CONTROL OF VOLTAGE SAG/SWELL IN THREE PHASE DISTRIBUTION LINE

Transcription

1 ISSN International Journal of Advance Research, IJOAR.org Volume 1, Issue 3, March 2013, Online: ISSN CONTROL OF VOLTAGE SAG/SWELL IN THREE PHASE DISTRIBUTION LINE USING UPQC R.Senthil Kumar, R.Prasanna Krishnan Department of Electrical and Electronic Engineering, SRM University Kattankulathur Abstract--- The paper presents a three phase four wire distribution system for measurement of Voltage sag and voltage swell. Considering unbalanced condition of sags occurring across two phases say A and B in the distribution line. Initially the sag events are minimized using FACTS device Unified Power Quality Conditioner (UPQC). Mitigation of the sags and swells is done with the help of Kaiser s formula of windowing technique, which controls the operation of the Unified Power Quality Conditioner. Comparison of the output is done with UPQC-Fuzzy controller technique along with UPQC-Kaiser window technique. KeyWords -- Power Quality, voltage sag, voltage swell, UPQC, Kaiser Window.

2 ISSN INTRODUCTION The power quality has become a challenging issue in our day to day life. As the consumers requirement increases day by day, the quality of the power supply has also to be improved accordingly. Both the electric utilities and end users of electric power are becoming increasingly concerned about the quality of electric power. The term power quality has become one of The Various Power Quality Issues includes Voltage sag, Voltage swell, Voltage notching, Interruption, Distortion etc. In order to minimize these issues we therefore need an additional device as a compensation for the power distribution system. Hence UPQC is preferred as it controls both the voltage and the Current variation in the distribution system. The basic concept of UPQC is explained under section 2, windowing techniques in section 3 and the simulation results are explained under section 4 respectively. UPQC. the most prolific buzzwords in the power industry since the late 1980s. It is an umbrella concept for a multitude of individual types of power system disturbances. The issues that fall under this umbrella are not necessarily new. What is new is that engineers are now attempting to deal with these issues using a system approach rather than handling them as individual problems. Fig 1: General Configuration of UPQC 2. UNIFIED POWER QUALITY CONDITIONER Unified power quality conditioners (UPQCs) consist of combined series and shunt active power filters (APFs) for simultaneous compensation of voltage and current disturbances and reactive power. They are applicable to power distribution systems, being connected at the point of common coupling (PCC) of loads that generate harmonic currents. The series APF compensate the source voltage disturbances, such as harmonics, dips or overvoltages, which might deteriorate the operation of the local load while the shunt APF attenuates the undesirable load current components (harmonic currents and the fundamental frequency component which contributes to the reactive load power). Moreover, the shunt APF must control the dc-bus voltage in order to ensure the compensation capability of the

3 ISSN CIIT-IJ-3936-International Journal November 2010 been reported on it. Sometimes it has been viewed as combination of series and shunt active filters. Fig 2: Equivalent Circuit of UPQC A Unified Power Quality Conditioner (UPQC) is a device that is similar in construction to a Unified Power Flow Conditioner (UPFC). The UPQC, just as in a UPFC, employs two voltage source inverters (VSIs) that connected to a d.c. energy storage capacitor. One of these two VSIs is connected in series with a.c. line while the other is connected in shunt with the a.c. system.a UPQC that combines the operations of a Distribution Static Compensator (DSTATCOM) and Dynamic Voltage Regulator (DVR) together. One of the serious problems in electrical systems is the increasing number of electronic components of devices that are used by industry as well as residences. These devices, which need high-quality energy to work properly, at the same time, are the most responsible ones for injections of harmonics in the distribution system. Therefore, devices that soften this drawback have been developed.one of them is the unifiedpower quality conditioner (UPQC),It consists of a shunt active filter together with a series-active filter. This combination allows a simultaneous compensation of the load currents and the supply voltages, so that compensated current drawn from the network and the compensated supply voltage delivered to the load are sinusoidal, balanced and minimized. The series- and shunt-active filters are connected in a back-to-back configuration, in which the shunt converter is responsible for regulating the common DC-link voltage. A UPQC is employed in a power transmission system to perform shunt and series compensation at the same time. A power distribution system may contain unbalance, distortionand even d.c. components. Therefore a UPQC operate, better than a UPFC, with all these aspects in order to provide shunt or series compensation. The UPQC is a 3. KAISER WINDOW TECHNIQUE In general, for any window a trade-off exists between the main lobe width and the side lobe amplitude. The main lobe width is inversely proportional to no: of samples (N). An increase in the window-length decreases the transition band of the filter. However, the minimum stop band attenuation is independent of N and is a function of the selected window. Thus, in order to achieve prescribed minimum stop band attenuation and pass band ripple, the designer must find a window with undesirable design specifications. To overcome this problem, Kaiser has chosen a near optimal window which is formed by using the zerothorder modified Bessel function. It is given by, [ ] ( ) for n (N-1)/2 0 otherwise Where α is the adjustable parameter (attenuation) and ( ) is the modified zeroth-order Bessel function of the first kind of order zero is given by ( ) = 1+ ( ) ^2. The frequency response equation of the Kaiser window is given by, ( ) [ ( ) ] relatively new device and not much work has yet

