SwePub - search: WFRF:(Bollen Math H.J.)

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1.	Ehnberg, Jimmy, 1976, et al. (author) Reliability of a small power system using solar power and hydro 2005 In: Electric Power Systems Research. - : Elsevier BV. - 0378-7796 .- 1873-2046. ; 74:1, s. 119-127 Journal article (peer-reviewed)abstract This paper studies the availability of the electricity supply when the sources consist of a combination of solar energy and a small hydro installation. Instead of flow-of-river, a small reservoir is used. By not using the hydro energy during sunny periods, the natural flow-of-river fills up the reservoir for later use. A model for global solar radiation is proposed with an astronomical part (deterministic) and a meteorological part (stochastic). The meteorological part is based on a Markov model of the cloud coverage. The solar model does not require solar radiation measurements, just cloud observations. A case study has been performed for Timbuktu (16.75degreesN, 0.07degreesW) in which generation availability is simulated for four different cases: solar power only; solar power with storage; solar and hydro power and solar and hydro, power with storage. To be able to use exclusively renewable energy sources, a combination of sources is needed to secure the reliability of the supply. Using solar cells in combination with a small reservoir is favorable. Even with a weak flow the affect of the flow on the day time reliability is minor, but great benefits can be found for reliability during low load hours (night time).
2.	Ehnberg, Jimmy, 1976, et al. (author) Simulation of global solar radiation based on cloud observations 2005 In: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 78:1, s. 157-162 Journal article (peer-reviewed)abstract A stochastic model for simulating global solar radiation on a horizontal surface has been developed for use in power systems reliability calculations. The importance of an appropriate model for global solar radiation has increased with the increased use of photovoltaic power generation. The global solar radiation shows not only regular yearly and daily variations but also a random behaviour. The yearly and daily variations can be described in a deterministic way while the random behaviour has a high correlation with the state of the atmosphere. The astronomic effects can easily be described mathematical with only some minor simplifications but the atmospheric effects are more complicated to describe. The transmittivity of solar radiation in the atmosphere depends on various factors, e.g. humidity, air pressure and cloud type. By using cloud observations as input for the simulations, the local meteorological conditions can be accounted for. The model is usable for any geographical location if cloud observations are available at the location or at locations with similar climatological conditions. This is especially useful for development countries where long-term solar radiation measurement can be hard to obtain. Cloud observations can be performed without any expensive equipment and have been a standard parameter for many years throughout the world. Standard observations are done according to the Oktas-scale. It is the interval between observations that sets the resolution of the simulation: the observations are normally only every hour or every third hour. The model can easily be combined with cloud coverage simulations, has been proposed, for a more general model. For some calculations higher resolution may be needed. This can be obtained by including a stochastic model for the short-term variations and simple model has been proposed. Errors and limitations of the model are estimated and discussed.
3.	Ahmed, Kazi Main Uddin, 1989-, et al. (author) A Novel Reliability Index to Assess the Computational Resource Adequacy in Data Centers 2021 In: IEEE Access. - NY : IEEE. - 2169-3536. ; 9, s. 54530-54541 Journal article (peer-reviewed)abstract The energy demand of data centers is increasing globally with the increasing demand for computational resources to ensure the quality of services. It is important to quantify the required resources to comply with the computational workloads at the rack-level. In this paper, a novel reliability index called loss of workload probability is presented to quantify the rack-level computational resource adequacy. The index defines the right-sizing of the rack-level computational resources that comply with the computational workloads, and the desired reliability level of the data center investor. The outage probability of the power supply units and the workload duration curve of servers are analyzed to define the loss of workload probability. The workload duration curve of the rack, hence, the power consumption of the servers is modeled as a function of server workloads. The server workloads are taken from a publicly available data set published by Google. The power consumption models of the major components of the internal power supply system are also presented which shows the power loss of the power distribution unit is the highest compared to the other components in the internal power supply system. The proposed reliability index and the power loss analysis could be used for rack-level computational resources expansion planning and ensures energy-efficient operation of the data center.
4.	Ahmed, Kazi Main Uddin, 1989-, et al. (author) A Review of Data Centers Energy Consumption And Reliability Modeling 2021 In: IEEE Access. - : IEEE. - 2169-3536. ; 9 Research review (peer-reviewed)abstract Enhancing the efficiency and the reliability of the data center are the technical challenges for maintaining the quality of services for the end-users in the data center operation. The energy consumption models of the data center components are pivotal for ensuring the optimal design of the internal facilities and limiting the energy consumption of the data center. The reliability modeling of the data center is also important since the end-user’s satisfaction depends on the availability of the data center services. In this review, the state-of-the-art and the research gaps of data center energy consumption and reliability modeling are identified, which could be beneficial for future research on data center design, planning, and operation. The energy consumption models of the data center components in major load sections i.e., information technology (IT), internal power conditioning system (IPCS), and cooling load section are systematically reviewed and classified, which reveals the advantages and disadvantages of the models for different applications. Based on this analysis and related findings it is concluded that the availability of the model parameters and variables are more important than the accuracy, and the energy consumption models are often necessary for data center reliability studies. Additionally, the lack of research on the IPCS consumption modeling is identified, while the IPCS power losses could cause reliability issues and should be considered with importance for designing the data center. The absence of a review on data center reliability analysis is identified that leads this paper to review the data center reliability assessment aspects, which is needed for ensuring the adaptation of new technologies and equipment in the data center. The state-of-the-art of the reliability indices, reliability models, and methodologies are systematically reviewed in this paper for the first time, where the methodologies are divided into two groups i.e., analytical and simulation-based approaches. There is a lack of research on the data center cooling section reliability analysis and the data center components’ failure data, which are identified as research gaps. In addition, the dependency of different load sections for reliability analysis of the data center is also included that shows the service reliability of the data center is impacted by the IPCS and the cooling section.
