It has identified three causes of electric vehicle battery fires: connector failures, thermal runaway on charge or failure in associated electronics – at the same time acknowledging freak puncturing incidents have also caused electric vehicle fires.
Its proposal for detecting impending battery failure is to combine conventional voltage, current and temperature sensing, with strain gauges and an ultrasonic detector that can ‘hear’ electrical arcs as they develop.
To detect sparking, signals between 20kHz and 300kHz from a custom MEMS sensor (see photos) are analysed to reject non-arc sources, then further analysis estimates the physical location of the problem within the battery pack.
Each module has a series disconnect relay, plus a relay that can short the module’s output terminals.
When a fault is detected in one 50V module, it can remove itself from the 400V string and replace itself with a short circuit so the vehicle can continue to operate on what has become a 350V battery.
This removal and bypass process can be initiated during: charge, driving, maintenance or a crash.
Within each modules are the two power switches and six series-connected battery sub-modules – allowing the module to be serviced.
Individual cell balancing within each sub-module and module maximises module storage capacity during charge and discharge.
Then at the module level, the two power switches can be used to implement module-level charge balancing – for example switching out the weakest module when it is depleted, allowing the vehicle to continue on seven others.
In a modelled example with eight ill-matched modules, a battery with power switches lasted 34% longer than a permanently connected battery – which is effectively empty once the weakest module is empty.
The strategy used in this case was to save the weakest module until last – it was only switched into the battery once the second weakest module had depleted to its charge level.
from News http://ift.tt/1Nsa4td
via Yuichun
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