Pitch control of a wind turbine blade in standby mode

Abstract

The present disclosure relates to an operating method of a wind turbine generator (WTG) including a pitch control system, the method comprising: a) operating the WTG in a normal mode while the WTG is connected to an external power grid; b) controlling the pitch angle of the blades using a normal pitch control mode while the WTG is operating in the normal mode; c) detecting a grid loss; d) operating the WTG in a standby mode during the grid loss; and e) controlling the pitch angle of the blades according to the monitored speed parameters of the WTG using a standby pitch control mode different from the normal pitch control mode while the WTG is operating in the standby mode, wherein the response of the standby pitch control mode is slower than that of the normal pitch control mode, so that the power consumption of the pitch control system is reduced when the WTG is operating in the standby mode.

Description

Technical Field

[0001] The present disclosure relates to a method of operating a wind turbine generator (WTG), and more particularly to a method of controlling the pitch angle of the blades of a WTG while the WTG is operating in a standby mode during a grid loss. Background Art

[0002] A wind power plant (WPP), also known as a wind farm or wind park, typically includes a number of wind turbines or wind turbine generators (WTGs) configured to generate electrical power to be supplied to an external power grid. During normal operating conditions, the WTGs of the WPP continuously generate electrical power to be supplied to the external power grid. However, during certain operating conditions, the WPP may experience a "grid loss", i.e., the WTGs are unable to supply electrical power to the external power grid, for example because the external power grid is unavailable or determined to be unstable. In such a case, the WTGs can switch to a standby mode in which the WTGs continue to operate (i.e., the rotors continue to rotate), but do not operate to generate electrical power to be supplied to the external power grid.

[0003] During a grid loss, the WTGs may be disconnected from their normal power sources. In such a case, critical subsystems of the WTGs (including, for example, the pitch control system of the WTGs) can continue to be powered by a backup power system that includes a battery energy storage system and / or a diesel generator. However, over time, these backup power systems may become depleted, in which case it may be necessary to completely stop the WTGs.

[0004] In some cases, the WTGs can operate to generate backup power while operating in a standby mode, and the backup power can be used to charge the backup power system. However, it is still possible for the backup power system to become depleted, for example, if the power consumption of the critical subsystems exceeds the power generation of the backup power over a long period of time.

[0005] The object of the present invention is to solve the disadvantages of the known WPPs of the above type. Summary of the Invention

[0006] According to one aspect of the present invention, there is provided a method of operating a wind turbine generator (WTG) including a pitch control system, the method comprising: a) operating the WTG in a normal mode while the WTG is connected to an external power grid; b) controlling the pitch angle of the blades using a normal pitch control mode while the WTG is operating in the normal mode; c) detecting a grid loss; d) operating the WTG in a standby mode during the grid loss; and e) controlling the pitch angle of the blades using a standby pitch control mode different from the normal pitch control mode based on monitored speed parameters of the WTG while the WTG is operating in the standby mode, wherein the standby pitch control mode has a slower response than the normal pitch control mode, such that when the WTG is operating in the standby mode, the power consumption of the pitch control system is reduced.

[0007] For example, when the normal pitch control mode is activated, the pitch angle of the blades can be adjusted substantially continuously, for example in response to minor and / or instantaneous changes in operating parameters such as generator speed and / or rotor speed, in order to provide precise control of the speed of the WTG and to optimize and / or maximize the power output of the WTG. However, when the WTG is operating in the standby mode, a higher activation threshold can be applied such that the pitch angle of the blades is adjusted only if the monitored speed parameter consistently deviates from the target speed over a duration (e.g., at least 30 seconds) and / or deviates from the target speed by a large or significant amount (e.g., at least +50% / -30%).

[0008] By controlling the pitch angle of the blades using a separate standby pitch control mode when the WTG is operating in the standby mode, the present invention enables the WTG to continue to control the pitch angle of the blades in order to control the rotor speed (and to control the generator speed in the case where the generator remains connected while the WTG is operating in the standby mode). However, since the standby pitch control mode has a slower response than the normal pitch control mode, the WTG will perform fewer pitch angle adjustment operations compared to the alternative case of continuously applying the normal pitch control mode while the WTG is operating in the standby mode, and thus use less energy while operating in the standby mode. This can prevent unnecessary conventional pitch angle adjustments from being performed while the WTG is operating in the standby mode and extend the time that the WTG can operate in the standby mode before the power supply for a critical subsystem of the WTG is depleted. Reducing the use of standby power can also reduce the required capacity of the standby power system of the WTG.

