A method, system, device and medium for protection of distribution lines with inverter-based distributed generation (IBDG)

Abstract

The application discloses a kind of distribution line protection method, system, equipment and medium of inverter type distributed power access, belong to distribution line protection technical field, including the following steps: in response to the original signal of distribution line exceeds preset starting threshold, the extraction of original signal, obtain relative characteristic quantity;Based on the normalization association of each described relative characteristic quantity, construct sequence current voltage normalization ratio;To the sequence current voltage normalization ratio is carried out one level condition judgment, in response to the judgment result is when fault occurs, output protection action instruction.The application constructs the judgment basis that can reflect inverter type distributed power controlled output characteristic by collecting the electrical quantity change before and after fault, and decision is carried out according to fault type using corresponding criterion, even if the fault current that inverter type distributed power outputs is far less than overcurrent protection setting value, protection device can still identify fault.

Description

Technical Field

[0001] This invention relates to the field of power distribution line protection technology, specifically to a power distribution line protection method, system, equipment, and medium for inverter-type distributed power source access. Background Technology

[0002] In scenarios where inverter-type distributed power sources are connected to the distribution network, when a fault occurs in the distribution line, the inverter-type distributed power source will output a fault current with limited amplitude and controlled according to the grid connection technology standard. This current is much smaller than the short-circuit current provided by the traditional synchronous power source, which causes the protection device based on the power frequency overcurrent principle to fail to start reliably.

[0003] For example, on a 10kV distribution line with a 0.5MW photovoltaic power station at the end, a two-phase short-circuit fault occurs 3km away from the protection installation point. Because the short-circuit current output by the photovoltaic power station is limited to 1.2 times the rated current, and the short-circuit current provided is also reduced due to the weak feedback characteristics of the inverter, the fault current at the protection installation point does not reach the overcurrent protection setting value, and the protection fails to operate.

[0004] At this time, the photovoltaic system continues to feed current into the fault point, and the fault arc cannot be extinguished on its own. This not only aggravates the damage to the line insulation, but may also cause subsequent reclosing to fail because the fault point is still energized, ultimately resulting in a large-scale unplanned power outage. Summary of the Invention

[0005] In view of the above-mentioned problems, the present invention provides a method, system, device and medium for the protection of distribution lines with inverter-type distributed power supply access.

[0006] Therefore, the technical problem solved by this invention is that after the inverter-type distributed power source is connected to the distribution network, the inverter outputs a controlled fault current with a limited amplitude according to the grid connection standard during the fault period, which causes the traditional overcurrent protection to fail to start reliably.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a power distribution line protection method for inverter-type distributed power supply access, comprising the following steps: in response to the original signal of the power distribution line exceeding a preset start threshold, extracting the original signal to obtain relative feature quantities; constructing a sequence current-voltage normalized ratio based on the normalized correlation of each of the relative feature quantities; performing a first-level condition judgment on the sequence current-voltage normalized ratio, and outputting a protection action command in response to the judgment result indicating a fault.

[0008] As a preferred embodiment of the distribution line protection method for inverter-type distributed power source access according to the present invention, the step of obtaining the relative characteristic quantity includes: performing sequence component separation on the original signal to obtain each sequence voltage component and each sequence current component; using each sequence voltage component as a reference, performing a first-level calculation on each sequence current component to obtain each sequence q-axis current; using the fault start time as a boundary, performing a second-level calculation on each sequence q-axis current to obtain each sequence q-axis abrupt change, and filtering the each sequence q-axis abrupt change; using the filtering result as the relative characteristic quantity.

[0009] As a preferred embodiment of the distribution line protection method for inverter-type distributed power source access described in this invention, the step of performing the first-level calculation includes: performing phase-locking on each sequence voltage component to obtain a positive sequence reference phase and a negative sequence reference phase; using the positive sequence reference phase and the negative sequence reference phase as a reference, performing coordinate transformation on each sequence current component to obtain each sequence q-axis current.

[0010] As a preferred embodiment of the power line protection method for inverter-type distributed power source access described in this invention, the step of performing the secondary calculation includes: taking the fault start time as the boundary, calculating the difference between the current of each sequence q-axis before and after the fault start time to obtain the sudden change of each sequence q-axis; in response to the fluctuation of the sudden change of each sequence q-axis being less than a preset range, recording the steady-state value of the sudden change of each sequence q-axis, and using the steady-state value as a relative characteristic quantity.

