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M.H.J. Bollen
Skellefte, United States, 93187

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Journal article
Published: 07 July 2021 in IEEE Transactions on Power Delivery
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This paper presents the role of the medium-voltage network and low-voltage loads in harmonic voltages with low-voltage customers and harmonic propagation. A general model, as well as a detailed transfer function-based model, are used. By applying them to an existing network, it is shown that remote low-voltage loads have a significant impact on the source and transfer impedance. The main impact occurs for a specific range of frequencies below the resonant frequency of the low-voltage network. The general model is able to estimate this frequency range with an acceptable level of accuracy. Furthermore, by utilizing the concept of overall transfer impedance, it is shown that voltage harmonic levels for harmonic orders around this frequency range are determined mainly by aggregated remote emission rather than local emission.

ACS Style

Naser Nakhodchi; Math Bollen; Tatiano Busatto. Transfer of Harmonics in Distribution Networks. IEEE Transactions on Power Delivery 2021, PP, 1 -1.

AMA Style

Naser Nakhodchi, Math Bollen, Tatiano Busatto. Transfer of Harmonics in Distribution Networks. IEEE Transactions on Power Delivery. 2021; PP (99):1-1.

Chicago/Turabian Style

Naser Nakhodchi; Math Bollen; Tatiano Busatto. 2021. "Transfer of Harmonics in Distribution Networks." IEEE Transactions on Power Delivery PP, no. 99: 1-1.

Journal article
Published: 30 April 2021 in IEEE Access
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The harmonic interaction mechanism in a wind park is examined in this paper. The paper investigates the feasibility of a solution to the yet challenging harmonic contribution estimation from multiple sources in a wind park with limited available information, via an extension of a simple modeling approach as well as from detailed analysis of field measurements. The paper has two distinct objectives in assessing harmonic interactions (a) one to extend the classical Norton equivalent model to a multi-measurement wind park system and to suggest potential areas for further model developments from field measurement analysis, and (b) second to draw inferences from field measurements and to develop a new independent concept of analysis from long-term field measurements in the wind park. From practical experience, a new concept of analysis with a ‘harmonic interaction break-even point’ is introduced. With the help of it, one could identify whether the primary emission (emission from considered source) or secondary emission (emission from a distant source) dominates in the analysis period. In this way, the highest responsibility between different interacting time-varying harmonic sources is evaluated. It was concluded that from long-term measurements one can define a magnitude of power production where a certain harmonic order is canceled or reaches its lowest magnitude. If one finds this cancellation point, one can define a level of secondary/primary emission or at least a feasible range. This knowledge is a step forward towards harmonic contribution analysis.

ACS Style

Vineetha Ravindran; Naser Nakhodchi; Sarah Ronnberg; Math H. J. Bollen. Assessing Time-Varying Harmonic Interactions in a Wind Park. IEEE Access 2021, 9, 68151 -68160.

AMA Style

Vineetha Ravindran, Naser Nakhodchi, Sarah Ronnberg, Math H. J. Bollen. Assessing Time-Varying Harmonic Interactions in a Wind Park. IEEE Access. 2021; 9 ():68151-68160.

Chicago/Turabian Style

Vineetha Ravindran; Naser Nakhodchi; Sarah Ronnberg; Math H. J. Bollen. 2021. "Assessing Time-Varying Harmonic Interactions in a Wind Park." IEEE Access 9, no. : 68151-68160.

