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In this paper, in MATLAB/SIMULINK, using the partial short circuit method of hysteresis current control, without the need of a DC-DC converter, the grid-connected residential photovoltaic system with maximum power point tracking capability is designed and simulated and compared with disturbance and observation (P&O) and incremental conductance (INC) methods. P&O and INC use a DC-DC converter for simulation, and in the simulation of the proposed short-circuit method, the DC-DC converter is eliminated. In the proposed structure, hysteresis current control is used to regulate the inverter switch (DC-AC). In this structure, the inverter voltage change caused by the panel output power change is not important. Increasing or decreasing the slope of the inverter current will change the power. The system consists of photovoltaic arrays, inverters and nonlinear AC loads. In this work, in order to reduce the cost, the idea of canceling the DC-DC converter was proposed and the local short-circuit current method was used to track the maximum power point which has a lower cost due to its fast response and easy implementation. In the last part of the article, the effect of partial shading mode on maximum power point tracking using short-circuit current is investigated.

In this paper, a novel knowledge-based method is proposed for mid-term load forecasting (MTLF) in electric substations. Since knowledge-based methods rely on the similar day strategy for estimating the load profile, novel techniques are proposed to properly select these days from historical datasets. As the maintenance of substations is inevitable during some days of the year, it can affect the load shapes and make them abnormal. Therefore, some errors occur in MTLF if similar days are selected from the days with abnormal load shapes. To tackle this problem in MTLF, a pre-processing procedure based on the flag concept is conducted to separate the misleading data causing the estimation error. In addition, a new categorization of historical data is proposed in order to select days with more similar load shapes. In this procedure, the effects of neighbor substation maintenance, holidays, and special cultural days such as Ramadan are considered in order to select similar days more carefully. Finally, the hourly load profile is forecasted using a linear equation. The performance of the proposed MTLF method is evaluated in a target substation in Tehran Regional Electric Company in Iran. The results show that each of the neglecting substation maintenance days with abnormal load shapes from the similar day selection process and monthly–weekly window of data can reduce the error of forecasting by about 8%. In addition, neglecting similar days, on which the connected neighbor substations have maintenance, can reduce 5% of forecasting error. It means that these considerations are very important and can be used for improving the results of load forecasting approaches. To prove the advantage of the proposed method over other load forecasting methods, the results are compared with those of the fuzzy-based load forecasting method, which is a well-known approach. The forecasting results are improved by approximately 4% compared with those of the recent approach using the fuzzy method, which shows the applicability and superiority of the proposed method.

Purpose This paper aims to present a hybrid model to mid-term forecast the load of transmission substations based on the knowledge of expert site and multi-objective posterior framework. The main important challenges in load forecasting are the different behavior of load in specific days. Regular days, holidays and special holidays, days after a holidays and days of load shifting are characterized by abnormal load profiles. The knowledge of these days is verified by expert operators in regional dispatching centers. Design/methodology/approach In this paper, a hybrid model for power prediction of transmission substations based on the combination of similar day selection and multi-objective posterior technique has been proposed. In the first step, the important data for prediction is provided. Posterior method is used in the second step for prediction that it is based on kernel functions. A multi-objective optimization has been formulated with three type of output accuracy measurement function that it is solved by non-dominated sorting genetic technique II (NSGT-II) method. TOPSIS way is used to find the best point of Pareto. Findings The presented method has been tested in four scenarios for three different transmission stations, and the test results have been compared. The presented results indicate that the presentation method has better results and is robust to different load characteristics, which can be used for better forecasting of different stations for better planning of repairs and network operation. Originality/value The main contributions of this paper can be categorized as follows: A hybrid model based on similar days selection and multi-objective framework posterior is presented. Similar day selection is done by expert site that the day type and days with scheduled repair are considered. Hyperparameters of posterior process are found by NSGT-II based on TOPSIS method.

