Method for controlling a wind turbine generator

Abstract

A method for controlling a wind turbine generator (1) of a wind power plant based on the condition of a power converter or a component forming part of the power converter in the wind power plant. The method includes determining an initial condition of the power converter or the component forming part of the power converter, and determining the evolution of the condition from the initial condition based on a nominal power reference value of the wind turbine generator (1). The method further includes comparing the evolution of the condition with a predetermined threshold, and determining, based on the comparison, a time period during which the condition of the power converter or the component forming part of the power converter will be substantially equal to the predetermined threshold.

Description

Field of the Invention

[0001] The present invention relates to a method for controlling a power converter in a wind turbine generator of a wind power plant. Background Art

[0002] A wind turbine generator converts the energy contained in the wind into electrical energy, which is typically fed into the power grid. Since the variability of the wind necessarily results in an electrical power output with varying characteristics, a power converter is also included to modify the electrical power with a varying frequency generated by the generator into an electrical power output with a fixed frequency that is more suitable for feeding into the power grid.

[0003] For this purpose, a converter controller is provided for regulating the output of the power converter according to ambient wind conditions. In view of safety considerations and physical constraints, the converter controller can also be used to manage the generator to maintain cost-effective energy production by preventing component failures and minimizing downtime.

[0004] It is based on this background that the present invention is designed. Summary of the Invention

[0005] One aspect of the present invention provides a method for controlling a wind turbine generator of a wind power plant based on the conditions of a power converter in the wind power plant or a component forming part of the power converter. The method includes determining an initial condition of the power converter or a component forming part of the power converter, and determining the evolution of the condition from the initial condition based on a nominal power reference value of the wind turbine generator. The method further includes comparing the evolution of the condition with a predetermined threshold, and determining a time period during which the condition of the power converter or a component forming part of the power converter will be substantially equal to the predetermined threshold according to the comparison. Preferably, the condition of the power converter is the temperature of the power converter or a component forming part of the power converter.

[0006] Preferably, the method further includes determining an active power limit and a reactive power limit based on the power reference value. Preferably, the active power limit and the reactive power limit are in the form of a P-Q chart.

[0007] Preferably, the method further includes prioritizing between active power and reactive power when determining the active power limit and the reactive power limit.

[0008] Preferably, the method further includes controlling the wind turbine generator at the nominal power reference value within a duration not exceeding the time period.

[0009] Preferably, the initial temperature and the temperature evolution are determined as a non-linear function based on the power losses and the ambient temperature of the power converter or a component forming part of the power converter under current operating parameters.

[0010] Preferably, the power losses of the power converter or a component forming part of the power converter are determined based on the voltage across the power converter and the current passing through the power converter. More preferably, the power losses of the power converter are the product of the voltage across the power converter and the current passing through the power converter. Each of these characteristics can be measured directly or estimated otherwise.

[0011] Preferably, when applied to multiple power converters, the method further includes selecting the shortest time period from among multiple time periods as the time period.

[0012] Preferably, the ambient temperature is the measurable temperature closest to the power converter. That is, the ambient temperature is the temperature of the area around the power converter measured within a reasonable and feasible range. This can include, for example, the ambient air temperature.

[0013] Preferably, the method further includes comparing the initial conditions of the power converter with a predetermined threshold, and if the conditions are substantially equal to or exceed the predetermined threshold, modifying the power reference value of the wind turbine generator. In particular, the step of modifying the current power reference value of the wind turbine generator includes derating (reducing) a parameter.

[0014] Another aspect of the present invention provides a controller for a wind turbine generator, the controller including data processing means and a memory module, wherein the memory module includes a set of program code instructions which, when executed by the data processing means, implement the method according to the first aspect of the present invention.

[0015] Another aspect of the present invention provides a computer program product downloadable from a communication network and / or stored on a machine-readable medium, the computer program product including program code instructions for implementing the method according to the first aspect of the present invention.

[0016] It should be understood that the preferred and / or optional features of the first aspect of the present invention may also be combined in the second aspect of the present invention individually or in suitable combinations. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other aspects of the present invention will now be described by way of example only with reference to the following drawings, in which:

[0018] Figure 1 is a schematic view of a wind turbine generator suitable for use with an embodiment of the present invention;

[0019] Figure 2 is a schematic diagram of the architecture of a full-scale converter-based wind power plant suitable for use with embodiments of the present invention;

[0020] Figure 3 is Figure 2 a block diagram representation of the converter controller of the converter in

[0021] Figure 4 is Figure 3 a block diagram of the thermal capacity manager of the converter controller of

[0022] Figure 5 is Figure 4 a block diagram of the component thermal model of the thermal capacity manager of

[0023] Figure 6 is Figure 5 the thermal model of the component thermal model of

[0024] Figure 7 is Figure 3 a representation of a typical P-Q chart used by the converter controller of

[0025] Figure 8 is a graph showing the evolution of the component temperature using Figure 5 the component thermal model of

[0026] Figure 9 is a schematic block diagram of the architecture of a DFIG arrangement suitable for use with embodiments of the present invention.

