SUPERCAPACITORS ENERGY STORAGE BASED DSTATCOM MODELING AND SIMULATION FOR DISTRIBUTION SYSTEM

Transcription

1 SUPERPITORS ENERGY STORGE SED DSTTOM MODELING ND SIMULTION FOR DISTRIUTION SYSTEM Kuldeep SHY and harti DWIVEDI Department of Eletrial Engineering, Institute of Engineering & Tehnology, Luknow, Uttar Pradesh Tehnial University, Luknow, UP -60, India. Tel.: , Fax: strat: - There is an exponential inrease in the numer of non-linear loads in power distriution networks espeially due to advanes in power eletronis tehnology. Loads suh as variale speed drives, IT equipment; fluoresent lights, et. form a major portion of non-linear loads. Domesti applianes suh as TVs, omputers, SMPS, UPS, et. ause harmoni pollution whih leads to inreased harmoni distortion of urrent and voltages. Single-phase loads on a three-phase supply system result in an unalane in the system voltage and supply urrent. Harmoni pollution resulting from these loads distriuted in an unalaned manner adversely affets proper funtioning of utility equipments. Unalane in the voltages affets the performane of other loads, mainly indution motors. DSTTOM is a ustom power devie that is used to regulate the voltage sags/swells in the distriution system for maintaining the rated voltage level at the terminal of load/sensitive loads. The DSTTOM an injet three-phase voltages at point of ommon oupling whose magnitude and phase angle an e regulated with PI ontroller, while the superapaitors are used to meet the instantaneous power demand sine they an store and quikly release signifiant amounts of energy. This paper explores the use of Superapaitors in DSTTOM in plae of attery for ontrol of load terminal voltage. Keywords: Distriution Stati ompensators (DSTTOM), Power onditioning System (PS), Superapaitors Energy Storage System (SESS), Voltage Sags, Voltage Swells.. Introdution DSTTOM are used for improvement of power quality in the distriution system. DSTTOM, however, are limited in their aility to improve system performane due to limited apaility of delivering quik/instantaneous real power. onventionally in the DSTTOM attery is used for energy storage purpose, though atteries have a high energy density ut do not posses instantaneous harge and disharge apailities and normalized voltage swing (U min /U max ) at open iruit for atteries is higher than 0.85.Therefore it annot handle transient state prolems effiiently. From the last deade, there have een onsiderale developments and improvements in energy storage tehnologies for example, SMES, Flywheel, Fuel ells and also in the attery tehnologies.on the ontrary, these tehnologies have some limitations, SMES require a lot of spae, high shielding for its magneti effet and omplex auxiliary system, fuel ells quite slow initial response and atteries life detoriates very fast in ase of full disharge and limited numer of harge/disharge yle [,,3]. The reent development of Superapaitors has given a hope in the field of energy storage tehnologies, whih an store a very large amount of energy and it have very fast instantaneous power/energy harge and disharge apailities in the regulated manner with the help of ustom power devies, independent of numer of harge and disharge yle, voltage swing is 0.5 and is limited y the power onditioning system whih do not allow the superapaitors depth of disharge to go aove 75%,very high effiieny, life aout 0-5 years and harge and disharge times are frations of a seond to several minutes [4]. The energy stored in the SESS is used to provide

