Dissertations / Theses on the topic 'On-state voltage'

This Ph.D. thesis aims at investigating the effect of state feedback cross‐coupling decoupling of the capacitor voltage on the dynamics performance of Voltage Source Inverters for standalone microgrids/Uninterruptible Power Supply systems. Computation and PWM delays are the main factors which limit the achievable bandwidth of current regulators in digital implementations. In particular, the performance of state feedback decoupling is degraded because of these delays. Two decoupling techniques aimed at improving the transient response of voltage and current regulators are investigated, named nonideal and ideal capacitor voltage decoupling respectively. In particular, the latter solution consists in leading the capacitor voltage on the state feedback decoupling path in order to compensate for system delays. Practical implementation issues are discussed with reference to both the decoupling techniques. Moreover, different resonant regulators structures for the inner current loop are analysed and compared to investigate which is the most suitable for standalone microgrid applications. A design methodology for the voltage loop, which considers the closed loop transfer functions developed for the inner current loop, is also provided. Proportional resonant voltage controllers tuned at specific harmonic frequencies are designed according to the Nyquist criterion taking into account application requirements. For this purpose, a mathematical expression based on root locus analysis is proposed to find the minimum value of the resonant gain at the fundamental frequency. The exact model of the output LC filter of a three‐phase inverter is derived in the z‐domain. The devised formulation allows the comparison of two techniques based on a lead compensator and Smith predictor structure. These solutions permit the bandwidth of the current regulator to be widened while still achieving good dynamic performance. As a consequence, the voltage regulator can be designed for a wide bandwidth and even mitigates odd harmonics arising with unbalance loads supply. Discrete‐time domain implementation issues of an anti‐wind up scheme are discussed as well, highlighting the limitations of some discretization methods. Experimental tests performed in accordance to Uninterruptible Power Supply standards verify the theoretical analysis.

This paper presents the study and development of a topology of nonisolated converter operating at high frequency, which is suitable for the integration of battery banks, photovoltaic panels, and a high voltage dc link in a single conversion stage. The topology is based on the bidirectional version of the three-state switching cell and is recommended for battery charging, while a 200V dc link can be obtained in a single conversion stage using photovoltaic (PV) panels. The presented converter is able to supply a 200V dc link using a battery bank and a PV array and, depending on the solar irradiance level, it is also possible to charge the batteries by using a single conversion stage. Moreover, all the switches of the converter are able to operate under zero voltage switching (ZVS) condition over a wide operation range. The experimental results are obtained from a 500W laboratory prototype, which has been developed and tested in three situations: energy flow from the battery bank to the load, energy flow from the PV panel to the load; and energy flow from the panel to the battery bank, achieving the efficiency of 94,18%, 96,09% e 94,67% respectively. The high gain afforded by this topology and the excellent performance obtained in all operations mode, shows as a solution where the requirement of increasing the voltage to 200V or 400V from low input voltage energy sources, typically 12V, 24V or 48V, provided by batteries, solar panels or others sources of energy, for Uninterruptable Power Supply (UPS), or a DC link, for example.
