chapter 10 automatic solar tracking system

7/27/2019 Chapter 10 Automatic Solar Tracking System

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Study of Solar Module & Its Efficient Use in Bangladesh

106Automatic Solar Tracking System

Chapter 10

Automatic Solar Tracking System

10.1 Purpose

Nowadays the importance of solar cells and R&D in this field is steadily increasing. Themost important parameter of a solar cell is the generated power, which can be enhancedby use of solar tracking. The sun's position in the sky varies both with the seasons andtime of day as the sun moves across the sky. Solar powered equipment works bestwhen pointed at or near the sun, so a solar tracker can increase the effectiveness of suchequipment over any fixed position, at the cost of additional system complexity. A solartracker is a device for orienting a day lighting reflector, solar photovoltaic panel orconcentrating solar reflector or lens toward the sun.

Implementation

OVERALL DESIGN CONSIDERATIONS

Many factors influenced the component selection and the design of the MPPT.

In terms of optimal functionality, the barrier between the two LDR should beadjusted based on the location where to implement.

To protect the photovoltaic array from damage, protection diodes wereemployed.

Two 12V lead acid battery banks were utilized. Only one battery bank will becharged at a time. (The other will be employed to run other components circuit).

In order to trickle charge the batteries, a voltage exceeding 10V must be fed to thebank.

Voltage regulators may need a very large heat sink to operate properly.


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Fig 51: Proposed solar tracking system is being configured

Fig 52: Proposed Solar Tracker


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10.2 System Description

This is a power generating method from sunlight. This method of power generation issimple and is taken from natural resource. This needs only maximum sunlight to gene-rate power. This project helps for power generation by setting the equipment to getmaximum sunlight automatically. This system tracks maximum intensity of light. Whenthere is decrease in intensity of light, this system automatically changes its direction toget maximum intensity of light. In this work we present a microcontroller-based auto-matic position control scheme based on solar energy as primary source and batteries assecondary source. This solution permits a simple solar panels moving from east to westand returning from west to the east, within the angle regulation range of 0-80deg. Thesolar energy conversion unit with tracking module consists of an array of solar panels,battery, charge controller, LED, relay, a stepper motor, a driver, an AC mains powersource and a microcontroller based control unit. There are two sensors in two directionsto sense the direction of maximum intensity of light. The difference between the outputs

of the sensors is given to the microcontroller unit. The microcontroller will process theinput voltage from the comparison circuit and control the direction in which the motorhas to be rotated so that it will receive maximum intensity of light from the sun. Thepower generated from this process is then stored in a lead acid battery and is made tocharge an emergency light and is made to glow during night.


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Fig 53: Schematic Diagram of Automatic Solar Tracker

10.3 How it works: Flow Chart


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10.4 Advantage


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This increases the amount of energy gathered from the direct component of theincoming light.Independent on PV array characteristics.High convergence speed

Easy to constructParts are availableReliableSimple Design

10.5 Software

The AVR Microcontroller chosen had sufficient memory to meet the demands of thedesign. The ADCs were also included in the AVR, which reduced the amount ofadditional external parts. We use AVR Studio as the program compiler.

10.6 Code

#include #include #include #define delay_1 2000#define delay_2 1000

double ADC_RES_1=0,ADC_RES_2=0;short s=1,i=0,j=0,k=0,CW[4]={12,6,3,9},ACW[4]={12,9,3,6};{

DDRD &=~(1


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TCNT1L=0x7C;TCNT1H=0xE1;TCCR1B |=(5


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ADC_RES_2 = ADCL | (ADCH


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10.7 Components

Microcontroller (ATmega32) [20]

3-Terminal Positive Voltage Regulator (L7805) [21]

Stepper Motor (35BY412-16) [22]

Crystal Oscillator (12MHZ)

Relay (SRD-12VDC) [23]

High-Voltage, High-Current Darlington Arrays (ULN2804) [24]

LDR [25]

Capacitor

10.8 Components Description

Microcontroller

Description

The ATmega32 is a low-power CMOS 8-bit microcontroller based on the AVR enhancedRISC architecture. By executing powerful instructions in a single clock cycle, theATmega32 achieves throughputs approaching 1 MIPS per MHz allowing the system

designer to optimize power consumption versus processing speed. The AVR corecombines a rich instruction set with 32 general purpose working registers.