[0027] In the drawings, like parts are denoted by like reference numerals. Detailed Description

[0028] To provide the content of the present invention, Figure 1 a single wind turbine generator 1 of the type that can be controlled according to embodiments of the present invention is shown. It should be understood that the wind turbine generator 1 is only mentioned here by way of example, Figure 1 and it is possible to implement embodiments of the present invention into many different types of wind turbine systems.

[0029] The wind turbine generator 1 shown is a three-blade upwind horizontal axis wind turbine (HAWT), which is the most common type of turbine in use. The wind turbine generator 1 includes a turbine rotor 2 having three blades 3, and the rotor 2 is supported in the front part of the nacelle 4 in a conventional manner. It should be noted that although three blades are common, a different number of blades can be used in alternative embodiments. The nacelle 4 is in turn mounted on top of a support tower 5, and the support tower 5 is fixed to a base (not shown) embedded in the ground.

[0030] The nacelle 4 contains a generator driven by the rotor 2 to generate electrical energy ( Figure 1 not shown in the figure). Thus, the wind turbine generator 1 is capable of generating electrical power from the wind flow that passes through the swept area of the rotor 2, thereby causing the blades 3 to rotate.

[0031] Now referring to Figure 2 , an example of a wind power plant 12 to which the method according to an embodiment of the present invention can be applied is shown. The example shown is merely representative, and those skilled in the art will understand that the methods described below can be applied to many different configurations. For example, although Figure 2 the example shown is based on a full-scale converter architecture, in practice the present invention can be used with other types of converters, and in general, the present invention is suitable for use with all topologies (such as DFIG arrangements).

[0032] Furthermore, the power converter of the wind power plant 12 or components forming part of the power converter are conventional and familiar to those skilled in the art, and will therefore only be outlined.

[0033] Figure 2 The wind power plant 12 shown in Figure 1 includes a single wind turbine generator 1 (such as the wind turbine generator shown in

[0034] Figure 2 ), but in practice may include other wind turbine generators. As already noted, the wind turbine generator 1 includes a generator 20 that is driven by a rotor (

[0035] not shown in the figure) to generate electrical power. The wind turbine generator 1 includes a low-voltage link 14 defined by a bundle of low-voltage lines 16 that terminate at a coupling transformer 18, which serves as a terminal for connecting the wind turbine generator 1 to a grid transmission line that is in turn connected to the grid. The electrical power generated by the wind turbine generator 1 is delivered to the grid through the coupling transformer 18.

[0036] The power converter 22 provides AC-to-AC conversion by feeding current through a series of an AC-DC (alternating current - direct current) converter 26 and a subsequent DC-AC converter 28. The AC-DC converter 26 is connected to the DC-AC converter 28 through a conventional DC link 30, which includes: a switch 31 and a resistor 32 in series therewith, which serves as a dumping load to enable excess energy to be released; and a capacitor 34, which provides smoothing of the DC output.

[0037] Any suitable power converter 22 can be used. In this embodiment, the AC-DC and DC-AC portions of the power converter 22 are defined by respective bridges of switching devices (not shown) (e.g., in the configuration of a conventional two-level back-to-back converter). Suitable switching devices for this purpose include insulated gate bipolar transistors (IGBTs) or metal oxide semiconductor field effect transistors (MOSFETs). The switching devices are typically operated using pulse width modulated drive signals.

[0038] The smoothed DC output of the AC-DC converter 26 is received by the DC-AC converter 28 as a DC input and creates a three-phase AC output for delivery to the coupling transformer 18.

[0039] As described above, in a full-scale architecture, the DC-AC converter 28 is configured to provide a certain level of control over the characteristics of the generated AC power, such as to increase the relative reactive power according to grid demand. Note that the amplitude, angle, and frequency of the output are specified by the grid requirements, and the voltage is set to a constant level according to the specifications of the low-voltage link 14. In practice, only the current of the AC output is controlled, and a converter controller 36 is provided for this purpose. The converter controller 36 forms part of the overall control system that controls the operation of the wind power plant 12 and will be described in more detail later with reference to Figure 3 be described in more detail.