Este trabalho tem por escopo apresentar o estudo e desenvolvimento de um conversor CC-CC nÃo isolado de trÃs portas, adequado à integraÃÃo em um Ãnico estÃgio de conversÃo: um banco de baterias, um conjunto de painÃis fotovoltaicos e o link CC. A topologia proposta apresenta um conversor boost de alto ganho baseado na versÃo bidirecional da cÃlula de comutaÃÃo de trÃs estados na qual se tem integrado um banco de baterias e um conjunto de painÃis fotovoltaicos com capacidade para gerar um barramento CC de 200V em um Ãnico estÃgio de processamento. A caracterÃstica bidirecional da topologia permite aos painÃis fotovoltaicos carregar as bateiras e alimentar a carga dependendo da incidÃncia solar. No caso de ausÃncia de sol, o banco de baterias supre a carga. Outra importante caracterÃstica deste conversor à a comutaÃÃo suave em modo ZVS para todas as chaves. Foi desenvolvido um protÃtipo experimental com potÃncia nominal de 500W de forma a validar todo o embasamento teÃrico e de simulaÃÃo apresentados. O conversor desenvolvido foi submetido a trÃs condiÃÃes: o fluxo de energia da bateria para a carga, do painel fotovoltaico para a carga e do painel para o banco de baterias, sendo obtido o rendimento de 94,18%, 96,09% e 94,67% respectivamente para cada condiÃÃo. AlÃm disso, as formas de ondas experimentais e de simulaÃÃo para cada condiÃÃo e o comparativo de rendimento de topologias, tambÃm sÃo apresentados. O alto ganho e o rendimento alcanÃado nesta topologia, a torna uma forte soluÃÃo quando hà necessidade de elevar a tensÃo a partir de baterias ou painÃis fotovoltaicos, quando os valores fornecidos por estes geralmente sÃo de 12V, 24V ou 48V. Ressalte-se que este trabalho contribui cientificamente na Ãrea da eletrÃnica de potÃncia, mais especificamente, no que concerne ao estudo e desenvolvimento de novas topologias de conversores CC-CC nÃo isolados de trÃs portas para aplicaÃÃes em energias renovÃveis.

Previously, conventional state estimation techniques have been used for state estimation in power systems. These conventional methods are based on steady state models. As a result of this, power system dynamics during disturbances or transient conditions are not adequately captured. This makes it challenging for operators in control centers to perform visual tracking of the system, proper fault diagnosis and even take adequate preemtive control measures to ensure system stability during voltage dips. Another challenge is that power systems are nonlinear in nature. There are multiple power components in operation at any given time making the system highly dynamic in nature. Consequently, the need to study and implement better dynamic estimation tools that capture system dynamics during disturbances and transient conditions is necessary. For this thesis work, we present the Unscented Kalman Filter (UKF) which integrates Unscented Transformation (UT) to Kalman Filtering. Our algorithm takes as input the output of a synchronous machine modeled in MATLAB/Simulink as well as data from a PMU device assumed to be installed at the terminal bus of the synchronous machine, and estimate the dynamic states of the system using a Kalman Filter. We have presented a detailed and analytical study of our proposed algorithm in estimating two dynamic states of the synchronous machine, rotor angle and rotor speed. Our study and result shows that our proposed methodology has better efficiency when compared to the results of the Extended Kalman Filter (EKF) algorithm in estimating dynamic states of a power system.  Our results are presented and analyzed on the basis of how accurately the algorithm estimates the system states following various simulated transient and small-signal disturbances.

Multi functional health monitoring wearable devices are quite prominent these days. Usually these devices are battery-operated and consequently are limited by their battery life (from few hours to a few weeks depending on the application). Of late, it was realized that these devices, which are currently being operated at fixed voltage and frequency, are capable of operating at multiple voltages and frequencies. By switching these voltages and frequencies to lower values based upon power requirements, these devices can achieve tremendous benefits in the form of energy savings. Dynamic Voltage and Frequency Scaling (DVFS) techniques have proven to be handy in this situation for an efficient trade-off between energy and timely behavior. Within imec, wearable devices make use of the indigenously developed MUSEIC v2 (Multi Sensor Integrated circuit version 2.0). This system is optimized for efficient and accurate collection, processing, and transfer of data from multiple (health) sensors. MUSEIC v2 has limited means in controlling the voltage and frequency dynamically. In this thesis we explore how traditional DVFS techniques can be applied to the MUSEIC v2. Experiments were conducted to find out the optimum power modes to efficiently operate and also to scale up-down the supply voltage and frequency. Considering the overhead caused when switching voltage and frequency, transition analysis was also done. Real-time and non real-time benchmarks were implemented based on these techniques and their performance results were obtained and analyzed. In this process, several state of the art scheduling algorithms and scaling techniques were reviewed in identifying a suitable technique. Using our proposed scaling technique implementation, we have achieved 86.95% power reduction in average, in contrast to the conventional way of the MUSEIC v2 chip’s processor operating at a fixed voltage and frequency. Techniques that include light sleep and deep sleep mode were also studied and implemented, which tested the system’s capability in accommodating Dynamic Power Management (DPM) techniques that can achieve greater benefits. A novel approach for implementing the deep sleep mechanism was also proposed and found that it can obtain up to 71.54% power savings, when compared to a traditional way of executing deep sleep mode.
