A new energy grid-connected line adaptive differential protection method and system

Abstract

The application discloses a new energy grid-connected line adaptive differential protection method and system, comprising the following steps: acquiring system side voltage and system side current at the system side protection installation of the grid-connected line system, and acquiring new energy side voltage and new energy side current at the new energy side protection installation; calculating phase voltage change value and phase current change value of the line two sides; when the preset protection starting criterion is met, the line three-phase protection is started; after the protection is started, the amplitude and phase of the power frequency component of the current on the two sides of the grid-connected line are calculated respectively, and the amplitude and phase information of the opposite side current are acquired; the amplitude ratio of the current on the two sides of the line is calculated, and the phase compensation function and the amplitude compensation function are constructed based on the amplitude ratio; the phase difference of the current on the two sides of the line is calculated, and compensation is carried out based on the phase difference, the phase compensation function and the amplitude compensation function, so as to determine the system side compensation current and the new energy side compensation current; and based on the system side compensation current and the new energy side compensation current, the line internal and external faults are identified.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system relay protection, and more particularly, to a self-adaptive differential protection method and system for a new energy grid-connected line. BACKGROUND

[0002] In a new energy station sending out system through an AC power grid, new energy exhibits a weak feeding characteristic, and after a grid-connected line fault, the fault current amplitude provided by the new energy is limited and the phase is controlled. The nonlinear fault characteristics of the new energy seriously affect the action performance of the differential protection of the grid-connected line, and a new principle of new energy grid-connected line protection capable of improving reliability and sensitivity needs to be urgently researched.

[0003] In order to improve the action performance of the traditional differential protection, scholars at home and abroad have made certain research. According to the amplitude ratio of the fault currents on both sides of the new energy grid-connected line, the line internal and external faults are identified, but the action sensitivity of the protection principle will decrease significantly with the increase of the new energy proportion. The adaptive product-form differential protection principle according to the amplitude ratio of the fault currents on both sides of the line with distributed power access increases the action area of the traditional differential protection, but still cannot accurately identify all line internal faults under high proportion of new energy access.

[0004] Therefore, it is necessary to invent a self-adaptive differential protection method for a new energy grid-connected line. SUMMARY

[0005] The present application proposes a self-adaptive differential protection method and system for a new energy grid-connected line to solve the problem of how to efficiently protect the new energy grid-connected line.

[0006] In order to solve the above problems, according to one aspect of the present application, a self-adaptive differential protection method for a new energy grid-connected line is provided, which comprises:

[0007] The system side voltage and the system side current at the system side protection installation of the grid-connected line system are obtained respectively, and the new energy side voltage and the new energy side current at the new energy side protection installation are obtained respectively;

[0008] The phase voltage variation 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 respectively, and the phase current variation 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;

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

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

[0011] calculating the amplitude ratio of the currents on both sides of the grid-connected line based on the amplitude information of the power frequency components of the currents 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] calculating the phase difference of the currents on both sides of the grid-connected line based on the phase information of the power frequency components of the currents on both sides of the grid-connected line, and compensating the currents on both sides of the grid-connected 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;

[0013] identifying the in-zone fault and the out-of-zone fault based on the system-side compensation current and the new energy-side compensation current.

[0014] Preferably, the method determines whether the phase voltage change value and the phase current change value meet the preset protection starting criterion by using the following method:

[0015] 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 ,

[0016] |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 ,

[0017] wherein, if the phase voltage change value ΔU S or ΔU R of any phase on both sides of the line is less than or equal to -0.2U N , and the absolute value of the phase current change value ΔI S or ΔI R of any phase on both sides of the line is greater than or equal to 0.5A, it is determined that the preset protection criterion is met, and the three-phase protection of the line is started; ΔU S and ΔU R are the phase voltage change values of the system side and the new energy side, respectively; ΔI S and ΔI R are the phase current change values of the system side and the new energy side, respectively; U N and I NThe rated voltage and rated current of the line are respectively N, where N is the sampling point; T is the period of the electrical quantity of the AC system.

[0018] Preferably, the construction of the phase compensation function and the amplitude compensation function based on the amplitude ratio includes:

[0019]

[0020]

[0021] Where γ is the amplitude ratio; f1(γ) is the phase compensation function; and f2(γ) is the amplitude compensation function.

