Dynamic current limiting control method for full power converter wind turbine under power grid fault

Abstract

The present application provides a dynamic current limiting control method for a full-power converter wind turbine under a grid fault, including: obtaining the phase parameters generated by the grid-side converter under the grid-type control strategy; obtaining the three-phase voltage and three-phase current of the grid-connected point and performing coordinate transformation to obtain the voltage dq component and the current dq component under the dq coordinate axis; obtaining the reference value of the current dq component according to the reference value of the voltage dq component and the voltage dq component; when a grid fault occurs in the system, based on the virtual impedance parameter of the grid-side controller and the current dq component, adjusting the reference value of the current dq component to obtain the adjusted reference value of the current dq component; performing inner loop control according to the adjusted reference value of the current dq component to obtain the three-phase voltage of the converter. The reference value of the current is adjusted online through the virtual impedance parameter of the grid-side controller, the value of the fault current is reduced, and the overcurrent problem of the converter during the fault is suppressed.

Description

Technical Field

[0001] The present application relates to the technical field of wind power system control, and in particular to a dynamic current limiting control method for a full-power converter wind turbine set under a power grid fault. Background Art

[0002] With the proposal of the dual carbon goals, new energy will be connected to the power system on a large scale and at a high proportion. Offshore wind power has the advantages of relatively stable output and great potential for large-scale development, and will gradually become the main force of new energy. Large-power wind turbines basically use full-power converters, which are composed of a large number of power electronic devices connected in series. When a wind turbine is connected to the power grid and fails, a large fault current will flow through the power electronic devices.

[0003] In order to prevent power electronic devices from being damaged due to overcurrent problems, the current is usually limited through the power inner loop during the fault period. There is currently no better solution to the overcurrent problem of grid-connected full-power converters under grid voltage drops. Summary of the invention

[0004] The present application provides a method and device for dynamic current limiting control of a full-power converter wind turbine under a grid fault to suppress converter overcurrent problems during a fault. The technical solution of the present application is as follows:

[0005] The embodiment of the present application provides a dynamic current limiting control method for a full-power converter wind turbine generator set under a power grid fault, comprising:

[0006] Obtain the phase parameters generated by the grid-side converter under the grid-type control strategy;

[0007] Acquire the three-phase voltage and three-phase current of the grid connection point, and transform the three-phase voltage and the three-phase current through the Park matrix based on the phase parameter to obtain the voltage dq component and the current dq component under the dq coordinate axis respectively;

[0008] Obtaining a reference value of the current dq component according to the reference value of the voltage dq component and the voltage dq component;

[0009] When a grid fault occurs in the system, based on the virtual impedance parameter of the grid-side controller and the current dq component, the reference value of the current dq component is adjusted to obtain an adjusted reference value of the current dq component;

[0010] Inner loop control is performed according to the reference value of the adjusted current dq component to obtain the three-phase voltage of the converter at the grid-side converter end.

[0011] In some implementations, before adjusting the reference value of the current dq component based on the virtual impedance parameter of the grid-side controller and the current dq component, the method further includes:

[0012] The reference value of the current dq component is subjected to maximum value limiting processing by a first formula, wherein the first formula is expressed as follows:

[0013] I dref1 =max(I max ,I dref )

[0014]

[0015] Among them, I max is the maximum limit of the reference value of the current dq component, I dref ,I qref is the reference value of the current dq component; I dref1 ,I qref1 It is the reference value of the current dq component after the maximum value limit processing.

[0016] In some implementations, adjusting the reference value of the current dq component based on the virtual impedance parameter of the grid-side controller and the current dq component to obtain the adjusted reference value of the current dq component includes:

[0017] The reference value of the current dq component is adjusted by a second formula, wherein the second formula is expressed as follows:

[0018] I dref2 =I dref1 +R0I d -ωL0I q

[0019] I qref2 =I qref1 +R0 I d +ωL0 I q

[0020] Among them, I dref2 ,I qref2 is the reference value of the adjusted current dq component, R0 and L0 are the virtual impedance parameters of the grid-side controller; I d ,I q is the dq component of the current, and ω is the angular frequency of the grid connection point.

[0021] In some implementations, the method further includes:

[0022] The virtual inductance parameter L0 in the virtual impedance parameter of the grid-side controller is obtained by multiple iterations and updates according to the third formula, and the third formula is expressed as follows:

[0023]

[0024] Wherein, L0 is the virtual inductance parameter in the virtual impedance parameter of the grid-side controller, i ld 、i lq are the components of the AC side current of the grid-side converter on the dq axis respectively; is the component of the inner loop current reference value on the dq axis, k1 and k2 are the control parameters of the grid-side controller.

