System and method for operating a wind turbine power system during low wind speeds

Abstract

This invention relates to systems and methods for operating wind turbine power systems during low wind speeds. A method for operating a wind turbine power system supplying active and reactive power to the power grid includes operating the generator of the wind turbine power system up to a first speed limit. The method also includes monitoring the wind speed at the wind turbine power system. When the wind speed drops below a predetermined threshold, the method includes reducing the first speed limit of the generator to a reduced speed limit of the generator. Furthermore, the method includes operating the generator at the reduced speed limit for a period of time during which the wind speed remains below the predetermined threshold to optimize the tip speed ratio of the wind turbine power system during low wind speeds, thereby increasing the power output of the wind turbine power system at low wind speeds.

Description

Technical Field

[0001] This disclosure generally relates to wind turbines, and more particularly to systems and methods for operating wind turbine power systems during low wind speeds to optimize the tip speed ratio (TSR), thereby increasing annual power generation (AEP). Background Technology

[0002] Generally, during wind turbine operation, wind strikes the rotor blades, and the blades convert wind energy into mechanical rotational torque that drives a low-speed shaft. The low-speed shaft drives a gearbox, which then progressively increases the low rotational speed of the low-speed shaft to drive a high-speed shaft at an increased rotational speed, whereby the high-speed shaft rotatably drives the generator rotor. In many conventional wind turbine configurations, the generator is electrically connected to a bidirectional power converter, which includes a rotor-side converter (RSC) that is connected to a line-side converter (LSC) via a regulated DC link. Each of the RSC and LSC typically includes groups of pulse-width modulated switching devices, such as insulated-gate bipolar transistor (IGBT) modules. The LSC converts the DC power on the DC link into AC output power, which is combined with power from the generator stator to provide multiphase power at a frequency substantially maintained at the grid bus frequency (e.g., 50 Hz or 60 Hz).

[0003] The aforementioned system is broadly referred to as a doubly-fed induction generator (DFIG) system. Its operating principle includes: rotor windings connected to the grid via slip rings; and a power converter controlling the rotor current and voltage. Control of the rotor voltage and current allows the generator to maintain synchronization with the grid frequency when wind turbine speeds change (e.g., the rotor frequency may differ from the grid frequency). Furthermore, the primary sources of reactive power from the DFIG system are the RSC (generator stator-side reactive power) and the LSC (generator line-side reactive power) via the generator. Using a power converter (specifically, the RSC) to control the rotor current / voltage makes it possible to adjust the reactive power (and active power) fed to the grid from the RSC independently of the generator's rotational speed. Additionally, the generator can input or output reactive power, allowing the system to support the grid during extreme voltage fluctuations.

[0004] Typically, the amount of reactive power supplied from the wind farm to the grid during steady and transient periods is established by specifications defined by the grid operator, whereby the wind farm controller determines the reactive power demand for each wind turbine within the wind farm. Local controllers at each wind turbine receive the reactive power demand and distribute it among the generator sources (e.g., between generator-side reactive power and line-side reactive power).

[0005] Generally, the minimum speed of the DFIG (i.e., the cut-in speed) is determined based on the voltage limit imposed by the RSC. Lowering or extending the turbine's minimum speed increases the DFIG's operating slip, requiring the RSC to operate at a higher voltage. In addition to the minimum turbine speed, the reactive power requirements from the DFIG also affect the voltage at the RSC terminals. Furthermore, as mentioned, most grid specifications require rated reactive power support throughout the entire operation of the wind turbine (i.e., from cut-in speed to rated speed). Providing rated reactive power at the minimum turbine speed further compels the RSC to operate at a higher voltage.

[0006] During periods of low wind speeds (e.g., from approximately 3 m / s to approximately 5 m / s), wind turbines should rotate at their minimum speed limit. To meet this requirement, the turbine controller commands the DFIG to operate at a higher TSR (beyond the optimal value). However, operating wind turbines at a higher TSR is not efficient and results in energy waste.

[0007] Therefore, the following improved systems and methods would be desirable in industry for operating wind turbine power systems during low wind speeds to allow for lower or optimized TSR, thereby improving AEP. Summary of the Invention

[0008] Aspects and advantages of the invention will be set forth in part in the description which follows, or may be apparent from the description, or may be learned by practice of the invention.

[0009] In one aspect, this disclosure relates to a method for operating a wind turbine power system that supplies active and reactive power to a power grid. The wind turbine power system includes a generator coupled to a power converter. The method includes operating the generator of the wind turbine power system up to a first speed limit. The method also includes monitoring the wind speed at the wind turbine power system. When the wind speed drops below a predetermined threshold, the method includes reducing the first speed limit of the generator to a reduced speed limit of the generator. Furthermore, the method includes operating the generator at the reduced speed limit for a period of time during which the wind speed remains below the predetermined threshold to optimize the tip speed ratio of the wind turbine power system during low wind speeds, thereby increasing the power output of the wind turbine power system at low wind speeds. In other words, at low wind speeds, the TSR is typically greater than the optimal TSR; therefore, reducing the speed limit of the generator reduces the TSR to a value closer to the optimal TSR.

[0010] In one embodiment, the predetermined threshold may include wind speeds up to approximately 5 meters per second (m / s). In another embodiment, the reduced speed limit may be in the range of approximately 85% to approximately 95% of the first speed limit. In yet another embodiment, reducing the generator's first speed limit to the reduced speed limit of the generator increases the power factor of the wind turbine power system during low wind speeds.

