| In practical applications,lithium-ion batteries typically form a battery pack to meet the system’s need for output voltage,output power,and available capacity.But at the same time,with the gradual degradation of the performance of the battery pack,its output voltage and available capacity may not meet the energy requirements of the power system,and even can’t maintain the normal operation of the power system.Therefore,comprehensive and accurate evaluation of the degraded state of the lithium-ion battery pack provides a reference for the maintenance and use strategy of the battery pack,and is of great significance for maintaining the safe and reliable operation of the battery pack and the power system.At present,the battery pack has few measurable parameters,and it is difficult to directly characterize the performance degradation of the battery pack only by relying on its end node voltage and dry circuit current.Aiming at this problem,this paper looks for the requirements of direct measurement parameters and its test technical indicators from the characteristic parameters that can characterize degradation,and develops a lithium ion battery performance degradation test system.In this way,the external measurement parameters such as voltage and current are collected and the battery degradation evaluation is performed.Firstly,review current battery degradation assessment methods and analyze relevant parameters and test methods that can be used to characterize lithium ion battery degradation.Based on the definition of the battery degradation characterization parameters and the measurement principle,the test and data acquisition requirements are derived.The technical indicators and functional requirements corresponding to the degradation characterization parameters are analyzed,and the indicators are verified by simulation experiments.On this basis,the overall scheme design of the lithium ion battery performance degradation test system is completed.Secondly,complete the system hardware and controller firmware design according to the overall scheme of the battery performance degradation test system.The system hardware design includes a current excitation unit and a parameter acquisition unit.It provides current excitation for battery test and collects measurable parameters for the battery pack and its internal components.It also provides parameter support for degradation characterization parameter analysis and battery pack degradation assessment.The controller firmware design includes the control logic of each functional module and the design of the step operation control program.Thereby implementing the configuration and control of each hardware function module of the battery test system function.Thirdly,design the lithium ion battery performance degradation test system software according to the functional requirements of the test system.Design the static structure of the software according to the requirements,and design the control program of the software for the five functional use cases.These five functional use cases include: battery pack basic test,parameter analysis,status evaluation,data management,and status display.At the same time provide users with an interactive interface.The user can set up test operations and visually view the operating status of the battery pack.Finally,the lithium ion battery performance degradation test system developed by the company was debugged and functional verification was performed.Build a debugging environment to perform functional tests on the hardware modules and correct the accuracy.On this basis,the joint debugging of the test system software and hardware is carried out.Then verify the test system functionality and analyze the test results.The test results show that the test system can realize battery pack charge/discharge test(step setting and parameter acquisition),characteristic parameters(capacity,internal resistance and other parameters)monitoring and battery pack degradation status evaluation.Capable of meeting the functional requirements of battery pack performance degradation testing,as well as technical indicators for degradation characterization parameter testing and acquisition. |
