M. Piton

Characterization and Implementation of Dual-SiC MOSFET Modules for Future Use in Traction Converters

Silicon (Si) insulated-gate bipolar transistors are widely used in railway traction converters. In the near future, silicon carbide (SiC) technology will push the limits of switching devices in three directions: higher blocking voltage, higher operating temperature, and higher switching speeds. The first silicon carbide (SiC) MOSFET modules are available on the market and look promising. Although they are still limited in breakdown voltage, these wide-bandgap components should improve traction-chain efficiency. Particularly, a significant reduction in the switching losses is expected which should lead to improvements in power-weight ratios. Nevertheless, because of the high switching speed and the high current levels required by traction applications, the implementation of these new modules is critical. An original method is proposed to compare, in terms of stray inductance, several dc bus-bar designs. To evaluate the potential of these new devices, a first set of measurements, based on a single-pulse test-bench, was obtained. The switching behavior of SiC devices was well understood at turn-off and turn-on. To complete this work, the authors use an opposition method to compare Si-IGBT and SiC-MOSFET modules in voltage source inverter operation. For this purpose, a second test-bench, allowing electrical and thermal measurements, was developed. Experimental results confirm the theoretical loss-calculation of the single-pulse tests and the correct operation of up to three modules directly connected in parallel. This analysis provides guidelines for a full SiC inverter design, and prospects for developments in traction applications are presented.

Failure-relevant abnormal events in power inverters considering measured IGBT module temperature inhomogeneities

In this work, temperature inhomogeneities inside IGBT modules are measured to assess their relevance for the component reliability. Such issue has not been considered in many previous studies, since it is often assumed that the electro-thermal characteristics of IGBTs compensate for such temperature differences. Starting from real temperature measurements, this work discusses such aspect aided by electro-thermal simulations. This method provides useful information for the reliable thermal design of power modules, also considering the actual cooling system.

Revisiting power cycling test for better life-time prediction in traction

This paper discusses the commonly accepted method for life-time prediction for power converters in traction. The method is based on junction temperature estimation and thermal cycles on a given duty cycle. The predicted numbers of thermal cycles are compared to the curves giving the number of cycles to failure versus temperature cycles. These curves are extrapolated from power cycling tests. Power cycling tests and extrapolation method will be discussed, particularly under the aspect of failure mechanisms that are induced. In order to generate the same failure mechanisms in power cycling than in the real applications, a new power cycling approach is presented.

A study of the threshold-voltage suitability as an application-related reliability indicator for planar-gate non-punch-through IGBTs

This paper proposes an analysis of the stress level affecting non-punch-through IGBTs featuring different threshold-voltage values during their operation in inverter applications. Experimental results are interpreted and complemented by electro-thermal simulation, employing a partially self-developed transistor model. The outcome of this study is that the threshold-voltage value is a good performance and reliability indicator for transistors operated in parallel.

Local thermal cycles determination in thermosyphon-cooled traction IGBT modules reproducing mission profiles

Temperature mapping in two IGBT modules cooled by a thermosyphon-based system is performed under realistic power mission profiles. The power mission profiles are inferred from a traction design tool results based on feedback data extracted from the field, in which the service line, the train characteristics, and its speed profile are taken into account. Thereby, the chips which are more prone to fail due to a temperature-activated failure are detected by means of the experienced thermal cycles.

Robustness test and failure analysis of IGBT modules during turn-off.

Considering the typical operational conditions of railway traction applications, this paper proposes an insightful study of the failure mechanism of IGBT modules when exposed to various limit load conditions during turn-off. First, the results of extensive experimental analysis are presented. These are based on a dedicated test-circuit and point out a repetitive failure mechanism. This is subsequently investigated by means of simulations based on a compact model which includes all major and secondary electro-thermal effects (i.e. latch-up). The results enable an interpretation of the observations and point out how the limits of transient safe operation can be significantly reduced by parasitic effects.

Experimental analysis and modeling of multi-chip IGBT modules short-circuit behavior

Considering the case of railway-traction applications, this paper proposes an extensive experimental characterization of multi-chip IGBT-modules, combining fast-transient short-circuit electrical measurements with infrared thermal mapping under realistic operation-like working-conditions. Then, it presents the development of a comprehensive electro-thermal compact model of the multi-chip assembly, which accounts for all major functional and structural electro-thermal effects and which can be used in common circuit simulation environments with great flexibility. A selection of simulation examples demonstrates the usefulness of the model in extending and complementing the information that can be gained by experiment. The results provide precious information for a reliable application of these components.

Methodological framework for implementation of a prediction reliability model of IGBT power modules used in railway applications

The control of critical electronic components reliability is one of the main issues in railway traction applications. Insulated Gate Bipolar Transistors (IGBT) modules are part of these components. They are subjected to high stresses due to severe conditions of use of the train. The increase of requirements in terms of reliability and safety imposes to be able to assess these dependability measures. This paper introduces a methodological framework for predicting reliability of IGBT based on an innovative and structured Bayesian approach.

Temperature Distribution and Short Circuit Events in IGBT-Modules used in Traction Inverters

This paper proposes the study of IGBT-modules combining both inhomogeneous temperature distribution and short circuit events under realistic operational conditions. For this purpose, an IGBT-module compact model experimentally assisted by thermal mappings reproduces a railway traction application scenario. The results provide precious information for a reliable application of these components. Concretely, it is evidenced how package parasitics can strongly influence the electro-thermal behavior of the analysed IGBT-modules.