The three-port converter (TPC) obtains major attention due to its power density and ability to dispose different electric powers flexibly. Since the control models of the TPC are derived from particular steady state work point through small signal modeling method, the model parameters usually be deviated from their normal values with the change of operation and load conditions. Furthermore, there are couplings and interactions in power delivery between different ports, which have a significant influence in the dynamic control performance of the system. In this paper, the H∞ mixed sensitivity method is employed to design robust controllers for a TPC control system. Simulation results are given to demonstrate the effectiveness of the proposed scheme, and experimental studies are conducted on a prototype circuit to further validate the developed method. Compared to a traditional PI controller, it shows that a mixed sensitivity based robust controller manifest balanced performance in model... [more]

Wind power forecasting plays a vital role in renewable energy production. Accurately forecasting wind energy is a significant challenge due to the uncertain and complex behavior of wind signals. For this purpose, accurate prediction methods are required. This paper presents a new hybrid approach of principal component analysis (PCA) and deep learning to uncover the hidden patterns from wind data and to forecast accurate wind power. PCA is applied to wind data to extract the hidden features from wind data and to identify meaningful information. It is also used to remove high correlation among the values. Further, an optimized deep learning algorithm with a TensorFlow framework is used to accurately forecast wind power from significant features. Finally, the deep learning algorithm is fine-tuned with learning error rate, optimizer function, dropout layer, activation and loss function. The algorithm uses a neural network and intelligent algorithm to predict the wind signals. The proposed... [more]

This paper presents findings on mitigating the negative impact of renewable energy resources variability on the energy scheduling problem, in particular for island grids and microgrids. The methods and findings presented in this paper are twofold. First, data obtained from the City of Summerside in the province of Prince Edward Island, Canada, is leveraged to demonstrate the effectiveness of state-of-the-art time series predictors in mitigating energy scheduling inaccuracy. Second, the outcome of the time series prediction analysis is used to propose a novel data-driven battery energy storage system (BESS) sizing study for energy scheduling purposes. The proposed probabilistic method accounts for intra-interval variations of generation and demand, thus mitigating the trade-off between time resolution of the problem formulation and the solution accuracy. In addition, as part of the sizing study, a BESS management strategy is proposed to minimize energy scheduling inaccuracies, and is th... [more]

This particular study focuses on investigating the heat and mass transport characteristics of a liquid flow across the conical gap (CG) of a cone-disk apparatus (CDA). The cone and disk may be taken as stationary or rotating at varying angular velocities. Consideration is given to heat transport affected by solar radiation. The Rosseland approximation is used for heat radiation calculations in the current work. To observe the mass deposition variation on the surface, the effect of thermophoresis is taken into account. Appropriate similarity transformations are used to convert the three-dimensional boundary-layer governing partial differential equations (PDEs) into a nonlinear ordinary differential equations (ODEs) system. Particularly for the flow, thermal and concentration profiles, plots are provided and examined. Results reveal that the flow field upsurges significantly with upward values of Reynolds numbers for both cone and disk rotations. The increase in values of the radiation p... [more]

Heat cost allocation is commonly used in existing buildings supplied by centralized sources of heating/cooling and provided with individual metering systems. However, this process is not always fair for the users, since “fairness” strongly depends on the methods established to allocate variable and fixed costs among the dwellings. That is why unrealistic cost for heating may be allocated for specific flats. However, there is a lack of evidence about procedures as to how maximum and minimum variable cost of heating may be calculated for specific flats in multifamily building for a specific heating season. This paper presents different methods for estimation of maximum and minimum variable cost of heating of flat in multifamily buildings, the use of which depends of the availability of input data for specific buildings. Evaluation of the proposed methods is made on the example of a case study multifamily building located in Poland. It was shown that the maximum variable costs of heat pur... [more]

