Wavelet based Harmonic Analysis of Wind Connected System for Power Quality Improvement using STATCOM

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Wavelet based Harmonic Analysis of Wind Connected System for Power Quality Improvement using STATCOM

Special Issue – 2020 International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 NCSMSD – 2020 Conference Proceedings Wavelet based Harmonic Analysis of Wind Connected System for Power Quality Improvement using STATCOM J. Pardha Saradhi R. Srinivasarao V. Ganesh Department of EEE Department of EEE Department of EEE Bapatla Engineering College JNT University JNTUA College of Engineering Bapatla, India Kakinada, India Pulivendula, India Abstract A wind farm under non linear load conditions, mitigation and power system stability enhancement. The when connected to a power system creates the power quality revolution in using the FACTS parallel compensators led to problems of which the voltage variations and the harmonics are the utilization of the static synchronous compensators (ST severe. Here in this research paper, a power system connected ATCOM). with a wind form is taken for the study of reactive power Faster response, ability to compensate flickers, its compensation and harmonic reduction capability of a static flexibility in compensation and minimum interaction between compensator (STATCOM) in the presence of non-linear load. STATCOM and the power supply are the advantages of the The performance of the controller is studied under the presence of a non-linear load. At the point of common coupling the STATCOM compared to other conventional FACTS devices. variation in voltage, power factor are measured with a switch Here in this paper the STATIC COMPENSATOR connected to study the system both in the presence and absence (STATCOM) is used to mitigate the problems that are raised of the compensating device. The harmonic components in the due to the presence of the wind farm in a healthy power currents are studied using Wavelet transformation. Bi- system with a non-linear load. orthogonal 4.4 wavelet at level 4 is used to decompose the Wavelet based power quality analysis has been disturbances in power quality signals. The entire system is shown in [4], wavelet based fault identification in the presence simulated using MATLAB/SIMULINK software. The harmonic of FACTS devices has been shown in [5]. analysis also performed for the given and compares the performance of the proposed method with THD with the results II. WIND FARM DESIGN obtained using wavelet harmonic analysis. The wind generation is based on constant speed Keywords Wind farm, Harmonics, Compensator, STATCOM, topologies along with pitch control of the turbine blades. In Wavelet transformation the current scheme an induction generator is used because of its wide advantages like simplicity, no need of a separate field I. INTRODUCTION circuit, applicability for both constant and variable loads, and In an effort to meet the ever increasing demand for the its natural protection capability against short circuit. electrical power the present day engineers and environmentalists are pointing towards the non-conventional energy sources such as the energy present in solar radiation, III. BANG-BANG CONTROLLER FOR STATCOM energy possessed by the wind currents, geo-thermal energy A bang-bang controller is used to make the source etc., in order to ensure the sufficient conventional source for current sinusoidal by injecting required current components the future generations. Hence the use of these non- into the grid. Hysteresis type of current control technique is conventional energy sources is growing rapidly all across the employed here in this for a better control over the source world. This also will slowly show a positive impact on the current. The switching pulses required by the STATCOM are climate condition. generated by this bang-bang controller which is realized using Along with the positive impacts the injection of these a hysteresis current controller. The STATCOM here is DGs [1] also creates some problems like voltage variations, operated for controlling current and so the current control harmonic injection etc. These negative results impact the block in Bang-bang controller receives input current as functioning of the consumers equipment and sometimes the reference and actual current. power system may collapse. Hence in order to provide the end The R.M.S voltage of the source is given in the consumer a quality power, FACTS concept has been equation below introduced. The FACTS devices help in enhancing the power handling and transfer capabilities of a power system. Also the FACTS devices offer many other features