Journal of Computing::Optimization of Maximum Power …cisjournal.org/journalofcomputing/archive/vol4no8/vol4no8_11.pdf · Optimization of Maximum Power Point Tracking ... the power

Vol. 4, No. 8 Aug 2013 ISSN 2079-8407 Journal of Emerging Trends in Computing and Information Sciences

©2009-2013 CIS Journal. All rights reserved.

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Optimization of Maximum Power Point Tracking (MPPT) of Photovoltaic System using Artificial Intelligence (AI) Algorithms

1 Raal Mandour, 2 I. Elamvazuthi 1, 2 Department of Electrical Engineering, University Technology PETRONAS

31750, Bandar Seri Iskandar, 31750 Tronoh, Malaysia

1. INTRODUCTION Today’s world is developing at an extremely

rapid pace requiring more energy every day. This growing energy demand, tied with the decrease of conventional energy sources have urged researchers to turn to the renewable ones.One of the alternatives is solar energy. However, Solar Panel efficiency of energy conversion is not high [1]. This limitation has encouraged research work aiming to extract the maximum power and optimize the power output from theses panels to achieve optimum efficiency in operation.

There are two distinctive and only lightly related

concepts called tracking. It is important to differentiate between the two. The two concepts are:

ABSTRACT Although solar energy is one of the most available renewable energy resources, its usage is strongly influenced by environmental and technological aspects. Photovoltaic (PV) offers an environmentally friendly source of electricity, which is however still relatively costly today. In order to minimize the output power cost, the maximum power point tracking (MPPT) of the PV output for all sunshine conditions is a key factor to maximize the power output of a PV system for assigned conditions of radiation and temperature. The core of the MPPT is represented by the implemented algorithm devoted to find and maintain the operation near to the Maximum Power Point (MPP). In this paper, starting from the set of equations modeling a PV module, an innovative procedure to optimize the performance and efficiency of the MPPT algorithms is presented, simulated and verified. Artificial intelligence algorithms, specifically PSO and PSO combined with Incremental conductance algorithm, are used to achieve the stated goals. Studies on the conventional and intelligent algorithms are conducted and a comparison between their efficiencies and drawbacks is presented. Flowcharts are developed and simulation tools are identified. MATLAB simulations are shown and resulting graph and efficiencies under several irradiance values are specified along with comparison with the previously achieved performance of MPPT algorithms and different set of data. Keywords: MPPT, particle swarm optimization, PSO, Artificial Intelligence, AI

• Maximum Power Point Tracking (MPPT): an electronic function that regulates voltage / current parameters to allows the modules to produce all the power they are capable of out of a solar panel. Additional power harvested from the modules is then made available as increased battery charge current

• Mechanical Tracking: a method to physically move the solar panels to keep them facing the sun at an angle that changes with time depending on the sun position.

Electronics and programming are used in MPPT

to change the electrical operating point (usually the voltage) of the modules so that the modules are able to deliver maximum available power. Monitoring the Current (I) vs. Voltage (V) curve also known as the IV curve that is knee shaped, by slightly moving the voltage level a significantly higher current can be achieved.

Since Maximum Power Point Tracking (MPPT) is developed to get the maximum possible power from one or more solar panels, several algorithms and techniques have been proposed for MPPT. Most commonly used techniques of MPPT are Perturb and Observation (P&O), Constant Voltage and Current, Hill-climbing method, Incremental Conductance, Parasitic Capacitance along with some DSP based methods[2]. Each of the above techniques is accompanied with problems. For instance, P&O method is simple but has a large steady state error accompanied with oscillation at the maximum power point [3]. In Incremental conductance method, the power of solar panel is a non-linear function of duty cycle. Hill climbing algorithm suffers from getting stuck at local maxima or minima. Also, the modified algorithms based of the earlier mentioned ones were able to improve some of the drawbacks but not the efficiency such as the modified P&O technique that improved the convergence problem at rapidly changing weather but couldn’t increase the efficiency[1][4][5].

Similarly, Artificial intelligence algorithms are

used to improve MPPT and it began to increase the efficiency of the solar panels while presenting other trade-offs and disadvantages. Algorithms such as Stimulated Annealing (SA) technique will eliminate stability problems and getting stuck in maxima or minima. On the other hand, there is a trade-off between quick settling time and steady state error. Other problems and drawbacks are present to other AI algorithms such as Fuzzy logic and PSO [1]. Nevertheless, AI algorithms can be improved further. The objectives of this research are:




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a. To enhance MPPT efficiency using AI algorithm b. To explore the use of AI techniques in MPPT

such asPSO c. To validate the results

2. LITERATURE REVIEW 2.1 PV Module Model

An electrical equivalent circuit of solar cell can be obtained as shown in Fig. 1.

