Wind turbines and their control systems and methods

Abstract

A method for controlling a wind turbine connected to a power grid is provided. The method includes generating a turbine control reference signal and a power grid control reference signal. The turbine control reference signal is provided to a machine-side unit of a power or torque control system of the turbine to control the amount of energy generated by the turbine. The power grid control reference signal is provided to a line-side unit of the power or torque control system to control the amount of energy transmitted to the power grid based on the power grid control reference signal.

Description

Technical Field

[0001] This invention relates to a method for controlling a wind turbine using a power reference signal, and to a control system for a wind turbine. Background Technology

[0002] Modern wind turbines are typically variable-speed turbines. In such turbines, power output is controlled, at least in specific operating modes, by controlling the speed at which the blades can rotate. For example, torque can be applied to the rotor to limit the rotational speed during periods of high wind. A power controller or torque control system can be used to control the rotor speed. A power reference signal, typically generated by the turbine's main controller, is then used to control the power or torque control system. As used herein, a power or torque control system can refer to the wind turbine's converter, power controller, or torque controller.

[0003] A power reference signal can be generated based on the requirements of various turbine control systems. For example, the power reference signal can be based on an average rotor speed set under semi-static wind conditions, and small variations can be provided to that average rotor speed in response to temporary changes in conditions. For instance, small variations in the power reference signal can be used to provide damping to counteract changes in the turbine.

[0004] However, the extent to which such a control system can alter the power generated by the turbine is limited by the demand of the grid to which the turbine is connected. Power fluctuations caused by the control system pose a risk of being transmitted to the grid. Consequently, it may be necessary to limit the amount of power variation that the turbine control system can impose, thus limiting the effectiveness of these systems.

[0005] Some grid operators are introducing new turbines that should mimic the requirements of synchronous generators. In a synchronous generator, there is a direct link between the grid and the generator rotor, allowing the generator to eliminate power disturbances in the grid. When this virtual synchronous generator concept is implemented in wind turbines, it means that disturbances in the grid are directly fed back into the turbine's mechanical power, thus interfering with the turbine's control system. Summary of the Invention

[0006] A first aspect of the present invention provides a method for controlling a wind turbine connected to a power grid, the method comprising:

[0007] Generate a turbine control reference signal that includes a primary static power level signal and one or more auxiliary control system signals, the auxiliary control system signals including a damping signal to suppress oscillations in the wind turbine;

[0008] Generate a power grid control reference signal as the main static power level signal;

[0009] Provide turbine control reference signals to the machine-side unit of the power or torque control system of the wind turbine;

[0010] The amount of energy generated by the wind turbine is controlled using a machine-side unit based on turbine control reference signals.

[0011] Providing grid control reference signals to the line-side units of the power or torque control system; and

[0012] The line-side unit uses grid control reference signals to control the amount of energy transmitted to the grid.

[0013] The turbine control reference signal is the sum of the grid control reference signal and the one or more auxiliary control system signals, and the time correlation difference between the turbine control reference signal and the grid control reference signal is zero on average within a predetermined time window.

[0014] The turbine control reference signal thus includes the main signal and one or more auxiliary control system signals. The main static power level signal can be a semi-static signal, meaning that any change is noise-dependent.

[0015] In some embodiments, the duration of the predetermined time window may be, for example, between 10 seconds and 2 minutes, or between 30 seconds and 1 minute.

[0016] In some embodiments, controlling the amount of energy generated by the wind turbine may include controlling the amount of energy supplied by the machine-side unit to a battery connected between the machine-side unit and the line-side unit, or the amount of energy extracted by the machine-side unit from the battery. Alternatively or additionally, controlling the amount of energy transmitted to the grid may include controlling the amount of energy extracted by the grid from the battery, or the amount of energy supplied by the grid to the battery.

[0017] In some embodiments, the method may further include receiving grid performance indicators. Controlling the amount of energy supplied to or extracted from the battery may be based on grid performance indicators.

[0018] In some embodiments, the method may further include adjusting the turbine control reference signal and / or the grid control reference signal based on the remaining storage capacity of the battery.

[0019] In some embodiments, controlling the amount of energy generated by a wind turbine may include controlling the amount of energy supplied by the turbine to a resistor connected between a machine-side unit and a line-side unit.

