The study involves the following stages: First, coupled-inductor and integrated magnetic structure used in Cuk converter circuit topologies are analyzed and the necessary information about these elements in circuit design is gathered. Also, benefits of using these magnetic elements are presented. Secondly / steady-state model, dynamic model and transfer functions of coupled-inductor Cuk converter topology are obtained via state-space averaging method. Third stage deals with determining the design criteria to be fulfilled by the implemented circuit. The selection of the circuit components and the design of the coupled-inductor providing ripple-free input current waveform are performed at this stage. Fourth stage introduces the experimental results of the implemented circuit operating in open loop mode. Besides, the controller design is carried out and the closed loop performance of the implemented circuit is presented in this stage.

Ce travail de th`ese est consacré à la conception, la réalisation technologique et la caractérisation fonctionnelle d'un nouveau type de capteur de champ magnétique MEMS 3D. Différent de l'approche classique utilisée pour des magnétomètres MEMS 3D, le capteur conçu dans le cadre de cette thèse n'a pas comme base le principe de la force de Lorentz, mais se sert des avantages qu'offrent les matériaux magnétiques intégrés dans des systèmes MEMS. Le matériau magnétique subit un moment lorsqu'il est soumis à un champ magnétique environnant. Le principe de détection du signal est basé sur la piézorésistivité et utilise des jauges en silicium mono-crystallin avec une section nanométrique. Le concept technologique convient également pour la fabrication de capteurs inertiels et est donc une approche prometteuse pour la fabrication des centrales de mesure inertielle (IMUs). La conception est principalement basée sur un modèle de bruit. En dehors de la considération des limitations technologiques, des aspects mécaniques, magnétiques et thermiques sont également pris en compte. Deux pistes ont été étudiées pour l'intégration du matériau magnétique. Une première option consiste dans l'intégration d'aimants terres-rares comme SmCo et NdFeB. Une deuxième option a pour objet l'intégration des multi-couches antiferromagnétiques et ferromagnétiques, couplées par le couplage d'échange. La réalisation technologique bien exigeante des ces deux approches sera présentée avec une concentration particulière sur les propriétés magnétiques des matériaux utilisés. Une autre partie sera consacrée à la caractérisation des contraintes mécaniques dans des couches minces qui peuvent devenir problématiques pour les micro-systèmes conçus dans le cadre de ce travail. Au final, la fabrication du capteur ainsi que des caractérisations fondamentales seront présentées afin d'établir une preuve expérimentale pour le concept du capteur. / This PhD thesis deals with the design, the technological implementation, and functional characterizations of a new type of monolothic 3D MEMS magnetometer. Other than for the classical approach used for 3D MEMS magnetometers, the sensor developed in this work is not based on the principle of Lorentz force, but takes advantage of magnetic material which is integrated into the MEMS device and experiences a torque when surrounded by a magnetic field. Signal detection is based on piezoresistive detection using gauges of monocrystalline silicon with nanometric section. The technological concept is also suitable for the fabrication of inertial sensors and thus a very promising approach for fabrication of inertial measurement units (IMUs). Sensor design mainly relies on a noise model. Besides technological limitations, mechanical, magnetic and thermal aspects are also taken into account. Two different methods for integration of magnetic material were explored. A first option consists in the integration of rare-earth magnets like SmCo and NdFeB, a second option is about the integration of exchange-bias coupled antiferromagnetic and ferromagnetic multilayers. The technologically challenging implentation of both approaches will be discussed with a special focus on magnetic properties of the used materials. A further part will be dedicated to the characterization of mechanical stress in thin layers, which may become problematic for the microsystems conceived in this work. Finally, sensor fabrication and fundamental characterizations will be presented as experimental proof of concept for the sensor.

