Dissertations / Theses on the topic 'Current width'

The concept of soft-switching pulse-width-modulated (PWM) technique was proposed aimed at combining the advantages of both the conventional PWM technique and the resonant technique. This work presents four new families of soft-switching PWM converters: the zero-voltage-switched (ZVS) PWM converters, the zero-current-switched (ZCS) PWM converters, the zerovoltage- transition (ZVT) PWM converters, and the zero-current-transition (ZCT) PWM converters. The family of ZVS- and ZCS-PWM converters are developed to improve the performance of the ZVS and ZCS quasi-resonant converters, respectively. The principles of operations of these two families of converters are presented, and the merits and limitations are assessed. A number of experimental converters are breadboarded to verify the theoretical analysis. Both the ZVT-PWM and ZCT-PWM techniques use the concept of shunt resonant network to achieve soft-switching. In this way, the new converters achieve soft-switching without increasing the voltage and current stresses of the power switches and diodes. By using the boost topology as an example, a complete dc analysis of the ZVT-PWM and ZCT-PWM converters is presented, and the dc Voltage-conversion ratio characteristics are derived. Design trade-offs are examined, and design procedures are established. The theoretical analysis and novel features of the proposed converters are verified on a number of breadboarded converters. Finally, the typical small-signal characteristics of the ZVT -PWM converters are analyzed and verified experimentally by using the boost converter as an example.
Ph. D.

In marine environments and where de-icing salts are applied, the degradation of reinforced concrete structures due to chloride induced corrosion of the reinforcement is a major problem. The expansive nature of the corrosion process results in cracking of the concrete and eventually spalling. In order to select suitable remedial measures it is necessary to make an assessment of the residual strength and the residual life. In order to investigate the effect of corrosion on bond strength of the reinforcement, specimens comprising square prismatic sections containing steel reinforcement in the four corners have been subjected to a wet-dry cycle and corrosion has been accelerated by polarising the bars. The research has studied the change of bond strength with level of corrosion for 12 mm and 16 mm bars with concrete cover of 1 and 3 times the bar size. The bond strength is assessed by means of pull out tests and the corresponding extent of corrosion has been assessed in terms of the mass loss. Observations and measurements of the form of the corrosion (pit dimensions and loss of bar diameter) are also presented. The relationship between bond strength and surface crack width has been investigated. Results show that the surface crack width may be a good indicator of residual bond strength. In addition, the influence on bond strength of concrete compressive strength, reinforcement cover, bar position and bar size on the change of bond strength has been explored. It should be noted that all conclusions drawn in this project are based on tests on specimens without shear reinforcement (unconfined) and that accelerated corrosion (by impressed current) has been adopted. Consequently, care should be exercised in applying these results directly to structures in the field. Additional research is needed to assess the influence of impressed current on crack patterns and the effect of shear reinforcement.

This research work is devoted to the analysis, design and development of the Current-Source Converter (CSC) based distribution-type Static Synchronous Compensator (D-STATCOM) for low-voltage applications in reactive-power control in order to achieve i) faster transient response in reactive-power control, ii) lower current harmonic distortion, iii) lower power losses and iv) minimum storage elements in comparison with conventional solutions. The developed CSC-D-STATCOM includes a low-pass input filter and a three phase forced-commutated CSC which is composed of six insulated gate bipolar transistors (IGBT) with built-in series diodes. The analysis and the control of the CSC-D-STATCOM are carried out in dq-synchronous reference frame in order to obtain the reference current waveform which is to be generated by switching the IGBTs at 3kHz with the use of space vector modulation.

This thesis aims to design and build a power electronics system for the rectification and control of magnetization currents in synchronous generators with rotating exciters.The rotating exciter provides three-phase AC while the generator rotor needs DC with a high degree of control. The system needs to be able to rectify the three-phase AC to a stable DC without unwanted harmonic content, neither on the DC or the AC side. For control purposes it is also important that the current in the rotor can be changed very swiftly, preferably by several amperes during a single revolution ofthe machine.The system of choice is a synchronous rectifier bridge consisting of six MOSFET switches operated using the Space vector pulse width modulation (SVPWM) algorithm. This method gives a stable and controllable DC voltage while it keeps the harmonic content of the input currents at a minimum. However the DC voltage will always be higher than the peak line-to-line voltage from the exciter. To be able to lower the voltage below this value a Buck-converter is placed after the rectifier bridge.To gain a higher degree of control of the current density in the rotor windings the windings have been subdivided into three parts. To provide individual control of the current in the three rotor parts each part have been outfitted with a Push and Pull H-bridge.The proposed system has been both simulated using MATLAB Simulink and built and tested in the laboratory with satisfactory results.
I detta examensarbete presenteras ett kraftelektroniksystem för förbättrad kontroll av magnetiseringsstömmar i vattenkraftsgeneratorer som är utrustade med roterande matare.Generatorer används för att konvertera energi från rörelseenergi till elektrisk energi. Detta görs genom att man utsätter spolar för varierande magnetfält; då induceras spänning i spolarna. I vattenkraftsgeneratorer används oftast stora elektromagneter placerade i en rotor för att skapa dessa magnetfält. För att magnetisera elektromagneterna behövs ström som på något sätt måste överföras mellan den statiska och den roterande sidan i generatorn. Traditionellt görs detta med hjälp av släpringar och kolborstar som genom mekanisk kontakt överför elektriciteten. En roterande matare kan beskrivas som en liten generator som har sina elektriska utgångar på den roterande sidan istället för på den statiska sidan. Genom att placera en roterande matare på samma axel som den stora generatorn kan man istället alstra den elektricitet som behövs för att magnetisera generatorn direkt på den roterande sidan. Däregenom undviks många problem som är associerade med lösningen med släpringar.Den roterande mataren ger dock växelström medan magnetiseringsströmmen måste vara likström. Det är här kraftelektroniken kommer in i bilden. Det finns flera sätt att åstadkomma likriktning av ström. I det här projektet har ett fullständigt aktivt system byggts. Systemet är uppbyggt av transistorer av MOSFET typ och kan kontrolleras trådlöst med hjälp av Bluetoothteknik. Systemet ger full kontroll över strömmar och spänningar både på växelströmssidan och på likströmssidan och ska användas till en testgenerator på avdelningen för ellära vid Uppsala Universitet. Där ska den utökade kontroll som systemet ger förutsättningar till användas för att undersöka hur den här typen av system kan optimera de magnetiska krafterna inuti generatorn. En sådan optimering kan minska vibrationerna i generatorn och därigenom minska slitaget på lager och andra delar i maskinen.

This research work is devoted to the design, development and implementation of a Current Source Converter (CSC) based Active Power Filter (APF) for Medium Voltage (MV) applications. A new approach has been proposed to the design of the CSC based APF for reducing the converter kVA rating considerably. This design approach is called the Selective Harmonic Amplification Method (SHAM), and is based on the amplification of some selected harmoniccurrent components of the CSC by the input filter, and the CSC control system, which is specifically designed for this purpose. The proposed SHAM has been implemented on the first industrial CSC based APF for the elimination of 11th and 13th current harmonics of 12-pulse rectifiers fed from Medium Voltage (MV) underground cables in order to comply with IEEE Std. 519-1992. 450 kVA rated APF with only 205 kVA CSC rating has been connected to the MV bus via a coupling transformer of 600kVA, 34.5/1.1 kV. The power stage of the CSC based APF is composed of water-cooled high voltage IGBT and diode modules. Reference currents to be generated by the CSC are obtained by the use of a selective harmonic extraction method, by mploying synchronously rotating reference frames for each selected harmonic component. An Active damping method is also used to suppress the oscillations around the natural frequency of the input filter, excluding the harmonic components to be eliminated by APF. Simulation and field test results have shown that SHAM can successfully be applied to a CSC based APF for reduction of converter kVA rating, thus making it a cost- competitive alternative to voltage source converter based APFs traditionally used in industry applications.

