Robust local controllers design for the AC grid voltage control of an offshore wind farm

Abstract

In this paper we deal with the problem of voltage control of the AC grid in an offshore wind farm by means of several converters, all of them connected to the AC offshore grid at the Point of Common Coupling (PCC) through different transmission lines. We propose to control the voltage simultaneously by all the connected converters, i.e., we have multiple actuators with the same goal. However, the number of operative converters can change during the wind farm operation and dynamics changes. Thus, it is necessary to assure the stability of the whole system in all different scenarios. In order to achieve a global design and implementation strategy, we propose the use of same controller parameters for all converters. For this kind of wind farm topology, we address the design of controllers as an optimization problem where we seek to maximize the robustness against uncertainty in the model of transmission lines and changes in the number of connected wind turbines guaranteeing the stability of the whole system in all different scenarios as well as a given settling time. Due to the proposed design strategy it is not necessary communication between different converters and controllers do not need to be re-tuned when the number of connected converters changes.