Download power factor correction using microcontroller

POWER FACTOR CORRECTION USING
MICROCONTROLLER
ABIEW FRANCIS WOGBE
&
KUDZIE KORKU JULIUS
ACCRA INSTITUTE OF TECHNOLOGY (AIT)
2012
ACCRA INSTITUTE OF TECHNOLOGY (AIT)
SCHOOL OF ENGINEERING AND APPLIED SCIENCE
1
POWER FACTOR CORRECTION USING MICROCONTROLLER
ABIEW FRANCIS WOGBE
&
KUDZIE KORKU JULIUS
A Thesis Submitted in Partial Fulfillment of the Requirements for the
Bachelor of Engineering (BEng) in Electrical and Electronic Engneering
JULY 2012
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CHAPTER 1
GENERAL INTRODUCTION AND SUMMARY
1.0 Introduction
The power factor of an ac electric power system is defined as the ratio of the real
power to the apparent power, and is a number between 0 and 1. Real power is the
capacity of the electric load for performing work in a particular time. Apparent power
is the product of the current and voltage of the electric load. Due to energy stored in
the load and returned to the source, or due to a non-linear load that distorts the wave
shape of the current drawn from the source, the apparent power can be greater than
the real power. Low-power-factor loads increase losses in a power distribution system
and result in increased energy costs.
In a purely resistive ac circuit, voltage and current waveforms are in phase, changing
polarity at the same instant in each cycle. Where reactive loads are present, such as
with capacitors or inductors, energy storage in the loads result in a time difference
between the current and voltage waveforms. This stored energy returns to the source
and is not available to do work at the load. a circuit with a low power factor will have
thus higher currents to transfer a given quantity of real power than a circuit with a
high power factor.
Circuits containing purely resistive heating elements such as filament lamps and
cooking stoves have a power factor of 1.0. Circuits containing inductive or capacitive
elements such as lamp ballasts and motors, often have a power factor below 1.0.
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The significance of power factor lies in the fact that utility companies supply
customers with volt-amperes but bill them for watts. Power factors below 1.0 require
a utility to generate more than the minimum volt-amperes necessary to supply the real
power (watts). this increases generation and transmission costs. alternatively all
components of the system such as generators, conductors, transformers, and
switchgear would be increased in size and cost to carry the extra current. hence the
need for correction of low power factor.
1.1 The Research Field and Subject Area of the Study
The research field of study is Electrical and Electronic Engineering and the subject
area of focus is Electrical Power System.
1.2 The Study Objectives
General objective
The aim of this project is to find a good solution to high energy consumption by
industries, through a sustainable development of automatic system that corrects low
power factor. The advantages of correcting power factor reduced demand charges,
increased load carrying capabilities in existing circuits, improved voltage and reduced
power system loses.
Specific Objectives
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In light of the above objective, specific objectives of the study are as follows:

Develop a prototype of an automatic power factor corrector with
microcontroller as the brain of the control system.

The overall purpose is to improve low power factor, improve energy
consumption by industries, improve stability and efficiency of the
transmission network.
1.3 The Research Problem
Electrical power generators are design to produce quality, reliable and stable power to
consumers. It came to light that most of the loads in commercial use are inductive
loads that produce inductive reactance and if not immediately checked, contributes to
low power factor thereby increasing the amount of electrical energy that flows
through the electrical network from the generating station, example of industrial and
commercial loads are (inductive motors, furnaces, arc welding machines, etc.) and (air
conditions, washing machines, deep freezers, refrigerators heaters, etc.) respectively.
Attempts are made over the years to improve the low factor close to unity using
capacitors banks to generate capacitive reactance to compensate for the inductive
reactance. Switching on and off of the capacitor banks for the compensation also
produces harmonics in the system.
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Therefore the need for improving the power factor using microcontroller to do the
switching of the capacitor banks on/off the system and also eliminate harmonic effect
in the system.
1.4 Background And Justification Of The Study/Project.
Historically, utility companies have implemented power factor correction at their
substations by installing capacitors banks. The problem with implementing power
factor correction at the substations is that the reactive power present on the
distribution system, not serviced by those capacitors, is inducing thermal losses.
Furthermore, the distribution system with its lower voltages and higher currents
already accounts for the majority of the losses on the system. In addition, more
thermal losses occur on the customer side of electric meter, within the customer
premises.
The increased low power factor due to inductive loads are alway estimated based on
power produced daily or monthly. A generator, ttansmision line and distribution
transformers may operate below their capacity due to inductive loads with low power
factor in the system. An accurate and applicable method is needed to estimate the
effect of
low power factor
and harmonics on the power system that leads to
instability, unreliable and non – quality power, hence this project is to minimise the
inductive component of the current and thereby reducing the losses in the system,
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minimising wasted energy and hence improving the efficiency of a generating plant,
transmission line and distribution transformers thereby reducing high tariffs.
1.5 Expected Outcome Of The Project And Possible Usage
The expected out come of this project is to measuring the power factor value and to improve
power factor using capacitor bank and reduce current draw by the load using microcontroller
and proper algorithm to turn on capacitor automatically, determine and trigger sufficient
switching of capacitor in order to compensate excessive reactive components, thus bringing
power factor near to unity and remove harmonics in the system there by improving the
efficiency of the system and reducing the electricity bill.
1.6 Safety, Environmental And Economic Aspects
1.6.1 Safety

The project, if under taken and implemented, posses no known hazard to
personnel or the network on which it is installed.

It must however be installed, maintained and serviced by a qualified person to
achieve optimum performance.
1.6.2 Economic

The project if implemented shall cut cost for the service provider.
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
The project when completed will make the electrical transmission system
efficient and stable.

