Modeling and Simulation of TSR-based SVC on Voltage Regulation for Three-Bus System

Transcription

1 International Symposium and Exhibition on Electrical, Electronic and Computer Engineering, (ISEECE-6), pp: 67-7, - 5 Nov. 6, Near East University, Nicosia, TRNC. Modeling and Simulation of TSR-based SVC on Voltage Regulation for Three-Bus System Ayetul KARA Department of Electrical & Electronics Engineering, University of Nigde Nigde, Turkey ayetulkara@nigde.edu.tr Tankut YALCINOZ Department of Electrical & Electronics Engineering, University of Nigde Nigde, Turkey tyalcinoz@nigde.edu.tr Abstract This paper presents, modeling and simulation of Thyristor Switched Reactor (TSR)-Based Static VAr Compensator (SVC), which is one of Flexible AC Systems (FACTS) controllers. The effects of on load bus voltage are simulated on MATLAB 7.4 environment. The results show that significant improvement on reactive power compensation and bus voltage regulation could be achieved by using the TSR-based SVC. Also, harmonic levels generated by TSR based which is a three-bus system SVC structure do not cause to instability in the test system. Keywords Flexible AC Systems, Thyristor Switched Reactors, SVC, Compensation, Voltage Regulation, MATLAB.. INTRODUCTION Voltage control, voltage regulation, reactive power control, steady state stability etc. are important problems of power systems. Flexible AC Systems (FACTS) controllers can be used for solving these problems. Different types of FACTS controllers are described in IEEE, CIGRE and EPRI documents [-4]. Reactors combined with thyristors provide well flexible control of voltage in power systems []. The FACTS are obtained from application of power electronics technology. The shunt connected Static VAr Compensator (SVC) of one of FACTS devices are used for voltage regulation []. The SVC is both reactive power generator and reactive power absorber. The basic structures of a Static VAr Compensator (SVC) are fixed shunt capacitor (FC) and Thyristor Controlled Reactor (TCR) [-5]. Furthermore, the SVC is investigated in TSC (Thyristor Switched Capacitor)-TCR, MSC (Mechanically Switched Capacitor)-TCR and TSC-TSR configurations [4, 6-]. To date, some authors have simulated Thyristor Switched Reactor (TSR), which is one of FACTS devices, using different computer programs such as NETOMAC (Network Torsion Machine Control), MICROCAP that is a SPICE compatible software package [7, ]. Endres et. all. [7] presented the design and operational testing of valves for SVC which consisted of one TSR and two TSCs. They installed the SVC at Kemps Creek substation in Australia. In this paper, the effect of the thyristor switched reactor-based SVC to load voltages has been proposed in the three-bus system at static load conditions. The design and testing of TSR-based SVC are verified using the MATLAB/Simulink 7.4 and Power Systems Toolbox.. PRINCIPLES OF TSR Thyristor Switched Reactors are shunt compensators that can absorb reactive power [4]. The TSRs have following properties: its operating principle simple, delay of one half a cycle and no generation of harmonics [, 4, 7]. The Fig. illustrates an equivalent circuit of the TSR. According to Fig., the TSR consists of two thyristors in anti-parallel and a reactor to be switched.

2 International Symposium and Exhibition on Electrical, Electronic and Computer Engineering, (ISEECE-6), pp: 67-7, - 5 Nov. 6, Near East University, Nicosia, TRNC. The SVC is acquired to reactive and capacitive operation interval. In this paper, thyristors in structure of TSR are fired at the positive/negative peak of the source voltage or at the zero crossing of the line current. Thus, the harmonic generation has been prevented in the energy system.. DESIGN AND IMPLEMENTATION Fig.. Main structure of TSR In the -phase applications, the basic TSR elements are connected in delta [7]. The control technique of the TSR is in two states only: either fully on or fully off. Control schemes of the TSR have been found detailed in Ref., Ref. 4 and Ref Modeling of in MATLAB The has been modeled using the MATLAB/Simulink 7.4 and Power Systems Toolbox [4]. A schematic diagram of a single phase TSR-Based SVC is shown in Fig.. A three-phase model consists of three single-phase TSR and a fixed capacitor connected in delta configuration. It is in parallel connected to the load bus. A six-pulse generator has been used to fire six thyristors of the TSR. Load Bus.. TSR-based SVC As mentioned above, the most general structures of a Static VAr Compensator (SVC) are fixed shunt capacitor (FC) and Thyristor Controlled Reactor (TCR) [-5]. In this paper, in order to abstain harmonic generation it was decided to use a TSR instead of a TCR [7]. Also, with choice of TSR both voltage stability and stepwise control of bus voltage have been provided. The Fig. demonstrates an equivalent circuit of the. According to Fig., the TSR-Based SVC consists of one TSR and one fixed capacitor (FC). T g m a k g m a k T FC Load Bus Trigger L Trigger Δ Connected TSR Fig.. configuration L Δ Connected FC Fig.. A single phase configuration. Modeling of Loads and Power System in MATLAB In this study, a three-bus system with a km, 5 km and km transmission line modeled as a π- equivalent circuit is used to show the effect of the TSR- Based SVC on voltage regulation. Table shows parameters of static load, the transmission line and the source.

