Various Maximum Power Point Tracking Techniques Engineering Essay

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Solar energy is a type of renewable energy that is generated from natural resource. Different from oil and gas, solar energy is free, does not need fuel, and clean from wastage that will results in pollution. PV cell is needed to convert sunlight directly into electricity. Figure 1.1 shows the result of an international study about the world's energy consumption. Today, the solar energy covers only 0.5% of the world energy consumption, but will become one of the most important renewable energy sources in the future. In 2050, it has been estimated that about 30 to 60 Terawatt energy per year being needed and solar system is the biggest contributor (Roslan, 2009).

Figure 1.1: The world's energy consumption (Roslan, 2009)

Malaysia has the advantage of using this type of energy because of the location in the tropical zone which will get sunlight all over the year. The government realized about the importance of the solar energy and had spent about RM 469 million for rural electrical program, under Seventh Malaysian Plan.

Compared to the non-renewable energies such as coal, gasoline and oil, solar energy has become increasingly popular as an environmental friendly renewable energy source that produces no pollution and only needs minimal maintenance. The energy from the sun is free and has the advantage of reducing the power losses when converting the energy.

This type of energy also had its own disadvantage. The major disadvantage is low conversion efficiency of electric power generation (9% to 16%), especially under low irradiation conditions and the amount of electric power generated by solar array change continuously with the weather conditions.

PV array is needed to harvest solar energy. There is an optimum operating point in every PV array which varies on the condition of temperature and current insolation level. To use solar energy efficiently, a device called MPPT is invented. MPPT is an electronic system that operates the photovoltaic (PV) modules in a manner that allows the module to produce all the power they are capable of. The MPPT device is fully electric and did not use any mechanical moving device to attract sunlight.

The main use of the solar energy is still little. The main use can be found in the water solar heating in hotel, small food industry and rich man house. Not less than 10,000 unit of water solar heater had been used now.

The project was decided not to use analogue systems even it will results in a cheaper components. This is because the analogue system will insult problem in maintaining the accuracy under extreme operating conditions like wide temperature conditions that usually occur in an outdoor vehicle. So, it is more reliable to use the digitally controlled because it will not be influenced by temperature changes.

Objective

One of the objective for this project is to study various MPPT technique that usually been used. The other purpose is to model and simulate MPPT using MATLAB/SIMULINK. The simulated circuit of the MPPT is analyzed to see its performance in maximizing the efficiency of the solar energy.

Problem Statements

Photovoltaic power generation systems have intensively been investigated as an environmental friendly and as an alternative to oil, coal and gas. The system has the advantages of infinite energy resources and does not caused pollution. However, low efficiency and high cost per unit output power are the main problem of the system that prevents it to be used widely.

Scope

In order to achieve the objectives, there are several scope had been outlined. The work has been divided into few parts. The first part to be done is the literature review. During the literature review, many important facts will be glanced thru to ensure enough information and understanding on the projects. The subtopics will be on PV cells, types of PV cells, solar cell circuits, types of converters and MPPT. Three best MPPT methods will be choose to be used in this project. The scope of this project includes simulating each of the MPPT model using Matlab software for experimental verification purpose. As to mark the end of the work, the three MPPT models results will be analyzed to find the advantage and disadvantage of using each of them.

In this project, Constant voltage method, Incremental conductance method and Perturb and Observe method will be used in analyzing the best MPPT method between them. These three methods will be simulated and the result of the simulation will determine which MPPT bring better efficiency and performance with minimize power loss during the conversion.

1.5 Methodology

The approach that I have applied in completing this final year project can be divided into two major segments. The first segment is my literature review and the second part is on my circuitry simulation. In the beginning, the literature review will help me to understand the photovoltaic cell by understanding their types, and identifying the PV system components. Then my literature part will continue as the studies will be extended to analyzing the circuit.

