Reference Signal Generators for Distributed Compensation

Transcription

1 Herbert L. GINN III Unversty of Soth Carolna do: / Reference Sgnal Generators for Dstrbted Compensaton Abstract. Varos methods are sed to generate the control reference sgnals for power electroncs based compensators n three-phase dstrbton systems. In cases where ncreased flexblty and sharng dtes across mltple compensators provdes a cost beneft the applcablty of reference sgnal generaton methods for dstrbted compensaton applcatons shold be evalated. Shared compensaton reqres an nderstandng of power components that are present to enable prorty based decsons wth respect to the sharng. Ths paper provdes an overvew of several reference sgnal generaton methods for power electronc converters when sed n a cooperatve fashon for sharng compensaton dtes wthn an electrcal grd. Streszczene. Wele różnych metod stosje sę dla generowana sygnałów sterowana kompensatorów energoelektroncznych w systemach rozdzelczych. W sytacjach w których rosnąca elestyczność podzał zadań kompensatorów rozproszonych daje korzyśc fnansowe sterowane takch kompensatorów jest ważnym przedmotem zanteresowana. Kompensacja rozproszona wymaga ops energetycznego system możlwającego podzał ról kompensatorów. Nnejszy artykł przedstawa przegląd metod generowana sygnalów sterjących kompensatorów rozproszonych.(orównane przydatnośc różnych teor mocy do sterowana kompensatorów klczjących) Keywords: voltage-sorce converters actve compensator actve flters dstrbted compensaton mcrogrd. Słowa klczowe: Konwertery ze źrółem napęcowym kompensatory aktywne fltry aktywne kompensacja rozproszona mkro-sec Introdcton The sbject of components not assocated wth actve power sometmes referred to as seless components and ther compensaton has long been a topc of dscsson among researchers. In addton ncreasng se of power electroncs n power systems as well as n mcrogrds provdes opportntes for dstrbted compensaton f those power electroncs have flexblty to allow for varos compensaton fnctons as well as ther coordnaton to acheve the overall compensaton objectves. Ths there have been recent trends toward mlt-fnctonalty of power electronc converters combnng compensaton wth other fnctons or reqrng flexble compensaton. For example t may be desrable to perform compensaton wth converters sed for nterfacng of renewable sorces drng tme ntervals that they are not flly tlzed for renewable genererated energy transfer. Also non-deal spply condtons are warrantng more attenton as weak grds sch as mcrogrd systems are ganng nterest. Wth ncreased flexblty reqrements and the need to share dtes across mltple compensators the applcablty of reference sgnal generaton methods for dstrbted compensaton applcatons shold be evalated. Varos methods are sed to generate the control reference sgnals for power electroncs based compensaton systems. These systems when harmonc compensaton s nclded are sally referred to as actve flters actve power flters or actve harmonc flters. In some cases compensaton objectves may not nclde harmoncs and the more general term actve compensator s sed to ndcate that any component or grop of components of the crrent may be compensated. Sch power electroncs based compensators are referred to n ths paper as swtchng compensators as n [1] snce they rely on semcondctor swtchng n order to compensate for some ndesrable components of crrent or voltage n a system. Ths paper provdes an overvew of several methods for the generaton of reference sgnals sed n control of power electronc converters that mst share compensaton dtes wth other devces. ower electronc converter based compensators ower electronc converters sed n compensaton applcatons can be groped nto one of three broad categores: shnt connected crrent compensators seres connected voltage compensators and combnatons thereof. The shnt connected crrent compensator s the most prevalent and wll be the focs of compensaton examples n ths paper. Fgre 1 depcts a generalzed voltage sorce converter (VSC) based crrent compensator wth the control fnctons parttoned nto several herarchcal layers. Fgre 1. Fnctonal dagram of a generalzed three-phase Voltage Sorce Converter. The control layers can be groped nto two man parts. The frst s the crrent controller [2] and lower level controls that case the power electroncs hardware to behave as a controlled crrent sorce as depcted by the dashed lne. The power electronc eqpment and control sb-systems wthn the