Intermittent Problems Research Articles

Stability Assessment and Reactive Power Compensation Strategies for Grid-Connected Wind Power Generations

With the acceleration of global economic integration and the rapid increase in population, the reserves of mineral resources on the earth are becoming increasingly scarce, and non-renewable resources are becoming increasingly scarce. Technological advances have significantly reduced the cost of photovoltaic and wind power, improved energy storage efficiency and smart grid technology, and solved the intermittent problem of new energy. How to boost the utilization rate of new energy and ensure its secure and reliable operation during grid connection is an important challenge that the current development of electric power technology must tackle. To serve as a guide for the creation of new wind power, this article analyses the two most widely used reactive power compensation devices, studies the method of restoring the stable state through reactive power compensation after the grid-connected wind power becomes unstable, and introduces several control methods for power compensation using reactive power compensation devices. The main objective of this article is to summarize the current mainstream stability assessment methods in the world and compare their benefits and drawbacks.

Review of the Coupled System of Solar and Air Source Heat Pump

The coupled operation of solar energy and air source heat pump (ASHP) can effectively solve the intermittent problem of solar energy systems running alone and the problem of performance degradation of ASHP systems running alone in winter. The coupled system of solar energy and ASHP can be divided into direct expansion type and indirect expansion type according to the structure form, and the indirect expansion type can be divided into series type, parallel type, and hybrid type. Various architectural forms of the solar-air source heat pump coupled system (S–ASHP) have achieved enhanced energy efficiency by means of a series of strategies, including the optimization of collectors, the refinement of evaporator structures, and the regulation of the temperature within hot water storage tanks. Choosing the appropriate architecture needs to comprehensively consider factors such as the external environment and load demand. In this paper, a variety of S–ASHP are summarized in order to provide some guidance for the future application of S–ASHP systems in the field of heating.

Photo-thermal conversion and energy storage characteristics of magnetic phase change composites

The problem of solar intermittency can be effectively addressed by solar-to-thermal energy storage using phase change materials (PCMs). Nevertheless, intricate operating scenarios and the extreme environment of PCMs restrict their uses, and the solar energy selective absorption also impedes the attainment of high photo-thermal conversion. In this study, paraffin wax (PW) was combined with styrene-ethylene-butylene-styrene (SEBS) and magnetic nanoparticles Fe3O4 to synthesize a novel kind of magnetic PCMs (PW/SEBS/Fe3O4). Experimental verification and simulation analysis were carried out. The results have showed that the PW/SEBS/Fe3O4 achieved an overall solar absorptance of 95 %, whose energy storage capacity and photo-thermal conversion were superior to those of pure PW. The PW/SEBS/Fe3O4 showed exceptional thermal and cyclic stability, completed phase transition rapidly, and reached a greater equilibrium temperature with the rise in light intensity. Although the PW/SEBS/Fe3O4 with 1.2 g Fe3O4 has better photo-thermal storage capacity, the PW/SEBS/Fe3O4 with 2.4 g Fe3O4 has more flexible application when considering the magneto-thermal effect. Furthermore, based on the thermo-physical property, the magneto-thermal effect of the magnetic PCMs was simulated using commercial software. This research offers a new concept for solar-thermal uses of building insulation and magnetic thermal switches.

An adaptive prediction method for carbon emissions of power systems containing new energy based on least-squares support vector machine

Aiming at the problem of high volatility and intermittency of new energy-containing power systems, which affects the prediction accuracy of carbon emissions, we study the adaptive prediction method of carbon emissions of a new energy-containing power system based on a least-squares support vector machine. The carbon emission coefficients of the nodes of the new energy-containing power system are determined based on the trend analysis method. Historical carbon emissions and carbon emission coefficients of the power system are collected, and the rough set method is used to simplify the carbon emission attributes and obtain a simplified attribute set for carbon emission prediction. The least-squares support vector mechanism is used to construct the carbon emission prediction model, and the simplified attribute set is used as the input of the carbon emission prediction model. The whale optimization algorithm was selected to determine the optimal parameters of the least-squares support vector machine through the process of encircling prey, hunting behavior, searching for predation, and adaptively optimizing the least-squares support vector machine to output carbon emission prediction results. The experimental results show that the method can accurately predict the carbon emissions of the power system, and the mean square error of the carbon emissions prediction is lower than 7.