In current study, a method for achieving a load-independent output current with the ability to optimize the parameter tuning, which is applied to wireless power transfer (WPT) systems, is analyzed. The proposed technique is based on the immittance property in a passive resonant network (PRN) with the purpose of transforming a voltage/current resource into a current/voltage resource. This study determines an immittance conditions-qualified family of PRN, which is associated with a more appropriate topological description in WPT applications. Considering the resource and sink type, a comprehensive specification of the coupling coefficient-based design condition and operating point is carried out. Moreover, the parameters of each proposed topology are reconfigured by adjusting the proportion of active power to reactive power ratios as an index to optimize the topology size as well as a reduction of voltage/current stresses on their elements without changing the specified system-level parameters, such as the loosely coupled transformer operating frequency, and specified constant current outputs. The sample topology selection is also carried out with respect to the absorption of the parasitic components and achieving the inherent dc-blocked transformer. Zero-voltage-switching (ZVS) operation of the switches, minimum conduction losses of the rectifier diodes within an extensive variety of load variations, and capability of consistent generation of stable load-regulated current are also achieved. Analytical results show that the proposed compensation has the minimum output current fluctuation versus variations of the coupling coefficient and other parameters. Finally, the effectiveness of the proposed methodology is evaluated through simulations, and practical experiments, and compared with the conventional design method.

Under unbalanced grid condition, in a Doubly-Fed Induction Generator (DFIG), voltage, current, and flux of the stator become asymmetric. Therefore, active-reactive power and torque will be oscillating. In DFIG controlling Rotor Side Converter (RSC) aims to eliminate power and torque oscillations. However, simultaneous elimination of the power and torque oscillations is not possible. Also, Grid Side Converter (GSC) aims to regulate DC-Link voltage. In this paper, in order to regulate DC-Link voltage, an Extended State Observer (ESO) based on a Generalized Proportional-Integral (GPI) controller, is employed. In this controlling method, DC-Link voltage is controlled without measuring the GSC current, and due to using the GPI controller, the improved dynamic response is resistant against voltage changes, and the settling time is reduced. To improve the transient stability and Low Voltage Fault Ride Through (LVRT) capability of DFIG, Statistic Fault Current Limiter (S-FCL) and Magnetic Energy Storage Fault Current Limiter (MES-FCL) are proposed in this paper. The proposed FCL does not only limit the fault current but also fasten voltage recovery. The simulations are implemented by MATLAB software in the synchronous positive and negative sequence reference (d-q).

The objective of this paper is to propose a new topology for high step-up multiport DC–DC converter. The proposed converter has two-input single-output ports, and its voltage gain is significantly increased using diode–capacitor cells, which are modified Dickson’s charge pump. Moreover, the voltage stress on the switching devices is reduced. Thus, this converter is very useful for high-power applications. The voltage gain of the proposed converter can be further increased by increasing the number of diode–capacitor cells. The main advantage of this expandable structure is the use of only two inductors in its structure, which considerably decreases the losses and even the size of the converter. The conversion ratios, voltage stress on switches and diodes, as well as the average current of switches and diodes, are formulated, and the theoretical analysis of the converter is proposed. In order to experimentally validate the performance of the proposed converter and theoretical calculations, a converter with the first input voltage source of 10 V and the second input voltage source of 15 V is designed and the output voltage level of 312.5 V is measured, which confirm the simulation results. Moreover, the maximum efficiency occurred at 100 W and full load efficiency is 93.5%, which are all noticeable achievements.

