A method and system for reducing frequent operation of a tapping switch at a receiving converter station

Abstract

This invention relates to a method and system for reducing frequent tap changer operations at receiving-end converter stations. The method includes: determining the dead zone range of the receiving-end converter station's shut-off angle; determining the relationship between the dynamic proportional coefficient h and the number of tap changer operations based on the operating characteristics of the UHVDC transmission system; and determining an initial value for the shut-off angle that reduces frequent tap changer operations at the receiving-end converter station based on the determined dead zone range of the receiving-end converter station's shut-off angle and the relationship between the dynamic proportional coefficient h and the number of tap changer operations. This invention can significantly reduce the number of tap changer operations at receiving-end converter stations, thereby reducing the probability of converter transformer failures and improving the operational reliability of converter transformers at the converter station. This invention can be widely applied in the field of power transmission system technology.

Description

Technical Field

[0001] This invention belongs to the field of power transmission system technology, and in particular relates to a method and system for reducing the frequent operation of tap changers at receiving-end converter stations in ultra-high voltage direct current transmission projects. Background Technology

[0002] Ultra-high voltage direct current (UHVDC) transmission is the main technical means for transmitting power resources from large-scale energy bases in western China to load centers in central and eastern my country over long distances. With the continuous development of new power systems, the power grid has put forward higher requirements for the operational reliability, control flexibility, and equipment safety of UHVDC transmission.

[0003] With the large-scale integration of new energy sources into the UHVDC system, converter station voltage fluctuations are frequent and stability issues are prominent. When DC power or voltage repeatedly deviates from the target value, it can cause the tap changer to operate continuously, creating safety hazards for the converter transformer and on-load tap changer equipment. Summary of the Invention

[0004] To address the aforementioned problems, the purpose of this invention is to provide a method and system for reducing the frequent operation of tap changers in receiving-end converter stations. This method can significantly reduce the frequency of tap changer operation in receiving-end converter stations, is simple to implement, does not require changes to the converter station configuration, and can greatly improve the operational reliability of tap changers.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for reducing frequent operation of tap changers in receiving-end converter stations, comprising:

[0007] Determine the dead zone range of the turn-off angle of the receiving-end converter station;

[0008] Based on the operating characteristics of the UHVDC transmission system, the relationship between the dynamic proportional coefficient h and the number of tap changer operations is determined.

[0009] Based on the determined dead zone range of the cut-off angle of the receiving-end converter station and the relationship between the dynamic proportional coefficient h and the number of tap changer operations, the initial value of the cut-off angle that can reduce the frequent operation of the tap changer of the receiving-end converter station is determined.

[0010] Furthermore, the dead zone range of the shut-off angle of the receiving-end converter station is [17.5°, 25°].

[0011] Furthermore, determining the relationship between the dynamic proportional coefficient h and the number of tap changer operations based on the operating characteristics of the UHVDC transmission system includes:

[0012] Based on DC transmission theory, the relationship between the turn-off angle and DC current is established.

[0013] Based on the relationship between the turn-off angle and the DC current, the functional relationship between the dynamic proportional coefficient h and different operating modes of the UHVDC transmission system is determined.

[0014] Statistical analysis was conducted on the number of tap changer operations under different operating modes of the UHVDC transmission system to determine the relationship between the dynamic proportional coefficient h and the number of tap changer operations.

[0015] Furthermore, the functional relationship between the dynamic proportional coefficient h and different operating modes of the UHVDC transmission system is as follows:

[0016]

[0017] In the formula, R d d is the DC circuit line resistance; n is the number of converters put into operation at the receiving-end converter station; xI For the commutation reactance on the inverter side; I dN Rated DC current; U di0IN This is the ideal DC no-load DC voltage.

[0018] Furthermore, the determination of the initial value of the shut-off angle that can reduce frequent tap changer operations at the receiving-end converter station, based on the determined dead zone range of the shut-off angle of the receiving-end converter station and the relationship between the dynamic proportional coefficient h and the number of tap changer operations, includes:

[0019] Based on the operating mode of the UHVDC transmission system to be analyzed, determine the specific value of the dynamic proportional coefficient h.

[0020] The initial value of the shut-off angle is determined based on the specific value of the dynamic proportional coefficient and the relationship between the dynamic proportional coefficient h and the number of tap changer operations.

