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Made available in DSpace on 2020-12-12T02:25:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 One of the impacts of harmonic resonances in wind parks is to overload wind park components. The process of identifying a problematic component may be time-consuming due to the number of scenarios and different components (capacitors, transformers, cables and generators) that must be analyzed. In this context, this paper develops a first-screening approach to narrow down the number of scenarios that must be studied in detail. It first identifies that the capacitor bank is the most critical component. Then, it uses the operating limits of the capacitor bank and the harmonic distortions measured at the wind park entrance to obtain a chart that maps the problematic operating conditions of the park. Detailed investigations are needed only if the wind park condition is in specific regions of the chart. The proposed chart is attractive for practical applications as it is obtained with a simple equation, without the need to run any computer simulation, and can be consulted with few information from the wind park that is readily available to engineers. Electrical Engineering School, Universidad de Costa Rica, 27915 San Jose, San Jose Costa Rica 11501-2060 (e-mail: andres.arguello.guillen@gmail.com) Department of Systems and Energy, University of Campinas, Campinas, Sao Paulo Brazil 13083-852 (e-mail: torquato@ieee.org) State University of Campinas, 28132 Campinas Brazil 13083-872 (e-mail: walmir@unicamp.br) Engenharia Eletrica, UNESP, Ilha Solteira Brazil 15385-000 (e-mail: padilha@dee.feis.unesp.br)

Multipulse ac/dc rectifiers (MPRs) are widely used in aviation applications due to their rugged structure, cost effective, and high-reliability features. In this article, an overview of the recent advances and trends on the MPR technology, mainly the autoconfigured transformer-based MPRs, and its application in more electric aircrafts is performed. This article covers system topologies, transformer configurations, passive and active harmonic reduction schemes, case study, practical selection and design guidelines, and applications. To fairly evaluate the performances of MPRs with different pulse numbers, necessary simulation studies are carried out under comparable conditions, including power rating, input and output specifications, and transformer configuration. Then, an 18-pulse asymmetric delta-polygon configured prototype is established based on the simulation evaluation and experimental verification is performed. It is expected that this article can provide a broad perspective on MPR technology, and, in particular, highlight the latest emerged technology that significantly promotes the performances of MPRs. More importantly, it is desired that the results obtained in this article can provide an effective selection guideline and design suggestion for researchers and engineers engaged in designing MPRs, especially for aviation applications.

This letter demonstrates for the first time the usefulness of the X-parameters under 50- $\Omega $ load condition (conventional X-parameters) for simulating and designing RF feedback oscillator circuits. The measurement procedure to characterize a GaAs FET ATF34143 with conventional X-parameters is presented. The measured X-parameters’ data are subsequently used in the design of an RF feedback oscillator at 2.47 GHz. The comparison of the experimental results with the harmonic balance simulations demonstrates the strengths and weakness that conventional X-parameters have to predict the electrical behavior of the feedback oscillator.

Due to significant increment in harmonic polluting loads in the power system, there has been enhanced attention of the power professionals towards the estimation of harmonic signals and identification of their sources in the system. Harmonic source identification is an important step for proper accountability, monitoring, and mitigation of any harmonic pollution. The active power direction (APD) method is one of the conventional approaches for harmonic source detection in the distribution system. Although it is simple and easy to implement, serious concerns were raised on its validity, as the direction of active power is dependent on the phase angle. In this paper, APD is augmented with distorting and non-distorting power to improve its accuracy and reliability for harmonic source identification. The distorting and non-distorting portions of the loads are separated, and the distorting and non-distorting powers are calculated at each node. These calculated powers, in addition to the direction of the harmonic active power, are used to formulate the logic required for deciding the severity index at each node. The validity of the method has been tested on a single-phase network, an IEEE-5 bus system, and an IEEE-14 bus system. It has been observed that the proposed method provides good results than conventional APD with the same measurement requirement.

