Solar Freaks

1.1 Solar Photovoltaic and Renewable Energy

Electricity is most popular form of energy and used in homes, businesses, industries and transportation. It is clean, convenient, easily transferable and usable. Such positive attributes of electricity require high demand for electrical energy and as demand rises these energy sources diminish accordingly. Unfortunately, electrical energy sources we use, such as petroleum, coal, and natural gas is mainly from fossil fuels. These sources have two unwanted consequences. First, they are proportionally diminishing against high demand and second they are contributing to the raise of carbon dioxide (CO2) emission gases. These gases are the ground for climate change which causes temperature rising, droughts, floats and hurricanes. The pollution free ‘green’ energy sources such as solar, wind and thermal are becoming alternative to those black energy sources to tackle these problems. Renewable energy will not diminish over time, therefore it is sustainable and clean.



Source: [2]

Fig 1.1: The solar potential around the world.

Solar energy is one amongst the other renewable energy source and the vast abundance of solar potential available all over the world makes it very popular (Fig 1.1).The sun light reaches earth’s surface is enough to provide 10 thousand times of global energy consumption [2]. On average, each square meter is exposed to produce 1700 kWh energy every year [2]. From the above figure we can see that Australia has great potential of solar incident falling almost all over the continent. Solar energy has many friendly attributes. Solar energy can be easily install on houses and buildings, and can run with low maintenance after initial setup. It can be very economical in remote areas where grid connection is unavailable or costly. It does not create any sorts of noise and emissions. As all other renewable energy sources, it is independent of fluctuations in price [1].

Photovoltaic energy production will increase in the near future and will create over three millions jobs worldwide (Figure 2). Grid connected PV system is the most developed PV System, it is expected to reach around 50 thousands MW production and overall the PV production is expected to reach over 60 thousands MW by 2025.

Employment in PV related jobs shows that there will be half millions jobs by 2015 and over 3 millions jobs will be created by 2025, mostly in installation and retailing as well as production.



Source: [2]

Figure 1.2: Growth in world solar market and employment in PV related jobs worldwide respectively.


1.2 Battery Charger from Solar Cell

Solar (photovoltaic) cell is a device that converts energy in the photon of light into an electrical current, generates electricity from light. If properly captured and stored, it can give continuous supply of electrical energy. Storing the electrical energy into the batteries is preferred method used in remote areas where it is very difficult and expensive to connect to a grid. Unfortunately, the photovoltaic cell has non linear characteristics and availability of sun light varies depending on the season and atmospheric conditions.

With proper electronic and control system, we can obtain maximum possible power from photovoltaic cell. Maximum power point happens at the knee of the PV I-V curves called an operation point where voltage and current intersect to produce maximum available power (P = V*I). For this purpose, maximum power point tracker (MPPT) used to keep the operating point at the knee of the PV I-V curve throughout the day with changing insolation, temperature and load conditions.

Figure 1.3: Battery charger from solar cell system.


Above figure shows the battery charger from solar cell system. In our case, MPPT is a microcontroller which tracks the maximum power point from the PV module. The transducer sensor and the voltage divider are used to obtain the current and voltage respectively. The microcontroller senses values and changes the duty cycle accordingly and sends a PWM signal to H-Bridge power converter. Output of the H-Bridge converter connected to the transformer which steps up the voltage and through rectifier it is converted to DC. Finally, rectified voltage charges the 12 V battery.

2.1 PV Systems

Grid Connected (Utility Interactive) PV System

Grid connected is the most popular type of PV systems for houses and businesses in the developed world (Fig1.2). Grid connected PV system is connected to the utility grid and the generated power feed into the utility grid. Photovoltaic solar panel delivers dc power to a power conditioning unit (PCU) that converts dc to ac and sends power to the building. The grid connected system allows excess power produced to be sold to the utility during the daylight hours. Then outside daylight hours, electricity can be taken from the utility. The power conditioning unit is designed to cut the PV system from the grid in the case of power outrage. In the case of outrage, breakers isolate a section of the utility.


Source: [1]

Fig 2.1 Grid connected PV System.


