Chapter 5: Energy Storage System Modeling and Control
Advanced ESSs are providing dramatic new opportunities in the automotive industry. The algorithms relative to ESSs play a central role in hybrid vehicle applications, for example, the SOC of a battery system is often a critical factor in hybrid vehicle performance, fuel economy, and emissions. From simple voltage, current, and temperature measurements that establish the values of operation variables to SOC estimation, power capability prediction, and state of life (SOL) of a battery system, battery algorithms have permeated every aspect of hybrid vehicle systems. An ESS algorithm functionality diagram is shown in Fig. 5.1, and a short description is given below.
- Initialization Initialization is done to set all necessary parameters and variables to ensure the algorithm starts properly. Battery cells may still undergo dynamics during the key-down period, including mainly Li-ion diffusion and “self-discharge”. During the initialization, the stored previous cycle data need to be reloaded, including previous SOC, previous SOL, estimated open-circuit voltage, and key-off time. The controller should also check the system status to see if the level of self-discharge is too high or other fault conditions are diagnosed.
- Battery Measurement Data Acquisition The ESS controller receives cell voltages, temperatures, and pack voltage and current in real time. In addition, measurements have to be synchronized and meet accuracy ...