Commonly Used Algorithms for MPPT

The amount of electrical power generated by a photovoltaic system depends on solar irradiance (solar energy per unit area of the solar panel’s surface) and other conditions such as temperature and cloud cover. The current and voltage at which a solar module generates the maximum power is known as the maximum power point. The location of the maximum power point is not known in advance.Solar inverters or charge controllers use maximum power point tracking (MPPT) to get the maximum possible power from the PV array. Solar cells have a complex relationship between solar irradiation, temperature and total resistance that produces a non-linear output efficiency known as the I-V curve.
It is the purpose of the MPPT system to sample the output of the cells and determine a resistance (load) to obtain maximum power f or any given environmental conditions. Essentially, this defines the current that the inverter should draw from the PV in order to get the maximum possible power (since power equals voltage times current).

The current and voltage at which a solar module generates the maximum power is known as the maximum power point

Maximum power point tracking (MPPT) modifies the electrical operating point of a solar energy system to ensure it generates the maximum amount of power. This involves finding the current or voltage of the solar panel at which maximum power can be generated. MPPT improves the electrical efficiency of a solar energy system, thus reducing the number of solar panels or arrays required to generate a desired output.

Different Types of MPPT Algorithm

There are various methods or algorithms available to implement Maximum Power Point Tracking. Among them, the most efficient and commonly used methods are-

• Perturb & Observe Method (P&O)

• Incremental Conductance Method (INC)

• Constant Voltage Method

• Current Sweep Method

I'll Discuss briefly on  P & O Method and INC as these two methods used commonly.

• Perturb & Observe Method (P&O)

In this method, the device (controller/inverter) adjusts the voltage by a small amount from the array and measures power; if the power increases, further adjustments in that direction are tried until power no longer increases. This method is most common, although this method can result in oscillations of power output. It is referred to as a hill climbing method, because it depends on the rise of the curve of power against voltage below the maximum power point, and the fall above that point. Perturb and observe is the most commonly used MPPT method due to its ease of implementation. This method may result in top-level efficiency, provided that a proper predictive and adaptive hill climbing strategy is adopted.
I've added a flowchart for better understanding of this Method.

• Incremental Conductance Method

In the incremental conductance method, the controller measures incremental changes in array current and voltage to predict the effect of a voltage change. This method requires more computation in the controller, but can track changing conditions more rapidly than the perturb and observe method (P&O). Like the P&O algorithm, it can produce oscillations in power output. This method utilizes the incremental conductance (dI/dV) of the photovoltaic array to compute the sign of the change in power with respect to voltage (dP/dV).
The incremental conductance method computes the maximum power point by comparison of the incremental conductance (ΔI/ΔV) to the array conductance (I/V). When these two are the same (I/V=ΔI/ΔV), the output voltage is the MPP voltage. The controller maintains this voltage until the irradiation changes and the process is repeated.

For Further details on Perturb and Observe Method, please follow this link: Perturb and Observe Method

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Maximum Power Point Tracking : Basic Overview

Solar inverters or charge controllers use maximum power point tracking (MPPT) to get the maximum possible power from the PV array. Solar cells have a complex relationship between solar irradiation, temperature and total resistance that produces a non-linear output efficiency known as the I-V curve. It is the purpose of the MPPT system to sample the output of the cells and determine a resistance (load) to obtain maximum power f or any given environmental conditions.
Essentially, this defines the current that the inverter should draw from the PV in order to get the maximum possible power (since power equals voltage times current).

Working Principle of Maximum Power Point Tracking:

A Maximum Power Point Tracking solar regulator will simulate the load required by the solar panel to achieve the maximum power from the cell.  The regulator will work out at which point the cell will output the maximum power and derive from this the voltage and current outputs required for maximum power to be achieved.  It will then calculate the load that it must simulate based on these voltage and current levels R=V/I.  The regulator, now receiving the maximum amount of power in, will then regulate the output according to what it is designed for.