[0021] Furthermore, determining the initial value of the shut-off angle based on the specific value of the dynamic proportional coefficient and the relationship between the dynamic proportional coefficient h and the number of tap changer operations includes:

[0022] ① When h>0, the pre-adjusted tap changer makes the turn-off angle at the lower limit of the dead zone 17.5° when unlocking. At this time, the margin between the turn-off angle and the upper limit of the dead zone 25° is the largest. As the DC current increases, the turn-off angle will gradually increase and the number of tap changer operations will decrease.

[0023] ②When h=0, the pre-adjusted tap changer makes the turn-off angle at the rated value of 19.5° when unlocked. As the DC current increases, the turn-off angle can always remain unchanged, with the same margin range of 17.5° and 25°.

[0024] ③ When h<0, the pre-adjusted tap changer makes the turn-off angle at the upper limit of the dead zone 25° when unlocking. At this time, the margin between the turn-off angle and the lower limit of the dead zone 17.5° is the largest. As the DC current increases, the turn-off angle gradually decreases and the number of tap changer operations decreases.

[0025] Furthermore, in step ①, when h > 0 and there is no available reactive power compensation equipment, after adjusting the dead zone range of the shut-off angle to [17.5°, 21.5°], the tap changer is pre-adjusted so that the shut-off angle is the rated value of 19.5° when unlocked.

[0026] Secondly, the present invention provides a system for reducing frequent operation of tap changers in receiving-end converter stations, comprising:

[0027] Angle range determination module, used to determine the dead zone range of the shut-off angle of the receiving-end converter station;

[0028] The function relationship establishment module is used to determine the relationship between the dynamic proportional coefficient h and the number of tap changer operations based on the operating characteristics of the UHVDC transmission system.

[0029] The adjustment module is used to determine the initial value of the shut-off angle that can reduce the frequent operation of the tap changer at the receiving-end converter station, based on the dead zone range of the shut-off angle of the receiving-end converter station and the relationship between the dynamic proportional coefficient h and the number of tap changer operations.

[0030] Thirdly, the present invention provides a computer-readable storage medium for storing one or more programs, the one or more programs including instructions that, when executed by a computing device, cause the computing device to perform any of the methods.

[0031] Fourthly, the present invention provides a computing device comprising: one or more processors and a memory, wherein the memory stores one or more programs and is configured to be executed by the one or more processors, the one or more programs including instructions for performing any method.

[0032] The present invention has the following advantages due to the adoption of the above technical solutions:

[0033] 1. This invention is for receiving-end converter stations, which need to calculate the value of the dynamic proportional coefficient h according to different operating modes of the DC system, and further dynamically adjust the initial value of the firing angle at the initial power according to the value of the dynamic proportional coefficient h;

[0034] 2. By adjusting the angle adjustment range of the shut-off angle from the traditional [17.5°, 21°] to [17.5°, 25°], this invention can effectively reduce the number of tap changer operations, greatly reduce the risk of tap changer failure, and improve the operational reliability of the converter station.

[0035] 3. According to the specific operating conditions of the DC system, for the operating condition with an initial angle of 17.5 degrees, the trigger angle range needs to be adjusted to [17.5°, 21.5°] when there is no available reactive power equipment.

[0036] 4. This invention only requires modification to the soft pressure plate, without modifying the hardware, and does not affect other operating performance of the converter station, and can be flexibly applied to existing and newly built projects.

[0037] Therefore, this invention can be widely applied in the field of power transmission system technology. Attached Figure Description

[0038] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings:

[0039] Figure 1 This is a flowchart of a method for reducing frequent operation of tap changers in receiving-end converter stations, provided by an embodiment of the present invention.

[0040] Figure 2 The DC power of the bipolar full-voltage operation mode provided in this embodiment of the invention is increased from 0.1 pu to 1.0 pu;

[0041] Figure 3 The DC power of the single-pole full-voltage metal loop operation mode provided in this embodiment of the invention is increased from 0.1 pu to 1.0 pu;

[0042] Figure 4 The DC power of the single-pole semi-voltage metal loop operation mode provided in this embodiment of the invention is increased from 0.1 pu to 1.0 pu. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0044] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0045] This invention relates to a method for reducing frequent tap changer operations at receiving-end converter stations. The method includes: for receiving-end converter stations in UHVDC transmission projects, determining the value of a dynamic proportional coefficient h based on the relationship between the shut-off angle and the DC current; determining the initial range of the shut-off angle based on the value of the dynamic proportional coefficient h, wherein the shut-off angle range is set to [17.5°, 25°]. When the dynamic proportional coefficient h is greater than 0, the shut-off angle needs to be adjusted to [17.5°, 21.5°] when no available reactive power compensation equipment is available. This invention can significantly reduce the number of tap changer operations at receiving-end converter stations, thereby reducing the probability of converter transformer failure and improving the operational reliability of the converter transformers at the converter station.

