http://hdl.handle.net/2117/3651 Tue, 21 May 2013 15:26:59 GMT 2013-05-21T15:26:59Z webmaster.bupc@upc.edu Universitat Politècnica de Catalunya. Servei de Biblioteques i Documentació no http://hdl.handle.net/2117/17783 Title: Model of discharge lamps with magnetic ballast Authors: Molina, Julio; Sainz Sapera, Luis; Mesas García, Juan José; Bergas Jané, Joan Gabriel Abstract: Magnetic ballast discharge lamp modeling has been extensively studied because these lamps can be an important source of harmonics. Discharge lamp models usually represent the arc voltage by a square waveform. However, this waveform can be far from actual arc voltages, which affects the accuracy of the lamp models. This paper investigates the actual arc voltage behavior of discharge lamps from laboratory measurements and proposes a novel characterization of these voltages to reformulate the conventional models. The accuracy of the new model is validated with experimental measurements. Fri, 15 Feb 2013 10:49:21 GMT http://hdl.handle.net/2117/17783 2013-02-15T10:49:21Z Molina, Julio; Sainz Sapera, Luis; Mesas García, Juan José; Bergas Jané, Joan Gabriel no Magnetic ballast discharge lamp modeling has been extensively studied because these lamps can be an important source of harmonics. Discharge lamp models usually represent the arc voltage by a square waveform. However, this waveform can be far from actual arc voltages, which affects the accuracy of the lamp models. This paper investigates the actual arc voltage behavior of discharge lamps from laboratory measurements and proposes a novel characterization of these voltages to reformulate the conventional models. The accuracy of the new model is validated with experimental measurements. http://hdl.handle.net/2117/17751 Title: Saturation effects on torque- and current–slip curves of squirrel-cage induction motors Authors: Monjo Mur, Lluís; Córcoles López, Felipe; Pedra Durán, Joaquim Abstract: This paper measures and analyzes the saturation effects on torque- and current–slip curves of three squirrel-cage induction motors.Motor saturation is illustrated by three sets of measurements: I) torque and current for each slip measured at three voltage levels; II) short-circuit impedance measured at different current levels; and III) no-load impedance measured at different voltage levels. In test I, torque and current measured at reduced voltage are prorated to full voltage for comparison purposes. A double-cage model is used to model the motors, and the nonlinearity of their reactances is examined. In order to evaluate the individual weight of every nonlinear reactance on the observed saturated behavior, we try to fit the measurements considering that only one reactance of the double-cage model is nonlinear. Good agreement is obtained only when the stator leakage reactance is considered nonlinear. On the contrary, when magnetizing or remaining leakage reactances are considered nonlinear, they predict machine behaviors inconsistent with measurements. In otherwords, the saturation of the stator leakage reactance is the main contributor to torque and current behavior, while the saturation of the remaining reactances has a negligible influence. Consequently, when all voltage levels are considered, the squirrel-cage induction motors can be accurately modeled (with reasonable accuracy) with a double-cage modelwhere only the stator leakage reactance is considered nonlinear. When only a constant voltage level is considered, the paper also proves that a linear double-cage model (all reactances are linear) accurately predicts machine behavior at such voltage level. Thu, 14 Feb 2013 10:08:24 GMT http://hdl.handle.net/2117/17751 2013-02-14T10:08:24Z Monjo Mur, Lluís; Córcoles López, Felipe; Pedra Durán, Joaquim no This paper measures and analyzes the saturation effects on torque- and current–slip curves of three squirrel-cage induction motors.Motor saturation is illustrated by three sets of measurements: I) torque and current for each slip measured at three voltage levels; II) short-circuit impedance measured at different current levels; and III) no-load impedance measured at different voltage levels. In test I, torque and current measured at reduced voltage are prorated to full voltage for comparison purposes. A double-cage model is used to model the motors, and the nonlinearity of their reactances is examined. In order to evaluate the individual weight of every nonlinear reactance on the observed saturated behavior, we try to fit the measurements considering that only one reactance of the double-cage model is nonlinear. Good agreement is obtained only when the stator leakage reactance is considered nonlinear. On the contrary, when magnetizing or remaining leakage reactances are considered nonlinear, they predict machine behaviors inconsistent with measurements. In otherwords, the saturation of the stator leakage