It will reduce electricity costs by eliminating power factor surcharges.

The project when completed will enhance equipment operation by improving
voltage.

The project when completed will reduce line losses.

The project when completed will free up transformer and distribution system
capacity.
1.6.3 Environmental

The device/components in the set up are not likely to pose any environmental
problems, however the device/components
ought to be kept free from
obstruction, free from dirt and fumes, free from touch by children, and be
maintain within recommended design temperature

In case of faulty device/components ,disposal shall be done in an
environmentally friendly manner.
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1.7 Layout of Thesis.
This report will be in five chapters.

The Chapter One, consisting of an introduction, the research field and subject area
of the study, study objective, research problem, background and justification of
the research, expected outcome and possible usage, safety, environmental and
economic aspects, layout of thesis and summary of study result.

Chapter Two contains the literature review of power facto correction Brief
description of the uses of automatic power factor capacitors and fixed versus
automatic capacitors is also included in this chapter.
1.8

Chapter Three consist of methodology and hardware description.

Chapter Four consist of the system design.

Chapter Five contains conclusion and recommendations of the work.
Summary of Study Results

Designing a good microcontroller based power factor corection device to
help improve power factor, reduce high current drawn form the system and
also reduce harmonic in the system.

Improving the efficiency of the system and reducing high electricity
tariffs.

It is applicable on a commercial sinlge phase system.
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CHAPTER 2
LITERATURE REVIEW
2.0 Introduction
Though correction of power factor is very old practice, we have considered the work
done in recent years in our Thesis. Many of the authors below have suggested and
prescribe many ways of power factor correction but this work concentrates on
Barsoum model:
We have considered the work done in the previous years, starting from 1988.
Sharkawi et al. proposed a continuing effort to develop an effective, reliable, and
inexpensive adaptive power factor controller (APFC). The APFC was able to
compensate adaptively the reactive power of rapidly varying loads without adding
harmonics or transients to the power system. Based on thousands of hours of field
operation, the APFC had substantially modified to improve its reliability and
effectiveness. (Sharkawi et al. 1988)
Ioannides and Papadopoulos proposed the speed and power factor of an adjustable
speed slip power recovery drive were controlled in order to optimize the operation.
This was accomplished by means of a variable-voltage-variable-frequencies power
converter. The function of the digital controller of the power converter was to provide
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the online speed and power factor regulation. (Ioannides and Papadopoulos 1991)
Manual et al. reports a laboratory model of a microcomputer-based power factor
controller (PFC) for compensating the reactive power of rapidly varying loads by
switching capacitors sized in a binary ratio, with the help of zero voltage static
switches. Four types of control strategies were tried, viz., (1) unity step control
method, (2) binary search method, (3) successive approximation method, and (4)
look-up table method. Features like (a) independent control of current in each phase,
(b) reactive current sensing and capacitor switching in one cycle, (c) zero voltage
switching of static switches to prevent the occurrence of transients and harmonics,
and (d) switch failure detection logic and their display, are all incorporated in the
software programming. (Manual et al. 1994)
Wolfle,W.H. investigates the use of variable inductance (the inductance varies with
current), which provides adequate harmonic reduction. Three types of inductors are
investigated: an inductor with a fixed air-gap operating with a saturated core, a
swinging inductor which has a stepped gap and a novel inductor construction with a
sloped air-gap (SAG). Results are presented for a 200 W power supply and it is shown
that the SAG inductor has the best performance in terms of harmonic response and
size. (Wolfle,W.H. 1994)
Kurachi et al. proposed a detailed analysis of the ripple current of an electrolytic
capacitor in a boost-type power factor control circuit. The ripple current was divided
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into two components, namely the low-frequency and the high-frequency components.
The root-mean-square value of the capacitor current was derived for both
components. (Kurachi et al. 1995)
Barsoum proposed the programming of PIC micro-controller for power factor
correction that described the design and development of a three-phase power factor
corrector using PIC (Programmable Interface Microcontroller) chip. This involved
sensing and measuring the power factor value from the load using PIC and sensors,
then using proper algorithm to determine and trigger sufficient switching capacitors in
order to compensate excessive reactive components, thus withdraw PF near to unity.
(Barsoum 2007)
Tinggren proposed a new integrated power quality device-power factor controller
(PFC) for power distribution system and industrial power circuit applications. A PFC
integrated breaker-switched capacitor banks into a compact design with low cost
sensing elements and an intelligent control unit. The device provided more accurate
voltage control and power factor correction than traditional shunt capacitor bank
installations. (Tinggren 1999)
Ali et al. proposed a power factor controller (PFC) for a three-phase induction motor
(IM) utilized the programmable logic controller (PLC). It focused on the
implementation of a laboratory model for a PLC based PFC to improve the power
factor of a three-phase induction motor. During the online process a set of capacitors
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sized in a binary ratio would be switched on or off with the help of zero voltage static
switches according to a control strategy to obtain a pre-specified power factor. This
control strategy relied on a look-up table and an expert system. (Ali et al. 2000)
Consoli et al. proposed an innovative converter topology that improved the
performance of a switched reluctance motor drive, aimed to equip home appliances. It
was based on a modified C-dump converter configuration, where the energy recovery
stage acted as an active power factor controller for off-line operation. (Consoli et al.
2001)
Borlotti et al. proposed a general description of new functions integrated in the
medium voltage switchboard to meet the power quality challenge. They described
circuit breakers with magnetic actuators that were easy to justify economically and
gave low cost power quality solutions. (Borlotti et al. 2001)
Mather, B.A. introduces a single-phase digital power-factor correction (PFC) control
approach that requires no input voltage sensing or explicit current-loop compensation,
yet results in low-harmonic operation over a universal input voltage range and loads
ranging from high-power operation in continuous conduction mode down to the nearzero load. The controller is based on low-resolution A/D converters and digital pulse
width modulator, requires no microcontroller or DSP programming, and is well suited
for a simple, low-cost integrated-circuit realization, or as a hardware description
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language core suitable for integration with other power control and power
management functions. (Mather, B.A. 2011)
Venkateswarlu, N. proposed a novel compensator, where in-phase and quadrature
components of the supply current are vector-controlled. Implementation of this
compensator in a power electronic system operating with a very poor power factor
(and hence high THD) shows that the system then draws a leading current. A
conventional power electronic system with one of the traditional static VAR
compensators and the conventional power electronic system incorporated with the
proposed compensator are simulated and the simulation results are obtained. It is
shown that the proposed method offers only 0.7% THD, which also implies that the
power factor is improved. (Venkateswarlu, N. 2011)
Shuffling presents an intelligent power factor compensation controller that can
perform power factor correction without exciting harmonic resonance under varying
demand conditions. Practical and robust control algorithms are proposed for the
purpose of easy implementation in a micro-controller. In addition, the controller relies
on common low cost sensing devices and does not require additional measurements.
As a result, the proposed controller can be constructed as a retrofitting device to
replace existing power factor correction controllers with little effort. (Shuffling 2012)
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2.1 Power Factor
Power factor is an energy concept that is related to power flow in electrical systems.
To understand power factor, it is helpful to understand three different types of power
in electrical systems.
Real Power is the power that is actually converted into useful work for creating heat,
light and motion. Real power is measured in kilowatts (kW)q and is totalized by the
electric billing meter in kilowatt-hours (kWH). An example of real power is the useful
work that directly turns the shaft of a motor.
Reactive Power is the power used to sustain the electromagnetic field in inductive and
capacitive equipment. It is the non- working power component. Reactive power is
measured in kilovolt-amperes reactive (kVAR). Reactive power does not appear on
the customer billing statement.
Total Power or Apparent power is the combination of real power and reactive power.
Total power is measured in kilovolt-amperes (kVA) and is totalized by the electric
billing meter in kilovolt-ampere-hours (kVAH).
Power factor (PF) is defined as the ratio of real power to total power, and is expressed
as a percentage (%).
Power factor =
Real Power (kWH)
x 100
Total Power (kVAH)

