A grid-connected t-type rectifier fault diagnosis method and diagnosis device thereof

Abstract

The application discloses a grid-connected T-type rectifier fault diagnosis method, takes the ratio of three-phase current sampling frequency and grid frequency as a sliding window sampling number L, moves the sliding window with a sampling point as a moving step, takes each adjacent KL sliding window as an inner ring, takes each adjacent KL inner ring as a detection period, carries out detection in each detection period, respectively carries out three-phase normalization processing on each-phase current, determines the median current of three-phase normalized current of each sampling point, calculates the cumulative current of each inner ring, wherein, I mL is the sum of the absolute values of the median currents of the corresponding inner ring and the mLth sliding window; calculates the fundamental frequency quantity G and the direct current quantity Z and the ratio F of the two based on the cumulative current of the KL inner rings in the detection period, when F>T1, determines that the rectifier has a power tube fault, and when F≤T1, determines that the rectifier does not have a power tube fault. The application can realize rectifier fault diagnosis through fewer sampling signals, has simple calculation and good robustness.

Description

Technical Field

[0001] This invention belongs to the field of online fault diagnosis technology for grid-connected rectifiers, and more specifically, relates to a fault diagnosis method and device for grid-connected T-type rectifiers. Background Technology

[0002] With the continuous development of new energy vehicles, the supporting charging infrastructure is also constantly improving, making charging reliability and safety crucial considerations. As a core energy conversion component, the grid-connected T-type rectifier's reliability is severely affected by power transistor failures. Open-circuit faults in power transistors are the primary type of failure, leading to degraded charging performance and even jeopardizing equipment and personnel safety. Research into the diagnosis of open-circuit faults in power transistors can enable timely detection of these faults and prevent further catastrophic failures.

[0003] Currently, there is limited research on fault diagnosis methods for T-type rectifiers. Some model-based methods use a large number of system signals or parameters, resulting in poor usability. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a fault diagnosis method and device for grid-connected T-type rectifiers, the purpose of which is to accurately detect faults with less signal.

[0005] To achieve the above objectives, according to one aspect of the present invention, a fault diagnosis method for a grid-connected T-type rectifier is provided, which samples the three-phase current i at a set sampling frequency. x x = a, b, c, take the ratio of the three-phase current sampling frequency to the grid frequency as a sampling number L of a sliding window, move the sliding window with a sampling point as the moving step size, take each adjacent KL sliding window as an inner loop, take each adjacent KL inner loops as a detection cycle, and detect the fault based on the selected three-phase current in each detection cycle.

[0006] The fault detection process, based on selected three-phase currents, is performed within each detection cycle, including:

[0007] For each phase current i x Perform three-phase normalization processing separately to obtain the three-phase normalized current, and determine the median current of the three-phase normalized current at each sampling point;

[0008] Calculate the cumulative current of each inner loop s. Among them, I mL K is the sum of the absolute values ​​of the median current of the mL-th sliding window in the inner ring, and K is a preset value, K≥2;

[0009] The fundamental frequency quantity G and the direct current quantity Z, as well as the ratio F of the fundamental frequency quantity G and the direct current quantity Z, are calculated based on the cumulative current of KL inner loops within the detection period.

[0010]

[0011] Compare the ratio F with the first fault threshold T1. If F > T1, it is determined that the rectifier has a power transistor fault. If F ≤ T1, it is determined that the rectifier has not a power transistor fault.

[0012] In one embodiment, the method further includes fault phase location, wherein the fault phase location method includes:

[0013] Using the last L sampling points of the current detection cycle as the change point prediction set B, and determining the sampling change point t,

[0014]

[0015] Among them, I′ B(j-1) Z represents the cumulative current of the inner loop obtained by moving the sliding window to the (j-1)th sampling point in the variable point prediction set. B(j-1) Let I′ be the direct current obtained by moving the sliding window to the (j-1)th sampling point in the variable point prediction set. B(j+1) Z represents the cumulative current of the inner loop obtained by moving the sliding window to the (j+1)th sampling point in the variable point prediction set. B(j+1) Let I' be the direct current obtained by moving the sliding window to the (j+1)th sampling point in the variable point prediction set, and let I' be the direct current. B0 =I′ BL , I′ B(L+1) =I′ B1 Z B0 =Z BL Z B(L+1) =Z B1 ;

[0016] The phase state corresponding to the minimum absolute value of the three-phase normalized current at the sampling point t is taken as the fault phase.

