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About

About

Diogo Varajão received the M.Sc. degree in Electrical and Computer Engineering from the Faculty of Engineering of the University of Porto (FEUP), Portugal, in 2012. Since then he has been a researcher at the Smart Grids and Electric Vehicles Laboratory of INESC-TEC where he work in research projects in partnership with industry. He is also working toward the Ph.D. degree with the development of a Single-stage Bidirectional and Isolated AC-DC Matrix Converter for Energy Storage Systems. An international patent application under the PCT has already been filled regarding the invented technology. His research interests include the application of matrix converters to increase the power density and efficiency of battery chargers for electric vehicles and energy storage.

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Topics
Details

Details

  • Name

    Diogo André Varajão
  • Cluster

    Power and Energy
  • Role

    External Research Collaborator
  • Since

    15th November 2011
Publications

2017

Control of an isolated single-phase bidirectional AC-DC matrix converter for V2G applications

Authors
Varajão, D; Araújo, RE; Miranda, LM; Lopes, JP; Weise, ND;

Publication
Electric Power Systems Research

Abstract
This paper describes a new current control method that enhances the dynamic performance of a single-phase bidirectional AC-DC battery charger to provide a high-frequency link between the grid and electric vehicle. The single-stage structure and the bidirectional power flow make the matrix converter an attractive solution for electric vehicle (EV) battery charging applications in the context of smart grids. The operating principles and modulation method are analyzed and discussed in detail. Furthermore, a current controller improved with a Smith predictor is proposed to decrease the phase delay in the measurement of the average current in the battery pack. The SP reduces the rise time to around a third and the settling time to half when compared with a PI controller. Simulations and experimental results from a laboratory prototype are shown to verify the feasibility of the proposed control scheme. © 2017 Elsevier B.V.

2017

Modulation Strategy for a Single-stage Bidirectional and Isolated AC-DC Matrix Converter for Energy Storage Systems

Authors
Varajao, D; Araujo, RE; Miranda, LM; Pecas Lopes, JAP;

Publication
IEEE Transactions on Industrial Electronics

Abstract
This paper presents a new modulation and control strategies for high-frequency link matrix converter. The proposed method aims to achieve controllable power factor in the grid interface as well voltage and current regulation for a battery energy storage device. The matrix converter is a key element of the system, since performs a direct AC to AC conversion between the grid and the power transformer, dispensing the traditional DC-link capacitors. Therefore, the circuit volume and weight are reduced and a longer service life is expected when compared with the existing technical solutions. A prototype was built to validate the mathematical analysis and the simulation results. Experimental tests developed in this research show the capability to control the grid currents in the synchronous reference frame in order to provide grid services. Simultaneously, the battery current is well regulated with small ripple which makes this converter ideal for battery charging of electric vehicles and energy storage applications. IEEE

2016

Power Transformer for a Single-stage Bidirectional and Isolated AC-DC Matrix Converter for Energy Storage Systems

Authors
Varajao, D; Miranda, LM; Araujo, RE; Pecas Lopes, JP;

Publication
PROCEEDINGS OF THE IECON 2016 - 42ND ANNUAL CONFERENCE OF THE IEEE INDUSTRIAL ELECTRONICS SOCIETY

Abstract
This paper presents an approach to design the transformer and the link inductor for the high-frequency link matrix converter. The proposed method aims to systematize the design process of the HF-link using analytic and software tools. The models for the characterization of the core and winding losses have been reviewed. Considerations about the practical implementation and construction of the magnetic devices are also provided. The software receives the inputs from the mathematical analysis and runs the optimization to find the best design. A 10 kW / 20 kHz transformer plus a link inductor are designed using this strategy achieving a combined efficiency of 99.32%.

2014

Towards a new technological solution for Community Energy Storage

Authors
Varajao, D; Miranda, LM; Araujo, RE;

Publication
2014 16TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'14-ECCE EUROPE)

Abstract
Energy storage in low voltage grid is receiving increased attention due to renewables integration and consumption growth, challenges faced nowadays by grid operators. In this work, a study of main implementation issues for community energy storage (CES) is presented along with a comparison between possible solutions for the bidirectional isolated power conversion system (PCS) to interface a battery pack with the electric power grid. The aim of this research is to increase the power density of the power converter and keeping simultaneously the same reliability of traditional solutions. These goals are pursued to be achieved through the reduction of the conversion stages and utilization of new optimization methodologies to reduce the volume of the passive components. The proposed topology for the PCS is based on a matrix converter (MC) that performs a direct AC to AC conversion between the grid and a high-frequency transformer (HFT). With this solution it is possible to eliminate the traditional DC-link capacitor and obtain a single-stage power conversion with bidirectional power flow capability. This proposed solution is evaluated and compared with a conventional two-stage topology through extensive simulation. Two prototypes systems were designed for a 10kW PCS to connect the three-phase 230/400Vrms, 50Hz mains to a battery pack with voltage range of 320V to 490V. Simulation results are presented to assess the power quality provided by the front-end and the battery side converters, as well as performance evaluation and efficiency analysis.

2013

Microgrid Service Restoration The Role of Plugged-In Electric Vehicles

Authors
Gouveia, C; Moreira, CL; Pecas Lopes, JAP; Varajao, D; Araujo, RE;

Publication
IEEE INDUSTRIAL ELECTRONICS MAGAZINE

Abstract
The development of the microgrid (MG) concept endows distribution networks with increased reliability and resilience and offers an adequate management and control solution for massive deployment of microgeneration and electric vehicles (EVs). Within an MG, local generation can be exploited to launch a local restoration procedure following a blackout. EVs are flexible resources that can also be actively included in the restoration procedure, thus contributing to the improvement of MG operating conditions. The feasibility of MG service restoration, including the active participation of EVs, is demonstrated in this article through extensive numerical simulation and experimentation in a laboratorial setup. © 2007-2011 IEEE.