Method for reducing high torque levels and torque gradients in a wind turbine generator

Abstract

Aspects of the invention relate to a method (100) for reducing a high torque level and / or a high rate of change of torque in a wind turbine generator (10) comprising a machine-side converter (28) and a line-side converter (30) connected by a DC link (32), and the line-side converter (30) operating according to a virtual synchronous machine control scheme. The method (100) comprises: determining (102) a generator torque (T ref ); determining (104) a torque surplus (T surplus ) indicative of an amount by which the generator torque (T ref ) exceeds a torque limit; determining (106) an active power surplus (P surplus ) corresponding to the torque surplus (T surplus ); controlling (108) the line-side converter (30) according to the virtual synchronous machine control scheme, the virtual synchronous machine control scheme using input parameters and being configured to reduce an active power output of the line-side converter (30) by the active power surplus (P surplus ).

Description

Technical Field

[0001] This disclosure relates to a method for reducing high torque levels and high torque gradients in wind turbine generators, and to a power plant controller for implementing this method. The method particularly relates to wind turbine generators operating using a virtual synchronous generator control scheme and / or wind turbine generators configured to exhibit virtual synchronous generator responses. Background Technology

[0002] To allow for higher penetration of renewable energy sources such as wind turbines into the power grid, some countries have proposed requirements for equipping power converters with grid-forming characteristics similar to those of traditional synchronous generators. These requirements can be addressed by configuring wind turbines as virtual synchronous machines or by using virtual synchronous machine control schemes. Virtual synchronous machines are also known as virtual synchronous generators.

[0003] One characteristic of virtual synchronous generator control is that the power contribution of the wind turbine generator is adjusted to be proportional to the deviation angle between the grid voltage and the internal virtual rotor angle. The internal virtual rotor angle is determined by modeling the synchronous generator's response to power error values.

[0004] When a wind turbine generator is controlled as a virtual synchronous machine, abrupt changes in voltage or phase cause variations in the deviation angles. Large abrupt changes in voltage or phase result in large and significant variations in these deviations. This is translated into large variations in power contribution requirements through virtual synchronous machine control. These abrupt changes in power contribution requirements lead to the achievement of high torque gradients and / or high torque levels, and thus result in high mechanical stress on the wind turbine generator's power generation system.

[0005] High mechanical loads on generators are undesirable. Instantaneous peak loads can cause damage and, when repeated, can shorten turbine life. Large torque gradients can cause damage unrelated to peak loads, such as film bearing breaking through.

[0006] The purpose of this invention is to address one or more drawbacks associated with the prior art. Summary of the Invention

[0007] According to one aspect of the present invention, a method is provided for reducing high torque levels and / or high torque variation rates in a wind turbine generator. The wind turbine generator includes a machine-side converter and a line-side converter connected via a DC link. The line-side converter operates according to a virtual synchronous machine control scheme. The method includes:

[0008] - Determine the generator torque;

[0009] - Determine the remaining torque, which indicates the amount by which the generator torque exceeds the torque limit;

[0010] - Determine the remaining active power corresponding to the remaining torque; and

[0011] - Control the line-side converter according to the virtual synchronous machine control scheme.

[0012] The control scheme has input parameters based on the remaining active power. The control scheme is configured to reduce the active power output of the line-side converter based on the remaining active power.

[0013] The virtual synchronous generator control scheme means that the wind turbine generator is controlled as a simulated synchronous generator by analogy to a voltage source facing the grid instead of a current source, by providing virtual inertia, and by controlling the line-side converter based on the phase angle difference between the virtual generator and the grid.

[0014] Regarding torque surplus and active power surplus, the term "surplus" is intended to indicate the amount exceeding the limit requested or to be requested from the generator. In other words, torque surplus indicates the amount of torque included in the generator torque value that exceeds the torque limit. This surplus may be referred to as excess torque or over-torque. The torque surplus in the above method can be considered as primary torque surplus, to distinguish it from the preliminary torque surplus used below.

