DESIGN OF A DRIVER CIRCUIT FOR COMPACT FLUORESCENT LAMP TO IMPROVE THE POWER QUALITY
Kalins Bhattacharjee
Department of Electrical and Electronic Engineering
Dhaka University of Engineering & Technology, Gazipur
January 2018
DESIGN OF A DRIVER CIRCUIT FOR COMPACT FLUORESCENT LAMP TO IMPROVE THE POWER QUALITY
A dissertation submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Electrical and Electronic Engineering By Kalins Bhattacharjee Student No. 122201-P
Under Supervision of
Dr. Md. Raju Ahmed Professor, Department of Electrical and Electronic Engineering
Department of Electrical and Electronic Engineering
Dhaka University of Engineering & Technology, Gazipur
January 2018
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The project titled “Design of a driver circuit for compact fluorescent lamp to improve the power quality” submitted by Mr. Kalins Bhattacharjee, Student ID: 122201-P, has been accepted as satisfactory in partial fulfillment of requirement for the degree of Master of Engineering in Electrical and Electronic Engineering on 11th January, 2018.
Boards of Examiners
…………………………………….. Dr. Md. Raju Ahmed Chairman Professor and Head of the Department, (Supervisor) Department of Electrical and Electronic Engineering, (Ex-officio) Dhaka University of Engineering & Technology, Gazipur.
…………………………………….. Dr. Md. Bashir Uddin Member Professor, Department of Electrical and Electronic Engineering, Dhaka University of Engineering & Technology, Gazipur.
…………………………………….. Dr. Md. Sharafat Hossain Member Professor, Department of Electrical and Electronic Engineering, Dhaka University of Engineering & Technology, Gazipur.
…………………………………….. Dr. Md. Monirul Kabir Member Associate Professor, Department of Electrical and Electronic Engineering, Dhaka University of Engineering & Technology, Gazipur.
…………………………………….. Dr. Md. Aynal Haque Member Professor, (External) Department of Electrical and Electronic Engineering, Bangladesh University of Engineering and Technology, Dhaka.
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Declaration
I declare that this project is my own work and has not been submitted in any form for another degree or diploma at any university or other institute of tertiary education. Information derived from the published and unpublished work of others has been acknowledged in the text and a list of references is given.
Kalins Bhattacharjee Date: 11/01/2018
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Acknowledgements
First of all, I thank the Almighty, who gave me the opportunity and strength to carry out this research work.
I would like to express my sincere gratitude to my supervisor, Dr. Md. Raju Ahmed for his continuous encouragement, guidance and support. His extreme enthusiasm toward research has motivated me during my entire recharge life. I feel very proud to have worked with him. Without his inspiring enthusiasm and encouragement, this work could not have been completed.
I show gratitude all my teachers and staffs at the Department of EEE, Dhaka University of Engineering & Technology for their support and encouragement.
I would like to express my most sincere gratitude to my wife, family members, friends, colleagues and well-wishers who are taking lot of pains for progress in my life and for their sacrifices, blessings and constant prayers for my advancement.
I wish to thank the members of my project committee, Dr. Md. Bashir Uddin, Dr. Md. Sharafat Hossain, Dr. Md. Monirul Kabir and Dr. Md. Aynal Haque for their invaluable feedback on my work.
I would like to show my gratitude to Mohammad Saiful Kabir, Executive Director – Admin and Production, Paradise Cables Limited for his continuous guidance and support.
Finally, last but not least, I am also thankful to those, who have directly or indirectly helped me and encouraged me to complete my project. I feel sorry for not able to express my appreciation to each of my well-wishers and ask forgiveness for my improper behavior with anyone who was intending to help me.
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Abstract
In this project the performance of existing CFL (Compact Fluorescent Lamp) driver circuits analyzed and the drawbacks of existing circuits is discussed. A CFL presents a non-linear load to the power supply and introduces harmonic distortion on the current drawn from the supply. Measured Characteristics of existing CFL's has low power factor (40 to 65%) and total harmonic distortion (THD) of relative current is high. The relative current distortion expressed in percent of the fundamental may exceed 100%. High harmonics distortion causes increase in line losses and decrease to equipment lifetimes. Focus mainly on the high relative current distortion. Then a driver circuit of CFL is proposed to improve the performance of Total Harmonic Distortion (THD) and Power Factor (PF). The proposed circuit is simulated and practically implemented in the laboratory. The performance of the proposed driver circuit is analyzed and compared with the existing CFL driver circuits. In this project, find out the comparison between proposed driver circuit and existing circuits for 30 Watt are - the VTHD calculated was 4.0% which is almost similar to both proposed driver circuit and existing circuits. But the ATHD calculated was 37.6 % which is almost 86.2% in existing driver circuit. So it can be concluded that in existing circuit for 30W, VTHD is 5.9% and ATHD 86.2% where ATHD is almost 15 times higher than VTHD and causes (i) Low Power Factor (ii) Total Harmonics Distortion is High (iii) Generated heating etc. where 9 times higher ATHD from VTHD in proposed CFL driver circuit. Power Factor calculated was 0.689 in existing circuit for 30 Watt but Power Factor is 0.934 in proposed driver circuit which are close to the unit value.
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List of Abbreviations
Abbreviation Full Meaning
SV Sodium Vapor PF Power factor CFL Compact Fluorescent Lamp MV Mercury Vapor Hg Mercury PQ Power Quality LED Light Emitting Diode IEC International Electrotechnical Commission EN European Norms THD Harmonic Distortion HID High Intensity Discharge CCT Correlated Color Temperature CRI Color Rendering Index FL Fluorescent Lamps IL Incandescent Lamps PFC Power Factor Correction SMPS Switch Mode Power Supplies EMI Electromagnetic Interference VTHD Voltage Total Harmonics Distortion ATHD Current Total Harmonics Distortion CLP Constant Load Power DCF Driver Circuit Factor DCEF Driver Circuit Efficacy Factor AC Alternating Current DC Direct Current RMS Root Mean Square
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List of Contents Page No.
Declaration iii Acknowledgements iv Abstract v List of Abbreviations vi List of Figures ix List of Tables x
1. Introduction 1 1.1. Total Harmonic Distortion 4 1.1.1. Measurement of Power Distortion 4 1.2. Electronic Driver circuit 5 1.3. Gas Discharge Lamps 5 1.3.1. Different Types of Discharge Lamps 6 1.3.2. Description of Fluorescent Lamp 7 1.3.2.1. Advantage of Fluorescent Lamps 7 1.3.2.2. Disadvantage of Fluorescent Lamps 7 1.3.3. Description of Compact Fluorescent Lamp 8 1.3.3.1. Advantage of Compact Fluorescent Lamps 9 1.4. Objective of the Project 9 1.5. Project Organization 10
2. Studies of Existing CFL Driver Circuit 11 2.1. Electronic Driver Circuit 11 2.2. Work Procedure of Electronic Driver Circuit 13 2.3. Different Types of Electronic Driver Circuit 14 2.4. Experimental Tests Performed on Compact Fluorescent Lamp 15 2.5. Measurements and simulations result of exiting 23W CFL 17 2.6. Designing of Electronic Driver Circuit 18 2.7. Factors Affecting on Driver Circuit Performance 20 2.8. Problems Related to Electronic Driver Circuit 21
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3. Design of Proposed CFL Driver Circuit 22 3.1 Driver Circuit Design 23 3.1.1. Rectifier 25 3.1.2. Valley-Fill Circuit with Electrolytic Capacitor 27 3.1.3. Royer oscillator and Inverter 28 3.1.4. Resonant Tank Circuit to Ignite and Run the Lamp 30
4. Implementation and Performance Analysis 32 4.1. Power Quality Analysis of the Measurements Results for CFL 33 4.2. Benefits of High Power Factor CFL 40
5. Conclusion And Future Recommendation 42 5.1. Conclusion 42 5.2. Recommendation for Future Work 43
List of References 44
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List of Figures
Figure No. Page No.