[0011] As a preferred embodiment of the distribution line protection method for inverter-type distributed power source access described in this invention, the step of constructing the sequence current-voltage normalization ratio includes: normalizing and correlating the positive sequence q-axis mutation of each sequence q-axis mutation with the drop depth of the positive sequence voltage component in each sequence voltage component to obtain a positive sequence normalization ratio; normalizing and correlating the negative sequence q-axis mutation of each sequence q-axis mutation with the amplitude of the negative sequence voltage component in each sequence voltage component to obtain a negative sequence normalization ratio; and using the positive sequence normalization ratio and the negative sequence normalization ratio together to constitute the sequence current-voltage normalization ratio.

[0012] In a preferred embodiment of the distribution line protection method for inverter-type distributed power source access according to the present invention, the step of performing the first-level condition judgment includes: classifying the fault into symmetrical faults and asymmetrical faults based on the amplitude of the negative sequence voltage component among the sequence voltage components; under symmetrical faults, judging based on the positive sequence normalized ratio; under asymmetrical faults, judging based on the combined positive sequence normalized ratio and the negative sequence normalized ratio; and in response to the judgment result satisfying the controlled output characteristics of the inverter-type distributed power source, confirming the occurrence of a fault and outputting a protection action command.

[0013] As a preferred embodiment of the distribution line protection method for inverter-type distributed power source access described in this invention, the step of determining based on the positive sequence normalized ratio includes: under symmetrical fault conditions, if the positive sequence normalized ratio falls within the positive sequence characteristic range, then a fault is determined to have occurred; otherwise, it is determined not to have occurred. Under asymmetrical fault conditions, if both the positive sequence normalized ratio and the negative sequence normalized ratio simultaneously satisfy the joint characteristic range, then a fault is determined to have occurred; otherwise, it is determined not to have occurred.

[0014] This invention provides a power distribution line protection system for inverter-type distributed power source access.

[0015] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a power distribution line protection system for inverter-type distributed power source access, comprising: The feature extraction module is used to extract the raw signals of the power distribution line and obtain relative feature quantities; The calculation module constructs the normalized ratio of sequence current to voltage by normalizing and correlating the various relative characteristic quantities. The execution module performs a first-level condition judgment on the normalized ratio of the sequence current and voltage, and outputs a protection action command when the judgment result indicates that a fault has occurred.

[0016] The present invention provides a computer device, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, it implements the steps of the power distribution line protection method for inverter-type distributed power source access.

[0017] The present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the power distribution line protection method for inverter-type distributed power source access.

[0018] The beneficial effects of this invention are as follows: By collecting changes in electrical quantities before and after a fault, a judgment criterion reflecting the controlled output characteristics of the inverter-type distributed power source is constructed, and a decision is made based on the corresponding criteria according to the fault type. Therefore, even if the fault current output by the inverter-type distributed power source is much smaller than the overcurrent protection setting value, the protection device can still identify the fault. This eliminates the persistence of faults caused by protection failure to operate, allowing the fault point to be extinguished in a timely manner. Simultaneously, by distinguishing between symmetrical and asymmetrical faults and employing different judgment logics, this invention prevents maloperation of the local protection when adjacent line faults occur, achieving fault section isolation and reducing the scope of unplanned power outages. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a general flowchart of a power distribution line protection method for inverter-type distributed power source access provided in one embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of an inverter-type distributed power source access method for power distribution line protection provided in an embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram of the steady-state values ​​of the q-axis currents in a power distribution line protection method for inverter-type distributed power source access, provided as an embodiment of the present invention.

[0023] Figure 4 This is a schematic diagram of the sequence voltage amplitudes of a power distribution line protection method for inverter-type distributed power source access provided in an embodiment of the present invention. Detailed Implementation

[0024] To make the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0025] Example 1, referring to Figure 1 This is one embodiment of the present invention, which provides a method for protecting distribution lines with inverter-type distributed power source access, including the following steps: S1. When the original signal of the power distribution line exceeds the preset start threshold, the original signal is extracted to obtain the relative characteristic quantity.

[0026] S2. Based on the normalized correlation of each of the relative characteristic quantities, construct the normalized ratio of sequence current and voltage.

[0027] S3. Perform a first-level condition judgment on the normalized ratio of the sequence current and voltage, and output a protection action command when the judgment result indicates that a fault has occurred.

[0028] On a 10kV distribution line with a 0.5MW photovoltaic power station at the end, a two-phase short-circuit fault occurred 3km away from the protection installation point. Because the short-circuit current output by the photovoltaic power station is limited to 1.2 times the rated current, and the short-circuit current provided is also reduced due to the weak feedback characteristics of the inverter, the fault current at the protection installation point did not reach the overcurrent protection setting value, and the protection failed to operate.

