Method and system for reducing adjusting times of tap switch of sending-end hybrid direct current system

Abstract

The invention discloses a method and system for reducing the adjusting times of a tap switch of a sending-end hybrid direct current system, and the method comprises the steps: obtaining an alternating voltage variation required for enabling a trigger angle to return to a set range when the trigger angle of a commutation converter of a power grid of a sending-end converter station exceeds a limit; adjusting an initial reactive power control reference value of a voltage source converter according to the alternating current voltage variable quantity to obtain an actual reactive power control reference value; acquiring a power grid commutation converter trigger angle based on the actual reactive power control reference value, and if the trigger angle is within a set range, updating the actual reactive power control reference value to an initial reactive power control reference value; and if the trigger angle is still out of limit, adjusting the tap switch. According to the method, unnecessary tap switch adjustment caused by power grid alternating voltage fluctuation can be reduced through coordinated reactive power control of the voltage source converter and the power grid commutation converter.

Description

Technical Field

[0001] This invention belongs to the field of hybrid DC transmission technology, specifically relating to a method for reducing the number of tap changer adjustments in a hybrid DC system at the sending end. Background Technology

[0002] Conventional UHVDC transmission based on grid-commutated converters has advantages such as high voltage levels, large transmission capacity, and mature operating experience, and also has the function of blocking AC / DC fault currents. However, conventional UHVDC transmission faces significant technical bottlenecks in large-scale isolated renewable energy transmission. These bottlenecks mainly stem from the fact that UHVDC converter stations cannot provide the voltage support required for grid connection of renewable energy plants, and there are problems such as high reactive power consumption, severe AC / DC coupling, and the risk of renewable energy disconnection due to AC overvoltage at the sending end. Flexible DC technology based on voltage source converters can achieve independent decoupling control of active and reactive power, offers flexible operation, strong grid support, and facilitates the construction of multi-terminal DC transmission systems and flexible DC grids, giving it a technical advantage in large-scale isolated renewable energy transmission. With the rapid growth in application demand, flexible DC has entered a stage of large-scale practical application. However, flexible DC is limited by the current-carrying capacity of its devices, and the capacity of a single converter station is still somewhat lower than that of conventional UHVDC transmission projects. Furthermore, although the investment cost of flexible DC is rapidly decreasing, it is still much higher than that of conventional UHVDC, which is not conducive to large-scale promotion and application from a technical and economic perspective. By cascading grid-connected phase-change converters and voltage source converters, their respective advantages can be integrated. This can fully combine the advantages of UHVDC transmission, such as large capacity, strong overcurrent capability, low loss, and low cost, while leveraging the advantages of flexible DC active and reactive power regulation, thereby improving the grid voltage support capability and enhancing the stability of the AC system.

[0003] When a hybrid DC power grid is connected to a weak grid, AC voltage fluctuations may occur more frequently, causing the converter transformer tap changer of the grid commutator to be adjusted frequently, affecting the equipment lifespan and the safe and stable operation level of the DC power grid. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for reducing the number of tap changer adjustments in a hybrid DC system at the sending end. This method can reduce unnecessary tap changer adjustments caused by AC voltage fluctuations in the power grid by coordinating reactive power control between the voltage source converter and the grid commutation converter.

[0005] To achieve the above objectives, the solution of the present invention is:

[0006] A method for reducing the number of tap changer adjustments in a hybrid DC system at the sending end includes,

[0007] When the firing angle of the grid phase converter in the sending-end converter station exceeds the limit, the amount of AC voltage change required to bring the firing angle back to the set range is obtained.

[0008] Based on the change in AC voltage, the initial reactive power control reference value of the voltage source converter is adjusted to obtain the actual reactive power control reference value.

[0009] Obtain the grid commutator trigger angle based on the actual reactive power control reference value. If the trigger angle is within the set range, update the actual reactive power control reference value to the initial reactive power control reference value. If the trigger angle still exceeds the limit, adjust the tap changer.

