Gotowa bibliografia na temat „Switched Mode Converters”

This paper presents three new and improved non-isolated topologies of quadratic boost converters (QBC). Reduced voltage stress across switching devices and high voltage gain with single switch operation are the main advantages of the proposed topologies. These topologies utilize voltage multiplier cells (VMC) made of switched capacitors and switched inductors to increase the converter’s voltage gain. The analysis in continuous conduction mode is discussed in detail. The proposed converter’s voltage gain is higher than the conventional quadratic boost converter, and other recently introduced boost converters. The proposed topologies utilize only a single switch and have continuous input current and low voltage stress across switch, capacitors, and diodes, which leads to the selection of low voltage rating components. The converter’s non-ideal voltage gain is also determined by considering the parasitic capacitance and ON state resistances of switch and diodes. The efficiency analysis incorporating switching and conduction losses of the switching and passive elements is done using PLECS software (Plexim, Zurich, Switzerland). The hardware prototype of the proposed converters is developed and tested for verification.

Switched capacitor DC/DC converters are new prototype of DC/DC conversion technology. Since switched capacitor can be integrated into a power IC chip, consequently, these converters have small size and high power density. Switched capacitor can be used in voltage-lift technique to construct DC/DC converters. The clue is that for the converters operating in discontinuous input current mode (DICM) the switched capacitors can be charged during the input current discontinuous period. The switched capacitors are charged to the source voltage during the switch-off period. They will join the conversion operation during switch-on period, and the stored energy in them will be delivered through further elements to the load. These converters are called switched-capacitorized DC/DC converters. Simulation and experimental results are provided for verification of this design.

The article considers the problems of analyzing DC-DC voltage converters and analyzes the advantages, disadvantages, as well as the scope of full switched and averaged continuous models of the converters. The feasibility of using the complex of two models (full switch model and averaged continuous model) for analyzing their operation is proved. The general approach to the construction of continuous models of DC-DC voltage converters based on state-space averaging method is considered. Disadvantages of the averaged models using a classic approach are shown. The relevance of the development of universal continuous models of DC-DC converters is substantiated. The possibility of creating such models using averaged models of PWM switching structure included in the DC-DC voltage converter is shown. Analyzed the typical structure of the switch-mode power supply with feedback. An averaged model of the switching structure is proposed, basing on which continuous models of DC-DC converters with any topology can be built. The processes occurring in this switching structure in the mode of continuous and discontinuous choke current are analyzed. A method for constructing continuous models of the main types of DC-DC voltage converters based on switching structure averaged model is proposed. The adequacy of continuous models obtained by this method has been proven. The results of modeling transients on the continuous and full switch models for inverting voltage regulator are demonstrated. The possibility of accounting in the model of active resistances of switches and cumulative choke is shown. The possibility of using the proposed model to obtain the open loop transfer functions is demonstrated, in particular, the characteristics of the duty factor - output voltage. These transfer functions can be used to synthesize control system compensating circuits of the switch-mode power supply. The possibility of using a single generalized averaged model of the switching structure to build continuous models of converters with complex topology using both the Voltage Mode and Current Mode is shown. This creates prerequisites for developing a universal averaged continuous model for DC-DC converter based on this principle

In recent times, important contributions and the incorporation of renewable sources, such as photovoltaic, fuel cells, etc., are the main reasons for the popularity of DC microgrids. Integrating renewable sources into the microgrid requires high-voltage, high-efficiency DC-to-DC converters. Without modification, traditional converters are not suitable for achieving the required voltage in microgrid applications, due to the requirement for a large duty cycle, inductor resistance, voltage rating of switches, reverse recovery of the diode, high current rating inductors, etc. Various converters based on the circuitry of voltage multipliers, switched inductors/capacitors, coupled inductors, transformers, etc., have been proposed in the literature and have their drawbacks. In this paper, to realize significant voltage gain with two duty cycle controls, a new multi-leg (ML) converter is recommended as a solution for use in DC microgrids. The converter is designed by incorporating multiple legs into the boost converter. The implications of the proposed converter are reduced device voltage stress, small inductors and capacitors, two-duty cycle control, triple mode operation, single-stage conversion, etc. The proposed converter’s power circuits, mode of operation, and design equations of the converter are presented. The non-ideal model of the proposed converter is discussed, and efficiency is analyzed. The effect of unequal insurance on the operation of the converter is discussed. Comparative studies of converters are provided to draw attention to the benefits of the converter. The results of the experiments are shown to prove that the analysis and performance of the converter are correct. The discontinuous mode of operation and unequal inductance case of the converter are studied with the help of a simulation model.

<p><span>DC-DC converters are devices which convert direct current (DC) from one voltage level to another by changing the duty cycle of the main switches in the circuits. These converters are widely used in switched mode power supplies and it is important to supply a constant output voltage, regardless of disturbances on the input voltage. In this work, the performance of three different converters such as Single-Ended Primary-Inductance Converter (SEPIC), Luo converter and ZETA converter have been analyzed. Further, the parameters values such as ripple voltage, switching losses and efficiency of the proposed three different converters were compared with each other. Also, the simulation work has been carried out using MATLAB/SIMULINK software. From the comparison of obtained results, it is observed that the ZETA converter has high significance than the SEPIC and Luo converter.</span></p>

Abstract: Nowadays Switched-mode power converters are playing a significant role in the industries by providing higher efficiency for various applications. There are various applications that implement power supply and battery charge circuits for devices like smartphones, TVs, and various electronic devices When it comes to DC-DC Converters the most popular among the industries are buck converters and the efficient version of the buck converter is the Synchronous buck converter. The SBC steps down the voltage from higher to lower levels. Efficiency is a crucial parameter as the industry’s focus is on delivering greater performance devices. The power converter's design must be optimized to maximize performance to achieve customer expectations. As a result, a thorough understanding of the synchronous buck converter and how to properly select the circuit components is critical. The proposed work aims at optimizing the Synchronous Buck Converter components such as Inductors, Capacitors, and Resistors. The idea of this optimization study is to improve the performance of the converter and reduce power losses and cost-cutting. In this paper, the control mode considered is peak current mode control.

