1,720,960 research outputs found
Voltage stabilization and efficiency improvements on DC railways by stand alone energy storage systems
No full textStand Alone Energy Storage Systems (ESS) can be placed along railway lines to stabilize the catenary voltage and perform braking energy savings; this action reduces line power losses and saves energy normally wasted by train rheostats. The global result is both economic and technical, lower consumptions and a better utilization of the traditional substation rectifiers. This work analyzes a portion of a regional 3 kV DC railway; system efficiency and power savings are simulated with and without a stand alone ESS. Equipment is placed inside a passengers stop, so also infrastructures costs are low
Control and Thermal Design of a Bi-Directional Grid Interface Converter for Fast-Recharging Stations Developed in the Framework of the Italian PNRR Research Activities
No full textMulti-level converters are a possible solution for
increasing the power density and efficiency in many power
electronic systems. The increase in the number of switching
components on a single device leads to a growth both in the cost
of the converter and in its complexity compared to two-level
solutions. However, these drawbacks are counterbalanced by a
better harmonic content on the AC quantities, allowing a
significant decrease in the size of the output filters and reactive
power as well. Thus, three-level converters represent a good
compromise between costs, system complexity and efficiency.
More specifically, this paper focuses on the development of a
bidirectional control for a three-phase three-level T-type
converter working as an active front end to be coupled with
DC/DC converters in off-board recharging stations or in
renewable power plants. Moreover, a thermal analysis of the
power electronics is carried out aimed to the design and the
development of an ad hoc cooling system for a prototype
working at 80 kW
Hybrid battery-supercapacitor system for full electric forklifts
No full textDespite the yearly rise in the market quota of full electric vehicles, the main limitations on the deployment of electric vehicles are the real performances of the battery storage during operation. In this study, the authors focus on hybrid electrical storage systems composed of lead acid batteries and supercapacitors. Two different coupling methods are investigated: (i) the direct parallel coupling of the two storage devices and (ii) coupling by means of a step-up converter between the supercapacitor bank and direct current (DC) link of the entire power-train, where lead acid batteries are also connected. A specific control strategy is proposed and implemented in the step-up converter to guarantee the correct power management of the power train and in particular: (i) to save the power request to the lead acid battery pack, (ii) maintain an adequate state of charge of the supercapacitor bank, and (iii) guarantee an adequate voltage level on the DC link. A prototype of the hybrid battery, integrating the proposed control technique, was realised and tested on a real forklift. The performances of the entire power-train were experimentally measured in a warehouse test cycle emulating a typical daily working cycle
Power control of series connected passive-active rectifiers for a dual-star PMS wind generator
No full textIn this paper, a hybrid topology of series-connected passive-active rectifiers is proposed for offshore wind energy conversion systems (WECSs). In particular a combined structure of a voltage-source converter (VSC) and a diode rectifier (DR) is connected to a double-star permanent magnet synchronous generator (2S-PMSG) reducing cost and losses. Nonetheless, the current harmonics due to diodes behavior are mitigated without using large AC filters using an appropriate control structure. The VSC is downsized compared to a fully active rectifier stage. The potential benefits of this hybrid topology include low power losses, low costs, and smaller footprint resulting from diode-based component. The simulation results for 20 kW generation system are shown to verify the effectiveness of the proposed approach and the control method
Design of a Rotary Transformer for Installations on Large Shafts
Full text linkRotary transformers are adopted to transfer energy from primary to secondary in situations in which the two sides are in relative rotation. These devices are cylindrical transformers with two cores and the corresponding winding separated by an air gap. Their employment became quite convenient with the availability of power electronics, allowing the operation of electrical systems at relatively high frequencies. In particular, this paper proposes the design of a light and efficient transformer which can be used in applications involving large shafts. Moreover, a sliced arrangement for the magnetic core is proposed together with the experimental validation of this solution on a reduced-size prototype
Rotor position estimation in a large airgap Active Magnetic Bearing
No full textIn recent years, Active Magnetic Bears (AMBs) becoming attractive for several reason such as frictionless rotation, high reliability and high speed operation. Moreover, AMBs are today an interesting alternative to standard bearing due to power electronics and control hardware price reduction, but the main disadvantage of AMBs is that they are design to have a small airgap and a high stiffness. This paper presents a new large airgap magnetic bearing that allows to add dumping features thanks to a dedicated control. A simplified analytical model has been introduced, a study of the airgap estimation has been presented and some experimental results are provided to validate the approach
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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