In this image you can see that if we use a inverter which works without an MPPT algorithm, then the system become in-efficient or in other words there will be losses in utilizing the solar power. But we use an inverter which works on a MPPT algorithm then the utilizing of power is far better.

Now let's talk about the Fill Factor (FF) which is a very important and of course an integral part of the MPPT methodology.

The fill factor, more commonly known by its abbreviation FF, is a parameter which, in conjunction with the open circuit voltage and short circuit current of the panel, determines the maximum power from a solar cell. A solar micro-inverter in the process of being installed . The ground wire is attached to the lug and the panel's DC connections are attached to the cables on the lower right. The AC parallel trunk open circuit voltage and short circuit current of the panel, determines the maximum power from a solar cell. Fill factor is defined as the ratio of the maximum power from the solar cell to the product of Voc and Isc.

So, the mathematical expression of Fill Factor is FF=(Imp x Vmp) / (Isc x Voc)

Benefits By Using MPPT Based Devices In Solar PV System 

MPPT ensures that you get the most power possible from your solar panels at any point in time. It is particularly effective during low light level conditions. These calculations result in an output that delivers maximum current at the required voltage at any point in time.  During low light level situations it will compensate for the low light level and find the new point at which the solar cell delivers its maximum power output.

For Details on the Classification of MPPT and the MPPT Algorithm, please see the other posts.


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Solar Tracker : Advantage and Disadvantage

Solar tracker is a component/tool/plugin in solar PV system which let the solar panels/arrays facing the sunlight directly or you can say at 90 degree angle respect to the sun-light. In other words-"A solar tracker is a device that orients a payload toward the sun. Payloads can be photovoltaic panels, reflectors, lenses or other optical devices."
In flat-panel photovoltaic (PV) applications, trackers are used to minimize the angle of incidence between the incoming sunlight and a photovoltaic panel. This increases the amount of energy produced from a fixed amount of installed power generating capacity.
In standard photovoltaic applications, it is estimated that trackers are used in at least 85% of commercial installations greater than 1MW from 2009 to 2012.

Advantages:

The advantages of solar tracker are listed below:

• Solar tracking systems are used to continually orient photovoltaic panels towards the sun and can help maximize the investment in PV system.

• They are beneficial as the sun's position in the sky will change gradually over the course of a day and over the seasons throughout the year.

• Advantages to using a tracker system like this will depend mainly on it's placement in determining how well it will increase the effectiveness of the panels.

• energy production is at an optimum and energy output is increased year round. This is especially significant through out the summer months with its long days of sunlight available to capture and no energy will be lost.

• For those with limited space this means that a smaller array only needs to be installed, a huge advantage for those smaller sites with only a small area to place solar tracker.

Comparison between fixed and with-tracking solar PV system

Disadvantages

Now let's discuss about the disadvantages of solar tracking system. Today, with boom in solar technology, the use of solar tracker is not necessary as it increases the total set-up cost of the system. The main disadvantages of using solar tracking system are listed below:

• The stand alone PV home kit system is a very reliable and uncomplicated source of energy production; the panels don't move and require little maintenance. By adding a solar tracking system to your solar panels, you are adding moving parts and gears which will require regular maintenance of your solar system and repair or replacement of broken parts.

• The main disadvantage is the investment problem. It has seen that in comparison to the cost and increment in the efficiency, setup and maintenance cost of the tracking system leads. By using the solar tracker the overall efficiency of the system increased by 23-30% whereas the system cost increases by 31-35%  (in most of the cases).

• Also the maintenance and repairing of mechanical and electronic parts of the tracking system requires extra man-power and of course extra investment.

Last of all i'd like to conclude that the use of solar tracker in the solar PV installtation is not that much important. We can save this money and put it on utilising the Maximum Power Point Tracking which yields more output from the solar array than the tracker system.