Dc–dc converters with a high gain, continuous input current, and common ground are usually employed in renewable energy applications to boost the generated output voltage of renewable energy sources. In this paper, a high-gain dc–dc converter comprising a voltage multiplier cell (VMC) and a common ground with continuous input current and low-voltage stress across semiconductor devices is proposed. The converter produces a voltage gain of about ten times compared to the conventional boost converter at a duty ratio of 50% by utilizing switched capacitors and switched inductors. The simultaneous operation of both the switches with the same gate pulse offers easy and simple control of the proposed converter with a wide range of operations. The boundary operation of the converter is analyzed and presented in both modes, i.e., continuous conduction mode (CCM) and discontinuous conduction mode (DCM). Ideal and nonideal analysis of the converter is carried out by integrating real models of passive elements and semiconductor devices by using PLECS software. The simulation is also used to calculate the losses and hence the working efficiency of the converter. The performance of the converter analyzed in the steady state is compared with various similar converters based on the voltage boosting capability and switching stresses. A hardware prototype is also developed to confirm and validate the theoretical analysis and simulation of the proposed converter.

Single stage isolated AC to DC converters find prominence due to simplicity and efficiency in addition to economics. Boundary control Mode BCM Flyback converters are widely used for such applications up to power levels of 200 watts. For higher power levels, average current control mode PFCs are used and two stage conversion is incorporated. In this paper, a novel technique for building a single stage PFC with a Continuous Conduction Mode CCM Flyback AC DC converter is proposed for 500 watts power. A practicalsingle stage converter is built with power factor correction and input output isolation. The unique feature of the new configuration lies in having only one primary MOSFET switch and adapting BCM control in a CCM Flyback configuration and achieving ZVS and ZCS while in CCM operation. Proposed configuration is best suited for battery charger applications. Also, the absence of high voltage bulk capacitor at the mains input adds lot of advantages in terms of eliminating inrush current and saving PCB area. A working model of 130 V Dc output and 4.0A is built and the test data are presented depicting the complete soft switching of all power devices and exhibiting the efficiencies in excess of 95%.

Switched-mode power converters are some of the most widely used power electronics circuits due to their advantages of high conversion efficiency, flexible output voltage, light weight. A variety of control methods have been developed for the switched-mode power converters. However, in many practical situation, additional constraints need to be considered, e.g., safety measurement, current limiting or soft-starting, gross changes of operation point with guaranteed system stability, which has not been fully addressed in the available research works. On the other hand, the majority of the control design for power converters are based on the state-space averaged approach which involves considerable approximation in analysis and synthesis. Hence, advanced control techniques are in demand, which should be more constraints friendly and based on more precise models. In this thesis, much attention has been spent on designing controllers for both DC-DC converters and DC-AC inverters based on hybrid modelling and Lyapunov stability theory. Due to the existence of the power switches, switched-mode power converters are hybrid systems with both continuous dynamics and discrete transition events. Instead of linearizing the converter model around a specific operating point, hybrid modelling captures both dynamics, which results in more accurate models. Firstly, a novel sampled-data control approach is proposed for DC-DC converters. DC-DC converters are modeled as sampled-data switched affine systems according to the status of the power switch. In order to avoid the delay of the switching signal, an on-line prediction method is adopted to estimate the system state at the next switching instant. Based on the switched affine model and the predicted system state, a novel switching control algorithm is synthesized by using the switched Lyapunov theory. The proposed approach is able to not only drive the output to a prescribed set point from any initial condition, but also track a varying reference signal, and the switching frequency can be adjusted online with guaranteed stability. In addition, with this approach, Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM) operations can be treated in a unified way. Experimental verification has been carried out to test the effectiveness and merits of the proposed method. Furthermore, to compensate the information loss due to limited access to the state, a multiple sampling scheme is employed to derive a discrete-time switched affine model with an augmented measurement output for DC-DC converters. Based on the model, an output-feedback switching control law, which drives the system state to a set of attainable switched equilibria, is synthesized by using a quadratic state-space partition. The multiple sampling scheme not only facilitates the controller synthesis, but also improves the energy efficiency of the converter by allowing a lower switching frequency. In addition, hybrid modelling techniques have been extended to more complicated cases – DC-AC inverters as the increasing number of power switches and the time-variant nature of the references. A current controller based on the hybrid model of the three-phase two-level inverter has been developed, which can drive the inverter currents tracking the desired power references in realtime and keep a unity power factor at the same time. This method has been extended to three-phase NPC inverters later on. However, in order to solve the neutral point balancing issue, a capacitor voltages prediction algorithm, modified from model predictive control, has been adopted. It should also be mentioned that a novel hybrid model for a grid-connected single-phase NPC inverter also has been presented, which models not only the dynamic of the inverter but also the dynamic of the current reference. An experimental test platform including a three-phase NPC inverter and a FPGA control board has been designed to demonstrate the implementation of the proposed control scheme in practice.

