Investigation of the inductor’s parasitic capacitance in the high frequency switching of the high voltage cascode GaN HEMT:

by N. Galanos

Institution: Delft University of Technology
Year: 2015
Keywords: Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT); cascode configuration; double-pulse tester (DPT); analytical model; hard switching; inductor's equivalent parasitic capacitance (EPC)
Record ID: 1241522
Full text PDF: http://resolver.tudelft.nl/uuid:9c196c93-5990-45ca-bf82-001ccde69555


The concept of the More Electric Aircraft, where the majority of the aircraft’s secondary needs will be supplied by electrical power, is under continuous research over a number of years in order to conform the recent demand for more efficient and environmentally friendly aircrafts. Advancements in power electronics have contributed towards the realization of that demand, by introducing lightweight, high-power density and highly efficient in harsh environment power electronics. The increase in power density of power electronic systems was made feasible, so far, by developments in the semiconductors field, namely by semiconductors that can operate at higher switching frequencies and generate less power loss. Wide-bandgap devices, such as Gallium Nitride (GaN) transistors, have emerged as possible candidates to replace silicon and even silicon carbide devices in various power conversion applications offering potential benefits for high frequency power conversion due to their intrinsic material properties. Another step towards higher power densities is to utilize appropriate circuit topologies since they can reduce the stress upon the components and the cooling requirements. However, as the frequency goes up, the switching behavior of the device is not only influenced by the die itself and the device package’s and circuit’s parasitic elements can not be neglected any more. One of these parasitic elements is the the equivalent parasitic capacitance (EPC) of the magnetic component, which is part of almost every topology. This thesis project aims at two things: first, to observe the switching behavior of a high-voltage cascode GaN High Electron Mobility Transistor (HEMT) under inductive clamped load condition, which is the same commutation mode for the power devices as switching in a PWM, hard-switching type converter and second, to investigate the influence of the magnetic component’s EPC on the switching behavior of the GaN HEMT. For this, an analytical loss model of the device was developed and a double-pulse tester (DPT), which is considered to be a very good example of that load condition, was optimally designed and manufactured in order to verify the analytical model. Two pulses are launched to the device under test (DUT) and the switching transitions of the DUT can be captured for any desired current and voltage rating under hard-switching conditions. Moreover, when operating under that load conditions, applying active devices with reverse recovery charge has significant influence on the switching behavior of the DUT, so both cases will be examined. Finally, in order to characterize the device and eventually verify the analytical loss model, current and voltage measurements need to be taken during the turn-on and turn-off switching transitions. As the GaN HEMT is capable of switching are very high speed, there are issues and limitations that need to be taken into consideration in order to ensure the fidelity and the accuracy of these high frequency measurements