Protection of Low Voltage Ring Bus Type DC Microgrid System with Probe Power Unit

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1 2015 IJEDR Volue 3, Issue 2 ISSN: Protection of Low Voltge Ring Bus Type DC Microgrid Syste with Probe Power Unit 1 S.Srny, 2 S.Airthrj 1 PG Student [Power Syste Engineering], 2 Assistnt professor Deprtent of Electricl nd Electronics Engineering G.K.M College of Engineering And Tecnology, Chenni, Tilndu, Indi Abstrct A ultiterinl DC power systes cnnot surie or sustin high gnitude fults during fult conditions nd conerters will shut down to protect theseles under fulted conditions. This es locting fults in DC syste difficult, nd cuses the DC bus to deenergize. A fult protection ethod for lowoltge DCbus icrogrid syste is presented. The in gol of the project is to detect nd isolte fults in the DCbus bsed icrogrid syste without interruption in the entire DC bus. A ring bus topology is utilized s the in DC bus nd then bus is segented into indiidul zones with solid stte bidirectionl switches used to isolte the zone in the eent of fult. Ech zone is onitored nd controlled by n indiidul segent controller. Also fter fult clernce the circuit breer recloses by copring with the progred threshold lue. The DC ring bus is odelled with sources nd lod. A probe power unit is ipleented to test the fult sttus. A fult cretion, detection, isoltion nd reclosing opertion concept is siulted nd siultion result is erified using MATLAB/SIMULINK. Index ters DC Power Systes, Microgrid, Power Syste Protection, Segent Controller, SolidStte Switch I. INTRODUCTION Mny distributed power systes he been reserched nd deeloped, especilly to eet the dend for high penetrtion of renewble energy resources, such s wind turbines nd photooltic systes. The distributed power systes he dntges, such s the cpcity relief of trnsission nd distribution, better opertionl nd econoicl genertion efficiency, iproed relibility, ecofriendliness, nd higher power qulity. Copred to higholtge dc (HVDC) trnsission systes, the dc distribution syste is reltiely new concept in electric power systes. DC icrogrids he ny dntges oer trditionl c distribution systes. Furtherore, for gien cble, dc systes cn delier ties ore power thn c systes. This is becuse the usble power is bsed on the rs lues in n c syste, while the dc power is bsed on constnt current nd oltge. DC systes do not suffer fro sin effect, which llows the current to flow through the entire cble, nd not just the outer edge. Protection deices for c systes re ery ture nd they re generlly uch cheper thn dc breers since they re not specilty ites. AC breers rely on the nturl zero crossings of the c current; hence, these breers cnnot be pplied in dc systes due to the lc of zero crossing in the dc current. Modifiction to existing circuit breers (CBs) is possible, but this dries up cost nd led ties. DC switchger nd CBs re expensie nd y not lwys be ilble for certin systes. Also, the current power electronic deices cnnot surie or sustin high gnitude fults. Conerters will shut down to protect theseles under fulted conditions. This es locting fults in DC syste difficult, nd cuses the DC bus to deenergize. A fult protection lgorith nd ethod for lowoltge DCbus icrogrid syste is presented in order to reole the boe issues. This pper proposes dc bus icrogrid fult protection ethod including bcup protection tht llows the fult to be detected nd isolted without deenergizing the entire syste. II. MICROGRID SYSTEM The icrogrid syste is sllscle distributed power syste consists of distributed energy sources nd lods, nd it cn be redily integrted with the renewble energy sources. Due to the distributed nture of icrogrid pproch, the connection to the centrl disptch cn be reoed or iniized nd in turn the power qulity to sensitie lods cn be enhnced. Most icrogrid systes he their connected distributed energy sources interfced through power electronics conerters. Generlly they he two opertion odes: stndlone (islnded) nd gridconnected opertion. Microgrid systes cn be diided into ACbus nd DCbus systes, bsed on the bus tht the coponent systes such s energy sources, lods nd storges re connected. The chllenge ssocited with protection of VSCbsed icrogrid systes is tht the fult current ust be detected nd extinguished ery quicly s the fult current withstnd rting of typicl VSCs is generlly only twice the conerter fulllod rting. Seiconductorbsed CBs he been inestigted nd they he been used for fst dc current interruption nd oer current liittion. A. Possible Fults in LVDC For DC syste two types of fults exist linetoline nd linetoground. A linetoline fult occurs when pth between the positie nd negtie line is creted, shorting the two together. A linetoground fult occurs when pth between either the positie or negtie pole nd ground is creted. A linetoground fult is the ost coon type of fult. VSCs y experience internl switch fults tht cn cuse line to line short fult. This is terinl fult for deice tht cn't be clered nd in ost IJEDR Interntionl Journl of Engineering Deelopent nd Reserch ( 436

