Method and system for reducing action times of tap switch of converter transformer and storage medium

Abstract

The invention relates to the technical field of tap switch control, and discloses a method and system for reducing the number of actions of a tap switch of a converter transformer and a storage medium, and the method comprises the steps: selecting a corresponding step length regulation and control model according to the operation state of the converter transformer, and obtaining an input parameter corresponding to a step according to the operation parameter of the converter transformer; the action frequency reduction proportion, the initial step length and the input parameters are input into a step length regulation and control model to obtain a regulation and control step length, and the span of the tap switch is adjusted according to the regulation and control step length; and according to the regulation step length and the adaptive adjustment function, obtaining an angle adjustment amount, and according to the angle adjustment amount, adjusting the dead zone angle range of the tap switch. According to the invention, the step length of the tap switch of the converter transformer is adjusted to reduce the action times of the tap switch; the step length of the tap switch and the control dead zone are matched through the dead zone self-adaptive adjustment algorithm, frequent adjustment of the tap switch is avoided, the action frequency of the tap switch can be effectively reduced, and the safety and reliability of converter transformer operation are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of tap changer control technology, and in particular to a method, system, and storage medium for reducing the number of tap changer operations in a converter transformer. Background Technology

[0002] Converter stations are a crucial component of high-voltage direct current (HVDC) transmission projects. The converter transformer, as the core equipment of the converter station, directly determines the stable operation of the entire station. The tap changer, as the core control component of the converter transformer, plays a vital role in dynamically regulating voltage and matching AC system voltage fluctuations with DC power variations. With the continuous expansion of HVDC transmission projects, operational problems caused by frequent tap changer operation are becoming increasingly prominent. In some existing projects, excessive tap changer operation has led to abnormal gas generation inside the converter transformer, seriously threatening the safe and stable operation of the converter station. Therefore, developing optimized control strategies to efficiently reduce the frequency of tap changer operation has become a core technical requirement for ensuring the reliable operation of converter stations in HVDC transmission projects. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method, system, and storage medium for reducing the number of tap changer operations in a converter transformer. By controlling the step size of the tap changer and adaptively adjusting its dead zone range, the number of tap changer operations is reduced, thereby ensuring the safe and reliable operation of the converter transformer.

[0004] In a first aspect, the present invention provides a method for reducing the number of tap changer operations in a converter transformer, the method comprising:

[0005] In response to receiving a command to reduce the number of tap changer operations of the converter transformer, the operating status, operating parameters, and the reduction ratio and initial step size of the tap changer operations of the converter transformer are obtained.

[0006] Based on the operating status of the converter transformer, a corresponding step size control model is selected from the preset step size control model set, and the input parameters corresponding to the step size control model are obtained based on the operating parameters of the converter transformer. The input parameters include the per-unit value of the converter transformer ratio and the voltage reduction level.

[0007] The reduction ratio of the number of actions, the initial step size, and the input parameters are input into the step size control model to obtain the control step size, and the tap changer distance is adjusted according to the control step size.

[0008] Based on the control step size and the preset adaptive adjustment function, the angle adjustment amount is obtained, and the dead zone angle range of the tap changer is adjusted according to the angle adjustment amount.

[0009] Furthermore, the set of step size control models includes several step size control models, each of which is constructed based on different operating states of the converter transformer, including DC power range, AC voltage range, and step-down state.

[0010] Furthermore, the step of selecting a corresponding step size control model from a preset set of step size control models based on the operating state of the converter transformer, and obtaining the input parameters corresponding to the step size control model based on the operating parameters of the converter transformer includes:

[0011] In response to the operating state of the converter transformer being the rated AC system voltage and the full DC power range, the first step length control model is selected from the preset set of step length control models.

[0012] Based on the operating parameters of the converter transformer, calculate the first per-unit value and the second per-unit value of the turns ratio. The first per-unit value of the turns ratio is the turns ratio per-unit value corresponding to a DC power of 1.0 pu, and the second per-unit value of the turns ratio is the turns ratio per-unit value corresponding to a DC power of 0.1 pu.

[0013] In response to the converter transformer's operating state being the full AC system voltage range and the full DC power range, a second step size control model is selected from the preset step size control model set;

[0014] Calculate the maximum and minimum per-unit ratio values ​​based on the operating parameters of the converter transformer;

[0015] In response to the converter transformer's operating state being the full AC system voltage range, the full DC power range, and step-down operation, the third step-size control model is selected from the preset set of step-size control models.

[0016] Extract the step-down level from the operating parameters of the converter transformer.

[0017] Furthermore, the first-step long-term regulation model is represented by the following formula:

[0018]

[0019] In the formula, Δη1 represents the first control step size output by the first step length control model, m represents the reduction ratio of the number of actions, Δη represents the initial step size, and n 1.0pu This represents the per-unit value of the first ratio, n. 0.1pu This represents the per-unit value of the second ratio, and j represents the correction factor;

[0020] The second step size control model is represented by the following formula:

[0021]

[0022] In the formula, Δη2 represents the second control step size output by the second step size control model, and nmaxpu n represents the per-unit value of the maximum ratio. minpu This represents the per-unit value of the minimum ratio;

[0023] The third step size control model is represented by the following formula:

[0024] Δη3=(1-k) / (m((1-k) / Δη-1)+j)

[0025] In the formula, Δη3 represents the third control step size output by the third step size control model, and k represents the pressure reduction level.

[0026] Further, the step of obtaining the angle adjustment amount based on the control step size and the preset adaptive adjustment function, and adjusting the dead zone angle range of the tap changer based on the angle adjustment amount includes:

[0027] The adjustment step size is compared with the step size threshold, and the angle adjustment amount is calculated based on the comparison result and the preset adaptive adjustment function.

[0028] Based on the angle adjustment amount, the dead zone angle range of the tap changer is increased to obtain the adjusted dead zone angle range.

[0029] Furthermore, the adaptive adjustment function is expressed by the following formula:

[0030]

[0031] In the formula, Δα represents the angle adjustment amount, η represents the control step size, and round(*) represents the rounding function;

[0032] The left endpoint value of the adjusted dead zone angle range is expressed by the following formula:

[0033] α′ min =α min -Δα

[0034] The right endpoint value of the adjusted dead zone angle range is expressed by the following formula:

[0035] α′ max =α max +Δα

[0036] In the formula, α′ min α represents the left endpoint value of the adjusted dead zone angle range. min α′ represents the left endpoint value of the dead zone angle range before adjustment. max α represents the right endpoint value of the adjusted dead zone angle range. max This represents the right endpoint value of the dead zone angle range before adjustment.

