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Solar tracking system - Report

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info4eee | Information For Electrical & Electronics Engineering
1. INTRODUCTION
One of the most promising renewable ener...
2
info4eee | Information For Electrical & Electronics Engineering
1.1 Background
A Solar Tracker is a device onto which so...
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info4eee | Information For Electrical & Electronics Engineering
2. Literature Research
This chapter aims to provide a br...
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Solar tracking system - Report

  1. 1. 1 info4eee | Information For Electrical & Electronics Engineering 1. INTRODUCTION One of the most promising renewable energy sources characterized by a huge potential of conversion into electrical power is the solar energy. The conversion of solar radiation into electrical energy by Photo-Voltaic (PV) effect is a very promising technology, being clean, silent and reliable, with very small maintenance costs and small ecological impact. The interest in the Photo Voltaic conversion systems is visibly reflected by the exponential increase of sales in this market segment with a strong growth projection for the next decades. According to recent market research reports carried out by European Photovoltaic Industry Association (EPIA), the total installed power of PV conversion equipment increased from about 1 GW in 2001up to nearly 23 GW in 2009. The continuous evolution of the technology determined a sustained increase of the conversion efficiency of PV panels, but nonetheless the most part of the commercial panels have efficiencies no more than 20%. A constant research preoccupation of the technical community involved in the solar energy harnessing technology refers to various solutions to increase the PV panel‟s conversion efficiency. Among PV efficiency improving solutions we can mention: solar tracking, optimization of solar cells geometry, enhancement of light trapping capability, use of new materials, etc. The output power produced by the PV panels depends strongly on the incident light radiation. The continuous modification of the sun-earth relative position determines a continuously changing of incident radiation on a fixed PV panel. The point of maximum received energy is reached when the direction of solar radiation is perpendicular on the panel surface. Thus an increase of the output energy of a given PV panel can be obtained by mounting the panel on a solar tracking device that follows the sun trajectory. Unlike the classical fixed PV panels, the mobile ones driven by solar trackers are kept under optimum insolation for all positions of the Sun, boosting thus the PV conversion efficiency of the system. The output energy of PV panels equipped with solar trackers may increase with tens of percents, especially during the summer when the energy harnessed from the sun is more important. Photo-Voltaic or PV cells, known commonly as solar cells, convert the energy from sunlight into DC electricity. PVs offer added advantages over other renewable energy sources in that they give off no noise and require practically no maintenance. A tracking system must be able to follow the sun with a certain degree of accuracy, return the collector to its original position at the end of the day and also track during periods of cloud over. The major components of this system are as follows. Light dependent resistor Microcontroller. Output mechanical transducer (stepper motor)
  2. 2. 2 info4eee | Information For Electrical & Electronics Engineering 1.1 Background A Solar Tracker is a device onto which solar panels are fitted which tracks the motion of the sun across the sky ensuring that the maximum amount of sunlight strikes the panels throughout the day. The Solar Tracker will attempt to navigate to the best angle of exposure of light from the sun. This report aims to let the reader understand the project work which I have done. A brief introduction to Solar Panel and Solar Tracker is explained in the Literature Research section. Basically the Solar Tracker is divided into two main categories, hardware and software. It is further subdivided into six main functionalities: Method of Tracker Mount, Drives, Sensors, RTC, Motors, and Power Supply of the Solar Tracker is also explained and explored. The reader would then be brief with some analysis and perceptions of the information. By using solar arrays, a series of solar cells electrically connected, a DC voltage is generated which can be physically used on a load. Solar arrays or panels are being used increasingly as efficiencies reach higher levels, and are especially popular in remote areas where placement of electricity lines is not economically viable. This alternative power source is continuously achieving greater popularity especially since the realisation of fossil fuels shortcomings. Renewable energy in the form of electricity has been in use to some degree as long as 75 or 100 years ago. Sources such as Solar, Wind, Hydro and Geothermal have all been utilised with varying levels of success. The most widely used are hydro and wind power, with solar power being moderately used worldwide. This can be attributed to the relatively high cost of solar cells and their low conversion efficiency. Solar power is being heavily researched, and solar energy costs have now reached within a few cents per kW/h of other forms of electricity generation, and will drop further with new technologies such as titanium oxide cells. With a peak laboratory efficiency of 32% and average efficiency of 15-20%, it is necessary to recover as much energy as possible from a solar power system. This includes reducing inverter losses, storage losses, and light gathering losses. Light gathering is dependent on the angle of incidence of the light source providing power (i.e. the sun) to the solar cell‟s surface, and the closer to perpendicular, the greater the power. If a flat solar panel is mounted on level ground, it is obvious that over the course of the day the sunlight will have an angle of incidence close to 90° in the morning and the evening. At such an angle, the light gathering ability of the cell is essentially zero, resulting in no output. As the day progresses to midday, the angle of incidence approaches 0°, causing a steady increase in power until at the point where the light incident on the panel is completely perpendicular, and maximum power is achieved. As the day continues toward dusk, the reverse happens, and the increasing angle causes the power to decrease again toward minimum again. From this background, we see the need to maintain the maximum power output from the panel by maintaining an angle of incidence as close to 0° as possible. By tilting the solar panel to continuously face the sun, this can be achieved. This process of sensing and following the position of the sun is known as Solar Tracking. It was resolved that real-time tracking would be necessary to follow the sun effectively, so that no external data would be required in operation.
  3. 3. 3 info4eee | Information For Electrical & Electronics Engineering 2. Literature Research This chapter aims to provide a brief knowledge of Solar Panel, Solar Tracker and the components which made up Solar Tracker. 2.1 Technology of Solar Panel Solar panels are devices that convert light into electricity. They are called solar after the sun because the sun is the most powerful source of the light available for use. They are sometimes called photovoltaic which means "light-electricity". Solar cells or PV cells rely on the photovoltaic effect to absorb the energy of the sun and cause current to flow between two oppositely charge layers. A solar panel is a collection of solar cells. Although each solar cell provides a relatively small amount of power, many solar cells spread over a large area can provide enough power to be useful. To get the most power, solar panels have to be pointed directly at the Sun. The development of solar cell technology begins with 1839 research of French physicist Antoine-Cesar Becquerel. He observed the photovoltaic effect while experimenting with a solid electrode in an electrolyte solution. After that he saw a voltage developed when light fell upon the electrode. According to Encyclopaedia Britannica the first genuine for solar panel was built around 1883 by Charles Fritts. He used junctions formed by coating selenium (a semiconductor) with an extremely thin layer of gold. Crystalline silicon and gallium arsenide are typical choices of materials for solar panels. Gallium arsenide crystals are grown especially for photovoltaic use, but silicon crystals are available in less-expensive standard ingots, which are produced mainly for consumption in the microelectronics industry. Norway‟s Renewable Energy Corporation has confirmed that it will build a solar manufacturing plant in Singapore by 2010 - the largest in the world. This plant will be able to produce products that can generate up to 1.5 Giga watts of energy every year. That is enough to power several million households at any one time. Last year the world as a whole produced products that could generate just 2 GW in total. 2.2 Evolution of Solar Tracker Since the sun moves across the sky throughout the day, in order to receive the best angle of exposure to sunlight for collection energy. A tracking mechanism is often incorporated into the solar arrays to keep the array pointed towards the sun. A solar tracker is a device onto which solar panels are fitted which tracks the motion of the sun across the sky ensuring that the maximum amount of sunlight strikes the panels throughout the day. When compare to the price of the PV solar panels, the cost of a solar tracker is relatively low. Most photovoltaic solar panels are fitted in a fixed location- for example on the sloping roof of a house, or on framework fixed to the ground. Since the sun moves across the sky though the day, this is far from an ideal solution. Solar panels are usually set up to be in full direct sunshine at the middle of the day facing South in
  4. 4. 4 info4eee | Information For Electrical & Electronics Engineering the Northern Hemisphere, or North in the Southern Hemisphere. Therefore morning and evening sunlight hits the panels at an acute angle reducing the total amount of electricity which can be generated each day. Fig 2.1 Sun‟s apparent motion During the day the sun appears to move across the sky from left to right and up and down above the horizon from sunrise to noon to sunset. Figure 2.1 shows the schematic above of the Sun's apparent motion as seen from the Northern Hemisphere. To keep up with other green energies, the solar cell market has to be as efficient as possible in order not to lose market shares on the global energy marketplace. The end-user will prefer the tracking solution rather than a fixed ground system to increase their earnings because: The efficiency increases by 30-40%. The space requirement for a solar park is reduced, and they keep the same output. The return of the investment timeline is reduced. The tracking system amortizes itself within 4 years. In terms of cost per Watt of the completed solar system, it is usually cheaper to use a solar tracker and less solar panels where space and planning permit. A good solar tracker can typically lead to an increase in electricity generation capacity of 30- 50%.