This thesis details novel control schemes and design techniques with the aim of improving the performance of several switched-mode power converter topologies. These improvements include higher steady-state and transient efficiencies for hard-switching converters and the automatic current limiting provision for LLC resonant converters. The thesis initially attempts to use linear closed-loop controllers to improve the transient response of synchronous buck converters, enabling them to be designed with a lower open-loop bandwidth so that the system can achieve higher efficiency. Three types of controllers were investigated viz: the PID, the state-feedback and the predictive controller. All three controllers exhibit similar step responses, which are the maximum transient responses achievable by the linear controllers with the given requirements. The thesis then examines the parallel converter (i.e. a converter with two parallel connected power modules (PMs)) in detail with a view to improve the efficiency and to minimise the current ripple experienced by the output capacitor. Two control schemes and a design technique for the parallel converter are proposed, to simultaneously improve its efficiency and power density. The parallel converter in this research consists of two non-identical rated PMs (termed main PM and auxiliary PM), with the transient response requirement allocated to the auxiliary PM, thereby allowing the main PM to operate at a lower frequency for higher steady-state efficiency. The first control scheme activates the auxiliary PM only when a pre-determined deviation in load/output voltage is exceeded under a load step. Thus, eliminating the losses contributed by the low efficiency auxiliary PM for small load step changes. The second control scheme shapes the auxiliary PM inductor current to be equal and opposite to the main PM current ripple, which when combined reduce the current ripple as experienced by the output filter capacitor, thereby allowing a lower value (and hence physically smaller) capacitor to be selected for higher power density. In order to improve the converter's steady-state efficiency further, the minimum load condition is allocated to the auxiliary PM in the new design technique. These allow both the main PM inductance and its switching frequency to be lower for higher efficiency. In recent years, the LLC has received much attention owing to its favourable operating characteristics including high efficiency and high power density. Usually one chooses to operate at or very close to the load independent point (LIP) since very little control effort is required to regulate the converter's output voltage in response to changes in the load. However under fault conditions where the load tends towards a short circuit, excessive currents can flow and thus control action need to be taken to protect both the converter and the load. The final topic of the thesis hence studies the characteristics of an LLC resonant converter with current-limiting capacitor-diode clamp and develops a new equivalent circuit model to predict the behaviour under overload conditions. A detailed analysis of the converter is presented using the proposed model, from which a design methodology is derived allowing the optimum circuit components to be selected to achieve the required current limiting/protection characteristics.

