A method for detecting open-circuit fault of power tubes in NPC three-phase four-wire rectifier

Abstract

The application discloses a kind of NPC three-phase four-wire rectifier inner power tube open-circuit fault detection methods, it is related to the technical field of early warning, the method can realize on-line fault early warning, guide fault-tolerant technology and operation and maintenance strategy, prevent catastrophic failure occurs.The method comprises the following steps: determining the positive sampling mean and the negative sampling mean of each phase current, and determining whether the inner power tube fails; if it is detected that the inner power tube fails, then locate the fault phase according to the positive sampling mean and the negative sampling mean of each phase current; compare the positive sampling mean and the negative sampling mean of the fault phase to locate the fault inner power tube.The application is suitable for detecting the open-circuit fault of the inner power tube in the symmetric power NPC three-phase four-wire rectifier, and has the advantages of low calculation cost, good robustness and fast diagnosis speed.

Description

Technical Field

[0001] This invention relates to the field of fault early warning technology, and in particular to a method for detecting open-circuit faults in the power transistors of an NPC three-phase four-wire rectifier. Background Technology

[0002] In recent years, with the rapid development of new energy technologies, more and more new energy vehicles have emerged. As a crucial charging module in new energy vehicle charging piles, the reliability of the rectifier is a key indicator of system quality. In rectifiers, power transistors are prone to open-circuit faults due to high-frequency switching on and off, directly affecting normal system operation. The NPC (Neutral Point Clamped) three-phase four-wire rectifier is widely used in charging pile rectifier modules due to its superior performance. This paper proposes a real-time and effective diagnostic method for open-circuit faults in NPC three-phase four-wire rectifiers, providing real-time and effective information for subsequent fault-tolerant control strategies, which has significant engineering application value for improving the reliability of rectifier modules.

[0003] Most of the published literature on real-time detection methods for open-circuit faults in three-phase three-level rectifiers is based on model residuals. The constructed models rely too much on model parameters and system signals, resulting in poor implementation capabilities and hindering the effective application of fault diagnosis technology. Summary of the Invention

[0004] To address the aforementioned problems and technical requirements, the inventors have proposed a method for detecting open-circuit faults in the power transistors of an NPC three-phase four-wire rectifier. The aim is to achieve online fault early warning, guide fault-tolerant technologies and operation and maintenance strategies, and prevent catastrophic failures. The technical solution of this invention is as follows:

[0005] A method for detecting open-circuit faults in the power transistors of an NPC three-phase four-wire rectifier includes the following steps:

[0006] Determine the positive and negative sampling mean values ​​of the current in each phase and determine whether the internal power transistor has failed.

[0007] If a fault is detected in the internal power transistor, the faulty phase is located based on the positive and negative sampling average values ​​of the current in each phase.

[0008] By comparing the positive and negative sampling mean values ​​of the faulty phase, the faulty power transistor can be located.

[0009] A further technical solution involves determining the positive and negative sampling averages of the current in each phase, including:

[0010] Collect three-phase current and perform normalization operation;

[0011] Determine the number L of sampling points in the sliding window;

[0012] Each normalized three-phase current sampled within the sliding window is compared to zero, dividing each phase current into positive and negative sampling points. Then, the mean of the positive and negative samples of the normalized current for each phase is calculated, expressed as:

[0013]

[0014] Among them, P x N represents the positive sampled mean of the normalized current of phase x. x i represents the negative sample mean of the normalized current of phase x. x_m Let x represent the m-th sampling point of the normalized current of phase x collected within the sliding window, where x = a, b, c.

[0015] A further technical solution involves determining whether the internal power transistor has malfunctioned, including the following methods:

[0016] Let M be the minimum of the absolute values ​​of the positive and negative sample mean values ​​of all phase currents; if M is greater than the threshold Th, then the internal power transistor is determined to be faulty, otherwise the internal power transistor is working normally.

[0017] A further technical solution involves locating the faulty phase based on the positive and negative sampling averages of the current in each phase, including:

[0018] Based on the positive sampling average value P of each phase current x and negative sample mean N x Calculate the mean offset D of the three-phase current. x D x =P x -N x , where x = a, b, c;

[0019] Take the average deviation D of the three-phase current x The phase corresponding to the minimum value is the faulty phase.

[0020] A further technical solution involves comparing the positive sampling mean P of the faulty phase. x and negative sample mean N x Methods for locating the faulty internal power transistor include:

[0021] If |P x |>|N x If |, then the internal power transistor of phase x is faulty;

[0022] If |P x |<|N x If |, then the faulty phase x has a faulty internal power transistor;

[0023] Where x = a, b, c.

[0024] A further technical solution involves a method for acquiring and normalizing three-phase currents, including:

[0025] Based on the collected three-phase current i a i b i c Calculate peak current i m The expression is:

[0026]

[0027] According to the peak current i m The normalized three-phase current value is calculated using the following expression:

[0028]

[0029] Where x = a, b, c.

