Control of VSC-HVDC with electromechanical characteristics and unified primary strategy

High voltage dc (HVDC) systems act as the prevailed solution for transmitting offshore wind energy to onshore main grids. Control of the voltage source converters (VSC) in HVDC systems is decisive for the performance. This paper proposes the control of VSC-HVDC with electromechanical characteristics and unified primary strategy, as a reaction to the updated requirements of the ac grid transmission system operators. As two important aspects of VSC-HVDC control, converter control and primary control are both designed in detail. Electromechanical characteristics make the VSC capable of providing inertia to the ac networks as well as simplicity in island operation. Besides, unified primary control is given as a universal primary strategy for VSC stations, and especially takes into account frequency support and control mode transition. The proposed converter control is validated in scaled-down 10 kW laboratory setups, while the proposed primary control is endorsed by the simulation tests on a CIGRE multi-terminal HVDC model.