CHAPTER
ONE https:/www.google.com.ng/
INTRODUCTION
The
invention of electricity and its advancements in the field of electrical
engineering has made electrical energy so vast in its applications. A modern
house today, cannot be said to be one if it has no use for electricity .This is
because most of the items required for making life fit and comfortable in a
home functions with electricity. Electrical appliances like water heaters,
radios, televisions, fans, and water pumps e.t.c all have absolute need for
electricity. Unfortunately though the poor availability of public utility power
in Nigeria has pushed her citizens to seek alternatives and in dependent means
of electricity this has resulted in individuals buying wind turbines, solar panels,
generating sets and so on. Unavoidably this requires careful selection of the
one to be ON to their use – alternative power or public power utility. Sequel
to this, phase absence is a very common and severe problem in any industry,
home or office. Many times one or two phases may not be live in the three phase
supply, because of this some electrical appliances will be ON in one room and
OFF in another room. This project is designed to check the availability of any
live phase, and the load will be connected to the live phase only. This feat is
achieved with AT89C52 MCU [C. N. Gary,
2003.]. This controller continuously checks for live condition of all the
phases connected to it, and the controller connects the load the load to the
active phase using a relay. The relay is driven with a transistor. If two or
three phases are live, the phase will be connected to the phase that is ON only
and automatically transferred to the phase that is ON in the event of a main
outage or from generator back to main when restored. An LCD is provided to
display the status of the phase condition. [M. E. Rajash K. E. Malhorta, 1980] Contrast control preset is given
for LCD contrast control. Furthermore the project uses a regulated 12V, 500mA power
supply. Bridge type full-wave rectifier was used to rectify the a.c output of
the secondary 230/12V step –down transformer [R. J. Maddock, D. M. Calcutta 1988]. In addition due to problems
incurred over interrupted power supply, this led to the discovery of
three-phase intelligent switching system which makes the selection process a
lot stress free, efficient and cost effective. The three-phase intelligent
switching system makes our network infrastructure smarter. Intelligent
switching systems are in a giving phase in that companies are continually
developing solutions that will make network systems smarter in the future [F. B. Fredrick, F.C. Robert, 1975]. The
demand for sensitive systems which are able to monitor the violent and
devastating effect of fire and vandals at homes, offices etc have increased.
This led to the idea of an intelligent switching system which has the ability
to monitor, control and switch between phases. It also provides the comfort of
starting a standby generator when there is power failure from the mains (PHCN)
without the aid of an operator. The switching between the mains and the
generator occurs in micro seconds.
1.2 BACKGROUND OF THE STUDY
Electrical power is an
indispensable form of energy. Residential, industrial and commercial setups all
require continuous supply of electric power to undertake their day- to-day
activities. After its generation, the electrical energy is transmitted and
finally distributed to be used by various consumers. The power system is never
foolproof as it is bedeviled with myriad of problems both natural and man
–made. These problems usually lead to power outages. Power system failures or
outages in general do not encourage development in the public and private
sectors, residential, and commercial Institutions. In countries where these failures
are frequent and often lead to prolong periods of outages, the power system can
be said to be unreliable. In these countries where government are encouraging
private sector participation in the development process, investors confidence
is low and investors do not find it prudent to channel their resources into
capital intensive ventures in such countries. These problems militate against
the development of Industries in such countries.
To lessen the effect of
outages, Institutions like Hospitals, banks, etc. that can not do with the
absence of electric power have resorted to the use of generators with enough
capacity to meet their energy requirements. In the event of power outages, the
changeover from power supplied by public utility to a generator is usually
performed manually. These practices often result in waste of critical time,
machine damage due to incompetence of personnel leading to financial losses.
There have being instances because of poorly designed changeover systems,
voltages generated by the generators have being fed back into the utility grid
system leading to severe shocks and injuries suffered by personnel working on
distribution lines.[ J. E. Angello 1960]
The above mentioned
problems have created the need for automating the control aspect of finding
alternative sources of power to back up the utility supply. Power automation
refers to the use of the control systems such as numerical controllers,
programmable logic controllers, and other industrial control system to control
industrial machinery and processes, reducing the need for human intervention.
Specialized hardened computers, referred to as programmable logic controllers
(PLC) are use to synchronize the flow of input from sensors and events with the
flow of the output to actuators and events.
This leads to precisely
controlled actions that permit a tight control of almost any individual process
[E. I. Owen, 1996]
In industries, power
automation is yet to catch up and thus many industries undertake manual
changeover switching. There are some changeover switches available in Nigerian
markets which incorporates little or no automation at all. These switches are
able to switch between two sources of power supply and do so upon detection of
a complete absence of power o one source. These changeovers use contactors,
which create chattering noises at half voltages or low voltages. Again, there
are time delays in the changeover processes (Hermant Joshi, 2008).
This project seeks to address the
problems inherent in the manual changeover process. This present the design and
construction of microcontroller based three phase changeover switch that would
be to switch electrical power from the utility to the generator installed in
the event of power outage or insufficient voltage automatically.
1.3 Motivations for embarking on the Project
From various surveys,
it is generally noticed that industries are vulnerable to long and short
interruption that are considered as ‘reliability issues’ in the power system
analysis. And the use of manual changeover switch has become a major problem
due to its greatest delays.
Thus, when the power supply is
reconnected, someone has to put OFF the generator and then change the source
line from generator to the public supply.
1.4 Specific
objectives of the project.
The objective of this
project is to solve the shortfall associated with power supply changeovers
available in the market. These shortfalls include:
a) Changeover delays, chattering which cause can
fire, inability to detect and change over at low voltage.
b) Design and construct a changeover switch that
can switch loads from the mains power supply (PHCN) to a back up power supply (GENERATOR
SET, SOLAR) with simplicity.
c)
Introduce a circuitry that can sense and
monitors phase failure in each of the three phase available in the supply unit
and switch to the next source.
Design a three phase
changeover switch which is Microcontroller based that can be used for domestic
applications, Industries and commercial loads without interruption in
production process.
d) Design
a microcontroller based changeover which is capable of switching 50 amperes per
phase.
