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Öğe Comparison of Typical PV Module Performances Based on the Circuit Models(Ieee, 2018) Tutkun, Nedim; Gegin, Keziban; Sarma, Nur; Salam, Z.In PV systems, it is usually expected that power generation under varying conditions at any time should be maximum as much as possible. Therefore, it is essential to build a circuit model based on a widely used single or double diode model under instantly varying conditions with minimum estimation error through the measured values in the manufacturers' data sheet. It is fact that these approximate circuits models ease the performance analysis of PV systems if the unknown parameters are accurately estimated at various temperatures and unchanged irradiance levels or vice versa. This paper comparatively studies the performances of the two approximate circuit models for the four types of PV modules using the real-coded genetic algorithms. The results indicated that I-V characteristics obtained from the identified parameters exhibit almost similar trend with those given in manufacturers' data sheets under the same conditions. Besides, the estimated parameters obtained from using both models slightly show difference from each other and it can be said that the single diode model is solely satisfactory to model a typical PV model as long as they are accurately estimated.Öğe DFIG current and controller signals' angular shaft misalignment signature - an experimental case study(Ieee, 2020) Wang, Yingzhao; Sarma, Nur; Mohammed, Anees; Djurovic, Sinisawith the continuous increase in wind turbine generator size the monitoring and diagnosis of drive train shaft misalignment is of growing importance, as this condition contributes to as much as 30% of turbine's downtime. Machine current signature analysis has been widely investigated in conventional machinery as a non-invasive diagnostic tool for shaft misalignment, via spectrum analysis of the stator current signal. This paper reports a practical case study of misalignment fault signature manifestation in the doubly-fed induction generator (DFIG) controller signals spectra, with a view to assessing the feasibility of low cost and non-invasive controller signal analysis based misalignment diagnosis. The study employs a laboratory test rig to undertake a series of tests to analyze the sensitivity of controller signals to a specific angular misalignment condition, and hence evaluate and characterize the manifestation of its spectral signatures.Öğe Double Fed Induction Generator Shaft Misalignment Monitoring by FBG Frame Strain Sensing(Ieee-Inst Electrical Electronics Engineers Inc, 2020) Wang, Yingzhao; Mohammed, Anees; Sarma, Nur; Djurovic, SinisaThis study explores the potential for using FBG strain sensing to enable recognition of the shaft misalignment condition in electric machine drivetrains through observation of machine frame distributed relative strain. The sensing principles, design and installation methods of the proposed technique are detailed in the paper. The scheme was applied on a purpose built wind turbine generator representative laboratory test rig and its performance evaluated in an extensive experimental study involving a range of healthy and misaligned shaft operating conditions. The obtained experimental data demonstrate the reported method's capability to enable recognition of generator shaft misalignment conditions and thus its health monitoring. Finally, it is shown that the thermal variation of the generator frame structure inherent to its operation, combined with the FBG sensor intrinsic thermo-mechanical cross sensitivity, has no detrimental impact on the fidelity and usability of the observed strain measurements.Öğe Early life failure modes and downtime analysis of onshore type-III wind turbines in Turkey(Elsevier Ltd, 2023) Sarma, Nur; Tuohy, P.M.; Özgönenel, O.; Djurovi?, S.Operations and maintenance costs, and unplanned downtime accounts for a significant proportion of the total expenditure of windfarms. Therefore, reduction of these costs is essential, which requires a better understanding of the wind turbines' reliability in terms of failure rates and downtime with operational lifetime. Failure rates and downtime are generally logged using condition monitoring systems, which mainly focus on Supervisory Control and Data Acquisition (SCADA) alarm signals. The aim of this paper is to use SCADA alarm statistics to provide a new failure rate and downtime survey and thus to evaluate reliability performance of the major wind turbine components and subsystems. The paper focuses on a modern onshore windfarm located in Turkey with Type-III wind turbines over the course of the first two years of operations, which is the first time reliability data from Turkey has been published in literature. The presented data can help to provide a better understanding of early life operations, since all maintenance activities, as well as stoppages that caused the wind turbines not to generate electricity were considered in this paper. Furthermore, the evaluation and categorisation of the recorded SCADA alarms, their origins and whether they were associated with planned or unplanned downtime is presented. This analysis shows that early life modern wind turbines have the highest alarm rates and downtime associated with ‘safety’ factors, followed by the ‘electrical systems’, which was found to be the most critical (or