Research On Design And Realization Of On-Line Measuring Device For AC Impedance Spectrum Of Lithium-Ion Battery

In recent years,fires or explosions have occurred frequently in the field of electrochemical energy storage represented by lithium ion batteries,the current battery management system cannot timely warn the occurrence of safety accidents due to insufficient awareness of the internal information of the battery.The research shows that the AC impedance spectrum of the battery is closely related to the internal information of the battery,such as the battery’s internal temperature,state of charge and state of health.The electrochemical workstation is a professional instrument for obtaining AC impedance spectrum in the laboratory,but it is expensive,has measurement site limitations and cannot be measured online,which hinders the application research of battery AC impedance spectroscopy.The purpose of this thesis is to develop a laboratory-oriented,low-cost on-line measurement system for AC impedance spectrum of lithium-ion battery.The main research contents are as follows:(1)According to the actual research needs of the AC impedance spectrum of lithium-ion batteries,the technical indicators of the AC impedance spectrum on-line measuring instrument are determined,and the overall measurement scheme is given.The demand analysis of the on-line measurement of the lithium-ion battery AC impedance spectrum of the measurement object is carried out,and the technical indicators such as the frequency range and measurement accuracy are determined,and different impedance measurement methods are compared through the research status of the battery impedance measurement,finally,the overall measurement scheme including power module,multi-channel selection module,voltage and current channel without phase offset and so on is designed.(2)The key technologies and difficulties of the on-line measurement of the AC impedance spectrum of lithium-ion batteries are analyzed,and the current source excitation generating device and the strong DC and weak AC separation scheme are designed.The current source excitation has the characteristics of large internal resistance,constant current and strong anti-interference ability,it is not affected by the running state of the battery,a set of wide-band and low harmonic current source generator is designed with FPGA and DAC as the core;the strong DC and weak AC separation module is designed with a differential amplifier as the core,an inverting superposition circuit is designed to remove the DC voltage of the battery itself and the residual DC bias caused by load interference and circuit components,the voltage of the battery itself is obtained by the differential amplifier,the DC offset is obtained by the designed tracking compensation algorithm.The circuit test shows that the DC removal effect is good.(3)Completed the overall hardware and software design of the system,complete circuit board fabrication and human-computer interaction face design.Completed the choice and design of main controller FPGA,the design of power supply module,multi-channel selection module,program-controlled amplifier module,communication module,data processing and computation module,human-computer interaction interface and PCB layout and wiring,and completed the overall circuit board soldering and software programming in the laboratory.(4)The circuit modules are tested,and the overall measurement accuracy verification is completed.The testing and analysis of each module of the battery was completed;taking 13Ah lithium iron phosphate battery as the object and the laboratory electrochemical workstation as the control equipment,the measurement accuracy verification is completed;the equivalent circuit model of 13 Ah lithium iron phosphate battery is established,the impedance fitting software ZSimpWin is used to fit the parameters and compare the results of the AC impedance spectra measured by the self-developed equipment and the electrochemical workstation;the comparison of offline and online measurement results is performed at 10MΩ precision resistance;in addition,the needling experiment of lithium iron phosphate battery is designed to further verify the effectiveness of the on-line measurement data of the measuring instrument.The experimental results show that the on-line measurement system of AC impedance spectrum of lithium-ion battery designed in this thesis can meet the measurement requirements.