  5. 5. 5 info4eee | Information For Electrical & Electronics Engineering 3. Project Description 3.1 Block Diagram Fig 3.1 Block Diagram of Project 3.2 Schematic Diagram Fig 3.2 Schematic Diagram of Project
  6. 6. 6 info4eee | Information For Electrical & Electronics Engineering 3.3 PRINTED CIRCUIT BOARD Almost all circuits encountered on electronic equipment (computers, TV, radio, industrial control equipment, etc.) are mounted on printed circuit boards. Close inspection of a PCB reveals that it contains a series of copper tracks printed on one or both sides of a fiber glass board. The copper tracks form the wiring pattern required to link the circuit devices according to a given circuit diagram. Hence, to construct a circuit the necessity of connecting insulated wires between components is eliminated, resulting in a cleaner arrangement and providing mechanical support for components. Moreover, the copper tracks are highly conductive and the whole PCB can be easily reproduced for mass production with increased reliability. 1) Types of PCB PCB's can be divided into three main categories: Single-sided Double-sided Multi-layered. Single-sided PCB A single-sided PCB contains copper tracks on one side of the board only, as shown in Figure 3.3. Holes are drilled at appropriate points on the track-so that each component can be inserted from the non-copper side of the board, as shown in Figure 3.4. Each pin is then soldered to the copper track. Fig 3.3 Printed circuit board
  7. 7. 7 info4eee | Information For Electrical & Electronics Engineering Fig 3.4 Single sided PCB Double-sided PCB Double-sided PCBs have copper tracks on both sides of the board. The track layout is designed so as not to allow shorts from one side to another, if it is required to link points between the two sides, electrical connections are made by small interconnecting holes which are plated with copper during manufacture. Fig 3.5 Double sided PCB Multi-layer PCB In multi-layer PCBs, each side contains several layers of track patterns which are insulated from one another. These layers are laminated under heat and high pressure. A multi-layer PCB is shown in Figure 3.6
  8. 8. 8 info4eee | Information For Electrical & Electronics Engineering Fig 3.6 Multi layered PCB 2) MAKING A PCB PCB's commonly available on the market are not particular circuits, but are available as copper clad boards. In other words, the whole area of one or both sides of the board is coated with copper. The user then draws his track layout on the copper surface, according to his circuit diagram. Next, the untraced copper area removed by a process called etching. Here, the unused copper area is dissolved away by an etching solution and only the required copper tracks remain. The board is then cleaned and drilled at points where each device is to be inserted. Finally, each component is soldered to the board. The etching process depends on whether board is of plain or photo-resist type. These are treated separately in the following section. a) Making a PCB out of a plain copper clad board Equipment required The following items are required: A single-sided copper clad board. Ferric chloride solution, which is the etching liquid. An etch-resist pen is with its ink resisting to ferric chloride. A PCB eraser. Track layout design The first step is to draw the track layout on the plain copper clad board, according to the circuit to be implemented which turns on an LED when the push-button is pressed. The lines joining different components will form the track layout on the PCB. Each component is inserted from the non-copper side of the board and its leads appear on the copper side. For example, when viewing the component side, the base of the BC109 transistor appears to the right of the collector, while from the track side, it appears at the left of the collector. b) Making a PCB out of a photo resist board Equipment required Photo-resist board Ferric chloride solution as etchant A white board marker Transparent polyester film for use as drafting sheet Sodium hydroxide solution as developer
  9. 9. 9 info4eee | Information For Electrical & Electronics Engineering Ultra-violet exposure unit Track layout design Using the same principles outlined in section a track layout is drawn to scale on the transparency using the white board' marker. It may be useful to insert graph paper below the transparent sheet for accurate dimensioning of the layout. Photo-etching The principle behind photo-etching is to place the transparency over the copper clad and to expose it to UV radiation, hence leaving the track regions intact and softening unused areas. First, the protective plastic film is removed from the board. The traced transparency is then placed over the board, being careful to ensure that the copper side of the design faces upwards. The combination is next placed in a UV exposure unit, with the transparency facing the fluorescent tubes inside the unit. At the track regions, UV radiation is prevented from reaching the board, and hence the photo sensitive remains hardened in these regions. After an exposure of about 5 minutes the board can be removed. The PCB is then placed in a solution of caustic soda which dissolves away any unhardened photo-sensitive area. After a few minutes of development time, the track layout is apparent. The board is finally removed and rinsed in cold water. Final etching After having allowed the tracks to harden for about half an hour, the unmarked copper area is etched by ferric chloride solution. 3) The following points should be noted: It is a good idea to draft the track layout on graph paper before drawing the final layout on the copper clad. Use an etch resist pen to draw the track layout on the copper clad (the latter must be cleaned initially). The following lead spacing can be used as a rule of thumb: allow 10 mm for a 1/4 W resistor, 8 mm for a signal diode, 4 mm for LED's and ceramic capacitors. The lead spacing may also be measured before drawing. Terminals for the power supply input leads must also be included on the layout. The arrangement of components must be well planned so as to minimize the amount of cooper clad board required. Allow the ink to dry before etching.
  10. 10. 10 info4eee | Information For Electrical & Electronics Engineering 4) Etching The copper clad is now ready to be etched. If the etchant is available in powder form, it needs to be mixed with water in anon-corrodible container. A powder to water ratio of 2:5 by mass is about right. Etching time may vary between 10 to as long as 90 minutes, depending on the concentration and temperature of the etchant. The process can be accelerated by warming the solution and by frequently agitating the etching bath. The ferric chloride solution gradually dissolves any untraced copper area. When etching is complete, only the track layout remains on the board. The latter is then removed the bath and rinsed with clean water. The etch resist ink is finally rubbed away with a PCB eraser, or with very fine grain sand paper. Making a PCB out of a photo-resist copper clad board The photo-resist board consists of a single or double sided copper clad coated with a light-sensitive and the latter is protected with a plastic which should be removed before use. Its advantage over the plain copper clad board is that the track layout does not need to be drawn directly on the board. The use of etch-resist transfers The use of pens to design track layouts may not give neat result, even when using a ruler. For instance, it may be difficult to draw tracks with the same line Width or to draw well aligned terminals for IC's and discrete devices, Etch-resist PCB symbols and tracks are available for direct transfer to the copper clad or to the transparency. Transfer is by rubbing down the relevant symbol with a soft pencil.