1.1 Typical Phase to Phase Voltage Distortion 05 2.1 Block Diagram of Electronic Driver Circuit 13 2.2 Block Diagram of Refined Driver circuit 13 2.3 Practical Analysis of Commercial CFL Driver Circuit 15 2.4 Circuit Diagram of Existing Driver Circuit of CFL 16 2.5 Input Voltage and Current Wave Shape of Existing 23W CFL 17 2.6 Output Voltage and Current Wave Shape of Existing 23W CFL 17 3.1 Proposed Driver Circuit of CFL 24 3.2 Proposed CFL Circuit Implementation on the Vero Board 24 3.3 A Full-bridge Rectifier 26 3.4 Wave-Shape with Using Capacitance 100µF 26 3.5 Valley-Fill Circuit 27 3.6 Current Wave-Shape with Using Electrolytic Capacitor 28 3.7 Royer Oscillator and Inverter Design 29 3.8 Wave-Shape across the Transistor 30 3.9 Wave-Shape across the Inverter 30 4.1 Input and Output Wave Shape of Proposed 30Watt CFL 33 4.2 Input and Output Wave Shape of Existing 30Watt CFL 34 4.3 Input and Output Wave Shape of Proposed 23Watt CFL 35 4.4 Input and Output Wave Shape of Existing 23Watt CFL 35 4.5 Input and Output Wave Shape of Proposed 14Watt CFL 36 4.6 Input and Output Wave Shape of Existing 14Watt CFL 36 4.7 Input and Output Wave Shape of Proposed 08Watt CFL 37 4.8 Input and Output Wave Shape of Existing 08Watt CFL 38 4.9 Harmonic Spectrum of 20 W Proposed CFL 38 4.10 Harmonic Spectrum of 20 W Existing CFL 39 4.11 Harmonic Spectrum of 10 W Existing CFL 39
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List of Tables
Table No. Page No.
2.1 Component List of Existing Driver Circuit of CFL 16 2.2 Power Quantities and Harmonics of CFL 18 3.1 Component List of Proposed Driver Circuit of CFL 25 4.1 Parameter Comparison between Proposed and Existing 30 Watt CFL 33 4.2 Parameter Comparison between Proposed and Existing 23 Watt CFL 34 4.3 Parameter Comparison between Proposed and Existing 14 Watt CFL 35 4.4 Parameter Comparison between Proposed and Existing 8 Watt CFL 37
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Chapter 1
Introduction
The power crisis problem is getting worse in the developing countries. Measures are being taken to overcome the power shortage problem by efficiently utilizing the available power. Replacement of high-power consumption lamps with energy efficient lamps is also among these steps. This paper presents a detailed comparative analysis among power factor (PF), efficiency and total harmonics distortion of voltage & current of compact fluorescent lamp (CFL). The first light sources created by humans were produced thousands of years ago in the Neolithic period by burning tree branches and dried grass to provide light in the nighttime darkness. Thus began the age of combustible light sources. Eventually, people learned to fashion oil lamps by placing animal and vegetable oils in containers made of stone, clay and shell and then dipping wicks into the oil. While it remains unclear where and when human beings first made the transition from small lamp fires to oil lamps, the oldest known lamp today is thought to be a sandstone lamp unearthed from the La Mouthe caves in France. Over the centuries, oil lamps passed through many stages of evolution, including lamps shaped like teapots, lamps made of stone, ceramics and metal, and they came to hold an important place in many homes. However, the invention of the kerosene lamp by an American B. Syrian resulted in the gradual disappearance of the oil lamp. Finally, the discovery of electrical energy brought the introduction of electric lamps and light bulbs and the age of electrical lighting supplanted the age of combustion lighting [1]. In golden age, incandescence and fluorescence lamps were the main focus in illumination technology. With development in SV (Sodium Vapor), MV (Mercury Vapor) and metal halide (in recent), make possible to replace this old technology. But none of these technologies could improve the efficacy exceeding 200 lumens per watt and efficiency beyond 60-70%. The current technology of Compact Fluorescence Lamp (CFL) has improved the efficiency and it has really proved standards. The obstacle in becoming popular is the initial cost and the decrease in illumination over the use. These days with
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support of government (in taxes) and improvement in manufacturing technology the initial cost has come to the vision of common man [2]. All the compact fluorescent lamps contain a small amount of elemental mercury (Hg), also known as quicksilver. When CFL are cold, some of the mercury in the CFL is in liquid form, but while the lamp is operating, or when the CFL is hot, most of the mercury is in an invisible vapor form. Mercury vapor is a highly toxic substance, with an “extreme” rating as a poison, which can be dangerous to our health. When a CFL is broken, this will release the mercury and contaminate the surrounding area. Liquid mercury will not burn, but instead becomes a vapor when heated. It eventually cools and condenses back to a liquid form, spreading the contamination to larger areas. Inhaling the vapor is the main cause of mercury poisoning, as the mercury is absorbed by the lungs. Mercury can cause severe respiratory tract damage, brain damage, kidney damage, central nervous system damage, and many other serious medical conditions even for extremely small doses. Mercury present in CFLs which are hazardous and when left untreated can cause a great damage to our ecosystem. This hazardous mercury can affect our life in many direct as well as indirect ways like- 1. Mercury can be carried through ocean, rivers, lakes, ponds etc. along with rain water and which can subsequently affect aquatic life as fish and other aquatic animals can get it bio-accumulated. 2. Mercury can be biologically accumulated in soil and which can eventually cause the crops to be poisonous and ultimately it’s the human beings who will have to face disastrous consequences [3]. CFL is the symbol of energy of saving since 1980. By 1990s the sales of CFLs grew very high because of the awareness programs. Compact Fluorescent Lamp (CFL) is the smaller form of fluorescent tubes, which is easy to install in any Lamp fixtures. National Lighting Product information Program defines CFL as fluorescent lamps that have a tube of diameter of 16 mm or less and circular CFLs1. CFLs as lamps intended to replace incandescent lamps and having overall lengths of eight inches (20 cm) or less. CFL bulbs require low energy than what other bulbs requires for operating2. For example, a 27-watt CFL generates approximately 1800 lumens, compared to 1750 lumens from a 100 watt
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incandescent. CFLs also have a significantly longer service life, 6000–15000 hours compared to 750–1000 hours for a standard incandescent [4]. In the developing countries, where there is a gap between demand and supply, measures are being taken for reduction in electricity consumptions as a part of their demand side management. As per research in Trifunovic et al. (2009), it is estimated that the energy reduction up to 27% in residential and 30% in commercial sector could be achieved by switching towards energy efficient technologies. This has resulted in the growth of power electronic based energy saving devices. The tremendous increment in unit electricity charges is also one of the reasons for the penetration of such devices in existing power system. However, the widespread use of these devices could have some harmful effects on power quality. With short-sightedness, one problem’s solution will create too many other problems. Experiences have shown that the prevention is more cost-effective after knowing the fact, rather than finding the solution of the next upcoming problem (Watson et al., 2009) [5]. The Power Quality (PQ) in electrical systems is regulated by IEC (International Electrotechnical Commission) and EN (European Norms) standards. In order to comply with these technical standards, the utilities have to guarantee admissible voltage levels established by the standards, also ensuring the supply continuity; the end-users have to guarantee current absorptions with adequate Power Factor (PF) and reduced harmonic current absorptions. Indeed, an inadequate PF and/or insufficient PQ (Power Quality) level dramatically increase the power losses in the distribution grid, the voltage drop and the voltage distortion. Power factor correction capacitors are suitable to compensate the reactive power required by linear loads [6]. Non-linear loads, like rectifiers or arc discharge devices such as fluorescent lamp, require filters to reduce their harmonic current injection. Among the non-linear loads used in household, Compact Fluorescent Lamps (CFLs) and LED (Light Emitting Diode) lamps are becoming more widespread, while incandescent lamps are intended to be replaced by these types of lighting devices. Although LED lamps work on a completely different principle than CFLs, both need a power supply system enabling their correct operation and both introduce nonlinearities into the electrical grid. Furthermore, dimming devices are usually used to adjust the luminosity of the lamps. As nonlinear loads, CFLs and LEDs produce highly distorted currents [6]. Therefore, a good understanding of the CFLs and LEDs
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harmonic production characteristics becomes necessary. Many studies about the PQ issues related to the lighting devices have been addressed to analyze these problems since the 90s. They generally estimate through simulations the mutual influence between loads and distribution grid. The measurement of device’s harmonic absorption represents the preliminary step for the assessment of loads impact on the distribution grid [6].
1.1 Total Harmonic Distortion The total harmonic distortion (THD) is a measurement of the harmonic distortion present in a signal and is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency.
1.1.1 Measurement of Power Distortion The distortion of a waveform relative to a pure sinewave can be measured either by using a THD analyzer to analyse the output wave into its constituent harmonics and noting the amplitude of each relative to the fundamental. Given a sinewave generator of very low inherent distortion in Fig. 1.1, it can be used as input to amplification equipment, whose distortion at different frequencies and signal levels can be measured by examining the output waveform. There is electronic equipment both to generate sinewaves and to measure distortion; but a general-purpose digital computer equipped with a sound card can carry out harmonic analysis with suitable software. For many purposes different types of harmonics are not equivalent. For instance, crossover distortion at a given THD is much more audible than clipping distortion at the same THD, since the harmonics produced are at higher frequencies, which are not as easily masked by the fundamental. Taking THD measurements at different output levels would expose whether the distortion is clipping (which increases with level) or crossover (which decreases with level) [9], [23], [24].