Later on the literature review continues with study on power converters. There are three types of dc-dc converters being study that is buck converter (step down converter), boost converter (step up converter) and buck-boost converter. Furthermore on the literature review, the basic concept and use of maximum power point is being identified. There are many types of maximum power point available. Three best types that being studied is incremental conductance method, constant voltage method and perturbs & observe method. On the second part, the mathematical equation of the three will be modelled. Then, the three types of MPPT will be simulated and analyzed. The best MPPT will be find out based on the results. Following are the summarized flow chart on this project.

Analyzing maximum power point tracker converter for PV system

Modelling and Simulation

Literature Review

B

C

A

Analyze the strength and weaknesses of each method

Compare each of the MPPT method based on simulation result

Choose and verify the best MPPT method

Figure 1.5.1: Methodology Flow Chart

A

Study the basic structure and information about solar cell

Study the basic structure and information about solar cell

Recognized types of PV cell

Study the basic structure and information about solar cell

Identify components, characteristics and circuit of solar cell.

Study and identify types of power converter

power converter

Study and identify types of MPPT

Figure 1.5.2: Flow Chart on Literature Review

B

Model and simulate photovoltaic panel

A/B

Yes / No

Verify the data analyzed

Model and simulate PWM module

A/B

Yes / No

Verify the data analyzed

Model and simulate MPPT

Yes / No

A/B

Verify the data analyzed

Simulate overall project

Figure 1.5.3: Flow Chart on Simulation

Figure 1.5.4: Implementation Chart for Semester 1

Figure 1.5.5: Implementation Chart for Semester II

1.6 Thesis Outline

This theses will is a compilation of many chapters that will elaborate in stages the research work that have been carried out. As in general this theses mainly consist of three main chapter; introduction, literature review and methodology.

In chapter I, this thesis will discuss the research project in collectively. Whereby in this chapter crucial aspect of the research work such as introduction, objectives, problem statements, scope, methodology, thesis outline and summary will be discussed.

Chapter II completely dedicated to literature review about the maximum power point tracker. This chapter will be solely theoretical in detail discussing on the types of photovoltaic cell, solar cell circuit, power converter, types of dc-dc converter and types of MPPT.

Chapter III will be explaining the methodology of the project. A few simulations will be done here. The first one is the simulation of the PV panel. Then, the process will continue with simulation on pulse width modulation (PWM) and maximum power point tracker (MPPT). Later, the simulation on overall of the project will be done.

1.7 Summary of works

Implementation and work of the project are summarized into a flow chart as

shown in Figure 1.7. Gantt chart of the project schedule is as given in APPENDIX A.

START

Search the information and article on MPPT from internet, books, journal and other sources.

Not

Suitable

Find more information

on various types of

MPPT

Suitable

Design the simulation of MPPT

using Matlab/Simulink to verify and analyze its operation.

ANALYZE THE RESULT

THESIS WRITING

END

Figure 1.7: Summary of Works

CHAPTER 2

LITERATURE REVIEW

Photovoltaic technology

2.1 Photovoltaic technology

There are many types of technology in thin film photovoltaic technology. For an example in this film technology there is Silicon based and Chalcogenide based cells. Table 2.1 belows shows the summary of the types that shall be discussed in this topic.

Thin Film Technologies

Silicon based

Single junction amorphous silicon

Multiple junction amorphous silicon

Crystalline Silicon on Glass

In the thin film technology it can be divided into two major parts which is silicon based and chalcogenide-based. As for beginning look at silicon based which consists of single junction amorphous silicon, multiple junction amorphous silicon and crystalline silicon on glass. Below in Figure 2.1(a) is the single junction amorphous silicon and Figure 2.1 (b) is the individual cells deposited onto a glass sheet are laterally connected in series by the approach shown .

Figure 2.1 (a): Single junction amorphous, Figure 2.1 (b): Cells deposited onto a glass sheet are laterally connected in series.

In the early 1980s the calculators and digital watches have been using the amorphous silicon solar. At that time, many efforts were carried out but currently Kaneka and Mitsubishi are the companies that successfully supplies single junction amorphous silicon. In low temperature, the amorphous silicon allows 10% hydrogen to be incorporated. The quality of the material is improved from day to day with the presence of the hydrogen atom. The amorphous silicon is not very conductive hence the transparent conductive tin oxide layer between the silicon and the glass being used and connected in series as depicted in Figure 2.1(b).