In recent years, high brightness light emitting diodes (HBLEDs) have increasingly attracted the interest of both industrial manufacturers and academic research community. Among the several aspects that make LED technology so attractive, the most appreciated characteristics are related to their robustness, high efficiency, small size, easy dimming capability, long lifetime, very short switch-on/switch-off times and mercury free manufacturing. Even if all such qualities would seem to give to solid state lighting a clear advantage over all the other kinds of competing technologies, the issues deriving from the need of LED technology improvement, on one hand, and of the development of suitable electronic ballasts to properly drive such solid state light sources, on the other, have so far hindered the expected practical applications. The latter problem, in particular, is nowadays considered the main bottleneck in view of a widespread diffusion of solid state technology in the general lighting market, as a suitable replacement of the still dominant solutions, namely halogen and fluorescent lamps. In fact, if it is true that some aspects of the devices’ technology (e.g. temperature dependent performance, light quality, efficiency droop, high price per lumen, etc…) still need further improvements, it is now generally recognized that one of the key requirements, for a large scale spread of solid state lighting, is the optimization of the driver. In particular, the most important specifications for a LED lamp ballast are: high reliability and efficiency, high power factor, output current regulation, dimming capability, low cost and volume minimization (especially in domestic general lighting applications). From this standpoint, the main goal is, therefore, to find out simple switched mode power converter topologies, characterized by reduced component count and low current/voltage stresses, that avoid the use of short lifetime devices like electrolytic capacitors. Moreover, if compactness is a major issue, also soft switching capability becomes mandatory, in order to enable volume minimization of the reactive components by increasing the switching frequency in the range of the hundreds of kHz without significantly affecting converter’s efficiency. It is worth mentioning that, in order to optimize HBLED operation, also other matters, like the lamp thermal management concern, should be properly addressed in order to minimize the stress suffered by the light emitting devices and, consequently, the deterioration of the light quality and of the expected lamp lifetime. However, being this work focused on the issues related to the research of innovative driving solutions, the aforementioned thermal management problems, as also all the topics related to the improvement of solid state devices’ technology, will be left aside. The main goal of the work presented in this thesis is, indeed, to find out, analyze and optimize new suitable topologies, capable of matching the previously described specifications and also of successfully facing the many challenges dictated by the future of general lighting. First of all, a general overview of solid state lighting features, of the state of the art of lighting market and of the main LED driving issues will be provided. After this first introduction, the offline driving concern will be extensively discussed and different ways of approaching the problem, depending on the specific application considered, will be described. The first kind of approach investigated is based on the use of a simple structure relying on a single power conversion stage, capable of concurrently ensuring: compliance with the standards limiting the input current harmonics, regulation of the load current and also galvanic isolation. The constraints deriving from the need to fulfil the EN 61000-3-2 harmonics standard requirements, when using such kind of solution for low power (<15W) LED driving purposes, will be extensively discussed. A low cost, low component count, high switching frequency converter, based on the asymmetrical half bridge flyback topology, has been studied, developed and optimized. The simplicity and high compactness, characterizing this solution, make it a very good option for CFL and bulb replacement applications, in which volume minimization is mandatory in order to reach the goal of placing the whole driving circuitry in the standard E27 sockets. The analysis performed will be presented, together with the design procedure, the simulation outcomes and the different control and optimization techniques that were studied, implemented and tested on the converter's laboratory prototype. Another interesting approach, that will be considered, is based on the use of integrated topologies in which two different power conversion stages are merged by sharing the same power switch and control circuitry. In the resulting converter, power factor correction and LED current regulation are thus performed by two combined semi-stages in which both the input power and the output current have to be managed by the same shared switch. Compared with a conventional two-stages configuration, lower circuit complexity and cost, reduced component count and higher compactness can be achieved through integration, at cost of increased stress levels on the power switch and of losing a degree of freedom in converter design. Galvanic isolation can be provided or not depending on the topologies selected for integration. If non-isolated topologies are considered for both semi-stages, the user safety has to be guaranteed by assuring mechanical isolation throughout the LED lamp case. The issue, deriving from the need of smoothing the pulsating power absorbed from the line while avoiding the use of short lifetime electrolytic capacitors, will be addressed. A set of integrated topologies, used as HBLED lamp power supplies, will be investigated and a generalized analysis will be presented. Their input line voltage ripple attenuation capability will be examined and a general design procedure will be described. Moreover, a novel integrated solution, based on the use of a double buck converter, for an about 15W rated down-lighting application will be presented. The analysis performed, together with converter design and power factor correction concerns will be carefully discussed and the main outcomes of the tests performed at simulation level will be provided. The last kind of approach to be discussed is based on a multi-stage structure that results to be a suitable option for medium power applications, like street lighting, in which compactness is not a major concern. By adopting such kind of solution it is, indeed, possible to optimize converter’s behavior both on line and on load side, thereby guaranteeing both an effective power factor correction at the input and proper current regulation and dimming capability at the output. Galvanic isolation can be provided either by the input or the output stage, resulting in a standard two stage configuration, or by an additional intermediate isolated DC-DC stage (operating in open loop with a constant input/output voltage conversion ratio) that namely turns the AC/DC converter topology into a three stage configuration. The efficiency issue, deriving from the need of multiple energy processing along the path between the utility grid and the LED load, can be effectively addressed thanks to the high flexibility guaranteed by this structure that, relaxing the design constraint, allows to easily optimize each stage. A 150W nominal power rated ballast for street solid state lighting applications, based on the latter (three stage) topology, has been investigated. The analysis performed, the design procedure and the simulations outcomes will be carefully described, as well as the experimental results of the tests made on the implemented laboratory prototype.