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Figure 1.1: Typical Phase to Phase Voltage Distortion [9].
1.2 Electronic Ballast The Electronic ballast is used as solid state electronic circuitry to deliver the suitable starting and working electrical conditions to power discharge lamps. An electronic ballast can be smaller and lighter than a comparably-rated magnetic one. An electronic ballast is usually quieter than a magnetic one, which produces a line-frequency vibration by vibration of the transformer laminations. Electronic ballasts usually supply power to the lamp at a higher frequency, rather than the mains frequency of 50 Hz, this substantially eliminates the stroboscopic effect of flicker, a product of the line frequency associated with compact fluorescent lighting. The operating currents of electronic ballast of lighting devices built on the principle of electrical gas discharge lamps.
1.3 Gas Discharge Lamps Gas-discharge lamps are a family of artificial light sources that generate light by sending an electrical discharge through an ionized gas. Typically, such lamps use a noble gas (argon, neon, krypton and xenon) or a mixture of these gases. Most lamps are filled with additional materials, like mercury, sodium, and/or metal halides. In operation the gas is ionized, and free electrons, accelerated by the electrical field in the tube, collide with gas and metal atoms. Some electrons in the atomic orbitals of these atoms are excited by these collisions to a higher energy state. When the excited atom falls back to a lower energy state, it emits a photon of a characteristic energy, resulting in infrared, visible light, or ultraviolet radiation. Gas-discharge lamps offer long life and high efficiency, but are more complicated to manufacture, and they require electronics to provide the correct current flow through the gas [27].
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1.3.1 Different Types of Discharge Lamps Discharge lamp in low pressure: This types of lamps have gas inside the tube, with lower pressure than the atmospheric pressure. Fluorescent and compact fluorescent lamps work based on the low pressure gas discharge standard. The glass tube on low pressure gas discharge lamps is filled with a noble gas at low pressure and a small quantity of mercury. The glass wall is coated with a fluorescent. Inside the housing, an electrical field develops between two electrodes and gas discharge occurs. The discharge process causes the mercury vapor to emit UV (Ultraviolet) rays. Visible light is emitted as soon as the UV radiation makes contact with the fluorescent. The light color generated can be varied using an appropriate fluorescent mixture. Thus it is possible to create fluorescent lamps for all kinds of applications. The operation principle of high-pressure discharge lamps differs considerably from that of standard incandescent lamps. Light is produced by gas discharge that occurs in an arc tube between two electrodes after ignition. Electrical conductivity is established by ionized filler components. The electrodes are fed into a completely sealed discharge vessel [9], [27].
Discharge lamp in high pressure: These lamps have pressurized gas inside the tube, with higher pressure than the atmospheric pressure. Some examples of high pressure discharge lamps is are the metal halide lamps, the high pressure sodium lamps and the high pressure mercury-vapor lamps which are very old, being replaced in most applications [9]. CCT (Correlated Color Temperature) and CRI (Color Rendering Index) are very important concepts to characterize the light produced by a discharge lamp. High-pressure lamps operate under slightly less to greater than atmospheric pressure. They include: (i) Metal halide lamps. (ii) High pressure sodium lamps. (iii) High pressure mercury-vapor lamps. The above three lamps are also well known as High Intensity Discharge (HID) lamps. The definition of high intensity discharge is related to the special type of electrode used in the lamps. Compared to other lamp types, relatively high arc power exists for the arc length [27].
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1.3.2 Description of Fluorescent Lamp These lamps belong to the category of low-pressure mercury vapor discharge lamps. The discharge generates two main lines at 185 and 253.7 nm and other weak lines in the visible range of the spectrum. A fluorescent powder on the inside wall of the discharge tube converts the ultraviolet radiation into visible radiation, resulting in a broadband spectral distribution and good color rendition. In these lamps, the optimum mercury vapor pressure (which gives the maximum luminous efficacy) is 0.8 Pa. For the tube diameters normally used, this pressure is reached at a wall temperature of about 40◦C, not much higher than typical ambient temperature. The heat generated inside the discharge is sufficient to attain the required operating temperature without using an outer bulb. However, this structure causes a great variation of the lamp lumen output with the temperature, which is one important drawback of the fluorescent lamps. One solution to this problem is the addition of amalgams to stabilize the light output. This is specially used in compact fluorescent lamps [9].
1.3.2.1 Advantages of Fluorescent Lamps Energy efficient- so far the best light for interior lighting Low production cost (of tubes, not of the ballasts) Long life of tubes Good selection of desired color temperature (cool whites to warm whites) Diffused light (good for general, even lighting, reducing harsh shadows).
1.3.2.2 Disadvantages of Fluorescent Lamps The flicker of the high frequency can be imitated to humans (eye strain, headaches and migraines) Flicker of common fluorescent light looks poor on video, and creates an ugly greenish or yellow hue on camera. Diffused light (not good when you need a focused beam such as in a
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headlight or flashlight) Poorly/cheaply designed ballasts can create radio interference that disturbs other electronics Poorly/cheaply designed ballasts can create fires when they overheat There is a small amount of mercury in the tubes An imitating licker at the end of the life cycle.
1.3.3 Description of Compact Fluorescent Lamp A compact fluorescent light bulb (CFL) is a fluorescent light bulb that has been compressed into the size of a standard-issue incandescent light bulb. Modern CFLs typically last at least six times as long and use at most a quarter of the power of an equivalent incandescent bulb. A compact fluorescent lamp (CFL), is also known as compact fluorescent light or energy saving lamp, is a type of fluorescent lamp. Compared to general service incandescent lamps giving the same amount of visible light, CFLs use less power and have a longer rated life. Downside is they have a higher purchase price. Like all fluorescent lamps, CFLs contain mercury, which complicates their disposal. CFLs radiate a different light spectrum compared to incandescent lamps. New phosphor compositions have improved the colour of the light emitted by CFLs in such a way that the best warm white CFLs are nearly similar in colour to standard incandescent lamps. A CFL bulb is cost effective in usage as it uses low amount of power and at the same time it is over than 90% efficient. However the problem with CFL bulbs is the internal circuitry due to the usage of ballast. These bulbs have to be supplied at high frequency with cannot be obtained from the line as the line frequency is 50Hz. Therefore ballast has to be used to enhance the frequency and due to this the bulb distorts the input current wave-shape and gives rise to harmonics which drains power in the form of reactive power. One other problem is the usage of mercury in these bulbs. Mercury is poisonous to all living being and once the blub gets damaged mercury could spill out and harm people.
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1.3.3.1 Advantages of Compact Fluorescent Lamps 1. They are cost-effective: While these bulbs cost more at first, they are actually less expensive in the long run because they last longer than incandescent bulbs. And since they consume about 60% less than incandescent bulbs, they can help cut down a substantial amount from bills.
2. They are efficient: It is said that CFLs are up to 400% more efficient than incandescent bulbs. This means that replace of 100 Watt incandescent bulbs with 22 watt CFLs for the same amount of light, with less energy used.
3. They come with versatility: With the versatility of CFLs, can use them in any setting of incandescent bulbs. Also, they come in various sizes and shapes that they can be used for table lamps, recessed fixtures, ceiling lighting and track lighting. There are even 3-way CFLs that offer more versatility.
4. They help reduce emissions of carbon dioxide: Switching to these lights will allow to reducing carbon emissions, where just a single bulb is said to reduce half a ton of this gas in the atmosphere.
1.4 Objective of the Project The specific issues that will be analyzed in this project can be summarized as follows
(a) To analysis the commercial circuits diagram operation and behavior of compact fluorescent lamp. (b) To analysis the total harmonic distortion and power factor of existing compact fluorescent lamp. (c) To analysis the reason of low power factor and higher harmonic distortion of commercially available of CFL. (d) The main objective of this Project is to design and implementation of a driver circuit for CFL lamp with higher power factor and lower harmonic distortion.
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1.5 Project Organization This project is organized as follows: chapter 1 presents the introduction of overall project. In chapter 2 consist the analysis and studies of existing CFL driver circuit which are commercially available. In chapter 3 presents design of proposed CFL driver circuit by simulation software. In chapter 4 presents implementation and performance comparison of proposed CFL driver circuit with existing CFL driver circuit which are commercially available. In chapter 5 consist the conclusion and discussion of this project.
