FOR 575:  Parasitic Effects at Elevated Frequency in Inverter-fed Drive Systems

• Subject Area: Computer Science, Systems and Electrical Engineering
• Term: from 2005 to 2008
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5471635

Inverter-fed drives with IGBTs (insulated gate bipolar transistors) are available up to blocking voltages of about 6 kV. The fast switching within several nano-seconds from zero to DC link voltage generates travelling wave phenomena between inverter and electrical machine, causing due to reflections at the machine terminals considerable over-shoot of voltage. Further the common-mode voltage, pulsating with switching frequency, leads to parasitic currents at elevated frequency e.g. in the machine bearings, causing bearing failure. The increased voltage stress of the machine winding forced manufacturers to insulate even low voltage windings with improved insulation systems for inverter operation. The development of IGBTs for higher blocking voltages transfers this problem also to medium voltage level (above 1 kV). To mitigate these effects, different filter topologies have been designed at the inverter output or at the motor input; special winding design has been developed to protect the first coils in the motors, which are most stressed. Upgrading of insulation materials was necessary for low and medium voltage insulation level.
With six projects the following aims are envisaged:
-- Numerical prediction of high-frequency capacitive currents of AC induction and permanent magnet (PM) synchronous machines between winding and housing, in the bearings and in other machine parts.
-- Numerical prediction and comparison of inverter-induced additional losses in AC induction machines, PM synchronous machines and switched reluctance machines.
-- Development of improved numerical models for electric stress in selected components of drive systems such as lubrication film of ball bearings, silicon structures of power modules, and in varistors for over-voltage protection.
-- Establishment of numerical models for calculating travelling wave phenomena in inverter-cable-motor systems, based on recent experimental experience of industry and research labs.
-- Testing and designing of special varistors for over-voltage protection due to reflections in inverter-motor systems, which is a demanding task due to the high repetition rate in kHz-range and is a new application for varistors.
-- Influencing the steep voltage surges at the inverter output by modifying the switching behaviour of the IGBT power modules, which shall be accomplished by special gate drive units.

• DFG Programme: Research Units

Projects

• Einsatz von Mikrovaristor-Füllstoffen in der Isolation umrichtergespeister Antriebe (Applicant Hinrichsen, Volker )
• Erweiterte Transmission-Line Modelle für elektrische Antriebe mit Multi-Rate Zeitintegration (Applicant Gjonaj, Erion )
• Feld-Netzwerk gekoppelte Simulation mittelfrequenter Phänomene in umrichtergespeisten Antrieben (Applicant De Gersem, Herbert )
• Höherfrequente Parasitäreffekte in Antrieben mit unkonventionellen Umrichtern (Applicant Mutschler, Peter )
• Lagerimpedanz und Lagerschädigung bei Stromdurchgang in umrichtergespreisten elektrischen Maschinen (Applicant Binder, Andreas )
• Motorfreundlicher hocheffizienter Antriebswechselrichter (Applicant Mutschler, Peter )
• Multiskalen-Modelle für Wicklungen mit heterogenen Materialverteilungen unter Berücksichtigung von kapazitiven Effekten (Applicant Weiland, Thomas )
• Vergleichende Untersuchung von Verlusten in umrichtergespeisten Maschinen durch höherfrequente Stromanteile in Zeitschrittverfahren (Applicant Binder, Andreas )

• Spokesperson: Professor Dr.-Ing. Andreas Binder