Low-voltage current limiting control method and device, storage medium, equipment and product

Abstract

The embodiment of the invention discloses a low-voltage current limiting control method and device, a storage medium, equipment and a product, and the method comprises the steps: determining an elliptic curve equation according to a static characteristic curve; the direct current side voltage value corresponding to the intersection point of the elliptic curve corresponding to the elliptic curve equation and the static characteristic curve is not less than the maximum allowable direct current side voltage value; a linear function in an initial function corresponding to the static characteristic curve is replaced with an elliptic curve equation, and a target function finally used for calculating a direct current instruction value is obtained; substituting a target direct-current side voltage value monitored by the high-voltage direct-current power transmission system at present into the target function to obtain a target direct-current instruction value; and controlling the direct current side current of the high-voltage direct current transmission system according to the target direct current instruction value. Thus, under the condition that a lower direct current instruction value can be output, commutation failure can be better inhibited in subsequent low-voltage current limiting control based on the direct current instruction value.

Description

Technical Field

[0001] This invention relates to the field of power distribution network system technology, and in particular to a low-voltage current limiting control method, device, storage medium, equipment and product. Background Technology

[0002] In the field of long-distance, high-capacity power transmission, line-commutated high-voltage direct current (LCC-HVDC) technology has become an indispensable solution. The thyristors used in this technology lack self-turn-off capability; their normal turn-off depends on the converter valves being subjected to a sufficiently long reverse voltage. This characteristic makes the stable operation of the LCC-HVDC system, especially the stable commutation on the inverter side, closely related to the voltage strength and stability of the connected AC system.

[0003] When a fault occurs in the AC system on the inverter side, it causes an AC voltage drop. This voltage drop directly leads to a decrease in the commutation voltage, resulting in insufficient reverse voltage time or amplitude for the thyristors in the converter valve after current transfer, thus preventing successful turn-off and causing "commutation failure." Commutation failure causes a sharp increase in the DC-side current of the LCC-HVDC system, generating significant electrical and thermal stress on expensive power electronic equipment such as the converter valve, severely impacting its operational lifespan. If the fault is not eliminated in time or is improperly controlled, a single commutation failure may escalate into consecutive commutation failures, ultimately forcing the LCC-HVDC system to implement DC blocking measures, causing an interruption of the entire transmission channel and posing a serious threat to the stability of the power grid and the reliability of power supply.

[0004] To suppress commutation failure, low-voltage current limiting controllers (VDCOLs) are commonly installed on the inverter side of LCC-HVDC DC transmission systems in engineering practice. The core function of VDCOL is to detect AC voltage drops and, based on a defined static characteristic curve, output a limited DC current command value according to the DC voltage (DC-side voltage) of the DC transmission system. The static characteristic curve represents the functional relationship between the DC voltage and the DC current command value. However, the DC current command value output by the static characteristic curve is not very effective for low-voltage current limiting control of LCC-HVDC systems.

[0005] Therefore, the existing DC current command value output by VDCOL is not very effective in suppressing commutation failure and urgently needs improvement. Summary of the Invention

[0006] Based on this, it is necessary to propose a low-voltage current limiting control method, device, storage medium, equipment and product to address the above problems, aiming to solve the problem that the existing VDCOL output DC current command value is not very effective in suppressing commutation failure.

[0007] In a first aspect, embodiments of this application provide a low-voltage current limiting control method, the method comprising: When the DC-side voltage or AC-side voltage of the high-voltage direct current transmission system drops below a preset voltage threshold, the determined static characteristic curve for low-voltage current limiting control of the high-voltage direct current transmission system is obtained. Based on the maximum and minimum allowable DC-side voltage values ​​corresponding to the static characteristic curve, and the corresponding maximum and minimum allowable DC current command values, the elliptic curve equation is determined; wherein, the elliptic curve equation characterizes the functional relationship between the DC current command value and the DC-side voltage of the high-voltage DC transmission system, and the DC-side voltage value corresponding to the intersection point of the elliptic curve corresponding to the elliptic curve equation and the static characteristic curve is not less than the maximum allowable DC-side voltage value; The linear function in the initial function corresponding to the static characteristic curve is replaced with the elliptic curve equation to obtain the final target function used to calculate the DC current command value. Substitute the target DC-side voltage value currently monitored for the high-voltage direct current transmission system into the target function to obtain the target DC current command value; The DC-side current of the high-voltage direct current transmission system is controlled according to the target DC current command value.

[0008] In some embodiments, determining the elliptic curve equation based on the maximum and minimum permissible DC-side voltage values ​​corresponding to the static characteristic curve, and the corresponding maximum and minimum permissible DC current command values, includes: determining the elliptic curve equation with the minimum and maximum permissible DC-side voltage values ​​corresponding to the static characteristic curve as the center of an ellipse, the target current difference as the minor semi-axis of the ellipse, and the sum of the target voltage difference and the fault coefficient as the major semi-axis of the ellipse; wherein, the target current difference is the difference between the maximum and minimum permissible DC current command values, the target voltage difference is the difference between the maximum and minimum permissible DC-side voltage values, and the fault coefficient is used to characterize the severity of the AC-side voltage fault in the high-voltage direct current transmission system.

