Analysis on the Stability of Smart Microgrids

The growing level of concern about climate change on a global scale is leading to changes in the infrastructure of the conventional electricity grid, which is largely based on burning fossil fuels. This migration towards renewable energy sources with a lower impact on carbon footprints responds to the imperative need to reduce greenhouse gas emissions.

This paradigm shift implies a transition towards a more decentralized and efficient electricity system, which is characterized by distributed generation and the emergence of microgrids, local energy production and distribution networks that can operate independently or be connected to the grid, making the operation of the main grid more flexible. In addition, these microgrids will integrate future advanced energy storage and management technologies, which would allow the creation of an energy ecosystem where these microgrids would be intelligently interconnected to achieve continuous optimization of both energy production and consumption.

In recent specialized literature, the analysis of stability in unbalanced microgrids has received little attention, which implies a lack of focus on unbalanced power systems, a scenario that take on great importance particularly in systems with distributed generation. Within this context, Dr Sauro J. Yagüe recently completed his doctoral thesis within the Industrial Products Engineering Group (GEPI) in the Department of Industrial Engineering at the IQS School of Engineering. His research consisted of a review of the techniques used to analyse stability in unbalanced power systems. This review addressed both voltage-dependent loads and constant power loads, using methods such as modal analysis and the impedance-based method. Entitled Stability analysis of unbalanced microgrids with grid-forming and grid-following electronic power converters, his thesis was supervised by Dr Pere Palacín Farré with IQS and Dr Aurelio García Cerrada with the ICAI Advanced Technical School of Engineering at the Pontifical University of Comillas.

The review procedure undertaken by Dr Yagüe began with a simple low-voltage (LV) case study, coveringGrid Forming (GFO) electronic power converters andGrid Following (GFL) converters, along with three distinct models of phase-locked loop (PLL) and unbalanced loads. The main objective was to investigate possible interactions between these components.

The results obtained by both methods, the modal analysis and the impedance-based method, were compared. While the latter is easier to implement using simulation or field data, modal analysis requires a deeper understanding of the characteristics of the system, although it offers a better understanding of the problem. Since both methods are based on an approximation of the system by small-signal perturbations, they provide identical results, but offer different information.

To deepen the research, a broader case study was finally considered, using a low voltage distribution system defined by CIGRE. In the analysis, a comprehensive model developed at Simulink, which incorporated electronic power converters, was used for the purpose of extracting and examining the results.

This thesis constitutes a significant advance towards the implementation of an effective model reduction technique to identify the most relevant modes of an unbalanced microgrid. Not only does this progress hold theoretical importance, but it also has significant practical implications by facilitating the implementation of more efficient control strategies in microgrids, thus promoting their viability and adoption in the transition to more sustainable and resilient electricity systems.

Related publications

Sauro J. Yagüe, Aurelio García Cerrada, Pere Palacín Farré, Comparison between modal analysis and impedance-based methods for analysing stability of unbalanced microgrids with grid-forming electronic power converters, Journal of Modern Power Systems and Clean Energy, vol. 11, no. 4, pp. 1269-1281, 2023.

This thesis has received funding from IQS and the “Community of Madrid Smart Microgrids Programme,” co-financed by the European Social Fund and the European Regional Development Fund (Ref. S2018/EMT-4366).