The switching loss of the secondary side rectifiers in LLC resonant converters can have a noticeable impact on the overall efficiency of the complete power supply and constrain the upper limit of the optimum switching frequencies of the converter. Two are the main contributions to the switching loss in the secondary side rectifiers: on the one hand, the reverse recovery loss (Qrr), most noticeably while operating above the series resonant frequency; and on the other hand, the output capacitance (Coss) hysteresis loss, not previously reported elsewhere, but present in all the operating modes of the converter (under and above the series resonant frequency). In this paper, a new technique is proposed for the measurement of the switching losses in the rectifiers of the LLC and other isolated converters. Moreover, two new circuits are introduced for the isolation and measurement of the Coss hysteresis loss, which can be applied to both high-voltage and low-voltage semiconductor devices. Fin... [more]

The world is transitioning from the conventional grid to the smart grid at a rapid pace. Innovation always comes with some flaws; such is the case with a smart grid. One of the major challenges in the smart grid is to protect it from potential cyberattacks. There are millions of sensors continuously sending and receiving data packets over the network, so managing such a gigantic network is the biggest challenge. Any cyberattack can damage the key elements, confidentiality, integrity, and availability of the smart grid. The overall smart grid network is comprised of customers accessing the network, communication network of the smart devices and sensors, and the people managing the network (decision makers); all three of these levels are vulnerable to cyberattacks. In this survey, we explore various threats and vulnerabilities that can affect the key elements of cybersecurity in the smart grid network and then present the security measures to avert those threats and vulnerabilities at th... [more]

Advances in power electronics and their use in Miscellaneous Electric Loads (MELs) in buildings have resulted in increased interest in using low-voltage direct current (DC) power distribution as a replacement for the standard alternating current (AC) power distribution in buildings. Both systems require an endpoint converter to convert the distribution system voltage to the MELs voltage requirements. This study focused on the efficiency of these endpoint converters by testing pairs of AC/DC and DC/DC power converters powering the same load profile. In contrast to prior studies, which estimated losses based on data sheet efficiency and rated loads, in this study, we used part load data derived from real-world time-series load measurements of MELs and experimentally characterized efficiency curves for all converters. The measurements performed for this study showed no systematic efficiency advantage for commercially available DC/DC endpoint converters relative to comparable, commercially... [more]

This paper presents the development and evaluation of EnnerSpectrum, a platform for electricity monitoring. The development was motivated by a gap between academic, fully custom-made monitoring solutions and commercial proprietary monitoring approaches. EnnerSpectrum is composed of two main entities, the back end, and the Gateway. The back end is a server comprised of flexible entities that can be configured to different monitoring scenarios. The Gateway interacts with equipment at a site that cannot interact directly with the back end. The paper presents the architecture and configuration of EnnerSpectrum for a long-term case study with 13 prosumers of electricity for approximately 36 months. During this period, the proposed system was able to adapt to several building and monitoring conditions while acquiring 95% of all the available consumption data. To finalize, the paper presents a set of lessons learned from running such a long-term study in the real world.

Advances in remote data acquisition techniques have contributed to the flooding of society with spatial data sets and information. Widely available spatial data sets, including digital terrain models (DTMs) from aerial laser scanning (ALS) data, are finding more and more new applications. The article analyses and compares the heights of the 14 highest peaks of the Polish Carpathians derived from different data sources. Global navigation satellite system (GNSS) geodetic measurements were used as reference. The comparison primarily involves ALS data, and selected peaks’ GNSS measurements carried out with Xiaomi Mi 8 smartphones were also compared. Recorded raw smartphone GNSS measurements were used for calculations in post-processing mode. Other data sources were, among others, global and local databases and models and topographic maps (modern and old). The article presents an in-depth comparison of Polish and Slovak point clouds for two peaks. The results indicate the possible use of la... [more]

This study is related to the heat energy transfer during 3D nanofluid (water-based) motion over a rotating surface by incorporating the combined impacts of thermal radiations and couple stress. The flow is modeled by a set of non-linear coupled PDEs, which is converted to a set of coupled non-linear ODEs by using suitable similarity transformations. The transformed equations are solved with the built-in NDSolve command. The effects of relevant interesting parameters on the nanofluid velocity components and temperature distribution are explained through various graphs. It is found that the velocity component f(η) is increased with higher values of γ and A0 while it drops with an increasing rotation parameter and nanoparticle volume fraction. The fluid temperature increases with higher αnf, Rd, ϵ2, ϵ3, A1 and drops with increasing Pr, ϵ1 and couple stress parameter (A0). The Nusselt number remains constant at a fixed Pr and Rd, whereas it increases with increasin... [more]