[0015] Advantageously, by applying the methods described above, torque levels above the maximum torque and torque variations exceeding the maximum rate of change of torque can be avoided. Identifying the remaining torque and introducing it as an input parameter for controlling the line-side converter introduces a feedforward element, which can react quickly to potentially problematic torque. Importantly, the determination of the remaining torque ensures that only torques exceeding the limit (i.e., torques that could cause damage) are used to alter the operation of the line-side converter. Torque at permissible levels is transmitted without adjustment.

[0016] The torque limit can be based on the maximum rate of change of torque. When the torque limit is based on the maximum rate of change of torque, the method may include:

[0017] - Determine the generator torque variation rate based on the determined generator torque and at least one previously determined generator torque;

[0018] - Compare the generator torque change rate with the maximum torque change rate; and

[0019] - A torque limit is generated based on this comparison.

[0020] If the determined rate of change of generator torque is equal to or less than the maximum rate of change of torque, the torque limit can be set to the determined generator torque. If the determined rate of change of generator torque is greater than the maximum rate of change of torque, the torque limit can be generated by adjusting the previously determined generator torque by integrating the maximum rate of change of torque.

[0021] The torque limit can be based on the maximum torque value. When the torque limit is based on the maximum torque value, the method includes:

[0022] - Compare the determined generator torque with the maximum torque value; and

[0023] - A torque limit is generated based on this comparison.

[0024] If the determined generator torque exceeds the maximum torque value, a torque limit can be generated as the maximum torque value. If the determined generator torque is equal to or less than the maximum torque value, a torque limit can be generated as the determined generator torque.

[0025] The method may include determining at least two preliminary torque remainders. These at least two preliminary torque remainders may include a first preliminary torque remainder and a second preliminary torque remainder, the first preliminary torque remainder indicating the amount by which the generator torque exceeds a torque limit based on a maximum torque change rate, and the second preliminary torque remainder indicating the amount by which the generator torque exceeds a torque limit based on a maximum torque value. In the case of determining two preliminary torque remainders, determining the torque remainder may include determining the largest remainder among the at least two preliminary torque remainders.

[0026] The initial torque surplus differs from the main torque surplus described above. Each initial torque surplus is calculated based on a specific torque limit, allowing more than one limit to be achieved. The use of the initial torque surplus and the selection of the maximum surplus ensures that the generator is controlled to prevent any exceedance of the limits.

[0027] Optionally, the input parameters include an active power value. This active power value can be used as input to the swing equation for the voltage angle of the virtual synchronous machine control scheme.

[0028] Alternatively, the input parameters may include an active power limit. This active power limit can be used as an input to a power limiter configured to generate an active power reference for a virtual synchronous machine control scheme.

[0029] In another alternative, the input parameters may optionally include a current limit. This current limit can be based on excess active power and the power grid voltage level. This current limit can be used as an input to a current limiter in a virtual synchronous machine control scheme. The current limiter can be configured to implement the current limit as a virtual resistance.

[0030] Using different input parameters brings different, varying benefits. For example, using current limits as input parameters is a fast method, while active power limits are less fast, and active power values ​​are even slower. Implementing active power or current limits allows for the interaction and implementation of multiple different schemes within a virtual synchronizer that might otherwise be impossible. For instance, when current or active power limits are already implemented, using these as input parameters makes integration easy, especially into existing systems where redesigning operating modes may not be straightforward. Although the slowest of the three options described here, using active power values ​​offers the added benefit of being directly input into the oscillation equations and thus having a direct impact on the output angle.

[0031] In some embodiments, the input parameters may include more than one value. The input parameters may include a combination of active power values, active power limits, and / or current limits.

[0032] Determining generator torque may include measuring the generator torque from the generator drive system.

[0033] Alternatively, determining the generator torque may include:

[0034] - Determine the active power reference for the machine-side converter;

[0035] - Determine the rotor speed; and

[0036] - Calculate generator torque based on active power reference and rotor speed.