Stand Alone (Off-grid) PV System

Stand alone (Off-grid) PV system, also the model for this treatise, is connected to a battery which stores the electricity generated (Figure 2.2). The battery acts as a main switch and the system can be supported by the back up generator if there is not enough energy stored in batteries. This system is very satisfactory and costly effective especially in remote areas where extending utility grid or high maintenance generators expensive and noisy. Apart from the back up generator, purpose of the treatise is very similar to the stand alone PV system, charge 12 V battery with maximum available power obtained from the PV panel. The combination charger –inverter can convert both ac to dc and dc to ac. As a charger, it converts from the generator to charge batteries and as an inverter it converts battery dc into ac load.





Source: [1]

Figure 2.2 Stand alone PV system with back up generator.


Water Pumping PV System

Another type of PV system is where PV system combined with another source of power such as water pump. The simples PV water pumping system may consist of a PV array attached to a DC pump. PV system can raise water from a well or spring and store it in pressurized tank, or it can circulate water through a solar water heating system.
Water is pumped when sun light is available or stored in a tank for later. The water pump system is very simple, low cost and reliable. More complex water pump systems may have a battery and inverter to run a conventional AC pump, along with a linear current booster (LCB) to improve performance in low-light conditions [1].



2.2 PV Cell

Characteristics of a Photovoltaic Cell

The theoretical explanation of the photovoltaic effect is developed by Albert Einstein as a part of quantum theory in 1904. PV cell has two layers of semiconductor materials, (mostly silicon) one positively charged p-type material and the other negatively charged n-type material. When PV cell exposed to the sunlight photons are absorbed and hole-electron pairs formed. Holes collected on the p-type and electrons on the n-type, creates a voltage that can be used to deliver current to the load. The voltage-current characteristic curve for the p-n junction diode is



where Id is the diode current (A), Vd is the voltage across the diode terminals (V), Io is the is the reverse saturation current (A), q is the charge of an electron (1.602*10^-19 C), k is the Boltzmann’s constant (1.381*10^-23 J/K) and T is temperature (K).

Source: [3]
Figure 2.3 Equivalent circuit of PV cell.



I-V characteristic of a PV circuit (neglecting the shunt resistance) is given by the formula



where Isc is the light generated current, Isat is the reverse saturation current , q is the electronic charged, K is the Boltzmann constant, A is a dimensionless factor, T is the temperature in °K,, Rs is the series resistance of the cell.

From above formula, we can observe that I-V output of PV cell is non-linear and changes with the temperature, insolation and load condition. Each curve has maximum power point which is the optimal operation point for the efficient use of the solar array [4].


Impacts of Temperature and Insolation on PV Cell

The output of PV module can change dramatically with changing insolation and temperature conditions. Figure 2.4 shows the changes in insolation and temperature respectively. The insolation drops the PV panel current in proportion. If the insolation reduces to half, the output power reduces by half too. The insolation drops also changes the PV panel voltage. The increase in temperature, decrease the open circuit voltage and only increase the short circuit current slightly. Photovoltaics may perform well better at cold than hot temperature conditions. PV cells may vary in temperature for ambient temperature changes and insolation changes. Only small fraction of insolation on cell can be converted into electricity and the rest converted to heat. To account for changes in cell performance with temperature, the designers indicate nominal operating cell temperature (NOCT).






Source: [4]

Figure 2.4: Insolation and Temperature Characteristics of PV Panel respectively.


The NOCT is cell temperature in a module when ambient is 20 °C, irradiation 0.8 kW/m^2 and wind speed is 1 m/s. Other ambient conditions



where Tcell is cell temperature(°C), Tamb is ambient temperature and S is solar insolation (kW/m^2).








2.3 Current–Voltage Load Curves

Resistive Load I-V Curves

When I-V curve for load plotted onto the same graph with the I-V curve for PV, the intersection point is one spot at which both load and PV are satisfied and this is called operating point.


Source: [1]

Figure 2.5: The operating of PV cell.

For load
V = I*R or

when we plot it on the I-V curve, it is a straight line with slope 1/R. As we increase the R, the operating point will move along PV I-V curve from left to right. If we use variable resistance as load and vary its resistance pairs of current and voltage can be obtained.



Since the power delivered to the load is

P = I * V

There will be one particular value of resistance that will provide maximum power



where Rm and Im are the voltage and current at maximum power point (MPP).




