Identification of the DQ Impedance Model for Three-Phase Power Converter Considering the Coupling Effect of the Grid Impedance

The impedance-based analysis has been widely applied for predicting the system stability based on the ratio of the impedance of the converter to the equivalent system impedance. However, the analytical impedance model is difficult to be obtained since system operators cannot access to the internal control details of the converters. Therefore, the impedance measurements can be utilized to obtain the black-box impedance model of converters. Due to the cross-coupling terms in converter impedance models in the dq-frame, perturbation injected on one channel would cause response on the other channel, which couples to the grid impedance. The interaction will influence the accuracy of the measured impedance of the converter. This paper investigates the mechanism of the coupling between the grid impedance and converter impedance during the impedance measurement. It is revealed that the coupling influence makes the measured impedance model behave as a multi-input-multi-output (MIMO) system instead of the decoupled single-input-single-output (SISO) systems. To mitigate the influence of grid impedance on the converter impedance measurement, a MIMO parametric identification method is proposed for the direct measurement of the converter impedance matrix with a single-measurement. Experimental results are presented to demonstrate the effectiveness of the proposed method.