With massive amounts of photovoltaics (PV) connected to the distribution grid

the operational flexibility of the system has been significantly enhanced

yet the complexity of its optimal scheduling and control has also increased dramatically. Coordinated operation between transmission and distribution (T&D) systems can effectively alleviate issues such as voltage violations and line overloading in distribution networks. However

coordinated optimization and control of T&D systems face critical challenges

including high- dimensional nonlinear models

multi-source uncertainty disturbances

and high computational complexity in large-scale optimization. To address these challenges

this paper focuses on the scenario of extremely high penetration of distributed PV-storage systems. First

the morphological characteristics of T&D coordination under extremely high penetration of PV-storage systems are analyzed. Then

the current research progress in three key technical areas

i.e. coordinated T&D power flow calculation and optimization

optimal scheduling and coordinated control

is systematically reviewed

and three key difficulties faced by optimal scheduling and coordinated control of integrated T&D systems in such scenarios are identified. Finally

considering that power networks inherently exhibit the properties of complex systems

complex system theory is introduced to reveal the key regulatory factors and overall dynamic characteristics of integrated T&D systems. On this basis

a research framework for optimal scheduling and coordinated control of integrated T&D systems is proposed based on complex system theory. The proposed framework is expected to enhance the optimal scheduling and coordinated control performance of integrated T&D systems under extremely high penetration of distributed PV-storage

providing theoretical support and methodological reference for the high-quality development of the new dispatch system.