Control of VSC-HVDC Connected Offshore Windfarms for Providing Synthetic Inertia

This paper presents a generator emulation control (GEC)-based method to provide synthetic inertia with a voltage source converter-based high-voltage direct current (VSC-HVdc) converter station, and furthermore, a coordinated control strategy for VSC-HVdc connected offshore windfarms (OWFs) to achieve enhanced ability of serving synthetic inertia. Given that the increasing penetration of renewable energy sources may lead to a significant reduction of system inertia and will thus result in a greater risk of instability, an extended control loop to emulate both the inertia and the droop characteristics of a synchronous generator is first added, with which the VSC-HVdc converter station can provide active power support by using the stored energy in the dc-link capacitors to increase the inertia of power system. To provide larger synthetic inertia with reasonable volume of dc-link capacitors, a coordinated control strategy for VSC-HVdc connected OWFs is further proposed to utilize the OWFs to supply additional energy needed by the GEC strategy. The validity of the proposed control methods is verified exemplarily by simulation results of a three-terminal VSC-HVdc system with two connected OWFs.