2 real power and reative power through the inverter to the distriution network. Therefore the DSTTOM ased on SESS would injet an appropriate voltage magnitude with appropriate phase angle in shunt to the distriution system, when the voltage sag ours; the voltage injetion is ahieved through the injetion of real and reative power. The aim of this researh is to investigate the use of the superapaitors energy storage ased DSTTOM to enhane power quality of distriution system y means of preise & fast regulation of voltage sags/swells and ontrol of SESS voltage level y simulating in MTL/SIMULINK POWER.. Design of Superapaitors Energy Storage System The purpose of onneting the SESS in DSTTOM for smoothing the power flutuation via harging and disharging the real power whih may e due to peak demand, transient fault and other reasons. nother appliation is voltage management aross the load terminal. The superapaitors voltage U s will drop to 0 V if all the stored energy is utilized then the onstraint rated power output apaility would e violated i.e. P stored P rated. Therefore a lower limit is fixed on the superapaitors voltage U min, is 50 % of U max, so that 75 % of stored energy an e utilized effiiently. Sine the voltage of superapaitors ell is low therefore the superapaitors ank would onsist of numer of superapaitors ells in series and parallel so that the required voltage level and suffiient useful energy an e stored. The shemati diagram is shown in the Fig.. superapaitors ells maximum voltage availale in the market or in the stak. Where N s are numer of ell onneted in series. () U max is maximum voltage of the superapaitors ank. U ell is rating of superapaitors ell. The numer of parallel ranh N p in the superapaitors ank an e found y () To have suffiient energy storage apaity numer of parallel ranhes must e more than or equal to the one (N p ) and rounded upward side to nearest integer. The equivalent apaitane of the superapaitors ank is represented y the following formula Where (3) eq is equivalent apaitane of superapaitors ank in Farad. ell is apaitane of eah ell in Farad. N s are numer of ell onneted in series. N p is ank. numer of parallel arms in superapaitors SESS R eq From equation (3) it is lear that to have net higher equivalent apaitane of the ank, numer of the parallel arms (N p ) should e always higher than N s,in that way higher energy storage apaity. Fig. Superapaitors Module. In general, the numer of series onneted ells N s in one ranh are imposed y the rating of Total numers of ell in Superapaitors ank would e (4)

3 Where N T is total numer of ells required in superapaitors ank. ut when the superapaitors works at minimum voltage point, rated power output apaility is still required, so V min limitation under power request is expressed as (5) (6) The appropriately designed SESS should onsider oth the power demand and energy apaity and the overall effiieny of SESS, therefore the useful energy stored in the SESS is expressed y (7) while keeping the voltage onstraints U min <U<U max Where s effiieny of superapaitor ank. (7) The proposed superapaitors energy storage system is designed to have storage of MWh (3600 MJ) of energy, 440 V voltage and peak power of 000 kw onneted to distriution system to supply the load in ase of voltage variation and additional power demand. The superapaitors used are of Nessap o. Ltd. Korea make having produt speifiations, Nominal apaitane 5 F, Rated voltage 340 V, Surge voltage 367. VESR <9 m,operating temperature range -40 to +65, Speifi Energy.3 Wh/kg,yles 500,000(at 5 ), Lifespan 0 years, Maximum peak urrent( se) 3,854. Then the SESS designed would e as following: Tale I SESS onfiguration Item Symol Value Maximum superapaitors U max 63 V Voltage Minimum superapaitors U min 3 V Voltage Equivalent apaitane of eq 39.9 F SESS Numer of units onneted in N s series Numer of parallel arms in N p 545 SESS Total numer of units required N T 090 in superapaitors ank Equivalent series resistane of R eq 66 µ SESS Disharge voltage ratio d 50% 3. Simulink modeling of the DSTTOM and its ontrol DSTTOM whih onsists of a two level voltage soure onverter as inverter, superapaitors ank as energy storage devie, a oupling transformer onneted in shunt to the distriution network.the voltage soure onverter onverts the d voltage of the superapaitors ank into sets of three phase a voltages as output.these voltages are in phase and oupled with the distriution system through reatane of the oupling transformer.the proper adjustment of the phase and magnitude of the DSTTOM output voltages allows effetive ontrol of the ative and reative power exhanges etween the D-STTOM and the distriution network[6,7]. The VS onneted in shunt with the distriution network an e used for voltage regulation and ompensation of reative power, power fator orretion and elimination of harmonis. The ontinuous voltage regulation of the distriution network is performed y injeting the shunt urrent for elimination of the voltage sag aross the system impedane. The value of urrent an e ontrolled y adjusting the output voltage of the onverter. The effiay of the DSTTOM in orreting voltage sag depends on the value of equivalent thevenin impedane of the system or the fault level of the load us. When the shunt injeted urrent is in quadrature with the load terminal voltage, the desired voltage orretion an e ahieved without injetion of the ative power into the distriution network. On the other hand, when the value of shunt urrent is minimized, the same voltage orretion an e ahieved with minimum apparent power injetion into the system. 3

