Adaptive differential protection method and system for new energy grid-connected line

Abstract

The invention discloses a self-adaptive differential protection method and system for a new energy grid-connected line, and the method comprises the steps: obtaining a system side voltage and a system side current at a system side protection installation part of the grid-connected line, and a new energy side voltage and a new energy side current at a new energy side protection installation part; calculating a phase voltage change value and a phase current change value at two sides of the line; when a preset protection starting criterion is met, starting three-phase protection of the line; after protection is started, the amplitudes and phases of current power frequency components on the two sides of the grid-connected line are calculated respectively, and the amplitude and phase information of current on the opposite side is obtained; calculating the amplitude ratio of the current on the two sides of the line, and constructing a phase compensation function and an amplitude compensation function based on the amplitude ratio; calculating the phase difference between the currents on the two sides of the line, performing compensation based on the phase difference, the phase compensation function and the amplitude compensation function, and determining a system side compensation current and a new energy side compensation current; and based on the system side compensation current and the new energy side compensation current, identifying internal and external faults of the line region.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection for power systems, and more specifically, to an adaptive differential protection method and system for a new energy grid-connected line. Background Art

[0002] In the transmission system of the new energy station through the AC power grid, the new energy presents weak feedback characteristics. After the grid-connected line fails, the fault current amplitude provided by the new energy is limited and the phase is controlled. The nonlinear fault characteristics of new energy seriously affect the operation performance of the grid-connected line differential protection. It is urgent to study new protection principles for new energy grid-connected lines that can improve reliability and sensitivity.

[0003] In order to improve the operating performance of traditional differential protection, domestic and foreign scholars have conducted some research. According to the amplitude ratio of the fault current on both sides of the renewable energy grid-connected line, the fault inside and outside the line area is identified, but the operating sensitivity of this protection principle will decrease significantly with the increase of the proportion of renewable energy. The adaptive scalar product differential protection principle that adjusts the braking coefficient according to the amplitude ratio of the fault current on both sides of the distributed power access line increases the operating area of ​​the traditional differential protection, but it still cannot accurately identify all faults in the line area when a high proportion of renewable energy is connected.

[0004] Therefore, it is necessary to invent an adaptive differential protection method for renewable energy grid-connected lines. Summary of the invention

[0005] The present invention proposes an adaptive differential protection method and system for a renewable energy grid-connected line, so as to solve the problem of how to efficiently protect the renewable energy grid-connected line.

[0006] In order to solve the above problem, according to one aspect of the present invention, an adaptive differential protection method for a new energy grid-connected line is provided, the method comprising:

[0007] Respectively obtain the system side voltage and system side current at the system side protection installation of the grid-connected line, and the new energy side voltage and new energy side current at the new energy side protection installation;

[0008] Calculate the phase voltage change value of each phase on both sides of the grid-connected line based on the system side voltage and the new energy side voltage, and calculate the phase current change value of each phase on both sides of the grid-connected line based on the system side current and the new energy side current;

[0009] When the phase voltage change value and the phase current change value meet the preset protection start criterion, the three-phase protection of the line is started;

[0010] When the protection is activated, the amplitude and phase of the power frequency component of the current on both sides of the grid-connected line are calculated respectively, and the amplitude and phase information of the power frequency component of the current on the opposite side is obtained;

[0011] Calculating the amplitude ratio of the current on both sides of the line based on the amplitude information of the power frequency component of the current on both sides of the grid-connected line, and constructing a phase compensation function and an amplitude compensation function based on the amplitude ratio;

[0012] Calculate the phase difference of the current on both sides of the line based on the phase information of the power frequency component of the current on both sides of the grid-connected line, and compensate the current on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function to determine the compensation current on the system side and the compensation current on the new energy side;

[0013] Based on the system-side compensation current and the renewable energy-side compensation current, faults inside and outside the line area are identified.

[0014] Preferably, the method uses the following method to determine whether the phase voltage change value and the phase current change value meet the preset protection start criterion, including:

[0015] ΔU S =U S (N)-U S (NT)≤-0.2U N or ΔU R =U R (N)-U R (NT)≤-0.2U N ,

[0016] |ΔI S |=|I S (N)-I S (NT)|≥0.5I N or |ΔI S |=|I S (N)-I S (NT)|≥0.5I N ,

[0017] Among them, if the phase voltage change value ΔU of any phase on both sides of the line S or ΔU R Less than or equal to -0.2U N , and at the same time satisfy the phase current change value ΔI of any phase on both sides of the line S or ΔI R If the absolute value of ΔU is greater than or equal to 0.5A, it is determined that the preset protection criteria are met and the three-phase protection of the line is activated; S and ΔU R are the phase voltage changes on the system side and the new energy side respectively; ΔI S and ΔI R are the phase current changes on the system side and the new energy side respectively; U N and I Nare the rated voltage and rated current of the line respectively; N is the sampling point; T is the period of the electrical quantity of the AC system.