[0030] A further technical solution is that the expression for calculating the number of sampling points L in the sliding window is:

[0031]

[0032] Where f represents the frequency of the three-phase power supply, and f1 represents the sampling frequency.

[0033] The further technical solution is that the threshold Th is set as follows:

[0034]

[0035] The beneficial technical effects of this invention are:

[0036] (1) This method only processes the real-time collected three-phase current to detect the open circuit fault of the power tube in the NPC three-phase four-wire rectifier. No additional hardware or model building is required, and the cost is low.

[0037] (2) The diagnosis is very fast, requiring only one current cycle.

[0038] (3) It has strong anti-interference ability and can cope with the impact of load current change, grid voltage change, system parameter change and other factors on the fault.

[0039] (4) The algorithm is simple to implement and has a small amount of computation, which significantly reduces the computational complexity. Attached Figure Description

[0040] Figure 1 This application provides the NPC three-phase four-wire rectifier topology and fault diagnosis module.

[0041] Figure 2This is a flowchart of the method for detecting open-circuit faults in the internal power transistors of the NPC three-phase four-wire rectifier provided in this application. Detailed Implementation

[0042] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0043] Figure 1 The diagram shows the topology of the NPC three-phase four-wire rectifier with a fault diagnosis module in this embodiment, including: power transistor S a1 S a2 S a3 S a4 S b1 S b2 S b3 S b4 S c1 S c2 S c3 S c4 The diode D corresponding to the power transistor a1 D a2 D a3 D a4 D b1 D b2 D b3 D b4 D c1 D c2 D c3 D c4 DC side capacitors C1 and C2. In the diagram, U... d This is the DC bus voltage. It is the output setpoint of the rectifier control system, u as u bs u cs For three-phase power supply, i a i b i c For three-phase current. In the topology of the NPC three-phase four-wire rectifier, U... d i a i b i c This provides feedback information to the rectifier control system. Based on this topology, this embodiment adds an inner tube fault diagnosis module to collect real-time three-phase current i. a i b i c As input variables, execute the steps of the method for detecting open-circuit faults in internal power transistors of an NPC three-phase four-wire rectifier provided in this embodiment, wherein S a2 S b2 S c2 For internal power transistor, S a3 Sb3 S c3 It is the lower power transistor.

[0044] like Figure 2 As shown, the method includes the following steps:

[0045] Step 1: Determine the positive and negative sampling mean values ​​of the current in each phase, including:

[0046] Step 1.1: Acquire three-phase current i a i b i c Then perform a normalization operation.

[0047] Based on the collected three-phase current i a i b i c Calculate peak current i m The expression is:

[0048]

[0049] According to the peak current i m Calculate the normalized three-phase current value i x_ The expression is:

[0050]

[0051] Where x = a, b, c.

[0052] Step 1.2: Based on the frequency f of the three-phase power supply and the sampling frequency f1, determine the number of sampling points L in the sliding window, expressed as:

[0053]

[0054] Step 1.3: Compare each normalized three-phase current sampled within the sliding window with zero, divide each phase current into positive and negative sampling points, and then calculate the positive and negative sampling mean values ​​of the normalized current for each phase. The expression is:

[0055]

[0056] Among them, P x N represents the positive sampled mean of the normalized current of phase x. x i represents the negative sampled mean of the normalized current of phase x. x_m This represents the m-th sampling point of the normalized current of phase x collected within the sliding window.

[0057] Step 2: Determine if the internal power transistor is faulty, including:

[0058] Step 2.1: Let M be the minimum of the absolute values ​​of the positive and negative sample mean values ​​of all phase currents, i.e., M = min(|P a |,|N a |,|P b |,|N b |,|P c |,|N c |).

[0059] Step 2.2: If M is greater than the threshold Th, then the internal power transistor is determined to be faulty; if M is less than or equal to the threshold Th, then the internal power transistor is working normally.

[0060] Wherein, the threshold Th is set as:

[0061] Step 3: If a fault is detected in the internal power transistor, locate the faulty phase based on the positive and negative sampling average values ​​of the current in each phase, including:

[0062] Step 3.1: Based on the positive sampled mean P of the normalized current of each phase obtained in Step 1 x and negative sample mean N x Calculate the mean offset D of the three-phase current. x D x =P x -N x .

[0063] Step 3.2: Calculate the mean offset D of the three-phase currents. x The phase corresponding to the minimum value is the faulty phase, that is:

[0064] D' x =min(D a D b D c If ), then phase x will fail.

[0065] Step 4: Compare the positive and negative sample mean values ​​of the faulty phase to locate the faulty power transistor, including:

[0066] If |P x |>|N x | Then locate the internal power transistor S of the faulty phase x. x2 A malfunction occurred;

[0067] If |P x |<|N x | Then locate the internal power transistor S of the faulty phase x. x3 A malfunction has occurred.

