Method, device and storage medium for monitoring power failure of AC section at receiving end of flexible direct current transmission

Abstract

The present invention relates to a method, device and storage medium for monitoring AC section power failure at the receiving end of flexible direct current transmission, and belongs to the technical field of direct current transmission. By comprehensively considering the AC voltage and AC current on the primary side of the receiving-end connection transformer and the active power of the receiving-end converter station, the misjudgment of AC section power failure is effectively avoided; by introducing the differential component of the AC voltage on the primary side of the receiving-end connection transformer, the threshold for judging the effective value of the AC voltage is reduced, thereby accelerating the judgment of AC section power failure. The present invention provides a favorable guarantee for the system to quickly monitor the AC section power failure at the receiving end and take fault protection measures at the first time. The method is simple and easy to implement.

Description

Technical Field

[0001] The present invention relates to the field of AC section power failure monitoring at a receiving end of flexible direct current transmission, and in particular to a method, a device and a storage medium for monitoring AC section power failure at a receiving end of flexible direct current transmission. Background Art

[0002] Compared with conventional DC transmission systems, flexible DC transmission systems based on modular multilevel converters have many advantages, such as being able to simultaneously adjust active and reactive power, not requiring reactive compensation, having no commutation failure problems, and being able to supply power to passive systems. These advantages make them the future development direction of DC transmission systems.

[0003] However, for high-power flexible DC transmission systems, the overvoltage problem caused by the AC section power failure at the receiving-end converter station endangers the reliable operation of the system. The AC section power failure at the receiving-end refers to the abnormal disconnection of the AC outgoing line of the receiving-end converter station, which causes the receiving-end converter station to be unable to deliver power. After the AC section of the receiving-end converter station loses power, the surplus active power will be injected into the capacitor of the sub-module of the modular multi-level converter, and then overvoltage will appear on the DC side; at the same time, the surplus power will also be injected into the AC filter capacitor, and then overvoltage will also appear on the AC side. For the AC section power failure at the receiving-end converter station, after receiving the fault signal, the project adopts the last circuit breaker protection logic to lock the converter station to ensure the reliable operation of the system.

[0004] Therefore, in order to ensure that the system can identify AC section power failure faults in the first time and take protective measures, it is urgent to study a method for monitoring AC section power failure at the receiving end converter station to speed up the fault identification without misjudgment. Summary of the invention

[0005] The purpose of the present invention is to provide a method, device and storage medium for monitoring power failure of AC section at the receiving end of flexible direct current transmission, so as to improve the recognition rate and reduce the misjudgment rate.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A method for monitoring power failure of AC section at a receiving end of flexible direct current transmission, comprising:

[0008] Collect the instantaneous value of the AC voltage U on the primary side of the connecting transformer at the receiving converter station ac , and calculate the AC voltage effective value U ac_RMS ;

[0009] Calculates the derivative U of the effective value of the AC voltage at a preconfigured period ac_RMS ', and with the preconfigured first set threshold (U ac_RMS ') th By comparison, if the derivative of the effective value of the AC voltage U ac_RMS'Exceeds the pre-configured first set threshold (U ac_RMS ') th , then the first process signal FLAG is output A is high level, otherwise the first process signal FLAG is output A is low level;

[0010] Compare the effective value of AC voltage U ac_RMS and a preconfigured second set threshold (U ac_RMS ) th , if U ac_RMS Exceed (U ac_RMS ) th , then the second process signal FLAG is output B is high level, otherwise it outputs the second process signal FLAG B is low level;

[0011] The first process signal FLAG A As the clock input, it captures the second process signal FLAG in the clock window where it is high B The rising edge of the overvoltage signal on the AC side is latched, and the first flag signal FLAG1 of the output AC side overvoltage signal is high level, otherwise the first flag signal FLAG1 is low level;

[0012] Collect the instantaneous value of the AC current on the primary side of the connecting transformer of the receiving converter station I ac , calculate the effective value of current I ac_RMS and with the preconfigured third set threshold (I ac_RMS ) th By comparison, if the effective value of the current I ac_RMS Exceeding the preconfigured third threshold (I ac_RMS ) th , then the second flag signal FLAG2 is output as a high level, otherwise the second flag signal FLAG2 is output as a low level;

[0013] Collect the actual active power P of the primary side of the connecting transformer of the receiving converter station ac , calculate its active power reference value P relative to the receiving converter station ac_ref Relative error ΔP a , if the relative error exceeds ΔP a Exceeding the preconfigured fourth set threshold (ΔP ac ) th , then the third flag signal FLAG3 is output as a high level, otherwise the third flag signal FLAG3 is output as a low level;

[0014] When the first flag signal FLAG1, the second flag signal FLAG2 and the third flag signal FLAG3 are all at high level, a diagnostic signal for indicating that a power failure of the AC section at the receiving end occurs is output.