[0018] Preferably, constructing a phase compensation function and an amplitude compensation function based on the amplitude ratio comprises:

[0019]

[0020]

[0021] Among them, γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function.

[0022] Preferably, the compensating the currents on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function to determine the system side compensation current and the new energy side compensation current includes:

[0023]

[0024] in, and are the compensation current on the system side and the compensation current on the new energy side respectively; γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function; and They are system side current and new energy side current respectively; and are the phases of the system side current and the new energy side current respectively; is the phase difference; j represents a complex number.

[0025] Preferably, the identifying of line faults inside and outside the area based on the system side compensation current and the new energy side compensation current includes:

[0026] If the system-side compensation current and the renewable energy-side compensation current of the grid-connected line meet the adaptive differential protection criteria If the duration reaches the preset time threshold, it is determined that a fault has occurred within the line area; otherwise, it is determined that a fault has occurred outside the line area; and They are the compensation current on the system side and the compensation current on the new energy side respectively; K is the braking coefficient.

[0027] According to another aspect of the present invention, an adaptive differential protection system for a new energy grid-connected line is provided, the system comprising:

[0028] A voltage and current acquisition unit, used to respectively acquire the system side voltage and system side current at the grid-connected line system side protection installation location, and the new energy side voltage and new energy side current at the new energy side protection installation location;

[0029] A change value calculation unit, used to calculate the phase voltage change value of each phase on both sides of the grid-connected line based on the system side voltage and the new energy side voltage, and calculate the phase current change value of each phase on both sides of the grid-connected line based on the system side current and the new energy side current;

[0030] A protection start unit, used to start all three-phase protections of the line when the phase voltage change value and the phase current change value meet the preset protection start criterion;

[0031] The phase and amplitude calculation unit is used to calculate the amplitude and phase of the power frequency component of the current on both sides of the grid-connected line after the protection is started, and obtain the amplitude and phase information of the power frequency component of the current on the opposite side;

[0032] A compensation function construction unit, used to calculate the amplitude ratio of the currents on both sides of the line based on the amplitude information of the power frequency components of the currents on both sides of the grid-connected line, and to construct a phase compensation function and an amplitude compensation function based on the amplitude ratio;

[0033] A current compensation unit, used to calculate the phase difference of the current on both sides of the line based on the phase information of the power frequency component of the current on both sides of the grid-connected line, and compensate the current on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function, to determine the system side compensation current and the new energy side compensation current;

[0034] The fault identification unit is used to identify the faults inside and outside the line area based on the system side compensation current and the new energy side compensation current.

[0035] Preferably, the protection start unit determines whether the phase voltage change value and the phase current change value meet the preset protection start criterion in the following manner, including:

[0036] ΔU S =U S (N)-U S (NT)≤-0.2U N or ΔU R =U R (N)-U R (NT)≤-0.2U N ,

[0037] |ΔI S |=|I S (N)-I S (NT)|≥0.5I N or |ΔI S |=|I S (N)-I S (NT)|≥0.5I N ,

[0038] Among them, if the phase voltage change value ΔU of any phase on both sides of the line S or ΔU R Less than or equal to -0.2U N , and at the same time satisfy the phase current change value ΔI of any phase on both sides of the line S or ΔI R If the absolute value of ΔU is greater than or equal to 0.5A, it is determined that the preset protection criteria are met and the three-phase protection of the line is activated; S and ΔU R are the phase voltage changes on the system side and the new energy side respectively; ΔI S and ΔI R are the phase current changes on the system side and the new energy side respectively; U N and I N are the rated voltage and rated current of the line respectively; N is the sampling point; T is the period of the electrical quantity of the AC system.

[0039] Preferably, the compensation function constructing unit constructs a phase compensation function and an amplitude compensation function based on the amplitude ratio, comprising:

[0040]

[0041]

[0042] Among them, γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function.

[0043] Preferably, the current compensation unit compensates the currents on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function to determine the system side compensation current and the new energy side compensation current, including:

[0044]

[0045] in, and are the compensation current on the system side and the compensation current on the new energy side respectively; γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function; and They are system side current and new energy side current respectively; and are the phases of the system side current and the new energy side current respectively; is the phase difference; j represents a complex number.

[0046] Preferably, the fault identification unit identifies the faults inside and outside the line area based on the system side compensation current and the new energy side compensation current, including:

[0047] If the system-side compensation current and the renewable energy-side compensation current of the grid-connected line meet the adaptive differential protection criteria If the duration reaches the preset time threshold, it is determined that a fault has occurred within the line area; otherwise, it is determined that a fault has occurred outside the line area; and They are the compensation current on the system side and the compensation current on the new energy side respectively; K is the braking coefficient.