15
Or Power factor cos ϕ is defined as the ratio between the Active component IR and
the total value of the current I; ϕ is the phase angle between the voltage and the
current.
Reactive
Power (Q)
Total Power (S) measured in kVAH
Measured in
kVAR
Ф
Real Power (P) measured in kW
Figure 2.0 Power Triangle.
2.2 Power Factor Correction
Power factor correction is the process of compensating for the lagging current by
creating a leading current by connecting capacitors to the supply. A sufficient
capacitance can be connected so that the power factor is adjusted to be as close to
unity as possible.
Power factor correction (PFC) is a system of counteracting the undesirable effects of
electric loads that create a power factor that is less than one (1). Power factor
correction may be applied either by an electrical power transmission utility to improve
the stability and efficiency of the transmission network or, correction may be installed
by individual electrical customers to reduce the costs charged to them by their
electricity service provider .
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An electrical load that operates on alternating current requires apparent power, which
consists of real power and reactive power. Real power is the power actually consumed
by the load. Reactive power is repeatedly demanded by the load and returned to the
power source, and it is the cyclical effect that occurs when alternating current passes
through a load that contains a reactive component. The presence of reactive power
causes the real power to be less than the apparent power, so the electric load has a
power factor of less than one.
The reactive power increases the current flowing between the power source and the
load, which increases the power losses through transmission and distribution lines.
This results in operational and financial losses for power companies. Therefore,
power companies require their customers, especially those with large loads, to
maintain their power factors above a specified amount especially around ally 0.90 or
higher, or be subject to additional charges. Electrical engineers involved with the
generation, transmission, distribution and consumption of electrical power have an
interest in the power factor of loads because power factors affect efficiencies and
costs for both the electrical power industry and the consumers. In addition to the
increased operating costs, reactive power can require the use of wiring, switches,
circuit breakers, transformers and transmission lines with higher current capacities.
Power factor correction attempts to adjust the power factor of an AC load or an AC
power transmission system to unity (1) through various methods. Simple methods
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include switching in or out banks of capacitors or inductors which act to cancel the
inductive or capacitive effects of the load, respectively.
For example, the inductive effect of motor loads may be offset by locally connected
capacitors. It is also possible to effect power factor correction with an unloaded
synchronous motor connect across the supply. The power factor of the motor is varied
by adjusting the field excitation and be made to behave like a capacitor when over
excited. Non-linear loads create harmonic currents in addition to the original AC
current.
There are two types of PFCs:
1. Passive.
2. Active
2.2.1 Passive PFC
The simplest way to control the harmonic current is to use a filter: it is possible to
design a filter that passes current only at line frequency 50Hz. This filter reduces the
harmonic current, which means that the non-linear device now looks like a linear
load. At this point the power factor can be brought to near unity, using capacitors or
inductors as required. This filter requires large-value high-current inductors, however,
which are bulky and expensive.
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A passive PFC requires an inductor larger than the inductor in an active PFC, but
costs less.
This is a simple way of correcting the nonlinearity of a load is by using capacitor
banks. It is not as effective as active PFC. Passive PFCs are typically more power
efficient than active PFCs. (Wolfle, W.H 2003) .
2.2.2 Active PFC
An "active power factor corrector" (active PFC) is a power electronic system that
controls the amount of power drawn by a load in order to obtain a power factor as
close as possible to unity. In most applications, the active PFC controls the input
current of the load so that the current waveform is proportional to the mains voltage
waveform (a sine wave). The purpose of making the power factor as close to unity (1)
as possible is to make the load circuitry that is power factor corrected appear purely
resistive (apparent power equal to real power). In this case, the voltage and current are
in phase and the reactive power consumption is zero. This enables the most efficient
delivery of electrical power from the power company to the consumer. Some types of
active PFC are: Boost, Buck and Buck-boost. Active power factor correctors can be
single-stage or multi-stage. Active PFC is the most effective and can produce a PFC
of 0.99 (99%). (Fairchild 2004)
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2.2.3 Advantages of Power Factor Correction
There are several advantages in utilizing power factor correction capacitors. These
include:
1.
reduced demand charges
2.
increased load carrying capabilities in existing circuits
3.
improved voltage
4. reduced power system loses
2.3 The disadvantages of a low power factor
The load draws greater current for the same value of the useful power.
A simple example showing the current required by a single phase electric motor is
given below:
Supply voltage = 240Volts single phase
Motor input
= 10KW
Power factor = 0.65
Current (I1) = Power (KW) = 10000
= 64.1Amps.
Volts (V) x P.F 240 x0.65
If the power factor of the motor is increased to 0.9 the current drawn by the motor
shall be:
20
Current (I2) = Power (kW) __ =
Volts (V) x PF
10000
= 46.3 Amp.
240 x 0.9
Thus, as the power factor decreases the current required for the same value of
active, or useful, power increases. The result is that the capacity of the equipment
