1,721,157 research outputs found
Input current and voltage ripple analysis in ldn cells for h-bridge multilevel inverters
Full text linkThis paper deals with the analysis of the input dc-link voltage ripple in multilevel inverter based on H-bridge and level doubling network (LDN). The LDN is basically a half-bridge fed by a floating capacitor, with voltage self-balancing capability, recalling the concept of a flying capacitor configuration. The amplitude of the LDN voltage ripple is analytically determined considering both the low-order and the switching harmonic components. In particular, peak-To-peak distributions of voltage ripples over the fundamental period are analytically determined, making possible the design of dc-link capacitor relying only on the dc-voltage ripple requirements. The case study makes reference to negligible switching ripple in the output current. It well represents either grid connection or passive load having almost sinusoidal currents. Numerical simulations carried out by MATLAB/Simulink and a complete set of experimental verifications are given to confirm the theoretical developments
Improvement of the integration of a grid-connected wind-photovoltaic hybrid system
No full textThis paper presents control strategies for the integration of a grid-connected wind-photovoltaic hybrid system via adaptation converters connected to a common DC bus. For both wind and solar system, adequate control algorithms have been implemented for the maximum power extraction. The grid side converter has been connected to the point of common coupling (PPC) through an RL filter. The control of the grid side converter (GSC) was made in order to control the power quality and quantity of the feed power to the grid. At the DC bus, a PI-regulation control was adopted to overcome the ripples caused by the power flow. Performances of the adopted control laws have been evaluated by MATLAB/Simulink simulations. © 2013 IEEE
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
Analysis of input voltage switching ripple in three-phase four-wire split capacitor PWM inverters
Full text linkThree-phase, four-wire split capacitor inverters are currently employed in many applications, such as photovoltaic systems, battery chargers for electric vehicles, active power filters, and, in general, in all grid-tied applications that deal with possible grid voltage and/or current unbalances. This paper provides a comprehensive evaluation of the capacitor-switching voltage ripple and dc-link switching voltage ripple for the three-phase, four-wire, split capacitor inverters. Specifically, analytical formulations of the peak-to-peak and rms values of the voltage ripples are originally pointed out in this paper and determined in the case of balanced three-phase and unbalanced (two-phase and single-phase) output (ac) currents. The obtained results can help in designing the considered inverter and sizing of the dc-link capacitors. Reference is made to the sinusoidal PWM modulation and sinusoidal three-phase output currents with an almost unity power factor, representing a grid-connected application. Extensive numerical simulations have been carried out to thoroughly verify all the analytical developments presented in this paper. Furthermore, some experimental tests, having balanced output currents on the ac side, have been accomplished, validating numerical simulations and analytical developments
Evaluation of AC Current Ripple in case of Split-Capacitor Three-Phase Four Wires Inverters
Full text linkThis paper deals with a split capacitor three-phase four-wire inverter, able to deal with unbalanced ac currents and/or voltages. The considered topology can be used in many applications such as photovoltaic systems, chargers for electrical vehicles, active filters, and in general all the grid-connected applications. One parameter that must be considered in the converter design is the ac (output) current ripple, which should be determined and minimized in order to improve the system efficiency. In this paper, the evaluation of the ac current ripple for the three-phase split-capacitor inverter is developed with reference to both balanced and unbalanced output conditions. In particular, the peak-to-peak and the rms current ripple are analytically determined as a function of the modulation index, for each phase. Initially, reference is made to single-carrier sinusoidal PWM, being, in general, a simple and effective solution. The interleaved multiple-carrier PWM strategy is then considered in order to mitigate the current ripple in the neutral wire, while not affecting its phase counterpart. Numerical simulations have been carried out in order to verify the analytical developments
Volatile compounds and oxidative stability of Pinus halepensis Mill. seed oil under heating conditions