Source: [1]

Figure 2.6: Operating point moves with resistance changes on I-V curve.




Battery Load I-V Curves

A real battery has an internal resistance that can be modelled with ideal battery of voltage VB series with internal resistance Ri. During the charge cycle positive flow into battery can be written as

V = VB + Ri*I

which can be plotted slightly tilted, straight line with slope 1/Ri. Because of the internal resistance that battery possesses, the applied voltage needs to be greater than VB during charging.

During discharging, the output voltage of the battery is less than VB, I-V curve moves back to the left and slope becomes -1/Ri.



Source: [1]

Figure 2.7: Battery I-V curves during charging and discharging.


2.4 Maximum Power Point Tracking

Maximum power point tracking is essential part of PV system. MPPT are used to control a PV panel at its maximum power point. There are many MPPT algorithms developed and implemented. The methods can vary in complexity, cost, speed, popularity, sensor required and range of effectiveness [6]. A few of these methods are examined:

• Perturb and Observation (PAO) Method
• Improved PAO Method
• Incremental Conduction (IC) Method
• High Climbing Method
• Modified Adaptive High Climbing Method

PAO and Incremental Conduction Methods are based on the same technology. They both regulate the PV panel’s to the voltage of maximum power operating point (VMPOP). This point is tracked and updated to satisfy the mathematical equation dP/dV = 0 where P and V are power and voltage respectively. Hill Climbing method based on the PV panel’s output power and switching duty cycle. Different from PAO and IC methods, High Climbing method can track the maximum power point if dP/dD = 0 where P and D is the power and duty cycle respectively.

There are number of requirements important for a successful maximum power point tracker [7].

 Stability
 Dynamic response
 Steady state error
 Robustness to disturbances
 Efficient in a large power scale


Perturb and Observation (PAO) Method

PAO method in the case of P-V characteristic is on the left of the MPP dP/dV > 0 and on the left MPP is dP/dV < 0. If the voltage of the PV panel perturbed in a given direction and dP/dV > 0 means that the perturbation moved toward the MPP. Then PAO will continue to perturb voltage until it reaches dP/dV = 0. However, if the dP/dV < 0 then change in operating point moved away from the MPP and PAO moves backward to reverse until it finds the dP/dV = 0 (Figure 2.8).



Source: [5]

Figure 2.8: Sign of dP/dV at different positions.

If we increase the voltage the power will increase and if we decrease the voltage power will decrease and on the right hand side if we increase voltage power will decrease. Therefore, if change in power is positive perturbation should keep to reach MPP (dP/dV=0) and change in power is negative perturbation should reversed.
The advantage of the PAO method is that is has low computational demands and it is easy to implement. The disadvantage of PAO method is that it can be tracking in the wrong direction under rapidly changing atmospheric conditions.


Improved Perturb and Observation (PAO) Method

PAO method can be confused in rapidly changing insolation conditions. If change in power is due to the change in the insolation intensity rather than the increment in the voltage, the MPPT can get confused. It will interpret the change in the power as an effect of its own. Improved PAO method performs an additional power measurement between two sampling period. The change in power between Pk and Pk-1 reflects the change in power due to the environmental changes, as no action has been made by MPPT.




Source: [5]

Figure 2.9: Measurement of power between MPPT sampling

Improved PAO method performs superior to the traditional PAO method during rapidly changing irradiance, resulting in the high dynamic efficiency and improved PAO is able to avoid wrong tracking during rapidly changing irradiance [5]. Flow chart of improved PAO method is shown in Figure 2.10.




Source: [5]

Figure 2.10: Flow chart of dp-P&O Method

Incremental Conduction Method

Incremental conduction method based on the fact that the PV power is zero at MPP, negative on the right and positive on the left. This is given by

dP/dV = 0 ΔI/ΔV = -I/V MPP
dP/dV > 0 ΔI/ΔV > -I/V left of MPP
dP/dV < 0 ΔI/ΔV < -I/V right of MPP

with considering,




Source: [6]

Figure 2.11: Incremental Conduction Algorithm.

In Figure 2.11, flow chart of Incremental Conduction method is shown. Once MPP obtained (VMPP = Vref) operation maintained at this point until further changes in ΔI. Then new MPP tracked by increasing or decreasing Vref. The increment size determines the how fast MPP tracking. Fast tracking can be achieved with bigger increments but the system may not operate exactly at MPP, oscillate about it instead [6].