[0010] Among them, when the firing angle of the phase converter in the power grid at the sending-end converter station exceeds the limit, the AC voltage change required to return the firing angle to the set range is obtained, including,

[0011] Get the current trigger angle over-limit value and angle adjustment value;

[0012] Based on the aforementioned over-limit value, the corresponding no-load DC bus voltage U is obtained. di0R,1 Based on the angle adjustment value, the corresponding no-load DC bus voltage U is obtained. di0R,2 ;

[0013] The required AC voltage change to bring the firing angle back to the set range can be calculated using the following formula.

[0014]

[0015] In the formula, ΔU ACR The amount of AC voltage change required to bring the firing angle back to the set range; U AC1R This represents the effective value of the AC line voltage at the moment when the firing angle of the grid-commutated converter exceeds the limit.

[0016] Specifically, the corresponding no-load DC bus voltage is obtained based on the over-limit value; the corresponding no-load DC bus voltage is obtained based on the angle adjustment value; including,

[0017] According to the following relationship

[0018]

[0019] In the formula, α is the over-limit value or angle adjustment value, and d xR d represents the relative inductive voltage drop of the converter transformer in the grid commutator. rR I is the relative resistive voltage drop of the converter transformer in the grid commutator. dR I is the measured value of DC current. dNR For the rated DC current, U di0NR U is the rated no-load DC bus voltage. TRFor the forward voltage drop of the grid commutator, U di0R U is the no-load DC bus voltage corresponding to the over-limit value or angle adjustment value. dR This refers to the DC-side voltage of the grid-commutated converter.

[0020] Specifically, based on the AC voltage change, the initial reactive power control reference value of the voltage source converter is adjusted to obtain the actual reactive power control reference value, including:

[0021] Based on the change in AC voltage, the corresponding change in reactive power can be obtained using the following formula.

[0022]

[0023] In the formula, ΔQ represents the change in reactive power required by the voltage source converter; ΔU ACR The amount of AC voltage change required for the firing angle to return to the set range, I SC This refers to the short-circuit current at the AC busbar. The phase difference between the line voltage and line current of the AC power supply;

[0024] The corresponding reactive power change is superimposed on the initial reactive power control reference value to obtain the actual reactive power control reference value.

[0025] A system for reducing the number of tap changer adjustments in a hybrid DC system at the sending end, comprising:

[0026] The AC voltage change acquisition module is configured to obtain the AC voltage change required to bring the firing angle back to the set range when the firing angle of the grid phase converter in the sending-end converter station exceeds the limit.

[0027] The actual reactive power control reference value acquisition module is configured to adjust the initial reactive power control reference value of the voltage source converter according to the AC voltage change to obtain the actual reactive power control reference value.

[0028] The trigger angle acquisition module is configured to acquire the grid commutator trigger angle based on the actual reactive power control reference value;

[0029] The reactive power control reference value adjustment module is configured to update the actual reactive power control reference value to the initial reactive power control reference value when the trigger angle is within a set range; and,

[0030] The tap changer adjustment module is configured to adjust the tap changer when the trigger angle is still out of limit.

[0031] The AC voltage change acquisition module obtains the AC voltage change required to return the firing angle to the set range when the firing angle of the grid commutator in the sending-end converter station exceeds the limit. This includes...

[0032] Get the current trigger angle over-limit value and angle adjustment value;

[0033] Based on the aforementioned over-limit value, the corresponding no-load DC bus voltage U is obtained. di0R,1 Based on the angle adjustment value, the corresponding no-load DC bus voltage U is obtained. di0R,2 ;

[0034] The required AC voltage change to bring the firing angle back to the set range can be calculated using the following formula.

[0035]

[0036] In the formula, ΔU ACR The amount of AC voltage change required to bring the firing angle back to the set range; U AC1R This represents the effective value of the AC line voltage at the moment when the firing angle of the grid-commutated converter exceeds the limit.

