A STUDY AND DEVELOPMENT OF TRANSFORMER-LESS UNINTERRUPABLE POWER SUPPLY THANARAJA S/O KANNIYAPAN UNIVERSITI TEKNOLOGI MALAYSIA

Transcription

1 A STUDY AND DEVELOPMENT OF TRANSFORMER-LESS UNINTERRUPABLE POWER SUPPLY THANARAJA S/O KANNIYAPAN UNIVERSITI TEKNOLOGI MALAYSIA

2 UNIVERSITI TEKNOLOGI MALAYSIA PSZ 19:16 (Pind. 1/07) DECLARATION OF THESIS / UNDERGRADUATE PROJECT PAPER AND COPYRIGHT Author s full name : THANARAJA S/O KANNIYAPAN Date of birth : 22 ND OCTOBER 1988 Title : A STUDY AND DEVELOPMENT OF TRANSFORMER-LESS UNINTERRUPABLE POWER SUPPLY Academic Session: 2011/2012 I declare that this thesis is classified as : CONFIDENTIAL RESTRICTED OPEN ACCESS (Contains confidential information under the Official Secret Act 1972)* (Contains restricted information as specified by the organization where research was done)* I agree that my thesis to be published as online open access I acknowledged that Universiti Teknologi Malaysia reserves the right as follows: 1. The thesis is the property of Universiti Teknologi Malaysia. 2. The Library of Universiti Teknologi Malaysia has the right to make copies for the purpose of research only. 3. The Library has the right to make copies of the thesis for academic exchange. Certified by : SIGNATURE SIGNATURE OF SUPERVISOR EN. ZULFAKAR ASPAR (NEW IC NO. /PASSPORT NO.) NAME OF SUPERVISOR Date : 25 JUNE 2012 Date : 25 JUNE 2012 NOTES : * If the thesis is CONFIDENTAL or RESTRICTED, please attach with the letter from the organization with period and reasons for confidentiality or restriction.

3 I hereby declare that I have read this report and in my opinion this report is sufficient in terms of scope and quality for the award of the degree of Bachelor of Electrical Engineering (Electronics) Signature : Supervisor s Name : En. Zulfakar bin Aspar Date : 25 June 2012

4 A STUDY AND DEVELOPMENT OF TRANSFORMER-LESS UNINTERRUPABLE POWER SUPPLY THANARAJA S/O KANNIYAPAN A report submitted in partial fulfilment of the requirements for the award of the degree of Bachelor of Electrical Engineering (Electronics) Faculty of Electrical Engineering Universiti Teknologi Malaysia JUNE 2012

5 ii I declare that this thesis entitled A study and Development of Transformer-less Uninterruptable power supply is the result of my own research except as cited in the references. The thesis has not been accepted for any degree and is not concurrently submitted in candidature of any other degree. Signature :... Name : Thanaraja s/o Kanniyapan Date : 25 June 2012

6 iii Dedicated to my beloved parents for their love, sacrifice and inspiration, To my siblings for their constant support, To my scintillating lecturers and friends.

7 iv ACKNOWLEDGEMENT First and foremost, all praise to the Divine for the blessings and guidance that I received to embark on this research project of mine. The author wishes his greatest acknowledgement for those who contributed to the completion of this project and not to forget En. Zulfakar bin Aspar for his guidance, advises, comments, and encouragement which had contributed a lot to the completion of this project. I also wish my greatest acknowledgement to my friends for their valuable assistance and support as they are my confidence booster and they are the solutions for the problems that I faced while constructing this project. Last but not least, I would like to thank my parents for their blessing and love as well as my sisters and brother for their constant support and encouragement.

8 v ABSTRACT Currently there is a major concern about size, weight and cost of certain apllications in many industrial sectors. Concurrently, this project is about studying and developing a high efficient and compact boost converter which will be very reliable in special applications such a in bio-medical industries. The objective of this project is to study different types of transformer-less uninterrupable power supply. Besides that, the performance of different types of boost technique will be studied and modeled as well to design a low cost, low weight and a compact boost converter. By using the basic principle, the boost converter will be modeled and simulated in part by part using different techniques. In other way, to generally explain the operation of the boost converter which has the switching part as the key element to produce the step-up voltage based on the correct design specification. This project comprises of two parts which is the software part and the hardware part. The software used for the modelling and simulation of the boost converter is the PSPICE software. The corresponding output of different types of boost techniques will be analyzed. After that, the hardware for the boost converter will be designed and developed in two parts which is firstly on strip board and finally on printed circuit board. Finally, the completed hardware will be tested and analyzed.

9 vi ABSTRAK Pada masa ini, isu mengenai saiz, berat dan kos aplikasi tertentu dalam banyak bidang sektor industri.telah menjadi satu faktor yang penting. Projek ini mengkaji dan membangunkan pengubag voltan DC yang tinggi yang cekap dan akan menjadi sangat berguna dalam aplikasi-aplikasi khas seperti dalam industri bioperubatan. Objektif projek ini adalah untuk mengkaji pelbagai jenis bekalan kuasa tidak terganggu tanpa mengunakan pengubah voltan. Selain itu, prestasi penaikan voltan terus bagi pelbagai jenis teknik penaikan voltan terus akan dikaji untuk mereka bentuk litar penaikan voltan terus yang berkos rendah, ringan dan mampat. Dengan menggunakan prinsip asas, litar penukar voltan arus terus ini akan dimodelkan dan disimulasikan dengan menggunakan teknik yang berbeza. Secara amnya, operasi penukar voltan arus terus ini mempunyai satu elemen yang penting untuk menghasilkan voltan langkah-naik iaitu pada bahagian pengsuisan dengan mengikuti spesifikasi reka bentuk yang betul. Seterusnya, projek ini terdiri daripada dua bahagian iaitu bahagian perisian(software) dan bahagian perkakasan(hardware). Perisian yang digunakan untuk pemodelan dan simulasi litar penukar voltan arus terus ini adalah perisian PSPICE. Keputusan yang terhasil daripada perisian PSPICE ini akan dianalisis. Tambahan pula, perkakasan untuk penukar voltan arus terus ini akan direka dan dibangunkan dalam dua bahagian iaitu pertama di papan jalur dan akhirnya di atas papan litar bercetak. Akhirnya, perkakasan yang telah dihasilkan ini akan diuji dan dianalisis.

