G. Radman

Tennessee Technological University, Cookeville, TN, United States

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Publications (46)0.62 Total impact

  • M.A. Tabrizi, G. Radman
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    ABSTRACT: Wind energy system as a renewable energy source has been developed remarkably during the last decade to supplement large scale power systems, micro grids and smart grids. While Considerable research efforts have been directed to wind energy system modeling and analysis, comprehensive model developments for grid integration studies have been relatively sparse. This paper presents a detailed dynamic modeling for wind energy conversion system based on Permanent Magnet Synchronous Generator. The wind turbine system is equipped with maximum power point tracking module and pitch angle control. The control system aims to regulate the generator shaft speed, DC link voltage, and output reactive power while minimizing generator losses. The overall system is simulated in MATLAB. The simulation result indicates the presented model adequately represents the details of the system performance while meeting all control objectives.
    Southeastcon, 2013 Proceedings of IEEE; 01/2013
  • A. Jamehbozorg, G. Radman
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    ABSTRACT: This paper presents a MATLAB Graphical User Interface (GUI) software package which enables users to study small signal behavior of power systems with wind unit and Energy Capacitor Systems (ECSs). For hybrid systems including wind and storage units, studying dynamic behavior of overall system is a complicated and time consuming task. The objective of this paper is to design a user friendly GUI as an educational tool that helps students study the effect of wind and storage units on power system. Modeling of wind units with squirrel-cage induction generators connected to the network through a full-scale AC/AC converter and ECS units consisting of Electric Double-Layer Capacitors and DC/AC converter are explained thoroughly. GUI let the users to choose load change disturbance in any bus or wind speed change in any wind unit and displays the variation of desired state variable after such disturbance.
    Southeastcon, 2013 Proceedings of IEEE; 01/2013
  • G. Cakir, G. Radman, K. Hatipoglu
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    ABSTRACT: Power system oscillation is one of the major problems in power system operation. If not damped, these oscillations can grow and decrease transmission capacity of the lines which may cause interruption in energy supply. Several methods for damping of these oscillations are reported in literature. Traditionally, these oscillations have been damped by power system stabilizers. Recently, FACTS devices such as static synchronous compensator (STATCOM) equipped with a power oscillation damper (POD) have been also efficiently used for damping oscillation. It should be noted that, the main objective of STATCOM is to regulate voltage at its terminal by changing the amount of reactive power exchanges with the power system and POD is a secondary function provided by this device. This paper proposes the application of the residue factor method to obtain the best location of STATCOM for damping oscillations. The residue factor used is related the critical oscillatory modes. Also presented in this paper is a comparison of power system stabilizer (PSS) and STATCOM for the enhancement of oscillations damping. IEEE 14-Bus test system was used to demonstrate the effectiveness of the proposed method for placement and the comparison of PSS and STATCOM on damping oscillations. From the simulation results it is seen that STATCOM has better ability in damping oscillation when compared to PSS.
    Southeastcon, 2013 Proceedings of IEEE; 01/2013
  • A. Jamehbozorg, G. Radman
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    ABSTRACT: This paper presents a dynamic analysis of a micro grid including Photovoltaic units. A four-bus system including an infinite bus is considered for the simulations. The system is modeled using MATLAB Simulink software package. Different combinations of synchronous generators and PV units are simulated and their dynamic performances during different disturbances are studied in the paper. From these studies it is concluded that using PV units in a micro grid will make the dynamic of the system faster and system reaches to its steady-state point faster using more PV units. But, because PV units have no governor and exciter system (unlike conventional synchronous generators), the steady-state point of the system may be unacceptable (due to under- or over-voltage).
    Energytech, 2012 IEEE; 01/2012
  • K. Hatipoglu, I. Fidan, G. Radman
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    ABSTRACT: This paper presents effects of voltage changes on static polynomial (ZIP) load under three phase fault in a microgrid environment. The objective of the paper is investigating the behavior of the ZIP load model under a faulty condition. Load representation is a crucial factor on approaching power system realistically. The static characteristics of the load can be classified into constant power, constant current and constant impedance load, depending on the power relation to the voltage. For a constant impedance load (Z), the power dependence on voltage is quadratic, for a constant current (I) it is linear, and for a constant power (P) the power it is independent of changes in voltage. The ZIP model is a polynomial model that represents the sum of these three categories. Behavior of the ZIP loads connected to the Microgrid test system will be investigated and overall changes will be discussed.
