The Frequency Dynamic Stability Quantification and Coordinated Control Method After DC Commutation Failure

The inertia level of the power grid at the receiving end, which is strongly coupled with large-scale renewable energy and multi-infeed DC systems, is relatively weak, and the frequency regulation capability is not strong. A single short-circuit fault can easily trigger large-scale renewable energy to enter low-voltage ride-through, compounded by DC commutation failure. The transient power shocks generated during this period can cause the frequency to rapidly breach the low-frequency load shedding threshold, leading to high and low-frequency chain faults, thus threatening grid frequency stability. Traditional transient frequency risk assessment methods struggle to distinguish the risk levels between frequency response curves with long durations and small offsets and those with severe drops in a short time. To address this issue, this paper proposes an improved transient frequency risk assessment method that takes into account the rate of frequency change. By introducing a weight gain factor to emphasize the impact of frequency change rate in different frequency bands on system stability, the method effectively distinguishes the risk levels of short-term power disturbances and permanent power disturbances. Based on the improved transient frequency risk assessment index, a frequency coordination control strategy involving energy storage is proposed. Simulations on the IEEE 10 -machine 39 -bus system show that the participation of energy storage in frequency emergency control can effectively prevent the system frequency from triggering the low-frequency load shedding threshold after short-term power disturbances.