[0037] Specifically, the corresponding no-load DC bus voltage is obtained based on the over-limit value; the corresponding no-load DC bus voltage is obtained based on the angle adjustment value; including,

[0038] According to the following relationship

[0039]

[0040] In the formula, α is the over-limit value or angle adjustment value, and d xR d represents the relative inductive voltage drop of the converter transformer in the grid commutator. rR I is the relative resistive voltage drop of the converter transformer in the grid commutator. dR I is the measured value of DC current. dNR For the rated DC current, U di0NR U is the rated no-load DC bus voltage. TR For the forward voltage drop of the grid commutator, U di0R U is the no-load DC bus voltage corresponding to the over-limit value or angle adjustment value. dR This refers to the DC-side voltage of the grid-commutated converter.

[0041] The actual reactive power control reference value acquisition module adjusts the initial reactive power control reference value of the voltage source converter based on the AC voltage change to obtain the actual reactive power control reference value, including:

[0042] Based on the change in AC voltage, the corresponding change in reactive power can be obtained using the following formula.

[0043]

[0044] In the formula, ΔQ represents the change in reactive power required by the voltage source converter; ΔUACR The amount of AC voltage change required for the firing angle to return to the set range, I SC This refers to the short-circuit current at the AC busbar. The phase difference between the line voltage and line current of the AC power supply;

[0045] The corresponding reactive power change is superimposed on the initial reactive power control reference value to obtain the actual reactive power control reference value.

[0046] A computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor; the processor, when executing the computer program, implements the steps of the method for reducing the number of tap changer adjustments in a hybrid DC system at the sending end as described above.

[0047] A computer-readable storage medium storing a computer program; when executed by a processor, the computer program implements the steps of the method for reducing the number of tap changer adjustments in a hybrid DC system at the sending end, as described above.

[0048] After adopting the above scheme, the sending-end converter station of the hybrid DC system in this invention uses a grid-commutated converter and a voltage source converter connected in series. When the AC system voltage fluctuates frequently, the tap changer of the grid-commutated converter will experience frequent adjustments. Therefore, this invention estimates the amount of AC voltage change required to restore the firing angle of the grid-commutated converter to a set range, and then adjusts the reactive power output or absorption of the voltage source converter, thereby reducing the repeated adjustments of the tap changer of the grid-commutated converter caused by AC voltage fluctuations. This invention does not require modification to the current converter station hardware configuration, has low implementation difficulty, and helps ensure the safety and lifespan of the converter station's tap changer. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the topology of a hybrid cascaded ultra-high voltage direct current transmission system for the sending end, which is the subject of this invention.

[0050] Figure 2 This is a schematic flowchart of a method for reducing the number of tap changer adjustments in a hybrid DC system at the sending end, provided by the present invention.

[0051] Figure 3 This is a response waveform diagram of a DC system in an embodiment of the present invention that reduces the adjustment of the tap changer of the grid commutator when the AC grid rises.

[0052] Among them, (a) is the power grid voltage waveform, (b) is the power grid phase-commutation converter firing angle waveform, (c) is the voltage source converter reactive power waveform, and (d) is the tap changer position waveform.

[0053] Figure 4This is a response waveform diagram of a DC system in an embodiment of the present invention that reduces the adjustment of the tap changer of the grid commutator when the AC grid voltage drops.

[0054] Among them, (a) is the power grid voltage waveform, (b) is the power grid phase-commutation converter firing angle waveform, (c) is the voltage source converter reactive power waveform, and (d) is the tap changer position waveform. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of protection of the invention.

