Low-voltage current-limiting control method and system based on fault detection

Abstract

The invention discloses a low-voltage current-limiting control method and system based on fault detection, and relates to the technical field of safety and stability analysis and control of an electric power system, and the method comprises the steps: detecting the voltage of a commutation bus of an AC system in real time; respectively carrying out asymmetric fault detection and symmetric fault detection by adopting a zero-sequence component detection method and a component detection method at the same time according to the voltage of the converter bus, so as to monitor the running state of the system; when it is monitored that the alternating current system breaks down, a low-voltage current-limiting controller is started to adjust an original direct current instruction in real time, and a final direct current instruction is output, so that the direct current instruction is rapidly reduced, and the first commutation failure of the direct current system is inhibited; wherein the adjustment of the original direct current instruction means that the original direct current instruction is adjusted to be reduced and limited at a low level according to a set adjustment amplitude. According to the invention, the commutation margin and the fault response sensitivity can be effectively improved, and the prevention and suppression capability of the first commutation failure is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of power system safety and stability analysis and control, and in particular to a low voltage current limiting control method and system based on fault detection. Background Art

[0002] Based on the current complex AC / DC hybrid power grid scenario, AC system failures can easily lead to commutation failures in the DC system. When the first commutation failure occurs, the DC voltage and current fluctuate violently, which impacts the power grid equipment and easily leads to subsequent commutation failures. In severe cases, it causes DC lockout and interrupts power transmission. In addition, due to the interaction between AC / DC systems and multiple DC systems, commutation failures may evolve into continuous or multiple DC system power shocks, seriously threatening the safe and stable operation of AC / DC hybrid power grids. To avoid the above situation, a DC protection control strategy that can suppress commutation failures has been proposed, among which the low voltage dependent current order limiter (VDCOL) strategy occupies a major position.

[0003] The VDCOL strategy reduces the DC current quickly after a fault based on the mathematical relationship between the shutdown angle and the AC and DC electrical quantities. This can compensate for the reduced commutation margin due to the commutation voltage drop, reduce the reactive power demand of the converter station during the recovery process, and suppress subsequent commutation failures. However, this VDCOL strategy has poor timeliness and sensitivity in starting and responding under different fault conditions, and is unable to start and respond quickly, resulting in weak ability to suppress the first commutation failure and insufficient ability to prevent the first commutation failure. Summary of the invention

[0004] In order to solve the deficiencies of the above-mentioned prior art, the present invention provides a low voltage current limiting control method and system based on fault detection, which monitors the operating status of the AC system in real time, and uses the judgment result of whether a fault occurs in the system operation as the adjustment start criterion, and introduces the adjustment start criterion into the low voltage current limiting control (VDCOL), so that after a fault occurs in the AC system, the controller can be started in time to control and adjust the DC current instruction, and first limit it to a low level to achieve a rapid reduction of the DC current instruction, thereby suppressing the first commutation failure; the above-mentioned control strategy can effectively improve the commutation margin and fault response sensitivity, and enhance the prevention and suppression capabilities of the first commutation failure.

[0005] In a first aspect, the present invention provides a low voltage current limiting control method based on fault detection.

[0006] A low voltage current limiting control method based on fault detection, comprising:

[0007] For AC / DC hybrid power grid, real-time detection of the commutation bus voltage of the AC system;

[0008] According to the commutation bus voltage, the zero-sequence component detection method and the αβ component detection method are used simultaneously to perform asymmetric fault detection and symmetric fault detection respectively, so as to monitor the system operation status;

[0009] When a fault is detected in the AC system, the low voltage current limiting controller is started to adjust the original DC current command in real time, and the final DC current command is output to quickly reduce the DC current command, thereby suppressing the first commutation failure of the DC system; wherein, adjusting the original DC current command means adjusting the original DC current command to reduce and limit it to a low level according to a set adjustment range.

