Academic literature on the topic 'Switched Mode Power Converters'

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.

Measurement-based behavioral electromagnetic interference (EMI) models have been shown earlier to accurately capture the EMI behavior of switched power converters. These models are compact, linear, and run in frequency domain, enabling faster and more stable simulations compared to the detailed lumped circuit models. So far, the behavioral EMI modeling techniques are developed and applied to the converter's input side only. The resulting models are therefore referred to as "terminated EMI models". Under the condition that the output side of the converter remains fixed, these models can predict the input side EMI for any change in the impedance of the input side network. However, any change at the output side would require re-extraction of the behavioral model. Thus the terminated EMI models are incapable of predicting the change in the input side EMI due to changes at the output side of the converter or vice versa. The above mentioned limitation has been overcome by an "un-terminated EMI model" proposed in this dissertation. Un-terminated EMI models are developed here to predict both the common-mode (CM) and the differential (DM) noise currents at the input and the output sides of a motor-drive system. The modeling procedure itself has been simplified and now requires fewer measurements and results in less noise in the identified model parameters. Both CM and DM models are then combined to predict the total noise in the motor drive system. All models are validated by experiments and their limitations identified. A significant portion of this dissertation is then devoted to the application of behavioral EMI models in the design of EMI filters. Comprehensive design procedures are developed for both DM and CM filters in a motor-drive system. The filters designed using the proposed methods are experimentally shown to satisfy the DO-160 conducted emissions standards. The dissertation ends with a summary of contributions, limitations, and some future research directions.<br>Ph. D.

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.<br>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.

A method to obtain the exact control-to-output and input-to-output transfer functions for switched DC-to-DC pulse-width modulated power converters is applied to different combinations of operating conditions such as continuous conduction mode (CCM), discontinuous conduction mode (DCM), and discontinuous voltage mode (DVM) and methods of control such as normal voltage mode (NVM), current programming mode (CPM), and V-squared control. The majority of these combinations have not previously had their transfer functions of interest derived to the accuracy provided by the method. The derivation of the method is covered, and the results from its application are verified by simulation. The simulation method is also justied and proposed as an improvement to the methods used by simulation engines for switched mode power supply design such as SIMPLIS.

Increasing the power density of power electronic converters while reducing or maintaining the same cost, offers a higher potential to meet the current trend inrelation to various power electronic applications. High power density converters can be achieved by increasing the switching frequency, due to which the bulkiest parts, such as transformer, inductors and the capacitor's size in the convertercircuit can be drastically reduced. In this regard, highly integrated planar magnetics are considered as an effective approach compared to the conventional wire wound transformers in modern switch mode power supplies (SMPS). However, as the operating frequency of the transformers increase from several hundred kHz to MHz, numerous problems arise such as skin and proximity effects due to the induced eddy currents in the windings, leakage inductance and unbalanced magnetic flux distribution. In addition to this, the core losses whichare functional dependent on frequency gets elevated as the operating frequency increases. Therefore, this thesis provides an insight towards the problems related to the high frequency magnetics and proposes a solution with regards to different aspects in relation to designing high power density, energy efficient transformers.The first part of the thesis concentrates on the investigation of high power density and highly energy efficient coreless printed circuit board (PCB) step-down transformers useful for stringent height DC-DC converter applications, where the core losses are being completely eliminated. These transformers also maintain the advantages offered by existing core based transformers such as, high coupling coefficient, sufficient input impedance, high energy efficiency and wide frequencyband width with the assistance of a resonant technique. In this regard, several coreless PCB step down transformers of different turn’s ratio for power transfer applications have been designed and evaluated. The designed multilayered coreless PCB transformers for telecom and PoE applications of 8,15 and 30W show that the volume reduction of approximately 40 - 90% is possible when compared to its existing core based counterparts while maintaining the energy efficiency of the transformers in the range of 90 - 97%. The estimation of EMI emissions from the designed transformers for the given power transfer application proves that the amount of radiated EMI from a multilayered transformer is lessthan that of the two layered transformer because of the decreased radius for thesame amount of inductance.The design guidelines for the multilayered coreless PCB step-down transformer for the given power transfer application has been proposed. The designed transformer of 10mm radius has been characterized up to the power level of 50Wand possesses a record power density of 107W/cm3 with a peak energy efficiency of 96%. In addition to this, the design guidelines of the signal transformer fordriving the high side MOSFET in double ended converter topologies have been proposed. The measured power consumption of the high side gate drive circuitvitogether with the designed signal transformer is 0.37W. Both these signal andpower transformers have been successfully implemented in a resonant converter topology in the switching frequency range of 2.4 – 2.75MHz for the maximum load power of 34.5W resulting in the peak energy efficiency of converter as 86.5%.This thesis also investigates the indirect effect of the dielectric laminate on the magnetic field intensity and current density distribution in the planar power transformers with the assistance of finite element analysis (FEA). The significanceof the high frequency dielectric laminate compared to FR-4 laminate in terms of energy efficiency of planar power transformers in MHz frequency region is also explored.The investigations were also conducted on different winding strategies such as conventional solid winding and the parallel winding strategies, which play an important role in the design and development of a high frequency transformer and suggested a better choice in the case of transformers operating in the MHz frequency region.In the second part of the thesis, a novel planar power transformer with hybrid core structure has been designed and evaluated in the MHz frequency region. The design guidelines of the energy efficient high frequency planar power transformerfor the given power transfer application have been proposed. The designed corebased planar transformer has been characterized up to the power level of 50W and possess a power density of 47W/cm3 with maximum energy efficiency of 97%. This transformer has been evaluated successfully in the resonant converter topology within the switching frequency range of 3 – 4.5MHz. The peak energy efficiency ofthe converter is reported to be 92% and the converter has been tested for the maximum power level of 45W, which is suitable for consumer applications such as laptop adapters. In addition to this, a record power density transformer has been designed with a custom made pot core and has been characterized in thefrequency range of 1 - 10MHz. The power density of this custom core transformer operating at 6.78MHz frequency is 67W/cm3 and with the peak energy efficiency of 98%.In conclusion, the research in this dissertation proposed a solution for obtaining high power density converters by designing the highly integrated, high frequency(1 - 10MHz) coreless and core based planar magnetics with energy efficiencies inthe range of 92 - 97%. This solution together with the latest semiconductor GaN/SiC switching devices provides an excellent choice to meet the requirements of the next generation ultra flat low profile switch mode power supplies (SMPS).