High Climbing (HC) Method

So far, the maximum power point tracking method we examined is based on PV’s Array voltage to optimum set point which represents the voltage of maximum power operating point [7]. The MPPT tracks and updates the mathematical equation dP/dV = 0 continuously. High climbing algorithm, on the other side, based on the relationship between the PV module power and a switching duty cycle. Figure 2.12 below shows the PV output power and D switching duty cycle of DC/DC converter. So at point dP/dD = 0 the MPPT will be at maximum (Figure 2.12).


Source: [7]

Figure 2.12: P-D relation curve with a switching mode converter between PV and load.

Parameter definitions for high climbing algorithm,
P –power level
D –duty cycle
Slope –is either ‘1’ or ‘-1’, indicates the direction in order to increase power output
a –increment step for duty cycle
X (k) –current power or duty cycle value
X (k-1) –previous measurement of power or duty cycle.


Source: [7]

Figure 2.13: High Climbing method algorithm.

High climbing method is preferred because its simplicity. Unfortunately, high climbing method as in PAO method is sometimes deviates from MPP in rapidly changing atmospheric conditions. Another disadvantage of high climbing method has difficulty in providing good performance in both dynamic and steady state response [7]. When the incremental step of duty cycle ‘a’ is small, the tracking time is long and there is slow dynamic response. When the incremental step of duty cycle is large output power fluctuates and average power is less than the maximum.


Modified Adaptive High Climbing (MAHC) Method

Modified adaptive high climbing method is further developed version of high climbing method. To solve the increment step of switching duty cycle problem in high climbing method this method offers to make “a” large during the transient state and “a” small during steady state.



“a” is linear equation given by



where |ΔP| = P(k)-P(k-1) and M is constant parameter.

Source: [7]

Figure 2.14: Modified adaptive high climbing algorithm.








Source: [7]

Table 2.1: Performance comparison between MA and ordinary HC method.

High climbing method demonstrates better steady state performance with small incremental step of duty cycle but poor dynamic response. Modified adaptive high climbing method control demonstrates smaller steady state error than high climbing method. MAHC method has tracking speed 5 seconds faster than high climbing. Modified adaptive high climbing control algorithm provides better steady state performance than high climbing algorithm. MAHC shows overall better performance than the HC algorithm in both transient and steady-state response [7].

3.1 Hardware Design

H-Bridge Converter

Non isolated 4-Quadrant converter designed to drive PWM signals into the transformer. PWM signals connected directly from the PIC microcontroller and the ICs supply voltage provided externally.

The MOSFETs, Q1 and Q4 form one pair and Q2 and Q3 form the other pair (Figure 3.1). Q1-Q4 and Q2-Q3 switch ON/OFF simultaneously. Transformer connected to the output and current flowing in one direction. When Q1-Q4 turn on (Q2-Q3 turn off) DC supply voltage (DC+) apply on the transformer and current flow from Q1 to Q4. When Q2-Q3 turn on (Q1-Q4 turn off) the current will flow from Q2 to Q3 to maintain the flow of the armature current.


Source [8]

Figure 3.1 Full Bridge converter.

The output voltage will be

Vo = Vdc*(2*D-1)

where Vo is the output voltage, Vdc is the DC supply voltage, D is the duty cycle of the Q1-Q4 (D-1 is the duty cycle of the Q2-Q3). Duty cycle provides magnitude and polarity control of the output voltage.

In order to make Q1-Q4 pair switching, the four PWM signals from PIC feed into the inputs of the converter. Note that the Q1-Q2 and Q3-Q4 are complementary signals. The PWM signals sent to the LED and gate drivers. The gate driver IR2101 provides gate signal to Q1and Q2 and second driver provides gate signal to Q3 and Q4. MOSFETs are voltage controlled devices and their switching action on the charge-discharge of input capacitances across the gate-source and gate-drain terminals. There are two capacitors (C2 and C4) across the pins of the gate drivers to charge MOSFETs. MOSFETs then provide average voltage (positive and negative) across the output load (to the primary side of transformer).



