Mirko Bernardoni

Thermal modeling of planar transformer for switching power converters

Abstract This paper presents thermal simulations for reliability-oriented design of planar transformers for medium-power, high-frequency DC–DC converters. The modeling approach is based on accurate 3D finite-element thermal simulation of the transformer structure; inputs to the finite-element thermal model are the magnetic and electrical power losses extracted by experimental characterization of a planar transformer test-bench we designed and assembled. The simulation results are compared with those of infra-red thermal measurements. The simulations allowed to evaluate the effect of frequency and output current on the temperature distribution inside the transformer, thus setting limits for reliable operation, and to analyze alternative designs aimed at improving thermal management and, consequently the transformer reliability.

Power converters for future LHC experiments

The paper describes power switching converters suitable for possible power supply distribution networks for the upgraded detectors at the High Luminosity LHC collider. The proposed topologies have been selected by considering their tolerance to the highly hostile environment where the converters will operate as well as their limited electromagnetic noise emission. The analysis focuses on the description of the power supplies for noble liquid calorimeters, such as the Atlas LAr calorimeters, though several outcomes of this research can be applied to other detectors of the future LHC experiments. Experimental results carried on demonstrators are provided.

Power supply distribution system for calorimeters at the LHC beyond the nominal luminosity

This paper investigates the use of switching converters for the power supply distribution to calorimeters in the ATLAS experiment when the Large Hadron Collider (LHC) will be upgraded beyond the nominal luminosity. Due to the highly hostile environment the converters must operate in, all the main aspects are considered in the investigation, from the selection of the switching converter topologies to the thermal analysis of components and PCBs, with attention to reliability issues of power devices subject to ionizing radiations. The analysis focuses on the particular, but crucial, case of the power supplies for calorimeters, though several outcomes of the research can profitably be applied to other detectors like muon chambers.

Heat management for power converters in sealed enclosures: A numerical study

This paper compares four assembly solutions for power converters operating in sealed enclosures with tight temperature specifications. The specific application of interest is one of the DC/DC converters of a power supply system to be used in high-energy-physics experiments: the sealed case must not significantly alter the temperature of the surrounding components (detectors and their electronics). The comparison is made using 3D Finite Element thermal modeling. The standard FR4 board solution is shown not to be viable under these tight temperature specs; we therefore explore alternative assemblies for the stack connecting the active devices to the heat-sink.

Large-signal GaN HEMT electro-thermal model with 3D dynamic description of self-heating

This paper shows a physical approach to large-signal electro-thermal simulation of AlGaN/GaN HEMTs. The dynamic thermal behavior of the HEMT is described by a 3D network of thermal resistances and capacitances describing the physical structure of the HEMT, and including features such as the thermal boundary resistance between GaN and SiC, and the die-attach, as well as temperature non-uniformity along the gate finger. The thermal network is self-consistently coupled inside ADS with an electro-thermal large-signal model.

A simple 1-D finite elements approach to model the effect of PCB in electronic assemblies

Abstract In this paper, a simple method to describe the effect of Printed Circuit Board (PCB) and environment on the thermal behavior of packaged devices is addressed. This approach aims at exploiting the benefit of compact thermal models, which are necessarily one-dimensional, together with the advantage of Finite Element (FE) modeling, which retains all the three-dimensional geometrical details, only in the regions of the model that must be accurately described. The main focus is on correct modeling of long power pulses for subsequent electro-thermal and thermo-mechanical analysis at chip level.

Dynamic electro-thermal modeling for power device assemblies

Abstract This paper reports on the development of a hybrid approach to electro-thermal modeling of power device assemblies, suitable for reliability-oriented thermal design of power modules and converters. The temperature-dependent electrical model of a power MOSFET is self-consistently coupled with a dynamic lumped-element thermal network representing the die – package – heat-sink assembly and convective boundary conditions. The lumped-element network elements are calculated on the basis of geometrical dimensions and materials physical characteristics. The results of the lumped-element model are compared with thermal measurements in both steady-state and transient conditions. The model is compared with measurement result over an extended time scale, ranging from microseconds to tens of minutes.

Self-consistent compact electrical and thermal modeling of power devices including package and heat-sink

This paper shows a hybrid approach to electro-thermal modeling of power device assemblies that aims at bridging the gap between compact models amenable to insertion into circuit simulators and physical models (such as finite-element ones) of the three-dimensional heat flow in the system. We self-consistently couple a standard analytical description of the temperature-dependent electrical behavior of a power MOSFET with a lumped-element thermal network representing the die - package - heat-sink assembly and convective boundary conditions. This lumped-element network is built by partitioning the system into elementary building blocks and assigning to the thermal resistances values determined by the geometrical dimensions and material thermal conductivities. The results of the lumped-element model are shown to be in good agreement with measurements and three-dimensional finite-element simulations.

Non-linear thermal simulation at system level: Compact modelling and experimental validation

Abstract In this work, a general methodology to extract compact, non-linear transient thermal models of complex thermal systems is presented and validated. The focus of the work is to show a robust method to develop compact and accurate non-linear thermal models in the general case of systems with multiple heat sources. A real example of such a system is manufactured and its thermal behaviour is analyzed by means of Infra-Red thermography measurements. A transient, non-linear Finite-Element-Method based model is therefore built and tuned on the measured thermal responses. From this model, the transient thermal responses of the system are calculated in the locations of interest. From these transient responses, non-linear compact transient thermal models are derived. These models are based on Foster network topology and they can capture the effect of thermal non-linearities present in any real thermal system, accounting for mutual interaction between different power sources. The followed methodology is described, verification of the model against measurements is performed and limitations of the approach are therefore discussed. The developed methodology shows that it is possible to capture strongly non-linear effects in multiple-heat source systems with very good accuracy, enabling fast and accurate thermal simulations in electrical solvers.

Combined experimental and numerical approach to study electro-mechanical resonant phenomena in GaN-on-Si heterostructures

Abstract Due to the intrinsic piezoelectric nature of Gallium Nitride (GaN), devices manufactured with such technology are in principle prone to experience electro-mechanically induced resonance phenomena under operating conditions. In this paper, we present the thorough approach combining simulation and experiment to study the occurrence and implications of such electro-mechanical resonances. A simple GaN-on-Si capacitor test structure was fabricated and electrically excited in order to activate the mechanical eigenmodes of the assembly which are measured by a Laser-Doppler-Scanning-Vibrometer. A multiphysics Finite Element (FE) model of the tested structures was built in order to perform harmonic analysis and to quantitatively study the effects of damping on displacement, stress and strain. A mathematical comparison on different aspects between the model and measurements show good agreement. This successfully verifies the methodology to model the dynamic resonance behaviour of piezoelectric active chips.