[0037] The active power reference can be determined based on the error between the voltage reference signal and the measured voltage level of the DC link.

[0038] Determining the remaining active power may include:

[0039] - Determine the rotor speed; and

[0040] - Calculate the remaining active power based on the remaining torque and rotor speed.

[0041] According to another aspect of the invention, a wind turbine controller is provided, which is configured to implement the above-described method.

[0042] According to another aspect of the invention, a computer program product is provided, which includes instructions that, when executed by a computer or a controller of a wind turbine, cause the computer or controller to perform the steps of the method described above.

[0043] Within the scope of this application, it is expressly indicated that aspects, embodiments, examples, and alternatives, and in particular their individual features, given in the foregoing paragraphs, claims, and / or the following description and drawings, may be used independently or combined in any way. That is, all embodiments and / or features of any embodiment may be combined in any way and / or in any combination, unless such features are incompatible. The applicant reserves the right to accordingly amend any originally filed claim or to file any new claim, including the right to modify any originally filed claim to include any feature subordinate to and / or incorporated into any other claim, even if the claim was not initially filed in this manner. Attached Figure Description

[0044] One or more embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which:

[0045] Figure 1 A wind turbine generator is shown;

[0046] Figure 2 It shows Figure 1 A schematic representation of a wind turbine generator power generation system;

[0047] Figure 3 It shows Figure 2 A control system block diagram of a portion of the DC link voltage controller of a power generation system;

[0048] Figure 4 A flowchart is shown for a method to reduce high torque levels and torque gradients in wind turbine generators; and

[0049] Figures 5 to 7 An example of a control system for implementing a virtual synchronous machine control scheme is shown. Detailed Implementation

[0050] In general, this invention provides a method for controlling a wind turbine generator, and more particularly a method for controlling the line-side converter of a wind turbine generator to reduce high torque levels and high torque gradients (also known as high torque level variation rates) that may be caused by virtual synchronous machine control schemes. The invention also provides a system. This method and system utilize torque levels to alter the active power output of the line-side converter, thereby reducing the torque levels required by the generator at the machine-side converter and earlier in the drivetrain. Reducing high torque levels and high torque gradients ensures optimized lifespan of the wind turbine generator and prevents component failure within the generator.

[0051] Figure 1An example of the invention, a wind turbine 10, is shown that can be incorporated therein. The wind turbine 10 includes a tower 12 supporting a nacelle 14, on which a rotor 16 is mounted. The rotor 16 includes a plurality of wind turbine blades 18 extending radially from a hub 20. In this example, the rotor 16 includes three blades 18, but other configurations are possible.

[0052] Rotor 16 is connected to a generator located in the nacelle via a transmission system. Figure 1 (The generator and transmission system are not shown in the diagram). The rotor 16 is configured to rotate under the action of wind on the blades 18. The rotation of the rotor 16 causes the transmission system and the generator to rotate. The generator is configured to generate electricity. Thus, the wind turbine 10 converts the kinetic energy of the wind into mechanical energy by means of the rotor blades 18, and then into electrical energy by means of the generator.

[0053] Figure 2 An example of a power generation system 22 including a generator 24 is shown. The generator is connected to a power converter 26, which includes a generator-side converter 28 and a line-side converter 30. The generator-side converter 28 (also referred to as a machine-side converter or MSC) converts the AC electricity generated by the rotating armature of the generator 24 into DC electricity. The line-side converter 30 converts the DC electricity into AC electricity for supplying the power grid to which the wind turbine generator 10 is connected.

[0054] Power converter 26 also includes a DC link 32 and a resistor 34 connected to a controllable switch 36. The resistor and switch form a power dissipation device, also known as a chopper 38, used to dissipate active power. The DC link 32 includes one or more DC link capacitors 40, which are charged by the DC output current from the generator-side converter 28 and supply DC power to the line-side converter 30. The output AC current from the line-side converter 30 is supplied to the power output line 42 to supply power to a wider power network. One or more additional components 44 may be provided between the line-side converter 30 and the output line 42 to transform, adjust, or filter the output before it is supplied to the network. For example, the additional components 44 may include an output inductor, a wind turbine transformer, and / or harmonic filter capacitors, as well as other components.

