Method for diagnosing and positioning open-circuit fault of switching tube of three-phase dual-active bridge converter

Abstract

The invention relates to the technical field of power electronic converter fault diagnosis, and particularly discloses a three-phase dual active bridge (3phi-DAB) converter switch tube open-circuit fault diagnosis and positioning method. Taking single phase shift control as an example, in order to realize open-circuit fault diagnosis of a 3 phi-DAB converter switching tube, the specific method comprises the following steps: firstly, carrying out open-circuit fault diagnosis on the converter switching tube, and calculating a current centroid vector length formed by three-phase inductive current according to the three-phase inductive current; judging whether the converter breaks down or not according to the current centroid vector length and preliminarily positioning a full bridge where the fault is located; the open-circuit fault positioning of the switch tubes of the 3phi-DAB converter is realized according to the characteristics of different line voltage average values when the 12 switch tubes of the converter have open-circuit faults. The 3phi-DAB converter fault diagnosis method is small in observed electrical quantity, low in cost and high in accuracy, and provides a new diagnosis thought for the fault diagnosis technology of the 3phi-DAB converter.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronic converter fault diagnosis, and in particular relates to a method for diagnosing and locating a 3Φ-DAB converter switch tube open circuit fault. Background Art

[0002] Nowadays, bidirectional DC / DC converters, as the core components of power conversion, have been widely used in distributed power generation, DC microgrids, electric vehicle charging piles, energy routers, etc. In order to achieve safe and stable power conversion, the reliability of key components in its equipment and systems needs to reach almost 99.999%, and semiconductor power electronic components are the main cause of converter failure and damage.

[0003] As a bidirectional DC / DC converter, the single-phase dual active fullbridge (1Φ-DAB) DC / DC converter is commonly used in power multi-level converters, grid charging of vehicles, and vehicle discharge to the outside. Compared with the 1Φ-DAB converter, the 3Φ-DAB converter not only has the advantages of galvanic isolation, high power density, inherent zero voltage switching, and bidirectional power transmission, but also has lower voltage and current ripples and smaller filter capacitors, thus having the potential to achieve the highest power density. However, due to its more semiconductor devices and more operating modes, the reliability and stability issues of the 3Φ-DAB converter need to be paid more attention. Although the converter can still work abnormally in the stable state of open circuit fault (OCF). However, OCF still causes asymmetry of inductor current, switch node voltage, and inductor voltage, resulting in current overshoot, capacitor voltage imbalance, and saturation of magnetic components in the DAB converter. These asymmetric effects seriously reduce the reliability and safety of the DAB converter under long-term operation. Therefore, studying the real-time diagnosis and location method of the open-circuit fault of the switch tube of the 3Φ-DAB converter is of great significance to improving maintenance efficiency and reducing system protection costs.

[0004] At present, although the research on developing more efficient fault isolation (FT) schemes for 3Φ-DAB converters has been intensified, the fault diagnosis (FD) and fault location (FI) schemes for 3Φ-DAB converters have not been widely studied. For most FT strategies of 3Φ-DAB converters, a clear method for detecting and locating switch OCF has not been established. In the FD and FI processes of 3Φ-DAB converters, the primary and secondary sides are FD simultaneously, which will inevitably increase the electrical quantities required to be observed and slow down the diagnosis speed. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for diagnosing and locating an open-circuit fault of a power converter switch tube. The method observes few electrical quantities and can accurately diagnose and locate the open-circuit fault switch tube based only on the three-phase inductor current and line voltage in the converter control. The method is simple, has low hardware cost and high accuracy.

[0006] The present invention discloses a method for diagnosing and locating an open-circuit fault of a power converter switch tube, and its technical solution is: real-time acquisition of three-phase inductor current and line voltage data of a 3Φ-DAB converter, and innovative analysis of the current centroid vector and line voltage average value characteristics formed by the three-phase inductor current to achieve open-circuit fault diagnosis and location.

