Control Strategy of VSC-HVDC System based on Frequency Trajectory Planning

In the voltage sourced converter based high voltage direct current (VSC-HVDC) system, the continuous increase of the proportion of new energy leads to the reduction of the system equivalent inertia level, and the frequency regulation faces serious challenges. The existing converter frequency regulation strategy relies on the time-varying inertia/damping parameters of the system and the random disturbances that are difficult to measure and fail to achieve a safe and economical frequency regulation effect. In this article, we propose a VSC-HVDC system frequency regulation (FR) strategy based on Frequency Trajectory Planning (FTP), which adds FR dead zones and safety margins and compares the system frequency with the planned frequency trajectory in real time. When the system frequency exceeds the safety range composed of the planning frequency trajectory and the rated frequency of the system, the converter provides additional FR energy, which not only guarantees the stability of the system frequency but also reduces the cost of FR. Finally, the advancement and economy of the FTP are verified by simulation.