A Fast-response Power-Flow Control Strategy of MMC-UPFC based on Active Disturbance Rejection Control

This paper proposes, the unified power flow controller (UPFC) based on the modular multilevel converter (MMC) requires stability and fast power-flow-regulation capabilities, whereas the linear active disturbance rejection control (LADRC) strategy precisely has the characteristics of strong disturbance rejection and fast response. Therefore, to improve the dynamic performance of UPFC when regulating the power flow, LADRC is introduced into the UPFC inner-loop controller. Meanwhile, to reduce the observed burden of the linear extended state observer (LESO) in LADRC, a disturbance observer (DOB) is introduced to compensate for the LESO's disturbance estimation error. The frequency characteristics of the voltage inner loop in MMC-UPFC with improved LADRC are then provided, indicating that the improved DOB-based LADRC has smaller perturbation gain at low frequency, and the cut-off frequency of the transfer function is also increased. Thus, these optimizations effectively improve the dynamic and anti-interference ability of LADRC. The power flow characteristics of MMC-UPFC were also analyzed, providing theoretical guidance for UPFC to regulate the grid power flow. Finally, the UPFC power-flow control strategy and corresponding DOB-based LADRC method are verified in PLECS, showing that the improved method has the advantages of faster response speed and strong anti-interference ability under different working conditions.

Keywords: modular multilevel converter, unified power flow controller, active disturbance rejection control, disturbance observer.