In order to address the inconsistency problem of series-connected lithium-ion battery groups in practice, a two-level balanced topology based on bidirectional Sepic-Zeta circuit is designed in this article. Two-level equalization topology uses bidirectional Sepic-Zeta circuits both within and between groups, which can achieve the equilibrium between any cells in a battery group and between any battery groups. With the state of charge (SOC) of the battery as th. In order to address the inconsistency problem of series-connected lithium-ion battery groups in practice, a two-level balanced topology based on bidirectional Sepic-Zeta circuit is designed in this article. Two-level equalization topology uses bidirectional Sepic-Zeta circuits both within and between groups, which can achieve the equilibrium between any cells in a battery group and between any battery groups. With the state of charge (SOC) of the battery as the equalization variable, and the equalization control strategy is designed based on the consistency controller and PI controller to achieve fast and efficient equalization by dynamic adjustment of equalization current, and to efficiently decrease the inconsistency of the equalized battery packs. The experiments are conducted by Matlab/Simulink platform. According to the experimental results it can be obtained that compared with the topology based on single Cuk equalizer, the topology based on single Sepic-Zeta equalizer and the adjacent topology based on Sepic-Zeta equalizer, the proposed topology shortens the equilibrium time by about 51.57 %, 51.43 % and 42.24 %, respectively. Under the same operating conditions, the equalization control strategy designed in this article shortens the equilibrium time by about 29.4 % and 11.19 % compared to the conventional fixed-threshold method and the Fuzzy Logic Control (FLC) algorithm, respectively, and also achieves better results in the equalization efficiency and consistency problem, which effectively verifies the feasibility of t. ••A two-level equalization topology based on bidirectional Sepic-Zeta circuit is proposed to reduce the equalization time.••A consistency control equalization strategy is designed for dynamically adjusting the equalization current.••To better quantify the equalization effect, the battery difference and energy utilization rate are defined for evaluation.Consistency control strategyBidirectional Sepic-Zeta circuitTwo-level equalizationSOCLithium-ion batteries are commonly applied to electric vehicles and energy storage technologies owing to their high energy density, low self-discharge rate, no memory effect, long cycle life, and low environmental pollution [1,2]. In actual production and application, for the purpose of meeting the requirements of large voltage and high power, lithium-ion batteries are often required to be used in packs [3,4]. Due to the differences in production techniques and usage environments, different individual batteries can have differences in parameters such as capacity and internal resistance. These differences will increase with the increase of battery usage time, which not only reduces the performance of the battery pack, but also has an explosion and other safety risks [,,, ]. With the purpose of maintaining that the battery system can be safely and efficiently operated and used, the research and improvement of the battery equalization technology is crucial [,,,, ].Depending on different energy transfer methods, battery equilibrium is categorized into two forms, passive and active [14,15]. Passive equalization uses energy-consuming components to consume excess energy in the battery pack in the form of heat. The cost of passive equalization is low, and the circuit is simple and reliable, but there are problems of energy waste, heat dissipation and low equalization efficiency [16,17]. Compared to passive equalization, acti. Buck-boost circuit and Cuk circuit are commonly used in existing studies for design modifications. The Buck-Boost circuit combines the features of Buck and Boost circuits and has both boost and buck functions, but the outstanding drawback of this circuit is its relatively low efficiency. When the Buck-Boost circuit is used as the balanced circuit, the operating current is often set to intermittent mode. The intermittent current has a high current peak, which can be used to promote the equalization speed. But the operating current in intermittent mode is unstable and not easy to control, which increases the burden on the equalization circuit, and the excessive operating current is not good for the battery life. Compared with the current intermittent mode, the time used in the current continuous mode is shorter when transferring the same amount of energy with the same operating current peak, and the current continuous mode can transfer more energy when transferring the same amount of energy with the same current peak in the same time. Therefore, the equalization current operating in continuous mode is characterized by stability, high energy transfer efficiency and fast equalization. The Cuk equalization circuit has continuous input and output currents, but its input and output polarities are reversed, a feature that requires attention when doing the design. The Sepic circuit is widely used in the design of DC-DC converters because of its good voltage conversion capability, excellent power distribution capability a.