[0037] Furthermore, after the step of adjusting the dead zone angle range of the tap changer, the method further includes:

[0038] In response to the converter transformer's operating state being the full AC system voltage range and the full DC power range, the maximum and minimum per-unit values ​​of the adjusted transformer ratio are calculated based on the adjusted operating parameters of the converter transformer after the dead zone angle range.

[0039] The reduction ratio of the number of actions, the initial step size, the maximum per-unit value of the adjusted ratio, and the minimum per-unit value of the adjusted ratio are input into the second step size control model to obtain the verification step size expression;

[0040] Based on the equivalence between the verification step size expression and the model expression for calculating the second control step size, the correction coefficient is calculated;

[0041] If the correction coefficient is within a preset range, the dead zone angle range adjustment is considered complete; otherwise, the angle adjustment amount is adjusted according to a preset adjustment correction function, and a new correction coefficient is calculated based on the adjusted angle adjustment amount until the new correction coefficient is within the preset range.

[0042] Furthermore, the adjustment correction function is expressed by the following formula:

[0043]

[0044] In the formula, Δα′ represents the adjusted angle adjustment amount, round(*) represents the rounding function, Δη2 represents the second control step size output by the second step size control model, k1 represents the large adjustment coefficient, and k2 represents the small adjustment coefficient.

[0045] Secondly, the present invention provides a system for reducing the number of tap changer operations of a converter transformer, the system comprising:

[0046] The parameter calculation module is used to respond to the received instruction to reduce the number of tap changer operations of the converter transformer, and to obtain the operating status, operating parameters, and the reduction ratio and initial step size of the number of tap changer operations of the converter transformer.

[0047] Based on the operating status of the converter transformer, a corresponding step size control model is selected from the preset step size control model set, and the input parameters corresponding to the step size control model are obtained based on the operating parameters of the converter transformer. The input parameters include the per-unit value of the converter transformer ratio and the voltage reduction level.

[0048] The gap adjustment module is used to input the reduction ratio of the number of actions, the initial step size and the input parameters into the step size control model to obtain the control step size, and adjust the gap of the tap changer according to the control step size;

[0049] The dead zone adjustment module is used to obtain the angle adjustment amount based on the control step size and the preset adaptive adjustment function, and to adjust the dead zone angle range of the tap changer according to the angle adjustment amount.

[0050] Thirdly, embodiments of the present invention also provide a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the above-described method.

[0051] This invention provides a method, system, and storage medium for reducing the number of tap changer operations in a converter transformer. By using the tap changer step size as the control target, this invention overcomes the limitations of traditional methods that fix the tap changer step size. It reduces the number of tap changer operations by adjusting the step size. Through setting multiple step size control models, accurate solutions for the tap changer step size under different operating conditions can be achieved. Furthermore, the adaptive dead-zone adjustment algorithm ensures the matching between the tap changer step size and the control dead zone, avoiding frequent tap changer adjustments. This invention significantly reduces the number of tap changer operations, thereby ensuring the safe and reliable operation of the converter transformer and further improving the safety and reliability of the converter station. Attached Figure Description

[0052] Figure 1 This is a flowchart illustrating a method for reducing the number of tap changer operations in a converter transformer according to an embodiment of the present invention.

[0053] Figure 2 This is a schematic diagram of the system for reducing the number of tap changer operations in an embodiment of the present invention;

[0054] Figure label:

[0055] 10. Parameter calculation module; 20. Gear distance adjustment module; 30. Dead zone adjustment module. Detailed Implementation

[0056] 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 embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] Please see Figure 1 The first embodiment of the present invention proposes a method for reducing the number of tap changer operations in a converter transformer, comprising steps S10 to S40:

[0058] Step S10: In response to receiving a command to reduce the number of tap changer operations of the converter transformer, obtain the operating status, operating parameters, and the reduction ratio and initial step size of the number of tap changer operations of the converter transformer.

[0059] Step S20: Based on the operating status of the converter transformer, select the corresponding step size control model from the preset step size control model set, and obtain the input parameters corresponding to the step size control model based on the operating parameters of the converter transformer. The input parameters include the per-unit value of the converter transformer ratio and the voltage reduction level.

[0060] Step S30: Input the reduction ratio of the number of actions, the initial step size, and the input parameters into the step size control model to obtain the control step size, and adjust the tap changer's range according to the control step size;

[0061] Step S40: Based on the control step size and the preset adaptive adjustment function, the angle adjustment amount is obtained, and the dead zone angle range of the tap changer is adjusted according to the angle adjustment amount.

[0062] This invention provides a method for reducing the number of tap changer operations in a converter transformer by using the tap position step size as the control target. Before describing the method provided by this invention, the traditional tap position and tap position setting methods of tap changers will first be explained. The converter transformer (referred to as converter transformer) is the core equipment of the converter station, and the tap changer is the core component of the converter transformer, used to regulate changes in DC power and AC system voltage. The tap changer step size is directly related to the total range of converter transformer parameters. In DC transmission projects connected to AC system voltages below 500kV, 330kV, and 220kV, the tap changer step size of the converter transformer is generally calculated uniformly at 1.25%. The tap position settings of the tap changer are also set based on the preset positions of the tap changer manufacturer. Based on the current manufacturing level, the total number of tap changer positions does not exceed 31, and the dead zone angle range of the tap changer is a fixed range, generally within the range of [12.5°, 17.5°]. The limitation of this traditional tap changer setting method is that tap changer manufacturers preset a large number of tap positions, but very few tap positions are actually used, resulting in a waste of tap position design. At the same time, too many tap positions will lead to frequent tap changer operation, threatening the safe operation of the converter station. Fixed step size is based on standardized converter transformer parameters and does not take into account parameter changes under different operating conditions, so it cannot effectively adapt to converter transformers under different operating conditions.

