The main objective of this project was to design
a half-bridge switching module with four
GaN HEMTs in parallel. The parallel operation
of GaN HEMTs was analysed to understand
how the parasitics would affect the operation.
Three different designs were created,
based on the previous analysis, using a digital
design process with the FEA software Ansys
Q3D to calculate the parasitic content. These
parasitics were then implemented in an LTspice
model to account for all the parasitics
and non-linearities in the designs. This process
was further optimised to minimise the
number of simulations needed as the parallel
designs required a high number of iterations
per design. A method of integrating LTspice
with Matlab was developed, where a simulation
could be looped, with each iteration containing
different component values. Using optimisation
theories, the components could be
evaluated, and an optimal component could
be selected. The switching performances of
the three designs were tested in the laboratory
with a double pulse test, where one of
the designs switched at 400V and 50A, but a
failure occured at 60A. Undesired ringings on
the gate-source voltage were observed in one
of the other designs, which is thought to be
caused by too high gate loop inductance.