Commutation failure detection method based on valve side current asymmetry

Abstract

The invention relates to the technical field of high-voltage direct current transmission, in particular to a commutation failure detection method based on valve side current asymmetry, which comprises the following steps of: 1, extracting valve side three-phase current of an inverter side converter transformer; step 2, carrying out per-unit treatment on the three-phase current on the valve side and taking an absolute value; and step 3, according to the valve side current after per unit, determining whether a condition that a certain phase current is close to zero and the other two phases of currents are increased sharply exists, and if yes, determining that commutation failure occurs in the converter transformer, the commutation failure detection method based on valve side current asymmetry is simple in criterion structure and easy to realize, and the detection method is suitable for large-scale popularization and application. According to the method, the accuracy of the detection result is not influenced by fault factors such as fault degree, SCR or different fault moments, and the LCC-HVDC power transmission system can quickly and accurately judge the multiple commutation failures under the alternating current fault.

Description

Technical Field

[0001] The present invention relates to the technical field of high voltage direct current transmission, and in particular to a commutation failure detection method based on valve side current asymmetry. Background Art

[0002] The line-commutated converter based high voltage direct current (LCC-HVDC) transmission system based on line-commutated converters has become the mainstream technology for cross-regional power transmission due to its significant advantages in long-distance and large-capacity transmission. However, since the LCC-HVDC system uses thyristor devices, its dependence on AC power supply makes it prone to commutation failure when the power grid is disturbed or fails. At present, commutation failure has become one of the most typical faults in LCC-HVDC transmission systems. It will cause abnormal increase of DC current, interruption or reduction of power transmission, and seriously affect the operational stability and safety of the system;

[0003] Current commutation failure detection methods are mainly divided into predictive methods and measurement methods. Predictive methods are usually based on the dynamic change analysis of system parameters, and judge potential commutation failures by detecting AC voltage fluctuations or faults in advance. Although such methods can respond quickly before commutation failures occur, they will also increase system reactive power or increase control complexity, which is not conducive to engineering applications in some cases. In contrast, the measurement method relies on real-time monitoring of actual operating data and accurately detects commutation failures by analyzing changes in key electrical quantities. Although its detection accuracy is high, its real-time requirements are high, and there are certain limitations in obtaining complex electrical data in engineering. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the deficiencies in the prior art, the present invention provides a commutation failure detection method based on valve-side current asymmetry.

[0006] (II) Technical solution

[0007] To achieve the above object, the present invention provides the following technical solution: a commutation failure detection method based on valve-side current asymmetry, comprising the following steps:

[0008] Step 1, extracting the valve-side three-phase current of the inverter-side converter transformer;

[0009] Step 2: normalize the three-phase current on the valve side and take the absolute value;

[0010] Step 3: According to the normalized valve-side current, determine whether there is a situation where the current of one phase is close to zero and the currents of the other two phases surge. If so, it is determined that the converter transformer has a commutation failure.

[0011] Preferably, the detailed steps of step 3 are:

[0012] Step 21: If the current of phase A is less than the preset threshold δ 1 , and the currents of phase B and phase C are both greater than the surge threshold δ 2 , the output value is 1, otherwise it is 0;

[0013] Step 22: If the current of phase B is less than the preset threshold δ 1 , and the currents of phase A and phase C are both greater than the surge threshold δ 2 , the output value is 1, otherwise it is 0;

[0014] Step 23: If the C phase current is less than the preset threshold δ 1 , and the currents of phase A and phase B are both greater than the surge threshold δ 2 , the output value is 1, otherwise it is 0;

[0015] Among them, δ 1 is the preset threshold used to determine whether the current is close to 0, δ 2 It is a preset threshold used to measure whether the current increases abnormally;

[0016] Step 24: For the Y / D connection converter transformer, check the three judgment output values ​​from step 21 to step 23. If the three judgment output values ​​are all 0, set the Y / D connection judgment variable P YD =0; if any output value is 1, set P YD =1;

[0017] Step 25: For the Y / Y connection converter transformer, check the three judgment output values ​​from step 21 to step 23. If the three judgment output values ​​are all 0, set the Y / Y connection judgment variable P YY =0; if any output value is 1, set P YY =1;

[0018] Step 26: When the variable P is determined YD or P YY When any of the output values ​​is 1, it is determined that the converter transformer has commutation failure.

[0019] Preferably, the preset threshold is determined according to a current fluctuation range during normal operation of the system.

[0020] Preferably, the surge threshold is determined based on empirical data of abnormal current increase when commutation fails.

[0021] Preferably, the sampling frequency for extracting the three-phase current on the valve side of the inverter-side converter transformer is not less than [X] Hz, where X is a value that meets the current detection accuracy requirement.

[0022] Preferably, the order of judging whether the A-phase current is less than a preset threshold, judging whether the B-phase current is less than a preset threshold, and judging whether the C-phase current is less than a preset threshold can be adjusted according to actual conditions.

[0023] Preferably, after determining that the commutation failure occurs in the converter transformer, the method further includes the step of issuing an alarm signal, wherein the alarm signal may be in the form of, but not limited to, a sound alarm, a light alarm, or sending fault information to a monitoring system.