Mitigating Intermittent Connectivity Problems in Vehicle-to-Vehicle Communication (V2VC): A Sparse Network Computational Model (SNCM)

INTRODUCTION: Wireless communication has made remarkable progress, by the rapid development of wireless technology in Artificial Intelligence (AI). Intelligent Transportation Systems (ITS), and Vehicular Ad Hoc Networks (VANETs) have received significant attention to ensure safety. However, V2V communication in VANETs faces uncontrollable challenges due to frequent intermittent connectivity issues in infrastructure-less networks. Addressing these problems in both safety and non-safety applications is a complex task.OBJECTIVES: To mitigate the intermittent connectivity problems, a novel Sparse Network Computational Model (SNCM) was proposed.METHODS: Extensive simulations using MATLAB to analyze the impact of spatial-temporal variations under different traffic flow densities. We varied the sensitivity factor (λ) at different time intervals while maintaining a constant traffic density. RESULTS: The findings indicate that there is no need to increase λ beyond certain thresholds for each level of service. The simulation results provide valuable guidelines for designing sparse networks, effectively mitigating frequent intermittent disconnections. Simulation experiments revealed an optimal threshold for the sensitivity factor λ for each level of service. Increasing λ beyond certain thresholds did not yield significant improvements in mitigating disconnections in V2V communication.CONCLUSION: The results provide valuable insights and guidelines for designing sparse networks to enhance connectivity and address intermittent disconnection issues. This paper presents a groundbreaking endeavor, and therefore, direct comparisons with existing protocols to evaluate its overall performance are beyond the scope of this paper. Instead, the SNCM protocol is intended to set a standard for future researchers to benchmark their research contributions against.

Reinforcement learning intermittent optimal formation control for multi-agent systems with disturbances

Abstract This paper investigates disturbance-resistant intermittent event-triggered optimal formation control problems of second-order multi-agent systems by using the reinforcement learning method, which takes into account the influence of network damage including denial-of-service (DoS) and deception attacks, stochastic noises, and unknown external disturbances. Firstly, we propose a novel disturbance observer based on adaptive control to estimate unknown external disturbances under an event-triggered mechanism. Secondly, by use of estimation of disturbances, an innovative intermittent event-triggered optimal formation algorithm is given. By applying theories such as Lyapunov stability and stochastic stability, sufficient conditions are derived to guarantee that all agents achieve the desired formation in mean square sense. Additionally, in the model-free case, the optimal controller is solved using the least squares method, which is computationally less complex than some existing approaches. Finally, the theoretical results are effectively validated through simulation examples.

Preparation of coconut oil/aluminum nitride/expanded graphite composite phase change materials with high thermal conductivity and stable shape for thermal energy storage

Phase change energy storage is one of the solutions to effectively deal with the problem of intermittency and spatial and temporal mismatch between supply and demand of new energy sources (solar, wind, etc.). However, phase change materials (PCMs) suffer from low thermal conductivity, which greatly affects energy storage and release efficiency. In this study, a novel shape-stable phase change material (SSPCM) was prepared by mixing coconut oil (CO) as a PCM with aluminum nitride (AlN) thermally conductive reinforcing particles and vacuum impregnated into expanded graphite (EG). The results showed that the thermal conductivity of the prepared SSPCM reached 2.985 W·m–1·K–1, which was 1765% higher than that of pure CO. The latent heat of SSPCM was 83.67 J·g–1, which was 99% of the theoretical value. Furthermore, SSPCM showed excellent thermal stability and thermal cycle reliability. The proposed SSPCMs have the advantages of being renewable and simple preparation methods, which have great potential for application.

