*3.6. Approaches to BMS Evaluation*

In References [15,16], systematic approaches were presented to validate BFG algorithms. Particularly, the following three BFG evaluation metrics were proposed and analyzed in References [15,16]:


consider this in voltage: A BFG can predict the time it takes to reach a certain voltage, given a constant load or constant charging current. Similar to how an EV can be driven to check the accuracy of the mileage prediction, the TTV metric is computed based on the predicted vs. actual time it took for the battery to reach a certain terminal voltage. One drawback of the TTV metric is that it requires a constant current to implement the metric. Most battery chargers employ constant current charging for a certain amount of time—this provides an opportunity to implement the TTV metric in real-time. It must be re-emphasized that the TTV metric is used to quantify the accuracy of the following BFG estimates at once: such as, SOC, battery capacity and ECM parameter estimates

In order to compute the *BFG evaluation metrics* (CC-metric, OCV-metric and TTV-metric), the battery needs to undergo a specific load profile that is named *BFG evaluation profile* in References [15,16]. Figure 11 shows a BFG evaluation profile that is designed to compute the above three metrics for a battery with a nominal capacity of 1.5 Ah. The evaluation profile requires to start the experiment with a fully charged battery and apply various discharge profiles and rest periods until the battery is given a final rest period of about 2 h before constant current profile of moderate to low magnitude is applied until the battery becomes empty; this procedure ensures the total capacity [17] of the battery can be accurately estimated—the estimated total capacity in return ensures the computation of a rigorous CC-metric. The constant current discharge at the end also allows to compute the TTV metric; this is particularly significant because remaining time prediction is crucial when the battery nears it end of charge.

**Figure 11. BFG evaluation profile.** The battery fuel gauge evaluation profile is a specially designed load current profile that allows to implement all three BFG evaluation metrics: *CC-metric*, *OCV-metric* and the *TTV-metric*. The profile starts with a full battery and ends when the battery becomes empty; this allows to compute the battery capacity accurately. Intermittent rest periods within the profile allows to compute the OCV metric and the constant current load profile allows to compute the TTV metric.
