Design of active equalizer for lithium-ion battery pack based on double-tiered modular resonance

The energy balance between individual lithium-ion batteries in electric vehicles is an important factor that affects the efficiency and long-time operation of the entire system. In the conventional modular switched capacitor method, small pressure difference between the batteries at the end of the equalization and the need for multi-stage transmission may cause the low efficiency of the equalization, slow speed and so on. To solve the issues, the control method of three-resonant-state LC converters is adopted in this paper. The resonance process not only improves the transferable energy of the capacitor, but also realizes the zero-current switching of the circuit, reducing the circuit switching loss and electromagnetic interference. A double-tiered modular resonance equalization structure is also proposed to provide more energy transfer paths and larger equilibrium current. By means of this, the inconsistency between the cells can be eliminated more quickly and efficiently when energy needs to be transferred in multiple stages. Comparative experiment is conducted by constructing a simulation platform and an experimental platform to demonstrate the superiority of the double-tiered resonance equalization.