The present disclosure relates to methods for operating wind turbines (10), in particular to methods for feeding wind turbine auxiliary systems when connection to the electrical grid (102) is lost. A method (100) comprises rotating a wind turbine rotor (18) at a first rotational speed by actively controlling a pitch angle of the plurality of rotor blades (22) while a safe condition is detected, and generating electric power; supplying at least part of the generated electric power to at least one wind turbine auxiliary system; detecting a specified condition; and in reply to the detection of the specified condition, rotating the wind turbine rotor (18) at a second rotational speed lower than the first rotational speed, and generating electric power.

A control system for controlling the operation of a doubly fed induction generator of an electrical power system, such as a wind turbine, is provided. A rotor side converter coupled to a rotor of the DFIG is controlled by the control system. The control system includes an outer controller to generate a reference value for a control variable in accordance with which the operation of the DFIG is to be controlled and an inner controller that receives the reference value and provides feedback control of the rotor side converter. The inner controller is a state feedback controller obtains at least one state of the power system or the power grid that is different from the control variable. The control structure of the state feedback controller causes the electrical power system to act as a passive system at least in a predefined frequency range.

A method of damping motion of a wind turbine, the wind turbine comprising a rotor and a floating platform. A motion signal is generated which is indicative of a motion of the wind turbine. A wind direction signal is generated which is indicative of a wind direction relative to the floating platform. A damping signal is generated on the basis of the motion signal and the wind direction signal, and the motion of the wind turbine is damped on the basis of the damping signal, for instance by adjusting the pitch of the rotor blades. A phase of the damping signal may be controlled on the basis of the wind direction signal.

A battery storage and/or a wind turbine including the battery storage. A generator for generation of an electric current. An electric flow path configured for conducting the electric current to an electric grid via a power converter, the power converter. The battery storage electrically connected to the electric flow path, the battery storage comprising a plurality of battery cells, each battery cell comprising at least one battery element and at least two semiconductor switches. A controller is configured for selectively controlling the voltage over the battery storage by controlling the status of the at least two semiconductor switches of a plurality of the battery cells, and thereby whether a current path through the battery storage is bypassing the at least one battery element or passing through the at least one battery element of one or more of the plurality of battery cells.

A method, an apparatus, a device and a system for controlling an oscillation damping caused by a series compensation for a wind power plant are provided. The method includes: extracting, a first dynamic small signal from first relevant parameters causing power oscillation, inputting the first dynamic small signal to a PID controller, and feeding an output control parameter from the PID to a rotor voltage controller as a first feedforward term; obtaining, according to second relevant parameters causing sub-synchronous oscillation, a virtual voltage, and feeding into a rotor voltage controller as a second feedforward term; and extracting a third dynamic small signal from third relevant parameters causing the oscillation of a rotor current loop and then performing phase and amplitude compensations on the third dynamic small signal, and feeding the output of the POD controller into the given position of a rotor current controller as a third feedforward term.