فصلنامه مهندسی و مدیریت انرژی
سال پنجم شماره 2 (پیاپی 16، تابستان 1394)

In solving the electrical power systems economic dispatch (ED) problems, the goal is to schedule the committed generating units outputs so as to meet the required load demand at the minimum operating cost while satisfying all units and system equality and inequality constraints. This paper presents a different approach to economic dispatch problems with particle swarm optimization (PSO) technique. In proposed method to achieve better control on the algorithm’s exploration and exploitation capabilities, particles velocity is dependent on both particle’s fitness and time. Perturbation module is adopted to perform perturbation on some particles and provide extra diversity for it to jump out from local optima and avoid premature convergence. The proposed P-PSO method solves both, the ED problem with nonconvex/nonsmooth cost functions due to valve-point loading and the ED problem that takes into account nonlinear generator characteristics such as ramp-rate limits and prohibited operating zones in the power system operation. The performance of the P-PSO method is evaluated on four different power systems, and compared with that of other effective optimization methods in terms of the solution quality and convergence performance. The outcome is very encouraging and suggests that the P- PSO algorithm is very efficient to solve power system economic dispatch problem.

Due to the ever-increasing use of Distributed Generations (DGs), and special attentions toward wind power plants in recent years, this research investigates the wind plants from the viewpoint of lightning protection. In comparison to all other type of generators connected to the electric power systems, wind turbine generators are placed in areas which are more likely to be stricken by lightning. Lightning damages are divided into two major categories: direct and indirect damages. This paper studies the strategies to reduce the indirect damages to the wind turbine. Modeling of wind turbine components, i.e., blades, towers and connected cables, are frequency-dependent. Lightening arresters are used to reduce over-voltages caused by lightning currents in wind farms. Lightning arrester placement in wind farm is performed based on the objective function composed of insulation risk constraint and lightning failure; and weighting coefficients are considered for the stress-exposed insulation devices. Optimization process is performed using Genetic Algorithm (GA), and finally the simulation results are analyzed.

Nowadays, due to significant increase in demands of electric motors for residential, commercial and industrial applications, and for optimum consumption of electrical energy, the design and manufacturing of high efficiency motors and related variable speed drives have been regarded by many suppliers. Among several kinds of motors, the brushless DC (BLDC) motor is employed in many applications due to its high efficiency, high power and torque density, and ease in control, simple fabrication, high reliability, and lower maintenance. This motor is similar to PMSM in construction, while is controlled as easy as of DC motor. This paper to help for development and employing BLDC motors, reviews the different aspects of BLDC motors including performance, modeling, employed inverters, assessment of control methods for BLDC motor and implementation of its drive. Advantages and disadvantages of different control methods, remarks on various position sensorless methods, the effectiveness of various minimization schemes for commutation torque ripple, and control of BLDC motor in constant power region or flux-weakening are described in more details. Finally, some practical points are suggested for manufacturing of a commercial BLDC motor drive.

Due to the climatic change and raising the living standards, internal air quality of the buildings has become a major challenge. The increased cooling demand results a peak in electrical power demand during the hottest summer hours. The Phase Change Materials (PCMs) used in Thermal Energy Storage (TES) systems, can be a proper solution to overcome this problem. In the present study by solving a mathematical model in which effective heat capacity is used, performance of a latent heat thermal energy storage has been simulated for free cooling application of a hypothetical residential apartment placed in the desert region of Iran. Moreover, for better evaluation of the proposed system, the absorbed excess heat has been compared with the energy consumption of the fan. The Results have shown that the excess heat absorbed by the PCM is triple the energy consumption of the fan. Another advantage of this coolant system is that, 70 percent of the fan power consumption takes place during the off peak midnights.

Exergy analysis is a method of evaluating the contribution proportion of each process on transmission of initial availability of the system and determining the positions of useful energy losses. In this research exergic analysis of an internal combustion engine equipped with turbocharger and intercooler is attended. To do this, at first, the procedure of performance simulation of the system components i.e. engine, compressor, turbine and intercooler is briefly explained. Then by defining exergy terms and using related exergy equilibrium equations for open and closed systems necessary conceptual basis for exergy analysis, is introduced. Also exergoeconomic analysis, as a powerful tool for cost study and optimization of complex energy systems is developed by combining the second law of thermodynamics concept with economics point of view. The results show that combustion process produces the most proportion of the system irreversibility. Furthermore, regarding exergoeconomic parameters, engine has the most suitable performance among the related components of the system.

Since ordinary gas turbine cycles in actual condition comprise simple cycle, regenerative cycle, reheat cycle and intercooler cycle between High Pressure and Low pressure compressors, these cycles include 16 combined cycles by combining with a Rankine cycle that consists of three organic fluids and steam. In the present work, the thermodynamic analysis of the above combined cycles with three organic fluids and steam was considered in terms of the first law and the second law of thermodynamics, and efficiency curves were compared together. The amount of exergy destruction and exergy efficiency of all cycles computed. Finally the effect of important parameters of the systems on the energy and exergy efficiencies has been shown. Results indicate that toluene fluid has the best efficiency regarding the first and the second law among all considered organic fluids. Results also show that, when the pressure ratio is more than 12, the efficiency of the first and second law of thermodynamics has the highest amount for the combination of reheat gas turbine cycle and Rankine cycle however it has the lowest amount for the combination of simple gas turbine and Rankine cycle.