CN113193561A

CN113193561A - Direct current transformation control method for power distribution network

Info

Publication number: CN113193561A
Application number: CN202110341213.0A
Authority: CN
Inventors: 张璐; 张博; 唐巍; 王辰; 赵春雪
Original assignee: China Agricultural University
Current assignee: China Agricultural University
Priority date: 2021-03-30
Filing date: 2021-03-30
Publication date: 2021-07-30
Anticipated expiration: 2041-03-30
Also published as: CN113193561B

Abstract

The invention provides a direct current transformation control method of a power distribution network, which comprises the following steps: performing direct current transformation on the three-phase four-wire system low-voltage power distribution network by using a voltage source converter to obtain an alternating current-direct current hybrid low-voltage power distribution network; in the running process of the AC/DC hybrid low-voltage distribution network, obtaining running parameters of the AC/DC hybrid low-voltage distribution network so as to determine the running abnormal state of the AC/DC hybrid low-voltage distribution network; adjusting the output state of the voltage source converter according to the abnormal operation state; abnormal operating conditions include distribution transformer overload, voltage violations, and three-phase imbalances. According to the direct current transformation control method and system for the power distribution network, the existing resources of the low-voltage alternating current power distribution network are fully utilized, the direct current transformation is carried out on the alternating current power grid, the transformed power grid is controlled by adjusting the active power and the reactive power of the VSC, the coordination control and the comprehensive treatment of various power quality problems of three-phase imbalance, overload and voltage out-of-limit are realized, and the power quality and the power supply reliability of the power grid are improved.

Description

Direct current transformation control method for power distribution network

Technical Field

The invention relates to the technical field of electric power, in particular to a direct current transformation control method and a direct current transformation control system for a power distribution network.

Background

The low-voltage distribution network is used as a bottom layer power supply network directly connected with users, and the power supply quality and the power supply reliability of the low-voltage distribution network are directly related to the daily life of residents. However, imbalance in three-phase loads and line parameters can cause three-phase imbalance problems, resulting in degraded voltage quality and increased network losses. The problem of imbalance in the low-voltage distribution network is further exacerbated as the charging load of photovoltaic and electric vehicles for single-phase users increases. In addition, the rapid growth of distributed power and loads can result in overloading distribution transformers and low voltage lines. Due to the limited power capacity and voltage control capabilities of ac low voltage power distribution networks, the intermittency of distributed power sources and loads increases the risk of voltage violations. Therefore, a method for solving various power quality problems of three-phase imbalance, overload, voltage out-of-limit and the like of a low-voltage distribution network is needed.

In the prior art, the problem of power quality is generally solved by newly building a distribution line and a transformer, but the method has high investment cost and limited urban power supply space, and is difficult to effectively solve the problem of three-phase imbalance. Or the reactive power is controlled by power electronic equipment such as SVG; however, the high R/X ratio of the low voltage distribution network limits the performance of the voltage-reactive control. The problems of unbalanced three phases, overload and out-of-limit voltage are solved through control of active power and reactive power between low-voltage lines and between three phases, however, a low-voltage alternating-current power distribution network is mostly a radial network and cannot realize interconnection of multiple lines, a phase change switch can only be installed in a place with a three-phase power supply condition, and the problem of voltage sag can be caused by switch operation. Or direct current transformation of a three-phase three-wire medium-voltage distribution network is aimed at, and because a low-voltage alternating-current distribution network is generally of a three-phase four-wire system structure, the capacity of a low-voltage line cannot be fully utilized by the conventional transformation method.

The technologies all have the problem that the targets such as three-phase unbalance, overload, voltage out-of-limit and the like cannot be coordinately controlled.

Disclosure of Invention

Aiming at the problem that coordination control cannot be performed in the prior art, the embodiment of the invention provides a direct current transformation control method for a power distribution network.

The invention provides a direct current transformation control method of a power distribution network, which comprises the following steps: performing direct current transformation on the three-phase four-wire system low-voltage power distribution network by using a voltage source converter to obtain an alternating current-direct current hybrid low-voltage power distribution network; in the running process of the AC/DC hybrid low-voltage distribution network, obtaining running parameters of the AC/DC hybrid low-voltage distribution network so as to determine the running abnormal state of the AC/DC hybrid low-voltage distribution network; adjusting the output state of the voltage source converter according to the abnormal running state of the AC/DC hybrid low-voltage power distribution network; abnormal operating conditions include distribution transformer overload, voltage violations, and three-phase imbalances.

