A Bidirectional LLC-Based Integrated Equalizer for Large-Scale Energy Storage Systems: A Parallel Transformer Approach for Efficient and Compact

The existing transformer-based equalization systems have the advantages of simple circuitry and ease of control. However, their application in large-scale energy storage systems is often hampered by scalability issues, as the number of magnetic components typically scales linearly with the cell count. A bidirectional LLC-based integrated equalizer employing a parallel modular transformer architecture to overcome this scalability challenge in large-scale energy storage systems is proposed. By leveraging the symmetrical voltage and current waveforms inherent to the LLC converter, the proposed equalizer enables a single secondary winding to balance two adjacent cells, thereby halving the required number of transformers. Furthermore, the proposed circuit can achieve balancing during charging, discharging, and idle states in the energy storage system. The proposed design was validated on an eight-cell supercapacitor prototype, demonstrating rapid voltage convergence under all operating conditions. The system achieved peak efficiencies of 95.5% (charging) and 95.7% (discharging) within a 10 W to 30 W power range.