2 2015 IJEDR Volue 3, Issue 2 ISSN: cses it requires replceent of the deice. A linetoground fult (ground fult) occurs when the positie or negtie line is shorted to ground. In oerhed lines fults y occur when lightning stries the line. This y cuse the line to bre, fll to the ground nd crete fult. In this sitution the fult is lwys pernent nd the line ust be isolted for repir. Ground fults y lso occur by objects flling onto the line, such s trees, proiding pth to ground. In soe cses when n object cuses the ground fult it y fll wy fro the line nd the syste cn be restored. If the fult persists the line would he to be ten out of serice until the fult pth cn be clered. III. PROPOSED PROTECTION SCHEME The solid stte circuit breer nd segent controller bsed protection ethod for the DC bus icrogrid syste is proposed. Unlie other ethods, the proposed schee does not require interruption of serice of the grid. Rther, only the ffected section of the icrogrid is isolted nd deenergized. This is chieed through use of ring bus configurtion for the in DC bus, creting seerl zones of protection within the ring bus. This is done for both the positie nd negtie bus. The ring bus will be split into zones nd ech zone is onitored by n segent controller s shown in Fig. 1. It will continuously onitor the current through it's ssigned breers. Once fult is detected the controller will open the zone breers. Ensuring tht ll of the breers he opened nd tht the fulted zone is deenergized. If the zone hs not been deenergized the zone controller will send signls to djcent segent controller until the fult is extinguished. If the zone ws successfully deenergized the segent controller will ttept to restore the fulted zone by reclosing the breers. If fult is then detected the zone breers re gin tripped nd the zone is isolted. The proposed segent controller for one segent is shown below in Fig.2. The noel protection ethod nd lgorith for the DC bus icrogrid syste is proposed in this project. Unlie y other ethod the proposed schee does not require coplete shutdown of the grid. Rther, only the ffected section of the icrogrid is isolted nd deenergized. This is chieed through use of ring bus configurtion for the in DC bus, creting seerl zones of protection within the ring bus, nd instlling grounding resistor to liit the fult current. This is done for both the positie nd negtie bus. The proposed protection schee cn be split into three sections: Fult Detection Fult Isoltion Breer Filure Detection Reclose nd Restore Fig.1 Bloc digr of DC ring bus icrogrid. Fig.2 Segent Controller The ring bus will be split into zones nd ech zone is onitored by n segent controller. The segent controller will continully onitor the current through it's ssigned breers. Once fult is detected the segent controller will open the zone breers. The segent controller will then ensure tht ll of the breers he opened nd tht the fulted zone is deenergized. If the zone hs not been deenergized the zone segent controller will send signls to djcent segent controller until the fult is extinguished. If the zone ws successfully deenergized the segent controller will ttept to restore the fulted zone by reclosing the breers. If fult is then detected the zone breers re gin tripped nd the zone is isolted. A. Fult Detection nd Isoltion The icrogrid under study consists zones of protection. Ech zone is clssified by the type of energy deice it hs been ssigned to. The zones cn be split into 4 ctegories: unidirectionl, bidirectionl, lod, nd lin. Ech zone consists of 23 breers nd section of cble. A locl segent controller is ssigned to ech zone. The segent controller will onitor nd control ech of the breers within its ssigned zone. Ech segent controller is progred with the specific set of rules tht define norl zone opertion. This is dependent on the source tht the segent controller is onitoring. It should be noted tht due to the ring bus configurtion, current hs seerl pths to flow. Therefore seerl norl operting conditions ust be ccounted for, nd they ust ll fil before fult is declred. Once fult hs been detected ll breers in the ffected zone re tripped, regrdless of the pole the fult is on. This is done to eep the icrogrid nd conerters in blnce. In the exples specific rules tht re needed to define fult re proided. One rule for ech zone type is gien. Once the fulted segent is isolted, the reinder of the sources nd lods cn continue to IJEDR Interntionl Journl of Engineering Deelopent nd Reserch ( 437