Research on the Design of Multi-Rope Friction Hoisting System of Vertical Shaft Gravity Energy Storage System

Renewable energy generation methods such as wind power and photovoltaic power have problems of randomness, intermittency, and volatility. Gravity energy storage technology can realize the stable and controllable conversion of gravity potential energy and electric energy by lifting and lowering heavy loads. The hoisting system is an important component of a gravity energy storage system, and its lifting capacity and speed seriously restrict its energy storage capacity, energy conversion efficiency, and operational safety and reliability. In this paper, a design method for a multi-rope friction hoisting system of a vertical shaft gravity energy storage system is proposed. The parameter design and calculation of the hoisting rope, balance rope, and friction wheel of the friction hoisting system under typical conditions were carried out. The static and dynamic anti-slip capabilities of the friction hoisting system under the typical condition were explored. The results show that the maximum acceleration and deceleration speed of the compacted strand wire rope scheme is the largest, and the lifting and lowering time is the shortest. The maximum acceleration and deceleration speed of the triangular strand wire rope scheme is the lowest, and the lifting and lowering time is the longest. The dynamic tension of the hoisting rope at the heavy-load end is positively correlated with the acceleration, and the maximum value occurs in the accelerated lifting stage and decelerated lowering stage of the heavy load. The static anti-slip safety factor between the hoisting rope and the friction lining and the specific pressure between the hoisting rope and the friction lining comply with the requirements of China’s Safety Regulations for Coal Mines. The dynamic anti-slip safety factor of the hoisting system under different rope selection schemes is greater than the minimum value of 1.25 stipulated in the Safety Regulations for Metal and Nonmetal Mines. The research results are of great significance for the safety, reliability, and stable and efficient energy storage of a gravity energy storage system.

Potential-Dependent BDAC Adsorption on Zinc Enabling ‘Selective’ Suppression of Zinc Corrosion for Energy Storage Applications

Utility-scale zinc (Zn) batteries are a promising solution to address the problem of intermittency of renewable energy sources[1],[2]; however, Zn-metal anodes in these batteries suffer from capacity loss due to spontaneous corrosion of the Zn especially when high-surface area anode configurations are employed[3]. Additionally, Zn dendrites are known to form during battery charging which limits the cycle-life of these batteries. Electrolyte additives have been explored that prevent the aforementioned issues[4],[5], but these too come at a cost, i.e., surface-blocking additives polarize the electrode surface leading to loss in the voltaic and energy efficiencies of the battery. In this presentation, a novel electrolyte additive, benzyldimethylhexadecylammonium chloride (BDAC), will be presented for its ability to suppresses corrosion of Zn in a mildly acidic (pH = 3) electrolyte. An attribute of BDAC distinct from previously studied additives is that it ‘selectively’ suppresses corrosion when the Zn electrode is held near its mixed potential; however, during high-rate Zn deposition (charging) or stripping (discharging), BDAC is essentially deactivated and thus does not appreciably polarize the electrode surface. This selective corrosion suppression behavior is explored using slow-scan cyclic voltammetry, which reveals a hysteretic response. The response implies a current-dependent BDAC adsorption mechanism in which BDAC reaches higher surface coverages when the partial currents at the Zn surface are low (e.g., at or near the corrosion mixed potential), but BDAC coverage is reduced considerably when the Zn deposition-stripping rates are increased. Numerical simulations of the BDAC diffusion-adsorption process are used to corroborate this model. Ramifications of our approach to the selective suppression of Zn dendrites will also be discussed.

The short-term intermittency evaluation of distributed photovoltaic power

Uncertainty of distributed photovoltaic(PV) power brings great challenges to the safe and stable operation of power system, in which the intermittency problem is more challenging than the fluctuation. This paper focuses on the intermittency problem of distributed PV power, firstly, an intermittency evaluation method based on generalized extreme value(GEV) theory is proposed to solve the problem of the lack of "small-sample big-gap" events. Secondly, focusing on high risk events such as high-frequency and warning mutation events, probabilistic evaluation indexes were established, including T-hour-period mutation intensity and T-hour-period mutation frequency. Finally, a two-dimensional joint probability distribution of intermittency elements is established, and the concepts of return period and return level are introduced into the photovoltaic field to provide data support for the configuration of energy storage capacity and duration, and to provide auxiliary decision-making for the execution time and development cycle of interactive projects. The proposed method provides a solution for intermittency evaluation in small sample status quo with strong data compatibility and engineering replicability.