This report examines two power theories - one in the time domain and the other in so called hybrid domain. Both power theories are applied in the analysis of an urban electrical transport and a comparative analysis between them is made.

According to current energy efficiency labels, the majority of light-emitting diode (LED) lamps on the market are considered as highly efficient devices. This makes it difficult to distinguish between lamps with different operational characteristics and performance. This paper introduces a comprehensive experimental-based labeling methodology for comparing LED lamp performance with reference to two additional important characteristics: light flicker and power factor. The new labeling methodology reveals that there is high diversity between different LED lamps with different circuit topologies but also for a given topology with different design choices. General consumers and design engineers can benefit from the simple and clear information presented by the set of comparative labels when comparing LED lamp performance.

Current transformers for ac power systems applications are usually calibrated by applying sinusoidal currents at different frequencies. The main limitation of this approach is that it does not take into account nonlinearities that may have a significant impact on harmonic current measurement. A more accurate characterization should be based on test currents that are similar to those found in normal working conditions. However, this demands a proper current generator able to generate multitone waveforms with proper accuracy, which is seldom available in laboratories. This paper proposes a simple approach to implement a current generator, based on a waveform generator, a power amplifier, and a transformer which allows boosting the output current capability. Its uneven input–output response can be compensated through linear prefiltering of the desired current waveform. When the generator is employed to reproduce a specific class of current waveforms, such as those typically found in ac distribution grids, an optimal compensation filter can be easily designed. This approach allows canceling systematic nonlinearities introduced by the transformer and the power amplifier, thus significantly increasing accuracy with respect to a conventional frequency response compensation, as confirmed by experimental results.

This chapter discusses one of the inevitable power quality problems, that is harmonics. Causes, types, impacts, and examples of harmonics are given. Various harmonics producing loads recorded through a power quality analyzer are presented.The evaluation of harmonics like total harmonic distortion (THD), total demand distortion (TDD), and total rated current distortion (TRD) are explained with practical examples.

Conventional current transformers (CTs) suffer from nonlinearities due to their ferromagnetic cores. On one hand, it is well-known that severe core saturation may occur because of large overcurrents or unidirectional transient components: this may substantially impact the operation of relays. On the other hand, weaker nonlinear effects are also present during regular working conditions. In particular, the spectral content of typical current waveforms is characterized by a strong fundamental term responsible for harmonic distortion affecting the frequency components at the secondary side. In turn, this has a significant impact on the accuracy that can be reached as long as current harmonics must be monitored. The target of this work is implementing a simple signal processing technique that allows compensating for this effect. The method, characterized by extremely low computational complexity, is first introduced and validated using numerical simulations. After this, it was tested experimentally to improve the harmonic measurement capability of inductive CTs. The achieved results highlight a noticeable reduction of errors at low-order harmonics over a wide range of primary current amplitudes. It is worth noting that the black-box approach makes the technique suitable also for compensating nonlinearities introduced by current transducers based on different operating principles. Thanks to this peculiarity and to the low computational complexity, the proposed method is suitable to be employed in power quality analyzers and merging units. In this way, high-accuracy monitoring of current harmonics in power systems can be achieved, opening the way to advanced power quality management and to the location of disturbing users.

The number of nonlinear devices in distribution grids has rapidly grown in the last years, and this trend is likely to increase in a near future. In this scenario, power quality monitoring and identification of disturbance sources are critical aspects. Inductive transformers are often employed for this purpose, although their metrological performances are guaranteed only near rated frequency. Secondary voltage harmonics are affected by the filtering behavior of the transformer, but also by nonlinearities due to the iron core that may have remarkable impact. In this work a novel post-processing technique allowing to dramatically reduce the detrimental effects of nonlinearities is proposed and discussed. After explaining the methodology, it has been applied to enhance the harmonic measurement accuracy that can be obtained by using an inductive medium voltage instrument transformer. Experimental tests carried out in laboratory show the significant performance improvement achieved thanks to the proposed approach.

