Pre-synchronization method in grid-connected and off-grid switching process of network construction type converter

Abstract

The invention discloses a pre-synchronization method in a grid-connected and off-grid switching process of a grid-forming converter. The pre-synchronization method comprises the following steps of: converting an output voltage of the grid-forming converter and a power grid voltage into an alpha-beta coordinate system; according to the converter output voltage, the power grid voltage, the converter output voltage phase and the power grid voltage phase under the alpha-beta coordinate system, calculating an equivalent phase difference value and an amplitude deviation between the grid-forming converter and the power grid; if the equivalent phase difference value is not 0, adjusting the converter output voltage phase of the grid-forming converter, and returning to execute the step of calculating the equivalent phase difference value between the grid-forming converter and the power grid until the equivalent phase difference value is 0 so as to realize the frequency pre-synchronization of the grid-forming converter and the power grid; and if the amplitude deviation is not 0, adjusting the converter output voltage of the network construction type converter, and returning to execute the step of calculating the amplitude deviation between the network construction type converter and the power grid until the amplitude deviation is 0 so as to realize amplitude pre-synchronization of the network construction type converter and the power grid.

Description

Technical Field

[0001] The present invention relates to the technical field of converter control, and more specifically, to a pre-synchronization method in a grid-connected and off-grid switching process of a grid-connected converter. Background Art

[0002] Generally speaking, VSG type inverters operate in grid-connected mode, which can meet the power demand of local loads while being able to connect to the grid with surplus power. If the local load is too large to be met, the grid will help the inverter make up for the power shortfall and improve the economic efficiency of system operation. However, when the grid fails or needs maintenance, the VSG type grid-connected inverter cannot continue to operate in grid-connected mode, but must switch to off-grid operation mode and supply power to local loads alone. This process can achieve seamless switching without additional control. When the grid resumes normal operation, the VSG type inverter can be connected to the grid again to obtain maximum economic benefits. However, if it is directly connected to the grid without any pre-synchronization control method, it will cause a greater impact on the grid and damage the equipment, which is not worth the loss. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention provides a pre-synchronization method for a grid-connected converter during grid-connected and off-grid switching.

[0004] According to one aspect of the present invention, a pre-synchronization method for a grid-connected converter during grid-connected and off-grid switching is provided, comprising:

[0005] Convert the grid-forming converter output voltage and grid voltage to the αβ coordinate system;

[0006] According to the converter output voltage, the grid voltage, the converter output voltage phase and the grid voltage phase in the αβ coordinate system, the equivalent phase difference and the amplitude deviation between the grid-forming converter and the grid are calculated;

[0007] If the equivalent phase difference is not 0, after adjusting the converter output voltage phase of the grid-forming converter according to the equivalent phase difference, return to the step of calculating the equivalent phase difference between the grid-forming converter and the grid until the equivalent phase difference is 0, so as to achieve frequency pre-synchronization of the grid-forming converter and the grid;

[0008] If the amplitude deviation is not 0, the output voltage of the grid-type converter is adjusted according to the amplitude deviation, and then the step of calculating the amplitude deviation between the grid-type converter and the power grid is returned until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-type converter and the power grid.

[0009] Optionally, the calculation formula of the equivalent phase difference value sinΔθ is:

[0010]

[0011] Where U gα and U gβ are the components of the grid voltage on the α and β axes of the coordinate system; U vα and U vβ are the components of the converter output voltage on the α and β axes of the coordinate system; θ g ,θ v and Δθ are the grid voltage phase, the converter output voltage phase and the phase difference between the two, respectively, where sinΔθ≈Δθ,Δθ=θ g -θ v .

[0012] Optionally, the calculation formula of the amplitude deviation ΔU is:

[0013]

[0014] Where U g and U v are the grid voltage and the converter output voltage respectively; U gα and U gβ are the components of the grid voltage on the α and β axes of the two-phase coordinate system; U vα and U vβ They are the components of the converter output voltage on the α and β axes in the two-phase coordinate system respectively.

[0015] Optionally, if the equivalent phase difference is not 0, after adjusting the converter output voltage phase of the grid-forming converter according to the equivalent phase difference, returning to execute the step of calculating the equivalent phase difference between the grid-forming converter and the grid until the equivalent phase difference is 0, so as to achieve frequency pre-synchronization of the grid-forming converter and the grid, including:

[0016] If the equivalent phase difference value is not 0, the equivalent phase difference is superimposed on the active loop output frequency of the grid-forming converter through the phase regulator to obtain the adjusted output frequency;

[0017] Integrating the regulated output power to obtain the output voltage phase of the grid-type converter after the converter output voltage is regulated;

[0018] Based on the adjusted converter output voltage phase, return to the step of calculating the equivalent phase difference between the grid-forming converter and the grid until the equivalent phase difference is 0, so as to achieve frequency pre-synchronization between the grid-forming converter and the grid.