[0040] This control system works based on sampled data obtained by a sampling system that probes the wind turbine generator 1 at various stages to sample electrical signals indicating, for example, current and / or voltage. In particular, as is typical for a full-scale architecture, the sampling system collects raw data related to the current and voltage from the stator 23 of the generator 20 and the output of the power converter 22 on the grid side. This raw data is processed into sampled data, which is then passed to, for example, the converter controller 36. The converter controller 36 uses the sampled data to determine the operating parameters of the wind turbine generator 1. For example, the duty cycle of the control signal for the generator-side IGBTs of the power converter 22 can be determined at least in part based on the instantaneous characteristics of the generated power provided by the generator 20.

[0041] The AC output leaves the power converter 22 via three power lines 16, each power line carrying a phase, and the three power lines together define a low-voltage link 14. The low-voltage link 14 includes a filter 24 which, in this embodiment, includes respective inductors 38 having shunt filter capacitors 40 for each of the three power lines 16 to provide low-pass filtering to remove switching harmonics from the AC waveform.

[0042] The three power lines 16 may each also include respective circuit breakers (not shown) for managing faults within the wind power plant 12.

[0043] As described above, the low-voltage link 14 terminates at a coupling transformer 18 which provides the required voltage boost. The high voltage output from the coupling transformer 18 defines a wind turbine generator terminal 42 which serves as a point of common coupling for the wind power plant 12.

[0044] The low-voltage link 14 also includes three branches (one for each phase) which define an auxiliary power line 44 that diverts some of the power output from the filter 24 for powering auxiliary systems (such as yaw, pitch, and cooling systems) of the wind power plant 12.

[0045] Since some of the power output from the power converter 22 (or P CONV ) is diverted to provide power for the auxiliary systems (or P AUX ), P CONV is greater than the power delivered to the grid (or "line power" P L ).

[0046] The converter controller 36 may be configured to prioritize the various power references it receives and accordingly adjust the total power reference according to which it controls the power converter 22.

[0047] For example, if the total required power (i.e., the total grid demand P L combined with the total demand P AUX for powering the auxiliary systems) is greater than the total power P CONV that the wind power plant 12 is capable of generating relative to the ambient temperature and wind conditions, the demand somewhere in the system will not be met. In such a case, the converter controller 36 may control the power converter 22 according to a list of prioritized power references to ensure that the total grid demand is met. Alternatively, the total grid demand may be sacrificed in favor of the total demand for powering the auxiliary systems.

[0048] As Figure 3As shown, the converter controller 36 of this embodiment includes an active power controller 46, a reactive power controller 48, a software block defining a power management module 50, and a thermal capacity manager 49. Those skilled in the art will understand that in practice, the converter controller 36 may include various other control modules, but for the purposes of this disclosure, only those control modules related to power control are mentioned.

[0049] The active power controller 46 and the reactive power controller 48 operate in series to interface with a current controller (not shown), which sends drive signals to the switching devices of the power converter 22 to control the active and reactive components of its AC output based on the signals received from the active power controller 46 and the reactive power controller 48. The active power controller 46 is configured to receive an active power reference from the power management module 50, and the reactive power manager 48 is configured to receive a reactive power reference from the power management module 50.

[0050] The power management module 50 provides a set of functions that enable the processing and optimization of power references that occur within the wind power plant 12, as well as those received from external sources such as a transmission system operator responsible for the power grid, a power plant controller responsible for multiple wind turbine generators within a single wind power plant, or a turbine controller.

[0051] The power management module 50 is modular because it includes a set of discrete modules, each providing a specific function. In this embodiment, those modules are implemented as individual software blocks within a common processing unit, but in other arrangements, dedicated hardware modules may be used.

[0052] The modular arrangement enhances the integration with the converter controller 36, especially because it enables the development and upgrade of individual functions without affecting other functions. In addition, a well-defined hierarchy can be created between different functions, thereby improving the interaction between functions and thus increasing the efficiency of the converter controller 36.

[0053] More specifically, in this embodiment, the power management module 50 includes a power reference manager 52, a power capacity manager 54, and a degradation mode manager 56. These modules are sorted according to the following hierarchy: the degradation mode manager 56 provides an input to the power capacity manager 54, which in turn provides an input to the power reference manager 52, and the power reference manager 52 then delivers the active power reference and the reactive power reference to the active power controller 46 and the reactive power controller 48, respectively.