[0009] In some embodiments, replacing the linear function in the initial function corresponding to the static characteristic curve with the elliptic curve equation to obtain the final target function used to calculate the DC current command value includes: The DC-side voltage value corresponding to the intersection point of the elliptic curve corresponding to the elliptic curve equation and the static characteristic curve is determined as the new maximum allowable DC-side voltage value of the high-voltage direct current transmission system. A portion of the interval function in the initial function corresponding to the static characteristic curve is replaced with the elliptic curve equation to obtain the final target function used to calculate the DC current command value. The portion of the interval function is the function corresponding to the interval from the minimum allowable DC-side voltage value to the new maximum allowable DC-side voltage value in the initial function, and the portion of the interval function includes the linear function.

[0010] In some embodiments, substituting the target DC-side voltage value currently monitored for the HVDC transmission system into the objective function to obtain the target DC current command value includes: when the target DC-side voltage value currently monitored for the HVDC transmission system is less than the minimum allowable DC-side voltage value, determining the target DC command value as the minimum allowable DC current command value based on the objective function; when the target DC-side voltage value is greater than the new maximum allowable DC-side voltage value, determining the target DC command value as the maximum allowable DC current command value based on the objective function; and when the target DC-side voltage value is located within the closed interval formed by the minimum allowable DC-side voltage value and the new maximum allowable DC-side voltage value, substituting the target DC-side voltage value into the elliptic curve equation in the objective function to calculate and determine the target DC current command value.

[0011] In some embodiments, the formula for calculating the above-mentioned failure coefficient is as follows: K=D×U ac / U acN , ; Wherein, K represents the fault coefficient. U represents the preset coefficient. ac U represents the AC side voltage. acN This indicates the rated value of the AC side voltage.

[0012] Secondly, embodiments of this application provide a low-voltage current limiting control device, the device comprising: The curve acquisition module is used to acquire a predetermined static characteristic curve for low-voltage current limiting control of the high-voltage direct current transmission system when the DC side voltage value or AC side voltage value of the high-voltage direct current transmission system drops below a preset voltage threshold. The equation determination module is used to determine the elliptic curve equation based on the maximum and minimum allowable DC-side voltage values ​​corresponding to the static characteristic curve, as well as the corresponding maximum and minimum allowable DC current command values; wherein, the elliptic curve equation represents the functional relationship between the DC current command value and the DC-side voltage of the high-voltage DC transmission system, and the DC-side voltage value corresponding to the intersection point of the elliptic curve corresponding to the elliptic curve equation and the static characteristic curve is not less than the maximum allowable DC-side voltage value; The function determination module is used to replace the linear function in the initial function corresponding to the static characteristic curve with the elliptic curve equation to obtain the final target function used to calculate the DC current command value. The instruction calculation module is used to substitute the target DC side voltage value currently monitored for the high voltage DC transmission system into the target function to obtain the target DC current instruction value; The current control module is used to control the DC-side current of the high-voltage DC transmission system according to the target DC current command value.

[0013] In some embodiments, the equation determining module is further configured to: determine the equation of an elliptic curve with the minimum allowable DC-side voltage value and the maximum allowable DC-side current command value corresponding to the static characteristic curve as the center of an ellipse, the target current difference as the minor semi-axis of the ellipse, and the sum of the target voltage difference and the fault coefficient as the major semi-axis of the ellipse; wherein the target current difference is the difference between the maximum allowable DC-side voltage command value and the minimum allowable DC-side voltage command value, the target voltage difference is the difference between the maximum allowable DC-side voltage value and the minimum allowable DC-side voltage value, and the fault coefficient is used to characterize the fault severity of the AC-side voltage of the high-voltage direct current transmission system.

[0014] Thirdly, embodiments of this application provide a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the method described in the first aspect.

[0015] Fourthly, embodiments of this application provide a computer device including a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor performs the steps of the method described in the first aspect.

[0016] Fifthly, embodiments of this application provide a computer program product in which instructions, when executed by a processor of a computer device, cause the processor to perform the steps of the method described in the first aspect.

[0017] The low-voltage current limiting control method, apparatus, storage medium, device, and product of this application determine an elliptic curve equation based on the maximum and minimum allowable DC-side voltage values ​​corresponding to the static characteristic curve, as well as the corresponding maximum and minimum allowable DC current command values. The elliptic curve equation characterizes the functional relationship between the DC current command value and the DC-side voltage of the high-voltage direct current transmission system. The DC-side voltage value corresponding to the intersection of the elliptic curve and the static characteristic curve is not less than the maximum allowable DC-side voltage value. The linear function in the initial function corresponding to the static characteristic curve is replaced with the elliptic curve equation to obtain the final target function used to calculate the DC current command value. The target DC-side voltage value currently monitored by the high-voltage direct current transmission system is substituted into the target function to obtain the target DC current command value. The DC-side current of the high-voltage direct current transmission system is controlled according to the target DC current command value. Thus, since the elliptic curve corresponding to the elliptic curve equation is concave, the DC current command value output by the elliptic curve equation can be less than the DC current command value determined by the static characteristic curve when the input DC-side voltage value is the same. Since a smaller output DC current command value results in a larger commutation margin and reduces the probability of commutation failure, this embodiment, by outputting a lower DC current command value, can better suppress commutation failure in subsequent low-voltage current limiting control based on the DC current command value. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] in: Figure 1 A schematic flowchart of the low-voltage current limiting control method provided in the embodiments of this application; Figure 2 A schematic diagram of static characteristic curves provided for embodiments of this application; Figure 3 This is a schematic diagram illustrating the intersection of an elliptic curve and a static characteristic curve, provided in an embodiment of this application. Figure 4 This is a structural block diagram of the low-voltage current limiting control device provided in the embodiments of this application; Figure 5 This is a structural block diagram of a computer device provided in an embodiment of this application. Detailed Implementation

[0020] 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, and 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.

