SLUUB65B May 2015 – December 2022
At low temperatures and very high rate discharges, SOC convergence to 0 using the interpolated resistances can lead to higher errors. Fast Resistance Scaling provides improved SOC convergence to 0% (that is, Terminate Voltage) by scaling resistance values used in capacity prediction simulations instead of using interpolated resistance table values as-is. The algorithm becomes active once one of the following is true:
It then begins scaling resistance values every 30 seconds based on the ratio of most recent measured resistance (Rnew) to stored resistance (Rold) at the present SOC. This allows the predicted remaining capacity to gradually converge to the cell's empty point and avoids potential for SOC jumps to empty near the end of discharge. The minimum and maximum scaling factors that can be employed in the Fast Resistance Scaling algorithm are stored in Min Res Scale and Max Res Scale, respectively, where a value of 1000 corresponds to 1x and 200 corresponds to 0.2x. For most applications, the default value of Term V Delta and Fast Scale Start SOC are recommended. Further, it is typically best to keep (Terminate Voltage + Term V Delta) below 3.6 V for most battery applications. The feature is enabled via the [FConvEn] bit in Pack Configuration B.
Thermal modeling is designed to estimate cell heating based on current flow through the battery and compensates the predicted RemainingCapacity() based on the true cell temperature output from the model. However, it is possible to overestimate cell self-heating in particular cases and this could result in overestimation of RemainingCapacity(). As a result, thermal modeling is disabled by default in the Fast Resistance Scaling region but can be enabled for a given application using the Pack Configuration C [FConvTempEn] configuration bit.
For better flexibility, users can configure an independent load profile for use during Fast Resistance Scaling, using the Fast Scale Load Select parameter. This parameter can be set to any value supported by the standard Load Select and is useful for systems that exhibit significant load changes near the end of discharge, enabling the gauge to better predict remaining SOC in such cases. The default value for Fast Scale Load Select is set to 3 (14 s average of the current/power). This makes it more responsive to changes in load near empty and to help it converge better to 0%. This helps in cases where the discharge was at a relatively light load during most of the discharge, but the load increases dramatically near the end.
If typical load behavior is consistent throughout the entirety of the battery discharge curve, then the feature can be disabled by setting Fast Scaling Load Select to the same value as Load Select.
Ra Scaling is reset under the following conditions:
In CHARGE mode when:
Voltage > Terminate Voltage + Term V Delta AND SOC > Fast Scale Start SOC
RaScl Ocv Rst Temp Thresh determines the temperature threshold at which the scaling factor used in FAST RESISTANCE SCALING mode is reset if a new open-circuit voltage measurement is captured.
Subclass ID | Subclass | Offset | Name | Data Type | Value | Unit | ||
---|---|---|---|---|---|---|---|---|
Min | Max | Default | ||||||
80 | IT Cfg | 66 | Term V Delta | I2 | 0 | 4200 | 200 | mV |
100 | Max Res Scale | U2 | 0 | 32767 | 5000 | Num | ||
102 | Min Res Scale | U2 | 0 | 32767 | 200 | Num | ||
104 | Fast Scale Start SOC | U1 | 0 | 100 | 10 | % | ||
105 | Fast Scale Load Select | U1 | 0 | 6 | 3 | Number | ||
108 | RaScl OCV Rst Temp Thresh | U1 | 0 | 127 | 15 | °C |