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Fig 54: Pin configuration


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Fig 55: Block diagram


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Pin Description

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 notused. Port pins can provide internal pull-up resistors (selected for each bit). ThePort A output buffers have symmetrical drive characteristics with both high sinkand source capability.

When pins PA0 to PA7 are used as inputs and are externally pulled low, theywill source current if the internal pull-up resistors are activated. The Port A pinsare 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-upresistors (selected for each bit). The Port B output buffers have symmetrical drivecharacteristics with both high sink and source capability. As inputs, Port B pinsthat are externally pulled low will source current if the pull-up resistors areactivated. 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-upresistors (selected for each bit). The Port C output buffers have symmetrical drivecharacteristics with both high sink and source capability. As inputs, Port C pinsthat are externally pulled low will source current if the pull-up resistors areactivated. 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-upresistors on pins PC5(TDI), PC3(TMS) and PC2(TCK) will be activated even if areset occurs.

Port D (PD7..PD0) : Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each bit). The Port D output buffers have symmetrical

drive characteristics with both high sink and source capability. As inputs, Port Dpins that are externally pulled low will source current if the pull-up resistors areactivated. The Port D pins are tri-stated when a reset condition becomes active,even if the clock is not running.


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RESET : Reset Input. A low level on this pin for longer than the minimum pulselength will generate a reset, even if the clock is not running. Shorter pulses arenot guaranteed to generate a reset.

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. Itshould be externally connected to VCC, even if the ADC is not used. If the ADCis used, it should be connected to VCC through a low-pass filter.

AREF : AREF is the analog reference pin for the A/D Converter.

Oscillator Characteristics

XTAL1 and XTAL2 are input and output, respectively, of an inverting amplifier whichcan be configured for use as an On-chip Oscillator, as shown in Figure 12. Either aquartz crystal or a ceramic resonator may be used. The CKOPT Fuse selects betweentwo different Oscillator amplifier modes. When CKOPT is programmed, the Oscillatoroutput will oscillate will a full rail-to-rail swing on the output. This mode is suitablewhen operating in a very noisy environment or when the output from XTAL2 drives asecond clock buffer. This mode has a wide frequency range. When CKOPT isunprogrammed, the Oscillator has a smaller output swing. This reduces power

consumption considerably. This mode has a limited frequency range and it can not beused to drive other clock buffers. For resonators, the maximum frequency is 8 MHzwith CKOPT unprogrammed and 16 MHz with CKOPT programmed. C1 and C2should always be equal for both crystals and resonators. The optimal value of thecapacitors depends on the crystal or resonator in use, the amount of stray capacitance,and the electromagnetic noise of the environment.


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Figure 56: Crystal Oscillator Connections

10.9 Relay

A relay is an electrically operated switch. Current flowing through the coil of the relaycreates a magnetic field which attracts a lever and changes the switch contacts. The coilcurrent can be on or off so relays have two switch positions and most have doublethrow (changeover) switch contacts as shown in the diagram.

Relays allow one circuit to switch a second circuit which can be completely separate

from the first. For example a low voltage battery circuit can use a relay to switch a 230VAC mains circuit. There is no electrical connection inside the relay between the twocircuits; the link is magnetic and mechanical.


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The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but itcan be as much as 100mA for relays designed to operate from lower voltages. Most ICs(chips) cannot provide this current and a transistor is usually used to amplify the smallIC current to the larger value required for the relay coil. The maximum output currentfor the popular 555 timer IC is 200mA so these devices can supply relay coils directly

without amplification.

Circuit symbol for relay

Fig 57: Relay

10.10 High-Voltage, High-Current Darlington Arrays

Darlington pair

This is two transistors connected together so that the current amplified by the first isamplified further by the second transistor. The overall current gain is equal to the twoindividual gains multiplied together: Darlington pair current gain, hFE = hFE1 hFE2(hFE1 and hFE2 are the gains of the individual transistors).This gives the Darlingtonpair a very high current gain, such as 10000, so that only a tiny base current is requiredto make the pair switch on. A Darlington pair behaves like a single transistor with avery high current gain. It has three leads (B, C and E) which are equivalent to the leads

of a standard individual transistor. To turn on there must be 0.7V across both the base-emitter junctions who are connected in series inside the Darlington pair, therefore itrequires 1.4V to turn on.