Nuförtiden så har multifunktionella bärbara hälsoenheter fått en betydande roll. Dessa enheter drivs vanligtvis av batterier och är därför begränsade av batteritiden (från ett par timmar till ett par veckor beroende på tillämpningen). På senaste tiden har det framkommit att dessa enheter som används vid en fast spänning och frekvens kan användas vid flera spänningar och frekvenser. Genom att byta till lägre spänning och frekvens på grund av effektbehov så kan enheterna få enorma fördelar när det kommer till energibesparing. Dynamisk skalning av spänning och frekvens-tekniker (såkallad Dynamic Voltage and Frequency Scaling, DVFS) har visat sig vara användbara i detta sammanhang för en effektiv avvägning mellan energi och beteende. Hos Imec så använder sig bärbara enheter av den internt utvecklade MUSEIC v2 (Multi Sensor Integrated circuit version 2.0). Systemet är optimerat för effektiv och korrekt insamling, bearbetning och överföring av data från flera (hälso) sensorer. MUSEIC v2 har begränsad möjlighet att styra spänningen och frekvensen dynamiskt. I detta examensarbete undersöker vi hur traditionella DVFS-tekniker kan appliceras på MUSEIC v2. Experiment utfördes för att ta reda på de optimala effektlägena och för att effektivt kunna styra och även skala upp matningsspänningen och frekvensen. Eftersom att ”overhead” skapades vid växling av spänning och frekvens gjordes också en övergångsanalys. Realtidsoch icke-realtidskalkyler genomfördes baserat på dessa tekniker och resultaten sammanställdes och analyserades. I denna process granskades flera toppmoderna schemaläggningsalgoritmer och skalningstekniker för att hitta en lämplig teknik. Genom att använda vår föreslagna skalningsteknikimplementering har vi uppnått 86,95% effektreduktion i jämförelse med det konventionella sättet att MUSEIC v2-chipets processor arbetar med en fast spänning och frekvens. Tekniker som inkluderar lätt sömn och djupt sömnläge studerades och implementerades, vilket testade systemets förmåga att tillgodose DPM-tekniker (Dynamic Power Management) som kan uppnå ännu större fördelar. En ny metod för att genomföra den djupa sömnmekanismen föreslogs också och enligt erhållna resultat så kan den ge upp till 71,54% lägre energiförbrukning jämfört med det traditionella sättet att implementera djupt sömnläge.

