Behavioral analysis of insulated gate bipolar transistors during hard and soft turn-off

2007·5.8 MB·English

by  Banerjee, Abhishek

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BEHAVIORAL ANALYSIS OF INSULATED GATE BIPOLAR TRANSISTORS
DURING HARD AND SOFT TURN-OFF
BY
ABHISHEK BANERJEE
B.S., Kettering University, 2006
THESIS
Submitted in partial fulfillment of the requirements
for the degree of Master of Science in Electrical and Computer Engineering
in the Graduate College of the
University of Illinois at Urbana-Champaign, 2007
Urbana, Illinois
Adviser:
Professor Philip T. Krein

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ABSTRACT
This thesis examines hard and soft turn-off behavior of insulated gate bipolar
transistors. Insulated gate bipolar transistors are used as switching devices in power
converters for machine drives. Faults during operation of converters occurring due to
reasons such as loss of control, device parasitics, and load-side malfunctions might
necessitate shutdown of the devices to protect them from destruction. Hard turn-off
entails a direct shutdown when a fault is detected, whereas soft turn-off involves a
relatively slower shutdown to prevent overvoltage stress and consequent breakdown
of the device. For short-circuit conditions, soft turn-off helps reduce overvoltage.
However, for overcurrent situations, several factors are evaluated to determine
whether soft turn-off should be used: the amount of parasitic inductance, the turn-off
overvoltage, and the capability of the power device to handle higher current for brief
intervals. Also, soft turn-off uses excess pulse energy due to longer turn-off time.
This excess energy leads to increased losses and potential to hurt the device. Thus, the
trade-off is to maximize overvoltage reduction for the least increase in pulse area.
Through simulations and hardware tests, it is shown that soft turn-off for short-circuit
current is necessary but for overcurrent conditions, the decision whether to use hard
or soft turn-off is application based.
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