Online smooth switching method of control loop and converter

Abstract

The invention discloses an online smooth switching method of a control loop and a converter, and the method comprises the steps: carrying out the switching between a network following control mode and a network construction control mode according to a voltage vector transformation relation between a coordinate system corresponding to a control mode before switching and a coordinate system corresponding to a control mode after switching, calculating to obtain a voltage vector module value of the switched control mode; calculating a rotation angle between a coordinate system corresponding to the control mode before switching and a coordinate system corresponding to the control mode after switching according to the voltage vector module value; and taking the voltage vector module value as a reference voltage of a switched control mode, and superposing the rotation angle to a phase angle of a control loop so as to complete switching between the network following control mode and the network construction control mode. The external characteristics of the converter can be kept unchanged, smooth transition of the port voltage of the converter in the switching process is guaranteed, the switching response speed is high, and voltage fluctuation is small.

Description

Technical Field

[0001] The present application relates to the technical field of converters, and in particular to an online smooth switching method of a control loop and a converter. Background Art

[0002] With the incorporation of a large number of converters for wind power, photovoltaic power, energy storage, etc. into the power grid, the anti-interference ability of the power grid has been reduced. Existing converters generally operate in a grid-following control mode and do not actively support the frequency and voltage of the power grid. However, as a voltage source converter, the grid-building converter can provide the power grid with fast frequency, voltage and transient current support capabilities, which helps to improve the stability of the power grid. The large-scale application of grid-building converters will be a potential trend. The fluctuation of the power grid strength also causes some power grids to reserve and apply voltage source grid-building converters. Therefore, a large number of grid-building converters appear in the power grid to participate in the grid regulation. It may be necessary to select different control strategies according to the power grid conditions. The smooth switching between grid-following control and grid-building control is an urgent problem that needs to be solved.

[0003] The switching between grid construction and grid following control, on the one hand, during the switching of different control strategies, the power grid cannot accept large power and voltage disturbances and requires a smooth transition; on the other hand, the change of the two control methods causes problems with the jump of voltage phase and the smooth transition of power, voltage and current commands. Summary of the invention

[0004] In view of this, an object of the present application is to provide an online smooth switching method of a control loop and a converter to reduce voltage shock when switching between different control modes.

[0005] The technical solutions adopted by this application to solve the above technical problems are as follows:

[0006] In a first aspect, the present application provides an online smooth switching method of a control loop, which is applied to a converter; the method comprises:

[0007] When switching between the grid-following control mode and the grid-building control mode is executed, the voltage vector modulus value of the control mode after switching is calculated according to the voltage vector transformation relationship between the coordinate system corresponding to the control mode before switching and the coordinate system corresponding to the control mode after switching;

[0008] According to the voltage vector modulus, a rotation angle between a coordinate system corresponding to the control mode before switching and a coordinate system corresponding to the control mode after switching is calculated;

[0009] The voltage vector modulus is used as a reference voltage for the control mode after switching, and the rotation angle is superimposed on the phase angle of the control loop, thereby completing the switching between the following network control mode and the building network control mode.

[0010] A second aspect of the present application provides a converter, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the online smooth switching method of the control loop described in the first invention.

[0011] The online smooth switching method and converter of the control loop provided in the present application use the voltage vector modulus as the reference voltage of the control mode after switching, and superimpose the rotation angle on the phase angle of the control loop, thereby completing the switching between the grid-following control mode and the grid-building control mode; it can keep the external characteristics of the converter unchanged, ensure that the port voltage of the converter transitions smoothly during the switching process, the switching response speed is fast, and the voltage fluctuation is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A schematic diagram of an online smooth switching method of a control loop provided in an embodiment of the present application;

[0013] Figure 2 A schematic diagram of relative coordinate vectors provided in an embodiment of the present application;

[0014] Figure 3 A schematic diagram of the switching effect between the network following control mode and the network building control mode provided in an embodiment of the present application;

[0015] Figure 4 A schematic diagram of another switching effect between the network following control mode and the network building control mode provided in an embodiment of the present application.

