A Static Var Compensator Controlled Topology Based on TCR-TSC for a Grid Connected Photovoltaic System

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1 International Conferene on Control, Engineering & Information Tehnology (CEIT 4) Proeedings - Coyright IPCO-4 ISSN A Stati Var Comensator Controlled Toology Based on TCR-TSC for a Grid Conneted Photovoltai System Salwa Akermi, Noureddine Hidouri, Lassâad Sbita akremi.salwa@gmail.om, noureddine.hidouri@yahoo.fr, lassaad.sbita@enig.rnu.tn Researh Unit of Photovoltai, Wind turbine and Geothermal Systems National Engineering Shool of Gabes, Tunisia Abstrat This aer illustrates the use of Stati Var Comensators (SVC) to ontrol the erformane of a grid onneted hotovoltai system (GCPS). The omensator onsidered in this work ontains one Thyristor Controlled Reator (TCR) and three Thyristors Swithed Caaitors (TSC), whih are two of the shunt Flexible Altering Current Transmission Systems (FACTS) devies. The roosed onfiguration inororates a hotovoltai array, a boost onverter, an inverter that generates a three hase suly that will be filtered and onneted to the grid through a ste u transformer and a non linear load. The ositive effet of the TCR and TSC-based SVC on the non linear load urrent is onfirmed by the simulations results. Keywords GCPS, TCR, TSC, Nonlinear load, SVC. I. INTRODUCTION The use of renewable energy suh as hotovoltai is the subjet of ountless studies, sine this kind of soures is nature, renewable and environmentally friend. The Grid Conneted Photovoltai System is one of the many aliations of hotovoltai areas [], [], [5]. When onneting a PV system to the grid many undesirable imats may our suh as raid hanges in ower, urrent harmonis that an ause the ollution of the grid, inluding the instability of the grid system. To solve those roblems Flexible Alternating Current Transmission Systems (FACTS) an be develoed. FACTS devies have been inreasingly used in many eletrial ower systems, this tehnology based on eletroni ower devies, an imrove the erformane of ower system by ontrolling the ative and reative ower flow and inreasing the stability of the system [6], [7], []. The FACT Systems an also eliminate urrent harmonis that an be injeted into the ower system. The SVC (Stati Var Comensator) is a arallel omensator of FACTS family; it an regulate the voltage in the ower system by generating or absorbing reative ower from the system. The reative ower ontrolled by the SVC an be either aaitive or indutive deending whether the SVC generates or absorbs reative ower [8], [9]. There are many tyes of SVC ontroller, the Thyristor Swithed Caaitor (TSC), whih an erform the variation of reative ower by swithing on and off a shunt aaitors banks using two anti-arallel thyristors [9], [] and the Thyristor Controlled Reator (TCR) whih is a shunt reators banks that an be swithed on and off by two anti-arallel thyristors to ontrol the variation of reative ower in the system [6]. In many ases we an ombine the TCR and the TSC; this onfiguration an inrease the stability of the system, ensured a ontinuous ontrol of the reative ower, and eliminate the harmonis omonents [6]. In this aer we will resent a tehnique for ontrolling the grid onneted hotovoltai system using the SVC ontroller, rinially three TSCs and one TRC as shown in fig. 7

2 Bus Bus PV Array TCR Ste u Transmision line Boost onverter Inverter Grid Transformer Transmision line Transmision line TSC TSC TSC Synhronized - Pulse Generator Re tifier Load Bus SVC Controllers Load Ste down Transformer Fig.. Proosed toology of the grid onneted hotovoltai system. II. THE GRID CONNECTED SYSTEM MODEL A. Modeling of the ell and PV array The solar ell is an eletri devie that an onvert the solar energy into eletrial one. In the literature many models are roosed for solar ells [-5]. The eletri equivalent iruit roosed in this work is shown in fig. [-4] I h D I D R R s Fig.. Equivalent solar ell s eletri iruit. The harateristi equation of the ell s urrent ell s voltage V is reresented by equation (). I ( V + R I ) q I = I h Irs ex( ( V + Rs I ) β kt R s Where I h is the hotourrent ell given by relation () ( _ ( _ )) h s ref SCT ref Gref V I and G I = I + K T T () Denote by G, T, K SCT resetively the solar irradiation, the ell juntion temerature and the short iruit urrent temerature oeffiient. The hotourrent I is equal to the reverse saturation urrent s _ ref defined by T _ ref and G ref [4], [4]. h _ ref () I at the referene ondition the semiondutor, the eletron harge, the ideal fator of the solar ell and the βoltzman onstant. T qe g Irs = Irs _ ref ex () T _ ref β k T T _ ref A module PV an ontain ns ells assoiated in series, a solar anel is omosed of N array of modules assoiated in arallel; eah array an be omosed of N s modules assembled in series. Aording to this onsideration, we an exress the relations between the anel s and the ells arameters in relation (4). I = N I V = ns NsV ns Ns Rs = R (4) s N ns Ns R = R N In this onsideration, the equation related the anel urrent I to its voltage V is given in (5). q V Rs I P I = N I h N Irs ex + β kt ns Ns N N V R I + R ns Ns N s P B. Model of the Boost onverter Fig., show the struture of the boost onverter onneted to the hotovoltai system and used in this work []. (5) I rs is the reverse saturation urrent given by relation (), where E, q, k and β are resetively the band ga energy of g

