Volume 114 No. 10 2017, 397-405 ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version) url: http://www.ijpam.eu ijpam.eu Performance Improvement of Hydro-Thermal System with Superconducting Magnetic Energy Storage G.SreenivasaReddy 1 and T.BramhanandaReddy 2 and Sateesh.G 3 1,2,3 Dept.of EEE, GPREC,Kurnool,AP,India. nivasa7hills@gmail.com Abstract This paper deals with the improvement of dynamic performance of load following based Hydro-Thermal system employing Superconducting Magnetic Energy Storage[1]. It is encountered many advantages for using superconducting magnetic energy storage as a replacement for other energy storage methods. Since it has less time delay during the charging and discharging, with an availability of instantaneous and high power within a stipulated time. But other storage methods like pumped hydro or compressed air have a considerable large time delay for conversion of energy as stored mechanical into useful electrical energy back. If the load demand is varying continuously and frequently then selection of SMES is the best method. Also, it has negligible power loss than the other storage methods because of no/low resistance. In addition that, SMES has no moving parts and thus it has a better efficiency which results in the reliable operation. SMES is incorporated in two area system in consequence improving the response of the system with the help of computer simulations, and the dynamic performance of the system is effectively improved. The main objectives of this paper are to develop the SMES model in two area hydrothermal system using MATLAB/Simulink in addition that the comparative study for the improvement of dynamic performance of the system with and without SMES. 1. Introduction: Key Words: Load Following, SMES, hydrothermal system, AGC, load profile. A pool power system having more number of power generating sources or control areas are interconnected. These stations are a combination of different generators 397
like hydro, Thermal, Nuclear or other renewable sources, depending on the load demand here conventional generation hydro and steam is considered. Usually, nuclear plants are for base loads close to their maximum output due to their better efficiency. Gas power generation plant is to meet the continuous varying load demand. Thus the common choice for AGC is either thermal or hydro units or coordinately Hydro - Thermal. The area of AGC concern to less attention pays on AGC of an interconnected hydrothermal system compared to thermal stations which are interconnected to each other. For a system, Automatic Generation Control (AGC) with the considerations of Generation rate constraints (GRCs) is studied. [2] give the idea of frequency deviations and linearity of the system. When Generation Rate Constraint (GRC) is considered, the system dynamic model becomes non-linear and frequency deviation is less when GRC is not considered. The controllers so designed to regulate the area control error to zero and match the generation with the frequent change of loads along with the losses with the neighboring systems so that the important system parameters like frequency, real power, reactive power and desired voltage levels are maintained continuously with the help of SMES[3].The most interesting in present power system, especially generation and transmission system Flexible AC Transmission Systems (FACTS) opens up new opportunities for controlling and enhancing the usable power because of the fast, high-speed control and protection[4].the use of proposed SMES model for Hydro- Thermal system effectively minimizes frequency variations [5-7]. 2. Model Analysis: A power system can't feed with an individual power generating station even with sufficient generation, a meaning of pool operation that may divide into a number of load frequency control (LFC) areas, which are interconnected by tie lines. A power pool is a synchronous interconnection of the different power systems of individual utilities/ individual state electricity board Distribution companies (Discom's). Each element in LFC system (Governor, turbine, and load). reference [11] says that for a small load variations the LFC system can be represented by first order transfer function. The below figure (Fig.1) represents the block diagram of a two area interconnected system under deregulated scenario, the different parameters used in this model are shown in Appendix. 398