[0055] As should be understood, power output line 42 may be a medium-voltage power bus that receives power from other wind turbine generators forming a renewable energy power plant, or it may be connected to a high-voltage network, for example, via an additional transformer. The power converter may be a full-scale converter configured according to different principles including forced commutation and line commutation converters.

[0056] In order to respond to commands from the power plant controller and supply power in a responsive manner, the wind turbine generator 10 includes a control system. This control system includes at least a machine-side converter controller (MSC controller) 46 and a line-side converter controller (LSC controller) 48. Controllers 46 and 48 control corresponding converters 28 and 30, typically by controlling the pulse wave modulation of converters 28 and 30, to control the amount of active power P and reactive power Q generated by the wind turbine generator 10.

[0057] In the embodiments discussed herein, the wind turbine generator 10 is controlled according to a Virtual Synchronous Machine (VSM) control scheme. The VSM control scheme is a protocol used to control the converter of the wind turbine generator to mimic or simulate a synchronous generator. An angle is calculated for the virtual synchronous machine based on the measured grid voltage. This angle, referred to as θVSM, is used to control the power output of the line-side converter 30 based on the difference between the VSM angle and the grid angle. The VSM angle is generated based on the VSM oscillation equation.

[0058] The VSM acceleration (the double-time derivative of θVSM) indicates the difference between the power reference of the wind turbine's desired power output and the grid power supplied by the wind turbine to the grid. Therefore, controlling the converter based on this angle ensures that the wind turbine's power output matches grid requirements.

[0059] The VSM angle θVSM can be used to transform signals between rotating and non-rotating coordinate systems, such as between the V∠θ coordinate system or DQ coordinate system (rotating) and the αβ coordinate system or abc coordinate system (non-rotating). Based on the synchro angle θVSM and the voltage amplitude reference Vqref, control signals for the desired active and reactive power are determined and transmitted to the pulse width modulator of the line-side converter 30.

[0060] The line-side converter 30 is thus controlled to change its active power output and reactive power output according to the change in the difference between the angle and voltage amplitude reference.

[0061] To maintain the voltage level of DC link 32, the power flowing into and out of DC link 32 is kept at substantially equal levels. Since the line-side converter 30 is responsible for achieving power output relative to the desired voltage angle and therefore controls active power according to a reference value, the machine-side converter 28 is used to match the active power flowing out of DC link 32 to maintain the voltage level of DC link 32. The difference between the power flowing into and out of DC link 32 results in a change in the voltage level on DC link 32.

[0062] To supply power to DC link 32 and prevent voltage fluctuations on DC link 32, machine-side converter 28 is configured according to the DC link controller ( Figure 2 The power reference (not shown in the image) is used for control. The DC link controller determines the difference between the DC link reference voltage and the DC link measured voltage, and generates a power reference accordingly.

[0063] In traditional systems, this control stemming from the control of the line-side converter can result in high torque and a high rate of torque variation imposed on the generator. For example, changes in grid conditions and the occurrence of phase jumps or voltage drops cause variations in angle. Sudden changes in angle lead to sudden changes in the power reference at the line-side converter. Therefore, to maintain voltage on the DC link, the machine-side converter must also implement a similar change in the power reference. Large jumps in the power reference, and large jumps in the power demanded by the generator, can result in high torque and a high rate of torque variation, which is transmitted through the wind turbine's drivetrain and generation system. At a constant rotational speed, power generation is directly proportional to torque. Since the generator speed is uncontrollable, torque is controlled to change the power passing through the converter, typically by modifying the power reference or by tilting the blades differently depending on whether the generator's output is below or at rated power. Therefore, sudden changes in power demand cause sudden changes in load on the blades and turbine to achieve a sudden increase in torque to match the power demand. High torque and a high rate of torque variation can lead to damage to components in the drivetrain.