Journal article
Published: 17 March 2021 in International Journal of Electrical Power & Energy Systems
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This paper proposes a stochastic method, ''mixed aleatory-epistemic“, for estimating solar PV hosting capacity (HC) of low-voltage (LV) distribution networks. The approach treats the aleatory and epistemic uncertainties in a different way. The HC is estimated by applying the transfer impedance matrix, 'which is only calculated once', and the superposition principle to determine the voltage magnitude rise due to solar PV. By distinguishing between aleatory and epistemic uncertainties, the calculations are limited to the relevant hours (time-of-day or time-of-year) during which high solar PV production is expected. In this way, the random aleatory uncertainties (background voltage, solar PV production, local consumption) are modelled by their probability distributions during the selected time period. The distributions for the epistemic uncertainties (installed capacity per customer, number of customers with solar PV, phase to which single-phase units are connected) are created with simple models involving the interval value and possible occurrence. The stochastic approach proposed is applied to three LV distribution networks to illustrate the method. The results show that both types of uncertainties affect the HC. The need for distribution network planners to identify and distinguish between the types of uncertainties is emphasised.

ACS Style

Enock Mulenga; Math H.J. Bollen; Nicholas Etherden. Solar PV stochastic hosting capacity in distribution networks considering aleatory and epistemic uncertainties. International Journal of Electrical Power & Energy Systems 2021, 130, 106928 .

AMA Style

Enock Mulenga, Math H.J. Bollen, Nicholas Etherden. Solar PV stochastic hosting capacity in distribution networks considering aleatory and epistemic uncertainties. International Journal of Electrical Power & Energy Systems. 2021; 130 ():106928.

Chicago/Turabian Style

Enock Mulenga; Math H.J. Bollen; Nicholas Etherden. 2021. "Solar PV stochastic hosting capacity in distribution networks considering aleatory and epistemic uncertainties." International Journal of Electrical Power & Energy Systems 130, no. : 106928.

Journal article
Published: 01 March 2021 in Renewable Energy
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Swedish government’s target is to have 100% renewable electricity production by 2040. Currently, hydropower contributes the majority of renewable electricity generation of the country. The wind power capacity has increased significantly in the past decade. In this paper, practical data is used to study the possibility of reaching the 100% renewable electricity generation goal by replacing existing thermal generations with wind power generations. It is found that the Swedish electricity generation system can reach 100% renewable by tripling the existing wind power capacity combined with the existing hydropower in the country. Based on current growth rate of wind power installation, the goal could be reached within 20 years. Hourly simulation shows that 100% renewable energy generation system composed by wind power and hydropower satisfy hourly operation requirements.

ACS Style

Jin Zhong; Math Bollen; Sarah Rönnberg. Towards a 100% renewable energy electricity generation system in Sweden. Renewable Energy 2021, 171, 812 -824.

AMA Style

Jin Zhong, Math Bollen, Sarah Rönnberg. Towards a 100% renewable energy electricity generation system in Sweden. Renewable Energy. 2021; 171 ():812-824.

Chicago/Turabian Style

Jin Zhong; Math Bollen; Sarah Rönnberg. 2021. "Towards a 100% renewable energy electricity generation system in Sweden." Renewable Energy 171, no. : 812-824.

Journal article
Published: 22 February 2021 in Energy
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A techno-economic energy flow model for a standalone microgrid was developed to investigate the investment risks related to consumption changes and compare the results to a conventional grid-connection in Sweden. Two different design strategies for a standalone microgrid was used, one with the objective to minimize the life-cycle cost and the other to provide a lower investment risk. It was shown that the largest investment risk for both design strategies was a potential increase in annual energy consumption within the standalone microgrid. The design strategy with the objective to reduce the investment risk eliminated the influence on the life-cycle cost from an increase in peak consumption and reduced the overall investment risk in comparison to the design strategy with the objective to minimize the life-cycle cost. However, a larger life-cycle cost was the drawback of that design strategy. It was concluded that locations with larger annual mean capacity factors reduced the investment risk for standalone microgrids due to lower diesel fuel dependence. It was also concluded that a conventional grid-connection had a lower investment risk than a standalone microgrid, since adverse changes in consumption always increased the life-cycle cost less for a conventional grid-connection than for a standalone microgrid.

ACS Style

Jakob Nömm; Sarah K. Rönnberg; Math H.J. Bollen. Techno-economic analysis with energy flow modeling for investigating the investment risks related to consumption changes within a standalone microgrid in Sweden. Energy 2021, 225, 120156 .