AC/DC adapters mostly employ two-stage topology: Power Factor Correction (PFC) pre-regulation stage followed by an isolated DC/DC converter stage. Low power AC/DC adapters require a small size to be competitive. Among their components, the bulk DC-link capacitor is one of the largest because it should keep the output voltage with low ripple. Also, the size of this capacitor is penalized due to the universal line voltage application. Synchronization through employing leading edge modulation for the first PFC stage and trailing edge modulation for the second DC/DC converter stage can significantly reduce the ripple current and ripple voltage of the DC-link capacitor. Thus, a smaller DC-link capacitance can be used, lowering the cost and size of the AC/DC adapter. Benefits of the synchronous switching scheme were already demonstrated experimentally. However, no mathematical analysis was presented. In this thesis, detailed mathematical analyses in per-unit quantity are given to facilitate the calculation of the DC-link capacitor ripple current reduction with Leading/Trailing Edge Modulation strategies. One of the limitations of leading/trailing edge modulation is that the switching frequencies of the two stages need to be equal to achieve the best reduction of the DC-link capacitor ripple current. The DC-link capacitor ripple current will become larger if the switching frequency of the DC/DC converter is larger than that of the PFC pre-regulator, which blocks us to employ higher frequency for isolated DC/DC converter to reduce its transformer size. This thesis proposed a new Leading/Trailing Edge Modulation strategy to further reduce the DC-link bulk capacitor ripple current when switching frequency of DC/DC converter stage is twice the switching frequency of PFC stage. This proposed pulse width modulation scheme was verified by simulation. Experimental results obtained through digital control based on FPGA are also presented in this thesis.

The aim of the Master´s thesis is proposing and implementation of computer controlled optical radiation source. The theoretical part describes the photometric, the radiometric quantities, applied components such as LED, the microcontroller and possible methods for the LED brightness control. The development of the device is described from the selection of the individual LEDs to the end of the device assembling and programing. On the several LEDs were made properties measurement. A circuit with microcontroller was designed and then was fabricated. The device was programmed for communication and control from the PC. The entire electronic is fitted in the metal frame of the construction box and finally the device functionality is tested.

A voltage source inverter is commonly used to supply a variable frequency variable voltage to a three phase induction motor in a variable speed application. A suitable pulse width modulation (PWM) technique is employed to obtain the required output voltage in the line side of the inverter. Real-time methods for PWM generation can be broadly classified into triangle comparison based PWM (TCPWM) and space vector based PWM (SVPWM). In TCPWM methods such as sine-triangle PWM, three phase reference modulating signals are compared against a common triangular carrier to generate the PWM signals for the three phases. In SVPWM methods, a revolving reference voltage vector is provided as voltage reference instead of three phase modulating waves. The magnitude and frequency of the fundamental component in the line side are controlled by the magnitude and frequency, respectively, of the reference vector. The fundamental line side voltage is proportional to the reference magnitude during linear modulation. With sine-triangle PWM, the highest possible peak phase fundamental voltage is 0.5Vdc, where Vdc is the DC bus voltage, in the linear modulation zone. With techniques such as third harmonic injection PWM and space vector based PWM, the peak phase fundamental voltage can be as high as (formula) (i.e., 0:577Vdc)during linear modulation. To increase the line side voltage further, the operation of the VSI must be extended into the overmodulation region. The overmodulation region extends upto the six-step mode, which gives the highest possible ac voltage for a given (formula). In TCPWM based methods, increasing the reference magnitude beyond a certain level leads to pulse dropping, and gradually leads to six-step operation. However, in SVPWM methods, an overmodulation algorithm is required for controlling the line-side voltage during overmodulation and to achieve a smooth transition from PWM to six-step mode. Numerous overmodulation algorithms have been proposed in the literature for space vector modulated inverter. A well known algorithm among these divides the overmodulation zone into two zones, namely zone-I and zone-II. This is termed as the 'existing overmodulation algorithm' here. This algorithm is modified in the present work to reduce computational burden without much increase in the line current distortion. During overmodulation, the fundamental line side voltage and the reference magnitude are not proportional, which is undesirable from the control point of view. The present work ensures a linear relationship between the two. Apart from the fundamental component, the inverter output voltage mainly consists of harmonic components at high frequencies (around switching frequency and the integral multiples) during linear modulation. However, during overmodulation, low order harmonic components such as 5th, 7th, 11th, 13th etc., are also present in the output voltage. These low order harmonic voltages lead to low order harmonic currents in the motor. The sum of the lower order harmonic currents is termed as 'lower order current ripple'. The present thesis proposes a method for estimation of lower order current ripple in real-time. In closed loop current control, the motor current is fed back to the current controller. During overmodulation, the motor current contains low order harmonics, which appear in the current error fed to the controller. These harmonic currents are amplified by the current error amplifier deteriorating the performance of the drive. It is possible to filter the lower order harmonic currents before being fed back. However, filtering introduces delay in the current loop, and reduces the bandwidth even during linear modulation. In the present work, the estimated lower order current ripple is subtracted from the measured current before the latter is fed back to the controller. The estimation of lower order current ripple and the proposed current control are verified through simulation using MATLAB/SIMULINK and also experimentally on a laboratory prototype. The experimental setup comprises of a field programmable gate arrays (FPGA) based digital controller, an IGBT based inverter and a four-pole squirrel cage induction motor. (Pl refer the original document for formula)