[0029] At this time, the photovoltaic system continues to feed current into the fault point, and the fault arc cannot be extinguished on its own. This not only aggravates the damage to the line insulation, but may also cause subsequent reclosing to fail because the fault point is still energized, ultimately resulting in a large-scale unplanned power outage.

[0030] According to steps S1-S3, by collecting changes in electrical quantities before and after the fault, a judgment criterion reflecting the controlled output characteristics of the inverter-type distributed power source is constructed, and a decision is made based on the corresponding criteria according to the fault type. Therefore, even if the fault current output by the inverter-type distributed power source is much smaller than the overcurrent protection setting value, the protection device can still identify the fault. This eliminates the persistence of faults caused by protection failure to operate, allowing the fault point to extinguish the arc in a timely manner. Simultaneously, by distinguishing between symmetrical and asymmetrical faults and employing different judgment logics, this invention prevents maloperation of the local protection when adjacent line faults occur, achieving fault section isolation and reducing the scope of unplanned power outages.

[0031] Example 2, refer to Figures 1-4 As an embodiment of the present invention, a method for protecting distribution lines with inverter-type distributed power source access is provided based on the previous embodiment, including the following steps: S1. When the original signal of the power distribution line exceeds the preset start threshold, the original signal is extracted to obtain the relative characteristic quantity.

[0032] The protection device is installed at the protection installation point, continuously collecting the instantaneous values ​​of the three-phase voltage and the three-phase current at the protection installation point, and calculating the amplitude of the three-phase line voltage and the amplitude of the negative sequence voltage in real time.

[0033] The protection algorithm is activated when the amplitude of the three-phase line voltage is less than the preset activation threshold. After the protection algorithm is activated, the time-domain data of the three-phase voltage and three-phase current are extracted from the 20ms before the activation time to the steady-state control period after the activation time, using the activation time as a reference.

[0034] The time-domain data of three-phase voltage and three-phase current are used as the raw signals.

[0035] Reference Figure 2 As shown, Figure 2This is a topology diagram of a 10kV distribution system connected to an inverter-type distributed power source (represented by photovoltaic). Point R is the protection installation point. Under normal operation, the three-phase line voltage amplitude at the protection installation point is 9.98kV, and the preset start-up threshold is 0.85. When a metallic two-phase AB short-circuit fault occurs at point F, 3km downstream of the protection installation point, the three-phase line voltage amplitude of phases AB drops to approximately 0, satisfying the start-up condition of 0 < 0.85. The protection algorithm runs at the start-up moment and extracts the three-phase voltage and three-phase current time-domain data from 20ms before the start-up moment to the steady state after the fault as the raw input signal.

[0036] The steps for obtaining the relative characteristic quantity include S1.1 to S1.4: S1.1 Perform sequence component separation on the original signal to obtain each sequence voltage component and each sequence current component.

[0037] The three-phase voltage and three-phase current in the original signal are separated into positive and negative sequences using a phase-locked loop based on a dual second-order generalized integrator. This yields the three-phase positive-sequence voltage time-domain signal, the three-phase negative-sequence voltage time-domain signal, the three-phase positive-sequence current time-domain signal, and the three-phase negative-sequence current time-domain signal, which are collectively referred to as the sequence voltage component and the sequence current component.

[0038] Based on the separated sequence voltage components, the negative sequence voltage amplitude is calculated, and the negative sequence voltage amplitude is compared with the preset negative sequence voltage threshold to determine the fault type: if the negative sequence voltage amplitude is less than or equal to the negative sequence voltage threshold, it is determined to be a symmetrical fault; otherwise, it is determined to be an asymmetrical fault.

[0039] Specifically, the phase-locked loop processes the three-phase voltage and current signals collected at the protection installation point. The amplitudes of each sequence component are expressed as follows: positive sequence voltage amplitude is 2.9029kV, per-unit value is 0.5031; negative sequence voltage amplitude is 2.8364kV, per-unit value is 0.4915; the time-domain signals of positive and negative sequence currents are extracted synchronously. Since 0.4915 > the negative sequence voltage threshold, this fault is determined to be an asymmetrical fault. (Refer to...) Figure 4 As shown, the variation process of the positive sequence voltage amplitude of 2.9029kV and the negative sequence voltage amplitude of 2.8364kV is presented.

[0040] S1.2. Based on the sequence voltage components, perform a first-level calculation on the sequence current components to obtain the q-axis current of each sequence.

