CN111769524B - Method, device and system for adjusting grounding resistance of self-adaptive symmetrical monopole direct current power distribution network - Google Patents
Method, device and system for adjusting grounding resistance of self-adaptive symmetrical monopole direct current power distribution network Download PDFInfo
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Abstract
The invention discloses a method, a device and a system for adjusting the grounding resistance of a self-adaptive symmetrical monopole direct current power distribution network, wherein the method comprises the steps of continuously acquiring the voltage of a neutral point on the valve side of a connecting transformer in the symmetrical monopole direct current power distribution network; determining the number of the grounding resistance units based on the relation between the number of the grounding resistance units and the voltage of a neutral point on the valve side of the connecting transformer, and realizing automatic adjustment of the number of the grounding resistance units, wherein each grounding resistance unit comprises two reverse parallel-connected IGBTs and a resistor r 0 The grounding resistor units are connected in parallel, and all the grounding resistor units are sequentially connected in series to form a grounding resistor. When a high-resistance grounding fault occurs, the resistance value of the grounding resistor is automatically reduced, so that the fault component of the short-circuit current can meet the requirements of protection and sensitivity of a light current transformer to the maximum extent, and the fault can be accurately identified and removed.
Description
Technical Field
The invention belongs to the technical field of power distribution networks of power systems, and particularly relates to a method, a device and a system for adjusting the ground resistance of a self-adaptive symmetrical monopole direct-current power distribution network.
Background
In recent years, the direct current distribution network receives more and more attention by virtue of the advantages of the direct current distribution network in the aspects of electric energy quality, power supply reliability, load compatibility, active and reactive control flexibility and the like. Unlike a direct-current transmission network, a direct-current distribution network usually adopts a symmetrical monopole structure to reduce cost. For a dc distribution network in the form of a symmetrical monopole structure, there are many possibilities for grounding. At present, most direct current distribution projects often adopt a mode that a neutral point on a valve side of a transformer is connected with an alternating current side to be grounded. The grounding mode needs to be grounded through a resistor with a certain resistance value so as to reduce the short-circuit current flowing through the converter when the single-pole grounding fault of the direct-current system occurs, and ensure that the converter can maintain normal operation for a long time after the fault occurs, thereby improving the power supply reliability of the direct-current power distribution network.
At present, a plurality of direct current distribution network demonstration projects are built in China, and the selection of the grounding resistance on the valve side of the connecting transformer of the demonstration projects is always based on the principle that when a direct current system has a unipolar metallic grounding fault, the short-circuit current flowing through a power electronic device in a converter does not exceed a limit value of the short-circuit current. Although the selection principle can ensure that the converter can keep normal operation for a long time after the fault occurs, for a high-resistance grounding fault, the short-circuit current fault component is too small and is lower than the sensitivity of protection and even a photocurrent transformer, so that the protection is refused to operate, the fault cannot be cleared, and the fault always has great threat to the safe and stable operation of a direct current distribution network.
Disclosure of Invention
Aiming at the problems, the invention provides a method, a device and a system for adjusting the ground resistance of a self-adaptive symmetrical unipolar direct current power distribution network, which automatically reduce the resistance value of the ground resistance when a high-resistance ground fault occurs, so as to ensure that the short-circuit current fault component can meet the requirements of protection and the sensitivity of a photocurrent transformer to the maximum extent, thereby ensuring that the fault can be accurately identified and removed.
In order to achieve the technical purpose and achieve the technical effects, the invention is realized by the following technical scheme:
in a first aspect, the present invention provides a method for adjusting a ground resistance of a self-adaptive symmetric unipolar dc power distribution network, including:
continuously acquiring neutral point voltage on the valve side of a connecting transformer in a symmetrical unipolar direct-current power distribution network;
determining the number of the grounding resistance units based on the relation between the number of the grounding resistance units and the voltage of a neutral point on the valve side of the connecting transformer, and realizing automatic adjustment of the number of the grounding resistance units, wherein each grounding resistance unit comprises two reverse parallel-connected IGBTs and a resistor r 0 The grounding resistor units are connected in parallel, and all the grounding resistor units are sequentially connected in series to form a grounding resistor.