Fig 1: PV cell equivalent circuit

The circuit contains a current source with a diode, a shunt resistance and a series resistance [6]. The current Id is mainly responsible for producing the nonlinear I-V characteristics of the PV cell [7, 8]. Using KCL:

𝐼𝐼𝑠𝑠𝑠𝑠 − 𝐼𝐼𝐷𝐷 −𝑉𝑉𝐷𝐷𝑅𝑅𝑃𝑃− 𝐼𝐼𝑃𝑃𝑉𝑉 = 0 (1)

Diode characteristic:

𝐼𝐼𝐷𝐷 = 𝐼𝐼𝑂𝑂 �𝑒𝑒𝑉𝑉𝐷𝐷

𝑉𝑉𝑇𝑇� − 1� (2) KVL:

𝑉𝑉𝑃𝑃𝑉𝑉𝑠𝑠𝑒𝑒𝑃𝑃𝑃𝑃 = 𝑉𝑉𝐷𝐷 − 𝑅𝑅𝑠𝑠𝐼𝐼𝑃𝑃𝑉𝑉 (3) Where:

𝐼𝐼𝑠𝑠𝑠𝑠 : Short circuit current of PV cell 𝐼𝐼𝐷𝐷: Diode current 𝐼𝐼𝑂𝑂: pn junction reverse saturation current 𝐼𝐼𝑃𝑃𝑉𝑉 : PV current 𝑉𝑉𝑃𝑃𝑉𝑉 : PV voltage 𝑉𝑉𝐷𝐷: Diode voltage 𝑅𝑅𝑠𝑠: Series resistance 𝑅𝑅𝑝𝑝 : Parallel resistance

A group of current-voltage characteristics

defines the behaviour of a PV. Every curve is plotted for a constant uniform irradiance and a given temperature. Fig. 2 shows V-I curve of a PV module for different sun irradiations [9].

Fig 2: V-I curves of a PV module for different sun irradiations [7]

MPP is the point on the curve where the PV

module operates with maximum efficiency and produces the maximum power output: every curve has a single MPP as shown in Fig. 3.

Fig 3: Typical V-I curve of a PV module 2.2 Conventional MPPT algorithms: Incremental

Conductance (INC) Algorithm In this algorithm, the PV array’s incremental

conductance is used to determine the direction of perturbation. It compares the incremental conductance (dI/dV) with the instantaneous conductance (I/V).The major drawbacks of this algorithm since it uses a fixed step size (duty cycle) are excessive steady state oscillations resulting in a relatively low efficiency. A trade-off between dynamics and oscillations is always present [10, 11].A modification was done to this algorithm by introducing a variable step size.Fig. 4 indicates the algorithm.




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Fig 4: Variable step size INC flowchart

2.3 Particle Swarm Optimization In order to improve the currently used algorithms,

criteria that are to be enhanced have to be defined. Among these criteria [12]:

• efficiency of algorithm. In order to reduce the

energy generation cost and acquire better energy generation, efficiency should be increased

• recognition of Tracking Direction: In order to respond to rapidly changing environment, the MPPT controller should keep the correct sense of direction

• reduction of steady state errors.

To optimize complex problems with multivariable objective function, PSO method is always used. This method is effective in the case of the presence of multiple local maximum power points. PSO adapts the behaviour and searches for the best solution-vector in the search space. A single solution is called particle. Each particle has a fitness/cost value that is evaluated by the function to be minimized, and each particle has a velocity that directs the flying of the particles. The particles fly through the search space by following the optimum particles. The algorithm is initialized with particles at random positions, and then it explores the search space to find better solutions. In every iteration, each particle adjusts its velocity to follow two best solutions. The first is the cognitive part, where the particle follows its own best solution found so far. This is the solution that produces the lowest cost (has the highest fitness). This value is called pBest (particle best). The other best value is the current best solution of the swarm.

The PSO algorithm is based on the cooperation of multiple agents that exchange information obtained in their respective search process [12][13].Since MPPT algorithm algorithms get stuck in local minima and maxima, PSO can help overcome the problem as well as decrease steady state error and increase the efficiency.The velocity and position update follows the below equations:

𝑉𝑉𝑖𝑖𝑘𝑘+1 = 𝑤𝑤𝑉𝑉𝑖𝑖𝑘𝑘 + 𝑠𝑠1𝑟𝑟1�𝑃𝑃𝑃𝑃𝑘𝑘 − 𝑋𝑋𝑃𝑃𝑘𝑘� + 𝑠𝑠2𝑟𝑟2�𝑃𝑃𝑔𝑔𝑘𝑘 − 𝑋𝑋𝑃𝑃𝑘𝑘� (4) 𝑋𝑋𝑖𝑖𝑘𝑘+1 = 𝑋𝑋𝑖𝑖𝐾𝐾 + 𝑉𝑉𝑖𝑖𝑘𝑘+1 (5)

Where

𝑉𝑉𝑖𝑖𝑘𝑘+1: particle velocity, 𝑋𝑋𝑖𝑖𝑘𝑘+1 : current Position of a particle, 𝑃𝑃𝑃𝑃𝑘𝑘 : local best position 𝑃𝑃𝑔𝑔𝑘𝑘 : global best position r1, r2: random number between 0 & 1 c1, c2: learning factors.