[0010] A further technical solution is to take the minimum value of the adjusted DC current instruction and the DC current instruction output by the VDCOL characteristic curve as the final DC current instruction and output it.

[0011] A further technical solution is that after the controller is started, it continues for a set time period, and then determines the current fault detection result based on real-time detection data. If no fault is detected, the controller exits. Otherwise, the controller is started again for a set time period, and the detection steps are repeated in a cycle until no fault is detected, and the controller exits.

[0012] A further technical solution is to monitor the system operation status in real time, determine whether the system fails, and use the determination result as a criterion for adjusting the start, including:

[0013] The zero-sequence component detection method is used for asymmetric fault detection, which is: according to the three-phase voltage of the commutation bus obtained in real time, the zero-sequence voltage component is calculated, and then the zero-sequence voltage component is compared with the preset zero-sequence voltage threshold value, and whether an asymmetric fault occurs is determined according to the comparison result; wherein, when the zero-sequence voltage component is greater than the preset zero-sequence voltage threshold value, it is determined that an asymmetric fault occurs, and the regulation control is started at this time, otherwise it is not started;

[0014] The αβ component detection method is used for symmetrical fault detection, which is: according to the three-phase phase voltage of the commutation bus obtained in real time, the angular velocity rotation vector amplitude is calculated, and the difference between the angular velocity rotation vector amplitudes before and after the fault is calculated, and then the difference is compared with the preset voltage amplitude threshold value, and whether a symmetrical fault occurs is determined according to the comparison result; wherein, when the difference is greater than the preset voltage amplitude threshold value, it is determined that a symmetrical fault occurs, and the regulation control is started at this time, otherwise it is not started.

[0015] In a further technical solution, the calculation of the zero-sequence voltage component includes:

[0016] According to the real-time acquisition of the three-phase phase voltage U a , U b , U c, through the average operation, the zero-sequence voltage component U is calculated 0 , the formula is:

[0017] The calculation of the angular velocity rotation vector amplitude includes:

[0018] The real-time three-phase phase voltage U a , U b , U c Perform Clark transformation to obtain the transformed two-phase voltage U α , U β , and calculate the angular velocity rotation vector amplitude U αβ , the formula is:

[0019]

[0020]

[0021] A further technical solution introduces the adjustment start criterion into the low voltage current limit control, with the goal of preventing the first commutation failure, and calculates the set adjustment amplitude and the preset voltage threshold value of the DC current command; the preset voltage threshold value includes a preset zero-sequence voltage threshold value and a preset voltage amplitude threshold value; the calculation and determination of the set adjustment amplitude includes:

[0022] Based on the current loop equation satisfied during the commutation process, the voltage-time area expression required to complete the commutation is obtained;

[0023] Derive the expressions of the turn-off angle and the DC current on the inverter side when the phase voltage zero-crossing offset is ignored;

[0024] According to the voltage-time area expression, the analysis is performed, and based on the expressions of the turn-off angle and DC current, the DC voltage on the inverter side and the Echizen trigger angle are set. The corresponding relationship between the change amplitude of the DC current on the inverter side and the change amplitude of the turn-off angle is calculated to determine the DC current command adjustment amplitude that can suppress commutation failure and is used as the set adjustment amplitude.

[0025] In a further technical solution, the calculation and determination of the preset voltage threshold value includes:

[0026] Only the voltage threshold value is used as a variable, and the variation range of the voltage threshold value variable is set. At the same time, a simulation scenario of a three-phase ground short circuit fault occurring in the commutation bus through different transition inductances is set; wherein the three-phase ground short circuit fault includes a symmetrical fault and an asymmetrical fault;

[0027] Based on the simulation results, the situations of suppressing the first commutation failure corresponding to different voltage threshold values ​​under various faults are determined, and the optimal parameter value of the voltage threshold value is selected and used as the preset voltage threshold value.

[0028] In a second aspect, the present invention provides a low voltage current limiting control system based on fault detection.