[0021] This low-voltage current limiting control method can be executed by computer equipment, which can be a server or cloud server, or an electronic product such as a computer, tablet or mobile phone.

[0022] This low-voltage current limiting control method can be applied to low-voltage current limiting control scenarios in high-voltage direct current transmission (LCC-HVDC) systems, and the aforementioned computer equipment can be a low-voltage current limiting controller (VDCOL).

[0023] refer to Figure 1 , Figure 1 This is a flowchart illustrating the low-voltage current limiting control method provided in this application embodiment. Specifically, it includes the following steps S1-S5: Step S1: When the DC side voltage or AC side voltage of the high voltage direct current transmission system drops below the preset voltage threshold, obtain the determined static characteristic curve for low voltage current limiting control of the high voltage direct current transmission system.

[0024] In this embodiment, the DC voltage or AC voltage of the high-voltage direct current transmission system can be monitored in real time. The DC voltage (DC side voltage) can be, for example, the DC line voltage, the DC bus voltage of the converter, etc., and the AC voltage (AC side voltage) can be, for example, the AC bus voltage on the grid side or valve side of the converter transformer, the AC grid connection point voltage, etc.

[0025] The aforementioned preset voltage threshold can be a fixed value (e.g., a nominal voltage of 0.9 pu) or a dynamically calculated value (e.g., a threshold that is adaptively adjusted based on the current system operating power, frequency, or environmental conditions).

[0026] When the monitored voltage value is lower than the preset voltage threshold, the voltage drop condition is determined to be met. Alternatively, the voltage value can be set as met if it remains below the preset voltage threshold for a preset delay period (e.g., 10 milliseconds) to avoid false triggering.

[0027] Among them, the static characteristic curve is used to determine the DC current command value I for low-voltage current limiting control of the high-voltage direct current transmission system. ord .

[0028] The aforementioned static characteristic curve describes the static mapping relationship between the DC-side current and DC-side voltage (also known as the startup voltage in low-voltage current limiting control) of an LCC-HVDC system. The static characteristic curve is used for the DC-side voltage U of a high-voltage direct current transmission system. dc Determine the DC current command value I for low-voltage current limiting control of the high-voltage direct current transmission system. ord .

[0029] Generally, the static characteristic curve can be determined by some fixed parameters, including the maximum and minimum allowable DC-side current values ​​of the LCC-HVDC system, and the DC-side voltage U. dc The maximum allowable voltage value (i.e., the maximum allowable DC-side voltage value) and the minimum allowable voltage value (i.e., the minimum allowable DC-side voltage value) are fixed parameters that can be determined by the performance of the high-voltage direct current transmission system.

[0030] The maximum allowable current value is used as the maximum allowable DC current command value I for the static characteristic curve. max And the minimum allowable current value as the minimum allowable DC current command value I for the static characteristic curve. min In the static characteristic curve, when the DC side voltage U dc If the DC current command value is less than the minimum allowable DC side voltage, then the corresponding DC current command value I... ord For I min When the DC side voltage U dc If the DC current command value is greater than the maximum allowable DC side voltage value, then the corresponding DC current command value I ord For I max When the DC side voltage U dc When the voltage is located within the closed interval formed by the minimum allowable DC-side voltage value and the maximum allowable DC-side voltage value, the corresponding DC current command value I is used to calculate the DC current. ord The linear function is determined, and the linear function is shown in the following formula: , ; The function corresponding to the static characteristic curve is as follows: ; like Figure 2 As shown, Figure 2 This is a schematic diagram of static characteristic curves provided for an embodiment of this application.

[0031] Step S2: Determine the elliptic curve equation based on the maximum and minimum allowable DC side voltage values, as well as the maximum and minimum allowable DC current command values ​​corresponding to the static characteristic curve.

[0032] Elliptic curve equations are used to calculate the DC current command value for low-voltage current limiting control of the HVDC transmission system. Elliptic curve equations characterize the functional relationship between the DC current command value and the DC side voltage of the HVDC transmission system.

[0033] The DC-side voltage value corresponding to the intersection point of the elliptic curve corresponding to the above elliptic curve equation and the static characteristic curve shall not be less than the maximum allowable DC-side voltage value.

[0034] Step S3: Replace the linear function in the initial function corresponding to the static characteristic curve with an elliptic curve equation to obtain the final objective function used to calculate the DC current command value.

[0035] Since the arc corresponding to the elliptic curve equation is concave, the DC current command value calculated by the elliptic curve equation based on the DC side voltage value of the high voltage direct current transmission system will be less than or equal to the DC current command value calculated by the static characteristic curve based on the same DC side voltage value.

