A new energy power station single-circuit outgoing line non-impact reclosing method and system

Abstract

The application discloses a new energy power station single-circuit outgoing line non-impact reclosing method and system. The method comprises the following steps: after the arc breaking and ionization time T of the circuit breakers at both ends of the line, the circuit breaker on the side close to the new energy power station is reclosed, and a circuit containing an energy storage unit or a new energy circuit containing an energy storage unit is selected, and the circuit breaker on the circuit is closed; the control strategy of the converter of the energy storage unit or the grid-side converter of the new energy is switched to a positive sequence voltage frequency control strategy based on current amplitude limiting control, and the converter is unlocked; the three-phase voltage and three-phase current flowing through the line are monitored, and whether the line fault is a permanent fault or a transient fault is judged according to the voltage and current; if the line is judged to be a permanent fault, reclosing is not performed; if the line is judged to be a transient fault, reclosing timing is entered. The application realizes the discrimination of the transient fault or the permanent fault of the line, and can effectively reduce the reclosing time.

Description

Technical Field

[0001] This invention belongs to the field of power grid technology, specifically a method and system for impact-free reclosing of a single outgoing line in a new energy power station. Background Technology

[0002] With the introduction of the "dual carbon" target and the construction of new power systems, the construction and application of new energy power plants such as wind power and photovoltaic power are expanding, providing strong support for ensuring energy security. Because new energy power plants are affected by weather and other factors, their power generation is intermittent and fluctuates. Therefore, they are generally equipped with energy storage systems to smooth out fluctuations in the output power of new energy sources and improve grid stability.

[0003] For small-scale renewable energy power plants, a single AC transmission line is typically used. When a fault occurs on this line, the circuit breaker closest to the grid is usually reclosed to identify both transient and permanent faults and restore line operation. However, for the power grid, when the AC output of a renewable energy power plant is briefly interrupted due to a fault, a power deficit occurs instantaneously. If the fault is permanent, the reclosing of the grid-side circuit breaker will cause a secondary fault disturbance to the grid. The renewable energy deficit combined with this secondary disturbance further increases the grid's safety risks. Therefore, it is crucial to minimize the occurrence of secondary disturbances caused by reclosing during faults and to restore the line to operation as quickly as possible after a transient fault to reduce the duration of the renewable energy power deficit. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method and system for impact-free reclosing of a single outgoing line in a new energy power plant. It utilizes the energy storage unit within the new energy power plant for power supply and the converter for optimized control to achieve rapid and impact-free identification of transient or permanent line faults, thereby reducing line reclosing time and minimizing disturbance to the power grid.

[0005] Therefore, one technical solution adopted by the present invention is: a method for impact-free reclosing of a single outgoing line in a new energy power station, wherein the new energy power station is connected to the main power grid via a single AC line through a step-up system, and circuit breakers are provided at both ends of the line; the new energy power station contains an energy storage unit; and the method includes:

[0006] Step 1: After the arc ionization time T is completed by the circuit breakers at both ends of the line, the circuit breaker on the side of the line closest to the new energy power station is closed again. At the same time, select a circuit containing an energy storage unit or a new energy circuit containing an energy storage unit and close the circuit breaker on that circuit.

[0007] Step 2: The control strategy of the converter of the energy storage unit or the converter on the new energy grid side is switched to a positive sequence voltage frequency control strategy based on current limiting control, and the converter is unlocked to establish a stable positive sequence AC voltage.

[0008] Step 3: Monitor the three-phase voltage and three-phase current flowing through the line, and determine whether the line fault is permanent or transient based on the voltage and current conditions.

[0009] Step 4: If the line is determined to be a permanent fault, then reclosing will not be performed; if the line is determined to be a transient fault, then the reclosing sequence will be initiated.

[0010] Furthermore, in step 1, the arc deionization time T is preferably 0.2 to 0.3 s.

[0011] Furthermore, in step 2, the positive-sequence voltage frequency control strategy based on current limiting control is as follows:

[0012] Set the voltage amplitude U1, set the maximum amplitude of the line current I1, and combine I1 with the maximum amplitude of the line current I. mx After subtraction, the voltage is compared with the minimum value of the voltage amplitude U1 by the proportional-integral controller to obtain the voltage setpoint U. ref , will U ref The power frequency f0 is input to the positive sequence voltage frequency controller.

[0013] Among them, I mx =max(I a ,I b ,I c ),

[0014] In the formula, I a I b I c These are the amplitudes of the three-phase currents of the line.