[0063] To address the aforementioned problems, this invention provides a method for calculating the tap changer step size of a converter transformer. Based on the operating status of the converter transformer, the tap changer's positions are reduced by adjusting the tap changer step size, thereby reducing the number of tap changer operations. Specifically, based on the DC power range and AC voltage range of the converter transformer, its operating status can be divided into three operating conditions. The first operating condition is operating within the rated AC system voltage and the full DC power range. The rated AC system voltage refers to the converter transformer operating at the set rated voltage, such as 525kV. The full DC power range refers to the range of DC power, with a minimum DC power of 0.1pu and a maximum DC power of 1.0pu. The second operating condition is operating within the full AC system voltage range and the full DC power range. The full AC system voltage range refers to the converter transformer operating within a preset voltage range, such as 500kV to 550kV. The third operating condition is operating within the full AC system voltage range and the full DC power range, but with reduced voltage operation. Reduced voltage operation refers to an operating mode in which the DC system voltage is reduced while the power remains constant. It should be noted that the present invention can be extended to the calculation of tap changer step length with the goal of reducing the number of tap changer operations under any AC voltage level and any DC power range within the AC system voltage range. Here, the above three operating conditions are preferred rather than specifically limited.

[0064] When a command to reduce the number of tap changer operations of the converter transformer is received from the system, the reduction ratio of the number of tap changer operations is extracted from the reduction command. At the same time, the current operating status, operating parameters, and initial step size of the tap changer of the converter transformer are obtained. Based on the operating status of the converter transformer, the corresponding step size control model is selected from the preset step size control model set, and the input parameters corresponding to the model are calculated based on the operating parameters of the converter transformer.

[0065] In this embodiment, the step-size control model set includes several step-size control models, each constructed based on different operating states of the converter transformer, including DC power range, AC voltage range, and step-down state. Taking the above three operating conditions as examples, the step-size control model set includes three step-size control models: the first step-size control model, the second step-size control model, and the third step-size control model. The corresponding converter transformer operating states are the first, second, and third operating conditions, respectively. Based on the step-size control model set, the specific steps for model selection and input parameter calculation include:

[0066] In response to the operating state of the converter transformer being the rated AC system voltage and the full DC power range, the first step length control model is selected from the preset set of step length control models.

[0067] Based on the operating parameters of the converter transformer, calculate the first per-unit value and the second per-unit value of the turns ratio. The first per-unit value of the turns ratio is the turns ratio per-unit value corresponding to a DC power of 1.0 pu, and the second per-unit value of the turns ratio is the turns ratio per-unit value corresponding to a DC power of 0.1 pu.

[0068] In response to the converter transformer's operating state being the full AC system voltage range and the full DC power range, a second step size control model is selected from the preset step size control model set;

[0069] Calculate the maximum and minimum per-unit ratio values ​​based on the operating parameters of the converter transformer;

[0070] In response to the converter transformer's operating state being the full AC system voltage range, the full DC power range, and step-down operation, the third step-size control model is selected from the preset set of step-size control models.

[0071] Extract the step-down level from the operating parameters of the converter transformer.

[0072] In this embodiment, the converter transformer is the core equipment in the high-voltage direct current transmission system, realizing the transformation of AC voltage. Because the converter transformer has tap switches, different taps can be selected to adjust the ratio of the primary and secondary sides, i.e., the transformation ratio. Essentially, this is an adjustment of the ratio of the primary grid side voltage and the secondary valve side voltage of the converter transformer. Since the valve side voltage cannot be directly calculated, it needs to be calculated by calculating the ideal no-load DC voltage. The relationship between the valve side voltage and the ideal no-load DC voltage is as follows:

[0073]

[0074] In the formula, U v U represents the valve-side voltage. di0 This represents the ideal no-load DC voltage.

[0075] Therefore, the calculation of the maximum and minimum values ​​of the converter transformer valve-side voltage is transformed into the calculation of the ideal no-load DC voltage of the converter transformer. The ideal no-load DC voltage of the converter transformer can be calculated using parameters such as DC voltage, DC current, inductive impedance, and resistive impedance. Taking the ideal no-load DC voltage on the rectifier side of the converter transformer as an example, its calculation formula can be expressed as:

[0076]

[0077] In the formula, U di0R U represents the ideal no-load DC voltage on the rectifier side. dR This represents the DC voltage on the rectifier side, n represents the number of pulses in the commutator transformer, and d represents the DC voltage on the rectifier side. xR d represents the commutation variable inductive impedance. rR I represents the commutation variable resistive impedance. d I represents direct current. dNU represents the rated DC current, α represents the firing angle, and U represents the rated DC current. di0NR U represents the rated ideal no-load DC voltage on the rectifier side. TR This indicates the forward conduction pressure drop of the rectifier-side converter valve.

[0078] Based on the ideal no-load DC voltage under different operating conditions, the step-size calculation process of the converter transformer step-size control model under different operating conditions is explained in detail below. When the converter transformer operates at the rated AC system voltage and the full DC power range, firstly, based on the converter transformer's operating parameters, the rated ideal no-load DC voltage is calculated, and the ideal no-load DC voltage at DC power of 0.1 pu and 1.0 pu is also calculated. The calculation of the no-load DC voltage refers to the conventional formula for no-load DC voltage mentioned above, and the corresponding parameters are substituted; the calculation process is not explained in detail here. Then, based on the rated ideal no-load DC voltage and the ideal no-load DC voltage at DC power of 0.1 pu and 1.0 pu, the per-unit value of the converter transformer's turns ratio corresponding to the two DC power values ​​under the rated AC system voltage is calculated. The formula is expressed as:

[0079]

[0080] In the formula, U di0N U represents the rated ideal no-load DC voltage. di01.0pu U represents the ideal no-load DC voltage at a DC power of 1.0 pu. di00.1pu n represents the ideal no-load DC voltage at a DC power of 0.1 pu. 1.0pu This represents the per-unit value of the turns ratio at a DC power of 1.0 pu, also known as the first per-unit value of the turns ratio, n. 0.1pu This represents the per-unit value of the turns ratio at a DC power of 0.1 pu, also known as the second per-unit value of the turns ratio, U. lN This indicates the rated primary grid-side voltage of the converter transformer.

