Study of resonances in 1 x 25 kV AC traction systems with external balancing equipment

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.AC traction systems are 1 × 25 or 2 × 25 kV/50 Hz single-phase, nonlinear, time-varying loads that can cause power-quality problems, such as unbalanced or distorted voltages. To reduce unbalance, external balancing equipment is usually connected to these systems, forming the Steinmetz circuit. Parallel resonances can occur in these types of circuits, exciting the harmonic emissions (below 2 kHz) of railway-adjustable speed drives. This paper studies these resonances at pantograph terminals and provides analytical expressions to determine their harmonic frequencies. The expressions are validated from several traction systems in the literature and PSCAD simulations.Postprint (author's final draft

Disseny d’un generador eòlic de petita potència

En l’actualitat l’energia eòlica està assolint un protagonisme molt important en termes de grans parc de molt alta potència per generador. Tanmateix, un segment encara poc desenvolupat però amb símptomes d’un gran creixement és el dels petits generadors per aplicacions domèstiques, rurals, o d’abastiment en zones de difícil accés. En aquest projecte es presenten quins són els passos a seguir per poder dissenyar els generadors elèctrics síncrons d’imans permanents per a aquest tipus d’aplicacions. Al llarg del projecte es presenten les metodologies per a analitzar la potencialitat dels recursos eòlics d’una localització determinada, una pauta de càlcul per a màquines elèctriques síncrones d’imans permanents, tant pel disseny electromagnètic com per al disseny tèrmic, així com una proposta de simulació basada en software especialitzat

Aportacions a la modelització de la màquina d'inducció de gàbia d'esquirol

En aquesta tesi es tracten en profunditat diversos aspectes sobre la modelització de la màquina d’inducció de gàbia d’esquirol. En el primer capítol, a partir dels paràmetres i de les característiques elèctriques i mecàniques pels fabricants d’aerogeneradors de velocitat fixa, s’analitza la bondat dels models lineals clàssics de la literatura: el model de simple gàbia i el model de doble gàbia. Els resultats de l’estudi permeten concloure que, el model de doble gàbia és més flexible i permet ajustar completament tots els requeriments. Aquests resultats teòrics, són validats en diferents motors de baixa potència. En el segon capítol s’analitza el comportament no lineal de la màquina degut a l’efecte de la saturació magnètica. L’assaig de diferents motors amb diferents nivells de saturació, mostra experimentalment que les corbes de parelllliscament i corrent-lliscament es veuen afectades pel grau de saturació de la màquina. Per modelitzar analíticament la saturació es proposa una funció que ajusta les mesures experimentals. Com a solució òptima es proposa la utilització del model de doble gàbia en el què la reactància de dispersió de l’estator és no lineal. En el tercer capítol, s’analitza el comportament de la màquina en la zona de fre i es presenten mesures experimentals que mostren que es deformen el alguns motors les corbes de parell-lliscament en aquesta zona de treball. Aquest efecte pot ser explicat per la presència d’harmònics de camp, motiu pel que els models lineals no són capaços de reproduir-lo. En aquest capítol s’analitza la presència d’aquests harmònics de camp i s’utilitza un esquema equivalent que ajusta de manera satisfactòria els resultats obtinguts al laboratori. Finalment en el quart capítol, s’analitzen els efectes dels sots de tensió en els aerogeneradors de velocitat fixa. S’estudia l’efecte del model de la màquina i de la debilitat o no de la xarxa a la què roman connectada la màquina quan aquesta es veu sotmesa a un sot de tensió. Es proposa alguns indicadors per avaluar l’estabilitat de la màquina en aquestes condicions.This Thesis analyzes some aspects of the modelisation of the squirrel-cage induction machine. The first step analyzed is, from parameters and conditions given from a manufacturer of fixed-speed induction generators, the Thesis studies the classic linear models in the literature: the single- and double-cage induction machine models. The study results confirm that the double-cage model is able to fit all the requirements. Results of the theoretical study are also validated with experimental measurements obtained from several test in different motors. Secondly, the non-linear behavior of the induction machine due to the magnetic saturation has been treated. From experimental measurements, it could be demonstrated that the torque- and current-slip curves are affected by the saturation. In order to model this phenomenon, a magnetic saturation function is presented and its goodness is validated with the experimental data. To fit the torque- and current-slip curves, a steady-state equivalent circuit with a non-linear leakage stator reactance is presented as the best solution. The following step is to analyze the behavior of the induction machine in the braking regime. Measurements in these conditions are made, and they show how torque-slip curves are deformed with and high increase of the torque. This behavior cannot be reproduced by the single- and the double-cage model. One explanation of this phenomenon is the presence of space harmonics. In this chapter, space harmonics are presented and a justification of the equivalent chain single-cage circuit is made. With this steady-state equivalent circuit it is possible to estimate parameters that can fit the measurements made in laboratory. Finally, the Thesis analyzes the effects of the voltage sags in fixed-speed wind turbines which are based in squirrelcage induction machines. For this task, the effects of the modelisation of the induction machine and the weakness of the grid are studied. In this point, some indicators are presented to evaluate the stability of the machine in these conditions

