A Modularized Bidirectional Charge Equalizer for Series-Connected Cell Strings

In this article, a modularized charge equalizer is proposed. In the proposed topology, N series cells are divided into K modules and each module consists of J series cells and its multiplexer switches. A multioutput transformer is used as temporary energy storage. Each of the transformer outputs is connected to one of the K modules and targets the cells in its module. In this way, at the same time K cells are targeted simultaneously and the speed of balancing has increased. In the proposed circuit, energy can be transferred by string to cell, cell to string, and cell to cell methods. In addition, it can be transferred between modules and equalize them. Therefore, the proposed topology is very flexible and can circumvent the limitations of each method and use the appropriate method in the right place. Also, a step-by-step method for command the multiplex switches is proposed. To illustrate the correctness of the circuit operation, a prototype is implemented to balance the charge of four lithium-ion battery cells. The experimental results confirm the correctness of the proposed circuit operation.