ICEGES 2009 International Conference and Exhibition on Green Energy & Sustainability for Arid Regions & Mediterranean Countries

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1 CEGES 29 nternational Conference and Exhiition on Green Energy & Sustainaility for Arid Regions & Mediterranean Countries Le Royal Hotel Amman, Jordan Novemer, PERORMANCES O PHOTOVOLTAC GENERATOR MULT-LEVEL CASCADE Adelaziz Talha 1 Dalila Berier 2 Laoratoire d nstrumentation aculté d Electronique et d nformatique, Université des Sciences et de la Technologie Houari Boumediene Laoratoire d nstrumentation aculté d Electronique et d nformatique. Université des Sciences et de la B.P.32, El-Alia, Ba-Ezzouar, Alger Technologie Houari Boumediene. B.P.32, El-Alia, Ba-Ezzouar, Alger atalha@hotmail.com derier@yahoo.fr. Astract n this paper, we study the performances of the cascade of the solar cell panels with the multilevel inverter. n the first part, we develop a knowledge model of the inverter y using connection functions of this converter. A PWM strategy which uses four ipolar carriers is developed to control this converter. n this part, the inverter is fed y constant input DC voltages. The performance of the algorithm is studied on the ase of the harmonic rate. Then, we present the solar cell model. n the last part, we study the staility prolem of the input DC voltages of the inverter. Thus, we study a cascade constituted y two photovoltaic cell panels five-level NPC VS - permanent magnet synchronous machine (PMSM). This studied lets to find a solution to solve this prolem. The performances otained with this cascade are full of promise to e using this inverter in renewale energy 29 nternational Conference and Exhiition on Green Energy & Sustainaility for Arid Regions & Mediterranean Countries All rights reserved Keywords: Multilevel inverter; generator Cells; Renewale; PMSM,. 1. ntroduction * During last century, the consumption of electrical energy has greatly increased ecause the industry growth. The energy demand predictions for next years confirm the growth of the energy consumption. Consequently, the traditional energy sources (fossil) will last few more decades. And this will produce an outage of the energy in the word. On the other hand the consumption of the traditional sources contriutes greatly to the greenhouse effect, for this reason, it is necessary to use the renewale energy sources no polluting such as solar cell. The industrial consumers need to e fed y sinusoidal voltage generators. n the last decade the power electronic technology has made a very important advance their development. On the one hand, the power switches used in the structures of converters are ale to switch more quickly, On the other hand, new structures have emerged converters. Some of them promote high switching frequencies. And instead to transfer significant levels of power (multi-level structures, ). n this paper, we are interested to study the cascade of a multilevel inverter and solar cell generator. The performances otained with this cascade are full of promise to e used in renewale energy production systems. 2.Modelling of ive Level NPC Voltage Source nverter The three-phase five-level NPC VS is a new conversion structure used to feed, with variale frequency and voltage, power alternating current machines. Several structures are possile for five-level inverters [1]. n this paper, we study the Neutral Point Clamping (NPC) structure (igure1). This converter is constituted y three arms and four DC voltages sources. Every arm has eight i-directional switches, six in series and two in parallel, and two diodes DD k and DD k1 which let to have zero voltage for V km.. Every switch is composed y a transistor and a diode in anti-parallel. or an arm k of the three-phase five-level NPC VS, several complementary laws controls are possile. The control law which lets an optimal working of this inverter is [1]: B B B K 4 K 5 K 6 = B = B = B K 2 K1 K 3 Where B ks represents the gate control of the switch T ks

