I. Introduction
In recent years, the proportion of renewable energy on power grid has increased further around China [1]. The significant uncertainty of renewable energy has led to the power grid facing depth peak load and power supply ensuring pressure successively, which needs to be calmed down by flexibility resources. Especially, after the large-scale thermal power units have been transformed for heating and flexibility, their upward peaking capacity is limited by their downward regulating capacity, resulting in the grid facing extremely severe power supply challenges [2]. The proportion of renewable energy will further increase in the future, when it will face even more serious problems of peak operation. The power grid needs to fully employ the flexibility resources with upward regulating capacity [3].