[0020] In some embodiments, the power or torque control system may be or includes a converter. And it is to be understood herein that the term converter is used in a broad sense to include both power electronics and logic controllers, such that the converter as a whole can control the actual counter-torque applied to the rotor and / or control the actual power injected into the power grid.

[0021] In some embodiments, controlling the energy transmitted to the power grid may include an analog synchronous generator.

[0022] A second aspect of the present invention provides a wind turbine control system, the wind turbine control system being configured to:

[0023] A turbine control reference signal is generated, comprising a primary static power level signal and one or more auxiliary control system signals, wherein the auxiliary control system signals include a damping signal to suppress oscillations in the wind turbine.

[0024] Generate power grid control reference signals;

[0025] Turbine control reference signals are provided to the machine-side unit of the power or torque control system of the wind turbine to control the amount of energy generated by the wind turbine.

[0026] The grid control reference signal is provided to the line-side unit of the power or torque control system to control the amount of energy transmitted to the grid.

[0027] The turbine control reference signal is the sum of the grid control reference signal and the one or more auxiliary control system signals, and the time correlation difference between the turbine control reference signal and the grid control reference signal is zero on average within a predetermined time window.

[0028] The control system may also be configured to perform the method described according to any embodiment of the first aspect.

[0029] A third aspect of the invention provides a wind turbine that includes a control system according to any embodiment of the second aspect. Attached Figure Description

[0030] Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

[0031] Figure 1 This is a schematic diagram of a wind turbine;

[0032] Figure 2 This is a schematic diagram of the control system of a wind turbine;

[0033] Figure 3 The response of the virtual synchronizer to grid disturbances is shown;

[0034] Figure 4 The components of a turbine control system according to an embodiment of the present invention are shown;

[0035] Figure 5 A converter including a battery is shown;

[0036] Figure 6 The method according to the present invention is shown. Detailed Implementation

[0037] Figure 1 An example of a wind turbine 100 is shown in a schematic perspective view. The wind turbine 100 includes a tower 102, a nacelle 103 at the top of the tower, and a rotor 104 operatively coupled to a generator housed within the nacelle 103. In addition to the generator, the nacelle houses various components necessary for converting wind energy into electrical energy, as well as various components necessary for operating, controlling, and optimizing the performance of the wind turbine 100. The rotor 104 of the wind turbine includes a central hub 105 and a plurality of blades 106 projecting outward from the central hub 105. In the illustrated embodiment, the rotor 104 includes three blades 106, but the number can vary. Furthermore, the wind turbine includes a control system. The control system can be located inside the nacelle or distributed at several locations within the turbine and is communicatively connected.

[0038] Wind turbine 100 may be included in a collection of other wind turbines belonging to a wind farm, also known as a wind power plant or wind park, which serves as a power generation facility connected to the power grid via transmission lines. The power grid typically consists of a power plant network, transmission circuits, and substations coupled to the transmission line network, which delivers power to end-user loads and other customers of the public utility.

[0039] Figure 2 An embodiment of a turbine control system 200 and components of a wind turbine 100 are schematically illustrated. The wind turbine includes rotor blades 106 mechanically connected to a generator 202 via a gearbox 203. In direct drive systems and other systems, the gearbox 203 may be omitted. The electricity generated by the generator 202 is injected into the power grid 204 via a power converter 205. The converter 205 includes a machine-side unit, a DC link, and a line-side unit. The power generated by the turbine 100 is transferred from the machine-side unit to the DC link and then to the line-side unit to be delivered to the power grid 204. The generator 202 and converter 205 may be based on a full-size converter (FSC) architecture or a doubly-fed induction generator (DFIG) architecture, but other types may be used.

[0040] The turbine control system 200 includes several components, including at least one main controller 220 with a processor and memory, enabling the processor to perform computational tasks based on instructions stored in the memory. Typically, the wind turbine controller ensures that, during operation, the wind turbine generates the requested power output level. This is achieved by adjusting the pitch angle of the blades 106 and / or the power extraction of the converter 205. To this end, the control system includes a pitch system and a power system, the pitch system including a pitch controller 207 controlled using a pitch reference signal 208, and the power system including a power controller 209 controlled using a power reference signal 206. The wind turbine rotor includes rotor blades whose pitch can be adjusted by a pitch mechanism. The rotor includes individual pitch systems capable of adjusting the pitch of the rotor blades individually, and may include a common pitch system that simultaneously adjusts all pitch angles on all rotor blades. The turbine control system or components of the turbine control system may be housed in a power plant controller (not shown) so that the turbine can be operated based on externally provided instructions.