The impact of the establishment of the cross-border balancing market on the integration of RES into the regional electricity grid

Nowadays, it has become of great importance to obtain electricity from renewable, clean sources that do not pollute the nature. Wind power plants and photovoltaic-based solar power plants, which are among the leading renewable energy technologies, pose difficulties in monitoring the system for transmission system operators because their production is intermittent and not always continuous. Production from these sources varies with changing weather conditions and can be difficult to predict. Although new renewable capacities are available, including in the power system, the problem of intermittency of meteorological uncertainty is a major problem for the system stability of the power grid. The electricity obtained from RES based on intermittent wind and solar energy can vary significantly in a short time depending on changing weather conditions. The greater the share of these intermittent power supplies connected to the grid, the greater the risk of instability in the system. In this sense, integrating Turkey's large capacity in wind, solar and hydroelectric energy with the energy system of neighboring countries will greatly increase system reliability. Establishing regional energy markets and cross-border electricity collaborations are of great importance for the integration of this discrete renewable energy capacity into the system. In this study, Turkey's contribution to the integration of renewable resources into the cross-border power balancing market and regional load transfer is investigated. The electrical load transfer potential was examined in the light of the current capacity and planned future capacity increases, and the benefits and necessity of the system to be installed were revealed.

An enhanced hybrid scheme for ship roll prediction using support vector regression and TVF-EMD

In order to represent the complex characteristics of ship roll motion such as nonlinearity, uncertainty, and time-varying dynamics thus improving the ship roll prediction accuracy, an enhanced hybrid prediction scheme is proposed by using improved swarm intelligent optimization, time series decomposition, and machine learning. Firstly, the novel time-varying filtering-based empirical mode decomposition (TVF-EMD) is employed to decompose the ship roll motion data into multiple mode components with dynamic time-varying characteristics, which immunes of the mode mixing and intermittency problems of traditional empirical mode decomposition (EMD). Then, the support vector regression is utilized to train and predict mode components. Finally, the predicted results of individual components are reconstructed to achieve the final ship roll prediction angles. To avoid the unfavorable influence of manual parameter selection for TVF-EMD, an improved black widow optimization algorithm is employed to optimize the parameter configuration. The feasibility and effectiveness of the enhanced hybrid model are validated by ship roll prediction simulation based on the measured data of M.V. YuKun at sea. The experimental results show that the enhanced hybrid scheme can improve the prediction accuracy of ship roll motion and outrank those by using methods of EMD, ensemble empirical mode decomposition, and variational mode decomposition.

Dynamic event-triggered-based adaptive fuzzy optimized control for slowly switched nonlinear system with intermittent state constrains

This article presents a novel fuzzy event-triggered optimized strategy for slowly switched nonlinear system using reinforcement learning technique. For addressing intermittent state constraints problem, some improved shifting functions and barrier functions are designed in the adaptive backstepping process. Subsequently, by designing global performance functions with the discount term, the corresponding Hamilton-Jacobi-Bellman equation is derived and the optimal solution can be obtained under critic-actor structure. Different from the existing event-triggered methods, a novel dynamic event-triggered scheme for subsystem is developed, which not only saves communication resources, but also solves the mismatch behaviour between controller and subsystem without restriction on maximum asynchronous intervals and the number of switch within a triggering interval. Furthermore, by using modified average cycle dwell time method and Lyapunov stability theorem, all signals of system are proved to be bounded. Eventually, numerical simulation results validate the superiority of the proposed approach, and this new scheme is applied to single-link robotic manipulator.

Numerical analysis of the thermal behavior of a solar heat exchanger using multiple phase change materials

Currently, solar energy is the most abundant and cleanest source of renewable energy, making it a good substitute for increasing energy efficiency. Solar water heaters can significantly reduce the cost of electricity consumption in homes and help reduce greenhouse gas emissions. Most homes use water heaters to produce domestic hot water at a temperature between 50 °C and 60 °C. A latent heat phase change module is created to account for variations in energy supply to solve the inherent intermittency problem. The solar water/PCM heat exchanger, a phase change heat storage system, is designed in this work. A numerical analysis was conducted to examine the impact of various cooling temperatures on the solidification thermal cycle of the phase change material. As this temperature range is suitable for its melting. The phase change material (PCM) can be used to effectively control the temperature. Depending on the PCM and its storage capacity, the temperature of the produced water is controlled. Through the tubes, the water used for heat transfer from the solar collector transfers the heat from the sun’s rays to the PCM. During the discharge phase, the heat that has been stored in the PCMs is then transferred to the water and heats it up. In order to quantitatively evaluate the thermal performance of the water heat exchanger, a numerical simulation using the finite volume method was also analyzed.