Developing wind energy in Lithuania is one of the most important ways to achieve green energy goals. Observational data show that the decline in wind speeds in the region may pose challenges for wind energy development. This study analyzed the long-term variation of the observed 2006−2020 and projected 2006−2100 near-surface wind speed at the height of 10 m over Lithuanian territory using data of three models included in the Coupled Model Intercomparison Project phase 5 (CMIP5). A slight decrease in wind speeds was found in the whole territory of Lithuania for the projected wind speed data of three global circulation models for the scenarios RCP2.6, RCP4.5, and RCP8.5. It was found that the most favorable scenario for wind energy production is RCP2.6, and the most unfavorable is the RCP4.5 scenario under which the decrease in wind speed may reach 12%. At the Baltic Sea coastal region, the decline was smaller than in the country’s inner regions by the end of the century. The highest red... [more]

Pyrolysis is an optimal thermochemical process for obtaining valuable products (char, oil, and gas) from waste tires. The preliminary research was done on the three groups of samples acquired by cutting the same waste tire of a passenger vehicle into cylindrical granules with a base diameter of 3, 7, and 11 mm. Each batch weighed 10 g. The heating rate was 14 °C/min, and the final pyrolysis temperature was 750 °C, with 90 s residence time. After the pyrolysis product yields were determined for all of the three sample groups, further research was performed only on 3 mm granules, with the same heating rate, but with altered final pyrolytic temperatures (400, 450, 500, 550, 600, 650, 700, and 750 °C). The results of this study show that thermochemical decomposition of the waste tire sample takes place in the temperature range of 200−500 °C, with three distinct phases of degradation. The highest yield of the pyrolytic oil was achieved at a temperature of 500 °C, but further heating of vola... [more]

Smart electricity meters are a cornerstone for the realization of next-generation electrical power grids [...]

This book contains the successful invited submissions [...]

Systems of two immiscible liquid phases—aqueous phase (i.e., distilled water (dH2O) or phosphate-buffered saline (PBS)) and liquid perfluorochemical (i.e., perfluorodecalin (PFD))—were subjected to wave-assisted agitation, i.e., oscillatory rocked, in a disposable bag-like container in a ReadyToProcess WAVETM25 bioreactor, to recognize oxygen transfer effects and effectivity of the surface aeration. According to the DoE methodology, values of the volumetric liquid-side mass transfer (kLa) coefficient for dH2O, PBS, dH2O-PFD, and PBS-PFD systems were determined for the whole range of operating parameters of the WAVE 25 bioreactor. A significantly higher maximal value of kLa was found for waving dH2O than for dH2O-PFD (i.e., 0.00460 s−1 vs. 0.00331 s−1, respectively) compared to more equal maximal values of kLa reached for PBS and PBS-PFD (0.00355 s−1 vs. 0.00341 s−1, respectively). The interface development factor (f) depended on the interfacial area a, and the enhancement factor (EPFD)... [more]

A fluidic oscillator with a bent outlet nozzle was investigated to find the effects of the bending angle on the characteristics of the oscillator with and without external flow. Unsteady aerodynamic analyses were performed on the internal flow of the oscillator with two feedback channels and the interaction between oscillator jets and external flow on a NACA0015 airfoil. The analyses were performed using three-dimensional unsteady Reynolds-averaged Navier-Stokes equations with a shear stress transport turbulence model. The bending angle was tested in a range of 0−40°. The results suggest that the jet frequency increases with the bending angle for high mass flow rates, but at a bending angle of 40°, the oscillation of the jet disappears. The pressure drop through the oscillator increases with the bending angle for positive bending angles. The external flow generally suppresses the jet oscillation, and the effect of external flow on the frequency increases as the bending angle increases.... [more]

