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Seediscussions,stats,andauthorprofilesforthispublicationat:/publication/224166909AMaximumPowerPointControlPhotovoltaicSystemConferencePaperJuly2010DOI:10.1109/MED.2010.5547824Source:IEEEXploreCITATIONS3READS802authors,including:RachidElBachtiriUniversitSidiMohamedBenAbdellah31PUBLICATIONS93CITATIONSSEEPROFILEAllin-textreferencesunderlinedinbluearelinkedtopublicationsonResearchGate,lettingyouaccessandreadthemimmediately.Availablefrom:RachidElBachtiriRetrievedon:25April2016A Maximum Power Point Control Photovoltaic System M. Salhi, and R. El-Bachtiri Abstract A maximum power point tracking control (MPPT) is used for a photovoltaic (PV) system in order to maximize the output power irrespective of the temperature and irradiation conditions and of the load electrical characteristics. In this paper, we consider a photovoltaic panel supplying a battery. For maximizing its output power, we have used a boost DC/DC converter controlled by a PI regulator. The synthesis of this regulator parameters has been achieved by using Bode method. For having a transfer function of the system, we have used a small signal modeling. Theoretical and simulated results are presented. Experimental results are conclusive. KeywordsPhotovoltaic systems, maximum power point tracking, Boost dc/dc converter, PI regulator. I. INTRODUCTION photovoltaic generator has a nonlinear behaviour. The typical power-voltage and current-voltage characteristics of photovoltaic panel are shown in Fig. 1. The product of PV output voltage and current has a maximum value at a point called Maximum Power Point “MPP”. For the best utilization, the photovoltaic panel must operate at its MPP. However, the PV system operating point shifts out of MPP due to solar irradiation, cell temperature or load changes. When a maximum power point tracking “MPPT” regulator is inserted between the PV system and the load, it forces the system to operate at its MPP under all conditions, resulting in improved efficiency 1. Many MPPT regulators use a microcontroller or a personal computer for implementing sophistical algorithms 2-5, or even neural networks 6. These systems ensure very high performances. However they are very expensive and often need a separated, stable power supply for its operation; therefore they are only suitable for high power applications 7. Another algorithm is based on the searching of operating point which verifies . 0=VP Since the sign of “VP ” gives the direction of MPPT searching; it is possible to determine the maximum power operating by continuous measurement of power and voltage. In recent years, many MPPT applications based on this searching algorithm have been presented 8. In 9 and 10, an analog MPPT control-system is proposed, where a boost DC/DC converter is handed for having “VoutI” equals zero Fig. 3, where outI is the DC/DC converter output current. In this method, in order to reduce the complexity of the Manuscript received January 13, 2010. M. Salhi is member of LESSI Laboratory in Faculty of Sciences Dhar Mehraz (FSDM), Fez, Morocco. R. El-Bachtiri is a professor in High School of Technology, Fez, Morocco. system, the battery is considered as a constant voltageEand the converter is assumed to be ideal. So, the output power bPof DC/DC converter equals the PV output power .P A similar work is proposed in 11, that the battery is considered as a constant voltage in series with a constant resistance .bR This work is improved in 12 by taking into account the losses in the DC/DC converter, particularly, the switch losses in the MOSFET transistor. In this paper, we reconsider works proposed in 9-12 for experimental implementation. A block diagram of the proposed system is shown in Fig 3(a). A boost DC/DC converter is used to interface the PV output to the battery in order to track the maximum power point of the PV module. For That the MPPT controller must keep “VP” equals zero. What is possible with action on the duty cycle ()10 according to solar irradiation and temperature .T Duty cycle is the one of a signal generated by the PI regulator. For synthesizing the parameters of this regulator, we have developed a transfer function for the system using a small signal model. The PI regulator coefficients pK and iKare obtained by frequency synthesis. The synoptic scheme of the proposed method is shown in Fig. 3(b). With measurements of the PV panel voltage and current, the output power is calculated and derived with respect to voltage in order to obtain the dVdP who is compared to zero. The resulting difference signal (error signal) is used as an input signal to the PI regulator which delivers a control signal GSV for the boost DC/DC. II. THEORETICAL STUDY The power electronic converter is a boost converter inserted between the PV generator and the battery Fig. 2(a). It is controlled by a signal with a duty cycle ) 10(that gives the ratio between the input and the output voltage when the conduction is continuous. The transistor is ON during Tand OFF during the rest of the period (i.e., T)1 (). The diode state, in continuous conduction mode is complementary of the transistor one. The inductance is charged through the transistor, and it is discharged, output through the diode, in the battery. If the chopping frequency is enough higher than the system characteristic frequencies, we can replace the converter with an equivalent continuous model. We will consider so the mean values, over the chopping period, of the electric quantities Fig. 2(b). A 18th Mediterranean Conference on Control & AutomationCongress Palace Hotel, Marrakech, MoroccoJune 23-25, 2010978-1-4244-8092-0/10/$26.00 2010 IEEE1579 Fig. 1. PV characteristics: (a) current vs voltage and (b) power vs voltage Fig. 2. (a) Boost dc/dc converter and (b) boost converter “mean” equivalent circuit The transistor can be replaced by voltage source whose value equals its mean voltage. At the same, the diode can be replaced by a current source. A. PV module optimal operating point The equivalent circuit of the PV module considered in this paper is shown in Fig. 4. Relationship between PV output voltage Vand PV output current I is given by 13, 14: ()shRIsRVIsRVkTqosIsolII+=1exp (1) Where: =TrTkGOqErTTorIosI11exp3 (2) ()100018.298+=TIKSCIsolI (3) And sRshRorIGOEsolIIKscIqkosI,),(,= Fig. 3. Control system: (a) block diagram and (b) MPPT command. and T are respectively, cell reverse saturation current, Boltzmanns constant (1.381e-23 J/K), electronic charge (1.602e-19 C), short-circuit current at 25 C and 1000 W/m2, short-circuit current temperature coefficient at “Isc”, solar irradiation in W/m2, light-generated current, band gap for silicon (=1.12 eV), ideality factor, cell saturation current at reference temperature Tr (=298.18 K), shunt resistance, series resistance and cell temperature in kelvin. PV panel output power ,VIP= at optimal point, verifies: VIVIVIVIVP=+=0 (4) So: ()()+=shRIsRVAAosIIsRVI1exp (5) Where: )(/cellkTNqA= and Ncell is the number of series cells in the module. The PV module considered in this paper is the SM55. It has 36 series connected mono-crystalline cells. The manufacturer ratings of this PV photovoltaic under standard conditions (irradiation = 1000 W/m2, A.M. 1.5, solar spectrum and cell temperature T = 25 C ) is shown in tableI. The values of the rest parameters are as follows 15: =6500,1124. 0,74. 1shRsR, and 842. 4=orIA. 0PV output voltage (V)PV output current (A)MPP0PV output voltage (V)PV output power (W)MPP(a)(b)0PV output voltage (V)PV output current (A)MPP0PV output voltage (V)PV output power (W)MPP(a)(b)IVERbVout(L)CbatteryIoutIL(b)IVERbVout(L)CbatteryIoutIL(b)IVMOSFETERbVout(L)CbatteryIL(t)Iout(t)VGTsTstime(a)TDIVMOSFETERbVout(L)CbatteryIL(t)Iout(t)VGTsTstime(a)VGTsTstime(a)TD(a)PVarrayIVMPPT Control-systemBattery+-DC/DCconverter+-VGS control signalTsTstimeIoutprocessingcircuit of PVoutput powerIoscillatorVVoscPI regulator and comparatordP/dV+-(b)-+GroundPICircuitVreg+-VGScontrolsignalMPPT control-system(a)PVarrayIVMPPT Control-systemBattery+-DC/DCconverterDC/DCconverter+-VGS