With the integration of a large amount of renewable energy generation into the AC power grid through power electronic equipment, the dynamic characteristics of the system are influenced by the multi-timescale control of these electronic devices. The grid-connected converters, operated under various types of controls, exhibit strong nonlinearity and low inertia during operation, posing synchronization stability issues for power grids with a high proportion of renewable energy.Especially when large-scale renewable energydevicesare connected to the weak grid, the multi-time scale and the multi-machine interaction between the devices are easy to cause the stability problem of the grid-connected system. For the grid-following converters, the synchronization stability of PLL under weak grid has received much attention due to the disturbance of the converter terminal voltage. Thegrid-formingconvertershave the risk of instability in strong grid, due the line impedance of resistive characteristics will cause power coupling and multi-machine power oscillation. In the large-disturbance analysis of synchronous stability, the influence of nonlinearity, limiting protection and switching control of grid-following/grid-forming converters is more obvious.The synchronous stability mechanism of the grid-connected converter system under control needs to be further sorted out. This article provides an overview of the research on the synchronization stability of renewable energy grid-connected systems under multi-time scale control. It comprehensively reviews the modeling and stability analysis techniques for grid-connected systems under single-time scale synchronization control, multi-time scale interaction, and multi-machine multi-time scale interaction. Firstly, under the synchronous control time scale, the synchronous stability analysis methods of grid-following and grid-forming converters are summarized. Secondly, The multi-time scale control interaction is mainly embodied in the interaction between synchronization control andvoltage/current loop. The interaction of grid-following converters is particularly significant under the condition of weak grid. The non-negligible interactionis existed between the active and reactive power control loops in the grid-forming converter due to their close time scale.Thirdly, in new energy plants and stations, there is a complex dynamic process of multi-machine multi-time scale interaction. Under the condition of non-ideal weak grid, the interaction between the control loops of multiple grid-connected converters in parallel has synchronous-synchronous control interaction of the same time scale, and the interaction of different time scales between voltage/current loops. On this basis, a construction framework for the synchronization mechanism of renewable energy grid-connected systems is proposed. In the grid-connected converter system with multi-time scale and mass distributed generation, it is not considered in the traditional methods that the deterioration of the overall coordination of the system caused by the dynamic interaction of multi-timescale massive converters. Based on this, a construction framework for the synchronization mechanism of renewable energy grid-connected systems is proposed, considering both global design and distributed implementation of synchronization performance, while taking into account resource and network constraints. The analysis and review of synchronization technology in renewable energy grid-connected systems in this article provide a systematic overview of the current state of research on analysis methods. Moreover, a reliable outlook on the direction of synchronous operation mechanism and method, especially high-order nonlinear system analysis is presented. © 2024 China Machine Press. All rights reserved.