3 i L L V C i C i a C R Load In a fixed Conordia frame referene the outut inverter voltage is given by (), the following relation is built all around ( 4, 5 and 6 ) as Boolean variables defining the states of the inverter lower keys and the inut DC voltage, [], [5]. Fig.. Shemati of the boost onverter We suose that the ower devies in this model are ideal. The ommand of the boost onverter deends on the state of the swith that is ontrolled by a PWM signal haraterized by the duty yle (α) and the oerating eriod (T), so during the oerating time eriod (T), the swith is losed in αt, so takes value (=) and the diode is swithed off. In (-α)t, the swith is oen, takes value (=) and the diode is swithed on. Aording to this idea, the global model of the boost onverter is given as: RL i L L L i L = LV V + (6) anel C V C C RLoadC [ ][ ] V i V t d = L C (7) C. Modeling of the three hase voltage inverter Fig.4 gives the general diagram of a three-hase voltage inverter used in this work. [], [5]. The Swithes of eah arm are omlementary and it is the same for the assoiated ommand signals. [], [5] so: 4 = - 5 = - (8) 6 = - V d i id i i4 i i5 i i6 i sa i sb i s v sa v sb v s Fig. 4. Inverter-Load Configuration. Load When the natural frame is used, the three outut inverter voltage an be exressed by the relation (9) v = vd + jvq = Vd e + e + e 5 j j j () Aording to relation (), the inverter voltage vetors exression are given by (), [], [5]. vsk = if k = or k = 7 ( k -) vsk = q v s () vs = Vd if k =,,...6 j q = e the inverter vetors exression are suorted by 8 vetors that an be lassified in two grous; the first one is omosed of two null vetors, the seond is omosed of 6 vetors that an be resented as a geometri rogression defined by the first term j V and the ratio e. Taking those into d onsiderations, the ative vetors form a balaned voltage system; having the same module and a regular hases. The sae reresentation of these is illustrated by fig.5. v v v v4 v6 v5 q Fig. 5. Diagram of the three-hase inverter voltage vetors. D. Modeling of the Thyristor Swithed Caaitor (TSC) Fig.6 shows the single hase struture of the Thyristor Swithed Caaitor (TSC). The TSC onsists of two antiarallel thyristors in series with a aaitor that will be swithed on or off, a small series resistane and indutane [], []. C u( t) L R i( t) d vsa i 4 Vd v sb = v s i5 i6 (9) Fig. 6. Main struture of TSC.

4 The mathemati equations of the iruit when the series resistane is ignored are given as follow: di u = U m sin( ωt + ϕ) = L + idt dt C () U m d i i + = os( ωt + ϕ) () dt LC L The indutane initial urrent and the aaitane initial voltage are given by (4) + i( ) = i( ) = + u( ) = u( ) = uo (4) Using those onditions the solution of relation () is given by(5) i = I os( ωt + ϕ) I os( ϕ)os( ω t) u ω C sin( ω t) m m o o o o UmωoC sin( ϕ) + sin( ωot ) ω LC Where ωo = eak urrent (5) LC is the osillation frequeny and I m is the The urrent (5) reahes diretly into stable state when the onditions given by (6) are satisfied, thus the urrent of this iruit an be exressed as (7). Um uo = ± ω LC ϕ = ± (6) i Im os( ω t + ) (7) E. Thyristor Controlled Reator Model A basi single-hase TCR omrises two anti-arallel thyristor onneted in series with a reator, as illustrated in Fig.7 [7]. The TCR is able to ontrol the undesirable imats of the load and redue them u( t) L i( t) ( ) i t = u( t) dt L (9) U m i = os( ωt) + C () ωl Where C is a onstant Using the initial ondition given by (), the solution of (9) is given by relation () i( α ) = () U m ( os( ωt) os( α )) i = () ωl Where α is the TCR firing angle at whih the thyristors are turned on and ondut a full half-eriod 9< <8 α. III. SIMULATION RESULTS The simulation in this work has been arried out in Matlab/Simulink environment. Fig. 8 and fig.9 give resetively the outut anel and the outut boost onverter voltages Panel voltage(v) Boost onverter voltage(v) Fig. 8. Panel voltage resonse Fig. 9. Outut boost onverter voltage. The outut boost voltage is used as an inut of the PWM ontrolled inverter. Fig., gives the resonse of the three hase voltage inverter. 5 Fig. 7. TCR onfiguration Using the struture given in fig.7, the mathemati relations are given by the following equations: di u = U m sin( ωt) = L (8) dt Integrating (8), we get relation (9) Inverter voltage(v) Fig.. Outut inverter voltage.

