Francois Forest

Ageing and Failure Modes of IGBT Modules in High-Temperature Power Cycling

This paper presents an experimental study on the ageing of insulated-gate bipolar transistor (IGBT) power modules. The aim is to identify the effects of power cycling on these devices with high baseplate temperatures (60 °C to 90 °C) and wide temperature swings (60 °C to 100 °C). These values for thermal stresses have been defined according to automotive applications. The test conditions are provided by two types of test benches that will be described in this paper. The changes in electrical and thermal indicators are observed regularly by a monitoring system. At the end of the test (reaching damage criterion or failure), different analyses are performed (acoustic scanning and SEM imaging), and the damage is listed systematically. Nineteen samples of 600-V 200-A IGBT modules were thus aged using five different power-cycling protocols. The final summary of results shows that ageing mechanisms mainly concern wire bonds and emitter metallization, with gradual impact depending on protocol severity.

Multicell converters: derived topologies

Multicell converters were introduced ten years ago and, over this period, their properties have been thoroughly analyzed. Since then, this concept has lead to some other innovative topologies which are briefly presented in this paper. Different ways to introduce soft switching in multicell converters are investigated. The concept of distributing power over several switches, giving more degrees of freedom and using less passive components, is extended further with the stacked multicell topology. Finally, direct AC-AC converters using the multicell approach are described.

Principle of a multi-load/single converter system for low power induction heating

The induction heating appliances used for cooking generally include two or four inductors and in the most common solution, a converter is connected to each inductor. The main aim of this paper is to suggest a way of building a multi-load/single converter system, based on the use of a series-resonant ZVS inverter supplying several resonant loads. The principle can be probably extended to different applications (DC-to-DC converters, high power induction heating applications) but their study has been restricted to a low power induction heating context. In order to make this study, suitable models for the loaded inductors had to be found. Therefore, in the first part of this document, a number of different electrical inductor models, from the basic L-R equivalent circuit to a representation taking into account eddy currents effects, are presented. The second part describes the multi-load operating principle with respecting ZVS conditions, by the analysis of an R-L inductor model. Finally, the third part completes this work with simulations, including a more realistic model of the inductors and the associated experimental validation. These emphasize the interest of this original system that is currently being evaluated for an industrial application.

Frequency-Synchronized Resonant Converters for the Supply of Multiwinding Coils in Induction Cooking Appliances

The induction heating principle has been successfully introduced for about 20 years in domestic cooking appliances. The technical developments now concern the improvement of the current appliances and the introduction of new functions. So, one tendency is the design of multiwinding induction coils that are very adaptive concerning the shape and the power capability. This paper describes different original converter topologies designed to supply multiwinding coils, and, in addition, multicoil systems. The proposed topologies are based on particular use and associations of zero-voltage switching series-resonant converters. They are all characterized by a frequency-synchronized operating mode, in order to prevent any acoustic harm that could result from beating frequency-interferences

Fault management of multicell converters

Component counts and oversimplified reliability rules may lead to the conclusion that multilevel converters are less safe than two-level converters, just because they use more components. A better approach might be to consider that they use a different arrangement of components and also that the consequence of faults may be very different. This paper is focused on the study of the consequences of faults in hard-switching and soft-switching multicell converters. Solutions to minimize the consequences of major faults are described.

A Theoretical Approach to InterCell Transformers, Application to Interleaved Converters

The theoretical advantage of InterCell transformers over separate inductors is demonstrated in an interleaved power converter. Different practical ways to build InterCell transformers are described. A theoretical approach dedicated to interleaved converters and InterCell Transformers analysis is presented. This analysis tool is used to understand and overcome the main drawback of InterCell transformers. It is shown how the phase shifts between two adjacent phases must be modified to reduce the maximum flux density that influences core sizing and core losses.

Optimization of the Supply Voltage System in Interleaved Converters Using Intercell Transformers

Interleaved power converters are now used in many different conversion systems involving various topologies (series or parallel) and related to different fields or loads. This paper deals with interleaved parallel commutation cells using coupling transformers with a possibly high number of cells. The first part of the paper is a reminder of the basics of magnetic couplers addressing monolithic as well as distributed implementations. The limits associated with the conventional supply of such couplers (supply voltages forming a direct polyphase system) are described. In the second part of the paper, an optimized voltage supply improving the performances of the system is introduced. Experimental results obtained on a seven-cells test bench validate the approach

Evaluation of

The supervision of semiconductor power devices in operation demonstrates an obvious interest to improve the operating safety of electronic power converters used in critical applications. Unfortunately, this is a significant challenge due to the variability of stress conditions on the one hand and to the difficulty to implement accurate measurement systems in power stages on the other. Using VCE measurement as a real-time supervision method is evaluated here by using aging test results obtained on insulated gate bipolar transistor (IGBT) modules stressed by power cycling. These results are related to the aging of bond wires and metallization, on the top part of the module. Results were obtained in original test benches whose characteristics are overviewed briefly in the first part of this paper, along with a description of test conditions. The second part presents selected results extracted from a larger work and focusing on the VCE evolution with respect to degradations of the modules top part. Their analysis highlights the potential of VCE measurement. The last part proposes the principle of a specific system able to achieve real-time VCE supervision in the test benches in operation.

V_{\rm ce}

This paper presents an original design option dedicated to output-filtered pulsewidth modulation inverters used in uninterruptible power systems, embedded networks, or motor drives operating on long cables. It is based on the coupling of interleaved inverter cells by means of intercell transformers (ICTs) and is characterized by very good dynamic behavior on load transients, which is an important issue in such applications. ICT solutions are compared with the classical interleaved solutions using separate inductors. A specific design method is developed to achieve this comparison based on toroidal core shapes. The results obtained with a 600 V, 7.5 kW inverter show the usefulness of ICT-based designs, especially when nanocrystalline magnetic material is used; high specific power and very good dynamic performances are obtained.

Monitoring as a Real-Time Method to Estimate Aging of Bond Wire-IGBT Modules Stressed by Power Cycling

An original converter composed of interleaved flyback is presented. The cells are interconnected through intercell transformers replacing the standard multi-winding inductors used as insulation and storage magnetic device in the flyback. The combination of the interleaving effects and of the intercell transformer characteristics allows eliminating the mains limitations of the standard flyback due to the low performances of multiwindings inductors. In a first part, the different ways to interleave galvanic insulated converters as forward or flyback are briefly recalled. The second part presents the intercell transformers and shows that they can be used to interconnect interleaved converters cells. In the third and last part, this particular magnetic interconnection is applied to interleaved flyback cells and leads to create an ldquointercell transformer flybackrdquo. Its specific properties and advantages are described. Experimental results, obtained on a 2-kW test bench are finally presented.