2.4 Comparative Analysis Table 1 show the efficiency of each algorithm

and their drawbacks.

Table 1: MPPT algorithms efficiency

The recorded efficiencies are considered high. However for each case, few drawbacks arise such as getting caught in maxima, high steady state error and inability to follow the direction of change in perturbation in which hinders the overall performance of the MPPT as shown in Table 2.

Table 2: Reported MPPT Algorithms drawbacks




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3. METHODOLOGY 3.1 Research Methodology

Simulation is an increasingly significant methodological approach yielding to new prototypes and thus products. In this study, simulation of MPPT algorithms and development of AI based MPPT algorithms are achieved using MATLAB. The simulation requires creation of flow charts and diagrams of the targeted algorithms. Figs 5 and 6 show the general algorithm and the flowchart respectively.

Fig 5: General Algorithm flow chart

Fig 6: PSO Flowchart

As shown in Fig.6, PSO algorithm is very simple yet it offers a great deal of flexibility to suit changing weather conditions by adjusting few parameters. Two parameters defined as position and velocity areupdated at each iteration of the fitness function. As the iteration number increases the maximum power is updated and output the maximum power obtained until the final iteration. 3.2 PSO-INC Structure

The PSO-INC algorithm uses the same block for the PSO section. In addition to this, a derivative block that takes the derivative of the output PV power is added to produce a pulse width modulation (PWM) signal. The later serves as a duty cycle tuner and one of the inputs to a DC-DC converter that generates the adequate input voltage to the PV module.To control the photovoltaic power system is necessary to use a DC-DC converter; the most adequate is the Buck converter. It reduces the input voltage. Fig. 7 shows the topology used.

Fig 7: Buck converter topology used in DC-DC converter

The Simulink Model was created using the following differential equations that define the behaviour of the buck converter of Fig.7.

𝐿𝐿 𝑑𝑑𝑖𝑖𝑃𝑃𝑑𝑑𝑑𝑑

= 𝑉𝑉𝑃𝑃𝑉𝑉 .𝐷𝐷 − 𝑉𝑉𝐵𝐵𝐵𝐵𝑇𝑇 (6)

𝐿𝐿 𝑑𝑑𝑉𝑉𝑃𝑃𝑉𝑉𝑑𝑑𝑑𝑑

= 𝐼𝐼𝑃𝑃𝑉𝑉 − 𝑖𝑖𝑃𝑃 .𝐷𝐷 (7) where:

𝑖𝑖𝑃𝑃 : Current of the battery D: PWM parameter Control {0, 1}

Fig. 8 shows the model.

Fig 1: DC-DC Simulink Model




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The capacitor needed in this converter has to be a power capacitor in order to be able to support large currents. 𝐼𝐼𝐶𝐶 = 𝑃𝑃

𝑁𝑁𝑆𝑆 .𝑉𝑉𝑃𝑃𝑉𝑉= 1600

32.9= 48.6 𝐵𝐵 (8)

The efficacy value is expressed as follows:

𝐼𝐼𝐶𝐶𝑒𝑒𝐶𝐶𝐶𝐶 �1𝑇𝑇 ∫ 𝐼𝐼

2 = 13𝐼𝐼𝐶𝐶 = 16.2 𝐵𝐵 (9)

The value of the capacitor is 33mF.

As for the inductor, the equation to model the function of inductor is:

𝐿𝐿 = 𝑉𝑉𝑉𝑉𝑉𝑉𝑑𝑑𝑉𝑉𝑇𝑇

𝑉𝑉𝑖𝑖𝑃𝑃= 24×25×10−6

5= 125µ𝐻𝐻 (10)

The PWM controller is based on the Incremental

conductance section of the algorithm where the change in the output power of PV panel result in changes in the voltage of the panel and therefore a change in the pulse width (duty cycle). Fig.9 shows the PWM model.

Fig 2: PWM controller Simulink Model

4. RESULTS AND DISCUSSION 4.1 PSO

The PSO model developed is shown in Fig. 10.