[0036] Step S4: Substitute the target DC side voltage value currently monitored for the high voltage DC transmission system into the objective function to obtain the target DC current command value.

[0037] Step S5: Control the DC side current of the high-voltage direct current transmission system according to the target DC current command value.

[0038] The target DC-side voltage value mentioned above is the DC voltage currently monitored for the high-voltage direct current transmission system.

[0039] The aforementioned target DC current command value is a "safe" DC current level that the high-voltage direct current transmission system should strive to achieve and maintain under fault conditions.

[0040] Step S5 above can be: generating a control signal based on the error between the target DC current command value and the measured DC side current value, so as to adjust the converter of the high voltage DC transmission system so that the measured DC side current value tracks the target DC current command value.

[0041] In this embodiment, the static characteristic curve is adjusted based on fixed parameters corresponding to it to determine the objective function used to calculate the DC current command value. Given the same input DC-side voltage value, the DC current command value output by the objective function is less than or equal to the DC current command value determined by the static characteristic curve. Since a smaller output DC current command value results in a larger commutation margin and a better reduction in the probability of commutation failure, this embodiment... In lower cases, it can be based on subsequent In low-voltage current limiting control, commutation failure can be better suppressed.

[0042] In some embodiments, step S2 may include, but is not limited to, the following steps: The equation of the elliptic curve is determined by taking the minimum allowable DC side voltage value and the maximum allowable DC current command value corresponding to the static characteristic curve as the center of the ellipse, the target current difference as the minor semi-axis of the ellipse, and the sum of the target voltage difference and the fault coefficient as the major semi-axis of the ellipse.

[0043] That is, the center of the ellipse is ( , ).

[0044] The target current difference mentioned above is the difference between the maximum allowable DC-side voltage value and the minimum allowable DC-side voltage value, that is, the target current difference is... The target voltage difference mentioned above is the difference between the maximum allowable DC-side voltage value and the minimum allowable DC-side voltage value, that is, the target voltage difference is... .

[0045] The aforementioned fault factor K is used to characterize the severity of faults in the AC side voltage of a high-voltage direct current (HVDC) transmission system. The fault factor K can be calculated using the following formula: K=D×U ac / U acN , ; Where K represents the failure coefficient, U represents the preset coefficient. ac U represents the AC side voltage. acN This indicates the rated value of the AC side voltage.

[0046] In one embodiment, the above It can be set according to your needs; it can be set to 0.1, that is... .

[0047] In this embodiment, the sum of the target voltage difference and the fault coefficient is used as the major semi-axis of the ellipse, so that the elliptic curve equation can be dynamically adjusted based on different fault degrees, rather than a fixed curve, which can improve the flexibility of the curve function used to determine the DC current command value.

[0048] In some embodiments, step S3 may include, but is not limited to, the following steps: The DC-side voltage value corresponding to the intersection point of the elliptic curve corresponding to the elliptic curve equation and the static characteristic curve is determined as the new maximum allowable DC-side voltage value of the high-voltage direct current transmission system.

[0049] By replacing some interval functions in the initial function corresponding to the static characteristic curve with elliptic curve equations, the final objective function used to calculate the DC current command value is obtained.

[0050] Among them, the partial interval function is the function corresponding to the interval from the minimum allowable DC-side voltage value to the new maximum allowable DC-side voltage value in the initial function.

[0051] Because the interval corresponding to a linear function is a closed interval formed by the minimum allowable DC-side voltage value and the maximum allowable DC-side voltage value, some interval functions include linear functions.

[0052] Reference Figure 3 , Figure 3 This is a schematic diagram illustrating the intersection of an elliptic curve and a static characteristic curve provided in an embodiment of this application. The elliptic curve includes curve 1, curve 2, and curve 3, each corresponding to a different elliptic curve equation. The static characteristic curve... 0.9 pu 0.4 pu For 1pu and The fault coefficient K is 0.55 pu. The center of the ellipse in the elliptic curve equation is (0.4, 1), the minor semi-axis is 0.45, and the major semi-axis is defined as 0.5 + K. That is, the fault coefficient K values ​​corresponding to curves 1, 2, and 3 are different. Figure 3 As shown, the red solid lines of curves 1, 2 and 3 intersect the static characteristic curve at one point, and the DC-side voltage value corresponding to this intersection point is the new maximum allowable DC-side voltage value.

[0053] The objective function described above can be represented by the following formula: ; in, This indicates the new maximum permissible DC-side voltage value.

[0054] Therefore, in the objective function, when the DC-side voltage value is less than the minimum allowable DC-side voltage value, the calculated DC current command value is the minimum allowable DC current command value; when the DC-side voltage value is greater than the new maximum allowable DC-side voltage value, the calculated DC current command value is the maximum allowable DC current command value; and when the DC-side voltage value is within the closed interval formed by the minimum allowable DC-side voltage value and the new maximum allowable DC-side voltage value, the DC current command value is determined by the elliptic curve equation.

[0055] In this embodiment, since the major semi-axis corresponding to the elliptic curve equation can be determined by the fault coefficient, the maximum allowable DC side voltage value of the high voltage direct current transmission system can dynamically change with the different fault degrees. As the fault severity increases, the elliptic curve shifts to the right, and the maximum allowable DC side voltage value is larger. The low voltage current limiting link using the elliptic curve equation is accelerated, which can better suppress commutation failure.

