Method for controlling falling fault of power grid of network-forming converter

Abstract

The invention provides a grid construction type converter power grid drop fault control method, which comprises the following steps: when a grid construction type converter is in a low-pass recovery state, obtaining operation state parameters of the grid construction type converter; determining at least one phase angle offset corresponding to the operation state parameter according to the operation state parameter; superposing a corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle; and controlling wave emission of the network-forming converter based on the adjusted phase angle. The method provided by the invention inhibits the active power from flowing backwards from the power grid to the converter in the low-voltage-crossing recovery process of the network-forming converter.

Description

Technical Field

[0001] The present invention relates to the technical field of converter control, and in particular to a method for controlling a grid drop fault of a grid-forming converter. Background Art

[0002] With growing energy demand and increasing consumption of traditional fossil fuels, the energy crisis is an unavoidable challenge facing humanity. To address this, countries around the world are vigorously developing renewable energy sources, such as wind power and photovoltaics. my country also attaches great importance to the development of renewable energy. These renewable energy sources are often connected to the grid through converters. Compared to hydropower and thermal power, traditional grid-connected renewable energy sources lack mechanical inertia and also face small-signal stability issues when connected to weak grids. The integration of a large proportion of renewable energy sources will reduce the inertia level of the entire power system, further reducing the short-circuit ratio in some areas, leading to increased system frequency fluctuations and reduced system stability.

[0003] To solve this problem, a large number of experts and scholars have pointed out that the use of grid-type control converters can solve the problems of weak inertia and weak grid stability caused by the integration of new energy into the grid.

[0004] However, when conducting grid low-pass tests on converters using grid-type control, it was found that during the low-pass fault recovery process, active power would flow back from the grid to the converter. This phenomenon, on the one hand, increased the voltage of the DC capacitor, and on the other hand, had a negative impact on the active power balance during the grid recovery process. Summary of the Invention

[0005] The present invention provides a method for controlling a grid drop fault of a grid-forming converter, which suppresses the backflow of active power from the grid to the converter during the low-breakdown recovery process of the grid-forming converter.

[0006] According to a first aspect of an embodiment of the present invention, a method for controlling a grid drop fault of a grid-connected converter is provided, the method comprising:

[0007] When the grid-type converter is in a low-power recovery state, obtaining operating state parameters of the grid-type converter;

[0008] Determining at least one phase angle offset corresponding to the operating state parameter according to the operating state parameter;

[0009] Superimposing a corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle;

[0010] The wave generation of the grid-type converter is controlled based on the adjusted phase angle.

[0011] In one possible implementation, at least one link in the control link includes a frequency control link; and determining, based on the operating state parameter, at least one phase angle offset corresponding to the operating state parameter includes:

[0012] Determining, based on the operating state parameter, at least a first phase angle offset corresponding to the operating state parameter;

[0013] The corresponding phase angle offset is superimposed on the phase angle of at least one link in the control link to obtain the adjusted phase angle, including:

[0014] A first phase angle offset is superimposed on the phase angle of the frequency control link.

[0015] In one possible implementation, at least one link in the control link includes a voltage control link; and determining, based on an operating state parameter, at least one phase angle offset corresponding to the operating state parameter includes:

[0016] Determining, based on the operating state parameter, at least a second phase angle offset corresponding to the operating state parameter;

[0017] The corresponding phase angle offset is superimposed on the phase angle of at least one link in the control link to obtain the adjusted phase angle, including:

[0018] A second phase angle offset is superimposed on the phase angle of the voltage control link.

[0019] In one possible implementation, at least one link in the control link includes a current control link; and determining, based on an operating state parameter, at least one phase angle offset corresponding to the operating state parameter includes:

[0020] Determining at least a third phase angle offset corresponding to the operating state parameter according to the operating state parameter;

[0021] The corresponding phase angle offset is superimposed on the phase angle of at least one link in the control link to obtain the adjusted phase angle, including:

[0022] A third phase angle offset is superimposed on the phase angle of the current control link.

[0023] In one possible implementation, at least one link in the control link includes a dq-abc coordinate transformation link; and determining, based on the operating state parameter, at least one phase angle offset corresponding to the operating state parameter includes:

[0024] determining, based on the operating state parameter, at least a fourth phase angle offset corresponding to the operating state parameter;

[0025] The corresponding phase angle offset is superimposed on the phase angle of at least one link in the control link to obtain the adjusted phase angle, including:

[0026] A fourth phase angle offset is superimposed on the phase angle of the dq-abc coordinate transformation link.