With the fast advance in VLSI technology, smaller, more powerful digital system is available. It requires power supply with higher power density, lower profile and higher efficiency. PWM topologies have been widely used for this application. Unfortunately, hold up time requirement put huge penalties on the performance of these topologies. Also, high switching loss limited the power density achievable for these topologies. Two techniques to deal with hold up time issue are discussed in this dissertation: range winding solution and asymmetric winding solution, the efficiency at normal operation point could be improved with these methods. To reduce secondary rectifier conduction loss, QSW synchronous rectifier is developed, which also helps to achieve ZVS for symmetrical half bridge converter. Although with these methods, the efficiency of front end DC/DC converter could be improved, the excessive switching loss prohibited higher switching frequency. To achieve the targets, topologies with high switching frequency and high efficiency must be developed. Three resonant topologies: SRC, PRC and SPRC, are been investigated for this application because of their fame of low switching loss. Unfortunately, to design with hold up requirement, none of them could provide significant improvements over PWM converter. Although the negative outcome, the desired characteristic for front end application could be derived. Base on the desired characteristic, a thorough search is performed for three elements resonant tanks. LLC resonant topology is found to posses the desired characteristic. From comparison, LLC resonant converter could reduce the total loss by 40% at same switching frequency. With doubled switching frequency, efficiency of LLC resonant converter is still far better than PWM converters. To design the power stage of LLC resonant converter, DC analysis is performed with two methods: simulation and fundamental component simplification. Magnetic design is also discussed. The proposed integrated magnetic structure could achieve smaller volume, higher efficiency and easy manufacture. To make practical use of the topology, over load protection is a critical issue. Three methods to limit the stress under over load situation are discussed. With these methods, the converter could not only survive the over load condition, but also operate for long time under over load condition. Next small signal characteristic of the converter is investigated in order to design the feedback control. For resonant converter, state space average method is no longer valid. Two methods are used to investigate the small signal characteristic of LLC resonant converter: simulation and extended describing function method. Compare with test results, both methods could provide satisfactory results. To achieve both breadth and depth, two methods are both used to reveal the myth. With this information, compensator for feedback control could be designed. Test circuit of LLC resonant converter was developed for front end DC/DC application. With LLC topology, power density of 48W/in3 could be achieved compare with 13W/in3 for PWM converter. / Ph. D.

The extensive use of nonlinear loads in today’s world has inspired considerable research interest in the area of power quality improvement. This thesis proposes an integrated magnetics based compact solution which provides regulated, balanced and sinusoidal load voltage drawing sinusoidal and balanced currents from the grid. Thus, it supplies clean power to the load without polluting the grid. It consists of an EI shaped magnetic core and two compensators known as the series and shunt compensators. The series compensator ensures the quality of output voltage, where as the shunt one takes care of quality of the current drawn from the grid. The magnetic circuit acts as a common domain for interaction between the energy ports. It also provides galvanic isolation between the inverters, load and the grid. The magnetic circuit incorporates a virtual arm switching mechanism to have an option of connecting the inverters either in series or in parallel with each other depending on the requirements. During normal mode when the switch remains inactive, the series inverter is effectively in series with the load and the shunt inverter is effectively connected across the load. Therefore, the voltage source inverters can be independently controlled to serve the purpose of series and shunt compensation. The shunt inverter is always connected in shunt with the grid. The magnetic arm switch is activated during grid power failure. Then the switch ensures parallel connection of the inverters and the load. The inverters are controlled to share the load power according to the respective ratings. Thus the magnetic arm switching mechanism helps in improving the system reliability. The series inverter also can be connected in parallel with the shunt one in presence of the grid to supplement the shunt inverter by supplying harmonic and reactive currents. The design, modelling and implementation issues for single phase applications are considered first. A simple controller structure for this application is also discussed in the thesis. The individual compensation actions are then verified by simulation and experimental results. The three phase power quality compensator is in principle an extension of the single phase quality power supply. It is realized by combining three single phase units with minor modification in terms of windings. A more compact structure is also proposed wherein a single integrated magnetic circuit for the three phase application can be used. The composite magnetic circuit is modelled and designed considering a laboratory prototype. A synchronously rotating reference frame based controller structure for the series and shunt compensators are discussed. The control of the inverters in power sharing mode (with parallel connected inverters) are also proposed and discussed. Experimental and simulated results are presented to verify and validate the operation of this compensator in different operating modes. An effective improvement in the control dynamics is achieved for handling unbalanced and nonlinear loading without increasing inverter switching frequency and controller parameters. In other words, the modified control scheme can handle nonlinear and unbalanced loading with relatively slow proportional integral (PI) controllers. Suitable feed forward compensation terms corresponding to each harmonic component are added to the output of the PI controllers in order to achieve this effective improvement. Experimental results show good improvement in this regard (for both series and shunt compensations).