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Chapter 2
Studies of Existing CFL Driver Circuit
The rapidly increasing use of Fluorescent Lamps (FLs) and Compact Fluorescent Lamps (CFLs) nowadays increase concerns regarding the harmonics and their impacts on the quality of supply. In general, nonlinear loads such as FLs and CFLs can cause severe problems to power systems and end users such as voltage distortion, conductors and transformers overloading, increased system losses, interference with communications networks, impact on energy metering, improper operations of electronic devices, thermal effects on rotating machines, incorrect tripping of circuit breakers, a decrease in the overall system efficiency and reduced system reliability. Lighting is considered one of the most important loads in power systems. It has been estimated that lighting consumes about 25%- 35% of the global generated power. Due to the advancement in power electronics technology nowadays, CFLs are becoming increasingly more attractive for many reasons. First, the efficiency of CFLs is three to four times the efficiency of Incandescent Lamps (ILs). Second, lifetime of a typical CFL is thousands times that of an IL. Third, due to the high switching frequencies used in CFLs (>25 kHz), they are less in weight and size compare to ILs. To establish a high initial voltage across the lamp tube, CFLs require electronic ballasts. Ballasts are also important for proper lamp ignition and to limit the lamp current once the arc is established. These electronic ballasts use Switch Mode Power Supplies (SMPSs); therefore, their current distortion could be low or as high as 100% depending on whether a Power Factor Correction (PFC) circuit is used [25]. Details of existing driver circuit performance of CFL are given in below.
2.1 Electronic Driver Circuit A device required by electric-discharge light sources such as fluorescent or HID lamps to regulate voltage and current supplied to the lamp during start and throughout
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operation. To achieve full rated light output and rated lamp life from a fluorescent lighting system, a ballast’s output characteristics must precisely match the electrical requirements of the lamps it operates. A conversant and broadly used example is the inductive driver circuit used in fluorescent lamps, to limit the current through the tube, which would otherwise rise to destructive levels due to the tube's negative resistance characteristic. Driver circuits vary in design complexity. They can be as simple as a series resistor or inductor, capacitors, or a combination thereof or as complex as electronic driver circuits used with fluorescent lamps and high-intensity discharge lamps [9], [18]. The driver circuit regulates the current to the lamps and provides sufficient voltage to start the lamps. Without a driver circuit to limit its current, a fluorescent lamp connected directly to a high voltage power source would rapidly and uncontrollably increase its current draw. Within a second the lamp would overheat and burn out. During lamp starting, the driver circuit must briefly supply high voltage to establish an arc between the two lamp electrodes. Once the arc is established, the driver circuit quickly reduces the voltage and regulates the electric current to produce a steady light output [20]. Achieving full rated light output and rated lamp life from a fluorescent lighting system, driver circuit’s output characteristics must precisely match the electrical requirements of the lamps it operates. Traditionally, driver circuits are designed to operate a specific number and type of lamp at a specific voltage. Driver circuits are used with high intensity discharge lamps which emit strong light, imitating sunlight and facilitating plant cultivation in indoor settings. These lamps save on money because they are energy efficient and last longer than the ordinary light bulbs. Driver circuits function to start and control the electricity flow through a lamp. So, there is sufficient electrical current and light is emitted without destroying the bulb. The electronic driver circuits use power Royer oscillators which are basically low-cost, small sized and power efficient. The benefits of using electronic driver circuit are: Lighting quality increased Increased lamp life Reduced driver circuit size and weight Overall lamp and driver circuit efficiency
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2.2 Working Method of Electronic Driver circuit
Figure 2.1: Block Diagram of Electronic Driver circuit
There are several stages through which driver circuit works in supplying a discharge lamp as presents in Fig. 2.1 and Fig. 2.2. The stages are:
EMI filter of Electronic Driver circuit: In this stage the EMI filter is used in electronic ballasts so that the electromagnetic interference that is generated while increasing the frequency of the input current are removed [9].
Figure 2.2: Block Diagram of Refined Driver circuit AC-DC converter of Electronic Driver circuit: In this block, the DC voltage level is produced from the AC supply of the input voltage. Generally a full-bridge rectifier and a capacitor are used so that the output is as nearer to a dc voltage as it can be. Conversely the efficiency of this phase is quite low and has a corrupt voltage regulation [9].
DC-AC inverter of Electronic Driver circuit: This stage is intended to supply the discharge lamps with power at high frequency. The inverter commonly creates very high
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frequency waves and the ballast is needed to limit the discharge current. Inductors and capacitors are organized used in this stage for the function [9].
Starting Circuit of Electronic Driver circuit: In this circuit is mostly used while using high-pressure discharge lamps. The main purpose of this circuit is to ignite the discharge lamp. In low-pressure discharge lamps the driver circuit is used in both burning the lamp and also to limit the current. Conversely in high-pressure discharge lamps the starting voltage can be very high and so a changed ignition circuit is needed mainly while reigniting an already heated up lamp. Therefore the starting circuit is used to rise lamp life [9].
Control and Protection circuit of Electronic Driver circuit: This circuit is applied as a safety stage which makes sure the total system is not injured in any way. The circuit is surrounded by error amplifiers, main oscillators, output over-voltage protection, over- current protection, timers which control ignition, failure protection etc. [9].
2.3 Different Types of Electronic Driver Circuit There are different kinds of driver circuits, such as electronic driver circuits, magnetic driver circuits and digital driver circuits.
Electronic and High Frequency Electronic Driver Circuit: Electronic driver circuits control the electric flow inside the bulb complete electronic circuitry. Occasionally referred to as control gear, the electronic driver circuit restrictions the current which flows in an electric circuit. This category of driver circuit is active to balance the negative resistance to power supplies with positive resistance. As a result, the current is hold at a level that prevents the bulb from burning out. Electronic driver circuits may function in parallel or in a series mode. The series mode is preferred because the failure of a single lamp does not interrupt the working of all other lamps. The high frequency electronic driver circuit is additional type that makes use of electric circuitry. It uses frequencies that are above 21 KHz [7].
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Digital Driver Circuits: Digital driver circuits function at higher frequencies and generate larger amount of light while using less energy. The digital component controls temperature levels so that the bulb lasts longer. With digital driver circuits, the flow is low at the initial point and increases when temperature goes up inside the bulb. It is important to note that the consistency of digital driver circuits may depending on the manufacturer. Effective digital driver circuits shut down automatically if a damaged or defective bulb is identified or in case of a short circuit [7], [21].
2.4 Experimental Tests Performed on Compact Fluorescent Lamp A 23W existing CFL driver circuit implementation on vero board as presented in the Fig. 2.3.
Figure 2.3: Practical Analysis of Commercial CFL Driver Circuit.
Circuit design and simulation is categories as the first stage of learning. That is, by assemble all the electronics components entail in the design into the schematic editing window of Proteus with the aid of virtual electrical wire as showing in Fig. 2.4 and component list are given in table 2.1.
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L1 FUSE C2 0.89mH BR1 CY28 1N4007 VSINE C1
VA=312V
CY28 1
FREQ=50 0
t
D1 u p
t C1 (450V) 1N4007 u 10uF O Q1 13005SD C3 C4 MZ6 CY16KV C5 R3 (1W) R2 280k CY3A
2 22R R1 0
t
1R5 D2 u p 1N4007 t u O L2 D3 1N4007 TR1-30W
L3 R5 (1W) 560K D4 R4 Q2 1N4007 13005SD 0.3mH-2.23mH 22R C6 DIAC R3 DB3 1R5 2X2A L4 D6 1N4007
Figure 2.4: Circuit Diagram of Existing Driver Circuit of CFL.
Resister Value in Ohm Inductor Value R1 1R5 L 0.3Mh-2.23Mh R2 22R EMC Coil 3.8Mh R3 280K NPC 22D7 R4 22R 3 Turns R5 560K O-Core Coil 6 Turns Capacitor Value 3 Turns 10 micro - Farad, 450V C1 Diode Value (Electrolytic) C2 CY28 D1 IN4007 C3 MZ6 D2 IN4007 C4 CY16KV D3 IN4007 C5 CY3A, 272J D4 IN4007 C6 2X2A, 400V, 223J D5 IN4007 Transistor Value D6 IN4007 Q1 13005SD (NPN) DIAC DB3 Q2 13005SD (NPN) Fuse 5 ohm
Table 2.1: Component List of Existing Driver Circuit of CFL.
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2.5 Measurements and simulations result of exiting 23W CFL. A 23 W existing CFL was monitored and the harmonics, power factor and typical waveform can be shown in Figs. 2.5, Figs. 2.6 and Table 2.2.
