فصلنامه مهندسی و مدیریت انرژی
سال دوازدهم شماره 4 (پیاپی 46، زمستان 1401)

To reduce the uncertainty nature of tidal stream turbines connected to the bulk power system, energy storage systems with high capacity should be used. Among different energy storage systems, vanadium redox flow batteries with large capacity can be used in power systems. In this paper, an economic analysis is performed, and the impact of vanadium redox batteries on the power system containing tidal turbines considering reliability effect is evaluated. For this purpose, a multi-state reliability model is developed for tidal-stream turbines connected to battery units. The multi-state reliability model is used to study the adequacy of the power systems containing tidal turbines in conjunction with vanadium redox batteries. In the proposed reliability model, the failure rate of the composed components and variation in the generated power arisen from variation in tidal current speed are taken into account. Fuzzy c-means clustering technique and Xie-Beni index are utilized to determine an optimal number of clusters and probability of them in the reliability model of the system including tidal stream turbines and vanadium redox batteries. Numerical results of Roy-Billinton and IEEE reliability test systems are evaluated to study the effect of tidal stream turbines and vanadium redox batteries on the reliability of power systems and verify the effectiveness of the proposed model.

Recent promotions in renewable energy technology along with an increasing demand and the need for clean and cheap energy have led to an increasing trend towards distributed generation resources, especially solar cells, in distribution networks. Moreover, with the rapid development of electronic devices such as computers, televisions, and mobile phone chargers in the consumer sector and the use of power electronic devices such as converters in the industrial sector, the power quality of distribution networks has been seriously threatened. Therefore, it is very important to consider load compensation in distribution networks. In this paper, the use of a PV-grid interface converter for complete load compensation in a four-wire, three-phase distribution network is proposed. The proposed converter consists of a single-stage DC/AC inverter to connect solar cells to the grid. Maximum power point tracking of solar cells and injection of this power into the grid along with complete load compensation are done by the proposed DC/AC inverter. To achieve these aims, a new control strategy is proposed. Simulations wer performed in MATLAB/SIMULINK to evaluate the performance of the proposed structure and control strategy for the PV-grid interface converter. The simulation results for a four-wire, three-phase distribution system indicated complete nonlinear load compensation, reactive power compensation, load current harmonic elimination, and maximum PV power injection into the grid.

This paper presents a novel energy management strategy (EMS) for the hybrid electric vehicle with fuel cell/battery/ultra-capacitor energy sources (FCHEV). For improving the durability and fuel economy of the fuel cell system in FCHEV, the proposed EMS utilized a close-loop control strategy that combines fuzzy logic control (FLC) and a frequency decoupling-based model based on an adaptive low-pass filter and wavelet transform methods. Uncertainty as a powerful tool is utilized to design flexible strategies using type-II FLC based on the charge state of power storage systems. Furthermore, the designed frequency decoupling-based control system separates three optimal frequency components of the required power to supply it by fuel cell, battery, and ultra-capacitor systems based on their individual characteristics and limitation of the power fluctuation on the fuel cell system. Finally, a dynamic performance test used the ADVISOR simulator under the World Light Vehicle Test Cycle (WLTC) to compare the proposed strategy with different strategies. According to the simulation results, the proposed strategy ensures the safety of the ultra-capacitor and battery park and improves the durability of the fuel cell while reducing the hydrogen consumption maximum by 14.6% in comparison with different strategies under similar driving conditions.

The production of electricity from the pressure difference inside the water transmission lines is one of the new issues in the renewable energy fields, which is achieved by replacing pressure relief valves with micro-hydropower.  For this purpose, extensive research has been done for the technical and economic evaluation of the construction of micro-hydropower on different points of water transmission lines. The main challenge in conducted studies is that these studies cannot be generalized to other points. In other words, considering that the hydraulic parameters of the lines and their operating conditions are completely different, so each line needs feasibility and separate studies. To this end, in this paper, different stages of designing micro-hydropower from a technical and economic point of view were described; then, these steps were carried out for a real case study, that is, the Kohrang-Shahrkord water transmission line. The design of micro-hydropower in this paper was done with the cost function of the ratio of income to initial capital. The results of the designs for different scenarios showed the importance of studying the daily flow rate changes that may have been affected by climate change. Also, the results showed that by choosing the Crossflow turbine for the points with large flow rate changes, the highest value of the profit index was obtained at the cost of 1.92, which led to the production of 2742,000 kW-hr of energy per year. In similar hydraulic conditions, with the choice of Torgo turbine, the value of this index was 1.34 and the annual energy production was 2141,000 kW-hr.

