Micro-grid Control of PV -Wind-Diesel Hybrid System with Islanded and Grid Connected Operations

Transcription

1 EEE CSET Dec 2010, Kandy, Sri Lanka Micrgrid Cntrl f PV WindDiesel Hybrid System with slanded and Grid Cnnected Operatins A. Arulampalam Department f Electrical and Electrnic Engineering, University f Peradeniya, Sri Lanka atpu@ee.pdn.ac.lk N. Mithulananthan, R.C. Bansal, T.K. Saba Schl f nfrmatin Technlgy & Electrical Engineering, The University f Queensland, Australia mithulan@itee.ug.edu.au, bansal@itee.ug.edu.au, saha@itee.ug.edu.au AbstractThis paper discusses mdeling f a micrgrid with PVWindDiesel generatr hybrid system and its peratins. The PV system is mdeled with a DC/AC inverter with a predefined Maximum Pwer Pint Tracking (MPPT) cntrl. Fixed speed inductin generatr based wind turbines are used t mdel the wind farm. The diesel generatr cntrls are mdeled with drp gvernr and autmatic vltage regulatr (A VR). The PV inverter cntrls, including MPPT and vltage drp, are mdeled in the DC/AC inverter itself. The prpsed MPPT cntrl is mre stable with additinal input f PV cell temperature. The cmplete system is mdeled in PSCADEMTDC sftware. Perfrmance f this system is studied n (i) fault tripping f the main grid and (ii) islanded peratin f micrgrid with intermittent pwer frm the wind and PV plants. The simulatin results cnfirm the smth peratins f the prpsed cncept fr disturbances frm main grid as well as due t the intermittent wind and PV renewable pwer plants. Keywrds PVwinddiesel hybrid system, PV plant cntrls, drp cntrl, maximum pwer pint tracking cntrl, islanded and grid cnnected peratins.. NTRODUCTON The renewable pwer plants are mstly implemented in rural areas as they cver large grund surface. The rural areas are far away frm the main grid netwrk and cnnectin is pssible thrugh a weak transmissin line. The cncept f Micrgrid (MG) is prpsed as effective slutin fr such weak systems [1]. The peratin can be smthened by the hybrid generatin technlgies while mmlmlzmg the disturbances due t intermittent nature f energy frm PV and Wind generatin. Als pwer exchange is pssible with the main grid when excess/shrtage ccurrs in the MG. A MG cncept with hybrid peratin f generatrs is studied in this paper. A mdel is develped t study the peratins f integrated PVWindDiesel generatrs in a MG. Simplified active and reactive pwer cntrllers are develped t the PV inverter and diesel generatr. Finally the system's peratins are studied with grid cnnected and islanding mdes with intermittent pwer frm renewable plants. This paper includes detailed discussins n (i) literature review, (ii) MG circuit cnfiguratin, (iii) active and reactive pwer f the PV systems and diesel generatr and (iv) simulatin results. The simulatin results cnfirm the smth peratins with prpsed cntrller f the MG.. EXSTNG MCROGRD TECHNOLOGES Micrgrid is defined as a cluster (typically tw t three) f DG units and lads which perates in a crdinated and independent manner as a single entity that can be integrated int a distributin system r standalne system. n a mre advanced MG, energy strages such as super capacitrs, super cnducting magnetic energy strage (SMES), Flywheel and batteries are als integrated alng with generating units and lads [1]. MG appears t the main grid as a single lad r surce depending n whether lad is higher than the generating surces in the area. MG architecture ensures that it fllws grid and/r distributin cdes and des n harm t existing cnsumers and the rest f the grid. MG cncept will allw a higher penetratin f renewable energy in the frm f DG units withut requiring redesign and reengineering f distributin system. Hwever, cntrl aspect f MG is critical fr allwing maximum penetratin f desirable energy withut hampering the grid integrity. Pwer cntrl strategies f