Figure 2.5: Input Voltage and Current Wave Shape of Existing 23W CFL.
Figure 2.6: Output Voltage and Current Wave Shape of Existing 23W CFL.
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Power quantities and harmonics of different types of CFL
PARAMETER LAMP A (14 W) LAMP B (23 W) LAMP C (30 W) FREQUENCY (HZ) 49.88 50.27 50.17 Power (W) 13.0 21.0 28.2 Voltage (V) 217.21 220.3 219.3 Current (A) 0.09 0.146 0.186 Power Factor 0.661 0.65 0.689 Light Out (lm) 520 1185 1776 Rated Light Out (lm) 840 1380 1800 Efficacy (lm/W) 28.43 49.58 43.7
HARMONICS (%) VTHD 5.8 4.6 5.9 ATHD 104.6 107.0 86.2
Table 2.2: Power Quantities and Harmonics of CFL
It can be seen from the results that the existing driver circuits, basically for 23W are - the VTHD calculated was 4.6% and the ATHD calculated was 107.0 %. So it can be concluded that in existing circuit for 23W, VTHD is 4.6% and ATHD 107.0% where ATHD is almost 24 times higher than VTHD and causes (i) Low Power Factor (ii) Current Total Harmonics Distortion is High (iii) Generated heating etc. Due to the fact that a PFC (Power Factor Correction) circuit is not used in the CFL, its harmonics ATHD (Current Total Harmonics Distortion) is too high. Noted that the harmonics filter will be introduced to shape the current waveforms of the CFL. Hence, this paper suggests that waveforms of this kind of loads are measured first. Then, the CLP (constant load power) can be used with the help of the harmonic filters to simulate the behaviors of these loads precisely.
2.6 Designing of Electronic Driver Circuit Consider a number of factors while making a blue print of the driver circuit which is needed. There are basically five factors that considered: 1) Lamp Requirements: A fluorescent lamp requires preheating of the filaments, a
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high ignition voltage to strike, current or power control for dimming, and additional filament heating during low dimming levels. 2) Operating Frequency of Electronic Driver Circuit: Driver circuits are worked at a specific frequency range and this is due to a number of reasons. The frequency at which it is functioned should be high as reactive components are used such as inductors and capacitors which a little in size and at high frequencies they give the finest possible output. The frequency should be work higher than 21 KHz as noise interference should be ignored. The frequency used should also be lower than 100 kHz as very high frequencies can outcome in switching losses. The ranges of 30 to 40 kHz have to be ignored as well as they are often used in Infrared remote controls and can interfere with the process. Generally the driver circuit is used in the frequency range of 50 to 60 kHz for the output to be optimal and to ignore very high losses [9], [22], [26].
3) Discharge Lamp Current Wave-Shape of Electronic Driver Circuit: This reason has to be occupied into concern to extend lamp life. The lamp has maximum life the input current should be highly sinusoidal, that is both the electrodes of the lamp should be used instantaneously. If the input current is not sinusoidal it might lead to initially lamp aging and so would therefore not be cost effective. The Crest Factor (CF) of the lamp which is ratio of the peak-current value to the r.m.s. value of the current of the lamp. The higher the Crest Factor the lower is the lamp life and therefore it should be contained. The CF value should therefore be lower than 1.7 to make sure the lamp does not get damaged early [9], [22].
4) Starting Process of the Lamp of Electronic Driver Circuit: This is another significant reason for better lamp life. The main problem is that a lamp will get less damaged if it is started accurately. The method of starting a lamp is perfect if only the following steps are applied effectively. The steps are:
a) If the lamp is started the electrodes have to be heated and no high voltage should be applied unless an optimum temperature is extended. b) If the electrodes are heated to the optimum temperature the starting voltage can be applied and the lamp can be burned.
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c) The starting voltage should be as low as the minimum value needed to burn the lamp as higher voltages can reduce the lamp life [9]. 5) Dimming Control Method of Electronic Driver Circuit: This is an important reason in monitoring the lamp’s light output. Switching frequency is used in this method to control the driver circuit impedances and therefore to adjust the discharge current. That is by using high frequency the inductor reactance can be improved and by that the impedance is also improved and so the lamp current is decreased. Dimming has to be executed effectively by making sure that the lamp power does not change rapidly and also if the power is lost then the lamp should be restarted form the same light intensity level and slowly brought down to the needed level [9]. 6) Resonant output stage of Electronic Driver Circuit: A resonant RCL output stage is used to control the fluorescent lamp. The resonant behavior of the circuit is used to preheat, ignite and dim the lamp. During preheat, the lamp is not conducting and the circuit is a high-Q series L and C. The frequency is held constant and above resonance for a fixed time to preheat the filaments with a given current. When high intensity discharge lamps are supplied at very high frequencies they start showing unusual characteristics. The bulb starts flickering due to changes in the power as the core becomes unstable. This problem can be ignored by choosing frequencies that are above 100 KHz or under 1 KHz [9], [26].
2.7 Factors Affecting on Driver Circuit Performance There are certain reasons that should be taken into consideration while using electronic driver circuits. Driver Circuit Factor (DCF): It is the portion of light output by definite driver circuit to the light output by reference driver circuit. Electronic driver circuit has a DCF of range between “0.73 to 1.50”. A fluorescent lamps light output typically depends on current which flows through the lamp as discussed earlier. A lamp’s rated output lighting is given by functioning the lamp at the line frequency that is 50-60 Hz. If a lamp is
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worked at a frequency in the kilo hertz range low amount of current is required for the lamp to give the same lighting ratings as they worked more efficiently. Driver circuits with very high DCF value are additional likely to damage the lamp and can create the lumen depreciate faster due to high lamp current. Driver circuits with very low DCF value can also be wicked for lamp life due to low lamp current. Driver Circuit Efficacy Factor (DCEF): It is the ratio of driver circuit factor to input power. The comparison of efficacy is define as DCEF value of the fluorescent lamp to driver circuit combination.
2.8 Problems Related to Electronic Driver Circuit 1. Frequent Switching Causes Early Failures: If the lamp is installed where it is frequently switched on and off, it will age rapidly. Under extreme conditions, its lifespan may be much shorter than a cheap incandescent lamp. Each start cycle slightly erodes the electron-emitting surface of the cathodes; when all the emission material is gone, the lamp cannot start with the available driver circuit voltage. 2. Power Quality and Radio Interference: Inductive driver circuits include power factor correction capacitors. Simple electronic driver circuits may also have low power factor due to their rectifier input stage. Fluorescent lamps are a non-linear load and generate harmonic currents in the electrical power supply. The arc within the lamp may generate radio frequency noise, which can be conducted through power wiring. Suppression of radio interference is possible. 3. Fluorescent Lights Give Off Ultraviolet Light: Very sensitive individuals may experience a variety of health problems relating to light sensitivity that is aggravated by artificial lighting. Ultraviolet light can affect sensitive paintings, especially watercolors and many textiles. 4. Fluorescent Bulbs Contain Mercury: If a fluorescent lamp is broken, a very small amount of mercury can contaminate the surrounding environment. About 99% of the mercury is typically contained in the phosphor, especially on lamps that are near the end of their life.
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Chapter 3
Design of Proposed CFL Driver Circuit
The focus area of this Project is the internal driver circuit. The existing circuits were simulated by using Proteus Circuit Simulator Software and finding the problems of commercial driver circuit which is discussed. As discussed beforehand now-a-days the usage of electronic driver circuit is growing manifold and replacing the high power consuming and heavy weighted electromagnetic driver circuit. The electronic driver circuits are smaller in size and can be integrated within a lamp without increasing its size of weight significantly. Thus the overall cost of driving and supplying the lamp decreases due to usage of electronic driver circuit circuitry. CFL lamps are used mostly these days giving the rise in popularity of the usage and manufacture of electronic driver circuits. The CFL lamps mostly used due to the low consumption of power and also the reduction in size but at the same time getting enough luminous intensity compared to any fluorescent lamp. As discussed before the CFL bulb is ignited through a complicated circuitry known as electronic driver circuit and its circuit consists of multiple components using Royer oscillator switches and diodes and capacitors. Inside the circuit of driver contains of two main blocks which are a diode-bridge rectifier to change the input AC voltage to DC and then a Royer oscillator switch to change the DC voltage to AC again. The entire process is done to increase the overall frequency of the supply as the CFL lamps are commonly driven at high frequencies. A capacitor is associated with the output terminal of the rectifier to obtain as much DC like voltage as can be attained. High frequency AC is then supplied to the driver circuit which in turn performing as a starter circuit of the lamp which is then driven by it and thus the lamp is ignited. But the main problem is the generation of impulses of current in the form of spikes which changes the sinusoidal input voltage shapes which come directly from the line. This is called Total Harmonic Distortion and is quite dangerous for electronic equipment’s and at the same time gives rise to reactive power loss due to the existence of diodes and switches
22
existing in the driver circuitry which are not linear as a resistor. The power lost is in the form of reactive power and is an additional loss due to the spikes in current wave-shape. For example if allow a CFL lamp with a power rating of 30W then see that the apparent power used is greater because of these non-linear components existent in the circuit. The additional power drawn is useless and yet has to pay for it. Thus the efficiency of the lamp along with the circuit is reduced due to the appearance of distortion in the current. The main concern of this project was to design a complete driver circuit and therefore reduce the THD by reducing the distortion in current and thereby cumulative the efficiency of the generally circuit and also to continue the linearity as far as possible of the sinusoidal voltage wave- shape. Part by part circuits are designed and implemented giving rise to the whole block circuit. In order to evaluate the power quality analysis as described in below, an experimental procedure based on the measurement of the voltage and current waveforms at terminals has been developed. Considering that supply of single phase, with voltage of 230 V RMS and frequency of 50 Hz. The oscilloscope uses two channels to sample and store the waveforms.
