Control and protection of a doubly-fed induction generator system

A control system for a double-fed induction generator (DFIG) comprising a rotor (1) having rotor windings and a stator (2) having stator windings connectable to a grid for electric power distribution;

• said control system comprising a converter (170, 171), said converter comprising the following components:
• a rotor-inverter (71-73) connectable to the rotor windings of the generator,
• a grid-inverter (74-76) connectable to the grid and/or to the stator windings, and
• a DC-link (77) for feeding the rotor-inverter;
• the converter (170, 171) further comprising a clamping unit (190) for protecting the converter from damage due to over-currents in the rotor windings, said clamping unit (190) being connectable over the rotor windings and arranged to be triggered from a non-operating state to an operating state following detection of an over-current in the rotor-windings, said clamping unit comprising a clamping element (290) arranged so that
• when the clamping unit is in its non-operating state, currents in the rotor windings cannot pass through said clamping element, and
• when the clamping unit is in its operating state, currents in the rotor windings can pass through said clamping element,
• the clamping unit further comprising for each phase of the rotor, a connector (300) for connection to the respective rotor phase, each connector being connected to a trigger branch comprising, in series:
• a point of connection (297) of the clamping unit, to the connector (300) for connection to the respective rotor phase;
• a thyristor (295) for triggering the clamping unit;
• the clamping element (290);
• a diode (296);
• and the point of connection (297) to the connector (300) for connection to the respective rotor phase,
• said clamping element comprising at least one passive voltage-dependent resistor element (291, 292, 293, 294) for providing a clamping voltage over the rotor windings.