An Elegant Solution Using Hybrid Power Filter to Improve the Line Current Spectrum of Multiphase PWM Locomotive Rectifiers with Load Unbalance

Locomotive PWM Rectifiers employed in A.C traction systems represent several megawatts of electrical load. Typically they use multiple rectifiers/converters in parallel in order to secure high power ratings and high frequency operation. The rectifiers are supplied from a single-phase A.C. traction transformer with multiple secondaries of high leakage inductance. The switching instants of the PWM rectifiers are phase shifted and interlaced in order to achieve high ripple current cancellation, assuming that the converter loads are balanced. This would ensure the rectifiers to provide better harmonic performance and also redundancy of operation with multiple units in operation. However, in practice, rectifiers may be closely coupled to a traction inverter supplying an axle or a group of axles and the real power developed will depend upon the traction conditions. Creep and slip can give rise to variations in power and perfect power balance at the rectifiers is an improbable proposition.There is high degree of interest to examine the possibility locomotive systems that degrade gracefully with equipment failure. Failure of one traction inverter would lead to load unbalance for the rectifier modules. Or sometimes, partial failures may result in unbalanced operation which can cause reduced ripple current cancellation and generate switching frequency harmonic current components. This may adversely impact the signalling systems and/or result in over voltage effects due to resonance in the overhead supply system. This paper examines a 4 MW locomotive with three rectifier modules and a device switching frequency of 900 Hz. This results in a 5400 Hz ripple frequency in the mains current. And this paper will consider what may be the most frequently occurring case; that of loss of load in one traction motor due to wheel slip. Current ripple cancellation is partially lost in this case and lower frequency current components can be produced. Traditionally, number of solutions has been employed in the industry like passive filters, active filters etc., for this type of a problem. However, this paper explores an elegant, attractive and economical solution of using hybrid filters in order to achieve a level of acceptable satisfactory harmonic performance and thereby improving the power quality of the rail systems

Chi: a scalable and programmable control plane for distributed stream processing systems

Stream-processing workloads and modern shared cluster environments exhibit high variability and unpredictability. Combined with the large parameter space and the diverse set of user SLOs, this makes modern streaming systems very challenging to statically configure and tune. To address these issues, in this paper we investigate a novel control-plane design, Chi, which supports continuous monitoring and feedback, and enables dynamic re-configuration. Chi leverages the key insight of embedding control-plane messages in the data-plane channels to achieve a low-latency and flexible control plane for stream-processing systems. Chi introduces a new reactive programming model and design mechanisms to asynchronously execute control policies, thus avoiding global synchronization. We show how this allows us to easily implement a wide spectrum of control policies targeting different use cases observed in production. Large-scale experiments using production workloads from a popular cloud provider demonstrate the flexibility and efficiency of our approach

Rare-earth monosulfides as durable and efficient cold cathodes

In their rocksalt structure, rare-earth monosulfides offer a more stable alternative to alkali metals to attain low or negative electron affinity when deposited on various III-V and II-VI semiconductor surfaces. In this article, we first describe the successful deposition of Lanthanum Monosulfide via pulsed laser deposition on Si and MgO substrates and alumina templates. These thin films have been characterized by X-ray diffraction, atomic force microscopy, high resolution transmission electron microscopy, ellipsometry, Raman spectroscopy, ultraviolet photoelectron spectroscopy and Kelvin probe measurements. For both LaS/Si and LaS/MgO thin films, the effective work function of the submicron thick thin films was determined to be about 1 eV from field emission measurements using the Scanning Anode Field Emission Microscopy technique. The physical reasons for these highly desirable low work function properties were explained using a patchwork field emission model of the emitting surface. In this model, nanocrystals of low work function materials having a orientation perpendicular to the surface and outcropping it are surrounded by a matrix of amorphous materials with higher work function. To date, LaS thin films have been used successfully as cold cathode emitters with measured emitted current densities as high as 50 A/cm2. Finally, we describe the successful growth of LaS thin films on InP substrates and, more recently, the production of LaS nanoballs and nanoclusters using Pulsed Laser Ablation.Comment: 61 pages, 24 figure

Conformational and Structural Relaxations of Poly(ethylene oxide) and Poly(propylene oxide) Melts: Molecular Dynamics Study of Spatial Heterogeneity, Cooperativity, and Correlated Forward-Backward Motion

Performing molecular dynamics simulations for all-atom models, we characterize the conformational and structural relaxations of poly(ethylene oxide) and poly(propylene oxide) melts. The temperature dependence of these relaxation processes deviates from an Arrhenius law for both polymers. We demonstrate that mode-coupling theory captures some aspects of the glassy slowdown, but it does not enable a complete explanation of the dynamical behavior. When the temperature is decreased, spatially heterogeneous and cooperative translational dynamics are found to become more important for the structural relaxation. Moreover, the transitions between the conformational states cease to obey Poisson statistics. In particular, we show that, at sufficiently low temperatures, correlated forward-backward motion is an important aspect of the conformational relaxation, leading to strongly nonexponential distributions for the waiting times of the dihedrals in the various conformational statesComment: 13 pages, 13 figure