[0041] Power controller 209 and converter 205 (including machine-side converter unit, DC link, and line-side converter unit) can be considered together as an example of a power or torque control system. Power controller 209 may include independent control blocks for controlling each of the machine-side unit and line-side unit of the converter. As used herein, "machine-side unit" and "line-side unit" are to be understood as generally referring to both the corresponding power electronics system and the corresponding logic controller, such that the line-side unit / machine-side unit as a whole can control the actual counter-torque applied to the rotor / the actual power injected into the grid. Thus, in the embodiments described below, where the machine-side unit receives a turbine control reference signal and controls the power extracted from the wind based on the reference signal, it is to be understood that the machine-side logic controller receives the turbine control reference signal and controls the machine-side power electronics system to control the power extracted from the wind. Similarly, where the line-side unit bases the amount of power transmitted to the grid on a grid control reference signal, it is to be understood that the line-side logic controller receives the grid control reference signal and controls the line-side power electronics system to control the power transmitted to the grid. The machine-side logic controller and / or the line-side logic controller can be incorporated into the power controller 209.

[0042] In a conventional system, a single power reference signal 206 is generated to control the amount of power extracted from wind power and delivered to the grid by the turbine 100. In an embodiment, such a single power reference signal 206 may include a primary component and an auxiliary component. The primary component sets the static power output of the turbine 100. The auxiliary component includes signals from one or more auxiliary control systems, such as a damping system for the turbine 100, which serve as small variations on the primary signal. These small variations in the power reference signal 206 provide time-limited fluctuations in the mechanical power or torque of the turbine 100 and can therefore be used, for example, to suppress variations in the turbine. The auxiliary control system feeding into the auxiliary component may include a side-to-side tower damping (SSTD) system, a drivetrain damping (DTD) system, and / or an extended power control (EPC) system.

[0043] The auxiliary component of the power reference signal 206 causes variations in the amount of power generated by the turbine 100. These variations can then be transmitted to the power grid 204 via the line-side unit of the converter 205, resulting in power fluctuations such as flickering. Consequently, it is necessary to limit the amount of power variation that the turbine's auxiliary control system can apply.

[0044] Grid operators are also implementing new requirements for wind turbines to be used as virtual synchronous generators (VSMs), simulating the response of conventional synchronous generators. In a synchronous generator, there is a direct link between the rotor used for power generation and the grid. Disturbances on the grid are fed back into the generator to eliminate them. While this is beneficial for grid operation, it can have a detrimental effect on the performance of wind turbines used as VSMs.

[0045] Figure 3 Various grid disturbances and expected VSM generator responses are shown in (a)-(f). Figure 3 (a), (c), and (e) illustrate disturbances on the power grid, and Figure 3 (b), (d), and (f) show the expected corresponding responses of the virtual synchronizer.

[0046] Figure 3 (a) shows the oscillation of the AC electrical frequency of the power in the grid with a small time correlation to its nominal value of 50 Hz. Figure 3 (b) illustrates the expected response of the VSM, where the power generated by the VSM oscillates accordingly to suppress oscillations in the power grid. Such power oscillations in a wind turbine would resist the turbine's own damping system (e.g., SSTD) and thus limit the mechanical damping control available to the turbine.

[0047] Figure 3 (c) shows a large deviation in the AC frequency, and Figure 3(d) shows the corresponding VSM response. In this case, the VSM is expected to increase or decrease the generated power by approximately 20% to smooth out changes in grid frequency. Such a large-scale power change conflicts with the purpose of the power (or partial load) controller, reduces turbine efficiency, and may damage turbine mechanical components.

[0048] Figure 3 (e) illustrates the abrupt change in the grid angle (i.e., the phase difference between current and voltage in the grid). Figure 3 As shown in (f), the VSM is expected to compensate with large pulses in the generated power. Such large pulses could potentially damage components of the wind turbine, especially the drivetrain.