[0041] The steps for performing the first-level calculation include A1 to A2: A1. Phase-locked loops are applied to each sequence voltage component to obtain the positive sequence reference phase and the negative sequence reference phase.

[0042] Phase-locked loop (PLL) processing was performed independently on the three-phase positive-sequence voltage and the three-phase negative-sequence voltage to obtain the phase angles of the fundamental components of the positive-sequence voltage and the negative-sequence voltage, respectively. These phase angles will be used as the references for the positive-sequence current coordinate transformation and the negative-sequence current coordinate transformation, respectively.

[0043] After a two-phase short-circuit fault in phases A and B, phase-locked loop (PLL) is performed on the positive-sequence voltage to obtain the positive-sequence reference phase; and phase-locked loop (PLL) is performed on the negative-sequence voltage to obtain the negative-sequence reference phase.

[0044] Before the fault occurred, the three-phase voltages at the protection installation point were basically symmetrical, the negative sequence component was small, and the phase-locked loop result existed, but the signal corresponding to the amplitude was extremely weak.

[0045] After the fault occurred, the negative sequence voltage amplitude was established to 2.8364kV, and the negative sequence reference phase was able to track stably.

[0046] A2. Using the positive-sequence reference phase and the negative-sequence reference phase as a reference, perform coordinate transformation on each sequence current component to obtain the q-axis current of each sequence.

[0047] Using the positive-sequence reference phase from step A1 as a reference, perform a dq0 transformation on the three-phase positive-sequence current to obtain the components of the positive-sequence current in the dq0 coordinate system. , , Using the negative-sequence reference phase as a reference, a dq0 transformation is performed on the three-phase negative-sequence current to obtain the components of the negative-sequence current in the dq0 coordinate system. , , . and This refers to the q-axis current of each sequence, where the q-axis direction is orthogonal to the phase of the corresponding sequence voltage and corresponds to the reactive current component.

[0048] The three-phase positive-sequence current is subjected to dq0 transformation with the positive-sequence reference phase as a reference, and the three-phase negative-sequence current is subjected to dq0 transformation with the negative-sequence reference phase as a reference.

[0049] Before the A and B phase short circuit fault occurred, the inverter at the protection installation point was operating under rated conditions, and both the positive sequence q-axis current and the negative sequence q-axis current were approximately zero. That is, before the fault, the steady-state value of the positive sequence q-axis current (start-up time - 20ms) ≈ 0kA and the steady-state value of the negative sequence q-axis current (start-up time - 20ms) ≈ 0kA.

[0050] Reference Figure 3 As shown, after the fault occurs and the inverter enters steady state through low voltage ride-through control, the steady-state value of the positive sequence q-axis current is -0.015kA (the negative sign indicates that the inverter injects inductive reactive power into the grid side, and the direction is the opposite of the reference direction), and the steady-state value of the negative sequence q-axis current is +0.02725kA (the positive sign indicates that the inverter absorbs negative sequence reactive power).

[0051] S1.3. Taking the fault start time as the boundary, perform secondary calculations on the q-axis current of each sequence to obtain the q-axis mutation amount of each sequence, and then filter the q-axis mutation amounts of each sequence.

[0052] The steps for performing the second-level calculation include B1 to B2: B1. Taking the fault start time as the boundary, calculate the difference between the current of each sequence q-axis before and after the fault start time to obtain the sudden change of each sequence q-axis.

[0053] Taking the protection start-up time t0 as a reference, the difference between the real-time value of each sequence q-axis current and the steady-state value before the fault is calculated at each calculation time N, thus obtaining the positive sequence q-axis sudden change at time N. Negative q-axis mutation at time N The calculation formula is expressed as: ; ; in, and The q-axis current values ​​of each sequence are collected and saved 20ms before the fault starts, representing the steady-state reference during normal operation before the fault.

[0054] In this embodiment, during a two-phase A / B short-circuit fault, the positive-sequence q-axis current is 0 kA and the negative-sequence q-axis current is 0 kA before the fault. After the fault, the inverter's low-voltage ride-through control kicks in, and the q-axis currents of each sequence gradually build up during the control adjustment process. The sudden change is calculated in real time at each calculation moment N. For example, when the control enters a steady state, the parameters are substituted into the formula to obtain the positive-sequence q-axis sudden change as -0.015 - 0 = -0.015 kA and the negative-sequence q-axis sudden change as 0.02725 - 0 = +0.02725 kA.

