فصلنامه مهندسی و مدیریت انرژی
سال یازدهم شماره 2 (پیاپی 40، تابستان 1400)

This paperproposes a method for accurate sharing of harmonic and unbalanced loads in islanded microgrids. The proposed method can adaptively improve the load sharing among Distributed Generation (DG) units based on the circulating current rules and the harmonic and unbalanced power provided by each DG. Compared with previous methods, the proposed method does not require a dedicated central controller, and a relation should only be established among the adjacent DGs. Moreover, in this method, there is no need to know the values of the impedance of the DGs feeder and the loading conditions, and the effect of the proposed method on the quality of the output voltage of the DGs is less. The design process of the proposed method has fully been described; furthermore, to demonstrate the efficiency of the method, studies on the simulation have been performed on a sample islanded microgrids in MATLAB/Simulink environment.

This paper presents the system stability-constrianted optimal protection coordination (SSCOPC) as stochastic problem in the microgrid with grid-connected and islanded operation modes, including renewable energy sources (RESs) and energy storage systems (ESSs). To regulate optimally the dual setting overcurrent relays (DSORs) and to selectin the reactance size of fault current limiter (FCL), the system minimizes the total relays operation time in the primary and backup protection modes. Also, it is subject to the limits of the coordination time interval (CTI), DSORs setting parameters, FCL size, and microgrid stability in the fault condition. Generally, the microgrid includes RESs and ESSs; thus, the proposed SSCOPC needs a daily operation of microgrid as stochastic model to calculate network variables before fault occurrence. Hence, s this situation minimizes the microgrid operation cost and load shedding cost of islanded microgid which are subjected to optimal power flow equations in the presence of RESs and ESSswhile considering the uncertainty of the load and its generation. Therefore, by applying the proposed problem on the 9 and 32 bus microgrid, solving the problem by the Crow Search Algorithm (CSA), and selecting optimal size of RESs and ESSs, based on operation and protection coordination indices, the proposed SSCOPC can obtain a fast protection solution that considers system stability in faulty conditions.

Insufficient electrical endurance of equipment and insulation failure against overvoltage are one of the most effective reasons for the failure of the power lines. Lightening, switching, or other disruptive parameters can cause line outage or distribution substation failure. There are different devices used to improve the safety, reliability, and power quality of the system. Surge arresters are one of the insulation protection subsystems used against surge and switching overvoltages. In this paper, the effects of surge arrester performance have been investigated on the insulation system of distribution substation. The study has been done under normal and also transient conditions due to lightning overvoltage. The effects of failure rate, production quality, voltage stress, temperature and surge arrester permutation have been evaluated on surge arrester performances. The influence of surge arrester aging, as the most influential factor on the surge arrester performance, has been investigated as one of the factors involved in the present study. Obtained results have verified the great impact of surge arrester aging effect on the reliability of protection system.

The use of distributed generation units in distribution networks has attracted the attention of network managers due to their great benefits. In this research, the location and determination of the capacity of distributed generation (DG) units for different purposes has been studied simultaneously. The multi-objective functions in optimization model are reducing the losses of the system line, reducing voltage deviation, increasing voltage stability margin, and decreasing network's short circuit when DG units are considered in the distribution network (DN). To calculate the values ​​of mentioned multi-objective functions, a backward and forward sweep load-flow and a short circuit calculation are used. To solve the problem, a multi-objective optimization algorithm called improved non-dominated sorting genetic algorithm–II (INSGA-II) is used. This algorithm leads to the creation of various responses that the user can choose, as needed, for each one. A tradeoff method, based on fuzzy set theory, is used to obtain the best optimal solution.The proposed method is examined on the IEEE 33-bus test case while considering different scenarios. In the end, the feasibility and the effectiveness of the proposed algorithm for optimal placement and the sizing of DG in distribution systems have been proved.

The unprecedented penetration of distributed generation in distribution networks provides utilities with a unique opportunity to manage the portions of networks by microgrids (MG). The implementation of an MG may offer many benefits such as capital investment deferral, a reduction of greenhouse gas emissions, an improvement in reliability, and a reduction in network losses. In order to draw the most effective performance from MG systems with multiple energies, appropriate designs and operations are essential. This paper represents a compound co-optimization strategy to find the best type and size of components as well as the associated optimum dispatch in a MG with multiple energies considering the reliability criterion. The mixed-integer nonlinear programming technique of GAMS and the genetic algorithm of MATLAB software have been utilized to solve the optimization problem. In addition, a novel time-based demand response program is modeled to prevent the energy usage at the peak. Numerical simulations have proved the effectiveness of the proposed expansion planning.