1.5 Significance of the project:
The
purpose of this project is to design and construct a microcontroller based
three phase changeover switch that can provide solution to the fluctuation of
power supply problem we are facing in Nigeria today. The microcontroller based changeover switch is a unique switching
system that can be used to effect the change from one power supply to another as well as ensuring
consistency and reliability in the supply to a particular load or network. The
envisaged another changeover switch is to interface between two different
electrical power sources e.g., the mains supply and the generator, (Blalock Thomas, 2006).
1.6 The scope of Project
The
scope of this project work seeks to look at how changeover switching affects
the users of electricity (consumers) and how to come out with a simple device
to protect consumers from these effects. The design and construction of a three
phase microcontroller based changeover switch would solve the problem of work
force and the danger likely to be encountered by the changeover. The electronic
control switch monitors the incoming public supply voltage and detects when the
voltage drops below a level that an electrical or electronic gadgets can
function depending on the utility services, Michael Valcarcel, (1988)
CHAPTER
TWO
LITERATURE REVIEW
According to Donald G.
Fink and Wayne (1998), Emergency power systems were used
as early as World War II on naval ships. In combat, a ship may lose the
function of its steam engines, which powers the steam driven turbines for the
generators. Early transfer switches relied on manual operation; two switches
would be placed horizontally in line and the ‘ON’ position facing each other, a
rod is placed in between. In order to operate the switch one source must be
turned ‘OFF’, the rod moved to the other side and the other turned ‘ON’.
Switches allow
switching from a primary source to a secondary or tertiary power source and are
employed in some electrical power distribution system, (M.A. Mazidi and J.G Mazidi. 200). Power Instability in developing
countries have necessitated the need for automation between public power supply
and alternative generators to back up the utility power supply, and as the rate
of power instability becomes predominately high, the need for automation also
becomes high. And since the industrial and commercial processes require
uninterrupted power supply, if the process of power supply changeover is
manual, it will not only waste time by slowly the process, but could also cause
device, process or product to damage. There could be an error during the manual
changeover as a result of human factor, and in some cases, this can lead to massive
loss of revenue. Therefore, the major aim of this project is to exploit the
ubiquitous microcontroller facilities in bringing about automation of change
over process. One of the most critical needs of an embedded system such as to
decrease the power consumption and space,(http://www.journal.au.edu/eu techn/2006) and this is
achieved in this work. It has caused companies to lose millions of dollar each
time there is power failures and when power is restored. This can be clearly
seen in companies like Telecommunication, Breweries, Cold-rooms, etc .This
study is carried out to proffer solution to the shortcomings of the already
existing manual changeover switch by has the ability to eliminate the stress of
manual switching; monitors phase failures, line drops, and then switch over to
the alternate source (generator).
2.1 Review
of Existing work
To ensure the
continuity of power supply, many commercial/industrial facilities depend on
both utility service and on-site generation. And because of the growing
complexity of electrical; systems it becomes imperative to give attention to power
supply reliability and stability, [P. J.
Hurst) 2001]. Over the years many
approaches have been implored in configuring a change over system. Some of them
are discussed below:
2.1.1 Manual changeover switches box
Manual
changeover switch box separates the source between a generator and public
supply-Jonathan Gana Kolo (2007). Whenever
there is power failure, switching over to other source of supply is done
manually by human intervention and the same happens when the public power is
restored and this is usually accompanied with loud noise and electrical sparks.
2.1.2 Limitations of a Manual changeover switch
Below are some of the limitations of
manual changeover switches;
a) Time wastage whenever
there is power failure
b)
It is strengthous to operate
c)
Its causes devices, process or product to damage
d)
It makes a lot of noise
e)
Maintenance is more frequent as the changeover action causes wear and tear.
2.1.2
Automatic changeover system with electromagnetic Relays (EMRs)
A relay is an
electromagnetic device that is activated by varying its input in order to get a
desired output. Relays are of two types, the normally closed and the normally
open-Paul Horowitz and Winfreid (2008)
Recently
electromagnetic relays (EMRs) have been used with other components to implement
automatic changeover .Such component can be logic gates, transistors, opt-coupler,
microcontroller, etc. Most of these components makes use of 5volts since they
are transistor-transistor logic (TTL) based,
[ B. M. Weedy 1972]. Such control system
must be properly isolated from the relay as shown in the block diagram below:
Isolator
|
Electronic control
|
Mains
|
Electromagnetic
Relay
|
Load
|
Figure 1: Block diagram for control system
This type of changeover is better than
manual changeover type because it is automatic and faster, but has its
limitations listed below:
1)
Noise associated with switching relays,
2)
Wear and tear,
3)
Arcing which can cause fire outbreak,
4) High components count making the
system more prone to failures.
2.3.1 CHANGEOVER WITH AUTOMATIC TRANSFER SWITCH
(ATS)
This
type of changeover has an automatic transfer switch –Jerry C. Whitaker, IEE press, Page 1030-1031, which monitors the
alternating current ac, voltage coming from the utility company line for power
failure conditions upon detection of power failure for predetermined period of
time, the standby generator is activated (started) after which the load is transferred
from utility to the standby generator. Then, on return of the utility fed, the
load is switched back after some time and the generator is stopped. The
limitations of this approach are more or less than the same thing with
automatic changeover system with electromagnetic relays.
2.4 DEVELOPMENT
THAT HAVE TAKEN PLACE UNDER THIS PROJECT
In
view of the limitations of the above previous works, this project proposes and
implements a changeover system that drastically reduced the shortcomings. The noise,
arcing, wear and tear associated with EMRs are eliminated totally by the
introduction of solid state relays. Digital components were also used to make
the work more reliable unlike the previously existing ones that make use of
circuit breakers. Also AT89C52 microcontroller was also incorporated to help
improve the speed of automation. The system is controlled by a software program
embedded in the microcontroller,
J.Boyle, 2001.
