فصلنامه مهندسی و مدیریت انرژی
سال سیزدهم شماره 3 (پیاپی 49، پاییز 1402)

Due to renewable generation increment in power systems and the complexity of control and protection of them, the evaluation of   transient stability is necessary. This paper aims at analyzing the impact of wind power generation on the transient stability of power systems. To this end, doubly fed induction generator (DFIG) converters were first investigated in a closed-loop control mode. More detailed controls were used for the rotor side converter. Controls of the DC link converter on the network side were assumed to be ideal. Then, through using Gershgorin's theory, a new approach to adjust converter control parameters was presented. The simulation results in different operating modes confirmed the capability of this method in adjusting the converter’s control parameters. Also, by using performed simulations, the effect of increasing wind power production penetration and the changes of reactive power compensation by DFIG on the transient stability of power system were investigated. Finally, the effect of power system strength and DFIG parameters change, in the presence of DFIG-based wind power generation, on transient stability was analyzed. The simulation results showed that an increase in wind power generation initially led to an improvement and finally to the weakening of the transient stability of the system. In fact, this paper provides a professional and valuable perspective towards the investors and operators of the power systems with wind power generation from the viewpoint of transient stability.

In this paper an off-grid microgrid, based on 100% renewable energy, integrated with an electric vehicle charging station, an electric vehicle parking station, and a demand-response program was modeled. The electric vehicle charging station operated based on a battery swapping model in order to charge the electric vehicles in the shortest time possible. The electric vehicle parking station was used to park vehicles during various hours of the 24-hour period. The vehicles inside the parking had to be fully charged by the microgrid when leaving the parking station. Since these vehicles were parked for several hours, their charging time was not limited, and they are charged by direct chargers rather than battery swapping. The loads of the microgrid were under a demand-response program, and they were curtailable, non-curtailable, shiftable, and interruptible loads. The only energy source of microgrid was solar PV systems; the solar-energy related issues such as zero energy during night, output power variations, and the possibility of losing the whole or a part of energy due to shade should be dealt with. In the proposed method, an optimal programming was applied to the charging-discharging of the swapping batteries in charging station, to the charging-discharging of electric vehicles in the parking station, and to the energy management of loads (i.e., curtailable, non-curtailable, shiftable, and interruptible loads). The mismatch of energy and the lack of solar energy were compensated by the discharging power from charging and parking stations as well as by the management of the power of loads. Simulation results demonstrated that the unavailability of solar energy during the night resulted in paying 50% of the daily revenue as penalty cost. During hours such as 7 to 19, when the solar energy was available, the plan used the solar power as much as possible and limited the extracted energy from other energy resources. The energy of shiftable loads was supplied mostly from 13 to 15 hours, when solar energy was at the maximum level.

Multi-area economic distribution of load (MAED) is a generalization of the basic problems of economic distribution of load (ED), which evaluate the optimal power distribution of multiple areas in terms of operating costs. In the following parts of this paper, the concept of MAED is extended to multi-regional economic/environmental distribution (MAEED) by considering environmental issues. The purpose of MAEED is to distribute power among different areas by minimizing operating costs and emissions at the same time. In this paper, first the MAEED problem was expressed as a formula; then, a multi-objective and advanced particle optimization (MOPSO) algorithm was expressed to deduce its Pareto optimal solutions, during the optimization process. The transmission limits of communication lines were expressed as a set of constraints to ensure the security of the system. In addition, the rotating storage area was to increase the reliability of the system. A reserve sharing pattern was applied to ensure each region's capability to meet reserve demand. The simulation was based on the four-zone experimental power system, and it showed the effect of the proposed optimization process and the effects caused by different issues.

In this paper, the operation of electrical, heat and gas networks with flexible energy hubs is presented, where hubs is contributed in energy market that is based on market clearing price. This scheme maximizes the difference between energy hubs profit and operation cost of generation units subjected to operation model of sources, storages and responsible load in hub format, flexibility limits of hubs, and optimal power flow model of energy networks. This formulation is based on market clearing price model, so that it obtain value of energy price according to balancing between the generation and demand in different buses if energy networks. Penalty function method in this paper uses to calculate of primal variables and some dual variables (energy prices). In the following, the stochastic optimization uses to model the uncertainties of load and renewable power. Finally, the obtained numerical results show the capabilities of the proposed scheme in the improving flexibility and economic situations of hubs. Also, optimal operation of hubs is able to improve the economic and operation induces of energy networks in comparison to load flow study, and it improves the social welfare based on reducing of energy price. So that 100% flexibility condition obtains for Hubs. In this condition, the operation cost, energy loss, voltage drop and temperature drop are reduced about to 19.8%, 7.1%, 19.5% and 16.7%, respectively, with respect to load flow analysis, but the pressure drop increases about to 4.9%.

The environmental concerns of the use of fossil fuels and the financial interests of governments have raised the necessity of installing renewable power plants in the distribution network. In order to make maximum use of these resources, it is necessary to calculate the hosting capacity of the network. The hosting capacity of the distribution network is the maximum allowed capacity for installing distributed generation in the network, according to operating restrictions. Wind farms are one of the renewable resources used in the power system. The presence of wind farms intensifies the uncertainties of network operation. In this article, the theory of Information Gap Decision has been used to model the uncertainties in the production of wind farms and the amount of hourly load to calculate the hosting capacity of the network.  The strategies of energy management of the network have been taken into account in order to increase the capacity. The network energy management strategies, considered in this article, include static var compensators, network reconfiguration, and power factor control of wind turbines. The correctness and the accuracy of the proposed modeling has been studied on 33 bus IEEE networks.