control signalTsTstimeTsTstimeIoutprocessingcircuit of PVoutput powerIoscillatorVVoscVoscPI regulator and comparatordP/dV+-(b)-+GroundGroundPICircuitVreg+-VGScontrolsignalMPPT control-system1580. Fig. 4. Equivalent circuit of a PV module. TABLE I PV MODULE SPECIFICATION UNDER STANDARD TEST CONDITIONS B. Frequencial synthesis of PI regulator parameters We deduce, from the continuous model equations Fig. 3(b), the following equations: LIIdtdVC= (8) outVLILrdtLdILV+= (9) ()()+=1sVEoutIBRLIDSonRoutV (10) ()LIoutI=1 (11) where bRDSonRLr,and sV are respectively, inductor resistance, transistor resistance at ON sate, battery resistance and threshold voltage of the diode. For expanding in series equations (8-11) around an optimal operating point, we write: ,qmppqq+= for each quantity q in the set outIILIV, defining the operating point. At steady state, we have: LmppImppI= (12) ()()()mppsVEoutmppIbRLmppIDSonRmppLrmppV+=1 (13) LmppImppoutmppI=)1 ( (14) For a small variation around an optimal operating point, the system can be shown by the following functional diagram: Fig. 5. System functional diagram of the system Where )()(tVPty= and .)()(ssoRoKsoG= oK is the static gain, )(soRis the rational fraction with 1)0(=oR and is the integration number. ()()GkLmppIDSonRbRsVEkGkoK3121+= (15) 13132311)(+=sGkCkGLsGkLCsoR (16) Where: ()()()(),12,111GmppGsRdmppRmppVmppIsRAkmppGsRdmppRmppVmppIsRsARk+=+= mppGsRmppGGmppbRDSonRmppLrk+=+=1, )1 (3 dmppRmppG1= and ()mppIsRmppVAAosIdmppR+=exp1 III. SIMULATION METHOD We have built our model by using Simulink Matlab. The block used for simulations is given by Fig. 6. In PV module block, equations (1-3) are used; and in block (converter + battery), equations (8-11) are used. The proposed controller circuit that forces the system to operate at its optimal operating point under variable temperature and irradiation conditions is shown in Fig. 7. Fig. 6. Block diagram for system simulation IsolRshVIRsIsolRshVIRs0.0004 A/Kshort-circuit current temperature coefficient at IscKI55 Wmaximum powerPmax17.4 Vmaximum power voltageVmpp3.15 Amaximum power currentImpp3.45 Ashort-circuit currentIsc21.7 Vopen-circuit voltageVo25 Ccell temperatureTValueQuantitySymbol0.0004 A/Kshort-circuit current temperature coefficient at IscKI55 Wmaximum powerPmax17.4 Vmaximum power voltageVmpp3.15 Amaximum power currentImpp3.45 Ashort-circuit currentIsc21.7 Vopen-circuit voltageVo25 Ccell temperatureTValueQuantitySymbolY(s)0+-PIG0(s)(s)(s)Y(s)0+-PIG0(s)(s)(s)PVMPPT Control-systemIVPconverter+ batteryTemperature(T)VTIPV moduleIrradiation ()PVMPPT Control-systemIVPconverter+ batteryTemperature(T)VTIPV moduleIrradiation ()1581 Fig. 7. Block diagram for MPPT tracker circuit. IV. PROPOSED SYSTEM Block diagrams of the proposed system are shown in Fig. 2(a) and Fig. 3(b). DC/DC converter consists of a RFP50N06 power MOSFET rated at 60V 50A .022. 0=DSonRThe flyback diode D is a fast-switching diode. The input inductor is wound around a ferrite-core with air-gap to prevent saturation that might be caused by a large DC current component value. DC/DC converter output is connected to two 12V/85Ah battery. The MPPT control-system consists of the PI regulator circuit, comparators and PV output power processing circuit. The later circuit uses the AD633JN integrated circuit for product and dividing signals. For a higher accuracy, a Hall-effect sensor is used to pick up the PV output current. The PV output voltage is collected by a differential circuit. The oscillator circuit used to obtain duty cycle is based on NE555 integrated circuit. V. RESULTS AND DISCUSSION A. Theoretical results PI controller gain and integral time constant obtained by frequency synthesis using Bode method are respectively 01. 0=pK and msiKiT8 . 1)1(=9. The boost inductance choice is 1=LmH, and the choice of input capacitance is 7 . 