New energy transmission line current impedance differential coordinated protection method and system

Abstract

The application provides a new energy sending line current impedance differential coordination protection method and system, relates to the field of power system relay protection, and the method comprises the following steps: obtaining two-side current phasor information, performing current differential first-stage discrimination on the two-side current phasor information in a preset first time period after a fault; if the current differential first-stage discrimination result is not determined as an internal fault, the protection is not locked out, and the new energy converter current inner loop reference value is actively adjusted in a preset second time period; sampling is performed in a preset third time period, the average value of the positive sequence impedance sum of all sampling points is calculated through a sliding window, the absolute value of the difference between the average value and a preset line positive sequence impedance is calculated, the absolute value is compared with a preset setting value, and impedance differential second-stage discrimination is performed; if the absolute value is greater than the preset setting value, the internal fault is determined, and protection action is performed; otherwise, the external fault is determined, and no protection action is performed.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, specifically to a method and system for differential coordinated protection of current impedance of new energy transmission lines. Background Technology

[0002] With the large-scale integration of new energy sources, such as wind power and photovoltaics, into the power grid via power electronic converters, the fault characteristics of the power system have undergone fundamental changes. As a controlled current source, the fault output current of new energy converters has the characteristics of limited amplitude, controlled phase, and fast response. This poses a severe challenge to traditional line protection schemes based on the assumption of symmetrical short-circuit faults of synchronous generators.

[0003] First, current differential protection, as the main protection, may suffer from insufficient sensitivity or even failure to operate on renewable energy transmission lines. Because the amplitude and phase of the fault current on the renewable energy side are controlled, the amplitude ratio and phase difference of the fault currents on both sides of the line may deviate significantly from traditional setting principles. Especially in the event of high-resistance grounding or asymmetrical faults, the sum of the current phasors on both sides may not reliably exceed the operating threshold, posing a serious risk of failure to operate during faults within the designated zone and severely threatening system safety.

[0004] To address the adaptability issue of current differential protection, researchers have proposed a novel differential protection scheme based on impedance principles. This scheme calculates the equivalent impedance on both sides of the line and constructs a criterion using the difference in impedance sums during faults inside and outside the protection zone, theoretically offering better robustness against new energy fault characteristics. However, traditional impedance differential protection methods suffer from two prominent problems in practice:

[0005] The problem of failure to operate under special operating conditions within the zone: Under the influence of the control strategy on the new energy side, when certain special types or locations of faults occur within the zone, there may be an extreme situation where the sum of the equivalent impedances on both sides of the line is exactly equal to or close to the positive sequence impedance of the line. At this time, the impedance differential protection will misjudge it as a fault outside the zone and fail to operate, forming a new protection dead zone.

[0006] Transient process calculation error problem: In the initial stage of a fault, electrical quantities are in a transient process of drastic changes. Directly using the FFT (Fast Fourier Transform) algorithm to extract power frequency quantities during this stage will result in significant spectral leakage and calculation errors, potentially leading to misjudgments by protection systems. Existing methods often ignore this error or merely mitigate it by extending the waiting time, failing to fundamentally solve the problem.

[0007] Traditional current differential protection, while fast-acting, suffers from insufficient reliability. Improved impedance differential protection, though theoretically more reliable, is limited by the risk of failure to operate under special conditions and the constraints of transient calculation errors on its speed, making it difficult to achieve rapid, accurate, and reliable fault identification in complex new energy fault scenarios. Therefore, a new line protection method that can fundamentally balance speed, selectivity, and calculation accuracy is urgently needed. Summary of the Invention

[0008] This invention addresses the problems existing in the prior art by providing a method and system for coordinated protection of current and impedance differential in new energy transmission lines. It achieves coordinated operation of current differential and impedance differential in new energy transmission lines, solving the problems of potential failure of traditional current differential protection to operate and the problems of action delay and transient calculation error in traditional impedance differential protection.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: Acquire current phasor information from both sides and perform first-level differential current discrimination on the current phasor information from both sides within a preset first time period after the fault. If the first-stage current differential judgment result is an in-zone fault, the protection action will be performed directly; if the first-stage current differential judgment result is not an in-zone fault, the protection will not be blocked, and the reference value of the inner loop current of the new energy converter will be actively adjusted within the preset second time period. Sampling is performed in a preset third time period. The average value of the positive sequence impedance of all sampling points is calculated through a sliding window. The absolute value of the difference between the average value and the preset positive sequence impedance of the line is calculated. The absolute value of the difference is compared with the preset setting value to perform the second level of impedance differential discrimination. If the absolute value of the difference is greater than the preset setting value, it is determined to be an intra-zone fault and protection action is performed; otherwise, it is determined to be an extra-zone fault and protection action is not performed.

[0010] In some embodiments, the step of acquiring the current phasor information on both sides and performing a first-level differential current discrimination on the current phasor information on both sides within a preset first time period after the fault includes: Obtain current phasor information from the new energy side and the system side, and define the positive direction of the current as the flow from the bus to the line; Based on the new energy side current phasor information and the system side current phasor information, the differential current and braking current are calculated. The braking current, the preset minimum operating current, and the preset ratio braking coefficient are used as the criteria. The differential current is compared with the criterion to perform the first stage of current differential discrimination. If the criterion is met, it is determined to be an intra-zone fault; if the criterion is not met, it proceeds to the second stage of active control and impedance differential discrimination.

[0011] In some embodiments, the process of actively adjusting the inner loop reference value of the new energy converter current within a preset second time period includes: Obtain the current d-axis reference value and q-axis reference value of the inner current loop of the new energy converter; The d-axis reference value and the q-axis reference value are adjusted according to the preset amplitude adjustment amount and / or preset phase adjustment amount to obtain the active control reference value; During the preset second time period, the inner loop reference value of the new energy converter current is switched to the active control reference value to change the amplitude and / or phase of the fault current on the new energy side. At the end of the preset second time period, the inner loop reference value of the new energy converter current is restored to the d-axis reference value and the q-axis reference value before the active control is activated.

[0012] In some embodiments, the process of sampling during a preset third time period and calculating the average value of the positive sequence impedance of all sampling points using a sliding window includes: Set the sliding window length to the fourth time period; Sampling is performed in the preset third time period. The time corresponding to each sampling point is the end time of the sliding window. The fourth time period is moved forward as the start time of the sliding window. The sum of the positive sequence impedance measurement value of the new energy side and the positive sequence impedance measurement value of the system side of the sampling point is calculated from the start time to the end time as the positive sequence impedance sum. Collect the positive sequence impedance sum of all sampling points and calculate the average value of the positive sequence impedance sum.

[0013] In some embodiments, the time corresponding to each sampling point is the end time of the sliding window, and the fourth time period forward is taken as the start time of the sliding window. The process of calculating the positive sequence impedance of the sampling points from the start time to the end time includes: The time corresponding to each sampling point is the end time of the sliding window, and the fourth time period forward is the start time of the sliding window; The voltage and current phasors on the new energy side and the system side are continuously collected from the start time to the end time. The positive sequence voltage phasor and positive sequence current phasor of the new energy source side and the system side are calculated by the FFT algorithm, and the positive sequence impedance measurement values ​​of the new energy source side and the system side are obtained based on the positive sequence voltage phasor and the positive sequence current phasor. The positive sequence impedance measurement values ​​on the new energy side and the system side are added together to obtain the positive sequence impedance sum of the sampling points.

