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Publications

Publications by João Peças Lopes

2011

On the micro-grid and multi micro-grid impact assessment: Cost and benefits evaluation: Towards the power system of the future: Active distribution networks

Authors
Vasiljevska, J; Pecas Lopes, JA;

Publication
CIGRE 2011 Bologna Symposium - The Electric Power System of the Future: Integrating Supergrids and Microgrids

Abstract
The implementation of innovative network solutions to allow for an increase of micro-generation and demand side integration are highly dependent on building scale and cost effective infrastructures, where sharing of responsibilities among different stakeholders is the basis for a proper implementation of an active distribution network concept. In order to integrate large amounts of small and micro-generation (µG) units that exploit different power sources (with high or no intermittency) together with controllable loads and storage devices it is necessary to develop flexible management and control solutions where responsibilities for the system operation are shared between Distribution System Operators (DSO), customers and Distributed Generation (DG) units according to a regulatory environment. The incentives provided to the different parties (stakeholders) may have a major impact on their decision to adopt Micro-grid and Multi Micro-grid concepts. Therefore, an identification of the benefits and costs associated with these concepts adoption is needed in order to recognize the real value of their deployment. Moreover, only by proper allocation of these costs and benefits, each stakeholder affected may receive the right incentive to opt for Micro-grid and Multi Micro-grid solutions. The DSO is interested in maximizing profits, by minimizing the capital and operational costs related to the distribution service (for instance, loss reduction and reinforcement costs) and at the same time achieving the performance goals imposed by the regulators [1]. Micro-generation developers make decision considering capital and operational expenditures, the connection costs, and use of system charges. Incomes from energy selling (which may include RES incentives) are the main goals (benefits) for the µG investors. Therefore, one of the priorities of regulators is to ensure that these benefits are perceived by µG developers. Finally, customers may be asked to share with the DSO the responsibility for an increased reliable system and for having the possibility to reduce their bills when exploiting the best market options offered by different traders. This paper presents a detailed identification and characterization of the different benefits and costs for each stakeholder involved. Some of these benefits can be identified and allocated directly to a certain stakeholder, while others need to be shared among a large group of players, involving the society in general (for example CO2 emissions reduction, job creation).

2011

Exploiting the potential of electric vehicles to improve operating conditions in islanded grids: Towards the power system of the future: Active distribution networks

Authors
Rocha Almeida, PM; Moreira, CL; Soares, F; Pecas Lopes, JA;

Publication
CIGRE 2011 Bologna Symposium - The Electric Power System of the Future: Integrating Supergrids and Microgrids

Abstract
From the studies developed so far, it is a general consensus that Electric Vehicles (EV), when properly managed, can provide many benefits to the grid operation. In the power systems of islands the potential benefits may be even larger. The case of S. Miguel Island, in the Azorean archipelago, may be one of such cases. This island achieves typically an annual peak power of 75 MW and a valley slightly higher than 30 MW. Currently, around 75% of its installed capacity is formed by fuel units, 22% by geothermal units and the rest by small hydro units. Yet, there are numerous unexplored endogenous resources in this place, especially geothermal and wind power, which cannot be used due to technical restrictions. Geothermal is limited by the valley load as the involved technology is not suited for load following, even with very small ramp rates. Wind power requires sufficient conventional spinning reserve to be safely integrated due to the variability of the wind resource. High EV integration, with an adequate charging management, would then increase base load allowing further geothermal and a reduced need for conventional spinning reserves. This paper evaluates the benefits of the presence of EV as controllable loads performing frequency control in a scenario with abundant wind resource availability, where a sudden loss of wind power production over a short period of time occurs. Ultimately, this work will show that S. Miguel power system would benefit from the presence of EV. A comparison with the conventional approach considering EV as regular loads will also be performed for benchmarking purposes.

2011

Inertial control in off-shore wind farms connected to AC networks through multi-terminal HVDC grids with VSC: The supergrid(s): HVDC and power electronics, HVDC Grids and hybrid AC/DC systems

Authors
Moreira, CL; Silva, B; Soares, FJ; Seca, L; Pecas Lopes, JA;

Publication
CIGRE 2011 Bologna Symposium - The Electric Power System of the Future: Integrating Supergrids and Microgrids

Abstract
The massive interconnection of offshore Wind Farms (WF) brings challenges for the operation of electric grids. The predicted amount of offshore wind power will lead to a smaller ratio of conventional units operating in the system. Thus, the power system will have less capability to provide fast dynamic regulation. Despite of offshore WF being able to inject power on the AC grid through High Voltage Direct Current (HVDC) convertors, they cannot participate on frequency support by the intrinsic decoupling that DC adoption brings. This paper proposes a control methodology, based on local controllers, to enable the participation of offshore WF in primary frequency control. Additionally, enhancements were made on the Wind Energy Converters (WEC) controller to make them capable of emulating inertial behaviour. Tests were performed in a multi-terminal DC network with two off shore wind farms to assess the feasibility and effectiveness of the concept in a communication-free framework.