Negli ultimi anni i dispositivi LED di potenza ad elevata luminosità (HBLED) hanno attirato in misura sempre crescente l'interesse della comunità scientifica, sia all'interno del mondo accademico che di quello industriale. Tra le varie caratteristiche, che rendono questo tipo di tecnologia interessante, le qualità più apprezzate sono certamente: la robustezza, l'elevata efficienza, le piccole dimensioni, la facilità di modulazione dell'intensità luminosa, il lungo tempo di vita, l'estrema rapidità di accensione e spegnimento e l'assenza di mercurio. Nonostante tutti questi aspetti sembrino dare alla tecnologia a stato solido un netto vantaggio rispetto alle tecnologie concorrenti, l'utilizzo dei LED di potenza nel campo dell'illuminazione rimane a tutt'oggi abbastanza limitato. La necessità di ulteriori progressi nella tecnologia dei dispositivi, da un lato, e dello sviluppo di soluzioni in grado di garantirne il corretto ed efficiente pilotaggio, dall'altro, ne hanno, infatti, fino ad ora frenato la diffusione rispetto alle attese. Quest'ultimo aspetto, in particolare, è al giorno d'oggi considerata il vero "collo di bottiglia" in vista dell'impiego su larga scala della tecnologia a stato solido, in sostituzione delle soluzioni, tutt'ora dominanti nel mercato dell'illuminazione, basate sull'utilizzo di lampade alogene e a fluorescenza. Se, da un lato, infatti, è vero che alcuni aspetti della tecnologia dei dispositivi (e.g. variabilità delle prestazioni con la temperatura, qualità della luce, calo dell'efficienza luminosa con l'aumentare della corrente, elevato costo per lumen, ecc...) necessitano di essere ulteriormente perfezionati, dall'altro è ormai universalmente riconosciuto che l'elemento chiave per l'ampia diffusione dell'illuminazione a stato solido è proprio l'ottimizzazione dello stadio di alimentazione. In particolare, le specifiche più importati che un ballast per lampade a LED è tenuto a soddisfare sono: elevata affidabilità ed efficienza, elevato fattore di potenza, capacità di regolazione della corrente di uscita e di modulazione del flusso luminoso, basso costo e minimo ingombro (soprattutto nell'illuminazione domestica). L'obiettivo principale è, quindi, riuscire ad ideare soluzioni basate sull'utilizzo di topologie semplici, caratterizzate da ridotto numero di componenti e limitati livelli di stress di corrente e tensione, che non prevedano l'impiego di componenti con breve tempo di vita come i condensatori elettrolitici. Inoltre, nelle applicazioni in cui la compattezza è considerata uno degli aspetti di maggior rilievo, anche la capacità di operare in soft-switching diviene una specifica indispensabile. Ciò è infatti necessario al fine di permettere la minimizzazione del volume delle componenti reattive, tramite l'aumento della frequenza di commutazione nel range delle centinaia di kHz, senza compromettere l'efficienza del convertitore. Per completezza, vale la pena di ricordare che, per ottimizzare il funzionamento dei LED ad elevata luminosità, andrebbero presi in considerazione anche altri aspetti, come ad esempio le problematiche legate alla gestione del calore dissipato dalla lampada, importanti al fine di limitare gli stress termici subiti dai dispositivi e, di conseguenza, migliorare la qualità della luce emessa e massimizzare il tempo di vita della lampada. Tuttavia, essendo il lavoro presentato in questa tesi centrato sulle questioni relative allo stadio di alimentazione, i suddetti problemi di gestione termica, come anche gli aspetti relativi allo sviluppo della tecnologia dei dispositivi non verranno esaminati. L'obiettivo principale del lavoro che verrà descritto nel corso dei prossimi capitoli, è, infatti, la ricerca di soluzioni innovative per il pilotaggio da rete elettrica di lampade basate su tecnologia a stato solido. Verranno pertanto approfonditamente trattate le tematiche relative ad analisi, ottimizzazione e sviluppo di topologie che siano in grado di soddisfare i requisiti precedentemente enunciati e di affrontare con successo le sfide proposte dalla continua evoluzione dello scenario del "general lighting". Per prima cosa, sarà fornita una visione di insieme riguardante lo stato dell'arte del mercato dell'illuminazione, le caratteristiche dei dispositivi di illuminazione a stato solido ed i principali aspetti relativi al loro pilotaggio. Dopo questa prima sezione introduttiva, la tematica relativa all'alimentazione da rete elettrica di tali dispositivi verrà approfonditamente discussa. Differenti modi di approcciare il problema, a seconda della specifica applicazione considerata, verranno discussi. Il primo tipo di approccio che verrà esaminato si basa sull'uso di una semplice struttura, formata da un singolo stadio di conversione di potenza. Essa è in grado di fornire al contempo il rispetto degli standard che limitano il contenuto armonico della corrente di ingresso, l'isolamento galvanico e la regolazione della corrente e dell'intensità luminosa in uscita. I vincoli, dettati dall'esigenza di garantire il rispetto della normativa EN 61000-3-2, in applicazioni di bassa potenza (<15W) prive di uno stadio dedicato alla correzione del fattore di potenza, verranno approfonditamente trattati. Saranno, poi, illustrati i risultati dello studio, sviluppo ed ottimizzazione di un convertitore a singolo stadio, operante ad elevata frequenza di commutazione, basato sulla topologia flyback a mezzo ponte asimmetrico. La semplicità, il ridotto numero di componenti ed il basso costo, che caratterizzano tale tipo di soluzione, la rendono adatta all'alimentazione di lampade per il settore residenziale, in cui la compattezza dello stadio di alimentazione è di fondamentale importanza al fine di consentirne l'alloggiamento nei classici socket E27. L'analisi effettuata, la procedura di progetto ed risultati ottenuti in simulazione ed a livello sperimentale durante lo studio di tale topologia verranno accuratamente descritti e discussi. Un altro interessante tipo di approccio che verrà considerato si basa sull'utilizzo di topologie integrate, nelle quali due diversi stadi di conversione vengono uniti tramite la condivisione dello stesso interruttore di potenza e della relativa circuiteria di comando. Nel convertitore che ne risulta, la correzione del fattore di potenza e la regolazione della corrente nei LED saranno dunque garantite dalla combinazione dei due semi-stadi, il cui interruttore comune dovrà essere in grado di gestire sia la potenza di ingresso che la corrente di uscita. Rispetto alla configurazione a due stadi convenzionale, la soluzione ottenuta tramite l'integrazione consente una minore complessità circuitale, un ridotto numero di componenti e, di conseguenza, una maggiore compattezza ed un minor costo. Tutto ciò viene guadagnato a scapito di un maggiore livello di stress nei componenti e della perdita di un grado di libertà nel progetto del convertitore. L'isolamento galvanico può essere garantito o meno a seconda del tipo di topologie che vengono selezionate per l'integrazione. Se la scelta ricade su topologie non isolate, la sicurezza dell'utente andrà comunque garantita isolando meccanicamente l'involucro della lampada. I problemi legati alla necessità di smorzare la componente alternata della potenza assorbita dalla rete, evitando al contempo l'utilizzo di componenti con basso tempo di vita, come i condensatori elettrolitici, verranno discussi. A tal proposito si studieranno le caratteristiche di un insieme di topologie integrate, al fine di fornirne un'analisi ed una procedura di design generalizzate. Se ne esaminerà, inoltre, la capacità di attenuare la componente ondulatoria della tensione di ingresso che viene trasferita al carico, dove si traduce in un'oscillazione della corrente di alimentazione fornita ai LED. Verrà proposta, poi, una soluzione basata su una topologia derivante dall'integrazione di due convertitori di tipo step-down (abbassatori di tensione), per applicazioni di "down-lighting", dimensionata per una potenza di circa 15W. Se ne discuteranno, in particolare, i dettagli di maggiore interesse relativi all'analisi effettuata, alla procedura di progetto ed ai risultati dei test effettuati in ambiente di simulazione. L'ultimo tipo di approccio considerato prevede, infine, l'utilizzo di una topologia multi-stadio, ritenuta una scelta appropriata soprattutto per applicazioni lighting di potenza elevata (>60W), come l'illuminazione stradale, in cui la compattezza dell'alimentatore non è ritenuta un aspetto di primaria importanza. Tramite questo tipo di soluzione è, infatti, possibile ottimizzare le prestazioni del convertitore sia dal lato della rete che dal lato del carico. Si riescono a garantire, in tal modo, un'efficace correzione del fattore di potenza, un adeguato controllo della corrente di uscita ed un'appropriata modulazione del flusso luminoso emesso dalla lampada. L'isolamento galvanico può essere fornito dallo stadio di ingresso o da quello di uscita o da un aggiuntivo stadio DC-DC intermedio, operante a catena aperta con rapporto di conversione di tensione costante. In quest'ultimo caso la struttura del convertitore, si trasforma, dalla classica configurazione a due stadi, in una topologia a triplo stadio. Il problema che nasce dalla necessità di assicurare un elevato livello di efficienza del sistema, nonostante l'interposizione di ripetuti stadi di conversione dell'energia tra la rete ed il carico a LED, può essere efficacemente risolto grazie alla flessibilità che caratterizza tale tipo di struttura. L'aumento del numero dei gradi di libertà in fase progettuale permette, infatti, di ottimizzare con semplicità ogni singolo stadio. Per comprovare limiti e potenzialità di tale tipo di approccio, si è deciso di studiare un ballast (dimensionato per una potenza nominale di 150W) basato sulla topologia a triplo stadio precedentemente menzionata, per applicazioni nell'ambito dell'illuminazione stradale. L'analisi condotta, la procedura di progetto ed i risultati delle simulazioni effettuate verranno discussi nel dettaglio, così come i risultati sperimentali dei test di laboratorio effettuati sul prototipo costruito.

