Batteries play an important role in a micro-grid system and an electric vehicle. A proper charging method is necessary to prolong battery life and prevent battery from being damaged. Two-step charging is one of a charging method. It is combination of constant current charging and constant voltage charging. This method prevents the batteries being overcharged yet speed up charging time.
In this thesis, a two-step charging method is implemented to charge 12 units lead-acid batteries that connected in series. A half-bridge converter is used and the battery charged from DC power supply acting as DC bus with fixed voltage. Other than that, this thesis also built interface based on LabVIEW. The interface designed to monitor battery voltage, battery current, and battery state-of-charge (SOC) estimation. The SOC estimation in this thesis use Open Circuit Voltage (OCV) prediction method and coulometric counting method. Experiment results show that the system could implement two-step method without any problem and the SOC estimation shows accurate measurements with error no more than 6%.

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