[0009] The WTG can selectively operate while in standby mode to generate backup power, so as to further extend the time the WTG can operate in standby mode. The backup power generated by the WTG can be used, for example, to charge an energy storage system associated with the WTG and / or to power one or more subsystems of the WTG. Since the response ability of the standby pitch control mode is relatively low, the backup power generated by the WTG in standby mode is generally of lower quality than the power generated during normal operation. However, the reduction in standby power usage offsets the reduction in quality due to the reduced number of pitch angle adjustment operations.

[0010] Compared with when the WTG operates in normal mode, the WTG preferably operates at a lower speed when in standby mode. For example, the WTG can operate at a target generator speed within the range of 40 - 100 rpm. The generator speed within the range of 40 - 100 rpm has been determined to be particularly suitable for generating backup power in standby mode.

[0011] It can be understood that different manufacturers may use different terms to refer to different operating modes. However, the term "standby mode" used in this specification refers to the mode used during a grid loss, in which the WTG continues to operate (i.e., the rotor continues to rotate), but the WTG does not operate to supply power to the external grid.

[0012] When the WTG operates in standby mode, if a first activation condition is met, the pitch angle of the blade can be adjusted, but if the first activation condition is not met, it remains unadjusted; the first activation condition includes that the monitored speed parameter falls outside a first threshold during a specific time period. In this way, it can be ensured that the pitch angle of the blade is adjusted in response to continuous changes in operating conditions, rather than in response to short - term or instantaneous changes. For the sake of clarity, the speed parameter can be the generator speed or the rotor speed. For embodiments where the generator supplies backup power to the WTG, such as to store in an energy storage system or directly power one or more subsystems of the WTG, it may be preferable to directly monitor the generator speed.

[0013] The first threshold can have an upper limit of at least +20% of the target speed and / or a lower limit of at least -20% of the target speed. Defined in another way, the first threshold can have an upper limit of at least +10 rpm of the target generator speed and / or a lower limit of at least -10 rpm of the target generator speed. The target speed can be a clearly defined target speed, or alternatively can be the mid - point between the upper and lower limits of the first threshold. It can be understood that the lower limit is not crucial, and in some cases, the first threshold can only include the upper limit.

[0014] The first threshold can span a generator speed range of at least 20 rpm.

[0015] The first threshold may have an upper limit corresponding to a generator speed in the range of 70 - 120 rpm and / or a lower limit corresponding to a generator speed in the range of 30 - 50 rpm.

[0016] The specific time period may be at least 30 seconds, and preferably at least 100 seconds.

[0017] Alternatively or additionally, while the WTG is operating in standby mode, if a second activation condition is met, the pitch angle of the blade may be adjusted, but if the second activation condition is not met, it remains unadjusted; the second activation condition includes the monitored speed parameter falling outside a second threshold. The second threshold is preferably greater than the first threshold (e.g., wider). The second activation condition may not change over time. In other words, it may not be necessary for the monitored speed parameter to fall outside the second threshold for a significant period of time in order to meet the second activation condition. Instead, the pitch angle of the blade may be adjusted immediately after the monitored speed parameter has fallen outside the second threshold (regardless of how long the monitored speed parameter has deviated from the second threshold). In this way, it can be ensured that the pitch angle of the blade is quickly adjusted in response to a large or significant change in operating conditions, but not in response to a small change.

[0018] The second threshold may have an upper limit of at least +50% of the target speed and / or a lower limit of at least -30% of the target speed. Defined in another way, the second threshold may have an upper limit of at least +30 rpm of the target generator speed and / or a lower limit of at least -20 rpm of the target generator speed. The target speed may be a clearly defined target speed, or alternatively may be the midpoint between the upper and lower limits of the second threshold. It can be understood that the lower limit is not important, and in some cases, the second threshold may only include the upper limit.

[0019] The second threshold may span a generator speed range of at least 50 rpm.

[0020] The second threshold may have an upper limit corresponding to a generator speed in the range of 90 - 200 rpm and / or a lower limit corresponding to a generator speed in the range of 10 - 40 rpm.