In this paper, an interleaved fly-back-forward boost converter with a new auxiliary circuit was presented. An auxiliary circuit with a low number of elements provided zero voltage switching conditions to turn the switches on and off; besides, the energy of the transformer leakage inductance was properly absorbed by the auxiliary circuit and prevented voltage spikes on the switch. Furthermore, the third winding in the auxiliary circuit not only transfered the energy of the auxiliary circuit to the output but also caused a complete discharge of the snubber capacitors of the main switches in the resonance process. This auxiliary circuit could be expanded, and the number of auxiliary switches did not increase with the addition of converter branches. The performance of the proposed converter was fully analyzed, and a 120 W laboratory prototype was implemented to demonstrate its correct operation. The results showed a 6.5% increase in the efficiency compared with the converter without an auxiliary circuit.

In this paper, the thermoelectric properties of graphene-based structures are assessed by tight-binding method using Landauer-Buttiker formulas. Although a decline in the width of the grapheme nanoribbon can increase the thermoelectric figure of merit, the proper design of the nanostructures is still possible. Based on the results, a periodic alteration in the width of the ribbon, also known as the ribbon width modulation, could enhance the figure of merit twice compared with that of the narrow ribbon. Moreover, for the case with gradual changes in the ribbon width, three-fold enhancement could be achieved in the thermoelectric figure of merit compared to that of narrow ribbons. Such an increment could be assigned to an increase in the bandgap and, thus, the increment in the Seebeck coefficient, the power factor as well as the thermal conductance reduction.

CFTS semiconductor particles with the structure of Cu2FeSnS4 have attracted the attention of researchers as one of the newest materials in the field of absorber layer of thin film solar cells and interlayer layer in perovskite solar cells. This P-type structure has greatly raised the hopes to achieve an efficient low-cost structure due to the use of abundant elements in the earth's crust, direct band gap in the range of solar radiation intensity, and high absorption coefficient (104 cm−1). The synthesis of CFTS semiconductor nanoparticles was performed through a solvothermal process with simple and cheap precursors. The degree of crystallinity and the direction of crystal growth of the structure were evaluated by XRD analysis. The topography of the particles was carried out through a field emission scanning electron microscope (FE-SEM), and the percentage of the elements of the structure was determined through EDS analysis. The band gap of the particles was calculated through UV-Vis spectroscopy and the absorption spectrum of the structure. The results of the XRD analysis indicated the formation of a structure with high purity and a favorable degree of crystallinity. The average size of the particles was obtained to be in the range of 1-2 µm, and the particles were uniform spheres with a sheet-like surface. The results of EDS analysis indicated an optimal percentage of structural elements and a band gap of particles in the range of 1.43 eV, indicating good agreement with the reported values.

In this research, the effects of a sinusoidal middle plate with variable wavelength on the melting process of a vertical triple-tube heat storage unit were investigated. The middle enclosure was filled with the phase change material (PCM) while the heat transfer fluids (HTFs) passed through the inner and outer tubes. The enthalpy-porosity approach was applied in order to simulate the PCM phase change process, using ANSYS FLUENT 2020 R2 software. The flow regime was supposed to be laminar while the velocity and pressure fields were coupled using the SIMPLE approach. For the evaluation of the efficacy of the heat exchange unit with wavy middle plate, the outcomes of various scenarios were compared with those cases in the absence of the middle plate. Therefore, the performance of the thermal energy unit was assessed via comparing the liquid fraction and temperature contours as well as the melting times and heat storage values of various scenarios. The numerical results showed that the sinusoidal middle plate with variable wavelength decreased the melting time by 67.59%, while the heat storage rate increased by 200% compared with the cases in the absence of the middle plate.

Iran is one of the countries with a radiation potential that is very suitable for the construction of solar carports. Considering the high initial cost of constructing these parking lots, the importance of their feasibility and optimal design is very high. In the present study, the design and simulation of a solar carport connected to the power grid that was implemented at the Faculty of Agriculture of Tarbiat Modares University (TMU) in Tehran was carried out. For this purpose, the photovoltaic system was calculated in PVsyst software considering the geographical location and weather conditions of Tehran. In this case, the optimal side angle for installing the photovoltaic modules on the parking lot was set at 35 degrees to maximize the annual electricity production. Then, in determining the type and model of the photovoltaic modules and the solar inverter, their optimal electrical arrangement was designed. In addition, the losses of the various parts of the system were calculated, including the losses caused by shading, temperature rise, connecting wires, and so on; besides, the optimal spacing and arrangement of the modules were presented. Based on the final results of the simulation, the amount of electricity generated by the parking lot was 48.2 MWh/year; the annual power factor was 0.791; the reduction rate of CO2 production was 499.89 tons in a total of 30 years, and the sensitivity analysis and lower return on investment were calculated from 5 years onwards. The results of this study showed that the implementation of the project at the investigated site was economically justified in addition to the benefit of providing renewable electricity.