[0046] Correspondingly, in other embodiments of the present invention, a system, device, and medium are provided to reduce the frequent operation of tap changers in receiving-end converter stations.

[0047] Example 1

[0048] like Figure 1 As shown, this embodiment provides a method for reducing frequent operation of tap changers in receiving-end converter stations, which includes the following steps:

[0049] 1) Based on engineering experience, determine the dead zone range of the cut-off angle of the receiving-end converter station.

[0050] In ultra-high voltage direct current (UHVDC) projects with a DC power of 8 GW or above, a constant DC voltage control strategy is typically adopted on the inverter side. In this strategy, the firing angle control maintains the DC voltage at the target value, while the tap changer is used to control the turn-off angle γ within the dead zone. For example, in the Qinghai-Henan, Ya'an-Jiangxi, and Shaanxi-Wuhan projects already in operation, the rated turn-off angle on the inverter side is 19.5°. When the turn-off angle γ exceeds the dead zone range of [17.5°, 21.5°], adjusting the tap changer to change the valve-side voltage can bring the turn-off angle γ back within the dead zone.

[0051] Based on the long-term operational experience of ultra-high voltage direct current (UHVDC) projects such as Qinghai-Henan and Yajiang, where the sending end has a large angle of 25 degrees, this invention adjusts the dead zone range of the receiving end converter station's turn-off angle to [17.5°, 25°]. The rated turn-off angle on the inverter side is 19.5°. When the turn-off angle γ exceeds the range of [17.5°, 25°], the valve-side voltage is changed by adjusting the tap changer, so that the turn-off angle γ returns to the dead zone range. This range is expanded from the original 4-degree dead zone space to 7.5 degrees, approximately doubled, and the number of tap changer operations can be significantly improved.

[0052] 2) Based on the operating characteristics of the UHVDC transmission system, determine the relationship between the dynamic proportional coefficient h and the number of tap changer operations.

[0053] Specifically, it includes the following steps:

[0054] 2.1) Based on the DC transmission theory, establish the relationship between the turn-off angle and the DC current.

[0055] According to DC transmission theory, the DC voltage on the rectifier side can be expressed as:

[0056]

[0057]

[0058] In the formula, n is the number of converters put into operation at the receiving-end converter station; U dR The rectifier side has a 6-pulse DC voltage; R d For DC circuit line resistance, R is the resistance of the metal circuit. d =2R m Regarding the Earth's orbital mode, R d =R m +R e , where R e R is the grounding resistance. m For DC line resistance; I d γ is the DC current; γ is the inverter-side turn-off angle; d xI For the commutation reactance on the inverter side; I dN Rated DC current; U di0IN U is the ideal DC no-load DC voltage; di0I This is the ideal no-load DC voltage with 6 pulsations on the inverter side.

[0059] Equation (2) above reflects the 6-pulse DC voltage U on the rectifier side. dR Inverter-side turn-off angle γ, inverter-side commutation reactance d xI DC line resistance R m and DC current I d The relationship between them. In the constant DC voltage control strategy, U dR For ultra-high voltage direct current (UHVDC) projects, the target value is typically 800kV, which is also the value in equation (2), except for the inverter side turn-off angle γ and the DC current I. d Apart from that, all other quantities are constants.

[0060] 2.2) Based on the relationship between the turn-off angle and the DC current, determine the functional relationship between the dynamic proportional coefficient h and different operating modes of the UHVDC transmission system.

[0061] Based on the above analysis of formula (2), the dynamic scaling factor h is defined as follows in this embodiment:

[0062]

[0063] For ultra-high voltage direct current (UHVDC) transmission projects, the operating mode determines the number of converters n that are put into operation at the receiving-end converter station. Specifically, the different operating modes of UHVDC transmission projects and the corresponding number of converters n put into operation at the receiving-end converter station are shown in Table 1 below.