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Fig 58: Darlington Pair

Here we use ULN2804 to solve this purpose

The eight NPN Darlington connected transistors in this family of arrays are ideallysuited for interfacing between low logic level digital circuitry (such as TTL, CMOS orPMOS/NMOS) and the higher current/voltage requirements of lamps, relays, printerhammers or other similar loads for a broad range of computer, industrial, andconsumer applications. All devices feature opencollector outputs and free wheelingclamp diodes for transient suppression. The ULN2803 is designed to be compatible withstandard TTL families while the ULN2804 is optimized for 6 to 15 volt high level CMOSor PMOS.


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Fig 59: ULN2804

10.11 Voltage Regulator

A Voltage Regulator (also called a "regulator") has only three legs and appears to be acomparatively simple device but it is actually a very complex integrated circuit. Aregulator converts varying input voltage and produces a constant "regulated" outputvoltage. Voltage regulators are available in a variety of outputs, typically 5 volts, 9 voltsand 12 volts.


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Fig 60: Voltage Regulator

How it Works:

The transformer drops the 220-240 volt 'mains' voltage to 8.5 volts. The diode 'bridge'rectifies the 8.5 volts AC from the output side of the power transformer into DC. The2500uF capacitor helps to maintain a constant input into the regulator. As a generalguide this capacitor should be rated at a minimum of 1000uF for each amp of currentdrawn and at least TWICE the input voltage. The 0.1uF capacitor eliminates any highfrequency pulses that could otherwise interfere with the operation of the regulator.Voltage regulators are very robust. They can withstand over-current draw due to shortcircuits and also over-heating. In both cases the regulator will shut down beforedamage occurs. The only way to destroy a regulator is to apply reverse voltage to itsinput.

Reverse polarity destroys the regulator almost instantly. To avoid this possibility youshould always use diode protection of the power supply. This is especially importantwhen using nine volt battery supplies as it is common for people to 'test' the battery byconnecting it one way and then the other. Even this short 'test' could destroy theregulator if a protection diode is not used.

All of the interfaces described on this site have protection diodes connected into thepower supply circuit to prevent damage due to incorrect polarity. Generally a 1N4004, 1amp power diode is connected in series with the power supply. If the supply is

connected the wrong way around, the regulator will be protected from damage.

Input Voltage:

As a general rule the input voltage should be limited to 2 to 3 volts above the outputvoltage. The LM78XX series can handle up to 30 volts input, but the power differencebetween the input voltage/current ratio and output voltage/current ratio appears as


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Fig 62: Schematic Diagram of Voltage Regulator

10. 13 Light Dependent Resistors (LDR)

Fig 63: Light Dependent Resistors

LDRs or Light Dependent Resistors are very useful especially in light/dark sensorcircuits. Normally the resistance of an LDR is very high, sometimes as high as 1000 000ohms, but when they are illuminated with light resistance drops dramatically.


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10.13 Stepper Motor Systems

Stepper Motor Systems Overview

Motion Control, in electronic terms, means to accurately control the movement of an

object based on speed, distance, load, inertia or a combination of all these factors. Thereare numerous types of motion control systems, including; Stepper Motor, Linear StepMotor, DC Brush, Brushless, Servo, Brushless Servo and more. This document willconcentrate on Step Motor technology. In Theory, a Stepper motor is a marvel insimplicity. It has no brushes, or contacts. Basically it's a synchronous motor with themagnetic field electronically switched to rotate the armature magnet around. AStepping Motor System consists of three basic elements, often combined with some typeof user interface (Host Computer, PLC or Dumb Terminal):

Fig 64: Stepper Motor Overview

The Indexer (or Controller) is a microprocessor capable of generating step pulses anddirection signals for the driver. In addition, the indexer is typically required to perform

many other sophisticated command functions.

The Driver (or Amplifier) converts the indexer command signals into the powernecessary to energize the motor windings. There are numerous types of drivers, withdifferent current/amperage ratings and construction technology. Not all drivers aresuitable to run all motors, so when designing a Motion Control System the driverselection process is critical.

