Electrochemical State-Based Sinusoidal Ripple Current Charging Control

This paper presents a sinusoidal ripple current charging algorithm based on embedded impedance measurements. Existing battery charging strategies typically do not take into account the electrochemical properties of batteries, because these factors are difficult to obtain during charging operation. Factors of concern include lithium plating, growth of a solid electrolyte interphase, limited exchange current, and slow diffusion rates. It is beneficial to utilize these parameters during charging operation, because the charging current can adapt to the time-varying characteristics of a battery. Consequently, battery life cycle, charging speed, and charging efficiency all improve. In this paper, rigorous analysis of electrochemical characteristics is performed and a method for minimization of variations of charge transfer impedance is explained based on a sinusoidal ripple current charging algorithm. To obtain the optimal ripple current frequency, ac impedance analysis based on the dq transformation method is proposed. As a result, this method improved charging efficiency and reduced lithium plating by activation polarization. Simulation and experimental results using a 14.6-V LiFeMgPO₄ battery are used to validate and demonstrate the performance of the proposed control scheme. Based on the proposed control scheme, the charging time and efficiency of the Li-ion battery are improved by 5.1% and 5.6%, respectively.