Model card: Power subsystem¶

Module: src/nous/subsystems/power.py

Backlog: BL-003

Scope¶

A single Li-ion battery pack. State is integrated over a tick loop using coulomb counting against an effective capacity that combines a Peukert correction (high-current discharge) and a thermal derate (high cell temperature). Terminal voltage is a linear open-circuit curve between voltage_v_min (0% SoC) and voltage_v_max (100% SoC), reduced by the ohmic drop I * internal_resistance_ohm.

The subsystem is primary: every load served by nous ultimately draws from this pack. The APU contributes only charge, never load (ADR-0015).

Inputs¶

Input	Source	Notes
`load_w`	engine (compute + accessories; BL-007 wires the real value)	Watts, >= 0
`charge_w`	`ApuSubsystem.total_w`	Bus regulator clips to `charge_limit_w`
`cell_c`	thermal subsystem (BL-005); defaults to ambient	Degrees C

State (truth())¶

Field	Units	Notes
`soc_pct`	%	Coulomb-counted, clamped to [0, 100]
`voltage_v`	V	Linear OCV minus ohmic drop
`current_a`	A	Net (positive on discharge, negative on charge)
`remaining_wh`	Wh	`battery_wh * soc_pct / 100`
`endurance_min`	min or None	None when `load_w <= charge_w`
`flag`	enum	`nominal`, `low`, `critical`, `empty`, `full`

Outputs (sensor_obs())¶

Field	Units	Sigma
`soc_pct`	%	0.5 (calibrated bound; see estimator covariance)
`voltage_v`	V	0.05
`current_a`	A	0.10

Profile fields¶

power:
  battery_wh: 588               # nominal pack capacity (Wh)
  voltage_v_nominal: 14.4
  voltage_v_min: 12.0           # at 0% SoC
  voltage_v_max: 16.8           # at 100% SoC
  internal_resistance_ohm: 0.05
  rated_current_a: 5.0          # Peukert reference current
  peukert_k: 1.04
  soc_pct_low_threshold: 20     # ``flag = low`` below this
  soc_pct_critical_threshold: 5
  thermal_derate_c: 45          # capacity derate starts at this cell temperature
  thermal_derate_slope_per_c: 0.02
  charge_limit_w: 100           # bus regulator: max accepted from APU

Known limitations¶

Linear OCV. Real Li-ion is a piecewise curve with a flat plateau between roughly 20% and 80% SoC. The simulator's slope is sufficient to drive a voltage estimator but is not calibrated against any particular cell.
One-iteration fixed point between current and terminal voltage. The simulator does not solve the implicit system; instead it uses the previous tick's current. At a 2 Hz tick the error is small.
Single thermal node. Cell temperature is treated as uniform across the pack; pack-level thermal gradients are not modelled.
Li-ion only. Other chemistries are tracked under BL-042. See LIMITATIONS.md L8.