[0056] In some embodiments, step S4 may also include, but is not limited to, the following steps: When the target DC-side voltage value monitored for the current high-voltage direct current transmission system is less than the minimum allowable DC-side voltage value, the target DC command value is determined to be the minimum allowable DC current command value based on the objective function.

[0057] When the target DC-side voltage value is greater than the new maximum allowable DC-side voltage value, the target DC command value is determined to be the maximum allowable DC current command value based on the objective function.

[0058] When the target DC-side voltage value is within the closed interval formed by the minimum allowable DC-side voltage value and the new maximum allowable DC-side voltage value, the target DC-side voltage value is substituted into the elliptic curve equation in the objective function to calculate and determine the target DC current command value.

[0059] In this embodiment, if the target DC-side voltage value is located within the closed interval formed by the minimum allowable DC-side voltage value and the new maximum allowable DC-side voltage value, then the target DC-side voltage value is substituted into the elliptic curve equation, and the target DC current command value is calculated and determined by the elliptic curve equation.

[0060] In this embodiment, the target function can output a DC current command value that is less than or equal to the static characteristic curve. Therefore, in this embodiment, the output... In lower cases, based on In low-voltage current limiting control, it can better suppress commutation failure.

[0061] To better understand the above solution, the embodiments of this application provide a more detailed description, as follows: In the field of long-distance, high-capacity power transmission, line-commutated high-voltage direct current (LCC-HVDC) transmission has been widely adopted due to its cost-effectiveness and technological maturity. However, the thyristors used in LCC-HVDC systems lack self-turn-off capability, making their operation highly dependent on the stability of the AC system. If a fault occurs in the AC system on the inverter side, the thyristors in the converter valve may fail to turn off normally due to insufficient reverse turn-off voltage, leading to commutation failure. Commutation failure causes a sudden increase in DC current, impacting power electronic equipment and affecting its lifespan. In severe cases, a single commutation failure may evolve into consecutive commutation failures, ultimately causing DC blockage and a complete power outage.

[0062] Low-voltage current limiting controllers (VDCOLs) are an important component of DC transmission inverter-side control, capable of suppressing commutation failures in the event of a fault. However, conventional VDCOLs have a fixed maximum starting voltage, and the starting voltage and output current command follow a linear curve, resulting in low sensitivity to faults of varying degrees and types. Consequently, during fault recovery, the balance between active power recovery and reactive power fluctuations is poor.

[0063] This invention provides an improved nonlinear VDCOL strategy for suppressing continuous commutation failures in high-voltage direct current transmission. It replaces the conventional linear VDCOL curve with an elliptic curve whose focus varies with the AC side voltage. Under the same input voltage, the elliptic curve has a smaller output current command, increasing the commutation margin and reducing the probability of commutation failure. During fault recovery, it effectively balances active power recovery and reactive power fluctuations. Furthermore, the maximum starting voltage of the VDCOL can be adjusted according to the severity of the AC side fault.

[0064] The function of a low-voltage current limiting controller (VDCOL) is to limit the DC current command when the DC or AC voltage drops to a specified value, thereby limiting the increase of DC current and accelerating the voltage drop. Reducing the current increases the commutation margin and reduces the possibility of commutation failure. The static characteristic curve of VDCOL is shown below. Figure 2 As shown.

[0065] Figure 2 middle VDCOL is the startup voltage. The VDCOL output current command value. , The maximum and minimum values ​​are the output current commands. , These are the maximum and minimum starting voltage values. Their characteristics are expressed by the following equation (1): (1); Conventional VDCOL uses fixed parameters, for example, It is 0.9 pu. It is 0.4 pu. It is 1 pu. The value is 0.55 pu. Fixed parameters result in insufficient VDCOL suppression of commutation failure. This paper employs an elliptic curve-modified VDCOL to suppress commutation failure, as follows: Figure 3 As shown, Figure 3 For the improved VDCOL curve.

[0066] The expression for the turn-off angle of a DC system is shown in equation (2) below: (2); In the formula, L r For commutation inductance, U L This is the commutation voltage on the inverter side. For the AC bus angular frequency, I dc It is direct current. To trigger the leading angle.

[0067] Depend on Figure 3 It can be seen that the VDCOL improved by elliptic curves, at the same starting voltage... Below, the current command value is output to the rectifier side. Lower values ​​better limit the increase in DC current at the onset of commutation failure. According to equation (2), using the VDCOL curve improved by elliptic curves can increase the turn-off angle and suppress commutation failure. When the voltage recovers, if the DC voltage is low, the AC side voltage and reactive power levels are low, and the VDCOL current command value improved by elliptic curves changes slowly, which can slow down the absorption of AC side reactive power by the inverter-side converter, causing the AC side reactive voltage to drop further and resulting in continuous commutation failure. If the DC voltage level is high, the AC side voltage level is high, which can provide more reactive power, and the DC current command value of the elliptic curve changes quickly, which can accelerate the recovery of active power transmission. The focus of the elliptic curve is related to the fault coefficient. As the severity of the fault increases, the elliptic curve shifts to the right, which speeds up the entry into the stage of using the elliptic curve equation to achieve low-voltage current limiting, and better suppresses commutation failure.

