Load changes affect the frequency of electrical networks. frequency stabilization is very important due to the increasing penetration of renewable energy sources in power systems. Load frequency control (LFC) is used in the power system, so that the frequency of the programmed system and the power of the connection line of an interconnected area are within the specified limits. To improve the dynamic performance of the power system and control the frequency stability, LFC is used in power systems. The main task of LFC is to keep the system frequency according to the specified nominal value and to maintain the correct amount of exchange power between the control areas. In this paper, load frequency control in two-area power system is studied and simulated. Each area has a steam generating unit with a reheat steam turbine. The system equations are expressed in the state space and the system model is determined based on the transfer function. The simulation results have been obtained using Matlab software. The simulation results show the effect of Richter's parameters on the transient dynamic behavior of the system.

In this paper, the effect of a battery energy storage system (BESS) as a spinning reserve is considered to control the frequency of a ‎microgrid consisting of a diesel generator, photovoltaic, BESS, and electrical loads. In this stand-alone microgrid, the output power of ‎diesel generators and the BESS are subject to variations to compensate for power fluctuations caused by the load and output power of ‎photovoltaic. Therefore, secondary control, in addition to the primary control, has been proposed to deal with frequency deviation and ‎accelerate the operation of spinning reserve. The scheme is simulated in a hybrid power plant, where results show the effectiveness of the ‎secondary control on frequency deviation damping of the microgrid, thus improving dynamic stability.

Introduction: Usually osseointegration takes between three to six months after implant placement but patients are interested to have early loading. There are no definitive criteria for measuring bone mineral density (BMD), insertion torque (IT) (final torque force) and resonance frequency analysis (RFA) (primary implant stability) to determine exact loading time based on the relationship between the above-mentioned parameters. The aim of this study was to determine the relationship between IT, RFA and BMD in screw-type implants.Materials and Methods: This clinical trial was conducted on 18 patients who were candidates for ITI implant placement. Written consent was taken and jaw bone density was determined via a digital radiography technique before surgery. After implant placement, RFA and IT were measured. Fifty-five ITI implants of the total 62 implants placed were evaluated; the implants were 12 mm long with a diameter of 4.1 mm. Data was analyzed with Pearson’s test using SPSS.15 software (a=0.05).Results: There was a significant relationship between IT, RFA and BMD. Pearson’s test showed a correlation coefficient of 0.872 to 0.789 between the three parameters, indicating a strong relationship between them. The mean bone density was 1.468±0.042 g/cm2; the mean RFA was 66.01±2.2 ISQ and the mean IT was 34.62±3.33 N/cm2.Conclusion: Based on the results of the present study there is a significant relationship between, IT, RFA and BMD (p value=0.001).

This paper applies a new state feedback control to a distributed secondary voltage and frequency control in an islanded microgrid. The problem is focused on the output consensus of the multi-agent systems, which is converted to a first-order dynamic system. The inverter-based distributed generations play as agents in the proposed control strategy. It is assumed that the distributed generators communicate through a communication network modeled by a directed graph (digraph). The distributed output consensus is used to design the secondary controllers. Such innovative controllers synchronize distributed generators' output voltages and frequencies to their reference values by a novel state feedback approach. Compared to the existing consensus protocols, the proposed method provides a different innovative solution to the secondary voltage and frequency control of microgrids, which has a better response in case of communication failures. Finally, extensive and comparative simulations have been presented to verify the validity of the proposed control strategy and the system performance.

In this paper, a hybrid of Neural Network (NN) and Fast Traversal Filter (FTF) based controller in each area is used to determine the optimal parameters of Load frequency control (LFC) of a realistic two area power system. The two area power system is modeled considering the various non -linearities like governor dead band, generation rate constraint (GRC) and boiler dynamics. Input to the controller i.e. the error signal is divided into two parts- linear and non- linear. The linear part of the input signal is minimized by the FTF algorithm, whereas the non- linear part is minimized by the NN algorithm. The output of the controller is the sum of the outputs of NN and FTF networks. The proposed hybrid controller requires less number of samples for training of weights, thus making the system fast. This is highly desirable in power quality problems. The various components of power system are reduced to transfer functions and the system performance is analyzed for 1% step load perturbation in area1 with different control lersproportional and integral (PI), neural network (NN) and NN+FTF based controllers. The simulations demonstrate the fast and smooth performance of the power system with the proposed controller. Simulated results evince the superiority of the proposed hybrid controller.

Purpose: Managers are one of the important elements of an organization, for this reason, in order to draw the future of the organization, it is necessary for the planners to specify the conditions of their selection and appointment. Therefore, the current research has been done with the aim of identifying and analyzing the components of selecting future principals.Method: In this research, comparative and benchmarking method is used as a prospective approach. This approach is based on the belief that today's advanced organizations/countries can be considered as a model for the future of another organization/countries in their respective subjects. For this, first, the fields of comparison and benchmarking were determined using Brody's four-step comparison method; then the countries of Canada, Finland, Australia, South Africa, and Japan were selected according to the qualitative balance value in the international advanced TEAMS test, human development index, life quality index(health, instruction, and welfare), education quality index, and other scientific-scholarly indexes; finally, by extracting the criteria for the selection and appointment of principals through content analysis and comparison with Iran, the proposed framework for Iran has been presented.Findings: A total of 61 components for the selection of secondary school principals were identified from among the studies conducted in the selected countries in this article. By extracting the commonalities and differences of each of the components among the countries, it was found that the highest index of manager selection and appointment belongs to Japan and the lowest one is related to Finland.Conclusion: There are similarities between the components of selection of principals of secondary schools in Iran and selected countries. In Iran, special attention should be paid to important components such as adherence to religious principles, appropriate personality traits, creativity and innovation, motivation to develop capabilities, professional growth, power of supervision and accountability, social image, leader skills, and purposefulness and foresight.

Compared to individual DC or AC microgrids, Hybrid Microgrids (HMGs) are more efficient and inexpensive due to the elimination of multiple DC-AC-DC conversions. In HMGs, where AC loads are supplied by a DC link, load demand disturbance has direct negative effects on the DC link voltage. In this study, primary and secondary controllers are applied to realize suitable operation conditions and control the microgrid converters. Each converter has a primary controller to compensate for the demand power fluctuations. A secondary controller is also designed for extra demand varieties to send the proper control signals to the primary controllers. The expressed capability of the primary controllers can be obtained by designing a simple and robust secondary controller. Hence, the effects of demand fluctuations are eliminated and the system is stabilized. The overall state space model of the system is conducted for stability analysis. To demonstrate the proposed controller efficiency, a prototype HMG is modeled and simulated. The stability analysis reveals that the system is stable when the secondary controller tracks the error signal of the DC link. Simulation results show that the proposed method could efficiently manage the AC side voltage under load fluctuations.