Wind turbine and method for controlling wind turbine

A wind turbine is provided. The wind turbine includes a mechanical system, an electrical system and a controller. The controller is for determining an electrical capability limit of the electrical system according at least in part to one or more operating conditions of the wind turbine and one or more environment conditions of a site of the wind turbine, comparing the electrical capability limit of the electrical system and a mechanical capability limit of the mechanical system, and controlling the electrical system to operate at the smaller one of the electrical capability limit and the mechanical capability limit. A method for controlling a wind turbine comprising a mechanical system and an electrical system is also provided.

BACKGROUND

Embodiments of the invention relate to a wind turbine and a method for controlling the wind turbine.

Wind turbines convert wind energy to electrical energy and transmit the electrical energy to a power system. A wind turbine includes a mechanical system, an electrical system and a control system. The control system includes a turbine controller for controlling the mechanical system and a converter controller for controlling the electrical system, for example a generator and a converter. During operation, the turbine controller sends commands, for example a torque or power command to the converter controller, and the converter controller follows the command to control the electrical system to deliver electrical power to the power system (for example, a power grid). However, the turbine controller does not have detailed and dynamic information of the electrical system, e.g. maximum active power that can be delivered via the electrical system. Hence, on one hand, the turbine controller usually uses conservative fixed limits of the electrical system to control the wind turbine. Further the limits used in the turbine controller usually keep large margins from physical limits of the electrical systems. On the other hand, the capability of the electrical system varies as grid and environment conditions change, for example grid voltage increases or ambient temperature drops, in turn the electrical margins described above also change. There are opportunities to better manage these dynamic margins to increase the turbine output power when the mechanical system also has capability to capture more wind energy. That is, as grid and environment change, the wind turbine can dynamically boost its power output instead of following a fixed or pre-determined power curve.

It is desirable to provide a wind turbine and a method to address at least one of the above-mentioned problems.

BRIEF DESCRIPTION

In accordance with one embodiment disclosed herein, a wind turbine is provided. The wind turbine includes a mechanical system, an electrical system and a controller. The controller is for determining an electrical capability limit of the electrical system according at least in part to one or more operating conditions of the wind turbine and one or more environment conditions of a site of the wind turbine, comparing the electrical capability limit of the electrical system and a mechanical capability limit of the mechanical system, and controlling the electrical system to operate at the smaller one of the electrical capability limit and the mechanical capability limit.

In accordance with another embodiment disclosed herein, a method for controlling a wind turbine comprising a mechanical system and an electrical system is provided. The method includes determining an electrical capability limit of the electrical system according at least in part to one or more operating conditions of the wind turbine and one or more environment conditions of a site of the wind turbine; comparing the electrical capability limit of the electrical system and a mechanical capability limit of the mechanical system; and controlling the electrical system to operate at the smaller one of the electrical capability limit and the mechanical capability limit.

DETAILED DESCRIPTION

Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The use of “including,” “comprising” or “having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect. The terms “first”, “second” and the like in the description and the claims do not mean any sequential order, number or importance, but are only used for distinguishing different components.

FIG. 1illustrates a schematic diagram of a wind turbine10for delivering electrical power to a power grid12in accordance with an embodiment. The wind turbine10described and shown herein is a wind turbine generator for generating electrical power from wind energy. The wind turbine10includes a mechanical system14, an electrical system16and a controller18. The mechanical system14transforms the wind energy into a rotational torque or force that drives one or more generators of the electrical system16that may be rotationally coupled to a rotor20through a gearbox28. The electrical system16transforms the rotational torque or force from the mechanical system14into the electrical power for the power grid12. The controller18controls the mechanical system14and the electrical system16.

The mechanical system14includes the rotor20including a hub22and multiple blades24(sometimes referred to as “airfoils”) extending radially outwardly from the hub22for converting the wind energy into rotational energy. The rotor20may generally face upwind to harness the wind energy, and/or the rotor20may generally face downwind to harness the wind energy. Of course, in any embodiments, the rotor20may not face exactly upwind and/or downwind, but may face generally at any angle (which may be variable) with respect to a direction of the wind to harness energy therefrom. The rotor20includes a rotor shaft26coupled to the rotor hub22for rotation therewith. In an embodiment, the mechanical system14includes the gearbox28coupled with the rotor shaft26, which steps up the inherently low rotational speed of the rotor20for the generator30to efficiently convert the mechanical energy to the electrical energy. In other embodiments, the gearbox28may be omitted. In an embodiment, the mechanical system14may include other components not shown inFIG. 1, such as a nacelle, a tower.