5.	Ahmed, Kazi Main Uddin, 1989-, et al. (author) Characterizing Failure and Repair Time of Servers in a Hyper-scale Data Center 2020 In: Proceedings of 2020 IEEE PES Innovative Smart Grid Technologies Europe (ISGT-Europe) 26-28 October, 2020. - : IEEE. ; , s. 660-664 Conference paper (peer-reviewed)abstract Hyper-scale data centers are used to host cloud computing interfaces to support the increasing demand for storage and computational resources. For achieving specific service level agreements (SLA), this infrastructure demands highly available cloud computing systems. It is necessary to analyze the server failure incidents to determine the way of improving the reliability of the system since the computational interruption causes financial losses for the data center owners. Regarding the reliability analysis, it is important to characterize the time to failure and time to repair of the servers. In this paper, a publicly available data set from Google cloud-cluster data center will be analyzed to find the distribution function for the time to failure and the time to repair for the servers in a cloud based data centers.
6.	Ahmed, Kazi Main Uddin, 1989-, et al. (author) Reliability Analysis of Internal Power Supply Architecture of Data Centers in Terms of Power Losses 2021 In: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 193 Journal article (peer-reviewed)abstract The number of data centers and the energy demand are increasing globally with the development of information and communication technology (ICT). The data center operators are facing challenges to limit the internal power losses and the unexpected outages of the computational resources or servers. The power losses of the internal power supply system (IPSS) increase with the increasing number of servers that causes power supply capacity shortage for the devices in IPSS. The aim of this paper is to address the outage probability of the computational resources or servers due to the power supply capacity shortage of the power distribution units (PDUs) in the IPSS. The servers outage probability at rack-level defines the service availability of the data center since the servers are the main computational resource of it. The overall availability of the IPSS and the power consumption models of the IPSS devices are also presented in this paper. Quantitative studies are performed to show the impacts of the power losses on the service availability and the overall availability of the IPSS for two different IPSS architectures, which are equivalent to the Tier I and Tier IV models of the data center.
7.	Ahmed, Kazi Main Uddin, 1989-, et al. (author) The Impacts of Voltage Disturbances Due to Faults In the Power Supply System of A Data Center 2022 In: 2022 20th International Conference on Harmonics & Quality of Power (ICHQP) Proceedings. - : IEEE. Conference paper (peer-reviewed)abstract The internal power condition system (IPCS) in data centers is prone to have cable faults that cause voltage dips and swells. The voltage dips and swells impact the power supply units (PSUs) with the servers. The servers connected with the PUSs restart or turn-off when the input voltage comes out of the voltage-tolerance range. This paper analyses the impact of such voltage disturbances on server outages due to a single-phase fault in the IPCS. The voltage-tolerance range of the PSUs is considered according to the guideline of the Information Technology Industry Council (ITIC). The voltage dip propagates to the healthy load sections from the fault location, while voltage swells are also observed due to sudden load reduction. Moreover, the current limitation mode of the inverter in the uninterrupted power supply (UPS) is identified as a cause of voltage dip to almost zero experienced by the PSUs. The reliability of the data center considering the outage probability of the servers are finally quantified to show the impacts of the voltage dips and swells in the IPCS.
8.	Axelberg, Peter G. V., et al. (author) A Measurement Method for Determining the Direction of Propagation of Flicker and for Tracing a Flicker Source. 2007 Conference paper (peer-reviewed)
9.	Axelberg, Peter G. V., et al. (author) Automatic classification of voltage events using the support Vector 2007 Conference paper (peer-reviewed)
10.	Axelberg, Peter G.V. 1959, et al. (author) AUTOMATIC CLASSIFICATION OF VOLTAGE EVENTS USING THE SUPPORT VECTOR MACHINE METHOD 2007 In: 19th International Conference on Electricity Distribution (SIRED 2007) , Vienna, Austria, 21-24 May, 2007. Conference paper (peer-reviewed)abstract Statistically based classification systems need to be trained on a large number of training data in order to classify unseen data accurately. However, it is difficult to gather enough voltage events for the training purpose from real recordings. Therefore, a classification system trained to accurately classify real voltage events, but based on synthetic training data is highly in demand. This paper therefore proposes the design of a statistically based classification system trained on synthetic data. The paper gives also the results of conducted performance tests when the proposed classification system was trained to classify seven common types of voltage events. The experiments showed an overall detection rate of 81.6%, 91.9% and 99.5% respectively.
11.	Axelberg, Peter G.V., et al. (author) Performance Tests of a Support Vector Machine used for Classification of Voltage Disturbances 2006 In: in proc. of 12th International conf. on Harmonics and Quality of Power (ICHQP 2006), Cascais, Portugal, Oct.1-5, 2006. Conference paper (peer-reviewed)abstract This paper proposes a novel method for classifying voltage disturbances in electric power systems by using the Support Vector Machine (SVM) method. The proposed SVM classifier is designed to classify five common types of voltage disturbances and experiments have been conducted on recorded disturbances with good classification results. The proposed SVM classifier is also shown to be robust in terms of using training data and testing data that originate from two different power networks.
