• Energy Research

As Guest Editors of this Special Issue, it was our responsibility to ensure that the contributions to the issue related to the extensive field of electromechanical energy conversion, with a special focus on the design, materials, and modeling of electrical machines [...]

Energy storage concept that supports important technologies for electrical systems is well established and widely recognized. Several energy storage techniques are available, including an electrochemical energy storage system used to support electrical systems. These storage systems require interfaces based on power electronic converters for interconnection with an electrical system. This paper reviews the literature covering the various types of interfaces developed for electrochemical energy storage systems. Different electrochemical energy storage devices and their specificities regarding to integration with the electrical systems are described. . The various power converter interfaces that can be used for electrochemical energy storage systems are presented. These interfaces have been divided into standard, multilevel and multiport technology. The main characteristics and specificity of each topology considering its application to electrochemical energy storage systems are presented. The review also covers the smart storage concept and the requirements of the interface to integrate the electrochemical energy storage devices upon this concept.

A fast and robust control strategy for a multilevel inverter in grid-connected photovoltaic system is presented. The multilevel inverter is based on a dual two-level inverter topology. There are two isolated PV generators that feeding each bridge inverter. The output of each inverter is connected to a three-phase transformer. The active and reactive powers flowing into the grid are controlled by a sliding mode algorithm. An alfa–beta space vector modulator is also used. The inverters DC voltages are also controller by a sliding mode controller. In this way, a fast and robust system controller is obtained. Several test results are presented in order to verify the effectiveness of the proposed system controller.

Abstract A new approach to fault location for parallel double-circuit distribution power lines is presented. This approach uses the Clarke–Concordia transformation and an artificial neural network based learning algorithm. The α, β, 0 components of double line currents resulting from the Clarke–Concordia transformation are used to characterize different states of the system. The neural network is trained to map the non-linear relationship existing between fault location and characteristic eigenvalue. The proposed approach is able to identify and to locate different types of faults such as: phase-to-earth, phase-to-phase, two-phase-to-earth and three-phase. Using the eigenvalue as neural network inputs the proposed algorithm locates the fault distance. Results are presented which shows the effectiveness of the proposed algorithm for a correct fault location on a parallel double-circuit distribution line.

AbstractThis paper presents a three-phase STATic synchronous COMpensator (STATCOM) based on a current source inverter. Instead of the typical three-phase current bridge inverter it is used a power converter topology with only a single-phase current bridge inverter. A dynamic model of the STATCOM in αβ coordinates is used as a basis for control design. The control system uses a cascade structure where a fast ac current inner loop and a slow dc current control outer loop is used. For the inner loop, is used a sliding mode technique to generate αβ space-vector modulation. This fast and robust controller the ac currents of the STATCOM are actively shaped, being possible to maintain the desired currents even with high ripple DC inductor current. For the outer loop, is used a PI controller. Computer simulations are presented allowing validating the proposed STATCOM and their control system.

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.

The use of a solar photovoltaic (PV) panel simulator can be a valued tool for the design and evaluation of the several components of a photovoltaic system. This simulator is based on power electronic converter controlled in such a way that will behave as a PV panel. Thus, in this paper a PV panel simulator based on a two quadrant DC/DC power converter is proposed. This topology will allow to achieve fast responses, like suddenly changes in the irradiation and temperature. To control the power converter it will be used a fast and robust sliding mode controller. Therefore, with the proposed system I–V curve simulation of a PV panel is obtained. Experimental results from a laboratory prototype are presented in order to confirm the theoretical operation.

The use of distributed architectures for PV panels present several advantages over centralized solutions, such as better harnessing of the generated energy and improved reliability of the system. Therefore, several inverter structures have been proposed to ensure proper operation of distributed architectures and at the same time generate multilevel voltages. A newly proposed structure uses three three-phase two-level inverters. Thus, in this paper a new control system is proposed for grid-connected PV systems with this structure. The proposed control system is based on a sliding mode AC current controller that uses space-vector voltage modulators. The proposed control system is also designed to inject unbalanced power into the grid to provide an ancillary service regarding power unbalances. The proposed controller for the mentioned structure is then tested through several simulations considering different case studies.

Abstract With the growth of Distributed Energy Resources (DER) in electrical systems, an increase in the benefits with the reconfiguration of radial networks related to the use of renewable energy is expected. However, in some countries the reconfiguration of radial networks has some limitations like the impossibility of island operation. Also, many of them have contracts with Distributed Generation (DG) operators that force them to buy all the available generation of electricity. After a fault these limitations increase DG unavailability resulting in a waste of resources in the form of payments of available electricity generation not used. In this paper we propose a multiobjective optimal placement of switching devices considering DG unavailability, network reliability and equipment cost, with no island network operation. Two approaches are proposed in this multiobjective problem. In the first approach, besides the minimization of the equipment cost and the reliability indices, it is proposed an extra objective function that considers the minimization of the Distributed Generation Unavailability Index (DGUI). In the second approach two new composite indices comprising DG, interruption duration and interruption frequency are presented. Results obtained from a case study using a real utility distribution network are presented and discussed.