[0064] To counteract this effect, a design has been developed. Figure 3 System 50 and Figure 4 Method 100. System 50 and method 100 monitor the power reference of machine-side converter 46 established based on DC link voltage to identify potentially damaging changes in torque and torque rate of change, and feed the signal forward to line-side converter 48 to reduce parameters based on the potentially damaging torque level. For convenience, the torque rate of change will be referred to as the torque gradient below.

[0065] exist Figure 3 In the middle, starting from the left-hand side, the DC link controller 52 (also referred to as the DC link voltage controller or more simply as a voltage controller) is provided as part of the machine-side converter controller 46. The DC link voltage controller 52 receives the measured voltage level V on the DC link 32. DC and DC link reference voltage V DCref At the difference junction 54 within the DC link voltage controller 52, the difference between these values ​​is determined to provide an error value. Using the PI controller 56, the error value is converted into a power reference P. refThe power reference is then used to control the machine-side converter 46. Since this application does not involve the control of the machine-side converter, the machine-side converter controller following the generation of this power reference is not described in detail or discussed further.

[0066] According to the present invention, a high-torque module 60 is provided. The high-torque module 60 also receives a power reference generated by a DC link voltage controller 52. At block 62, the power reference is converted into a torque value T. ref The method involves dividing the power reference by the generator's rotational speed, also known as the rotor speed. The rotor speed can be determined using a rotor speed sensor (such as a tachometer) or a speed observer familiar to technicians.

[0067] A power reference from the DC link voltage controller 52 is used to effectively preemptively prevent high torque values. The system identifies power references that will lead to high power changes and reduces them at the line-side converter before the torque is converted through the drivetrain. This is why a DC link voltage controller value is used—high power reference values ​​can be identified before they are realized. In other embodiments, measured torque or other parameters or values ​​from which that torque can be derived can be used.

[0068] Back Figure 3 The remaining torque is determined based on the established torque value. Remaining torque refers to the amount of torque exceeding the torque limit. If the torque does not exceed the limit, the remaining torque can be zero; if the torque does exceed the limit, the remaining torque can be positive.

[0069] like Figure 3 As shown, the remaining torque is identified based on two tests. In the first test 64, indicated by the upper box, the torque gradient is determined and compared to a torque gradient limit (i.e., the maximum rate of torque change) to determine the remaining torque. In the second test 66, indicated by the lower box, the torque value is directly compared to a torque limit to determine the remaining torque. These two tests avoid any potentially destructive torque variations.

[0070] In the first test, the torque value is passed through constraint box 68. Within constraint box 68, a torque gradient is calculated based on the determined torque value and one or more previously determined torque values. The torque gradient is compared to a torque gradient limit. If the torque gradient does not exceed the torque gradient limit, the output of box 68 is the torque value. If the torque gradient exceeds the torque gradient limit, the output of box 68 is a new torque value calculated based on the previous torque value and the allowable rate of torque change (i.e., the torque gradient limit).

[0071] The output of constraint box 68 is passed to difference connection point 70 to determine the first preliminary residual, where the difference between the original torque value and the output of that box is calculated. If the torque gradient does not exceed the gradient limit, the output of difference connection point 70 is zero because the output of box 68 is the same as the torque value. If the gradient limit is exceeded, a positive first preliminary torque residual value is output from difference connection point 70.

[0072] In the second test, the torque value is passed through limit box 72. The torque value is compared to a torque limit, which is the maximum or peak torque value. If the torque value does not exceed the torque limit, the output of box 72 is the torque value. If the torque value exceeds the torque limit, the output of box 72 is the torque limit.

[0073] The output of the limiting box is passed to the difference connection point 74 to determine the second preliminary residual, where the difference between the original torque value and the output of box 72 is calculated. If the torque value does not exceed the limit, the output of the difference connection point 74 is zero because the output of box 72 is the same as the torque value. If the limit is exceeded, a positive second preliminary torque residual value is output from the difference connection point 74.

