Voltage-Current and Harmonic Characteristic Analysis of Different FC-TCR Based SVC

Transcription

1 Voltage-Current and Harmonic Characteristic Analysis of Different FC-TCR Based SVC Mohammad Hasanuzzaman Shawon, Zbigniew Hanzelka, Aleksander Dziadecki Dept. of Electrical Drive & Industrial Equipment AGH University of Science & Technology Krakow, Poland Abstract Static Var Compensator (SVC) is one of the most popular modern power system elements to stabilize voltage as well as to compensate reactive power demand. There are varieties of such circuit which deal with different technical arrangement, reactive power compensation technique, contribution to power system stability and individual features as well. In this paper simulation and experimental results of different types of SVC, more specifically Fixed Capacitor-Thyristor controlled reactor (FC-TCR), are presented. The experiments are carried out to verify the simulation result of two different configuration of FC- TCR. Finally, a comprehensive analysis on current-voltage characteristics and harmonic characteristics are reported in this paper. Keywords-SVC, FACTS, FACDS, FC-TCR, Harmonics I. INTRODUCTION In recent years, electric power has become a major concern due to the increasing complexity of modern power system as well as fulfilling the demand with better power quality. As a result nowadays, advanced technologies like Flexible AC Transmission System (FACTS) and Flexible AC Distribution System (FACDS) are being introduced in the modern power system to improve power system stability as well as maintaining better power quality [1,2]. The role of such device is to provide secured, stable and better quality power as well as facilitating power flow control and with increased power transfer capability [3,4]. FACTS and FACDS are power electronic based devices which have the ability to absorb or inject reactive power to the power system. FACTS/FACDS are a family or group of devices which can be inserted into power grids in series, in shunt, and in some cases, both in shunt and series [5]. They play the main role to attain some benefits in a power system [6] such as improved power transmission capability, improved system stability and availability and better power quality. In this study, a special kind of FACDS device named as Static Var Compensator (SVC) is been highlighted in terms of voltage, current characteristics as well as Harmonic analysis. II. STATIC VAR COMPENSATOR (SVC) BACKGROUND Static Var Compensators(SVC) are shunt connected static generators / absorbers whose outputs are varied so as to control reactive power flowing in order to control power factor or voltage level of the electric power systems [7]. SVC has an important role in power system transmission and distribution performance. Installation of SVC increases transfer capability and minimizes losses as well as maintains a smooth voltage profile under various network conditions. One of the salient features of SVC is to improve the dynamic stability of the grid and mitigation of active power oscillations [8]. An SVC fig. 1 typically comprises a transformer, reactors, capacitors and bidirectional thyristor valves. There is a variety of main circuit arrangements. The main two types are Fixed Capacitor(filter) - Thyristor-Controlled Reactor(FC-TCR) and Thyristor Switched Capacitors- Thyristor Controlled Reactor (TSC-TCR). In FC-TCR type SVC configuration, a capacitor is connected in parallel with a thyristor controlled reactor. Such device (FC-TCR) is capable to provide continuous lagging and leading vars to the system [9]. By controlling the firing of back-back thyristor valves, circulating current through the reactor (I L ) is controlled where as capacitor provides leading var to the system. Figure 1: Schematic Diagram of FC-TCR I. DIFFERENT CONFIGURATION FC-TCR can be arranged into other configuration as well. The advantage of other configuration is that it provides wide operation region with lower total harmonic distortion (THD). The Fig. 2 describes different configuration of TCR where X L indicates inductive reactance, R indicates resistance and T 1 and T 2 indicates Thyristor 1 and Thyristor 2 respectively.

2 . (a) A. Simulation Result In this paper, MATLAB/Simulink is used to simulate both the theoretical and simulation result. First, a single phase SVC system is simulated in MATLAB/SIMULINK environment and current and voltage are presented in fig. 3 and fig. 4. In the second step, the equation of current and voltage is plotted using MATLAB and both of the results are verified in fig. 5,6,7 and 8 respectively. In all the cases, voltage and current values are divided by the maximum value ( full conduction) in order to obtain per unit value of them. (b) Figure 3: Different Reactor current with respect to delay (c) Figure 2: Different configuration of FC/TCR: (a) Classical; (b) Configuration 02; (3) Configuration 03 II. CURRENT & VOLTAGE CHARACTERISTICS OF CLASSICAL FC-TCR In order to analysis the characteristics of TCR, several parameters have been taken into consideration in this study. These parameters are: Average and R.M.S value of the voltage of the reactor and average and R.M.S value of the reactor current. The table I represents the theoretical equation for these parameters Figure 4: Different Reactor voltage with respect to delay TABLE I. CHARECTERISTIC EQUATION Parameters Average Voltage of the reactor Characteristic Equation 2V V = m avg (1 + cosα) π Figure 5: Average Reactor current with respect to delay (comparison of simulated and theoretical result) R.M.S Voltage of the reactor V Vrms = m 2 2α sin 2α 2 + π π Average value of the current 2I I = m avg [( π α)cosα + sinα) π R.M.S Value of current Irms = Im 2π 2 2( π α ) + 4( π α ) cos α + 3sin 2α Figure 6: R.M.S Reactor current with respect to delay (comparison of simulated and theoretical result)

