F ACTS Devices for Stability Enhancements

F ACTS Devices for Stability Enhancements Sajan Varma Department of Electrical Engineering Ferozepur College of Engineering & Technology Ferozeshah, Ferozepur, India sanjuvermaOOO@gmail.com damping out the disturbances an effective, conventional and economical solution have to install in power system stabilizer. Abstract: FACTS devices are used to control the voltage profile and stability of power system by improving transient and dynamic stability. Particle swarm optimization (PSO) technique is used in place of Genetic Algorithm (GA) for minimization of losses and simulation process. There are several types of FACTS devices but we have discussed only SVC (Static Var Compensator), Thyristor Controlled Series Compensator (TCSC) and Unified Power Flow Controller (UPFC) for this purpose. The mathematical model of these FACTS devices are also discussed with their applications in 3 machine 9 bus system. Keywords- Transients, dynamic stability, FACTS, PSO, The concept of Flexible Alternating Current Transmission System (FACTS) is based on the significant combination of power electronic devices and methods within the high­ voltage side of a network, to make it automatically controllable and to increase power transfer capability. FACTS controllers are being used in various parts of the world. The most famous FACTS controllers are: Tap changers of load, phase-angle regulators, static var compensators (SVC), thyristor-controlled series compensators (TCSC), inter phase power controllers, static compensators (STATCOM), static synchronous series compensator (SSSC) and unified power flow controllers (UPFC). These controllers further can be divided into four categories: 1. Series FACTS controllers ii. Shunt FACTS controllers iii. Combined series-series FACTS controllers iv. Combined series-shunt FACTS controllers GA, modeling, current injection etc. I. INTRODUCTION Power System is a network of electrical components/devices forming a single unit and providing electrical energy; it can be a generating station, distribution system and transmission system. Power generation stations and distribution stations/systems are connected all the way through transmission lines, and they also connects one power station/system (grid, area) to another. All the loads in a particular area of distribution system are connected to the transmission lines. no --<@II eG �II ��Li� T. Transmission T, Benefits of FACTS Controllers: � Lion ,------' .......................... • Power flow can be controlled. • The loading capacity of line is increased closer to thermal capability. • System security is increased with raise of transient stability limit, limiting short circuit currents and overloads, managing cascading blackouts and damping electromechanical. • For setting new generation it will provide greater flexibility. • Transmission lines are upgraded. • It reduces reactive power flows; because of this lines can carry more active power. • It provides secured tie line connections to nearest utilities and regions in that way decreasing overall generation reserve requirements on both sides. Subtransmlssion . l Distribution L. .��!�E!!!' Fig 1: Power System basic structure __ __ . __ ._. Stability of a power system is very important aspect and it is necessary to maintain to minimize the load losses and to achieve a desired output from power system. Damping in power system oscillations is one of the major challenges to electrical utilities. As the load grows, generations are increased, as a result of increased generation there can be possibilities of steady-state and transient stability problems in power system. To improve the power system stability by 978-1-4673-7910-6115/$31.00 ©2015 IEEE 69 • Loop flows are reduced. • The utility of lowest cost generation is increased. S. No Fact dev ices Power Load System Flow Stability Enhancement Control Voltage Stability Stability I UPFC YES HIGH HIGH MEDIUM MEDIUM 2 TCSC YES MEDIU LOW HIGH MEDIUM 3 SVC YES LOW HIGH LOW MEDIUM 4 SSSC YES LOW HIGH MEDIUM MEDIUM M : �U. --yB� Dynamic Transient Control Fig 3: SVC Total Susceptance Model 1 = �-----'-� --------� -----� J>< II. MODELLING OF 3 