[0011] In an additional embodiment, reducing the generator's first speed limit to a reduced speed limit further includes transferring at least a portion of the reactive power to a reactive power compensation device. In such an embodiment, the power converter may include, for example, a line-side converter and a rotor-side converter, and the reactive power compensation device may include at least one of a line-side power converter, a VAR box, or an electrical balance of plant located at the interconnection point of the wind turbine power system.

[0012] In some embodiments, the generator may be a doubly-fed induction generator (DFIG). In another embodiment, the wind turbine power system may be one of multiple wind turbine power systems located within a wind farm that supplies active and reactive power to the grid. In such an embodiment, all or more wind turbine power systems may be connected to a common bus located within the wind farm.

[0013] In another aspect, this disclosure relates to a wind turbine power system configured to supply active and reactive power to a power grid. The wind turbine power system includes a wind turbine having a rotor. The rotor has a hub with a plurality of blades coupled thereto. The wind turbine also includes a generator coupled to the rotor and a power converter coupled to the generator. The wind turbine power system further includes a controller for controlling the operation of the wind turbine. The controller includes at least one processor configured to perform a plurality of operations, including but not limited to: operating the generator of the wind turbine up to a first speed limit; monitoring the wind speed at the wind turbine; reducing the first speed limit of the generator to a reduced speed limit of the generator when the wind speed drops below a predetermined threshold; and operating the generator at the reduced speed limit for a period of time during which the wind speed remains below the predetermined threshold, in order to optimize the tip speed ratio of the wind turbine during low wind speeds, thereby increasing the power output of the wind turbine at low wind speeds.

[0014] In another aspect, this disclosure relates to a method for operating a wind turbine power system that supplies active and reactive power to a power grid. The wind turbine power system includes a doubly-fed induction generator (DFIG) coupled to a power converter. The method includes monitoring the wind speed at the wind turbine power system. When the wind speed drops below a predetermined threshold, the method includes reducing the speed limit of the DFIG by a predetermined amount. Furthermore, the method includes maintaining the reduced speed limit for a period of time during which the wind speed remains below the predetermined threshold, in order to reduce the tip speed ratio of the wind turbine power system during low wind speeds, thereby increasing the power output of the wind turbine power system at low wind speeds.

[0015] Technical Solution 1. A method for operating a wind turbine power system that supplies active and reactive power to a power grid, the wind turbine power system including a generator connected to a power converter, the method comprising:

[0016] The generator of the wind turbine power system is operated up to a first speed limit;

[0017] Monitor the wind speed at the wind turbine power system;

[0018] When the wind speed drops below a predetermined threshold, the first speed limit of the generator is reduced to the reduced speed limit of the generator; and

[0019] The generator is operated at the reduced speed limit for a period of time during which the wind speed remains below the predetermined threshold in order to optimize the tip speed ratio of the wind turbine power system during low wind speeds, thereby increasing the power output of the wind turbine power system at low wind speeds.

[0020] Technical Solution 2. The method according to Technical Solution 1, characterized in that the predetermined threshold includes wind speeds up to approximately 5 meters per second (m / s).

[0021] Technical Solution 3. The method according to Technical Solution 1, characterized in that the reduced speed limit is in the range of approximately 85% to approximately 95% of the first speed limit.

[0022] Technical Solution 4. The method according to Technical Solution 1, characterized in that reducing the first speed limit of the generator to the reduced speed limit of the generator increases the power coefficient of the wind turbine power system during the low wind speed period.

[0023] Technical Solution 5. The method according to Technical Solution 1, characterized in that reducing the first speed limit of the generator to the reduced speed limit of the generator further includes transferring at least a portion of the reactive power to a reactive power compensation device.

[0024] Technical Solution 6. The method according to Technical Solution 5, characterized in that the power converter includes a line-side converter and a rotor-side converter, and the reactive power compensation device includes at least one of the line-side power converter, a VAR box, or a factory power balancing device located at the interconnection point of the wind turbine power system.

[0025] Technical Solution 7. The method according to Technical Solution 1, characterized in that the generator includes a doubly fed induction generator (DFIG), and the wind turbine power system is one of a plurality of wind turbine power systems located in a wind farm that supplies the active power and the reactive power to the power grid.

[0026] Technical Solution 8. The method according to Technical Solution 7, characterized in that all or more of the wind turbine power systems are connected to a common aggregation bus located within the wind farm.

[0027] Technical Solution 9. A wind turbine power system configured to supply active and reactive power to the power grid, the wind turbine power system comprising:

[0028] Wind turbines, which include:

[0029] A rotor, comprising a hub and a plurality of blades coupled to the hub.

[0030] A generator, which is connected to the rotor, and

[0031] A power converter, which is connected to the generator; and

[0032] A controller for controlling the operation of the wind turbine, the controller including at least one processor configured to perform a plurality of operations, the plurality of operations including:

[0033] The generator of the wind turbine is operated up to a first speed limit;

[0034] Monitor the wind speed at the wind turbine;

[0035] When the wind speed drops below a predetermined threshold, the first speed limit of the generator is reduced to the reduced speed limit of the generator; and

[0036] The generator is operated at the reduced speed limit for a period of time during which the wind speed remains below the predetermined threshold in order to optimize the tip speed ratio of the wind turbine during low wind speeds, thereby increasing the power output of the wind turbine at low wind speeds.

[0037] Technical Solution 10. The wind turbine power system according to Technical Solution 9, characterized in that the predetermined threshold includes wind speeds up to approximately 5 m / s.

