High-low voltage continuous ride-through control method and system for permanent magnet direct-drive wind power generating set

1. A method for controlling continuous low voltage ride-through and high voltage ride-through of a permanent magnet direct-driven wind turbine, comprising:

monitoring a voltage at a point of common coupling of a wind farm, wherein the wind turbine experiences a low voltage ride-through state in a first time period from a first time point to a second time point and a high voltage ride-through state in a second time period from a third time point to a fourth time point, wherein the wind turbine provides an active current at a first level before the first time point and a second level during the first time period from the first time point to the second time point, wherein the second level is lower than the first level;

determining a transient time period from the second time point to the third time point during which the wind turbine is transitioned from the low voltage ride-through state to the high voltage ride-through state;

controlling the wind turbine to provide, during the transient time period, the active current to the point of common coupling, the active current being gradually increasing from;

controlling the wind turbine to provide, during the transient time period, a reactive current to the point of common coupling according to an operation state of the wind turbine before the low voltage ride-through state; and

controlling the wind turbine to increase, at the third time point which is the end of the transient time period, the active current to a third level which is higher than the second level during the first time period but lower than a the first level before the first time point wherein the wind turbine provides the active current at the third level during the second time period from the third time point to the fourth time point.

2. The method according to claim 1 , wherein the controlling the wind turbine to provide, during the transient time period, the active current to the point of common coupling comprises:

increasing the active current at a preset recovery rate.

3. The method according to claim 1 , wherein the controlling the wind turbine to provide, during the transient time period, the reactive current to the point of common coupling according to the operation state of the wind turbine before the low voltage ride-through state comprises:

controlling the wind turbine to provide a zero reactive current o the point of common coupling when the operation state indicates that the wind turbine provides a zero reactive power to the point of common coupling before the low voltage ride-through state;

controlling the wind turbine to provide a gradually increasing capacitive reactive current to the point of common coupling when the operation state indicates that the wind turbine provides a capacitive reactive power to the point of common coupling before the low voltage ride-through state; or

controlling the wind turbine to provide an inductive reactive current to the point of common coupling when the operationstate indicates that the wind turbine provides an inductive reactive power to the point of commoncoupling before the low voltage ride-through state, wherein the provided inductive reactive current is the same as an inductive reactive current of the wind turbine before the low voltage ride-through state.

4. The method according to claim 3 , wherein he controlling the wind turbine to provide the gradually increasing capacitive reactive current to the point of common coupling comprises:

controlling an increase rate of the capacitive reactive current o be consistent with an increase rate of an output active power of the wind turbine; and

controlling the ind turbine to provide the gradually increasing capacitive reactive current to the point of common coupling according to the increase rate of the capacitive reactive current.

5. The method according to claim 1 , wherein the determining the transient tune period during which the wind turbine is transitioned from the low voltage ride-through state to the high voltage ride-through state comprises:

determining that the transient e period begins at the second time point if the monitored voltage at the point of common coupling at the second time point is increased as compared with a voltage at the point of common coupling at the first time point and an increased amount is not less than a preset threshold; and

determining that the transient tune period ends at the third time point if the monitored voltage at the point of common coupling at the third time point is increased to a preset high voltage ride-through threshold.

6. The method according to claim 1 , further comprising:

controlling the wind turbine to enter the high voltage ride-through state upon completion of the transient tine period, and to provide an inductive reactive power to the point of common coupling according to a degree of increase of the voltage at the point of common coupling and a reactive power of the wind turbine before the low voltage ride-through state.

7. A system for controlling continuous low voltage ride-through and high voltage ride-through of a permanent magnet direct-driven d turbine, comprising:

a monitoring module configured to monitor a voltage at a point of common coupling of a wind farm, wherein the wind turbine experiences a low voltage ride-through state in a first time period from a first time.point to a second time point and a high voltage ride-through state in a second time period from a third time point to a fourth time point, wherein the wind turbine provides an activecurrent at a first level before the first time point and a second level during the first time period from the first time point to the second time point, wherein the second level is lower than the first level; and

a controller configured to:

determine a transient time period from the second time point to the third time point during which the wind turbine is transitioned from the low voltage ride-through state to the high voltage ride-through state;

control the wind turbine to provide, during the transient time period, the active current to the point of common coupling, the active current being gradually increasing from the second level;

control the wind turbine to provide, during the transient time period, a reactive current to the point of common coupling according to an operation state of the wind turbine before the low voltage ride-through; and

control the wind turbine to increase, at the third time point which is the end of the transient time period, the active current to a third level which is higher than the second level during the first time period but lower than the first level before the first time point, wherein the wind turbine provides the active current at the third level during the second time period from the third time point to the fourth time point.

8. The system according to claim 7 , wherein the controllers further configured to increase the active current at a preset recovery rate.