[0055] B2. When the fluctuation of the q-axis mutation amount of each sequence is less than a preset range, record the steady-state value of the q-axis mutation amount of each sequence and use the steady-state value as a relative characteristic quantity.

[0056] For each calculation time N, the positive and negative q-axis abrupt changes are continuously detected. When the difference between two adjacent calculation times satisfies: ; ; Where ε is a preset steady-state determination threshold, at which point the positive-order q-axis abrupt change occurs. With negative q-axis mutation amount The steady-state values ​​of the positive-order q-axis mutation and the negative-order q-axis mutation are recorded as the final relative feature quantities. In this embodiment, the preset steady-state determination threshold is set empirically.

[0057] Following a two-phase short-circuit fault (A and B), the inverter's low-voltage ride-through control completes adjustment and enters steady state within tens of milliseconds. At a certain calculated time N, a fault is detected. and Both values ​​are less than the preset steady-state threshold, indicating that steady-state has been reached. The final steady-state values ​​are recorded as -0.015kA and +0.02725kA.

[0058] S1.4. Use the screening results as the relative feature quantity.

[0059] In the AB two-phase short-circuit fault, after steady-state screening, the finally confirmed relative characteristic quantities are: positive sequence q-axis mutation amount is -0.015kA, and negative sequence q-axis mutation amount is +0.02725kA.

[0060] S2. Based on the normalized correlation of each of the relative characteristic quantities, construct the normalized ratio of sequence current and voltage.

[0061] The steps for constructing the normalized ratio of the sequence current to voltage include S2.1 to S2.3: S2.1. Normalize and correlate the positive q-axis mutation of each sequence q-axis mutation with the drop depth of the positive sequence voltage component in each sequence voltage component to obtain the positive sequence normalization ratio.

[0062] According to GB / T 29319—2024, which specifies the dynamic reactive current output law during low-voltage ride-through of inverter-type distributed power sources, when the per-unit value of the positive-sequence voltage at the grid connection point satisfies 0 ≤ positive-sequence voltage per-unit value ≤ 0.85, the inverter should inject a dynamic positive-sequence reactive current increment into the grid that is proportional to the positive-sequence voltage drop depth. Normalizing this to the rated current yields the normalized positive-sequence ratio. The calculation formula is expressed as: ; In the formula, This represents the steady-state value of the positive-sequence q-axis abrupt change. This represents the per-unit value of the positive-sequence voltage component amplitude; The rated current of the inverter-type distributed power source is used as a known parameter; The theoretical driving force of the positive-sequence dynamic reactive current increment as specified in the characterization standard.

[0063] The positive-sequence normalization ratio reflects the degree of agreement between the measured positive-sequence q-axis current response and the theoretical expectation of the inverter's standard control law. Under normal operation or external fault conditions, the inverter's positive-sequence q-axis current does not undergo controlled abrupt changes, and the positive-sequence normalization ratio approaches zero. When a fault occurs in the downstream line of the protection installation point and the inverter enters the low voltage ride-through state, the controlled injected positive sequence reactive current causes the positive sequence normalized ratio to deviate from zero and fall into a specific interval corresponding to the range of control law parameters, thereby achieving fault identification.

[0064] According to step S1.1, the per-unit value of the positive sequence voltage at the protection installation point after the fault is 0.5031; according to step S1.3, the steady-state value of the positive sequence q-axis mutation is -0.015kA; the photovoltaic rated current IN = 0.0289kA. Substituting these values ​​into the formula for calculating the positive sequence normalized ratio, we can obtain: ; The positive sequence normalization ratio is -1.4962, which is negative and conforms to the direction convention for the inverter's injection of inductive reactive current.

[0065] S2.2. Normalize and correlate the negative q-axis mutation of each sequence q-axis mutation with the amplitude of the negative sequence voltage component in each sequence voltage component to obtain the negative sequence normalization ratio.

[0066] According to GB / T 29319—2024, which specifies the negative-sequence dynamic reactive current output law for inverter-type distributed power sources during asymmetrical faults, when a negative-sequence voltage component appears at the grid connection point, the inverter should absorb a dynamic negative-sequence reactive current increment from the grid that is proportional to the per-unit value U- of the negative-sequence voltage amplitude. Normalization with the rated current yields the negative-sequence normalized ratio. The calculation formula is expressed as: ; In the formula, This represents the steady-state value of the negative q-axis mutation rate; IN is the per-unit value of the negative sequence voltage component amplitude; IN is the rated current of the inverter-type distributed power source. The theoretical driving force of the negative sequence dynamic reactive current increment as specified in the characterization standard.