[0038] Technical Solution 11. The wind turbine power system according to Technical Solution 9, characterized in that the reduced speed limit is in the range of approximately 85% to approximately 95% of the first speed limit.

[0039] Technical Solution 12. The wind turbine power system according to Technical Solution 9, characterized in that reducing the first speed limit of the generator to the reduced speed limit of the generator increases the power coefficient of the wind turbine during the low wind speed period.

[0040] Technical Solution 13. The wind turbine power system according to Technical Solution 9, characterized in that reducing the first speed limit of the generator to the reduced speed limit of the generator further includes transferring at least a portion of the reactive power to a reactive power compensation device.

[0041] Technical Solution 14. The wind turbine power system according to Technical Solution 13, characterized in that the power converter includes a line-side converter and a rotor-side converter, and the reactive power compensation device includes at least one of the line-side power converter, a VAR box, or a factory power balancing device located at the interconnection point of the wind turbine.

[0042] Technical Solution 15. The wind turbine power system according to Technical Solution 14, characterized in that the generator includes a doubly fed induction generator (DFIG), and the wind turbine is one of a plurality of wind turbines located in a wind farm that supplies the active power and the reactive power to the power grid.

[0043] Technical Solution 16. The wind turbine power system according to Technical Solution 15, characterized in that all or more of the wind turbines are connected to a common collection bus located within the wind farm.

[0044] Technical Solution 17. A method for operating a wind turbine power system that supplies active and reactive power to a power grid, the wind turbine power system comprising a doubly-fed induction generator (DFIG) coupled to a power converter, the method comprising:

[0045] Monitor the wind speed at the wind turbine power system;

[0046] When the wind speed drops below a predetermined threshold, the speed limit of the DFIG is reduced by a predetermined amount.

[0047] The reduced speed limit is maintained for a period of time during which the wind speed remains below the predetermined threshold in order to reduce the tip speed ratio of the wind turbine power system during low wind speeds, thereby increasing the power output of the wind turbine power system at low wind speeds.

[0048] Technical Solution 18. The method according to Technical Solution 17, wherein the predetermined threshold includes wind speeds up to approximately 5 meters per second (m / s).

[0049] Technical Solution 19. The method according to Technical Solution 17, characterized in that the predetermined amount is in the range of about 5% to about 15%.

[0050] Technical Solution 20. The method according to Technical Solution 17, characterized in that reducing the speed limit of the DFIG by the predetermined amount further includes transferring at least a portion of the reactive power to a reactive power compensation device, the reactive power compensation device comprising at least one of a line-side power converter, a VAR box, or a factory power balancing device located at the interconnection point of the wind turbine.

[0051] It should be understood that methods and systems may further include any combination of additional features and / or steps as described herein.

[0052] These and other features, aspects, and advantages of the invention will become more readily understood with reference to the following description and the appended claims. The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. Attached Figure Description

[0053] The invention (including its preferred mode) is fully disclosed and can be practiced by one of ordinary skill in the art in the description with reference to the accompanying drawings, in which:

[0054] Figure 1 The illustration shows a perspective view of an embodiment of a wind turbine according to the present disclosure;

[0055] Figure 2 The diagram illustrates what is suitable for and Figure 1 A schematic diagram of one embodiment of a wind turbine electric power system used in conjunction with a wind turbine is shown.

[0056] Figure 3 The illustration shows a schematic diagram of one embodiment of a power converter for a wind turbine according to the present disclosure;

[0057] Figure 4 The illustration shows a system configuration of a wind farm according to one embodiment of the present disclosure;

[0058] Figure 5The illustration shows a flowchart of an embodiment of a method for operating a wind turbine power system for supplying active and reactive power to the power grid according to the present disclosure; and

[0059] Figure 6 The illustration shows a flowchart of another embodiment of a method for operating a wind turbine power system for supplying active and reactive power to the power grid according to the present disclosure. Detailed Implementation

[0060] Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The various examples are provided by way of explanation rather than limitation of the invention. Indeed, it will be apparent to those skilled in the art that many modifications and variations can be made to the invention without departing from its scope. For example, features illustrated or described as part of one embodiment may be used in conjunction with another embodiment to produce yet another embodiment. Therefore, it is intended that the invention cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0061] Generally, as discussed above, this disclosure relates to a system and method for operating a wind turbine with a generator (such as a doubly fed induction generator system (DFIG)) coupled to a power converter. Accordingly, the DFIG can be operated up to a first speed limit. During this period, one or more sensors can monitor the wind speed at the wind turbine. When the wind speed drops below a predetermined threshold, the first speed limit of the DFIG can be reduced to a reduced speed limit and maintained at the reduced speed limit for a period of time during which the wind speed remains below the predetermined threshold. Accordingly, the tip speed ratio of the wind turbine is optimized during low wind speeds, thereby increasing the power output of the wind turbine at low wind speeds. At low wind speeds, the TSR is typically greater than the optimal TSR; therefore, reducing the speed limit of the generator reduces the TSR to a value closer to the optimal TSR.

[0062] Therefore, this disclosure aims to improve the operating power coefficient (C) of wind turbines during low wind speeds by extending the minimum speed of the wind turbine. p By transferring reactive power to line-side converters (LSCs), VAR boxes, and / or eBOPs located at generator / interconnection points, the minimum speed limit of wind turbines can be extended. Additionally, by lowering the minimum speed limit, wind turbines can operate with optimized TSR and pitch angles during low wind speeds, thereby operating with improved turbine efficiency.