12.	Axelberg, Peter G.V. 1959, et al. (author) Support Vector Machine for Classification of Voltage Disturbances 2007 In: accepted for publication in IEEE Transactions on Power Delivery. ; 22:3, s. 1297-1303, July, 2007 Journal article (peer-reviewed)abstract The Support Vector Machine (SVM) is a powerful method for statistical classification of data used in a number of different applications. However, the usefulness of the method in a commercial available system is very much dependent on whether the SVM classifier can be pre-trained from a factory since it is not realistic that the SVM classifier must be trained by the customers themselves before it can be used. We first propose a novel SVM classification system for voltage disturbances. Our aim also includes investigating the performance of the proposed SVM classifier when the voltage disturbance data used for training and testing are originated from different sources. The data used in the experiments were originated from both real disturbances recorded in two different power networks and from synthetic data. The experimental results have shown excellent accuracy in classification when training data were originated from one power network and unseen testing data from another. High accuracy was also achieved when the SVM classifier was trained on data from a real power network and test data originated from synthetic data. Slightly less accuracy was achieved when the SVM classifier was trained on synthetic data and test data were originated from the power network.
13.	Axelberg, Peter G.V. 1959, et al. (author) Trace of flicker sources by using the quantity of flicker power 2007 In: IEEE transactions on Power Delivery. ; 23:1, s. pp.465-471 Journal article (peer-reviewed)abstract Industries that produce flicker are often placed close to each other and connected to the same power grid system. This implies that the measured flicker level at the point of common coupling (PCC) is a result of contribution from a number of different flicker sources. In a mitigation process it is essential to know which one of the flicker sources is the dominant one. We propose a method to determine the flicker propagations and trace the flicker sources by using flicker power measurements. Flicker power is considered as a quantity containing both sign and magnitude. The sign determines if a flicker source is placed downstream or upstream with respect to a given monitoring point and the magnitude is used to determine the propagation of flicker power throughout the power network and to trace the dominant flicker source. This paper covers the theoretical background of flicker power and describes a novel method for calculation of flicker power that can be implemented in a power network analyzer. Also conducted simulations and a field test based on the proposed method will be described in the paper.
14.	Axelberg, P., et al. (author) Trace of Flicker Sources by using the Quantity of Flicker power. 2008 In: IEEE Transactions on Power Delivery. - : IEEE. - 0885-8977 .- 1937-4208. ; 23:1, s. 465-471 Journal article (peer-reviewed)abstract Industries that produce flicker are often placed close to each other and connected to the same power grid system. This implies that the measured flicker level at the point of common coupling (PCC) is a result of contribution from a number of different flicker sources. In a mitigation process it is essential to know which one of the flicker sources is the dominant one. We propose a method to determine the flicker propagations and trace the flicker sources by using flicker power measurements. Flicker power is considered as a quantity containing both sign and magnitude. The sign determines if a flicker source is placed downstream or upstream with respect to a given monitoring point and the magnitude is used to determine the propagation of flicker power throughout the power network and to trace the dominant flicker source. This paper covers the theoretical background of flicker power and describes a novel method for calculation of flicker power that can be implemented in a power network analyzer. Also conducted simulations and a field test based on the proposed method will be described in the paper.
15.	Bagheri, Azam, et al. (author) A Framework Based on Machine Learning for Analytics of Voltage Quality Disturbances 2022 In: Energies. - : MDPI. - 1996-1073. ; 15:4 Journal article (peer-reviewed)abstract This paper proposes a machine-learning-based framework for voltage quality analytics, where the space phasor model (SPM) of the three-phase voltages before, during, and after the event is applied as input data. The framework proceeds along with three main steps: (a) event extraction, (b) event characterization, and (c) additional information extraction. During the first step, it utilizes a Gaussian-based anomaly detection (GAD) technique to extract the event data from the recording. Principal component analysis (PCA) is adopted during the second step, where it is shown that the principal components correspond to the semi-minor and semi-major axis of the ellipse formed by the SPM. During the third step, these characteristics are interpreted to extract additional information about the underlying cause of the event. The performance of the framework was verified through experiments conducted on datasets containing synthetic and measured power quality events. The results show that the combination of semi-major axis, semi-minor axis, and direction of the major axis forms a sufficient base to characterize, classify, and eventually extract additional information from recorded event data.
16.	Bagheri, Azam, et al. (author) The Novel Method for Voltage Transient Detection and Characterization 2019 In: 2019 IEEE Milan PowerTech. - : IEEE. Conference paper (peer-reviewed)abstract This paper proposes a novel method for voltage transient detection and characterization using space phasor model (SPM) of the three phase-to-neutral voltages as basis. A Gaussian model based anomaly detection technique is used to extract transient samples as anomalous samples. The proposed method introduces and calculates a set of 'single-transient characteristics'(STC) for voltage transient events. This facilitates quantification of transients, leads to additional information about transient origin, and enables comparing different transients. The proposed method is not sensitive to shallow harmonic distortion particularly in deal with oscillating transients.A number of transients measured at distribution or transmission level have been applied to the proposed method. The simulation results support the effectiveness of the SPM for voltage transient analytics.
