A two‐step tie‐line scheduling method considering variable renewable energy variations

Abstract

A promising way to promote variable renewable energy (VRE) integration is to enable more power transmission through tie-lines between distant areas. Practically, because of the dispatching independence of regions, tie-line flows need to be carefully scheduled. The daily energy transmitted follows the daily mean load with a limited variation. Moreover, within a day, the tie-line flow's variation range, its ramping rate, and the number of changes in flows should be limited. Thus, current tie-line scheduling fixes transmission power to relatively constant levels, failing to fit VRE variations and further restricting VRE accommodations. This paper proposes a two-step tie-line scheduling method to promote VRE accommodations by considering VRE variations and above practical constraints, while also considering the cost of the system for providing flexibility. Regarding VRE's daily variability, the annual energy transmission plan between regions is decomposed into daily plans based on both VRE generation and load. For VRE's intraday variability, a dispatch model determining tie-line flows is built with constraints on tie-line flow's variation range, ramping rate, and change numbers. In addition, the regulation costs involving generator deep peak shaving cost and generator ramping cost are modeled with binary variables and included. Numerical studies for Chinese provincial systems show that the regulation costs account for 9% of the total cost and the VRE consumption increases by 8.6% while the cost reduces by 9.5%.