BMS carrier is the board which is responsible for monitoring and managing the main battery pack. It interfaces with the AFE (analog front end) board and the Current Sense board to get readings from the main pack.
Other Resources:
FWXIV BMS Carrier notes
...
Components
Current Sense - connected via I2C, and provides current readings and ambient temperature,
AFEs - 3 AFE boards, daisy-chained over iso-spi. These provide per-cell-unit voltage readings and cell temperature readings, as well as perform load balancing
Relays + killswitch monitoring - Positive and negative relays must both be closed for the battery to be connected to the rest of the car. Killswitch monitor reads state of manual killswitch to batteries
HV Neg relay
HV Pos Relay
HV Solar Relay
Fans - Used to provide cooling to batteries. Controlled via PWM
Fault Conditions
These are all fault conditions which will trigger a BPS fault. They are split into Minor, in which the issue is likely to not be dangerous and the driver can take time coming to a stop, and Major in which the driver should exit the car as quickly as possible due to dangerous conditions or the potential for thermal runaway.
...
BMS_FAULT_OVERVOLTAGE
BMS_FAULT_UNBALANCE
BMS_FAULT_OVERTEMP_AMBIENT
BMS_FAULT_COMMS_LOSS_AFE
BMS_FAULT_COMMS_LOSS_CURR_SENSE
BMS_FAULT_OVERTEMP_CELL
BMS_FAULT_OVERCURRENT
BMS_FAULT_UNDERVOLTAGE
BMS_FAULT_KILLSWITCH
Operation
BMS Checks
These are the checks that are done at every cycle in each FSM state, at the highest frequency possible. They should happen as follows. If any error is detected, we should exit our check function and transition to fault immediately. We also set the requisite bit in bms_status_bms_faults signal.
...
Communication Loss: We will keep a running count of communication errors separately for AFEs and Current sense (CRC invalid, no data returned, etc). If 3 occur, we BPS fault.
Shared Memory
Readings from the AFEs and current sense should be stored into a struct shared between the BMS FSM and master task. This will allow for Fan monitor to access temp data, and any data broadcasting to happen from master task
Fan Monitor
This will be a function called from master task medium cycle which will:
Update fan PWM based on temp readings
Relay Sequence
These are the actions needed to achieve a certain relay state:
...
| Expand | ||
|---|---|---|
| ||
TX:
|
AFEs Additional info
The AFEs (analog front end) handle interactions with the main battery pack. There are multiple AFEs (LTC6811 chips) which handle reading cell voltages, reading thermistors to determine cell temperatures, and doing load balancing for the cells. These multiple AFE units are daisy-chained through one SPI interface. This SPI interface through hardware is translated to isoSPI and back to SPI for improved reliability. We do this because of the high potential differences and different grounds on BMS and AFE boards.
AFE Configuration
The AFE operation revolves around two main data structures.
...
The storage struct holds the information from the settings, as well as memory for all of the readings taken.
AFE Readings
AFE readings are taken via the daisy-chain method, meaning that a read of a certain register on one AFE will be replied to with the values of all of the AFEs connected. (For example, the reading of the voltage register A of one of the AFE will be replied to with x 64 bit readings, where x is the number of AFEs connected)
...