17.	Bakhtiari, Hamed, et al. (author) A stochastic modelling of electrical vehicle load and its impacts on a Swedish distribution network 2021 In: CIRED 2021 - The 26th International Conference and Exhibition on Electricity Distribution. - : Institution of Engineering and Technology. ; , s. 2406-2410 Conference paper (peer-reviewed)
18.	Bhattacharya, Kankar, et al. (author) Operation of Restructured Power Systems 2001 Book (other academic/artistic)
19.	Bollen, Math H.J., et al. (author) Analysis and Classification of Power Quality Disturbances: Ideas, Methods and Technquies 2006 In: in Proc. 12th International conf. on harmonics and quality of power (ICHQP 06), Cascais, Portugal, Oct. 1-5, 2006. Conference paper (peer-reviewed)
20.	Bollen, Math H.J. 1960, et al. (author) BRIDGING THE GAP BETWEEN SIGNAL AND POWER: assessing power system quality using signal processing techniques 2009 In: IEEE Signal Processing Magazine. - 1558-0792 .- 1053-5888. ; 26:4, s. 12-31 Journal article (peer-reviewed)
21.	Bollen, Math H J, et al. (author) Harmonics and Wind Power Installations 2021 In: CIRED 2021 - The 26th International Conference and Exhibition on Electricity Distribution. - : IEEE. ; , s. 648-652 Conference paper (peer-reviewed)
22.	Bollen, Math H. J., et al. (author) Is there a place for power quality in the smart grid? 2014 In: Proceedings - International Conference on Harmonics and Quality of Power. - : IEEE. - 1540-6008 .- 2164-0610. ; , s. 713-717 Journal article (peer-reviewed)abstract This paper contains some thoughts on the relations between power quality and smart grids. It includes some of the, in our opinion, important research and development activities that are needed within power quality as part of the transition to the smart grid.
23.	Bollen, Math H.J., et al. (author) On the Analysis of Voltage and Current Transients in Three-Phase Power Systems 2007 In: IEEE Transactions on Power Delivery. ; 22:2, s. 1194-1201, April 2007 Journal article (peer-reviewed)abstract This paper presents a method for analysis measurementsof voltage transients in three-phase systems. The method is based on the Clarke transform introduced in 1950 forcalculations of travelling waves along three-phase transmission lines. The proposed method also shows close similarities with the classification of three-phase unbalanced voltage dips into types C and D. After extracting the actual transient, e.g. by using a notch filter centered on the power-system frequency, the three signals are decomposed into seven components. From the relationbetween these seven components, the dominant component isidentified. The method is successfully applied to a number of measured transients. The paper also identifies the limitations of the method and gives suggestions for future work.
24.	Bollen, Math H. J., et al. (author) Overload and overvoltage in low-voltage and medium-voltage networks due to renewable energy — Some illustrative case studies 2012 In: 2nd IEEE PES International Conference and Exhibition on Innovative Smart Grid Technologies (ISGT Europe). - Piscataway, NJ : IEEE Communications Society. - 9781457714221 - 9781457714207 Conference paper (peer-reviewed)abstract This paper presents the use of curtailment to allowmore wind or solar power to be connected to a distributionnetwork when overcurrent or overvoltage set a limit. For fourcase studies, all based on measurements, the gain in producedenergy is calculated. It is shown that the curtailment method hasa large impact on this gain. The paper further discusses details ofthe curtailment algorithm and the communication needs as wellas some further applications of curtailment.
25.	Bollen, Math H. J., et al. (author) Signal processing of power-quality disturbances 2006 In: Johh Wiley & Sons - IEEE Press. - Piscataway, NJ : IEEE Communications Society. - 0471731684 ; , s. 888- Book (pop. science, debate, etc.)abstract Bridging the gap between power quality and signal processing This innovative new text brings together two leading experts, one from signal processing and the other from power quality. Combining their fields of expertise, they set forth and investigate various types of power quality disturbances, how measurements of these disturbances are processed and interpreted, and, finally, the use and interpretation of power quality standards documents. As a practical aid to readers, the authors make a clear distinction between two types of power quality disturbances: Variations: disturbances that are continuously present Events: disturbances that occur occasionally A complete analysis and full set of tools are provided for each type of disturbance: Detailed examination of the origin of the disturbance Signal processing measurement techniques, including advanced techniques and those techniques set forth in standards documents Interpretation and analysis of measurement data Methods for further processing the features extracted from the signal processing into site and system indices The depth of coverage is outstanding: the authors present and analyze material that is not covered in the standards nor found in the scientific literature. This text is intended for two groups of readers: students and researchers in power engineering who need to use signal processing techniques for power system applications, and students and researchers in signal processing who need to perform power system disturbance analyses and diagnostics. It is also highly recommended for any engineer or utility professional involved in power quality monitoring.
26.	Bollen, Math H.J., et al. (author) The power grid as part of a 100% renewable energy system 2017 In: Large Scale Grid Integration of Renewable Energy Sources. - : Institution of Engineering and Technology. ; , s. 1-27 Book chapter (other academic/artistic)
27.	Busatto, Tatiano, et al. (author) Experimental Harmonic Analysis of the Impact of LED Lamps on PV Inverters Performance 2019 In: 2019 Electric Power Quality and Supply Reliability Conference (PQ) & 2019 Symposium on Electrical Engineering and Mechatronics (SEEM). - : IEEE. Conference paper (peer-reviewed)abstract It is known for instance that voltage waveform distortion and network impedance have a significant impact on PV inverter current emissions. Because this, much research is still required to better understand their behavior and impact when multiple common household devices are placed to operate together in the same low-voltage installation. In particular, this paper addresses the harmonic impact of LED lamps on PV inverters performance considering different technologies and number of lamps. The analysis has been carried out with different scenarios considering two types of LED lamps, with and without power factor correction feature, and three different PV inverter technologies. The evaluation of the impacts is simply performed by frequency and time domain analysis, establishing the correlation between the devices current harmonics. The results obtained from the experiments have shown that LED lamps are prone to add a significant impact on the PV inverter current harmonics, and this impact is mainly dependent on the devices used technology.