10 vii TABLE OF CONTENTS CHAPTER TITLE PAGE DECLARATION DEDICATION ACKNOWLEDEGEMENTS ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF FIGURES LIST OF TABLES LIST OF ABBREVIATIONS ii iii iv v vi vii x xiii xiv 1 INTRODUCTION 1.1 Background Objective of Research Scope of Research Statement of Problem 4 2 LITERATURE REVIEW Introduction Types of UPS Configuration Standby or Off-Line UPS Line-Interactive UPS DC power UPS 7

11 viii Rotary UPS Single-Phase Double Conversion UPS Configuration (Online UPS) Normal Mode Stored Energy Mode Bypass Mode Summary of Comparison Between Different Types of UPS Advantages and Disadvantages of Double Conversion UPS Advantages Of Double Conversion UPS Disadvantages of Double Conversion UPS Comparison Between Transformer Based and Transformer-Less UPS System 15 3 METHODOLOGY Introduction Method Used DC to DC Converter Step Down (Buck Converter) Step Up (Boost Converter) SEPIC (Single-Ended Primary Inductor Converter) Buck- Boost Converter DC to DC Converter Continuous Mode Discontinuous Mode DC to AC Converter Project Flow 24 4 DEVELOPMENT PROCESS Introduction 26

12 ix 4.2 Design Specification Inductor Selection Diode Selection Input Capacitor Selection Output Capacitor Selection Power Switches Selection The 555 Timer Selection Simulation Process Hardware Development 34 5 RESULTS AND DISCUSSION Introduction Simulation and Technique Used for the DC to DC Converter Simulation of Single Stage Boost Converter Simulation of Interleaved Boost Converter Simulation of Cascaded Interleaved Boos Converter Hardware Result of The Cascaded Interleaved Boost 42 Converter 5.4 Discussions 44 6 CONCLUSION AND RECOMMENDATIONS Introduction Recommendations 47 REFERENCES 48 APPENDIXES 50 Appendix A 50 Appendix B 52 Appendix C 54 Appendix D 60 Appendix E 69

13 x LIST OF FIGURES FIGURE NO. TITLE PAGE 1.1 A basic diagram of transformer-less UPS system The basic operation block diagram of off-line 6 UPS system 2.2 The block diagram of line interactive UPS 7 System 2.3 The diagram of DC power UPS system A block diagram of a general rotary UPS system Operation modes block diagram of double 10 Conversion UPS System. 2.6 A block diagram of online single phase double 12 Conversion UPS system 2.7 Efficiency versus load of a transformer-less UPS Basic buck converter circuits Basic boost converter circuits Basic SEPIC converter circuits Basic buck-boost converter circuits Switch is closed Switch is opened Schematic diagram of an inverter Project flow The pulse width modulation of the 555 timer The circuit diagram of single stage boost converter The output simulation of the single stage boost 34 Converter

14 xi 4.4 The circuit diagram of interleaved boost converter The output simulation of the interleaved boost 37 Converter 4.6 The circuit diagram of cascaded interleaved boost 38 Converter 4.7 The output simulation of the cascaded interleaved 39 Boost converter 4.8 The picture of cascaded interleaved boost 40 Converter on strip board 4.9 The picture of cascaded interleaved boost 40 Converter on PCB board 4.10 The picture of output result from the millimetre 41 Reading

15 xiii LIST OF TABLES TABLE NO. TITLE PAGE 2.1 Benefits and limitation of different types of UPS Benefits and limitation of different types of UPS Characteristic comparison between transformers 17 Based and transformer-less UPS system 2.4 Performance comparison of two UPS topologies Summary comparison between transformers 18 Based and transformer-less UPS system 4.1 The desired parameters which were used in the 28 Simulation 5.1 Simulation result versus hardware result 38

16 xiv LIST OF ABBREVIATIONS UPS - Uninterruptable Power Supply DC - Direct Current AC - Alternating Current SEPIC - Single-Ended Primary-Inductor Converter PSPICE - Personal Computer Simulation Program With Integrated Circuit Emphasis ESR - Equivalent Series Resistance PWM - Pulse Width Modulation MOSFET - Metal-Oxide-Semiconductor Field-Effect Transistor

17 CHAPTER 1 INTRODUCTION 1.1 Background In this thesis, a transformer-less based UPS system will be studied and developed. A transformer-less UPS is an electrical equipment that supply back up power supply when there is sudden power loss or blackouts. Many critical loads are susceptible to power spikes. Critical loads are the loads such as computers, printers and many others that are most commonly used in industries. There is a great demand for transformer-less UPS in the low power range. The desirable features in such UPS are low cost, low weight, silent operation and compactness. In the conventional UPS, the presence transformer makes the system heavy and bulky. The existence of the transformer makes the UPS system more expensive and they also contribute most of the weight to the system. Besides that, there is also a major concern on the efficiency of the UPS system design. A conventional UPS system is not very efficient because most of the power is used by the transformer and also produces more heat. So by removing the transformer in a UPS system, a more efficient design will be produced with less heat and higher efficiency..

