1,721,123 research outputs found
Decoupled d-q Axes Current-Sharing Control of Multi-Three-Phase Induction Machines
Full text linkMulti three-phase drives are a particular case of multiphase systems, which are often used in high-power applications, such as wind-energy generation, naval and railway propulsion. In a multi three-phase system the electric machine is fed by more than one three-phase converter. A current sharing algorithm for multi three-phase drives allows setting unequal current references among the converters so that each of them differently contributes to the generation of the magnetic torque and flux. Suitable current sharing control systems already exist and have been presented for multi three-phase machines. This paper illustrates a current sharing technique where the contributions to the rotor flux for the three-phase inverters, related to the d-axis current, is decoupled from the contributions to the electromagnetic torque, which depends on the q-axis current. Also, the presented algorithm minimizes the Joule losses in the stator winding. Finally, the advantages of the proposed method are analyzed and confirmed by experimental tests. The effectiveness of the control strategy is validated on a scaled prototype of a quadruple three-phase starter/generator for more-electric-aircraft applications
Effects of input voltage measurement on stability of matrix converter drive system
No full textThe effects of different input voltage measurement methods on the stability of a matrix converter drive system are analysed. In particular, with the aim of improving the maximum output power of the matrix converter, the duty cycles of the switching configurations are calculated using input voltages filtered by a digital lowpass filter. A variable state average model of the whole system, which takes into account the grid impedance, the input L–C filter parameters and the load, is used for the theoretical analysis. The stability of the system is evaluated by analysing the migration of eigenvalues of the system, which is linearised around a steady-state operating point. The analytical approach allows the determination of the maximum power for a stable operation of the matrix converter as a function of the time constant of the digital lowpass input voltage filter. Theoretical considerations are supported by simulation results, showing the varying behaviour of the matrix converter that can be achieved in terms of stability as the time constant of the digital filter is changed
Modeling and Simulation of Grid Connected Wind Energy Conversion System Based on a Doubly Fed Induction Generator (DFIG)
No full textThis paper deals with the analysis, modeling, and control of a grid connected doubly-fed induction generator (DFIG) driven by the wind turbine. Recent advancements in size and technology of wind turbines require sophisticated control systems to effectively optimize energy conversion and enhance grid integration. This article investigates the power flow analysis of grid connected Wind Energy Conversion System (WECS) in a highly fluctuating wind environment. The WECS is equipped with a DFIG and a back-to-back converter in the rotor circuit. A control technique is presented for extracting the maximum power from the wind turbine. The grid side converter maintains the DC link voltage and the task of the rotor side converter is to track the maximum power point for the wind turbine. The description for the proposed system is presented with the detailed dynamic modeling equations. Simulation results for different operating conditions are presented
Voltage feedback of an LLC resonant converter with a rotary transformer
No full textRotary assembly platforms are used in several automation applications, such as box-fill systems. In modern automatic machines, several actuators may be mounted on the rotating platform, but this architecture raises the problem of their feeding. The solution developed in this paper consists in adopting a LLC resonant converter that uses the leakage and magnetizing inductances of a rotary transformer as inductors of the resonant network. Furthermore, since the output voltage on the rotating platform cannot be directly measured, a sensorless control scheme has been developed to improve load regulation. Experimental results are provided to show the effectiveness of the converter and its control scheme
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Sensorless speed observer based on third-order spatial field harmonic for multiphase induction motor drives
No full textThis paper presents an electric drive consisting of a multiphase induction motor fed by a multiphase inverter. The control system is similar to that of a traditional field-oriented control for three-phase motors, but the machine speed is estimated by a novel sensorless observer. Since multiphase motors with M phases (M is supposed odd) have the capability of controlling the odd spatial harmonics of the magnetic field up to the (M-2)th order, the developed observer excites the third-order spatial harmonic of the magnetic field to estimate the rotor speed. Simulation results are provided to assess the performance of the observer
Closed-loop control impact on the detectability of stator high-resistance connection in Doubly-fed WRIMs based on rotor power spectral analysis
No full textDesign of modern Wind Energy Conversion Systems (WECSs) must take into account two crucial aspects: efficient control strategies and reliable monitoring and diagnosis techniques. Wind turbine generators based on Wound Rotor Induction Machine (WRIM) is actually the preferred technology mainly because of the lower rating of the power converter connected to the rotor side. With the association of a back-to back converter on the rotor side a Stator-Flux-Oriented-Control (SFOC) system can be used to obtain a decoupled control of the active and reactive power on the stator side with high efficiency. In this context, the influence of the Closed-Loop (CL) control scheme must be considered when the diagnosis of stator asymmetry is derived from the signature analysis of electrical quantities. Therefore, an examination of the spectral content of the investigated quantities for different bandwidths of CL regulators is necessary to assess the effectiveness of the derived fault indexes. In this paper, the performances of three different techniques based on rotor electrical quantities, for detecting stator asymmetry are investigated. Results with numerical simulations and experimental tests are here presented showing the validity of the established comparative study
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