The Step Motor is an electromagnetic device that converts digital pulses into mechanicalshaft rotation. Advantages of step motors are low cost, high reliability, high torque at

low speeds and a simple, rugged construction that operates in almost any environment.The main disadvantages in using a step motor is the resonance effect often exhibited atlow speeds and decreasing torque with increasing speed.


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Fig 65: Hybrid stepper motor combines features of the permanent magnet stepperand the variable reluctance stepper motors.

STEPPING MOTORS

Types of Stepper Motors

There are basically three types of stepping motors; variable reluctance, permanentmagnet and hybrid. They differ in terms of construction based on the use of permanentmagnets and/or iron rotors with laminated steel stators.

Variable Reluctance

The variable reluctance motor does not use a permanent magnet. As a result, the motorrotor can move without constraint or "detent" torque. This type of construction is good

in non industrial applications that do not require a high degree of motor torque, such asthe positioning of a micro slide.


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Fig 66: Variable Reluctance

The variable reluctance motor in the above illustration has three "stator pole sets" (A, B,C,), set 15 degrees apart. Current applied to pole A through the motor winding causes amagnetic attraction that aligns the rotor (tooth) to pole A. Energizing stator pole Bcauses the rotor to rotate 15 degrees in alignment with pole B. This process will

continue with pole C and back to A in a clockwise direction. Reversing the procedure (Cto A) would result in a counterclockwise rotation.

Permanent Magnet

The permanent magnet motor, also referred to as a "canstack" motor, has, as the nameimplies, a permanent magnet rotor. It is a relatively low speed, low torque device withlarge step angles of either 45 or 90 degrees. It's simple construction and low cost make itan ideal choice for non industrial applications, such as a line printer print wheelpositioned. Unlike the other stepping motors, the PM motor rotor has no teeth and is

designed to be magnetized at a right angle to it's axis. The above illustration shows asimple, 90 degree PM motor with four phases (A-D). Applying current to each phase insequence will cause the rotor to rotate by adjusting to the changing magnetic fields.Although it operates at fairly low speed the PM motor has a relatively high torquecharacteristic.

Fig 67: Permanent Magnet


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Hybrid

Hybrid motors combine the best characteristics of the variable reluctance andpermanent magnet motors. They are constructed with multi-toothed stator poles and a

permanent magnet rotor. Standard hybrid motors have 200 rotor teeth and rotate at 1.80step angles. Other hybrid motors are available in 0.9and 3.6 step angle configurations.Because they exhibit high static and dynamic torque and run at very high step rates,hybrid motors are used in a wide variety of industrial applications.

Fig 68: Hybrid Motor

Motor Windings

Unifilar

Unifilar, as the name implies, has only one winding per stator pole. Stepper motorswith a unifilar winding will have 4 lead wires. The following wiring diagram illustratesa typical unifilar motor:

Fig 69: 4 Lead Unifilar Motor


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Bifilar

Bifilar wound motors means that there are two identical sets of windings on each statorpole. This type of winding configuration simplifies operation in that transferringcurrent from one coil to another one, wound in the opposite direction, will reverse the

rotation of the motor shaft. Whereas in a unifilar application, to change direction requir-es reversing the current in the same winding. The most common wiring configurationfor bifilar wound stepping motors is 8 leads because they offer the flexibility of either aSeries or parallel connection. There are however, many 6 lead stepping motors availablefor Series connection applications.

Figure 70: 6 and 8 lead Bifilar Motor Winding

Step Modes:

Stepper motor "step modes" include Full, Half and Microstep. The type of step modeoutput of any motor is dependent on the design of the driver.

Full Step

Standard (hybrid) stepping motors have 200 rotor teeth, or 200 full steps per revolutionof the motor shaft. Dividing the 200 steps into the 360's rotation equals a 1.8 full stepangle. Normally, full step mode is achieved by energizing both windings while

reversing the current alternately. Essentially one digital input from the driver isequivalent to one step.


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Half Step

Half step simply means that the motor is rotating at 400 steps per revolution. In thismode, one winding is energized and then two windings are energized alternately,causing the rotor to rotate at half the distance, or 0.9's. (The same effect can be achieved

by operating in full step mode with a 400 step per revolution motor). Half stepping is amore practical solution however, in industrial applications. Although it providesslightly less torque, half step mode reduces the amount "jumpiness" inherent in runningin a full step mode.

