A method and system for calculating the capacity of distributed photovoltaic access to an active distribution network

Abstract

The present invention proposes a method and system for calculating the access capacity of distributed photovoltaic in an active distribution network, comprising: calculating the mismatch current of outgoing line and branch protection; considering the coordination of outgoing line and branch, obtaining the maximum capacity that can be accessed by the current bus based on the calculated outgoing line and branch protection mismatch current as the first capacity; calculating the mismatch current of outgoing line and boundary protection; considering the coordination of outgoing line and boundary, obtaining the maximum capacity that can be accessed by the current bus based on the calculated outgoing line and boundary protection mismatch current as the second capacity; comprehensively considering the coordination of outgoing line and branch, outgoing line and boundary, and taking the minimum value between the first capacity and the second capacity as the maximum capacity that can be accessed by the current bus.

Description

Technical Field

[0001] The present invention belongs to the technical field of distributed photovoltaic access capacity calculation, and in particular relates to a method and system for calculating the access capacity of distributed photovoltaic in an active distribution network. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] For distributed power sources that are directly connected to the public grid at a 10 kV voltage level and connected to the grid at a 35 kV grid level, they should have low voltage ride-through capability. When the grid connection point voltage is within the standard medium voltage-time curve profile and above, the distributed power source should not be disconnected from the grid and continue to operate; otherwise, the distributed power source is allowed to be cut out. Therefore, this requires that when a fault occurs, the distributed photovoltaic can continuously and effectively provide short-circuit current.

[0004] At present, the protection scheme for phase-to-phase faults in 10kV distribution networks is generally set up according to the three-level switch protection of "outgoing line + branch + boundary". The outgoing line switch is equipped with three-stage overcurrent protection, most of which have directional locking function, the branch switch is equipped with two-stage overcurrent protection, and the boundary switch is equipped with one or two-stage overcurrent protection. Both the outgoing line switch and the branch switch have the function of reclosing. Among them, the branch circuit breaker is installed at an appropriate position on the line, and the circuit breaker is isolated from the phase-to-phase short-circuit fault and the single-phase grounding fault by local protection; the boundary circuit breaker is installed in front of the user's power distribution device, and the circuit breaker is isolated from the phase-to-phase short-circuit fault and the single-phase grounding fault by local protection.

[0005] There are relevant corporate standards: the installed capacity of distributed power sources that can be connected to the 10 kV voltage distribution network is 0.4 MW-6 MW, and the installed capacity of distributed power sources that can be connected to the 35 kV grid distribution network is 6 MW-20 MW. This standard defines the maximum capacity of distributed power sources that can be connected in terms of system stability, but lacks the impact on the coordination of relay protection setting. It is possible that the unreasonable configuration of distributed photovoltaics in the 10 kV feeder line of a substation may lead to improper coordination of the feeder line setting and branch setting. In severe cases, there may be a loss of coordination, resulting in the expansion of the accident. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a method for calculating the access capacity of distributed photovoltaic in an active distribution network. Based on the coordination ability of the feeder outgoing line setting and branch setting, the outgoing line setting and boundary setting of the traditional distribution network, the maximum distributed photovoltaic capacity that the current bus can carry is evaluated, so as to avoid the expansion of accidents due to improper coordination of the setting.

[0007] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0008] In a first aspect, a method for calculating the access capacity of distributed photovoltaic power generation in an active distribution network is disclosed, comprising:

[0009] Calculate the mismatch current of outgoing line and branch protection;

[0010] Considering the coordination of outgoing and branch lines, the maximum capacity that can be connected to the current busbar is obtained based on the calculated outgoing and branch line protection mismatch currents as the first capacity;

[0011] Calculate the mismatch current of outgoing and boundary protection;

[0012] Considering the coordination of outgoing and boundary lines, the maximum capacity that can be connected to the current busbar is obtained based on the calculated outgoing and boundary protection mismatch currents as the second capacity;

[0013] Taking into account the coordination between outgoing lines and branches, outgoing lines and boundaries, the minimum value between the first capacity and the second capacity is taken as the maximum capacity that can be connected to the current bus.

