Battery Management System Reference Design

ID 683279
Date 4/02/2016
Document Table of Contents

1.3.2. BMS Reference Design Battery Model

The battery model can simulate a number of series-connected cells.

The only input is the battery current, which is the same for all the series-connected cells. For the output, at each time step, the model generates the arrays of the cell voltages V i, SOC, and the current values of the model parameters.

Figure 12. Battery cell equivalent circuit model

The left hand side models the cell capacity Q n and evaluates the SOC as the voltage across a linear capacitor with a capacity equal to Q n (expressed in Coulomb) divided by 1V. The cell voltage v M is the sum of the open-circuit voltage V OC and a dynamic term, which accounts for the internal Ohmic resistance R 0 and the double layer effect (V RC1 ) and diffusion (V RC2 ) of the Li-ion during charging and discharging (two RC branches). The model parameters change with manufacturing variations, ageing and operating conditions, such as temperature and state of charge. To model the temperature and SOC dependences, the reference design stores the parameter values in two-dimensional LUTs. You see the variability of the cell behaviour by setting the model parameters, temperature, and capacity of each cell individually