[0007] A method for diagnosing and locating an open circuit fault of a power converter switch tube of the present invention comprises the following steps:

[0008] Step 1: Calculate the length of the current centroid vector formed by the three-phase inductor current. When the current centroid vector length exceeds the preset threshold of the primary side fault, it is determined that an open circuit fault occurs in the switch tube on the primary side of the 3Φ-DAB converter. When the current centroid vector length is between the preset threshold of no fault and the preset threshold of the primary side fault, it is determined that an open circuit fault occurs in the switch tube on the secondary side of the 3Φ-DAB converter;

[0009] Step 2: Based on the average value of the line voltage on the fault side as an effective fault judgment criterion, it is compared and judged with the average line voltage characteristics of each switch tube when the switch tube has an open circuit fault (Table II, Table III), so as to locate the switch tube with the open circuit fault of the 3Φ-DAB converter.

[0010] The step 1 is specifically as follows:

[0011] Step 1.1: When an open circuit fault occurs, the three-phase inductor current will generate a DC bias, causing the average value of the phase current to change significantly within a switching cycle. The primary side open circuit fault has a larger change than the secondary side open circuit fault. Therefore, a current centroid vector that can reflect this feature is constructed. The calculated vector length is used to detect faults and identify the faulty side. It is the average value of the phase current within a switching cycle.

[0012] Since the current centroid vector It contains amplitude and phase angle, and its length calculation is relatively complicated, so it is decomposed into the αβ coordinate system through equal-amplitude coordinate transformation.

[0013]

[0014] Then the current centroid vector Size It can be calculated as

[0015]

[0016] Step 1.2: Define thresholds to determine if a failure has occurred Among them, A and B are weight coefficients, is the magnitude of the current centroid vector when a fault occurs, is the magnitude of the current centroid vector during normal operation, is the primary side fault threshold, is the secondary side fault threshold. In addition, in order to ensure the sensitivity and accuracy of fault diagnosis, the magnitude of the current centroid vector should account for a larger proportion when a fault occurs in the threshold, that is, the weight coefficient A should be larger, and its magnitude depends on the noise level of normal operation. If the noise is large, the influence of the noise should be reduced, the magnitude of B should be reduced, that is, the magnitude of A should be increased, and vice versa. After repeated testing and adjustment, the present invention believes that A=0.8 and B=0.2 are suitable values ​​to ensure the stability and effectiveness of the proposed detection method.

[0017] Will By comparing with Table I, the fault side can be found. The proposed fault diagnosis technique is as follows Figure 4 (a). Here, the normalized analysis is To express it in units, the reference value is the input current i in The average value of .

[0018] Table I Fault identification scheme based on current centroid vector

[0019]

[0020] The step 2 is specifically as follows:

[0021] Step 2.1: In order to ensure the accuracy of fault diagnosis, threshold voltages λ and δ are introduced to avoid misoperation or failure. Among them, λ is the threshold voltage for primary side faults, and δ is the threshold voltage for secondary side faults. Secondly, in order to ensure that the converter can operate normally under noise conditions, λ and δ should be small enough to eliminate the influence of noise and ensure sensitivity to faulty operating conditions. After repeated testing and adjustment, the present invention believes that λ=2V and δ=1V are suitable values ​​to ensure the stability and effectiveness of the proposed detection method.

[0022] If step 1 determines that an open circuit fault occurs on the primary or secondary side of the converter, Figure 4 As shown in (b), the average value of two line voltages on the fault side is calculated and compared with the threshold voltage λ or δ to determine whether it is positive or negative, which is used as the positioning criterion.

[0023] Step 2.2: If Figure 4As shown in (c), the positioning criteria obtained in step 2.1 are input into the logic-based fault positioning scheme to locate the open-circuit fault of the switch tube of the 3Φ-DAB converter.