This paper focuses on studying the phenomenon of harmonic distortion propagation through distribution networks. This phenomenon is governed by a combination of factors involving the nature of harmonic loads and their dynamic interaction, the influence of background voltage distortion, and harmonic impedance values. The objective of the proposed research includes evaluation of the network response at different nodes to harmonic current injections via utilizing a time-synchronized distributed measurement system. The study is performed in a fully controlled and flexible test network with three medium voltage/low voltage (MV/LV) distribution substations and several managed LV harmonic sources, namely PV inverter, single-phase EV charger and emulated harmonic load with reference current injections. A selection of the results is analyzed and interpretation of the observed phenomena is given with implications that synchronized harmonic measurements can be considered as potential powerful instruments for analyzing power quality disturbances.

The complexity of modes of operation of energy systems with distributed generation requires new analyses methods which take into account the modes of distributed generation sources operation. The analyses and optimization methods presented in this paper allow to perform analyses and optimization in the real time taking into account power quality issues from different types of distributed generation sources.

Light emitting diode (LED) lamps are now an established lighting technology, which is becoming prevalent in all load sectors. However, LED lamps are non-linear electrical loads, and their impact on distribution system voltage quality must be evaluated. This paper provides a detailed analysis of time domain and frequency domain approaches for developing and evaluating models suitable for use in large scale steady-state harmonic power flow analysis of the low frequency (LF) emission of LED lamps. The considered approaches are illustrated using four general categories of LED lamps, which have been shown to cover the vast majority of LED lamps currently available on the market. The aim is an in-depth assessment of the ability of commonly applied models to represent the specific design characteristics of different categories of LED lamps. The accuracy of the models is quantitatively evaluated by means of laboratory tests, numerical simulations, and statistical analyses. This provides an example, for each LED lamp category, of comprehensive information about the overall accuracy that can be achieved in the general framework of large scale LF harmonic penetration studies, particularly in the assessment of voltage quality in low voltage networks and their future evolution.

The importance of monitoring voltage harmonics in distribution grids has raised because of the increasing diffusion of power electronics-based nonlinear devices. In this respect, the role of voltage transformers (VTs) is vital since they represent the input stage in power quality monitoring systems, and they are responsible for one of the major uncertainty contributions. Nevertheless, their metrological performances are still quantified in terms of accuracy class, namely, rating maximum ratio error and phase displacement. The aim of this article is moving from the concept of maximum error to that of uncertainty, while proposing a new approach to evaluate and express the accuracy of VTs employed for harmonic measurements. The method is applied to the calibration of a conventional inductive VT by means of a proper setup that allows injecting complex multitone waveforms. Experimental results clearly show the advantages of the proposed approach, which permits a better description of the metrological behavior with respect to the usual ratio error and phase displacement.

Owing to the particular distribution of energy and load, the high-voltage direct current transmission system has been greatly developed in China. A number of areas have formed the multi-infeed direct current (MIDC) transmission systems. In MIDC transmission systems, the electrical distance between the inverter stations is close and the coupling effect is strong, therefore, the interaction influence of harmonics is complex. In order to analyse this complex interaction influence, this study first introduces the influence factors multi-infeed influence factors of power (MIIF-Pd) and multi-infeed total harmonic voltage distortion (MITHDu), which are used to describe the interaction influence degree of harmonics between inverter stations. Then based on the Shanghai power grid, a simulation model of the MIDC transmission systems was built in PSCAD/EMTDC, and the interaction influence degree of harmonics in MIDC transmission systems was studied in the case of large disturbance and small disturbance exists in the inverter stations. The results show that the interaction influence of harmonics between inverter stations is related to the electrical distance, the style of disturbance, transmission power and so on. Meanwhile, the disturbance on a commutation bus mainly leads to the increase of the harmonic distortion rate in this inverter station, and has less influence on the other stations.

