Soft-Switching GaN-Based Isolated Power Conversion System for Small Satellites with Wide Input Voltage Range

As we pursue the advancement of small satellites for space missions with more capabilities, there is a significant need for cutting-edge, modularly configurable, high density power converters. This article proposes a fixed switching frequency, high efficiency, compact isolated converter for sensitive loads such as radar, communication systems, or other instruments on small satellites

The 77 K operation of a multi-resonant power converter

The liquid-nitrogen temperature (77 K) operation of a 55 W, 200 kHz, 48/28 V zero-voltage switching multi-resonant dc/dc converter designed with commercially available components is reported. Upon dipping the complete converter (power and control circuits) into liquid-nitrogen, the converter performance improved as compared to the room-temperature operation. The switching frequency, resonant frequency, and the characteristic impedance did not change significantly. Accordingly, the zero-voltage switching was maintained from no-load to full-load for the specified line variations. Cryoelectronics can provide high density power converters, especially for high power applications

Constraint-Aware, Scalable, and Efficient Algorithms for Multi-Chip Power Module Layout Optimization

Moving towards an electrified world requires ultra high-density power converters. Electric vehicles, electrified aerospace, data centers, etc. are just a few fields among wide application areas of power electronic systems, where high-density power converters are essential. As a critical part of these power converters, power semiconductor modules and their layout optimization has been identified as a crucial step in achieving the maximum performance and density for wide bandgap technologies (i.e., GaN and SiC). New packaging technologies are also introduced to produce reliable and efficient multichip power module (MCPM) designs to push the current limits. The complexity of the emerging MCPM layouts is surpassing the capability of a manual, iterative design process to produce an optimum design with agile development requirements. An electronic design automation tool called PowerSynth has been introduced with ongoing research toward enhanced capabilities to speed up the optimized MCPM layout design process. This dissertation presents the PowerSynth progression timeline with the methodology updates and corresponding critical results compared to v1.1. The first released version (v1.1) of PowerSynth demonstrated the benefits of layout abstraction, and reduced-order modeling techniques to perform rapid optimization of the MCPM module compared to the traditional, manual, and iterative design approach. However, that version is limited by several key factors: layout representation technique, layout generation algorithms, iterative design-rule-checking (DRC), optimization algorithm candidates, etc. To address these limitations, and enhance PowerSynth’s capabilities, constraint-aware, scalable, and efficient algorithms have been developed and implemented. PowerSynth layout engine has evolved from v1.3 to v2.0 throughout the last five years to incorporate the algorithm updates and generate all 2D/2.5D/3D Manhattan layout solutions. These fundamental changes in the layout generation methodology have also called for updates in the performance modeling techniques and enabled exploring different optimization algorithms. The latest PowerSynth 2 architecture has been implemented to enable electro-thermo-mechanical and reliability optimization on 2D/2.5D/3D MCPM layouts, and set up a path toward cabinet-level optimization. PowerSynth v2.0 computer-aided design (CAD) flow has been hardware-validated through manufacturing and testing of an optimized novel 3D MCPM layout. The flow has shown significant speedup compared to the manual design flow with a comparable optimization result

Evaluation of the off-state base-emitter voltage requirement of the SiC BJT with a regenerative proportional base driver circuit and their application in an inverter

A strong candidate device for use in high-efficiency and high-density power converters is the SiC bipolar junction transistor, which requires a continuous gate (base) current to maintain its on-state. A base driver circuit with regenerative collector current feedback using a current transformer, and a negative off-state base-emitter voltage is presented in this article. The off-state base-emitter voltage required to prevent simultaneous conduction of a commercially available device when subjected to dv/dt's is assessed. The device is then utilized in a three-phase dc-To-Ac power converter where the efficacy of using the proposed base driver is evaluated. The off-state base-emitter voltage used is informed by the dv/dt tests. The converter is supplied from a 600-V dc rail, switches at 50 kHz and supplies a 4.1-kW load at a modulation index of 0.9. An efficiency of 97.4% was measured

