With the increase dependency on electricity to provide correct form of electricity for lightning, machines, and home and office appliances, the need for the introduction of high reliability power electronics in converting the raw form of electricity into efficient electricity for these applications is uprising. One of the most common failures in power electronics is temperature related failure such as overheating. To address the issue of overheating, thermal management becomes an important mission in the design of the power electronics to ensure the functional power electronics. Different approaches are taken by academia and industry researchers to provide efficient power electronics. In particular, the Center for Power Electronics System (CPES) at Virginia Tech and four other universities presented the IPEM approach by introducing integrated power electronics modules (IPEM) as standardized units that will enable greater integration within power electronics systems and their end-use application. The IPEM approach increases the integration in the components that make up a power electronics system through novel a packaging technique known as Embedded Power technology. While the thermal behavior of commonly used packages such as pin grid arrays (PGA), ball grid array (BGA), or quad flat pack (QFP) are well-studied, the influence of the Embedded Power packaging architecture on the overall thermal performance of the IPEMs is not well known. This motivates the presentation of this dissertation in developing an in-depth understanding on the thermal behavior of the Embedded Power modules. In addition, this dissertation outlines some general guidelines for the thermal modeling and thermal testing for the Embedded Power modules. Finally, this dissertation summarizes a few thermal design guidelines for the Embedded Power modules. Hence, this dissertation aims to present significant and generalized scientific findings for the Embedded Power packaging from the thermal perspective. Both numerical and experimental approaches were used in the studies. Three-dimensional mathematical modeling and computational fluid dynamics (CFD) thermal analyses were performed using commercial numerical software, I-DEAS. Experiments were conducted to validate the numerical models, characterize the thermal performance of the Embedded Power modules, and investigate various cooling strategies for the Embedded Power modules. Validated thermal models were used for various thermal analyses including identifying potential thermal problems, recognizing critical thermal design parameters, and exploring different integrated cooling strategies. This research quantifies various thermal design parameters such as the geometrical effect and the material properties on the thermal performance of the Embedded Power modules. These parameters include the chip-to-chip distance, the copper trace area, the polyimide thickness, and the ceramic materials. Since the Embedded Power technology utilizes metallization bonding as interconnection, specific design parameters such as the interconnect via holes pattern and size, the metallization thickness, as well as the metallization materials were also explored to achieve best results based on thermal and stress analyses. With identified potential thermal problems and critical thermal design parameters, different integrated cooling strategies were studied. The concept of integrated cooling is to incorporate the cooling mechanisms into the structure of Embedded Power modules. The results showed that simple structural modifications to the current Embedded Power modules can reduce the maximum temperature of the module by as much as 24%. Further improvement can be achieved by employing double-sided cooling to the Embedded Power modules. Based on the findings from the thermal analyses, general design guidelines were developed for future design of such Embedded Power modules. In addition, thermal modeling and testing guidelines for the Embedded Power modules were also outlined in this dissertation. / Ph. D.