in power quality issues like power factor correction, voltage variation (1) Volume 8, Issue 16 Published by, www.ijert.org 175 Special Issue – 2020 International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 NCSMSD – 2020 Conference Proceedings absence of the STATCOM. Basically wavelet analysis expands the given functions or waveforms into small signals, which are generated in the form of translations and dilations of a fixed function called the mother wavelet. A mother wavelet is a function that oscillates, has finite energy and zero mean value. Using wavelet transformations one can obtain both time and frequency information of the given signal, but Fourier transformation can only give the frequency information. In the current paper Bi-Orthogonal 4.4 wavelet transformation is used at level 4 for decomposing the output source currents into approximate and detailed coefficients. As the approximate coefficient is close to the actual waveforms they are used to study the operation of the controller is studied. Wavelet analysis gives DWT coefficients which start from separating the original signal s of length N to 2 set of coefficients: approximate coefficients CA1 by low pass filter and detail coefficients CD1 by high pass filter. The length of each filter is equal to half of originals length by down sampling function. The next step splits the approximate Fig.1: Basic STATCOM controller coefficients CA1 in two parts again by the same process but And the in-phase vectors are replace s by CA1 and producing CA2 and CD2 and so on. The detail and approximate coefficients at scale j are written as CDj and CAj, which are used to detect the order of harmonics in distribution system. The sampling frequency (2) selected is 1.6 kHz. In this paper, the fundamental frequency is The in-phase reference currents generated are given by, 50 hertz and 4 level decomposition is made. [6]The sub band of output signal as follows. CD1: 0.4 kHz ~ 0.8 kHz (3) CD2: 0.2 kHz~ 0.4 kHz Here I is proportional to the magnitude of filtered CD3: 0.1 kHz ~ 0.2 kHz source voltage for respective phase. The source current is CD4: 0.05 kHz~ 0.1 kHz controlled to be sinusoidal. CA4: 0 kHz ~ 0.05 kHz The bang-bang controller shown below is also called The harmonic distortions included in the each frequency as hysteresis controller. Bang-bang current controller is ranges can be detected by using approximation and detail implemented in the current control scheme. The so called coefficients which measure from sub-band harmonics in term hysteresis controller produces the ON and OFF switching of RMS values .Total Harmonics can be calculated by using signals required for switching of IGBTs of the controller (STATCOM). (4) Where Nj is the number of detail coefficients at scale -j. V. TEST SYSTEM A simple system with a source of AC currents is taken and the wind farm is developed by using an induction generator for which a constant is given as the input which is equivalent to the speed of wind. A non-linear load is considered to be at the load of the system. The harmonics are made to be introduced into the system by connecting a power electroic converter to Fig.2: Controller for STATCOM the load. A STATCOM is connected at the point of common coupling of the source, wind farm and the load. This system is IV. WAVELET HARMONIC ANALYSIS the designed with Bang-bang controller [6]based STATCOM Wavelet tool is used in the present paper for the harmonic .The Harmonic analysis is made at Source side by using THD analysis of the output currents both in the presence and method and wavelet based harmonic analysis. The power Volume 8, Issue 16 Published by, www.ijert.org 176 Special Issue – 2020 International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 NCSMSD – 2020 Conference Proceedings quality effecting and dependant variables like the currents, voltages and phase angles at different points in the system are measured. Fig.3: Matlab Simulink model of test system To judge the performance of the STATCOM [7]in the system the system is first run without any controller. And later the controller i.e. STATCOM is connected and the Fig.5: Source, load currents and phase voltage of controller control capability is analyzed in the presence of a load. And from the above Fig.5 it is observed that the presence of the non-linear load made the source current non- sinusoidal even though the voltages are sinusoidal. The total harmonic distortion is observed from wavelet transform is to be 19.2%. From Fig.6 the same system is applied a multi resolution analysis is made using Bi-orthogonal 4.4wavelet and its value is observed that 22.7%. Fig.4: One Line Diagram of the Test System VI. SIMULATION