Optionally, the relationship between the number of the input ground resistance units and the valve-side neutral point voltage of the coupling transformer is as follows:
wherein U is the neutral point voltage on the valve side of the connecting transformer, U n The rated interelectrode voltage of the symmetrical monopole direct current distribution network.
Optionally, the resistance r 0 The calculation formula of (2) is as follows:
in the formula, k 0 To a reliability factor, I n For rated current of power electronics, U n The rated interelectrode voltage of the symmetrical monopole direct current distribution network.
Optionally, the determining the number of input ground resistance units based on the relationship between the number of input ground resistance units and the voltage of the neutral point on the valve side of the coupling transformer includes:
comparing the voltage of the neutral point on the valve side of the connecting transformer with a preset threshold value;
and starting time delay of set time when the voltage of the neutral point on the valve side of the connecting transformer exceeds a threshold value, and determining the number of the input grounding resistance units based on the relation between the number of the input grounding resistance units and the voltage of the neutral point on the valve side of the connecting transformer after time delay if the voltage of the neutral point on the valve side of the connecting transformer still exceeds the threshold value.
Optionally, the threshold value is 0.05U n 。
In a second aspect, the present invention provides an adaptive symmetrical unipolar dc power distribution network ground resistance adjusting device, including:
the acquisition unit is used for continuously acquiring neutral point voltage on the valve side of the connecting transformer in the symmetrical unipolar direct-current power distribution network;
an adjusting unit for determining the number of the grounding resistance units based on the relation between the number of the grounding resistance units and the voltage of the neutral point at the valve side of the connecting transformer, and realizing automatic adjustment of the number of the grounding resistance units, wherein each grounding resistance unit comprises two reverse parallel IGBTs and a resistor r 0 The grounding resistor units are connected in parallel, and all the grounding resistor units are sequentially connected in series to form a grounding resistor.
Optionally, the relationship between the number of the input ground resistance units and the valve-side neutral point voltage of the coupling transformer is as follows:
wherein U is neutral point voltage of valve side of coupling transformer, U n The rated interelectrode voltage of the symmetrical monopole direct current distribution network.
Optionally, the resistance r 0 The calculation formula of (2) is as follows:
in the formula, k 0 To a reliability factor, I n For rated current of power electronics, U n Rated for symmetrical monopole DC distribution networkThe interelectrode voltage.
Optionally, the determining the number of input ground resistance units based on the relationship between the number of input ground resistance units and the voltage of the neutral point on the valve side of the coupling transformer includes:
comparing the voltage of the neutral point on the valve side of the connecting transformer with a preset threshold value;
and starting time delay of set time when the voltage of the neutral point on the valve side of the connecting transformer exceeds a threshold value, and determining the number of the input grounding resistance units based on the relation between the number of the input grounding resistance units and the voltage of the neutral point on the valve side of the connecting transformer after time delay if the voltage of the neutral point on the valve side of the connecting transformer still exceeds the threshold value.
In a third aspect, the invention provides a self-adaptive symmetrical unipolar direct current distribution network ground resistance adjustment system, which comprises a storage medium and a processor;
the storage medium is used for storing instructions;
the processor is configured to operate in accordance with the instructions to perform the steps of the method according to any one of the first aspects.
Compared with the prior art, the invention has the following beneficial effects:
the invention can solve the contradiction between weak overcurrent capacity and protection of the power electronic devices of the direct current distribution network and insufficient sensitivity of the photocurrent transformer by only arranging the grounding resistors in sections and adaptively adding the number of the grounding resistor units according to the adding principle and method of the grounding resistor units. The method has the advantages that the direct-current power distribution network can be guaranteed to keep running for a long time when the single-pole earth fault occurs, the power supply reliability is high, meanwhile, the condition of protection failure caused by the problems of protection and sensitivity of the photocurrent transformer can be avoided, the method has good engineering application value, and powerful guarantee can be provided for popularization and application of the medium-low voltage direct-current power distribution network.
Drawings
In order that the manner in which the present invention is more fully understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings, wherein:
FIG. 1 is a diagram of a typical valve-side grounded topology of a DC distribution network coupling transformer;
FIG. 2 is a DC side single pole ground fault loop diagram;
FIG. 3 is a topological diagram of the grounding resistor segment arrangement;
FIG. 4 is a circuit diagram of the equivalent circuit of the fault component in case of a single-pole ground fault;
fig. 5 is a schematic flow chart of a method for adjusting the ground resistance of the adaptive symmetric unipolar direct-current distribution network.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of the invention.
