Power grid adaptive direction distance protection method and system based on apparent power supply

Abstract

The invention discloses a power grid adaptive direction distance protection method and system based on an apparent power supply, and the method comprises the steps: building a home terminal dynamic equivalent apparent power supply model based on a voltage phasor and a current phasor obtained through measurement at a protection installation part, and enabling the model to be defined by two key parameters, namely, an apparent power supply voltage amplitude and equivalent impedance; three-phase voltage and three-phase current at a protection installation position are collected in real time, positive sequence voltage is calculated through a symmetrical component method, and the real-time phase difference between the dynamic equivalent apparent power source at the terminal and the three-phase voltage and the three-phase current is calculated; comparing the real-time phase difference with a preset action interval; when the real-time phase difference is in a set action interval, judging that a fault is a forward fault, and starting a protection action; and otherwise, a reverse fault is determined, and latching protection output is carried out. According to the method, the dependence of traditional protection on fixed source impedance parameters is effectively overcome, multiple control strategies such as unit power factor control, low voltage ride through and negative sequence current suppression of the wind turbine generator are adaptively compatible, and the interference of harmonic waves and power fluctuation on protection is remarkably suppressed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power system relay protection, and particularly relates to a power grid adaptive directional distance protection method and system based on apparent power source, especially an adaptive protection technology for phase-to-phase fault in a direct-drive permanent magnet synchronous generator wind farm grid-connected system. BACKGROUND

[0002] With the accelerated global energy transformation, large-scale centralized access of new energy such as wind power and photovoltaic to power grids, the power system presents a significant power electronic characteristic. As the key channel for new energy power transmission, the safe and stable operation of high-voltage and ultra-high-voltage transmission lines is crucial to energy supply. Distance protection is most widely used in high-voltage and ultra-high-voltage transmission lines due to its mature principle and stable performance, but its traditional design concept is mainly based on the characteristics of power systems dominated by synchronous generators, which is difficult to adapt to the complex working conditions after the access of new energy.

[0003] In recent years, there have been several cases of incorrect operation of distance protection due to the access of new energy, such as the incorrect operation of 220kV line protection in Qian'an, Jilin, and the incorrect operation of 500kV AC out-of-line distance protection in the flexible HVDC station of the Rudong offshore wind power transmission project. The action logic of traditional distance protection is highly dependent on the inertia characteristics of the power source, while new energy power sources such as wind power and photovoltaic inverters have characteristics such as non-constant internal potential and significant weak feedback characteristics. The output characteristics after a fault are dominated by control strategies, which directly leads to the failure of the mechanism discrimination logic relied on by traditional protection, making it unable to adapt to the complex fault characteristics after the access of new energy.

[0004] Existing improvement schemes for distance protection have obvious limitations: traditional circular characteristic distance protection has poor anti-interference ability; adaptive distance protection relies on communication systems to transmit real-time parameters, with high algorithm complexity; parameter identification-based schemes are limited by the transparency of new energy unit parameters; time-domain protection, polygon impedance characteristic protection, etc. require high-precision sampling equipment, and the setting calculation is complex, which are difficult to meet the protection needs of power electronic systems. At the same time, existing research focuses on power source impedance analysis relying on system source characteristics, and there is a lack of research on apparent impedance reflecting the inherent characteristics of the line. The protection research for power electronic systems is mostly based on the superposition principle, and the exploration of equivalent modeling methods is limited, making it difficult to establish an effective fault discrimination logic.

[0005] Therefore, in view of the adaptability defects of the traditional distance protection in the new energy high proportion access scene, it is urgent to research a new phase comparison type distance protection scheme suitable for the power electronic regulation environment, to improve the sensitivity and reliability of the distance protection in the power electronic system by reconstructing the theoretical basis and action logic of the protection criterion. This has important significance for guaranteeing the safe grid connection of new energy, improving the protection performance of transmission lines, and promoting the progress of relay protection technology of power system, and can provide key technical support for the safe and stable operation of new type power system. SUMMARY

[0006] The application discloses a new phase comparison type distance protection scheme suitable for power electronic regulation, and aims to solve the misoperation and refusal of the traditional distance protection in the new energy high proportion access scene due to the change of internal potential, weak feeding characteristics and power angle relationship, and improve the sensitivity and reliability of the distance protection in the power electronic system.

[0007] To solve the above technical problems, the technical scheme adopted by the application is as follows: The first aspect of the application discloses a power grid adaptive directional distance protection method based on an apparent power source, comprising the following steps: S1: based on the voltage phase sequence and the current phase sequence measured at the protection installation place, a dynamic equivalent apparent power source model of the local end is established, the model is defined by two key parameters of an apparent power source voltage amplitude and an equivalent impedance ; S2: real-time acquisition of three-phase voltage and three-phase current at the protection installation place, calculation of positive sequence voltage by the symmetrical component method calculation of the dynamic equivalent apparent power source of the local end and the real-time phase difference between the two ; S3: comparison of the real-time phase difference with a preset action interval; when is in the set action interval, it is determined as a forward fault, and the protection action is started; otherwise, it is determined as a reverse fault, and the protection output is locked.