[0014] In some embodiments, the third time period covers the input transient phase after the new energy converter current inner loop reference value is switched to the active control reference value, and the exit transient phase after the new energy converter current inner loop reference value is restored to the d-axis reference value and q-axis reference value before active control input; The input transient phase and the exit transient phase are time-symmetric, and the calculation errors of the input transient phase and the exit transient phase alternate between positive and negative on the time axis, which are used to cancel each other out when calculating the average value of the positive sequence impedance.

[0015] In some embodiments, the first time period is preset to be the time window from the occurrence of the fault to the completion of the first stage of current differential judgment; The second time period is preset to be the time window during which the inner loop reference value of the new energy converter current is maintained at the active control reference value. The preset third time period is a sampling time window used to calculate the average value of the positive sequence impedance. That is, the third time period includes the preset second time period and the transient recovery time period that follows the preset second time period.

[0016] This invention proposes a current impedance differential coordinated protection system for new energy transmission lines, comprising: The acquisition unit is configured to acquire current phasor information from both sides and perform differential current discrimination on the current phasor information from both sides within a preset first time period after the fault. The first-stage current differential judgment unit is configured to directly perform protection action if the first-stage current differential judgment result is an in-zone fault; if the first-stage current differential judgment result is not an in-zone fault, the protection is not blocked, and the reference value of the inner loop current of the new energy converter is actively adjusted within a preset second time period. The calculation unit is configured to perform sampling in a preset third time period, calculate the average value of the positive sequence impedance of all sampling points through a sliding window, calculate the absolute value of the difference between the average value and the preset positive sequence impedance of the line, compare the absolute value of the difference with a preset setting value, and perform impedance differential second-level discrimination. The impedance differential second-stage discrimination unit is configured to determine that if the absolute value of the difference is greater than the preset setting value, it is a fault within the zone and protection action is performed; otherwise, it is a fault outside the zone and protection action is not performed.

[0017] This invention proposes a computer device, comprising: At least one processor; and a memory storing a computer program executable on the processor, wherein the processor, when executing the program, performs the steps of the method for differential coordinated protection of current impedance of new energy transmission lines.

[0018] The present invention proposes a computer-readable storage medium storing a computer program, which, when executed by a processor, performs the steps of the method for differential coordinated protection of current impedance of new energy transmission lines.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention proposes a method and system for differential coordinated protection of current impedance in new energy transmission lines. The method includes: Acquire current phasor information from both sides and perform first-level differential current discrimination on the current phasor information from both sides within a preset first time period after the fault. If the first-stage current differential judgment result is an in-zone fault, the protection action will be performed directly; if the first-stage current differential judgment result is not an in-zone fault, the protection will not be blocked, and the reference value of the inner loop current of the new energy converter will be actively adjusted within the preset second time period. Sampling is performed in a preset third time period. The average value of the positive sequence impedance of all sampling points is calculated through a sliding window. The absolute value of the difference between the average value and the preset positive sequence impedance of the line is calculated. The absolute value of the difference is compared with the preset setting value to perform the second level of impedance differential discrimination. If the absolute value of the difference is greater than the preset setting value, it is determined to be an intra-zone fault and protection action is performed; otherwise, it is determined to be an extra-zone fault and protection action is not performed.

[0020] This invention rapidly identifies faults within the protection zone and directly activates the protection system within a very short time after a fault occurs through the first stage of current differential discrimination, ensuring the protection's speed requirement. For faults outside the protection zone, active control is introduced to adjust the inner loop reference value of the renewable energy converter current, effectively eliminating the adverse effects of renewable energy side fault current on the differential protection. The method of calculating the positive sequence impedance and average value using a sliding window and utilizing the time symmetry of the transient process to cancel out errors significantly improves the accuracy of the second stage of impedance differential discrimination.

[0021] This invention constructs a hierarchical protection system that balances speed and reliability. While retaining the rapidity of current differential protection, it addresses the adaptability issues of traditional protection systems in new energy scenarios by introducing actively controlled impedance differential protection. It innovatively employs a transient symmetric error cancellation mechanism, effectively eliminating calculation errors in the FFT algorithm during transient processes, significantly improving the accuracy of impedance measurement and protection accuracy. It fundamentally solves the problem of protection failure and maloperation under special operating conditions, ensuring reliable identification and correct operation under various complex faults by actively controlling and altering fault characteristics. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0023] Figure 1 The flowchart of the method for differential collaborative protection of current impedance of new energy transmission lines provided by the present invention is shown.

[0024] Figure 2 The system module diagram of the differential collaborative protection of current impedance for new energy transmission lines provided by the present invention is shown.

[0025] Figure 3 A schematic diagram of the structure of an embodiment of the computer device provided by the present invention.

[0026] Figure 4 This is a schematic diagram of an embodiment of the computer-readable storage medium provided by the present invention.

[0027] Figure 5 This is a topology diagram of a new energy grid-connected system.

[0028] Figure 6(a) is a positive sequence fault component network diagram when a short circuit fault occurs at point f1 outside the new energy side zone of the new energy transmission line.

[0029] Figure 6(b) is a positive sequence fault component network diagram when a short circuit fault occurs at point f2 in the area of ​​the new energy transmission line.

[0030] Figure 6(c) is a positive sequence fault component network diagram when a short circuit fault occurs at point f3 outside the system side zone of the new energy transmission line.

[0031] Figure 7 This is a graph showing the error analysis of FFT calculation based on active control.

[0032] Figure 8(a1) is a curve showing the amplitude change of the sum of the positive sequence impedance measurements on both sides when a two-phase phase-to-phase fault occurs at point f1 outside the new energy side zone of the new energy transmission line.

[0033] Figure 8(a2) is a curve showing the impedance angle change of the sum of the positive sequence impedance measurements on both sides of the new energy transmission line when a two-phase phase-to-phase fault occurs at point f1 outside the new energy side zone.

[0034] Figure 8(b1) is a curve showing the amplitude change of the sum of the positive sequence impedance measurements on both sides when a two-phase phase-to-phase fault occurs at point f3 outside the system side zone of the new energy transmission line.

[0035] Figure 8(b2) is a curve showing the impedance angle change of the sum of the positive sequence impedance measurements on both sides when a two-phase phase-to-phase fault occurs at point f3 outside the system side zone of the new energy transmission line.

[0036] Figure 8(c1) is a curve showing the amplitude change of the sum of the positive sequence impedance measurements on both sides when a two-phase phase-to-phase fault occurs at point f2 in the area of ​​the new energy transmission line.

[0037] Figure 8(c2) is a curve showing the change in impedance angle of the sum of the positive sequence impedance measurements on both sides when a two-phase fault occurs at point f2 in the area of ​​the new energy transmission line.

[0038] Figure 9 This is a flowchart of the new energy transmission line current impedance differential collaborative protection scheme based on the control transient response symmetry of the present invention. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application.

[0040] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0041] This invention proposes a method for differential coordinated protection of current impedance in new energy transmission lines. Please refer to [link / reference]. Figure 1 , Figure 5 and Figure 9 ,include: Acquire current phasor information from both sides and perform first-level differential current discrimination on the current phasor information from both sides within a preset first time period after the fault. If the first-stage current differential judgment result is an in-zone fault, the protection action will be performed directly; if the first-stage current differential judgment result is not an in-zone fault, the protection will not be blocked, and the reference value of the inner loop current of the new energy converter will be actively adjusted within the preset second time period. Sampling is performed in a preset third time period. The average value of the positive sequence impedance of all sampling points is calculated through a sliding window. The absolute value of the difference between the average value and the preset positive sequence impedance of the line is calculated. The absolute value of the difference is compared with the preset setting value to perform the second level of impedance differential discrimination. If the absolute value of the difference is greater than the preset setting value, it is determined to be an intra-zone fault and protection action is performed; otherwise, it is determined to be an extra-zone fault and protection action is not performed.

