Solution to Coordination of Transmission and Distribution for Renewable Energy Integration into Power Grids: An Integrated Flexibility Market

Nowadays, transmission system operators (TSOs) encounter the challenges of securely operating power grids with high penetration of renewables. In this context, more flexibility is needed than ever to maintain system reliability. With rapid development of coordinated transmission and distribution technology recently, active distribution networks (ADNs) which have abundant flexible resources, have the potential to provide flexibility to the TSO. Hence, an integrated transmission-distribution flexibility market is proposed in this paper. In the proposed framework, the energy market is first cleared to obtain baseline generation schedules. Then the baseline generation schedules are treated as inputs to the flexibility market. Furthermore, the integrated flexibility market is cleared to facilitate flexibility trading between transmission and distribution networks. To preserve the data privacy of different market participants, an alternating direction method of multipliers (ADMM) based method is utilized to clear the markets in a distributed manner. In the energy market and flexibility market-clearing model, transmission network market clearing models are linear programming (LP) models, and distribution network market clearing models are second order cone programming (SOCP) models. Through the proposed method, only limited information is exchanged between TSO and DSOs. Case studies are conducted on a revised IEEE 30-bus transmission network with two 33-node ADNs. Numerical results demonstrate the proposed flexibility market framework can enhance competitiveness of generation companies in the transmission network and distributed generators (DGs) in the ADNs. Moreover, flexibility purchasing cost is reduced by 17.7% compared to traditional flexibility supplied by generators according to the case study results, and ADNs can gain additional flexibility profit by providing flexibility.