[0067] The negative-sequence normalized ratio reflects the degree of agreement between the measured negative-sequence q-axis current response and the inverter's standard control law on the negative-sequence path. Under normal operation or symmetrical fault conditions, the negative-sequence voltage component of the system is extremely small, and the negative-sequence q-axis current does not undergo controlled abrupt changes, with the negative-sequence normalized ratio approaching zero. When an asymmetrical fault occurs and the inverter enters a low-voltage ride-through state, the controlled absorption of negative-sequence reactive current causes the negative-sequence normalized ratio to deviate from zero and fall into a specific interval corresponding to the range of control law parameters.

[0068] From S1.1, we know that the per-unit value of the negative sequence voltage at the protection installation point after the fault is 0.4915; the steady-state value of the negative sequence q-axis mutation is +0.02725kA; and the rated photovoltaic current I of the system is... N=0.0289kA. Substituting this into the formula for calculating the negative order normalized ratio, we get: ; The negative sequence normalization ratio is +1.9184, which is a positive value and conforms to the direction convention for inverters to absorb negative sequence reactive current.

[0069] S2.3 The positive sequence normalization ratio and the negative sequence normalization ratio together constitute the sequence current-voltage normalization ratio.

[0070] Orthogonal normalized ratio k + The ratio of negative order normalization k - Each is calculated independently, and together they form an ordered pair (k) + k - This ordered pair serves as the normalized ratio of the sequence current and voltage.

[0071] S3. Perform a first-level condition judgment on the normalized ratio of the sequence current and voltage, and output a protection action command when the judgment result indicates that a fault has occurred.

[0072] The normalized ratio of sequence current to voltage (k) constructed in step S2 + k - Taking the input as the fault type determined in step S1.1, the positive sequence normalized ratio and the negative sequence normalized ratio are judged according to the symmetrical fault criterion and the asymmetrical fault criterion, respectively. It is verified whether they fall into the characteristic range that matches the controlled output characteristics of the inverter-type distributed power source, so as to confirm whether a fault has occurred in the zone. When the judgment result is that a fault has occurred, a protection action command is output.

[0073] The steps for performing the first-level condition judgment include S3.1 to S3.4: S3.1 Based on the amplitude of the negative sequence voltage component in each sequence voltage component, the fault is classified into symmetrical faults and asymmetrical faults.

[0074] Based on the per-unit value of the negative sequence voltage amplitude output in step S1.1, and compared with the preset negative sequence voltage threshold, the fault types corresponding to this protection activation event are classified as follows: When the per-unit value of the negative sequence voltage amplitude is less than or equal to the preset negative sequence voltage threshold, the negative sequence voltage component can be ignored, the three phases of the system are basically symmetrical, the fault is determined to be a symmetrical fault, and then enters S3.2, where only the positive sequence normalization ratio is used for single-channel determination. When the per-unit value of the negative sequence voltage amplitude is greater than the preset negative sequence voltage threshold, the system has a significant negative sequence voltage component and three-phase asymmetry. The fault is determined to be an asymmetrical fault, and then proceeds to S3.3, where the positive sequence normalization ratio and the negative sequence normalization ratio are used together for dual-channel determination.

[0075] S3.2 Under symmetrical faults, the determination is made based on the positive order normalization ratio.

[0076] Under symmetrical fault conditions, if the positive sequence normalized ratio falls within the positive sequence characteristic range, it is determined that a fault has occurred; otherwise, it is determined that no fault has occurred.

[0077] Under symmetrical fault conditions, the system is three-phase symmetrical, with only a positive-sequence component. According to GB / T 29319—2024, the proportionality coefficient between the positive-sequence dynamic reactive current increment injected by the inverter-type distributed power source during the low-voltage ride-through of a symmetrical fault and the positive-sequence voltage drop depth ranges from [1.5, 3], and the theoretical range of the corresponding positive-sequence normalized ratio is [-4.0, -1.0].

[0078] When the positive sequence normalization ratio falls within the above positive sequence characteristic range, it is determined that the positive sequence q-axis current response of the inverter is consistent with the low voltage ride-through control law, confirming a symmetrical fault in the occurrence zone, and entering S3.4 to output protection action command; If the normalized ratio does not fall within the above range, it is determined that the protection activation event is not a symmetrical fault within the zone (it may be a fault outside the zone or a transient disturbance), the protection resets, and no action command is output.

