Control Strategy of Bi-directional Converter for Battery Energy Storage System

Transcription

1 Control Strategy of Bi-diretional Converter for Battery Energy Storage Sytem Zhangang Yang *, Yinghuan Ma, Junhao Qu, Xudong Shi Aeronautial Automation College, Civil Aviation Univerity of China, 898 Jinei Road, Dongli Ditrit,Tianjin,, China, telp/fax: /978, Atrat - To enure the tale operation of the ytem, a i-diretional onverter i eential to ditriuted generation ytem. In thi paper, a harge/diharge ontrol trategy of ingle-tage power eletroni topologie with three phae i-diretional onverter wa propoed. When working in grid-onneted ondition, the external DC-link voltage loop ontrol trategy wa ued for attery harge, and the external power ontrol loop and the inner deadeat ontrol wa ued for attery diharge. When working in ilanded ondition, the inner deadeat ontrol and the external voltage ontrol loop wa ued for attery diharge. It i demontrated that the propoed ontrol trategy i effetive for attery harge/diharge in ilanded and grid-onneted mode, and it i exhiit atifatory tranient repone and routne to load variation. eyword - Mirogrid; Bi-diretional Converter;Grid-onneted;Ilanded;Deadeat ontrol I. INTRODUCTION Reently, ditriuted generator are a fat-developing trend and will reult in an inreae in reliale and power quality [],[]. When lot of ditriuted generator are onneting to the grid, there may e many prolem eaue of the flutuation of the ditriuted generator. In order to improve the utilization of ditriuted generator, the oneption of mirogrid wa propoed in []. A mirogrid i a low voltage ytem that ha different ditriuted generator, load and energy torage unit. A mirogrid an working in grid-onneted mode under normal ondition and will tranfer to ilanded mode under network fault ondition [],[5], o the power quality and upply reliaility are inreaed. To enure the tale operation, a i-diretional onverter whih an injet and draw power from the grid i eential to the mirogrid. When power i injeted into or drawn from the energy torage unit, a i-diretional onverter an meet the intantaneou power alaning etween load requirement and ditriuted generator in mirogrid. The ontroller of the onverter i reponile for keeping voltage and frequeny within the given limit, o how to ontrol the onverter i the key tehnology for mirogrid tale operation. Now there are numerou tudie aout the ontrol method of the i-diretional onverter [6],[7]. In [8], a harge/diharge ontrol trategy for i-diretional onverter wa propoed. Compared to traditional ontrol trategy, higher harge-diharge effiieny wa otained. In [9], a ingle phae i-diretional inverter wa ued in the mirogrid whih ontain PV, wind generation and attery, the flutuation of the olar or wind energy wa alaned y the inverter. The doule loed loop ontrol of voltage and urrent wa applied in the i-diretional onverter ytem in [],[], and the fat dynami repone wa gained. However, the teady error i inevitale when there i a load diturane. In [], a droop ontrol method wa propoed, and the eamle tranform wa gained etween girdonneted mode and ilanded mode, o the reliaility of energy upplie wa inreae, ut the mall ignal taility and routne of the ytem i weak [],[]. So at the moment, droop ontrol i merely experimental, a udden reakthrough ould poe ome triky quetion. Thi paper diue the iue related to the ontrol trategy of a three phae i-diretional onverter, and a feaile ontrol trategy aed on deadeat ontrol wa propoed, alo the dynami ehavior of i-diretional onverter wa reearhed. Thi ha een demontrated uing imulation reult. II. BI-DIRECTIONAL CONVERTER CONFIGURATIONS The attery energy torage ytem i onneted to the grid through a i-diretional onverter, and the typial topology of the onverter i hown in Fig. (), the idiretional onverter i a voltage oure PWM onverter. A the input of the onverter, a apaitor whih i ued to uppre the harmoni urrent i in parallel with the attery. Through the PWM onverter, the input of the DC voltage i onverted into a three-phae, high frequeny hopper voltage, and after a three-phae low-pa filter, a threephae inuoidal voltage i otained. In order to avoid interferene etween the attery energy torage ytem and the grid, an iolation tranformer i ued. DOI.5/IJSSST.a ISSN: 7-8x online, 7-8 print

