First self-resonant frequency of power inductors based on approximated corrected stray capacitances

Inductive devices are extensively employed in power electronic systems due to their magnetic energy storage and power transfer capabilities. The current trend is towards increasing the frequency of operation in order to reduce the size of the magnetic components, but the main drawback is that the parasitic capacitance effect can become significant, and degrade the performance of the system. This work analyses the influence of this stray capacitance, and considers how to improve the performance of the device. In general, the impact of the stray capacitance on a magnetic component can be reduced by two methods: reducing the parasitic capacitance between turns of the winding or, alternatively, modifying the arrangement of the connection between turns. To evaluate the last option, an approximated expression of the first self-resonant frequency of the magnetic device is proposed. This gives a rapid assessment of the performance of different devices maintaining the overall equivalent inductance. The proposed expression accounts for the influence of the connection between turns in the bandwidth of the component. Finally, some numerical results are verified with planar coils manufactured on two-layer printed circuit boards

Design and Control of Power Converters for High Power-Quality Interface with Utility and Aviation Grids

Power electronics as a subject integrating power devices, electric and electronic circuits, control, and thermal and mechanic design, requires not only knowledge and engineering insight for each subarea, but also understanding of interface issues when incorporating these different areas into high performance converter design.Addressing these fundamental questions, the dissertation studies design and control issues in three types of power converters applied in low-frequency high-power transmission, medium-frequency converter emulated grid, and high-frequency high-density aviation grid, respectively, with the focus on discovering, understanding, and mitigating interface issues to improve power quality and converter performance, and to reduce the noise emission.For hybrid ac/dc power transmission,• Analyze the interface transformer saturation issue between ac and dc power flow under line unbalances.• Proposed both passive transformer design and active hybrid-line-impedance-conditioner to suppress this issue.For transmission line emulator,• Propose general transmission line emulation schemes with extension capability.• Analyze and actively suppress the effects of sensing/sampling bias and PWM ripple on emulation considering interfaced grid impedance.• Analyze the stability issue caused by interaction of the emulator and its interfaced impedance. A criterion that determines the stability and impedance boundary of the emulator is proposed.For aircraft battery charger,• Investigate architectures for dual-input and dual-output battery charger, and a three-level integrated topology using GaN devices is proposed to achieve high density.• Identify and analyze the mechanisms and impacts of high switching frequency, di/dt, dv/dt on sensing and power quality control; mitigate solutions are proposed.• Model and compensate the distortion due to charging transition of device junction capacitances in three-level converters.• Find the previously overlooked device junction capacitance of the nonactive devices in three-level converters, and analyze the impacts on switching loss, device stress, and current distortion. A loss calculation method is proposed using the data from the conventional double pulse tester.• Establish fundamental knowledge on performance degradation of EMI filters. The impacts and mechanisms of both inductive and capacitive coupling on different filter structures are understood. Characterization methodology including measuring, modeling, and prediction of filter insertion loss is proposed. Mitigation solutions are proposed to reduce inter-component coupling and self-parasitics

A 1-MHz Series Resonant DC-DC Converter with a Dual-Mode Rectifier for PV Microinverters

The photovoltaic (PV) output voltage varies over a wide range depending on operating conditions. Thus, the PV-connected converters should be capable of handling a wide input voltage range while maintaining high efficiencies. This paper proposes a new series resonant dc-dc converter for PV microinverter applications. Compared with the conventional series resonant converter, a dual-mode rectifier is configured on the secondary side, which enables a twofold voltage gain range for the proposed converter with a fixed-frequency phase-shift modulation scheme. The zero-voltage switching turn-on and zero-current switching turn-off can be achieved for active switches and diodes, thereby, minimizing the switching losses. Moreover, a variable dc-link voltage control scheme is introduced to the proposed converter, leading to a further efficiency improvement and input-voltage-range extension. The operation principle and essential characteristics (e.g., voltage gain, soft-switching, and root-mean-square current) of the proposed converter are detailed in this paper, and the power loss modeling and design optimization of components are also presented. A 1-MHz 250-W converter prototype with an input voltage range of 17-43 V is built and tested to verify the feasibility of the proposed converter

Power converters in WBG device technology for automotive applications and characterization setups for GaN power transistors