[0048] The present invention provides an adaptive differential protection method and system for a renewable energy grid-connected line, comprising: respectively obtaining the system side voltage and the system side current at the grid-connected line system side protection installation location, and the new energy side voltage and the new energy side current at the new energy side protection installation location; respectively calculating the phase voltage change value of each phase on both sides of the grid-connected line based on the system side voltage and the new energy side voltage, and calculating the phase current change value of each phase on both sides of the grid-connected line based on the system side current and the new energy side current; when the phase voltage change value and the phase current change value meet the preset protection start criterion, all three-phase protection of the line are started; after the protection is started, the grid-connected line is calculated respectively. The amplitude and phase of the power frequency component of the current on both sides of the line are calculated, and the amplitude and phase information of the power frequency component of the current on the opposite side is obtained; the amplitude ratio of the current on both sides of the line is calculated based on the amplitude information of the power frequency component of the current on both sides of the grid-connected line, and a phase compensation function and an amplitude compensation function are constructed based on the amplitude ratio; the phase difference of the current on both sides of the line is calculated based on the phase information of the power frequency component of the current on both sides of the grid-connected line, and the current on both sides of the line is compensated based on the phase difference, the phase compensation function and the amplitude compensation function to determine the compensation current on the system side and the compensation current on the new energy side; based on the compensation current on the system side and the compensation current on the new energy side, the faults inside and outside the line area are identified. The method of the present invention can well adapt to the grid connection of a high proportion of renewable energy, has high reliability under different fault types, and effectively solves the problem of refusal of traditional differential protection under faults within the zone; the protection action response speed is high, and the higher the SCR, the shorter the response time, which meets the quick action requirements of the main protection of the AC transmission line; it can tolerate 500Ω transition resistance and 30dB noise, has strong robustness, only uses the amplitude and phase information of the current, is simple to calculate, is convenient for the implementation of the protection device, and has high engineering value. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0050] Figure 1 It is a flow chart of an adaptive differential protection method 100 for a new energy grid-connected line according to an embodiment of the present invention;

[0051] Figure 2 A protection algorithm flow chart according to an embodiment of the present invention;

[0052] Figure 3 A schematic diagram of the topological structure of a new energy station grid-connected system according to an embodiment of the present invention;

[0053] Figure 4 (a), (b), (c), (d) and (e) are respectively simulation waveform diagrams of the voltage change on the system side, the voltage change on the new energy side, the current change on the system side, the current change on the new energy side, and the ratio of the differential current to the braking current of the method of the present invention and the traditional differential protection when the SCR is 2.5:1 and a three-phase metallic short circuit fault occurs at F1 according to an embodiment of the present invention;

[0054] Figure 5 (a), (b), (c), (d) and (e) are respectively simulation waveform diagrams of the voltage change on the system side, the voltage change on the new energy side, the current change on the system side, the current change on the new energy side, and the ratio of the differential current to the braking current of the method of the present invention and the traditional differential protection when the SCR is 2.5:1 and the transition resistance at F2 is 25Ω for a two-phase short circuit fault according to an embodiment of the present invention;

[0055] Figure 6 It is a simulation waveform diagram of the ratio of the differential current to the braking current when the SCR is 2.5:1 and a metallic three-phase short circuit fault occurs at F3 according to an embodiment of the present invention;

[0056] Figure 7 Schematic diagram of the structure of an adaptive differential protection system 700 for a new energy grid-connected line according to an embodiment of the present invention. DETAILED DESCRIPTION

[0057] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0058] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0059] In order to solve the problems existing in the differential protection of the grid-connected lines of renewable energy stations, a differential protection method was invented which can adapt to the high proportion of renewable energy grid connection, has high reliability, strong speed, no protection dead zone, and can tolerate high transition resistance and noise.

[0060] Figure 1 FIG. 1 is a flow chart of an adaptive differential protection method 100 for a new energy grid-connected line according to an embodiment of the present invention. Figure 1 As shown, the adaptive differential protection method for the new energy grid-connected line provided by the embodiment of the present invention can well adapt to the grid connection of a high proportion of new energy, has high reliability under different fault types, and effectively solves the problem of the traditional differential protection refusing to operate under faults in the zone; the protection action response speed is high, and the higher the SCR, the shorter the response time, which meets the fast-acting requirements of the main protection of the AC transmission line; it can tolerate 500Ω transition resistance and 30dB noise, and has strong robustness; it only uses the amplitude and phase information of the current, the calculation is simple, and it is convenient to realize the protection device, and the engineering value is high. The adaptive differential protection method 100 for the new energy grid-connected line provided by the embodiment of the present invention starts from step 101. In step 101, the system side voltage and system side current of the grid-connected line system side protection installation, and the new energy side voltage and new energy side current of the new energy side protection installation are respectively obtained.