2 Fig. The lok diagram of i-diretional onverter When harging the attery energy torage ytem, the idiretional onverter i working in retifier mode, the power will flow from grid to the DC ide, and the energy will e tored in the attery. When the attery energy torage ytem diharging, the i-diretional onverter i working in inverter mode, the power will flow from DC ide to the grid, and the energy whih wa tored in the attery will e releaed. III. CHARGE CONTROL OF BI-DIRECTIONAL CONVERTER Aording to different requirement, the harge proe i divided into two tep whih are ontant voltage harge and ontant urrent harge when onneted to grid, the onverter work a a retifier and the power flow from the grid to the attery energy torage ytem. In ontant voltage harging, for example, the dual-loop ontrol i ued, the external DC voltage ontrol loop, whih ontrol the output voltage of the onverter, V d trak the given referene voltage V dref. The error etween the real DC u voltage and the referene DC u voltage i given to a proportional-integral ontroller. The output of the proportional-integral ontroller, i d-ref i ued a d axe input of internal urrent loop. For the power fator i et a, the q axe input of internal urrent loop, i q-ref i et to. The inner urrent ontrol loop, i reponile for fat dynami adjutment of the urrent. The error etween the real urrent and the referene urrent i alo given to a proportional-integral ontroller, then the modulated ignal m d and m q, are finally otained. The ontrol funtion of thi ontrol i given a equation (). id iq m m d q di dp V S di dp i d _ S qi qp i q _ S _ ref _ ref dref ref ref V i i The parameter meaning of harge ontrol i hown in tale I. TABLE I. THE PARAMETERS OF GRID-CONNECTED MODE CHARGE CONTROL d q d () Parameter Vd,Vdref id,id-ref iq,iq_ref dp,di dp, di qp,qi The parameter meaning DC u voltage, the referene DC u voltage d axe urrent, the referene d axe urrent q axe urrent, the referene q axe urrent proportional and integral oeffiient of external loop proportional and integral oeffiient of d axe proportional and integral oeffiient of q axe The lok diagram for thi ontrol i hown in Fig. di di dp dp qi qp Fig. Blok diagram of grid-onneted mode harge ontrol Fig. how the DC u voltage when the onverter i onneted to a utility, the referene DC u voltage i 5V, and the DC u voltage will reah 5V at. eond. The reult of imulation how that the ytem ha quiker repone peed and higher teady preiion. Voltage/V Fig. DC u voltage of i-diretional onverter in grid-onneted mode harge ontrol It an e een that, when onneted to utility, the external voltage loop ontrol trategy whih ontrol the DC-link voltage an realized the ontant voltage harge and ontant urrent harge of the attery, and meet the need of attery harge. IV. DISCHARGE CONTROL OF BI-DIRECTIONAL CONVERTER There are two type of proe when the attery i diharged: the grid-onneted mode diharge ontrol and ilanded mode diharge ontrol. A. The grid-onneted mode diharge ontrol When in grid-onneted mode diharge ontrol proe, the i-diretional onverter i the grid-following unit. Baed on the et point for reative and real power, the idiretional onverter will end orreponding reative and real power to the grid. The ontroller of the onverter inlude two different etion. One i an external power ontrol loop whih i realized y a ommon proportional integral ontroller. The output of the external real and DOI.5/IJSSST.a ISSN: 7-8x online, 7-8 print

