The coordinated operation of coal-fired power units and large-scale energy storage systems can give full play to the flexible resources of energy storage systems and the adjustment capabilities of coal power units

enhancing the flexibility of the power system and promoting the low-carbon transformation of power system. In this paper

a compressed air energy storage system coupled with coal-fired power unit is proposed. In the air compression stage

the condensed water is used to absorb the heat of air compression

and in the air expansion stage

the feed water/extraction steam is used to realize cascade heating of the air at the expander inlet. The different coupling schemes of compression and energy storage processes are compared

and the optimal scheme of the coupling system with given parameters is proposed. Moreover

the operation efficiency of this system and the conventional compressed air energy storage system with heat storage device is compared. The results show that

the system efficiency can be increased by 5 percentage points through reasonable coupling of compressed air energy storage system and coal power unit.