Next, the multiple junction amorphous silicon devices is designed in thinner layers to accommodate the decreased material quality under light exposure such as in single junction amorphous. It's made possible by stacking two or more cells on top of one and another as in Figure 2.2. In effort to boost its performance the upper cells bandgap is made larger compared to the lower cells.

Figure 2.2: Multiple-junction stacked or tandem solar cells where two or more current matched cells are stacked on top of one another.

As discussed above, by increasing the bandgap of the uppercell there's a change in performance and the earliest effort made in reducing the bandgap by alloying it with germanium. This result in the performance was around the 6-7% range, compared to the best of the single junction amorphous silicon (a-Si). Currently there's another way of doing it whereby an a-Si as top cell combined with a bottom cell which consists a mixture of amorphous and microcrystalline as in Figure 2.3. This technology can improve the performance by 8-10%. This cell is still in small scale and hasn't been commercialized yet.

Figure 2.3: (a) Mixed-phase microcrystalline/amorphous material; (b) single-phase

polycrystalline film

Another type of solar cell is crystalline silicon on glass as depicted in Figure 2.4 whereby this technology uses high temperature to transform the amorphous silicon material to polycrystalline. This technology has some similarity with the polycrystalline wafer. The advantage of this technology is that the material is more conductive and there's no need for a transparent conducting oxide that results in cost reduction. The instability possessed by a-Si is also solved using this material [8]. The glass texture is also another plus point in this technology as it allows the silicon layer to be very thin.

Figure 2.4: Crystalline silicon on glass (CSG) unit cell structure.

A fault tolerant metallization approach and the use of higher grade borosilicate float glass compared to the soda-lime glass has improve the ruggedness in the CSG technology compared to the module.

Earlier we were discussing regarding the silicon based, now let's have a preview on the Chalcogenide-based cells. The Chalcogenide-based cells kick off with the cadmium sulphite technology in the early 1980s. Yet this technology was beat down by the biggest contender at the time; amorphous silicon. Besides that, the instability issue with cadmium sulphite was another major issue. When the amorphous silicon was going thru dark ages as it had problem with commercialization, this technology had a good time and became famous.

BP solar and Matsushita were manufacturing Cadmium Telluride solar cell and then later move on to other technology due to environmental issues. The toxicity of cadmium was one of the reasons. A layer of cadmium sulphide is deposited from

solution onto a glass sheet coated with a transparent conducting layer of tin oxide. This is followed by the deposition of the main cadmium telluride cell by as variety of techniques including close-spaced sublimation, vapour transport, chemical spraying, or electroplating.[8]. The cadmium telluride structure has been depicted in Figure 2.5.

Figure 2.5: Device schematic for a cadmium telluride cell

Copper Indium diselenide known as CIS technology has demonstrated 19.5% efficiency in experiments yet it's hard to commercialize. CIS technology generally involves deposition onto a glass substrate and then interconnected as in Figure 2.6 [8]. An additional glass top-cover is then laminated to the cell/substrate combination.

Research are being conducted in order to replace the thin layer of CdS as many environmental controversy issues submerged as noted earlier. Yet the CIS technology is one of available resources as reserves of indium would only produce enough solar cells to provide a capacity equal to all present wind generators [8].

Figure 2.6: Basic CIS (copper indium diselenide) cell structure

2.3 Circuit of Solar Cell

The design of the solar cell circuit is very much influenced by the solar array characteristic. Solar cell is a non-linear device. (Roslan, 2009).The equivalent circuit model of a solar cell consists of a current generator and a diode plus series and parallel resistance as shown in Figure.

In this circuit, ILG is the light generated current, Rsh is the shunt resistance, Rs is the series parasitic resistance of the connection of the PV panel to the converter, RL is the load resistance and D, a diode which having breakdown voltage equivalent to the rated one of the panel.