Voltage-source inverter has been used widely in traditional photovoltaic systems which have limitations. To overcome, Z-source inverter has been introduced. In spite of all the features introduced in Z-source inverter, its configuration has been improved over the years, like trans-Z-source inverter which has added advantages compared to traditional inverters, namely buck–boost feature, lesser passive elements, and higher voltage boost gain. In this paper, photovoltaic arrays are connected to the grid via the trans-Z-source inverter with the aim of improving its power quality. Moreover, the shoot-through duty ratio is kept constant in the switching control method to add features like lower voltage stress (higher reliability), lower total harmonic distortion (lower maintenance cost), and higher voltage boost ratio. To evaluate the precision of the proposed system, the photovoltaic system is simulated on a standard grid and under partial shading condition which brings about voltage sag, and hence, a dynamic voltage restorer is used to mitigate voltage sag. Simulation results are presented to verify the validation of the proposed photovoltaic system in terms of voltage and current THD reducing 78.2% and 19.7%, respectively.

This paper deals with a new islanding detection method based on parallel inductive impedance (PII) switching at distributed generation (DG) connection point, and monitoring the rate of change of voltage $(dv\!/\!dt)$ at DG output. In the proposed approach, switching the PII causes variation in the $dv\!/\!dt$ . This variation is very small in the case that DG operates in parallel with the main grid, whereas the changes will be very large during the occurrence of islanding. Therefore, the $dv\!/\!dt$ is employed to identify both the islanding and nonislanding situations; however, to better analyze the $dv\!/\!dt$ changes, a fast Fourier transform (FFT) is employed to process the variation of the $dv\!/\!dt$ . To select the type of inserted impedance, the effect of switching various impedance types on the $\text{FFT}$ $(dv\!/\!dt)$ is thoroughly analyzed. It is demonstrated that the purely inductive impedance has better performance than other impedance types. The performance of the proposed method is examined through comprehensive simulation studies in MATLAB. The simulation results indicate that the proposed method retains its efficiency for both inverters- and synchronous-based DGs. Moreover, the proposed method not only has a substantial influence on the reduction of disturbances due to the small amount of PII but also eliminates the nondetection zone entirely in comparison with other available methods.

Advantages of combined heat and power system such as high efficiency, low environmental pollution, reliability and controllable output result in its widely application in commercial and residential buildings. Finding the optimal number and capacity of combined heat and power (CHP) units in commercial buildings is a challengeable issue. In this paper, an optimization method based on constrained index of reliability is used for optimal allocation of these systems. Hence, the value of lost load is considered as the reliability index. The random prediction errors of load and energy in CHP systems are modelled as a scenario based on Monte Carlo sampling procedure. Optimization is formulated by using a two-stage stochastic integer linear programming. To reduce the computation time, the number of scenarios has been reduced. Finally, the proposed model is used in a commercial building as a case study.

Hybrid energy systems such as PV-battery-diesel have been identified as an effective option to solve the power-supply problem and, therefore, the optimal sizing of such hybrid PV systems becomes important. Also, activities related to the demand side of the power system such as demand response programs are interested and, electric vehicle to grid (V2G) parking lot as a controllable load unit is recently used with demand response potential through charging and discharging V2Gs according to electricity price variations. The goal of this study is to develop and examine a heuristic optimization algorithm to solve the optimal sizing for hybrid PV-battery-diesel system with considerations for V2G parking lot as a controllable load. Simulation results show that utilization of V2G parking lot can reduce total cost for optimal sizing of hybrid PV-battery-diesel system by 5.21%.

This paper presents a novel method for islanding detection of synchronous distributed generation (SDG) based on the inherent feature extracted from the mechanical power signal. The proposed method is based on this feature that during the transient phenomena, the load angle changes and it creates stress in the SDG shaft due to small inertia. Accordingly, the mechanical power signal of the SDG is oscillated until it becomes stable. However, in islanding mode, we are faced with a new configuration of power system in which the SDG control system is operated immediately and tries to stabilize the islanded system. This condition leads to non-swinging changes in the mechanical power signal. Therefore, this inherent feature can be used as an important factor in distinguishing between islanding and other events. One of the most important advantages of the proposed method in comparison with other passive methods is that there is no need for any threshold values to discriminate between islanding and other conditions. The proposed method is tested on two sample power system networks in the presence of single DG and multiple DGs and loads using MATLAB/Simulink software. The simulation results indicate that the proposed method works properly for the synchronous DG units with different inertia constant, power level, installation location as well as DG numbers. Furthermore, it eliminates the non-detection zone completely.

