A Spearman-based method for diagnosing open-circuit faults in DC charging pile rectifiers

Abstract

The present invention relates to a method for diagnosing open circuit faults of a DC charging pile rectifier based on Spearman, and belongs to the field of fault diagnosis technology. It includes three parts: fault data collection, open circuit fault identification, and open circuit fault location. The three-phase current data of the AC side of the DC charging pile rectifier is collected, and the mean absolute value of the current of each phase is calculated; in order to identify the rectifier open circuit fault bridge arm, an open circuit fault identification feature quantity is constructed, and the absolute value of the current mean corresponding to the bridge arm where the open circuit fault may occur is numerically compared, and the phase corresponding to the maximum value of the three-phase current mean absolute value is taken to determine it as the rectifier open circuit fault bridge arm; if an open circuit fault bridge arm exists, the phase current data within the integer multiple period of the fault phase is used, combined with the normal three-phase current historical data, and the open circuit fault location feature quantity is constructed to realize the location of the open circuit fault of a single power device of the rectifier. The present invention only requires the three-phase current data on the AC side to realize the diagnosis of the DC charging pile rectifier open circuit fault.

Description

Technical Field

[0001] The present invention belongs to the technical field of fault diagnosis and relates to a Spearman-based method for diagnosing open-circuit faults of a DC charging pile rectifier. Background Art

[0002] The rapid growth in the number of electric vehicles is leading to a rapid increase in the number of DC charging stations, particularly those using fast chargers. These stations operate in harsh environments, with most operating outdoors in high temperatures, extreme cold, and humidity. This makes them susceptible to sudden failures, a significant concern for operators and manufacturers. According to statistics, approximately 34% of failures in charging station rectifiers are caused by IGBT (Insulated Gate Bipolar Transistor) power device failures, with open-circuit failures being the most common. An open-circuit IGBT failure does not significantly impact the continued operation of the charging station, generating no excessive current or voltage, and can even hinder the effective triggering of relevant protective measures. This makes it difficult to detect and conceal. If not promptly detected and repaired, it can cause long-term harmonics to the power grid, impact vehicle charging times, and ultimately lead to secondary failures and sudden downtime of the charging station. Therefore, it is necessary to develop diagnostic methods for open-circuit failures in DC charging station rectifier power devices.

[0003] Currently, DC charging pile rectifier modules mostly use three-phase two-level rectifier circuits and three-phase Vienna rectifier circuits. Considering that three-phase Vienna rectifier circuits cannot achieve bidirectional energy flow, three-phase two-level rectifier circuits can achieve bidirectional energy interaction between vehicle and grid, and have important application value in smoothing grid power fluctuations and providing emergency support for grid faults. Therefore, this paper proposes a DC charging pile rectifier open circuit fault diagnosis method based on the Spearman correlation coefficient for the three-phase two-level rectifier of DC charging piles. The three-phase current data on the AC side of the DC charging pile rectifier is collected, and the mean absolute value of each phase current is calculated. To identify the rectifier open-circuit fault bridge arm, an open-circuit fault identification feature is constructed. The mean absolute values ​​of the currents corresponding to the bridge arm where the open-circuit fault may occur are numerically compared, and the phase corresponding to the largest value among the three-phase current mean absolute values ​​is determined as the rectifier open-circuit fault bridge arm. If an open-circuit fault bridge arm exists, the phase current data within the period of the fault phase is combined with the normal three-phase current historical data using the Spearman correlation coefficient to construct an open-circuit fault location feature to locate the open-circuit fault of a single power device in the rectifier. The proposed DC charging pile rectifier open-circuit fault diagnosis method based on the Spearman correlation coefficient only requires the AC side three-phase current data to perform DC charging pile rectifier open-circuit fault diagnosis, providing technical support for the safe and reliable operation of DC charging piles in charging stations. It is of great significance to reduce the impact of faults on grid power quality, improve charging pile maintenance efficiency, and reduce maintenance costs. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a Spearman-based DC charging pile rectifier open circuit fault diagnosis method for obtaining the open circuit fault condition of the DC charging pile rectifier power device.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A Spearman-based DC charging pile rectifier open circuit fault diagnosis method includes the following steps:

[0007] (1) Collect the three-phase current data of the rectifier AC side with T integer multiple cycles, and use formula (1) to calculate the mean absolute value of each phase current.

