Transmission grid and distribution grid flexible planning under high level renewable energy

The grow prominence of renewable energy has highlighted the need for coordinated planning between transmission and distribution with flexibility. With rapidly increasing levels of renewable energy penetration, flexibility plays an ever more critical role in power system due to the uncertainty and variability of renewable energy generation. Also, there is an urgent need to integrate flexibility in coordinated planning models to effectively manage high levels of renewable energy. In this paper, a novel tri-level method for coordinated planning of flexible transmission grid and distribution grid (TSG-DSG) is proposed considering normal operational conditions and severe fault conditions; moreover, a novel network structure regulation as well as coal-fired power units and energy storage systems are employed as flexible tools for flexibility enhancement of transmission and distribution system under static security and transient stability framework. The model employs a parallel tri-level Benders decomposition & heterogeneous decomposition algorithm to improve computational efficiency. Upper level of the tri-level model minimizes the investment and operational costs under normal operational conditions, while the middle and lower levels minimize expectation of operational costs under faults in the transmission and distribution grids. The proposed method is applied to a real case study HRPTD-20 system. Results demonstrate that the coordinated planning method is both cost effective and computationally efficient. With the proposed methodology, the cost is reduced by 3.3 billion CNY and the renewable energy consumption rate is improved by 6 %.