# Multi-Mode Lithium-Ion Battery Balancing Circuit Based on Forward Converter with Resonant Reset
###### Abstract  
A multi-mode active balancing circuit based on a forward converter with resonant reset is proposed to deal with unbalanced states of lithium-ion battery packs. The balancing circuit utilizes the forward converter, enabling high-power balancing. SPST relays are selected to constitute the switching matrix, and the proposed balancing circuit completes the connection of serial battery clusters to the main circuit by controlling the SPST relays, realizing the Multi-Cell-to-Multi-Cell (MC2 MC) balancing method. An \"adaptive selection mode based on the state of high energy battery\" balancing strategy is proposed. The proposed balancing strategy allows the proposed balancing circuit to have multiple balancing modes, flexible balancing paths, and switching between different balancing processes in real time, significantly improving the balancing speed. The inherent LC resonant reset structure of the forward converter is employed to achieve MOSFET zero-voltage switching (ZVS). To optimize the balancing performance, the circuit model is built and the balancing parameters in the circuit are analyzed. An experiment with an eight-cell lithium-ion battery pack was performed to verify the balancing effect of the proposed circuit, and comparison with a typical balancing circuit was carried out. Experimental results show that the proposed balancing circuit has a faster balancing speed. lithium-ion battery; active balancing circuit; Multicell-to-Multicell (MC2 MC); forward converter; zero-voltage switching (ZVS) +
Footnote †: journal: Applied  
cell to dissipate excess energy in the cell. The advantages of this balancing method include simple circuit structure, low circuit cost, and lack of requirement of complex control strategies, but the thermal management problem caused by energy consumption is the main drawback of this method [14; 15]. Active balancing uses active circuits to transfer energy from a high-energy cell to a low-energy cell. It is important to mention that active balancing and its circuits are now widely applied in PV to address the adverse effects of partial shading conditions (PSCs) on series-connected PV modules/submodules, removing the obstacles to maximum power extraction [16; 17; 18; 19]. According to the path of energy transfer during balancing, active balancing can be further divided into the following categories: Adjacent Cell-to-Cell (AC2C), Direct Cell-to-Cell (DC2C), Cell-to-Pack (C2P), Pack-to-Cell (P2C), Any Cell-to Any Cell (AC2 AC), and Multicell-to-Multicell (MC2 MC) [20]. The characteristic of Adjacent Cell-to-Cell (AC2C) is the transfer of energy by setting balancing main circuits between adjacent cells [21; 22; 23; 24]. The advantage of this approach is that the whole balancing circuit can be controlled using an easy approach, and the balancing process has high reliability. However, when the cells involved in balancing are located far apart, the balancing energy needs to be sequentially transferred through multiple balancing main circuits, resulting in slow balancing speed and energy loss during the balancing process, thereby reducing the balancing efficiency. To address the drawbacks of AC2C, Direct Cell-to-Cell (DC2C) is studied in [25; 26; 27]. Compared to AC2C, DC2C typically requires only a single universal circuit for balancing, simplifying the structural design of the balancing circuit and reducing cost. In addition, since the balancing energy can be directly transferred between any two cells, DC2C addresses the problem present in AC2C where the energy transfer efficiency is low when the cells being equalized are located far apart, thus improving balancing efficiency. However, the disadvantage of DC2C is also obvious: only two cells can be balanced at a time, which means that when a larger number of cells are involved in the balancing process, the other cells have to wait, resulting in longer balancing time. Cell-to-Pack (C2P), as shown in [28; 29; 30], involves transferring energy from a cell to the whole battery pack.