No full textHeating conditions of Pinus halepensis seed oil were monitored to evaluate the effect of thermo-oxidation processes on the bioactive compounds contained in the samples. The following parameters were monitored: ultra violet absorption at 232 and 270 nm, fatty acid composition, oxidative stability, antiradical activity and aromatic profiles. Under thermo-oxidation process, trans fatty acids (TFA) increased and conjugated linoleic acid isomers appeared. The antiradical activity significantly decreased from 73.3% to 52.5% after 120 min of heating. Oxidative stability decreased (r = 0.70). The volatile profile was heavily influenced by heating with the formation of new volatile compounds, such as the two isomers (E,Z)-2,4-decadienal and (E,E)-2,4-decadienal. a-pinene, and the main terpene compound was very vulnerable to heating conditions. Despite its peculiar pleasant aroma and nutritional value, the P. halepensis seed oil should not be used for cooking. Indeed, under frying conditions, its antioxidant properties and oxidative stability are lost and potential toxic compounds, such as TFA and unsaturated aldehydes, are forme
Ac current ripple harmonic pollution in three-phase four-leg active front-end ac/dc converter for on-board EV chargers
Full text linkThree-phase four-leg voltage-source converters have been considered for some recent projects in smart grids and in the automotive industry, projects such as on-board electric vehicles (EVs) chargers, thanks to their built-in ability to handle unbalanced AC currents through the 4th wire (neutral). Although conventional carrier-based modulations (CBMs) and space vector modulations (SVMs) have been commonly applied and extensively studied for three-phase four-leg voltage-source converters, very little has been reported concerning their pollution impact on AC grid in terms of switching ripple currents. This paper introduces a thorough analytical derivation of peak-to-peak and RMS values of the AC current ripple under balanced and unbalanced working conditions, in the case of three-phase four-leg converters with uncoupled AC-link inductors. The proposed mathematical approach covers both phase and neutral currents. All analytical findings have been applied to two industry recognized CBM methods, namely sinusoidal pulse-width modulation (PWM) and centered PWM (equivalent to SVM). The derived equations are effective, simple, and ready-to-use for accurate AC current ripple calculations. At the same time, the proposed equations and diagrams can be successfully adopted to design the conversion system basing on the grid codes in terms of current ripple (or total harmonic distortion (THD)/total demand distortion (TDD)) restrictions, enabling the sizing of AC-link inductors and the determination of the proper switching frequency for the given operating conditions. The analytical developments have been thoroughly verified by numerical simulations in MATLAB/Simulink and by extensive experimental tests
Theoretical Analysis of the AC Current Ripple in Three-Phase Four-Leg Sinusoidal PWM Inverters
No full textThree-phase four-leg voltage-source inverters (VSIs) are currently considered for several renewable-energy and automotive applications, due to their inherent ability to deal with unbalanced ac currents through the 4th wire (neutral). Although conventional carrier-based and space vector modulations have been commonly applied and extensively studied for various power electronic configurations, very little has been reported concerning the impact of these modulation strategies on ac current switching ripple for three-phase four-leg VSIs. This paper presents a comprehensive analytical derivation of peak-to-peak profile and rms value of the ac current ripple for this converter topology in case of sinusoidal pulse-width modulation, also including the neutral wire. The analytical developments for all examined subcases have been verified by numerical simulations, carried out in the MATLAB/Simulink environment
A DC/DC Fast Charger for Electric Vehicles with Minimum Input/Output Ripple Based on Multiphase Interleaved Converters
No full textAn off-board dc fast battery charger for electric vehicles (EVs) with an original control strategy aimed to provide minimum input voltage ripple and zero output current ripple in the typical EV batteries voltage range is presented in this paper. Currently, due to an infant development stage of high-power, high-energy batteries for EV application, there is no clear consensus on allowable output current ripple for fast chargers. However, there are different charging protocols, which are optimized for short charging time and efficiency, while maintaining a long-life cycle of a battery. Common feature of these protocols is an underlying assumption of minimum (or null) instantaneous charging current ripple. The fast charger configuration proposed in this paper is based on a modular three-phase interleaved converter, used as an interface between the dc-link (dc supply) and the battery. The use of low-cost, standard and industry-recognized three-phase power modules for high-power fast EV charging stations enables the reduction of capital and maintenance costs of the charging facilities, enhancing further expansion of the eco-friendly transport. Numerical simulations are carried out in Matlab/Simulink to confirm the feasibility and the effectiveness of the whole EV fast charging configuration, with emphasis to input voltage ripple and output current ripple of the interleaved three-phase dc/dc converter
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