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About

About

Nayara Brandão de Freitas received the M.S. and D.Sc. degrees in Power Electronics Engineering, Electrical Engineering, in 2016 and 2020, respectively, from the Federal University of Campina Grande (UFCG), Campina Grande, Brazil. She received a B.S. in Automation and Control Engineering, Electrical Engineering, from UFCG in 2015. As an undergraduate student, she was a member of the Tutorial Education Program of the UFCG Bachelor’s in Electrical Engineering Program from 2010 to 2012. In 2013, she was an exchange student at Purdue University, US, with the sponsorship of the Science without Borders Program. From 2014 to 2015, she received scholarships from the Institutional Scientific Initiation Scholarship Program (PIBIC). Nayara received the Professor Mário Toyotaro Hattori Award, granted to the students with the best academic performance within the UFCG Electrical Engineering and Computer Science departments who graduated in the class of 2015.1. During the M.S. and D.Sc. studies, Nayara was sponsored by the Brazilian National Council for Scientific and Technological Development (CNPq). From December 2018 to November 2019, she was a Visiting Scholar at the Center for Power Electronics Systems, Virginia Tech, US. From April 2020 to May 2021, she was a Postdoctoral Researcher at UFCG. Since June 2021, Nayara has been a Researcher at the Center for Power and Energy Systems, Institute for Systems and Computer Engineering, Technology and Science (INESC TEC), Portugal. Her current research interests include power electronics for Renewable Energy Systems (RESs) integration. She is a member of the Industry Applications Society (IAS) e Power Electronics Society (PELS) of the Institute of Electrical and Electronics Engineers (IEEE). She graduated from the IEEE Volunteer Leadership Training Program (VoLT) in 2018. She co-founded and was the first chair of the UFCG PELS/IAS Student Branch Chapter from January 2017 to March 2018. She was PELS Student Membership Chair from September 2018 to October 2020. Nayara is currently a member of the PELS Students and Young Professionals Committee and the PELS Women in Engineering (WIE) Committee.

Interest
Topics
Details

Details

  • Name

    Nayara Brandão de Freitas
  • Cluster

    Power and Energy
  • Role

    Assistant Researcher
  • Since

    22nd June 2021
Publications

2021

Grid-Connected Induction Motor Using a Floating DC-Link Converter Under Unbalanced Voltage Sag

Authors
Cunha, MF; Jacobina, CB; de Freitas, NB;

Publication
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS

Abstract
This article proposes a series compensator with unbalanced voltage sag ride-through capability applied to grid-connected induction motors. A conventional three-phase voltage source inverter (VSI) is intended to regulate the motor voltages. The VSI is connected in series with the grid and a three-phase machine with open-ended windings. The proposed system is suitable for applications in which no frequency variation is required, like large pumps or fans. The VSI dc-link voltage operates as a floating capacitor through the energy minimized compensation (EMC) technique, in which there is no dc source or injection transformer. The motor load condition determines the minimum grid voltage positive component (sag severity) to keep EMC operation. Meanwhile, a voltage unbalance may increase the dc-link voltage requirements. A 1.5-hp four-pole induction motor has been used to verify the ride-through capability of the proposed compensator under grid voltage disturbances. A total harmonic distortion (THD) analysis of grid currents demonstrates that the proposed system provides low THD even if no passive filter is used. The operating principle, converter output voltage analysis, pulsewidth modulation technique, control strategy, and components ratings are discussed as well. Simulation and experimental results are presented to demonstrate the feasibility of the system.

