Examenspresentation för Henrik Zander och Shaurya Sharma

Opponent: Shijie Zhang and Pranav Katta

Abstract
Formula Student is an international competition which challenges engineering students to design, manufacture, test and compete with a formula style race car. The Chalmers Formula Student (CFS) team has participated in the competition since 2002 and has competed with an electric car since 2015. In this study, both the
hardware and the software of a two-level three phase silicon carbide inverter was designed and, subsequently, manufactured and verified. This inverter was designed
as a replacement to the current inverter being used by CFS, which means that it had to fulfill or exceed the performance specifications of the current inverter, for it
to be a viable solution for CFS’s future cars. As a consequence of this, it was decide that the designed inverter should be able to output phase currents of 120 A RMS,
tolerate DC-link voltages up to 600 V, have a volume of less than 2 litres, weigh less than 2 kg and finally have less than 200 mV of peak-to-peak DC-link ripple.

The necessary hardware circuits of the inverter were organised into three main printed circuit boards called the power board, the gate driver board and the communication board. These boards were stacked on top of each other and connected using board-to-board connectors, which created an inverter package with small physical dimensions. This was particularly important to the CFS team since it would enable them to create smaller and lighter cars in the future. Once the inverter had been assembled the hardware characteristics of it were measured, which revealed significant problems with the switching behaviour of the SiC MOSFETs. It was identified that this was due to the quite low gate resistance that was added to the MOSFETs, as well as the stray inductance between the DC-link capacitance and the MOSFETs. The result of this was that severe voltage oscillation could be observed between the drain and source pin of the SiC MOSFETs. This issue lead to a second hardware revision which introduced snubber circuits, more DC-link capacitance closer to the MOSFETs and more aggressive over-voltage protection on the communication board.

Welcome!

Henrik, Shaurya and Stefan