Abstract
The research activity, carried out during the three-years doctorate course, has been divided in two general topics. The first one was focused on the thermal problems within the power electronic devices and systems while the second one consisted of the design, simulation, practical realization and testing of power electronic circuits for AC voltages regulation within motorcycles.
Within the first topic, a new steady-state thermal simulation code, purposely designed for the power electronic devices and systems, with their assembling structures, was developed.
This code, which has been called DJOSER, is based on the direct analytical resolution of the heat transfer equations for a structure composed by a stack of homogeneous layers. Due to its speed and the wide set of available boundary conditions, it is a strong candidate to replace the commercial expensive programs based of the finite elements calculation technique, with the same accuracy degree. Other activities directly connected to this argument include the theoretical and experimental validations of the DJOSER results and several thermal analyses on real systems suggested by industrial partners within close collaborations. Finally, the DJOSER thermal simulator was successfully used in a electro- thermal simulation loop program, developed for the study of the electro-thermal behaviour of power bipolar transistors with cellular structures. In particular the so-called HOT-SPOT phenomenon was extensively studied and some countermeasures were proposed.
A further research activity concerned the practical and experimental implementation of the thermo-reflectance measurement system for the dynamic temperature characterization of power electronic device. This technique allows a contact-less temperature measurement of a surface, by using the reflected beam at a fixed wavelength in the near infra-red (where both lasers and detectors are available) and using the temperature dependence of the reflection coefficient. The optical apparatus was built and the control electronics was designed and realized. It was possible to record the thermal transient of a purposely built sample in order to apply the thermal resistance measurement method TRAIT, able to yield the dynamic equivalent thermal circuit of the sample with its packaging structure. The results were also validated by means of accurate thermal analyses performed with DJOSER.
In the framework of the second general topic, a new and innovative AC voltage regulator for permanent magnets generators, and specifically for electronics of motorbikes without battery and for low power eolic generation systems has been designed . The innovative aspect of the project is the kind of regulation, series instead of parallel (switches are connected in series to the generator), which avoid short circuiting of the generator, supplying of high currents and breaking torques. The project has been made and experimentally proven directly on an alternator, both in the first version with the control part built with discrete and integrate analog components, and in one other version in which the control was realized directly with a microcontroller. The project has an Italian patent and is waiting for the approval of the international patent (PCT).