[0021] In a preferred embodiment, the first (time - varying) activation condition and the second (non - time - varying) activation condition are used in combination such that if any one (or both) of the first and second activation conditions are met, the pitch angle of the blade is adjusted, but if neither the first nor the second activation condition is met, it remains unadjusted. However, in other embodiments, it may be more preferable to apply only one of the first and second activation conditions.

[0022] If it is determined that the pitch angle of the blade is to be adjusted while the WTG is operating in the standby mode, for example if the first and / or second activation conditions have been met, the method may include increasing the gain coefficient used to control the pitch angle of the blade. Otherwise, the gain coefficient may remain at its current value without adjustment, for example at the value 0, such that no pitch angle adjustment operation is performed.

[0023] If the first activation condition has been met, the gain coefficient may be increased to a first predetermined value. The first predetermined value may be the value 1. The gain coefficient may be increased at a first gain rate over a period of time to avoid a step change in the gain coefficient. After the pitch angle of the blade has been adjusted, the gain coefficient may subsequently be decreased, for example back to the value 0.

[0024] If the second activation condition has been met, the gain coefficient may be increased above the value 1. Thus, if the second activation condition has been met, the responsiveness of the pitch angle control may be artificially increased. The gain coefficient may be increased at a second gain rate, which may be different from the first gain rate. After the pitch angle of the blade has been adjusted, the gain coefficient may subsequently be decreased, for example back to the value 0.

[0025] The method may include, while the WTG is operating in the standby mode, shutting down the pitch angle control module that is normally used to set the pitch angle of the blade. The pitch angle control module may be automatically shut down when the WTG enters the standby mode. In some cases, shutting down the pitch angle control module may include completely stopping the power supply to the pitch angle control module. However, in other cases, it may simply be prevented from adjusting the pitch angle of the blade in accordance with the normal pitch control mode while the WTG is operating in the standby mode. (It can be understood that the pitch angle control module may not be an independent unit, but part of a broader control system, such as the WTG controller.)

[0026] The WTG may also be configured to shut down one or more other non-critical subsystems while the WTG is operating in the standby mode, including for example the lifting system, lighting system, heating system, cooling system, ventilation system, hydraulic pump system, and / or non-critical sensor system.

[0027] The method may further include reactivating the pitch angle control module and using the pitch angle control module to set the pitch angle of the blade if it is determined that the pitch angle of the blade is to be adjusted while the WTG is operating in the standby mode, for example if the first and / or second activation conditions have been met. The pitch angle control module may subsequently be shut down after it has been used to reset the pitch angle of the blade. If it is determined that the pitch angle of the blade is to be adjusted while the WTG is operating in the standby mode, the pitch angle of the blade may be adjusted in accordance with the normal pitch control mode.

[0028] Alternatively, the pitch angle of the blade can be set by a separate control module while the WTG is operating in standby mode. The separate control module can be a relatively simple controller with lower power consumption than the pitch angle control module.

[0029] When the WTG is operating in standby mode, a lower pitch rate can be applied when adjusting the pitch angle of the blade compared to when the WTG is operating in normal mode. For example, when the WTG is operating in standby mode, the pitch rate can be reduced by at least 30%.

[0030] When the WTG is operating in standby mode, the monitored speed parameter can be monitored at a lower frequency (e.g., compared with a target speed and / or one or more activation thresholds) compared to when the WTG is operating in normal mode. For example, when the WTG is operating in standby mode, a monitoring period of at least 5 seconds can be applied.

[0031] According to another aspect of the present invention, there is provided a controller configured to control the operation of the WTG according to the above method. The controller can include one or more memory modules for storing instructions and one or more processing modules for executing the stored instructions. The controller can form part of a WTG controller associated with the WTG and / or a power plant controller associated with the power plant where the WTG is located. It will be understood that the memory module and the processing module do not need to be co-located in a single location and, in some cases, can be distributed between the WTG controller and the power plant controller.

[0032] According to another aspect of the present invention, there is provided a computer program downloadable from a communication network and / or stored on a machine-readable storage medium, the computer program including program code instructions for implementing a method according to the above method.

