نشریه تحقیقات نوین در سیستم های قدرت هوشمند
سال دوم شماره 2 (پیاپی 5، تابستان 1392)

In this paper for more efficient use of fossil fuels in order to reduce fuel costs, reserve and reduce emissions at the same time on the network, taking into account constraints such as the effects of the valve point the ramp rate, frequency constraints, etc., an intelligent algorithm for solving multi – objective economic Dispatch pollution is presented. Finally, the performance of the proposed algorithm with other methods such as non liner programing, genetic algorithm , particle swarm optimization algorithm, bacterial foring algorithm and bacterial foring – nyldr mead hybrid algorithm were compared. Simulation results, the advantages of frequency constraints on production costs and advantages of the proposed method in improving the accuracy and convergence results compared to the algorithm of the show.

The daily economic dispatching of hydrothermal system (DHS), which is a large-scale dynamic nonlinear constrained optimization problem, plays an important role in economic operation of electric power systems. This paper proposes a novel enhanced gravitational search algorithm (GSA) to solve DHS problem. These are non-convex economic dispatch problems including the valve-point effect. The feasibility and using the GSA methods in solving the economic dispatching load in hydro thermal systems at Matlab are simulated by computer and the simulation results are compared and analyzed with and without the valve-point effect. The proposed programming computer aided is applied on a hydro thermal system and by analyzing the results, efficiency and ability of using method (GSA) is proposed in comparing to other methods.

Regarding the growing use of distributed generation resources, optimal design of these units is necessary in the power system especially in the distribution network. In this paper, Cuckoo Optimization Algorithm with multiple purposes was used to determine optimal location and size of distributed generation resources. The investigated purposes include reducing line losses, reducing medium voltage deviation and voltage stability. Cuckoo Algorithm is an algorithm based on population which is derived from the life of cuckoos in nature. Using this algorithm leads to increased accuracy and speed of convergence. In order for the implementation of the proposed algorithm, distributed generation resources are considered in two modes. In the first mode, distributed generation resources only produce active power; but in the second mode, they produce reactive power too. Simulation is done in 33 bus bar radial system. The results of simulation show optimal convergence of the suggested algorithm. In addition, the obtained results were compared with the results of optimization algorithm of the aggregation of particles and genetics algorithm in order to show the efficiency of the suggested algorithm. The comparison indicated tangible superiority of Cuckoo Algorithm in comparison with the mentioned methods.

Placement and installation of capacitors in electrical power distribution systems have being done in order to reducing losses , improving voltage profile and realising network lines capacity. In this Thesis , capacitor Placement and sizing of it are reviewed in radial distribution systems to minimizing three objective’s functions , system’s losses , Compensation costs and Voltage Profile Index and it implemented in the actual system by using teaching and learning Algorithm (TLBO) .This Algorithm based on real class’s relationships and including two phases of teacher and student. Also because of the relationships in this algorithm compare to the other algorithm’s methods , there are fewer formula and involves less inputs, therefore, the convergence speed is high and the response time is fewer. locate and determine the optimal capacity of the capacitor with respect to the fixed load modle and three objective functions have been studied. This Algorithm has been Implemented on a distributed networks of 22 - 69 – 85 bus and 4 bus distribution network of Nezamieh’s Ahvaz relevant to Oil Pipelines and Telecommunication Company of Iran and The results were analyzed by MATLAB simulation.These results represent better situation compare to other technics with 55% reducing of total cost in cost function and 53% reducting of losses in losses function and up to 99% improving in voltage profile index..

This paper presents new series grid interface topologies for enhancing the low voltage ridethrough capability of self-excited induction generator-based wind turbines. Two proposed schemes: static synchronous series compensator (SSSC) and controllable series braking resistor (CSBR) have been designed and simulated. The test system simulated represents a wind turbine connected to an electric grid with alternatively employing SSSC and CSBR. The potential of the two schemes is evaluated and analyzed using positive and negative-sequence reference frames in response to balanced and unbalanced fault scenarios. The simulation results using MATLAB demonstrate the performance of the proposed schemes for improving the fault ridethrough capability and transient stability margin in response to severe symmetrical and asymmetrical grid faults. The schemes have shown successful and fast mitigation of voltage disturbance consequences on the mechanical system. The schemes helped the wind turbine to remain connected with considerable isolation from grid faults.

The operation of the wind power plant has problems due to the changing nature of wind and network. Because of the lack of stability in wind speed, wind power plant output is variable. This uncertainty is reduced controllability of wind power plants. Another problem, island power plants from the national grid by the fault. In this situation, an imbalance between power produced and power requirements in the isolated system, whereby away voltage of the desired value. The next problem is specific DFIG, increasing the current of rotor-side converter when the fault is in the network. In this paper, discussed the effect of energy storage tank on the behavior of wind power plant with Doubly Fed Induction Generator in a micro-grid. The purpose of this paper smoothing DFIG output power when changes in wind speed and protect and prevent it from leaving the circuit with the battery and super capacitor energy storage tank with two different connector type. Using simulation done by PSCAD shown that energy storage system has an important role in improving the dynamic stability of the grid and DFIG. Also compare two different control systems have been studied and shown that distributed ESS for internal changes of DFIG and complex ESS for the network faults have greater impact in improving the network.

Short-Term Scheduling of a standalone microgrid in the presence of renewable energy sources which is used to determine optimal daily operation is presented. The Necessity of this work is to use green and low-cost distributed energy resources that leads to lower costs and less pollution to the environment. Here, the commitment decisions are determined by minimizing the Lagrangian Function of the optimal power and then a duality-based analysis isapplied to derive closedform solutions. Finally, an efficient subgradientbased method is introduced to numerically compute the optimal solutions. The under study microgrid consists of five DG units, including solar photovoltaic, wind turbines, micro turbines and fuel cells. In islanded mode, the unit commitment problem is solved with respect of load demand and electrical power generated by WT and PV in different hours, so as to meet the load demand and related system operating constraints, several senarios are studied. The intermittency nature of the renewable energy sources, as well as microgrid’s capacity to operate either in parallel with, or autonomously of, the traditional power grid, pose new challenges to this classic optimization task. Using of an Energy Storage System with guidelines in deciding of its size is proposed to compensate the intermittent of the renewable energy sources.

In recent years, many comprehensive researches have been done on multilevel inverters used in high power and voltage applications mainly due to their beneficial points such as less harmonic distortion of output waveforms, less voltage variation of switches, and less intervention of system’s electromagnetic waves. These researches on multilevel inverters mainly concentrate on two general aspects: structure of inverters and their control techniques. Most of the multilevel inverters consist of power electronic switches, DC voltage sources, transformators, and capacitors. Electronic devices used in these inverters cause a harmonic injection to the circuit of power lines. Therefore it makes the waveforms of the circuit and power system’s voltage curved, which leads to the reduction of quality in the system power. Consequently, using less number of electronic devices in the structure of inverters leads to the reduction of switching loss, cost, and circuit size. In this paper, it is tried to show that using multilevel inverters with less power electronic devices brings about lower circuit loss and higher production and power quality of the system.