28.	Busatto, Tatiano, et al. (author) Harmonic Analysis of Electric Vehicle Charging on the Distribution System Network with Distributed Solar Generation 2020 In: The Renewable Energies and Power Quality Journal. - : European Association for the Development of Renewable Energies, Environment and Power Quality. - 2172-038X. ; 18, s. 103-108 Journal article (peer-reviewed)abstract Electric vehicle chargers and solar photovoltaic inverters are two types of household loads that can potentially impact the power quality of the grid. This paper presents a view of the consequences that the connection of these two nonlinear loads into a low-voltage installation can create on voltage harmonic distortion. The analysis considers the combined impact on network impedance and current harmonic distortion. First, the network impedance for phase-to-neutral connections is obtained considering the uncertainty in customer impedance. For this, a Monte Carlo simulation and the concept of transfer impedance are used. Second, based on real measurements, the current harmonic distortion of these two nonlinear loads are used to calculate the resulting voltage distortion at any bus of interest in the network. The analysis is applied to an existing low-voltage network in Sweden. Based on the study case, results show that some harmonics may increase by about 83 % as a function of the penetration of electric vehicles and photovoltaic installations.
29.	Carvalho, J. M., et al. (author) Voltage sag index calculation: Comparison between time-domain simulation and short-circuit calculation 2008 In: Electric Power Systems Research. - : Elsevier BV. - 0378-7796 .- 1873-2046. ; 78:4, s. 676-682 Journal article (peer-reviewed)abstract This paper describes a case study where voltage sags indices are estimated using Monte Carlo approach combined with ATP (Alternative Transient Program) and short-circuit calculation program. Voltage sag magnitude and frequency are used to evaluate the correlation between both programs. The results indicate that time-domain simulation and short-circuit calculation gives similar voltage sag indices. Considering the high correlation between the results, short-circuit calculation programs are preferable over the time-domain simulation tools as the modelling for time-domain simulation is more complex, time consuming, and rarely covers the whole network. (C) 2007 Elsevier B.V. All rights reserved.
30.	Chen, Cheng, et al. (author) Power Quality Knowledge Application for Low Voltage Ride Through Studies of Wind Turbine Generator 2019 In: Proceedings of 2019 IEEE PES Innovative Smart Grid Technologies Europe (ISGT-Europe). - : IEEE. Conference paper (peer-reviewed)abstract Low voltage ride through (LVRT) of wind turbines is an important grid integration issue and the subject of many studies. However, in many such studies, the voltage dip waveforms used to test the performance of LVRT methods are not the one that can occur at the terminal of a wind turbine in reality. This paper provides a critical review of existing works and summarizes the power quality knowledge needed to study LVRT. Characteristics of voltage dips at the terminals of a wind turbine generator (WTG) will be analyzed based on realistic wind farm topology and transformer winding configuration. The impact of collection system transformer winding configuration on low voltage ride through of DFIG is revealed for the first time. Also, the impact of phase angle jump (PAJ) is shown in simulation. The changes of PAJ and point on wave (POW) characteristics in propagation between point of common connection (PCC) and terminal are analyzed to inspire further works. These issues are important but widely neglected by current works.
31.	Chouhy Leborgne, Roberto, 1972, et al. (author) Effect of PQ-monitor connection on voltage dip indices: PN vs PP voltages 2006 In: Electric Power Quality and Utilisation Magazine. ; 2:1 Journal article (peer-reviewed)abstract This work addresses the influence of the PQ-monitor connection on the estimation of voltage dip site and system indices. Voltage dip indices are estimated for a set of events obtained from simulation and measurement of voltage dips. The simulated dips are obtained applying the method of fault positions on a large transmission network and the measured dips come from a one-year survey realized on three buses of a sub-transmission and distribution network.The site and system indices estimated to compare phase-to-phase and phase-to-neutral dips are SARFI-90, SARFI-70, SARFI-ITIC, expected voltage dip amplitude (µ[VDA]), and the cumulative distribution frequency of voltage dip amplitude. These indices are estimated at the bus level and then they are aggregated to estimate the system performance. The comparison of phase-to-phase and phase-to-neutral indices indicates that, at high voltage level, phase-to-neutral dips are more frequent and more severe than phase-to-phase ones. However, these differences are damped at low voltage level, where the monitored bus presented similar indices for phase and line voltages. These observations must be taken in consideration to compare voltage dip benchmark because the lack of information about the type of the measured voltages may lead to derive inaccurate conclusions about the site and system performance regarding voltage dips.
32.	de Oliveira, Roger Alves, et al. (author) Analysing Waveform Distortion in Wind Power Plants by a Deep Learning-Based Graphical Tool 2022 In: 2022 20th International Conference on Harmonics & Quality of Power (ICHQP) Proceedings. - : IEEE. Conference paper (peer-reviewed)abstract This work shows an application of a deep learning-based graphical tool for analyzing waveform distortion in wind power plants. The tool consists of a deep autoencoder followed by a clustering algorithm. Previous applications of such a tool have covered harmonic emission which follows daily patterns. The challenge of measurements in wind power plants is the intermittence of the power production, which can vary in a time frame of minutes and hours. To this point, this work proposes a modification of a DL method presented in the literature to address measurements from wind power plants. The method can automatically obtain the number of clusters. The method is applied to harmonic measurements from H2 to H50 and active power in a Brazilian wind power plant. The graphical results allowed obtaining the correlation between patterns of odd and even current harmonic with the active power generated by a wind power plant.