Interfacial structuring of Mn[sbnd]N and Mn[sbnd]C bonds by defect engineering for high-performance Zn-Mn battery

Zinc‑manganese batteries (ZMBs), with their non-flammable aqueous electrolyte and lower electrode material costs, offer a safer and more economical solution to the problem of energy intermittency. However, current ZMBs still face significant challenges, such as the presence of low electrical conductivity and poor structural stability of the manganese-based cathode, as well as unclear mechanisms of structural changes during charge storage. Here, we present a strategy to construct MnO2 containing MnC and MnN bonds (PAMO) by defect engineering and interface bonding design. This strategy benefits from the fact that MnN and MnC bonds can stabilize the structure and promote the interfacial dynamics of MnO2, thus effectively mitigating manganese dissolution. Meanwhile, the oxygen defects generated by interfacial bonding increase the electrical conductivity of MnO2. In addition, in terms of morphology and structure, the leafy vein-like secondary compartmentalized structure formed by PAMO provides more reactive sites for the redox reaction of MnO2, accelerating charge transfer and ion diffusion. The experimental results show that compared with pure MnO2 (326.8 mAh g−1), the capacity of PAMO material is enhanced by 30.1% (426.6 mAh g−1), and the battery still has 85.4% residual capacity (144.2–123.1 mAh g−1) after 6000 cycles, and coulombic efficiency is always maintained above 99.5%. This heterostructure design strategy of C- and N-doped MnO2 provides high electronic conductivity while playing an important role in improving structural stability.

Diffusion with two resetting points.

We study the problem of a target search by a Brownian particle subject to stochastic resetting to a pair of sites. The mean search time is minimized by an optimal resetting rate which does not vary smoothly, in contrast with the well-known single site case, but exhibits a discontinuous transition as the position of one resetting site is varied while keeping the initial position of the particle fixed, or vice versa. The discontinuity vanishes at a "liquid-gas" critical point in position space. This critical point exists provided that the relative weight m of the further site is comprised in the interval [2.9028...,8.5603...]. When the initial position is a random variable that follows the resetting point distribution, a discontinuous transition also exists for the optimal rate as the distance between the resetting points is varied, provided that m exceeds the critical value m_{c}=6.6008.... This setup can be mapped onto an intermittent search problem with switching diffusion coefficients and represents a minimal model for the study of distributed resetting.

Potential–Dependent BDAC Adsorption on Zinc Enabling Selective Suppression of Zinc Corrosion for Energy Storage Applications

Utility-scale zinc (Zn) batteries are a promising solution to address the problem of intermittency of renewable energy sources; however, Zn-metal anodes in these batteries suffer from capacity loss due to spontaneous corrosion of the Zn especially when high-surface area anode configurations are employed. Additionally, Zn dendrites are known to form during battery charging limiting the cycle-life of these batteries. Electrolyte additives have been explored that prevent aforementioned issues, but these too come at a cost, i.e., surface-blocking additives polarize the electrode surface leading to loss in the voltaic and energy efficiencies of the battery. In this contribution, a novel electrolyte additive, benzyldimethylhexadecylammonium chloride (BDAC), is investigated for its ability to suppresses corrosion of Zn in an acidic (pH = 3) electrolyte. An attribute of BDAC distinct from previously studied additives is that it selectively suppresses electrochemical activity when the Zn electrode is at its corrosion potential; however, during high-rate Zn deposition (charging) or stripping (discharging), BDAC is essentially deactivated and thus it does not appreciably polarize the electrode surface, thus minimizing voltaic efficiency losses. This selective corrosion suppression behavior is explored using slow-scan voltammetry, which reveals hysteresis implying a potential- or current-dependent BDAC adsorption mechanism in which BDAC reaches higher surface coverages when the partial currents at the Zn surface are low (e.g., at or near the corrosion potential), but BDAC coverage is reduced considerably when the Zn deposition or stripping rates are increased. Numerical simulations of the BDAC diffusion-adsorption process corroborate this mechanism. Ramifications of our approach to the selective suppression of Zn dendrites are discussed.