Figure 2.3.1: Circuit of PV Cell

The PV circuit above is related by an equation as below. The interval of Rsh, shunt resistance is neglected.

Io = Iq - Isat{exp|(Vo+ IoRs)|} (2.1)

Reviewing the equation, Iq is the light generated current, Io is the reserve saturation current while Isat , saturation current. Then, q is the electronic charge, A is a dimensionless factor, K is the Boltzmann constant, T is the temperature in oK while Rs is the series resistance of the cell. Based on this parameter, the equation for output voltage (Vo) is:

Vo = - IoRs + ln [] (2.2)

In order to make sure that the PV circuit is ideal, Rs is put to zero while Rsh is put with infinitely large number. The interval shunt resistance is neglected. The above equations are used to simulate the PV circuit.

Figure 2.3.2: I-V Characteristic Curve, the Effect of the Solar Radiation. (Ramaprabha, Mathur, & Sharanya, 2009)

Figure 2.2.3: I-V Characteristic Curve, the Effect of Temperature

Figure 2.2.4: P-V Characteristic Curve, the Effect of the Solar Radiation.

Figure 2.2.5: P-V Characteristic Curve, the Effect of Temperature.

The solar array depends on solar irradiation and temperature to produce power output. All the figure above ( Figure ) showed the result of simulations ran to see the effect of both the solar radiation and temperature on the I-V and P-V characteristics.

Based on Figure, it is showed that the short circuit current is proportional to the solar radiation. There is more radiation, more current and more maximum output power. Based on Figure, the temperature is inversely proportional to the open-circuit voltage. Hence, the maximum output power is also reduced. The results really depend on the surrounding condition. These situations make the needs to track the maximum power point efficiently.

2.4 Power Converter

Dc-dc power converters are widely used in regulated switch-mode d.c. power supplies and in d.c. motor adrive applications. (Singh & Khanchandani, 2007) D.C.-D.C. power converters also used in many applications such as power supplies for personal computers, office equipment, spacecraft power systems, laptop computers, and telecommunications equipment. Normally, the input to a dc-dc converter is an unregulated dc voltage Vg, which is obtained by rectifying the line voltage and therefore will fluctuate due to changes in the line voltage magnitude. The converter produces a regulated output voltage V, which got a magnitude that differs from Vg.

High efficiency is invariably required, since cooling of inefficient power converters is difficult and expensive. The ideal dc-dc converter exhibits 100% efficiency; in practice, efficiencies of 70% to 95% are typically obtained. (Erickson, 1999) These efficiencies can be achieved by using switched-mode or chopper. Pulse-width modulation (PWM) is used to allow control and regulation of the total output voltage. This approach is also employed in applications involving alternating current, including high-efficiency dc-ac power converters (inverters and power amplifiers), A.C.-A.C. power converters, and some A.C.-D.C. power converters (low-harmonic rectifiers). (Erickson, 1999)

The DC-DC converter is based on linear regulator and switching regulator. The transistor is operated in linear mode in the linear regulator. (Roslan, 2009) The output voltage can be calculated using this equation:

Vo = Vin - Vce

(a)

(b)

Figure 2.4.1: (a) Linear Regulator circuit (b) Equivalent Circuit (Roslan, 2009)

Vin = input voltage

Vout = output voltage

Vce = voltage across transistor

Figure (b) showed that the transistor can be conveniently modelled by the equivalent variable resistor. There is power loss happened here at high current and can be calculated by using this equation:

P0 = IL2 x RL

IL2 = Vce

Where,

Po = output power

IL = load current

RL = load resistance

Transistor is operating in switched-mode for switching regulator. There is no current flow in it when the switch is open. When the switch is closed, there is no voltage drop across it. Below are figures showing switching regulator circuit and its equivalent circuit.