[0033] Within the scope of the present application, the aspects, embodiments, examples, and alternatives set forth in the preceding paragraphs, the claims, and / or the following description and drawings, in particular their respective features, can be taken independently or combined in any way. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless these features are incompatible. The applicant reserves the right to correspondingly change any originally filed claim or file any new claim, including the right to modify any originally filed claim to depend on and / or incorporate any feature of any other claim, even though it was not originally claimed in this way. Description of the Drawings

[0034] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0035] Figure 1Schematically shows a wind power plant, its connection to an external power grid, and its control system;

[0036] Figure 2 Schematically shows in Figure 1 a front view of a wind turbine generator of the wind power plant shown in;

[0037] Figure 3 Schematically shows in Figure 2 the power generation and conversion equipment and various subsystems of the wind turbine generator shown in;

[0038] Figure 4 is a flow chart showing method steps by which the wind turbine generators of the power plant shown in Figure 1 are controlled during normal operating conditions and during a power grid loss; and

[0039] Figure 5 shows a method by which the pitch angle of the blades can be adjusted while the wind turbine generator is operating according to a standby pitch control mode during a power grid loss. DETAILED DESCRIPTION

[0040] Figure 1 Schematically shows a part of a power transmission network including a wind power plant (WPP) 1 according to a possible non - limiting embodiment of the present invention. The wind power plant may also be referred to as a wind farm or a wind park. The wind power plant 1 includes a plurality of wind turbines or wind turbine generators (WTG) 10 which are configured to generate electrical power to be supplied to an external power grid 2 during normal operation of the WPP 1. As Figure 1 shown, each of the WTGs 10 is connected to a local power grid 3 of the WPP 1. The local power grid 3 is in turn connected to an interconnection point (POI) bus 6, and electrical power is fed into the external power grid 2 via the interconnection point bus through a power transmission line 4 including a main step - up transformer 5. The external power grid 2 may be a regional, national or international power transmission network, such as the National Grid of Great Britain.

[0041] The WPP 1 is equipped with a power plant controller (PPC) 7. The PPC 7 is connected to the power transmission network at a measurement point (POM) 8 from where it can monitor the state of the power transmission network, and is connected to a grid operator or a transmission system operator (TSO) 9 from where the PPC 7 can receive instructions regarding the operation of the WPP 1. The PPC 7 is further connected to the WPP 1 and is configured to control the operation of the WPP 1 according to a stored set of operating instructions and instructions received from the TSO 9. In particular, the PPC 7 is configured to communicate information and instructions to the controller 20 of the respective WTG 10 which in turn controls the operation of the WTG and its various subsystems.

[0042] It is understood that Figure 1 the shown power transmission network is schematic and highly simplified, for illustrative purposes only, and WPP 1 may include any desired number of WTGs 10, which may be connected to each other and to the external power grid 2 in any suitable manner.

[0043] Figure 2 A front view schematically showing one typical WTG 10 of WPP 1. As Figure 2 shown, the WTG 10 includes a rotor 11, which includes a plurality of blades 12 extending outward from a hub 13. The rotor 11 is connected to a nacelle 14, which in turn is connected to a tower 15. The nacelle 14 houses a generator configured to be driven by the rotor 11. The WTG 10 is an onshore horizontal axis wind turbine (HAWT) with three blades. However, it is understood that the present invention can equally be applied to other types of WTGs, including offshore WTGs.

[0044] Figure 3 Schematically showing the power generation and conversion equipment and various subsystems of the WTG 10 shown in Figure 2 . As Figure 3 shown, the power generation and conversion equipment includes a generator 16 driven by the rotor 11 via a transmission 17. The transmission 17 may optionally include a gearbox or may alternatively be a direct drive transmission. The generator 16 is configured to generate electrical power to be supplied to the external power grid 2 in a conventional manner. The power generation and conversion equipment also includes a power converter 19, which is configured to convert the output of the generator 16 into a frequency compatible with the external power grid 2. The power converter 19 may optionally be a full-scale converter including a machine-side AC-DC converter 19a, a DC link 19b, and a grid-side DC-AC converter 19c, as Figure 3 shown, although other types of converters may also be used in other embodiments. The power generation and conversion equipment of the WTG 10 is generally controlled by a WTG controller 20.

[0045] Figure 3As shown, the WTG 10 further includes a power system 23, which includes a battery storage system (BSS) 24 configured to be charged by the generator 16 in any suitable manner according to the design of the WTG 10. In some cases, the power system 23 can be connected to and configured to be charged by the power converter 19 (as shown by connection 25). In this case, the power system can be selectively connected to the DC link 19b of the power converter 19, or alternatively connected to any other suitable part of the power converter 19. However, in other cases, the power system 23 can be configured to be charged by the generator 16 via a separate connection including another AC-DC converter (see connection 26). The power system 23 is also connected to and configured to supply DC current to various electrical sub-systems of the WTG at least in the event of a grid loss, which is described in more detail below.