[0054] The derating mode manager 56 is arranged to derate or reduce the power generation capacity of the generator 20 based on transient operating parameters. For example, if the temperature of the coolant system of the wind turbine generator 1 is higher than it should be, or if a module within the power converter 22 fails, the power generation capacity of the generator 20 may be derated.

[0055] Therefore, in view of safety considerations or physical constraints, the derating mode manager 56 relates to the power level that the wind turbine generator 1 is capable of producing at a basic level.

[0056] To this end, the derating mode manager 56 is also arranged to derate the power generation capacity of the generator 20 based on the temperature of at least one component of the wind power plant 12. For example, if it is determined that the temperature of a component is close to or exceeds a predetermined threshold of the component (the predetermined threshold may be the operating temperature limit or the overall temperature limit of the component), the power generation capacity may be derated. A temperature exceeding the former limit may damage the performance of the component, while a temperature exceeding the latter limit will put the component at risk of failure and becoming a fire hazard. This means that the wind turbine generator 1 will need to be shut down to repair or otherwise replace the component, resulting in a loss of production time.

[0057] Some examples of components whose temperature can be used to derate the power generation capacity of the generator 20 are as follows: inductor 38; AC-DC converter 26; DC-AC converter 28; switch 31; resistor 32; stator breaker (not shown) used in the generator 20; and, corresponding breaker (not shown) used in the power line 16. However, it will be obvious to those skilled in the art that this list of components is not exclusive, and the temperature of other components of the wind power plant 12 can be used when determining whether to derate the power generation capacity of the generator 20.

[0058] The thermal capacity manager 49 is arranged to calculate the temperature of the components of the power converter and output a derating reference to the power management module 36 based on a comparison between the calculated temperature and a predetermined threshold of the power converter or a component forming part of the power converter. The operation of the thermal capacity manager 49 will be described in more detail below focusing on a single component of the wind power plant 12. However, it will be obvious to those skilled in the art that the thermal capacity manager 49 is capable of simultaneously calculating the temperatures of multiple power converters or components forming part of the power converter and performing comparisons of the temperatures of multiple power converters or components forming part of the power converter.

[0059] Figure 4The architecture of the thermal capacity manager 49 is shown in schematic form. The thermal capacity manager 49 includes a series of modules, each providing a dedicated function, which process the sampled data received from the sampling system in a sequential phase to generate a derating reference that is passed to the power management module 52. This derating reference limits the output of the generator 20 and the converter 22 based on the estimated temperature of the power converter of the wind power plant 12 or a component forming part of the power converter. Those skilled in the art will understand that, where possible, the derating reference can also be generated based on a direct measurement of the component temperature.

[0060] Specifically, the thermal capacity manager 49 includes four modules: an operating point disturber 60; a component thermal module 62; a converter capacity evaluator 64; and a derating controller 66. These modules can be embodied as, for example, software blocks or, alternatively, as dedicated hardware components. Although only one component thermal model 62 is shown for simplicity, in practice, each component to be monitored includes a corresponding component thermal model.

[0061] The operating point disturber 60 receives input data including the current active power reference and reactive power reference, as well as sampled data indicating operating parameters such as the voltage and current at various sections of the wind power plant 12 and the ambient temperature.

[0062] Referring Figure 5 , the component thermal model 62 includes three software blocks: a component circuit model 67; a component loss model 68; and a thermal model 70.

[0063] The component circuit model 67 simulates the voltage across the component and the current through the component based on the input data received from the operating point disturber 60 related to the current active power reference and reactive power reference.

[0064] Once the voltage and current have been determined, they are used as inputs to the component loss model 68, which is configured to determine the associated power dissipated by the component. The dissipated power, together with the ambient temperature of the component, is then used as an input to the thermal model 70, which estimates the current temperature of the component.

[0065] In this case, the ambient temperature is the measurable temperature closest to the component. That is, the ambient temperature is an indication of the temperature of the area surrounding the component measured within the reasonable and practicable range. For example, this can include the air temperature or the temperature of the cooling system near the component. Conventional methods or systems can be used to estimate or measure the ambient temperature, all of which are familiar to those skilled in the art.

