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The system equivalent inertia of the power grid is gradually decreased with the increasing penetration of renewable energy resources, which leads to a higher risk of frequency fluctuation after a major fault. For the frequency emergency control in the scenario of a high-voltage direct current (HVDC) line block fault, a novel criterion for enabling the fast response of user-end distributed loads is proposed in this study based on voltage feature identification and frequency drop detection. The reactive power to voltage sensitivity coefficient is combined with the Hausdorff algorithm to increase the accuracy of the calculation. The proposed criterion can realise the HVDC block fault identification at the end of the distribution grid, so as to achieve fast decentralised decision-making for distributed loads. This method may greatly reduce the need for high-speed communication and take actions faster than the primary and secondary frequency controls of the traditional units. The criterion makes it possible for low voltage small load in the user-end to be controlled precisely and selectively to fill the large power imbalanced caused by an HVDC block fault. The validity and superiority of the criterion are verified by simulation experiments using multiple test systems. [ABSTRACT FROM AUTHOR]

The Central China Power Grid (CCPG) and North China Power Grid (NCPG) are connected together by a single AC ultra‐high‐voltage (UHV) transmission link. When suffering power disturbances, power oscillation with high magnitude and long period would happen on the UHV tie‐line, which may affect the synchronous and stable operation of the interconnected two power grids. This study proposes a novel emergency control scheme for high‐voltage direct current (HVDC) in CCPG to suppress the high peak value of the power oscillation. Based on a two‐machine equivalent model, the maximum rising slope of power oscillat'ion is used to predict the peak value of power oscillation and power disturbance which is used as the reference of emergency power modulation. Simulation verification is carried out based on the full model of the CCPG and NCPG, using Power System Analysis Software Package. Moreover, field test has also been carried out in CCPG. Both simulation results and recorded wave curve show that the proposed HVDC emergency control scheme can effectively suppress the peak value under different power disturbances. This significantly improves the transient performance of the interconnected power system and the power transfer capacity of the UHV tie‐line. [ABSTRACT FROM AUTHOR]