A valve state-based direct current protection judgment method

Abstract

The present application relates to a kind of valve state-based DC protection judging method, belong to high voltage direct current transmission technology relay protection technical field.The present application first calculates the maximum of each phase valve conduction time width and the maximum of each phase valve turn-off time width in three-phase;Then according to the maximum of each phase valve conduction time width and the maximum of each phase valve turn-off time width, the state of valve is discriminated;Finally, using the difference of each phase valve time width in two states, according to the maximum of each phase valve conduction time width and the maximum of each phase valve turn-off time width in three-phase, comprehensive criterion is made.The present application proposes constraint from the safety angle of valve, based on the valve state constructed on the basis of valve side current timing characteristics, valve state characteristics are used for DC protection protection judgment, solve the problem that criterion and valve state do not match in DC valve area protection, improve the adaptability of DC protection to fault.

Description

Technical Field

[0001] This invention relates to a DC protection judgment method based on valve status, belonging to the field of relay protection technology for high voltage DC transmission technology. Background Technology

[0002] In traditional HVDC transmission power grid projects, DC valve zone protection relies on criteria constructed from the amplitude characteristics of external electrical quantities of converter valves, and DC protection operates with fixed settings. Under AC faults outside the zone, maloperation of the DC valve zone protection can lead to DC system shutdown, impacting system stability. From the perspective of the four characteristics of protection: the similarity between external AC faults and internal faults causes maloperation, resulting in insufficient selectivity; the non-one-to-one correspondence between protection actions and fault locations, and the uncertainty between them, leads to insufficient protection sensitivity; the number and types of actions affected by the fault time in DC valve zone protection also differ, resulting in time discreteness and insufficient protection speed; and the reliance on converter port electrical quantity characteristics to reflect internal valve characteristics is relatively simplistic, leading to insufficient protection reliability.

[0003] Existing research, regarding protection principles, reveals a disconnect between the left-side criteria and right-side protection settings and time delays in the mapping process of DC protection. Furthermore, while existing research analyzes the mechanisms of protection maloperation, it fails to fundamentally explain the time discreteness of DC protection. Based on these two issues, the existing DC protection criteria, including AC quantities, DC quantities, and fault times, cannot form a complete system. Therefore, the use of simple electrical quantity amplitude characteristics in DC valve zone protection is mismatched with the actual operating valve state, resulting in a mismatch between DC protection criteria and valve state characteristics. Summary of the Invention

[0004] The purpose of this invention is to provide a DC protection judgment method based on valve status to solve the problem of low accuracy in judging converter asymmetry.

[0005] To solve the above-mentioned technical problems, this invention provides a DC protection judgment method based on valve status, which includes the following steps:

[0006] 1) Detect the AC current on the valve side of the three-phase converter, and calculate the maximum value of the on-time width and the maximum value of the off-time width of each phase valve in the three phases;

[0007] 2) Compare the maximum value of the on-time width and the maximum value of the off-time width of each phase valve with the continuous on-time width and continuous off-time width of each phase valve during normal operation to obtain the difference in the on-time width and the difference in the off-time width of each phase valve, and use this to determine the valve status.

[0008] 3) Utilizing the difference in the time width of each phase valve in the two states, the maximum value of the conduction time width and the maximum value of the turn-off time width of each phase valve in the three phases are used as the comprehensive criterion, and the fault classification is hierarchically determined according to the number of valve phase switching failures.

[0009] This invention determines the valve state by utilizing the relationship between the maximum values ​​of the on-time and off-time widths of each phase valve and the continuous on-time and continuous off-time widths of each phase valve during normal operation. It uses a comprehensive criterion based on the maximum values ​​of the on-time and off-time widths of each phase valve across the three phases, and hierarchically classifies faults according to the number of valve commutation failures. This invention proposes constraints from a valve safety perspective. Based on the valve state constructed from the valve-side current timing characteristics, it uses valve state characteristics for DC protection judgment, solving the problem of mismatch between the criteria for DC valve zone protection and the valve state, and improving the adaptability of DC protection to faults.

[0010] Furthermore, the hierarchical discrimination in step 3) includes:

[0011] The judgment of valve asymmetric operation, single valve commutation failure and multiple valve commutation failure is made based on the maximum value of the conduction time width of each phase and the minimum value of the disconnection time width of each phase in the three phases; the judgment of continuous commutation failure is made based on the maximum value of the conduction time width of each phase and the maximum value of the disconnection time width of each phase in the three phases.

[0012] The present invention can perform hierarchical discrimination based on the maximum value of the conduction time width of each phase in the three phases and the minimum value of the maximum value of the disconnection time width of each phase, as well as the maximum value of the conduction time width of each phase in the three phases and the maximum value of the disconnection time width of each phase.