Inductive coordination between power lines and pipelines has been focused on the 60Hz/50Hz component in the past. Through field measurements and circuit-model based analysis, this research shows that harmonic currents in power lines can cause more significant voltage induction on pipelines. It is due to the relatively higher frequency and zero-sequence nature of some of the harmonic currents. In view of the findings, this paper presents two methods for assessing the severity of harmonic voltage induction. One is a circuit-model based method and the other is a field measurement based method.

Interleaved converter legs are typically modulated with individual carriers per leg and phase-shifted PWM (PS-PWM) as it facilitates current balancing amongst the legs. Phase-disposition PWM (PD-PWM), despite the better harmonic performance, cannot be directly used due to the resulting current imbalance that may damage the converter. This paper addresses the current sharing issue and proposes a single-carrier PD-PWM technique for multiple leg two-level converters based on a hierarchy scheme derived from current sorting algorithms. An extension of the proposed algorithm through a switching state feedback loop, limiting the average switching frequency, is also developed. In both cases, the load current is shared amongst the legs and the high-quality of the output voltages and currents is maintained while the circulating currents amongst the converter legs are kept to a minimum. Simulation results demonstrate the method for multiple interleaved legs as well as its current sharing capabilities for high-power applications. Experimental results from a low-power laboratory prototype validate the operation of the proposed approach.

Electric vehicles (EVs) can be utilized as mobile storages in a power system. The use of battery chargers can cause current harmonics in the supplied AC system. In order to analyze the impact of different EVs with regardto their number and their emission of current harmonics, a generic harmonic current model of EV types was built and implemented in the power system simulation tool PSS®NETOMAC. Based on the measurement data for different types of EVs three standardized harmonic EV models were developed and parametrized. Further, the identified harmonic models are used by the computation of load flow in a modeled, German power distribution system. As a benchmark, a case scenario was studied regarding a high market penetration of EVs in the year 2030 for Germany. The impact of the EV charging on the power distribution system was analyzed and evaluated with valid power quality standards.

The frequency range between 2 and 150 kHz has recently gained significant attention, triggered by standardization needs and increased emission in this wide frequency range. This paper gives an overview of the state-of-the-art concerning these so-called supraharmonics, and noticeably indicates the research challenges associated with waveform distortion in this frequency range, with emphasis on the following aspects: emission; propagation; interference; measurements; standardization; modelling and simulation.

Electric transportation systems are a challenging load for three-phase transmission lines due to load variations, reactive power, imbalance, and harmonic pollution. Many power quality conditioners and compensation technologies have been developed to ensure compatibility with power systems. The most important ones are investigated, identifying parameters and performances for comparison, including evaluation of cost and size. A reference case is used for simulation, focusing on three-phase current intensity, current rate of rise, dc-link voltage, and dynamic response under various combinations of traction line load. The objective is to identify key characteristics supporting the selection of the appropriate compensation strategy for a new electrified railway system.

Energy saving policies have boosted the use of light emitting diode (LED) lamps in distribution networks. These lamps are non-linear loads which inject harmonic currents into the distribution system, which has led to a decrease in the system power quality. Study of the modelling of these lamps would allow the prediction of harmonic emissions into distribution systems. This study presents a frequency-domain LED lamp model for harmonic emission calculation, together with a simple estimation procedure for model parameter determination from experimental measurements. Both were validated by laboratory tests. Finally, an application illustrates the effect of widespread use of LED lamps in a typical distribution system and allows LED lamp models to be compared.

Photovoltaic systems are the important part of the energy market in many countries around the world. Such systems contain several parts and one of them is the inverter to produce the AC signal. In this paper, an estimation method is used to obtain the value of frequency, amplitude and phase of the grid signal used to drive the inverter in a proper way. The method is based on the 3-point spectrum interpolation and I class Rife-Vincent time windows. The tested signal contains harmonics and AWGN noise to reflect real and practical measurement conditions. Additionally, simulations were performed for various values of measurement parameters to show broadly properties of the method. The estimation time is only up to two CiR (cycles of the signal in the measurement window). Harmonic components and noise negatively affect the accuracy but the method is so flexible that it can be adjusted to the needs of a current estimation. The estimation error for SNR = 50–60 dB and for two additional harmonics is in the order of approximately 10^−3.