AMA Style

Jakob Nömm, Sarah K. Rönnberg, Math H.J. Bollen. Techno-economic analysis with energy flow modeling for investigating the investment risks related to consumption changes within a standalone microgrid in Sweden. Energy. 2021; 225 ():120156.

Chicago/Turabian Style

Jakob Nömm; Sarah K. Rönnberg; Math H.J. Bollen. 2021. "Techno-economic analysis with energy flow modeling for investigating the investment risks related to consumption changes within a standalone microgrid in Sweden." Energy 225, no. : 120156.

Journal article
Published: 19 February 2021 in Energies
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Power converters with high switching frequency used to integrate renewable power sources to medium and low voltage networks are sources of emission in the supraharmonic range (2 to 150 kHz). When such converters are connected to a medium voltage (MV) network these supraharmonics propagate through the MV network and can impact network and customer equipment over a wide range. This paper evaluates an existing Swedish MV electrical network and studies the pattern of supraharmonic resonance and the propagation of supraharmonics. The MV network consists of eight feeders including a small wind farm. Simulations reveal that, the bigger the MV network, the more resonant frequencies, but also the lower the amplitude of the resonance peaks in the driving point impedance. It was also identified that for short feeders as length increases, the magnitude of the transfer impedance at supraharmonic frequency decreases. For further increment in feeder length, the magnitude increases or becomes almost constant. For very long feeders, the transfer impedance further starts decreasing. The eight feeders in the network under study are similar but show completely different impedance versus frequency characteristics. Measurements at the MV side of the wind farm show time varying emissions in the supraharmonic range during low power production. The impact of these emissions coupled with system resonance is examined.

ACS Style

Sudha Shimi; Angela Delgado; Sarah Rönnberg; Math Bollen. Evaluation of Medium Voltage Network for Propagation of Supraharmonics Resonance. Energies 2021, 14, 1093 .

AMA Style

Sudha Shimi, Angela Delgado, Sarah Rönnberg, Math Bollen. Evaluation of Medium Voltage Network for Propagation of Supraharmonics Resonance. Energies. 2021; 14 (4):1093.

Chicago/Turabian Style

Sudha Shimi; Angela Delgado; Sarah Rönnberg; Math Bollen. 2021. "Evaluation of Medium Voltage Network for Propagation of Supraharmonics Resonance." Energies 14, no. 4: 1093.

Journal article
Published: 27 January 2021 in Electric Power Systems Research
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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.

ACS Style

Kazi Main Uddin Ahmed; Manuel Alvarez; Math H.J. Bollen. Reliability Analysis of Internal Power Supply Architecture of Data Centers in Terms of Power Losses. Electric Power Systems Research 2021, 193, 107025 .

AMA Style

Kazi Main Uddin Ahmed, Manuel Alvarez, Math H.J. Bollen. Reliability Analysis of Internal Power Supply Architecture of Data Centers in Terms of Power Losses. Electric Power Systems Research. 2021; 193 ():107025.

Chicago/Turabian Style

Kazi Main Uddin Ahmed; Manuel Alvarez; Math H.J. Bollen. 2021. "Reliability Analysis of Internal Power Supply Architecture of Data Centers in Terms of Power Losses." Electric Power Systems Research 193, no. : 107025.

Journal article
Published: 29 December 2020 in IEEE Transactions on Power Electronics
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More and more devices connected to low voltage networks inject currents in the frequency range above 2 kHz, so called supraharmonics. Supraharmonics can appear as synchronized or non-synchronized to the power system frequency. A device exposed to a fixed supraharmonic frequency are here shown to generate low order interharmonics when the power system frequency deviates from the ideal 50/60 Hz. Resulting interharmonic frequency and magnitude are determined by three factors; the frequency at which a supraharmonic component exist, the voltage magnitude of that component and the deviation from 50/60 Hz of the power system frequency. Formation of interharmonics is confirmed in a functional model and validated through the measurements and numerical simulations.