[0013] Furthermore, the criterion used to determine valve asymmetry is as follows:

[0014]

[0015] Among them, t VL The continuous shut-off time width of each phase valve during normal operation, t VH The normal operating valve conduction time width is given by Δt, where Δt is the sampling rate, and max(max(t)) is the maximum sampling rate. aH ),max(t bH ),max(t cH The maximum conduction width (max(t)) of each phase in the three-phase system is given by the given value. aH ), max(t) bH ), max(t) cH The maximum value of ), min(max(t) aL ),max(t bL ),max(t cLThe maximum value of the disconnection width for each phase in the three phases is max(t). aL ), max(t) bL ), max(t) cL The minimum value of ).

[0016] This invention can construct a criterion for valve asymmetric operation based on the maximum value of the conduction time width of each phase and the minimum value of the disconnection time width of each phase in the three phases, and can accurately determine valve asymmetric operation.

[0017] Furthermore, the criterion used to determine the failure of a single valve commutation is as follows:

[0018]

[0019] Among them, t VL The continuous shut-off time width of each phase valve during normal operation, t VH The normal operating valve conduction time width is given by Δt, where Δt is the sampling rate, and max(max(t)) is the maximum sampling rate. aH ),max(t bH ),max(t cH The maximum conduction width (max(t)) of each phase in the three-phase system is given by the given value. aH ), max(t) bH ), max(t) cH The maximum value of ), min(max(t) aL ),max(t bL ),max(t cL The maximum value of the disconnection width for each phase in the three phases is max(t). aL ), max(t) bL ), max(t) cL The minimum value of ).

[0020] This invention can construct a criterion for single valve commutation failure based on the maximum value of the conduction time width of each phase and the minimum value of the disconnection time width of each phase in the three phases, and can accurately determine the commutation failure of a single valve.

[0021] Furthermore, the criteria used to determine multiple valve commutation failures are as follows:

[0022]

[0023] Among them, t VL The continuous shut-off time width of each phase valve during normal operation, t VH The normal operating valve conduction time width is given by Δt, where Δt is the sampling rate, and max(max(t)) is the maximum sampling rate. aH ),max(t bH ),max(t cH The maximum conduction width (max(t)) of each phase in the three-phase system is given by the given value.aH ), max(t) bH ), max(t) cH The maximum value of ), min(max(t) aL ),max(t bL ),max(t cL The maximum value of the disconnection width for each phase in the three phases is max(t). aL ), max(t) bL ), max(t) cL The minimum value of ).

[0024] This invention can construct a criterion for multiple valve commutation failures based on the maximum value of the conduction time width of each phase and the minimum value of the disconnection time width of each phase in the three phases, and can accurately determine the commutation failure of multiple valves.

[0025] Furthermore, the criterion used to determine continuous commutation failure is as follows:

[0026]

[0027] t VL The continuous shut-off time width of each phase valve during normal operation, t VH The normal operating valve conduction time width is given by Δt, where Δt is the sampling rate, and max(max(t)) is the maximum sampling rate. aH ),max(t bH ),max(t cH The maximum conduction width (max(t)) of each phase in the three-phase system is given by the given value. aH ), max(t) bH ), max(t) cH The maximum value of ), max(max(t) aL ),max(t bL ),max(t cL The maximum value of the disconnection width for each phase in the three phases is max(t). aL ), max(t) bL ), max(t) cL The maximum value of ).

[0028] This invention can construct a criterion for continuous commutation failure of a valve based on the maximum value of the conduction time width of each phase and the maximum value of the disconnection time width of each phase in the three phases, and can accurately determine the continuous commutation failure.

[0029] Furthermore, in step 2), the valve state includes an asymmetrical state and a symmetrical state. The criterion for determining the asymmetrical state is as follows:

[0030]

[0031] max(t kH) represents the conduction time width t for each phase. aH t bH t cH The maximum value, max(t) kL ) represents the time width t of each correlation interruption. aL t bL t cL The maximum value is given by k = a, b, c, and Δt is the sampling rate. Attached Figure Description

[0032] Figure 1 This is a flowchart of the DC protection judgment method based on valve status of the present invention;

[0033] Figure 2 This is a flowchart of the hierarchical timing discrimination of the present invention. Detailed Implementation

[0034] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0035] The DC protection judgment method based on valve status of this invention first detects the AC current on the three-phase valve side of the converter and calculates the maximum value of the on-time width and the maximum value of the off-time width of each phase valve. Then, it compares the maximum values ​​of the on-time width and off-time width of each phase valve with the continuous on-time width and continuous off-time width of each phase valve during normal operation to obtain the difference in the on-time width and the difference in the off-time width of each phase valve, and uses this to determine the asymmetrical state of the valve. Finally, using the difference in the time width of each phase valve in the two states, and based on the maximum values ​​of the on-time width and the off-time width of each phase valve in the three phases, a comprehensive judgment is made, and the fault is classified hierarchically according to the number of valve commutation failures. The implementation process of this method is as follows: Figure 1 As shown below, a detailed explanation will be provided with specific examples.