[0061] In step 102, the phase voltage change value of each phase on both sides of the grid-connected line is calculated based on the system side voltage and the new energy side voltage, and the phase current change value of each phase on both sides of the grid-connected line is calculated based on the system side current and the new energy side current.

[0062] In step 103, when the phase voltage change value and the phase current change value meet the preset protection start criterion, the three-phase protection of the line is started.

[0063] Preferably, the method uses the following method to determine whether the phase voltage change value and the phase current change value meet the preset protection start criterion, including:

[0064] ΔU S =U S (N)-U S (NT)≤-0.2U N or ΔU R =U R (N)-U R (NT)≤-0.2U N ,

[0065] |ΔI S |=|I S (N)-I S (NT)|≥0.5I N or |ΔI S |=|I S (N)-I S (NT)|≥0.5I N ,

[0066] Among them, if the phase voltage change value ΔU of any phase on both sides of the line S or ΔU R Less than or equal to -0.2U N , and at the same time satisfy the phase current change value ΔI of any phase on both sides of the line S or ΔI R If the absolute value of ΔU is greater than or equal to 0.5A, it is determined that the preset protection criteria are met and the three-phase protection of the line is activated; S and ΔU R are the phase voltage changes on the system side and the new energy side respectively; ΔI S and ΔI R are the phase current changes on the system side and the new energy side respectively; U N and I N are the rated voltage and rated current of the line respectively; N is the sampling point; T is the period of the electrical quantity of the AC system.

[0067] Combination Figure 2 As shown, in the present invention, the voltage U at the protection installation location on the grid-connected line system side and the protection installation location on the new energy side are measured and collected respectively. S , U R and current I S ,I R ; Then, based on the acquired voltage and current, the phase voltage change value and phase current change value of each phase on both sides of the line are calculated respectively; Then, based on the phase voltage change value and phase current change value, it is determined whether to start the protection.

[0068] Specifically, for any side of the grid-connected line, if the phase voltage change value of any phase is less than -0.2U N , and at the same time, if the absolute value of the phase current change value of any phase is greater than or equal to 0.5A, then the three-phase protection of the line will be activated. That is, the protection activation criterion is to simultaneously satisfy equations (1) and (2):

[0069] ΔU S =U S (N)-U S (NT)≤-0.2U N or ΔU R =U R (N)-U R (NT)≤-0.2U N (1)

[0070] |ΔI S |=|I S (N)-I S (NT)|≥0.5I N or |ΔI S |=|I S (N)-I S(NT)|≥0.5I N (2)

[0071] Among them, ΔU S and ΔU R are the phase voltage changes on the system side and the new energy side respectively; ΔI S and ΔI R are the phase current changes on the system side and the new energy side respectively; U N and I N are the rated voltage and rated current of the line respectively; N is the sampling point; T is the period of the electrical quantity of the AC system.

[0072] In step 104, after the protection is started, the amplitude and phase of the power frequency component of the current on both sides of the grid-connected line are calculated respectively, and the amplitude and phase information of the power frequency component of the current on the opposite side are obtained.

[0073] In step 105, the amplitude ratio of the currents on both sides of the grid-connected line is calculated based on the amplitude information of the power frequency components of the currents on both sides of the grid-connected line, and a phase compensation function and an amplitude compensation function are constructed based on the amplitude ratio.

[0074] Preferably, constructing a phase compensation function and an amplitude compensation function based on the amplitude ratio comprises:

[0075]

[0076] Among them, γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function.

[0077] Combination Figure 2 As shown, in the present invention, after the protection is started, the protection devices on both sides of the line respectively calculate the phase of the power frequency component of the current at both ends of the line, and obtain the amplitude information and phase information of the current on the opposite side, so that the protection devices on both sides of the line can perform calculations respectively.

[0078] After obtaining the amplitude and phase, the protection devices on both sides of the line calculate the amplitude ratio γ of the current on both sides of the line respectively, and use γ as the independent variable to construct the phase compensation function f1(γ) and the amplitude compensation function f2(γ), as shown in equations (3) and (4):

[0079]

[0080] In step 106, the phase difference of the current on both sides of the grid-connected line is calculated based on the phase information of the power frequency component of the current on both sides of the grid-connected line, and the current on both sides of the line is compensated based on the phase difference, the phase compensation function and the amplitude compensation function to determine the system side compensation current and the new energy side compensation current.

[0081] Preferably, the compensating the currents on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function to determine the system side compensation current and the new energy side compensation current includes:

[0082]

[0083] in, and are the compensation current on the system side and the compensation current on the new energy side respectively; γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function; and They are system side current and new energy side current respectively; and are the phases of the system side current and the new energy side current respectively; is the phase difference; j represents a complex number.