reactance is the main contributor to torque and current behavior, while the saturation of the remaining reactances has a negligible influence. Consequently, when all voltage levels are considered, the squirrel-cage induction motors can be accurately modeled (with reasonable accuracy) with a double-cage modelwhere only the stator leakage reactance is considered nonlinear. When only a constant voltage level is considered, the paper also proves that a linear double-cage model (all reactances are linear) accurately predicts machine behavior at such voltage level. http://hdl.handle.net/2117/17060 Title: Study of the steinmetz circuit influence on AC traction system resonance Authors: Sainz Sapera, Luis; Monjo Mur, Lluís; Riera, Sara; Pedra Durán, Joaquim Abstract: Traction systems are single-phase, nonlinear loads, which can unbalance and pollute supply voltages. To reduce voltage unbalance, reactances are usually connected in delta configuration with traction systems. This setup is called the Steinmetz circuit. Parallel and series resonances can occur between the Steinmetz capacitor and system inductors, increasing voltage distortion. Thus, it is important to analyze the parallel resonance “observed” from the traction system to avoid harmonic problems due to its injected harmonic currents. This paper studies this resonance analytically and presents simple expressions to locate it. Experimental measurements are also provided to validate the obtained analytical results. These expressions are also used to analyze resonance in several power systems in the literature. Mon, 03 Dec 2012 15:46:40 GMT http://hdl.handle.net/2117/17060 2012-12-03T15:46:40Z Sainz Sapera, Luis; Monjo Mur, Lluís; Riera, Sara; Pedra Durán, Joaquim no Traction systems are single-phase, nonlinear loads, which can unbalance and pollute supply voltages. To reduce voltage unbalance, reactances are usually connected in delta configuration with traction systems. This setup is called the Steinmetz circuit. Parallel and series resonances can occur between the Steinmetz capacitor and system inductors, increasing voltage distortion. Thus, it is important to analyze the parallel resonance “observed” from the traction system to avoid harmonic problems due to its injected harmonic currents. This paper studies this resonance analytically and presents simple expressions to locate it. Experimental measurements are also provided to validate the obtained analytical results. These expressions are also used to analyze resonance in several power systems in the literature. http://hdl.handle.net/2117/16812 Title: Behaviour of the doubly fed induction generator exposed to unsymmetrical voltage sags Authors: Rolán Blanco, Alejandro; Córcoles López, Felipe; Pedra Durán, Joaquim Abstract: This study analyses the dynamic behaviour of the doubly fed induction generator exposed to unsymmetrical voltage sags, providing insights into wind turbine fault ride-through capability. The sags are assumed to be caused by faults. An analytical approach assuming that the rotor-side converter can keep constant the rotor current in the synchronous reference frame during the event is used. The voltage limit of the rotor-side converter is also considered in order to determine the situations where the rotor current can be controlled. The effects of sags on grid-connected equipments depend on the sag characteristics (duration and depth), but also on the fault clearing process. In this process, the fault is not cleared instantaneously, as in the case of abrupt sags (which is the usual approach in the literature), but in the successive natural fault-current zeros, leading to a voltage recovery in several steps known as discrete sags. The effects of both abrupt and discrete sags on the doubly fed induction generator behaviour are compared. This comparison reveals that the discrete clearing process smoothes the sag effects on the generator. Mon, 29 Oct 2012 14:30:39 GMT http://hdl.handle.net/2117/16812 2012-10-29T14:30:39Z Rolán Blanco, Alejandro; Córcoles López, Felipe; Pedra Durán, Joaquim no Analytical approach, Clearing process, Doubly fed induction generator (DFIG), Dynamic behaviours, Fault clearing, Fault ride through capability, Grid-connected, Rotor current, Rotor-side converter, Synchronous reference frame, Unsymmetrical voltages, Voltage limits, Voltage recovery This study analyses the dynamic behaviour of the doubly fed induction generator exposed to unsymmetrical voltage sags, providing insights into wind turbine fault ride-through capability. The sags are assumed to be caused by faults. An analytical approach assuming that the rotor-side converter can keep constant the rotor current in the synchronous reference frame during the event is used. The voltage limit of the rotor-side converter is also considered in order to determine the situations where the rotor current can be controlled. The