Darlan A. Fernandes

A Traveling-Wave Detection Method Based on Park's Transformation for Fault Locators

A novel algorithm for transient detection based on Parks transformation is proposed. It is very simple, self-adapts to electrical noise and phase imbalances, and is appropriate to be used in connection with traveling-wave fault location (TWFL) methods. The proposed technique is evaluated through Electromagnetic Transients Program simulations. A 230-kV transmission system case study is carried out, in which power system voltage and current waveforms are picked up one sample at a time. It is shown that the method is very reliable and suitable for multiterminal TWFL algorithms.

Harmonic Analysis Based on Kalman Filtering and Prony's Method

This work proposes a technique for harmonic analysis in electrical power systems. Towards this end, a frequency estimator, the Pronys method, has been matched to a Kalman filter. In the proposed technique, the sinusoid amplitudes of electrical power signals are estimated by the Kalman filter. The Kalman filter regressors are built up using the frequencies estimated by the Pronys method. The technique have been tested to both synthetical and experimental signals.

Real-Time Traveling-Wave-Based Fault Location Using Two-Terminal Unsynchronized Data

In this paper, a new two-terminal traveling-wave-based fault-location algorithm is proposed. Its main advantage over similar two-terminal algorithms lies in the fact it does not require the data from both line terminals to be synchronized. In order to do so, the algorithm is applied in real time, and a communication system is used, whose data-transmission latency is taken into account in the proposed formulation. The fault locator routines were implemented using the real-time digital simulator (RTDS), such that a wide variety of fault scenarios in a 230-kV transmission line 200 km long was evaluated in real time, considering communication systems with different latency variability levels. The obtained results indicate the proposed algorithm is able to locate faults using either synchronized or unsynchronized two-terminal data, whereas classical methods work properly for synchronized measurements only.

A Method for Averting Saturation From Series Transformers of Dynamic Voltage Restorers

This paper proposes a technique for preventing saturation in series transformers from dynamic voltage restorer (DVR) systems. The method consists in correcting the voltages which are injected through the transformers into the power system to compensate voltage sags. It restricts the compensating voltages during the sag whenever it predicts that a maximum limit for the flux linkage is about to be exceeded. The prediction is carried out at the beginning of a stabilized voltage sag. Moreover, the technique allows a certain level of sag compensation even when the estimated flux is expected to exceed the saturation limit. The voltage sag level and phase are computed through an adaptive recursive least squares (RLS). The RLS estimation incorporates a transient period before it achieves a stable state whenever there is a sag event. The DVR is not supposed to operate in this period. Therefore, this paper also outlines a simple procedure for detecting the RLS estimation stable level. Simulation of different scenarios of voltage sags and the results from the experimental implementation of a DVR show the effectiveness of the method.

Single-phase current source converter with new modulation approach and power decoupling

In this work it is presented a Current Source Converter (CSC) topology that helps to mitigate double line frequency power ripple (low frequency) effect. Low frequency power ripple presented in single-phase systems propagates through DC-bus converter. This low frequency ripple reduction allows to increase the power converter density by reducing the volume of the DC inductor, without lack of stiffness at the DC-bus. The low frequency mitigation is achieved by using a different single-phase CSC topology that uses three series-connected switches per leg. Thus, it allows independent control for two merged CSCs which share the same DC-bus and the middle switches of the leg. This solution is adequate to connect photovoltaic panels to the electrical grid, among others applications. Evaluation of such a solution by assuming grid modeling is useful and may require powerful simulation tools such as real-time simulator. In order to comply with power processing restrictions, a low frequency model is derived. Performance of both models (high and low frequency) are compared to ensure usability of the low frequency model. Control strategies and modulation are presented. Simulation results are provided to validate the theoretical approach, and real-time simulation results, as well.

A hybrid current control for a controlled rectifier

A current controller must satisfy the contradictory requirements of having a fast dynamic response in transient and a low harmonic content in steady state, characteristics that are found in linear and hysteresis controllers, respectively. Predictive current controllers partly satisfy these requirements but at expenses of complexity. The present work proposes an alternative approach for modifying the linear controller in order to have a faster response. This consists of the One Cycle Control (OCC) current controller modified by the use of a lead-lag compensator. An additional feature of this controller is that it can be implemented with DSP. Besides mathematical analysis, simulation and experimental results are presented to validate the proposed controller.

Double four-quadrants single-phase current source converter sharing the same DC-bus

In this work it is presented a novel topology of Current Source Converter (CSC) that allows to control two single-phase AC converters independently sharing the same DC-bus, with the advantage of having a reduced number of conducting switches, less switching and a lower DC-bus current. A conventional double single-phase CSC that uses the same DC-bus needs to have two two-legs (H-bridge) converters connected in series, which means that it will always have four conducting switches. The new topology proposed allows to generate any two AC output currents with the same number of switches, however having always only three conducting switches in a switching period, representing 25% less conducting losses comparing on the equivalent conventional double single-phase CSC. It is also presented a Scalar Pulse Width Modulation (SPWM) and Space Vector Modulation (SVM) to control the converters with switching optimization, which reduces the switching losses. Details of topology, control strategy and modulation are presented. Simulation results are provided to validate the theoretical approach.

Torque control of induction motor drives based on One-Cycle Control method

The first work on direct torque control (DTC) of induction motor (IM) was based on hysteresis controllers and Switching Tables. Although it has the advantage of simplicity, it has a few drawbacks such as current, torque and flux distortions, and variable frequency operation. Posterior DTC works have solved most of these problems, but with added complexity to the control algorithm. This paper presents a new flux and torque controllers, for DTC of IM drives, based on One Cycle Control (OCC). The proposed control method (DTC-OCC) is capable of solving most of the original problems of DTC such as operation at fixed frequency with reduced ripple on flux, torque and current, while recovering at the same time, the simplicity of the DTC algorithm. As OCC has been considered as a generalized PWM modulator, the theoretical foundations of the new method are provided from both PWM and OCC approaches. Simulation and DSP-based experimental results show good performance of the proposed control and confirm the theoretical analysis and assumptions.

Modeling and state-space feedback control of a DC-DC converter for photovoltaic systems

In this work is proposed a model of a photovoltaic (PV) system comprised by PV-arrays connected to a dc-dc converter. Toward this purpose, the PV panels, dc-dc converter and the controller are modeled as a set of state-space equations suitable for adjusting the transient and steady-state performances of the system. The photovoltaic system is evaluated with the average state variable method and the controllers are designed by means of concepts of the characteristic polynomial and the system controllability. These concepts in state-space formulation allow the controllers can be determined by the ackermanns method. The modeling and proposed control are tested by simulations and experimental procedures. The results corroborate the performance of the method.

A family of single-phase Current Source Converters with double outputs

This work introduces a family of Current Source Converters (CSCs) that allows to control single-phase AC converters with two outputs independently sharing the same DC-bus. It is presented four different topologies which have their own advantages and disadvantages compared to each other. The comparison criterias are the total number of switches, the number of conducting switches per switching cycle, quadrant operations and DC-bus current. One of the topologies needs to always have four conducting switches with full-quadrant operation (named Fq4c), while another topology (Lq2c) needs only two, however with limited-quadrant operation. The last two presented topologies have three conducting switches in a switching period, one with full-quadrant operation (Fq3c) and another with limited-quadrant operation (Lq3c). Also it is presented the Scalar Pulse Width Modulations (SPWMs) to control each converter with switching optimization. Details of the topologies, operation and modulation logic are presented. Simulations and experimental results are provided to validate the theoretical approach.