Voltage source converter AC voltage controller design and dynamic response for a large offshore wind farm network

Abstract

The small footprint and controllability of voltage source converters are ideal for long distance high voltage direct current (HVDC) connection of large offshore wind farms in the future. The popularity of fully rated converters for wind turbines is also increasing in wind turbines. The converters decouple the generator from the offshore network, which is already decoupled from the onshore grid by HVDC. The offshore network effectively becomes islanded and inertia-less. The voltage control of offshore wind farm network needs to be fast for stiff regulation control under extreme disturbances. The control design and dynamics response of the offshore AC network voltage controller is studied in this paper. It is composed of the decoupled inner current control loop and outer voltage loop. Small-signal analysis is used to observe the eigenvalue damping in the system for a range of control response speed ratios between control loops in order to find suitable control designs. A lead compensator in the outer voltage control loop significantly improved the dynamics response in the control design.