Disseny d’un generador eòlic de petita potència

En l’actualitat l’energia eòlica està assolint un protagonisme molt important en termes de grans parc de molt alta potència per generador. Tanmateix, un segment encara poc desenvolupat però amb símptomes d’un gran creixement és el dels petits generadors per aplicacions domèstiques, rurals, o d’abastiment en zones de difícil accés. En aquest projecte es presenten quins són els passos a seguir per poder dissenyar els generadors elèctrics síncrons d’imans permanents per a aquest tipus d’aplicacions. Al llarg del projecte es presenten les metodologies per a analitzar la potencialitat dels recursos eòlics d’una localització determinada, una pauta de càlcul per a màquines elèctriques síncrones d’imans permanents, tant pel disseny electromagnètic com per al disseny tèrmic, així com una proposta de simulació basada en software especialitzat

Study of resonances in 1 x 25 kV AC traction systems

AC traction systems are 1 x 25 or 2 x 25 kV 50-Hz single-phase, non-linear, time-varying loads that can cause power quality problems. One of the main concerns about these systems is voltage distortion, because adjustable-speed drives for trains may inject harmonic currents of frequencies below 2kHz. Since the presence of parallel resonances in the contact feeder section of the traction circuit worsens the scenario, traction system resonance phenomena should be analyzed to prevent problems. Several works addressed these phenomena, but they only drew weak numerical conclusions based on the frequency scan method. This article studies 1 x 25 kV traction system resonances at pantograph terminals and provides more effective analytical expressions to locate them and determine the impact of traction system parameters on them. These expressions are validated from several traction systems in the literature.Postprint (author's final draft

Parameter estimation of squirrel-cage motors with parasitic torques in the torque–slip curve

This paper studies parasitic torques in steady-state torque–slip curves of squirrel-cage induction motors. The curves of nine motors (small, medium and large size units), three of which were measured in the range s = 2 to 0, are analysed. The torque–slip curves of eight of these nine motors differ significantly from the smooth curves predicted by the classical single- and double-cage models: a torque dip at large slips in the motoring regime and a notable torque increase in the braking regime occur. As parasitic torques have been traditionally associated with space harmonics, two singlecage chain models (which consider the space harmonics) are tested to fit the measured torque and current of the three measured motors: one neglects the skin effect, leading to the wrong torque prediction, whereas the other (the chain model proposed in the early 60s in the literature) considers the skin effect, leading to an accurate torque prediction.Postprint (author's final draft

