Negative sequence current control method and system applicable to following network and constructing network type converters

Abstract

The invention discloses a negative-sequence current control method and system applicable to a grid-following and grid-constructing converter, and relates to the technical field of grid-connected converter control, and the method comprises the steps: obtaining the negative-sequence voltage of an alpha-beta coordinate system of a converter grid-connected point and the negative-sequence voltage of a dq coordinate system of the converter grid-connected point; calculating an alpha-axis component and a beta-axis component of the negative-sequence control voltage of the converter based on the negative-sequence voltage of the alpha-beta coordinate system of the grid-connected point; calculating to obtain a d-axis component and a q-axis component of the negative-sequence control voltage of the converter based on the negative-sequence voltage of the dq coordinate system of the grid-connected point; and calculating the control voltage of the converter based on the negative sequence control voltage of the alpha-beta coordinate system or the negative sequence control voltage of the dq coordinate system. The method does not depend on a current loop, the rising time of the negative sequence current is less than or equal to 100ms, and the method improves the negative sequence reactive power support speed of the converter to the system under the asymmetric fault.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-connected converter control, and in particular to a negative-sequence current control method and system applicable to grid-following and grid-forming converters. Background Art

[0002] When an asymmetric short-circuit fault occurs in the power system, the converter needs to support negative-sequence reactive power. If it is not controlled, the converter may generate unreasonable negative-sequence current, which will not only fail to support the power grid, but also cause additional losses and equipment aging. At present, both grid-following and grid-building converters are used in engineering, and it is necessary to propose a negative-sequence current control method that is applicable to both grid-following and grid-building converters. Summary of the invention

[0003] In view of the above-mentioned problems, the present invention is proposed.

[0004] Therefore, the problem to be solved by the present invention is: how to solve the problem of providing rapid negative sequence reactive power support to the power grid.

[0005] To solve the above technical problems, the present invention provides the following technical solutions: a negative-sequence current control method applicable to grid-following and grid-forming converters, comprising: obtaining the negative-sequence voltage of the converter grid-connected point in αβ coordinate system and the negative-sequence voltage of the grid-connected point in dq coordinate system; calculating the α-axis component and β-axis component of the converter negative-sequence control voltage based on the negative-sequence voltage of the grid-connected point; calculating the d-axis component and q-axis component of the converter negative-sequence control voltage based on the negative-sequence voltage of the grid-connected point in dq coordinate system; and calculating the converter control voltage based on the negative-sequence control voltage of the αβ coordinate system or the negative-sequence control voltage of the dq coordinate system.

[0006] As a preferred scheme of the negative-sequence current control method applicable to grid-following and grid-forming converters described in the present invention, wherein: the obtaining of the negative-sequence voltage of the converter grid-connected point in the αβ coordinate system and the negative-sequence voltage of the grid-connected point in the dq coordinate system includes obtaining the α-axis component and β-axis component of the negative-sequence voltage of the converter grid-connected point through the three-phase AC voltage of the converter grid-connected point by the symmetrical component method and Clark transformation, and obtaining the d-axis component and q-axis component of the negative-sequence voltage of the converter grid-connected point through the three-phase AC voltage of the converter grid-connected point by the dual synchronous coordinate system decoupling method.

[0007] As a preferred solution of the negative sequence current control method applicable to the grid-following and grid-forming converters of the present invention, the α-axis component and the β-axis component of the negative sequence control voltage of the converter obtained by calculation are expressed as:

[0008]

[0009] in, is the α-axis component of the negative sequence control voltage, is the α-axis component of the negative sequence voltage at the grid-connected point of the converter, is the β-axis component of the negative sequence control voltage, is the β-axis component of the negative sequence voltage at the grid-connected point of the converter, ω is the grid angular frequency, L1 is the grid-side filter inductor of the converter, is the negative sequence voltage modulus of the converter grid connection point, It is the negative sequence reactive current command.

[0010] As a preferred solution of the negative sequence current control method applicable to the grid-following and grid-forming converters of the present invention, the d-axis component and q-axis component of the negative sequence control voltage of the converter obtained by calculation are expressed as:

[0011]

[0012] in, represents the d-axis component of the negative sequence control voltage, represents the d-axis component of the negative sequence voltage at the grid connection point of the converter, represents the q-axis component of the negative sequence control voltage, represents the q-axis component of the negative sequence voltage at the grid-connected point of the converter, ω represents the grid angular frequency, L1 represents the grid-side filter inductance of the converter, Indicates the negative sequence voltage modulus of the converter grid connection point, Indicates negative sequence reactive current command.