In recent years, multilevel converters are becoming more popular and attractive than traditional converters in high voltage and high power applications. Multilevel converters are particularly suitable for harmonic reduction in high power applications where semiconductor devices are not able to operate at high switching frequencies or in high voltage applications where multilevel converters reduce the need to connect devices in series to achieve high switch voltage ratings. This thesis investigated two aspects of multilevel converters: structure and control. The first part of this thesis focuses on inductance between a DC supply and inverter components in order to minimise loop inductance, which causes overvoltages and stored energy losses during switching. Three dimensional finite element simulations and experimental tests have been carried out for all sections to verify theoretical developments. The major contributions of this section of the thesis are as follows: The use of a large area thin conductor sheet with a rectangular cross section separated by dielectric sheets (planar busbar) instead of circular cross section wires, contributes to a reduction of the stray inductance. A number of approximate equations exist for calculating the inductance of a rectangular conductor but an assumption was made that the current density was uniform throughout the conductors. This assumption is not valid for an inverter with a point injection of current. A mathematical analysis of a planar bus bar has been performed at low and high frequencies and the inductance and the resistance values between the two points of the planar busbar have been determined. A new physical structure for a voltage source inverter with symmetrical planar bus bar structure called Reduced Layer Planar Bus bar, is proposed in this thesis based on the current point injection theory. This new type of planar busbar minimises the variation in stray inductance for different switching states. The reduced layer planar busbar is a new innovation in planar busbars for high power inverters with minimum separation between busbars, optimum stray inductance and improved thermal performances. This type of the planar busbar is suitable for high power inverters, where the voltage source is supported by several capacitors in parallel in order to provide a low ripple DC voltage during operation. A two layer planar busbar with different materials has been analysed theoretically in order to determine the resistance of bus bars during switching. Increasing the resistance of the planar busbar can gain a damping ratio between stray inductance and capacitance and affects the performance of current loop during switching. The aim of this section is to increase the resistance of the planar bus bar at high frequencies (during switching) and without significantly increasing the planar busbar resistance at low frequency (50 Hz) using the skin effect. This contribution shows a novel structure of busbar suitable for high power applications where high resistance is required at switching times. In multilevel converters there are different loop inductances between busbars and power switches associated with different switching states. The aim of this research is to consider all combinations of the switching states for each multilevel converter topology and identify the loop inductance for each switching state. Results show that the physical layout of the busbars is very important for minimisation of the loop inductance at each switch state. Novel symmetrical busbar structures are proposed for multilevel converters with diode-clamp and flying-capacitor topologies which minimise the worst case in stray inductance for different switching states. Overshoot voltages and thermal problems are considered for each topology to optimise the planar busbar structure. In the second part of the thesis, closed loop current techniques have been investigated for single and three phase multilevel converters. The aims of this section are to investigate and propose suitable current controllers such as hysteresis and predictive techniques for multilevel converters with low harmonic distortion and switching losses. This section of the thesis can be classified into three parts as follows: An optimum space vector modulation technique for a three-phase voltage source inverter based on a minimum-loss strategy is proposed. One of the degrees of freedom for optimisation of the space vector modulation is the selection of the zero vectors in the switching sequence. This new method improves switching transitions per cycle for a given level of distortion as the zero vector does not alternate between each sector. The harmonic spectrum and weighted total harmonic distortion for these strategies are compared and results show up to 7% weighted total harmonic distortion improvement over the previous minimum-loss strategy. The concept of SVM technique is a very convenient representation of a set of three-phase voltages or currents used for current control techniques. A new hysteresis current control technique for a single-phase multilevel converter with flying-capacitor topology is developed. This technique is based on magnitude and time errors to optimise the level change of converter output voltage. This method also considers how to improve unbalanced voltages of capacitors using voltage vectors in order to minimise switching losses. Logic controls require handling a large number of switches and a Programmable Logic Device (PLD) is a natural implementation for state transition description. The simulation and experimental results describe and verify the current control technique for the converter. A novel predictive current control technique is proposed for a three-phase multilevel converter, which controls the capacitors' voltage and load current with minimum current ripple and switching losses. The advantage of this contribution is that the technique can be applied to more voltage levels without significantly changing the control circuit. The three-phase five-level inverter with a pure inductive load has been implemented to track three-phase reference currents using analogue circuits and a programmable logic device.

Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Webster, Don; Committee Member: Sturm, Terry; Committee Member: Weissburg, Marc. Part of the SMARTech Electronic Thesis and Dissertation Collection.

