Battery Management System and its Applications

9 SoC Estimation of a Battery

9.1 Different Understandings of the SoC Definition

The SoC estimation is an important function of the BMS and is the basis for the implementation of the control strategies. For example, many battery equilibrium control methods are based on SoC estimation results. If the same BMS development team has different understandings of the SoC definition, it is detrimental to the efficiency and robustness of the system.

9.1.1 Difference on the Understanding of SoC

It is found that the SoC is an interesting term: people acknowledge its importance and propose a variety of different ways to implement it, but there is little literature to strictly define the SoC, with the subtext “you should understand such a simple problem without explanation.” However, in fact, if the SoC is not strictly defined, the definition may vary with the people, and it is difficult to verify a certain SoC estimation method.

However, in any case, most people still have some basic consensus to the definition of SoC. The SoC is often defined often by the following equation:

(9.1)

where the numerator and the denominator refer to the electric charge quantity (rather than energy), in coulombs (C) or ampere-hours (A h or Ah), and

According to Equation (9.1), the SoC value is in the range ...