[0049] Figure 4 Elements of a turbine control system 400 for a wind turbine 100 are shown, which can be used to decouple the power generated by the turbine 100 from the power supplied to the power grid 204. This decoupling protects the power grid 204 from power variations used to control the turbine 100 and protects the turbine 100 from requirements of the power grid 204 (e.g., VSM requirements).

[0050] Decoupling the turbine 100 and the power grid 204 in this manner offers several advantages. The damping system of the turbine 100 can apply larger amplitude variations to the generated power than is conventionally possible, since the variations are no longer transmitted to the power grid 204. This allows for reduced pitching activity, as more power control can be prioritized over pitching control. Pitching activity can also be reduced because constant power instability of speed control is limited. Similarly, drivetrain load can be reduced by using DTD damping more aggressively than is conventionally possible and limiting constant power strategy instability. Reduced pitching activity and drivetrain load lower the fatigue rate of turbine 100 components and thus extend turbine life. Furthermore, decoupling reduces flicker in the power grid 204 because turbine damping system activity is no longer seen in the grid, and the turbine's annual energy production (AEP) can be increased due to more efficient turbine control.

[0051] The control system 400 generates two distinct power control reference signals: a turbine control reference signal 401 and a power grid control reference signal 402. The turbine control reference signal 401 is provided to the machine-side unit 409 of the power or torque control system of the turbine 100, such as the machine-side unit of the converter 205. The machine-side unit 409 adjusts the mechanical operation of the turbine 100 based on the turbine control reference signal 401 to control the amount of energy extracted by the turbine 100 from wind power.

[0052] A grid control reference signal 402 is provided to a line-side unit 410 of a power or torque control system (e.g., the line-side unit of converter 205), which is configured to control the amount of energy transferred from turbine 100 to grid 204 based on the grid control reference signal. The line-side unit 410 can also make the power supplied to grid 204 based on current grid conditions, for example, to simulate the response of a synchronous machine to disturbances on grid 204. In some embodiments, a feedback mechanism from grid 204 can be used to provide the turbine controller with information about the current state of the grid, such as grid performance indicators. Grid performance indicators can provide an assessment of the health of grid 204 and / or can indicate any disturbances in grid 204, such as changes in frequency or grid angle. This feedback can be used to inform the generation of control reference signals 401, 402, such that the reference signals are partially based on the current conditions of grid 204.

[0053] Each turbine 100 in a wind farm can be associated with an individual line-side unit 410, or multiple turbines can supply energy to a common line-side unit.

[0054] In a conventional system with only a single power control signal, the power generated by turbine 100 is equal to the power transmitted to grid 204 at all times. In this invention, turbine control reference signal 401 can be different from grid control reference signal 402, so the energy generated by the turbine at a particular time may be different from the energy transmitted to grid 204 at that time, thus providing the decoupling between turbine 100 and grid 204 as described above.

[0055] The turbine control reference signal 401 includes a main component, which sets the static power level for turbine operation based on the current conditions experienced by the turbine. The main component can be generated by the main controller 220 (or a partial load controller) of the turbine 100. Figure 4 As shown, this principal component can be the power grid control reference signal 402.

[0056] like Figure 4As shown, the turbine control reference signal 401 also includes several auxiliary control system signals 403-405, each of which is generated by a corresponding auxiliary control system 406-408. The auxiliary control system signals 403-405 are summed with the principal component of the turbine reference signal (i.e., the grid control reference signal 402 in the illustrated embodiment) to form the turbine control reference signal 401. The auxiliary control system signals 403-405 include damping system signals designed to suppress oscillations in the turbine by applying small variations to the static power generated by the turbine 100. The auxiliary control system signals are therefore time-varying signals. In this embodiment, the signal may be an oscillating signal whose amplitude and phase are set or determined by the corresponding auxiliary control system according to the desired damping result. Figure 4 In the specific embodiment shown, the damping system signals include an SSTD control signal 403 generated by the SSTD controller 406 and a DTD control signal 404 generated by the DTD controller 407. The turbine control reference signal 401 is also formed by the EPC control signal 405 generated by the EPC controller 408. Although shown as different components, any of the auxiliary control systems 406-408 can actually be implemented in the main controller 220 of the turbine 100.