[0019] Optionally, if the amplitude deviation is not 0, after adjusting the converter output voltage of the grid-forming converter according to the amplitude deviation, returning to the step of calculating the amplitude deviation between the grid-forming converter and the grid until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-forming converter and the grid, including:

[0020] If the amplitude deviation is not 0, the amplitude deviation is superimposed on the output voltage of the reactive loop of the grid-forming converter by using a voltage regulator to obtain the regulated output voltage of the regulated converter;

[0021] Based on the adjusted output voltage of the regulating converter, return to the step of calculating the amplitude deviation between the grid-forming converter and the grid until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-forming converter and the grid.

[0022] According to another aspect of the present invention, a pre-synchronization device for a grid-connected converter during grid-connected and grid-offline switching is provided, comprising:

[0023] A conversion module, used for converting the grid-forming converter output voltage and the grid voltage into an αβ coordinate system;

[0024] A calculation module is used to calculate the equivalent phase difference and amplitude deviation between the grid-forming converter and the grid according to the converter output voltage, the grid voltage, the converter output voltage phase and the grid voltage phase in the αβ coordinate system;

[0025] A first pre-synchronization module is used for, if the equivalent phase difference value is not 0, adjusting the converter output voltage phase of the grid-type converter according to the equivalent phase difference value, and returning to execute the step of calculating the equivalent phase difference value between the grid-type converter and the grid until the equivalent phase difference value is 0, so as to achieve frequency pre-synchronization of the grid-type converter and the grid;

[0026] The second pre-synchronization module is used to adjust the converter output voltage of the grid-type converter according to the amplitude deviation if the amplitude deviation is not 0, and then return to execute the step of calculating the amplitude deviation between the grid-type converter and the power grid until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-type converter and the power grid.

[0027] Optionally, the calculation formula of the equivalent phase difference value sinΔθ is:

[0028]

[0029] Where U gα and U gβ are the components of the grid voltage on the α and β axes of the coordinate system; U vα and U vβ are the components of the converter output voltage on the α and β axes of the coordinate system; θ g ,θ v and Δθ are the grid voltage phase, the converter output voltage phase and the phase difference between the two, respectively, where sinΔθ≈Δθ,Δθ=θ g -θ v .

[0030] Optionally, the calculation formula of the amplitude deviation ΔU is:

[0031]

[0032] Where U g and U v are the grid voltage and the converter output voltage respectively; U gα and U gβ are the components of the grid voltage on the α and β axes of the two-phase coordinate system; U vα and U vβ They are the components of the converter output voltage on the α and β axes in the two-phase coordinate system respectively.

[0033] Optionally, the first pre-synchronization module includes:

[0034] A first superposition submodule is used for superimposing the equivalent phase difference to the active loop output frequency of the grid-forming converter through a phase regulator if the equivalent phase difference value is not 0, so as to obtain an adjusted output frequency after adjustment;

[0035] An integration submodule, used for integrating the regulated output power to obtain the output voltage phase of the grid-type converter after the converter output voltage is regulated;

[0036] The first pre-synchronization submodule is used to return to the step of calculating the equivalent phase difference between the grid-forming converter and the power grid based on the adjusted converter output voltage phase until the equivalent phase difference is 0, so as to achieve frequency pre-synchronization between the grid-forming converter and the power grid.

[0037] Optionally, the second pre-synchronization module includes:

[0038] The second superposition submodule is used for superimposing the amplitude deviation on the output voltage of the reactive loop of the grid-type converter by using the voltage regulator if the amplitude deviation is not 0, so as to obtain the adjusted output voltage of the regulating converter;

[0039] The second pre-synchronization submodule is used to return to the step of calculating the amplitude deviation between the grid-forming converter and the grid based on the adjusted output voltage of the regulated converter until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-forming converter and the grid.

[0040] According to another aspect of the present invention, a computer-readable storage medium is provided, wherein the storage medium stores a computer program, and the computer program is used to execute the method described in any one of the above aspects of the present invention.