This study focuses on development a planar power module with low thermal impedance and thermo-mechanical stress for high density integration of power electronics systems. With the development semiconductor technology, the heat flux generated in power device keeps increasing. As a result, more and more stringent requirements were imposed on the thermal and reliability design of power electronics packaging. In this dissertation, a boundary-dependent RC transient thermal model was developed to predict the peak transient temperature of semiconductor device in the power module. Compared to conventional RC thermal models, the RC values in the proposed model are functions of boundary conditions, geometries, and the material properties of the power module. Thus, the proposed model can provide more accurate prediction for the junction temperature of power devices under variable conditions. In addition, the transient thermal model can be extracted based on only steady-state thermal simulation, which significantly reduced the computing time. To detect the peak transient temperature in a fully packaged power module, a method for thermal impedance measurement was proposed. In the proposed method, the gate-emitter voltage of an IGBT which is much more sensitive to the temperature change than the widely used forward voltage drop of a pn junction was monitored and used as temperature sensitive parameter. A completed test circuit was designed to measure the thermal impedance of the power module using the gate-emitter voltage. With the designed test set-up, in spite of the temperature dependency of the IGBT electrical characteristics, the power dissipation in the IGBT can be regulated to be constant by adjusting the gate voltage via feedback control during the heating phase. The developed measurement system was used to evaluate thermal performance and reliability of three different die-attach materials. From the prediction of the proposed thermal model, it was found that the conventional single-sided power module with wirebond connection cannot achieve both good steady-state and transient thermal performance under high heat transfer coefficient conditions. As a result, a plate-bonded planar power module was designed to resolve the issue. The comparison of thermal performance for conventional power module and the plate-bonded power module shows that the plate-bonded power module has both better steady-state and transient thermal performance than the wirebonded power module. However, due to CTE mismatch between the copper plate and the silicon device, large thermo-mechanical stress is induced in the bonding layer of the power module. To reduce the stress in the plate-bonded power module, an improved structure called trenched copper plate structure was proposed. In the proposed structure, the large copper plate on top of the semiconductor can be partitioned into several smaller pieces that are connected together using a thin layer copper foil. The FEM simulation shows that, with the improved structure, the maximum von Mises stress and plastic strain in the solder layer were reduced by 18.7% and 67.8%, respectively. However, the thermal impedance of the power module increases with reduction of the stress. Therefore, the trade-off between these two factors was discussed. To verify better reliability brought by the trenched copper plate structure, twenty-four samples with three different copper plate structures were fabricated and thermally cycled from -40°C to 105°C. To detect the failure at the bonding layer, the curvature of these samples were measured using laser scanning before and after cycling. By monitoring the change of curvature, the degradation of bonding layer can be detected. Experimental results showed that the samples with different copper plate structure had similar curvature before thermal cycle. The curvatures of the samples with single copper plate decreased more than 80% after only 100 cycles. For the samples with 2 × 2 copper plate and the samples with 3 × 3 copper plate, the curvatures became 75.8% and 77.5% of the original values, respectively, indicating better reliability than the samples with single copper plate. The x-ray pictures of cross-sectioned samples confirmed that after 300 cycles, the bonding layer for the sample with single copper plate has many cracks and delaminations starting from the edge. / Ph. D.

This work reports the experimental and numerical study of the thermal management of Li-ion battery packs under the context of electric vehicle (EV) or hybrid EV (HEV) applications. Li-ion batteries have been extensively demonstrated as an important power source for EVs or HEVs. However, thermal management is a critical challenge for their widespread deployment, due to their highly dynamic operation and the wide range of environments under which they operate. To address these challenges, this work developed several experimental platforms to study adaptive thermal management strategies. Parallel to the experimental effort, multi-disciplinary models integrating heat transfer, fluid mechanics, and electro-thermal dynamics have been developed and validated, including detailed CFD models and lumped parameter models. The major contributions are twofold. First, this work developed actively controlled strategies and experimentally demonstrated their effectiveness on a practical sized battery pack and dynamic thermal loads. The results show that these strategies effectively reduced both the parasitic energy consumption and the temperature non-uniformity while maintaining the maximum temperature rise in the pack. Second, this work established a new two dimensional lumped parameter thermal model to overcome the limitations of existing thermal models and extend their applicable range. This new model provides accurate surface and core temperatures simulations comparable to detailed CFD models with a fraction of the computational cost. / Ph. D.

<p dir="ltr">Increasing power density and power consumption in electronic devices require heat dissipating components with high thermal conductivity to prevent overheating and improve performance and reliability. Polymers offer the advantages of low cost and weight over conventional metallic components, but their intrinsic thermal conductivity is low. Previous studies have shown that the thermal conductivity of polymers can be enhanced by aligning the polymer chains or by adding high thermal conductivity fillers to create percolation paths within the polymeric matrix. To further enhance the in-plane thermal conductivity, the conductive fillers can be aligned preferentially, but this leads to a lower increase in performance in the cross-plane direction. Yet, the cross-plane thermal conductivity plays a vital role in dissipating heat from active devices and transmitting it to the surrounding environment. Alternatively, when the fillers are aligned to enhance cross-plane thermal transport, the enhancement in the in-plane direction is limited. There is a need to develop polymer composites with an approximately isotropic increase in thermal performance compared to their neat counterparts.</p><p dir="ltr">To achieve this goal, in this study, I combine conductive fibers and fillers to enhance thermal conductivity of polymers without significantly inducing thermal anisotropy while preserving the mechanical performance of the matrix. I employ three approaches to enhance the thermal conductivity () of thermoset polymeric matrices. In the first approach, I fabricate thermally conductive polymer composites by creating an emulsion consisting of eutectic gallium indium alloy (EGaIn) liquid metal in the uncured polydimethylsiloxane (PDMS) matrix. In the second approach, I infiltrate mats formed from chopped fibers of Ultra High Molecular Weight Polyethylene (UHMWPE) with an uncured epoxy resin. Finally, the third approach combines the two previous methods by infiltrating the UHMWPE fiber mat with an emulsion of the liquid metal and uncured epoxy matrix.</p><p dir="ltr">To evaluate the thermal performance of the composites, I use infrared thermal microscopy with two different experimental setups, enabling independent measurement of in-plane and cross-plane thermal conductivity. The results demonstrate that incorporating thermally conductive fillers enhances the overall conductivity of the polymer composite. Moreover, I demonstrate that the network structure achieved by the fiber mat, in combination with the presence of liquid metal, promotes a more uniform increase in the thermal conductivity of the composite in all directions. Additionally, I assess the impact of filler incorporation and filler concentration on matrix performance through tension, indentation, and bending tests for mechanical characterization of my materials.</p><p dir="ltr">This work demonstrates the potential of strategic composite design to achieve polymeric materials with isotropically high thermal conductivity. These new materials offer a solution to the challenges posed by higher power density and consumption in electronics and providing improved heat dissipation capabilities for more reliable devices.</p>