[0015] Furthermore, in step 2, U1 is preferably 5% of the AC voltage rating, and I1 is preferably 5A or less.

[0016] Furthermore, in step 3, if there is an asymmetry in the three-phase current or three-phase voltage on the line, and the degree of current asymmetry η i Or voltage asymmetry η u If the percentage exceeds 5%, it indicates that a fault still exists in the line and is classified as a permanent fault. If the three-phase voltage or three-phase current is symmetrical, and the previous protection criterion was a three-phase symmetrical fault, then calculate the line impedance for each phase and between phases. If the minimum absolute value of the impedance for each phase and between phases is Z... mx If Z is greater than Z0, it indicates that the line fault has disappeared and is judged as a transient fault. mxIf the value is less than Z0, it indicates that the line fault still exists and is judged as a permanent fault; if the three-phase voltage or current is symmetrical and the previous protection criterion was an asymmetrical fault, it indicates that the line fault has disappeared and is judged as a transient fault.

[0017] Where Z0 is the line's no-load impedance value divided by 3.

[0018] Furthermore,

[0019]

[0020]

[0021]

[0022] In the formula, U a U b U c U represents the amplitude of the three-phase voltage of the line. ab U bc U ac I represents the phase-to-phase voltage amplitude of the line. ab I bc I ac I represents the amplitude of the phase-to-phase current in the line. a I b I c These are the amplitudes of the three-phase currents of the line.

[0023] Furthermore, in step 4, the reclosing timing sequence is as follows:

[0024] 1) Lockout converter;

[0025] 2) Disconnect the circuit breaker connected to the converter;

[0026] 3) Circuit breakers on the closed circuit side closest to the power grid;

[0027] 4) New energy power plants are connected to the grid according to the conventional grid connection process.

[0028] Another technical solution adopted in this invention is: a single-circuit outgoing line impact-free reclosing system for a new energy power station, wherein the new energy power station is connected to the main power grid via a single AC line through a step-up system, and circuit breakers are installed at both ends of the line; the new energy power station contains an energy storage unit; and the system includes:

[0029] Arc deionization unit: After the circuit breakers at both ends of the line have interrupted the arc deionization time T, the circuit breaker on the side of the line closest to the new energy power station is reclosed. At the same time, a circuit containing an energy storage unit or a new energy circuit containing an energy storage unit is selected, and the circuit breaker on that circuit is closed.

[0030] Control strategy switching unit: The control strategy of the converter of the energy storage unit or the converter on the new energy grid side is switched to a positive sequence voltage frequency control strategy based on current limiting control, and the converter is unlocked to establish a stable positive sequence AC voltage.

[0031] Fault diagnosis unit: Monitors the three-phase voltage and three-phase current flowing through the line, and determines whether the line fault is permanent or transient based on the voltage and current conditions;

[0032] Action execution unit: If the line is determined to be a permanent fault, it will not reclose; if the line is determined to be a transient fault, it will enter the reclosing sequence.

[0033] Compared with the prior art, the present invention has the following beneficial technical effects:

[0034] (1) This invention utilizes the energy storage unit in the new energy power station for power supply and the converter for optimized control to identify transient or permanent line faults, which can effectively reduce reclosing time.

[0035] (2) The present invention can avoid reclosing and permanent faults, avoid secondary disturbances to the power grid or power equipment, and improve the stability of the power grid. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the single-circuit outgoing line system of the new energy power plant of the present invention.

[0038] Figure 2 This is a flowchart of the non-impact reclosing method for a single outgoing line of a new energy power plant according to the present invention.

[0039] Figure 3 This is a schematic diagram of the positive sequence voltage frequency control strategy based on current limiting control of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1

[0042] Single-circuit outgoing line system of new energy power plant, such as Figure 1 As shown, the new energy power station is connected to the main power grid via a transformer and other step-up systems, and then via a single-circuit AC line. The circuit breakers at both ends of the single-circuit AC line are marked as S1 and S2, respectively. The new energy power station in this invention includes energy storage units. These energy storage units can be independently arranged energy storage systems or distributed energy storage systems integrated with new energy sources. Distributed energy storage systems are generally located in the DC links of wind and photovoltaic converters; they can be fully or partially installed, depending on the actual engineering requirements. Taking a direct-drive wind turbine as an example, the wind turbine unit is connected to the grid through a DC back-to-back converter, and the energy storage system is located on the DC bus, forming a new energy + energy storage configuration.