[0017] In one embodiment, the method for locating faults in the inner and outer pipes includes:

[0018] Calculate the sum of the normalized three-phase currents for each phase state within the last sliding window of the current detection cycle.

[0019] Pick The maximum absolute value I in * Compare the maximum value I * With the second fault threshold T2, when I * When I ≤ T2 / 2, it is determined to be an internal tube fault. *When the value is greater than T2 / 2, the problem is determined to be an external pipe fault.

[0020] The inner tube is a power transistor on the neutral point bridge arm of the grid-connected T-type rectifier, and the outer tube is a power transistor on the upper bridge arm of the grid-connected T-type rectifier.

[0021] In one embodiment, the formula for calculating the second fault threshold T2 is:

[0022]

[0023] In one embodiment, the method further includes power transistor fault location, wherein the power transistor fault location method includes:

[0024] When an internal tube fault is identified, the sum of the normalized three-phase currents is further compared. With 0, when When, determine the power transistor S x3 When a malfunction occurs, When, determine the power transistor S x2 A malfunction occurred;

[0025] When the fault is determined to be an external pipe fault, the sampled variable point t is backtracked to the sampled point t′ within the variable point prediction set.

[0026]

[0027] Determine the normalized three-phase current at sampling point t′ The polarity, when When, determine the power transistor S x4 When a malfunction occurs, When, determine the power transistor S x1 A malfunction occurred;

[0028] Among them, S x1 S represents the power transistor in the upper arm of phase x. x4 S represents the power transistor in the lower arm of phase x. x2 S represents the power transistor in the x-phase bridge arm connected to the center point of the busbar. x3 This represents the power transistor in the x-phase middle arm connected to the center point of the upper and lower arms.

[0029] In one embodiment, the three-phase normalized current is calculated. The formula is:

[0030]

[0031] In one embodiment, K = 3.

[0032] According to another aspect of the present invention, a grid-connected T-type rectifier fault diagnosis device is provided, comprising:

[0033] The normalization processing unit is used to process the sampled phase currents i x Perform three-phase normalization processing separately to obtain the three-phase normalized current;

[0034] The median determination unit is used to determine the median current of the three-phase normalized current at each sampling point;

[0035] The inner loop calculation unit is used to calculate the cumulative current of each inner loop s. Among them, I mL K is a preset value, K≥2, which is the sum of the absolute values ​​of the median current of the mL-th sliding window in the inner loop. The sampling number L of a sliding window is the ratio of the three-phase current sampling frequency to the grid frequency. The sliding window is moved backward with a sampling point as the moving step size. Each adjacent KL sliding window is a single inner loop.

[0036] The fundamental frequency calculation unit is used to calculate the fundamental frequency based on the cumulative current of KL inner loops within the current detection period. Each KL adjacent inner rings constitutes one detection cycle;

[0037] The DC calculation unit is used to calculate the DC quantity based on the cumulative current of KL inner loops within the current detection cycle.

[0038] The ratio calculation unit is used to calculate the ratio of the fundamental frequency quantity G to the DC quantity Z;

[0039] The fault determination unit is used to compare the ratio F with the first fault threshold T1. When F > T1, it is determined that the rectifier has a power transistor fault. When F ≤ T1, it is determined that the rectifier has not a power transistor fault.

[0040] In one embodiment, it further includes a sampling change point determination unit and a fault phase location unit; wherein,

[0041] The sampling change point determination unit is used to determine the sampling change point t = arg min by taking the last L sampling points of the current detection period as the change point prediction set B. 1≤j≤L ((max(I′ B(j-1) -Z B(j-1) ,0))·(max(I′ B(j+1) -Z B(j+1) ,0))), where I′ B(j-1) Z represents the cumulative current of the inner loop obtained by moving the sliding window to the (j-1)th sampling point in the variable point prediction set. B(j-1) Let I′ be the direct current obtained by moving the sliding window to the (j-1)th sampling point in the variable point prediction set. B(j+1) Z represents the cumulative current of the inner loop obtained by moving the sliding window to the (j+1)th sampling point in the variable point prediction set. B(j+1)Let I' be the direct current obtained by moving the sliding window to the (j+1)th sampling point in the variable point prediction set, and let I' be the direct current. B0 =I′ BL , I′ B(L+1) =I′ B1 Z B0 =Z BL Z B(L+1) =Z B1 ;

[0042] The fault phase location unit is used to take the phase state corresponding to the minimum absolute value of the three-phase normalized current at the sampling point t as the fault phase.

[0043] In one embodiment, it further includes an inner and outer tube positioning unit and a power tube positioning unit;

[0044] The outer tube positioning unit includes a current summation unit, a maximum value determination unit, and a first determination unit, wherein...

