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On the Electrostatic Inertia in Microgrids with Inverter-Based Generation Only—An Analysis on Dynamic Stability

1
Faculty of Power Engineering, University Politehnica of Bucharest, 060042 Bucharest, Romania
2
KIOS Research and Innovation Centre of Excellence, University of Cyprus, Nicosia 1678, Cyprus
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Faculty of Sciences and Technology, Universidade NOVA de Lisboa, CTS-UNINOVA, 2829-516 Caparica, Portugal
4
Polytechnic Institute of Setúbal, INESC-ID Lisboa, 2910-761 Setúbal, Portugal
*
Author to whom correspondence should be addressed.
Energies 2019, 12(17), 3274; https://doi.org/10.3390/en12173274
Received: 31 July 2019 / Revised: 18 August 2019 / Accepted: 22 August 2019 / Published: 26 August 2019
Microgrids are about to change the architecture and the operation principles of the future power systems towards smartness and resiliency. Power electronics technologies are key enablers for novel solutions. In this paper we analyze the benefits of a “microgrid by design” architecture (MDA), using a solid-state transformer (SST) as a low-voltage grid-former and inverter-based generation only. In this context, the microgrid stability is maintained with the help of “electrostatic energy inertia” that can be provided by the capacitor connected to the DC busbar behind the SST inverter topology. This happens in a natural way, alike the mechanical inertia in power systems with synchronous machines, however without depending on frequency and without the need of a rotational inertia. This type of microgrid always operates (both fully connected to the main grid or in islanding mode) with all the necessary mechanisms needed to maintain the microgrid stable—no matter of the perturbations in the upstream of the point of common coupling (PCC). In the case of microgrids with inverter-based generation only (including the energy storage systems), there is no mechanical inertia and different stability mechanisms need to be applied compared to the stability principle of the classical power systems. Our proposed mechanism differentiates from the recently proposed stability assessments of microgrids based on virtual synchronous generators from the control theory perspective. This paper is a continuation of our previous work where the MDA was first introduced. The use-cases and scenarios are based on realistic and yet reasonable complexities, by coupling the disturbance magnitude with the voltage stability limit in power grids. The paper finds meaningful disturbances to test the electrostatic energy inertia at the boundaries of grid stability, as guidance to understand the range of voltage variation for extreme conditions. The results show that in microgrids with inverter-based generation only and passive loads (RLC type) the operation is no longer frequency dependent. The energy of the DC busbar capacitor as electrostatic energy inertia of the MDA has a role similar to that of the rotational machines in classical grids in terms of maintaining dynamic stability, however impacting two different types of stability. View Full-Text
Keywords: microgrid; electrostatic energy inertia; inverter-based generation; solid state transformer; dynamic stability; resilience; immunity microgrid; electrostatic energy inertia; inverter-based generation; solid state transformer; dynamic stability; resilience; immunity
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Sanduleac, M.; Toma, L.; Eremia, M.; Ciornei, I.; Bulac, C.; Triștiu, I.; Iantoc, A.; Martins, J.F.; Pires, V.F. On the Electrostatic Inertia in Microgrids with Inverter-Based Generation Only—An Analysis on Dynamic Stability. Energies 2019, 12, 3274.

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