2021

Single-Phase Three-Wire Power Converters Based on Two-Level and Three-Level Legs Using a Space-Vector PWM-Based Voltage Balancing

Authors
Gehrke, BS; Jacobina, CB; de Sousa, RPR; da Silva, IRFMP; de Freitas, NB; Correa, MBD;

Publication
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS

Abstract
This article proposes four converters for interfacing a single dc power source and loads of a single-phase three-wire system. The topologies of the proposed converters are based on two-level (2L) and three-level neutral point clamped (NPC) legs. For regulating the dc-link capacitors of the NPC-based converters, a dc-link voltage-balancing technique is proposed to balance the neutral-point voltage using the space-vector pulsewidth modulation, considering the harmonic distortion of the output voltages and the semiconductor losses from an algorithm that defines the vector sequences to be applied. These characteristics make the proposed converters suitable for applications in microgrid employing dc distributed energy resources or ac power supply by adding ac-dc stage. The proposed converters are compared to a conventional 2 L converter from simulated results for evaluating the semiconductor losses in balanced and unbalanced load scenarios. Experimental results are presented to verify the effectiveness of the proposed voltage-balancing technique and to validate the converters.

2020

Multilevel Single-Phase Converter With Two DC Links

Authors
de Freitas, NB; Jacobina, CB; Cunha, MF;

Publication
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS

Abstract
In this article, a multilevel single-phase converter is proposed and investigated. Its structure is based on cascaded-transformer systems, which are very interesting in applications in which a single dc source is available. The features of well-known multilevel cascaded H-bridge and transformer-based solutions are integrated into the proposed converter. As a result, the number of synthesized voltage levels can be optimized without excessively increasing the number of transformers. The basic configuration has six two-level insulated-gate bipolar transistor legs, two injection transformers, and two dc links (the lowest voltage dc link may be a floating capacitor or be connected to a small dc power source). The configuration is generalized and the calculation of the transformer's turns ratios as well as the dc-link voltages to maximize the number of voltage levels is provided. The proposed configuration is compared with cascaded H-bridge and a single-phase shared leg converter, which are also cascaded by means of transformers. Compared with the conventional converters, the proposed one has lower switching losses and higher conduction losses. Thus, the proposed configuration is more interesting in terms of semiconductor losses for high-voltage and low-current applications. Experimental and simulation results are shown to demonstrate the feasibility of the system.

2020

Two Novel Open-End Winding Multilevel Unidirectional Six-Phase Rectifiers With Reduced Switch Count

Authors
da Silva, I; Jacobina, CB; de Freitas, IS; Sousa, RPR; Maia, ACN; de Freitas, NB;

Publication
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS

Abstract
In this article, two new unidirectional multilevel six-phase power rectifier topologies are proposed and investigated. Such topologies may be applied to ac-dc systems such as wind energy conversions systems, aerospace generator drives, telecommunications or any other application where regenerative operation is either not required or prohibited. The first topology is composed of two three-level neutral-point-clamped (NPC) converters connected to the open-end windings of a six-phase permanent magnet synchronous generator, and a three-phase noncontrolled diode bridge converter. The second topology is composed of three modified NPC converters with the substitution of two controlled switches by diodes in each leg. The use of a noncontrolled converter with diodes aims to reduce the controlled switches count, the system complexity, and the costs. However, it makes both systems nonreversible. The system models, operating principles, the space vector pulsewidth modulation strategies, the dc-links balance, and the control system to ensure the elimination of the zero-crossover distortion caused by the use of the diodes are presented. Due to the high number of levels generated, the systems are suitable for high power applications with voltage and current ratings restrictions. A study concerning harmonic distortion and semiconductor losses for both systems is performed, in order to be compared with a standard configuration. The feasibility of the system is demonstrated by simulation and experimental results.

2020

Capacitor Voltage Balancing for Single-Phase Asymmetric Cascaded H-Bridge Inverters

Authors
Monteiro, AP; Jacobina, CB; Mello, JPRA; de Freitas, NB; Matias, RR;

Publication
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS

Abstract
This article presents an analysis of conventional single-phase cascaded H-bridge multilevel inverters composed of two and three cells. The dc-link can be a dc source or a floating capacitor. Two methods are given to regulate the floating capacitor voltage. In this way, according to the capacitor voltage balancing method used, operating regions and power distribution on the floating capacitor are presented for different dc-link voltage ratios and several ranges of modulation index and load power factor. A mathematical analysis is done in order to demonstrate the influence of the modulation index and load power factor over the power distribution. Finally, simulation and experimental results are provided to validate the theoretical considerations.