[0014] As a further technical solution, the three-stage overcurrent protection of the active distribution network includes: protection coordination of outgoing lines, branches and boundaries;

[0015] Among them, the three-stage setting value of the outgoing line protection of a certain feeder is:

[0016] (1) Overcurrent I stage constant: Current constant I CX-I , delay 0 seconds;

[0017] (2) Overcurrent II stage setting: Current setting I CX-II , delay 0.4 seconds;

[0018] (3) Overcurrent stage III setting: Current setting I CX-III , delay 0.6 seconds;

[0019] The branches of the current feeder are generally equipped with two-stage protection, and their settings are:

[0020] (1) Overcurrent I stage constant: Current constant I FZ-I , delay 0 seconds;

[0021] (2) Overcurrent II stage setting: Current setting I FZ-II , delay 0.2 seconds;

[0022] The current feeder boundary is generally configured with two-stage protection, and its setting value is:

[0023] (1) Overcurrent I stage constant: Current constant I FJ-I , delay 0 seconds;

[0024] (2) Overcurrent II stage setting: Current setting I FJ-II , delay 0.2 seconds.

[0025] As a further technical solution, when calculating the mismatch current of the outgoing line and branch protection, specifically:

[0026] The difference between the overcurrent I-section current setting value in the outgoing line protection of the feeder and the overcurrent I-section current setting value in the branch protection of the feeder is taken as the outgoing line and branch protection mismatch current. The above-mentioned overcurrent I-section current setting value in the outgoing line protection of the feeder and the overcurrent I-section current setting value in the branch protection of the feeder can be obtained from the dispatching agency.

[0027] As a further technical solution, the maximum capacity that can be connected to the current busbar is obtained based on the calculated outgoing line and branch protection mismatch currents as the first capacity:

[0028]

[0029] Among them, I SP.1 It represents the nominal value of the instantaneous mismatch current between the outgoing line and the branch, in kiloamperes; U represents the nominal value of the calculated network voltage, in kilovolts; k represents the multiple of the short-circuit current provided by the distributed system at the time of fault and the rated current, and k is generally taken as 1.1 to 1.5.

[0030] As a further technical solution, when calculating the mismatch current of the outgoing line and the boundary protection, it is specifically as follows:

[0031] The difference between the overcurrent I section current setting value in the outgoing line protection of the feeder and the overcurrent I section current setting value in the boundary protection of the feeder is taken as the outgoing line and boundary protection mismatch current. The overcurrent I section current setting value in the outgoing line protection of the feeder and the overcurrent I section current setting value in the boundary protection of the feeder can be obtained from the dispatching agency.

[0032] As a further technical solution, the maximum capacity that can be connected to the current busbar is obtained based on the calculated outgoing line and boundary protection mismatch currents as the second capacity:

[0033]

[0034] Among them, I SP.2 It represents the nominal value of the instantaneous mismatch current between the outgoing line and the branch, in kiloamperes; U represents the nominal value of the calculated network voltage, in kilovolts; k represents the multiple of the short-circuit current provided by the distributed system at the time of fault and the rated current, and k is generally taken as 1.1 to 1.5.

[0035] As a further technical solution, the method is applicable to planning distributed photovoltaic access in 35 kV or 10 kV distribution networks.

[0036] The present invention takes a branch or boundary line fault as an example, taking into account the loss of coordination between the overcurrent section I of the outgoing line protection and the branch protection, and the overcurrent section I of the outgoing line protection and the boundary protection, and the maximum distributed photovoltaic capacity that can be connected to the busbar connected to the current feeder is calculated by the above method.

[0037] One or more of the above technical solutions have the following beneficial effects:

[0038] The present invention evaluates the maximum distributed photovoltaic capacity that can be accessed through other feeders on the bus connected to the current feeder according to the set value coordination of the feeder "outgoing line + branch" or "outgoing line + boundary", so as to prevent the distributed photovoltaic capacity connected to the bus from being too high, resulting in improper coordination of the set values ​​of the outgoing line and the branch, the outgoing line and the boundary when a branch or boundary fault occurs, resulting in malfunction of the outgoing line protection, causing the circuit breaker to trip, and causing the accident to expand.