[0074] These two initial torque residual values, whether zero or positive, are passed to box 76, where the larger of the two values ​​is determined. This larger value is the torque residual value T. surplus .

[0075] Based on the torque surplus, the active power surplus is obtained by multiplying it by the rotational speed at box 78. As shown by arrow 80, the active power surplus P surplus This is then used as an input parameter for the line-side converter. The remaining active power is used to control the line-side converter to reduce the particular value that would result in the required high torque.

[0076] Residual active power P surplus It can be used as the input of a line-side converter in one or more ways, which will be described below. Before that, a brief discussion will follow. Figure 4 .

[0077] Figure 4A general method 100 for operating a torque module is illustrated. As can be understood from the above discussion, this method typically includes steps 102, 104, 106, and 108: determining the generator torque, which may be a calculated generator torque based on rotor speed and power references, a measured generator torque, or others; determining torque surplus, which indicates the amount by which the generator torque exceeds a torque limit; determining the active power surplus corresponding to the torque surplus; and controlling the line-side converter according to a virtual synchronous machine control scheme having input parameters based on the active power surplus and configured to reduce the active power output of the line-side converter through the active power surplus.

[0078] It is worth noting that, with Figure 3 Compared to the previous embodiment, Figure 4 Method 100 is a general method. As indicated by Method 100, the tests performed to determine the remaining torque can be based on multiple parameters and limits. Therefore, although Figure 3 The embodiments illustrate two tests 64 and 66, but it should be understood that only one of the tests may be performed, or more than two tests may be performed.

[0079] Now consider the use of surplus active power, a value typically used to reduce the active power output of line-side converters. Reducing this output value ensures that the power demand of machine-side converters is also reduced, thus avoiding high torque gradients and torque values.

[0080] Figures 5 to 7 Three different examples are shown, which involve how to use the surplus active power as input to a virtual synchronous machine control scheme for a line-side converter to reduce the active power output of the line-side converter.

[0081] In reference Figure 5 In the first example of the explanation, the input from the torque module to the line-side converter is the residual active power P. surplus The surplus active power is used as an input parameter and requires no further modification or calculation. The surplus active power is input into the swing equation for the voltage angle used to calculate the virtual synchronous machine control scheme.

[0082] exist Figure 5 An example of the oscillation equation and its implementation is shown in the control system 120. Figure 5 In the above, the power error ΔP is determined as the difference P at connection point 122. ref -P grid -P surplus P ref It is a power reference for the expected active power output of a wind turbine, P grid It is the value of the grid power, P surplus This is the remaining active power value. Another parameter, P... dIt can also be subtracted at this connection point 122, but it is not shown here for clarity. P d This includes other input power terms, such as damped power fed back from the swing equation. In some embodiments, the grid power P grid It can be determined elsewhere and adjusted based on the virtual power calculated from the virtual resistance. Under steady-state conditions, the power error ΔP is zero because the power reference value equals the grid power, and any feedback or feedforward power adjustments (including residual power) are also zero.

[0083] exist Figure 5 In this process, the residual active power is passed through an optional filter 128 before being used at connection point 122. Filter 128 is configured to correct for hysteresis introduced by rotor simulation.

[0084] In response to changes in the power reference or grid power, the power error ΔP becomes non-zero, causing the angle θVSM to increase or decrease in order to reduce the power error ΔP. In response to fluctuations in the power reference or grid power, the synthesized inertial response becomes non-zero, causing the virtual machine to accelerate or decelerate to reach a new equilibrium state. When the grid power P... grid Follow P again ref At that time, a new equilibrium state is reached.

[0085] By directly injecting the remaining active power value into this part of the oscillation equation, the variation in error value is mitigated to prevent the torque value from exceeding the limit or to prevent it from rising faster than the maximum torque change rate.

