**Alan:** Mühendislik ve Temel Bilimler **Tür:** Hakemli Dergi

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**Yazar(lar):** YINGPEI LIU, RAN LI

The voltage source converter-high voltage direct current (VSC-HVDC) transmission is the ideal integration technology for grid-connected wind farms. A passivity-based control (PBC) method for VSC-HVDC when the wind farm voltage is unbalanced is proposed in this paper. The mathematical model of a VSC with unbalanced voltage is established. The PBC theory including dissipation inequality and system strict passivity is introduced, and then the stability of PBC is proven in light of the Lyapunov stability theory. According to PBC theory, a Euler--Lagrange mathematical model of a VSC is constructed. After that, the strict passivity of the VSC is proven. On the premise of the power factor being 1, the PBC controller for the VSC-HVDC system is designed under d-q coordination. The control law is deduced in detail. In order to accelerate the convergence speed, dampers are added to the PBC controller. The decoupled control of the active power and the reactive power is achieved by this method. The dynamic and steady performances of the VSC-HVDC system in a grid-connected wind farm when the wind farm voltage is unbalanced are significantly improved. Furthermore, the robustness of the system is enhanced. The simulation results verify the feasibility and correctness of the method.

**Yazar(lar):** İLKER MERT, CUMA KARAKUŞ

The wind energy potential of the Antakya area was statistically analyzed based 8 years of wind data sets (2002--2009). The 4-parameter Burr, 3-parameter generalized gamma, and conventional Weibull distributions were regarded as suitable statistical models for describing wind speed profiles. The suitability of the models was tested by $R^{2}$, textit{RMSE}, chi-squared, and Kolmogorov--Smirnov analysis. According to goodness-of-fit tests, the Burr distribution was found to be more suitable than the generalized gamma or Weibull distributions for representing the actual probability of wind speed data for Antakya. Based on the capacity factors estimated by the Burr model at a hub height, the power generation potential of a commercial 330-kW wind turbine was also determined. The results show that the available wind energy potential to generate electricity in Antakya is low; consequently, wind power would be suitable only for stand-alone electrical and mechanical applications, such as water pumps, battery charging units, and local consumption in off-grid areas.

**Yazar(lar):** Sabir Rüstemli, Mehmet Sait Cengiz

Recent developments in power electronics have increased the usage of nonlinear loads in energy systems. With increases in the usage of semiconductor-sourced nonlinear loads, the adverse effects of harmonics-sensitive loads (e.g., protection control circuits and circuit breakers) have also increased. Generally, the negative effects of harmonics in power systems include the following: increased power losses; motor, generator, and transformer overheating; faulty operation of measurement and protection systems; lifetime shortening of electrical components; and parallel and series resonance problems. Therefore, harmonics has become a serious problem in current power electronics systems. However, harmonics can be reduced, particularly through drainage using filters. In this study, some power losses were detected in different facilities in the city of Van, Turkey, on the basis of the variable measurements (e.g., instantaneous electrical values, harmonics, flow, and voltage waveforms) obtained using ZERA MT 310 power analyzers. The harmonics causing these power losses were examined. Some simulation results for active filters were evaluated, and the overall effects of the harmonics are discussed. Shunt active power filter (SAPF) simulation was conducted using Simplorer 6.0, which is known to produce successful results in power electronics simulation applications. SAPF simulation requires the use of measurement points. This utilization of SAPF simulation has demonstrated that voltage drop and power loss in power distribution systems can be reduced. However, it was found that owing to their structure, semiconductor components produce harmonics and consume power.

**Yazar(lar):** Mehmet Fatih IŞIK, YILMAZ UYAROĞLU

Transformers are an indispensable element in the transmission and distribution of electricity. While they are highly efficient, the increasing global demand for electrical energy has prompted efforts to improve their performance. No-load power losses constitute the majority of total losses within electrical energy distribution, especially when looking at load ratio. In recent years, some studies have found that no-load power losses of amorphous core transformers are less than those of laminated steel core transformers by as much as 60{%} to 70{%}. For this paper, we have manufactured an amorphous distribution transformer prototype rated 33 kV and 1 MVA. By quantifying its design considerations, power losses, and the energy efficiency value, we studied the outcome of replacing laminated steel core transformers with this new type of machine.

