Self-synchronization Decoupling Control Strategy for Improving Inertia Support Capability of MMC-HVDC Transmission System

For frequency stabilization problems caused by low inertia of power electronic systems, this paper presents a self-synchronization decoupling control strategy for improving inertia support ability of MMC-HVDC transmission system to actively support the system inertia. By analyzing the available energy to support the inertia of the MMC-HVDC, quantitative analysis of the feasibility of using its energy margin to improve the inertia level of the grid at the receiving end is proposed; analogous to the rotor equation of motion of the synchronous unit, a self-synchronization control strategy of the converter station that takes into account the energy margins of the energy storage components in the MMC-HVDC transmission system is proposed to actively support the inertia of the power grid at the receiving end while realizing self-synchronization without a phase-locked loop; On this basis, taking the DC voltage into account constraints on the utilization of capacitor energy margin, a decoupling control strategy between DC voltage and sub-module capacitor voltage is proposed for the system, which fully utilizes of the energy margin of energy storage components in the MMC-HVDC through the adaptive adjustment of the number of inputs of the sub-modules and the reference value of capacitor voltage and effectively enhances the inertia level and frequency stability of the power grid at the receiving end. Finally, the effectiveness of the proposed control strategy is verified by real-time digital simulation.