Matlab/Simulink Model of Solar PV Array with Perturb and Observe MPPT for Maximising PV Array Efficiency Oladimeji Ibrahim, Member IEEE
Nor Zaihar Yahaya, Member IEEE,
Department of Electrical and Electronics Engineering Universiti Teknologi PETRONAS, Bander Seri Iskander, Perak 32610, Malaysia
[email protected]
Nordin Saad, Member IEEE Muhammad Wasif Umar Universiti Teknologi PETRONAS Bandar Seri Iskandar, Perak 32610, Malaysia
[email protected] [email protected] [email protected] The performance of a PV cell largely depends on quality of cell material such as absorption capacity and reflectance of the surface. The operating condition like solar irradiance level, incident angle, temperature and load current plays a big role in dictating the performance of PV array output voltage, current and power delivery [2, 3]. The available commercial solar PV cells have low efficiency in the range of 10-25 % necessitating the need to ensure that maximum available power is extracted for better utilization efficiency and cost reduction. Research effort in solar energy studies are directed towards increasing cell efficiency via manufacturing technologies, improving power quality of PV power generation for grid connection and extracting maximum output power termed maximum power point tracking (MPPT).
Abstract—The efficiency of commercially available solar PV module is very low in the range of 10-25 %. In order to maximise their operating efficiency and to reduce installation cost, maximum power point trackers (MPPT) are coupled with the system. The output power of solar PV depends on solar irradiance level, incident angle, temperature and load current which all contribute to non-linear varying I-V characteristic during operation. MPPT ensures that a PV cell, module or panel is operated and maintained at the reference voltage that correspond to maximum power point for particular operating solar irradiance and cell temperature. A 220 W solar PV panel is modelled in Matlab-Simulink to study solar PV characteristics under different solar irradiance and working cell temperature. A Perturb & Observation MPPT technique incorporated for maximising the output power of the PV panel shows that the percentage deviation from the ideal PV power is about 10 % for different operating solar irradiance and cell temperature.
MPPT are used for operating PV array at the point of maximum power irrespective of irradiance, temperature and load current variation. In literature, different MPPT techniques have been proposed but their suitability largely depends on factors like the end application, dynamic of irradiance, design simplicity, convergence speed, hardware implementation and the cost [4]. The available MPPT methods ranges from simple voltage relationships to complex multiple sample based analysis which includes but not limited to constant voltage method, short current pulse method, open voltage method, perturb and observe method, incremental conductance method, and temperature method [5]. The design and implementation simplicity coupled with good performance has make perturb and observe (P&O) MPPT to be one of the most widely used MPPT techniques for solar PV applications [4, 6].
Keywords: Solar PV; Perturb and Observe; Solar Irradiance; DC-DC boost converter; PV cell temperature
I. INTRODUCTION Solar energy is a readily available, clean, and inexhaustible energy source considered as a sustainable alternative energy source for electricity generation. The contribution of solar energy to the world total electricity generation has been on increase in the past decades. The global installed capacity of solar photovoltaic (PV) system increased from below 10 GW in 2007 to over 100 GW capacity in year 2012 [1]. Solar energy system generates electricity by direct conversion of solar photon (light) energy to electricity using solar cells and indirectly using solar thermal to produce superheated steam for driving electrical turbines. Solar photovoltaic cells used in solar PV system are made of a light absorber materials of p-n junction semiconductor that absorbs solar photons above certain minimum threshold energy called “energy gap” or “band gap” (Eg) to free electrons generate electricity.
This paper presents studies on solar PV model module, the energy pattern was investigated under different operating weather conditions and MPPT was incorporated to maximize energy harvesting. A model a 220 W solar PV panel intended to be fed to an inverter for stand-alone AC network system is
This work was supported by Electrical & Electronics Engineering, Universiti Teknologi PETRONAS
978-1-4799-8598-2/15/$31.00 ©2015 IEEE
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2 I r = irradiance in W/m covering cell surface
modelled in Matlab-Simulink environment. T The characteristic behaviour of the PV panel is analysed considering different operating conditions of irradiance and tempeerature level and P&O MPPT algorithm was used for maximum m power tracking. The simulation results shows that sysstem performed satisfactorily as the maximum output power from m solar PV panel with MPPT show a close relationship with the m maximum power available from the PV under test at different irraadiance levels. II.
perature at STC T , T = cell working and reference temp c r
To show the non-linear characcteristic of PV array under different irradiance and temperatture, a 220 W solar panel comprises of 3 modules with eaach module having 36 cells connected in series. The electricaal specifications of the solar panel based on standard test cond ditions (STC) at 1000 W/m2 irradiance, AM of 1.5 and, 25 °C is presented in Table I.
