Analysis and Design of a Regenerative EnergyConversion System Based on an Active Simulator

Byoung-Kuk Lee, Senior IEEE, Su-Jin Jang, Han-Min Lee*, Gil-Dong Kim*

School of Information and Communication Engineering, Sungkyunkwan, Suwon, Korea*Korea Railroad Research Institute, Uiwang, Korea

Tel: +82-31-299-4581 Fax: +82-31-299-4612 E-mail:bkleeskku@skku.edu

Abstract - In this paper, a regenerative energy conversion system lot of research such as energy storage equipment has beenfor subway is proposed. In order to simulate the actual voltage studied.and current fluctuation in subway system, a active simulator,which is based on pwm ac-dc converter, is developed andimplemented. Also, the energy storage system is designed using Utility A DC linebi-directional dc-dc converter and super capacitors. The Voltage X 'A

theoretical explanation is carried out and the validity of the Vproposed system is verified by simulation and experimental _results.Index Terms -Active simulator, regenerative energy, bi-directionaldc-dc converter.

CapacitorI . INTRODUCTION Bank

Bidirectional Energy storage systemThe DC subway system consumed a lot of electric energy converter wxith supercapacitorand according to movement of electric car in moving field, Braking resistorthere is generated regenerative energy. In other word, if the Fig. 2. Regeneration energy store device.movement range is download stream or braking range, there ischanged in 4500 of input energy to regenerative energy. Figl Fig. 2 is flow chart for regenerative energy storageis a distribution chart of regenerative energy [1]. equipment in subway system. In this state, it is not possible toThe 5500 of input energy consumed in electric car. All of the simulate the real size scale to test DC line voltage which has

4500 of energy generated in form of regenerative energy, there got enormous rate in regenerative energy using equipment. Sois used 25% to the adjacency vehicles' start and accelerating, it could not efficiently control the real system. Therefore inand remaining 20% of regenerative energy, there is pretended this study has been adapted to solve the problem cause bycould've recycled energy [2]-[3] risen the DC line voltage, and propose the active simulator toIn DC subway system, this type of regenerative energy efficiently control the energy storage equipment, and also

raised the DC line voltage so that became a main cause the control the both direction DC/DC Converter.problem making such as malfunction of protecting equipmentand coil burning. But in this time, there is no other equipment If THE DC VOLTAGE ACCORDING TO CHARACTERISTIC OFto store or to use in this regenerative energy in DC subway ELECTRIC CAR IN DC RAILWAY SYSTEMsystem, so the DC line voltage rose over determined level, itis consumed by using residence burden. In DC subway system, the electric car operated in

combination of 4ea of operating mode such as start-move-brake-stop when it moved in station to station. The

enerative Elergy combination method of this operation mode affected to the

5,yo \ \electric car's run time and also affected to energy25%\\OJ°/O consumption and amount of revived energy. We could divide

5i\ _ 1the characteristic of electric car's operation mode to energy

I2 consumption mode and energy regenerative mode. Fig. 3indicated the standard operation chart in electric car.

Consume Ener_ The constantly maintained DC link voltage in the level of1500V by 3-phase rectifier, affected by regenerative energy

Fig. 1. Distribution chart of regenerativeenergy. which was cause of standard operation characteristic pattern,it is changed like Fig. 4 which is included in regenerative

Therefore, to solve the problem cause by raised the DC line energy, so it has got non-linear wire voltage pattern.voltage and raise the using method of regenerative energy; a

0-7803-9761-4/07/$20.00 ©2007 IEEE 659

d-q voltage equations are shown in (2) in the stationary- - 4 coordinate system.

_ ~~~~~~~~~~~~~~~~~~~~~~~di,'*0 e8 = L dd s> / \ d dtd (2)

e8=L diq +VDistance [kml q dt q

Fig. 3. Standard operation chart in electric car.