a grid cnnected hybrid system r MG fr versatile pwer transfer have been prpsed in [2]. The hybrid system includes PV array, Wind turbine and battery strage alng with cmmn DC bus and the versatile pwer transfer is defined as multimde f peratin, including nrmal peratin withut battery strage, pwer dispatching and "pwer averaging". A supervisry cntrl that regulates pwer generatin f generating elements has been used fr the hybrid system t perate in the varius peratin mdes and a hysteresis cntrl strategy was applied in the cnverter f battery. An interesting study f a standalne PVWind hybrid system has been reprted in [3]. n this wrk, as the hybrid system cannt always prvide stable utput with weather cnditins, an auxiliary generatin apparatus that uses elastic f energy is used t frm energy strage. Rtary energy in the spring was used t pwer a small scale generatr. Hwever, the auxiliary generatr utput was limited t a maximum f 240 W. Relatively larger WindPV hybrid generatin system design, experimental as well as simulatin results have been presented in [4]. A cntrller which includes PWM chpping technlgy in charging cntrl f batteries used in the wind PV hybrid system. This cntrl perates the system at maximum pwer pint. Further cnstant vltage and limited current lps cntrl f battery charge and SPWM cnversin with frnt end high frequency DC t DC mdel tgether with The authrs wuld like t thank the Australian Research Cuncil (ARC) discvery grant scheme, the University f Queensland, Australia and the University f Peradeniya, Sri Lanka fr their supprts t cnduct this research wrk /10/$ EEE

2 special micrchip cntrl, are als used hybrid system. in 1 kw t 5 kw f. PROPOSED MCROGRD FOR HYBRD GENERA TrONS Anther standalne PV Diesel hybrid generatin system fr a small island has been presented in [5]. The hybrid generatin that cnsists f 750 kw f phtvltaic pwer and 300 kw f diesel pwer as auxiliary surce was designed t supply pwer t private huses in the island and far away frm utility distributin grid. Thugh this is a practical wrk, the cntrl aspect and maximizing the PV yield and strage facilities have nt been discussed. Reference [] reprted a 500 W hybrid system that cnsists f PV and fuel cell. An electrlysed cuple t the PV array is emplyed fr hydrgen prductin in this hybrid cnfiguratin. A cntrller is designed t ensure cntinuus and cnstant pwer generatin thrughut day and night via the cmbinatin f PV and fuel stack. The details f the cntrller were nt presented in the wrk. A standalne PVWind hybrid system fr a small scale applicatin with a cntrller MPPT f bth PV and Wind system is discussed in [7]. The wind energy generatin system is based n variable speed wind turbine. The MPPT cntrller is based n terminal vltage r current accrding t the pen circuit vltage r shrt circuit current and the cntrl relatinship f the turbine speed and dclink vltage that was btained using simple calculatins. t is imprtant t nte that the cntrller was implemented withut measuring the envirnmental cnditins such as irradiance and wind speed. Pwer fluctuatin in the standalne MG architecture has been suppressed using battery strage. The issues relating t sizing and cntrl f battery strage culd be identified as the drawback f the paper. A variable structure cntrller t regulate utput pwer f a standalne hybrid generating systems cnsists f PV Wind and battery bank strage is presented in [8]. The cntrl presented in the paper admits tw mdes f peratins. The first mde takes place when the islatin regime is sufficient t satisry pwer demand. The secnd mde f peratin takes place under insufficient inslatin regimes which leads the system peratins at the maximum pwer perating pint. Reference [9] presented pwer cntrl f a gridcnnected hybrid generating system which cnsists f PV, Wind and Battery strage. The