The origins of fast segmental dynamics in 2 nm thin confined polymer films

Molecular-Dynamics computer simulations were used to study 2 nm wide polystyrene films confined in slit pores, defined by inorganic crystalline surfaces. The simulated systems mimic experimentally studied hybrid materials, where polystyrene is intercalated between mica-type, atomically smooth, crystalline layers. A comparison between the experimental findings and the simulation results aims at revealing the molecular origins of the macroscopically observed behavior, and thus provide insight about polymers in severe/nanoscopic confinements, as well as polymers in the immediate vicinity of solid surfaces. Pronounced dynamic inhomogeneities are found across the 2 nm thin film, with fast relaxing moieties located in low local density regions throughout the film. The origins of this behavior are traced to the confinement-induced density inhomogeneities, which are stabilized over extended time scales by the solid surfaces

Control of traction supply power quality using locomotive PWM converter controls

Wolfs, PJ ORCiD: 0000-0001-7048-1231Railway traction systems are highly susceptible to severe harmonic distortion, poor voltage regulation and line resonances. Electric locomotives, which are concentrated high power loads, move continuously along the supply line, rendering the topography of the supply system, a time-variable. Under those conditions, the resonant impedances vary as the traction vehicle moves along the track. Parallel resonances with feeder line inductance and capacitance between feeder line and earth, cause harmonic magnification. This paper will examine the use of small retrofit converters to improve the performance of multiphase PWM rectifiers as found in locomotive applications

An Active Power Filter Method to Improve the Line Current Spectrum of PWM Locomotive Rectifiers with Load Unbalance

Locomotives in heavy haul and high speed passenger operations represent several megawatts of electrical load. Single phase power collected by a pantograph is typically rectified by multiple PWM converters. The converter switching instants are phased to ensure ripple current cancellation, assuming that the converter loads are balanced. Partial failures may result in unbalanced operation with reduced cancellation. The resulting harmonics may adversely impact the signalling systems and/or result in over voltage effects due to resonance in the overhead supply system. This paper examines a 4 MW locomotive with three rectifier modules and a device switching frequency of 900 Hz. This results in a5400 Hz ripple frequency in the mains current. Ideal balanced operation of converters is compared to anunbalanced operation case. Unbalanced cases include rectifier failures, inverter failures and changes in the relative balance of power delivered to each axle of the locomotive. This paper will consider what may be the most frequently occurring case; that of loss of load in one traction motor due to wheel slip. Current ripple cancellation is partially lost in this case and lower frequency current components can be produced. An active filter is proposed as a means to retain an acceptable harmonic performance for the locomotive

Segmental dynamics of polymers in nanoscopic confinements, as probed by simulations of polymer/layered-silicate nanocomposites

In this paper we review molecular modeling investigations of polymer/layered-silicate intercalates, as model systems to explore polymers in nanoscopically confined spaces. The atomic-scale picture, as revealed by computer simulations, is presented in the context of salient results from a wide range of experimental techniques. This approach provides insights into how polymeric segmental dynamics are affected by severe geometric constraints. Focusing on intercalated systems, i.e. polystyrene (PS) in 2 nm wide slit-pores and polyethylene-oxide (PEO) in 1 nm wide slit-pores, a very rich picture for the segmental dynamics is unveiled, despite the topological constraints imposed by the confining solid surfaces. On a local scale, intercalated polymers exhibit a very wide distribution of segmental relaxation times (ranging from ultra-fast to ultra-slow, over a wide range of temperatures). In both cases (PS and PEO), the segmental relaxations originate from the confinement-induced local density variations. Additionally, where there exist special interactions between the polymer and the confining surfaces (e.g., PEO) more molecular mechanisms are identified

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Not AvailableA hurdle technology-based approach for the reduction in immunogenicity of shrimp major allergen, tropomyosin was investigated by combining electron beam irradiation at 5 kGy and boiling, autoclaving, trypsin and chymotrypsin treatments along with peeled raw shrimp as control. Shrimp extracts were prepared from the irradiated sample and evaluated SDS PAGE profile, IgE binding ability and immunogenicity of tropomyosin using pooled sera of shrimp sensitive individuals. Electron beam irradiation resulted in significant (p < 0.05) decrease in the IgE activity in the case of all treatments. The SDS PAGE analysis showed the presence of tropomyosin in all the treatments except autoclaving in combination with or without electron beam irradiation. A pronounced reduction in allergenicity was observed in the treatment of autoclaving in combination with electron beam irradiation. The combined application of autoclaving and electron beam irradiation can be utilized for the preparation of hypoallergic shrimp.Not Availabl