[0039] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0041] Figure 1 The figure is a schematic diagram of a network configuration according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0043] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0044] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0045] The overall idea proposed by the present invention is:

[0046] The present invention evaluates the maximum distributed photovoltaic capacity that the current bus can carry based on the coordination capabilities of the traditional distribution network feeder outgoing line setting and branch setting, outgoing line setting and boundary setting, and can avoid the expansion of accidents caused by improper setting coordination.

[0047] Embodiment 1

[0048] This embodiment discloses a method for calculating the access capacity of distributed photovoltaic power generation in an active distribution network, including:

[0049] Calculate the mismatch current of outgoing line and branch protection;

[0050] Considering the coordination of outgoing and branch lines, the maximum capacity that can be connected to the current busbar is obtained based on the calculated outgoing and branch protection mismatch currents as the first capacity. This method can avoid the misoperation of the outgoing line protection caused by faults at the branch outlet;

[0051] Calculate the mismatch current of outgoing and boundary protection;

[0052] Considering the coordination between outgoing and boundary, the maximum capacity that can be connected to the current bus is obtained based on the calculated outgoing and boundary protection mismatch currents as the second capacity. This method can avoid the misoperation of the outgoing protection caused by faults at the boundary outlet.

[0053] Taking into account the coordination between outgoing lines and branches, outgoing lines and boundaries, the minimum value between the first capacity and the second capacity is taken as the maximum capacity that can be connected to the current bus.

[0054] When the above branches and boundaries exist at the same time, taking a conservative value, that is, the minimum value, can ensure the security of the system.

[0055] Specifically, in a real power grid, the topology diagram of a 10 kV distribution network is as follows: Figure 1 QF represents the outgoing line circuit breaker, equipped with outgoing line protection, tripping, and the protection setting is:

[0056] (1) Stage I, current setting 6000A, delay 0 seconds;

[0057] (2) Section II, current setting 1200A, delay 0.4 seconds;

[0058] (3) Section III, current setting 900A, delay 0.6 seconds.

[0059] FZ1~FZ3 represent branch circuit breakers, equipped with branch protection, tripping, and protection settings are:

[0060] (1) Stage I, current setting 900A, delay 0 seconds;

[0061] (2) Section II, current setting 600A, delay 0.2s.

[0062] FJ1~FJ2 represent boundary circuit breakers, equipped with boundary protection, tripping, and protection setting value:

[0063] (1) Stage I, current setting 600A, delay 0 seconds;

[0064] (2) Section II, current setting 480A, delay 0.2 seconds

[0065] FD1~FD2 represent section circuit breakers, which are equipped with section protection and alarm, and are not considered here.

[0066] The calculation method for the maximum distributed photovoltaic capacity that can be connected to the current 10 kV bus is:

[0067] (1) Calculate the mismatch current of the outgoing line and branch protection as follows:

[0068] I SP.1 =6000-900=5100 amperes (6)

[0069] (2) Considering the coordination of outgoing lines and branches, according to conservative calculations, in the event of a fault, the distributed photovoltaic can provide a short-circuit current of 1.5 times the rated current. The maximum capacity that can be connected to the current bus is

[0070]

[0071] (3) Calculate the mismatch current of the outgoing line and boundary protection as

[0072] I SP.2 =6000-600=5400 amperes (8)

[0073] (4) Considering the coordination of outgoing lines and boundaries, according to conservative calculations, in the event of a fault, the distributed photovoltaic can provide a short-circuit current of 1.5 times the rated current. The maximum capacity that can be connected to the current bus is

[0074]

[0075] (5) Taking into account the coordination between outgoing and branching, outgoing and boundary, the current maximum capacity that can be connected to the bus is

[0076] S max = min (61.8 MW, 65.5 MW) = 61.8 MW (10)

[0077] It can be seen from this that in order to ensure the reliability of the set value coordination, the maximum total distributed photovoltaic capacity that the current bus can carry is 61.8 MW.