Image courtesy: http://www.rimlifegreentech.com/



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MPPT based (Perturb & Observe) Solar Charge controller:: Paper Work

Maximum power point tracking (MPPT) based solar charger/charge controller plays a vital role in increasing the overall efficiency of solar PV based system. Implementing a MPPT algorithm in charge controller of a solar PV system is necessary because the current-voltage characteristics of solar PV arrays is non-linear where at a particular point the power output is maximum. So to extract the maximum power from the solar PV system, implementation of MPPT algorithm is must. Maximum Power Point tracking can be done in a few different methodology; they are i) Perturb and Observe (P & O) Method,
ii) Incremental Conductance (INC) Method and iii) Constant Voltage Method. In this paper, the details of Perturb & Observe (P & O) method algorithm and designing and implementing of the algorithm in a charge controller of a Solar PV system (applicable for both grid-tie and stand-alone system) has been presented.

Because of the limited function of this post editor I have to post the the original document of my work here.
Please read the document provided here and give your valuable feedback.



I'm providing the flowchart and block diagram that i've made in the above paper for better and clear view.

Algorithm



Block Diagram

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Internet Access Through LED bulb: Li-Fi

Imagine you are standing under a street light to get public internet access, or downloading a HD full movie from the lamp of your desk in  a few seconds, or posting your just clicked snap during a flight. No, I'm not talking about an upcoming Sci-Fi movie. There  is a newborn technology, which could meet the ever-increasing demand for high-speed wireless connectivity. Radio waves are replaced by light waves in a new method of data transmission which is being called Li-Fi.

Genesis

The technology Li-Fi was pioneered by German physicist Harald Haas, currently based at the University of Edinburgh in the UK. Haas coined the term Li-Fi in 2011 in the context of a talk presenting the new technology at the TED (Technology Entertainment and Design) Global conference. The word quickly entered common parlance as an instantly recognizable alternative to WiFi. Both terms are examples of abbreviations linguists sometimes describe as clipped forms, i.e. WiFi = wireless fidelity, Li-Fi = light fidelity. Haas's research project, originally known as D-Light (short for Data Light), is now set to launch a prototype Li-Fi application under the name of newly-formed company VLC (Visible Light Communication) Ltd, which was set up to commercialize the technology. 

Prof. Harald Haas, Edinburgh, Germany

According to researchers led by a team from the University of Strathclyde, it could be possible to combine domestic lighting to also illuminate homes with the technology, which claims to offer high-definition film downloads in under a minute. Professor Martin Dawson, of Strathclyde, who is leading the four-year initiative, said “Imagine an LED array beside a motorway helping to light the road, displaying the latest traffic updates and transmitting internet information wirelessly to passengers’ laptops, netbooks and smartphones. This is the kind of extraordinary, energy-saving parallelism that we believe our pioneering technology could deliver.”

How Li-Fi Works?

Li-Fi is typically implemented using white LED light bulbs at the downlink transmitter. These devices are normally used for illumination only by applying a constant current. However, by fast and subtle variations of the current, the optical output can be made to vary at extremely high speeds. This very property of optical current is used in Li-Fi setup. The operational procedure is very simple-, if the LED is on, you transmit a

digital 1, if it’s off you transmit a 0. The LEDs can be switched on and off very quickly, which gives nice opportunities for transmitting data. Hence all that is required is some LEDs and a controller that code data into those LEDs. All one has to do is to vary the rate at which the LED’s flicker depending upon the data we want to encode. Further enhancements can be made in this method, like using an array of LEDs for parallel data transmission, or using mixtures of red, green and blue LEDs to alter the light’s frequency with each frequency encoding a different data channel. Such advancements promise a theoretical speed of 10 Gbps – meaning one can download a full high-definition film in just 30 seconds.

 A novel modulation technique coined SIM-OFDM was recently proposed. SIM-OFDM uses different frequency carrier states to convey information and leads to increased performance in comparison to conventional OFDM. Additionally, its innovative structure can lead to a decrease of the peak system power, which is highly beneficial in the context of optical wireless communication.