[0081] Assuming ΔTC represents the tap changer range difference across the entire DC power range under rated AC system voltage, i.e., the number of tap changer operations during the DC power increase from 0.1 pu to 1.0 pu, TC 1.0pu and TC 0.1pu Let Δη be the tap position at 1.0 pu and 0.1 pu under rated AC system voltage, and Δη be the initial step size of the tap changer. Then, the tap positions at 1.0 pu and 0.1 pu under rated AC system voltage, and the number of tap changer operations, can be expressed as:

[0082]

[0083] Based on the reduction ratio m in the reduction instruction, multiplying it by the initial number of actions △TC, the new number of actions △TC1 can be calculated. Since the number of actions should be an integer, the new number of actions can be expressed as:

[0084]

[0085] In the formula, △TC1 represents the number of new operations within the full power range under the rated AC system voltage, and m represents the percentage reduction in the number of operations. Indicates rounding up. Indicates rounding down;

[0086] Based on the expression for the number of actions above, the corresponding control step size under a new number of actions should be expressed as:

[0087]

[0088] Taking the above formula as the first step of the control model, Δη1 represents the first control step size output by the first step of the control model, j represents the correction coefficient, and the correction coefficient is a decimal between [-1,1], keeping one decimal place.

[0089] Here, we need to explain the correction factor. For the number of tap changer operations, its value must be an integer. For the initial number of operations ΔTC, when it is multiplied by the operation reduction ratio m, the resulting value is either an integer or a non-integer. For example, if the initial number of operations ΔTC is 30 and the operation reduction ratio m is 50%, then 30 * 50% = 15, which is an integer. If the initial number of operations ΔTC is 25 and the operation reduction ratio m is 50%, then 25 * 50% = 12.5, which is a non-integer.

[0090] when If j is zero, the denominator of the step size formula can be directly taken as the new number of movements without correction. It's important to note that this formula indicates the new number of movements is an integer, not that m△TC is rounded up to obtain the new number of movements. In other words, when the calculated number of new actions is not an integer, the parameter after the decimal point in the denominator needs to be fine-tuned using the correction coefficient j. Furthermore, the rounding and other operations in the step-size control model described above are all aimed at ensuring the number of actions is an integer. Moreover, the new number of actions cannot be directly rounded; instead, it's necessary to determine if the calculated value is an integer. This is because forcibly rounding to ensure the number of actions is an integer would lead to a final calculated result that does not conform to the reduction ratio specified in the reduction instruction.

[0091] In this embodiment, the fine-tuning of the correction coefficient j includes positive and negative adjustments. Positive adjustment of j involves gradually increasing it from 0 to 1, known as positive increase adjustment. Negative adjustment involves decreasing the step size from 0 to -1, known as negative increase adjustment. Positive increase decreases the step size, while negative increase increases the step size. Besides the need for j correction adjustment when the gear position is not an integer, a suitable step size can be selected non-uniquely according to engineering requirements. For example, when the step size can be anywhere from 0.023 to 0.028, the fine-tuning of j allows for flexible selection of the step size. For instance, if the AC system voltage variation range is large, j should be negative to obtain a large step size to cover this AC voltage variation; if the actual AC voltage variation range is small, j can be positive to obtain a small step size to cover the current AC voltage range. This way, the tap changer does not need to operate back and forth due to real-time changes in AC voltage.

[0092] When the converter transformer operates within the full AC system voltage range and the full DC power range, similarly, based on the converter transformer's operating parameters, calculate the rated ideal no-load DC voltage of the converter transformer, and calculate the minimum ideal no-load DC voltage at 0.1 pu and the maximum ideal no-load DC voltage at 1.0 pu. The maximum ideal no-load DC voltage represents the maximum voltage that the converter transformer's secondary valve side voltage may operate at, and the minimum ideal no-load DC voltage represents the minimum voltage that the converter transformer's secondary valve side voltage may operate at. First, calculate the rated converter transformer ratio relative to the 0 tap position. The rated ratio is the ratio of the rated primary grid side voltage to the rated secondary valve side voltage.

[0093]

[0094] In the formula, n nom U represents the rated transformer ratio. lN U represents the rated primary grid-side voltage of the converter transformer. vN This indicates the rated secondary valve-side voltage of the converter transformer.

[0095] The maximum per-unit value of the converter transformer is calculated by normalizing the maximum AC system voltage and the minimum valve-side voltage using the rated transformation ratio as the reference value. The formula is as follows:

[0096]

[0097] In the formula, n maxpu U represents the per-unit value of the maximum ratio. lmax U represents the maximum voltage of the AC system. lN U represents the rated voltage of the AC system. di0N U represents the rated ideal no-load DC voltage. di0min This represents the minimum ideal no-load DC voltage;

[0098] The minimum turns ratio of a converter transformer is calculated by taking the minimum AC system voltage and the maximum valve-side voltage, and then normalizing it using the rated turns ratio as a reference value to obtain the per-unit value of the minimum turns ratio. The formula is as follows:

[0099]

[0100] In the formula, n minpu U represents the minimum ratio per unit value. lmin U represents the minimum voltage of an AC system. lN U represents the rated voltage of the AC system, which is also the rated primary grid-side voltage of the converter transformer. di0N U represents the rated ideal no-load DC voltage. di0max This represents the maximum ideal no-load DC voltage.

[0101] Based on the initial step size, minimum transformer ratio per unit value, and maximum transformer ratio per unit value, the number of tap changer operations △TC under the current operating state can be obtained:

[0102]

[0103] Based on the reduction ratio m in the reduction instruction, multiplying it by the initial number of actions △TC, the new number of actions △TC2 can be calculated, and the formula is expressed as:

[0104]

[0105] By deriving the above formula, we can obtain the corresponding adjustment step size for a new number of actions:

[0106]

[0107] Using the above formula as the second step size control model, Δη2 represents the second control step size output by the second step size control model, and j represents the correction coefficient, which is a decimal between [-1, 1], keeping one decimal place. The criteria for determining the value of the correction coefficient j and the explanation of fine-tuning can be found in the explanation of j in the first step size control model section, and will not be repeated here.

[0108] When the converter transformer operates within the full AC system voltage range, the full DC power range, and in step-down mode, the positive position corresponds to the highest adjustment range under the maximum per-unit value of the maximum turns ratio, i.e.:

[0109]

[0110] The negative gear corresponds to the highest adjustment range at the minimum gear ratio per unit value, that is:

[0111]

[0112] Without considering voltage reduction, the total range of positive and negative taps is [-A, B0], where A and B0 are the absolute values ​​of the negative and positive taps, respectively. Therefore, the total number of taps of the tap changer is TC = (B0 + A + 1).

