Search

Efficiency degradation due to modules soiling is a key factor in photovoltaic plants, which must be accurately taken into account in order to set a maintenance program, which optimizes the production/cost ratio. In this paper a model is developed, which accounts for the losses in the energy production due to dust and other kind of dirt. A small PV system with a proper measurement bench and a reference panel kept clean was set up allowing to identify different shading effects due to different kinds of soiling. Early results allowed identifying different soiling factors on current and voltage. This will enable the development of a smart system optimizing the PV plant maintenance, especially for the module cleaning interventions.

This work proposes a SPICE-CFD/FEM based methodology for an optimized design of water heatsinks for high power electronic converters. Cold plates are a key issue for power electronics systems, in order to obtain reliable applications. Often the design of custom heatsinks is done by manual procedures, which require the fabrication of several prototypes. On the other hand, CFD + FEM analysis is a powerful tool to design optimized cold plates, but it requires skilled technicians and long simulation studies. In this paper a SPICE based methodology, with negligible simulation cost and limited use of CFD + FEM simulations and prototypes, is demonstrated to be adequate to design cold plates with the lowest thermal resistance and the lowest surface temperature gradient. A prototype made with the proposed methodology was used to validate the approach. Results show a good agreement between cold plate thermal-fluid dynamic 3D numerical simulations and the SPICE based methodology. A software tool was developed to easily exploit the proposed methodology in customized design of cold plates for any specific application, and to extract necessary data for the datasheet: pressure drop, and thermal resistance.

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.

In this research work, a high-frequency converter with GaN devices is proposed for a reliable specific automotive application. Core of the circuit is a high-frequency transformer, able to work at 5 MHz switching frequency with relevant power absorption peaks. 3D finite element method (FEM) simulations are provided for different transformers and a first prototype has been tested. Considerations about geometry, mutual inductance, current limitations, and thermal behavior are explored through dedicated simulations.

In this work we present a system-simulation approach to model the behavior of PROFET™ devices for automotive applications. Attention has been paid to the simulation speed, given the necessity to simulate long mission profiles in a short amount of time. PLECS has been chosen as a simulation tool, thanks to its system-level approach to the solution of electrical circuits and systems; the work shows how to implement the basic behavioral features described in the PROFET™ datasheet, and how some typical electric features, which would normally be analyzed with a SPICE-like simulator, have been included.

Many power electronics applications require high tolerance to faults such as short circuit or open circuit of the control signals. One such application is the CERN High energy AcceleRator Mixed-field (CHARM) facility, where maintenance may be precluded for long periods of time due to radiation and, therefore, high reliability is necessary. A redundant interconnection architecture for the control signals is proposed, where each signal is individually processed by different CPUs and transmitted through separate interconnection lines. During normal operation, the CPUs are synchronized and produce the same signals. The purpose of the proposed hardware and firmware strategy is to allow the actuator to continue operating even in case of fault; regardless of the fault type (open circuit, short circuit to ground or to positive supply), a fault on one of the parallel lines would not inhibit the correct operation of the remaining line. This solution can be used to control the movements of a target system using a remote joystick in a safe environment. The architecture features reliable transmission of PWM signals driving a half-bridge power converter. Moreover, it is possible to extend it to any type of converter such as three-phase bridges, three-level NPC, or buck-boost converters. Simulations and experimental results show a good agreement, proving the effectiveness of the proposed fault-tolerant circuitry.

In this work we propose a new sensor concept to evaluate the degradation of PV arrays due to soiling. It is based on I-V curve analysis coupled with artificial vision inspection of a reference PV module to quantify and identify the type of dirt. In order to assess the usefulness of this approach in the automatic scheduling of maintenance interventions in smart-grid PV modules, we developed a Simulink model of a DC nanogrid to test different control strategies. Early experimental results are also shown demonstrating the feasibility of the approach.

In this work a new concept of liquid cold plate for high power press-pack assemblies is investigated. In industrial applications it is very important to reduce the volume and weight of the device-heatsink stack, in order to improve reliability and availability of the whole system. The potential of aluminum additive manufacturing technology is investigated by means of coupled thermal fluid-dynamic 3D modeling in order to get the best trade-off between thickness, thermal performance, and pressure drop. The validation of the numerical model was conducted by means of thermal characterization of a prototype with a properly built test bench. The numerical model was used to explore different solutions for the cold plate internal layout, such as with classical coils, deformed coils, or specific textures impossible with standard mechanical machining. Early results are shown to demonstrate the usefulness of our coupled thermal fluid-dynamic approach. Mechanical analysis was also taken into consideration, to account for possible weakness induced by the reduction in metal content typical of the advanced structures built with additive technology.

In this work we propose a procedure based on finite element simulations to compute a lumped-parameter thermal model of capacitors. The extracted Foster or Cauer network coupled to the electrical model can be useful to evaluate the temperature of capacitors in circuit simulators as SPICE or Simulink. In this way, it is possible to evaluate the expected maximum operative temperature of the capacitor embedded in a circuit before its real application, avoiding unexpected failures since the prototyping stage. Here, we describe the workflow of the method and, finally, the proposed approach will be used for designing snubber capacitors for medium power (60 kW) high frequency AC/AC converter.

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.

