As the penetration rate of renewable energy sources (RES) gradually increases

demand-side resources (DSR) should be fully utilized to provide flexibility and rapidly respond to real-time power supply-demand imbalance. However

scheduling a large number of DSR clusters will inevitably bring unbearable transmission delay

and computation delay

which in turn lead to lower response speeds. This paper examines flexibility scheduling of DSR clusters within a smart distribution network (SDN) in view of both kinds of delay. Building upon a SDN model

maximum schedulable flexibility of DSR clusters is first quantified. Then

a flexibility response curve is analyzed to reflect the effect of delay on flexibility scheduling. Aiming at reducing flexibility shortage brought by delay

we propose a modified flexibility scheduling strategy based on cloud-edge collaboration. Compared with traditional strategy

centralized optimization is replaced by distributed optimization to consider both economic efficiency and effect of delay. Besides

an offloading strategy is also formulated to decide optimal edge nodes and corresponding wired paths for edge computations. In a case study

we evaluate scheduled flexibility

operational cost

average delay and the chosen edge nodes for edge computations with traditional strategy and our proposed strategy. Evaluation results show the proposed strategy can significantly reduce the effect of delay on flexibility scheduling

and guarantee the optimality of operational cost to some extent.