DSpace Angular ::Πλοήγηση Σχολή Ηλεκτρολόγων Μηχανικών και Μηχανικών Υπολογιστών ανά Ημερομηνία έκδοσης

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Power Optimization of Wind Electric Conversion Systems Integrated into the Utility Grid

(Wind Engineering, 1982) Kalaitzakis K.C; Vachtsevanos, G.J

This paper is concerned with the interconnected operation of WECS with the utility grid.Specifically ,it addresses problems of stability , protection and power flow optimization from the WECS to the power lines. The approach followed contains both a theoritical and a experimental component.A variable-speed constant-frequency wind electric system utilizing a synchronous generator and line-commutated inverter provides experimental verification of computer simulation studies for the dynamic and steady-state performance of the interconnected system. Simulation results indicate that the transient bahavior of the wind electric-power grid system is satisfactory with appropriate devices providing adequate protection to both the wind generator and the utility grid from a variety of fault conditions. A maximum power tracking mechanism has been designed for the continuous matching of the wind-electric generator to the grid impedance characteristics.As a result,maximum electric power is transferred from the wind machine to the power lines.Computer simulation studies of this type of operation indicate the substantial improvement in power transfer that is achieved. The proposed scheme tends to minimize equipment and maintenance costs while maximizing the energy transfer capabilities of the wind-electric conversion system and maintaining a high degree of reliability in overall system performance.

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Design of a Power Conditioning Unit for Nonlinear Source-Load Systems

(Institute of Electrical and Electronics Engineers, 1984) Kalaitzakis K.C; Vachtsevanos, G.J

This paper describes the development, design, and operation of an electronic device which performs dynamic matching between electric energy sources and their respective loads. This matching is achieved by monitoring the output power of the energy source and modulating a control signal which, in turn, regulates appropriately the operation of a source-load interface device. This device is characterized by a simple structure and an ability to continuously match the characteristics of the source to those of the load, for maximum power transfer, even when these characteristics are randomly time-varying. The device may be used with existing energy systems, without significant changes, and operates effectively even when the utility grid substitutes for the load. Its operation is described in terms of a configuration involving renewable energy sources, such as wind electric conversion systems and photovoltaic arrays, as the primary energy generators. The latter are attracting the growing interest of many investigators recently.

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Maximum Power Transfer in Non-Linear Source-Load Systems

(John Wiley and Sons, 1984) Vachtsevanos, G.J; Kalaitzakis K.C

This paper is concerned with the conceptual design and realization of matching networks for the continuous transfer of maximum power from a non-linear source with randomly varying characteristics to a load. Such sources are commonly encountered in the use of photovoltaic arrays or wind energy conversion systems for the production of electric power. Experimental studies as well as computer simulation results verify the validity of the design and point to methods for its practical implementation.

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Correlation Study of Arterial Blood Pressure Level to the Amplitude of the Pressure Pulse Waveform

(Butterworth & Co Ltd, 1984) Vachtsevanos, G.J; Kalaitzakis K.C; Papamarkos, N; Ziakas G.; Economou K.; Gemitzis K.

Automated blood pressure measurements are usually characterized by poor operational reliability and a considerable degree of complexity in performing the measurement. This paper introduces a new technique for the indirect measurement of the systolic and diastolic blood pressure of an individual. The technique is based upon a statistically consistent relationship between the amplitude of the pulsative pressure waveform at the systolic and diastolic points, and the amplitude of pulse signals detected when the artery is fully occluded. Clinical testing and statistical analysis techniques are used to derive appropriate numerical values for these relationships. The proposed procedure thus incorporates an adaptive measurement philosophy achieving minimum observer involvement and consequently high instrument accuracy. Overall measurement errors are maintained well within proposed standards for automated sphygmomanometers.

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Penetration of Wind Electric Conversion Systems into the Utility Grid

(Institute of Electrical and Electronics Engineers, 1985) Vachtsevanos, G.J; Kalaitzakis K.C

This paper is concerned with the development of appropriate models for the interconnected operation of wind generator clusters with an autonomous power system and simulation techniques for the study of the degree of penetration of such wind electric conversion devices when operating in parallel with the utility grid. The quality of the interconnected system performance is specified in terms of operational constraints and the resultant penetration strategy is implemented via a microprocessor-based control scheme. The strategy assures a satisfactory level of system performance while optimizing the available energy transfer from the wind generators to the utility grid.

