The insulation pressboard is very important in the insulation of oil-immersed transformers, which determines the useful life of the transformer. In order to analyze the change in the micro topography of the pressboard under the condition of thermal aging in detail, the insulation pressboard samples of different thermal aging periods were made. Image enhancement, denoising, segmentation, optimization, edge detection, expansion, and corrosion were used to process SEM images of the pressboard after thermal aging, so as to extract the fiber width, hole size, and surface roughness. By comparing the relationship between the micro topography and the degree of polymerization of the insulation pressboard in different thermal aging periods, it can be concluded that when the fiber width was 91% of the unaged pressboard fiber width, and the corresponding roughness was 0.162, the insulation life was only approximately half of its original value, and when the fiber width was 79% of that of the unage... [more]

In order to obtain the calibration law of rock macro and meso parameters under three-dimensional conditions, based on the parallel bond model, starting with the basic theory of PFC and the qualitative relationship between macro and meso parameters, an orthogonal experimental scheme is designed. An improved BP algorithm is proposed, which has a function with gradient factor, adaptive Nesterov momentum method, and adaptive learning rate for the lightweight analysis of meso parameters. The sensitivity between macro and meso parameters is quantified, and the key meso parameters are screened out. Based on the lightweight model, the correlation and influence mechanisms between macro and meso parameters are analyzed. It was found that the elastic modulus increases linearly with the increase in equivalent modulus. The parallel bond stiffness ratio can inhibit the growth of the elastic modulus, and the elastic modulus decreases greatly when the stiffness is relatively high. There is a linear re... [more]

This research presents an optimal scheme for the integration of renewable resources with the utility grid to minimize the operational cost of the residential and industrial microgrids. With the changing paradigm of solar photovoltaic in low-voltage distribution networks, utilities have allowed net metering and feed-in tariff (FiT). These incentives encourage residential and industrial consumers to contribute toward energy generation. However, in conventional mode, the system may underperform if resources are not scheduled optimally. To compensate for the price difference during off-peak and on-peak hours, the energy should be taken from the grid when electricity prices are lower and supplied to the grid when the electricity price is higher. The proposed models will therefore allow optimal resource utilization considering intermittent renewable generation as well as a time-varying utility tariff. A complete comparative analysis of on-grid and off-grid models was carried out. The results... [more]

The power-sharing possibility amongst microgrids (MGs) in networked microgrids (NMGs) offers multiple profits to the NMG by employing an applicable energy management system. An efficient energy management system can provide an adequate compromise in terms of the component sizing of NMGs through MG collaboration. This paper proposes a procedure to size the component for an isolated networked hybrid microgrid. The proposed design procedure relies on the optimum operation of individual MGs. The defined Reduced Factor (RF) identifies the possible size reduction for the dispatchable components, such as diesel generators and the energy storage system of each MG. The introduced RF is based on the operating reserve evaluation obtained from the optimal operation of individual MGs and the correlation between load profiles. Eventually, the simulation and practical results of a networked hybrid MG consisting of three MGs are presented to verify the proposed component sizing procedure. The practica... [more]

This paper presents automatic software for E-liked shaped contactless inductive power transfer (CIPT) device study and design that provides attended-free, multiple-case auto-generating and auto-deploying analysis in one go. It provides visualized and listed results in a design space or for optimizing solutions. To satisfy the demand for static and dynamic charging devices, the software provides specific cores, such as EE-, EI-, IE-, and II-shaped, with or without legs as optional core structures. The software contains three main parts: a user-friendly interface, analytic approaches providing grid analysis that represent the general performance in a designated parameter range, and optimal analysis for multi-objective optimization using a genetic algorithm (GA). The post-analysis processor converts the analysis results to easy-to-read outputs. Users can customize various parameters, such as core type, structural size, circuit configuration, materials, and analysis setting. Automatic func... [more]

The organic Rankine cycles (ORCs) have been used to convert low-enthalpy geothermal brine into power. Parameter optimization and working fluid selection are the main approaches to enhance geothermal ORC performance. This work uses environmentally friendly fluids, including R1224yd(Z), R1233zd(E), R1336mzz(Z), R601 and R601a, as the geothermal ORC working fluids. The evaporation temperatures of the selected fluids were optimized to maximize the cycle net power outputs. The thermodynamic characteristics are investigated with the consideration of the influence of the allowed reinjection temperature (ARIT). Among the selected fluids, R1224yd(Z) has the highest optimal evaporation temperature with the maximum turbine power output for a brine inlet temperature (BIT) higher than 120 °C, especially at a lower allowed reinjection temperature. However, the parasitic power consumption by the pumps in an ORC with R1224yd(Z) is also higher than with the other four fluids. The net power output for O... [more]