3 Figure 7: Average Reactor voltage with respect to delay (comparison of simulated and theoretical result) Figure 10: Different Reactor current with respect to delay Figure 11: Different Reactor voltage with respect to delay Figure 8: RMS Reactor voltage with respect to delay (comparison of simulated and theoretical result) B. Laboratory Result of A laboratory test has been performed in the Laboratory stand of AGH University of Science & Technology. Fig. 10 presents experimental result (Reactor current characteristics) which matches simulation results and hence both the results are verified by obtaining the same characteristics. In case of experimental result of voltage characteristics of FC-TCR, some deviations are observed in case of peak values only. These deviations are due to the only measurement and all other parameters yield same result and hence verify simulation result. III. HARMONIC CHARACTERISTICS OF CLASSICAL FC-TCR Discontinuous current conduction of the thyristor controlled reactor is responsible for generating harmonic currents. Simulation has been carried to represent the harmonic characteristics of a single phase FC-TCR. Figure 9: Laboratory set up for the FC-TCR In laboratory, PQ analyzer Topas is used to measure the thyristor current and reactor voltage. Varying the delay (from 90 degree to 180 degree),three types of voltage and current (RMS value, AVG value for half cycle and Peak value) has been recorded using Topas. This recorded data has been plotted using MATLAB/SIMULINK to verify the simulation result. Figure 10 and figure 11 represents experimental result of such system and they also verify the simulated result. In all the cases, voltage and current values are divided by the maximum value ( full conduction) in order to obtain per unit value of them. A. Simulation Result Figure 12 represents firing versus first harmonics expressed with respect to the maximum value of the fundamental. It is seen that as the delay increases from 90 degree to 180 degree, the rms value of first harmonic is decreased. Figure 12: Basic Harmonic characteristic with respect to delay

4 Figure 13 represents harmonics characteristics of odd harmonics (3 rd, 5 th,7 th,9 th and 11 th ) versus delay. The harmonics are calculated in terms of percentage of maximum fundamental harmonic. B. Laboratory Result Laboratory test has been performed in the Laboratory stand of AGH University of Science & Technology to record the harmonics. Using Topas harmonics data are recorded for different firing. Using Matlab/Simulink the recorded harmonics are plotted to verify the simulated and theoretical result. Figure 16 indicates delay versus first harmonics expressed with respect to the maximum value of the fundamental. It is seen that as the delay increases from 90 degree to 180 degree, the rms value of first harmonic is decreased. Figure 13: Harmonic component (3 rd, 5 th,7 th,9 th, 11 th ) with respect to delay Another representation of harmonic is presented in Fig. 14 and Fig. 15. In figure 17, X axis has fundamental harmonics (expressed as percentage of maximum fundamental harmonic) and Y axis has all odd harmonics (3 rd,5 th, 7 th, ) which are expressed in terms of percentage of maximum fundamental current. Figure 16: Fundamental Harmonic with respect to delay Figure 17 represents harmonics characteristics of odd harmonics (3 rd, 5 th,7 th,9 th and 11 th ) versus delay. The harmonics are calculated in terms of percentage of maximum fundamental harmonic. Figure 14: Harmonic component (3 rd, 5 th,7 th,9 th, 11 th ) with respect basic component In figure 14, X axis has fundamental harmonics (expressed as percentage of maximum fundamental harmonic) and Y axis has all odd harmonics (3 rd,5 th, 7 th, ) which are expressed in terms of percentage of individual fundamental current. Figure 17: Harmonic component (3 rd, 5 th,7 th,9 th, 11 th ) with respect to delay Both Fig. 16 and Fig. 17 present harmonics characters at different firing which also verify previously obtained simulated result. IV. ANALYSIS OF MARTHUR FC-TCR CONFIGURATION FC-TCR arranged into Marthur configuration are analyzed in this section. Figure 15: Harmonic component (3 rd, 5 th,7 th,9 th, 11 th ) with respect to basic harmonic (%) A. Simulation Result A single phase FC-TCR system (second configuration) has been modeled in MATLAB/SIMULINK. The analysis has focused on two characteristics such configuration. They are current-voltage characteristics and harmonic characteristics respectively.