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

[0023]

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

[0025] Preferably, the identification of faults within and outside the line 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 a preset time threshold, a fault is determined to have occurred within the line area; otherwise, a fault is determined to have occurred outside the line area. and These are the system-side compensation current and the new energy-side compensation current, 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] The voltage and current acquisition unit is used to acquire the system-side voltage and system-side current at the grid-connected line system-side protection installation point, and the new energy-side voltage and new energy-side current at the new energy-side protection installation point, respectively.

[0029] The change value calculation unit 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.

[0030] The protection activation unit is used to activate all three phase protections of the line when the phase voltage change value and the phase current change value meet the preset protection activation criteria.

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

[0032] The compensation function construction unit is used to calculate the amplitude ratio of the current on both sides of the line based on the amplitude information of the power frequency components of the current on both sides of the grid-connected line, and to construct the phase compensation function and the amplitude compensation function based on the amplitude ratio.

[0033] The current compensation unit is used to calculate the phase difference of the current on both sides of the line based on the phase information of the power frequency components of the current on both sides of the grid-connected line, and to compensate the current on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function, so as to determine the system-side compensation current and the new energy-side compensation current.

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

[0035] Preferably, the protection start-up unit determines whether the phase voltage change value and the phase current change value meet the preset protection start-up criteria using the following method:

[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 simultaneously 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, then the preset protection criterion is met, and all three-phase protections of the line are activated; S and ΔU R These are the phase voltage changes on the system side and the new energy side, respectively; ΔI S and ΔI R These are the phase current changes on the system side and the new energy side, respectively; U N and I N These represent the line's rated voltage and rated current, respectively; N is the sampling point; and T is the period of the AC system's electrical quantities.

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

[0040]

[0041]

[0042] Where γ is the amplitude ratio; f1(γ) is the phase compensation function; and 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, phase compensation function, and amplitude compensation function, and determines the system-side compensation current and the new energy-side compensation current, including:

[0044]

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

[0046] Preferably, the fault identification unit identifies faults within 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 a preset time threshold, a fault is determined to have occurred within the line area; otherwise, a fault is determined to have occurred outside the line area. and These are the system-side compensation current and the new energy-side compensation current, respectively; K is the braking coefficient.

[0048] This invention provides an adaptive differential protection method and system for a renewable energy grid-connected line, comprising: acquiring the system-side voltage and system-side current at the system-side protection installation point of the grid-connected line, and the renewable energy-side voltage and renewable energy-side current at the renewable energy-side protection installation point; calculating the phase voltage change value of each phase on both sides of the grid-connected line based on the system-side voltage and renewable 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 renewable energy-side current; when the phase voltage change value and phase current change value meet the preset protection start criterion, all three phases of the line protection are activated; after the protection is activated, the grid-connected line protection is calculated... The system obtains the amplitude and phase of the power frequency components of the current on both sides of the line, and acquires the amplitude and phase information of the power frequency components of the current on the opposite side; it calculates 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 line, and constructs a phase compensation function and an amplitude compensation function based on the amplitude ratio; it calculates the phase difference of the currents on both sides of the line based on the phase information of the power frequency components of the currents on both sides of the line, and 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; based on the compensation current on the system side and the compensation current on the new energy side, it identifies faults within and outside the line area. The method of this invention can adapt well to the grid connection of high proportion of new energy sources, and has high reliability under different fault types. It effectively solves the problem of traditional differential protection failing to operate 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 speed requirement of AC transmission line main protection. It can withstand 500Ω transition resistance and 30dB noise, and has strong robustness. It only uses the amplitude and phase information of the current, which is simple to calculate and easy to implement in the protection device, and has high engineering value. Attached Figure Description

[0049] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0050] Figure 1 A flowchart 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 This is a flowchart of the protection algorithm according to an embodiment of the present invention;

[0052] Figure 3 This is a schematic diagram of the topology of a new energy power station grid connection system according to an embodiment of the present invention;

[0053] Figure 4 (a), (b), (c), (d), and (e) are simulation waveforms of the system-side voltage change, new energy-side voltage change, system-side current change, new energy-side current change, and the ratio of differential current to braking current of the method of the present invention and the traditional differential protection when the SCR is 2.5:1 according to the embodiment of the present invention.

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

[0055] Figure 6 The simulation waveform of the ratio of differential current to braking current during a metallic three-phase short-circuit fault at F3 is shown in the embodiment of the present invention, where the SCR ratio is 2.5:1.