4 ISSN The Parameters of Kaiser Window include: 1. Length: (M+1) 2. Shape Parameter: β Where, β= { }

5 ISSN And M = The computation is done under three cases viz a) Normal condition, b) Without UPQC c) With UPQC d) UPQC with Kaiser Window. CIIT-IJ-3936-International Journal November 2010 Where A = -20 approximation, the low pass filter peak error. - Where =0.35, = 0.5 and = = =0.021 According to the filter design, 1- β value can be 2.6 and M =24 according to the Kaiser's formula. The advantages of using Kaiser s window in control operation over other controllers are the Window function does not depend on any reference value of any signal. According to the window, whatever signal its almost the same and operates only if it detects any unwanted disturbance in the incoming signal, here we call it as a Voltage or Current signal. 4. SIMULATION RESULTS The Simulations are done using MATLAB 2010A version software. The system taken for the research is the three phase distribution system 11KV/440V.Consider an unbalanced condition of Sags across Phases B and C. The Comparison of the results are based on some predetermined results of the paper, Role of PI and Fuzzy Controllers in Unified Power Quality Conditioner - VOL. 2, NO. 2, APRIL 2007 ISSN ARPN Journal of Engineering and Applied Sciences -by A. Jaya Laxmi, G. Tulasi Ram Das, Department of Electrical and Electronics Engineering, JNTU College of Engineering, Hyderabad and K.Uma Rao,Department of Electrical and Electronics Engineering, RS Institute of Science and Technology, Bangalore, India.In the above mentioned paper, the Controlof UPQC using Fuzzy controller is done. Computation under various operating conditions:

6 ISSN Fig 3: Normal phase Voltage Now consider the double line to the ground fault occurring across Phase B and C such that Voltage Swell occurs along Phase A as shown below. Fig 4: Sag-swell along the line without UPQC In the above fig, the transaction time is between 0.01 to 0.03 cycles. Due to the absence of UPQC in this case, the output voltage to the consumers will be very poor as shown below from which we can easily understand the necessity of UPQC. Fig 5: Poor Output to Consumer From this above simulation waveform, it s very clear that the consumers' equipments will be damaged and hence an additional device has to be installed to the line for a conditioned voltage supply. Hence UPQC is then injected as soon as the sag and swell event occurs (due to phase disconnection swell occurs) to minimize the sag and swell occurring on the line as shown below.

7 ISSN The above results are based on the computational research works done in one of my reference as mentioned earlier. When the Kaiser window is used Fig 6: Voltage-sag/swell with UPQC Injection The above waveforms confirms that the UPQC reduces the sag/ swell events in the distribution line. Now we need an additional controller along with the FACTS device for obtaining a conditioned output voltage as shown below. Fig 7: Output Voltage with UPQC Comparison of UPQC-Fuzzy with UPQC- Kaiser The Test system voltage taken is 230V rms output voltage. When the sag event occurs, the Unified Power Quality Conditioner is controlled by Fuzzy controller, the sag events get minimized but not completely mitigated as shown below: Fig 8: UPQC-Fuzzy controller