4=CmF 16. For different values of irradiation and temperature T, the computation of the theoretical optimum quantities of PV output voltage mppV and power mppPare assembled in table II. TABLE II THEORETICAL QUANTITIES Vmpp AND Pmpp FOR DIFFERENT VALUES OF IRRADIATION AND TEMPERATURE T. Fifteen kilohertz switching frequency is used. B. Simulation results Simulations were made to illustrate the response of the controlled system to temperature and solar irradiance rapid change. For this purpose, the irradiance and the temperature T, which are initially 100 W/m2 and 298.18 K, are switched, at 0.02 s and 0.05 s, to 1000 W/m2 and 320.18K respectively Fig. 8(a) and (b). And vice versa Fig. 9(a) and (b). , i.e., the solar irradiance changes from 1000 W/m2 to 100 W/m2 at 0.02 s and the temperature changes from 320.18 K to 298.18 K at 0.05 s. Optimum values of PV output power and voltage obtained by simulations are assembled in table III. Locking table II and table III, it is clear, on one hand that the average PV output power and voltage are very close to their optimal values Vmpp and Pmpp. And, on the other hand, the values obtained by simulation coincide with those obtained by programming. Simulations of the MPPT behaviour show that the system is stable. Oscillations around the computed optimal operating point are due to the switching action of the DC/DC converter. TABLE III SIMULATED QUANTITIES Vmpp AND Pmpp FOR DIFFERENT VALUES OF IRRADIATION AND TEMPERATURE T. C. Experimental results A prototype of the MPPT system has been developed using the above-described method and tested in the laboratory. The boost DC/DC converter, consisting of a MOSFET transistor, a fast switching diode, and an input inductor, has been carried out. Not having a material for measuring irradiation , in order to perform experience, we have proceeded as follows: In a dark room (no wind nor daylight), we have used LMP EJH 24V - 250 W overhead projector to give out the light to the PV array for a given temperature T1 (285 K) and irradiation 1. In these conditions (1 and T1 are supposed unvarying), we have measured, on one hand, the open-circuit voltage oV (= 19.5 V) and the Short-circuit current scI(=80.5mA). On the other hand, we have achieved a series of measurements of PV output current and voltage by varying a load. Results of measurements are used to plot the PV power-voltage characteristic in order to determine the optimal operating point “MPP1” corresponding to irradiation 1 and temperature T1 Fig. 10. Values of (W/m2) and T (K)Vmpp(V)Pmpp(W) = 100 and T = 298.18 = 1000 and T = 298.18 = 1000 and T = 320.18 = 100 and T = 320.1814.2517.3915.6512.314.39354.8048.613.715Values of (W/m2) and T (K)Vmpp(V)Pmpp(W) = 100 and T = 298.18 = 1000 and T = 298.18 = 1000 and T = 320.18 = 100 and T = 320.1814.2517.3915.6512.314.39354.8048.613.715Values of (W/m2) and T (K)Vmpp(V)Pmpp(W) = 100 and T = 298.18 = 1000 and T = 298.18 = 1000 and T = 320.18 = 100 and T = 320.1814.2517.4115.6612.314.39654.8348.643.549Values of (W/m2) and T (K)Vmpp(V)Pmpp(W) = 100 and T = 298.18 = 1000 and T = 298.18 = 1000 and T = 320.18 = 100 and T = 320.1814.2517.4115.6612.314.39654.8348.643.549AlphaPdP/dtMATLAB1/(dV/dt)dV/dtVPIregulator-+FunctionGround(dP/dV)AlphaPdP/dtMATLAB1/(dV/dt)dV/dtVPIregulator-+FunctionGround(dP/dV)1582 First, we have connected the PV module to the input of DC/DC converter and we have connected the output of the DC/DC converter to the battery. After that, we have used the output signal VGS provided from the MPPT control-system Fig. 12 to control the gate of MOSFET transistor. The MPPT tracker led operating point to reach its optimal value “MPP1”. Experimental results are shown in Fig. 10, Fig. 11(a) and (b), and Fig. 12. Using the power-voltage characteristic for = 1 and T = T1 Fig. 10, PV optimal voltage and optimal corresponding power to The MPP1 are: 121=mppVV and 6 .7171max=P mW. Measured corresponding current is 8 .591=mppImA. Using the MPPT tracker, we have obtained an optimal operating point corresponding to the maximum power voltage Fig. 11(a) 5 .122=mppVV and the maximum power current Fig. 11(b) 592=mppI mA. So, the maximum corresponding power is 5 .7372max=P mW. Fig. 8. Variation of: (a) PV output power and (b) PV output voltage for a step change on irradiation and temperature from 100 W/m2 to 1000 W/m2 and 298.18 K to 320.18 K respectively. These results show that the use of the proposed MPPT control increases the PV output power, voltage, and current like 2.77 %, 4% and 1.36 % respectively. VI. CONCLUSION The PV system output power can be maximized using MPPT control system. It consists of a power converter to interfacing the PV output to the load, driven by a control unit to extract the maximum power from a PV generator. A low-cost MPPT system for battery charging has been developed and tested. The power converter is a boost dc/dc converter. Its controlled by a PI regulator. This PI regulator has been synthesized by frequencial synthesis using Bode method. For a given temperature T and solar irradiance , we have calculated the corresponding optimal values Vmpp and Pmpp. Experimental and simulation results show that the proposed method was able to track the maximum power point for a given temperature T and irradiance. Our proposed MPPTs charge controller is easier and cheaper to build. Fig. 9. Variation of: (a) PV output power and (b) PV output voltage for a step change on irradiation and temperature from 1000 W/m2 to 100 W/m2 and 320.18 K to 298.18 K respectively. PV output voltage (V)00.020.040.060.080.10510152025Time (s)(b)PV output voltage (V)00.020.040.060.080.10510152025Time (s)(b)00.020.040.060.080.1-30-20-100102030405060Time (s)PV output power (W)(a)00.020.040.060.080.1-30-20-100102030405060Time (s)PV output power (W)(a)00.020.040.060.080.1-20-15-10-50510152025Time (s)PV output voltage (V)(b)00.020.040.060.080.1-20-15-10-50510152025Time (s)PV output voltage (V)00.020.040.060.080.1-20-15-10-50510152025Time (s)PV output voltage (V)(b)00.020.040.060.080.1-50-40-30-20-1001020304050Time (s)PV output power (W)(a)00.020.040.060.080.1-50-40-30-20-1001020304050Time (s)PV output power (W)00.020.040.060.080.1-50-40-30-20-1001020304050Time (s)PV output power (W)(a)1583 Fig. 10. Power-voltage characteristic for irradiation 1 and temperature T1. Fig. 11. Measured (a) PV output voltage and (b) PV output current under MPPT conditions (T = T1 and = 1). Fig. 12. MPPT output VG signal for driving the gate of MOSFET transistor. REFERENCES 1 R. E. Katan, G. Agelidis, C. V. Nayar, “Performance analysis of a solar water pumping system,” in Proc. of IEEE International Conf. on Power Electronic Drives and Energy Systems for Industrial Growth, New Delhi, 1996, pp. 81-87. 2 K. H. Hussein, I. Muta, T. Hoshino, and M. Osakada, “Maximum photovoltaic power tracking: an algorithm for rapidly changing atmospheric conditions,” IEE Proc. Generation Transmission Distrib., vol. 142, 1995, pp. 59-64. 3 M. Bodur, and M. Ermis, “Maximum power point tracking for low power photovoltaic solar panels,” Proc. IEEE Electrotechnic Conference. 1992, pp. 758-761. 4 V. Salas, M.J. Manzanas, A. Lazaro, A. Barrado, and E. Olias, “Analysis of control strategies for solar regulators,” Industrial Electronics ISIE 2002, Proc. of the 2002 IEEE International, vol. 3, May 2002, pp. 936-941. 5 D. Hohmn and M. E. Ropp, “Comparative study of maximum power point tracking algorithms,” Proc. Photovoltaic, Res. Appl., vol 11, 2003, pp. 47-62. 6 A. Al-Amoudi, and L. Zhang. “Application of radial basis function networks for solar-array modeling and maximum power-point prediction,” IEE Proc. Generation Trans. Distrib., vol 147, 2000, pp. 310-315. 7 J. H. R. Enslin, and D. B. Snyman “Combined low-cost, high-efficiency inverter, peak power tracker and regulator for PV applications,” IEEE Trans. Power Electron., vol. 6, pp. 73-82, 1991. 8 V. Salas, E. Olias, A. Barrado, and A. Lzaro, “Review of the maximum power point tracking algorithms for stand-alone photovoltaic systems,” Solar Energy Materials & Solar Cells, vol. 89, issue 1, pp. 1-24, Oct. 2005. 9 M. Salhi, and R. El-Bachtiri, “A PI regulator synthesis for tracking the optimal operating point of photovoltaic system supplying a battery” RT
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