Universal protection method and device for distribution network suitable for distributed photovoltaic boosting

Abstract

The present invention discloses a universal protection method and device for distribution networks suitable for distributed photovoltaic power generation. The present invention introduces the overcurrent protection principle and the distance protection principle, and proposes a composite criterion for outgoing line protection section I. When the measured current amplitude of the fault point is greater than the maximum theoretical limit of the protection current flowing under the photovoltaic power generation, the composite criterion for outgoing line protection section I determines that the fault point is within the protection range of the preset outgoing line protection section I, and the protection can be reliably actuated. When the current amplitude of the fault point is less than or equal to the maximum theoretical limit, and the measured impedance value is less than or equal to the preset impedance constant, the composite criterion for outgoing line protection section I determines that the fault point is within the protection range of the preset outgoing line protection section I, and the protection can be reliably actuated. Thus, the present invention improves the reliability and selectivity of active distribution network protection, and can be widely applied to distribution network protection in different high-proportion photovoltaic access and operation scenarios.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network protection, and more particularly to a universal distribution network protection method and device suitable for distributed photovoltaic auxiliary function. Background Art

[0002] In the context of developing new power systems, the increased integration of distributed power sources into distribution networks is an inevitable trend for improving the local consumption of renewable energy. Distributed photovoltaics are the primary form of renewable energy integration into distribution networks. The widespread integration of distributed photovoltaics will alter the existing radial flow pattern of single-source power sources in distribution networks and, in the event of a fault, affect the short-circuit current provided by the primary power source, leading to current boosting, current draining, or reverse current flow. This degrades the reliability of traditional distribution network line protection settings and the coordination between multi-level protection systems, leading to frequent false or failed protection trips.

[0003] Specifically, distribution networks usually adopt the principle of staged overcurrent protection. The quick-break section (Section I) is a fast fault-clearing section with no delay (<0.1s). Rural distribution lines are long and have many branches. Except for the line outlet switch protection (referred to as outgoing line protection), all levels of protection must exit Section I to avoid over-tripping. Only Section I of the outgoing line protection is retained to prevent the main transformer from bearing high overcurrent for a long time when a fault occurs near the busbar. However, when the distributed photovoltaic access capacity is large, the auxiliary effect of photovoltaics will increase the current flowing through the outgoing line protection after the fault, thereby expanding the protection range of Section I of the outgoing line protection, resulting in an increase in the probability of over-tripping and the scope of power outage, which limits the application of Section I of the outgoing line protection.

[0004] Protection methods for distributed PV access primarily fall into two categories: communication-based distributed protection and local protection relying solely on local information. While the former offers high reliability, due to the complex and multi-branch distribution network structure, its widespread adoption faces multiple constraints, including communication quality, network security, and construction costs. Therefore, practical improvements to traditional local multi-level protection will remain the primary approach for distribution network protection in the foreseeable future. Currently, these improvements primarily involve leveraging voltage and current signals, introducing sequence component information, constructing novel directional criteria, and employing high-frequency transient characteristics. However, the characteristic analysis processes underlying these improved protection methods are often not generalizable, suffering from overly sophisticated modeling and overly specific scenarios, which reduces their applicability to operating conditions outside the scope of this discussion. The complex and ever-changing topology of actual distribution networks, the diverse PV control strategies, the evolving connection locations and penetration rates, and the intermittent nature of output all contribute to variations in the fault characteristics perceived by protection.

[0005] Therefore, in view of the boosting effect of distributed photovoltaics, it is urgent to develop a universal protection method that can be widely applied to distributed photovoltaic distribution networks under different operating modes. Summary of the Invention

[0006] In order to solve the problem of reduced reliability of traditional distribution network protection principles and coordination schemes under distributed photovoltaic access, the present invention provides a general distribution network protection method and device suitable for distributed photovoltaic auxiliary function.

[0007] According to one aspect of the present invention, a general distribution network protection method applicable to distributed photovoltaic power generation is provided, comprising:

[0008] After the distributed photovoltaic system is connected to the distribution network, when a fault occurs somewhere on the line, the current amplitude and impedance value at the outgoing line protection installation location at the busbar outlet are measured;

[0009] Based on the measured current amplitude and impedance value, the system determines whether the fault point is within the protection range of the preset outgoing line protection section I according to the preset outgoing line protection section I composite criterion, where the outgoing line protection section I composite criterion is derived from the combination of the overcurrent protection principle and the distance protection principle;

[0010] When the fault point is within the protection range of the preset outgoing line protection section I, the protection will operate reliably.

[0011] Optionally, the expression of the composite criterion of the outgoing line protection stage I is:

[0012]

[0013] Where, is the current amplitude measured at the fault point, It represents the maximum theoretical limit of the protection current under the photovoltaic boost effect, |Z M | is the impedance value measured at the fault point, |Z set | is the preset impedance value, l set0 Indicates the protection range of the outgoing line protection section I corresponding to the impedance setting value, |z L | represents unit impedance.

[0014] Optionally, the composite criterion for the outgoing line protection stage I is determined by the following steps:

[0015] Assume that the target protection range of outgoing line protection section I is l set0 , target protection range l set0 The corresponding maximum fault current is I set0 ;

[0016] Based on the overcurrent protection principle, the outgoing line protection section I is set to Time action, Determined by the total photovoltaic capacity that produces the boosting effect;

[0017] Based on the distance protection principle, the target protection range l is obtained set0 The corresponding equivalent impedance is |z L |l set0 , based on the equivalent impedance |z L |l set0 Obtain impedance constant |Z set |=|z L |l set0 , when the current amplitude is less than And the measured impedance is less than |Z set |When the outgoing line protection I stage is activated;

[0018] The overcurrent protection principle is combined with the distance protection principle to obtain the composite criterion for the outgoing line protection stage I.