This thesis deals with the effect of frequency inverter on the lifetime of roller bearings. The measurement has been carried out on the frequency inverter and induction motor by Siemens in the Switchgear laboratory of Fakulty of elektrical engineering and communication. Data has been recorded and processed on Adash VA4 Pro analyzer. Methods of measuring RMS values and frequency analysis of vibration and current were used for the analysis. Based on the mutual similarity of frequency spectrum, the presence of the high frequency capacitive current in the bearings has been proven. To prevent this, possible solutions have been presented. In the second part of the experiment an effect of changing pulse width modulation (PWM) on vibration was examined. The goal was to make a basic analysis and to provide background material for further research.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.22.09 "Електротранспорт". — АТ "Українська залізниця", філія "Проектно-вишукувальний інститут залізничного транспорту", Харківське відділення, Міністерство інфраструктури України, Національний технічний університет "Харківський політехнічний інститут", МОН України. Харків, 2020. Дисертація присвячена актуальній науково-технічній проблемі підвищення енергетичної ефективності електрорухомого складу змінного струму з колекторними тяговими двигунами за рахунок вдосконалення тягових перетворювачів. Основу парку вантажних та пасажирських електровозів змінного струму "Укрзалізниці" складають електровози з колекторними тяговими двигунами. Такі електровози мають порівняно низький коефіцієнт потужності. Для електровозів з діодними випрямлячами (ВЛ80К, ВЛ80Т) його величина становить 0,65…0,85, а для електровозів з тиристорними перетворювачами (2ЭС5К, 2ЕЛ5) — 0,3…0,84. Сукупність енергетичних недоліків електрорухомого складу і тягового електропостачання обумовлює порівняно низький коефіцієнт потужності електрифікованих залізниць змінного струму — приблизно 0,7, при цьому за сучасними світовими нормами високим вважається коефіцієнт потужності не нижче 0,95. Тому підвищення енергетичної ефективності тягового навантаження є актуальною задачею. На сьогодні вітчизняними та зарубіжними спеціалістами розроблено ряд технічних рішень, які забезпечують підвищення енергетичних характеристик електровозів змінного струму. Ці рішення можна умовно об’єднати в три групи: 1) удосконалені схеми тягових перетворювачів та алгоритми їх управління; 2) пасивні і активні компенсатори реактивної потужності, встановлені на елкетрорухомому складі; 3) перетворювачі на повністю керованих напівпровідникових приладах (активні перетворювачі). Незважаючи на високі енергетичні характеристики активних перетворювачів, робіт, присвячених дослідженню режимів роботи таких перетворювачів при живленні тягових двигунів постійного струму, на сьогодні недостатньо. Отже, подальший розвиток цього напрямку досліджень можна вважати актуальним. Базовою ланкою перетворювача для живлення двигуна постійного струму є однофазний активний випрямляч струму. У роботі отримано математичний опис роботи активного випрямляча струму в режимах випрямлення та інвертування. На основі математичного апарату алгебри логіки розроблено уніфікований опис алгоритмів широтно-імпульсної модуляції з синусоїдальним, трапецеїдальним та прямокутно-ступінчатим модуляційним сигналом. Дослідження електромагнітних процесів і порівняння енергетичних характеристик активного випрямляча струму при обраних алгоритмах ШІМ і частоті модуляції 900 Гц, 1200 Гц і 1800 Гц проведено шляхом імітаційного моделювання в MATLAB. Дослідження показали, що при всіх трьох алгоритмах при коефіцієнті модуляції 0,2…1,0 коефіцієнт потужності на вході активного випрямляча струму складає 0,6…0,99 незалежно від частоти модуляції. Запропоновано силову схему з двозонним регулюванням випрямленої напруги і алгоритм управління активного тягового перетворювача електровоза. Обґрунтовано використання прямокутно-ступінчатої ШІМ з чаостою модуляції 1200 Гц. Регулювання випрямленої напруги з коефіцієнтом модуляції менше 0,5 використовується лише в короткочасних режимах роботи. Розроблено математичну модель системи електричної тяги змінного струму напруги 25 кВ, 50 Гц з урахуванням двох варіантів тягового перетворювача — тиристорного та активного перетворювача з широтно-імпульсною модуляцією. З точки зору моделювання систем управління перетворювачами розроблена модель є універсальною, оскільки на основі логічних функцій формування та розподілу імпульсів розроблено уніфікований математичний опис алгоритмів управління тиристорним та активним тяговим перетворювачем. Ця модель реалізована в програмному пакеті MATLAB. Комп’ютерне моделювання електромагнітних процесів в системі "тягова мережа — електровоз" дозволило дослідити енергетичну ефективність електровоза з активним тяговим перетворювачем. Так, коефіцієнт потужності електровоза становить 0,839…0,991, а його значення більше 0,9 забезпечується при коефіцієнті модуляції більше 0,5. У номінальному режимі коефіцієнт потужності електровоза з активним тяговим перетворювачем на 19,4 % вище, ніж у електровоза з тиристорним перетворювачем. Коефіцієнт спотворення синусоїдальності кривої напруги на струмоприймач і електровоза з активним тяговим перетворювачем KU в усьому діапазоні регулювання змінюється в межах 3…11 %, а коефіцієнт спотворення синусоїдальності кривої струму KI — в межах 9…17 %. При зміні відстані від електровоза до тягової підстанції в діапазоні 0…10 км коефіцієнт спотворення синусоїдальності кривої напруги електровоза в номінальному режимі складає 5…9 %. Проведені експерименти показали, що активний тяговий перетворювач є джерелом широкого спектру гармонік напруги та струму. Найменш вигідним при цьому є режим з коефіцієнтом модуляції 0,5…0,6. Результати гармонічного аналізу дозволили встановити характерні групи гармонік, які в основному визначають несинусоїдальність форми відповідних кривих напруги та струму. Тому подальші дослідження активного тягового перетворювача електровоза повинні враховувати необхідність корекції форми напруги та струму. У цілому, результати проведених досліджень показали, що активний тяговий перетворювач забезпечує більш високі енергетичні характеристики, ніж традиційні випрямлячі на основі діодних і тиристорних схем.
Thesis for candidate degree of technical sciences of speсialty 05.22.09 — Electric transport. Joint-Stock Company “Ukrainian zaliznytsia”, Branch “Design and survey institute of railway transport”, Ministry of Infrastructure of Ukraine, National Technical University “Kharkiv Polytechnic Institute”, MES of Ukraine. Kharkiv, 2020. The dissertation is devoted to the actual scientific and technical problem of increasing the energy efficiency of the AC electric locomotives with DC traction motors due to the improvement of traction converters. The basis of the park of freight and passenger AC electric locomotives of “Ukrzaliznytsya” are electric locomotives with DC traction motors. Such electric locomotives have a relatively low power factor. For electric locomotives with diode rectifiers (VL80K, VL80T) its value is 0.65...0.85, and for electric locomotives with thyristor converters (2ES5K, 2EL5) — 0.3...0.84. The aggregate of the energy defects of the electromotive force and traction power causes a relatively low power factor of the AC electrified railways — about 0.7, while according to modern world standards the power factor is not lower than 0.95. Therefore, increasing the energy efficiency of the traction load is an urgent task. Today, Ukrainian, Russian and foreign specialists have developed a number of technical solutions that provide an increase in the power characteristics of electric locomotives. These solutions can be conventionally grouped into three groups: 1) improved schemes of traction converters and control algorithms; 2) passive and active reactive power compensators installed on the electric locomotives; 3) converters on fully controlled semiconductor devices (active converters). Despite the high energy characteristics of the active converters, investigations of the operation modes of such converters with DC traction motors, today is not enough. Consequently, further development of this research direction can be considered relevant. The base element of the converter for DC motor is a single-phase active current source rectifier. In the paper a mathematical description of the active current source rectifier in the rectifier and inverter modes is obtained. On the basis of the mathematical apparatus of logic algebra, a unified description of pulse-width modulation algorithms with sinusoidal, trapezoidal, and rectangular-step modulation signals is obtained. Investigation of electromagnetic processes and the comparison of the energy characteristics of the active current source rectifier with selected PWM algorithms and modulation frequencies of 900 Hz, 1,200 Hz and 1,800 Hz is carried out by simulation in MATLAB. Studies have shown that for all three algorithms, at a modulation index of 0.2...1.0, the input power factor of the active current source rectifier is 0.6...0.99 regardless of the modulation frequency. The power circuit with two-zone regulation of DC voltage and the control algorithm of the active traction converter of the electric locomotive are proposed. The use of rectangular-stepped PWM with a modulation frequency of 1,200 Hz has been substantiated. The regulation of the DC voltage with a modulation index of less than 0.5 is used only in short-term operating modes. A mathematical model of the AC electric traction system (25 kV, 50 Hz) was developed, taking into account two variants of the traction converter — a thyristor and active converter with pulse-width modulation. From the point of view of modeling of converters control systems, the developed model is universal because on the basis of logic functions of pulse formation and distribution a unified mathematical description of algorithms of thyristor control and active traction converter is developed. This model is implemented in MATLAB. Computer simulation of electromagnetic processes in the “traction network — electric locomotive” system has allowed to investigate the energy efficiency of an electric locomotive with an active traction converter. So, the power factor is 0.839...0.991, and its value is more than 0.9 provided with a modulation index of more than 0.5. In nominal mode, the power factor of an electric locomotive with an active traction converter is 19.4 % higher than that of an electric locomotive with a thyristor converter. The THD of the contact wire voltage of the electric locomotive with the active traction converter in the whole range of regulation varies within the range of 3...11 %, and the THD of the contact wire current is within the range of 9...17 %. When changing the distance from the electric locomotive to the traction substation in the range 0...10 km, the THD of contact wire voltage in nominal mode is 5...9 %. The virtual experiments showed that the active traction converter is the source of a wide spectrum of voltage and current harmonics. The least advantageous is the mode with a modulation index of 0.5...0.6. The results of harmonic analysis allowed to establish characteristic groups of harmonics, which basically determine the nonsinusoidal form of the of voltage and current waveforms. Therefore, in further research works of the active traction converter we must focus on correction of the voltage and current waveforms. In general, the results of the research showed that the active traction converter have higher energy characteristics than traditional rectifiers based on diode and thyristor schemes.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.22.09 — електротранспорт. — АТ "Укрзалізниця", філія "Проектно-вишукувальний інститут залізничного транспорту", Харківське відділення, Міністерство інфраструктури України, Національний технічний університет «Харківський політехнічний інститут», МОН України. Харків, 2020. Одним з ефективних засобів підвищення коефіцієнта потужності електрорухомого складу змінного струму з колекторними тяговими двигунами є акитвні випрямлячі. У дисертації розроблено математичний опис активного випрямляча струму з тяговим двигуном постійного струму, проведено аналіз енергетичної ефективності випрямляча при широтно-імпульсній модуляції з синсуоїдальним, трапецеїдальним та прямокутно-ступінчатим модуляційним сигналом. Запропоновано силову схему активного тягового перетворювача з двозонним регулюванням напруги і алгоритм управління транзисторами в режимах тяги і рекуперації. Результати комп’ютерного моделювання показали, що активний тяговий перетворювач забезпечує високий коефіцієнт потужності електровоза (0,83…0,99) і більш низький рівень несинусоїдальності струму первинної обмотки тягового трансформатора (THDi до 17 %) у порівнянні з тиристорним перетворювачем, що дає змогу скоротити витрати електроенергії на тягу поїздів.
Thesis for candidate degree of technical sciences of specialty 05.22.09 — electric transport. — Joint-Stock Company “Ukrainian zaliznytsia”, Branch “Design and survey institute of railway transport”, Ministry of Infrastructure of Ukraine, National Technical University “Kharkiv Polytechnic Institute”, MES of Ukraine. Kharkiv, 2020. Active rectifiers are one of the effective ways to increase the power factor on AC electric locomotives with DC traction motors. In this thesis, the mathematical description of the active current source rectifier with DC motor is improved. The analysis of the active rectifier energy efficiency with a sinusoidal, trapezoidal and rectangular-stepped pulsewidth modulation (modulation frequency 900 Hz, 1,200 Hz and 1,800 Hz) is performed. The power circuit of the active traction converter with two-zone DC voltage regulation and the algorithm for controlling transistors in traction and recuperation modes has been developed. The results of computer simulation showed that the active traction converter can provide a high power factor of electric locomotive (0.83...0.99). The trolley wire current THD is 9...17%, which is less than with a thyristor converter. This reduces the consumption of electricity for traction.