[0045] The current summation unit is used to calculate the sum of the three-phase normalized currents for each phase in the last sliding window of the current detection cycle.

[0046] The maximum value determination unit is used to determine the maximum value. The maximum absolute value I in * ;

[0047] The first determination unit is used to compare the maximum value I. * With the second fault threshold T2, when I * When I ≤ T2 / 2, it is determined to be an internal tube fault. * When the value is greater than T2 / 2, the problem is determined to be an external pipe fault.

[0048] The power transistor positioning unit includes a second determination unit, a change-point backtracking unit, and a third determination unit, wherein...

[0049] The second determination unit is used to compare the sum of the three-phase normalized currents when the first determination unit determines that the inner tube is faulty. With 0, when When, determine the power transistor S x3 When a malfunction occurs, When, determine the power transistor S x2 A malfunction occurred;

[0050] The variable point backtracking unit is used to backtrack the sampled variable point t to the sampling point within the variable point prediction set when the first determination unit determines that the external pipe is faulty.

[0051] The third determination unit is used to determine the three-phase normalized current at sampling point t′. The polarity, when When, determine the power transistor S x4 When a malfunction occurs, When, determine the power transistor S x1 A malfunction occurred;

[0052] Among them, S x1 S represents the power transistor in the upper arm of phase x. x4 S represents the power transistor in the lower arm of phase x. x2 S represents the power transistor in the x-phase bridge arm connected to the center point of the busbar. x3 This represents the power transistor in the x-phase middle arm connected to the center point of the upper and lower arms.

[0053] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0054] (1) Low cost. This invention only uses three-phase current signals for fault detection and location, and does not require any hardware sensors other than those necessary for the normal control system. It has strong portability.

[0055] (2) It has good robustness and can cope with transient conditions of rectifiers;

[0056] (3) Simple to implement. This invention is implemented in software, which consumes less CPU resources and has low computational complexity.

[0057] Moreover, in the preferred embodiment, all single-tube fault diagnosis can also be achieved. Attached Figure Description

[0058] Figure 1 This is a T-type three-phase four-wire rectifier topology in one embodiment;

[0059] Figure 2 This is a schematic diagram of data division within a detection cycle in one embodiment;

[0060] Figure 3 This is a flowchart of the steps for determining whether a fault has occurred in a grid-connected T-type rectifier fault diagnosis method in one embodiment;

[0061] Figure 4 This is a flowchart of the steps for locating the faulty phase in a grid-connected T-type rectifier fault diagnosis method in one embodiment;

[0062] Figure 5 This is a flowchart of the steps for locating faults in the inner and outer tubes in a fault diagnosis method for a grid-connected T-type rectifier in one embodiment.

[0063] Figure 6 This is a flowchart of the steps for locating a specific power transistor in a grid-connected T-type rectifier fault diagnosis method in one embodiment;

[0064] Figure 7 This is a structural block diagram of a grid-connected T-type rectifier fault diagnosis device in one embodiment;

[0065] Figure 8 This is a diagram showing the physical experimental results of fault detection according to the present invention in one embodiment, wherein (a) represents the original sampled three-phase current i x (b) represents the normalized three-phase current after normalization. (c) represents the median current i at each sampling point. z (d) represents the cumulative current I′ s And DC flow rate Z, (e) represents the comparison result of ratio F and fault threshold T1, (f) represents the maximum value I * The second fault threshold T2, (g) represents the minimum absolute value of the three-phase normalized current and the absolute value of the b-phase normalized current. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0067] like Figure 1 The diagram shows the topology of a T-type three-phase four-wire rectifier. The system consists of power transistors (S... a1 ,S a2 ,S a3 ,S a4 ,S b1 ,S b2 ,S b3 ,S b4 ,S c1 ,S c2 ,S c3 ,S c4 ) Corresponding diode (D a1 D a2 D a3 D a4 D b1 D b2 D b3 D b4 D c1 D c2 D c3 D c4 The busbar energy storage capacitors (C1, C2) constitute the system. c1 U c2The voltages of the two capacitors are U and U, respectively. d This is the DC bus voltage. Where S... x1 S represents the power transistor in the upper arm of phase x. x4 S represents the power transistor in the lower arm of phase x. x2 S represents the power transistor in the x-phase bridge arm connected to the center point of the busbar. x3 This represents the power transistor in phase x, connected to the center point of the upper and lower bridge arms. Where S... x2 ,S x3 For the inner tube, S x1 ,S x4 For the outer tube. a i b i c For three-phase current, in the fault diagnosis algorithm, i a i b i c For variables that need to be collected in real time.

