Simulation and Modeling of a Five -Level (NPC) Inverter Fed by a Photovoltaic Generator and Integrated in a Hybrid Wind-PV Power System

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1 Engineering, Technology & Alied Science Reearch Vol. 7, No. 4, 07, Simulation and odeling of a Five -Level (NPC) Inverter Fed by a Photovoltaic Generator and Integrated in a Hybrid Wind-PV Power Sytem. Rezki Deartment of Electrical Engineering Faculty of Science and Alied Science Univerity of Bouira Bouira, Algeria mohamedrezki97@yahoo.fr I. Griche Deartment of Electrical Engineering Faculty of Science and Alied Science Univerity of Bouira Bouira, Algeria griche_iam@yahoo.fr Abtract A ditributed hybrid coordinated wind hotovoltaic (PV) ower ytem wa rooed in thi aer. A oil and coal reerve are being deleted whilt at the ame time the energy demand i growing, it i imortant to conider alternative energy generating technique. Today, the five-level (NPC) inverter rereent a good alternative for everal indutrial alication. To take advantage of the five-level inverter toology and the benefit of renewable energy rereented by a hotovoltaic generator, a new cheme of thee controller i rooed in thi work. Thi aer outline the deign of a hybrid ower ytem coniting of a olar hotovoltaic (PV) and a wind ower ytem. The ytem i modeled in atlab Simulink and teted for variou condition. The model and reult are dicued in thi aer. Keyword-five-level inverter; olar v; wind energy; hybrid ower ytem I. INTRODUCTION The limited reerve of foil fuel and environmental ollution have ignificantly increaed the interet in renewable energy ource. Hybrid Wind-PV ower ytem a a ditributed generation network tructure have received coniderable attention. Such a ytem ha the merit of ulying the difference in time and zone between wind ower ytem and PV ytem. Hybrid wind-pv ytem have become a romiing ower generation form, a they can imrove ower reliability in certain remote area uch a deert, lateau etc. The hybrid wind-pv generation ytem can achieve otimal erformance by deigning the rational ytem tructure and chooing the coordinated otimization algorithm [, ]. Active Power Filter (APF) i the modern olution ued to eliminate the undeired current comonent by injection comenation current in ooition to them [3]. The univeral ower converter toology ued i the two level voltage ource inverter [4-6]. Due to ower handling caabilitie of ower emiconductor, thee converter are limited to low ower alication. Princially, the deign of any APF ytem a through three eential criteria: ower inverter toology, current controller and trategy control. ulti level inverter are uccefully ued in medium and high ower alication [7, 8]. Intantaneou ower theory [9] and ynchronou reference frame detection method [0] have alo been widely ued. Thee technique rovide good reult under different voltage ource condition but reent ome drawback uch a a large calculation number, comlex mathematical tranformation and difficult ractical imlementation. The ynchronou current detection method i another intereting method. It i concie and require le comutational calculation comared to the two other method. In thi work, the ynchronou current detection technique i adoted uing a five-level (NPC) inverter after ome neceary modification. II. THE HYBRID PHOTOVOLTAIC-WIND SYSTE A chematic reentation of the rooed hybrid energy converion ytem i given in Figure. The ytem conit of the following element: a doubly fed induction generator (DFIG), a wind turbine, a PV generator and an inverter of fivelevel NPC VSI. The wind turbine convert the wind kinetic energy into mechanical energy, which i tranformed in electrical by the DFIG and tranmitted to the network. The DFIG rotor i connected to the inverter. The uroe of the multilevel converter i to yntheize a inuoidal form of the voltage with le harmonic ditortion. However, it reent a fluctuating otential of mid-oint inducing intability of it inut voltage, and then intability of it outut voltage. Different PW algorithm for the five-level NPC VSI are available with the vector modulation trategy with four biolar carrier [3, 4] to be conidered one of the bet. Fig.. PV-Wind hybrid ytem.