dashed lne act as a controlled sorce. The second part s the reference sgnal generator that generates the crrent reference sgnal for the controlled crrent sorce accordng to the msson of the partclar shnt connected VSC. Ths an approprate reference sgnal generator can enable the VSC to operate as a compensator by extractng the desred components of the crrent n an approprate manner [3-11]. It wll also nclde a voltage reference sb-system when the VSC operates as a solated mcrogrd spply. A hgher level or system control may or may not be present. In the general control strctre consdered here a hgher level control s assmed that selects the partclar crrent components present n the AC lnes of the VSC and determnes how dtes are dstrbted among mltple compensators. RZEGLĄD ELEKTROTECHNICZNY ISSN R. 91 NR 6/

2 Types of Dstrbted Compensaton In the broadest sense dstrbted compensaton means tlzaton of two or more power electronc devces wth compensaton fnctons that are coordnated n order to acheve an overall compensaton objectve. Two man types are dstrbted grd connected compensators and dstrbted solated mcrogrd compensators. In addton they may be co-located compensators or network dstrbted compensators. a. Co-located compensators Co-located compensators are connected at the same cross secton of the dstrbton system as shown n Fg 2. Ths confgraton s sed when t s not desrable to tlze a sngle compensator to generate all compensatng crrent components. Crrent components at the fndamental freqency are typcally mch larger than harmonc components. Therefore low freqency swtchng power electronc converters may be sed for the lower freqency components of the crrent whle hgh freqency swtchng converters wth lower ratng may be sed for hgh freqency component compensaton. Some compensators for fndamental freqency components may generate harmonc components f they are composed of thyrstor based crcts. In that case the hgh freqency compensator shold be located on the sorce sde of the thyrstor based compensator n order to elmnate compensator generated as well as load generated harmoncs. Also larger capacty energy storage may be reqred for some compensaton goals f actve crrent s needed. j j j n Fg 4. In ths confgraton the converters are not only compensators bt also they are the spples and provde the sorce of voltage. In ths confgraton compensaton means that each converter shares non-actve crrents reqred by the loads n sch a way that voltage at the load bs s mantaned accordng to a desred power qalty target. Fgre 4. Dstrbted solated mcrogrd compensators Compensaton objectves The desred form of compensaton depends pon the objectves. Some common objectves are: 1. Sorce crrent shold have a mnmm RMS vale 2. Sorce crrent shold be snsodal and may also be reqred to have a partclar phase and degree of symmetry 3. Bs voltage shold be snsodal and may also be reqred to have a partclar degree of symmetry 4. Instantaneos actve power at the spply shold be constant Here both voltage and crrent are consdered to be dstorted and asymmetrcal. The crrents and voltages measred wth respect to an artfcal zero may be expressed n vector form as (1) Rn Rn Sn Sn nn nn Tn Tn where N s the set of voltage and crrent harmoncs ncldng the fndamental. Fgre 2. Co-located grd connected compensators b. Dstrbted grd connected compensators Dstrbted grd connected compensators are connected at dfferent dstrbton system bsses as depcted n Fg 3. In ths confgraton the man grd s the sorce of voltage and each compensator operates as a controlled crrent sorce. A control method s needed to determne sharng of the crrent components njected or drawn by the compensators. Fgre 3. Dstrbtted grd connected compensators c. Dstrbted solated mcrogrd compensators Dstrbted solated mcrogrd compensators are connected at dfferent dstrbton system bses as depcted N (2) 1 1 where 1 s the fndamental postve seqence snsodal voltage vector 1 N s the fndamental negatve seqence snsodal voltage vector and h s the dstored component of the voltage. Under the condton that the spply voltage s non-snsodal and/or asymmetrcal the compensaton goals cannot be smltaneosly met. The tradeoff between varos compensaton optons are best descrbed n the freqency doman. The CC theory developed n the freqency doman by Czarneck [14-16] s based on orthogonal decomposton of the crrent. For each harmonc the theory decomposes the crrent nto actve scattered reactve and nbalanced components. In order to perform ths decomposton the load s expressed n terms of two admttances for any harmonc freqency the eqvalent admttance and the nbalanced admttance. The eqvalent admttance of the fndamental s expressed as (3) Ye1 Ge1 jbe1 YRS1YST1Y TR1 where G e1 and B e1 are the eqvalent condctance and eqvalent ssceptance respectvely. The nbalanced postve seqence admttance of the fndamental s h 182 RZEGLĄD ELEKTROTECHNICZNY ISSN R. 91 NR 6/2015