[0068] In this invention, a fixed sampling frequency is set for real-time sampling i. a i b i c This invention utilizes three-phase current to perform fault diagnosis. Fault diagnosis requires acquiring and analyzing multiple sets of data. This invention selects multiple sets of sampled data using a sliding window, where the length L of the sliding window is calculated using the following formula:

[0069]

[0070] Among them, f s f is the power grid frequency. i The current sampling frequency is used. When the ratio result is a small value, it is rounded down to L.

[0071] Simultaneously, a sliding window is moved backward with a sampling point as the moving step size, each adjacent KL sliding window forms an inner loop, and each adjacent KL inner loops form a detection cycle. Fault detection is performed based on the selected three-phase current within each detection cycle. To facilitate understanding of the relationship between the sampling point sliding window, inner loop, and detection cycle, as follows... Figure 2 As shown, with a distance of L=2 and K=5, the sliding window has a length of 2 sampling points. The movement step is one sampling point. Starting from the initial sampling point t1, a new sliding window is formed after each new sampling point is acquired. When sampling point t11 ​​is acquired, 10 sliding windows have been formed. Every 10 sliding windows form a group, creating an inner loop. Figure 2 In the process, the inner loop 1 includes sampling points t1 to t11. After that, each new sampling point is added to form a new inner loop. When sampling point t20 is obtained, 10 inner loops have been formed. The 10 inner loops constitute a detection cycle, and fault diagnosis is performed based on the sampling data in this detection cycle.

[0072] Specifically, such as Figure 3 As shown, the methods for fault detection based on selected three-phase currents mainly include:

[0073] Step S110: For each phase current i x Perform three-phase normalization processing separately to obtain the three-phase normalized current, and determine the median current of the three-phase normalized current at each sampling point.

[0074] For three-phase current i x Normalization yields the normalized current. Where: x equals a, b, c:

[0075]

[0076] And extract the median current i z :

[0077]

[0078] Step S120: Calculate the cumulative current of each inner loop s. Among them, I mL K is the sum of the absolute values ​​of the median current of the mL-th sliding window in the inner ring, and K is a preset value, K≥2.

[0079] First, calculate the sum of the absolute values ​​of the median currents of each sliding window w, I. w :

[0080]

[0081] Among them, i zj Let be the median current at the j-th sampling point within the current sliding window.

[0082] Then calculate the cumulative current I′ of each inner loop s. s :

[0083]

[0084] In the current cycle, among the KL sliding windows from the 1st to the KLth, the sum of the absolute values ​​of the median currents of the sliding windows whose serial numbers are integer multiples of L is taken, and then averaged to obtain the cumulative current of the corresponding inner loop. For example, in the previous embodiment, when L=2 and K=5, the sum of the absolute values ​​of the median currents of the 2nd, 4th, 6th, 8th, and 10th sliding windows in each inner loop, I2, I4, I6, I8, and I... 10 Perform a summation and average calculation.

[0085] K can be an integer greater than or equal to 2, specifically 3, to ensure the correctness of the result.

[0086] Step S130: Calculate the fundamental frequency quantity G, the DC quantity Z, and the ratio F of the fundamental frequency quantity G and the DC quantity Z based on the cumulative current of KL inner loops within the detection period.

[0087] Specifically, let G sin and G cos Intermediate quantities for calculating the fundamental frequency G:

[0088]

[0089]

[0090]

[0091] Therefore, by forming KL consecutive inner loops, we can obtain a fundamental frequency G, a DC quantity Z, and the corresponding ratio F.

[0092] Step S140: Compare the ratio F with the first fault threshold T1. When F > T1, it is determined that the rectifier has a power transistor fault. When F ≤ T1, it is determined that the rectifier has not a power transistor fault.

[0093] The first fault threshold is the maximum value of F when no fault occurs, which can be obtained through simulation. Under normal circumstances, the DC quantity is much larger than the fundamental frequency quantity, and the ratio between the two is close to 0. Considering the fluctuation, the range of the first fault threshold can be set to (0.02, 0.03).

[0094] By following steps S110 to S140 above, it can be diagnosed that the power transistor of the current rectifier has failed.

[0095] If no fault is detected, sampling data can continue to be acquired and the data of the current cycle can be continuously updated. The diagnosis can then be performed again following the steps described above. It is understandable that when performing fault diagnosis in the next cycle, if the information used has already been calculated in the previous detection cycle, it can be used directly without recalculation.