**Yazar(lar):** MAHALAKSHMI MAHADEVAN, LATHA SALAI

This paper focuses on the design and analysis of a hybrid biomass-solar photovoltaic system for the textile industry with the goal of minimizing the cost and greenhouse gas emissions. The feasibility analysis of the hybrid system is performed based on the resource availability and the power generation potential of the existing biomass power plant near the textile plant at T.Kallupatti in Tamil Nadu, India. The power plant located at the site (9.66$^{circ}$N, 77.79$^{circ}$E) has an average daily global horizontal irradiance of 4.86 kWh/m$^{2}$, which has been validated through NASA Surface Meteorology and Solar Energy data. The chosen site also has adequate biomass fuel availability. The biomass feedstock fuel price varies from {$}38.5 to {$}42 per ton on average for the fuels juliflora, bagasse, coconut shell, paddy husk, etc., which are purchased from nearby villages of the chosen region. The comparative analysis of grid-alone, standalone biomass-solar hybrid, and grid connected biomass-solar hybrid systems is performed using HOMER 2.81 software. In particular, an economic and environmental evaluation of the hybrid system is carried out based on the results of the optimization of biomass feedstock combination for maximum power output using the Neural Network toolbox of MATLAB 2010a. The results prove the effectiveness of the stand-alone solar-biomass hybrid system for the textile industry in terms of cost combined with emission reductions.

**Yazar(lar):** RAJAMANICKAM MANICKARAJ SASIRAJA, VELU SURESH KUMAR, SANKARALINGAM PONMANI

After the implementation of deregulation in a power system, an appreciable volume of renewable energy sources is used to generate electric power. Even though they are intended to improve the reliability of the power system, the unpredictable outages of generators or transmission lines, an impulsive increase in demand, and failures of other equipment lead to congestion in one or more transmission lines. There are several ways to alleviate this transmission congestion, such as the installation of new generation facilities in the place where the demand is high, the addition of a new transmission facility, generation rescheduling, and curtailment of load demand processes. Among the above methods generation rescheduling and load shedding are normally preferred, since the other methods require additional investments. However, some critical cases require improved methods to alleviate congestion. With the extensive application of distributed generation (DG), congestion management is also accomplished by the optimal placement of multiple DG units. It is well known that incorrect sizes and improper locations of DG undoubtedly create higher power losses and an undesirable voltage profile. Hence, this research effort employs the line flow sensitivity index to establish the optimal location of DG units and genetic algorithm-based optimization for determining the optimal sizes of DG units. The objective of this research is to minimize the total losses and real power flow performance index and to improve the voltage shape of the modified IEEE 30-bus test system. The results of this proposed approach are encouraging and help in anticipating higher efficiency by satisfying all the objectives.

**Yazar(lar):** MUSTAFA ENGİN BAŞOĞLU, Bekir ÇAKIR

This paper presents a new maximum power point tracking (MPPT) method based on an incremental conductance (IC) algorithm, constant voltage, and look-up table approach. Convergence time, one of the indicators of MPPT quality, is considered for improving MPPT performance of photovoltaic (PV) modules. In this context, a novel hybrid MPPT approach has been proposed. This proposed method consists of three stages. In the first stage, the value of load resistance is calculated. Then the initial operation point of the PV module is determined by using the constant voltage method or look-up table approach. An IC algorithm is used in order to increase MPPT accuracy in the last stage. One of the novelties of this proposed approach is the determination criterion related to sample numbers of PV module current or solar irradiance. With the help of this approach, the initial operation point of the PV module is optimized before MPPT starts. Thus, convergence time is reduced. In this paper, a DC--DC boost converter has been designed to show the performance of the proposed approach. Then the proposed approach is compared with an IC algorithm. Experimental results show that the performance of the proposed approach is better than that of the IC algorithm in terms of convergence time. On the other hand, since the proposed approach is convenient for reducing convergence time, it can be used instead of variable step size algorithms. Furthermore, there are no topological constraints in the proposed approach. Therefore, this method can be easily applied to other converter topologies for low power or microconverter (module-based converter)-based applications.

**Yazar(lar):** CHENGJIN YE, MINXIANG HUANG

Complementary renewable energies like wind and solar power may be more sufficient to satisfy reliability requirements. This paper proposes a quantitative capacity allocation method of a hybrid wind and solar energy system. First, discrete probability distributions are established to model the random factors including the volatility of power outputs and the failure of components. Then a multiobjective optimization model is formulated with objectives of minimization of the total investment, the nodal voltages violating limits probability, and power supply inadequacy probability. For the purpose of fast probability computing with a satisfactory precision degree, an innovative probabilistic load flow algorithm is introduced, which deals with means and increments of random variables separately and uses cumulants as well as Gram--Charlier series to obtain probabilistic distributions of state variables. A modified parallel elitist nondominated sorting genetic algorithm II is used to search the Pareto optimal configuration solutions.

