Flyback converter based charge balancing control with cell-load and cell-cell operation modes in battery system

This paper presents a flyback converter based charge balancing control algorithm in a dual-output battery system. The system configures multiple battery cells in series to produce main bus output. In the meanwhile, multiple isolated low-power converters are connected to each battery cell at the inputs, and the outputs of converters are connected in parallel to generate a secondary output. Three operation modes within SOC balancing algorithm are introduced in this paper, including cell-load, cell-cell and current-reset mode. Cell-load/cell modes are the primary balancing operation modes, designed for scenarios with and without secondary loads, and current-reset mode is the intermediate process of transitioning between these two modes. In cell-load mode, the SOC value of each battery can be balanced by adjusting the discharge current rate at the battery side, and the secondary bus voltage is under regulation. In cell-cell mode, where the secondary bus power path is not available, charges are transferred from the cells with higher SOC values to the cells with lower SOC values through the converters. During SOC balancing process, the normal operation of main bus shall not be impacted. The presented controller is proven by experiment on a scaled-down proof-of-concept prototype.