[0096] In one embodiment, when a power transistor failure is diagnosed in the current rectifier, the faulty phase is also located. Therefore, as Figure 4 As shown, the rectifier fault diagnosis method also includes:

[0097] Step S210: Use the last L sampling points of the current detection cycle as the variable point prediction set B and determine the sampling variable point t.

[0098] The sampling point t is determined by the following formula:

[0099]

[0100] As explained earlier, after acquiring a certain number of sampling points, each additional sampling point will move to form a new sliding window. Each time the sliding window moves, the nearest KL sliding windows will form a new inner loop. Each update of the inner loop will form a detection cycle based on the nearest KL inner loops and obtain the corresponding DC value. That is, each additional sampling point will calculate an inner loop cumulative current and a DC value. Among the parameters used to determine the sampling point, I′ B(j-1) and Z B(j-1) Let I′ be the inner loop cumulative current and DC current, respectively, when the sliding window moves to the (j-1)th sampling point in the variable point prediction set B. B(j+1) and Z B(j+1) These are the inner-loop cumulative current and DC current, respectively, when the sliding window moves to the (j+1)th sampling point in the variable-point prediction set B. Furthermore, the values ​​of these parameters are cyclically selected within a window; that is, when j=1, I′... B0 =I′ BL Z B0 =Z BL When j = L, I′ B(L+1) =I′ B1 Z B(L+1) =Z B1 By iterating through each sampling point in the variable point prediction set B, the sampling point corresponding to the minimum value obtained by the above formula is taken as the sampling variable point.

[0101] Step S220: The phase state corresponding to the minimum absolute value of the three-phase normalized current at the sampling point t is taken as the fault phase.

[0102] After determining the sampling point t, the minimum absolute value of the three-phase normalized current at the current sampling point is determined to be...

[0103]

[0104] in, Let represent the normalized three-phase currents of phases a, b, and c at the sampling point t, respectively. Let y be the three-phase normalized current with the smallest absolute value, and y be the faulty phase located.

[0105] It should be noted that the faulty phase can be located after a fault is determined to have occurred, or it can be located simultaneously during the determination of whether a fault has occurred. Only the faulty phase located when a fault is determined to have occurred is valid; the faulty phase located when a fault is not determined to have occurred is invalid data.

[0106] In one embodiment, when a power transistor in the current rectifier is diagnosed to be faulty, the faulty power transistor is also located. Since power transistors are divided into inner and outer transistors, the rectifier fault diagnosis method can also locate faults in both the inner and outer transistors. Therefore, as... Figure 5 As shown, the rectifier fault diagnosis method also includes:

[0107] Step S310: Calculate the sum of the normalized three-phase currents for each phase state within the last sliding window of the current detection cycle.

[0108] As mentioned earlier, a sliding window has L sampling points. The sum of the normalized three-phase currents for each phase at the L sampling points is calculated, i.e.

[0109]

[0110] in, This represents the normalized three-phase current at the j-th sampling point in the current sliding window, from which we obtain...

[0111] Step S320: Take The maximum absolute value in.

[0112]

[0113] Step S330: Compare the maximum value I * With the second fault threshold T2, when I * When I ≤ T2 / 2, it is determined to be an internal tube fault. * When the value is greater than T2 / 2, it is determined to be an external pipe fault.

[0114] The second fault threshold can be obtained through simulation or calculated using a fitted formula, which is as follows:

[0115]

[0116] It should be noted that the fault location of the inner and outer tubes can be determined after the fault has occurred, or the fault location of the inner and outer tubes can be determined simultaneously during the fault determination process. Only the fault location located when the fault has been determined is valid; the fault location located when the fault has not been determined is invalid information.

[0117] Furthermore, after locating the faults in the internal and external transistors, it is possible to continue locating the specific power transistor. Therefore, if... Figure 6 As shown, the rectifier fault diagnosis method also includes:

[0118] When an internal tube malfunction is detected, execute:

[0119] Step S340: Continue comparing the sum of the normalized three-phase currents. With 0, when When, determine the power transistor S x3 When a malfunction occurs, When, determine the power transistor S x2 A malfunction has occurred.

[0120] When an external pipe fault is detected, execute:

[0121] Step S351: Backtrack the sampled variable point t to the sampled point t′ within the variable point prediction set.

[0122]

[0123] when If the number is a decimal, then take the integer part before the decimal point.

[0124] Step S352: Determine the three-phase normalized current at sampling point t′. The polarity, when When, determine the power transistor S x4 When a malfunction occurs, When, determine the power transistor S x1 A malfunction has occurred.

