An operation region determination method for modular multilevel converter high-voltage direction current (MMC-HVDC) system is proposed in this paper. Firstly, the mathematical model of MMC-HVDC system is illustrated, where the voltage stability constraint, voltage magnitude constraint and the current constraint is considered. Secondly, the operation region determination problem is transformed into checking the possible solution for a series of equations. Thirdly, the proposed method is applied based on the planning Xiamen-Jinmen power system inter-connection project, which aims to provide electricity supply for Jinmen with safety and economy. It is illustrated by numerical case study that the operation region of MMC-HVDC is not ideally as a unit circle, in which case the region is limited by the system parameter of Jinmen power system, voltage magnitude and operation current. Furthermore, it is shown that the operation region is reduced with the decrease of short circuit ratio (SCR), in which case the Jinmen power system should be strengthened to improve its system characteristic.

MMC-HVDC, operation region, power system inter-connection, SCR