| Energy storage is an important technology choice for effective utilization of renewable energy.Liquid metal battery is a newly developed battery energy storage technology with the advantages of low-price and high efficiency.Low energy storage cost and long cycle life make the technology have a broad application prospect in current energy storage markets.In order to further promote the commercialization of liquid metal batteries,it is very important to analyze the energy storage characteristics of the batteries and establish the battery model to master the dynamic response characteristics.In addition,the balanced control measures for the series liquid metal battery pack should be taken to raise the capacity utilization rate and prolong the service life.Modeling for battery monomer and battery pack equilibrium control are important contents of building battery management system(BMS).The BMS plays a "escort" role for the safe and efficient use of the whole battery group.Focusing on the above requirements,the main contents of this paper are as follows:1.The basic output characteristics of liquid metal batteries,including open circuit voltage characteristics,ratio characteristics and cycle characteristics,are analyzed.Voltage characteristics show that the voltage platform of liquid metal batteries is low and wide.The cycle characteristics show that the battery has a high efficiency and a lower capacity attenuation rate.The cycle characteristics of liquid metal battery group are introduced in detail.The experimental results show that the capacity utilization ratio of the pack under the unbalanced control is obviously lower than that of the battery monomer.2.This paper improves the method of battery test step and parameter identification for modeling,and further constructs the two order Thevenin equivalent circuit model of liquid metal battery,and verifies the output of the model.The simulation results show that the model can better simulate the real dynamic output characteristics of the battery no matter the condition of the pulse test or the different ratio test.3.The inductor balanced circuit based on switch matrix is studied,and a balanced control strategy of "variable step" equilibrium current control mode is proposed,which takes state of charge(SOC)as the equilibrium variable.The equilibrium simulation analysis is made for the pack of three liquid metal batteries in series.The results show that the balanced control strategy has better comprehensive performance.4.A BMS prototype for 16 liquid metal batteries is preliminarily designed.The principle of hardware design and the overall design framework of the software are described in detail.The function verification for the battery group,which is made of the series of three liquid metal batteries in series,shows that the BMS has high accuracy of voltage and current detection and SOC estimation.And the passive equalization can achieve a certain voltage balancing effect. |
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