[0125] By following the steps above, it is possible to diagnose whether a fault has occurred. If a fault is diagnosed, the specific location of the faulty power transistor can be quickly determined by combining the location of the faulty phase and the power transistor.

[0126] Accordingly, the present invention also relates to a fault diagnosis device for a grid-connected T-type rectifier, such as... Figure 7 As shown, the device includes a normalization processing unit, a median determination unit, an inner loop calculation unit, a fundamental frequency calculation unit, a DC calculation unit, and a fault determination unit. Among them,

[0127] The normalization processing unit is used to process the sampled phase currents i x Perform three-phase normalization processing separately to obtain the three-phase normalized current;

[0128] The median determination unit is used to determine the median current of the three-phase normalized current at each sampling point;

[0129] The inner loop calculation unit is used to calculate the cumulative current of each inner loop s and Among them, I mL K is a preset value, K≥2, which is the sum of the absolute values ​​of the median current of the mL-th sliding window in the inner loop. The sampling number L of a sliding window is the ratio of the three-phase current sampling frequency to the grid frequency. The sliding window is moved backward with a sampling point as the moving step size. Each adjacent KL sliding window is a single inner loop.

[0130] The fundamental frequency calculation unit is used to calculate the fundamental frequency based on the cumulative current of KL inner loops within the current detection period. Each KL adjacent inner rings constitutes one detection cycle;

[0131] The DC calculation unit is used to calculate the DC quantity based on the cumulative current of KL inner loops within the current detection cycle.

[0132] The ratio calculation unit is used to calculate the ratio of the fundamental frequency quantity G to the direct current quantity Z;

[0133] The fault determination unit is used to compare the ratio F with the first fault threshold T1. When F > T1, it is determined that the rectifier has a power transistor fault. When F ≤ T1, it is determined that the rectifier has not a power transistor fault.

[0134] Furthermore, the fault diagnosis device also includes a sampling change point determination unit and a fault phase location unit. Among them,

[0135] The sampling change point determination unit is used to determine the sampling change point t = arg min by taking the last L sampling points of the current detection period as the change point prediction set B. 1≤j≤L ((max(I′ B(j-1) -Z B(j-1) ,0))·(max(I′ B(j+1) -Z B(j+1) ,0))), where I′ B(j-1) Z represents the cumulative current of the inner loop obtained by moving the sliding window to the (j-1)th sampling point in the variable point prediction set. B(j-1) Let I′ be the direct current obtained by moving the sliding window to the (j-1)th sampling point in the variable point prediction set. B(j+1) Z represents the cumulative current of the inner loop obtained by moving the sliding window to the (j+1)th sampling point in the variable point prediction set. B(j+1) Let I' be the direct current obtained by moving the sliding window to the (j+1)th sampling point in the variable point prediction set, and let I' be the direct current. B0 =I′ BL , I′ B(L+1) =I′ B1 Z B0 =Z BL Z B(L+1) =Z B1 .

[0136] The fault phase location unit is used to identify the phase state corresponding to the minimum absolute value of the three-phase normalized current at the sampling point t as the fault phase.

[0137] Furthermore, the fault diagnosis device also includes an inner and outer tube positioning unit, which comprises a current summation unit, a maximum value determination unit, and a first determination unit. Among these,

[0138] The current summation unit is used to calculate the sum of the normalized three-phase currents for each phase state within the last sliding window of the current detection cycle.

[0139] The maximum value determination unit is used to determine the maximum value. The maximum absolute value I in * ;

[0140] The first decision unit is used to compare the maximum value I. * With the second fault threshold T2, when I * When I ≤ T2 / 2, it is determined to be an internal tube fault. * When the value is greater than T2 / 2, it is determined to be an external pipe fault.

[0141] Furthermore, the fault diagnosis device also includes a power transistor location unit, comprising a second determination unit, a change-point tracing unit, and a third determination unit, wherein...

[0142] The second determination unit is used to compare the sum of the three-phase normalized currents when the first determination unit determines that the internal tube is faulty. With 0, when When, determine the power transistor S x3 When a malfunction occurs, When, determine the power transistor S x2 A malfunction occurred;

[0143] The change-point backtracking unit is used to backtrack the sampled change point t to the sampling point within the change-point prediction set when the first determination unit determines that the external pipe is faulty.

[0144] The third determination unit is used to determine the three-phase normalized current at sampling point t′. The polarity, when When, determine the power transistor S x4 When a malfunction occurs, When, determine the power transistor S x1 A malfunction has occurred.