3 s S g D 2015 IJEDR Volue 3, Issue 2 ISSN: operte on the ring bus. Een with ultiple fulted segents, the syste cn operte prtilly if the segents fro the in source to soe lods re intct. It hs been ssued tht the segent controllers cn detect it nd open/close Solid Stte Circuit Breers in 500 µsec. B. Reclose And Restore Once the fulted lin ws successfully seprted nd deenergized, the segent controller will ttept to reclose nd restore. Fults re often teporry, cused by debris, nils, or other trnsients (e.g., lightning) contcting n energized line or bus. The teporry fults will cler theseles fter current flows through the fult pth. The reclose nd restore ode llows the segent controller to utonoously restore power bc to the deenergized zone. This is done by witing certin ount of tie fter the trip signls he been sent. After tht, the segent controller will send close conds to ll of the breers. The witing tie depends on syste configurtion. IV. DC RING BUS FORMATION DC ring fortion is de by odelling the two or ore renewble energy sources, AC nd DC lod, bttery, in grid these re connected to the DC bus through respectie conerters y be uni directionl or bi directionl ccording to the need. DC bus is de to rrnged s loop type or ring bus fortion. Here DC ring bus fortion is odelled in which the solr energy syste, wind energy syste, AC chine, AC nd DC lod, bttery bcup, bidirectionl conerter nd in grid ll re connected to DC ring bus with circuit breers in ech segent of the DC bus. Also segent controller which controls the opening nd closing of circuit breer is ipleented nd operted through control syste. Oerll DC ring bus with ll sources nd lod with protection is designed for nlysis of fult detection nd isoltion. A. Wind nd Solr Energy Syste The odelling of wind turbine nd AC to DC conerter is done using the Mtlb 7.11 softwre. Here pernent gnet synchronous genertor is used thn induction genertor becuse of its reduced size nd high efficiency. It is shown in Fig.3. In wind turbine odel the first input is the genertor speed in per unit of the genertor bse speed for pernent gnet genertor the bse speed is the speed producing noinl oltge t no lod. The second input is the blde pitch ngle in degrees nd the third input is the wind speed in /s. The output is the torque pplied to the genertor shft in per unit of the genertor rtings. A wind turbine cn only extrct prt of the power fro the wind which is liited by pitch ngle controller nd PMSG is de to wor in genertor ode by giing input s negtie echnicl torque. As DC icrogrid is used AC oltge hs to be conerted to DC thus AC to DC conerter is coupled with the genertor. The odel for solr energy syste is siulted in tlb softwre shown in Fig.4. Solr energy syste is considered s one of the sources in DC icrogrid syste it supplies DC oltge to the DC lod nd AC lod which is connected to the ring bus. It is considered s the priority source of supply thn wind energy syste. If the pulse genertor genertes 0 switch will be in closed condition. If it generte 1 ens the switch open nd store the chrge fro solr in the cpcitor. Also subsyste of solr energy syste odel consist of solr cells, current sensor nd oltge sensor to sense current nd oltge respectiely, diode, MOSFET switch for production of DC current. 1 R1 Series RLC Brnch Diode4 1 Pulse Genertor2 wr1 Pitch_ngle1 Pitch_nglecontroller Genertor speed (pu) Pitch ngle (deg) T (pu) Wind speed (/s) Wind Turbine odel PMSG T A B C Scope Voltge Source Scope3 C1 Scope5 Vout 2 Solr Syste 2 Fig.3. Wind energy syste odelling Fig.4. Solr energy syste odel. C. Segent Controller A segent controller is plced in bus segent to control the operttion of circuit breers. Once fult is detected then controller sends opening signl to open the respectie circuit breer which isolte the syste. By the se it connects to the other sources to supply power to the lod thus it hndles fult detection, isoltion nd uninteruptted power to lod. V. PROTECTION WITH PROBE POWER UNIT Once the fulted lin ws successfully seprted nd deenergized, the segent controller will ttept to reclose nd restore. The teporry fults lie trnsients or nils contcting n energized line will cler theseles fter current flows through the fult pth. This is done by witing certin ount of tie fter the trip signls he been sent. So fr, the bus CBs he been reclosed without nowing the sttus of the fult. If the fult hs not been clered, the se fult current would flow gin nd it could dge the syste. A probe power unit is to test the fult sttus of the bus segent before reclosing the circuit breer. The probe unit consist of cpcitor, inductor, power sources nd connection switches. The power source pplies certin oltge tht is just high enough to inject probe current to see if the fult persists. The reclosing of circuit breer cn be conducted uch sfer becuse the in CB will be closed only when nofult sttus is confired. IJEDR Interntionl Journl of Engineering Deelopent nd Reserch ( 438

1= Closed/ 0= Open 2015 IJEDR Volue 3, Issue 2 ISSN: 23219939 VI. V. SIMULATION RESULT The proposed protection schee ws perfored with coputer siultions using MATLAB.

Siultion of probe power unit During norl operting conditions solr is chosen s in priority os sources to supply AC nd DC lod.

2sec fter the fult occurrence the current gnitude rises ieditely which is detected by segent controller.

Thus solr energy syste is isolted without ny interruption in power supply to the lod. Fig.7. Siultion result for solr supplying 24V to DC lod. Fig.8. Siultion result for AC lod t 24V.