[0113] When the DC system is stepped down, that is, when the lowest voltage level of the DC system corresponds to the voltage after step-down, it is necessary to adjust the tap changer to adapt to the step-down operation. The step-down level k refers to the DC system's ability to operate in a stable state when the DC voltage is reduced to the rated voltage by a preset ratio k. Generally, the step-down level k is not less than 70%.

[0114] When considering the voltage reduction level k, assume the total range of positive and negative positions is [-A, B1], where A and B1 are the absolute values ​​of the negative and positive positions, respectively. In this case, the total tap position of the tap changer is TC = (B1 + A + 1).

[0115] The total adjustment range of the gear position must cover the adjustment range of the AC system voltage. The product of the total gear position range and the step size represents the total voltage regulation range. The total voltage regulation range needs to be greater than or equal to the DC voltage drop range 1-k, that is:

[0116] (B1+A+1)·Δη≥(1-k)

[0117] The above expression is derived as follows:

[0118] (B1-A)≥(1-k) / Δη-1

[0119] This can be understood as B1-A representing the number of actions. By taking the minimum value of the above inequality, the initial number of actions △TC under the reduced voltage operation state can be obtained:

[0120] ΔTC=((1-k) / Δη-1)

[0121] Similarly, when the number of actions decreases by a percentage of m, the new number of actions ΔTC3 can be expressed as:

[0122] ΔTC3=m·((1-k) / Δη-1)

[0123] Similarly, considering the rounding of the number of actions, the corresponding adjustment step size under the new number of actions should be expressed as:

[0124] Δη3=(1-k) / (m((1-k) / Δη-1)+j)

[0125] Using the above formula as the third-step control model, Δη3 represents the third control step output by the third-step control model, k represents the pressure reduction level, and j represents the correction coefficient, which is a decimal between -1 and 1, kept to one decimal place. The criteria for determining the value of the correction coefficient j and the explanation of fine-tuning can be found in the explanation of j in the first-step control model section, and will not be repeated here.

[0126] Based on the above step size control model, the control step size of the converter transformer in different operating states can be calculated. Then, the tap gap of the tap changer is adjusted according to the control step size. The tap gap refers to the step size between adjacent taps, which can be understood as adjusting the initial step size.

[0127] When the tap changer's span is adjusted, increasing the span will inevitably reduce the total number of tap positions, thus reducing the number of tap changer operations. However, increasing the tap changer's span allows it to adapt to larger AC system voltage variations or DC power changes. In this case, the tap changer's dead zone needs to be matched to the span range to cope with changes in external conditions. Otherwise, the increased step size will lead to an excessively narrow dead zone, causing frequent tap changer operations. In practical engineering applications, the step size for AC voltages of 500kV and below is 1.25%. Therefore, any step size adjustment based on this requires angle compensation to accommodate the effects of increased tap size.

[0128] In this embodiment, the adjustment range of the tap changer dead zone should be appropriately increased according to the multiple of the tap gap increase. Assuming the dead zone angle range is [α...] min ,α max If the dead zone angle adjustment is Δα, then the adjusted dead zone angle range is [α′]. min ,α′ max ],in,

[0129] α′ min =α min -Δα

[0130] α′ max =α max +Δα

[0131] In the formula, α′ min α represents the left endpoint value of the adjusted dead zone angle range. min α′ represents the left endpoint value of the dead zone angle range before adjustment. max α represents the right endpoint value of the adjusted dead zone angle range. max This represents the right endpoint value of the dead zone angle range before adjustment.

[0132] The traditional dead zone angle range is [12.5, 17.5]. Therefore, the adjusted dead zone angle range can be obtained by calculating the angle adjustment amount Δα. Since an excessively low converter valve angle can cause the trigger angle to drop below 5 degrees during DC power step transitions, α′ should, in principle... min It should be greater than or equal to 10, so take α. min If the value is 12.5, then △α should be less than or equal to 2.5. In addition to considering that the minimum trigger angle cannot be lower than 10 degrees, it is also necessary to ensure strict matching in the step size calculation process, so that the change in step size after the angle increases cannot be too large. If it is too large, it will lead to a situation where there is no solution even if the original step size cannot be finely adjusted.

[0133] Based on the above considerations, this embodiment uses an adaptive adjustment function to calculate the angle adjustment amount, and its formula is expressed as:

[0134]

[0135] In the formula, Δα represents the angle adjustment amount, η represents the control step size, and round(*) represents the rounding function; the value of the control step size η is determined according to the control step size output by the step size control model, that is, the control step size η includes the first control step size, the second control step size, and the third control step size.

[0136] According to the adaptive adjustment function, when the step size is 1.25% of the initial step size, the angle adjustment is 0, meaning there is no need to adjust the dead zone angle range. When the ratio of the control step size to the initial step size is greater than or equal to 2.5%, the angle adjustment takes the maximum value, i.e., 2.5. When the ratio of the control step size to the initial step size is less than 2.5%, the angle adjustment takes the rounded value of the ratio of the control step size to the initial step size.

[0137] In a preferred embodiment, the present invention also provides a method for verifying and secondary adjusting the adjusted dead zone angle range, the specific steps of which include:

[0138] In response to the converter transformer's operating state being the full AC system voltage range and the full DC power range, the maximum and minimum per-unit values ​​of the adjusted transformer ratio are calculated based on the adjusted operating parameters of the converter transformer after the dead zone angle range.

[0139] The reduction ratio of the number of actions, the initial step size, the maximum per-unit value of the adjusted ratio, and the minimum per-unit value of the adjusted ratio are input into the second step size control model to obtain the verification step size expression;

[0140] Based on the equivalence between the verification step size expression and the model expression for calculating the second control step size, the correction coefficient is calculated;

[0141] If the correction coefficient is within a preset range, the dead zone angle range adjustment is considered complete; otherwise, the angle adjustment amount is adjusted according to a preset adjustment correction function, and a new correction coefficient is calculated based on the adjusted angle adjustment amount until the new correction coefficient is within the preset range.

[0142] As can be seen from the above embodiments, in each step-size control model, when the converter transformer operates within the full AC system voltage range and the full DC power range, the expression of the second step-size control model uses the maximum and minimum per-unit values ​​of the turns ratio. However, when the dead zone angle range changes, the maximum and minimum per-unit values ​​of the turns ratio will change after calculating the step size covering the AC system voltage and power range. This is because the firing angle is based on the dead zone angle range when calculating the maximum and minimum per-unit values ​​of the turns ratio. Since the calculation of the turns ratio per-unit value is a conventional calculation, the specific parameter values ​​in the calculation process will not be explained in detail here, but only the relevant parameters will be explained.