3 International Symposium and Exhibition on Electrical, Electronic and Computer Engineering, (ISEECE-6), pp: 67-7, - 5 Nov. 6, Near East University, Nicosia, TRNC. Table. The Loads and Systems Parameters Source (-) voltage 8 kvrms (LL) System frequency R L Bus - line length Bus -Load Bus line length Bus -Load Bus line length Static load P Static load Q 5 Hz 6.5 Ω 45 mh km 5 km km 5 MW 7 MVAr Fig. 4 demonstrates a three-bus test system with a static load model. Two source as 8 kv link is connected between Bus and Bus, respectively. Another bus is selected as the load bus. Resistive and inductive parts of the static load are occurred from 5 MW as active power and 7 MVAr as reactive power, respectively. Souce 8 kv Bus Bus Fixed C km 5 km TSR km Load Bus LOAD Fig. 4. A three-bus test system with static load 4. SIMULATION RESULTS Source 8 kv In this study, a three-bus system is used to show the performance of the device on voltage regulation for the static load. The parameters of the system and the static load are given in Table. A sixpulse generator is used to control of firing angle of the TSR. Firstly, the system without the thyristor switched reactor-based SVC is considered. In this case study, Table shows obtained simulation results and gives the load voltage as rms value, (V LL (kv)); total active power of the load as P load (MW); total reactive power of the load as Q load (MVAr) and power factor as Cos φ. Table. Simulation Results for the system without VLL 8. Vsource (kvll) VLL 8. VLL 8. VLL 65.7 Vload (kvll) VLL 65.9 VLL 66.4 Pload (MW) 4.5 Qload (MVAr) 648. Cos φ.447 It is clearly seen from Table that the static load absorbs active power of 4.5 MW and reactive power of 648. MVAr at.447 power factor lagging. Required active and reactive powers of the static load are far from nominal values given in Table. Therefore the power factor would be desired to correct for improving power quality. Fig. 5 illustrates variations of the load voltage and the source voltage. It is clearly seen that the load voltage of 65 kv, which is.96 pu for a base of 8 kv, is less than the source voltage for the static load model. The reactive power compensation should be definitely made for voltage regulation. Source and Load Voltage (kvrms) 4 x Fig. 5 Source and load voltage at a -Bus system without Here, the effect of will be examined for reactive power compensation and voltage regulation. In this test system, TSR has a reactor of MVAr and the fixed capacitor is (FC).6 μf. The simulation results of the test system with TSR-Based SVC are given in Table.

4 International Symposium and Exhibition on Electrical, Electronic and Computer Engineering, (ISEECE-6), pp: 67-7, - 5 Nov. 6, Near East University, Nicosia, TRNC. Table. Simulation Results for the system with VLL 8. Vsource (kvll) VLL 8. VLL 8. VLL Vload (kvll) VLL 75. VLL Pload (MW) 4.77 Qload (MVAr) 7.9 Cos φ.8 As given in Table, the load voltage is close to nominal value of the source. For a base of 8 kv, the load voltage is increased by using from.96 pu to.987 pu. Correspondingly, measured active power of the static load is very close to nominal value of the static load and measured reactive power at the load bus is 7.9 MVAr. The reactive power compensation is made by using. Hence power factor (Cos φ) is increased from.447 to.8 and installation of it in the system is caused to improve power factor and voltage profile in the conditions. Figure 6 demonstrates the source voltage and the load voltage for the. Source and Load Voltage (kvrms) 4 x Fig. 6 Source and load voltage at a -Bus system with As can be seen from Fig. 6, located at Load Bus provides the reactive powers for the static load around its base value to keep the load voltage at the acceptable level. Now, the waveforms of total harmonic distortion of voltage (THD V) and total harmonic distortion of current (THD C) are investigated. Fig. 7 shows THD V and THD C for the system without. THD V THD C Fig. 7. THD V and THD C without Fig. 7 demonstrates that the system without TSR- Based SVC inject forever harmonic components of voltages and harmonic component of currents into the line. Hence, the test system without is needed a harmonic filter, because this harmonic levels cause to instability in the systems. THD V THD C Fig. 8. THD V and THD C with Fig. 8 shows THD V and THD C for the system with. This system does not inject harmonic components of voltages and harmonic component of currents into the line. Hence, the test system with TSR- Based SVC is not needed a harmonic filter and this is a great advantage of the device. 5. CONCLUSION The voltage flicker and voltage stability have become important subjects in power systems. One of solutions of these problems is the reactive power