The electrical system16includes a generator30coupled to the rotor20for generating electrical power from the rotational energy generated by the rotor20. The generator30may be any suitable type of electrical generator, such as, but not limited to, a wound rotor induction generator, a double-fed induction generator (DFIG, also known as dual-fed asynchronous generators), a permanent magnet (PM) synchronous generator, an electrically-excited synchronous generator, and a switched reluctance generator.

The generator30includes a generator rotor32and a generator stator34with an air gap included therebetween. The generator30is coupled to the rotor shaft26such that rotation of the rotor shaft26drives rotation of the generator rotor32, and therefore operation of the generator30. In an embodiment, the generator rotor32has a generator shaft36coupled thereto and coupled to the rotor shaft26such that rotation of the rotor shaft26drives rotation of the generator rotor32. In the illustrated embodiment, the generator shaft36is coupled to the rotor shaft26through the gearbox28. In another embodiment, the generator rotor32is directly coupled to the rotor shaft26, sometimes referred to as a “direct-drive wind turbine.” Torque of the rotor20drives the generator rotor32to thereby generate variable frequency alternating current (AC) electrical power from rotation of the rotor20. The generator stator34is coupled to the power grid12through a transformer38.

The electrical system16includes a converter unit40coupled to the generator30for converting the variable frequency AC to a fixed frequency AC for delivery to the power grid12. In an embodiment, the converter unit40may include a single phase converter or a multi-phase converter configured to convert electricity generated by the generator30to electricity suitable for delivery over the power grid12. In the illustrated embodiment, the converter unit40may include a rotor-side converter42, a line-side converter44and a direct current (DC) link46. The DC link46connects the rotor-side converter42and the line-side converter44. The rotor-side converter42is configured to convert the AC power from the generator rotor32of the generator30into DC power. The line-side converter44is configured to convert the DC power to AC power at a frequency compatible with the grid12.

The rotor-side converter42may include an AC-DC converter which converts an AC voltage from the generator30to a DC voltage on the DC link46. The DC link46may include one or more capacitors coupled either in series or parallel for maintaining the DC voltage of the DC link46at a certain level, and thus the energy flow from the DC link46to the grid12can be managed. The line-side converter44may include a DC-AC inverter which converts the DC voltage on the DC link46to AC voltage with suitable frequency, phase, and magnitude for feeding to the power grid12. In another embodiment, the converter unit40may include one AC-AC converter.

The transformer38is configured to provide voltage or current transformation of the power from the converter unit40and the power from the generator stator34. The transformer38is configured to step up the magnitude of the AC voltages output from the line-side converter44and the generator stator34to match the power grid12. The electrical system16in the illustrated embodiment is only a non-limited example, but in some other embodiments the electrical system16may include one or more other elements or have other connections between elements.

The controller18is for determining an electrical capability limit of the electrical system16according at least in part to one or more operating conditions of the wind turbine10and one or more environment conditions of a site of the wind turbine10, comparing the electrical capability limit of the electrical system16and a mechanical capability limit of the mechanical system14, and controlling the electrical system16to operate at the smaller one of the electrical capability limit and the mechanical capability limit. The term “electrical capability limit” refers to maximum operating parameter(s) the electrical system16can operate at under the current operating conditions thereof and the current environment conditions, which is dynamic. The electrical capability limit includes at least one of a torque limit and a rotational speed limit of the generator30. The term “mechanical capability limit” refers to maximum operating parameter(s) the mechanical system14can provide to the electrical system16, which may be pre-determined and fixed in a non-limited example. The mechanical capability limit includes at least one of a torque limit and a rotational speed limit provided by the mechanical system14.