Figure 2.4.2(a): Switching Regulator

Figure 2.4.2 (b): Equivalent Circuit

2.4.1 Buck Converter

The buck converter is a device that used to lower the output voltage. The circuit

diagram is shown in Figure. The waveform applied to the low-pass L-C

filter. The low-pass filter removes all the high frequency components in Vin,

and the output becomes just the DC component. (Siti Noorhaninah, 2009)

Figure 2.4.3: Buck Converter (Rashid, 2004)

When switch is turn on (closed), diode is reverse biased and switch will conducts inductor current. When switch is turn off (opened), diode is forward biased. The inductive energy storage results on the inductor current, iL to flow. The current will flows through diode.The duty cycle, D can be calculated using following calculation

Vo = output voltage and Vd = input voltage

In continuous current mode (CCM), inductor value is chosen greater than minimum inductor current to ensure continuous mode of operation. (Roslan, 2009)

L ≥ Lmin =

Lmin = minimum inductor, D = duty cycle, f = frequency, R = resistance

2.4.2 Boost Converter

The boost converter is also known as step up converter. The boost converter is used to produce output voltage greater to the input voltage. The circuit diagram is shown in Figure 2.14.

Figure 2.4.4: Boost Converter (Rashid, 2004)

When switch is closed, the inductor is charged and the diode is reversed. When the switch opens, the inductor discharged into the capacitor. Then, the charges slowly discharge into the load. (Siti Noorhaninah, 2009)Output voltage is maintained constant by virtue of large C. The off state voltage impressed across power device is output voltage, Vo .(Roslan, 2009) The duty cycle, D can be calculated using following calculation

Vo = output voltage and Vd = input voltage

In continuous current mode (CCM), inductor value is chosen greater than minimum inductor current to ensure continuous mode of operation. (Roslan, 2009)

L ≥ Lmin =

Lmin = minimum inductor, D = duty cycle, f = frequency, R = resistance

2.4.3 Buck-Boost Converter

The buck-boost converter or Step-down/Step-up converter is used to raise or lower the output voltage. The circuit diagram is shown in Figure. The buck-boost converter is like a combination of buck and boost converter.

Figure 2.4.5: Buck-Boost Converter circuit (Rashid, 2004)

Besides that, this converter is known as inverting regulator (Siti Noorhaninah, 2009).

The circuit operation can be divided into two modes. During the mode 1, the power switch is turned on and the freewheeling diode D is reversed biased. The current is only flow through the inductor and power switch. During the mode 2, the power switch is turned off and the current would be flowing through the inductor L, capacitor C, load resistance R, and the diode D. In this condition, the freewheeling diode is forwarded biased (Rashid, 2004). In this circuit, Vo can be calculated by using equation:

Vo = -Vin (

D = duty cycle, Vo = output voltage and Vd = input voltage

When the duty cycle, D>0.5, output is higher than input ( as Buck Converter). When the duty cycle, D<0.5, output is lower than input (as Boost Converter) (Roslan, 2009).

2.4.4 Comparison of dc-dc converter efficiency

The most efficient dc-dc converter will be chosen to be used. Figure 3.2.1 (a)-(c) shows the PV power tracking waveforms for buck, boost and buck-boost converters under rapidly changing atmospheric conditions (about 40-85 mW/cm2). Figure 3.2.1 (d) shows the simulated tracking waveforms. Figure 3.2.2 (a)-(c) shows the tracking waveforms for buck, boost and buck-boost converters under slowly changing atmospheric conditions (about 80 mW/cm2). Figure 3.2.2 (d) shows the simulated tracking waveforms. From Figures 3.2.1 and 3.2.2, it is observed that the designed dc-dc converters successfully followed the variations of solar insolation

(a)

(b)

(c)

(d)

Figure 3.2.1: Tracking waveforms of dc-dc converter under rapidly changing atmospheric conditions. (Roslan, 2009)

(a)

(b)

(c)

(d)

Figure 3.2.2: Tracking waveforms of dc-dc converter under rapidly changing atmospheric conditions. (Roslan, 2009)

Figure 3.2.3 shows the graph of efficiency against the output for buck, boost and buck-boost converters. The plot shows the differences in the converters efficiency for buck, boost and buck-boost converters. The efficiency of buck converter is a little bit higher than boost and buck-boost converters. With the proposed maximum power point controller, these converters operate with high efficiencies under the maximum power point tracking (Ivan & Marko, 2007).