[0027] In a possible implementation, before obtaining the operating status parameters of the grid-connected converter, the method further includes:

[0028] At least one phase angle offset corresponding to at least one set of operating status parameters is determined through parameter debugging.

[0029] In a possible implementation, before obtaining the operating status parameters of the grid-connected converter, the method further includes:

[0030] During the low-voltage recovery process of the grid-connected converter, the grid voltage at the grid connection point is monitored;

[0031] When the grid voltage has not returned to the normal range, the low-voltage recovery signal is set to 0, indicating that the grid-connected converter is not in the low-voltage recovery state;

[0032] When the grid voltage returns to the normal range, the low-voltage recovery signal is set to 1, indicating that the grid-connected converter is in the low-voltage recovery state.

[0033] In one possible implementation, the normal range is U g ≥0.9U0, where U g Indicates the grid voltage, U0 indicates the rated grid voltage.

[0034] According to a second aspect of an embodiment of the present invention, a grid-type converter is provided, which includes a control unit, which is used to execute the grid drop fault control method of the grid-type converter in the first aspect or any possible implementation of the first aspect.

[0035] An embodiment of the present invention provides a grid-sag fault control method for a grid-type converter. When the grid-type converter is in a low-pass recovery state, the operating state parameters of the grid-type converter are obtained; at least one phase angle offset corresponding to the operating state parameters is determined based on the operating state parameters; the corresponding phase angle offset is superimposed on the phase angle of at least one link within the control link to obtain an adjusted phase angle; and the grid-type converter's wave generation is controlled based on the adjusted phase angle. By adjusting the phase angle of the converter's control link, the converter's short-term phase angle relative to the grid voltage is changed during the low-pass recovery process, thereby changing the short-term phase angle of the AC current, thereby suppressing the backflow of active power from the grid into the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0037] Figure 1 This is a typical schematic diagram of a network control structure;

[0038] Figure 2 A schematic flow chart of a method for controlling a grid drop fault of a grid-connected converter provided in an embodiment of the present invention;

[0039] Figure 3 A schematic diagram of the structure of a frequency control link provided by an embodiment of the present invention;

[0040] Figure 4 A schematic diagram of a structure for performing abc-dq coordinate transformation in a voltage control link provided by an embodiment of the present invention;

[0041] Figure 5 A schematic diagram of a structure for performing abc-dq coordinate transformation in a current control link provided by an embodiment of the present invention;

[0042] Figure 6 A structural diagram of a dq-abc coordinate transformation link for performing dq-abc coordinate transformation is provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0044] Converter: An electrical device that changes the voltage, frequency, number of phases, and other electrical quantities or characteristics of a power system. This includes rectifiers (converting AC to DC), inverters (converting DC to AC), AC converters, and DC converters. Renewable energy generation is connected to the grid through converters.

[0045] The method provided in the embodiment of the present invention is applied to a grid-type converter, such as Figure 1 As shown in FIG, the control link of the grid-type converter includes the frequency control link, the voltage control link, the current control link, and the dq-abc coordinate transformation link, among which:

[0046] P ref_pu: Converter output power command value

[0047] P fdb : Converter output power acquisition value

[0048] ΔP pu : Power deviation value

[0049] Δω pu : Frequency offset value

[0050] Δω: frequency offset value

[0051] ω: converter output frequency

[0052] ω0: rated frequency of the power grid

[0053] θ vsc : Output phase angle of the frequency control link

[0054] u abc : Grid voltage at the grid connection point

[0055] E ref : Output voltage reference value

[0056] U od 、U oq : d-axis component and q-axis component of the grid voltage

[0057] I ref_d , I ref_q : d-axis component and q-axis component of the current reference value

[0058] i abc : Grid-side AC current

[0059] I d , I q : d-axis component and q-axis component of the grid-side AC current

[0060] e d 、e q : d-axis component and q-axis component of the modulation voltage

[0061] e abc : AC modulation voltage

[0062] In the frequency control link based on P ref_pu 、P fdb , ω0, generating a phase angle θ vsc ; Voltage control link is based on E ref 、u abc and θ vsc Generate I ref_d , I ref_q ; The current control link is based on U od 、U oq , Iref_d , I ref_q 、i abc and θ vsc , generating e d 、e q ; dq-abc coordinate transformation link is based on e d 、e q and θ vsc Generate e abc .