The controller18includes a mechanical system controller48, an electrical system controller50and an electrical system optimizer52. The mechanical system controller48is configured to control the mechanical system14. The mechanical system controller48is for controlling (e.g., changing) pitch angles of the blades24with respect to a wind direction. The mechanical system controller48may control pitch actuators (not shown) coupled to the hub22and the blades24to change the pitch angle of the blades24by rotating the blades24with respect to the hub22. The pitch actuators may include any suitable structure, configuration, arrangement, means, and/or components, whether described and/or shown herein, such as, but not limited to, electrical motors, hydraulic cylinders, springs, and/or servomechanisms. Moreover, the pitch actuators may be driven by any suitable means, whether described and/or shown herein, such as, but not limited to, hydraulic fluid, electrical power, electro-chemical power, and/or mechanical power, such as, but not limited to, spring force.

The mechanical system controller48is programmed to generate command signals to the electrical system controller50through implementation of analog circuitry and/or digital control algorithms based at least in part on wind speed of wind, current torque of the generator30, current rotational speed of the generator30, and the electrical capability limit of the electrical system16from the electrical system optimizer52.

The electrical system controller50is configured to control the electrical system16. In an embodiment, the electrical system controller50is configured to control operations of the converter unit40through implementation of analog circuitry and/or digital control algorithms in response to the command signals from the mechanical system controller48. The electrical system controller50monitors operation of the electrical system16. For example, the electrical system controller50monitors the current torque and the current rotational speed of the generator30via sensors35at the generator shaft36, and monitors a grid voltage of the power grid12through a sensor37, but it is not limited.

The electrical system optimizer52is for determining the electrical capability limit of the electrical system16and providing the electrical capability limit to the mechanical system controller48. The mechanical system controller48is for comparing the electrical capability limit of the electrical system16and the mechanical capability limit of the mechanical system14and provides optimized command signals based on the smaller one of the electrical capability limit and the mechanical capability limit to the electrical system controller50. The electrical system controller50controls the converter unit40of the electrical system16in response to the optimized command signals from the mechanical system controller48, so that the generator30operates at the smaller one of the electrical capability limit and the mechanical capability limit.

With reference toFIG. 2, when the wind speed is lower than a wind speed threshold, the electrical power generated by the wind turbine10rises rapidly as the wind speed rises. However, when the wind speed rises higher than the wind speed threshold, the wind turbine10generates substantially the same electrical power due to limits of the electrical system16and the mechanical system14. The wind speed threshold may be 12 m/s, for example. In the condition that the wind speed is higher than the wind speed threshold, the electrical limit of the electrical system16is dynamic with the operating conditions and the environment conditions, the electrical system optimizer52may determine a higher electrical capability limit than a traditional fixed electrical limit, and the mechanical system controller48may generate a higher torque command for the electrical system16and a higher rotational speed command for the mechanical system14under the mechanical capability limit of the mechanical system14, so the torque of the generator30is boosted and an electrical power Pnewgenerated by the wind turbine10inFIG. 1is higher than an electrical power Poldgenerated by the traditional wind turbine. Accordingly, annual energy production (AEP) increases.

FIG. 3illustrates a block diagram of the wind turbine10in accordance with an embodiment. The mechanical system controller48determines a first torque command T1, which is an initial torque command, according to the wind speed, the current torque Tcurrentand the current rotational speed ωcurrentof the generator30. The wind speed of wind may be detected by sensor(s) near the rotor20of the wind turbine10. The current torque Tcurrentand the current rotational speed ωcurrentof the generator30may be provided by the electrical system controller50.

The first torque command T1is provided to the electrical system optimizer52. The electrical system optimizer52is for generating one or more state variables of the electrical system16according at least in part to the first torque command T1and the operating conditions of the wind turbine, determining a command margin ΔT according at least in part to the state variables and the environment conditions, and adjusting the first torque command T1using the command margin ΔT in an iteration method until at least one of the state variables substantially reaches to a corresponding state variable limit to obtain an optimized torque command Toptimized.