3 j (4) 1 A1 A1 e ( YST1YTR1 Y RS1) relatng components of the nbalanced load crrent to the spply postve seqence voltage and nbalanced negatve seqence admttance s N N j (5) 1 A1 A1 e ( YST1 YTR1Y RS1) relatng components of the nbalanced load crrent to the spply negatve seqence voltage where =1e j120 and =1e -j120. In the case of asymmetrcal spply voltage and nbalanced load an addtonal eqvalent admttance referred to as the asymmetry dependent admttance [15] has a non-zero vale eqal to Yd1 Gd1 jbd1 (6) Ye1- Y ST1UR1+YTR1US1 YRS1UT1 2 Assmng that the spply voltage s symmetrcal then Y d1 s zero and the three-phase crrent vector of the fndamental can be decomposed nto mtally orthogonal components as (7) a r1s11 h where a s the actve component of the crrent and the fndamental actve component of the crrent s j t a1 e1 R1 S1 T1 e (8) 2Re G U U U 1 the fndamental reactve component of the crrent s j t r1 e1 R1 S1 T1 e (9) 2Re jb U U U 1 and the fndamental nbalanced component of the crrent s j 1t 1 1 R1 T1 S1 e (10) 2Re A U U U h s the lmped harmonc components of the crrent and s1 s the fndamental component of the scattered crrent eqal to T j t s1 Ge1 Ge R1 S1 T1 e (11) 2Re ( ) U U U 1. A compensatng crrent can be based on ths decomposton. If only the crrent components at the fndamental are compted then the compensatng crrent s expressed as (12) j r11h r11 ( a1r1 1) where the harmonc components of the crrent are determned by sbtractng the fndamental components. In ths case the spply crrent after compensaton s eqal to (13) j a1 a sn an nn nn where N h denotes the set of orders n wthot the fndamental. Only the eqvalent condctance of the fndamental s compted and not the eqvalent condctance. Therefore f voltage dstorton s not redced h. to zero by the compensaton of the harmonc components of the crrent then the spply crrent RMS vale wll always be hgher than ts mnmm. However the spply crrent wll be snsodal. If the scattered crrents are compted then the spply crrent RMS vale can be mnmzed however some dstorton wll reman snce the actve crrent a s not snsodal. Althogh compensatng all seless components of the crrent s deal t s often desrable to target a sb-set of the possble components of the crrent de to power electronc converter power and swtchng speed lmtatons etc. Frthermore the compensaton objectves may vary over tme. An example of a swtchng compensator reference sgnal [10] for varable compensaton objectves and snsodal spply crrent s the lnear form (14) j K K K K aa1 rr1 1 hh c where K a K r K and K h are scalng coeffcents of the actve reactve nbalanced and harmonc components respectvely. The fnal term n the expresson s the swtchng compensator actve power whch s needed to actve mantan power balance as well as to spply power to the compensator de to losses. Dependng on the compensaton goals and power components present n the system the compensator actve crrent may also consst of actve power at harmonc freqences or negatve seqence. In the case that the spply voltage s asymmetrcal then the fndamental nbalanced crrent s composed of both postve and negatve seqence components (15) and (16) 1 A1 U U U 2Re e Y d1 U U U R1 S1 T1 R1 T1 S1 j 1t N N N N A1 N U U U R1 T1 S1 j 2Re 1t e 1 N N N Y d1 U U U R1 S1 T1 where the asymmetry dependent admttance Y d1 removes the porton of opposte seqence crrent that occrs de to spply asymmetry for the balanced eqvalent load. The reference sgnal wll take on dfferent forms dependng on the goals of compensaton and whether t s expressed n the tme doman freqency doman or both. Generaton of reference sgnals Whether a reference sgnal generaton method s based on a tme-doman or freqency doman approach the basc elements are the same. ower or crrent components present at a measrement pont are determned followed by extracton of selected sbsets of those components. Fnally a compensaton command sgnal s constrcted from the selected sbset. Compensator control n the freqency doman based on (14) can be acheved n ether the synchronos or statonary reference frames. In ether case an effcent recrsve dscrete Forer Transform (RDFT) algorthm [10-11] for comptng components of the measred qanttes and a crrent decomposton algorthm sed to provde separate control of orthogonal crrent components s reqred. In the case that the spply s asymmetrcal voltage seqence mst be separated n order for the nbalanced RZEGLĄD ELEKTROTECHNICZNY ISSN R. 91 NR 6/

