Martin Helsper

Challenges in using the latest generation of IGBTs in traction converters

Summary The voltage class 6.5kV was the last step to now cover completely the whole range of voltages for traction starting with 1.7kV and 3.3kV. This lead to the general introduction of the IGBT across the whole power range of traction. In first IGBT generations the Non Punch Through design dominated here. The latest generation of IGBTs feature characteristics like field-stop design or trench design. Thus high cosmic ray withstand capability can be combined with low VCesat. For the high-power high-voltage application as used in traction, the introduction of the field stop leads to a significant change in the switching behavior compared to the conventional NPT-design. It will be shown how the IGBT and diode turn-off characteristics change and how sensitive it is to parasitic circuit characteristics. Especially in high-power circuits with relatively large stray inductances, this is a device and application challenge. Further more it will be shown that the IGBT overvoltage during turn-off transients can be controlled only by using a highly dynamic gate driver. Since no active control ofthe diode turn-offis possible, the peak-voltage must be limited by appropriate circuit and device design. For new generations of IGBT and diode, this behavior should be considered carefully by the semiconductor development.

Next generation of IGBT-modules applied to high power traction

Modern high power traction converters are equipped with IGBT-modules. For a reliable operation the modules have to fulfil the following requirements: High junction temperature limit, large safe operating area, high surge current capability and sufficient thermal cycling capability. In this paper current and next generation of IGBT modules will be characterised regarding the first three aspects.

Multicommutation of IGBTs in large inverters

Large inverter-systems are characterized by a significant number of parallel IGBTs operating on the same dc-link. The IGBT-phases are cross coupled by their mutual stray inductance. This paper investigates the special effects occurring due to nearly simultaneous switching of multiple IGBTs. This operation can cause a significant increase in stress on the IGBT and on the free wheel diode. Countermeasures to cope with these problems are discussed

Explaining the short-circuit capability of SiC MOSFETs by using a simple thermal transmission-line model

In this paper the short-circuit robustness of state of the art SiC MOSFETs is analysed and their short-circuit behaviour is compared to that of a modern IGBT. A simplified thermal model of the chip itself is used to explain the difference between the behaviour of IGBT and SiC MOSFET under short-circuit conditions. Further, this model is used to derive the requirements for short-circuit detection methods for SiC MOSFETs.

Multiple turn on of IGBTs in Large Inverters

Large inverter-systems are characterized by a significant number of parallel IGBTs operating on the same DC-link. The IGBT-phases are cross coupled by their mutual stray inductance. This paper investigates the special effects occurring due to nearly simultaneous turn on of multiple IGBTs. This operation can cause a significant increase in stress on the IGBT and especially on the free wheeling diode. Countermeasures to cope with these problems will be discussed

Requirements to change from IGBT to Full SiC modules in an on-board railway power supply

In this paper the difference in switching characteristic and switching losses together with the effects of parasitic elements between silicon and silicon-carbide devices on the loss distribution are reviewed. A comparison between a standard silicon IGBT module and a Full SiC MOSFET module is being made on the basis of equal voltage overshoot and maximum switching speed of both devices. Potentials and limitations between the both devices are discussed for the use of Full SiC power module in on-board power supplies for railway application.

Requirements of hybrid and electric buses - a huge challenge for power electronics

The ongoing development of drives for city buses is marked by an increasing hybridization and electrification. A high operation time and the utilization of new drive concepts using permanent-magnet synchronous machines (PMSM) require very durable power electronic and hence power semiconductor technology. First of all the article will initially explain current and future city bus drive concepts and then look at the resultant requirements on power electronics. Starting with state-of-the-art drives it will be shown that future drive concepts using PMSM will result in new requirements for power electronics and especially on the load-cycling capability of IGBT. Strategies to fulfill these requirements will be discussed in the second part. The last chapter provides an overview of promising new packaging technologies for power semiconductors. The potential thermal cycling capability of these new technologies will be estimated. Finally the potential of SiC for the lifetime of electric drives will be briefly evaluated.