[0084] Combination Figure 2 As shown, in the present invention, the protection devices on both sides of the line respectively calculate the phase difference of the current on both sides of the line According to the phase difference, the current on both sides of the line is compensated in different ways using the amplitude and phase compensation functions. The measured current on the new energy side Compensation is performed according to equations (5) and (6) respectively, and the current after compensation is and

[0085]

[0086] in, and are the compensation current on the system side and the compensation current on the new energy side respectively; γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function; and They are system side current and new energy side current respectively; and are the phases of the system side current and the new energy side current respectively; is the phase difference; j represents a complex number;

[0087] In step 107, based on the system-side compensation current and the new energy-side compensation current, the faults inside and outside the line area are identified.

[0088] Preferably, the identifying of line faults inside and outside the area based on the system side compensation current and the new energy side compensation current includes:

[0089] If the system-side compensation current and the renewable energy-side compensation current of the grid-connected line meet the adaptive differential protection criteria If the duration reaches the preset time threshold, it is determined that a fault has occurred within the line area; otherwise, it is determined that a fault has occurred outside the line area; and They are the compensation current on the system side and the compensation current on the new energy side respectively; K is the braking coefficient.

[0090] Combination Figure 2 As shown, in the present invention, the protection devices on both sides of the line form a new differential protection criterion by adaptively compensating the phase and amplitude of the current on both sides of the grid-connected line, as shown in formula (7):

[0091]

[0092] Among them, K is the braking coefficient, which is 0.7.

[0093] For both sides of the line, if the currents on both sides of the grid-connected line satisfy equation (7) for 5 ms continuously, it is determined to be a fault within the line area; otherwise, it is determined to be a fault outside the line area.

[0094] The present invention analyzes the characteristics of the fault current provided by the renewable energy station and the action characteristics of the traditional current differential protection, targets the problems existing in the traditional current differential protection in the grid-connected lines of the renewable energy station, and utilizes the characteristic that the amplitude of the fault current provided by the renewable energy is limited. An adaptive differential protection method for renewable energy grid-connected lines based on compensation function is proposed.

[0095] When the present invention is simulated and verified, a simulation is built on Matlab / Simulink. Figure 3 The new energy station grid-connected system shown. The new energy station is controlled by a virtual synchronous machine with a rated power of P N 80kW, Q N The lengths of the 35kV collection line and the 220kV transmission line are 100m and 50km respectively. and The positive direction is from the busbar to the line. The short-circuit ratio between the system side and the renewable energy side is 2.5:1, which is a high-proportion renewable energy grid-connected system. N with I N They are 220kV and 1A respectively. Fault points F1 and F2 are on the new energy export side and system export side of the transmission line respectively, F3 is on the 35kV busbar, and F4 is on the low voltage side of T1. The fault time is set to 0.5s.

[0096] Simulation of faults within the area:

[0097] In order to verify the reliability of the present invention under the most difficult to identify fault in the zone, a metallic three-phase short circuit fault is set at F1, and an AB two-phase short circuit fault with a transition resistance of 25Ω is set at F2. The simulation waveforms of the change in the voltage on the new energy side are as follows: Figure 4 (a) and Figure 5 As shown in (a), the simulated waveforms of the voltage changes on the system side are as follows: Figure 4 (b) and Figure 5 As shown in (b), the simulation waveforms of the change in the current on the new energy side are as follows: Figure 4 (c) and Figure 5 As shown in (c), the simulated waveforms of the voltage changes on the new energy side are as follows: Figure 4 (d) and Figure 5 (d) as shown. d and I r Indicates differential current and braking current. The present invention is different from the traditional differential protection under I d / I r The simulation waveforms are as follows Figure 4 (e) and Figure 5 (e) is shown. The simulation results are shown in Table 1. d / I r and(I d / I r ) T They represent the action quantities of the proposed adaptive differential protection and the traditional differential protection respectively. If the protection can be operated, this paper gives the continuous 5ms I d / I r and(I d / I r ) T If the protection fails to work, the I d / I r and(I d / I r ) T The range of variation of t and t T They represent the action response time of the proposed adaptive differential protection and the traditional differential protection respectively, and × represents that the protection cannot be operated.

[0098] Table 1. Simulation results of faults within the zone

[0099]

[0100] From the above simulation results, it can be seen that after the above two faults occur, the voltage change rate and current change rate on both sides of the line meet the start-up criteria. After the protection is started, the traditional differential protection cannot accurately identify all fault phases, but the proposed adaptive differential protection After the amplitude and phase of the power supply are compensated to different degrees, all fault phases can be reliably identified, and the non-fault phases are reliably inactive. In addition, the response time of the three-phase protection does not exceed 14ms, which meets the requirements of the main protection speed. Therefore, the present invention can accurately identify the faults in the line area when a high proportion of new energy is connected to the grid, and has strong reliability.

