Multiterminal grid for offshore wind
With the aim to investigate the best ways of integrating large scale offshore wind power by means of a transnational grid in the North Sea, we are working with ECN and TU Delft - in the context of the North Sea Transnational Grid (NSTG) project - to assess the challenges of operating multiterminal direct current transmission networks.
More specifically, aim of the cooperation is to test and validate new control strategies for AC/DC converters operating inside a multi-terminal DC (MTDC) grid.
For this validation a down-scaled MTDC grid will be built and tested in the JRC Smart Grid Simulation centre. First a stand-alone configuration will be tested consisting of three Voltage Source Converters (VSCs). Subsequently, a real-time digital simulator will be connected to perform testing of the VSC and its controls, interactively with the MTDC grid model in combination with real-time validation of the different models (f.i. wind farm models) and control strategies previously developed in the NSTG project.
For the testing phase, 3 voltage-source converters (VSC), each rated at 5 kVA, have been acquired. With the VSCs, it is possible to use PC-based controllers directly developed in Simulink™ together with the actual power hardware. This provides a straight-forward platform for obtaining practical results from the developed control strategies in the simulation phase. The advantage of using a real-time simulator in this scenario lies in the fact that it becomes possible to exchange signals with external devices, such as the VSCs, and use them in real-time, making this a valuable setup for PHIL (power-hardware-in-the-loop) testing.
The development of a multi-terminal (MT) high voltage DC (HVDC) grid based on voltage source converter (VSC) technology has been envisaged as a key development for harnessing the vast offshore wind production potential of the North Seas. In this paper, market integration of a centrally dispatched MT HVDC Grid based on droop control is examined. Particular emphasis is given on the management of onshore imbalance volumes due to offshore wind power forecast errors.
The economic importance of the control choices of the operator of such an active transmission grid is highlighted, and regulatory implications are briefly discussed. The main contribution of the paper is the coherent development of a droop-controlled MT HVDC grid scheme that integrates optimal power flow (OPF) dispatch, and imbalance volume management.