Julio C. Teixeira

Separating Components of the Hysteresis Loss of Non-Oriented Electrical Steels

This paper shows that the separation of quasi-static hysteresis losses into two components, one related to Low Induction and other to High Induction levels. The separation line between those two regions has been arbitrarily chosen as the induction at maximum permeability. Results show that the grain size has stronger effect on the low induction component, while the high induction component is more sensitive to sample measuring direction. This may provide basis for better materialsproperties correlation modeling and product development.

Optimal Allocation of Capacitor Banks using Genetic Algorithm and Sensitivity Analysis

This paper presents a methodology for allocation of Bank of Capacitor (BC), based on the genetic algorithm (GA) and in the use of Sensitivity Analysis (SA). The AS is used to evaluate the candidate solutions directly instead of using a Optimal Power Flow (OPF), which is an iterative method. The proposed methodology was applied on three distribution systems, containing 34, 70 bus, respectively. Scenarios were analyzed for the insertion of two units of BC in each system. The proposed methodology AG - AS was compared with exhaustive methodology, solved by only OPF method and the gain in computational processing time is showed. As a main result, it was obtained the best locations for placement of BC units considering the minimization of real power losses, and consequently an improvement in the voltage levels in the buses of the system.

Methodology for grid current unbalance compensation appling DFIG as a parallel active filter

This paper presents a new control strategy for the DFIG working under grid voltage unbalance, intending not only the ideal machine operation, but also to compensate the current unbalance in the point of common coupling (PCC). Models that allow the DFIG to inject negative sequence current in the grid to compensate unbalances in the PCC have been already proposed, but they are limited by the residual power of the Grid Side Converter (GSC) or by the oscillations in the electromagnetic torque when the Rotor Side Converter (RSC) control is used. To overcome these limitations, this paper proposes a control that not only injects negative sequence current by the machine stator but also sets the stator negative sequence voltage, reducing the oscillations in the electromagnetic torque. A third converter is coupled to the machine terminals to allow the stator voltage control. Therefore, the use of the proposed control reaches two objectives simultaneously, the support to the grid power quality, and the ideal operation of the machine.

Method for adaptive overcurrent protection of distribution systems with Distributed synchronous Generators

The increase of Distributed Generators (DG) has encouraged the operation of these generators in islanded mode or intentional islanding. Such operation mode can increase the system reliability, once in the event of network failure the supply of critical consumers will be maintained by the DGs. However, it is necessary to consider that the fault current is considerably reduced when the system is in intentional islanding, and the overcurrent protection setting must be adapted in order to take into account the new fault current level. This paper proposes the use of adaptive protection to change the overcurrent protection setting based on the identification of the system operating state. The system operating state is identified by the use of an active measurement technique, which identifies its operating condition by the impedance level of the grid. Simulation results show that the proposed scheme can be used to update the protection settings for the islanded operation condition.

Methodology for grid voltage unbalance compensation appling a two-converter series DFIG topology

This paper presents a new control strategy for the DFIG replacing the conventional Grid Side Converter for a series one, namely series grid side converter (SGSC). The control strategy for operation under grid voltage unbalance intends not only the ideal machine operation, but also to attenuate the grid voltage unbalance. This compensation is performed injecting unbalanced currents in the point of common coupling (PCC). The SGSC promotes a higher operational capacity during grid disturbances as voltage unbalances. The proposed methodology uses the machine electromagnetic power equation decomposed by the symmetrical components to obtain a relationship between the rotor negative sequence current and the stator negative sequence voltage, where the oscillating components of the electromagnetic power are zero. Appling this relationship is possible to reduce the electromagnetic torque oscillations when injecting negative sequence current by the machine stator.

3D cross coupling effect for flux control in magnetic circuit with permanent magnet

Permanent magnet synchronous motors are used in several industrial applications. A flux control is necessary for some applications such as in wide speed range electrical vehicles. This paper presents theoretical and experimental results that show the possibility of using the 3D cross coupling effect in electrical steel to control the flux in the machine air gap. A simple experimental device was constructed and a 34 percent of flux variation has been attained.

A Simple Device for Measuring Losses in Soft Magnetic Materials

The aim of this work is the development of an electronic device for the rapid characterization of soft ferromagnetic materials for electrical purposes named single sheet tester (sst). The basis of this study consists in determining the magnetic induction, B and the magnetic field, H, by using a simplified circuit. Results are compared with classical epstein test and the obtained losses present an error less than 10%.