[0024] Preferably, before the current determination is performed, a step of filtering the collected current data is also included to remove noise interference.

[0025] (III) Beneficial effects

[0026] Compared with the prior art, the present invention provides a commutation failure detection method based on valve-side current asymmetry, which has the following beneficial effects:

[0027] The commutation failure detection method based on valve-side current asymmetry has a simple criterion structure and is easy to implement. The accuracy of the detection result of the present invention is not affected by fault factors such as the fault degree, SCR or at different fault moments, and can quickly and accurately realize the judgment of multiple commutation failures in the LCC-HVDC transmission system under AC faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart of commutation failure detection;

[0029] Figure 2 This is the logic diagram for judging the current on the valve side of the Y / D converter transformer;

[0030] Figure 3 It is the logic diagram of the current discrimination on the valve side of the Y / Y converter transformer;

[0031] Figure 4 A diagram showing the commutation failure detection result based on valve-side current asymmetry provided in Embodiment 1 of the present invention;

[0032] Figure 5 A result diagram of a single-phase grounding fault detection based on asymmetry of valve-side current provided in Embodiment 2 of the present invention;

[0033] Figure 6 A three-phase fault result diagram of commutation failure detection based on valve-side current asymmetry provided in Embodiment 2 of the present invention;

[0034] Figure 7A result diagram of a single-phase grounding fault detection based on asymmetric current on the valve side of the commutation failure provided in Embodiment 3 of the present invention;

[0035] Figure 8 This is a three-phase fault result diagram of commutation failure detection based on valve-side current asymmetry provided in Example 3 of the present invention. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] See also Figure 1-8 , a flow chart of a commutation failure detection method based on valve side current asymmetry, the method comprising the following steps:

[0038] Step 1: Extract the three-phase current on the valve side of the inverter-side converter transformer to obtain the three-phase current waveforms of phase A, phase B, and phase C.

[0039] Step 2: Normalize the three-phase current on the valve side and take its absolute value to remove the influence of system voltage fluctuation, thereby improving the stability and accuracy of the detection result.

[0040] Step 3: Based on the normalized valve-side current, determine whether a phase current is close to zero and the other two phase currents are significantly increased. If this condition is met, it is determined that the converter transformer has failed to commutate. This step includes the following specific judgment process:

[0041] Step 3.1: Determine whether the current of phase A is less than the preset threshold δ 1 If yes, then further determine whether the currents of phase B and phase C are both greater than the surge threshold δ 2 If both conditions are met, the output value is set to 1; otherwise, the output value is 0.

[0042] Step 3.2: Determine whether the current of phase B is less than the preset threshold δ 1 If yes, then further determine whether the currents of phase A and phase C are both greater than the surge threshold δ 2 If both conditions are met, the output value is set to 1; otherwise, the output value is 0.

[0043] Step 3.3: Determine whether the C phase current is less than the preset threshold δ 1 If so, further determine whether the currents of phase A and phase B are both greater than the surge threshold δ 2If both conditions are met, the output value is set to 1; otherwise, the output value is 0.

[0044] Among them, δ 1 is the preset threshold used to determine whether the current is close to 0, δ 2 It is a preset threshold used to measure whether the current increases abnormally.

[0045] Step 4: For the Y / D connected converter transformer, analyze the output values ​​in steps 3.1 to 3.3. The specific judgment logic is as follows: Figure 2 If the three outputs are all 0, set the judgment variable P of the Y / D connection YD =0; if any output value is 1, set P YD =1.

[0046] Step 5: For the Y / Y connected converter transformer, analyze the output values ​​in steps 3.1 to 3.3. The specific judgment logic is as follows: Figure 3 If the three outputs are all 0, then set the judgment variable P of the Y / Y connection YY =0; if any output value is 1, set P YY =1.

[0047] Step 6: Determine the decision variable P YD and P YY If P YD or P YY If any one of them is 1, it is determined that the converter transformer has a commutation failure.

[0048] Through the above steps, the method of the present invention can accurately detect the commutation failure of the LCC-HVDC system under AC fault and achieve rapid response;

[0049] Invention implementation example 1:

[0050] The CIGRE LCC-HVDC transmission system simulation model is analyzed based on the PSCAD / EMTDC simulation platform. Different fault levels are set and the commutation failure is identified through the above steps. The specific results are as follows: Figure 4 As shown. "Yellow box" indicates that the detection result is a commutation failure, "white box" indicates that the simulation result is 0 commutation failure, "blue box" indicates that the simulation result is 1 commutation failure, "red box" indicates that the simulation result is 2 commutation failures, and "green box" indicates that the simulation result is 3 commutation failures; no further details will be given later.

[0051] Depend on Figure 4It can be seen that the commutation failure of the LCC-HVDC transmission system has a strong spatial discreteness. Different fault types have different effects on the number of commutation failures at different fault levels. However, despite the different fault types, the commutation failure detection method proposed in the present invention still shows good accuracy at different fault levels, proving that the method is not affected by the fault type and fault level.