[0043] Before reclosing a single AC line in a new energy power plant, the three-phase circuit breakers S1 and S2 at both ends of the single AC line are usually in the open state due to the operation of line protection and other actions. At the same time, the new energy and energy storage systems will also be in the off-grid state, that is, the output circuit breaker is in the open state. Figure 2 A flowchart of a non-impact reclosing method for a single outgoing line of a new energy power plant is presented, and its steps are as follows:

[0044] Step 1: After the circuit breakers at both ends of the line (i.e., a single-circuit AC line) have been open for a time T, the arc deionization on the line is basically complete. At this time, the circuit breaker closest to the new energy power station is reclosed. Simultaneously, a circuit containing an energy storage unit or a new energy circuit containing an energy storage unit is selected, and the circuit breaker on that circuit is closed. The arc deionization time T is generally 0.2s to 0.3s.

[0045] Step 2: The control strategy of the converter of the energy storage unit or the converter on the new energy grid side is switched to a positive sequence voltage frequency control strategy based on current limiting control, and the converter is unlocked to establish a stable positive sequence AC voltage.

[0046] Positive sequence voltage-frequency control strategy based on current limiting control, such as Figure 3 As shown, the voltage amplitude U1 is set, which is generally taken as 5% of the rated AC voltage; the maximum amplitude I1 of the line current is set, which is generally taken as below 5A. I1 and the maximum amplitude I of the line current are then compared. mx After subtraction, the voltage is compared with the minimum value of U1 by the proportional-integral controller (PI controller) to obtain the voltage setting value U. ref . Will U ref The power frequency f0 is input to the now relatively mature positive sequence voltage-frequency controller.

[0047] in,

[0048] I mx =max(I a ,I b ,I c ),

[0049] In the formula, I a I b I c This represents the amplitude of the three-phase current in the line.

[0050] Step 3: Monitor the three-phase voltage and three-phase current flowing through the line, and determine whether the line fault is permanent or transient based on the voltage and current conditions.

[0051] If there is an imbalance in the three-phase current or three-phase voltage on the line, and the degree of current imbalance η i Or voltage asymmetry η u If the percentage exceeds 5%, it indicates that a fault still exists in the line, and is judged as a permanent line fault. If the three-phase voltage or three-phase current is symmetrical, and the previous protection criterion was a three-phase symmetrical fault, then calculate the line impedance of each phase and between phases. If the minimum absolute value of the impedance of each phase and between phases is Z... mx If Z is greater than Z0, it indicates that the line fault has disappeared and is judged as a transient fault. mx If the value is less than Z0, it indicates that the line fault still exists and is judged as a permanent fault; if the three-phase voltage or current is symmetrical and the previous protection criterion was an asymmetrical fault, it indicates that the line fault has disappeared and is judged as a transient fault.

[0052] Where Z0 is the line's no-load impedance value divided by 3.

[0053]

[0054]

[0055]

[0056] U a U b U c U represents the amplitude of the three-phase voltage of the line. ab U bc U ac I represents the phase-to-phase voltage amplitude of the line. ab I bc I ac This represents the amplitude of the phase-to-phase current in the line.

[0057] Step 4: If the line is determined to be a permanent fault, then reclosing will not be performed; if the line is determined to be a transient fault, then the reclosing sequence will be initiated.

[0058] The reclosing timing sequence is as follows:

[0059] 1) Lockout converter;

[0060] 2) Disconnect the circuit breaker connected to the converter;

[0061] 3) Circuit breakers on the closed circuit side closest to the power grid;

[0062] 4) New energy power plants are connected to the grid according to the conventional grid connection process.

[0063] Example 2

[0064] This embodiment describes a single-circuit, impact-free reclosing system for a new energy power station. The new energy power station is connected to the main power grid via a single AC line through a step-up system. Circuit breakers are installed at both ends of the line. The new energy power station includes an energy storage unit. The system comprises:

[0065] Arc deionization unit: After the circuit breakers at both ends of the line have interrupted the arc deionization time T, the circuit breaker on the side of the line closest to the new energy power station is reclosed. At the same time, a circuit containing an energy storage unit or a new energy circuit containing an energy storage unit is selected, and the circuit breaker on that circuit is closed.

[0066] Control strategy switching unit: The control strategy of the converter of the energy storage unit or the converter on the new energy grid side is switched to a positive sequence voltage frequency control strategy based on current limiting control, and the converter is unlocked to establish a stable positive sequence AC voltage.