[0013] As a preferred solution of the negative sequence current control method applicable to the grid-following and grid-forming converters of the present invention, the calculation of the converter control voltage includes: directly selecting the negative sequence control voltage of the αβ coordinate system Or the negative sequence control voltage of the dq coordinate system is transformed by inverse Park to obtain the negative sequence control voltage of the αβ coordinate system It is superimposed with the positive sequence component of the control voltage obtained by the original positive sequence control module of the converter to obtain the control voltage finally output by the converter.

[0014] Another object of the present invention is to provide a system of negative-sequence current control methods applicable to grid-following and grid-forming converters, which can solve the negative-sequence current control problem applicable to grid-following and grid-forming converters by constructing a negative-sequence current control system applicable to grid-following and grid-forming converters.

[0015] To solve the above technical problems, the present invention provides the following technical solutions: a negative-sequence current control system applicable to grid-following and grid-forming converters, comprising a first module, a second module, a third module and a fourth module; the first module is a module for obtaining the negative-sequence voltage of the converter grid-connected point αβ coordinate system and the negative-sequence voltage of the converter grid-connected point dq coordinate system; the second module is a module for calculating the negative-sequence control voltage component of the αβ coordinate system; the third module is a module for calculating the negative-sequence control voltage component of the dq coordinate system; and the fourth module is a module for calculating the converter control voltage.

[0016] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the negative sequence current control method applicable to grid-following and grid-forming converters as described above are implemented.

[0017] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the negative-sequence current control method applicable to grid-following and grid-forming converters as described above.

[0018] The beneficial effects of the present invention are as follows: the conventional strategy of directly controlling negative sequence current relies on the current loop, and the negative sequence current rise time is about 300 to 500 ms; the negative sequence current control method applicable to grid-following and grid-forming converters provided by the present invention does not rely on the current loop, and the negative sequence current rise time is ≤100 ms. Under asymmetric faults, this method improves the negative sequence reactive power support speed of the converter for the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0020] Figure 1 A flowchart of a negative sequence current control method applicable to grid-following and grid-forming converters provided in the first embodiment of the present invention.

[0021] Figure 2 An equivalent model diagram of a grid-connected converter connected to an AC power grid, which is applicable to a negative-sequence current control method for grid-following and grid-forming converters, provided in the first embodiment of the present invention.

[0022] Figure 3 A structural diagram of a negative-sequence current control system applicable to grid-following and grid-forming converters provided in the second embodiment of the present invention.

[0023] Figure 4A schematic diagram of a negative sequence current control method applicable to grid-following and grid-forming converters provided in the third embodiment of the present invention.

[0024] Figure 5 This is a rendering of the effect of a negative-sequence current control method applicable to grid-following and grid-forming converters provided in the third embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0026] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0027] Example 1, reference Figure 1 and Figure 2 , which is the first embodiment of the present invention, provides a negative-sequence current control method applicable to grid-following and grid-forming converters, including: obtaining the negative-sequence voltage of the converter grid-connected point αβ coordinate system and the negative-sequence voltage of the grid-connected point dq coordinate system; calculating the α-axis component and β-axis component of the converter negative-sequence control voltage based on the negative-sequence voltage of the grid-connected point αβ coordinate system; calculating the d-axis component and q-axis component of the converter negative-sequence control voltage based on the negative-sequence voltage of the grid-connected point dq coordinate system; calculating the converter control voltage based on the negative-sequence control voltage of the αβ coordinate system or the negative-sequence control voltage of the dq coordinate system.

[0028] The equivalent model of wind turbines connected to the AC grid is shown in the attached figure. Figure 2 As shown in the figure, the voltage sampling point of the wind turbine is the voltage of the converter grid connection point. The traditional wind turbine grid-side converter does not have special control for negative sequence. When an asymmetric fault occurs in the power grid, the converter may generate unreasonable negative sequence current, which not only fails to support the power grid, but also causes additional losses and equipment aging. Therefore, it is necessary to control the negative sequence current.