[0041] According to another aspect of the present invention, an electronic device is provided, comprising: a processor; a memory for storing instructions executable by the processor; the processor is configured to read the executable instructions from the memory and execute the instructions to implement the method described in any one of the above aspects of the present invention.

[0042] Therefore, the present invention converts the output voltage of the grid-type converter and the grid voltage to the αβ coordinate system; calculates the equivalent phase difference and amplitude deviation between the grid-type converter and the grid according to the converter output voltage, grid voltage, converter output voltage phase and grid voltage phase in the αβ coordinate system; adjusts the converter output voltage phase of the grid-type converter according to the equivalent phase difference and then calculates the equivalent phase difference until the equivalent phase difference is 0, thereby achieving frequency pre-synchronization of the grid-type converter and the grid; until the amplitude deviation is 0, achieving amplitude pre-synchronization of the grid-type converter and the grid. Compared with conventional pre-synchronization control, the proposed control strategy is simpler, has no complex phase-locked link, and can achieve the purpose of seamless switching between on-grid and off-grid, which has obvious advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0044] Figure 1 It is a flow chart of a pre-synchronization method in a grid-connected and off-grid switching process of a grid-connected converter provided by an exemplary embodiment of the present invention;

[0045] Figure 2 is a block diagram of a VSG type converter pre-synchronization control provided by an exemplary embodiment of the present invention;

[0046] Figure 3 is a phasor diagram of a converter output voltage and a grid voltage provided by an exemplary embodiment of the present invention;

[0047] Figure 4 is a VSG simulation main circuit diagram provided by an exemplary embodiment of the present invention;

[0048] Figure 5 is a schematic diagram of a voltage phase pre-synchronization waveform provided by an exemplary embodiment of the present invention;

[0049] Figure 6 is a schematic diagram of a voltage amplitude difference waveform provided by an exemplary embodiment of the present invention;

[0050] Figure 7 is a schematic diagram of a voltage pre-synchronization waveform provided by an exemplary embodiment of the present invention;

[0051] Figure 8It is a structural schematic diagram of a pre-synchronization device in a grid-connected and off-grid switching process of a grid-connected converter provided by an exemplary embodiment of the present invention;

[0052] Fig. 9 This is a structure of an electronic device provided by an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0053] Below, the exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments of the present invention, and it should be understood that the present invention is not limited to the exemplary embodiments described here.

[0054] It should be noted that the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise.

[0055] Those skilled in the art can understand that the terms "first" and "second" in the embodiments of the present invention are only used to distinguish different steps, devices or modules, etc., and neither represent any specific technical meaning nor indicate the necessary logical order between them.

[0056] It should also be understood that, in the embodiments of the present invention, “plurality” may refer to two or more than two, and “at least one” may refer to one, two or more than two.

[0057] It should also be understood that any component, data or structure mentioned in the embodiments of the present invention can generally be understood as one or more, unless explicitly limited or otherwise indicated in the context.

[0058] In addition, the term "and / or" in the present invention is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects before and after are in an "or" relationship.

[0059] It should also be understood that the description of the various embodiments of the present invention focuses on the differences between the various embodiments, and the same or similar aspects thereof can be referenced to each other, and for the sake of brevity, they will not be described one by one.

[0060] At the same time, it should be understood that for the convenience of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship.

[0061] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0062] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0063] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0064] Embodiments of the present invention can be applied to electronic devices such as terminal devices, computer systems, servers, etc., which can operate with many other general or special computing system environments or configurations. Examples of well-known terminal devices, computing systems, environments and / or configurations suitable for use with electronic devices such as terminal devices, computer systems, servers, etc. include, but are not limited to: personal computer systems, server computer systems, thin clients, thick clients, handheld or laptop devices, microprocessor-based systems, set-top boxes, programmable consumer electronics, network personal computers, small computer systems, large computer systems, and distributed cloud computing technology environments including any of the above systems, etc.

[0065] Electronic devices such as terminal devices, computer systems, servers, etc. can be described in the general context of computer system executable instructions (such as program modules) executed by computer systems. Generally, program modules can include routines, programs, object programs, components, logic, data structures, etc., which perform specific tasks or implement specific abstract data types. Computer systems / servers can be implemented in a distributed cloud computing environment, where tasks are performed by remote processing devices linked through a communication network. In a distributed cloud computing environment, program modules can be located on local or remote computing system storage media including storage devices.