Aiming at the problem of large vibration of a high-subside stator inner cavity curve vane pump, the force analysis of the vane at the transition curve is carried out, and the functional relationship between the vane turning angle θ, the large arc radius R, the small arc radius r and the sliding friction is established. The particle swarm algorithm is used to optimize the solution of the objective function, and the optimized parameter values are brought into the MATLAB simulation program to obtain the optimized stator curve profile diagram. The dynamic performance of the vane pump before and after optimization is simulated using ADAMS. The results show that: the acceleration of the vane pump slide is significantly reduced; the friction between the slide and the slide groove is significantly reduced; the contact force between the slide and the stator is significantly reduced; the impact vibration of the optimized vane pump is significantly reduced; and the dynamic performance of the vane... [more]

Grid integration of renewable resources such as solar and wind energy can significantly raise the level of uncertainty in power systems, making the scheduled operation of generating units difficult. Therefore, the importance of operating reserves is more emphasized to prevent disruption by sudden changes in outputs of generators. In this paper, a stochastic unit commitment (UC) model to reflect uncertainty due to a large amount of renewable resources is proposed, in which upward and downward operating reserves are deployed simultaneously, and feasibility of the reserves is examined to make the deployed reserves supplied reliably. Uncertain parameters considered in the model are wind power availability, solar direct normal irradiance, and electric load. Two-stage stochastic programming is applied to the mathematical formulation, where UC decisions including dispatch are modeled as non-anticipative variables at the first stage, and redispatch decisions to serve realized electric demand a... [more]

The maintenance of wireless sensor networks involves challenges such as the periodic replacement of batteries or energy sources in remote locations that are often inaccessible. Therefore, onboard energy harvesting solutions can provide a viable alternative. Experimental energy harvesting from fluid flow, specifically from air flow, is typically restricted to a rotor and stator design or a model that strikes a piezoelectric. On the other hand, energy harvesting from mechanical vibrations routinely uses the linear motion of a magnet passing through a coil or vibrating piezoelectric elements. In this paper, we propose a novel V-twin harvester design that converts wind energy from a rotational input into the linear motion of a magnet inside a coil via a crank-slider mechanism. This design allows for high performance with a smoother voltage output when compared to a reference rotor/stator harvester design or piezoelectric method. At 0.5 Hz, a single crank-slider generated a voltage of 0.176... [more]

Local Energy Markets (LEMs) were recently proposed as a measure to coordinate an increasing amount of distributed energy resources on a distribution grid level. A variety of market models for LEMs are currently being discussed; however, a consistent analysis of various proposed grid tariff designs is missing. We address this gap by formulating a linear optimization-based market matching algorithm capable of modeling a variation of grid tariff designs. A comprehensive simulative study is performed for yearly simulations of a rural, semiurban, and urban grids in Germany, focusing on electric vehicles, heat pumps, battery storage, and photovoltaics in residential and commercial buildings. We compare energy-based grid tariffs with constant, topology-dependent and time-variable cost components and power-based tariffs to a benchmark case. The results show that grid tariffs with power fees show a significantly higher potential for the reduction of peak demand and feed-in (30−64%) than energy... [more]

This paper proposes new eccentric (ECC) auxiliary salient poles (ASPs) applied in spoke permanent-magnet (PM) motors. These ECC ASPs optimize flux density harmonics and further reduce torque pulsation. Then, the optimization procedure is proposed to reveal the relationship between the ECC method and ASP, and optimization steps are reduced. Firstly, the design of the ECC ASPs is based on the stairs, which are equivalent to sinusoidal flux density. Second, the expressions of offset length for maximum air gap, pole arc angle, and thickness ratio are revealed. Through theoretical analysis and the finite element method (FEM), the proposed ECC ASPs can generate low torque pulsation and improve sound and vibration features.

With the participation of wind power in grid frequency modulation, the fatigue load of the wind turbine increases accordingly. A new control method that considers both fatigue load and output power of wind turbine (WT) is proposed in this paper. A linear active disturbance rejection control (LADRC) is designed and applied for the pitch angle in the wind turbine load reduction control. The particle swarm optimization (PSO) algorithm is used to optimize the parameters of the wind turbine controller, and the total variation of the wind turbine shaft torque and tower bending moment is added to construct a new objective function to further reduce the fatigue load of the wind turbine. The design-optimized controller is validated on a 5 MW wind turbine in SimWindFarm. The simulation results show that the LADRC controller can accurately track the reference power of the wind turbine, reduce the pitch angle fluctuation of the wind turbine, reduce the fatigue load of the wind turbine, and improve... [more]