[0042] This invention provides a current-impedance differential coordinated protection scheme for renewable energy transmission lines based on the symmetry of control transient response. The method first uses current differential protection for rapid identification. If the fault is identified as within the protection zone, the protection operates directly. If the first-stage current differential protection does not identify the fault as within the protection zone, it enters the second-stage active control and impedance differential protection stage, briefly adjusting the inner loop reference value of the renewable energy converter current. Utilizing the transient symmetry of the active control activation and deactivation process, FFT calculation errors are mutually canceled. By calculating the average of the sum of the positive sequence impedance measurements on both sides during this period and comparing it with the line impedance, an impedance differential criterion is formed, ultimately accurately distinguishing between faults within and outside the protection zone. While retaining rapid operation, this method solves the problems of insufficient sensitivity of traditional current differential protection, transient errors in impedance differential protection, and failure to operate within the protection zone, significantly improving the reliability and adaptability of the protection.

[0043] The present invention first utilizes the fault after 20 Within 5ms, the current phasor information on both sides of the line is used for differential current discrimination. If the fault is determined to be within the zone, the protection operates directly; if the fault is determined to be outside the zone, the active control loop is activated. If the first-stage current differential discrimination does not determine that the fault is within the zone, the active control and impedance differential second-stage discrimination are initiated. Next, in the active control loop, the inner loop reference value of the new energy converter current is adjusted for 5ms. Finally, after the active control is activated, impedance differential protection is used to calculate the sum of the positive sequence impedance measurements on both sides of the line. 45 seconds after the fault... At 10ms, the calculation errors of FFT can cancel each other out. The average value of the calculated impedance is then compared with the positive sequence impedance of the line. If the absolute difference is greater than the setting value, it is determined to be an internal fault and the protection will operate; otherwise, it is determined to be an external fault and the protection will not operate.

[0044] Step (1): After the fault occurs, immediately start the current differential protection calculation, and in 20 The first-level judgment is completed within 5ms; if the fault is determined to be within the zone, the protection will operate directly; if the fault is determined to be outside the zone, the active control loop will be activated. Step (2): Start active control and adjust the inverter current inner loop reference value. and The active control phase lasts for 5ms. Step (3): After intervention of active control, start using impedance differential protection to calculate the sum of the positive sequence impedance measurements on both sides of the line; Step (4): 25 days after active control intervention 5ms (i.e., 45 seconds after the fault) (10ms) The calculation error of FFT reaches symmetry and thus cancels it out. The average value of the impedance during this time period is calculated and compared with the positive sequence impedance of the line. If the absolute difference is greater than the setting value, it is determined to be an internal fault and the protection will operate; otherwise, it is determined to be an external fault and the protection will not operate.

[0045] This invention provides a current impedance differential coordinated protection method for new energy transmission lines. After a power system fault occurs, the protection device immediately activates and enters a preset first time period, from 0ms to 25ms after the fault. During this period, the system acquires current phasor information from both the new energy side and the system side and performs the first level of current differential judgment. If the judgment result indicates an intra-zone fault, the protection device issues a trip command directly without any delay, with the protection action time controlled within 25ms, fully meeting the strict requirements of the main protection for speed. If the first-level judgment result indicates an inter-zone fault, the protection device does not act immediately but enters a preset second time period, lasting 5ms, i.e., from 20ms after the fault. 5ms to 25 For 5ms, the system actively controls the inner loop reference value of the new energy converter's current, adjusting the d-axis and q-axis reference values ​​to change the fault current output characteristics on the new energy side, preventing it from misleading the differential protection. The protection device enters a preset third time period, from the start of active control intervention to 25±5ms after intervention, or from 20±5ms to 45±10ms after the fault. During this period, the system continuously samples and calculates the average of the positive sequence impedances of all sampling points using a sliding window. The absolute value of the difference between this average and the preset positive sequence impedance is compared with a preset setting value for impedance differential second-level discrimination. If the absolute value of the difference is greater than the setting value, it is determined to be an in-zone fault and protection action is executed; otherwise, it is determined to be an out-of-zone fault and no action is taken.

[0046] Assume a new energy transmission line has a rated voltage of 220kV, a positive sequence impedance setting of 700Ω, and a set value of 30Ω. When a fault occurs within the line zone, the first stage of the current differential detection determines it to be a fault within the zone within 25ms, and the protection trips directly, with a total operating time of 25ms. When an external fault occurs on the line, after the first-level identification, the system actively adjusts the d-axis reference value of the new energy converter from 500A to 150A and the q-axis reference value from 300A to 80A within 25ms to 30ms. The final judgment is completed through the second-level identification of impedance differential. Since the active control effectively suppresses the fault current on the new energy side and the sliding window eliminates measurement errors by utilizing time symmetry, the input and recovery processes of the active control reference value form an input transient stage and an exit transient stage, respectively. The two transient stages are generated by the dynamic response of the same current inner loop. Therefore, the impedance calculation error alternates between positive and negative on the time axis. The system accurately determines that it is an external fault and does not operate. By combining the rapid initial judgment of current differential and the accurate final judgment of impedance differential, a two-level coordinated protection logic is formed, which satisfies both the speed requirement and the selectivity.

[0047] In some embodiments, please refer to Figure 1 , Figure 5 and Figure 9 The step of acquiring the current phasor information on both sides and performing a first-level differential current discrimination on the current phasor information on both sides within a preset first time period after the fault includes: Obtain current phasor information from the new energy side and the system side, and define the positive direction of the current as the flow from the bus to the line; Based on the new energy side current phasor information and the system side current phasor information, the differential current and braking current are calculated. The braking current, the preset minimum operating current, and the preset ratio braking coefficient are used as the criteria. The differential current is compared with the criterion to perform the first stage of current differential discrimination. If the criterion is met, it is determined to be an intra-zone fault; if the criterion is not met, it proceeds to the second stage of active control and impedance differential discrimination.

[0048] The specific implementation process of the first-level current differential judgment is as follows: The protection device first obtains the current phasor information of the new energy side and the current phasor information of the system side, and defines the positive direction of the current as the direction of the current from the bus to the line. That is, the direction of the current from the new energy bus to the line on the new energy side is defined as the positive direction, and the direction of the current from the system bus to the line on the system side is also defined as the positive direction.

[0049] Based on the current phasor information of the new energy side and the current phasor information of the system side, the protection device calculates the differential current and the braking current. The differential current is equal to the magnitude of the difference between the current phasor of the new energy side and the current phasor of the system side, and the braking current is equal to half the magnitude of the sum of the current phasor of the new energy side and the current phasor of the system side.

[0050] Assuming the fault current phasor on the new energy side is 500∠30°A and the fault current phasor on the system side is 480∠-25°A, then the differential current Id, equal to the magnitude of the difference between the two phasors, is approximately 460A, and the braking current Ir, equal to half the magnitude of the sum of the two phasors, is approximately 470A. The braking current, the preset minimum operating current Id0, and the preset ratio braking coefficient K are then used to construct a criterion: the criterion is valid when Id is greater than Id0 plus K multiplied by Ir. The calculated differential current Id is compared with this criterion; if Id is greater than Id0 plus K multiplied by Ir, it is determined to be an in-zone fault; otherwise, it is determined to be an out-of-zone fault.