[0064] Table 1. Number of converters put into operation at receiving-end converter stations under different operating modes of UHVDC transmission projects.

[0065] Operating mode n Bipolar 4 Unipolar 4 Monopolar metal 4 Bipolar half-pressure 2 Single-element half-pressure 2 Monopolar metal half-pressure 2

[0066] 2.3) Statistical analysis was conducted on the number of tap changer operations under different operating modes of the UHVDC transmission system to determine the relationship between the dynamic proportional coefficient h and the number of tap changer operations.

[0067] In this embodiment, after statistically analyzing the bipolar full-voltage operation times of currently operational UHVDC projects such as the Xiangshang, Hazheng, Jinsu, Xizhe, Jiuhu, and Xizhe projects, it was found that when the relative inductive voltage drop d... x When the resistance is close to that of the DC circuit line, the tap changer at the receiving end converter station operates less frequently. The statistical results are shown in Table 2 below.

[0068] Among them, the relative inductive pressure drop d x It can be represented as:

[0069] d x =1 / 2×U k %×U dioN / I dN (4)

[0070] In the formula, U k % represents the short-circuit impedance of the converter transformer.

[0071] Table 2. Statistics on the number of receiving-end operations under different DC circuit line resistances in different DC transmission projects during bipolar full-voltage operation.

[0072]

[0073] Table 2 only shows the statistical results. Further analysis shows that the DC circuit line resistance Rd is divided into different voltages on each 6-pulse under different operating modes, with the full-voltage ground operating mode being the most common. Therefore, the DC resistance is divided into four 6-pulse valve groups, and then compared using h = RN / 4 - dx. The results are shown in Table 3. The results show that the number of times the bipolar full-voltage tap changer operates is related to the h value. The larger the h value, the more times the tap changer operates.

[0074] Table 3. Statistics on the number of receiving-end operations under different resistances in different DC transmission projects during bipolar full-voltage operation.

[0075]

[0076] As shown in Equation 2, for a certain operating mode, h is fixed and Ud remains unchanged. However, as the DC power increases, Id increases. The factor affecting the tap changer operation is Udi0I. To minimize tap changer operations, Udi0I should remain as constant as possible. In this case, cosγ should decrease to maintain the validity of Equation 2. Therefore, when h > 0, the initial angle of γ should be 17.5 degrees. As the power gradually increases from 0.1 to 1.0 pu, cosγ gradually decreases, Id gradually increases, Ud remains constant, and Udi0I remains essentially constant, thus reducing the number of tap changer operations. Similarly, when h < 0, the initial angle of γ should be 25 degrees. As the power gradually increases from 0.1 to 1.0 pu, cosγ gradually increases, Id gradually increases, Ud remains constant, and Udi0I remains essentially constant, reducing the number of tap changer operations. When h = 0, γ can be maintained at the rated angle of 19.5 degrees.

[0077] 3) Based on the determined dead zone range of the cut-off angle of the receiving-end converter station and the relationship between the dynamic proportional coefficient h and the number of tap changer operations, the initial value of the cut-off angle is determined to reduce the frequent operation of the tap changer of the receiving-end converter station.

[0078] For a specific DC project, under a certain main wiring operation mode (e.g., full voltage / half voltage, earth return / metal return), h is a fixed value. For a constant DC voltage control strategy, when the turn-off angle γ exceeds the dead zone, the tap changer will actuate to bring the turn-off angle γ back into the dead zone. If the tap changer position can be adjusted before unlocking or even before the converter transformer is charged, it is possible to ensure that the turn-off angle γ is within the dead zone as much as possible during the power increase process, thereby reducing the number of tap changer actuations.

[0079] Specifically, it includes the following steps:

[0080] 3.1) Determine the specific value of the dynamic proportional coefficient h based on the operating mode of the UHVDC transmission system to be analyzed.

[0081] 3.2) Determine the initial value of the shut-off angle based on the specific value of the dynamic proportional coefficient and the relationship between the dynamic proportional coefficient h and the number of tap changer operations.

[0082] The specific strategies are as follows:

[0083] ① When h>0, the pre-adjusted tap changer makes the turn-off angle at the lower limit of the dead zone of 17.5 degrees when unlocking. As the DC current increases, the turn-off angle will gradually increase, and the margin in the range of 25 degrees is large, reducing the number of tap changer operations.

