Application of Wavelet Transform for the Detection and Minimization of Harmonics using Shunt Active Filter

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1 Application of Wavelet Transform for the Detection and Minimization of Harmonics using Shunt Active Filter Priyadharshini. A, Hans John D cruz, Naresh. B Ragul.J & Swathy. S Department of Electrical and Electronics Engineering, Sri Krishna College of Technology, Coimbatore priyadharshini_a@yahoo.co.in, hansdcruz@gmail.com, nareshb13@gmail.com, ragul.j40@gmail.com, srhswathy@gmail.com Abstract In the recent days the use of non linear loads have increased thereby creating distortions in voltage and current waveforms. These disturbances cause Harmonic distortions which cause reduction in power quality. Hence harmonic reduction becomes a necessary I. INTRODUCTION Unlike in linear loads Ohm's law is not applicable to non-linear Loads. Load current contains all ODD Harmonics. The loads cannot be categorized as leading or lagging loads. The primary devices used will be diodes and capacitors.foremost among loads meeting their definition are gas discharge lighting having saturated ballast coils and Thyristor (SCR) controlled loads. The nature of non-linear loads is to generate harmonics in the current waveform. This distortion of the current waveform leads to distortion of the voltage waveform. Under these conditions, the voltage waveform is no longer proportional to the current. grid are a frequent cause of power quality problems. Harmonic components should be reduced as much as possible. Causes : In a normal alternating current power system, the voltage varies sinusoidally at a specific frequency(50 hertz).when a linear electrical load is connected to the system, it draws a sinusoidal current at the same frequency as the voltage. When a non-linear load, (rectifier) is connected to the system, it draws a current that is not necessarily sinusoidal. The current waveform can become quite complex, depending on the type of load and its interaction with other components of the system. Fig.1: A non linear load drawing current in short pulses when compared to linear load. II. HARMONICS - CAUSES AND EFFECTS: Harmonics are electric voltages and currents that appear on the electric power system as a result of nonlinear electric loads. Harmonic frequencies in the power Fig. 2 : Three phase shunt active power filter connected at the point of common coupling. Effects : One of the major effects of power system harmonics is to increase the current in the system. This is particularly the case for the third harmonic, which causes a sharp increase in the zero sequence current, and therefore increases the current in the neutral conductor. This effect can require special consideration 23

2 in the design of an electric system to serve non-linear loads. III. CONTROL STRATEGY OF SHUNT ACTIVE FILTER: Among the several methods present the Synchronous Reference Frame method (SRF) is one of the most common and probably it is widely used method. In the SRF, the load current signals are transformed into the conventional rotating frame d-q. If theta is the transformation angle, the transformation is defined by: values were noted. An inverter circuit was designed and tested for effective operation. This inverter is used as a Shunt Active Filter in place of Passive filter and its THD values are noted. Now the circuit is made closed loop by triggering the IGBT based on load current and thus the closed loop circuit is completed. This is done using Synchronous Reference Frame Theory. Wavelet analysis is included for detection and the final outcome of the THD values are noted and tabulated. It is again converted back to a b c values which acts as reference voltage and current. These values of reference voltages and current are converted to triggering pulses for the Shunt active filter using PWM pulse generation. IV. WAVELET TRANSFORM: The wavelet transform is often compared with the Fourier transform. Fourier transform is a powerful tool for analyzing the components of a stationary signal (a stationary signal is a signal where there is no change in the properties of signal). Fourier transform is a powerful tool for processing signals that are composed of some combination of sine and cosine signals (sinusoids). Wavelet transforms allow the components of a non-stationary signal to be analyzed. Wavelets also allow filters to be constructed for stationary and nonstationary signals. The main difference is that wavelets are well localized in both time and frequency domain whereas the standard Fourier transform is only localized in frequency domain. The Short-time Fourier transform (STFT) is also time and frequency localized but there are issues with the frequency time resolution and wavelets often give a better signal representation using Multiresolution analysis (MRA). Wavelet Transform can generate a two-parameter family of functions. V. SIMULATION OF SHUNT ACTIVE FILTER The first step was to simulate a non-linear load. The most critical load among all the non-linear loads, three phase rectifier was simulated. FFT analysis of the harmonics was done for source current and the THD values were noted. Passive filter for compensating 5th Harmonic was introduced and the corresponding THD Fig. 3 : Simulated circuit of three phase shunt active filter connected at PCC. VI. SIMULATION RESULTS The simulated waveforms are as shown below. Fig. 4 : Waveforms with non-linear load without filter: a.source voltage, b. Source current,c. Load voltage, d. Load current waveforms 24

Fig. 5 : FFT analysis of supply current waveform

8 : Waveforms using Shunt Active Filter (Open

9 : FFT analysis of supply current waveform using

7 : FFT analysis of supply current waveform using

3 Fig. 5 : FFT analysis of supply current waveform for nonlinear load without filter Fig. 8 : Waveforms using Shunt Active Filter (Open Loop) Fig. 6 : Waveforms using Passive Filter Fig. 9 : FFT analysis of supply current waveform using Shunt Active Filter (Open Loop) Fig. 7 : FFT analysis of supply current waveform using Passive Filter Fig. 10 : Waveforms using Shunt Active Filter (Closed Loop) 25

Fig. 11 : FFT analysis of supply current

waveform for non-linear load without filter.