[0025] In some implementations, the component i of the AC side current of the grid-side converter on the dq axis is ld 、i lq Methods for obtaining include:

[0026] Substitute the virtual inductance parameter L0 updated in the last iteration into the state space equation of the grid-side converter to obtain the component i of the AC side current of the grid-side converter on the dq axis after the last iteration update. ld 、i lq .

[0027] In some implementations, obtaining the reference value of the current dq component according to the reference value of the voltage dq component and the voltage dq component includes:

[0028] V dref Superimposed voltage V d Then the current I is obtained through the proportional integral controller PI d Reference value I dref ;

[0029] V qref Superimposed voltage V q Then the current I is obtained through the proportional integral controller PI q Reference value I qref

[0030] Among them, V dref 、V qref is the reference value of the voltage dq component, V d 、V q is the voltage dq component.

[0031] In some implementations, performing inner loop control according to the adjusted reference value of the current dq component to obtain the three-phase voltage of the converter at the grid-side converter end includes:

[0032] The current I d Adjusted reference value Idref2 Superposition current I d Then the proportional integral controller PI is used to obtain the first value, and the first value is superimposed with the voltage V d and the coupling term ωLI q , and obtain the d-axis component of the voltage V cdref ;

[0033] The current I q Adjusted reference value I qref2 Superposition current I q Then the proportional integral controller PI is used to obtain the second value, and the second value is superimposed on the voltage V q and the coupling term ωLI d , we get the q-axis component of the voltage V cqref ;

[0034] Then, the obtained V cdref 、V cqref Perform dq / abc coordinate transformation to obtain the three-phase voltage V cAref 、V cBref 、V cCref , the three-phase voltage is the modulation reference wave of the converter.

[0035] In some implementations, the obtaining of the phase parameter generated by the grid-side converter under the grid-type control strategy includes:

[0036] Based on the rated frequency ω of the grid connection point ref , DC voltage rated voltage value U dcref , DC voltage measurement value U dc , control parameters D of the grid-side controller p / J p / s generates phase θ.

[0037] Based on the above technical solution, the method of the embodiment of the present application adjusts the reference value of the current online through the virtual impedance parameter of the grid-side controller, that is, the dynamic virtual impedance control strategy adjusts the reference value of the current online, reduces the value of the fault current, thereby suppressing the overcurrent problem of the converter during the fault, and solves the overcurrent problem of the grid-connected full-power converter under the grid voltage drop.

[0038] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present application, and together with the specification are used to explain the principles of the present application, and do not constitute an improper limitation on the present application.

[0040] Figure 1 It is a schematic flow chart of a dynamic current limiting control method for a full power converter wind turbine set under a grid fault according to an embodiment of the present application.

[0041] Figure 2 It is a topological structure diagram of a full-power converter wind turbine set according to an embodiment of the present application.

[0042] Figure 3 It is a networking strategy diagram according to an embodiment of the present application.

[0043] Figure 4 4 is a logic diagram for obtaining reference values ​​of current dq components according to an embodiment of the present application.

[0044] Figure 5 is a schematic block diagram of an electronic device according to an embodiment of the present application. DETAILED DESCRIPTION

[0045] In order to enable ordinary persons in the art to better understand the technical solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings.

[0046] It should be noted that the terms "first", "second", etc. in this application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the application described here can be implemented in an order other than those illustrated or described here. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0047] like Figure 1 As shown, the embodiment of the present application provides a dynamic current limiting control method for a full power converter wind turbine set under a power grid fault. The dynamic current limiting control method for a full power converter wind turbine set under a power grid fault may include the following steps S101-S103.

[0048] In step S101, a phase parameter generated by a grid-side converter under a grid-type control strategy is obtained.

[0049] The topological structure of the full power converter wind turbine in this embodiment is as follows: Figure 2As shown in the figure, the full power converter is a back-to-back frequency conversion system consisting of two groups of power electronic converters connected by a DC link. The two converters are the generator side converter and the grid side converter. The generator side converter receives the active power generated by the generator and sends the power to the grid side converter through the DC link. The generator side converter is also used to excite the induction generator through the stator end of the induction generator. The grid side converter receives the active power transmitted through the DC link and transmits it to the grid, which balances the voltage on both sides of the DC link.