The electrical system optimizer52includes a judgment unit53, a system model unit54, a margin management unit56and a limit determine unit57. In an embodiment, the judgment unit53, the system model unit54and the margin management unit56of the electrical system optimizer52operate in loops in the iteration method to generate the optimized torque command Toptimizedat a corresponding rotational speed of the generator30. In an embodiment, the rotational speed herein may be selected from a series of rotational speeds [ω0, ω1, . . . , ωn] (n is a positive integer). A series of the optimized torque commands [Toptimized,0, Toptimized,1, . . . , Toptimized,n] at corresponding rotational speeds [ω0, ω1, . . . , ωn] are generated respectively in such a method.

The judgment unit53judges if an estimated command Testimatedis the optimized command Toptimized, where the estimated command Testimatedis a sum of the command margin ΔT determined by the margin management unit56and the first torque command T1. In a first loop of the iteration method, the initial command margin ΔT can be set zero, so the estimated command Testimatedis equal to the first torque command T1. If the estimated command Testimatedis the optimized command Toptimized, the estimated command Testimatedis provided to the limit determine unit57as the optimized command Toptimized, otherwise the estimated command Testimatedis provided to the system model unit54to enter into the next loop.

The system model unit54is for generating the state variables of the wind turbine10according to the estimated command Testimatedand one or more operating conditions of the wind turbine10. The system model unit54may include at least one of a converter control model of the electrical system controller50, an electrical model of the electrical system16and a thermal model of the electrical system16, and generate the state variables based on at least one model thereof.

In an embodiment, the system model unit54includes the converter control model and the electrical models of the converter unit40and the generator30. The operating conditions of the wind turbine10includes at least one of the grid voltage of the power grid12, the series of rotational speeds [ω0, ω1, . . . , ωn] of the generator30, and a power factor of the generator30. The state variables may be the electrical state variables including at least one of currents of the generator30, currents of the converter unit40and voltages of the generator30in an embodiment.

In another embodiment, the system model unit54includes the thermal model of the electrical system16which may include a thermal model of the generator30, a thermal model of cables of the electrical system16and any other thermal models of electrical components, such as reactor, fuse, bridge circuit. The system model unit54generates the state variables according to the first torque command T1and the operating conditions based on the thermal model of the electrical system16. The state variables may include thermal state variables indicating component temperatures at the operating conditions. In another embodiment, the system model unit54may include one or more other models of the electrical system16.

The state variables from the system model unit54is provided to the margin management unit56. The margin management unit56is for determining the command margin ΔT according at least in part to the state variables and the environment conditions. In an embodiment, the command margin ΔT is a torque margin. The command margin ΔT from the margin management unit56is sent back to adjust the first command T1, i.e., estimate the estimated command Testimatedwhich is provided to the judgment unit53again.

The judgment unit53, the system model unit54and the margin management unit56operate in such loops until at least one of the state variables substantially reaches a corresponding state variable limit thereof to obtain the optimized torque command Toptimizedin such iteration method. And the series of the optimized torque commands [Toptimized,0, Toptimized,1, . . . , Toptimized,n] corresponding to the series of rotational speeds [ω0, ω1, . . . , ωn] are generated.

The limit determine unit57may store the optimized torque commands [Toptimized,0, Toptimized,1, . . . , Toptimized,n] and the corresponding rotational speeds [ω0, ω1, . . . , ωn] in a table. The limit determine unit57estimates a series of powers [P0, P1, . . . , Pn] from the optimized torque commands [Toptimized,0, Toptimized,1, . . . , Toptimized,n] and the corresponding rotational speeds [ω0, ω1, . . . , ωn], and determines the maximum power Pk(k is an integer from 0 to n) from the powers [P0, P1, . . . , Pn]. The maximum power Pkis a power limit of the electrical capability limit. The limit determine unit57determines the optimized torque command which is the torque limit Toptimized,kand the optimized rotational speed command which is the rotational speed limit ωkto the mechanical system controller48. The torque limit Toptimized,kand the corresponding rotational speed limit ωkare the electrical capability limit of the electrical system16in an embodiment.

The mechanical system controller48generates a second torque command T2according to the electrical capability limit which is the torque limit Toptimized,kherein and the first torque command T1to the electrical system controller50. And the mechanical system controller48also generates a new rotational speed command ωnewaccording to the electrical capability limit which is the rotational speed limit ωkherein and the mechanical capability limit to the mechanical system14. The mechanical system controller48may control the mechanical system14to change the pitch angles of the blades24according to the new rotational speed command ωnew.