[0016] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0017] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer and more understandable, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0018] like Figure 1 As shown, the online smooth switching method of the control loop provided in the embodiment of the present application includes the following steps:

[0019] S11, when switching between the grid-following control mode and the grid-building control mode, according to the voltage vector transformation relationship between the coordinate system corresponding to the control mode before switching and the coordinate system corresponding to the control mode after switching, the voltage vector modulus value of the control mode after switching is calculated;

[0020] The switching between the network following control mode and the network building control mode includes: switching from the network following control mode to the network building control mode, and switching from the network building control mode to the network following control mode.

[0021] In one example, the method further includes:

[0022] When the switching instruction is obtained, the switching between the following network control mode and the building network control mode is executed.

[0023] That is, the converter switches between the grid-following control mode and the grid-building control mode when the switching instruction is obtained. The switching instruction may be an instruction generated by an external trigger or an instruction generated by an internal trigger.

[0024] In one example, the method further includes:

[0025] Obtaining the voltage and current at the converter terminal;

[0026] The voltage vector transformation relationship is determined at least according to the voltage and current at the converter terminal.

[0027] Wherein, determining the voltage vector transformation relationship at least according to the voltage and current at the converter terminal includes:

[0028] Converting the voltage and current at the converter machine end into the voltage value and current value in the coordinate system corresponding to the control mode before switching;

[0029] The voltage vector transformation relationship is obtained at least according to the converted voltage value and current value.

[0030] For example, the coordinate system corresponding to the control mode before switching is the dq coordinate system, and the voltage and current sampled at the converter machine end are transformed into voltage and current values ​​U and U respectively after dq coordinate transformation. gd , U gq ,I d ,I q When switching from grid control to grid control mode, the voltage vector transformation relationship is obtained based on the converted voltage and current values ​​and the connection impedance as V dref =U gd +I d RI q X, V qref =U gq +I d X+I q R, X, R include virtual impedance and line impedance, etc.; when the network control switches to the network control mode, according to the converted voltage and current values, the voltage vector transformation relationship is obtained as V dref =U gd , V qref =Ugq .

[0031] According to the voltage vector transformation relationship, the voltage vector modulus value of the control mode after switching can be obtained:

[0032] S12, calculating a rotation angle between a coordinate system corresponding to a control mode before switching and a coordinate system corresponding to a control mode after switching according to the voltage vector modulus value;

[0033] In one example, calculating the rotation angle between the coordinate system corresponding to the control mode before switching and the coordinate system corresponding to the control mode after switching according to the voltage vector modulus includes:

[0034] Calculating the sine value and cosine value of the voltage vector according to the voltage vector modulus;

[0035] The rotation angle between the coordinate system corresponding to the control mode before switching and the coordinate system corresponding to the control mode after switching is calculated according to the sine value and the cosine value of the voltage vector.

[0036] Continuing with the above example, the voltage vector modulus V m The sine and cosine values ​​of the voltage vector are calculated to be sinσ=V qref / V m , cosσ=V dref / V m Then, the rotation angle σ=arctan(sinσ / cosσ) between the coordinate system corresponding to the control mode before switching and the coordinate system corresponding to the control mode after switching is obtained.

[0037] S13, using the voltage vector modulus as a reference voltage for the control mode after switching, and superimposing the rotation angle on the phase angle of the control loop, thereby completing the switching between the following network control mode and the building network control mode.

[0038] In one example, the method further includes:

[0039] Before completing the switching between the grid-following control mode and the grid-building control mode, the grid voltage and current instructions of the coordinate system corresponding to the control mode after switching are calculated.