  11. 11. 11 info4eee | Information For Electrical & Electronics Engineering 4. Components Description 4.1 Solar Tracker Solar Tracker is basically a device onto which solar panels are fitted which tracks the motion of the sun across the sky ensuring that the maximum amount of sunlight strikes the panels throughout the day. After finding the sunlight, the tracker will try to navigate through the path ensuring the best sunlight is detected. The design of the Solar Tracker requires many components. The design and construction of it could be divided into six main parts that would need to work together harmoniously to achieve a smooth run for the Solar Tracker, each with their main function. They are: Methods of Tracker Mount Methods of Drives Sensor and Sensor Controller Motor and Motor Controller Tracker Solving Algorithm Data Acquisition/Interface Card 4.2Methods of Tracker Mount 1. Single axis solar trackers Single axis solar trackers can either have a horizontal or a vertical axle. The horizontal type is used in tropical regions where the sun gets very high at noon, but the days are short. The vertical type is used in high latitudes where the sun does not get very high, but summer days can be very long. The single axis tracking system is the simplest solution and the most common one used. 2. Double axis solar trackers Double axis solar trackers have both a horizontal and a vertical axle and so can track the Sun's apparent motion exactly anywhere in the World. This type of system is used to control astronomical telescopes, and so there is plenty of software available to automatically predict and track the motion of the sun across the sky. By tracking the sun, the efficiency of the solar panels can be increased by 30-40%.The dual axis tracking system is also used for concentrating a solar reflector toward the concentrator on heliostat systems. 4.3 Methods of Drive 1. Active Trackers Active Trackers use motors and gear trains to direct the tracker as commanded by a controller responding to the solar direction. Light-sensing trackers typically have two photo sensors, such as photodiodes, configured differentially so that they output a null when receiving the same light flux.
  12. 12. 12 info4eee | Information For Electrical & Electronics Engineering Mechanically, they should be omnidirectional and are aimed 90 degrees apart. This will cause the steepest part of their cosine transfer functions to balance at the steepest part, which translates into maximum sensitivity. 2. Passive Trackers Passive Trackers use a low boiling point compressed gas fluid that is driven to one side or the other by solar heat creating gas pressure to cause the tracker to move in response to an imbalance. 4.4 Sensors A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. 1. Light Dependent Resistor Light Dependent Resistor is made of a high-resistance semiconductor. It can also be referred to as a photoconductor. If light falling on the device is of the high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron conducts electricity, thereby lowering resistance. Hence, Light Dependent Resistors is very useful in light sensor circuits. LDR is very high-resistance, sometimes as high as 10MΩ, when they are illuminated with light resistance drops dramatically. A Light Dependent Resistor is a resistor that changes in value according to the light falling on it. A commonly used device, the ORP-12, has a high resistance in the dark, and a low resistance in the light. Connecting the LDR to the microcontroller is very straight forward, but some software „calibrating‟ is required. It should be remembered that the LDR response is not linear, and so the readings will not change in exactly the same way as with a potentiometer. In general there is a larger resistance change at brighter light levels. This can be compensated for in the software by using a smaller range at darker light levels. Fig 4.1 Light Dependent Resistor
  13. 13. 13 info4eee | Information For Electrical & Electronics Engineering 2. Photodiode Photodiode is a light sensor which has a high speed and high sensitive silicon PIN photodiode in a miniature flat plastic package. A photodiode is designed to be responsive to optical input. Due to its water clear epoxy the device is sensitive to visible and infrared radiation. The large active area combined with a flat case gives a high sensitivity at a wide viewing angle. Photodiodes can be used in either zero bias or reverse bias. In zero bias, light falling on the diode causes a voltage to develop across the device, leading to a current in the forward bias direction. This is called the photovoltaic effect, and is the basis for solar cells - in fact a solar cell is just a large number of big, cheap photodiodes. Diodes usually have extremely high resistance when reverse biased. This resistance is reduced when light of an appropriate frequency shines on the junction. Hence, a reverse biased diode can be used as a detector by monitoring the current running through it. Circuits based on this effect are more sensitive to light than ones based on the photovoltaic effect. Fig 4.2 different type of photo diodes 4.5 Motor Motor is use to drive the Solar Tracker to the best angle of exposure of light. For this section, we are using stepper motor. Stepper Motor Features Linear speed control of stepper motor Control of acceleration, deceleration, max speed and number of steps to move Driven by one timer interrupt Full - or half-stepping driving mode Supports all AVR devices with 16bit timer
  14. 14. 14 info4eee | Information For Electrical & Electronics Engineering Introduction This application note describes how to implement an exact linear speed controller for stepper motors. The stepper motor is an electromagnetic device that converts digital pulses into mechanical shaft rotation. Many advantages are achieved using this kind of motors, such as higher simplicity, since no brushes or contacts are present, low cost, high reliability, high torque at low speeds, and high accuracy of motion. Many systems with stepper motors need to control the acceleration/deceleration when changing the speed. This application note presents a driver with a demo application, capable of controlling acceleration as well as position and speed. Fig 4.3 Stepper Motors Theory Stepper motor This application note covers the theory about linear speed ramp stepper motor control as well as the realization of the controller itself. It is assumed that the reader is familiar with basic stepper motor operation, but a summary of the most relevant topics will be given. Bipolar vs. Unipolar stepper motors The two common types of stepper motors are the bipolar motor and the Unipolar motor. The bipolar and unipolar motors are similar, except that the Unipolar has a centre tap on each winding as shown in Figure 4.4
  15. 15. 15 info4eee | Information For Electrical & Electronics Engineering Fig 4.4 Bipolar and Unipolar stepper Motor Unipolar stepper motor Stepper motors are very accurate motors that are commonly used in computer disk drives, printers and clocks. Unlike dc motors, which spin round freely when power is applied, stepper motors require that their power supply be continuously pulsed in specific patterns. For each pulse the stepper motor moves around one step often 15 degrees giving 24 steps in a full revolution.There are two main types of stepper motors - Unipolar and Bipolar. Unipolar motors usually have four coils which are switched on and off in a particular sequence. Bipolar motors have two coils in which the current flow is reversed in a similar sequence. Each of the four coils in a Unipolar stepper motor must be switched on and off in a certain order to make the motor turn. Many microprocessor systems use four output lines to control the stepper motor, each output line controlling the power to one of the coils. As the stepper motor operates at 5V, the standard transistor circuit is required to switch each coil. As the coils create a back emf when switched off, a suppression diode on each coil is also required. The table below show the four different steps required to make the motor turn. Table 4.1 Unipolar stepper motor operation Step Coil 1 Coil 2 Coil 3 Coil 4 1 1 0 1 0 2 1 0 0 1 3 0 1 0 1 4 0 1 1 0 1 1 0 1 0 Look carefully at the table 4.1 and notice that a pattern is visible. Coil 2 is always the opposite or logical NOT of coil 1. The same applies for coils 3 and 4. It is therefore possible to cut down the number of microcontroller pins required to just two by the use of two additional NOT gates. Fortunately the Darlington
