A Central Control Strategy of Parallel Inverters in AC Microgrid

Transcription

1 A Central Cntrl Strategy f Parallel Inverter n AC Mcrgrd Gang Ya, Yu Lu, Tanha Tang, Mhamed Benbuzd, Yuka Zheng, Wang Tanzhen T cte th vern: Gang Ya, Yu Lu, Tanha Tang, Mhamed Benbuzd, Yuka Zheng, et al.. A Central Cntrl Strategy f Parallel Inverter n AC Mcrgrd. IEEE. IECON, Dec 13, Venne, Autra. IEEE, Prceedng f the 13 IEEE IECON, pp , 13, Prceedng f the 13 IEEE IECON. <hal-11837> HAL Id: hal Submtted n Jan 15 HAL a mult-dcplnary pen acce archve fr the dept and demnatn f centfc reearch dcument, whether they are publhed r nt. The dcument may cme frm teachng and reearch nttutn n France r abrad, r frm publc r prvate reearch center. L archve uverte plurdcplnare HAL, et detnée au dépôt et à la dffun de dcument centfque de nveau recherche, publé u nn, émanant de établement d enegnement et de recherche frança u étranger, de labratre publc u prvé.

2 A Central Cntrl Strategy f Parallel Inverter n AC Mcrgrd Gang Ya 1, Yu Lu, Tanha Tang 3 Electrcal Engneerng and Autmatn Department Shangha Martme Unverty Shangha, Chna 1 gangya@hmtu.edu.cn, luyu948@163.cm, 3 thtang@hmtu.edu.cn Mhamed Benbuzd 4, Yuka Zheng 5, Tanzhen Wang 6 4 EA 435 LBMS, Unverty f Bret, France, Mhamed.Benbuzd@unv-bret.fr 5 Cllege f Phyc Scence and Technlgy, Suzhu Unverty, Suzhu 156, Chna 6 Electrcal Engneerng and Autmatn Department Shangha Martme Unverty, Shangha, Chna Abtract Th paper fcue n the mcrgrd cntrl methd n dfferent peratng mde. The cnventnal drp cntrl cheme typcally ued t acheve autnmu vltage and frequency regulatn, whch cnder nly lcal nfrmatn, and the glbal ptmal perfrmance can't be guaranteed. In land mde, when the lad r generatn nde the MG change, crculatn wll be generated between the nverter n cae the lne mpedance are mmatch. Furthermre, the MG actve pwer utput de nt fllw the reference n grd cnnected mde. Dealng wth the abve prblem, a central cntrller degned t mantan the table peratn f the mcrgrd n dfferent mde n th paper. Sme mulatn are carred ut and the reult valdate the effcency f the prped methd. Keywrd Mcrgrd; Dtrbuted generatn (DG; Pwer cnverter; Drp cntrl; Parallel peratn I. INTRODUCTION Mcrgrd a cntrllable unt that upple pwer t cnumer n the cmbnatn f dtrbuted generatn (DG, energy trage equpment, cntrl devce and lad, whch mprve the relablty f pwer upply and repreent a new develpment drectn f pwer ytem [1, ]. The nterface between the DG unt and MG are ften bae n cnverter, and the fnal tage f thee cnverter cnt f dc/ac nverter. When multple nverter are paralleled n grd cnnected, ynchrnzatn r landng mde, a drp cntrl cheme typcally adpted, whch adjut the frequency and ampltude f the utput vltage, thu actve and reactve pwer can be hared amng the nverter [3-4]. But th methd tll ha everal drawback that lmt t applcatn. Frtly, due t the mpedance mmatch between the DG unt and the lne mpedance, the cnventnal drp cntrl ubject t reactve pwer cuplng. In [5] and [6], the nnerlp utput mpedance f the nverter can be nductve by degnng the parameter f the nner cntrller, But t cmplcate the cntrller degn. In [7], vrtual utput Th wrk wa upprted by Shangha Natural Scence Fundatn (11ZR14151, Specalzed Reearch Fund fr the Dctral Prgram f Hgher Educatn ( , and Innvatn Prgram f Shangha Muncpal Educatn Cmmn (11YZ139. mpedance lp can lve th prblem uccefully. In th ene, the utput mpedance can be een a a cntrl varable. Further, n