[0051] In actual settings, the minimum operating current Id0 is usually set to 0.1 to 0.3 times the rated current. For example, for a line with a rated current of 1000A, Id0 can be set to 100A to 300A. The ratio braking coefficient K is usually set to 0.3 to 0.7, for example, K equals 0.5. Taking Id0 equal to 200A and K equal to 0.5 as an example, when the braking current Ir is 470A, the criterion threshold is 200 plus 0.5 multiplied by 470 equals 435A. Since the differential current Id is 460A, which is greater than 435A, the criterion is met, and the fault is determined to be within the zone.

[0052] Assuming the current on the new energy side is 200∠60°A, the system side current is 180∠-40°A, the differential current Id is approximately 190A, and the braking current Ir is approximately 185A, the criterion threshold is 200 + 0.5 multiplied by 185, which equals 292.5A. Since 190A is less than 292.5A, the criterion is not met, and the fault is determined to be outside the fault zone. The ratio braking characteristic increases the braking current when an outside fault is accompanied by a large load current, thus raising the criterion threshold and effectively preventing false tripping during outside faults. Conversely, during inside faults, the differential current increases significantly, ensuring reliable operation. The entire first-level discrimination is completed within 20ms to 25ms after the fault occurs.

[0053] In some embodiments, please refer to Figure 1 , Figure 5 and Figure 9 The process of actively adjusting the inner loop reference value of the new energy converter current within a preset second time period includes: Obtain the current d-axis reference value and q-axis reference value of the inner current loop of the new energy converter; The d-axis reference value and the q-axis reference value are adjusted according to the preset amplitude adjustment amount and / or preset phase adjustment amount to obtain the active control reference value; During the preset second time period, the inner loop reference value of the new energy converter current is switched to the active control reference value to change the amplitude and / or phase of the fault current on the new energy side. At the end of the preset second time period, the inner loop reference value of the new energy converter current is restored to the d-axis reference value and the q-axis reference value before the active control is activated.

[0054] When the first-stage current differential judgment result indicates an external fault, the system will, within a preset second time period (20 seconds after the fault),... 5ms to 25 Active control is performed within 5ms to adjust the inner loop reference value of the new energy converter current. The specific implementation of this process is as follows: The protection device first obtains the current d-axis reference value Id_ref and q-axis reference value Iq_ref of the new energy converter current inner loop. These two reference values ​​are the current control target values ​​of the new energy converter in the dq rotating coordinate system. In actual operation, assuming the current d-axis reference value is 500A and the q-axis reference value is 300A, this means that the current current control target of the converter is to output a current of 500A in the d-axis direction and 300A in the q-axis direction. At this time, the converter output current amplitude is approximately 583A. Then, according to the preset control command, the d-axis reference value and q-axis reference value are adjusted to new reference values ​​Id_ref_new and Iq_ref_new. The purpose of the adjustment is to significantly reduce the fault current injected into the line by the new energy converter, so that it will no longer mislead the current differential protection during external faults. For example, the control command can adjust the d-axis reference value from 500A to 150A and the q-axis reference value from 300A to 80A, so that the output current on the new energy side is reduced from about 583A to about 170A, and the adjustment process is completed within 5ms.

[0055] It should be noted that, in this embodiment of the invention, the d-axis reference value refers to the current setpoint of the inner current loop of the new energy converter in the d-axis direction, and the q-axis reference value refers to the current setpoint of the inner current loop of the new energy converter in the q-axis direction. Together, they constitute the current reference vector. The preset amplitude adjustment amount may include an amplitude adjustment coefficient, and the preset phase adjustment amount may include a phase offset angle. When the d-axis reference value before active control is engaged is Id_ref, the q-axis reference value is Iq_ref, the amplitude adjustment coefficient is k, and the phase offset angle is Δθ, the active control reference value can be obtained as follows: ; ; Wherein, Id_ref_new is the adjusted d-axis reference value, and Iq_ref_new is the adjusted q-axis reference value. Through the above conversion, the preset amplitude adjustment amount acts on the amplitude of the current reference vector, and the preset phase adjustment amount acts on the direction of the current reference vector in the dq coordinate system, thereby converting the amplitude adjustment and phase adjustment into d-axis and q-axis reference values ​​that can be directly received by the inner current loop of the new energy converter.

[0056] In another possible implementation, the preset amplitude adjustment amount can also be an amplitude increment. The system first obtains the current reference vector amplitude based on the d-axis reference value and q-axis reference value before active control is activated, then superimposes the current reference vector amplitude with the amplitude increment, and recalculates the adjusted d-axis reference value and q-axis reference value in combination with the preset phase adjustment amount.

[0057] In another embodiment, the control command can also adjust both the d-axis and q-axis reference values ​​to near zero, for example, adjusting the d-axis reference value to 20A and the q-axis reference value to 10A, so that the renewable energy converter provides almost no fault current to the fault point during an external fault, with an output current of only about 22A. The duration of this active control is the preset second time period, controlled within 5ms. After the active control is deactivated, the current characteristics on the renewable energy side have changed significantly, because even if an external fault occurs at this time, the interference of the renewable energy side to the differential protection has been effectively suppressed, and the impedance differential criterion can more accurately identify the fault location.

[0058] In some embodiments, please refer to Figure 1 , Figure 5 and Figure 9 The process of sampling during a preset third time period and calculating the average value of the positive sequence impedance of all sampling points using a sliding window includes: Set the sliding window length to the fourth time period; Sampling is performed in the preset third time period. The time corresponding to each sampling point is the end time of the sliding window. The fourth time period is moved forward as the start time of the sliding window. The sum of the positive sequence impedance measurement value of the new energy side and the positive sequence impedance measurement value of the system side of the sampling point is calculated from the start time to the end time as the positive sequence impedance sum. Collect the positive sequence impedance sum of all sampling points and calculate the average value of the positive sequence impedance sum.

[0059] The process of sampling and calculating the positive sequence impedance and average value through a sliding window in the preset third time period is as follows: First, the sliding window length is set to the fourth time period, which is usually set to one power frequency cycle, i.e., 20ms. Continuous sampling is performed within the preset third time period, which is from the start of active control intervention to 25ms after active control intervention. The sampling period is 5ms (i.e., from 20±5ms to 45±10ms after the fault). The system samples at a frequency of once per millisecond. The time corresponding to each sampling point is the end time of the sliding window. Moving forward four time intervals (20ms) from this end time is taken as the start time of the sliding window. The positive-sequence impedance sum for each sampling point is calculated from the start time to the end time. The positive-sequence impedance sum within the corresponding sliding window is calculated for each sampling point. After collecting the positive-sequence impedance sums for all sampling points, the arithmetic mean of the positive-sequence impedance sums is obtained to obtain the average value. By using the sliding window method, the positive-sequence impedance sum of each sampling point utilizes electrical quantity information within a 20ms time range before and after it, effectively smoothing impedance measurement fluctuations caused by DC components and decaying aperiodic components during transient processes, thus improving the stability and reliability of impedance calculation.