[0029] A low voltage current limiting control system based on fault detection, comprising:

[0030] A data acquisition module is used to detect the commutation bus voltage of the AC system in real time for the AC / DC hybrid power grid;

[0031] A fault detection module is used to perform asymmetric fault detection and symmetric fault detection respectively according to the commutation bus voltage by using a zero-sequence component detection method and an αβ component detection method, so as to monitor the system operation status;

[0032] The DC current command adjustment module is used to start the low voltage current limiting controller to adjust the original DC current command in real time when a fault in the AC system is detected, and output the final DC current command to quickly reduce the DC current command, thereby suppressing the first commutation failure of the DC system; wherein, adjusting the original DC current command means adjusting the original DC current command to reduce and limit it to a low level according to a set adjustment range.

[0033] One or more of the above technical solutions have the following beneficial effects:

[0034] 1. The present invention provides a low voltage current limiting control method and system based on fault detection, which monitors the operating status of the AC system in real time, uses the judgment result of whether a fault occurs in the system operation as the adjustment start criterion, and introduces the adjustment start criterion into the low voltage current limiting control (VDCOL), so that after a fault occurs in the AC system, the controller can be started in time to control and adjust the DC current instruction, and it is first limited to a low level to achieve a rapid reduction of the DC current instruction, thereby suppressing the first commutation failure.

[0035] 2. Compared with the existing low voltage current limiting control (VDCOL) strategy, the low voltage current limiting control method based on fault detection proposed in the present invention can start and respond promptly and quickly under different fault conditions, effectively improve the commutation margin and fault response sensitivity, thereby reducing the risk of the first commutation failure, enhancing the prevention and suppression capabilities of the first commutation failure, and contributing to the safe and stable operation of the AC / DC hybrid power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0037] Figure 1This is an overall flow chart of the low voltage current limiting control method based on fault detection according to an embodiment of the present invention;

[0038] Figure 2 The figure is a schematic diagram of the comparison curve of the electrical quantity simulation corresponding to the first commutation failure prevention effect of the method described in the embodiment of the present invention and the existing VDCOL control strategy under symmetrical fault; wherein (a) is the turn-off angle curve, (b) is the DC current curve, (c) is the commutation bus voltage curve, and (d) is the DC current command curve. DETAILED DESCRIPTION

[0039] It should be noted that the following detailed descriptions are exemplary only, are intended to describe specific embodiments, are intended to provide further explanation of the present invention, and are not intended to limit exemplary embodiments according to the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those of ordinary skill in the art to which the present invention belongs. In addition, it should also be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0040] Embodiment 1

[0041] This embodiment provides a low voltage current limiting control method based on fault detection, including:

[0042] For AC / DC hybrid power grid, real-time detection of the commutation bus voltage of the AC system;

[0043] According to the commutation bus voltage, the zero-sequence component detection method and the αβ component detection method are used simultaneously to perform asymmetric fault detection and symmetric fault detection respectively, so as to monitor the system operation status;

[0044] When a fault is detected in the AC system, the low voltage current limiting controller is started to adjust the original DC current command in real time, and the final DC current command is output to quickly reduce the DC current command, thereby suppressing the first commutation failure of the DC system; wherein, adjusting the original DC current command means adjusting the original DC current command to reduce and limit it to a low level according to a set adjustment range.

[0045] The low voltage current limiting control method based on fault detection proposed in this embodiment is introduced in more detail through the following content.

[0046] like Figure 1 As shown, first, the operating status of the AC system is monitored in real time to detect the occurrence of system failures in a timely manner.

[0047] For the AC / DC hybrid power grid, the commutation bus voltage of the AC system is collected and detected in real time, and the system state is sensed and judged according to the corresponding detection data. In this embodiment, a PMU measurement device is configured, and the voltage data of the device is used for high-frequency acquisition, which can reach the microsecond to millisecond level. On this basis, the zero-sequence component detection method and the αβ component detection method are used at the same time to perform asymmetric fault detection and symmetric fault detection respectively, so as to judge whether the system has a fault; the judgment result is used as the adjustment start criterion, and the asymmetric fault detection and symmetric fault detection modules are set. When it is detected that the detection signal output by any detection module of symmetrical fault or asymmetric fault is valid (that is, the fault is detected), the controller is started in time to adjust the DC current command. Through the above method, it is possible to achieve timely and rapid start response under different fault conditions.

