SOLAR POWERED SWITCHING DC POWER SUPPLY

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1 3 r Internatonal onference on Energy Systems an Technologes 6 9 Feb. 5, aro, Egypt SOAR POWERED SWITHING D POWER SUPPY Mohame Ahme Azab enter For Renewable Energy - Yanbu Research enter, olleges an Insttutes Sector,Royal ommson-yanbu, KSA azabm@rcyc.eu.sa, pe_bht@yahoo.com The objecte of ths paper s to stuy an nestgate a PV powere swtchng c power supply base on SEPI conerter whch can be employe n seeral applcatons n ar regons such as water pumpng systems an battery chargng systems n ar regons foun n Mle East. The output oltage of the solar powere SEPI conerter s well controlle to the esre alue usng two feeback control loops; an outer oltage control loop s employe to regulate the loa oltage, an an nner current control loop to lmt the swtch current to a safe alue. The parameters of both oltage an current PID controllers are off-lne etermne by partcle swarm technque. The performance of the swtchng conerter s stue uner fferent operatng contons nclung nput oltage araton, loa araton an also for step change n the reference loa oltage. Both smulaton an expermental results proe the effecteness of the nestgate system to control an regulate the loa oltage to the esre alue. Keywors: photooltac, swtchng regulator, p controller, partcle swarm.. INTRODUTION Solar powere systems hae gane great nterest n recent years n Mle East countres owng to the conserable hgh leel of solar rraance fallng on such regon most the year. Eently, the accumulate an ncreasng utlzaton of such systems can enhance the efforts of enronment reserng an protecton. Salent applcatons of such renewable energy systems are battery chargng an water pumpng systems. Bascally, power electronc conerters an ther control unts are the core of such systems. Among seeral swtchng conerters, the SEPI topology s preferre n eelopng such systems owng to ts merts of non-nertng polarty, easy-to re the power swtch, an low nput-current pulsatng []. Snce the SEPI conerter proes both step own or step up operaton epenng on the uty cycle of the swtch control sgnal, ths feature wens ts applcaton an ntegraton wth PV systems where the output oltage from the PV s a aryng c source relate to solar rraance, ambent temperature, an the loang pont tself. Accorng to seeral lteratures, the transfer functon of the SEPI conerter s a fourth orer system wth a rght-half-plane (RHP zero n the contnuous conucton moe that shoul be compensate [,3,4]. Unfortunately, gans etermnaton of the PID controllers of such non-lnear power electronc conerters wth conentonal methos ether woul lea to unsatsfactory performance or een unstable operaton.

2 In aton, the successful close loop operaton of the SEPI conerter shoul take nto conseraton the swtch current through an nner current control loop to lmt ths current to a safe alue aong a transstor falure. Therefore, eolutonary computaton technques propose to tune the PID controller n lteratures [5,6,7,8] can be employe to etermne the gans of PID controllers of such power electroncs systems. One of the powerful optmzaton technques s the partcle swarm (PSO that oes not requre complcate computatons, thus t can be mplemente n real tme wth the most aalable μ or DSP cars. In ths paper the PSO technque s utlze to etermne the optmal gans of the PID controllers to both oltage an current control of a SEPI conerter ren by a PV moule. The system s stue an teste for fferent transent an steay state operatng contons through a smulaton an an expermental prototype. Both Smulaton an expermental results emonstrate the successful operaton of the nestgate system.. MODEING OF THE SEPI ONVERTER The power crcut of the SEPI conerter s shown n Fg.. The power crcut has two separate nuctors. The nuctor smoothes the current rawn from the supply an elmnates the nee to an nput flter. In aton, the capactor connecte between the prmary nuctor an seconary nuctor offers D solaton between nput an output []. Moreoer, t elmnates the nee for a snubber crcut across the power transstor. D V n T V o - Fg. rcut agram of SEPI onerter. State Space Moel The conerter can be moele wth the state space representaton n the form: (x = Ax Bu, where: x s chosen to be nuctor current, x s chosen to be nuctor current, x 3 s chosen to be capactor oltage V, an x 4 s chosen to be capactor oltage V. When the transstor s turne ON for the uraton (T on = T swt the state space moel takes the form (x = A xb u presente n equaton ( where s the uty cycle, T swt s the swtchng pero, an u s the nput oltage V n.