**Yazar(lar):** Hayati MAMUR

In this study, design, implementation, and power performance analyses of a micro wind turbine (MWT) system are presented. An original permanent magnet synchronous generator (PMSG) that reduced cogging torque was employed as a generator in the MWT. A novel blade form offering better performance at low wind speeds was also utilized for the MWT blades. Power performance analyses of the MWT were carried out for different wind regimes by truck testing. Performance coefficient, cut-in, and cut-out of the MWT were determined as 27.7{%}, 2.7 m/s, and 20 m/s at the end of the truck testing, respectively. Moreover, a new supervisory control and data acquisition (SCADA) program based on a programmable logic controller was written to measure the electrical power of the MWT, and hence the analyses of the MWT were easily fulfilled through the SCADA.

**Yazar(lar):** ZHIWEI ZHANG, LIBING ZHOU

This paper presents the design and analysis of fractional slot multilayer interior permanent magnet synchronous machines (PMSMs) with concentrated winding for electric vehicles applications. The major advantages of concentrated winding will be analyzed first. The significant design consideration of multilayer interior permanent magnet machines will be illustrated, as well. Finally, the advanced finite element method will be employed to verify the detailed electromagnetic performance of the proposed interior PMSMs.

**Yazar(lar):** MILETA ZARKOVIC, IVAN SKOKLJEV

This study presents a possible process of simulating power plant generation planning. The process combines expected overall industry costs, associated cost uncertainty, and expected CO$_{2}$ emissions for different generations, variations of future fossil fuel costs, carbon prices, plant investment costs, and demand, including price elasticity impacts. Uncertainty in the decision stems from the elasticity of prices of fuel and electricity. The aim of this paper is to apply fuzzy numbers to power generation planning and to use a Monte Carlo simulation to check. Simulations are demonstrated through a case study of an electricity industry with coal and lignite, combined cycle gas turbines, and supercritical boilers facing future uncertainties. The same simulation was used in planning the generation of electricity from wind, solar, and hydro energy. Comparing the results, decisions were made about the profitability of investments in renewable energy. Based on the results, it can be concluded that the use of fuzzy numbers is a simple and flexible approach to planning and that it can be a serious competitor compared to other methods of planning.

**Yazar(lar):** SERKAN ABBASOĞLU, AKINOLA ADEYINKA BABATUNDE

The objective of this study is to examine the conformity of different simulation tools in analyzing the performance of photovoltaic (PV) systems in countries with high solar radiation. Primarily an installed system was evaluated and the results were compared with the simulation results of 3 globally known PV software tools: pvPlanner, PVsyst, and Homer. The parameters evaluated in this study are energy production, specific yield, performance ratio, and capacity factor. Detailed explanations are presented for monthly, seasonal, and annual variation of installed system data and simulation results. Northern Cyprus is selected as a case study due to high solar radiation and duration values. The total annual energy production of the installed 5.76 kW system amounts to 12,216 kWh for the year studied. All the simulation tools appear to underestimate the installed system's energy production and the variances observed are 5.3{%}, 9.3{%}, and 7.5{%} for pvPlanner, PVsyst, and Homer, respectively. Energy production in summer was observed to be about twice the production in winter. The percentage shares with respect to energy production are 34{%}, 28{%}, 22{%}, and 16{%} in summer, spring, autumn, and winter, respectively. The performance ratio of the system is 80.8{%}. However, the average performance ratio of the 3 simulators was found to be 78.6{%}. PVsyst modeled a performance ratio with the least deviation from the system with 79.2{%}. The specific yield and capacity factor of the installed system are 2121 kWh/kW$_{p}$ and 25.06{%}, respectively. The average specific yield value and average capacity factor of the 3 simulators are nearly 7{%} lower than the measured data of the installed system. Different factors led to the difference between real-world application and simulation results. These are discussed in this study in detail.