prpsed system has reprted several mdes f peratins similar t what is presented in [2]. Thugh the MG cnfiguratin has been verified with test results, the hybrid system is relatively small and the islanded mde f peratin is nt cvered in the wrk. Based n the abve, in this paper relatively large MG, in few MW range, with PVWindDiesel hybrid system has been prpsed. The PV system is mdelled with predefined MPPT. While the wind energy system is mdelled as fixed speed inductin generatr, the Diesel generatr cntrls are mdelled with drp gvernr and A YR. The MG architecture prpsed has been analysed fr bth grid cnnected as well as islanded peratins. Equivalent :/1 t the Main Grid (MG) generatr ( MW) Diesel generatr (5.MW) Figure. Micrgrid netwrk used t study the hybrid peratin f the PV WindDiesel generatin. Table Netwrk parameters Lad and PFC at the related busbars, Parameters Details Values Psitive sequence resistance Psitive sequence reactance 0.30 Netwrk Zer sequence resistance 0.27 parameters Zer sequence reactance (hmslkm) Psitive sequence charging admittance 3.82 Zer sequence charging admittance At Bus 1 4.5,3 lad At Bus 2,4.5 (MW, MVAr) At Bus 3 3,1.5 At Bus 1 3 PFC At Bus 2 4 (MVAr) At Bus Figure 1 shws simple MG t study the hybrid peratin f the PVWindDiesel generatins. The diesel generatr is engaged with Autmatic Vltage Regulatr (A VR) and gvernr drpcntrl. The A VR maintains the vltage at bus 2. The wind generatr is a fixed speed inductin generatr and its input trque is applied with fluctuatin t reflect the intermittent nature f wind speed. The PV system is designed with DClAC full inverter mdel. The inverter reactive pwer injectin is cntrlled thrugh a drp t keep Bus 3 vltage within the acceptable limit. The inverter active pwer injectin is based n DClink vltage regulatin. The PV side is mdeled as a DC current surce, which varies the current injectin based n the sun energy variatins. Lads are cnnected at all three busses. Pwer Factr crrectin Capacitr (PFC) banks are cnnected at Bus 1 and 3 t minimize reactive pwer requirement frm the netwrk thus supprts the vltages. Main grid is cnnected at Bus 1 thrugh a lng transmissin line and mdeled by a vltage surce with equivalent grid impedance. The 33 kv netwrk line parameters per km and ther lads, PFC ratings are given in Table 1.

3 V. ACTVE AND REACTVE POWER CONTROLS This sectin discusses active and reactive pwer cntrl f PVwinddiesel hybrid system. n this paper, cntrls f PV inverter and Diesel generatr are presented. Fr wind, a Fixed Speed nductin Generatr is cnsidered hence n special cntrl is described. A. Cntrl circuits f the DCAC inverter f the PV system The PV system DC/AC inverter active and reactive pwer cntrls are shwn in Figures 2 and 3. Figure 2 shws the reactive pwer cntrl, which maintains the AC terminal vltage magnitude within the acceptable limits. Here the drp cntrl is develped with a Prprtinal ntegral (P) regulatr. The P regulatr is tuned t be slw t avid any malfunctin due drp fast actin f the drp. t als maintains the steady state peratin alng the predefined vltage drp curve. VPVmeas VPVref VPVmag Figure 2. Reactive pwer cntrl f the PV inverter vltage drp cntrl. be changed t get the maximum pwer. Hwever, the DC vltage has t be varied with varying cell temperature. Therefre, the cell temperature was taken as an input t the MPPT cntrl t vary the DClink vltage reference accrdingly. This cntrl technique is very stable when cmpared t the cnventinal MPPT cntrls. This cntrl is designed t accmmdate all in ne mdule. As a result, it avids the needs f additinal DC/DC inverter mdule, which cnventinally used t keep the PV utput DC vltage at cnstant. The mdulatin index is varied accrding t the reference DClink vltage variatin t prevent any effect n the respnse f the AC terminal vltage