[0046] The WTG 10 further includes various electrical sub-systems 21, for example, including: a pitch control actuation system 22 including one or more actuators for controlling the pitch angle of the blades 12, a yaw control actuation system including one or more actuators for controlling the yaw angle of the nacelle 14, a lubrication system, a lifting system, a lighting system, a heating system, a cooling system, a ventilation system, a hydraulic pump system, and various sensor systems, which are also generally controlled by the WTG controller 20.

[0047] The electrical sub-systems 21 can be powered in any suitable manner according to the design of the WTG 10 and the WPP 1 during the normal operation of the WTG 10 while the WPP 1 remains connected to the external grid 2. For example, the electrical sub-systems 21 can be powered by the local grid 3 and / or the external grid 2, selectively via a dedicated power supply grid. In this case, the WTG power system 23 can operate only as a backup power system. Alternatively, during the normal operation of the WTG 10, the electrical sub-systems 21 can be powered by the WTG power system 23. However, in either case, the WTG power system 23 is configured to supply DC current to at least some of the electrical sub-systems 21 during a grid loss, such that the WTG 10 can continue to operate during a grid loss, even when the electrical sub-systems 21 have been disconnected from their normal power sources.

[0048] The WTG controller 20 is a control system including various different control modules, which are configured to control the operation of the WTG 10 and its various subsystems 21. In particular, the WTG controller 20 includes a speed control module 30 and a pitch angle control module 40 (as well as other modules). The speed control module 30 is configured to at least substantially real-time monitor the speed of the WTG 10 (i.e., the rotor speed and / or the generator speed) by using a speed sensor or alternatively by calculating or estimating the speed of the WTG, and to adjust the speeds of the rotor 11 and the generator 16. The pitch angle control module 40 is configured to set the pitch angle of the blade 12, for example, by calculating a pitch angle setpoint and controlling the operation of the pitch control actuation system 22 so as to achieve the desired blade pitch angle. The pitch angle setpoint can be calculated, for example, based on the current wind turbine speed and the power demand received from the PPC 7, although other operating parameters can be additionally considered when setting the pitch angle setpoint.

[0049] It can be understood that Figure 3 the basic WTG architecture shown is schematic and highly simplified for illustrative purposes only, and the WTG 10 can further include other subsystems and control modules arranged in any suitable manner.

[0050] Now, the operation of the WTG 10 during normal operating conditions and during a grid loss will be described with reference to Figure 4 the flowchart. The following description refers to the control of a single WTG 10, although it can be understood that each WTG 10 can be controlled in an equivalent manner.

[0051] Under normal operating conditions, when the WPP 1 is connected to the external grid 2 and the external grid 2 can receive power from the WPP 1, the WTG 10 operates in a normal mode to generate power to be supplied to the external grid 2 via the local grid 3 and the transmission line 4, as shown in step 1.

[0052] While the WTG 10 is operating in the normal mode, the pitch angle control module 40 continuously operates to calculate the pitch angle setpoint of the blade 12 in accordance with the normal pitch control mode and to control the operation of the pitch control actuation system 22 so as to achieve the desired blade pitch angle, as shown in step 2. The normal pitch control mode has a lower threshold for performing the pitch angle adjustment operation, thus providing substantially continuous adjustment of the pitch angle of the blade 12, including in response to smaller and / or instantaneous changes in the operating conditions, so as to provide precise control of the rotor speed and the generator speed and to optimize and / or maximize the power output of the WTG 10.

[0053] During certain operating conditions, such as when the external power grid 2 is completely unavailable or determined to be unstable, the WTG 10 can be disconnected from the external power grid 2 and prevented from supplying power to it. In this case, for example, a "grid loss" situation is detected by the PPC 7 and / or the WTG controller 20, and the WTG 10 automatically switches from the normal mode to a separate standby mode, in which the WTG 10 continues to operate (i.e., the rotor 11 continues to rotate), but the WTG 10 does not operate to supply power to the external power grid 2, as shown in step 3. In some cases, the rotor 11 can continue to rotate without interruption, although in other cases, the rotor 11 can initially stop when a grid loss is detected and then restart, for example, by feathering the blades 12.