4 crrent n (7) to have meanng. In order for the converter to nject or draw balanced crrents only postve-seqence voltage s sed by the reference sgnal generator. To extract the postve seqence component the RDFT can be taken for each phase qantty wth respect to the axs of that phase so that real and magnary parts are eqal to (17) Re{ X } Re{ X } xc x C Im{ X } Im{ X } xs x S 1 k 1 k1 k k kn k 1 k 1 k1 k k kn k where C k and S k for each phase are gven by CkR CkS CkT cos( gk ) (18) T 1 SkR SkS SkT sn( gk ) (19) T 1 and (20) T. Otpts of the RDFT wth respect to ths modfed reference system are denoted by wth a sperscrpt β. Then the CRMS vale of the postve seqence component of the spply voltage fndamental s gven by (21) (22) 1 Re{ U } Re{ U R} Re{ U S} Re{ U T} 3 1 Im{ U } Im{ U R} Im{ U S} Im{ U T}. 3 Ths s smlar to the approach gven n [12] except that there a recrsve bandpass flter s sed to extract the fndamental. Smply changng the sgn of the terms n (20) wll yeld the negatve seqence component. Calclatng the CRMS vales of the measred voltages and crrents sng a RDFT ther rato can be nterpreted as admttances for the fndamental freqency. The vale of these admttances can change as the RDFT movng wndow advances. Therefore the admttances are consdered as tme varyng qanttes and the two necessary admttances are referred to as tme varyng admttances of an eqvalent load. They are calclated by (23) Y I R I S TR ST U Y U. RT ST Havng these two admttances the tme varyng eqvalent admttance s gven by Y G jb Y Y (24) e e e ST TR and the tme varyng nbalanced admttance postve seqence component s gven by j (25) A A e ( Y Y ) ST etc. In ths manner any needed tme varyng versons of the fcttos admttances needed for decomposton of crrent components can be generated. a. references for grd connected compensators Grd connected compensators whether co-located or dstrbted connected as shown n Fg. 2 and Fg. 3 act as crrent sorces. Ther man dfference s n the method for determnng how dtes are shared among the compensators. For co-located compensators n order to provde flexblty of the compensaton objectves among the compensators the crrent control reference sgnal for each one can be expressed as the lnear form gven n (14). Snce the compensators are co-located a central control can determne sharng among each by settng the scalng coeffcents. In the case that the spply s asymmetrcal voltage seqence mst be separated n order for nbalanced crrent to have meanng. If the compensaton goal s snsodal balanced crrent on the spply sde of the compensator only postve-seqence voltage s sed by the reference sgnal generator. Ths actve component of the converter Ca s eqal to (26) Ca TR sc N a1 N 1 an n nnh 2 1 where sc are losses of the converter. Sperscrpts and N denote postve and negatve seqences respectvely. Actve component of the converter s adjsted by the DC bs voltage control as needed to satsfy the power balance. 1 Fgre 5. General crrent reference sgnal generator n the statonary reference frame. 184 RZEGLĄD ELEKTROTECHNICZNY ISSN R. 91 NR 6/2015

5 K a K Kr K h 1 j a j r U 1 j a1 U 1 1 j M sn 1g t cos 1g t U 1 A 1 Y d1 j h A1 U 1 Yd1 R h 1 j r U 1 N h Fgre 6. Reference sgnal generator for stand alone mcrogrd operaton wth crrent sharng control. A smplfed block dagram of a CC reference sgnal generaton strategy to realze (14) s shown n Fg. 5. The man featre of ths archtectre s the RDFT and orthogonal crrent decomposton that provdes the crrent reference sgnals. The reference sgnal generator s comprsed of several parts: the RDFT measrement and decomposton algorthm sed for measrng the necessary voltages and crrents and decomposng them nto eqvalent and nbalanced admttances and the crrent waveform reconstrcton algorthm that transforms the freqencydoman references back to tme-doman crrent waveforms. In addton to these there are two feedback control loops assocated wth the reference sgnal generaton. These are crrent controllers that ensre the reactve and nbalanced crrents are eqal to the set-pont n the presence of any RDFT ndced phase error. The RDFT calclaton of the measred voltage can contan