[0068] An improved nonlinear VDCOL strategy for suppressing continuous commutation failure in high-voltage direct current transmission includes the following steps: Step 1: In order to make the maximum starting voltage for low-voltage current limiting vary according to the severity of AC side faults, the fault factor K is defined as shown in equation (3): (3); In the formula U ac For AC side voltage, U acN This refers to the rated value of the AC side voltage.

[0069] Step 2: Determine the center of the elliptic curve and the lengths of its minor and major semi-axis. (From...) Figure 3 It can be seen that the center of the ellipse is (0.4, 1), the minor semi-axis is 0.45, and the major semi-axis is defined as 0.5+K.

[0070] Step 3: Based on the parameters from Step 2, the equation of the elliptic curve is: (4); Step 4: Derive the DC current command under the elliptic curve based on Step 3. expression: (5); Step 5: Verify the maximum starting voltage for different fault degrees based on the fault coefficient. The regulatory effect.

[0071] During normal operation, U ac =1, K=0, substituting into (5) gives: (6); Substituting the special points (0.4, 0.55) and (0.9, 1) into equation (6) for verification, we find that the points lie on equation (6). Figure 3For curve 1.

[0072] During severe fault operation, assume U ac =0, K=1, substituting into (5) gives: (7); Substituting the special points (0.4, 0.55) and (1, 1) into equation (6) for verification, we obtain that the points lie on equation (7). Figure 2 This is curve 3. Therefore, introducing a fault factor can change the VDCOL startup voltage, which better suppresses commutation failure.

[0073] Compared with the prior art, the advantages and positive effects of the present invention are: Using elliptic curves to improve VDCOL results in a smaller DC current command output value at the same input voltage, which can better reduce the DC current amplitude, increase commutation margin, and suppress commutation failure.

[0074] The elliptic curve used results in a low DC current command growth rate when the DC voltage is low, which can reduce the fluctuation of reactive power absorbed by the converter to the AC system and prevent continuous commutation loss caused by AC side voltage fluctuations. When the voltage value is high, the AC system voltage level is high and the reactive power is relatively sufficient, and the DC current command changes rapidly, which can accelerate the recovery of active power transmitted by the system.

[0075] By introducing a fault factor, the maximum starting voltage Umax of VDCOL can be changed according to the degree of voltage drop on the AC side during a fault, effectively suppressing continuous commutation failures.

[0076] To better implement the aforementioned low-voltage current limiting control method, this application provides a low-voltage current limiting control device, referring to... Figure 4 , Figure 4 This is a structural block diagram of the current command value calculation device provided in the embodiments of this application. The low-voltage current limiting control device 400 includes: The curve acquisition module 401 is used to acquire a determined static characteristic curve for low-voltage current limiting control of the high-voltage direct current transmission system when the DC side voltage value or AC side voltage value of the high-voltage direct current transmission system drops below a preset voltage threshold. The equation determination module 402 is used to determine the elliptic curve equation based on the maximum and minimum allowable DC-side voltage values ​​corresponding to the static characteristic curve, as well as the corresponding maximum and minimum allowable DC current command values. The elliptic curve equation represents the functional relationship between the DC current command value and the DC-side voltage of the high-voltage DC transmission system. The DC-side voltage value corresponding to the intersection point of the elliptic curve and the static characteristic curve is not less than the maximum allowable DC-side voltage value. The function determination module 403 is used to replace the linear function in the initial function corresponding to the static characteristic curve with the elliptic curve equation to obtain the final target function used to calculate the DC current command value. The instruction calculation module 404 is used to substitute the target DC side voltage value currently monitored for the high voltage DC transmission system into the objective function to obtain the target DC current instruction value; The current control module 405 is used to control the DC side current of the high voltage DC transmission system according to the target DC current command value.

[0077] In some embodiments, the equation determination module 402 can be specifically used to: determine the equation of an elliptic curve with the minimum allowable DC-side voltage value and the maximum allowable DC-side current command value corresponding to the static characteristic curve as the center of the ellipse, the target current difference as the minor semi-axis of the ellipse, and the sum of the target voltage difference and the fault coefficient as the major semi-axis of the ellipse; wherein, the target current difference is the difference between the maximum allowable DC-side voltage command value and the minimum allowable DC-side voltage command value, the target voltage difference is the difference between the maximum allowable DC-side voltage value and the minimum allowable DC-side voltage value, and the fault coefficient is used to characterize the fault severity of the AC-side voltage of the high-voltage DC transmission system.

[0078] In some embodiments, the formula for calculating the fault coefficient in module 502 determined by the above equation is as follows: K=D×U ac / U acN , ; Where K represents the fault coefficient of the elliptic curve equation. U represents the preset coefficient. ac U represents the AC side voltage represented by the elliptic curve equation. acN This indicates the rated value of the AC side voltage.

[0079] In some embodiments, the function determination module 403 may be specifically used to: determine the DC-side voltage value corresponding to the intersection point of the elliptic curve corresponding to the elliptic curve equation and the static characteristic curve as the new maximum allowable DC-side voltage value of the high-voltage direct current transmission system; replace a portion of the interval function in the initial function corresponding to the static characteristic curve with the elliptic curve equation to obtain the final target function used to calculate the DC current command value; wherein, the portion of the interval function is the function corresponding to the interval from the minimum allowable DC-side voltage value to the new maximum allowable DC-side voltage value in the initial function, and the portion of the interval function includes linear functions.