cntrl. Here the reference vltage is used t calculate the mdulatin index. t is t slw dwn the variatin in mdulatin index cmpared t the DClink vltage regulatin. This is satisfied because the MPPT cntrl is slwer than the DClink vltage regulatin cntrl. Figure 4 shws the three phase vltage vectr Phase Lck Lp (PLL) used t btain the phase angle f the PV terminal vltage vectr (SPLd. The vltage vectr angle is added with the DClink vltage regulatr utput angle shift (Dpv) t get the inverter internal vltage vectr angle (Spv). The internal vltage vectr magnitude ( V PVmag) and the angle (Spv) are used t calculate the three phase instantaneus vltages f the PV inverter unit. The cnventinal sinetriangular Pulse Width Mdulatin (PWM) technique is used t prduce the firing pulses t the nsulated Gate Biplar Transistr (lgbt) switches f the inverter. 980 V"" 980 V B. Cntrl circuits f the diesel generatr T Mech F 50 V + Vcref 25 C 75 C VOCmeas Figure 3. Active pwer cntrl f the PV inverter DC link vltage regulatin tgether with MPPT cntrl. (Omeas TM initial Figure 5. Simple gvernr Drp cntrl f the diesel generatr. VOref QJs (50 Hz) Resettable ntegratr 2n V Omeas V Dref Figure. Simple autmatic vltage regulatr cntrl f the diesel generatr. Figure 4. Three phase vltage vectr PLL fr the PV inverter cntrl. Figure 3 shws the active pwer cntrl. The active pwer cntrl regulates the DClink vltage t the desired level. The P cntrller is tuned t be fast enugh t regulate the DClink vltage within 50 millisecnds. Here MPPT cntrl is integrated at the DClink reference vltage. The MPPT is designed t be a slw acting steady state cntrl t avid unnecessary pwer flickering. PV data sheets indicate that fr any changes in sun radiatin, the DC vltage des nt need t The diesel generatr is emplyed with a simple drp gvernr cntrl and P based A VR cntrl. Figure 5 shws drp gvernr cntrller. The purpse f the drp cntrller is t balance the lad t the generatin during slw changes either in demand r generatin. Hwever, any pwer mismatch due t fast changes will affect the energy in the magnetic field f the netwrk thus the grid vltage. Therefre, mismatch due t fast pwer variatin is addressed indirectly thrugh the A VR cntrl by adjusting the generatr terminal vltage. Simplified A VR cntrller emplyed at diesel generatr is shwn in Figure.

4 V. and directins are indicated in Figure 1. Figures 7 shws SMULATON RESULTS The netwrk with three generatr technlgies f PV, wind and diesel shwn in Figure 1 was mdeled in PSCADEMTDC variatins f pwer frm main grid, diesel generatr, lads, PV and wind pwer plants. with the cntrls discussed in Sectin. The PV cells are represented by a DC current surce injecting t the DClink f the inverter ci rcui t. A/G r l c«> /./" '_,run '"'Jiili1l 0 ",''"'"' 1.20 '''llmnllll Fgen "'U P3L FfV l l9' gna t";nnpn :g; '0 10 7"\1\ d ria A y f\ "CY \] re /\ \T.= 03L :0 (pj ntermjttl iff na mre., Tatlvll, 11.( t W rn:.,!, wasin t at Q i ' \.J\i''''''l; i = ONind 7\ fl, t.r, 1'\0' q V \111 \? \/ T \ r ntpi Tl;tt'S. f", ind speed was initiated.)1".' 1 A f'\ fj) )j '\...A..,; CEltaPJ ntermjtt nt nature t slar 'adlatlon (l fj1r f'j' T was i itiated 'V'1i '!]' V B v, ta :::J ",.. Vdc <t cr!=wind SB V am "g c QVG O F=< 00 "' D V2. V3 "ft" "ci! "'"' T V nr 1...,,.l11li.1 TW P Figure 8. Simulatin results f the prpsed system when it was perated at islanded mde. Figure 7. Simulatin results f the prpsed system when it was perated at islanded mde. The simulatins were carried ut t check the peratin f the system with prpsed cntrllers in islanding and grid cnnected mdes. The simulatin results are shwn in Figures 7 t 9 fr the islanding peratin. The measured parameters Figure 8 shws the variatins n internal vltage magnitude (Vpvmag) and phase angle (DeltaPV) f the PV inverter, DC link vltage, AC rms vltages at the netwrk bus bars and line pwer flws. The main grid was discnnected at 4 secnds. The intermittent nature was intrduced at the wind farm input trque at secnds. Then the intermittent nature was