33.	de Oliveira, Roger Alves, et al. (author) Comparative Analysis of Transformer-Energizing and Fault-Caused Voltage Dips on the Dynamic Behavior of DFIG-Based Wind Turbines 2020 In: Proceedings of 2020 IEEE PES Innovative Smart Grid Technologies Europe (ISGT-Europe) 26-28 October, 2020. - : IEEE. ; , s. 589-593 Conference paper (peer-reviewed)abstract This work compares the response of DFIG-based wind turbines under voltage dips caused by transformer-energizing and caused by an asymmetrical fault. Voltage dips with similar retained voltage and duration and the two distinct causes are applied to an equivalent model of a DFIG-based wind park. The dips are different in terms of harmonic content and unbalance during the recovery after the dip. Due to its slow recovery, the transformer-energizing dip results in longer fluctuation in torque, longer overshoot in DC-link voltage, and longer recovery to the pre-dip active power. Also, due to its harmonic content, the harmonic distortion in the rotor and stator current is higher for the transformer-energizing dip. As the impact is different between the transformer-energizing dip and the fault-caused dip, it is recommended to consider both events separately during low-voltage-ride-through studies.
34.	de Oliveira, Roger Alves, et al. (author) Deep Learning Method With Manual Post-Processing for Identification of Spectral Patterns of Waveform Distortion in PV Installations 2021 In: IEEE Transactions on Smart Grid. - : IEEE. - 1949-3053 .- 1949-3061. ; 12:6, s. 5444-5456 Journal article (peer-reviewed)abstract This paper proposes a deep learning (DL) method for the identification of spectral patterns of timevarying waveform distortion in photovoltaic (PV) installations. The PQ big data with information on harmonic and/or interharmonics in PV installations is handled by a deep autoencoder followed by feature clustering. Measurements of voltage and current from four distinct PV installations are used to illustrate the method. This paper shows that the DL method can be used as a starting point for further data analysis. The main contributions of the paper include: (a) providing a novel DL method for finding patterns in spectra; (b) guiding the manual post-processing based on the patterns found by the DL method; and (c) obtaining information about the emission from four PV installations.
35.	de Oliveira, Roger Alves, et al. (author) Impact of Voltage Dips Originated in the Transmission Grid on EV Charging Stations 2022 In: 2022 20th International Conference on Harmonics & Quality of Power (ICHQP) Proceedings. - : IEEE. Conference paper (peer-reviewed)abstract This work aims to verify the impact of voltage dips propagated from the transmission grid on EV charging stations. Previous works in this topic have applied voltage dips directly to the terminals of the EV chargers, i.e. neglecting the transfer between the source of the dip and the EV chargers stations. Moreover, some works limited their analysis by considering only the magnitude and duration of voltage dips. This work aims to verify if the impact of dips on EV charging stations is distinct when considering the propagation and detailed characteristics of the dips. This work shows that the non-consideration of the propagation and detailed characteristics of the voltage dips might underestimate the impact on the EV charging station.
36.	de Oliveira, Roger Alves, et al. (author) Short-Term Distortion and Protection Operation in DFIG-Based Wind Parks during Voltage Dips 2020 In: Proceedings of 2020 IEEE PES Innovative Smart Grid Technologies Europe (ISGT-Europe) 26-28 October, 2020. - : IEEE. ; , s. 819-823 Conference paper (peer-reviewed)abstract Due to the increasing penetration of wind power, grid codes require that the wind farms remain connected to the grid during voltage dips. The harmonic distortion might change during the short-term reduction in the voltage magnitude. Although the distortion only occurs during the short period of the voltage dip, high levels of harmonic might cause mal-operation of the protective devices in a wind power plant. The main negative influence that harmonics can have on wind power plant protection is that it can act unnecessarily. This work analysis the changes in the harmonic content in the voltages and currents during dips in a DFIG-based wind power plant. The results showed that the total harmonic distortion for the voltages in the collector system and at the terminals of the wind turbines increases during asymmetrical dips. The currents were affected for both symmetrical and asymmetrical dips. The third and seventh harmonics were the voltage components that most increased. For the currents, the increase was in the third harmonic and interharmonics.
37.	de Oliveira, Roger Alves, et al. (author) Susceptibility of Large Wind Power Plants to Voltage Disturbances – Recommendations to Stakeholders 2022 In: Journal of Modern Power Systems and Clean Energy. - : State Grid Electric Power Research Institute (SGERPI). - 2196-5625 .- 2196-5420. ; 10:2, s. 416-429 Journal article (peer-reviewed)abstract Sufficient fault-ride-through (FRT) of large wind power plants (WPPs) is essential for ensuring transmission-grid operational security. The majority of FRT studies do not include all disturbances originated in the transmission grid or include disturbances not relevant for operational security. Using knowledge of power quality, this paper provides a guide to stakeholders in different aspects of FRT for wind turbines (WTs) and wind power plants. This work details the characteristics of the most common disturbances originated in the transmission grid, how they propagate to the wind turbines terminals, and how they impact the dynamic behavior of a large WPP. This work shows that the details of the voltage disturbances at the WT terminals should be considered and not just the voltage disturbance in the transmission grid. Moreover, detailed representation or characterization of voltage dips is important in FRT studies. The simplified models used in the literature are insufficient. This paper strongly recommends that distinct events and additional characteristics as the phase-angle jump and oscillations in the transition segments are considered in FRT analysis.