[0143] Based on the calculation process of the maximum and minimum per-unit ratio values, it can be seen that when the dead zone angle range changes, new maximum and minimum per-unit ratio values ​​will be obtained. Substituting these new values ​​into the second-step control model yields a new control step size Δη4, expressed by the following formula:

[0144]

[0145] In the formula, n′ maxpu This represents the new maximum ratio per unit value, n′ minpu This represents the new minimum ratio per unit value.

[0146] As can be seen, in the new formula for calculating the control step size, the correction coefficient j is 0, and the step size is the initial step size. This is because all step sizes are control targets set based on the initial step size. The reduction ratio m of the tap changer action is all based on the initial step size (e.g., 1.25%). Therefore, the original step size is used when calculating the new step size.

[0147] Since the per-unit value of the transformer ratio has changed, the new control step size must be different from the second control step size. At this point, the new control step size is compared with the second control step size. Using the correction coefficient in the second step size control model, the step size is adjusted to achieve consistency between the step size before and after iteration, because the target number of pressure reductions *m* under the two step sizes is exactly the same. Now, let the new control step size equal to the second control step size, i.e.: Δη4 = Δη2, then:

[0148]

[0149] In the equivalent formula above, the correction coefficient j is used as the variable, and all other parameters are known values. The value of j can then be calculated. If the result of j is a number between -1 and 1, it indicates that the dead zone angle correction is successful. If the result of j exceeds this range, the angle range is fine-tuned until the j correction meets the requirements. Since the adaptive adjustment function itself has fully considered this situation, in principle, this situation will not occur. However, to improve the accuracy of dead zone adjustment and avoid j exceeding the range under extreme working conditions, this embodiment also provides an adjustment correction function to adjust the angle adjustment amount to achieve fine-tuning of the dead zone angle range, thereby ensuring that the step size verification meets the correction requirements. The adjustment correction function is represented by the following formula:

[0150]

[0151] In the formula, Δα′ represents the adjusted angle adjustment amount, round(*) represents the rounding function, Δη2 represents the second adjustment step size output by the second step size control model, k1 represents the large adjustment coefficient, and k2 represents the small adjustment coefficient. k1 and k2 are integers, which can be understood as coarse and fine adjustment of the dead zone angle through k1 and k2. The adjustment process is as follows:

[0152] When j exceeds the range [-1, 1], k1 = 1 and k2 = 0 are set to obtain a new angle adjustment amount. A new dead zone angle range is then calculated based on this new adjustment amount, leading to the calculation of a new control step size Δη4. This new control step size is then set equal to the second control step size, and the correction coefficient j is calculated. If j is within the range of -1 to 1, the iteration ends, and the new dead zone angle range is the final dead zone angle range. If j still does not meet the range requirements, k1 = 1 is kept constant, and the value of k2 is increased sequentially (e.g., to 2, 3, etc.), and the correction coefficient is calculated again until j meets the range requirements, thus obtaining the final dead zone angle range. It should be noted that the above embodiment's verification and secondary adjustment of the adjusted dead zone angle range only applies to the converter transformer operating in the full power range and the full AC system voltage range. Under rated AC system voltage and considering reduced voltage operation, the dead zone angle correction does not affect the overall range, therefore, secondary adjustment of the dead zone angle is not required under these two conditions.

[0153] The calculation process of the method provided by the present invention will be explained below through specific embodiments. Taking a certain AC-to-DC conversion project as an example, the AC system voltage of this DC transmission project is 220kV, the rated voltage is ±200kV, the rated current is 3000A, the transmission capacity is 1200MW, and the total line length is 111km. When the converter transformer operates in the full power range under the rated AC system voltage, assuming the initial step size is 1.25% and the reduction ratio m of the number of operations is 50%, the rated ideal no-load DC voltage, the ideal no-load DC voltage under DC power of 1.0pu, and the ideal no-load DC voltage under DC power of 0.1pu are calculated according to the operating parameters of the converter transformer, and are assumed to be 224.32kV, 224.32kV, and 209.06kV respectively. Then the initial number of operations ΔTC is:

[0154]

[0155] Since m is 50%, the new number of actions △TC1 is:

[0156]

[0157] Substituting the above parameters into the first step of the long-term regulation model, we can obtain:

[0158]

[0159] That is, Δη1 = 2.4%, at which point the number of tap changer operations is reduced from the original 6 times to 3 times.

[0160] When the converter transformer operates within the full power range and the full AC system voltage range, its minimum and maximum per-unit ratio values ​​are calculated. Assuming the calculated minimum and maximum per-unit ratio values ​​are 0.952 and 1.129 respectively, and using an initial step size of 1.25% and a reduction in the number of operations m of 50% as an example, the initial number of operations is:

[0161]

[0162] The new number of actions, ΔTC2 = m * 15 = 7.5, means that the value of ΔTC2 is not an integer. At this point, fine-tuning is performed using the correction coefficient j. Assuming the direction of fine-tuning is to increase the adjustment capability, then:

[0163]

[0164] Based on the second adjustment step size, the new number of actions is obtained as follows:

[0165]

[0166] It should be noted that since the step size is determined, the number of actions after the step size update can be calculated according to the formula for calculating △TC. In other words, △TC2 can be calculated according to the corresponding formula for calculating △TC.

[0167] Since the dead zone angle range is adjusted accordingly after the step size is adjusted, the new n calculated at this time... minpu And the new n maxpu If the values ​​are 1.121 and 0.957 respectively, then the new adjustment step size is:

[0168]

[0169] make:

[0170]

[0171] The calculation yields j = 0.2, meaning the correction coefficient meets the range requirements. At this point, the new step size and the new dead zone angle range can be determined, and the number of tap changer operations can be reduced from 15 to 8.

[0172] When the converter transformer operates within the full power range and the full AC system voltage range, and is in step-down mode, assuming the step-down level k is 70%, the initial step size is 1.25%, and the reduction ratio m of the number of operations is 50%, then the initial number of operations ΔTC is 23. The third control step size is then:

[0173] Δη3=(1-70%) / (50%((1-70%) / 0.0125-1)+1)=2.4%

[0174] At this point, to ensure the new number of actions is an integer, the correction coefficient is set to 1. Similarly, the number of actions under the new control step size can be obtained based on the formula for calculating ΔTC:

[0175] ΔTC3=(1-70%) / 0.024-1-(0.909-1) / 0.024=16

[0176] As can be seen, after adjusting the step size, the number of movements decreased from 23 to 16.