land mde, when the lad r generatn nde the MG change, the drp cntrl regulate the utput pwer by changng the ampltude and frequency f vltage [8]. Frequency and vltage devatn are nherent t th methd [9]. The pwer balance caue the devatn f vltage and frequency, and the vltage drp n the lne mpedance lead t greater devatn [1]. When the lne mpedance f DG unt mmatch, the utput vltage f nverter nt equal, and then the crculatn wll be generated between the nverter [11]. Mrever, n grd cnnected mde, the vltage and frequency f PCC can be upprted by man grd. Due t the vltage drp n the mpedance f lne and nverter unt, the utput actve pwer f the nverter nt a ratng,thu t caue the devatn between the utput pwer f nverter and reference value. T vercme the afrementned drawback, n th paper, a central cntrl trategy prped. In land mde, the applcatn f a ecndary regulatn cntrl lp elmnate vltage devatn, and an actve cmpenatr mplemented t elmnate the crculatn. In grd cnnected mde, an external cntrl lp prped t regulate the utput pwer f an nverter. II. LOCAL CONTROL SYSTEM OF THE DG INVERTER Fg.1 hw the lcal cntrl tructure f a DG nverter. It cnt f nner cntrl lp, drp cntrl lp and P/Q calculatn. v and are the utput vltage and current f the DG nverter repectvely. The P/Q calculatr calculate ntantaneu value f actve and reactve pwer; the drp cntrl generate the reference vltage f nner lp; and the nner lp cntrl the utput vltage f nverter. v v Z ( D Fg. 1. Blck dagram f the nverter lcal cntrl

3 A. Inner Cntrl Lp Wth The Vrtual Output Impedance The nner cntrl lp f the three-phae vltage urce nverter (VSI hwn n Fg. degned n d-q reference frame. S Park tranfrmatn ued t tranfrm the varable between abc and d-q frame. In Fg., Ld Cd and d are the Inductr current, capactr current and utput current f the nverter repectvely. The nner cntrl lp cnt f an nner current lp, an external vltage lp and a vrtual mpedance lp. The prprtnal ntegral cntrl ued n vltage lp t mantan the tablty f the utput vltage. The utput f vltage lp a a reference f current lp. In rder t cntrl the renant peak f LC flter and enhance the dynamc repne, prprtnal cntrl be ued n current lp. The utput mpedance f the cled-lp nverter affect the pwer harng accuracy. The applcatn f vrtual mpedance lp can fx the utput mpedance f the nverter and btan the dered utput mpedance. u d K K K u up K p pwm 1 SL d Ld Cd 1 Fg.. Blck dagram f nner cntrl lp wth vrtual utput mpedance The cled-lp utput vltage can be expreed a fllw ( ( d d d SC u d u = G u Z (1 where G( the vltage gan and Z ( the utput mpedance, u d the utput vltage reference. G( and Z ( can be btaned n ( and (3 a kkk kkk G ( = LC Ckk kkk kkk up p pwm u p pwm 3 p pwm up p pwm u p pwm ( 1 ( 1 ( 1 Z( = LC Ckk kkk kkk (3 L Rkup kk u pwm Rkkk u p pwm 3 p pwm up p pwm u p pwm where K up and K u are the prprtnal and ntegral ceffcent f vltage lp, K p the prprtnal ceffcent f current lp, K pwm the fundamental wave magnfcatn f nverter, R the vrtual retve-mpedance. It can be berved that addng vrtual retve-mpedance whch de nt affect the tablty f the ytem and jut change the utput mpedance f the nverter. Ung the parameter lted n Table I, the frequency repne f Inverter utput mpedance btaned, and llutrated n Fg. 3. It can be een that the utput mpedance f the nverter nductve wthut vrtual retve mpedance. After addng the vrtual retve mpedance, the utput mpedance becme almt retve, and the utput mpedance at lne