  16. 16. 16 info4eee | Information For Electrical & Electronics Engineering driver IC ULN2003 can be used to provide both the NOT and Darlington driver circuits. It also contains the back emf suppression diodes so no external diodes are required. Bipolar Stepper motor The bipolar stepper motor has two coils that must be controlled so that the current flows in different directions through the coils in a certain order. The changing magnetic fields that these coils create cause the rotor of the motor to move around in steps. The bipolar motor needs current to be driven in both directions through the windings, and a full bridge driver is needed as shown in Figure 4.5 (a). The centre tap on the Unipolar motor allows a simpler driving circuit shown in Figure 4.5 (b), limiting the current flow to one direction. The main drawback with the Unipolar motor is the limited capability to energize all windings at any time, resulting in a lower torque compared to the bipolar motor. The Unipolar stepper motor can be used as a bipolar motor by disconnecting the centre tap. (a) (b) Fig 4.5 Bipolar and Unipolar drivers with MOS transistors Implementation A working implementation written in C is included with this application note. Full documentation of the source code and compilation information is found by opening the „readme.html‟ file included with the source code. The demo application demonstrates linear speed control of a stepper motor. The user can control the stepper motor speed profile by issuing different commands using the serial port, and the AVR will drive the connected stepper motor accordingly. The demo application is divided in three major blocks,
  17. 17. 17 info4eee | Information For Electrical & Electronics Engineering as shown in the block diagram in Figure 4.6. There is one file for each block and also a file for UART routines used by the main routine. Fig 4.6 Block diagram of demo application Main c has a menu and a command interface, giving the user control of the stepper motor by a terminal connected to the serial line. Speed controller c calculates the needed data and generates step pulses to make the stepper motor follow the desired speed profile. Smdriver.c counts the steps and outputs the correct signals to control the stepper motor. Timer interrupt The timer interrupt generates the step pulses calls the function Step Counter ( ) and is only running when the stepper motor is moving. The timer interrupt will operate in four different states according to the speed profile shown in Figure 4.7 and this behaviour is realized with a state machine in the timer interrupt shown in Figure 4.8. Fig 4.7 Operating states for different speed profile parts
  18. 18. 18 info4eee | Information For Electrical & Electronics Engineering Fig 4.8 State machine for timer interrupt When the application starts or when the stepper motor is stopped the state-machine remains in the state STOP. When setup calculations are done, a new state is set and the timer interrupt is enabled. When moving more than one step the state-machine goes to ACCEL. If moving only 1 step, the state is changed to DECEL. When the state is changed to ACCEL, the application accelerates the stepper motor until either the desired speed is reached and the state is changed to RUN, or deceleration must start, changing the state to DECEL. When the state is set to RUN, the stepper motor is kept at constant speed until deceleration must start, then the state is changed to DECEL.It will stay in DECEL and decelerate until the speed reaches zero desired number of steps. The state is then changed to STOP. 4.6 Microcontroller A microcontroller is a single chip that contains the processor, non-volatile memory for the program, volatile memory for input and output, a clock and an I/O control unit also called a computer on a chip, billions of microcontroller units are embedded each year in a myriad of products from toys to appliances to automobiles. For example, a single vehicle can use 70 or more microcontrollers. The following picture describes a general block diagram of microcontroller. Features High-performance, Low-power AVR 8-bit Microcontroller Advanced RISC Architecture 131 Powerful Instructions – Most Single-clock Cycle Execution 32 x 8 General Purpose Working Registers Fully Static Operation Up to 16 MIPS Throughput at 16 MHz On-chip 2-cycle Multiplier High Endurance Non-volatile Memory segments 16K Bytes of In-System Self-programmable Flash program memory 512 Bytes EEPROM 1K Byte Internal SRAM Write/Erase Cycles: 10,000 Flash/100,000 EEPROM Data retention: 20 years at 85°C/100 years at 25°C Optional Boot Code Section with Independent Lock Bits In-System Programming by On-chip Boot Program True Read-While-Write Operation Programming Lock for Software Security
  19. 19. 19 info4eee | Information For Electrical & Electronics Engineering JTAG Interface Boundary-scan Capabilities According to the JTAG Standard Extensive On-chip Debug Support Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface Peripheral Features Two 8-bit Timer/Counters with Separate Prescalers and Compare Modes One 16-bit Timer/Counter with Separate Prescalers, Compare Mode, and Capture Mode Real Time Counter with Separate Oscillator Four PWM Channels 8-channel, 10-bit ADC 8 Single-ended Channels 7 Differential Channels in TQFP Package Only 2 Differential Channels with Programmable Gain at 1x, 10x, or 200x Byte-oriented Two-wire Serial Interface Programmable Serial USART Master/Slave SPI Serial Interface Programmable Watchdog Timer with Separate On-chip Oscillator On-chip Analog Comparator Special Microcontroller Features Power-on Reset and Programmable Brown-out Detection Internal Calibrated RC Oscillator External and Internal Interrupt Sources Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standby and Extended Standby I/O and Packages 32 Programmable I/O Lines 40-pin PDIP, 44-lead TQFP, and 44-pad QFN/MLF Operating Voltages 2.7 - 5.5V for ATmega16L 4.5 - 5.5V for ATmega16 Speed Grades 0 - 8 MHz for ATmega16L 0 - 16 MHz for ATmega16
  20. 20. 20 info4eee | Information For Electrical & Electronics Engineering Power Consumption @ 1 MHz, 3V, and 25°C for ATmega16L Active: 1.1 mA Idle Mode: 0.35 mA Power-down Mode: < 1 μA ATmega16: The ATmega16 is a low-power, high-performance advance RISC8-bit microcontroller with 32K bytes of in- system programmable Flash memory. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional non-volatile memory programmer. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel ATmega16 is a powerful microcontroller, which provides a highly flexible and cost-effective solution to many, embedded control applications. The ATmega16 provides the following standard features:32K bytes of Flash, 1024 byte of EEPROM & 2KB INTERNAL S RAM ,32 I/O lines, Watch dog timer, two data pointers, two 16-bit timer/counters, a six- vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator,8-channel 10 bit ADC and clock circuitry. In addition, the ATmega16 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-down mode saves the RAM con-tents but freezes the oscillator, disabling all other chip functions until the next interrupt.
  21. 21. 21 info4eee | Information For Electrical & Electronics Engineering Fig 4.9 Pin diagram of ATmega16 Overview- The ATmega16 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC architecture. By executing powerful instructions in a single clock cycle, the ATmega16 achieves throughputs approaching 1 MIPS per MHz allowing the system designed to optimize power consumption versus processing speed. Pin Descriptions VCC Digital supply voltage GND Ground Port A (PA7 - PA0) Port A serves as the analog inputs to the A/D Converter. Port A also serves as an 8-bit bi-directional I/O port, if the A/D Converter is not used. Port pin scan provide internal pull-up resistors. The Port A output buffers have symmetrical drive characteristics with both high sink and source capability. When pins PA0 to PA7are used as inputs and are externally pulled low, they will source current if the internal pull-up resistors are activated. The Port A pins are tri-stated when a reset condition becomes active, even if the clock is not running. Port B (PB7 - PB0) Port B is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port B output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port B pins that are externally pulled low will source current if the pull-up resistors are activated. The Port B pins are tri-stated when a reset condition becomes active, even if the clock is not running. Port C (PC7 - PC0) Port C is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port C output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port C pins that are externally pulled low will source current if the pull-up resistors are activated. The Port C pins are tri-stated when a reset condition becomes active, even if the clock is not running. If the JTAG interface is enabled, the pull-up resistors on pins PC5 (TDI), PC3 (TMS) and PC2 (TCK) will be activated even if a reset occurs. Port D (PD7 - PD0) Port D is an 8-bit bi-directional I/O port with internal pull-up resistors. The Port D output buffers have symmetrical drive characteristics with both high sink and source capability. As inputs, Port D pins that are externally pulled low will source current if the pull-up resistors are activated. The Port D pins are tri-stated when a reset condition becomes active, even if the clock is not running. RESET Reset Input. A low level on this pin for longer than the minimum pulse length will generate a reset, even if the clock is not running.