This
work is handy and portable compared to the bulky works done previously. It also
has some important features like an alarm system for indicating generator
failure units and line drops.
2.5 MICROCONTROLLER
A
microcontroller is a computing device capable of executing a program (i.e. a
sequence of instructions) and is often referred to as the “brain” or “control
center” in a robot or SMART system since it is usually responsible for all
computations, decision making, and communications.
In order to interact with the outside
world, a microcontroller possesses a series of pins (electrical signal
connections) that can be turned HIGH (1/ON), or LOW (0/OFF) through programming
instructions. These pins can also be used to read electrical signals (coming
form sensors or other devices) and tell whether they are HIGH or LOW.
It is also a self-contained system
with peripherals, memory and a processor that can be used as an embedded
system. Most programmable microcontrollers that are used today are embedded in
other consumer’s product or machinery including phones, peripherals,
automobiles and household appliances for computer systems. Due to that, another
name for a microcontroller is “Embedded controller”. Some embedded systems are
more sophisticated, while others have minimal requirement for memory and
programming length and a low software complexity.
Input
and output devices include solenoids, LCD displays, relays, switches and
sensors for data like humidity, temperature or light level, amongst others
2.5.1 Microprocessors versus
Microcontrollers
The
primary difference between a microprocessor and a microcontroller is that the
microcontroller includes more supporting functions such as on-board memory and
I/O than the microprocessor.
Until
recently, microcontroller units (MCU's) were considered less powerful than
microprocessors, however, continued development has lead to MCU's that meet or
exceed the throughput (number of equivalent instructions per second) of
high-end microprocessors.
2.5.2
Types of microcontrollers
There
are several types of Microcontrollers are:
>
8051 Family e.g. AT89C52,AT89S52
> PIC Family, e.g.
PIC16F84,
> AVR Family, e.g.
ATmega8, ATmega32.
> Digital
Signal Processors
Digital
Signal Processors (DSP's) are types of microcontrollers that are more
specialized for a particular application.
DSP represent around 20% of the total MCU market. DSP's are particularly
well suited to real-time operations in which a data stream, video, audio, etc. is
modified in someway as it is passed along to another device or component. Most DSP's are based on the Harvard
Architecture. DSP's commonly include
analog-to-digital (A/D) conversion for their inputs and digital-to-analog (D/A)
conversion of their outputs.
Figure 2: Digital Signal Processors
Architecture.
2.5.3
Purpose
of microcontrollers in this project
a) The embedded controller (microcontroller), in
this project will make it precise and accurate in operation
b)
It measures load current-true RMS
c)
Monitors over voltage and under voltage cut-off for EB and DG (optional)
d)
Significant saving on wall space and wiring.
f)
For tropicalized and rugged design.
2.5.4.
Communication Protocols of Microcontrollers
The
various types of Microcontroller communication Protocols are listed as shown bellow.
a) The SPI Communication Protocol
b)
The chip-to-chip protocol
c)
The Master slave protocol
a)
I2C
and CAN Bus communication Protocol
b) Serial I/O Interface (UART)
c) 1-Wire®
Communication
1.
The Universal Asynchronous Receiver/Transmitter (UART)
is a popular form of serial communication between digital devices.
A number of bits are
presented to the UART in parallel and are then serialized, transmitted to
another UART where they are converted back into a binary vector.
The UART specification
does not include details of the communication details.
In fact, there are
several interface standards in common use (e.g. RS232, RS422 and RS485). For embedded systems the RS232 standard is
the most popular.
1. The Serial Peripheral Interface (SPI)
This
is a communications protocol used on most MCU's as an inexpensive alternative
to multiple pin parallel communications. SPI is used for many applications in
MCU including memory data block transfers.
The SPI interface include a clock line, a data-in, a data-out and a chip
enable line, named as, SCLK - serial clock
MISO - master input, slave output MOSI - master output, slave input CS -
chip select (optional, usually inverted polarity)
Figure .3: The Serial Peripheral Interface (SPI)
3.
I2C
Communications
The
Inter-Integrated Circuit (I2C) computer bus is used to interface
many different types of peripherals to MCU's or other embedded systems when a
high data throughput is not required.
The
I2C uses bidirectional data and clock lines with open-collector
logic. The standard data rate for the I2C is 100 kilobits/second. It
also supports a low-speed 10 Kbits/s or lower.
The
I2C protocol is ideal for sending control signals to remote devices,
collecting A/D signals from sensors and accessing slow-speed non-volatile
RAM.
One
of the most valuable features is that peripherals can be connected and removed
from the I2C bus while powered up.
This is possible because of the open-collector logic in which a bus line
is either set to ground or no-connection.
In
open-collector circuits, a logical high is achieved by placing pull-up resistor
one each open-collector line.
4 Controller
Area Network (CAN) Bus
This
is a multicast shared serial bus standard.
The CAN bus was designed to operate in high noise conditions, which
makes it a preferred communications standard for applications involving
electrical motors and internal combustion engines.
The
CAN protocol uses error-correcting codes to automatically detect and recover
bit errors in data words. The full data
transfer rate of 1Mbit/s the total length of the CAN network is limited to less
than 50 metres.
Figure 4: Controller Area Network (CAN) Bus
5. 1-Wire Communication with PIC
Microcontroller
This application note
introduces the user to the 1-Wire communication protocol and describes how a
1-Wire device can be interfaced to the PIC microcontrollers. 1-Wire protocol is
a registered trade mark of Maxim/ Dallas Semiconductor.
A software stack for
the basic, standard speed, 1-Wire master communication is provided with this
application note along with an example application
5(a) OVERVIEW OF THE 1-Wire BUS
The PIC
microcontrollers have multiple General Purpose Input/output (GPIO) pins, and
can be easily configured to implement Maxim/Dallas Semiconductor’s 1-Wire
protocol.
The 1-Wire protocol
allows interaction with many Maxim/Dallas Semiconductor parts, including
battery and thermal management devices, memory, Buttons®, etc.
