Transmission Grid Expansion Planning of a High Proportion Renewable Energy Power System Based on Flexibility and Economy

The large-scale grid connection of renewable energy causes great uncertainty in power system planning and operation. The power system flexibility index can quantify the system's ability to adjust to uncertain events such as renewable energy, load fluctuations, and faults. Compared with traditional planning methods, the flexibility planning method can accurately evaluate the impact of various uncertain events on the system during the planning process, thus effectively ensuring the safe and economic operation of renewable energy systems. First, from the perspective of power transmission and safe operation, the flexibility index of the transmission line is defined. On this basis, considering the system's economic operation strategy, aiming at the optimization of flexibility, investment cost, operation cost, and renewable energy consumption, a multi-objective transmission grid planning model based on flexibility and economy is proposed. The NSGAII optimization algorithm is used to solve the model. Finally, the simulation is performed in the modified Garver-6 and IEEE RTS-24 node systems to analyze the effectiveness of the proposed model. The results show that the planning model can meet the needs of flexibility and economy, improve the transmission capacity of power grids, reduce the probability of renewable energy abandonment or exceeding power flow, as well as enhance the flexibility, economy, and reliability of power systems.