There were many promising superconducting materials discovered in the last decades that can significantly increase the efficiency of large power transformers. However, these large machines are generally custom-made and tailored to the given application. During the design process the most economical design should be selected from thousands of applicable solutions in a short design period. Due to the nonlinearity of the task, the cost-optimal transformer design, which has the smallest costs during the transformers’ planned lifetime, is usually not the design with the highest efficiency. Due to the topic’s importance, many simplified transformer models were published in the literature to resolve this problem. However, only a few papers considered this preliminary design optimization problem in the case of superconducting transformers and none of them made a comparison with a validated conventional transformer optimization model. This paper proposes a novel FEM-based two-winding transforme... [more]

A power system’s nonlinearity and complexity increase from time to time due to increases of power demand. Therefore, properly designed power system controlsare required. Without these, system instability will cause equipment failures, and possibly even cascading events and blackouts. To cope with this, intelligent controllers using soft computing are necessary for real time operation. In this paper, the reheat type three-area thermal power system is considered, and the output scaling factors, gain parameters of fuzzy membership functions, and parameters of fuzzy-proportional integral derivative (FPID) controllers are optimized using a differential evolution (DE) optimization techniqueand integral time multiplied absolute error (ITAE) as objective functions. To improve the limitations of the controller and to enhance stability of the system, high voltage direct current (HVDC) technology is advantageous due to its quickresponse capabilities. In this paper, a HVDC is connected in parallel... [more]

Renewable energy transition creates unprecedented issues in power system control, operation and protection [...]

Harmonic pollution sources in microgrids have the characteristics of high penetration and decentralization, as well as forming a full network. Local harmonic mitigation is a traditional harmonic mitigation method, which has the disadvantages of complexity and costly operation. Based on the idea of the decentralized autonomy of power quality, this paper establishes a comprehensive optimization model of the active power and harmonic mitigation capacities of grid-connected inverters based on two-layer optimization and realizes harmonic mitigation. Firstly, based on the harmonic sensitivity analysis, the calculation method of harmonic mitigation capacity is given. Secondly, a two-layer model of harmonic mitigation optimization is established. The upper-layer optimization model takes the minimum operation cost of the microgrid as the objective and the active power reduction in the multi-functional grid-connected inverter (MFGCI) as the optimization variable. The lower-layer optimization mod... [more]

This study presents the optimization of a multilayer wire-on-tube condenser exposed to forced convection, using the Optimized Multi-objective Particle Swarm Optimization (OMOPSO) algorithm. The maximization of the heat transfer and the minimization of the heat exchange area were defined as objective functions. In the optimization process, the variations of eight geometric parameters of the condenser were analyzed, and the Multi-objective Evolutionary Algorithm based on Decomposition (MOEAD), Non-dominated Sorting Genetic Algorithm-II (NSGAII), and OMOPSO algorithms were statistically explored. Furthermore, the condenser optimization analysis was extended to the use of alternative refrigerants to R134a such as R600a and R513A. Among the relevant results, it can be commented that the OMOPSO algorithm presented the best option from the statistical point of view compared to the other two algorithms. Thus, optimal designs for the wire-on-tube condenser were defined for three proposed study... [more]

The operation of the photovoltaic (PV) system under partial shading conditions (PSC) is complicated since the output characteristic of the PV system is profoundly affected by the heterogeneous irradiance of PSC. This paper proposes a dynamic reconfiguration framework to tackle PSC in the PV array. Continuous operation of the dynamic PV array reconfiguration under cloud-induced partial shading is considered by developing an emulator of the moving cloud. In addition, the Particle Swarm Optimization and Rao algorithms are improved to obtain the optimal PV array configuration under PSC. The operation of switching is enhanced by simultaneously considering the total switching times and the operation of highly active switches. The simulation results on the 9×9 PV array demonstrate the effectiveness of the proposed framework in terms of reducing the number of local maximum power points on the power-voltage characteristic, enhancing power output, and relieving stress on the switching operation... [more]

Although the proportional integral derivative (PID) is a well-known control technique applied to many applications, it has performance limitations compared to nonlinear controllers. GAPID (Gaussian Adaptive PID) is a non-linear adaptive control technique that achieves considerably better performance by using optimization techniques to determine its nine parameters instead of deterministic methods. GAPID represents a multimodal problem, which opens up the possibility of having several distinct near-optimal solutions, which is a complex task to solve. The objective of this article is to examine the behavior of many optimization algorithms in solving this problem. Then, 10 variations of bio-inspired metaheuristic strategies based on Genetic Algorithms (GA), Differential Evolution (DE), and Particle Swarm Optimization (PSO) are selected to optimize the GAPID control of a Buck DC−DC converter. The computational results reveal that, in general, the variants implemented for PSO and DE present... [more]

