Hybrid Ac/dc Transmission Expansion Planning Coordinated With Distribution Networks Under High Shares Of Renewable Energy

The integration of high shares of renewable energy is a significant feature of future power systems.New characteristics such as the diversity of operation modes,the reduction of inertia,the bidirectional power flow between transmission and distribution networks,and the hybrid AC/DC transmission will bring new challenges to transmission expansion planning(TEP).Based on the robust planning and stochastic planning theory,this paper aims to study and solve the security,stability and renewable energy consumption issues in TEP under high shares of renewable energy.The main work is as follows:(1)Given the diversity of operation modes caused by high shares of renewable energy,a security-constrained robust TEP method under massive scenarios is proposed.The quick convex hull method is used to handle the spatial-temporal distribution characteristics of renewable energy,and the adaptive robust optimization technique is used to dynamically find the worst-case scenario and the most serious fault in the convex combination of scenarios.A security-constrained robust TEP model is established to ensure the static security of the obtained planning scheme under massive scenarios.(2)Given the reduction of inertia caused by high shares of renewable energy,a transient stability-constrained robust TEP method is proposed.Based on the extended equal area criterion,the transient stability margin is calculated,and the linearized transient stability cut constraint is formed by using the quasi-linear relationship between transient stability margin and mechanical power.A transient stability-constrained robust TEP model is established to ensure the transient stability of the obtained planning scheme under the anticipated fault set.(3)Given that the high shares of renewable energy are connected to different voltage level grids,a stochastic TEP method coordinated with distribution networks is proposed.An extended DC power flow model considering voltage magnitudes is derived to support the coordinated optimization calculation of transmission and distribution networks.Based on the generalized master-slave splitting theory,a stochastic TEP model coordinated with distribution networks is established to promote renewable energy consumption.(4)Given that high shares of renewable energy are transmitted and consumed through different transmission modes,a risk-constrained hybrid AC/DC stochastic TEP method is proposed.The superquantile is used to measure the risk of renewable energy curtailment,and the decomposition coordination optimization technique is used to deal with the AC power flow constraints and the steady-state constraints of DC transmission systems.A risk-constrained hybrid AC/DC stochastic TEP model is established to reduce the risk of renewable energy curtailment of the obtained planning scheme.(5)Combining robust planning and stochastic planning methods,a hybrid AC/DC stochastic robust TEP method coordinated with distribution networks is proposed.Considering static security,transient stability,the coordination of transmission and distribution,and hybrid AC/DC,a hybrid AC/DC stochastic robust TEP model coordinated with distribution networks is established to promote renewable energy consumption when ensuring the security and stability of the obtained planning scheme.The effectiveness of the proposed planning methods is verified by the test system constructed from power grids with high shares of renewable energy.Each planning method can provide a theoretical basis for high shares of renewable energy TEP from different aspects.