ITER experiment will be built at Cadarache (France) and its main goal will be to prove the viability of fusion as an energy source. In a fusion reactor, the plasma (an ionized gas of Deuterium and Tritium) has to be heated up to temperatures of millions of Celsius degrees in order to sustain the fusion reaction. No materials are able to withstand these temperatures; therefore the plasma is kept away from the walls of the reactor vacuum vessel by means of appropriate magnetic fields, produced by the currents flowing in the superconducting coils, which interact with the charged particles of the plasma. Besides the ohmic heating, two additional sources are foreseen in ITER, based on radiofrequency electromagnetic waves and neutral beam injection. Two Neutral Beam Injectors (NBIs) will heat the plasma; each of them is based on five 200 kV stages in series accelerating negative ions of deuterium or hydrogen, which are neutralized and injected in ITER plasma. The high energy (1 MeV) and beam power (16.7 MW) make this design very complex, close to the state of the art of the components. The ac/dc conversion system necessary to supply the superconducting coils of the magnet system and the auxiliary systems (as the NBIs) may consume a total active and reactive power respectively up to 500 MW and 900 Mvar. In the past years many studies have been carried out on the ITER power supply system and its impact on the electrical network (called Pulsed Power Electrical Network PPEN). Several methods have been considered to improve the power factor, based both on Q reduction and compensation techniques. As for the first, sequential and asymmetric controls, with internal bypass or external freewheeling have been evaluated. Concerning the compensation approach, the current reference design is based on Static Var Compensation System with nominal power of 750 Mvar based on Thyristor Controlled Reactor (TCR) + Tuned Filter (as fixed capacitor). Nevertheless, studies are still in progress aimed to further improvements. This PhD thesis aims to investigate two topics related to the impact on the PPEN of the ITER power supply system with a novel approach. The former concerns the study of the stability of the PPEN and mainly aims to investigate interaction phenomena among the ac/dc conversion and Q compensation and filtering systems, due in particular to the relatively high power ratings and operating scenarios with significant power transients during the plasma pulses. It is not an easy task: the overall system is very complex, the numerical simulation of its operation via programs capable of reproducing the instantaneous current and voltage profiles requires very long calculation time and most of all it does not provide any sensitivity data concerning the stability of the whole power system. Therefore I have followed an analytical approach. The study took the starting points from the methods developed for the HVDC applications, which however can not be directly applied to the ITER case; therefore I have developed specific analytical models. The former model is a Quasi Static Model, which aims to evaluate the strength of the electrical network feeding the ITER power supply system by sensitivity analysis. I have derived the equations of the model by the power flow equations as a function of some relevant parameters in order to carry out sensitivity analysis. This model allows the calculation of some indexes as the Critical Short Circuit Ratio (CSCR) and Voltage Sensitivity Factor (VSF). No critical conditions have been found. The latter is a Dynamic Model; it is based on the state space formulation and it aims to investigate the dynamic stability of the whole system, including also the control system. Nevertheless the ac/dc conversion and the TCR systems are non-linear and discrete, thus difficult to be modelled; therefore, taking the starting point from the methods described in literature, I have approximated the discrete phenomena by continuous transfer functions, and I have worked out the linearization around an equilibrium point such that the small signal analysis approach can be used. I have adopted a modular approach, developing an analytical Dynamic Model for each subsystem (Tuned Filters, TCR and ac/dc conversion system). Then I have built numerical models of the subsystems with a program (PSIM) capable to reproduce the instantaneous waveforms for the validation of the analytical Dynamic Models (run in Matlab Simulink program, state space tool) in frequency and time domain by a comparison between the simulation results. Finally I have built the Dynamic Model of the whole system and validated by comparison with the PSIM one. From the results of the frequency analysis, the dynamic