a phase error de to lack of synchronzaton of the RDFT wth the fndamental [17]. The same reference sgnal generator can be sed for dstrbted grd connected compensators wth the excepton of how the crrent component scalng coeffcents are sed for sharng allocaton. Commncaton based approaches to dstrbted compensaton are descrbed n [18] where nformaton based on local converter measrements mst be commncated n order to determne sharng coeffcent settngs. Often droop based approaches are sed to accomplsh sharng when commncaton lnks are not preferred [19-22]. b. references for solated mcrogrd compensators Converters sed n solated mcrogrds mst act as the sorce of voltage when dsconnected from the man grd. Therefore they act as voltage sorces and a voltage generator secton mst be added to the reference sgnal generator. The converters can stll be vewed as compensators snce n general varos components of crrent sppled by the converters shold be shared n sch a way that the power qalty at load bsses s mantaned [20]. A coordnatng control secton s added to the CC based reference generator shown n Fg. 5 along wth a voltage reglator as shown n Fg. 6. The RDFT and CC decompostons sectons are the same except that only the converter crrent needs to be measred n ths case. Coordnated control of actve and reactve crrent s performed by the se of crrent based droop control. Smlar to actve and reactve power based droop control crrent based droop can be gven as (27) (28) o s j a1 U1 Uo s j r1. In these eqatons ω 0 and U 0 are the rated vales of freqency and voltage magntde whle s ω and s are slopes of droop characterstc lnes whch are determned based on the rato of actve and reactve crrent sharng and wth consderaton of freqency and voltage lmts. Harmonc crrent sharng the harmonc component of the crrent whch s extracted based on CC power theory s mltpled by a harmonc resstance. Ths can be seen as a droop characterstc lne for harmonc sharng. The slope of ths characterstc s nversely proportonal to the amont of harmonc crrent generated by the converter and can be adjsted by the harmonc sharng factor K h. Unbalanced loadng may be present and the nbalanced crrent shold be shared between the converters n sch a way that voltage asymmetry at the load bsses s redced. A method s developed [21] whch s based on settng the negatve seqence voltage to compensate a part of the negatve seqence crrent prodced by postve seqence voltage that occrs drng nbalanced loadng. The amont of ths part depends on the share of converter for nbalanced crrent generaton. As mentoned above nbalanced crrent of an asymmetrcally sppled load n terms of CC power theory has two conter-rotatng parts. One s wth respect to postve seqence voltage and the other wth respect to negatve seqence voltage. Here the calclaton s formed to share the negatve seqence part of the nbalance crrent as N 1 (29) U1 A U1 Y d1 Smlatons for a system n the confgraton of Fg. 4 were performed to valdate the reference generator shown n Fg. 6. It was assmed that de to dfferent ratngs of the power converters sharng of varos components of the load crrent shold be n dfferent proportons. De to smaller capacty of the energy spply as well as a smaller converter ratng VSC 1 s able to generate half as mch actve and reactve power as VSC 2. Unbalanced crrent also s consdered to be shared between the two converters wth RZEGLĄD ELEKTROTECHNICZNY ISSN R. 91 NR 6/

6 proporton to half for VSC 1 wth respect to VSC 2. Snce harmonc crrents shold be mch less than fndamental crrent components VSC 1 s tasked to generate twce as mch harmonc crrent as VSC 2. Fgres and 10 show actve reactve harmonc and nbalance crrent sharng between the two sorces both wth and wthot the nbalanced and harmonc generatng loads. There s a constant balanced load n the grd and an nbalanced and a harmonc generatng load are swtched on at t=1s and swtched off at t=2s. It can be seen that crrent components are shared between the two sorces wth the predefned sharng factors. Coordnated control of the demanded crrent among converters n an atonomos mcrogrd provdes a mechansm for optmzaton of the mcrogrd operaton. Capabltes of nterface power converters n provdng each component of crrent may vary de to the avalablty of prmary sorces sch as photo or wnd converter ratng converter strctre and swtchng freqency of the converter. A reference sgnal generaton method that allows ndependent control of load crrent components to be shared among sorces n a