Detection of inflection point in secondary-battery charging process by

Abstract

A secondary battery charging method that utilizes a standard, characteristic reference curve for that type of battery for identifying the voltage inflection point during a constant-current charging process. The voltage response of a battery being charged is sampled periodically and compared to the reference curve to establish the degree of completion of battery charge by tracking the reference curve. The charging stage of the battery is determined as the fast-charge operation progresses by identifying a place on the reference curve corresponding to the observed response. When a satisfactory match is found, the time remaining to reach a fast-charge termination point is predicted by assuming that the voltage response will track the reference curve to the inflection point. Accordingly, the voltage response is no longer monitored and the time remaining to reach the inflection point is used to complete the fast-charge operation. For the purpose of developing the reference curve, the functionality of the derivative of the standard voltage-versus-time response for the system is simulated by assuming an exponential relation during the early stages of fast-charge and a sinc function relation as the battery approaches the voltage inflection point indicating optimal termination of the fast-charge process.