Research On Active Equalization Strategy Of Lithium-ion Battery Pack Applied To AGV Car

In recent years,Automated Guided Vehicles(AGVs)have been rapidly developed and widely used in the field of industrial handling.The battery system is an AGV power source.Due to the special operating conditions of the AGV vehicle,the inconsistency problem caused by the inconsistency of the battery pack during use is very prominent.If high efficiency and balanced management measures are not adopted,the battery pack life will be seriously affected.This paper proposes a bidirectional DC / DC type equalization circuit topology based on a switch matrix,and designs an active equalization control strategy with three-threshold control,which can adapt to the special working conditions of AGV,quickly complete the equalization,and the equalization loss is small.The thesis conducts the following aspects:1)The causes of inconsistencies in lithium-ion batteries are analyzed,as well as the effects of special operating conditions of AGV high-current charging,short charging time,and high frequency on inconsistencies.By studying the inconsistent characteristic parameter descriptions of lithium-ion batteries,SOC was determined as the evaluation parameter for active equalization.In order to improve the equalization effect,EKF algorithm was used to estimate SOC to improve the estimation accuracy;2)In order to improve the equalization efficiency,based on factors such as hardware cost,energy efficiency,equalization speed,control complexity,size and weight,combined with the actual situation of AGV,a bidirectional DC / DC type equalization circuit based on a switch matrix is proposed.The equalization circuit Can reduce the energy loss in the AGV equalization process.3)Propose a three-threshold control active equalization strategy suitable for a single equalizer equalization circuit.According to the SOC offset,the battery is divided into an action area,a pre-action area,and a non-action area.The end threshold is added to reduce the repetition of the equalizer.The number of actions,and at the same time,by increasing the pre-action threshold,the battery in the pre-action zone will be equalized in advance when the equalizer is not operating,reducing the occurrence of unbalanced situations.For the special working conditions of large AGV charging current and short charging time,during the charging process The fuzzy control of the equalization current is designed to further increase the equalization speed.4)Charge and discharge experiments were performed to simulate typical AGV operating conditions.The experimental results show that the active equalization strategy in this paper is suitable for AGV operating conditions.Compared with the traditional equalization strategy,the speed is increased by about 14%,and the equilibrium energy loss is reduced by about 10%.The equilibrium topology of this paper has small equilibrium loss.The proposed three-threshold equalization strategy can adapt to AGV working conditions,and the equalization speed is fast,which has certain practical significance.