9. The system according to claim 7 , wherein the controller is further configured to:

control the wind turbine to provide a zero reactive current to the point of common coupling when the operation state indicates that the wind turbine provides a zero reactive power to the point of common coupling before the low voltage ride-through state;

control the wind turbine to provide a gradually increasing capacitive reactive current to the point of common coupling when the operation state indicates that the wind turbine provides a capacitive reactive power to the point of common coupling before the low voltage ride-through state; or

control the wind turbine to provide an inductive reactive current to the point of common coupling when the operation state indicates that the wind turbine provides an inductive reactive power to the point of common coupling before the low voltage ride-through state, wherein the provided inductive reactive current is the same as an inductive reactive current of the wind turbine before the low voltage ride-through state.

10. The system according to according to claim 9 , wherein controller is further configured to:

wherein the controller is further configured control an increase rate of the capacitive reactive current to be consistentith an increase rate of an output active power of the wind turbine; and

control the wind turbine to provide the gradually increasing capacitive reactive current to the point of common coupling according to the increase rate of the capacitive reactive current.

11. The system according to claim 7 , wherein the controller is further configured to:

determine that the transient time period begins at the second time point if the monitored voltage at the point of common coupling at the second time point is increased as compared with a voltage at the point of common coupling at the first time point and an increased amount is not less than a preset threshold; and

determine that the transient time period ends at the third time point if the monitored voltage at the point of common coupling at the third time point is increased to a preset high voltage ride- through threshold.

12. The system according to claim 7 , wherein the controller is further configured to:

control the wind turbine to enter the high voltage ride-through state upon completion of the transient time period, and to provide an inductive reactive power to the point of common coupling according to a degree of increase of the voltage at the point of common coupling and a reactive power of the wind turbine before the low voltage ride-through state.

13. A non-transitory computer-readable storage medium having computerprogram instructions stored thereon, wherein the computer program instructions, when executed by a processor, implement a method for controlling continuous low voltage ride-through and high voltage ride-through of a permanent magnet direct-driven wind turbine, the method comprising:

monitoring a voltage at a point of common coupling of a wind farm. wherein the wind turbine experiences a low voltage ride-through state in a first time period from a first time point to a second time point and a high voltage ride-through state in a second time period from a third time point to a fourth time point, wherein the wind turbine provides an active current at a first level before the first time point and a second level during the first time period from the first time point to the second time point, wherein the second level is lower than the first level;

determining a transient time period from the second time point to the third time point during which the wind turbine is transitioned from the low voltage ride-through state to the high voltage ride-through state;

controlling the wind turbine to provide, during the transient time period, the active current to the point of common coupling, the active current being gradually increasing from;

controlling the wind turbine to provide, during the transient time period, a reactive current to the point of common coupling according to an operation state of the wind turbine before the low voltage ride-through state; and

controlling the wind turbine to increase, at the third time point which is the end of the transient time period, the active current to a third level which is higher than the second level during the first time period but lower than the first level before the first time point, wherein the wind turbine provides the active current at the third level during the second time period from the third time point to the fourth time point.

14. The non-transitory computer-readable storage medium according to claim 13 , wherein controlling the wind turbine to provide, during the transient time period, the active current to the point of common coupling comprises:

increasing the active current at a preset recovery rate.

15. The non-transitory computer-readable storage medium according to claim 13 , wherein controlling the wind turbine to provide, during the transient time period, the reactive current to the point of common coupling according to the operation state of the wind turbine before the low voltage ride-through state comprises:

controlling the wind turbine to provide a zero reactive current to the point of common coupling when the operation state indicates that the wind turbine provides a zero reactive power to the point of common coupling before the low voltage ride-through state;

controlling the wind turbine to provide a gradually increasing capacitive reactive current to the point of common coupling when the operation state indicates that the wind turbine provides a capacitive reactive power to the point of common coupling before the low voltage ride-through state; or

controlling the wind turbine to provide an inductive reactivecurrent to the point of common coupling when the operation state indicates that the wind turbine provides an inductive reactive power to the point of common coupling before the low voltage ride-through state, wherein the provided inductive reactive current is the same as an inductive reactive current of the wind turbine before the low voltage ride-through state.

16. The non-transitory computer-readable storage medium according to claim 15 , wherein controlling the wind turbine to provide the gradually increasing capacitive reactive current to the point of common coupling comprises:

controlling an increase rate of the capacitive reactive current to be consistent with an increase rate of an output active power of the wind turbine; and

controlling the wind turbine to provide the gradually increasing capacitive reactive current to the point of common coupling according to the increase rate of the capacitive reactive current.

17. The non-transitory computer-readable storage medium according to claim 13 , wherein determining the transient time period during which the wind turbine is transitioned from the low voltage ride-through state to the high voltage ride-through state comprises:

determining that the transient time period begins at the second time point if the monitored voltage at the point of common coupling at the second time point is increased as compared with a voltage at the point of common coupling at the first time point and an increased amount is not less than a preset threshold; and

determining that the transient time period ends at the third time point if the monitored voltage at the point of common coupling at the third time point is increased to a preset high voltage ride-through threshold.

18. The non-transitory computer-readable storage medium according to claim 13 , wherein the method further comprises:

controlling the wind turbine to enter the high voltage ride-through state upon completion of the transient time period, and to provide an inductive reactive power the point of common coupling according to a degree of increase of the voltage at the point of common coupling and a reactive power of the wind turbine before the low voltage ride-through state.