Deviation-Free Frequency Control of MMC-MTDC Converter Based on Improved VSG

As an important issue of the future AC-DC hybrid power system, the research of coordinated control between MMC-MTDC transmission system and AC network is attracting more and more attention. Based on the conventional virtual synchronous generator (CVSG) control method, the converter connected with AC network can simulate the traditional synchronous generator participating in primary frequency regulation of AC system, but its frequency control accuracy needs to be improved. To address this issue, this paper proposes an improved frequency regulation control strategy for the virtual synchronous generator (IVSG) converter. This strategy introduces the frequency deviation based on the inertial parameters and damping parameters in the CVSG control, which enables the grid-connected converter to cooperate with the thermal power unit to participate in the AC system's error-free frequency regulation in real time, and then realize the high-precision frequency support of the converter to the AC system frequency. Based on the Opal-RT simulation platform, a five-terminal 31-level MMC-MTDC transmission system model including the cluster wind field is built. The proposed control strategy is verified by real-time simulation under two operating conditions: DC power change and AC load fluctuation. The simulation results show that the proposed control strategy can effectively improve the frequency regulation accuracy of AC system.