[0063] Now refer to the attached diagram, Figure 1A perspective view of one embodiment of a wind turbine 10 is illustrated. As shown, the wind turbine 10 generally includes: a tower 12 extending from a support surface 14; a nacelle 16 mounted on the tower 12; and a rotor 18 coupled to the nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to and extending outward from the hub 20. For example, in the illustrated embodiment, the rotor 18 includes three rotor blades 22. However, in alternative embodiments, the rotor 18 may include more or fewer than three rotor blades 22. The individual rotor blades 22 may be spaced apart around the hub 20 to facilitate rotation of the rotor 18 so that kinetic energy can be converted from wind into usable mechanical energy, and subsequently into electrical energy. For example, as will be described below, the rotor 18 may be rotatably coupled to a generator 120 (…). Figure 2 The wind turbine can be used to generate electricity. One or more wind conditions (such as wind speed and / or wind direction) can also be monitored via a wind sensor 24 (such as an anemometer) located in the nacelle 16 or in any other suitable location near the wind turbine 10.

[0064] Wind power generation typically consists of a large number (usually 100 or more) of associated wind turbine generators 120 ( Figure 2 The wind farm provides wind turbines 10, wherein each individual wind turbine 10 is typically subjected to a unique wind force. Therefore, the output power of the individual wind turbine generator 120 can vary from one wind turbine 10 to another within the wind farm.

[0065] As generally understood, active and reactive power are provided by individual wind turbine generators 120. In some embodiments, the field-level controller provides reactive power commands (Qcmd) to the wind turbine generators 120 based on grid transmission needs (which may be specified by the grid operator or determined based on grid voltage). The reactive power demand may be identical for each individual wind turbine generator. In alternative control methods, reactive power commands may be individually tailored for each wind turbine generator 120 in the wind farm based on the different power generation characteristics of the respective wind turbine generators 120. It should be understood that the invention is not limited to the manner or method of generating reactive power commands for individual wind turbine generators 120.

[0066] Now for reference Figure 2 The illustration shows a schematic diagram of one embodiment of a wind turbine DFIG power system 100 (“wind turbine system”) according to aspects of the present disclosure. Although reference will generally be made herein... Figure 2The present disclosure is described in connection with the system 100 shown herein, but those skilled in the art who use the disclosure provided herein will understand that aspects of the present disclosure are also applicable to other power generation systems, and, as mentioned above, the present invention is not limited to wind turbine systems.

[0067] exist Figure 2 In the embodiment, the wind turbine 10 ( Figure 1 The rotor 18 of the DFIG 120 can optionally be connected to a gearbox 118, which in turn is connected to a generator 120, which may be a doubly-fed induction generator (DFIG). As shown, the DFIG 120 can be connected to a stator bus 154. Furthermore, as shown, a power converter 162 can be connected to the DFIG 120 via a rotor bus 156 and to the stator bus 154 via a line-side bus 188. Accordingly, the stator bus 154 can provide multiphase power output (e.g., three-phase power) from the stator of the DFIG 120, and the rotor bus 156 can provide multiphase power output (e.g., three-phase power) from the rotor of the DFIG 120. The power converter 162 may also include a rotor-side converter (RSC) 166 and a line-side converter (LSC) 168. The DFIG 120 is connected to the rotor-side converter 166 via the rotor bus 156. Additionally, RSC 166 is connected to LSC 168 via DC link 136, which is traversed by DC link capacitor 138. LSC 168 is then connected to line-side bus 188.

[0068] The RSC 166 and LSC 168 can be configured for normal operating modes in a three-phase pulse width modulation (PWM) arrangement using insulated gate bipolar transistor (IGBT) switching elements, as per the relevant provisions. Figure 3 As discussed in more detail.

[0069] Additionally, power converter 162 can be coupled to controller 174 to control the operation of rotor-side converter 166 and line-side converter 168. It should be noted that converter controller 174 can be configured as an interface between power converter 162 and local wind turbine control system 176, and can include any number of control devices. In one embodiment, controller 174 may include processing means (e.g., microprocessor, microcontroller, etc.) that executes computer-readable instructions stored in a computer-readable medium. When executed by the processing means, the instructions can cause the processing means to perform operations, including providing control commands (e.g., switching frequency commands) to the switching elements of power converter 162.

[0070] As mentioned, for an individual DFIG wind turbine power system 100, reactive power can be mainly supplied by RSC 166 via generator 120 and LSC 168.

[0071] In a typical configuration, various line contactors and circuit breakers (including, for example, grid circuit breaker 182) may also be included to isolate various components necessary for normal operation of the DFIG 120 during connection to and disconnection from a load (such as grid 184). For example, system circuit breaker 178 may connect system bus 160 to transformer 180, which may be connected to grid 184 via grid circuit breaker 182. In alternative embodiments, fuses may replace some or all of the circuit breakers.

[0072] In operation, AC power generated at DFIG 120 by rotating rotor 18 is supplied to the power grid 184 via a dual path defined by stator bus 154 and rotor bus 156. On the rotor bus side 156, sinusoidal multiphase (e.g., three-phase) AC power is supplied to power converter 162. Rotor-side power converter 166 converts the AC power supplied from rotor bus 156 into direct current (DC) power and supplies DC power to DC link 136. As generally understood, the switching elements (e.g., IGBTs) used in the bridge circuit of rotor-side power converter 166 can be modulated to convert the AC power supplied from rotor bus 156 into DC power suitable for DC link 136.

