Circuit arrangement for speed control of three-phase motors

摘要

If a medium power three-phase motor (1) is supplied via a converter (1) for speed control purposes, and if a transformer (6) is connected between the converter (1) and the three-phase motor (2) for voltage matching to a medium-voltage network, the starting of the three-phase motor (2) at a very low voltage and frequency leads to saturation of the transformer (6). In order to avoid this situation, the converter (1) is connected directly to the motor (2) in the lower frequency and voltage range, bypassing the transformer (6). Once the converter (1) has reached its maximum possible voltage, the transformer is initially magnetised and is subsequently connected between the converter (1) and the three-phase motor (2), so that it is possible to increase the motor voltage further. <IMAGE>