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Publications

Publications by CPES

2021

Agent-based models in power systems-a literature review

Authors
Dos Santos, AF; Saraiva, JT;

Publication
U.Porto Journal of Engineering

Abstract
In the last two decades, power systems have experienced several changes, mainly related to organizational and operational restructuring. The appearance of new actors contributes to developing new business models and modifies its traditional operation activities. As a direct result, there is a need for new control solutions and strategies to integrate these different players. Agent-Based Models (ABM) have been increasingly used to model complex systems since they are especially suited to model systems influenced by social interactions between flexible, autonomous, and proactive agents. This paper provides a review of the literature regarding ABM in power systems followed by an analysis in more detail regarding specific applications that are becoming relevant in this new paradigm.

2021

A techno-economic analysis of floating photovoltaic systems, for southern european countries

Authors
Baptista J.; Vargas P.; Ferreira J.R.;

Publication
Renewable Energy and Power Quality Journal

Abstract
In the last few decades, the vast majority of world states have faced increased energy consumption using more environmentally friendly production technologies. The use of traditional renewable energies like hydro, wind and solar has been the solution found. Despite this, new technical solutions and strategies are beginning to emerge, of which Floating Solar Photovoltaic (FSPV) systems are part. In this framework, southern European countries have excellent climate conditions for reinforcing the use of solar energy. This research assess the existing Portuguese potential for floating PV systems and its integration in the power grid. A floating solar power plant of 1MW in Gouvães dam included in the Tâmega hydroelectric complex, under construction in northern Portugal was sizing and evaluated its energy potential. A techno-economic feasibility study was also carried out taking into account the current investment costs and energy tariffs in the Iberian liberalized market. This integrated analysis allowed to obtain important results on the current state of the art, types of technologies available, their costs and the payback period for this type of projects.

2021

Influence of Load Dynamics on Converter-Dominated Isolated Power Systems

Authors
Gouveia, J; Moreira, CL; Lopes, JAP;

Publication
APPLIED SCIENCES-BASEL

Abstract
The operation of isolated power systems with 100% converter-based generation requires the integration of battery energy storage systems (BESS) using grid-forming-type power converters. Under these operating conditions, load dynamics influences the network frequency and voltage following large voltage disturbances. In this sense, the inclusion of induction motor (IM) load models is required to be properly considered in BESS power converter sizing. Thus, this paper presents an extensive sensitivity analysis, demonstrating how load modeling affects the BESS power converter capacity when adopting conventional control strategies while aiming to assure the successful recovery of all IM loads following a network fault. Furthermore, this work highlights that generators with converter interfaces can actively contribute to mitigate the negative impacts resulting from IM loads following a network fault. Thereby, two distinct control strategies are proposed to be integrated in the power electronic interfaces of the available converter-based generators: one to be adopted in grid-following converters and another one suitable for grid-forming converters. The proposed control strategies provide an important contribution to consolidating insular grid codes, aiming to achieve operational scenarios accommodating 100% penetration of converter-based generation with a significative percentage of the IM load composition without resorting to a significative increase in BESS power converter sizing.

2021

Rule-based adaptive control strategy for grid-forming inverters in islanded power systems for improving frequency stability

Authors
Gouveia, J; Moreira, CL; Lopes, JAP;

Publication
ELECTRIC POWER SYSTEMS RESEARCH

Abstract
Operating isolated power systems with increasing shares of renewable energy sources requires the integration of battery energy storage systems in order to assure enhanced frequency regulation capabilities. The control mode of power converters interfacing battery energy storage systems to the grid can be based on grid-forming type structures given its superior performance with respect to the mitigation of network frequency disturbances. Nevertheless, in case of network faults, the interactions between existing synchronous units and the grid-forming type converters may adversely affect the global system behavior. Therefore, this paper addresses the study-case of a MW-scale isolated power system with large shares of converter-interfaced renewable generation, operating with both synchronous machines and a grid-forming type power converter. An optimal grid-forming control parameter tuning procedure considering different disturbances is presented, aiming to reduce the associated battery energy storage system power regulating effort following the disturbances. Moreover, it is proposed and discussed the need of a novel rule-based adaptive control solution to switch between different sets of control parameters used in grid-forming type converters depending on the network status following a fault-type disturbance. Extensive numerical simulations performed over different operating scenarios illustrate the performance of the proposed solution.

2021

Hydrogen and the transition from gas networks to a new energy carrier paradigm: Portuguese challenges of the national roadmap

Authors
Santos, BH; Peças Lopes, JA;

Publication
U.Porto Journal of Engineering

Abstract
Portugal has developed a national roadmap for hydrogen deployment as a key element of the Portuguese energy transition towards carbon neutrality, with a major contribution towards the electrification of society, generating synergies between the electric and gas systems. Considering the government goals for hydrogen injection within natural gas infrastructures for 2025 and 2030, as long as the indicative trajectories for 2040 and 2050, the authors used the natural gas forecast of the security of supply official report in order to obtain the hydrogen demand and power plant capacity, evaluating the system effort to meet public policy goals. Several alternative scenarios were developed for sensitive analysis, in order to assess the different strategies of hydrogen deployment, considering production from an electrolyzer. Regarding the current Portuguese situation and every scenario outcome, the authors stated that major efforts must be undertaken in order to develop full-scale hydrogen projects in order to meet the national goals.

2021

Fault-Ride-Through Approach for Grid-Tied Smart Transformers without Local Energy Storage

Authors
Rodrigues, J; Moreira, C; Lopes, JP;

Publication
ENERGIES

Abstract
The Smart Transformer (ST) is being envisioned as the possible backbone of future distribution grids given the enhanced controllability it provides. Moreover, the ST offers DC-link connectivity, making it an attractive solution for the deployment of hybrid AC/DC distribution grids which offer important advantages for the deployment of Renewable Energy Sources, Energy Storage Systems (ESSs) and Electric Vehicles. However, compared to traditional low-frequency magnetic transformers, the ST is inherently more vulnerable to fault disturbances which may force the ST to disconnect in order to protect its power electronic converters, posing important challenges to the hybrid AC/DC grid connected to it. This paper proposes a Fault-Ride-Through (FRT) strategy suited for grid-tied ST with no locally available ESS, which exploits a dump-load and the sensitivity of the hybrid AC/DC distribution grid's power to voltage and frequency to provide enhanced control to the ST in order to handle AC-side voltage sags. The proposed FRT strategy can exploit all the hybrid AC/DC distribution grid (including the MV DC sub-network) and existing controllable DER resources, providing FRT against balanced and unbalanced faults in the upstream AC grid. The proposed strategy is demonstrated in this paper through computational simulation.

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