4 Fig. 11 : FFT analysis of supply current waveform using Shunt Active Filter (Closed Loop) Fig. 13 : Wavelet analysis of supply current waveform using Passive Filter Fig. 12 : Wavelet analysis of supply current waveform for non-linear load without filter. Fig. 14 : Wavelet analysis of supply current waveform using Shunt Active Filter (Open Loop) 26

5 VII. CONCLUSION The tabulated values show that the source voltage THD are well below the specified limit. The source current THD is found to be more than the IEEE 519 standards, hence by using the filters, the current THD also has been brought within the permissible limits. VIII. REFERENCES Fig. 15 : Wavelet analysis of supply current waveform using Shunt Active Filter (Closed Loop) Three phase Rectifier Load Passive Filter Shunt Active Filter % THD Table 1. Parameters Used R load = 10.6Ω L load = 58.2mH L ppf =20.17mH C ppf = 625µF L sapf = 3.5mH R sapf = 0.001Ω C dc = 6800µF Table 2. Tabulation of THD values Without Filter With Passive Filter With Shunt Active Filter (Open Loop) With Shunt Active Filter (Closed Loop) V SA V SB V SC I SA I SB I SC [1] Akagi.H, Modern active filter and traditional passive filters, Bulletin of the polish academy of sciences technical sciences vol.54.no.3, [2] J. Arrillaga, N. R. Watson : Power System Harmonics. New York: John Wiley, c2003 [3] T.Lachman, A.P.Memon, T.R.Mohamad, Z.A.Memon Detection of Power Quality Disturbances Using Wavelet Transform Technique, International Journal For The Advancement Of Science & Arts, VOL. 1, NO. 1, 2010 [4] Jaume Miret, Member, IEEE, Miguel Castilla, José Matas, Josep M. Guerrero, Senior Member, IEEE, and Juan C. Vasquez Selective Harmonic-Compensation Control for Single-Phase Active Power Filter With High Harmonic Rejection IEEE Transactions On Industrial Electronics, VOL. 56, NO. 8, August 2009 [5] Hideaki Fujita Hirofumi, The unifed power quality conditioner : the integration of series and shunt-active filters Akagi Okayama University Okayama University. Lib.okayamau.ac.jp/eletrical_engineering/8. [6] T.Mahalekshmi, Current harmonics compensation and power factor improvement by hybrid shunt active power filter, International Journal. of Computer Applications ( ) Volume 4 No.3, July [7] Prof. P.C.Panda Investigations On Shunt Active Power Filter For Power Quality Improvement Dept.of Electrical Engg. National Institute of Technology Rourkela [8] Schaffner EMV AG, white paper Rating of harmonic filters, December [9] Tamkang, Ying-Tung Hsiao. Design of Filters for Reducing Harmonic Distortion and Correcting Power Factor in Industrial Distribution Systems Journal of Science and Engineering, Vol. 4, No. 3, pp (2001),193. [10] Daniel J.Carnovale,P.E and Thomas M. Blooming P.E Application of IEEE STD on harmonic limits International Journal of Advances in Engineering & Technology, May 2011.ISSN: [11] Sangu Ravindra, Dr.V.C.Veera Reddy, Dr.S.Sivanagaraju, Devineni Gireesh Kumar Design of Shunt Active Power Filter to eliminate the harmonic cur-rents and to compensate the reactive power under 27

6 distorted and/or imbalanced source voltages in steady state, International Journal of Scientific & Engineering Research, Volume 3, Issue 1, January ISSN [12] C. Venkatesh, D. Srikanth Kumar, Student Members, IEEE, D.V.S.S. Siva Sarma, Senior Member, IEEE and M. Sydulu, IEEE Member Modelling of Nonlinear Loads and Estimationof Harmonics in Industrial Distribution System, Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008 [13] M. Sifuzzaman, M.R. Islam1 and M.Z. Ali Application of Wavelet Transform and its AdvantagesCompared to Fourier Transform Journal of Physical Sciences, Vol. 13, 2009, ISSN: : [14] Stephane G. Mallat. A Theory for Multiresolution Signal Decomposition IEEE Transactions On Pattern Analysis And Machine Intelligence.V Ol. Ii, No. 7. July 28

Implementation of SRF based Multilevel Shunt Active Filter for Harmonic Control

International Journal of Engineering Research and Development e-issn: 2278-067X, p-issn: 2278-800X, www.ijerd.com Volume 3, Issue 8 (September 2012), PP. 16-20 Implementation of SRF based Multilevel Shunt