e-ISSN: 2582-5208 International Research Journal of Modernization in Engineering Technology and Science Volume:02/Issue:12/December -2020
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SYNCHRONOUS REFERENCE FRAME THEORY BASED CONTROL OF SERIES ACTIVE POWER FILTER Faliqa Mushtaq *1 *1Bachelor
of Technology, Department of Electrical Engineering, Baba Ghulam Shah Badshah University, India.
ABSTRACT Presence of power electronic devices in the power system has created a number of power quality problems such as voltage sags, interruptions, voltage swells, harmonics. Of all these problems, presence of harmonics is the most troublesome for consumers as it causes malfunctioning of all the electrical equipments connected to the supply among other bunch of power quality problems. Solution to this problem is to connect a device named filter with the electrical system. Of all the existing filters, active power filter is the most efficient in filtering out harmonics. In this paper it is planned to present the simulation model and performance of synchronous reference theory controlled series active power filter. It can be concluded that synchronous reference theory is effective in filtering out voltage harmonics from a three phase electrical system. Keywords: Harmonic, Total Harmonic Distortion (THD), Synchronous reference frame theory (SRF), Series APF, Hysteresis Controller, Pulse width modulation (PWM),
I.
INTRODUCTION
Power quality is said to be poor when there is a change in supply voltage, current or frequency beyond permissible limits. It causes a range of power quality problems such as voltage sag, swell, inter harmonic, harmonics, interruption, blackout etc. The presence of harmonics in an electrical system is of grave concern as it causes malfunctioning of the electrical equipments connected to the supply, overheating of underground cables, insulation failure etc. [1] Solution to this problem is to connect filters to remove harmonics from the supply. There are two types of filters: passive and active. Passive filters do selective filtering and suffer from other drawbacks as well such as ageing, resonance etc. To overcome these limitations, active power filters were introduced. Active power filters(APF) have proved to be most efficient in harmonic and reactive power compensation. APF are of two major types: shunt and series. APFs injects harmonics into the supply at the point of common coupling. The harmonics produced by APF are the same as produced by loads but displaced by 180 degrees. Thus, it cancels out the effect of the harmonic generated by loads smoothening the supply waveform. Shunt APFs inject current harmonics into the supply system while as series APF inject voltage harmonics. Shunt APF is used for harmonic current compensation while as series APF is used for harmonic voltage compensation.[2]
II.
METHODOLOGY
Basic configuration of series APF Figure 1.1 shows a series APF connected to mains circuit which consists of supply and non-linear load. APFs are constructed with either a voltage source inverter or current source inverter, a reference generator and a control circuit. The series APF used for the power quality mitigation is realized as a six legged VSI which consists of IGBTs. The VSI is connected in series with the source impedance through a transformer. A capacitor is used at the input side of VSI to provide constant input to the VSI.
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e-ISSN: 2582-5208 International Research Journal of Modernization in Engineering Technology and Science Volume:02/Issue:12/December -2020
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Fig.-1: Basic configuration of series APF Reference generator is the harmonic extractor. It estimates the quantity of harmonics the filter should compensate for. Its output is the reference signal for controller circuit. There are different techniques used for reference signal generation namely pq. theory, dq theory etc. [3][1]This paper describes synchronous reference frame theory for extraction of three phase reference voltages. Control circuit produces pulses in order to drive the VSI in such a way that it produces compensating voltages similar to reference voltages produced by reference generator. [3]In this paper hysteresis current control is used to accomplish this task. Synchronous reference frame theory(SRF) In this method three phase supply voltages is transformed into d and q synchronous reference voltage using park transformation.Then, these d and q components of voltage are fed to low pass filters to eliminate harmonics from fundamental component of voltage.[3][4] Later inverse park transform is used to convert d and q components to abc frame of reference. dq components of voltages are obtained from abc refrence frame by using the given below equation
[
]
(
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)
(
(
)
)
(
][
]
)
Phase locked loop(PLL) is used for determining mains voltage phase.[3]abc components of voltages are obtained from dq refrence frame by using the given below equation
[
] [
III.
(
)
(
)
(
)
(
)]
[
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MODELING AND ANALYSIS
Modelling of proposed filter is carried out in MATLAB Simulink. Simulation models are presented below
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e-ISSN: 2582-5208 International Research Journal of Modernization in Engineering Technology and Science Volume:02/Issue:12/December -2020
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Fig.-2: Simulation of three phase electrical vircuit with series active power filter
Fig.-3: Simulation of SRF based reference voltage generator
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Fig.-4: Simulation of hysteresis controller
Fig.-5: Simulation of phase locked loop
IV.
RESULTS AND DISCUSSION
Performance of series active power filter is checked with the use of MATLAB software.
Fig.-6: Source voltage without a filter
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Fig.-7: FFT analysis of source voltage waveform without filter
Fig.-8: i)source voltage with series APF ii) load voltage iii)compensating voltage injected by series APF
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Fig.-9 : FFT analysis of source voltage waveform with series APF
Comparison of individual harmonics(%) 16 14 12 10 8 6 4 2 0 5th 7th 11th 13th 17th 19th Harmonics Harmonics Harmonics Harmonics Harmonics Harmonics Without filter
With series active filters
Fig.-10: Comparison of individual voltage harmonics before and after compensation
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THD OF SOURCE VOLTAGE (%) 20
18.77
18 16 14 12 Without filter
10
With active filters
8 6 3.32
4 2 0
THD
Fig.-11: Comparison of THD before and after compensation Fig. 6 and Fig. 8 (i) show the source voltage waveform before and after the insertion of series active power filter. From which it is observed that before the insertion of series active power filter is applied to the system, the source voltage is highly distorted. But once the series active power filter is applied the source voltage becomes very much near the ideal sinusoidal waveform. Fig. 7 and Fig.9 shows the FFT analysis of source voltage. Fig. 10 show the comparison of individual harmonic before and after harmonic mitigation using series active power filter. Fig. 11 shows the comparison of overall mitigation in source voltage and after insertion of series active power filter.
V.
CONCLUSION
In this paper the performance analysis of series active power filter using synchronous reference frame theory has been carried out. Simulation results show the effectiveness of series active power filter for harmonic elimination in distorted source voltage. THD of source voltage is reduced from 18.77% to 3.32% which comply with IEEE standard.
VI. [1]
[2]
[3] [4]
REFERENCES
A. Ullah, I.U.H. Sheikh, S. Arshad, F. Saleem, Digital Active Power Filter Controller Design for Current Harmonics in Power System, Proc. 2019 16th Int. Bhurban Conf. Appl. Sci. Technol. IBCAST 2019. (2019) 384–388. https://doi.org/10.1109/IBCAST.2019.8667169. B.S.R. -Ankita P. Bagde, Rupali B. Ambatkar, Rupali G. Bhure, Power Quality Improvement By Series Active Power Filter- a Review, Int. Res. J. Eng. Technol. 4 (2017) 1730–1733. https://irjet.net/archives/V4/i1/IRJET-V4I1345.pdf. P. Datar, V. Datar, S.B. Halbhavi, S.G. Kulkarni, Synchronous Reference Frame Theory For Nonlinear Loads using Mat-lab Simulink, 3 (2016) 241–245. A Review on Shunt Active Power Filter Control Strategies _ Singh _ International Journal of Engineering & Technology.pdf, (n.d.).
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