This paper presents a new islanding detection method for synchronous distributed generation (DG). The proposed method is developed based on the combination of rate of change of exciter voltage (RCEV) and open–close circuit breaker (OCCB) at a DG connection point. Whenever the RCEV parameter is not sufficient enough to detect an islanding condition efficiently and correctly, the OCCB strategy will be triggered. The proposed OCCB strategy sends a switching command to one phase of the three-phase circuit breaker (CB), which connects the DG to the grid. In this way, the CB will be immediately opened and then closed. This switching condition will cause a variation in the value of RCEV. This variation is small for the conditions when DG operates in parallel with the main grid, whereas it will be large during the occurrence of islanding. The implementation of the proposed strategy is cost-effective because it only uses the CB at the DG output and does not require any extra equipment. The proposed approach is tested on two different systems including a hypothetical power system and the IEEE 33-bus test system in MATLAB/Simulink environment. The simulation results show that the proposed method eliminates the nondetection zone and also reveals high accuracy compared with previously introduced methods. Moreover, it has been proved that the performance of the proposed approach is not affected by DG capacity, DG location, the number of DG units, as well as network configuration.

Voltage control and Voltage stability are the most important issues in the power system. The purpose of this paper is to investigate the emergency voltage control in power systems. One of the most important proposed methods to solve this issue is optimal coordinated voltage control (OCVC), which is based on the model predictive control (MPC). Time limitations for preventing voltage collapse is the most critical constraint to solve an OCVC problem. In this paper, the Modified WARD-PV will be proposed to reduce the dimension of the power system and consequently, the speed of solving problem is increased. In this method, immediately after occurrence a fault, the power system is partitioned to into three subsystems by spectral graph partitioning method. Partitioning is based on reactive power flow through the lines. The subsystems, which are far from fault, will be replaced by the reduced model. This method will drastically reduce the number of system equations and will boost the speed of solving problem. The simulations results obtained on New England IEEE 39-Bus System reveals that the proposed method acts more precise than dimension reduction of power system based on linearization of external subsystems, but the speed of solving problem decrease.

Under unbalanced grid condition, in a doubly-fed induction generator (DFIG), voltage, current, and flux of the stator become asymmetric. Therefore, active-reactive power and torque will be oscillating. In DFIG controlling rotor side converter (RSC) aims to eliminate power and torque oscillations. However, simultaneous elimination of the power and torque oscillations is not possible. Also, grid side converter (GSC) aims to regulate DC-Link voltage. In this paper, in order to regulate DC-Link voltage, an extended state observer (ESO) based on a generalized proportional-integral (GPI) controller, is employed. In this controlling method, DC-Link voltage is controlled without measuring the GSC current, and due to using the GPI controller, the improved dynamic response is resistant against voltage changes, and the settling time is reduced. A versatile rotor position computation algorithm (RPCA) is utilized to measure the rotor speed. This algorithm is simple, yet it is accurate and is resistant to changes in the resistance of the rotor and stator. The simulations are implemented by MATLAB software in the synchronous positive and negative sequence reference (d-q).

For the purposes of lowering environmental emission and total cost, energy efficient combined cooling, heat, and power (CCHP) units can be integrated with conventional separate cooling, heat, and power production units to meet demands. The goal of this study is to develop and examine a heuristic and deterministic optimization algorithm for solving the unit commitment problem for integrated CCHP-thermal-heat only system for (i) satisfying demands for cooling, heat, and power, (ii) providing spinning reserve for power, (iii) reducing environmental emission, and (iv) accounting for valve-point effects for steam turbines of thermal units. When environmental emission cost and valve-point effects are considered, the utilization of CCHP units in an integrated CCHP-thermal-heat only system results in environmental emission and total cost reduction by and 38.37 and 0.03%, respectively, as compared with those resulting from operating thermal and heat only units separately.

