1,721,032 research outputs found
Experimental Validation of a Semi-Two-Stage Traction System Based on the NPC Multi-Source Inverter for Fuel Cell Rail Vehicles
No full textHydrogen trains have been increasingly considered as an alternative to diesel-powered trains on long-range medium-traffic routes, for which electrification lacks economic attractiveness. In fact, very long autonomies can be reached by hydrogen fuel cell plants with a single refueling. In fuel cell systems, a high-power dc/dc converter must be included to boost the voltage of the fuel cell, which can vary significantly from no load to full load condition. In this paper, a semi-two-stage traction system for hydrogen-powered rail vehicles is investigated and tested. The architecture employs an NPC multi-source inverter as main traction converter to provide an additional connection between the fuel cells and the traction motors. With the coordinated control of the two power converters, the boost converter can be partly bypassed during operation, and its peak power rating and round-trip energy losses reduced. Experimental tests on a lab prototype show significant reductions in the peak current and round-trip energy processed by the dc/dc converter, with expected benefits in terms of weight and volume of its passive filters and heatsinks
Performance analysis of a full order sensorless control adaptive observer for doubly-fed induction generator in grid connected operation
Full text linkThis paper focuses on the performance analysis of a sensorless control for a Doubly Fed Induction Generator (DFIG) in grid-connected operation for turbine-based wind generation systems. With reference to a conventional stator flux based Field Oriented Control (FOC), a full-order adaptive observer is implemented and a criterion to calculate the observer gain matrix is provided. The observer provides the estimated stator flux and an estimation of the rotor position is also obtained through the measurements of stator and rotor phase currents. Due to parameter inaccuracy, the rotor position estimation is affected by an error. As a novelty of the discussed approach, the rotor position estimation error is considered as an additional machine parameter, and an error tracking procedure is envisioned in order to track the DFIG rotor position with better accuracy. In particular, an adaptive law based on the Lyapunov theory is implemented for the tracking of the rotor position estimation error, and a current injection strategy is developed in order to ensure the necessary tracking sensitivity around zero rotor voltages. The roughly evaluated rotor position can be corrected by means of the tracked rotor position estimation error, so that the corrected rotor position is sent to the FOC for the necessary rotating coordinate transformation. An extensive experimental analysis is carried out on an 11 kW, 4 poles, 400 V/50 Hz induction machine testifying the quality of the sensorless control
A Perturb-and-Observe based MTPA Algorithm for Mono-Inverter Multi PMSM Electric Drives
No full textSingle inverter multi motor architectures enable the possibility of a significant system simplification, with a remarkable reduction of required components, resulting in cheaper, lighter, and more compact structure. This solution has been extensively studied for Induction Motors and only for two parallel-connected Permanent Magnet Synchronous Motors (PMSM). The case of multi PMSMs, instead, is in its early stage. This paper contributes to enrich the study of the optimized control problem for Single Inverter Multi PMSM system proposing two methods for the Maximum Torque Per Ampere point tracking, also in presence of motor parameter deviations. The optimum trajectories are studied, and the effect of motor parameter deviations highlighted. Two suitable MTPA tracking methods are selected and their performance evaluated by means of an extensive numerical investigation. The results comparison allowed to highlight pros and cons of the two methods, testifying the feasibility to effectively track the optimum point both during steady-state and transient conditions and during the motor parameter variations
Size, Efficiency, Reliability and Cost Analysis of a Multiport Traction Inverter with Downsized DC-DC Converter for a Catenary/Battery Tram
Full text linkThe use of a NPC-type multilevel converter as multiport inverter (MPI) has recently been considered a promising solution for the compact integration of multisource systems in various applications. Despite increasing research interest in this topic, a comprehensive study of an MPI-based power conversion system for multisource rail applications is still lacking in the literature. This paper presents a broad analysis of a quasi-single stage propulsion system (QSS) that employs an NPC-type MPI and a downsized boost dc-dc converter for an urban tram vehicle with overhead line connection and onboard batteries. The control and dynamic performance are detailed and validated experimentally. Furthermore, the efficiency, weight, volume, reliability and cost of the QSS system are evaluated and benchmarked against a conventional architecture for a case-study catenary/battery tram model. To this aim, analytical design equations, manufacturers’ data, electrothermal time-domain simulations, finite element method (FEM) simulations, and Monte Carlo-based lifetime analyses are employed. The analysis reveals that the QSS system can achieve significant savings in volume, weight, and round-trip energy efficiency, higher reliability due to intrinsic redundancy, but with increased part count, complexity, and cost
Semi-Two-Stage Traction System based on the NPC Multisource Inverter for Tram Vehicles with Onboard Supercapacitors
No full textThis paper proposes an innovative semi-two-stage topology for the traction system of trams equipped with supercapacitors, with the aim to downsize the onboard dc/dc converters. The configuration is obtained through a non-conventional connection of a half-bridge chopper and 3L Neutral Point Clamped (NPC) inverter to the dc sources and ac traction motors. By means of a proper modulation strategy, the NPC converter works as a Multi-Source Inverter and can independently control the power absorbed or supplied by the catenary and supercapacitors. Due to limitations in the power-processing domain of the NPC circuit, a chopper must be also included in the traction circuit. However, it processes only a fraction of the total power of the supercapacitors. The proposed solution is compared against a traditional two-stage architecture, where a dc/dc converter processes the entire power of the capacitors and a 2L Voltage Source Inverter drives the traction motors. Extensive numerical analyses testify that the envisioned architecture shows encouraging performance and can yield a significant reduction of the dc/dc converter ratings, losses, volume, and weight
Current waveforms distribution among electrochemical cells of Modular Multilevel Converters in Battery Electric Vehicles
No full textIn the context of Battery Electric Vehicles, conventional Voltage Source Inverters (VSI) have been associated with several types of Battery Management System, mainly to balance the state of charge of electrochemical cells and extend their lifetime. Modular Multilevel Converters (MMC) with embedded elementary cells represent a valid alternative, thanks to the possibility of integrating the balancing functionality, ensuring a negligible harmonic content of the output currents and reducing the ringing phenomenon. On the other hand, the MMC topology exposes the cells to a different current waveform, increasing the cells losses in comparison with VSI solutions. This paper analyzes how the cells current waveforms of a MMC topology produce an unbalanced distribution of active power among the cells and evaluates their loss increase with respect to VSI configurations
Propulsion System Based on the NPC Multi-Source Inverter for Battery Hybrid Trams: Experimental Validation
No full textHybrid tram vehicles with a connection to the overhead line and onboard batteries present many advantages, including effective braking energy recovery, reduced current absorption from the overhead wire, and partial catenary-free operation. For their connection to the vehicle dc bus, the batteries require bulky and heavy dc/dc converters that are sized for the peak power rating of the storage system. This paper presents the experimental validation of a non-conventional battery hybrid propulsion system employing the NPC Multi-Source Inverter. The Multi-Source Inverter provides an additional connection between the battery and the traction motors and can thus be used to partly bypass the dc/dc converter and reduce its power rating. The experiments on a small-scale lab prototype validate the envisioned control of the architecture and attest to its potential of reducing significantly the peak current rating of the dc/dc converter, with expected savings in terms of weight, volume, and power losses
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
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