[0060] Assuming the positive sequence impedance of 55 sampling points fluctuates between 700Ω and 760Ω, with an average of 730Ω, this average has a smaller standard deviation than the measurement of a single sampling point. After a fault, 45... The 10ms interval forms two time-symmetric transient phases of electrical quantities, during which calculation errors can alternate between positive and negative on the time axis and cancel each other out.

[0061] In some embodiments, please refer to Figure 1 , Figure 5 and Figure 9 The time corresponding to each sampling point is the end time of the sliding window, and the fourth time interval forward is taken as the start time of the sliding window. The process of calculating the positive sequence impedance of the sampling points from the start time to the end time includes: The time corresponding to each sampling point is the end time of the sliding window, and the fourth time period forward is the start time of the sliding window; The voltage and current phasors on the new energy side and the system side are continuously collected from the start time to the end time. The positive sequence voltage phasor and positive sequence current phasor of the new energy source side and the system side are calculated by the FFT algorithm, and the positive sequence impedance measurement values ​​of the new energy source side and the system side are obtained based on the positive sequence voltage phasor and the positive sequence current phasor. The positive sequence impedance measurement values ​​on the new energy side and the system side are added together to obtain the positive sequence impedance sum of the sampling points.

[0062] For each sampling point, after determining the end and start times of its sliding window, voltage and current phasors from the renewable energy source and the system side are continuously acquired from the start to the end time. These voltage and current phasors are used to calculate the corresponding fundamental positive-sequence components using an FFT algorithm, thereby calculating the positive-sequence impedance measurement Zn on the renewable energy source side and the positive-sequence impedance measurement Zs on the system side. The calculation of positive-sequence impedance is based on Ohm's law, i.e., positive-sequence impedance equals positive-sequence voltage divided by positive-sequence current.

[0063] In one specific embodiment, for a certain sampling point, the positive-sequence voltage on the renewable energy side is calculated to be 220kV and the positive-sequence current is 500A using the FFT algorithm. Therefore, the measured positive-sequence impedance Zn on the renewable energy side is equal to 220000 divided by 500, which equals 440Ω. Simultaneously, the positive-sequence voltage on the system side is 230kV and the positive-sequence current is 800A. Therefore, the measured positive-sequence impedance Zs on the system side is equal to 230000 divided by 800, which equals 287.5Ω. Adding the measured positive-sequence impedance of 440Ω on the renewable energy side and the measured positive-sequence impedance of 287.5Ω on the system side yields a total positive-sequence impedance of 727.5Ω for this sampling point. The FFT algorithm can accurately extract the 50Hz fundamental positive-sequence component from the original sampled signal containing abundant harmonics and noise. Its frequency resolution depends on the sampling time length; for a 20ms data window, the frequency resolution is 50Hz, effectively separating the fundamental frequency from the harmonics.

[0064] In another embodiment, for a sampling point where the positive sequence voltage on the renewable energy side is 110kV and the positive sequence current is 250A, the measured positive sequence impedance is 440Ω. When the system side positive sequence voltage is 115kV and the positive sequence current is 400A, the measured positive sequence impedance is 287.5Ω. The sum of the positive sequence impedances is also 727.5Ω, indicating that the sum of the positive sequence impedances has a certain degree of stability under different fault conditions. In actual engineering, the line positive sequence impedance setting is 700Ω, while the measured value of the sum of the positive sequence impedances is approximately 727.5Ω, with a difference of 27.5Ω. If the setting is set to 30Ω, then 27.5Ω is less than 30Ω, indicating an external fault and no action is taken. If it is an internal fault, the measured value of the sum of the positive sequence impedances deviates significantly from 700Ω, for example, reaching 800Ω, with a difference of 100Ω, which is greater than 30Ω, indicating an internal fault and action is taken.

[0065] In some embodiments, please refer to Figure 1 , Figure 5 and Figure 9 The third time period covers the input transient phase after the new energy converter current inner loop reference value is switched to the active control reference value, and the exit transient phase after the new energy converter current inner loop reference value is restored to the d-axis reference value and q-axis reference value before active control input. The input transient phase and the exit transient phase are time-symmetric, and the calculation errors of the input transient phase and the exit transient phase alternate between positive and negative on the time axis, which are used to cancel each other out when calculating the average value of the positive sequence impedance.

[0066] The third time period, from 20±5ms to 45±10ms after the fault, forms two time-symmetric transient phases of electrical quantities. During the transient process following a power system fault, the changes in electrical quantities typically exhibit time symmetry; that is, the trend of change in electrical quantities in the first half of the period after the fault occurs mirrors the trend in the second half. This time symmetry causes the calculation errors generated by the two transient phases to alternate between positive and negative on the time axis when calculating the sum of positive-sequence impedances. For example, from 20ms to 32.5ms after the fault, due to the influence of the DC component and the decaying aperiodic component in the fault current, the positive-sequence impedance measurement calculated by the FFT algorithm is too large, assuming a positive error of 15Ω. From 32.5ms to 45ms, due to the exponential decay of the transient components, the positive-sequence impedance measurement is too small, assuming a negative error of 14Ω. These two errors are approximately equal in absolute value but opposite in sign, and can cancel each other out when calculating the average of the sum of positive-sequence impedances.

[0067] In some embodiments, please refer to Figure 1 , Figure 5 and Figure 9 The first time period is preset to be the time window from the occurrence of the fault to the completion of the first stage of current differential judgment; The second time period is preset to be the time window during which the inner loop reference value of the new energy converter current is maintained at the active control reference value. The preset third time period is a sampling time window used to calculate the average value of the positive sequence impedance. That is, the third time period includes the preset second time period and the transient recovery time period that follows the preset second time period.

[0068] The first time period is preset as the time window for the first stage of current differential judgment. The first stage judgment is completed within 20±5ms. Within this time, the rapid initial judgment of current differential is completed, ensuring the speed of protection and enabling the protection to issue a trip command within 25ms when there is a fault in the zone.

[0069] The second time period is preset as the time window from the start to the end of the active control. The duration of the active control phase is 5ms. During this period, the new energy converter operates according to the adjusted d-axis and q-axis reference values, which effectively suppresses the adverse effects of the fault current on the differential protection.

[0070] The third time period is preset to be the time window from the start of active control to the time when the calculation errors of impedance and sum reach mutual cancellation. Specifically, it is from the start of active control intervention to 25±5ms after active control intervention, or from 20±5ms to 45±10ms after the fault, when the FFT calculation error reaches symmetry and thus cancels out.

[0071] This invention proposes a current impedance differential coordinated protection system for new energy transmission lines. Please refer to [link / reference]. Figure 2 and Figure 5 ,include: The acquisition unit is configured to acquire current phasor information from both sides and perform differential current discrimination on the current phasor information from both sides within a preset first time period after the fault. The first-stage current differential judgment unit is configured to directly perform protection action if the first-stage current differential judgment result is an in-zone fault; if the first-stage current differential judgment result is not an in-zone fault, the protection is not blocked, and the reference value of the inner loop current of the new energy converter is actively adjusted within a preset second time period. The calculation unit is configured to perform sampling in a preset third time period, calculate the average value of the positive sequence impedance of all sampling points through a sliding window, calculate the absolute value of the difference between the average value and the preset positive sequence impedance of the line, compare the absolute value of the difference with a preset setting value, and perform impedance differential second-level discrimination. The impedance differential second-stage discrimination unit is configured to determine that if the absolute value of the difference is greater than the preset setting value, it is a fault within the zone and protection action is performed; otherwise, it is a fault outside the zone and protection action is not performed.