unreliable) subsystem. The presented results therefore suggest that early life focus should be on the electrical systems of wind turbines for maximising their operating time and availability. Monthly distributions of both SCADA alarms and downtime rates are also presented to highlight the effects of environmental conditions. © 2022Öğe The Effect of Conducted Emissions of Grid-Tied Three-Phase Adjustable Drives(Elsevier - Division Reed Elsevier India Pvt Ltd, 2023) Genc, Secil; Muneeswaran, Venkatkumar; Thomas, David; Greedy, Steve; Gundogdu, Burcu; Sarma, Nur; Ozgonenel, OkanElectromagnetic Interference (EMI) is generated and mitigated in power converters. EMI problems are related to high-speed power converters. This article focuses on conducted electromagnetic interference in adjustable-speed drive (ASD) systems. The electromagnetic compatibility of three-phase/level grid-connected drive inverters is investigated. The test setup is built per the CISPR16-1-2 standard, and the interferences produced from the inverter to the grid are measured. The main dependencies of conducted emissions of a power inverter, changes in the length/shape of main cables, and motor speed have been investigated under load and no load conditions. Factors affecting EMI performance and filter design issues will be addressed. A statistical approach to quantifying the frequency domain impact of conducted emission noise created on the three-phase system by operating various emission sources. Fast Fourier Transform (FFT) was applied for time-frequency domain conversion, and to evaluate with a statistical approach Minitab software was used. Then, a filter design is created to prevent these interferences from being conducted to the grid. Also, the noise attenuation of the EMI filter has been validated in the simulation. Briefly, this study fills in the blanks of uncertainties involved in measuring three-phase emissions, which helps the engineers at the design stage of three-phase converters.Öğe Electrical & mechanical diagnostic indicators of wind turbine induction generator rotor faults(Pergamon-Elsevier Science Ltd, 2019) Zappala, Donatella; Sarma, Nur; Djurovic, Sinisa; Crabtree, Cristopher J.; Mohammad, Anees; Tavner, P.J.In MW-sized wind turbines, the most widely-used generator is the wound rotor induction machine, with a partially-rated voltage source converter connected to the rotor. This generator is a significant cause of wind turbine fault modes. In this paper, a harmonic time-stepped generator model is applied to derive wound rotor induction generator electrical & mechanical signals for fault measurement, and propose simple closed-form analytical expressions to describe them. Predictions are then validated with tests on a 30 kW induction generator test rig. Results show that generator rotor unbalance produces substantial increases in the side-bands of supply frequency and slotting harmonic frequencies in the spectra of current, power, speed, mechanical torque and vibration measurements. It is believed that this is the first occasion in which such comprehensive approach has been presented for this type of machine, with healthy & faulty conditions at varying loads and rotor faults. Clear recommendations of the relative merits of various electrical & mechanical signals for detecting rotor faults are given, and reliable fault indicators are identified for incorporation into wind turbine condition monitoring systems. Finally, the paper proposes that fault detectability and reliability could be improved by data fusion of some of these electrical & mechanical signals. (C) 2018 The Authors. Published by Elsevier Ltd.Öğe Intelligent Condition Monitoring of Wind Power Systems: State of the Art Review(Mdpi, 2021) Benbouzid, Mohamed; Berghout, Tarek; Sarma, Nur; Djurovic, Sinisa; Wu, Yueqi; Ma, XiandongModern wind turbines operate in continuously transient conditions, with varying speed, torque, and power based on the stochastic nature of the wind resource. This variability affects not only the operational performance of the wind power system, but can also affect its integrity under service conditions. Condition monitoring continues to play an important role in achieving reliable and economic operation of wind turbines. This paper reviews the current advances in wind turbine condition monitoring, ranging from conventional condition monitoring and signal processing tools to machine-learning-based condition monitoring and usage of big data mining for predictive maintenance. A systematic review is presented of signal-based and data-driven modeling methodologies using intelligent and machine learning approaches, with the view to providing a critical evaluation of the recent developments in this area, and their applications in diagnosis, prognosis, health assessment, and predictive maintenance of wind turbines and farms.Öğe Investigation of Grid Supply Harmonic Effects in Wound Rotor Induction Machines(Ieee, 2018) Sarma, Nur; Tuohy, Paul MichaelThis paper presents an in-depth investigation of the effects of several grid supply harmonic voltages on the stator currents of an example wound rotor induction machine. The observed effects of higher order grid supply harmonics are identified using a finite element time stepping transient model, as well as a time-stepping electromagnetic model. In addition, a number of analytical equations to calculate the spectral content of the stator currents are presented in the paper. The presented equations are validated through comparison with the obtained spectra predicted using the finite element and electromagnetic models. The presented study provides a better understanding of the origin of supply harmonic effects identified in the stator currents of the example wound rotor induction machine. Furthermore, the study helps to understand the effects of higher order supply harmonics on the harmonic emissions of an example wound rotor induction machine.