Frequency-dependent impedance of transformer in mesh network for converter-driven stability analysis

With the large-scale penetration of power electronic converters into the grid, new stability problems such as converter-driven stability are a concern to both utilities and manufacturers. One of the suitable approaches for stability analysis of power electronic converters connected to AC gird is impedance-based stability, which models the whole system as two subsystems that can be represented with frequency-dependent equivalent impedances. Hence, the representation of the power system by frequency-dependent equivalent impedance is required to carry out an impedance-based stability analysis. As there are various components in a power system, accordingly, this paper focuses on representing the frequency-dependent impedance of transformers in the network for assessment of converter-driven stability. For this purpose, the transformer model is implemented in the frequency domain using a two-port ABCD parameter and it is validated in the time domain by comparing the frequency response obtained from the PSCAD. Further, the transformer model is integrated into the frequency domain meshed test network and the nodal network impedance is validated. It is understood that the frequency-dependent impedance seen from the primary and secondary side of transformer is different and therefore it should be considered independently while calculating the nodal network impedances.