Formal stability assessment of hybrid distribution grids based on the correct modeling of the effect of synchronization of the power electronics interfaces
Hybrid grids, which incorporate both AC and DC technologies, use power electronics converters to interface distributed energy resources, energy storage systems, and modern types of loads (such as EV charging stations) with high or medium voltage AC or DC grids. Such grid-connected converters rely on control algorithms and synchronization systems, and (as of late) on commu-nication infrastructures, with the aim of providing smart grid functionalities. It has been demonstrated that the widespread use of grid-connected converters may lead to a scenario where the grid is largely decreasing its inertia. If a network features a lack of inertia as well as a topology and line characteristics that result in operation close to voltage collapse, it is classi-fied as weak. In a weak network, the stability of the system is a major concern. This project fo-cuses on stability issues in weak microgrids. Currently, there are no quantitative methods that would allow assessing the stability margin as a function of the system topology, the system state, and the primary control laws. In particular, the influence of the synchronization elements and the communication infrastructure on the stability has not been well investigated in the ex-isting literature, although it has been demonstrated that they do indeed have an impact. Due to the general lack of investigations in this field, adequate models to describing such effects as well as standardized approaches for thoroughly validating such models are currently missing. This project aims at filling these major gaps in the existing works by developing a general framework for investigating stability issues in hybrid grids. To start with, formal methods for quantifying the static and dynamic stability margin of hybrid grids, while taking into account the effects of synchronization and communication, shall be elaborated. Such methods are an ena-bling factor for real-time stability assessment and the design of robust controllers. Moreover, a benchmark library of accurate time-domain models of hybrid distribution grids shall be devel-oped. In doing so, special attention will be given to modeling the finite bandwidth of synchroni-zation elements and the finite latency communication network. Finally, a thorough validation of the developed stability assessment tools and time-domain models shall be conducted using a combination of power-hardware-in-the-loop and real-scale microgrid experiments. Thereby, close-to-reality experimental conditions can be achieved while ensuring a minimum level of approximation. This framework is expected to grant deeper insights into the stability issues en-countered in hybrid distribution grids, and how they can be modeled and detected.
Prof. Dr. Marco Liserre