The power quality analysis is an essential issue in the integration of distributed energy resources to the grid. Recent standards regulate the harmonics disturbances due to the increasing penetration of intermittent energy sources interconnected with the grid employing power converters. This paper aims to analyze the power quality of an interconnected wind turbine system based on a Squirrel Cage Induction Generator (SCIG) driven by an Electromagnetic Frequency Regulator (EFR). The steady state of the EFR harmonic model is developed in the stationary frame based on the conventional induction generator modeling, which allows the study of the harmonic disturbances in the electrical and mechanical variables due to the PWM inverter of the EFR’s armature voltage. There is no electrical connection between the EFR and SCIG, and the results show that the inherent system inertia contributes to the mitigation of the harmonic content at the grid side generated by the switching. In addition to the... [more]

Partial discharge measurement is part of the monitoring of equipment in power engineering systems. It provides important information about the condition of the equipment and in particular the condition of the insulation components. This information serves to take necessary preventive measures at an early stage to avoid failures of the affected energy system and thus ensure a high level of energy supply security. Possible causes of partial discharges in energy technology equipment include high field strengths at edges with small radii or defects within insulation materials itself. Depending on the location and extent of the occurrence, partial discharge events may cause lasting damage to components of equipment. In order to be able to interpret the measurement results of partial discharge monitoring with regard to the exact cause and, if necessary, to evaluate them automatically, a precise understanding of the physical phenomena that occur during a partial discharge is necessary. The ph... [more]

Long-term transition pathways to a low-carbon energy system are analysed by applying the energy system model REMod. All in all, the paper contributes to the current research through an innovative scenario approach, using assumptions for societal trends and quantitative results for scenarios, analysing the paths towards climate neutrality and defossilization in 2050. In the case study of Germany, these trends and drivers influence the results and the technology composition in each consumption sector (buildings, transport, and industry). Across all scenarios, it can be observed that the electrification of all sectors is important for the defossilization of the energy system, as the direct use of electricity from renewable energy is more efficient than the consumption of carbon-neutral synthetic energy carriers. However, different consumer behavior (e.g., non-acceptance or resistance against specific technologies) influences not only the efficient use of (green) electricity, it also chang... [more]

High-frequency components of common-mode voltage (CMV) induce the shaft voltage and bearing current, which lead to premature failures in motors. In addition, due to non-zero average CMV, the low-frequency components of CMV, particularly the third-order harmonic component, have been reported to cause difficulties in common-mode filter design. Furthermore, the utilization of distant voltage vectors in the pulse-width modulation (PWM) with reduced CMV magnitudes gives rise to high output harmonic distortion compared to PWM ones without CMV reduction. In an attempt to solve the aforementioned issues, this article presents a PWM strategy that features reduced CMV magnitudes, zero average CMV, and improved output harmonic distortion for a five-level cascaded H-bridge (CHB) converter. In addition, the carrier rotation technique based on the phase-leg redundancy of the CHB topology is also combined with the proposed scheme to achieve equal power loss distribution among power switching devices.... [more]

Eco-drive is a widely used concept. It can improve fuel economy for different driving behaviors such as vehicle acceleration or accelerator pedal operation, deceleration or coasting while slowing down, and gear shift timing difference. The feasibility of improving the fuel economy of urban buses by applying eco-drive was verified by analyzing data from drivers who achieved high fuel efficiencies in urban buses with a high frequency of acceleration/deceleration and frequent operation. The items that were monitored for eco-drive were: rapid take-off/acceleration/deceleration, accelerator pedal gradient, coasting rate, shift indicator violation, average engine speed, over speed, and gear shifting under low-end engine speed. The monitoring method for each monitored item was set up, and an index was produced using driving data. A fuel economy prediction model was created using machine learning to determine the contribution of each index to the fuel economy. Furthermore, the contribution of... [more]

The design of gear pumps and motors is focused on more efficient units which are possible to achieve using advanced numerical simulation techniques. The flow that appears inside the gear pump is very complex, despite the simple design of the pump itself. The identification of fluid flow phenomena in areas inside the pump, considering the entire range of operating parameters, is a major challenge. This paper presents the results of simulation studies of leakages in axial and radial gaps in an external gear pump carried out for different gap shapes and sizes, as well as various operating parameters. To investigate the processes that affect pump efficiency and visualize the fluid flow phenomena during the pump’s operation, a CFD model was built. It allows for a detailed analysis of the impact of the gears’ eccentricity on leakages and pressure build-up on the circumference. Performed simulations made it possible to indicate the relationship between leakages resulting from the axial and ra... [more]