    North American Power Symposium (NAPS), 2012; 01/2012
  • A. Jamehbozorg, G. Radman
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    ABSTRACT: This paper proposes an Energy Capacitor System (ECS) designed to enhance the dynamics of micro-grids in presence of wind generation units. The output power of wind units fluctuates due to continuous variations in wind speed. In a power system with high penetration of wind units - like a microgrid - this can considerably deteriorate the dynamics of the entire system. To study the negative impacts of high penetration of wind power on power system dynamics and compensation of this negative impact through ECS, the following tasks are undertaken in this paper. First, a micro grid test system is modeled using MATLAB Simulink software. Then, an ECS unit is designed to mitigate the negative effects caused by the wind unit due to wind speed fluctuations. Finally, the dynamics of the test system for a short-circuit fault is studied. The simulation results show that ECS units can effectively improve the dynamics of the system, thus compensating for negative effects of wind speed fluctuations (in normal steady state operation) and during/after a major short circuit fault.
    North American Power Symposium (NAPS), 2012; 01/2012
  • R. Hassan, M. Abdallah, G. Radman
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    ABSTRACT: Load shedding is required when there is an imbalance between electricity demand (customers' usage) and electricity supply (the ability of the electricity network to generate and transport the required amount of electricity to meet this demand). Hybrid novel design methodology is proposed to enhance the underfrequency load shedding in terms of consumer satisfaction level. A Consumer Priority Assignment Unit (CPAU) is proposed to be placed in each smart house. It gives the consumer the option to decide which loads to be shed. A reliable efficient self-pruning Ad-Hoc broadcast algorithm is proposed. The performance of the proposed algorithm is tested. The results indicate that the proposed algorithm nearly maintain the efficiency of the generic algorithm, at the same time it enforces higher reliability and prevents nodes (CPAUs) from taking wrong decisions.
    01/2012;
  • Gang Zheng, Yilu Liu, G. Radman
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    ABSTRACT: This paper presents the latest development in wide-area frequency-based generation trip event location. Real-time generation trip location information is very useful to system operators and also to power producers. Using synchronized frequency data from wide-area frequency monitoring network (FNET) as input, the event location estimation is expressed as nonlinear optimization problem. In this paper, we address a systematic way of dealing with coordinates conversion issue in solving this problem. The coordinates of event location, the time at which event occurred, and the propagating speed of the electromechanical wave, are solved simultaneously using Gauss-Newton method. The presented computation process is concise and efficient. Using actual event data, the proposed procedure is examined for implementation feasibility.
    Power and Energy Society General Meeting, 2012 IEEE; 01/2012
  • A. Jamehbozorg, G. Radman
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    ABSTRACT: This paper presents dynamic analysis of multi-machine power systems with large penetration of Photovoltaic (PV) units. The actual non-linear characteristics of the PV-units is included in the modeling of the overall power system and the influence of this non-linear dynamics is studied through various simulations. These simulations (performed in MATLAB Simulink software package) are applied on a modified IEEE 30-bus system, where one of the major generators is replaced by a large PV power plant. Three case studies are considered. From these studies it is concluded that large penetration of PV-units deteriorates the dynamics of the overall system.
    Power and Energy Society General Meeting, 2012 IEEE; 01/2012
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    ABSTRACT: At this time, the restructuring of power system is going to pass the early stages and become a well-known concept. However, it is impossible to say that supplying electricity is perfect now. There are still many works undergoing to increase the efficiency and functionality of restructured electricity markets. In this paper, a new concept for electricity markets has been proposed. This new concept is FDO which stands for FACTS Devices Owner. In this paper it has been tried to introduce this new participant and clarify some of its duties. Removing the Transmission Owner market power by increasing the line capacity, optimum unit commitment by distributing the generation, less emission by using units with lower emission and renewable energies which directly affects on social health and welfare, are some of the benefits that come along with FDOs. In the case study part, the FDO has been implemented on an assumed market with two areas and four Generation Companies and it is shown that introducing FDO to the market is a useful action toward full free competition vision.
    Southeastcon, 2011 Proceedings of IEEE; 04/2011
  • R. Hassan, G. Radman, D. Gao
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    ABSTRACT: A photovoltaic (PV) array performance depends on various operating conditions. Solar irradiation is considered the most important factor. The shading on PV array can result from passing clouds, trees, utility, telephone poles, or neighboring buildings. It causes not only power losses, but also increases non-linearity of V-I characteristics of PV array. This phenomenon has been studied in many research works using different software packages. In this paper, user-friendly LabView tool is proposed to simulate effects of PV shading on its characteristics. Simulation results are verified through different case studies.