The following detailed description of the principles of the invention is provided in connection with the accompanying drawings.
Example 1
FIG. 1 shows a typical valve-side grounding topology of a DC distribution network connection transformer, and a valve-side grounding resistor R of the connection transformer in FIG. 1 g Is a grounding resistance, V, which needs to be adjusted adaptively in the invention p And V n Respectively represent direct current positive and negative voltages, and the CT represents a photocurrent transformer.
The photocurrent transformer and the power electronics in fig. 1 should have the following requirements:
(1) the sensitivity of the photocurrent transformer is more than or equal to I 0 ；
(2) The short-time overcurrent stress allowed by a power electronic device (a plurality of power electronic devices jointly form an MMC) does not exceed the rated current I of the power electronic device n 1.35 times of the rated current I, and allows long-time overcurrent stress not to exceed the rated current I generally n 1.2 times of the total weight of the composition.
The key points of the self-adaptive grounding resistance adjusting method provided by the invention are three:
firstly, the selection principle of the grounding resistor:
the ground resistance selection principle has two principles: (1) when the direct current side single-pole ground fault is ensured, the short-circuit current flowing through the power electronic device does not exceed the short-circuit current allowed to flow for a long time; (2) the short-circuit current fault component is ensured to be larger than the sensitivity requirement value of the protection and photocurrent transformer to the maximum extent. According to the fault loop in the case of the dc-side single-pole ground fault shown in fig. 2, the above principle can be quantified as follows:
in the formula of U f Representing a fault voltage component having a value equal to 0.5U of the unipolar voltage during normal operation n ；R g And R f Respectively representing a valve side grounding resistor and a fault transition resistor of the coupling transformer; I.C. A 0 And I n Respectively representing the sensitivity of the photocurrent transformer and the rated current of the power electronics. According to the formula (1), the reliability coefficient k is added while taking into consideration the protection of the power electronic device 0 Get 1.25, get the ground resistance R g Satisfies the formula:
in order to meet the requirement of sensitivity of protection and ensure reliable action of protection, it is desirable to make the grounding resistance as small as possible under the condition of satisfying the formula (2), so as to obtain a larger short-circuit current to correctly identify the fault. Thus, R g Is taken as
Secondly, the sectional arrangement method of the grounding resistor comprises the following steps:
r obtained in step one g Is decomposed into n same resistors in series configuration and resistance value
Considering the difference of the directions of fault current components when the positive and negative electrodes are in fault, each resistor r needs to be provided 0 Tool for configuring bidirectional power electronic device and arranging grounding resistors in sectionsThe body topology is shown in FIG. 3, the dotted line frame is a ground resistor unit, which is composed of two reverse parallel IGBTs and a resistor r 0 The whole grounding resistor is formed by connecting n grounding resistor units in series. When the IGBT in the grounding resistance unit is locked, r 0 When the IGBT is turned on, r 0 And (4) cutting.
Third, the method of utilizing neutral point voltage on valve side of connecting transformer to adaptively switch into grounding resistance
There is a need for an adaptive method of determining ground resistance on a one and two basis. The invention utilizes the neutral point voltage on the valve side of the connecting transformer to control the input quantity of the grounding resistor. Fig. 4 shows an equivalent circuit of a fault component in a single-pole earth fault on a direct-current side, wherein U represents a valve-side neutral point voltage of a coupling transformer, and an expression of the U is shown in formula (3):
in order to meet the sensitivity requirement of protection, ensure the reliable action of protection and ensure that the grounding resistance is as small as possible, thereby obtaining larger short-circuit current to correctly identify faults, when the fault transition resistance is increased, the grounding resistance is gradually cut off, and the relation between the number of the grounding resistances and the fault transition resistance is put into use satisfies the formula (4).