model is accurate for frequency range less than 50 Hz, but it may be used to obtain some insight about the system stability also for frequency range up to 100 Hz. Some unstable operating conditions have been discovered, and the cause has been identified due to resonance between the tuned filters and the grid. It is highlighted that this model may be easily implemented with more detail to the whole ITER power supply system and it can be a very useful and fast tool to aid the design of the power supply system and set the parameters of the control system. As the second topic of my PhD thesis, I have studied the feasibility of adopting a more advanced technology based on the Active Front End approach for the design of the main ac/dc conversion system (called AGPS) of the NBI power supply (56 MW, 88 MVar) to improve its impact in ITER PPEN in terms of current harmonic and reactive power minimization. After giving a short description of the AGPS reference design, based on thyristor technology, the conceptual design of the AFE alternative topology that I have developed for the input ac/dc rectifier is illustrated; its feasibility, and the advantages and drawbacks with respect to the thyristor solution are evaluated and discussed. The results obtained by the analysis show that the AFE solution is feasible and it significantly improves the impact of the AGPS on the Pulsed Power Electrical Network of ITER with respect to thyristor one. The modifications of the present design parameters to allow the full compliance with the requirements of the technical specifications with the implementation of the AFE solution are also proposed and discussed. This thesis is organized as follows. In the Chapter 1 a brief introduction to the fusion research framework is given. The ITER power supply system is described in the chapter 2. The first part of the PhD thesis related to the development of the analytical model starts in the chapter 3, with the description of the simplified equivalent scheme of the ITER Power Supply. The Quasi-Static and Dynamic Models are described in chapter 4 and 5 respectively, and in the chapter 6 are given the conclusions related to this part. The second part of the PhD thesis related to Study of Active-Front-End design for the Acceleration Grid Power Supply of ITER Neutral Beam Injector start in the chapter 7, describing the reference design of the AGPS based on thyristor solution. Then an overview of the AFE converter topologies and control systems is given and their application to AGPS is discussed in the chapter 8. In chapter 9 the conceptual design of the AGPS based on AFE approach is described in detail. In the chapter 10 the AFE and thyristor solution are compared in terms of impact on the PPEN (reactive power and ac current harmonic)
L’esperimento ITER sarà costruito a Cadarache (Francia) e il suo obiettivo principale sarà quello di dimostrare la fattibilità tecnologica di produzione di grandi quantità d’energia attraverso la fusione in un plasma di deuterio e trizio In un reattore a fusione, il plasma (un gas ionizzato di deuterio e trizio) deve essere riscaldato fino a temperature di milioni di gradi Celsius al fine di sostenere la reazione di fusione. Non vi sono materiali in grado di resistere a tali temperature, per cui il plasma è tenuto lontano dalle pareti della camera da vuoto del reattore per mezzo di opportuni campi magnetici, prodotto dalle correnti nelle bobine superconduttrici, che interagiscono con gli ioni del plasma. Oltre al riscaldamento ohmico, altri due sistemi di riscaldamento sono previsti nel progetto di ITER, basati sulle onde elettromagnetiche a radiofrequenza e iniezione di neutri. Due iniettori di fasci di neutri (Neutral Beam Injectors NBIs) saranno utilizzati per scaldare il plasma; ciascuno è composto da un sistema di griglie che formano cinque stadi di accelerazione da 200 kV ciascuno, che accelerano gli ioni negativi di deuterio o idrogeno, che vengono poi neutralizzati e iniettati nel plasma di ITER. L'alta energia (1 MeV) e la potenza del fascio (16,7 MW) rendono questo progetto molto complesso, vicino alla stato dell'arte dei componenti. Il sistema di conversione ac/dc necessario per alimentare le bobine superconduttrici del sistema di magneti e dei sistemi ausiliari (come i NBIs) può consumare complessivamente una potenza attiva e reattiva rispettivamente fino a 500 MW e 900 Mvar. Negli ultimi anni molti studi sono stati effettuati sul sistema di alimentazione ITER e sul suo impatto sulla rete elettrica (chiamata Pulsed Power Electrica Networ PPEN). Diverse tecniche sono state considerate per migliorare il fattore di potenza dei sistemi di conversione ac/dc a tiristori di ITER. Per quanto riguarda la riduzione