[0019] Optionally, let the total photovoltaic capacity that generates the auxiliary effect for a certain outgoing line be S DG1 , The expression is:

[0020]

[0021] Where, Indicates the ratio of the photovoltaic boost current to the main grid short-circuit current; h DG1 =S DG1 / ∑S DG , h DG1 Indicates the total photovoltaic capacity S DG1 and total photovoltaic capacity ∑S DG The ratio of h DG∑ =∑S DG / S T , h DG∑ Represents the total photovoltaic capacity ∑S DG With the main transformer capacity S T The ratio of Indicates the short-circuit current flowing from the main network to the fault point; Indicates the photovoltaic output current that produces the boost effect; c represents the voltage coefficient, reflecting the ratio of the main grid power supply voltage to the rated voltage; Indicates the per-unit value of transformer impedance.

[0022] Optionally, the comprehensive performance of the composite criterion of the outgoing line protection stage I is determined based on the photovoltaic access capacity constraint of the distribution network; wherein the photovoltaic access capacity constraint is: the photovoltaic access capacity downstream of the fault point does not exceed 30% of the total photovoltaic capacity.

[0023] Optionally, when the fault point is within the protection range of the preset outgoing line protection section I, the reliable protection action includes:

[0024] When the fault point is within the protection range of the preset outgoing line protection section I, the fault type is determined, where the fault type includes transient fault and permanent fault;

[0025] If it is a transient fault, the outgoing line switch will reclose and restore power supply by checking synchronization; if it is a permanent fault, when the fault is on the main feeder, the outgoing line switch will reclose and accelerate the tripping of the fault. When the fault is on the branch line within the protection range of the outgoing line protection section I, the outgoing line switch will be reclosed twice and the feeder automation will be coordinated to operate the branch line switch where the fault is located, so as to achieve fault isolation and main feeder power supply restoration.

[0026] According to another aspect of the present invention, a universal protection device for distribution networks suitable for distributed photovoltaic power generation is provided, comprising:

[0027] The measurement module is used to measure the current amplitude and impedance value at the outgoing line protection installation location at the busbar outlet when a fault occurs somewhere on the line after the distributed photovoltaic system is connected to the distribution network;

[0028] A judgment module is used to judge whether the fault point is within the protection range of the preset outgoing line protection section I based on the measured current amplitude and impedance value and according to the preset outgoing line protection section I composite judgment criterion, wherein the outgoing line protection section I composite judgment criterion is obtained by combining the overcurrent protection principle and the distance protection principle;

[0029] The protection module is used to ensure reliable protection when the fault point is within the protection range of the preset outgoing line protection section I.

[0030] Optionally, the expression of the composite criterion of the outgoing line protection stage I is:

[0031]

[0032] Where, is the current amplitude measured at the fault point, It represents the maximum theoretical limit of the protection current under the photovoltaic boost effect, |Z M | is the impedance value measured at the fault point, |Z set | is the preset impedance value, l set0 Indicates the protection range of the outgoing line protection section I corresponding to the impedance setting value, |z L | represents unit impedance.

[0033] Optionally, the device further includes a criterion determination module, configured to determine the outgoing line protection section I composite criterion through the following steps:

[0034] Assume that the target protection range of outgoing line protection section I is l set0 , target protection range l set0 The corresponding maximum fault current is I set0 ;

[0035] Based on the overcurrent protection principle, the outgoing line protection section I is set to Time action, Determined by the total photovoltaic capacity that produces the boosting effect;

[0036] Based on the distance protection principle, the target protection range l is obtained set0 The corresponding equivalent impedance is |z L |l set0 , based on the equivalent impedance |z L |l set0 Obtain impedance constant |Z set |=|z L |l set0 , when the current amplitude is less than And the measured impedance is less than |Z set |When the outgoing line protection I stage is activated;

[0037] The overcurrent protection principle is combined with the distance protection principle to obtain the composite criterion for the outgoing line protection stage I.

[0038] Optionally, let the total photovoltaic capacity that generates the auxiliary effect for a certain outgoing line be S DG1 , The expression is:

[0039]

[0040] Where, Indicates the ratio of the photovoltaic boost current to the main grid short-circuit current; h DG1 =S DG1 / ∑S DG , h DG1 Indicates the total photovoltaic capacity S DG1 and total photovoltaic capacity ∑S DG The ratio of h DG∑ =∑S DG / S T , h DG∑ Represents the total photovoltaic capacity ∑S DG With the main transformer capacity S T The ratio of Indicates the short-circuit current flowing from the main network to the fault point; Indicates the photovoltaic output current that produces the boost effect; c represents the voltage coefficient, reflecting the ratio of the main grid power supply voltage to the rated voltage; Indicates the per-unit value of transformer impedance.

[0041] Optionally, the comprehensive performance of the composite criterion of the outgoing line protection stage I is determined based on the photovoltaic access capacity constraint of the distribution network; wherein the photovoltaic access capacity constraint is: the photovoltaic access capacity downstream of the fault point does not exceed 30% of the total photovoltaic capacity.

[0042] Optionally, the protection module is specifically configured to:

[0043] When the fault point is within the protection range of the preset outgoing line protection section I, the fault type is determined, where the fault type includes transient fault and permanent fault;

[0044] If it is a transient fault, the outgoing line switch will reclose and restore power supply by checking synchronization; if it is a permanent fault, when the fault is on the main feeder, the outgoing line switch will reclose and accelerate the tripping of the fault. When the fault is on the branch line within the protection range of the outgoing line protection section I, the outgoing line switch will be reclosed twice and the feeder automation will be coordinated to operate the branch line switch where the fault is located, ultimately achieving fault isolation and main feeder power supply restoration.

[0045] According to another aspect of the present invention, a computer-readable storage medium is provided, wherein the storage medium stores a computer program, and the computer program is used to execute the method according to any one of the above aspects of the present invention.

[0046] According to another aspect of the present invention, an electronic device is provided, comprising: a processor; a memory for storing instructions executable by the processor; and the processor for reading the executable instructions from the memory and executing the instructions to implement the method described in any one of the above aspects of the present invention.

