The existing connection compliance process for inverter-based resources (IBRs) is based on a relatively simple grid model which cannot necessarily capture the risk of IBR-induced sub-synchronous oscillations (SSO). Once an IBR is implicated for its role in SSO, the relevant IBR vendor/developer can investigate using their detailed IBR model but, with a simple grid model which could not cover large impedance spectra to check for extreme scenarios. In parallel, the NESO could undertake an investigation using detailed grid models but black-box IBR models. The difficulty is over how black-box IBR models and grid models are exchanged with richness of operating points and frequency spectrum retained. The project will study the effectiveness of using a bank of grid impedance spectra that covers extreme grid conditions and suggest small-signal tests to be carried out with the model bank. We will establish principles/rules to shape the response of an IBR to mitigate further risk of SSO. 

Benefits

NESO is keen to capture the risk of potential IBR-induced SSO during connection compliance itself. However, the current approach cannot always foresee poorly damped SSO as evident from the SSO events in Scotland in recent years. The outcome of this project is expected to make IBR connection compliance more robust in terms of its ability to foresee potential risk of SSO. Nonetheless, if an SSO event happens, NESO will be able to specify to the vendor/developer how the response of the implicated IBR(s) needs to be shaped to mitigate further risk of SSO.