Frequency Stability Enhancement of Integrated AC/VSC-MTDC Systems With Massive Infeed of Offshore Wind Generation

This paper investigates how the operation of the onshore AC grid and the offshore voltage source converter-based multiterminal dc (VSC-MTDC) grid can be cooptimized within the unit commitment (UC) framework to enhance system frequency stability following various contingencies. Frequency dynamic constraints corresponding to three typical types of outages (i.e., loss of a synchronous unit, loss of a grid-side VSC, and loss of a wind farm-side VSC) are established. A novel frequency dynamics constrained UC for integrated AC/VSC-MTDC systems is then proposed. Case studies on three integrated AC/VSC-MTDC systems demonstrate that major frequency disturbances caused by credible contingencies occurring in either the AC grid or VSC-MTDC grid can be effectively stabilized by the proposed approach.