ACS Style

Selcuk Sakar; Sarah K. Ronnberg; Math Bollen. Interharmonic Emission in AC–DC Converters Exposed to Nonsynchronized High-Frequency Voltage Above 2 kHz. IEEE Transactions on Power Electronics 2020, 36, 7705 -7715.

AMA Style

Selcuk Sakar, Sarah K. Ronnberg, Math Bollen. Interharmonic Emission in AC–DC Converters Exposed to Nonsynchronized High-Frequency Voltage Above 2 kHz. IEEE Transactions on Power Electronics. 2020; 36 (7):7705-7715.

Chicago/Turabian Style

Selcuk Sakar; Sarah K. Ronnberg; Math Bollen. 2020. "Interharmonic Emission in AC–DC Converters Exposed to Nonsynchronized High-Frequency Voltage Above 2 kHz." IEEE Transactions on Power Electronics 36, no. 7: 7705-7715.

Journal article
Published: 29 November 2020 in Electric Power Systems Research
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Solar photovoltaics in electricity distribution networks is often limited by the rise in voltage magnitude. The pre-connection voltage magnitude is an important factor that determines the hosting capacity. This paper studies to which extent details of the pre-connection voltage magnitude impact the hosting capacity. Extensive measurements of voltage magnitude and solar power production were obtained for a number of distribution networks with 10-minute resolution. The measured background voltage during the sunny-hours from the two-year measurements was used to obtain representative probability distribution functions. A guide for selecting the time-of-day (ToD) used is presented. The obtained probability distribution functions are applied to estimate the stochastic hosting capacity for a low-voltage distribution network with 83 customers. The impact of various details on the hosting capacity are studied. The results show that general knowledge about the range of the pre-connection voltage are essential for the hosting capacity estimation. Measurements over one year were shown to be sufficient to estimate the hosting capacity. The hosting capacity considering the entire day was underestimated by 11 % when compared to the 10 am – 2 pm sunny-hours. The proposed method is general and can be applied to other aleatory uncertainties and other types of hosting capacity studies.

ACS Style

Enock Mulenga; Math H.J. Bollen; Nicholas Etherden. Distribution networks measured background voltage variations, probability distributions characterization and Solar PV hosting capacity estimations. Electric Power Systems Research 2020, 192, 106979 .

AMA Style

Enock Mulenga, Math H.J. Bollen, Nicholas Etherden. Distribution networks measured background voltage variations, probability distributions characterization and Solar PV hosting capacity estimations. Electric Power Systems Research. 2020; 192 ():106979.

Chicago/Turabian Style

Enock Mulenga; Math H.J. Bollen; Nicholas Etherden. 2020. "Distribution networks measured background voltage variations, probability distributions characterization and Solar PV hosting capacity estimations." Electric Power Systems Research 192, no. : 106979.

Journal article
Published: 13 August 2020 in IEEE Transactions on Instrumentation and Measurement
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This paper proposes a novel scheme for analyzing power system measurement data. The main question 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 followed by feature clustering. 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 paper include: 1) providing a new unsupervised deep feature learning approach for seeking possible underlying patterns of power system variation measurements; 2) proposing an effective empirical analysis approach for understanding the measurements through examining the underlying feature clusters and the associated reconstructed data by deep autoencoder.

ACS Style

Chenjie Ge; Roger Alves De Oliveira; Irene Yu-Hua Gu; Math H. J. Bollen. Deep Feature Clustering for Seeking Patterns in Daily Harmonic Variations. IEEE Transactions on Instrumentation and Measurement 2020, 70, 1 -10.

AMA Style

Chenjie Ge, Roger Alves De Oliveira, Irene Yu-Hua Gu, Math H. J. Bollen. Deep Feature Clustering for Seeking Patterns in Daily Harmonic Variations. IEEE Transactions on Instrumentation and Measurement. 2020; 70 (99):1-10.