This PhD dissertation envisages the design of innovative power converters exploiting WBG devices to get state-of-the-art performance in products intended for industrial applications of automotive field. The collaborations with different specialized companies, provided the opportunity to access commercially-available state-of-the-art SiC and GaN technologies and the possibility to realize innovative converter prototypes. Concerning SiC technology, the complete design of a $350kW$ Battery Emulator instrument in collaboration with a company leader in the automotive testing sector, was carried out from scratch exploiting state-of-the-art SiC power-modules, planar magnetics and top-notch MCU technologies. Discrete high-voltage GaN switches were exploited in the Power Supplies design for automotive charger application to target improved performances compared to the market state-of-the-art. Specifically, two high-efficiency prototypes, an AC/DC converter and a DC/DC converter of $7.5kW$, have been realized for this purpose. To further investigate the characteristics of state-of-the-art GaN power devices two measurement set-ups have been designed. In particular, the trapping phenomenon causing the collapse of drain current during ON-state with a consequent degradation of ON-resistance has been analyzed

Bidirectional Electric Vehicles Service Integration in Smart Power Grid with Renewable Energy Resources

As electric vehicles (EVs) become more popular, the utility companies are forced to increase power generations in the grid. However, these EVs are capable of providing power to the grid to deliver different grid ancillary services in a concept known as vehicle-to-grid (V2G) and grid-to-vehicle (G2V), in which the EV can serve as a load or source at the same time. These services can provide more benefits when they are integrated with Photovoltaic (PV) generation. The proper modeling, design and control for the power conversion systems that provide the optimum integration among the EVs, PV generations and grid are investigated in this thesis. The coupling between the PV generation and integration bus is accomplished through a unidirectional converter. Precise dynamic and small-signal models for the grid-connected PV power system are developed and utilized to predict the system’s performance during the different operating conditions. An advanced intelligent maximum power point tracker based on fuzzy logic control is developed and designed using a mix between the analytical model and genetic algorithm optimization. The EV is connected to the integration bus through a bidirectional inductive wireless power transfer system (BIWPTS), which allows the EV to be charged and discharged wirelessly during the long-term parking, transient stops and movement. Accurate analytical and physics-based models for the BIWPTS are developed and utilized to forecast its performance, and novel practical limitations for the active and reactive power-flow during G2V and V2G operations are stated. A comparative and assessment analysis for the different compensation topologies in the symmetrical BIWPTS was performed based on analytical, simulation and experimental data. Also, a magnetic design optimization for the double-D power pad based on finite-element analysis is achieved. The nonlinearities in the BIWPTS due to the magnetic material and the high-frequency components are investigated rely on a physics-based co-simulation platform. Also, a novel two-layer predictive power-flow controller that manages the bidirectional power-flow between the EV and grid is developed, implemented and tested. In addition, the feasibility of deploying the quasi-dynamic wireless power transfer technology on the road to charge the EV during the transient stops at the traffic signals is proven

Overview study of Space Power Technologies for the advanced energetics program

Space power technologies are reviewed to determine the state-of-the-art and to identify advanced or novel concepts which promise large increases in performance. The potential for incresed performance is judged relative to benchmarks based on technologies which have been flight tested. Space power technology concepts selected for their potentially high performance are prioritized in a list of R & D topical recommendations for the NASA program on Advanced Energetics. The technology categories studied are solar collection, nuclear power sources, energy conversion, energy storage, power transmission, and power processing. The emphasis is on electric power generation in space for satellite on board electric power, for electric propulsion, or for beamed power to spacecraft. Generic mission categories such as low Earth orbit missions and geosynchronous orbit missions are used to distinguish general requirements placed on the performance of power conversion technology. Each space power technology is judged on its own merits without reference to specific missions or power systems. Recommendations include 31 space power concepts which span the entire collection of technology categories studied and represent the critical technologies needed for higher power, lighter weight, more efficient power conversion in space

Desenvolvimento de conetores sem contactos (Contactless) para aplicações de elevada potência, baseados em acoplamento indutivo ressonante