[0063] From the above, we can see that in the frequency control link, θ is generated vsc , input θ in the voltage control link, current control link and dq-abc coordinate transformation link vsc .

[0064] Example 1

[0065] The embodiment of the present invention provides a grid-type converter power grid drop fault control method, which is applied to the grid-type converter, such as Figure 2 As shown, the method may include the following steps:

[0066] S210 : When the grid-type converter is in a low-power recovery state, obtain operating state parameters of the grid-type converter.

[0067] Monitor the operating status of the converter. When the grid-type converter experiences a low-current breakdown and is in a low-current breakdown recovery state, obtain the operating status parameters of the grid-type converter, where the operating status parameters may include parameters such as current, voltage, frequency or power.

[0068] The low-voltage recovery state indicates that the grid voltage of the grid-type converter has risen to the normal range and keeps rising or stable. The normal range can be U g ≥0.9U0, where U g Indicates the grid voltage, U0 indicates the rated grid voltage.

[0069] S220: Determine, according to the operating state parameter, at least one phase angle offset corresponding to the operating state parameter.

[0070] According to the operating state parameter, at least one pre-configured phase angle offset corresponding to the operating state parameter is searched.

[0071] S230 , superimposing a corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle.

[0072] A corresponding phase angle offset is superimposed on at least one of the phase angles generated by the frequency control link, the phase angle of the input voltage control link, the phase angle of the input current control link, and the phase angle of the input dq-abc coordinate transformation link to obtain an adjusted phase angle.

[0073] S240, controlling the wave generation of the grid-type converter based on the adjusted phase angle.

[0074] An embodiment of the present invention provides a method for controlling a grid drop fault in a grid-type converter. When the grid-type converter is in a low-pass recovery state, the method obtains operating state parameters of the grid-type converter; determines at least one phase angle offset corresponding to the operating state parameters based on the operating state parameters; superimposes the corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle; and controls the wave generation of the grid-type converter based on the adjusted phase angle. By adjusting the phase angle of the converter control link, the short-term phase angle of the grid-type converter relative to the grid voltage during the low-pass recovery process is changed, thereby changing the short-term phase angle of the AC current, thereby suppressing the backflow of active power from the grid to the converter.

[0075] In one embodiment, before S210: obtaining the operating status parameters of the grid-connected converter, the method further includes the following steps:

[0076] At least one phase angle offset corresponding to at least one set of operating status parameters is determined through parameter debugging.

[0077] Specifically, through modeling and simulation, the grid-type converter can be debugged to suppress the phase angle offset of active power flowing back from the grid to the converter under each set of operating state parameters in multiple sets of operating state parameters, and the phase angle offset corresponding to each set of operating parameters can be obtained.

[0078] The phase angle offset corresponding to the debugged operating status parameter includes: at least one phase angle offset among: a first phase angle offset acting on the frequency control link, a second phase angle offset acting on the voltage control link, a third phase angle offset acting on the current control link, and a fourth phase angle offset acting on the dq-abc coordinate transformation link.

[0079] The method provided by the embodiment of the present invention debugs the phase angle offset corresponding to the operating status parameter of the grid-type converter, providing a data basis for suppressing the backflow of active power from the grid to the converter.

[0080] In one embodiment, before S210: obtaining the operating status parameters of the grid-connected converter, the method further includes the following steps:

[0081] During the low-voltage recovery process of the grid-connected converter, the grid voltage at the grid connection point is monitored;

[0082] When the grid voltage does not return to the normal range, the low-voltage recovery signal is set to 0, indicating that the grid-connected converter is not in the low-voltage recovery state; the normal range is U g ≥0.9U0, where U gIndicates the grid voltage, U0 indicates the rated grid voltage.

[0083] When the grid voltage returns to the normal range, the low-voltage recovery signal is set to 1, indicating that the grid-connected converter is in the low-voltage recovery state.

[0084] The method provided by the embodiment of the present invention identifies whether a grid-type converter is in a low-throughput recovery state.

[0085] In one embodiment, at least one link in the control link includes a frequency control link, then:

[0086] S220: Determining, based on the operating state parameter, at least one phase angle offset corresponding to the operating state parameter, including:

[0087] Based on the operating state parameter, at least a first phase angle offset corresponding to the operating state parameter is determined.

