Adding solar trackers to a solar panel array is a good idea. These solar trackers actually increase the time a panel may face the sun which helps them produce power more effectively. However these solar trackers which are commercial made are too expensive therefore we have decided to design our own solar trackers thus making the deal a bit affordable. We have used the concept of using time to track the sun, and not the device which could sense the presence of sun and move the panel in that particular direction.
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The main goal of the project is to position a solar panel according to the motion of the sun so that it can produce maximum power. Methodology: This project uses solar panels, Microcontroller, RTC, and Stepper motor (along with its driving circuit). RTC, here, plays the role in finding the position of the sun. 1) INTRODUCTION Importance of renewable energy (to be used as an energy source) is increasing day by day. Therefore, it is vital for the students of technology field to understand the need of the hour and appreciate the skills and machineries related with renewable energy.
Solar energy is one of the well-known sources of renewable energy. You will find many recent researches conducted with an objective to enhance the efficiency of solar panels (also known as Photo Voltaic systems). One of the ways to attain this objective is solar tracking system. Our project also suggests the same solution but it deals with the solar tracking system which is RTC based. Solar tracking system has always proved to be an effective way to generate more energy because it helps the solar panel remain exactly in front of the solar rays. The concept behind these researches is that it is a fact that the sun keep on moving across the sky, the whole day long therefore it’s a good idea to track its location so that the solar panel can remain exactly in front of it absorbing more power. By applying this concept tracking systems were designed which help increase the amount of energy a solar panel may accumulate. It is been calculated that by using tracking systems the output may increase by 30% to 60%. Therefore it’s a feasible thing to opt for rather than to incur cost in the system enhancement. One way to do sun to solar panel alignment is by using an electronic control which can track the sun. This can be done using a microcontroller. Design requirements: 1) when sun is high up in the sky, the tracking system must follow its position. 2) An active control can help achieve this purpose by using time movements. The system need to be automatic thus making it simple and easy to use. The operator interference need to be negligible and must be restricted. The key components of the system are:
Output mechanical transducer.
RTC (stands for Real Time Clock)
Fig 1: Block Diagram of Time Operated Solar Tracking System
It is a fact that learning about a computer asks to have a deep look at it so as to get familiarize with its capability, and definitely it is possible by studying internal design (devices structural design) and by knowing the size and number of the records.
A microcontroller chip is a small entity made up of the processor, stable memory (ROM), unstable memory (RAM), an input output control unit and a clock. A microcontroller is also called as a small computer on the chip and is used in many items each year including toys, automobiles and home appliances etc. see below the picture of a microcontroller.
AT89S52: With in-built flash memory of 8K bytes, AT89S52 is high performance and low power 8-bit microcontroller. This device has used Atmel’s unstable memory technique and matches the 80C51 instruction according to industry standard. The flash memory in the chip allows reprogramming of the memory. This chip works like a wonder as it is highly flexible as it combines 8-bit CPU along with a programmable device which is in-built on the chip thus its quite cost effective and convenient to be used inside many control applications. Standard features of the AT89S52 are: Flash (of 8K bytes), RAM (256 bytes), input/out lines (32), timer, data pointers (two), counters (16-bit, three in number), oscillator (on-ship), clock circuit, serial port (duplex), interrupt design (6 vector, 2-level). Moreover, the AT89S52 design allows power saving by using static logic which makes the operation to zero. This idle or static mode only stops the working of the CPU whereas RAM, serial port, counters and interrupt system, keep on working. When the system is on a halt i.e. when its idle (in power saving mode) the RAM volatile memory’s contents are safe but oscillator is frozen till the next interrupt.
There are set instructions to guide the functioning of the hardware. Once the user become familiar with the HW and SW, he can then look after the microcontrollers problems easily.
The 8051 pin diagram clearly shows the microcontroller specific I/O pins:
8051 microcontroller’s capabilities are as follows:
Internal RAM and ROM
Input/Output ports having programmable pins
Counters and timers
Communication (serial data type)
Specific features of 8051 design are as follows:
DPTR (data pointer) and 16bit PC
8 bit PSW (Program Status Word)
8 bit SP (Stack Pointer)
4k ROM (internal)
128 bytes RAM (Internal)
Register banks (4 in number with 8 registers in each bank)
General data memory (80 bits)
8bit ports (four in number): making a total of 32 I/O pins: P0-P3
16bit counters/timers (two in number): T0-T1
Oscillator and circuits (3 internal and 2 external)
Features of RTC DS12C887:
IBM AT clock’s drop in replacement.