  22. 22. 22 info4eee | Information For Electrical & Electronics Engineering XTAL1 Input to the inverting Oscillator amplifier and input to the internal clock operating circuit. XTAL2 Output from the inverting Oscillator amplifier. AVCC AVCC is the supply voltage pin for Port A and the A/D Converter. It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter. AREF AREF is the analog reference pin for the A/D Converter. Alternate Functions of Port A Port A has an alternate function as analog input for the ADC as shown in Table 4.2. If some Port A pins are configured as outputs, it is essential that these do not switch when a conversion is in progress. This might corrupt the result of the conversion. Table 4.2 Port A Pins Alternate Functions Port Pin Alternate Function PA7 ADC7 (ADC input channel 7) PA6 ADC6 (ADC input channel 6) PA5 ADC5 (ADC input channel 5) PA4 ADC4 (ADC input channel 4) PA3 ADC3 (ADC input channel 3) PA2 ADC2 (ADC input channel 2) PA1 ADC1 (ADC input channel 1) PA0 ADC0 (ADC input channel 0) The alternate pin configuration of Port B is as follows: • SCK – Port B, Bit 7 SCK: Master Clock output, Slave Clock input pin for SPI channel. When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB7. When the SPI is enabled as a Master, the data direction of this pin is controlled by DDB7. When the pin is forced by the SPI to be an input, the pull- up can still be controlled by the PORTB7 bit. • MISO – Port B, Bit 6 MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is enabled as a Master, this pin is configured as an input regardless of the setting of DDB6. When the SPI is enabled as a Slave, the data
  23. 23. 23 info4eee | Information For Electrical & Electronics Engineering direction of this pin is controlled by DDB6. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB6 bit. • MOSI – Port B, Bit 5 MOSI: SPI Master Data output, Slave Data input for SPI channel. When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB5. When the SPI is enabled as a Master, the data direction of this pin is controlled by DDB5. When the pin is forced by the SPI to be an input, the pull- up can still be controlled by the PORTB5 bit. • SS – Port B, Bit 4 SS: Slave Select input. When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB4. As a Slave, the SPI is activated when this pin is driven low. When the SPI is enabled as a Master, the data direction of this pin is controlled by DDB4. When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the PORTB4 bit. • AIN1/OC0 – Port B, Bit 3 AIN1, Analog Comparator Negative Input Configure the port pin as input with the internal pull-up switched off to avoid the digital port function from interfering with the function of the analog comparator. OC0, Output Compare Match output: The PB3 pin can serve as an external output for the Timer/Counter 0 Compare Match. The PB3 pin has to be configured as an output to serve this function. The OC0 pin is also the output pin for the PWM mode timer function. • AIN0/INT2 – Port B, Bit 2 AIN0, Analog Comparator Positive input Configure the port pin as input with the internal pull-up switched off to avoid the digital port function from interfering with the function of the Analog Comparator. INT2, External Interrupt Source 2: The PB2 pin can serve as an external interrupt source to the MCU. • T1 – Port B, Bit 1 T1, Timer/Counter1 Counter Source. • T0/XCK – Port B, Bit 0
  24. 24. 24 info4eee | Information For Electrical & Electronics Engineering T0 Timer/Counter 0 Counter Source XCK USART External Clock. The Data Direction Register DDB0 controls whether the clock is output DDB0 set or input DDB0 cleared. The XCK pin is active only when the USART operates in Synchronous mode. The alternate pin configuration of Port C is as follows: • TOSC2 – Port C, Bit 7 TOSC2, Timer Oscillator pin 2: When the AS2 bit in ASSR is set one to enable asynchronous clocking of Timer/Counter2, pin PC7 is disconnected from the port, and becomes the inverting output of the Oscillator amplifier. In this mode, a Crystal Oscillator is connected to this pin, and the pin cannot be used as an I/O pin. • TOSC1 – Port C, Bit 6 TOSC1, Timer Oscillator pin 1: When the AS2 bit in ASSR is set one to enable asynchronous clocking of Timer/Counter2, pin PC6 is disconnected from the port, and becomes the input of the inverting Oscillator amplifier. In this mode, a Crystal Oscillator is connected to this pin, and the pin cannot be used as an I/O pin. • TDI – Port C, Bit 5 TDI, JTAG Test Data In: Serial input data to be shifted in to the Instruction Register or Data Register. When the JTAG interface is enabled, this pin cannot be used as an I/O pin. • TDO – Port C, Bit 4 TDO, JTAG Test Data Out: Serial output data from Instruction Register or Data Register. When the JTAG interface is enabled, this pin cannot be used as an I/O pin. The TD0 pin is tri-stated unless TAP states that shifts out data are entered. • TMS – Port C, Bit 3 TMS, JTAG Test Mode Select: This pin is used for navigating through the TAP-controller state machine. When the JTAG interface is enabled, this pin cannot be used as an I/O pin. • TCK – Port C, Bit 2 TCK, JTAG Test Clock: JTAG operation is synchronous to TCK. When the JTAG interface is enabled, this pin cannot be used as an I/O pin. SDA – Port C, Bit 1 SDA, Two-wire Serial Interface Data: When the TWEN bit in TWCR is set one to enable the Two-wire Serial Interface, pin PC1 is disconnected from the port and becomes the Serial Data I/O pin for the Two-wire Serial Interface. In this mode, there is a spike filter on the pin to suppress spikes shorter than 50 ns on the
  25. 25. 25 info4eee | Information For Electrical & Electronics Engineering input signal, and the pin is driven by an open drain driver with slew-rate limitation. When this pin is used by the Two-wire Serial Interface, the pull-up can still be controlled by the PORTC1 bit. • SCL – Port C, Bit 0 SCL, Two-wire Serial Interface Clock: When the TWEN bit in TWCR is set one to enable the Two-wire Serial Interface, pin PC0 is disconnected from the port and becomes the Serial Clock I/O pin for the Two- wire Serial Interface. In this mode, there is a spike filter on the pin to suppress spikes shorter than 50 ns on the input signal, and the pin is driven by an open drain driver with slew-rate limitation. When this pin is used by the Two-wire Serial Interface, the pull-up can still be controlled by the PORT C0 bit. 4.7 LCD Display A Liquid Crystal Display is an electronic device that can be used to show numbers or text. There are two main types of LCD display, numeric display and alphanumeric text displays. The display is made up of a number of shaped „crystals‟. In numeric displays these crystals are shaped into „bars‟, and in alphanumeric displays the crystals are simply arranged into patterns of „dots‟. Each crystal has an individual electrical connection so that each crystal can be controlled independently. When the crystal is „off‟ i.e. when no current is passed through the crystal, the crystal reflect the same amount of light as the background material, and so the crystals cannot be seen. However when the crystal has an electric current passed through it, it changes shape and so absorbs more light. This makes the crystal appear darker to the human eye - and so the shape of the dot or bar can be seen against the background. It is important to realise the difference between a LCD display and an LED display. An LED display often used in clock radios is made up of a number of LEDs which actually give off light and so can be seen in the dark. An LCD display only reflect slight, and so cannot be seen in the dark. The dot-matrix liquid crystal display controller and driver LSI displays alphanumeric, characters, and symbols. It can be configured to drive a dot-matrix liquid crystal display under the control of a 4 or 8-bit microprocessor. Since all the functions such as display RAM, character generator, and liquid crystal driver, required for driving a dot-matrix liquid crystal display are internally provided on one chip, a minimal system can be interfaced with this controller/driver. A single HD44780U can display up to two 8-character lines 16 x 2. A 16 x 2 line LCD module to display user information. Fig 4.10 2 x16 LCD Display