[0056] Figure 7 This is a schematic diagram of the adaptive differential protection system 700 for a new energy grid-connected line according to an embodiment of the present invention. Detailed Implementation

[0057] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0058] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0059] To address the problems existing in the differential protection of grid-connected lines of new energy power plants, a differential protection method was invented that can adapt to a high proportion of new energy grid connection, has high reliability, strong speed, no protection dead zone, and can withstand high transition resistance and noise.

[0060] Figure 1 This is a flowchart 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 new energy grid-connected lines provided by this invention can adapt well to the grid connection of high-proportion new energy sources, and has high reliability under different fault types, effectively solving the problem of traditional differential protection failing to operate under faults within the protection zone; the protection action response speed is high, and the higher the SCR, the shorter the response time, meeting the fast-acting requirements of the main protection of AC transmission lines; it can withstand 500Ω transition resistance and 30dB noise, and has strong robustness; it only uses the amplitude and phase information of the current, making the calculation simple, easy to implement the protection device, and of high engineering value. The adaptive differential protection method 100 for new energy grid-connected lines provided by this invention starts from step 101. In step 101, the system side voltage and system side current at the system side protection installation point of the grid-connected line, and the new energy side voltage and new energy side current at the new energy side protection installation point are obtained respectively.

[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, all three phase protections of the line are activated.

[0063] Preferably, the method determines whether the phase voltage change value and the phase current change value meet the preset protection start criterion using the following methods:

[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 simultaneously 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, then the preset protection criterion is met, and all three-phase protections of the line are activated; S and ΔU R These are the phase voltage changes on the system side and the new energy side, respectively; ΔI S and ΔI R These are the phase current changes on the system side and the new energy side, respectively; U N and I N These represent the line's rated voltage and rated current, respectively; N is the sampling point; and T is the period of the AC system's electrical quantities.

[0067] Combination Figure 2 As shown, in this invention, the voltage U at the protection installation points on the grid-connected line system side and the new energy side is measured and collected respectively. S U R and current I S I R Then, based on the acquired voltage and current, calculate the phase voltage change and phase current change values ​​for each phase on both sides of the line; then, based on the phase voltage change and phase current change values, determine whether to activate the protection.

[0068] Specifically, for any side of the grid-connected line, if the phase voltage change of any phase is less than -0.2U... N Furthermore, if the absolute value of the phase current change in any phase is greater than or equal to 0.5A, then all three phase protections of the line will be activated. That is, the protection activation criterion is that both equation (1) and equation (2) must be satisfied simultaneously:

[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] Wherein, ΔU S and ΔU R These are the phase voltage changes on the system side and the new energy side, respectively; ΔI S and ΔI R These are the phase current changes on the system side and the new energy side, respectively; U N and I N These represent the line's rated voltage and rated current, respectively; N is the sampling point; and T is the period of the AC system's electrical quantities.

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

[0073] In step 105, the amplitude ratio of the current on both sides of the line is calculated based on the amplitude information of the power frequency components 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.

[0074] Preferably, the construction of the phase compensation function and the amplitude compensation function based on the amplitude ratio includes:

[0075]

[0076] Where γ is the amplitude ratio; f1(γ) is the phase compensation function; and f2(γ) is the amplitude compensation function.

[0077] Combination Figure 2 As shown, in this invention, after the protection is activated, the protection devices on both sides of the line calculate the phase of the power frequency component of the current at both ends of the line, and obtain the amplitude 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, and construct the phase compensation function f1(γ) and amplitude compensation function f2(γ) with γ as the independent variable, as shown in equations (3) and (4):

[0079]

[0080] In step 106, the phase difference between the currents on both sides of the grid-connected line is calculated based on the phase information of the power frequency components of the currents on both sides of the line, and the currents on both sides of the line are 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 method for compensating the currents on both sides of the line based on the phase difference, phase compensation function, and amplitude compensation function to determine the system-side compensation current and the new energy-side compensation current includes:

[0082]

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

[0084] Combination Figure 2 As shown, in this invention, the protection devices on both sides of the line calculate the phase difference of the current on both sides of the line. Based on the magnitude of the phase difference, amplitude and phase compensation functions are used to compensate the current on both sides of the line in different ways. Specifically, the measured current on the grid-connected line system side... Measurement current with the new energy side Compensation is performed according to equations (5) and (6) respectively, and the compensated current is: and

[0085]

[0086] in, and These are the system-side compensation current and the new energy-side compensation current, respectively; γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function; and These are the system-side current and the new energy-side current, respectively. and These represent the phases of the system-side current and the new energy-side current, respectively. The phase difference is represented by j; j represents a complex number.

