Undersynchronous and oversynchronous current rectifier cascade and method for operating it

摘要

Undersynchronous and oversynchronous rectifier cascades having an asynchronous machine (5) with a slip-ring rotor, in which the slip power released when running undersynchronously as a motor or over- synchronously as a generator is fed back to the power supply network (1) via an invertor (36), are used for driving pumps, ventilators and compressors in the power range from 500 kW to 5 MW. in order that the undersynchronous and oversynchronous rectifier cascade can also be used as a generator in the undersynchronous region and as a motor in the oversynchronous region, the invertor (36) is operated with a DC intermediate circuit such that the intermediate circuit current (Id) disappears for a short period so that commutation of the valves of a rectifier (10) on the machine side is possible. In this way, the rotor current of the asynchronous machine (5) is predetermined by means of a coordinate converter (31), via a trigger pulse transmitter (23) on the machine side, in terms of its magnitude (Is) and phase angle ( phi ). A zero-current detector (26) is used to determine whether the intermediate circuit current (Id) is 10 A for a predeterminable short time interval of 10 mu s, and the voltage on the thyristors of a rectifier (12) on the mains side is 20 V, in order that the commutation of the thyristors of the rectifier (10) on the machine side can be released via the trigger pulse transmitter (23) on the machine side. IMAGE