Kalman Filter-Based State and Parameter Estimation of an Electric Scooter Battery Pack

摘要

Battery packs in modern vehicles are built from the network of lithium-ion (Li-Ion) battery cells, and present one of the most important parts of hybrid (HEV), plug-in hybrid (PHEV), or fully electric (EV) vehicle powertrains. For larger battery packs, such as those found in the beforementioned vehicles, battery management system (BMS) is required to ensure optimal battery operation in terms of battery lifetime and vehicle electric range. Modern BMSs, contain numerous algorithms for estimation of the key battery model state variables (e.g. State-of-Charge (SoC)), and model parameters (e.g. battery pack internal resistance). SoC estimate can be used for the vehicle available range evaluation, as well as for identification of battery operating point, which is important from the battery safety and lifetime standpoint. Furthermore, the internal resistance can be used for tracking the battery degradation level (i.e. State of Health (SoH)).This poster first outlines the experimental setup, an electric scooter with 4 kWh, 72 V Li-Ion battery pack, consisting of Li-NMC cells. Battery measurement and telemetry system that collects vehicle and battery data used in this research is also described. Then, a simple first-order state-space equivalent-circuit model (ECM) of the battery is described, along with the results of the off-line identification of model parameters (e.g. open-circuit voltage (OCV) characteristic). Two Extended Kalman Filters (EKF) are then designed based on this model. The first EKF estimates battery pack SoC by combining the Coulomb counting method (CC) with the voltage-based estimation based on the OCV(SoC) characteristic. The second EKF is used for estimation of total battery DC resistance as a random-walk state variable. In this case, estimated SoC is taken as an input to the filter, and is estimated using the CC method. At the end of the poster, estimation results are presented and discussed with respect to the available results documented in literature for similar battery pack and specified battery chemistry.