[0101] Simulation of out-of-zone faults:

[0102] A metallic three-phase short-circuit fault and an AB two-phase grounding fault are set at F3 and F4 respectively. Taking the most serious out-of-zone fault F3 as an example, the proposed adaptive differential protection d / I r The simulation waveforms are as follows Figure 6 The simulation results of all the above faults are shown in Table 2.

[0103] Table 2 Simulation results of out-of-zone faults

[0104]

[0105] From the simulation results, it can be seen that after the fault occurs at F3 and F4, the protection is activated. γ≈1, the phase compensation function f1(γ) is close to 0, and the amplitude compensation function f2(γ) is 1. The amplitude and phase are not compensated. d / I r They are all much smaller than the braking coefficient, and the present invention is reliable and will not act.

[0106] Simulation of different fault types:

[0107] To further verify that the proposed adaptive differential protection is effective under different fault types, taking the high-resistance fault at F2 as an example, the A-phase grounding fault and the AB two-phase grounding fault with a transition resistance of 500Ω are set respectively. The simulation results are shown in Table 3.

[0108] Table 3 Simulation results of different fault types

[0109]

[0110] From the simulation results in Table 3, it can be seen that after various types of grounding faults with a transition resistance of 500Ω occur at F2, the protection is activated, and the proposed adaptive differential protection can accurately identify all fault phases within 14ms after the fault, and the non-fault phases are reliably inactive. The present invention has a high ability to withstand transition resistance, and has high reliability and speed under different fault types.

[0111] White Noise:

[0112] To further verify the influence of noise on the adaptive differential protection, 30dB white noise is added to the three-phase current. A metallic three-phase short-circuit fault is set at F1 and F3, and an AB two-phase short-circuit fault with a transition resistance of 25Ω is set at F2. The simulation results are shown in Table 5.

[0113] Table 5 Simulation results under 30dB white noise

[0114]

[0115] It can be seen from the simulation results that the present invention can still accurately identify the faulty phase within 14ms after the fault under 30dB white noise, and the non-faulty phase will not operate reliably. Therefore, when the SCR is 2.5:1 and above, the proposed adaptive differential protection can tolerate 30dB noise and has strong robustness.

[0116] In summary, the present invention has the following advantages: (1) It can adapt well to the grid connection of a high proportion of renewable energy, has high reliability under different fault types, and effectively avoids the risk of traditional differential protection refusing to operate under faults within the zone. (2) The protection action response speed is high. When the SCR is 2.5:1, the response time does not exceed 14ms, which meets the speed requirements of the main protection of the AC transmission line. (3) It can tolerate 500Ω transition resistance and 30dB noise, and has strong robustness. (4) Only the amplitude and phase information of the current are used, the calculation is simple, which is convenient for the implementation of the protection device and has high engineering value.

[0117] Figure 7 FIG. 7 is a schematic diagram of the structure of an adaptive differential protection system 700 for a new energy grid-connected line according to an embodiment of the present invention. Figure 7 As shown, the adaptive differential protection system 700 for the new energy grid-connected line provided in an embodiment of the present invention includes: a voltage and current acquisition unit 701, a change value calculation unit 702, a protection start unit 703, a phase and amplitude calculation unit 704, a compensation function construction unit 705, a current compensation unit 706 and a fault identification unit 707.

[0118] Preferably, the voltage and current acquisition unit 701 is used to respectively acquire the system side voltage and system side current at the system side protection installation of the grid-connected line, and the new energy side voltage and new energy side current at the new energy side protection installation.

[0119] Preferably, the change value calculation unit 702 is used to calculate the phase voltage change value of each phase on both sides of the grid-connected line based on the system side voltage and the new energy side voltage, and to calculate the phase current change value of each phase on both sides of the grid-connected line based on the system side current and the new energy side current.

[0120] Preferably, the protection starting unit 703 is used to start all three-phase protections of the line when the phase voltage change value and the phase current change value meet preset protection starting criteria.

[0121] Preferably, the protection start unit 703 uses the following method to determine whether the phase voltage change value and the phase current change value meet the preset protection start criterion, including:

[0122] ΔU S =U S (N)-U S (NT)≤-0.2U N or ΔU R =U R (N)-U R (NT)≤-0.2U N ,

[0123] |ΔI S |=|I S (N)-I S (NT)|≥0.5I N or |ΔI S |=|I S (N)-I S (NT)|≥0.5I N ,

[0124] Among them, if the phase voltage change value ΔU of any phase on both sides of the line S or ΔU R Less than or equal to -0.2U N , and at the same time satisfy the phase current change value ΔI of any phase on both sides of the line S or ΔI R If the absolute value of ΔU is greater than or equal to 0.5A, it is determined that the preset protection criteria are met and the three-phase protection of the line is activated; S and ΔU R are the phase voltage changes on the system side and the new energy side respectively; ΔI S and ΔI R are the phase current changes on the system side and the new energy side respectively; U N and I N are the rated voltage and rated current of the line respectively; N is the sampling point; T is the period of the electrical quantity of the AC system.