Fossil fuels vehicles are considered as the most problematic factor of air pollution in metropolitan cities. Electric vehicles (EVs) are presented as the most paramount solution in response...

This paper proposes a mathematical optimization approach based on semidefinite programing (SDP) for optimal operation of a microgrid (MG) equipped with renewable energy resources (RERs) as well as energy storage systems (ESSs) including compressed air energy storage (CAES) and electric vehicles (EVs). The SDP converts nonlinear and non-convex models proposed for day-ahead optimal operation into a convex approximation, which is easily implemented by commercial software. An optimization problem is formulated such that it minimizes the costs related to operation and environmental effects limited to several technical limitations. It is clear that there is an intrinsic deviation between predicted and actual uncertainty variables in MG. This paper presents a stochastic optimal operation model based on Information Gap Decision Theory (IGDT) with risk averse strategy to overcome this information gap and to help Microgrid Operator (MGO). As demand response programs (DRPs), the shiftable load and time of use (ToU) are considered for enhancing the flexibility of MG. Employing the presented model in the 21-bus test system shows that CAES and EVs, as novel ESSs, have good capability to reduce the costs. The total cost, including operation cost and emission cost can be reduced by 3.8% compared to without considering these ESSs in the day-ahead optimal operation.

In this article, the minimisation of total harmonic distortion (THD) of the output voltage of a multilevel inverter is studied. The harmonic component of output voltage in the inverter is reduced in THD minimisation. The output voltage THD in multilevel inverters is minimised by proper selection of switching angles. The teaching–learning-based optimisation algorithm is used to find the optimum switching angles in order to generate the desired voltage value in the possible minimum THD. Experimental and simulation results depict advantages of this approach compared to published papers which discus this concept using genetic algorithm. The experiments conducted on a seven-level inverter confirm the feasibility of this approach.

Nowadays, penetration of DG resources into the power systems due to their advantages is rapidly increasing. Islanding performance is one of the most disadvantages of using DGs, which should be considered, because this option may lead to negative effects on the protection, performance, and operation management of distributed systems implementation. An island must be detected in less than 2 sec based on IEEE STD 1547-2003 standard, and DG resources must be disconnected from distribution network immediately. In this paper, a novel hybrid algorithm to identify the islanding has been proposed based on the passive parameters (ROCOV and ROCORP) and capacitor bank connection strategy. In the incompatibility conditions of the large-scale power, by combining two parameters i.e. ROCOV and ROCORP and investigating their changes, the islanding is carefully and quickly identified. This strategy is completely verified in the mismatch conditions of small-scale power by applying the capacitor bank connection strat...

This study is aimed to evaluate the grid-connected PV system in partial shading conditions through the three-level SVM inverter and compensation of inverter output voltage sag caused by the partial shading using the dynamic voltage restorer (DVR). A function per time and the amount of radiation has been used to create the partial shading condition in the photovoltaic system. The advantages of three-level SVM inverter include the complete region detection method even in the boundary points between two regions through boundary lines equations and complete online solution of those equations. Also the reduction of total harmonic distortion (THD) through the switching table is appropriate. The results show that in the partial shading conditions the three-level SVM inverter decreased THD in the presence or absence of DVR. DVR also compensate the voltage sag to a suitable level. MATLAB/Simulink based simulation results are presented for validation of the entire system.