2011

Hierarchical frequency control in multi-microgrids: The participation of electric vehicles

Authors
Gil, N; Issicaba, D; Rocha Almeida, PM; Pecas Lopes, JA;

Publication
CIGRE 2011 Bologna Symposium - The Electric Power System of the Future: Integrating Supergrids and Microgrids

Abstract
The operation and planning of Low Voltage (LV) and Medium Voltage (MV) distribution networks have been changing over the last decade. Due to the presence of Distributed Generation (DG) and microgeneration, an active role has been attributed to these networks in grid operation. For this accomplishment, different conceptual approaches were developed. In [1], a hierarchical control structure was defined, considering that DG units, onload tap changer transformers, static var compensators and loads can be controlled by a hierarchically higher entity, the Central Autonomous Management Unit (CAMC). The CAMC is also responsible for the management of specific LV networks, the MicroGrids (MG), which in turn have autonomy to manage their loads and microgeneration units through an entity called MicroGrid Central Controller (MGCC). A MV grid with these characteristics plus some storage devices would then be called a Multi-MicroGrid (MMG), being, among other functionalities, able to operate isolated from the upstream network. The recent appearance of a new type of load to the system, the Electric Vehicle (EV), expected to be largely integrated in the electricity grids in the upcoming years, has a great potential for adding controllability to the MMG. In this paper, an EV control droop (see [2]) will be introduced to improve the MMG performance when EVs operate as active elements. EV controllers are then able to receive setpoints from the CAMC and also actively update the droop settings in order to deal with different events that may occur on the MMG, for instance when moving from interconnected to islanded mode of operation. The performance of the MMG with controllable EV will be compared with a MMG without the participation of EV. Additionally, multiple philosophies for setting the droops will be tested, considering that EV may inject power into the grid as storage devices or just act as controllable loads. Simulation results were obtained exploiting a dynamic simulation platform developed using the EUROSTAG and MATLAB environments.

2006

Microgrids - Large scale integration of microgeneration to low voltage grids

Authors
Hatziargyriou, N; Jenkins, N; Strbac, G; Pecas Lopes, JA; Ruela, J; Engler, A; Oyarzabal, J; Kariniotakis, G; Amorim, A;

Publication
41st International Conference on Large High Voltage Electric Systems 2006, CIGRE 2006

Abstract
Microgrids comprise Low Voltage distribution systems with distributed energy sources, such as micro-turbines, fuel cells, PVs, etc., together with storage devices, i.e. flywheels, energy capacitors and batteries, and controllable loads, offering considerable control capabilities over the network operation. These systems are interconnected to the Medium Voltage Distribution network, but they can be also operated isolated from the main grid, in case of faults in the upstream network. From the customer point of view, Microgrids provide both thermal and electricity needs, and in addition enhance local reliability, reduce emissions, improve power quality by supporting voltage and reducing voltage dips, and potentially lower costs of energy supply. This paper outlines selected research findings of the EU funded MICROGRIDS project (Contract ENK-CT-2002-00610). These include: • Development and enhancement of Microsource controllers to support frequency and voltage based on droops. Application of software agents for secondary control. • Development of the Microgrid Central Controller (MGCC). Economic Scheduling functions have been developed and integrated in a software package able to simulate the capabilities of the MGCC to place bids to the market operator under various policies and to evaluate the resulting environmental benefits. • Analysis of the communication requirements of the Microgrids control architecture • Investigation of alternative market designs for trading energy and ancillary services within a Microgrid. Development of methods for the quantification of reliability and loss reduction. • Initial measurements from an actual LV installation.

2012

Impact of electric and plug-in hybrid vehicles on grid infrastructure - Results from the merge project

Authors
Hatziargyriou, N; Pecas Lopes, JA; Bower, ET; Strunz, K; Rivier, M; Lioliou, V; Wu, J; Papathanassiou, S; Karfopoulos, E; Gonzalez Bordagaray, A; Cabral, P; Llanos Lecum, C; Walsh, A; Kanellopoulos, K; Joyce, C; Hartmann, N; Willums, JO;

Publication
44th International Conference on Large High Voltage Electric Systems 2012

Abstract
This paper highlights findings of the European Commission funded project called MERGE (Mobile Energy Resources in Grids of Electricity). MERGE is a collaborative research project that includes utilities, regulators, commercial organisations and universities with interests in the power generation, automotive, electronic commerce and hybrid and electric vehicle sectors across the entire European Union (EU). This major two-year research initiative began in January 2010. The MERGE project mission is to evaluate the impacts that electric vehicles (EV) will have on the European Union (EU) electric power systems with regards to planning, operation and market functioning. The focus is placed on EV and SmartGrid/MicroGrid simultaneous deployment, together with renewable energy increase, leading to CO2 emission reduction through the identification of enabling technologies and advanced control approaches. In this paper indicative results from the impact of the additional EV load will have in the daily and yearly system load diagrams and in the operation of the transmission and distribution networks of five European countries (Greece, UK, Spain, Portugal, and Germany) in 2020 are presented. General conclusions are drawn.

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