[0066] Exemplary Methods

[0067] Figure 1 1 is a flow chart of a pre-synchronization method in a grid-connected and off-grid switching process of a grid-connected converter provided by an exemplary embodiment of the present invention. This embodiment can be applied to electronic devices, such as Figure 1 As shown, the pre-synchronization method 100 in the process of grid-connected and off-grid switching of a grid-connected converter includes the following steps:

[0068] Step 101, converting the grid-connected converter output voltage and the grid voltage into an αβ coordinate system;

[0069] Step 102, calculating an equivalent phase difference and an amplitude deviation between the grid-forming converter and the grid according to the converter output voltage, the grid voltage, the converter output voltage phase, and the grid voltage phase in the αβ coordinate system;

[0070] Step 103, if the equivalent phase difference is not 0, then after adjusting the converter output voltage phase of the grid-forming converter according to the equivalent phase difference, return to the step of calculating the equivalent phase difference between the grid-forming converter and the grid until the equivalent phase difference is 0, so as to achieve frequency pre-synchronization of the grid-forming converter and the grid;

[0071] Step 104, if the amplitude deviation is not 0, then after adjusting the converter output voltage of the grid-type converter according to the amplitude deviation, return to execute the step of calculating the amplitude deviation between the grid-type converter and the grid until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-type converter and the grid.

[0072] Specifically, the present invention aims at the problems of grid instability that may exist in the process of switching between grid-connected and off-grid operation modes of VSG converters, and proposes a pre-synchronization control method for VSG converters that is not based on a phase-locked loop. Compared with conventional pre-synchronization control, the proposed control strategy is simpler, has no complex phase-locked link, and can achieve the purpose of seamless switching between grid-connected and off-grid operation, which has obvious advantages. The specific scheme is as follows:

[0073] The pre-synchronization control block diagram is as follows Figure 2 As shown. v is the output angular frequency of the frequency pre-synchronization loop, θ v is the output voltage phase of the frequency pre-synchronization loop, ω1 is the output angular frequency of the active frequency loop, ω0 is the rated angular frequency, J is the VSG moment of inertia, K D is the VSG damping coefficient, P e Active power measurement value, P eref Active power reference value, K Q is the reactive voltage regulation coefficient. Here, V v is the output inner loop control voltage, Q e Reactive power measurement, Q eref Reactive reference value, U1 is the VSG reactive loop output voltage, U0 is the voltage target value, U g is the grid voltage, U v is the output voltage of the converter. First, the system output voltage is transformed by Clark to obtain the value in the α and β coordinate systems, and then the voltage value in the αβ coordinate system is substituted into equations (1) and (2) to obtain the approximate phase deviation sinΔθ and the amplitude deviation ΔU. Finally, the two deviation values ​​are adjusted by the phase regulator and the voltage regulator (both using PI regulators) respectively and then sent to the power loop to form the frequency pre-synchronization link and the amplitude pre-synchronization link.

[0074] Figure 3 is the phasor diagram of the converter output voltage and the grid voltage in the αβ coordinate system, U g and U vare the grid voltage and the converter output voltage, U gα and U gβ are the components of the grid voltage on the α and β axes respectively; U vα and U vβ are the components of the converter side voltage on the α and β axes respectively; θ g ,θ v and Δθ are the grid voltage phase, the converter side output voltage phase and the phase difference between them respectively.

[0075] Normally, the phase angle difference Δθ between the system output voltage and the grid voltage is very small, that is:

[0076] sinΔθ≈Δθ,Δθ=θ g -θ v (1)

[0077] Therefore, the sine value of the phase difference can be calculated to be equivalent to the phase difference value, combined with Figure 3 And formula (1) we can get:

[0078]

[0079] The working principle of the frequency pre-synchronization link is as follows: First, the approximate value of the phase deviation sinΔθ is calculated by equation (3), and then the difference is input into the phase regulator. The output of the phase regulator is superimposed on the active loop output frequency ω1 of the VSG, thereby obtaining the VSG output frequency ω after being adjusted by the frequency pre-synchronization link. v Finally, ω v The phase θ of the VSG output voltage is obtained by integration calculation v If sinΔθ>0, then θ g >θ v , the output value of the phase regulator is positive, which will make ω v Increase (and as long as sinΔθ>0, ω v will continue to increase), which will make θ v It also increases until θ v =θ g , that is, let the phase deviation gradually decrease until it is 0.