[0008]

[0009] Where m is phase A, B or C respectively; t is the current i m The total number of samples. It can be seen that the mean absolute value I can be calculated by formula (1) A , I B , I C .

[0010] (2) The absolute value of the current mean I m Based on this, the open circuit fault identification feature D is constructed m for:

[0011]

[0012] Where k1 is the open circuit fault identification threshold. m =1, it means that the m-phase bridge arm may have an open circuit fault; if the fault identification characteristic value D m =0, it means that there is no open circuit fault in the m-phase bridge arm.

[0013] The absolute values ​​of the mean currents corresponding to the bridge arms where the open circuit fault may occur are compared numerically, and the bridge arm corresponding to the phase with the largest absolute value among the three-phase current mean currents is determined as the bridge arm with the rectifier open circuit fault.

[0014] (3) If there is a rectifier open circuit fault phase, the above step 3 should be used to locate the power device of the rectifier open circuit fault. The Spearman correlation coefficient S of the positive half cycle of the fault phase is calculated using formula (3). mp and the negative half-cycle Spearman correlation coefficient S mn , the calculation formula is as follows:

[0015]

[0016] Among them, i m and i'm are the collected m-phase current data and normal m-phase current history data respectively; L is the total number of collected m-phase current positive half-cycle or negative half-cycle data, L = 0.5t; S m is the correlation coefficient, and -1≤S m ≤1; when S m =1, it means the two waveforms are completely consistent; when S m =-1, it means that the two waveforms have the same amplitude but opposite polarity.

[0017] The constructed power device fault location feature R is:

[0018]

[0019] Among them, S mp represents the positive half-cycle correlation coefficient, S mn represents the negative half-cycle correlation coefficient, and k2 is the fault location threshold.

[0020] If the power device positioning characteristic value R=U, it means that the upper arm power device of the fault phase m has an open circuit fault; if the power device positioning characteristic value R=D, it means that the lower arm power device of the fault phase m has an open circuit fault.

[0021] The beneficial effects of the present invention are: collecting the three-phase current data of the AC side of the DC charging pile rectifier and calculating the mean absolute value of the current of each phase; in order to identify the rectifier open circuit fault bridge arm, the open circuit fault identification feature quantity is constructed, the current mean absolute value corresponding to the bridge arm where the open circuit fault may occur is numerically compared, and the phase corresponding to the maximum value of the three-phase current mean absolute value is determined as the rectifier open circuit fault bridge arm; if an open circuit fault bridge arm exists, the phase current data within the integer multiple period of the fault phase is used, combined with the normal three-phase current historical data, and the Spearman correlation coefficient is used to construct the open circuit fault positioning feature quantity to realize the open circuit fault positioning of a single power device of the rectifier. The DC charging pile rectifier open circuit fault diagnosis method based on the Spearman correlation coefficient proposed by the present invention only requires the three-phase current data on the AC side to realize the DC charging pile rectifier open circuit fault diagnosis, and can provide technical support for the status monitoring of the DC charging pile in the charging station.