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Design and development of a new electronic sphygmomanometer

(Kluwer Academic Publishers, 1985) Vachtsevanos, G.J; Kalaitzakis K.C; Papamarkos, N

The paper introduces a new technique for the indirect measurement of the systolic and diastolic blood pressure in humans. The technique is based upon a statistically consistent relationship between the amplitude of the pulsatile pressure waveform at the systolic and diastolic points and the amplitude of pulse signals detected when the artery is fully occluded. An adaptive measurement philosophy has been implemented in the design of an electronic sphygmomanometer which, in addition to a pressure transducer, contains suitable electronic instrumentation for processing and displaying the electronic signals. Verification of overall system accuracy is accomplished with direct comparison with manual auscultatory measurements. Clinical testing of a prototype indicates a satisfactory performance; measurement errors are maintained well within proposed standards for automated sphygmomanometers.

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On the control and stability of grid connected photovoltaic sources

(Institute of Electrical and Electronics Engineers, 1987) Kalaitzakis Kostas; Καλαϊτζακης Κωστας; Vachtsevanos, G.J

A methodology is proposed for the effective integration of photovoltaic (PV) devices into the electric utility distribution network operations. The dispersed PV generator is viewed as an active device used to improve system stability by appropriately modulating the power conditioning unit's output power. Disturbances on the utility system can be damped out by injecting this power into the grid in such a way so that the net effect is a cancellation of undesirable oscillations. The approach is implemented by monitoring the oscillating power and generating control signals which shape accordingly the interface unit's output power. Successful implementation of the scheme relies heavily on the speed and flexibility with which the electronic inverter moves power from the primary source/storage facility to the utility lines. Simulation studies, using the proposed control approach, indicate that application of these policies may result in reduced load following requirements for conventional power generating units, increase the value and acceptability of new energy technologies, and improve power quality and stability of the interconnected system.

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A Methodology for Dynamic Utility Interactive Operation of Dispersed Storage and Generation Devices

(Institute of Electrical and Electronics Engineers, 1987) Vachtsevanos, G.J; Kalaitzakis K.C

This paper is introducing a new methodology for the dynamic integration of dispersed storage and generation devices into the electric utility distribution network operations. The dispersed source is viewed as an active device contributing towards the regulation of real and reactive power flows while improving the stability of the power system. Conceptual means are developed for an effective DSG-utility grid interface. Computer models of appropriate interconnection and control equipment are used in simulation studies to test the effectiveness of control strategies and optimize design parameters. Simulation results indicate that load frequency control and voltage regulation may be effectively accomplished with dispersed generators within a fraction of the time required for conventional regulating units. Appropriate modulation and conditioning of the DSG-output power can assist in damping out undesirable power oscillations. Implementation of the proposed policies may result in reduced load following requirements for conventional power generating units, increase the value and acceptability of new energy technologies, and improve power quality and stability of the interconnected system.

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A Hybrid Photovoltaic Simulator for Utility Interactive Studies

(Institute of Electrical and Electronics Engineers, 1987) Vachtsevanos, G.J; Kalaitzakis K.C

An analog-digital photovoltaic (PV) array simulator is considered. The analog section is designed on the basis of an equivalent solar cell model while the digital section is constructed realizing the mathematical representation of the array. Fast time responses achieved by the analog section make this part suitable for the study of transient phenomena associated with the interconnected operation of PVs and the utility grid. Its digital counterpart is more appropriate for long-term experimental investigations due to its inherent accuracy and reliability. The combined hybrid simulator offers a versatile and flexible piece of apparatus capable of simulating the performance of any PV array under a variety of operating conditions. The device can be constructed with low-cost components in a compact arrangement offering transportability and ease of operation. Experimental results derived from a laboratory constructed prototype match closely the theoretically computed characteristics.

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Development of a microprocessor-based adaptive technique for blood pressure measurements.

(Kluwer Academic Publishers, 1989) Kalaitzakis Kostas; Καλαϊτζακης Κωστας; Papamarkos, N; Vachtsevanos, G.J

The paper introduces a new microprocessor-based adaptive technique for the indirect measurement of the systolic and diastolic pressure in humans. The technique is based upon a statistically consistent relationship between the amplitude of the pulsative pressure waveform at the systolic and diastolic points and the amplitude of pulse signals detected when the artery is fully occluded. An adaptive measurement philosophy has been implemented in the design of an electronic analog-digital sphygmomanometer which, in addition to a pressure transducer, contains suitable electronic instrumentation for processing and displaying the electronic signals. A dedicated microprocessor is used to store statistical relations and control the operation of the device. Verification of overall system accuracy is accomplished via direct comparison with manual auscultatory measurements. Clinical testing of a prototype indicates satisfactory performance; measurement errors are maintained well within proposed standards for automated sphygmomanometers.