[0084] ②When h=0, the pre-adjusted tap changer makes the turn-off angle at the rated value of 19.5 degrees when unlocked. As the DC current increases, the turn-off angle can always remain unchanged, and the margin range of 17.5 degrees and 25 degrees is the same.

[0085] ③ When h<0, the pre-adjusted tap changer makes the turn-off angle at the upper limit of the dead zone of 25 degrees when unlocking. As the DC current increases, the turn-off angle gradually decreases, and the margin in the range of 17.5 degrees is large, reducing the number of tap changer operations.

[0086] This method of pre-adjusting the tap changer based on the main wiring operation mode maximizes the utilization of the dead zone of the turn-off angle. The pre-adjusted tap changer ensures that the turn-off angle after unlocking is at the upper limit of the dead zone. Although the angle is large at this point, the reactive power consumption is low due to the low power output. As the power increases, the turn-off angle naturally decreases, resulting in less reactive power consumption compared to situations with a larger turn-off angle at the same power output.

[0087] Preferably, in step 3.1) above, when h > 0 and there is no available reactive power compensation equipment, the initial angle range of the shut-off angle needs to be adjusted to [17.5°, 21.5°]. This is because the receiving-end shut-off angle of a typical UHVDC converter station is [17.5°, 21.5°], and reactive power configuration is also configured according to this angle range. When the angle is expanded to 25 degrees, it may cause insufficient reactive power. Therefore, when there is no available reactive power compensation equipment, the shut-off angle range is adjusted to [17.5°, 21.5°].

[0088] Example 2

[0089] This embodiment uses the Shaanxi-Wuhan DC transmission project as an example to illustrate the design results of the project.

[0090] 1. Design Results

[0091] 1) Comparison of effects with the original strategy

[0092] like Figures 2-4 As shown, taking the Shaanxi-Wuhan UHVDC transmission line as an example, the method for reducing the frequent operation of tap changers proposed in this invention was verified. Based on the main circuit calculation results for three typical operating modes—double-polar full-voltage return line, single-polar full-voltage metal return line, and single-polar half-voltage metal return line—after adopting the improved tap changer control strategy, the number of tap changer operations is significantly reduced when the power increases from 0.1 pu to 1.0 pu, as shown in Table 4.

[0093] Table 4 Comparison of the number of actions for different strategies as power increases from 0.1 pu to 1.0 pu

[0094]

[0095] 2) Operating characteristics

[0096] In the following calculation results for the main circuit under different operating modes, the converter bus voltage of the Shaanbei converter station is 775kV, the converter bus voltage of the Wuhan converter station is 525kV, and the DC line resistance is 4.37Ω.

[0097] 2.1) Double Extreme Total Pressure Operation Mode

[0098] Table 5. Calculation results of the main circuit of the original strategy (bipolar full-pressure operation mode)

[0099]

[0100]

[0101] Table 6. Calculation results of the main circuit of the improved strategy (bipolar maximum total pressure operation mode)

[0102]

[0103] 2) Single-pole metal full-voltage operation mode

[0104] Table 7. Calculation results of the main circuit of the original strategy (single-pole metal full-voltage operation mode)

[0105]

[0106]

[0107] Table 8. Calculation results of the main circuit of the improved strategy (single-pole metal full-voltage operation mode)

[0108]

[0109] 3) Single-pole metal semi-pressure operation mode

[0110] Table 9. Calculation results of the main circuit of the original strategy (single-pole metal half-voltage operation mode)

[0111]

[0112]

[0113] Table 10 Calculation results of the main circuit of the improved strategy (single-pole metal half-voltage operation mode)

[0114]

[0115] 2. RTDS Simulation Results

[0116] Taking the Bai-Zhe DC project as an example, a closed-loop simulation and commissioning test of DC control and protection equipment was carried out using the UHV project RTDS simulation test platform. The RTDS simulation verification was performed using a DC control and protection system with the same model as the Bai-Zhe DC field equipment, the same core program functions, and simplified redundant configuration and interface, to verify the test effect of the project.

[0117] 1) Main circuit operating characteristics

[0118] Under the conventional strategy of the Bai Zhe Project, the main circuit operating characteristics of the rated AC system voltage under various operating conditions are shown in Tables 11, 12 and 13, respectively.