[0125] Preferably, the phase and amplitude calculation unit 704 is used to calculate the amplitude and phase of the power frequency component of the current on both sides of the grid-connected line respectively after the protection is started, and obtain the amplitude and phase information of the power frequency component of the current on the opposite side.

[0126] Preferably, the compensation function constructing unit 705 is used to calculate the amplitude ratio of the currents on both sides of the line based on the amplitude information of the power frequency components of the currents on both sides of the grid-connected line, and construct a phase compensation function and an amplitude compensation function based on the amplitude ratio.

[0127] Preferably, the compensation function constructing unit 705 constructs a phase compensation function and an amplitude compensation function based on the amplitude ratio, including:

[0128]

[0129] Among them, γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function.

[0130] Preferably, the current compensation unit 706 is used to calculate the phase difference of the current on both sides of the line based on the phase information of the current on both sides of the grid-connected line, and compensate the current on both sides of the line based on the phase difference, phase compensation function and amplitude compensation function to determine the first compensation current on the system side and the second compensation current on the new energy side.

[0131] Preferably, the current compensation unit 706 compensates the currents on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function to determine the compensation current on the system side and the compensation current on the new energy side, including:

[0132]

[0133] in, and are the compensation current on the system side and the compensation current on the new energy side respectively; γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function; and They are system side current and new energy side current respectively; and are the phases of the system side current and the new energy side current respectively; is the phase difference; j represents a complex number.

[0134] Preferably, the fault identification unit 707 is used to identify the faults inside and outside the line area based on the system side compensation current and the new energy side compensation current.

[0135] Preferably, the fault identification unit identifies the faults inside and outside the line area based on the system side compensation current and the new energy side compensation current, including:

[0136] If the system-side compensation current and the renewable energy-side compensation current of the grid-connected line meet the adaptive differential protection criteria If the duration reaches the preset time threshold, it is determined that a fault has occurred within the line area; otherwise, it is determined that a fault has occurred outside the line area; and They are the compensation current on the system side and the compensation current on the new energy side respectively; K is the braking coefficient.

[0137] The adaptive differential protection system 700 for a renewable energy grid-connected line according to an embodiment of the present invention corresponds to the adaptive differential protection method 100 for a renewable energy grid-connected line according to another embodiment of the present invention, and will not be described in detail herein.

[0138] The invention has been described above with reference to a few embodiments. However, it is readily apparent to a person skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

[0139] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise therein. All references to "a / said / the [means, components, etc.]" are to be openly interpreted as at least one instance of said means, components, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily have to be performed in the exact order disclosed, unless explicitly stated otherwise.

[0140] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0141] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0142] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0143] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0144] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An adaptive differential protection method for a new energy grid-connected line, characterized in that: The method comprises: Respectively obtain the system side voltage and system side current at the system side protection installation of the grid-connected line, and the new energy side voltage and new energy side current at the new energy side protection installation; Calculate the phase voltage change value of each phase on both sides of the grid-connected line based on the system side voltage and the new energy side voltage, and calculate the phase current change value of each phase on both sides of the grid-connected line based on the system side current and the new energy side current; When the phase voltage change value and the phase current change value meet the preset protection start criterion, the three-phase protection of the line is started; When the protection is activated, the amplitude and phase of the power frequency component of the current on both sides of the grid-connected line are calculated respectively, and the amplitude and phase information of the power frequency component of the current on the opposite side is obtained; Calculating the amplitude ratio of the current on both sides of the line based on the amplitude information of the power frequency component of the current on both sides of the grid-connected line, and constructing a phase compensation function and an amplitude compensation function based on the amplitude ratio; Calculate the phase difference of the current on both sides of the line based on the phase information of the power frequency component of the current on both sides of the grid-connected line, and compensate the current on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function to determine the compensation current on the system side and the compensation current on the new energy side; Based on the system-side compensation current and the renewable energy-side compensation current, faults inside and outside the line area are identified.

2. The method according to claim 1, characterized in that: The method uses the following method to determine whether the phase voltage change value and the phase current change value meet the preset protection start criterion, including: ΔU S = U S (N) - U S (N - T) ≤ -0.2U N or ΔU R = U R (N) - U R (N - T) ≤ -0.2U N , |ΔI S | = | I S (N) - I S (N - T)| ≥ 0.5I N or |ΔI S | = | I S (N) - I S (N - T)| ≥ 0.5I N , Among them, if the phase voltage change value ΔU of any phase on both sides of the line S or ΔU R Less than or equal to -0.2U N , and at the same time satisfy the phase current change value ΔI of any phase on both sides of the line S or ΔI R If the absolute value of ΔU is greater than or equal to 0.5A, it is determined that the preset protection criteria are met and the three-phase protection of the line is activated; S and ΔU R are the phase voltage changes on the system side and the new energy side respectively; ΔI S and ΔI R are the phase current changes on the system side and the new energy side respectively; U N and I N are the rated voltage and rated current of the line respectively; N is the sampling point; T is the period of the electrical quantity of the AC system.

