Design Overview
Battery pack structure
BeVolt’s battery pack uses 434 Samsung INR18650-30Q li-ion cells.
There are 31 modules connected in series, with 14 cells connected in parallel in each module.
Note
Due to weight requirements, we may remove a module from the pack during the scrutineering phase.
Each module will have at least two temperature sensors.
Architecture
BeVolt’s BPS v1.x uses a leader-minion architecture. The minion boards measure all the data and send it to the master board. There are two types of minion boards: Amperes and module.
The Amperes minion board only measures the current of the whole battery pack. The module minion boards measure both the temperature and voltage of the battery modules.
The leader board analyzes all the data and determines whether the batteries are safe. It also controls the contactor, which can connects the battery to the rest of the car and can disconnect it if needed, which shuts down the car.
The STM32F413 microcontroller runs the BPS software.
BPS Software Configurations
The BPS has a file inside the config folder called config.h that contains all data pertinent to the BPS.
Most importantly, it contains all the fault conditions that can trip the BPS (e.g. MAX_VOLTAGE_LIMIT).
It also has some hardware information that the BPS uses (e.g. NUM_BATTERY_MODULES). All of these
parameters are contained within #define and descriptions of each parameter are located in the comments.
Communications
The BPS communicates with the rest of the car through the CAN protocol, an automotive communication standard. It is powered by a 12V line outside the battery box. The emergency switch is connected to this line.
When the switch is pressed, the BPS powers off, which also grounds the contactor MOSFET driver and de-energizes the contactor, which shuts down the car.
Board functions
The minion boards will be daisy-chained to minimize wire clutter from the leader board. The Amperes minion board uses Shunt Resistor sensors to measure the current in the high-voltage line.
Note
The minion boards all use isolated SPI.
Each minion board can evaluate up to 12 modules and 16 temperature sensors.
Two display boards are present, one on the dashboard and one for the BPS. The BPS Display board is separate from the dashboard to keep it independent from all other systems while debugging.
The BPS will also power the fans in the battery box.
Overview of system
Interrupts
SPI
SPI1 - for sending commands to LTC6811 minions, has subpriority level 0SPI3 - for sending current data to LTC2315, has subpriority level 1UART
UART2 - for BLE/CLI, has subpriority level 1UART3 - for USB, has subpriority level 0Note: The OS interrupts (PendSV and Systick) should have the lowest priority amongst all other interrupts.