[0040] Continuing with the above example, the calculation can be performed as follows: Grid voltage coordinate before switching, U d II , U q II Grid voltage coordinates in the control mode after switching. The current before switching, is the current instruction after switching. In one example, the method further includes:

[0041] When the network building control mode is switched to the network following control mode, an integral of the power control loop of the network following control mode is generated according to the current instruction.

[0042] In one example, the method further includes:

[0043] During the switching process between the grid-following control mode and the grid-building control mode, a power compensation instruction is calculated according to the frequency deviation and / or the voltage deviation, so as to perform power compensation according to the power compensation instruction.

[0044] In this example, in order to ensure the disturbance suppression performance of power, frequency and voltage after switching, power, frequency and voltage compensation are added. For example, the calculated active power compensation instruction P ref =k w Δf, reactive power compensation command Q ref =k u ΔU; where k w is the frequency modulation coefficient, Δf is the frequency deviation or change during the switching process, k u is the voltage regulation coefficient, and ΔU is the voltage deviation or change during the switching process.

[0045] In one example, the method further includes:

[0046] After the switching between the following network control mode and the building network control mode is completed, a switching success flag is generated.

[0047] The following combination Figure 2 The relative coordinate vector is explained as follows:

[0048] Assuming that the coordinate system corresponding to the control mode before switching is the dq coordinate system, when the external trigger mode switching operation is performed or the converter receives the control mode switching instruction, the converter establishes the coordinate transformation relationship between the current coordinate system 1 and the coordinate system 2 that will take effect, and converts the control variables of the current coordinate system 1 to the control variables corresponding to the coordinate system 2 through this coordinate transformation relationship, keeping the external characteristics unchanged. The switching process does not depend on the loop parameters of the coordinate system 2, the phase-locked loop PLL and other control parameters, and estimates the relative relationship between the coordinate system 1 and the coordinate system 2 in real time, with small constraints on the control parameters, small amount of calculation and fast calculation speed. The specific operations include:

[0049] The converter obtains the voltage and current at the machine end, and converts the voltage and current at the machine end into U through dq coordinate transformation. gd , U gq ,Id ,I q , the voltage in coordinate system 2 is constructed by the current flowing through the line according to the relationship between the connection impedance X and R;

[0050] When the coordinate transformation relationship of different control systems before and after the conversion is established through the above vector information, the specific implementation is:

[0051] When the grid-following control mode is switched to the grid-building control mode, the voltage at the generator end is used as the control synchronization reference U q =0, dq coordinate system is the current coordinate system 1, d 1 q 1 The coordinate system 2 corresponds to the switched control mode. The relationship between the converter virtual voltage reference and the connection impedance and voltage is V dref =U gd +I d RI q X, V qref =U gq +I d X+I q R, where V dref 、V qref is the projection of the virtual voltage reference in the current coordinate system 1; X and R include virtual impedance and line impedance, etc.; according to the coordinates of the switched voltage vector in the current coordinate system 1, the modulus of the switched voltage vector is calculated Then, the sine and cosine of the vector are calculated from the voltage vector modulus: cosσ=V dref / V m , sinσ=V qref / V m , phase σ = arctan(sinσ / cosσ).

[0052] When the network control mode is switched to the network control mode, d 1 q 1 is coordinate system 1, dq is coordinate system 2, and the voltage coordinate of the switched voltage in coordinate system 1 is: V dref =U gd , V qref =U gq ;

[0053] Calculate the voltage vector modulus in the target mode

[0054] Calculate sine and cosine: cosσ=V dref / V m , sinσ=V qref / V m ;

[0055] Calculate the phase σ = arctan (sinσ / cosσ);

[0056] Furthermore, in the process of switching the control mode from coordinate system 1 to coordinate system 2, in order to ensure the smooth transition of each parameter variable, the grid voltage and current instructions of the switched coordinate system 2 are calculated:

[0057] Current grid voltage coordinate, U d II , U q II Grid voltage coordinates in target control mode. is the current at the current moment, is the current command of the target control mode.