Parking lots for Electric Vehicles (EVs) can pave the way for a better utilization of EVs' battery capacity due to the large number of EVs. However, the location and size of parking lots will affect the condition of the distribution network. In this paper, a mixed-integer linear programming (MILP) model is proposed for locating and determining the optimal capacity of EVs' parking lots while considering the constraints of distribution network and the traffic patterns of different urban areas. In the proposed model, the purpose of trips, the number of EVs', and their arrival and departure time in different areas are considered. Distribution network constraints are also taken into account by using linearized load flow equations. The objective of the model was maximizing the profit of parking owners. The model was implemented in a distribution system with 37 buses which covered four different areas in terms of EVs' travel type. The results showed the effectiveness of the proposed model for locating EVs' parking lots.

Because of the high capacity of Phase Change Materials (PCM), the application of these materials in the variant parts of buildings leads to an improvement in temperature conditions as well as a reduction in energy consumption. Due to the high dependency of the performance of these materials on ambient temperature fluctuations, their application in climates with extreme temperature fluctuations has significant impacts on reducing the temperature fluctuations inside buildings as well as the consumption of energy. In this study, the high temperature of Kashan, as ambient temperature, and the walls of normal concrete with the thickness of 10 and 20 cm and the height of 100 cm were modeled in FLUENT software. Some kinds of PCM for these temperature conditions were considered, and the best was chosen. Numerical results show that the presence of PCM has reduced the temperature fluctuations of the inner surface of the walls about 4 ° C, and the position in the inner surface has better result. However, totally the changing in PCM position has not had great impacts on the ultimate results. Moreover, a change in the number of PCM thickness does not have a great influence on the temperature function. Based on the results, it can be concluded that parafin has a better function for Kashan’s climate and that every climate requires an appropriate PCM.

In this paper, a thermodynamic modeling and a comprehensive performance analysis of a real integrated solar combined cycle (ISCC) power plant are performed. The performance of the plant cycle is assessed in an off-design condition and in two operation modes of power-boosting and of fuel-saving. Such an approach has not been considered for an ISCC plant in previous studies. Yazd ISCC, as a case study, consists of parabolic collectors which are connected to a combined cycle section. The presented simulation results cover different times of the day and the twelve months of the year. According to these results, in the power-boosting mode, the steam production of the fossil section is reduced by 12 kg/s from 6:00 AM to 3:00 PM on the design day while the solar steam increases by 36 kg/s. By stabilizing the oil temperature on 392°C, the control philosophy of the starting of steam production in the solar field is also discussed. In the fuel-saving mode, if the solar field is in service, the fuel consumption of the auxiliary burners is reduced by 28,000 kg on the design day. The results of this paper indicate that the power output of ISCCs is more stable than the conventional combined cycles on the hot days of the year.

Due to the effect of temperature on the output power of a photovoltaic module, this research tries to calculate temperature distribution in a photovoltaic module by numerical solving of the energy balance equations. Therefore, its output power can be accurately predicted. For this purpose, several photovoltaic modules are modeled in detail in the COMSOL software. A new method for calculating power output, as a function of the PV modules temperature, has also been presented to solve it using thermal equations simultaneously. Different layers of PV module are considered separately in the present three dimensional and transient models. The effect of different correlations for heat convection in the temperature distribution and output power has also been studied. Results show that the aforementioned features end in an accurate prediction of temperature distribution and, thus, of the performance of the PV module.

The application of guide blades is an appropriate method for improving the aerodynamic performance of Savonius wind turbines. Guide blades gather wind energy around the turbine and guide them into the concave side of the Savonius rotor. In this paper, a numerical investigation is conducted to evaluate the effect of the guide blades on the performance of Savonius turbines. ANSYS Fluent 16.0 software is applied for the simulation of turbulent and transient flow around the turbine. Suggested designs for guide blades are 4, 5, and 6 blades which are located in the angles of 30, 40, 50, and 60 degrees. The numerical results of power and torque coefficients show that guide blades have significantly improved the performance of Savonius turbines.  For a turbine with 5 guide blades located at the angle of 30 degrees, maximum power coefficient is 0.51, which indicates an increase of 183% compared to a single Savonius turbine without the guide blades. For turbines with 4 and 6 guide blades, maximum power coefficients are 0.42 and 0.49 respectively; this finding shows an increase of 133% and 171% in comparison with a single Savonius rotor without guide blades.