For offshore wind power, HVDC is more economically advantageous than AC transmission due to the longer transmission distance to the demand point when the coastal distance is greater. In addition, the recent introduction of large amounts of VRE (variable renewable energy) into the grid has led to a relative reduction in the amount of synchronous generators connected, which presents challenges such as reduced inertia. For this reason, studies are underway to add control with frequency fluctuation suppression to VRE.

Converter control used in HVDC systems for offshore wind power is generally applied with GFL, but GFM systems are more advantageous for delivering the inertia from the offshore wind power side faster to the AC grid side. Although there have been cases where GFM control has been applied to one of the converters at either the transmission side or the receiving side, studies have not progressed with GFM control at both the transmission side and the receiving side, and it will be verified whether the power is transmitted to the AC system at a sufficient speed via the two converters.

As a model configuration, HVDC model consisting of two converters, one at the transmission side and one at the receiving side, in a monopolar configuration is used, and as converter control, the transmission side and receiving side are GFM-type and F-Droop control is implemented on the receiving side converter. Load variations are generated in the AC system and the frequency changes are compared with the case of a conventional configuration.

It was first confirmed that start-up and steady-state can be implemented in both-side GFM-type DC transmission system. Next, differences in characteristics were clarified for the behaviour during frequency fluctuations in comparison with conventional control.