[0008] Further preferably, in S1, the apparent power source voltage amplitude is set as a constant unit value; the impedance angle of the equivalent impedance is constrained to be equal to the positive sequence impedance angle of the power grid line.

[0009] Further preferably, the constant unit value is 1.1 .

[0010] Further preferably, In S1, the new energy or grid-side power supply system is equivalent to a dynamic apparent power source wherein the apparent power phase angle and the equivalent impedance amplitude The dynamic equivalent apparent power source changes in real time with the change of the grid topology, the injection of new energy, and the switching of the control strategy of the new energy unit.

[0011] Further preferably, The local end is equivalent to a single-port network at the protection installation, wherein the dynamic equivalent apparent power source is used as a single-port network power source, and the internal impedance angle of the single-port network is equal to the internal impedance angle, which is equal to the positive sequence impedance angle of the protected line; The voltage and current collected at the protection installation are substituted into the single-port network circuit equation, and the dynamic equivalent apparent power impedance amplitude and the phase angle ε of the dynamic equivalent apparent power source are solved under the constraint conditions of the apparent power voltage amplitude and the internal impedance angle .

[0012] Further preferably, The phase angle ε of the dynamic equivalent apparent power source is calculated according to the following formula:

[0013] wherein, , are the voltage and current phase quantities measured at the protection installation, respectively, and Z L is the full-length positive sequence impedance of the line.

[0014] Further preferably, In S2, the real-time phase difference is: .

[0015] Further preferably, The set action interval is .

[0016] The second aspect of the present application discloses a grid adaptive directional distance protection system based on an apparent power source using the distance protection method, comprising an electrical quantity acquisition module, a dynamic equivalent apparent power source model module, a real-time phase difference calculation module, and an action criterion module. The electrical quantity acquisition module acquires the three-phase voltage and three-phase current at the protection installation in real time. The dynamic equivalent apparent power source model module establishes a dynamic equivalent apparent power source model of the local end based on the voltage and current phase quantities measured at the protection installation. The real-time phase difference calculation module calculates the positive sequence voltage through a symmetrical component method Calculate the dynamic equivalent apparent power at the local end With The real-time phase difference between them ; The action criterion module compares the real-time phase difference With the preset action interval;When In the set action interval, it is determined as a forward fault, and the protection action is started;Otherwise, it is determined as a reverse fault, and the protection output is locked.

[0017] The third aspect of the application discloses a computer readable storage medium, which stores a computer program, and the program is executed by a processor to realize the steps of the power grid adaptive directional distance protection method based on apparent power. The fourth aspect of the application discloses a computer device, which comprises a memory, a processor and a computer program stored in the memory;The processor executes the computer program to realize the steps of the power grid adaptive directional distance protection method based on apparent power.

[0018] By adopting the above technical scheme, the application has the following beneficial effects: First, the line voltage and current signals are collected in real time, and E aps And the voltage phase angle epsilon are calculated through the dynamic new energy dynamic equivalent power model, and the improved phase comparison criterion is input to identify the direction, and the distance protection I, II and III section setting range is combined to realize the fast fault removal.

[0019] Second, different fault types, transition resistances, new energy control strategies and interference environments are simulated, and the results show that the scheme can accurately identify the fault direction in all scenarios without rejection and misoperation. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The apparent power equivalent circuit diagram of the direct drive wind turbine; Figure 2 The critical power angle voltage phasor diagram; Figure 3 The phase comparison distance protection direction determination diagram; Figure 4 The flow chart of the power grid adaptive directional distance protection method based on apparent power; Figure 5 The positive and negative direction phasor angle difference curve of the sending end; Figure 6 The positive and negative direction phasor angle difference curve of the receiving end. DETAILED DESCRIPTION

[0021] 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, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0022] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0023] As attached Figure 4 As shown, this invention discloses a power grid adaptive directional distance protection method based on apparent power sources, specifically including the following steps: Step 1: Based on the voltage and current phasors measured at the protection installation point, establish a dynamic equivalent apparent power source model for this terminal. The model is composed of the apparent power source voltage amplitude. and equivalent impedance Two key parameters are defined; This invention proposes a phase comparison protection logic implementation mechanism, including a new energy dynamic equivalent source construction mechanism and a phase difference direction criterion generation mechanism.

[0024] The model constraints include setting the internal electromotive force amplitude to... (Constant per-unit value) to ensure numerical stability. Internal impedance angle constraint is... (Consistent with the positive sequence impedance angle of the line), preserving the inherent characteristics of the line. Under the above two constraints, the core parameter that truly changes dynamically in the model is the magnitude of the equivalent impedance. Voltage phase angle with equivalent power source .

