The vortex rope in the draft tube is considered as the major contributor to pressure pulsation at partial load (PL) conditions, which causes the hydro unit to operate unstably. Based on the prototype Francis turbine HLA551-LJ-43 in the laboratory, J-grooves are designed on its conical section in this paper. We used numerical simulation to study the effect of the J-grooves on vortex suppression and energy dissipation in the draft tube. Four typical operating conditions were chosen to analyze the vortex suppression; the corresponding flow ratios Q* are 100%, 82%, 69%, and 53%, respectively. Entropy production theory is used to calculate the energy losses and assess the effect of the J-groove on energy dissipation under part-load conditions. By comparing entropy production, circumferential and axial velocity components, swirl intensity, pressure pulsation, and vortex distribution in a draft tube with and without J-grooves at different operating conditions, it can be concluded that the ent... [more]

Several North American utilities are planning to blend hydrogen into gas grids, as a short-term way of addressing the scalable demand for hydrogen and as a long-term decarbonization strategy for ‘difficult-to-electrify’ end uses. This study documents the impact of 0−30% hydrogen blends by volume on the performance, emissions, and safety of unadjusted equipment in a simulated use environment, focusing on prevalent partially premixed combustion designs. Following a thorough literature review, the authors describe three sets of results: operating standard and “ultra-low NOx” burners from common heating equipment in “simulators” with hydrogen/methane blends up to 30% by volume, in situ testing of the same heating equipment, and field sampling of a wider range of equipment with 0−10% hydrogen/natural gas blends at a utility-owned training facility. The equipment was successfully operated with up to 30% hydrogen-blended fuels, with limited visual changes to flames, and key trends emerged: (a... [more]

This paper proposes a type-2 fuzzy controller for floating tension-leg platforms in wind turbines. Its main objective is to stabilize and control offshore floating wind turbines exposed to oscillating motions. The proposed approach assumes that the dynamics of all units are completely unknown. The latter are approximated using the proposed Sugeno-based type-2 fuzzy approach. A nonlinear Kalman-based algorithm is developed for parameter optimization, and linear matrix inequalities are derived to analyze the system’s stability. For the fuzzy system, both rules and membership functions are optimized. Additionally, in the designed approach, the estimation error of the type-2 fuzzy approach is also considered in the stability analysis. The effectiveness and performance of the proposed approach is assessed using a simulation study of a tension leg platform subject to various disturbance modes.

This paper presents a novel method for current control for a modular multilevel converter (MMC). The proposed current control methodology is based on a modified sliding mode control (SMC) with proportional and integral (PI) sliding surface which allows fast transient responses and improves the robustness of the MMC control performance. As the proposed method is derived via Lyapunov direct method, the closed-loop stability is ensured and results in globally asymptotically stable. Furthermore, the reaching time is also guaranteed by the proposed method, leading to fast transient responses. The proposed method is validated by comparing with some existing methods, which are proportional integral controller and conventional SMC, via offline and hardware-in-loop (HIL) simulations where a 10 MW, medium-voltage MMC system is tested. According to these results, the proposed method is able to provide fast transient responses, zero overshoot, and robustness to the weak grid and short-circuit cond... [more]

The article reviews the history and the direction of development for railway CCTV (Closed-Circuit TeleVision) systems. The authors described the CCTV system at PKP Polskie Linie Kolejowe S.A. and the associated network and server infrastructure. The authors proposed an operational model for a centralized CCTV system that assumes states of partial fitness, in accordance with the regulations of the national railway infrastructure administrator. The aim of the paper is to review, analyse, and evaluate the operational reliability of railroad video monitoring systems in relation to the assumptions of the national railroad infrastructure manager using an operational model. A unified system structure is presented in the article. The model was used as a base to calculate the probabilities for the system while staying in the assumed states. Calculations showed that a centralized CCTV system is characterized by high reliability and satisfies the expectations of PKP Polskie Linie Kolejowe S.A. in... [more]

Construction of the Włocławek Barrage on the Vistula River in 1970 became an important source of energy; however, it discontinued sediment transport in the Vistula River. This phenomenon resulted in accumulation before and erosion below the barrage; a similar problem can be expected due to the planned construction of the Lower Vistula Cascade. This study is dedicated to finding an effective and feasible solution to sediment transport management, acceptable to a wide group of users (e.g., navigation, energy producers, and ecologists). A numerical 1D model was applied to carry out analysis of hydrodynamics and sediment transport in the river section from Włocławek Barrage to the Vistula River mouth in the Baltic Sea. For calibration, historical data describing the accumulation and erosion created by the Włocławek Barrage were used. The proposed model allowed incorporation of new barrages chronologically, in accordance with the proposed time schedules. Analysis was carried out in a 50-yea... [more]