[0080] The working principle of the amplitude pre-synchronization link is as follows: First, the amplitude deviation ΔU can be obtained by equation (4), and then the difference is input into the voltage regulator. The output of the voltage regulator is superimposed on the VSG reactive loop output voltage U1, thereby obtaining the VSG voltage amplitude set value U after adjustment by the amplitude pre-synchronization link. v If ΔU>0, that is, U g >U v , the output of the voltage regulator is positive, which will make U vIncrease (and as long as ΔU>0, V v will continue to increase), which will make U v It also becomes larger until U v =U g , that is, let the amplitude deviation gradually decrease until it reaches 0.

[0081] In order to verify the effectiveness and correctness of the proposed grid-connected / off-grid seamless switching method for grid-connected converters based on presynchronization control, a model of a single-machine VSG grid-connected converter was built. Figure 4 The main circuit shown and Figure 2 The pre-synchronization control method shown, Figure 4 Medium in is the output power of the constant DC voltage source, U dc is the constant DC voltage source capacitor voltage, e a 、e b 、e c are the potentials in phases a, b, and c respectively, L f is the inductance inside the VSG, R f is the internal resistance of VSG, i sa 、i sb 、i sc are the line currents of phases a, b, and c at the output end of VSG, u sa 、u sb 、u sc are the line voltages of phases a, b, and c respectively, i ga 、i gb 、i gc are the a, b, and c phase currents of the AC grid, respectively, and u ga 、u gb 、u gc are the phase voltages of the AC grid a, b, and c respectively. The specific control parameters are shown in Table 1.

[0082] Table 1 VSG type grid-connected converter on-grid and off-grid seamless switching control parameters

[0083]

[0084] At the beginning of the system simulation, switch KM1 is always in the closed state, VSG carries a load of 10kW / 0kVar alone, and the active power and reactive power reference P are given. eref =10kW and Q eref =0kVar. Simulation conditions: 0.5s gives the pre-synchronization control start signal; 0.7s closes the switch KM2, and the VSG converter switches from off-grid mode to grid-connected mode; 1.2s opens the switch KM2, and the VSG converter runs off-grid again.

[0085] After starting the pre-synchronization control, the phase pre-synchronization waveform is as follows Figure 5As shown, it can be seen that the system output voltage phase coincides with the grid voltage phase about 0.06s after the pre-synchronization control is started, and the synchronization is rapid.

[0086] The waveform of the difference between the grid voltage and the system output voltage is as follows: Figure 6 As shown, it can be seen that after the pre-synchronization control is started, the voltage amplitude difference quickly stabilizes to 0V after a short oscillation link. The whole process takes about 0.03s, and the synchronization is rapid.

[0087] The grid voltage and system output voltage pre-synchronization waveform is as follows Figure 7 As shown in the figure, it can be seen that after starting pre-synchronization, the two voltage waveforms overlap at about 0.02s, the synchronization is rapid, and the tracking effect is good, which is consistent with the theoretical analysis.

[0088] Therefore, the present invention proposes a presynchronization control method for a VSG type converter. Compared with conventional presynchronization control, the proposed control strategy is simpler, has no complicated phase-locked link, and can achieve the purpose of seamless switching between on-grid and off-grid, which has obvious advantages.

[0089] Exemplary Devices

[0090] Figure 8 1 is a schematic diagram of the structure of a pre-synchronization device in a grid-connected and off-grid switching process of a grid-connected converter provided by an exemplary embodiment of the present invention. Figure 8 As shown, the device 800 includes:

[0091] A conversion module 810, used to convert the grid-connected converter output voltage and the grid voltage into an αβ coordinate system;

[0092] A calculation module 820 is used to calculate an equivalent phase difference and an amplitude deviation between the grid-forming converter and the grid according to the converter output voltage, the grid voltage, the converter output voltage phase and the grid voltage phase in the αβ coordinate system;

[0093] A first pre-synchronization module 830 is used for, if the equivalent phase difference value is not 0, adjusting the converter output voltage phase of the grid-type converter according to the equivalent phase difference value, and returning to the step of calculating the equivalent phase difference value between the grid-type converter and the grid until the equivalent phase difference value is 0, so as to achieve frequency pre-synchronization of the grid-type converter and the grid;

[0094] The second pre-synchronization module 840 is used to adjust the converter output voltage of the grid-type converter according to the amplitude deviation if the amplitude deviation is not 0, and then return to execute the step of calculating the amplitude deviation between the grid-type converter and the power grid until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-type converter and the power grid.

[0095] Optionally, the calculation formula of the equivalent phase difference value sinΔθ is:

[0096]

[0097] Where U gα and U gβ are the components of the grid voltage on the α and β axes of the coordinate system; U vα and U vβ are the components of the converter output voltage on the α and β axes of the coordinate system; θ g ,θ v and Δθ are the grid voltage phase, the converter output voltage phase and the phase difference between the two, respectively, where sinΔθ≈Δθ,Δθ=θ g -θ v .