The relation between the number of input ground resistors and the voltage of the neutral point on the valve side of the coupling transformer obtained by the formula (3) and the formula (4) is as follows:
the specific flow of the method for adjusting the ground resistance in the embodiment of the invention is shown in fig. 5. When the transformer normally operates, all n grounding resistors are put into use, and then the voltage of the neutral point on the valve side of the connecting transformer is continuously detected. In normal operation, inThe theoretical value of the voltage of the neutral point is 0, and a certain threshold value of 0.05U is set for the voltage in consideration of the measurement error of the voltage transformer n When the voltage exceeds the threshold value of 0.05U n Starting 3ms time delay to prevent abnormal adjustment of the resistance value of the grounding resistor caused by system fluctuation, and if the voltage still exceeds the threshold value by 0.05U after 3ms time delay n And automatically adjusting the quantity of the input ground resistors according to the rule of the formula (5), so that the fluctuation in normal operation can be avoided, and the ground resistor input device is prevented from frequently acting in normal operation.
According to the process, the resistance value of the grounding resistor of the direct-current power distribution network can be adjusted in a self-adaptive mode, so that the contradiction between weak overcurrent capacity and insufficient protection and photocurrent transformer sensitivity of a power electronic device of the direct-current power distribution network is solved, and the power supply reliability of the direct-current power distribution network is improved.
Example 2
Based on the same inventive concept as embodiment 1, the embodiment of the present invention provides a device for adjusting ground resistance of a self-adaptive symmetric unipolar dc power distribution network, including:
the acquisition unit is used for continuously acquiring neutral point voltage on the valve side of the connecting transformer in the symmetrical monopole direct-current power distribution network;
an adjusting unit for determining the number of the grounding resistance units based on the relation between the number of the grounding resistance units and the voltage of the neutral point at the valve side of the connecting transformer, and realizing automatic adjustment of the number of the grounding resistance units, wherein each grounding resistance unit comprises two reverse parallel IGBTs and a resistor r 0 The grounding resistor units are connected in parallel, and all the grounding resistor units are sequentially connected in series to form a grounding resistor.
In a specific implementation manner of the embodiment of the present invention, a relationship between the number of the input ground resistance units and the voltage of the neutral point on the valve side of the coupling transformer is as follows:
wherein U is the neutral point voltage on the valve side of the connecting transformer, U n For symmetrical unipolar DC distributionThe grid is rated for interelectrode voltage.
In a specific implementation manner of the embodiment of the invention, the resistor r 0 The calculation formula of (2) is as follows:
in the formula, k 0 To a reliability factor, I n For rated current of power electronics, U n The rated interelectrode voltage of the symmetrical monopole direct current distribution network.
In a specific implementation manner of the embodiment of the present invention, the determining the number of the input ground resistance units based on a relationship between the number of the input ground resistance units and a voltage of a neutral point on a valve side of the coupling transformer includes the following steps:
comparing the voltage of the neutral point on the valve side of the connecting transformer with a preset threshold value;
and starting time delay of set time when the voltage of the neutral point on the valve side of the connecting transformer exceeds a threshold value, and determining the number of the input grounding resistance units based on the relation between the number of the input grounding resistance units and the voltage of the neutral point on the valve side of the connecting transformer after time delay if the voltage of the neutral point on the valve side of the connecting transformer still exceeds the threshold value.
Example 3
Based on the same inventive concept as embodiment 1, the embodiment of the invention provides a self-adaptive symmetrical unipolar direct-current power distribution network ground resistance adjusting system, which comprises a storage medium and a processor;
the storage medium is used for storing instructions;
the processor is configured to operate in accordance with the instructions to perform the steps of the method according to any of embodiment 1.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
The foregoing shows and describes the general principles and features of the present invention, together with the advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (8)
1. A self-adaptive symmetrical monopole direct current distribution network ground resistance adjusting method is characterized by comprising the following steps:
continuously acquiring neutral point voltage on the valve side of a connecting transformer in the symmetrical monopole direct-current power distribution network;
determining the number of the grounding resistance units based on the relation between the number of the grounding resistance units and the voltage of a neutral point on the valve side of the connecting transformer, and realizing automatic adjustment of the number of the grounding resistance units, wherein each grounding resistance unit comprises two reverse parallel-connected IGBTs and a resistor r 0 The grounding resistor units are connected in parallel, and all the grounding resistor units are sequentially connected in series to form a grounding resistor;
the relation between the number of the input grounding resistor units and the voltage of the neutral point at the valve side of the coupling transformer is as follows:
wherein U is the neutral point voltage on the valve side of the connecting transformer, U n The rated interelectrode voltage of the symmetrical monopole direct current distribution network.