Economic value

• A free band that does not need license.
• High installment cost but very low maintenance cost.
• Cheaper than Wi-Fi.
• Theoretical speed up to 1 GB per second : Less time & energy consumption.
• No more monthly broadband bills.
• Lower electricity costs.
• Longevity of LED bulb : saves money.
• Light doesn't penetrate through walls : secured access.

Limitations

The main problem is that light can't pass through objects, so if the receiver is inadvertently blocked in any way, then the signal will immediately cut out. "If the light signal is blocked, or when you need to use your device to send information -- you can seamlessly switch back over to radio waves", Harald says.

Reliability and network coverage are the major issues to be considered by the companies while providing VLC services. Interferences from external light sources like sun light, normal bulbs; and opaque materials in the path of transmission will cause interruption in the communication. High installation cost of the VLC systems can be complemented by large-scale implementation of VLC though Adopting VLC technology will reduce further operating costs like electricity charges, maintenance charges etc.

Future Prospects

This research report categorizes the global VLC technology market; based on component, applications, and geography. Li-Fi uses light-emitting diodes (LEDs) which are rapidly gaining in popularity for standard lightbulbs and other domestic and commercial purposes. They are expected to be ubiquitous in 20 years. VLC is not in competition with WiFi, Prof. Haas says, it is a complimentary technology that should eventually help free up much needed space within the radio wave spectrum.

"We still need Wi-Fi, we still need radio frequency cellular systems. You can't have a light bulb that provides data to a high-speed moving object or to provide data in a remote area where there are trees and walls and obstacles behind," he says.

some hotspots are:

• the remote control devices under the ocean : radio wave doesn't work there.

• petrochemical plants : radio wave data tranmission is not secured there.

• hospitals : for medical purpose.

• street lights, traffic signals : for traffic update.

• aircraft cabins : for emmegency conversations.

A power point slideshow on this topic provided here.Please give your valuable feedback.

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Lead-Acid Battery charger circuit

In this article i'm going to discuss about a lead-acid battery chrager construction and a very basic principle of charging ckt. Also i'll share my own battery charger that i've built to use my project.

Brief Description

Input of this prototype is 12v,1amp DC power supply.using a voltage regulator IC, a comparator IC and a Double transistor package module the circuit gives output of 6v DC.  A 6v, 5Ah lead-acid battery can be charged using this circuit.

Circuit Design:

LM 317

Components Used:
ICs:
a) LM 317 (v-reg) - 1
b) IC 741 (comparator) - 1
c) TIP 122 (transistors) - 1
Resistors:(all are 1/4 watts)
470 ohms: 1
220 ohms: 1
100 ohms: 1
10k ohms: 1
1k   ohms: 1
100kohms:1
2k2 preset pot:1
10k preset pot:1
Diodes:
1N4007 : 2
3.3v Zener : 2
0.1uF capacitor : 1(disk type)
LED: green & red : one each

IC 741

Testing of the Circuit

1)    The input to the circuit can be fed from a standard 12V 1 amp adapter.

2)    To set up the circuit initially do not connect any battery.

3)    Feed 12V input, adjust the 2K2 pot to get 7v across the battery charging terminals.

4)    Next, adjust the 10K preset such that the green LED just lights up fully and the red LED shuts off.

5)    Circuit has been set.

6)    Switch OFF power. Connect a discharged battery and switch ON power, the circuit will do the rest.it will cut off as as soon as the battery voltage reaches 7V.

The prototype model i've built:

 1. this is the circuit set-up in 3.5x6 inches box. Input of this circuit comes from two 6v, 3watt solar modules connected in series to get 12v,1amp DC output.

2. the output of the circuit is connected to a 6v,5Ah lead-acid battery which is fully charged.
that' why the RED LED is lighted up.

3. you can see the multi-meter reading.
It shows that the battery-voltage is 6.36v. and because of that the RED LED is blinking.