8 ISSN for the control operation of UPQC, the sag events as well as the swell events are completely mitigated. It adjusts the trade lobe width and the side lobe width and thus we obtain a completely mitigated output. The test system taken for this is 230V rms voltage distribution system which is done in that reference paper. [1] Performance of UPQC for power quality improvement /10/$ IEEE by Yash Pal, A. Swarup, Senior Member, IEEE, and Bhim Singh2 Senior Member, IEEE Fig 9: UPQC- Kaiser Window 5. CONCLUSION Thus in order to mitigate the voltage sag and voltage swell, we therefore require an additional FACTS device, UPQC (Unified Power Quality Conditioner). All the computations are done and the results are compared with that of the predetermined results of that of PI control technique with that of the Kaiser window control technique. From the above simulation result it is clear that, the window technique is the better control technique when compared to that of PI controller control technique. Hence in order to get a better mitigated output, it is better to use window technique instead of any controller with UPQC. Infuture, there will be more shortage of power and that is mainly because of transmission losses or sags in the line. Prevention is better than cure. Better be safe than sorry. 6. REFERENCES

9 ISSN [2] UPQC-S: A Novel Concept of Simultaneous Voltage Sag/Swell and Load Reactive Power Compensations Utilizing Series Inverter of UPQC - IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 26, NO. 9, SEPTEMBER by VinodKhadkikar, Member, IEEE, and Ambrish Chandra, Senior Member, IEEE. Capability - Víctor M. Moreno, Alberto Pigazo, Marco Liserre and Antonio DellAquilaDepartamento [3] Electrical Systems Power Quality - Roger C. Duhan, Mark F. McGranaghan [4] Applications of UPQC for Power Quality Improvement - 16th NATIONAL POWER SYSTEMS CONFERENCE, 15th-17th DECEMBER, 2010 by Yash Pal, A. Swarup, Senior Member, IEEE, and Bhim Singh Fellow, IEEE,. [5] Mitigation of voltage sags, imbalances and harmonics in sensitive industrial loads by means of a series power line conditioner - Electric Power Systems Research 84 (2012) by Pablo Fernandez-Comesana, Francisco D. Freijedo, Jesus Doval-Gandoy, Oscar Lopez, Alejandro G. Yepes, JanoMalvar. [6] Rule-based classification of power quality disturbances using S-transform - Electric Power Systems Research 86 (2012) by A. Rodríguez, J.A. Aguado, F. Martín, J.J. López, F. Mu noz, J.E. Ruiz. [7] Digital Signal Processing - by John Proakis.. [8] Extension of Fourier Transform for very fast reference generation of UPQC - December 2011 Issue 9 Volume 3- by A. Mokhtarpour H.A. Shayanfar S.M.T. Bathaee, Department of Electrical Engineering, Science and Research Branch, Islamic Azad University, Tehran. [9] Role of PI and Fuzzy Controllers in Unified Power Quality Conditioner - VOL. 2, NO. 2, APRIL 2007 ISSN ARPN Journal of Engineering and Applied Sciences -by A. Jaya Laxmi, G. Tulasi Ram Das, Department of Electrical and Electronics Engineering, JNTU College of Engineering, Hyderabad and K. Uma Rao, Department of Electrical and Electronics Engineering, RS Institute of Science and Technology, Bangalore, India. [10] Unified Power Quality Conditioner (UPQC) with Voltage Dips and Over-voltagesCompensation

10 ISSN de Electronica y Computadores Universidad de Cantabria Avda. de los Castros s/n, Santander (Spain). About Authors: the R.PrasannaKrishnan was born in 8 th sep He did his B.E in Electrical and Electronic Engineering at Raja College of Engineering and Technology, Madurai. Currently he is pursuing his M.Tech Power System, Final Year in SRM University, Kattankulathur. His area of interest includes: Power Quality Issues, Power System Protection and FACTS. R.Senthil Kumar was born in 6 th April He completed his B.E in Electrical and Electronic Engineering at Thiyagarajar College of Engineering, Madurai and M.E in Instrumentation and Control Engineering in Bharath University, Chennai. Currently he is pursuing his Ph.D in SRM University and working as an Assistant Professor of EEE Dept. His area of interest includes Power Electronics and Drives, Power Quality Issues and Induction machines.