[0079] During normal operation, the positive sequence normalization ratio is 0, which does not meet the operating conditions. When there is an external fault, the inverter does not meet the low voltage ride-through triggering conditions or the drop depth is limited because the voltage drop at the grid connection point does not meet the low voltage ride-through triggering conditions. Therefore, the positive sequence normalization ratio does not fall into this range, thus ensuring the selectivity of the protection.

[0080] Suppose that a three-phase metallic short circuit occurs in the system. The positive sequence normalization ratio is calculated to be -2.1 in step S2.1 (assumed value, satisfying the control coefficient scenario of K1=2.1 under three-phase short circuit). Determine whether the positive sequence normalization ratio falls within the positive sequence characteristic range [-4.0, -1.0].

[0081] Since -4.0≤-2.1≤-1.0 is true, the conditions for symmetrical fault operation are met, the symmetrical fault in the occurrence zone is confirmed, and the protection operation command is output in S3.4.

[0082] When an external fault causes the positive sequence voltage per unit value at the grid connection point to drop only from 0.998 to 0.90, the drop depth is insufficient, the inverter's dynamic reactive power response is minimal, the positive sequence normalization ratio approaches zero, and it does not fall within [-4.0, -1.0], ensuring correct protection reset and preventing false tripping.

[0083] S3.3 Under asymmetric faults, the determination is made by combining the positive-order normalization ratio and the negative-order normalization ratio.

[0084] Under asymmetrical fault conditions, the inverter, according to GB / T 29319—2024, injects inductive reactive current in the positive-sequence channel and absorbs capacitive reactive current in the negative-sequence channel. According to the standard, the values ​​of both the positive-sequence dynamic reactive current proportionality coefficient K2+ and the negative-sequence dynamic reactive current proportionality coefficient K2- are not less than 1.0, corresponding to a theoretical value of less than -1 for the positive-sequence normalized ratio and a theoretical value of greater than +1 for the negative-sequence normalized ratio. In this example, the joint action criterion under asymmetrical fault conditions is set as follows: ; If only the positive-sequence normalized ratio meets the condition but the negative-sequence normalized ratio does not, or if only the negative-sequence normalized ratio meets the condition but the positive-sequence normalized ratio does not, the protection action will not be triggered, and the protection will reset.

[0085] The significance of employing dual-channel joint judgment lies in the fact that, compared to single-channel judgment, the joint criterion significantly improves the reliability of asymmetric fault identification. During normal system operation or external asymmetric disturbances, the inverter response is limited, k + and k - Both values ​​approach zero, making it impossible to simultaneously satisfy both threshold values; during asymmetrical faults within the zone, the inverter's low-voltage ride-through control produces significant controlled responses in both the positive and negative sequence channels, k + and k - At the same time, it deviates from zero and falls into the corresponding range, thereby triggering the protection action.

[0086] S3.4 When the judgment result satisfies the controlled output characteristics of the inverter-type distributed power source, the fault is confirmed and a protection action command is output.

[0087] When k + or (k) + k - If the current falls within the corresponding characteristic range, it is confirmed that the fault is within the corresponding range of this protection activation event. The measured positive and negative sequence q-axis current response of the inverter during the fault period is consistent with its theoretical expectation of performing low voltage ride-through control according to GB / T 29319—2024. The protection device outputs a protection action command to drive the circuit breaker on the inverter-type distributed power supply side to trip, reliably isolate the inverter-type distributed power supply from the faulty line, and terminate the continuous current feed from the inverter to the fault point.

[0088] Example 3 is an embodiment of the present invention, which provides a power line protection system for inverter-type distributed power source access, including: The feature extraction module is used to extract the raw signals of the power distribution line and obtain relative feature quantities; The calculation module constructs the normalized ratio of sequence current to voltage by normalizing and correlating the various relative characteristic quantities. The execution module performs a first-level condition judgment on the normalized ratio of the sequence current and voltage, and outputs a protection action command when the judgment result indicates that a fault has occurred.

[0089] This embodiment also provides an electronic device applicable to a power distribution line protection method with inverter-type distributed power source access, comprising: a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions to implement the power distribution line protection method with inverter-type distributed power source access as proposed in the above embodiment.

[0090] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements a power distribution line protection method for inverter-type distributed power source access as proposed in the above embodiments.

[0091] The storage medium proposed in this embodiment belongs to the same inventive concept as the distribution line protection method for implementing inverter-type distributed power supply access proposed in the above embodiments. Technical details not described in detail in this embodiment can be found in the above embodiments, and this embodiment has the same beneficial effects as the above embodiments.

