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Publications

Publications by CPES

2019

Grid-forming inverters replacing Diesel generators in small-scale islanded power systems

Authors
Beires, PP; Moreira, CL; Lopes, JP;

Publication
2019 IEEE MILAN POWERTECH

Abstract
This paper addresses the stability analysis of a real island power system following the transformation occurring in the generation portfolio: from a 100 % synchronous-generation-based system (associated to a fleet of diesel generators) to a hybrid power system dominated by power electronics converters. The integration of a battery-wind-photovoltaic power plant in the island creates the necessary conditions for operating the system without synchronous units scenarios with a system dominated by power electronics - or, at least to minimize its use - scenarios with a reduced number of synchronous units in operation. The possibility of operating the system under these conditions is assured by grid-forming inverters connected to battery energy storage systems, that are responsible for performing frequency and voltage control tasks either in parallel with synchronous units or when synchronous units are disconnected. The resulting transient stability issues for the aforementioned operational scenarios are discussed and evaluated through dynamic simulations.

2019

Smart Transformers - Enabling Power-Frequency Regulation Services for Hybrid AC/DC Networks

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

Publication
2019 IEEE MILAN POWERTECH

Abstract
The progressive decommissioning of large synchronous generators that should take place in face of increasing penetration ratios of Distributed Generation (DG) will demand additional control mechanisms for inertia provision and frequency and voltage regulation in the power system. The need to cope with increasing penetration ratios of DG in distribution grids, added to the necessity to integrate an expected massification of EV and distributed ESS, and to the necessity to enhance Power System resilience and controllability, makes the Smart-Transformer (ST) a suitable solution. In this paper it is demonstrated the feasibility of the ST to contribute to frequency control through the control of the resources available in the distribution AC/DC hybrid networks created from the ST. The feasibility of local droop controllers, acting on frequency and voltage magnitude of the AC/DC hybrid networks created from the ST, to achieve the aforementioned goal, is demonstrated through computational simulation.

2019

Grid-Forming Inverters Sizing in Islanded Power Systems- A stability perspective

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

Publication
SEST 2019 - 2nd International Conference on Smart Energy Systems and Technologies

Abstract
The large scale integration of inverter-based renewable generation in isolated power systems is posing stability concerns as a result of the displacement of the conventional synchronous machines (SM). In this sense, the integration of battery energy storage systems (BESS) connected to the grid through power converters operating as grid-forming units is mandatory in order to ensure system stability. Therefore, this paper aims to perform a dynamic stability analysis of an isolated power system regarding the installation of a BESS, where it is intended to determine the minimum required grid-forming power capacity of the associated power converter that guarantees system stability under several operational scenarios. Moreover, the expected interactions between the grid-forming inverter and the conventional SM are also addressed. © 2019 IEEE.

2019

On the development of a framework for the advanced monitoring of LV grids

Authors
Kotsalos, K; Marques, L; Sampaio, G; Pereira, J; Gouveia, C; Teixeira, H; Fernandes, R; Campos, F;

Publication
2019 2ND INTERNATIONAL CONFERENCE ON SMART ENERGY SYSTEMS AND TECHNOLOGIES (SEST 2019)

Abstract
This paper aims to describe the main outcomes of the ADMS4LV project which stands for Advanced Distribution Management System for Active Management of LV Grids. ADMS4LV targets the development and demonstration of a framework with adequate tools to optimize the management and operation of Low Voltage (LV) networks towards the effective implementation of Smart Grids. This work details the main functionalities of ADMS4LV and discusses their implementation. The validation of the functionalities is presented from demonstrations in a laboratorial setup, namely regarding the algorithms which using advanced data analytics, accomplish to operate LV networks with low observability, (i.e., with few real-time measurements) and without having full knowledge of the networks' technical characteristics, such as the consumers' phase connection to the grid. The assessment of the results shows the adequacy of the ADMS4LV solutions for deployment in distribution networks with current infrastructures, differing unnecessary investments in sensory devices. © 2019 IEEE.

2019

Optimal Prosumer Scheduling in Transactive Energy Networks Based on Energy Value Signals

Authors
Lotfi, M; Monteiro, C; Javadi, MS; Shafie khah, M; Catalao, JPS;

Publication
2019 2ND INTERNATIONAL CONFERENCE ON SMART ENERGY SYSTEMS AND TECHNOLOGIES (SEST 2019)

Abstract
We present a novel fully distributed strategy for joint scheduling of consumption and trading within transactive energy networks. The aim is maximizing social welfare, which itself is redefined and adapted for peer-to-peer prosumer-based markets. In the proposed scheme, hourly energy values are calculated to coordinate the joint scheduling of consumption and trading, taking into consideration both preferences and needs of all network participants. Electricity market prices are scaled locally based on hourly energy values of each prosumer. This creates a system where energy consumption and trading are coordinated based on the value of energy use throughout the day, rather than only the market price. For each prosumer, scheduling is done by allocating load (consumption) and supply (trading) blocks, maximizing the energy value globally and locally within the network. The proposed strategy was tested using a case study of typical residential prosumers. It was shown that the proposed model could provide potential benefits for both prosumers and the grid, albeit with a user-centered, fully distributed management model which relies solely on local scheduling in transactive energy networks. © 2019 IEEE.

2019

Energy performance of buildings with on-site energy generation and storage - An integrated assessment using dynamic simulation

Authors
Bot, K; Ramos, NMM; Almeida, RMSF; Pereira, PF; Monteiro, C;

Publication
JOURNAL OF BUILDING ENGINEERING

Abstract
The European Union aims to achieve a nearly zero energy balance in buildings by 2020. The present study takes into consideration the passive systems of the building, energy demand, and energy generated by the on-site photovoltaic and storage system, and how they interact in different scenarios. The study also considers the energy demand from the grid and the surplus of renewable energy. The software EnergyPlus was used and the parametric sensitivity simulation method was applied, taking into account blinds operation, ventilation strategies, HVAC operation schemes and battery storage capacity, in 96 scenarios. The results highlight that there is great variability between the considered scenarios, highlighting the importance of sizing methodologies for the passive systems and the use of optimized home management algorithms. It was found that the use of batteries with higher storage capacity increases the demand-supply from the on-site PV energy but decreases the amount of energy injected into the grid. The design of the PV and battery system based on yearly integrated simulations allows for an optimized solution. This study also emphasizes the importance of knowing the expected occupancy during the design phase, as a significant input to the sizing methodologies of the storage capacity and on-site generation.

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