  26. 26. 26 info4eee | Information For Electrical & Electronics Engineering 4.8 TRANSFORMER: A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors - the transformer's coils or windings. Except for air-core transformers, the conductors are commonly wound around a single iron-rich core, or around separate but magnetically coupled cores. A varying current in the first or primary winding creates a varying magnetic field in the core of the transformer. This varying magnetic field induces a varying electromotive force or voltage in the secondary winding. This effect is called mutual induction. Fig 4.11 Transformer If a load is connected to the secondary circuit, electric charge will flow in the secondary winding of the transformer and transfer energy from the primary circuit to the load connected in the secondary circuit. The secondary induced voltage VS, of an ideal transformer, is scaled from the primary VP by a factor equal to the ratio of the number of turns of wire in their respective windings: By appropriate selection of the numbers of turns, a transformer thus allows an alternating voltage to be stepped up - by making NS more than NP or stepped down, by making it. BASIC PARTS OF A TRANSFORMER In its most basic form a transformer consists of: A primary coil or winding. A secondary coil or winding. A core that supports the coils or windings. Refer to the transformer circuit in figure as you read the following explanation: The primary winding is connected to a 50-hertz ac voltage source. The magnetic field builds up and collapses about the primary
  27. 27. 27 info4eee | Information For Electrical & Electronics Engineering winding. The expanding and contracting magnetic field around the primary winding cuts the secondary winding and induces an alternating voltage into the winding. This voltage causes alternating current to flow through the load. The voltage may be stepped up or down depending on the design of the primary and secondary windings. THE COMPONENTS OF A TRANSFORMER Two coils of wire are wound on some type of core material. In some cases the coils of wire are wound on a cylindrical or rectangular cardboard form. In effect, the core material is air and the transformer is called an air-core transformer. Transformers used at low frequencies, such as 50 hertz and 400 hertz, require a core of low-reluctance magnetic material, usually iron. This type of transformer is called an iron-core transformer. Most power transformers are of the iron-core type. The principle parts of a transformer and their functions are: The core, which provides a path for the magnetic lines of flux. The Primary winding, this receives energy from the ac source. The secondary winding, this receives energy from the primary winding and delivers it to the load. The enclosure, this protects the above components from dirt, moisture, and mechanical damage. 4.9BRIDGE RECTIFIER A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave rectification. This is a widely used configuration, both with individual diodes wired as shown and with single component bridges where the diode bridge is wired internally. Basic operation According to the conventional model of current flow originally established by Benjamin Franklin and still followed by most engineers today, current is assumed to flow through electrical conductors from the positive to the negative pole. In actuality, free electrons in a conductor nearly always flow from the negative to the positive pole. In the vast majority of applications, however, the actual direction of current flow is irrelevant. Therefore, in the discussion below the conventional model is retained. In the diagrams below, when the input connected to the left corner of the diamond is positive, and the input connected to the right corner is negative, current flows from the upper supply terminal to the right along the red(positive) path to the output, and returns to the lower supply terminal via the blue (negative) path.
  28. 28. 28 info4eee | Information For Electrical & Electronics Engineering Fig 4.12 Bridge rectifier When the input connected to the left corner is negative, and the input connected to the right corner is positive, current flows from the lower supply terminal to the right along the red path to the output, and returns to the upper supply terminal via the blue path. In each case, the upper right output remains positive and lower right output negative. Since this is true whether the input is AC or DC, this circuit not only produces a DC output from an AC input, it can also provide what is sometimes called "reverse polarity protection". That is, it permits normal functioning of DC- powered equipment when batteries have been installed backwards, or when the leads from a DC power source have been reversed, and protects the equipment from potential damage caused by reverse polarity. Prior to availability of integrated electronics, such a bridge rectifier was always constructed from discrete components. Since about 1950, a single four terminal component containing the four diodes connected in the bridge configuration became a standard commercial component and is now available with various voltage and current ratings. Output smoothing For many applications, especially with single phase AC where the full-wave bridge serves to convert an AC input into a DC output, the addition of a capacitor may be desired because the bridge alone supplies an output of fixed polarity but continuously varying or pulsating magnitude.
  29. 29. 29 info4eee | Information For Electrical & Electronics Engineering Fig 4.13 Bridge rectifier in parallel capacitor at the output The function of this capacitor, known as a reservoir capacitor is to lessen the variation in the rectified AC output voltage waveform from the bridge. One explanation of smoothing is that the capacitor provides a low impedance path to the AC component of the output, reducing the AC voltage across, and AC current through, the resistive load. In less technical terms, any drop in the output voltage and current of the bridge tends to be cancelled by loss of charge in the capacitor. This charge flows out as additional current through the load. Thus the change of load current and voltage is reduced relative to what would occur without the capacitor. Increases of voltage correspondingly store excess charge in the capacitor, thus moderating the change in output voltage / current. The simplified circuit shown has a well-deserved reputation for being dangerous, because, in some applications, the capacitor can retain a lethal charge after the AC power source is removed. If supplying a dangerous voltage, a practical circuit should include a reliable way to safely discharge the capacitor. If the normal load cannot be guaranteed to perform this function, perhaps because it can be disconnected, the circuit should include a bleeder resistor connected as close as practical across the capacitor. This resistor should consume a current large enough to discharge the capacitor in a reasonable time, but small enough to minimize unnecessary power waste. Because a bleeder sets a minimum current drain, the regulation of the circuit, defined as percentage voltage change from minimum to maximum load, is improved. However in many cases the improvement is of in significant magnitude. capacitor and the load resistance have a typical time constant τ = RC where C and R are the capacitance and load resistance respectively. As long as the load resistor is large enough so that this time constant is much longer than the time of one ripple cycle, the above configuration will produce a smoothed DC voltage across the load. In some designs, a series resistor at the load side of the capacitor is added. The smoothing can then be improved by adding additional stages of capacitor–resistor pairs, often done only for sub-supplies to critical high-gain circuits that tend to be sensitive to supply voltage noise. The idealized waveforms shown above are seen for both voltage and current when the load on the bridge is resistive. When the load includes a smoothing capacitor, both the voltage and the current waveforms will be greatly changed. While the voltage is smoothed, as described above, current will flow through the bridge only during the time when the input
  30. 30. 30 info4eee | Information For Electrical & Electronics Engineering voltage is greater than the capacitor voltage. For example, if the load draws an average current of n Amps, and the diodes conduct for 10% of the time, the average diode current during conduction must be 10n Amps. This non-sinusoidal current leads to harmonic distortion and a poor power factor in the AC supply. In a practical circuit, when a capacitor is directly connected to the output of abridge, the bridge diodes must be sized to withstand the current surge that occurs when the power is turned on at the peak of the AC voltage and the capacitor is fully discharged. Sometimes a small series resistor is included before the capacitor to limit this current, though in most applications the power supply transformer's resistance is already sufficient. Output can also be smoothed using a choke and second capacitor. The choke tends to keep the current rather than the voltage more constant. Due to the relatively high cost of an effective choke compared to a resistor and capacitor this is not employed in modern equipment. 4.10 REGULATOR IC It is a three pin IC used as a voltage regulator. It converts unregulated DC current into regulated DC current. First pin is used for input, second for ground and third pin gives the rectified and filtered output. It has an inbuilt filtering circuit which removes the ripples present in the rectified DC obtained from full bridge rectifier circuit. Fig 4.14 MCT7805CT voltage regulator Normally we get fixed output by connecting the voltage regulator at the output of the filtered DC see in above diagram. It can also be used in circuits to get a low DC voltage from a high DC voltage for example we use 7805 to get 5V from 12V. There are two types of voltage regulators 1. fixed voltage regulators 78xx,