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

[0025] 1. By detecting the three-phase inductor current, calculating the length of the current centroid vector formed by it, and comparing the current centroid vector length with the preset threshold value of no fault and the preset threshold value of primary side fault, the open circuit fault of the switch tube of the 3Φ-DAB converter can be quickly diagnosed;

[0026] 2. If it is determined that an open-circuit fault occurs on the primary or secondary side of the converter, the average value of the primary or secondary line voltage under the open-circuit fault is further calculated and used as the fault location criterion. Based on the different fault location criteria when the 12 switch tubes have an open-circuit fault, a fault location algorithm is designed to locate the open-circuit fault of the switch tube of the 3Φ-DAB converter;

[0027] 3. The present invention can accurately diagnose and locate the open circuit fault of the switch tube only based on the current centroid vector formed by the three-phase inductor current of the converter and part of the line voltage, with a small amount of electrical observation, low cost and high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The circuit topology and equivalent circuit of 3Φ-DAB converter are shown in Figure 2.

[0029] Figure 2 This is the normal operating waveform of the 3Φ-DAB converter

[0030] Figure 3 The waveform of the 3Φ-DAB converter with the switch tube open circuit fault

[0031] Figure 4 Diagram of the open circuit fault diagnosis and location strategy of the switch tube of the 3Φ-DAB converter DETAILED DESCRIPTION

[0032] 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.

[0033] In order to better understand the present invention, the following introduction is given before explaining the present invention.

[0034] The topology of 3Φ-DAB is as follows: Figure 1As shown in (a), it is composed of two three-phase full bridges connected through energy storage inductors and a three-phase high-frequency transformer. The primary bridge converts the DC input voltage into a high-frequency AC voltage. The AC voltage and current are converted according to the turns ratio of the three-phase high-frequency transformer, and then rectified by the secondary bridge. Among them, the connection method of the three-phase transformer is flexible, including YY connection, Y-△ connection and △-△ connection. In order to analyze without loss of generality, the present invention selects the transformer as a YY-connected 3Φ-DAB converter for analysis, and equates it to the following: Figure 1 The analysis process of 3Φ-DAB converter with other transformer connection methods is similar to that of the circuit shown in (b).

[0035] The traditional modulation strategy of 3Φ-DAB converter is single phase shift (SPS) modulation. Its basic principle is that the three phases are staggered by 120° and each switching component is switched in one switching cycle T. s The internal conduction is 180°, and the transmission power is changed by changing the phase relationship between its primary side and secondary side. When the primary side voltage phase leads the secondary side phase, forward power is transmitted, and vice versa. The present invention is explained by taking forward power transmission as an example, and the analysis of reverse power transmission is similar. Figure 2 (a)(b) shows the voltage and current waveforms of phase A of single phase shift modulation. In the figure, D3 represents the phase shift ratio, T hs Represents half a switching cycle, i.e. 2T hs =T s =1 / f s When the monotonicity of the system transmission power is considered, the value range of D3 in the single phase shift modulation strategy is 0≤D3≤1. From the figure, it can be found that with different values ​​of D3, there are two different modes of single phase shift modulation.

[0036] Next, the normal operating characteristics of the 3Φ-DAB converter are analyzed.

[0037] To simplify the analysis, a switching function S is first defined for each bridge arm of the 3Φ-DAB converter. x (t)(x=A,B,C,a,b,c), the specific expression is

[0038]

[0039] In the formula, t0 represents the turn-on time of the upper bridge arm switch device, D c For the duty cycle of each switching device, for single phase shift modulation D c = 1. By switching function S x The definition of (t) can calculate the phase voltage of each phase on the primary and secondary sides, and its expression is:

[0040]

[0041] From the above formula, we can find that the number of phase voltage levels of the 3Φ-DAB converter is related to the switching function S in one switching cycle. x (t). Then, the expression of line voltage can be obtained based on the equivalent circuit:

[0042]

[0043] The state equation of the three-phase transformer inductor current can be expressed as

[0044]

[0045] Considering the symmetry of the three-phase parameters of the 3Φ-DAB converter, the average transmission power of the 3Φ-DAB converter can be expressed as

[0046]

[0047] Therefore, in the steady state, the expression of the average transmission power under single phase shift modulation can be obtained by the segmented analytical method:

[0048]

[0049] In the formula, n is the transformation ratio of the three-phase transformer, U in is the DC voltage at the input terminal, U out is the DC voltage at the output end, L s is the leakage inductance of each phase of the three-phase transformer. According to the symmetry of the three-phase transformer parameters, the leakage inductance of the three-phase transformer satisfies L s =L A =L B =L C .

