Modular Equalization System Using Dual Phase-Shift-Controlled Capacitively Isolated Dual Active Bridge Converters to Equalize Cells and Modules in Series-Connected Lithium-Ion Batteries

Abstract

Conventional lithium-ion battery (LIB) packs comprising series-connected modules need cell and module equalizers separately, resulting in increased system complexity. This article proposes a modular equalization system using dual phase-shift (DPS)-controlled capacitively isolated dual active bridge (CIDAB) converters. Each module contains an intramodule CIDAB converter that performs direct cell-to-cell equalization. Meanwhile, switching legs of adjacent modules' CIDAB converters are connected through an LC tank to configure an intermodule CIDAB converter that equalizes module voltages. The switching legs of CIDAB converters are utilized for both the intra- and intermodule equalizers, achieving the simplified system. Based on the proposed DPS control, the PS angles of both the intra- and intermodule CIDAB converters are manipulated to perform cell and module equalization. The prototype of the proposed modular equalization system for two LIB modules, each consisting of 12 cells was built and tested. Cells and module voltages in the proposed system were sufficiently equalized, demonstrating the efficacy of the proposed equalization system.