Non-linear stability of inverter-dominated power grids

继续推动现有电力系统的脱碳，与在其中安装越来越多的可再生能源有直接关系。这些可再生资源需要电力电子逆变器才能与现有电网连接。电力电子逆变器以控制算法为主，尽管与传统的同步发电机相比，它们在电网的运行和控制方面具有更大的灵活性，但它们也给电网带来了前所未有的新的动态，威胁着电力系统的稳定。对未来电力网络的顺利运行来说，能够保证网络的稳定和避免对公众服务的中断是至关重要的。我的博士研究重点是研究电力电子高渗透率下的电力网络稳定性。更具体地说，它集中于研究和分析它们的暂态稳定性，即系统在发生诸如短路故障、断线和跳相等大扰动后的稳定性。所使用的电力电子逆变器根据其与电网同步的方法和其运行方式分为两种主要类型的逆变器。这两种类型是电网跟随式逆变器，它通过形成电流并跟随电网的电压向电网注入电力，以及电网形成逆变器，它形成一个电压源，可以从中获取电力。这些类型的逆变器使用不同的同步控制器来保持它们与电网的同步，因此它们在来自电网的不同干扰下与网络的交互是不同的。我的研究旨在提供对它们在网络中发生扰动后的个体行为的洞察，并得出关于如何在网络中配置和使用它们以尽可能减少系统潜在不稳定性的有价值的结论。该方法包括对描述逆变器在不同环境和一系列网络配置下的行为的微分方程式进行解析推导。这些配置将包括连接到几个示例电网的不同数量的逆变器，覆盖不同强度和结构的电网，旨在涵盖广泛的可能场景，并得出关于这些逆变器如何影响系统稳定性的综合结果。推导出的解析方程将被用来执行系统的相平面分析，并获得对其行为的直观了解，以及采用其他用于研究非线性系统稳定性的技术和方法。在此分析之后，将在仿真软件中对所检查的系统进行时域仿真，以验证所获得的理论结果。预计该分析将有助于电网系统运营商选择如何规划和配置其电网。

The continuous drive towards the decarbonisation of existing power systems is directly connected with the increasing installation of renewable energy resources in them. These renewable resources require power electronic inverters in order to interface them to the existing power networks. The power electronic inverters are dominated by control algorithms and despite the fact that they can offer increased flexibility in operation and control of the network compared to the traditional synchronous generators, they also introduce new and unprecedented dynamics to the network that are threatening the stability of the power systems. It is of vital importance for the smooth operation of future power networks to be able to guarantee the stability of the networks and avoid in this way interruption of services to the public. My PhD research focuses on investigating the stability of the power networks under high penetration of power electronics. More specifically it concentrates on studying and analysing their transient stability, which is the stability of the system after large disturbances, such as short circuit faults, line disconnections and phase jumps, take place in it. The power electronic inverters that are used are distinguished into two main types of inverter depending on their method of synchronisation with the grid and their operation. These two types are the Grid-Following inverters, which inject power to the grid by forming the current and following the grid's voltage and the Grid-Forming inverters which form a voltage source from which power can be drawn. These types of inverters utilize different synchronisation controllers to sustain their synchronisation with the network and therefore their interaction with the network under different disturbances from the grid differs. My research aims to provide insights into their individual behaviours after disturbances take place in the network and deduce valuable conclusions on how they should be configured and used in the network to reduce as much as possible potential instabilities to the system. The approach includes analytical derivations of differential equations describing the behaviour of the inverters under different circumstances and in a range of network configurations. These configurations will include different number of inverters connected to several example grids, covering grids of different strengths and structures aiming to cover a large range of possible scenarios and derive comprehensive results on how these inverters affect the system's stability. The derived analytical equations will be used to perform Phase Plane analysis of the systems and gain visual insights on their behaviours as well as employ other techniques and methods that are used for investigating the stability of non-linear systems. This analysis will be followed by time-domain simulations of the examined systems in simulation software for validation of theoretical results obtained. It is anticipated that the analysis will be useful to grid system operators in choosing how to plan and configure their power grids.