MACHNE 9 Bus SYSTEM A. Case Study The integrated multi-machine power system model consisting of 3 generators and 9 buses used for simulation process are shown as single line diagram in figure 2. The generator 1, 2 and 3 are connected to the busses 1, 5 and 9 respectively. Seven transformers T1 to T7 are also connected in the integrated power system for transmission purpose i.e. for step up and step down purposes. TCSC and SVC are connected between buses 2-3. UPFC is connected between buses 6-7. A voltage source is connected near to bus 8. Fig 4: SVC Firing Angle Model Representation of SVC in a transmission line is shown in fig. 5. 'v"; I j l3 s v= Fig 5: Representation of a SVC Voltage S ource Fig 2: 3 Machine 9 Bus System B. Mathematical Model of SVC SVC is a shunt connected FACTS family controller whose main function is to regulate the voltage by controlling equivalent reactance at a given bus. There are two components in SVC i.e. a fixed shunt capacitor (FC) and a thyristor controlled reactor (TCR). Generally there are two types of configurations of the SVC. a) A dynamic susceptance Bsvc representing the basic frequency equivalent susceptance of all shunt modules creating up the SVC total susceptance model as shown in Fig. 3. b) The equivalent reactance Xsvc, which is function of a dynamic firing angle denoted by a, a is made up of a parallel combination of TCR having equal admittance and a fixed capacitive reactance as shown in Fig. 4. This model is called as firing angle model of SVC which provides information on the SVC firing angle required to achieve a given level of compensation. 70 2015 Current injection model of SVC is shown in fig. 6, where I svc represents the composite current injected by SVC at j node j, V i and V j represents complex voltages at node i and j respectively. The reactive power injected at node j is given by: (l.l) Where Bsve = Be - BL, Be and Be represents the susceptance of the fixed capacitor and thyristor controlled reactor respectively. The reactive power that may be transferred to injection current at bus j is given by: (1.2) Ijsvc = jVj Bsvc Vii I Vj n -+.--jXJ I. � I Fig 6: Current injection model of a SVC Figure 7 shows control system block diagram of SVC where Vt represents the voltage magnitude at the terminal of SVC and voltage maintained by SVC is denoted by Vref, K represents gain of controller, time constant correlated with the SVC control action is denoted by T, llBmin and llBmax denotes the limits of the SVC susceptance and Cdamp represents the signal coming from damping controller. International Conference on Green Computing and Internet of Things (ICGCloT) From Fig. 9 the line current I.e is given by: (1 A) svc k/(1 +sT) The impact of capacitor is equal to a voltage source which depends on node voltages i.e. Vi and Vj. The current injection model of the TCSC can be obtained by replacement of voltage across the TCSC with an equivalent current source Is as seen in Fig. 10. In Fig.9, Ps = -jxcI.e, and from Fig. 10 follows �B V,er Is Fig 7: SVC control system r] + _ C. Mathematical Model of TCSC I 'Vi Figure 8 shows the basic topology of TCSC, which is composed of a series capacitor C, a thyristor controlled reactor L is also connected in its parallel branch. TCSC is used in power system for the purpose of dynamically controlling and increasing power transfer level by varying the apparent impedance of a specific transmission line. A TCSC operates in different modes and can be utilized in a mannered way for contingencies to enhance transient stability, dynamic stability and load flow control in power system. The different modes of operations of TCSC depending upon when the thyristors for inductive branch are triggered are blocking mode, bypass mode and capacitive boost mode. Apart from this, TCSC is also being used to mitigate sub synchronous resonance (SSR). . jx] Ps --jxclse (1.5) f]+jXl I v. III -+j XI I 'j E:> I" Fig 10: Replacement of a Voltage Source by a Current Source Current injections into nodes i and j are [- SJ = -JXc -f] + jXI ­ Vi - Vj x ---'----' (1.6) f] + j(Xl - xc) (1.7) I.i = -[Sj And as a result the suitable current injection model of TCSC can be represented as shown