Decibels Lab

The battery state of charge (SOC) is an important parameter of the battery capacity state. Accurate estimation of SOC is one of the key problems in a battery management system. As Li-ion cell behaves dynamically, characteristics depend on the function of temperature, discharge charge cycles, charge & discharge pattern, ageing, utilised SOC and more. The coulomb counting technique with correction (after rest periods) using an OCV-SOC correlation curve is not practical for cells exhibiting hysteresis since the battery cell takes a long time to reach a steady-state OCV after a current pulse. Current SOC- estimation models are unable to take care of all of these complications. 

A more robust algorithm is needed to estimate the instantaneous total charge available. The EKF technique, an adaptive estimator, has emerged as one of the practical solutions to enhance the accuracy of SOC determination, but is complicated and needs heavy computing resources on-board the vehicle. Available embedded technology is capable to process complex computations. This is the direction ahead to industry, EKF based estimations are predominantly used for real-time applications. 

This course will help you understand & build the MBD based approach for SOC based on the EKF approach. By the end, of course, you will have the solid exposure to estimation approaches, limitations, calculations, cell behaviour, cell characteristics, end to end functional model for SOC estimations, comparison of simulation data and real-time test data.

Course content

• Introduction
• BMS Functionalities
• SOC Estimation Strategies

Coulomb Counting Methodology

Current Integration Methodology

Voltage Lookup Based Estimation Methodology

Kalman Filter Based Estimation

Example Calculations

Basic Introduction to UKF, EKF

Understanding the EKF flow process

Predict and Update Steps

State Equations

Discretization of the State Equations

State Space Representation of the Equations

Discretization of the State Space Equations

SOC Estimation for Constant Current Discharge/ Charge

SOC Estimation for Dynamic Profiles

7. Model-Based SOC Estimation

Predict Step Modelling

Update Step Modelling

Thevenin Circuit Modelling

8. Post Processing 

9. Results and Discussion

SOC Estimations Plots

Voltage Variation w.r.t Discharge Capacity

Voltage Variation across R0 and RC Circuit

Estimation Errors

10. Model prediction validation w.r.t tested data

11.  Future Scope of Study