Research On Measurement Method Of Capacitance And Equivalent Series Resistance Of Supercapacitor

The supercapacitor(SC)is a new type of capacitor based on the theory of the electrical double layer.It has the advantages of both traditional capacitor and battery.The capacitance is three to four orders larger than that of an ordinary capacitor.Compared with batteries,there's no chemical reaction occurs in the energy storage process,and the charge and discharge can be repeated one hundred thousand times.It also has the advantages of high speed of charging and discharging,no pollution to the environment and long cycle life.SC is a breakthrough components which can be used to improve and solve the power performance of electric energy.With the development of manufacturing technology,its application in electric power,automobile,energy,railway,communication and other fields will be developed rapidly.Because of the low single open circuit voltage(common capacitor: 2.7V),it needs used in series.In order to improve the energy storage,it needs more than one capacitor used in parallel.The parameters of each capacitor monomer are not same in series and parallel,so the voltage of SC is easy to be unbalanced in the process of charging and discharging with large current.This can cause excessive charging and discharging of some SC,which affect the lifetime of SC and the reliability of the whole circuit.Therefore,the research on measurement of the capacitance and equlvalent series resistance(ESR)of SC is significance.In this paper,the DC charging and discharging method is used to measure the capacitance of SC.AC method is used to measure the ESR of SC.The main contents are as follows:1.Capacitance measurement of SC based on charge method and discharge method with constant current:When using the constant current charging method,this paper studies the effect of charging current and initial voltage on the measurement result.When using constant current discharge method,this paper studies the effect of charging current,discharging current and initial voltage on the measurement result.2.Capacitance measurement of SC based on discharge method with constant resistor:Charge and discharge method with constant current is widely used in capacitance measurement of SC,which has higher requirements for the stability of charge and discharge current during measuring.Discharge method with constant resistance can eliminate the influence of current stability and accelerate measurement speed.Based on the frequency-domain analysis of the measurement circuit,the calculation formula of capacitance is inferred.This method is simulated by using Multisim software to verify correctness.This paper also studies the influence of resistance value on the measurement result.3.Study on calculation method of capacitance:Different from IEC62391-1-2015,QCT741-2014 and other standards in which the capacitance is measured as a constant value,this project researches the method of curve fitting,integration of electric quantity,discharge with constant resistance to calculate the dynamic capacitance.4.Research on AC Measurement Method of ESR:ESR of supercapacitor was measured by alternating current which is at 1kHz frequency and 1mA~10mA amplitude.The non-periodic DFT algorithm is adopted to eliminate the influence of noise and improve the accuracy of internal resistance measurement.5.Analogue AC resistance method of calibrating the battery resistance tester:The voltage on the standard AC resistor is divided by using a multidigit two-stage inductive voltage divider,a low value AC resistance standard device is developed to solve the problem that the battery resistance tester can't be calibrated at low range.Through the research,this project developed a device for measuring the capacitance and ESR of SC.The voltage sampling,current sampling,the range of capacitance measurement and the accuracy of ESR measurement were verified.The uncertainty of measurement is evaluated.The result shows that the measuring device developed in this paper can meet the testing requirements.