[0022] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0024] Figure 1 This is a fault diagnosis flowchart;

[0025] Figure 2 This is the circuit structure diagram of the DC charging pile rectifier;

[0026] Figure 3 The three-phase current of the power device VT1 open circuit fault;

[0027] Figure 4 The absolute value change of the current mean when the power device VT1 has an open circuit fault. DETAILED DESCRIPTION

[0028] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0029] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0030] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0031] A method for diagnosing open circuit faults of rectifiers of DC charging piles based on the Spearman correlation coefficient, wherein the object is a three-phase two-level rectifier of a DC charging pile, mainly includes three parts: fault data acquisition, open circuit fault identification, and open circuit fault location. Collect the three-phase current data of the AC side of the DC charging pile rectifier, and calculate the mean absolute value of the current of each phase; in order to identify the rectifier open circuit fault bridge arm, construct an open circuit fault identification feature, compare the absolute value of the current mean corresponding to the bridge arm where the open circuit fault may occur, and take the phase corresponding to the maximum value of the absolute value of the three-phase current mean as the rectifier open circuit fault bridge arm; if there is an open circuit fault bridge arm, use the phase current data within the integer multiple period of the fault phase, combined with the normal three-phase current historical data, adopt the Spearman correlation coefficient, and construct an open circuit fault location feature to realize the location of the open circuit fault of a single power device of the rectifier. The method for diagnosing open circuit faults of rectifiers of DC charging piles based on the Spearman correlation coefficient proposed in the present invention only requires the three-phase current data on the AC side to realize the diagnosis of open circuit faults of DC charging pile rectifiers. Combined with Figure 1 The open circuit fault diagnosis method and implementation steps of the DC charging pile rectifier based on the Spearman correlation coefficient are described in detail.

[0032] The circuit topology of the three-phase two-level rectifier of the DC charging pile is as follows: Figure 2 Next, Figure 2 The effectiveness of the present invention is illustrated by taking the open circuit fault of the A-phase bridge arm power device VT1 as an example.

[0033] S1: Fault data collection part. Collect the three-phase current data of the rectifier AC side, extract the rectifier three-phase current data of T cycles, and use formula (1) to calculate the average absolute value of each phase current. For example, when Figure 2 When the A-phase bridge arm power device VT1 has an open circuit fault, the three-phase current of the AC side fault of the DC charging pile rectifier is collected. When the time of a single cycle is t = 0.02s and the sampling frequency is 5kHz, T = 5 is taken. At 1.04s, the A-phase bridge arm VT1 has an open circuit fault. Figure 3 As shown. According to the absolute value of the mean current of each phase calculated by formula (1), see Figure 4 As shown in Figure 1, it can be seen that the absolute values ​​of the mean currents of the three phases are 0 before the open circuit fault occurs, and the absolute values ​​of the mean currents of each phase are greater than 0 after the fault occurs.

[0034] S2: Fault identification part. Construct the open circuit fault identification feature D based on the mean absolute value. m, determine the arm of the bridge where an open - circuit fault may occur, compare the absolute values of the average currents corresponding to the arms of the bridge where an open - circuit fault may occur numerically, and determine the arm of the bridge corresponding to the maximum value among the absolute values of the average three - phase currents as the open - circuit fault arm of the rectifier. For example, the threshold k1 in Equation (2) is set based on experience, and its value range is between 0.05 and 0.08 times the maximum normal current. In this example, k1 is taken as 0.3 A. Further, the fault identification feature quantity D after 1.04 s is obtained through Equation (2): D A = 1, D B = 1, D C = 1, and then it is inferred that open - circuit faults may occur in the arms of the rectifier in phases A, B, and C. According to the method of determining the arm of the bridge corresponding to the maximum value among the absolute values of the average three - phase currents as the open - circuit fault arm of the rectifier, as shown in Figure 4 , it is obvious that an open - circuit fault has occurred in the arm of phase A.