1-Wire devices provide
solutions for identification, memory, timekeeping, measurement and control.
1-Wire data interface
is reduced to the absolute minimum (single data line with a ground reference).
As most 1-Wire devices provide a relatively small amount of data, the typical
data rate of 16 kbps is sufficient for the intended tasks. It is often
convenient to use a GPIO pin of an 8-bit or 16-bit microcontroller in a “bit
banging” manner to act as the bus master. 1-Wire devices communicate using a
single data line and well-defined, time tested protocols.
5(b) 1-Wire Protocol
• The protocol is
called 1-Wire because it uses 1 wire to transfer data. 1-Wire architecture uses
a pull-up resistor to pull voltage off the data line at the master side.
• 1-Wire protocol uses
CMOS/TTL logic and operates at a supply voltage ranging from 2.8V to 6V.
• Master and slave can
be receivers and transmitters, but transfer only one direction at a time (half
duplex). The master initiates and controls all 1-Wire operations.
• It is a bit-oriented
operation with data read and write, Least Significant bit (LSB) first, and is
transferred in time slots.
• The system clock is
not required as each part is self-clocked and synchronized by the falling edge
of the master.
5© Prerequisites
The requirements of any
1-Wire bus are:
• The system must be
capable of generating an accurate and repeatable 1μs delay for standard speed
and 0.25μs delay for overdrive speed.
• The communication
port must be bidirectional; its output must be open-drain and there should be a
weak pull-up on the line.
• The communication
operations should not be interrupted while being generated
5(d) OPERATIONS OF THE 1-Wire BUS
The four basic
operations of a 1-Wire bus are Reset, Write 0 bit, Write 1 bit and Read bit.
Using these bit
operations, one has to derive a byte or a frame of bytes.
The bus master
initiates and controls all of the 1-Wire communication. Figure 2 illustrates
the 1-Wire communication timing diagram. It is similar to Pulse-Width
Modulation (PWM) because, the data is transmitted by wide (logic ‘0’) and
narrow (logic ‘1’) pulse widths during data bit time periods or time slots. The
timing diagram also contains the recommended time values for robust
communication across various line conditions.
Table 1 provides a list
of operations with descriptions and also implementation steps; this is for
standard speed.
A communication
sequence starts when the bus master drives a defined length “Reset” pulse that
synchronizes the entire bus. Every slave responds to the “Reset” pulse with a
logic-low “Presence” pulse (http://www.maxim-ic.com/quick_view2.cfm/qv_pk/
3711/t/al)
To
write the data, the master first initiates a time slot by driving the 1-Wire
line low, and then, either holds the line low (wide pulse) to transmit a logic
‘0’ or releases the line (short pulse) to allow the bus to return to the logic
‘1’ state. To read the data, the master again initiates a time slot by driving
the line with a narrow low pulse. A slave can then either return a logic ‘0’ by
turning on its open-drain output and holding the line low to extend the pulse,
or return a logic ‘1’ by leaving its open-drain output off to allow the line to
recover.( http://www.maxim-ic.com/)
• Most 1-Wire devices
support two data rates: standard speed of about 15 kbps and overdrive speed of about 111 kbps.
The protocol is
self-clocking and tolerates long inter-bit delays, which ensures smooth
operation in interrupted software environments. (http://www.maxim-ic.com/1-Wire)
appnotes.cfm?appnote_number=126)
5) The SPI protocol
The SPI protocol is a
widely accepted and easily used serial transfer protocol. It is fast and
efficient, allowing for simultaneous bi-directional data transfer. The protocol
involves a master-slave configuration which includes a master device and one or
more slave devices. However, the protocol does allow for multiple slave devices
to simultaneously communicate with a single master device. This application
note provides information on both the hardware and software aspects of a single
master, multi-slave SPI setup under two operating conditions: (1) when both
master and slave are operating from the same source voltage and (2) when master
and slave are operating from different source voltages.
This application note
shows the hardware and software for an SST89E/V516RDx microcontroller utilizing
its 8-bit hardware SPI to communicate with several SST25VFxxx Serial Flash
memory devices. The software routines, written in C, contain extensive comments
to describe the function of each routine. Port 1 of the MCU is used to
interface 25VFxxx devices, and Port 2 of the MCU can contain LEDs for
debugging. Companion product data sheets for the SST89E/ V516RDx MCU and
25VFxxx Serial Flash should be reviewed in conjunction with this application
note for a complete understanding of the hardware and software examples
provided here.
(a) Master-Slave Running from the Same Voltage
Source
Figure 2-1 shows the
hardware setup of master and slaves operating at a single supply voltage. P1.2
- P1.4 control the Chip-Enable inputs for the three 25 series memory chips.
P1.5 - P1.7 provide the SI, SO, and SCK interfaces respectively to each chip.
This means that all three memory chips are clocked off the same clock and
communicate on the same serial bus. Also note that the SO outputs on the memory
are in a Hi-Z state when CE is HIGH. For this reason, no buffers are required
between the memory and the MCU. For the same reason, only one memory chip may
be enabled at one time. Enabling more than 1 memory chip at one time risks data
corruption and possible hardware damage. Although there are extra port pins
available on the MCU to implement the HOLD and Write-Protect features, such
implementation is up to customer preference and beyond the scope of this
application note.
Figure 5:
Master-Slave Running from the Same Voltage Source
(b) Master-Slave Running from Different Source
Voltages
The schematic in Figure
2-2 shows how the same master-slave setup can be achieved when the master is
running at a different voltage than the slaves. As you can see, the first
modification is the addition of a voltage regulator. Any suitable voltage
regulator will be adequate. The one used with the above system is a
STMicroelectronics LF30CV. Next, the addition of the high-speed Texas
Instruments SN74LVC4245A level shifters is necessary due to the voltage
differences between the master and slave devices. P1.2 - P1.4 outputs are still
used to control the Chip- Enables of the three memory chips. The only
difference now is that they are routed through the level shifters first so that
the proper voltage levels can be conveyed to the memory devices. Level shifters
are also used between the MCU and the SI, SO and SCK signals of the serial
flash. Even with the addition of the level shifters, there is no software
driver change between the formal single voltage system and the latter dual
voltage system. One possible design concern is making sure the maximum data
transmission speed for the level shifters matches or (preferably) exceeds the
maximum desired transmission speed of the SPI bus.