3 V n = R ( When the power transstor s turne OFF for the rest of the swtchng pero (T off = [-] T swt the state space moel has the form (x = A xb u presente n equaton (: V n = R ( Equatons ( an ( can be combne together to complete the state space representaton of the SEPI conerter urng the whole swtchng pero, where A matrx an B matrx are compute base on the followng relatons: A = A (- A (3 B = B (- B (4 Therefore, the A matrx becomes : ( ( ( ( ( ( = R A Whle the B matrx becomes : = B (5

4 3. DESRIPTION OF THE INVESTIGATED SYSTEM The block agram of the nestgate system s shown n Fg., where a SEPI conerter s supple from a PV moule. The SEPI conerter s controlle a oltage an current control loops usng analog PI controllers wth lmte outputs an ant saturaton ntegrators. The gans of PI controllers are compute OFF-ne wth the a of partcle swarm optmzaton program as explane later n secton 4. The PWM unt generates the swtch control sgnal of arable uty cycle. PV SEPI ONVERTER O A D Swtchng control sgnal U control PWM unt PID - SWT - PID V V o V ref Fg. Block agram of the nestgate system 4. PID TUNING WITH PARTIE SWARM 4. PSO oncept PSO s one of eolutonary computaton technques where t s nspre by socal behaor of br flockng or fsh schoolng. It s apple effcently n solng nonlnear problems as n [7,]. PSO algorthm s ntalze wth a group of ranom partcles (solutons, an searches for optma by upatng generatons. Each partcle n swarm represents a soluton to the problem an t s efne wth ts poston an elocty [7]. The partcles are place n a search space of a certan problem or functon. All partcles hae eloctes, whch rect the flght of the partcles. In eery teraton, each partcle s upate by two best alues. The frst one s the best soluton the partcle has achee so far. Ths alue s calle local best (. The secon best alue s the best alue obtane so far by any partcle wthn the neghborhoo. It s calle global best (G. Velocty an poston of the partcles are upate usng equatons (6 an (7 respectely: [ ( k x ( k ] c r [ G( k x ( ] ( k = w ( k c r k (6 x ( k = x ( k ( k (7 Where: w s the nerta weght factor; (k s the partcle elocty at teraton k; x (k s the partcle poston n the search space at teraton k; c an c are poste constants calle acceleraton constants; r an r ranom numbers between (,.

5 Eentually the swarm as a whole, lke a flock of brs moes close to an optmum of the ftness functon. A large alue of w faors hgher ablty for the global search, whle lower alue of w mples a hgher ablty for the local search. 4. Off-lne Tunng Algorthm The PSO algorthm has the followng major steps:. Intalzaton: In ths step, the PIDs gans (K pv, K V, K pi, K I are ntalze ranomly.. Ealuaton of the ntal soluton: where the objecte functon for all partcles n the ntal populaton s ealuate. 3. Upatng poston an elocty: The elocty an poston of the partcles are upate accorng to equatons (6 an (7. 4. Ealuaton of the upate soluton: The upate poston of partcles are ealuate accorng to ther ftness; the local best ( an global best (G partcles wll be upate. 5. Repeat the upatng process: If the termnal conton (number of teratons has not been satsfe, the upatng process wll be repeate; otherwse, the optmzaton process ens. 6. Get the fnal results: The best soluton for all PIDs gans obtane urng the optmzaton process s (G. Tunng the parameters of PID controllers s treate as an optmzaton problem to satsfy a certan performance nex. In ths paper, the performance nex s selecte to be ITAE efne by the followng equaton: J = t e( t t (8 The optmzaton metho ams to search the proper alues of (K pv, K V of oltage control loop, an K pi, K I of the current control loop that mnmze the performance nex J. Where e(t s the error sgnal. e PSO K p K V ref PI V PI I u SEPI ONVERTER V o _ - I SWT Fg. 3 Tunng system of PI controllers

