ACTIVE CELL BALANCING WITH ZCS SWITCHED CAPACITOR AND MODULARIZED BUCK-BOOST + CUK CONVERTER FOR LITHIUM-ION BATTERIES

Abstract

This work presents the design and analysis of Zero-Current Switching Switched-Capacitor and Innovative Buck-Boost + Cuk Converter cell equalizing circuits for series-connected batteries. The study has two main objectives. The first objective is to develop a voltage equalizer for series batteries using a two-resonant state switched capacitor technique. Unlike traditional voltage equalizers, this approach does not require large magnetic components or a complicated monitoring and control mechanism. Switched-capacitor battery balancing circuits have potential among active balancing techniques due to their affordability, compact design, and simplicity. However, achieving full cell equalization with switched-capacitor equalizers is challenging and a higher voltage difference between cells reduces equalizing efficiency, while a smaller voltage difference slows down the balancing process. The proposed circuit improves on current switched-capacitor based cell balancing circuits as its balancing speed is independent of the number of battery cells and the starting misfit of distribution of cell voltages. All switches in the stated equalizing circuit operate under zero-current switching. It can also be integrated with a bidirectional buck-boost converter for charging and discharging along with equalization. The second objective is toperform active cell balancing using a dc-dc converter—the Buck-Boost + Cuk converter for the battery cells connected in series. Traditionally, the buck-boost converter or the Cuk converter would be used to balance 𝑛 battery cells in a battery pack that would require (2𝑛 − 1) switches. Nevertheless, by combining the buck-boost converter and the Cuk converter, the final buck-boost + Cuk converter requires only 𝑛 switches. Unlike many previous one-switch-per-cell configurations, this design decreases the switch count by approximately half without sacrificing the benefits of modularization or raising device voltage stress. A SEPIC converter-based charger is also integrated in parallel with this topology to perform cell balancing and charging simultaneously. Both circuits can be controlled using just two complementary square-wave signals with a 50% duty cycle, similar to existing switched-capacitor-based cell balancing systems or buck-boost and Cuk converter-based battery charge equalizers. Simulation results show that the first architecture performs well in terms of equalization, achieving zero current switching and zero voltage gap between cells, whilethe second architecture provides zero voltage gap with a faster equalization. The designed systemoutcomes are validated using MATLAB-Simulink.