Cpf 11 Cpf 12 p.u load of Disco 1 Cpf 21 Cpf 22 p.u load of Disco 2 B 1 R 1 1 R 2 Area-I P D1 (s) P SMES - K 11 a s - - -1 a a - - 1 1 1 sk r T r 1 s T g 1 s T t 1 s T r 1 1 s T 1-1 1 s T 1-1 st R 1 s T 2 1 st R 1 s T 2 1 - st w 1 0.5s T w 1 - st w 1 0.5s T w K - 12 1 1 1 sk r T r a s 1 s T g 1 s T t 1 s T r - - - Area-II 1 1 P SMES PD2 (s) B R 3 R 4 - K p1 1 s T p1 Demand of discos in area 1 to Gencos in area 2 2 T 12 s - - -1 Demand of discos in area 2 to Gencos in area 1 K P 2 1 s T P 2 Cpf 13 Cpf 14 p.u load of Disco 3 Cpf 23 Cpf 24 p.u load of Disco 4 3. The Design of SMES: Fig.1: Block diagram representation of a two area interconnected system. The Fig.2 shows the arrangement of a power semiconductor device controlled SMES unit. It consists of a 12-pulse converter and superconducting coil and coil is enclosed in a helium vessel, This arrangement is fed by Y Δ/Y Y transformer. Here the working fluid as a helium, to wash out excessive heat generated with the help of refrigerator and the energy switched over between superconducting coil and thus the electrical system is effectively controlled by a converter. Without any loss, it will conduct as soon as the superconducting coil gets charged. But in 399
practical the load is fluctuating and for the concentration of increasing load demand, the energy which is stored in the form of an inductor is released and converted into an alternating current through the convertor. Hence the power system is in steady state. Similarly, during sudden reduction of load demand, the coil starts charging to its rating, thereby diverting part of a energy from system to load, and the system retains to its original steady state even in the light load conditions. The firing angle control of a converter provides a dc voltage (Ed ) appears across the inductor and it is to be varying continuously within a specified range. Due to the superconducting of the coil the inductor voltage reduces once the current gets its rated current (Ido) and maintaining constantly the voltage across inductor become to zero. Figure 2. Schematic diagram of SMES The stored energy of a coil in magnetic energy form is equal to the product of half of its inductance value and square of the current. E=... (1) in above equation, I = Current in amperes L = Inductance measured in henries, E = Energy in joules. 3.1 Control of SMES Unit: According to Sabita Chaine, M. Tripathy (12) says the operation and control of Superconducting Magnetic Energy Storage by applying a sufficient positive or negative voltage at the inductor during its charging, discharging, steady state and power modulating dynamic oscillatory period are achieved(by considering load pattern). Fig.3 represents the transfer function for the control methodology of SMES. to derive the simultaneous changes in converter voltage (ΔEd), ACE is given as an input to the proportional block (KSMES ) as shown in below equation (2). Δ Δ ) -...(2) to regain the inductor current (Id) quickly with respect to change in load 400
demand, in SMES control loop the ΔId used as a negative feedback. 4. Results and Discussions : Fig 3: Transfer function model of SMES Simulation studies are performed to find out the performance of a two-area hydrothermal system under deregulated concept, in each area of a two-area hydrothermal system three Generation companies and two distribution companies (Discom's) are considered. It is assumed that there is only one Generation company (Genco's) under AGC in each of the area and the remaining Generation companies will participate in the two-sided contracts and also assumed 0.2% step load disturbance of each Discom's, resulting in the total step load disturbance in each area accounts to 0.4%. Each Generation company participates in AGC as defined as area participation factors (apfs): apf1 =0.25, apf2 =0.25, apf3 =0.5, apf4 =0.25, apf5 =0.25, apf6 =0.5 and the Discos contract with the Gencos as per the following Distribution company Participation Matrix (DPM) and in both the areas the gain setting of integral controller is considered as nominal value of 0.5. Table.1 gives the comparison between the system dynamic performance with/without SMES, and it is cleared and identified with SMES the system has better dynamic performance than at of the system without SMES. Also, this paper pointed out the contract violation case, that is the Discom1 demands additional load of 0.3% after 30 sec and Discom4 in area 2 demands additional load of 0.3% after 60 sec. It can be cleared that the un contracted additional power has to supply by the Gencos in the same area. DPM = 0.25 0.25 0 0.25 0.25 0 0.3 0.1 0 0.4 0.4 0 0.1 0.4 0 0.3 0.3 0 0.3 0.4 0 0 401