[0025] The protection device measures the voltage phasor at the installation point in real time. and current phasor .Will , With two constraints Substitute them together into the basic circuit equations The solution is obtained by performing the following steps.

[0026] By decomposing the above phasor equation into real and imaginary parts, and eliminating the voltage phase angle ε using the sum of squares operation, a equation concerning |Z| can be derived. aps | A quadratic equation in one variable. Solving this equation yields a unique, dynamic equation under the current system state (considering all factors such as new energy injection, control strategy switching, and faults). value.

[0027] In obtaining Then, by substituting back into the equation, the voltage phase angle ε of the current equivalent power source can be calculated. Thus, a complete and dynamically adaptive equivalent source that adjusts according to the system state is obtained. and The construction is now complete. The phase angle ε of the dynamic equivalent apparent power source is calculated using the following formula:

[0028] in, , These are the voltage phasors and current phasors measured at the protection installation location, Z. L The positive sequence impedance is the total length of the line. The protection scheme of this invention is implemented through a dynamic equivalent source construction mechanism within the analysis framework of a single-port equivalent circuit. The single-port equivalent circuit defines the system structure observed from the relay installation point and obtains local electrical quantities; the dynamic equivalent source is an adaptive power supply model dynamically generated by an algorithm and injected into the circuit. Its parameters are updated in real time with the system state, thereby ensuring that the equivalent circuit accurately reflects the actual operating characteristics of the system including new energy access.

[0029] Step 2: Real-time acquisition of three-phase voltage and three-phase current at the protection installation location, and calculation of the positive sequence voltage using the symmetrical component method. Calculate the dynamic equivalent apparent power supply at this end. and Real-time phase difference between the two ; The real-time phase difference for: .

[0030] Step 3: Convert the real-time phase difference Compare with the preset action range; when When the fault is within the set operating range, it is determined to be a positive fault and the protection action is initiated; otherwise, it is determined to be a reverse fault and the protection output is blocked.

[0031] This invention proposes a design method for directional adaptive distance protection criterion based on critical power angle. Figure 2 This study reveals the voltage phasor relationship of traditional phase-comparison distance protection at the critical power angle. In traditional protection, the polarization voltage... Phase reference (such as system-side power supply) The value is fixed. As shown in the figure, when the power angle δ is 90°, there is a clear operating boundary: during a forward fault, the operating voltage... With polarization voltage The phase difference of the equivalent source voltage is exactly 90°, which is the critical operating point; when the fault is reversed, the phase difference of 90° is the critical blocking point. However, in a system with a high proportion of new energy, the equivalent source power angle δ may greatly exceed 90°, resulting in incorrect operation of the traditional protection due to the reference reference.

[0032] Figure 3 The adaptive direction criterion principle proposed in the application is demonstrated. The core innovation of the application is that the dynamic equivalent source voltage calculated in real time is used as a new adaptive phase reference to replace the fixed polarization voltage reference in the traditional protection. The protection device calculates the real-time phase difference between the positive sequence voltage at the installation point of the protection device and the positive sequence voltage of the equivalent source, and determines whether the real-time phase difference is within the preset fixed operating interval (such as -40° to 140°), to reliably distinguish between forward and reverse faults. This method fundamentally overcomes the polarization voltage pollution problem caused by changes in the power angle and fluctuations in the system strength.

[0033] The deep mechanism of the failure of the traditional protection is that, in the phase comparison type distance protection based on the polarization of the positive sequence voltage, the tracking characteristics of the polarization voltage are closely related to the system impedance parameters. The system strength ratio (wherein and are the equivalent system impedances observed from the busbars and respectively, and is the full-length impedance of the line) quantitatively characterizes the characteristics. For example, when the system impedance on the side significantly increases (i.e., the strong side system strength condition, > 5), the polarization voltage presents significant tracking characteristics of the opposite side system power , and this deviation directly distorts the phase relationship between the operating voltage and the polarization voltage, which is the key mechanism leading to incorrect operation of the traditional protection in the power electronic system. The application introduces the dynamic equivalent source , the phase of which itself contains the dynamic information of the system strength, so that the criterion has inherent adaptive ability.

[0034] As shown in Figure 3 , the phase comparison protection logic implementation mechanism adapted to the power electronic regulation of the application is shown. Key definitions and criteria: System strength definition: the application defines that when the system strength ratio , it is the weak power side (M side); is the strong power side (M side). Wherein and​​ From the busbar and The observed equivalent system impedance, The impedance is the total length of the line.

[0035] Core Action Equation: The specific action equation for the new criterion is as follows. The protection device calculates the dynamic equivalent source voltage in real time. Positive sequence voltage at the protection installation point phase difference between And perform the following judgment: like If so, it is determined to be a positive fault, and the protection is activated. or If the fault is detected, it is determined to be a reverse fault, and the protection output is immediately blocked.