Figure 3.2 Build H-Bridge converter

Transformer

Transformer is designed to step up the voltage at a ratio of 1:2. AC signal from the H-Bridge converter injected into the transformer. Transformer boosts the voltage and sends to the rectifier to convert to the DC. The specifications of the core material are given in Table 3.1 and the date sheet is given in Appendix E.


pk i Bmax G Le mm Ae mm2 Amin mm2 ALmin nH/1000T
1590 225 - 114 211 209 2910

Table 3.1 Specifications for ETD N67 49 core.

The switching frequency is 5 kHz and this makes the period is 0.0002 second. Then the duty cycle


is 0.583. Then the inductance is


=
is 291.5 micro H. Finally we can calculate the number of turns from the equation

= 31.65


and since it is 1:2 transformer the secondary side is going to have a turn of 64. The transformer designed according to the values obtained from calculations is shown in Figure 3.3.




Figure 3.3 Transformer designed for the project.

When current flows through a conductor, it generates a flux. This flux induces the eddy currents to oppose the ac flux. So the eddy currents reduce the current density at the center of the conductor and the majority of the current flows near or surface of the conductor. The skin effect causes the effective resistance of the conductor to increase with frequency. Setting the maximum frequency of the project 5 kHz, the skin effect

is 1.066 mm. Thus the diameter is 1.066 mm and the radius is 0.533 mm. This size of radius is thick and it is hard to round around transformer and also the inductor. To tackle this problem the diameter halved. Two wires with diameter 0.533 mm chosen and rounded together to make it equal to the skin effect diameter value founded. Same wire used for the inductor design as well.


Rectifier, Inductor and Capacitor

Rectifier is used to convert AC to DC. Bridge rectifier used and build between transformer and inductor and capacitor. Details of the rectifier are given in Appendix F. 35 V and 470 micro Farad valued capacitor used to smooth voltage at the output. Inductor is used to smooth the current at the output. When designing the inductor the minimum PV voltage and output voltages are picked, so 5 V and 12 V respectively. We find period to be 0.0002. Maximum current ripple is 0.3 A, duty cycle is 0.583 and the switching frequency is 5 kHz.

Therefore the inductance


is 0.0019 mH. Inductance used to find the number of turns.

The number of turns



where L is 0.0019 and AL is , we obtain the number of turns to be 144. Also skin effect is the same in the transformer which 1.065 mm (Figure 3.4).




Figure 3.4 Inductor, rectifier (Appendix F) and capacitor


Sensor

Sensor is designed to sense the current from the PV and send it to PIC microcontroller (Figure 3.5). Also the voltage divider added to circuit to calculate the voltage and send it to PIC microcontroller. INPUT is connected to the PV panel and OUTPUT is connected to the H-Bridge converter. I and V are hooked up to the PIC microcontroller to update the MPPT.


Figure 3.5 Sensor circuit design

The HX10 NP transducer date sheet also is provided in the Appendix C. The current range for the current transducer is the 5 to 10 A. The transducer needs to be set to +15 V and -15 V. To obtain proper +15 V and -15 V the dual DC Power Supply used. Positive and Ground of one supply and negative and ground of the second supply short circuited in order to create -15 V and +15 V respectively. Then the remaining negative and positive sockets used to supply voltage to the Transducer (Figure 3.6).


Figure 3.6 Sensor designed for the project.


3.2 Software Design


Microcontroller

PIC18F4431 microcontroller used to control the system. PIC18 microcontrollers have high computational performance at a low economical price with high endurance enhanced Flash program memory and a high speed 10-bit Analog Digital Converter [9]. The PIC18 microcontrollers mostly used in power control and motor control applications. PIC18 microcontrollers have following specifications

• 14-bit resolution power control PWM module (PCPWM) with programmable
Dead-Time Insertion
• Motion Feedback Module (MFM) including a 3 Channel Input Capture (IC)
• High Speed 10-bit A/D Converter (HSADC)

PWM module provides 1, 2 or 4 modulated outputs for controlling the half-bridge or full-bridge converters. Since full bridge converter used in this project, 4 modulated outputs are selected to control H-Bridge driver. High Speed 10-Bit Analog Digital Converter incorporates programmable acquisition time allowing a channel to be selected and reducing the code overhead with conversation initiation while not waiting for sampling period.

