S. M'Rad

University of Lyon, Lyons, Rhône-Alpes, France

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Publications (6)4.08 Total impact

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    ABSTRACT: The virtual prototyping of power electronic converters requires electrothermal models with various abstraction levels and easy identification. Numerous methods for the construction of compact thermal models have been presented in this paper. Few of them propose state-space models, where the model order can be controlled according to the necessity of the virtual prototyping analyses. Moreover, the model reduction methods require the experience of the engineer and previous calibration. Diffusive representation (DR) is proposed here as an original and efficient method to build compact thermal models as state-space models. The model reduction is obtained through the model parameter identification and/or the time horizon of the measurement data provided for the identification. Instead of eigenvalue elimination, the method enables to specify adequately inside the model the frequency domain wished for the virtual analysis at hand. The proposed method is particularly dedicated to the system optimization phases. Experimental and simulation results are in good agreement. The advantages and limitations of the DR are discussed in comparison to published methods.
    IEEE Transactions on Power Electronics 01/2010; · 4.08 Impact Factor
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    ABSTRACT: Ladders of RC-cell are usually used for compact thermal representation of power modules or assemblies. A large number of cells are considered in order to balance the intrinsic poor dynamic accuracy of the representation. However the number is limited by convergence problems in simulation. The RC-cells representation is also questionable in terms of relation to physical quantities. These limitations may be overcome using the so-called diffusive representation to build systematically a low-order but accurate thermal model of any assembly, and including thermal couplings. The paper intends to demonstrate how to build practically a diffusive model and assert its validation by experiment and through confrontation to finite-element simulations. A compact diffusive model comes as a state space model and main be easily implemented in circuit simulator.
    Power Electronics and Applications, 2007 European Conference on; 10/2007
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    ABSTRACT: The feasibility of a hybrid inverter based on commercial silicon carbide vertical JFETs was tested. The Ron-resistance, mainly due to the vertical channel, increases with the temperature, from 1.1 Omega measured at RT to 2.98 Omega at 300deg C. These devices can drive current in both forward and reverse direction, eliminating the need for an external anti-parallel diode. A transient current-limited short circuit is observed with duration of 100 ns in turn-on. The power losses estimated involve for the hybrid inverter a working frequency up to 300 kHz. Good results obtained for hybrid inverter predict a SiC monolithic inverter realization. For this propose, SiC lateral JFETs (LJFETs) were studied and designed by finite-element method. A double RESURF structure is retained for the SiC LJFET, in order to reduce the on-resistance and to improve the blocking voltage. The obtained Ron-resistances are one order of magnitude lower than in vertical SiC JFETs. This result is obtained thanks to the high doping lateral channel and RESURF structure. Switching times of the LJFETs during turn-off and turn-on, are obtained in the 20 to 30 ns range. Eight levels of masks are designed to fabricate these devices. The masks structures were optimized in order to minimize both the Ron-resistance and the device size by utilizing inter-fingers structures.
    Integrated Power Systems (CIPS), 2006 4th International Conference on; 07/2006
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    ABSTRACT: The paper deals with so-called ¿diffusive representation¿ method and its application to efficient thermal modelling. The interest of this approach is to build a compact electro-thermal model as an input-output state-space model, accurate and easy to simulate compared with finite-element (FEM) or finite-difference (FDM) approaches. In the first part, a diffusive thermal model has been developed for a Direct Bonding Copper (DBC) package with a wire-bonding attached IGBT die (600v / 50A). The obtained state-space thermal model is implemented in SABER simulator and allows transient thermal responses. The hottest point in the die is the channel extremity and adequate thermal measurement methods have been implemented to validate the developed diffusive thermal model. In the second part of the paper, a fast and accurate analytic thermal model of self-heating VDMOSFET was developed from only one result of a 2D finite element electro-thermal simulation with ISE-TCAD. The diffusive thermal model is then simulated in SABER and compared with FEM simulations.
    Integrated Power Systems (CIPS), 2006 4th International Conference on; 07/2006
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    ABSTRACT: A silicon carbide JFET cascade sample is characterized at temperatures up to 300degC with the design of a diode-less inverter in mind. The JFET is considered as a power switch, on-off gate voltages are applied during testing, conduction capability and blocking are measured, reverse conduction is investigated experimentally. Switching losses are considered and total losses of the inverter leg are estimated
    01/2005;
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    ABSTRACT: The paper presents different modeling approaches that yield a same bond graph representation structure. The first one is based on a variational approximation of the Magnetic Induction Diffusion Equation and supplies various degrees of modeling starting from the simple standard electrical inductor. The second approach is based on the diffusion representation and may be simply connected to numerical simulation of the Maxwell's Equations in Frequency Domain. Finally such approaches should be applied to advanced modeling of Integrated Power Systems that operate at high switching frequency.