[0073] Additionally, the line-side converter 168 converts the DC power on DC link 136 into AC output power suitable for the power grid 184. Specifically, the switching elements (e.g., IGBTs) used in the bridge circuit of the line-side power converter 168 can be modulated to convert the DC power on DC link 136 into AC power on the line-side bus 188. The AC power from the power converter 162 can be combined with the power from the stator of the DFIG 120 to provide multiphase power (e.g., three-phase power) with a frequency substantially maintained at the frequency of the power grid 184 (e.g., 50 Hz or 60 Hz).

[0074] Additionally, various circuit breakers and switches (such as grid circuit breaker 182, system circuit breaker 178, stator synchronizing switch 158, converter circuit breaker 186, and line contactor 172) may be included in the wind turbine power system 100 to connect or disconnect the corresponding bus, for example, in the event of excessive current that could damage components of the wind turbine power system 100, or for other operational considerations. Additional protective components may also be included in the wind turbine power system 100.

[0075] Furthermore, the power converter 162 can receive control signals from, for example, a local control system 176 via the converter controller 174. The control signals can be based, in particular, on sensed states or operating characteristics of the wind turbine power system 100. Typically, the control signals provide control over the operation of the power converter 162. For example, feedback in the form of sensed speed of the DFIG 120 can be used to control the conversion of output power from the rotor bus 156 to maintain an appropriate and balanced multiphase (e.g., three-phase) power supply. Other feedback from other sensors (including, for example, stator and rotor bus voltage and current feedback) can also be used by the controller 174 or the control system 176 to control the power converter 162. Various forms of feedback information can be used to generate switching control signals (e.g., gate timing commands for IGBTs), stator synchronization control signals, and circuit breaker signals.

[0076] The power converter 162 also compensates for or adjusts the frequency of the three-phase power from the rotor for changes in wind speed, such as at hub 20 and blades 22. Therefore, the mechanical rotor frequency and the electric rotor frequency are decoupled, and the matching of the electric stator frequency with the electric rotor frequency is facilitated substantially independently of the mechanical rotor speed.

[0077] In some states, the bidirectional nature of power converter 162, and specifically the bidirectional nature of LSC 168 and RSC 166, facilitates the feedback of at least some of the generated electrical power to the generator rotor. More specifically, electrical power can be transferred from stator bus 154 to line-side bus 188, and subsequently via line contactor 172, and to power converter 162 (specifically, LSC 168), which acts as a rectifier and rectifies the sinusoidal three-phase AC power into DC power. The DC power is transferred to DC link 136. Capacitor 138 facilitates the mitigation of DC link voltage amplitude variations by mitigating DC ripple, which is sometimes associated with three-phase AC rectification.

[0078] The DC power is then transmitted to RSC 166, which converts the DC power into three-phase sinusoidal AC power by adjusting the voltage, current, and frequency. This conversion is monitored and controlled via converter controller 174. The converted AC power is transmitted from RSC 166 to the generator rotor via rotor bus 156. In this way, reactive power control of the generator is facilitated by controlling the rotor current and voltage.

[0079] Now for reference Figure 3 The illustration shows aspects according to this disclosure. Figure 2A detailed schematic diagram of one embodiment of the power converter shown is provided. As illustrated, RSC 166 includes multiple bridge circuits (e.g., H-bridge circuits) wherein each phase of the rotor bus 156 input to the rotor-side converter 166 is connected to a single bridge circuit. Additionally, LSC 168 may also include multiple bridge circuits. Similar to the rotor-side converter 166, the line-side converter 168 also includes a single bridge circuit for each output phase of the line-side converter 168. In other embodiments, without departing from the scope of this disclosure, the line-side converter 168, the rotor-side converter 166, or both the line-side converter 168 and the rotor-side converter 166 may include parallel bridge circuits.

[0080] Each bridge circuit can generally consist of multiple switching elements (e.g., IGBTs) connected in series with each other. For example, such as... Figure 3 The bridge circuits shown include an upper IGBT (e.g., IGBT 212) and a lower IGBT (e.g., IGBT 214). Additionally, diodes may be connected in parallel with the IGBTs. In an alternative embodiment, the parallel IGBTs and diodes can be used to increase the current rating of the converter. As generally understood, the line-side converter 168 and rotor-side converter 166 can be controlled, for example, by providing control commands to the gates of the IGBTs using suitable driver circuitry. For example, the converter controller 174 can provide suitable gate timing commands to the gates of the IGBTs in the bridge circuit. The control commands can control the switching frequency of the IGBTs to provide the desired output. Those skilled in the art will recognize that, as an alternative to the IGBTs, the power converter 162 may include any other suitable switching elements.

[0081] General reference Figure 4 The diagram illustrates a block diagram of a wind farm 175 having multiple wind turbine systems 100 connected to a transmission grid 184. For example, as shown, each wind turbine system 100 may include a local controller 176 that responds to the state of the wind turbine generator being controlled. In one embodiment, the local controller 176 senses only terminal voltages and currents (via potentiometers and current transformers), which are used by the local controller 176 to provide an appropriate response so that the wind turbine generator provides the desired reactive power or power factor and voltage.

[0082] Each wind turbine system 100 can be connected to a collector bus 183 via a generator connection converter 180 to provide active and reactive power (denoted as Pwg and Qwg, respectively) to the collector bus 183. Generator connection converters and collector buses are known in the art.

[0083] Wind farm 175 provides farm-level active and reactive power outputs (denoted as Pwf and Qwf, respectively) via wind farm main converter 179. Farm-level controller 190 senses the wind farm output and the voltage at the common coupling point 181 with the grid 184 to provide farm-level reactive power command (farm-level Q_Cmd).

