Abstract
When large-capacity HVDC (high voltage direct current) transmission line blocking occurs in a hybrid AC/DC (alternating current/direct current) power grid, the receiving-end system will encounter a huge power imbalance, which will lead to a frequency drop and redistribution of the power flow, and which may further lead to the overload of other transmission lines, cascading failures and a large-scale blackout. To resolve these problems, an emergency load-shedding strategy for the DC receiving-end system is proposed from the perspective of a quasi-steady state. The proposed method can accurately calculate the actual total power imbalance by modeling more detailed stochastic loads with static frequency/voltage characteristics and involving the inertia effect of the generator during the response delay period, which can effectively reduce the amount of load curtailment. In addition, several factors affecting the power imbalance estimation in stochastic scenarios and their mechanisms are analyzed in detail, and the key aspects relevant to the DC blocking fault analysis are identified as well. Finally, the influence of different load-shedding strategies on the receiving-end system security after a DC blocking fault is compared with the security indices, including those that are relevant to the frequency/load change proposed herein, and a uniform load-shedding coefficient is obtained via the proposed method, even for different power imbalances under a stochastic context, which makes the load-shedding strategy more practical.
Highlights
In recent years, the total electricity consumption has been increasing with the development of the economy, but the distributions of energy sources do not coordinate well with the power demands in some countries, such as China
The receiving-end power grid with a large capacity DC infeed needs to be equipped with an appropriate emergency load-shedding countermeasure, in particular for such DC blocking faults
It can be seen that most of the above literature focuses on how to optimize the distribution of power shortage in the steady-state control process after a DC blocking fault, but the accurate determination of the actual total power shortage is an important premise for evaluating whether the load-shedding strategy is reasonable
Summary
The total electricity consumption has been increasing with the development of the economy, but the distributions of energy sources do not coordinate well with the power demands in some countries, such as China. It can be seen that most of the above literature focuses on how to optimize the distribution of power shortage in the steady-state control process after a DC blocking fault, but the accurate determination of the actual total power shortage is an important premise for evaluating whether the load-shedding strategy is reasonable. In order to address the above issues, an emergency load-shedding strategy of the DC blocking fault is proposed in this paper, which considers the fluctuations of renewable energy and the stochastic load with the static frequency and voltage characteristics, to accurately calculate the actual power shortage after the serious fault. (1) The stochastic load model is established for the first time considering the static frequency and voltage characteristics This proposed load model can be solved via a probabilistic power flow calculation and can be used for the DC blocking fault analysis in the receiving-end system. Establishment and Solution of Stochastic, Static Characteristics-Dependent Load Model
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