[0066] Figure 6An example of a thermal model generally designated by 70 used in the component thermal model 62 is shown. The thermal model 70 is a high-order model including a plurality of Foster circuits 72 arranged in series. However, it will be apparent to those skilled in the art that the thermal model 70 can also be implemented as a first-order, second-order, or higher-order model. In this example, the same heat flow (which is equivalent to the power loss determined using the component loss model) passes through each Foster circuit 72. However, it will be apparent to those skilled in the art that the component may be exposed to more than one heat flow, where the same thermal model is shared among the components. Each Foster circuit 72 includes a capacitor 74 and a resistor 76 arranged in parallel, and the sum of the voltage drops across each section is equal to the temperature difference between the component temperature and the ambient temperature. This can be simply expressed as:

[0067]

[0068] Each Foster circuit 72 is a first-order function, which can be described by a time constant and a gain (H):

[0069]

[0070] Where,

[0071] τ i =R i ·C i

[0072] Then the component temperature can be estimated as:

[0073] T component (s)=H(s)P loss (s)+T amb (s)

[0074] The output from the component thermal model 62 is passed to the converter capability evaluator 64, which compares the temperature of the component with a predetermined threshold.

[0075] The converter capability evaluator 64 outputs an indication as to whether the estimated temperature of the component is substantially equal to or exceeds the predetermined threshold to the derating controller 66. If it is determined that the estimated temperature of the component is substantially equal to or exceeds the predetermined threshold, the derating controller 66 correspondingly generates corresponding derating factors for the active power and the reactive power. The derating factors are passed to the derating mode manager 56 of the power management module 50, and the derating mode manager 56 updates the active power reference and the reactive power reference used to control the operation of the converter 22 and the generator 20 using the derating factors. In the case where the temperature of the component exceeds the predetermined threshold, the derating factor may be in a proportional relationship or a non-linear relationship with the degree to which the threshold is exceeded.

[0076] The derating mode manager 56 calculates a derating factor between 0 and 1 that is globally applied across the system. In a simplified example, if the derating mode manager 56 determines that the generator 20 can only output half of its normal capacity (in terms of active power) due to excessive component temperature, then the derating mode manager 56 calculates a derating factor of 0.5 for the active power.

[0077] In this regard, it should be noted that since excessive component temperatures should be avoided, in this embodiment, the derating factor calculated by the derating controller 66 limits the maximum capabilities of the converter 22 and, in turn, the generator 20. Then, any other factors that could cause further derating (such as those mentioned below) are applied within the parameters established by the derating factor. Thus, for example, if the derating factor is set to 0.8, the derating mode manager will output a derating factor ranging from 0 to 0.8.

[0078] The derating factors calculated by the derating mode manager 56 are output to the power capability manager 54, which uses these factors to update the P-Q chart that defines the ratio of active power to reactive power that the wind turbine generator 1 can produce, as well as the absolute magnitude of each type of power. An example of the P-Q chart 80 that can be used by the converter controller 36 is shown in Figure 7 which plots active power in kilowatts on the x-axis and reactive power in kilovolt-amperes reactive on the y-axis.

[0079] The solid line 82 that forms a trapezoidal shape represents the capabilities of the generator 20 when operating at its normal capacity. Those skilled in the art will understand that this shape is typical for any P-Q chart of the generator 20 of a wind turbine generator. Inside the solid line 82, the dashed line 84 that forms a smaller trapezoid represents the derated capabilities of the generator 20.

[0080] Note that in the Figure 7 example shown, both the active power and the reactive power are derated with the derated capabilities represented by the dashed line 84 and are derated by equal amounts. However, in other operating modes, only one of them may be derated, or different weights can be applied to each type of power. For example, if the active power has a higher priority than the reactive power, the reactive power is derated to a greater extent than the active power, and optionally, only the reactive power is derated. Correspondingly, if the reactive power has a higher priority ranking, the active power is derated to a greater extent than the reactive power.

[0081] Thus, the lines shown on the P-Q chart 80 define the long-term power generation capabilities of the wind turbine generator 1. If the derating factors generated by the derating mode manager 56 drop below 1, the power capability manager 54 updates the P-Q chart 80 based on these factors.

[0082] Then, the power capability manager 54 generates active power limits and reactive power limits by checking the updated P-Q diagram 80 for the prioritization of active power and reactive power, which is defined by the operating mode of the wind turbine generator 1 indicated by the power plant controller or the turbine controller.

[0083] For example, if the prioritization of reactive power is higher, but the reactive power reference provided by the power plant controller or the turbine controller cannot be satisfied within the limits of the updated P-Q diagram 80, the power capability manager 54 will adjust the active power limits and reactive power limits accordingly by further reducing the active power limits so that the reactive power demand can be met.