[0088] S230: superimposing the corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle, such as Figure 3 Shown, including:

[0089] A first phase angle offset is superimposed on the phase angle of the frequency control link.

[0090] Specifically, if the low-pass recovery signal is 1, the first phase angle offset Δθ1 is superimposed on the phase angle θ generated by the frequency control link to obtain the adjusted phase angle θ vsc ,θ vsc As the phase angle of the subsequent control link input.

[0091] If the low-pass recovery signal is 0, the phase angle θ generated by the frequency control link is used as the phase angle θ of the subsequent control link. vsc .

[0092] The method provided in the embodiment of the present invention suppresses the backflow of active power from the power grid to the converter by adjusting the phase angle of the frequency control link.

[0093] In one embodiment, at least one link in the control link includes a voltage control link, then:

[0094] S220: Determining, based on the operating state parameter, at least one phase angle offset corresponding to the operating state parameter, including:

[0095] Based on the operating state parameter, at least a second phase angle offset corresponding to the operating state parameter is determined.

[0096] S230: superimposing the corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle, such as Figure 4 Shown, including:

[0097] A second phase angle offset is superimposed on the phase angle of the voltage control link.

[0098] Specifically, if the low-through recovery signal is 1, then at the phase angle θ vsc On the , the second phase angle offset Δθ2 is superimposed to obtain the adjusted phase angle θ u ,θ u As the voltage control link abc The phase angle used when performing abc-dq coordinate transformation is u abc Convert to U od 、U oq .

[0099] If the low penetration recovery signal is 0, the phase angle θ vsc As the phase angle used when performing abc-dq coordinate transformation in the voltage control link.

[0100] The method provided by the embodiment of the present invention suppresses the backflow of active power from the power grid to the converter by adjusting the phase angle of the voltage control link.

[0101] In one embodiment, at least one link in the control link includes a current control link, then:

[0102] S220: Determining, based on the operating state parameter, at least one phase angle offset corresponding to the operating state parameter, including:

[0103] Determining at least a third phase angle offset corresponding to the operating state parameter according to the operating state parameter;

[0104] S230: superimposing the corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle, such as Figure 5 Shown, including:

[0105] A third phase angle offset is superimposed on the phase angle of the current control link.

[0106] Specifically, if the low-through recovery signal is 1, then at the phase angle θ vsc On the , the third phase angle offset Δθ3 is superimposed to obtain the adjusted phase angle θ i ,θ i As the current control link of i abc The phase angle used when performing abc-dq coordinate transformation is i abc Convert to I d , I q .

[0107] If the low penetration recovery signal is 0, the phase angle θ vsc As the phase angle used in the abc-dq coordinate transformation in the current control link.

[0108] The method provided by the embodiment of the present invention suppresses the backflow of active power from the power grid to the converter by adjusting the phase angle of the current control link.

[0109] In one embodiment, at least one link in the control link includes a dq-abc coordinate transformation link, then:

[0110] S220: Determining, based on the operating state parameter, at least one phase angle offset corresponding to the operating state parameter, including:

[0111] According to the operating state parameter, at least a fourth phase angle offset corresponding to the operating state parameter is determined.

[0112] S230: superimposing the corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle, such as Figure 6 Shown, including:

[0113] A fourth phase angle offset is superimposed on the phase angle of the dq-abc coordinate transformation link.

[0114] Specifically, if the low-through recovery signal is 1, then at the phase angle θ vsc On the , the fourth phase angle offset Δθ4 is superimposed to obtain the adjusted phase angle θ e ,θ e As the coordinate transformation link of dq-abc d 、e q The phase angle used in the dq-abc coordinate transformation is e d 、e q Convert to e abc .

[0115] If the low penetration recovery signal is 0, the phase angle θ vsc As the phase angle used in the dq-abc coordinate transformation in the dq-abc coordinate transformation link.

[0116] The method provided by the embodiment of the present invention suppresses the backflow of active power from the power grid to the converter by adjusting the phase angle of the dq-abc coordinate transformation link.

[0117] This embodiment also provides a grid-type converter, which is based on the same inventive concept as the grid-type converter grid drop fault control method provided in the above-mentioned embodiments of the present invention. It can execute the grid-type converter grid drop fault control method provided in any of the above-mentioned embodiments of the present invention and has the corresponding functional modules and beneficial effects of executing the grid-type converter grid drop fault control method. For technical details not fully described in this embodiment, please refer to the specific processing content of the grid-type converter grid drop fault control method provided in the above-mentioned embodiments of the present invention, and will not be repeated here.

[0118] For simplicity of description, the aforementioned method embodiments are described as a series of actions. However, those skilled in the art should be aware that the present invention is not limited by the order of the actions described, as certain steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also be aware that the embodiments described in this specification are preferred embodiments, and the actions and modules involved are not necessarily required for the present invention.

[0119] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similarities between the various embodiments can be referred to in conjunction with each other. For device embodiments, since they are generally similar to method embodiments, their description is relatively simple, and for relevant details, reference can be made to the description of the method embodiments.

[0120] The steps in the methods of the various embodiments of the present invention can be adjusted in sequence, combined, and deleted according to actual needs, and the technical features recorded in the various embodiments can be replaced or combined.

[0121] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the above description has generally described the components and steps of each example according to their functions. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0122] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein may be implemented directly using hardware, software units executed by a processor, or a combination of the two. The software units may be placed in random access memory (RAM), internal memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0123] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

[0124] The above description of the disclosed embodiments will enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling grid drop faults of a grid-connected converter, characterized in that: The method comprises: When the grid-type converter is in a low-power recovery state, obtaining an operating state parameter of the grid-type converter; determining, based on the operating state parameter, at least one phase angle offset corresponding to the operating state parameter; Superimposing a corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle; The wave generation of the grid-type converter is controlled based on the adjusted phase angle.

2. The method according to claim 1, characterized in that At least one link in the control link includes a frequency control link; and determining at least one phase angle offset corresponding to the operating state parameter according to the operating state parameter includes: Determining, based on the operating state parameter, at least a first phase angle offset corresponding to the operating state parameter; The step of superimposing a corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle includes: The first phase angle offset is superimposed on the phase angle of the frequency control link.

3. The method according to claim 1, characterized in that At least one link in the control link includes a voltage control link; and determining at least one phase angle offset corresponding to the operating state parameter according to the operating state parameter includes: Determining, based on the operating state parameter, at least a second phase angle offset corresponding to the operating state parameter; The step of superimposing a corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle includes: The second phase angle offset is superimposed on the phase angle of the voltage control link.

4. The method according to claim 1, wherein At least one link in the control link includes a current control link; and determining at least one phase angle offset corresponding to the operating state parameter according to the operating state parameter includes: determining, based on the operating state parameter, at least a third phase angle offset corresponding to the operating state parameter; The step of superimposing a corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle includes: The third phase angle offset is superimposed on the phase angle of the current control link.

5. The method according to claim 1, wherein At least one link in the control link includes a dq-abc coordinate transformation link; and determining at least one phase angle offset corresponding to the operating state parameter according to the operating state parameter includes: determining, based on the operating state parameter, at least a fourth phase angle offset corresponding to the operating state parameter; The step of superimposing a corresponding phase angle offset on the phase angle of at least one link in the control link to obtain an adjusted phase angle includes: The fourth phase angle offset is superimposed on the phase angle of the dq-abc coordinate transformation link.

6. The method according to claim 1, characterized in that Before obtaining the operating status parameters of the grid-connected converter, the method further includes: At least one phase angle offset corresponding to at least one set of operating status parameters is determined through parameter debugging.

7. The method according to claim 1, characterized in that Before obtaining the operating status parameters of the grid-connected converter, the method further includes: During the low-voltage recovery process of the grid-connected converter, the grid voltage at the grid connection point is monitored; When the grid voltage has not recovered to the normal range, the low-voltage recovery signal is set to 0, indicating that the grid-connected converter is not in the low-voltage recovery state; When the grid voltage returns to a normal range, the low-voltage recovery signal is set to 1, indicating that the grid-connected converter is in a low-voltage recovery state.

8. The method according to claim 7, characterized in that The normal range is U g ≥0.9U0, where U g Indicates the grid voltage, U0 indicates the rated grid voltage.

9. A grid-type converter, characterized in that: The grid-type converter includes a control unit, which is used to execute the grid-type converter power grid drop fault control method according to any one of claims 1 to 8.

Images