[0048] Specifically, when a single-phase ground short circuit or two-phase short circuit ground fault (both are asymmetric faults) occurs in the AC system, a zero-sequence component will appear in the commutation bus voltage. Therefore, the zero-sequence component detection method can be used to detect asymmetric faults at this time, specifically:

[0049] First, according to the real-time three-phase voltage U a , U b , U c , through the average operation, the zero-sequence voltage component U is calculated 0 , the formula is shown in the following formula (1):

[0050]

[0051] Secondly, the zero-sequence voltage component U 0 and the preset zero-sequence voltage threshold U threshold_0 Compare and judge whether an asymmetric fault occurs according to the comparison result. 0 Greater than the preset zero-sequence voltage threshold U threshold_0 When an asymmetric fault occurs, it is judged that the regulation control occurs, and otherwise it is not started.

[0052] Similarly, the αβ component detection method is used for symmetrical fault detection, specifically:

[0053] First, according to the real-time three-phase voltage U a , U b , U c , calculate the angular velocity rotation vector amplitude. That is, the three-phase phase voltage U a , U b , U c Perform Clark transformation (Clark transformation is a method of converting three-phase current or voltage into two-phase current or voltage) to obtain the transformed two-phase voltage Uα , U β , and calculate the angular velocity rotation vector amplitude U αβ , i.e., the αβ component, which is essentially the difference between the phase voltages, and the calculation formula is shown in the following equations (2) and (3):

[0054]

[0055] Secondly, calculate the angular velocity rotation vector amplitude U before and after the fault αβ The difference is then compared with the preset voltage amplitude threshold value U threshold_αβ A comparison is made, and whether a symmetrical fault occurs is determined based on the comparison result. When the difference is greater than a preset voltage amplitude threshold, it is determined that a symmetrical fault occurs, and the regulation control is started at this time, otherwise it is not started.

[0056] Since no matter what kind of fault occurs, the components are calculated only from the positive-sequence components and negative-sequence components of the AC voltage, and do not include the zero-sequence component, the components need to cooperate with the zero-sequence component fault detection algorithm to effectively cover various types of faults.

[0057] Secondly, based on the monitoring results of the AC system operation status, when the AC system is detected to have a fault, the low voltage current limiting controller is started to control the original DC current command I res (The command here actually refers to the command value) to make real-time adjustments and output the final DC current command I order , so that the DC current command is reduced quickly, thereby suppressing the first commutation failure of the DC system. res Adjusting means that the original DC current command is adjusted according to the set adjustment range to reduce and limit it to a low level.

[0058] In the above process, starting the low voltage current limiting controller to adjust the original DC current command is one of the important steps to suppress the first commutation failure of the DC system, and how to adjust is the top priority. In this embodiment, the original DC current command is reduced by adjusting the adjustment amplitude according to the set adjustment amplitude, and the adjusted command value is limited to a low level; similarly, in order to ensure the suppression of the first commutation failure of the DC system, timely starting the low voltage current limiting controller is also one of the important steps. This embodiment achieves timely response through the above system operation status monitoring, wherein setting an accurate fault judgment threshold can ensure timely detection and identification of faults, and then ensure timely response at the start. In this embodiment, the adjustment start criterion is introduced into the low voltage current limiting control, with the goal of preventing the first commutation failure, and the set adjustment amplitude and preset voltage threshold value (including preset zero-sequence voltage threshold value and preset voltage amplitude threshold value) of the DC current command are calculated and determined.

