Hello zg,
if it needs to be in simpowersystems, now called specialized power systems, you need to do a few steps. First, you need to fit the frequency response to a transfer function using the system ID toolbox. You then need to use that transfer function to build your own custom impedance block, similar to how this time varying inductor is implemented, only using the transfer function to calcute either your output voltage, or your output current, depending on wether you use voltage or current as your input signal.
Regards,
Joel
