What is parameter extraction?

Battery characterization provides experimental measurements of the battery's electrical behaviour, but these measurements cannot be used directly in the Thevenin Battery Model. Instead, the measured data must be analysed to determine the electrical parameters that describe the battery. This process is known as parameter extraction.

The objective of parameter extraction is to identify the values of the parameters that enable the Thevenin Battery Model to accurately reproduce the measured voltage response of the battery.

For the second-order Thevenin model, the parameters to be identified are:

• Open Circuit Voltage (OCV)
• Ohmic resistance ($R_0$)
• First polarization resistance ($R_1$)
• First polarization capacitance ($C_1$)
• Second polarization resistance ($R_2$)
• Second polarization capacitance ($C_2$)

These parameters are obtained by analysing the measurements collected during the Open Circuit Voltage (OCV) and Hybrid Pulse Power Characterization (HPPC) tests.

The OCV characterization data are used to determine the relationship between Open Circuit Voltage and State of Charge, while the HPPC data are analysed to identify the resistive and capacitive parameters that describe the battery's dynamic response.

The following sections explain how each parameter of the Thevenin Battery Model is identified from the experimental measurements.