The existing switched-capacitor (SC)-based equalizers either have slow equalizing speed and low efficiency or have bulky volume and low reliability. Therefore, an optimized mesh-structured switched-capacitor (SC) equalizer (MSSCE) is introduced to achieve a trade-off between the equalization performances and size as well as cost. The proposed MSSCE achieves all the shortest balancing paths from one cell to any cell in a battery string, significantly improving the equalization speed and efficiency. The switching impedance of the proposed MSSCE is derived and analyzed, which provides a design guidance for the switching frequency and the capacitance. A four-cell prototype was set up. Experiment results confirm that the proposed MSSCE enhances the balancing speed with a high efficiency of 91.7%, moreover which is robust to the imbalanced cell voltages.

Due to the low switching loss, compact size, and low price, the LC series resonant converter (LCSRC) as an energy carrier is promising in battery equalizers. However, the conventional equalizers based on LCSRC only can realize the one-cell-to-one-cell balancing for a high-voltage series-connected battery pack, causing a low equalizing speed and efficiency. Therefore, two direct multicell-to-multicell (MC2MC) balancing topologies based on matrix LC converter and half-bridge LC converter are proposed, respectively, which achieve the direct energy transfer from a consecutive more-charged-cell group to a consecutive less-charged-cell group, significantly improving the equalizing speed and efficiency. An analytical model for the LCSRC is developed to provide a guidance for the optimal design of the proposed equalizers. The prototypes for the proposed two balancing topologies are constructed. The MC2MC balancing performances are verified though the comparative experimental results at different initial voltage distributions. In particular, the proposed equalizers simultaneously achieve the fast balancing speed and high equalization efficiency. The measured peak efficiency is about 87.9% at the four-cell-to-four-cell equalization.