Coordinated Flexible Damping Mechanism With Inertia Emulation Capability for MMC-MTDC Transmission Systems

The rapid growth in penetration levels of power-electronics-interfaced renewable power generation into grids has been reducing system kinetic inertia, which results in degraded frequency stability and oscillation damping. In an attempt to address this challenge, this article proposes a control scheme that realizes a coordinated flexible damping mechanism (CFDM) with inertia emulation capability for modular multilevel converter-based multiterminal dc (MMC-MTDC) transmission systems. The proposed CFDM scheme allows the MMC-MTDC system to autonomously provide an emulated inertial response with a flexible damping effect to ac systems in a similar fashion of synchronous generator, without the need for communication. To ensure the precision of the total provided damping power, the power losses of the converter stations and MTDC networks are also compensated in the algorithm. The CFDM controller parameters are optimized by the small-signal stability analysis. The effectiveness of the proposed CFDM scheme is demonstrated in a power system model simulated in MATLAB/Simulink, which consists of a three-terminal MMC-MTDC transmission system and three asynchronous ac girds. It is verified that the proposed CFDM scheme can effectively minimize grid frequency deviation and damp angular oscillation in grid events of load changes and faults.