4.1.1. State estimation

foxBMS 2 performs various state estimations for the battery system:

  • state-of-charge (SOC)

  • state-of-energy (SOE)

  • state-of-health (SOH)

  • state-of-function (SOF)

The SOC estimation is used to estimate the currently remaining charge (Ah) within the battery system whereas the SOE estimation provides the remaining available energy (Wh) that can be drawn from the battery. The SOH estimation tries to assess the degradation state of the battery pack (aging) - how much charge or energy can the battery pack store compared to its initial value.

The SOF calculation provides a metric for the current capability of the battery pack. For example, to prevent an accelerated degeneration of the battery materials (aging) through operation near the limits given by their electrochemical properties the SOF is reduced. Especially fast charging at low temperatures leads to accelerated aging. To attenuate these conditions, the lowered current capability, the maximum recommended battery current is calculated and communicated to other control units. The operator or the supervisory control unit is encouraged to respect these suggested limits, but violation of the current ranges is not resulting in an opening of the contactors.

In an airborne application, where in extreme cases the full availability of the system must be ensured, the operating area has to be widened at the expense of the batteries health state. A typical automotive application would rather prefer to enter a limp home mode with reduced system performance. Instead, a stationary application would use more sensitive settings for the safe operating area, as the long-term availability of the battery packs is of major importance.

Different estimation algorithms for SOC, SOE and SOH can be selected via the battery system configuration file (bms.json).

This is achieved as all state estimation implementations follow the State estimation API. State estimation API