[0080] In some embodiments, the instruction calculation module 404 may be specifically used to: when the target DC side voltage value currently monitored for the high voltage DC transmission system is less than the minimum allowable DC side voltage value, determine the target DC instruction value as the minimum allowable DC current instruction value based on the objective function; when the target DC side voltage value is greater than the new maximum allowable DC side voltage value, determine the target DC instruction value as the maximum allowable DC current instruction value based on the objective function; when the target DC side voltage value is within the closed interval formed by the minimum allowable DC side voltage value and the new maximum allowable DC side voltage value, substitute the target DC side voltage value into the elliptic curve equation in the objective function to calculate and determine the target DC current instruction value.

[0081] The low-voltage current limiting control device 400 provided in this application embodiment can execute the technical solution shown in the above method embodiment. Its implementation principle and beneficial effects are similar, and will not be repeated here.

[0082] Figure 5 An internal structural diagram of a computer device in one embodiment is shown. This computer device can specifically be a terminal or a server. Figure 5 As shown, the computer device includes a processor, memory, and a network interface connected via a system bus. The memory includes a non-volatile storage medium and internal memory. The non-volatile storage medium stores an operating system and may also store a computer program that, when executed by the processor, enables the processor to implement an age recognition method. The internal memory may also store a computer program that, when executed by the processor, enables the processor to implement the age recognition method. Those skilled in the art will understand that... Figure 5 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0083] In one embodiment, a computer device is provided, including a memory and a processor, the memory storing a computer program that, when executed by the processor, causes the processor to perform the following steps: When the DC-side voltage or AC-side voltage of the high-voltage direct current transmission system drops below a preset voltage threshold, the determined static characteristic curve for low-voltage current limiting control of the high-voltage direct current transmission system is obtained. Based on the maximum and minimum allowable DC-side voltage values ​​corresponding to the static characteristic curve, as well as the corresponding maximum and minimum allowable DC current command values, the elliptic curve equation is determined. The elliptic curve equation characterizes the functional relationship between the DC current command value and the DC-side voltage of the high-voltage DC transmission system. The DC-side voltage value corresponding to the intersection of the elliptic curve equation and the static characteristic curve is not less than the maximum allowable DC-side voltage value. The linear function in the initial function corresponding to the static characteristic curve is replaced with an elliptic curve equation to obtain the final objective function used to calculate the DC current command value. Substitute the target DC side voltage value currently monitored for the high-voltage direct current transmission system into the objective function to obtain the target DC current command value; The DC-side current of the high-voltage direct current transmission system is controlled according to the target DC current command value.

[0084] In one embodiment, a computer-readable storage medium is provided storing a computer program that, when executed by a processor, causes the processor to perform the following steps: When the DC-side voltage or AC-side voltage of the high-voltage direct current transmission system drops below a preset voltage threshold, the determined static characteristic curve for low-voltage current limiting control of the high-voltage direct current transmission system is obtained. Based on the maximum and minimum allowable DC-side voltage values ​​corresponding to the static characteristic curve, as well as the corresponding maximum and minimum allowable DC current command values, the elliptic curve equation is determined. The elliptic curve equation characterizes the functional relationship between the DC current command value and the DC-side voltage of the high-voltage DC transmission system. The DC-side voltage value corresponding to the intersection of the elliptic curve equation and the static characteristic curve is not less than the maximum allowable DC-side voltage value. The linear function in the initial function corresponding to the static characteristic curve is replaced with an elliptic curve equation to obtain the final objective function used to calculate the DC current command value. Substitute the target DC side voltage value currently monitored for the high-voltage direct current transmission system into the objective function to obtain the target DC current command value; The DC-side current of the high-voltage direct current transmission system is controlled according to the target DC current command value.

[0085] In conjunction with the methods in the above embodiments, this application also provides a computer program product, wherein the instructions in the computer program product, when executed by the processor of a computer device, cause the computer device to implement the low-voltage current limiting control method in the above embodiments.

[0086] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments described above. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and RAMbus dynamic RAM (RDRAM), etc.

[0087] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims. Please enter the specific implementation details.

Claims

1. A low voltage current limit control method, characterized by, The method comprises: In the case that the DC side voltage value or the AC side voltage value of the high-voltage direct current power transmission system falls below a preset voltage threshold, a determined static characteristic curve for low-voltage current limiting control of the high-voltage direct current power transmission system is acquired; An elliptic curve equation is determined according to the maximum allowable DC side voltage value and the minimum allowable DC side voltage value corresponding to the static characteristic curve, and the maximum allowable DC current instruction value and the minimum allowable DC current instruction value; wherein the elliptic curve equation represents a functional relationship between a DC current instruction value and a DC side voltage of the high-voltage direct current power transmission system, and a DC side voltage value corresponding to an intersection point of the elliptic curve corresponding to the elliptic curve equation and the static characteristic curve is not less than the maximum allowable DC side voltage value; A linear function in an initial function corresponding to the static characteristic curve is replaced by the elliptic curve equation to obtain a target function for calculating a DC current instruction value; A target DC side voltage value currently monitored for the high-voltage direct current power transmission system is substituted into the target function to obtain a target DC current instruction value; The DC side current of the high-voltage direct current power transmission system is controlled according to the target DC current instruction value.

