Syseng68k #902
Hi, I'm an Electronics engineer working in another industry, involving MW size power electronics, UPS systems, and IEC61508 P/P/E.
2) There is a single hall effect current sensor ("dc current tranformer"), where two might have been expected for redundancy reasons, for such a critical function.
I would prefer two, not only for redundancy, but also for insulation monitoring.
The battery is in a conductive casing, and is expected to be insulated from the power circuits. But one single fault in a battery could connect it to the casing, thereby creating a circuit that can't be disconnected. I would insert a HAL sensor in both the positive and the negative connection, for insulation detection.
5) The battery isolation contactor has normally closed contacts. Trivial item, you may think, but in fact, it has very serious implications.
This is serious, it seems the designers has been more concerned with the risk of the system failing so it can't provide power, than the system failing so it can't protect itself. (against high currents, and high/low charge).
I would prefer two separate contactors (or at least a two pole), with normally open contact sets, one installed in the positive and the other in the negative connection. The contactors and BMS has to be able to detect and break the highest possible short circuit current.
The contactor operation could then be a part of a daily self-test (Feedback from forcefully guided contact sets).
This would also allow the battery box to have unpowered terminals during installation, the power could be connected when the communication link is established.
This would then create a chicken and egg problem, since the contactors has to be unpowered, when the aircraft is parked in order not to drain the battery, and the system needed to wake-up the battery has to be powered from the same battery. This could be solved by providing power via. the data communication connector to the charger/DC bus controller.
If Boeing continues with the hot-box solution then the energy-density would be lower than the current solution, and more rack-space would then be required.
Such a battery box would probably have a MTBF (safe faults) in the range of 5 years, for extra availability of backup power a 2oo3 architecture could be used.