Offshore wind power direct current collection line fault identification method based on current transient state quantity area comparison

Abstract

The invention discloses an offshore wind power direct current collection line fault identification method based on current transient state quantity area comparison, and the method achieves the area selection and pole selection of a fault line through extracting the current transient state quantity of a collection line. The method comprises the following steps: firstly, establishing an offshore wind power direct-current collecting and sending-out system, and obtaining transient current data when a fault occurs; then, the area value of the transient current is obtained through calculation; then, by searching for the cluster with the maximum transient current area value, the cluster where the fault is located is determined; and finally, judging a fault pole according to the positive and negative relation of the positive and negative current of the cluster with the maximum transient current area value. According to the method, faults can be recognized more quickly and effectively, and meanwhile, due to the fact that the area method can reduce interference of noise on fault recognition, the method has important significance in the aspect of guaranteeing safe and stable operation of the offshore wind power direct current collection system.

Description

Technical Field

[0001] The present invention belongs to the technical field of offshore wind power protection, and in particular relates to a method for identifying faults in offshore wind power DC collection lines based on current transient quantity area comparison. Background Art

[0002] Wind power is currently the most technologically mature and widely used renewable energy source. Furthermore, compared to offshore wind power, offshore wind power has fewer constraints and more stable and powerful winds, which facilitates the continuous and efficient provision of power output. Compared to onshore and offshore wind power, the construction and operation of offshore wind farms have less impact on the surrounding environment.

[0003] Traditional AC collection and transmission methods are limited by factors such as transmission losses, cable capacity, and reactive power compensation, making them unsuitable for offshore wind power applications. In contrast, offshore wind power collection systems based on DC architectures offer advantages such as high efficiency, compact size, and the absence of reactive power compensation, making them more suitable for long-distance offshore wind power transmission.

[0004] However, DC collection systems face significant challenges in terms of protection. They rely on power electronic converters, which have poor tolerance to sustained overcurrent and are prone to damage, impacting safe and stable system operation. Furthermore, DC system fault currents rise rapidly, making them difficult to isolate using conventional circuit breakers. Communication delays within offshore wind farms complicate fault handling and hinder the real-time nature of fault detection. Rapid fault identification and isolation are essential to minimize the impact and avoid significant power loss and impact on the onshore power grid. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, the present invention provides a method for identifying faults in offshore wind turbine DC transmission lines based on current transient area comparison. This method obtains the area and proportion of the transient current at the positive and negative poles of each turbine cluster within 1ms when a fault occurs. The faulty turbine cluster is located and the fault type identified based on the proportion and positive and negative directions. This method has low requirements for system topology and is unaffected by the number of turbine clusters and line length, making it both interference-resistant and universally applicable.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The method for identifying faults in an offshore wind power DC collection line based on current transient area includes the following steps:

[0008] Step 1: The current collector on the bus collects the instantaneous current flowing from the bus into the positive and negative poles of the group. When the starting criterion is activated, the instantaneous value of the positive current of each group within 1ms after the fault occurs is recorded. k,P (i) and the instantaneous value of the negative electrode current ik,N (i) Save as positive transient current and negative transient current respectively;

[0009] The specific implementation methods are as follows:

[0010] When the bus voltage U dc Less than the set voltage U set When the fault occurs, the set voltage is set to 50% of the rated voltage. When the fault occurs:

[0011] U dc ≤U set

[0012] The positive and negative transient currents within 1ms of a fault are:

[0013] i k,P (i)=(i k,P (0),i k,P (1)...i k,P (0.001*f))

[0014] i k,N (i)=(i k,N (0),i k,N (1)...i k,N (0.001*f))

[0015] Where f is the sampling frequency.

[0016] Step 2: Based on the acquired transient current data, calculate the transient current area values ​​of the positive and negative currents of each group within 1ms after the fault occurs;

[0017] The specific implementation methods are as follows:

[0018] The transient current area values ​​of the positive and negative currents of each group within 1ms are:

[0019]

[0020]

[0021] Where S k,P is the positive electrode current integral area of ​​the kth group, S k,N is the integrated area of ​​negative electrode current of the kth group; i k,P (i) is the instantaneous value of the positive current of the i-th unit recorded within 1ms of the k-th unit failure. k,N (i) is the instantaneous value of the negative electrode current of the i-th unit recorded within 1ms of the k-th unit failure; i k,P (0) is the instantaneous value of the initial positive current when the k-th group fault occurs, i k,N(0) is the instantaneous value of the initial negative electrode current when the k-th group fault occurs; f is the sampling frequency.