In emerging countries, energy service users generally pay high rates of return to transmission system operators (TSOs). One of the causes of this situation is the application of the CAPM with the comparable beta method when estimating the cost of equity in the WACC. The purpose of this article is to present a new methodology for calculating the cost of equity of TSOs in Colombia. To achieve this objective, a multifactor model has been built to explain the variation in returns on the electric utilities portfolio in Colombia between April 2008 and March 2022 and then recalculate the WACC approved by the country’s regulatory commission. It was found that, in addition to the estimated market risk in the CAPM, there is a risk due to the regulatory framework and changes in interest rates, which helps to explain 73% of the variations in the electric utilities portfolio, resulting in a lower cost of equity, and therefore a lower WACC of 5.28% compared to the WACC estimated by the regulator of... [more]

Standing out for their remarkable benefits, such as lower voltage stress on integrated semiconductor devices, reduction in total harmonic distortion, as well as lower electromagnetic effects, multilevel inverters (MLIs) increase their share in the field of energy supply. The multilevel inverter is an interesting research topic that realizes the generation of desired output voltage waveforms composed of small voltage steps. However, many studies have put a premium on the structure, efficiency, and output of the multilevel inverter, but there are relatively few studies on the THD and practical product applications. Consequently, in this brief perspective, some puzzles for MLIs are pointed out to explore new ideas as well as to present new questions.

Microalgae is a promising metabolism microorganism for the fixation of CO2 from industrial gas while accumulating microalgae biomass. The process of CO2 fixation by microalgae is able to be significantly improved by the regulation of phytohormones. However, the complex metabolic mechanism of microalgae regulated by phytohormones and abiotic stress on CO2 fixation deserves to be explored. To systematically understand the existing status and establish a foundation for promoting the technology, this paper reviews investigations on the metabolic mechanism of microalgae regulated by phytohormones. The influences of nitrogen stress, light intensity stress, heavy metal stress, and salinity stress on CO2 fixation and lipid production are summarized. In addition, a comprehensive overview of the multistage regulation of phytohormones and abiotic stress on CO2 fixation and lipid production through microalgae is presented. The recent advances in CO2 transfer reinforcement and light transmission re... [more]

Here, we seek to review the relevant literature and published articles on the subjects of electricity markets, electricity prices and green energy transition [...]

The aim of the paper is to present the change in the radiation noise of the single-phase voltage source inverter (VSI) when the Si-MOSFET transistors are replaced by the wide-band-gap (WBG) SiC-MOSFET and GaN transistors. The power spectral density of the near-field interference is used to visualise the change of the radiation noise of the VSI. The conclusions concern the results of the experimental replacement of the switches to the WBG technology in the existing inverters. Three switching frequencies and two gate circuits were used to show the change in the radiation noise. The measurements of the experimental VSI are presented.

The Special Issue “Demand Response in Smart Grids” includes 10 papers [...]

As non-isolated step-up and step-down DC−DC converters are at present widely used in various fields, this review will summarize and introduce non-isolated step-up and step-down DC−DC converters in various aspects. First of all, the origin and development of power electronics technology and the generation and principle of certain basic non-isolated step-up and step-down DC−DC converters are briefly stated. Subsequently, according to their different characteristics, including whether they are unidirectional or bidirectional, voltage-fed or current-fed, or hard-switching or soft-switching, the review will classify them and analyze their advantages and disadvantages. Meanwhile, in order to change the voltage gains of the DC−DC converters, different voltage change techniques are applied to them. The review will elaborate on the four technologies (switched capacitors, voltage multipliers, switched inductors and different ways of connecting), providing examples and analyzing the topologies in... [more]

The construction industry is one of the three major worldwide energy consumers, producing nearly 30% of global carbon emissions [...]

Accurate analysis of the air gap magnetic field is the focus of research in the field of precision permanent magnet linear synchronous motors. In this paper, the two-dimensional air gap magnetic field of a secondary trapezoidal Halbach permanent magnet array coreless permanent magnet linear synchronous motor (PMLSM) was taken as our research object. On the basis of the equivalent surface current method, we proposed an improved equivalent analytical algorithm with a trapezoidal side length unit. The equivalent analytical model of the magnetic induction vector of the two-dimensional air gap was established, and the air gap magnetic field of the trapezoidal Halbach array coreless PMLSM was calculated. At the same time, we analyzed the influence of the bottom angle α of a trapezoidal permanent magnet equivalent width coefficient αw, pole height coefficient αh, and air gap height coefficient αg on the amplitude (Bpeak) and total harmonic distortion (THDB) of the central magnetic field in th... [more]

