Laboratoire de Génie Électrique de Grenoble

REBCO HTS material makes it possible to consider very high engineering current densities and energy densities in coil windings Their use for very high field insert is already extensively studied, but they are also attractive for high field outserts or other meter-scale standalone magnets. In this work present preliminary studies for an insulated 500 mm split REBCO magnet concept. The conductor consist of co-wound REBCO and Hastelloy reinforcement tapes, In order to use efficiently the conductor, full impregnation is considered to enable effective stress averaging in the winding. Such impregnation is made possible by the use of thin film insulation on the co-wound metal reinforcement tape limiting the risk of delamination when cooling down. This concept was validated on a small-scale pancake tested under high stress in background field. Mechanical modelling compared to experimental strain measurement demonstrate the stress redistribution.

The transition toward intelligent and sustainable power systems requires practical schemes to integrate industrial demand flexibility into short-term operation, particularly in emerging electricity markets. This paper proposes an integrated framework that combines data-driven flexibility characterisation with a bi-level optimisation model for an industrial demand-side aggregator participating in the short-term balancing market. Flexibility is identified from AMI data and process information of large consumers, yielding around 2 MW of interruptible load and 3 MW of reducible load over a 24 h horizon. At the upper level, the aggregator maximises its profit by submitting flexibility offers; at the lower level, the system operator minimises balancing costs by co-optimising thermal generation and activated flexibility. The problem is formulated as a mixed-integer linear programming model and is evaluated on a real subtransmission and distribution network of a local utility in Ecuador, with ex-post power flow validation in DIgSILENT PowerFactory. Numerical results show that, despite the limited flexible capacity, the aggregator reduces the maximum energy price from USD/MWh 172.32 to 139.59 (about 19%), generating a daily revenue of USD 2475.15. From a network perspective, demand flexibility eliminates undervoltage at the most critical bus (from 0.93 to 1.03 p.u.) without creating overvoltages, while line loadings remain below 50% in all cases and total daily technical losses decrease from 89.46 to 89.10 MWh (about 0.4%). These results highlight both the potential and current limitations of industrial demand flexibility in short-term markets.

The integration of inverters into modern electrical distribution systems has introduced new challenges in maintaining system stability and protection. Traditional protection mechanisms, such as overcurrent (OC) protection, may not be effective in detecting faults in the presence of inverters, particularly line-to-line faults where the fault current is around 85% of the three- phase fault current. This issue arises because the contribution of inverters to the fault reduces the phase current of the affected phases, leading to the potential failure of overcurrent protection relays to detect the fault, a phenomenon known as protecti on relay blinding. This paper explores negative sequence current protection as an approach to safeguard distribution systems with inverters during line-to-line (LL) and line-to-line-to-ground (LLG) faults. Our research has shown that inverters, by injecting positive sequence currents, reduce the positive sequence current contribution from the grid while keeping the negative sequence current nearly unchanged when inverters are located close to the substation. However, this current increase when inverters ar e connected further from the substation. This indicates that the negative sequence current is favourably influenced from the perspective of negative sequence relay protection. The study provides a comprehensive analysis of the principles underlying negative sequence current protection, along with the implementation and settings of such protection. Simulation results and case studies are presented to demonstrate the effectiveness of negative sequence current protection in enhancing the reliability a nd safety of distribution systems with high inverter penetration.

In the rapidly advancing field of power electronics, the exploration and dynamic testing of Schottky diamond diodes represent a significant leap forward. This article presents comprehensive dynamic tests on these diodes, showcasing their performance under various conditions. The results indicate that diamond components are not only viable but also that they might become alternatives to traditional materials used in power electronics. With their exceptional thermal dependent behavior and electrical properties, diamond diodes will play a crucial role in the future landscape of power electronics. This study confirms the potential of diamond-based components to revolutionize the industry, offering a glimpse towards the future of power electronics.

International audience

To improve the reliability of power systems, Model Predictive Control (MPC) has emerged as a highly effective approach for optimizing parameters in Battery Energy Storage Systems (BESS) and other components. This study utilized MPC to identify the ideal settings for an island microgrid across two scenarios: one focused solely on optimizing BESS controller parameters, and the other addressing the simultaneous optimization of parameters for the BESS controller, photovoltaic (PVs) units, and wind turbines (WTs). By analyzing system performance under varying conditions, the researchers developed a detailed and accurate perspective on its operational behavior. The MPC algorithm was programmed in Python and integrated with DigSilent PowerFactory for simulation purposes, ensuring practicality for practise applications. Simulations in the time domain showcased the capability of the MPC-driven BESS and Renewable Energy Sources (RES) system to mitigate power system oscillations effectively.

Medium Frequency Transformers are essential for achieving galvanic isolation in isolated converter topologies, but challenges in insulation and cooling arise due to their compact nature. This study introduces a versatile thermal circuit tailored for shell-type medium frequency transformers. By addressing dielectric losses and incorporating diverse insulation materials, heatsink integration, and air gap considerations, this research enhances the adaptability of thermal modeling in the design process. The derived analytical model is verified against measurements from a 5kW test bench featuring a solid insulated transformer prototype, with a maximum hotspot relative error not exceeding 11.1% at all tested operating conditions.

The wide band gap transistors allow high or very high frequency operation of power converters. But the losses due to the magnetic materials increase a lot at these frequencies. Designers might consider not using magnetic materials at all. This paper addresses the question of the frequency range at which air core inductors will have a lower volume than counterparts with magnetic material for a given quality factor.

The paper deals with a modeling approach for a hybrid excitation synchronous machine using equivalent reluctance networks. From a finite element modeling (used as a reference model), it aims to define a computationally efficient model suitable for integration with optimization algorithms. Therefore, it propose to perform a parameter design model of the electrical machine. One of the main ideas is to have a model enabling the machine design with or without permanent magnet. Firstly, the paper depicts the geometric parameterization of the machine. Then, it presents the development of a reluctance network model. This approach offers a compromise between accuracy and computational efficiency, making it suitable for future optimization tasks in the design and control of synchronous machines.