Design considerations for primary control in multi-terminal VSC-HVDC grids

Abstract

Multi-terminal dc networks based on voltage source converters (VSC) are the latest trend in dc-systems; the interest in the area is being fueled by the increased feasibility of these systems for the large scale integration of remote offshore wind resources. Despite the active research effort in the field, at the moment, issues related to the operation and control of these networks, as well as sizing, are still uncertain. This paper intends to make a contribution in this field by analyzing the sizing of droop control for VSC together with the output capacitors. Analytical formulas are developed for estimating the voltage peaks during transients, and then it is shown how these values can be used to dimension the dc-bus capacitor of each VSC. Further on, an improved droop control strategy that attenuates the voltage oscillations during transients is proposed. The proposed methods are validated on the dc-grid benchmark proposed by the CIGRE B4 working group. Starting from the structure of the network and the power rating of the converters at each terminal, the output capacitors and the primary control layer are designed together in order to ensure acceptable voltage transients.(C) 2014 Elsevier B.V. All rights reserved.Peer ReviewedPostprint (author’s final draft

A new sequential power flow algorithm for AC/DC systems including independent multiterminal DC subsystems

“…(2,4,6), and reactive power flowing from the i th bus to other buses in the AC system given by Eqs. (3,5,7), respectively.…”

“…High-voltage direct current (HVDC) systems have been used in electrical power systems integrated to AC systems for a long time [1][2][3][4][5]. Many methods have been proposed for AC/DC power flow calculation in integrated AC/DC systems.…”

Control of multi-terminal HVDC networks towards wind power integration: A review

“…Sometimes communications are needed for achieving a proper power flow [28]. Besides, large droop gains can provoke oscillations in the DC voltage [29][30][31]. To improve performance under various loading conditions, references [12,32,33] have proposed an adaptive scheme that modified the droop gains depending on the system state.…”

HVDC meshed multi-terminal networks for offshore wind farms: Dynamic model, load flow and equilibrium

“…All numerical results are available in [10] The system is represented in per unit with a P base = 1000M W and V base(dc) = 400kV . The matrix Y bus for this case yields: The Parameters of the system were taken from [11] and the recommendations from [12], [13]. For the sake of completeness, they are presented in Tables I and II.…”