    Southeastcon, 2011 Proceedings of IEEE; 04/2011
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    ABSTRACT: Trajectory extrapolation is important for stability analysis and control of modern power systems. Many functions such as security warning and time-delay compensation for wide-area feedback control can be developed through trajectory extrapolation. But as of now, there are no effective methods to extrapolate power system trajectories except for time-consuming numerical integration methods. The difficulties for trajectory extrapolation in power systems lie within the fact that the underlying dynamic equations are nonlinear, and thus analytical solutions are not possible. In this paper, a method is proposed to approximate the analytical solution of power system dynamics, by which trajectories can be extrapolated. First, the dynamic equations of power system are modified to an equivalent set of equations by polynomial projection technique. Based on the modified equations, an approximate analytical solution is obtained using algebraic Picard iteration without integration operation. This solution depends on the initial values and can be used for on-line trajectory extrapolation. Following a disturbance, with values at the instant of disturbance clearance known (i.e. through PMU - measurements), one can easily extrapolate the system trajectory by extending the approximate analytical solution and updating initial values. Finally, some simulation results are presented to show the effectiveness of the method. Index Terms—Power systems, trajectory extrapolation, analytical solution approximation, nonlinear differential equations, Picard iteration.
    01/2011;
  • Gang Zheng, Ghadir Radman
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    ABSTRACT: For evaluating the first swing stability (FSS) of power systems in the presence of doubly fed induction generator (DFIG) wind farms, a simple and unified model of DFIG is proposed in this paper. In addition the proposed DFIG model is carefully incorporated into the power system for fast FSS evaluation. The evaluation algorithm is also presented in details in the paper. Without losing generality, DFIG is represented by an equivalent circuit according to various rated active and reactive powers output. The limitation of rotor current was considered during the evaluation process as well. The effectiveness of the proposed DFIG model and the evaluation algorithm are tested on modified IEEE 14-bus test system. The proposed DFIG model and the evaluation algorithm are very general and can be easily applied to a large power system.
    01/2011;
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    ABSTRACT: Although deregulation of power systems in most of the cases is considered as a worthy progress, however, for the operation and maintenance of this brand new environment, the associated new issues have to be clarified and solved. In this paper, a new method for pricing the transmission loss is proposed. The proposed method is fundamentally based on zero cash balance of the market. The idea of this paper for the loss allocation process is to consider and integrate the time of consumption into the cost of allocated losses to one party. That means the price of loss would not be the same as the price of power at same interval. This price of loss is a function of both market clearing price and the time of transmitting power. The method has been implemented and tested on several types of markets and two samples are summarized in the paper. The results show that the method has an acceptable performance in various situations. HE restructuring in electricity power systems brings along many new issues that the power system operation has never faced before. Although deregulation of power systems in most of the cases is considered as a worthy progress, however, for the operation and maintenance of this brand new environment, these issues have to be clarified and solved. One of the issues related to the transmission system of liberalized power markets is allocating the transmission losses to the participants who use the transmission system. On the other hand, global trend to increase the penetration of wind energy in power system is growing. It is proved that wind energy is environmentally and economically valuable in long-term planning. However, this kind of energy is at early stages of being commercially operated and needs to be supported. Production and renewable credits based on federal and state subsidies are examples for supporting wind energy which are in effect right now. In spite of current support of wind energy, other ways to promote it are always welcome. The transmission losses cost of a national wide transmission network can reach to millions of dollars each year, and as long as the electricity market is a non-profit organization, this money should be subtracted from the generator's income and load's fee simultaneously to keep the cash-flow in balanced state. This cost is considered as variable
    01/2011;
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    ABSTRACT:  Abstract - Photovoltaic systems are being considered as one of the major sources of electrical energy for next decades. The cost of PV cells is decreasing more and more and this will help increase its penetration in power systems. One of the main issues of PV systems is their dependency on irradiance of the sun and temperature of the cells. As during day-time both these factors are changing continuously, the output power of PV cells would have considerable fluctuations that would not be acceptable in power systems with high penetration of PVs. In order to solve this problem, this paper proposes a system to smooth the output power of the PV using Energy Capacitor System. A case study for investigating the performance of the proposed configuration is simulated and results show that it can considerably smooth the output power of the PV system. I. NOMENCLATURE - Output current of the PV cell (A), - Current generated by the incident light (A), - Reverse saturation current of the diode (A), - Output voltage of the PV cell (V), - Series resistance of the PV model (Ω), - Shunt resistance of the PV model (Ω), - Ideality factor, - Nominal saturation current (A), - Temperature of the PV cell (K), - Nominal temperature (K), - Material band gap energy (eV), - Nominal ideality factor of the PV cell (K), - Open circuit of the PV module (V), - Thermal voltage (V), - Number of series cells, - Boltzmann constant = (J/K), - Electron charge = (C), - Short circuit current of the PV (A), - Short circuit current/temperature coefficient (A/K), - Irradiance of the sun (W/m 2 ), - Nominal irradiance of the sun (W/m 2 ).
