# Multi-Mode Lithium-Ion Battery Balancing Circuit Based on Forward Converter with Resonant Reset
## 6 Discussion  
This section systematically evaluates the balancing circuits in terms of their size, cost, balancing speed, and switch driving. Assuming a battery pack is composed of n cells, the component requirements for different balancing circuits are shown in Table 5.  
To provide a more detailed comparison of different balancing circuits, a battery pack of eight cells is selected for analysis in Table 5. The component prices were referenced from [30], where the approximate unit prices for each component are as follows: M (MOSFET, USD 0.2), D (Diode, USD 0.15), L (Inductor, USD 0.6), C (Capacitor, USD 0.2), RE (Relay, USD 0.2), T (Transformer, USD 1), DR (Switch Driver IC, USD 0.8). According to the comparisons in Tables 5 and 6, the SC circuit in [24] needs 2n MOSFETs to switch, and it requires n-1 capacitors and inductors for ZCS, resulting in a larger circuit size Although each switch is configured with a driver IC, the control of each switch group is achieved through a pair of complementary PWM signals, simplifying the overall driving scheme. However, the inclusion of numerous driver ICs, MOSFETs, inductors, and capacitors significantly increases the cost of the balancing circuit. Furthermore, the AC2C balancing approach employed by this circuit leads to long balancing time and slower speed, which remains its major drawback. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Balancing Circuit** & **Type** & **Size** & **Cost (USD)** & **Speed** & **Drive** \\ \hline SC circuit [24] & AC2C & Large & 21.6 & Very High & Poor & Good \\ LCSR circuit [26] & DC2C & Small & 17 & High & Normal & Poor \\ Flyback circuit [30] & C2P & Small & 9.3 & Very Low & Normal & Good \\ Forward circuit [35] & AC2 AC & Medium & 18.8 & High & Normal & Good \\ BRLC circuit [37] & MC2 MC & Small & 23 & Very High & Good & Poor \\ Proposed circuit & MC2 MC & Large & 13.9 & Low & Excellent & Excellent \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Comparisons for 8 cells battery pack. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Balancing Circuit** & **Balancing Time/s** & **Balancing Voltage/V** \\ \hline Balancing Circuit in ref. [35] & 7250 & 3.533–3.58 \\ Proposed Balancing Circuit & 1260 & 3.151–3.193 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of balancing results. The LCSR circuit utilized in [26] results in a significant reduction in the size of the balancing circuit and enables ZCS, thus reducing switching loss. However, the use of bipolar switches in the switch matrix of the circuit still requires many MOSFETs to be implemented, which increases the complexity of the driver design. Although only one inductor and capacitor are needed, the adoption of bipolar switches still requires a large number of driver ICs, resulting in relatively high cost. In addition, this circuit achieves DC2C balancing, which is faster than AC2C, but the overall balancing speed is generally moderate. In [30], C2P balancing is achieved by multi-winding flyback converters. Although a certain number of MOSFETs and ICs are needed to be switches and drivers, no additional inductor and capacitor are required in this circuit. As a result, the circuit structure is simple, and the design of the drive scheme is easy. Therefore, the circuit has low cost and a small size. However, this balancing circuit requires a longer balancing time and the balancing speed is moderate. In [35], the modularized forward converter with resonant reset introduces size and cost issues for the circuit. It achieves AC2 AC balancing, but the energy transfer is more dispersed, resulting in a longer balancing time for the circuit. In terms of switch driving, the adoption of phase-locked loop control simplifies the design of the driving scheme. Like [26], the HBLC circuit in ref. [37] only uses one inductor and capacitor. It has a smaller size and reduces switch losses by achieving ZCS.