Sub-ns Shaping of Switching Transients in GaN HEMT Bridge-legs

Abstract

The thesis that follows this abstract describes the development of a high bandwidth active gate driving testbed and the investigation of effects that multi-GHz bandwidth gate signals have on the switching of 650 V GaN HEMT power devices. It covers the development of the support hardware required to drive a proto-type active gate driver capable of updating its output impedance every 100 ps to deliver between ±10 A of gate current. The challenges caused by 150 V/ns and 10 A/ns slew rates on the support circuitry are investigated to select DC-DC converters and digital signal isolators which allow the testbed to be self-immune to the transitions it can produce. Measurement techniques suitable for GaN HEMT devices and optimised power circuits are explored and evaluated. Considerations on the impact of a measurement technique on circuit layout and the parasitic inductance present are explored as this impacts the viability of power circuit current measurement methods. High bandwidth active gate driving is used to demonstrate beneficial control via the gate of <5 KW scale transitions during double pulse tests with 650 V normally off GaN HEMTs. Reductions in drain oscillation of up to 10% and switch node voltage spectra by 9 dB above 125 MHz were observed depending on the load configuration. The impact of environmental and electrical operating parameters on the robustness of demonstrated improvements is investigated and discussed. For load current variations of ±3 A a resistance sequence is shown to keep drain current peak spectral content within 10 dB of the minimum achieved with a fixed gate resistance sequence. Finally, a method is proposed that allows the established resistance sequence to be compensated for changing load current and keep peak spectral content within 5 dB of minimum for a new optimised point.

Date of Award	7 May 2019
Original language	English
Awarding Institution	University of Bristol
Supervisor	David Drury (Supervisor) & Bernard H Stark (Supervisor)