| Series equivalent resistance is one of the important parameters of supercapacitor and an important indicator for evaluating the performance of supercapacitors.The supercapacitor internal resistance detection provides a basis for ensuring the reliability,safety and prolonging the service life of the super capacitor during use.To this end,this paper,under the support of the research project of the measurement method of supercapacitor internal resistance of the research project of Hunan Institute of Metrology and Measurement,carried out research on the detection method of supercapacitor internal resistance,and designed two methods of supercapacitor internal resistance detection by AC injection method.The scheme is based on the supercapacitor internal resistance detection method based on the lock-in amplification circuit,the supercapacitor internal resistance detection method based on FFT and Goertzel algorithm,and the comparison results are given.This paper first introduces the method of detecting the internal resistance of super capacitor based on AC injection method.The AC signal is injected into the super capacitor,and the internal resistance of the super capacitor is calculated by measuring the output voltage,current,and phase difference of the super capacitor.On this basis,(1)Design a supercapacitor internal resistance measurement circuit based on phase-locked amplification,including AC signal source circuit(ie,AC constant current source with frequency of 1 kHz and effective value of 0.1 V),signal conditioning circuit The locking amplifier circuit,the low-pass filter circuit,etc.,and the comparison test of two different super capacitors verify the accuracy of the circuit and give the test data.(2)A method for detecting the internal resistance of supercapacitor based on FFT and Goertzel algorithm is proposed.The phase difference of the output signal of the supercapacitor output voltage hysteresis(ie,the AC constant current signal)is obtained,and the internal resistance of the supercapacitor is calculated.The software design of this algorithm and experimental verification prove the accuracy of the two algorithms.Experimental results show that the supercapacitor internal resistance detection system designed in this paper can effectively detect the internal resistance of supercapacitors.Among them,the internal resistance of the super capacitor based on the lock-in amplifier circuit is adopted.The repeatability error of the detection result is less than 3%,the repeatability error of the detection result based on the FFT algorithm is less than 3%,and the repeatability error of the detection result using the Goertzel algorithm is less than 5%,which meets the requirements of the supercapacitor internal resistance detection. |