The paper provides an analysis of a transportation system with a long stator linear drive. The presented analysis for an in-house transportation system may be easily scaled into large transportation systems like maglev and hyperloop. It investigates the impact of the division of the stator into shorter parts which are sequentially supplied. Then it compares the concept of single-inverter and multi-inverter drive systems. The presented research includes the analysis of drive system power parameters. The drive system characteristics depending on the length of the active part of the linear motor are presented for each configuration, followed by a description of differences in the required inverter power and the obtained average thrust force. The paper proposes a new arrangement of the multi-inverter drive system incorporating multi-level inverters, which allows decreasing voltage oscillations in the DC circuit of drive inverters. The operation of the transportation system is presented in... [more]

Fifth-generation district heating and cooling (5th DHC) systems offer promising approaches to decarbonizing space heating, cooling and domestic hot water supply. By using these systems, clustered buildings combined with industrial waste heat can achieve a net-zero energy balance on a variety of time scales. Thanks to the low exergy approach, these systems are highly efficient. As part of the Smart Anergy Quarter Baden (SANBA) project, the thermal energy grid simulation tool TEGSim has been further developed and used to design an ultra-low-temperature district heating (ULTDH) network with hydraulic and thermal components fitted to the specific regional characteristics of the investigated case. Borehole thermal energy storage (BTES) used as seasonal storage ensures long-term feasibility. The annual discrepancy of input of thermal energy provided by space cooling and output of energy demanded by space heating and domestic hot water is supplied by an external low-grade industrial waste hea... [more]

This article investigates the potential of selected urban typologies in Vienna to reach the state of Positive Energy Districts (PED) by achieving a positive annual energy balance. It follows the EU initiative for implementing at least 100 PED in Europe by 2025. Four urban typologies have been assessed using the bottom-up energy modelling tool MAPED that enables a simplified energy demand-supply analysis at the district scale. Considering relevant urban typologies in different construction periods, the analysis focused on converting the allocated building stocks into PED by employing comprehensive thermal refurbishment and energy efficiency measures, electrification of end-uses and fuel switching, exploitation of local renewable energy potential, and flexible interaction with the regional energy system. The results reveal that a detached housing district can achieve a positive annual energy balance (for heat and power) of 110% due to the fact that there are sufficient surfaces (roofs, f... [more]

A climate resilient city, perforce, has an efficient and robust energy infrastructure that can harvest local energy resources and match energy sources and sinks that vary over space and time. This paper explores the use of an urban building energy model (UBEM) to examine the potential for creating a near-zero carbon neighbourhood in Dublin (Ireland) that is characterised by diverse land-uses and old and new building stock. UBEMs are a relatively new tool that allows the simulation of building energy demand across an urbanised landscape and can account for building layout, including the effects of overshadowing and the potential for facade retrofits and energy generation. In this research, a novel geographic database of buildings is created using archetypes, and the associated information on dimensions, fabric and energy systems is integrated into the Urban Modelling Interface (UMI). The model is used to simulate current and future energy demand based on climate change projections and t... [more]

The general wideband modeling method of the power converter is presented on the example of DC-DC buck converter with GaN High Electron Mobility Transistors (HEMT). The models of all basic and parasitic components are briefly described. The two methods of Printed Circuit Board (PCB) layout parameter extraction are presented. The results of simulation in Saber@Sketch simulation software and measurements are compared. Next, the model of the converter is reduced to obtain one lumped inductance of the input filter PCB for the analytical prediction of transistor turn-off ringing frequency and overvoltage. The practical use of the model is presented for sizing optimal capacitance of snubber.

Deep mining results in an increasingly serious hazard. Based on the principle of heat transfer and radiant cooling, a three-dimensional heat transfer model of the working face was established. The influence of the inlet airflow parameter, the surrounding wall temperature and other parameters on the temperature distribution of airflow along the working face were analyzed under the radiation cooling mode. The results show that the increment of airflow temperature in several sections along the working face decreases by 0.67 °C, 0.48 °C, 0.40 °C, 0.36 °C, 0.33 °C, 0.29 °C respectively. The farther away from the airflow inlet, the more obvious the cooling effect was. The airflow temperature of the working face is positively correlated with the airflow inlet temperature and the surrounding wall temperature, and is negatively correlated with the airflow velocity. The research provides a good solution for the working face cooling of deep mines, and also provides a theoretical reference for the... [more]

The present study focuses on investigating the aerodynamic interaction between a three-element wing and wheel in ground effect, following the Formula One regulation change set for 2022, among which is the simplification of the front wing. This was accomplished by conducting a three-dimensional computational fluid dynamics analysis, using a Detached-Eddy Simulation approach, on a simplified one-quarter model of a Formula One racing car. The main goal was to examine how changing the front wing pressure distribution, by changing the incidence of the second flap, affected the wheel wake. The flow investigation indicated that the wheel wake is influenced by the flap configuration, which is mainly due to the fact that different flap configurations produce different upwash flow fields, leading to a variation of the separation point on top of the tire. As the separation point moves rearwards, the downwash generated in the central region (for a vertical plane) of the wheel wake increases increm... [more]