Thesis (MTech (Oceanography))Cape Peninsula University of Technology, 2010
The current dynamics along the Tsitsikamma coast is described from a combination of acoustic current measurements. satellite-tracked surface drifters and underwater temperature recordings made between November 2006 and March 2008. The Tsitsikamma coast is largely a Marine Protected Area (MPA) that protects a rich marine biodiversity. The nearshore currents are important in the dispersal of eggs and larvae of many marine species. including the paralarvae of the commercially caught chokka squid. LoNgo reynaudii. Changes in the environment, including the currents. can affect the successful recruitment of chokka squid, and can bring about large annual fluctuations in biomass that creates economic uncertainty in the squid fishery. Results confirm the existence of a predominantly alongshore current off the Tsitsikamma coast. At Middelbank eastward flow was slightly dominant, with a percentage occurrence of 58% vs. 41% westward flow near the surface. The percentage eastward flow decreased with depth, with 41% vs. 58% westward flow near the seabed. At Thyspunt westward and eastward flow occurred at near equal percentages. but westward flow was slightly dominant throughout the water column. The alongshore current was strongest near the surface during eastward flow (maximum = 141 crn.s1: average = 27 crn.s '). while westward surface currents were weaker (maximum velocity = 78 cm.s1: average = 19 crn.s1). Current speed generally decreased with depth and opposing surface and bottom currents, associated with a thermal stratified water column, were occasionally recorded. The nearshore flow regime was characterised by frequent barotropic alongshore reversals that occurred year round. An increase in strong eastward episodes, and opposing surface and bottom currents during spring and summer months have implications for the dispersal of squid paralarvae during the summer and winter spawning seasons. In summer, the combination of strong eastward pulses in the current and upwelling at the capes favoured dispersal onto the midshelf of the Agulhas Bank. In winter, alongshore oscillations without the offshore displacement associated with upwelling. restricted offshore dispersal which caused surface particles to be retained inshore. Drifter trajectories show that both the eastward and westward nearshore current can link the inshore spawning grounds with the nursery grounds, offshore on the central Agulhas Bank; and that passive, neutrally buoyant material in the surface layer can reach the vicinity of the cold ridge in as little as eight days. The wind-driven processes of upwelling and coastal trapped waves (CTWs). and the influence of the greater shelf circulation are discussed as possible driving forces of variability in the currents off the Tsitsikamma coast. The occurrence of coastal trapped waves during thermal stratification appears to drive the jet-like, eastward pulses in the current. and results suggest that the propagation of CTWs may regulate and even enhance upwelling and downwelling along the Tsitsikamma coast.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 196-205).
This thesis advances our understanding of how transport properties of turbidity currents are mediated by interactions with seafloor topography, specifically channelized surfaces. Turbidity currents are responsible for crafting the morphology of continental margins. Unfortunately, very few direct observations exists defining turbidity current interactions with submarine channels and canyons because infrequent occurrence, great water depths, and high current velocities make measurements difficult to obtain. To overcome this problem, I utilize reduced scale laboratory experiments, remote sensing of the seafloor and subsurface deposits, and numerical analysis of transport processes. I focus on resolving the topography and composition of the evolving water-sediment interface with additional measurements that characterize the sediment transport and flow fields. I begin by quantifying interactions between turbidity currents and channel-bounding levees. Levees are the primary elements of self-formed channels and act to confine flows within channels, thereby increasing transport efficiency. I quantify the morphology and growth of levees in a submarine channel network offshore Borneo. Levee deposit trends are interpreted using laboratory observations and a morphodynamic model describing levee growth. Channel and levee deposits resulting from interactions between turbidity currents and sinuous submarine channels are then studied using reduced-scale laboratory experiments. Measurements of current superelevation in channel bends are used to illustrate the importance of current runup onto the outer banks of channel bends. This runup resulted in focused overbank flow and production of thick, coarse, steep levees at these sites.
(cont.) Additional laboratory experiments illustrate the importance of current-channel bend interactions to the runout length of turbidity currents. I observed enhanced mixing in channel bends that reduced proximal deposition rates in sinuous channels compared to straight channels. I hypothesize that a wholesale vertical mixing of suspended sediment within turbidity currents at channel bends is a necessary condition for the construction of submarine channels greater than 100 km in length. Finally, I document the deepening of submarine canyons under net depositional conditions using an industry-grade seismic volume from the continental slope offshore Borneo. Interpretation of seismic horizons suggests deposition resulted from sheet-like turbidity currents, highlighting the importance of unconfined currents to the evolution of seascapes.
by Kyle M. Straub.
Ph.D.

AC motors are largely used in a wide range of modern systems, from household appliances to automated industry applications such as: ventilations systems, fans, pumps, conveyors and machine tool drives. Inverters are widely used in industrial and commercial applications due to the growing need for speed control in ASD systems. Fast switching transients and the common mode voltage, in interaction with parasitic capacitive couplings, may cause many unwanted problems in the ASD applications. These include shaft voltage and leakage currents. One of the inherent characteristics of Pulse Width Modulation (PWM) techniques is the generation of the common mode voltage, which is defined as the voltage between the electrical neutral of the inverter output and the ground. Shaft voltage can cause bearing currents when it exceeds the amount of breakdown voltage level of the thin lubricant film between the inner and outer rings of the bearing. This phenomenon is the main reason for early bearing failures. A rapid development in power switches technology has lead to a drastic decrement of switching rise and fall times. Because there is considerable capacitance between the stator windings and the frame, there can be a significant capacitive current (ground current escaping to earth through stray capacitors inside a motor) if the common mode voltage has high frequency components. This current leads to noises and Electromagnetic Interferences (EMI) issues in motor drive systems. These problems have been dealt with using a variety of methods which have been reported in the literature. However, cost and maintenance issues have prevented these methods from being widely accepted. Extra cost or rating of the inverter switches is usually the price to pay for such approaches. Thus, the determination of cost-effective techniques for shaft and common mode voltage reduction in ASD systems, with the focus on the first step of the design process, is the targeted scope of this thesis. An introduction to this research – including a description of the research problem, the literature review and an account of the research progress linking the research papers – is presented in Chapter 1. Electrical power generation from renewable energy sources, such as wind energy systems, has become a crucial issue because of environmental problems and a predicted future shortage of traditional energy sources. Thus, Chapter 2 focuses on the shaft voltage analysis of stator-fed induction generators (IG) and Doubly Fed Induction Generators DFIGs in wind turbine applications. This shaft voltage analysis includes: topologies, high frequency modelling, calculation and mitigation techniques. A back-to-back AC-DC-AC converter is investigated in terms of shaft voltage generation in a DFIG. Different topologies of LC filter placement are analysed in an effort to eliminate the shaft voltage. Different capacitive couplings exist in the motor/generator structure and any change in design parameters affects the capacitive couplings. Thus, an appropriate design for AC motors should lead to the smallest possible shaft voltage. Calculation of the shaft voltage based on different capacitive couplings, and an investigation of the effects of different design parameters are discussed in Chapter 3. This is achieved through 2-D and 3-D finite element simulation and experimental analysis. End-winding parameters of the motor are also effective factors in the calculation of the shaft voltage and have not been taken into account in previous reported studies. Calculation of the end-winding capacitances is rather complex because of the diversity of end winding shapes and the complexity of their geometry. A comprehensive analysis of these capacitances has been carried out with 3-D finite element simulations and experimental studies to determine their effective design parameters. These are documented in Chapter 4. Results of this analysis show that, by choosing appropriate design parameters, it is possible to decrease the shaft voltage and resultant bearing current in the primary stage of generator/motor design without using any additional active and passive filter-based techniques. The common mode voltage is defined by a switching pattern and, by using the appropriate pattern; the common mode voltage level can be controlled. Therefore, any PWM pattern which eliminates or minimizes the common mode voltage will be an effective shaft voltage reduction technique. Thus, common mode voltage reduction of a three-phase AC motor supplied with a single-phase diode rectifier is the focus of Chapter 5. The proposed strategy is mainly based on proper utilization of the zero vectors. Multilevel inverters are also used in ASD systems which have more voltage levels and switching states, and can provide more possibilities to reduce common mode voltage. A description of common mode voltage of multilevel inverters is investigated in Chapter 6. Chapter 7 investigates the elimination techniques of the shaft voltage in a DFIG based on the methods presented in the literature by the use of simulation results. However, it could be shown that every solution to reduce the shaft voltage in DFIG systems has its own characteristics, and these have to be taken into account in determining the most effective strategy. Calculation of the capacitive coupling and electric fields between the outer and inner races and the balls at different motor speeds in symmetrical and asymmetrical shaft and balls positions is discussed in Chapter 8. The analysis is carried out using finite element simulations to determine the conditions which will increase the probability of high rates of bearing failure due to current discharges through the balls and races.