[0056] This invention provides a method for reducing the number of tap changer adjustments in a hybrid DC system at the sending end. The sending-end converter station of the hybrid DC system employs a grid-commutated converter and a voltage source converter connected in series. When AC system voltage fluctuations cause the grid-commutated converter angle at the sending-end converter station to exceed its limit, triggering a tap changer adjustment command, the tap changer is not adjusted initially. The AC voltage change required for the trigger angle to return to the set range is calculated. Based on the required AC voltage change, the reactive power change ΔQ required by the voltage source converter is calculated, and the reactive power reference value of the voltage source converter is updated. If the trigger angle returns to the set range at this point, the tap changer is no longer adjusted. If the trigger angle continues to exceed the limit, the tap changer is adjusted. When the trigger angle is detected to have returned to the set range, the reactive power change ΔQ of the voltage source converter is reduced to 0.

[0057] The specific method for calculating the required reactive power change ΔQ of the voltage source converter based on the required AC voltage change is as follows:

[0058]

[0059] In the formula, ΔU ACR The amount of AC voltage change required for the firing angle to return to the set range, I SC This refers to the short-circuit current at the AC busbar. This represents the phase difference between the line voltage and line current of the AC power supply.

[0060] Among them, the AC voltage change ΔU required to bring the firing angle of the grid commutator back within the set range. ACR The calculation method is as follows:

[0061]

[0062] In the formula, U AC1R U is the effective value of the AC line voltage corresponding to the moment when the firing angle of the grid commutator exceeds the limit. di0R,1U is the no-load DC bus voltage corresponding to the moment when the firing angle of the grid commutator exceeds the limit. di0R,2 This refers to the no-load DC bus voltage when the firing angle of the grid-commutated converter is equal to the preset reference value.

[0063] The relationship between the no-load DC bus voltage and the firing angle of the grid-commutated converter is as follows:

[0064]

[0065] In the formula, α is the firing angle of the grid commutator converter, and d xR d represents the relative inductive voltage drop of the converter transformer in the grid commutator. rR I is the relative resistive voltage drop of the converter transformer in the grid commutator. dR I is the measured value of DC current. dNR For the rated DC current, U di0NR U is the rated no-load DC bus voltage. di0R U represents the actual no-load DC bus voltage of the tap changer. TR For the forward voltage drop of the grid commutator, U dR This refers to the DC-side voltage of the grid-commutated converter.

[0066] In the operation of the sending-end hybrid DC transmission system, when the firing angle of the grid commutator needs to exceed the lower limit α... min When the adjustment command is about to be issued, do not adjust the tap changer first. Calculate the reactive power compensation amount ΔQ required to increase the angle by Δα, and add ΔQ to the original reactive power control reference value of the voltage source converter. When the angle returns to α... ref After that, reduce ΔQ to 0. When the firing angle of the grid commutator needs to exceed the upper limit α... max When the adjustment command is about to be issued, do not adjust the tap changer first. Calculate the reactive power compensation amount ΔQ required to lower the angle by Δα, and add ΔQ to the original reactive power control reference value of the voltage source converter. When the angle returns to α... ref After that, reduce ΔQ to 0.

[0067] Where, α min The value range is [10, 12.5] degrees, α max The value range of is [17.5, 25] degrees, and the value range of Δα is [1, 1.5] degrees. ref The value range is [15, 17] degrees.

[0068] Among them, the grid-commutated converter and the voltage source converter need to be connected to the same AC grid.

[0069] The method of the present invention will now be described in detail with reference to a specific embodiment. First, as... Figure 1The diagram shown is a schematic diagram of the topology of a single converter station in a hybrid cascaded ultra-high voltage direct current system applied in this invention. The positive and negative terminals of the DC side of the converter station are each composed of a grid-commutated converter 1 and a voltage source converter 2 connected in series. The grid-commutated converter 1 is a high-end converter, and the voltage source converter 2 is a low-end converter. The AC side of each converter is connected to the AC bus 4, and each AC filter group 3 is connected to the AC bus 4. The AC bus 4 is connected to the power grid.

[0070] Cooperate Figure 2 The method for reducing the number of tap changer adjustments in a hybrid DC system at the sending end specifically includes the following steps:

[0071] Step S110: When the trigger angle of the grid phase converter is about to trigger the tap changer adjustment command due to exceeding the limit, do not adjust the tap changer first, and calculate the amount of AC voltage change required to adjust the trigger angle back to the set range.