[0036] The following is a simulation test verification of the above-disclosed power grid adaptive directional distance protection method based on apparent power sources disclosed in this invention.

[0037] (1) Verification at the power supply end: High-power-side scenario: Traditional protection systems are prone to malfunction in this scenario due to reverse faults. This invention, through the aforementioned operating equation, addresses the phase difference of reverse faults. Reliably isolated within the locked section, thereby achieving effective locking.

[0038] In weak power supply scenarios, traditional protection systems are prone to failing to operate under forward faults. This invention, by setting the effective operating range to -40° to 140°, covers the phase difference distribution range of forward faults under weak power supply conditions, ensuring the reliability of protection operation.

[0039] (2) Power receiving end verification: Simulations under various operating conditions demonstrate that the criterion of this invention has clear distinguishability: the phase difference of all positive faults The phase differences of all reverse faults are concentrated in the range of -140° to 40°; the phase differences of all reverse faults are strictly distributed in the complementary region of this range.

[0040] The present invention further improves the reliability of fault diagnosis through auxiliary measures, specifically as follows: By tracking and stabilizing the phase of the fundamental voltage component using a high-precision phase-locked loop (PLL), harmonic and interharmonic interference is effectively suppressed. In high-resistance grounding fault scenarios, the discrimination results of the zero-sequence direction element can be combined with the main criterion of this invention to form an AND logic, further improving the reliability of grounding fault discrimination.

[0041] Compared to the above embodiments, the topology and control components are existing technologies and will not be described in detail here.

[0042] The technical contribution of this application is as follows: (1) Dynamic equivalent source construction mechanism and phase difference direction criterion generation mechanism. The dynamic equivalent source construction mechanism is applicable to all power grid scenes at the relay protection installation place (M end or N end), whether the place is a strong power source side (such as a traditional large power grid), a weak power source side (such as a remote sea wind power sending end), or a high proportion of new energy access side (such as a wind power plant or a photovoltaic power station collection line). The core purpose is to accurately equivalent the dynamic characteristics of various power sources during a fault through a unified and adaptive model, and to provide a reliable phase reference for subsequent direction discrimination.

[0043] The model constraint conditions include that the internal electromotive force amplitude is set as (constant in per unit), ensuring numerical stability. The internal impedance angle constraint is (the same as the line positive sequence impedance angle), retaining the inherent characteristics of the line. Under the above two constraints, the core parameters of the model that truly change dynamically are the equivalent impedance amplitude and the voltage phase angle ε of the equivalent power source.

[0044] The model is implemented in a single-port equivalent circuit. Specifically, local interphase electrical quantities are collected at the relay installation place (M end or N end), taking the BC phase as an example, that is, the voltage and the current . New energy (such as direct-drive wind turbines) or complex systems are equivalent to a dynamic apparent power source , the phase angle of which is dynamically changing in real time. The fault condition is set as: the BC two-phase short circuit through the transition resistance , and the line impedance from the protection installation point to the fault point is defined as . Among them, is the positive sequence impedance of the entire line, is the fault position coefficient, which is a preset setting parameter, and the value range is (corresponding to the line I section protection range, such as α=0.8). The coefficient is used to set the protection range when calculating the operating voltage, and its value determines the length proportion of the line that the protection can reliably act on.

[0045] The protection scheme of the application is implemented through a dynamic equivalent source construction mechanism under the analysis framework of a single-port equivalent circuit. The single-port equivalent circuit is used to define the system structure observed from the relay installation place and obtain local electrical quantities. The dynamic equivalent source is an adaptive power source model dynamically generated by an algorithm and injected into the circuit, and the parameters and are updated in real time with the system state, thereby ensuring that the equivalent circuit can accurately reflect the real operating characteristics of the system with new energy access.

[0046] (2) By constructing a dynamic equivalent power source model, writing and solving the equivalent circuit equations at the measurement points, the dynamic equivalent power source parameters of the new energy source of the direct-drive wind turbine after the fault are obtained, and the polarization voltage change is calculated, thus returning the analysis process to the traditional power angle theory framework.

[0047] The protection device measures the voltage phasor at the installation point in real time. and current phasor .Will , With two constraints Substitute them together into the basic circuit equations The solution is obtained by performing the following steps.

[0048] By decomposing the above phasor equation into real and imaginary parts, and using the sum of squares operation to eliminate the voltage phase angle ε, a formula for... can be derived. The quadratic equation in one variable is given. Solving this equation yields a unique, dynamic equation under the current system state (considering all factors such as new energy injection, control strategy switching, and faults). value.