2 Engineering, Technology & Alied Science Reearch Vol. 7, No. 4, 07, III. HYBRID SYSTE ODELING A. odeling of the Aeroturbine The wind model ued ha been develoed at RISØ National Laboratory baed on the Kaimal ectra []. The wind eed i calculated a an average value of the fixed-oint wind eed over the whole rotor, and it take the tower hadow and the rotational turbulence into account. A main comonent in thi model i the normally ditributed white noie. Therefore, in order to obtain the ame wind time erie in all conidered imulation tool ued in the imulation latform, ome invetigation have been done. It ha been found that the builtin white noie generator from different imulation tool ue a different algorithm and thu a different wind time erie i obtained. In order to validate the new white noie generator model, ome comarion have been done. A wind time erie for 3600 ec with 0.05 ec amle time i hown in Figure. The equivalent model of a wind turbine drive train i reented in Figure 3. The mae correond to a large ma of the wind turbine rotor, mae for the gearbox wheel and a ma for generator reectively. [] Fig. 3. odel of a wind turbine drive train 4 3 Wind rofile Taking into account the tiffne and the daming factor for both haft, the dynamic equation can be written a follow: eed (m/) time () Fig.. The wind rofile. The aerodynamic model of the wind turbine (WT) rotor i baed on the torque coefficient CQ or the ower coefficientc P. The torque coefficient C Q i ued to determine the aerodynamic torque directly by uing: T wt 0.5 () 3 R V CQ ςhere i the air denity, R i the blade radiu,v i the wind eed, C Q i the torque coefficient. Alternatively, the aerodynamic torque can be determined uing the ower coefficient C baed on: P T wt 0.5 () 3 R V CP It i imortant to underline that both coefficient C P and C Q can be function of the ti eed ratio for aive-tall wind turbine or function of ti eed ratio and itch angle for active tall and variable itch/eed wind turbine. The arameter for thi model are: blade radiu, air denity, cut-in and cut-out wind eed, a hown in aendix. Uing a reduced look-u table in reect with the variation of the torque coefficient/ower coefficient with the itch angle ( 0 0 ), the model for the active-tall wind turbine i obtained. Imoing a zero value for the itch angle the model for aive tall wind turbine can be obtained. d wtr Twtr Jwtr Dwtr wtr Kwtr wtr (3) d T J DwtrKwtr wtr (4) d d T J Dgen Kgen gen (5) d gen Tgen Jgen Dgen gen Kgen gen (6) T T K gear (7) Such a: d d wtr gen di wtr, gen ; i ; i,; K gear, (8) Where: Twtr i the wind turbine torque, T i torque that goe in the gearbox, T i the torque out from the gearbox, Jwtr i the WT moment of inertia, wtr i the WT mechanical eed, K wtr i the ring contant indicating the torion tiffne of the haft on wind turbine art, T gen i the generator torque, J gen i the generator moment of inertia, gen i the generator mechanical eed, K gen i the ring contant indicating the torion tiffne of the haft on generator art. B. odeling of the DFIG Some of the machine inductance are function of the rotor eed, whereuon the coefficient of the tate-ace equation (voltage equation), which decribe the behavior of the induction machine, are time varying (excet when the rotor i at tand-till). A change of variable i often ued to reduce the comlexity of thee tate-ace equation. There are everal

3 Engineering, Technology & Alied Science Reearch Vol. 7, No. 4, 07, change of variable, which are ued but there i jut one general tranformation [8]. Thi general tranformation refer the machine variable to a frame of reference, which rotate at an arbitrary angular velocity g. In thi reference frame, the machine winding are relaced with ome equivalent winding a hown in Figure 4. Fig. 4. Induction machine winding in the dq0- reference frame The baic equation of the machine i: d V RI (9) Baed on (9) and uing the general tranformation, the voltage equation in the arbitrary reference frame can be written a: d V RI (0) The relation between the linkage fluxe and current i given by: L I () The electromagnetic torque can be obtained tarting from eq. () and multilying it from the left with the tranoe of the current vector: i t t t I V I RI I I Where: t d () t i the intantaneou ower. P t coer I RI t d P I P I V are the coer loe in the machine blade. mag i the magnetic ower tored in machine (due to the variation in time of the magnetic energy) and P t m I i the mechanical ower. The electromagnetic torque i then: Pm Pm 3 Te diq qid (3) r r With i the number of ole air and r i the mechanical eed of the rotor. ynchronou rotating eed. To achieve thi, two aroache are oible to know the direct control and indirect control [3, 4]. In thi work, the indirect control i ued. Choice of reference By chooing two axe d-q reoitory related to rotating tator field and aligning the tator flux illutration with axi d, we can write: d (4) q 0 Therefore, the torque electromagnetic of DFIG i given by: C i i (5) em d rq L And the current in the tator and