Capacitor performance limitations in high power converter applications

Background: Over the last 80 years the association between social class and obesity has changed. In the 1930s obesity rates were low and wealthy people tended to have a higher risk of obesity than poor people. However, rising affluence and industrialisation has lead to both rising rates of obesity and an obesogenic environment in which socioeconomically disadvantaged people have the highest risk of obesity. This study investigates the magnitude of these changes by modelling trajectories of adiposity by social class and cohort using the Twenty-07 study. Methods: The Twenty-07 study contains three cohorts of people (n = 4510), born in Glasgow in the 1930s, 1950s and 1970s. Two measures of adiposity, BMI and Waist to Height Ratio (WHtR), were recorded at baseline in 1987/8 when study participants were aged 15, 35 or 55, and again on 4 further occasions over 20 years. Parental social class (manual/non-manual) was collected at baseline. For each gender, we apply multilevel models to identify trajectories of adiposity by cohort and social class. Results: The trajectories indicated that adiposity increased with age and rates of increase varied by cohort, social class and gender. For any given age the youngest cohort had the fastest rate of increase and the highest predicted adiposity. For example, at age 35 for non-manual men, BMI was 24.2 (95% CI 23.7, 24.8) for the 1950s cohort and 27.2 (26.8, 27.5) for the 1970s cohort. By the end of the study respondents in more recent cohorts had BMI values approximately equivalent to those of people aged 20 years older in an earlier cohort. Cohort variation was much greater than socioeconomic variation. The smallest cohort difference in BMI was 2.10 (0.94, 3.26), a comparison of the 1950 and 1930s cohorts for non-manual men at age 55. In contrast, the largest social class difference in BMI, a comparison of manual and non manual women at age 64, was only 1.18 (0.37, 1.98). Socioeconomic inequalities tended to be smaller for men than women, particularly for the 1930s cohort where there was no evidence of a socioeconomic gradient for men unlike for women. The main difference between WHtR and BMI was that increases in WHtR accelerated with age whilst increases in BMI slowed with age. Conclusion: Increases in adiposity for younger cohorts across all socioeconomic groups dwarf any socioeconomic inequalities in adiposity. This highlights the damaging impact for the whole population of living in an obesogenic environment

High Temperature Testingand Noise Integration of a Buck Converter usingSilicon and Silicon Carbide Diodes.

This project includes comparison of the advantages of enhanced SiC device performance at elevated temperatures over Si devices in a buck type DC/DC converter circuit. Being that elevated temperatures in a circuit have always caused energy losses and deviation in results, the manufacturers of silicon technology came up with a much more sophisticated Silicon Carbide technology which dramatically reduces the above mentioned two factors. The scope is mainly to examine thermal effects at high temperatures on the performance characteristics of the buck converter circuit, diode losses, switching losses and overall system losses. This project also includes effect of noise integrated buck converter circuit. So, comparison is being made between that of noise integrated and noiseless circuit both of which are being varied from a low temperature up to temperature of 300 Celsius. This project mainly utilizes PSPICE software to achieve the above stated results. Reasons and causes as to the increase of losses as the increase of temperature have been discussed in this project. Also the source of noise and practical ways of reducing noises in buck converter circuits is being stated in this project. Withpropertabulation and graphs of results this project enables to deeply understand Silicon Carbide technology used in buck converter circuit, which is a subject to elevated temperatures and noise

