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Hybrid AC/DC Grid
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Hybrid AC/DC Grid

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "F: Electrical Engineering".

Deadline for manuscript submissions: closed (20 November 2021) | Viewed by 9915

Special Issue Editor

Dr. Gilney Damm

E-Mail Website
Guest Editor
Laboratory Instrumentation, Modélisation, Simulation et Expérimentation (IMSE) , University Gustave Eiffel, Campus Marne-la-Vallée, 77420 Champs-sur-Marne, France
Interests: nonlinear control of power systems; power system stability; control of power converters; fast ancillary services; microGrid; multi-terminal HVDC; supergrid

Special Issue Information

Dear Colleagues,

The electrical power system is currently undergoing a dramatic change from centralized generation to distributed generation. Most of these distributed/renewable-energy generators comprise variable-frequency AC sources or DC sources, and hence, they need power converters to interface with the public utility grid. These changes are happening in most voltage levels, from the high voltage connection of offshore wind farms to the low voltage connection of solar panels. In the same way, DC links are reinforcing the grid, creating backbones, firstly in high voltage, but now arriving to medium voltage. This process will most likely continue with the deployment of DC MicroGrids connecting the new elements of SmartGrids, most of them inherently DC, such as solar panels, electric vehicles, batteries, and intelligent buildings.

This coexistence of AC and DC grids and their interconnection may bring several problems, in particular power system stability. If frequency and voltage stability are well-known problems that must be tackled in this new configuration, the natural reduction of inertia brough by those power converter interfaces will create even more challenges and is already causing large problems around the world, such as the 2019 UK blackout. In the same way, in the framework of islanded MicroGrid, and in particular mixed AC/DC MicroGrid, they may only be composed of power converters. In all these cases, AC and DC grids will necessarily support each other with ancillary services in both directions.

This Special Issue of Energies on “Hybrid AC/DC Grids” will address all these common aspects of AC/DC grids’ interconnection, support, and stability. Topics of interest for publication include but are not limited to:

  • Interaction of AC and DC dynamics;
  • Low inertia AC grids;
  • Means to provide ancillary services with and without storage;
  • Synthetic inertia emulation and control;
  • Synchronverters and their use to support power grids;
  • Stability analysis of power network;
  • Voltage, frequency, and inertial support;
  • Mixed AC/DC MicroGrids;
  • HVDC and its interaction to AC grids;
  • Ancillary services from renewables’ power plants connected by power converters.

Prof. Dr. Gilney Damm
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (4 papers)