The contemporary world is uneven not only in terms of the quality of life and economic development, but also in cultural issues that define awareness of global development processes. Geographies of energy co-create various energy paradigms and territorial development scenarios. This paper has two general aims. First, we want to identify the main fields of study within the geographies of energy. We try to define a general model of geographic analysis in terms of key concepts. The second aim concerns the definition of perspectives of geography of energy as a growing field of interest for researchers. We believe that geographies of energy should undertake a contemporary transition in this area from the point of view of scale and relativity resulting from the presented dimensions of spatiality and locality, i.e., differential, vertical, horizontal and transversal approaches.

This paper presents a method for determining the load capacity of three-phase squirrel-cage induction motors supplied with a balanced distorted voltage containing rotating harmonics (1st, 5th, 7th, 11th, 13th,...). The method is based on the dependence of the motor load capacity on the load power losses in the rotor cage. The load capacity was determined based on motor short-circuit measurements made for frequencies equal to harmonic frequencies. To evaluate the load capacity, a factor with the proposed name Harmonic Losses Factor (HLF) was introduced. Its expression is a generalization of the well-known HVF expression. However, it has been shown that a more accurate estimation of the load capacity is obtained using the sum of load power losses in the rotor cage from higher harmonics. Measurements and calculations were carried out for a low-voltage squirrel-cage motor with a rated power of 22 kW and a synchronous speed of 1500 rpm. Calculations showed that the derating power curves giv... [more]

Anaerobic digestion plays a starring role in the development of a bioeconomy due to the practical advantages that gaseous fuels have over solid fuels (i [...]

Substation (SS) auxiliary systems (SAux) are facilities responsible for hosting the alternating (AC) and direct current (DC) busbar to serve the equipment and systems that perform the substation’s protection, control, and supervision. External and internal power supplies typically ensure the continuity of such a facility. The electricity support will be restricted to diesel emergency generators (DG) if the external power supply is unavailable due to a contingency. The DG present a slower response time and are susceptible to starting failures. Microgrids with Battery Energy Storage Systems (BESS) paired with photovoltaic systems (PV) are presented as an innovative and reliable solution for powering the SAux. In this article, tests were carried out on the microgrid of the Edson Mororó Moura Institute of Technology (ITEMM) in Brazil to support the use of microgrids BESS/PV in the SAux of a transmission SS of the São Francisco Hydroelectric Company (Chesf). Without an external power supply... [more]

Large-scale grids have gradually become the dominant trend in power systems, which has increased the importance of solving the challenges associated with large-scale economic dispatch (LED). An increase in the number of decision variables enlarges the search-space scale in LED. In addition to increasing the difficulty of solving algorithms, huge amounts of computing resources are consumed. To overcome this problem, we proposed a surrogate-assisted adaptive bat algorithm (GARCBA). On the one hand, to reduce the execution time of LED problems, we proposed a generalized regression neural network surrogate model based on a self-adaptive “minimizing the predictor” sampling strategy, which replaces the original fuel cost functions with a shorter computing time. On the other hand, we also proposed an improved hybrid bat algorithm (RCBA) named GARCBA to execute LED optimization problems. Specifically, we developed an evolutionary state evaluation (ESE) method to increase the performance of the... [more]

In recent years, industries in the suburb have retrofitted their power supply units with solar power supply systems. Using solar power supply systems for various applications, such as food processing, enables energy expense saving. A promising opportunity in the food industry is solar-powered Pulsed Electric Field (PEF) used in the treatment of fruits and their by-products. For this application, a converter is proposed in this paper with a combination of a passive switched inductor cell and a switched capacitor cell. Furthermore, the derived topology possesses an extendable feature. This topology generates high voltage repetitive pulses with a single semiconductor switch and a reduced component count. Dynamic study of the converter is also performed with the derivation of the transfer function. Cost effective, reliable, and simple circuitry are the critical features of this topology. The circuit topology can generate high voltage pulses by increasing the number of switched inductors an... [more]