6 5. SIMUATION STUDY The performance of the nestgate SEPI regulator powere from PV moule s stue uner fferent operatng contons nclung both steay state an transent performance. The smulaton parameters are summarze n Appenx. 5. Steay State Performance To nestgate the steay state performance, the esre loa oltage s ajuste to be V (buck operaton. The corresponng obtane steay state output oltage s plotte n Fg 4. The regulator s loae wth a resste loa of Ω. The results ncate that the output was well controlle to V wth small rpple oltage. In aton, the steay state boost operaton s also stue. The reference loa oltage s set to 4 V. The corresponng waeform of loa oltage s shown n Fg. 5. Accorng to the result of Fg. 5, the loa oltage (blue cure s well controlle to the esre 4 V (whte lne Fg. 4 Steay state loa oltage V ref = V, PV oltage = 9 V t [s] Fg. 5 oa oltage at steay state V ref = 4 V, PV oltage = 9 V t [s] 5. Transent Response The step change n reference sgnal an the loa regulaton ssue hae been stue. Frstly, the reference loa oltage s change from V to 4 V. The corresponng output oltage s plotte n Fg. 6. The results proe that the system offers goo transent performance. After reachng to the steay state operaton, the loa resstance s change from Ω to 5 Ω (at tme =.6 s. The corresponng response s plotte n Fg. 6. The results show that the controller succeee to return the loa oltage to the set pont (4 V although the conerter s loae.

7 t [s] Fg. 6 Transent response for both step changes n reference oltage an step change n loang resstance Fnally, the nput oltage s change n a snusoal form from 6 V up to 8 V. The esre output oltage s ajuste to V, the corresponng results of the output oltage s shown n Fg. 7. The results ncate that the SEPI regulator was able to regulate the loa oltage to the esre alue rrespecte the nput oltage araton. 4 8 V n V o Fg. 7 Transent response of the SEPI loa oltage uner we range of araton of nput oltage The smulaton results proe that the SEPI regulator succeee to satsfy all operatng contons (nput oltage araton, loa araton, an reference oltage araton, so the partcle swarm optmzaton technque s effecte to etermne the alues of PID controllers of both oltage an current loops. t [s] 6. EXPERIMENTA SET UP An expermental prototype has been mplemente to erfy the stue smulaton system. The prototype conssts of the followng parts: - 8 W PV moule (BP 38J. - SEPI power crcut forme by MOSFET transstor IRF 64, an a fast recoery oe. 3- Two Analog PI controllers wth ant saturaton capablty, an wth lmte outputs n orer to lmt the generate control oltage an consequently the uty cycle between a reasonable range (5 % - 8 %. 4- PWM unt, to generate a arable uty cycle swtch control sgnal. The swtchng frequency s khz. 5- Hall effect current transucer s use to measure the current of the MOSFET transstor. 6- Hall effect oltage transucer s use to measure the loa oltage.

8 7. EXPERIMENTA RESUTS The expermental results are e nto two major groups: steay state performance, an transent response results. 7. Steay State Performance ase : In ths case, the reference oltage s set to V. The conerter s loae wth a resstor of 7 Ω. The gans of PI controllers are set to the optmum alues obtane from the off-lne tunng process. The corresponng loa oltage s plotte n Fg. 8. Goo steay state performance s obsere. Fg. 8 Steay state loa oltage at full loa V ref = V, optmum gans, 5 /,.5 s/ ase : n ths case the steay state performance s obsere for the same operatng contons of case except that the ntegrator gan of the current controller s ncrease behn the preetermne optmum alue. So, sustane oscllatons are obsere aroun the aerage alue of V as shown n Fg. 9. Fg. 9 Steay state loa oltage at full loa V ref = V, hgh ntegrator gan, 5 /, ms/