The Queensland University of Technology (QUT) allows the presentation of theses for the Degree of Doctor of Philosophy in the format of published or submitted papers, where such papers have been published, accepted or submitted during the period of candidature. This thesis is composed of ten published /submitted papers and book chapters of which nine have been published and one is under review. This project is financially supported by an Australian Research Council (ARC) Discovery Grant with the aim of investigating multilevel topologies for high quality and high power applications, with specific emphasis on renewable energy systems. The rapid evolution of renewable energy within the last several years has resulted in the design of efficient power converters suitable for medium and high-power applications such as wind turbine and photovoltaic (PV) systems. Today, the industrial trend is moving away from heavy and bulky passive components to power converter systems that use more and more semiconductor elements controlled by powerful processor systems. However, it is hard to connect the traditional converters to the high and medium voltage grids, as a single power switch cannot stand at high voltage. For these reasons, a new family of multilevel inverters has appeared as a solution for working with higher voltage levels. Besides this important feature, multilevel converters have the capability to generate stepped waveforms. Consequently, in comparison with conventional two-level inverters, they present lower switching losses, lower voltage stress across loads, lower electromagnetic interference (EMI) and higher quality output waveforms. These properties enable the connection of renewable energy sources directly to the grid without using expensive, bulky, heavy line transformers. Additionally, they minimize the size of the passive filter and increase the durability of electrical devices. However, multilevel converters have only been utilised in very particular applications, mainly due to the structural limitations, high cost and complexity of the multilevel converter system and control. New developments in the fields of power semiconductor switches and processors will favor the multilevel converters for many other fields of application. The main application for the multilevel converter presented in this work is the front-end power converter in renewable energy systems. Diode-clamped and cascade converters are the most common type of multilevel converters widely used in different renewable energy system applications. However, some drawbacks – such as capacitor voltage imbalance, number of components, and complexity of the control system – still exist, and these are investigated in the framework of this thesis. Various simulations using software simulation tools are undertaken and are used to study different cases. The feasibility of the developments is underlined with a series of experimental results. This thesis is divided into two main sections. The first section focuses on solving the capacitor voltage imbalance for a wide range of applications, and on decreasing the complexity of the control strategy on the inverter side. The idea of using sharing switches at the output structure of the DC-DC front-end converters is proposed to balance the series DC link capacitors. A new family of multioutput DC-DC converters is proposed for renewable energy systems connected to the DC link voltage of diode-clamped converters. The main objective of this type of converter is the sharing of the total output voltage into several series voltage levels using sharing switches. This solves the problems associated with capacitor voltage imbalance in diode-clamped multilevel converters. These converters adjust the variable and unregulated DC voltage generated by renewable energy systems (such as PV) to the desirable series multiple voltage levels at the inverter DC side. A multi-output boost (MOB) converter, with one inductor and series output voltage, is presented. This converter is suitable for renewable energy systems based on diode-clamped converters because it boosts the low output voltage and provides the series capacitor at the output side. A simple control strategy using cross voltage control with internal current loop is presented to obtain the desired voltage levels at the output voltage. The proposed topology and control strategy are validated by simulation and hardware results. Using the idea of voltage sharing switches, the circuit structure of different topologies of multi-output DC-DC converters – or multi-output voltage sharing (MOVS) converters – have been proposed. In order to verify the feasibility of this topology and its application, steady state and dynamic analyses have been carried out. Simulation and experiments using the proposed control strategy have verified the mathematical analysis. The second part of this thesis addresses the second problem of multilevel converters: the need to improve their quality with minimum cost and complexity. This is related to utilising asymmetrical multilevel topologies instead of conventional multilevel converters; this can increase the quality of output waveforms with a minimum number of components. It also allows for a reduction in the cost and complexity of systems while maintaining the same output quality, or for an increase in the quality while maintaining the same cost and complexity. Therefore, the asymmetrical configuration for two common types of multilevel converters – diode-clamped and cascade converters – is investigated. Also, as well as addressing the maximisation of the output voltage resolution, some technical issues – such as adjacent switching vectors – should be taken into account in asymmetrical multilevel configurations to keep the total harmonic distortion (THD) and switching losses to a minimum. Thus, the asymmetrical diode-clamped converter is proposed. An appropriate asymmetrical DC link arrangement is presented for four-level diode-clamped converters by keeping adjacent switching vectors. In this way, five-level inverter performance is achieved for the same level of complexity of the four-level inverter. Dealing with the capacitor voltage imbalance problem in asymmetrical diodeclamped converters has inspired the proposal for two different DC-DC topologies with a suitable control strategy. A Triple-Output Boost (TOB) converter and a Boost 3-Output Voltage Sharing (Boost-3OVS) converter connected to the four-level diode-clamped converter are proposed to arrange the proposed asymmetrical DC link for the high modulation indices and unity power factor. Cascade converters have shown their abilities and strengths in medium and high power applications. Using asymmetrical H-bridge inverters, more voltage levels can be generated in output voltage with the same number of components as the symmetrical converters. The concept of cascading multilevel H-bridge cells is used to propose a fifteen-level cascade inverter using a four-level H-bridge symmetrical diode-clamped converter, cascaded with classical two-level Hbridge inverters. A DC voltage ratio of cells is presented to obtain maximum voltage levels on output voltage, with adjacent switching vectors between all possible voltage levels; this can minimize the switching losses. This structure can save five isolated DC sources and twelve switches in comparison to conventional cascade converters with series two-level H bridge inverters. To increase the quality in presented hybrid topology with minimum number of components, a new cascade inverter is verified by cascading an asymmetrical four-level H-bridge diode-clamped inverter. An inverter with nineteen-level performance was achieved. This synthesizes more voltage levels with lower voltage and current THD, rather than using a symmetrical diode-clamped inverter with the same configuration and equivalent number of power components. Two different predictive current control methods for the switching states selection are proposed to minimise either losses or THD of voltage in hybrid converters. High voltage spikes at switching time in experimental results and investigation of a diode-clamped inverter structure raised another problem associated with high-level high voltage multilevel converters. Power switching components with fast switching, combined with hard switched-converters, produce high di/dt during turn off time. Thus, stray inductance of interconnections becomes an important issue and raises overvoltage and EMI issues correlated to the number of components. Planar busbar is a good candidate to reduce interconnection inductance in high power inverters compared with cables. The effect of different transient current loops on busbar physical structure of the high-voltage highlevel diode-clamped converters is highlighted. Design considerations of proper planar busbar are also presented to optimise the overall design of diode-clamped converters.