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What does 64K means In a SIM Card?

Many of us don’t know the meaning of 64k written on the SIM card. In many forum it is said the the 64K is refer to the total memory available in the SIM card. I don’t know whether it is correct or not. Recently I was studying the digital communication subject. In this subject there is a chapter of Pulse Code Modulation (PCM) and Digital Multiplexers. In this chapter, I found a topic on TI carrier system(PCM-TDM System). It says that according to North-American hierarchy of telephony system-both for analog and digital system- a PCM voice signal represents 64k bits/sec i.e., 8000 samples per sec x 8 bits per sec.. also that due to 8000 samples per sec, the sampling rate, the time duration between adjacent samples will be (1/8000) or 125 micro seconds.
Now you can see that in actual telephony system, 64K stands for the data transfer rate and of course the speed of data (digital signal) transfer. higher the rate, higher speed of data accessing and transferring. Some years back, when the mobile phones came into market, you might have noticed that 32K was written on the place of 64K of now-a-days SIM card. that means the data transfer rate was very low then and we could not surf/browse internet thru’ our mobile phones. Today, 64K, 128K SIM Cards are available. We all know that 64K is 2G and 128K SIMs are 3G.
So , according to my limited knowledge, 64K should stands for the data transfer rate or to be more precious, the sampling rate of that particular SIM card. I’m posting details of T1 carrier system here. To know more please go thru’ the next part.
T1-carrier System
The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system that supported digitized voice transmission. The original transmission rate (1.544 Mbps) in the T1 line is in common use today in Internet service provider (ISP) connections to the Internet. Another level, the T3 line, providing 44.736 Mbps, is also commonly used by Internet service providers.

The T-carrier system is entirely digital, using pulse code modulation (PCM) and time-division multiplexing (TDM). The system uses four wires and provides duplex capability (two wires for receiving and two for sending at the same time). The T1 digital stream consists of 24 64-Kbps channels that are multiplexed. (The standardized 64 Kbps channel is based on the bandwidth required for a voice conversation.) The four wires were originally a pair of twisted pair copper wires, but can now also include coaxial cable, optical fiber, digital microwave, and other media. A number of variations on the number and use of channels are possible.
A T1 line in which each channel serves a different application is known as integrated T1 or channelized T1. Another commonly installed service is a fractional T1, which is the rental of some portion of the 24 channels in a T1 line, with the other channels going unused.

In the T1 system, voice or other analog signals are sampled 8,000 times a second and each sample is digitized into an 8-bit word. With 24 channels being digitized at the same time, a 192-bit frame (24 channels each with an 8-bit word) is thus being transmitted 8,000 times a second. Each frame is separated from the next by a single bit, making a 193-bit block. The 192 bit frame multiplied by 8,000 and the additional 8,000 framing bits make up the T1's 1.544 Mbps data rate. The signaling bits are the least significant bits in each frame.

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Features of a Solar Inverter

When it comes to setting up a solar inverter (for any type), the engineer/installer have to ask for certain features or you can say the qualities to the manufacturer because lacking of these feature in a inverter causing the system in-efficient. So in this post, i'll discuss about those particular features that we are looking for at the time of purchasing/installing solar inverter.

1.    Maximum Power Point Tracking

Solar inverters use maximum power point tracking (MPPT) to get the maximum possible power from the PV array. Solar cells have a complex relationship between solar irradiation, temperature and total resistance that produces a non-linear output efficiency known as the I-V curve. It is the purpose of the MPPT system to sample the output of the cells and determine a resistance (load) to obtain maximum power f or any given environmental conditions. Essentially, this defines the current that the inverter should draw from the PV in order to get the maximum possible power (since power equals voltage times current).

In this image you can see that if we use a inverter which works without an MPPT algorithm, then the system become in-efficient or in other words there will be losses in utilizing the solar power. But we use an inverter which works on a MPPT algorithm thenthe utilizing of power is far better.