A mathematical model that governs unsteady coupled moisture and heat energy transport through an exterior wall covered with vegetation is described. The unknown temperature and moisture content of the plants and canopy air are represented by a system of nonlinear ordinary differential equations (ODEs). The transport of moisture and heat through the support structure, which includes insulation and soil layers, is defined in a series of nonlinear partial differential equations (PDEs). After setting out the model, this article presents and discusses a set of numerical applications. First, a simplified system consisting of a brick wall covered with climbing vegetation is used to study the role of individual variables (e.g., wind speed, minimum stomatal internal leaf resistance, leaf area index, and short-wave extinction coefficient) on the hygrothermal behaviour of the green wall. Thereafter, more complex green wall systems comprising a bare concrete wall, mortar, cork-based insulation (IC... [more]

Printed circuit heat exchangers (PCHEs) have the characteristics of high temperature and high pressure resistance, as well as compact structure, so they are widely used in the supercritical carbon dioxide (S-CO2) Brayton cycle. In order to fully study the heat transfer process of the Z-type PCHE, a numerical model of traditional Z-type PCHE was established and the accuracy of the model was verified. On this basis, a new type of spiral PCHE (S-ZPCHE) is proposed in this paper. The segmental design method was used to compare the pressure changes under 5 different spiral angles, and it was found that increasing the spiral angle θ of the spiral structure will reduce the pressure drop of the fluid. The effects of different spiral angles on the thermal-hydraulic performance of S-ZPCHE were compared. The results show that the pressure loss of fluid is greatly reduced, while the heat transfer performance is slightly reduced, and it was concluded that the spiral angle of 20° is optimal. The loc... [more]

The development of urban strategies for the reduction of environmental impacts and decarbonization requires ongoing monitoring from the local scale and further deployment of actions to improve transport demand (user characteristics and modal choice) and supply (infrastructure and services). The analysis of pollution sources and the evaluation of possible scenarios are preliminary to the mitigation of impacts. In particular, the study of geometrical and functional characteristics of infrastructures through micro-simulation allows understanding of which schemes can support the reduction of emissions and guarantee high levels of service (LOS), reducing the problem of vehicular congestion in urban areas. The present work focuses on the small-scale analysis of vehicular traffic emissions at a multi-lane roundabout road intersection and the comparison of geometric schemes (current and design) and use with a turbo roundabout scheme as traffic volumes changes. These volumes have plummeted due... [more]

The latent heat storage in the layer of phase change material (PCM) exposed to dynamic changes in boundary temperature was investigated numerically and experimentally. The original numerical model of heat transfer with phase change using a mushy volume approach was proposed and validated. The main improvement in the proposed model in comparison to others is that the compaction of the mesh and longitude of the time step were chosen after analysis of its impact in the field of error. The model was tested in the case of thin layer structure of the triple glazing window with one cavity filled with phase change material paraffin RT18HC. The experimental validation was carried out in the climatic chamber under dynamic changes in external temperature (from 10 to 50 °C) in a daily cycle. The highest accuracy was obtained for space discretization of the control volume 1 mm thick (12 CV for 12 mm of PCM layer) and 5 min time step. The obtained RMSE values, although they cannot be directly compar... [more]

This paper proposes a multimodal deep learning method for forecasting the daily power generation of small hydropower stations that considers the temporal and spatial distribution of precipitation, which compensates for the shortcomings of traditional forecasting methods that do not consider differences in the spatial distribution of precipitation. First, the actual precipitation values measured by ground weather stations and the spatial distribution of precipitation observed by meteorological satellite remote sensing are used to complete the missing precipitation data through linear interpolation, and the gridded precipitation data covering a group of small hydropower stations are constructed. Then, considering the time lag between changes in the daily power generation of the group of small hydropower stations and precipitation, the partial mutual information method is used to estimate the “time difference” between the two, and combined with the precipitation grid data, a data set of t... [more]

Submersible mixers are widely used in the sewage treatment process in various fields, such as agriculture and industry. They are mainly responsible for pushing flow and mixing activated sludge particles in a pool. Based on the CFD-DEM coupling method under the Euler−Lagrange framework, the solid−liquid two-phase flow of a submersible mixer was simulated in this paper, and the motion characteristics and distribution laws of particles in the pool were studied in axial, horizontal, and lateral directions, respectively. An evaluation method of distribution uniformity was proposed to analyze the velocity distribution of the flow field, the velocity distribution of particles, and the mixing uniformity of particles. The results show that the movement process of activated sludge particles in the pool can be roughly divided into three stages: the horizontal development stage, absorption−injection stage, and reflux-mixing stage, in which the reflux-mixing stage is the main stage for the uniform... [more]