18 2 1.2 Objective of Research The main objectives of this project are as below: i) To study a transformer-less based UPS system. i) To study the performance of different types of boost techniques. ii) To design a low cost, low weight and a compact boost converter. 1.3 Scope of Research It is not practical to design a UPS for unlimited applications. Thus, this project focuses on limited maximum power being produced. Furthermore, design from previous student can be used to build the battery charger. Besides that, the power supply to convert from AC to DC can be easily acquired in the market to speed up development cycle. The scope of this project is as stated below: i) Model a boost converter based on design specification. The model of the boost converter will be done using the PSPICE software simulation. ii) Design a transformer less DC to DC converter which able to have a very high gain atleast 30 times the original input.

19 3 Figure 1.1 A basic diagram of transformer-less UPS system A transformer-less based UPS system is basically consist of AC to DC converter, battery charger and a DC to DC converter. In this project, the scope is limited to only designing the DC to DC converter and DC to AC converter. The front end which is the AC to DC converter is not required in this project because it has already been done by the previous student. Figure 1.1 above shows the basic diagram of the transformer-less UPS system.

20 4 1.4 Statement of Problem The main role of a UPS system is to provide short term back up power during the input power fails. However, choosing between a conventional and a transformerless based UPS system has become a major concern. Transformer based UPS system produces more disadvantages compare to transformerless UPS system as stated below: i) Transformer based UPS system are bulky and heavy. One of the most important factor for choosing the transformer-less UPS is the size. By removing the transformer, the size of the system can be saved for up to 60%. Besides that, the weight of the UPS is also very important factor since it will make the UPS system more portable and save in cost. ii) Conventional UPS system leads to high power usage and expensive. In a transformer based UPS, most of the power is wasted by the transformer itself compare to a transformer-less UPS. Besides that, the transformer is very expensive and can lead to high cost to build the system. iii) Transformer based UPS system generates more noisy and less efficient. The transformer inside the conventional UPS produces heat and noise due to the size of it. On the other hand, for a transformer-less UPS switching frequency is applied to the MOSFETS and the use of other small components making the system more efficient compare to the transformer based UPS.

21 CHAPTER 2 LITERATURE REVIEW 2.1 Introduction The main role of a transformer-less UPS system is to provide backup power when the main power source fails [1]. The UPS system is used many critical equipment in various industries. There are many types of UPS system designed by manufacturer which is available in the market and each type has their own advantages and disadvantages [2]. This chapter focuses on the classification of the single phase double conversion UPS system configuration and how it operates. 2.2 Types of UPS Configuration Standby or Off-Line UPS

22 6 This type of UPS is the most basic, small and cheaper compare to other UPS system. The load is directly connected to the power supply. When the power supply fails the UPS, it will turn on its internal DC-AC inverter circuitry. The UPS then mechanically switches the connected load on its DC-AC inverter output. It disconnects the main power supply until it returns to an acceptable level [4]. This UPS only charge the battery when it is running on utility power. The inverter immediately operates from battery power when the load is transferred to inverter.the figure bellow shows the basic operation of the standby or off-line UPS [4]. Figure 2.1 The basic operation block diagram of off-line UPS system Line-Interactive UPS This type of UPS system is the most common design for small business operation. The charger and inverter is always connected to the output of the UPS [5]. When blackout occurs, the transfer switch will open and the power flows from the

23 7 battery to the output. Since the inverter is always connected to the output of the UPS, additional filtering is provided and this reduces the switching transient. The figure below shows a basic block diagram of line interactive UPS [6]. Figure 2.2 The block diagram of line interactive UPS system DC power UPS A DC power UPS created to provide power to dc equipment which is similar to an online UPS except it does not have an inverter circuit [8]. This ups system does not need an external power supply. This UPS system is obviously known as rectifier. This UPS was created to use in telecommunication system because a lot of equipment need dc power supply. Figure 2.3 shows the dc power UPS system [8]. Figure 2.3 The diagram of DC power UPS system [8].

24 Rotary UPS A rotary UPS is emergency energy source which were created for the usage of 10,000 watts of protection [9]. A rotary UPS uses inertia of a high mass spinning flywheel energy to supply current in the duration of power loss. This UPS system can be considered as online UPS because it spins continuously under normal mode but it is not battery based UPS [9]. This UPS provide about 20 seconds protection before the flywheel has slowed and power output stopped. Figure 2.4 shows the rotary UPS system [10]. Figure 2.4 A block diagram of a general rotary UPS system Single-Phase Double Conversion UPS Configuration (Online UPS) This type of UPS system has two power conversion stages. First it operates by converting the AC voltage to DC voltage and then converts back the DC voltage to AC voltage to supply the load as shown in figure 2.5 [1,3]. There is no need for power transfer switch because the batteries are directly connected to the inverter. It has three operating mode which are bypass mode, normal mode and stored mode. When main power loss occurs the battery will keep the power of the circuit steady

25 9 and constant. After that, when the main supply arrives, the rectifier will charge the batteries and continues its operation. The benefit of this UPS system is, it can provide a firewall between the electronic equipment and the incoming power supply. Besides that, it also help to control the frequency and output voltage regardless of input frequency and input voltage. Figure 2.5 Operation modes block diagram of double conversion UPS System. The three types of operating modes for the single phase double conversion method are defined as below.

