Operation of a wind turbine during grid loss using a power storage unit

Abstract

The present invention relates to operation of a wind turbine using a power storage unit, such as a rechargeable battery, to power a group of power consuming units during grid loss. The wind turbine comprises a number of power consuming units being grouped into at least a first group and a second group, a first electrical converter for connecting the generator to the electrical grid, and a second electrical converter for connecting the electrical generator to the power storage unit. Upon detecting an occurrence of the grid loss, the generator is operated to ensure sufficient power of the power storage unit to operate the first group of power consuming units.

Claims

1. A method of operating a wind turbine comprising a rotor with a number of pitch-adjustable rotor blades, the rotor being arranged to drive an electrical generator, the wind turbine further comprises: a power storage unit; a number of power consuming units being grouped into at least a first group of power consuming units and a second group of power consuming units, the first group of power consuming units being powered by the power storage unit; and a first electrical converter for connecting the electrical generator to an electrical grid; and a second electrical converter for connecting the electrical generator to the power storage unit; the method comprising: in response to detecting an occurrence of loss of the electrical grid: disconnecting the first electrical converter from the electrical generator; and connecting the second electrical converter to the electrical generator, wherein the electrical generator is operated with a reduced rotation speed; and in response to detecting that the electrical grid has returned: connecting the first electrical converter to the electrical generator; and disconnecting the second electrical converter from the electrical generator.

2. The method according to claim 1, wherein the first group of power consuming units comprises at least one of: pitch actuators, equipment for lubrication of bearings, yaw actuators, or a control unit.

3. The method according to claim 1, wherein the second group of power consuming units are not powered during the loss of the electrical grid.

4. The method according to claim 1, wherein the power storage unit is a rechargeable power storing unit, and wherein connecting the second electrical convertor to the electrical generator is further conditioned upon detection of a voltage level of the rechargeable power storing unit is below a first voltage threshold.

5. The method according to claim 1, wherein the second electrical convertor is disconnected from the electrical generator upon detection of an output voltage level of the electrical generator is below a first output threshold and connected to the electrical generator upon detection of the output voltage level of the electrical generator is above a second output threshold, the second output threshold being larger than the first output threshold.

6. The method according claim 1, wherein during the loss of the electrical grid, a speed of the electrical generator is controlled by adjusting the pitch-adjustable rotor blades.

7. The method according to claim 6, wherein the speed is controlled to be within a speed range.

8. The method according to claim 1, wherein the pitch-adjustable rotor blades during the loss of the electrical grid are operated in a reduced mode with slower pitch angle adjustment as compared to normal mode operation.

9. The method according to claim 1, wherein the first group of power consuming units comprise a hydraulic system that comprises one or more check valves which can be selectively controlled.

10. The method according to claim 1, further comprising upon detection of a voltage level of the power storage unit being below a second voltage threshold, stopping a rotation of the rotor and entering a sleep mode.

11. The method according to claim 10, further comprising detecting a wind speed and comparing the wind speed with a wind speed threshold, upon detection of the wind speed being above a wind speed threshold, starting the rotation of the rotor and exiting the sleep mode.

12. The method according to claim 1, further comprising: upon detecting the occurrence of the loss of the electrical grid, stopping a rotation of the rotor; while a voltage level of the power storage unit is above a first voltage threshold, powering the first group of power consuming units by the power storage unit; and upon detecting that the voltage level of the power storage unit is below the first voltage threshold, rotating the rotor to ensure sufficient power of the power storage unit to operate the first group of power consuming units.

13. The method according to claim 1, wherein the electrical generator is operated in an idling mode of operation with a reduced rotation speed.

14. The method according to claim 1, further comprising operating controllable switches to selectively connect the first or second electrical converters to the electrical generator.

15. The method according to claim 1, wherein the second electrical converter is connected to the electrical generator at a time when a rotation of the electrical generator is reducing to stop.

16. The method according to claim 1, wherein the second electrical converter is further arranged to generate AC electrical power for powering the second group of power consuming units.

