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Publications

Publications by João Peças Lopes

2012

Impact of Phase-shift Modulation on the Performance of a Single-stage Bidirectional Electric Vehicle Charger

Authors
Varajao, D; Araujo, RE; Moreira, C; Lopes, JP;

Publication
38TH ANNUAL CONFERENCE ON IEEE INDUSTRIAL ELECTRONICS SOCIETY (IECON 2012)

Abstract
The Smart Vehicle-to-Grid Project at INESC TEC is currently studying the application of matrix converters to implement an isolated bidirectional AC-DC power converter using a single power conversion stage to provide a high-frequency link between the grid and vehicle. The single-stage structure and bidirectional power flow make the matrix converter an attractive solution for the charging applications of electric vehicles. A very brief overview of the matrix converter and its modulation strategy is presented, followed by detailed analysis. The power conversion system performance is investigated in terms of the switching commutation, input filter and input power factor. Simulations and experimental results of a prototype are also presented to further validate the proposed topology and operating principle.

2009

Using Vehicle-to-Grid to Maximize the Integration of Intermittent Renewable Energy Resources in Islanded Electric Grids

Authors
Pecas Lopes, JAP; Rocha Almeida, PMR; Soares, FJ;

Publication
2009 INTERNATIONAL CONFERENCE ON CLEAN ELECTRICAL POWER (ICCEP 2009), VOLS 1 AND 2

Abstract
This paper presents the results of a dynamic behaviour analysis study developed with the objective of quantifying the amount of wind power that can he safely, integrated in an isolated electricity grid where Electric Vehicles (EVs) are present. The assessment was performed considering two distinct situations: a) when EVs are only, in charging mode and b) when EVs participate in primary frequency, control. The test system, a small island, contains, in addition to wind generation, a small amount of solar PV plants and four conventional diesel generators. Only wind power influence in system's frequency, was assessed since, from a dynamic perspective, this is the renewable resource whose high intermittency level might be more harmful for the electric system operation. Sudden wind variations were simulated and, for both situations, a) and b), the amount of Intermittent Renewable Energy Sources was maximized, keeping always the grid frequency, within the limits defined by: the power quality standards.

2007

MicroGrids dynamic security assessment

Authors
Moreira, CL; Pecas Lopes, JA;

Publication
2007 International Conference on Clean Electrical Power, ICCEP '07

Abstract
MicroGrids comprise low voltage distribution systems with distributed energy sources, storage devices and controllable loads, operated interconnected with the main power grid or autonomously, in a controlled coordinated way. Storage devices are absolutely essential for MicroGrid autonomous operation. However, depending on the operating conditions, their limited storage capacity is a major drawback and might compromise successful MicroGrid islanded operation. In this paper is proposed an index to evaluate MicroGrids security regarding an unplanned transition to islanded operation due to disturbances in the upstream Medium Voltage network. An Artificial Neural Network tool is proposed to forecast the security index for a credible range of operating scenarios. The usage of Artificial Neural Networks is emphasized due to its computational speed for on-line performance and its flexibility for providing corrective actions for insecure operating conditions in order to achieve a seamless transition from interconnected to islanded operation. © 2007 IEEE.

2009

Quantification of Technical Impacts and Environmental Benefits of Electric Vehicles Integration on Electricity Grids

Authors
Pecas Lopes, JAP; Soares, FJ; Rocha Almeida, PMR; Baptista, PC; Silva, CM; Farias, TL;

Publication
2009 8TH INTERNATIONAL SYMPOSIUM ON ADVANCED ELECTROMECHANICAL MOTION SYSTEMS (ELECTROMOTION 2009)

Abstract
In this paper a typical electricity distribution network for a residential area in Portugal is used in order to assess the impact of integrating different levels of pure electric vehicles and plug-in hybrid vehicles in the grid and in pollutants emissions. First, the amount of vehicles that can be safely accommodated in the grid will be determined. Second, changes in pollutants emissions will be evaluated, by applying a vehicle full life cycle analysis.

2010

A Monte Carlo method to evaluate electric vehicles impacts in distribution networks

Authors
Soares, FJ; Pecas Lopes, JA; Rocha Almeida, PM;

Publication
2010 IEEE Conference on Innovative Technologies for an Efficient and Reliable Electricity Supply, CITRES 2010

Abstract
This paper describes a statistical approach developed for assessing the impacts resulting from EV presence in a given electricity network was developed. The algorithm, developed for this purpose, is based on a Monte Carlo method and can be seen as a planning tool that allows obtaining average values for several system indexes, like buses voltages, branches loading and energy losses. Additionally, it also allows identifying the most critical operation scenarios and the network components that are subjected to more demanding conditions and that might need to be upgraded. The example of a small grid from one of the Azores islands, Flores Island, was used for illustration purposes and two scenarios of EV integration were considered: 25% and 50% of the current light vehicles fleet replaced by EV. ©2010 IEEE.

2009

Coordinated voltage support in distribution networks with distributed generation and microgrids

Authors
Madureira, AG; Pecas Lopes, JAP;

Publication
IET RENEWABLE POWER GENERATION

Abstract
This paper proposes a new methodology for coordinated voltage support in distribution networks with large integration of distributed generation and microgrids. Given the characteristics of the LV networks, it is shown that traditional control strategies using only reactive power control may not be sufficient in order to perform efficient voltage control. Therefore, microgeneration shedding must also be employed, especially in scenarios with extreme microgeneration penetration. An optimisation tool based on a meta-heuristic approach was developed to address the voltage control problem. In addition, neural networks were employed in order to decrease computational time, thus enabling the use of the tool for online operation. The results obtained revealed good performance of this control approach.

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