[0036] Step 1. Detect the three-phase AC current i a i b i c Determine the on-time width and off-time width of each phase valve in the converter.

[0037] Step 11: Measure the three-phase AC current i on the converter valve side. a i b i c The absolute value is calculated to obtain the amplitude |i of the three-phase alternating current. a |、|i b |、|i c |;

[0038] Step 12, Measure the amplitude |i of the three-phase alternating current a |、|i b |、|ic After maximization and smoothing, the maximum value of the three-phase AC current amplitude, max(i), is obtained. a |,|i b |,|i c |);

[0039] Step 13: Compare the amplitude of the three-phase AC current obtained in Step 11 with the maximum amplitude of the three-phase AC current obtained in Step 12. Define the ratio of the amplitude of each phase current to the maximum amplitude of the three-phase current as the relative relationship S of the phase current. a S b S c As shown in formula (1):

[0040]

[0041] Where: k = a, b, c, S k This refers to the relative relationship of current in each phase;

[0042] Step 14: Determine the conduction state of each phase based on the relative relationship of the currents in each phase in Step 13. In this implementation, a relative relationship of the currents in each phase greater than K is defined as the conduction state S of each phase. aH S bH S cH As shown in formula (2), in this implementation, the relative relationship of current in each phase is defined as less than K as the phase disconnection state S. aL S bL S cL As shown in formula (3):

[0043] The formula for the conduction state is as follows:

[0044] S kH >K (2)

[0045] The formula for the shutdown state is as follows:

[0046] S kL =1-S kH <K (3)

[0047] Where: K is a constant;

[0048] Step 15: Summate the on-state and off-state of each phase in Step 14, and calculate the on-time width t of each phase by integration. aH t bH t cH and the width of each correlation interruption time t aL t bL t cL As shown in formula (4):

[0049]

[0050] Where: k = a, b, c, t kH t is the conduction time width of phase k. kL The turn-off time width of phase k.

[0051] Through the above process, the three-phase alternating current i can be determined. a i b i c Determine the on-time width and off-time width of each phase valve in the converter.

[0052] Step 2. Compare the maximum value of the on-time width and the maximum value of the off-time width of each phase valve in Step 1 with the continuous on-time width and continuous off-time width of each phase valve during normal operation to determine the valve status.

[0053] Step 21: According to Step 1, during normal operation, the three-phase continuous conduction time width and the three-phase continuous turn-off time width are as shown in Formula (5);

[0054]

[0055] t VL The continuous shut-off time width of each phase valve during normal operation, t VH This refers to the conduction time width of each phase valve during normal operation.

[0056] Step 22: Based on the conduction time width and turn-off time width of each phase valve of the converter obtained in Step 1 and the results of Step 21, the maximum value of the three-phase continuous conduction time width and the maximum value of the three-phase continuous turn-off time width are compared with the criteria for the continuous conduction time width and turn-off time width of each phase during normal operation as shown in Formula (6).

[0057]

[0058] Where: max(t) kH ) represents the conduction time width t for each phase. aH t bH t cH The maximum value, max(t) kL ) represents the time width t of each correlation interruption. aL t bL t cL The maximum value, k = a, b, c, Δt is the sampling rate;

[0059] If there is a difference in time width, as shown in formula (7), then the asymmetric state of the valve is determined:

[0060]

[0061] Where: t VH For normal operation, the conduction time width of each phase valve and t VL For normal operation, the continuous shut-off time width of each phase valve and

[0062] Step 3. Utilize the maximum value of the actual continuous conduction width of each phase valve, max(t). kH ) and the maximum value of the continuous shut-off width of each phase valve, max(t) kL ) and the conduction width t per phase during normal operation VH and the shutdown width t VL The differences are used to classify the valve asymmetry state in step 2 according to the number of asymmetries and commutation failures as criteria. The flowchart of the criteria is as follows: Figure 2 As shown, the specific process is as follows:

[0063] Step 31: Construct the valve asymmetric operation criterion by taking the maximum value of the conduction time width of each phase and the minimum value of the disconnection time width of each phase in the three phases;

[0064]

[0065] Where: max(max(t) aH ),max(t bH ),max(t cH The maximum conduction width (max(t)) of each phase in the three-phase system is given by the given value. aH ), max(t) bH ), max(t) cH The maximum value of ), min(max(t) aL ),max(t bL ),max(t cL The maximum value of the disconnection width for each phase in the three phases is max(t). aL ), max(t) bL ), max(t) cL The minimum value of ).