Since the TI level
shifters shown above can transmit data much faster than the SPI protocol would
allow, this is not an issue in our design. However, if your design uses
different level shifters, make sure the new level shifters can keep up with the
SPI bus speed being used.
Figure 6: Master-Slave Running from Different Source Voltages
2.6
PROGRAMMING SOFTWARE
2.6.1 Driver
Description
Custom
code
is required for proper communication between a single master and multi slave
devices. The following code is written for this purpose. It is also highly
modular so it can be flexible while efficient. The code can be used in its
entirety or modified to suit different application needs. The code contained
within this application note is designed as a driver set for communication
between a single master device and multiple slave devices via the SPI bus as
illustrated in the preceding hardware section. As such, the functions shown
below are meant to be called from the customer’s main program. A sample MAIN
program is provided to illustrate proper use of the driver functions. The
sample MAIN will initialize all three memory chips and perform a chip erase to
all three chips. Then it will write the byte values 0-19 to the first memory
chip, 20-39 to the second chip, and 40-59 to the third chip. All chips are
being written to starting at memory address 0000H.
Name Function
HWSPI_Init Initializes
SPI.
SST_Master IO Handles
byte transfer to and
From
slave device.
CE_High Sets Chip Enable of the serial flash
high
CE_Low Clears
Chip Enable of the serial flash low
Read Status_ Register
Reads the status register of
The
serial flash
EWSR Enables the Write Status
Register
WRSR Performs
a write to the status
Register
WREN Write enables the serial flash
WRDI Write
disables the serial
Flash
Read_ID Reads the
manufacturer ID and
device ID
Reads one byte from the serial
flash and returns byte
Read_Cont Reads multiple
bytes
Byte Program Program one byte to the serial
flash
Auto_Add_IncA Initial Auto Address
Increment process
Auto_Add_IncB Successive Auto
Address_ Increment
process after AAI
Initiation
Chip_Erase Erases entire
serial flash
Sector_Erase Erases one
sector (4 KB) of the
serial flash
Block_Erase Erases one
block (32 KB) of
the serial flash
Wait_Busy Polls status
register until busy
bit is low
2.10 Description of solid state Relays
With
emergence of semiconductor technology, the productions of solid state relays
were made possible which in many applications out perform their predecessors. A
typical solid state relay consists of a light emitting diode (LED) optically
coupled to a photovoltaic device such as a Field effect Transistor (FET)
Light
from the Led creates s voltage across the photovoltaic array and activates the
output FET. FET is the preferred switching element in a solid state relay
because it is comparatively less electric resistant when it is in a conductive
state than a Traic in the same state and therefore generates less heat.
(Alexander C. King, 2003) As a result of this, FET requires smaller heat
dissipating fins and can reduce the overall size of the solid state relay. The
internal circuitry of a solid states relay is shown above.
Advantages
of Solid state Relay over Electromagnetic Relay
Solid
state relay has the following properties which give it an edge over the EMR:
1. It has no moving coil part,
2, It has long
operating life.
3. It is bounce-free
operation
4. It has immunity to
electromagnetic interference
5. It has high switching speed
6.
It can be controlled by a low signal of about 3volts
7. It has multifunction
integration
8. High reliability
9. Resistance to shock
and vibration
10. Wide input voltage
range
11. No arcing or
sparking
12. No acoustical noise
13. High input-output isolation
(John Saltford, 2003).
Because
of the low signal control feature, solid state relays can be driven directly by
the microcontroller without the use of interface drivers. This can save space,
time and money, reduce component count as well as improve product life,
performance and reliability.
2.11. Liquid Crystal Display
In
the early 1970's, digital watches started showing up in the marketplace with a
new and different type of display-the liquid crystal display or LCD. The LCD
displays used in these early digital watches were very different from the LEDs
they replaced. While even a tiny LED display consumes a few mill watts of
power, the LCD consumes just microwatts of power. Hence, the
LCDs are over 1000
times more efficient at their job than the LEDs.
Since their
commercialization in the '70s, LCDs are the most popular electronic display
device, except one-the CRT. LCD flat full color panels are now challenging the
CRT as displays for television and computers. There are also many hybrid
systems that use LCD display technology,
R. Perez, (1988).
2.12
Liquid crystals
There are 3 states of
matter: solid, liquid, gas.
Solids states can be
further categorized into: crystalline which has regular arrangement of
molecules; and amorphous where there is no regular structure. It is well known that
Crystalline solids
heat → Isotropic liquid.
In 1888, an
intermediate phase is discovered and is known as the crystalline liquid or
liquid crystal. This phase is called the nematic phase. An example is
4-n-pentyl-4'-cyano-biphenyl (PCB). Since than, over 20,000 known compounds
have been found to have the nematic phase, B.
Bahadur, (1990).
The main interest in
these types of compound is that the nematic phase compounds with rod-like
molecules can be aligned by varying an external electric field.
Most of the liquid
crystal displays (LCDs) produced today uses either the twisted nematic (TN) or
super twisted nematic (STN) electro-optical effects.
2.11.1
Types of LCDs
There are many types of
LCDs.
• Dynamic Scattering:
Higher voltage, higher power, less legible, now obsolete.
LIQUID
CRYSTAL DISPLAYS 2
• FLC (Ferroelectric
Liquid Crystal) Bi-stable, faster switching times (~2MHz), can achieve good
grayscale by rubbing process.
• TN: Twisted Nematic
• STN: Super-twisted
Nematic
• TFT: Thin Film
Transistor Active Matrix TN
We will only cover the
last three types in our lectures.
2.11.2
Power Requirements
The LCDs have minimal
power requirements. Currently manufactured LCDs consume between 1 and 300
microwatts per square centimeter. This is the lowest power consumption of any
display type now available. This very low power consumption allows most LCD
products to be battery operated.