[0078] It should be noted that the above-mentioned FZ1 setting of 900A and FJ1 setting of 600A do not take into account the short-circuit current provided entirely by the system side in the event of a fault at the branch or boundary outlet in the case of distributed photovoltaic access.

[0079] Assuming that all the distributed photovoltaics connected to the bus can output a maximum short-circuit current of 5100 amperes, according to the superposition principle, when a fault occurs at the FZ1 outlet, in addition to the 900 amperes short-circuit current provided by the system, the remaining distributed photovoltaics connected to the bus provide a short-circuit current of 5100 amperes, which adds up to 6000 amperes, reaching the QF protection setting of the outgoing line circuit breaker. This causes the fault at the branch outlet to cause the outgoing line protection to malfunction. (The photovoltaic grid-connected capacity can be derived from 5100 amperes)

[0080] Therefore, the above measures can avoid false operation of the outgoing line protection caused by faults at the branch outlet.

[0081] Embodiment 2

[0082] The purpose of this embodiment is to provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the steps of the above method are implemented when the processor executes the program.

[0083] Embodiment 3

[0084] The purpose of this embodiment is to provide a computer-readable storage medium.

[0085] A computer-readable storage medium stores a computer program, which executes the steps of the above method when executed by a processor.

[0086] Embodiment 4

[0087] The purpose of this embodiment is to provide a distributed photovoltaic access capacity calculation system for an active distribution network, including:

[0088] The first capacity calculation module is configured as follows:

[0089] Calculate the mismatch current of outgoing line and branch protection;

[0090] Considering the coordination of outgoing and branch lines, the maximum capacity that can be connected to the current busbar is obtained based on the calculated outgoing and branch line protection mismatch currents as the first capacity;

[0091] The second capacity calculation module is configured as follows:

[0092] Calculate the mismatch current of outgoing and boundary protection;

[0093] Considering the coordination of outgoing and boundary lines, the maximum capacity that can be connected to the current busbar is obtained based on the calculated outgoing and boundary protection mismatch currents as the second capacity;

[0094] The module for determining the maximum accessible capacity is configured to: comprehensively consider the coordination between outgoing lines and branches, and outgoing lines and boundaries, and take the minimum value between the first capacity and the second capacity as the maximum accessible capacity of the current bus.

[0095] The steps involved in the apparatuses of the above embodiments 2, 3 and 4 correspond to the method embodiment 1, and the specific implementation methods can refer to the relevant description part of embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood to include any medium that can store, encode or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

[0096] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0097] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A method for calculating the access capacity of distributed photovoltaic power generation in an active distribution network, characterized in that: include: Calculate the mismatch current of outgoing line and branch protection; Considering the coordination of outgoing and branch lines, the maximum capacity that can be connected to the current busbar is obtained based on the calculated outgoing and branch protection mismatch currents as the first capacity. This method can avoid the misoperation of the outgoing line protection caused by the fault at the branch outlet; Calculate the mismatch current of outgoing and boundary protection; Considering the coordination between outgoing and boundary, the maximum capacity that can be connected to the current busbar is obtained based on the calculated outgoing and boundary protection mismatch current, which is used as the second capacity. This method can avoid the misoperation of the outgoing line protection caused by the fault at the boundary outlet; Taking into account the coordination between outgoing and branch lines, outgoing and boundary lines, the minimum value between the first capacity and the second capacity is taken as the maximum capacity that can be connected to the current bus; When calculating the mismatch current of the outgoing line and branch protection, the specific calculation is: The difference between the overcurrent I-stage current setting value in the feeder outgoing line protection and the overcurrent I-stage current setting value in the feeder branch protection is taken as the outgoing line and branch protection mismatch current; Based on the calculated outgoing line and branch protection mismatch current, the maximum capacity that can be connected to the current bus is obtained as the first capacity: in, Indicates the nominal value of the instantaneous mismatch current between the outgoing line and the branch, in kiloamperes. U It indicates the nominal value of the calculated network voltage, in kilovolts, and k indicates the multiple of the short-circuit current provided by the distributed system at the time of the fault and the rated current; When calculating the mismatch current of the outgoing line and boundary protection, it is specifically: The difference between the overcurrent I section current setting value in the feeder outgoing line protection and the overcurrent I section current setting value in the feeder boundary protection is taken as the outgoing line and boundary protection mismatch current; Based on the calculated outgoing line and boundary protection mismatch current, the maximum capacity that can be connected to the current bus is obtained as the second capacity: in, Indicates the nominal value of the instantaneous mismatch current between the outgoing line and the branch, in kiloamperes. U It represents the nominal value of the calculated network voltage in kilovolts. k represents the multiple of the short-circuit current provided by the distributed system at the time of fault and the rated current. The value of k is 1.1~1.