3.1 Driver Circuit Design For this Project using non-resonant driver circuit design due to the fact that dealing with 30W CFL lamps which consume as 28W to 33W. We have designed the driver circuit in parts and taken values of each part and made comparisons where necessary. The circuit consists of four parts which are – (i) The Rectifier, (ii) Valley-Fill Circuit with Electrolytic Capacitor, (iii) Royer oscillator & Inverter and (iv) Resonant Tank Circuit. The sole purpose is to convert the input sinusoidal AC voltage into DC voltage and then finally converting the DC voltage to AC voltage while increasing the frequency significantly as the main purpose of driver circuit is to supply the CFL at high frequencies. A full design has also been given in Fig. 3.1, vero board in Fig. 3.2 and component list as presented in Table 3.1. Proposed Driver Circuit of CFL at the end along with the
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improvements we have made to fulfill our purpose of creating and improving a theoretical model of an electronic driver circuit for CFL.
D2 D3 1N4007 1N4007 L1 C5 FUSE 10uF
0.89mH BR1 D6 D8 1N4007 VSINE D1 1N4007 1N4007 1
VA=312V 0
1N4007 t FREQ=50 C2 u p C8 10uF t u
C7 47uF O 100nF C9 47uF
C C4 C3 5 T P MZ11A C1 R2 R1 2XCB829 L4 470R 470R 223J D11
7 C6 0
O-Coil Arrangement 6 0 R7 4 F N 470k p 1 L4 4 D4 Q1 0 1 FR102 13005SD 2 0
t u
D10 p 6 5 3 t
R4 u O L3 L3 D5 22R FR102 1N4007 R3 1R 4 L5 4 3
3mH L2 1 R5 Q2 L2 13005SD 2 1 22R 2 D9 D7 R6
1R 1N4007 DB3 Figure 3.1: Proposed Driver Circuit of CFL.
Figure 3.2: Proposed CFL Circuit Implementation on the Vero Board.
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In this segment, skills acquired during the first and second platform exercises were merged together (simulation and Vero boarding) and to produce a 30 Watt proposed driver circuit by soldering all the electronics and electrical wire together to functions as a unit on a Vero board as presented in the fig4.6.
Component List of Proposed Driver Circuit of CFL
Resister Value in Ohm Inductor Value R1 470R EMC Coil, L1 0.89 mH R2 470R 3 Turns R3 1R O-Core Coil 6 Turns R4 22R 3 Turns R5 22R L5 or TR 3 mH, 30 Watt R6 1R Diode Value R7 470R D1 IN4007 Capacitor Value D2 IN4007 C1 2X2A, 400V, 223J D3 IN4007 10 micro - Farad, C2 D4 FR102 450V, Electrolytic C3 2XCB829 D5 FR102 C4 MZ11A D6 IN4007 10 micro - Farad, C5 D7 IN4007 450V, Electrolytic 104 pico - Farad, C6 D8 IN4007 450V, Electrolytic C7 100 micro - Farad D9 or DIAC DB3 47 micro - Farad, C8 D10 IN4007 450V, Electrolytic 47 micro - Farad, C9 D11 IN4007 450V, Electrolytic Transistor Value BR1 IN4007 Q1 13005SD (NPN) Q2 13005SD (NPN) Fuse 5 ohm Table 3.1: Component List of Proposed Driver Circuit of CFL
3.1.1 Rectifier The rectifier circuit used is a full-bridge diode rectifier along with capacitance connected to the output terminals as shown in Fig. 3.3. The main objective of this circuit is
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to ensure that the output voltage is as close to that of the DC level. Four diodes are placed as shown in the diagram.
Figure 3.3: A Full-bridge Rectifier
An ammeter is placed with the input voltage to measure the distortion in current due to placement of diodes which direct the current in one single direction. The input voltage is 312V peak which has an rms value of 220V and the frequency used is 50Hz which is the line frequency of this country. The diodes are numbered from D1 to D4 and are placed according to the diagram. When the voltage cycle of the input source is positive diodes D1 and D4 are active and diodes D2 and D3 are open circuited and the current travels in the direction from P1 to P2 for the half cycle. The voltage of the resistor therefore shows a positive peak. In the negative half cycle of the input source diodes D2 and D3 are active and diodes D1 and D4 are open circuited and so the current travels in the direction from P1 to P2 the same as before. The wave-shave obtained for the circuit is as shown in Fig. 3.4:
Figure 3.4: Wave-Shape with Using Capacitance 100µF
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The voltage again shows a positive peak. The capacitor is placed so that once it is charged to the full voltage it takes time to discharge and thus due to its use the voltage never falls to zero. The wave-shape shows that the input voltage which was an AC- sinusoidal supply is altered to a much resembling DC voltage. The capacitor used for the wave-shape is 100µF. However this rectifier which converts the AC voltage to DC voltage has one big drawback. The usage of diodes itself distorts the input current wave-shape giving rise to THD which is quite harmful for other electronic equipment’s and also draws in over power. The capacitor used with a very small value of 100µF also gives rise to distortion and thus the power factor of the circuit lessens and more power is drawn from the source which should not have been drawn.
3.1.2 Valley-Fill Circuit with Electrolytic Capacitor The valley-fill current shaper permits input current conduction from 30° to 150°, and then from 210° to 330°. Due to the discontinuities from 0° to 30° and from 150° to 210°, substantial amount of harmonics were introduced into the input current waveform. This article presents an improved version of the valley-fill circuit as shown in Fig. 3.5 which extends the conduction angle to near 360°, thus lowering unwanted harmonics as well as improving power line current waveform. Improvements are made with passive components. Proteus Circuit simulations compare original circuit with different improved versions of the circuit. 98% power factor is achievable with this new circuit.
Figure 3.5: Valley-Fill Circuit.
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The capacitors C2 and C5 are charged in series, and discharged, via the diodes D6 and D3, in parallel. Current is drawn from the line from 30° to 150° and then from 210° to 330°. Discontinuities occur from 150° to 210° and from 330° to 360° and then the cycle repeat itself. Diode D2 is inserted to prevent C2 from discharging via C5. The current wave- shape is shown in Fig. 3.6.
Figure 3.6: Current Wave-Shape with Using Electrolytic Capacitor.
The capacitors C5 and C2 are charged in series, and discharged via the diodes D6 and D3 in parallel. Current is drawn from the line from 30° to 150° and then from 210° to 330°. Discontinuity occur from 150° to 210° and from 330° to 360° and then the cycle repeats itself. Diode D2 is inserted to prevent C2 from discharging via C5. By this circuit, we achieved better power factor which is about 0.934 leading.
3.1.3 Royer oscillator and Inverter Royer Oscillator A Royer oscillator is an electronic relaxation oscillator that employs a saturable-core transformer as presented in Fig. 3.7. It has the advantages of simplicity, low component count, rectangle waveforms, and easy transformer isolation.
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Figure 3.7: Royer Oscillator and Inverter Design
By making maximum use of the transformer core, it also minimizes the size and weight of the transformer. The classic Royer circuit outputs square waves; a modified version, essentially by adding a capacitor, turns it into a harmonic oscillator, outputting sine waves. Both versions are widely used, mainly as power inverters.