PIC18F4431 Motor Control Development Board is designed to allow PIC18F4431 microcontroller to be easily interfaced to existing Labvolt motor control power electronics [10]. The Motor Control Development Board has following features

• 6-channel (3 complementary pairs) PWM output buffer, with sync
• 4 pushbutton switches
• 3 finger adjust pots for analog inputs with VREF or VDD as reference
• Analog voltage reference VREF (4.1V)
• RS232 port with level translator and RTS/CTS handshake capability
• Serial EEPROM or FRAM support
• Serial 8-bit LED indicator
• Power supply reverse polarity protection
• 2mm and 4mm sockets for power supply connection
• 2 programming sockets- one general-purpose 5-pin header for use with PRESTO
programmer or similar; one RJ12 Microchip ICSP programmer compatible.
• Processor Reset switch
• External access to all processor pins via 2 banks of 20 pin headers. -Allows an external PCB or circuit to be easily connected. (*With the exception of RA6, RA7 and /MCLR)

C language was chosen to program the PIC18F4431 microcontroller. It is faster and requires less coding compare to the assembly language. MPLAB C18 compiler also downloaded to convert C code into assembly code. The works done by previous years’ students and also the codes from ELEC3204 Power Electronics and Drives project was used. But there has to be slight changes because no computer interface used in this project and codes from ELEC3204 was in assembly language.

The input reference voltage is set to 5 V. The clock frequency chosen the PICF4431 microcontroller is 5 kHz. To generate PWM signal modules from the previous years used. So reference voltage set up to 5 V in ADCON1 register. For reading purposes ADC conversation set to 16 acquisition times.

10-bit Analog to Digital conversion (A/D) set to channels RA0 and RA1 for voltage and current respectively. But to initialize A/D conversion certain steps need to be adopted

• Configure A/D module
• Turn on ADC
• Start sample/conversion sequence
• Wait for A/D conversations to complete
• Read ADC results, clear ADIF flag, and reconfigure
For the MPPT, the High Climbing (HC) method is used. The microcontroller follows the HC algorithm step by step. At first, it detects voltage and current values from the PV panel then multiples it to obtain the power (P=V*I). Then it gets the next values calculates power and compares with previous value. If it is bigger than previous value the duty cycle incremented, if not it is decremented. The code written in C language is in Appendix A.

3.3 Testing

The tests of the project carried out in the level 4 laboratory in Electrical Engineering building. The set up is as seen from the Figure 3.7. Two light sources provide light to fall on the solar panel. Solar panel is connected to the sensor. Between sensor and the panel there is voltage and current meters connected to observe the input readings. The sensor sends the voltage and current readings to the PIC microcontroller and the PIC microcontroller calculates the MPPT and sends the PWM signals to the H-Bridge converter. Transformer connected to the H-bridge steps up the voltage and through rectifier the voltage converted to the DC. Inductor used to smooth the output voltage. The voltage and current meters also connected to the load for the output readings. The sketches and graphs of the testing will be discussed in the next section.



Figure 3.7 Testing of the project.

4.1 Results and Discussions

The results obtained during the testing will be discussed in this section. The theoretical research and information in Chapter 2 will be compared with the results and information obtained during the practical experiment. Experiments are done in the Level 4 laboratories in Electrical Engineering building. Solar energy provided with the lights and BP solar panels are used. The results are taken under different changing environmental conditions such as temperature and irradiation and also the different loads. The maximum power point tracking and different duty cycles are shown with graphs and tables. Finally the 12 V power battery tests are taken and demonstrated.





Temperature Impact

In Figure 4.1 below voltage and current readings are taken at 23, 27 and 37 °C in each 30 second periods. The temperature on the panel measured with the thermometer and then values recorded. If the graph is compared with the Temperature Characteristics graph in Figure 2.4 we can see that current is low at low temperatures and high at high temperatures. The Figure 4.1 proves that as temperatures raise the current rises and as a result the output power increases. The values for voltage is not shown on the graph because it is practically the same all different temperatures but it will be mentioned when the power calculations done and the maximum power point tracking results discussed.




Figure 4.1 Temperature Characteristics of the system.