DC Admittance Model of VSCs for Stability Studies in VSC-HVDC Systems

High-voltage direct current (HVDC) systems linked to AC grids with converters are promising energy transmission systems. These systems present complex AC- and DC-side dynamic interactions. Impedance-based stability studies have recently been proposed to assess DC-side dynamics from DC-side characterization of voltage source converters (VSCs) considering AC-side dynamics. However, the existing approaches used for stability studies in VSC-HVDC systems do not completely model VSCs because they do not consider together the VSC delay, the grid voltage feedforward filter, and all the d- and q-reference current controls. Moreover, these approaches are analytically characterized from dq-real space vectors (less related to circuit theory than dq-complex space vectors), and some work with simple AC grids. The main contribution of this paper is a detailed and complete DC admittance model of VSCs from dq-complex space vectors, which considers the VSC delay, feedforward filter, and d- and q-reference current controls, and also a general AC grid. The proposed model can be used for DC-side stability studies in VSC-HVDC systems considering AC grid dynamics. The capabilities and drawbacks of impedance-based stability methods for DC-side stability assessment were analyzed, and the positive-net-damping criterion was validated as a robust approach. The model was validated by PSCAD/EMTDC simulations and applied to a stability study in a VSC-HVDC system.info:eu-repo/grantAgreement/AEI/Plan Estatal de Investigación Científica y Técnica y de Innovación 2021-2023/PID2021-123633OB-C33/ES/Estabilidad de microrredes formadas por agrupaciones de clustersObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energiaObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.b - Per a 2030, ampliar la infraestructura i millorar la tecnologia per tal d’oferir serveis d’energia moderns i sos­tenibles per a tots els països en desenvolupament, en particular els països menys avançats, els petits estats insulars en desenvolupament i els països en desenvolupament sense litoral, d’acord amb els programes de suport respectiusObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura::9.4 - Per a 2030, modernitzar les infraestructures i reconvertir les indústries perquè siguin sostenibles, usant els recursos amb més eficàcia i promovent l’adopció de tecnologies i processos industrials nets i racionals ambiental­ment, i aconseguint que tots els països adoptin mesures d’acord amb les capacitats respectivesPostprint (published version

Replacing induction motors without defined efficiency class by IE class: example of energy, economic, and environmental evaluation in 1.5 kW—IE3 motors

This paper shows the results obtained from the study on the variables that have the greatest influence on the decision to replace three-phase induction motors, without a defined efficiency class and installed in industrial applications, with IE3 efficiency class induction motors. The work has been carried out on motors with a nominal power of 1.5 kW due to the availability of laboratory tests that have allowed us to accurately quantify the selected study variables. According to IEC 60034-30, between 0.75 kW and 4 kW is the greatest potential for energy savings in electric motors installed within the industrial sector. The tests carried out have made it possible to assess different operating conditions of the motor: direct power supply from the grid, electronic power supply using scalar control, and electronic power supply using direct torque control. The study has focused on three aspects: energy evaluation, assessing the savings potential; economic evaluation, based on indicators such as Payback Period and Net Present Value; environmental assessment, quantifying the impact indicators proposed by the Methodology for Ecodesign of Energy-related Products (MEErP). A sensitivity analysis has been carried out to quantify, through ratios, different operating points from those directly analyzed in the article.This work was supported by the Universitat Politècnica de atalunya under the project AGRUPS R-02140.Peer ReviewedPostprint (published version

Study of resonance in wind parks

Wind turbine harmonic current emissions are a well-known power quality problem. These emissions flow through wind park impedances, leading to grid voltage distortion. Parallel resonance may worsen the problem because it increases voltage distortion around the resonance frequency. Hence, it is interesting to analyze the parallel resonance phenomenon. The paper explores this phenomenon in wind parks and provides analytical expressions to determine parallel resonances. (C) 2015 The Authors. Published by Elsevier B.V.Postprint (author's final draft

Assessment of subsynchronous oscillations in AC grid-connected VSC systems with type-4 wind turbines

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Converters are the key for increasing the development of renewable energy generation but their dynamic interaction with the grid has an important impact on stability. Oscillatory instabilities in different grid-connected converter systems at several frequency ranges are reported. In particular, sub and supersynchronous oscillatory instabilities in AC power systems with type-3 and type-4 wind turbine generators (WTGs) were recently registered at several wind farm areas. A number of works based on eigenvalue analysis and frequency domain approaches are carried out to analyse this new stability issue and more research is going on to analyse in detail the electric and control parameters that may affect this phenomenon. This study contributes analysing in detail the influence of system parameters on the subsynchronous oscillations (SSOs) in AC power systems with type-4 WTGs. This study is based on a new approach for subsynchronous stability assessment which could also be used for analysing other types of SSOs (e.g. subsynchronous control interactions between doubly-fed induction generators and series-compensated networks) as well as supersynchronous oscillations. A representative example of weak AC grids with type-4 WTGs is used to illustrate the contributions of the study. Results are validated with PSCAD/EMTDC time-domain simulations.Postprint (author's final draft