[0015] The calculation obtains the AC voltage effective value U ac_RMS Specifically, the AC voltage effective value U is calculated using half of the mains cycle as a sliding window. ac_RMS .

[0016] The calculation obtains the effective value of the current I ac_RMS Specifically, the current effective value I is calculated using half of the mains cycle as a sliding window. ac_RMS .

[0017] All process signals and flag signals are blanked.

[0018] The first set threshold (U ac_RMS ') th Take 50% of the maximum differential value of the AC side voltage effective value after the AC section loses power.

[0019] The second set threshold (U ac_RMS ) th Take 1.3 times the effective value of the AC side voltage under normal operating conditions.

[0020] The third set threshold value (I ac_RMS ) th Take 0.08 times the effective value of the rated current.

[0021] The fourth set threshold (ΔP ac ) th Take 0.2.

[0022] A device for quickly monitoring power failure of AC section at a receiving end of flexible direct current transmission comprises a memory, a processor, and a program stored in the memory and executed by the processor. When the processor executes the program, the method described above is implemented.

[0023] A storage medium stores a program, which implements the above method when executed.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention can reduce the misjudgment rate of AC section power failure at the receiving end and avoid misjudgment caused by fault interference on the AC and DC sides.

[0026] 2. The present invention can improve the speed of judging power failure of the AC section at the receiving end, and avoid the judgment delay caused by the excessively high threshold value of the effective value of the AC side voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a topological structure diagram of a point-to-point flexible direct current transmission system in an embodiment of the present invention;

[0028] Figure 2 Schematic diagram of a method for rapid monitoring of AC power failure in an embodiment of the present invention;

[0029] Figure 3 It is a schematic diagram of the differential component of the effective value of the voltage on the AC side after the AC section loses power in an embodiment of the present invention;

[0030] Figure 4 Schematic diagram of the effective value of the voltage on the AC side after the AC section loses power in an embodiment of the present invention;

[0031] Figure 5 is a schematic diagram of AC side overvoltage judgment in an embodiment of the present invention;

[0032] Figure 6 is a schematic diagram of the comprehensive criteria in an embodiment of the present invention;

[0033] Figure 7 It is a schematic diagram of the final judgment result of AC section power failure in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0035] Figure 1 The topological structure diagram of the point-to-point two-terminal flexible direct current transmission system provided for this application, wherein MMC1 represents the sending-end converter station and MMC2 represents the receiving-end converter station. In this application, the AC section power failure at the receiving end refers to the abnormal disconnection of the AC outgoing line of MMC2, that is, the part connected to the receiving-end transformer, resulting in a surplus of active power at the sending end, and then an overvoltage on the AC and DC sides of the receiving end. In this embodiment, it is assumed that the AC section power failure occurs at 3s.

[0036] Figure 2 Schematic diagram of the AC section power failure rapid monitoring method in the embodiment of the present invention, wherein the AC side voltage instantaneous value U ac , instantaneous value of AC side current I ac , the actual active power P of the receiving converter station ac , active power reference value P of receiving converter station ac_ref The original signals of the four inputs; the voltage mutation signal FLAG A , voltage over threshold signal FLAG BAs the first process signal and the second process signal, the AC side overvoltage signal FLAG1, the AC side current loss signal FLAG2, and the active power surplus signal FLAG3 are respectively used as the first flag signal, the second flag signal, and the third flag signal, and finally FLAG is the output AC section power failure diagnosis signal. When each flag signal is set to 1, it means that the judgment criterion is met.

