Current matching control system for multi-terminal DC transmission to integrate offshore wind farms

Abstract

The inherent features of Voltage Source Converters (VSCs) are attractive for practical implementation of Multi-Terminal HVDC transmission systems (MTDC). MTDC can be used for large-scale integration of offshore wind power with onshore grids. However, many of the control strategies for MTDC that have been proposed previously for offshore wind farm integration depend on local control of the wind turbine generators. This paper proposes a new control strategy, termed Current Matching Control (CMC), which can be used with any number of converter terminals, and is independent of the types of wind turbines used within each wind farm. The proposed CMC matches the current reference of the grid side converter to that of the wind farm side converters. In order to achieve such current matching, a telecommunication system will be required to facilitate calculations of the grid side current references to be carried out in real time. To validate the performance of the proposed control strategy, a generic four-terminal MTDC network, which integrates two offshore wind farms with two mainland grids, is simulated and results relating to several steady state and transient scenarios are presented.