[0052] Invention implementation example 2:

[0053] The CIGRE LCC-HVDC transmission system simulation model is analyzed based on the PSCAD / EMTDC simulation platform. By changing the impedance of the inverter-side AC system and the system short-circuit ratio (SCR), the most typical single-phase grounding fault and three-phase fault are selected to identify the commutation failure through the above steps. The specific results are as follows: Figure 5-6 shown.

[0054] Depend on Figure 5-6 It can be seen that the commutation failure of the LCC-HVDC transmission system is significantly correlated with the strength of the AC system. The commutation failure detection method proposed in the present invention can quickly and accurately detect the commutation failure under different SCRs, indicating that the method has strong adaptability in terms of system strength.

[0055] Invention implementation example 3:

[0056] The CIGRE LCC-HVDC transmission system simulation model is analyzed based on the PSCAD / EMTDC simulation platform. Different fault inductances are selected at different fault moments to identify the commutation failure through the above steps. The specific results are as follows: Figure 7-8 shown.

[0057] like Figure 7-8 The method of the present invention uses the CIGRE model to select the detection results of different fault inductances at different fault moments. Figure 7-8 It can be seen that commutation failure has strong temporal and spatial discreteness. The commutation failure detection method proposed in the present invention is not affected by the temporal and spatial discreteness of commutation failure and can accurately identify commutation failure.

[0058] In summary, the detection method of the present invention can quickly and effectively realize the judgment of multiple commutation failures under different fault factors, has high accuracy, reliability and robustness, and has practical engineering application value.

[0059] Reference to "embodiment" herein means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The term "embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or association with other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the various technical features mentioned in the embodiments can be combined in any way to form a corresponding implementable technical solution.

[0060] Unless otherwise defined, the technical terms used in this document have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms in this document is only for describing specific embodiments and is not intended to limit this application.

[0061] While the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that many changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the invention.

Claims

1. A commutation failure detection method based on valve side current asymmetry, characterized in that: The steps include: Step 1, extracting the valve-side three-phase current of the inverter-side converter transformer; Step 2: normalize the three-phase current on the valve side and take the absolute value; Step 3: According to the normalized valve-side current, determine whether there is a situation where the current of one phase is close to zero and the currents of the other two phases surge. If so, it is determined that the converter transformer has a commutation failure.

2. The commutation failure detection method based on valve side current asymmetry according to claim 1, characterized in that: The detailed steps of step 3 are: Step 21: If the current of phase A is less than the preset threshold value δ1, and the currents of phases B and C are both greater than the surge threshold value δ2, the output value is 1, otherwise it is 0; Step 22: If the current of phase B is less than the preset threshold value δ1, and the currents of phase A and phase C are both greater than the surge threshold value δ2, the output value is 1, otherwise it is 0; Step 23: If the C phase current is less than the preset threshold value δ1, and the A phase and B phase currents are both greater than the surge threshold value δ2, the output value is 1, otherwise it is 0; Among them, δ1 is a preset threshold used to determine whether the current is close to 0, and δ2 is a preset threshold used to measure whether the current increases abnormally; Step 24: For the Y / D connection converter transformer, check the three judgment output values ​​from step 21 to step 23. If the three judgment output values ​​are all 0, set the Y / D connection judgment variable P YD =0; if any output value is 1, set P YD =1; Step 25: For the Y / Y connection converter transformer, check the three judgment output values ​​from step 21 to step 23. If the three judgment output values ​​are all 0, set the Y / Y connection judgment variable P YY =0; if any output value is 1, set P YY =1; Step 26: When the variable P is determined YD or P YY When any of the output values ​​is 1, it is determined that the converter transformer has commutation failure.

3. The commutation failure detection method based on valve-side current asymmetry according to claim 2 is characterized in that: The preset threshold is determined according to the current fluctuation range during normal operation of the system.

4. The commutation failure detection method based on valve-side current asymmetry according to claim 3 is characterized in that: The surge threshold is determined based on empirical data of abnormal current increase when commutation fails.

5. The commutation failure detection method based on valve-side current asymmetry according to claim 4 is characterized in that: The sampling frequency for extracting the three-phase current on the valve side of the inverter-side converter transformer is not less than [X] Hz, where X is a value that meets the current detection accuracy requirement.

6. The commutation failure detection method based on valve-side current asymmetry according to claim 5 is characterized in that: The order of judging whether the A-phase current is less than the preset threshold, judging whether the B-phase current is less than the preset threshold, and judging whether the C-phase current is less than the preset threshold can be adjusted according to actual conditions.

7. The commutation failure detection method based on valve-side current asymmetry according to claim 6, characterized in that: After determining that the commutation failure occurs in the converter transformer, the method further includes the step of sending an alarm signal, wherein the form of the alarm signal includes but is not limited to a sound alarm, a light alarm, or sending fault information to a monitoring system.

8. The commutation failure detection method based on valve-side current asymmetry according to claim 7 is characterized in that: Before the current determination is performed, a step of filtering the collected current data is also included to remove noise interference.

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