dell’assorbimento sono state studiate tecniche quali il controllo sequenziale ed asimmetrico, con bypass interno o con freewheeling esterno. Per quanto riguarda invece la compensazione, l’attuale progetto di riferimento è basato sulla tecnologia Static Var Compensator (SVC) con potenza nominale di 750 Mvar, composto da Thyristor Controlled Reactor (TCR) + Filtri per le armonche di corrente (che hanno la funzione di fornire potenza reattiva). Tuttavia, gli studi sono ancora in corso con l'obiettivo di ulteriori miglioramenti. Questa tesi di dottorato studia due aspetti legati all'impatto sulla rete PPEN del sistema di alimentazione di ITER, con un approccio diverso rispetto a quelli già effettuati. Il primo riguarda lo studio della stabilità della rete elettrica PPEN e principalmente si propone di studiare i fenomeni di interazione tra i sistemi di conversione ac/dc e di compensazione della reattiva, dovuti in particolare all’elevato consumo di potenza durante gli scenari di funzionamento di ITER. Non è un compito facile: il sistema di alimenatzione di ITER è molto complesso, le simulazioni numeriche del suo funzionamento attraverso programmi in grado di riprodurre i profili istantanei di tensione e corrente richiede tempi di calcolo molto lunghi e soprattutto non forniscono alcuna sensibilità riguardo la stabilità del sistema. Ho quindi applicato un approccio analitico e, considerando i metodi sviluppati per le applicazioni HVDC che però non possono essere direttamente applicati al caso ITER, ho sviluppato specifici modelli analitici. Il primo modello è il “Quasi-Static Model”, che ha lo scopo di valutare l’adeguatezza della rete elettrica del sistema di alimentazione di ITER attraverso un’analisi di sensibilità. Ho ricavato le equazioni del modello dalle equazioni ai flussi di potenza in funzione di alcuni parametri rilevanti per l’analisi di sensibilità. Con questo modello ho potuto calcolare alcuni indici come il rapporto critico cortocircuito (Critical Short Circuit Ratio) e il fattore di sensibilità di tensione (Voltage Sensitivity Factor). Nessuna condizione criticha è stata trovata. Il secondo è un modello dinamico (chiamato Dynamic Model), ed è basato sulla formulazione alle variabili di stato e si propone di indagare la stabilità dinamica di tutto il sistema, tra cui anche il sistema di controllo. Tuttavia il sistema di conversione ac/dc e i TCR sono componenti non lineari e discreti, e sono difficili da modellare; considerando i metodi descritti in bibliografia, ho approssimato i fenomeni discreti con funzioni di trasferimento continue, e ho eseguito la linearizzazione attorno ad un punto di equilibrio, utilizzando così l’approccio ai piccoli segnali. Ho adottato un approccio modulare, sviluppando cioè un modello dinamico per ogni sottosistema (i filtri delle armoniche di corrente, i TCR e il sistema di conversione ac/dc). Poi ho costruito modelli numerici dei sottosistemi, con un programma (PSIM) in grado di riprodurre le forme d'onda istantanee per la validazione dei modelli dinamici (implementato con il programma Matlab Simulink, state space tool) attraverso il confronto dei risultati nel dominio della frequenza e del tempo. Infine ho costruito il modello dinamico di tutto il sistema e validato con il modello equivalente in PSIM. Dai risultati delle analisi in frequenza, il modello dinamico è accurato per frequenze inferiori a 50 Hz, ma può essere utilizzato per ottenere qualche informazione circa la stabilità del sistema anche per frequenze fino a 100 Hz. Alcune condizioni di funzionamento instabili sono state individuate e sono dovute alla risonanza tra i filtri e la griglia. Questo modello può essere facilmente implementato con maggiori dettagli per l'intero sistema di alimentazione ITER e può essere uno strumento molto utile e veloce per aiutare la progettazione del sistema di alimentazione e impostare i parametri del sistema di controllo. Come secondo argomento della mia tesi di dottorato, ho studiato la fattibilità tecnologica di utilizzare una tecnologia più avanzata basata su un approccio di rettificazione attiva (Active Front End AFE) per la progettazione del principale sistema di conversione ac/dc (chiamato Acceleration Grid Power Supply AGPS) del sistema di alimentazione del NBI (56 MW , 88 MVAr) per migliorare il suo impatto in sulla rete PPEN in termini di minimizzazione della potenza reattiva e delle armoniche di corrente. In questa parte della tesi, dopo una breve descrizione del progetto di riferimento dell’AGPS basato sulla tecnologia a tiristori, ho descritto il progetto concettuale del sistema di rettificazione dell’AGPS basato sulla soluzione alternativa AFE che ho sviluppato; la sua fattibilità ed i vantaggi e gli svantaggi rispetto alla