Claudionor F. Nascimento

A teaching method applied in the power electronics laboratory

The use of power electronics-based equipment has been steadily increasing in industrial and consumer applications, leading professional training in the field to be increasingly predicated on economic growth, and resulting in the motivation of electrical engineering students which choose this discipline. This paper presents a teaching and problem-based learning experience in power electronics, as well as a proposal and experimental project developed by student groups.

Analysis of Noncharacteristic Harmonics Generated by Voltage-Source Converters Operating Under Unbalanced Voltage

This paper deals with an analytical model to evaluate the noncharacteristic harmonics that are generated by three-phase three-wire voltage-source converters (VSCs) operating under unbalanced sinusoidal voltage conditions. This model permits the calculation of the oscillating current on the VSC dc side by considering the unbalanced voltages on its ac side. It can be used to prove that the use of dc voltage control techniques to eliminate VSC dc-side double frequency voltage ripple necessarily creates three-phase currents with undesirable low-frequency harmonic components on the VSC ac side. In this paper, the attention is directed to the instantaneous oscillating real power component at twice the line frequency, rather than to other power components. The noncharacteristic current components analyzed in this paper, such as the fundamental negative sequence and third-order harmonic components of positive and negative sequences are calculated using the proposed model in time-domain simulations. A simple model to calculate the dc-side capacitor to mitigate these noncharacteristic harmonic problems is presented.

Non-characteristic harmonics and DC side capacitor calculation in VSC connected to a distribution system with unbalanced voltage

This paper presents a model of typical three-phase, three-wire and two-level PWM controlled voltage-source converters (VSC) suitable to investigate the non-characteristic harmonic generation at dc- and ac-side of the converter under sinusoidal unbalanced voltage condition, e.g., third order current harmonic component of positive-sequence in the VSC ac-side current. The proposed model, based on instantaneous power as well as switching functions concepts, permits to evaluate the oscillating voltage that appears on the VSC dc-side. The effect of the negative-sequence voltage component is considered on the dc capacitance calculation which consequently enables to size the dc capacitor accurately in order to keep the dc voltage ripple under pre-defined limits. The model also shows the exact dc-side voltage ripple due to the VSC ac-side negative-sequence voltage component. The dc capacitor size and the non-characteristic harmonics obtained based on the proposed model are assessed using time-domain simulation in the PSCAD program.

Evaluating Harmonic Voltage in Electric Distribution Systems due to Six-Pulse Static Power Converter

The circulation of harmonic currents in power systems, caused by particular nonlinear loads, leads to harmonic voltages which depend on the circuit and on the load it drives. Harmonic currents in the system also contribute with a portion of the system technical losses and produce a series of undesirable effects. This paper presents an alternative approach based on an efficient harmonic load flow algorithm in order to evaluate harmonic voltages along distribution systems due to nonlinear loads, more specifically a six-pulse static power converter. The proposed methodology uses frequency-domain formulations which allow dealing directly with voltage and current phasors. Tests were carried out on 04 and 34 bus distribution systems in order to evaluate the proposed technique performance.

Artificial neural networks applied to single-phase load harmonic characterization

In this paper, an alternative method based on artificial neural networks is presented for the determination of load current harmonic components in a single-phase electric power system. The first six harmonic components are calculated from current waveforms of an AC controller and a single-phase diode bridge rectifier, which are the most common loads in industrial, commercial and residential applications. The influences of such nonlinear loads in power quality issues are also characterized. The proposed method is compared with truncated FFT. Simulation and experimental results are presented in order to validate the proposed approach.

Diagnosability of Hybrid Systems

Modern industrial systems combine discrete and continuous behaviors and thus are hybrid systems (HSs). In this brief, we introduce a new definition of diagnosability of HSs called

Allocation of Static Var Compensator in Electric Power Systems Considering Different Load Levels

h

Analysis of non-characteristic harmonics generated by voltage-source converters operating under unbalanced voltage

-diagnosability, and we present a method to verify this property. The method is based on a verifier automaton that can be constructed in polynomial time, leading to a smaller computational complexity for the verification of the diagnosability of HS than methods using diagnoser automata. The main idea is to build a verifier of the underlying discrete-event system, taking into account the distinguishability of the system modes based on the continuous state models of the HS.