Accurate Identification of Frequency-Coupling Admittance for Grid-Connected Converters Under all Operating Conditions

Accurate identification for the frequency-coupling admittance of the grid-connected converters is a key factor in impedance stability analysis. However, not all information about the grid-connected converters is available, which results in the "black/grey-box" phenomenon. It is challenging to identify the frequency-coupling admittance of black/grey-box devices under all operating conditions. An accurate identification method of the frequency-coupling admittance under all operating conditions is proposed in this article, which can be used for grey-box devices. The influence of the transmission power on frequency-coupling admittance is quantified, which can be used to analyze the amplitude and phase characteristics. A capacitor identification method based on voltage disturbance is proposed, which can be used to accurately solve the actual capacitor parameter. Therefore, the impact of capacitance parameter mismatch on frequency-coupling admittance can be eliminated. In addition, the frequency-coupling admittance under all operating conditions is modeled, which can quantify the impact of capacitor parameter mismatch. Finally, a hardware prototype of the grid-connected converter is built; the accurate identification method of frequency-coupling admittance for the grid-connected converter under all operating conditions is verified by simulation and experimental results.