This paper shows an elaboration of an equivalent electrical circuit of a Dual Active Bridge (DAB) and its application as a versatile tool for steady-states analysis in wide range of operating conditions. This work analyses the converter which is controlled with a coherently defined Triple Phase-Shift (TPS) modulation which allows appropriate switching functions to be written, thus enabling the circuit’s state-space equations to be derived. Due to this approach, a Fourier series expansion may be easily applied to utilize Generalized Averaged Modeling (GAM)—a convenient method for modeling resonant and quasi-resonant power converters. Moreover, this paper shows the utilization of the GAM model higher harmonics’ complex magnitudes to calculate the steady-state power characteristics for bidirectional operation; additionally, a method for a particular state variable waveform signal reconstruction is presented. All the discussed model properites are validated with a 1.5 kW 100 kHz SiC-based... [more]

Residential buildings are an important sector in the urban environment as they provide essential dwelling space, but they are also responsible for a significant share of final energy consumption. In addition, residential buildings that were built with outdated standards usually face difficulty meeting current energy performance standards. The situation is especially common in Europe, as 35% of buildings were built over fifty years ago. Building retrofitting techniques provide a choice to improve building energy efficiency while maintaining the usable main structures, as opposed to demolition. The retrofit assessment requires the building stock information, including energy demand and material compositions. Therefore, understanding the building stock at scale becomes a critical demand. A significant piece of information is the building geometry, which is essential in building energy modelling and stock analysis. In this investigation, an approach has been developed to automatically meas... [more]

This paper presents a simple novel mathematical model of a heat accumulator with an arranged packing in the form of ceramic cylinders. The accumulator analysed in the paper can be heated with inexpensive electricity overnight or excess electricity from wind farms. It can be used as a heat source in a hydronic heating system or for domestic hot water. The differential equations describing the transient temperature of the accumulator packing and flowing air were solved using the explicit Euler and Crank−Nicolson methods. The accuracy of both methods was assessed using exact analytical solutions and the superposition method for a uniform initial temperature and accounted for time changes in inlet air temperature. A numerical simulation of the accumulator cooled by flowing air was carried out. The correlation for the air-side Nusselt number was determined using the method of least squares based on experimental data. The calculated exit air temperature was compared with the measured data. T... [more]

The current use of health index algorithms is mainly limited to single assessments of the unit’s condition or the device comparison. The paper focuses on the changes in the health index values between the consecutive analyses. The algorithm used for this purpose was previously developed by the authors. The test group included 359 complete oil evaluation results from 86 power transformers monitored over several years. For each outcome, the influence of the sub-components of the main score was calculated. Additional health index increase simulations were performed based on the IEC 60599 standard guidelines. The highest increases and decreases in the total score were listed and analyzed to determine the main factors behind the changes. The study has shown that the changes in dissolved gases concentrations have a much more significant influence on the health index values than the changes in physicochemical properties of the oil and furfural content. Based on the magnitude of the observed c... [more]

Plastic waste accumulation has been growing due to the increase in plastic generation and the lack of infrastructure for recycling. One of the approaches is to treat the mixed plastic waste (MPW) through thermal processes to produce feedstocks for other applications. However, the presence of polyvinyl chloride (PVC) in MPW would produce HCl during processing and has negative impacts (emission, catalyst poisoning, etc.). In addition, due to the high heterogeneity of MPW, it is difficult to generate consistent experimental data. In this study, MPW was homogenized through double compounding−extrusion and then formed into a sheet to be treated at 400 °C. The solid products at various mass losses were characterized by heat and chlorine content, Fourier-transform infrared (FTIR) spectroscopy, and elemental composition analysis. It was found that the thermal degradation of MPW started at ~260 °C. The chlorine removal efficiency increased with mass loss and reached an asymptotic value of ~84%... [more]

High-Frequency Pressure Fluctuation (HFPF) is an extensively observed hydraulic phenomenon in pumped-storage power stations and water conveyance projects. The investigation of the propagation characteristics of the pressure perturbation is of great significance for the safe operation of hydraulic facilities. In this study, a one-dimensional (1D)−three-dimensional (3D) coupling model is established based on the combination of the Method of Characteristics (MOC) and Computational Fluid Dynamics (CFD) and implanted in the open source software OpenFOAM. The established model in this study implants the dynamic mesh module into the original OpenFOAM solver sonicLiquidFoam and presents the complete solution procedure of the CFD model with the dynamic mesh considered. The vibration of the pipe walls modeled by the mesh motion is employed to numerically generate the HFPF in the hydraulic system, which could not be implemented in the traditional MOC model. The independence of the pressure pertur... [more]