soluzione tiristori sono stati valutati e discussi. I risultati ottenuti dalle analisi mostrano che la soluzione AFE è fattibile e migliora significativamente l'impatto della AGPS sulla rete PPEN di ITER rispetto a quella a tiristori. Inoltre sono state proposte e discusse alcune modifiche di alcuni parametri del progetto di riferimento per consentire la piena conformità con i requisiti delle specifiche tecniche con l'implementazione della soluzione AFE. Questa tesi è organizzata come segue. Nel capitolo 1, una breve introduzione descrive la ricerca sulla fusione. Il sistema di alimentazione di ITER è descritto nel capitolo 2. La prima parte della tesi di dottorato relativa allo sviluppo dei modelli analitici inizia nel capitolo 3, con la descrizione dello schema equivalente semplificato del sistema di alimentazione ITER. I modelli quasi-statico e dinamico sono descritti rispettivamente nei capitoli 4 e 5, e nel capitolo 6 sono presenti le conclusioni relative a questa parte. La seconda parte della tesi di dottorato relativa allo studio di una soluzione di rettifficazione attiva applicata al sistema d’alimentazione dell griglie (AGPS) dell’iniettore di fasci di neutri inizia nel capitolo 7, che descrive il progetto di riferimento della AGPS basato sulla soluzione tiristori. Poi sono descritte diverse soluzioni AFE e dei sistemi di controllo trovati in bibliografia, e la loro applicazione alla AGPS è discussa nel capitolo 8. Nel capitolo 9 il progetto concettuale della AGPS basato sull’approccio AFE è descritto in dettaglio. Nel capitolo 10 la soluzioni AFE e tiristori sono confrontati in termini di impatto sulla rete PPEN (potenza reattiva e armoniche di corrente)

碩士
建國科技大學
電機工程系暨研究所
97
The main purpose of this thesis is to analyze the steady-state operation characteristics for a low-voltage AC microgrid with various distributed energy resources. First of all, the low-voltage AC microgrid integrated with a 30 kW micro-turbine generator, a 13 kW photovoltaic generation system, a 10 kW fuel cell generation system, a 10 kVA wind-turbine generator, and a 30 kW batteries storage system as well as loads was proposed by realizing the related researches and current development all over the world; secondary, the sequential three-phase power flow program is developed by Implicated ZBUS Gauss Method and tested to ensure its accuracy in the Matlab environment; finally, the system naturals and steady-state operation characteristics of the proposed microgrid are discussed by using the developed three-phase power flow program to analyze two cases, which are microgrid without distributed resources and grid-tied microgrid. Furthermore, the outcomes will provide the related researchers to realize the operation characteristics for the AC low-voltage microgrids, and are helpful for the development of microgrids in Taiwan.

碩士
國立澎湖科技大學
電機工程系電資碩士班
106
With the rapid advancement of technology, the society pays increasing attention to the power quality, but there is a little manpower for maintenance in the industry. The high-voltage apparatuses are likely to fail in long running. Therefore, the high-voltage apparatus measurement data are collected by long-term monitoring and Cloud transmission, insulation state of high-voltage apparatuses can be mastered instantly, to avoid unwarned malfunction of high-voltage apparatuses, so as to upgrade the power quality and stability. The cause of partial discharge is comprehended first, and the partial discharge detection method is studied, combined with domestic and foreign standards and regulations for design. The partial discharge measuring system designed in this paper uses wavelet filtering to filter the background noise off the field environment before data analysis. The data analysis result is uploaded via network to the Cloud to create database. The supervisor only needs to use the remote monitoring system designed in this paper. This system receives the database data in the Cloud hard disk via internet, combined with Regression Analysis and Moving average to draw a tendency chart, so as to monitor insulation state deterioration of high-voltage apparatuses in different places for a long time, and to reduce the occurrences of unwarned malfunction. The actual measurement was implemented at Penghu Chienshan Power Plant of Taiwan Power Company, with the field staff's assistance, a considerable result has been obtained, providing a new method for monitoring insulation state of high-voltage apparatuses in the future. Keywords: Partial Discharge; Regression Analysis; Moving Average; Equipment Insulation State

博士
國立清華大學
電機工程學系
98