mcrogrd was presented. Fgre 10. Unbalance crrent sharng between two converters. Fgre 7. Actve crrent sharng between two converters. Fgre 8. Reactve crrent sharng between two converters. Fgre 9. Harmonc crrent sharng between two converters. Conclsons The applcablty of a partclar reference generaton technqe to swtchng compensator control depends on the goals of compensaton as well as expected system condtons. For the case of non-snsodal and asymmetrcal spply condtons the extracton of postve seqence voltage fndamental s needed. REFERENCES [1] Czarneck L. S. earce S. E. Compensaton Objectves and CC Based Generaton of Reference Sgnals for Shnt Swtchng Compensator Control IET Trans. ower Electroncs March (2008). [2] Bso S. Malesan L. Mattavell. Comparson of Crrent Control Technqes for Actve Flter Applcatons IEEE Trans. On Indstal Electroncs Vol. 45 (1998) No [3] M. Dolen R. D. Lorenz An Indstrally Usefl Means for Decomposton and Dfferentaton of Harmonc Components of erodc Waveforms IEEE Indstry Applcatons Conference Vol pp October [4] Maza Ortega J. M. et al. Reference Crrent Comptaton Methods for Actve ower Flters: Accracy Assessment n the Freqency Doman IEEE Trans. ower Electroncs Vol. 20 (2005) No [5] S. Rechka E. Ngand J. X. Scard A Comparatve Stdy of Harmonc Detecton Algorthms for Actve Flters and Hybrd Actve Flters roceedngs of IEEE 33rd ower Electroncs Specalst Conference Vol Jne 2002 pp [6] Bso S. Malesan L. Mattavell. Comparson of Crrent Control Technqes for Actve Flter Applcatons IEEE Trans. On Indstal Electroncs Vol. 45 (1998) No [7] Asmnoae L. Blaabjerg F. Hansen S. Evalaton of harmonc detecton methods for actve power flter applcatons Twenteth Annal IEEE Appled ower Electroncs Conference and Exposton (2005) Vol [8] Frlt A. Crrent s hyscal Components Theory and p-q ower Theory n the Control of the Three-phase Shnt Actve ower Flter Electrcal ower Qalty and Utlsaton Jonal Volme XIII (2007) Nmber [9] Konstantn Borsov Herbert L. Gnn III Mltfnctonal VSC Based on a Novel Fortesce Reference Sgnal Generator IEEE Transactons on Indstral Electroncs Vol. 57 No pp [10] H. Gnn G. Chen Flexble Actve Compensator Control for Varable Compensaton Objectves IEEE Trans. on ower Electroncs Vol. 23 Isse 6 Nov pp [11] Herbert L. Gnn Gangda Chen CC based converter control for systems wth non-deal spply voltage rzeglad Elecktrotechnczny (Electrcal Revew) Vol. 87 Jan pp [12] T. Ln and A. Domjan" Recrsve Algorthm for Real-Tme Measrement of Electrcal Varables n ower Systems" IEEE 186 RZEGLĄD ELEKTROTECHNICZNY ISSN R. 91 NR 6/2015

7 Trans On ower Delvery Volme 21 No. 1 Jan pp [13] Gnn H. L. III A Hybrd Reference Sgnal Generator for Actve Compensators Electrcal ower Qalty and Utlsaton Jonal Volme XIII (2007) Nmber [14] Czarneck L. S. ower Theory of Electrcal Crcts wth Qas-erodc Waveforms of Voltages and Crrents ETE Vol. 6 (1996) No. 5. [15] Czarneck L. S. Orthogonal decomposton of the crrent n a three-phase nonlnear asymmetrcal crct wth non-snsodal voltage IEEE Trans. Instrm. Meas. Vol. IM-37 (1988) [16] Czarneck L.S. owers of Asymmetrcally Sppled Loads n Terms of the CC ower Theory Electrcal ower Qalty and Utlsaton Jornal Vol.XIII nº pp [17] Gnn H.L. "Control method for grd-connected converters n systems wth non-deal spply voltage" roceedngs of Appled Measrements for ower Systems (AMS) 2011 IEEE Internatonal Workshop on 2011 age(s): [18] Bengn A. Gnn H.L. Lowen A. onc F. Mont A. An embedded solton for mlt-agent control of EBB based power electronc systems Intellgent Energy Systems (IWIES) 2014 IEEE Internatonal Workshop on pp [19] o-ta Cheng; Tzng-Ln Lee "Dstrbted Actve Flter Systems (DAFSs): A New Approach to ower System Harmoncs" Indstry Applcatons IEEE Transactons on vol.42 no.5 pp Sept.-Oct [20] Tzng-Ln Lee o-ta Cheng "Desgn of a New Cooperatve Harmonc Flterng Strategy for Dstrbted Generaton Interface Converters n an Islandng Network" IEEE Transacton on power electroncs vol. 22 pp September [21] Gholamreza Dehnav Herbert L. Gnn III Concrrent Dstrbted Control of all ower Components n an Atonomos Mcrogrd IEEE ower & Energy Socety General Meetng [22] Gholamreza Dehnav Herbert L. Gnn III Dstrbted Control of Orthogonal Crrent Components among Converters n an Atonomos Mcrogrd IEEE Energy Converson Congress & Exposton Athor: dr nż. Herbert Gnn Unversty of Soth Carolna Dept. of Electrcal Engneerng Swearngen Engneerng Center 3A30 Colmba SC U.S.A E-mal: gnnhl@cec.sc.ed RZEGLĄD ELEKTROTECHNICZNY ISSN R. 91 NR 6/