Frequency converter for a double-fed asynchronous generator with variable power output and method for its operation

A method for operating a frequency converter for a double-fed asynchronous generator having a rotor, a stator and a variable power output, and which can be connected to a voltage network, the frequency converter comprising:

• a rotor rectifier, adapted to be connected to the rotor of the asynchronous generator, said rotor having two direct voltage outputs;
• a network frequency converter, adapted to be connected to the voltage network:
• two direct voltage inputs;
• and
• an intermediate circuit, which can be connected to each direct voltage input via a first connecting line;
• wherein said intermediate circuit contains a semiconductor switch disposed between the direct voltage outputs, an intermediate circuit capacitor disposed between said direct voltage inputs, second and third connecting lines connecting said semiconductor switch and the intermediate circuit capacitor and a diode disposed in one of said connecting lines,
• wherein the method comprises the steps of:
• closing said semiconductor switch during sub-synchronous operation of the asynchronous generator, and
• opening said semiconductor switch during at least portions of synchronous or super-synchronous operation of the asynchronous generator;
• and
• wherein the network frequency converter is operated while the asynchronous generator is not in operation.