[0067] Fault diagnosis unit: Monitors the three-phase voltage and three-phase current flowing through the line, and determines whether the line fault is permanent or transient based on the voltage and current conditions;

[0068] Action execution unit: If the line is determined to be a permanent fault, it will not reclose; if the line is determined to be a transient fault, it will enter the reclosing sequence.

[0069] Specifically, in the arc deionization unit, the arc deionization time T is 0.2 to 0.3 s.

[0070] Specifically, in the control strategy switching unit, the positive sequence voltage frequency control strategy based on current limiting control is as follows:

[0071] Set the voltage amplitude U1, taking 5% of the rated AC voltage; set the maximum amplitude of the line current I1, taking I1 as below 5A; combine I1 and the maximum amplitude of the line current I... mx After subtraction, the voltage is compared with the minimum value of the voltage amplitude U1 by the proportional-integral controller to obtain the voltage setpoint U. ref , will U ref The power frequency f0 is input to the positive sequence voltage frequency controller.

[0072] Among them, Imx =max(I a ,I b ,I c ),

[0073] In the formula, I a I b I c These are the amplitudes of the three-phase currents of the line.

[0074] Specifically, in the fault judgment unit, if there is an asymmetry in the three-phase current or three-phase voltage on the line, and the degree of current asymmetry η i Or voltage asymmetry η u If the percentage exceeds 5%, it indicates that a fault still exists in the line and is classified as a permanent fault. If the three-phase voltage or three-phase current is symmetrical, and the previous protection criterion was a three-phase symmetrical fault, then calculate the line impedance for each phase and between phases. If the minimum absolute value of the impedance for each phase and between phases is Z... mx If Z is greater than Z0, it indicates that the line fault has disappeared and is judged as a transient fault. mx If the value is less than Z0, it indicates that the line fault still exists and is judged as a permanent fault; if the three-phase voltage or current is symmetrical and the previous protection criterion was an asymmetrical fault, it indicates that the line fault has disappeared and is judged as a transient fault.

[0075] Where Z0 is the line no-load impedance value divided by 3;

[0076]

[0077]

[0078]

[0079] In the formula, U a U b U c U represents the amplitude of the three-phase voltage of the line. ab U bc U ac I represents the phase-to-phase voltage amplitude of the line. ab I bc I ac I represents the amplitude of the phase-to-phase current in the line. a I b I c These are the amplitudes of the three-phase currents of the line.

[0080] Specifically, in the aforementioned action execution unit, the reclosing timing sequence is as follows:

[0081] 1) Lockout converter;

[0082] 2) Disconnect the circuit breaker connected to the converter;

[0083] 3) Circuit breakers on the closed circuit side closest to the power grid;

[0084] 4) New energy power plants are connected to the grid according to the conventional grid connection process.

[0085] 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 them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for impact-free reclosing of a single outgoing line in a new energy power station, wherein the new energy power station is connected to the main power grid via a single AC line through a step-up system, and circuit breakers are installed at both ends of the line; the new energy power station includes an energy storage unit, characterized in that... The method includes: Step 1: After the arc ionization time T is completed by the circuit breakers at both ends of the line, the circuit breaker on the side of the line closest to the new energy power station is closed again. At the same time, select a circuit containing an energy storage unit or a new energy circuit containing an energy storage unit and close the circuit breaker on that circuit. Step 2: The control strategy of the converter of the energy storage system or the converter on the new energy grid side is switched to the positive sequence voltage frequency control strategy based on current limiting control, and the converter is unlocked to establish a stable positive sequence AC voltage. Step 3: Monitor the three-phase voltage and three-phase current flowing through the line, and determine whether the line fault is permanent or transient based on the voltage and current conditions. Step 4: If the line fault is determined to be permanent, reclosing will not be performed; if the line fault is determined to be transient, the reclosing sequence will be initiated. In step 2, the positive sequence voltage frequency control strategy based on current limiting control is as follows: Set the voltage amplitude U1, set the maximum amplitude of the line current I1, and combine I1 with the maximum amplitude of the line current. I mx After subtraction, the voltage is compared with the minimum value of the voltage amplitude U1 by the proportional-integral controller to obtain the voltage setpoint U. ref , will U ref The power frequency f0 is input to the positive sequence voltage frequency controller. in, In the formula, , , These are the amplitudes of the three-phase currents of the line; In step 3, if there is an asymmetry in the three-phase current or three-phase voltage on the line, and the degree of current asymmetry η i Or voltage asymmetry η u If the percentage exceeds 5%, it indicates that a fault still exists in the line and is classified as a permanent fault. If the three-phase voltage or three-phase current is symmetrical, and the previous protection criterion was a three-phase symmetrical fault, then calculate the line impedance for each phase and between phases. If the minimum absolute value of the impedance for each phase and between phases is Z... mx If Z is greater than Z0, it indicates that the line fault has disappeared and is judged as a transient fault. mx If the value is less than Z0, it indicates that the line fault still exists and is judged as a permanent fault; if the three-phase voltage or current is symmetrical and the previous protection criterion was an asymmetrical fault, it indicates that the line fault has disappeared and is judged as a transient fault. Where Z0 is the line's no-load impedance value divided by 3.