and assoceries, like the switchgear, cables, transformers, etc., will have to be
increased to cater for the higher current in the circuit. All this adds to the cost.
2
Further, the greater current causes increased power loss or I R losses in the
circuits. Also due to higher current, the conductor temperature rises and hence the
life of the insulation is reduced.
Also, with the increased current the voltage drop increases; thereby the voltage at the
supply point is reduced. For different loads it causes voltage drop resulting in:
a. Lower output of the illumination system.
b. Less current is drawn by the heating devices so that the operating temperature
drops. This results in increased consumption for the same rise of temperature
c. The induction motors slow down and therefore draw more current to produce a
fixed torque for the loads.
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2.3.1 The advantages of an improved power factor
Higher power factors result in:
a) Reduction in system losses, and the losses in the cables, lines, and feeder circuits
and therefore lower cable sizes could be opted for.
b) Improved system voltages, thus enable maintaining rated voltage to motors, pumps
and other equipment. The voltage drop in supply conductors is a resistive loss, and
wastes power heating the conductors. Improving the power factor, especially at the
motor terminals, can improve the efficiency by reducing the line current and the line
losses.
c) Improved voltage regulation.
d) Increased system capacity, by release of KVA capacity of transformers and cables
for the same KW, thus permitting additional loading without immediate expansion.
2.4 Power Factor and Electrical Loads
In general, electrical systems are made up of three components: resistors, inductors
and capacitors. Inductive equipment requires an electromagnetic field to operate.
Because of this, inductive loads require both real and reactive power to operate. The
power factor of inductive loads is referred to as lagging, or less than 100%, based
upon our power factor ratio.
22
In most commercial and industrial facilities, a majority of the electrical equipment
acts as a resistor or an inductor. Resistive loads include incandescent lights, baseboard
heaters and cooking ovens. Inductive loads include fluorescent lights, AC induction
motors, arc welders and transformers.
Typical average power factor values for some inductive loads:
Load
PF %
Induction Motor7
70-90
Small Adjustable Speed Drive
90-98
Fluorescent Lights
Magnetic Ballast & Electronic Ballast
70-80 & 90-95 resp.
Arc Welders
35-80
2.5 Capacitor
A capacitor (originally known as condenser) is a passive two-terminal electrical
component used to store energy in an electric field. The forms of practical capacitors
vary widely, but all contain at least two electrical conductors separated by a dielectric
(insulator); for example, one common construction consists of metal foils separated
by a thin layer of insulating film. Capacitors are widely used as parts of electrical
circuits in many common electrical devices.
When there is a potential difference (voltage) across the conductors, a static electric
field develops across the dielectric, causing positive charge to collect on one plate and
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negative charge on the other plate. Energy is stored in the electrostatic field. An ideal
capacitor is characterized by a single constant value, capacitance, measured in farads.
This is the ratio of the electric charge on each conductor to the potential difference
between them.
The capacitance is greatest when there is a narrow separation between large areas of
conductor; hence capacitor conductors are often called plates, referring to an early
means of construction. In practice, the dielectric between the plates passes a small
amount of leakage current and also has an electric field strength limit, resulting in a
breakdown voltage, while the conductors and leads introduce an undesired inductance
and resistance.
Capacitors are widely used in electronic circuits for blocking direct current while
allowing alternating current to pass, in filter networks, for smoothing the output of
power supplies, in the resonant circuits that tune radios to particular frequencies, in
electric power transmission systems for stabilizing voltage and power flow, and for
many other purposes.
Capacitors also require reactive power to operate. However, capacitors and inductors
have an opposite affect on reactive power. The power factors for capacitors are
leading. Therefore capacitors are installed to counteract the effect of reactive power
used by inductive equipment. (Hammond, P 1964).
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2.5.1 Power Factor capacitors
Power factor capacitors may conveniently be switched on and off with individual
motors. This assures that the capacitor is energized only during the times when the
motor is energized - when you need power factor correction. For this type of
application, typically a Fixed Capacitor Bank is used. This is the simplest and most
economical form of power factor correction. Depending on the manner in which you
connect the capacitor, you may or may not need to include fuses
Harmonics will reduce the life of power factor capacitors. Whenever there are
harmonic producing loads on the power system, the capacitor bank should include a
capacitor protection reactor that will ―
detune‖ the capacitor bank to a frequency where
no harmonic energy exists. Instead of the capacitor protection reactor we intend using
a microcontroller to detune the capacitor bank to a frequency where no harmonics
energy can exist thereby improving the correction of Power factor.
2.5.2 Uses of Automatic Power Factor Capacitors
When the load conditions and power factor in a facility change frequently, the
demand for power factor improving capacitors also changes frequently. In order to
assure that the proper amount of power factor capacitor kVARs are always connected
to the system (without over-correcting), an Automatic Type Capacitor System should
be used for applications involving multiple loads. A microcontroller automatic
compensation system is formed by:
25
