Development of Methodology for Small-Signal Stability Assessment in Energy Island Type Systems

Abstract: There is an increasing number of renewables being integrated into the power system around the world, due to the shift from producing electricity based on fossil fuels and instead relying on renewable energy sources. In order to scale up the renewable energy production and more easily transport the electricity between countries the interest in energy island (i.e., energy hub) type systems have grown, which mainly consist of wind power plants and high-voltage direct current (HVDC) interconnections used to transfer the electricity to onshore systems. More specifically, the energy island type system will consist of a combination of converter-based technologies, such as grid-following (GFL) and grid-forming (GFM), which for small disturbances may result in phenomena such as synchronization challenges and interactions among the converters, e.g., controller interactions and sub-synchronous oscillations, which can cause the system to become unstable for small disturbances. The small-signal stability assessment can be performed utilizing methods such as the eigenvalue-based or the impedance-based method, which can give physical insight into the cause for instability, and aid in tracing the root-cause for instability. Hence, the small-signal stability assessment complements the result obtained from the electromagnetic transient (EMT) simulations, which on their own can be difficult to interpret. However, the small-signal stability assessment is based on a single operating point, and a given energy island type system will contain a vast range of operating conditions. Further, the transmission system operator (TSO) receives black-box models of the vendor-specific converter-based resources in the energy island, which complicates the process of identifying the root-cause for instability, if required. Therefore, it is of interest to develop a methodology for scanning the risks of small-signal instability of energy islands, and to address the above-mentioned challenges, this PhD project aims at studying the following three objectives:
1. Develop a systematic method for identifying the root-causes for small-signal instability based on a system-level stability analysis considering different operating scenarios in practical energy island type systems.
2. Develop a general methodology for performing a sufficient small-signal stability assessment that covers the worst-case operating points by considering practical operational constraints of energy island type systems.
3. Identification of the level of detail of information required from the black-box model to enable the use of the developed methods in the above objectives 1. and 2., considering vendor-specific converters and the expansion of energy island type systems.


Funding: Energinet