[0047] After a distributed photovoltaic system is connected to a distribution network, when a fault occurs somewhere on the line, the present invention measures the current amplitude and impedance value at the outgoing line protection installation location at the busbar outlet. Based on the measured current amplitude and impedance value, the present invention determines whether the fault point is within the protection range of the preset outgoing line protection section I according to the outgoing line protection section I composite criterion obtained by combining the overcurrent protection principle and the distance protection principle. When the fault point is within the protection range of the preset outgoing line protection section I, the protection is reliably activated. The present invention introduces the overcurrent protection principle and the distance protection principle and proposes the outgoing line protection section I composite criterion. When the measured current amplitude is greater than the maximum theoretical limit of the current flowing under photovoltaic power generation, the outgoing line protection section I composite criterion determines that the fault point is within the protection range of the preset outgoing line protection section I, and the protection is reliably activated. When the measured current amplitude is less than or equal to the maximum theoretical limit, and the measured impedance value is less than or equal to the preset impedance constant, the outgoing line protection section I composite criterion determines that the fault point is within the protection range of the preset outgoing line protection section I, and the protection is reliably activated. Therefore, the present invention improves the reliability and selectivity of active distribution network protection and can be widely applied to distribution network protection in different high-proportion photovoltaic access and operation scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0049] Figure 1 This is a flow chart of a general protection method for a distribution network applicable to distributed photovoltaic power generation, provided by an exemplary embodiment of the present invention;

[0050] Figure 2 is a schematic diagram of a distributed photovoltaic system connected to a power distribution network according to an exemplary embodiment of the present invention;

[0051] Figure 3 Schematic diagram of the impact of photovoltaic boost on the protection range of the criterion under different operating scenarios provided by an exemplary embodiment of the present invention;

[0052] Figure 4 1 is a schematic diagram comparing the protection ranges of outgoing line I-section protections based on different principles provided by an exemplary embodiment of the present invention;

[0053] Figure 5 1 is a schematic structural diagram of a universal protection device for a distribution network applicable to distributed photovoltaic boosting provided by an exemplary embodiment of the present invention;

[0054] Figure 6 This is a structure of an electronic device provided by an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0055] Below, the exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments of the present invention, and it should be understood that the present invention is not limited to the exemplary embodiments described herein.

[0056] It should be noted that the relative arrangement of components and steps, the numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise.

[0057] Figure 1 The figure shows a flow chart of a general protection method for distribution network applicable to distributed photovoltaic power generation provided by the present invention. Figure 1 As shown in the figure, the general protection method for distribution network applicable to distributed photovoltaic boosting includes:

[0058] Step S10: After the distributed photovoltaic system is connected to the power distribution network, when a fault occurs somewhere on the line, the current amplitude and impedance value at the outgoing line protection installation location at the busbar outlet are measured.

[0059] Step S20: Based on the measured current amplitude and impedance value, and in accordance with the preset outgoing line protection section I composite criterion, determine whether the fault point is within the protection range of the preset outgoing line protection section I, wherein the outgoing line protection section I composite criterion is obtained by combining the overcurrent protection principle with the distance protection principle.

[0060] Optionally, the expression of the composite criterion of the outgoing line protection stage I is:

[0061]

[0062] Where, is the current amplitude measured at the fault point, It represents the maximum theoretical limit of the protection current under the photovoltaic boost effect, |Z M | is the impedance value measured at the fault point, |Z set | is the preset impedance value, l set0 Indicates the protection range of the outgoing line protection section I corresponding to the impedance setting value, |z L | represents unit impedance.

[0063] Optionally, the composite criterion for the outgoing line protection stage I is determined by the following steps:

[0064] The function of the outgoing line protection stage I is to prevent the main transformer from overcurrent. The target protection range of the outgoing line protection stage I is l set0 , the target protection range is l set0 The corresponding maximum fault current is I set0 Based on the overcurrent protection principle, the outgoing line protection section I is set to Time action, It is determined by the total photovoltaic capacity that generates the boosting effect, that is, the total photovoltaic capacity of all other outgoing lines; based on the distance protection principle, the target protection range l is obtained set0 The corresponding equivalent impedance is |z L |l set0 , based on the equivalent impedance |z L |l set0 Obtain impedance constant |Z set |=|z L |l set0 , when the current amplitude is less than And the measured impedance is less than |Z set |When the outgoing line protection stage I is activated.

[0065] Optionally, let the total photovoltaic capacity that generates the auxiliary effect for a certain outgoing line be S DG1 , The expression is:

[0066]

[0067] Where, Indicates the ratio of the photovoltaic boost current to the main grid short-circuit current; h DG1 =S DG1 / ∑S DG , h DG1 Indicates the total photovoltaic capacity S DG1 and total photovoltaic capacity ∑S DG The ratio of h DG∑ =∑S DG / S T , h DG∑ Represents the total photovoltaic capacity ∑S DG With the main transformer capacity S T The ratio of Indicates the short-circuit current flowing from the main network to the fault point; Indicates the photovoltaic output current that produces the boost effect; c represents the voltage coefficient, reflecting the ratio of the main grid power supply voltage to the rated voltage; Indicates the per-unit value of transformer impedance.

[0068] Optionally, the comprehensive performance of the composite criterion of the outgoing line protection stage I is determined based on the photovoltaic access capacity constraint of the distribution network; wherein the photovoltaic access capacity constraint is: the photovoltaic access capacity downstream of the fault point does not exceed 30% of the total photovoltaic capacity.

[0069] In the embodiment of the present invention, Figure 2 The figure shows a typical multi-stage protection configuration diagram for a distribution network. Based on this, the steps for determining the composite criterion for the outgoing line protection stage I adapted to the photovoltaic current boosting effect proposed by the present invention are as follows:

[0070] Considering that the primary function of the outgoing line protection stage I is to instantly clear a fault near the outgoing line to prevent the main transformer from sustaining excessive current and potentially damaging it, while also accommodating the photovoltaic boost, the protection stage I must maintain its original purpose of protecting the main transformer, ensuring that the protection operates at the original overcurrent level.