Kyoto University (京都大学)
0048
新制・課程博士
博士(エネルギー科学)
甲第9051号
エネ博第38号
新制||エネ||10(附属図書館)
UT51-2001-F381
京都大学大学院エネルギー科学研究科エネルギー応用科学専攻
(主査)教授 塩津 正博, 教授 岩瀬 正則, 教授 牟田 一弥
学位規則第4条第1項該当

Thesis (M.S.)--University of Kentucky, 2003.
Title from document title page (viewed Sept. 10, 2004). Document formatted into pages; contains xi, 128 p. : ill. Includes abstract and vita. Includes bibliographical references (p. 127-128).

Загальна сума зовнішніх державних і гарантованих державою боргів на кінець лютого 2020 року склала 49,81 млрд доларів. З 2009 року державний борг, який тоді становив 26,5 мільярдів доларів, з кожним роком зростає. Виняток становить 2013 рік, коли борги зменшилися з 38,7 до 37,5 млрд доларів. наступного року, а також у 2019-му – з 50,5 до 48,9 млрд дол. Найбільші запозичення Україні довелося зробити в 2011 році, коли борг зріс з 34,8 до 37,5 млрд грн, а в 2015 році борг зріс з 38,8 до 43,4 млрд доларів.
Общая сумма внешней государственной и гарантированной государством задолженности на конец февраля 2020 года составила 49,81 миллиарда долларов. С 2009 года государственный долг, который тогда составлял 26,5 миллиарда долларов, ежегодно растет. Исключение составляет 2013 год, когда долги снизились с 38,7 до 37,5 миллиарда долларов. в следующем году, как и в 2019 году - с 50,5 до 48,9 миллиарда долларов. Самые крупные заимствования Украине пришлось сделать в 2011 году, когда долг увеличился с 34,8 до 37,5 миллиарда гривен, а в 2015 году долг увеличился с 38,8 до 43,4 миллиарда долларов.
The total amount of external public and state-guaranteed debts at the end of February 2020 amounted to 49.81 billion dollars. Since 2009, the public debt, which then amounted to 26.5 billion dollars, has been growing every year. The exception is 2013, when debts decreased from 38.7 to 37.5 billion dollars. next year, as well as in 2019 - from 50.5 to 48.9 billion dollars. Ukraine had to make the largest borrowings in 2011, when the debt increased from 34.8 to 37.5 billion hryvnias, and in 2015 the debt increased from 38.8 to 43.4 billion dollars.

碩士
崑山科技大學
電機工程研究所
96
This thesis presents a novel zero-current-transition (ZCT) pulse-width-modulation (PWM) dc-dc converter for battery chargers. With an auxiliary power switch in series with the resonant capacitor, all of the semiconductor devices in the charger circuit are turned on and off under soft switching. The proposed charger topology practically eliminates the charging current ripple in the battery, thus maximizing battery life without penalizing the volume of the converter. Accordingly, a battery charger with the proposed ZCT-PWM dc-dc converter can be operated at low switching power losses conditions. No additional voltage and current stresses on the auxiliary switch and auxiliary diode occur. Also, the main switch and main diode are subjected to voltage and current values at allowable levels. Furthermore, the proposed ZCT-PWM dc-dc battery charger has a simple structure, low cost, easy control, and high efficiency. The operating principles and design procedure are analyzed and discussed in detail. The optimal values of the resonant components are determined by applying the characteristic curve and the electric functions derived from the circuit configuration. Simulation and experimental results from a laboratory prototype are shown to demonstrate the feasibility of the proposed scheme. Finally, a prototype circuit designed for a 12V-48Ah lead-acid battery is built and tested to verify the theoretical predictions. Satisfactory performance is obtained from the experimental results.

Line current distortion is an important issue to a high-power current source rectifier(CSR) system. There are two main challenges related to this issue. First, the CSR input LC resonance can be affected by the variation of the source inductance from the power system and the effects of the CSR DC side circuit, which may lead to a line current distortion higher than expected. Another challenge is that the traditional high-power CSR using Selective Harmonic Elimination (SHE) pulse-width modulation (PWM) technique attempts to eliminate certain harmonics in the PWM current, which limits its ability for line current harmonic control. To control the CSR line current harmonics, this thesis focuses on two aspects: 1) the analysis and design of CSR input filter to avoid unexpected input LC resonance, and 2) the development of a new PWM scheme that can compensate the effects of the grid voltage harmonics and DC link current ripples. The thesis work has been validated by simulations and on an experimental CSR prototype.
Power Engineering and Power Electronics

Thesis (Ph. D.)--University of Wisconsin--Madison, 1985.
Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 187-190).

碩士
國立臺北科技大學
電腦與通訊研究所
96
The use of white LED can accord with the current issue in energy saving and environmental protection in the world. Due to the features of small size and longer life, this LED is widely used in the backlight of portable device display. The backlight can change the life time of battery and the brightness of display. In the thesis, switching mode boost DC-DC converter can make higher efficiency, and current sensing circuit can increase current matching of each output, and make the brightness of every white LED lightbulbs uniform. The structure of whole system is consisted of three major parts:(1) Boost DC-DC converter will offer the voltage for white LED, and the circuit includes a compensator, a pulse-width-modulation, a non-overlapping circuit and a driver circuit. The pulse-width-modulation circuit is composed of ring oscillator and pseudo hyperbola charge current generator, and it can enhance the efficiency because the power consumption is lower than sawtooth generator. (2)Current sensing circuit is composed of current mirror and operational amplifier. (3)White LED brightness control circuit can be adjusted to the suitable brightness. White LED driver is implemented by TSMC 0.35μm 2P4M CMOS 5V process and whole chip area is 1.503x1.218mm2 without pads. The range of the operation voltage is from 2.7V to 3.7V, and the output voltage is 4V. The output maximum current is at 105mA, the driver efficiency will reach to 90%, and the minimum mean error of each output current can reach to 1.6% matching.

碩士
崑山科技大學
電機工程研究所
95
This thesis applies a zero-current-transition pulse-width-modulated boost converter in a battery charger. The battery charger with zero-current-transition pulse-width-modulated technology can significantly reduce the switching losses, constant-frequency control and maintain the voltage/current stress on the circuit components when the power transistor is switched under zero-current condition. The equivalent circuits of various modes are constructed based on analyzing the operating principles of the circuit according to the turn-on conditions of the switches.Experimental results have demonstrated the theoretical effectiveness of the presented battery charger circuit. The practical mean charging efficiency of the proposed battery charger is 92.87%.