below in Fig. II. Vi Fig 8: Basic TCSC topology Vi Fig 11: Current Injection Model for a TCSC TCSC generally express its control action in terms of percentage of the compensation denoted by kc which is defined as: (1.3) Where XI: line reactance Xc: effective capacitive reactance contributed by TCSC. TCSC control system is shown in Fig. 12, where the control strategy of power flow controller is based on linearization of power flow equations. The output of the control system block is the change in the compensation degree is given by: L1kc L1P(rI2 ( - xc/)/ {2(V/ - Vi Vj cos 8ij) (1 kc) - rl (Vi Vj cos 8ij) � Vi Vj cos 8ij(1 - kc)} (1. 8) Where L1P Pref - P (input in the block) = + Xl + = TCSC is supposed to be placed between buses i and j in transmission line as shown in Figure 9, Where the TCSC is represented as a continuously controllable reactance (capacitive). Fig 9: TCSC in a Transmission Line 2015 Fig 12: TCSC Control System Ked represents the proportional constant and Ted denotes the integral time constant of the TCSC PI controller. The time International Conference on Green Computing and Internet of Things (ICGCloT) 71 constant T approximates interruption due to major circuit attributes and control system. P denotes line active power of TCSC and the active power of line to be maintained by TCSC are represented by Pref. Change is compensation degree limits are denoted by L'lkmin and L'lkmax. Fig 14: UPFC Schematic Arrangement D. Mathematical Modelling of UPFC UPFC provides simulation control of transmission voltage, impedance, line reactance, phase angle, active and reactive power flow of transmission line. UPFC is made of two branches i.e. one is parallel and other is series. Both branches of UPFC consist of dc capacitor, transformer and voltage source converter. In parallel branch, transformer is shunt connected and in the series branch a series injected transformer is used. The converter, labelled "Converter 1" and "Converter 2" are operated from a common dc link provided by a dc storage capacitor, Fig. 13. The active power demand of series converter is mainly supplied by the shunt converter with the help of common dc link. Converter 1 can also produce or absorb reactive power, if it is required, and in this way allows self-governing shunt reactive compensation for transmission line in a power system. Converter 2 plays the major role of the UPFC by injecting a voltage i.e. Vse with controlled magnitude (OSVseSVsemax) and phase angle in series with the line, Fig. 14. The reactance seen from terminals of the series transformer is denoted by Xs and is given as (1.9) Xk Xs = r�axCSB/ Ss) Where Xk: series transformer reactance rmax: maximum per unit value of injected voltage magnitude SB : base power of the system Ss: nominal power rating of the series converter In Fig. 15, the voltage source Vse has been replaced by current source l;n -jbs �e in parallel with Xs. j = I-------{--- }------j Fig 15: Transformed Series Voltage Source The active power supplied by shunt current source is calculated by the equation PCONVl = Re [V, (-I;h)] (1.11) -V;lt With the UPFC losses neglected, PCONVI PCONV2 = (1.12) = The apparent power supplied by series voltage source converter is calculated by the equation = rejyv, t�::j)* (1.13) Active and reactive power contributed by "Converter 2" are distinguished as below rbs VjVj sin(Sj - Sj + y) - rbs V/ siny PCONV2 (1.14) = rbs VjVj cos(Sj - Sj + y) + rbs V/cosy QCONV2 (1.15) Substituting Eqs. (1.11) and (1.14) in Eq. (1.12) gives = It (1.16) -rbs VjVj sin(Sj - Sj + y) + rbs Vjsiny The current of the shunt source can be calculated by the equation = Ish Fig 13: Implementation of UPFC by back-to-back voltage Schematic arrangement of UPFC controller is shown in figure 14, where an ideal series voltage is used as series voltage source which is controllable in magnitude and phase, and the shunt converter is represented or used as an ideal shunt current source. In Figure 14, Ish = It + Iq (It + jIq)ej8j = Where It is the current in phase with in quadrature with Vi. (1.10) Vi and Iq is the current (It + jIq) ej(Jj i ( -rbs Vj sin(Sjj + y) + rbs Vj siny + jIq) ejIJ = (l.l7) From Fig. 15 current injections