RESULTS The test system is developed in the environment of MATLAB/SIMULINK. First the system is simulated with a non-linear load without the controller and the simulated results are as shown below. Fig.6: Wavelet analysis of approximated source current at Bi-Orthogonal 4.4 at level 4 Volume 8, Issue 16 Published by, www.ijert.org 177 Special Issue – 2020 International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 NCSMSD – 2020 Conference Proceedings done and the quality of power being supplied is also been improved. The STATCOM which is provides with a DC battery system injects the required current components into the line. The FFT analysis gave the THD in the source current as 3%. This says the controller is very effective in the reduction of harmonics. The wavelet analysis of the source current in the Bi- Orthogonal 4.4 wavelet transform in level four is given below. The Harmonics are obtained by using Bi-Orthogonal 4.4 wavelet transform it its value is 3.6%. Fig.7: wave form decomposition of approximated source current Fig.7 gives the approximate and detailed coefficients by using bi-orthogonal wavelet at level-4. Further the bang-bang controller based STATCOM is designed for harmonic reduction in the source current. The can also do the THD reduction, power Quality improvement such as keeping the voltages, currents, power factor etc., in their limits. The simulated results of the test system with the STATCOM by using Bang controller are as shown in the figure below Fig.9: waveform decomposition of approximated source current Fig.10: Wavelet analysis of approximated source current with Bi-Orthogonal 4.4 at level 4 Fig.8: Source, load and STATCOM currents and phase voltage of compensator The waveforms in the above figure are the source The harmonics are obtained by using FFT analysis with and without controller. Similarly harmonic analysis also current, load current, the compensator current and the phase voltage of the controller. made with wavelet transform The presence of the STATCOM made the non- sinusoidal source current in the absence of controller into the sinusoidal wave thus we can say the harmonic reduction is Volume 8, Issue 16 Published by, www.ijert.org 178 Special Issue – 2020 International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 NCSMSD – 2020 Conference Proceedings Table.1: Harmonics obtained in the source side Sl.No Type of Current By FFT By Discrete REFERENCES signal technique Wavelet [1] Z.Chen, E. Spooner, Grid Power Quality with Variable speed wind at Source side Transform Turbines, IEEE Transaction on Energy Conversion , Vol.16, no.2, (DWT) pp.148-154, June 2001. 1 Without any 19.2% 22.7% [2] Lee,S.S, Juyi Park, Loparo.K.A, Schrader.C.B, Pyung Hun Chang, compensating device Bang- Bang impact control using impedance/time-delay control 2 With Bang bang 3% 3.6% Mechatronics, IEEE Transactions on Volume:8 Issue: 2 2003. controller based [3] C. Han, A. Huang, M. Baran, S. Bhattacharya, W. Litzenberger, L. STATCOM Anderson, A. Johnson, and A.-A. Edris, Statcom impact study on the integration of a large wind farm into a weak loop power system, IEEE Trans.Energy Convers., vol. 23, no. 1, pp. 226-233, Mar. 2008. VII.CONCLUSION [4] J. Pardha Saradhi, R. Srinivasa Rao, V.Ganesh Wavelet Based This research paper is discussed in the presence of a non- Power Quality Assessment of Wind Energy Source Integrated 5-Bus linear load is modeled and simulated in the System under Sudden Load Conditions in Presence of FACTS MATLAB/SIMULINK environment. The performance of the Devices2019, International Journal of Engineering and Advanced Technology (IJEAT) ISSN: 2249 – 8958, Volume-8, Issue-6S3, system with and without a controller (STATCOM) is studied September 2019 and it is observed that the total harmonic distortion of the [5] J. Pardha Saradhi, R. Srinivasa Rao, V.Ganesh Wavelet-Based source current has been reduced to a greater extent. The Algorithm for Fault Detection and Discrimination in UPFC- wavelet tool box is used to decompose the source currents into Compensated Multiterminal Transmission Network Lecturer Notes in Electrical Engineering 661,https://doi.org/10.1007/978-981-15- the detailed and approximated coefficients and analyzed with 4692-1_7 Springer Nature Singapore 2020 Bi-Orthogonal 4.4 level 4 transformations. The results [6] G. Sunil Kumar, D.V.S.S. Siva Sarma, C. VenkateshWavelet obtained from discrete wavelet harmonic analysis in the Transform Based Harmonic Analysis and Real Power system network system are compared with THD obtained MeasurementIEEE conference 2011. from FFT analysis. Volume 8, Issue 16 Published by, www.ijert.org 179

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