Compatible pin with MC146818B as well as DS1287
Can operate without power for over 10 years as its totally stable (non-volatile)
Enclosed subsystem having quartz, support circuitry and lithium.
Counts each time frame (sec, min, hours, day, week, month, date and year) for until 2100
Binary representation of alarm, calendar and time.
12 hour mode with PM AM options or 24 hours clock
Include the daylight saving option.
Both Motorola and Intel timing available to choose from
Pin efficiency is ensured by multiplex bus
128 RAM destined interface
15 bytes of control registers
113 bytes RAM (for general purpose)
Output signal programmable
Interrupt signals are bus compatible (IRQ)
Testable and maskable interrupts
Alarm with time of day option one per second, one per day
Periodic rates (122ms – 500ms)
Update cycle for end of clock
Multiplexed Data Bus AD0-AD7
NC = No Connection
CS = Chip Select
R/W = Read/Write Input
AS = Address Strobe
RESET = Reset Input
DS = Data Strobe
SQW = Square Wave Output
IRQ = Interrupt Request Output
GND = Ground
VCC = +5 Volt Supply
MOT = Selection of Bus Type
DS12C887 RAM is an up-gradation of DS12887 in personal computers line of IBM, adding hardware. As specified by PC AT a century byte has been added towards 50, 32h memory location. Quartz crystal, lithium and write-protected circuit is present there within the package of 24-pin. DS12C887 has replaced 16 components of the old application thus becoming a complete subsystem. Its functions include: alarm clock, completely stable clock, interrupt which is programmable, calendar, wave generator, and static RAM (113 bytes). The provision of real time clock can be different, in that it allows the time to run even if the power is not present.
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Step motor, as it is also called, is a brushless electric motor with a synchronized feature and is capable of dividing a wholesome rotation into steps. It’s an open-loop controller which means there is no feedback mechanism and hence the position of the motor is controlled exactly. The stepper motor’s functioning is somehow related to reluctance motors (huge stepping motors with lesser pole count and close loop mechanism)
Fundamentals of Operation:
A stepper motor working is different from that of Direct current brush motors which only start working when the current is supplied to their terminals. These motors contain several electromagnets present around a central piece of iron which just look like a gear. A microcontroller, working as an external circuit, provides energy to the electromagnets. To start the run, the first electromagnet when receives the power attracts the gear’s teeth toward itself – the electromagnet teeth. Thus upon the alignment of the first gear’s teeth with that of electromagnet the second teeth comes in line and when the alignment with the second teeth is turned on, the first one is turned off thus making the gear rotate. Each slight rotation from first teeth to the second one and from second to the third one and so on is called as a ‘step’ and thus the rotations of all these steps together form a rotation.
Characteristics of Stepper motor:
They are power devices
With the increase in motor speed, the torque decreases
By increasing the voltage and using limiting drivers the torque curve can be increased.
Stepper motors has more vibrations than other types of motors.
This vibration may result in loss of torque if motor is too speedy.
By applying micro-stepping driver this vibration effect may be minimized.
The operation can also be effected by the number of phases i.e. high number of phases offer smooth operation and vice versa.
Closed-loop versus Open-loop commutation
Stepper motors work on open-loop mechanism which means there is no feedback on which they can act. Therefore it is very important to make them efficiently so that they might not lose steps in case of high or varying loads. This is the main reason why sometimes the designers need to see the cost of going for servomechanism system that is a bit expensive as compared to cheaper but oversized stepper machine.
A new thing which is found effective while designing stepper control is the incorporation of feedback on rotor position (for example, a resolver or encoder). This insertion will help torque generation more effective depending on the rotor position. The reason of this effective operation is that the stepper motor will be converted into brushless servo motor which has a proper position resolution and low speed torque. The normal practice in this regard is to make the stepper motor run according to the open loop mechanism but to switch to close loop system only if the errors of rotor position become unbearable – thus also avoiding oscillating issues (most common servo error) at the same time.