Circuit Description of Royer Oscillator: The circuit consists of a saturable-core transformer with a center-tapped primary winding, a feedback winding and (optionally) a secondary winding. The two halves of the primary are driven by two transistors in push-pull configuration. The feedback winding couples a small amount of the transformer flux back in to the transistor bases to provide positive feedback, generating oscillation. The oscillation frequency is determined by the maximum magnetic flux density, the power supply voltage, and the inductance of the primary winding. The current wave-shape is shown in Fig. 3.8:
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Figure 3.8: Wave-Shape across the Transistor.
The inverter circuit used is an O-core coil with diodes connected in parallel. The objective of this circuit is to convert the input DC voltage to AC voltage which is then supplied to the resistive load. The following figure displays a simulation done by me of an inverter. The current wave-shape is shown in Fig. 3.9.
Figure 3.9: Wave-Shape across the Inverter.
3.1.4 Resonant Tank Circuit to Ignite and Run the Lamp The AC mains voltage is full-wave rectified and then peak-charges a capacitor to produce a smooth DC bus voltage. The DC bus voltage is then converted into a high- frequency, 50% duty-cycle, AC square-wave voltage using a standard half-bridge switching circuit. The high-frequency AC square-wave voltage then drives the resonant tank circuit and becomes filtered to produce a sinusoidal current and voltage at the lamp. During pre-
30
ignition, the resonant tank is a series-LC circuit with a high Q-factor. After ignition and during running, the tank is a series-L, parallel-RC circuit, with a Q-factor somewhere between a high and low value, depending on the lamp dimming level. The frequency keeps decreasing until the lamp voltage exceeds the lamp ignition voltage threshold and the lamp ignites. Once the lamp ignites, the lamp current is controlled such that the lamp runs at the desired power and brightness level. To dim the fluorescent lamp, the frequency of the half- bridge is increased, causing the gain of the resonant tank circuit to decrease and therefore lamp current to decrease. A closed-loop feedback circuit is then used to measure the lamp current and regulate the current to the dimming reference level by continuously adjusting the half-bridge operating frequency. The feedback circuit regulates the valley of the AC+DC signal to COM as the DC dimming level is increased or decreased by continuously adjusting the half-bridge frequency. This causes the amplitude of the lamp current to then increase or decrease for dimming. If the DC reference is increased, the valley of the AC+DC signal will increase above COM and the feedback circuit will decrease the frequency to increase the gain of the resonant tank. This will increase the lamp current, as well as the amplitude of the AC+DC signal at the DIM pin, until the valley reaches COM again. If the DC reference is decreased, the valley will decrease below COM. The feedback circuit will then increase the frequency to decrease the gain of the resonant tank until the valley reaches COM again.
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Chapter 4
Implementation and Performance Analysis
We know that in generally two methods are familiar for correcting power factor. One is passive method and another is active methods. Simple power factor correction can be accomplished using a capacitor to shift phase angles until the line current and voltage is in phase, i.e. power factor is unity. The electronic correction of power factor and suppression of harmonic distortion is more complex. The front end of electronic fluorescent driver circuits converts the alternating line current to DC. This is accomplished using a full-wave rectifier bridge followed by a filter capacitor. The bridge conducts during the period of the cycle when the line current exceeds the capacitor voltage as shown in Fig. 3.1. The effect is that current is drawn from the power source over a very short time, as shown in Fig. 4.1. The line current is no longer sinusoidal, which results in the generation of harmonics. The amount of harmonic distortion is generally expressed as a percentage of the fundamental current. To solving the harmonic problem is the elimination of the filter capacitor that causes the problem. Unfortunately, without the filter capacitor, the unfiltered DC is 100% modulated. This modulated to wave is undesirable for fluorescent systems, reducing system efficacy and lamp life while increasing the flickers. Experimental tests have been performed on five compact fluorescent lamps, four CFLs of earlier generation in commercially by two manufacturer and one CFL of new generation in Laboratory. The proposed driver circuit of CFL is designed in Vero board as simulated circuit design in laboratory. The rated specifications of commercial CFL are – CFL-A: 8 W commercially generation CFL from manufacturer 1. CFL-B: 14 W commercially generation CFL from manufacturer 1. CFL-C: 23 W commercially generation CFL from manufacturer 2. CFL-D: 30 W commercially generation CFL from manufacturer 2. CFL-E: 30 W Proposed driver circuit of CFL in Laboratory.
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4.1 Power Quality Analysis of the Measurements Results for CFL Parameter comparison between proposed and existing 30 Watt CFL Harmonics CFL Frequency Power Voltage Current Power Factor Light Out Rated Light Efficacy VTHD ATHD (Hz) (W) (V) (A) (P.F.) (lm) Out (lm) (lm/W) (%) (%)
Proposed 50.95 32.5 229.7 0.151 0.934 1985 1800 61.10 4.0 37.6
Exiting 50.17 28.2 219.3 0.186 0.689 1336 1800 47.37 5.9 86.2
Table 4.1: Parameter Comparison between Proposed and Existing 30 Watt CFL
Table 4.1 shows the power quality analysis of the measurements results between proposed CFL driver circuit and existing 30 watt CFL driver circuit. The VTHD calculated was 4.0% which was almost similar to both proposed and existing. The ATHD calculated was 37.6 % which was almost 86.2% in existing driver circuit. So it can be concluded that In existing circuit of 30W, VTHD is 5.9% and ATHD 86.2% where ATHD was almost 15 times higher than VTHD and 9 times higher ATHD from VTHD in proposed CFL driver circuit. For the proposed driver circuit of 30W CFL, PF is close to the unit value, as shown in Fig. 4.1, which compared with existing driver circuit, as shown in Fig. 4.2. This means that voltage and current first harmonics have a small phase shift in proposed driver circuit and the significant harmonics in current waveform are few and small in amplitude.
Figure 4.1: Input and Output Wave Shape of Proposed 30Watt CFL
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Figure 4.2: Input and Output Wave Shape of Existing 30Watt CFL
Parameter comparison between proposed and existing 23 Watt CFL Harmonics CFL Frequency Power Voltage Current Power Factor Light Out Rated Light Efficacy VTHD ATHD (Hz) (W) (V) (A) (P.F.) (lm) Out (lm) (lm/W) (%) (%)
Proposed 50.56 23.9 218.8 0.115 0.946 1489 1380 62.30 5.9 28.9
Exiting 50.27 21.0 220.3 0.146 0.650 1048 1380 49.87 4.6 107.0
Table 4.2: Parameter Comparison between Proposed and Existing 23 Watt CFL
Table 4.2 shows the power quality analysis of the measurements results between proposed CFL driver circuit and existing 23 watt CFL driver circuit. The VTHD calculated was 5.9% which was almost similar to both propose and existing. The ATHD calculated was 28.9 % which is almost 107.0% in existing driver circuit. So it can be concluded that in existing circuit of 23W, VTHD is 4.6% and ATHD 107.0% where ATHD is almost 24 times higher than VTHD and 5 times higher ATHD from VTHD in proposed CFL driver circuit. For the proposed driver circuit of 23W CFL, PF is close to the unit value, as shown in Fig. 4.3, which compared with existing driver circuit, as shows in Fig. 4.4. This means that voltage and current first harmonics have a small phase shift in proposed driver circuit and the significant harmonics in current waveform are few and small in amplitude.
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Figure 4.3: Input and Output Wave Shape of Proposed 23Watt CFL
Figure 4.4: Input and Output Wave Shape of Existing 23Watt CFL
Parameter comparison between proposed and existing 14 Watt CFL Harmonics CFL Frequency Power Voltage Current Power Factor Light Out Rated Light Efficacy VTHD ATHD (Hz) (W) (V) (A) (P.F.) (lm) Out (lm) (lm/W) (%) (%)
Proposed 50.36 14.2 221.7 0.069 0.926 847 840 59.63 4.4 34.7
Exiting 49.88 13.0 217.1 0.090 0.661 605 840 46.53 5.8 104.6
Table 4.3: Parameter comparison between proposed and existing 14 Watt CFL
Table 4.3 shows the power quality analysis of the measurements results between proposed CFL driver circuit and existing 14 watt CFL driver circuit. The VTHD calculated was 5.8% which was almost similar to both propose and existing driver circuit of CFL. The
35
ATHD calculated was 34.7 % which was almost 104.6% in existing driver circuit. So it can be concluded that in existing circuit of 14W, VTHD is 5.8% and ATHD 104.6% where ATHD is almost 18 times higher than VTHD and 8 times higher ATHD from VTHD in proposed CFL driver circuit. For the proposed driver circuit of 14W CFL, PF is near to the unit value, as shown in Fig. 4.5 which compared with existing driver circuit, as shows in Fig. 4.6. This means that voltage and current first harmonics have a small phase shift in proposed driver circuit and the significant harmonics in current waveform are few and small in amplitude.