4 The ontrol sheme for the DSTTOM is shown in the Fig..The ontroller input is an error signal otained from the D referene voltage and the measured terminal voltage of the SESS.Suh error is proessed y a disrete PI ontroller and the output is I d_ref, whih is provided to urrent regulator. The urrent regulator output is passed to sinusoidal voltage error generator; this error signal is provided to disrete PWM signal generator. The PWM generator, generates the pulse signals that are passed to voltage soure onverter to generate the output voltage as per load requirement on the point of ommon oupling. Freq Va Va (pu) wt Sin_os Disrete 3-phase PLL Ia sin_os IdIq Va Vmag Ia Measuremnt Unit == -- Vmag Iq_Ref e3 Va_Ref Voltage Regulator Swith IdIq IdIq_Ref VdVq urrent Regulators VdVq Va (t) m_phi->va(t) Disrete PWM Generator Uref Pulses z pulses 3e6 Vmag Iq_Ref Qref Iq_ref manual 3 Vd 500 Vd Id_Ref Vd_Ref D Voltage Regulator Fig. ontrol Sheme of DSTTOM Fig. 3 shows the test system used to arry out the various DSTTOM simulations in MTL/Sim- Power SIMULINK. The test system omprises of a kv,50hz transmission system-setion of 5 km long and T-setion of km long, feeding into the primary side of -winding transformer onneted in Y/,kV/440V,00MV the load is onneted to 440 V, seondary side of the transformer. The D voltage is applied to IGT/Diode s of twolevel inverter generating 50 Hz. The IGT of the inverter uses pulse width modulation at 680 Hz arrier frequeny, disretized sample time of 5.8e -6 se. The load voltage is regulated at pu y PI voltage regulators of d regulator, the input of D regulator are voltage of P, urrent of P, SESS voltage and the output is a vetor ontaining the three modulating signals used y the disrete pulse width modulation generator to generate the 6 IGT pulses. The harmonis generated y the inverter are filtered y L filter. The three oupling transformer of 440V/ kv, 00MV are used to onnet the DSTTOM to the distriution network. SESS of 39.9 F are onneted on the d side to provide the energy/real power. The effetiveness of this arrangement in voltage regulation an e seen on simulating the test system with and without DSTTOM/SESS. 4

5 KV 00 MV a 5 km a 4 a Tr a Va Ia a 3 voltage To Workspae3 urrent To Workspae4 0 time Disrete, lok Ts = 5.8e-006 s. To Workspae [Va_] [Ia_] Sope4 [Va_4] [Ia_4] Three-Phase Parallel RL Load Three-Phase reaker T T a T3 + - v Voltage Measurement Va Ia a 5 L Sope5 voltage To Workspae urrent To Workspae [Va_] [Ia_] Sope Va Ia pulses L Filter Sope L Sope6 Vd 0 D Regulator Multimeter Internal reistane of soure Universal ridge g + SESS v Voltage Measurement Sope3 Fig.3 Developed Test System for DSTTOM 4. Simulation and Result nalysis ase:- Simulation Results when Superapaitors are not harged The first simulation was performed when the DSTTOM s superapaitors was not harged and the main supply to load is swithed off y the three phase iruit reaker for period of seond,during this period the voltage aross the load approahes to zero and urrent through the load also eomes zero as shown in the Fig.4 and Fig.5. Fig.4 Voltage aross the load when superapaitors are not harged. 5