17. The method according to claim 1, wherein the second electrical converter comprises an AC boosting circuit.

18. The method according to claim 1, wherein the second electrical converter comprises a DC boosting circuit.

19. The method according to claim 1, wherein the second electrical converter comprises a rectifying circuit followed by a DC to DC boosting circuit.

20. The method according to claim 1, wherein the first electrical converter is dimensioned to handle a rated power of the wind turbine, whereas the second electrical converter is dimensioned to handle less than 10% of the rated power of the wind turbine.

21. The method according to claim 1, wherein the electrical generator is a permanent magnet electrical generator.

22. A wind turbine comprising: an electrical generator; a rotor with a number of pitch-adjustable rotor blades, the rotor being arranged to drive the electrical generator; a power storage unit; a number of power consuming units being grouped into at least a first group of power consuming units and a second group of power consuming units, the first group of power consuming units being powered by the power storage unit; a first electrical converter for connecting the electrical generator to an electrical grid; a second electrical converter for connecting the electrical generator to the power storage unit; a grid sensor for detecting an electrical state of the electrical grid; a data processing system configured to perform an operation, comprising: in response to detecting an occurrence of loss of the electrical grid: disconnecting the first electrical converter from the electrical generator; connecting the second electrical converter to the electrical generator; and operating the electrical generator with a reduced rotation speed; and in response to detecting that the electrical grid has returned: connecting the first electrical converter to the electrical generator; and disconnecting the second electrical converter from the electrical generator.

23. A non-transitory computer readable medium containing a program which, when executed by one or more processors, performs an operation for controlling a wind turbine during a grid loss, the wind turbine comprising a rotor with a number of pitch-adjustable rotor blades, the rotor being arranged to drive an electrical generator; the operation comprising: in response to detecting an occurrence of the grid loss: disconnecting a first electrical converter from the electrical generator, wherein the first electrical converter is configured for selectively connecting the electrical generator to an electrical grid; and connecting a second electrical converter to the electrical generator, upon which the electrical generator is operated with a reduced rotation speed, and wherein the second electrical converter is configured for selectively connecting the electrical generator to a power storage unit that powers a first group of power consuming units of a number of power consuming units; and in response to detecting that the electrical grid has returned: connecting the first electrical converter to the electrical generator; and disconnecting the second electrical converter from the electrical generator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

(2) FIG. 1 schematically illustrates an embodiment of elements of a wind turbine together with example elements inside a nacelle housing;

(3) FIG. 2 schematically illustrates elements of an embodiment of the present invention, including an embodiment comprising the second electrical converter;

(4) FIG. 3 illustrates an example of the operation cycle of the second electrical converter;

(5) FIG. 4 illustrates an example of pitch angle settings in dependency upon the wind speed; and

(6) FIG. 5 illustrates a flow chart of operation of a wind turbine in accordance with embodiments of the present invention.

DESCRIPTION OF EMBODIMENTS

(7) FIG. 1 schematically illustrates an embodiment of elements of a wind turbine 1 together with example elements inside a nacelle housing 3. The wind turbine comprises pitch-adjustable rotor blades 6 which are mechanically connected to drive an electrical generator 2. The electrical generator 2 is connected to electrical components 4, including the first and second electrical converters. Also a number of power consuming units 7 are schematically illustrated. While not shown, the wind turbine may optionally comprise a gearbox, as well as further electrical and mechanical components.

(8) One of the power consuming units is the control unit 5. The control unit may further comprise a number of elements, including at least one central controller with a processor and a memory, so that the processor is capable of executing computing tasks based on instructions stored in the memory. While the control unit is illustrated as a single entity, it may in embodiments be distributed both in location and in function. In normal operation, the wind turbine controller ensures that the wind turbine generates a requested power output level. This is obtained by adjusting the pitch angle and/or the power extraction of the (first) converter.

(9) FIG. 2 schematically illustrates elements of an embodiment of the present invention.