[0084] Subsequently, once the power capability manager 54 has updated the P-Q diagram 80 based on the derating factors provided by the derating mode manager 56 and generated the active power limits and reactive power limits based on the prioritization between the two types of power, these power limits will be transmitted back to the power plant controller or the turbine controller as a request to reduce power. Then, when generating the next set of power references, the power plant controller and the turbine controller can take this request into account, thus providing a feedback loop for this control element. In this way, the changes defined by the derating factors based on the comparison of the component temperatures with their respective predetermined thresholds propagate throughout the wind power plant 12.

[0085] The updated P-Q diagram 80 is transmitted to the power reference manager 52, which also receives a number of power references from various sources. In this regard, the power reference manager 52 includes an input (not shown) configured to receive various power references. The power reference manager 52 also includes a processor 58, which is arranged to analyze the input power references to determine the output active power reference and reactive power reference; and an output (not shown) configured to transmit those references to the power converter 22 as will be described.

[0086] The references received at the input of the power reference manager 52 include the active power reference and the reactive power reference received from the power plant controller or the turbine controller, as well as various internal active power references that jointly define the auxiliary demand.

[0087] The power reference manager 52 also prioritizes reactive power over active power (or vice versa) in the short term according to the same priority order imposed by the power capability manager 54. This requires setting the active power reference or the reactive power reference outside the P-Q diagram 80 within a short time period to meet the type of prioritization of the demand, as will be described in more detail below.

[0088] Typically, a power plant controller or a turbine controller issues an active power reference indicating the real power level that the wind power plant 12 must deliver, as well as a reactive power reference. As an alternative to, or in addition to, the reactive power reference, the power plant controller or the turbine controller may also provide a power factor (or "CosPhi") reference, which defines the ratio of real power to the total power dissipated in the system (or "apparent power"). In this case, the power reference manager 52 is responsible for determining the reactive power reference based on the active power reference and the power factor reference. As those skilled in the art will understand, the reactive power reference can be derived from these inputs using basic geometric and trigonometric relationships. The power reference manager 52 may have the option to calculate the reactive power reference based on the power factor and the active power reference, or to use the reactive power reference provided by the power plant controller or the turbine controller.

[0089] The power reference manager 52 compares the power references it receives with the current capabilities of the wind turbine generator 1 (as indicated by the P-Q chart 80 received from the power capability manager 54) and determines whether all of the requirements associated with those references can be met while providing sufficient reactive power.

[0090] If the requirements can be met, the power reference manager 52 simply generates active power references and reactive power references representing the respective sums of the different active power references and reactive power references it receives. If the requirements cannot be met within the constraints of the P-Q chart 80, the power reference manager 52 prioritizes the references it receives according to a predetermined scheme.

[0091] By creating the active power references and reactive power references based on the various requirements that occur throughout the system, the power reference manager 52 avoids always operating the wind turbine generator 1 at its operating capacity (as indicated by the power capability manager 54). This in turn improves the operating efficiency and reduces the risk of failure due to overheating of components.

[0092] In summary, the present invention utilizes the functionality of the thermal capability manager 49 to monitor the temperature of components within the wind power plant 12. This is then used to update the derating factor, which is transmitted to the power management module 52 and incorporated into the derating factor that defines the capacity limit of the converter 22 (as defined by the P-Q chart 80). By monitoring several components, the capability manager 49 provides an overall derating for the evaluated component system. This ultimately feeds into the final active power reference and reactive power reference output by the power reference manager 52 and accordingly transmitted to the active power controller 46 and the reactive power controller 48. This in turn feeds back to the turbine controller and thus affects the limitation of the output of the generator 20 as needed.

[0093] If the wind turbine generator 1 is operated up to its operating limits, the thermal capacity manager 49 of this embodiment can also be used to model the variation over time of this influence on the power converter or on components forming part of the power converter. In this case, the thermal model 62 of the power converter or of the components forming part of the power converter serves the purpose of determining the temperature evolution of the components starting from their initial temperature, based on the nominal or perturbed power reference. The nominal power reference defines a short-term limit of the apparent power generated by the generator 20 that lies outside the normal operating limits defined by the P-Q diagram 80. This short-term limit is represented by the dashed line 86 in Figure 7 and is related to operating the wind turbine generator 1 at its operating limits. As can be seen from this figure, the dashed line 86 forms a trapezoidal shape. However, it will be obvious to a person skilled in the art that the dashed line 86 defining the short-term limit of the wind turbine generator 1 can also form a different shape. Within the apparent power limits, the reactive power component and the active power component can be varied to suit the instantaneous prioritization. In this context, "short-term" typically requires a duration of up to a few minutes. Other nominal power references defining medium-term limits (lying between the normal operating limits 82 and the short-term limits 86) can also be considered, but are not given here. Additionally, multiple short-term limits and / or medium-term limits can be evaluated continuously.