6 Fig.5 urrent through the load when superapaitors are not harged ase:- Simulation Results when superapaitors are harged elow U min. Similarly, a new set of simulations was arried out ut the now the DSTTOM superapaitors had disharged elow the U min level, while the threephase iruit reaker for duration se in whih main line supply was utoff, ut now the voltage aross the load in phases is ale to maintain ut for the third phase the DSTTOM was not ale to supply the power properly as required. The voltage and urrent waveforms are shown respetively in Fig.6 and Fig.7. Fig.6 Voltage aross the load when superapaitors are harged elow U min. 6

7 Fig.7 urrent through the load when superapaitors are harged elow U min ase: 3 Simulation Results when superapaitors are harged properly Similarly, a new set of simulations was arried out ut the now in the DSTTOM the superapaitors are harged properly, a transient load was swithed in test system for the duration se in whih main line supply was also utoff with the help of three phase iruit reaker. The Superapaitors ased DSTTOM is quit effiient to support the load without any unalane in phase and having no harmonis also ale to maintain its amplitude of.0 pu. The voltage and urrent waveforms are shown respetively in Fig.8 and Fig.9. Fig.8 Voltage aross the load when the superapaitors are harged properly 7

8 Fig.9 urrent through the load when the superapaitors are harged properly 5. onlusions Superapaitors energy storage has een used as a storage devie in plae of attery of a DSTTOM devie. This allows the DSTTOM to deliver the real power into grid for short periods of the time. The highly developed graphi failities availale in MTL/SIM-Power Simulink were used to ondut all aspets of model implementation and to arry out extensive simulation studies on developed test systems. PWM ased ontrol sheme has een implemented to ontrol the swithes (IGT/Diode) in the two level voltage soure onverters whih ontrols the superapaitors to deliver/asor the real power as per the requirement and also maintains the loads power fator unity. This harateristi make it suitale for ustom power appliations where very sensitive loads are onneted, sine performane of the ontrol sheme has een studied with sudden disruption of the main supply and swithing in a ulk load into the test system and found ale to mitigate the voltage sag and at the same time maintaining the load power fator unity. Referenes:-. Srithorn, P. Sumner, M. Liangzhong Yao Parashar, R., Power System Stailisation Using STTOM with Superapaitors, Industry ppliations Soiety nnual Meeting, 008. IS '08. IEEE, Edmonton, lta, Dated: 5-9Ot.008, page(s):-8.. Srithorn, P. Sumner, M. Liangzhong Yao Parashar, R., The ontrol of a Statom with superapaitor energy storage for improved power quality Smart Grids for Distriution, 008. IET- IRED Seminar, Frankfurt, Dated: 3-4 June 008, page(s): Nasiraghdam,H., and Jalilian. alaned and Unalaned voltage sag Mitigation Using Dstatom with Linear and Nonlinear loads International Journal of Eletrial, omputer and Systems Engineering ; 007,Page(s) Zhai, N.S. Yao, Y.Y. Zhang, D.L. Xu, D.G., Design and Optimization for a Superapaitor ppliation System, International onferene on Power System Tehnology, Poweron 006, hongqing, Dated -6 Ot. 006, page(s): Xiao Li hangsheng Hu hangjin Liu Dehong Xu, Modeling and ontrol of aggregated Super- apaitor Energy Storage system for wind power generation, Industrial Eletronis, 008. IEON th nnual onferene of IEEE, Dated: 0-3 Nov. 008, Orlando, FL, page(s): Ravi Kumar, S.V. and S.Siva Nagaraju Power Quality Improvement using D-Statom and DVR International Journal of Eletrial and Power Engineering (3): , 007, Medwell Online Journals. 7. Van Voorden,.M. Elizondo, L.M.R. Paap, G.. Veroomen, J. Van der Sluis, L., The ppliation of Super apaitors to relieve attery-storage systems in utonomous Renewale Energy Systems, Power Teh, 007 IEEE Lausanne, Date: -5 July 007, page (s):