[0084] A local reactive power command (operator Q_Cmd) is generated and transmitted to the individual wind turbine systems 100 in the wind farm. In one embodiment, the total reactive power demand (Qwf) set on the wind farm 175 can be substantially equally distributed among the wind turbine systems 100, such that the local operator Q_Cmd command is the same for all wind turbine systems 100. In an alternative embodiment, the local operator Q_Cmd command can be based on the available reactive power value for that wind turbine generator. For example, a wind turbine generator providing relatively more active power (Pwg) can receive a relatively smaller individualized operator Q_Cmd command, and a wind turbine generator providing relatively less active power Pwg can receive a relatively larger individualized operator Q_Cmd command. This reduces the reduction of individual wind turbine generators that provide relatively more active power, thus increasing the active power (Pwf) generated by wind farm 175 relative to the increased farm-level reactive power command (Qwf).

[0085] It should be recognized that the converter controller 174, the local wind turbine controller 176, and the field-level controller 190 may each correspond to any suitable computing device and / or any combination of computing devices. For example, the controller may include one or more processors and associated memory devices(s) configured to perform a variety of computer-implemented functions. As used herein, the term "processor" refers not only to an integrated circuit included in a computer as known in the art, but also to a controller, microcontroller, microcomputer, programmable logic controller (PLC), application-specific integrated circuit, and other programmable circuits. Additionally, the memory devices(s) may generally include one or more memory elements, including but not limited to computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), floppy disks, compact disc-read-only memory (CD-ROM), magneto-optical disks (MOD), digital versatile discs (DVDs), and / or other suitable memory elements. Such memory devices(s) may be generally configured to store suitable computer-readable instructions that, when implemented by the processor(s), configure the controller to perform a variety of functions, such as the steps disclosed herein.

[0086] exist Figure 4In the embodiments depicted herein, each wind turbine system 100 may also be configured with an individual reactive power compensation device 200 (also referred to herein as a modular VAR box (MVB)). In additional or alternative embodiments, the reactive power compensation device 200 may also include, for example, an LSC 168 and / or a plant power balancer (also referred to as an eBOP) located at the interconnection point 181 of the wind farm 175.

[0087] Now for reference Figure 5 The diagram illustrates a flowchart of an embodiment of a method 300 for operating a wind turbine power system according to aspects of this disclosure. Generally, method 300 is described herein as being implemented using, for example, the DFIG wind turbine power system 100 described above. However, it should be appreciated that the disclosed method 300 can be implemented using any other suitable wind power generation system configured to supply power (including reactive power) applied to a load (such as a power grid). Additionally, although... Figure 5 The steps performed in a specific order are depicted for illustrative and discussion purposes, but the methods described herein are not limited to any particular order or arrangement. Those skilled in the art using the disclosures provided herein will recognize that various steps of the methods can be omitted, rearranged, combined, and / or modified in a variety of ways.

[0088] As shown at (302), method 300 includes operating the generator of the wind turbine power system 100 up to a first speed limit. As shown at (304), method 300 includes monitoring the wind speed at the wind turbine power system 100. As shown at (306), method 300 includes comparing the wind speed to a predetermined threshold. As shown at (308), when the wind speed drops below the predetermined threshold, method 300 includes reducing the first speed limit of the generator to a reduced speed limit of the generator. If the wind speed remains above the predetermined threshold, the operation of the generator remains at the first speed limit. In one embodiment, the predetermined threshold may include wind speeds up to about 5 m / s, such as cut-in wind speeds from about 3 m / s to about 5 m / s. In another embodiment, for example, the reduced speed limit may be in the range of about 85% to about 95% of the first speed limit.

[0089] As shown at (310), method 300 operates the generator at a reduced speed limit for a period of time during which the wind speed remains below a predetermined threshold in order to optimize the tip speed ratio of the wind turbine power system 100 during low wind speeds, thereby increasing the power output of the wind turbine power system 100 at low wind speeds. For example, in some embodiments, reducing the generator's first speed limit to a reduced speed limit increases the power factor of the wind turbine power system 100 during low wind speeds, thereby increasing power output. Additionally, at low wind speeds, the TSR is typically greater than the optimal TSR; therefore, reducing the generator's speed limit also reduces the TSR to a value closer to the optimal TSR.

[0090] In a particular embodiment, by transferring at least a portion of the reactive power to a reactive power compensation device (such as the reactive power compensation device 200 described herein), the generator's first speed limit can be reduced to a reduced speed limit of the generator.

[0091] Now for reference Figure 6 The diagram illustrates a flowchart of an embodiment of a method 400 for operating a wind turbine power system according to aspects of this disclosure. Generally, method 400 is described herein as being implemented using, for example, the DFIG wind turbine power system 100 described above. However, it should be appreciated that the disclosed method 400 can be implemented using any other suitable wind power generation system configured to supply power (including reactive power) applied to a load (such as a power grid). Additionally, although... Figure 6 The steps performed in a specific order are depicted for illustrative and discussion purposes, but the methods described herein are not limited to any particular order or arrangement. Those skilled in the art using the disclosures provided herein will recognize that various steps of the methods can be omitted, rearranged, combined, and / or modified in a variety of ways.