This paper deals with a well-known problem of the transient DC-bias current occurring during a phase shift transition in dual active bridge (DAB) DC/DC converters. This phenomenon, if not compensated, can cause damage to the converter or deteriorate its performance. One aim of this paper is to present a solution which allows for the elimination of the undesired transient DC-bias component in current waveforms. This solution is the dual rising edge shift (DRES) compensation algorithm. It provides a very simple implementation and fast settling time within the first half of a switching period. Moreover, the solution is independent on any measurements or system parameter values. It is based on the double-sided single phase shift (DSSPS) modulation, which is described in detail along with a converter model in steady-state. Then, the mechanisms leading to the transient DC-bias are explained, and the compensation algorithm is derived. The performance of the algorithm has been tested using a l... [more]

A method for computation of the lightning channel base current from the corresponding vertical component of lightning electric field was presented. The algorithm was developed by applying Laplace transform. The lightning current was estimated from its deconvolution with a special transfer function. The transfer function includes information about geometry and physical properties of entire lightning impulse generation system. The method was verified for a Heidler-type base current and a MTLL model of its propagation within the lightning channel. Research was done for close, middle, and far distance to the lightning strike point. Optimum performance was obtained for the middle distance of several kilometers where the electrostatic, induction, and radiation components of the transfer function were of the same range. An analysis was done for input electric field with and without noise superimposed on its time domain waveform. Relative uncertainties for the electric field and calculated lig... [more]

The aim of this study was to identify the factors inducing customers to choose cashless payments made with payment cards at retail and service outlets during the COVID-19 pandemic. We identified factors that are crucial for consumers’ functioning under pandemic conditions, but which have so far been neglected in research. The estimated logit model indicates that the variables significantly influencing the more frequent choice of payment cards at retail outlets are related to the fear of infection and perception of the advantages of new technological solutions in connection with social distancing. Our study shows that, in addition to sociodemographic characteristics such as age and level of education, emotionally motivated factors induced by the pandemic have begun to play an important role in the transition to cashless payment.

The transverse vibration frequency of conveyor belts is an important parameter describing the dynamic characteristics of a belt conveyor. This parameter is most often identified from theoretical relationships, which are derived on the basis of an assumption that the belt is a stationary elastic string. Belt vibrations have a number of analogies to other tension member systems, such as, for example, power transmission belts. Some research findings suggest that in the case of a limited length of the belt section, a more accurate description of its vibration can be obtained with a beam model rather than with a string model. Experimental research has so far mostly revolved around measurements of stationary belts. This article presents the results of vibration measurements performed for a moving belt and obtained for various operating parameters of the conveyor, as well as for several configurations of the distance between idler supports. The analysis was conducted on a moving steel-cord be... [more]

The new energy industry (NEI) is key to achieving a clean and low-carbon economy. Improving its technical efficiency, a factor reflecting the ability of an enterprise or industry to produce maximum economic outputs from a given set of inputs and production technologies, is vital for the healthy development of the NEI. Nevertheless, due to the fragmentation of industry data, it is still difficult to accurately measure the technical efficiency of China’s NEI and understand the driving factors behind it. Based on the panel data derived from 17,457 observations on new energy enterprises in 29 Chinese provinces during 1998 and 2013 (latest data available), this paper uses data envelopment analysis (DEA) and geographically and temporally weighted regression (GTWR) for the first time to investigate the spatiotemporal characteristics and driving factors of the technical efficiency of China’s NEI. The results show that the technical efficiency of China’s NEI was relatively low and increased mod... [more]

In this study, the lightning protection system and grounding system of one plant of the petrochemical industry were investigated, evaluated, and improved. The methods used in this study were rolling sphere and angle protection methods. The grounding system of the building under study was modeled and simulated using ATP/EMTP (Alternative Transient Program/Electromagnetic Transient Program) software. The results show that the external lightning protection system of the prilling tower studied does not adhere to IEC 62305 and IEC 1024-1-1 standards. Moreover, the grounding configuration of the DCS building was not appropriate for protecting sensitive equipment inside. Lightning causes an enormous potential difference between lightning ground rods in the grounding system. Additionally, disabling the existing surge protective device (SPD) causes an increase in the magnitude of Ground Potential Rise at the DCS building. Improvement of the lightning protection system of the prilling tower and... [more]

The influence of lighting on crime was investigated by considering the effect of ambient light level on crimes recorded in three US cities for the ten-year period 2010 to 2019. Crime counts were compared for similar times of day, before and after the biannual clock change, therefore employing an abrupt change of light level but without an obvious intervention such as improving road lighting in an area. The results suggest a significant increase in robbery during darkness, confirming previous studies. The results also suggest darkness leads to an increase in arson and curfew loitering offenses, and to a decrease in disorderly conduct, family offences (non-violent) and prostitution. Future research investigating the effectiveness of improved street lighting should consider that this may not be beneficial for all types of crime.