[0037] A method for monitoring power failure of AC section at a receiving end of flexible direct current transmission, comprising:

[0038] 1) Collect the instantaneous value of the AC voltage U on the primary side of the connecting transformer at the receiving converter station ac , the instantaneous value of AC current I ac , the actual active power P of the converter station ac , active power reference value P of receiving converter station ac_ref As the original signal for monitoring power failure of AC section at the receiving end;

[0039] 2) Taking half of the mains cycle as the sliding window, calculate the effective value of the AC side voltage U ac_RMS The AC side voltage effective value U is calculated with ΔT as the period ac_RMS The derivative U ac_RMS ', as shown in formula (1):

[0040]

[0041] Among them, U ac_RMS (k) is the AC voltage effective value data of the kth point, U ac_RMS (k-1) is the AC voltage effective value data of the k-1th point;

[0042] 3) The differential value of the AC side voltage RMS U ac_RMS 'With the set threshold (U ac_RMS ') th Compare, if it exceeds the threshold, perform blanking link A processing, and obtain voltage mutation signal FLAG A =1;

[0043] 4) The AC side voltage effective value U ac_RMS With the set threshold (U ac_RMS ) th Compare, if it exceeds the threshold, perform blanking link B processing, and obtain voltage over-threshold signal FLAG B =1;

[0044] 5) Set the pulse signal FLAG A As clock input, in the clock window (FLAG A =1) Internal capture FLAG B The rising edge is latched and the AC side overvoltage signal FLAG1=1 is output;

[0045] 6) Using half of the mains cycle as the sliding window, calculate the effective value of the AC side current I ac_RMS and set the threshold value (I ac_RMS ) th Compare, if it is lower than the threshold, perform blanking link C processing, and obtain AC side current loss signal FLAG2 = 1;

[0046] 7) Calculate the actual active power P of the converter station ac Relative to the reference active power P ac_ref Relative error ΔP ac and set the threshold value (ΔP ac ) th In comparison, if the threshold is exceeded, the blanking link D is processed to obtain the active power surplus signal FLAG3=1. The active power relative error is shown in formula (2):

[0047]

[0048] 8) Comprehensively consider the AC side overvoltage signal FLAG1, the AC side current loss signal FLAG2 and the active power surplus signal FLAG3, and perform AND logic operation on the three signals. When FLAG1=FLAG2=FLAG3=1 is satisfied, the receiving end AC section power failure signal FLAG=1 is output, and it is determined that an AC section power failure has occurred at the receiving end.

[0049] The present application introduces a differential component criterion of the effective value of the AC side voltage to effectively identify the steep increase trend when the AC side is overvoltage, thereby reducing the threshold setting of the effective value of the AC side voltage and accelerating the judgment speed of AC section power failure; by integrating the AC side voltage overvoltage, AC side current loss and active power surplus signals, the AC section power failure at the receiving end can be accurately and quickly judged, effectively reducing the misjudgment rate of AC section power failure.

[0050] The three conditions of AC side overvoltage, AC side current loss and active power surplus must be met at the same time, that is, FLAG1 = FLAG2 = FLAG3 = 1, otherwise it is not considered that there is an AC section fault at the receiving end. Each threshold judgment criterion needs to be blanked, that is, the judgment must be maintained for a period of time, otherwise it is considered an invalid judgment and no flag signal is output.

[0051] In this embodiment, the AC side voltage effective value differential value setting threshold (U ac_RMS ') th The typical value is 50% of the maximum differential value of the AC side voltage effective value after the AC section loses power; the AC side voltage effective value setting threshold (U ac_RMS ) thThe typical value of is 1.3 times the effective value of the AC side voltage under normal working conditions; the effective value of the AC side current setting threshold (I ac_RMS ) th The typical value is 0.08 times the rated current effective value; the setting threshold of the relative error of active power (ΔP ac ) th A typical value is 0.2.

[0052] Figure 3 Schematic diagram of the differential component of the effective value of the AC side voltage after the AC section loses power in the embodiment of the present invention. Obviously, when the AC section at the receiving end loses power, the sharp increase of the effective value of the AC side voltage will cause U ac_RMS ' increases sharply. The threshold value criterion of the differential value of the AC side voltage effective value can be used to determine that the AC side voltage effective value has a sharp increase trend.

[0053] Figure 4 It is a schematic diagram of the effective value of the AC side voltage after the AC section loses power in the embodiment of the present invention. When the AC section loses power and causes the effective value of the AC side voltage to rise, the threshold judgment criterion of the effective value of the AC side voltage can be used to judge that the effective value of the AC side voltage exceeds the threshold. When the effective value of the AC side voltage has a steep increase trend, the threshold setting of the effective value can be reduced, thereby speeding up the judgment speed of AC power failure.

