نشریه تحقیقات نوین در سیستم های قدرت هوشمند
سال هشتم شماره 4 (پیاپی 20، زمستان 1398)

Unified Power Flow Controller (UPFC) is one of the most efficient FACTS devices that can be individually or combinatorial on all effective parameters in the transmission power of the transmission lines. With the flexibility of effective parameters in power passage, the power system operation can be improved. in this study, the optimization algorithm based on location and optimal capacity of UPFC has been proposed to improve the stability of power system stability. The proposed method innovation is demonstrated by improving search functionality, stochastic reduction, and complexity reduction. In this regard, the generator error affects power system operation constraints, including voltage, real and reactive power dissipation, as well as computational cost. The UPFC modeling is a power injection and load injection model of the Newton - Raphson method. Power system operation conditions are formulated with the objective of minimizing the power loss, minimization of voltage variation, and installation cost of UPFC. in matlab software, an optimization algorithm for solving the problem on the ieee 14 and 30 bus test systems is implemented and the results of investigation are compared with other methods.

The active-frequency and reactive-voltage droop control method is one of the most widely used decentralized control methods in island-controlled microgrids. With the active-frequency droop control, it can be used to divide the exact active power between distributed energy sources, but the reactive-voltage droop, due to the high dependence on the line impedance and the load rate, often makes it worse to divide the reactive power between resources. Another challenge of the droop control is the frequency deviation and voltage mediated by load changes. In this paper, a new independent method for accurate account of reactive power between the distributed energy resources and the recovery of the micro-grid frequency has been provided. The proposed method improves the reliability and simplicity of the network. Simulation results show that the performance accuracy of the proposed method is especially about the correct splitting of reactive power and retrieval of the network frequency, as the difference in the reactive power of resources is reduced from approximately 1200 to 700 var and the network frequency is maintained on 314 radians per second.

The stator of the doubly-fed induction generator-based wind turbine is connected directly to the grid, which makes possible reactive power compensation of the grid. In this paper, controlling reactive power in DFIG in two modes, the first assumption is neglecting stator resistance while the second one is considering stator resistance and its flux variations in four performance modes including maximum stator reactive power absorption, maximum stator reactive power generation, mode minimum casualties and minimization modes are provided. For each mode in each of assumptions and optimization problem introduced and PSO algorithm utilized to find a feasible solution. By solving the optimization problems with aim of PSO algorithm, the required for controlling reactive power in each mode is achieved. To demonstrate the efficiency of proposed method, the results compared with another method based on an iterative algorithm. Simulation results show that considering linkage flux variations of stator as a constraint of the optimization problems has led to good performance in controlling reactive power of DFIG.

Dynamic Voltage Restorer (DVR) is one of the voltage compensation equipment. Voltage quality injected by of this equipment depends on the quality of DC link voltage and the type of control system modulation. The photovoltaic array can be used to store the DC link of this equipment. To increase the output voltage of the photovoltaic array to the required DC voltage level, a standard boost chopper is used which reduces the quality of the compensator voltage due to the high voltage ripple. Using well-designed choppers such as interleave can in addition to increasing the photovoltaic array voltage, reduce the ripple DC link voltage and thus the harmonic content of the voltage injected by the compensator. Applying appropriate pulse bandwidth modulation to the control system of this equipment can also be effective in reducing harmonic content and improving voltage quality. In this paper, in order to reduce the total harmonic distortion (THD) of the compensator injected voltage and consequently to improve the load voltage quality, the interleave boost converter at DC compensator link and the hysteresis modulation in the controller scheme of this hybrid compensator are used and the simulation results are presented. The result of the proposed system is compared with the results of the hybrid compensator based on conventional boost chopper and sinusoidal modulation.The simulations are done using Matlab/Simulink.

Static reactive power compensators (SVCs) have been widely used to improve voltage and power factor ratios in factory and industrial substations. Therefore, these two functions are independent of each other and it is necessary to improve the power factor in order to regulate the voltage. In this paper, the new SVC startup method for induction motors is suggested. In this method, the amount of reactive power is precisely and controllable according to the load requirements. A hybrid controller includes slow suspension control and rapid voltage control that gives the SVC the ability to achieve power factor correction and creates a constant voltage characteristic during the start of the large induction motor. An ideal compensation method is recommended for both optimal voltage regulation and power factor correction. A case study on the operation of a large 1.4MW induction motor is presented with several startup methods. The comparative study is done by simulation with MATLAB software for different startup cases. Finally, the results of safe and reliable performance simulation guarantee the proposed method for effective design of operational posts.

Wind energy conversion systems (WECS) are designed to convert the wind motion energy into mechanical energy, which provides the energy needed for generators to generate electrical energy. The wind energy conversion system consists of four parts, including wind turbines, generators, control systems and interface devices. In this paper, an overview of each part is given. The structure of the WECS is first described. Then, the types of wind turbines are expressed along with their production capacity and performance areas. Then, the types of induction generators and their application in WECS are mentioned.