Fault ride through method for load impact minimization

A control system for controlling a wind turbine during a grid fault where the grid voltage drops below a nominal grid voltage, wherein the wind turbine comprises a doubly fed induction generator (DFIG) connected to a grid, a power converter connected between the grid and rotor windings of the DFIG, wherein the power converter comprises a rotor inverter and a grid inverter, wherein the rotor inverter is controllable to control production of active and reactive output currents based on respective active and reactive current references, wherein the active and reactive output currents are based on current delivered by the DFIG and current delivered or consumed by the grid inverter, wherein a vector-sum of active output current and reactive output current is limited according to a total current limit, and wherein the control system is arranged to perform an operation comprising:

• determining a presence of the grid fault;
• setting the total current limit to a total maximum overload current limit;
• determining the active and reactive current references based on a control function which determines the active current reference so that a reduction in active power production due to the grid voltage drop is minimized, wherein the active and reactive current references are determined subject to a condition that the vector-sum of the active output current and the active current reference is based on the active power production before the grid fault and an obtained grid voltage corresponding to the grid voltage drop, and that the reactive output current is limited according to the total maximum overload current limit;
• determining a maximum period of time in which the power converter can be controlled based on the active and reactive current references;
• and
• controlling the power converter based on the active and reactive current references.

A computer program product comprising software code adapted to control a wind turbine when executed on a data processing system, the computer program product being adapted to perform an operation for controlling a wind turbine during a grid fault where the grid voltage drops below a nominal grid voltage, wherein the wind turbine comprises a doubly fed induction generator (DFIG) connected to a grid, a power converter connected between the grid and rotor windings of the DFIG, wherein the power converter comprises a rotor inverter and a grid inverter, wherein the rotor inverter is controllable to control production of active and reactive output currents based on respective active and reactive current references, where the active and reactive output currents are based on current delivered by the DFIG and current delivered or consumed by the grid inverter, and wherein a vector-sum of active output current and reactive output current is limited according to a total current limit, the operation comprising:

• determining a presence of the grid fault;
• setting the total current limit to a total maximum overload current limit;
• determining the active and reactive current references based on a control function which determines the active current reference so that a reduction in active power production due to the grid voltage drop is minimized, wherein the active and reactive current references are determined subject to a condition that the vector-sum of the active output current and the active current reference is based on the active power production before the grid fault and an obtained grid voltage corresponding to the grid voltage drop, and the reactive output current is limited according to the total maximum overload current limit;
• determining a maximum period of time in which the power converter can be controlled based on the active and reactive current references;
• and
• controlling the power converter based on the active and reactive current references.

A wind turbine, comprising:

• a tower;
• a nacelle disposed on the tower;
• a doubly fed induction generator (DFIG) disposed in the nacelle and connected to a grid;
• a power converter connected between the grid and rotor windings of the DFIG, where the power converter comprises a rotor inverter and a grid inverter, wherein the rotor inverter is controllable to control production of active and reactive output currents based on respective active and reactive current references, wherein the active and reactive output currents are based on current delivered by the DFIG and current delivered or consumed by the grid inverter, wherein a vector-sum of active output current and reactive output current is limited according to a total current limit;
• and
• a control system configured to perform an operation, comprising:
• determining a presence of a grid fault;
• setting the total current limit to a total maximum overload current limit;
• determining the active and reactive current references based on a control function which determines the active current reference so that a reduction in active power production due to the grid voltage drop is minimized, wherein the active and reactive current references are determined subject to the condition that the vector-sum of the active output current and the active current reference is based on the active power production before the grid fault and an obtained grid voltage corresponding to the grid voltage drop, and the reactive output current is limited according to the total maximum overload current limit;
• determining a maximum period of time in which the power converter can be controlled based on the active and reactive current references;
• and
• controlling the power converter based on the active and reactive current references.