[0049] In obtaining Then, by substituting back into the equation, the voltage phase angle ε of the current equivalent power source can be calculated. Thus, a complete and dynamically adaptive equivalent source E is obtained. aps =E mag ∠ε and Z aps =∣Z aps The construction of |∣∠θ is now complete.

[0050] After a fault occurs, the protection device collects the instantaneous three-phase voltage values ​​at the protection installation location in real time. The positive-sequence voltage component is calculated by matrix transformation using the symmetric component method and decoupling. (Right now ,in ).this It is one of the reference quantities for subsequent phase comparisons.

[0051] (3) Design of an adaptive fault direction decision mechanism to achieve protection triggering based on real-time phase difference determination results: This invention aims to solve the inherent defects of traditional distance protection based on positive sequence voltage polarization in power electronic systems. The mechanism of this defect is as follows: Traditional polarization voltage U j The tracking characteristics are dominated by the grid strength ratio Kz (e.g., in a strong M-side grid, U j It will track the power supply on the opposite side E N This uncontrollable offset will distort the phase relationship with the working voltage, causing the critical action boundary to be inaccurate, resulting in false operation or failure to operate when the power angle δ>90°.

[0052] To address the aforementioned problems, this invention employs a completely different technical approach from existing technologies: using a dynamic equivalent source voltage as an adaptive polarization reference. This invention no longer uses the traditional fixed memory voltage or system power supply voltage as the polarization reference. The dynamic equivalent source voltage E is obtained through real-time calculation. aps As a new, adaptive polarization voltage, the protection device directly compares E. aps The phase difference Δθ between the voltage and the local positive sequence voltage U1 is used for discrimination, and a fixed operating range is employed: This scheme eliminates the dependence of protection criteria on volatile system impedance parameters. Regardless of changes in the system power angle or the distribution of renewable energy sources, information about the fault direction is stably mapped to E. aps Regarding the phase relationship with U1, reliable and adaptive direction discrimination can be achieved through the aforementioned fixed interval. Based on the dynamic equivalent power supply voltage phasor diagram of new energy sources, phase-to-phase short-circuit faults in new energy scenarios may cause the power angle to exceed the critical power angle, thereby obtaining the system oscillation center and polarization voltage offset law through the grid strength ratio Kz.

[0053] This application also discloses a power grid adaptive directional distance protection system based on apparent power source using the distance protection method, including an electrical quantity acquisition module, a dynamic equivalent apparent power source model module, a real-time phase difference calculation module, and an action criterion module; The electrical quantity acquisition module collects the three-phase voltage and three-phase current at the protection installation location in real time. The dynamic equivalent apparent power model module establishes a local dynamic equivalent apparent power model based on the voltage phasors and current phasors measured at the protection installation location. The real-time phase difference calculation module calculates the positive sequence voltage using the symmetrical component method. Calculate the dynamic equivalent apparent power supply at this end. and Real-time phase difference between the two ; The action criterion module will determine the real-time phase difference. Compare with the preset action range; when When the fault is within the set operating range, it is determined to be a positive fault and the protection action is initiated; otherwise, it is determined to be a reverse fault and the protection output is blocked.

[0054] Example 1: with Figure 1 The technical solution of the present invention will be described in detail using the circuit diagram shown as an example. Figure 1 The figure shown is the equivalent circuit diagram of the apparent power supply of a direct-drive fan. Figure 1 middle, For a total installed capacity of 150MW of direct-drive wind turbines, System power supply; M, N are two sides of the system bus. F1, F2 and F3, F4 are the positive and negative direction near zone fault of relay M, N, and the protection range of the I section of the distance protection is 80% of the full length of the line.

[0055] The method comprises the following steps: Step 1: Construct a dynamic equivalent apparent power model; The constructed new energy dynamic equivalent power model needs to meet the following constraint conditions: the internal electromotive force amplitude is constant 1.1 times the rated voltage; the internal impedance angle is equal to the positive sequence impedance angle of the protected line.

[0056] The equivalent circuit equation presented by the model at the fault port needs to meet the above two constraints at the same time, and the equivalent equation is: (1) In the formula, is the equivalent apparent power voltage, is the relay measured voltage phasor, is the relay measured voltage phasor; is the equivalent apparent power impedance.

[0057] 1.1 Solution of the modulus: Substitute and into the circuit equation. Separate the equation into real and imaginary parts: (2) In the formula, U r , U i is the real part and the imaginary part of the measured point voltage phasor, I r , I i is the real part and the imaginary part of the measured point current phasor, is the equivalent apparent power impedance amplitude, and θ is the line impedance angle, is the equivalent apparent power voltage amplitude, and ε is the apparent power voltage phase angle.

[0058] Arrange a quadratic equation , solve the expression, so as to obtain , the coefficients are as follows: (3) In the formula, α, β and χ are equation parameters of the equivalent apparent power impedance amplitude, which are used to solve the equivalent apparent power impedance amplitude .

