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Passive Filter For Harmonic Mitigation Of Power
Diode Rectifier And SCR Rectifier Fed Loads
C L Anooja, N Leena
Abstract— Power electronic devices find tremendous applications in industry as well as in domestic appliances. The excessive use of these devices causes major problems to the power system due to generation of current harmonics. These harmonic current pollute the power system and produce many adverse effect like malfunction of sensitive equipment, reduced power factor, overloading of capacitor, flickering lights, over heated equipments, reduced system capacity etc.
This work deals with the investigation of current harmonics mitigation by using passive filters. Passive filters provide low impedance path to di- vert harmonic current to the ground and thus clears harmonics from the circuit. The design and simulation of passive filters for diode rectifier and SCR rectifier fed loads is discussed in this paper. A comparison is also made between diode rectifier and SCR rectifier in six pulse and twelve pulse configura- tion. Simulation results are presented to prove that THD is reduced with the use of these filters, and in the twelve pulse configuration harmonics is re- duced in both SCR and diode rectifier than the six pulse configuration. In the SCR rectifier, when firing angle is increased the THD is also increased.
Index Terms— Diode rectifier, Harmonics, Passive filter, SCR rectifier, Total harmonic distortion (THD)
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odern consumers of power such as variable speed drives, switch mode power supplies in home electronics etc. significantly contribute to energy saving and more
efficient use of electricity. The power handling capacity of modern power electronics devices such as power diodes, SCR, IGBT are very large. So such power electronic equipments are widely used in industry as well as in home appliances. How- ever the nature of their operation will cause a non sinusoidal current flow from the supply. This current consists of funda- mental wave and its integer multiples, called harmonics.
The main sources of the current harmonics are magnetic core equipments, power electronics devices and arc furnaces. Harmonic currents flow through such systems cause problems like reduction in equipment service life, function and reliabil- ity [1-2]. Harmonics have a serious impact; it will reduce sys- tem efficiency and waste precious energy. It also results in overloading and heating of electrical equipments, transform- ers, fuses and conductors. It will also cause derating of the equipment, overloading of the capacitor bank and causes mal- function in electronics control. Passive filters are the most ef- fective and simple method to reduce the adverse effect of harmonics [3-7].
The paper is organized as follows: Section II presents the so- lutions for harmonic problems. Design of passive filter is dis- cussed in Section III. The simulation results of how the passive filter alleviates the harmonic currents are provided in Section IV. Section V explains conclusion of this work.
A Line Reactor (choke) is a 3-phase series inductance on the line side of a drive. Line reactors are available in various val- ues of percent impedance, typically 1-1.5%, 3%, and 5%. The main advantages of line reactors are the low cost, it provide moderate reduction in voltage and current harmonics and in- put protection from line transients.
Figure 1. Line reactor
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(This information is optional; change it according to your need.)
A 12 Pulse Converter consists of two separate input semicon- ductor bridges, which are fed from 30 degree phase shifted power sources with identical impedance. The two isolation
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International Journal of Scientific & Engineering Research, Volume 4, Issue 6, June-2013 1616
ISSN 2229-5518
transformers, where one is a wye /delta design (which pro- vides the phase shift) and the second a wye/wye design (which does not phase shift) which is fed to these two bridges. It may also be a “three-winding” transformer with a primary wye winding, wye and delta are secondary windings. The 12- pulse arrangement allows certain harmonics (primarily 5th and 7th) from the first converter to cancel the harmonics of the second. Up to approximately 85% reduction of harmonic cur- rent and voltage distortion may be achieved (over standard 6- pulse converter). Advantage of 12- pulse converter is substan- tial reduction in voltage and current .
Figure 3. Passive filter
The system considered here is ,input vltage VS = 415V, Reac- tive power = 168.62 kW, XC = (V2/ Q), XC = (1/2πFC), C = (1/2πF XC), L = (1/4Cπ2 F2). For the system according to these equations, the capacitance, inductance and resistance values are obtained are given in table 1.
TABLE 1
PASSIVE FILTERS FOR RECTIFIERS
Figure 2. 12- Pulse rectifier
Tuned harmonic filters consist of the combination of an induc- tor, resistor and capacitor elements. It is sometimes desirable to have circuits capable of selectively filtering one frequency or range of frequencies out of a mix of different frequencies in a circuit. For mitigating the harmonic distortion passive filter- ing is the simplest conventional solution. The most commonly used passive filter is the single-tuned filter. This filter is sim- ple and least expensive as compared with other means for mit- igating the harmonic problems. Passive filter provide a low impedance path for harmonic current. These currents are then "sucked off” and the network is cleaned of damaging harmon- ic currents.
FILTER C(µF) L(H) R(Ω)
5TH 11.09 0.0365 0.54
7TH 11.09 0.0186 0.38
11TH 11.09 0.0075 0.24
13TH 11.09 0.0054 0.21
The different types of filters are Band-pass filters and High- pass filters. Band-pass filters, which are used to filter lowest order harmonics ,it can be tuned at a single frequency called single-tuned filter or at two frequencies called double-tuned filter. High-pass filters are used to filter high-order harmonics. One type of high-pass filters are the C-type high-pass filter, is used to filter low order harmonics and provide reactive pow- er. C type filter avoids parallel resonance.