Stepper motors are available in three main types:
First one, Hybrid Synchronous Stepper
Second is Variable Reluctance Stepper and
Permanent Magnet Stepper
Permanent motors are generally called so because they use a rotor’s permanent magnet (PM) and work on the basic principle of attraction and repulsion between the magnet and electromagnetic stators. Whereas Variable reluctance stepper motors operate on the mechanism that more the gap, more will be the reluctance and thus the iron rotor points and magnet poles of stator are made to be attracted closely towards each other. Then lastly, Hybrid Synchronous Motors achieve maximum power and are called so as they are the combination of the permanent magnet and variable reluctance technique.
2 phase stepper motors
Two-phase motors caters unipolar and bipolar phases, these names are basically given on the basis of electromagnetic coils’ winding arrangements.
These stepper motors are called unipolar as they have two windings (one for each magnetic field’s direction) per phase. Because we can reverse the magnetic pole without disturbing the direction of the current thus this arrangement is quite simple and requires only one transistor per winding. Generally, in a single phase, each winding has one common end: thus per phase it is three leads and therefore for two-phase motor it is 6 leads (2*3). As a general practice, commons of two phases are joined together to make it five leads.
If one want to rigger transistors to make it activated properly stepper controllers are best as the offer easy operation. This is one of the reasons of stepper motor’s popularity as they are excellent when it comes to getting perfect movements at cheap rates.
Stepper motor coils – Unipolar
(If one wants to distinguish between the common wire and the coil-end, one can do so by calculating resistance. Common and the coil-end wire resist from each other half than the resistance shown by coil-end wires and coil-end. Reason being coil’s length is double in coil-end wires as compared to common wire at the ends.) One of the easiest ways to check the stepper motor’s proper working is by rotating the shaft and if high resistance is felt this means there exist a closed circuit and phase is working normally.
These motors have a solo winding in each phase which means the current has to reverse if one wants to reverse the magnetic pole. Thus a complex H-bridge organization is required in the circuit. There are no common leads as in unipolar motors; rather each phase has two leads.
Nevertheless, windings in bipolar motors are better used as compared to unipolar motors because they are considered to be more powerful due to H-Bridge arrangement.
It is same as unipolar motor in winding but the internal common joint is missing. Thus 8-lead stepper can use different configurations when it comes to wiring:
Bipolar(using series windings). It is high in induction but each winding has lower current requirement.
Bipolar(using parallel windings). Current requirement is higher but due to lower inductance requirement performance is improved.
Bipolar(using single winding). Single winding each phase will allow motor to run partially on the windings available. Thus reducing the current requirement and torque speed requirement.
Higher-phase count motors:
These higher phase motors being high in the number of phases have less vibration but are expensive.
Drive circuits of Stepper motor
Drive circuit will decide how the motor will perform. Depending upon the quickness with which stator poles are rotated, torque curve speed may increase. The whole thing depends upon the winding inductance. In order to make windings run quickly by overcoming the resistance, we need to increase the voltage of the drive. Moreover high current induced by high voltages may also require controlling.
L/R Drive circuits
These circuits are also known as ‘constant voltage drives’ because each winding is supplied with a stable +ve and -ve current to set position steps. But voltage doesn’t apply torque; it is actually the winding current. We refer to Ohm’s law in this regard which states I=V/R. in the equation:
I = Current per winding
V = Applied Voltage
R = Winding resistance
Winding inductance L also plays a role in deciding I. R i.e. resistance will decide the current. L is generally related to change in current i.e. change in I. According to inductor formula dI/dt = V/L. L/R drive controllers, when used in stepper, will limit inductance due to the reason that v and I might be changing at different rates/speeds.
Thus with the help of L/R drive resistive motor having a low voltage can be managed easily with the help of a drive high in voltage. This can be done by placing an additional resistor in the winding series. It causes the high voltage to be wasted in the resistors. Although it is not an excellent option, still it’s a simple solution in low-cost.
Chopper drive circuits
These are also known as constant drives as they produce constant current and not the constant voltage. Initially each winding gets a high voltage by which current in each and every winding shoot instantly according to dI/dt = V/L (As V is quite high). Each winding is properly look after for current production and supply with the help of a resistor which is present in each winding. Whenever a high current is noticed the voltage gets ‘off’ (by the use of transistors). And of course when the current level normalizes, the voltage gets started again thus the constant current supply per step is ensured. This whole system needs extra electronics to work properly so that current can be identified and switched correctly. Chopper drive circuits allow high torque and speed as compared to L/R drives.