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Design of a Microprocessor-Based Sphygmomanometer.

(Biomedical Instrumentation and Technology, 1990) Kalaitzakis Kostas; Καλαϊτζακης Κωστας; Papamarkos, N; Vachtsevanos, G.J

This paper describes the implementation on a microprocessor of a new method for the indirect measurement and recording of the systolic and diastolic blood pressure in humans. The technique is based on a statistical analysis of the cardiac pulse pressure signal. Polynomial relations are derived between the amplitude of the pulsatile pressure waveforms at the systolic and diastolic points and the amplitude of pulse signals detected when the artery is fully occluded. With the dual objective of automating the measurement procedure and minimizing errors, an electronic analog-digital sphygmomanometer that contains suitable electronic instrumentation was developed. The functions of processing the pressure signal, automating the measurement, and recording the results are performed and controlled by a microprocessor. A laboratory prototype embodying this approach was constructed and its performance and reliability were verified using a series of clinical tests. The test results indicate that the device is accurate within acceptable bounds for automated blood pressure instruments.

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A Simulation Model for the Reliable Integration of a 4.5MW Wind Farm into the Power Grid of the Crete Island

(Taylor & Francis, 1990) Kalaitzakis Kostas; Καλαϊτζακης Κωστας; Stavrakakis Georgios; Σταυρακακης Γεωργιος

This paper describes a computer simulation model which has been developed to study the effects of integrating wind energy conversion systems (WECS) into autonomous power systems. The quality of the interconnected system performance is specified in terms of operational constraints. Load-flow and power-system-stability studies were preformed in order to evaluate the penetration impact of a 4·5 MW wind farm on the local grid fo Sitia-Crete. The results show that the above wind energy penetration level will not cause any problem to the existing electric power grid.

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Έμπειρο σύστημα ασαφούς λογικής για τον έλεγχο της θερμικής και οπτικής άνεσης στα κτίρια

(Πολυτεχνείο Κρήτης, 1992) Ντούνης Αναστάσιος Ι.

Μη διαθέσιμο

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Optimal PV system dimensioning with obstructed solar radiation

(Elsevier, 1996) Kalaitzakis Kostas; Καλαϊτζακης Κωστας

This paper describes an analytical methodology for the optimised design of stand-alone photovoltaic (PV) systems installed at locations where the solar radiation is considerably shortened by obstacles, i.e. at the bottom of a gorge. A method for the computation of the real available solar energy incident on the PV panel is proposed, based on easily conducted measurements. The optimum tilt of the PV array, under such conditions, is obtained and a dimensioning procedure provides the optimal size of the PV-array/storage. The resulting system is tested by a verification routine. A case study, employing the complete algorithm proposed, is illustrated.

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Size optimization of a PV system installed close to sun obstacles.

(Elsevier, 1996) Kalaitzakis Kostas; Καλαϊτζακης Κωστας; Stavrakakis Georgios; Σταυρακακης Γεωργιος

The assessment of the optimal size of a PV-array/battery-storage system, when the incident solar radiation is considerably obstructed, is presented in this article. An optimal dimensioning method is proposed based on a new procedure for the calculation of the actual solar radiation on the array surface, for installations located near obstacles. The optimum tilt of the PV array is also computed and the resulting optimal PV-array/battery-storage system is evaluated by an appropriate routine. The results of the application of the complete algorithm for a real case study inside a gorge are illustrated.

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Σχεδιασμός και υλοποίηση περιβάλλοντος μάθησης από απόσταση στο διαδίκτυο

(Μη διαθέσιμο, 2000) Στελλάκης Δημοσθένης

Μη διαθέσιμο

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Advanced fuzzy logic controllers design and evaluation for buildings’ occupants thermal–visual comfort and indoor air quality satisfaction

(Elsevier, 2001) Kolokotsa Dionysia; Κολοκοτσα Διονυσια; Tsiavos D.; Stavrakakis Georgios; Σταυρακακης Γεωργιος; Kalaitzakis Kostas; Καλαϊτζακης Κωστας; Antonidakis E.

