BQ27426: self-learning condition for BQ27426

chengxiaobin

Part Number: BQ27426
Other Parts Discussed in Thread: BQSTUDIO

Hello TI engineers

BQ27426使用的阻抗跟踪算法，关于自学习部分，我们目前了解到的信息如下：

1. Qmax：在DOD累计变化超过35%的后，静置5小时或者OCV稳定后，采集OCV，并更新Qmax。

2. Ra Table：放电持续500s后，此后每 50 秒计算一次，实时计算的阻抗 R(DOD, T)会存储在 RAM 里。每当 DOD 经过这个些格点时，RAM 里的阻抗 R(DOD, T) 就会按公式(6)经过归一化处理，存储到 data flash，更新已有的阻抗表 Ra table: Ra 0 ~ Ra 14。

如果在如下的使用场景中，BQQ27426是否可以完成自学习，更新Qmax和Ra？

1. 电池仅用于供电电源断开的情况下使用，正常使用场景下，电池保持在不充电和不放电的场景下。

2. 在供电电源断开的情况下，电池会以0.2C放电1分钟，然后低功耗模式（10mA<dsg current threshold(15mA)）维持30分钟；重复6次耗电约30mAh后关机。

The impedance tracking algorithm used by the BQ27426, regarding the self-learning part, we currently know the following information:

1. Qmax: after a cumulative change in DOD of more than 35%, after 5 hours of resting or after the OCV has stabilised, the OCV is collected and Qmax is updated.

2. Ra Table: After 500s of discharge and every 50 seconds thereafter, the impedance R(DOD, T) is calculated in real time and stored in RAM. Whenever DOD passes through this grid point, the impedance R(DOD, T) in RAM will be normalised according to equation (6) and stored in data flash, updating the existing impedance table Ra table: Ra 0 ~ Ra 14.

Can the BQQ27426 be self-learning and update Qmax and Ra in the following scenarios?

1. The battery is only used when the power supply is disconnected, and in normal use scenarios the battery is kept in a non-charging and non-discharging state.

2. With the power supply disconnected, the battery will discharge at 0.2C for 1 minute, then low power mode (10mA < dsg current threshold (15mA)) is maintained for 30 minutes; repeat 6 times to drain about 30mAh and then switch off.

over 2 years ago

0 Dominik Hartl11 over 2 years ago

TI__Guru 61936 points

The Ra table updates not every 50s but only when DOD crosses a grid point after other time conditions are met (e.g. 500s, depending on configuration).

#1: Yes. The gauge will still learn Qmax and Ra during a discharge as long as the Qmax and Ra update conditions are met.

#2: What's the total capacity of the cell? 30mAh is very little so depending on the capacity of the cell this may not be enough for Qmax updates nor Ra updates.

0 chengxiaobin over 2 years ago in reply to Dominik Hartl11

Intellectual 300 points

电池的总容量为1230mAh。我司的产品在正常使用过程中，不会断开常供电，所以电池不会进行放电，仅是保持在一个固定的容量区间。

1. 500sec的时间可以修改，对应的参数为哪一个，请指导下？针对与这个使用场景下，为了实现自学习，是否还有其它参数需要修改？

2. 自学习更新Ra和Qmax，是否有环境温度或是其他外部条件的限制？

The total capacity of the battery is 1230 mAh and our products are not disconnected from the regular power supply during normal use, so the battery is not discharged and is only kept at a fixed capacity interval.

1. Which configuration does it correspond to 500s for time conditions, please advise? Are there any other parameters that need to be modified in order to achieve self-learning for this scenario?

2. Is there an ambient temperature or other external condition that limits the self-learning update of Ra and Qmax?

0 Dominik Hartl11 over 2 years ago in reply to chengxiaobin

TI__Guru 61936 points

#1: It's a private parameter and not visible in bqStudio. It affects other behavior of the algorithm, which I can't discuss on E2E for intellectual property reasons. It's not possible for the gauge to learn anything if you don't discharge or charge the cell regularly. You will have to discharge periodically for the gauge to learn cell resistance and/or chemical capacity.

#2: The gauge will learn cell resistance for any temperature. It will limit Qmax learning to between +10 deg.C and +40 deg.C

0 chengxiaobin over 2 years ago in reply to Dominik Hartl11

Intellectual 300 points

我们的电池使用场景如附件所示，请确认如何配置电量计才能更新Ra Table。

并基于附件的FS文件，更新下对应参数给我们谢谢

注1：

关于RaTable的更新条件，我们在白皮书中，发现如关键参数（如存在，我们认为都要针对性的调整）：

Prime Relax Time 默认500秒
Sec. Relax Time 默认50秒
Resistance Parameter Filter 滤波时间常数，默认41秒
Res Relax Time 默认500秒
Dis Relax Time Min，默认值未知
Dsg Current Threshold TRC设置15mA

注2：

希望一并提供以上参数修改前后的对比值。

Our battery usage scenario is shown in the attachment. Please confirm how to configure the power meter in order to update the Ra Table.
Please also update us with the corresponding parameters based on the attached FS file, thank you.

Note 1:
Regarding the update conditions of RaTable, we found in the white paper that the following key parameters (if they exist, we think they should be adjusted accordingly)
1. Prime Relax Time 500 seconds by default
2. Sec. Relax Time default 50 seconds
3. Resistance Parameter Filter Filter time constant, default 41 seconds
4. Res Relax Time default 500 seconds
5. Dis Relax Time Min, default value unknown
6. Dsg Current Threshold TRC setting 15mA

Note 2:
We would like to provide a comparison of the above parameters before and after modification.

add current FS file used.

Fullscreen prepp_fs.txt Download

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0 Dominik Hartl11 over 2 years ago in reply to chengxiaobin

TI__Guru 61936 points

The reason why there's a 500s setting for Prime Relax Time is due to the cell voltage not immediately settling to the voltage = OCV - I.R.

So if you configure the gauge to make cell resistance measurements sooner (e.g. in your max. 2 minute window), the gauge will calculate incorrect cell resistance. Please check with your cell vendor how fast the cell voltage settles before changing this private parameter.

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BQ27426: self-learning condition for BQ27426