rotor are: id idr L L idr iqr L The active and reactive ower are given by: (6) P V iqr L (7) V V Q idr L L In teady tate, the term involving the derivative of the two-hae rotor current diaear. We can therefore write: V R i g ( L ) i L dr r dr r qr V Vdq Rridq g ( Lr ) iqd g L L (8) Indirect vector control The indirect method i to relicate revere the block diagram of the ytem to be controlled. Thi build a block diagram for exreing the rotor voltage function and ower. The roortional-integral (PI) controller i ued to control the DFIG. C. Flux oriented control of the DFIG The rincile of the vector control require the knowledge of the exact oition of the tream to orient at all time and make it coincide with the direct axi "d" at the ame Fig. 5. Indirect control block diagram without ower loo

4 Engineering, Technology & Alied Science Reearch Vol. 7, No. 4, 07, Figure 5 how a cloed loo ytem corrected by a PI controller given in the equation: K i R( ) K (9) S where K : i the roortional gain controller and K i : i the integral controller gain. Fig. 6. Block diagram of the current control D. odeling of the PV module Among the modeling method of PV module, the two-diode model i known to be an accurate model a deicted in Figure 7 [5]. The outut current of the module can be decribed a: V IR I I PV Id (0) R Where: V IR Id I0 ex () av T And: V IR Id I0 ex () av T Where I PV i the generated current by the incidence of light; I 0 and I 0 are the reerve aturation current of diode and diode, reectively. The term I 0 i introduced to comenate for the recombination lo in the deletion region a decribed in [9]. Other variable are defined a follow: V T and V T (both equal to N kt / q ) are the thermal voltage of the PV module having N cell connected in erie, q i the 9 electron charge ( C ), k i the Boltzmann 3 contant ( J / K ) and T i the temerature of the n junction in Kelvin. The variable a and a rereent the diode ideality contant; a and a rereent the diffuion and recombination current comonent, reectively. Although greater accuracy can be achieved uing thi model than the ingle diode model [6], it require the comutation of even arameter, namely I PV, I 0, I 0, R, R, a and a. Recently, a fat and imle two-diode model i rooed in [7]. The imlified current equation i given a: V IR I I PV I0 I R (3) Where: V IR V IR I ex ex VT ( ) VT (4) And a (5) IV. FIVE -LEVEL INVERTER ultilevel inverter are being invetigated and recently ued for active filter toologie. Five-level inverter are becoming very oular today for mot inverter alication, uch a machine drive and ower factor comenator. Thee advantage are the reduction of the harmonic content generated by the active filter and the decreae the voltage or current rating of the emiconductor. Figure 8 how the circuit toology of a diode-clamed five-level inverter baed on the ix main witche (T, T, T 3, T 4, T 4, T 34 ) of the traditional two-level inverter, adding two auxiliary witche (T, T 3, T, T 3, T 3, T 33 ) and two neutral clamed diode on each bridge arm reectively. The diode are ued to make the connection with the oint of reference to obtain midoint voltage. Such tructure allow the witche to endure larger dc voltage inut on the remie of not raiing the level of their withtand voltage. oreover, take hae-a a examle, three kind of voltage level Udc/, 0 and Udc/. Fig. 7. Two-diode model of PV cell Fig. 8. Five level inverter NPC

5 Engineering, Technology & Alied Science Reearch Vol. 7, No. 4, 07, V. CASE STUDY RESULTS AND DISCUSSION Figure 9 illutrate a chematic rereentation in it mot imle form of hybrid energy converion chain. Thi chain i made u of element, which are: A doubly fed induction generator (DFIG). A wind turbine convert energy of wind into mechanical energy injected directly to the rotor of DFIG. Four hotovoltaic olar anel that rovide a DC voltage from olar energy. Each anel conit of 36 cell connected in erie. A three-hae voltage inverter with five level in NPC tructure whoe role i to convert the DC voltage of the hotovoltaic anel into an alternating voltage ulied to the tator of DFIG. The chematic model of hybrid ytem i imlemented in atlab / Simulink. Figure 0 how the erformance of the vector control and reactive ower in the tator alied to a doubly fed induction machine. Note that the active and reactive and current (ird, irq) are identified with their reference ower. Proortionality aear between the rotor current quadrature Iqr and active ower, and between direct current Idr and reactive ower. The quadrature comonent of flux i almot zero in teady tate, which confirm the hyothei of the vector control. Note the effect of couling between the two ower P and Q, becaue that Pref a (0 to -800) to (t = ) there i a mall ocillation in the grah of the reactive ower Q. It can be noted that the electromagnetic torque react ontaneouly when there i a demand for active ower, reactive ower indeendent. In addition, the voltage reone time iued by the anel i big. The voltage Va i a conequence of the inut voltage