[0072] Step S120: Calculate the reactive power change ΔQ of the voltage source converter output based on the required AC voltage change, and update the reactive power reference value of the voltage source converter.

[0073] Step S130: When the firing angle is detected to have returned to the set range, reduce the reactive power change ΔQ of the voltage source converter to 0.

[0074] Figure 3 This is the response waveform of the DC system in this embodiment of the invention, which reduces the regulation of the tap changer of the grid commutator when the AC grid voltage rises. (a) represents the grid voltage U. s Waveform diagrams: (b) shows the firing angle waveform of the grid-commutated converter; (c) shows the reactive power Q waveform of the voltage source converter. vsc Waveform diagram, (d) is the tap position waveform diagram of the tap changer.

[0075] Figure 4 This is the response waveform of the DC system in this embodiment of the invention, which reduces the regulation of the tap changer of the grid commutator when the AC grid voltage drops, where (a) is the grid voltage U. s Waveform diagrams: (b) shows the firing angle waveform of the grid-commutated converter; (c) shows the reactive power Q waveform of the voltage source converter. vsc Waveform diagram, (d) is the tap position waveform diagram of the tap changer.

[0076] The following is combined with Figures 1 to 4 Here we will introduce Example 1 and Example 2.

[0077] Example 1: Targeting Figure 1 The topology shown has a normal operating range of [12.5, 17.5] degrees for the grid-commutated converter firing angle. (From...) Figure 3 As can be seen, when the DC system is in steady-state operation, the DC active power is 2000MW, the reactive power output of the voltage source converter is 0Mvar, and the AC system voltage starts to rise at 0.8s, causing the angle of the grid commutator converter to exceed the upper limit of 17.5 degrees. According to the traditional control method, the tap changer will adjust at this time to bring the firing angle back within the range. However, according to the method proposed by this invention, the tap changer is not adjusted at this time. At 2s, the control system adjusts the reactive power reference value of the voltage source converter according to the method proposed by this invention. The voltage source converter absorbs about 75Mvar of reactive power from the grid, thereby reducing the AC voltage and bringing the angle of the grid commutator converter back to the normal operating range. The tap changer position remains unchanged throughout the process.

[0078] Example 2: Targeting Figure 1 The topology shown has a normal operating range of [12.5, 17.5] degrees for the grid-commutated converter firing angle. (From...) Figure 4 As can be seen, when the DC system is in steady-state operation, the DC active power is 2000MW, the reactive power output of the voltage source converter is 0Mvar, and the AC system voltage begins to drop at 0.8s, causing the angle of the grid commutator converter to exceed the lower limit of 12.5 degrees. According to the traditional control method, the tap changer will adjust at this time to bring the firing angle back within the range. However, according to the method proposed by this invention, the tap changer is not adjusted at this time. At 2s, the control system adjusts the reactive power reference value of the voltage source converter according to the method proposed by this invention. The voltage source converter sends about 95Mvar of reactive power to the grid, thereby increasing the AC voltage and bringing the angle of the grid commutator converter back to the normal operating range. The tap changer position remains unchanged throughout the process.

[0079] This invention also provides a system for reducing the number of tap changer adjustments in a hybrid DC system at the sending end, comprising:

[0080] The AC voltage change acquisition module is configured to obtain the AC voltage change required to bring the firing angle back to the set range when the firing angle of the grid phase converter in the sending-end converter station exceeds the limit.

[0081] The actual reactive power control reference value acquisition module is configured to adjust the initial reactive power control reference value of the voltage source converter according to the AC voltage change to obtain the actual reactive power control reference value.

[0082] The trigger angle acquisition module is configured to acquire the grid commutator trigger angle based on the actual reactive power control reference value;

[0083] The reactive power control reference value adjustment module is configured to update the actual reactive power control reference value to the initial reactive power control reference value when the trigger angle is within a set range; and,

[0084] The tap changer adjustment module is configured to adjust the tap changer when the trigger angle is still out of limit.