    01/2011;
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    ABSTRACT: Under-Frequency Load Shedding (UFLS) can increase power system reliability by preventing total system collapse during emergency operating situations when load exceeds generation. UFLS is required by The North American Electric Reliability Council (NERC) for large consumers and has been implemented by utilities across the country. When the frequency drops to some predefined set points, feeder breakers are opened to shed loads in favor of maintaining generation/load balance. With increasing pressure to improve system reliability through more sophisticated controls and SCADA (Supervisory Control And Data Acquisition) equipments, electric utilities are encouraged to apply more localized frequency sensing and load shedding schemes on the distribution system. This research work aims at studying the effects of voluntary load shedding for different load shedding scenarios using the simulation package PSS/E. In addition, a consumer- based load shedding controller is proposed, designed and developed.
    01/2011;
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    ABSTRACT: Although there is considerable progress in the wind energy conversion technology, most of the currently installed wind turbines are using induction generators to convert mechanical energy to electrical one. The induction generators which are utilized in wind turbines and wind farms consume high amount of reactive power. Beside, since there is no voltage regulation installed for induction machines and they draw reactive power from power system, these machines are source of voltage fluctuations. Therefore, reactive power compensation is needed to provide expected voltage support where the wind turbines are connected. Minimizing the cost of compensation is the next important step. In this paper a practical method is proposed to find the minimum cost of reactive power compensation for use in radial connection of wind power turbines to power systems.
    01/2011;
  • Conference Proceeding: Survey on Smart Grid
    R. Hassan, G. Radman
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    ABSTRACT: Creation of a Smart Grid provides utilities and their customers a significant improvement in power reliability and services. To date, Smart Grid has attracted various researchers from different perspectives. This paper presents a review of Smart Grid technologies and its characteristics. An extensive literature review is introduced. One can see variety of problems and challenges in the field of Smart Grid. Hence, this paper can provide a help to find a new research point in this field.
    IEEE SoutheastCon 2010 (SoutheastCon), Proceedings of the; 04/2010
  • Jiaxin Ning, Wenzhong Gao, Ghadir Radman, Jane Liu
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    ABSTRACT: Power flow study is one of the most dominant subjects in the field of power system. This paper applies the Groebner Basis (GB) technique to solve power flow problem. The GB technique is a systematic mathematical tool to solve nonlinear polynomial algebraic equations. The technique has capabilities of uncoupling any given set of coupled equations. Uncoupling not only facilitates numerical work, but also provides the possibility of solving uncoupled equations of up to the fifth degree analytically in symbolic form. For higher degree, since the new set of equations is decoupled, the overall solution is simplified. The superior property of the technique brings an alternative method for power flow study. 3-bus and 5-bus power system are used to test and discuss the GB technique. The effectiveness of this technique is validated with solution from Newton-Raphson method.
    North American Power Symposium (NAPS), 2009; 11/2009
  • Alex Pama, Ghadir Radman
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    ABSTRACT: The MW-distance to voltage collapse is a good indicator of voltage stability at a given operating condition in power systems. This indicator is determined using PV-curves obtained through continuation power flow (CPF) program. The CPF method performs several power flow runs requiring a large amount of computing time. This method is reliable for off-line voltage stability studies, but not very much suitable for real-time operation of today's stressed power systems. Given that, it is essential for system operators to have quick information about voltage stability, a new method is needed for a fast estimation of voltage collapse point. This is the main thrust of the presented paper. It is well known that PV-curves are approximately quadratic functions and become exactly quadratic in close neighborhood of the collapse point. Some authors used this fact and suggested methods that use two to three power flow solutions for a relatively quick, but approximate, calculation of the collapse point. The present paper, also based on quadratic approach, proposes a new method for the determination of voltage collapse that uses only one power flow solution and gives more accurate estimate of the collapse point when compared with other existing methods. Another advantage of the presented method is that the estimation becomes more accurate for stressed power systems. In addition, application of the presented method for performing the top/stable portion of the PV-curves provides an effective step-size that reduces the number of power flow runs. The method is tested using the New England 39-bus and the IEEE 300-bus test systems. The results confirm the effectiveness of the presented method.
    Electric Power Systems Research - ELEC POWER SYST RES. 01/2009; 79(4):653-659.