[0059] 1.2 Solution of the angle of Based on the model constraints, the following simplification can be made: (4) In the formula, the impedance Z is re-derived. aps After solving, we can obtain E. aps The angle. Specifically as follows: (5) In the formula, Z L Given the positive sequence impedance of the entire line, we obtain the equivalent equation E. aps After considering the angle ε, the system with new energy access can return to the voltage phasor diagram analysis of the traditional system.

[0060] Step 2: Real-time acquisition of current and voltage at the protection installation location, and calculation of the relationship between the equivalent apparent power supply and the positive sequence voltage phase angle; like Figure 2 The figure shows the voltage phasor diagram under the apparent power source critical power angle. The phase-to-phase distance protection criterion is considered first as follows: (6) In the formula, The operating voltage, Polarization voltage, , and The measurement voltage, positive sequence voltage, and measurement current of the grounding impedance relay are... , and The measurement voltage, positive sequence voltage, and current of the phase-to-phase impedance relay are... This is the protection impedance setting value.

[0061] Considering the following expression for measuring impedance: (7) In the formula, To measure impedance for grounding distance protection, For phase-to-phase distance protection, the impedance is measured. This is the zero-sequence current compensation coefficient. To protect against the zero-sequence current measured at the installation location, the expression for the measured impedance is substituted into the distance protection criterion. The protection criterion expression is as follows: (8) In the formula, the criterion is re-expressed using measured impedance, and then the dynamic equivalent power source of the new energy source is substituted to obtain the expression: (9) In the formula, This is the equivalent apparent power supply voltage. This is the equivalent apparent power supply impedance. The operating voltage, Polarization voltage, and The positive sequence voltage and measuring current of the grounding impedance relay are given. and The positive sequence voltage and measuring current of the phase-to-phase impedance relay are given. To protect the impedance setting value To measure impedance for grounding distance protection, The impedance is measured for phase-to-phase distance protection.

[0062] The criteria are expressed using the dynamic equivalent power supply parameters of the new energy source. For a two-phase short circuit of phases B and C, the protection criteria for the phase-to-phase impedance relay are as follows: (10) The expression can be divided into angles A and B. Angle A requires in-depth analysis, while angle B is related to the location of the fault and is a constant. After re-establishing the voltage phasor diagram, the critical power angle and the operating voltage U can be obtained. op Unaffected by the access of new energy sources, the polarization voltage U j The impact of new energy sources is mainly related to the oscillation center. A power angle of 90° is the critical case, and the expression for the polarization voltage angle at this time is as follows: (11) In the formula Z M Z N E represents the impedance on the M and N sides of the system. M E N The electromotive force of the power supply on the M and N sides of the system is... A rotation factor for the added phase shift. The system power angle is denoted as , where For power grid strength K z It is very sensitive, and its expression is as follows: (12) In the formula K z For grid strength, the system impedance on the M side accounts for a high proportion of the total impedance (K z >5), polarization voltage U j Tracking E N This leads to malfunction in the opposite direction. The N-side system impedance accounts for a high proportion of the total impedance (K). z <0.5), polarization voltage U j Tracking E M This leads to failure to move in the positive direction. The above analysis shows that the reliability of the traditional direction criterion relies on a flawed assumption: the polarization voltage... The phase is stable. In fact, The phase is constrained by the grid strength ratio This is precisely the root cause of its failure.

[0063] In stark contrast, the direction criterion proposed in this invention does not depend on the volatile system impedance parameters for reliability, but rather on the operating voltage. With dynamic equivalent power supply voltage The inherent and stable phase relationship between them. Under forward and reverse fault conditions, the phase relationship between them differs fundamentally from that of conventional power supplies, which forms the solid basis for the adaptive criterion of this invention.

[0064] The orientation criterion of this invention is constructed based on the operating voltage. With dynamic equivalent power supply voltage The phase difference is used for discrimination. In the case of forward and reverse faults, the operating voltage... With dynamic equivalent power supply voltage The phase relationship between them is as follows: a) Fault in the positive direction: (13) b) Fault in the opposite direction: (14) In Chapter 1, Z k For distance protection, the measuring impedance and the operating voltage U for near-field faults are measured. op and dynamic equivalent power supply E aps With a fixed phase difference of 180°, this stable phase relationship provides a key criterion for accurately distinguishing between positive and negative faults.

[0065] After a fault occurs, the protection device collects the instantaneous three-phase voltage values ​​at the protection installation location in real time. The positive-sequence voltage component is calculated by matrix transformation using the symmetric component method and decoupling. .this It is one of the reference quantities for subsequent phase comparisons.

[0066] Step 3: Convert the real-time phase difference Compare with the preset action range; when When the fault is within the set operating range, it is determined to be a positive fault and the protection action is initiated; otherwise, it is determined to be a reverse fault and the protection output is blocked.

