نشریه تحقیقات نوین در سیستم های قدرت هوشمند
پیاپی 2 (پاییز 1391)

In this paper, Z-Source Inverter base DVR is used. In this system, the size of energy storage elements and nominal values of power electronic devices are decreased in compare with the conventional DVR which uses VSI. Here, four different topologies of  Z-source inverter based DVR are analyzed and compared, which two of them have energy storage devices, and two topologies have no energy storage that take energy from the grid during the period of compensation. Simulation tests based on comparison parameters can be used to compare the performance of different proposed topologies. The mentioned topologies of z-source inverter based DVR are simulated in MATLAB/ SIMULINK software.

The measure of Reactive power optimization of main power network mainly considers on-load tap changer, the optimal capacity of the capacitor, the voltage of generator under the steady load. In This paper, a multi-objective optimization methodology to the Optimal Reactive Power Flow (ORPF) problem is proposed in which the e-constrained approach is implemented for the Multi-objective Mathematical Programming (MMP) formulation. The objective functions of the proposed model include optimize the total fuel cost, the active power losses, and the system load ability. Since the control variables include discrete variables (var sources and transformer tap ratios), the ORPF is inherently a mixed-integer nonlinear programming (MINLP) problem. The optimum tap settings of transformers are directly determined in terms of the admittance matrix of the network since the admittance matrix is constructed in the optimization framework as additional equality constraints. To show the effectiveness of proposed method the results are compared with single-objective, two-objectives and three-objectives. Finally, the method has been implemented in GAMS and solved using DICOPT solver to obtain optimal solutions. In this research, for selection of the best compromising answer among the Pareto optimal solutions has been designed a fuzzy decision-maker tool. The algorithm is tested on standard IEEE 14- bus test system. Simulation results show that the proposed algorithm is able to control reactive power flow effectively and optimize the selected objective functions.

In recent years, due to shortage of energy resources, use of new energies such as wind energy has been rising. Therefore, the study for the optimal use of these energy resources is very necessary. Nowadays, doubly fed induction generators (DFIGs) are used in modern wind power plants. Stability investigation of power system connected to DFIG is very essential. Static VAR compensator (SVC) and static synchronous compensator (STATCOM) are installed in parallel with transmission lines. The main applications of these compensators are fixing and adjusting of the voltage in a certain amount and stability improvement. Parameters tuning of these compensators is very important. In this research, at first, an appropriate way is suggested in order to choose the objective function for minimizing oscillations resulted from disturbances. Then optimal tuning of SVC and STATCOM control parameters will be done by genetic algorithm in the form of an optimization. Ultimately, efficiency of suggested methods will be considered in order to improve the stability of DFIG voltage, DFIG rotor speed, DFIG active power and the rotor speed of synchronous generators. This topic is evaluated and analyzed in a sample network with considering and comparison of results in the presence and absence of SVC and STATCOM. All simulation and optimization steps are done by the MATLAB software.

In this paper automatic generation control (AGC) of three and five unequal-areas interconnected thermal systems with reheat turbine and generation rate constraints of 3% has been investigated. New fuzzy logic controller for AGC in multi area thermal system is suggested. Fuzzy logic controller is optimized by evolutionary computation Genetic Algorithm (GA). A comparison dynamic response of systems reveals that the dynamic performance of suggested fuzzy controller is superior to conventional controllers. Sensitivity analyses reveals robustness of the fuzzy logic PD controller (FLPD) to wide changes in the system parameters (Inertia constant H, Reheater time constant Tr and Reheater coefficient Kr).

In this paper, the effect of SSSC on voltage sag following transformeris investigated. Static synchronous Series Capacitor (SSSC) as a dynamic system, besides its capability in increasing power transfer in transmission lines, can be used to enhance different power system issues. Hence, voltage sag as one of the key components of the power quality is alleviated for the sensitive loads that are connected to the same bus which the power transformer is energized from.

this paper presents the application of biogeography based optimization (BBO) algorithm to find optimal location and parameter setting of unified power flow controller (UPFC) for minimizing generation cost and real power losses. UPFC is one of the most complete and the most comprehensive of FACTS devices that many researches have used to control the flow and reduce system losses. BBO is a novel evolutionary algorithm that is based on the mathematics of biogeography. Biogeography describes how species migrate from one island to another, how new species arise and how species become extinct. Simulations are performed on  IEEE 14 bus system for optimal location and parameter setting of UPFC and the results show the efficiency and robustness of BBO algorithm.

Nowadays, phasor measurement units are used in power networks for different purposes, such as Linearization of state estimation equations and speed improvement of controlling and protecting systems. Optimization of position and number of these equipments is considerably important because of their high costs. Effective parameters on position and number of PMUs optimization are: Network topology, zero injection buses and commonly used measurement devices in power networks. In this paper an objective function based on integer linear programming (ILP) is presented to determine the number and optimized position of PMUs, in order to complete observability of power systems. The effect of zero injection buses and prevalent measurement devices on objective function in power networks is evaluated. Simulation results are presented for the IEEE 9, 14, 30, 39, 57 and 118 buses systems. The optimization method is numerically solved using MATLAB software environment and formation of parameters of objective function in IEEE 14 buses network has been studied.

In this paper, the performance of two types of FACTS devices in order to enhance the power system static voltage stability has been investigated. These devices include Static Var Compensator (SVC) and Thyristor Controlled Series Capacitor (TCSC). The modeling of the Single Machine Infinite Bus (SMIB) and aforesaid devices has been made up in steady state mode with disregarding of the generator limitations. The incremental load changes will cause the voltage collapse phenomenon, load power factor decrease and load current increase. Consequently, the voltage will have more decrement and therefore voltage will collapse, and then the power system will be encountered with instability problem. This paper presents a scale of the Voltage Collapse Proximity Indicator (VCPI) for evaluation of voltage stability and its role in transmission line power flow. Application of the mentioned compensators in power system will improve the voltage stability and power flow in transmission line. The simulation results of this paper reveal the good efficiency of TCSC and SVC in reducing the voltage collapse and improving the bus voltage.