[0085] This invention also provides another computer device, including a processor and a memory configured to store a computer program capable of running on the processor; wherein, when the processor is configured to run the computer program, it performs the method steps described in the foregoing embodiments.

[0086] In practical applications, the aforementioned processor includes a Field-Programmable Gate Array (FPGA), and the processor can be a Central Processing Unit (CPU) or a Digital Signal Processor (DSP). It is understood that for different devices, the electronic devices used to implement the functions of the aforementioned processor can also be other types, and this embodiment of the invention does not impose specific limitations.

[0087] The aforementioned memory can be volatile memory, such as random-access memory (RAM); or non-volatile memory, such as read-only memory (ROM), flash memory, hard disk drive (HDD), or solid-state drive (SSD); or a combination of the above types of memory, and provides instructions and data to the processor.

[0088] In an exemplary embodiment, the present invention also provides a computer-readable storage medium for storing a computer program.

[0089] Optionally, the computer-readable storage medium can be applied to any of the methods in the embodiments of the present invention, and the computer program causes the computer to execute the corresponding processes implemented by the processor in the various methods of the embodiments of the present invention. For the sake of brevity, these will not be described in detail here.

[0090] In the several embodiments provided by this invention, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods, such as: multiple units or components can be combined, or integrated into another system, or some features can be ignored or not executed. In addition, the coupling, direct coupling, or communication connection between the various components shown or discussed can be through some interfaces, and the indirect coupling or communication connection between devices or units can be electrical, mechanical, or other forms.

[0091] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0092] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0093] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0094] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0095] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0096] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for reducing the number of tap changer adjustments in a hybrid DC system at the sending end, characterized in that: include, When the firing angle of the grid phase converter in the sending-end converter station exceeds the limit, the amount of AC voltage change required to bring the firing angle back to the set range is obtained. Based on the change in AC voltage, the initial reactive power control reference value of the voltage source converter is adjusted to obtain the actual reactive power control reference value. Obtain the grid commutator trigger angle based on the actual reactive power control reference value. If the trigger angle is within the set range, update the actual reactive power control reference value to the initial reactive power control reference value. If the trigger angle still exceeds the limit, adjust the tap changer.

2. The method as described in claim 1, characterized in that: When the firing angle of the phase converter in the power grid at the sending-end converter station exceeds the limit, the AC voltage change required to bring the firing angle back to the set range is obtained. include, Get the current trigger angle over-limit value and angle adjustment value; Based on the aforementioned over-limit value, the corresponding no-load DC bus voltage U is obtained. di0R,1 Based on the angle adjustment value, the corresponding no-load DC bus voltage U is obtained. di0R,2 ; The required AC voltage change to bring the firing angle back to the set range can be calculated using the following formula. In the formula, ΔU ACR The amount of AC voltage change required to bring the firing angle back to the set range; U AC1R This represents the effective value of the AC line voltage at the moment when the firing angle of the grid-commutated converter exceeds the limit.

3. The method as described in claim 2, characterized in that: Based on the over-limit value, the corresponding no-load DC bus voltage is obtained; based on the angle adjustment value, the corresponding no-load DC bus voltage is obtained. include, According to the following relationship In the formula, α is the over-limit value or angle adjustment value, and d xR d represents the relative inductive voltage drop of the converter transformer in the grid commutator. rR I is the relative resistive voltage drop of the converter transformer in the grid commutator. dR I is the measured value of DC current. dNR For the rated DC current, U di0NR U is the rated no-load DC bus voltage. TR For the forward voltage drop of the grid commutator, U di0R U is the no-load DC bus voltage corresponding to the over-limit value or angle adjustment value. dR This refers to the DC-side voltage of the grid-commutated converter.