Insolation Impact

Figure 4.2 shows the current variation at different insolation. The insolation changes are taken at angles of 10, 40 and 50 ° in 30 second each. When the graph is compared with the Figure 2.4 the insolation characteristics, it can be observed that the greater insolations causes the larger current run through the PV module and vice versa. The insolation which measure kW per meter square could not be able to measure directly but obtained through the changing the panel angles and light sources. The voltage variations did not take place in graph as there is only small changes occurred for every degree. However it will be examined in the power calculations and maximum power point tracking.




Figure 4.2 The Insolation characteristics of the system.






Load Impact

The system also tested with different loads. In Figure 2.6 the graph shows the operating point with different resistances. The figure shows that the as we increase the resistance the voltage increases and the current decreases. In the experiment the current meter connected series with the circuit and the current recorded. The voltage graphs are printed on the oscillator (Figure 4.4). Then voltage and the output power calculated. The results are shown in Table 4.1. Table shows that the output power increases with the resistance. Also the graph obtained from the readings and calculations shows similarity with Figure 2.6. By comparing both current versus voltage graphs, we can guess that the maximum power point is just at the knee of the curve which points around 10 V.

Resistance (Ω) Current (A) Voltage (V) Output Power (W)
15 0.33 4.95 1.634
30 0.28 8.4 2.352
45 0.23 10.35 2.381

Table 4.1 Resistance and current readings and, voltage and power calculations.
FFigure 4.3 The voltage versus current graph as load varies.








Figure 4.4 Load voltages at 15, 30 and 45 Ω respectively.



Maximum Power Point Tracking

One of the important parts of analysis section is to prove that the system is tracking the maximum power point. This will be proved with two results obtained previously but not completed yet. The temperature and insolation characteristics and changing duty cycle accordingly will be compared with the High Climbing (HC) algorithm and demonstrated that the MPPT is working.


Temperature (°C) Voltage (V) Current (A) Power (W)
23 18.5 0.028 0.52
23 18.3 0.043 0.79
23 18.4 0.034 0.63
23 18.4 0.034 0.63
23 18.4 0.028 0.52
37 18.8 0.507 9.50
37 17.4 0.489 8.51
37 17.4 0.461 8.02
37 15.5 0.442 7.24
37 17.5 0.440 7.70
27 18.6 0.108 2.00
27 18.0 0.117 2.10
27 18.8 0.960 1.80
27 16.1 0.121 1.95
27 18.8 0.108 2.03

Table 4.2 Power calculations from changing temperature.










Figure 4.5 Duty cycle changes shown with 23, 37 and 27 ° respectively.




In Chapter 2, HC algorithm explained and Figure 2.12 shows the P-D relation. Table 4.2 and Figure 4.5 shows output powers and duty cycles at 23, 37 and 27 °C respectively. There are three different temperatures and three different duty cycles in the figures. At 23°C, power is low and duty cycle is around 10-15 %. When temperature raises to 37°, power increases and duty cycle reaches around 30-40 %. HC method proposes that the duty cycle changes according to the power increment and decrement. When power increase it means change in power is positive the duty cycle will increase. That is just what happened when power went up. Now if the temperature goes down to 27°C which power will reduce around 5 W (Table 4.2), so the change in power will be negative and duty cycle will go down. As it can be seen from Figure 4.5 duty cycle is now 15-20 %. This shows that duty cycle is tracking the maximum power point according to the change in power.

Similarly, the same conclusion can be obtained from the insolation changes. Table 4.3 and Figure 4.6 shows the power calculations made with changing insolation and duty cycle responses respectively. By observing the power changes at different insolations, the duty cycle can be recorded. Change in power is low at 10° around 2.5 W and power rapidly increases to around 7 W and the duty cycle increases dramatically. Again after insolation reduces at 40° the power decreases and change in power is negative now and the duty cycle reduces slightly.

These two different temperature and insolation analysis show that the MPPT is tracking the maximum power with changing environmental conditions such as temperature and insolation.









Insolation (°) Voltage (V) Current (A) Power (W)
10 14.9 0.187 2.34
10 15.9 0.192 3.05
10 16.0 0.179 2.86
10 16.1 0.185 2.98
10 16.8 0.173 2.91
50 16.2 0.420 6.80
50 18.6 0.337 6.27
50 17.1 0.425 7.27
50 16.3 0.429 7.00
50 15.9 0.418 6.65
40 15.9 0.372 5.91
40 17.4 0.301 5.24
40 17.1 0.327 5.60
40 17.2 0.325 5.56
27 13.7 0.371 5.08

Table 4.3 Power calculations from changing insolation.