at bus can be defined as (1.18) I; Ish - Ijnj = � Where = Ijnj = Ijnj = (1.19) -jbs Vs e -jbs Vjejy (1.20) Substituting Eqs. (1.17) and (1.20) in Eqs (1.18) and (1.19) gives = Ij ( -ebs Vj sine Sjj +y) + rbs Vj siny + jIq)ejIJj + (1.21) +jrbs VjejC8j+Y) (1.20) � -jbSVjejC8j+Y) = = Where Iq is an independent controllable variable, signifying a reactive shunt source. From Eqs. (1.20) and (1.21), the 72 2015 International Conference on Green Computing and Internet of Things (ICGCloT) current injection model of UPFC can be presented as shown in Fig. 16. Fig 16: UPFC Current Injection Model The active and reactive power flows at the UPFC shunt side are given as �l = (1.22) -rbs ViVj sin(8ij + y) - bs ViVj sin(8ij) V/ Qil -rbs cosy + Qconvl - bs (1.23) Whereas at the series side they are = �2 Qj2 = V/ + bs ViVj cos 8ij rbs ViVj sin(8ij + y) + bs ViVj sin(8ij) rbs ViVj cos( 8ij + y) - bs V/ + bs ViVj cos 8ij (1.24) (1.2S) Current injection model of UPFC can be defined by the constant susceptance i.e. bs connected in series branch, which is integrated as bus admittance matrix of system, and bus current injections i.e. Ii and Ij. To achieve control objective of system, the bus current injections can be modified by changing the control parameters of UPFC i.e. r, y and Iq• To keep active and reactive power flow of a line at specific values i.e. at Pref and Qref, the UPFC should work as the automatic power flow controller or in automatic mode. = through the problem space by following the current optimal particles. It is applicable to find variety of issues wherever native strategies fails or their usage become in-effective. PSO can be used as optimizing technique in massive and complicated multi-criteria issues or combinatorial issues, wherever the matter with the planning of criteria operate arises, as an example, it's laborious to derive or is not continuous. PSO provides easier methodology of providing new solutions as compared to GA. PSO basically uses two variables i.e. velocity and position with two linear equations. Every attainable solution described by a particle, files within the problem space area, which is restricted within maximum and minimum values, toward the present optimum position. The particle may also arbitrarily commit to move at the best position but it also has a speed of movement and a direction. Each particle keeps of its coordinates within the drawback area that are related to the best solution it has achieved up to now and this value is known as Pbest. Another 'best' value tracked by the particle swarm optimizer, obtained up to now by any particle within the neighbours of the particle. Once the particle takes all the population as its topological neighbours, the best value is a global best and is called gbest. Each particle is updated with its pbest and gbest. �� � " � � , �l. t )....: .L""' � 1, " \\\, � � � ') � - Fig 18: Flock of Birds Collectively Foraging for Food The Advantages of PSO over different ancient optimization techniques [8-9): P ref Qref ilr ily = = 1. Fig 17: UPFC control system llP s inCSij + y) HQcos CSij + y) (1.26) bs ViVj i i i s s n c o j S Q P S J +_-Y,-,-) _Il _ _ _ C,- ..:... _+ Y ....:. ,-) -_Il_ .::... _ -'.C � ·,(1.27) rb s ViVj II. III. OVERVIEW OF PARTICLE SWARM OPTIMIZATION (PSO) III. Particle Swarm Optimization (PSO) technique is developed by Kennedy and Eberhart is a computational method which is much better than G.A and has been used extensively in solving various problems in power systems. PSO is a modern heuristic technique which yields better results. In PS�, the potential solutions called particles are "flown" 2015 IV. PSO is a population-based search algorithmic rule i.e., PSO has latent compatibility. This feature makes PSO to be less vulnerable to obtain treed on native minima. PSO use objective perform info to guide the search within the drawback area. Therefore, non­ differentiable objective functions may be simply dealt by PSo. PSO uses probabilistic transition rules, not settled rules. a lot of difficult and uncertain space may be simply search by PSO algorithmic rule. From this we will conclude that when compared to traditional ways PSO is a lot of versatile