This paper proposes a novel pole-to-ground fault protection strategy for HVDC grids under symmetrical monopolar configuration employing low-speed DC breakers and pole rebalancing reactor (PRR) located at AC side to manage the rebalancing of the pole voltages. The first part of the paper is dedicated to the detailed description of the primary and backup protection sequences. In the second part, the proposed concept is validated through EMT simulations performed on a 4-terminal HVDC grid.
Effect of the Surge Arrester Configuration in MMC-HVDC Systems under DC and Converter Fault Conditions
Different surge arrester configurations are studied for a modular multilevel converter (MMC) in a symmetrical monopole configuration. Each configuration is analyzed under fault conditions including DC side faults and faults inside the converter station. The configurations considered are compared in terms of overvoltages, current levels and energy dissipation. It is found that the selection of the surge arrester parameters does not only depend on the overvoltage levels of the equipment, but also on the surge arrester configuration considered. The action of the surge arresters could result in higher longitudinal withstand voltage requirements of the arm reactors. Furthermore, special attention shall also be given to the possible low inductance loops created by the conduction of the arresters during a transient event.
SuperGrid Institute is proud to have been an active participant in the PROMOTioN project since 2016. This project is part of the European Union’s Horizon 2020 program and is made up of several work packages (WP) that share a common aim: developing meshed HVDC offshore grids that are both cost effective and reliable, through technological innovation. SuperGrid Institute is an active member of several Work Packages, including WP9 whose objective is to develop fault clearing strategies using Hardware-in-the-Loop (HIL) real-time simulation (RTS).
A New Energy Management Control of Modular Multilevel Converters for Coping with Voltage Stress on Sub-Modules
This paper investigates the impact of the operating condition on the SM voltage ripples. In particular, it is revealed that under the classical control scheme where the Modular Multilevel Converter internal energy varies naturally with the DC grid voltage, the traditional sizing approach based on the analytical expression of instantaneous SM voltage may fail to respect the SM voltage constraint. To tackle this problem, this paper presents a solution by incorporating the advantages of the explicit energy management and the developed analytical expressions of the SM voltage ripple, which achieves a better utilization of the converter asset.
PhD Amjad MOUHAIDALI « Contribution to the modelling of HVDC cables for electromagnetic transient simulations »
The integration of new technologies in the electric grids made them more and more complex, and most likely future growth of power grids will be based more on underground cables than overhead lines. One problem here, is that the mathematical model for electromagnetic simulation of power cables still has some shortcomings regarding stability, accuracy and passivity. In this thesis, we evaluate the cable parameters using analytical and numerical methods.
PhD Juan-Carlos GONZALEZ « Transient stability of high voltage AC-DC electric transmission systems »
This thesis addresses the transient stability analysis of hybrid AC/DC electric transmission systems. More precisely two questions sought to be investigated: What is the impact of a DC contingency on AC transient stability? How can we take advantage of the DC transmission systems as control inputs in order to enhance AC transient stability?
SuperGrid Institute and IMDEA joint forces with the support of REE, and created a consortium. This consortium was selected from more than 80 projects. Through the "Reduced Inertia Transient Stability Enhancement" (RITSE) project, SuperGrid Institute will strive to improve the transient stability of the AC networks by coordinating the use of batteries and HVDC links.
This work proposes a method for the full development, from conception to implementation, of the supervisory control of a multi-terminal HVDC (MT-HVDC) system.
In this paper, a thorough analysis of the converter arm behavior is presented, which gives an analytic expression of the lower limit of the energy as a function of the converter operating point and the connected grid conditions. The relation between the lower energy limit and the operating power is analyzed by using the practical MMC specifications of an HVDC application. An experimental test of a small-scale MMC mock-up demonstrates the validity of the theoretical analysis.
Multi-terminal high voltage direct current (MTDC) grids, or supergrids, are considered an interesting solution to integrate large amounts of renewable power and release congestion of existing AC power grids. Nonetheless, safe and reliable operation of such grids require the development of new DC protection systems.