[0059] (1) Calculation and determination of the adjustment range, including:

[0060] First, based on the current loop equation satisfied during the commutation process, as shown in the following equation (4), the voltage-time area expression required to complete the commutation is obtained, as shown in the following equation (5).

[0061]

[0062] Where U d and I d They represent the DC voltage and DC current on the inverter side, respectively, and e a 、e b and e c Represents three-phase AC voltage, X r =2ωL r is the commutation reactance, L r is the equivalent commutation inductance, i 1 is the current flowing in thyristor 1, γ is the inverter side turn-off angle; ω is the AC side angular frequency; β is the Echizen trigger angle.

[0063] Based on the above formula, it can be seen that during the commutation period, if the DC current is suppressed to a smaller value, the voltage-time area required for commutation can be reduced accordingly, thereby reducing the probability of commutation failure.

[0064] Secondly, according to the system circuit, the expressions of the turn-off angle and the inverter-side DC current when the phase voltage zero-crossing offset is ignored are derived, as shown in the following equations (6) and (7):

[0065]

[0066] Where, γ is the inverter side turn-off angle; ω is the AC side angular frequency; U L is the effective value of the inverter side commutation bus line voltage; β is the Echizen trigger angle.

[0067] Finally, based on the above expressions of the turn-off angle and the DC current, the inverter side DC voltage and the Echizen trigger angle are set. In this embodiment, U L As a constant and β is taken as 38° (usually 38° when the DC system is operating normally), the corresponding relationship between the DC current change amplitude on the inverter side and the turn-off angle change amplitude is calculated, that is, the turn-off angle change amplitude corresponding to the DC current change amplitude is calculated to obtain the DC current command adjustment amplitude that can suppress commutation failure and effectively reduce the risk of commutation failure, and this value is used as the set adjustment amplitude. At this time, formula (7) can be approximately expressed as the following formula (8):

[0068] I d ≈c(cosγ-cos38°)(8)

[0069] In the formula, c can be regarded as a constant.

[0070] Furthermore, considering that the turn-off angle γ must be at least greater than 7° to avoid commutation failure, the above formula shows that when I d When the decrease is 10%, the turn-off angle will increase from 0° to 11.8°, which means that when the DC current command decreases by 10%, the commutation failure can be avoided, effectively reducing the risk of commutation failure. res When controlling, the magnitude of the reduction is set to 0.1.

[0071] (2) Calculation and determination of the preset voltage threshold value, including:

[0072] Firstly, only the voltage threshold value is used as a variable, and the variation range of the voltage threshold value variable is set. At the same time, a simulation scenario is set in which a three-phase ground short-circuit fault occurs in the commutation bus through different transition inductors; wherein the three-phase ground short-circuit fault includes a symmetrical fault and an asymmetrical fault; secondly, based on the simulation results, the situations of suppressing the first commutation failure corresponding to different voltage threshold values ​​under various faults are determined, and the lowest value is selected as the optimal parameter value of the voltage threshold value, and the optimal parameter value is used as the preset voltage threshold value.

[0073] Specifically, this embodiment summarizes that, in PSCAD / EMTDC, taking the CIGRE-HVDC (high voltage direct current transmission) standard test system as an example, the influence of the preset voltage threshold value in the fault detection process in the DC current command control method based on fault voltage detection on the first commutation failure prevention effect is analyzed, and the optimal parameter value is selected. Among them, only the voltage threshold value is set as a variable, and the variation range of the voltage threshold value variable is set, and the preset voltage threshold value U of the symmetrical fault detection is used. threshold_αβ As an example, assume that the variation range is 0.1pu to 0.15pu, the variation interval is 0.025pu, and a simulation scenario is set in which a three-phase ground short circuit fault occurs in the commutation busbar through different transition inductors (any inductor can be used to simulate different fault conditions, and different inductors indicate different fault severity), the fault duration is 0.05s, and the fault start time is 1.000s as the reference point. A group of simulations is performed every 1ms. Based on the simulation results, the commutation conditions corresponding to different preset threshold values ​​under various faults are analyzed. In this embodiment, the lower value of the two voltage threshold values ​​is selected as the optimal value according to the simulation results, U threshold_αβ Take 0.1pu, U threshold_0 The lower value is selected as the optimal value here because if the lowest value is selected, the strategy will be started frequently. However, for some minor faults, it will not actually cause commutation failure and there is no need to start the strategy.