3 reative power regulator i ued a d axe input and q axe input of internal urrent loop repetively. The ontrol funtion of thi ontrol i given a equation (), and the parameter meaning of grid-onneted mode diharge ontrol i hown in tale II. di id _ ref dp Pref P S () qi i q _ ref qp Qref Q S TABLE II. THE PARAMETERS OF GRID-CONNECTED MODE DISCHARGE CONTROL Parameter P,Pref Q,Qref, id,id-ref iq,iq_ref dp,di qp,qi The parameter meaning real power, the referene real power reative power, the referene reative power d axe urrent, the referene d axe urrent q axe urrent, the referene q axe urrent proportional and integral oeffiient of external real power loop proportional and integral oeffiient of external reative power loop After getting the et point for urrent, the ommonly ued method i the inner urrent ontrol whih i realized y a ommon PI ontroller, ut there i teady tate error etween the referene urrent and meaured urrent when the load ditured. In thi paper, the deadeat ontrol trategy i ued in the inner urrent ontrol. The i-diretional onverter variale on the d-q frame, i d-ref, i q-ref are tranformed to variale i a-ref on the three tationary axe a,, and. For a uffiiently hort PWM arrier period, T, the duty yle of the onverter are d A, d B,d C, and d A +d B +d C =.5, then it i poile to alulate the tranfer funtion of the deadeat ontroller from equation() to equation(6). U U U an n n U U U n n an dia L V di L V di L V AB BC CA di L di L dia L () L A L A i i i i U U aref U T d i i i i U U ref a ref ref U d T an n n T T (5) Then the duty yle of eah phae i given a following equation (6): d A A B.5 / d B A B.5 / (6) dc A B.5 / The inner deadeat ontroller i preented in Fig. (). P ref Q ref V a I a PQ aulation Q + - P di dp + - qi qp I d_ref I q_ref dq/a I aref Deat-eat ontrol Pule Fig. Blok diagram of grid-onneted mode diharge ontrol When working in the grid-onneted mode diharge, the imulation waveform i hown in Fig. 5. In thi phae, the real power P ref i etting to 8kW, the reative power i etting to kvar. The three-phae load are unalaned load, P a=kw,p =kw,p =5kW,Q =kvar. In a hortly repone time (.), the real and reative power of the onverter will reahed the teady tate(8kw,kvar), and the teady tate error i almot zero, a hown in Fig. (5-a), (5-). For the totally three phae load i kw,kvar, the utility power output will inreae to kw,kvar orrepondingly, a hown in Fig. (5-), (5-d). The real and reative power output of the onverter maintain ontant, the unalane power requirement will e upplied y the grid, a hown in Fig. (5-f). 9 x di i a di i di i aref ref ref i T i T i Defining the variale A, B a T a () Q/Var x (a)real power of the onverter ()Reative power of the onverter DOI.5/IJSSST.a ISSN: 7-8x online, 7-8 print

4 Q/Var 6 x x ()Real power of the grid ahieved in d-q frame. The ontroller of the onverter inlude two different part. One i an external voltage ontrol loop whih i ahieved with a tandard proportional-integral ontroller, ut the referene voltage i etting aording to the ytem requirement whoe premie i the yntheizing voltage vetor magnitude are equal etween three-phae and ynhronou referene frame, and the phae angle of oordinate tranformation i alo given diretly aording to the output frequeny. The ontrol funtion of thi ontrol i given a equation (7) (d)reative power of the grid di id _ ref dp Vd _ ref Vd i V V qi q _ ref qp q _ ref q (7) (e)current of the onverter (f)current of the grid Fig.5 Grid-onneted mode diharge of i-diretional onverter When the onverter i working in grid-onneted diharge mode, from the imulation waveform in Fig.5, it may e oerved that i-diretional onverter whih wa ontrolled y external power ontrol loop and the inner deadeat ontrol will end orreponding reative and real power to the utility aed on the et point for reative and real power, and the flutuation of the load will e alaned y the grid. B. The ilanded mode diharge ontrol When in ilanded mode diharge ontrol proe, the idiretional onverter i the grid-forming unit and etting the voltage and frequeny of the mirogrid. The attery energy torage ytem work a a high quality AC voltage oure, the V/f ontrol of i-diretional onverter i hown in Fig. (6). Compare to equation (6), the inner urrent ontrol i alo deadeat ontrol in ilanded diharge ontrol. Fig.7 give the ilanded diharge mode operation urve of unalaned load ondition. In -.5, three phae load i alaned, and eah phae load i kw, o the total load i kw, a hown in Fig. (7-a). In thi time, the idiretional onverter i etting the frequeny and voltage of the mirogrid. A hown in Fig. (7-), the frequeny and voltage of the ytem i 5Hz, V, alo the three phae urrent are alane, a hown in Fig. (7-). At.5, there i a tep hange of the phae A load, from kw to kw. For the V/f ontrol of the i-diretional onverter, the attery power output of phae A will inreae from kw to kw orrepondingly. Thi mean that the total three phae power will inreae from kw to kw, a hown in Fig. (7-a). The output voltage of the onverter remain unhanged, ut the urrent of phae A will inreae with the load, a hown in Fig. (7-), (7-). 5 x (a)real power of the onverter Voltage/V - dp qi qp di ()Voltage of the onverter Fig.6 Blok diagram of ilanded mode diharge ontrol During ilanded diharge mode, the V/f ontrol i alo DOI.5/IJSSST.a ISSN: 7-8x online, 7-8 print

