Microcontroller based control card of an AC drive

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Dr. Varjasi István
Department of Automation and Applied Informatics

With renewal energy sources becoming more widely used, and electric drives requiring more sophisticated design methods, the manufacturers of these devices face a great challenge. One of these companies is PROCON Hajtástechnika Ltd. One of their most succesful product line is the low power V3D family used in the control of electric motors in many industrial applications. An inverter of this type is also used by the Power Electronics laboratory of the Budapest University of Technology for industrial applications with their custom programs. The device is controlled by a card built around a TMS320F2808 microprocessor by Texas Instruments. The Texas 28xx series controllers are developed specifically for usage in switching power converters such as power supplies or in the drive of electric motors. The processors feature built-in support for these applications with their advanced peripherals. Howewer, in recent years the MCU has started to show its limitations. It does not support floating point operations, making the development process longer, while the on-chip memory limits the number of applications. My supervisor and I came to the conclusion that a replacement was needed using one of the more recent foating point MCUs of the same product family. The TMS320F28069 seemed to be the best solution, offering backwards compatibility with the functions of the older card. My task was to design a new card with the selected processor, that can fulfill the duties of the previous one. To begin the design process, I studied the previus card, as well as the functions and peripherals of the MCU. When selecting the replacement I had to make sure that it has all the required peripherals. I also had to select a packaging suitable for manual soldering in the laboratory, without the need for industrial equipment. The size of the packaging was constrained by the size of the board. The new MCU required a different voltage regulator, a new external crystal oscillator, and several other components. For the design I used Altium Designer, in which I had to create these components including their schematic symbols and footprints. When designing the schematic the parameters provided by the manufacturer, and the needs by my supervisor had to be considered. The aforementioned requirements were necessary to make the board suitable for other inverters, and to be modified for further applications. The final stage of development was creating the printed circuit board. Since the card will be used in high power applications, it had to be designed in a way that it will remain functional in these environments. The technological limitations of the PCB manufacturer was also taken into consideration. Finally I compared the software requirements for each MCU to ensure compatibility with existing applications. The new card offers faster development, as well as larger memory for more paralell applications, thus easing the work of the department.


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