A Hierarchical Active Balancing Architecture for Lithium-Ion Batteries

Abstract

This paper proposes a hierarchical active balancing architecture for the series-connected lithium-ion batteries. The key point of the architecture is that by grouping the battery string into different packs and introducing the top layer, the coupled influence among the cells in different packs is eliminated, which reduces the required balancing time and the energy loss. The repeated charging and discharging problem is avoided, which is beneficial for increasing the State-of-Health (SOH). Moreover, the proposed architecture can lower the current rating of the balancing circuits, which helps decrease the required cost and improve the system efficiency. On the basis of the architecture, a balancing control using the State-of-Charge (SOC) of each cell is proposed to achieve the balance for all the cells. Furthermore, to deliver the energy from one pack to any other pack bi-directionally, a multi-directional multi-port converter along with the current control method is proposed to serve as the top layer. This converter is different from the conventional three-port converter as it can achieve the arbitrary current flow direction control for any number of ports. The experimental results based on 24 series-connected 200 Ah lithium-ion batteries verified the benefits of the proposed architecture and the balancing circuits. After balancing, 4.1% of the total energy of the battery string is saved. Compared to the conventional Adjacent Cell-to-Cell (A-C2C) architecture, the proposed architecture can decrease the balancing time and the energy loss during the balancing process by 27.6% and 44.0%respectively. In addition, the current rating and the cost of the balancing circuits in the proposed architecture is only 37.5% and 11.5% of that in other references.

A Modular Cell Balancer Based on Multi-Winding Transformer and Switched-Capacitor Circuits for a Series-Connected Battery String in Electric Vehicles

“…Therefore, the novel MCBC needs to be considered carefully to reduce the mentioned disadvantages as shown in Section 2.2. Figure 7 illustrates an SCBS structure based on a conventional and modular balancing circuit [2,[31][32][33]. The conventional cell balancer used the series-connected battery cell string, which consists of N × M cells.…”

A Modularized Discharge-Type Balancing Topology for Series-Connected Super Capacitor String

“…The output voltage of the cascaded converter voltage U e can be assumed to be invariant when the PWM frequency is high; however, U e changes with the inductor current i L when the PWM frequency is low. So, the average voltage U e is used to replace U e to calculate the frequency in Equation (18). Assume that the average voltage U e = u omax / √ 2, u omax is the maximum output voltage of the cascaded converter.…”

“…The higher voltage SCs are discharged indirectly with a small current. Many charge-type balancing topologies are researched, such as the topology based on the voltage multiplier [16,17], based on the fly-back circuit [18,19], based on the forward circuit [20,21], and so on. These topologies are not aimed at the discharging of the higher voltage SCs, but the charging of the lower voltage SCs and the discharging speed of the higher voltage SCs is slow.…”

A Novel Lithium Battery Equalization Circuit with Any Number of Inductors

“…In order to equalize the cells, a large number of battery equalization circuits have been proposed [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. These circuits can be divided into two types: dissipative circuits and non-dissipative circuits [4].…”

“…But the volume, control complexity and cost are higher than the first type. Figure 3 shows the third type, the number of energy storage components of this type is greater than or equal to the number of batteries [1,[11][12][13][14][15][16][17]. This type of circuit has a large number of cells and buck-boost circuits working at the same time, and the equalization current is large, which means this type of circuit has the fastest equalization speed of the three types.…”