Voltage transformers are vital components for the operation of power systems. Because of the increasing diffusion of power electronics, nonlinear devices in distribution grids, their role is becoming even more important, since they represent the input stage in power quality monitoring instruments. Nevertheless, their metrological performances are still expressed in terms of accuracy class, namely rating maximum ratio and phase errors at fundamental and harmonic frequencies. The aim of this work is providing a contribution that allows migrating from the concept of maximum error to that of uncertainty. Calibration of an inductive voltage transformer has been considered as a case study and simulated through detailed modeling; this allows neglecting the impact of noise and that of the reference transducer. The statistical features of the measurement error are evaluated, and a method to quantify and express uncertainty is proposed.

Monitoring voltage harmonics represents one of the most important tasks in power quality assessment. In particular, the employed instrument transformer plays a key role in the achieved accuracy. Its harmonic measurement performance is typically evaluated by measuring its frequency response function. However, nonlinearities may have a nonnegligible impact on measurement uncertainty; for example, this occurs as far as the inductive voltage transformers are considered. This paper proposes a simple technique allowing the compensation of the most significant nonlinear effect that is the harmonic distortion produced by the large fundamental primary voltage. The method is first derived and introduced by means of numerical simulations and then implemented through a proper experimental setup. Results highlight remarkable accuracy improvements when realistic voltage waveforms are measured.

Due to the increase of sensitive loads on the mains power grid, measurement and monitoring of the power quality (PQ) have become an important factor for both consumers and operators. As is well-known, PQ problems occur in a very short time period with specific characteristics. In transmission or distribution systems, power quality data are collected from monitoring devices such as digital fault recorders, power quality and dynamic system monitors, etc. The recorded data has to be analysed in order to understand system anomalies. These anomalies may be due to sources of broadband noise. In this study, we employ broadband subspace decomposition, using polynomial eigenvalue decomposition, to detect these anomalies. Results demonstrate that this method may be considered as a new and effective tool for measurement and monitoring of PQ problems.

© The Institution of Engineering and Technology. The recently proposed parallel hybrid modular multilevel converter is considered to be a low loss, low component count converter with soft switching capability of the 'main' H-bridge. The converter has similar advantages to other emerging modular multilevel converter circuits being considered for high-voltage, direct current power transmission and can be made compact which is desirable for offshore application. However, during ac network unbalance the individual 'chain-links' (CL) exchange unequal amounts of power with the grid which requires appropriate remedial action. This study presents research into the performance of the converter and proposes a suitable control method that enables the converter to operate during grid voltage unbalance. The proposed control concept involves the use of asymmetric third harmonic voltage generation in the 'CL' of the converter to redistribute the power exchanged between the individual 'CL' and the grid. Mathematical analysis and simulation modelling with results are presented to support the work described.

This study presents control algorithms for a new unified power quality conditioner (UPQC) without the series transformers that are frequently used to make the insertion of the series converter of the UPQC between the power supply and the load. The behaviour of the proposed UPQC is evaluated in presence of voltage imbalances, as well as under non-sinusoidal voltage-and current conditions. The presented algorithms derive from the concepts involving the active and non-active currents, together with a phase-locked-loop circuit. Based on these real-time algorithms, and considering the proposed hardware topology, the UPQC is able to compensate the harmonic components of the voltages and currents, correct the power factor, and keep the load voltages regulated, all of this in a dynamic way, responding instantaneously to changes in the loads or in the electrical power system. The control algorithms were distributed in a two-DSP digital control architecture, without any communication between them. Consequently, can be increased the sampling frequency of the acquired voltages and currents and improve the UPQC performance. Furthermore, some constraints of the proposed UPQC are evidenced, particularly when the main voltages are imbalanced. Simulation and experimental results are presented to verify the UPQC performance under transient and steady state conditions., info:eu-repo/semantics/publishedVersion

This paper describes a three phase shunt active power filter with selective harmonics elimination. The control algorithm is based on a digital filter bank. The moving Discrete Fourier Transformation is used as an analysis filter bank. The correctness of the algorithm has been verified by simulation and experimental research. The paper includes exemplary results of current waveforms and their spectra from a three phase active power filter.