[0072] Step (1): After the fault occurs, immediately start the current differential protection calculation, and in 20 The first level of discrimination is completed within 5ms: New energy grid connection system such as Figure 5 As shown, the new energy power station is stepped up to 220kV by the main transformer and then connected to the power grid through the AC transmission line. Figure 5 In the diagram, S and W represent the system-side and new energy-side busbars, respectively, and f1, f2, and f3 represent the fault points of the new energy-side outlet fault outside the zone, the system-side outlet fault outside the zone, and the zone fault inside the zone. The research object is the AC transmission line SW.

[0073] After the fault occurs, the protection device immediately activates and collects the current phasors on both sides of the line, namely the new energy side W and the system side S. and The positive direction of the current on both sides is defined as the flow from the busbar to the line. Based on the traditional current differential protection principle, the typical operating criteria for ratio-controlled current differential protection are as follows:

[0074] In the formula, It is the minimum operating current, and due to the braking characteristics, its value increases as the braking current increases; This is the ratio braking coefficient for differential protection, typically ranging from 0.5 to 0.8.

[0075] The protection device will be activated 20 days after the fault. The above calculation and judgment are completed within 5ms. If the judgment is true, it is determined to be a fault within the zone, and the protection system operates directly; if the judgment is false, active control is initiated.

[0076] Step (2): Start active control and adjust the inverter current inner loop reference value. and The control duration is 5ms. When a short-circuit fault occurs in the renewable energy grid-connected system, the renewable energy power source first enters the low-voltage ride-through operation mode, and the positive sequence current command of the converter is determined by the following control equations:

[0077] In the formula, P is the per-unit value of the positive sequence voltage at the grid connection point; P is the reference value of the converter output power; Imax is the maximum current value that the converter is allowed to pass. , These are the d-axis and q-axis reference values ​​for the positive-sequence short-circuit current on the renewable energy side in the dq rotating coordinate system. The phasor expression for the positive-sequence short-circuit current output on the renewable energy side during a fault is shown below:

[0078] In the formula, This refers to the rated current of the new energy power supply. This represents the positive-sequence voltage phase at the grid connection point. Space current vector. Angle in the dq rotating coordinate system .

[0079] Depend on From the expression, we can see that The phase of the positive sequence voltage at the grid connection point and Regarding this, by adjusting the current reference value , Adjustment angle of value , thereby regulating The phase. During active control, the original control command value of the positive sequence current ( , Adjust to , For different voltage drop levels, the control command value of the positive sequence current during active control is also different. This can not only meet the reactive power support requirements of new energy power sources, but also deviate the original fault state as long as the short-circuit current does not exceed the limit, thus creating conditions for the correct operation of the protection.

[0080] Step (3): After intervention of active control, start using impedance differential protection to calculate the sum of the positive sequence impedance measurements on both sides of the line: like Figure 5 As shown in the diagram of a new energy grid-connected transmission line, neglecting the distributed capacitance of the line when a fault occurs at different locations, analyze the impedance characteristics of the following three fault scenarios: (1) When a short-circuit fault occurs at point f1 outside the new energy side zone of the transmission line, the following KVL and KCL equations can be established according to Figure 6(a):

[0081] By combining the KVL and KCL equations with the definition of the positive sequence impedance measurement, the positive sequence impedance measurement value at the new energy side protection installation point can be obtained. and the positive sequence impedance measurement at the system-side protection installation location. :

[0082] At this time, impedance and equal to line impedance ; (2) When a short-circuit fault occurs at point f3 outside the side zone of the transmission line system, the KVL and KCL equations are written according to Figure 6(c) as follows:

[0083] By simultaneously applying the KVL and KCL equations and the definition of positive-sequence equivalent impedance, we can further obtain:

[0084] At this time, impedance and equal to line impedance ; (3) When a fault occurs at point f2 within the transmission line area, write the KVL and KCL equations according to Figure 6(b):

[0085] By simultaneously applying the KVL and KCL equations and the definition of positive-sequence equivalent impedance, we can further obtain:

[0086] UW and US are the positive sequence voltage phasors at the protection installation points on the new energy side and the system side, respectively; IW and IS are the current phasors on the new energy side and the system side, respectively. , These represent the positive-sequence impedance measurements on the new energy side and the system side, respectively; ZL represents the line positive-sequence impedance. In most cases, during an in-zone fault, the sum of the impedances is not equal to the line impedance. However, due to factors such as line distributed capacitance and control strategies, in extremely rare cases, the sum of the impedances may equal the line impedance, leading to failure to operate within the traditional impedance differential protection zone. To overcome this problem, this invention, based on active control, proactively changes the phase and amplitude of the output current on the new energy side by briefly adjusting the converter current reference value, thereby breaking the original fault impedance balance and fundamentally avoiding failure to operate within the zone.

[0087] Step (4): 25 days after active control intervention After 5ms, the calculation error of FFT reaches symmetry and is thus canceled out. The average value of the impedance during this time period is calculated and compared with the positive sequence impedance of the line. If the absolute difference is greater than the setting value, it is determined to be an internal fault and the protection will operate; otherwise, it is determined to be an external fault and the protection will not operate.

[0088] The active control adjusts the inverter current inner loop reference value instantly upon command issuance, while the actual current output undergoes a dynamic tracking process and cannot change abruptly. This process lasts approximately 5ms, characterized by the current amplitude or phase gradually approaching the target value, and recovering with similar dynamic characteristics after control ends. Thus, two time-symmetric transient electrical quantity phases are formed at the control activation and deactivation points. To address the spectral leakage and calculation errors caused by asynchronous truncation of the data window in integer-cycle Fourier transform (FFT), this invention is based on the following mechanism: throughout the entire time window from active control activation to the electrical quantity stabilization (approximately 25ms),... Within 5ms, the positive sequence impedance measurements on both sides of the line are continuously calculated, and the impedance sum is obtained in real time. Due to the waveform symmetry of the two transient stages, the introduced impedance sum calculation error is also symmetrical, exhibiting an alternating positive and negative characteristic on the time axis.

[0089] By calculating the average impedance over the complete time period, the aforementioned symmetrical transient errors can cancel each other out during the integral averaging process, thus obtaining stable and accurate impedance estimates. This average value is then compared with the known positive-sequence impedance of the line to form the final protection criterion.

[0090] In the formula For impedance and satisfy ; Here, Kset1 represents the impedance and average value; Kset1 is the preset scaling factor. To preset the positive sequence impedance of the line, factors such as the magnitude of the output line impedance and the error of the current transformer are taken into account.

[0091] If the criteria are met, the fault is determined to be within the protection zone, and the protection system will activate; otherwise, the fault is determined to be outside the protection zone, and no protection system will activate.

[0092] Based on the above analysis, the feasibility of the protection scheme is verified by setting up a fault simulation test for both in-zone and out-of-zone conditions. Considering the reduced sensitivity or even the risk of failure to operate of traditional current differential protection when phase-to-phase faults occur, a simulation verification is conducted using phase-to-phase faults as an example.

[0093] (1) Two-phase short circuit fault outside the new energy side zone (at f1, Rf=0Ω) exist Figure 5 In a typical new energy grid-connected transmission system topology diagram, taking line WS as the research object, it is assumed that a two-phase short-circuit fault occurs on the new energy side outside the zone at 1.0s (at f1, Rf=0Ω).