[0119] Table 11 Operation status of double-pole full-voltage tap changers

[0120] P(pu) Id(kA) UdR(kV) γ(°) TCI 0.1 0.5 800 19.5 2.1 0.2 1 800 19.5 1.9 0.3 1.5 800 19.5 1.6 0.4 2 800 19.5 1.4 0.5 2.5 800 19.5 1.2 0.6 3 800 19.5 0.9 0.7 3.5 800 19.5 0.7 0.82 4.1 800 19.5 0.5 0.98 4.9 800 19.5 0.2 1 5 800 19.5 0.0

[0121] Table 12 Operation status of single-pole metal tap changers

[0122] P(pu) Id(kA) UdR(kV) γ(°) TCI 0.1 0.5 800 19.50 2.7 0.2 1 800 19.50 3.0 0.3 1.5 800 19.50 3.3 0.4 2 800 19.50 3.6 0.5 2.5 800 19.50 3.9 0.6 3 800 19.50 4.2 0.7 3.5 800 19.50 4.5 0.82 4.1 800 19.50 4.7 0.98 4.9 800 19.50 5.0 1 5 800 19.50 5.3

[0123] Table 13 Operation status of single-pole metal half-voltage tap changer

[0124]

[0125]

[0126] After adopting improved strategies on the rectifier and inverter sides of the Bai Zhe project, the main circuit operating characteristics under various operating conditions of the rated AC system voltage are shown in Tables 14, 15, and 16, respectively.

[0127] Table 14 Operation status of double-pole full-voltage tap changers

[0128] P(pu) Id(kA) UdR(kV) γ(°) TCI 0.1 0.5 800 25.00 -1.1 0.2 1 800 24.64 -1.1 0.3 1.5 800 24.27 -1.1 0.4 2 800 23.90 -1.1 0.5 2.5 800 23.52 -1.1 0.6 3 800 23.14 -1.1 0.7 3.5 800 22.75 -1.1 0.8 4 800 22.36 -1.1 0.9 4.5 800 21.96 -1.1 1 5 800 19.50 0.0

[0129] Table 15 Operation of Single-Pole Metallic Tap Changers

[0130]

[0131]

[0132] Table 16 Operation status of single-pole metal half-voltage tap changer

[0133] P(pu) Id(kA) UdR(kV) γ(°) TCI 0.1 0.5 800 17.50 4.7 0.2 1 800 20.38 4.7 0.3 1.5 800 22.91 4.7 0.4 2 800 23.31 6.0 0.5 2.5 800 24.17 7.0 0.6 3 800 23.62 9.0 0.7 3.5 800 24.60 10.0 0.8 4 800 24.25 12.0 0.9 4.5 800 24.01 14.0 1.0 5 800 23.87 16.0

[0134] Table 17 shows the operation of the tap changer in the Baizhe Project before and after adopting the improved control strategy.

[0135]

[0136] According to Table 17, when the AC system voltage remains constant, after adopting a large-angle control strategy at the receiving end, during the process of DC power changing from 0.1pu to 1.0pu, the number of tap changer operations decreases from 2 to 1 when the bipolar full voltage is applied, the number of tap changer operations decreases from 2 to 0 when the unipolar metal full voltage is applied, and the number of tap changer operations decreases from 15 to 11 when the unipolar metal half voltage is applied.

[0137] 2) RTDS simulation

[0138] To verify the effectiveness of this strategy, a verification experiment was conducted on a real-time simulation platform for UHVDC control and protection in laboratory engineering.

[0139] 2.1) Dual Extreme Total Pressure Operation

[0140] During the process of increasing the DC power from 0.1 pu to 1.0 pu, the inverter side tap changer remained at position 23, and the test results were consistent with expectations.

[0141] Table 18 shows the operation of the tap changer under improved strategy with full-voltage operation.

[0142]

[0143] 2.2) Single-pole metal loop full-voltage operation

[0144] During the process of increasing the DC power from 0.1 pu to 1.0 pu, the inverter side tap changer remained at 21 positions, and the test results were consistent with expectations.

[0145] Table 19 shows the operation of the tap changer under the improved strategy with full voltage operation of the single-pole metal return line.

[0146]

[0147] 2.3) Monopolar metal semi-pressure operation

[0148] During the process of increasing the DC power from 0.1 pu to 1.0 pu, the inverter side tap changer was reduced from 21 positions to 9 positions, and the test results were consistent with expectations.

[0149] Table 20 shows the operation of single-pole metal half-voltage tap changers using the improved strategy.