[0098] Optionally, the calculation formula of the amplitude deviation ΔU is:

[0099]

[0100] Where U g and U v are the grid voltage and the converter output voltage respectively; U gα and U gβ are the components of the grid voltage on the α and β axes of the two-phase coordinate system; U vα and U vβ They are the components of the converter output voltage on the α and β axes in the two-phase coordinate system respectively.

[0101] Optionally, the first pre-synchronization module 830 includes:

[0102] A first superposition submodule is used for superimposing the equivalent phase difference to the active loop output frequency of the grid-forming converter through a phase regulator if the equivalent phase difference value is not 0, so as to obtain an adjusted output frequency after adjustment;

[0103] An integration submodule, used for integrating the regulated output power to obtain the output voltage phase of the grid-type converter after the converter output voltage is regulated;

[0104] The first pre-synchronization submodule is used to return to the step of calculating the equivalent phase difference between the grid-forming converter and the power grid based on the adjusted converter output voltage phase until the equivalent phase difference is 0, so as to achieve frequency pre-synchronization between the grid-forming converter and the power grid.

[0105] Optionally, the second pre-synchronization module 840 includes:

[0106] The second superposition submodule is used for superimposing the amplitude deviation on the output voltage of the reactive loop of the grid-type converter by using the voltage regulator if the amplitude deviation is not 0, so as to obtain the adjusted output voltage of the regulating converter;

[0107] The second pre-synchronization submodule is used to return to the step of calculating the amplitude deviation between the grid-forming converter and the grid based on the adjusted output voltage of the regulating converter until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-forming converter and the grid.

[0108] Exemplary Electronic Devices

[0109] Fig. 9 This is a structure of an electronic device provided by an exemplary embodiment of the present invention. Fig. 9 As shown, the electronic device 90 includes one or more processors 91 and a memory 92 .

[0110] The processor 91 may be a central processing unit (CPU) or other forms of processing units having data processing capabilities and / or instruction execution capabilities, and may control other components in the electronic device to perform desired functions.

[0111] The memory 92 may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may include, for example, random access memory (RAM) and / or cache memory (cache), etc. The non-volatile memory may include, for example, read-only memory (ROM), hard disk, flash memory, etc. One or more computer program instructions may be stored on the computer-readable storage medium, and the processor 91 may run the program instructions to implement the methods of the software programs of the various embodiments of the present invention described above and / or other desired functions. In one example, the electronic device may also include: an input device 93 and an output device 94, which are interconnected via a bus system and / or other forms of connection mechanisms (not shown).

[0112] In addition, the input device 93 may also include, for example, a keyboard, a mouse, and the like.

[0113] The output device 94 can output various information to the outside. The output device 94 can include, for example, a display, a speaker, a printer, a communication network and a remote output device connected thereto.

[0114] Of course, to simplify, Fig. 9Only some of the components related to the present invention in the electronic device are shown, and components such as a bus, an input / output interface, etc. are omitted. In addition, the electronic device may further include any other appropriate components according to specific application conditions.

[0115] Exemplary computer program products and computer-readable storage media

[0116] In addition to the above-mentioned methods and devices, an embodiment of the present invention may also be a computer program product, which includes computer program instructions, which, when executed by a processor, enable the processor to execute the steps of the method according to various embodiments of the present invention described in the above-mentioned "Exemplary Method" section of this specification.

[0117] The computer program product may be written in any combination of one or more programming languages ​​to write program code for performing the operations of the embodiments of the present invention, including object-oriented programming languages ​​such as Java, C++, etc., and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user computing device, partially on the user device, as a separate software package, partially on the user computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0118] In addition, an embodiment of the present invention may also be a computer-readable storage medium having computer program instructions stored thereon, which, when executed by a processor, enable the processor to execute the steps of the method according to various embodiments of the present invention described in the above “Exemplary Method” section of this specification.

[0119] The computer readable storage medium can adopt any combination of one or more readable media. The readable medium can be a readable signal medium or a readable storage medium. The readable storage medium can include, for example, but is not limited to, a system, system or device of electricity, magnetism, light, electromagnetic, infrared, or semiconductor, or any combination of the above. More specific examples (non-exhaustive list) of readable storage media include: an electrical connection with one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above.

