Suppression of torsional vibrations in rotor shaft systems by a thyristor controlled device

Torsional vibrations and resonances can cause problems in many applications of electrical machines ranging from industrial drives to large synchronous generators. The paper presents examples for torsional resonances measured in the IPP experimental power supply, an isolated power system based on flywheel generators. After a routine check of these synchronous machines, damage to a coupling of one rotor shaft system was revealed which can only be explained by an electromechanical resonance, it excited by active power transients from thyristor converter loads. Once the coupling was repaired, a novel power electronic device for damping the torsional vibrations was developed. The power circuitry of the device consists of a six-pulse thyristor bridge, which is connected to a magnet coil acting as a buffer storage of magnetic energy. The thyristor converter is feedback controlled with the measured first natural frequency of the shaft assembly. Thus, only little damping power is needed which results in a compact converter design. Up to now, two thyristor controlled devices were applied on different synchronous machines in more than 2000 dynamic load cases. Since they work demonstrably reliable and do not require modifications to the existing control or drive system, applications to special-purpose industrial drives are presently investigated.