[0054] Figure 5 This is a schematic diagram of the AC side overvoltage judgment in the embodiment of the present invention. When an AC power failure occurs, the voltage mutation signal FLAG A A pulse flag signal will be output, and at the same time, the voltage in the pulse exceeds the threshold signal FLAG B A step flag signal will be output, and the rising edge of FLAGB will be latched, indicating that an overvoltage has occurred on the AC side.

[0055] Figure 6 It is a comprehensive schematic diagram of criteria in an embodiment of the present invention. When the three criteria of AC side overvoltage, AC side current loss and active power surplus of the receiving-end converter station are met at the same time, FLAG1=FLAG2=FLAG3=1 exists.

[0056] Figure 7 1 is a schematic diagram of the final judgment result of AC section power failure in an embodiment of the present invention. AND logic operation is performed on FLAG1, FLAG2 and FLAG3. When the three flag signals are 1 at the same time, it is judged that AC section power failure has occurred.

[0057] If the above functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program code.

Claims

1. A method for monitoring power failure of AC section at the receiving end of flexible direct current transmission, characterized in that: include: Collect the instantaneous value of the AC voltage U on the primary side of the connecting transformer at the receiving converter station ac , and calculate the AC voltage effective value U ac_RMS ; Calculates the derivative U of the effective value of the AC voltage at a preconfigured period ac_RMS ', and with the preconfigured first set threshold (U ac_RMS ') th By comparison, if the derivative of the effective value of the AC voltage U ac_RMS 'Exceeds the pre-configured first set threshold (U ac_RMS ') th , then the first process signal FLAG is output A is high level, otherwise the first process signal FLAG is output A is low level; Compare the effective value of AC voltage U ac_RMS and a preconfigured second set threshold (U ac_RMS ) th , if U ac_RMS Exceed (U ac_RMS ) th , then the second process signal FLAG is output B is high level, otherwise it outputs the second process signal FLAG B is low level; The first process signal FLAG A As the clock input, it captures the second process signal FLAG in the clock window where it is high B The rising edge of the overvoltage signal on the AC side is latched, and the first flag signal FLAG1 of the output AC side overvoltage signal is high level, otherwise the first flag signal FLAG1 is low level; Collect the instantaneous value of the AC current on the primary side of the connecting transformer of the receiving converter station I ac , calculate the effective value of current I ac_RMS and with the preconfigured third set threshold (I ac_RMS ) th By comparison, if the effective value of the current I ac_RMS Exceeding the preconfigured third threshold (I ac_RMS ) th , then the second flag signal FLAG2 is output as a high level, otherwise the second flag signal FLAG2 is output as a low level; Collect the actual active power P of the primary side of the connecting transformer of the receiving converter station ac , calculate its active power reference value P relative to the receiving converter station ac_ref Relative error ΔP a , if the relative error ΔP a Exceeding the preconfigured fourth set threshold (ΔP ac ) th , then the third flag signal FLAG3 is output as a high level, otherwise the third flag signal FLAG3 is output as a low level; When the first flag signal FLAG1, the second flag signal FLAG2 and the third flag signal FLAG3 are all at high level, a diagnostic signal for indicating that a power failure has occurred in the AC section of the receiving end is output; The derivative of the effective value of the AC voltage U ac_RMS 'for: Among them, U ac_RMS (k) is the AC voltage effective value data of the kth point, U ac_RMS (k-1) is the AC voltage effective value data of the k-1th point; The relative error of active power is: The calculation obtains the AC voltage effective value U ac_RMS Specifically, the AC voltage effective value U is calculated using half of the mains cycle as a sliding window. ac_RMS ; The calculation obtains the effective value of the current I ac_RMS Specifically, the current effective value I is calculated using half of the mains cycle as a sliding window. ac_RMS ; All process signals and flag signals are blanked; The first set threshold (U ac_RMS ') th Take 50% of the maximum differential value of the AC side voltage effective value after the AC section loses power; The second set threshold (U ac_RMS ) th Take 1.3 times the effective value of the AC side voltage under normal working conditions; The third set threshold value (I ac_RMS ) th Take 0.08 times the effective value of the rated current; The fourth set threshold (ΔP ac ) th Take 0.

2.

2. A device for quickly monitoring AC section power failure at a receiving end of flexible direct current transmission, comprising a memory, a processor, and a program stored in the memory and executed by the processor, characterized in that: When the processor executes the program, the method according to claim 1 is implemented.

3. A storage medium having a program stored thereon, characterized in that: When the program is executed, the method according to claim 1 is implemented.

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