Lithium Battery Management Subsystem
Per-Cell EKF SOC/SOH Estimator with Active Balancing
Embedded BMS hierarchy with per-module slave controllers and a per-rack master, performing per-cell voltage/temperature monitoring, Extended Kalman Filter (EKF) state-of-charge estimation, state-of-health tracking, cell balancing, and safety enforcement.
Purpose
Maximize usable energy, extend cell life through tight operating-window control, identify degraded cells early, balance state-of-charge across cells, and trip the battery offline before damage propagates — without burdening the central CDH with high-rate cell data.
Context
Slave controllers embedded in each L3-ESS-LITH-MOD; rack-master in each L3-ESS-LITH-RACK; aggregates upward to L2-ESS-MGMT. Issues commands to L3-ESS-LITH-ISOL contactors for emergency disconnect.
Principles
- ▸Per-cell voltage measurement (10-bit min, sample rate ≥1 Hz) detects imbalance and weak cells
- ▸Extended Kalman Filter (EKF) and adaptive Unscented KF (AUKF) achieve <1% SOC error during operation
- ▸State-of-health (SOH) estimated from capacity fade and impedance growth — joint EKF approach correlates the two
- ▸Active cell balancing (capacitive or inductive transfer) is more efficient than passive resistor dissipation
- ▸Coulomb counting paired with voltage-based EKF provides robust SOC estimates across operating temperatures
- ▸Thermal-electric coupled models capture self-heating during high-rate operation
Typical implementations
- ▸Analog Devices LTC68xx and AD7280 multi-cell monitor ICs (terrestrial automotive heritage)
- ▸Saft BMS for spacecraft (proprietary, used on ESA missions)
- ▸Texas Instruments BQ7969x rad-tolerant battery monitors
- ▸Microchip ATmega/PIC32 master controllers (rad-tolerant variants)
- ▸NASA Glenn BMS designs for lunar lander demonstrators
- ▸Recent (Dec 2024) advanced BMS publications: 0.32–1% SOC error with EKF vs. 5% traditional
Lunar considerations
- ▸Long-mission BMS must correct drift in coulomb counters via periodic full-cell calibration cycles
- ▸Sense lines run between rack modules pose risk of dust shorting — shielded shielded connectors mandatory
- ▸Temperature sensors per cell (or per cell-block) must be radiation-tolerant; PT100 or PT1000 RTDs preferred
- ▸Active balancing topology favored to recover energy across full-cycle losses (passive ~0.5% loss per balance, active ~0.05%)
- ▸Algorithms must handle replaced modules joining mid-life rack — initial SOC unknown, gradually converged
Specifications
Functional
| primary function | Monitor, estimate state, balance, and protect lithium battery cells/modules |
| inputs | Per-cell voltage and temperature signals from L3-ESS-LITH-MOD, Rack-level current from L3-ESS-LITH-RACK shunts, Coolant temperature from L3-ESS-LITH-COOL, Commands from L2-ESS-MGMT (charge/discharge profiles) |
| outputs | SOC, SOH, and remaining-life estimates to L2-ESS-MGMT, Balancing currents to active balancers in L3-ESS-LITH-MOD, Trip signals to L3-ESS-LITH-ISOL contactors, Detailed telemetry log to L1-DVT |
| cell voltage resolution mv | 1 |
| cell voltage sample rate hz | 10 |
| temperature resolution c | 0.1 |
| soc estimation error percent | 1.0 |
| soh estimation error percent | 2.0 |
| balancing topology | Active capacitive switched-capacitor |
| balancing current a | 2 |
| fault response time ms max | 100 |
| supported cells per module | 14 |
| supported modules per rack | 16 |
Physical
| mass kg per slave | 0.3 |
| mass kg per master | 0.8 |
| dimensions slave mm | 100 × 80 × 15 |
| dimensions master mm | 150 × 100 × 25 |
| materials | FR4 or polyimide PCB, Rad-tolerant analog front-end ICs (Microsemi LX76xx or equivalent), Rad-hard microcontroller (Microchip CRYO MCU or LEON3FT), Anodized aluminum chassis, Conformal coating |
| operating temperature c | -40, 70 |
| radiation tid krad | 50 |
Operational
| power consumption w slave | 0.5 |
| power consumption w master | 3 |
| thermal range c | -40, 70 |
| lifetime years | 25 |
| mtbf hours | 250000 |
Interfaces
Provides
- Aggregated battery SOC/SOH, fault flags, dispatchable capacity
- Balancing commands per cell
- Trip commands for emergency disconnect
Requires
- Per-cell voltage, temperature, optional pressure
- Coolant temperature for thermal model
- Always-on 3.3 V/5 V supplies
Cite this entry
Lunar Ark Codex. "Lithium Battery Management Subsystem" (L3-ESS-LITH-BMS). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-ESS-LITH-BMS
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.