**Yazar(lar):** YINGJIE WANG, HAIYUAN LIU, XUELONG HAN, KANGAN WANG

With some of the intermittent new energy and large nonlinear loads, grid voltage unbalance, harmonics, and frequency deviation are increasing year by year. The voltage source converter (VSC) is seriously affected by the various unexpected factors, and the presence of grid impedance makes the situation worse. In order to make the VSC track the nonideal grid quickly and accurately, this paper proposes a frequency-adaptive grid-virtual-flux synchronization by multiple second-order generalized integrators (MSOGI-GVFS). Key expressions of the MSOGI-GVFS and its frequency response characteristics are described in this paper. A second-order generalized integrator configured as a quadrature signal generator generates a specific-frequency virtual flux. A harmonics decoupling network achieves fundamental and harmonic components of the virtual flux. The positive- and negative-sequence components are separated by multiple positive- and negative-sequence calculators. A frequency-locked loop is used to track the grid angular frequency. Finally, after compensating the voltage and the flux on the grid impedance and the filtering inductor, it accurately achieves the estimation of the grid virtual flux in the highly polluted grid environment. This method may reduce the voltage sensors, eliminate the influence of grid impedance, and track the grid frequency quickly, which contributes to the stability of the VSC. The good performance of MSOGI-GVFS is verified by simulation and experimental results.

**Yazar(lar):** SID AHMED EL MEHDI ARDJOUN, Mohamed Abid

In this paper an indirect vector control using fuzzy sliding mode control is proposed for a double-fed induction generator (DFIG), applied for a wind energy conversion system in variable speed. The objective is to independently control the active and reactive power generated by the DFIG, which is decoupled by the orientation of the flux. The sliding mode control finds its strongest justification for the problem concerning the use of a robust nonlinear control law for the model uncertainties. As far as the fuzzy mode control is concerned, it aims at reducing the chattering effect. The obtained results show the increasing interest of such control in this system

**Yazar(lar):** SUNIL SEMWAL, MUNENDRA SINGH, RAI SACHINDRA PRASAD

Identifying and controlling (ON/OFF) electrical appliance(s) from a remote location is an essential part of energy management. This motivated us to design a system that can collect the aggregate load signature from a single point, obtain the features, and finally identify the ON state of electrical appliance(s). The proposed disaggregation technique can be divided into two modules: the first part proposes an electrical installation system to disaggregate the appliance at the circuit level, whereas the second part consists of feature selection, dimension reduction, and classification algorithms. Load signatures of electrical appliances were combined with white Gaussian noise to analyze how noise affects the classification results. Amplitudes of the major eight harmonics of load signatures were selected as a feature for the classification. Various classification algorithms were applied to data to check their feasibility. The comparative evaluation showed that among the considered classifiers, the multilayer perceptron-artificial neural network (MLP-ANN) classifier leads in classification accuracy with 99.18{%}. If the system is combined with noise, the accuracy decreases to 93.10{%}. This paper also shows that the proposed technique reduces the space complexity and decision time of the smart meter.

**Yazar(lar):** SOHEL UDDIN, HUSSAIN SHAREF, OLAV KRAUSE, AZAH MOHAMED, MOHAMMAD ABDUL HANNAN, NAZ NIAMUL ISLAM

The aim of this paper was to examine the utilization of a large number of nonlinear light emitting diode (LED) lamps in a distribution system and its impact on system power quality. Initially, harmonic and others electrical characteristics were identified by carrying out an experiment on four types of LED lamps available on the local market. On the basis of the identified characteristics, a new LED lamp model was developed in MATLAB Simulink. This model is called the time-dependent current source model and gives more accurate results than the fixed current source model. Then this model was applied to a distribution network together other linear and nonlinear loads, namely incandescent lighting, computer loads, and compact fluorescent lamps (CFLs). The simulated results show that the harmonic voltage distortion can exceed the 8{%} IEC standard limit when 80{%} incandescent lamps in a distribution power network are replaced with LED lamps. Furthermore, the simulation results show that the active power loss can drastically increase across distribution transformers due to the presence large numbers of LED lamps.

**Yazar(lar):** AMANY EL ZONKOLY

Integration of wind farms into power systems may increase the risk of power system blackouts due to the uncertain nature of their output power. In the meantime, wind turbines have relatively short starting time when compared to non-black-start (NBS) generating units. For this reason, wind farms need to participate in power system restoration after blackouts. The decision of restoring a wind farm depends on its output power and the characteristics of the power system. The power system restoration should be accomplished as soon as possible. For complete power system restoration, three stages must be completed: generation restoration, transmission system restoration, and load pick up. To achieve a faster restoration process, an optimal schedule for the black-start units to crank the NBS units is required with optimal transmission path selection. During the restoration process, to maintain the stability of the system and satisfy the system's operational constraints, an optimal load pick up sequence is required. In this paper, the firefly optimization algorithm is used to find the optimal final sequence of NBS unit restoration, the optimal transmission paths, and the optimal load pick up sequence with and without integration of wind farms in the system. The objective is to minimize the overall restoration time and the unserved load, which maximizes the energy capability and improves the sustainability of the system. The proposed algorithm is applied successfully to the IEEE 39-bus system.