Öğe Modeling of a Typical Photovoltaic Module using Matlab/Simulink(Ieee, 2018) Sarma, Nur; Gegin, Keziban; Şimşir, Mehmet; Tutkun, NedimThis paper presents detailed modeling principles of a typical photovoltaic (PV) module using the Matlab/Simulink software. The presented model is based on equations that are obtained from equivalent circuits of the single and double diode models. The presented models are designed with user-friendly blocks from the Simulink block library. The models provide better understanding of the output characteristics of a typical PV module and its changes, since the models can predict the behavior when it operates under various design parameters, as well as environmental conditions. The P-V and I-V output characteristics are determined using the developed models under various temperature and solar irradiation conditions. The accuracy of the developed models is validated by comparing the predicted results with the parameters provided in the datasheet of the investigated PV module.Öğe Modeling, Analysis, and Validation of Controller Signal Interharmonic Effects in DFIG Drives(Ieee-Inst Electrical Electronics Engineers Inc, 2020) Sarma, Nur; Tuohy, Paul Michael; Djurovic, SinisaThis paper presents the development of a doubly fed induction machine (DFIG) harmonic model in matlab/Simulink, which is used to examine the spectral content of DFIG controller signals and improve the understanding of their behavior and spectral nature. The reported DFIG harmonic model has the capability of representing the effects of higher order time and space harmonics and thus, allows detailed analysis of the controller signals embedded spectral effects. The model consists of a wound rotor induction machine (WRIM) harmonic model coupled with a stator flux oriented controller model. The WRIM space harmonic effects are represented using the conductor distribution function approach to enable the calculation of winding inductances as a harmonic series. In addition, analytical expressions are derived to define the possible spectral content in the controller signals of DFIGs. Both the reported DFIG harmonic model and the analytical expressions are validated by comparison with measurements taken from a purpose built vector-controlled DFIG laboratory test rig. The findings confirm the capability of the developed DFIG harmonic model in representing the controller signals embedded spectral effects, as well as the accuracy of the reported analytical expressions, and enables a much improved understanding of the spectral nature of the DFIG controller signals.Öğe Rotor Electrical Fault Detection in DFIGs Using Wide-Band Controller Signals(Ieee-Inst Electrical Electronics Engineers Inc, 2021) Sarma, Nur; Tuohy, Paul M.; Mohammed, Anees; Djurovic, SinisaThis paper presents a novel study of the wide-band spectral signatures in the controller signals of doubly fed induction generators (DFIGs) for the identification of rotor electrical faults. The aim is to advance the understanding of diagnostic information obtainable from the readily available DFIG controller signals. Analytical equations defining the controller signals possible spectral contents are derived to enable characterization of spectral signatures and their correlation to operating conditions and rotor faults. The equations are verified in a DFIG harmonic model study and also validated by undertaking a range of experiments on a laboratory DFIG test-rig. It is shown that the calculated, simulated and experimental results are in good agreement with regards to representing fault induced signatures in the examined DFIG controller signals spectra. Furthermore, it is shown that wide-band rotor electrical fault related spectral signatures in the controller signals carry considerable diagnostic potential for recognition of rotor electrical faults.Öğe Stator Electrical Fault Detection in DFIGs Using Wide-Band Analysis of the Embedded Signals From the Controllers(Ieee-Inst Electrical Electronics Engineers Inc, 2021) Sarma, Nur; Tuohy, Paul M.; Djurovic, SinisaThis article presents a novel study of stator electrical faults detection using the wide-band spectral signatures in the controller signals of doubly fed induction generators (DFIGs). The possible wide-band spectral content of the controller signals are first defined with a set of analytical equations in order to characterize the wide-band spectral signatures and their correlation to operating conditions including stator electrical faults. A DFIG harmonic model and laboratory test-rig are used to validate the derived equations. The calculated, simulated and experimental results are in good agreement. Furthermore, it is shown that the wide-band stator electrical fault related spectral signatures carry considerable diagnostic potential for recognition of stator electrical faults, and therefore, can potentially be used to advance controller embedded fault detection techniques.