[0035] S3: Open - circuit fault location part. If an open - circuit fault of the rectifier is identified, use the phase - current data within the integral multiple periods of the faulty phase, combined with the historical data of the normal three - phase currents i' m , and adopt the Spearman correlation coefficient to construct an open - circuit fault location feature quantity to achieve the location of the open - circuit fault of the rectifier. For example, from S2, it has been identified that an open - circuit fault has occurred in the arm of phase A of the rectifier. The phase - A current data and the historical data of phase A are as shown in Figure 3 . There are obvious waveform - missing phenomena in the positive and negative half - cycles. Extract the upper - half - cycle and lower - half - cycle data of the phase - A current in Figure 3 respectively, combine them with the historical data of the normal phase - A current, and calculate the correlation coefficients according to Equation (3) as shown in Table 1: S Ap = 0.6307, S An = 0.2775. According to Equation (4), the power - device location feature quantity R = U is obtained, where the judgment threshold k2 is set through experience. In this example, k2 is taken as 0.5. It can be seen that S An = 0.2775 < k2, and it can be judged that the power device VT1 in the upper arm of phase A has a fault. The fault - location result is consistent with the above assumption, and the fault location is accurate. It can be seen that the invented fault - diagnosis method is effective.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A Spearman-based DC charging pile rectifier open circuit fault diagnosis method, characterized by: The method comprises the following steps: Step 1: Collect the three-phase current data of the AC side of the DC charging pile rectifier and calculate the average absolute value of each phase current; Step 2: To identify the rectifier open-circuit fault bridge arm, construct an open-circuit fault identification feature, compare the current mean absolute values ​​corresponding to the bridge arm where the open-circuit fault may occur, and take the phase with the largest value among the three-phase current mean absolute values ​​to determine it as the rectifier open-circuit fault bridge arm; Step 3: If an open-circuit fault is identified in the rectifier, the open-circuit fault location feature is constructed by using the phase current data within the integer multiple period of the fault phase, combined with the normal three-phase current historical data, and the Spearman correlation coefficient to locate the open-circuit fault of a single power device in the rectifier. If there is a rectifier open circuit fault phase, locate the power device of the rectifier open circuit fault; use formula (3) to calculate the positive half cycle Spearman correlation coefficient S of the fault phase respectively. mp and the negative half-cycle Spearman correlation coefficient S mn , the calculation formula is as follows: Among them, i m and i' m They are respectively the collected m-phase current data and the fault-free m-phase current historical data; L is the total number of collected m-phase current positive half-cycle or negative half-cycle data, L = 0.5t, t is the current i m Total number of samples; S m is the correlation coefficient, and -1≤S m ≤1; when S m =1, it means the two waveforms are completely consistent; when S m =-1, indicating that the two waveforms have the same amplitude but opposite polarity; The constructed power device fault location feature R is: Among them, S mp represents the positive half-cycle correlation coefficient, S mn represents the negative half-cycle correlation coefficient, k2 is the fault location threshold; If the power device positioning characteristic value R=U, it means that the upper arm power device of the fault phase m has an open circuit fault; if the power device positioning characteristic value R=D, it means that the lower arm power device of the fault phase m has an open circuit fault.

2. The Spearman-based DC charging pile rectifier open circuit fault diagnosis method according to claim 1, characterized in that: In the step 1, the three-phase current data of the AC side of the DC charging pile rectifier is collected, and the m-phase current data i with T cycles is extracted. m , use formula (1) to obtain the mean absolute value of the m-phase current I m ; Where m is phase A, B or C respectively; t is the current i m The total number of samples; the mean absolute value I is calculated by formula (1) A , I B , I C .

3. The Spearman-based DC charging pile rectifier open circuit fault diagnosis method according to claim 2, characterized in that: In the step 2, based on the absolute value of the mean of the three-phase current, the open circuit fault identification feature D is constructed. m for: Among them, k1 is the open circuit fault recognition threshold; when the fault recognition feature quantity D m =1, it means that the m-phase bridge arm may have an open circuit fault; if the fault identification characteristic value D m =0, it means that there is no open circuit fault in the m-phase bridge arm; The absolute values ​​of the mean currents corresponding to the bridge arms where the open circuit fault may occur are compared numerically, and the phase corresponding to the maximum absolute value of the three-phase current mean current is selected to determine the bridge arm with the rectifier open circuit fault.

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