MODELING OF SOLAR PV CEELL
TABLE I: ELECTRICAL CHARAC CTERISTICS OF PV PANEL
Solar PV cell is the basic unit of solar PV array/panel, they are combined in series and parallel to achievee require voltage and current level. A PV cell is a p–n junction semiconductor that generate current when exposed to light. Thhe mathematical model of PV cell is useful for simulation purpose to reveal the voltage, current and power behaviour under diifferent operating conditions. A simplified equivalent circuit off PV cell with 5 parameter is presented in Fig. 1. A cell series rresistance ሺܴ௦ ሻ is connected in series with a parallel combbination of cell photocurrentሺܫ ሻ, exponential diodeሺ)ܦ,, and shunt resistanceሺܴ௦ ሻ . ܫ௩ , and ܸ௩ are the PV cell’s current and voltage respectively.
Parameters Rated power Open circuit voltage Short circuit current Voltage at maximum power Current at maximum power Total number of cells in series Total number of cells in parallel
Symbol P MP V OC I SC V MP I MP NS NP
Value 220W 54V 5.52A 44.63V 4.94A 108 1
Matlab-Simulink tools was used d to simulate the solar panel I-V and P-V curve under variable irradiance i and temperature as presented in Fig. 2. The simulattion result of I-V and P-V characteristic at 1000 W/m2, 80 00 W/m2, and 600 W/m2 irradiance at constant temperature of o 25 °C is presented in Fig. 3 and Fig. 4 respectively. The resullt shows that the PV output current and power increases as solarr irradiance increase.
Fig. 1. Equivalent circuit of PV celll
The PV cell output current ܫ௩ is expressed as:
§ q(VPV +I PV ∗Rs )nKT · I PV = I ph − I s ¨¨e −1¸¸ − (vPV + I PVV ∗ Rs ) / Rsh (1) © ¹ Where: I ph = Solar-induced current
Fig. 2. Simulink model of solar panel
I s = Diode saturation current
q = Electron charge (1.6e −19C ) K = Boltzmann constant (1.38e −23 J / K ) n = Ideality factor (1 ~ 2) 0
T =Temperature K
The solar induced current of the solar PV celll depends on the solar irradiation level and the working temperatture expressed as eq. (2): Ir (2) I ph = I sc + K ( T − T ) ∗ i c r 1000 I sc = short-circuit current of cell at STC
d solar irradiance Fig. 3. I-V curve for different
K = cell short-circuit current/temperature coefficientt ( A / K ) i
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installation cost. MPPT automaatically finds the voltage (reference voltage ሺܸ ሻ at wh hich the PV array outputs maximum power and ensure thaat it maintains the system operation at the point under differen nt irradiance, temperature and load current. The basic unit of max ximum power point tracker is shown in Fig. 7 with MPPT powerr stage and the MPPT control algorithm [7]. VPV,IPV
MPPT M po ower ciircuit
Vo,Io Load
D
Fig. 4. P-V curve for different solar iirradiance
PV Array
The simulation result of I-V and P-V charactteristic of the PV panel for different working temperature 25 °C, 50 °C and 75° C with constant irradiance are shown in Fig. 5 andd Fig. 6. The PV output voltage and power decreases with incrreasing solar cell operating temperature.
