AC drive main circuit conducted electromagnetic interference design during concept phase of the development cycle
Leppäaho, Oskari (2015)
2015
Teknis-luonnontieteellinen koulutusohjelma
Luonnontieteiden tiedekunta - Faculty of Natural Sciences
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Hyväksymispäivämäärä
2015-03-04
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201502161063
https://urn.fi/URN:NBN:fi:tty-201502161063
Tiivistelmä
Variable frequency drives (VFDs), also known as AC Drives, are used to control the rotational speed and torque of electric motors. They do the control mostly by applying short voltage pulses that generate a controlled current in the motor winding to provide the desired speed and torque of the motor. The voltage pulses are changed in microsecond scale, but their edges show voltage changes happening in nanosecond scale. This causes unwanted high frequency currents that flow through the electrical grid supplying the drive. Those currents are called as conducted electromagnetic interference (EMI).
Previously, a common way to address the electromagnetic interference problems has been to test against standards and use the knowledge gained for filter design. This can lead to serious delays in the product development. In this thesis, the target is to find a method to secure the VFD EMI performance already in the concept phase of the product design and to use that knowledge for filter design considerably earlier than before.
The voltage pulses generated by the drive are analyzed in frequency domain and that excitation is then transferred to source interference for filter design work. After the filter has been designed, the results are verified with a prototype drive measurements.
The thorough analysis of the main circuit emission sources and propagation routes provides a lot of insight to the emergence of the conducted emissions and their significant routes. The most important properties are the used voltage and switching speed in the emissions side and the motor cable in the propagation route side.
For future, a lot of work remains to be done in comparing different design choices e.g. motor cable type, dimensions, and materials. To advance further in the product design, the next step would be to improve the models to take into account the challenges of development phase with coupling of different filters and current routes. The excitation source could be improved to take into account the intermodulation products of different phases and also the practical limits in the modulation diverging from the ideal as e.g. dead time. Also, analysis of different inverter bridge realizations would provide more future insight.
Previously, a common way to address the electromagnetic interference problems has been to test against standards and use the knowledge gained for filter design. This can lead to serious delays in the product development. In this thesis, the target is to find a method to secure the VFD EMI performance already in the concept phase of the product design and to use that knowledge for filter design considerably earlier than before.
The voltage pulses generated by the drive are analyzed in frequency domain and that excitation is then transferred to source interference for filter design work. After the filter has been designed, the results are verified with a prototype drive measurements.
The thorough analysis of the main circuit emission sources and propagation routes provides a lot of insight to the emergence of the conducted emissions and their significant routes. The most important properties are the used voltage and switching speed in the emissions side and the motor cable in the propagation route side.
For future, a lot of work remains to be done in comparing different design choices e.g. motor cable type, dimensions, and materials. To advance further in the product design, the next step would be to improve the models to take into account the challenges of development phase with coupling of different filters and current routes. The excitation source could be improved to take into account the intermodulation products of different phases and also the practical limits in the modulation diverging from the ideal as e.g. dead time. Also, analysis of different inverter bridge realizations would provide more future insight.