of the PV anel. We ee an aearance of rile level of the tator flux, the rotor current and the electromagnetic torque. Thi i due to the nature of the voltage of the olar anel. Figure 0 how the erformance of the vector control and reactive ower in the tator alied to a doubly fed induction machine. Note that the active and reactive and current (ird, irq) are identified with their reference ower. Proortionality aear between the rotor current quadrature Iqr and active ower, and between direct current Idr and reactive ower. The quadrature comonent of flux i almot zero in teady tate, which confirm the hyothei of the vector control. Note the effect of couling between the two ower P and Q, becaue that Pref a (0 to -800) to (t = ) there i a mall ocillation in the grah of the reactive ower Q. It can be noted that the electromagnetic torque react ontaneouly when there i a demand for active ower, reactive ower indeendent. In addition, the voltage reone time iued by the anel i big. The voltage Va i a conequence of the inut voltage of the PV anel. We ee an aearance of rile level of the tator flux, the rotor current and the electromagnetic torque. Thi i due to the nature of the voltage of the olar anel. ( a) ( b) Fig. 9. Cae tudy Fig. 0. Simulation reult without PPT and a) without and b) with vector control)

6 Engineering, Technology & Alied Science Reearch Vol. 7, No. 4, 07, VI. CONCLUSIONS A ditributed coordinated hybrid wind-pv ytem tructure baed on DFIG rereenting an iolated renewable energy ite i invetigated in thi aer. Five-level (NPC) inverter neutraloint diode clamed toology with the integration of a PV generator i rooed to rovide a great imrovement in the quality of the outut voltage. The doubly-fed induction machine for the five level inverter i flux oriented controlled in order to imrove the inverter erformance. For future work, it i recommended to examine the erformance of the rooed methodology by uing other technique uch a fuzzy logic and liding mode controller. REFERENCES [] O. Vodyakho, T. Kim, S. Kwak, Comaraion of the ace vector current control for hunt active ower filter, IET Power Electronic, Vol.,No. 6, , 009 [] U. Khruathe, S. Premrudeereechacharn, Y. Kumuwan, Imlementation of hunt active ower filter uing ource voltage and ource current detection, ICIEA 008, 3rd IEEE Conference on Indutrial Electronic and Alication, Singaore, 3-5 June 008 [3] E. E. El-Kholy, A. El-Hefnawy, H.. ahrou, Three-hae active ower baed on current controlled voltage ource inverter, Electric Power and Energy Sytem, Vol. 8, , 006 [4] N. G. Ate, V. N. Baat, A. N. Jog, A hunt active filter for reactive ower comenation and harmonic mitigation, IEEE 7 th International Conference on Power Electronic, , 008 [5] S. Bhattacharya, T. Frank, D. Divan, B. Banerjee, Active filter ytem imlementation, IEEE Tranaction on Indutry Alication, Vol. 4, No. 5, , 998 [6]. Routimo,. Salo, H. Tuua, Comaraion of voltage ource and current ource hunt active ower filter, IEEE Tranaction on Power Electronic, Vol., No., , 007 [7] O. Vodyakho, C. C. i, Three-level inverter-baed hunt active ower filter in three-hae three-wire and four-wire ytem, IEEE Tranaction on Power Electronic, Vol. 4, No. 5, , 009 [8] O. Vodyakho, D. Hacktein, A. Steimel, T. Kim, Novel direct currentace vector control for hunt active ower filter baed on three-level inverter, IEEE Tranaction on Power Electronic, Vol. 3, No. 4, , 008 [9] R. H. Herrera, P. Salemeron, H. Kim, Intantaneou reactive ower theory alied to active ower filter comenation: different aroache, aement, and exerimental reult, IEEE Tranaction on Indutrial Electronic, Vol. 55, No., , 008 [0] S. Bhattachrya, D. Divan, Synchronou frame baed controller imlementation for a hybrid erie active filter ytem, IEEE Thirtieth IAS Annual eeting Indutry Alication Conference IAS '95, Vol. 3, , 995 [] A. Shaltout, Analyi of torional torque in tarting of large quirrel cage induction motor, IEEE Tranaction on Energy Converion, Vol. 9, No.,. 35-4, 994 [] A. S. Neri, N. A. Vovo, G. B. Giannakooulo, A variable eed wind energy converion cheme for connection to weak AC ytem, IEEE Tranaction on Energy Converion, Vol. 4, No.,. -7, 999 [3] T. Petru, T. Thiringer, odeling of wind turbine for ower ytem tudie, IEEE Tranaction on Power Sytem, Vol. 7, No. 4,. 3 39, 00 [4] S. Seman, S. Kanerva, J. Niiranen, A. Arkkio, Tranient analyi of wind ower doubly fed induction generator uing couled field circuit model, 6th International Conference on Electrical achine ICE 004, Cracow, Poland, Setember 5-8, 004 [5] D. S. H. Chan, J. C. H. Phang, Analytical method for the extraction of olar-cell ingle- and double-diode model arameter from I-V characteritic, IEEE Tranaction on Electron Device, Vol. 34, No., , 987 [6] K. Ihaque, Z. Salam, H. Taheri, Simle, fat and accurate twodiode model for hotovoltaic module, Solar Energy aterial and Solar Cell, Vol. 95, No., , 0 [7] KC00GT High Efficiency ulticrytal Photovoltaic odule dataheetkyocera, available at htt:// olar/ df/kc00gt.df