frequency (5 Hz abut.3 db and.6. In th tuatn, the decuplng between P and Q can be guaranteed. ( Magntude (db Phae (deg Bde Dagram Fg. 3. Bde dagram f nverter utput mpedance wth (ld lne and wthut (dahed lne vrtual retve-mpedance B. Drp cntrl ytem Fg. 4 hw the equvalent crcut f tw nverter cnnected t a cmmn lad. The utput actve pwer and reactve pwer f nverter can be expreed a fllw: EV V EV P= cφ c θ n φn θ (4 Z Z Z EV V EV Q= c φ n θ n φc θ (5 Z Z Z where =1,, Z and θ are the magntude and the phae f the utput mpedance, the pwer angle, E and V are the ampltude f the nverter utput vltage and the cmmn bu vltage. Z1 θ1 = R1 jx1 V Z θ = R jx E E φ 1 φ 1 Z L Fg. 4. Equvalent crcut f Parallel peratn f tw nverter The utput mpedance f the nverter and the lne mpedance are manly Retve, and cnderng mall phae dfference between E and V (c 1 and n. The equatn (4 and (5 can be mplfed a E E = m( P P (6 f f = n( Q Q where f and E are the frequency and ampltude f the utput vltage reference, f and E are ther reference, P and Q are the actve and reactve pwer, P and Q are ther reference, and m and n are the drp frequency and ampltude ceffcent. It can be een that actve pwer P regulated by the nverter utput vltage ampltude E, whle reactve pwer Q can be cntrlled by the nverter utput vltage frequency, whch the ppte trategy t the cnventnal drp methd. The drp ceffcent (m and n can be degned a fllw m = ΔV Pmax (7 n =Δf Qmax where P max and Q max are the maxmum actve and reactve

4 pwer f the nverter utput, ΔV and Δf are the maxmum frequency and vltage allwed f the nverter. The value f drp ceffcent relate t the ytem ynchrnzed and the vltage tablty lmt. III. IMPROVED CONTROL SYSTEM DESIGN The MG can perate n land, grd cnnected and wtchng mde. Ung lcal cntrller, the glbal ptmal perfrmance can't be guaranteed. The central cntrller huld be degned t mantan the table peratn f the MG n dfferent mde. A. Cntrl Strategy n Iland Mde In land peratn, the nverter perate a a vltage urce. When the lne mpedance f the nverter mmatch, the utput vltage ampltude f the nverter nt equal. It affect the actve pwer harng f DG unt and prduce crculatn between the nverter. Further drp cntrl regulate the utput pwer by changng the ampltude and frequency f vltage, when the lad r generatn nde the MG change. The nherent trade ff f drp cntrl between frequency ampltude regulatn and actve, reactve pwer harng accuracy cannt be avded. The tablty f the vltage at the PCC affect the qualty f pwer upply and eamle wtch the mcrgrd between the dfferent peratng mde. In rder t retre the devatn f the PCC vltage and elmnate the crculatn between the nverter, the crrepndng cntrller prped. It mplemented a expreed n E = E m( P P Δ E1ΔE (8 f = f n( Q Q Δf where ΔE 1 and Δf are the devatn, that can be btaned n (8 and (9 a KE Δ E1 = ( KpE ( EPCC EPCC (9 Kf Δ f = ( Kpf ( fpcc fpcc (1 where f PCC, E PCC are the frequency and ampltude f vltage at PCC, f PCC and E PCC are ther reference repectvely, K pe, K E, K pf, and K f are the cntrl parameter f PI regulatn. The frequency and ampltude f the MG, f PCC and E PCC, are meaured then cmpared wth the reference f PCC and E PCC. After PI regulatn, the devatn are ent t all the DG unt t retre the utput-vltage frequency and ampltude. Take the P-V drp a an example, and analy the cntrl prncple. In Fg. 5, the nterectn a f the pwer curve P G and the lad curve P L a nmnal peratng pnt f the MG. The lad curve