4 1= Closed/ 0= Open 2015 IJEDR Volue 3, Issue 2 ISSN: VI. V. SIMULATION RESULT The proposed protection schee ws perfored with coputer siultions using MATLAB. The oeriew of entire DC icrogrid protection is shown Fig 5 nd A probe power unit is shown in Fig.6. Fig.5. Oeriew of DC icrogrid protection. Fig 6. Siultion of probe power unit During norl operting conditions solr is chosen s in priority os sources to supply AC nd DC lod. The siultion result for solr supplying lod before the fult occurrence is shown in Fig.7 nd 8. A line to ground fult is creted t the solr lin circuit breer t 0.2sec fter the fult occurrence the current gnitude rises ieditely which is detected by segent controller. The breer ner the solr energy syste opened nd AC nd DC lod which is connected to solr syste is supplied through the wind energy syste. Thus solr energy syste is isolted without ny interruption in power supply to the lod. Fig.7. Siultion result for solr supplying 24V to DC lod. Fig.8. Siultion result for AC lod t 24V. If the wind speed is low nd unble to supply these lod then the breers AFTER opened nd connected FAULT to ISOLATION the AC grid. Thus AC grid supplies BREAKER required oltge SIGNAL to the AFTER lods. FAULT The breer OCCURENCE conditions under no fult nd fter fult occurrence is shown in Fig.9. SOLAR Siultion result for AC lod fter fult isoltion SOLAR LINK WIND WIND LINK GRID GRID LINK V O L T A G E DC LOAD FAULT OCCURRED AT 0.2S Fig.9. Breer signl fter fult occurrence. FAULT OCCURRED AT 0.2S Fig.10. Siultion result for AC lod fter fult isoltion. After the fult isoltion the AC lod is supplied by the wind energy syste with ny interruption in serice is shown in Fig.10. Since solr is isolted fter the fult occurrence its output current becoes zero is shown in Fig.11. IJEDR Interntionl Journl of Engineering Deelopent nd Reserch ( 439

2015 IJEDR Volue 3, Issue 2 ISSN: 23219939 C U R R E N T Fig.11. Siultion result for solr output current fter fult isoltion. Fig 12. Siultion result for probe power unit VII.

The proposed protection schee consists of segent controllers cpble of detecting bnorl fult current in the bus nd seprting the fulted segent to oid the entire syste shutdown.

5 2015 IJEDR Volue 3, Issue 2 ISSN: C U R R E N T Fig.11. Siultion result for solr output current fter fult isoltion. Fig 12. Siultion result for probe power unit VII. CONCLUSION This pper hs presented fult detection nd isoltion schee for the lowoltge dcbus icrogrid syste. The proposed protection schee consists of segent controllers cpble of detecting bnorl fult current in the bus nd seprting the fulted segent to oid the entire syste shutdown. A looptype dcbusbsed icrogrid syste with segent controllers between connected coponents hs been proposed. The proposed protection concepts he been lidted by coputer siultions nd experients. A probe power unit is ipleented to test the fult sttus. The proposed schee cn be pplied to dc power systes, such s Green Buildings, with sustinble energy resources nd dt centers with serer rry. Chllenges, such s reduction of conduction loss in the solidstte CBs nd fult ride through cpbility, nd fultloction techniques need to be inestigted. REFERENCES [1] M. Seedifrd, M. Groc, R. Dis, nd R. Irni, DC power systes:chllenges nd opportunities, in Proc. IEEE Power nd Energy Society Gen. Meeting, Jul. 2010, pp [2] R. Cuzner nd G. Ventrnn, The sttus of DC icrogrid protection, in Proc. IEEE Ind. App. Soc. Annu. Meeting, Oct. 2008, pp.1 8. [3] D. Sloonsson, L. Soder, nd A. Snnino, Protection of lowoltge DC icrogrids, IEEE Trns. Power Del., ol. 24, no. 3, pp , Jul [4] P. Slonen, P. Nuutinen, P. Peltoniei, nd J. Prtnen, LVDC distribution syste protection: Solutions, ipleenttion nd esureents, in Proc.13th Eur. Conf. Power Electron. App., 2009, pp [5] J. Cndelri nd J.D. Pr, VSCHVDC syste protection: A reiew of current ethods, in Proc. IEEE/Power Energy Soc. Power Syst. Conf. Expo., Mr. 2011, pp [6] C. Jin nd R. Dougl, Current liiting technique bsed protection strtegy for n industril DC distribution syste, in Proc. IEEE Int. Syp. Ind. Electron., Jul. 2006, ol. 2, pp [7] M. Steurer, K. Frohlich, W. Holus, nd K. Kltenegger, A noel hybrid currentliiting circuit breer for ediu oltge: Principle nd test results, IEEE Trns. Power Del., ol. 18, no. 2, pp , Apr IJEDR Interntionl Journl of Engineering Deelopent nd Reserch ( 440

Technical and Performance Aspects of a Dynamic Voltage Restorer

Technical and Performance Aspects of a Dynamic Voltage Restorer Technicl nd Perfornce Aspects of Dynic Voltge Restorer Author: K. Chn, ABB High Voltge Technologies Ltd., Syste ngineering Division, Switzerlnd Keywords: Voltge sgs itigtion, DVR, GCT, Rel-tie siultor,