Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This Ph.D. Dissertation focuses on the proposal of a novel converter topology applied to the connection of an energy storage system, composed of a supercapacitor bank and a battery bank, to the dc bus of a residential microgrid. The proposed full-bridge-forward integrated dc-dc converter presents high voltage gain between the input and output, a fundamental requirement for the desired application, bidirectional power flow, galvanic isolation, among other features. The integration process, operation stages (including converter waveforms and equations), design methodology, dc modeling, among others, are presented. Three different clamping circuits structures are studied and applied to the proposed converter. Moreover, a comparison including several parameters with the dual active bridge converter, which is one of the most used topologies for similar applications is performed, highlighting the lesser number of active switches. Experimental results of the proposed converter in different operation modes are presented, validating the theoretical analysis. Experimental results of the dual active bridge converter are also presented and its performance is compared to the proposed converter, where it can be seen that the efficiency of the proposed converter is higher. The topology application is directed to microgrid systems, which attract high attention nowadays due to the possibility of renewable electric energy generation through distributed energy resources and with high reliability. / Esta Tese de Doutorado tem como foco a proposta de uma nova topologia de conversor aplicado para conexão de um sistema de armazenamento de energia, composto de um banco de supercapacitores e um banco de baterias, ao barramento CC de uma microrrede residencial. O conversor CC-CC integrado full-bridge-forward proposto apresenta alto ganho de tensão entre a entrada e saída, requisito fundamental para a aplicação desejada, fluxo de potência bidirecional, isolação galvânica, entre outras características. O processo de integração, etapas de operação (incluindo formas de onda e equações do conversor), metodologia de projeto, modelagem CC, entre outros, são apresentados. Três diferentes estruturas de circuitos grampeadores são estudadas e aplicadas ao conversor proposto. Além disso, uma comparação de diversos parâmetros com o conversor dual active bridge, que é uma das topologias mais utilizadas para aplicações semelhantes é realizada, destacando o menor número de interruptores. Resultados experimentais do conversor proposto em diferentes modos de operação são apresentados, validando as análises teóricas. Resultados experimentais do conversor dual active bridge também são apresentados e o seu desempenho é comparado ao do conversor proposto, onde se observa que o rendimento do conversor proposto é superior. A aplicação da topologia é voltada para sistemas de microrrede, os quais atraem grande atenção atualmente devido à possibilidade de geração de energia elétrica de maneira renovável através de fontes distribuídas e com elevada confiabilidade.

Switched-capacitor (SC) DC-DC converters provide a viable solution for on-chip DC-DC conversion as all the components required are available in most processes. However, power efficiency, power density characteristics of SC converters are adversely affected by the integration, and characteristics such as response time and noise can be further improved with an on-chip converter. An analysis on speed, power efficiency, and noise performance of SC converters is presented and verified using simulations. Based on the analysis two techniques, converter-gating and adaptive gain control, are developed. Converter-gating uses a combination of smaller stages and reconfiguration during transient load steps to improve the power efficiency and transient response speed. The stages of the converter are also distributed across the die to reduce the voltage drop and noise on power supply. Adaptive gain control improves transient response through manipulation of the gain of the integrator in the control loop. This technique focuses on improving the response time during converter reconfiguration and offers a general solution to transient response improvement instead of focusing on the worst case scenario which is usually the largest transient load step. The techniques developed are then implemented in ST 28nm FDSOI process and test methodologies are discussed.

Doctor of Philosophy / Department of Electrical and Computer Engineering / Medhat M. Morcos / Characterized by variable impedances, DC power sources normal operation, reliability, and life-time is negatively affected by the sequential switching within any DC power system. The impedances of Nickel-Cadmium (NiCd) storage batteries and Direct Ethanol Fuel Cells (DEFC) vary nonlinearly; therefore, existing DC power system models, that employ averaging of the sequential switching process, are inaccurate in describing the system output voltage. In this research, Fourier-series models of DC–DC converters are developed and evaluated, through numerical computations and computer simulations. Both NiCd-DC converter and DEFC-DC converter power systems are experimentally evaluated over a selected switching frequency range. Input voltage and output voltage characteristics of two types of DEFC-DC converter systems (Nickel-mesh and Nickel-foam electrode assembly) are determined. Experimental results are compared to computer simulations, thus validating the Fourier-series models. Experimental results show a correlation between the DC converter switching frequency and the output of the DC power system. Sequential switching operation, along with the type of DC converter employed, are factors determining the maximum power transfer of the system. The models developed in this work are flexible over a large switching frequency range, and for any desired duty cycle. Correction factors, accounting for the source-converter impedance matching, are easily implemented in Fourier-series models. The research demonstrates the advantages of Fourier-series models, as compared to both large-signal and small-signal models, with regard to accuracy and ease of implementation to any DC–DC converter-driven power system.

The increasing use of electrical technologies within on-board (aircraft, road vehicle, train and ship) power systems is resulting in complex and highly dynamic networks in which energy storage devices have an important role to play, for example to resolve the instantaneous mismatch between load demand and power availability or to provide the flexibility to optimise overall performance. In this thesis, a multi-level controller for a super-capacitor based energy storage system (ESS) is designed, simulated, emulated and validated experimentally to show its effectiveness in smoothing load and managing state-of-charge of the energy storage system. This thesis first investigates the low level control of the dual-interleaved converter, particularly at light load where seven discontinuous conduction modes (DCMs) appear. A thorough analysis of these operating modes is given and validated by simulations and experiments. Based on the analysis, an inverse-model-based feed-forward current controller is implemented, offering a low level converter control interface which serves the high level supervisory controller within the energy storage system. Two supervisory control methods have been proposed in this thesis, both producing a super-capacitor current reference for the low level controller. The first supervisory control not only manages the energy within the ESS but also shields the primary power source from rapid load transients , which has been examined through an emulated ESS in the Intelligent Electrical Power Network Evaluation Facility (IEPNEF). A more advanced supervisory controller is then proposed which in addition to the benefits of the first control, regulates the rate-of-change in power that is drawn from the primary power source in the system. The proposed second control method is implemented within a real super-capacitor energy storage system in IEPNEF, with both simulation and experimental results successfully demonstrating and validating its operation.