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

[0088] Preferably, the identification of faults within and outside the line 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 a preset time threshold, a fault is determined to have occurred within the line area; otherwise, a fault is determined to have occurred outside the line area. and These are the system-side compensation current and the new energy-side compensation current, respectively; K is the braking coefficient.

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

[0091]

[0092] Where K is the braking coefficient, which is taken as 0.7.

[0093] If the current on both sides of the line satisfies 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] This invention analyzes the characteristics of fault currents provided by renewable energy power plants and the operating characteristics of traditional current differential protection. Addressing the problems of traditional current differential protection in renewable energy power plant grid-connected lines, this invention proposes an adaptive differential protection method for renewable energy grid-connected lines based on a compensation function, taking advantage of the limited amplitude of fault currents provided by renewable energy.

[0095] During simulation verification, this invention is built on Matlab / Simulink. Figure 3 The diagram shows a new energy power station grid connection system. The new energy power station uses virtual synchronous machine control, with a rated power P. N 80kW and Q respectively N The lengths of the 0.35kV collection line and the 220kV transmission line are 100m and 50km respectively. and All positive directions are from the busbar to the line. The short-circuit ratio between the system side and the renewable energy side is 2.5:1, indicating a high proportion of renewable energy grid connection. N with I N The voltage levels are 220kV and 1A, respectively. Fault points F1 and F2 are located on the new energy output side and system output side of the transmission line, respectively; F3 is on the 35kV busbar; and F4 is on the T1 low-voltage side. The fault time for each fault is set to 0.5s.

[0096] Simulation of faults within the zone:

[0097] To verify the reliability of this invention under the most difficult-to-identify fault conditions within the fault zone, a metallic three-phase short-circuit fault was first set at F1, and a two-phase AB short-circuit fault with a transition resistance of 25Ω was set at F2. The simulated waveforms of the voltage change on the new energy side are shown below. Figure 4 (a) and Figure 5 As shown in (a), the simulated waveforms of the system-side voltage change are as follows: Figure 4 (b) and Figure 5 As shown in (b), the simulated waveforms of the change in 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 change on the new energy side are as follows: Figure 4 (d) and Figure 5 As shown in (d). I d and I r This invention represents the differential current and braking current, and differs from traditional differential protection methods in that it uses I... d / I r The simulated waveforms are as follows: Figure 4 (e) and Figure 5 As shown in (e). The simulation results are shown in Table 1, I d / I r and(I d / I r ) T These represent the operating parameters of the proposed adaptive differential protection and the traditional differential protection, respectively. If the protection can operate, this paper provides the I value within a continuous 5ms that satisfies the protection criterion. d / I r and(I d / I r ) T The range of variation. If the protection fails to operate, the I value within 20ms after the fault is given. d / I r and(I d / I r ) T The range of variation of t and t. T These represent the action response time of the proposed adaptive differential protection and the traditional differential protection, respectively. × indicates that the protection cannot operate.

[0098] Table 1. Fault simulation results within the area

[0099]

[0100] The simulation results above show that after the occurrence of the two faults mentioned above, both the voltage and current change rates on both sides of the line meet the start-up criteria. After the protection is started, traditional differential protection cannot accurately identify all faulty phases, while the proposed adaptive differential protection... After compensation of amplitude and phase to varying degrees, all faulty phases can be reliably identified, while non-faulty phases reliably remain inactive. Furthermore, the response time of all three-phase protections does not exceed 14ms, meeting the requirements for fast operation of the main protection. Therefore, this invention can accurately identify faults within the line area under conditions of high-proportion renewable energy grid connection, demonstrating strong reliability.

[0101] Simulation of external faults:

[0102] Metallic three-phase short-circuit faults and A / B two-phase ground faults are respectively set at F3 and F4. Taking the most severe external fault F3 as an example, the adaptive differential protection proposed in this paper... d / I r The simulated waveforms are as follows: Figure 6 As shown in Table 2, the simulation results for all the above faults are as follows.

[0103] Table 2 Simulation results of faults outside the zone

[0104]

[0105] Simulation results show that the protection system activates after faults occur at points F3 and F4. 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. Three-phase I d / I r All values ​​are much smaller than the braking coefficient, ensuring the invention remains reliable and does not activate.

[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, we set up an A-phase ground fault and an AB two-phase ground fault with a transition resistance of 500Ω respectively. The simulation results are shown in Table 3.

