Showing papers by "V. Fernao Pires published in 2011"

Power quality disturbances classification using the 3-D space representation and PCA based neuro-fuzzy approach

Abstract: In this paper a new approach for power quality (PQ) event detection and classification is proposed. This approach is based on an automatic four step algorithm. First the acquired voltage signals are represented in a 3-D space referential. Then principal component analysis is performed. In the third, features are extracted from the obtained eigenvalues of each disturbance waveforms. Finally a neuro-fuzzy based classifier automatically classifies the PQ disturbances. To show the effectiveness of the proposed method several case studies are presented. From the obtained results it is possible to confirm that the proposed approach can effectively classify different PQ disturbances.

Self-learning as a tool for teaching power electronics

Abstract: Teaching power electronics is a complex task. The classical approach is based on lectures and laboratories assisted by teachers. However, teaching power electronics it is not easy due to the student's motivation related to the difficult of this subject. In this way, this paper presents an approach to teach power electronics based on the students self learning. Instead of using the classical approach, students must develop a research work and a complete power converter prototype. Since students must have some background, this is a second course of power electronics. It is finally here that they clearly understand how a power converter works.

Three-phase multilevel inverter based on LeBlanc transformer

Abstract: A new power conversion structure for a three-phase multilevel inverter is proposed in this paper. This structure uses a LeBlanc transformer and three single-phase voltage source inverters. The power converter topology has two single-phase outputs that connect to the LeBlanc transformer. This transformer allows deriving two-phase voltage to a three-phase source. This multilevel power conversion structure allows obtaining a five-level three-phase inverter. To control the proposed converter a sliding mode controller with a vectorial modulator was used. Simulation results of the proposed converter structure with their control system are presented. From the obtained results it possible to confirm the voltage multilevel waveforms and the effectiveness of the proposed control system technique.

A modular multilevel power converter system for photovoltaic applications

Abstract: In this paper a novel power conversion structure for grid-connected photovoltaic applications is presented. The proposed structure uses a four-wire voltage source inverter, two single-phase voltage source inverters and a scott transformer. PV modules arrangements can be divided in several groups. This power conversion structure is suitable for multi-string technology. The proposed structure allows multilevel output voltage. A sinusoidal pulse with modulator particularly adapted to this power converter structure is also proposed. Several simulation results are presented in order to verify the effectiveness of the proposed system.

Phase-locked loop topology based on a synchronous reference frame and sliding mode approach for DVR applications

Abstract: Phase-Locked Loop (PLL) circuits capable of fast tracking the utility voltage have been used for an increased number of power system equipments. This paper presents a new PLL structure for three-phase power systems. The proposed structure uses a synchronous reference frame and a sliding mode approach to detect phase angle, frequency and amplitude of the system three-phase voltages. The use of the sliding mode approach allows having a fast and robust phase and frequency detection of the power system voltages. In order to verify the behavior of the proposed PLL structure several simulation results are presented. From the obtained results it is possible to verify that this system can be applied to equipments such as dynamic voltage restores.

Dynamic voltage restorer using a multilevel converter with a novel cell structure

Abstract: Voltage sags and swells have a severe impact on sensitive loads. To overcome this problem Dynamic Voltage Restores (DVR) are often used. The DVR is very attractive due to its potential for fast dynamic response to sags disturbances. In this paper, a new multilevel power converter structure for the DVR is proposed. This structure uses three single phase inverters and one three-phase inverter. In this way, a power converter with a five level output voltage is obtained. To control the proposed multilevel power converter a sliding mode controller is used. This control system presents important characteristics such as fast dynamic response and robustness to external perturbations. Several computer simulation results are presented in order to verify the proposed DVR structure.

Fault diagnosis method for three-phase high power factor rectifier based on a pattern recognition algorithm

Abstract: This paper proposes a new fault diagnosis methodology for of high power factor rectifiers. This method Is based on the combined with input line currents three dimensional space and the use of the on Principal Component Analysis (PCA). With the proposed method it is possible to detect and identify the power switch in which the fault has occurred. Such detection requires only the measurement the rectifier input currents. Simulation and experimental results are presented, considering for both healthy and faulty cases, to demonstrate the correctness of the proposed method.

New real coordinates model for an asymmetrical six-phase induction machine

Abstract: This article presents an approach for the modulation of an asymmetric six-phase induction machine. The developed model is formed by two sets of three-phase stator windings that are displaced by 60 degrees. Since this kind of machines can have stator windings displaced with different angles this model also allows choosing another angle. Due to the fact that the induction machine was fully implemented in real coordinates, it is possible to simulate stator and rotor faults without being necessary to change system equations, only system parameters. The simulated results are used to validate the model.

FPGA implementation of a speed controller for three phase induction machines based on the inversion of the electromagnetic field

Abstract: In the paper a field-programmable gate array (FPGA) implementation of a speed controller for the induction machine is presented. This control system is based on the modulation of the rotating field from two others that rotate in opposing directions. To implement this strategy it is used a sliding mode controller. In this way, the controller invert the direction of the field, by inverting the sequence of the three phase stator voltages applied, and in such a way that there is no risk of exceeding the operating currents of the drive. The sliding mode controller is embedded in the core of the Hardware Description Language (HDL) code. As for the FPGA itself, there are several tasks that have to be handled in parallel: calculate the rotor shaft speed from the linear encoder, read the speed set point value from the man-machine interface, apply the commutation switching law from the sliding mode controller, and finally, generate the PWM commands to the inverter. Experimental results from a laboratory prototype system are also presented.

A multilevel voltage source inverter for two-phase AC motor drive systems

Abstract: This paper presents and studies a multilevel converter with two DC voltage sources and three H Bridges The inverter modulates two independent single-phase voltages using a four wires output The design of the inverter allows five levels to the modulated voltages that feed an asymmetrical two windings phase induction motor The classical SPWM technique was used to modulate the multilevel power inverter switches; the frequency of the carrier (a triangular wave) was varied and total harmonic distortion (THD) of voltages and currents were compared The simulation results were obtained using the Matlab/Simulink®/SimPowerSystems software