[0120] The basic principle of the present invention is described above in conjunction with specific embodiments. However, it should be pointed out that the advantages, strengths, effects, etc. mentioned in the present invention are only examples and not limitations, and it cannot be considered that these advantages, strengths, effects, etc. must be possessed by each embodiment of the present invention. In addition, the specific details disclosed above are only for the purpose of illustration and facilitation of understanding, rather than limitation, and the above details do not limit the present invention to being implemented by adopting the above specific details.

[0121] Each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system embodiment, since it basically corresponds to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0122] The block diagrams of the devices, systems, equipment, and systems involved in the present invention are only illustrative examples and are not intended to require or imply that they must be connected, arranged, and configured in the manner shown in the block diagram. As will be appreciated by those skilled in the art, these devices, systems, equipment, and systems can be connected, arranged, and configured in any manner. Words such as "including", "comprising", "having", etc. are open words, referring to "including but not limited to", and can be used interchangeably with them. The words "or" and "and" used here refer to the words "and / or" and can be used interchangeably with them, unless the context clearly indicates otherwise. The word "such as" used here refers to the phrase "such as but not limited to", and can be used interchangeably with it.

[0123] The method and system of the present invention may be implemented in many ways. For example, the method and system of the present invention may be implemented by software, hardware, firmware or any combination of software, hardware, firmware. The above order of steps for the method is only for illustration, and the steps of the method of the present invention are not limited to the order specifically described above, unless otherwise specifically stated. In addition, in some embodiments, the present invention may also be implemented as a program recorded in a recording medium, which includes machine-readable instructions for implementing the method according to the present invention. Thus, the present invention also covers a recording medium storing a program for executing the method according to the present invention.

[0124] It should also be noted that in the system, device and method of the present invention, each component or each step can be decomposed and / or recombined. These decompositions and / or recombinations should be regarded as equivalent schemes of the present invention. The above description of the disclosed aspects is provided to enable any technician in the field to make or use the present invention. Various modifications to these aspects are very obvious to those skilled in the art, and the general principles defined here can be applied to other aspects without departing from the scope of the present invention. Therefore, the present invention is not intended to be limited to the aspects shown here, but in accordance with the widest range consistent with the principles and novel features disclosed here.

[0125] The above description has been given for the purpose of illustration and description. In addition, this description is not intended to limit the embodiments of the present invention to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, changes, additions and sub-combinations thereof.

Claims

1. A pre-synchronization method for a grid-connected converter in a grid-connected or grid-offline switching process, characterized in that: include: Convert the grid-forming converter output voltage and grid voltage to the αβ coordinate system; Calculate the equivalent phase difference and amplitude deviation between the grid-forming converter and the grid according to the converter output voltage, the grid voltage, the converter output voltage phase and the grid voltage phase in the αβ coordinate system; If the equivalent phase difference is not 0, after adjusting the converter output voltage phase of the grid-type converter according to the equivalent phase difference, return to the step of calculating the equivalent phase difference between the grid-type converter and the grid until the equivalent phase difference is 0, so as to achieve frequency pre-synchronization of the grid-type converter and the grid; If the amplitude deviation is not 0, after adjusting the converter output voltage of the grid-type converter according to the amplitude deviation, return to the step of calculating the amplitude deviation between the grid-type converter and the power grid until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-type converter and the power grid.

2. The method according to claim 1, characterized in that The calculation formula of the equivalent phase difference sinΔθ is: Where U gα and U gβ are the components of the grid voltage on the α and β axes of the coordinate system; U vα and U vβ are the components of the converter output voltage on the α and β axes of the coordinate system; θ g ,θ v and Δθ are the grid voltage phase, the converter output voltage phase and the phase difference between the two, respectively, where sinΔθ≈Δθ,Δθ=θ g -θ v .

3. The method according to claim 1, characterized in that: The calculation formula of the amplitude deviation ΔU is: Where U g and U v are the grid voltage and the converter output voltage respectively; U gα and U gβ are the components of the grid voltage on the α and β axes of the two-phase coordinate system; U vα and U vβ They are the components of the converter output voltage on the α and β axes in the two-phase coordinate system respectively.

