6545(Print), ISSN (Online) Volume 4, Issue 1, January- February (2013), IAEME & TECHNOLOGY (IJEET)

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1 INTERNATIONAL International Journal of JOURNAL Electrical Engineering OF ELECTRICAL and Technology (IJEET), ENGINEERING ISSN 0976 & TECHNOLOGY (IJEET) ISSN (Print) ISSN (Online) Volume 4, Issue 1, January- February (2013), pp IAEME: Journal Impact Factor (2012): (Calculated by GISI) IJEET I A E M E OPTIMAL ALLOCATION OF FACTS DEVICES IN DIFFERENT OVER LOAD CONDITIONS M.V.RAMESH, M.Tech Associate Professor, Priyadarashini college of Engineering & technology, Nellore, AP, India Dr. V.C. VEERA REDDY, PhD Professor & Head of the Dept, EEE S.V.University, Tirupathi, AP, India ABSTRACT This paper gives a solution to an optimal allocation of multi-type FACTS devices using a partial swarm optimization technique. This technique is useful to find the solution of three parameters i.e. the location the devices, their types and their ratings. In this paper, SVC and IPFC types of FACTS controllers are optimally located for different over load conditions. Optimal allocation of these FACTS devices improves the power transfer capability and voltage profile of the system. Simulations are performed on a modified IEEE 30-bus system at normal and overvoltage conditions and results are presented. Keywords: SVC, IPFC, PSO, Power losses, Load flow studies, modified IEEE 30 bus. 1. INTRODUCTION With ever increasing demand of electric power, the existing transmission networks are found to be weak which results in poor quality of unreliable supply. Also it is seen that in order to expand or enhance the power transfer capability of the existing transmission network huge sum of finances are required and sometimes even difficulties are encountered in finding right-of-way for the new lines. Lot of research has gone to gain increased efficiency from the existing power system. This programme is known as Flexible Alternating Current Transmission System abbreviated as FACTS. The main objective of FACTS devices is to replace the existing slow acting mechanical controls required to react to the changing system 208

2 conditions by rather fast acting electronic controls. Various FACTS devices are developed with the passage of time. Some of them are static VAR Compensator, Thyristor controlled series capacitor, Interline power flow controller, unified power flow controller, Static Synchronous series capacitor, Static Synchronous compensator, Static Synchronous generator etc. The purpose of reactive power (VAR) optimization is to improve the voltage profile in the system and to minimize the real power transmission losses while satisfying the unit and system constraints. This goal is achieved by proper adjustment of reactive power control variables like generator bus voltage magnitudes, transformer tap settings, and reactive power generation of the devices such as capacitor, reactor, synchronous condensers and the static VAR compensators (SVC). As power transfer grows, the power system can become increasingly more difficult to operate, and the system becomes more insecure with unscheduled power flows and higher losses. The rapid development of self-commutated semiconductor devices, have made it possible to design power electronic equipments. These equipments are well known as Flexible AC Transmission systems (FACTS) devices. The FACTS controllers, such as Static VAR Compensator (SVC), Thyristor Controlled Series Compensator (TCSC) and Static Synchronous Compensator (STATCOM) can increase or reduce reactive power according to the demand of reactive power in the network to improve the stability, reduces system loss and also improves the loadability of the system [1-4]. Unified power-flow controllers (UPFC) enable the operation of power transmission networks near their maximum ratings, by enforcing power flow through well-defined lines. The UPFC regulates the active and reactive power control as well as adaptive to voltage magnitude control simultaneously or any combination of them. Controlling the power flows in the network help to reduce flows in heavily loaded lines, reduce system power loss, and improve stability and performance of the system without generation rescheduling or topological changes. Interline power flow controller (IPFC) is a new concept of FACTS controller for series compensation with the unique capability of power flow management among multi-line of a substation [5], [8]. In this paper, multi-type FACTS devices like SVC and IPFC are optimally located on a modified IEEE 30-bus using Partial Swarm Optimization Technique. 2. STATIC VAR COMPENSATOR (SVC) It is the first device in the first generation of FACTS controller introduced to provide fast-acting reactive power compensation in the transmission network. Static VAR Compensator as shown in Fig 1 composed of Thyristor Controlled Reactor (TCR), Thyristor Switched Capacitor (TSC) and harmonic filters connected in parallel to provide dynamic shunt compensation. The current in the Thyristor Controlled Reactor is controlled by the thyristor valve that controls the fundamental current by changing the firing angle, ensuring the voltage limited to an acceptable range at the injected node. Current harmonics are inevitable during the operation of thyristor controlled rectifiers, thus it is essential to have filters to eliminate harmonics in the SVC system. The filter bank not only absorbs the risk harmonics but also produce the capacitive reactive power. 209