Most loads in the power distribution system of Tehran Metro (Subway) are inductive and lead to poor power factor (PF) especially in Lighting and Power Substation. One of the methods of PF correction is adding or producing the capacitive components within the circuit to eliminate the effect of inductive loads. Optimal capacitor placement (OCP), with the objects of power system voltage profile improvement, PF correction, loss reduction, and line reactive power decrease are of particular importance in power system control and planning. These objects depend on how the capacitive components are installation and to achieve them, since the capacitor placement is nonlinear problem and has some equally and inequality constraint. This article investigates OCP in the actual power distribution grid of Tehran Metro (Line 2) in the presence of nonlinear loads. The placement problem is solved using Genetic Algorithms as implemented in the Electrical Transient Analyser Program software. Results (capacity release, total generation, loading, demand, power losses and number of capacitor banks, costs and annual benefits) are obtained and analysed. This study and simulation shows that by OCP can calculate reduce annual losses and release capacity of equipment in power distribution grid of Tehran Metro such as cables and transformers from reactive power and that will maximize profits. © 2016 Wiley Periodicals, Inc. Complexity, 2016

As flexible AC transmission systems (FACTS) have come to maturity, major advances have been made in the field of power system dynamic stability and low frequency oscillation damping. Interline power flow controllers (IPFC) and static var compensators (SVC) members of FACT devices family which are used to, respectively, realize optimal power flow over transmission lines and inject reactive power to transmission lines for maintaining voltage magnitude. In this paper, following to the modeling of a single-machine infinite bus system equipped with IPFC and SVC, a power system stabilizer (PSS), without FACT devices controller, is designed. After selecting the most effectual IPFC control signal, with the use of residue theory, a coordinated control design of IPFC and SVC in absence of PSS is carried out. Moreover, the parameters of proposed controllers are optimized using imperialist competitive algorithm.

A number of referenced materials in the area of real-time tracking have been considered to present a novel intelligent estimation framework (IBEF). The main idea behind the research is to realize an approach that is applicable and efficient with respect to the final outcomes in the same way. The IBEF is realized, as a decision maker, in association with the neural network, where all the types of chosen objects, such as military, private vehicles, animals and other related objects, may be tracked in a set of frames of video through their approach. Then, the IBEF in each frame should be corrected to re-organize the estimation, in a constructive manner. The main goals may be chosen as solid, non-solid, stationary and non-stationary objects, as long as all of them can be taken in different quantities. The applicability of the approach can be presented in the areas of flight control, collision avoidance, etc. The process of realizing the approach can be continued by extracting some prominent features regarding the tracked objects, in order to apply them to the IBEF. The desirable performance of the proposed approach is guaranteed though a standard scenario. The results are finally compared with a benchmark approach, where the improvement of the approach performance can be verified.

Summary The application of the turbo-expander in the auxiliary service system of Neka power plant in Iran causes considerable voltage sag, which is very dangerous to the auxiliary service system. To reduce the voltage sag, the dynamic voltage restorer (DVR) is proposed. The auxiliary service system and main substation of the power plant with compensators are simulated by Power System Computer Aided Design (PSCAD/EMTDC) software. The application of the static synchronous compensator in different scenarios is discussed, and the results are compared with the results of the application of the DVR, which has a new topology and minimum injection power control strategy. It is shown that the results of the DVR application are better in all tested scenarios. Also, the economic assessment shows that the payback period is reduced to half in case of using DVR instead of static synchronous compensator. Copyright © 2015 John Wiley & Sons, Ltd.

This paper presents a novel anti-islanding protection method for synchronous Distributed Generation (DG). The proposed method is developed based on the combination of rate of change of exciter voltage (ROCOEV) and mechanical power (MP) and open-close circuit breaker (OCCB) strategy. Whenever the ROCOEV and MP parameters cannot be detected, the OCCB initiates its action. For the practical application of OCCB strategy, the circuit breaker (CB) which connects the DG to the grid is equipped with a recloser. Therefore, by sending a switching command, one-phase of CB at DG connection point, is opened and then immediately closed. This switching causes a variation in the ROCOEV parameter, which is used to detect the islanding. Meanwhile, one-pole opening instead three-poles can limit the transient changes caused by its operation and the amortizations of other poles of breaker are prevented. The proposed strategy only uses the CB at the DG connection point, so it is quite economical. Furthermore, the proposed method does not have any negative impact on the DG stability. The proposed approach is tested on a typical network in MATLAB/Simulink software. The simulation results show that the proposed method has advantages in reduction of non-detection zone (NDZ) and high accuracy compared with previously introduced methods.