• Some sensors detecting current and voltage signals;
• An intelligent unit that compares the measured power factor with the desired
one and operates the connection and disconnection of the capacitor banks with
the necessary reactive power (power factor regulator);
• An electric power board comprising switching and protection devices;
• Some capacitor banks.
2.6 Power Factor in Resistor, Inductance and capacitance circuit
In a purely resistive AC circuit, voltage and current waveforms are in phase, changing
polarity at the same instant in each cycle. Where reactive loads are present, such as
with capacitors or inductors, energy storage in the loads result in a time difference
between the current and voltage waveforms. This stored energy returns to the source
and is not available to do work at that load. A circuit with low power factor will have
a higher current to transfer a given quality of real power than a circuit with a high
power factor.
In order to get the current reading with the oscilloscope for the diagram for pure
resistive, capacitive and inductive loads below.
A resistor with a negligible value was introduced in the circuit and the current value
was measured across it. This assumption was made using ohms law:
Ohms law:
V=IR but R‘s value is negligible therefore V=I, This assumption was used to get the
waveform for current I.
26
Figure 2.1 Show pure resistive load circuit
Figure 2.2: The waveform for pure resistive load, Voltage and current are in phase.
27
Figure 2.3. Show pure inductive load circuit.
Figure 2.4: The wave form for pure inductive load, the current lags the voltage by
90°C.
28
Figure 2.5 Show pure capacitive load circuit.
Figure 2.6 The wave form for pure capacitive load, current leads the voltage by 90°C.
29
2.7 Power factor Harmonics
Harmonics are sinusoidal voltages or currents having frequencies that are whole
multiples of the frequency at which the supply system is designed to operate (e.g.
50Hz or 60 Hz).
E.g. a 250 Hz sine-wave signal, superposed onto the fundamental 50 Hz mains
frequency, will be designated as the 5th harmonic or as the harmonic of 5th order (5 x
50 Hz).
Any signal component having a frequency which is not an integer multiple of the
fundamental frequency is designated as an interharmonic component or referred to
more simply as an interharmonic.
Harmonics and interharmonics are basically the result of modern developments in
electricity utilization and the use of electronic power conditioning modules. Using
switching power supplies to control loads and to reduce power consumption results in
unwanted frequencies superimposed on the supply voltage. The presence of voltage at
other frequencies is, as far as possible, to be avoided.
30
2.7.1 Potential Sources of Harmonics
• Switched mode power supplies • Dimmer‗s • Current Regulators • Frequency
Converters.
• Voltage source inverters with pulse width modulated converters.
• Low power consumption lamps.
• Electrical arc-furnaces.
• Arc welding machines.
• Induction motors with irregular magnetizing current associated with saturation
of the iron.
• All equipment with built-in switching devices or with internal loads with nonlinear voltage/current characteristics.
2.7.2 Effects of Harmonics on Mains supplies
• Distortion of main supply voltage, unwanted currents flowing in the supply
network generate additional energy losses.
• Defective operation of regulating devices, disturbed operation of florescent
lamps, television receivers or other equipment.
• Malfunction of ripple control and other mains signaling systems, protective
relays and, possibly, other of control systems.
• Additional losses in capacitors and rotating machines.
• Additional acoustic noise from motors and other apparatus, reducing the
31
efficiency of motors.
• Telephone interference.
• High harmonic amplitudes may not only cause malfunctions, additional losses
and overheating, but also overload the power distribution network and
overheat the neutral conductor and cause it to burn out.
2.7.3 For the purpose of harmonic current limitation, equipment is classified as
follows:
Class A: Balanced three-phase equipment;
• Household appliances excluding equipment identified as Class D;
• Tools excluding portable tools;
• Dimmers for incandescent lamps;
• Audio equipment;
• Equipment not specified in one of the three other classes shall be considered as
Class A equipment.
Class B: Portable tools.
Class C: Lighting equipment
Class D: Equipment having a specified power < 600W of the following types:
• Personal computers and personal monitors;
• Television receivers.
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2.8 Fixed Versus Automatic Capacitors
Fixed capacitor banks are always on at all times, regardless of the load in the facility,
while an automatic capacitor bank varies the amount of correction supplied to an
electrical system. An automatic capacitor is much more expensive per kVAr than a
fixed system. 100 kVAr of fixed capacitors will save as much power factor penalties
as a 100 kVAr automatic capacitor. Generally, when a capacitor is connected to a
system there is a reduction in amperage on the system. This reduction in amperage
reduces the voltage drop across a transformer, which results in a higher voltage in the
system. If 100 kVAr is connected to a 1000 KVA transformer, there is approximately
a ¾% voltage rise on the system (if there are no other loads on the system). The more
kVAr connected, the higher the voltage rise. This voltage rise is counter acted by the
increase of load in the facility. Typically, in the night and on weekends, utility voltage
are higher than normal, and facilities that are not normally loaded during these times,
could experience a higher than normal voltage rise if too much capacitance is
connected to their system. Based on this, we generally limit fixed capacitors to 10% to
15% fixed kVAr to KVA of transformer size. We would recommend an automatic
capacitor bank if the amount of kVAr exceeds 20% of the KVA size of the
transformer.
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CHAPTER 3
METHODOLOGY AND HARDWARE
3.0 Methodology
The aim is to monitor the power factor continuously and in the event of change in
power factor, which usually result in the demand of higher current a correction action