[0022] Step 3: Compare the absolute value of the transient current area of ​​the positive and negative currents of each cluster with the sum of the absolute values ​​of the transient current areas of the positive and negative currents of all clusters to obtain the transient current proportions of the positive and negative currents of each cluster;

[0023] The specific implementation methods are as follows:

[0024] The absolute value of the transient current area of ​​the positive or negative electrode of each cluster is compared with the sum of the absolute values ​​of the transient current area of ​​the positive or negative electrode current of all clusters to obtain the transient current proportion of the positive and negative electrodes of each cluster:

[0025]

[0026]

[0027] Where, P k,p is the percentage of the positive electrode area of ​​the kth group to the total positive electrode area, P k,N is the percentage of the negative electrode area of ​​the kth cluster to the total negative electrode area; m is the number of clusters.

[0028] Step 4: Use the transient current ratio to find the faulty cluster. The cluster with the largest transient current ratio is the faulty cluster. Use the positive and negative transient current area of ​​the faulty cluster and the fault type comparison table to identify the fault type.

[0029] The specific implementation methods are as follows:

[0030] When a positive grounding fault occurs, the relationship between the positive current of the faulty group and the positive current of the non-faulty group is:

[0031] |i f,P |=|i 1,P |+|i 2,P |+...|i f-1,P |+|i f+1,P |+|i m,P |+|i D |

[0032] Where i f,P is the positive current of the faulty group; i m,P is the positive electrode current of the mth group; i f-1,P and i f+1,P is the positive current of the cluster adjacent to the faulty cluster; i D is the transformer current.

[0033] When a negative grounding fault occurs, the relationship between the negative current of the faulty group and the negative current of the non-faulty group is:

[0034] |i f,N |=|i 1,N |+|i 2,N |+...|i f-1,N |+|i f+1,N |+|i m,n |+|i D |

[0035] Where i f,N is the negative current of the faulty generator set; i m,N is the negative electrode current of the mth group; i f-1,N and i f+1,N is the negative current of the cluster adjacent to the faulty cluster; i D is the transformer current. When an inter-pole fault occurs, the positive and negative poles satisfy the above expression at the same time. It can be obtained that the positive or negative pole current of the faulty group accounts for the largest proportion. Since the capacitor discharge is the main source when the fault occurs, its equivalent power supply is U dc / 2, then the initial direction of the current fault should be consistent with the equivalent power supply voltage, so:

[0036]

[0037] The method to find the largest proportion of transient current is the direct traversal method.

[0038] 1) Select the positive transient current proportion of group 1 as the maximum value P max,P ;

[0039] 2) The positive transient current ratios of other groups are compared with the maximum value in turn. If the maximum value is greater than the maximum value, it is used as the new maximum value. The positive transient current ratios of all groups are traversed, compared and updated one by one.

[0040] 3) The traversal ends, P max,P The group where the positive transient current is located is the group with the largest proportion

[0041] For the negative electrode transient current ratio, the same method is used to obtain P max,N , P max,P With P max,N Compare, the larger corresponding group is the fault group. Then, compare the positive and negative transient current areas of the group with 0.

[0042]

[0043] Query the fault type comparison table to obtain the fault type.

[0044] Compared with the prior art, the present invention has the following advantages:

[0045] 1. Good anti-interference ability: Due to the transient current area method, it can effectively filter out noise interference.

[0046] 2. High applicability: It can correctly identify a variety of faults. At the same time, the number of clusters and line length have little impact on the accuracy of fault identification.

[0047] 3. High identification efficiency: The present invention only requires the positive and negative currents of each cluster within 1ms of the fault, and can quickly identify the fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of the method of the present invention;

[0049] Figure 2 This is the topology diagram of the offshore wind power DC collection and transmission system. DETAILED DESCRIPTION

[0050] Below in conjunction with accompanying drawing and accompanying table and embodiment, the present invention is described in further detail:

[0051] like Figure 1 FIG2 is a flow chart of a method for identifying faults in an offshore wind power DC collection line based on current transient area comparison according to an embodiment of the present invention, comprising the following steps:

[0052] Step 1: After determining that a fault has occurred, obtain the positive and negative transient current data within 1ms after the fault.