[0071] The present invention first introduces the principle of distance protection. Obviously, the photovoltaic boost current will not affect the measured impedance of the protection position, thereby avoiding the influence of the photovoltaic boost effect. This principle is only used for the outgoing line protection section I, and its advantages are: 1) It does not need to cooperate with the lower-level protection; 2) The protection range of section I is only 2 to 3 kilometers from the outlet, and the impedance setting is small, generally less than 2Ω. The distribution network load impedance is relatively large, generally reaching tens of Ω, and there is basically no risk of false operation; 3) The transition resistance will not affect the performance of the protection action of section I. The essential goal of section I protection is to prevent overcurrent in the main transformer. The protection range (distance) of section I is only a manifestation of the above goal. The distance protection setting is set to the impedance reflected by the overcurrent level that the main transformer can withstand. Although the transition resistance will cause the measured distance to deviate from the original protection range, it does not affect the equivalent distance between the main transformer and the fault point reflected by the above impedance, and does not affect the protection action at the original main transformer overcurrent level.

[0072] Considering the current-bearing capacity of the main transformer, the outgoing line protection section I should be set when the current amplitude reaches I set0 The protection range and equivalent impedance corresponding to the set value are l set0 and |z L |l set0 , that is, the impedance constant |Z set |=|z L |l set0 .

[0073] Furthermore, the inherent defect of distance protection principle needs to be addressed when it is applied: when there are a large number of distributed photovoltaics downstream of the fault point and the fault transition resistance is not zero, the measured impedance will be too large. Specifically, when a fault occurs somewhere within the protection range and the distance from the busbar is l0, the impedance constant |Z set |Greater than the actual impedance|Z R | is smaller than the measured impedance |Z M |, resulting in the current exceeding the original threshold but the protection refuses to operate, as shown in the following formula (1). In the extreme case, when the photovoltaic output current that produces the boost effect is zero The short-circuit current output by the downstream photovoltaic power station to the fault point of this line is Short-circuit current flowing from the main grid to the fault point Equal amplitude and same direction When the protection range is 0.01, the protection range is only half of the original target range, that is, the protection may not operate when the current reaches twice the original target current.

[0074] in,

[0075] Therefore, the present invention proposes a composite criterion combining the overcurrent protection principle and the distance protection principle, as shown in the following formula:

[0076]

[0077] Where, The current amplitude measured to protect the position, It represents the maximum theoretical limit of the protection current under the photovoltaic boost effect, |Z M | is the impedance value measured at the protection position, |Z set | is the preset impedance value, l set0 Indicates the protection range corresponding to the impedance setting value, |z L | represents unit impedance.

[0078] Assume that the total photovoltaic capacity that generates auxiliary power for a certain outgoing line is S DG1 ,but It can be written as:

[0079]

[0080] Where, It represents the ratio of the photovoltaic boost current to the main grid short-circuit current, h DG1 =S DG1 / ∑S DG , h DG1 It represents the ratio of auxiliary photovoltaic capacity to total photovoltaic capacity, h DG∑ =∑S DG / S T , h DG∑ Indicates the ratio of auxiliary photovoltaic capacity to total photovoltaic capacity and the ratio of total photovoltaic capacity to main transformer capacity; Indicates the short-circuit current flowing from the main network to the fault point; Indicates the photovoltaic output current that produces the boost effect; c represents the voltage coefficient, reflecting the ratio of the main grid power supply voltage to the rated voltage; Indicates the per-unit value of transformer impedance.

[0081] For the action characteristics of the above composite criterion, it is necessary to analyze the maximum and minimum range of protection in various scenarios. Suppose the protection range of the composite criterion is l set , whose value is l set1 and l set2 The maximum value of , that is:

[0082] l set =max{l set1 , l set2} (4)

[0083] Regarding the maximum range, let the original I-segment protection range be l set0 , when the protection current is greater than The fault point must be within the protection range of stage I. According to criterion 1, the protection should be activated. When the fault occurs outside the original protection range, the current must be less than The impedance criterion in criterion 2 is used to judge, so the protection range will not be expanded due to the influence of the auxiliary current. Therefore, the maximum protection range of the composite criterion is the original protection range, that is, max{l set}=l set0 .

[0084] Regarding the minimum range, we need to solve equation (5). Equation (5) shows the protection range of criteria 1 and 2 in the composite criterion. set1 and l set2 From formula (1), we can see that the protection range of criterion 2 changes with P DG2 and Z f When the conditions of formula (1) are satisfied and |z L l0+Z f |When the minimum is taken (i.e. l0=0, Criterion 2: Scope of equivalent protection set2 The most severe reduction is

[0085]

[0086] The minimum protection range of the composite criterion is the result of the above formula under the most stringent conditions. set1 The solution of the expression is relatively clear, l set2 The inequality must be equalized to obtain its minimum value, that is, the following conditions must be met simultaneously: i) all photovoltaics on the fault line are located downstream of the fault point, ii) all photovoltaic output current flows into the fault point (excluding load) and the current flowing on both sides of the fault point ( and ) in phase. On this basis, the equations involve multiple uncertain parameters of the line, transformer, and photovoltaic. Among them, h DG∑ =1, that is, when the total photovoltaic capacity is the largest, l set1 and l set2 The protection range is reduced to the greatest extent. In addition, due to the variety of line and transformer models, the line unit impedance |z L |, line impedance angle θ2, main transformer capacity S TThere is no unified corresponding standard between them, but there is a general corresponding trend. Taking the commonly used model JKLGYJ of 10kV overhead line as an example, Table 1 summarizes the corresponding relationship between unit impedance and impedance angle reflected by lines of different specifications, as well as the approximate matching level between the current carrying capacity corresponding to unit resistance and the main transformer capacity. Based on the above corresponding relationship, the fitting function θ2=f(|z L |) and S T =g(|r L |)=g(|z L |·cos(θ2)). Substituting the above fitting function into formula (5), the composite criterion protection range l can be calculated. set About variable |z L |、 and h DG1 The law of change.