3 Fig: 1 Circuit Diagram of Static VAR Compensator (SVC) Fig: 2 (a) SVC Firing angle model (b) SVC susceptance model SVC placed in a transmission network provides a dynamic voltage control to increase the transient stability, enhancing the damping power oscillations and improve the power flow control of the power systems. In real time scenario, it effectively controls the reactive power, improves the power factor, reduces the voltage levels caused by the nonlinear loads, improves the power quality and reduces the energy consumption. The main advantage of SVC application is to maintain bus voltage approximately near a constant level in addition used to improve transient stability. It is widely used in metallurgy, electrified railway, wind power generation etc. In general, the transfer admittance equation for the variable shunt compensator is i = jbvk..(1) and the reactive power equation is Q K= - VK 2 (2) SVC Total Susceptance Model H = BSVC (i) (i) P K = 0 0 θ k Q K 0 Q K BSCV..(3) B SCV 210

4 The liberalized SVC Equation is given by Where i (i) 0 0 (i) P K = Q K Q K.(4) Q K 0 α α QK 2VK α = COS (2α) - 1 (5) X L At the end of iteration, the firing angle is updated according to equation (6) α i +1 = α + α i.(6) Fig:3 steady-state and dynamic voltage/current 3. INTERLINE POWER FLOW CONTROLLER (IPFC) The IPFC, proposed by Gyugyi and Schauder addresses the problem of compensating a number of transmission lines at a given substation. The IPFC scheme, together with independently controllable reactive series compensation of each individual line, provides a capability to directly transfer real power between the compensated lines. This capability makes it possible to equalize: both real and reactive power flow between the lines reduce the burden of overload line by real power transfer; compensate against resistive line voltage drops and the corresponding reactive power demand; and increase the effectiveness of the overall compensating system for dynamic disturbances. It is common that, the IPFC employs a number of dc to ac inverters in order to offer series compensation for each line. As a new concept for the compensation and effective power flow management, it addresses the target of compensating a number of transmission lines at a given substation. The IPFC is a combination of two or more independently controllable SSSC which are solid-state voltage source converters. As shown in Fig. 4, the unit 1 of IPFC can be operated as SSSC. 211

5 Fig: 4 Basic Configuration Of Interline Power Flow Controller Conventionally, series capacitive compensation fixed, thyristor controlled or SSSC based, is employed to increase the transmittable real power over a given line and to balance the loading of a normally encountered multi-line transmission system. They are controlled to provide a capability to directly transfer independent real power between the compensated lines while maintaining the desired distribution of reactive flow among the line. Fig: 5 Two-Inverter Interline Power Flow Controller The simplified schematic of IPFC model is shown in Fig.6, with this scheme an addition to provide series reactive compensation, any converter can be controlled to supply real power to the common dc link from its own transmission line. 212

6 Fig: 6 Schematic diagram of two converter IPFC Fig: 7 Equivalent circuit of two converter IPFC Fig: 8 Power injection model of two converter IPFC Thus an overall surplus power can be made from the underutilized lines which then can be used by other lines for real power compensation. In this way some of the converters, compensating overloaded lines or lines with heavy burden of reactive power flow, can be equipped with full two dimensional, reactive and real power control capability, similar to that offered by the UPFC. Evidently, this arrangement mandates the rigorous maintenance of the overall power balance at the common dc terminal by appropriate control action, using the general principle that the overloaded lines are to provide help in the form of appropriate real power transfer, for the overloaded lines. 213