[0053] Step 2: Obtain the transient current area value and proportion value based on the fault current data;

[0054] Step 3: Find the cluster with the largest transient current ratio, which is the faulty cluster;

[0055] Step 4: Determine the fault type based on the positive and negative relationship between the positive and negative transient current area values ​​of the faulty generator group and the fault type comparison table.

[0056] Example:

[0057] Build as Figure 1 The offshore wind power DC collection system shown in the figure has four wind turbines connected in series in each cluster. There are four clusters in total. All simulated faults are set to 0ms and last for 1s. The sampling frequency is 50kHz. The fault location is as follows: Figure 2 Various fault conditions were simulated, including positive pole ground fault, negative pole ground fault, double pole ground fault, and ground fault between wind turbines.

[0058] The positive and negative transient current area values ​​and proportions of each group within 1ms for different fault types are shown in Table 1.

[0059] Table 1: Positive and negative transient current area and proportion of each group within 1ms for each fault type

[0060]

[0061] When a positive grounding fault occurs between the fan and busbar of cluster 1, it can be seen that cluster 1 has the largest proportion of positive and negative transient current among the four clusters, so cluster 1 can be determined to be the faulty cluster. Based on the positive and negative relationship between the positive and negative transient current areas of cluster 1, querying fault comparison table 2 shows that the fault type is a positive grounding fault.

[0062] Table 2: Fault type comparison table

[0063] Fault type Positive current area Negative current area Positive ground fault 1 1 Negative ground fault 0 0 Bipolar fault 1 0

[0064] Similarly, negative ground faults and bipolar faults between the fan and busbar are correctly identified. A special case is the ground fault between clusters 2 and 3. Because a single cluster in this model consists of four fans connected in series, the point between clusters 2 and 3 is at zero potential. Even a ground short-circuit here would not cause overcurrent in the system. Furthermore, as shown in the last two columns of Table 1, ground faults between fans can also be correctly identified.

Claims

1. A fault identification method for offshore wind power DC collection lines based on current transient area comparison, characterized in that: The steps include: Step 1: Build an offshore wind power DC collection and transmission system to collect positive and negative current data from the busbar into the turbine cluster, and obtain positive and negative transient current data when a fault occurs in the offshore wind power DC collection line; Step 2: Based on the acquired transient current data, calculate the transient current area values ​​of the positive and negative currents of each group within 1ms after the fault occurs; Step 3: Compare the absolute value of the transient current area of ​​the positive and negative currents of each cluster with the sum of the absolute values ​​of the transient current areas of the positive and negative currents of all clusters to obtain the transient current proportions of the positive and negative currents of each cluster; Step 4: Use the transient current ratio to find the faulty cluster. The cluster with the largest transient current ratio is the faulty cluster. Use the positive and negative transient current area of ​​the faulty cluster and the fault type comparison table to identify the fault type.

2. The method for identifying faults in offshore wind power DC collection lines based on current transient area comparison according to claim 1, characterized in that: In step 2, the transient current area values ​​of the positive and negative currents of each cluster within 1ms are: Where S k,P is the positive electrode current integral area of ​​the kth group, S k,N is the integrated area of ​​negative electrode current of the kth group; i k,P (i) is the instantaneous value of the positive current of the i-th unit recorded within 1ms of the k-th unit failure. k,N (i) is the instantaneous value of the negative electrode current of the i-th unit recorded within 1ms of the k-th unit failure; i k,P (0) is the instantaneous value of the initial positive current when the k-th group fault occurs, i k,N (0) is the instantaneous value of the initial negative electrode current when the k-th group fault occurs; f is the sampling frequency.

3. The method for identifying faults in offshore wind power DC collection lines based on current transient area comparison according to claim 1, characterized in that: In step 3, the absolute value of the transient current area of ​​the positive and negative currents of each group obtained in step 2 is compared with the sum of the absolute values ​​of the transient current areas of the positive and negative currents of all groups, and the proportion thereof is obtained. Where, P k,p is the percentage of the positive electrode area of ​​the kth group to the total positive electrode area, P k,N is the percentage of the negative electrode area of ​​the kth cluster to the total negative electrode area; m is the number of clusters.

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