With SMES Table -1: Performance of the system with and without SMES Area- Area- Peak time Settling Peak Settling Overshoot Overshoot (sec) Time time Time 0.804 0.00416939 2.305 0.729 0.00464404 2.22 Without SMES 0.835 0.0106458 4.39 0.79 0.0112863 4.5 TABLE-2: Comparison of System Performance Index Values With and Without SMES Performance Index Value (Base case) With SMES 5.201*10-6 Without SMES Performance Index Value (contract 2.363*10-5 1.748*10-5 5.006*10-5 Figure 4 shows the comparison between frequency deviations( (f ) and tie line power error deviations ( P tie(e) ) for both control areas with and without SMES. Fig.5 and 6 explain about the generation of Gencos of area 1 and area 2 (three generating stations are considered). Fig.7 gives the comparison of frequency deviations and tie line power error deviations during the contract power violation. Fig.8 and 9 illustrate the various generation of Gencos during contract violation. from fig.10 and 11 it is observed that the system with SMES has less performance index than the system without SMES which indicates that the system has less error in the presence of SMES. Fig. 4: Comparison of Frequency deviations and tie line power error deviations. Fig.5: Generation Area I Fig.6: Generation of Area II 402
Fig 7: Comparison of Frequency deviations and tie line power error deviations during contract violation. Fig 8: Generation of Area I during contract violation Fig 9: Generation of Area II during contract violation Fig.10: Comparison of performance index values during normal case 5. Conclusion : Fig.11: Comparison of performance index values during contract violation An efficient method in order to design a Superconducting Magnetic Energy Storage (SMES) for a two area system under deregulated scenario has suggested. Under frequent load varying conditions, this paper suggests performance improvements with the SMES balance system frequency and the tie line power of the multi-area system. The simulation results of proposed system indeed shows that methodology successfully mitigates the tie line power as well as frequency deviations during a continuous load demand and the performance index of the system with SMES is less than the system without SMES, which indicates the essentiality of the SMES. Also, it gives a way to enhance the power handling capability of a system with frequent load variations. Appendix : (a) System data : R =2.4 Hz/p.u.MW; D = 8.33 10 3 p.u. MW/Hz; K g =1; T g =0.08 sec; K t =1; T t =0.3 sec; K r =0.5; T r =10 sec; T 1,T 2,T R =41.6, 0.513, 5 sec; T w =1 sec; K p =120 Hz/p.u. MW; T p =:20 sec; 403
B =0.425 p.u. MW/Hz; c g=1; b g=0.05; X G=0.6; Y G=1; K SMES 0.3; T SMES 0.0352 References: [1] A. Suresh Babu, Ch.Saibabu, S.Sivanagaraju "Improvement of Dynamic Performance of Multi Area System under Load Following Employing FACTS Devices". [2] C. Concordia and L.K.Kirchmayer, Tie-Line Power and Frequency Control of Electric Power System -Part II, AIEE Transaction, vol. 73, Part- 111-A, pp. 133-146, April 1954. [3] M.L.Kothari, B.L.Kaul and J.Nanda, Automatic Generation Control of Hydro- Thermal system, journal of Institute of Engineers(India), vo1.61, pt EL2, pp85-91, Oct 1980. [4] Chun-Feng Lu, Chun-Chang Liu and Chi-Jui Wu. Effect of battery energy storage system on load frequency control considering governor dead band and generation rate constraints IEEE transactions on energy conversions Vol. 10 September1995,pp.555-561. [5] Banerjee S, Chatterjee JK, Tripathy SC. Application of magnetic energy storage unit as continuous var controller. IEEE Trans Energy Conver 1990;5 (1):39 45. [6] Tripathy S C, Kalantar M, Balasubramanian R. Dynamics and stability of wind and diesel turbine generators with superconducting magnetic energy storage unit on an isolated power system. IEEE Trans Energy Conver 1991;6 (4):579 85. [7] Banerjee S, Chatterjee JK, Tripathy SC. Application of magnetic energy storage unit as load frequency stabilizer. IEEE Trans Energy Conver 1990;5 (1):46 51. [8] Jayant Kumar, Kah-Koeng and Gerald Sheble, AGC simulator for price based operation Part1, IEEE Transactions on Power Systems, vol.12, no.2, May 1997, pp. 527-532. [9] Jayant Kumar, Kah-Hoeng and Gerald Sheble, AGC simulator for price based operation part- 2, IEEE Transactions on Power Systems, Vol.12, no. 2, May 1997, pp 533-538. [10] Bjorn H.Bakken and OvesGrande, Automatic generation control in a deregulated environment, IEEE Transactions on Power Systems, vol.13, no.4, Nov 1998,pp. 1401-1406. [11] V. Donde, M. A. Pai and I. A. Hiskens, Simulation and optimization in an AGC system after deregulation, IEEE Trans. on Power systems, Vol. 16, No 3, Aug 2001, pp 481-489. [12] "Design of an optimal SMES for automatic generation control of two-area thermal power system using Cuckoo search algorithm" Sabita Chaine, M.Tripathy [13] Dynamic Models for steam and Hydro Turbines in Power system studies, IEEE committee report. Transactions in Power Apparatus & Systems Vol.92,No.6,Nov./Dec.1973,pp.1904-915. 404
405
406