2 nternational Conference and Exhiition on Green Energy & Sustainaility for Arid Regions & Mediterranean Countries n this part, we present a PWM algorithm of the fivelevel NPC VS: the space vector modulation strategy with four ipolar carriers. This strategy is characterised y two parameters [1], [2]: - The modulation index m is defined as a ratio etween the carrier frequency f p and the reference voltage frequency f:. m = f f p The modulation rate r is the ratio etween the magnitude V m of the reference voltage and three times of the carrier s magnitude U pm :. Vm r = U igure2 shows the signals of this strategy pm ig. 1. A ive-level NPC voltage source inverter The switch connection function ks indicates the opened or closed state of the switch TD ks. We define too a half arm connection function km with: k : arm numer for the lower m = 1 for the upper half half arm arm ig. 2. Space vector modulation strategy associated to four ipolar carriers and: K1 K = = K1 K4 K2 K5 K3 K6 The output voltages of the inverter relatively to the middle point M are defined as follows V V V AM BM CM = U c1 + 21U c U c3 2U 3 c4 The system (3) shows that a five-level NPC VS can e considered as four two-level voltage source inverters in series. This characteristic lets us to extrapolate the strategies used for the two-level inverter to the five-level NPC inverter. The input currents of the inverter are given as follows: id 1 = 17i1 + 27i2 + 37i3 id 2 = 11i1 + 21i2 + 31i3 id 3 = 18i1 + 28i2 + 38i3 id 4 = i1 + 2i2 + 3i3 i The current i d is given as follows ( i + i + i + i ) ( i + i ) d = d1 + i3 3. PWM Strategy of the ive Level NPC VS ig. 3. The simple voltage of the inverter and its spectrum (m=) or even values of m, the output voltages present symmetry relatively to the quarter of the period. Then, only odd harmonics exist. These harmonics gather y families centred around frequencies multiple of 4mf. The first family centred around frequency 4mf is the most important in view of its magnitude 4. Modelling of Photovoltaic Generator

3 nternational Conference and Exhiition on Green Energy & Sustainaility for Arid Regions & Mediterranean Countries Since the invention of solar cells in en 1954, several models have een proposed to descrie its function and ehaviour under different weather conditions (light and temperature) [3]. n this paper, we present the model with one exponential (diode) [4][5]. The electrical scheme is given in figure 4 The figures 6, 7 and 8 represents respectively current voltage characteristics, power voltage and current voltage (reel case) of panel MSX-83, for a temperature T=25 and light E=W/m2 ig. 4. Electrical Scheme of a photovoltaic cell with one diode The expression of the current-voltage characteristic is given as follows q ( V + R ) A k T s = ph S [exp( ) 1] V + Rs R sh ig. 7. Current voltage Characteristic PG Thus, the equivalent scheme of a photovoltaic generator (PG) is given in figure5 ig. 8. Power voltage Characteristic PG ig. 5. Equivalent scheme of photovoltaic generator The expression of the current-voltage characteristic of photovoltaic generator is given as follows: Vg + Rs, g g Vg + Rs, g g g ph, g s, g[exp q 1] AkNmsT Rsh, g The functional scheme of photovoltaic generator uses Matla/Simulink is given in figure6. n this paper, we have used photovoltaic generator MSX- 83 composed y 36 cells in en series ig. 9. Real Characteristic current voltage of PG We can note that the simulation results used the proposed model are nearly of the real case and then we can validate our model 5. Cascade of Two Photovoltaic Generator ive-level NPC VS - PMSM Until now, we have supposed the input DC voltages of the five-level NPC VS constants. n this part, the authors study a generation input DC voltage technique. or this, we propose a cascade constituted y two photovoltaic generator-five-level NPC VS which feeds a PMSM (igure). ig. 6. unctional Scheme of photovoltaic generator

4 nternational Conference and Exhiition on Green Energy & Sustainaility for Arid Regions & Mediterranean Countries ig.. Two photovoltaic generator-filter-five-level NPC VS- PMSM cascade ig. 12. nput voltages of the inverter and their differences 5.1. Modelling of ntermediate ilter igure11 shows the structure of the intermediate filter of the studied cascade. ig. 13. Output voltage of photovoltaic generator ig. 11. Structure of the intermediate filter The model of this filter is defined y the following system The different input voltages of the VS are not stales and their differences are not null (igure12). The output voltages of the photovoltaic generator decrease continually (igure13). 6. Stailisation of nput Voltage of ive Level NPC VS To improve the input voltages of the five-level NPC inverter, we propose to use a clamping ridge, constituted y a transistor and a resistor [1]. The transistors are controlled to maintain equal the different input DC voltages of the inverter (igure14) i r(i+1) rect(i+1) i ri i c(i+1) i ci i di T i rect(i-1) R p C i U ci i d(i-1) 5.2. Simulation results The five-level NPC inverter is controlled y the space vector modulation strategy with four ipolar carriers, any photovoltaic generator delivered a voltage Vpvi=14V. We note : Uc13=Uc1-Uc4, Uc24=Uc2-Uc4 et U= UPV1+UPV2. The parameters of the intermediate capacitors filter are: C1=C2=C3=C4=2m i r(i-1) i c(i-1) ig. 14. Clamping ridge cell The model of the clamping ridge-filter set is defined y the following equation