and robust. When compared with GA and different heuristic algorithms, PSO has a lot of flexibility to control International Conference on Green Computing and Internet of Things (ICGCloT) 73 V. VI. VII. VIII. IX. X. the balance between the worldwide and local exploration of the search area. Coding implementation is very easy with the help of PSO. PSO provides feature of stable convergence. PSO has very less parameters to adjust. PSO is less sensitive to the nature of objective function. PSO is much efficient to perform a global search. With the help of PSO we can obtain high quality solutions within shorter calculation time. Journal, Vo!'2, (2011), No.2, pp 543 - 549. iSSN 2078 - [13] 2365. Akhilesh A. Nimje, D. P. Kothari, "Energy Function Based Transient Series Stability Capacitor", Assessment of International Thyristor Journal Technology and Advanced Engineering, Controlled of Emerging Vol. 4, issue 12, December 2014, pp 461-467. ABOUT AUTHORS Er. Sajan Varma obtained B.Tech Electrical Engineering (EE) in 2013 in from Punjab Technical University, India. He is IV. CONCLUSION currently FACTS devices are the most powerful devices to control the voltage and power system enhancement by improving the transient and dynamic stability of Power system [10-12]. In this paper different FACTS devices are discussed with their respective mode of operations, representation and mathematical model as well. It is found that the performance and mode of operation of UPFC is higher and much better than the other FACTS devices such as TCSC, SVC, SSSC etc respectively. UPFC can stable the power system comparatively faster than the rest of FACTS devices. pursuing M.Tech Assistant Professor Electrical College in of at DevelepTech IT Solutions Department of Electrical Engineering His research areas are Power System systems-modeling, IEEE Transactions on 15.2 (2000): 817-824. K. R. Padiyar "FACTS Controllers in power transmission [4] N. G. Hingorani and L. Gyugyi, "Understanding FACTS" [5] and distribution",New Age International Publishers, 2007. Delhi, india:Standard PublishersDistributors, 2001. 1. Kennedy, and R. Eberhart, "Particle Swarm Optimization," iEEE international Conference on Neural Networks, vol. 4, [6] pp.i942-1948, November i995. Noroozian, M., et al. "Use of UPFC for optimal power flow contro1." iEEE Transactions on Power Delivery, [7] (1997): i629-1634. Noroozian, M., Angquist, L., Ghandhari, M., & Andersson, G. "Use of UPFC for optimal power flow control", iEEE [8] Transactions on Power Delivery, 12(4), i629-1634. Hingorani, Narain G., and Laszlo Gyugyi. "Understanding FACTS: Concepts and Technology of Flexible AC Transmission Systems" Ed. Mohamed El-Hawary. Vol. 1. [9] New York: IEEE press, 2000. Gan, Deqiang, Robert J. Thomas, and Ray D. Zimmerman. "Stability-constrained [10] optimal power flow." IEEE Transactions on Power Systems 15.2 (2000): 535-540. Kennedy, James. "Particle swarm optimization." Encyclopedia of Machine Learning. Springer [II] US, 2010. 760-766. Akhilesh A. Nimje, C. K. Panigrahi, A. K. Mohanty, "Enhanced Power Transfer Capability by using SSSC", Journal of Mechanical Engineering and Research, Vol. 3 (2), [12] pp 48 - 56, February 2011. Akhilesh A. Nimje, C. K. Panigrahi, A. K. Mohanty, "Energy Function Based Transient Stability Assessment of SSSC 74 and IPFC", international Electrical Engineering 2015 International Conference Ltd., at Saint Kabir modelling and Simulation, Power System Stability and Control, FACTS and interface, control strategy, and case study." Power Systems, [3] Pvt. Polytechnic College, Fazilka, India. He is member ofIAENG. i994). power Technology Chandigarh, India. He also has worked as a Lecturer in Huang, Zhengyu, et al. "Application of unified power flow interconnected of Ferozepur Previously he was working in Department of Research and development P. Kundur, "Power System Stability and Control", EPRI in & Engineering Power System Engineering Series (Mc Graw-Hill, New York, controller at Ferozeshah, Ferozepur, Punjab,India. Renewable Energy Sources. [2] Punjab Department Engineering REFERENCES [1] in Technical University and working as an on Green Computing and Internet of Things (ICGCloT)