  31. 31. 31 info4eee | Information For Electrical & Electronics Engineering 79xx 2. Variable voltage regulators in fixed voltage regulators there is another classification 1. + ve voltage regulators 2.–vevoltage regulators positive voltage regulators this include 78xx voltage regulators. The most commonly used ones are 7805 and 7812. 7805 gives fixed 5V DC voltage if input voltage is in 7.5V, 20V. 7805 is a voltage regulator integrated circuit. It is a member of 78xx series of fixed linear voltage regulator ICs. The voltage source in a circuit may have fluctuations and would not give the fixed voltage output. The voltage regulator IC maintains the output voltage at a constant value. The xx in 78xx indicates the fixed output voltage it is designed to provide. 7805 provides +5V regulated power supply. Capacitors of suitable values can be connected at input and output pins depending upon the respective voltage levels. 4.11 The Capacitor Filter The simple capacitor filter is the most basic type of power supply filter. The application of the simple capacitor filter is very limited. It is sometimes used on extremely high-voltage, low current power supplies for cathode ray and similar electron tubes, which require very little load current from the supply. The capacitor filter is also used where the power-supply ripple frequency is not critical; this frequency can be relatively high. The capacitor C1 shown in figure 4.15 is a simple filter connected across the output of the rectifier in parallel with the load. Fig 4.15 Full wave rectifier with a capacitor filter When this filter is used, the RC charge time of the filter capacitor C1 must be short and the RC discharge time must be long to eliminate ripple action. In other words, the capacitor must charge up fast, preferably with no discharge a tall. Better filtering also results when the input frequency is high; therefore, the full- wave rectifier output is easier to filter than that of the half-wave rectifier because of its higher frequency. For you to have a better understanding of the effect that filtering has on Eavg, a comparison of a rectifier circuit with a filter and one without a filter is illustrated in figure 4.16 and figure 4.17. The output waveforms in figure 4.16 represent the unfiltered and figure 4.17 represents filtered outputs of the half-wave rectifier circuit. Current pulses flow through the load resistance RL each time a diode conducts. The dashed line
  32. 32. 32 info4eee | Information For Electrical & Electronics Engineering indicates the average value of output voltage. For the half-wave rectifier, Eavg is less than half of the peak output voltage. This value is still much less than that of the applied voltage. With no capacitor connected across the output of the rectifier circuit, the waveform in figure 4.16 has a large pulsating component compared with the average or dc component. When a capacitor is connected across the output figure 4.17, the average value of output voltage Eavg is increased due to the filtering action of capacitor C1 UNFILTERED Fig 4.16 Half-wave rectifier without filtering FILTERED Fig 4.17 Half-wave rectifier with filtering The value of the capacitor is fairly large, several microfarads, thus it presents a relatively low reactance to the pulsating current and it stores a substantial charge. The rate of charge for the capacitor is limited only by the resistance of the conducting diode, which is relatively low. Therefore, the RC charge time of the circuit is relatively short. As a result, when the pulsating voltage is first applied to the circuit, the capacitor charges rapidly and almost reaches the peak value of the rectified voltage within the first few cycles. The capacitor attempts to charge to the peak value of the rectified voltage anytime a diode is conducting, and tends to
  33. 33. 33 info4eee | Information For Electrical & Electronics Engineering retain its charge when the rectifier output falls to zero. The capacitor slowly discharges through the load resistance RL during the time the rectifier is non-conducting. The rate of discharge of the capacitor is determined by the value of capacitance and the value of the load resistance. If the capacitance and load resistance values are large, the RC discharge time for the circuit is relative Long. A comparison of the waveforms shown in figure 4.16 and figure 4.17 illustrates that the addition of C1 to the circuit results in an increase in the average of the output voltage Eavg and a reduction in the amplitude of the ripple component Er, which is normally present across the load resistance. Now, let's consider a complete cycle of operation using a half-wave rectifier, a capacitive filter C1, and a load resistor RL. As shown in figure 4.16, the capacitive filter C1 is assumed to be large enough to ensure a small reactance to the pulsating rectified current. The resistance of RL is assumed to be much greater than the reactance of C1 at the input frequency. When the circuit is energized, the diode conducts on the positive half cycle and current flows through the circuit, allowing C1 to charge. C1 will charge to approximately the peak value of the input voltage. The charge is less than the peak value because of the voltage drop across the diode D1. In the figure 4.16 the heavy solid line on the waveform indicates the charge on C1. In the figure 4.17 the diode cannot conduct on the negative half cycle because the anode of D1 is negative with respect to the cathode. During this interval C1 discharges through the load resistor RL. The discharge of C1 produces the downward slope as indicated by the solid line on the wave form in the figure 4.17. In contrast to the abrupt fall of the applied ac voltage from peak value to zero, the voltage across C1 and thus across RL during the discharge period gradually decreases until the time of the next half cycle of rectifier operation. Keep in mind that for good filtering, the filter capacitor should charge up as fast as possible and discharge as little as possible as shown in Figure 4.18 and figure 4.19. POSITIVE HALF-CYCLE Fig 4.18 Capacitor filter circuit NEGATIVE HALF-CYCLE
  34. 34. 34 info4eee | Information For Electrical & Electronics Engineering Fig 4.19 Capacitor filter circuit Since practical values of C1 and RL ensure a more or less gradual decrease of the discharge voltage, a substantial charge remains on the capacitor at the time of the next half cycle of operation. As a result, no current can flow through the diode until the rising ac input voltage at the anode of the diode exceeds the voltage on the charge remaining on C1. The charge on C1 is the cathode potential of the diode. When the potential on the anode exceeds the potential on the cathode the charge on C1, the diode again conducts and C1 begins to charge to approximately the peak value of the applied voltage. After the capacitor has charged to its peak value, the diode will cut off and the capacitor will start to discharge. Since the fall of the ac input voltage on the anode is considerably more rapid than the decrease on the capacitor voltage, the cathode quickly become more positive than the anode and the diode ceases to conduct. Operation of the simple capacitor filter using a full-wave rectifier is basically the same as that discussed for the half-wave rectifier. Referring to figure, you should notice that because one of the diodes is always conducting on alternation, the filter capacitor charges and discharges during each half cycle. Note that each diode conducts only for that portion of time when the peak secondary voltage is greater than the charge across the capacitor. Fig 4.20 Full-wave rectifier with capacitor filter Another thing to keep in mind is that the ripple component Er of the output voltage is an ac voltage and the average output voltage Eavg is the dc component of the output. Since the filter capacitor offers relatively low
