SOC和SOH定义

作者：储电侠 来源：鲍教授说电池

和电池打交道的都绕不开SOX，今天聊一下SOC和SOH，这里说的SOC和SOH和BMS里面的还是有较大差距，属于理论版和简化版，但是用于大数据分析也够用。

主要资料来源于USABC。

定义一（USABC，Battery Technology Life Verification Test Manual, February 2005）

State of Charge (SOC)-The available capacity in a battery expressed as a percentage of actual capacity. This is normally referenced to a constant current discharge at the C1/1 rate. For this manual, it may also be determined by a voltage obtained from a correlation of capacity to voltage fixed at beginning of life. SOC = (100 – DOD) if the rated capacity is equal to the actual capacity, %.

SOC=可用容量/实际容量。

实际容量=1C恒流放电容量。

定义二（USABC，United States Advanced Battery Consortium Battery Test Manual For Electric Vehicles, JUNE 2015）

State of Charge (SOC)-an estimate of the device charge capability expressed as a percentage of the BOL rated or operating capacity and typically reached by obtaining specified voltages.

SOC=充电能力/BOL额定容量或者运行容量。

充电能力即从放空至充满的充电容量；BOL额定容量即额定容量；运行容量即实际容量。

现实问题

以上SOC定义在EV大数据应用过程中均面临实际容量不可知的难题，因为根本 不具备条件进行1C恒流放电来测试实际容量。

此外，BMS给出的SOC就像薛定谔的猫一样，根本无法知道SOC是否准确。如果相信BMS给出的SOC准确，那么市场上那么多SOC不准确的案例不应该发生；如果相信BMS给出的SOC不准确，那么需要基于GBT 32960.3-2016定义的数据进行SOC计算。可用的字段有总电压、总电流、电池单体电压最高值、电池单体电压最低值、最高温度值、最低温度值，这些字段的采样周期为30S。基于公式（2）推导，由于实际充电过程极少从放空至充满的情况，因此取充电起始和充电截止的差值（△SOC），充电容量通过积分得到，关键问题转换为充电起始和充电截止SOC的识别。

SOC可通过OCV与容量在BOL时的关系获得。

通过OCV-SOC-T组成的MAPPING表即可求得SOC，那么OCV如何选取？

USABC中定义了两个稳定条件，即SOC稳定条件和电压稳定条件，至此，实际容量计算理论依据基本解决。

Stable SOC (state of charge) Condition – For a device at thermal equilibrium, its state of charge under clamped voltage conditions is considered to have reached a stable value when the current declines to less than 1% of its original or limiting value, averaged over at least 5 minutes. (For example, if a device is discharged at a C1/1 rate and then clamped at a final voltage, the SOC would be considered stable when the current declines to 0.01 C1/1 or less.)

稳定SOC为热平衡时电流小于0.01C且持续时间超过5min时的SOC。

Stable Voltage Condition – For a device at thermal equilibrium, its open circuit voltage (OCV) is considered stable if it is changing at a rate of less than 1% per hour when measured over at least 30 minutes. (Note that a stable voltage condition can also be reached by setting an arbitrary OCV rest interval (e.g., 1 hour), which is long enough to ensure that voltage equilibrium is reached at any SOC and temperature condition of interest. This is much simpler to implement with most battery testers than a rate-of-change criterion. However, it would result in a longer test and in longer rest intervals, which could be undesirable if a device had high self-discharge at the temperature where the test was conducted.)

稳定电压为热平衡时OCV在30min内变化率小于1%/h。

USABC中对SOH也进行了定义

State-of-health (SOH) – The present fraction of allowable performance deterioration remaining before EOL. (SOH = 100% at beginning of life and 0% at end of life.)

SOH=可用性能剩余的比例。

SOH这里进行简化，只看容量。

由于容量与温度有强依赖关系，因此需要对额定容量进行温度补偿，补偿后的SOH公式见公式（5）。LG-E63电芯的容量与温度依赖关系如表1所示，绘制散点图并进行拟合，结果如图1所示。将电池平均温度代入拟合公式即可得到温度补偿后的额定容量。

表1 LG-E63电芯的容量与温度依赖关系

图1 散点图及拟合曲线

实际情况，充电温度一般在0℃以上，特别是充电截止温度一般在10℃以上，因此额定容量的补偿量不大。图2中不同区域乘用车月平均电池启动温度情况也证实了电池的充电温度一般在0℃以上。

图2 不同区域乘用车月平均电池启动温度情况（中国新能源汽车大数据研究报告2018）

综上，SOC和SOH定义完毕，希望对对家有帮助。

来源：鲍教授说电池