Research On Measurement Technology Of Power Battery Internal Resistance

Power lithium-ion battery has been widely used in the field of new energy vehicles.This article points out that the battery core internal resistance is one of the most important factors to influence and judge the energy storage process,and the real time change of the battery core internal resistance can accurately reflect the running state and health state of the battery.Now the standard to measure the battery internal core resistance has been recognized gradually by people.Because the measurement of the internal resistance range of the lithium-ion battery is a weak signal detection at the level of the milliohmeter,for the detection of such high precision weak signal,whether in the detection technology,the measurement method or in the circuit design must retain the effective signal,and in the signal amplification and filtering circuit,the disturbance of the power frequency signal and the disturbance signal of the peripheral circuit are removed to ensure that detection accuracy is in expected range.Analysis starting from the lithium-ion battery internal core resistance formation mechanism,according to the battery core internal resistance is mainly composed of ohmic resistance and polarization resistance,the equivalent model of second order battery internal resistance is established,at that time,the improved four terminal AC injection method was used to detect the internal resistance of the battery.The chemiacal impedance spectroscopy of the battery is made,and the suitable frequency range of the internal resistance of the battery is selected by the chemical impedance spectroscopy.When the frequency range is 100~10kHz,the dynamic change of the internal resistance of the battery tends to be stable,which is convenient for measuring and testing.The battery internal resistance detection system is respectively introduced and designed that AC excitation constant current source,difference enlargement electric circuit,analog multiplication circuit,filter circuit,A/D conversion module,and the main control circuit unit.Through the sine signal generator as a separate module,contrast effect of signal amplification,and comparison of signal input and output before and after filtering to verify the effectiveness of design.In the software design part,the program flow chart and communication interface module are designed.According to the program flow chart,the software is programmed.Simulation model based on Matlab is constructed,First of all,the detection of each part of the circuit module debugging,comparison,to test the performance of the system is in line with the standard.Secondly,the internal resistance of the battery by repeated sampling detection,and take the average value and variance to evaluate the volatility and stability of internal resistance of the battery,From the Simulation model based on Matlab,it testify that the design of the battery internal resistance detection error is controlled in the range of ±1.1%,indicating the effectiveness of the proposed scheme and the feasibility of the battery internal resistance detection.