26 Normal Mode In the normal mode, the load is continuously supplied by the AC power supply through rectifier and charger-inverter [ 11, 12]. The rectifier converts the AC power to DC power. The DC power will charge batteries and at the same time the DC power pass-through inverter where the inverter convert the DC power to AC power to supply the load [11, 12]. This process is called as the double conversion (AC-DC-AC) Stored Energy Mode Stored energy mode happens, when the AC input supply voltage fails or when the power loss occurs [11, 12]. In this case, the rectifier simply drops out of the circuit where the batteries and the inverter continue to supply the load. The UPS will run in the stored energy mode until the AC input supply return. When the power is restored, the rectifier will continue to support the most of the load and begin to charge the batteries, through the charging current may be limited to prevent the high power rectifier from overheating the batteries. At this point the ups will return to normal mode [11, 12] Bypass Mode A static bypass is often called as a static switch, which allows the instantaneous transfer of the load to the bypass AC input. This bypass mode was created in case of ups internal malfunctioning, overload or the end of the batteries backup time [11, 12]. In the bypass mode the input voltage and frequency must be same or identical with the output voltage and frequency. If the voltage of the input and output were not same means, a transformer must be installed for the bypass mode process function [11, 12].

27 11 The figure below shows the proposed basic structure of the online single phase double conversion ups system for this project. From the figure below a DC to DC converter is introduced to the UPS system. This DC to DC converter is needed to boost or step up the battery voltage. Boost circuit not only functions as regulation of DC voltage (switching power supply) but also checks effectively harmonic wave noise of electric power network. Figure 2.6 A block diagram of online single phase double conversion UPS system 2.3 Summary of Comparison Between Different Types of UPS The tables below show the characteristics of different types of UPS. These factors must be evaluated thoroughly because the implementation and manufactured quality strongly impact the characteristics of the UPS.

28 12 Table 2.1: Benefits and limitation of different types of UPS Practical power range Voltage conditioning Cost per VA Efficiency Inverter always operating (KVA) Standby Low Low Very high No Line interactive Design dependant Medium Very high Design dependant Standby High High Low Partially on-line hybrid Double conversion on-line High Medium Low Yes Table 2.2: Benefits and limitation of different types of UPS Benefits Limitation Functionality Standby Low cost, high efficiency, compact Uses battery during burnouts, impractical over Best value for personal workstations 2kVA Line interactive High reliability, high efficiency, good voltage conditioning Impractical over 5kVA Most popular UPS type in existence due to high reliability, ideal for rack or distributed servers and harsh power environments Standby on-line Excellent voltage conditioning, low efficiency, low Impractical over 5kVA Line interactive provides better reliability and

29 13 reliability, high similar cost conditioning at a better value Double Excellent voltage Low efficiency, Well suited for conversion on- conditioning, ease expensive under N+1 designs line of paralleling 5kVA. 2.4 Advantages and Disadvantages of Double Conversion UPS Double conversion UPS are largely used to protect critical load, so it present some benefit and drawbacks Advantages Of Double Conversion UPS i) The load is always isolated from the upstream distribution system, so it eliminates the transmission of any upstream fluctuations such as overvoltages and spikes [3, 12]. ii) The inverter in the UPS system provides continuous protection for the load [3, 12]. iii) This UPS have very wide input-voltage and accuracy in regulation of the output [3, 12] iv) This UPS have higher performance levels in the steady-state and transient

30 14 v) This UPS can instantaneous transfer to stored-energy mode in the condition of the AC supply failure [12]. vi) This UPS also have manual bypass which is designed to facilitate maintenance [12]. vii) It has a low Total Harmonic Distortion (THD) output voltage [12] Disadvantages of Double Conversion UPS Although double conversion UPS system have several advantages, it have a marginally lower efficiency compare to the other UPS system [3]. Additionally, this double conversion system cost much more than other, because it have two power conversion stages. 2.5 Comparison Between Transformer Based and Transformer-Less UPS System The main difference between the two types of UPS is the usage of transformer in the implementation. The subsequent table below shows a basic comparison between a transformers based UPS and a transformer-less UPS system [3, 12].

31 15 Table 2.3: Characteristic comparison between transformers based And transformer-less UPS system Transformer-less UPS Transformer based UPS Susceptible to interference Transformer used to provide from spikes two main functions Reduce size and cost -voltage conversion ratio Generates far less noise and -DC isolation heat EMI generation High efficiency leakage inductance of the transformers Table 2.4: Performance comparison of two UPS topologies Transformer-less UPS Transformer based UPS Rated UPS power 300 KVA 300 KVA Effective power Power factor = 0.9 Losses at full load at 200kw 232kW (86% of UPS rated power) 14kW (93% efficiency) 182kW 10% OVERLOAD! Need for larger UPS 22kW (89% efficiency losses) Sizing factor Leads to increase in cost

32 16 Table 2.5: Summary comparison between transformer based and transformer-less UPS system Types and criteria Transformer-less Transformer based Location flexibility Size and weight Input waveform management System efficiency Initial system costs Adaptability/scalability Fuzzy growth plans Robustness Input/output configuration flexibility Reduced need for paralleling for capacity Input/DC/output isolation Component count Availability Fault management Best = +++ Better = ++ Good = + The transformer-less UPS was designed with a main concern on efficiency. Currently, many industries are giving attention on maintaining high efficiency and high performance over a wide range of load. The figure below shows the graph of efficiency for a transformer-less UPS system. From the graph, the efficiency of the transformer-less UPS is reduced for more than 1.5 percent. This makes the transformer-less UPS system more efficient and effective..