Microstep

Microstepping technology controls the current in the motor winding to a degree thatfurther subdivides the number of positions between poles. AMS microstep drives arecapable of rotating at 1/256 of a step (per step) which corresponds to 51200 steps per

revolution (for a 1.8 step angle motor).

Fig 71: Microstep

Microstepping is typically used in applications that require accurate positioning and afine resolution over a wide range of speeds. MAX-410/MAX-420 microstep drivesintegrate state-of-the-art hardware with "VRMC" (Variable Resolution MicrostepControl) technology developed by AMS. At slow shaft speeds, VRMCs produces highresolution microstep positioning for silent, resonance-free operation. As shaft speedincreases, the output step resolution is expanded using "on-motor-pole"synchronization. At the completion of a coarse index, the target micro position istrimmed to 1/100 of a (command) step to achieve and maintain precise positioning.


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Design Considerations

The electrical compatibility between the motor and the driver are the most criticalfactors in a stepper motor system design. Some general guidelines in the selection ofthese components are:

Inductance

Stepper motors are rated with a varying degree of inductance. A high inductance motorwill provide a greater amount of torque at low speeds and lower torque at higherspeeds.

Motor Stiffness

By design, stepping motors tend to run stiff. Reducing the current flow to the motor by

a small percentage will smooth the rotation. Likewise, increasing the motor current willincrease the stiffness but will also provide more torque. Trade-offs between speed,torque and resolution are a main consideration in designing a step motor system.

Motor Heat

Step motors are designed to run hot (50-90 C). However, too much current may causeexcessive heating and damage to the motor insulation and windings. AMS step motorproducts reduce the risk of overheating by providing a programmable Run/Holdcurrent feature.

10.14 Power Supply

Voltage

The higher the output voltage from the driver, the higher is the level of torque versusspeed. You can think of the voltage as the driver of the current. The higher the voltage,the faster will the current in the windings reach its new target value from one step tothe next. Therefore it is conceivable why a higher voltage will result in better speedperformance.


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Fig 72: Speed in Full Steps per Second

The torque versus speed behavior varies strongly across stepping motors. Parameters

such as the inductance of the coils and their resistance play an important role. Thehigher the inductance, the worse the performance will be at higher speeds. Whenselecting a motor for an application, make sure that it is capable of delivering adequatetorque at one target speeds of operation. If anyone has to use bifilar motors with 6 or 8leads, one may be able to optimize performance by selecting either the series or parallelconfiguration.

The voltage applied to the step motor should be higher than the rated motor voltage. Itis common to use a voltage that is 3 to 25 times the rated motor voltage. As an example,for a motor that is rated at 3.7V, supply voltages in the range of 11V to 92V are typical.

Again, the higher the voltage, the better the performance will be.

The rated motor voltage does not represent the maximum voltage that can be applied tothe motor. In fact, the motor will normally not operate properly at the rated motorvoltage.

Type

Unregulated power supplies are best suited for step motor applications. Their behavioris superior to other power supplies such as switching power supplies especially insituations where there is a sudden increase in current demand. These instances can

occur in step motor applications depending on usage. Nevertheless, switching powersupplies are also successfully used in many step motor applications. They tend to beattractive due to their price competitiveness. An important consideration in the designof such power supplies is the buffering capacitor. It needs to be adequately sized toprovide the required current during the response time of the power supply.


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10.15 Overview of the Solar Tracker:

Equipment/Component

Capacity Quantity Model Other Specifications

Solar Panel 5 Watt peak 1 SLP005-12 Vmp = 17VImp = .29 A

ChargeController

1

Battery 9 Volt 1 Lead Acid

Stepper Motor 1 35BY412-16 MotorType

Hybrid

MotorWinding

Unifilar

StepMode

Half Step

StepPulse

7.5

Rotations 48

Driver 1 ULN2804 High-Voltage, High-Current DarlingtonArrays

Microcontroller

Unit

1 ATmega32

VoltageRegulator

Input: upto30

1 LM78053-Terminal PositiveVoltage RegulatorOutput 5 Volt

Resistors 470 220

25

Capacitors 33 pf22 pf

100 f

22

1

Used for Filtering

LDR 2 VAC54

Relay 1 SRD-12VDC

CrystalOscillator

12 MHz 1

chapter 10 automatic solar tracking system

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