[0050] It can be understood that, in this embodiment, abc / dq coordinate transformation needs to be performed, and the phase parameter θ required for the abc / dq coordinate transformation is generated by the grid-side converter, so the phase parameter θ needs to be acquired first.

[0051] For grid-side converters, with the access of large-scale wind turbines, grid-type control strategies are gradually proposed.

[0052] The networking strategy of this embodiment is as follows Figure 3 As shown, based on the rated frequency ω of the grid connection point ref , DC voltage rated voltage value U dcref , DC voltage measurement value U dc , control parameters D of the grid-side controller p / J p / s can generate a phase θ. Based on the reactive power Q provided by the converter of the grid-side converter and the reactive power reference value Q of the converter of the grid-side converter ref , Rated voltage amplitude of grid connection point V mref , the control parameters Dq / Jq / S of the grid-side controller can generate amplitude reference values.

[0053] In step S102, the three-phase voltage and the three-phase current of the grid connection point are obtained, and the three-phase voltage and the three-phase current are transformed by Park matrix based on the phase parameters to obtain the voltage dq component and the current dq component under the dq coordinate axis respectively.

[0054] In this embodiment, the three-phase voltage Vabc of the grid connection point is collected, and the Park matrix is ​​changed to generate the dq components of Vabc, V d 、V q Similarly, the three-phase current Iabc of the grid point is collected and the Park matrix is ​​changed to generate the dq components of Iabc, I d ,I q .

[0055] In step S103, a reference value of the current dq component is obtained according to the reference value of the voltage dq component and the voltage dq component.

[0056] Optionally, by Figure 4 The logic diagram shown in the figure generates I d and I q Reference value I dref and I qref .

[0057] That is, V dref Superimposed voltage V d , and then the current I is obtained through the proportional integral controller PI d Reference value I dref ; V qref Superimposed voltage V q , and then the current I is obtained through the proportional integral controller PI q Reference value I qref .

[0058] In step S104, when a grid fault occurs in the system, the reference value of the current dq component is adjusted based on the virtual impedance parameter of the grid-side controller and the current dq component to obtain an adjusted reference value of the current dq component.

[0059] Preferably, before adjusting the reference value of the current dq component, the method further includes:

[0060] The reference value of the current dq component is subjected to maximum value limiting processing by the following formula:

[0061] I dref1 =max(I max ,I dref )

[0062]

[0063] Among them, I max is the maximum limit of the reference value of the current dq component, I dref ,I qref is the reference value of the current dq component; I dref1 ,I qref1 It is the reference value of the current dq component after the maximum value limit processing.

[0064] In this embodiment, the maximum limit is set to I d and I q Reference value I dref and I qref Perform preliminary limiting to avoid obtaining the reference value I dref and I qref Out of limit range.

[0065] Preferably, the method for obtaining the reference value of the adjusted current dq component includes:

[0066] The reference value of the current dq component is adjusted by the following formula:

[0067] I dref2 =I dref1 +R0I d -ωL0I q

[0068] I qref2 =I qref1 +R0 I d +ωL0 I q (2)

[0069] Among them, I dref2 ,I qref2 is the reference value of the adjusted current dq component, R0 and L0 are the virtual impedance parameters of the grid-side controller; I d ,I q is the dq component of the current, and ω is the angular frequency of the grid connection point.

[0070] Based on this, the reference value of the current is adjusted online through the virtual impedance parameter of the grid-side controller, that is, the reference value of the current is adjusted online through the dynamic virtual impedance control strategy, so as to achieve the following in the event of a fault: dref2 ,I qref2 The design can reduce the value of the fault current.

[0071] In step S105, inner loop control is performed according to the reference value of the adjusted current dq component to obtain the three-phase voltage of the converter at the grid-side converter end.

[0072] Optionally, by Figure 5 The logic diagram shown generates the three-phase voltage of the converter at the grid-side converter end.

[0073] The current I d Adjusted reference value I dref2 Superposition current I d Then the proportional integral controller PI is used to obtain the first value, and the first value is superimposed with the voltage V d and the coupling term ωLI q , and obtain the d-axis component of the voltage V cdref ;

[0074] The current I q Adjusted reference value I qref2 Superposition current I q Then the proportional integral controller PI is used to obtain the second value, and the second value is superimposed on the voltage V q and the coupling term ωLI d , we get the q-axis component of the voltage V cqref ;

[0075] Then, the obtained V cdref 、V cqref Perform dq / abc coordinate transformation to obtain the three-phase voltage V cAref 、V cBref 、V cCref , the three-phase voltage is the converter modulation reference wave.