3. The method according to claim 1, characterized in that The constructing of a phase compensation function and an amplitude compensation function based on the amplitude ratio comprises: Among them, γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function.

4. The method according to claim 1, characterized in that: The compensating the currents on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function to determine the system side compensation current and the new energy side compensation current includes: in, and are the compensation current on the system side and the compensation current on the new energy side respectively; γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function; and They are the system side current and the new energy side current respectively; and are the phases of the system side current and the new energy side current respectively; is the phase difference; j represents a complex number.

5. The method according to claim 1, characterized in that The identifying of faults inside and outside the line area based on the system side compensation current and the new energy side compensation current includes: If the system-side compensation current and the renewable energy-side compensation current of the grid-connected line meet the adaptive differential protection criteria If the duration reaches the preset time threshold, it is determined that a fault has occurred within the line area; otherwise, it is determined that a fault has occurred outside the line area; and They are the compensation current on the system side and the compensation current on the new energy side respectively; K is the braking coefficient.

6. An adaptive differential protection system for a new energy grid-connected line, characterized in that: The system comprises: A voltage and current acquisition unit, used to respectively acquire the system side voltage and system side current at the grid-connected line system side protection installation location, and the new energy side voltage and new energy side current at the new energy side protection installation location; A change value calculation unit, used to calculate the phase voltage change value of each phase on both sides of the grid-connected line based on the system side voltage and the new energy side voltage, and calculate the phase current change value of each phase on both sides of the grid-connected line based on the system side current and the new energy side current; A protection start unit, used to start all three-phase protections of the line when the phase voltage change value and the phase current change value meet the preset protection start criterion; The phase and amplitude calculation unit is used to calculate the amplitude and phase of the power frequency component of the current on both sides of the grid-connected line after the protection is started, and obtain the amplitude and phase information of the power frequency component of the current on the opposite side; A compensation function construction unit, used to calculate the amplitude ratio of the currents on both sides of the line based on the amplitude information of the power frequency components of the currents on both sides of the grid-connected line, and to construct a phase compensation function and an amplitude compensation function based on the amplitude ratio; A current compensation unit, used to calculate the phase difference of the current on both sides of the line based on the phase information of the power frequency component of the current on both sides of the grid-connected line, and compensate the current on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function, to determine the system side compensation current and the new energy side compensation current; The fault identification unit is used to identify the faults inside and outside the line area based on the system side compensation current and the new energy side compensation current.

7. The system according to claim 6, characterized in that The protection start unit determines whether the phase voltage change value and the phase current change value meet the preset protection start criterion in the following manner, including: ΔU S = U S (N) - U S (N - T) ≤ -0.2U N or ΔU R = U R (N) - U R (N - T) ≤ -0.2U N , |ΔI S | = | I S (N) - I S (N - T) | ≥ 0.5I N or | ΔI S | = | I S (N) - I S (N - T) | ≥ 0.5I N , Among them, if the phase voltage change value ΔU of any phase on both sides of the line S or ΔU R Less than or equal to -0.2U N , and at the same time satisfy the phase current change value ΔI of any phase on both sides of the line S or ΔI R If the absolute value of ΔU is greater than or equal to 0.5A, it is determined that the preset protection criteria are met and the three-phase protection of the line is activated; S and ΔU R are the phase voltage changes on the system side and the new energy side respectively; ΔI S and ΔI R are the phase current changes on the system side and the new energy side respectively; U N and I N are the rated voltage and rated current of the line respectively; N is the sampling point; T is the period of the electrical quantity of the AC system.

8. The system according to claim 6, characterized in that The compensation function construction unit constructs a phase compensation function and an amplitude compensation function based on the amplitude ratio, including: Among them, γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function.

9. The system according to claim 6, characterized in that The current compensation unit compensates the currents on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function to determine the system side compensation current and the new energy side compensation current, including: in, and are the compensation current on the system side and the compensation current on the new energy side respectively; γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function; and They are the system side current and the new energy side current respectively; and are the phases of the system side current and the new energy side current respectively; is the phase difference; j represents a complex number.

10. The system according to claim 6, characterized in that The fault identification unit identifies the faults inside and outside the line area based on the system side compensation current and the new energy side compensation current, including: If the system-side compensation current and the renewable energy-side compensation current of the grid-connected line meet the adaptive differential protection criteria If the duration reaches the preset time threshold, it is determined that a fault has occurred within the line area; otherwise, it is determined that a fault has occurred outside the line area; and They are the compensation current on the system side and the compensation current on the new energy side respectively; K is the braking coefficient.

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