33 Figure 2.7 Efficiency versus load of a transformer-less UPS 17

34 CHAPTER 3 METHODOLOGY 3.1 Introduction This chapter presents the configuration and the fundamental of a transformerless uninterruptible power supply. This chapter will go through the basics of the flow of the project in designing the hardware for both converters. Furthermore, this chapter also focuses on the configuration of DC to DC and DC to AC and the operations of circuits. 3.2 Method Used DC to DC Converter Step Down (Buck Converter) The output voltage is lower than the input voltage and of the same polarity. This is a switched-mode power supply that uses two switches (a transistor and a diode) [11]..

35 19 Figure 3.1 Basic buck converter circuits The operation mode of this converter is simple. Energy in the inductor will increase when the switch is closed and decrease when the switch is open. The inductor is used to transfer energy from input to output of the converter. This converter is very potential to over voltage the output if the switch shorts. Besides that, this converter also requires high side switch drive and has high input ripple current Step Up (Boost Converter) The output voltage is higher than the input voltage. This converter is built up with a diode, transistor and a energy storage element which is an inductor. Figure 3.2 Basic boost converter circuits The operation of this boost converter is first during the on state, the switch is closed. During this time the inductor current is increased and during the off state, the `

36 20 switch is open. So when the switch is open, the current from inductor will go through the diode and to the capacitor and the load [11]. This is where the energy stored in the inductor will be transfered into the capacitor SEPIC (Single-Ended Primary Inductor Converter) Figure 3.3 Basic SEPIC converter circuits SEPIC is a type of DC to DC converter that allows the voltage at its output to be greater than, less than, or equal to its input voltage. Duty cycle is used to control the output from the transistor. The advantage of this converter is that the output voltage is same polarity as the input voltage. The disadvantage of this converter is that it has pulsating output current Buck- Boost Converter This type of converter has an output voltage magnitude that is either less than or greater than the input voltage. `

37 21 Figure 3.4 Basic buck-boost converter circuits Based on the duty cycle, the output voltage can be adjusted with a switching transistor. The disadvantage of this circuit is that the switch is not directly connected to the ground, so it will have problem at the switching part. From all of the different methods of DC to DC converter, the best method that has to be chosen is the boost converter. This is because the need of a converter to step up the DC voltage from a battery and not to step down. Besides that, this method is simple, low cost and has the ability to achieve up conversion efficiently. Furthermore, the other two converters which is the SEPIC and the buck-boost converter is complex and the function for step down is not needed. Moreover, both the SEPIC converter and the buck- boost converter have a pulsating output current and do not have any real impact on the efficiency of the converter. 3.3 DC to DC Converter A boost converter is a power converter which converts the input voltage to a higher voltage. It is a switching-mode power supply consists of at least two semiconductor switches which are a diode and a transistor and at least one energy storage element [12].This DC to DC converter is needed to boost or step up the battery voltage from 9v dc to 300v dc. Boost circuit not only functions as regulation `

38 22 of DC voltage (switching power supply) but also checks effectively harmonic wave noise of electric power network. A boost converter operates in two modes which are in continuous mode and discontinuous mode [13] Continuous Mode During the continuous mode, the current through the inductor never falls to zero. When in On-state, the switch S is closed, which makes the input voltage (Vi) appear across the inductor. This will cause the current (IL) flowing through the inductor change with time period (t). This state is also known as charging state of the inductor as shown in figure 3.5. When in the Off-state, the switch S is open, so the inductor current flows through the load. At this mode the inductor is discharging its energy to the load as shown in figure 3.6. Figure 3.5 Switch is closed Figure 3.6 Switch is opened `

39 Discontinuous Mode In the discontinuous mode, the energy needed by the load is very small enough to be transferred in a smaller time. For this case, the current through the inductor falls to zero at some part of time. The only change with the continuous mode mentioned earlier is that the inductor is completely discharged at the end of the cycle. 3.4 DC to AC Converter A DC to AC converter is also known as inverter. It is an electrical device that converts direct current to alternating current. Basically, an inverter operates in the opposite way from the rectifier. A basic inverter circuit is consisting of 4 transistors, an inductor and a capacitor as the filtering function. The operation of the inverter is very simple, when transistor Q1 and Q3 on, transistor Q2 and Q4 will in off state. So this will produce the alternating current at positive cycle and the other way round [11, 12]. Therefore, these continuous alternating cycles of positive cycle and negative cycle will finally produce a AC voltage at the output. Figure 3.7 Schematic diagram of an inverter `

40 Project Flow The figure below shows the project flow and the method used to run this project. Start Preliminary studies Circuit Design and Simulation Device development Testing the device performance Success? YES NO Device Modification End Figure 3.8 Project flow The method that will be used in this project is, firstly by doing some research on the different types of technique used in the transformer-less boost converter. Then choose the best technique based on the suitable configuration for this project by looking at the advantages and disadvantages. Next this technique will be simulated using PSPICE simulation. PSPICE is a SPICE analog circuit and digital logic simulation program for Microsoft Windows. `

41 25 The next step is to design the hardware part for the DC to DC converter. The hardware will be build both on the strip board and printed circuit board. After that the circuit will be tested and troubleshoot the circuit if any problem occurs. Finally, the circuit will be modified and improved if it requires. `

