BEST - Battery SOC estimator

Description

The BEST (Battery ESTimator) module implements a battery state estimation algorithm. It estimates the SOC (State Of Charge) and SOH (State Of Health) of a configured battery pack based on current and voltage readings.

The estimation combines two approaches:

• Coulomb counting — integrating the current flowing through the controller
• Voltage estimation — estimating SOC from the battery voltage using an OCV (Open Circuit Voltage) model

These two methods work together to compute the SOC.

There are two variants of the OCV model, depending on the product:

• 4-point OCV — used in ESC controllers. The cell OCV curve is approximated by 4 voltage breakpoints at 0%, 10%, 85%, and 100% SOC, with a single scalar cell resistance.
• OCV table — used in BMS. The cell OCV curve is defined by a multi-point lookup table with temperature-dependent interpolation and per-temperature cell resistance values.

tip

• For controllers, the BEST parameters are located at /best.
• For BMS, the BEST parameters are located at /driver/best.

Voltage estimation

By increasing soc_gain or reset_gain, the BEST module will rely more on voltage estimation for SOC correction.

Coulomb counting

There is no explicit setting for coulomb counting strength. It can be disabled by setting P to 0.

When to disable coulomb counting?

If the siliXcon controller is not the only power device connected to the battery, coulomb counting should be disabled since the controller cannot measure the total battery current.

Parameters

Common parameters

These parameters are present in both OCV model variants.

Parameter	Unit	Description
S	-	Number of cells in series
P	-	Number of cells in parallel. Set to 0 to disable coulomb counting
soc_gain		SOC voltage correction weight. Set to 0 to disable voltage correction during run (voltage correction will still work during BEST reset)
reset_time	ms	SOC reset time at device startup. Negative value for manual-only reset via breset command or from the app. Set to 0 to disable the reset feature
reset_gain		SOC reset correction weight. Same role as soc_gain, but applied during the BEST reset period
Rs	Ohm	Pack wiring resistance (not present in single-cell mode)
Cc	mAh	Cell nominal capacity

OCV model parameters

4-Point OCV (Controllers)

The 4-point model approximates the cell OCV curve using four voltage breakpoints. A single scalar resistance value is used for the cell.

Parameter	Unit	Description
Rc	Ohm	Cell nominal resistance
U100	V	OCV for cell when SOC = 100%
U85	V	OCV for cell when SOC = 85%
U10	V	OCV for cell when SOC = 10%
U0	V	OCV for cell when SOC = 0%

OCV

OCV = Open Circuit Voltage — the voltage on a single battery cell without load.

OCV Table (BMS)

The OCV table model uses multi-point lookup tables with bilinear interpolation across SOC and temperature. Up to 6 temperature breakpoints are supported, each with its own OCV table and cell resistance value.

Parameter	Unit	Description
T	C	Temperature breakpoints array (up to 6 values)
Rc	Ohm	Cell resistance per temperature (array, one value per temperature breakpoint)
ocv_T1	V	OCV table for temperature T[0] (index 0 = 0% SOC, last index = 100% SOC)
ocv_T2	V	OCV table for temperature T[1]
ocv_T3	V	OCV table for temperature T[2]
ocv_T4	V	OCV table for temperature T[3]
ocv_T5	V	OCV table for temperature T[4]
ocv_T6	V	OCV table for temperature T[5]

info

The number of OCV tables and resistance values depends on the number of configured temperature breakpoints. Not all ocv_T* tables may be present.

States

State	Unit	Description
SOC	0-1	Battery state of charge
OCV	V	Extrapolated cell open circuit voltage

Permanents

tip

Located at folder /permanents.

Permanent	Unit	Description
Cmax	mAh	Maximum battery capacity (at 100% charge)
Cact	mAh	Actual battery capacity

Shell commands

Command	Description
breset	Reset BEST module SOC and SOH. During reset_time, SOC is corrected using reset_gain