Fuzzy controlled lithium-ion battery equalization with state-of-charge estimator

A fuzzy controlled method for the equalization of series connected lithium-ion batteries is presented. The state-space representation of bi-directional dc-to-dc equalizer that modified from Cuk-converter is derived for design the battery equalization controller. A PWM switching control and equalization with the intelligent state-of-charge (SOC) estimator is employed to balance the cell voltage of the battery strings. An intelligent SOC estimator is designed based on a fuzzy logic control (FLC) with a set of membership function, it can predict the complex cell equalizing dynamics with an accurate state determination of batteries. A designed procedure is presented for constructing the FLC SOC estimator for the battery equalizer of the battery strings. The validity of the controller design method is further verified by using computer simulation and experiment. The numerical results indicate that the battery equalizer with the FLC SOC estimator can improve the equalization performance under the safe operating region of lithium-ion batteries.