[0057] The inclusion of auxiliary control system signals 403-405 in the turbine control reference signal 401 implies that, at a given moment, the amount of energy extracted by the turbine from the wind can be greater than the energy transferred to the power grid 204. This excess energy can be channeled into a resistor connected between the machine-side and line-side units, for example, a resistor connected in the DC link between the machine-side and line-side units of converter 205. In such a case, the difference between control reference signals 401 and 402 can be controlled to ensure that the machine-side-line-side power difference can be safely channeled into the resistor without causing it to overheat. For example, a feedback mechanism can exist from the resistor to the turbine controller, allowing control reference signals 401 and 402 to be generated based on the current state of the resistor and the current conditions experienced by turbine 100.

[0058] Alternatively, excess energy can be stored in a battery connected between the machine-side unit and the line-side unit. Figure 5 The components of the converter 500, which incorporates this battery 504, are shown.

[0059] The converter 500 includes a machine-side unit 501 connected to the line-side unit 502 via a DC link 503. The line-side unit 502 transmits power to the power grid 504.

[0060] Machine-side unit 501 supplies generated energy to DC link 503 based on turbine control reference signal 401 generated as described above. Line-side unit 502 extracts energy from DC link 503 and supplies it to grid 504 based on grid control reference signal 402 also generated as described above. In some embodiments, line-side unit 502 may additionally extract energy from DC link 503 based on current grid conditions, for example, to provide a virtual synchronizer response.

[0061] As described above, converter 500, along with its machine-side unit 501 and line-side unit 502, should generally be considered to refer to both the logic controllers that receive control reference signals 401 and 402 and the power electronic systems controlled by these logic controllers. Thus, converter 500 can be considered an example of a power or torque controller. The logic controller can be implemented within a power controller (e.g., power controller 209). In such a case, the converter power electronic system, together with the power controller, can be considered to form a power or torque controller.

[0062] Due to the different control reference signals 401 and 402, at any given time, the energy transmitted from machine-side unit 501 to DC link 503 may not be equal to the energy extracted from DC link by line-side unit 502. Battery 505, connected to DC link 503, provides a buffer for this energy difference. When turbine 100 provides excess energy, the excess energy can be stored in battery 505. When the power grid 204 requires more energy than turbine 100 currently generates, for example, to smooth out disturbances in the power grid 204 by providing a VSM response, excess energy can be extracted from battery 505.

[0063] Since battery 505 has a limited storage capacity, a feedback mechanism can be used to provide the turbine controller with information about the current state of battery 505. In this way, turbine control reference signal 401 and grid control reference signal 402 can be generated based on the current state of battery 505, thereby ensuring that excess energy can be safely stored in battery 505. Specifically, the difference between the generated power and the extracted power can be limited based on the current capacity of battery 505.

[0064] The capacity of battery 505, which can be used to buffer the difference between the generated and extracted power, can also be dynamically determined based on current grid conditions. The storage controller can receive a grid performance indicator representing the current state or health of grid 504. Based on this grid performance indicator, the storage controller can determine the capacity of battery 505 that should be retained to meet the requirements of grid 504 (e.g., to provide VSM response). Therefore, only the non-reserved capacity of battery 505 can be used as a buffer. The dynamically determined non-reserved capacity of battery 505 can be fed back to the turbine controller, causing turbine control reference signal 401 and grid control reference signal 402 to be generated based on the current dynamic capacity of battery 505.

[0065] It should be understood that, when averaged over time, the power generated by turbine 100 should be substantially equal to the energy supplied to grids 204 and 504 (minus any inefficiency losses). Turbine control reference signal 401 and grid control reference signal 402 can be generated to ensure that the difference between the generated energy and the energy transmitted to grids 204 and 504 is averaged to zero over a specific time window. For example, the time window could be between 10 seconds and 2 minutes, or between 30 seconds and 1 minute.

[0066] Figure 6 A method 600 for controlling a wind turbine 100 according to the present invention is shown.

