arXiv subjects

Willem Lambrichts

Publications and source records attributed to Willem Lambrichts.

4 recordsLinked to original sources

arXiv2025

Grid-Aware Islanding and Resynchronisation of AC/DC Microgrids

This paper proposes an optimal, grid-aware control framework for the islanding, island-operation and resynchronisation of hybrid AC/DC microgrids. The optimal control framework is based on a formally derived linearized load-flow model for multiterminal hybrid AC/DC networks. The load flow model integrates the AC grid, DC grid, and interfacing converters (IC) into a unified representation. This work extends an existing load flow model to include the ICs' grid-forming operation. In traditional islanding control frameworks, the grid-forming converter is typically interfaced with an energy storage system that can provide bidirectional power to maintain the power balance. The proposed framework, however, allows the ICs to operate as the grid-forming unit while being connected to a DC grid rather than a single resource. This configuration allows for a wider operating range and, thus, a more flexible control. Furthermore, the optimal grid-aware control framework can steer the system to ensure a feasible operation without any grid constraint violations before, during, and after the islanding manoeuvre. The framework also guarantees smooth transitions, i.e., without any significant transient behaviour, when transitioning between grid-connected and islanding operations. The optimal control framework is experimentally validated on a 27-bus hybrid AC/DC network consisting of 3 ICs that interface the AC and DC networks. The hybrid grid hosts various controllable and stochastic resources.

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arXiv2023

Analytically Computation of Sensitivity Coefficients in Hybrid AC/DC Micro-Grid

In this paper, we present a closed-form model for the analytical computation of the power flow sensitivity coefficients (SCs) for hybrid AC/DC networks. The SCs are defined as the partial derivates of the nodal voltages with respect to the active and reactive power injections. The proposed method is inspired by an existing SC computation process proposed for AC networks and here extended to include both the DC grid and the relevant AC/DC Interfacing Converters (ICs). The ICs can operate under different control modes i.e. voltage or power. Additionally, the model is able to compute the SCs for three-phase networks subjected to unbalanced loading conditions. The proposed method is numerically validated by means of a comparison with a detailed time-domain simulation model solved within the EMTP-RV simulation environment. Furthermore, we provide a formal proof regarding the uniqueness of the proposed SCs computational model for hybrid AC/DC networks.

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arXiv2023

Experimental Validation of a Grid-Aware Optimal Control of Hybrid AC/DC Microgrids

This paper presents the experimental validation of a grid-aware real-time control method for hybrid AC/DC microgrids. The optimal control is leveraged by the voltage sensitivity coefficients (SC) that are computed analytically using the close-form expression proposed in the authors' previous work. The SCs are based on the unified power flow model for hybrid AC/DC grids that accounts for the AC grid, DC grid, and the Interfacing Converters (IC), which can operate in different control modes, e.g. voltage or power control. The SCs are used to express the grid constraints in the optimal control problem in a fully linear way and, therefore, allow for second- to subsecond control actions. The validation of the model is performed on the hybrid AC/DC grid, available at the EPFL. The network consists of 18 AC nodes, 8 DC nodes, and 4 converters to interface the AC and DC network. The network hosts multiple controllable and uncontrollable resources. The SC-based optimal control is validated in a generic experiment. It is shown that the real-time control is able to control the ICs optimally to redirect power through the DC grid, to avoid grid constraint violations while providing reactive power support to the upper layer AC grid. Furthermore, the computational time of the optimal control is analysed to validate its application in critical real-time applications.

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arXiv2023

General and Unified Model of the Power Flow Problem in Multiterminal AC/DC Networks

This paper proposes a generic and unified model of the power flow (PF) problem for multiterminal hybrid AC/DC networks. The proposed model is an extension of the standard AC-PF. The DC network is treated as an AC one and, in addition to the Slack, PV and PQ nodes, four new node types are introduced to model the DC buses and the buses connecting the AC/DC interfacing converters (IC). The unified model is solved using the Newton-Raphson method. The extended PF equations can be used in the presence of multiple ICs operating under different control modes. Compared to other recent works, the proposed method allows multiple ICs to regulate the DC voltage simultaneously. This corresponds to more realistic operational conditions that ensure redundancy and allow for more flexible control of the hybrid grid. The proposed model can be used for networks under unbalanced conditions and allows for an intentionally negative sequence power injection. In addition to the operational advantages of this method, it is shown that the computational performance of the proposed method is one order of magnitude better than that of other methods presented in the existing recent literature while having the same accuracy.

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