[0058] Furthermore, the grid-following control mode under different coordinate systems is switched to the grid-building control mode. The voltage reference value of the current grid-following control mode coordinate system 1 switched to the grid-building control mode coordinate system 2 is the voltage vector modulus value V m ; The grid-building control mode is switched to the grid-following control mode, and the integral of the power control loop of the grid-following control mode is generated according to the current command.

[0059] Furthermore, when the control loop is switched to the switched coordinate system, the coordinate system angle needs to be rotated toward the switched coordinate system. The coordinate rotation method is to superimpose the phase σ on the phase integral of the current control loop.

[0060] When all the above pre-switching preparations are completed, the switching begins.

[0061] Furthermore, in order to ensure the disturbance suppression performance of power, frequency and voltage after switching, power, frequency and voltage compensation are added; the power-frequency deviation compensation of the converter during the control loop switching process, the active power compensation instruction P ref =k w Δf; power-voltage deviation compensation of the converter during the control loop switching process, reactive power compensation instruction Q ref =k u ΔU; loop switching is completed and feedback loop switching success flag is given.

[0062] Assuming that the coordinate system corresponding to the control mode before switching is the αβ coordinate system, when the external trigger mode switching operation or the converter receives the control mode switching instruction, the converter obtains the voltage and current at the machine end, and converts them into U after αβ coordinate transformation. gα , U gβ ,I α ,I β , the voltage in coordinate system 2 is constructed by the current flowing through the line according to the relationship between the connection impedance X and R;

[0063] When the coordinate transformation relationship of different control systems before and after the conversion is established through the above vector information, the specific implementation is: when the network control mode is switched to the network control mode, the αβ before the switch is used as the current reference coordinate system 1, α 1 β 1 The reference coordinate system 2 after switching, the relationship between the converter virtual voltage reference and the connection impedance and voltage is V αref =U gα +I α RI β X, V βref =U gβ +I α X+I β R, where V αref 、V βref is the projection of the virtual voltage reference in the current coordinate system 1; X and R include virtual impedance and line impedance, etc.; according to the coordinates of the switched voltage vector in the current coordinate system 1, the modulus of the switched voltage vector is calculated Then, the sine and cosine of the vector are calculated from the vector modulus of the voltage: cosσ=V αref / V m , sinσ=V βref / V m , phase σ = arctan(sinσ / cosσ).

[0064] The network control mode switches to the network control mode, α 1 β 1 is coordinate system 1, αβ is coordinate system 2, and the voltage coordinate of the switched voltage in the current coordinate system 1 is: V αref =U gα , V βref =U gβ ;

[0065] Calculate the voltage vector modulus in the target mode

[0066] Calculate sine and cosine: cosσ=V αref / V m , sinσ=V βref / V m ;

[0067] Calculate the phase σ = arctan (sinσ / cosσ);

[0068] Furthermore, in the process of switching the control mode from coordinate system 1 to coordinate system 2, in order to ensure the smooth transition of each parameter variable, the grid voltage and current instructions of the switched coordinate system 2 are calculated:

[0069] Current grid voltage coordinate, Uα II , U β II Grid voltage coordinates in target control mode. is the current at the current moment, It is the current command of the target control mode.

[0070] Furthermore, the grid-following control mode under different coordinate systems is switched to the grid-building control mode. The voltage reference value of the current grid-following control mode coordinate system 1 switched to the grid-building control mode coordinate system 2 is the voltage vector modulus value V m ; The grid control mode is switched to grid-following control, and the integral of the power control loop of the grid-following control mode is generated according to the current command.

[0071] Furthermore, when the control loop is switched to the switched coordinate system, the coordinate system angle needs to be rotated toward the switched coordinate system. The coordinate rotation method is to superimpose the phase σ on the phase integral of the current control loop.

[0072] When all the above pre-switching preparations are completed, the switching begins.