7 The IPFC is placed in between two transmission lines. The active and reactive powers injected at each bus using IPFC are given as, = Σ Vi Vsein bin sin (Өi-Өsein) n=j,k, = -Σ Vi Vsein bin cos (Өi-Өsein) n=j,k, = - Vn Vsein bin sin (Өi-Өsein), = Vn Vsein bin cos (Өi-Өsein) Where n= i,j. The active power exchange between the lines is zero. i.e ( Vsein Iji * + Vseik Iki * ) =0 The resistances of the transmission line and series coupling transformer are neglected. i.e Σ Pinj,m=0 m=i,j,k The active and reactive power flow control constraints are Pni = Pni spec =0 Qni = Qni spec =0 Where n=j,k; Pni spec, Qni spec are the specified active and reactive power flow control references respectively, and Pni = ( Vn Ini * ) Qni = ( Vn Ini * ) Thus the power balance equations are as follows( Zhang, 2003) Pgm + Pinj,m Plm Pline,m=0 Qgm + Qinj,m Qlm Qline,m=0 Where Pgm and Qgm are the generated active and reactive powers, Plm and Qlm are load and active and reactive powers, Pline,m and Qline,m are conventional transmitted active and reactive powers at the buses m=i,j,k. 214

8 5. PARTIAL SWARM OPTIMIZATION PSO was originally developed by a social psychologist (James kennedy) and the electrical engineer (Russell Eberhart) in 1995 and emerged the flocking behavior seen in many species of birds. To the simple rules the birds used to set their direction and velocity (essentially, each bird is trying to stay in the middle of the it is near while also trying not to run into any of them) a bird pulling away from the flock in order to land at the roost would result in nearby birds moving towards the roost. As these birds discovered to roost, they would land there, pulling more birds towards it and so on until the entire flock had landed. Let S and V denote a particle co-ordinates (position) and its corresponding flight speed(velocity) in a search space, respectively. Therefore, the k th particle is particle is represented as x k =(x ki,x k2,..x kd ) in the d-dimensional space. The best previous position of the k th particle is recorded and represented as p bestk =(p bestk1,p bestk2 p bestkd ). The index of the best particle among all the particles in the group is represented by the g bestd. The rate of the velocity for particle can be calculated using the current velocity and the distance from p bestkd and g bestd as show in the following equation. The modification of the particle s position can be mathematically modeled according the following equation: V i k+1 = wv i k +c 1 rand 1 ( ) x (pbest i -s i k ) + c 2 rand 2 ( ) x (gbest-s i k ) where, v i k : velocity of agent i at iteration k, w: weighting function, c j : weighting factor, rand : uniformly distributed random number between 0 and 1, s i k : current position of agent i at iteration k, pbest i : pbest of agent i, gbest: gbest of the group. for k=1,2..n and d=1,2..m. Using above equation a certain velocity that gradually gets close to p best and g best can be calculated. The current position (searching point the solution space) can be modified by the following equation. X id (t+1) =x id (t) +v id (t+1) The inertia weight w is employed to control the impact of the previous history of velocities on the current velocity and thus influences the tradeoff between global and local exploration abilities of the flying point. Suitable selection of the inertia weight w can provide a balance between global and local exploration abilities and thus requires less iteration on average to find the optimum. W can be calculated according to the following equation. 215

9 W= Wmax ( Wmax Wmin) iter itermax Where W max and W min are set at 0.9 and 0.4 respectively. SOLUTION ALGORITHM The goal of optimization is to perform a best utilization of existing transmission lines. In this respect, the SVC and IPFC devices are located in order to minimum the power losses and maximum the system loadability while considering voltage constraints and cost of installation. The problem has four variables: optimal location of SVC & IPFC, the rating of the devices, the total power losses and voltage magnitude. The step by step procedure for the proposed optimal placement of SVC and IPFC devices using PSO is given below: Step 1: The number of devices to be placed is declared. The load flow is performed. Step 2: The initial population of individuals is created satisfying the SVC & IPFC constraints. Step 3: For each individual in the population, the fitness function is evaluated after running the load flow. Step 4: The velocity is updated and new population is created. Step 5: If maximum iteration number is reached, then go to next step else go to step 3. Step 6: Print the best results. Step 7: stop. A CASE STUDY The PSO based optimal location of multi-type FACTS devices was implemented using MATLAB 7.5. The system tested and described here the modified IEEE 30-bus system. The following parameters are used for PSO based optimal location of FACTS devices. Population =50 Maximum iterations=200 Wmax=0.9 and Wmin=0.4 Acceleration constants C1=1.4 and C2=1.4 The voltage magnitude at each bus of the system is given table 1 and the Power flows through the each line of the system are given in table

