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ISSN 2348–2370 Vol.07,Issue.08, July-2015, Pages:1298-1303 www.ijatir.org PV Cell Fed Unified Power Quality Conditioner for Voltage Sag Compensation C. ANITHA1, G. VIJAYA LAKSHMI2 1 2 PG Scholar, Dept of EEE, Arjun College of Technology & Sciences, Ranga Reddy(Dt), Hyderabad, TS, India. Assistant Professor, Dept of EEE, Arjun College of Technology & Sciences, Ranga Reddy(Dt), Hyderabad, TS, India. Abstract: Power quality has become an important factor in power systems, for consumer and household appliances with proliferation of various electric and electronic equipment and computer systems. The main causes of poor power quality are harmonic currents, poor power factor, supply voltage variations etc., A technique of achieving both active current distortion compensation ,power factor correction and also mitigating the supply voltage variations at load side, is compensated by unique device UPQC presented in this paper and this concept presents a multi loop based controller to compensate power quality problems through a three phase four wire unified power quality conditioner(UPQC) under unbalanced and distorted load conditions. The UPQC is constituted of two voltage source converters (vsc) connected via power link. The series compensator is connected to the line in series and injects the voltage and thus compensates for voltage issues; whereas the shunt compensator injects current thus compensating for current issues, and is connected in shunt to the line. The voltage injection to the line uses an injecting transformer. The proposed concept has been extended with RES for the dc link of the UPQC which supplies the active power whenever the grid is at block out conditions or else at peak power demands this extension works also increases the power quality improvement efficiently. The simulation results have to conform that the proposed UPQC with RES for very efficient, very simple continuous power generation to load as compared to the contemporary ones. Keywords: FACTS, Series-Shunt Controllers, Power Quality, RES. I. INTRODUCTION The integration of renewable energy into existing power system presents technical challenges and that requires consideration of voltage regulation, stability, power quality problems [13]. The power quality is an essential customer focused measure and it’s greatly affected by the operation of a distribution and transmission network. Nowadays, generation of electricity from renewable sources has improved very much. Since most renewable energy sources are intermittent in nature, it is a challenging task to integrate a significant portion of renewable energy resources into the power grid infrastructure. Traditional electricity grid was designed to transmit and distribute electricity generated by large conventional power plants. The electricity flow mainly takes place in one direction from the centralized plants to consumers. In contrast to large power plants, renewable energy plants have less capacity, and are installed in a more distributed manner at different locations. The integration of distributed renewable energy generators has great impacts on the operation of the grid and calls for new grid infrastructure. UPQC was widely studied by many researchers as an eventual method to improve power quality in distribution system. A small distributed generation (DG) should be interconnected with the power system in order to maintain the frequency and voltage. Several studies proposed on the interconnection system for distributed generation with the power system through the inverter because the inverter gives versatile functions in proving the ability of distributed generation. The attention to distributed generating sources is increasing day by day. The reason is their important roll they will likely play in the future of power systems. Recently, several studies are accomplished in the field of connecting DG to grid using power electronic converters [9]. Here grid interface shunt inverters are considered more where the reason is low sensitiveness of DG to grid parameters and DG power transferring facility using this approach. Although DG needs more controls to reduce the problems like grid power quality and reliability. PV and WECS distributed generation sources which provides a part of human required energy now a day and will provide in the future. The greatest share of this kind of energy in the future will be its usage in interconnected system. II. SYSTEM DESCRIPTION A. Basic System with Injection Transformer The circuit diagram of the UPQC system with injection transformer is shown in Fig. 1. The series and shunt VSC are in full bridge configuration and are interconnected via a DC link. DC link is constituted of a single capacitor alone. The UPQC module is constituted of the VSCs in full bridge configuration and a DC link. Out of the two bridged VSCs, one acts as the series VSC and other as Parallel VSC. This conventional UPQC works when there is disturbance in the line. The control signals/gating signals are obtained from the control strategy used. This control signal activates the VSCs. Copyright @ 2015 IJATIR. All rights reserved. C. ANITHA, G. VIJAYA LAKSHMI The VSC acting as series VSC compensates for the The circuit diagram of UPQC with the injection capacitor voltage. Hence, when an over-voltage occurs, the system shows the filter inductances in both sides of the VSCs through balances itself by injecting a voltage