This article introduces an advanced converter harmonic model that can be used to study harmonic resonance when the ultra-fast charging station (UFCS) is connected to the medium-voltage (MV) grid. A small demonstration network is created to verify the effectiveness of the converter harmonic model in the harmonic resonance interaction study compared with the traditional ideal current source model approach (all benchmarked to the detailed Electromagnetic Transient PSCAD ® model). A case study is performed on the Dutch Bronsbergen MV grid when a UFCS is connected. The harmonic resonance is calculated with both the ideal current source model and the converter harmonic model. When the converter harmonic model is used for the impedance sweep calculation, its output filter capacitance plus control circuit gain creates one extra parallel impedance resonance peak at 1250 Hz providing good insight for harmonic resonance risk investigation. To conclude, this article highlights the risk of harmonic resonance when a voltage source converter such as an UFCS is introduced in a MV grid. The advanced converter harmonic model, as applied in the Dutch MV grid, delivers the required level of insight for the distribution network operators when it comes to large-scale integration of UFCS in the future.