is initialized to compensate for this difference by continuous changing variable
capacitors value through switching process. The overall system requires only one PIC
chip, a few power electronic components and bank of capacitors.
3.1 Research Approach and Strategy
Research approach and strategy are about organizing research activity embodying
data collection in ways that are most likely to achieve the research objective. Making
decision about research approach, strategy and design is fundamental to both the
viewpoint reinforcing the research and the contributions that the research is likely to
make. These in turns influence the actual research methods that are used to investigate
the problem and to collect; analysis and interpret data.
In mostly reported that a continuum of methods that underline philosophical position
of research is largely manifested as experiment, survey, interviews, case study, action
research and ethnography.
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It is important to note that the research is going to be based on this two main
approach and strategy which are qualitative and quantitative research.
3.1.1 Qualitative Research Method
A qualitative evaluation shall be utilized for this research project lever aging
subjective method such as interviews, documents, and participant observation data, to
understand and explain social phenomena to collect substantive and relevant data.
This interviews and observation shall be conducted with practicing workers from the
generating, transmission and distribution company in the country. Such a qualitative
approach is valuable here due to the varying experience of the workers in the power
industries.
3.1.2 Quantitative research methods
Quantitative evaluations were originally developed in the natural sciences to study
natural phenomena. Examples of quantitative methods now well accepted in the social
sciences include survey methods, laboratory experiments, formal methods (e.g.
econometrics) and numerical methods such as mathematical modelling.
Quantitative research follows a deductive approach in relation to theory and is
concerned with the design measurement and sample. The strategy employs the use of
mathematical and statistical technique to identify facts and causal relationships; it
follows the practices and norms of natural scientific model and particularly,
positivism and viewing social reality as an external and objective reality.
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Quantitative research is therefore, objective in nature and based on testing a
hypothesis or theory composed of variable.
There are mainly four types of quantitative research namely, correlation, descriptive,
experimental and causal comparative. So this research adopted the descriptive type
because of its relative significance in addressing the research concerns.
But our project work is not quantitative in nature since it is a simulation design of a
microcontroller power factor correction.
3.1.3 Framework Analysis
Due to constraints in getting physical electronic components in our analysis, we opted
for the use of National Instrument Multisim 11.0 electronic workbench simulation
software, which have almost the electronic components we needed in testing the
Design of a microcontroller power factor correction.
Framework analysis is an establish method of data analysis used in qualitative
research, the method is developed by specialist researchers to explored the important
aspects of the project in order to influence the outcome result.
The method form a methodical and rigorous framework, these phase enable the
research to understand and interpret the data and move from description explanation
into the data of providing solution to the problem, this method is transparent and
enables the research to give a good result.
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As in any other empirical study, the investigation needed theories which provide the
framework for the systematic analysis and accumulation of the existing stock of
knowledge as well as to serve as guide for developing research direction.
3.1.4 Qualitative Techniques for Data Collection
There was no qualitative method used in our collection of data.
3.1.5 Modes of Analysis
National instrument Multisim 11.0,an electronic workbench was used as the mode of
analysis
3.2 Microcontroller
A microcontroller is a type of microprocessor emphasizing self-sufficiency and cost
effectiveness, which have additional parts that allow them to control external devices,
in contrast to a general purpose microprocessor. The MCU executes a user program
which is loaded in this program memory. Under control of this program, data is
received from external devices (Inputs), manipulated and then data is sent to external
output devices. A typical microcontroller contains all the memory and I/O interfaces
needed, whereas a general purpose microprocessor requires additional chips to
provide these necessary functions. A microcontroller differs from a microprocessor in
that the first one is easy to implement into electronic system with a minimum of
external support chips. The idea is that the microcontroller will be placed in the
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device to control, hooked up to power and any information it needs. A traditional μP
will not allow doing this. It requires all of these tasks to be handled by other chips.
For example, some number of RAM memory chips must be added. The amount of
memory provided is more flexible in the traditional approach, but at least a few
external memory chips must be provided, and additionally requires that many
connections must made to pass the data back and forth to them with external bus.
3.3 Description of complete system
Voltage,
Current step
down
arrangement
Switching drivers
ADC
Phase angle
calculation
and control
Capacitor bank
PIC 16F84A
Figure 3.1 Block diagram of PIC 32-bits based PFC
Block diagram of PIC based PFC is shown in figure 3.1. Whole system may be
divided into four stages. First stage is concern with the conversion of incoming
voltage and current into the PIC level voltage (e.g. 5V). Here we have to use the step