[0067] At step 601, a turbine control reference signal is generated, and at step 602, a power grid control reference signal is generated. (As described above...) Figure 4 The turbine control reference signal and the power grid control reference signal can be generated by the controller of the turbine 100. The turbine control reference signal can be a power reference signal or a torque reference signal.

[0068] At step 603, a turbine control reference signal is provided to the machine-side unit of the turbine's power or torque control system, such as the machine-side unit of the converter.

[0069] At step 604, the machine-side unit controls the amount of energy generated by turbine 100 based on turbine control reference signals.

[0070] At step 605, a grid control reference signal is provided to the line-side unit of the power or torque control system, such as the line-side unit of a converter. The line-side unit can be connected to the machine-side unit via a DC link.

[0071] At step 606, the line-side unit can be used to control the amount of energy transmitted to the grid based on the grid control reference signal.

[0072] A wind turbine control system (e.g., wind turbine control system 200) can be configured to execute method 600. Specifically, a memory associated with the turbine control system can store instructions that, when executed by one or more controllers of the wind turbine control system, execute method 600.

[0073] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method for controlling a wind turbine connected to a power grid, the method comprising: A turbine control reference signal is generated, comprising a primary static power level signal and one or more auxiliary control system signals, wherein the auxiliary control system signals include a damping signal to suppress oscillations in the wind turbine. A power grid control reference signal is generated as the main static power level signal; The turbine control reference signal is provided to the machine-side unit of the power or torque control system of the wind turbine; The machine-side unit uses the turbine control reference signal to control the amount of energy generated by the wind turbine. The power grid control reference signal is provided to the line-side unit of the power or torque control system; as well as The line-side unit uses the grid control reference signal to control the amount of energy transmitted to the grid. The turbine control reference signal is the sum of the grid control reference signal and the one or more auxiliary control system signals, and the time correlation difference between the turbine control reference signal and the grid control reference signal is zero on average within a predetermined time window.

2. The method according to claim 1, wherein, The auxiliary control system signal is a time-varying signal.

3. The method according to claim 1 or 2, wherein, The one or more auxiliary control system signals are oscillating signals with amplitude and phase determined by the corresponding control system.

4. The method according to claim 1, wherein, The duration of the predetermined time window is between 10 seconds and 2 minutes, or between 30 seconds and 1 minute.

5. The method according to claim 1 or 2, wherein, Controlling the amount of energy generated by the wind turbine includes controlling the amount of energy supplied by the machine-side unit to the battery connected between the machine-side unit and the line-side unit, or the amount of energy extracted by the machine-side unit from the battery.

6. The method according to claim 5, further comprising: Receive power grid performance indicators; as well as The amount of energy supplied to or extracted from the battery is controlled based on the power grid performance indicators.

7. The method of claim 5, further comprising adjusting the turbine control reference signal and / or the grid control reference signal based on the remaining storage capacity of the battery.

8. The method according to claim 1 or 2, wherein, Controlling the amount of energy generated by the wind turbine includes controlling the amount of energy supplied by the machine-side unit to a resistor connected between the machine-side unit and the line-side unit.

9. The method according to claim 1 or 2, wherein, The power or torque control system is a converter.

10. The method according to claim 1 or 2, wherein, The control of the energy transmitted to the power grid includes analog synchronous generators.

11. A wind turbine control system, wherein the wind turbine control system is configured to: A turbine control reference signal is generated, comprising a primary static power level signal and one or more auxiliary control system signals, wherein the auxiliary control system signals include a damping signal to suppress oscillations in the wind turbine. A power grid control reference signal is generated as the main static power level signal; The turbine control reference signal is provided to the machine-side unit of the power or torque control system of the wind turbine to control the amount of energy generated by the wind turbine. The grid control reference signal is provided to the line-side unit of the power or torque system to control the amount of energy transmitted to the grid. in, The turbine control reference signal is the sum of the grid control reference signal and the one or more auxiliary control system signals, wherein the time correlation difference between the turbine control reference signal and the grid control reference signal is zero on average within a predetermined time window.

12. The wind turbine control system according to claim 11, wherein, The wind turbine control system is also configured to perform the method according to any one of claims 2-10.

13. A wind turbine, the wind turbine comprising a wind turbine control system according to claim 11 or claim 12.

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