5 The three hase voltages generated by the inverter shown in fig. are filtered using a filter grid, and then a ste u transformer was used to adat those voltages to the grid as shown in fig.. The filtered inverter voltage generated to the grid is shown in fig.. Filtered inverter voltage(v) Fig.. Inverter voltage resonse. In order to rove the influene the SVC, we have onsidered three ases; - First ase: at t =.8 s a nonlinear load is onneted to the grid and the TCR-TSCs is not used. Fig. gives the wave of the DC Bus load urrent. DC Bus load urrent (A) Fig.. DC Bus load urrent without SVC. As shown in fig., the wave shae of the urrent is affeted by the harmoni henomena aused by the nonlinear load, the harmoni setrum and the THD value are given in fig. DC Bus Current Magnitude (A) Fundamental (5Hz) = 7.6, THD= 4.9% Frequeny (Hz) Fig.. Harmoni setrum of the DC Bus load urrent without SVC. - Seond ase: only the TSCs are onneted to DC Bus load at t =.6 s.fig. 4 shows that the wave of urrent is reovered by the use of the TSCs and the harmoni omonents have been almost eliminated. DC Bus load urrent (A) Fig. 4. DC Bus load urrent with TSCs. The FFT analysis of fig.4 at t=.6s, leads to fig.5 whih reresent the harmoni setrum and the THD of the studied urrent with only TSCs. Comared to fig., this figure shows that the transient omonent of the load urrent is eliminated. DC Bus load urrent magnitude (A) 4 Fundamental (5Hz) = 4.4, THD=.4% Frequeny (Hz) Fig. 5. Harmoni setrum and THD of the DC bus load urrent using only three TSCs. -Third ase: at t=.4s a TCR is onneted in arallel with the three TSCs to DC Bus load to show the erformane of the whole omensator in harmoni elimination. Fig.6 and fig.7 gives resetively the wave of the DC Bus load urrent with both TCR and TSCs and the FFT analysis of the studied urrent DC Bus load urrent (A) DC Bus load urrent magnitude (A) Fig. 6. DC Bus load urrent with TCR-TSCs Fundamental (5Hz) = 47.5, THD=.47% Frequeny (Hz) Fig. 7. Harmoni setrum and THD of the DC bus load urrent using TCR- TSCs. Comared the setrum in fig.7 with those in fig.5 and fig., this setrum show that the transient omonents of the load urrent are eliminated, and the result obtained by ombining the TCR and the TSCs is better than using only

6 TSCs. The THD has dereased from 4.9% to.4% by using TSCs, while it reahes.47% with both TCR and TSCs. IV. CONCLUSION This aer introdues a ontrolled toology for a grid onneted hotovoltai system based on SVC devies. Two most widely SVC devies TCR and TSC are used, modeled, and simulated in this aer. The simulation has been develoed in Matlab/Simulink environment. The ase studied illustrate the imat of SVC devies rinially the TCR-TSCs devies on a non linear load and the simulation results demonstrate that those devies an signifiantly eliminate the undesirable omonents generated by the load and injeted into the system, whih mean redue the Total Harmoni Distortion. With the three TSCs the THD has been redued from 4.9% to.4%, and it reahes to.4% when using the TCR with the three TSCs. Aendix TABLE I. Soure voltage System frequeny Line R Line L TABLE II. Caaitane of TSC Indutane Resistane TABLE III. Indutane TABLE IV. GRID PARAMETERS PARAMETERS OF TSC PARAMETERS OF TCR PARAMETERS OF CELL PV 5KV 5 Hz 6.7 Ω H 8.4e-6 F.e- H 4.6e- Ω 8.7e-9 H Oen iruit voltage Vo.658 V Short iruit urrent Is 8. A Parallel ell s resistane R.8 Ω Series ell s