change t P L1, a the lad ncreang, then the MG perate n the pnt b. It can be een that there a devatn between the vltage ampltude and the ratng. The applcatn f ecndary regulatn lead t the tranlatn f pwer curve. When the pwer curve P L1, the MG perate n the pnt c, and the vltage f the MG equal t the ratng. E E a P L c b P L 1 P G P P G 1 Fg. 5. the dagram f the vltage devatn retre ΔE the actve cmpenatn value, that can be btaned n (1 and (11 a Kc Δ E = ( Kpc ( P P (11 P = Pttal n (1 where P utput actve f the nverter, P ttal the actve utput by all the nverter, n the number f nverter, P the actve pwer demand f the nverter, K pc, and K c are the cntrl parameter f PI regulatn. Thrugh calculatn the um f actve pwer utput t btan actve pwer reference f the nverter [11]. The central cntrller regulate the actve pwer f each nverter va PI cntrller. B. Synchrnzatn Cntrl Strategy In rder t mthly wtch the MG between the landng mde and the cnnectn mde, t requred t mplement the ynchrnu cntrl lp. In ynchrnzatn mde, the frequency and vltage f the MG and man grd huld be meaured, and the θ m, E m can be cmpared wth the θ g and E g, the cntrl law can be expreed a n the fllwng E = E m( P P ΔEt (13 f = f n( Q Q Δft where ΔE t and Δf t can be btaned n (14 and (15 a k 1 Eref = E kp1 ( Eg Em (14 k fref = f kp ( θg θm (15 where θ g, E g are the phae-angle and ampltude f man grd vltage, θ m, E m are the phae-angle and ampltude f MG vltage, k p1, k 1, k p,and k are the cntrl parameter f the ynchrnu cntrl lp. After everal cycle, the ynchrnzatn prce wll fnh, and then the MG can be cnnected t the man grd thrugh the tatc bypa wtch. Operatn mde f MG frm landng t grd cnnected. Then the ynchrnu cntrl lp qut peratn. C. cntrl trategy n grd cnnected mde After ynchrnzatn prcedure, t allwed that cnnect the mcrgrd t the man grd. In grd cnnected mde, the ampltude and frequency f the MG vltage depend n the man grd. Suppng the frequency f man grd reman pwer frequency (5HZ and the vltage f man grd tay the ame, equalng t the nmnal vltage f nverter. Frm (1, t can be een that the utput reactve pwer f nverter the rated pwer. Due t the vltage drp n the mpedance f lne and nverter unt, whch prduce devatn between the Q G Q G1 f f a b c Q L Q L1 Q

5 utput vltage f the nverter unt and the nmnal vltage. The utput actve pwer f the nverter nt a ratng. An advanced cntrl trategy prped t mprve th weakne. The blck dagram f cntrl law preented n Fg. 6, and t can be expreed a n the fllwng kp E = E m( P P kpp ( Pref P (15 where P and P ref are the utput actve pwer f nverter and t reference. K pp and K P are the cntrl parameter f actve pwer cntrl lp. By meaurng the actve utput pwer f the nverter, P can be cmpared wth the P ref, after PI cntrller, the devatn are ent t the drp cntrl lp t regulate ampltude reference f the nverter. The utput actve vltage can be cntrlled by th mean. When the mcrgrd perate n the grd cnnectng mde, the cntant pwer cntrl can be acheved. Accrdng t the cntrl trategy prped abve, the cntrl cheme hwn n Fg. 6. E f ΔE 3 ΔE t Δf t ΔE 1 ΔE Δf Δ E3 = Kpp( Pref P Kp ( Pref P dt Δ E = K ( E E K ( E E dt t p1 g m 1 g m Δ f = K ( θ θ K ( θ θ dt t p g m g Δ E = K ( E E K ( E E dt 1 pe PCC PCC E PCC PCC pf ( PCC PCC f ( PCC PCC Δ= f K f f K f f dt Δ E = K ( P P K ( P P dt pc c Fg. 6. Blck dagram f the prped cntrl cheme m θm v IV. SIMULATION RESULTS In th paper, a mcrgrd mdel ha been etablhed ung MATLAB/Smulnk t verfy