  35. 35. 35 info4eee | Information For Electrical & Electronics Engineering impedance to ac, the majority of the ac component flows through the filter capacitor. The ac component is therefore bypassed around the load resistance and the entire dc component Eavg flows through the load resistance. This statement can be clarified by using the formula for XC in a half wave and full-wave rectifier. First, you must establish some values for the circuit. As you can see from the calculations by doubling the frequency of the rectifier, you reduce the impedance of the capacitor by one-half. This allows the ac component to pass through the capacitor more easily. As a result, a full wave rectifier output is much easier to filter than that of a half-wave rectifier. Remember the smaller the XC of the filter capacitor with respect to the load resistance the better the filtering action. Xc = Since the largest possible capacitor will provide the best filtering. Remember, also, that the load resistance is an important consideration. If load resistance is made small, the load current increases, and the average value of output voltage Eavg decreases. The RC discharge time constant is a direct function of the value of the load resistance therefore the rate of capacitor voltage discharge is a direct function of the current through the load. The greater load current the more rapid the discharge of the capacitor and the lower the average value of output voltage. For this reason, the simple capacitive filter is seldom used with rectifier circuits that must supply a relatively large load current. Using the simple capacitive filter in conjunction with a full-wave or bridge rectifier provides improved filtering because the increased ripple frequency decreases the capacitive reactance of the filter capacitor. 4.12 Light Emitting Diode An LED is a very simple electronics component which lights up when electricity flows through it. Since it is a diode, electricity can only flow one way. There is usually a flat section on the side of the LED to mark its polarity: this side should be connected to ground. This side usually also has a shorter leg. In order to prevent too much current flowing through an LED and damaging it, it should be connected in series with a resistor. Fig 4.21 Light Emitting Diode 4.13 Resistor A resistor is a component of a circuit that resists the flow of electrical current. It has two terminals across which electricity must pass, and it is designed to drop the voltage of the current as it flows from one terminal
  36. 36. 36 info4eee | Information For Electrical & Electronics Engineering to the other. Resistors are primarily used to create and maintain known safe currents within electrical components. Resistance is measured in ohms, after Ohm's law. This law states that electrical resistance is equal to the drop in voltage across the terminals of the resistor divided by the current being applied. A high ohm rating indicates a high resistance to current. This rating can be written in a number of different ways - for example, 81R represents 81 ohms, while 81K represents 81,000 ohms. Materials in general have a characteristic behavior of opposing the flow of electric charge. This opposition is due to the collisions between electrons that make up the materials. This physical property, or ability to resist current, is known as resistance and is represented by the symbol R. Resistance is expressed in ohms which is symbolized by the capital Greek letter omega. The resistance of any material is dictated by four factors: Material property-each material will oppose the flow of current differently. Length-the longer the length, the more is the probability of collisions and, hence, the larger the resistance. Cross-sectional area-the larger the area A, the easier it becomes for electrons to flow and, hence, the lower the resistance. Temperature-typically, for metals, as temperature increases, the resistance increases. The amount of resistance offered by a resistor is determined by its physical construction. A carbon composition resistor has resistive carbon packed into a ceramic cylinder, while a carbon film resistor consists of a similar ceramic tube, but has conductive carbon film wrapped around the outside. Metal film or metal oxide resistors are made much the same way, but with metal instead of carbon. A wire wound resistor, made with metal wire wrapped around clay, plastic, or fibre glass tubing, offers resistance at higher power levels. Those used for applications that must withstand high temperatures are typically made of materials such as cermets, a ceramic-metal composite, or tantalum, a rare metal, so that they can endure the heat. Resistors are coated with paint or enamel, or covered in moulded plastic to protect them. Because they are often too small to be written on, a standardized color-coding system is used to identify them. The first three colors represent ohm value, and a fourth indicates the tolerance, or how close by percentage the resistor is to its ohm value. This is important for two reasons: the nature of its construction is imprecise, and if used above its maximum current, the value can change or the unit itself can burn up. The circuit element used to model the current-resisting behavior of a material is the resistor. For the purpose of constructing circuits, resistors shown in Figure 4.22 are usually made from metallic alloys and carbon compounds. The resistor is the simplest passive element.
  37. 37. 37 info4eee | Information For Electrical & Electronics Engineering Fig 4.22 from top to bottom: W, W, and 1-W resistors TYPES OF RESISTER Different types of resistors have been created to meet different requirements. Some resistors are shown in Figure 4.23. The primary functions of resistors are to limit current, divide voltage and dissipate heat. A resistor is either fixed or variable. Most resistors are of the fixed type that is their resistance remains constant. The two common types of fixed resistors wire wound and composition are shown in Figure 4.24. Wire wound resistors are used when there is a need to dissipate a large amount of heat while the composition resistors are used when large resistance is needed. Fig 4.23 Different types of resistors
  38. 38. 38 info4eee | Information For Electrical & Electronics Engineering (a) (b) Fig 4.24 Fixed resistors: (a) wire wound type (b) Carbon film type RESISTOR COLOUR CODE Some resistors are physically large enough to have their values printed on them. Other resistors are too small to have their values printed on them. For such small resistors color coding provides a way of determining the value of resistance. As shown in Figure 4.25 the color coding consists of three, four, or five bands of color around the resistor. Fig 4.25 Color coding The first three bands specify the value of the resistance. Bands A and B represent the first and second digits of the resistance value and C is usually given as a power of 10 as shown in figure 4.25. If present the fourth band D indicates the tolerance percentage. For example a 5 percent tolerance indicates that the actual value of the resistance is within ± 5 of the color-coded value. When the fourth band is absent, the tolerance is taken by default to be ± 20 percent. The fifth band E, if present is used to indicate a reliability factor which is a Statistical indication of the expected number of components that will fail to have the indicated resistance after working for 1,000 hours. As shown in Figure 4.25 the statement “Big Boys Race Our Young Girls, But Violet Generally Wins” can serve as a memory aid in remembering the color code.
  39. 39. 39 info4eee | Information For Electrical & Electronics Engineering 5. CONCLUSION From the design of experimental set up with Micro Controller Based Solar Tracking System Using Stepper Motor If we compare Tracking by the use of LDR with Fixed Solar Panel System we found that the efficiency of Micro Controller Based Solar Tracking System is improved by 30-45% and it was found that all the parts of the experimental setup are giving good results. The required Power is used to run the motor by using Step-Down T/F by using 220V AC. Moreover, this tracking system does track the sun in a continuous manner. And this system is more efficient and cost effective in long run. From the results it is found that, by automatic tracking system, there is 30 % gain in increase of efficiency when compared with non-tracking system. The solar tracker can be still enhanced additional features like rain protection and wind protection which can be done as future work.
  40. 40. 40 info4eee | Information For Electrical & Electronics Engineering 6. REFERENCES [1] Rizk J. and Chaiko Y. “Solar Tracking System: More Efficient Use of Solar Panels”, World Academy of Science, Engineering and Technology 41 2008. [2] Filfil Ahmed Nasir, Mohussen Deia Halboot, Dr. Zidan Khamis A. “Microcontroller-Based Sun Path Tracking System”, Eng. & Tech. Journal, Vol. 29, No.7, 2011. [3] Alimazidi Mohammad, Gillispie J, Mazidi, Rolin D. McKinlay, “The 8051 Microcontroller and Embedded Systems”, An imprint of Pearson Education. [4] Mehta V K, Mehta Rohit, “Principles of Electronics”, S. Chand & Company Ltd. [5] Balagurusamy E, “Programming in ANSI C”, Tata McGraw-Hill Publishing Company Limited. [6] Damm, J. Issue #17, June/July 1990. An active solar tracking system, Home Brew Magazine. [7] Koyuncu B and Balasubramanian K, “A microprocessor controlled automatic sun tracker,” IEEE Trans. Consumer Electron., vol. 37, no. 4,pp. 913-917, 1991. [8] Konar A and Mandal A K, “Microprocessor based automatic sun tracker,” IEE Proc. Sci., Meas. Technol., vol. 138, no. 4, pp. 237-241,1991.

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