38.	de Oliveira, Roger Alves, et al. (author) Third Harmonic and its Relation to Solar Elevation Angle in a PV Installation with Solar Tracking Systems 2022 In: 2022 20th International Conference on Harmonics & Quality of Power (ICHQP) Proceedings. - : IEEE. Conference paper (peer-reviewed)abstract This paper shows an application of a deep learning method to a solar installation with a solar tracking system. The method consists of a deep autoencoder followed by clustering. The deep learning method allows defining the most dominant component in harmonic spectra during long-term measurements. Power Quality measurements were accessed over two years in 3ϕ PV installation of 6 kVA with 2-axis tracking in northern Sweden. The deep learning results indicate that the third harmonic of current is the component that changes most over the two years. This paper demonstrates that there is a correlation between the daily and seasonal variations of the third harmonic with the solar elevation angle at the location. The main conclusion for this cause was associated with the operation of the solar tracking systems which are based on single-phase motors. The paper also discusses the possibility of correlation of the third harmonic with cloud coverage, snow on the panels, and reactive power unbalance.
39.	Du, C., et al. (author) A new control strategy of a VSC-HVDC System for high-quality supply of industrial plants 2007 In: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 22:4, s. 2386-2394 Journal article (peer-reviewed)abstract This paper proposes a control strategy for a VSC-HVDC for improving the quality of power supply to industrial plants. The new idea of this control strategy is to give high priority to keep up the ac voltage and slightly decrease the frequency during disturbances. The motivation for choosing this strategy is that the sensitive processing industries are much more sensitive to voltage drops as compared with frequency deviations. In order to test this control strategy, the dynamic performance of a VSC-HVDC supplied industrial plant is investigated during sudden load disturbances, balanced and unbalanced faults from the grid. Simulation results obtained using PSCAD/EMTDC show that with the use of the proposed control strategy, the system can ride through disturbances such as motor starting and faults by slightly decreasing the frequency. The current limit of the VSC-HVDC converters has a significant influence on the dynamics of the system. An increase of the current limit significantly improves the power quality of the system. The comparison of the behavior between a pure ac supplied industrial plant and a VSC-HVDC supplied industrial plant clearly shows the capability of the VSC-HVDC to mitigate voltage dips during faults.
40.	Ehnberg, Jimmy S.G., et al. (author) Generation Reliability for Small Isolated Power Systems entirely based on Renewable Sources 2004 In: Power Engineering Society General Meeting, 2004. IEEE. - 0780384652 ; , s. 2322-2327 Vol 2 Conference paper (peer-reviewed)
41.	Ehnberg, Jimmy S.G. 1976-, et al. (author) Reliability of a small isolated power system in remote areas based on wind power 2004 In: Nordic Wind Power Conference 2004 NWPC'04. Conference paper (other academic/artistic)
42.	Espín-Delgado, Ángela, et al. (author) Failure of MV Cable Terminations due to Supraharmonic Voltages : A Risk Indicator 2020 In: IEEE Open Journal of Industry Applications. - : IEEE. - 2644-1241. ; 1, s. 42-51 Journal article (peer-reviewed)abstract This paper addresses the accelerated aging of medium-voltage (MV) cable terminations with resistive stress-grading due to supraharmonics. The paper introduces a simple and quick way to relate the risk of cable termination failure to the characteristics of supraharmonic distortion in the system. The motivation is to give practical recommendations and guidelines to evaluate the risk of failure of cable terminations under the presence of supraharmonics in MV networks. The underlying model relates the heating in the cable termination linearly with the frequency of the voltage applied and proportionally with the square of the magnitude of the voltage. The indicator can be used to decide whether given levels and frequencies of supraharmonics in the MV network represent a risk to cable terminations. The parameters of the cable termination design are not needed for that decision. However, the decision criterion is based on one sample data (Eagle Pass) and more field information is crucial to improve the approach.
43.	Espín-Delgado, Angela, et al. (author) Uncertainties in the Quantification of Supraharmonic Emission: Variations over Time 2020 In: PAPERS0 ICREPQ'20. - : European Association for the Development of Renewable Energies, Environment and Power Quality (EA4EPQ). Conference paper (peer-reviewed)abstract This paper shows a study of the variations of the supraharmonic distortion emitted by an LED lamp during and after its thermal stabilization. The study is aimed to contribute to map the uncertainties existing when quantifying supraharmonics. Measurements of the current drawn by five lamps of the same type and manufacturer are performed. Then, analysis in the frequency domain is performed and the Total Supraharmonic Current (TSHC) index is used to quantify the supraharmonic emission of the lamps. The TSHC is calculated over bands of different widths, whose outcomes are then compared to decide which bandwidth results in a less time-varying-TSHC index. It is demonstrated that the supraharmonic distortion emitted by the lamp under study experiences both an increase in magnitude and a shift in frequency during the thermal stabilization of the lamp. It is also shown how the frequency grouping impacts the quantification. It is concluded that the best choice of a grouping bandwidth is one wide enough so that it includes the whole emission band of interest. This result is a step forward to set up references for the analysis and quantification of broadband supraharmonic emission.
