Electrical & Computer Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2765
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Item A BARE-DIE SIC-BASED ELECTRO-THERMALLY CO-DESIGNED WIRE-BONDLESS HIGH-FREQUENCY DC-DC CONVERTER(2021) Park, Yongwan; Khaligh, Alireza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The current technological status of switch-mode power converters requires a paradigm shift to enable a substantial enhancement in power density. The emergence of wide-bandgap (WBG) devices such as Silicon Carbide (SiC) MOSFETs o↵ers the possibility to achieve high power-density by enabling higher switching frequency and higher temperature operation. This dissertation addresses the following shortcomings of conventional designs: 1) High values of commutation loop inductances and parasitic capacitances which prohibit fast, reliable and efficient switching performance, 2) inadequate thermal design capable of handling very high heat-fluxes (exceeding hundreds of W/cm2), which naturally stem from highly compact design and high allowable losses of the SiC devices, and 3) decoupled and sequential electrical and thermal designs, which leads to sub-optimal electro-thermal performance. As a solution to these challenges, this dissertation investigates two design strategies: 1) a novel switch module structure with low parasitics, and 2) a novel planar transformer structure with integrated leakage inductance and cooling system. Both approaches result in enhanced thermal performance, optimized through simultaneous electro-thermal co-design. A common key highlight of the proposed solutions is the high degree of integration realized by use of sub-components that integrate both electrical and thermal performance. This will save real estate by reducing component count and by lessening electrical and thermal burdens. In the first part of this dissertation, a detailed electrical characterization of a novel, wire-bondless, three-dimensional (3D), half-bridge switch module using bare-die SiC MOSFETs is presented. The switch assembly features the use of electro- thermally multi-functional components, simultaneously serving as bus-bars and heat sinks. A highly compact composition with embedded decoupling capacitors and gate driver components is realized with vertical loop structures for both power and gate drive circuits. Besides, the wire-bondless structure enables double-sided cooling, which significantly improves the thermal performance. 3D finite element analysis simulations and experiments demonstrate that the proposed switch module can achieve extremely low values of parasitic loop inductances (Lloop,power = 1.35 nH, Lloop,gate = 5.1 nH at a parasitic oscillation frequency of 100 MHz) as well as high thermal performance without entailing significant layout capacitances and resistances. The second part of this dissertation proposes an electro-thermal design optimization method of a high-frequency planar transformer with an integrated leakage inductance and thermal management system. Aiming at the use in a high-frequency (>500 kHz) dual-active-bridge (DAB) converter, an optimal leakage inductance selection process is explored based on highly accurate analyses of the DAB converter operation for maximizing the efficiency. Effect of design variables like the number of turns of the transformer and cooler height on the transformer’s electrical parameters such as leakage inductance, ac resistance and parasitic capacitance is further analyzed in detail. The dependence of converter efficiency on these parameters is estimated using realistic simulations and analyses, and potential trade-o↵s of the design are investigated. Thermal modeling is used to evaluate the thermal performance of different designs. Based on a combination of the analyses, optimal designs are identified, which simultaneously ensure good electrical and thermal performance. Finally, a compact DAB converter is designed based on the investigated components, operating at a switching frequency of 500 kHz. Robust gate-driver circuitry and auxiliary parts are also developed to tolerate such high switching frequency as well as high dv/dt. The optimal design processes, operation strategies and analytical models are validated through diverse experiments on 3.3 kW dc-dc converter operation. As a result of the investigations, the converter achieves zero-voltage-switching over various load conditions with satisfactory high-frequency waveforms and a peak efficiency of 98%. The converter’s operation at high power is validated through a designed loss-emulation test corresponding to 8.4 kW operation.Item Electromagnetic Interference Reduction using Electromagnetic Bandgap Structures in Packages, Enclosures, Cavities, and Antennas(2007-11-26) Mohajer Iravani, Baharak; Ramahi, Omar M.; Granatstein, Victor L.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Electromagnetic interference (EMI) is a source of noise problems in electronic devices. The EMI is attributed to coupling between sources of radiation and components placed in the same media such as package or chassis. This coupling can be either through conducting currents or through radiation. The radiation of electromagnetic (EM) fields is supported by surface currents. Thus, minimizing these surface currents is considered a major and critical step to suppress EMI. In this work, we present novel strategies to confine surface currents in different applications including packages, enclosures, cavities, and antennas. The efficiency of present methods of EM noise suppression is limited due to different drawbacks. For example, the traditional use of lossy materials and absorbers suffers from considerable disadvantages including mechanical and thermal reliability leading to limited life time, cost, volume, and weight. In this work, we consider the use of Electromagnetic Band Gap (EBG) structures. These structures are suitable for suppressing surface currents within a frequency band denoted as the bandgap. Their design is straight forward, they are inexpensive to implement, and they do not suffer from the limitations of the previous methods. A new method of EM noise suppression in enclosures and cavity-backed antennas using mushroom-type EBG structures is introduced. The effectiveness of the EBG as an EMI suppresser is demonstrated using numerical simulations and experimental measurements. To allow integration of EBGs in printed circuit boards and packages, novel miniaturized simple planar EBG structures based on use of high-k dielectric material (r > 100) are proposed. The design consists of meander lines and patches. The inductive meander lines serve to provide current continuity bridges between the capacitive patches. The high-k dielectric material increases the effective capacitive load substantially in comparison to commonly used material with much lower dielectric constant. Meander lines can increase the effective inductive load which pushes down the lower edge of bandgap, thus resulting in a wider bandgap. Simulation results are included to show that the proposed EBG structures provide very wide bandgap (~10GHz) covering the multiple harmonics of of currently available microprocessors and its harmonics. To speed up the design procedure, a model based on combination of lumped elements and transmission lines is proposed. The derived model predicts accurately the starting edge of bandgap. This result is verified with full-wave analysis. Finally, another novel compact wide band mushroom-type EBG structure using magneto-dielectric materials is designed. Numerical simulations show that the proposed EBG structure provides in-phase reflection bandgap which is several times greater than the one obtained from a conventional EBG operating at the same frequency while its cell size is smaller. This type of EBG structure can be used efficiently as a ground plane for low-profile wideband antennas.