4. The method according to claim 1, characterized in that: If the equivalent phase difference is not 0, after adjusting the converter output voltage phase of the grid-type converter according to the equivalent phase difference, returning to the step of calculating the equivalent phase difference between the grid-type converter and the grid until the equivalent phase difference is 0, so as to achieve frequency pre-synchronization of the grid-type converter and the grid, including: If the equivalent phase difference value is not 0, the equivalent phase difference is superimposed on the active loop output frequency of the grid-type converter through a phase regulator to obtain an adjusted output frequency; Integrating the regulated output power to obtain a converter output voltage phase after the converter output voltage of the grid-type converter is regulated; Based on the adjusted converter output voltage phase, return to the step of calculating the equivalent phase difference between the grid-forming converter and the grid until the equivalent phase difference is 0, so as to achieve frequency pre-synchronization of the grid-forming converter and the grid.

5. The method according to claim 1, characterized in that If the amplitude deviation is not 0, after adjusting the converter output voltage of the grid-type converter according to the amplitude deviation, returning to the step of calculating the amplitude deviation between the grid-type converter and the grid until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-type converter and the grid, including: If the amplitude deviation is not 0, the amplitude deviation is superimposed on the output voltage of the reactive loop of the grid-type converter by a voltage regulator to obtain an adjusted output voltage of the regulated converter; Based on the adjusted output voltage of the regulating converter, return to the step of calculating the amplitude deviation between the grid-forming converter and the grid until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-forming converter and the grid.

6. A pre-synchronization device for a grid-connected and off-grid switching process of a grid-connected converter, characterized in that: include: A conversion module, used for converting the grid-forming converter output voltage and the grid voltage into an αβ coordinate system; A calculation module, used to calculate the equivalent phase difference and amplitude deviation between the grid-forming converter and the grid according to the converter output voltage, the grid voltage, the converter output voltage phase and the grid voltage phase in the αβ coordinate system; A first pre-synchronization module, for, if the equivalent phase difference is not 0, adjusting the converter output voltage phase of the grid-type converter according to the equivalent phase difference, and returning to the step of calculating the equivalent phase difference between the grid-type converter and the grid until the equivalent phase difference is 0, so as to achieve frequency pre-synchronization of the grid-type converter and the grid; The second pre-synchronization module is used to adjust the converter output voltage of the grid-type converter according to the amplitude deviation if the amplitude deviation is not 0, and then return to the step of calculating the amplitude deviation between the grid-type converter and the grid until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-type converter and the grid.

7. The device according to claim 6, characterized in that The calculation formula of the equivalent phase difference sinΔθ is: Where U gα and U gβ are the components of the grid voltage on the α and β axes of the coordinate system; U vα and U vβ are the components of the converter output voltage on the α and β axes of the coordinate system; θ g ,θ v and Δθ are the grid voltage phase, the converter output voltage phase and the phase difference between the two, respectively, where sinΔθ≈Δθ,Δθ=θ g -θ v .

8. The device according to claim 6, characterized in that The calculation formula of the amplitude deviation ΔU is: Where U g and U v are the grid voltage and the converter output voltage respectively; U gα and U gβ are the components of the grid voltage on the α and β axes of the two-phase coordinate system; U vα and U vβ They are the components of the converter output voltage on the α and β axes in the two-phase coordinate system respectively.

9. The device according to claim 6, characterized in that The first pre-synchronization module includes: A first superposition submodule is used for superimposing the equivalent phase difference to the active loop output frequency of the grid-type converter through a phase regulator to obtain an adjusted output frequency if the equivalent phase difference value is not 0; An integration submodule, used for integrating the regulated output power to obtain a converter output voltage phase after the converter output voltage of the grid-type converter is regulated; The first pre-synchronization submodule is used to return to the step of calculating the equivalent phase difference between the grid-forming converter and the grid based on the adjusted converter output voltage phase until the equivalent phase difference is 0, so as to achieve frequency pre-synchronization of the grid-forming converter and the grid.

10. The device according to claim 6, characterized in that The second pre-synchronization module includes: A second superposition submodule is used for, if the amplitude deviation is not 0, using a voltage regulator to superimpose the amplitude deviation on the output voltage of the reactive loop of the grid-type converter to obtain an adjusted output voltage of the regulating converter; The second pre-synchronization submodule is used to return to the step of calculating the amplitude deviation between the grid-forming converter and the grid based on the adjusted output voltage of the regulating converter until the amplitude deviation is 0, so as to achieve amplitude pre-synchronization of the grid-forming converter and the grid.

11. A computer-readable storage medium, characterized in that: The storage medium stores a computer program, and the computer program is used to execute the method according to any one of claims 1 to 5.

12. An electronic device, characterized in that: The electronic device comprises: processor; a memory for storing instructions executable by the processor; The processor is used to read the executable instructions from the memory and execute the instructions to implement the method described in any one of claims 1 to 5.

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