2.11.3 Principle of Operation of LCD
The LCD uses a system
of filters to display information that is similar to the operation of the
polarizer. Ambient light enters the LCD display through the front polarizing
filter. The coherent light then passes through the liquid crystal medium. This
liquid crystal medium is a collection of specific organic molecules which
rotate the light passing through them. They change the polarization of the
coherent light passed to them.
This rotation of the
light's polarization may be from just a few degrees to over 270 degrees, M. Slater, (1989).
In most liquid crystal
compounds used in manufacturing LCDs, the amount of rotation of the light's
polarization is 90 degrees.
Figure 9: Simple diagram for working
Principle of LCD
CHAPTER THREE
DESIGN METHODOLOGY
3.1
MATERIALS
The
materials to be used in the design of this project are highlighted as shown below:
> The
microcontroller device ,AT89S52 and ATmeg8, Voice activator
> Step down transformer,
220V/12V or 12Volt Battery,
> Cables,
> Electronic
Components which are : Diodes, Capacitor, varactor, Resistors,
> Relays, e.g.,
solid state and Electromagnetic relays, Liquid Crystal Display (LCD) 20X8, Ammeter,
Voltmeter, Transistors, Operational Amplifiers, IC regulator, etc
> Casing, etc.
3.2.
Method used in the design
The different modules
of three-phase Microcontroller based switching system are presented here. These
include:
3.3.
POWER SUPPLY UNIT: This unit is designed to produce power
of 12volts to the loads. The circuit takes in an alternating current power from
the supply and step it down to 12volts ac and then convert it to a direct
current. This is achieved using some electronic components such as, diodes,
resistors such as choke resistors, capacitors such as mica capacitors, etc.
Using the following materials above in the conversion of ac power into a dc
power is a transformer-less power supply unit .The conversion of ac power into
a dc power is known as “Rectification”. The figure below shows the circuit diagram
of the power supply.
Figure 10: Power supply
unit
3.4. Voltage Comparator unit: This
is the decision making unit of the system. Sample voltages are compared based
on the reference values set. The unit has variable resistor used as potential
zener diodes for voltage references, operational amplifiers as voltage
comparators and industrial relays for interfacing the D.C outputs with the A.C
inputs, J.E Angello, (1960).
The
voltage reference settings are Zener diode D13 = 3V, Zener diode D14 =4.7V,
Zener diode D15= 10V, Potentiometer VR1 = 13V, and the D.C. output from each
phase after filtration equals 18V.
Figure
11: Voltage comparative circuit.
In the design, as seen in fig 1 the
reference voltage for the IC comparator is from VR1 potentiometer. Once the
input source at pin 3 of the IC is greater, a high output is produced at its
pin terminal 6 to energize relay RLA. The energized relay immediately closes on
the phase one supply to the A.C load- Bulb.
But when phase two has higher voltage
than phase one, the reference voltage at pin 2 of IC1 increases to make the
operational amplifier go low, and de-energizes relay RLA. Phase one supply is
then shifted to the comparator two i.e. IC2. The reference voltage for IC2 is
from the output of IC1. As far as output voltage of IC1 is high, pin 2 terminal
of the second comparator will remain greater than the input value at pin 3 of
IC2. This will make it impossible for the second relay, RLB to be energized.
But one, IC1 goes low, voltage at pin 2 of IC2 immediately gets to OV,
comparator 2 is pushed to energize relay RLB. Phase two supply can only be
connected to the load when the other two phases are out of supply. Then, the
reference of 10V from the diode D15 will be at the terminal 3 of IC3. The
positive difference resulting from the two inputs of the comparator puts relay RLC
in active form, P.J. Hurst, 2001,
thus, this units monitors the line or voltage drop in each phases.
3.5 The Charging Unit
This
is like the normal power supply that converts high ac input to a low dc output.
The unit transform the high ac input to a low one, rectifies it to produce a dc
output. A relay is connected in parallel with the dc output to disconnect the
battery from the inverter section while it is charging, F. B. Fredreck, (1975). The values of the components used for the
power charging unit are previously calculated. The circuit is as shown in
figure 3.3.
Figure 12: Charging circuit
3.6 Phase / line drop
detector circuit.
This
module of the design monitors the phase or line drop from any of the supply
phases. The circuit monitors the phases and sends a feed back to the
microcontroller. The microcontroller then signals the relay and energizes it to
trip, thereby switching over to next available source.
Figure 13: Phase/line drop detector
circuit
3.7 Phase failure
detector
The
Microcontroller monitors the mains supply through the phase failure unit and
switches the appropriate phase to the load through the solid state relay
arrangement.
In
case of total power failure, the system sustained by the back up battery,
switches on a three phase generator, whose output is also connected to the load
through the solid state relay arrangement.
Figure 14: Phase
failure detector
3.8 The display unit
In the early 1970's,
digital watches started showing up in the marketplace with a new and different
type of display-the liquid crystal display or LCD. The LCD displays used in
these early digital watches were very different from the LEDs they replaced.
While even a tiny LED display consumes a few milliwatts of power, the LCD
consumes just microwatts of power. Hence, the LCDs are over 1000 times more
efficient at their job than the LEDs.
Since their
commercialization in the '70s, LCDs are the most popular electronic display
device, except one-the CRT. LCD flat full color panels are now challenging the
CRT as displays for television and computers. There are also many hybrid
systems that use LCD display technology. LCD is used in this project is
provided to display the status of the three phase condition. It also has some
important features which makes the system user friendly, an alarm system for
indicating generator failure, phase failure display of the three phases,
over-voltage and under-voltage level monitoring. Contrast control preset is
given for LCD contrast control.
Figure
15: Diagram of LCD
3.9 Block Diagram
The
different modules of three-phase Microcontroller based switching system are
presented in block diagram below in figure 7.
The
Microcontroller used in this project design is from the Atmel family, such as AT89S52.