42 26 CHAPTER 4 DEVELOPMENT PROCESS 4.1 Introduction The development process of this project will be discussed in this chapter. The main part of this project is DC to DC converter (boost converter). This project consists of three main approaches of development process and that are design, simulate and construct. Figure 4.1 shows the flow of process in this project. Table 4.1 shows the parameters involved in the development of DC to DC converter (boost type). Further calculations on the design parameters will be shown in the design specification. Designing of boost converter Simulation of boost converter Constructing of boost converter Figure 4.1 The flow of the development process

43 27 Table 4.1: Parameter involved in designing the boost converter Parameter Value Unit Input voltage 9 V Switching frequency 3200 Hertz Duty cycle 97 % Inductor 2.2m Henry The inductor current 0.11 Ampere Input capacitor 47u Farad Output capacitor 33u Farad The table above shows the parameter value involved for designing the boost converter. The parameter was studied and researched from an international conference paper on DC to DC boost converter design for solar electric system [13]. 4.2 Design Specification The main concern of this circuit is to step up the voltage. So the main element focused here is the voltage level at the output. The boost converter is controlled by the 555 timer. The probe is used to measure the output result of the boost converter. There were few assumptions made in this simulation as stated below: i) The circuit is operating in steady state. ii) The inductor current is continuous (always positive). iii) The capacitor is very large and the output voltage is held constant at voltage Vo.

44 28 iv) The components are ideal Inductor Selection Figure 4.2 Picture of 2.2mH inductor The higher the maximum output current, the higher the inductor value because of the reduced ripple current. So, when the inductor value is small, the size of the circuit design also becomes smaller. If the inductor ripple current is high, then the peak current for the inductor will increase and this will cause the saturation of the inductor to be greater. So the value below is the optimum value chosen based on the datasheet. Below is the equation to find the value of an inductor: Vin = typical input voltage. Vout = desired output voltage. Fs = minimum switching frequency of the converter.

45 29 ΔIl = estimated inductor ripple current. The estimation for the inductor ripple current is 20% to 40% of the output current. The inductor ripple current is chosen to be 0.37 based on the research on the master thesis paper on full bridge boost converter [14]. ΔIl = estimated inductor ripple current. Iout(max) = maximum output current necessary Diode Selection Figure 4.3 Picture of 1N4002 diode There are various types of diodes. Among them, Schottky diodes were found to be having least energy losses. The DC blocking voltage must be greater or at least

46 30 equal output voltage. The main idea of using the diode is to allow the current to flow in one direction. The peak current rating for schottky diodes is much higher than the average current rating. A higher peak current is not a problem in the system Input Capacitor Selection Figure 4.4 Picture of 47uF capacitor This input capacitor is necessary to stabilize the input voltage due to the peak current requirement of a switching power supply. The best material is to use low equivalent series resistance (ESR) ceramic capacitors. Otherwise, the capacitor cane lose much of its capacitance due to DC bias or temperature. The value of the input capacitor can be increased if the input voltage is noisy Output Capacitor Selection Figure 4.5 Picture of 33uF, 250v capacitor Output capacitor is used to minimize the ripple on the output voltage. Besides that the voltage rating of the output capacitor is also very important as it is the

47 31 amount of charge the capacitor can keep. Basically, the output of the boost converter is depending on the output capacitor with the help of the inductor. The following equations can be used to adjust the output capacitor values for a desired output voltage ripple [15]: Cout(min) = minimum output capacitance Iout(max) = maximum output current of the application D = duty cycle Fs = minimum switching frequency of the converter ΔVout = desired output voltage ripple Power Switches Selection Figure 4.6 Picture of power MOSFET Several parameters are needed to be considered when selecting a power MOSFET. The input voltage should be lower than the drain-source breakdown. RDS

48 32 (ON) value will determine conduction losses and must low enough to keep junction temperatures within specifications at the maximum drain current condition. The thermal resistance rating will determine heat sink. Finally, the voltage rating of the MOSFET must be higher than the maximum output voltage The 555 Timer Selection Figure 4.7 Picture of 555 timer The 555 timer is the pulse generator for the boost converter. It provides a PWM (pulse width modulation) to the power MOSFET to switch it on and off. The idea here is that the more time the switch is in on state, the more time the current will go through the inductor and the more energy will be stored in the inductor. So the equation for duty cycle is: t DC T HIGH 100% Duty cycle is the amount of time the pulse width modulation is in high state. Since, we need the pulse width modulation to be on high state most of the time so we choose a 97% duty cycle. Based on the duty cycle, the value of resistors, period and frequency can be calculated from the equation below: t t HIGH LOW T t HIGH t R R B LOW A C R B C

49 33 F F 1 T R A 2R B C The figure below shows the pulse width modulation of the 555 timer. From the signal waveform, the on time and the off time of the pulse width modulation can be estimated as well as the duty cycle which is the amount of time the pulse width modulation in on state. on duration duty cycle = 97% off duration Figure 4.8 The pulse width modulation of the 555 timer Based on the design specification and the desired parameters, the expected output voltage can be calculated. The formula for output voltage is given below.