This paper presents a current converter that uses an inductor based approach for interim energy storage. A family of the circuits for step down conversion is examined for both non-inverting and inverting operations. The paper has disclosed the method of the generation, so that any order of 1/n conversion ratio can be made. One of the features is to use two transistors only in the common half-bridge style. The main contribution is its special current conversion capability and soft-switching, because it eliminates switching loss and the spike in the devices using a resonant capacitor with the switched-inductor. The performance has been proved to work well for current bucking. This is a new concept for the power converter and is an advanced development of the conventional switched-inductor converter, switched-capacitor, and resonant converter; it is a duality of the switched-capacitor converter. The paper provides a theoretical approach for the current source topology and its formation. I... [more]

We provide an open, available, and ready-to-use data set covering 40 years of hourly wind speeds and synthetic hourly production signals for the 29 biggest offshore wind farms in Europe. It enables researchers and industry experts to include realistic offshore time series into their analyses. In particular, we provide data from 1980 to 2019 for wind farms already in operation and those that will be in operation by 2024. We document in detail how the data set was generated from publicly available sources and provide manually collected details on the wind farms, such as the turbine power curves. Correspondingly, the users can easily keep the data set up to date and add further wind farm locations as needed. We give a descriptive analysis of the data and its correlation structure and find a relatively high volatility and intermittency for single locations, with balancing effects across wind farms.

An essential challenge in generation scheduling (GS) problems of hydrothermal power systems is the inclusion of adequate modeling of the hydroelectric production function (HPF). The HPF is a nonlinear and nonconvex function that depends on the head and turbined outflow. Although the hydropower plants have multiple generating units (GUs), due to a series of complexities, the most attractive modeling practice is to represent one HPF per plant, i.e., a single function is built for representing the plant generation instead of the generation of each GU. Furthermore, due to the computation time constraints and representation of nonlinearities, the HPF must be given by a piecewise linear (PWL) model. This paper presented some continuous PWL models to include the HPF per plant in GS problems of hydrothermal systems. Depending on the type of application, the framework allows a choice between the concave PWL for HPF modeled with one or two variables and the nonconvex (more accurate) PWL for HPF... [more]

Considering the development of the hybrid wind and solar photovoltaic generation and smart grid, Active Front-End (AFE) converters for high-power applications are facing significant opportunities and challenges related to power quality and efficiency. The Pre-programmed Pulse-Width Modulation (PPWM) techniques can strictly control the harmonic spectrum of a specified voltage or current waveform generated by a high-power AFE converters, and have been extensively applied to reduce or even eliminate the harmonic distortion with low switching losses for high-power converters in order to deal with these issues aforementioned. For the PPWM techniques with low switching frequency, Selective Harmonic Elimination (SHE) and Selective Harmonic Mitigation (SHM) have been the prevailing solutions and gain widespread popularity, among which SHM can provide further control of the harmonic spectrum in cases of similar switching losses to SHE. Over the past several decades, the applications of SHE and... [more]

A natural gas transportation pipeline with a gas−water two-phase flow containing CO2 is prone to severe flow-assisted corrosion (FAC). The accumulation location of the water phase in the pipeline and the wall shear stress distribution are important factors affecting the severity of this phenomenon. In this work, computational fluid dynamics (CFD) simulations were performed using the realizable k-ε model and volume of fluid (VOF) model to determine the gas−water volume fraction distribution and wall shear stress in a gas−water two-phase pipeline and established a pipeline corrosion prediction model. By determining where the water phase accumulates in the pipeline, the potential corrosion area could be predicted. By alleviating the phenomena of excessive local wall shear stress and bubble cavitation, the FAC due to the formation of stress and acid gas can be controlled. The simulation results lay a certain foundation for the corrosion research of gas−liquid two-phase flow pipelines.

The control of the battery-thermal-management-system (BTMS) is key to prevent catastrophic events and to ensure long lifespans of the batteries. Nonetheless, to achieve a high-quality control of BTMS, several technical challenges must be faced: safe and homogeneous control in a multi element system with just one actuator, limited computational resources, and energy consumption restrictions. To address those challenges and restrictions, we propose a surrogate BTMS control model consisting of a classification machine-learning model that defines the optimum cooling-heating power of the actuator according to several temperature measurements. The la-belled-data required to build the control model is generated from a simulation environment that integrates model-predictive-control and linear optimization concepts. As a result, a controller that optimally controls the actuator with multi-input temperature signals in a multi-objective optimization problem is constructed. This paper benchmarks t... [more]