[0067] like Figure 3 The diagram shown is a direction determination diagram for phase-to-phase distance protection. Simulations were performed on positive and negative fault conditions in the near-zone of the power supply end M and the power receiving end N, using a unity power factor strategy and a low-voltage ride-through strategy, respectively. Through negative sequence current suppression loop control, the simulation yielded E... aps -E apsq E aps -U 1q Eaps -U1, U1-U 1q , E apsq -U 1q (q represents the electrical quantity before the fault), where E aps -U1 has a clear boundary. A new protection boundary can be designed according to the difference in the phasor, and its expression is as follows: (15) According to the newly designed standard, the calculated source voltage E APS as the reference phasor, when the angle of the voltage U1 is within the nominal range of -40° to 140°, the fault is determined to be a positive direction fault. Therefore, the complementary angle region is classified as a reverse direction fault.

[0068] The simulation results show clear and effective direction discrimination: all positive faults are always distributed in the orange-red region, while all reverse faults are only located in the blue region. This obvious spatial separation on the characteristic plane visually and quantitatively verifies the ability of the method and system to reliably distinguish the direction of positive and reverse faults under all test conditions, as shown in Figure 3 .

[0069] As shown in Figure 4 , it is a flow chart of the power grid adaptive directional distance protection method based on apparent source. In order to accurately calculate the power frequency phasor required by the protection, the system first preprocesses the sampling signal. The fundamental component is extracted by the discrete Fourier transform algorithm to generate the voltage and current phasor used for distance protection criterion calculation. This preprocessing step significantly improves the accuracy of the calculation of the fundamental component, avoids the direction discrimination error caused by transient interference, and thus enhances the reliability of the protection.

[0070] As shown in Figure 5 , it is a curve diagram of the phase angle difference of positive and reverse direction phasors at the sending end. It shows the distribution curve of the phase angle difference of different phasor combinations when a near-zone positive direction and reverse direction fault occurs at the sending end (M side). The horizontal axis of the figure is the system side impedance Z N , and the vertical axis is the phase angle difference, which compares the relationships of E aps -E apsq , E aps -U 1q , E aps -U1, U1-U 1q , E apsq -U 1q , etc. (where subscript q represents the steady-state electrical quantity before the fault). Among the many phasor relationships, the real-time phase angle difference between the dynamic apparent source electromotive force and the positive sequence voltage at the protection installation exhibits the most significant distinguishing characteristics. Under different control strategies, the E apsThe -U1 angle difference is stably distributed between two clearly separated regions with very low overlap, forming a very distinct boundary.

[0071] When a near-field positive direction fault occurs, under both unity power factor and low voltage ride-through control strategies, E aps - The phase angle difference of U1 remains stable within the range of 20° to 100°. However, when a near-field reverse fault occurs, this phase angle difference is tightly clustered within a narrow range of 162° to 178°. The phase angle differences of forward and reverse faults not only form a clear interval band of more than 60 degrees, but also exhibit low dispersion of their respective clusters, demonstrating extremely high internal consistency and external isolation.

[0072] like Figure 6 The figure shows the phasor phase angle difference curves for the forward and reverse directions at the receiving end. It illustrates the phase angle difference distribution curves for different phasor combinations when a near-field forward and reverse fault occurs at the transmitting end (N side). The horizontal axis in the figure represents the system-side impedance Z. N The vertical axis represents the phase angle difference, compared to E. aps -E apsq E aps -U 1q E aps -U1、U1-U 1q E apsq -U 1q Multiple phasor relationships are presented (where the subscript q represents the steady-state electrical quantity before the fault). Among these phasor relationships, the real-time phase angle difference between the dynamic apparent power supply electromotive force and the positive sequence voltage at the protection installation point exhibits the most significant distinguishing characteristic. Under different control strategies, the E corresponding to forward and reverse direction faults... aps The -U1 angle difference is stably distributed between two clearly separated regions with very low overlap, forming a very distinct boundary.

[0073] At the receiving end (N side), this characteristic quantity also exhibits strong resolution, but its numerical distribution differs significantly from that at the transmitting end. When a near-field positive direction fault occurs at the receiving end, E aps - The phase angle difference of U1 is distributed in the negative range of 0° to -14°; while when a reverse fault occurs, it is widely distributed in the range of -70° to -150°. Although the angle value of the receiving end is different from that of the sending end, there is still a clear safety boundary with a width of more than 50 degrees and no data overlap between the forward and reverse faults.