[0150]

[0151] In summary, RTDS simulations show that the improved tap changer strategy can reduce the number of tap changer operations. Under various operating modes such as bipolar and single-pole single-pole metal, the receiving-end tap changer remains basically stationary. For the extreme metal half-voltage operating mode, the number of tap changer operations can also be significantly reduced, which is consistent with the design results.

[0152] Example 2

[0153] Embodiment 1 above provides a method for reducing frequent tap changer operation at receiving-end converter stations. Correspondingly, this embodiment provides a system for reducing frequent tap changer operation at receiving-end converter stations. The system provided in this embodiment can implement the method for reducing frequent tap changer operation at receiving-end converter stations described in Embodiment 1. This system can be implemented through software, hardware, or a combination of both. For example, the system may include integrated or separate functional modules or units to execute the corresponding steps in the methods of Embodiment 1. Since the system in this embodiment is basically similar to the method embodiment, the description process in this embodiment is relatively simple. Relevant details can be found in the description of Embodiment 1. The system embodiment provided in this embodiment is merely illustrative.

[0154] The system provided in this embodiment for reducing frequent tap changer operation at the receiving-end converter station includes:

[0155] Angle range determination module, used to determine the dead zone range of the shut-off angle of the receiving-end converter station;

[0156] The function relationship establishment module is used to determine the relationship between the dynamic proportional coefficient h and the number of tap changer operations based on the operating characteristics of the UHVDC transmission system.

[0157] The adjustment module is used to determine the initial value of the shut-off angle based on the dead zone range of the shut-off angle of the receiving-end converter station and the relationship between the dynamic proportional coefficient h and the number of tap changer operations, thereby reducing the frequent operation of the tap changer of the receiving-end converter station.

[0158] Example 3

[0159] This embodiment provides a processing device corresponding to the method for reducing frequent operation of tap changers in receiving-end converter stations provided in Embodiment 1. The processing device can be a processing device for clients, such as mobile phones, laptops, tablets, desktop computers, etc., to execute the method of Embodiment 1.

[0160] The processing device includes a processor, a memory, a communication interface, and a bus. The processor, memory, and communication interface are connected via the bus to enable communication between them. The memory stores a computer program that can run on the processor. When the processor runs the computer program, it executes the method provided in Embodiment 1 for reducing frequent tap changer operations at the receiving-end converter station.

[0161] Preferably, the memory may be high-speed random access memory (RAM), and may also include non-volatile memory, such as at least one disk storage device.

[0162] Preferably, the processor can be any type of general-purpose processor such as a central processing unit (CPU) or a digital signal processor (DSP), and there is no limitation herein.

[0163] Example 4

[0164] The method for reducing frequent operation of tap changers in receiving-end converter stations according to Embodiment 1 can be specifically implemented as a computer program product. The computer program product may include a computer-readable storage medium on which computer-readable program instructions are loaded for executing the method for reducing frequent operation of tap changers in receiving-end converter stations as described in Embodiment 1.

[0165] A computer-readable storage medium can be a tangible device that holds and stores instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination thereof.

[0166] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied 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.

[0167] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. 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... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0168] 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.

[0169] 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.

[0170] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for reducing frequent operation of tap changers in receiving-end converter stations, characterized in that... include: Determine the dead zone range of the turn-off angle of the receiving-end converter station; Based on the operating characteristics of the UHVDC transmission system, the relationship between the dynamic proportional coefficient h and the number of tap changer operations is determined. Based on the determined dead zone range of the cut-off angle of the receiving-end converter station, and the relationship between the dynamic proportional coefficient h and the number of tap changer operations, the initial value of the cut-off angle that can reduce the frequent operation of the tap changer of the receiving-end converter station is determined. The determination of the relationship between the dynamic proportional coefficient h and the number of tap changer operations based on the operating characteristics of the UHVDC transmission system includes: Based on DC transmission theory, the relationship between the turn-off angle and DC current is established. Based on the relationship between the turn-off angle and the DC current, the functional relationship between the dynamic proportional coefficient h and different operating modes of the UHVDC transmission system is determined. Statistical analysis was conducted on the number of tap changer operations under different operating modes of the UHVDC transmission system to determine the relationship between the dynamic proportional coefficient h and the number of tap changer operations. The functional relationship between the dynamic proportional coefficient h and different operating modes of the UHVDC transmission system is as follows: In the formula, R d is the DC loop line resistance; n is the number of converter inputs of the receiving end converter station; d xI is the commutation reactance on the inverter side; I dN is the rated DC current; U di0IN is the ideal no-load DC voltage of the DC.