In this survey paper, typical solutions that focus on the reduction in negative effects resulting from the common-mode voltage influence in AC motor drive applications are re-examined. The critical effectiveness evaluation of the considered methods is based on experimental results of tests performed in a laboratory setup with an induction machine fed by an inverter. The capacity of a common-mode voltage level reduction and voltage gradient du/dt limitation is discussed to extend motor bearings’ lifetime and increase motor windings’ safety. The characteristic features of the described solutions are compared and demonstrated using laboratory results.

Wood chips and logging residues currently comprise the largest share of biomass fuels used for heat generation in district heating plants and are provided by a variety of suppliers. Ash and moisture contents, as well as the calorific value, may vary considerably depending on the composition of the fuel, seasonality, location, and other factors. This paper provides the summarized results of the main characteristics of wood chip moisture and ash content and calorific value, experimentally tested for a significant range of samples. Chip samples were collected from two district heating companies and tested for a significant range of samples. Chip samples were collected from two district heating companies and tested for a 3-year period. The data on fuel chip prices were taken from the electronic wood chip trading platform. The tests were performed using standard express methods, where two sub-samples were taken and analyzed from every chip sample. It was determined that the moisture content... [more]

Sound localization is a vast field of research and advancement which is used in many useful applications to facilitate communication, radars, medical aid, and speech enhancement to but name a few. Many different methods are presented in recent times in this field to gain benefits. Various types of microphone arrays serve the purpose of sensing the incoming sound. This paper presents an overview of the importance of using sound localization in different applications along with the use and limitations of ad-hoc microphones over other microphones. In order to overcome these limitations certain approaches are also presented. Detailed explanation of some of the existing methods that are used for sound localization using microphone arrays in the recent literature is given. Existing methods are studied in a comparative fashion along with the factors that influence the choice of one method over the others. This review is done in order to form a basis for choosing the best fit method for our us... [more]

With the increase in PV system installations, the available free land and rooftops for these systems may become scarcer, and therefore sloped fields facing the north may be utilized for that purpose. In deployments of PV collectors in multiple rows, either on horizontal or sloped planes, the second and subsequent rows are subject to two effects: shading and masking. Both effects reduce the electric energy generated by the PV systems. Multiple rows of collectors are deployed on horizontal planes and on sloped planes facing south, and literature on the topic has been published. No literature deals analytically with deployments of PV fields on north-facing slopes in the northern hemisphere, to the best of our knowledge. The present study develops explicit analytical expressions for the shadow height and length cast on a collector row by a row in front in multiple-row PV systems installed on slopes facing north. In addition, analytical expressions are developed for row spacing and sky view... [more]

The existence of a growing myopia pandemic is an unquestionable fact for health authorities around the world. Different possible causes have been put forward over the years, such as a possible genetic origin, the current excess of children’s close-up work compared to previous stages in history, insufficient natural light, or a multifactorial cause. Scientists are looking for different possible solutions to alleviate it, such as a reduction of time or a greater distance for children’s work, the use of drugs, optometric correction methods, surgical procedures, and spending more time outdoors. There is a growing number of articles suggesting insufficient natural light as a possible cause of the increasing levels of childhood myopia around the globe. Technological progress in the world of lighting is making it possible to have more monochromatic LED emission peaks, and because of this, it is possible to create spectral distributions of visible light that increasingly resemble natural light... [more]

This paper presents a novel output voltage regulator in the cascade structure under the consideration of both the parameter and load uncertainties. It leads to the first-order closed-loop inner and outer loop dynamics in the low-pass filter form by the pole-zero cancellation through the active damping injection, which is the main contribution of this study. Moreover, it is proved that the active damping injection level determines the disturbance rejection capability of the closed-loop system. A 3-kW DC/DC boost converter confirms the actual advantages from these two contributions.