New energy grid-connected transmission line protection method and system

Abstract

The invention provides a new energy grid-connected transmission line protection method and system, and relates to the technical field of power protection. The method comprises the following steps: calculating positive-sequence comprehensive impedance of a to-be-evaluated sending-out line by using positive-sequence voltage and current fault components at protection installation positions on two sides of the new energy sending-out line and line positive-sequence impedance; based on the calculated positive sequence comprehensive impedance of the to-be-evaluated sending-out line, performing first judgment to determine whether to enter an active control link; when it is determined that an active control link is entered, changing a new energy power supply inner loop current reference value to change a fault state; and calculating the positive sequence comprehensive impedance of the to-be-evaluated sending-out line in the master control period, and performing second judgment to determine whether the relay protection device acts or not. According to the invention, faults inside and outside the new energy grid-connected transmission line area can be effectively judged, and the protection sensitivity and reliability are improved.

Description

Technical Field

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

[0002] With the transformation of the global energy structure, large-scale grid connection of new energy sources such as wind power and photovoltaics has become a trend. However, the fault characteristics of new energy power sources, especially those connected to the grid based on power electronic converters, differ significantly from those of traditional synchronous generators. When a grid fault occurs, the weak inertia, current limiting characteristics, and complex control strategies of new energy power sources result in fault current amplitude and direction that differ from those of traditional power sources, and the fault current often exhibits nonlinear and non-power frequency characteristics.

[0003] When a fault occurs on the AC side of a renewable energy grid connection system, the fault characteristics of the converter differ significantly from those of a synchronous generator. The short-circuit current amplitude is limited, and the phase angle is controlled, challenging the adaptability of protection principles designed based on synchronous generator characteristics. Distance protection impedance measurements may be capacitive, exceeding the protection setting range; the phase angle of the fault currents on both sides may exceed 90°, reducing the sensitivity of current differential protection or even causing it to fail to operate, severely impacting accurate fault identification and rapid isolation. In the protection of renewable energy grid-connected transmission lines, traditional current differential protection is a commonly used primary protection method. However, due to the aforementioned unique fault characteristics of renewable energy sources, when a phase-to-phase fault occurs, the fault current injected into both sides of the line may not meet the operating conditions of traditional current differential protection, leading to insufficient protection sensitivity or even failure to operate. This seriously threatens the operational stability and reliability of the renewable energy grid-connected system.

[0004] Therefore, there is an urgent need for a protection method for new energy grid-connected transmission lines to solve the above problems. Summary of the Invention

[0005] This invention addresses the technical problem that traditional current differential protection is insufficiently sensitive and cannot effectively cope with faults in new energy grid-connected transmission lines when phase-to-phase faults occur. It provides a protection method and system for new energy grid-connected transmission lines.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of this invention proposes a protection method for a new energy grid-connected transmission line, comprising: calculating the positive sequence comprehensive impedance of the transmission line to be evaluated using the positive sequence voltage and current fault components at the protection installation points on both sides of the new energy transmission line and the positive sequence impedance of the line; performing a first discrimination based on the calculated positive sequence comprehensive impedance of the transmission line to be evaluated to determine whether to enter the active control loop; when it is determined that the active control loop has been entered, changing the reference values ​​of relevant parameters in the inner loop of the new energy power supply to change the fault state; calculating the positive sequence comprehensive impedance of the transmission line to be evaluated during the main control period and performing a second discrimination to determine whether the relay protection device has operated.

[0008] The second aspect of this invention proposes a protection system for renewable energy grid-connected transmission lines, employing the renewable energy grid-connected transmission line protection method described in the first aspect of this invention. The renewable energy grid-connected transmission line protection system includes: a calculation module, which calculates the positive-sequence comprehensive impedance of the transmission line to be evaluated using the positive-sequence voltage and current fault components at the protection installation points on both sides of the renewable energy transmission line, as well as the positive-sequence impedance of the line; a first discrimination module, which performs a first discrimination based on the calculated positive-sequence comprehensive impedance of the transmission line to be evaluated to determine whether to enter the active control phase; an active control module, which, when it is determined to enter the active control phase, changes the fault state by altering the reference values ​​of relevant parameters within the renewable energy power supply loop; and a second discrimination module, which calculates the positive-sequence comprehensive impedance of the transmission line to be evaluated during the main control processing and performs a second discrimination to determine whether the relay protection device operates.

[0009] A third aspect of the present invention provides an electronic device comprising: one or more processors; a storage device for storing one or more programs; wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the method described in the first aspect of the present invention.

[0010] A fourth aspect of the present invention provides a computer-readable medium having a computer program stored thereon, which, when executed by a processor, implements the method described in the first aspect of the present invention.

[0011] Compared with existing technologies, this invention solves the problem of insufficient sensitivity of current differential protection when phase-to-phase faults occur in new energy grid-connected transmission lines, and improves protection reliability through active control methods. It can enable relay protection devices to perform correct actions under various fault conditions, and has high sensitivity and reliability. Attached Figure Description

[0012] Figure 1 This is a flowchart illustrating an example of the new energy grid-connected transmission line protection method of the present invention;

[0013] Figure 2 This is an application example diagram of the new energy grid-connected transmission line protection method of the present invention;

[0014] Figure 3 This is an example diagram of an external fault in the new energy side zone of the new energy grid-connected transmission line protection method of the present invention;

[0015] Figure 4 This is an example diagram of an external fault in the system side zone of the new energy grid-connected transmission line protection method of the present invention;

[0016] Figure 5 This is an example diagram of an intra-regional fault in the new energy grid-connected transmission line protection method of the present invention;

[0017] Figure 6 This is an example diagram showing the calculation results after filtering and preprocessing the voltage and current sampling data collected when a two-phase short-circuit fault occurs outside the zone at point f1 on the new energy side of the AC transmission line.