Exponential growth of heat flux densities in commercial and industrial electronics, and compact heat exchangers demand surfaces and heat sinks with high dissipation rate capabilities. Among different technologies proposed to meet these demands, high-porosity metal foams have attracted the attention of many investigators due to their higher surface area densities as well as higher thermal performance due to the turbulence and tortuosity generated in the flow due to their structure. One of the disadvantages of such metal foams, however, is the attendant higher pressure drop or pumping power penalty. This thesis was undertaken to investigate whether channels partially filled with metal foams can reduce the required pumping power with a minimal loss in thermal performance. The thermo-hydraulic (T-H) performance factor J/F<sup>1/3, where J is the Colburn-J factor and F is the friction factor, was used to compare the relative performance of foams for various values of blocking fractions (B), where B is defined as the ratio of the height of the foam to the height of the channel. The metal foam samples considered were 10 PPI (pores per inch) 6101-T6 Aluminum, with porosity of ∼ 94 − 96%, and B of 1/6, 1/3, 2/3, 5/6, and 1. Each of these samples was attached to an aluminum slab embedded in one of the walls, which had a patch heater that acted as a heat source. A modification was made to all B < 1 configurations by attaching an aluminum plate on top, which then separated the foam-free and the foam-filled flows completely. These configurations are denoted by a 'P' in their names (e.g. B = 1/3P is the plated modification of B = 1/3). Experiments were conducted in an in-house designed wind tunnel, with a test section of 45" in length and a cross-section of 3"X3". Reynolds number (based on channel hydraulic diameter and inlet velocity) was varied from 1,000 to 15,000 to capture the flow domains from laminar to turbulent. The data obtained for the three scenarios namely - 1. Controlled-Flow Scenario 2. Pumping Power Variation with Temperature Difference, and 3. Fan-Based System were analyzed for their thermo-hydraulic performance. The extreme low blocking fractions are evaluated and compared against the dimpled/protruded surfaces, and were found to give superior performance, hence displaying potential as good turbulators. The plated configurations were found to perform better in almost all scenarios when compared to their non-plated counterparts. Furthermore, a new simplified analytical model is introduced that considers the flow in the partially-blocked region as two separate 'parallel' flows, one in the foam-free region and the other in the foam-filled region. The comparison between this novel approach and the analytical solution from the literature shows good agreement, suggesting that this simplified model may be appropriate. This model is then used for determining the foam-filled region flow ratios for the performed experiments, and a correlation is presented. / Master of Science / Portable devices, such as laptops, and mobile phones are trending towards miniaturization and simultaneously becoming more power-hungry, leading to ever-increasing heat flux densities. Growing energy and technology demands require high thermal dissipation rates to be achieved in equipment such as industrial and commercial electronics, data centers, heat exchangers in automobiles, and power plants - both renewable and non-renewable. One of the best ways to enhance convective heat transfer is by increasing the heat transfer surface area. This is traditionally done using fins. A much higher surface area can be achieved using a metal foam instead, along with improving the turbulent mixing of the fluid. The flow through the metal foam, however, faces a higher pressure drop penalty which is one of the major reasons for a continued preference for fins. In this experimental study, we aim at minimizing this pressure drop penalty of a metal-foam heat-sink along with maintaining a respectable heat transfer performance through 'partial-blocking' (filling) of the channel, where the height of the foam is lower than the total channel height. The ratio of metal foam height to the channel height is named as blocking fraction B. A general comparison of the hydraulic, thermal, and thermo-hydraulic (T-H) performance reveals that the ∼ 83.3% plated configuration is capable of superseding the baseline of full blockage. The 'plating' here denotes a slight modification - a solid plate rests on top of the metal foam, separating the foam-free and foam-filled flow. For applications with Re > 10000, ∼ 33.3% plated configuration is highly recommended. For fan-based systems, ∼ 83.3% plated, ∼ 33.3% plated, and 33.3% non-plated configurations emerge as possible alternatives to the fully-blocked case. Furthermore, while considering partial configurations, it is shown that one should go for lower PPI metal foams to improve the flow ratio inside the metal foam. For pressure-drop critical equipment, ∼ 16.7% configuration is found to perform better than the conventional double-protruded walls and other turbulence-enhancing surface treatments. Finally, this thesis presents a novel and simplified approach for estimating the flow ratios for partially-blocked channels using scaling analysis.