[0177] When the step size of the converter transformer tap changers changes, the dead zone angle range needs to be expanded according to the adaptive adjustment function. Taking the above DC project as an example, assuming the step size is adjusted to 1.8%, the sending end transmits 0.9 pu DC power, and the AC system voltage is 224~228kV, the tap changer operation is shown in Table 1 below:

[0178] Table 1. Tap switch operation before and after trigger angle adjustment.

[0179]

[0180] In the table above, Power represents the per-unit value of DC power, PdR represents the nominal value of DC power, Uac represents the AC system voltage, and the dead zone angle range of 12.5 to 17.5 degrees is the dead zone angle range before angle adjustment, while the dead zone angle range of 11.5 to 18.5 degrees is the dead zone angle range after angle adjustment. Based on the table, before the trigger angle adjustment, when the AC system voltage is 224kV, assuming the trigger angle corresponding to the tap changer at position -1 is 14.41 degrees, when the AC system voltage fluctuates to 228kV, the trigger angle increases to 17.91 degrees, exceeding 17.5 degrees, and the tap changer operates from position one to position 0, with the angle reaching 14.75 degrees. After the trigger angle adjustment, when the AC system voltage is 224kV, the trigger angle corresponding to the tap changer at position -1 is 14.41 degrees. When the AC system voltage fluctuates to 228kV, the trigger angle increases to 17.91 degrees, not exceeding the 18.5-degree dead zone limit, and the tap changer remains at position -1. In other words, the trigger angle needs to be increased appropriately to match the increase in the tap changer step size. When the angle is adjusted to the range of 11.5 to 18.5 degrees, the AC system voltage fluctuates between 222kV and 228kV, and the tap changer can still maintain the -1 position, thereby effectively reducing the number of tap changer operations.

[0181] This embodiment provides a method for reducing the number of tap changer operations in a converter transformer. This embodiment uses the tap changer step size as the control target, breaking through the traditional method of fixing the tap changer step size. It reduces the number of tap changer operations by adjusting the tap changer step size. In the process of calculating the tap changer step size, this embodiment sets multiple step size control models to accurately solve the tap changer step size under different operating conditions. Simultaneously, this embodiment uses an adaptive dead-zone adjustment algorithm to ensure the matching between the tap changer step size and the control dead zone, avoiding frequent tap changer adjustments. This embodiment can significantly reduce the number of tap changer operations, ensuring the safe and reliable operation of the converter transformer and further improving the safe and reliable operation of the converter station.

[0182] Please see Figure 2 Based on the same inventive concept, the second embodiment of the present invention proposes a system for reducing the number of tap changer operations in a converter transformer, comprising:

[0183] The parameter calculation module 10 is used to respond to the received instruction to reduce the number of tap changer operations of the converter transformer, and to obtain the operating status, operating parameters, and the reduction ratio and initial step size of the number of tap changer operations of the converter transformer.

[0184] Based on the operating status of the converter transformer, a corresponding step size control model is selected from the preset step size control model set, and the input parameters corresponding to the step size control model are obtained based on the operating parameters of the converter transformer. The input parameters include the per-unit value of the converter transformer ratio and the voltage reduction level.

[0185] The gear adjustment module 20 is used to input the reduction ratio of the number of actions, the initial step size and the input parameters into the step size control model to obtain the control step size, and adjust the gear size of the tap changer according to the control step size;

[0186] The dead zone adjustment module 30 is used to obtain the angle adjustment amount according to the control step size and the preset adaptive adjustment function, and to adjust the dead zone angle range of the tap changer according to the angle adjustment amount.

[0187] The technical features and effects of the system for reducing the number of tap changer operations in converter transformers proposed in this invention are the same as those of the method proposed in this invention, and will not be repeated here. Each module in the above-mentioned system for reducing the number of tap changer operations in converter transformers can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0188] Furthermore, embodiments of the present invention also propose a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the above-described method.

[0189] In summary, the embodiments of this invention propose a method, system, and storage medium for reducing the number of tap changer operations in a converter transformer. The method, in response to a received instruction to reduce the number of tap changer operations in a converter transformer, acquires the operating status, operating parameters, and the reduction ratio and initial step size of the tap changer operations. Based on the operating status of the converter transformer, a corresponding step size control model is selected from a preset set of step size control models. Based on the operating parameters of the converter transformer, input parameters corresponding to the step size control model are obtained. These input parameters include the converter transformer's per-unit ratio and voltage reduction level. The reduction ratio, the initial step size, and the input parameters are input into the step size control model to obtain a control step size. The tap changer's tap spacing is adjusted according to the control step size. Based on the control step size and a preset adaptive adjustment function, an angle adjustment amount is obtained. Based on the angle adjustment amount, the dead zone angle range of the tap changer is adjusted. This invention uses the tap changer step size of the converter transformer as the control target, breaking through the traditional method of fixing the tap changer step size. It reduces the number of tap changer operations by adjusting the tap changer step size. During the tap changer step size calculation, multiple step size control models are set up to accurately solve the tap changer step size under different operating conditions. Simultaneously, this invention uses an adaptive dead-zone adjustment algorithm to ensure the matching between the tap changer step size and the control dead zone, avoiding frequent tap changer adjustments. This invention significantly reduces the number of tap changer operations, ensuring the safe and reliable operation of the converter transformer, thereby further improving the safety and reliability of the converter station operation.

[0190] The various embodiments in this specification are described in a progressive manner. For directly identical or similar parts of the embodiments, refer to each other. Each embodiment focuses on its differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. It should be noted that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0191] The embodiments described above are merely preferred embodiments of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the technical principles of this invention, and these improvements and substitutions should also be considered within the scope of protection of this application. Therefore, the scope of protection of this patent application should be determined by the scope of the claims.