[0074] Furthermore, in the above process, the low voltage current limiting controller is started to control the original DC current instruction Ires Real-time regulation is performed, that is, the original DC current instruction is adjusted to be reduced and limited to a low level according to the set adjustment amplitude. In this embodiment, when the detection signal is valid, I res The value of will first be reduced from 1.0pu to 0.9pu, thereby quickly limiting the DC current to prevent the first commutation failure. On this basis, preferably, based on the adjusted DC current command I res The DC current command I output by the VDCOL characteristic curve ord , take the minimum value as the final DC current command I order And output, where the DC current command I output by the VDCOL characteristic curve ord It can be expressed by the following formula (9): the final output DC current command I order It can be expressed by the following formula (10):

[0075]

[0076] Where U d_2 is the high voltage threshold; U d_1 is the low voltage threshold; I d_1 is the lower limit of current command; I d_2 It is the upper limit of current command, usually the rated current value of DC system operation.

[0077] Finally, the final DC current command I order , so that the DC current command is reduced quickly, thereby suppressing the first commutation failure of the DC system. Further, after the controller is started, it continues for a set time period, which is 100ms in this embodiment, and then judges the current fault detection result according to the real-time detection data. If no fault is detected (that is, the detection signal is invalid), the controller exits. Otherwise, the controller is started again for a set time period, and the detection steps are repeated in a loop until no fault is detected at present, and the controller exits, thereby avoiding unnecessary DC current regulation and causing large power loss.

[0078] In the above scheme, rapid fault detection can be achieved through microsecond / millisecond level voltage data collection and simple operation of voltage signals. At the same time, the starting threshold is preset offline according to the simulation results, and no longer needs to participate in the online process, so timely start-up adjustment can be achieved. Moreover, the DC system is a power electronic device, and the adjustment of current is at the millisecond level. Therefore, the above control strategy proposed in this embodiment can effectively guarantee the timeliness and sensitivity of its regulation and avoid the first commutation failure.

[0079] The effectiveness and superiority of the improved VDCOL control strategy proposed in this embodiment for preventing the first commutation failure are further analyzed and verified through the following examples.

[0080] A three-phase symmetrical fault is set at the inverter side commutation bus of the DC system. The fault occurs at 1.001s and lasts for 0.05s. The grounding inductance is 1.59H. The prevention effect of the control strategy described in this embodiment and the existing control strategy on the first commutation failure under symmetrical fault is obtained and observed. The corresponding electrical quantity simulation comparison curve is as follows: Figure 2 As shown. Figure 2 It can be seen that under the original control, the shutdown angle of the DC system after the fault was lower than the limit shutdown angle and commutation failure occurred; when the proposed improved control strategy was adopted, the shutdown angle was successfully increased to above 7°, thus avoiding the first commutation failure. In addition, since the surge amplitude of the DC current was suppressed and quickly reduced to a smaller value, the reactive power consumption of the DC system was reduced, thereby improving the commutation voltage level to a certain extent.

[0081] In summary, the control strategy proposed in this embodiment starts faster than the existing control strategy, and can quickly reduce the current command to limit the DC current in advance, successfully preventing the first commutation failure. That is, compared with the existing method, the method proposed in this embodiment has higher fault response sensitivity to different fault conditions, and effectively enhances the ability of DC to resist the first commutation failure.