Current environmental concerns and fuel scarcity are leading to the progressive introduction of Electric Vehicles (EV) in the global fleet vehicle population. This requires significant design and research efforts from scientific community and industry to provide reliable automotive electric propulsion systems. The power modules used for automotive traction inverters can be considered as central elements of such systems. As they are subject to high electro-thermal stress during operation, Design-for-Reliability (DfR) approaches should be adopted. Thus, accurate models for electro-thermal simulations are relevant since the early design stages. However, such simulations become highly time consuming and complex when accurate thermal characterization through standardized or real driving conditions needs to be provided. In this context, this work proposes a simulation methodology that combines real-time simulation for electro-thermal characterization of the whole EV propulsion system, using a 1D equivalent thermal impedance circuit, in conjunction with 3D FEM thermal simulation. In this way, an accurate thermal characterization of the power module under driving cycles with long duration (of hundreds of seconds) can be obtained without computing heavy 3D FEM simulations. The proposed procedure allows to simplify and speed up the early design stages while maintaining high accuracy in the results.

Power cycling is the most realistic stress test for thermo-mechanical accelerated failure mechanisms in power devices. The fast evolution in solder materials and packaging techniques makes it necessary to find the proper accelerate test conditions for any specific package/mounting solution. This paper deals with a procedure for determining the power cycling optimal parameters (power rating, period, duty-cycle, cooling conditions) for accelerated stress tests on solder joints of SMD power devices mounted on a specific board. The procedure is based on FEM numerical analysis and preliminary experimental tests. Simulation results are presented; they are validated by comparison with measurements performed using an ad-hoc experimental setup. Early power cycling is also shown.

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.

This work deals with optimization of boards with commercial discrete power GaN FETs in applications where natural air convection is a strict constraint. In these cases, both thermal and electromagnetic behaviours are critical reliability issues for the board design, and they are modeled by Finite Element (FE) analysis, starting from literature description of the device structure, and measurements on a simple test circuit. For improved accuracy and more realistic modeling, verification and validation simulation steps are introduced, in order to evaluate the relevant error parameters for different FEM solutions. The results obtained demonstrate a good fitting with experimental and make it possible to improve board thermal characteristic. The electromagnetic simulations allow the evaluation, and possibly the reduction, of parasitic inductances for different layouts. Then, the proposed approach enables thermal and electromagnetic optimization of the layout design by simple FEM simulations, without any preliminary prototype, with time and cost saving.

We show results of temperature-dependent reverse-bias step-stressing of normally-off high-power GaN FETs. In the range 250–350 K, the stress voltage at which the FETs fail catastrophically does not show a clear temperature dependence, while some correlation is observed with the initial leakage current value. Our results, consistent with other published reports, point to the activation of a deep gate-to-drain leakage path as the responsible for fatal device degradation at large values of the drain–gate reverse bias.

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.

The aim of this work is to show how it is possible to improve the reliability of a power converter by means of thermal–fluid dynamic numerical analysis. Power electronic converters such as those for High Energy Physics Experiments (HEPEs), must operate in hostile environment with tight thermal constraints and the reliability must be high because of the inaccessibility during the experiments and the high costs of the overall setup. Due to the high power density, the presence of closed environments and the requirement of non-thermal interaction with other subsystems, a liquid cooling system is mandatory. 3D FEM and/or FVM simulations can be used to analyze thermal fluid dynamic behavior of those systems and can be a useful support to design heat sinks optimized for specific applications. We show a comparison of different heat sink solutions to improve the thermal management of a 1.5 kW DC/DC hybrid power module.

The aim of this paper is to show and discuss results of 3D finite-element simulations for thermal management design with tight constraints taking care of reliability aspects of hybrid power converters. A procedure to obtain simplified but accurate device models has been shown together with experimental validation. The simplified models have been used for converter module modeling. The same procedure has been applied to analyze the thermo-fluid dynamic problem of a whole converter comprising of three modules, inner air and enclosure.

The paper describes the design of switching converters suitable for power supply application in the LHC proton accelerator, in operation since 2010 at the European Organization for Nuclear Research (CERN) in Geneva (Switzerland). Experiments running at LHC must reliably operate in a harsh environment, due to radiation, high magnetic fields, and stringent thermal constraints. The followed approach takes into account the very tight reliability requirements during all the design stages, from the choice of circuit topologies and radiation hard power components, to the thermal layout and material optimization. Results carried out on prototypes are reported.

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.

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.

Reliability requirements for very high power devices are growing for their importance in industrial drives and renewable energy; testing those devices in operating condition is more and more difficult. A coupled measurement-simulation based design procedure is presented and applied to high power PiN diodes for application with fast IGBTs or IGCTs, in which high di/dt’s can result in too high current or voltage or energy peaks during turn-off, limiting the reliability of the circuit. Appropriately tuned simulation of the semiconductor device embedded in the test circuit allows to overcome measurement capability limits and to properly design the diode itself and a specific test circuit.

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.

The aim of this paper is to show and discuss results of three-dimensional finite-element thermal simulation of GaN HEMT structures. HEMTs differing by geometry, substrate material, passivation, and cooling strategy are simulated and compared in order to give a picture of the complex interplay of factors that must be reckoned with for proper thermal modeling and management.

This work focuses on the accurate thermal modeling of magnetic components for power converters. The inductors of a 1.8 MHz DC–DC switching converter are simulated using the Finite-Element (FE) approach with a three-step procedure: (i) electrical simulation for Joule power loss; (ii) electromagnetic simulation for core losses and eddy currents; (iii) thermal simulation for temperature distribution calculation. The magnetic component models can be used in the full converter FE thermal simulation for design optimization and estimation of reliability hazards.

We have developed and experimentally validated a 3D model for thermal analysis and reliability-conscious design of hybrid power converters, using the commercial finite-element solver COMSOL™. The model was tuned using an accurate packaged MOSFET model and a specially-designed test board for multi-point temperature measurements. Measured and modeled temperatures showed good agreement for various dissipated power levels. A simplified version of the packaged MOSFET was then used in a bridge configuration to build a thermal model of the converter. After thermal studies, we performed preliminary finite-element analysis of the thermally-induced stress distributions.