Design of a power limiter for an FSAE electric racecar

Abstract

MIT Motorsports is the Formula SAE team at MIT that has competed in Lincoln, NE since 2013. Last year's racecar performed exceptionally in all dynamic events but was disqualified from the endurance event due to a power violation. In order to prevent a violation in the following year, a power limiter was developed to ensure that the power consumption of the vehicle is reliably under the limit. Since weight and space come at a premium when it comes to an electric racecar, the power limiting approaches were implemented through C code in the car's Vehicle Control Unit. The power limiter makes use of a feed-forward mechanical power limiter combined with an electrical power limiter that makes use of the battery's power consumption with the use of a PI closed-loop controller. Powertrain efficiency calculations were performed to best model the power consumption of the vehicle. Testing became an essential tool used to develop, debug, and validate the power limiter. This year's power limiter will reliably keep the team under the power limit while minimally affecting performance to increase our potential at the next competition.