Generalized Passivity-Based Control for Obtaining Passive Impedance of Grid-forming VSC Above 2f1

This paper presents a generalized passivity-based control approach for grid-forming voltage-source converter (GFM-VSC), termed as "passivation control", to achieve passive impedance characteristic above the second harmonic frequency. The passivation control uses phase current and voltage feedforward to cancel the effect of the controllers and the associated control delay on the impedance of the GFM-VSC. As a result, the impedance of the GFM-VSC converges to that of its filter (i.e., L, LC, or LCL) and remains passive above the second harmonic frequency, thereby effectively avoiding high-frequency oscillations. Note that the effectiveness of the proposed passivation control is independent of the control delay, control structure, and filter type. In addition, this passivation control maintains the passive characteristics of the GFM-VSC impedance even beyond the Nyquist frequency (i.e., half of the sampling frequency), thereby complementing existing methods in the literature. Case studies are presented to verify the proposed designs.