1,720,968 research outputs found
Performance analysis of envelope modelling applied to resonant converters
Full text linkResonant converters are often studied using their envelope models, i.e. the transfer functions that relate the envelope of the output quantities to those of the input ones. Transfer functions can accurately represent only the input-output relation of linear systems and hence any method used to develop the envelope model cannot be accurate if the resonant converter processes the envelopes in a non-linear way. This paper works out a general criterion that recognizes whether the envelope processing is linear or not, the type of the eventual non-linearity and its amount. The criterion is expressed in terms of conditions that have to be fulfilled by the input-output Bode diagram of the converter. These conditions are of general validity and do not depend on the converter topology; their applicability is not limited to resonant converters, but it can be extended to any system. The conditions have been derived by reviewing the procedure that leads to the Modulated Variables Laplace Transform method for the development of the envelope models. The theoretical results are verified at first by simulations and then by experimental tests carried out on two different resonant topologies of a prototypal converter that works as wireless battery charger
Design and Experimentation of a Single-Phase PLL With Novel OSG Method
Full text linkDifferent phase-locked loop algorithms applied to three-phase grid voltages implement a closed control loop based on the Park transform to obtain the grid voltage instantaneous phase and frequency. When a single-phase grid voltage must be processed, one of the inputs of the Park transform is generated by a block that, starting from the available voltage, computes an additional signal with the same frequency of the grid voltage and ideally orthogonal to it. This paper introduces a novel method for the orthogonal signal generation and gives a detailed analysis of its functioning. Then, after sizing the control loop of the phase-locked loop, the paper considers different aspects relevant to implementation of the presented orthogonal signal generation and of the phase-locked loop on a digital signal controller, such as the finite numerical resolution, the memory usage and the computation time. Finally, the paper checks the comprehensive performance of the orthogonal signal generation and phase-locked loop pair by experimental tests and compares the obtained results with those available in the literature
Automatic optimization of the compensation networks of a wireless power transfer system
Full text linkThis paper addresses the optimization of the compensation networks of a wireless power transfer system. Optimization is performed by means of a genetic algorithm that looks for the reactances of the elements of the compensation networks that maximize the power transfer efficiency and the power transferred to the load. In addition, the algorithm selects the solutions that are less sensitive to the difference between the theoretical and actual reactances. The last part of the paper describes the prototypal setup used for the tests and supports the theoretical findings by reporting experimental results
Demand-side power paradigm-oriented analysis of reactive electric spring stabilization capabilities
Full text linkElectric Spring (ES) technique is a user-level solution developed to stabilize the supply voltage of a user under variations of the grid voltage. This paper analyzes the stabilization capabilities of a reactive ES that operates according to the demand-side power paradigm. By help of a convenient ES modeling, the extreme values of the active power that a user can draw under the ES action are first determined. Then, it is demonstrated that the demand-side power paradigm is fulfilled only if the distribution line impedance has a resistive component while its reactive component weakens such fulfillment. Lastly, the variations of the grid voltage that ES is able to cope with are worked out. All findings are formulated in terms of normalized quantities and consequently are of general validity. Computer-aided simulation of a case study exemplifies the theoretical findings
Application of Smart Transformer Load Control to mitigate Voltage Fluctuations in Medium Voltage Networks
No full textPenetration of renewable energy sources introduces variability in the electric power generation. It causes grid voltage fluctuations that adversely affect operation of critical loads. Mitigation of these fluctuations is traditionally achieved by compensating for the reactive power absorbed at the point of common coupling. In the paper, the Smart Transformer (ST) load control is applied to adjust the active power absorbed by the noncritical loads. In the paper, this application of ST load control is explicated showing its enforceability in the presence of distribution lines with resistive parameters of the same order as the reactive ones. Results obtained for a study case are also given that support the theoretical findings
Design of a Bidirectional Wireless Power Transfer System for Vehicle-to-Home Applications
Full text linkEnergy storage plays a fundamental role in balancing the power fluctuations induced by the distributed generation of renewable energy sources. In this scenario, electric vehicles can strongly contribute to exchange power with the grid through their on-board batteries. When the vehicle is parked, the battery can be discharged, injecting active power into the grid, provided that its state of charge will be restored before vehicle utilization. This paper presents a comprehensive step-by-step design of a wireless charger for a Vehicle-to-Home application. The design procedure begins from the constraints disposed by the Italian reference technical rules for Low Voltage utilities and by the standard SAE J2954 for Wireless Power Transfer for electric vehicles. The selection of the output power of the battery is followed by the power sizing of each stage of the bidirectional wireless charger
Dynamic Behavior Analysis and Control of Reactive Electric Springs
No full textElectric Spring (ES) technology is an innovative user-level solution developed to stabilize the supply voltage of the loads against variations of the grid voltage. Two basic ES versions exist: reactive and active, whereas the former operates by exchanging only reactive power with the non-critical user loads whilst the latter exchanges both reactive and active power with them. Several strategies have been developed for the ES control, mainly considering loads of R type and focusing on the arrangement of the ES command. This paper deals with a user of RL type equipped with a reactive ES, and pursues the twofold objective of analyzing the dynamic behavior of the user quantities and designing an effective ES control system. The analysis reveals the slightly damped behavior of the user supply voltage in response to an ES command. The designed control system provides a fast and smooth voltage stabilization; to this end, a nested scheme is proposed and the individual controllers are properly synthesized. The performance of the ES control system is validated by Matlab/Simulink simulations
Stabilization characteristics of user load equipped with electric spring for various types of line impedance
Full text linkIn the last years, Renewable Energy Sources (RESs) have increasingly contributed to the power delivered by the grid. Despite the environmental benefits made by RESs, their unpredictable power production is responsible of variations in the voltage of the distribution lines that can be disruptive for the functioning of the supplied loads. Electric Spring (ES) is a device that faces such an issue by stabilizing the supply voltage of the critical load of a user in a simple but effective way. This paper is concerned with the stabilization characteristics of a user load supplied by a low-voltage distribution line and equipped with a reactive power-operated ES. After working out an ES model that facilitates the analysis of an ES-equipped user load, its stabilization characteristics are found for three types of line impedance, namely pure resistive, pure inductive and resistive-inductive. Comparison of the resultant characteristics shows the different performance of the ES-equipped user load under various types of line impedance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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