[0082] Embodiment 2

[0083] This embodiment provides a low voltage current limiting control system based on fault detection, including:

[0084] A data acquisition module is used to detect the commutation bus voltage of the AC system in real time for the AC / DC hybrid power grid;

[0085] A fault detection module is used to perform asymmetric fault detection and symmetric fault detection respectively according to the commutation bus voltage by using a zero-sequence component detection method and an αβ component detection method, so as to monitor the system operation status;

[0086] The DC current command adjustment module is used to start the low voltage current limiting controller to adjust the original DC current command in real time when a fault in the AC system is detected, and output the final DC current command to quickly reduce the DC current command, thereby suppressing the first commutation failure of the DC system; wherein, adjusting the original DC current command means adjusting the original DC current command to reduce and limit it to a low level according to a set adjustment range.

[0087] Based on the above system, the low voltage current limiting controller is started to control the original DC current command I res Real-time adjustment is performed, that is, the original DC current instruction is adjusted to be reduced and limited to a low level according to the set adjustment range. On this basis, preferably, based on the adjusted DC current instruction I res The DC current command I output by the VDCOL characteristic curve ord, take the minimum value as the final DC current command I order And output.

[0088] Finally, the final output DC current command I order , so that the DC current command is reduced quickly, thereby suppressing the first commutation failure of the DC system. Furthermore, after the controller is started, it continues to set a time period, and then judges the current fault detection result according to the real-time detection data. If there is no fault (that is, the detection signal is invalid), the controller exits. Otherwise, the controller is started again for a set time period, and the detection steps are repeated in a cycle until there is no fault at present, and the controller exits, thereby avoiding unnecessary DC current regulation and causing large power loss.

[0089] The steps involved in the above embodiment 2 correspond to those in the method embodiment 1. For the specific implementation method, please refer to the relevant description part of the embodiment 1.

[0090] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0091] The above description is only a preferred embodiment of the present invention. Although the specific implementation mode of the present invention is described in conjunction with the accompanying drawings, it is not a limitation of the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative work are still within the protection scope of the present invention.

Claims

1. A low voltage current limiting control method based on fault detection, characterized in that: include: For AC / DC hybrid power grid, real-time detection of the commutation bus voltage of the AC system; According to the commutation bus voltage, the zero-sequence component detection method and the component detection method are used simultaneously to perform asymmetric fault detection and symmetric fault detection respectively, so as to monitor the system operation status; When a fault is detected in the AC system, the low voltage current limiting controller is started to adjust the original DC current command in real time, and the final DC current command is output to quickly reduce the DC current command, thereby suppressing the first commutation failure of the DC system; wherein, adjusting the original DC current command means adjusting the original DC current command to reduce and limit it to a low level according to a set adjustment range.

2. A low voltage current limiting control method based on fault detection as claimed in claim 1, characterized in that: Based on the adjusted DC current command value and the DC current command value output by the VDCOL characteristic curve, the minimum value is taken as the final DC current command value and output.

3. A low voltage current limiting control method based on fault detection as claimed in claim 1, characterized in that: After the controller is started, it will continue to run for a set time period, and then judge the current fault detection result based on the real-time detection data. If no fault is detected, the controller will exit. Otherwise, the controller will continue to be started for a set time period, and the detection steps will be repeated in a cycle until no fault is detected, and the controller will exit.

4. A low voltage current limiting control method based on fault detection as claimed in claim 1, characterized in that: Monitor the system operating status in real time, determine whether the system has a fault, and use the judgment result as the adjustment start criterion, including: The zero-sequence component detection method is adopted to calculate the zero-sequence voltage component according to the three-phase voltage of the commutation bus obtained in real time, and then the zero-sequence voltage component is compared with the preset zero-sequence voltage threshold value, and whether an asymmetric fault occurs is determined according to the comparison result; wherein, when the zero-sequence voltage component is greater than the preset zero-sequence voltage threshold value, it is determined that an asymmetric fault occurs, and the regulation control is started at this time, otherwise it is not started; At the same time, a symmetrical fault detection method is adopted. According to the three-phase phase voltage of the commutation bus obtained in real time, the amplitude of the angular velocity rotation vector is calculated, and the difference between the amplitudes of the angular velocity rotation vector before and after the fault is calculated. The difference is then compared with the preset voltage amplitude threshold value, and it is determined whether a symmetrical fault has occurred based on the comparison result. When the difference is greater than the preset voltage amplitude threshold value, it is determined that a symmetrical fault has occurred, and the regulation control is started at this time, otherwise it is not started.

