Modularized buck-boost + Cuk converter for high voltage series connected battery cells

This paper proposes a new bidirectional dc-dc converter - buck-boost + Cuk converter - for series connected battery cells. Traditionally, in order to balance n battery cells in a string, (2n-1) switches are required by either the buck-boost converter or the Cuk converter. However, by nicely combine the buck-boost converter and the Cuk converter together, the proposed buck-boost + Cuk converter only requires n switches. It achieves almost half of the switch count reduction, without losing the advantage of modularization or sacrificing the device voltage stress, unlike many other existing one-switch-per-cell topologies. Meanwhile, it still maintains the buck-boost battery charge equalizer´s best characteristic - simple pulse width modulation (PWM) - 50% duty cycle. Moreover, it offers a solution to bypass the open-circuit faulty cells, and prolong the life time of the whole battery string. Simulation and experimental results are given to demonstrate the functionality of the proposed buck-boost + Cuk converter.