Chicago/Turabian Style

Chenjie Ge; Roger Alves De Oliveira; Irene Yu-Hua Gu; Math H. J. Bollen. 2020. "Deep Feature Clustering for Seeking Patterns in Daily Harmonic Variations." IEEE Transactions on Instrumentation and Measurement 70, no. 99: 1-10.

Journal article
Published: 06 July 2020 in Electric Power Systems Research
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A number of changes in the power system have increased the risk for more serious resonances in the harmonic frequency range. The changes also result in an increased uncertainty with regard to the frequency and damping of those resonances. Uncertainties could be related to variations with time, uncertain future developments in the grid, and the modelling of individual components. This article investigates uncertainties affecting resonant overvoltages caused by transformer energization. Several study cases investigating the impact of different uncertainties on resonances and resonant overvoltages, performed in PSCAD, are presented. The results show that some uncertainties may have a significant impact on the resulting impedance characteristics and on the resulting overvoltage levels.

ACS Style

Oscar Lennerhag; Math H.J. Bollen. Impact of uncertainties on resonant overvoltages following transformer energization. Electric Power Systems Research 2020, 187, 106503 .

AMA Style

Oscar Lennerhag, Math H.J. Bollen. Impact of uncertainties on resonant overvoltages following transformer energization. Electric Power Systems Research. 2020; 187 ():106503.

Chicago/Turabian Style

Oscar Lennerhag; Math H.J. Bollen. 2020. "Impact of uncertainties on resonant overvoltages following transformer energization." Electric Power Systems Research 187, no. : 106503.

Journal article
Published: 27 May 2020 in IEEE Open Journal of Industry Applications
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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.

ACS Style

Angela Espin-Delgado; Shimi Sudha Letha; Sarah K. Ronnberg; Math H. J. Bollen. Failure of MV Cable Terminations Due to Supraharmonic Voltages: A Risk Indicator. IEEE Open Journal of Industry Applications 2020, 1, 42 -51.

AMA Style

Angela Espin-Delgado, Shimi Sudha Letha, Sarah K. Ronnberg, Math H. J. Bollen. Failure of MV Cable Terminations Due to Supraharmonic Voltages: A Risk Indicator. IEEE Open Journal of Industry Applications. 2020; 1 (99):42-51.

Chicago/Turabian Style

Angela Espin-Delgado; Shimi Sudha Letha; Sarah K. Ronnberg; Math H. J. Bollen. 2020. "Failure of MV Cable Terminations Due to Supraharmonic Voltages: A Risk Indicator." IEEE Open Journal of Industry Applications 1, no. 99: 42-51.

Journal article
Published: 23 May 2020 in Electric Power Systems Research
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Photovoltaic (PV) systems, Electric vehicles (EV) and LED lamps have gained significant popularity in our current society. It is therefore common to find customer installations with all three operating together. PV and EV are known sources of voltage variations on the grid. The impact of these voltage variations on LED lamps situated in close proximity to PV or EV in a low voltage installation, in terms of overvoltage, undervoltage, and rapid voltage changes is systematically studied in a laboratory environment in this paper. Such variations can cause malfunctioning of the lamp based on its immunity and tolerance level or be disturbing to the end-user based on the intensity of variations and rate of recurrence of being subjected to such variations. In this work, the observed impacts on LED lamps are illustrated as 15 different cases. The scope of this work is to identify the possible impacts due to voltage variations induced by PV and EV systems on LED lamps and the potential problems that could happen long term due to recurrent subjection of such voltage variations.

ACS Style

Vineetha Ravindran; Selcuk Sakar; Sarah Rönnberg; Math H.J. Bollen. Characterization of the impact of PV and EV induced voltage variations on LED lamps in a low voltage installation. Electric Power Systems Research 2020, 185, 106352 .