A worldwide awareness of the environment is accelerating fuel cell vehicle development. With respect to power electronics, special requirement is on the development of high efficiency, high voltage ratio bi-directional DC/DC converter for fuel cell energy system management. In this paper, two bi-directional DC/DC converters, which are developed for Ford Motor Company’s fuel cell vehicle, are compared from different aspects. Comparison is concentrated on the circuit topology and EMI performance. Emphasis is placed on soft-switch, hard-switch, synchronized rectification, auxiliary start-up winding and their effect on EMI performance in this kind of isolated bi-directional converter. Comparison includes circuits analysis and test result. The EMI test setup is described. EMI measurements are given and explained. EMI solutions for bi-directional DC/DC converter are discussed. An EMI filter is designed and final test result is given. / Master of Science

The DC House project relies primarily on renewable energy sources to provide DC power to the various loads of the house. However, not all renewable sources are capable of providing power at all times of the day. A back-up energy source in the form of a battery storage system must be available to meet the electrical needs of the house. A bi-directional flyback power converter was initially designed to allow a battery to charge from as well as discharge to the 48V bus line of the DC House. The design provided a 35W prototype to demonstrate the converter’s feasibility. Further improvements to increase power output through changes in design as well as improving the control scheme of the bi-directional converter were conducted. Results allowed an increase of output power to 48W with efficiency at 82% for both charging and discharging. The improvements to the control scheme allowed for better management of charging and discharging cycles of the battery.

Energy Harvesting from Exercise Machines (EHFEM) is an ongoing project pursuing alternate forms of sustainable energy for Cal Poly State University. The EHFEM project seeks to acquire user-generated DC power from exercise machines and sell that energy back to the local grid as AC power. The end goal of the EHFEM project aims to integrate a final design with existing elliptical fitness trainers for student and faculty use in Cal Poly’s Recreational Center. This report examines whether including the DC-DC converter in the EHFEM setup produces AC power to the electric grid more efficiently and consistently than an EHFEM system that excludes a DC-DC converter. The project integrates an overvoltage protection circuit, a DC-DC converter, and a DC-AC microinverter with an available elliptical trainer modified to include an energy converting circuit. The initial expectation was that a DC-DC converter would increase, when averaged over time, the overall energy conversion efficiency of the EHFEM system, and provide a stable voltage and current level for the microinverter to convert DC power into AC power. In actuality, while including a DC-DC converter in a test setup allows the EHFEM system to function with less frequent interruptions, this occurs at the cost of lower efficiency. Testing demonstrates the EHFEM project can convert user-generated DC mechanical power into usable AC electrical power. Retrofitting existing equipment with the EHFEM project can reduce Cal Poly’s energy cost.

In this work, a modified boost converter design has been implemented in a multiphase configuration with a condensed topology. The modified aspect of the design has already been proven to drastically reduce input current ripple by about 40% in a single-phase implementation. By placing two modified boost converters in parallel with interleaving main switches (multiphase), the input inductors and modified capacitors of the modified topology can be reduced to just one of each, lowering the number of components, size, and cost. Additionally, multiphase DC/DC converters lower input/output voltage and current ripples while delivering more power compared to single-phase converters. By combining the modified and multiphase benefits, this thesis creates a topology with low ripple and noise while providing high power capability. This thesis covers the analysis, simulation, hardware implementation, and testing of the Modified-Multiphase Boost Converter as well as an equivalent Standard-Multiphase Boost Converter for comparison. Simulation and hardware test results exhibited a 9% input current ripple reduction with the Modified-Multiphase design, presenting a high-power converter with considerable input noise reduction. Keywords: dc/dc, boost, multiphase, interleave, modified, power, ripple

The master thesis deals with the development of buck-boost DC-DC converter which supplies matrix beam module. The design is focused on testing two-phase boost converter and three channel buck converter manufactured by NXP Semiconductors. Part of the design is implementation of microcontroller for converter control and communication with computer. Part of the thesis is also to design user interface on Windows platform for easy system configuration. Next thing the thesis deals with is designing load for DC-DC converter that is variable and can make different current consumption. One part of this thesis is focused to achieve the lowest conducted emissions and to maximize conducted immunity. Part of this project is production of a prototype and prototype testing.

A boost converter is one of the most efficient techniques to step up DC input voltage to a higher needed DC output voltage. The boost converter has many possible applications, such as in a photovoltaic system, hybrid car and battery charger. The proposed prototype in this report is a proof of concept that a Two-Phase Boost Converter is a possible improvement topology to offer higher efficiency without compromising any advantages readily offered by a basic boost. The prototype is designed to be able to handle up to 200 watts of output power with an input of 36 volts and an output of 48 volts. This paper goes through step-by-step the calculation, design, build and test of a Two-Phase Boost Converter. Calculations found in this paper were done on Mathcad and the simulations were done on LTSpice and Pspice. These include converter’s efficiency and other measures of converter’s performance. Advantages, disadvantages as well as possible improvements of the proposed topology will be presented. Data collected and analyzed from the prototype were done on a bench test, not through an actual application.