Phase current waveforms
Stepper motor is basically an AC motor (consider below mentioned theory) which uses sinusoidal current. Full form wave is not a proper description of a sinusoid. Thus it has much vibration. To overcome these issue techniques like micro stepping and half stepping are used.
Full step drive
With full step drive, the two phases are always kept on and thus the motor have a high speed torque.
A single phase can be activated using wave drive. Wave drive is used occasionally because its torque is very less. Nevertheless steps are same as in full step drive.
During half stepping, swapping of the drive takes place between one phase on and two phases on. It improves the angular resolution a lot but when only one phase is on (position: half step), stepper could have low torque. This torque can be increased by raising the current in windings.
The technical full name of microstepping is “Sine cosine microstepping” and is common waveforms used. In this stepping type current in each wind is roughly equal to sinusoidal AC waveform. Whatever waveform is used, whether AC or winding when steps become small, the smoothness of operations increases thus reducing resistance in motor and its parts. It is worth noticing that although it seems that microstepping allows high resolution achievement and high speeds but practically speaking it is not that feasible no matter even if controller is used. Mostly if angular resolution is required to set high gearheads is the most preferred way.
A very significant stepper motor feature is the repeatability of the step size. Example: A general criteria to rate the hybrid motors available these days is the motion of every complete step. The criterion is that if operated under ideal circumstances each full step travel must be within 3 to 5% of every next full step. Many producers claim their motors falls in this range of 3 to 5% travel size as the stepping falls down to one tenth. But then with the increase in the number of step the repeatability of the step size decreases considerably. If the step size is larger many commands for microsteps can be issued before motion and hence it could be taken to a very new position thereafter.
Step motor is basically a synchronized Alternate Current motor with several poles (both on stator and rotor) but no general denominator. Moreover, teeth on stator and rotor have a magnetic material that increases the poles number at cheap rate. New stepper motors combine both permanent magnet and reluctance motor, thus forming a hybrid design.
If one wants to have higher torque the stepper motor’s coils must receive full current in each step. The inductance and reverse flow of current in rotor doesn’t allow this and whenever the motor is at its full speed, time in which it receives full current is very limited which limits and lessen the torque. As the speed keep on increasing the torque decreases thus the desired level is not attained.
If stepper motor is not in its full speed the torque state is called as pull-in torque. Low speeds allow motor synchronization but friction needs to be overcome during pull-in torque.
To measure pull-out torque we need to run the motor at a desired speed thus increasing torque till the moment the motor halt. This method is tested at different speeds to judge the motor’s performance. It helps make the performance curve. Many things affects this curve, it includes current, voltage and current switching methods. Safety factor of 50% to 100% is to be practiced while comparing results of torque output.
Motors with synchronous options plus permanent magnets have torque even when they are electrically numb. Variable reluctance having core of soft iron doesn’t show detent torque.
Specifications and ratings of Stepper motor
Only winding current options are mentioned in stepper motors specifications and it is very rare to find winding or voltage resistance mark over there. The rating that winding current produces the rated voltage at DC is not up to the mark because mostly all recent drivers do so i.e. driver voltage is always higher than rated voltage.
The motors torque will depend upon the current. The inductance, voltage and circuit to which the driver is connected will decide that at what speed torque will fall off.
A very important care while selecting stepper is that the selection should be based on torque curve published by the manufacturer. Although the results and performance you may get after the purchase may vary depending upon the circuitry manufacturer had used and you are using but still torque curve is a standard measure.
Steppers that are controlled in a computerized manner are used widely when it comes to positioning systems. These are controlled digitally and have a simple operation than servo systems. Moreover steppers are open-loop thus precise control is possible.
As far as industrial applications of stepper motor are concerned it is most commonly used in heavy and speedy picking and moving equipments/machinery. CNC machines also use steppers. They are used a positioning machine in optics and laser field like in mirror mounts, linear actuators, goniometry and linear actuators. It is also used in fluid control mechanism systems etc.
If we look at its commercial applications it is widely used in printers/scanners, floppy drives slots and many other devices like plotters etc.
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