[0094] This short-term limit is determined based on the duration for which the wind turbine generator 1 can be operated at its operating limits before the temperature of the power converter or of the components forming part of the power converter reaches its predetermined threshold.

[0095] To this end, the operating point perturbator 60 receives input data including the current active power reference and reactive power reference, the nominal power reference defining the operating limits of the wind turbine generator 1, and indicating operating parameters such as the voltage and current at various sections of the wind power plant 12, as well as the ambient temperature and the temperature of the components. The nominal power reference can be fixed or can be online commanded / regulated.

[0096] The component circuit model 67 simulates the voltage across the component and the current through the component based on the input data received from the operating point perturbator 60 related to the current power reference and the nominal power reference.

[0097] Once the voltage and current have been determined, they are used as input to the component loss model 68, which is configured to determine the associated power dissipated by the component. The dissipated power is then used together with the ambient temperature of the component as input to the thermal model 70, which determines the temperature evolution of the component under the current power reference and the nominal power reference.

[0098] Figure 8Shows two examples of the temperature evolution of a component, one example based on the current power reference (as indicated by line 90) and the other example based on the nominal power reference (as represented by line 92). The horizontal line 93 indicates a predefined threshold for the component. In this embodiment, the predefined threshold is the operating temperature of the component, but it can also be related to the component temperature limit. As can be seen from this figure, the wind turbine generator 1 can operate indefinitely at the current power reference without the temperature of the component reaching its operating temperature limit. However, line 92 indicates that the wind turbine generator 1 can only operate at the nominal power reference for a limited period of time (denoted by T LIMIT before the temperature of the component reaches its limit or heat capacity). In this case, T LIMIT corresponds to the short-term limit beyond which the apparent power generated by the generator 20 lies outside the normal operating limits defined by the P-Q diagram 80. That is, T LIMIT corresponds to the short-term limit for operating the generator 20 at the input nominal power reference. Several short-term limits can be calculated for different nominal power references.

[0099] The converter capacity estimator 64 calculates T LIMIT , and then T LIMIT is passed to the power management module 50. The power management module 50 then uses T LIMIT to update the active power reference and the reactive power reference for controlling the operation of the converter 22 and the generator 20 as described above. That is, T LIMIT is transmitted to the power plant controller or the wind turbine generator controller in order to establish the heat capacity of the component.

[0100] For example, if the power reference manager 52 determines that basic services cannot be maintained while also supplying some power to the grid, it can provide a short-term boost by setting the active power priority to be higher than the reactive power. In other words, if the basic services and the active power demand of the grid exceed the active power that can be provided as indicated by the P-Q diagram 80, the power reference manager 52 increases the active power reference above the normal P-Q diagram limit and correspondingly reduces the reactive power reference within the constraint of the total electric power that the generator 20 can generate.

[0101] In another scenario, if the power plant controller or the turbine controller sets the reactive power priority to be higher for improved stability, the power reference manager 52 increases the reactive power reference outside the P-Q diagram 80 (within the bounds defined by the short-term apparent power limit 86) for a short period of time.

[0102] This shows that the power reference manager 52 provides a boosting function so that active power and / or reactive power can be provided to the power grid in the short term (e.g., when the local wind speed is low and thus the power generation capacity of the wind turbine generator 1 is reduced). In this way, the power reference manager 52 enables the wind turbine generator 1 to operate at its maximum power generation potential in a safe manner for a short period of time.

[0103] As described above, multiple short-term limits and / or medium-term limits can be continuously evaluated. This means that the calculation of T LIMIT is iterative and updated based on information from the previous iteration. Thus, if the short-term heat capacity of a component is used, T LIMIT will be reduced to zero. Then, when the component cools, T LIMIT will increase. The reduction of T LIMIT effectively allows short-term operation outside the normal P-Q diagram 80 while still ensuring that the component does not reach or exceed its operating limits.

[0104] In the long term, the normal limit 80 or the derating limit 84 determined by the power capability manager 54 must be adhered to so that the wind turbine generator 1 does not operate outside its expected range for a long period of time to avoid long-term thermal stress within the wind turbine generator 1, which may lead to wear or failure as described above. Therefore, whenever the power reference manager 52 determines that the demands of the power plant controller or the turbine controller for active power and reactive power can be met while operating within the normal P-Q diagram 80 defined by the power capability manager 54 and also satisfying the current prioritization between active power and reactive power, the power reference manager 52 calculates the active power reference and the reactive power reference that fall within these limits for the corresponding controller. If power cannot be provided to the power grid without operating outside the P-Q diagram 80 for a long period of time, the wind power plant 12 must be shut down until the power generation capacity becomes sufficient for stable operation.