[0087] Table 1 Parameters of 10kV overhead lines of different specifications (JKLGYJ) and their corresponding relationship with main transformer capacity

[0088]

[0089]

[0090] Furthermore, based on the original protection scope l set0 Take 2.0km as an example, Figure 3 Shows the proportion of photovoltaic capacity downstream of the fault point h DG1 l when 20% and 30% respectively set , and various h including two cases DG1 Take the value l set The minimum value of . It can be seen that The smaller the value, the greater the impact of the downstream photovoltaic access on the protection criterion. L The overall impact on the protection criteria is minimal. Without any restrictions on PV access, under the most stringent operating conditions, the minimum protection range of this composite criterion is reduced to approximately 1.5 km. When the PV access capacity downstream of the fault point does not exceed 30% of the total PV capacity, the minimum protection range can be controlled to over 1.7 km. Therefore, the PV access capacity constraint for the composite criterion is: the PV access capacity downstream of the fault point does not exceed 30% of the total PV capacity.

[0091] The minimum boundary of this protection range can only be achieved when many of the aforementioned boundary conditions are met simultaneously, including but not limited to: the currents flowing into the fault point from both sides are in phase, the ratio of photovoltaic power generation to main transformer capacity reaches a maximum, and all photovoltaic output currents flow into the fault point without loss. Therefore, it can be seen that in actual scenarios, the composite criterion proposed by this invention is less affected by photovoltaic power generation than the theoretical results shown in the above figure.

[0092] Therefore, in combination with the composite criterion proposed in the present invention and the photovoltaic access capacity constraint of the composite criterion given, the protection range of the composite criterion and the safety protection capability of the main transformer are basically not affected.

[0093] Step S30: When the fault point is located within the protection range of the preset outgoing line protection section I, the protection is reliably activated.

[0094] Optionally, when the fault point is located within the protection range of the preset outgoing line protection section I, the protection is reliably actuated, including: when the fault point is located within the protection range of the preset outgoing line protection section I, judging the fault type, wherein the fault type includes transient fault and permanent fault; if it is a transient fault, the outgoing line switch is reclosed to restore power supply by checking synchronization; if it is a permanent fault, when the fault is located on the main feeder line, the outgoing line switch is reclosed to accelerate tripping of the fault, and when the fault is located on the branch line within the protection range of the outgoing line protection section I, the outgoing line switch is reclosed twice and the feeder automation is coordinated to operate the branch line switch where the fault is located, thereby ultimately achieving fault isolation and main feeder power supply restoration.

[0095] In an embodiment of the present invention, combined with the composite criterion of the I-stage protection of the present invention, when the fault is within the protection range, the protection is reliably activated. If it is a transient fault, the outgoing line switch is reclosed to restore power supply by checking synchronization. If it is a permanent fault, when the fault is on the main feeder, the outgoing line switch is reclosed to accelerate the tripping of the fault. When the fault is on the branch line within the I-stage protection range, the outgoing line switch is reclosed twice and the feeder automation is coordinated to operate the branch line switch where the fault is located, thereby ultimately achieving fault isolation and main feeder power supply restoration.

[0096] A specific application example of the present invention is given below to illustrate the technical effects that can be achieved by the present invention:

[0097] In PSCAD, create Figure 2 The distribution network shown has a line unit impedance of 0.26+j0.25Ω / km and a main transformer capacity of 50MVA, which is close to the reference value in Table 1 above. Figure 3 The maximum value is set to 0.3. The photovoltaic system adopts a PQ control strategy and has a voltage ride-through control function. The output of the energy storage system can be flexibly controlled to approach the stable operation boundary.

[0098] Table 2 shows the main measurement signals for faults set at different distances from the line outlet, with and without PV boost. The protection range for Section I is set to 0 to 2.1 km from the busbar, with the relevant fixed values ​​noted below.

[0099] Table 2 Simulation analysis of protection measurement signals under auxiliary boosting

[0100]

[0101]

[0102] Note: 1. The data marked with parentheses are the measurement results after photovoltaic connection. 2. The protection range of section I is set to 0 to 2.1 km at the line exit, and the impedance constant is |Z set |=0.76Ω, when there is no photovoltaic access, the current flowing through the main transformer and outgoing line protection when the three-phase metallic short circuit occurs at the end of the protection range is 5394A and 4231A respectively (the latter is ). According to the criterion of formula (2) and the calculation method of formula (3), The values ​​are taken when the auxiliary photovoltaic accounts for 100%, 70% and 0% respectively. and

[0103] From cases 1 to 6, it can be seen that the current at the outgoing line protection increases due to the influence of photovoltaic boost, but the measured impedance is not affected. The fault in the zone can be reliably operated, and the fault outside the zone can be reliably inactive. In cases 7 to 9, the transition resistance increases the measured impedance. The measured impedance of cases 8 and 9 is greater than |Z set | and the current does not exceed In case 8, although the fault spatial location is within the protection range, the measured impedance exceeds the line impedance of the original protection range. In addition, the photovoltaic power generation function of the main transformer is not affected, so the safety of the main transformer equipment is not affected. Cases 10 and 11 verify the minimum range of the protection criterion according to the proportion of 30% of the photovoltaic capacity downstream of the fault point. According to formula (5), the minimum range is when the fault occurs at the outgoing line protection outlet and the transition resistance is close to the fixed value |Z set |, it can be seen that when the transition resistance reaches 0.73Ω, the impedance criterion is not satisfied but the current criterion is satisfied. When the transition resistance exceeds 0.74Ω, both criteria are not satisfied, and the minimum protection range is shortened by about Much smaller than Figure 3 The theoretical limit of about 0.3 km is not only because it is difficult to meet all theoretical extreme values ​​at the same time, but also because the theoretical limit assumes that all photovoltaic current flows into the fault point. In reality, after a fault, a considerable portion of the photovoltaic current still flows to the local and nearby loads, thus further reducing the impact on the protection criterion.

[0104] like Figure 4 A comparison of existing I-stage protection principles reveals that traditional overcurrent I-stage and distance I-stage protection are significantly affected by upstream and downstream photovoltaic systems, leading to significant increases and decreases in protection range, respectively. Adjusting the I-stage constant based on the level of photovoltaic power generation is inadequate for the intermittent nature of photovoltaic output. The composite criterion proposed in this paper, however, significantly enhances its adaptability to photovoltaic power generation. Furthermore, based on the photovoltaic power generation constraints described in this paper, the composite criterion is virtually unaffected by photovoltaic power generation.