[0054] During a grid loss, while the WTG 10 is operating in the standby mode, the electronic system 21 can be disconnected from its normal power source. To enable the WTG 10 to continue operating during a grid loss, the WTG controller 20 and various other critical subsystems are at least intermittently powered by the WTG power system 23. However, to minimize the use of standby power and maintain the life of the BSS 24, power supply to non-critical subsystems including, for example, the lift system, lighting system, heating system, cooling system, ventilation system, hydraulic pump system, and non-critical sensor system can be automatically stopped in the standby mode.

[0055] While the WTG 10 is operating in the standby mode and the rotor 11 continues to rotate, the WTG 10 can be operated, optionally using the same generator 16 and power converter 19 used during the normal operation of the WTG 10, to generate backup power to be supplied to the BSS 24, as shown in step 4. In some cases, the BSS 24 can be charged at least substantially continuously, for example, by trickle charging, although in other cases, the BSS 24 can be charged only when charging conditions are met, such as when the BSS 24 is below an energy threshold.

[0056] When the WTG 10 enters the standby mode, power supply to the pitch angle control module 40 is also stopped, such that the pitch angle of the blades 12 is no longer controlled using the normal pitch control mode. Instead, the pitch angle of the blades 12 is controlled according to a separate standby pitch control mode, as shown in step 5.

[0057] In the standby pitch control mode, the speed control module 30 continues to monitor the generator speed. In some embodiments, the generator speed can be monitored at a lower frequency, e.g., with a monitoring period of 10 seconds, when the WTG is operating in the standby mode compared to when it is operating in the normal mode. The generator speed is then compared with a target generator speed, as shown in step 6. The target generator speed can be a preset speed, which can be set, for example, during the design, installation, or calibration of the WTG 10. Alternatively, the target generator speed can be variable and can be calculated during the operation of the WTG 10. The target generator speed is preferably a speed that is well-suited for generating backup power during a grid loss. In this embodiment, the target generator speed is preset to 60 rpm, although other values, such as 80 rpm or 100 rpm, can equally be selected. It has been determined that generator speeds in the range of 40 - 100 rpm are particularly suitable for generating backup power in the standby mode.

[0058] In the standby pitch control mode, if the speed control module 30 determines that the current generator speed deviates from the target generator speed for a duration or to a greater or significant extent, the pitch angle of the blade 12 is adjusted, as shown in step 7. In particular, if the generator speed continuously falls outside a first threshold of + / - 20 rpm (or + / - 30%) of the target generator speed for a period of at least 300 seconds (i.e., above 80 rpm or below 40 rpm), it is determined that a first activation condition corresponding to a persistent error in the generator speed has been met, and the pitch angle of the blade is adjusted to reduce or eliminate the speed error. Similarly, if the generator speed falls outside a second threshold of +60 rpm / -40 rpm (or +100% / -65%) of the target generator speed (i.e., above 120 rpm or below 20 rpm), it is determined that a second activation condition corresponding to a greater or significant error in the generator speed has been met, and the pitch angle of the blade is adjusted to reduce or eliminate the speed error. However, if neither of these activation conditions is met, it is determined that no pitch angle adjustment is required, in which case the pitch angle of the blade 12 remains unadjusted.

[0059] In this way, the pitch angle of the blade is adjusted only in response to persistent or significant changes in the operating conditions and not in response to transient or small changes, such that the rotor speed and the generator speed can be kept within an acceptable range while also minimizing the power consumed by the WTG 10 in performing the pitch angle adjustment operation. In some embodiments, the pitch angle of the blade 12 can be adjusted at a lower pitch rate, e.g., 20% of the normal pitch rate, when the WTG is operating in the standby mode compared to when it is operating in the normal mode, in order to further reduce power consumption.

[0060] According to a possible embodiment, if the speed control module 30 determines that the pitch angle of the blade 12 is to be adjusted while the WTG 10 is operating in the standby mode (e.g., if the first and / or second activation conditions have been met), the pitch angle control module 40 is reactivated and operated to control the pitch angle of the blade 12 so as to reduce or eliminate the error between the generator speed and the target generator speed, as shown in step 8. In some cases, if it is determined that the pitch angle of the blade 12 is to be adjusted while the WTG 10 is operating in the standby mode, the pitch angle of the blade 12 can be adjusted according to the normal pitch control mode. However, once the pitch angle of the blade 12 has been adjusted, the pitch angle control module 40 is shut down to prevent further unnecessary pitch angle adjustment operations from being performed. In other embodiments, when the WTG is operating in the standby mode, the pitch angle adjustment can be controlled by a separate control module, such as the speed control module 30 or another module forming part of the WTG controller 20. In this case, it may not be necessary to reactivate the pitch angle control module 40.