Uno de los campos más importantes de la Electrónica de Potencia es el de los convertidores de potencia conmutados, que debido a sus características de alto rendimiento energético, reducido tamaño, posibilidades de regulación del factor de potencia y de elevación de tensión, etc., están presentes en un gran número de las etapas de alimentación de los equipos electrónicos actuales.
Las mejoras tecnológicas en ámbitos como el de la integración de circuitos han permitido importantes reducciones en el tamaño de los equipos (por ejemplo en los ordenadores). Sin embargo, este proceso de reducción de tamaño que, además, suele venir unido a unas especificaciones más rígidas en cuanto a costes, rendimiento, seguridad y prestaciones en general, no se ha producido en igual medida en las etapas de alimentación. El estudio de los convertidores conmutados es por lo tanto un campo necesitado de esfuerzos de investigación y desarrollo.
Para potencias superiores a 25 W, y especialmente en potencias superiores a 150 W, una de las estrategias utilizadas para mejorar las prestaciones de los convertidores es el uso del denominado "interleaving" o entrelazado , definido como la puesta en paralelo de N convertidores idénticos desfasando sus señales de control de forma uniforme a lo largo del periodo de conmutación.
Con el objetivo principal de reducir al máximo los rizados de la tensión de salida y de la corriente de entrada, en esta tesis se estudian casos particulares de "interleaving" en estructuras convertidoras continua-continua que utilizan el convertidor elevador ("boost") como célula básica y cuyas tensiones de salida son, idealmente y operando en modo de conducción continua, múltiplos enteros positivos de la tensión de entrada, de ahí la denominación de multiplicadores de tensión que aparece en el título de tesis propuesto. Posteriormente se analizan las posibilidades de regulación de tensión que presentan algunos de los casos de estudio, a costa de incrementar los rizados.

