Francesco Giuliani

Developments on DC/DC converters for the LHC experiment upgrades

Prototypes of DC/DC power and Point of Load (PoL) converters were designed and built with the aim of satisfying the foreseen working parameters of the High Luminosity (HL) LHC experiments, using both Silicon (Si) MOSFETs and/or more recent devices substantiated of better power performance, like Silicon Carbide (SiC) and Gallium Nitride (GaN) transistors. Optimization of their design, based on the comparison between the simulated and measured thermal, electrical and mechanical performance, is in progress, and many improvements with respect to the previous versions are under implementation. We discuss in this paper the results of the last modifications. In addition, many tens of discrete component samples, chosen among the devices commercially available in the three different technologies (Si, SiC and GaN), were electrically characterized and tested under γ-rays, neutron, proton and heavy ion radiation, also using a combined run method. We have also planned to test some commercial DC/DCs under the extreme conditions of radiation and magnetic field expected in the upgrades of the LHC experiments. Here we show the first results on few samples.

Review of Oscillating Water Column Converters

Ocean waves are a huge largely unexploited energy resource, and the potential for extracting energy from waves is great. Research in this area is driven by the need to meet renewable-energy targets, but it is relatively immature compared to other renewable-energy technologies. This review introduces some device types that represent the state of the art of oscillating water column technology, a kind of wave energy converter (WEC). Unlike other works in literature, typically limited to specific aspects of WECs, in this paper, a system-wide perspective will be pursued, from the sea waves to the grid connection.

Analysis of Heavy Ion Irradiation Induced Thermal Damage in SiC Schottky Diodes

A study is presented aimed at describing phenomena involved in Single Event Burnout induced by heavy ion irradiation in SiC Schottky diodes. On the basis of experimental data obtained for 79Br irradiation at different energies, electro-thermal FEM is used to demonstrate that the failure is caused by a strong local increase of the semiconductor temperature. With respect to previous studies the temperature dependent thermal material properties were added. The critical ion energy calculated by this model is in agreement with literature experimental results. The substrate doping dependence of the SEE robustness was analyzed, proving the effectiveness of the developed model for device technological improvements.

A main converter for future LHC experiments: Features measurement and reliability considerations

Devices used in future experiments at LHC will be called to work in very hostile environment. Power supply is a key aspects in this scenario and new converter will be re-designed in order to meet the future requirements. In this paper a main DC-DC power converter, developed by authors in the framework of the APOLLO R&D project, has been proposed and the experimental activity devoted to its characterization is presented and discussed.

Metrological characterization of a cold plate test bench

The reliability of a power converter can be improved using a well-dimensioned cold plate. At this aim it is necessary to realize a state of the art cold plate by means of thermal-fluid dynamic numerical analysis and ad-hoc designed experimental test bench. Features and metrological characterization of test bench for cold plate design and verification will be discussed in this paper.

Thermal damage in SiC Schottky diodes induced by SE heavy ions

Abstract The failure of SiC Schottky diodes due to the impact of high energy heavy ions is investigated by means of electro-thermal and thermal finite element simulations. In particular, 3D ATLAS simulation of a small portion of the diode structure is used for computing the dissipated power density, which is subsequently used as input for the thermal COMSOL simulation of the complete system including chip and packaging. Results show that, as a consequence of the ion penetrating through the device, the temperature at the Schottky barrier becomes bigger than the SiC melting point for a time large enough to cause permanent damages to the SiC lattice. Simulation results are in good agreement with experiments presented in the literature.

Finite element modeling and characterization of lead-free solder joints fatigue life during power cycling of surface mounting power devices

Abstract In this work it is developed a numerical model for thermo-mechanical fatigue of SMD chip solder joints in power converters that can be useful for reliability prediction. By this model the thermo-mechanical stress–strain distribution in the structure is studied by means of Finite Elements (FE) method and operational life of the solder joints can be calculated. As a case study the estimation of the fatigue life of lead-free solder joints in SO8-packaged power MOSFETs is investigated. A stress bench for power cycling was set up to tune the developed FE model by experimental results and dynamic thermal measurements are reported. Results obtained by either simply applying the Coffin–Manson law or also accounting for creep, depending on cycle period, are discussed.

Oscillating water column power conversion: A technology review

Ocean waves are a huge, largely unexploited energy resource, and the potential for extracting energy from waves is great. Research in this area is driven by the need to meet renewable energy targets, but it is relatively immature compared to other renewable energy technologies. This brief review introduces some device types that represent the state of the art of Oscillating Water Column (OWC) technologies, a kind of Wave Energy Converter (WEC). Unlike other works in literature, typically limited to specific aspects of WECs, in this paper will be pursued a system wide perspective, from the sea waves to the grid connection, with a particular focus on the power electronics.

Metrological Characterization of Cold Plates for Power Converters

The reliability of a power converter can be improved using a well-dimensioned cold plate. For this purpose, it is necessary to realize a state-of-the-art cold plate by means of thermal-fluid dynamic numerical analysis and an ad hoc experimental test bench. Features and metrological characterization of a test bench for cold plate characterization are discussed in this paper. An infrared camera is used to measure the outer surfaces, and thermocouples are employed to measure the temperatures of some inner points, but not all the points of a structure under test are accessible to probes and sensing. An accurate 3-D numerical model has been set to widen the cold plate characterization investigating the values of the variables of interest, such as the temperature and the water velocity field, in all the points of the geometry. A case study is described, showing that using modeling with potentially high accuracy in designing new systems can be useful not only to choose, by comparison, the best solution, saving time and prototyping costs, but also to foresee the system performance.

Soft-starting procedure for dual active bridge converter

Dual Active Bridge converter is extensively used to manage the power flow in high power and high density applications, as energy storage systems, renewable sources integration and electrical vehicles. This paper focuses on a digital starting process - suitable for all operating conditions - aiming at minimizing the inrush current at the turn on. The output voltage is initially built up by the secondary side body diodes, then phase-shift control is enabled and the reference is smoothly increased till the nominal value. A FPGA controlled 1.2kW 270V/28V converter is developed and experimental results are provided to assess the proposed method.