The synchronous d-q voltage equations can be shown using

die_~~~~~~~~~~~~~~~~ je_ ~~~~~~~~~~~~~~~ed = Li I+ ct)Liq Vddt (3)die

a ~~~~~~~~~~~~~~~~ee= Li -q _ CLie + Ve8eq ' dt d q

If the ac source is a three- phase sinusoidal voltage with anangular frequency, the three-phase line voltage on basis of a-phase is presented by (4).Fig. 4. DC line voltage affected by regeneration energy.

Like this, In DC line voltage which was regenerative energy, ea = -E sin cotif there is non-existence of adjacency vehicles or there is no ( 2<T (4)energy consumption, the maximum value of DC line voltage eC -Esint- 3positioned more than 1800V, so it produce a cause ofimportant system's problem such as burning of coil or e = -E sincot±+malfunction of protecting equipment. [4][5] a 3)

111. REGENERATIVE ENERGY CONVERSION SYSTEM In (4), E is the maximum phase voltage and the ac sourcevoltage in d-q stationary and synchronous coordinate is (5),

A. Active Simulator (6).The proposed active simulator is both direction AC/DC

converter type. Fig. 5 indicates the AC/DC converter which ee=Esincdwas used of active simulator. (5)

<? =-Ecosotc ~~~e>~

T oX E (6)

By (3), Equation (6) can be expressed by using (7).

Fig. 5. Regeneration energy simulator. dideEE=L d cLibl + Vdeidt q d7The regeneration power flows from traction to the ac source. ed (7)

For this mode, voltage equations are below. d=Ldie tLi + Ve0 idt d q

a iL di ±V The error between the transformed three-phase current todi (1) synchronous coordinates and the dc line voltage is the inputeh-L dt bvalue of the PI controller and makes d-axis current reference.

di This d-axis current reference compensates q-axis interferenceec Li dt±+Vc and makes d-axis voltage reference. [6]

660

(IC 'Load electric car, the down stream of DC line voltage could'vedisplayed like as figure 8(b).

VC 'Kr traction FV FX F Input voltage

I~~~~~~~~~~~~R~ oi kVuItSg

iqS t f u i;v t ^ vj s. ~~~~~~~~(a)Up stream of DC line voltage

St(] ti<wila1 , q S t (tie)n(1wtractio1

I:lcl:<, < > Is:lcluncc.sF JsF 1, 3repthfiese Input voltage~~~~~~~~~~~~Inptvotag

q q = d i ye iye > > D X a <~ Aci

Gate Signal

Fig. 6. Ov erall cor bo di rmDSP Control lCD I Board

PlIase~~irX p|aeT N Board |Real DC l0000 Dtag

patter t

Therefore, the notion of the proposed scheme in this paper (b) Down streamofnDC lin vlaeuses a three-phase SVPWM inverter for regeneration of Fig 8. stream ofDC line voltagesurplus power. Fig. 6 show the overall control block diagramof active simulatorFig. 7 show the active regeneration energy simulator system. B. Bidirectional DC/DC converter ofregenerative energyThe active simulator has been connected with output of storage systemrectifier to the type of D.C, so it could control the wire Regenerative energy which is increasing the DC line voltagevoltage in 1500V type of included regenerative energy. In this controlled by bidirectional DC-DC converter throughtime, the reference of simulator taken the sensing of voltage charge/discharge operation of super-capacitor.and current by actually measured DC line voltage and Bidirectional DC-DC converter controlled power flow ofcompared then compensate the tolerance. regenerative energy by variation of DC line voltage. This

paper used non-isolation half-bridge type converter to realizel Actiesimultor3hase 3phasethe bidirectional DC-DC converter because half-bridge;~~ +> {$trectiInpt voltge converter has a low inductance value and low capacitance of1 T + 5 J Jd d ~~~passive elements and low rated voltage of active elements

||||T T l I ~~~~~appropriated in energy storage system in DC tractionlllll application. Fig. 9 Show the Non-isolation half-bridgelll ~~bidirectionalDC-DC converter

Gate Signa[

Boadl DEl inVlhe ncs

patter S 1

Fig.=7.eRegenerationenergysimulatorsystem

The simulator's energy flow which was cause of occurredbyll|revived energy could've displayed like as Fig. 8 In the

movement rag of elcrccrwsdontemrneo Fig. 9. Non-isolation half-bridge bidirectional DC-DC converter.