50 Simulation Process The circuit designed is simulated in PSPICE software. The software simulation of the boost converter is basically consisting of three parts. The first part is the basic conventional boost converter. From the simulation of this boost converter, the maximum output achieved is only 100v. This is due the limited number of storage element which is the inductor. So, the problem faced here is how to increase the voltage. Based on studies and researches, interleaving technique is used on the boost converter [12]. The idea of this technique is to make the single stage boost converter interleaved each other which means connecting the circuit in parallel with each other. This is the second part of the simulation. From the simulation, the output increased slightly to 175v. Although the output voltage increase slightly compare to the first stage, it is still not sufficient enough to supply the load. Finally, the third part of this simulation is to cascade the interleaved boost converter in series to accomplish the objective. Previously the research was done on positive output cascade boost converter [16]. So, in order to sort the converters differently from existing boost converter, there are several subseries shown below [16]. Based on the simulation result, the voltage conversion was successful and the output voltage increased significantly compared to the previous technique. The simulation results will be discussed in the next chapter. Generally, the objective of this project is achieved. There are several subseries of cascaded boost converter [16] : i) Main series Each circuit of the main series has one switch S, n inductors, n capacitors and (2n-1) diodes. ii) Additional series Each circuit of the additional series has one switch S, n inductors, (n+2) capacitor and (2n+1) diodes. iii) Double series Each circuit of the double series has one switch S, n inductors, 3n capacitors and (3n-1) diodes.

51 35 iv) Triple series Each circuit of the triple series has one switch S, n inductors, 5n capacitors and (5n-1) diodes. v) Multiple series Each multiple series circuit has one switch S and a higher number of capacitors and diodes. 4.4 Hardware Development The final part of this process is developing the hardware of the designed circuit. In developing and constructing process, the practical circuit that shown in Figure 4.9 is developed and constructed. Figure 4.9 The circuit diagram of cascaded interleaved boost converter The hardware for the cascaded interleaved boost converter was constructed in two parts. The first part is the construction of the circuit on strip board and followed by printed circuit board. Both construction of the circuit was developed successfully and tested. Further discussion will be discussed in the next chapter.

52 36 CHAPTER 5 RESULTS AND DISCUSSION 5.1 Introduction The transformer-less Dc to Dc converter was designed using PSPICE software. There are several techniques used for the implementation of the boost converter. Both the software simulation and hardware implementation will be discussed in this chapter. 5.2 Simulation and Technique Used for the DC to DC Converter Simulation of Single Stage Boost Converter The Figure 5.1 shows the designed simulation of single stage boost converter. The simulation was run for 10 seconds using the PSPICE software.

53 37 Figure 5.1 The circuit diagram of single stage boost converter Figure 5.2 shows the resulting outcome of the single stage boost converter from the PSPICE simulation. Based on the output result, it is clearly shows that the output is highly stepped up which is 100v DC from the 9v DC input voltage with the corresponding pulse width modulation. Output = 100v DC Input = 9v DC PWM Figure 5.2 The output simulation of the single stage boost converter

54 38 The basic operating principal of the boost converter is: i. The switch is turned on and the current will flow through the inductor and the energy is stored. ii. The switch is turned off and the energy stored in the inductor will be collapsed and transferred to the output capacitor. So the output capacitor will be charged and produces the output voltage higher than the input voltage. This can be written as: The equation above shows the input and output relation of the boost converter. From the equation above, the duty cycle of the boost converter can be calculated with the following equation: From the above equation, the output voltage is always higher than the input voltage as the duty cycle goes from 0 to 1and that it increases with D, theoretically to infinity as D approaches 1. This is the reason why this converter is called a step up converter.

55 Simulation of Interleaved Boost Converter The figure 5.3 shows the designed simulation of interleaved boost converter. The simulation was run for 20 seconds using the PSPICE software. Figure 5.3 The circuit diagram of interleaved boost converter Figure 5.4 shows the resulting outcome of the interleaved boost converter from the PSPICE simulation. Based on the output result, it is clearly shows that the output is highly stepped up which is 175v dc from the 9v dc input voltage with the corresponding pulse width modulation.

56 40 Output = 175v DC Input = 9v DC PWM Figure 5.4 The output simulation of the interleaved boost converter The interleaved technique is used in this circuit is basically to increase the energy storage element which eventually will contribute to a higher output voltage. The operation of the circuit is when M1 turns on, current is interleaved in L2 with a slope depending on the input voltage, storing energy in L2. Once M1 turns off, it will deliver part of its stored energy to the output capacitor. Current in L2 goes down with a slope depending on the difference between the input and output voltage. At the same time, M2 and M3 also turn on since the power from interleaving part and the single stage part are combined at the output capacitor. This in turns provide a high output voltage.

57 Simulation of Cascaded Interleaved Boost Converter The figure 5.5 shows the designed simulation of cascaded interleaved boost converter. The simulation was run for 30 seconds using the PSPICE software. Figure 5.5 The circuit diagram of cascaded interleaved boost converter Figure 5.6 shows the resulting outcome of the cascaded interleaved boost converter from the PSPICE simulation. Based on the output result, it shows that the output is highly increased which is 325v dc from the 9v dc input voltage with the corresponding pulse width modulation. Second Second stage output stage output = 325v = DC 325v dc First stage output = 165v DC Input = 9v DC PWM Figure 5.6 The output simulation of the cascaded interleaved boost converter

58 42 The cascaded interleaved technique is used in this circuit to improve the output voltage of the converter. The operation of this circuit is same as the previous interleaved technique. This is because this cascading technique basically uses two circuits of the previous interleaved technique and cascaded each other. So by cascading each other we will have 2 stages of output. The idea here is that the output voltage from the first stage will be transferred to the second stage and thus it will boost to higher voltage compare to the first stage. The capacitor used in this technique is has the voltage rating of 300v DC. This capacitor is the main cause providing the output voltage. So if the voltage rating of the capacitor is small, the output voltage becomes smaller and vice versa. This is because the higher the voltage rating of the capacitor, the more energy it can store and thus providing a higher output voltage. 5.3 Hardware Result of The Cascaded Interleaved Boost Converter The Figure 5.6 shows the hardware diagram of the cascaded interleaved boost converter implemented on strip board. First stage Second stage 555 timer control circuit Figure 5.6 The picture of cascaded interleaved boost converter on strip board.

