Robust Current Sensorless Control of VSC-Based MTDC Transmissions for Integrating Wind Farms

This article presents an observer-based robust current sensorless control (RCSC) scheme for voltage-source-converter (VSC)-based multiterminal direct-current (MTDC) transmission system integrated with wind farms. Perturbation observer-based point of common coupling (PCC) voltage controller and dc-link voltage controller are designed for wind farm station (WFS) and grid-side station (GSS) of MTDC, respectively, for grid integration of multiple wind farms. Perturbation states are defined to describe the interactions of voltage control loops of nonlinear VSC model, and the feedback linearization control is realized based on the state estimations provided by perturbation observers to achieve the decoupled voltage control of MTDC. Neither current sensors nor parameters of MTDC are required in the RCSC scheme, thus achieving the robust sensor fault-tolerant operation of the MTDC system. Simulation and experimental studies are undertaken on a three-terminal MTDC transmission system integrated with two wind farms to verify the control performance of the RCSC scheme under the conditions of wind speed variations, sudden load changes, parameter variations, and current sensor faults.