Harmonic emissions of power electronic (PE) devices connected to transmission networks are introducing new and rising trends of harmonic distortion. Analyses, which focus on assessing the harmonic levels in PE-rich power networks of the future, are mostly based on digital simulations, which require accurate models of the power system and connected devices. The simulations are usually performed with the use of electro-magnetic transient (EMT) models, resulting in long simulation times or the use of oversimplified load-flow models. In this paper, we propose a methodology that can be used to define accurate frequency-domain simulation models of PE devices. The models are derived by frequency-dependent multiparameter scanning. The resulting models can be employed for harmonic load-flow simulations in different network and PE-device operating conditions. They enable the assessment of the impact of frequency-dependent network-impedance characteristics and, moreover, the effect of cross coupling between different frequency components. The analysis is focused on high-power high-voltage PE devices, which cannot be easily measured or analyzed for harmonic characteristics. Therefore, the methodology requires detailed EMT models of the devices, which are analyzed within different operating conditions. The accurate equivalent models of PE devices represent a crucial element within the context of harmonic emission studies in large transmission networks.

The parallel connection of multiple electronic power converters is typically used to connect renewable power sources to the electricity grid, like often done, for example, in photovoltaic farms. This interconnection of systems can be affected by instability issues above the fundamental grid frequency, which has detrimental effects on power quality, protection effectiveness, and reliability. This paper proposes an accurate multi-input multi-output methodology to stability analysis that allows us to highlight and analyze all the relevant stability contributions linked to converters as well as grid dynamics. The analytical study of a generic system representation is first discussed to introduce the approach. Then, the impedance multiplication effect, commonly applied when all the parallel connected inverters are equal, is herein extended to the case of converters with different parameters. The outcome of the study is an approach featuring both accurate stability analysis, as in multi-input-multi-output-based approaches, and modularity, as in impedance-based approaches. The results of the study are validated by means of extensive simulation and experimental tests on an experimental setup composed of three 5-kVA parallel inverters.

Measurement of voltage harmonics has become a crucial task in power quality assessment for several years. The achieved accuracy strictly depends on the employed transducer, which in many cases is represented by a conventional inductive voltage transformer. It is well known that such transducers suffer from an uneven frequency response that undermines their harmonic measurement performance; for this reason, compensation techniques based on a linear modeling have been proposed in the literature. However, the accuracy of inductive voltage transformers at low-order harmonics is severely jeopardized by nonlinear effects and in particular by the harmonic distortion due to the strong fundamental component typical of voltage waveforms in ac power systems. For the first time, this paper proposes a simple technique able to compensate also this nonlinear phenomenon, thus achieving a significant improvement in overall accuracy. The performance of the method is assessed by means of numerical simulations and the achieved results are extensively discussed.

Resonances in electrical distribution systems can result in amplification of harmonics, which is undesirable in electrical networks. To avoid intrusive measurement techniques, in the majority of the cases network modeling is used to validate if there is an issue with resonance. In this paper a new, innovative but simple, concept is presented which uses relatively basic measurements to segregate the power related to specific harmonics into active and non-active harmonic power. These results are subsequently used in order to find if there is resonance in the electrical network. In this paper the concepts are explained on a theoretical basis and are test cased by numerical modeling. The initial results look promising but additional research is needed to validate the method.