The use of SMPS (Switched mode power supply) in embedded systems is continuously increasing. The technological requirements of these systems include simultaneously a very good voltage regulation and a strong compactness of components. SEPIC ( Single-Ended Primary Inductor Converter) is a DC/DC switching converter which possesses several advantages with regard to the other classical converters. Due to the difficulty in control of its 4th-order and non linear property, it is still not well-exploited. The objective of this work is the development of successful strategies of control for a SEPIC converter on one hand and on the other hand the effective implementation of the control algorithm developed for embedded applications (FPGA, ASIC) where the constraints of Silicon surface and the loss reduction factor are important. To do it, two non linear controls and two observers of states and load have been studied: a control and an observer based on the principle of sliding mode, a deadbeat predictive control and an Extended Kalman observer. The implementation of both control laws and the Extended Kalman observer are implemented in FPGA. An 11-bit digital PWM has been developed by combining a 4-bit Δ-Σ modulation, a 4-bit segmented DCM (Digital Clock Management) phase-shift and a 3-bit counter-comparator. All the proposed approaches are experimentally validated and constitute a good base for the integration of embedded switching mode converters

Orientador: Ernesto Ruppert Filho
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Resumo: O estudo da utilização de conversores CC/CC isolados e elevadores de tensão para a alimentação de moduladores de pulsos é apresentado neste trabalho. Foi selecionada a topologia em ponte completa, dando-se enfoque ao problema das capacitâncias parasitas envolvidas no circuito, que aparecem de forma acentuada em transformadores elevadores de tensão e filtros indutivos de saída e são altamente indesejáveis quando se opera em regime chaveado. Essas capacitâncias são tratadas através de uma forma de amortecimento, onde a energia armazenada nas mesmas é devolvida à fonte primária ao final de cada semiciclo de chaveamento, tentando obter-se menor volume, maior rendimento e menor dissipação de calor no conversor. Além disso, um circuito de regulação de carga é utilizado para garantir uma maior estabilidade de pulso e contornar problemas típicos de moduladores de pulsos utilizados em radares, como o efeito de backswing. O modulador de pulsos utilizado como carga para esse sistema opera com uma tensão de alimentação de 1kV, frequência de repetição de pulsos (PRF) de 585Hz e consome uma potência da ordem de 2,1kW. O conversor CC/CC é alimentado por um barramento CC não regulado de 280V
Abstract: The study of high-voltage isolated DC/DC converters used to supply pulse modulators is presented on this dissertation. The Full Bridge topology was selected, focusing in problems caused by parasitic capacitances in the circuit. This characteristic, which appears sharply in high voltage transformers and in inductors of output filter, is highly undesirable when the circuit is operated in switching mode. These capacitances are handled using a soft commutation technique, where their stored energy are returned to the primary source in the end of each switching cycle, trying to get a low size, high efficiency and low heat dissipation in the converter. Moreover, a charging regulator circuit is used to ensure good pulse stability and avoid typical problems in the pulse modulators use, such as the backswing effect. The pulse modulator used as load for this converter operates with a supply voltage of 1kV, pulse repetition frequency (PRF) of 585Hz and consumes 2.1 kW. The converter input is supplied by a 280V unregulated DC bus
Mestrado
Energia Eletrica
Mestre em Engenharia Elétrica

En aquesta tesi s'utilitza la noció de resistor lliure de pèrdues (LFR) per dissenyar fonts d'alimentació destinades a iluminació eficient com son els light emmiting diodes (LEDs), làmpades d'alta intensitat de descàrrega (HID) i làmpades d'inducció sense electrodes (IEFL), amb la finalitat de reduir el consum elèctric tant en aplicacions domèstiques com industrials. Aprofitant la naturalesa del LFR, es a dir, un resistència emulada al port d'entrada y una font de potència al port de sortida, les làmpades mencionades anteriorment son alimentades a potència constant independentment del tipus de làmpada i de la seva impedància. La técnica de control en mode de lliscament ha sigut aplicada als convertidors per imposar el comportament de LFR treballant en mode de conducció contínu (CCM) en alguns casos, i en d'altres a la frontera entre CCM i mode de conducció discontinu (DCM). Aquesta técnica de control que s'ha utilitzat al llarg de la tesi, ha estat implementada mitjançant técniques de control analògiques i digitals, permetent regular la llum de les làmpades.
En esta tesis se usa la noción de resistor libre de pérdidas (LFR) para diseñar fuentes de alimentación destinadas iluminación eficiente como por ejemplo light emmiting diodes (LEDs), lamparas de alta intensidad de descarga (HID) y lámparas de inducción sin electrodos (IEFL), con el fin de reducir el consumo eléctrico tanto en aplicaciones domésticas como industriales. Aprovechando la naturaleza del LFR, es decir, una resistencia emulada en el puerto de entrada y una fuente de potencia en el puerto de salida, las lámparas mencionadas anteriormente son alimentadas a potencia constante independientemente del tipo de lámpara e impedancia de la misma, . La técnica de control en modo de deslizamiento es aplicada en los convertidores para imponer el comportamiento de LFR trabajando en modo de conducción continuo (CCM) en algunos casos, y en otros en la frontera entre CCM y modo de conducción discontinuo (DCM). Ésta técnica de control que se a implementado a lo largo de toda la tesis ha sido implementada mediante técnicas de control tanto analógicas como digitales permitiendo regular la luz de las lámparas.
In this thesis, the notion of loss-free resistor (LFR) is used systematically to design power supplies for efficient lighting, namely light emitting diodes (LEDs), high intensity-discharge lamps (HID) and induction electrode-less fluorescent lamps (IEFLs) with the aim of reducing the electrical energy consumption in domestic or industrial applications. The different lamps previously mentioned are supplied at constant power independently of the lamp type and impedance, taking advantage of the LFR nature, i.e. an emulated resistance in the input port and a power source in the output port. The sliding -mode control technique is applied in the converters to impose the LFR behaviour in continuous conduction mode (CCM) in some cases, and in the boundary between CCM and discontinuous conduction mode (DCM) in other cases. This control technique has been implemented throughout the thesis by either analogue or digital controllers and allows regulating the light emitted by the lamps.

Electrical switched-mode DC-DC converters have become ubiquitous in the last decade, primarily driven by their high energy efficiency. Although considerable academic research has been performed on the analogous hydraulic switched-inertance converters, widespread adoption has lagged. This paper presents a comparison of the two technologies, comparing theoretical and practical limits to their performance. First we develop a simple model for the efficiency and specific power capacities of buck and boost converters in the ideal case, so that critical parameters can be identified as well as their physical limitations. We then expand our analysis to include practical effects such as wave propagation, switching losses and operating limits, in an attempt to identify if there are any reasons to continue or discontinue development of the hydraulic switched-inertance converter.