Claims

1. A method for reducing the number of tap changer operations in a converter transformer, characterized in that, include: In response to receiving a command to reduce the number of tap changer operations of the converter transformer, the operating status, operating parameters, and the reduction ratio and initial step size of the tap changer operations of the converter transformer are obtained. Based on the operating status of the converter transformer, a corresponding step size control model is selected from the preset step size control model set, and the input parameters corresponding to the step size control model are obtained based on the operating parameters of the converter transformer. The input parameters include the per-unit value of the converter transformer ratio and the voltage reduction level. The reduction ratio of the number of actions, the initial step size, and the input parameters are input into the step size control model to obtain the control step size, and the tap changer distance is adjusted according to the control step size. Based on the control step size and the preset adaptive adjustment function, the angle adjustment amount is obtained, and the dead zone angle range of the tap changer is adjusted according to the angle adjustment amount.

2. The method for reducing the number of tap changer operations of a converter transformer according to claim 1, characterized in that, The set of step size control models includes several step size control models, each of which is constructed based on different operating states of the converter transformer, including DC power range, AC voltage range, and step-down state.

3. The method for reducing the number of tap changer operations of a converter transformer according to claim 2, characterized in that, The steps of selecting a corresponding step size control model from a preset set of step size control models based on the operating state of the converter transformer, and obtaining the input parameters corresponding to the step size control model based on the operating parameters of the converter transformer, include: In response to the operating state of the converter transformer being the rated AC system voltage and the full DC power range, the first step length control model is selected from the preset set of step length control models. Based on the operating parameters of the converter transformer, calculate the first per-unit value and the second per-unit value of the turns ratio. The first per-unit value of the turns ratio is the turns ratio per-unit value corresponding to a DC power of 1.0 pu, and the second per-unit value of the turns ratio is the turns ratio per-unit value corresponding to a DC power of 0.1 pu. In response to the converter transformer's operating state being the full AC system voltage range and the full DC power range, a second step size control model is selected from the preset step size control model set; Calculate the maximum and minimum per-unit ratio values ​​based on the operating parameters of the converter transformer; In response to the converter transformer's operating state being the full AC system voltage range, the full DC power range, and step-down operation, the third step-size control model is selected from the preset set of step-size control models. Extract the step-down level from the operating parameters of the converter transformer.

4. The method for reducing the number of tap changer operations of a converter transformer according to claim 3, characterized in that, The first step of the long-term regulation model is represented by the following formula: In the formula, Δη1 represents the first control step size output by the first step length control model, m represents the reduction ratio of the number of actions, Δη represents the initial step size, and n 1.0pu This represents the per-unit value of the first ratio, n. 0.1pu This represents the per-unit value of the second ratio, and j represents the correction factor; The second step size control model is represented by the following formula: In the formula, Δη2 represents the second control step size output by the second step size control model, and n maxpu n represents the per-unit value of the maximum ratio. minpu This represents the per-unit value of the minimum ratio; The third step size control model is represented by the following formula: Δη3=(1-k) / (m((1-k) / Δη-1)+j) In the formula, Δη3 represents the third control step size output by the third step size control model, and k represents the pressure reduction level.

5. The method for reducing the number of tap changer operations of a converter transformer according to claim 1, characterized in that, The step of obtaining the angle adjustment amount based on the control step size and the preset adaptive adjustment function, and adjusting the dead zone angle range of the tap changer based on the angle adjustment amount includes: The adjustment step size is compared with the step size threshold, and the angle adjustment amount is calculated based on the comparison result and the preset adaptive adjustment function. Based on the angle adjustment amount, the dead zone angle range of the tap changer is increased to obtain the adjusted dead zone angle range.

6. The method for reducing the number of tap changer operations of a converter transformer according to claim 5, characterized in that, The adaptive adjustment function is represented by the following formula: In the formula, Δα represents the angle adjustment amount, η represents the control step size, and round(*) represents the rounding function; The left endpoint value of the adjusted dead zone angle range is expressed by the following formula: a' min =a min -Yes The right endpoint value of the adjusted dead zone angle range is expressed by the following formula: a' max =a max +Da In the formula, α′ m in represents the left endpoint value of the adjusted dead zone angle range, α m in represents the left endpoint value of the dead zone angle range before adjustment, α′ max α represents the right endpoint value of the adjusted dead zone angle range. max This represents the right endpoint value of the dead zone angle range before adjustment.

7. The method for reducing the number of tap changer operations of a converter transformer according to claim 4, characterized in that, After the step of adjusting the dead zone angle range of the tap changer, the method further includes: In response to the converter transformer's operating state being the full AC system voltage range and the full DC power range, the maximum and minimum per-unit values ​​of the adjusted transformer ratio are calculated based on the adjusted operating parameters of the converter transformer after the dead zone angle range. The reduction ratio of the number of actions, the initial step size, the maximum per-unit value of the adjusted ratio, and the minimum per-unit value of the adjusted ratio are input into the second step size control model to obtain the verification step size expression; Based on the equivalence between the verification step size expression and the model expression for calculating the second control step size, the correction coefficient is calculated; If the correction coefficient is within a preset range, the dead zone angle range adjustment is considered complete; otherwise, the angle adjustment amount is adjusted according to a preset adjustment correction function, and a new correction coefficient is calculated based on the adjusted angle adjustment amount until the new correction coefficient is within the preset range.

8. The method for reducing the number of tap changer operations of a converter transformer according to claim 7, characterized in that, The adjustment correction function is expressed by the following formula: In the formula, Δα′ represents the adjusted angle adjustment amount, round(*) represents the rounding function, Δη2 represents the second control step size output by the second step size control model, k1 represents the large adjustment coefficient, and k2 represents the small adjustment coefficient.

9. A system for reducing the number of tap changer operations in a converter transformer, characterized in that, include: The parameter calculation module is used to respond to the received instruction to reduce the number of tap changer operations of the converter transformer, and to obtain the operating status, operating parameters, and the reduction ratio and initial step size of the number of tap changer operations of the converter transformer. Based on the operating status of the converter transformer, a corresponding step size control model is selected from the preset step size control model set, and the input parameters corresponding to the step size control model are obtained based on the operating parameters of the converter transformer. The input parameters include the per-unit value of the converter transformer ratio and the voltage reduction level. The gap adjustment module is used to input the reduction ratio of the number of actions, the initial step size and the input parameters into the step size control model to obtain the control step size, and adjust the gap of the tap changer according to the control step size; The dead zone adjustment module is used to obtain the angle adjustment amount based on the control step size and the preset adaptive adjustment function, and to adjust the dead zone angle range of the tap changer according to the angle adjustment amount.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 8.

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