[0092] As shown at (402), method 400 includes monitoring wind speed at the wind turbine power system 100. For example, in some embodiments, wind speed may be monitored via wind sensor 24. Alternatively or additionally, wind speed may be estimated via various controllers described herein. As shown at (404), wind speed is compared to a predetermined threshold. When wind speed drops below the predetermined threshold, as shown at (406), method 400 includes reducing the speed limit of DFIG 120 by a predetermined amount. For example, in some embodiments, the predetermined amount may be in the range of about 5% to about 15%. Alternatively, if wind speed remains at approximately the predetermined threshold, wind speed may be further monitored without any reduction in operating speed. As shown at (408), method 400 includes maintaining a reduced speed limit for a period of time during which the wind speed remains below a predetermined threshold in order to reduce the tip speed ratio of the wind turbine power system 100 during low wind speeds, thereby increasing the power output of the wind turbine power system 100 at low wind speeds.

[0093] Various aspects and embodiments of the present invention are defined by the following numbered clauses:

[0094] Clause 1. A method for operating a wind turbine power system supplying active and reactive power to a power grid, the wind turbine power system including a generator coupled to a power converter, the method comprising:

[0095] The generator of the wind turbine power system is operated up to the first speed limit;

[0096] Monitor the wind speed at the wind turbine power system;

[0097] When the wind speed drops below a predetermined threshold, the generator's first speed limit is reduced to the generator's reduced speed limit; and

[0098] The generator is operated at reduced speed limits for a period of time when the wind speed remains below a predetermined threshold in order to optimize the tip speed ratio of the wind turbine power system during low wind speeds, thereby increasing the power output of the wind turbine power system at low wind speeds.

[0099] Clause 2. According to the method of Clause 1, wherein the predetermined thresholds include wind speeds up to approximately 5 meters per second (m / s).

[0100] Clause 3. The method according to any of the preceding clauses, wherein the reduced speed limit is in the range of approximately 85% to approximately 95% of the first speed limit.

[0101] Clause 4. The method of any of the preceding clauses, wherein reducing the first speed limit of the generator to the reduced speed limit of the generator increases the power factor of the wind turbine power system during low wind speeds.

[0102] Clause 5. The method according to any of the preceding clauses, wherein reducing the first speed limit of the generator to the reduced speed limit of the generator further comprises transferring at least a portion of the reactive power to a reactive power compensation device.

[0103] Clause 6. The method according to Clause 5, wherein the power converter includes a line-side converter and a rotor-side converter, and the reactive power compensation device includes at least one of a line-side power converter, a VAR box, or a factory balancing unit located at the interconnection point of the wind turbine power system.

[0104] Clause 7. The method according to any of the foregoing clauses, wherein the generator includes a doubly fed induction generator (DFIG) and the wind turbine power system is one of a plurality of wind turbine power systems located within a wind farm supplying active and reactive power to the grid.

[0105] Clause 8. The method of Clause 7, wherein all or more wind turbine power systems are connected to a common collection bus located within the wind farm.

[0106] Clause 9. A wind turbine power system configured to supply active and reactive power to the power grid, the wind turbine comprising:

[0107] Wind turbines, which include:

[0108] The rotor includes a hub and multiple blades connected to the hub.

[0109] The generator, which is connected to the rotor, and

[0110] A power converter that is connected to a generator; and

[0111] A controller for controlling the operation of a wind turbine, the controller including at least one processor configured to perform a plurality of operations, the plurality of operations including:

[0112] The generator of the wind turbine is operated to the first speed limit;

[0113] Monitor the wind speed at the wind turbine;

[0114] When the wind speed drops below a predetermined threshold, the generator's first speed limit is reduced to the generator's reduced speed limit; and

[0115] The generator is operated at reduced speed limits for a period of time when the wind speed remains below a predetermined threshold in order to optimize the tip speed ratio of the wind turbine during low wind speeds, thereby increasing the power output of the wind turbine at low wind speeds.

[0116] Clause 10. A wind turbine power system pursuant to Clause 9, wherein the predetermined thresholds include wind speeds up to approximately 5 m / s.

[0117] Clause 11. A wind turbine power system pursuant to Clause 9, wherein the reduced speed limit is in the range of approximately 85% to approximately 95% of the first speed limit.

[0118] Clause 12. A wind turbine power system pursuant to Clause 9, wherein reducing the generator’s first speed limit to a reduced speed limit increases the power coefficient of the wind turbine during low wind speeds.

[0119] Clause 13. The wind turbine power system according to Clause 9, wherein reducing the first speed limit of the generator to the reduced speed limit of the generator further includes transferring at least a portion of the reactive power to a reactive power compensation device.

[0120] Clause 14. A wind turbine power system pursuant to Clause 13, wherein the power converter includes a line-side converter and a rotor-side converter, and the reactive power compensation device includes at least one of a line-side power converter, a VAR box, or a factory electrical balancer located at the interconnection point of the wind turbine.

[0121] Clause 15. A wind turbine power system pursuant to Clause 14, wherein the generator comprises a doubly fed induction generator (DFIG), and the wind turbine is one of a plurality of wind turbines located within a wind farm supplying active and reactive power to the grid.

[0122] Clause 16. A wind turbine power system pursuant to Clause 15, wherein all or more wind turbines are connected to a common collection bus located within the wind farm.

[0123] Clause 17. A method for operating a wind turbine power system supplying active and reactive power to a power grid, the wind turbine power system including a doubly-fed induction generator (DFIG) coupled to a power converter, the method comprising:

[0124] Monitor the wind speed at the wind turbine power system;

[0125] When the wind speed drops below a predetermined threshold, the speed limit of the DFIG is reduced by a predetermined amount.

[0126] The reduced speed limit is maintained for a period of time when the wind speed remains below a predetermined threshold in order to reduce the tip speed ratio of the wind turbine power system during low wind speeds, thereby increasing the power output of the wind turbine power system at low wind speeds.