**Yazar(lar):** ABDELHAK DJOUDI, HACHEMI CHEKIREB, EL madjid Berkouk, Seddik Bacha

The aim of this work is to developing sliding mode control of active and reactive stator powers produced by a wind energy conversion system (WECS), based on doubly fed induction generator (DFIG). A flux estimation model and rotor current sensor are no longer required. The controller is developed from the DFIG nonlinear-coupled model. Moreover, the global stability and the DFIG states' boundedness when our low-cost sliding mode control is applied are established analytically. It is revealed that the $(dq)$ components of the rotor flux remain near their nominal values. Our approach is validated via simulation in the case of a WECS based on DFIG rating at 1.5 MW. The robustness and the performances are verified with the presence of parametric variations and disturbances in the case of an unbalanced grid.

**Yazar(lar):** Ayhan Özdemir, İrfan YAZICIOĞLU, Nihal Zekiye ERDEM

This paper proposes a discrete-time model-reference sliding mode control of three-phase four-leg voltage source inverters for stand-alone distributed generation systems. Three-phase four-leg voltage source inverters (VSIs) are used in a broad area. A discrete-time model-reference sliding mode controller, having superior advantages such as insensitivity to external disturbances, system parameter variations, and modeling errors, is applied to control the output voltage of three-phase four-leg VSIs. As a new study, the discrete-time model-reference sliding mode control with a supplemented output feedback integral controller is proposed so that the controlled output voltages of the VSI tracks the input reference signal. The controller is designed using the augmented discrete-time error dynamics presented in this paper and is applied to control the output voltage control of a three-phase four-leg based uninterruptable power supply. It is shown that the output voltage of the VSI controlled by the proposed method is accurately regulated for various load conditions such as linear balanced/unbalanced, nonlinear balanced/unbalanced, and instantaneous load changes. The robustness of the proposed method against variations by 20{%}--50{%} in R, L, and C filter parameters and 5 different cases are showed. vs{1mm}

**Yazar(lar):** LIHUA WANG, XUEYE WEI, YUQIN SHAO, TIANLONG ZHU, JUNHONG ZHANG

In order to achieve maximum efficiency, a maximum power point tracking (MPPT) scheme should be applied in photovoltaic systems. Among all the MPPT schemes, the chaos optimization scheme is one of the hot topics in recent years. In this study, a novel stepped-up chaos optimization algorithm is presented. A chaos mapping $x_{n+1} =mu sin (pi x_{n} )$ is used as a chaos generator to produce a chaos variable. In the process of MPPT, a coarse search is done to find the current optimal solution in a certain range, and then a fine search reduces the space of optimized variables. Compared with the algorithm of traditional chaos searches, the proposed algorithm is more accurate and can respond quickly. Simulation and experimental results confirm the goodness of the proposed algorithm.

**Yazar(lar):** JUAN ZHOU, MALONG LIU, CHEN WEI, CHAOXU GAO, XIAOJIE WU

The photovoltaic power generation and active filter (PV-AF) system can realize photovoltaic grid-connected power regulation, and meanwhile it can also improve the power quality of power grid effectively. The four-leg grid-connected inverter has successfully been used in the three-phase four-wire system. In this paper, a three-dimensional space vector pulse width modulation (3D-SVPWM) method based on the gh$gamma $ coordinate system for a four-leg inverter has been proposed. As the switching vectors of the four-leg inverter are in the three-dimensional space, it is difficult to realize the complex modulation process. In order to simplify the modulation process, the reference vector is placed into gh$gamma $ coordinates in the proposed modulation strategy, and then the vectors are selected and the duration times are acquired directly by a group of intermediate variables, which could be obtained by linear transformation of the coordinates. As the intermediate variables are used, the modulation can be easily implemented by the proposed modulation strategy without excessive mathematical calculations. The simulation and experimental results all confirmed the validity and effectiveness of this strategy.