[0076] The dynamic current limiting control method for a full-power converter wind turbine set under a grid fault in an embodiment of the present application adjusts the reference value of the current online through a dynamic virtual impedance control strategy, reduces the value of the fault current, thereby suppressing the overcurrent problem of the converter during the fault, and solves the overcurrent problem of the grid-connected full-power converter under a grid voltage drop.

[0077] On the basis of the above embodiment, the virtual inductance parameter L0 in the virtual impedance parameter may be adaptively adjusted, and the reference value of the current may be adjusted online by the adaptively adjusted virtual inductance parameter L0, so that the value of the fault current can be reduced more accurately.

[0078] Preferably, the virtual inductance parameter L0 in the virtual impedance parameter of the grid-side controller is obtained by multiple iterations and updates using the following formula:

[0079]

[0080] Wherein, L0 is the virtual inductance parameter in the virtual impedance parameter of the grid-side controller, i ld 、i lq are the components of the AC side current of the grid-side converter on the dq axis respectively; is the component of the inner loop current reference value on the dq axis, k1 and k2 are the control parameters of the grid-side controller.

[0081] Among them, the component i of the AC side current of the grid-side converter on the dq axis is ld 、i lq Methods for obtaining include:

[0082] Substitute the virtual inductance parameter L0 updated in the last iteration into the state space equation of the grid-side converter to obtain the component i of the AC side current of the grid-side converter on the dq axis after the last iteration update. ld 、i lq .

[0083] It can be understood that the power grid is generally regarded as a very strong power grid. At this time, the equivalent inductance L between the AC side converter of the grid-side converter and the power grid comes from two parts, namely the equivalent inductance of the reactor on the AC side of the grid-side converter (i.e. the equivalent inductance on the AC side) and the equivalent inductance of the transformer. The equivalent inductance of these two parts can be accurately obtained from the equipment parameters. However, when the wind power system is connected to a weak power grid, the weak power grid will have its own impedance. At this time, the equivalent inductance L between the converter and the power grid comes from four parts, namely the equivalent inductance on the AC side, the equivalent inductance of the transformer, the line inductance and the equivalent inductance of the weak power grid. The equivalent inductance on the AC side and the equivalent inductance of the transformer can be obtained from the equipment parameters, but the line inductance and the equivalent inductance of the weak power grid cannot be accurately obtained. The equivalent inductance L between the converter and the power grid is a very important parameter. If the value of L is inaccurate, some overcurrent conditions may occur.

[0084] In this embodiment, the value of the equivalent inductance L is uncertain. In this case, L is not a given value. Assuming that the value of L is set to L0 in the controller, L0 is updated online and converged to a fixed value, thereby improving the control algorithm of the controller. Therefore, L0 is the equivalent inductance value given by the iterative algorithm in the grid-side controller.

[0085] Specifically, an iterative update includes:

[0086] Get the value of the equivalent inductance after the last iteration update;

[0087] Substituting the value of the equivalent inductance after the last iteration update into the state space equation of the grid-side converter to obtain the AC side current of the grid-side converter after the last iteration update;

[0088] updating the value of the equivalent inductance after the previous iteration update according to the AC side current of the grid-side converter after the previous iteration update, to obtain the value of the equivalent inductance after the current iteration update;

[0089] If the value of the equivalent inductance after the current iterative update does not meet the preset convergence condition, the value of the equivalent inductance is iteratively updated for the next time.

[0090] As an example, at the initial moment, L0 has an initial value. Substituting the initial value into the state space equation of the grid-side converter, we get i at the current moment. ld 、i lq , then, the current moment i ld 、i lq Substitute into formula (3) to get L0 at the next moment, and then substitute L0 at the next moment into the state space equation to get i at the next moment ld、i lq , then, the next moment i ld 、i lq Substituting into formula (3) to obtain the new L0 at the next moment, after iterative calculation, L0 will converge to a value (preset convergence condition), that is, through formula (3), it converges to a value that makes the system stable, and finally the whole system converges to an equilibrium point.

[0091] In this embodiment, the reference value of the current is adjusted online through the adaptively adjusted virtual inductance parameter L0, so that the value of the fault current can be reduced more accurately.

[0092] It should also be noted that the exemplary embodiments mentioned in the present invention describe some methods or systems based on a series of steps or devices. However, the present invention is not limited to the order of the above steps, that is, the steps can be performed in the order mentioned in the embodiments, or in a different order from the embodiments, or several steps can be performed simultaneously.

