Online Monitoring of Supercapacitor SOH Using PWM High-frequency Switching Oscillations

The health status of supercapacitors is directly impacting their performance, making the online monitoring of their health status highly significant. In view of the issues existing in the current online monitoring technology for the state of health(SOH) of supercapacitors, such as low monitoring accuracy, ease of overfitting, and complex measurement process, a new method based on PWM high-frequency switching oscillation is proposed. The high-frequency oscillating current generated by the self-excitation of the PWM switching voltage during the operation of the converter is utilized. Fast Fourier transform(FFT) combined with the half-power bandwidth method is used to extract the natural frequency and damping ratio characteristics from the oscillation signal, enabling the estimation of the supercapacitor's high-frequency impedance online. Through pre-calibration of the relationship between high-frequency impedance and SOH, the accurate quantification of the supercapacitor SOH is achieved. A small supercapacitor energy storage experimental system is constructed to verify the feasibility and effectiveness of this proposed method. The experimental results indicate that this proposed method can effectively monitor the changes in the supercapacitor SOH, and it possesses the advantages of high safety, good sensitivity, and support for continuous monitoring.