According to the direct current transformation control method for the power distribution network, provided by the invention, a three-phase four-wire system low-voltage power distribution network is subjected to direct current transformation by using a voltage source converter, and an alternating current and direct current hybrid low-voltage power distribution network is obtained, and the method comprises the following steps: aiming at an urban low-voltage distribution network, acquiring an alternating current-direct current hybrid low-voltage distribution network by adopting a first preset transformation scheme; aiming at the town low-voltage power distribution network, acquiring an alternating current-direct current hybrid low-voltage power distribution network by adopting a second preset transformation scheme; aiming at a rural low-voltage power distribution network, a third preset transformation scheme is adopted to obtain an alternating current-direct current hybrid low-voltage power distribution network; the first preset retrofit solution comprises: transforming a three-phase four-wire system low-voltage distribution network into an alternating current-direct current hybrid line with a parallel monopole structure; the second preset reconstruction scheme comprises: transforming a three-phase four-wire system low-voltage distribution network into an alternating current-direct current hybrid line with a loop and a bipolar structure; the third preset reconstruction scheme comprises the following steps: a three-phase four-wire system low-voltage distribution network is transformed into an improved alternating current-direct current hybrid line with a loop bipolar structure.

According to the direct current transformation control method of the power distribution network, provided by the invention, in the running process of the alternating current-direct current hybrid low-voltage power distribution network, the running parameters of the alternating current-direct current hybrid low-voltage power distribution network are obtained so as to determine the running abnormal state of the alternating current-direct current hybrid low-voltage power distribution network; adjusting the output state of the voltage source converter according to the abnormal running state of the AC/DC hybrid low-voltage power distribution network; the method comprises the following steps:

step 1, in the running process of the alternating current-direct current hybrid low-voltage power distribution network, under the condition that the alternating current-direct current hybrid low-voltage power distribution network is in communication, active power of all distribution transformers in the alternating current-direct current hybrid low-voltage power distribution network is obtained based on a communication network, and step 2 is executed; under the condition that the alternating current-direct current hybrid low-voltage power distribution network is not in communication, executing the step 3;

step 2, executing step 3 under the condition that all distribution transformers are determined not to be overloaded;

step 3, acquiring direct-current voltage of a direct-current line in the alternating-current and direct-current hybrid low-voltage power distribution network; if the direct-current voltage is determined to be in the preset direct-current voltage interval, executing the step 4;

step 4, acquiring alternating-current voltage of an alternating-current line in the alternating-current and direct-current hybrid low-voltage power distribution network, and executing step 5 under the condition that the alternating-current voltage is determined to be in a preset alternating-current voltage interval;

step 5, under the condition that the alternating current-direct current hybrid low-voltage power distribution network is not in communication, after a preset time interval, re-executing the step 1;

under the condition of communication, acquiring the three-phase unbalance of each preset node in the alternating-current and direct-current hybrid low-voltage power distribution network based on a communication network, and under the condition that the three-phase unbalance of any preset node is determined not to be in a threshold interval, acquiring the reactive capacity of the VSC;

under the condition that the reactive capacity is determined to be sufficient, adjusting the reactive power of the voltage source converter until the three-phase unbalance degree is within a threshold interval, and after a preset time interval, re-executing the step 1;

and under the condition that the reactive capacity is determined to be insufficient, adjusting the active power and the reactive power of the voltage source converter until the three-phase unbalance degree is within a threshold interval, and after a preset time interval, re-executing the step 1.

According to the direct current transformation control method of the power distribution network provided by the invention, the step 2 further comprises the following steps: and under the condition that the distribution transformer is determined to be overloaded, adjusting the active power of the voltage source converter until all the distribution transformers are not overloaded, and executing the step 3.