The electrical system controller50controls the converter unit40according to the second torque command T2. The electrical system controller50generates pulse-width modulation (PWM) signals under limits of currents, voltages, and/or temperatures of the electrical system16to the converter unit40according to the second torque command T2and the converter unit40convers voltages for the generator30. The generator30and the converter unit40as shown inFIG. 1both provide the electrical power to the power grid12. In another embodiment, the generator30provides the electrical power to the power grid12.

FIG. 4illustrates a block diagram of the electrical system optimizer52in accordance with an embodiment. In the illustrated embodiment, the system module unit54includes the converter control model58and the electrical system model60. The converter control model58generates converter control signals according to the operating conditions and the estimated command Testimatedestimated from the first torque command T1and the command margin ΔT. The converter control signals are provided to the electrical system model60for generating the state variables [x1, x2, . . . , xm] (m is a positive integer) of the electrical system16at the operating conditions.

The margin management unit56includes a constraint generation unit62and a margin governor64. The constraint generation unit62generates first limits of the state variables according to the environment conditions and the series of rotational speeds [ω0, ω1, . . . , ωn] under physical limits of the electrical system16. The physical limits are maximum state variables at which the electrical system16can operate. For example, the first limit of a generator current cannot beyond the physical limit of the generator current, the first limit of a generator voltage cannot beyond the physical limit of the generator voltage, the first limit of heat of the electrical system16cannot beyond the heat that the electrical system16can afford.

The margin governor64determines margins under the first limits of the state variables to generate second limits [x1lim, x2lim, . . . , xmlim] of the state variables to keep the margins under different conditions, for example, to keep current margins in case of transient events. The margins may be determined according to particular applications.

Differences between the second limits [x1lim, x2lim, . . . , xmlim] and the corresponding state variables [x1, x2, . . . , xm] are estimated respectively by a summator70. The margin management unit56includes a determine unit72and a margin regulator74. The determine unit72determines a minimum difference Δxminfrom the differences. The margin regulator74estimates the command margin ΔT according to the minimum difference Δxminthrough a PI controller. An absolute value unit68estimates an absolute value of the minimum difference |Δxmin| from the determine unit72. The estimated command Testimatedis the optimized torque command Toptimizedprovided to the limit determine unit57through the judgement unit53until the minimum difference |Δxmin| is zero or lower than a threshold, such as 0.1, 0.2, that is to say, at least one of the state variables substantially reaches the corresponding second limit thereof.

FIG. 5illustrates a block diagram of the mechanical system controller48in accordance with an embodiment. The mechanical system controller48includes a torque determine unit76and a speed determine unit78. The torque determine unit76is for determining the second torque command T2for the electrical system controller50according to the first torque command T1and the torque limit Toptimized,k. The torque determine unit76includes a summator80for calculating a deference between the first torque command T1and the optimized torque command Toptimizedand a filter82for filtering the difference from the summator80. The torque determine unit76includes a summator84for calculating a sum of the filtered difference from the filter82and the first torque command T1. The torque determine unit76includes a first limit unit86for limiting the sum from the summator84under the mechanical limit and a second limit unit88for limiting the sum from the summator84under the torque command limit Toptimized,kso as to obtain the second torque command T2.

The speed determine unit78is for determining the new rotational speed command ωnewaccording to an old rotational speed command ωoldand the rotational speed limit ωkcorresponding to the torque limit Toptimized,k. The speed determine unit78includes a summator90for calculating a deference between the old rotational speed command ωoldand the rotational speed limit ωkand a filter92for filtering the difference from the summator90. The speed determine unit78includes a summator94for calculating a sum of the filtered difference from the filter92and the old rotational speed command ωold. The speed determine unit78includes a third limit unit96for limiting the sum from the summator94under the mechanical limit and a forth limit unit98for limiting the sum from the third limit unit96under the rotational speed limit ωkso as to obtain the new rotational speed command ωnew. The mechanical system controller48controls the rotor20according to the new rotational speed command ωnew.

Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. The various features described, as well as other known equivalents for each feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure.