A Comprehensive Review of Various Topologies and Control Techniques for DC-DC Converter-Based Lithium-Ion Battery Charge Equalization

Table 3

Comparison of the direct measurement method of SOC estimation.

Methods	Principle	Merits	Demerits
OCV [92]	SOC and OCV have a linear relationship. This will be accomplished by putting a pulse load on the battery and then allowing it to stabilise. Depending on the battery, this relationship will change.	(i) Simple method; (ii) Cost-effective; (iii) Easy implementation	(i) Long time required for equilibrium; (ii) Less accuracy
TV [93]	Internal impedance causes the terminal voltage of the battery to decline; the terminal voltage is proportional to the electrical motive force (EMF), which is proportional to the state of charge (SOC). As a result, the terminal voltage can be used to calculate SOC.	(i) Simple method; (ii) Suitable for all batteries	(i) The error will occur due to a sudden voltage drop at the discharge end
Impedance [94]	Internal resistance is measured using the battery voltage and current in this manner. The internal resistance value is calculated using the voltage and current ratio to estimate SOC.	(i) Very flexible; (ii) Easy implementation	(i) Less accuracy; (ii) Very difficult to observe when a slight change in internal resistance causes wide variation in SOC
IS [95]	To assess impedance, multiple frequencies are applied across the battery. SOC is calculated using this impedance.	(i) Suitable for online estimation; (ii) Low cost; (iii) Good accuracy	(i) The battery temperature and ageing will affect the assessment