5 ()Current of the onverter Fig.7 Ilanded mode diharge of i-diretional onverter in unalaned load ondition Voltage/V 7 x (a)real power of the onverter ()Voltage of the onverter urrent will flutuate aordingly with the load. V. CONCLUSION In thi paper, a ontrol trategy for i-diretional onverter in different mode wa propoed. When working in grid-onneted ondition, the external DC-link voltage loop ontrol trategy wa ued for attery harge, and the external power ontrol loop and the inner deadeat ontrol wa ued for attery diharge. When working in ilanded ondition, the inner deadeat ontrol and the external voltage ontrol loop wa ued for attery diharge. Simulation reult how that the propoed ontrol trategy wa effetive in ilanded and grid-onneted mode harge and diharge, alo it wa imple, exhiit atifatory tranient repone and routne to load variation. CONFLICT OF INTEREST The author onfirm that thi artile ontent ha no onflit of interet. ACNOWLEDGMENT Projet upported y the National Natural Siene Foundation of China(5785,5776), Sientifi Reearh Foundation for Civil Aviation Univerity of China (QDX).. REFERENCES ()Current of the onverter Fig.8 Ilanded mode diharge of i-diretional onverter in udden load hange ondition In -.5, the three phae alaned load i kw, o the output power of the onverter i kw, a hown in Fig. (8- a). Both the voltage and urrent are alaned, a hown in Fig. (8-), (8-). At.5, the three phae load will inreae from kw to 6kW uddenly. For the V/f ontrol of the i-diretional onverter, the output power of the attery will inreae from kw to 6kW orrepondingly, a hown in Fig. (8- a). The three phae voltage of the onverter till remain unhanged, ut the three phae urrent will inreae with the load, a hown in Fig. (8-), (8-). When the i-diretional onverter i working in ilanded diharge mode, from the real power, voltage and urrent imulation reult in Fig. (7) and Fig. (8), it may e oerved that the i-diretional onverter whih wa ontrolled y external voltage ontrol loop and the inner deadeat ontrol will maintain the voltage even there i a uddenly hange of one phae or three phae load, and the [] WANG Jian, LI Xing-yuan, QIU Xiao-yan. Power ytem reearh on ditriuted generation penetration. Automation of Eletri Power Sytem, 9(): [] M.F. Baharom, M.H. Jali, M. Fani, et al. Multi population evolutionary programming approah for ditriuted generation intallation. TELOMNIA,():5-58. [] Hatziargyriou N., Aano H., Iravani R., Marnay C., Mirogrid, IEEE Power Energy. 5(): [] WANG Cheng-han, WANG Shou-xiang. Study on ome key prolem related to ditriuted generation ytem. Automation of Eletri Power Sytem, ():-.8 [5] Rudy Setiaudy, Hartono BS, Budiyanto. Analyi harateriti of on/off grid tie inverter and implementation in Mirogrid. TELOMNIA,():-5. [6] Hajizadeh A.Golkar M A.Control of Hyrid Fuel Cell Battery Ditriuted Power Generation Sytem with Voltage Sag Ride- Through Capaility.nd IEEE International Conferene on Power and Energy,Johor Baharu, pp:6~67,8 [7] Chiang S J, Chang T, Yen C Y.Reidential Photovoltai Energy Storage Sytem.IEEE Tranation on Indutrial Eletroni, 5() :85~9,998 [8] Inoue S, Akagi H.A Bidiretional Iolated DC DC Converter a a Core Ciruit of the Next-Generation Medium-Voltage Power Converion Sytem.Power Eletroni Speialit Conferene, Jeju, pp:-7,6. [9] YANG Zhangang, WANG Chenghan, CHE Yano. a mall-ale Mirogrid Sytem with Fexile Mode of Operation. Automation of Eletri Power Sytem. (): DOI.5/IJSSST.a ISSN: 7-8x online, 7-8 print

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