[0066] Step 32: Based on Step 31, construct a single valve commutation failure criterion by taking the maximum value of the conduction time width of each phase and the minimum value of the disconnection time width of each phase.

[0067]

[0068] Step 33: Based on Step 31, construct multiple valve commutation failure criteria by taking the maximum value of the conduction time width of each phase and the minimum value of the disconnection time width of each phase in the three phases:

[0069]

[0070] Step 34: Based on step 31, construct the continuous commutation failure criterion by taking the maximum value of the conduction time width of each phase and the maximum value of the disconnection time width of each phase in the three phases.

[0071]

[0072] Where: max(max(t) aL ),max(t bL ),max(t cL The maximum value of the disconnection width for each phase in the three phases is max(t). aL ), max(t) bL ), max(t) cL The maximum value of ).

[0073] To verify the effectiveness of this invention, a single-phase ground fault occurred at the converter bus during actual power grid operation. The fault time was varied, and the conduction time width and turn-off time width of each phase were recorded to verify the feasibility of hierarchical discrimination. The recorded results and verification results are shown in Table 1. Where t YaH t YbH t YcH t is the conduction width of each phase of the YY bridge; YaL t YbL t YcL t represents the width of each disconnection of the YY bridge. DaH t DbH t DcH t is the conduction width of each phase of the YD bridge; DaL t DbL t DcL The width of each disconnection of the YD bridge.

[0074] Table 1

[0075]

[0076]

[0077] As can be seen from Table 1, the conduction width and turn-off width of each phase change by altering the fault time. Based on the hierarchical discrimination method of this invention, the number of commutation failures can be determined, and the severity of the fault can be characterized.

Claims

1. A DC protection judgment method based on valve status, characterized in that, The determination method includes the following steps: 1) Detect the AC current on the valve side of the three-phase converter, and calculate the maximum value of the on-time width and the maximum value of the off-time width of each valve in the three phases; 2) Compare the maximum value of the on-time width and the maximum value of the off-time width of each phase valve with the continuous on-time width and continuous off-time width of each phase valve during normal operation to obtain the difference in the on-time width and the difference in the off-time width of each phase valve, and use this to determine the valve status. 3) Utilizing the difference in the time width of each phase valve in the two states, the maximum value of the conduction time width and the maximum value of the turn-off time width of each phase valve in the three phases are used as the comprehensive criterion, and the fault classification is hierarchically determined according to the number of valve commutation failures. The criterion used to determine valve asymmetry is: The criterion used to determine the failure of a single valve commutation is: The criteria used to determine multiple valve commutation failures are as follows: The criteria used to determine successive commutation failures are as follows: in, This is the width of the continuous shut-off time for each phase valve during normal operation. For the normal operation of each phase valve conduction time width, Sampling rate, The maximum conduction width of each phase in the three phases , , The maximum value, The maximum disconnection width for each of the three phases. , , The minimum value, The maximum disconnection width for each of the three phases. , , The maximum value.

2. The DC protection judgment method based on valve status according to claim 1, characterized in that, In step 2), the valve state includes an asymmetrical state and a symmetrical state. The criterion for determining the asymmetrical state is as follows: The conduction time width per phase , , The maximum value, For each correlation interruption time width , , The maximum value, , The sampling rate.

3. The DC protection judgment method based on valve status according to claim 2, characterized in that, The criteria for determining the maximum value of the three-phase continuous on-time width and the maximum value of the three-phase continuous off-time width, and the normal operating continuous on-time width and off-time width of each phase, are as follows: in, The conduction time width per phase , , The maximum value, For each correlation interruption time width , , The maximum value, , The sampling rate.

4. The DC protection judgment method based on valve status according to any one of claims 1-3, characterized in that, The conduction time width per phase , , and the width of each disconnection time , , The following formula can be used to obtain: in, Let k be the conduction time width of phase k. The turn-off time width of phase k, and the conduction state of each phase. This refers to the relative relationship of current in each phase being greater than K, and the disconnection state of each phase. This refers to the fact that the relative current of each phase is less than K, where K is a constant.

5. The DC protection judgment method based on valve status according to claim 4, characterized in that, The relative relationships of the currents in each phase are obtained by the following formula: in, The relative relationship of current in each phase. This represents the maximum value of the three-phase current amplitude. This represents the current amplitude per phase.

6. The DC protection judgment method based on valve status according to claim 5, characterized in that, The maximum value of the three-phase current amplitude It is the amplitude of the three-phase current , , It is obtained through a maximum value module and smoothing processing.

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