New ways in high voltage protection

Topics & Trends27. July 2022 by Philipp Teepe - Reading Time 3 min.

Electronic vehicles are already a mass market. Relatively long charging times, expensive batteries and rather low ranges are still critical challenges, but are being improved quickly. We also support the development of sustainable mobility and provide some insight into current and future high-voltage battery switching and protection concepts.

We work on the electrical vehicles of the future

There are currently two common basic principles for disconnecting an HV battery from the HV intermediate circuit in normal operation and in the event of an error.

HV switch and protection combinations

The HV switch is intended to maintain the vehicle in a ready-to-drive condition by connecting or disconnecting the HV battery to or from the HV intermediate circuit. The HV fuse only provides a safe system condition in the event of a short circuit. This technique has proven itself in 450 V systems, but is associated with large heat losses and fuse ageing.

HV switch and pyrofuse combinations

Blade fuses are often replaced by pyrofuses in order to avoid the problems of heat loss and ageing and also possible safety issues of the HV switch and protection combinations - e.g. bonded relay contacts combined with a lack of fuse tripping. They can disconnect the battery management system (BMS) if necessary. An ignition kit disconnects the busbar, connecting the battery with the intermediate circuit within milliseconds. Pyrofuses prevail in the market, particularly in 800 V systems, that are relevant for shorter charging times and a more compact design.

The need for new protection concepts, increasing battery capacities and charging currents, as well as decreasing internal battery resistance of future vehicle generations leads to higher demands for rated and short circuit currents in future pyrofuses. Solutions for this challenge are still in development. The demand for lower costs, increased safety and higher availability – especially in the utility vehicle sector – are questioning the pyrofuse concept, too:

In the event of an error, the pyrofuse must trip externally, reliably and quickly, which means additional effort and costs in the BMS. Self-tripping devices offer great beneﬁts in this case.
In the event of a short circuit, a fast disconnection is not the only demand for the maximum transmission energy, but also an early current limitation.
In case of utility vehicles with several batteries, this can lead to a breakdown, when all pyrofuses in each battery pack are ignited, although only one battery pack is defective.
Using explosives makes handling more difﬁcult, as a disconnection via pyrofuse can damage the battery or make maintenance more complicated.

So, not only the improvement of pyro-technical disconnection systems, but also the self-tripping, current limiting and resettable switching and protection element combinations are becoming increasingly important for the system design. This is why we are working on pyro-technical and electro-mechanical HV protection and switching solutions. They are designed to provide our customers better performance, decreased costs and higher availability. It will still take some time until series production, historically speaking, the era of battery-electrical vehicles has only just begun.

Your benefits

Higher availability through resettability and reduced components
Better performance by taking into account future charging and short circuit currents
Reduced total costs through minimised system complexity and increased typical life