[0074] The application relates to the technical field of power system relay protection, and particularly relates to adaptive protection technology for phase-to-phase faults in a direct-drive permanent magnet synchronous generator wind farm grid-connected system. In order to solve the technical problem that traditional distance protection malfunctions and refuses to act due to the fault response of power electronic equipment in a new energy power grid, on the basis of revealing the dynamic characteristics of equivalent power source power angle and the phase offset mechanism of positive sequence voltage, the dynamic equivalent power source model is constructed, and the phase difference between the equivalent power source voltage and the positive sequence voltage is innovatively used as the direction discrimination basis, so that the fault direction is accurately identified. The method and system not only effectively overcome the problems of malfunctions of reverse faults outside the area and refusal to act of faults near the area, but also maintain reliable action characteristics under various converter control strategies such as unit power factor control, low voltage ride through and negative sequence current suppression. The protection adaptability under the protection of transition resistance and asymmetric fault scenes is significantly improved, and the existing protection device hardware architecture is compatible, and only software upgrading is needed to deploy. The application provides an engineering universal technical solution for solving the distance protection mismatch problem of a high proportion of new energy power grid, and has guiding significance for the design of a new generation of power system protection algorithm.

[0075] The present disclosure can be a system, a method, and / or a computer program product. The computer program product can include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present disclosure.

[0076] The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium can be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium include the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or punched tape, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.

[0077] 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.

[0078] 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.

[0079] 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 power grid adaptive directional distance protection method based on apparent power sources, characterized in that, Includes the following steps: S1: Based on the voltage and current phasors measured at the protection installation point, a dynamic equivalent apparent power source model is established at this terminal. This model is composed of the apparent power source voltage amplitude. and equivalent impedance Two key parameters are defined; S2: Real-time acquisition of three-phase voltage and three-phase current at the protection installation location, and calculation of positive sequence voltage using the symmetrical component method. Calculate the dynamic equivalent apparent power supply at this end. and Real-time phase difference between the two ; S3: Real-time phase difference Compare with the preset action range; when When the fault is within the set operating range, it is determined to be a positive fault and the protection action is initiated; otherwise, it is determined to be a reverse fault and the protection output is blocked.

2. The adaptive directional distance protection method for power grids based on apparent power sources according to claim 1, characterized in that: In S1, the apparent power supply voltage amplitude It is set to a constant per-unit value; The equivalent impedance The impedance angle is constrained to be equal to the positive sequence impedance angle of the power grid line.

3. The grid adaptive directional distance protection method based on apparent power sources according to claim 2, characterized in that: The constant per-unit value is 1.1 .

4. The adaptive directional distance protection method for power grids based on apparent power sources according to claim 2, characterized in that: In S1, the new energy or grid-side power system is equivalent to a dynamic apparent power source. Among them, the apparent power supply phase angle and equivalent impedance magnitude It changes dynamically in real time with changes in grid topology, injection of new energy sources, and switching of control strategies for new energy units.

5. The grid adaptive directional distance protection method based on apparent power sources according to claim 1, characterized in that: At the protection installation point, this end is equivalent to a single-port network, wherein the dynamic equivalent apparent power supply is used as the power supply of the single-port network, and the internal impedance angle of the single-port network is equal to the positive sequence impedance angle of the protected line. Substituting the voltage and current collected at the protection installation location into the single-port network circuit equations, the apparent power supply voltage amplitude... and internal impedance angle Solving for the dynamic equivalent apparent power supply impedance magnitude under constraints The phase angle ε of the dynamic equivalent apparent power source.

6. The adaptive directional distance protection method for power grids based on apparent power sources according to claim 5, characterized in that: The phase angle ε of the dynamic equivalent apparent power source is calculated using the following formula: in, , These are the voltage phasors and current phasors measured at the protection installation location, Z. L This is the positive sequence impedance of the entire line.

7. The grid adaptive directional distance protection method based on apparent power source according to claim 1 or 6, characterized in that: In S2, the real-time phase difference for: 。 8. The adaptive directional distance protection method for power grids based on apparent power sources according to claim 1, characterized in that: The set action range is .

9. A power grid adaptive directional distance protection system based on apparent power source using the distance protection method according to any one of claims 1-8, comprising an electrical quantity acquisition module, a dynamic equivalent apparent power source model module, a real-time phase difference calculation module, and an action criterion module; characterized in that: The electrical quantity acquisition module collects the three-phase voltage and three-phase current at the protection installation location in real time. The dynamic equivalent apparent power model module establishes a local dynamic equivalent apparent power model based on the voltage phasors and current phasors measured at the protection installation location. The real-time phase difference calculation module calculates the positive sequence voltage using the symmetrical component method. Calculate the dynamic equivalent apparent power supply at this end. and Real-time phase difference between the two ; The action criterion module will determine the real-time phase difference. Compare with the preset action range; when When the fault is within the set operating range, it is determined to be a positive fault and the protection action is initiated; otherwise, it is determined to be a reverse fault and the protection output is blocked.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps of the method as described in any one of claims 1-8.

11. A computer device, comprising a memory, a processor, and a computer program stored in the memory; characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1-8.

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