59 43 The Figure 5.7 shows the hardware diagram of the cascaded interleaved boost converter implemented on PCB board. Figure 5.7 The picture of cascaded interleaved boost converter on PCB board. The Figure 5.8 shows the corresponding output from the hardware implementation. The output from the hardware is measured using digital multimeter. Figure 5.8 The picture of output result from the multimeter reading.

60 44 The Input power supply is 9v dc from a single battery. This 9v dc was passed through the first stage of the circuit. Then the output from the first stage will then be transferred to the second stage of the circuit to provide a 237v dc at the output. The circuit was controlled by a single 555 timer which produced pulse width modulation to all the power MOSFETS simultaneously. 5.4 Discussions The cascaded interleaved boost converter was simulated using PSPICE simulation software and it was implemented in small scale hardware. The simulation was divided into three stages. The first part of the simulation was a single stage boost converter. The second part of the simulation is the interleaved boost converter and the final part of the simulation is the cascaded interleaved boost converter. The theory was proven that the dc voltage was stepped up from a lower voltage to a higher voltage using an inductor as an energy storage with the appropriate duty cycle. The output voltage for all three simulation reached steady state very fast which is at three milliseconds. A PWM technique was used to control the power MOSFETS and based on calculation the values of resistors for the 555 timer were found to compensate at 97% duty cycle. To prove the simulation a small scale of hardware was build. The hardware was implemented using the cascaded interleaved boost technique. The hardware delivers a continuous output voltage of 237v dc from a 9v dc at a small period of time and it will gradually drop since the input power supply is limited due to the usage of a small battery. Besides that, the output voltage difference between the simulation and the hardware is comparable because in hardware implementation there are small amount of power loss in the power MOSFETS and other critical components.

61 45 The table below shows the comparisons of output voltage between the simulation and hardware implementation. Based on the result shown below the simulation result and hardware result is comparable. As we can see in the first stage result both the software and hardware achieved the same result. In the second stage the hardware result reduced by 8% compare to the simulation result and finally in third stage the hardware result reduced to 27% compare to the simulation result. This is because in simulation the 9v DC input supply is ideal, which means the current is constant. On the other hand, in hardware implementation, the 9v DC supply from battery will consume energy gradually and the current is limited. Besides that, the amount of power loss is also depends on the amount of electronic component used in the circuit. This is why in the third stage, the difference between simulation result and hardware result is higher than the other two stages. Table 5.1: Simulation result versus hardware result Stage Input voltage Simulation result Hardware result 1 9v 100v 100v 2 9v 175v 160v 3. 9v 325v 237v The DC to DC converter (boost type) was successfully developed and constructed. The project is able to convert 9v dc to approximately 237v dc. Although the output current is very low, it is still applicable in small applications especially in medical lab instruments.

62 CHAPTER 6 CONCLUSION AND RECOMMENDATIONS 6.1 Conclusion As a conclusion, the objectives of this project were achieved. From this project, I have understood what UPS system is and how the UPS system functioning and providing emergency power to the load. Besides that, a complete PSPICE simulation for the boost converter using different techniques was simulated stage by stage and the simulation result was the same as the theory. Furthermore, since the scope of the project is focused on simulation and development of a boost converter, I have learned various techniques used in boost converter for high voltage conversion by using basic electronic components. Besides that, the hardware of the cascaded interleaved boost converter was successfully build and was able to provide high voltage conversion. In addition, there is also a major concern on the efficiency of the UPS system design. A conventional UPS system is not very efficient because most of the power is used by the transformer and also produces more heat. So by removing the transformer in a UPS system, a more efficient design will be produced with less heat, since energy efficiency and conservation of energy is an important issue now a day.

63 Recommendations There are few recommendations to further improve the cascaded interleaved boost converter used in the transformer-less UPS system in the future as stated below: 1) Design and develop a battery rechargeable control circuit to monitor and control the state of the battery. This is to make sure the battery was fully charged and overcharged which will damage the battery. So, the battery rechargeable control circuit can be build based on the capacity of the battery. 2) Develop and improve the cascaded interleaved boost converter to produce high power to be used in bigger applications. By using boost technique, there is only one variable can be changed at one time. Since the project focuses on high voltage conversion, the current is very small and limited. 3) Design and build a full bridge inverter using PWM switching method. The hardware of full bridge inverter can be build using a suitable PWM IC (integrated circuit). Building an inverter circuit using PWM IC is cheaper than buying an inverter circuit. 4) Replace 555 timer with a microcontroller so that the output voltage can be made more flexible 5) Instead of using a single cell battery, the design can be implemented using a higher current power source such as a switching power supply or a car battery.

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66 50 APPENDIX A LAYOUT OF CASCADED INTERLEAVED BOOST CONVERTER ON PRINTED CIRCUIT BOARD

67 51 Figure 1 Layout design of cascaded interleaved boost converter Table 1 component parameters used in the design Parameter Inductor Input capacitor Output capacitor Diode Resistor MOSFET Value 2.2mH, 4.4mH 47uF, 16v 33uF, 300v 1N4004 1K ohm IRF610