[0050] The relationship between the current and voltage across the phase inductor is given by

[0051]

[0052] In normal operation, the phase currents contain no DC bias and are offset by 120° from each other. Under ideal conditions, within one cycle (T s ) can be divided into 18 states according to the conductive devices. Figure 2 (c) shows the phase current waveforms and the conduction conditions of each switch tube in the normal mode operation of the three-phase DAB. On the primary side, each switch tube conducts 8 of the 18 conduction states, while on the secondary side, each switch tube conducts only 1 of the 18 conduction states. This shows that the impact of the primary side OCF is more obvious than the secondary side OCF. This feature can be used to develop fault diagnosis technology for the primary and secondary sides of the converter.

[0053] Next, the operating characteristics of the 3Φ-DAB converter with a switch open-circuit fault are analyzed.

[0054] 1) Primary side fault (T A1 ):

[0055] For T A1 Open circuit fault, such as Figure 3 (a) Through L A The positive voltage time decreases, the current i A Generates a negative DC bias, current i B and i C Generates a positive DC bias. Figure 3 (b) shows the primary side T A1 The steady-state waveform of the three-phase current when a fault occurs. Since there is no path for positive current to flow in phase A, i A Completely shifted below the time axis, resulting in a large negative DC offset. Figure 3 (c) shows T A1 The impact of open circuit fault on the primary line voltage waveform. According to the line voltage expression, T A1 When a failure occurs, it will cause u AB and u CA The waveform is distorted. Specifically, it will make u AB The waveform above the positive half axis is missing, making u CA The waveform below the positive half axis is also missing. Therefore, this will inevitably change the line voltage u related to the fault bridge arm AB ,u CA The average value of .

[0056] 2) Secondary side fault (T a1 ):

[0057] For T a1 Open circuit fault, such as Figure 3 (d) Through L A The negative voltage time decreases, the current i A Generates a positive DC bias, current i B and i C Generates a negative DC bias. Figure 3 (e) shows the secondary side T a1 The steady-state waveform of the three-phase current when a fault occurs. It can be seen that the primary side T A1 Compared with the fault, the impact on phase current is much smaller, which is consistent with the above analysis. Figure 3 (f) shows the secondary side T a1 The impact of fault on line voltage waveform. According to the expression of line voltage, when T a1 When a failure occurs, it will cause u ab and u caWaveform distortion. A1 Similarly, it will make u ab The waveform above the positive half axis is missing, making u ca The waveform above the positive half axis increases, so the line voltage u related to the fault bridge arm ab ,u ca The average value of also changes accordingly.

[0058] Based on the above analysis, the average line voltage characteristics of each faulty switch tube in the converter are different, and the average line voltage characteristics of the top and bottom switches of each bridge arm are opposite. A1 Take a fault as an example, u AB The absence of positive voltage will cause its average value to be significantly less than 0. CA The absence of negative voltage will cause its average value to be significantly greater than 0. A2 On the contrary, the average line voltage characteristics of other switch tubes when an open circuit fault occurs can also be obtained similarly and listed in Table II and Table III for developing fault diagnosis and location technology.

[0059] Table II Characteristics of average line voltage of primary side fault switch

[0060]

[0061] Table III Characteristics of average line voltage of secondary side fault switch tube

[0062]

[0063] The present invention discloses a method for diagnosing and locating an open-circuit fault of a power converter switch tube, and its technical solution is: real-time acquisition of three-phase inductor current and line voltage data of a 3Φ-DAB converter, and innovative analysis of the current centroid vector and line voltage average value characteristics formed by the three-phase inductor current to achieve open-circuit fault diagnosis and location.