which in effect which the VSCs are connected to the transmission line. The reduces the line voltage and maintains the desired voltage controller for series VSC produces a proportional signal level. But whenever there is a voltage sag/dip, an according to the signal obtained from the comparison of the additional voltage will be added to the line with the help of desired/reference voltage with the actual voltage measured the injecting transformer. The shunt VSC compensates for from the system. This error voltage is used for PWM the reactive component and thus conditions the current and generation. This PWM signals generated is used for switching reduces the harmonics. Thus the UPQC conditions power of the IGBT switches which constitutes the series VSC. The totally. shunt VSC of the UPQC module is the responsible for the compensation of the current and elimination of the unwanted frequencies in the system. The PWM signal switches the VSC according to the changes in the system by producing a PWM signal accordingly so that the output of the VSC injected to the line conditions the power flow through t he line. The switching frequency of the IGBT switches used for the comparative study is taken as 5 kHz. Fig .1.Circuit diagram of UPQC with injection transformer. B. Basic System with Injection Capacitor The major difference between the conventional system and the proposed system are listed: Replacement of the injection transformer with a capacitor. The voltage across the capacitor is adjusted so that voltage compensation is obtained in the system. DC link between the VSCs is constituted of two capacitance- split capacitance. The split capacitance provides one terminal for the injection capacitor. III. CONTROL STRATEGY The control strategy used here is a multi-loop based controller which is based on the feedbacks obtained from the systems. The control strategies for the series and shunt controllers are discussed below: A. Control Strategy for the Series VSC The flowchart for the series control strategy is shown in Fig 3. The control signals obtained from the PWM generator is used for switching the switches of the series VSC. The feedbacks from the systems is taken and compared with various parameters. The reference voltage generation is done by extracting the positive sequence component and its phase from the system voltage. The Phase Locked Loops (PLL) along with the positive extraction is used to generate the positive sequence component. The following equation (1) represents the reference capacitor voltage. The single line diagram of the device is shown. Both the VSCs are connected to the transmission line via a filter circuit. Here a filter inductance is used in both sides which is shown in the circuit diagrams for the both proposed system (Fig 2) & conventional system (Fig 1). Fig.3.Flowchart for Series VSC Controller. (1) Fig.2.Circuit capacitor. diagram of UPQC with injection International Journal of Advanced Technology and Innovative Research Volume.07, IssueNo.08, July-2015, Pages: 1298-1303 (2) PV Cell Fed Unified Power Quality Conditioner for Voltage Sag Compensation Vl* is the peak value of the line voltage. This is set by user. θp is the phase angle of the positive sequence component. (3) The equation (2) shows the reference source voltage used to obtain the required capacitor reference voltage. The Where, the voltages Vα, Vβ are given as below voltages Vsp and Vsn are the peak voltages of positive sequence component and negative sequence component respectively. θn is the phase angle of the negative sequence (4) component of the line voltage. Thus the generated voltage Vsd is the positive sequence component of supply. The is compared is with actual voltage and as per the algorithm reference current generated in α-β reference frame is gating signals are obtained the generated signal controls the converted to abc reference frame. And we obtain the reference switching of the switches of the series VSC. frame currents – I*a, I*b& I*c. B. Control Strategy for the Shunt VSC The algorithm for the generation of control signals for the shunt VSC is shown in fig.4. The feedbacks obtained from the system are compared and then used generate the PWM signals used for switching the switches of the shunt VSC. IV. PHOTOVOLTAIC MODULE Here we are taking photovoltaic cells are the renewable energy sources. In the crystalline silicon PV module, the complex physics of the PV cell can be represented by the equivalent electrical circuit shown in Fig.5. For that equivalent circuit, a set of equations have been derived, based on standard theory, which allows the operation of a single solar cell to be simulated using data from manufacturers or field experiments. Fig 4 .Flowchart for Shunt VSC Controller. Fig.5. Equivalent electrical circuit of a PV module. The series resistance RS represents the internal losses due to the current flow. Shunt resistance Rsh, in parallel with diode, this corresponds to the leakage current to the ground. The single exponential equation which models a PV cell is extracted from the physics of the PN junction and is widely agreed as echoing the behaviour of the PV cell Fig.5.Reference current generation. The reference current generation for the shunt VSC controller is obtained using power balance theory. The reference currents generated are in α-β reference frame. This is transformed to abc reference frame and used as the reference current for the PWM generation. The generation of