MPPT control algorithm
Fig. 7. Block diagram of MPPT M control
In this work, a DC-DC boost con nverter is used at power stage to achieve the source to load imped dance matching controlled by variable switching duty cycle. Th he Perturb and Observation (P&O) MPPT algorithm is used for the duty cycle ሺܦሻ control to mum power point. The flow obtain reference voltage for maxim chart of P&O algorithm is shown in Fig. 8, where the PV o the output power. The voltage and current are sensed to obtain power is checked by varying the voltage, v with increase voltage the power also increased, then the duty d cycle ሺܦሻis increased in the same direction otherwise du uty cycle decreases with a stepሺ߂ܦሻ. The iteration continues until u maximum power point is reached and the converter output voltage is maintained at the point [8-11]. The output voltage ሺܸ௨௧ ሻ of the converter is maintained constant by varying the duty cycle which determines the output voltage value from the solar PV att every switching cycle. The solar PV array output voltage whicch is input to the converter is defined by (3) [12]:
Fig. 5. I-V curve for different cell tem mperature
VPV = (1 − D)Vouut
(3)
The solar irradiation or temperaturre changes will results in PV array output voltage variation expreessed as:
/ ΔVPV / = / ΔD / Vout
(4)
Where ΔV PV and Δ D are the PV output voltage and converter T P&O coding was done in duty cycle variations. The MPPT Matlab m file and embedded in the Simulink using Matlabfunction block. In order to ensurre that the possible voltage oscillation around the maximum po ower point is minimised and at the same time achieving fast trracking, the duty cycle step change was Δ D chosen as 0.0005.
Fig. 6. P-V curve for different cell tem mperature
III. MPPT CONTROL TECHNIQU UE PV arrays exhibits non-linear varying I--V characteristic during operation based on solar irradiance andd temperature at particular time. In order to ensure that PV arrrays operates at maximum power point under different operaating conditions, maximum power point tracker (MPPT) are inccorporated. This will improve the PV panel efficiency and reduce the system
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TABLE II: BOOST CONVE ERTER PARAMETERS
Start
Parameters Input voltage Output voltage Load resistance Inductor Output capacitor Switching frequency
Sample V(k), I(k)
P(k) = V(k)*I(k)
Y
N P(k)>P(k-1)
Y
N
Y
V(k)>V(k-1)
D=D1+ǻD
D=D1-ǻD
V(k)> >V(k-1)
D=D1+ǻD
N
RL
L C fs
IV. RESULTS AND D DISCUSSIONS
D=D1-ǻD
Return
Fig. 8. Flow chart of P&O MPPT methood
A DC-DC boost converter is used to achhieve the MPPT power stage owing to the advantage of highh reliability, less component parts to reduce implementation ccost. The boost converter configuration comprises of power M MOSFET as the switching transistor with input inductor ሺܮሻ placced in series with the PV voltage ሺܸ ሻ as shown in Fig. 9. Thee boost converter parameters used in this project is shown in Tablee II.
iin(t)
Vout
Value 45 [V] 90 [V] at D=0.5 36.8 [] 500 [μH] 100 [μF] 5 [kHz]
The Matlab_Simulink model off PV panel developed with the n Fig. 10 for studying the MPPT controller is presented in performance of the MPPT at different irradiances and cell temperatures is presented in Fig. 10 0. The results of output power from the PV at different solar irrradiance of 1000 W/m2, 800 W/m2, 600 W/m2 and cell temperatu ure of 25 °C, 50 °C, 75 °C are presented in Fig. 11 and Fig. 12 reespectively. The results show decrease in MPPT duty cycle and d PV output power as solar irradiance decreases and with cell teemperature increases. The PV output power from application off MPPT power is closed to maximum available power from th he PV panel test parameters. The comparative output power resullts are given in Table III.
k = k+1
L
Symboll V in
D
iL(t)
+
ic(t) Vin
Q1
Vc(t)
PWM
RL Vout(t) C
Fig. 10. Simulink model of PV P array with P&O MPPT
Fig. 9. Equivalent circuit of DC-DC boost connverter
The steady state conversion ratio (input-outpuut voltage) of the converter is given by:
Vin (5) 1− D The magnitude of peak-to-peak inductor curreent ripple ΔI L is given by: Vout =
ΔI L =
Vin D fs L
(6)
And, also the output capacitor voltage ripple ΔVc is: ΔVc = ΔVout =
Io D f sC
(7)
Fig. 11. Duty cycle and PV output po ower at 25 °C cell temperature
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ACKNOWLEDGMENT The authors would like to thank Univeersiti Teknologi PETRONAS for financial support in the publication of th his work.
