifting Transformer (+7.5 deg)
Out1
Conn2
+ PWM2
C
c3
Out1
Conn2
g
Conn3
+ PWM3
a3
A
C+ ABC-
C
c3
Conn1 Out1
Conn2
g
Conn3 B+
+ PWM4
a3
A
C+ A-
B
b3
BC-
C
c3
Zigzag Phase Shifting Transformer (-7.5 deg)
Conn1 Out1
Conn2
A+
g +
PWM5
a3
A
C+ A-
B
b3
BC-
C
c3
Zigzag Phase Shifting Transformer (-15 deg)
Conn1 Out1
Conn2
A+
g +
PWM6
a3
A
C+ A-
b3
B
c3
C
BC-
Zigzag Phase Shifting Transformer (-22.5 deg)
B+
a3
C+ A-
Out1
Conn2
g
C-
+ PWM7
A
b3
B
c3
C
B-
-
In1 Conn1 Conn3
A+
-
In1
Conn3 B+
-
In1
Conn3 B+
-
In1
A+
Continuous powergui
B
b3
Zigzag Phase Shifting Transformer (+22.5 deg)
-
In1 Conn1
A+ B+
v
B
BC-
-
A
b3
Zigzag Phase Shifting Transformer (+15 deg)
+
g
Conn3 a3
C+ A-
-
In1
B. Analysis of Ripple Content Table 5: % Ripple Content Observed on Simulation No. of Pulses Ripple Content 06 12.13 12 35.44 18 4.499 24 3.334 30 2.56 36 2.127 48 1.606
Conn1
A+ B+
i -
-
In1
A+ B+
+
B
b3
40
-
C. Analysis of Form Factor Table 6: Form Factor Observed on Simulation No. of Pulses Form Factor 06 1.007 12 1.002 18 1.001 24 1.001 30 1 36 1 48 1
Zigzag Phase Shifting Transformer (-30 deg)
Fig. 29. Controlled Forty-Eight Pulse Converter
VIII. CONCLUSION
66
International Journal of Scientific Engineering and Technology www.ijset.com, Volume No.1, Issue No.4, pg : 61-70
Uncontrolled Controlled Uncontrolled 0.45 0.4 0.35 0.3
THD
A. Simulation The various isolated multi-pulse configurations were simulated using the software MATLAB/SIMULINK[5] and the results have been presented in this chapter in Table 1 to Table 6. The effect of load variation on different multi-pulse converters reveals that with RL load because of inductance there is smoothing effect on current, therefore current THD decreases. The effect is similar for different multi-pulse converters, i.e. it increases current discontinuity and hence affecting the harmonic spectrum adversely.
(ISSN : 2277-1581) 01 Oct. 2012
0.25 0.2 Controlled 0.15 0.1 0.05 0
18 pulse converter 0.41 0.11
Uncontrolled Controlled
(c) Eighteen Pulse Converter Uncontrolled Controlled Controlled 0.14 0.12 0.1 0.08
Uncontrolled
THD
B. Performance Analysis And Comparison All the data obtained after simulation of aforesaid models using MATLAB/SIMULINK has been collected here so as to ease the comparison of factors accounted for i.e. THD, Ripple Content and Form Factor between Uncontrolled & Controlled Multi-pulse converters. All the results obtained have been collected from Tables 5.1 to 5.6 and categorised on the basis of Load provided so as to ease the comparison.
