Unmanned Systems Technology 036

10 Platform one An electronic module has been developed to safeguard emergency operation in autonomous vehicles (writes Nick Flaherty). The module, developed by a European project led by the Fraunhofer Institute for Reliability and Microintegration (IZM) in Germany, provides protection for the entire electrical system in microseconds. Autonomous electric vehicles draw power from their high-voltage battery at 400 or 800 V and from the conventional 12 V battery that supplies the vehicle when idling or in high-load driving situations. Safety-critical systems such as brakes and steering can therefore be connected to two sources of power, providing the degree of redundancy needed for the highest level of reliability certification, ASIL-D. To help maintain that safety level, the HiBord project developed an electronic disconnection device that can isolate any short-circuits in a vehicle’s electrical systems. Current autonomous vehicle designs use overload protection in an electronic fuse to isolate areas that might be affected by a fault, shutting down a device within 20 ms before it is damaged by a short-circuit. However, this only works if there is redundancy for all components and the onboard electrical system. That is expensive though, and increases the vehicle’s weight, reducing the operating range from the battery pack. Instead, the new module shuts off faulty components in the onboard electrical system while still safeguarding the supply of power to safety-critical components. That guarantees safe driving without the need to install a duplicate onboard electrical system. “In conventional systems, any undervoltage while on the road can trigger a sudden and uncontrolled failure of the entire onboard electronics – including the braking and steering systems,” said Phillip Arnold, research associate at the IZM. “That presents an unacceptable risk, particularly when travelling at high speeds. But with our module, part of the onboard electrical system continues to function as before, so a fully automated vehicle would still have enough time to convey passengers to somewhere safe.” The module uses 16 silicon MOSFET switches that can each redirect up to 180 A. If that threshold value is exceeded, for example by a short-circuit, the electrical switch opens and shuts off the power. Each MOSFET has a maximum rating of 300 A, well below their maximum permissible load, so they have a much longer lifetime than conventional solutions. In tests where researchers intentionally triggered short-circuits, results showed that the module is capable of reliably isolating a current of up to 700 A without any propagation of the initial short-circuit. The disconnection module detects a fault within 10 µs and only requires a further 300 µs before tripping. That makes it more than 60 times faster than current fuse systems. The module has been successfully tested in an electrically powered BMW i3 demonstrator, and is designed in such a way that it can, in principle, be used in any electric vehicle, although the focus is on autonomous vehicles. Super-fast shut-off system Driverless cars February/March 2021 | Unmanned Systems Technology Conventional systems trigger a sudden and uncontrolled failure of the entire electronics, but our module doesn’t do that The module protects electrical systems in microseconds rather than milliseconds