the reference current in abc frame is depicted in fig.4 The Cpq-1 is a transformation matrix and is given by the following equations, (5) The number of PV modules connected in parallel and series in PV array are used in expression. The Vt is also Defined in terms of the ideality factor of PN junction (n), Boltzmann’s constant (KB), temperature of photovoltaic array (T), and the electron charge (q). applied a dynamical electrical array reconfiguration (EAR) strategy on the photovoltaic (PV) generator of a grid-connected PV system based on a plant-oriented configuration, in order to improve its energy production when the operating conditions of the solar panels are different. The EAR strategy is carried out by inserting a controllable switching matrix between the PV generator and the central inverter, which allows the electrical reconnection of the available PV modules. International Journal of Advanced Technology and Innovative Research Volume.07, IssueNo.08, July-2015, Pages: 1298-1303 C. ANITHA, G. VIJAYA LAKSHMI V. MATLAB/SIMULINK RESULTS Simulation results of this paper is shown in bellow Figs.6 to 15. Fig.6. Simulink circuit for without UPQC. Fig.10.Simulation results for load voltage and load current. Fig.7. Simulation results for source voltage without UPQC. Fig.11.FFT analysis for load voltage. Fig.8. Simulation results for source current without UPQC. Fig.9. Simulink circuit with injecting transformer. Fig.12. Simulink circuit for with UPQC having ultra capacitance. International Journal of Advanced Technology and Innovative Research Volume.07, IssueNo.08, July-2015, Pages: 1298-1303 PV Cell Fed Unified Power Quality Conditioner for Voltage Sag Compensation VI. CONCLUSION The major power quality problems were minimized with the implementation of the UPQC in the system. The UPQC with three types of injecting devices were compared here to find out the efficiency and effectiveness of the UPQC with the change in the injecting devices. Thus the proposed injecting device (injecting capacitor) was found effective for minimizing the power quality issues over the conventional injecting device (injecting transformer).And by using renewable energy sources the injection capability is increases. Fig.13. Simulation results for load voltage and load current. Fig.14. FFT analysis for load voltage. VII. REFERENCES [1] Sruthi Raghunath, P.Venkatesh Kumar: ‘Transformer less Cross Phase Connected Unified Power Quality Conditioner’, IEEE Conference proceedings- 2013 International Conference on Circuits, Power and Computing Technologies, page no. 450-455. [2] Ghosh, A., Jindal, A.K., Joshi, A.: ‘A unified power quality conditioner for voltage regulation of critical load bus’. IEEE Power Engineering Society General Meeting, 6–10 June 2004, vol. 1, pp. 471–476 [3] Ghosh, Led wich. G, Power Quality Enhancement Using Custom, Power Devices, Boston: Kluwer. IET Power Electron, Vol. 5, Iss. 5, pp. 600–608, 2002. [4] Hideaki Fujita, Hirofumi Akagi: ‘The Unified Power Quality Conditioner: The Integration of Series- and ShuntActive Filters’. IEEE Transactions On Power Electronics, Vol. 13, No. 2, March 1998,pp 1088- 1093 [5] Zhang, Y., Zhang, S., Chen, J.: ‘The applications of bidirectional full bridge DC–DC isolated converter in UPQC’. Int. Conf. on Electrical Machines and Systems, 17–20 October 2008, pp. 1916–1921 [6] Choi.S.S, Eng Kian Kenneth Sng, Mahinda Vilathgamuwa. D, ,’ Analysis of Series Compensation and DC-Link Voltage Controls of a Transformer less SelfCharging Dynamic Voltage Restorer’, IEEE transactions on power delivery, vol. 19, no. 3, Pages 0885-8977, 2004. [7] G.J. Li, F. Ma,S.S. Choi, X.P. Zhang,Control Strategy Of A Cross-phase connected Unified Power Quality Conditioner, IET Power Electron., 2012, Vol. 5, Iss. 5, pp. 600–608, doi: 10.1049/iet-pel.2011.0272 [8] Khadkikar, V., Chandra, A.: ‘A novel structure for threephase four-wire distribution system utilizing unified power quality conditioner (UPQC)’. Int. Conf. on Power Electronics, Drives and Energy Systems, 12–15 December 2006, pp. 1–6 [9] Kazemi, A., Mokhtarpour, A., Tarafdar Haque, M.: ‘A new control strategy for unified power quality conditioner (UPQC) in distribution systems’. 2006 Int. Conf. on Power System Technology, 22–26 October 2006, pp. 1–5 [10] Elnady, A., Goauda, A., Salama, M.M.A.: ‘Unified power quality conditioner with a novel control algorithm based on wavelet transform’. Canadian Conf. on Electrical and Computer Engineering, 13–16 May 2001, vol. 2, pp. 1041–1045 [11] Tey, L.H., So, P.L., Chu, Y.C.: ‘Neural networkcontrolled unified power quality conditioner for system harmonics compensation’. IEEE PES Transmission and Distribution Conf. and Exhibition 2002 Asia Pacific, 6–10 October 2002, vol. 2, pp. 1038–1043 Fig.15. Simulation results for upqc having photovoltaic cell. International Journal of Advanced Technology and Innovative Research Volume.07, IssueNo.08, July-2015, Pages: 1298-1303 C. ANITHA, G. VIJAYA LAKSHMI [12] Singh, B.N., Chandra, H., Al-Haddad, K., Singh, B.: ‘Fuzzy control algorithm for universal active filter’. Power Quality’98, 18 June 1998, pp. 73–80 [13] Khadkikar, V., Chandra, A.: ‘A new control philosophy for a unified power quality conditioner (UPQC) to coordinate load-reactive power demand between shunt and series inverters’, IEEE Trans. Power Deliv., 2008, 23, (4), pp. 2522–2534. International Journal of Advanced Technology and Innovative Research Volume.07, IssueNo.08, July-2015, Pages: 1298-1303