The operating license of Kori units 3 and 4 are to be expired in 2024 and 2025. If the plants are decided to be decommissioned, the spent nuclear fuels in the spent fuel storage pool (SFP) have to be removed from the site. However, no proper storage facility is currently available in Korea. To overcome the difficulty, this study proposes application of an independent temporary SFP cooling system. It is expected to safely isolate the SFP from the plant. The case study conducted showed this concept is achievable and technically mature. Moreover, the installation cost per unit is USD 9.51 million obtained from an analogous estimating. This is much lower cost than the dry cask options. Then, system requirements and applicable design are developed. Maximum heat generation of unit 4 is estimated as 1.67 MW, through fuel characteristics categorizations and ORIGEN calculations. To remove the decay heat, installation of an indirect air-cooled method is selected by evaluating three cooling metho... [more]

This study discusses the assessment of OE (operational efficiency) and RTS (returns to scale) over a time horizon. Many previous DEA (Data Envelopment Analysis) studies have discussed how to measure OE/RTS. However, their works did not consider the measurement over time. The important feature of the proposed approach is that our models are different from standard ones in terms of factor (inputs and outputs) unification. A problem with standard models is that they produce different efficiency measures for input and output orientations. Consequently, they yield different OE and RTS estimates depending upon which production factor is used for measurement. To handle the difficulty, we develop a new DEA formulation whose efficiency measure is determined after combining inputs and outputs, and then we discuss how to measure the types of RTS. The other methodological feature is that the proposed model incorporates a time horizon. As an empirical application, this study considers electricity g... [more]

This paper presents findings from an experimental study investigating the secondary atomization of liquid fuel droplets widely used in the heat and power industry exemplified by fuel oil and environmentally promising fuel oil/water emulsion. The scientific novelty comes from the comparative analysis of the critical conditions and integral characteristics of the secondary atomization of the liquid and composite fuels with the greatest potential for power plants. Here, we used two fuel atomization schemes: droplet−droplet collisions in a gas and droplets impinging on a heated solid wall. The temperature of the liquids under study was 80 °C. The velocities before collision ranged from 0.1 m/s to 7 m/s, while the initial droplet sizes varied from 0.3 mm to 2.7 mm. A copper substrate served as a solid wall; its temperature was varied from 20 °C to 300 °C. The main characteristics of droplet interaction were recorded by a high-speed camera. Regime maps were constructed using the experimental... [more]

Aiming at the melt splashing behavior in the smelting process of an oxygen-enriched side-blowing furnace, the volume of fluid model and the realizable k−ε turbulence model are coupled and simulated. The effects of different operating parameters (injection velocity, immersion depth, liquid level) on splash height are explored, and the simulation results are verified by water model experiments. The results show that the bubbles with residual kinetic energy escape to the slag surface and cause slag splashing. The slag splashing height gradually increases with the increase in injection velocity, and the time-averaged splashing height reaches 1.01 m when the injection speed is 160 m/s. Increasing the immersion depth of the lance, and the slag splashing height gradually decreases. When the immersion depth is 0.12 m, the time-averaged splashing height is 0.85 m. Increasing the liquid level is beneficial to reduce the splash height, when the liquid level is 2.7 m, the splash height reduces to... [more]

This article describes the results of laboratory tests on an oil-wedge-type electrode system, which were supplemented by FEM (finite element method) simulations. The studies were focused on the comparison of the partial-discharge inception voltage (PDIV) in the abovementioned system when immersed in different liquid dielectrics, namely inhibited mineral oil, uninhibited mineral oil, synthetic ester, and natural ester. In addition, the electric field stress obtained from the simulations was used in each case to determine the safe level for the actual transformer insulation. The studies were performed under AC voltage. Both electrical and optical detection methods were applied in order to properly determine the discharge inception. The statistical analysis of the results obtained from the laboratory measurements was carried out using Weibull distribution. We found that both mineral oils demonstrated better properties than the ester liquids in terms of resistance against partial-discharge... [more]