The embedded controller has 40 pins and is able to communicate with the
hardware using master slave communication protocol to communicate with the
hardware part of the system (project) The Master slave communication protocol
is explained in details in chapter two of this project write-up.
Figure 16: Shows the block diagram of the
system.
3.10. PRINCIPLE OF
OPERATION
The implementation of
this system was achieved by using the AT89S52 as the host controller. The
microcontroller does the control through the software program embedded in it.
The phase failure, over voltage and under voltage monitoring was achieved using
the operational amplifier LM3914 interfaced to microcontroller. LM3914 is a
single IC that has ten separate op-amps embedded in it, J.B. Calverthree, (2001).The host microcontroller was connected
to the hardware through cable, and the master microcontroller communicates
through cable to the slave, (the hardware).
Below is the summary of
the operations of the entire system:
•
The microcontroller monitors the mains supply through the phase failure detector,
over/under voltage detector units, and switches the appropriate three phases to
the load through the solid relay arrangement.
•
In the case of total power failure, the system, sustained by back up battery or
make use of the generator battery
switches on the three Phase generator, whose output is also connected to the
load through the solid relay arrangement.
The
switching of the three phase generator is controlled by the generator control unit.
•
In case of starting failure after three attempts, the system sounds an alarm
through the voice activator and automatically goes to manual mode (where the
user will have to start the generator manually after putting it in order).
•
The system connects the load back to utility power and automatically turns off
the generator as soon as utility power is restored.
• The liquid crystal display (LCD)
displays all the activities of the system, making it user friendly, R. Perez, (1988).
3.11. Switching Unit. This
unit consists of the solid state relays. Each relay is capable of switching at
least 80amperes per phase, and each relay handles a phase. The circuit diagram
of the switching unit is shown below:
Solid state Relay
|
Figure 17: Solid State Relay arrangement
3.12.
Voice Activator: This device will enable you to
wirelessly control the switching of various devices in the room environment,
merely using the spoken command. It is aimed at the handicapped user who cannot
push buttons on a remote but also has universal appeal as an easy and
comfortable way to switch devices, without interrupting the work at hand.
3.12.1 Mode of operation
There are two basic modes of operation
of the system –
• Training
• Recognition
But
the scope of this project is only limited to the recognition mode of operation
and it is explained as below:
3.12.2 Recognition
This mode is valid only
when system has been programmed fully. In this mode, the system continuously
samples the incoming signal and detects the start of the word. This is
indicated by blinking of state LED. On capturing the word, it extracts the
parameters and compares them with the previously stored template.
On identifying the
match, the word number flashed on the word LEDs and the transmission of
corresponding device code begins. The word LEDs remain unchanged till the
transmission continues. On detecting the mismatch, the red state LED is
flashed.
The recognition mode
continues till the system is forced into training mode using DIP switches.
The diagram is shown
below:
Figure 18: Circuit
diagram of voice activation
3.13. Mains Detector
Unit:
This unit detects the availability of the mains supply coming from the PHCN and
sends signal to the Microcontroller through the phase failure detector units.
The diagram is shown below:
Figure
19: Mains Detector Unit:
3.14. CALCULATION OF POWER FOR A THREE PHASE SYSTEM
If the change over is to be applied on a
220V/415V, 40KVA generator operating at 50Hz and a power factor of about 0.8.
To determine rating of
relay to be used as well as cable size
Recall:
Apparent power = 40 x 1000 VA (40KVA)
Line voltage = VL = 415V
Phase voltage = VsP = 240V
Active power “P” = Apparent power x
power factor
= 40 x 1000 x 0.8
=
32KW
Assuming a balanced three phase load is
being used,
P = 3* Ip*Vp* cos ᶲ
40000 = 3 x Ip x 240 x 0.8
Ip = 45000 = 69.4A
Ip ≈ 69.4A
The relay required will have a minimum
current rating of 69.4A
For increased
efficiency a tolerance of about +25% will be given
Thus relay rating will be
15% of 69.4A
= 0.15 x 69.4A
=10.41A
=69.4+10.41
= 79.81Amps or nearest allowable.
Ip = 69.4A deduced is current per phase.
Thus any cable used should be capable of carrying about 1.5 times the current.
The operating environment will also play a role.
:. Required cable
should carry a current of at least
69.4 + (50% x 69.4)
= 18.3 + 34.7
= 104.1Ampere
However, if the operating environment is
very hot, a larger cable size will be required.
CHAPTER FOUR
CONSTRUCTION
ANDS DESIGN OF THE
MICROCONTROLLER BASED THREE PHASE
CHANGEOVER SWITCH PANEL
The
Panel was constructed and designed in such a way as to make it look robust and
self explanatory. Starting with the casing, it was fabricated from a steel
metal (22.0mm thick) and has a dimension of (450X350X170) mm. The Hanger from
mounting on the wall was also constructed with key lock facility for safety
purposes.
Figure 20: Pictorial of internal
arrangement of the panel showing the solid relay.
Figure 21: Pictorial diagram of the outer look of the project.
Figure: 22: Internal diagram of the
project showing the Microcontroller.
The
panel was designed to carry a total load of 80amperes and can work with
approximately a 40KVA three phase generator (maximum). It can not be used for
single phase generator. The design was according to the formula shown below:
Power
= IV
Nominal
voltage =240V
Nominal
Current =80A
Nominal
Power =240X80
=20KVA
(approx.)
The
size of the cable used for the power circuit was 16mm²
4.1. Testing and performance Analysis: The
following test was carried out after the construction of the project and the
following results were observed
1. Activate the
generator start key and off the utility power supply
2. The power supply still
off and generator start key deactivated
3. The power supply still
off and generator start key deactivated and generator disengaged.
4. The power supply still
off and generator start key deactivated and generator engaged.
5. Switch on the
utility power supply and activate the utility power start key.
6. Switch on the
utility power supply and deactivate the utility power start key and reduce the
mains to 170V using variable transformer
7.
Switch on the utility power supply and deactivate the utility power override
and return the mains to 220V using variable transformer.