Figure 4.6 Duty cycle change with insolation.



Battery Charger

As proposed in the first chapter, the aim of the project is to design the solar system to charge 12 V battery. Also mentioned in section 2.3, that voltage needs to be greater than 12 V because of the internal resistance the battery possesses. To achieve this, first the 12 V battery short circuited to the PV panel, voltage and current values read. Then the 12 V battery connected to the load and measurements took again. The results are given in the Table 4.4.

Voltage (V) Current (A) Power (W)
P SC 12.8 0.44 5.632
Load 12.60 0.32 4.032

Table 4.4 12 V battery results.

Then the efficiency is



72 %. Despite the loss in the system the voltage is greater than 12 V and the current reading is 0.32 A. The power delivered to the battery is 4.032 Watts. Since the current is flowing into the battery is positive the battery is being charged. If the current was negative it would tell us that battery voltage is less than 12 V and current would be negative. Therefore the generated power was able to charge battery. The voltage measured with duty cycle shown in the same graph is given in the Figure 4.7.










Table 4.6 The 12 V battery charger.

5.1 Conclusion

The maximum power point tracking is an incredibly complex system and needs to be very carefully designed and implemented. The complexity of the system only can be solved with deep understanding of the theoretical details of the maximum power point tracking and to carry it well to the practical work. The project both software and hardware parts also must be integrated to obtain precise accuracy.

In conclusion, this project successfully achieved to track maximum available power from solar panel which able to charge 12 V battery at the output. Also the theoretical explanations and practical results compared and henceforth the maximum power point tracking proved. The maximum power point tracker implemented in this project is working around 72 % duty cycle.


On the other side there is the power loss in the system. But despite the loss, the system was able to charge the battery which is primary objective of the project. Along the battery other appliances working in DC voltage can be used and charged.

BIBLIOGRAPHY

[1] Masters, Gilbert M. “Renewable and Efficient Electrical Power Systems”
John Wiley and Sons., 2004

[2] Dr, Hoffman, Winfried (EPIA) and Teske, Sven (Greenpeace), “Solar Generation”,
September 2006,

[3] Hua, Chihchiang and Shen Chihming, “Control of DC/DC Converters for Solar
Energy System with Maximum Power Tracking”
National Yunlin University of Science & Technology, Taiwan

[4] Abu Tariq, Jamil Asghar M.S. “Development of an Analog Maximum Power Point
Tracker for Photovoltaic Panel”
2002, India Aligarh Muslim University

[5] Sera, D. ,Kerekes, T. , Teodorescu, R. , Blaabjerg, F. “Improved MPPT Method for
Rapidly Changing Enviromental Conditions”
Aalborg University Denmark, 2006

[6] Esram, Trishan, Chapman Patrick L., “Comparision of Photovoltaic Array Maximum
Power Point Tracking Array Tecniques”
Transactions of Energy Conversion, Vol. 22 No. 2, June 2007

[7] Xiao, Weidong, Dunford, William G. “A modified Adaptive Hill Climbing MPPT
Method for Photovoltaic Power Systems”
IEEE Power Electronics Specialist Conference, Aachen, Germany, 2004

[8] Full bridge converter
www.maxim-ic.com.cn


[9] Microchip PIC18F4431 Data Sheet
www.microchip.com

[10] M. N. F. Nashed “Low Cost Highly Efficient of Complete PV System”
Electronic Research Institute, National Research Centre. Cairo, Egypt.

[11] R.M.Ramaison, J.Bordonau, A. Esquivel, J. Peracaula “Analysis and Design of a Resonant Battery Charger for PV System”
Universitat Politecnica de Catalunya (UPC), CETYS Universidad-Campus Tijuana.

[12] Trishan Esram, Patrick L. Chapman, “Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques”

Could you please upload the Pics and photgraphs

i need to figures you which you talked about,especailly mppt circles.I am working on solar boat and we are using mppt charger so please give links of figures...

Guys here is my mates thesis with all the figures in it.. I have posted it unsecured with his permission..
There are a few errors etc..