[0018] Figure 7 This is an example diagram showing the calculation results of voltage and current sampling data collected when a two-phase short-circuit fault occurs outside the zone at point f1 on the new energy side of the AC transmission line, without filtering preprocessing.

[0019] Figure 8 This shows the positive sequence composite impedance modulus value corresponding to the occurrence of a two-phase short-circuit fault in the zone at point f2 on the new energy side of the AC transmission line.

[0020] Figure 9 This is a schematic diagram of the calculation results after filtering and preprocessing the voltage and current sampling data collected when a two-phase phase-to-phase short-circuit fault occurs at point f2 on the new energy side of the AC transmission line.

[0021] Figure 10 This is a schematic diagram of the calculation results of voltage and current sampling data collected when a two-phase short-circuit fault occurs at point f2 on the new energy side of the AC transmission line, without filtering.

[0022] Figure 11 This is a schematic diagram of the calculation results after filtering and preprocessing the voltage and current sampling data collected when a two-phase short-circuit fault occurs outside the zone at point f3 on the new energy side of the AC transmission line.

[0023] Figure 12 This is a schematic diagram of the calculation results of the voltage and current sampling data collected when a two-phase short-circuit fault occurs outside the zone at point f3 on the new energy side of the AC transmission line, without filtering preprocessing.

[0024] Figure 13 This is a structural block diagram of the new energy grid-connected transmission line protection system of the present invention;

[0025] Figure 14 This is a schematic diagram of the structure of an electronic device according to an embodiment of the present invention;

[0026] Figure 15 This is a schematic diagram of a computer-readable medium embodiment according to the present invention. Detailed Implementation

[0027] 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.

[0028] In view of the above problems, this invention provides a protection method for new energy grid-connected transmission lines. This method calculates the positive-sequence comprehensive impedance using the positive-sequence voltage and current fault components at the protection installation points on both sides of the new energy grid-connected transmission line, as well as the positive-sequence impedance of the line. If the absolute value of the positive-sequence comprehensive impedance is greater than the setting value, it is determined to be an in-zone fault, and the protection operates. If the absolute value of the positive-sequence comprehensive impedance is less than the setting value, it is determined to be an out-of-zone fault or an in-zone failure to operate. In this case, the current reference value is changed by active control to change the fault state. The positive-sequence comprehensive impedance during the active control period is calculated and substituted into the protection criterion. If the absolute value of the positive-sequence comprehensive impedance is greater than the setting value, it is determined to be an in-zone fault, and the protection operates. If the absolute value of the positive-sequence comprehensive impedance is less than the setting value, it is determined to be an out-of-zone fault, and the protection does not operate. By utilizing the difference in positive-sequence comprehensive impedance characteristics between in-zone and out-of-zone faults to construct the protection criterion, the sensitivity and reliability are improved, solving the problem of insufficient sensitivity of current differential protection when phase-to-phase faults occur in new energy grid-connected transmission lines, and eliminating the situation of protection failure to operate through active control.

[0029] It should be noted that the above is only an optional example and should not be construed as a limitation of the present invention.

[0030] Example 1

[0031] Figure 1 This is a flowchart illustrating an example of the new energy grid-connected transmission line protection method of the present invention. Figure 2 This is an application example diagram of the new energy grid-connected transmission line protection method of the present invention.

[0032] The following will refer to Figures 1 to 12 This invention provides a detailed explanation of the protection method for new energy grid-connected transmission lines.

[0033] exist Figure 2The system topology diagram for renewable energy grid connection shows the basic layout of the renewable energy transmission lines, surrounding power sources, and fault points. The "renewable energy source" on the left refers to wind power or photovoltaic power plants; the "system" on the right refers to the synchronous power system in the grid. Both the renewable energy source and the system are connected via a main transformer (corresponding to...). Figure 2 The voltage is boosted by the main transformer (as sometimes referred to as the "transmission line" in this text, which connects the renewable energy power source side and the system side). Here, W represents the busbar or protection installation point on the renewable energy side (or wind farm side). S represents the busbar or protection installation point on the system side (or main grid side). f1 is located to the left of point W, indicating an external fault point on the renewable energy side. f2 is located between W and S, indicating an internal fault point on the transmission line. f3 is located to the right of point S, indicating an external fault point on the system side. Specifically, the renewable energy power station is boosted to 220kV by the main transformer and then connected to the grid via the AC transmission line.

[0034] First, in step S101, the positive sequence comprehensive impedance of the transmission line to be evaluated is calculated using the positive sequence voltage and current fault components at the protection installation points on both sides of the new energy transmission line and the positive sequence impedance of the line.

[0035] exist Figure 2 In the application example, the positive sequence voltage fault component and current fault component measured at the protection installation point W on the new energy side are respectively The positive sequence voltage and current fault components measured at point S on the system-side protection installation point are respectively The positive sequence impedance of the transmitting line is Z. L1 .

[0036] The following expression represents the positive-sequence composite impedance of the outgoing line to be evaluated:

[0037]

[0038] Among them, Z eq1 This represents the positive-sequence composite impedance of the outgoing line to be evaluated. These represent the positive sequence voltage fault component and current fault component measured at the protection installation point W on the new energy side, respectively. Z represents the positive sequence voltage fault component and current fault component measured at point S on the system-side protection installation location, respectively; L1 This indicates the positive sequence impedance of the outgoing line to be evaluated.

[0039] It should be noted that the above is only an optional example and should not be construed as a limitation of the present invention.

[0040] Next, in step S102, based on the calculated positive sequence composite impedance of the outgoing line to be evaluated, a first discrimination is performed to determine whether to enter the active control stage.

[0041] Collect data related to faults outside the new energy side zone, faults outside the system side zone, and faults within the zone within a specified historical period, analyze and quantify the positive sequence comprehensive impedance characteristics under different fault conditions, and construct the first protection criterion.

[0042] The specified historical time period includes historical time periods calculated backwards from the current time, such as 3 months, 4 months, 5 months, 6 months, 12 months, etc.

[0043] When a fault occurs at different locations on the AC transmission line (corresponding to...) Figure 3 An example of a fault outside the new energy side zone, specifically a fault at point f1. Figure 4 The system side-area fault, i.e., the fault at point f3. Figure 5 (Example of a fault within the zone, i.e., a fault at point f2), and analyze its positive sequence comprehensive impedance characteristics.

[0044] exist Figure 3 In the example, when an out-of-area fault occurs at point f1 on the new energy side of the AC transmission line (i.e., the transmission line to be evaluated), the positive sequence fault component voltages on both sides of point f1 on the new energy side satisfy the following relationship:

[0045]

[0046] in, This represents the positive sequence voltage fault component measured at the protection installation point W on the new energy side; Z represents the positive sequence voltage fault component and current fault component measured at point S on the system-side protection installation location, respectively; L1 This indicates the positive sequence impedance of the AC output line.

[0047] At this point, the positive-sequence fault component currents on both sides of point f1 on the new energy side satisfy the following relationship:

[0048]

[0049] in, This represents the positive sequence current fault component measured at the protection installation point W on the new energy side; This represents the positive sequence current fault component measured at point S on the system-side protection installation location.

[0050] Substituting the above relations (2) and (3) into expression (1), i.e., the positive sequence composite impedance expression, we get the positive sequence composite impedance Z. eq1 =0.

[0051] exist Figure 4In the example, when an out-of-area fault occurs at point f3 on the system side of the AC transmission line (i.e., the transmission line to be evaluated), the positive sequence fault component voltages on both sides of point f3 on the system side satisfy the following relationship:

[0052]

[0053] in, This represents the positive sequence voltage fault component measured at point S on the system-side protection installation location; This represents the positive sequence voltage fault component measured at the protection installation point W on the new energy side; Z represents the positive sequence fault current component measured at point S on the system-side protection installation location; L1 This indicates the positive sequence impedance of the AC output line.

[0054] At this point, the positive-sequence fault component currents on both sides of the line are equal in magnitude and opposite in direction, as shown below:

[0055]

[0056] in, This represents the positive sequence current fault component measured at the protection installation point W on the new energy side; This represents the positive sequence current fault component measured at point S on the system-side protection installation location.

[0057] Substituting the above relations (4) and expressions (5) into expression (1), i.e., the positive sequence composite impedance expression, the positive sequence composite impedance Z is then obtained. eq1 =0.

[0058] exist Figure 5 In the example, when a fault occurs in the f2 region of the AC transmission line (i.e., the transmission line to be evaluated), the positive sequence fault component voltage and current on both sides of point f2 satisfy the following relationship:

[0059]

[0060] in, This represents the positive sequence voltage fault component measured at point S on the system-side protection installation location; This represents the positive sequence voltage fault component measured at the protection installation point W on the new energy side; This represents the positive sequence current fault component measured at the protection installation point W on the new energy side; Z represents the positive sequence fault current component measured at point S on the system-side protection installation location; L1 This indicates the positive sequence impedance of the AC output line.

[0061] Substituting this into the definition of positive-sequence composite impedance, we obtain the expression for the positive-sequence composite impedance when a fault occurs within the fault zone:

[0062]

[0063] It should be noted that in most cases, the positive-sequence composite impedance is not equal to 0 when a fault occurs within the zone, and the characteristics of the positive-sequence composite impedance differ significantly between faults occurring within and outside the zone. However, due to factors such as line distributed capacitance and control strategies, in very special cases, the positive-sequence composite impedance may be approximately equal to 0. In this case, the characteristics of the positive-sequence composite impedance will be similar when a fault occurs within or outside the zone.

[0064] By analyzing the positive-sequence composite impedance characteristics under different fault conditions, it is found that the positive-sequence composite impedance is approximately zero when an external fault occurs. However, when an internal fault occurs, the positive-sequence composite impedance is not equal to zero in most cases. Based on the difference in positive-sequence composite impedance characteristics between internal and external faults, a first protection criterion is constructed; that is, based on the above analysis results, a first protection criterion is constructed.

[0065] The first protection criterion includes setting a protection threshold value corresponding to the positive sequence comprehensive impedance, and determining whether it is an in-zone fault or an out-of-zone fault through the following discriminant formula.

[0066] |Z eq1 |>K set (8)

[0067] Among them, |Z eq1 | represents the positive-sequence composite impedance modulus of the outgoing line to be evaluated, K set The protection threshold value K is calculated using the following expression to determine the protection threshold value corresponding to the positive sequence composite impedance. set :

[0068] K set =K rel K z |z1|l (9)

[0069] Among them, K set K represents the protection threshold value corresponding to the positive-sequence composite impedance. rel Let K be the reliability coefficient. rel =1.1; |z1| is the impedance modulus per unit length of the transmission line to be evaluated, in Ω / km, and its value is related to the actual transmission line parameters to be evaluated; l is the length of the transmission line to be evaluated (km), and its value is related to the actual length of the transmission line to be evaluated; K z The composite impedance coefficient is taken as K, considering that in most cases the composite impedance is much greater when the fault occurs within the zone than when the fault occurs outside the zone. z =0.1. In this example, the impedance modulus per unit length of the line |z1| = 0.4Ω, the line length l = 100km, and the protection threshold value K set =4.4.

[0070] The first protection criterion includes the following protection logic: If the absolute value of the calculated positive sequence composite impedance of the outgoing line to be evaluated is greater than the protection threshold value, the protection is identified as an intra-zone fault. If the absolute value of the calculated positive sequence composite impedance of the outgoing line to be evaluated is less than or equal to the protection threshold value, the protection is identified as an extra-zone fault or an intra-zone failure to operate, requiring further differentiation between intra-zone and extra-zone faults.

[0071] Based on the constructed first protection criterion, a first discrimination is performed to determine whether it is an external or internal fault.

[0072] If the absolute value of the positive sequence composite impedance of the output line to be evaluated is less than or equal to the protection threshold value, the protection is judged as an external fault or an internal failure to operate. At this time, it is necessary to further distinguish whether it is an external fault or an internal failure to operate, so as to enter the active control loop to determine whether it is an external fault or an internal fault.

[0073] In one specific implementation, the relay protection device operates when the protection determines that the fault is within the zone.

[0074] In another specific implementation, when the protection is determined to be an external fault or an internal failure to operate, the protection action is not executed, and the active control phase is entered.

[0075] It should be noted that the above is only an optional example and should not be construed as a limitation of the present invention.

[0076] Next, in step S103, when it is determined that the active control loop has been entered, the fault state is changed by changing the reference values ​​of relevant parameters in the inner loop of the new energy power supply.

[0077] When a short circuit fault occurs, the reference value of the inner loop current of the new energy power supply is changed. Adjusting the phase of the positive sequence short-circuit current on the new energy side changes the fault state.

[0078] When a short-circuit fault occurs on the grid-connected transmission line of a new energy source, a low-voltage ride-through strategy is adopted. The control command value of the positive sequence current of the converter is expressed by the following expression:

[0079]

[0080] Among them, U p1 P is the per-unit value of the positive sequence voltage at the grid connection point of the new energy source; P is the reference value of the converter's output power; I max This is the maximum current withstand value of the converter; These represent the d-axis and q-axis reference values ​​of the positive-sequence short-circuit current on the renewable energy side in the dq rotating coordinate system, respectively. The phasor expression for the positive-sequence short-circuit current on the renewable energy side after a fault is:

[0081]

[0082] In the formula, For the positive sequence short-circuit current on the new energy side; I N The rated current of the new energy power supply; θ u1 This refers to the positive sequence voltage phase at the point where the new energy source is connected to the grid. Angle in the dq rotating coordinate system

[0083] It should be noted that the dq rotating coordinate system (also known as the dq0 coordinate system or the Park coordinate system) is a coordinate system used in motor control and power electronics for analyzing and controlling AC motors (such as permanent magnet synchronous motors (PMSM) and induction motors (IM). Specifically, it transforms the AC quantities (current and voltage that vary sinusoidally with time) in the three-phase stationary coordinate system (abc coordinate system) into a two-phase rotating coordinate system (dq coordinate system) that rotates synchronously with the motor rotor. This converts the AC quantities into DC quantities, greatly simplifying the design of the control system.

[0084] In one specific implementation, after a fault occurs, the system undergoes a first protection check to determine if it has entered the active control phase. This involves combining active control of the wind turbine's grid-side converter to adjust the fault state and further determine whether the fault is within or outside the designated area. As can be seen from the above analysis, The phase of the positive sequence voltage at the new energy grid connection point and Regarding this, by adjusting the current reference value Adjustment angle of value This, in turn, regulates the positive sequence short-circuit current on the new energy side. The phase. Phase changes also affect the amplitude and phase changes of other electrical quantities, thus altering the fault state. If a fault fails to operate within the protection zone, the active control mechanism can change the original balance state, creating conditions for correct protection operation. When an external fault occurs, the positive sequence fault components of the voltage and current on both sides of the transmitting line still satisfy the electrical quantity relationships in step S101, preventing false operation outside the protection zone. Therefore, the active control mechanism can further distinguish between internal and external faults, thereby improving protection reliability.

[0085] Optionally, the original command value (i.e., the original control command value) of the positive sequence current of the output line to be evaluated is adjusted to a specified value, maintained for a specified time, and then adjusted back to the original command value. The specified time is 20ms to 25ms, preferably 5ms. This active control adjustment time enables rapid fault clearing and improves protection speed.

[0086] In one specific implementation, the time of the first protection judgment is t=20ms, the time of the start of active control is t=20ms, and the time of the second protection judgment is t=25ms.

[0087] It should be noted that the above is only an optional example and should not be construed as limiting the present invention.

[0088] For the active control adjustment range, when a phase-to-phase nonmetallic fault occurs, the positive sequence voltage drop at the fault point is less than half of the voltage amplitude before the fault. Based on the calculation method for the converter's positive sequence current control command value, at this time... This means that while the renewable energy source provides reactive power support, it still generates active power. In this situation, the positive sequence current control command value still has room for adjustment. During active control, the original control command value of the positive sequence current can be adjusted. Adjust to Will Adjust to I max The two boundary values, 0 and 0, can meet the requirements of reactive power support for new energy power sources and can change the fault state as much as possible, making it deviate from the original fault state, thus creating conditions for the correct operation of the protection.

[0089] In one specific implementation, when the first protection detection indicates an external fault, no protection action is performed. Instead, an active control signal is issued, and the converter on the renewable energy power grid side enters the active control phase, adjusting the original control command value of the positive sequence current to... The duration is 5ms, after which it switches back to the original instruction value, and the active control phase ends.

[0090] Preferably, during active control, voltage sampling data and current sampling data at the protection installation points on both sides of the transmission line to be evaluated are collected in real time, and the fundamental frequency components of voltage and current are calculated.

[0091] Based on the calculated voltage fundamental frequency component and current fundamental frequency component, the positive sequence fault components of voltage and current at the protection installation points on both sides of the transmission line to be evaluated are calculated.

[0092] During the execution of the active control strategy, voltage and current data on both sides of the line are collected in real time. Based on the sampled data, the positive-sequence comprehensive impedance Z is calculated using the positive-sequence voltage fault component and the positive-sequence current fault component. eq1 The calculation method for the positive sequence composite impedance is consistent with that described in step S101.

[0093] It is important to note that during control strategy switching, the switching operations of power electronic devices inject a large number of broadband harmonics and high-frequency transient components into the system. These non-power frequency interferences will severely contaminate the power frequency components of the voltage and current sampling signals, leading to a decrease in the extraction accuracy of the positive sequence fault components of voltage and current. The positive sequence composite impedance calculated based on the contaminated data will have a large deviation, and may also cause incorrect judgments by the protection system (false tripping or failure to trip).

[0094] To eliminate harmonic interference and ensure calculation accuracy, a power frequency component extraction step was added before calculating the positive sequence fault components of voltage, current, and positive sequence composite impedance.

[0095] Specifically, a second-order Butterworth low-pass filter is used to preprocess the acquired original voltage and current sampling sequences to separate the power frequency fundamental component.

[0096] It should be noted that the selection of filters is based on two requirements: filtering performance and filtering delay. On the one hand, the selected filters can effectively suppress major harmonics above the fundamental frequency. On the other hand, compared with high-order filters, the phase delay introduced by the second-order structure is smaller, which meets the strict requirements of relay protection for speed and avoids the protection action speed being affected by filtering delay.

[0097] In this example, the filter cutoff frequency fc is set to 1.02 to 1.05 times the fundamental power frequency f0 (51Hz to 52.5Hz). This ensures that the power frequency signal passes through with an attenuation of less than 0.5dB, reducing amplitude distortion and achieving significant suppression of nearest-neighbor higher harmonics. The filter transfer function is:

[0098]

[0099] Where H(s) represents the filter transfer function, the behavior of a second-order low-pass filter, s represents the dynamic characteristics of the system used to analyze the system in the complex frequency domain; fc represents the cutoff frequency; w c ω represents the angular frequency, which is another way to characterize the cutoff frequency fc. c =2πf c .

[0100] The transfer function is transformed into the following discrete difference equation using the bilinear transformation method:

[0101] y[n]=b0x[n]+b1x[n-1]+b2x[n-2]-a1y[n-1]-a2y[n-2](13)

[0102] Where y[n] represents the output sequence, which is the pure power frequency fundamental component; n represents the current sampling time; x[n], x[n-1], x[n-2] represent the current input sample value, the previous historical input sample value, and the historical input sample value before that; y[n], y[n-1], y[n-2] represent the current output value, the previous historical output value, and the historical output value before that; b0, b1, b2, a1, a2 are pre-calculated coefficients determined by fc and the sampling rate fs, respectively; x[n] represents the voltage sampling sequence or the current sampling sequence at the current sampling time. Applying the above discrete difference equation to each voltage sampling point and current sampling point, the output sequence y[n] is the pure power frequency fundamental component.

[0103] During active control, the voltage fundamental frequency component and current fundamental frequency component of the above-mentioned filtered output are used to replace the original sampling points to calculate the positive sequence fault components of voltage and current, thereby calculating a high-precision positive sequence composite impedance.

[0104] It should be noted that the method for calculating the positive sequence composite impedance here is roughly the same as the method for calculating the positive sequence composite impedance in step S101. The difference is that the voltage and current are filtered before calculating the positive sequence composite impedance, so the calculated result is more accurate.

[0105] It should be noted that the above is only an optional example and should not be construed as a limitation of the present invention.

[0106] Next, in step S104, the positive sequence composite impedance of the transmission line to be evaluated during the main control process is calculated, and a second discrimination is performed to determine whether the relay protection device has been activated.

[0107] The positive sequence comprehensive impedance value after a fault occurs in the transmission line to be evaluated is calculated by using the calculated positive sequence voltage fault component and positive sequence current fault component.

[0108] The second discrimination is performed using the calculated positive sequence comprehensive impedance value after a fault occurs in the transmission line to be evaluated. Specifically, the calculated positive sequence comprehensive impedance value after a fault occurs in the transmission line to be evaluated is compared with the protection action threshold value to determine the fault type and the corresponding operation action.

[0109] If the absolute value of the positive sequence comprehensive impedance is greater than the protection threshold, it is determined to be an internal fault, and the protection will operate, i.e., the relay protection device will perform the protection action; if the absolute value of the positive sequence comprehensive impedance is still less than the protection action threshold, it is determined to be an external fault, and the protection will not operate, i.e., the relay protection device will not perform the protection action.

[0110] Considering that the sensitivity of the current differential protection decreases or even fails to operate when a phase-to-phase fault occurs, a simulation verification is conducted using a phase-to-phase fault as an example to verify the effectiveness of the present invention.

[0111] In one specific implementation, when a two-phase short-circuit fault occurs between phases outside the zone at point f1 on the new energy side of the AC transmission line, the transition resistance Rf = 0Ω. Figure 6 , Figure 7 This shows the positive sequence composite impedance modulus |Z| corresponding to the occurrence of a two-phase-to-phase short-circuit fault outside the zone at point f1 on the new energy side of the AC transmission line. eq1 |. Among them, Figure 6 This is an example diagram showing the calculation results after filtering and preprocessing the voltage and current sampling data collected when a two-phase short-circuit fault occurs outside the zone at point f1 on the new energy side of the AC transmission line. Figure 7 This is an example diagram showing the calculation results of voltage and current sampling data collected when a two-phase short-circuit fault occurs outside the zone at point f1 on the new energy side of the AC transmission line, without filtering preprocessing.

[0112] like Figure 6 As shown, 10ms after the fault, the positive sequence composite impedance magnitude stabilized at 0.24Ω, which is less than the protection action threshold value K. set =4.4, the protection is judged as an external fault or an internal failure to operate. Therefore, when t is 1.02s, the active control loop is entered, and when t = 1.025s, the active control loop ends. During the active control period, the positive sequence composite impedance modulus is still approximately equal to 0Ω. At t = 1.0248s, |Z eq1 |=0.663Ω, which is less than the protection action threshold value K set The protection system identifies the fault as occurring outside the designated area; if this is correct, the protection system will not activate. For example... Figure 7 As shown, the positive sequence composite impedance magnitude |Z| 20ms after the fault. eq1 |and Figure 6 The values ​​are consistent, but the positive-sequence composite impedance magnitude is larger during active control. When t is 1.0248s, |Z eq1 |=1.163Ω, although less than the protection action threshold value K set The protection system correctly identifies the fault as an external fault and does not operate. However, compared to using a filtering algorithm, the protection sensitivity is reduced when the filtering algorithm is not used.

[0113] When a two-phase short-circuit fault occurs at point f2 on the new energy side of the AC transmission line, the transition resistance Rf = 0Ω. Figure 8 This shows the positive sequence composite impedance modulus |Z| corresponding to the occurrence of a two-phase-to-phase short-circuit fault at point f2 on the new energy side of the AC transmission line. eq1 |. For example Figure 8 As shown, during the 20ms period after the fault, the positive sequence composite impedance magnitude is much greater than the protection action threshold. When t is 1.02s, |Z eq1The current is 589.25Ω, which is greater than the protection action threshold. The protection system identifies the fault as within the protection zone and operates correctly.

[0114] When a two-phase short-circuit fault occurs at point f2 on the new energy side of the AC transmission line, the transition resistance Rf = 200Ω. Figure 9 , Figure 10 This shows the positive sequence composite impedance modulus |Z| corresponding to the occurrence of a two-phase-to-phase short-circuit fault at point f2 on the new energy side of the AC transmission line. eq1 |. Among them, Figure 9 This is a schematic diagram of the calculation results after filtering and preprocessing the voltage and current sampling data collected when a two-phase phase-to-phase short-circuit fault occurs at point f2 on the new energy side of the AC transmission line. Figure 10 This is a schematic diagram illustrating the calculation results of voltage and current sampling data collected when a two-phase phase-to-phase short-circuit fault occurs at point f2 on the new energy side of the AC transmission line, without filtering. For example... Figure 9 As shown, at t = 1.02ms, the positive sequence composite impedance magnitude is 0.148Ω, which is less than the protection action threshold. The protection is judged as either an external fault or a failure to operate within the protection zone. Therefore, at t = 1.02ms, the active control loop is initiated; at t = 1.025ms, the active control loop ends; and at t = 1.0248s, |Z eq1 |=8.22Ω, which is greater than the protection action threshold. The protection is judged as failing to operate within the zone, and the protection operates correctly. For example Figure 10 As shown, the positive sequence composite impedance magnitude |Z 20ms after the fault eq1 |and Figure 9 Consistent, during active control, at t = 1.0248s, |Z eq1 |=15.03Ω, which is greater than the protection action threshold. The protection is judged as failing to operate within the zone, and the protection is operating correctly.

[0115] When a two-phase short-circuit fault occurs at point f3 on the new energy side of the AC transmission line, the transition resistance Rf = 0Ω. Figure 11 , 12 This shows the positive sequence composite impedance modulus |Z| corresponding to the occurrence of a two-phase interphase short-circuit fault outside the zone at point f3 on the new energy side of the AC transmission line. eq1 |. Among them, Figure 11 This is a schematic diagram showing the calculation results after filtering and preprocessing of voltage and current sampling data collected when a two-phase short-circuit fault occurs outside the zone at point f3 on the new energy side of the AC transmission line. Figure 12 This is a schematic diagram illustrating the calculation results of voltage and current sampling data collected when a two-phase phase-to-phase short-circuit fault occurs at point f3 on the new energy side of the AC transmission line, without prior filtering or preprocessing. For example... Figure 11As shown, the positive sequence composite impedance magnitude stabilizes at 0.127Ω 10ms after the fault, which is less than the protection action threshold. The protection is judged as an external fault or an internal failure to operate. Therefore, when t = 1.02ms, the active control loop is entered, and when t = 1.025ms, the active control loop ends. During the active control period, the positive sequence composite impedance magnitude is still approximately equal to 0Ω. When t = 1.0248ms, |Z eq1 |=0.794Ω, which is less than the protection action threshold. The protection is identified as an external fault, and the protection function is correct and does not operate. For example... Figure 12 As shown, the positive sequence composite impedance magnitude |Z|20ms after the fault eq1 |and Figure 6 The values ​​are consistent, but the positive-sequence composite impedance magnitude is larger during active control. When t = 1.0248s, |Z eq1 |=1.516Ω, although less than the protection action threshold, the protection is judged as an external fault and does not operate correctly. However, compared with the use of the filtering algorithm, the protection sensitivity is reduced when the filtering algorithm is not used.

[0116] Through the above simulation verification, this invention addresses the problem of protection misjudgment caused by the similarity of fault characteristics inside and outside the zone under special circumstances. It introduces an active control link, adopts a filtering algorithm, and changes the fault state by adjusting the control strategy of the new energy power source, thereby improving the protection sensitivity and reliability. It solves the problem of insufficient sensitivity of current differential protection when phase-to-phase faults occur in the grid-connected transmission lines of new energy sources, and eliminates the situation of protection failure to operate through the active control method.

[0117] It should be noted that the above is only an optional example and should not be construed as a limitation of the present invention.

[0118] Compared with existing technologies, this invention utilizes the different characteristics of the positive-sequence comprehensive impedance calculated from the electrical quantities on both sides of the renewable energy grid-connected transmission line during faults inside and outside the fault zone for discrimination. To address the problem of protection misjudgment caused by the similarity of fault characteristics inside and outside the fault zone in special circumstances, an active control loop is introduced. By adjusting the control strategy of the renewable energy power source to change the fault state, it assists the protection in making accurate judgments. The protection criterion is constructed using the difference in positive-sequence comprehensive impedance characteristics during faults inside and outside the fault zone, improving protection sensitivity and reliability. This solves the problem of insufficient sensitivity of current differential protection when phase-to-phase faults occur on renewable energy grid-connected transmission lines, and eliminates the situation of protection failure to operate through active control.

[0119] Example 2

[0120] The following are system embodiments of the present invention, which can be used to execute the method embodiments of the present invention. For details not disclosed in the system embodiments of the present invention, please refer to the method embodiments of the present invention.

[0121] Figure 13This is a schematic diagram of an example of a new energy grid-connected transmission line protection system according to the present invention.

[0122] The following will refer to Figure 13 The new energy grid-connected transmission line protection system 300 is described below. The new energy grid-connected transmission line protection system 300 implements the new energy grid-connected transmission line protection method described in Embodiment 1 of the present invention.

[0123] The new energy grid-connected transmission line protection system 300 includes a calculation module 310, a first discrimination module 320, an active control module 330, and a second discrimination module 340.

[0124] In one specific embodiment, the calculation module 310 calculates the positive-sequence comprehensive impedance of the transmission line to be evaluated using the positive-sequence voltage and current fault components at the protection installation points on both sides of the new energy transmission line and the positive-sequence impedance of the line. The first discrimination module 320 performs a first discrimination based on the calculated positive-sequence comprehensive impedance of the transmission line to be evaluated to determine whether to enter the active control phase. When the active control module 330 determines that it has entered the active control phase, it changes the fault state by altering the reference values ​​of relevant parameters within the inner loop of the new energy power supply. The second discrimination module 340 calculates the positive-sequence comprehensive impedance of the transmission line to be evaluated during the main control processing and performs a second discrimination to determine whether the relay protection device operates.

[0125] According to an optional implementation, the first discrimination based on the calculated positive sequence comprehensive impedance of the outgoing line to be evaluated to determine whether to enter the active control loop includes: constructing a first protection criterion based on the difference in positive sequence comprehensive impedance characteristics when there is a fault inside or outside the zone; and performing a first discrimination based on the constructed first protection criterion to determine whether it is an external or internal fault, and further determining whether to enter the active control loop.

[0126] According to the optional implementation, when it is determined that the active control link is entered, the fault state is changed by changing the reference value of the relevant parameters in the inner loop of the new energy power supply. This includes: adjusting the original command value of the positive sequence current of the transmission line to be evaluated to a specified value, and after a specified time, adjusting it back to the original command value. The specified time is 20ms to 25ms.

[0127] According to the optional implementation method, when a short circuit fault occurs, the phase of the positive sequence short circuit current on the new energy side is adjusted by changing the reference value of the inner loop current of the new energy power source, thereby changing the fault state.

[0128] According to the optional implementation method, during active control, voltage sampling data and current sampling data of the output line to be evaluated are collected in real time, and the fundamental frequency components of voltage and current are calculated.

[0129] According to an optional implementation, based on the calculated voltage fundamental frequency component and current fundamental frequency component, the positive-sequence voltage fault component and positive-sequence current fault component of the transmission line to be evaluated are calculated. The positive-sequence composite impedance value after a fault occurs in the transmission line to be evaluated is then calculated using the calculated voltage and current positive-sequence fault components.

[0130] According to the optional implementation method, the positive sequence comprehensive impedance value after the fault occurs in the transmission line to be evaluated is used for the second discrimination. Specifically, the positive sequence comprehensive impedance value after the fault occurs in the transmission line to be evaluated is compared with the protection action threshold value to determine the fault type and whether the relay protection device has been activated.

[0131] It should be noted that, due to Figure 13 The protection method for new energy grid-connected transmission lines implemented by the protection system for new energy grid-connected transmission lines is the same as... Figure 1 The protection methods for new energy grid-connected transmission lines in the examples are largely the same, therefore, the descriptions of the same parts have been omitted.

[0132] Figure 14 This is a schematic diagram of an embodiment of an electronic device according to the present invention.

[0133] like Figure 14 As shown, the electronic device is embodied in the form of a general-purpose computing device. There can be one or more processors working collaboratively. This invention also does not preclude distributed processing, meaning that processors can be distributed across different physical devices. The electronic device of this invention is not limited to a single entity, but can also be the sum of multiple physical devices.

[0134] The memory stores a computer-executable program, typically machine-readable code. The computer-readable program can be executed by the processor to enable the electronic device to perform the method of the present invention, or at least some steps of the method.

[0135] The memory includes volatile memory, such as random access memory (RAM) and / or cache memory, and may also be non-volatile memory, such as read-only memory (ROM).

[0136] Optionally, in this embodiment, the electronic device further includes an I / O interface for exchanging data with external devices. The I / O interface can represent one or more of several bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus using any of the various bus structures.

[0137] It should be understood that Figure 14The electronic device shown is merely one example of the present invention, and the electronic device of the present invention may also include elements or components not shown in the above examples. For example, some electronic devices also include display units such as displays, and some electronic devices also include human-computer interaction elements such as buttons and keyboards. Any electronic device capable of executing a computer-readable program in memory to implement the method of the present invention or at least some steps of the method can be considered as an electronic device covered by the present invention.

[0138] From the above description of the embodiments, those skilled in the art will readily understand that the exemplary embodiments described herein can be implemented by software, or by combining software with necessary hardware. Therefore, as... Figure 15 As shown, the technical solution according to the embodiments of the present invention can be embodied in the form of a software product. The software product can be stored in a non-volatile storage medium (such as a CD-ROM, USB flash drive, mobile hard drive, etc.) or on a network, and includes several commands to cause a computing device (such as a personal computer, server, or network device, etc.) to execute the above-described method according to the embodiments of the present invention.

[0139] The software product may employ any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of readable storage media (a non-exhaustive list) include: electrical connections with one or more wires, portable disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof.

[0140] The computer-readable storage medium may include data signals propagated in baseband or as part of a carrier wave, carrying readable program code. Such propagated data signals may take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. The readable storage medium may also be any readable medium other than a readable storage medium, capable of transmitting, propagating, or transmitting programs for use by or in connection with a command execution system, apparatus, or device. The program code contained on the readable storage medium may be transmitted using any suitable medium, including but not limited to wireless, wired, optical fiber, RF, etc., or any suitable combination thereof.

[0141] Program code for performing the operations of this invention can be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java and C++, and conventional procedural programming languages ​​such as C or similar languages. The program code can execute entirely on the user's computing device, partially on the user's device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0142] The aforementioned computer-readable medium carries one or more programs, which, when executed by a device, enable the computer-readable medium to implement the data interaction method of this disclosure.

[0143] Those skilled in the art will understand that the above modules can be distributed in the device as described in the embodiments, or they can be modified accordingly and placed in one or more devices that are unique to this embodiment. The modules in the above embodiments can be combined into one module, or they can be further divided into multiple sub-modules.

[0144] Through the description of the above embodiments, those skilled in the art will readily understand that the exemplary embodiments described herein can be implemented by software or by combining software with necessary hardware. Therefore, the technical solutions of the embodiments of the present invention can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (such as a CD-ROM, USB flash drive, portable hard drive, etc.) or on a network, including several commands to cause a computing device (such as a personal computer, server, mobile terminal, or network device, etc.) to execute the methods according to the embodiments of the present invention.

[0145] It should be noted that the above detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0146] In the detailed description above, reference has been made to the accompanying drawings, which form part of this document. In the drawings, similar symbols typically identify similar parts unless the context otherwise indicates otherwise. The illustrated embodiments described in the detailed specification, drawings, and claims are not intended to be limiting. Other embodiments may be used and other changes may be made without departing from the spirit or scope of the subject matter presented herein.

[0147] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A protection method for a new energy grid-connected transmission line, characterized in that, include: The positive sequence comprehensive impedance of the transmission line to be evaluated is calculated by using the positive sequence voltage and current fault components at the protection installation points on both sides of the new energy transmission line and the positive sequence impedance of the line. Based on the calculated positive sequence composite impedance of the outgoing line to be evaluated, a first discrimination is made to determine whether to enter the active control stage. When it is determined that the active control phase has been entered, the fault state is changed by altering the reference values ​​of relevant parameters in the inner loop of the new energy power supply. Calculate the positive sequence composite impedance of the transmission line to be evaluated during the main control period, and perform a second discrimination to determine whether the relay protection device has operated.

2. The method for protecting new energy grid-connected transmission lines according to claim 1, characterized in that, The first discrimination is performed based on the calculated positive-sequence composite impedance of the outgoing line to be evaluated to determine whether to enter the active control stage, including: The first protection criterion is constructed based on the difference in positive sequence comprehensive impedance characteristics during faults inside and outside the zone. Based on the constructed first protection criterion, a first discrimination is performed to determine whether it is an external or internal fault, and then it is further determined to enter the active control stage.

3. The method for protecting new energy grid-connected transmission lines according to claim 1, characterized in that, When it is determined that the active control phase has been entered, the fault state is changed by altering the reference values ​​of relevant parameters within the inner loop of the new energy power supply, including: The original command value of the positive sequence current of the output line to be evaluated is adjusted to a specified value and maintained for a specified time, and then adjusted back to the original command value. The specified time is 20ms to 25ms.

4. The method for protecting new energy grid-connected transmission lines according to claim 1, characterized in that, When a short-circuit fault occurs, the phase of the positive-sequence short-circuit current on the new energy side is adjusted by changing the reference value of the inner loop current of the new energy power source, thereby changing the fault state.

5. The method for protecting new energy grid-connected transmission lines according to claim 1 or 3, characterized in that, The term includes: During active control, voltage and current sampling data of the output line to be evaluated are collected in real time, and the fundamental frequency components of voltage and current are calculated.

6. The method for protecting new energy grid-connected transmission lines according to claim 5, characterized in that, Based on the calculated voltage fundamental frequency component and current fundamental frequency component, calculate the voltage positive sequence fault component and current positive sequence fault component of the transmission line to be evaluated. The positive sequence comprehensive impedance value after a fault occurs in the transmission line to be evaluated is calculated by using the calculated positive sequence voltage fault component and positive sequence current fault component.

7. The method for protecting new energy grid-connected transmission lines according to claim 6, characterized in that, The second discrimination is performed using the calculated positive sequence comprehensive impedance value after a fault occurs in the transmission line to be evaluated. Specifically, the calculated positive sequence comprehensive impedance value after a fault occurs in the transmission line to be evaluated is compared with the protection action threshold value to determine the fault type and whether the relay protection device has been activated.

8. A protection system for a new energy grid-connected transmission line, characterized in that, The method for protecting new energy grid-connected transmission lines according to any one of claims 1 to 7, wherein the new energy grid-connected transmission line protection system comprises: The calculation module uses the positive sequence voltage and current fault components at the protection installation points on both sides of the new energy transmission line and the positive sequence impedance of the line to calculate the positive sequence comprehensive impedance of the transmission line to be evaluated. The first discrimination module performs a first discrimination based on the calculated positive sequence comprehensive impedance of the outgoing line to be evaluated, in order to determine whether to enter the active control stage; The active control module, when it determines that it is entering the active control phase, changes the reference values ​​of relevant parameters in the inner loop of the new energy power supply to change the fault state. The second discrimination module calculates the positive sequence comprehensive impedance of the transmission line to be evaluated during the main control process and performs a second discrimination to determine whether the relay protection device has been activated.

9. The new energy grid-connected transmission line protection system according to claim 8, characterized in that, include: The first protection criterion is constructed based on the difference in positive sequence comprehensive impedance characteristics during faults inside and outside the zone. Based on the constructed first protection criterion, a first discrimination is performed to determine whether it is an external or internal fault, and then it is further determined to enter the active control stage.

10. The new energy grid-connected transmission line protection system according to claim 8, characterized in that, include: The original command value of the positive sequence current of the output line to be evaluated is adjusted to a specified value and maintained for a specified time, and then adjusted back to the original command value. The specified time is 20ms to 25ms.

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