A method for locating harmonic producing source in the low-voltage distribution network is presented. The method aims to employ natural load variability of the existing non-linear installations. By performing multi-point time-synchronized acquisition of the voltage and current waveforms and analysing spectral characteristics of the signals, harmonic impedance of the cable section associated with non-linear load is estimated. A certain rejection algorithm is applied in order to discard data sets with unreliable information. To validate the method, a field test was established in the low-voltage grid. The results demonstrate capability of the proposed technique to accurately estimate harmonic impedances and successfully identify location of harmonic current source in the grid.

LCL filters feature low inductance; thus, the injected grid current from an LCL -filtered voltage-source inverter can be easily distorted by grid-voltage harmonics. This problem is especially tough for the control system with inverter-side current feedback (ICF), since the grid-current harmonics can freely flow into the filter capacitor. In this case, because of the loss of harmonic information, traditional harmonic controllers fail to mitigate the grid-current distortion. Although this problem may be avoided using the grid-voltage feedforward scheme, the required differentiators may cause the noise amplification. In light of the above issue, this paper develops a simple method for the ICF control system to mitigate the grid-current harmonics without extra sensors. In the proposed method, resonant harmonic controllers and an additional compensation loop are adopted at the same time. The potential instability introduced by the compensation loop can be avoided through a special design of the compensation position. Finally, the effectiveness of the proposed method for harmonic rejection is verified by detailed experimental results.

This study presents the preliminary results of a new methodology for detecting high-impedance faults in distribution systems based on interharmonic signatures. The methodology involves incorporation of an interharmonic current analysis system into a conventional protection system, such as automatic reclosers and sectionalisers. To check the functionality of the proposed methodology, the authors carried out field tests on different types of soil, involving instantaneous current waveform measurements during the occurrence of faults. The results suggest that the methodology, based on interharmonic currents produced by variations in electric arc length during the occurrence of high-impedance faults, shows great promise when it comes to detection of the disturbance.

Nowadays, voltage transducers in medium-voltage (MV) distribution networks operate in nonsinusoidal conditions while their calibration is still based on simple sine-wave tests. A more significant characterization could be achieved using complex multitone signals. However, this requires an MV generator able to apply arbitrary voltage waveforms to the transducer under test. The authors have recently proposed a simple MV signal generator that can be effectively employed for this purpose. In this paper, the performance of this MV generator has been carefully analyzed. A characterization procedure based on multisine excitation has been proposed and tested. In particular, the main causes of uncertainty have been identified and their impact on the accuracy of the generated voltage evaluated. The analysis considers both linear and nonlinear effects, such as harmonic distortion and hysteresis.

Low-watt compact fluorescent lamps (CFLs) may account for significant energy consumption of power distribution feeders in future years. This can lead to power-quality concerns because these devices consume highly distorted currents. In order to predict CFL harmonic current emissions into networks, CFL models capable of predicting these emissions accurately are being studied. On the other hand, these models require great computational effort in large-scale CFL penetration studies. This paper presents and discusses several approximate CFL models based on the harmonic-coupled admittance matrix model which reduces the computational effort while maintaining reasonable accuracy. The performance of the models is validated with CFL laboratory measurements.

A multi-functional distributed generation unit (MFDGU) and its control strategy are proposed in this paper for the purpose of enhancing power quality in low-voltage networks. By using the 3H-bridge converter structure, an MFDGU can be applied in 3-phase 4-wire low-voltage distribution networks to compensate harmonic, reactive, and unbalanced currents. A reduced-order model of the MFDGU is derived through a weighted-average-current-feedback (WACF) approach, showing the robustness and stability of the proposed approach. The Fryze-Buchholz-Dpenbrock (FBD) power theory is employed to generate the current reference of the MFDGU, which can be easily implemented in three-phase networks. A 15kVA prototype consisting of three full bridge converters has been built and tested. Experimental results show the feasibility of the proposed topology and control strategy.