In order to explore the axial electromagnetic dynamic balance force curve of a scroll compressor under the action of thermal energy, radial clearance, mechanism friction, and other factors in actual working conditions, an axial force exploration method that can automatically approach sections is proposed in this paper. Considering the dynamic response ability of the electromagnetic balance system, an automatic optimization algorithm of the partition number was proposed to find the optimal partition number in order to achieve the optimal tracking effect. An experimental platform was built to test the effect of the segmented tracking method on calibrating the deviation between the theoretical axial force curve and the real curve. The results show that the curve construction method proposed in this paper has convergence. This method can automatically and accurately construct the axial balance force curve required by the electromagnetic dynamic balance. Through the automatic optimization a... [more]

A brushless parallel hybrid excitation claw pole generator (HECPG) is proposed for electric vehicle (EV) application. Permanent magnet (PM) excitation method can reduce the volume of the machine and improve the power density and efficiency. Moreover, the voltage regulation can be ensured by field excitation. The flux path of the proposed HECPG is complex, and it will take a long time for 3D finite element analysis (FEA) to process it. To reduce simulation time, the mathematical model of the generator is given by a mesh-based 3D magnet equivalent circuit (MEC) network method considering radial and axial flux, magnetic saturation, and magnetic flux leakage. The performance of the generator is analyzed by FEA and prototype experiment. Finally, the results of 3D MEC, FEA, and experiment are compared. There is little difference between the three results, so 3D MEC can ensure the accuracy and significantly reduce the simulation time. The efficiency of the proposed HECPG is 90%, and the DC-Bu... [more]

The article presents an extended computer model of a HTS (high temperature superconducting) 21 MVA 70/10.5 kV transformer with severalfold compound windings, based on a verified PSpice model of 10 kVA transformer with single windings. Two superconducting tapes: SCS12050 (with a copper stabiliser layer) and SF12050 (without a stabiliser) were used in the windings. The circuit model of the transformer developed in the PSpice environment considers Rhyner’s power law and the Jiles−Atherton description of the magnetic hysteresis loop. Two types of transient states were analysed: switching on a superconducting transformer to the network and an emergency short-circuit of the secondary winding. For the first five unidirectional current pulses generated when connecting an unloaded transformer to the network, the values of the pulse duration (γ angle), the temperature increase in the primary winding as well as the mean and effective values of the switch-on current were calculated. The waveforms... [more]

Intense economic, social and environmental changes are creating new challenges for both consumers and businesses. Today’s consumer is becoming increasingly conscious of the importance of living in harmony with both ethical standards and the environment. Access to global resources, including utilities such as water, sewage collection, electricity or gas, is so ubiquitous that modern man cannot imagine functioning without them. The aim of this article is to show how the statistical Polish consumer has, or wants to have, an impact on improving the quality of the natural environment by using available resources and technological solutions. The novelty here is the use of the structural equation model (SEM) to build a model of pro-environmental behaviors in relation to the motivating and limiting factors for undertaking such behaviors in Poland. The hypothesis that the statistical Polish consumer undertakes pro-environmental behaviors because of their positive impact on the natural environme... [more]

Detection and diagnosis of the malfunction of the heating, ventilation, and air conditioning (HVAC) systems result in more energy efficient systems with a higher level of indoor comfort. The information from the system combined with the artificial intelligence methods contributes to powerful fault detection and diagnosis. The paper presents a novel method for the detection and diagnosis of multiple dependent faults in an air handling unit (AHU) of HVAC system of an institutional building during heating season. The proposed method guided the search for faults, by using the information and operation flow between sensors. Support vector regression (SVR) models, developed from building automation system (BAS) trend data, predicted air temperature of two target sensors, under normal operation conditions without known problems. The fault symptom was detected when the residual of measured and predicted values exceeded the threshold. The recurrent neural network (RNN) models predicted the norm... [more]

This article investigates the influence of four causal frequency-dependent (FD) soil models and their impact on the responses of a multiphase overhead transmission line (OHTL) with ground wires, generated by a lightning strike. The FD models proposed by Longmire-Smith (LS), Messier (M), Portela (P) and Alípio-Visacro (AV) are considered. The ground-return impedance and admittance matrices are computed with the Nagakawa approach for both frequency-constant and FD soil models. The frequency-domain modal voltages and time-domain transient voltages are assessed in this work. Modal decomposition technique is used to study the attenuation constant, propagation velocity and voltages for each propagation mode. Simulations are carried out in a frequency range of 100 Hz to 10 MHz, for OHTLs with lengths of 1 and 10 km, on soils of 700 and 4000 Ω·m. Simulation results demonstrated that the Portela (P) model has resulted in more significant variation in the ground-return impedance and admittance,... [more]

