Investigation of the influence on the AC system frequency due to DC voltage fluctuations in MMC-HVDC by analogue simulator

With the large-scale introduction of inverter-based resources (IBRs), there are concerns about increased frequency fluctuations during accidents such as a large generator trip out due to reduced system inertia. To mitigate these fluctuations, Grid-Forming (GFM) inverters with droop control are gaining attention, and their implementation is being considered for IBRs, including offshore wind turbine generators. As offshore wind turbine generators are often installed far from the demand area, HVDC transmission is more advantageous than AC power transmission in terms of reactive power current limitation. HVDC transmission models for the application of offshore wind turbine generators have therefore been studied all over the world. In actual generator operation, when generator trips due to a fault or other contingency event, the voltage in the HVDC transmission line may fluctuate temporarily because some parts of the wind power are momentarily interrupted. Under such circumstances, it is important to verify how the frequency fluctuation suppression effect of IBRs is affected. Therefore, this paper compares the performance of GFL and GFM controllers on the receiving side ac grid to supress the frequency fluctuation by means of an analogue simulator.