44.	Etherden, Nicholas, et al. (author) Quantification of ancillary services from a virtual power plant in an existing subtransmision network 2013 In: Innovative Smart Grid Technologies Europe (ISGT EUROPE). - Piscataway, NJ : IEEE Communications Society. - 9781479929849 ; , s. 1-5 Conference paper (peer-reviewed)abstract This paper presents the results of a feasibility study of a virtual power plant (VPP) in central Sweden designed to provide ancillary services to a 50-kV distribution network. The VPP consists of a wind park, hydro plant and reservoir as well as solar PVs and battery energy storage. The 50-kV subtransmission network was modeled in order to evaluate the ancillary services that could be provided by coordinating existing distributed energy resources in the network. Simulations were performed using measured hourly variations in production and consumption at all network nodes. The studied ancillary services include both reactive and active power control. Contribution from the VPP is evaluated for balancing, to enable a producer to meet spot markets bids and avoid purchases of balancing power minimize peak load in order to reduce subscribed power and tariff to the regional 130-kV network decrease network losses the contribution from reactive power control using the power converters to reduce the reactive power flow to the overlying network. Quantification of the economic gains from each operation case is provided.
45.	Etherden, Nicholas, et al. (author) Technical dimensioning of an energy storage for a Swedish distribution company 2013 In: 22nd International Conference and Exhibition on Electricity Distribution (CIRED 2013). - Red Hook, NY : Curran Associates, Inc.. - 9781849197328 Conference paper (peer-reviewed)
46.	Faiz, J., et al. (author) Wavelet based Mann and Morrison algorithm for improvement of three-phase unbalanced voltage dips characterization 2007 In: IET Generation, Transmission & Distribution. - : Institution of Engineering and Technology (IET). - 1751-8687 .- 1751-8695. ; 1:4, s. 640-646 Journal article (peer-reviewed)
47.	Fornari, Federica, et al. (author) SSC compensation capability of unbalanced voltage sags 2005 In: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 20:3, s. 2030-2037 Journal article (peer-reviewed)abstract In this paper, the capacity of a static series compensator (SSC) to compensate for voltage sags is discussed, and a complete analysis of the effects of unbalanced Sags on the SSC compensation capability is carried out. Expressions are obtained for the missing voltage during unbalanced voltage sags. These expressions are used to estimate how often a voltage sag occurs where the missing voltage exceeds the injection capability of the SSC. The method is applied to a typical Italian network configuration.
48.	Ge, Chenjie, 1991, et al. (author) Deep Feature Clustering for Seeking Patterns in Daily Harmonic Variations 2021 In: IEEE Transactions on Instrumentation and Measurement. - : IEEE. - 0018-9456 .- 1557-9662. ; 70 Journal article (peer-reviewed)abstract This article proposes a novel scheme for analyzing power system measurement data. The main question that we seek answers in this study is on “whether one can find some important patterns that are hidden in the large data of power system measurements such as variational data.” The proposed scheme uses an unsupervised deep feature learning approach by first employing a deep autoencoder (DAE) followed by feature clustering. An analysis is performed by examining the patterns of clusters and reconstructing the representative data sequence for the clustering centers. The scheme is illustrated by applying it to the daily variations of harmonic voltage distortion in a low-voltage network. The main contributions of the article include: 1) providing a new unsupervised deep feature learning approach for seeking possible underlying patterns of power system variation measurements and 2) proposing an effective empirical analysis approach for understanding the measurements through examining the underlying feature clusters and the associated reconstructed data by DAE.
49.	Ge, Chenjie, 1991, et al. (author) Unsupervised deep learning and analysis of harmonic variation patterns using big data from multiple locations 2021 In: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 194 Journal article (peer-reviewed)abstract This paper addresses the issue of automatically seeking and identifying daily, weekly and seasonal patterns in harmonic voltage from measurement data at multiple locations. We propose a novel framework that employs deep autoencoder (DAE) followed by k-mean clustering. The DAE is used for extracting principal features from time series of harmonic voltages. A new strategy is used for training the encoder in DAE from data at one selected location that is effective for subsequent feature extraction from data at multiple locations. To analyze the patterns, several empirical analysis approaches are applied on the clustered principal features, including the distribution of daily patterns over the week and the year, representative waveform sequences of individual classes, and feature maps for visualizing high-dimensional feature space through low-dimensional embedding. The proposed scheme has been tested on a dataset containing harmonic measurements at 10 low-voltage locations in Sweden for the whole year of 2017. Results show distinct principal patterns for most harmonics that can be related to the use of equipment causing harmonic distortion. This information can assist network operators in finding the origin of harmonic distortion and deciding about mitigation actions. The proposed scheme is the first to provide a useful analysis tool and insight for finding and analyzing underlying patterns from harmonic variation data at multiple locations.
50.	Gil-de-Castro, Aurora, et al. (author) Variations in harmonic voltage at the sub-10-minute time scale 2021 In: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 195 Journal article (peer-reviewed)abstract This paper presents the statistical analysis of variations in harmonic voltage in the time scale between 1 second and 10 min, a time scale that is rarely considered in studies but that is of relevance for incorrect operation of end-user equipment. The paper also introduces a set of novel power-quality indices quantifying these variations and it gives recommendations on how to include these indices in the power-quality-monitoring framework provided by IEC 61000–4–30. The statistics and the illustration of the novel indices are based on measurements of harmonic 2 through 40 with 1-second time resolution at 154 locations in 16 countries. The proposed power-quality indices are a compromise between storing large amounts of raw data with high time resolution, resulting in the different big-data challenges, and completely neglecting this time scale. Two important findings from this paper are that this time scale should not be completely neglected and that information on this time scale can be recorded without excessive increase in the need for data transmission and storage.

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