Conventional inductive contactless power transfer (ICPT) systems have only one energy transmission path, which makes it challenging to meet the power transmission requirements of high-power and reliability. This study proposes a novel multiple-input multiple-output (MIMO) ICPT system. The three-dimensional finite element analysis tool COMSOL is utilised to study various magnetic coupling structures, analyse the influence of cross-coupling between coils on the same side, design the circuit based on this, propose a parameter configuration method for resonance compensation, and, finally, build an experimental platform with small magnetic coupling structures for single-input single-output systems (SISO) and MIMO systems. The results indicate that the co-directional connection of the coils of the E-shaped and UE-shaped magnetic coupling structures has a strengthening effect on the secondary side coupling. The magnetic coupling structure of the E-shaped iron core exhibits the best transmissi... [more]

Operation of distribution networks involves a series of criteria that should be met, aiming for the correct and optimal behavior of such systems. Some of the major drawbacks found when studying these networks is the real losses related to them. To overcome this problem, distribution network reconfiguration (DNR) is an efficient tool due to the low costs involved in its implementation. The majority of studies regarding this subject treat the problem by considering networks only as three-phase balanced, modeled as single-phase grids with fixed power demand, which is far from representing the characteristics of real networks (e.g., unbalanced loads, variable power and unbalance indexes). Due to the combinatorial nature of the problem, metaheuristic techniques are powerful tools for the inclusion of such characteristics. In this sense, this paper proposes a study of DNR considering balanced and unbalanced systems with variable power demand. An analysis of the direct influence of voltage un... [more]

With the development of intelligent manufacturing, automated data acquisition techniques are widely used. The autocorrelations between data that are collected from production processes have become more common. Residual charts are a good approach to monitoring the process with data autocorrelation. An improved hidden Markov model (IHMM) for the prediction of autocorrelated observations and a new expectation maximization (EM) algorithm is proposed. A residual chart based on IHMM is employed to monitor the autocorrelated process. The numerical experiment shows that, in general, IHMMs outperform both conventional hidden Markov models (HMMs) and autoregressive (AR) models in quality shift diagnosis, decreasing the cost of missing alarms. Moreover, the times taken by IHMMs for training and prediction are found to be much less than those of HMMs.

Global CO2 concentration level in the air is unprecedently high and should be rapidly and significantly reduced to avoid a global climate catastrophe. The work indicates the possibility of quickly lowering the impact of changes that have already happened and those we know will happen, especially in terms of the CO2 emitted and stored in the atmosphere, by implanting a virgin ivy plant on the available area of walls and roofs of the houses. The proposed concept of reducing CO2 from the atmosphere is one of the technologies with significant potential for implementation entirely and successfully. For the first time, we showed that the proposed concept allows over 3.5 billion tons of CO2 to be captured annually directly from the atmosphere, which makes even up 6.9% of global greenhouse gas emissions. The value constitutes enough high CO2 reduction to consider the concept as one of the applicable technologies allowing to decelerate global warming. Additional advantages of the presented conc... [more]

To date, hydropower dams raise numerous interpretations about their impact on the Lancang-Mekong River. While most research studies analyze the negative aspects of hydropower development on people’s livelihoods and local environments, the hydropower sector was historically one of the most iconic economic segments facilitating transboundary water cooperation for decades. By using the constructive discourse analysis and critical political ecology approach, the presented text (1) outlines the current environmental narratives over the Lancang-Mekong hydropower development and (2) explores the politicization of the Chinese mainstream dams. The data were collected upon the multi-level content analysis of relevant sources and double-checked with the Lancang-Mekong Cooperation and Conflict Database (LMCCD) monitoring over 4000 water-related events among six riparian countries between 1990 and 2021. Our data show that (i) there is a stark contrast in positive and negative narratives over the ra... [more]

Voltage sag in a power system is an unavoidable power quality issue, and it is also an urgent concern of sensitive industrial users. To ensure the power quality demand and economical operation of the power system, voltage sag management has always drawn great attention from researchers around the world. The latest research that realizes the power quality conditioning has used dynamic voltage restorers (DVRs), static VAR compensator (SVCs), adaptive neuro-fuzzy inference systems (ANFISs), and fuzzy logic controllers based on DVR to mitigate voltage sag. These devices, methods, and control strategies that have been recently used for voltage sag mitigation have some limitations, including high cost, increased complexity, and lower performance. This article proposes a novel, efficient, reliable, and cost-effective voltage sag mitigation scheme based on a modular multilevel converter (MMC) that ensures effective power delivery at nominal power under transient voltage conditions. The propose... [more]

This Special Issue was intended as a forum to advance research and apply machine-learning and data-mining methods in order to facilitate the development of modern electric power systems, grids and devices, smart grids and protection devices, as well as to develop tools for more accurate and efficient power system analysis [...]