Salient Features of Transmission-Distribution Coordination for Secure System Operation

A high level of renewable integration has emerged the requirement of flexibility-based services such as congestion, frequency, and voltage control for system operators at both transmission and distribution levels. Distributed energy resources can fulfil these requirements in the form of flexibility. However, procurement of their flexibility will result in the possible interaction between the transmission and distribution system operators (TSO & DSO). There is a strong need for system operators to identify the set of areas where they have to coordinate with each other in the RE-rich grid. Previous review articles are limited to the required market arrangements, also known as coordination schemes. Salient elements such as identifying the benchmark coordination schemes among all the possible market arrangements and flexibility integration at the TSO-DSO node are prerequisites for TSO-DSO coordination. This manuscript proposes potential research directions and recommendations for coordination between TSO and DSO. Salient elements to implement this coordination are also discussed. Furthermore, the current study presents a comprehensive review of coordination schemes to identify benchmark coordination schemes. This manuscript also summarizes different methods to obtain flexibility estimation at the TSO-DSO node. Overall, this article provides a rich and fruitful summary of ongoing research works for positive interaction between TSO and DSO.