According to the direct current transformation control method of the power distribution network provided by the invention, the step 3 further comprises the following steps: under the condition that the direct-current voltage exceeds a preset direct-current voltage interval, acquiring the active power regulating quantity of the voltage source converter; under the condition that the active power regulating quantity is determined not to exceed the capacity constraint of the voltage source converter, the active power of the voltage source converter is regulated until the direct-current voltage is in a preset direct-current voltage interval, and the step 4 is executed; and under the condition that the active power regulating quantity exceeds the capacity constraint of the voltage source converter, regulating the active power and the reactive power of the voltage source converter until the direct-current voltage is in a preset direct-current voltage interval, and executing the step 4.

According to the direct current transformation control method of the power distribution network provided by the invention, the step 4 further comprises the following steps: under the condition that the alternating voltage is determined to exceed the preset alternating voltage interval, acquiring the reactive power regulating quantity of the voltage source converter; under the condition that the reactive power regulating quantity is determined not to exceed the capacity constraint of the voltage source converter, regulating the reactive power of the voltage source converter until the alternating voltage is in a preset alternating voltage interval, and executing the step 5; and under the condition that the reactive power regulating quantity is determined to exceed the capacity constraint of the voltage source converter, regulating the active power and the reactive power of the voltage source converter until the alternating voltage is in a preset alternating voltage interval, and executing the step 5.

According to the direct current transformation control method of the power distribution network provided by the invention, the step 5 further comprises the following steps: and under the condition that the three-phase unbalance degrees of all the preset nodes do not exceed the threshold value, after a preset time interval, re-executing the step 1.

According to the direct current transformation control system of the power distribution network provided by the invention, the direct current transformation control system comprises:

the transformation unit is used for carrying out direct current transformation on the three-phase four-wire system low-voltage power distribution network by using the voltage source converter to obtain an alternating current-direct current hybrid low-voltage power distribution network;

the control unit is used for acquiring the operation parameters of the AC/DC hybrid low-voltage distribution network in the operation process of the AC/DC hybrid low-voltage distribution network so as to determine the abnormal operation state of the AC/DC hybrid low-voltage distribution network; adjusting the output state of the voltage source converter according to the abnormal running state of the AC/DC hybrid low-voltage power distribution network; abnormal operating conditions include distribution transformer overload, voltage violations, and three-phase imbalances.

The invention also provides an electronic device, which comprises a memory, a processor and a computer program which is stored on the memory and can run on the processor, wherein when the processor executes the program, the steps of the direct current transformation control method of the power distribution network are realized.

The invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, implements the steps of any of the above-mentioned direct current modification control methods for a power distribution network.

According to the direct current transformation control method and system for the power distribution network, the existing resources of the low-voltage alternating current power distribution network are fully utilized, the active power and the reactive power of the VSC are adjusted by performing direct current transformation on the alternating current power grid, the coordination control and the comprehensive treatment of various power quality problems of three-phase imbalance, overload and voltage out-of-limit are realized, and the power quality and the power supply reliability of the power distribution network are improved.

Drawings

In order to more clearly illustrate the technical solutions of the present invention or the prior art, the drawings needed for the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.

Fig. 1 is a schematic flow chart of a dc modification control method for a power distribution network according to the present invention;

FIG. 2 is a schematic diagram of a looped monopole asymmetric structure provided by the present invention;

FIG. 3 is a schematic view of a monopole symmetrical structure provided by the present invention;

FIG. 4 is a schematic view of a parallel monopole configuration provided by the present invention;

FIG. 5 is a schematic diagram of a bipolar structure provided by the present invention;

FIG. 6 is a schematic diagram of a looped bipolar configuration provided by the present invention;

FIG. 7 is an improved looped bipolar configuration provided by the present invention;

fig. 8 is a schematic structural diagram of an urban low-voltage distribution network before direct current transformation provided by the invention;

fig. 9 is a schematic diagram of an alternating current-direct current transformation scheme of an urban low-voltage distribution network provided by the invention;

fig. 10 is a schematic structural diagram of a town low-voltage distribution network before direct current transformation provided by the invention;

fig. 11 is a schematic diagram of an alternating current-direct current transformation scheme of a town low-voltage distribution network provided by the invention;

FIG. 12 is a schematic structural diagram of a rural low-voltage distribution network before direct-current transformation provided by the invention

FIG. 13 is a schematic diagram of the AC/DC transformation scheme of the rural low-voltage distribution network provided by the invention