[0094] ① First-level discrimination (0~20 after fault) 5ms) After the fault occurred, the protection device immediately initiated current differential protection calculations. Since the fault was located outside the renewable energy zone, the current on both sides of the line exhibited through-current characteristics, and the differential current was less than the operating threshold, thus the ratio-restrained current differential protection criterion was not met. The protection did not operate and entered the active control phase.

[0095] ②Active control intervention (after fault 20) 5~25 5ms) The protection system initiates active control, adjusts the inner loop reference value of the new energy inverter current for 5ms, and actively changes the amplitude and phase of the output current on the new energy side.

[0096] ③ Second-level discrimination (20 after the fault) 5~45 10ms) As shown in Figures 8(a1) and 8(a2), after the active control is intervened, the sum of the positive sequence impedance measurements on both sides of the line is calculated using impedance differential protection. 45 The calculation errors cancel each other out at 10ms, and the calculation is performed 20 seconds after the fault. 5~45 The average value of the sum of positive sequence impedance measurements within a 10ms time interval Positive sequence impedance of the line According to the impedance differential protection criterion: Much smaller than the protection setting value The preset setting value is the impedance difference threshold, with the unit being Ω. It can be set according to the positive sequence impedance of the line, the error of the current transformer, the error of the voltage transformer, and the protection sensitivity requirements. If the criterion is not met at this time, it is determined to be an external fault, and the protection will not operate correctly.

[0097] (2) Two-phase short circuit fault outside the system side zone (at f3, Rf=0Ω) exist Figure 5 In a typical new energy grid-connected transmission system topology diagram, taking line WS as the research object, it is assumed that a two-phase short-circuit fault occurs on the system side outside the zone at 1.0s (at f3, Rf=0Ω).

[0098] ① First-level discrimination (0~20 after fault) 5ms) The calculation results for the current differential protection show that the differential current does not exceed the operating threshold, so the criterion is not valid. The protection does not operate and enters the active control phase.

[0099] ②Active control intervention (after fault 20) 5~25 5ms) Active control is initiated, and the inverter current inner loop reference value is adjusted for 5ms.

[0100] ③ Second-level discrimination (20 after the fault) 5~45 10ms) As shown in Figures 8(b1) and 8(b2), the calculation of 20 after the fault 5~45 The average value of the sum of positive sequence impedance measurements within a 10ms time interval According to the impedance differential protection criterion: The current is much smaller than the protection setting value of 2.44Ω. At this point, the criterion is not valid, and the fault is determined to be outside the protection zone. The protection is correct and does not operate.

[0101] (3) Two-phase short circuit fault within the zone (at f2, Rf=20Ω) exist Figure 5 In a typical topology diagram of a renewable energy grid-connected transmission system, taking line WS as the research object, it is assumed that a two-phase short-circuit fault occurs in the line at 1.0s (at point f2, Rf=20Ω). Under this condition, due to the low-voltage ride-through control strategy of the renewable energy converter, the amplitude of the output current on the renewable energy side is limited and the phase is controlled, and traditional current differential protection has the risk of failing to operate.

[0102] ① First-level discrimination (0~20 after fault) 5ms) Because the fault current contribution from the renewable energy side is insufficient, the sum of the current phasors on both sides does not exceed the operating threshold, and the current differential criterion is not established. The protection does not operate directly and enters the active control phase.

[0103] ②Active control intervention (after fault 20) 5~25 5ms) Active control is initiated, and the inverter current inner loop reference value is adjusted for 5ms.

[0104] ③ Second-level discrimination (20 after the fault) 5~45 10ms) As shown in Figures 8(c1) and 8(c2), the calculation of the fault after 25 5~45 The average value of the sum of positive sequence impedance measurements within a 10ms time interval According to the impedance differential protection criterion: The current is much greater than the protection setting value of 2.44Ω. At this point, the criterion is met, and the fault is determined to be within the zone. The protection operates correctly.

[0105] The simulation results above show that: When a fault occurs outside the protection zone, the current differential protection is correctly blocked. After the active control intervenes, the impedance differential protection still determines that the fault is outside the protection zone and the protection reliably does not operate, which verifies the selectivity of the method. In the event of a high-resistance fault within the zone, traditional current differential protection fails to operate due to insufficient sensitivity. The proposed method actively disrupts the impedance balance through control, enabling the impedance differential protection to operate within 45 seconds after the fault. The method accurately identifies faults within the protection zone and operates correctly within 10ms, verifying its effectiveness in overcoming the problem of traditional protection malfunction. 45 after the malfunction At 10ms, by utilizing the transient symmetry of the active control input and output process, the FFT calculation errors cancel each other out, and the impedance and measurement accuracy are significantly improved, verifying the feasibility of the transient symmetry error cancellation mechanism.

[0106] The proposed new energy transmission line current impedance differential collaborative protection scheme based on the control transient response symmetry effectively solves the problems of insufficient sensitivity of traditional current differential protection, transient error and failure to operate within the zone of traditional impedance differential protection while retaining the speed of operation, thus significantly improving the reliability and adaptability of new energy transmission line protection.

[0107] Based on the same inventive concept, according to another aspect of the present invention, such as Figure 3 As shown, an embodiment of the present invention also provides a computer device 30, which includes a processor 310 and a memory 320. The memory 320 stores a memory computer program 321 that can run on the processor. When the processor 310 executes the program, it performs the steps of the method described above.

[0108] Based on the same inventive concept, according to another aspect of the present invention, such as Figure 4As shown, embodiments of the present invention also provide a computer-readable storage medium 40, which stores a readable medium computer program 410 that, when executed by a processor, performs the methods described above.

[0109] Embodiments of the present invention may also include a corresponding computer device. The computer device includes a memory, at least one processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes any of the methods described above when executing the program.

[0110] The memory, as a non-volatile computer-readable storage medium, can be used to store non-volatile software programs, non-volatile computer-executable programs, and modules, such as program instructions / modules in the embodiments of this application. The processor executes various functional applications and data processing of the device by running the non-volatile software programs, instructions, and modules stored in the memory, thereby implementing the above-described method.

[0111] The memory may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created based on the use of the device. Furthermore, the memory may include high-speed random access memory and non-volatile memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In embodiments, the memory may optionally include memory remotely located relative to the processor, which can be connected to the local module via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0112] Finally, it should be noted that those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the methods described above. The storage medium for the program can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc. The above computer program embodiments can achieve the same or similar effects as any of the corresponding foregoing method embodiments.

[0113] Those skilled in the art will also understand that the various exemplary logic blocks, modules, circuits, and algorithm steps described in conjunction with the disclosure herein can be implemented as electronic hardware, computer software, or a combination of both. To clearly illustrate this interchangeability between hardware and software, the functionality of various illustrative components, blocks, modules, circuits, and steps has been generally described. Whether this functionality is implemented as software or as hardware depends on the specific application and the design constraints imposed on the system as a whole. Those skilled in the art can implement the functionality in various ways for each specific application, but such implementation decisions should not be construed as departing from the scope of the embodiments disclosed herein.

[0114] The above are exemplary embodiments disclosed in this invention. However, it should be noted that various changes and modifications can be made without departing from the scope of the embodiments of this invention as defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. The sequence numbers of the disclosed embodiments of this invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular number.

[0115] It should be understood that, as used herein, the singular form “a” is intended to include the plural form as well, unless the context clearly supports an exception. It should also be understood that, as used herein, “and / or” refers to any and all possible combinations of one or more of the associated listed items.

[0116] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of different aspects of the invention exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for differential coordinated protection of current impedance in new energy transmission lines, characterized in that, Includes the following steps: Acquire current phasor information from both sides and perform first-level differential current discrimination on the current phasor information from both sides within a preset first time period after the fault. If the first-stage current differential judgment result indicates an intra-zone fault, then the protection action will be performed directly; If the first-stage current differential judgment result does not determine that it is an in-zone fault, the protection will not be blocked, and the inner loop reference value of the new energy converter current will be actively adjusted within a preset second time period. Specifically, the current d-axis and q-axis reference values ​​of the new energy converter current inner loop will be obtained; the d-axis and q-axis reference values ​​will be adjusted according to a preset amplitude adjustment amount and / or a preset phase adjustment amount to obtain an active control reference value; within the preset second time period, the inner loop reference value of the new energy converter current will be switched to the active control reference value to change the amplitude and / or phase of the fault current on the new energy side; at the end of the preset second time period, the inner loop reference value of the new energy converter current will be restored to the d-axis and q-axis reference values ​​before the active control was activated. Sampling is performed during a preset third time period. The average value of the positive sequence impedance sum of all sampling points is calculated using a sliding window. The absolute value of the difference between the average value and the preset positive sequence impedance is calculated, and the absolute value of the difference is compared with a preset setting value for impedance differential second-level discrimination. The sliding window length is set as a fourth time period. Sampling is performed during the preset third time period, with the time corresponding to each sampling point being the end time of the sliding window. Moving forward four time periods is taken as the start time of the sliding window. From the start time to the end time, the sum of the positive sequence impedance measurements on the renewable energy side and the system side is calculated as the positive sequence impedance sum. The positive sequence impedance sum of all sampling points is collected, and the average value of the positive sequence impedance sum is obtained. The time corresponding to each sampling point is taken as the end time of the sliding window, and moving forward four time periods is taken as the start time of the sliding window. From the start time to the end time, voltage phasors and current phasors on the renewable energy side and the system side are continuously collected. The positive sequence voltage phasors and current phasors on the renewable energy side and the system side are calculated using an FFT algorithm, and a new positive sequence impedance is obtained based on the voltage positive sequence phasors and the current positive sequence phasors. The positive sequence impedance measurements on the energy side and the system side are used to obtain the positive sequence impedance sum at the sampling point. The third time period covers the transient phase after the inner loop reference value of the new energy converter current is switched to the active control reference value, and the transient phase after the inner loop reference value of the new energy converter current recovers to the d-axis and q-axis reference values ​​before active control is activated. The transient phase and the transient phase have time symmetry, and the calculation errors of the transient phase and the transient phase alternate between positive and negative on the time axis to cancel each other out when calculating the average value of the positive sequence impedance sum. The first time period is the time window from the occurrence of the fault to the completion of the first stage of current differential discrimination. The second time period is the time window during which the inner loop reference value of the new energy converter current remains at the active control reference value. The third time period is the sampling time window for calculating the average value of the positive sequence impedance sum, that is, the third time period includes the second time period and the transient recovery time period after the second time period. If the absolute value of the difference is greater than the preset setting value, it is determined to be an intra-zone fault and protection action is performed; otherwise, it is determined to be an extra-zone fault and protection action is not performed.

2. The method for differential coordinated protection of current impedance of new energy transmission lines according to claim 1, characterized in that, The step of acquiring the current phasor information on both sides and performing a first-level differential current discrimination on the current phasor information on both sides within a preset first time period after the fault includes: Obtain current phasor information from the new energy side and the system side, and define the positive direction of the current as the flow from the bus to the line; Based on the new energy side current phasor information and the system side current phasor information, the differential current and braking current are calculated. The braking current, the preset minimum operating current, and the preset ratio braking coefficient are used as the criteria. The differential current is compared with the criterion to perform the first stage of current differential discrimination. If the criterion is met, it is determined to be an intra-zone fault; if the criterion is not met, it proceeds to the second stage of active control and impedance differential discrimination.

3. A current impedance differential coordinated protection system for new energy transmission lines, characterized in that, include: The acquisition unit is configured to acquire current phasor information from both sides and perform differential current discrimination on the current phasor information from both sides within a preset first time period after the fault. The first-stage current differential discrimination unit is configured to directly perform protection action if the first-stage current differential discrimination result is an intra-zone fault. If the first-stage current differential judgment result does not determine that it is an in-zone fault, the protection will not be blocked, and the inner loop reference value of the new energy converter current will be actively adjusted within a preset second time period. Specifically, the current d-axis and q-axis reference values ​​of the new energy converter current inner loop will be obtained; the d-axis and q-axis reference values ​​will be adjusted according to a preset amplitude adjustment amount and / or a preset phase adjustment amount to obtain an active control reference value; within the preset second time period, the inner loop reference value of the new energy converter current will be switched to the active control reference value to change the amplitude and / or phase of the fault current on the new energy side; at the end of the preset second time period, the inner loop reference value of the new energy converter current will be restored to the d-axis and q-axis reference values ​​before the active control was activated. The calculation unit is configured to sample during a preset third time period, calculate the average of the positive sequence impedance sum of all sampling points through a sliding window, calculate the absolute value of the difference between the average value and the preset positive sequence impedance of the line, compare the absolute value of the difference with a preset setting value, and perform a second-level impedance differential discrimination. The sliding window length is set to a fourth time period. Sampling is performed during the preset third time period, with the time corresponding to each sampling point being the end time of the sliding window. Moving forward four time periods is used as the start time of the sliding window. From the start time to the end time, the sum of the positive sequence impedance measurements on the renewable energy side and the system side is calculated as the positive sequence impedance sum. The positive sequence impedance sum of all sampling points is collected, and the average value of the positive sequence impedance sum is obtained. The time corresponding to each sampling point is the end time of the sliding window, and moving forward four time periods is used as the start time of the sliding window. From the start time to the end time, voltage phasors and current phasors on the renewable energy side and the system side are continuously collected. The positive sequence voltage phasors and current phasors on the renewable energy side and the system side are calculated using an FFT algorithm, and the positive sequence impedance is calculated based on the voltage phasors and current phasors. The positive sequence impedance measurements on the new energy side and the system side are obtained using sequence phasors. These measurements are then added together to obtain the sum of the positive sequence impedances at the sampling points. The third time period covers the transitional phase after the new energy converter current inner loop reference value is switched to the active control reference value, and the transitional phase after the new energy converter current inner loop reference value recovers to the d-axis and q-axis reference values ​​before active control activation. The transitional phase and the transitional phase are time-symmetric, and their calculation errors alternate on the time axis to cancel each other out when calculating the average value of the sum of positive sequence impedances. The first preset time period is the time window from the occurrence of the fault to the completion of the first stage of current differential discrimination. The second preset time period is the time window during which the new energy converter current inner loop reference value remains at the active control reference value. The third preset time period is the sampling time window for calculating the average value of the sum of positive sequence impedances, i.e., the third time period includes the second preset time period and the transitional recovery time period following the second preset time period. The impedance differential second-stage discrimination unit is configured to determine that if the absolute value of the difference is greater than the preset setting value, it is a fault within the zone and protection action is performed; otherwise, it is a fault outside the zone and protection action is not performed.

4. A computer device, characterized in that, include: At least one processor; And a memory storing computer instructions executable on the processor, which, when executed by the processor, implement the steps of the method according to any one of claims 1-2.

5. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1-2.

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