2. The method for impact-free reclosing of a single outgoing line in a new energy power station according to claim 1, characterized in that, In step 1, the arc deionization time T is 0.2~0.3s.

3. The method for impact-free reclosing of a single outgoing line in a new energy power station according to claim 1, characterized in that, In step 2, U1 is taken as 5% of the rated AC voltage, and I1 is taken as less than 5A.

4. The method for impact-free reclosing of a single outgoing line in a new energy power station according to claim 1, characterized in that, ， ， ， In the formula, , , This refers to the amplitude of the three-phase voltage of the line. , , This refers to the phase-to-phase voltage amplitude of the line. , , This refers to the phase-to-phase current amplitude. , , These are the amplitudes of the three-phase currents of the line.

5. The method for impact-free reclosing of a single outgoing line in a new energy power station according to claim 1, characterized in that, In step 4, the reclosing timing sequence is as follows: 1) Blocking out the converter; 2) Disconnect the circuit breaker connected to the converter; 3) Circuit breakers on the closed circuit near the power grid side; 4) New energy power plants are connected to the grid according to the conventional grid connection process.

6. A single-circuit outgoing line impulse-free reclosing system for a new energy power station, wherein the new energy power station is connected to the main power grid via a single-circuit AC line through a step-up system, and circuit breakers are installed at both ends of the line; the new energy power station includes an energy storage unit, characterized in that... The system includes: Arc deionization unit: After the circuit breakers at both ends of the line have interrupted the arc deionization time T, the circuit breaker on the side of the line closest to the new energy power station is reclosed. At the same time, a circuit containing an energy storage unit or a new energy circuit containing an energy storage unit is selected, and the circuit breaker on that circuit is closed. Control strategy switching unit: The control strategy of the converter of the energy storage unit or the converter on the new energy grid side is switched to a positive sequence voltage frequency control strategy based on current limiting control, and the converter is unlocked to establish a stable positive sequence AC voltage. Fault diagnosis unit: Monitors the three-phase voltage and three-phase current flowing through the line, and determines whether the line fault is permanent or transient based on the voltage and current conditions; Action execution unit: If the line is determined to be a permanent fault, reclosing will not be performed; if the line is determined to be a transient fault, the reclosing sequence will be initiated. In the control strategy switching unit, the positive sequence voltage frequency control strategy based on current limiting control is as follows: Set the voltage amplitude U1, set the maximum amplitude of the line current I1, and combine I1 with the maximum amplitude of the line current. I mx After subtraction, the voltage is compared with the minimum value of the voltage amplitude U1 by the proportional-integral controller to obtain the voltage setpoint U. ref , will U ref The power frequency f0 is input to the positive sequence voltage frequency controller. in, In the formula, , , These are the amplitudes of the three-phase currents of the line; In the aforementioned fault diagnosis unit, if there is an asymmetry in the three-phase current or three-phase voltage on the line, and the degree of current asymmetry η i Or voltage asymmetry η u If the percentage exceeds 5%, it indicates that a fault still exists in the line and is classified as a permanent fault. If the three-phase voltage or three-phase current is symmetrical, and the previous protection criterion was a three-phase symmetrical fault, then calculate the line impedance for each phase and between phases. If the minimum absolute value of the impedance for each phase and between phases is Z... mx If Z is greater than Z0, it indicates that the line fault has disappeared and is judged as a transient fault. mx If the value is less than Z0, it indicates that the line fault still exists and is judged as a permanent fault; if the three-phase voltage or current is symmetrical and the previous protection criterion was an asymmetrical fault, it indicates that the line fault has disappeared and is judged as a transient fault. Where Z0 is the line's no-load impedance value divided by 3.

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