Programa Doutoral em Engenharia Eletrónica e de ComputadoresA implementação de conetores sem contactos (contactless) envolve a transmissão de energia sem fios a curta distância. Atualmente, este tipo de sistemas é já uma realidade em algum equipamento das tecnologias de informação (IT) de baixa potência e dimensões reduzidas (smartphones, sobretudo), onde é utilizado para carregamento das respetivas baterias. O presente trabalho tem como objetivo o estudo e a conceção de um sistema de conetores sem contactos de elevada potência (entre 100 W a 1000 W); o princípio subjacente é o acoplamento indutivo ressonante. O sistema destina‐se sobretudo a aplicações têxteis de aquecimento, onde pretende substituir os conetores tradicionais, baseados em contactos condutores. Considerando este domínio de aplicação, é importante que a dimensão do sistema seja a menor possível, o que implica uma otimização cuidada. Pretende‐se que o trabalho esteja sempre ancorado nos fundamentos físicos subjacentes. Assim sendo, começa‐se pela revisão do Eletromagnetismo Clássico, no contexto da área tecnológica em questão. Segue‐se o levantamento do estado da arte, onde os diferentes métodos de transmissão de energia sem fios são revistos e categorizados segundo o princípio físico subjacente. O acoplamento indutivo é então estudado em detalhe, com particular ênfase no transformador linear e respetivos modelos equivalentes. De seguida, aborda‐se o acoplamento indutivo ressonante, onde incide a maioria da componente de investigação do trabalho. Aqui, procura‐se estabelecer uma teoria unificadora no âmbito da Teoria de Circuitos em regime de excitação harmónica estacionária (domínio da frequência), que permita a sistematização do desenvolvimento dos sistemas baseados em acoplamento indutivo ressonante, o que constitui trabalho original. Para tal, recorreu‐se sobretudo ao conceito de alinhamento, usual no domínio dos filtros. A busca dessa teoria deveu‐se à constatação da sua falta aquando do levantamento do estado da arte, no qual ocorrem sobretudo abordagens ad hoc. Dentro dessa teoria, os principais resultados são a identificação e categorização dos diferentes regimes de acoplamento e a identificação de configurações ressonantes com capacidade de regulação de carga. Por fim, procede‐se à conceção de um sistema de conetores sem contactos experimental, sendo assistida por simulação FEA para Eletromagnetismo e por simulação SPICE. No ensaio experimental do sistema, a potência máxima conseguida sem ventilação foi de cerca de 250 W; com ventilação, chegou‐se a 350 W. Em ambos os casos, o rendimento do sistema foi de cerca de 95,5%, tendo‐se considerado que estes resultados demonstram a viabilidade do sistema. O trabalho termina com a indicação de alguns melhoramentos e sugestões de trabalho futuro.The deployment of contactless connectors involves short‐range wireless power transmission. Currently, this type of systems is already implemented in some low‐power and small‐size information technology equipment (IT), for battery charging (smartphones, mainly). The objective of the present work is the study and development of a high‐power system of contactless connectors (from 100 W to 1000 W), based on resonant inductive coupling. The system is primarily intended for textile heating applications, where it would replace traditional connectors, based on conductive contacts. Considering this application domain, the system size should be as small as possible, demanding a careful optimization process. The work should be always anchored on the underlying physical fundamentals. Being so, it begins by reviewing the Classical Electromagnetism in the context of the work’s technological field. Next, the state of the art is studied, and the different methods of wireless power transmission are reviewed and categorized according their underlying physical principle. The inductive coupling is then studied in detail, with particular emphasis on the linear transformer and its equivalent models. After that, the resonant inductive coupling is finally addressed, and this is where the main research component of the work begins. The main goal is the establishment of a tentative unifying theory in the context of Circuit Theory under sinusoidal steady‐state (frequency domain), that would enable the systematization of the development of systems based on resonant inductive coupling, which is original work. This theory is mainly based on the concept of alignment, more usual in the context of filters. The pursuit of such theory was motivated by its absence in the state of the art, in which mainly occur ad hoc approaches. Within this theory, the main results are the identification and categorization of different coupling regimes and the identification of resonant configurations with load regulation capability. Finally, the design of an experimental system of contactless connectors is carried on, with the assistance of FEA simulation for Electromagnetism and SPICE simulation. In the experimental tests, the maximum power achieved by the system without ventilation was about 250 W; with ventilation, the system reached 350 W. In both cases, system efficiency was about 95.5%. It was considered that these results demonstrate the viability of the system. The work ends with the indication of some improvements and future work suggestions

Bibliography of Lewis Research Center technical publications announced in 1977

This compilation of abstracts describes and indexes over 780 technical reports resulting from the scientific and engineering work performed and managed by the Lewis Research Center in 1977. All the publications were announced in the 1977 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Documents cited include research reports, journal articles, conference presentations, patents and patent applications, and theses