[0105] As already noted, embodiments of the present invention are also applicable to other types of wind turbine systems (including DFIG topologies having a converter connected to the rotor of a doubly-fed induction generator). Although those skilled in the art will be familiar with such an arrangement, for completeness, Figure 9 an example of a wind power plant 81 having such an architecture is schematically shown.

[0106] Figure 9 The wind power plant 81 of has a generator 83 that includes a set of rotor windings and a set of stator windings driven by a rotor 2. To enable the generator 83 to generate electrical power when the rotor windings rotate, an excitation current is fed into the rotor windings through a power converter 85.

[0107] The output of the generator 83 is connected to a three-way coupling transformer 87, which provides electrical connections to a common coupling point (not shown), to the power grid, and to the power converter 85. Subsequently, the power converter 85 is connected to the rotor winding of the generator 83, thereby defining a feedback loop. Thus, once power generation begins, the power converter 85 can use the output of the generator 83 to generate the excitation current that is delivered to the rotor winding.

[0108] In summary, the power management module 50 of the present embodiment divides the power management of the wind turbine generator 1 into two different categories, namely long-term power management for stable operation and short-term power management for temporarily boosting the active power and / or the reactive power when needed.

[0109] Those skilled in the art will understand that the above specific embodiments can be modified without departing from the inventive concept defined by the claims.

Claims

1. A method for controlling a wind turbine generator of a wind power plant based on conditions of a power converter or a component forming part of the power converter, the method comprising: Determining an initial condition of the power converter or the component forming part of the power converter; Determining an evolution of the condition from the initial condition based on a nominal power reference value of the wind turbine generator; Comparing the evolution of the condition with a predetermined threshold; Determining, based on the comparison, a time period during which the condition of the power converter or the component forming part of the power converter will be substantially equal to the predetermined threshold; The method further comprises: Comparing the initial condition of the power converter or the component forming part of the power converter with the predetermined threshold; If the initial condition is substantially equal to or exceeds the predetermined threshold, modifying the power reference value of the wind turbine generator; Wherein modifying the power reference value of the wind turbine generator comprises: Generating respective derating factors for active power and reactive power by a derating controller; Transmitting the respective derating factors to a derating mode manager, the derating mode manager using the respective derating factors to calculate a derating factor between 0 and 1 to be globally applied in the whole system; Outputting the derating factor to a power capability manager, the power capability manager using the derating factor to update a P-Q chart that defines a ratio of active power and reactive power that the wind turbine generator can generate and absolute magnitudes of the active power and the reactive power, and the power capability manager also generating an active power limit and a reactive power limit by checking the updated P-Q chart for prioritization of active power versus reactive power; and Transmitting the active power limit and the reactive power limit as a power reduction request back to a power plant controller or a turbine controller such that the power plant controller or the turbine controller takes the request into account when generating the next set of power references.

2. The method according to claim 1 further comprises: Controlling the wind turbine generator at the nominal power reference value for a duration not exceeding the time period.

3. The method according to claim 1, wherein, The condition is a temperature of the power converter or the component forming part of the power converter.

4. The method according to claim 3, wherein Determining the initial condition as a non-linear function based on power losses of the power converter or the component forming part of the power converter at current operating parameters and ambient temperature.

5. The method according to claim 3, wherein Determining the evolution as a non-linear function based on power losses of the power converter or the component forming part of the power converter at the nominal power reference value and ambient temperature.

6. The method according to claim 3 or 4, wherein The power losses of the power converter or the component forming part of the power converter are determined based on a voltage across the power converter or the component forming part of the power converter and a current passing through the power converter or the component forming part of the power converter.

7. The method according to claim 1, when applied to multiple power converters, the method further comprising: Selecting the shortest time period from a plurality of time periods as the time period.

8. A controller for a wind turbine generator, comprising data processing means and a memory module, wherein, The memory module includes a set of program code instructions which, when executed by the data processing device, implement the method according to any one of the preceding claims.

9. A wind turbine comprising the controller according to claim 8.

10. A computer program product downloadable from a communication network and / or storable on a machine-readable medium, comprising program code instructions for implementing the method according to any one of claims 1 to 7.

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