This dissertation presents a new flux control scheme for a solid-state transfer switch (STS) system and an uninterruptible power supply (UPS) system to accomplish fast load transfer and to mitigate the inrush current. Conventional STS system based on thyristors has been widely used in medium-voltage applications to enhance the power quality and reliability. However, conventional STS system often requires more than a quarter of cycle to complete the load transfer and its line transfer action also causes a considerable inrush current. In this dissertation, an improved STS with forced commutated circuit is presented to greatly reduce the transfer time and provide a better voltage sag ride-through capability for the critical loads. Based on this forced commutation capability, moreover, a flux estimation scheme and a thyristor gating scheme are presented to suppress the inrush current during the load transition process when the combination of the STS system and the transformer is used to serve the critical loads. Laboratory test results and design considerations are presented to validate the performance of proposed STS system. The inrush current issues associated with the solution for the UPS system are also presented in the dissertation. When the UPS systems are used for the voltage sag ride-through, the inrush current phenomenon often exists in the load transition process from a deformed grid voltage to battery power. To mitigate the inrush current, a closed-loop flux compensator is proposed and integrated with the voltage and current controllers. The proposed flux compensator can track the transformer flux and corrects the flux deviation in real time without sacrificing any voltage quality, thus completely avoiding the inrush current. Furthermore, the proposed flux control design is also extended to alleviate the inrush current when multiple transformers are energized by the UPS system. Detail description of the design issues and investigation of flux estimation error are given.

碩士
逢甲大學
資訊電機工程碩士在職專班
99
In this thesis, we integrate buried P+ layer and the vertical liner doping profile graded of the drift region into trench LDMOS to further improve the characteristics of the breakdown voltage and the specific on-resistance. Using high-energy implant buried P + layer enhances the RESURF principle, thus increasing the concentration of the drift region, effectively reducing the specific on-resistance. Vertical linear doping profile of the LDMOS structure exhibited obviously to reduce specific on-resistance while the breakdown voltage is not degraded. The purpose of this work is to develop the LDMOS response surface method (RSM) model and to design the optimum LDMOS device and to improve the trade-off between the breakdown voltage and the specific on-resistance. The RSM model is developed based upon the technology computer-aided design (TCAD) numerical simulations, which simulate the device characteristics. The optimized structure from the simulation are 107.3V and 1.332mΩ-cm2 for breakdown voltage and specific on-resistance, respectively. And with the conventional trench LDMOS comparison, the device performance improved by 25.3%.

In South Africa, live work is routinely performed on high voltage apparatus at various voltages up to 400 kV ac. With regard to HVDC, there are unqualified parameters relating to the development of the safe live work standards, which are currently based on extrapolation of ac and transient voltage test data. Furthermore, it is generally accepted that the mechanism for air breakdown under dc is different when compared between ac and dc voltage. The air breakdown mechanism under HVDC conditions and the corresponding live work related parameters need to be researched further before live work may be performed. Experimentation using floating objects, has in the past, been used to study parameters related to live working calculations. This research report presents the results of HVDC air breakdown tests using a 300 mm diameter floating metallic sphere with a 30 mm protrusion, in a point-to-plane configuration with a total gap length ranging between 0.75 m and 1.4 m. Both positive and negative polarity cases were tested. The results indicated that the position of the floating sphere does not significantly affect the flashover-voltage magnitude. There is, however, a definite reduction in the strength of the air gap, between 27 % and 29 %, for the cases tested. Further, the static charge on the floating object did not influence the breakdown voltage. There is also linearity in the air breakdown voltages of simple point-to-plane air gaps. Humidity and temperature also contribute to variations in the breakdown voltage. Two international publications have been published based on the research presented in this report. These are listed in Appendix D and E, respectively.