Dominique Bergogne

Electrothermal modeling of IGBTs: application to short-circuit conditions

This paper discusses the possible estimation of IGBT failure phenomena by means of simulation. The studied destruction mode addresses the large surges, especially the short-circuit of IGBTs. In this case the reason of the device destruction is a thermal runaway. Thus we have developed an electrothermal model of the IGBT. The developed model may be implemented in any circuit simulator featuring a high level description language (SABER, ELDO, SMASH, PACTE etc.). The used electrical model is based on the Hefner model of the IGBT. A bidimensional finite element thermal model is considered. This model has been optimized to give a good trade-off between accuracy and simulation cost. To validate the implemented model, finite element simulations have been performed with the ATLAS two-dimensional (2-D) numerical simulator. The study is completed with the comparison between experimental and simulation results. It is shown that the proposed electrothermal model allows the prediction of the IGBT destruction phases in the case of large surges. So, users of IGBT components have the possibility to estimate, by mean of simulation, the possible failure (due to large surges) of these devices in the case of complex converters. This enables the possibility for developing protection systems for IGBTs without any destructive test.

An estimation method of the channel temperature of power MOS devices

A method is presented to characterize the IGBT (insulated gate bipolar transistor) from a power module to obtain an internal temperature estimation. A prototype is described. The technique is compatible with operating PWM-based converters.

A 200 °C Safety System at Power-Up of Normally On SiC JFETs Inverters

Silicon carbide (SiC) power devices are the only commercialized components to run at high voltage and high temperature. Normally on junction field-effect transistors (JFETs) have lower on-state resistance and lower output capacitance than other SiC switches, which reduces conduction and switching losses. However, normally on power devices induce a short-circuit in voltage-fed inverters (VFI) when the gate driver is not powered prior to the bus supply. This is a power-up limitation that has not received much attention in the literature, especially for safety systems that can be used in an integrated circuit capable of running at elevated temperature. This paper describes an original solution based on SiC JFETs to secure the inverter operation at power-up without gate driver supply for the SiC JFETs. The reliability test of the protection circuit and his impact on the ageing of the JFET of the VFI are also presented. The safety system is capable of running in elevated ambient temperatures. Experimental results have been carried out in a 540 V, 10 A inverter and at ambient temperatures from 27 to 200 °C.

Paralleling of low-voltage MOSFETs operating in avalanche conditions

This paper addresses the behavior of low voltage MOSFETs under breakdown avalanche operation. The phenomena leading to avalanche operation of the MOSFET transistors in automotive applications are first presented. Then, after a brief description of the model and of the experimental identification of its parameters, electrothermal simulations are performed. A special focus is given to the current balance between paralleled MOSFETs, because in this case breakdown voltage mismatches are a well-known reliability issue. These simulations demonstrate the influence of the specific avalanche path resistance on current sharing. Calculations performed using the proposed model give results far less pessimistic (lower temperature rise on the most stressed transistor) than classical temperature-dependant-only avalanche models. This avoids expensive specifications narrowing when designing for mass-market applications (where wide manufacturing dispersions occur)

Thermal Stability of Silicon Carbide Power JFETs

Silicon carbide (SiC) JFETs are attractive devices, but they might suffer from thermal instability. An analysis shows that two mechanisms could lead to their failure: the loss of gate control, which can easily be avoided, and a thermal runaway caused by the conduction losses. Destructive experimental tests performed on a dedicated system show that the latter mechanism is more severe than initially expected. A low thermal resistance and gate driver equipped with protections systems are thus required to ensure safe operation of the SiC JFETs.

SiC power semiconductor devices for new applications in power electronics

This paper addresses the benefits of SiC semiconductor, owning excellent physical properties able to fulfill new scope of applications in terms of high temperature, high voltage and for more specific applications. Devices and applications developed at Ampere laboratory are detailed.

A high temperature ultrafast isolated converter to turn-off normally-on SiC JFETs

Silicon Carbide (SiC) components are accepted devices for high temperature and high efficiency applications. Normally-on SiC JFETs are now commercialized and will be used in future power converters. However, such devices are conducting when not driven with a sufficient negative voltage, which can lead to safety issues during start-up or abnormal operation of the gate driver. Therefore, it is needed to generate an auxiliary negative voltage to turn-off the JFET in order to protect the system. Moreover, insulation is necessary to cover all failure modes. Prior papers presented solution to protect such devices but no high temperature isolated solution were demonstrated. In this paper, a solution to protect JFETs used in a high temperature (200°C) voltage source inverter is proposed. The protection circuit, components selection and characterizations for high temperature application are detailed. Experimental results are provided and validate the design of the isolated normally-on protection circuit up to 200°C.

New Applications in Power Electronics Based on SiC Power Devices

Controlled switch devices are now available in silicon carbide. So new applications are possible. The SiC-JFET enables to develop high temperature inverters for the More Electric Aircraft for instance. The diode-less SiC-JFET inverter is a potentially nice solution, but specific drivers, passive components and packaging have to be developed. Besides high voltage applications need high voltage devices. In this case design rules have to be adapted to the extended short-circuit and breakdown voltage capabilities of SiC devices.

Statistical Study of Nanocrystalline Alloy Cut Cores From Two Different Manufacturers

The classic shape of a magnetic circuit made of nanocrystalline alloy is usually the toroidal one. In power electronics, this shape is not the best one in terms of size and congestion. For high power magnetic components, the UU or CC shape (the cores look like the letter U or C) is preferred. Recently, two manufacturers have commercialized new magnetic circuits made of nanocrystalline alloy in this last shape. But before using these new products in power electronics, we have to first know them well and to be sure that they will respond adequately to the peculiar needs of the application. In this paper, we compare several cut cores geometric dimensions and magnetic properties from two different manufacturers. Full amplitude characterizations are performed. The dispersions of the samples and the agreement to datasheets are presented.

Minimization of Drain-to-Gate Interaction in a SiC JFET Inverter Using an External Gate-Source Capacitor

This paper presents a study on a SiC JFET leg of a 3-leg Voltage Source Inverter (VSI). The switching curves obtained with the JFET working in free wheeling mode are shown to point out drain-to-gate interaction effects. Indeed, during the drain-source voltage variations, the JFET gate-source voltage can have considerable variations, because of the electrical coupling induced by the gate-drain capacitance Cgd. When the gate-source voltage variation becomes too negative, there is a risk of occurrence of the phenomenon of punch-through in the gate-source junction. Conversely, when it is enough positive, the JFET may conduct and lead to a leg short-circuit. To decrease these undesired effects for the JFET legs and consequently for the SiC JFET inverter, an external gate-source capacitor is used. This solution is studied and optimized by simulation on an inverter leg.