Frequency Regulation Control Strategy for Flexible DC Transmission System Based on Adaptive Virtual Inertia

In order to solve the problem that the flexible DC transmission system cannot provide inertia for the AC power grid and participate in frequency regulation with the traditional control strategy, this paper proposes a frequency regulation control strategy based on adaptive virtual inertia with consideration of frequency stability. With the proposed control strategy, the flexible DC transmission system can participate in the secondary frequency regulation and realize the zero-error regulation of AC-side frequency, while keeping the droop characteristic of DC side and automatically distributing DC power. In addition, the frequency stability and inertia of the system are further improved through virtual inertia control, and the transient fluctuation caused by secondary frequency regulation control is improved. For the problem that the choice of inertia coefficient is limited by DC voltage deviation, the adaptive inertia coefficient is adopted. When the voltage deviation is small, the inertia coefficient can be increased for better frequency stability effect. On the contrary, the inertia coefficient is reduced to prevent DC voltage from exceeding the limit. The simulation model of a five-terminal flexible DC power grid is built in the PSCAD environment, and the simulation results verify the feasibility and effectiveness of the proposed control strategy. © 2021 Automation of Electric Power Systems Press.