This paper observes that a number of new methods have emerged for efficient and effective testing of data converters, but there is no work comparing their strengths and weaknesses. The authors describes recent methods in detail, highlighting important aspects and contrasting their abilities to perform various test measurements.

The increasing penetration of renewable/distributed sources with non-linear characteristics demands a clear methodology for determining the amount of generation which can be connected to the system without deteriorating the performance (the hosting capacity). This paper proposes a methodology for determining the hosting capacity regarding harmonic distortions. The method includes aggregation effects of harmonic currents, the influence of harmonic distortion limits and harmonic generation profile. To exemplify an application of the proposed procedure, a simple case study is performed and analyzed.

Attention towards power quality issues in distribution grids has increased noticeably in the last decade. Power quality assessment and monitoring require voltage transducers capable of measuring both fundamental and harmonics with adequate accuracy. Beside this, a systematic but simple procedure for evaluating the measurement performance of voltage transducers, able to quantify the impact of linear and nonlinear effects separately has not been proposed yet. In this paper, a testing method based on the concept of Best Linear Approximation (BLA) is introduced. The excitation signals resemble the voltage waveforms typically found in distribution networks, while the impact of noise and nonlinearity is evaluated in terms of sample variances. The approach is applied to the model of a typical voltage transformer by means of numerical simulations.

Continuous development of electrical power systems has resulted in very complex relay protection system with associated numerical protection algorithms. Reliability, selectivity and speed are the basic design requirements for the development of new algorithms. Ideally the amplitude estimation algorithms should determinate the amplitude as fast as possible, theoretically with just one sampled value. Currently there are no algorithms which can do that with a high reliability. Abovementioned requirements are contradictory which makes it impossible to completely fulfil all of them. Current and voltage based phasor estimation algorithms are the core of all numerical protection relays, thus significantly defining protection function performances. A detailed overview of the most common numerical phase estimation algorithms is shown in this paper, including time responses on various input signal combinations. All algorithms are simulated in the LabVIEW development environment.

The characteristics of harmonic current emission of residential customers depends significantly on the number of users. While single users have a virtually random behavior, the low order harmonic current of a whole network with several hundreds of residential users usually shows a high level of prevalence with low variation. This paper discusses the aggregation characteristic of low order harmonic currents in residential low-voltage networks based on an extensive measurement database of single users and aggregated users. The first part of the paper compares the harmonic emission of single users and groups of users and shows, how the variation of harmonic magnitudes and phase angles changes with the number of users. The second part presents a systematic simulation of the harmonic currents for groups with stepwise increased number of users. Based on the results, recommendations for the development of probabilistic aggregate harmonic models of residential users are provided.

Enhanced Digital Functionality has captivated nearly every phase of society. The shift is overwhelming: Smart phones, smart TVs and smart cars are just a few examples of the trend. Enhanced digitization has also inspired a key development trend in Electrical Distribution Equipment. In fact, recommended practices to improve electrical safety by design are being developed that include digital features that can enhance safety in the design of Electrical Distribution Equipment.

This paper presents a method for the detection of series arc faults in electrical circuits, which has been developed starting from an experimental characterization of the arc fault phenomenon and an arcing current study in several test conditions. Starting from this, the authors have found that is it possible to suitably detect arc faults by means of a high-resolution low-frequency harmonic analysis of current signal, based on chirp zeta transform, and a proper set of indicators. The proposed method effectiveness is shown by means of experimental tests, which were carried in both arcing and nonarcing conditions and in the presence of different loads, chosen according to the UL 1699 standard requirements.

This contribution reports the design of an X-band MMIC power amplifier in a 0.25 um GaN technology, proposing for the first time a harmonic manipulation approach on a class C bias condition. Output network provides the power matching condition at fundamental frequency and an open circuit condition at the 3rd harmonic; the correct phase ratio between drain current components is assured by the proper input 2nd harmonic impedance. This solution allows to reach an efficiency higher than 60% in the frequency band 8.5 GHz–9.5 GHz.