Fault Detection Method for Permanent Magnet Synchronous Generator Wind Energy Converters Using Correlation Features Among Three-phase Currents
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In a permanent magnet synchronous generator (PMSG) system, conversion systems are major points of failure that create expensive and time-consuming problems. Fault detection is usually used to achieve a steady system. This paper presents a full analysis of a PMSG system for wind turbines (WT) and proposes a fault detection method using correlation features. The proposed method is motivated by the balance among the three-phase currents both before and after an open-circuit fault occurs in a converter of the PMSG system. It is unnecessary to analyze the output waveforms of a converter during fault detection. In this study, two correlation features of stator currents, the mean and covariation, are extracted to train an artificial neural network (ANN), thereby enhancing the performance of the proposed method under different wind speed conditions. Moreover, additional sensors and the collection of a massive amount of data are not required. Model simulations of an ideal inverter and a PMSG system are conducted using PSCAD software. The simulation results show that the proposed method can detect the locations of faulty switches with a diagnostic rate greater than 99.4% for the ideal inverter, and the PMSG drives settings at different wind speeds.Differential Power Processing (DPP) converters have been recently utilized for reducing the losses in partially shaded PV systems. Through enabling new paths for currents, shaded panels have less impact on blocking higher currents from series connected PV modules. This ultimately results in harvesting more power from partially shaded PV units. Unfortunately, the number of required DPP converters increases linearly with the number of series PV units. To address this challenge, this paper investigates the possibility of reconfiguring DPP converters reducing the number of needed converters. Instead of using a complete set of DPP converters, reconfiguring DPP converters could substantially reduce the number of needed converters. The used DPP converters will be connected to shaded units and reconfigured online with changes in shadings to reduce the mismatch power losses. Validation and verification through simulation is conducted to demonstration the effectiveness of the proposed idea.
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Ac-dc power conversion can either be done with two separate converter stages or with a single converter stage. Two-stage ac-dc converters, however, can be costly and complex and the performance of single-stage converters is compromised due to a reduced number of components. Several researchers have therefore proposed adding some sort of auxiliary circuit consisting of a second switch and some passive elements to single-stage converters to improve their performance. Although these quasi-single-stage (QSS) converters may have two converters, they are not two-stage converters as they do not have two separate and independently controlled converters that are always operating to convert power from one form to another. In the paper, the operation of ac-dc single-stage converters is first reviewed and their characteristics are noted. The operation of several QSS converters, including one proposed by the authors, is then discussed, and the paper concludes by presenting experimental results that confirm the feasibility of the proposed converter.
Single stage
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1. Terminology, specifications and evaluation techniques 2. Scaled D to A converters 3. High resolution scaled D to A converters 4. Feedback A to D converters 5. Algorithmic converters 6. Rampfunction converters 7. Delta-sigma converters 8. Fast A to D converters Appendix: simulations
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This paper addresses itself to the inter-influence on the stator and rotor fault detection in induction motors. The reason why the detection of stator fault is influenced adversely to a certain extent by rotor fault is clearly revealed by study based on the electromagnetic mechanism. Rotor fault results in edge frequency components emerged in stator current. The conventional algorithm of negative sequence component of stator current, which is usually regarded as the most typical indicator of stator fault, gives rise to a false negative sequence component due to the modulation of edge frequency components in stator current, and might influence the detection of stator fault. The problem whether stator fault influences the detection of rotor fault or not is quantitatively discussed on the standpoint of electromagnetic mechanism, and a few interesting conclusions have been drawn. Namely, stator fault indeed results in edge frequency components emerged in stator current, which is usually regarded as the most typical indicator of rotor fault, and thus influence the detection of rotor fault in theory. However, the amplitudes of the edge frequency components derived from incipient even some severe stator fault are rather small with respect to those derived from rotor fault, and not be detectable from the practice’s point of view, and thus do not confuse the indicator of rotor fault.
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In the past, and still today it has been hard to find good methods to locate and determine the magnitude of the iron losses in stator cores and from that obtain an overall quality check. In order to meet the future demands on high-effeciency motors with high power density it is essential to have a good knowledge where the stator losses are located and what size they have in specific parts of the stator. This paper presents a method to measure the stator core losses in different parts of the stator by means of a measurement device and determine the relative stator losses in the different parts. The paper gives a hint how to design an appropriate measurement device for a stator with certain dimensions. In the end of the paper results from measurements on sttator cores with different sheet qualities are presented.
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The authors present a new phase axesmodelof three phaseasynchronous machines considering the stator iron loss. The model can be used when the parameters of the machine's stator are unbalance. The simulation and experiment results show that the stator currents are influenced by the iron loss distinctly. The simulation results considering the stator iron loss is more consistent with the measured data in laboratory comparing with those neglecting the stator iron loss. The phase axes model considering the stator iron has better precision and very useful in the asynchronous machine's monitoring and control.
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In order to optimize the stator slots arrangement and get high-efficiency electromagnetic scheme for the turbine generators,study on the loss taken away by the stator cooling water as well as the outlet water temperature-rise of the upper and lower layers of the stator winding was conducted.The mathematical relationship between the stator slots arrangement and the loss taken away by the stator cooling water as well as the outlet water temperature-rise of the upper and lower layers of the stator winding was established.Such key points as height of the stator bar,thickness of hollow pipe,ratio between hollow and solid bar and optimization range were proposed to be taken into account.The 660 MW generator with both water-inner-cooled stator and rotor windings was taken as an example,in which the optimized design of stator slot arrangement was described in detail.
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Traditional passive stator winding model can not represent electromotive force(EMF) when stator is in working condition.This paper proposes an active stator winding model,taking into account the EMF occurring when stator winding cuts magnetic induction lines.Every stator slot will produce EMF with different phase angles,dividing and putting the EMF unit into every sub-bar of the winding model.Field-circuit comprehensive analysis using active stator model can calculate the electric field distribution of stator slot,and predict safety of stator insulation.The over-voltage simulation results show that using active stator model to reckon electric field distribution is more accurate than using the traditional stator model,and has higher accuracy of predicting winding insulation fault.
Electromotive force
Counter-electromotive force
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It is a challenge to diagnose insulation condition of stator bars using an ultrasonic technique, due to the complex structures of the stator bars and the high attenuation of the stator insulation. In this paper, five low frequency transducers were used in a pulse-echo configuration to try to test a standby stator bar of a generator (300 MW, 18 kV). With an available transducer, four types of insulation structures were tested on the stator bar. The short side insulation was compared with the large one of the stator bar in the slot. The stator bar near the exit from the slot and the end stator bar, were compared with the stator bar in the slot. The semiconductive coating covered stator insulation was compared with the uncoated one. The stator insulation having an insulation-copper interface was compared with that having an insulation-gas interface. In addition, insulation diagnosis tests in the laboratory were performed on two sets of stator bars, which had been in service for 18 and 23 years, respectively in two generators (300 MW, 18 kV). Field tests were performed on the stator bars near the exit from the slot and the end stator bars of a generator (300 MW, 18 kV). The experimental results demonstrated an availability of low frequency ultrasonic pulse-echo method for insulation condition diagnosis of large generators.
Bar (unit)
Insulation system
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The industrial application of power electronic converters and systems of converters are varied (Motorola, 1991, 1993). Power electronic converters of electrical energy for electrical engineering technologies have a wide spread in industry.
Power Electronics
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