Safety-Critical Systems Demand New Approach to Backup Power
Today’s vehicles increasingly include automated driving features and are moving toward hands-off or even fully autonomous driving. These technologies require high levels of functional safety so that a vehicle does not become a hazard in the event of a single-point or multipoint failure scenario. Designing for those scenarios presents major engineering challenges, including providing safety-critical components with highly reliable and fail-operational electrical power.
Battery electric vehicles use a high-voltage battery pack system and a large DC-to-DC converter to convert high-voltage power from the battery to 12V for the vehicle powernet. This is the primary power source, but the automaker must then also include a separate 12V battery for redundancy. The alternative solution is to use two DC-to-DC converters, but they must not share any common failure points in the high-voltage battery pack to maintain full redundancy. Plus, it is preferable to have dissimilar technologies providing the redundancy, so that the same conditions don’t necessarily cause the same failures in both.
Autonomous driving further increases the requirements for redundant power. Hands-free driving — that is, Level 3 or higher — requires not just redundant power sources but also redundant electrical systems. This can be imagined as a right-side and a left-side powernet, with each one having fully redundant power sources, fuse boxes and wire harnesses. If one of the powernets were to fail — for example, due to a collision — the powernet on the other side of the vehicle would continue to function. That way, the system could be fail-operational, and could potentially execute a minimum risk maneuver to bring the vehicle to a stop or transfer control to the human driver.
With so many critical functions in a vehicle increasingly dependent on uninterrupted electrical power, automakers require a solution that will continue to provide power even if the primary power source fails. The ideal solution would excel at providing quick bursts of power, have a long anticipated lifespan and be lighter and less expensive than competing solutions.
Enter the ultracapacitor — a compact, lightweight energy storage unit that can stabilize a vehicle’s 12V or 48V powernet while also supplying emergency power to safety-sensitive components should a collision or electrical failure occur. Coupling long-life ultracapacitors to the 12V powernet through a multiphase bidirectional DC-to-DC converter allows the module to both absorb and deliver electrical power.
This approach has distinct advantages over battery technology. Ultracapacitors weigh less than lead-acid batteries, are less expensive than lithium-ion batteries, have a much longer lifespan than either type and are ideally suited for quick bursts of power.
In short, such a module is the natural choice to meet the requirements of today’s vehicles, which increasingly rely on electrical power to perform functions that are essential for consumers’ safety.