9 7. Transent Response ase : In ths case, loa oltage regulaton s stue. The reference loa oltage s set to 4 V. The loa s perocally step change from 7 Ω to 85 Ω. The corresponng loa oltage s plotte n Fg.. At the moment of applyng the loa, the loa oltage s suenly reuce then t returne to the reference alue. Also, at the moment of reucng the loa, the loa oltage s suenly ncrease then t returne to the reference alue agan. The PV oltage was 9 V (re cure. Fg. Transent loa oltage uner loa araton V ref =4 V, 5 /,.5 s/ ase : n ths case the transent performance s obsere for step change n the reference sgnal from V to V. The PI controllers are set to the optmum alues. The result s shown n Fg.. The PV oltage s 9 V (re cure. Fg. loa oltage for step change n reference oltage from V to V, 5 /,. s/ 8. ONUSION Ths paper presente a hgh performance swtchng oltage regulator fe from a PV moule to be apple n ar zones. Both smulaton stuy an ts expermental erfcaton proe the effecteness of the propose system to control the loa oltage to the esre alue for fferent operatng contons.

10 9. REFERENES [] S. J. hang, H. J. Sheh, M.. hen, Moelng an ontrol of PV harger System Wth SEPI onerter,, IEEE Trans. on In. Electroncs, Vol. 56, No., pp , No. 9. [] A. Ezhlaras, M. Ramaswamy, A strategy for Assessng the Stablty of SEPI onerter, Int. Journal of Engneerng Scence an Technology, Vol., No. 5, pp ,. [3] A. De Naro, N. Fema, M. Ncolo, G. Petrone, S. Pagnulo, PA-base esgn of a SEPI conerter, IEEE Int. Symposum on In. Elect. onference ISIE8, pp , July 8. [4] N. Fema, F. Forrs, M. Granato, A Noel Desgn Metho to Preent SEPIs Instablty, Int. Workshop on ontrol an Moelng for Power Electroncs OMPE8, pp. -4, Aug. 8. [5] Y.B. Wang, X. Peng, B.Z.We, A New Partcle Swarm Optmzaton Base Auto-Tunng of PID ontroller, IEEE Int. onf. on Machne earnng an ybernetcs, pp , 8. [6] Donso S. Perera, GA Base System Ientfcaton an PID Tunng for Optmum Aapte ontrol, Internatonal onference on Aance Intellgent Mechatroncs, Monterey, alforna, USA, 4-8 July, pp.8~86, 5. [7] Mohame Azab, Tunng of a PID controller n a step-own oltage regulator usng partcle swarm optmzaton, Electromoton Journal, Vol. 8, No., pp.8-9, June. [8] Gang, Z.., A partcle swarm optmzaton approach for optmum esgn of PID controller n AVR system, IEEE Trans. Energy on. Vol. 9, No., pp , June4. [9] Y. Del Valle, Y. et al., Partcle swarm optmzaton: basc concepts, arants an applcatons n power systems, IEEE Transactons on Eolutonary omputaton, Aprl, Vol., No., pp. 7-95, 8. [] Mohame Azab, Harmonc Elmnaton n Three-Phase Voltage Source Inerters by Swarm Optmzaton, Korean Journal of Electrcal Engneerng an Technology JEET, Vol. 6, No. 3, pp ,. [] Mcrochp Applcaton Notes AN 6, 9. [] Vatché Vorpéran, Analyss of the Sepc onerter, [3] Ray Rley, Analyzng the Sepc onerter, Power Systems Desgns Europe, pp. 4-8, No. 6. Appenx ( Mathematcal Moel of a PV cell I = I I o (e q(v IR AkT V IR - R S sh S (a. Where: I s the cell current, I s the lght generate current (A, I o s the oe saturaton current, q s the charge of electron (coulomb, k s the Boltzmanns constant (j/k, A s the oe factor, T s the cell temperature (K, R S s cell seres resstance (Ω, R sh s cell shunt resstance (Ω, an V s the cell output oltage.

11 Appenx Table Parameters use for PSO Algorthm PSO parameter Value Swarm sze 5 Maxmum number of teratons 5 Inerta weght factor w.5 Appenx 3 Table Smulaton Parameters Parameter Value =. H = μf oa: R 5-3 Ω Soler Euler Step sze 3e-5 s Appenx 4 Table 3 Expermental Parameters Parameter Value PV moule BP 8 W Short cr. current I S 5. A Open cr. oltage V O 3 V MOSFET transstor IRF 64 oa: R 85-3 Ω =. H = 47 μf Swtchng frequency khz