[0108] Table 3 Simulation results for different fault types

[0109]

[0110] As shown in Table 3, the simulation results indicate that after various ground faults with a transition resistance of 500Ω occur at F2, the protection system activates in all cases. The proposed adaptive differential protection system can accurately identify all faulty phases within 14ms after the fault, and the non-faulty phases reliably do not operate. This invention possesses high resistance tolerance to transition resistance and exhibits high reliability and speed of operation under different fault types.

[0111] White noise:

[0112] To further verify the impact of noise on the adaptive differential protection, 30dB of white noise was added to the three-phase current. Metallic three-phase short-circuit faults were set at F1 and F3, respectively, and a two-phase A / B short-circuit fault with a transition resistance of 25Ω was set at F2. The simulation results are shown in Table 5.

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

[0114]

[0115] Simulation results show that the proposed invention can accurately identify the faulty phase within 14ms after a fault, even under 30dB white noise, while ensuring that the non-faulty phases remain reliably inactive. Therefore, when the SCR is 2.5:1 or higher, the proposed adaptive differential protection can withstand 30dB of noise and exhibits strong robustness.

[0116] In summary, the present invention has the following advantages: (1) It can adapt well to the grid connection of high proportion of new energy sources and has high reliability under different fault types, effectively avoiding the risk of traditional differential protection failing to operate under faults within the zone. (2) The protection action response speed is high, and the response time does not exceed 14ms when the SCR is 2.5:1, which meets the speed requirement of the main protection of AC transmission lines. (3) It can withstand 500Ω transition resistance and 30dB noise, and has strong robustness. (4) It only uses the amplitude and phase information of the current, which is simple to calculate, facilitates the implementation of protection devices, and has high engineering value.

[0117] Figure 7 This is a schematic diagram of the 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 new energy grid-connected lines provided in this embodiment of the 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 acquire the system-side voltage and system-side current at the grid-connected line system-side protection installation point, and the new energy-side voltage and new energy-side current at the new energy-side protection installation point.

[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 start 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 the preset protection start criterion.

[0121] Preferably, the protection start unit 703 determines whether the phase voltage change value and the phase current change value meet the preset protection start criterion in the following manner:

[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 simultaneously 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, then the preset protection criterion is met, and all three-phase protections of the line are activated; S and ΔU R These are the phase voltage changes on the system side and the new energy side, respectively; ΔI S and ΔI R These are the phase current changes on the system side and the new energy side, respectively; U N and I N These represent the line's rated voltage and rated current, respectively; N is the sampling point; and T is the period of the AC system's electrical quantities.

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

[0126] Preferably, the compensation function construction unit 705 is used to calculate the amplitude ratio of the current on both sides of the line based on the amplitude information of the power frequency components of the current 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.

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

[0128]

[0129] Where γ is the amplitude ratio; f1(γ) is the phase compensation function; and 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 grid-connected line based on the phase information of the current on both sides of the line, and to compensate the current on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function, so as 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, phase compensation function, and amplitude compensation function, and determines the compensation current on the system side and the compensation current on the new energy side, including:

[0132]

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

[0134] Preferably, the fault identification unit 707 is used to identify faults within 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 faults within 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 a preset time threshold, a fault is determined to have occurred within the line area; otherwise, a fault is determined to have occurred outside the line area. and These are the system-side compensation current and the new energy-side compensation current, respectively; K is the braking coefficient.

[0137] The adaptive differential protection system 700 for new energy grid-connected lines in an embodiment of the present invention corresponds to the adaptive differential protection method 100 for new energy grid-connected lines in another embodiment of the present invention, and will not be described again here.

[0138] The invention has been described with reference to a few embodiments. However, as will be known to those skilled in the art, and as defined in the appended claims, other embodiments besides those disclosed above fall equivalently within the scope of the invention.

[0139] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to “a / the / the [device, component, etc.]” ​​are openly interpreted as at least one instance of said device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed unless explicitly stated otherwise.