5.

2. A method for calculating the access capacity of distributed photovoltaic power generation in an active distribution network as claimed in claim 1, characterized in that: Three-stage overcurrent protection for active distribution networks, coordination of outgoing lines, branches and boundaries.

3. A method for calculating the access capacity of distributed photovoltaic power generation in an active distribution network as claimed in any one of claims 1 to 2, characterized in that: The method is applicable to planning distributed photovoltaic access in 35 kV or 10 kV distribution networks.

4. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the steps of the method described in any one of claims 1 to 2 are implemented.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method described in any one of claims 1 to 2 are performed.

6. An active distribution network distributed photovoltaic access capacity calculation system, characterized in that: include: The first capacity calculation module is configured as follows: Calculate the mismatch current of outgoing line and branch protection; Considering the coordination of outgoing and branch lines, the maximum capacity that can be connected to the current busbar is obtained based on the calculated outgoing and branch protection mismatch currents as the first capacity. This method can avoid the misoperation of the outgoing line protection caused by the fault at the branch outlet; The second capacity calculation module is configured as follows: Calculate the mismatch current of outgoing and boundary protection; Considering the coordination between outgoing and boundary, the maximum capacity that can be connected to the current busbar is obtained based on the calculated outgoing and boundary protection mismatch current, which is used as the second capacity. This method can avoid the misoperation of the outgoing line protection caused by the fault at the boundary outlet; The module for determining the maximum accessible capacity is configured to: comprehensively consider the coordination between the outgoing line and the branch, and between the outgoing line and the boundary, and take the minimum value between the first capacity and the second capacity as the maximum accessible capacity of the current bus; When calculating the mismatch current of the outgoing line and branch protection, the specific calculation is: The difference between the overcurrent I-stage current setting value in the feeder outgoing line protection and the overcurrent I-stage current setting value in the feeder branch protection is taken as the outgoing line and branch protection mismatch current; Based on the calculated outgoing line and branch protection mismatch current, the maximum capacity that can be connected to the current bus is obtained as the first capacity: in, Indicates the nominal value of the instantaneous mismatch current between the outgoing line and the branch, in kiloamperes. U It indicates the nominal value of the calculated network voltage, in kilovolts, and k indicates the multiple of the short-circuit current provided by the distributed system at the time of the fault and the rated current; When calculating the mismatch current of the outgoing line and boundary protection, it is specifically: The difference between the overcurrent I section current setting value in the feeder outgoing line protection and the overcurrent I section current setting value in the feeder boundary protection is taken as the outgoing line and boundary protection mismatch current; Based on the calculated outgoing line and boundary protection mismatch current, the maximum capacity that can be connected to the current bus is obtained as the second capacity: in, Indicates the nominal value of the instantaneous mismatch current between the outgoing line and the branch, in kiloamperes. U It represents the nominal value of the calculated network voltage in kilovolts. k represents the multiple of the short-circuit current provided by the distributed system at the time of fault and the rated current. The value of k is 1.1~1.5.

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