[0086] After calculating the error, the rotational speed ωVSM of the virtual synchronizer is determined based on the power error and the inertial integral model 124. The inertial integral model 124 is implemented as 1 / (2Hs), where H is the inertial time constant and 1 / s is the integral in the s-domain. Since the derivative of the synchronizer's rotational speed ωVSM is related to the power reference P... ref and grid power P grid The deviation between them is proportional, so the integral of the difference ΔP gives the rotational speed ωVSM of the synchronizer.

[0087] The synchronizing angle θVSM is determined at frame 126 based on the integral of the synchronizing speed ωVSM from ωr / s, where ωr is the rated speed of the synchronizing generator.

[0088] In reference Figure 6 In the second example of the explanation, the input from the torque module to the line-side converter includes an active power limit. The remaining active power is input as an upper limit to the limit box, through which the power reference used for the virtual synchro angle calculation passes. Once the power reference has passed the limiter, the output is input to the swing equation.

[0089] Figure 6 A system diagram 130 illustrating this second example is shown. Figure 6 It generally shows the relationship with Figure 5 The same oscillation equations are used, therefore similar elements are numbered using the same reference numbers. Figure 5 The difference lies in the absence of residual active power parameters input to connection point 122. Instead, Figure 6 The implementation method utilizes active power limits to modify the virtual synchronizing machine angle. From Figure 6 As can be seen from this, a limit box 132 is provided, and the input to the limit box 132 is the power limit P calculated by subtracting the residual value from the power reference of the machine-side converter. lim Therefore, the maximum permissible power is calculated and used as a limit input. The power limit is defined by limit box 132, which determines the change in angle value Δθ. The change in angle value can be determined based on the active power measurement signal or active power feedback signal, the inductor reactive power value, and the voltage value. An example of using the power limit to generate the angle change value is in "A VSM (Virtual Synchronous Machine) Converter Control ModelSuitable for RMS Studies for Resolving System Operator / Owner Challenges" (Roscoe, Andrew & Yu, Mengran & This is discussed in Adam & Booth, Campbell & Ierna, Richard & Zhu, Jiebei & Urdal, Helge, 15th Wind Integration Workshop, Vienna, 2016.

[0090] Once the change in angle value has been determined, at connection point 134, it is subtracted from the VSM angle θVSM to provide the constrained VSM angle θVSM. lim It was subsequently used to control the line-side converter.

[0091] In some embodiments, the power limit can also be used to directly limit the power reference value input to connection point 122.

[0092] In reference Figure 7 In the third example explained, the input from the torque module to the line-side converter controller includes a current limit. This current limit is generated based on the residual active power and the power grid voltage level. This current limit is then input to the current limiter of the line-side converter's control system.

[0093] Figure 7An example of a control system 140 for a line-side converter is shown. In this figure, the swing equation is labeled 120 and receives a power reference P. ref and the measured power level P grid This generates a virtual synchronizer angle θVSM. The current controller 142 is based on the received voltage reference V... ref Current reference I ref and maximum current value I max This generates a current-controlled voltage reference level V. ref，cc In box 144, the voltage reference level and angle are transformed from a rotating coordinate system to a non-rotating coordinate system to generate the voltage level V. abc This is used as input to the pulse width modulator 146. The pulse width modulator (PWM) 146 then controls the line-side converter accordingly.

[0094] In this embodiment, the active power surplus is converted into current surplus, i.e., I, by dividing the active power surplus by the absolute grid voltage. surplus The residual current is provided as an input to box 148, which generates a maximum current value I for input to current controller 142 based on the residual current value. max The current controller then modifies the voltage reference based on the maximum current value. For example, the maximum current value could be based on a measured current value limited by the remaining value, or based on the measured current value subtracted from it.

[0095] In some embodiments, the maximum current value can be implemented as a virtual resistance.

[0096] It should be understood that various changes and modifications can be made to this invention without departing from the scope of this application.