Figure 4.5: Input and Output Wave Shape of Proposed 14Watt CFL
Figure 4.6: Input and Output Wave Shape of Existing 14Watt CFL
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Parameter comparison between proposed and existing 8 Watt CFL Harmonics CFL Frequency Power Voltage Current Power Factor Light Out Rated Light Efficacy VTHD ATHD (Hz) (W) (V) (A) (P.F.) (lm) Out (lm) (lm/W) (%) (%)
Proposed 50.46 7.6 221.5 0.036 0.937 427 480 56.14 4.6 24.8
Exiting 50.13 9.5 218.5 0.070 0.620 475 480 48.97 5.4 112.1
Table 4.4: Parameter comparison between proposed and existing 8 Watt CFL
Table 4.4 shows the power quality analysis of the measurements results between proposed CFL driver circuit and existing 8 watt CFL driver circuit. The VTHD calculated was 4.6% which was almost similar to both propose and existing driver circuits of CFL. The ATHD calculated was 24.8% which was almost 112.1% in existing driver circuit. So it can be concluded that in existing circuit of 8W, VTHD is 5.4% and ATHD 112.1% where ATHD is almost 21 times higher than VTHD and 5 times higher ATHD from VTHD in proposed CFL driver circuit. For the proposed driver circuit of 8W CFL, PF is close to the unit value, as shown in Fig. 4.7, which compared with existing driver circuit, as shown in Fig. 4.8. This means that voltage and current first harmonics have a small phase shift in proposed driver circuit and the significant harmonics in current waveform are few and small in amplitude.
Figure 4.7: Input and Output Wave Shape of Proposed 08Watt CFL
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Figure 4.8: Input and Output Wave Shape of Existing 08Watt CFL
Fig. 4.9, Fig. 4.10 and Fig. 4.11 shows the harmonic spectrum of the proposed 20W CFL, existing 20W CFL and existing 10W CFL respectively. The results here reported are in agreement with the results obtained. Furthermore, the proposed CFL shows a further improvement of the PQ (Power Quality) behavior.
Figure 4.9: Harmonic Spectrum of 20 W Proposed CFL.
Harmonics with significant amplitude in the AC side current waveform of proposed driver circuit of 20W CFL can be found up to about the 10th harmonic; the 5th harmonic is
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the higher in Fig. 4.9. Moreover, the current waveforms show that the driver circuit input stage includes a valley-fill circuit for the passive correction of power factor.
Figure 4.10: Harmonic Spectrum of 20 W Existing CFL.
For the existing CFL, cosφ is less than in the proposed ones. Moreover, PF is very low indicating that harmonics in current waveform have a strong impact in reducing the quality in the energy conversion. The AC side current waveform of existing CFL is characterized by high derivative and a significant part of the period when current is nil, these characteristics are reflected in a spectrum rich in harmonics, and harmonics with high or significant amplitude can be found up to about the 40th harmonic as shown in Fig. 4.10 and Fig. 4.11.
Figure 4.11: Harmonic Spectrum of 10 W Existing CFL.
Passive correction methods are using a tuned series LC network before the input bridge. C7 is the filter capacitor shown in driver circuit in Fig. 3.1 and can be provide nearly
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ripple-free output, depending on the size of the capacitor. This circuits corrects the power factor and provides limited harmonic distortion improvements. Fig. 3.5 is a method of correction which is known as the “Valley Fill” circuit. It has adequate power factor correction and moderate amounts of harmonic distortion suppression. When the line voltage drops below the 50% point, the capacitor discharge, filling the valley and preventing the voltage from going to zero. The load must be able to tolerate or compensate for a ripple of about 50% and the harmonic distortion levels are reduced by about 75%. The current waveforms are affected by distortion while voltage is almost sinusoidal, as indicated by the THD indexes. Also in this case, voltage harmonics due to harmonic current absorption are negligible and the small value of VTHD is related only to the harmonic pollution already existing into the grid. The proposed compact fluorescent lamps show smaller current distortion than the commercially available CFL their ATHD is almost five times less than the ATHD of commercial compact fluorescent lamps. Therefore, for the commercial compact fluorescent lamp, PF is less than in the proposed CFL. Moreover, PF is very low indicating that harmonics in current waveform have a strong impact in reducing the quality in the energy conversion.
4.2 Benefits of High Power Factor CFL: For Customer Reduced effect of harmonics (electrical noise that may interfere with the operation of computers, receivers or sensitive equipment). Reduced potential for power quality problems Reduced power fluctuations caused by switching on heavy loads within installation. Many utilities provide incentives to consumers to improve their power factor and thereby reduce their demand for electric current. For Electric Power Utility Reduced electric current needs means energy saving Reduced transmission and transformer losses Improved voltage regulation
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An increase in available capacity throughout the power company’s system without additional investments in generation or distribution Reduced peak current demand can allow the utility to postpone the construction of new generating capacity Losses to the Power Utilities due to Low Power Factor Electronics Cost to Correct Power Quality - Harmonic Distortion reduces power quality. This requires expensive capacitive compensation and harmonic filtering equipment to be installed to dampen the effect. Equipment Damage and Reduce Life - Poor power quality can cause nuisance tripping of residential circuit breakers, reduced motor life and equipment damage due to overheating. Unreliable and Uncontrolled Electricity Supply - Leads to frequent occurrences Brown Outs and Black Outs.
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Chapter 5
Conclusion and Future Recommendation
5.1 Conclusion THD is an issue that is the main reason for all kinds of problems caused by power electronic circuitry and is needed to be resolved. In this Project, lean-to light on how much damage is caused by the distortion of the input current due to diodes and capacitors. Two types of driver circuits which are magnetic and electronic researched also. It is seen that the CFL uses electronic driver circuits and the components in the driver circuit are power electronic components consisting to two circuits which are a rectifier followed by an inverter. Performing below steps in this Project –
At first collected three different types of commercial CFL lamps and these are analyzed in Laboratory. Then the existing circuits were simulated by using Proteus Circuit Simulator Software and finding the problems of commercial driver circuit which is discussed. Then a HPF (high power factor) driver circuit is proposed to overcome the problems of commercially available CFL driver circuit. The propose driver circuit is simulated and practically implemented in the laboratory. Then performance of implemented circuit is analyzed in terms of Power Factor (PF), Efficiency and Total Harmonics Distortion of voltage & current.
In this project, find out the comparison between proposed driver circuit and existing circuits for 30 Watt are - the VTHD calculated was 4.0% which is almost similar to both proposed driver circuit and existing circuits. But the ATHD calculated was 37.6 % which is almost 86.2% in existing driver circuit. So it can be concluded that in existing circuit for 30W, VTHD is 5.9% and ATHD 86.2% where ATHD is almost 15 times higher than VTHD
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and causes (i) Low Power Factor (ii) Total Harmonics Distortion is High (iii) Generated heating etc. where 9 times higher ATHD from VTHD in proposed CFL driver circuit. Power Factor calculated was 0.689 in existing circuit for 30 Watt but Power Factor is 0.934 in proposed driver circuit which are very close to the unit value. This means that voltage and current first harmonics have a small phase shift and the significant harmonics in current waveform are few and small in amplitude.
The desire to reduce electrical loading by using energy efficient lighting has resulted in a high level of interest in replacing conventional incandescent lamp with Compact Fluorescent Lamps. However, their high harmonic content was always a problem for the power quality of the power system networks, especially the ones with a considerable share of nonlinear loads. The problem of harmonics cannot be neglected in cases of installations with high lighting load. This paper presents an analysis of harmonics in a network where lighting is one of the main loads. CFLs lamps with electronic gear are characterized by extremely distorted current, with high total current harmonic distortions. Hence they cause a significant voltage distortion in electrical installations. A comparative analysis is performed on the power quality, maximum loading and economics of CFL lamps.
5.2 Recommendation for Future Work There are still some scopes for future research as mentioned below: 1. The CFL bulbs manufacturers should improve on design of CFL bulbs to mitigate the high level of harmonic distortions and low power factor inherently associated with the CFL bulbs. 2. It is recommended to combine other loads (resistive and inductive) with the CFL bulbs to improve the power quality of the power supplied at the point of common coupling (PCC). 3. It can also mitigate voltage dips and over voltages, compensate reactive power of the load, unbalance in currents, and can compensate unbalance in load voltages. 4. In future cost-effective mitigation techniques can be developed to mitigate multiple power quality problems simultaneously.
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