[0064] A method for diagnosing and locating an open circuit fault of a power converter switch tube of the present invention is as follows: Figure 4 As shown, the following steps are included:

[0065] Step 1: Calculate the length of the current centroid vector formed by the three-phase inductor current. When the current centroid vector length exceeds the preset threshold of the primary side fault, it is determined that an open circuit fault occurs in the switch tube on the primary side of the 3Φ-DAB converter. When the current centroid vector length is between the preset threshold of no fault and the preset threshold of the primary side fault, it is determined that an open circuit fault occurs in the switch tube on the secondary side of the 3Φ-DAB converter;

[0066] Step 2: Based on the average value of the line voltage on the fault side as an effective fault judgment criterion, it is compared and judged with the average line voltage characteristics of each switch tube when the switch tube has an open circuit fault (Table II, Table III), so as to locate the switch tube with the open circuit fault of the 3Φ-DAB converter.

[0067] The step 1 is specifically as follows:

[0068] Step 1.1: When an open circuit fault occurs, the three-phase inductor current will generate a DC bias, causing the average value of the phase current to change significantly within a switching cycle. The primary side open circuit fault has a larger change than the secondary side open circuit fault. Therefore, a current centroid vector that can reflect this feature is constructed. The calculated vector length is used to detect faults and identify the faulty side. It is the average value of the phase current within a switching cycle.

[0069] Since the current centroid vector It contains amplitude and phase angle, and its length calculation is relatively complicated, so it is decomposed into the αβ coordinate system through equal-amplitude coordinate transformation.

[0070]

[0071] Then the current centroid vector Size It can be calculated as

[0072]

[0073] Step 1.2: Define thresholds to determine if a failure has occurred Among them, A and B are weight coefficients, is the magnitude of the current centroid vector when a fault occurs, is the magnitude of the current centroid vector during normal operation, is the primary side fault threshold, is the secondary side fault threshold. In addition, in order to ensure the sensitivity and accuracy of fault diagnosis, the magnitude of the current centroid vector should account for a larger proportion when a fault occurs in the threshold, that is, the weight coefficient A should be larger, and its magnitude depends on the noise level of normal operation. If the noise is large, the influence of the noise should be reduced, the magnitude of B should be reduced, that is, the magnitude of A should be increased, and vice versa. After repeated testing and adjustment, the present invention believes that A=0.8 and B=0.2 are suitable values ​​to ensure the stability and effectiveness of the proposed detection method.

[0074] Will By comparing with Table I, the fault side can be found. The proposed fault diagnosis technique is as follows Figure 4 (a). Here, the normalized analysis is To express it in units, the reference value is the input current iin The average value of .

[0075] Table I Fault identification scheme based on current centroid vector

[0076]

[0077] The step 2 is specifically as follows:

[0078] Step 2.1: In order to ensure the accuracy of fault diagnosis, threshold voltages λ and δ are introduced to avoid misoperation or failure. Among them, λ is the threshold voltage for primary side faults, and δ is the threshold voltage for secondary side faults. Secondly, in order to ensure that the converter can operate normally under noise conditions, λ and δ should be small enough to eliminate the influence of noise and ensure sensitivity to faulty operating conditions. After repeated testing and adjustment, the present invention believes that λ=2V and δ=1V are suitable values ​​to ensure the stability and effectiveness of the proposed detection method.

[0079] If step 1 determines that an open circuit fault occurs on the primary or secondary side of the converter, Figure 4 As shown in (b), the average value of two line voltages on the fault side is calculated and compared with the threshold voltage λ or δ to determine whether it is positive or negative, which is used as the positioning criterion.