Figure 3.2.3 : Efficiency of DC-DC Converter (Ivan & Marko, 2007)

2.5 Maximum Power Point

A solar cell can be operated at any point along its characteristic current voltage curve. There are two important points on this curve; the open circuit voltage (Voc) and the short circuit current (ISC). (Siti Nur Afiszah, 2009) As shown in Figure 2.5.1, the Voc is the maximum voltage which a solar cell can provide at a zero current, whereas the ISC is the maximum current which a solar cell can provide at zero voltage.

Figure 2.5.1: Current versus voltage (I-V) and Current versus Power (I-P) characteristic for a solar cell. (Siti Nur Afiszah, 2009)

A plot of power (P) against voltage (V) for this device shows that there is a unique point on the I-V curve in which the solar cell generates the maximum power. This is known as the maximum power point (Vmp, Imp). The maximum power conditions always occur at the knee of the characteristic curve. Therefore, every PV application should be able to operate at the maximum power point.

Silicon solar cell typically produces only about 0.5 V per cell [24], a number of cells needs to be connected in series (called PV module). A PV panel is a collection of PV modules grouped together on a support structure. A PV array is a collection of PV panels. The effect of a temperature on the performance of a silicon solar cell is described in Figure 2.3. ISC slightly increase in temperature, but VOC and maximum majority decrease in temperature (Chaisook).

According to Figure 2.5.2 and Figure 2.5.3, it can be concluded that the characteristic of a solar cell at a given radiation level and temperature consists of a constant-voltage segment and a constant-current segment. Its current is limited at the short circuit current and its voltage is limited at the open circuit voltage. The maximum power conditions always occur at the knee of the I-V characteristic curve.

Figure 2.5.2: Effect of temperature on solar cell (Siti Nur Afiszah, 2009).

Figure 2.5.3: Typical I-V characteristic curves for different radiation levels (Siti Nur Afiszah, 2009)

2.6 MPPT

Maximum power point tracker (MPPT) is an electronic system that is needed to maximum the amount of power obtained from PV array to the power supply. There are a few methods that usually used like constant voltage method, incremental conductance method (IncCond) and perturbation and observation method (P&O). There are other methods that are infamous, but sometimes very appropriate, methods such as maximizing load current or voltage , fractional short circuit current control, array reconfiguration , linear current control , fuzzy control , neural network , dc link capacitor droop control , pilot cells , current sweep and limit-cycle control.

The module P-V characteristics are shown in Figure 2.6.1 show further that the derivative is greater than zero to the left of the peak point and is less than zero to the right (Balakrishna, Rajamohan, Nabil, Kenneth, & Ling, 2002).

∂P/∂V = 0 for V = Vmp (1)

∂P/∂V > 0 for V <Vmp (2)

∂P/∂V < 0 for V >Vmp (3)

Figure 2.6.1: Basic algorithm of MPPT

So, it is the role of MPPT to find the maximum power point and converts the voltage to be the same with the main system. Maximum power point tracker is used to ensure that the system always work close to the maximum power point every time the environment condition changed. MPPT also provide high conversion efficiency to minimize power loss.

2.6.1 Constant Voltage Method

The Constant Voltage (CV) algorithm is one of the simplest MPPT control method available. The operating point of the PV array is kept near the MPP by regulating the array voltage and matching it to a fixed reference voltage equal to the maximum power point voltage (VMPP) of the characteristic PV module or another revaluated best voltage value (Carvalho, Pontes, Oliveira Jr, Riffel, Oliveira, & Mesquita, 2004).

This method only can be use if the insulation and temperature variations on the array are not significant, and that the constant reference voltage is an adequate approximation of the true MPP. When the insulation and temperature varied, the operating point also will changed hence the MPP will also changed. There will be different data be use for different locations. This technique is more effective than P&O method and Incremental conductance method when the PV panel is in low insulation conditions. Because of this effectiveness, this method often used together with other MPPT techniques.