[0068] The design principle of the above method is as follows: Under healthy system conditions, the three-phase current exhibits a near-sinusoidal variation, with a phase difference of 120 degrees. Normalization ensures that the three-phase current amplitude is 1. When an internal power transistor S occurs... x2 After an open-circuit fault, the negative half-cycle current of that phase collapses completely to near zero, while its positive half-cycle remains unaffected, and the currents of the other two phases are also unaffected; when the internal power transistor S occurs... x3 After an open-circuit fault, the positive half-cycle of the current in that phase collapses completely to near zero, while its negative half-cycle remains unaffected, as do the currents in the other two phases. Therefore, the positive and negative sampling averages proposed in this scheme can be used for fault detection, fault phase location, and faulty power transistor location. It should be noted that in step 4, when an open-circuit fault occurs, one of the values ​​in the positive and negative sampling averages will decrease significantly, thus preventing the positive and negative sampling averages from being equal.

[0069] This invention can detect open-circuit faults in NPC three-phase four-wire rectifiers in real time. The designed diagnostic method only requires real-time detection of the three-phase current, resulting in low detection cost and few limitations. Due to the use of normalization operation, it has good robustness to sudden changes in load R and given power, and will not cause false alarms. The proposed method does not depend on the system model, does not require the establishment of an accurate circuit model or accurate system signals, has strong implementation capability, and can be ported to other systems. The algorithm is simple and has a small computational load, which significantly reduces computational complexity.

[0070] The above descriptions are merely preferred embodiments of this application, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A method for detecting open-circuit faults in power transistors within an NPC three-phase four-wire rectifier, characterized in that, include: Determine the positive and negative sampling mean values ​​of the current in each phase and determine whether the internal power transistor has failed. If a fault is detected in the internal power transistor, the faulty phase is located based on the positive and negative sampling average values ​​of the current in each phase. By comparing the positive and negative sampling mean values ​​of the faulty phase, the faulty power transistor can be located. The method for locating the faulty phase based on the positive and negative sampling averages of the current in each phase includes: Based on the positive sampling average of the current in each phase P x and negative sample mean N x Calculate the mean offset of the three-phase current. D x , D x = P x - N x ,in x = a , b , c ; Take the average deviation of the three-phase current. D x The phase corresponding to the minimum value is the faulty phase.

2. The method for detecting open-circuit faults in the power transistors of an NPC three-phase four-wire rectifier according to claim 1, characterized in that, The method for determining the positive and negative sample mean values ​​of the current in each phase includes: Collect three-phase current and perform normalization operation; Determine the number of sampling points in the sliding window L ; Each normalized three-phase current sampled within the sliding window is compared to zero, dividing each phase current into positive and negative sampling points. Then, the mean of the positive and negative samples of the normalized current for each phase is calculated, expressed as: ； in, P x express x The positive sampling mean of the phase normalized current. N x express x The negative sampling mean of the phase normalized current. i x_m Indicates the data collected within the sliding window. x The first phase normalized current m One sampling point, x = a , b , c .

3. The method for detecting open-circuit faults in the power transistors of an NPC three-phase four-wire rectifier according to claim 1, characterized in that, Methods for determining whether the internal power transistor has failed include: set up M Let be the minimum absolute value of the positive and negative sample mean values ​​of all phase currents; if M Greater than the threshold Th If the internal power transistor fails, it indicates a fault; otherwise, the internal power transistor is functioning normally.

4. The method for detecting open-circuit faults in the power transistors of an NPC three-phase four-wire rectifier according to claim 1, characterized in that, Compare the positive sampled mean of the fault phase P x and negative sample mean N x Methods for locating the faulty internal power transistor include: like Then locate the faulty phase. x The internal power transistor failed; like Then locate the faulty phase. x The internal power transistor failed; in, x = a , b , c .

5. The method for detecting open-circuit faults in the power transistors of an NPC three-phase four-wire rectifier according to claim 2, characterized in that, The method for acquiring three-phase current and performing normalization includes: Based on the collected three-phase current i a , i b , i c Calculate peak current i m The expression is: ； Based on peak current i m The normalized three-phase current value is calculated using the following expression: ； in, x = a , b , c .

6. The method for detecting open-circuit faults in the power transistors of an NPC three-phase four-wire rectifier according to claim 2, characterized in that, Determine the number of sampling points in the sliding window L The calculation expression is: ； in, f Indicates the frequency of the three-phase power supply. f 1 indicates the sampling frequency.

7. The method for detecting open-circuit faults in the power transistors of an NPC three-phase four-wire rectifier according to claim 3, characterized in that, The threshold Th Set as: ； in L This represents the number of sampling points in the sliding window.

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