Fig. 14 is a schematic flow chart of a dc control method for a power distribution network according to the present invention;

fig. 15 is a schematic structural diagram of an exemplary ac/dc hybrid low-voltage distribution network provided by the present invention;

fig. 16 is a schematic structural diagram of a dc retrofit control system for a power distribution network according to the present invention;

fig. 17 is a schematic structural diagram of an electronic device provided by the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The direct-current power distribution network is large in transmission capacity, flexible in power control capacity and capable of coping with uncertainty of photovoltaic and electric vehicles. The AC lines can be interconnected with the DC lines to realize power dispatching among the lines. In addition, in an ac/dc hybrid distribution network, the three-phase power can be individually regulated by a Voltage Source Converter (VSC). The alternating current-direct current hybrid low-voltage power distribution network can be used as a substitute scheme for breaking the bottleneck of the traditional alternating current low-voltage power distribution network, and flexible power control between low-voltage lines and between three phases is achieved.

The following describes a dc modification control method for a power distribution network according to an embodiment of the present invention with reference to fig. 1 to 17.

Fig. 1 is a schematic flow chart of a dc modification control method for a power distribution network according to the present invention, as shown in fig. 1, including but not limited to:

s1, performing direct current transformation on the three-phase four-wire system low-voltage power distribution network by using a voltage source converter to obtain an alternating current-direct current hybrid low-voltage power distribution network;

s2, acquiring operation parameters of the AC/DC hybrid low-voltage distribution network in the operation process of the AC/DC hybrid low-voltage distribution network to determine the abnormal operation state of the AC/DC hybrid low-voltage distribution network; adjusting the output state of the voltage source converter according to the abnormal running state of the AC/DC hybrid low-voltage power distribution network; abnormal operating conditions include distribution transformer overload, voltage violations, and three-phase imbalances.

The invention aims at the transformation and control of a three-phase four-wire system alternating-current power distribution network.

The three-phase four-wire system low-voltage distribution network comprises a communication power grid and a non-communication power grid.

In step S1, in the three-phase four-wire system low-voltage distribution network in the original power grid, a part of the ac lines is transformed into dc lines by VSC, and an ac-dc hybrid low-voltage distribution network is obtained.

Optionally, the VSC may be installed at the junction of a low voltage distribution network retrofit.

Further, in step S2, in the operation process of the ac/dc hybrid low-voltage distribution network, obtaining operation parameters of the ac/dc hybrid low-voltage distribution network to determine an abnormal operation state of the ac/dc hybrid low-voltage distribution network; according to the abnormal operation state of the AC-DC hybrid low-voltage power distribution network, the DC active power injected to the DC side by the voltage source converter, and the AC active power and the AC reactive power injected to the AC side are adjusted; abnormal operating conditions include distribution transformer overload, voltage violations, and three-phase imbalances.

The operating parameters of the low-voltage distribution network may include active power at an outlet of the distribution transformer, a dc voltage at a side of the dc line, an ac voltage at a side of the ac line, and a three-phase imbalance of each node. Under the condition of communication, the VSC can acquire active power at the outlet of the distribution transformer, and alternating-current voltage, direct-current voltage and three-phase unbalance of each communication node through a communication network; without communication, the VSC can obtain the ac voltage, the dc voltage and the three-phase imbalance at the location.

According to the direct current transformation control method for the power distribution network, the existing resources of the low-voltage alternating current power distribution network are fully utilized, the direct current transformation is carried out on the alternating current power grid, the transformed power grid is controlled by adjusting the active power and the reactive power of the VSC, the coordination control and the comprehensive treatment of various power quality problems of three-phase imbalance, overload and voltage out-of-limit are realized, and the power quality and the power supply reliability of the power grid are improved.