2. The method of claim 1, wherein, The elliptic curve equation is determined according to the maximum allowable DC side voltage value and the minimum allowable DC side voltage value corresponding to the static characteristic curve, and the maximum allowable DC current instruction value and the minimum allowable DC current instruction value, comprising: An elliptic curve equation is determined with the minimum allowable DC side voltage value and the maximum allowable DC current instruction value corresponding to the static characteristic curve as the center of the ellipse, a target current difference value as the short semi-axis of the ellipse, and a sum of a target voltage difference value and a fault coefficient as the long semi-axis of the ellipse; wherein the target current difference value is a difference between the maximum allowable DC current instruction value and the minimum allowable DC current instruction value, the target voltage difference value is a difference between the maximum allowable DC side voltage value and the minimum allowable DC side voltage value, and the fault coefficient is used to represent the fault severity of the AC side voltage of the high-voltage direct current power transmission system.

3. The method of claim 1, wherein, The linear function in the initial function corresponding to the static characteristic curve is replaced by the elliptic curve equation to obtain the target function for calculating the DC current instruction value, comprising: A DC side voltage value corresponding to an intersection point of the elliptic curve corresponding to the elliptic curve equation and the static characteristic curve is determined as a new maximum allowable DC side voltage value of the high-voltage direct current power transmission system; A part interval function in the initial function corresponding to the static characteristic curve is replaced by the elliptic curve equation to obtain the target function for calculating the DC current instruction value; wherein the part interval function is a function corresponding to an interval from the minimum allowable DC side voltage value to the new maximum allowable DC side voltage value in the initial function, and the part interval function includes the linear function.

4. The method of claim 3, wherein, The target DC side voltage value currently monitored for the high-voltage direct current power transmission system is substituted into the target function to obtain the target DC current instruction value, comprising: when the target DC side voltage value currently monitored by the HVDC power transmission system is less than the minimum allowable DC side voltage value, determining the target DC instruction value as the minimum allowable DC current instruction value based on the target function; when the target DC side voltage value is greater than the new maximum allowable DC side voltage value, determining the target DC instruction value as the maximum allowable DC current instruction value based on the target function; when the target DC side voltage value is within the closed interval formed by the minimum allowable DC side voltage value and the new maximum allowable DC side voltage value, substituting the target DC side voltage value into the elliptic curve equation in the target function to determine the target DC current instruction value.

5. The method of claim 2, wherein, The calculation formula of the fault coefficient is as follows: K = D x U ac / U acN , ; wherein K represents the failure coefficient, represents a preset coefficient, U ac represents the AC side voltage, U acN represents an AC side voltage rated value.

6. A low voltage current limiting control device, characterized by, The device comprises: a curve acquisition module, configured to acquire a determined static characteristic curve for low-voltage current limiting control of the HVDC power transmission system when a DC side voltage value or an AC side voltage value of the HVDC power transmission system drops below a preset voltage threshold; an equation determination module, configured to determine an elliptic curve equation according to a maximum allowable DC side voltage value and a minimum allowable DC side voltage value corresponding to the static characteristic curve, and a maximum allowable DC current instruction value and a minimum allowable DC current instruction value corresponding to the static characteristic curve; wherein the elliptic curve equation represents a functional relationship between the DC current instruction value and the DC side voltage of the HVDC power transmission system, and a DC side voltage value corresponding to an intersection point of the elliptic curve corresponding to the elliptic curve equation and the static characteristic curve is not less than the maximum allowable DC side voltage value; a function determination module, configured to replace a linear function in an initial function corresponding to the static characteristic curve with the elliptic curve equation to obtain a target function for calculating a DC current instruction value; an instruction calculation module, configured to substitute a target DC side voltage value currently monitored by the HVDC power transmission system into the target function to obtain a target DC current instruction value; a current control module, configured to control a DC side current of the HVDC power transmission system according to the target DC current instruction value.

7. The apparatus of claim 6, wherein, The equation determination module is further configured to determine an elliptic curve equation with the minimum allowable DC side voltage value and the maximum allowable DC current instruction value corresponding to the static characteristic curve as the center of an ellipse, with a target current difference value as a short semi-axis of the ellipse, and with a sum of a target voltage difference value and a fault coefficient as a long semi-axis of the ellipse; wherein the target current difference value is a difference between the maximum allowable DC current instruction value and the minimum allowable DC current instruction value, the target voltage difference value is a difference between the maximum allowable DC side voltage value and the minimum allowable DC side voltage value, and the fault coefficient is used to represent the severity of an AC side voltage fault of the HVDC power transmission system.

8. A computer-readable storage medium storing a computer program, the computer program being executed by a processor to cause the processor to perform the steps of the method of any one of claims 1 to 5.

9. A computer device comprising a memory and a processor, the memory storing a computer program, the computer program, when executed by the processor, causing the processor to perform the steps of the method of any one of claims 1 to 5.

10. A computer program product, instructions in the computer program product, when executed by a processor of a computer device, causing the processor to perform the steps of the method of any one of claims 1 to 5.

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