Among the numerous renewable energy resources, the main advantage of water energy is that it utilizes the current of the streams and rivers regardless of the given time of the day or season. The main purpose of this study was to create a low capacity, floating hydropower plant that is suitable for shallow and even narrow water bodies. The device was designed to create electric energy while floating on the water’s surface; therefore, it can be used not only in natural streams but also in drainage channels and wastewater treatment plants. The prototype was tested under real circumstances to identify the impacts of various settings on the energy efficiency. Measurements were conducted in Veszprém, Hungary on the Brook Séd. The average depth of the riverbed was 36 cm. Based on the field measurements, optimal efficiency was achieved by using six paddles. On the other hand, much lower efficiency was achieved when low (two or three) or high numbers (12 or 15) of paddles were used. A design fr... [more]

Diesel engines are widely used in agricultural tractors. During field operations, the tractors operate at low speed and high load for a long time, the fuel efficiency is only about 15% to 35%, and the exhaust waste heat accounts for 38% to 45% of the energy released from the fuel. The use of tractor exhaust waste heat can effectively reduce fuel consumption and pollutant emissions, of which the organic Rankine cycle (ORC)-based waste heat recovery conversion efficiency is the highest. First, the diesel engine map is achieved through the test rig, a plate-fin evaporator is trial-produced based on the tractor size, and the thermodynamic and economic performance model of the ORC are established. Then, taking the thermal efficiency of ORC and the specific investment cost (SIC) as the objective function, the particle swarm optimization (PSO) algorithm and the technique for order of preference by similarity to ideal solution (TOPSIS) decision method were used to obtain the optimal operating... [more]

This paper presents the integrated optimal design of the powertrain of a hybrid regional aircraft using multidisciplinary design optimization (MDO). The sizing of the main components of the propulsion chain is performed over the flight mission under various scenarios regarding energy management strategies and technological assessments. For that purpose, a complete set of multidisciplinary surrogate models are integrated into the MDO process, taking account not only of the main electrical, thermal and mechanical aspects but also of environmental constraints such as partial discharges in electric motors regarding flight conditions. Several MDO formulations are investigated comparing local (i.e., motor mass minimization) and global optimizations (i.e., powertrain mass then fuel burn minimization at aircraft level). Results emphasize main systemic couplings showing that despite future technological progress, the series hybrid architecture is heavier than a conventional thermal aircraft. Ne... [more]

This paper proposes an effective approach to solve renewable distributed generators (RDGs) and electric vehicle charging station (EVCS) allocation problems in the distribution system (DS) to reduce power loss (PLoss) and enhance voltage profile. The RDGs considered for this work are solar, wind and fuel cell. The uncertainties related to RDGs are modelled using probability distribution functions (PDF). These sources’ best locations and sizes are identified by the voltage stability index (VSI) and political optimization algorithm (POA). Furthermore, EV charging strategies such as the conventional charging method (CCM) and optimized charging method (OCM) are considered to study the method’s efficacy. The developed approach is studied on Indian 28 bus DS. Different cases are considered, such as a single DG, multiple DGs and a combination of DGs and EVs. This placement of multiple DGs along with EVs, considering proper scheduling patterns, minimizes PLoss and considerably improves the volt... [more]

In this paper, a novel one-way single-wire power transfer structure is proposed. Different from the traditional single-wire power transfer system, power is one-way transmitted from the power source to the load, and no loop is constituted. The structure of one-way single-wire power transfer is studied in detail, and the influences of its length and shapes on the transmission efficiency are determined. Research shows that the length of the receiving structure plays a key role in improving the system’s efficiency, while the transmitting structure has a little effect. Based on ensuring transmission efficiency, the space volume optimization method is further applied. The expression of electromagnetic field distribution is derived theoretically, and the proposed structure is verified by simulation and experimental results.

This study selects five parameters as decision variables for the optimization design of an ocean thermal energy conversion system, including the evaporating temperature, the condensing temperature, the pinch-point temperature difference between the evaporator and condenser, and the working fluid flow rate. The optimization goal is to maximize the net output power per unit area and the exergy efficiency. The final scheme is comprehensively screened out from the Pareto solution set through some evaluation indexes. Finally, this study also analyzes the effects of four decision variables on the optimization objectives and the evaluation indexes. This study finds that evaporating temperature and condensing temperature have similar effects on the two objective functions. However, the pinch-point temperature difference has different effects on them. The back work ratio is obviously affected by the condensing temperature. A small pinch-point temperature difference is beneficial and improves th... [more]