An Experimental and Mechanistic Hybrid Impedance Modeling Approach for Grid-Connected Converters Considering Modulation Deviation

Impedance analysis is usually used to study the stability of high proportion new energy systems, which needs to know the impedance of the grid-connected converter. However, traditional impedance modeling methods usually simplify the modulation part to unit gain, which affects the modeling accuracy. To address this issue, an experimental and mechanistic hybrid impedance modeling approach for grid-connected converters considering modulation deviation is proposed. Since the deviation value between the modulation part and unit gain changes with working conditions and its deviation expression is difficult to accurately derive, experimental modeling is adopted for the modulation part. The modulation coefficient matrix is first introduced to describe the input and output relationship of the modulation part. Furthermore, the influencing factors of modulation coefficient matrix are analyzed in detail. On this basis, experimental modeling scheme of modulation part is designed. For the remaining part, the mechanism modeling is adopted and derived by establishing the small-signal impedance model. Finally, simulation and experimental results under different working conditions indicate that the proposed hybrid modeling method has high accuracy and simultaneously retains the control mechanism, which is convenient for conducting oscillation analysis and suppression strategies.