2. The method for reducing frequent operation of tap changers in receiving-end converter stations as described in claim 1, characterized in that, The deadband range of the receiving end converter station turn-off angle is [17.5 o ,25 o ].

3. The method for reducing frequent operation of tap changers in receiving-end converter stations as described in claim 1, characterized in that, The determination of the initial value of the shut-off angle that can reduce frequent tap changer operations at the receiving-end converter station, based on the determined dead zone range of the shut-off angle of the receiving-end converter station and the relationship between the dynamic proportional coefficient h and the number of tap changer operations, includes: Based on the operating mode of the UHVDC transmission system to be analyzed, determine the specific value of the dynamic proportional coefficient h. The initial value of the shut-off angle is determined based on the specific value of the dynamic proportional coefficient and the relationship between the dynamic proportional coefficient h and the number of tap changer operations.

4. The method for reducing frequent operation of tap changers in receiving-end converter stations as described in claim 3, characterized in that, The determination of the initial value of the shut-off angle based on the specific value of the dynamic proportional coefficient and the relationship between the dynamic proportional coefficient h and the number of tap changer operations includes: ① When h>0, the pre-adjusted tap changer ensures that the cut-off angle during unlocking is the lower limit of the dead zone, 17.5°. o At this point, the shut-off angle is 25 degrees above the dead zone limit. o The range margin is the largest. As the DC current increases, the turn-off angle will gradually increase, and the number of tap changer operations will decrease. (ii) when h = 0, the pre-adjustment of the tap switch makes the off angle 19.5 o when unlocked, which remains unchanged with the increase of the DC current, to 17.5 o and 25 o margin range is the same; ③ When h<0, the pre-adjusted tap changer ensures that the cut-off angle during unlocking is the upper limit of the dead zone, 25°. o At this point, the cutoff angle to the lower limit of the dead zone is 17.

5. o The range margin is the largest. As the DC current increases, the turn-off angle gradually decreases, and the number of tap changer operations decreases.

5. The method for reducing frequent operation of tap changers in receiving-end converter stations as described in claim 4, characterized in that, In step ①, when h > 0 and there is no available reactive power compensation equipment, the dead zone range of the shut-off angle is adjusted to [17.5]. o 21.5 o Afterwards, the pre-adjusted tap changer ensures that the closing angle is the rated value of 19.5 degrees when unlocked. o .

6. A system for reducing frequent tap changer operation at receiving-end converter stations, characterized in that... include: Angle range determination module, used to determine the dead zone range of the shut-off angle of the receiving-end converter station; The function relationship establishment module is used to determine the relationship between the dynamic proportional coefficient h and the number of tap changer operations based on the operating characteristics of the UHVDC transmission system. The adjustment module is used to determine the initial value of the shut-off angle that can reduce the frequent operation of the tap changer at the receiving-end converter station, based on the dead zone range of the shut-off angle of the receiving-end converter station and the relationship between the dynamic proportional coefficient h and the number of tap changer operations. The determination of the relationship between the dynamic proportional coefficient h and the number of tap changer operations based on the operating characteristics of the UHVDC transmission system includes: Based on DC transmission theory, the relationship between the turn-off angle and DC current is established. Based on the relationship between the turn-off angle and the DC current, the functional relationship between the dynamic proportional coefficient h and different operating modes of the UHVDC transmission system is determined. Statistical analysis was conducted on the number of tap changer operations under different operating modes of the UHVDC transmission system to determine the relationship between the dynamic proportional coefficient h and the number of tap changer operations. The functional relationship between the dynamic proportional coefficient h and different operating modes of the UHVDC transmission system is as follows: In the formula, R d d is the DC circuit line resistance; n is the number of converters put into operation at the receiving-end converter station; xI For the commutation reactance on the inverter side; I dN Rated DC current; U di0IN This is the ideal DC no-load DC voltage.

7. A computer-readable storage medium for storing one or more programs, characterized in that, The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any of the methods described in claims 1 to 5.

8. A computing device, characterized in that, include: One or more processors and a memory, wherein the memory stores one or more programs and is configured to be executed by the one or more processors, the one or more programs including instructions for performing any of the methods described in claims 1 to 5.

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