[0145] Finally, when a rectifier fault is detected, the final location of the faulty power transistor is determined based on the identified faulty phase and power transistor. For example, if the identified faulty phase is 'a' and the identified power transistor is 'S'... x1 When both factors are considered, the faulty power transistor can be identified as S. a1 .

[0146] like Figure 8 The diagram shows the physical experimental results of fault detection according to the present invention. The first vertical dashed line represents the actual fault point, and the fourth dashed line represents the fault point determined by the present invention. A brief delay occurs due to the time required for calculation. Specifically, (a) represents the original sampled three-phase current i. x (b) represents the normalized three-phase current after normalization. (c) represents the median current i at each sampling point. z (d) represents the cumulative current I′ sGiven the DC flow rate Z, the sampling variable point t can be obtained. (e) represents the comparison result between the ratio F and the fault threshold T1. It can be seen that the fault was identified at the position of the fourth vertical dashed line. After the fault is identified, the variable point t obtained in (d) is the valid variable point. (f) represents the maximum value I. * When a fault is identified, the comparison between the two, along with the second fault threshold T2, determines the fault information of the outer tube. (g) represents the minimum absolute value of the three-phase normalized current and the absolute value of the b-phase normalized current. At the change point t, the two are equal, meaning the absolute value of the b-phase normalized current is the minimum. This indicates that the faulty phase located at the change point t is the b-phase. Simultaneously, after locating the outer tube fault, the change point is traced back to obtain t′ in (b), and the three-phase normalized current at the sampling point t′ is determined. The polarity of S is determined b4 The fault was eventually located to the S power transistor. b4 The faults matched the actual fault settings perfectly, indicating that the present invention can perform accurate fault diagnosis.

[0147] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fault diagnosis method for a grid-connected T-type rectifier, characterized in that, The three-phase currents are sampled at the set sampling frequency. , The ratio of the three-phase current sampling frequency to the grid frequency is rounded down to form a sliding window sampling number. The sliding window moves backward with a sampling point as the step size, and then moves forward with each adjacent sampling point. The sliding window acts as an inner ring, with each adjacent... Each inner loop is considered as a detection cycle, and faults are detected based on the selected three-phase current within each detection cycle; The fault detection process, based on selected three-phase currents, is performed within each detection cycle, including: For each phase current Perform three-phase normalization processing separately to obtain the three-phase normalized current, and determine the median current of the three-phase normalized current at each sampling point; Calculate each inner loop cumulative current ,in, For the corresponding inner ring The sum of the absolute values ​​of the median current of each sliding window. As a preset value, ; Based on the detection period Calculate the fundamental frequency of the cumulative current of each inner loop. and direct traffic and fundamental frequency and direct traffic ratio , , , Comparison ratio Compared with the first fault threshold ,when When a power transistor fault is detected in the rectifier, it is determined that a fault has occurred. At that time, it was determined that the rectifier did not have a power transistor failure; The method further includes fault phase location, the fault phase location method comprising: At the end of the current testing cycle 1 sampling point as the change point prediction set And determine the sampling change point , ; in, To move the sliding window to the first point in the change point prediction set The cumulative current of the inner loop obtained from each sampling point, To move the sliding window to the first point in the change point prediction set The direct current obtained from each sampling point, To move the sliding window to the first point in the change point prediction set The cumulative current of the inner loop obtained from each sampling point, To move the sliding window to the first point in the change point prediction set The direct current obtained from each sampling point, and , , , ; With sampling variable point The phase state corresponding to the minimum absolute value of the three-phase normalized current is taken as the fault phase.

2. The fault diagnosis method for grid-connected T-type rectifiers as described in claim 1, characterized in that, It also includes fault location for internal and external pipes, and the methods for fault location for internal and external pipes include: Calculate the sum of the normalized three-phase currents for each phase state within the last sliding window of the current detection cycle. ; Pick , , The maximum absolute value in Compare the maximum values With the second fault threshold ,when When the problem is identified as an internal tube malfunction, At that time, it was determined to be an external pipe failure; The inner tube is a power transistor on the neutral point bridge arm of the grid-connected T-type rectifier, and the outer tube is a power transistor on the upper bridge arm of the grid-connected T-type rectifier.