2.6.2 Perturbation and Observation Method (P&O)

The most commonly used MPPT algorithm is P&O method and is also known as hill-climbing algorithm. In Figure 2.6.2, the operating voltage of the PV array is perturbed and the value of dP/dV is calculated. If the value is dP/dV > 0, it means that the perturbation moved the array's operating point toward the MPP.

Figure 2.6.2: Sign of the dP/dV at Different Positions on the Power Characteristic (Roslan, 2009)

Next, the P&O algorithm would then continue to perturb the PV array voltage in the same direction. If dP/dV < 0, it means that the operating point moved the PV array away from the MPP, and the P&O algorithm reverses the direction of the. Figure 2.6.3 shows the flowchart of P&O algorithm method.

Measure V(k), I(k)

Calculate Power

P(k)=V(k)I(k)

P(k)>P(k-1) ?

YES

NO

V(k)>V(k-1) ?

V(k)>V(k-1) ?

Vref(k)

=Vref(k-a)+C

Vref(k)

=Vref(k-a)-C

Vref(k)

=Vref(k-a)-C

Vref(k)

=Vref(k-a)+C

Return

Figure 2.6.3: Perturb and Observe Method Flowchart (Roslan, 2009)

The P & O method is easy to implement as few parameters are to be measured and gives moderate efficiencies of about 95%. However, the algorithm becomes complex when rapidly changing site conditions are present and the efficiency depends on how the method is optimized at design stage. The implementation cost of this method is relatively lower. The problems with this method are it gives arbitrary performance with oscillations around MPP particularly with rapidly changing conditions and provides slow response. Sometimes, this method is not reliable as it is difficult to judge whether the algorithm has located the MPP or not (Balakrishna, Rajamohan, Nabil, Kenneth, & Ling, 2002).

2.6.3 Incremental Conductance

This incremental conductance uses the source incremental conductance method as its MPP search algorithm. It is more efficient than Perturb and Observe method and independent on device physics. (Nguyen, 2001) The method uses the PV array's incremental conductance dI/dV to compute the sign of dP/dV (Hohm & Ropp, 2000). It does this using an expression derived from the condition that, at the maximum power point, dP/dV = 0.

Beginning with this condition, it is possible to show that, at the MPP dI/dV = -i/v (Hohm & Ropp, 2000) (Hussein, Muta, Hoshino, & Osakada, 1995). So, it can be determined that the MPPT has reached the MPP and stop perturbing the operating point. The perturbing process should be continuing if the condition is not met yet. The relationship between dI/dV and -i/v] can be use to find the direction where the MPPT operating point must be perturbed.

Figure 2.6.3 shows the flowchart for INC method. The INC can track rapidly increasing and decreasing irradiance conditions with higher accuracy than P&O (Hohm & Ropp, 2000). However, because of noise and errors due to measurement and quantization, this method also can produce oscillations around the maximum power point and it also can be confused in rapidly changing atmospheric conditions (Optimizing sampling rate of P&O MPPT technique", 2004). Another disadvantage of this algorithm is the increased complexity when compared to perturb and observe. This increases computational time, and slows down the sampling frequency of the array voltage and current (Hohm & Ropp, 2000).

Figure 2.6.4: The Flowchart of the INC Method (Roslan, 2009)

Chapter 3

METHODOLOGY

3.1 Design Procedure

Figure 3.1 below shows the overall view of this project. From the PV panel, the current, IPV and voltage, VPV will go through the dc-dc converter. Then, the maximum power point tracker algorithm will control the voltage/current before going to load.

DC/DC

Converter

DC Load

PV panel

Gate Drive

Microcontroller

Controller

PWM

MPPT Algorithm

Figure 3.1.1

Figure 3.1: Overall view of the project

Before starting any simulation, the important data need to be set and calculate Based on the model of Solarex MSX-60, a switching frequency is set to 50 kHz, buck input voltage, Vin is 17.1 V and buck output voltage, Vo is 14.5 V. Firstly, the value for duty cycle is finded by using Equation() . The duty cycle value is 84.8%.