10 Table 1: Voltage profile at each bus Bus number Voltage(p.u) before compensation Voltage(p.u) after compensation

11 Table 2: Power flow profile without compensation Line (between buses) Real power MW Reactive power Mvar From the above test results the total power loss of the system is MW 218

12 Table 3: Power flow profile with compensation Line (between buses) Real power MW Reactive power Mvar From the above test results the total power loss of the system is MW 219

13 without FACTS with FACTS min voltage p.u 1.2 Voltage(p.u) Bus Fig. Voltage Profile at each bus for both cases Power Loss (pu) Iterations Fig. Power losses at each bus Optimal location of SVC (at bus) Rating of the SVC in Mvar

14 Optimal location of IPFC Rating of the IPFC in Mvar (between the lines) By comparing the above two cases, the total power losses of the system by placing SVC and IPFC is reduced to MW and gives the optimal location of each device and its rating. Hence, the cost of the system is reduced. IEEE 30 Bus System 5. CONCLUSION In this, the optimal location of IPFC and SVC are studied at different overload conditions and various parameters such as voltage profile and real and reactive power flow in transmission lines are investigated using PSO. In this paper, we have proposed a PSO algorithm to place a combination of both SVC and IPFC devices. The future scope of this paper is a complete cost benefit analysis has to be carried out to justify the economic viability of the SVC and IPFC using different combination of optimization techniques. 221

15 REFERENCES [1] S.Gerbex, R.cherkaoui, and A.J.Germond, Optimal Allocation of FACTS Devices by Using Multi-Objective Optimal Power Flow and Genetic Algorithms. IEEE trans.power system, vol.16, pp , August [2] L.J.Cai, I.Erlich, G.Stamtsis Optimal Choice and Allocation of FACTS Devices in Deregulated Electricity Market using Genetic Algorithms IEEE transactions on [3] H.R.Bahaee, M.Jannati, B.Vahidi, S.H.Hosseinnian, H.Rastager: Improvement of voltage stability and reduce power system losses by optimal GA-base allocation of Multi-Type FACTS devices. The 11 th international IEEE conference on May 2008,OPTIM [4] K.Sundareswaran, P.Bharathram, M.siddharth, Vaishavi.G, Nitin Anand Srivastava, Harish Sharma: Voltage Profile enhancement through optimal placement of FACTS devices using Queen Bee Assisted GA. The 3 rd international conference on power systems, Kharagapur, December [5] S Teerathana, A. Yokoyama, An Optimal Power Flow Control Method of Power System using Interline Power Flow Controller (IPFC), IEEE Transactions on Power Delivery, Vol. 23,pp , Aug [6] P. Subburaj, N. Sudha, K. Rajeswari, K. Ramar,and L. Ganesan, Optimum Reactive Power Dispatch Using Genetic Algorithm, Academic Open Internet Journal, Vol.21, 2007, p6. [7] B.Geethalakshmi, T. Hajmunisa and P. Dhananjayan, Dynamic characteristics analysis of SSSC based on 48 pulse inverter, The 8 th International Power Engineering Conference (IPEC) pp , May [8]. A.V.Naresh Babu, S.Sivanagaraju, Ch.Padmanabharaju and T.Ramana Multi-Line Power Flow Control using Interline Power Flow Controller (IPFC) in Power Transmission Systems International Journal of Electrical and Electronics Engineering 4: [9] A. Ziane-Khodja and M. Adli et A. Kheireddine, Techniques Of Control Of The Transit Of Power By Facts-Series Devices International Journal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 1, 2012, pp , ISSN Print : , ISSN Online: Published by IAEME. AUTHORS M.V.Ramesh: B.Tech(EEE) from S.V.H.College of Engineering, Machilipatnam in M.Tech in Power Electronics from J.N.T. University, Hyderabad (Autonomous) in Pursuing PhD in J.N.T. University, Hyderabad. Dr. V.C.Veera Reddy: B.Tech(EEE) from J.N.T. University in M.Tech in power systems & operation control from S.V. University in Completed PhD from S.V. University in