Fig 10: PSO Simulink Model

The PV module is used as a platform to be able to test the algorithm. The MATLAB function block named PSO is the main section of the model.

4.1.1 PSO-Kuala Lumpur The resulting graphs are displayed in Fig.11, 12

and13.

Fig 11: Power vs. Voltage at different irradiance

Fig 12: I-V Characteristic at different irradiance

Fig 13: Fitness function (Ppso) vs. Ppv The efficiency is calculated and tabulated in Table .3

Table 3: Efficiency of PSO algorithm




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4.1.2 PSO-Saudi Arabia The results are shown in Fig.: 14,15 and 16.



Fig 4: Fitness function (Ppso) vs. Ppv

The efficiency is calculated and tabulated. Table 4 shows the results for KSA for 1 iteration.

Table 4: Efficiency of PSO algorithm

4.2 PSO-INC

The PSO-INC model developed is shown in Fig. 17:

Fig 17: PSO-INC Simulink model

4.2.1 PSO-INC-Kuala Lumpur

The resulting graphs are displayed in Fig. 18, 19 and 20.






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Fig 20: Fitness function vs. Ppv 4.2.1 PSO-INC-Saudi Arabia

The results are shown in Figs 21, 22 and 23.



Fig 8: Fitness function vs. Ppv

MPPT system using PSO-INC calculates the

voltage at which the module is able to produce maximum power and input to the PV module. In addition to increased efficiency and correct sense of tracking direction, the PSO–INC reaches steady state rapidly with no oscillations.The simulated results using PSO and PSO-INC techniques are successfully able to track the maximum power point for a PV panel at any given Irradiation. 4.3 Validation

The theoretical power, voltage and current output of the PV module (Kuala Lumpur Data set) are calculated for different irradiance and compared with the values obtained using Method 1 (PSO) and Method 2 (PSO-INC). This is shown in Table 5.

Table 5: Comparison between Calculated and obtained results

To validate the developed methods, the efficiency of PSO and PSO-INC techniques are compared to previously developed methods using conventional algorithms (INC, P&O...) as well as earlier developed PSO algorithms as shown in Table 6.

Table 6: Efficiency of suggested Methods for MPPT compared to previously developed methods

The results show that particle swarm optimization technique given better results. Efficiency of MPPT increases using PSO (98.6%) compared to the theoretical values, the Maximum Power output increases




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with increased irradiance using AI techniques. At higher irradiance value, the output value can surpass the theoretical power value. 5. CONCLUSION

Simulation of Maximum Power Point Tracking of a Solar PV panel using Particle Swarm Optimization and Incremental conductance techniques is presented. Comparison of Solar Photovoltaic panel output with and without optimization is presented. It can be deduced that the eefficiency of MPPT increases using PSO. Further work can be done by developing the hardware for the suggested method. ACKNOWLEDGEMENTS

The authors would like to thank Universiti Teknologi Petronas for supporting this work through grant, STIRF27/2011. REFERENCES [1] Azam, M.A., AshfanoorKabir, M., Imam, M. H.

and Abdullah-Al-Nahid, S., "Advanced Artificial Intelligence Algorithms for Microcontroller based Maximum Power Point Tracking of Photovoltaic," International Journal of Advanced Renewable Energy Research, Pp. 143-155, 2012.

[2] M. A. G. de Brito, L. P. Sampaio, G. Luigi Jr., G.

A. e Melo, and C. A. Canesin, “Comparative Analysis of MPPT Techniques for FV Applications,” International Conference on Clean Electrical Power (ICCEP), 2011, pp. 94-104.

[3] Gomathy, S., Saravanan, S. and Thangavel, D.S.,

"Design and Implementation of Maximum Power Point Tracking (MPPT) Algorithm for a Standalone PV System," International Journal of Scientific & Engineering Research Volume 3, Issue 3, 2012.

[4] Cha, H. and Lee, S., "Design and Implementation

of photovoltaic power conditioning system using a

current based Maximum Power Point tracking," in 43rd IEEE IAS, 2008.

[5] Liu, R.C., "Advanced Algorithm For MPPT

Control Of Photovoltaic Systems," 2004. [6] Padmanabhan, B., Modeling of solar cells, Arizona

State University, 2008. [7] "Solar cell model," [Online]. Available:

http://www.mathworks.com/help/physmod/elec/ref/solarcell.html, [Accessed 23 October 2012].

[8] N. C. Sahoo, I. Elamvazuthi, Nursyarizal Mohd

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Journal of Computing::Optimization of Maximum Power …cisjournal.org/journalofcomputing/archive/vol4no8/vol4no8_11.pdf · Optimization of Maximum Power Point Tracking ... the power