Influence of the phase-locked loop on the design of microgrids formed by diesel generators and grid-forming converters

D.P. Morán-Río, J. Roldán-Pérez, M. Prodanovic, A. García-Cerrada

IEEE Transactions on Power Electronics Vol. 37, nº. 5, pp. 5122 - 5137

Summary:

In recent years, Microgrids (MGs with renewable energy sources, diesel gen-sets and droop-controlled converters have been increasingly used to guarantee the continuity of power supply in remote areas. Renewable energy sources have been typically connected to MGs by using an electronic converter that features the two controllers: a current-control loop and a phase-locked loop (PLL . Stability issues related to the PLLs application in electrical grids have already been addressed in the literature, however, dynamic interactions in MGs caused by PLLs have not been sufficiently explored. In this paper, a MG that includes a grid-feeding voltage source converter and a grid-forming device (diesel gen-set or converter is studied. All network elements are modelled analytically and the eigenvalue and participation-factor analyses are used to analyse the interactions between the devices. It is demonstrated that MGs formed by diesel gen-sets have reduced stability limits. Also, it is shown that stability margins of MGs formed by droop-controlled converters can be improved by changing the control parameters (e.g. PLL and internal controllers bandwidths . The main findings and conclusions are summarised and presented as a practical MG design guide. Theoretical results are validated in a lab environment comprising two 15~kW converters and one 75~kW grid emulator.

Spanish layman's summary:

La incorporación de fuentes de energía renovables en la red eléctrica requiere de la participación de convertidores electrónicos. Este artículo estudia las posibles interacciones entre algunos aspectos del control de este tipo de convertidores y otros generadores conectados en la red. En particular, se estudia en detalle cómo el diseño del PLL que se usa para los llamados "convertidores seguidores de red" afecta a otros elementos de control del propio convertidor y de otros agentes en la misma red.

English layman's summary:

The connection of renewable energy sources to the electricity grid requires the use of electronic power converters. This paper studies possible interactions between control aspects in this type of converters and other generators connected to the same grid. Specifically, the paper addresses how the design of the PLL used in the so-called "Grig-Following Converters" affects other control elements of the same converter and other agents connected to the same grid.

Keywords: Microgrid, Phase-Locked Loop, Current Control, Diesel Generator, Droop Control, Small-Signal Analysis.

JCR Impact Factor and WoS quartile: 6,700 - Q1 (2022); 6,600 - Q1 (2023)

DOI reference: https://doi.org/10.1109/TPEL.2021.3127310

Published on paper: May 2022.

Published on-line: November 2021.

Citation:
D.P. Morán-Río, J. Roldán-Pérez, M. Prodanovic, A. García-Cerrada, Influence of the phase-locked loop on the design of microgrids formed by diesel generators and grid-forming converters. IEEE Transactions on Power Electronics. Vol. 37, nº. 5, pp. 5122 - 5137, May 2022. [Online: November 2021]