braking range, the DC line voltage shall be risen by means of Hl-rdeD-Ccnetroeae sbc ovreoccurrin regenerative energy. Fig. 8(a) showedqup the when charge mode and operated as boost converter when

electric current which was raised of DC line voltage. In dshremd.Hl-rdeD-C cnetrdsgreverse side, such as the case of start or acceleration of codto.anb.eninTbe1661cnee Tb1

CT1(~ ~ ~ ~ 6

Table 1. DESIGN PARAMETERS OF BIDIRECTIONAL DC-DCCONVERTER.

Means Value A 4EU

Maximum Discharge voltage 40[kW]

Voltage range of Supercapacitor 50100[V] . _ r X 2 $ * ,3 gg ti ... ..Maximum current of Superapacitor 50[A] :

Input current of Converter 10[A] NN

Switching Frequency 10 [kHz]

Input voltage of Converter 311 [V] F.1 T p r i(DC Line voltage) Fig. II. The proposed regenerative system.

This paper proposes new control algorithm of bidirectional Fig. 12 was a displayed waveform which was viewed byDC-DC converter which according to the characteristics of using program in DC line voltage which was measured insuper-capacitor. Fig. 10 shows the diagram of control block to Seo-Cho station substation. We could realize the fact that thecontrol the regenerative energy storage system. In this displayed DC line voltage was not uniform because of the

algorithm, super-capacitor needs initial charging time because regenerative energy.the system demanding a large voltage in early stage motion.

(START A

Completion of early SCcharging

Electric railwaysubstation start to supply

power

Voltage of D)C-line - StandardVotage No

YesElectric railway

substation stop to supplypower

I |; Fig. 12. Measured in Seo-Cho station substation.Start of SC charging

/Inpu~t voltage of SC e Stop of SCmrlndaagiespclMaximnum of the !t_

chargingThe DC line voltage data which were gained using special

\permissible voltaRge / c;gnpermissiblevoltage ch'ring |program has been simulated by 0.5 second interval used ofDLL of PSIM. Fig. 13 was displayed DLL of really measured

V<oltag3e of D)C-line < Standardi voltage Exhaustion of DC voltage datum.resister

Closing of SC discharging(Stop of resister operating)

Electric railwaysubstation start to supply

power V,~

Discharging of SC

Output voltage of SCMinimum of the Stop of SC discharging

permissible voltage Yes

No

Fig. 10. Control algorithm of regenerative energy storage system.

IV. SIMULATION RESULTSFig. 13. Displayed DLL of really measured DC voltage data.

The active simulator which was simulate the change of DCline voltage, both direction DC-DC converter which was In DC subway system, non-burden input was DC 1650V, butchanged the regenerative energy and capacitor which has got for the purpose of experiment, it is scaled for 350V, and in thefunction of energy storage, had been adapted real subway Seo-Cho station which was one of Seoul subway systemsystem and simulated. The Figi 1 indicated the circuit diagram picked up real data and simulated based of these. Fig. 14 waswhich was proposed in this paper non-burden DC line voltage of subway system

662

F iIg. 14. Non-burdenl DC li ne voltage of subway system.'

regenerative energy which were caused from electric car. Fig.15 showed up the DC voltage which was affected from Fig. 17. Actual hardware configuration ofregenerativeenergy storage system.regenerative energy of simulator.

X X <~~egen: ativi energYAI 2 .TOPPED

Fig. 15.Affecte fromreeneratie energyof simuator. Fg. 18. Output waveform of active simulator (D/A output)Fig. 15. Affected from regenerative energy of simulator.(5V/div, 2s/div).

Fig. 16 iS waveform of current which has been flown to Fig. 18 shows output waveform of DC line simulator. Thesimulator of regenerative energy. Simulator could control the otu auso iuao r dnia ihvle fraboth direction current, therefore to made energy balance. tasiso.I i.1,tevle hc vrtesadr

. ~~~~~~~~~~~~~~lineshow generated regenerative energy and the values whichdown the standard line show power consumption of DC

.. I~~~~~~~~~~~~~~~raction.