[0092] Based on the above description of the implementation methods, those skilled in the art can clearly understand that the present invention can be implemented using software and necessary general-purpose hardware, and of course, it can also be implemented using hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0093] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for protecting distribution lines with inverter-type distributed power source access, characterized in that, Includes the following steps: When the original signal of the power distribution line exceeds the preset start threshold, the original signal is extracted to obtain the relative characteristic quantity; Based on the normalized correlation of each of the relative characteristic quantities, the normalized ratio of sequence current to voltage is constructed. The normalized ratio of the sequence current and voltage is used for a first-level condition judgment. When the judgment result indicates that a fault has occurred, a protection action command is output.

2. The method for protecting distribution lines with inverter-type distributed power source access as described in claim 1, characterized in that, The steps for obtaining the relative characteristic quantity include: The original signal is subjected to sequence component separation to obtain each sequence voltage component and each sequence current component; Based on the voltage components of each sequence, a first-level calculation is performed on the current components of each sequence to obtain the q-axis current of each sequence. Using the fault initiation time as the boundary, a two-stage calculation is performed on the q-axis current of each sequence to obtain the q-axis mutation amount of each sequence, and the q-axis mutation amount of each sequence is then filtered. The screening results are used as the relative feature values.

3. The method for protecting distribution lines with inverter-type distributed power source access as described in claim 2, characterized in that, The steps for performing the first-level calculation include: Phase-locked loops are performed on each sequence voltage component to obtain the positive sequence reference phase and the negative sequence reference phase; Using the positive-sequence reference phase and the negative-sequence reference phase as a reference, coordinate transformation is performed on each sequence current component to obtain the q-axis current of each sequence.

4. The method for protecting distribution lines with inverter-type distributed power source access as described in claim 3, characterized in that, The steps for performing the second-level calculation include: Taking the fault start time as the boundary, calculate the difference between the current of each sequence q-axis before and after the fault start time to obtain the sudden change of each sequence q-axis. When the fluctuation of the q-axis mutation amount of each sequence is less than a preset range, the steady-state value of the q-axis mutation amount of each sequence is recorded, and the steady-state value is used as a relative characteristic quantity.

5. The method for protecting distribution lines with inverter-type distributed power source access as described in claim 4, characterized in that, The steps for constructing the normalized ratio of the sequence current to voltage include: The positive q-axis mutation of each sequence q-axis mutation is normalized and correlated with the drop depth of the positive sequence voltage component in each sequence voltage component to obtain the positive sequence normalization ratio. The negative q-axis mutation of each sequence q-axis mutation is normalized and correlated with the amplitude of the negative sequence voltage component in each sequence voltage component to obtain the negative sequence normalization ratio. The positive-sequence normalization ratio and the negative-sequence normalization ratio together constitute the sequence current-voltage normalization ratio.

6. The method for protecting distribution lines with inverter-type distributed power source access as described in claim 5, characterized in that, The steps for performing the first-level condition judgment include: Based on the amplitude of the negative sequence voltage component in each sequence voltage component, the faults are classified into symmetrical faults and asymmetrical faults. Under symmetrical faults, the determination is made based on the positive order normalization ratio; Under asymmetric faults, the determination is made by combining the positive-order normalization ratio and the negative-order normalization ratio; When the judgment result meets the controlled output characteristics of the inverter-type distributed power source, a fault is confirmed and a protection action command is output.

7. The method for protecting distribution lines with inverter-type distributed power source access as described in claim 6, characterized in that, The step of determining based on the positive order normalization ratio includes: Under symmetrical fault conditions, if the positive sequence normalized ratio falls within the positive sequence characteristic range, it is determined that a fault has occurred; otherwise, it is determined that no fault has occurred. Under asymmetric fault conditions, if the positive-order normalized ratio and the negative-order normalized ratio simultaneously satisfy the joint characteristic interval, then the fault is judged to have occurred; otherwise, the fault is judged not to have occurred.

8. A power distribution line protection system with inverter-type distributed power source access, employing the power distribution line protection method with inverter-type distributed power source access as described in any one of claims 1 to 7, characterized in that, include: The feature extraction module is used to extract the raw signals of the power distribution line and obtain relative feature quantities; The calculation module constructs the normalized ratio of sequence current to voltage by normalizing and correlating the various relative characteristic quantities. The execution module performs a first-level condition judgment on the normalized ratio of the sequence current and voltage, and outputs a protection action command when the judgment result indicates that a fault has occurred.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the power distribution line protection method for inverter-type distributed power source access as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the power distribution line protection method for inverter-type distributed power source access as described in any one of claims 1 to 7.

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