The task of thermal management in electrical systems has never been simple and has only become more difficult in recent years as the power electronics industry pushes towards devices with higher power densities. At the Center for Power Electronic Systems (CPES), a new approach to power electronic design is being implemented with the Integrated Power Electronic Module (IPEM). It is believed that an IPEM-based design approach will significantly enhance the competitiveness of the U.S. electronics industry, revolutionize the power electronics industry, and overcome many of the technology limits in today's industry by driving down the cost of manufacturing and design turnaround time. But with increased component integration comes the increased risk of component failure due to overheating. This thesis addresses the issues associated with the thermal management of integrated power electronic devices. Two studies are presented in this thesis. The focus of these studies is on the thermal design of a DC-DC front-end power converter developed at CPES with an IPEM-based approach. The first study investigates how the system would respond when the fan location and heat sink fin arrangement are varied in order to optimize the effects of conduction and forced-convection heat transfer to cool the system. The set-up of an experimental test is presented, and the results are compared to the thermal model. The second study presents an improved methodology for the thermal modeling of large-scale electrical systems and their many subsystems. A zoom-in/zoom-out approach is used to overcome the computational limitations associated with modeling large systems. The analysis performed in this paper was completed using I-DEAS©,, a three-dimensional finite element analysis (FEA) program which allows the thermal designer to simulate the affects of conduction and convection heat transfer in a forced-air cooling environment. / Master of Science

In this dissertation, three major contributions are presented in a photovoltaic (PV) energy system. Firstly, a three-port grid-forming (GFM) microinverter and a lithium-ion battery pack are integrated at the back of PV panel. As a result, they form an AC-PV energy system module that produces an AC output voltage. The technoeconomic analysis, battery capacity optimization, PV panel size optimization, electrical and thermal model of batteries, battery heat generation model, battery management system and thermal management system are discussed in the AC-PV module by using stochastic analysis and battery test results. Secondly, a three-phase 540 KVA bidirectional inverter and a 1.86 MWh lithium-ion battery energy storage system (BESS) were integrated at the Florida Solar Energy Center (FSEC). A case study is performed for this system by acquiring the energy consumption of the building, the reduced energy consumption, the battery testing, the load shifting, and the peak shaving. The total harmonic distortion (THD) values are also provided. Among eight power management scenarios, the scenarios that include PV panels are satisfied via simulation. However, the scenarios that do not include PV panels are analyzed and presented based on the real-world setting measurements. Thirdly, a modified droop control method is designed for grid-tied and off-grid scenarios. The simulation results are obtained based on three scenarios. The first one is that the voltage and frequency regulation control algorithm is discussed when GFM inverters have the equal power ratings. Then, the load sharing control algorithm is determined based on different GFM inverters' power ratings. The last scenario includes Grid connection. Loads are added and removed from the system to ensure that the frequency and voltage stability is the range of continuous operation. The coupling reactance effect on power sharing is investigated.

