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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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Publications

2020

Driving GaN HEMT high-voltage half-bridge with a single-channel non-isolated gate driver with truly differential inputs

Authors
Varajao, D; Ferianz, T; Zhang, VC; Matrisciano, CM;

Publication
PCIM Europe Conference Proceedings

Abstract
This paper describes the functional principle of a non-isolated gate driver with truly differential inputs (TDI) and the benefits of its application in GaN HEMT high-voltage resonant half-bridge DC-DC converters (LLC). This innovative gate driver is able to overcome the driving issues associated with DC ground-shift or AC noise between controller and driver IC ground potentials, enabling its application even in high-side driving as a replacement of isolated gate drivers. Test results obtained in a GaN HEMT based 600 W/400 V/300 kHz half-bridge resonant converter are provided. © VDE VERLAG GMBH · Berlin · Offenbach.

2020

High density cascaded zvs switched capacitor converter for 48-v data-center application

Authors
Rainer, C; Rizzolatti, R; Varajao, D;

Publication
PCIM Europe Conference Proceedings

Abstract
This paper presents a new intermediate bus converter topology based on a zero voltage switching switched capacitor circuit including a novel non-isolated gate driver ICs enabling high power density in 48-V data center applications. The proposed topology inherently ensure zero voltage switching operation enabling high switching frequency keeping high efficiency. The novel non-isolated driver IC, with truly differential input, works also as floating high side driver, which lead to a driver circuit footprint reduction by 75% compared to an equivalent dual isolated driver IC. Experimental results show the effectiveness of the proposed approach, the prototype achieves 3060 W=in3 power density and a peak efficiency of 97.13% at 48-V input voltage including auxiliary losses. © VDE VERLAG GMBH · Berlin · Offenbach.

2018

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

2018

EMI Filter Design for a Single-stage Bidirectional and Isolated AC–DC Matrix Converter

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

Publication
Electronics

Abstract
This paper describes the design of an electromagnetic interference (EMI) filter for the high-frequency link matrix converter (HFLMC). The proposed method aims to systematize the design process for pre-compliance with CISPR 11 Class B standard in the frequency range 150 kHz to 30 MHz. This approach can be extended to other current source converters which allows time-savings during the project of the filter. Conducted emissions are estimated through extended simulation and take into account the effect of the measurement apparatus. Differential-mode (DM) and common-mode (CM) filtering stages are projected separately and then integrated in a synergistic way in a single PCB to reduce volume and weight. A prototype of the filter was constructed and tested in the laboratory. Experimental results with the characterization of the insertion losses following the CISPR 17 standard are provided. The attenuation capability of the filter was demonstrated in the final part of the paper.

2017

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

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