Now, we should know about the Fill-Factor. what is Fill Factor or FF? 

The fill f actor, more commonly known by its abbreviation FF, is a parameter which, in conjunction with the open circuit voltage and short circuit current of the panel, determines the maximum power from a solar cell. A solar micro-inverter in the process of being installed . The ground wire is attached to the lug and the panel's DC connections are attached to the cables on the lower right. The AC parallel trunk open circuit voltage and short circuit current of the panel, determines the maximum power from a solar cell. Fill f actor is def ined as the ratio of the maximum power f rom the solar cell to the product of Voc and Isc.

 There are three main types of MPPT algorithms: perturb-and-observe, incremental conductance and constant voltage. The first two methods are often referred to as hill climbing methods; they rely on the curve of power plotted against voltage rising to the left of the maximum power point, and falling on the right.

MPPT With FF Display

A general algorithm of MPPT shown here.

2.   Anti-Islanding Protection

In the event of a power failure on the grid, it is generally required that any grid-tie inverters attached to the grid turn off in a short period of time. This prevents the inverters from continuing to feed power into small sections of the grid, known as "islands". Powered islands present a risk to workers who may expect the area to be unpowered, but equally important is the issue that without a grid signal to synchronize to, the power output of the inverters may drift from the tolerances required by customer equipment connected within the island. 

Detecting the presence or lack of a grid source would appear to be simple, and in the case of a single inverter in any given possible physical island (between disconnects on the distribution lines f or instance) the chance that an inverter would f ail to notice the loss of the grid is effectively zero. However, if there are two inverters in a given island, things become considerably more complex. It is possible that the signal from one can be interpreted  as a grid feed from the other, and vice versa, so both units continue operation. As they track each other's output, the two can drift away from the limits imposed by the grid connections, say in voltage or frequency.

 There are a wide variety of methodologies used to detect an islanding condition. None of these are considered fool-proof , and utility companies continue to impose limits on the number and total power of solar power systems connected in any given area. However, many in-field tests have failed to uncover any real-world islanding issues, and the issue remains contentious within the industry.

3.    Redundancy

Redundancy is one of the main reason string inverters and microinverters are chosen instead of central inverters because in case of failure a smaller part of the system will be affected. String inverters have the added benefit of being a standard readily available commercial component which means it’s possible to let a local installer or facility manager exchange the inverter if necessary; also extra inverters can be kept in stock for quick exchange. Conversely, service contracts should be offered with central inverters and they should be serviced only by trained experts.

4.  Total Harmonic Distortion

The total harmonic distortion, or THD, of a signal is a measurement of the harmonic distortion present and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency. THD is used to characterize the linearity of audio systems and the power quality of electric power systems.

So, it is desired that a inverter should have feature to cancel out the most of the higher harmonics as possible

.

When the input is a pure sine wave, the measurement is most commonly the ratio of the sum of the powers of all higher harmonic frequencies to the power at the first harmonic, or fundamental, frequency.

which can equivalently be written as

if there is no source of power other than the signal and its harmonics.

Measurements based on amplitudes (e.g. voltage or current) must be converted to powers to make addition of harmonics distortion meaningful. For a voltage signal, for example, the ratio of the squares of the RMS voltages is equivalent to the power ratio:

where V_i is the RMS voltage of ith harmonic and i = 1 is the fundamental frequency.

THD is also commonly defined as an amplitude ratio rather than a power ratio,^[3] resulting in a definition of THD which is the square root of that given above:

This latter definition is commonly used in audio distortion (percentage THD) specifications. It is unfortunate that these two conflicting definitions of THD (one as a power ratio and the other as an amplitude ratio) are both in common usage.

So, it is desired that a inverter should have feature to cancel out the most of the higher harmonics as possible.

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About the Author

Amrit Mandal is a final year B.tech (EE) Student, Admin of this blog. He likes to work in the renewable energy field-specially in solar energy field.
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