Recent years have observed the fast and continuous development of distributed energy resources (DERs) (e.g., rooftop PV and electric vehicles) in one distribution sub-system. For example, 167 GW of rooftop PV were installed globally during 2019–2021, whose resultant peak outputs can be higher than the joint peak consumption of France and Britain [1]. Observed from one transmission sub-system, the incorporation of such DERs into its interconnected distribution sub-system at the point of common coupling (PCC) transfers the role of distribution sub-systems from pure power consumers to flexible prosumers [2]. This can be achieved by the following two perspectives. Firstly, local demands in one distribution sub-system can be fulfilled by the local DERs (e.g., rooftop PV) in addition to power transfers from its interconnected transmission sub-system. Secondly, DERs enable flexible energy demands, such as discharging of electric vehicles during peak periods and charging during off-peak periods. Consequently, DERs pave one promising way towards the coordinated energy management between one distribution sub-system and its interconnected transmission sub-system through flexible PCC power flow exchanges.