Fuzzy-controlled individual-cell equaliser using discontinuous inductor current-mode Cuk convertor for lithium-ion chemistries

An intelligent battery equalisation-scheme based on fuzzy-logic control (FLC) is presented to adaptively control the equalising process for series-connected lithium-ion batteries. The proposed individual-cell equalisation scheme (ICE) is a bidirectional DC-DC convertor based on the Cuk convertor operated in the discontinuous inductor current mode (DICM). The proposed method can be used to achieve a zero-current-switching (ZCS) cell-balancing control scheme to reduce the switching losses in MOSFET switches. Further, a fuzzy-logic-controlled strategy is constructed with a set of membership functions to prescribe the cell equalising behaviour within a safe equalising region for reduced cell-equalisation time. The simulation and experimental results show the advantage of the predicted equalising performance for lithium-ion battery stacks. The proposed fuzzy-logic-control battery-equalisation controller (FLC-BEC) abridges the equalisation time by about 30% compared with the equaliser without FLC. The power losses of the MOSFET switch are significantly reduced by about 33.8%, and the equalisation efficiency is increased by about 8.5% compared with the same equalisation scheme in continuous-inductor-current mode (CICM). The proposed equalisation method maintains safe operations during the charge/discharge state to increase the charge capacity of lithium-ion battery-pack cells.