BMU + PCU
Designed the BMU and PCU in Altium Designer and brought them up. Together they control key functions of the FSAE car's HV system and include various safety circuits.
The old BMU had everything on one PCB: the HV battery control and the LV interlock circuitry on the same board. For 2025 I split it into HV and LV, which made the Ebox layout much cleaner.
- BMU: runs the interlock loop, drives the contactors, handles the last branch of the LTC6804 isoSPI chain, and interfaces with the rest of the HV system, IMD status in, fan power out
- PCU: precharge and discharge of the 588V bus
- Shunt: off the shelf, measures HV current and energy for safety checks, the precharge sequence and driver energy feedback
The Boards
The Interlock Loop
The interlock loop is a series hardware circuit. Every element in it has to be closed for the HV contactors to be supplied with power, and if any single point opens, the contactors de-energize and the car discharges. The switches and sensors are external, but the loop circuitry and the hardware sense are all on the BMU.
- Runs through the emergency stops, master switches, other safety switches and HV connectors around the car
- Three latched devices need a manual reset by someone other than the driver: the BSPD for brake plausibility, the AMS for cell limits and the IMD for insulation faults
- Hardware sense on each main part of the interlock loop, so software can read exactly where it is broken
Bringup and Validation
I built a bench setup that replicates every hardware interface on the BMU. All the new firmware was brought up on the bench, with the safety checks bypassed so the system could run without high voltage present. Once everything was brought up and validated on the bench, the board went into the car and the real HV system was brought up step by step.