**Yazar(lar):** MUHAMMAD NOMAN SIDDIQUE, Aftab Ahmad CHATHA, MUHAMMAD KASHIF NAWAZ, SYED BASIT ALI BUKHARI

Most energy worldwide is supplied through conventional energy sources, such as thermal, hydro, and nuclear. There have been serious energy crises in the last couple of years and so it is essential to consider renewable energy sources. This paper proposes a cost-effective solution for integrating a wind--solar system with an existing diesel power plant of a grid-connected site at Taxila, Pakistan. In the case of nonavailability of power from the grid, this diesel power plant acts as a standby system. Three cases were considered in this paper: 1) using the diesel power plant during load-shedding hours; 2) assisting the system using renewables when it is connected to the grid (on-grid); 3) completely relying on hybrid energy system to meet the daily load demand if excess energy is available (off-grid). The system was implemented in the software package Hybrid Optimization Model for Electric Renewables (HOMER) developed by the National Renewable Energy Laboratory. Different environmental factors were examined, including wind speeds, solar insolation, and their maximum and minimum differences from the average parameters. In the end, the most optimal solution for each case was proposed to meet the desired load demand while making the system operation economical.

**Yazar(lar):** Şaban YILMAZ, HASAN RIZA ÖZÇALIK

In today's world, the daily need for and cost of energy sources increase and this forces industrial institutions to seek for new ways to generate their own energy. The developments in photovoltaic systems have recently drawn attention in the business world. Although their installation costs are high, they are environmentally friendly and profitable investments in the long run. The cost analysis of a large-scale photovoltaic generator in the climatic conditions of Kahramanmarac{s} will lead the way to new investments. In this study, the modeling and cost analysis of an on-grid photovoltaic generator of 500 kW, which was installed to provide energy for a textile factory located in the Pazarc{i}k district of Kahramanmarac{s} Province (37.5$^{circ}$N, 37.3$^{circ}$E; altitude: 748 m), was performed. The findings suggest that the photovoltaic generator of 500 kW installed in the Pazarc{i}k district of Kahramanmarac{s} Province in August 2013 produces 816,639 MWh energy and reaches its initial cost in 6.2198 years. Therefore, photovoltaic generators are significantly useful when the climatic conditions in Kahramanmarac{s} are taken into account.

**Yazar(lar):** GÜRHAN ERTAŞGIN, WEN LIANG SOONG, NESIMI ERTUGRUL

This paper investigates the design and performance of a 150 W single-phase current-source grid-connected inverter topology that is based on a PV array and DC link inductor acting as a constant-current source. The inverter is implemented using a single boost switch, an H-bridge inverter, and a CL output filter. The inverter output current is simply controlled using the boost switch and open-loop or feedforward control. The dark I-V configuration is used to simulate two series PV modules. Comprehensive test results are obtained to validate the computer simulation results. Furthermore, the proposed inverter's ability to deliver a sinusoidal current to the grid while meeting the appropriate standards, i.e. total harmonic distortion and power factor requirements, is also examined for various modulation index values and irradiances.

**Yazar(lar):** ANIRBAN GHOSHAL, VINOD JOHN

Synchronous reference frame phase locked loop (SRF-PLL) is a well established technique used for maintaining synchronism of a grid connected VSI with an electric grid. Many methods of PLL are present in the literature to achieve improved performance under nonideal grid condition. These solutions are based on SRF-PLL structure along with some modification to achieve improved performance. It is observed that faster and better performance are achieved at the expense of more computations. Moving average filter (MAF) SRF-PLL structure is one such solution that consumes less resources and gives a reasonably fast response. In this work the performance of a MAF-SRF-PLL structure is evaluated in terms of unit vector distortion and settling time under various nonideal grid conditions. Its performance is compared with that of two differently designed SRF-PLLs. This evaluation gives a clear idea about possible utilizations of these PLL structures under different possible nonideal grid conditions.

**Yazar(lar):** JYOTIRMAYEE DALEI, KANUNGO BARADA MOHANTY

In this paper, the transient and steady-state performances of an isolated self-excited induction generator driven by a wind turbine and feeding power to a dynamic load such as a three-phase induction motor are analyzed. Mathematical modeling and simulation study of the whole system, including the wind turbine, induction generator, capacitor, pulse width modulated voltage source inverter, and dynamic load, are carried out with closed-loop voltage and frequency controller. The complete system is modeled in the stationary $d-q$ frame and validated by comparing simulation and experimental results at no-load. The same mathematical model is then used to study the transient performance of the self-excited induction generator supplying to a dynamic load. When the induction motor is connected to the induction generator without any voltage and frequency controller, it causes severe transients in electrical and mechanical variables of the generator. Due to the large starting-current requirement of the induction motor, there is a collapse of the terminal voltage of the generator. A bidirectional pulse width modulated source inverter with DC link battery is connected with the generator and operated in closed-loop control mode to maintain voltage and frequency and to operate the induction motor successfully with variable wind speed and mechanical load.