Fig. 1g Cr0Brentofactive simulator.0Th.rttp is ful buil an tete. Th eprimental Fig . g19... rChr I . s I.gingmod (Buc _mode)t=.W=_ ..... ._

-1|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~....................................I g i g I 1 1 01 ... I Sg W.W.~~~~~~~~~~~~~ ~~ ~~ ~~ ~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~....................................I | ggI gBX ... I .0... 0 I g~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.............

~~~~~~~~~~~~~~~~~~~~~~~~(0/iv 100V/div6, SOs/iv.

g0~ ~~~ ~~~~~~~~~~~2 shw chrg curn avfr f ue-apctr

663 ,

Figi1.Non-burdentDin oltactie ofsiubwator system.

Ah proomthingiamuntly buire vlagehasted.enhefxperimentaregenemrativ enetrgyowhihe werotye ase fromnielctig. ca.7i. Fig.17 .Aculhardwrecnfgmoe(uraio mofdege) atv1 showed uptheDC voltage which was affep:cSupeeapacitorechrgynstoltage,systtom:. wthotg

regenerative~~ ~ ~ ~ ~ ~ ~ ~ ~ ig enrgshow simunlatagorv.omofsue-cpcio

wiegnrtnthregenerative energy . syucnsei

Fig.19,voutptagofasuefrm-capactitor simuatrgedAoutput)Adig

Fig.16 s waefom ofcurentwhic ha bee flwn t Fi.20 showschrgourrent waveform of DCupier-capacitor. Th

siultr f eenraie neg. imlto cud onrl h otptvaue f imlto aeidntcl it aleso6ra

[4] A. Horn, R. H. Wilkinson, and T. H. R Enslin, "Evaluation of converterCtopologies for im proved power quality in DC traction substations," IEEE-

ISIE'96, vol.2, pp.802-807, 1996.[5] P. J. Randewijk and J. H. R Enslin, "Inverting DC traction substation with

active power filtering incorporated," IEEEPESC'95, Vol. 1, pp. 360-366,1995.

[6] H.I. Han, N. K. Hahm, N. K Sung, G.. D. Kim, D. K Kim, andK. H. Han, "A study on current controller comparision for three phasePWM converter," KIEE, pp. 1248-1250, 2000.

Fig. 20. Charging mode (Buck mode)Top: Supercapacitor charging current, Bottom: Input current

(4A/div, 50us/div).

Fig. 21. Discharging mode (Boost mode)Top: Supercapacitor discharging voltage, Bottom : discharging current

(4A/div, 50us/div).

Fig. 21, show the voltage and current output waveform ofsuper-capacitor which in discharge mode. It can be confirmedfrom Fig. 22 that Super-capacitor supplies an amount ofpower to DC line in an instant.

V. CONCLUSION

In this paper, based on the actual simulator, which cansimulate DC line voltage fluctuation of subway, regenerativeenergy storage system has been designed and implemented.Using supercapacitors as the energy storage system, an test-bed has been built and the static and dynamic performance ofthe proposed system has been analyzed. From theexperimental results, it can be expected that the proposedsystem can be utilized for energy efficient subway systems.

REFERENCE

[1] K. H Cho, S. J Jang, J. Y Kim, C. Y. Won and Y. K. Kim, "Regenerationinverter system for DC traction system," KIEE Annual SpringConference, 2007.

[2] K.W. Kim, I. S. Yoon, Y. M. Seo, D. Y. Yoon, and S. C. Hong, "A study on

thenspoercafacitorsimprovementfD oerg stregenrtgsystems," KIPte,t

vhpol. se6,teno. 5,epp.yed410415 2001

[3] K. W.h,S Jn,JKim,Y.M. Seon andS. C. Hong,"ARtdnteipementrationoinverter systems for regenratediowe control," KIPE, vonul.,n.2Spp.n205-213nc, 2002.

[2]K.. im,I.S.Yoo, . . So,D.Y.Yoo, ndS. . on, " 664o