The
corresponding expected results during the test are stated as shown below.
1. The system should
not attempt starting the generator despite the fact that there is no utility supply
2. The system should
attempt starting the generator.
3. The system should attempt starting the
generator three times and then sounds an alarm and display fault on LCD.
4.
The system should start the Generator
5. The system should
not switch on any of the three phases available from the utility supply
6. The system should not switch on any phase
but puts on gen if generator is not on.
7. The system should
switch on any of the phase and switch off the generator.
After
the project has been tested, the result oriented obtained are also stated as
follows;
1.
The system did not attempt starting the generator
2. The system did
attempt starting the generator
3. The system
immediately did start the generator three times and alarm was sounded and the
fault was displayed on LCD
4.
The system actually started the generator immediately
5. The system did not
switch on any of the available three phases available from the utility supply
6. The system did not
switch on any of the available three phases from the utility supply, but switch
on the generator immediately when it was not on previously
7.
The system switched on one of the phase and puts off the generator almost
immediately
4.2 Panel coupling
The Power supply unit is first coupled
after tested and its works. The next module/unit is the phase failure unit. The
circuit diagram below shows the order of arrangement of the project work.
4.3 Program Algorithm
The algorithm of the
program is shown as follows:
1
Start
2
Initialize the system
3
Check the utility supply
4 Is
there utility supply?
5
‘IF’ YES,
6
Reset utility control unit
7 IF
NO,
8 GO
TO 17
9
Is utility Power ON?
8
‘IF’ NO,
10
GO TO 3
11 ‘IF’ YES
12 Check the three phase Voltage
13 Are the three phases OK?
14 ‘IF’ YES,
15
Switch ON the three phases and
switch OFF Gen
16 ‘IF’ NO,
17 GO TO 4
18 Is Gen Ignition ON?
19 ‘IF’ NO,
20 GO TO 3
21 ‘IF’ YES,
22 Is Gen control unit OK?
23 ‘IF’ NO
24 GO TO 3
25 ‘IF’ YES,
26 Start
the Gen
27 Is the Gen ON?
28 ‘IF’ YES,
29 GO TO 37
30 ‘IF’ NO,
31 Start count
32 Is count =3?
33 ‘IF’ NO,
34 GO TO 2
35 ‘IF’ YES
36 Activate alarm and display fault on
LCD
37 Clear count
38 Activate switching action and connect
the load unit.
4.4. Program Flow chart: The
Program Flow Chart is shown in the space above.
4.5 BILL OF ENGINEERING
MEASUREMENT AND EVALUATION (BEME)
S/N Description
of materials Qty Rate (#) AMOUNT (#)
1 Molded case 1 4000 4000
2 Solid state relay 3 25000 75000
3 Atmega8 1 2500 2500
4 Comparators (LM324) 12 200 2400
5 Transistors (BC547) 10 100 1000
6 Electromagnetic relay 1 300 300
7 Capacitors: Electrolytic 10 25 250
Mica 10 25 250
8 Varactor (MOV) 1 200 200
9 Resistors: Fixed valued 25 10 250
i). Choke resistor 12 350 4200
ii).
Variable resistor 10 70 700
10 IC voltage regulator 10 150 1500
11 AT89S52 (MuC) 1 2500 2500
12 Vero board (small) 7 150 1050
13 Soldering Lead (Roll) 1 2000 2000
14 Connecting Leads /yard 10 30 300
15 Power cable (per yard) 1 800 800
16 Liquid Crystal Display 1 2500 2500
17 Diodes (IN4007) 10 30 300
18 Step-down
transformer 6 500 3000
19 Connectors 20 150 3000
20 Buzzer 1 1000 1000
21 Bolt and Nuts 12 30 360
22 Cable tie 10 60 600
23 Cable guard 9 100 900
24 Transportation -- --- 9140
Total = #120,000.00
CHAPTER
FIVE
SUMMARY,
CONCLUSION AND RECOMMENDATION
5.1 SUMMARY
From
the discussion so far it can be seen that the use of solid state relay in the
implementation of microcontroller based automatic changeover has a number of
advantages over the other devices used in changeover system implementation. It
eliminates all the noise, arching, wear and tear associated with EMRs and
manual changeover switch box. The microcontroller with its ability to execute
millions of instruction within seconds has also helped to improve the speed of
the automation besides miniaturizing the entire system.
5.2 CONCLUSION
Unfortunately though the poor
availability of public utility power in the developing countries has pushed her
citizens to seek alternatives and dependent means of electricity .This has
resulted in individuals buying wind turbines, solar panels, generating sets and
so on. Unavoidably this requires careful
selection of the one to be ON to their use – alternative power or public power
utility.
Sequel
to this, phase absence is a very common and severe problem in any industry, home
or office. Many times one or two phases may not be live in the three phase
supply, because of this, some electrical appliances will be ON in one room and
OFF in another room. This project is designed to check the availability of the
three phases, and the load will be connected to the three phase that are
available only. In addition, due to problems incurred over interrupted power
supply, this led to the discovery of three-phase microcontroller based
switching system which makes the changing over process a lot stress free,
efficient and cost effective. The three-phase microcontroller switching system
makes our network infrastructure smarter. Intelligent switching systems are in
a giving three phases in that companies are continually developing solutions
that will make network systems smarter in the future. The demand for sensitive
systems which are able to monitor the violent and devastating effect of fire
and vandals at homes, offices etc have increased. This led to the idea of an
intelligent switching system which has the ability to monitor, detects, control
and switch between the alternative sources of supply. It also provides the
comfort of starting a stand by generator when there is power failure from the
mains (PHCN) without the aid of an operator. The switching between the mains
and the generator occurs in micro seconds.
5.3 RECOMMENDATION
This project is recommended in areas
where continuous power supply is needed such as homes, banks, industries,
hospitals and so on. It is also recommended to the student in Electrical and
Electronic Engineering department of Rufus Giwa Polytechnic, Owo for a more
study and research in Electronic and programming.
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