[0029] A negative sequence current control method applicable to grid-following and grid-forming converters, comprising:

[0030] S1. Obtain the negative sequence voltage of the converter grid-connected point in the αβ coordinate system and the negative sequence voltage of the grid-connected point in the dq coordinate system.

[0031] Obtain the negative sequence voltage of the converter grid-connected point in the αβ coordinate system and the dq coordinate system:

[0032] The grid connection point voltage is a known quantity. The α-axis component of the negative sequence voltage at the grid connection point of the converter is obtained by using the symmetrical component method and Clark transformation of the three-phase AC voltage at the grid connection point of the converter. and the β-axis component The d-axis component of the negative sequence voltage at the grid-connected point of the converter is obtained by using the dual synchronous coordinate system decoupling method through the three-phase AC voltage at the grid-connected point of the converter. and the q-axis component

[0033] S2. Calculate the α-axis component and β-axis component of the negative-sequence control voltage of the converter based on the negative-sequence voltage of the αβ coordinate system of the grid-connected point.

[0034] Obtain the negative sequence control voltage in the αβ coordinate system:

[0035]

[0036] in, represents the α-axis component of the negative sequence control voltage, represents the β-axis component of the negative sequence control voltage, Represents the α-axis component of the negative sequence voltage at the grid-connected point of the converter, represents the β-axis component of the negative sequence voltage at the grid-connected point of the converter, ω represents the grid angular frequency, L1 represents the grid-side filter inductance of the converter, Indicates the negative sequence voltage modulus of the converter grid connection point, Indicates negative sequence reactive current command.

[0037] S3. Calculate the d-axis component and q-axis component of the negative-sequence control voltage of the converter based on the negative-sequence voltage of the dq coordinate system of the grid-connected point.

[0038] Obtain the negative sequence control voltage in the dq coordinate system:

[0039]

[0040] in, represents the d-axis component of the negative sequence control voltage, represents the q-axis component of the negative sequence control voltage, represents the d-axis component of the negative sequence voltage at the grid connection point of the converter, represents the q-axis component of the negative sequence voltage at the grid-connected point of the converter, ω represents the grid angular frequency, L1 represents the grid-side filter inductance of the converter, Indicates the negative sequence voltage modulus of the converter grid connection point, Indicates negative sequence reactive current command.

[0041] S4. Calculate the converter control voltage based on the negative sequence control voltage of the αβ coordinate system or the negative sequence control voltage of the dq coordinate system.

[0042] Directly select the negative sequence control voltage of the αβ coordinate system according to the conditions Or the negative sequence control voltage of the dq coordinate system is transformed by inverse Park to obtain the negative sequence control voltage of the αβ coordinate system It is superimposed with the positive sequence component of the control voltage obtained by the original positive sequence control module of the converter to obtain the control voltage finally output by the converter.

[0043] Example 2, reference Figure 3 , which is the second embodiment of the present invention, is different from the previous embodiment in that it provides a negative-sequence current control system applicable to grid-following and grid-forming converters, including: a first module 100, a second module 200, a third module 300 and a fourth module 400.

[0044] The first module 100 is a module for obtaining the negative sequence voltage of the converter grid-connected point αβ coordinate system and the negative sequence voltage of the converter grid-connected point dq coordinate system.

[0045] The second module 200 is a calculation module for the negative sequence control voltage in the αβ coordinate system.

[0046] The third module 300 is a calculation module for the negative sequence control voltage in the dq coordinate system.

[0047] The fourth module 400 is a calculation module for the converter control voltage.

[0048] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for 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 methods described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program codes.

[0049] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0050] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0051] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0052] Example 3, reference Figure 4 and Figure 5 , which is the third embodiment of the present invention, and which is different from the first two embodiments in that it is used to verify and illustrate the technical effects adopted in the present invention, so as to verify the real effects of this method.

[0053] Figure 4 It is a schematic diagram of a negative sequence current control method applicable to grid-following and grid-forming converters provided in an embodiment of the present invention. Figure 5This is a rendering of the negative-sequence current control method applicable to grid-following and grid-forming converters provided by an embodiment of the present invention. In the figure, an asymmetric short circuit occurs in the grid at the 5th second. At this time, the converter uses a positive-sequence reactive power control strategy and does not provide negative-sequence reactive power support. At the 6.5th second, the control method of the present invention is put into use. As can be seen from the figure, the converter absorbs negative-sequence reactive current, and the rise time of the negative-sequence reactive current is 60ms. Rapid negative-sequence reactive power support is provided to the grid, and the negative-sequence voltage at the grid-connected point of the converter decreases.