0.06 0.04 0.02 0
24 pulse converter
1) Total Harmonic Distortion Uncontrolled Controlled
0.06 0.13
Uncontrolled Controlled
(d) Twenty Four Pulse Converter
Uncontrolled 1.2
1
Uncontrolled Controlled
0.8
Uncontrolled
THD
0.4
Controlled
0.6
0.35 0.3
0.4
0.25
THD
0.2
0
0.15
1.07 0.44
0.1
Uncontrolled Controlled
Controlled
0.05
(a) Six Pulse Converter
0
30 pulse converter
Uncontrolled Controlled
0.7
0.2
6 pulse converter
0.36 0.1
Uncontrolled Controlled
(e) Thirty Pulse Converter
Uncontrolled
0.6 Uncontrolled Controlled
0.5 Uncontrolled 0.18
THD
0.4
0.16
0.3
0.14
Controlled
0.2
0.12
THD
0.1 0
12 pulse converter Uncontrolled Controlled
0.63 0.13
0.1 Controlled
0.08 0.06 0.04 0.02
(b) Twelve Pulse Converter
0
36 pulse converter Uncontrolled Controlled
0.17 0.06
(f)Thirty Six Pulse Converter
67
International Journal of Scientific Engineering and Technology www.ijset.com, Volume No.1, Issue No.4, pg : 61-70
(ISSN : 2277-1581) 01 Oct. 2012 Uncontrolled Controlled
Uncontrolled Controlled
Uncontrolled
Controlled 3.5
0.14
3
0.12 Controlled
2.5
RIPPLE % AGE
0.1
THD
0.08 0.06
2 1.5
0.04
1
0.02
0.5
0
0
24 pulse converter
48 pulse converter Uncontrolled Controlled
0.14 0.09
Uncontrolled Controlled
Uncontrolled
0.0588 3.334
(d) Twenty Four Pulse Converter
(g) Forty Eight Pulse Converter Fig. 31. %THD for RL Load: (a) – (g)
Uncontrolled Controlled
2) Percentage Ripple Content 3
Uncontrolled Controlled
Controlled
2.5 Controlled RIPPLE % AGE
14 12
RIPPLE % AGE
10 8
2
1.5
1 Uncontrolled
Uncontrolled
6
0.5
4
0
2
Uncontrolled Controlled
30 pulse converter
0
6 pulse converter
(e) Thirty Pulse Converter
4.352 12.13
Uncontrolled Controlled
0.313 2.56
(a) Six Pulse Converter
Uncontrolled Controlled 2.5
Uncontrolled Controlled
2
Controlled
RIPPLE % AGE
40 35 30
RIPPLE % AGE
Controlled
25
1.5
1 Uncontrolled
20
0.5 15
0
10
36 pulse converter
Uncontrolled 5
Uncontrolled Controlled
0
0.2739 2.127
12 pulse converter Uncontrolled Controlled
(f) Thirty Six Pulse Converter
0.9479 35.44
(b) Twelve Pulse Converter
Uncontrolled Controlled Controlled
1.8 Controlled
Uncontrolled Controlled
1.6 1.4 RIPPLE % AGE
4.5 4
RIPPLE % AGE
3.5 3 2.5
1.2 1 0.8 0.6
Uncontrolled
0.4
2
0.2
1.5 Uncontrolled 1
0
48 pulse converter
0.5
Uncontrolled Controlled
0
0.2988 1.606
18 pulse converter Uncontrolled Controlled
0.5821 4.499
(c) Eighteen Pulse Converter
68
(g) Forty Eight Pulse Converter Fig. 32. %Ripple Content for RL Load: (a) – (g)
International Journal of Scientific Engineering and Technology www.ijset.com, Volume No.1, Issue No.4, pg : 61-70
(ISSN : 2277-1581) 01 Oct. 2012
3) Form Factor Uncontrolled
Controlled
Uncontrolled Controlled
Controlled
Uncontrolled Controlled
1 0.9
1.007 0.8
1.006 FORM FACTOR
0.7
FORM FACTOR
1.005 1.004 1.003 Uncontrolled
1.002
0.6 0.5 0.4 0.3
1.001
0.2
1
0.1 0
0.999
30 pulse converter
0.998
1.001 1.007
Uncontrolled Controlled
1 1
Uncontrolled Controlled
6 pulse converter
(e) Thirty Pulse Converter
(a) Six Pulse Converter Uncontrolled Controlled
Uncontrolled Controlled
Controlled
Uncontrolled Controlled
1 0.9
1.002
0.8 0.7 FORM FACTOR
FORM FACTOR
1.0015
1.001
1.0005
Uncontrolled
0.6 0.5 0.4 0.3
1
0.2 0.1
0.9995
0
36 pulse converter 0.999
Uncontrolled Controlled
12 pulse converter Uncontrolled Controlled
1 1.002
1 1
(f) Thirty Six Pulse Converter
(b) Twelve Pulse Converter Uncontrolled Controlled
Uncontrolled Controlled
Controlled
Uncontrolled Controlled
1 0.9
1.001
0.8 1.0008 FORM FACTOR
0.7
FORM FACTOR
1.0006 1.0004 1.0002
Uncontrolled