=

=0.849

=84.8%

For inductor, Equation () is used for calculation and the value getting is 0.26 mH.

Data

Vin

Vo

Duty cycle

Rload

Linductor

C (capacitor)

3.2 Modelling using Matlab/Simulink

The MATLAB/SIMULINK software is chosen to be used for the modelling and simulation process. This software prepares all the electrical and mathematical blocks that needed in modelling and simulating the Maximum Power Point Tracker. This software is simple and easy to use because it is more on graphical user interface pertaining to build or model any circuits or mathematical equations.

In this chapter, the reader will be able to grasp some idea on the usage of MATLAB/SIMULINK software. In addition, the method and steps in modelling the solar cell, PV array and MPPT are shown clearly. The modelling process was done by stages. The first stage was to model the mathematical equation for the diode current and the light generated photovoltaic current. Later, the part will be extended for the array model. On the second stage will be modelling for mathematical equation for Im, model current. Next on the third stage will be on modelling the Maximum Power Point Tracker algorithm. On the fourth stage will be modelling for the pulse width modulation.

Stage 1

Modelling the solar cell

Modelling mathematical equation for Ipv

Modelling mathematical equation for Io

Figure 3.2.1: First stage in modelling the solar cell

Stage 2

Modelling the solar cell

Modelling mathematical equation for Im (model current)

Figure 3.2.2: Second stage in modelling the solar cell

Stage 3

Modelling the MPPT algorithm

Figure 3.2.3: Third stage in modelling the MPPT

Stage 4

Modelling the PWM

Figure 3.2.4: Fourth stage in modelling the PWM

3.3 Building the Mathematical Modelling and Circuit

The components being used in developing and modelling the mathematical equation and also the circuitry are taken from the MATLAB/SIMULINK library as discussed earlier. In order to model Shockley diode current, the light generated photovoltaic current and saturation current, the components that being use are the voltage measurement block and current measurement block. Besides that on the circuitry part, buck converter, PWM generator, diode and resistor needed to fulfil the model.

Figure 3.3.1 below shows the mathematical modelling for the reverse current saturation (I0/IRS) at the reference temperature which given by the equation 2.1 as below.

Figure 3.3.1: Mathematical Modelling Implementation for Io

Figure 3.3.2 below shows the mathematical modelling for the light generated current of the photovoltaic cell which depends linearly on the influence of temperature and solar radiation as given by the equation 3.2 below.

Figure 3.3.2: Mathematical modelling for the light generated current

Figure 3.3.3 below shows the mathematical modelling for the model current Im referring to the appropriate model circuit for which given by the equation 3.3 below.

Figure 3.3.4 depicts the PV array modelling, while Figure 3.3.5 shows the circuitry modelling part. The PV circuit is made as a subsystem and later put the mask.Next, Figure 3.3.6 shows theMaximum Power Point Tracking Algorithm circuit. Figure 3.3.7 depicts the Pulse Width Modulation.

Figure 3.3.4: PV array modelling

Figure 3.3.6: Maximum Power Point Tracking Algorithm Circuit

Figure 3.3.7: Pulse Width Modulation

Figure 3.3.8 below shows the whole PV system with attached MPPT.

3.2.1 Simulation Software

All simulation for this project will be done by using MATLAB software package.

3.2.2 PV Panel

The simulations of the PV panel will be done by referring to photovoltaic module Solarex MSX-60. The datasheet of the module can be reviewed in the appendix.

3.2.3 Dc-Dc Converter

3.2.4 MPPT algorithm

There will be three types of MPPT will be used in this project that is Incremental Conductance method, Perturb and Observation method and Constant Voltage method.

Each of the three types will be simulated using the Matlab software. The result will be analyzed based on efficiencies. The best with highest efficiencies will be chosen to be use in the project.

3.3 Simulation of Photovoltaic Panel

Simulation for photovoltaic panel was built by using Equation 2.1 and 2.2 in Chapter 2.

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