The aim of this paper is to present and evaluate control strategies for adjustment and preservation of air quality, thermal and visual comfort for buildings’ occupants while, simultaneously, energy consumption reduction is achieved. Fuzzy PID, fuzzy PD and adaptive fuzzy PD control methods are applied. The inputs to any controller are: the PMV index affecting thermal comfort, the CO2 concentration affecting indoor air quality and the illuminance level affecting visual comfort. The adaptive fuzzy PD controller adapts the inputs and outputs scaling factors and is based on a second order reference model. More specifically, the scaling factors are modified according to a sigmoid type function, in such a way that the measured variable to be as closer as possible to the reference model. The adaptive fuzzy PD controller is compared to a non-adaptive fuzzy PD and to an ON–OFF one. The comparison criteria are the energy required and the controlled variables response. Both, energy consumption and variables responses are improved if the adaptive fuzzy PD type controller is used. The buildings’ response to the control signals has been simulated using MATLAB/SIMULINK.

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Local operating networks technology aiming to improve building energy management system performance satisfying the users preferences

(Taylor & Francis, 2001) Kolokotsa Dionysia; Κολοκοτσα Διονυσια; Kalaitzakis Kostas; Καλαϊτζακης Κωστας; Stavrakakis Georgios; Σταυρακακης Γεωργιος; Sutherland George; Eftaxias George

The available Building Energy Management Systems (BEMS), although they contribute to a significant reduction of energy consumption and improvement of the indoor environment, they can only be implemented in new buildings. Their installation in existing buildings is far from being cost effective due to the incompatibility of communication protocols between BEMS designed by various manufacturers and unavoidable modifications for data transmission. On the other hand, current research for energy efficient buildings has proved that although the design and the facilities including BEMS aim to satisfy the thermal and visual comfort plus the air quality demands while minimising the energy needs, they often do not reach their goals due to users interference. Latest trends in designing Intelligent Building Energy Management Systems (IBEMS) offer a Man Machine Interface that could store the users preferences and adapt the control strategy accordingly. The objectives of the present paper are to present the advantages of the use of a man machine interface based on a smart card terminal together with fuzzy control techniques in satisfying the users preferences plus to underline the capabilities that the LON network offers to the design. A fuzzy PID controller is developed to reach the first of the above objectives. The monitoring of the energy consumption along with satisfying the users preferences is achieved by the use of a suitable cost function for the whole system. All the above parameters as well as the cost function are kept between acceptable limits. The overall control system including the cost function is modeled and tested using MATLAB/SIMULINK. The implementation of the control system in an existing building requires interconnection of sensors and actuators installed across the building, is well served by the LonWorks technology due to its high standards and flexibility features.

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A fuzzy knowledge based method for maintenance planning in a power system

(Elsevier, 2002) Sergaki Amalia; Σεργακη Αμαλια; Kalaitzakis Kostas; Καλαϊτζακης Κωστας

The inspection planning in electric power industry is used to assess the safety and reliability of system components and to increase the ability of failure situation identification before it actually occurs. It reflects the implications of the available information on the operational and maintenance history of the system. The output is a ranked list of components, with the most critical ones at the top, which indicates the selection of the components to be inspected. In this paper, we demonstrate the use of a fuzzy relational database model for manipulating the data required for the criticality component ranking in thermal power systems inspection planning, incorporating criteria concerning aspects of safety and reliability, economy, variable operational conditions and environmental impacts. Often, qualitative thresholds and linguistic terms are used for the component criticality analysis. Fuzzy linguistic terms for criteria definitions along with fuzzy inference mechanisms allow the exploitation of the operators' expertise. The proposed database model ensures the representation and handling of the aforementioned fuzzy information and additionally offers to the user the functionality for specifying the precision degree by which the conditions involved in a query are satisfied. In order to illustrate the behavior of the model, a case study is given using real inspection data.

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Genetic algorithms optimized fuzzy controller for the indoor environmental management in buildings implemented using PLC and local operating networks.

(Elsevier, 2002) Kolokotsa Dionysia; Κολοκοτσα Διονυσια; Stavrakakis Georgios; Σταυρακακης Γεωργιος; Kalaitzakis Kostas; Καλαϊτζακης Κωστας; Agoris D.

In this paper, an optimized fuzzy controller is presented for the control of the environmental parameters at the building zone level. The occupants’ preferences are monitored via a smart card unit. Genetic algorithm optimization techniques are applied to shift properly the membership functions of the fuzzy controller in order to satisfy the occupants’ preferences while minimizing energy consumption. The implementation of the system integrates a smart card unit, sensors, actuators, interfaces, a programmable logic controller (PLC), local operating network (LON) modules and devices, and a central PC which monitors the performance of the system. The communication of the PLC with the smart card unit is performed using an RS 485 port, while the PLC-PC communication is performed via the LON network. The integrated system is installed and tested in the building of the Laboratory of Electronics of the Technical University of Crete.

Σχολή Ηλεκτρολόγων Μηχανικών και Μηχανικών Υπολογιστών

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