Supergrid Institute

Superconducting Fault Current Limiters (SFCLs) have reached a mature Technology Readiness Level, making their deployment in power grids increasingly relevant. While applications in AC networks are well studied, HVDC grids pose distinct chal-lenges due to different fault dynamics and the reliance on Modular Multilevel Converters (MMCs). This work develops a mathematical model of a simplified DC grid including an SFCL based on High-Temperature Superconducting (HTS) tapes and an MMC repre-sented by an Averaged Value Model (AVM). The model couples net-work and converter dynamics with the nonlinear temperature- and current-dependent properties of the SFCL, enabling efficient para-metric studies under fault conditions. The analysis investigates key design parameters, such as the HTS tape length, highlighting their influence on SFCL and grid performance and providing guidelines for optimal device design.

The global transition to renewable energy is transforming power systems, necessitating advanced transmission solutions to ensure reliability and resilience. High-voltage direct current (HVdc) systems, particularly multiterminal dc (MTdc) networks, are pivotal in integrating diverse renewable energy sources into hybrid ac/dc networks. These systems facilitate efficient power transfer over long distances and enable dynamic energy sharing across regions. However, the increasing penetration of inverter-based resources introduces complex control challenges that must be addressed to maintain grid stability and resilience.

<p>DC power transmission technologies have achieved significant advancements, gaining widespread adoption within modern electrical systems. The use of superconducting cables in Magnesium Diboride (MgB<sub>2</sub>) cooled by liquid hydrogen (LH2) could drastically increase the performance of DC grids, enabling higher power transport capacity and extending transmission distance, while reducing energy loss and land occupation. Today, the transport of DC electrical energy is enabled through modular muti-level converters (MMCs) capable of effectively controlling currents, voltages and power flow. Designing an optimal DC power system, along with appropriate superconducting cable design and protection apparatus, needs accurate, yet simplified, models of the converters. This study presents simplified models that apply during the fault, able to adapt to any pre-fault scenario without a need to implement complex control systems. The developed model can be easily integrated, along with a model of a superconducting MgB<sub>2</sub> cable, in EMT power system simulators for analysing their mutual interaction during faults and for optimizing the cable design and its protection system.</p>

During the early stages of Railway Systems, the implementation of DC technology facilitated the deployment of lightweight and efficient traction locomotives. At that time, DC systems offered considerable advantages over AC systems, allowing an easy control of the motor torque and avoiding the need for heavy step-down transformers and rectifier bridges. Additionally, substations connected in parallel along the line ensured a consistent contact line voltage, contributing to high supply reliability and balanced load for the AC power grid. However, safeguarding this system against short circuits presented challenges due to potential configuration changes and the short-circuit currents, whose magnitude is often comparable to the substation rated current. While the current protection system effectively clears faults, it might be subjected to wrong fault detections in the case of major transient events not linked to faults, causing unnecessary protection trips. The current protection system, being a very mature technology, has reached its performance limit nowadays. To enhance system performance, new protection strategies must be explored. This paper proposes a new advanced Fault Detection Algorithm (FDA) capable of overcoming the limitations of the protection system nowadays deployed in DC railways systems.

The number of HVDC installations is increasing and the decarbonization of power systems makes it necessary to install storage systems. It might become relevant to assess the synergies between both trends by connecting storage systems on the DC side of HVDC systems. The contribution of this paper is to show the feasibility and the design of such a system to provide three different ancillary services: power oscillation damping (POD), fast frequency response (FFR), or wind power oscillation smoothing. The DC storage system consists of a series connection of sub-modules with energy storage devices connected to each sub-module through a DC-DC converter. For the proposed design methodology, a first simple average model of the DC storage converter is developed to run preliminary EMT simulations to obtain power profiles for the energy storage elements according to the system needs. These profiles are used as inputs for designing the storage system. The design methodology is validated by performing new EMT simulations with a more detailed model which includes a model of the storage elements. Results show that the designed system can provide the expected services and sizing results confirm the technical feasibility of the solution.

Medium voltage direct current is emerging in distribution and collection networks and the network codes are under construction. This article introduces the MVDC network fault ride-through (FRT) requirement and the response of a DC solid state transformer is analyzed. A novel control of the DC SST suitable in the MVDC PV collection network is proposed. The controls of the boost MPPT converter and the isolated DC-DC converter include a normal operation mode and an FRT mode without any additional hardware circuit components. The performance of the proposed solution is demonstrated in simulation.

International audience

Conventional magnetron discharge is a widely used technology for many applications. In the last decade, the high current density sputtering regime has been an interesting alternative for tailoring thin film properties. In this paper, we focused on the electrical characterization of the helium magnetron plasma operated at average gas pressure (5 Pa) with a molybdenum target. Optical emission spectroscopy diagnostics also supports this study by providing information on electron density evolution. The analysis of the plasma–surface interaction zone on the target unveiled the physical mechanisms associated with the high current density range (6 A cm−2), corresponding to different discharge regimes. The self-sputtering yield plays a key role in high-power impulse magnetron sputtering discharge operated with helium. The electron density is highly dependent on the presence of a metal.

At the early age of Railway Systems, the DC solution enabled the deployment of lightweight and efficient traction locomotives compared to AC systems as they do not have to carry a heavy step-down transformer and the rectifier bridge. Moreover, the contact line voltage is sustained by sub-stations connected in parallel along the line, determining a high supply reliability and a balanced load for the AC power grid. However, the protection of this system against short circuit is a challenging task as the configuration of the DC system can change and the short-circuit current is in the order of the sub-station rated current. The protection system currently installed in DC railway systems is effective in clearing faults, however, it has reached its performance limit, and in order to increase the global system performance, new protection technologies must be investigated. In this paper, a new model-based Fault Detection Algorithm (FDA) is proposed. The simulation results prove its ability to overcome the limitations of the current protection system and to localize the fault position in many operating conditions.