effects of sags on grid-connected equipments depend on the sag characteristics (duration and depth), but also on the fault clearing process. In this process, the fault is not cleared instantaneously, as in the case of abrupt sags (which is the usual approach in the literature), but in the successive natural fault-current zeros, leading to a voltage recovery in several steps known as discrete sags. The effects of both abrupt and discrete sags on the doubly fed induction generator behaviour are compared. This comparison reveals that the discrete clearing process smoothes the sag effects on the generator. http://hdl.handle.net/2117/15003 Title: Doubly fed induction generator subject to symmetrical voltage sags Authors: Rolán Blanco, Alejandro; Córcoles López, Felipe; Pedra Durán, Joaquim Abstract: The aim of this paper is to analyze the dynamic behavior of the doubly fed induction generator (DFIG) subject to symmetrical voltage sags caused by three-phase faults. A simple control algorithm is considered and assumed ideal: the rotor current irf in the synchronous reference frame is kept constant. This hypothesis allows the electrical transient to be solved analytically, providing a comprehensive description of DFIG behavior under symmetrical sags. The fault-clearing physics of symmetrical sags is also analyzed. That is, the fault is cleared in the successive natural fault-current zeros, leading to a voltage recovery in one, two, or three steps. This clearing process, called discrete fault clearing in this paper, results in a more accurate sag modeling than the abrupt or instantaneous fault clearing (the usual modeling in the literature). The fault-clearing process has a strong influence on the rotor voltage required to control the rotor current after fault clearing. To compare the effects of both abrupt and discrete sags, different wind turbine (WT) operating points, which determine different generated powers, are considered. This study helps in the understanding of WT fault ride-through capability. Wed, 08 Feb 2012 07:45:35 GMT http://hdl.handle.net/2117/15003 2012-02-08T07:45:35Z Rolán Blanco, Alejandro; Córcoles López, Felipe; Pedra Durán, Joaquim no Doubly fed induction generator (DFIG), fault clearing, fault ride-through capability, symmetrical voltage sag The aim of this paper is to analyze the dynamic behavior of the doubly fed induction generator (DFIG) subject to symmetrical voltage sags caused by three-phase faults. A simple control algorithm is considered and assumed ideal: the rotor current irf in the synchronous reference frame is kept constant. This hypothesis allows the electrical transient to be solved analytically, providing a comprehensive description of DFIG behavior under symmetrical sags. The fault-clearing physics of symmetrical sags is also analyzed. That is, the fault is cleared in the successive natural fault-current zeros, leading to a voltage recovery in one, two, or three steps. This clearing process, called discrete fault clearing in this paper, results in a more accurate sag modeling than the abrupt or instantaneous fault clearing (the usual modeling in the literature). The fault-clearing process has a strong influence on the rotor voltage required to control the rotor current after fault clearing. To compare the effects of both abrupt and discrete sags, different wind turbine (WT) operating points, which determine different generated powers, are considered. This study helps in the understanding of WT fault ride-through capability. http://hdl.handle.net/2117/14732 Title: On fixed-speed WT generator modeling for rotor speed stability studies Authors: Pedra Durán, Joaquim; Córcoles López, Felipe; Monjo Mur, Lluís; Bogarra Rodríguez, Santiago; Rolán Blanco, Alejandro Abstract: This paper analyzes fixed-speed induction generator modeling oriented to rotor speed stability studies. The single- and double-cage models are compared. The effects of symmetrical voltage sags on generator behavior are studied in detail. The rotor speed stability of the turbine is also examined and rotor speed recovery time is proposed as an indicator of system stability. Significant differences in the results obtained for both models were found, e.g., the double-cage model shows better speed and voltage stability. For some generator designs, the single-cage model can lead to erroneous stability predictions because manufacturer data of such designs can only be fulfilled with a double-cage model. The use of the latter to simulate fixed-speed wind turbines with this type of designs is therefore strongly recommended. The simulations were carried out using PSpice and PSCAD/EMTDC. Mon, 23 Jan 2012 11:04:16 GMT http://hdl.handle.net/2117/14732 2012-01-23T11:04:16Z Pedra Durán, Joaquim; Córcoles López, Felipe; Monjo Mur, Lluís; Bogarra Rodríguez, Santiago; Rolán Blanco, Alejandro no This paper analyzes fixed-speed induction