HIGH
PASS
FILTER
11.09 0.0031 49.66
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The system was simulated with the load fed by diode and SCR rectifier in a 6 pulses and 12 pulse configurations with and without passive filter. Figure 4 shows the circuit arrangement for 6- Pulse diode rectifier fed load without filter. A THD analysis was done and the result obtained is as shown in fig 5. Figure 6 shows the circuit arrangement for 6- pulse diode rec- tifier with tuned filter .The THD analysis of the system is giv- en in the figure 7. The circuit arrangement with a 12- pulse diode rectifier is shown in figure 8 and THD analysis is shown in figure 9. Figure 10 and 11 shows the circuit arrangement for
12- pulse diode rectifier and THD analysis result with filter condition.
Figure 6. 6- Pulse diode rectifier with filter
Figure 4. 6- Pulse diode rectifier without filter
Figure 7. 6 pulse diode rectifier with filter,THD =25.01%
Figure 5. 6- Pulse diode rectifier without filter,THD = 55.74%
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Figure 10. 12 Pulse diode rectifier with filter,
Figure 8. 12 pulse diode rectifier without filter
Figure 9. 12 Pulse diode rectifier without filter,THD =5.52%
Figure 11. 12 Pulse diode rectifier with filter,THD =2.43%
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The diode rectifiers are replaced by controlled rectifier and analysis done. The circuit arrangement for a 6- Pulse SCR Rec- tifier without filter condition and its THD analysis are shown in figure 12 and 13. Tuned filter were connected to the circuit as in figure 14 and THD analysis done shown in figure 15. It is known that 12 pulse rectifier can result in substantial reduc- tion in harmonics. Figure 16 and 17 shows the circuit ar- rangement for 12- pulse SCR rectifier without filter and its THD analysis result. The circuit arrangement for 12- pulse SCR rectifier with filter showed in figure 18 and its THD anal- ysis shown in figure 19.
Figure 12. 6 Pulse SCR rectifier without filter
Figure 14. 6 Pulse SCR rectifier with filter
Figure 13. 6 Pulse SCR rectifier without filter,THD =28.21%
Figure 15. 6 Pulse SCR rectifier with filter,THD = 5.10%
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Figure 16. 12 Pulse SCR rectifier without filter
Figure 18. 12 Pulse SCR rectifier with filter
Figure 17. 12 Pulse SCR rectifier without filter,THD = 16.13%
Figure 19. 12 Pulse SCR rectifier with filter,THD = 4.86%
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A comparison of the different topology with and with- out filter is presented in table 2.
TABLE 2
COMAPARISON OF THD VALUES
The above result shows that a 12 pulse configuration can re- duce current harmonics when compared to a 6 pulse configu- ration. There was about 89.6% reduction in harmonics for a 12 pulse diode rectifier when compared to 6 pulse diode rectifier. On addition of a filter there was a further reduction in har-
Parameters 6-Pulse Diode Rectifier Without Filter
6-Pulse Diode Rectifier With Filter
12-Pulse Diode Rectifier Without Filter
12-Pulse Diode Rectifier With Filter
monics, 95% reduction in harmonics was obtained on addition of tuned filter. In controlled rectifier THD increases with in- crease in firing angle.
THD (%) 55.77 25.01 5.76 2.36
The effect of variation in firing angle on harmonics was stud- ied.THD values are increases with increase in firing angle.
TABLE 3
THD VALUES OF A DIFFERENT FIRING ANGLES
Firing Angle
Types 100 400 500
Harmonics cause damage to electrical networks and can some- times be dangerous. This result in overload, reduced lifespan and under some circumstances can even lead to premature fail- ure of electrical and electronic equipments. The conventional method to mitigate the harmonics is by using passive filters. In this project, diode and SCR rectifier fed system are simulated in
6 pulse and 12 pulse configurations. From the simulation re- sults, the use of a 12 pulse rectifier can results in substantial re- duction in harmonics.
Fore mostly, I would like to express my sincere gratitude to our Principal: Dr K. S.M Panicker, for his guidance.I am also thank- ful to our HOD Dr Pailo Paul for imparting fundamental idea, which helped me a lot for my mini project.Iam extremely thank- ful to my guide Mrs Leena N for her guidance and suggections, I would also like to thank all my teachers who gave their full support and encouragement for doing this project. I owe my deepest gratitude to them.
6-Pulse SCR Rectifier Without Filter
6-Pulse SCR Rectifier With Filter
12-Pulse SCR Rectifier Without Filter
12-Pulse SCR Rectifier With Filter
49.80 54.19 72.87
3.20 5.10 5.13
5.21 16.13 19.12
1.41 4.86 5.21
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