Formula Student Racecar Propulsion Drive Converter

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Dr. Varjasi István
Department of Automation and Applied Informatics

Electric or hybrid vehicle drivetrains have recently gained importance. A few years ago only a few prototypes existed, which we have barely heard of. Today, the Tesla Model S electric car amazes everyone and many major manufacturers have their own electric cars. The evolution of the Formula Student competition well illustrates this growth: while electric racecars competed in a separate category in 2010, 2014 brought a direct competition of combustion and electric drivetrains on the racetrack, and an electric car managed to win the race. As of writing this paper, the first FIA (Fédération Internationale de l’Automobile) FormulaE season has already started, illustrating the interest of the topclass automotive competition.

Most of this segment uses PMSM (Permanent Magnet Synchronous Machine) technology due to its high power density. Moreover, the characteristics of this type of engine align much better with vehicle dynamics than their internal combustion counterpart. These drivetrains need three-phase power supply, therefore a power converter should be applied to convert the power source that is predominantly DC. This is not a new problem, of course; several motor control solutions have already been developed by the industry. The question is whether these motor controllers have sufficiently quick dynamics; in other words, are they capable of providing proper handling characteristic for road and racing purposes. This group of vehicles poses a significantly different set of requirements compared to those for example for ships, which have proven to be driven by an electric drivetrain efficiently. Ships can tolerate the delays of the drivetrain even up to the order of seconds. However, what if stability control electronics could only assist the driver with a one second delay? That would mean, for example, a situation when the throttle is released but the torque is only withdrawn a second later.

In this paper we introduce the hardware and software implementation of a design fulfilling the requirements described above for an engine control unit. The list of discussed topics includes conceptual hardware-level decisions, the emphasis on reduced weight, a robust design and its difficulties, a control loop structure and the means of reducing lag.


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