0.6 0.5 0.4 0.3
1
0.2 0.9998
0.1
0.9996
0
0.9994
Uncontrolled Controlled
48 pulse converter 18 pulse converter Uncontrolled Controlled
1 1.001
(g) Forty Eight Pulse Converter Fig. 33. Form Factor for RL Load: (a) – (g)
(c) Eighteen Pulse Converter
Controlled 1.001 1.0008
FORM FACTOR
1.0006 1.0004 1.0002
Uncontrolled
1 0.9998 0.9996 0.9994
24 pulse converter Uncontrolled Controlled
1 1
Uncontrolled Controlled
C. Result Of Simulation The objective of the present work is to investigate the performance of controlled and uncontrolled multi-pulse converters. These converters are studied in terms of harmonic spectrum of AC supply current, Total Harmonic Distortion, Ripple Content & form factor in the AC mains. It is concluded therefore that in general with increase in number of pulses in multi-pulse case the performance parameters of these converters are remarkably improved.
1 1.001
(d) Twenty Four Pulse Converter
IX. FUTURE SCOPE A back-to-back asynchronous tie comprised of VSC converters employing PWM may well represent the ultimate HVDC system. Besides controlling the through power flow,
69
International Journal of Scientific Engineering and Technology www.ijset.com, Volume No.1, Issue No.4, pg : 61-70 it can supply reactive power and provide independent dynamic voltage control at its two terminals. The two converters can be paralleled to double the reactive power capability supplied to one side or the other. The back-toback converters can be used for black start or to supply a passive load. Higher voltage designs can be used with transmission lines or cables to form point-to-point or multiterminal transmission links. More sophisticated controls can be used to provide additional network benefits. With the Eagle Pass project, CSW has realized the system advantages of deploying a VSC based back-to-back asynchronous Tie with standby dynamic voltage control during network contingencies. The controlled power transfer capability allows the exchange of power between the two networks while the voltage control stabilizes the voltage following line outages especially during peak load periods. The future scope of work could be the simulation of 6, 12, 18, 24, 30, 36, 48 multi pulse converter topologies in closed loop. With this technique, this work can be further extended to: i. Number of pulses can be increased. Even higher pulse converters can be used for high voltage and high power applications such as HVDC conversion.
ii. Closed Loop Multi-pulse conversion can be worked out for enhanced controlling and efficiency. iii. Other method of increasing the pulses can be used in place of phase shifting transformers as to derive multiphase supply from three phase AC mains
70
(ISSN : 2277-1581) 01 Oct. 2012
using different combinations of transformer windings such as star, delta, zigzag, fork, polygon, etc. REFERENCES [1] N.Mohan, T.M.Undeland, W.P.Robbins, “Power Electronics: Converters, Applications, and Design”, 3rd Edition, 2002 [2] D.A.Paice, Power Electronic Converter HarmonicsMulti-pulse Methods for Clean Power. New York, IEEE Press, 1996. [3] B.Singh, S.Gairola, B.N.Singh, A.Chandra, and K.A.Haddad, “Multi-pulse AC-DC Converter for Improving Power Quality: A Review”, IEEE Transactions, On Power Delivery, Vol.23 No.1 January 2008. [4] G.K.Dubey, S.R.Doradla, A.Joshi, R.M.K.Sinha, “Thyristorised Power Controllers”, New Age International publishers, July 1996. [5] Mathworks, “Matlab Users Guide”, Mathworks. Inc. Corporation