Power Design and Auxiliaries of an Electric Racecar

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Supervisor:
Dr. Balázs Gergely György
Department of Electric Power Engineering

The BME-motion team operating at the Department of Electrical Power Engineering in the Budapest University of Technology and Economics is building a Formula (SAE) racecar. The car is driven by two synchronous hub motors built in the rear wheels. I had two tasks as a member of the team.

The first task was to design and choose a high current cable from the types used in automotive applications, which is capable of supplying the two electric hub motors with power. The insulation of the cable was designed to the maximum rated voltage of the accumulators. The thickness of the conductor was first calculated by the voltage drop, then it was chosen according to the standards. From an earlier calculation it was obvious, that the ideal choice for conductor's material is aluminium. It is cheaper than copper and, even though for the same amperage a thicker conductor is needed, it still weighs less compared to copper and in racecar design weight reduction is one of the most important aspects. When every parameter was given, I chose the proper cable, then I made a temperature rise check with an Excel calculation and a Quickfield simulation.

The second task was to design a safety-critical auxiliary electronic circuit. This system switches on and off the high-voltage system according to the permitting and fault signals of the various electronic circuits operating in the car. At normal operation it also indicates if it is safe to switch off the low-voltage system, without causing failures to the electronic circuits' correct shutdown processes or the logging. In case of failure it switches off the high-voltage system immediately. The difficulty in the auxiliary system is that the Formula SEA rules do not allow the use any kind of programmable logic, so every operation had to be realized by hardwired logic.

Because this is a safety-critical circuit, the main aspect during design was to build the system as robust as possible and should I make any mistakes, safety would not be compromised.

During each task, I paid special attention to the weight and size of the designed products. In racecar design weight reduction is one of - if not - the most important aspects. Size reduction is justified because to fit all components in such a small formula racecar no space should be wasted.

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