[0061] While the WTG 10 is operating in the standby mode, the PPC 7 and the WTG controller 20 continue to monitor the availability of the external power grid 2. Once the fault has been cleared and the external power grid 2 can receive power again, the WTG 10 reconnects to the external power grid 2 and returns to the normal mode for supplying power to the external power grid 2, as shown in step 9. After the WTG 10 re-enters the normal mode, the pitch angle control module 40 is reactivated and operated to continuously control the pitch angle of the blade 12 according to the normal pitch control mode.

[0062] Now reference will be made to Figure 5 the control of the pitch angle of the blade 12 in the case where the first and / or second activation conditions are met in the standby pitch control mode.

[0063] The current generator speed is compared with the target generator speed, as described above in relation to step 7. As long as the generator speed remains within the first threshold (i.e., between the first / low threshold upper limit and the first / low threshold lower limit), no measures are taken to adjust the pitch angle of the blade 12 and the pitch angle control module 40 is not activated. However, if the generator speed continuously falls outside the first threshold for at least 300 seconds, it can be determined that the operating conditions of the WTG 10 have changed continuously, and the pitch angle control module 40 is reactivated and operated to adjust the pitch angle of the blade 12. In this case, the gain value "K" for setting the pitch angle of the blade increases to the value 1 at a first gain rate over a period of time, such that the pitch angle of the blade can be adjusted according to the normal pitch control mode.

[0064] If the generator speed error is reduced or eliminated, the gain value is reduced back to the value 0 (as Figure 5as shown by the line labeled "A" in ) and deactivate the pitch angle control module 40. On the other hand, if the generator speed error continues to increase and the generator speed subsequently falls outside the second threshold (e.g., above the second / high threshold upper limit or below the second / high threshold lower limit), it is determined that a large or significant change has occurred in the operating condition of the WTG 10, and the gain value K is further increased to a value above 1 at a second gain rate (as Figure 5 shown by the line labeled "B" in ) to artificially increase the responsiveness of the pitch angle control module 40. After the generator speed error has been eliminated, the gain value then decreases back to the value 0 and the pitch angle control module 40 is deactivated.

[0065] Figure 5 shows a situation where the second activation condition is only satisfied after the first activation condition has been satisfied. However, it is also possible for the second activation condition to be satisfied without the first activation condition being satisfied, e.g., in the case of a rapid increase or decrease in the generator speed. In such a case, the pitch angle control module 40 can be reactivated, and the gain value K can be increased from the value 0 without waiting for the first activation condition to also be satisfied before applying corrective measures.

[0066] The above description relates to one possible embodiment of the present invention. However, it is understood that many modifications and variations to the above embodiments are possible within the scope of the appended claims.

[0067] For example, the above standby pitch control mode includes first and second activation conditions for triggering pitch angle adjustment while the WTG is operating in the standby mode, each activation condition including a generator speed threshold based on the deviation from a target generator speed. However, it is understood that different activation conditions can equally be selected in other embodiments of the present invention. For example, in other embodiments, the standby pitch control mode can include only one of the above first and second activation conditions, or alternatively can include another activation condition in addition to the above first and second activation conditions. Furthermore, the thresholds for determining when to adjust the pitch angle of the blade can have values different from those above and can equally be based on different speed parameters other than the generator speed, such as the rotor speed or the speed of another drivetrain component. Additionally, the thresholds for determining when to adjust the pitch angle of the blade can have separately defined start and end points, which do not need to be based on any explicitly defined target speed.

[0068] In one embodiment, in the case where the power grid is lost for an extended period, e.g., due to damage to the export cable, the method of operating a wind turbine can be applied during installation. In such a case, the WTG can be operated with this method until normal mode operation can be established. In such a case, the embodiment is directed to:

[0069] A method for operating a wind turbine generator (WTG) including a pitch control system before connecting to an external power grid, the method comprising:

[0070] a) putting the WTG in a normal operation mode, including enabling the WTG to have the ability to control the pitch angle of the blades;

[0071] c) detecting that it is impossible to be in the normal operation mode because the WTG is not connected to the external power grid;

[0072] d) operating the WTG in a standby mode; and

[0073] e) while the WTG is operating in the standby mode, using a standby pitch control mode different from the normal pitch control mode to control the pitch angle of the blades according to the monitored speed parameter of the WTG, wherein the response of the standby pitch control mode is slower than that of the normal pitch control mode, so that when the WTG is operating in the standby mode, the power consumption of the pitch control system is reduced.