The goal of the work reported herein has been to model aspects of the electrical distribution system of an all-electric ship (AES) and to couple electrical load behavior with the thermal management network aboard the ship. The development of a thermally dependent electrical network has built upon an in-house thermal management simulation environment to replace the existing steady state heat loads with dynamic, thermally dependent, electrical heat loads. Quantifying the close relationship between thermal and electrical systems is of fundamental importance in a large, integrated system like the AES. This in-house thermal management environment, called the Dynamic Thermal Modeling and Simulation (DTMS) framework, provided the fundamental capabilities for modeling thermal systems and subsystems relevant to the AES. The motivation behind the initial work on DTMS was to understand the dynamics of thermal management aboard the ship. The first version, developed in 2007, captured the fundamental aspects of system-level thermal management while maintaining modularity and allowing for further development into other energy domains. The reconfigurable nature of the DTMS framework allowed for the expansion into the electrical domain with the creation of an electrical distribution network in support of thermal simulations. The dynamics of the electrical distribution system of the AES were captured using reconfigurable and physics-based circuit elements that allow for thermal feedback to affect the behavior of the system. Following the creation of the electrical network, subsystems and systems were created to simulate electrical distribution. Then, again using the modularity features of DTMS, a thermal resistive heat flow network was created to capture the transient behavior of heat flow from the electrical network to the existing thermal management framework. This network provides the intimate link between the thermal management framework and the electrical distribution system. Finally, the three frameworks (electrical, thermal resistive, and thermal management) were combined to quantify the impact that each system has relative to system-level operation. Simulations provide an indication of the unlimited configurations and potential design space a user of DTMS can explore to explore the design of an AES. / text

The thesis is focused on premature newborn thermomanagement. It is focused particularly on very premature and extremely premature newborns which suffer the highest level of thermolability. The theoretical part deals with the particularities of premature newborn thermoregulation, newborns' reactions to thermal stress, thermomanagement in the delivery room and providing a thermoneutral environment in the incubator. The thesis describes a method of servo-control mode of body temperature, which has not been utilised for premature newborns in Czech Republic. The aim of the thesis is to start using this method and compare it with the method of manual control. Based on the total time not meeting the standard, number of failures and other parameters to assess which method is more suitable for body temperature regulation. The research sample consists of 47 newborsn who were born between the 24th and 32nd gestational week. Quantitative data collection at one-minute intervals was conducted in the 72 hours after birth. The method choice was random. Statistically important differences between the two methods were measured regarding the total time not meeting the standards. The incidence of hyperthemia was higher during manual method, hypothermia when servo-control. Total failure amount was 19%. However, the...

The transportation sector continues to be a primary source of greenhouse gas (GHG) emissions, contributing more than any other sector in the United States in 2017. Medium-duty and heavy-duty trucks trail only passenger cars as the largest GHG contributor in this sector [1]. The intense operating requirements of these vehicles create a reliance on the diesel engine that is projected to last for many decades. Therefore, it is vital that the efficiency and environmental sustainability of diesel engines continue to be advanced.<br><br>Cylinder deactivation (CDA) is a promising technology to improve diesel engine fuel efficiency and aftertreatment thermal management for emissions reduction. This work presents original experimental results demonstrating fuel efficiency improvements of CDA implemented on a modern engine at idle operating conditions through testing of various CDA configurations. Idle calibration optimizations result in up to 28% fuel consumption reduction at steady-state unloaded idle operation and 0.7% fuel consumption reduction over HD-FTP drive cycles at equivalent emissions levels. The low-load thermal management performance of CDA is also investigated through creep and extended idle transient cycles, during which CDA is shown to reduce fuel consumption by up to 40% with similar thermal management performance and reduced NOx and soot emissions. <br><br>Variants of CDA implementation are explored through an experimental comparison of deactivation strategies. The effort described here compares charge trapping strategies through examination of in-cylinder pressures following deactivation because: (1) choice of trapping strategy dictates the in-cylinder pressure characteristics of the deactivated cylinders, and (2) deactivated cylinders can affect torque, oil consumption, and emissions upon reactivation. Results discussed here suggest no significant differences between the strategies. As an example, the in-cylinder pressures of both trapping strategies are shown to converge as quickly as 0.8 seconds after deactivation.<br><br>Finally, the NVH effects of CDA are characterized through studies of torsional vibration, linear vibration, and acoustics. CDA causes frequency content at reduced frequencies compared to conventional operation, which has effects on all aspects of NVH. This creates possible constraints on achievable fuel efficiency and thermal management performance by restricting CDA usage. An alternate form of CDA, dynamic cylinder activation (DCA), is explored as a possible option of avoiding undesirable frequency output while maintaining the desired engine performance. <br>