[0054] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A negative sequence current control method applicable to grid-following and grid-forming converters, characterized in that: include, Obtain the negative sequence voltage of the converter grid-connected point αβ coordinate system and the negative sequence voltage of the grid-connected point dq coordinate system; Based on the negative sequence voltage of the grid-connected point αβ coordinate system, the α-axis component and β-axis component of the negative sequence control voltage of the converter are calculated; Based on the negative sequence voltage of the dq coordinate system of the grid connection point, the d-axis component and the q-axis component of the negative sequence control voltage of the converter are calculated; The converter control voltage is calculated based on the negative sequence control voltage of the αβ coordinate system or the negative sequence control voltage of the dq coordinate system.

2. The negative sequence current control method applicable to grid-following and grid-forming converters according to claim 1, characterized in that: The method of obtaining the negative-sequence voltage of the inverter grid-connected point in the αβ coordinate system and the negative-sequence voltage of the grid-connected point in the dq coordinate system includes obtaining the α-axis component and the β-axis component of the negative-sequence voltage of the inverter grid-connected point through the three-phase AC voltage of the inverter grid-connected point by the symmetrical component method and the Clark transformation, and obtaining the d-axis component and the q-axis component of the negative-sequence voltage of the inverter grid-connected point through the three-phase AC voltage of the inverter grid-connected point by the dual synchronous coordinate system decoupling method.

3. The negative sequence current control method applicable to grid-following and grid-forming converters as claimed in claim 2, characterized in that: The α-axis component and β-axis component of the negative sequence control voltage of the converter obtained by the calculation are expressed as: in, is the α-axis component of the negative sequence control voltage, is the α-axis component of the negative sequence voltage at the grid-connected point of the converter, is the β-axis component of the negative sequence control voltage, is the β-axis component of the negative sequence voltage at the grid-connected point of the converter, ω is the grid angular frequency, L1 is the grid-side filter inductor of the converter, is the negative sequence voltage modulus of the converter grid connection point, It is the negative sequence reactive current command.

4. The negative sequence current control method applicable to grid-following and grid-forming converters as claimed in claim 3 is characterized in that: The d-axis component and q-axis component of the negative sequence control voltage of the converter obtained by the calculation are expressed as: in, represents the d-axis component of the negative sequence control voltage, represents the d-axis component of the negative sequence voltage at the grid connection point of the converter, represents the q-axis component of the negative sequence control voltage, represents the q-axis component of the negative sequence voltage at the grid-connected point of the converter, ω represents the grid angular frequency, L1 represents the grid-side filter inductance of the converter, Indicates the negative sequence voltage modulus of the converter grid connection point, Indicates negative sequence reactive current command.

5. The negative sequence current control method applicable to grid-following and grid-forming converters as claimed in claim 4, characterized in that: The calculation to obtain the converter control voltage includes: directly selecting the negative sequence control voltage of the αβ coordinate system Or the negative sequence control voltage of the dq coordinate system is transformed by inverse Park to obtain the negative sequence control voltage of the αβ coordinate system It is superimposed with the positive sequence component of the control voltage obtained by the original positive sequence control module of the converter to obtain the control voltage finally output by the converter.

6. A system using the negative sequence current control method applicable to grid-following and grid-forming converters as claimed in any one of claims 1 to 5, characterized in that: include, A first module (100), a second module (200), a third module (300) and a fourth module (400); The first module (100) is a module for obtaining the negative sequence voltage of the converter grid connection point αβ coordinate system and the negative sequence voltage of the converter grid connection point dq coordinate system; The second module (200) is a calculation module for the negative sequence control voltage component of the αβ coordinate system; The third module (300) is a calculation module for the negative sequence control voltage component of the dq coordinate system; The fourth module (400) is a module for calculating the converter control voltage.

7. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the negative sequence current control method applicable to grid-following and grid-forming converters described in any one of claims 1 to 5 are implemented.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the negative sequence current control method applicable to grid-following and grid-forming converters described in any one of claims 1 to 5 are implemented.

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