Showing papers in "Istanbul University - Journal of Electrical and Electronics Engineering in 2009"

Vector control of a dfig based wind turbine

Abstract: Variable speed wind turbines (WT) based on the Doubly-Fed Induction Generator (DFIG) is commercially offered and is frequently used in grid connected mode. The variable speed operation in such wind turbines is achieved by means of a four-quadrant ac-dc-ac power converter among the rotor winding and the grid while the stator is directly connected to the grid. Below rated wind speed, tracking the maximum power/torque curve realized by speed/current control mode while pitch control ensures the rated power for above rated wind speed. In this research, a maximum power control strategy is incorporated with the DFIG whereby the produced power serves as the dynamic active power reference for the DFIG. Stator flux oriented vector control is applied to decouple the control of active and reactive power generated by the DFIG based WT. Details of the control strategy and system simulation results in Simulink are presented in the paper to show the effectiveness of the proposed control strategy.

The modelling of electric power systems on the state space and controlling of optimal lqr load frequency

Abstract: The modelling of electric power systems on the state space and an optimal control system known as Linear Quadratic Regulator (LQR) for designing the load frequency control system are realized in this paper. In order to obtain high quality electric energy on electric power systems, the fluctuations on voltage and frequency must be decreased as much as possible. The frequency sensitivity of the system must be reduced to minimum level against to load changes. To obtain minimum frequency sensitivity against to load changes, an optimal control known as Linear Quadratic Regulator ( LQR) is designed. In the study, the simplified and block diagram of the electric power system is employed. By using this diagram, the state equations for the power system are obtained on the state space. In the load frequency control of power system, control system via pole-placement and optimal LQR control method known as modern control with high reability rate are used. The proposed optimal LQR load frequency has been compared with control system via pole-placement. Load frequency control system of electric power system has been developed designed by using MATLAB/SIMULINK.

An adaptive neuro-fuzzy inference system approach for prediction of power factor in wind turbines

Abstract: This paper introduces an adaptive neuro-fuzzy inference system (ANFIS) model for predicting the power factor of a wind turbine. This model based on the parameters involved for NACA 4415 and LS1 profile types with 3 and 4 blades. In model development, profile type, blade number, Schmitz coefficient, end loss, profile type loss, and blade number loss were taken as input variables, while the power factor was taken as output variable. After a successful learning and training process the proposed model produced reasonable mean errors. The results on a testing data indicate that the ANFIS model is found to be more successful than the ANN approach in estimating the power factor.

Modelling and fuzzy logic control of pem fuel cell system power generation for residential application

Abstract: This paper presents a dynamic model of Fuel cell system for residential power generation. The models proposed include a fuel cell stack model, reformer model and DC/AC inverter model. More then an analytical details of how active and reactive power output of a proton-exchange-membrane (PEM) fuel cell system is controlled. Furthermore a fuzzy logic (FLC) controller is used to control active power of PEM fuel cell system. The controller modifies the hydrogen flow feedback from the terminal load. Simulation results confirmed the high performance capability of the fuzzy logic controller to control power generation.

A microcontroller based generator design for ultrasonic cleaning machines

Abstract: In this study, driver and power units of a microcontroller based ultrasonic generator, which has advanced controlling functions are designed and implemented for 28 KHz ultrasonic cleaning machines. The importance and usage of ultrasonic frequencies for surface cleaning purposes are addressed. The designed generator has the ability of automatic frequency control as a solution to the problems of degradation on power and cleaning efficiencies results from the resonant frequency deviations of ultrasonic transducers due to load changes on cleaning tanks. For this purpose, a special software algorithm is developed. Since its operation has the property of frequency sweeping in a narrow frequency band, more homogenous cleaning patterns have been observed after the foil tests, and the related results are included in this article. Moreover, temperature and timing controls, and also protections against possible short circuits in the power unit are among the additional properties of the designed generator. It can easily be adapted to the multi-frequency ultrasonic cleaning systems by additional commands into the software running on the microcontroller. Keywods: Ultrasonic cleaning, microcontrollers, ultrasonic generators.

Separation of original paintings of matisse and his fakes using wavelet and artificial neural networks

Abstract: SEPARATION OF ORIGINAL PAINTINGS OF MATISSE AND HIS FAKES USING WAVELET AND ARTIFICIAL NEURAL NETWORKS

A single/double precision floating-point multiplier design for multimedia applications

Abstract: Modern graphic processors, multimedia processors, and general-purpose processors with multimedia extensions provide SIMD floating-point instructions. SIMD floating-point multiplication is commonly used in 2D and 3D applications, which mostly use single precision floating-point operands. Consequently, efficient single precision multiplier units are crucial for high performance systems. This paper introduces a novel floating point multiplier that can perform either a double precision or two parallel single-precision floating-point multiplications. The proposed design uses approximately 10% more hardware and has 33% more delay compared to a conventional double precision floatingpoint multiplier.

Optimal trajectory planning for control of nuclear research reactors using genetic algorithms and artificial neural networks

Abstract: In this study, an optimal trajectory planning based on artificial neural networks and genetic algorithms was proposed for control of nuclear research reactors. The trajectory being followed by the reactor power is composed of three parts. In order to calculate periods of all parts of the trajectory, a period generator was designed based on a feedforward neural network. Period values of the trajectory used to train the artificial neural network were acquired by utilizing genetic algorithms. The contribution of the proposed trajectory to the reactor control system was investigated. Furthermore, the behavior of the controller with the proposed trajectory was tested for various initial and desired power levels, as well as under disturbance. It was seen that the controller could control the system successfully under all conditions within the acceptable error tolerance.

Gps helix antenna design

Abstract: The Ground positioning through GPS-Global Positioning System has earned extreme significance in the recent years and has various applications. GPS is well-developed system which was initially established for military objectives and later showed itself in civil applications. It consists of three parts as control, space and user. Receiver antennas are one of most important mechanism which is used on the user side. These antennas have specific central frequency with narrow reception bandwidth and a beam width must be capable of receiving signals coming from low horizontal angles and also the structure should be sensitive to right-hand circular polarized waves. In this study, a receiver antenna which is designed in helix form has been implemented for civil GPS applications. In the case when the designed antenna did not meet the required criteria, it was observed that the problem arose from impedance mismatching between the antenna and transmission line and a passive impedance matching circuit has been used in order to eliminate this problem.