In recent years, the increasing application of nonlinear and unbalanced electronic equipment and large single phase loads have made voltage imbalance a serious problem in power distribution systems. A novel approach has been proposed to eliminate voltage imbalance and disturbances. The main strategy of this scheme is based on series active filter. By improving control circuit toward existing schemes and proposing a new strategy to control the voltage amplitude, simultaneous elimination of voltage imbalance, faults, voltage harmonics and also compensation of voltage drop in transmission lines become possible. Eventually, the voltage on the load side is a perfectly balanced three phase voltage with specific proper amplitude. The proposed scheme has been simulated in a test network and the results show high capability of this scheme for the complete elimination of imbalance without phase shift.

This study proposes a Pareto-based multi-objective distribution network reconfiguration (DNRC) method using discrete particle swarm optimisation algorithm. The objectives are minimisation of power loss, the number of switching operations and deviations of bus voltages from their rated values subjected to system constraints. Probabilistic heuristics and graph theory techniques are employed to improve the stochastic random search of the algorithm self-adaptively during the optimisation process. An external archive is used to store non-dominated solutions. The archive is updated iteratively based on the Pareto-dominance concept to guide the search towards the Pareto optimal set. The method is implemented on the IEEE 33-bus and IEEE 70-bus radial distribution systems, simulations are carried out and results are compared with other available approaches in the literature. To assess the performance of the proposed method, a quantitative performance assessment is done using several performance metrics. The obtained results demonstrate the effectiveness of the proposed method in solving multi-objective DNRC problems by obtaining a Pareto front with great diversity, high quality and proper distribution of non-dominated solutions in the objective space.

This paper presents an interactive fuzzy satisfying method, which is based on Hybrid Modified Shuffled Frog Leaping Algorithm, and should solve the problem of the Multi-objective optimal placement and sizing of DG (distributed generation) units in the distribution network. Minimizing total electrical energy losses, total electrical energy cost and total pollutant emissions produced are the objective functions in this problem. Also, the improvement of the voltage profile is considered as a constraint in determining the optimal placement. In the proposed method, the objective functions are modeled with fuzzy sets. The multi-objective problem is transformed into a mini–max problem, which is then handled by the proposed evolutionary algorithm. Finally, the proposed algorithm is tested on a 69-bus distribution test system based on technical, economical and environmental protection considerations. The simulation results illustrate the good performance and applicability of the proposed method.

This paper deals with the capability of a static synchronous series compensator (SSSC) to attenuate the subsynchronous resonance (SSR). Two well-known controllers are designed, namely a conventional damping controller (CDC) and fuzzy logic damping controller (FLDC). These 2 damping controllers are added to a main control loop of a SSSC operating as a SSR damping controller. It should be noted that, to optimize the parameters of the CDC, a versatile optimization technique is implemented, namely particle swarm optimization (PSO). A comprehensive comparison between the 2 control methods is carried out for different operational conditions. To observe the superior performance of the proposed FLDC, many operating points and different fault types are considered. The IEEE second benchmark model aggregated with the SSSC is utilized and simulations are presented.

Environmental and economical constrains to build more aggregate bulk power plants and transmission lines besides slow improvement of DG in compare with fast growth of demand, resulted in operation of heavily loaded power grids near their stability limits. Meanwhile, a disturbance occurrence may lead to voltage instability more probably than ever before. A smart methodology of load shedding, based on optimized fuzzy inference logic, is evaluated in this paper to mitigate instability state of the power system. The result indicates more reliable voltage maintenance while using optimized membership function in our defined fuzzy logic system