碩士
國立中山大學
電機工程學系研究所
102
In recent years, the traditional incandescent has life is short, low luminous efficiency, high replacement rate, does not meet the demands of environmental advocate, so being replaced by light emitting diode. Because LED has a long life, small size, light, fast response, environmental protection without the use of mercury and mercury materials, high luminous efficiency, but LED brightness depending on the forward current, therefore, how to supply constant current is becoming the most important topic of LED driving circuit. In this paper, the following three points to improve integrated circuit. The first, replace BJT with MOSFET to produce voltage of negative temperature coefficient for reducing layout area and power consumption. The second, this design circuit, the current controlled oscillator with temperature compensation to improve the PWM dimming. The final, the AND gate is combined with overheat protection circuit (OTP) signal and PWM signal. The advantage is that the output voltage does not affect the each channel current, increase switch speed and improve the accuracy of the protective effect. The duty cycle of PWM be controlled to by external dc bias 0.6V to 2.3V. Post-layout simulation shows that Vout channel provides dimming frequency about 100KHz changes from -25℃ to 100℃ and the duty cycle of PWM which adjustable from 10% to 90%. In addition, the current channel provides 30mA between -25℃ to 100℃, when power supply Vdd is 3.3V. Besides, It is fabricated with CIC provided by TSMC 0.35μm 2P4M 3.3V/5V CMOS process in an active area of 1.1 mm × 1.0 mm.

碩士
崑山科技大學
電機工程研究所
94
The resonant converter provides the advantages of low switching losses, small circuit volume, light weight and high power density. Various high-frequency switching converters have replaced traditional hard -switching converters. This thesis presents a novel zero-current-switching pulse-width-modulated buck converter for battery chargers to control resonant converters flexibly. An auxiliary switch is inserted into the resonant loop in the proposed novel battery charger to control the resonant time precisely. The developed charger has the advantages of the hard-switching converter and the resonant converter with constant -frequency control, reduced resonant time and the operation of all switching components in the charger under the zero-current-switching condition to reduce significantly switching losses. The developed charger circuit is highly suitable for high-frequency operation and high charging efficiency. This thesis employs the pulse-width-modulated control mode for the switching of two active switches. The operation modes of the circuit and the equivalent circuits are constructed by analyzing the operating principles of the circuit, based on the turn-on conditions of the active switches. The equations used to determine the circuit parameters are derived from the equivalent circuits. Experimental results have demonstrated the theoretical effectiveness of the proposed novel battery charger circuit. A practical mean charging efficiency of over 90% is quite satisfactory.

碩士
健行科技大學
電機工程系碩士班
103
This thesis proposes to use pulse-width modulation (PWM), instead of frequency modulation (FM), to regulate the output voltage and balance the module currents of an interleaved LLC resonant converter. The imbalance of module currents in power converters with modules connected in parallel is usually a problem caused by parameter errors of component, which is unavoidable and unsolvable by the regular FM method. The thesis combines the Fundamental component approximation method and the Fourier series analysis technique to explain the principle that a half bridge resonant converter can be controlled by the PWM method. Analysis and design of LLC resonant converter based on PWM control are performed. In addition, the control system is designed to include two PWM control loops. While the inner loop is to balancing the module currents by using the master-slave control logic, the outer loop is to regulating the output voltage of the converter. A 300W/380Vin/19Vout interleaved LLC resonant converter with two modules connected in parallel had been realized in this thesis to verify the proposed method, in which the DSP TMS320F28035 was used as the control platform. As a result, the experimental measure showed that all the half bridge switches can be turned on with zero voltage, the current balancing effect can be improved at least 75%, and the maximum converter efficiency obtained is 94%.

The Indonesian Throughflow (ITF) is the only low latitude connection of the global circulation and is an essential pathway for mass, heat and salt exchange between the Pacific and Indian Oceans. The ITF is a boundary current constrained by topography and is characterised by two source pathways, a western and an eastern. At the exit to the Indian Ocean, observations show the ITF partitions amongst the three major outflow straits. The westernmost, Lombok Strait, has the lowest transport even though it is expected to carry most of the flow given that the ITF is a boundary current and this strait is a direct continuation of the western pathway. Heat and saltwater transports are different in each outflow strait and thus exchanged properties depend on the partitioning, consequently affecting the contribution to the Indian Ocean. In this study, we explore the ITF circulation and local dynamics that control the ITF partitioning. To explore what controls ITF partitioning in the context of western boundary current theories, we simulate a steady ITF in a high-resolution (4-km) regional model. The forcing consists of time-averaged velocity, temperature and salinity fields from the global model Ocean Forecasting Australia Model v3 (OFAM3). We investigate what sets the amount of western pathway water that exits via Lombok Strait in the regional model. Our reference simulation confirms the two ITF pathways and gives a mean ITF of 14.1 Sv and an outflow partitioning of 0.2:0.4:0.4 (Lombok:Ombai:Timor), consistent with observations. Focusing on the western pathway, comprising 70% of the total ITF, we investigate the routes this water follows to the Indian Ocean. Here we consider partitioning as the ratio between transport in Lombok and Makassar Straits. Relative to only Makassar Strait transport, Lombok Strait still has the lowest transport portion of the three outflows (27%). Idealised perturbation experiments help us to investigate boundary current dynamics; combinations of slip/non-slip boundary conditions and linear/non-linear advection in the momentum equations illustrate the effects of current width (CW) on partitioning. Our key finding from this analysis is that the CW in the Makassar Strait controls the Lombok Strait transport; a narrower boundary current can fit more flow through a narrow strait. To understand what sets the CW, we perform a vorticity budget. The reference simulation reveals that the leading order term that balances change in planetary vorticity is advection of vorticity. The vorticity term diagnostics for the perturbation experiments suggest non-linearity is the main term controlling the ITF current width. We test how CW influences partitioning in more realistic conditions and evaluate how low-frequency variability affects partitioning, analysing 18-yr of a global fully-realistic model OFAM3. Consistent with our perturbation experiments, we find CW in Makassar Strait controls transport in Lombok Strait. Further, we find that, on the inter-annual scale, the Makassar Strait CW is approximately constant. This suggests that Makassar Strait may be saturated and similar dynamics could also take place upstream in the ITF western pathway. Specifically, we find that the width of Makassar Strait constrains the CW, independent of variations in CW at the upstream inflow ITF at Mindanao boundary current. As a consequence, during years when Mindanao current is wide at the Indonesian Seas entrance, the flow does not entirely fit in Makassar Strait. This flow that did not fit in Makassar Strait joins the eastern pathway. The increase of inflow in the eastern pathway produces a change in transport at Timor Passage, providing a link between variability at Timor Passage and that of the Mindanao. Our results suggest that, given the ITF complexity, the simple concept of partitioning cannot be easily used as a proxy for ITF transports and predictions cannot be made based on single strait measurements. The ITF western pathway provides a more direct connection to the Indian Ocean compared to the eastern pathway. The changes eastern pathway waters undergo while circulating in the Indonesian Seas are crucial for understanding heat and tracers exchange between the two oceans. Finally, understanding what controls the ITF circulation and its variability is critical to better predicting how the ITF responds to climate change.

碩士
國立臺北科技大學
電腦與通訊研究所
98
In the first part of this thesis, a new fast-transient-response buck converter is presented with an accelerated pulse-width-modulation technique. The traditional voltage-mode speed in the transient response is slow, so in this thesis add an accelerated pulse-width-modulation technique to solve the problem. The proposed buck converter has been fabricated with a TSMC 0.35 μm CMOS 2P4M process, the total chip area is about 1.32 x 1.22 mm2(include PADs). In the second part of this thesis, we present a dual-mode fast-transient average-current-mode buck converter is presented. The benefits of the average-current-mode are fast-transient response, simple-compensation design, and without slope-compensation. Furthermore, this technique eliminates some power management problems, such as electro magnetic interference(EMI), size, design complexity, and cost. The adaptive switching between pulse-width-modulation (PWM) and pulse-frequency modulation (PFM) are operated with very high conversion efficiency. The proposed buck converter has been fabricated with a TSMC 0.35 μm CMOS 2P4M process, the total chip area is about 1.45 x 1.11mm2(include PADs).