REFEREN NCES [1] REN21. (2012). Renewabless 2012 Global Status Report. Available: Available at: http://www.map.ren21.net/GSR/ GSR2012_low.pdf [Retrieved d December, 2013] [2] D. Shmilovitz, "On the con ntrol of photovoltaic maximum power point tracker via outpu ut parameters," in Electric Power Applications, IEE Proceeding gs-, 2005, pp. 239-248. [3] A. Cupertino, J. de Resende, H. Pereira, and S. S. Júnior, "A Grid-Connected Photovoltaic System with a Maximum Power Point Tracker using Passiviity-Based Control applied in a Boost Converter," the solar syystem, vol. 4, p. 6, 2012. [4] T. Esram and P. L. Chapmaan, "Comparison of photovoltaic array maximum power point tracking techniques," IEEE TRANSACTIONS ON ENERG GY CONVERSION EC, vol. 22, p. 439, 2007. [5] D. Freeman, "Introduction to photovoltaic systems maximum power point tracking," Texas Instruments Rapport d'application SLVA446-Novem mber, vol. 2010, 2010. [6] S. Jain and V. Agarwal, "Comparison of the performance of maximum power point track king schemes applied to singlestage grid-connected photov voltaic systems," IET Electric Power Applications, vol. 1, pp p. 753-762, 2007. [7] M. Killi and S. Samanta, "Modified " Perturb and Observe MPPT Algorithm for Drifft Avoidance in Photovoltaic Systems," IEEE Transactionss on Industrial Electronics, vol. 62, pp. 5549-5559, 2015. [8] A. Dolara, R. Faranda, and S. S Leva, "Energy comparison of seven MPPT techniques for f PV systems," Journal of Electromagnetic Analysis and d Applications, 2009. [9] A. K. Abdelsalam, A. M. Maassoud, S. Ahmed, and P. Enjeti, "High-performance adaptivee perturb and observe MPPT technique for photovoltaaic-based microgrids," IEEE Transactions on Power Electtronics, vol. 26, pp. 1010-1021, 2011. [10] M. Mohd Zainuri, M. Radzi,, M. Amran, A. C. Soh, and N. Rahim, "Development of adaaptive perturb and observe-fuzzy control maximum power poin nt tracking for photovoltaic boost dc-dc converter," Renewable Power Generation, IET, vol. 8, pp. 183-194, 2014. [11] M. A. De Brito, L. P. Samp paio, G. Luigi, and C. Canesin, "Comparative analysis of MPPT techniques for PV applications," in Internatiional Conference on Clean Electrical Power (ICCEP), 20 011 2011, pp. 99-104. [12] F. Liu, Y. Kang, Y. Zhang, and S. Duan, "Comparison of P&O and hill climbing MPPT T methods for grid-connected PV converter," in 3rd IEEE Confference on Industrial Electronics and Applications, 2008. ICIEA A 2008. , 2008, pp. 804-807.
Fig. 12. Duty cycle and PV output power at 1000 W//m2 irradiance TABLE III: COMPARISON OF PV AND MPPT OUTTPUT POWER Constant cell temperature of 25°C Solar Irradiance (W/m2)
PV maximum power (watt)
1000 220.47 800 172.87 600 125.82 Constant solar irradiance of 1000W/m2
PV with P&O ou utput power P PV (waatt)
% deviation
213.31 154.11 113.67
3.25 10.85 9.66
Cell temperature (°C)
PV maximum power (watt)
PV with P&O ou utput power P PV (waatt)
% deviation
25 50 75
220.47 185.34 151.46
213.31 174.32 139.95
3.25 5.96 8.22
V.
CONCLUSIONS
A solar PV panel has been modelled and perrturb and observe MPPT technique is developed for maximisinng its operating efficiency. Studies on the solar PV Simulink m model shows the nonlinear I-V and P-V characteristics of thhe PV panel to different solar irradiance of 1000 W/m2, 800 W W/m2, 600 W/m2 and cell temperature of 25 °C, 50 °C, 75 °C.. The PV output power decreases as the irradiance level decreaase and when the working temperature of the PV cells rises. T The P&O MPPT technique used for maximising the output powerr of the PV panel is able to effectively operate the system at a poiint very closed to maximum available power from the PV pannel source. The percentage deviation of the PV output power frrom the ideal PV power is about 10 % for the tested operating ccondition of solar irradiance and cell temperature.
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