AMA Style

Vineetha Ravindran, Selcuk Sakar, Sarah Rönnberg, Math H.J. Bollen. Characterization of the impact of PV and EV induced voltage variations on LED lamps in a low voltage installation. Electric Power Systems Research. 2020; 185 ():106352.

Chicago/Turabian Style

Vineetha Ravindran; Selcuk Sakar; Sarah Rönnberg; Math H.J. Bollen. 2020. "Characterization of the impact of PV and EV induced voltage variations on LED lamps in a low voltage installation." Electric Power Systems Research 185, no. : 106352.

Journal article
Published: 19 March 2020 in Electric Power Systems Research
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The development of methods to study the propagation of supraharmonics in LV and even MV grids is a current research topic among the power quality community, which has been motivated by the efforts to establish limits for non-intentional supraharmonic emissions and planning levels. The assessment of how much distortion a bulk use of power electronics devices can inject into the grid is necessary before stating emission limits and planning levels for supraharmonics. To address this issue, the development of suitable models that can predict the supraharmonic emission from a low-voltage installation as a whole is required. This article presents a comparison of models for the summation of supraharmonics. An improved model for the summation of supraharmonics is proposed, which is validated experimentally. It is shown that by using the proposed model, predictions of supraharmonic propagation can be accomplished. Furthermore, it is demonstrated experimentally that, with the increasing number of supraharmonic emitting devices, the supraharmonic current distortion injected into a grid by an installation increases up to a maximum value and then decreases due to the capacitive nature of power electronics appliances existing in low-voltage networks.

ACS Style

Ángela Espín-Delgado; Sarah Rönnberg; Tatiano Busatto; Vineetha Ravindran; Math Bollen. Summation law for supraharmonic currents (2–150 kHz) in low-voltage installations. Electric Power Systems Research 2020, 184, 106325 .

AMA Style

Ángela Espín-Delgado, Sarah Rönnberg, Tatiano Busatto, Vineetha Ravindran, Math Bollen. Summation law for supraharmonic currents (2–150 kHz) in low-voltage installations. Electric Power Systems Research. 2020; 184 ():106325.

Chicago/Turabian Style

Ángela Espín-Delgado; Sarah Rönnberg; Tatiano Busatto; Vineetha Ravindran; Math Bollen. 2020. "Summation law for supraharmonic currents (2–150 kHz) in low-voltage installations." Electric Power Systems Research 184, no. : 106325.

Journal article
Published: 16 March 2020 in Electric Power Systems Research
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Voltage magnitude deviation from its nominal value varies over a range of time scales. This paper concentrates on the range between 1 s and 10 min as part of the long-term aim of obtaining a complete picture of voltage magnitude variations at time scales below ten minutes. Time series of voltage with 1-s time resolution are obtained at 57 locations around the world. The main contributions of the paper are: the definition of additional indices in the sub-10-minute time scale from the 1-s rms voltages; statistics on the values of these indices for different locations; identifying the need for further research through a set of recommendations to the research community. It is shown, among others, that for the available data set, the voltage typically varies between 0.5 V and 5 V within a 10-min window; a range exceeding 1 or 2 V is common; a range exceeding 5 V is uncommon. The need for the indices proposed in this paper is justified as equipment connected to the grid is changing and to help managing and for storing the huge amount of data resulting from power-quality measurements at many sites during several years.

ACS Style

Math Bollen; Aurora Gil de Castro; Sarah Rönnberg. Characterization methods and typical levels of variations in rms voltage at the time scale between 1 second and 10 minutes. Electric Power Systems Research 2020, 184, 106322 .

AMA Style

Math Bollen, Aurora Gil de Castro, Sarah Rönnberg. Characterization methods and typical levels of variations in rms voltage at the time scale between 1 second and 10 minutes. Electric Power Systems Research. 2020; 184 ():106322.

