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1. Influence of Temperature and Frequency on Electric Field Reduction Method via a Nonlinear Field Dependent Conductivity Layer Combined with Protruding Substrate for Power Electronics Modules

   https://doi.org/10.1109/EIC47619.2020.9158768  

   Tousi, Maryam Mesgarpour; Ghassemi, Mona (June 2020, 2020 IEEE Electrical Insulation Conference (EIC))

   null (Ed.)

   As shown in our previous studies, geometrical field grading techniques such as stacked and protruding substrate designs cannot well mitigate high electric stress issue within power electronics modules. However, it was shown that a combination of protruding substrate design and applying a nonlinear field-dependent conductivity layer could address the issue. Electric filed (E) simulations were carried out according to IEC 61287-1 for the partial discharge test measurement step, where a 50/60 Hz AC voltage was applied. However, dielectrics, including ceramic substrate and silicone gel, in power devices undergo high temperatures up to a few hundred degrees and frequencies up to 1 MHz. Thus, E values obtained with electrical parameters of the mentioned dielectrics for room temperature and under 50/60 Hz may not be valid for high temperatures and frequencies mentioned above. In this paper, we address this technical gap through developing a finite element method (FEM) E calculation model developed in COMSOL Multiphysics where E calculations are carried out for different temperatures up to 250°C and frequencies up to 1 MHz. Using the model, the influence of temperature and frequency on our proposed electric field mitigation technique mentioned above is evaluated. 

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2. Class-D Amplifier-Based Core Loss Measurements for High Frequency Magnetic Materials

   https://doi.org/10.1109/COMPEL57542.2024.10614013  

   Anderson, Jacob R; Kirkby, Nick J; Ranjram, Mike K (June 2024, IEEE Workshop on Control and Modeling for Power Electronics)

   Magnetic core loss measurement methods suitable for high-frequency sinusoidal excitations are currently time intensive or inherently suffer from flux drive limitations due to the costly and ill-suited radio frequency (RF) equipment utilized in the measurement. The recent development of automated testers has enabled the collection of large core loss data sets across a broad range of operating frequencies and flux densities. Improper loading of the RF power amplifiers utilized in these measurements makes the collection of accurate core loss data impractical above certain drive levels. In this paper, we develop and demonstrate an automatable core loss testing method which replaces the commonly employed RF power amplifier with a high frequency switching inverter. An analytical framework for assessing flux harmonics in the core is also presented. An experimental demonstration is performed in the range of 1-7MHz for the following materials: (1) Fair-Rite 67, (2) Fair-Rite 80, and (3) Proterial ML91S. 

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3. TAPA: A Scalable Task-parallel Dataflow Programming Framework for Modern FPGAs with Co-optimization of HLS and Physical Design

   https://doi.org/10.1145/3609335  

   Guo, Licheng; Chi, Yuze; Lau, Jason; Song, Linghao; Tian, Xingyu; Khatti, Moazin; Qiao, Weikang; Wang, Jie; Ustun, Ecenur; Fang, Zhenman; et al (December 2023, ACM Transactions on Reconfigurable Technology and Systems)

   In this article, we propose TAPA, an end-to-end framework that compiles a C++ task-parallel dataflow program into a high-frequency FPGA accelerator. Compared to existing solutions, TAPA has two major advantages. First, TAPA provides a set of convenient APIs that allows users to easily express flexible and complex inter-task communication structures. Second, TAPA adopts a coarse-grained floorplanning step during HLS compilation for accurate pipelining of potential critical paths. In addition, TAPA implements several optimization techniques specifically tailored for modern HBM-based FPGAs. In our experiments with a total of 43 designs, we improve the average frequency from 147 MHz to 297 MHz (a 102% improvement) with no loss of throughput and a negligible change in resource utilization. Notably, in 16 experiments, we make the originally unroutable designs achieve 274 MHz, on average. The framework is available athttps://github.com/UCLA-VAST/tapaand the core floorplan module is available athttps://github.com/UCLA-VAST/AutoBridge 

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4. Understanding Timing Error Characteristics from Overclocked Systolic Multiply–Accumulate Arrays in FPGAs

   https://doi.org/10.3390/jlpea14010004  

   Chamberlin, Andrew; Gerber, Andrew; Palmer, Mason; Goodale, Tim; Gundi, Noel Daniel; Chakraborty, Koushik; Roy, Sanghamitra (March 2024, Journal of Low Power Electronics and Applications)

   Artificial Intelligence (AI) hardware accelerators have seen tremendous developments in recent years due to the rapid growth of AI in multiple fields. Many such accelerators comprise a Systolic Multiply–Accumulate Array (SMA) as its computational brain. In this paper, we investigate the faulty output characterization of an SMA in a real silicon FPGA board. Experiments were run on a single Zybo Z7-20 board to control for process variation at nominal voltage and in small batches to control for temperature. The FPGA is rated up to 800 MHz in the data sheet due to the max frequency of the PLL, but the design is written using Verilog for the FPGA and C++ for the processor and synthesized with a chosen constraint of a 125 MHz clock. We then operate the system at a frequency range of 125 MHz to 450 MHz for the FPGA and the nominal 667 MHz for the processor core to produce timing errors in the FPGA without affecting the processor. Our extensive experimental platform with a hardware–software ecosystem provides a methodological pathway that reveals fascinating characteristics of SMA behavior under an overclocked environment. While one may intuitively expect that timing errors resulting from overclocked hardware may produce a wide variation in output values, our post-silicon evaluation reveals a lack of variation in erroneous output values. We found an intriguing pattern where error output values are stable for a given input across a range of operating frequencies far exceeding the rated frequency of the FPGA. 

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5. An overall view of temperature oscillations in the solar chromosphere with ALMA

   https://doi.org/10.1098/rsta.2020.0174  

   Jafarzadeh, S.; Wedemeyer, S.; Fleck, B.; Stangalini, M.; Jess, D. B.; Morton, R. J.; Szydlarski, M.; Henriques, V. M.; Zhu, X.; Wiegelmann, T.; et al (February 2021, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences)

   null (Ed.)

   By direct measurements of the gas temperature, the Atacama Large Millimeter/submillimeter Array (ALMA) has yielded a new diagnostic tool to study the solar chromosphere. Here, we present an overview of the brightness-temperature fluctuations from several high-quality and high-temporal-resolution (i.e. 1 and 2 s cadence) time series of images obtained during the first 2 years of solar observations with ALMA, in Band 3 and Band 6, centred at around 3 mm (100 GHz) and 1.25 mm (239 GHz), respectively. The various datasets represent solar regions with different levels of magnetic flux. We perform fast Fourier and Lomb–Scargle transforms to measure both the spatial structuring of dominant frequencies and the average global frequency distributions of the oscillations (i.e. averaged over the entire field of view). We find that the observed frequencies significantly vary from one dataset to another, which is discussed in terms of the solar regions captured by the observations (i.e. linked to their underlying magnetic topology). While the presence of enhanced power within the frequency range 3–5 mHz is found for the most magnetically quiescent datasets, lower frequencies dominate when there is significant influence from strong underlying magnetic field concentrations (present inside and/or in the immediate vicinity of the observed field of view). We discuss here a number of reasons which could possibly contribute to the power suppression at around 5.5 mHz in the ALMA observations. However, it remains unclear how other chromospheric diagnostics (with an exception of H α line-core intensity) are unaffected by similar effects, i.e. they show very pronounced 3-min oscillations dominating the dynamics of the chromosphere, whereas only a very small fraction of all the pixels in the 10 ALMA datasets analysed here show peak power near 5.5 mHz. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’. 

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