Claims

1. A method (100) for reducing high torque levels and / or high torque rate of change in a wind turbine generator (10), the wind turbine generator (10) comprising a machine side converter (28) and a line side converter (30) connected by a DC link (32), and the line side converter (30) operating according to a virtual synchronous machine control scheme, the method (100) comprising: Determining generator torque T ref ; determining a torque residual T surplus , the torque residual indicating an amount by which the generator torque T ref exceeds a torque limit, wherein the torque limit is generated based on a comparison between a generator torque rate of change and a maximum torque rate of change, the generator torque rate of change being determined based on the determined generator torque and at least one previously determined generator torque; based on the torque surplus T surplus determining the active power surplus P surplus ; and controlling the line side converter (30) according to the virtual synchronous machine control scheme having input parameters based on the active power surplus P surplus and being configured to reduce the active power output of the line side converter (30) by the active power surplus P surplus .

2. The method (100) according to claim 1, wherein: if the determined generator torque rate of change is equal to or less than the maximum torque rate of change, the torque limit is set to the determined generator torque, and if the determined generator torque rate of change is greater than the maximum torque rate of change, the torque limit is generated by adjusting the previously determined generator torque by an integral of the maximum torque rate of change.

3. The method (100) according to any one of claims 1 to 2, wherein The torque limit is based on a maximum torque value.

4. The method (100) of claim 3, wherein The method comprises: determining the generator torque T ref comparing with the maximum torque value; and generating the torque limit based on the comparison, wherein: if the determined generator torque exceeds the maximum torque value, the torque limit is generated as the maximum torque value; and if the determined generator torque is equal to or less than the maximum torque value, the torque limit is generated as the determined generator torque.

5. The method (100) of claim 3, wherein, The method comprises: determining at least two preliminary torque residuals, the preliminary torque residuals comprising a first preliminary torque residual and a second preliminary torque residual, the first preliminary torque residual indicating an amount by which the generator torque exceeds the torque limit based on the maximum torque rate of change, the second preliminary torque residual indicating an amount by which the generator torque exceeds the torque limit based on the maximum torque value, and: determining the torque surplus T surplus comprising determining the maximum surplus of the at least two preliminary torque surpluses.

6. The method (100) according to any one of claims 1 to 2, wherein The input parameter comprises an active power value, and the active power value is used as an input to a swing equation (120) for calculating a voltage angle of the virtual synchronous machine control scheme.

7. The method (100) according to any one of claims 1 to 2, wherein The input parameters comprise an active power limit P lim and the active power limit P lim is used as an input for a power limiter (132) configured to generate an active power reference for the virtual synchronous machine control scheme.

8. The method (100) according to any one of claims 1 to 2, wherein The input parameters comprise a current limit I based on the active power surplus P surplus and the power network voltage level lim and the current limit is used as input to a current limiter (142) of the virtual synchronous machine control scheme.

9. The method (100) of claim 8, wherein, The current limiter (142) is configured to limit the current to the current limit value I lim implemented as a virtual resistance R vir .

10. The method (100) according to any one of claims 1 to 2, wherein Determining the generator torque comprises measuring the generator torque from a generator drive train.

11. The method (100) according to any one of claims 1 to 2, wherein Determining the generator torque comprises: determining an active power reference P for the machine side converter (28) ref ; determining a rotor speed; and based on the active power reference P ref and the rotor speed to calculate the generator torque.

12. The method (100) of claim 11, wherein, The active power reference P ref is determined on the basis of an error value between a voltage reference signal V DCref and a measured voltage level V DC of the DC link (32).

13. The method (100) according to any one of claims 1 to 2, wherein determining the active power surplus P surplus comprising: determining a rotor speed; and based on said torque surplus T surplus and said rotor speed to calculate said active power surplus P surplus .

14. A computer program product comprising instructions which, when executed by a computer or a wind turbine controller, cause the computer or the wind turbine controller to perform the steps of the method (100) according to any one of claims 1 to 13.

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