A New, Ultra-Low-Cost Power Quality and Energy Measurement Technology Bringing SmartGrid on the Factory and Automation Floor

This paper introduces a new application for Power Quality and Energy Monitoring: embedding power quality monitors inside sensitive industrial, commercial, automation, manufacturing and medical equipment – and bringing SmartGrid to the factory and automation floor. Using power quality monitors to solve intermittent problems has also been limited by the cost of monitors. In this case, the monitors are generally installed at the equipment terminals. So the monitors can either directly interface with the load, or they can interface via e-mail or WebServer with a remotely connected user. In addition the new technology also combines a high accuracy energy monitor that can precisely control loads based on the load profile. It also introduces IEC 61000-4-30 which is an excellent standard that ensures that all compliant power quality instruments, regardless of manufacturer, will produce the same results when connected to the same signal. However, instruments that comply with the Class A requirements of this standard have, until now, been too expensive for common use. Now a new set of technologies developed by an American company, in cooperation with a Japanese company, demonstrate that it is possible to manufacture three-phase power quality instruments that are fully compliant with the Class A requirements of IEC 61000-4-30, and to do so at ultra-low-cost, allowing these monitoring devices to be used even at entry levels of individual loads.

An analysis of the application of computer-assisted instruction in the teaching of physical education yoga

Abstract In this paper, according to the TOF method in the principle of Kinect V2.0 depth measurement, the Kinect data stream can be obtained, which can realize the real-time acquisition of the user’s yoga movement data. On the basis of the extraction of joint motion features, the position of each joint point in the model under the model coordinate system is calculated sequentially using the action redirection algorithm. For the intermittent problem of keyframes in the yoga action screen of the joints, it is necessary to optimize the analysis of yoga action recognition through the action keyframe interpolation method. Starting from the demand for sports yoga teaching, we determine the design scheme of a computer-aided yoga teaching system, realize the design of a computer-aided yoga teaching system based on the system development platform and programming program, and test the performance of the computer-aided yoga teaching system by using simulation analysis. The results show that the yoga movement redirection algorithm, when matching the data information of the same movement, the distance value is 1 to 2 orders of magnitude smaller compared to the matching distance between different yoga movement sequences, and the use of the joint angle value can find out the joints where the trainer’s movement is not up to the standard, and the yoga trainer can reasonably adjust the movement based on the similarity and the joint angle value given by the system to achieve the purpose of yoga training.

MXene nanosheets coated conjugated microporous polymers hollow microspheres incorporating with phase change material for continuous desalination

The inevitable intermittency of solar illumination during the interfacial evaporation process can cause a reduction in the evaporation performance of solar evaporators. Here, we report the fabrication of a new solar-driven interfacial evaporator using MXene nanosheets as the photothermal layer, modifying them with conjugated microporous polymer hollow microspheres, and then compounding them with the phase change material, in this case, cetyl alcohol, to form a composite evaporator (CE) that can perform all-weather solar interfacial evaporation. By combining interfacial evaporation photothermal conversion with energy storage, the evaporator achieves an evaporation rate of 1.57 kg⋅m−2⋅h−1 at a light intensity of 1 kW⋅m−2 and 2.79 kg⋅m−2⋅h−1 at a light intensity of 2 kW⋅m−2. In addition, the evaporator attains an excellent solar evaporation efficiency of over 91% in both cases and even in salt water. In addition, interestingly, our CE exhibits excellent continuous evaporation ability, e.g., the mass of evaporated water was increased by 0.36 kg⋅m−2 at a light intensity of 2 kW⋅m−2 compared to the cavity evaporator without the phase change material (PCM) when solar light was turned off. These results could be attributed to the fact that the energy released by the incorporated phase change material allows the evaporator to maintain stable evaporation under conditions of insufficient or intermittent solar irradiation, potentially providing a new opportunity for addressing the intermittent problem of evaporation at the solar interface due to unstable light intensity, thus showing great potential for practical continuous desalination.