the feablty f the cntrl methd. A hwn n Fg. 7,the mcrgrd nclude f tw parallel nverter and lad. The tw nverter (, DG parallel perate harng the lad. The nverter cnt f a Three-phae full-brdge wth an LC flter. The cntrller cnt f the vltage and current cntrl lp wth vrtual mpedance, the drp cntrl lp, the P/Q calculatr and the central cntrller. The pwer tage and cntrller parameter are lted n Table I and Table II. Swtchng frequency f the DG nverter et t 6 khz. The nverter actve and reactve pwer reference value are 5kW and kvar repectvely. The DC lnk vltage:v dc1 =65V,V dc =6V. The lne mpedance f the tw nverter: Z 1 =.64j.83, Z =.34j.83. v θg Fg. 7. The tructure f mcrgrd n the mulatn. Table I. Pwer tage and nner cntrller parameter Parameter Symbl Value Unt Grd vltage Grd frequency rated utput pwer(/ Inverter nductance Inverter capactance Ampltude drp ceffcent Frequency drp ceffcent vltage prprtnal term vltage Integral term current prprtnal term retve vrtual mpedance V f S L1,L C1,C m n K up K u K p R V Hz KVA mh µf W/V Var/rd V -1 S/V A -1 Ω Table II. The central cntrller parameter Parameter Symbl Value Unt Ampltude prprtnal term Ampltude ntegral term Frequency prprtnal term Frequency ntegral term Actve ampltude prprtnal term Actve ampltude ntegral term Actve prprtnal term Actve ntegral term K pe, K E, K pf, K f K pc K c K pp K P W/V W/V Var/rd Var/rd W/V W/V W/V W/V A. landng peratng Frt, the mcrgrd perate n landng mde and tw nverter hare the 5 kw lad. At.6, the lad change frm 5kW t 9kW, kvar. At.1, the lad decreae t 7kW, 1kVar. The reult hwn n Fg. 8 and Fg. 9. P (W Q (Var DG (a Actve pwer delvered by and DG DG (b Reactve pwer delvered by and DG

6 Vltage (V Frequency (HZ (c Mcrgrd vltage (d Mcrgrd frequency Frequency (HZ H (A H (A (d Mcrgrd frequency (e The crculatn between the tw nverter Fg. 8. The reult f the mcrgrd wthut the central cntrller. P (W Q (Var DG (a Actve pwer delvered by and DG DG (b Reactve pwer delvered by and DG (e The crculatn between the tw nverter Fg. 9. The reult f the mcrgrd wth the central cntrller Fg.8 and Fg.9 hw the actve and reactve pwer delvered by and DG, the tranent repne f the frequency and ampltude f the MG and the crculatn between the tw nverter fr lad change. It can be een frm the reult that the ncreae f utput pwer f nverter lead t the decreae f the vltage ampltude and the ncreae f the frequency, whch cnfrm t the P-V, Q-f cntrl charactertc. Frm the Fg. 8 (a and (e, the actve pwer utput f tw DG nt equal; the mmatch f the lne mpedance can prduce the crculatn between the tw nverter. Frm the Fg.8(c and (d, the lad change, the frequency and ampltude f vltage have devatn. Fg. 9 hw the reult f the MG wth the central cntrller. Frm the Fg. 8 (a and (e, the actve pwer utput f tw DG equal and the crculatn between tw nverter reduced. Frm the Fg.8 (c and (d, the applcatn f the central cntrller can quckly repnd t the change, the vltage frequency and ampltude devatn are regulated tward zer after every change f lad. The cntrl trategy enhanced the pwer qualty f the MG. B. Ilandng T Grd Cnnected Frt, the MG n landed mde, tw nverter hare the 5 kw lad. At.5 ynchrnzatn cntrl wrk t prepare fr cnnectng t the man grd. After the ynchrnzatn prce, at 1.3 the MG cnnected t the man grd. The mulatn reult hwed n Fg.1, Fg. 11 and Fg.1. 1 Vltage (V (c Mcrgrd vltage Vltage (V Fg. 1. Vltage dfference between the man grd and the MG durng the ynchrnzatn prce.