Chicago/Turabian Style

Math Bollen; Aurora Gil de Castro; Sarah Rönnberg. 2020. "Characterization methods and typical levels of variations in rms voltage at the time scale between 1 second and 10 minutes." Electric Power Systems Research 184, no. : 106322.

Journal article
Published: 06 March 2020 in IEEE Transactions on Power Delivery
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This letter proposes a measurement-based definition for the phase-angle of the negative-sequence voltage that fits in the general approach used in the IEC standard for power-quality measurements, IEC 61000-4-30. The definition is based on an expression that is obtained during a derivation of the classical expression for calculating the negative-sequence voltage from the rms values of the three line-to-line voltages. The definition can be applied to the 10/12 cycle, 150/180-cycle and 10-minute values.

ACS Style

Math H. J. Bollen; Sarah K. Ronnberg. A Measurement-Based Definition of Phase-Angle for Negative-Sequence Unbalance. IEEE Transactions on Power Delivery 2020, 35, 2561 -2564.

AMA Style

Math H. J. Bollen, Sarah K. Ronnberg. A Measurement-Based Definition of Phase-Angle for Negative-Sequence Unbalance. IEEE Transactions on Power Delivery. 2020; 35 (5):2561-2564.

Chicago/Turabian Style

Math H. J. Bollen; Sarah K. Ronnberg. 2020. "A Measurement-Based Definition of Phase-Angle for Negative-Sequence Unbalance." IEEE Transactions on Power Delivery 35, no. 5: 2561-2564.

Journal article
Published: 23 December 2019 in IEEE Transactions on Power Delivery
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This article presents a stochastic aggregate harmonic load model that can be used to accurately replicate the stochastic behavior of the network impedance downstream of a point of aggregation. The method has been applied to three low voltage networks and the results show that it is able to accurately represent their stochastic behavior while significantly reducing the computational burden compared to modelling the downstream network in detail.

ACS Style

Oscar Lennerhag; Math H. J. Bollen. A Stochastic Aggregate Harmonic Load Model. IEEE Transactions on Power Delivery 2019, 35, 2127 -2135.

AMA Style

Oscar Lennerhag, Math H. J. Bollen. A Stochastic Aggregate Harmonic Load Model. IEEE Transactions on Power Delivery. 2019; 35 (5):2127-2135.

Chicago/Turabian Style

Oscar Lennerhag; Math H. J. Bollen. 2019. "A Stochastic Aggregate Harmonic Load Model." IEEE Transactions on Power Delivery 35, no. 5: 2127-2135.

Journal article
Published: 18 December 2019 in IEEE Transactions on Power Delivery
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Point-on-wave (POW) is a single-event characteristic of voltage dips, influencing the performance of sensitive equipment, such as AC contactor and wind turbines. However, definition and calculation of POW are unsolved issues. The existing definition of POW is for single-phase dips; it does not consider three-phase dips. Moreover, existing POW calculation methods are inaccurate. This paper proposes a definition of POW as a single-event characteristic for three-phase voltage dips. Then, it proposes a POW calculation method based on space vector, including POW detection and angle calculation. The proposed method is based on the ellipse characteristics during the dip-stage and non-dip stage. The proposed method does not depend on zero crossing for angle reference. To verify the performance of the proposed method, a power-system simulation model is built to generate voltage dips with different origin. Furthermore, the accuracy of the proposed method is verified by 425 sets measured voltage dips, and compared with the published methods.

ACS Style

Ying Wang; Ling-Feng Deng; Math H. J. Bollen; Xian-Yong Xiao. Calculation of the Point-on-Wave for Voltage Dips in Three-Phase Systems. IEEE Transactions on Power Delivery 2019, 35, 2068 -2079.

AMA Style

Ying Wang, Ling-Feng Deng, Math H. J. Bollen, Xian-Yong Xiao. Calculation of the Point-on-Wave for Voltage Dips in Three-Phase Systems. IEEE Transactions on Power Delivery. 2019; 35 (4):2068-2079.