[0105] In summary, after distributed photovoltaic power is connected to the distribution network, the present invention first measures the current amplitude and impedance value at the fault point when a fault occurs somewhere away from the busbar. Then, based on the measured current amplitude and impedance value, the composite criterion for outgoing line protection section I obtained by combining the overcurrent protection principle and the distance protection principle is used to determine whether the fault point is within the protection range of the preset outgoing line protection section I. When the fault point is within the protection range of the preset outgoing line protection section I, the protection is reliably activated. The present invention introduces the overcurrent protection principle and the distance protection principle and proposes a composite criterion for outgoing line protection section I. When the measured current amplitude at the fault point is greater than the maximum theoretical limit of the protection current under photovoltaic power generation, the composite criterion for outgoing line protection section I determines that the fault point is within the protection range of the preset outgoing line protection section I, and the protection is reliably activated. When the current amplitude at the fault point is less than or equal to the maximum theoretical limit, and the measured impedance value is less than or equal to the preset impedance constant, the composite criterion for outgoing line protection section I determines that the fault point is within the protection range of the preset outgoing line protection section I, and the protection is reliably activated. Therefore, the present invention improves the reliability and selectivity of active distribution network protection and can be widely applied to distribution network protection in different high-proportion photovoltaic access and operation scenarios.

[0106] Exemplary devices

[0107] Figure 5 FIG. 1 is a schematic diagram of a general protection device for a distribution network applicable to distributed photovoltaic power generation, provided by an exemplary embodiment of the present invention. Figure 5 As shown, the apparatus 500 includes:

[0108] The measurement module 510 is used to measure the current amplitude and impedance value of the outgoing line protection installation location at the busbar outlet when a fault occurs somewhere on the line after the distributed photovoltaic system is connected to the distribution network;

[0109] A judgment module 520 is configured to determine whether the fault point is within the protection range of the preset outgoing line protection section I based on the measured current amplitude and impedance value and according to a preset outgoing line protection section I composite criterion, wherein the outgoing line protection section I composite criterion is derived from a combination of the overcurrent protection principle and the distance protection principle;

[0110] The protection module 530 is used to ensure reliable protection when the fault point is within the protection range of the preset outgoing line protection section I.

[0111] Optionally, the expression of the composite criterion of the outgoing line protection stage I is:

[0112]

[0113] Where, is the current amplitude measured at the fault point, It represents the maximum theoretical limit of the protection current under the photovoltaic boost effect, |Z M | is the impedance value measured at the fault point, |Z set | is the preset impedance value, l set0 Indicates the protection range of the outgoing line protection section I corresponding to the impedance setting value, |z L | represents unit impedance.

[0114] Optionally, the apparatus 500 further includes a criterion determination module, configured to determine the outgoing line protection stage I composite criterion through the following steps:

[0115] Assume that the target protection range of outgoing line protection section I is l set0 , target protection range l set0 The corresponding maximum fault current is I set0 ;

[0116] Based on the overcurrent protection principle, the outgoing line protection section I is set to Time action, Determined by the total photovoltaic capacity that produces the boosting effect;

[0117] Based on the distance protection principle, the target protection range l is obtained set0 The corresponding equivalent impedance is |z L |l set0 , based on the equivalent impedance |z L |l set0 Obtain impedance constant |Z set |=|z L |l set0 , when the current amplitude is less than And the measured impedance is less than |Z set |When the outgoing line protection I stage is activated;

[0118] The overcurrent protection principle is combined with the distance protection principle to obtain the composite criterion for the outgoing line protection stage I.

[0119] Optionally, let the total photovoltaic capacity that generates the auxiliary effect for a certain outgoing line be S DG1 , The expression is:

[0120]

[0121] Where, Indicates the ratio of the photovoltaic boost current to the main grid short-circuit current; h DG1 =S DG1 / ∑S DG , h DG1 Indicates the total photovoltaic capacity S DG1 and total photovoltaic capacity ∑SDG The ratio of h DG∑ =∑S DG / S T , h DG∑ Represents the total photovoltaic capacity ∑S DG With the main transformer capacity S T The ratio of Indicates the short-circuit current flowing from the main network to the fault point; Indicates the photovoltaic output current that produces the boost effect; c represents the voltage coefficient, reflecting the ratio of the main grid power supply voltage to the rated voltage; Indicates the per-unit value of transformer impedance.

[0122] Optionally, the comprehensive performance of the composite criterion of the outgoing line protection stage I is determined based on the photovoltaic access capacity constraint of the distribution network; wherein the photovoltaic access capacity constraint is: the photovoltaic access capacity downstream of the fault point does not exceed 30% of the total photovoltaic capacity.

[0123] Optionally, the protection module 530 is specifically configured to:

[0124] When the fault point is within the protection range of the preset outgoing line protection section I, the fault type is determined, where the fault type includes transient fault and permanent fault;

[0125] If it is a transient fault, the outgoing line switch will reclose and restore power supply by checking synchronization; if it is a permanent fault, when the fault is on the main feeder, the outgoing line switch will reclose and accelerate the tripping of the fault. When the fault is on the branch line within the protection range of the outgoing line protection section I, the outgoing line switch will be reclosed twice and the feeder automation will be coordinated to operate the branch line switch where the fault is located, ultimately achieving fault isolation and main feeder power supply restoration.

[0126] The universal protection device for distribution network applicable to distributed photovoltaic auxiliary function of an embodiment of the present invention corresponds to the universal protection method for distribution network applicable to distributed photovoltaic auxiliary function of another embodiment of the present invention, which will not be described in detail here.

[0127] Exemplary electronic devices

[0128] Figure 6 This is the structure of an electronic device provided by an exemplary embodiment of the present invention. Figure 6 As shown, the electronic device 60 includes one or more processors 61 and a memory 62 .

[0129] The processor 61 may be a central processing unit (CPU) or other forms of processing units having data processing capabilities and / or instruction execution capabilities, and may control other components in the electronic device to perform desired functions.