resistane Rs.8 mω Solar ell s ideal fator k.45 Reverse diode saturation urrent Irs.47e-7 A Short iruit urrent temerature.7eoeffiient KSCT A/ K Referene ell s temerature T_ref 5 C Boltzman s onstant β.8 e- Band ga energy Eg. ev TABLE V. Rated outut ower Oen iruit voltage: V o PARAMETERS OF PV MODULE Number of series ells: n 6 s 6W 6.5 V TABLE VI. Oen iruit voltage: V o Short iruit urrent : I s Number of series modules: PV ARRAY PARAMETERS Number of arallel modules: 9 V 8. A N 8 s N 8 REFERENCES [] M. A. Mahmud, H. R. Pota, and M. J. Hossain, Dynami Stability of Three-Phase Grid-Conneted Photovoltai System Using Zero Dynami Design Aroah, IEEE Journal of Photovoltais, Vol. (4), , Otober. [] K. Barra and D. Rahem, Preditive diret ower ontrol for hotovoltai grid onneted system: An aroah based on multilevel onverters, Energy Conversion and Management,. [] K. H. Chao, S. H. Ho and M. H. Wang, Modeling and fault diagnosis of a hotovoltai system, Eletri Power Systems Researh, vol. 78,. 97 5, 8. [4] R. Chenni, M. Makhlouf, T. Kerbahe, and A. Bouzid, A detailed modeling method for hotovoltai ells, Energy, vol.,. 74 7, 7. [5] L. S.Kim, Sliding mode ontroller for the single hase grid onneted hotovoltai system, Alied Energy, vol. 8,. 5, 6. [6] C. Rakenthai, S. Premrudeereehaharn and S. Uatrongjit, Power system with multi-tye FACTS devies states estimation based on reditor orretor interior oint algorithm, Eletrial Power and Energy Systems, vol.,. 6 66, 9. [7] A.D. Del Rosso, C.A. Cañizares and V.M. Dona, A Study of TCSC ontroller Design for Power Stability Imrovement, IEEE transations on ower systems. Vol. 8, , Nov.. [8] Ghorbani, M. Khederzadeh, and B.Mozafari, Imat of SVC on the rotetion of transmission lines, Eletrial Power and Energy Systems, vol. 4,. 7 79,. [9] S. K.M. Kodsi, C. A. Canizares, M. Kazerani, Reative urrent ontrol through SVC for load ower fator orretion,. Eletri Power Systems Researh, vol. 76,. 7 78, 6. [] A. Gelen and T. Yalinoz, An eduational software akage for Thyristor Swithed Reative Power Comensators using Matlab/Simulink, Simulation Modelling Pratie and Theory, vol. 8, ,. [] S. Akremi, N. Hidouri and L. Sbita, A Stati Var Comensator Controlled Toology For a Grid Conneted Photovoltai System, aeted in The International Renewable Energy Congress (IREC), Marh 5-7, 4 in Hammamet, Tunisia [] N. Hidouri and L. Sbita, A New DTC-SPMSM Drive Sheme for PV Puming System, International Journal of Systems Control, vol..,. -,. [] N. Hidouri, L. Sbita and T. Mhamdi, An Isolated Hybrid Fuzzy Controlled-Photovoltai Diesel-PMSG System, International Conferene on Control, Engineering & Information Tehnology (CEIT ), Proeedings Engineering & Tehnology (PET), Vol. 4,. 7-,. [4] N. Hidouri, T. Mhamdi, S. Hammadi and L. Sbita, A new hybrid hotovoltai-diesel system ontrol sheme for an isolated load, IJRRAS, vo. 9, issue,. 7-8,. [5] N. Hidouri, S. Hammadi and L. Sbita, An Advaned DPC-Self Exited Indution Generator Drive Sheme for an Isolated Wind turbine Boost System, International Review on Modelling and Simulations (IREMOS), vol. 5, No.,. 9-9,. [6] M. Hedayati, Tehnial Seifiation and Requirements of Stati VAR Comensation (SVC) Protetion Consist of TCR, TSC and Combined TCR/TSC, Universities Power Engineering Conferene, 4. UPEC 4. Vol.,. 6-64, 4. [7] R. Mohan Mathur and R.K. Varma, Thyristor-Based FACTS Controllers for Eletrial Transmission Systems,. IEEE Press, New York ().