This paper presents modified rotor designs for two conventional V- and Flat-type BLDC motors to reduce the torque ripple. For gaining an insight into design features, the torque production characteristics are described at the beginning of the paper. By analyzing and comparing performance parameters including cogging torque, air gap flux density, back EMF, and torque average, the paper tries to describe how the torque ripple can be affected and reduced by shaping the air gap and creating specific holes in the rotor magnetic path. First, the conventional V-type BLDC motor was analyzed. Sensitivity analysis was deployed to shape the air gap and to create holes in the rotor structure. Then, all the results for both conventional and proposed V-type models were compared. Consequently, the torque ripple was effectively reduced without affecting other performance parameters. Next, the Flat-type BLDC motor was considered. Following the sensitivity analysis, the air gap was shaped, and holes were created. Similar to the proposed V-type design, the proposed Flat-type design effectively reduced the torque ripple compared with the conventional design. The results were obtained using finite element analysis; it confirmed the effectiveness of the proposed designs in both V- and Flat-type BLDC motors.

This paper proposes a modified drive structure for switched reluctance motors considering a direct torque control strategy. In the proposed converter structure, standard inverter topologies are used with a few additional components to make the total SRM drive cost-effective. Like drives with conventional inverters, proposing a new general converter structure, appropriate regarding its total cost and controllability, has been one of the most critical challenges of the last two decades for switched reluctance motors. The use of such conventional three-phase inverters instead of SRM (Switched Reluctance Motor) exclusive converters, due to low cost and greater availability, has been analyzed and effectively implemented in this paper. The analysis showed that driving switched reluctance motors using conventional inverters could possibly lead to a high torque performance. In this paper, two new converter structures, based on conventional three and one phase inverters, are presented for a four-phase switched reluctance motor. In addition, the direct torque control strategy is used to reduce torque ripple sufficiently. The results showed the effectiveness of the proposed drive structure.

The limited resources of fossil fuels and the problems caused by greenhouse gas emissions have made it increasingly necessary to pay more attention to renewable energy sources, especially solar energy. Increasing the efficiency of equipment related to this group of energies will increase productivity, decrease fuel costs and electricity, and improve air quality. This study aims to design a new geometry for turbulators which increase efficiency in solar collectors, especially in higher Reynolds number (Re), with an increase in the Nusselt number (Nu) and a decrease in the pressure drop (DP). In this regard, the performance evaluation criterion (PEC) has been defined based on DP and Nu, and its changes have been investigated. Furthermore, the heat-transfer characteristics and performance of water-based CuO-SWCNT hybrid nanofluids (HNF), with volume fractions (ϕ) of 2% to 6% of nanoparticles in the Re = 12000 to 18000, have been investigated in the absorber tube of a solar collector. In order to couple velocity and pressure equations, a simple algorithm is used. Results from the study of two samples of twisted tape (TT) with two different scales (1 and 0.5) are examined for samples A and B respectively. Based on the results, the TT with a scale has the highest efficiency of 1.0 (Re =12000, f = 2% is 3.54) where it is 3.52, while considering a TT with a scale of 0.5 under the same conditions. Therefore, using a TT with a scale of 1 is more desirable from a thermal fluid dynamics point of view.

Due to high heat flux in electronic equipment, the better cooling of these equipment using microchannel heat sink is of interest to many researchers today. However, paying attention to reducing energy consumption is also one of the essential issues that has attracted the attention of researchers and manufacturers.Thermohydraulic characteristics and energy saving of a water-based graphene nanoplatelet-platinum hybrid nanofluid inside a manifold microchannel heat sink for laminar flow have been  investigated numerically for various nanofluid volume fractions (φ=0.02, 0.06, and 0.1%) and Reynolds number (Re=20 to 100). The Properties of hybrid nanofluid were considered temperature-dependent. According to studies conducted in this research, graphene nanoplatelet-platinum hybrid nanofluid in a manifold microchannel heat sink improves heat transfer performance. Cooling uniformity factor as a criterion for diagnosing of hotspot regions decreases with an increase in Reynolds number and nanofluid volume fraction. Nusselt number (Nu) increases with an increase in  the Reynolds and nanofluid volume fraction. Numax=38.10 is obtained for Re=100 and φ=0.1%  and Numin=24.17 is obtained for Re=20 and φ=0. Thermal resistance decreases with an increase in nanofluid volume fraction and Reynolds number. With an increase in Reynolds number andnanofluid volume fraction, pressure drop increases. Also, at low Reynolds numbers (Re=20), pressure drop differences in different volume fractions are insignifcant. For all nanofluid volume fraction values, the performane evaluation criterion (PEC) value is greater than 1, which indicates the improvement of manifold microchannel heat sink efficiency using nanofluids. Also, for all Reynolds values, the performance evaluation criterion with an increase in volume fraction increases. PECmax for Re=20 and φ= 0.02% is achieved. There is no significant difference in the performance evaluation criterion for higher volume concentrations (0.06% and 0.1%) and higher Reynolds numbers (40 to 100).