Investigation of Pulse current capabilities of IGBTs and MOSFETs

Abstract

TU Delft and KEMA laboratories are collaborating to create a Programmable high voltage test source by employing Modular Multilevel Converter MMC which can generate output voltage waveforms of any arbitrary shape. To produce an Impulse waveform of magnitude 250 kV across a capacitive load of 10 nF with a rise time of 1.2 µs as output voltage, each Power Electronic device incorporated into each Sub-Module of the MMC has to conduct pulse currents as high as 850 Amperes. Moreover, the Impulse Waveform has a very short time duration. Hence the Power Electronic devices need to conduct such high current magnitude only for a very short duration of time. This motivates this Master thesis to find out how many multiples of its rated current a Power Electronic device is able to conduct within such short time and what factor limits the peak current capability of the Power Electronic device. However, to produce an output voltage of any other waveshape each Power Electronic device of each Sub-Module of the MMC has to conduct only a few amperes of continuous current. Employing Power Electronic devices of current rating as high as pulse currents of Impulse waveform is not only uneconomical since other waveforms do not require such high continuous currents, but also such Power Electronic devices of high current rating would make the MMC bulkier.
To identify the Power Electronic device technology that is capable of conducting such high pulse currents, a literature review is conducted among IGBT, MOSFET and their types. Each device of IGBT and MOSFET is compared to one another. Finally, the most promising switching technology is chosen among MOSFET and IGBT based on three criteria namely, high peak current capability, high voltage blocking capability and high switching frequency.
A prototype of Pulse Current Test circuit is built to test the peak pulse current of the chosen switching technology. Then, the factors that can be utilized to achieve the peak pulse current are identified. Based on results of the pulse current test, the multiplication factor of the rated current of the Power Electronic device is identified. Switch technology for the MMC specifically for Impulse waveform is suggested.