Passive circuits and active circuits (i.e., switched-mode power converters) for vibration-energy harvesting are reviewed, focusing on power-extraction efficiency (PEE). Optimal battery voltage and resistance are given for maximal power extraction by passive circuits. Switched-mode converters are reviewed as means to match the actual battery voltage or load resistance to the optimal ones. To emulate the optimal battery voltage or load resistor, these converters could be controlled by pulse-width modulation (PWM) or by resonance, could operate in continuous or discontinuous conduction modes (CCM or DCM), and could leverage the piezoelectric (PZT) impedances in the energy extraction process. The large filter capacitor usually found after the bridge rectifier actually degrades the PEE. Resonance between the output capacitor of the PZT and the converter inductor improves the PEE at the expense of higher voltage and current stresses.

The project was originally aimed at investigating and developing new efficient methods for cost effective removal of ammonia (NH₃) and hydrogen sulfide (H₂S) from Concentrated Animal Feeding Operations (CAFO), in particular broiler and laying houses (NH₃) and hog houses (H₂S). In both cases, the principal idea was to design and operate a dedicated air collection system that would be used for the treatment of the gases, and that would work independently from the general ventilation system. The advantages envisaged: (1) if collected at a point close to the source of generation, pollutants would arrive at the treatment system at higher concentrations; (2) the air in the vicinity of the animals would be cleaner, a fact that would promote animal growth rates; and (3) collection efficiency would be improved and adverse environmental impact reduced. For practical reasons, the project was divided in two: one effort concentrated on NH₃₍g₎ removal from chicken houses and another on H₂S₍g₎ removal from hog houses. NH₃₍g₎ removal: a novel approach was developed to reduce ammonia emissions from CAFOs in general, and poultry houses in particular. Air sucked by the dedicated air capturing system from close to the litter was shown to have NH₃₍g₎ concentrations an order of magnitude higher than at the vents of the ventilation system. The NH₃₍g₎ rich waste air was conveyed to an acidic (0<pH<~5) bubble column reactor where NH₃ was converted to NH₄⁺. The reactor operated in batch mode, starting at pH 0 and was switched to a new acidic absorption solution just before NH₃₍g₎ breakthrough occurred, at pH ~5. Experiments with a wide range of NH₃₍g₎ concentrations showed that the absorption efficiency was practically 100% throughout the process as long as the face velocity was below 4 cm/s. The potential advantages of the method include high absorption efficiency, lower NH₃₍g₎ concentrations in the vicinity of the birds, generation of a valuable product and the separation between the ventilation and ammonia treatment systems. A small scale pilot operation conducted for 5 weeks in a broiler house showed the approach to be technically feasible. H₂S₍g₎ removal: The main goal of this part was to develop a specific treatment process for minimizing H₂S₍g₎ emissions from hog houses. The proposed process consists of three units: In the 1ˢᵗ H₂S₍g₎ is absorbed into an acidic (pH<2) ferric iron solution and oxidized by Fe(III) to S⁰ in a bubble column reactor. In parallel, Fe(III) is reduced to Fe(II). In the 2ⁿᵈ unit Fe(II) is bio-oxidized back to Fe(III) by Acidithiobacillus ferrooxidans (AF).In the 3ʳᵈ unit S⁰ is separated from solution in a gravity settler. The work focused on three sub-processes: the kinetics of H₂S absorption into a ferric solution at low pH, the kinetics of Fe²⁺ oxidation by AF and the factors that affect ferric iron precipitation (a main obstacle for a continuous operation of the process) under the operational conditions. H₂S removal efficiency was found higher at a higher Fe(III) concentration and also higher for higher H₂S₍g₎ concentrations and lower flow rates of the treated air. The rate limiting step of the H₂S reactive absorption was found to be the chemical reaction rather than the transition from gas to liquid phase. H₂S₍g₎ removal efficiency of >95% was recorded with Fe(III) concentration of 9 g/L using typical AFO air compositions. The 2ⁿᵈ part of the work focused on kinetics of Fe(II) oxidation by AF. A new lab technique was developed for determining the kinetic equation and kinetic parameters (KS, Kₚ and mₘₐₓ) for the bacteria. The 3ʳᵈ part focused on iron oxide precipitation under the operational conditions. It was found that at lower pH (1.5) jarosite accumulation is slower and that the performance of the AF at this pH was sufficient for successive operation of the proposed process at the H₂S fluxes predicted from AFOs. A laboratory-scale test was carried out at Purdue University on the use of the integrated system for simultaneous hydrogen sulfide removal from a H₂S bubble column filled with ferric sulfate solution and biological regeneration of ferric ions in a packed column immobilized with enriched AFbacteria. Results demonstrated the technical feasibility of the integrated system for H₂S removal and simultaneous biological regeneration of Fe(III) for potential continuous treatment of H₂S released from CAFO. NH₃ and H₂S gradient measurements at egg layer and swine barns were conducted in winter and summer at Purdue. Results showed high potential to concentrate NH₃ and H₂S in hog buildings, and NH₃ in layer houses. H₂S emissions from layer houses were too low for a significant gradient. An NH₃ capturing system was designed and tested in a 100-chicken broiler room. Five bell-type collecting devices were installed over the litter to collect NH₃ emissions. While the air extraction system moved only 10% of the total room ventilation airflow rate, the fraction of total ammonia removed was 18%, because of the higher concentration air taken from near the litter. The system demonstrated the potential to reduce emissions from broiler facilities and to concentrate the NH₃ effluent for use in an emission control system. In summary, the project laid a solid foundation for the implementation of both processes, and also resulted in a significant scientific contribution related to AF kinetic studies and ferrous analytical measurements.