5 International Symposium and Exhibition on Electrical, Electronic and Computer Engineering, (ISEECE-6), pp: 67-7, - 5 Nov. 6, Near East University, Nicosia, TRNC. compensation. In this paper, switching ON or OFF of a, which is of FACTS controller, has been proposed for the reactive power compensation and in particular voltage regulation. This FACTS device does not produce harmonics in power systems because of the control technique. In this paper, the effect of the thyristor switched reactor-based Static VAr Compensator on load voltages has been presented. The modelling and simulation of have been verified using the Matlab7.4 SimPowerSystems Blockset. The studied power system was a three-bus system with the static load. The simulation results demonstrated that installation of a in the system is caused to improve power factor and voltage profile for both static loads and systems with multiple buses. The proposed controller provides to rapid control of the voltage at week points at every load level in the test system. Test system with is not needed a harmonic filter and this is a great advantage of the TSR-based SVC. AKNOWLEDGMENT This work was supported in part by the Research Fund of the Turkish Scientific and Technical Research Council (TUBITAK) under the project number of TUBITAK 4M5. REFERENCES [] Povh D., Modelling of FACTS in Power System Studies, IEEE Power Engineering Society Winter Meeting, Vol., -7 January/, pp [] G. F. Ledwich, S. H. Hosseini, G. F. Shannon, Voltage Balancing Using Switched Capacitors, Electric Power Systems Research, Vol. 4, Issue, August/99, pp [] Hingorani N. G., Gyugyi L., Understanding FACTS: Concepts and Technolgy Flexible AC Systems, IEEE Press, New York, 999. [4] Mathur R. M., Varma R. K., Thyristor-Based FACTS Controllers for Electrical Systems, IEEE Press, USA,. [5] Kodsi S. K. M., Canizares C. A., Kazerani M., Reactive Current Control Through SVC for Load Power Factor Correction, Electric Power Systems Research, Vol. 76, Issue 9-, June/6, pp [6] Huesmann G., Habur K., Stump, K., Elliott W.H., Trujillo F.E., Design Considerations for The Eddy County Static VAr Compensators, IEEE Transactions on Power Delivery, Vol. 9, Issue, April/994, pp [7] Endres B., Thiele G., Bonfanti İ., Testi G., Design and Operational Testing on Thyristor Modules for The SVC Kemps Creek, IEEE Power Engineering Society Winter Meeting, November/989, pp. 6. [8] Hedayati M., Technical Spefication and Requirements of Static VAr Compensation (SVC) Protection Consist of TCR, TSC and Combined TCR/TSC, 9 th Int. UPEC 4, Vol., 6-8 Sept. 4, pp [9] Scott Z., Powsiri K., Ali F., Design of a Microprocessor- Controlled Personal Static Var Compensator (PSVC), IEEE. Power Engineering Society Summer Meeting,, Vol:, pp [] Ahmed T., Ogura K., Soshin K., Hiraki E., Nakaoka M., Small- Scale Wind Turbine Coupled Single-Phase Self-Excited Induction Generator with SVC for Isolated Renewable Energy Utilization, The 5th Int. Conf. on Power Electronics and Drive Systems, Vol., 7- Nov./, pp [] Thomas P. Y., Conard J. Ph., Labrique F., Buyse H., Analysis of A Three Phase TSC-TCR Static VAr Compensator by Recurrences Theory, IEEE 7th Mediterranean Electrotechnical Conference, Vol., -4 April/994, pp [] Y. H. Song, A. T. Johns, R. K. Aggarwal, Nonlinear Thyristor- Controlled Static VAR Compensation, Fifth European Conference on Power Electronics and Applications, -6 Sept. 99, Vol. 8, pp [] G. G. Karady, Concept of a Combined Short Circuit Limiter and Series Compensator, IEEE Transactions on Power Delivery, Vol. 6, Issue, July/99. pp. 7. [4] SimPowerSystems for Use with Simulink User s Guide, The Mathworks, Inc., Version: 4.