Control method and system for continuous high and low voltage ride through of permanent-magnet direct-drive wind-driven generator set

1. A method for controlling continuous high voltage ride-through and low 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;

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

controlling the wind turbine to provide, during the transient time period, an active current to the point of common coupling, the active current being gradually increasing from a first level at which the wind turbine provides during the high voltage-through state;

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 high voltage ride-through state; and

controlling the wind turbine to reduce, at the end of the transient time period, the active current to a second level lower than the first level.

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:

superimposing a transient active current increasing at a preset recovery rate on an active current provided by the wind turbine to the point of common coupling in the high voltage ride-through state.

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 high voltage ride-through state comprises:

controlling the wind turbine to provide a zero reactive current to the point of common coupling under a condition that the wind turbine provides a zero reactive power to the point of common coupling before the high voltage ride-through state;

controlling the wind turbine to provide a gradually increasing capacitive reactive current to the point of common coupling under a condition that the wind turbine provides a capacitive reactive power to the point of common coupling before the high voltage ride-through state;

controlling the wind turbine to provide an inductive reactive current to the point of common coupling under a condition that the wind turbine provides an inductive reactive power to the point of common coupling before the high voltage ride-through state, wherein the provided inductive reactive current is the same as an inductive reactive current of the wind turbine before the high voltage ride-through state.

4. The method according to claim 3 , wherein the 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.

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

determining that the transient time period begins if the monitored voltage at the point of common coupling is decreased as compared with a voltage at the point of common coupling at beginning of the high voltage ride-through state of the wind turbine and a decreased amount is not less than a preset threshold; and

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

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

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

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

a monitoring module configured to monitor a voltage at a point of common coupling of a wind farm; and

a controller configured to:

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

control the wind turbine to provide, during the transient time period, an active current to the point of common coupling, the active current being gradually increasing from a first level at which the wind turbine provides during the high voltage-through state;

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 high voltage ride-through; and

control the wind turbine to reduce, at the end of the transient time period, the active current to a second level lower than the first level.

8. The system according to claim 7 , wherein the controller is further configured to superimpose a transient active current increasing at a preset recovery rate on an active current provided by the wind turbine to the point of common coupling in the high voltage ride-through state.

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 under a condition that the wind turbine provides a zero reactive power to the point of common coupling before the high voltage ride-through state;

control the wind turbine to provide a gradually increasing capacitive reactive current to the point of common coupling under a condition that the wind turbine provides a capacitive reactive power to the point of common coupling before the high voltage ride-through state; or

control the wind turbine to provide an inductive reactive current to the point of common coupling under a condition that the wind turbine provides an inductive reactive power to the point of common coupling before the high voltage ride-through state, wherein the provided inductive reactive current is the same as an inductive reactive current of the wind turbine before the high voltage ride-through state.

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

control 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

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 if the monitored voltage at the point of common coupling is decreased as compared with a voltage at the point of common coupling at beginning of the high voltage ride-through state of the wind turbine and a decreased amount is not less than a preset threshold; and

determine that the transient time period ends if the monitored voltage at the point of common coupling is decreased to a preset low 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 low voltage ride-through state upon completion of the transient time period, and to provide a capacitive reactive power to the point of common coupling according to a degree of decrease of the voltage at the point of common coupling and a reactive power of the wind turbine before the high voltage ride-through state.

13. A non-transitory computer-readable storage medium having computer program instructions stored thereon, wherein the computer program instructions, when executed by a processor, implement a method for controlling continuous high voltage ride-through and low 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;

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

controlling the wind turbine to provide, during the transient time period, an active current to the point of common coupling, the active current being gradually increasing from a first level at which the wind turbine provides during the high voltage-through state;

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 high voltage ride-through state; and

controlling the wind turbine to reduce, at the end of the transient time period, the active current to a second level lower than the first level.

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:

superimposing a transient active current increasing at a preset recovery rate on an active current provided by the wind turbine to the point of common coupling in the high voltage ride-through state.

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 high voltage ride-through state comprises:

controlling the wind turbine to provide a zero reactive current to the point of common coupling under a condition that the wind turbine provides a zero reactive power to the point of common coupling before the high voltage ride-through state;

controlling the wind turbine to provide a gradually increasing capacitive reactive current to the point of common coupling under a condition that the wind turbine provides a capacitive reactive power to the point of common coupling before the high voltage ride-through state; or

controlling the wind turbine to provide an inductive reactive current to the point of common coupling under a condition that the wind turbine provides an inductive reactive power to the point of common coupling before the high voltage ride-through state, wherein the provided inductive reactive current is the same as an inductive reactive current of the wind turbine before the high 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 high voltage ride-through state to the low voltage ride-through state comprises:

determining that the transient time period begins if the monitored voltage at the point of common coupling is decreased as compared with a voltage at the point of common coupling at beginning of the high voltage ride-through state of the wind turbine and a decreased amount is not less than a preset threshold; and

determining that the transient time period ends if the monitored voltage at the point of common coupling is decreased to a preset low 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 low voltage ride-through state upon completion of the transient time period, and to provide a capacitive reactive power to the point of common coupling according to a degree of decrease of the voltage at the point of common coupling and a reactive power of the wind turbine before the high voltage ride-through state.