[0130] The memory 62 may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may, for example, include random access memory (RAM) and / or cache memory (cache), etc. The non-volatile memory may, for example, include read-only memory (ROM), a hard disk, a flash memory, etc. One or more computer program instructions may be stored on the computer-readable storage medium, and the processor 61 may run the program instructions to implement the method for information mining of historical change records and / or other desired functions of the software program of each embodiment of the present invention described above. In one example, the electronic device may further include: an input device 63 and an output device 64, which are interconnected via a bus system and / or other forms of connection mechanisms (not shown).

[0131] In addition, the input device 63 may also include, for example, a keyboard, a mouse, etc.

[0132] The output device 64 can output various information to the outside. The output device 64 can include, for example, a display, a speaker, a printer, a communication network and a remote output device connected thereto.

[0133] Of course, to simplify, Figure 6 Only some of the components related to the present invention in the electronic device are shown, and components such as a bus, an input / output interface, etc. are omitted. In addition, the electronic device may further include any other appropriate components according to specific application scenarios.

[0134] Exemplary computer program products and computer-readable storage media

[0135] In addition to the above-mentioned methods and devices, an embodiment of the present invention may also be a computer program product, which includes computer program instructions, which, when executed by a processor, enable the processor to perform the steps of the method according to various embodiments of the present invention described in the above "Exemplary Method" section of this specification.

[0136] The computer program product may be written in any combination of one or more programming languages ​​to implement the operations of embodiments of the present invention, including object-oriented programming languages ​​such as Java, C++, and conventional procedural programming languages ​​such as C or similar programming languages. The program code may be executed entirely on the user's computing device, partially on the user's computing device, as a stand-alone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0137] In addition, an embodiment of the present invention may also be a computer-readable storage medium having computer program instructions stored thereon, which, when executed by a processor, enables the processor to execute the steps of the method for information mining of historical change records according to various embodiments of the present invention described in the above "Exemplary Method" section of this specification.

[0138] The computer-readable storage medium can adopt any combination of one or more readable media. The readable medium can be a readable signal medium or a readable storage medium. The readable storage medium can, for example, include but is not limited to a system, system or device of electricity, magnetism, light, electromagnetic, infrared, or semiconductor, or any combination thereof. More specific examples (non-exhaustive list) of readable storage media include: an electrical connection with one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof.

[0139] The basic principles of the present invention have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in the present invention are merely illustrative and non-limiting, and should not be construed as necessarily possessed by each embodiment of the present invention. Furthermore, the specific details disclosed above are provided for illustrative purposes and to facilitate understanding, and are not intended to be limiting. These details do not necessarily limit the present invention to being implemented using these specific details.

[0140] Each embodiment in this specification is described in a progressive manner, with each embodiment focusing on its differences from the other embodiments. References to the same or similar parts between the various embodiments are sufficient. For system embodiments, since they largely correspond to method embodiments, their description is relatively simple. For relevant parts, references to the description of the method embodiments are sufficient.

[0141] The block diagrams of the devices, systems, equipment, and systems involved in the present invention are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As will be appreciated by those skilled in the art, these devices, systems, equipment, and systems can be connected, arranged, or configured in any manner. Words such as "including," "comprising," "having," and the like are open-ended words, meaning "including but not limited to," and can be used interchangeably therewith. The words "or" and "and" used herein refer to the words "and / or" and can be used interchangeably therewith, unless the context clearly indicates otherwise. The word "such as" used herein refers to the phrase "such as but not limited to," and can be used interchangeably therewith.

[0142] The method and system of the present invention may be implemented in many ways. For example, the method and system of the present invention may be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above sequence of steps for the method is for illustration only, and the steps of the method of the present invention are not limited to the sequence specifically described above, unless otherwise specified. In addition, in some embodiments, the present invention may also be implemented as a program recorded in a recording medium, which includes machine-readable instructions for implementing the method according to the present invention. Thus, the present invention also covers recording media that store programs for executing the method according to the present invention.

[0143] It should also be noted that, in the system, device and method of the present invention, each component or each step can be decomposed and / or recombined. These decompositions and / or recombinations should be regarded as equivalent schemes of the present invention. The above description of the disclosed aspects is provided to enable any technician in this field to make or use the present invention. Various modifications to these aspects will be very obvious to those skilled in the art, and the general principles defined here can be applied to other aspects without departing from the scope of the present invention. Therefore, the present invention is not intended to be limited to the aspects shown here, but according to the widest scope consistent with the principles disclosed here and novel features.

[0144] The above description has been provided for the purpose of illustration and description. Furthermore, this description is not intended to limit the embodiments of the present invention to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A universal protection method for distribution network suitable for distributed photovoltaic power generation, characterized in that: include: After the distributed photovoltaic system is connected to the distribution network, when a fault occurs somewhere on the line, the current amplitude and impedance value at the outgoing line protection installation location at the busbar outlet are measured; Based on the measured current amplitude and impedance value, the system determines whether the fault point is within the protection range of the preset outgoing line protection section I according to the preset outgoing line protection section I composite criterion, where the outgoing line protection section I composite criterion is derived from the combination of the overcurrent protection principle and the distance protection principle; The expression of the composite criterion of the outgoing line protection section I is: and |Z M | ≤ |Z set | = |z L |l set0 ; Where, is the current amplitude measured at the fault point, It represents the maximum theoretical limit of the protection current under the photovoltaic boost effect, |Z M | is the impedance value measured at the fault point, |Z set | is the preset impedance value, l set0 Indicates the protection range of the outgoing line protection section I corresponding to the impedance setting value, |z L | represents unit impedance; The composite criterion for the outgoing line protection stage I is determined by the following steps: Assume that the target protection range of outgoing line protection section I is l set0 , target protection range l set0 The corresponding maximum fault current is I set0 ; Based on the overcurrent protection principle, the outgoing line protection section I is set to Time action, Determined by the total photovoltaic capacity that produces the boosting effect; Based on the distance protection principle, the target protection range l is obtained set0 The corresponding equivalent impedance is |z L |l set0 , based on the equivalent impedance |z L |l set0 Obtain impedance constant |Z set |=|z L |l set0 , when the current amplitude is less than And the measured impedance is less than |Z set |When the outgoing line protection I stage is activated; Combining the overcurrent protection principle with the distance protection principle, the composite criterion for the outgoing line protection stage I is obtained; When the fault point is within the protection range of the preset outgoing line protection section I, the protection will operate reliably.