5 C C C C c1 c 2 c3 c 4 nternational Conference and Exhiition on Green Energy & Sustainaility for Arid Regions & Mediterranean Countries PV 1 PV 1 PV 2 PV 2 d 3 d1 r 2 d1 r1 d d1 r 3 d r 4 Where i r 1 = U ci Rp The control algorithm of the resistive clamping circuits can e summarized as follows if U c1 > U PV1 U 2 if U c2 > PV1 U 2 if U c3 > PV 2 U 2 if U c4 > PV 4 2 (T1=1) & (T2=) (T2=1) & (T1=) (T3=1) & (T4=) (T4=1) & (T3=) The parameters of the intermediate capacitors filter are: C 1 =C 2 =C 3 =C 4 =2m and R p =25Ω. The figures 15 and 16 show the simulation results when using the clamping ridge ig. 15. Tensions du pont de clamping et leurs différences ig. 16. Output voltage of two Photovoltaic generator

6 a (A) Cem (N/m) nternational Conference and Exhiition on Green Energy & Sustainaility for Arid Regions & Mediterranean Countries 2 Cem Cr ig.18. Performances of PMSM a (A) Wr (rad/s) Wr Wref [2] L.M. Tolert,.Z. Peng and T.G. Haelter, Multilevel PWM methods at Low Modulation indices, in Proceedings of 1999 Applied Power Electronics Conference and exposition (APEC), pp [3] M. Bayegan, Power electronic technologies for distriuted Power, 9th European conference on Power Electronics and Applications, EPE 1, 27th August 21, Graz, Austria 21. [4] B.Multon and al, "Analysis and Experimental Validation of Various Photovoltaic System Models", 7th nternational ELECTRMACS 22 Congress, Montréal, Canada 22, pp [5] E. Massada, "Power Converter for Renewale and Distriuted Sources", 9th nternational Conference on Power Electronics and Motion Controls, EPE-PEMC 2, Kosice, Slovak Repulic 2. We oserve that the differences etween the input voltages of the five-level NPC inverter are decreased to have a value practically null in steady state (igure15). The output voltage of the three two-level rectifiers is lightly increased (igure16). The current i d has a mean value practically null (igure17). The performance of the speed control algorithm of the PMSM shows that the current of the machine nearly is sinusoidal. The speed and the torque effect for the charge variation etween two instants t=1.5s and t=2.5s (igure18). 7. Conclusions n this paper, we have studied the performances of the cascade of the photovoltaic cell panels with the multilevel inverter. The modelling of the five-level NPC inverter shows that it is equivalent to four two-level inverters in series. This characteristic lets us to extrapolate the strategies used for the two-level inverter to the five-level NPC inverter. Also, we have presented a space vector modulation strategy with four ipolar carriers. The study of the staility prolem of the input DC voltages of five-level NPC inverter using a cascade constituted y two photovoltaic generator-five-level NPC VS shows that the different input voltages of this VS are not stales and their differences are not zero. To solve this prolem, we propose to use clamping ridge, ecause this ridge allows improve the input voltage of five-level inverter. The performances otained with this cascade are full of promise to e using this inverter in renewale energy Nomenclature : Current delivered y photovoltaic cell, V : Voltage delivered y photovoltaic cell, ph : Photo-current, s : Saturation current of diode dependants of temperature, R s : Series resistance, R sh : Shunt resistance, 19 q : Charge of electron = C, 23 K : Boltzmann Constant = J/K, A : Quality factor of diode, T : Cell Temperature in K. g : gap. References [1] A. Talha, E.M. Berkouk, M.S. Boucherit and G. Manesse, Study and control of two two-level PWM rectifier clamping ridge - seven-level NPC VS cascade. Application to PMSM speed control", European Transactions on Electrical Power Journal (ETEP) y John Wiley & Sons, Ltd, Volume16, No.1, 26, pp