5 1) Current-Voltage Characteristics: Figure 18 presents different current versus delay where as Fig 19 represents different voltage versus delay. Figure 21: Harmonic component (3 rd, 5 th,7 th,9 th, 11 th ) with respect to delay Figure 18: Different reactor voltage versus delay B. Laboratory Result Laboratory test has also been conducted to verify the simulated result. A single Phase SVC model (second configuration) has been built at AGH university of Science & Technology and different current, voltage and harmonics are recorded using Topas. Current-Voltage Characteristics: Figure 19: Different reactor current versus delay 2) Harmonics Characteristics: The system is simulated in MATLAB/SIMULINK environment and harmonics are also calculated. Figure 20 presents Fundamental harmonic character versus delay where as Fig 21 represents Odd harmonic character versus delay. In Fig. 22, first harmonics expressed with respect to the maximum value of the fundamental. The main feature of this characteristic is that with delay increment, the rms value of first harmonic is decreased. In Fig. 21, the odd harmonics are calculated in terms of percentage of maximum fundamental harmonic. In both the simulation, the operating range for thyristor delay is from 0 degree to 180 degree. Figure 22: Different reactor voltage versus delay Figure 23: Different reactor current versus delay 1) Harmonics Characteristics:: Figure 24 indicates delay versus first harmonics expressed with respect to the maximum value of the fundamental where as Fig 25 presents delay versus odd harmonics expressed with respect to the percentage of maximum value of the fundamental. Figure 20: Fundamental Harmonic component with respect to delay

6 Figure 24: Fundamental Harmonic component with respect to delay Figure 25: Reactive Power Compensation using FC-TCR Figure 25: Harmonic component (3 rd, 5 th,7 th,9 th, 11 th ) with respect to delay V. CONTROL SYSTEM FOR FC-TCR The control of the TCR in the FC TCR SVC has four basic Functions. 1. A phase-locked loop circuit that provides a timing circuit function and runs in synchronism with the system voltage and generates timing pulses with respect to the peak of that voltage. 2. A reactive power to firing conversion that can be implemented from the mathematical relationship between the reactive power and the delay. Figure 26: Q to Angle conversion controll 3. The fourth function is the thyristor firing pulse generation. Thus, the control circuit is designed using these four main functions. The MATLAB/SIMULINK model of the control circuit used here is depicted in Fig. 26. The delay α is then fed to the SVC firing circuit module. VI. CONCLUSION This study presents basic configuration and operation of one of the most popular FACTS/FACDS devices (FC/TCR). Various voltage and current properties as well as harmonic characters are also analyzed in this study. It also proposes different configuration of FC-TCR in terms of lower THD as well as operating region. FC-TCR system is modeled in MATLAB/SIMULINK environment and in laboratory and simulated results are verified with theoretical result. REFERENCES [1] N.G. Hingorani, "High Power Electronics and flexible AC Transmission System," IEEE Power Engineering Review, Volume: 8 Issue: 7, pp. 3-4, July. [2] L. Gyugyi, "A unified flow control concept for flexible AC transmission systems," AC and DC Power Transmission, 1991, International Conference on, pp [3] R.M. Mathur and R.K. Varma, Thyristor-Based FACTS Controllers for Electrical Transmission Systems, IEEE Press and Wiley Interscience, New York, USA, Feb [4] T. T. Lie, and W. Deng, "Optimal flexiable AC transmission systems (FACTS) devices allocation," Electrical power & Energy System, vol. 19, No. 2, pp , [5] D. J. Gotham, G.T. Heydt, "Power flow control and power flow studies for systems with FACTS devices," IEEE Transactions on power systems, vol. 13, NO.1, pp , February [6] N. G. Hingorani and L. Gyugyi, Understanding FACTS Concepts and Technology of Flexible AC Transmission Systems, 1999 :IEEE Press [7] Chopade, P.; Bikdash, M.; Kateeb, I.; Kelkar, A.D. "Reactive power management and voltage control of large Transmission System using SVC (Static VAR Compensator)", Southeastcon, 2011 Proceedings of IEEE, pp [8] Yuma, G.P.; Kusakana, K. "Damping of oscillations of the IEEE 14 bus power system by SVC with STATCOM", Environment and Electrical Engineering (EEEIC), th International Conference on, pp [9] K. Suzuki, T. Nakajima, S. Ueda, and Y. Eguchi, "Minimum harmonic PWM control for self-commutated SVC", Proc PCC, no. D1-7, pp