**Yazar(lar):** İSMAİL HAKKI ÇAVDAR, NERMIN SULJANOVIC, MUHAMMET UZUNTARLA

Prof Dr İsmail Hakkı Çavdar Department of Electrical and Electronics Engineering, Karadeniz Technical University, Trabzon, Turkey Prof Dr Nermin Suljanovic Faculty of Electrical Engineering, University of Tuzla, Tuzla, Bosnia and Herzegovina Assoc Prof Dr Muhammet Uzuntarla Department of Biomedical Engineering, Bülent Ecevit University, Zonguldak, Turkey

**Yazar(lar):** VLADIMIR YURCHENKO, EDUARD YURCHENKO, Mehmet ÇİYDEM, ONAT TOTUK

We present our developments in computer simulations and optimization of compound parabolic concentrators (CPCs) for solar heat collectors. Issues of both the optical and thermal optimization of CPC collectors of enclosed design are discussed. Ray tracing results for a CPC with a V-shaped absorber are presented. A range of optimal values for the apex angle of a V-shaped absorber is proposed for a CPC collector of typical design.

**Yazar(lar):** HOSSEIN DELAVARIPOUR, BEHZAD MIRZAEIAN DEHKORDI

This paper presents a reliability evaluation technique for a small standalone system including wind and conventional resources integrated with an energy storage system. A battery bank is considered as the energy storage system. The focus in this analysis is on the effect of battery modeling and its performance on system reliability. In this way, this paper presents an accurate model for the electrochemical batteries, which takes into account all the influential characteristics of the battery related to reliability studies, such as depth of charge, efficiency of charge, and rate of discharge. The proposed reliability evaluation method is based on the combination of a probabilistic production simulation technique as an analytical method and time series technique, in the domain of adequacy studies. By using the probabilistic production simulation technique, not only can the reliability of wind-conventional resources be assessed, but the fuel consumption can also be analyzed. On the other hand, by using the time series approach, the time variation of wind speed and operating constraints of the battery bank can be considered in evaluating the reliability indices. In this paper, a typical lead--acid battery bank is used. It is shown how the accurate modeling of the battery bank can affect the reliability indices. Beneficial results are obtained for different operating strategies and wind penetrations and are then compared.

**Yazar(lar):** ALEKSANDAR JANJIC, SUZANA SAVIC, LAZAR VELIMIROVIC, VESNA NIKOLIC

Unlike the traditional way of efficiency assessment of renewable energy sources integration, the smart grid concept is introducing new goals and objectives regarding increased use of renewable electricity sources, grid security, energy conservation, energy efficiency, and deregulated energy market. Possible benefits brought by renewable sources integration are evaluated by the degree of the approach to the ideal smart grid. In this paper, fuzzy analytical hierarchy process methodology for the integration efficiency has been proposed, taking into account the presence of multiple criteria of both qualitative and quantitative nature, different performance indicators, and the uncertain environment of the smart grid. The methodology has been illustrated on the choice of the size and location of a distributed generator in the radial distribution feeder.

**Yazar(lar):** SARA NOUROLLAH, ABOLFAZL PIRAYESH, PORIA HASANPOR DIVSHALI

This paper proposes sharing active and reactive power in autonomous voltage source inverter (VSI)-based microgrids with no physical communication links. In decentralized VSI-based microgrids, when the demand or generation changes, the output voltage of distributed generation units and the frequency of the system will also change. This study presents a novel adaptive nonlinear droop (ANLD) scheme for preserving network stability, improving the system's dynamics, and controlling power sharing in multibus microgrids in a decentralized manner. Subcontrollers are modeled in a state space and combined together so that a complete dynamic model of the network can be developed. Note that controller coefficients are optimized to improve small-signal stability and to obtain a good operating point. To this end, an optimization problem is formulated and solved using the particle swarm optimization method. For the purposes of comparison, the proposed ANLD method and three other schemes are applied to two case studies: a 5-bus microgrid and a modified 37-bus IEEE microgrid. The stability margin analysis and time response simulations prove that the proposed algorithm performs much better and can be applied to large-scale microgrids.