[0093] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the invention disclosed herein. The present application is intended to cover any modification, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary techniques in the art that are not disclosed in the present application. The specification and examples are intended to be exemplary only.

[0094] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A dynamic current limiting control method for a full power converter wind turbine generator set under a power grid fault, characterized in that: include: Obtain the phase parameters generated by the grid-side converter under the grid-type control strategy; Acquire the three-phase voltage and three-phase current of the grid connection point, and transform the three-phase voltage and the three-phase current through the Park matrix based on the phase parameter to obtain the voltage dq component and the current dq component under the dq coordinate axis respectively; Obtaining a reference value of the current dq component according to the reference value of the voltage dq component and the voltage dq component; When a grid fault occurs in the system, based on the virtual impedance parameter of the grid-side controller and the current dq component, the reference value of the current dq component is adjusted to obtain an adjusted reference value of the current dq component; Performing inner loop control according to the reference value of the adjusted current dq component to obtain the three-phase voltage of the converter at the grid-side converter end; Before adjusting the reference value of the current dq component based on the virtual impedance parameter of the grid-side controller and the current dq component, the method further includes: The reference value of the current dq component is subjected to maximum value limiting processing by a first formula, wherein the first formula is expressed as follows: I dref1 =max(I max ,I dref ) Among them, I max is the maximum limit of the reference value of the current dq component, I dref ,I qref is the reference value of the current dq component; I dref1 ,I qref1 is the reference value of the current dq component after the maximum value limit processing; The adjusting the reference value of the current dq component based on the virtual impedance parameter of the grid-side controller and the current dq component to obtain the adjusted reference value of the current dq component includes: The reference value of the current dq component is adjusted by a second formula, wherein the second formula is expressed as follows: I dref2 =I dref1 +R0I d -ωL0I q I qref2 =I qref1 +R0I d +ωL0I q Among them, I dref2 ,I qref2 is the reference value of the adjusted current dq component, R0 and L0 are the virtual impedance parameters of the grid-side controller; I d ,I q is the dq component of the current, and ω is the angular frequency of the grid connection point.

2. The method according to claim 1, characterized in that The method further comprises: The virtual inductance parameter L0 in the virtual impedance parameter of the grid-side controller is obtained by multiple iterations and updates according to the third formula, and the third formula is expressed as follows: Wherein, L0 is the virtual inductance parameter in the virtual impedance parameter of the grid-side controller, i ld 、i lq are the components of the AC side current of the grid-side converter on the dq axis respectively; is the component of the inner loop current reference value on the dq axis, k1 and k2 are the control parameters of the grid-side controller.

3. The method according to claim 2, characterized in that The component i of the AC side current of the grid-side converter on the dq axis ld 、i lq Methods for obtaining include: Substitute the virtual inductance parameter L0 updated in the last iteration into the state space equation of the grid-side converter to obtain the component i of the AC side current of the grid-side converter on the dq axis after the last iteration update. ld 、i lq .

4. The method according to claim 1, characterized in that: The obtaining the reference value of the current dq component according to the reference value of the voltage dq component and the voltage dq component comprises: V dref Superimposed voltage V d Then the current I is obtained through the proportional integral controller PI d Reference value I dref ; V qref Superimposed voltage V q Then the current I is obtained through the proportional integral controller PI q Reference value I qref Among them, V dref 、V qref is the reference value of the voltage dq component, V d 、V q is the voltage dq component.

5. The method according to claim 1, characterized in that The inner loop control is performed according to the reference value of the adjusted current dq component to obtain the three-phase voltage of the converter at the grid-side converter end, including: The current I d Adjusted reference value I dref2 Superposition current I d Then the proportional integral controller PI is used to obtain the first value, and the first value is superimposed with the voltage V d and the coupling term ωLI q , and obtain the d-axis component of the voltage V cdref ; The current I q Adjusted reference value I qref2 Superposition current I q Then the proportional integral controller PI is used to obtain the second value, and the second value is superimposed with the voltage V q and the coupling term ωLI d , we get the q-axis component of the voltage V cqref ; Then, the obtained V cdref 、V cqref Perform dq / abc coordinate transformation to obtain the three-phase voltage V cAref 、V cBref 、V cCref , the three-phase voltage is the modulation reference wave of the converter.

6. The method according to claim 1, characterized in that The obtaining of the phase parameters generated by the grid-side converter under the grid-type control strategy includes: Based on the rated frequency ω of the grid connection point ref , DC voltage rated voltage value U dcref , DC voltage measurement value U dc , control parameters D of the grid-side controller p / J p / s generates phase θ.

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