Research On Direct Equalization System For Series Power Batteries

Nowadays,the world gradually pays more attention to the concept of green environmental protection and strongly supports clean energy.The power lithium battery has high energy density and other superior performance,and is gradually applied to the new energy industry.Because of the low voltage level of lithium-ion,it is usually connected in series when applied in high-power applications.However,due to the manufacturing process,it is difficult to ensure that the parameters of the lithium-ion battery are exactly the same during charging and discharging,which will cause overcharging and overdischarging of individual cell,reducing the usable capacity of the battery pack and threatening the service life of battery pack.In order to solve the above problems,the equalization technology is used to balance the battery pack,so that the working state of each battery tends to be basically the same.To achive the object,a balanced topology with good reliability,high efficiency,and fast speed,and a balanced control strategy with simple control are required.In this paper,a multi-cell direct balanced topology is constructed.Through analysis and simulation verification of the working mode of the balanced topology,it is shown that it can achieve single-to-single equalization and single-to-multiple equalization between any monomers.And taking the non-adjacent monomers working in the flyback mode as an example,the equivalent circuit is modeled,a series of formulas are derived,and the factors affecting the equalization power and efficiency are analyzed.The relationship between battery voltage,loop resistance,switching frequency,inductance value,duty cycle,equalization power and equalization efficiency is studied.The related hardware in the multi-cell direct equalization circuit is designed.The analog front-end BQ79630 is used to collect the information of the battery pack;the drive circuit is optimized;the proper inductance value is determined by analyzing the influence of the inductance value on the equalization efficiency and power of the equalization circuit.And the DSP program is written so that it can generate the drive signal of the corresponding switch according to the equalization strategy.The reasons and consequences of the imbalance of series battery packs are analyzed,and the advantages and disadvantages of the commonly used equalization variables are summarized.The balancing strategy of the multi-cell equalization circuit is designed,using the working voltage as the equalization control quantity,determining the equalization strategy of hysteresis control combined with over equalization,and classifying the imbalance conditions to determine that the equalization circuit is used under different imbalance conditions of the duty cycle.And through the experimental platform of multi-cell equalization circuit,the equalization experiment of adjacent monomers and non-adjacent monomers were carried out.