4. The method as described in claim 1, characterized in that: Based on the AC voltage change, the initial reactive power control reference value of the voltage source converter is adjusted to obtain the actual reactive power control reference value, including: Based on the change in AC voltage, the corresponding change in reactive power can be obtained using the following formula. In the formula, ΔQ represents the change in reactive power required by the voltage source converter; ΔU ACR The amount of AC voltage change required for the firing angle to return to the set range, I SC This refers to the short-circuit current at the AC busbar. The phase difference between the line voltage and line current of the AC power supply; The corresponding reactive power change is superimposed on the initial reactive power control reference value to obtain the actual reactive power control reference value.

5. A system for reducing the number of tap changer adjustments in a hybrid DC system at the sending end, characterized in that: include, The AC voltage change acquisition module is configured to obtain the AC voltage change required to bring the firing angle back to the set range when the firing angle of the grid phase converter in the sending-end converter station exceeds the limit. The actual reactive power control reference value acquisition module is configured to adjust the initial reactive power control reference value of the voltage source converter according to the AC voltage change to obtain the actual reactive power control reference value. The trigger angle acquisition module is configured to acquire the grid commutator trigger angle based on the actual reactive power control reference value; The reactive power control reference value adjustment module is configured to update the actual reactive power control reference value to the initial reactive power control reference value when the trigger angle is within a set range. as well as, The tap changer adjustment module is configured to adjust the tap changer when the trigger angle is still out of limit.

6. The system as described in claim 5, characterized in that: When the firing angle of the phase converter in the power grid at the sending-end converter station exceeds the limit, the AC voltage change acquisition module obtains the AC voltage change required to return the firing angle to the set range. include, Get the current trigger angle over-limit value and angle adjustment value; Based on the aforementioned over-limit value, the corresponding no-load DC bus voltage U is obtained. di0R,1 Based on the angle adjustment value, the corresponding no-load DC bus voltage U is obtained. di0R,2 ; The required AC voltage change to bring the firing angle back to the set range can be calculated using the following formula. In the formula, ΔU ACR The amount of AC voltage change required to bring the firing angle back to the set range; U AC1R This represents the effective value of the AC line voltage at the moment when the firing angle of the grid-commutated converter exceeds the limit.

7. The system as described in claim 6, characterized in that: Based on the over-limit value, the corresponding no-load DC bus voltage is obtained; based on the angle adjustment value, the corresponding no-load DC bus voltage is obtained. include, According to the following relationship In the formula, α is the over-limit value or angle adjustment value, and d xR d represents the relative inductive voltage drop of the converter transformer in the grid commutator. rR I is the relative resistive voltage drop of the converter transformer in the grid commutator. dR I is the measured value of DC current. dNR For the rated DC current, U di0NR U is the rated no-load DC bus voltage. TR For the forward voltage drop of the grid commutator, U di0R U is the no-load DC bus voltage corresponding to the over-limit value or angle adjustment value. dR This refers to the DC-side voltage of the grid-commutated converter.

8. The system as described in claim 5, characterized in that: The actual reactive power control reference value acquisition module adjusts the initial reactive power control reference value of the voltage source converter based on the AC voltage change to obtain the actual reactive power control reference value, including: Based on the change in AC voltage, the corresponding change in reactive power can be obtained using the following formula. In the formula, ΔQ represents the change in reactive power required by the voltage source converter; ΔU ACR The amount of AC voltage change required for the firing angle to return to the set range, I SC This refers to the short-circuit current at the AC busbar. The phase difference between the line voltage and line current of the AC power supply; The corresponding reactive power change is superimposed on the initial reactive power control reference value to obtain the actual reactive power control reference value.

9. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor; characterized in that: When the processor executes the computer program, it implements the steps of the method for reducing the number of tap changer adjustments in a hybrid DC system as described in any one of claims 1 to 4.

10. A computer-readable storage medium storing a computer program; characterized in that: When the computer program is executed by the processor, it implements the steps of the method for reducing the number of tap changer adjustments in a hybrid DC system as described in any one of claims 1 to 4.

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