(10) The figure illustrates a rotor 20 with a number of pitch-adjustable rotor blades 6, the rotor being arranged to drive an electrical generator G. The wind turbine further comprises a power storage unit 21, a number of power consuming units 7 being grouped into at least a first group 22 of power consuming units and a second group 23 of power consuming units. The first group of power consuming units being powered by the power storage unit 21. In the illustrated embodiment, the second group being powered by the electrical grid 24. The electrical components 4 includes a first electrical converter 25 for connecting the generator G to the electrical grid 24. Such electrical converter typically comprises a machine side converter MSC and a grid side converter GSC connected by a DC link. In addition to the first electrical converter, also a second electrical converter 26 is illustrated. The second electrical converter 26 connecting the electrical generator G to the power storage unit 21.

(11) FIG. 2 further illustrates a grid detector 27 which is capable of detecting the state of the grid. The control unit 5 is implemented, upon detection of an occurrence of a grid loss, to instruct the generator to operate to ensure sufficient power of the power storage unit to operate the first group of power consuming units.

(12) In addition to the control unit 5, the first group 22 of power consuming units may further include pitch actuators, equipment for lubrication of bearings, yaw actuators, selected dehumidifiers and selected heaters, selected hydraulic pumps, controllable check valves.

(13) The second group 23 of power consuming units may comprise such units as power supplies for lifts, lights, cooling, heating, ventilation, hydraulic pumps, etc.

(14) The power storage unit 21 typically outputs DC power, and the first group of power consuming units are typically DC powered units, whereas the second group of power consuming units may be AC powered units. At least in the illustrated embodiment, where the second group of power consuming units are grid connected, via appropriate transformer equipment (not shown). The power storage unit may thus comprise an AC input and a DC output. The power storage unit may be a rechargeable battery, where the AC input is an input to a battery charger 200. The power storage unit may comprise a number of rechargeable battery cells 201.

(15) In the illustrated embodiment, upon grid loss, the first group of power consuming units are powered by the power storage unit, whereas the second group of power consuming units are not powered.

(16) In the illustrated embodiment, the second electrical converter is connected to the electrical generator via a switch 28, so that the second electrical converter can be selective connected to the electrical generator upon detection of the occurrence of the grid loss. Depending upon the type of generator and/or converter, it may be advantageous to be able to selective disconnected the first electrical converter during the grid loss. This may be done by switch 29.

(17) The second electrical converter may be an AC/AC boost converter which is arranged to provide a constant voltage and frequency AC output from a variable voltage and frequency input. The AC/AC boost converter may e.g. be arranged to convert a 64 V AC input at 10 Hz from the rotating generator at reduced speed, to a 400 V AC output suitable for the power storage unit. In this regard, the AC/AC boost converter may be arranged to accept a certain input range both in voltage and in frequency.

(18) The illustrated power storage unit is a rechargeable power storing unit, in which case the output of the second electrical converter 26 is used for recharging the power storage unit, which is drained from the powering of the first group of power consuming units.

(19) In an embodiment, the selective connection of the second electrical convertor to the electrical generator is further conditioned upon detection of the voltage level of the rechargeable power storing unit is below a first voltage threshold. The charging of the power storage unit may be obtained by trickle charging.

(20) In an embodiment, the output voltage level of the electrical generator is monitored to ensure that the second electrical converter is only connected to the generator if the generator output is above a certain level.

(21) During normal operation, i.e. when the grid is present, the second electrical converter 26 is disconnected and the power storage 21 is charged via the grid. In this regard the two switches between the grid 24 and the power storage 21 is connected. Moreover, further electrical equipment may be inserted between the grid and the power storage in order to enable such charging. Such further equipment is not shown, but it is with the skilled person's ability to select appropriate equipment.

(22) FIG. 3 illustrates an example of the operation cycle of the second electrical converter, which shows that the second electrical convertor is disconnected for an output voltage level of the electrical generator below a first output threshold OT1 and connected for an output voltage level of the electrical generator being above a second threshold OT2.

(23) During grid loss the generator speed is controlled by adjusting the pitch-adjustable rotor blades. An example of pitch angle settings in dependency upon the wind speed is illustrated in FIG. 4.

