Toward Flexible Risk-Limiting Operation of Multi-Terminal HVDC Grids With Vast Wind Generation

Contingencies occurring in multi-terminal high voltage direct current (MT-HVDC) grids can result in DC voltage/flow violations and also affect the frequency stability of the connected multiple asynchronous grids. To recognize and control such notable operating risks, a novel flexible risk-limiting optimal power flow (FROPF) for the MT-HVDC grid with vast wind generation is proposed in this paper. Within the two-stage FROPF structure, the pre-contingency operation of grid-side voltage-source converters (GVSCs) is optimized to minimize MT-HVDC grid power losses. Immediately following an outage occurring in the MT-HVDC grid, various fast-acting corrective actions of GVSCs are utilized to hedge against the overall risk exposure, including the wind power curtailment risk of the MT-HVDC grid and the rate-of-change-of-frequency (RoCoF) violation risk imposed on associated asynchronous grids. Reformulation techniques are introduced to ease the computational complexity of the optimization model. Case studies of two MT-HVDC grids demonstrate the effectiveness of the proposed FROPF.