Investigation of FACTS devices to improve power quality in distribution networks

Flexible AC transmission system (FACTS) technologies are power electronic solutions that improve power transmission through enhanced power transfer volume and stability, and resolve quality and reliability issues in distribution networks carrying sensitive equipment and non-linear loads. The use of FACTS in distribution systems is still in its infancy. Voltages and power ratings in distribution networks are at a level where realistic FACTS devices can be deployed. Efficient power converters and therefore loss minimisation are crucial prerequisites for deployment of FACTS devices. This thesis investigates high power semiconductor device losses in detail. Analytical closed form equations are developed for conduction loss in power devices as a function of device ratings and operating conditions. These formulae have been shown to predict losses very accurately, in line with manufacturer data. The developed formulae enable circuit designers to quickly estimate circuit losses and determine the sensitivity of those losses to device voltage and current ratings, and thus select the optimal semiconductor device for a specific application. It is shown that in the case of majority carrier devices (such as power MOSFETs), the conduction power loss (at rated current) increases linearly in relation to the varying rated current (at constant blocking voltage), but is a square root of the variable blocking voltage when rated current is fixed. For minority carrier devices (such as a pin diode or IGBT), a similar relationship is observed for varying current, however where the blocking voltage is altered, power losses are derived as a square root with an offset (from the origin). Finally, this thesis conducts a power loss-oriented evaluation of cascade type multilevel converters suited to reactive power compensation in 11kV and 33kV systems. The cascade cell converter is constructed from a series arrangement of cell modules. Two prospective structures of cascade type converters were compared as a case study: the traditional type which uses equal-sized cells in its chain, and a second with a ternary relationship between its dc-link voltages. Modelling (at 81 and 27 levels) was carried out under steady state conditions, with simplified models based on the switching function and using standard circuit simulators. A detailed survey of non punch through (NPT) and punch through (PT) IGBTs was completed for the purpose of designing the two cascaded converters. Results show that conduction losses are dominant in both types of converters in NPT and PT IGBTs for 11kV and 33kV systems. The equal-sized converter is only likely to be useful in one case (27-levels in the 33kV system). The ternary-sequence converter produces lower losses in all other cases, and this is especially noticeable for the 81-level converter operating in an 11kV network

A Simple Closed-Loop Active Gate Voltage Driver for Controlling diC/dt and dvCE/dt in IGBTs

The increase of the switching speed in power semiconductors leads to converters with better efficiency and high power density. On the other hand, fast switching generates some consequences like overshoots and higher switching transient, which provoke electromagnetic interference (EMI). This paper proposes a new closed-loop gate driver to improve switching trajectory in insulated gate bipolar transistors (IGBTs) at the hard switching condition. The proposed closed-loop gate driver is based on an active gate voltage control method, which deals with emitter voltage (VEe) for controlling diC/dt and gets feedback from the output voltage (vCE) in order to control dvCE/dt. The sampled voltage signals modify the profile of the applied gate voltage (vgg). As a result, the desired gate driver (GD) improves the switching transients with minimum switching loss. The operation principle and implementation of the controller in the GD are thoroughly described. It can be observed that the new GD controls both dvCE/dt and diC/dt accurately independent of the variable parameters. The new control method is verified by experimental results. As a current issue, the known trade-off between switching losses and EMI is improved by this simple and effective control method.Postprint (published version

Evaluating the Thermal Conductivity of Potting Materials using the Hot-Wire Method

This thesis is focused on the evaluation of the thermal conductivity of certain potting materials, in particular Aluminum Nitride (AlN), thermal putty, and silicone oil using the “hot-wire” method in order to allow volume reductions of inductors, and thus, increase the power density of converters. The main objective of this thesis is then to study the behavior of these specific materials intended for high-density power converters by mixing them with different proportions and placing the resulting compounds into a can for calculating their thermal conductivities, in order to evaluate the effects on the power density of inductor-based converters. One objective in calculating the thermal conductivity is to determine the duration of the various experiments since they are time-consuming. To this end, two rounds of experiments are performed up to 15 and 30 minutes, respectively, since there was a clear idea for the time needed for the various mixtures to reach steady-state temperatures. The “hot-wire” method is normally used to measure the thermal conductivity of a material. For this thesis work, the “hot-wire” method equipment needed for the experiments is adapted to the equipment available in the Engineering Research Center (ENRC) at the University of Arkansas. Errors occurring during the experiments could have many reasons; for example, external factors that affect external temperature readings (for example, individual performing tests in the same lab room and adding heat to the ambient, the thermocouple not being firmly placed on the resistor inside the can, errors in weighing the materials on the digital scale, etc). The analysis of the results for the 15- minute experiments has errors due to negative value results, so this time was not suitable for calculating the thermal conductivities. The experiments conducted to 30 minutes produced good results. Thus, the influence of time is important to get very good results. However, the experiments performed up to 30 minutes demonstrated a reduction in both maximum temperature ii rise and the time to reach a stable temperature which gives improvements in efficiency and performance in the system. Further experiment analysis of some other materials like silicone epoxy should be conducted to analyze the thermal conductivity behavior and determine if other materials can enable faster heat removal