Transient Frequency-Voltage Support Strategy for VSC-MTDC Integrated Offshore Wind Farms Based on Perturbation Observer and Funnel Control

Abstract

To address the transient frequency and voltage stability challenges posed by low-inertia offshore wind farms (OWFs) connected through voltage source converter (VSC) based multi-terminal high voltage direct current (VSC-MTDC) system, a nonlinear perturbation observer and funnel control-based transient frequency and voltage support (PFTFVS) control strategy is proposed for VSC-MTDC integrated OWFs system. This approach utilizes improved estimation ability of the observer and adaptive feature of the funnel controller to enhance transient support capability and disturbance rejection performance of the system. The strategy comprises three parts: 1) an adaptive transient frequency support and rotor speed control method for wind turbines is devised to enhance the frequency support capability of OWFs; 2) considering the energy storage capability of DC capacitor in VSC-MTDC system, a transient frequency support controller is designed for VSC station to swiftly manage transient frequency variations; and 3) utilizing the rapid power regulation ability of VSC-MTDC, a transient voltage support controller is developed for VSC station to enhance voltage stability and boost the power transmission capacity. Finally, dynamic simulations of VSC-MTDC integrated OWFs system are built to verify the validity and robustness of the proposed strategy.