[0073] Furthermore, in order to ensure the disturbance suppression performance of power, frequency and voltage after switching, power, frequency and voltage compensation are added; the power-frequency deviation compensation of the converter during the control loop switching process, the active power compensation instruction P ref =k w Δf; power-voltage deviation compensation of the converter during the control loop switching process, reactive power compensation instruction Q ref =k u ΔU; loop switching is completed and feedback loop switching success flag is given.

[0074] In the specific implementation process, after the loop switching is completed, a loop switching success flag is fed back.

[0075] like Figure 3-Figure 4 As shown in the figure, Rms is the effective value of the grid voltage; U_positive is the grid positive sequence voltage; Py is the grid active power; Qy is the grid reactive power; Id.y is the current Id at the current moment; Iq.y is the current Iq at the current moment. It can be seen from the figure that the power fluctuation is less than 2% and the voltage fluctuation is less than 1%.

[0076] Another embodiment of the present application provides a converter, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the aforementioned online smooth switching method of the control loop.

[0077] It should be noted that the converter includes but is not limited to wind power converters, photovoltaic inverters, energy storage converters, etc.

[0078] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0079] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0080] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0081] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0082] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a disk or an optical disk.

[0083] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An online smooth switching method of a control loop, applied to a converter; characterized in that: The method comprises: When switching between the grid-following control mode and the grid-building control mode is executed, the voltage vector modulus value of the control mode after switching is calculated according to the voltage vector transformation relationship between the coordinate system corresponding to the control mode before switching and the coordinate system corresponding to the control mode after switching; According to the voltage vector modulus, a rotation angle between a coordinate system corresponding to the control mode before switching and a coordinate system corresponding to the control mode after switching is calculated; The voltage vector modulus is used as a reference voltage for the control mode after switching, and the rotation angle is superimposed on the phase angle of the control loop, thereby completing the switching between the following network control mode and the building network control mode.

2. The method according to claim 1, characterized in that The method further comprises: When the switching instruction is obtained, the switching between the following network control mode and the building network control mode is executed.

3. The method according to claim 1, characterized in that The method further comprises: Obtaining the voltage and current at the converter terminal; The voltage vector transformation relationship is determined at least according to the voltage and current at the converter terminal.

4. The method according to claim 3, characterized in that The step of determining the voltage vector transformation relationship at least according to the voltage and current at the converter terminal includes: Converting the voltage and current at the converter machine end into the voltage value and current value in the coordinate system corresponding to the control mode before switching; The voltage vector transformation relationship is obtained at least according to the converted voltage value and current value.

5. The method according to claim 1, characterized in that The step of calculating the rotation angle between the coordinate system corresponding to the control mode before switching and the coordinate system corresponding to the control mode after switching according to the voltage vector modulus value includes: Calculating the sine value and cosine value of the voltage vector according to the voltage vector modulus; The rotation angle between the coordinate system corresponding to the control mode before switching and the coordinate system corresponding to the control mode after switching is calculated according to the sine value and the cosine value of the voltage vector.

6. The method according to claim 1, characterized in that The method further comprises: Before completing the switching between the grid-following control mode and the grid-building control mode, the grid voltage and current instructions of the coordinate system corresponding to the control mode after switching are calculated.

7. The method according to claim 6, characterized in that The method further comprises: When the network building control mode is switched to the network following control mode, an integral of the power control loop of the network following control mode is generated according to the current instruction.

8. The method according to claim 1, characterized in that The method further comprises: During the switching process between the grid-following control mode and the grid-building control mode, a power compensation instruction is calculated according to the frequency deviation and / or the voltage deviation, so as to perform power compensation according to the power compensation instruction.

9. The method according to claim 1, characterized in that: The method further comprises: After the switching between the following network control mode and the building network control mode is completed, a switching success flag is generated.

10. A converter, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the online smooth switching method of the control loop according to any one of claims 1 to 9.

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