**Yazar(lar):** GANGATHARAN SIVASANKAR, VELU SURESH KUMAR

The recent advancement in electric energy storage technologies provides an opportunity of using energy storage systems to address the issues of grid-integrated wind energy conversion systems. This paper proposes a novel configuration of a unified power quality conditioner (UPQC) with a supercapacitor-based short-term energy storage system for managing wind power intermittency during grid faults. The STATCOM-like compensation device can compensate only current related issues. The dynamic voltage restorer can compensate voltage-related issues but it can contribute only 50{%} voltage due to converter rating limitations. Moreover, real power handling capabilities of these devices are very poor. This new UPQC scheme can compensate voltage sag, negative sequence current, and real and reactive powers from 0.1 pu to 0.9 pu. The proposed system improves fault ride-through capability of the wind turbine generators and satisfies the grid code requirement. A synchronous reference frame-based control method is employed for the UPQC. The energy storage system is controlled using a two-quadrant DC/DC converter. The proposed model was developed and tested in the MATLAB/SIMULINK environment.

**Yazar(lar):** Zhijian YANG, DONGRAN SONG, HUA HAN, PENGSHA TONG, LING ZHOU

For a variable-speed wind turbine (VSWT), the primary objective of control is to maximize power generation while maintaining the desired rotor speed and avoiding equipment overloads. To fulfill the control objectives, the classical model-based control (MBC) has been widely used, which refers to two controllers: torque controller (TC) and pitch controller (PC). In this work, the drawbacks of MBC for VSWTs are studied extensively. It reveals that there are transition issues between the TC and PC, and over-speed problems under large turbulent wind when only MBC is taken. To improve the control performance of the VSWT, an integrated control solution is presented, in which three fuzzy logic control modules are designed to function in parallel with MBC modules. Potential integrated structures are also given and a structure suitable for industrial application is adopted in this study. The proposed solution is applied to update the raw control system of a 3.0 MW VSWT of the Chinese Ming Yang Wind Power, which is validated with nonlinear simulations by using the commercial wind turbine simulation tool Bladed in accordance with IEC standards. The results prove that good performance of the target wind turbine is guaranteed under the proposed integrated control structure.

**Yazar(lar):** AGHA FRANCIS NNACHI, JOSIAH MUNDA, DAN VALENTINE NICOLAE, AUGUSTIN MABWE MPANDA

The utilization of a DC-link transmission corridor of embedded VSC HVDC for a DC power injection from renewable energy sources to increase the power flow capability and AC network stability support is a promising technology. However, DC faults on the DC transmission line are likely to threaten the system's operation and stability, especially when the DC power injection exceeds certain limits. A DC single line-to-earth fault is the most likely fault scenario and its effect on the VSC HVDC operation will depend on the earth-loop impedance. Adding an injection point on the DC-link will reduce the earth-loop impedance, hence imposing a danger of increasing the earth fault current. Therefore, in this paper, a VSC HVDC with a DC power injection on the DC-link is studied, the DC-line-to-earth fault is analyzed in the time domain, and its effects on the DC and AC sides of the system are presented. The analysis is based on a developed state-space representation of the system under a single-line-to earth fault. The zero-input zero-state (ZIZS) response is used to find the solution of the state-space representation. In order to correlate the state-space solution with a simulation, the system is modeled in MATLAB/Simulink. Interestingly, it was observed that a quick recharging of the DC-link capacitor due to a power injection created an additional damping of the postfault oscillations of the AC-side power angle and the DC-side voltage and power oscillations, hence enhancing transient stability.

**Yazar(lar):** WEI CHAI, ZHENG LIU, XU CAI

A variable charge/discharge time-interval ($T_{C/D})$ control strategy of a battery energy storage system (BESS) for wind power dispatch is proposed in this paper, aiming at: 1) extending the BESS life, 2) reducing the total BESS energy loss, and 3) increasing the dispatch tracking accuracy. A multifactor life model of a large-scale BESS containing four factors, charge/discharge rate, times, $T_{C/D}$, and temperature, is developed, which has taken into account the cell series/parallel effects and BESS operational characteristics. A comprehensive evaluation system including BESS aging level (BAL), energy loss index (ELI), and tracking inaccuracy index (TII) is proposed, and the relationships between $T_{C/D}$ and the three indices are discussed. In order to combine the advantages of low BAL and low ELI under long $T_{C/D}$ and low TII under short $T_{C/D}$, a fuzzy controller is designed to regulate $T_{C/D}$ in real time. The effectiveness of the proposed control strategy is verified by actual data from a wind farm in eastern China.

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