Chicago/Turabian Style

Ying Wang; Ling-Feng Deng; Math H. J. Bollen; Xian-Yong Xiao. 2019. "Calculation of the Point-on-Wave for Voltage Dips in Three-Phase Systems." IEEE Transactions on Power Delivery 35, no. 4: 2068-2079.

Journal article
Published: 14 August 2019 in Energies
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HVDC cable systems connected to HVDC overhead lines are subject to fast front overvoltages emanating from the line when lightning strikes a shield wire (backflashover) or a pole conductor (shielding failure). Representative fast front overvoltage levels for HVDC cable systems are usually established without considering their statistical characteristics. A statistical method to determine overvoltages related to the acceptable mean time between failure (MTBF) for the cable system was developed previously. The method accounts for the statistical distribution of lightning current magnitudes as well as the attenuation of the overvoltage wave due to corona discharges on the line, since this effect dominates for system voltages up to about ±320 kV. To make the method suitable for higher system voltages as well, this article introduces an improved statistical method which also accounts for surge attenuation through resistive effects, soil ionization, and statistical treatment of overvoltages due to shielding failures. To illustrate the improved method, it is applied to a case study for a ±525 kV DC line.

ACS Style

Oscar Lennerhag; Jan Lundquist; Christiaan Engelbrecht; Tanumay Karmokar; Math H. J. Bollen. An Improved Statistical Method for Calculating Lightning Overvoltages in HVDC Overhead Line/Cable Systems. Energies 2019, 12, 3121 .

AMA Style

Oscar Lennerhag, Jan Lundquist, Christiaan Engelbrecht, Tanumay Karmokar, Math H. J. Bollen. An Improved Statistical Method for Calculating Lightning Overvoltages in HVDC Overhead Line/Cable Systems. Energies. 2019; 12 (16):3121.

Chicago/Turabian Style

Oscar Lennerhag; Jan Lundquist; Christiaan Engelbrecht; Tanumay Karmokar; Math H. J. Bollen. 2019. "An Improved Statistical Method for Calculating Lightning Overvoltages in HVDC Overhead Line/Cable Systems." Energies 12, no. 16: 3121.

Review
Published: 07 August 2019 in International Journal of Electrical Power & Energy Systems
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A literature review is presented in this paper of the methods for quantifying the solar PV hosting capacity of low-voltage distribution grids. Three fundamentally different methods are considered: i) deterministic ii) stochastic iii) time series. The methods’ outline of applications, merits and shortfalls are summarized. The methods differ in the input data, accuracy, accuracy, computation time, consideration of uncertainties, consideration of the time-related influence and the models used. Two types of uncertainties need to be considered: certain (aleatory) uncertainties and uncertain (epistemic) uncertainties. The latter ones are only included in some of the stochastic methods. In most of the reviewed publications, the voltage magnitude rise and increased loading with increased risk of overvoltage and overloading (for lines, cables and transformers) were the main phenomena considered in the hosting capacity study. This review offers guidelines for distribution system planners on which hosting-capacity method to be used and to researchers on research gaps.

ACS Style

Enock Mulenga; Math H.J. Bollen; Nicholas Etherden. A review of hosting capacity quantification methods for photovoltaics in low-voltage distribution grids. International Journal of Electrical Power & Energy Systems 2019, 115, 105445 .

AMA Style

Enock Mulenga, Math H.J. Bollen, Nicholas Etherden. A review of hosting capacity quantification methods for photovoltaics in low-voltage distribution grids. International Journal of Electrical Power & Energy Systems. 2019; 115 ():105445.

Chicago/Turabian Style

Enock Mulenga; Math H.J. Bollen; Nicholas Etherden. 2019. "A review of hosting capacity quantification methods for photovoltaics in low-voltage distribution grids." International Journal of Electrical Power & Energy Systems 115, no. : 105445.