(24) In one embodiment, the wind speed is measured or estimated when the self-powering mode is initiated. Here the initial pitch angle is set according to a predefined pitch angle, such as illustrated on FIG. 4. As the grid loss continues, the pitch angle may be controlled via speed control of the generator, either to ensure that the speed remains either at an appropriate level, or within an appropriate range. Typically approximately around 10% of nominal rotor speed. The graph illustrated in FIG. 4, may typically be implemented as a look-up table in the control unit. In an alternative embodiment, the rotor speed is not monitored. Instead the pitch angle is set in accordance with the wind speed. If the second electrical converter can accept a large variation in speed and frequency, there may not be a need for a speed control of the generator.

(25) Embodiments of the present invention allows for keeping the first group of power consuming units operational even in high wind situations. Above a certain wind speed there may be a need for shutting down the turbine, however the time period where the wind is so high that the rotor needs to be completely stopped is normally less that the time where the power storage unit can support operation of the first group of power consuming units.

(26) FIG. 5 illustrates a flow chart of operation of a wind turbine in accordance with embodiments of the present invention.

(27) In normal mode operation 50 the grid is monitored, and upon detection of a grid loss 51, e.g. using a grid detector 27, the turbine rotor is initially stopped 52, this is done by feathering the rotor blades, i.e. turning the blades to their feathering position typically around 90 degrees. When the turbine is stopped the voltage level of the power storage unit 21 is normally at nominal level allowing for powering of the first group of power consuming elements, typically, for a number of hours. While in off grid situation, the grid is continuously monitored 53 so that normal operation can be resumed upon grid availability. At the same time, also the voltage level of the power storage unit is monitored 54. While the voltage level of the power storage unit is above the first voltage threshold, the turbine remains stopped and the first group of power consuming units remains powered by the power storage unit. Upon detecting that the voltage level of the power storage unit gets below the first voltage threshold, self-powering mode is entered 55 operating the generator at reduced speed to ensure sufficient power of the power storage unit to operate the first group of power consuming units.

(28) For as long as the energy in the wind is sufficient to trickle charge the power storage unit, the self-powering mode can be maintained. The wind speed need not constantly be above a certain level, however, at least periods of sufficient wind need to be present to keep the voltage level of the power storage unit above a minimum threshold, the second voltage threshold.

(29) Upon detection of the voltage level of the rechargeable power storing unit gets below the second voltage threshold, the rotation of the rotor is stopped, and sleep mode of the turbine is entered.

(30) In sleep mode operation 57, in an embodiment, in addition to stopping the rotor, the first group of power consuming units, or at least a sub-group of the first group of power consuming units, are disconnected from the power storage unit, and only a wake-up circuit is powered. The wake-up circuit may be a simple timer circuit which at set time intervals wake up the control unit 5, or parts of the control unit 5, to detect the wind speed and compare the wind speed with a wind speed threshold, upon detection of the wind speed being above a second wind speed threshold, the sleep mode may be ended. In an alternative embodiment, the wind speed may also be monitored continually during sleep mode, and upon detecting the wind speed is sufficient high, the self-powering mode is re-entered. The wake-up circuit may be set to ensure that the wind speed has been above the wind speed threshold for a prolonged period of time, to ensure that the wind speed is stable.

(31) If the grid is restored, the normal mode is resumed, whereas if the grid is still not functioning, self-powering mode is entered.

(32) In an embodiment, as an alternative to a wake-up circuit, the turbine may also arranged for manual restart, e.g. via the SCADA system.

(33) In an embodiment, steps 52, 54 may be omitted so that the turbine upon detection of grid loss enters the self-power mode 55 directly.

(34) In embodiments, the discharge rate of the power storage unit may be monitored, e.g. by a monitoring module of the control system or via a data connection to a SCADA system. In the event of a rapid discharge of the energy storage device service personnel may be informed for mobile recharging. In general, the status of the charge level of the power storage unit may be communicated, e.g. via SCADA, to service personnel during idle mode to ensure that the service personal can react to a problematic situation.

(35) Example embodiments of the invention have been described for the purposes of illustration only, and not to limit the scope of the invention as defined in the accompanying claims.