[0074] Other variations and modifications will also be readily apparent to those skilled in the art.

Claims

1. A method of operating a wind turbine generator including a pitch control system, the method comprising: a) Operate the wind turbine generator in normal mode while connected to an external power grid; b) While operating the wind turbine generator in normal mode, use a normal pitch control mode to control the pitch angle of the blades; c) Detect a grid loss; d) During the grid loss, operate the wind turbine generator in standby mode, wherein, during standby mode, operate the wind turbine generator to: generate backup power to supply power to one or more subsystems of the wind turbine generator and charge an energy storage system associated with the wind turbine generator; or generate backup power to charge an energy storage system associated with the wind turbine generator; and e) While operating the wind turbine generator in standby mode, use a standby pitch control mode different from the normal pitch control mode to control the pitch angle of the blades according to monitored speed parameters of the wind turbine generator, wherein the response of the standby pitch control mode is slower than that of the normal pitch control mode, such that when the wind turbine generator is operating in standby mode, the power consumption of the pitch control system is reduced, wherein, while operating the wind turbine generator in standby mode, apply a higher activation threshold such that the pitch angle of the blades is adjusted only if the monitored speed parameter deviates from the target speed during a duration and / or to a significant extent, wherein, when the wind turbine generator is operating in standby mode, if a first activation condition is met, the pitch angle of the blades is adjusted, but if the first activation condition is not met, no adjustment is made; the first activation condition includes the monitored speed parameter falling outside a first threshold during a specified time period, wherein, while operating the wind turbine generator in standby mode, if a second activation condition is met, the pitch angle of the blades is adjusted, but if the second activation condition is not met, no adjustment is made; the second activation condition includes the monitored speed parameter falling outside a second threshold.

2. The method according to claim 1, wherein, The first threshold has an upper limit of +20% of the target speed and / or a lower limit of -20% of the target speed.

3. The method according to claim 1, wherein, The first threshold is greater than or equal to a generator speed range of 20 rpm.

4. The method according to claim 1, wherein, The specified time period is at least 30 seconds.

5. The method according to claim 1, wherein, The second threshold has an upper limit of +50% of the target speed and / or a lower limit of -30% of the target speed.

6. The method according to claim 1, wherein, The second threshold is greater than or equal to a generator speed range of 50 rpm.

7. The method according to any one of claims 1-4, wherein If it is determined that the pitch angle of the blades is to be adjusted while the wind turbine generator is operating in standby mode, the method includes increasing the gain coefficient for controlling the pitch angle of the blades.

8. The method according to claim 7, wherein If the first activation condition has been met, increase the gain coefficient to a first predetermined value.

9. The method according to claim 7, wherein, If the second activation condition has been met, increase the gain coefficient to a value greater than 1.

10. The method according to claim 1, wherein, The wind turbine generator is provided with a pitch angle control module for setting the pitch angle of the blades while the wind turbine generator is operating in normal mode, and the method includes shutting down the pitch angle control module while the wind turbine generator is operating in standby mode.

11. The method according to claim 10, the method further comprising re - activating the pitch angle control module and using the pitch angle control module to set the pitch angle of the blade if it is determined that the pitch angle of the blade is to be adjusted while the wind turbine generator is operating in standby mode.

12. The method according to claim 1, wherein, When the wind turbine generator is operating in standby mode, a lower pitch rate is applied when adjusting the pitch angle of the blade compared to when the wind turbine generator is operating in normal mode.

13. The method according to claim 1, wherein When the wind turbine generator is operating in standby mode, the speed parameter is monitored at a lower frequency compared to when the wind turbine generator is operating in normal mode.

14. A controller configured to control the operation of a wind turbine generator according to the method of any one of claims 1 - 13.

15. A computer program product downloadable from a communication network and / or stored on a machine - readable storage medium, the computer program product comprising program code instructions for implementing the method of any one of claims 1 to 13.

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