[0127] Clause 18. The method according to Clause 17, wherein the predetermined thresholds include wind speeds up to approximately 5 meters per second (m / s).

[0128] Clause 19. The method according to Clause 17 or 18, wherein the predetermined amount is in the range of approximately 5% to approximately 15%.

[0129] Clause 20. The method according to Clauses 17, 18 or 19, wherein reducing the speed limit of the DFIG by a predetermined amount further includes transferring at least a portion of the reactive power to a reactive power compensation device, which includes at least one of a line-side power converter, a VAR box or a factory balancing unit located at the interconnection point of the wind turbine.

Claims

1. A method for operating a wind turbine power system that supplies active and reactive power to a power grid, the wind turbine power system comprising a generator coupled to a power converter, the method comprising: The generator of the wind turbine power system is operated up to a first speed limit; Monitor the wind speed at the wind turbine power system; When the wind speed drops below a predetermined threshold, the first speed limit of the generator is reduced to the reduced speed limit of the generator. as well as The generator is operated at the reduced speed limit for a period of time during which the wind speed remains below the predetermined threshold in order to optimize the tip speed ratio of the wind turbine power system during low wind speeds, thereby increasing the power output of the wind turbine power system at low wind speeds. The reduction of the first speed limit of the generator to the reduced speed limit of the generator further includes transferring at least a portion of the reactive power to a reactive power compensation device.

2. The method according to claim 1, characterized in that, The predetermined thresholds include wind speeds up to 5 meters per second (m / s).

3. The method according to claim 1, characterized in that, The reduced speed limit is in the range of 85% to 95% of the first speed limit.

4. The method according to claim 1, characterized in that, Reducing the first speed limit of the generator to the reduced speed limit of the generator increases the power coefficient of the wind turbine power system during the low wind speed period.

5. The method according to claim 1, characterized in that, The power converter includes a line-side converter and a rotor-side converter, and the reactive power compensation device includes at least one of the line-side power converter, a VAR box, or a factory power balancing device located at the interconnection point of the wind turbine power system.

6. The method according to claim 1, characterized in that, The generator includes a doubly fed induction generator (DFIG), and the wind turbine power system is one of a plurality of wind turbine power systems located in a wind farm that supplies the active power and the reactive power to the grid.

7. The method according to claim 6, characterized in that, All or more of the aforementioned wind turbine power systems are connected to a common aggregation bus located within the wind farm.

8. A wind turbine power system configured to supply active power and reactive power to a power grid, the wind turbine power system comprising: Wind turbines, which include: A rotor, comprising a hub and a plurality of blades coupled to the hub. A generator, which is connected to the rotor, and A power converter, which is connected to the generator; and A controller for controlling the operation of the wind turbine, the controller including at least one processor configured to perform a plurality of operations, the plurality of operations including: The generator of the wind turbine is operated up to a first speed limit; Monitor the wind speed at the wind turbine; When the wind speed drops below a predetermined threshold, the first speed limit of the generator is reduced to the reduced speed limit of the generator; and The generator is operated at the reduced speed limit for a period of time during which the wind speed remains below the predetermined threshold in order to optimize the tip speed ratio of the wind turbine during low wind speeds, thereby increasing the power output of the wind turbine at low wind speeds. The reduction of the first speed limit of the generator to the reduced speed limit of the generator further includes transferring at least a portion of the reactive power to a reactive power compensation device.

9. The wind turbine power system according to claim 8, characterized in that, The predetermined thresholds include wind speeds up to 5 meters per second (m / s).

10. The wind turbine power system according to claim 8, characterized in that, The reduced speed limit is in the range of 85% to 95% of the first speed limit.

11. The wind turbine power system according to claim 8, characterized in that, Reducing the first speed limit of the generator to the reduced speed limit of the generator increases the power coefficient of the wind turbine during the low wind speed period.

12. The wind turbine power system according to claim 8, characterized in that, The power converter includes a line-side converter and a rotor-side converter, and the reactive power compensation device includes at least one of the line-side power converter, a VAR box, or a factory power balancing device located at the interconnection point of the wind turbine.

13. The wind turbine power system according to claim 12, characterized in that, The generator includes a doubly fed induction generator (DFIG), and the wind turbine is one of a plurality of wind turbines located in a wind farm that supplies the active power and the reactive power to the grid.

14. The wind turbine power system according to claim 13, characterized in that, All or more of the wind turbines are connected to a common hub bus located within the wind farm.

15. A method for operating a wind turbine power system supplying active and reactive power to a power grid, the wind turbine power system comprising a doubly-fed induction generator (DFIG) coupled to a power converter, the method comprising: Monitor the wind speed at the wind turbine power system; When the wind speed drops below a predetermined threshold, the speed limit of the DFIG is reduced by a predetermined amount. The reduced speed limit is maintained for a period of time during which the wind speed remains below the predetermined threshold in order to reduce the tip speed ratio of the wind turbine power system during low wind speeds, thereby increasing the power output of the wind turbine power system at low wind speeds. The reduction of the speed limit of the DFIG by the predetermined amount further includes transferring at least a portion of the reactive power to a reactive power compensation device.

16. The method according to claim 15, characterized in that, The predetermined thresholds include wind speeds up to 5 meters per second (m / s).

17. The method according to claim 15, characterized in that, The predetermined amount is in the range of 5% to 15%.

18. The method according to claim 15, characterized in that, The reactive power compensation device includes at least one of a line-side power converter, a VAR box, or a factory power balancing device located at the interconnection point of the wind turbine.

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