down arrangement like step down transformer.
38
Figure 3.2 Showing PIC based PFC Picture
Second stage is concerned with conversion of analogue to digital signal. This is done
by use of PIC. In this stage the phase angle between current and voltage is calculated
and it is continuously displayed on LCD as shown in figure 3.3. The digital voltage
and current signal so acquired are processed in the PIC with the help of appropriate
algorithm software. On the basis of phase angle, PIC controls the switching drivers
for on/off action of capacitor bank.
PIC 16F84A suits well to perform these tasks because of its following features: The
PIC 16F84A is a part of PIC 16FXXX microcontroller of 8 bit that accommodates
flash type program memory with 13 I/O‘s. Its maximum operation clock is 20 MHz
where 1 command has fix width of 14 bits with an operating voltage 5.0V.
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Figure 3.3: Continuously monitor on LCD
3.4 Relay
A relay is an electrical switch that opens and closes under the control of another
electrical circuit. In the original form, the switch is operated by an electromagnet to
open or close one or many sets of contacts. Because a relay is able to control an
output circuit of higher power than the input circuit, it can be considered, in a broad
sense, to be a form of an electrical amplifier. Current flowing through the coil of the
relay creates a magnetic field which attracts a lever and changes the switch contacts.
The coil current can be on or off so relays have two switch positions and they are
double throw (changeover) switches. Usually this is a spring, but gravity is also used
commonly in industrial motor starters. Most relays are manufactured to operate
quickly. In a low voltage application, it is used to reduce noise. In a high voltage or
40
high current application, it is used to reduce arcing. The relay is shown in Figure.3.4
Figure.3.4 Relay
3.5 Voltage Regulator
When the 12V through voltage regulator, the supply will be fixing to 5V and divide it
to switch ON the PIC 16F84A and relays. The type of the voltage regulator is LM
7805 shown in Figure 3.5.
Figure 3.5 Voltage regulator
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3.6 Architecture of PIC 16F84A
The figure below shows the internal architecture of a PIC 16F84A chip.
Figure 3.6 Architecture of PIC Chip.
The basic building block of PIC 16F84A is based on Harvard architecture. This
microcontroller also has many advanced features as mentioned in the previous post.
Here you can see the basic internal architecture and memory organisation of PIC
16F84A.
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3.6.1 PIC 16F84A features:
High-Performance RISC CPU
- Only 35 single word instructions to learn
- All instructions are single cycle (1µs) except for program branches
- Operating speed: DC - 20MHz clock input
- 1 k Bytes Flash Program Memory
- 68 Byte RAM Data Memory
- 68 Byte EEPROM Data Memory
- In-circuit serial programming
- Four Interrupt Sources
Peripheral Features
- High current sink/source for direct LED Drive
- One 8-bit timer/counter(TMR0) with 8-bit programmable prescalar
- One 16 bit timer/counter
- Watchdog Timer (WDT) with separate RC oscillator
Special Microcontroller Features
- Power-On Reset
- Power-up Timer (PWRT) and Oscillator Start-Up Timer (OST)
- 1,000 erase/write cycles Enhanced Flash program memory
- 1,000,000 typical erase/write cycles EEPROM data memory
- Selectable Oscillator Options
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CMOS Technology
- Low power, high speed CMOS FLASH technology
- Fully Static Design
- Low Power Consumption
- < 2mA @ 5V, 4MHz
- 15µA typical @ 3V, 32kHz
- < 0.5µA typical standby current
I/O and Packages
- 13 I/O pins with individual direction control
- 18-pin DIP
Pic 16f84a is a microcontroller of 8 bit that accommodates flash type program
memory. It is made up of CMOS and low power consumption. High speed RISC
(Reduced Instruction Set Computer) is being adapted in the CPU side. Maximum
operation clock is 20 MHz where 1 command has fix width of 14 bits.
3.6.2 PIC 16F84A CPU
CPU of pic 16f84a has the following features:
a) 35 instructions (instruction width 14 bits, data width 8 bits)
b) Maximum operating clock is 20 MHz
c) Program memory of size 1024 word
d) Data RAM of 68 byte
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e) Data EEPROM of 64 byte
3.6.3 PIC 16F84A peripherals
a) 13 I/O terminals indicated by input output successively
b) Source sinks current driven by LED for each pin maximum 25 mA
c) 8 bit timer counter module.
3.6.4 Pin diagram/Layout
Figure 3.6.1 Pin diagram of PIC 16f84A.
Inside 18 pin package of pic16f84a integrated together with CPU, ROM, RAM and
I/O. The I/O terminal that is necessary for running important computer functions are
extended outside of pic 16f84a.
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3.6.5: Pin Description
Pin Description
Pin Number
Description
1
RA2 - Port A
2
RA3 - Port A
3
RA4/TOCK1 - Port A
4
MCLR - Master clear input (active low)
5
Vss - Ground
6
RB0/INT - Port B
7
RB1 - Port B
8
RB2 - Port B
9
RB3 - Port B
10
RB4 - Port B
11
RB5 - Port B
12
RB6 - Port B
13
RB7 - Port B
14
Vdd - Positive Power Supply
15
OSC2/CLKOUT - Oscillator Output
16
OSC1/CLKIN - Oscillator Input
17
RA0 - Port A
18
RA1 - Port A
Description cription
Figure 3.6.2: Pin Description
3.7. Safety features
The dielectric is self-healing. In the case of a breakdown caused, for example, by
voltage overload, the self healing effect takes place. If the self healing process does
not operate (e.g. because of voltage, current or thermal overload) the cover plate,
46
which is designed as an overload valve, is raised and ruptures the internal connecting
wires to the coils, so that the capacitor is separated from the mains.
3.8 Wiring the PIC
J1
Ke y = Sp a ce
D3
U2
LM7805CT
1N 4001GP
LINE
VREG
VOLTAGE
U1
2A
220 Vp k
50kH z
0°
COMMON
C1
1000µF
V2
T2
C2
0.1µF
C3
10µF
T S_POW ER _10_T O_1
D1
1N 4001GP
Figure 3.7 Power supply circuit.
Power supply circuit diagram is shown in figure 3.7, which is used by the
programming voltage (VPP) pin and VDD pin. A 5V power supply circuit using LM
7805 IC. LM7805 is a famous positive voltage regulator IC comes in three terminals