5. A low voltage current limiting control method based on fault detection as claimed in claim 4, characterized in that: The calculation of the zero-sequence voltage component includes: According to the real-time acquisition of the three-phase phase voltage U a , U b , U c , through the average operation, the zero-sequence voltage component U0 is calculated, the formula is: The calculation of the angular velocity rotation vector amplitude includes: The real-time three-phase phase voltage U a , U b , U c Perform Clark transformation to obtain the transformed two-phase voltage U α , U β , and calculate the angular velocity rotation vector amplitude U αβ , the formula is:

6. A low voltage current limiting control method based on fault detection as claimed in claim 4, characterized in that: The adjustment start criterion is introduced into the low voltage current limit control, and the set adjustment range of the DC current command and the preset voltage threshold value are calculated with the goal of preventing the first commutation failure. The preset voltage threshold value includes a preset zero-sequence voltage threshold value and a preset voltage amplitude threshold value; The calculation and determination of the set adjustment range includes: Based on the current loop equation satisfied during the commutation process, the voltage-time area expression required to complete the commutation is obtained; Derive the expressions of the turn-off angle and the DC current on the inverter side when the phase voltage zero-crossing offset is ignored; According to the voltage-time area expression, the analysis is performed, and based on the expressions of the turn-off angle and DC current, the DC voltage on the inverter side and the Echizen trigger angle are set. The corresponding relationship between the change amplitude of the DC current on the inverter side and the change amplitude of the turn-off angle is calculated to determine the DC current command adjustment amplitude that can suppress commutation failure and is used as the set adjustment amplitude.

7. A low voltage current limiting control method based on fault detection as claimed in claim 6, characterized in that: The calculation and determination of the preset voltage threshold value includes: Only the voltage threshold value is used as a variable, and the variation range of the voltage threshold value variable is set. At the same time, a simulation scenario is set in which a three-phase ground short circuit fault occurs in the commutation bus through different transition inductances; wherein the three-phase ground short circuit fault includes a symmetrical fault and an asymmetrical fault; Based on the simulation results, the situations of suppressing the first commutation failure corresponding to different voltage threshold values ​​under various faults are determined, and the optimal parameter value of the voltage threshold value is selected and used as the preset voltage threshold value.

8. A low voltage current limiting control system based on fault detection, characterized in that: include: A data acquisition module is used to detect the commutation bus voltage of the AC system in real time for the AC / DC hybrid power grid; A fault detection module is used to perform asymmetric fault detection and symmetric fault detection respectively according to the commutation bus voltage by using a zero-sequence component detection method and a component detection method, so as to monitor the system operation status; The DC current command adjustment module is used to start the low voltage current limiting controller to adjust the original DC current command in real time when a fault in the AC system is detected, and output the final DC current command to quickly reduce the DC current command, thereby suppressing the first commutation failure of the DC system; wherein, adjusting the original DC current command means adjusting the original DC current command to reduce and limit it to a low level according to a set adjustment range.

9. A low voltage current limiting control system based on fault detection as claimed in claim 8, characterized in that: Based on the adjusted DC current command and the DC current command output by the VDCOL characteristic curve, the minimum value is taken as the final DC current command and output.

10. A low voltage current limiting control system based on fault detection as claimed in claim 8, characterized in that: After the controller is started, it will continue to run for a set time period, and then judge the current fault detection result based on the real-time detection data. If no fault is detected, the controller will exit. Otherwise, the controller will continue to be started for a set time period, and the detection steps will be repeated in a cycle until no fault is detected, and the controller will exit.

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