Fault ride-through capability for wind turbine

1. In a power generation system comprising a wind turbine energy resource connected to a grid, a method comprising:

setting a low DC bus voltage trip setpoint of the wind turbine energy resource;

supporting a voltage on the grid by providing reactive current to the grid from an inverter of the wind turbine energy resource during a period when the wind turbine energy resource is not providing active power to the grid;

monitoring a DC bus voltage of the wind turbine energy resource while supporting the voltage on the grid; and

reducing an amount of the reactive current being supplied to the grid when the monitored DC bus voltage drops to a predetermined threshold value which is set above the low DC bus voltage trip setpoint of the wind turbine energy resource, thereby preventing the monitored DC bus voltage from dropping further to the low DC bus voltage trip setpoint and avoiding tripping of the wind turbine energy resource.

2. The method of claim 1 , further comprising reducing the amount of the reactive current being supplied to the grid to zero when the DC bus voltage drops to the predetermined threshold value above the low DC bus voltage trip setpoint.

3. The method of claim 2 , further comprising

monitoring a turbine terminal voltage, and controlling the inverter to provide the reactive current to the grid when the turbine terminal voltage falls below a predetermined minimum voltage level.

4. The method of claim 1 , further comprising:

reducing the amount of the reactive current being supplied to the grid from a first programmed value to a second programmed value less than the first programmed value when the DC bus voltage drops to a first predetermined threshold value; and

reducing the amount of the reactive current being supplied to the grid to zero when the DC bus voltage drops to a second predetermined threshold value less than the first predetermined threshold value with the second predetermined threshold value being set above the low DC bus voltage trip setpoint.

5. The method of claim 1 , further comprising providing power to the DC bus to support the DC bus voltage while supporting the voltage on the grid.

6. The method of claim 5 , wherein the power to the DC bus is provided from an energy storage device.

7. The method of claim 6 , wherein the energy storage device is dimensioned to have sufficient capacity to maintain the DC bus voltage above the predetermined threshold value for at least a predetermined time period during a predetermined fault condition.

8. The method of claim 7 , wherein the predetermined time period is at least 150 ms.

9. The method of claim 2 , further comprising

receiving communication responsive to grid or collector system voltage;

monitoring the grid or collector system voltage, and when it falls below a predetermined level, controlling the inverter to provide the reactive current to the grid responsive to the monitored grid or collector system voltage; and

reducing the reactive current to zero when the DC bus voltage drops to the predetermined threshold value.

10. A wind turbine energy resource comprising:

a generator-side AC-DC converter that receives AC power from a generator and converts the AC power to a DC bus voltage,

a line-side DC-AC inverter that converts the DC bus voltage to a grid AC voltage of a grid at a grid frequency,

a DC bus connecting the DC bus voltage of the AC-AD converter and the DC-AC Inverter, and

a processor comprising an input receiving the DC bus voltage of the DC bus, the processor having control logic to control the line-side DC-AC inverter to provide reactive power to an electrical grid connected to the wind turbine energy resource in a synchronous condenser mode without producing active power by reducing

an amount of the reactive power supplied to the grid by the line-side DC-AC inverter when the DC bus voltage drops below a predetermined threshold value which is set above a DC bus low voltage trip setpoint of the wind turbine energy resource, thereby preventing the DC bus voltage from dropping further to the low DC bus voltage trip setpoint and avoiding tripping of the wind turbine energy resource.

11. The wind turbine energy resource of claim 10 , further comprising a battery connected to the DC bus, with the battery configured to provide current sufficient to maintain the DC bus voltage above the predetermined threshold value for at least 150 ms during a predetermined fault condition of the grid.

12. A computer program stored on a non-transitory storage medium and comprising program steps which, when the computer program is loaded into a memory of the processor and the program steps are executed by the processor, protects a power transmission system during a fault condition by causing the-processor to:

receive electronic communications that concurrently contain:

a) an indication of a low voltage condition on a grid powered by an inverter of a wind turbine generator system; and

b) an indication that the wind turbine generator system is in a synchronous condenser mode without producing active power;

provide a voltage regulation of the grid during the low voltage condition by controlling the inverter to provide reactive current to the grid or absorb reactive current therefrom in response to electrical conditions of the grid;

sense a voltage on a DC bus connected to the inverter; and

when the voltage on the DC bus falls below a predetermined threshold value, cease the voltage regulation of the grid to preserve a remaining voltage on the DC bus which is set above a DC bus low voltage trip setpoint of the wind turbine generator system, thereby preventing the sensed DC bus voltage from dropping further to the low DC bus voltage trip setpoint and avoiding tripping of the wind turbine generator system.

13. The computer program of claim 12 , further comprising:

providing energy to the DC bus from an energy storage device connected to the DC bus while providing voltage regulation.

14. The computer program of claim 13 , wherein the energy storage device is a battery with a capacity that maintains the voltage of the DC bus above the predetermined threshold value while providing the voltage regulation of the grid by the inverter for at least 150 ms during the low voltage condition.