2. The method for adjusting the ground resistance of the self-adaptive symmetrical unipolar direct-current power distribution network according to claim 1, wherein the method comprises the following steps: the resistance r 0 Is calculated byThe formula is as follows:
in the formula, k 0 To a reliability factor, I n For rated current of power electronics, U n The rated interelectrode voltage of the symmetrical monopole direct current distribution network.
3. The method for adjusting the ground resistance of the adaptive symmetrical unipolar direct-current power distribution network according to claim 1, wherein the determining the number of the input ground resistance units based on the relationship between the number of the input ground resistance units and the voltage of the neutral point on the valve side of the coupling transformer comprises the following steps:
comparing the voltage of the neutral point on the valve side of the connecting transformer with a preset threshold value;
and starting time delay of set time when the voltage of the neutral point on the valve side of the connecting transformer exceeds a threshold value, and determining the number of the input grounding resistance units based on the relation between the number of the input grounding resistance units and the voltage of the neutral point on the valve side of the connecting transformer after time delay if the voltage of the neutral point on the valve side of the connecting transformer still exceeds the threshold value.
4. The method for adjusting the ground resistance of the self-adaptive symmetrical unipolar direct-current power distribution network according to claim 1, wherein the method comprises the following steps: the threshold value is 0.05U n 。
5. The utility model provides a self-adaptation symmetry monopole direct current distribution network ground resistance adjusting device which characterized in that includes:
the acquisition unit is used for continuously acquiring neutral point voltage on the valve side of the connecting transformer in the symmetrical unipolar direct-current power distribution network;
an adjusting unit for determining the number of the grounding resistance units based on the relation between the number of the grounding resistance units and the voltage of the neutral point at the valve side of the connecting transformer, and automatically adjusting the number of the grounding resistance units, wherein each grounding resistance unitThe resistance unit consists of two reverse parallel IGBTs and a resistor r 0 The grounding resistor units are connected in parallel, and all the grounding resistor units are sequentially connected in series to form a grounding resistor;
the relation between the number of the input grounding resistor units and the voltage of the neutral point on the valve side of the connecting transformer is as follows:
wherein U is neutral point voltage of valve side of coupling transformer, U n The rated interelectrode voltage of the symmetrical monopole direct current distribution network.
6. The device of claim 5, wherein the resistor r is the resistor r 0 The calculation formula of (2) is as follows:
in the formula, k 0 As a reliability factor, I n For rated current of power electronics, U n The rated interelectrode voltage of the symmetrical monopole direct current distribution network.
7. The adaptive symmetrical unipolar direct current distribution network ground resistance adjusting device according to claim 5, wherein the determining of the number of input ground resistance units based on the relationship between the number of input ground resistance units and the neutral point voltage on the valve side of the coupling transformer comprises the following steps:
comparing the voltage of the neutral point on the valve side of the connecting transformer with a preset threshold value;
and starting time delay of set time when the voltage of the neutral point on the valve side of the connecting transformer exceeds a threshold value, and determining the number of the input grounding resistance units based on the relation between the number of the input grounding resistance units and the voltage of the neutral point on the valve side of the connecting transformer after time delay if the voltage of the neutral point on the valve side of the connecting transformer still exceeds the threshold value.
8. A self-adaptive symmetrical monopole direct current distribution network ground resistance adjusting system is characterized by comprising a storage medium and a processor;
the storage medium is used for storing instructions;
the processor is configured to operate in accordance with the instructions to perform the steps of the method according to any one of claims 1-4.
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| CN105119251A (en) * | 2015-07-23 | 2015-12-02 | 华南理工大学 | Method for determining scheme suitable for grounding resistance of flexible direct current power distribution system |
| CN110323726A (en) * | 2019-07-17 | 2019-10-11 | 国网江苏省电力有限公司 | A kind of DC distribution net adaptable line guard method and device |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN105119251A (en) * | 2015-07-23 | 2015-12-02 | 华南理工大学 | Method for determining scheme suitable for grounding resistance of flexible direct current power distribution system |
| CN110323726A (en) * | 2019-07-17 | 2019-10-11 | 国网江苏省电力有限公司 | A kind of DC distribution net adaptable line guard method and device |
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