HVDC Control and operation for the integration of extremely high-RES systems with focus on permanent DC faults

Abstract

This master thesis presents the control and analysis of a DC fault on a zero inertia offshore grid integrating multiple Voltage Source Converters. The system analyzed consists in an offshore grid which includes two wind power plants and two offshore converter platforms. These two offshore converter platforms are connected to two different onshore grids through High Voltage Direct Current (HVDC) point-to-point connections. First, the modeling and control of Voltage Source Converters for offshore wind energy HVDC systems are presented. Two control strategies are described for them depending on their operating mode which can be grid-forming or grid-following. Then, the complete model of the system, including the onshore grids, is presented. For simulation purposes an aggregated model is used for the WPPs. Further, two control methods for power reduction for the system to be able to perform correctly under DC faults are proposed. Finally, a simulation of the modelled system under a pole-to-pole DC fault on one of the HVDC transmission links is performed and evaluated by means of time domain simulations using Matlab Simulink®.