Research

Electrical Machines transient phenomena

The electrical machines’ dynamic behavior and the appearing transient phenomena is a very important domain of research for the machine's robust design and reliable operation. L.EM.E.C. has a wide volume of work to display in this area, concerning mainly the motors and generators transient behavior analysis, where many models have been introduced in order to study critical transient phenomena.

Electromechanical systems simulation

Many mathematical models have been developed in L.EM.E.C. in order to simulate and study transient states of complex systems and circuits consisting of electrical machines and electronic power converters. Systems of this kind are often characterized by significant lack of linearity and variable topology of the models describing the system. A number of special techniques that were developed in L.EM.E.C., helped in the further study of such complex systems consisting of electrical machines of all types and various electronic power converters. Particular attention was paid to systems consisted of synchronous and asynchronous machines and PWM power converters.

Design and Development of electronic drives for power semiconductors switch operation triggering

Many thyristors and power transistors triggering electronic devices were designed and developed in L.EM.E.C for use in AC/DC or DC/AC (single or three phase) voltage converters with variable frequency and active ratings. For these circuits both sequential electronics and programmable microprocessors have been used.

Design and development of motor drive systems and control systems for electric motors

Besides power electronics triggering devices, many other electronic systems for electrical machines' automation have been developed in L.EM.E.C. These machines are connected to power supply through special electronic power converters (bridges, PWM inverters, chopper etc.). Very significant for the machines' automatic control systems design is also the role of microprocessor circuits that leaded in powerful and flexible designs.

Electronic power inverters and synchronous machines powered electromotive systems

Problems related to starting of synchronous motors have been studied extensively. Original circuits and techniques have been invented in L.EM.E.C., concerning especially the synchronous machine inverters operation for the machine DC voltage supply during the starting phase, as the synchronous machine internal voltage is not sufficient to supply the power semiconductor circuits. (Machine speed <10% of the nominal rate). The research on this special issue is carried out in the lab by means of both computerized simulation and experimental work, while the necessary circuits have been constructed and tested by L.EM.E.C researchers.

Electrical vehicles electromotive system research

The propulsion system of an electrical car (motor, inverter, batteries and control) has been studied in L.EM.E.C. for the construction of a prototype vehicle. This project was carried out in cooperation with third party partners for an R&D program called "STRIDE-HELLAS" 1991-1993. A state-of-art electronic power converter based on IGBT technology was developed in L.EM.E.C. for this purpose. A simulation circuit setup was also developed to simulate the on-road load of an actual electrical car, in order to experiment in the lab with motor loading of a real electrical vehicle. A related area of research is being currently investigated regarding the functional characteristics of the electrical vehicle and the motor electromagnetic field interference through special measurements equipment.

Electronic power converters based on innovative power semiconductor elements research

A domain of research currently investigated in L.EM.E.C. is the use of new semiconductor elements G.T.O, I.G.B.T and MOSFET replacing thyristors in power electronic converters. These elements appear to have advantages concerning the ease of switching operation and a better performance in high frequency. The technical characteristics of the elements as well as the suitable techniques used allow the development of various PWM methods targeting in the higher harmonics reduction, as well as the reduction of the used passive elements size (inductors and transformers).

Photovoltaic energy conversion and storage research

L.EM.E.C. researchers have designed and constructed electronic devices based on power transistors for the batteries charging from photovoltaic resources. These applications have some special designing requirements regarding the high efficiency and small weight and size, as most of these converters target in mobile applications. Part of this research was also the accumulators modeling for a simulator's development in the lab, in order to help studying and testing the constructed converters. The whole system was a part of a project funded by Greek Renewable Energy Resources Center.

Aeolic to electrical energy conversion research

Many diploma projects concerning the fluid-mechanics behavior of wind generators and generally the aeolic to electrical energy conversion have been so far completed in L.EM.E.C. A low power installation for the aeolic to electrical energy conversion was designed and constructed for the basic study of the fundamental principles of this conversion. Many other projects have been worked out for the simulation and study of aeolic to electrical energy conversion integrated systems.

Electronic power converters design and construction

Electronic power converters of many kinds and sizes have been designed and developed in L.EM.E.C. (Network driven single phase and three phase bridge, choppers, forced driven single phase and three phase inverters, load driven inverters, PWM controlled inverters for constant V/f ratio, etc.). Vector control driven inverters for asynchronous machines control, using special purpose microprocessor circuits (i.e. DSP) have also been developed. Resonant type converters have been developed for use in induction heat installations. Quasi-Resonant type converters is another area were there has been done significant work through extensive study, simulation and system construction in applications for power semiconductor supply devices operating in high switching frequency (up to 1.5 MHz). Research has been done also in power factor correction circuits.

 

All the work done targets in the know-how acquisition in the scientific areas mentioned above. A number of several dozens of people work or have worked in L.EM.E.C. for these projects as permanent research associates, Ph.D. researchers or electrical engineering graduates working on their diploma project. Many of these projects were funded from third party research institutes, from the European Union, from state scientific organizations and the local or foreign industry. Besides all the acquired knowledge through the years, L.EM.E.C.'s work leaded in more than 200 diploma projects completed already, in over a dozen Ph.D. diplomas and in a large number of publications in world-wide distinguished scientific journals and conferences.

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