7 Q (Var P (W DG (a Actve pwer delvered by and DG DG (b Reactve pwer delvered by and DG Fg. 11. Pwer tranent repne frm landed t grd-cnnected mde Vltage/V Current/A t/ 4 - (a Current wavefrm at the PCC t/ (b Vltage wavefrm at the PCC Fg. 1. Tranent repne f the utput current and vltage f PCC Fg. 1 hw the vltage dfference between the MG and the man grd durng the ynchrnzatn prce. It can be een that the errr dfference between them decreang. t> 1.1, the vltage errr dfference apprache zer. Fg. 11 hw the pwer tranent repne f nverter. <t<1.3, the MG n landng mde, tw DG hare the 5 kw lad equally. At t=1.3, the MG cnnect t the man grd, the pwer utput f nverter fllw the pwer reference value. The utput pwer P 1, =5kW, Q 1, =kvar. The reult hw that the cntrl tratege perfrm uccefully durng land and grd cnnected mde and the trantn mde. Fg. 1 (a hw the Current wavefrm at the PCC, <t <1.3, MG n landng mde, the current at the PCC zer. t > 1.3, MG n grd cnnected mde, the pwer nject t the man grd. The current ttal harmnc dtrtn (THD value f THD=.45%, fundamental current=14.18a. THD<.5%, t meet the requrement f cnnectn t man grd [1]. Fg. 1 (a hw the Vltage wavefrm at the PCC, The THD value f THD=.1%, fundamental Vltage=311.1V. The reult hw that the Seamle wtchng frm landng t grd cnnected can be acheved. V. CONCLUSION In th paper, a central cntrl trategy wa prped by analyzng the peratn charactertc f the MG. Accrdng t the dfferent peratn mde f the MG, the crrepndng cntrl methd prped. In land mde, the mplement f ecndary regulatn lp elmnated vltage devatn f PCC, and enhanced the pwer qualty f the MG. The applcatn f actve cmpenatr elmnated the crculatn between tw nverter. In grd cnnected mde, the utput pwer f nverter fllwed the ratng ung an actve pwer cntrl lp. In addtn, the applcatn f ynchrnu cntrl trategy enhanced eamle wtchng mcrgrd between landng and grd cnnected mde. The mulatn reult hwed the hgh relablty and flexblty f the mcrgrd durng dfferent peratn mde. REFERENCES [1] Lu Zngxang,Wang Caxa,Mn Yng,et al.overvew n mcrgrd reearch [J]. Autmatn f Electrc Pwer Sytem, 7,31(19:1-17. [] Sheng Kun,Kng L,Q Zhpng,et al.a urvey n reearch f mcrgrd-a new pwer ytem[j].relay, 7, 35(1: [3] Rcabert J, Luna A, Blaabjerg F, etal. Cntrl f Pwer Cnverter n AC Mcrgrd[J]. IEEE TRANSACTIONS ON POWER ELECTRONICS, 1, 7(11: [4] Guerrer J M, Hang L, Uceda J. Cntrl f Dtrbuted Unnterruptble Pwer Supply Sytem[J]. IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, 8, 55(8: [5] Wang Chenghan, Ga Fe, L Peng, et al. Cntrl Strategy Reearch n Lw Vltage Mcrgrd [J]. Prceedng f the CSEE, 1, 3(5:-8. [6] Xa Zhaxa, Wang Chenghan, Wang Shuxang. Multple feedback lp cntrl cheme fr nverter f the mcr urce n mcrgrd[j]. Tranactn f Chna Electrtechncal Scety,9,4( :1-17. [7] Guerrer J M, Jé Mata, Lu García de Vcuña, et al. Decentralzed Cntrl fr Parallel Operatn f Dtrbuted Generatn Inverter Ung Retve Output Impedance[J]. IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, 7, 54(: [8] Yang Xangzhen, Su Janhu, Dng Mng, et al. Vltage Cntrl Stratege fr Mcrgrd Wth Multple Inverter [J]. Prceedng f the CSEE, 1, 3(7:7-13. [9] Guerrer J M, Vaquez J C, Mata J, etal. Herarchcal cntrl f drpcntrlled AC and DC mcrgrd: a general apprach tward tandardzatn[j]. IEEE Tranactn n Indutral Electrnc, 11, 58(1: [1] Savagheb M, Jallan A, Vaquez J C, etal. Secndary Cntrl Scheme fr Vltage Unbalance Cmpenatn n an Ilanded Drp-Cntrlled Mcrgrd[J]. IEEE TRANSACTIONS ON SMART GRID, 1, 3(: [11] A. Mcallef, M. Apap, C. Spter-Stane, J. M. Guerrer Secndary Cntrl fr Reactve Pwer Sharng n Drp-Cntrlled Ilanded McrGrd IEEE ISIE, 1. [1] Yang Zhchun, Le Jan, Lu Kape, etal. Study n the tandard f the grd-cnnected mcrgrd[j]. Pwer Sytem Prtectn and Cntrl, 1, 4(: