Method and system for identifying new energy power supply under asymmetric fault based on sequence impedance difference

Abstract

The method and system for identifying new energy power supply under asymmetric fault based on sequence impedance difference, the protection device collects three-phase current and three-phase voltage in real time, and calculates to obtain negative sequence current voltage, zero sequence current voltage and positive sequence current voltage; after the protection is started, the asymmetric fault type is judged; when the ground fault occurs, the modulus difference and impedance angle difference of the negative sequence impedance and the zero sequence impedance are compared to judge the fault characteristics of the power supply behind the protection; when the phase-to-phase fault occurs, the modulus difference of the negative sequence impedance and the positive sequence impedance is compared, and the impedance angle difference of the negative sequence impedance and the positive sequence impedance and the difference between the line positive sequence sensitive angle are combined to judge the fault characteristics of the power supply behind the protection; it is determined that the power supply behind the protection is a new energy power supply, the identification of the new energy power supply under asymmetric fault based on sequence impedance difference is realized, and the safety and reliability of the relay protection under the new energy access to the power system are improved.

Description

Technical Field

[0001] This invention belongs to the field of new energy power source fault identification technology, and relates to a method and system for identifying new energy power sources under asymmetrical faults based on sequence impedance differences. Background Technology

[0002] Currently, efforts are being accelerated to build a new power system with new energy sources as the mainstay. The proportion of new energy sources such as photovoltaics, wind power, and energy storage in the power system is constantly increasing, resulting in the long-term coexistence of new energy power sources and conventional synchronous generator power sources. However, when a fault occurs in the power grid, the transient output characteristics of the two power sources differ significantly.

[0003] A power system with a conventional synchronous generator exhibits transient constant voltage source characteristics and is a linear system, which can be approximated as a system with subtransient reactance X. d The voltage source. In the event of a power grid system fault, the relay protection analyzes the electromagnetic transient process through the superposition principle of linear systems and approximates that the positive sequence impedance Z1 and the negative sequence impedance Z2 are the same, which meets the requirements of field applications.

[0004] New energy power sources are considered voltage-controlled current sources, and a large number of power sources, loads, energy storage devices with diverse characteristics are connected to the existing power system through power electronic equipment interfaces. During grid faults, if wind power, photovoltaic, and other new energy power sources still disconnect from the system after protection tripping, it will lead to a significant reduction in active power input to the grid, increasing the difficulty of restoring the entire power system. Therefore, it is necessary to maintain uninterrupted grid connection for a certain period when grid faults cause voltage drops at the grid connection point, which is beneficial for system recovery. During low-voltage ride-through, to ensure the safety of grid-connected inverter devices, the magnitude of the grid-connected current needs to be limited, and a control strategy to suppress negative sequence current is adopted to achieve three-phase balance. Power electronic equipment exhibits strong controllability and nonlinear dynamic response characteristics during faults, resulting in limited short-circuit current, altered positive-sequence and negative-sequence equivalent circuit characteristics and voltage source characteristics, and the superposition principle of linear systems no longer applies, affecting phase selection and direction determination in asymmetrical faults. During faults within the zone, the original relay protection is difficult to adapt to the requirements of the underlying new energy power station; therefore, new strategies for new energy power sources have been added.

[0005] The same relay protection device employs different strategies for conventional synchronous generator systems and new energy power systems. Because the location of the fault point is not fixed, it is impossible to determine whether the source of the protection is a new energy power source by manually adjusting the protection settings. Therefore, there is an urgent need for a solution for online identification of the underlying new energy power source by the relay protection, providing protection components with corresponding strategies. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method and system for identifying new energy power sources under asymmetrical faults based on sequence impedance differences. This method is used to identify new energy power sources affected by power electronic device constraints and negative sequence suppression control strategies online. Since the fault transient output characteristics of synchronous power sources and new energy power sources differ significantly, this invention provides a way to rationally apply corresponding protection components, which is beneficial to improving the safety and reliability of relay protection under the access of new energy to the power system.

[0007] The present invention adopts the following technical solution.

[0008] The method for identifying new energy power sources under asymmetric faults based on sequence impedance differences includes the following steps:

[0009] Step 1: The protection device collects the three-phase current and three-phase voltage in real time, and calculates the negative sequence current voltage, zero sequence current voltage, and positive sequence current voltage.

[0010] Step 2: After the protection is started, the type of asymmetrical fault is determined based on the magnitude of the zero-sequence current voltage and the negative-sequence current voltage. If it is determined to be a ground fault, proceed to step 3; if it is determined to be a phase-to-phase fault, proceed to step 4; otherwise, return to step 1.

[0011] Step 3: In the event of a ground fault, calculate and compare the magnitude difference and impedance angle difference between the negative sequence impedance and the zero sequence impedance based on the zero sequence current voltage and the negative sequence current voltage to determine the fault characteristics of the power supply behind the protection. If the fault is determined to be a new energy characteristic, proceed to step 5; otherwise, return to step 1.

[0012] Step 4: In the event of a phase-to-phase fault, calculate and compare the difference in magnitude between the negative-sequence impedance and the positive-sequence impedance based on the negative-sequence current and voltage and the positive-sequence current and voltage. Combine the difference between the impedance angle of the negative-sequence impedance and the positive-sequence impedance and the line positive-sequence sensitivity angle to determine the fault characteristics of the power supply behind the protection. If it is determined to be a new energy characteristic, proceed to step 5; otherwise, return to step 1.

[0013] Step 5: Determine if the power source behind the protection is a new energy source, thus enabling the identification of new energy sources under asymmetrical faults based on sequence impedance differences.

[0014] Preferably, step 1 specifically includes:

[0015] Step 1.1: The protection device collects and stores the three-phase current and three-phase voltage in real time;

[0016] Step 1.2: The collected voltage and current at each sampling point are processed through a digital filtering algorithm to obtain the filtered power frequency components, i.e., the current and voltage vectors of each phase, which are the three-phase current vectors. Three-phase voltage vector

[0017] Step 1.3: Using the symmetrical component method, convert the current and voltage vectors of each phase into sequence components and store them. Each sequence component is the positive sequence current. Negative sequence current Zero-sequence current Positive sequence voltage Negative sequence voltage Zero-sequence voltage

[0018] Preferably, in step 2, the following conditions are met: or Under certain conditions, if and The asymmetrical fault type is then identified as a ground fault;

[0019] satisfy or If the conditions are not met and The asymmetrical fault type is then identified as a phase-to-phase fault.

[0020] in, I is the magnitude of the negative sequence current. 2set This is the threshold for negative sequence current. U is the magnitude of the negative sequence voltage. 2set This is the threshold for negative sequence voltage. I is the magnitude of the zero-sequence current. 0set This is the threshold for zero-sequence current. U is the magnitude of the zero-sequence voltage. 0set This is the threshold for zero-sequence voltage.

[0021] Preferably, in step 3, the formulas for calculating the negative-sequence impedance Z2 and the zero-sequence impedance Z0 are:

[0022]

[0023]

[0024] In the formula, |Z2| and |Z0| are the negative sequence impedance magnitude and the zero sequence impedance magnitude, respectively;

[0025] θ2 and θ0 are the negative sequence impedance angle and the zero sequence impedance angle, respectively;

[0026] These are negative sequence voltage and negative sequence current, respectively.

[0027] These are zero-sequence voltage and zero-sequence current, respectively.

[0028] Preferably, in step 3, if |Z2|>K1|Z0|, and If the new energy characteristics are met, proceed to step 5; otherwise, proceed to the following judgment:

[0029] If |θ2-θ0|>θ 20set ,and If the new energy characteristics are met, proceed to step 5; otherwise, return to step 1.

[0030] Wherein, |Z2| and |Z0| are the negative sequence impedance magnitude and the zero sequence impedance magnitude, respectively;

[0031] K1 is the ratio of the magnitudes of the negative-sequence impedance to the zero-sequence impedance;

[0032] For negative sequence current, I 2set This is the threshold for negative sequence current;

[0033] θ2 and θ0 are the negative sequence impedance angle and the zero sequence impedance angle, respectively;

[0034] θ 20set It is the threshold value for the angle difference between the negative sequence impedance angle and the zero sequence impedance angle.

[0035] Preferably, the value of K1 is 8.

[0036] θ 20set The value is 60°.

[0037] Preferably, in step 4, the formula for calculating the positive sequence impedance Z1 is:

[0038]

[0039] In the formula, |Z1| is the positive sequence impedance magnitude, and θ1 is the positive sequence impedance angle;

[0040] and These are the positive-sequence current surge and the positive-sequence voltage surge, respectively.

[0041]

[0042]

[0043] In the formula, and These are the positive sequence current and positive sequence voltage at the current moment, respectively;

[0044] and These are the positive sequence current and positive sequence voltage before the second wave, respectively.

[0045] Preferably, in step 4, if |Z2|>K2|Z1|, and If the new energy characteristics are met, proceed to step 5; otherwise, proceed to the following judgment:

[0046] like and or and If the new energy characteristics are met, proceed to step 5; otherwise, return to step 1.

[0047] Wherein, |Z2| and |Z1| are the negative sequence impedance magnitude and the positive sequence impedance magnitude, respectively;

[0048] For negative sequence current, I 2set This is the threshold for negative sequence current;

[0049] K2 is the ratio of the magnitudes of the negative-sequence impedance to the positive-sequence impedance;

[0050] This is the positive sequence sensitivity angle of the line, and the protection setting.

[0051] θ 21set It is the threshold value for the difference between the negative sequence impedance angle and the positive sequence impedance angle and the positive sequence sensitivity angle of the line.

[0052] Preferably, the value of K2 is 3;

[0053] θ 21set The value is 60°.

[0054] A system for identifying new energy power sources under asymmetric faults based on sequence impedance differences includes:

[0055] The analog sampling and storage module is used by the protection device to collect three-phase current and three-phase voltage in real time, and calculate the negative sequence current voltage, zero sequence current voltage and positive sequence current voltage.

[0056] The asymmetrical fault type discrimination module, after the protection is started, determines the asymmetrical fault type based on the magnitude of the zero-sequence current voltage and the negative-sequence current voltage. If it is determined to be a ground fault, it enters the ground fault fault characteristic discrimination module; if it is determined to be a phase-to-phase fault, it enters the phase-to-phase fault characteristic discrimination module; otherwise, it returns to the analog quantity sampling and storage module.

[0057] The fault characteristic discrimination module during ground faults is used to calculate and compare the difference in magnitude and impedance angle between the negative sequence impedance and the zero sequence impedance based on the zero sequence current voltage and negative sequence current voltage during ground faults, and to determine the fault characteristics of the power supply behind the protection. When the fault is determined to be a new energy characteristic, it enters the output module; otherwise, it returns to the analog quantity sampling and storage module.

[0058] The fault characteristic discrimination module for phase-to-phase faults is used to calculate and compare the difference in magnitude between negative-sequence impedance and positive-sequence impedance based on negative-sequence current and voltage and positive-sequence current and voltage. Combining the difference between the impedance angle of negative-sequence impedance and positive-sequence impedance and the positive-sequence sensitivity angle of the line, it determines the fault characteristics of the power supply behind the protection. When it is determined to be a new energy characteristic, it enters the output module; otherwise, it returns to the analog quantity sampling and storage module.

[0059] The output module is used to output the determination that the power supply behind the protection is a new energy power source, realizing the identification of the new energy power source under asymmetrical faults based on sequence impedance differences.

[0060] The beneficial effects of this invention are compared with those of the prior art:

[0061] When a ground fault occurs, the protection device compares the magnitude and impedance angle differences between the zero-sequence impedance and the negative-sequence impedance; it can identify the fault characteristics of the new energy power supply when the negative-sequence current is small or large.

[0062] When an ungrounded phase-to-phase fault occurs, the protection device compares the magnitudes of the negative-sequence impedance and the positive-sequence transient impedance, calculates the difference between the impedance angles of the negative-sequence impedance and the positive-sequence sensitivity angle of the line, and uses the comparison results of the magnitude difference and impedance angle difference to identify the fault characteristics of the new energy power supply when the negative-sequence current is small or large.

[0063] Online identification of fault characteristics of the underlying power source as a new energy source provides a way to rationally apply corresponding protection components, which is conducive to improving the safety and reliability of relay protection under the access of new energy to the power system. Attached Figure Description

[0064] Figure 1 This is a schematic diagram of a method for identifying new energy power sources under asymmetric faults based on sequence impedance differences.

[0065] Figure 2 This is a flowchart of a method for identifying new energy power sources under asymmetric faults based on sequence impedance differences. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0067] First, the following technical terms used in this invention will be explained or defined:

[0068] Protection Initiation: Protection initiation elements are used to monitor whether a fault has occurred in the power system. Upon confirmation of a fault, the power supply to the protection trip relay is turned on, and the protection fault handling procedure is initiated. Protection initiation elements include those for sudden current changes, zero-sequence auxiliary initiation, static stability failure, and weak feeder initiation. Based on the current and voltage collected by the protection system, the initiation conditions of the initiation elements are calculated and determined. If any initiation element operates, the protection function is activated and self-held until the entire system resets.

[0069] Asymmetrical faults: Asymmetrical faults include single-phase ground faults, two-phase ground faults, and phase-to-phase faults, but do not include three-phase short-circuit faults. Among them, single-phase ground faults and two-phase ground faults are ground faults.

[0070] Figure 1 This is a schematic diagram of the identification method for new energy power sources under asymmetrical faults based on sequence impedance differences, as proposed in this invention.

[0071] The M side of the line is powered by a new energy source and is equipped with line protection device 1. The N side of the line is powered by a synchronous machine and is equipped with line protection device 2.

[0072] Protection device 1 collects the three-phase AC current I on the M side. a I b and I c Three-phase AC voltage U a U b and U c .

[0073] Correspondingly, protection device 2 collects the three-phase AC current and voltage on the N side.

[0074] For protection device 1, when a fault occurs at point F1, the power supply behind it is the synchronous machine power supply, and the fault current provided by the synchronous machine power supply is collected. When faults occur at points F2 and F3, the power supply behind it is the new energy power supply, and the fault current provided by the new energy power supply is collected.

[0075] For protection device 2, when points F1 and F2 fail, the power supply behind it is the synchronous machine power supply, and the fault current provided by the synchronous machine power supply is collected. When point F3 fails, the power supply behind it is the new energy power supply, and the fault current provided by the new energy power supply is collected.

[0076] Figure 2 This is a schematic flowchart illustrating the steps of the new energy power source identification method based on sequence impedance difference under asymmetrical faults according to the present invention. Figure 2 As shown, Embodiment 1 of the present invention provides a method for identifying asymmetrical faults in new energy power sources based on sequence impedance differences. In a preferred but non-limiting embodiment of the present invention, the method includes the following steps:

[0077] Step 1: The protection device collects the three-phase current and three-phase voltage in real time, and calculates the negative sequence current voltage, zero sequence current voltage, and positive sequence current voltage.

[0078] Step 1.1: The protection device collects and stores the sampled values ​​of three-phase current and three-phase voltage in real time;

[0079] More preferably, the protection device typically samples at a frequency of 1200Hz to obtain and store the sampled values ​​of the three-phase AC current and voltage analog quantities at each sampling point in real time.

[0080] The storage time is no less than 4 cycles, used for calculating sudden changes in current and voltage, as well as protection recording, etc.

[0081] Step 1.2: Calculate the current and voltage vectors of each phase in real time based on the three-phase current and three-phase voltage collected in Step 1.1.

[0082] The collected voltage and current at each sampling point are processed through a digital filtering algorithm to obtain the filtered power frequency components, which are the three-phase current vectors. Three-phase voltage vector

[0083] Step 1.3: Calculate and store the sequence components of current and voltage in real time based on the current and voltage vectors of each phase.

[0084] The three-phase current is converted into sequence components using the symmetrical component method, namely, the positive sequence current. Negative sequence current Zero-sequence current The three-phase voltage is converted into its sequence components, namely, the positive sequence voltage. Negative sequence voltage Zero-sequence voltage

[0085] The storage time for the calculation results of positive sequence current and positive sequence voltage is no less than 2 cycles, which is used to calculate the positive sequence transient impedance.

[0086] Step 2: After the protection is started, the type of asymmetrical fault is determined based on the magnitude of the zero-sequence current voltage and the negative-sequence current voltage. If it is determined to be a ground fault, proceed to step 3; if it is determined to be a phase-to-phase fault, proceed to step 4; otherwise, return to step 1.

[0087] satisfy or Under certain conditions, if and The asymmetrical fault type is then identified as a ground fault;

[0088] satisfy or If the conditions are not met and The asymmetrical fault type is then identified as a phase-to-phase fault.

[0089] in, I is the magnitude of the negative sequence current. 2set This is the threshold for negative sequence current. U is the magnitude of the negative sequence voltage. 2set This is the threshold for negative sequence voltage. I is the magnitude of the zero-sequence current. 0set This is the threshold for zero-sequence current. U is the magnitude of the zero-sequence voltage. 0set This is the threshold for zero-sequence voltage.

[0090] Step 3: In the event of a ground fault, calculate and compare the magnitude difference and impedance angle difference between the negative sequence impedance and the zero sequence impedance based on the zero sequence current voltage and the negative sequence current voltage. Determine the fault characteristics of the power supply behind the protection. If it is determined to be a new energy characteristic, proceed to step 5; otherwise, return to step 1.

[0091] Step 3.1: Calculate the negative sequence impedance Z2 and the zero sequence impedance Z0, then proceed to step 3.2.

[0092] Negative-sequence impedance needs to be calculated using negative-sequence current and voltage at the same time, and zero-sequence impedance needs to be calculated using zero-sequence current and voltage at the same time.

[0093] The formulas for calculating the negative-sequence impedance Z2 and the zero-sequence impedance Z0 are:

[0094]

[0095]

[0096] In the formula, |Z2| and |Z0| are the negative sequence impedance magnitude and the zero sequence impedance magnitude, respectively;

[0097] θ2 and θ0 are the negative sequence impedance angle and the zero sequence impedance angle, respectively.

[0098] Step 3.2, if |Z2|>K1|Z0|, and If the new energy characteristics are met, proceed to step 5; otherwise, proceed to step 3.3.

[0099] Using the negative-sequence impedance and zero-sequence impedance at the same time, compare the magnitudes of the negative-sequence impedance and the zero-sequence impedance. If the magnitude of the negative-sequence impedance is greater than K1 times the magnitude of the zero-sequence impedance and the magnitude of the negative-sequence current is small, it is judged to meet the characteristics of new energy.

[0100] K1 is the ratio of the magnitudes of the negative-sequence impedance to the zero-sequence impedance.

[0101] Considering the characteristics of negative sequence impedance and zero sequence impedance in synchronous machine power supply faults, the value of K1 should be greater than 3, with 8 being the preferred value.

[0102] Step 3.3, if |θ2-θ0|>θ 20set ,and If the new energy characteristics are met, proceed to step 5; otherwise, return to step 1.

[0103] θ 20set It is the threshold value for the angle difference between the negative sequence impedance angle and the zero sequence impedance angle.

[0104] Compare the difference between the negative-sequence impedance angle and the zero-sequence impedance angle. When the difference between the negative-sequence impedance angle and the zero-sequence impedance angle is large, i.e., θ 20set If the angle is greater than 30°, preferably 60°, and the negative sequence current magnitude is large, it is judged to meet the characteristics of new energy.

[0105] Step 4: In the event of a phase-to-phase fault, calculate and compare the difference in magnitude between the negative-sequence impedance and the positive-sequence impedance based on the negative-sequence current and voltage and the positive-sequence current and voltage. Combine the difference between the impedance angle of the negative-sequence impedance and the positive-sequence impedance and the line positive-sequence sensitivity angle to determine the fault characteristics of the power supply behind the protection. If it is determined to be a new energy characteristic, proceed to step 5; otherwise, return to step 1.

[0106] Step 4.1, calculate the positive sequence current abrupt change. and positive sequence voltage mutation Proceed to step 4.2.

[0107] Positive sequence current abrupt change and positive sequence voltage mutation The formula is as follows:

[0108]

[0109]

[0110] In the formula, and These are the positive sequence current and positive sequence voltage at the current moment, respectively;

[0111] and These are the positive sequence current and positive sequence voltage before the second wave, respectively.

[0112] Step 4.2: Calculate the negative sequence impedance Z2 and the positive sequence impedance Z1, then proceed to step 4.3.

[0113] Negative-sequence impedance needs to be calculated using negative-sequence current and voltage at the same time, and positive-sequence impedance needs to be calculated using positive-sequence current and voltage abrupt changes at the same time.

[0114] The positive sequence impedance Z1 is calculated according to the following relationship:

[0115]

[0116] In the formula, |Z1| is the positive sequence impedance magnitude, and θ1 is the positive sequence impedance angle.

[0117] The calculation method for negative sequence impedance is shown in step 3.1.

[0118] Step 4.3, if |Z2|>K2|Z1|, and Proceed to step 5; otherwise, proceed to step 4.4.

[0119] Using the negative-sequence impedance and positive-sequence impedance at the same time, compare the magnitudes of the negative-sequence impedance and positive-sequence impedance. If the magnitude of the negative-sequence impedance is greater than K2 times the magnitude of the positive-sequence impedance and the magnitude of the negative-sequence current is small, it is judged to meet the characteristics of new energy.

[0120] K2 is the ratio of the magnitudes of the negative-sequence impedance to the positive-sequence impedance.

[0121] Considering that negative sequence impedance and positive sequence impedance are basically the same in synchronous machine power supply faults, the value of K2 should be greater than 1.5, and the preferred value is 3.

[0122] Step 4.4, if and or and Proceed to step 5; otherwise, return to step 1.

[0123] θ is the positive sequence sensitivity angle of the line, and θ is the protection setting. 21set It represents the difference between the negative sequence impedance angle and the positive sequence impedance angle and the positive sequence sensitivity angle of the line.

[0124] The negative sequence impedance angle or the positive sequence impedance angle is greater than the positive sequence impedance angle of the line by θ. 21set Furthermore, the negative sequence current magnitude is large, indicating that it meets the characteristics of new energy sources.

[0125] The positive sequence sensitivity angle of high-voltage line protection is approximately 80°, θ 21set The value should be greater than 30°, preferably 60°.

[0126] Step 5: Determine if the power source behind the protection is a new energy source, thus enabling the identification of new energy sources under asymmetrical faults based on sequence impedance differences.

[0127] When the new energy power source criteria in steps 3 and 4 are met, the protection is determined to be backed by a new energy power source.

[0128] Embodiment 2 of the present invention provides a system for identifying new energy power sources under asymmetrical faults based on sequence impedance differences. The system includes:

[0129] The analog sampling and storage module is used by the protection device to collect three-phase current and three-phase voltage in real time, and calculate the negative sequence current voltage, zero sequence current voltage and positive sequence current voltage.

[0130] The asymmetrical fault type discrimination module, after the protection is started, determines the asymmetrical fault type based on the magnitude of the zero-sequence current voltage and the negative-sequence current voltage. If it is determined to be a ground fault, it enters the ground fault fault characteristic discrimination module; if it is determined to be a phase-to-phase fault, it enters the phase-to-phase fault characteristic discrimination module; otherwise, it returns to the analog quantity sampling and storage module.

[0131] The fault characteristic discrimination module during ground faults is used to calculate and compare the difference in magnitude and impedance angle between the negative sequence impedance and the zero sequence impedance based on the zero sequence current voltage and negative sequence current voltage during ground faults, and to determine the fault characteristics of the power supply behind the protection. When the fault is determined to be a new energy characteristic, it enters the output module; otherwise, it returns to the analog quantity sampling and storage module.

[0132] The fault characteristic discrimination module for phase-to-phase faults is used to calculate and compare the difference in magnitude between negative-sequence impedance and positive-sequence impedance based on negative-sequence current and voltage and positive-sequence current and voltage. Combining the difference between the impedance angle of negative-sequence impedance and positive-sequence impedance and the positive-sequence sensitivity angle of the line, it determines the fault characteristics of the power supply behind the protection. When it is determined to be a new energy characteristic, it enters the output module; otherwise, it returns to the analog quantity sampling and storage module.

[0133] The output module is used to output the determination that the power supply behind the protection is a new energy power source, realizing the identification of the new energy power source under asymmetrical faults based on sequence impedance differences.

[0134] In practical implementation, the above modules involve:

[0135] Analog signal sampling and storage: The protection device collects and stores the three-phase current and three-phase voltage samples at the installation location for at least four cycles; the power frequency three-phase current vector is obtained through filtering. Three-phase voltage vector

[0136] Calculation of positive-sequence, negative-sequence, and zero-sequence current-voltage vectors: The positive-sequence components of the three-phase currents are obtained through transformation. Negative order components Zero-order component The positive sequence components of the three-phase voltages are obtained by transformation. Negative order components Zero-order component Stores 2 cycles and Calculate the positive sequence current surge after the fault occurs. and positive sequence voltage mutation Calculate the positive-sequence impedance, negative-sequence impedance, and zero-sequence impedance of the power supply. The positive-sequence impedance is the calculated result of the sudden change in voltage and current after the fault.

[0137] Comparison of negative sequence impedance and zero sequence impedance: When there is zero sequence current and zero sequence voltage, and negative sequence current or negative sequence voltage at the same time, it is judged as a ground fault. Compare the magnitudes of negative sequence impedance and zero sequence impedance, and calculate the difference in impedance angle.

[0138] Comparison of negative sequence impedance and positive sequence transient impedance: When there is no zero sequence current or zero sequence voltage, but there is negative sequence current or negative sequence voltage, it is judged as a two-phase short circuit. Compare the magnitudes of negative sequence impedance and positive sequence impedance, and calculate the difference between the impedance angles of negative sequence impedance and positive sequence impedance and the positive sequence sensitivity angle of the line.

[0139] Distinguishing characteristics of new energy power sources: During a ground fault, if the negative sequence impedance is much greater than the zero sequence impedance and the negative sequence current is small, it is judged as a new energy power source fault characteristic. If the negative sequence impedance angle differs greatly from the zero sequence impedance angle and the negative sequence current is large, it is judged as a new energy power source fault characteristic. During a two-phase short circuit, if the negative sequence impedance is much greater than the positive sequence impedance and the negative sequence current is small, it is judged as a new energy power source fault characteristic. If the negative sequence impedance angle or the positive sequence impedance angle is much greater than the positive sequence sensitivity angle of the line and the negative sequence current is large, it can be judged as a new energy power source fault.

[0140] The beneficial effect of this invention is that, compared with the prior art, it can identify the fault characteristics of new energy power sources under asymmetrical faults when the negative sequence current is small or large.

[0141] When a ground fault occurs, the protection device compares the magnitude and impedance angle differences between the zero-sequence impedance and the negative-sequence impedance.

[0142] When a phase-to-phase fault occurs without grounding, the protection device compares the magnitudes of the negative-sequence impedance and the positive-sequence transient impedance, calculates the difference between the impedance angles of the negative-sequence impedance and the positive-sequence sensitivity angle of the line, and uses the comparison results of the magnitude difference and the impedance angle difference.

[0143] Online identification of fault characteristics of the underlying power source as a new energy source provides a way to rationally apply corresponding protection components, which is conducive to improving the safety and reliability of relay protection under the access of new energy to the power system.

[0144] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0145] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination thereof. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0146] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0147] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for identifying new energy power sources under asymmetrical faults based on sequence impedance differences, characterized in that: The method includes the following steps: Step 1: The protection device collects the three-phase current and three-phase voltage in real time, and calculates the negative sequence current voltage, zero sequence current voltage, and positive sequence current voltage. Step 2: After the protection is started, the type of asymmetrical fault is determined based on the magnitude of the zero-sequence current voltage and the negative-sequence current voltage. If it is determined to be a ground fault, proceed to step 3; if it is determined to be a phase-to-phase fault, proceed to step 4; otherwise, return to step 1. Step 3: In the event of a ground fault, calculate and compare the magnitude difference and impedance angle difference between the negative sequence impedance and the zero sequence impedance based on the zero-sequence current voltage and negative sequence current voltage. Determine the fault characteristics of the power supply behind the protection. If the fault is determined to be a new energy source, proceed to step 5; otherwise, return to step 1. (Negative sequence impedance) Z 2 and zero sequence impedance Z The formula for calculating 0 is: = / = ∠ = / = ∠ In the formula, and These are the negative-sequence impedance magnitude and the zero-sequence impedance magnitude, respectively. 2 and 0 represents the negative sequence impedance angle and the zero sequence impedance angle, respectively; , These are negative sequence voltage and negative sequence current, respectively. These are zero-sequence voltage and zero-sequence current, respectively. like > K 1 ,and < I 2set If it meets the characteristics of new energy, proceed to step 5; otherwise, proceed to the following judgment: like > ,and > I 2set If it meets the characteristics of new energy, proceed to step 5; otherwise, return to step 1. and These are the negative-sequence impedance magnitude and the zero-sequence impedance magnitude, respectively. K 1 represents the ratio of the magnitudes of the negative-sequence impedance to the zero-sequence impedance; It is a negative sequence current. I 2set This is the threshold for negative sequence current; 2 and 0 represents the negative sequence impedance angle and the zero sequence impedance angle, respectively; 20set This is the threshold value for the angle difference between the negative sequence impedance angle and the zero sequence impedance angle; Step 4: In the event of a phase-to-phase fault, calculate and compare the magnitude difference between the negative-sequence impedance and the positive-sequence impedance based on the negative-sequence current and voltage, and the positive-sequence current and voltage. Combine this with the difference between the impedance angles of the negative-sequence and positive-sequence impedances and the line's positive-sequence sensitivity angle to determine the fault characteristics of the power source behind the protection. If the fault is determined to be a new energy source, proceed to Step 5; otherwise, return to Step 1. (Positive-sequence impedance) Z The calculation formula is: = / = ∠ In the formula, This is the positive sequence impedance magnitude. 1 is the positive sequence impedance angle; Δ and △ These are the positive-sequence current surge and the positive-sequence voltage surge, respectively. = - = - In the formula, and These are the positive sequence current and positive sequence voltage at the current moment, respectively; and These are the positive sequence current and positive sequence voltage two cycles before the wavefront; like > K 2 ,and < I 2set If it meets the characteristics of new energy, proceed to step 5; otherwise, proceed to the following judgment: like( - > and > I 2set ,or( - > and > I 2set If the result meets the characteristics of a new energy source, proceed to step 5; otherwise, return to step 1. and These are the negative-sequence impedance magnitude and the positive-sequence impedance magnitude, respectively. It is a negative sequence current. I 2set This is the threshold for negative sequence current; K 2 represents the ratio of the magnitudes of the negative-sequence impedance to the positive-sequence impedance; This is the positive sequence sensitivity angle of the line, and the protection setting. 21set It is the threshold value of the difference between the negative sequence impedance angle and the positive sequence impedance angle and the positive sequence sensitivity angle of the line; Step 5: Determine if the power source behind the protection is a new energy source, thus enabling the identification of new energy sources under asymmetrical faults based on sequence impedance differences.

2. The method for identifying new energy power sources under asymmetrical faults based on sequence impedance differences according to claim 1, characterized in that: Step 1 specifically includes: Step 1.1: The protection device collects and stores the three-phase current and three-phase voltage in real time; Step 1.2: The collected voltage and current at each sampling point are processed through a digital filtering algorithm to obtain the filtered power frequency components, i.e., the current and voltage vectors of each phase, which are the three-phase current vectors. , , Three-phase voltage vector , , ; Step 1.3: Using the symmetrical component method, convert the current and voltage vectors of each phase into sequence components and store them. Each sequence component is the positive sequence current. Negative sequence current Zero-sequence current Positive sequence voltage Negative sequence voltage Zero-sequence voltage .

3. The method for identifying new energy power sources under asymmetrical faults based on sequence impedance differences according to claim 1, characterized in that: In step 2, the following conditions are met. > I 2set or > U 2set Under certain conditions, if > I 0set and > U 0set If so, the asymmetrical fault type is identified as a ground fault; satisfy > I 2set or > U 2set If the conditions are not met > I 0set and > U 0set If so, the asymmetrical fault type is identified as a phase-to-phase fault; in, This represents the magnitude of the negative sequence current. I 2set This is the threshold for negative sequence current. This represents the magnitude of the negative sequence voltage. U 2set This is the threshold for negative sequence voltage. The magnitude of the zero-sequence current. I 0set This is the threshold for zero-sequence current. The magnitude of the zero-sequence voltage. U 0set This is the threshold for zero-sequence voltage.

4. The method for identifying new energy power sources under asymmetrical faults based on sequence impedance differences according to claim 1, characterized in that: K The value of 1 is 8; 20set The value is 60°.

5. The method for identifying new energy power sources under asymmetrical faults based on sequence impedance differences according to claim 1, characterized in that: K The value of 2 is 3; 21set The value is 60°.

6. A system for identifying new energy power sources under asymmetrical faults based on sequence impedance differences, used to implement the method described in any one of claims 1-5, characterized in that: The system includes: The analog sampling and storage module is used by the protection device to collect three-phase current and three-phase voltage in real time, and calculate the negative sequence current voltage, zero sequence current voltage and positive sequence current voltage. The asymmetrical fault type discrimination module, after the protection is started, determines the asymmetrical fault type based on the magnitude of the zero-sequence current voltage and the negative-sequence current voltage. If it is determined to be a ground fault, it enters the ground fault fault characteristic discrimination module; if it is determined to be a phase-to-phase fault, it enters the phase-to-phase fault characteristic discrimination module; otherwise, it returns to the analog quantity sampling and storage module. The fault characteristic discrimination module during ground faults is used to calculate and compare the difference in magnitude and impedance angle between the negative sequence impedance and the zero sequence impedance based on the zero sequence current voltage and negative sequence current voltage during ground faults, and to determine the fault characteristics of the power supply behind the protection. When the fault is determined to be a new energy characteristic, it enters the output module; otherwise, it returns to the analog quantity sampling and storage module. The fault characteristic discrimination module for phase-to-phase faults is used to calculate and compare the difference in magnitude between negative-sequence impedance and positive-sequence impedance based on negative-sequence current and voltage and positive-sequence current and voltage. Combining the difference between the impedance angle of negative-sequence impedance and positive-sequence impedance and the positive-sequence sensitivity angle of the line, it determines the fault characteristics of the power supply behind the protection. When it is determined to be a new energy characteristic, it enters the output module; otherwise, it returns to the analog quantity sampling and storage module. The output module is used to output the determination that the power supply behind the protection is a new energy power source, realizing the identification of the new energy power source under asymmetrical faults based on sequence impedance differences.

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