[0080] Step 2.2: If Figure 4 As shown in (c), the positioning criteria obtained in step 2.1 are input into the logic-based fault positioning scheme to locate the open-circuit fault of the switch tube of the 3Φ-DAB converter.

[0081] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0082] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for diagnosing and locating an open circuit fault of a power converter switch tube, characterized in that: Step 1: Calculate the length of the current centroid vector formed by the three-phase inductor current. When the current centroid vector length exceeds the preset threshold of the primary side fault, it is determined that an open circuit fault occurs in the switch tube on the primary side of the 3Φ-DAB converter. When the current centroid vector length is between the preset threshold of no fault and the preset threshold of the primary side fault, it is determined that an open circuit fault occurs in the switch tube on the secondary side of the 3Φ-DAB converter; Step 2: Based on the average value of the line voltage on the fault side as an effective fault judgment criterion, it is compared and judged with the average line voltage characteristics of each switch tube when the switch tube has an open circuit fault (Table II, Table III), so as to locate the switch tube with the open circuit fault of the 3Φ-DAB converter.

2. The method for diagnosing and locating the open circuit fault of the switch tube of the 3Φ-DAB converter according to claim 1 is characterized in that: The step 1 is specifically as follows: Step 1.1: When an open circuit fault occurs, the three-phase inductor current will generate a DC bias, causing the average value of the phase current to change significantly within a switching cycle. The primary side open circuit fault has a larger change than the secondary side open circuit fault. Therefore, a current centroid vector that can reflect this feature is constructed. The calculated vector length is used to detect faults and identify the faulty side. It is the average value of the phase current within a switching cycle. Since the current centroid vector It contains amplitude and phase angle, and its length calculation is relatively complicated, so it is decomposed into the αβ coordinate system through equal-amplitude coordinate transformation. Then the current centroid vector Size It can be calculated as Step 1.2: Define thresholds to determine if a failure has occurred Among them, A and B are weight coefficients, is the magnitude of the current centroid vector when a fault occurs, is the magnitude of the current centroid vector during normal operation, is the primary side fault threshold, is the secondary side fault threshold. In addition, in order to ensure the sensitivity and accuracy of fault diagnosis, the magnitude of the current centroid vector should account for a larger proportion when a fault occurs in the threshold, that is, the weight coefficient A should be larger, and its magnitude depends on the noise level of normal operation. If the noise is large, the influence of the noise should be reduced, the magnitude of B should be reduced, that is, the magnitude of A should be increased, and vice versa. After repeated testing and adjustment, the present invention believes that A=0.8 and B=0.2 are suitable values ​​to ensure the stability and effectiveness of the proposed detection method. Will By comparing with Table I, the fault side can be found. In order to normalize the analysis, To express it in units, the reference value is the input current i in The average value of . Table I Fault identification scheme based on current centroid vector 3. The method for diagnosing and locating the open circuit fault of the switch tube of the 3Φ-DAB converter according to claim 1 is characterized in that: The step 2 is specifically as follows: Step 2.1: In order to ensure the accuracy of fault diagnosis, threshold voltages λ and δ are introduced to avoid misoperation or failure. Among them, λ is the threshold voltage for primary side faults, and δ is the threshold voltage for secondary side faults. Secondly, in order to ensure that the converter can operate normally under noise conditions, λ and δ should be small enough to eliminate the influence of noise and ensure sensitivity to faulty operating conditions. After repeated testing and adjustment, the present invention believes that λ=2V and δ=1V are suitable values ​​to ensure the stability and effectiveness of the proposed detection method. If step 1 determines that an open circuit fault occurs on the primary or secondary side of the converter, as shown in FIG4( b ), the average values ​​of two line voltages on the faulty side are calculated and compared with the threshold voltage λ or δ to determine whether they are positive or negative, which is used as a positioning criterion. Step 2.2: As shown in FIG4(c), the positioning criteria obtained in step 2.1 are input into the logic-based fault location scheme to locate the open-circuit fault of the switch tube of the 3Φ-DAB converter.

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