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Research

20 pages, 1847 KiB  
Article
Nonlinear Hierarchical Easy-to-Implement Control for DC MicroGrids
by Sabah B. Siad, Alessio Iovine, Gilney Damm, Lilia Galai-Dol and Mariana Netto
Energies 2022, 15(3), 969; https://doi.org/10.3390/en15030969 - 28 Jan 2022
Cited by 5 | Viewed by 1858
Abstract
In this work is considered the connection of a photovoltaics (PV) solar plant to the main grid through a Direct Current (DC) MicroGrid and a hybrid storage system, composed of a battery and a supercapacitor, in order to satisfy constraints of grid connection [...] Read more.
In this work is considered the connection of a photovoltaics (PV) solar plant to the main grid through a Direct Current (DC) MicroGrid and a hybrid storage system, composed of a battery and a supercapacitor, in order to satisfy constraints of grid connection (the so-called Grid-Codes). The objective, and main contribution of this paper, is to stabilize the DC MicroGrid voltage in spite of large variations in production and consumption, using a nonlinear hierarchical easy-to-implement control strategy. Here is presented the MicroGrid’s control design based on detailed models of the photovoltaic energy sources and the storage systems. Such DC grids may present an unstable behavior caused by the PV’s intermittent output power, by switching ripples from the power converters and their power electronics, and oscillatory currents produced by some types of loads. Therefore, the system is subject to both fast and slow variations, and its stabilization is based on different technologies of storage, such as battery and supercapacitor, and control algorithms designed thanks to the use of time-scale separation between different components of the storage systems. The obtained nonlinear results are stronger than current linear controllers, allowing to keep operating margins around the voltage reference. At the same time, in this work, insights from power systems practice have been used, aiming to obtain a very simple and easy-to-implement control scheme. Detailed simulation results are provided to illustrate the behavior and effectiveness of the proposed stabilization technique. Full article
(This article belongs to the Special Issue Hybrid AC/DC Grid)
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25 pages, 2839 KiB  
Article
Stability Analysis of Grid-Forming MMC-HVDC Transmission Connected to Legacy Power Systems
by Luís F. N. Lourenço, Filipe Perez, Alessio Iovine, Gilney Damm, Renato M. Monaro and Maurício B. C. Salles
Energies 2021, 14(23), 8017; https://doi.org/10.3390/en14238017 - 01 Dec 2021
Cited by 11 | Viewed by 2817
Abstract
The power system is going through a change in its very foundations. More and more power converters are being integrated into the electric grid to interface renewable energy resources and in high-voltage direct-current (HVDC) transmission systems. This article presents a discussion on the [...] Read more.
The power system is going through a change in its very foundations. More and more power converters are being integrated into the electric grid to interface renewable energy resources and in high-voltage direct-current (HVDC) transmission systems. This article presents a discussion on the stability of power systems when HVDC transmission systems based on modular multilevel converters (MMC) are connected in grid-forming (GFM) mode to the legacy power system using concepts of energy functions and Lyapunov stability theory and considering aspects of the interoperability between GFM converter technologies. As a base for the stability analysis, we review the main GFM converter technologies (droop and virtual synchronous machine), highlighting their differences. Then, we present a model using the center-of-inertia formulation for a multi-machine/multi-GFM converter power system representing a close future scenario of power systems where GFM converters might adopt different technologies. To illustrate the theoretical Lyapunov-based stability analysis, simulations performed in Matlab/Simulink showed the behavior of a 12-bus test system during a frequency disturbance that originated from the sudden connection of a load. To reflect the interoperability of different GFM technologies and the power system, scenarios with one single GFM technology and a scenario with mixed technologies were investigated. For the test system considered, the frequency response with fewer oscillations and a higher frequency nadir was obtained when all GFM converters were operated as VSMs that have a higher inertial response contribution. Full article
(This article belongs to the Special Issue Hybrid AC/DC Grid)
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27 pages, 3386 KiB  
Article
A Hierarchical Control Approach for Power Loss Minimization and Optimal Power Flow within a Meshed DC Microgrid
by Igyso Zafeiratou, Ionela Prodan and Laurent Lefévre
Energies 2021, 14(16), 4846; https://doi.org/10.3390/en14164846 - 09 Aug 2021
Cited by 2 | Viewed by 1354
Abstract
This work considers the DC part of a hybrid AC/DC microgrid with a meshed topology. We address cost minimization, battery scheduling and the power loss minimization within the power distribution network through constrained optimization. The novelty comes from applying differential flatness properties to [...] Read more.
This work considers the DC part of a hybrid AC/DC microgrid with a meshed topology. We address cost minimization, battery scheduling and the power loss minimization within the power distribution network through constrained optimization. The novelty comes from applying differential flatness properties to the microgrid components and formulating the cost and constraints in terms of the associated B-splines parametrization of the flat outputs (the voltages and currents of the system). This allows us to obtain optimal power profiles to minimize the power dissipation and the cost of the electricity purchase from the external grid. These profiles are tracked by a model predictive controller at the higher level, while at a a lower level a controller deals with the operation of the switches within the DC/DC converters. Extensive simulations under nominal and fault-affected scenarios using realistic data validate the proposed approach. Full article
(This article belongs to the Special Issue Hybrid AC/DC Grid)
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27 pages, 3910 KiB  
Article
Investigating the Converter-Driven Stability of an Offshore HVDC System
by Matthias Quester, Fisnik Loku, Otmane El Azzati, Leonel Noris, Yongtao Yang and Albert Moser
Energies 2021, 14(8), 2341; https://doi.org/10.3390/en14082341 - 20 Apr 2021
Cited by 6 | Viewed by 2471
Abstract
Offshore wind farms are increasingly built in the North Sea and the number of HVDC systems transmitting the wind power to shore increases as well. To connect offshore wind farms to adjacent AC transmission systems, onshore and offshore modular multilevel converters transform the [...] Read more.
Offshore wind farms are increasingly built in the North Sea and the number of HVDC systems transmitting the wind power to shore increases as well. To connect offshore wind farms to adjacent AC transmission systems, onshore and offshore modular multilevel converters transform the transmitted power from AC to DC and vice versa. Additionally, modern wind farms mainly use wind turbines connected to the offshore point of common coupling via voltage source converters. However, converters and their control systems can cause unwanted interactions, referred to as converter-driven stability problems. The resulting instabilities can be predicted by applying an impedance-based analysis in the frequency domain. Considering that the converter models and system data are often confidential and cannot be exchanged in real systems, this paper proposes an enhanced impedance measurement method suitable for black-box applications to investigate the interactions. A frequency response analysis identifies coupling currents depending on the control system. The currents are subsequently added to the impedance models to achieve higher accuracy. The proposed method is applied to assess an offshore HVDC system’s converter-driven stability, using impedance measurements of laboratory converters and a wind turbine converter controller replica. The results show that the onshore modular multilevel converter interacts with AC grids of moderate short-circuit ratios. However, no interactions are identified between the offshore converter and the connected wind farm. Full article
(This article belongs to the Special Issue Hybrid AC/DC Grid)
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