3. The fault diagnosis method for grid-connected T-type rectifiers as described in claim 2, characterized in that, Second fault threshold The calculation formula is: 。 4. The fault diagnosis method for grid-connected T-type rectifiers as described in claim 2, characterized in that, It also includes power transistor fault location, the method for power transistor fault location includes: When an internal tube fault is identified, the sum of the normalized three-phase currents is further compared. With 0, when When determining the power transistor When a malfunction occurs, When determining the power transistor A malfunction occurred; When an external pipe fault is identified, the variable point will be sampled within the variable point prediction set. Tracing back to the sampling point , ； Determine sampling points Three-phase normalized current The polarity, when When determining the power transistor When a malfunction occurs, When determining the power transistor A malfunction occurred; in, express Phase upper arm power transistor, express Lower bridge arm power transistor, Indicates connection to the center point of the busbar. Phase bridge arm power transistor, Indicates connection to the center point of the upper and lower bridge arms Phase-selected bridge arm power transistor.

5. The fault diagnosis method for grid-connected T-type rectifiers as described in claim 1, characterized in that, Calculate the normalized three-phase current The formula is: 。 6. The fault diagnosis method for grid-connected T-type rectifiers as described in claim 1, characterized in that, 。 7. A fault diagnosis device for a grid-connected T-type rectifier, characterized in that, include: The normalization processing unit is used to process the sampled phase currents. Perform three-phase normalization processing separately to obtain the three-phase normalized current; The median determination unit is used to determine the median current of the three-phase normalized current at each sampling point; Inner loop calculation unit, used to calculate each inner loop cumulative current and ,in, For the corresponding inner ring The sum of the absolute values ​​of the median current of each sliding window. As a preset value, The sampling number of a sliding window is calculated by rounding down the ratio of the three-phase current sampling frequency to the grid frequency. The sliding window moves backward with a sampling point as the step size, and then moves forward with each adjacent sampling point. The sliding window acts as an inner ring; The fundamental frequency calculation unit is used to calculate the fundamental frequency based on the current detection period. Calculate the fundamental frequency of the cumulative current of each inner loop. ; where each adjacent Each inner ring is considered a detection cycle; DC calculation unit, used to calculate based on the current detection period Calculate the DC current of the cumulative current of each inner loop. ; The ratio calculation unit is used to calculate the fundamental frequency. and direct traffic The ratio; Fault determination unit, used for comparing ratios Compared with the first fault threshold ,when When a power transistor fault is detected in the rectifier, it is determined that a fault has occurred. At that time, it was determined that the rectifier did not have a power transistor failure; The device further includes a sampling change point determination unit and a fault phase location unit; wherein... The sampling change point determination unit is used to determine the last sampling point of the current detection cycle. 1 sampling point as the change point prediction set And determine the sampling change point ,in, To move the sliding window to the first point in the change point prediction set The cumulative current of the inner loop obtained from each sampling point, To move the sliding window to the first point in the change point prediction set The direct current obtained from each sampling point, To move the sliding window to the first point in the change point prediction set The cumulative current of the inner loop obtained from each sampling point, To move the sliding window to the first point in the change point prediction set The direct current obtained from each sampling point, and , , , ; The fault phase location unit is used to sample change points. The phase state corresponding to the minimum absolute value of the three-phase normalized current is taken as the fault phase.

8. The grid-connected T-type rectifier fault diagnosis device as described in claim 7, characterized in that, It also includes internal and external tube positioning units and power tube positioning units; The outer tube positioning unit includes a current summation unit, a maximum value determination unit, and a first determination unit, wherein... The current summation unit is used to calculate the sum of the three-phase normalized currents for each phase in the last sliding window of the current detection cycle. ; The maximum value determination unit is used to determine the maximum value. , , The maximum absolute value in ; The first determination unit is used to compare the maximum value. With the second fault threshold ,when When the problem is identified as an internal tube malfunction, At that time, it was determined to be an external pipe failure; The power transistor positioning unit includes a second determination unit, a change-point backtracking unit, and a third determination unit, wherein... The second determination unit is used to compare the sum of the three-phase normalized currents when the first determination unit determines that the inner tube is faulty. With 0, when When determining the power transistor When a malfunction occurs, When determining the power transistor A malfunction occurred; The change-point backtracking unit is used to sample change points within the change-point prediction set when the first determination unit determines that the external pipe is faulty. Tracing back to the sampling point ; The third determination unit is used to determine the sampling point. Three-phase normalized current The polarity, when When determining the power transistor When a malfunction occurs, When determining the power transistor A malfunction occurred; in, express Phase upper arm power transistor, express Lower bridge arm power transistor, Indicates connection to the center point of the busbar. Phase bridge arm power transistor, Indicates connection to the center point of the upper and lower bridge arms Phase-selected bridge arm power transistor.

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