generator modeling oriented to rotor speed stability studies. The single- and double-cage models are compared. The effects of symmetrical voltage sags on generator behavior are studied in detail. The rotor speed stability of the turbine is also examined and rotor speed recovery time is proposed as an indicator of system stability. Significant differences in the results obtained for both models were found, e.g., the double-cage model shows better speed and voltage stability. For some generator designs, the single-cage model can lead to erroneous stability predictions because manufacturer data of such designs can only be fulfilled with a double-cage model. The use of the latter to simulate fixed-speed wind turbines with this type of designs is therefore strongly recommended. The simulations were carried out using PSpice and PSCAD/EMTDC. http://hdl.handle.net/2117/13437 Title: Discrete fault-clearing instant influence on the simulation of voltage-source-inverter-fed adjustable-speed drives subjected to voltage sags Authors: Córcoles López, Felipe; Bogarra Rodríguez, Santiago; Pedra Durán, Joaquim; Luna Alloza, Álvaro Abstract: This study analyses the influence of modelling sags with discrete fault-clearing instants on the behaviour of adjustablespeed drives (ASDs) subjected to sags caused by faults. The effects are compared with those of sags modelled with simultaneous fault clearance in all faulted phases (i.e. abrupt fault clearance; the most common approach to voltage sag modelling). In many cases, abrupt fault clearance is far more severe than discrete fault clearance. Thus, if an ASD rides through a more severe case of an abrupt fault clearance test, it will likely ride through a discrete fault clearance sag. As current protocols for testing the immunity of ASDs to voltage sags only consider abrupt fault clearance, it is not necessary to consider the more complicated discrete fault clearance in equipment sag-testing methodology if more severe abrupt clearance sags are properly chosen and tested. Wed, 05 Oct 2011 14:09:11 GMT http://hdl.handle.net/2117/13437 2011-10-05T14:09:11Z Córcoles López, Felipe; Bogarra Rodríguez, Santiago; Pedra Durán, Joaquim; Luna Alloza, Álvaro no This study analyses the influence of modelling sags with discrete fault-clearing instants on the behaviour of adjustablespeed drives (ASDs) subjected to sags caused by faults. The effects are compared with those of sags modelled with simultaneous fault clearance in all faulted phases (i.e. abrupt fault clearance; the most common approach to voltage sag modelling). In many cases, abrupt fault clearance is far more severe than discrete fault clearance. Thus, if an ASD rides through a more severe case of an abrupt fault clearance test, it will likely ride through a discrete fault clearance sag. As current protocols for testing the immunity of ASDs to voltage sags only consider abrupt fault clearance, it is not necessary to consider the more complicated discrete fault clearance in equipment sag-testing methodology if more severe abrupt clearance sags are properly chosen and tested. http://hdl.handle.net/2117/10777 Title: Deterministic and stochastic study of wind farm harmonic currents Authors: Sainz Sapera, Luis; Mesas García, Juan José; Teodorescu, Remus; Rodríguez Cortés, Pedro Abstract: Wind farm harmonic emissions are a well-known power quality problem, but little data based on actual wind farm measurements are available in literature. In this paper, harmonic emissions of an 18MWwind farm are investigated using extensive measurements, and the deterministic and stochastic characterization of wind farm harmonic currents is analyzed. Specific issues addressed in the paper include the harmonic variation with the wind farm operating point and the random characteristics of their magnitude and phase angle. Tue, 28 Dec 2010 11:02:36 GMT http://hdl.handle.net/2117/10777 2010-12-28T11:02:36Z Sainz Sapera, Luis; Mesas García, Juan José; Teodorescu, Remus; Rodríguez Cortés, Pedro no Wind farm harmonic emissions are a well-known power quality problem, but little data based on actual wind farm measurements are available in literature. In this paper, harmonic emissions of an 18MWwind farm are investigated using extensive measurements, and the deterministic and stochastic characterization of wind farm harmonic currents is analyzed. Specific issues addressed in the paper include the harmonic variation with the wind farm operating point and the random characteristics of their magnitude and phase angle. http://hdl.handle.net/2117/10488 Title: Deterministic and stochastic assessment of the harmonic currents consumed by discharge lamps Authors: Mesas García, Juan José; Sainz Sapera, Luis; Ferrer Biosca, Alberto Wed, 01 Dec 2010 15:49:32 GMT http://hdl.handle.net/2117/10488 2010-12-01T15:49:32Z Mesas García, Juan José; Sainz Sapera, Luis; Ferrer Biosca, Alberto no