Study On Rapid Measuring Instrument For Health State Of Lithium Battery

Electric vehicles gradually replace the traditional fuel vehicles is an important development direction of the future automobile industry.As the energy source of electric vehicles,the development and improvement of the health status measurement technology of lithium battery has become a research topic for many researchers.In this paper,a rapid battery health state measuring instrument suitable for practical applications is designed.The detector not only successfully measures the health state of lithium batteries,but also takes into account the speed,accuracy and economy of the measurement process.Firstly,this paper introduced the physical structure,working principle and internal resistance characteristics of Li Fe PO4 batteries,then introduced four equivalent circuit models which are commonly used to analyze internal resistance characteristics of batteries,and it is pointed out that the equivalent circuit models are not suitable for the study of battery impedance in practical applications.In this paper,the battery impedance is used to characterize the health status of the battery,and the relationship between the battery impedance and health state is deduced theoretically.Electrochemical impedance spectroscopy reflects the functional relationship between impedance and detection current frequency,and the impedance value corresponding to some frequency points on the electrochemical impedance spectroscopy can directly reflect the health status of the battery.In this paper,combining the electrochemical impedance spectroscopy with the traditional AC-DC measurement method,a hybrid current measurement method with large multiplicity is proposed to estimate the battery health state by measuring the impedance of two representative frequency points on the impedance spectrum.Secondly,from the perspective of machine learning,this paper proposes a battery health state measurement algorithm based on support vector regression.This algorithm takes the hysteresis curve obtained by battery HPPC test as the feature vector,and estimates the health state of the battery to be tested according to the different concavity of the hysteresis curve.Some parameters show that this algorithm model has less error,better performance and better performance than other similar algorithms.In order to verify the above theory,the hardware and software design of the instrument are introduced in detail.The hardware part is divided into the main control chip and its peripheral circuit,power circuit,battery charge and discharge circuit,battery current and voltage detection circuit,and the main functions of each circuit are introduced one by one.Then,three characteristic technologies of the detector used to regulate and process the current are introduced: micro-current superposition technology,nonlinear PI controller and dual-channel digital lock amplifier.In the software part,four core function modules including system initialization,the generation and processing of measuring current,data storage,data display and human-computer interaction are completed.The above hardware and software design is the core component of the detector.Finally,this paper built a test platform to verify the feasibility of the instrument.The results of hardware test and software test show that the instrument works normally and the function meets the expected requirements.