5 intrduced at 9 secnds at the PV plant inverter DC link as current injectin. The results shw that the PV inverter DClink vltage is maintained at its set value and fluctuatin at the PV bus vltage is very small and acceptable. J S S S S Fgen D.Qa (\ n /\ 1\.. '" 1\ fl'> P' "'V b! l<;' y FfV Cl \_J \,.".,,( (1..,d "".,..4' ",',...J ';U'\ 1"'\11 'iii "' \fi "" 'l l' 'V.'l9" /' FWind Cl.QtiQ A \./ \ "" T\ 1'1!\/'\;.,...e. v V \ f v l/v V \ V "rtfv "...'" ""..,. "'. '.. ' '\./\ e'\ rv \f\ \. '\,..JE.. '".. CEtaFV L / ' 1 /"'10., 1 igj\ 'qmp 1...Jfl. V f \.f, V1 D V2 AY]} 'j ' '''f R:1fi. M '1 a' l ifi t! iii r = 'i=, i= V. CONCLUSONS A PVWindDiesel hybrid system is used in the prpsed MG. Drp vltage cntrl and DClink vltage regulatin tgether with simple predefined maximum pwer pint tractin cntrl are explained fr PV system inverter. Simple drp gvernr and AVR cntrls are discussed fr diesel generatr. Operatins f the prpsed system were studied fr islanded mde with intermittent nature f wind and PV pwer plants. The results cnfirm the smth peratin f MG. Further it prves that affects due t intermittent nature f renewable plants are minimized at the PV DClink vltage and its AC terminal vltage. REFERENCES [] R. Lasseter, A Akhil, C. Marnay, J. Stephens, J. Dagle, R. Guttrmsn, AS. Melipuls, R. Yinger and J. Et, "White paper n integratin f distributed energy resurces the CERTS MicrGrid cncept", Office f Pwer Technlgies f the US Department f Energy, Cntract DE AC037SFO0098, [2] S.K. Kim, J.H. Jen, C.H. Ch, J.B. Ahn, and S.H. Kwn, "Dynamic mdeling and cntrl f a gridcnnected hybrid generatin system with versatile pwer transfer", EEE Trans. ndustrial Electrnics, vl. 55, n. 4, April 2008, pp [3] S.J. Park, B.B. Kang, J.P. Yn,.S. Cha, and J. Y Lim, "A study n the stand,alne perating r phtvltaic/wind pwer hybrid generatin system", EEE 35 " Annual Pwer Electrnics Specialists Cnf (PESC 04), vl. 3, 20 th 25 th June 2004, pp [4] M. Meiqin, S. Jianhui, L. Chang, Z. Gurng, and Z. Yuzhu, "Cntrller fr kw5kw windslar hybrid generatin systems", Prc. Canadian Cnf Electrical and Cmputer Engineering (CCECE 2008), 4 th 7 th May 2008, pp [5] T. Tadkr, K. Taira, and M. Asaka, "A phtvltaicdiesel hybrid generatin system fr small islands", Prc. 24 t h EEE Phtvltaic Specialists Cnf, vl., 5 th 9 th Dec. 1994, pp [] F. Valenciaga and P. F. Pulestn, "Supervisr cntrl fr a standalne hybrid generatin system using wind and phtvltaic energy", EEE Trans. Energy Cnversin, vl. 20, n. 2, June 2005, pp [7] H.J. Chi, S.J. Park, J.S. Chi,.S. Cha, J. P. Yn, J.S. Suh, and S. d Gun, "An analysis f PEMFC & phtvltaic 500W hybrid system", Prc. 7 " nt. Cnf n Pwer Electrnics (CPE '07), 22 "" 2 th Oct. 2007, pp [8] N.A Ahmed and M. Miyatake, "A standalne hybrid generatin system cmbining slar phtvltaic and wind turbine with simple maximum pwer pint tracking cntrl", Prc. EEE 5th nt. Cnt n Pwer Electrnics and Mtin Cntrl (PEMC 200), vl. 1,14 1 th Au g. 200, pp. 7. [9] F. Valenciaga, P. F. Pulestn, and P.E. Battaitt, "Pwer cntrl f a phtvltaic array in a hybrid electric generatin system using sliding mde techniques", lee Prc. Cntrl Thery and Applicatins, vl. 148, n., Nv. 2001, pp Figure 9. Steady state simulatin results f the prpsed system when it was perated at islanded mde with all intermittent nature inputs. Figure 9 shws imprtant wavefrms at steady state peratin f the islanded system. Here all the intermittent nature inputs are engaged. This cnfirms that the prpsed cntrl maintains the DClink vltage at its set value while minimizes the effect n PV AC terminal vltage. The grid cnnected perfrmance was better than this.