2. The method according to claim 1, wherein For a certain outgoing line, the total photovoltaic capacity that produces the auxiliary effect is S DG1 , The expression is: Where, Indicates the ratio of the photovoltaic boost current to the main grid short-circuit current; h DG1 =S DG1 / ∑S DG , h DG1 Indicates the total photovoltaic capacity S DG1 and total photovoltaic capacity ∑S DG The ratio of h DG ∑=∑S DG / S T , h DG∑ Represents the total photovoltaic capacity ∑S DG With the main transformer capacity S T The ratio of Indicates the short-circuit current flowing from the main network to the fault point; Indicates the photovoltaic output current that produces the boost effect; c represents the voltage coefficient, reflecting the ratio of the main grid power supply voltage to the rated voltage; Indicates the per-unit value of transformer impedance.

3. The method according to claim 1, characterized in that The comprehensive performance of the composite criterion of the outgoing line protection stage I is determined based on the photovoltaic access capacity constraint of the distribution network; wherein, the photovoltaic access capacity constraint is: the photovoltaic access capacity downstream of the fault point does not exceed 30% of the total photovoltaic capacity.

4. The method according to claim 1, wherein When the fault point is within the protection range of the preset outgoing line protection section I, the protection is reliably actuated, including: When the fault point is within the protection range of the preset outgoing line protection section I, the fault type is determined, where the fault type includes transient fault and permanent fault; If it is a transient fault, the outgoing line switch will reclose and restore power supply by checking synchronization; if it is a permanent fault, when the fault is on the main feeder, the outgoing line switch will reclose and accelerate the tripping of the fault. When the fault is on the branch line within the protection range of the outgoing line protection section I, the outgoing line switch will be reclosed twice and the feeder automation will be coordinated to operate the branch line switch where the fault is located, so as to achieve fault isolation and main feeder power supply restoration.

5. A universal protection device for distribution network suitable for distributed photovoltaic power generation, characterized in that: include: The measurement module is used to measure the current amplitude and impedance value at the outgoing line protection installation location at the busbar outlet when a fault occurs somewhere on the line after the distributed photovoltaic system is connected to the distribution network; A judgment module is used to judge whether the fault point is within the protection range of the preset outgoing line protection section I based on the measured current amplitude and impedance value and according to the preset outgoing line protection section I composite judgment criterion, wherein the outgoing line protection section I composite judgment criterion is obtained by combining the overcurrent protection principle and the distance protection principle; The expression of the composite criterion of the outgoing line protection section I is: and |Z M | ≤ |Z set | = |z L |l set0 ; Where, is the current amplitude measured at the fault point, It represents the maximum theoretical limit of the protection current under the photovoltaic boost effect, |Z M | is the impedance value measured at the fault point, |Z set | is the preset impedance value, l set0 Indicates the protection range of the outgoing line protection section I corresponding to the impedance setting value, |z L | represents unit impedance; The criterion determination module is used to determine the composite criterion of the outgoing line protection section I through the following steps: Assume that the target protection range of outgoing line protection section I is l set0 , target protection range l set0 The corresponding maximum fault current is I set0 ; Based on the overcurrent protection principle, the outgoing line protection section I is set to Time action, Determined by the total photovoltaic capacity that produces the boosting effect; Based on the distance protection principle, the target protection range l is obtained set0 The corresponding equivalent impedance is |z L |l set0 , based on the equivalent impedance |z L |l set0 Obtain impedance constant |Z set |=|z L |l set0 , when the current amplitude is less than And the measured impedance is less than |Z set |When the outgoing line protection I stage is activated; Combining the overcurrent protection principle with the distance protection principle, the composite criterion for the outgoing line protection stage I is obtained; The protection module is used to ensure reliable protection when the fault point is within the protection range of the preset outgoing line protection section I.

6. The device according to claim 5, characterized in that For a certain outgoing line, the total photovoltaic capacity that produces the auxiliary effect is S DG1 , The expression is: Where, Indicates the ratio of the photovoltaic boost current to the main grid short-circuit current; h DG1 =S DG1 / ΣS DG , h DG1 Indicates the total photovoltaic capacity S DG1 and total photovoltaic capacity ΣS DG The ratio of h DGΣ =ΣS DG / S T , h DG∑ Represents the total photovoltaic capacity ∑S DG With the main transformer capacity S T The ratio of Indicates the short-circuit current flowing from the main network to the fault point; Indicates the photovoltaic output current that produces the boost effect; c represents the voltage coefficient, reflecting the ratio of the main grid power supply voltage to the rated voltage; Indicates the per-unit value of transformer impedance.

7. The device according to claim 5, characterized in that The comprehensive performance of the composite criterion of the outgoing line protection stage I is determined based on the photovoltaic access capacity constraint of the distribution network; wherein, the photovoltaic access capacity constraint is: the photovoltaic access capacity downstream of the fault point does not exceed 30% of the total photovoltaic capacity.

8. The device according to claim 5, characterized in that The protection module is specifically used for: When the fault point is within the protection range of the preset outgoing line protection section I, the fault type is determined, where the fault type includes transient fault and permanent fault; If it is a transient fault, the outgoing line switch will reclose and restore power supply by checking synchronization; if it is a permanent fault, when the fault is on the main feeder, the outgoing line switch will reclose and accelerate the tripping of the fault. When the fault is on the branch line within the protection range of the outgoing line protection section I, the outgoing line switch will be reclosed twice and the feeder automation will be coordinated to operate the branch line switch where the fault is located, ultimately achieving fault isolation and main feeder power supply restoration.

9. A computer-readable storage medium, characterized in that The storage medium stores a computer program, and the computer program is used to execute the method according to any one of claims 1 to 4.

10. An electronic device, characterized in that: The electronic device comprises: processor; a memory for storing instructions executable by the processor; The processor is configured to read the executable instructions from the memory and execute the instructions to implement the method according to any one of claims 1 to 4.

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