[0140] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied 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] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0142] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0143] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function 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 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 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 includes: The system-side voltage and system-side current at the grid-connected line system-side protection installation point, and the new energy-side voltage and new energy-side current at the new energy-side protection installation point are obtained respectively. 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. When the phase voltage change value and the phase current change value meet the preset protection start criterion, all three phase protections of the line are activated. After the protection is activated, the amplitude and phase of the power frequency components of the current on both sides of the grid-connected line are calculated respectively, and the amplitude and phase information of the power frequency components of the current on the opposite side are obtained. The amplitude ratio of the current on both sides of the line is calculated based on the amplitude information of the power frequency components of the current on both sides of the line, and a phase compensation function and an amplitude compensation function are constructed based on the amplitude ratio. The phase difference between the currents on both sides of the grid-connected line is calculated based on the phase information of the power frequency components of the currents on both sides of the line. The currents on both sides of the line are then 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. Based on the system-side compensation current and the new energy-side compensation current, faults within and outside the line area are identified. The construction of phase compensation function and amplitude compensation function based on the amplitude ratio includes: The process involves compensating the currents on both sides of the line based on the phase difference, phase compensation function, and amplitude compensation function to determine the system-side compensation current and the renewable energy-side compensation current, including: in, and These are the system-side compensation current and the new energy-side compensation current, respectively; γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function; and These are the system-side current and the new energy-side current, respectively. and These represent the phases of the system-side current and the new energy-side current, respectively. denoted as phase difference; j represents a complex number.

2. The method according to claim 1, characterized in that, The method determines whether the phase voltage change value and phase current change value meet the preset protection start criterion in the following ways: 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 simultaneously 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, then the preset protection criterion is met, and all three-phase protections of the line are activated; S and ΔU R These are the phase voltage changes on the system side and the new energy side, respectively; ΔI S and ΔI R These are the phase current changes on the system side and the new energy side, respectively; U N and I N These represent the line's rated voltage and rated current, respectively; N is the sampling point; and T is the period of the AC system's electrical quantities.

3. The method according to claim 1, characterized in that, The method of identifying faults within 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 a preset time threshold, a fault is determined to have occurred within the line area; otherwise, a fault is determined to have occurred outside the line area; where K is the braking coefficient.

4. An adaptive differential protection system for a new energy grid-connected line, characterized in that, The system includes: The voltage and current acquisition unit is used to acquire the system-side voltage and system-side current at the grid-connected line system-side protection installation point, and the new energy-side voltage and new energy-side current at the new energy-side protection installation point, respectively. The change value calculation unit 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. The protection activation unit is used to activate all three phase protections of the line when the phase voltage change value and the phase current change value meet the preset protection activation criteria. The phase and amplitude calculation unit is used to calculate the amplitude and phase of the power frequency components of the current on both sides of the grid-connected line after the protection is started, and to obtain the amplitude and phase information of the power frequency components of the current on the opposite side. The compensation function construction unit is used to calculate the amplitude ratio of the current on both sides of the line based on the amplitude information of the power frequency components of the current on both sides of the grid-connected line, and to construct the phase compensation function and the amplitude compensation function based on the amplitude ratio. The current compensation unit is used to calculate the phase difference of the current on both sides of the line based on the phase information of the power frequency components of the current on both sides of the grid-connected line, and to compensate the current on both sides of the line based on the phase difference, the phase compensation function and the amplitude compensation function, so as to determine the system-side compensation current and the new energy-side compensation current. The fault identification unit is used to identify faults within and outside the line area based on the system-side compensation current and the new energy-side compensation current. The compensation function construction unit, based on the amplitude ratio, constructs a phase compensation function and an amplitude compensation function, including: The current compensation unit, based on the phase difference, phase compensation function, and amplitude compensation function, compensates the current on both sides of the line to determine the system-side compensation current and the new energy-side compensation current, including: in, and These are the system-side compensation current and the new energy-side compensation current, respectively; γ is the amplitude ratio; f1(γ) is the phase compensation function; f2(γ) is the amplitude compensation function; and These are the system-side current and the new energy-side current, respectively. and These represent the phases of the system-side current and the new energy-side current, respectively. denoted as phase difference; j represents a complex number.

5. The system according to claim 4, characterized in that, The protection start-up unit determines whether the phase voltage change value and the phase current change value meet the preset protection start-up criteria using the following methods: 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 ,​ 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 simultaneously 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, then the preset protection criterion is met, and all three-phase protections of the line are activated; S and ΔU R These are the phase voltage changes on the system side and the new energy side, respectively; ΔI S and ΔI R These are the phase current changes on the system side and the new energy side, respectively; U N and I N These represent the line's rated voltage and rated current, respectively; N is the sampling point; and T is the period of the AC system's electrical quantities.

6. The system according to claim 4, characterized in that, The fault identification unit, based on the system-side compensation current and the new energy-side compensation current, identifies faults within and outside the line area, 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 a preset time threshold, a fault is determined to have occurred within the line area; otherwise, a fault is determined to have occurred outside the line area; where K is the braking coefficient.

Images