that provides 5V DC output. This IC has many built in features like internal current
limiting, thermal shut down, operating area protection etc. Transformer in this circuit
is 220V AC to 9V 2A DC, output current of this circuit is up to 2A. The IC will
become hot during the operation so it is essential to use a good heat sink.
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3.9 Clock generator oscillator
Even though the microcontroller has built in oscillator, it cannot operate without
external components which stabilize its operation and determine its frequency
(operating speed of the microcontroller). Owing to the fact that it is almost impossible
to make oscillator which operates sterilely over a wide frequency range, the
microcontroller must know which crystal is connected in order that it can adjust the
operation of its internal electronics to it. That is why all programs used for chip
loading contain an option for oscillator mode selection. ( Ritter, R. 2002)
3.9.1 Quartz resonator
In case a quartz crystal is used for frequency stabilization, the built in oscillator
operates at very precise frequency which is independent from changes in temperature
and voltage power supply as well. This frequency is normally labelled on the
microcontroller package. Apart from the crystal, in this case the capacitors C1 and C2
must be also connected as per scheme below. Their capacitance is not of great
importance, therefore, the values provided in the table 2.1 should be considered as a
recommendation rather than a strict rule. (Shinohara,1996).
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Figure 3.8: Quartz resonator circuit
Table 3.1: capacitor with
frequency.
3.9.2 System programming
In order to program a program memory, microcontroller must be set to special
working mode by bringing up Vpp pin to 13.5V, and supply voltage VDD has to be
stabilized between 4.5 to 5.0V. Program memory can be programmed serially using
two data/ clock pins which must previously be separated from device lines, so that
errors would not come up during programming.
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3.9.3 LCD and its connection with PIC
Figure 3.8.1: LCD connection diagram
A liquid crystal display (LCD) is a thin, flat display device made up of any number of
colour or monochrome pixels arrayed in front of a light source or reflector. It is often
utilized in battery-powered electronic devices because it uses very small amounts of
electric power. LCDs with a small number of segments, such as those used in digital
watches and pocket calculators, have individual electrical contacts for each segment.
An external dedicated circuit supplies an electric charge to control each segment. This
display structure is unwieldy for more than a few display elements. Small
monochrome displays such as those found in personal organizers, or older laptop
screens have a passive-matrix structure employing super-twisted pneumatic (STN) or
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double-layer STN (DSTN) technology—the latter of which addresses a colourshifting problem with the former—and colour-STN (CSTN)—wherein colour is
added by using an internal filter. Each row or column of the display has a single
electrical circuit. The pixels are addressed one at a time by row and column addresses.
This type of display is called passive-matrix addressed because the pixel must retain
its state between refreshes without the benefit of a steady electrical charge. As the
number of pixels increases, this type of display becomes less feasible. Very slow
response times and poor contrast are typical of passive-matrix addressed LCDs.
(Scheffer, 1984)
3.9.4 Capacitor banks used for power factor correction
Generally used capacitors for power factor controller are: LKT type power factor
correction capacitors; C and CB Type capacitor modules; SBA Type –
Automatically Controlled Capacitor Modules; SBC Type - Statically Controlled
Capacitor Modules.
3.9.5 LKT type power factor correction capacitors
These capacitors feature an all metallic construction within a cylindrical aluminium
case. Advanced safety features include; self healing qualities, an integral
overpressure disconnect device and non toxic impregnated polypropylene capacitor
elements. The unique construction of this product prevents leakage even if the casing
is punctured.
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3.9.6 C and CB type capacitor modules
The C and CB Type capacitor modules are designed for local correction of individual
loads, such as single motors, starters or control gear, where Power Factor Correction
is more appropriately located at the source. This project seeks to improve a power
factor of 0.75 to 0.95. The CB Series Incorporates an integral Circuit Breaker for
independent isolation and overload protection.
3.9.7 SBA type - Automatically controlled capacitor modules
Figure 3.9: SBA type capacitor modules
These automatic modules are designed to fit into existing switchgear, control panels
or pre-installed Power Factor Correction units. Control is provided automatically, via
an independent or existing Power Factor control relay. The equipment incorporates a
soft-switching contactor arrangement to minimize system disturbance caused by
capacitor switching. A pre-connection resistor system is integrated within the
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contactors, which reduces the effect of current inrush to a minimum. Highly reliable,
low loss capacitors with self healing properties. Safety protection system built into
each capacitor element. SBA type capacitor modules is shown in figure 3.9
3.9.8 SBC type - Statically controlled capacitor modules
Static Power Factor Correction modules for placement within an existing control
panel, switchgear cubicle or Power Factor Correction unit. These modules can be
independently switched, if required, via customers own control gear. Highly reliable,
low loss capacitors with self healing properties.
Figure 3.9.1: SBC type capacitor module
Safety protection system incorporated into each capacitor element. SBC type
capacitor module is shown in figure 3.9.1.
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