Stanimir VALTCHEV
Auxiliary Professor in the Department of Electrical Engineering, Faculty of Science and Technology, Universidade NOVA de Lisboa, Portugal, Invited Full Professor of Burgas Free University, Bulgaria
Research interests:
power converters, energy harvesting, wireless energy transfer, electric vehicles, energy management and storage, non-destructive testing, bio energy-harvesting, and biosensors
Keynote address:
Regulation and Command Systems in Power Converters with a Special Emphasis on the Resonant (and Wireless Energy) Converter
Abstract:
The regulation and control of the power converters depends mostly on the gradual development of the power processing electronic devices. In the middle of the XX century the vacuum tubes were substituted by ignited devices (ignitrons) which corresponded better to the principles of the lossless conversion (switching processes), but only for the lowest frequency of operation. The emerging thyristors took the place of switching devices and are recently replaced by new sophisticated devices, even in very high power applications, e.g. HVDC. All the time the technology was seeking for the best possible efficiency of conversion. As a result in the end of 1960s the resonant process of soft switching (later: soft-transition, as well) entered into the practical technology. For the thyristors this mode of operation was vital to reach a reasonably high frequency of operation but the resonance came out to be also useful for the newly emerging fully controlled devices: transistors, MOSFET, IGBT, etc. Recently the wireless energy transfer, together with the previously existing induction heating and other technological applications also obliged to resonance in their operation. Some examples are presented of the hard-switched and soft-switched converters. For the hard-switched converters the most used regulation is the PWM, but other methods are also listed. Unfortunately the resonant processes have a more complicated nature than the classical "hard-switching" process, because of the internal exchange of energy in the 2 or more reactive elements (energy tanks). Several basic control methods may be considered applicable, in order to maintain the operation of the resonant converter stable and efficient. Those methods must keep special attention to the stored energy when the converter transfers the energy wirelessly. Some basic solutions are described: frequency mode (FM), pulse-width mode (PWM), phase-shift mode (PhSM) and finally, instantaneous and predictive methods are described, based on the calculation of each individual energy portion sent through the reactive elements of the resonant tank (or tanks). Practical results are demonstrated to prove the viability of the method. Some higher-frequency resonant processes are not capable (for the moment) to be controlled instantly because of their speed. The resonant converters that correspond to this definition must be considered also, as they are applied to the coreless and waveguide transfer of energy (multi-megahertz dielectric heating, gigahertz rectenna grids, etc.).
The main goals of the keynote:
• to list systematically and historically the concepts of power converters regulation and command;
• to show a modern, fast (if possible, instantaneous) and safe method of resonant converter control;
• to predict the future control systems based on the necessities of the emerging power converters.
The main goals of the keynote:
• to list systematically and historically the concepts of power converters regulation and command;
• to show a modern, fast (if possible, instantaneous) and safe method of resonant converter control;
• to predict the future control systems based on the necessities of the emerging power converters.
Stanimir VALTCHEV was born in Bulgaria 1951, received M.Sc. from TU Sofia, awarded as the best of the year 1974, received PhD from IST in Lisbon. He worked on semiconductor technology, medical equipment, and then as a researcher in industrial electronics (laser supplies and high-frequency power converters). In the 1980s worked in the Robotics Laboratory of TU Sofia (also being Assistant Director of the Centre of Robotics). During 1987 and in 1991-1992 he worked in the Laboratory for Power Electronics of TU Delft in the Netherlands, as Assistant Professor. Since 1988 was Assistant Professor in TU Sofia and taught several courses on Power Supply Equipment and Power Transistor Converters to graduate and post-graduate students. He was the Deputy Dean of TU Sofia, responsible for the international students in 1990-1994. After 1980 he worked on high-frequency resonant power converters and published in numerous conferences and journals (IEEE Meritorious Paper Award, 1997). In 1994 being invited to Portugal to lead a project of a new soft-transition power converter, stayed and taught various subjects in different universities and has consulted various institutions in Portugal and in the Netherlands. He is currently Auxiliary Professor in UNL and Invited full professor in BFU, Bulgaria. His research includes power converters (also resonant and multilevel), energy harvesting, wireless energy transfer, electric vehicles, energy management and storage, bio energy-harvesting, and biosensors.
