With the increasing scale of power systems and the large-scale application of new energy technologies, the planning and construction of future power grids and the stable operation of systems face severe challenges. Among them, transient stability and short-circuit current are two key factors that determine the safe and stable operation of a power system. However, in traditional power-grid planning, there is little research on the strategy of coordinating the solution between transient stability, short-circuit current problems and planning forecasts. Based on the perspective of power-grid planning, this study proposes a method for the optimal planning of a power system's comprehensive stability margin that uses the external penalty function method. The coupling relationship between the transient stability margin and short-circuit current margin is developed through the system impedance in power-grid planning, and the line impedance optimization planning problem based on the comprehensive stability margin is formulated as a multiobjective optimization model. Finally, the optimal system impedance and the optimal comprehensive stability margin are determined by the external penalty function method. The simulation results of an IEEE 10-generator 39-bus system verify the effectiveness of the proposed method, and the system with the optimal planned impedance determined by this method yields the best comprehensive stability margin. Further simulation verification is conducted in a real power grid in China, and the strategy proposed in this article exhibits good economy and scalability. It provides a theoretical basis for the planning and construction of the future power grid, which is conducive to the safe and stable operation of the future power grid.INDEX TERMS comprehensive stability margin, power-grid planning, external penalty function method, optimal system impedance value.
With the construction and development of ultra-high voltage (UHV) power grids, large-scale, long-distance power transmission has become common. A failure of the connecting line between the sending-end power grid and the receiving-end power grid will cause a large-scale power shortage and a frequency drop in the receiving-end power grid, which can result in the frequency collapse. Presently, under-frequency load shedding (UFLS) is adopted for solving the frequency control problem in emergency under-frequency conditions, which can easily cause large load losses. In this context, a frequency coordination optimal control strategy is proposed, which combines the mode transition of pumped storage units with UFLS to deal with emergency under-frequency problems. First, a mathematical model of the frequency dynamic response is established, which combines the mode transition of pumped storage units with UFLS based on a single-machine equivalent model. Then, an optimal model of the minimal area of the power system’s operation frequency trajectory is introduced, yielding the optimal frequency trajectory, and is used for obtaining the action frequency of the joint control strategy. A simulated annealing algorithm based on the perturbation analysis is proposed for solving the optimal model, and the optimal action frequency is obtained that satisfies the transient frequency offset safety constraint of the power system. Thus, the joint optimal control of the mode transition of the pumped storage units and UFLS is realized. Finally, the EPRI-36 bus system and China’s actual power grid are considered, for demonstrating the efficiency of the proposed strategy.
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