Based on the content of above-mentioned embodiment, as an optional embodiment, carry out the direct current transformation to three-phase four-wire system low voltage distribution network with voltage source transverter, obtain the mixed low voltage distribution network of alternating current-direct current, include:

aiming at an urban low-voltage distribution network, acquiring an alternating current-direct current hybrid low-voltage distribution network by adopting a first preset transformation scheme;

aiming at the town low-voltage power distribution network, acquiring an alternating current-direct current hybrid low-voltage power distribution network by adopting a second preset transformation scheme;

aiming at a rural low-voltage power distribution network, a third preset transformation scheme is adopted to obtain an alternating current-direct current hybrid low-voltage power distribution network;

the first preset retrofit solution comprises: transforming a three-phase four-wire system low-voltage distribution network into an alternating current-direct current hybrid line with a parallel monopole structure;

the second preset reconstruction scheme comprises: transforming a three-phase four-wire system low-voltage distribution network into an alternating current-direct current hybrid line with a loop and a bipolar structure;

the third preset reconstruction scheme comprises the following steps: a three-phase four-wire system low-voltage distribution network is transformed into an improved alternating current-direct current hybrid line with a loop bipolar structure.

Firstly, the transformation scheme provided by the invention transforms a three-phase four-wire system low-voltage distribution network into an alternating-current and direct-current hybrid low-voltage distribution network. Because the low-voltage alternating-current power distribution network generally adopts a three-phase four-wire system to supply power, the direct-current transformation of the low-voltage power distribution network is obviously different from that of a three-phase three-wire system medium-voltage power distribution network.

The invention provides various transformation structures consisting of VSC, and a part of alternating current lines in a three-phase four-wire system low-voltage distribution network are transformed into direct current lines through the transformation structures. The transformation structure comprises: unipolar asymmetric structures, unipolar symmetric structures, parallel unipolar structures, bipolar structures with loops and improved bipolar structures with loops.

Fig. 2 is a schematic diagram of a looped monopole asymmetric structure according to the present invention, and as shown in fig. 2, the monopole asymmetric structure includes a VSC, an ac side of the VSC may be connected to an ac line, and four original wires in a low voltage distribution network may be used as anodes of the dc line and connected to an anode of a dc side of the VSC. And then, a newly-built line is used as a negative pole return line of the direct current line and is connected with the negative pole of the direct current side of the VSC, and the capacity of the newly-built line needs to meet the rated current of the load. Because the ground voltage of the newly-built loop line is zero, the insulation requirement can be relatively low. The load may be connected between any dc conductor and neutral. When any one of the original lines fails, the system is shut down, and the reliability is low. Due to the fact that one VSC is needed and one line is newly built, the economic input level is high.

Fig. 3 is a schematic diagram of a symmetrical monopole structure according to the present invention, and as shown in fig. 3, the symmetrical monopole structure includes a VSC, an ac side of the VSC is connected to an ac line, a positive electrode and a negative electrode on the dc side of the VSC are connected through two serially connected capacitors, and one connected electrode of the two capacitors is grounded. The original four conductors in the low-voltage distribution network are combined randomly, wherein two conductors are connected with the positive pole of the VSC direct current side to serve as the positive pole of the direct current circuit, and the other two conductors are connected with the negative pole of the VSC direct current side to serve as the negative pole of the direct current circuit. The load may be connected between any of the positive and negative leads of the dc link. The direct current structure does not need to build a new line, only needs one VSC, and therefore is low in cost. When any one of the original lines fails, the system is shut down, and the reliability is low. Since only one VSC is needed, the economic investment is low.

Fig. 4 is a schematic diagram of a parallel monopole structure provided by the present invention, as shown in fig. 4, the parallel monopole structure includes two VSCs whose ac sides are both connected to an ac line, the positive electrode and the negative electrode of the dc side of any VSC are connected through two series capacitors, and one electrode of each two series capacitors is grounded. The original four conductors in the low-voltage distribution network are randomly divided into combinations, and the positive electrode and the negative electrode of the direct-current side of each VSC are correspondingly connected with a group of circuits respectively and serve as the positive electrode and the negative electrode of the direct-current circuit. This configuration is more reliable than the unipolar symmetrical configuration shown in fig. 3 because a failure of one circuit does not affect the operation of the other circuit. In this configuration, the parallel monopole configuration does not require new wiring, but requires two VSCs with a capacity of half the maximum transmission capacity of the original ac line. The economic investment is moderate due to the need of two VSCs.

Fig. 5 is a schematic diagram of a bipolar structure provided by the present invention, as shown in fig. 5, the bipolar structure includes two VSCs with ac sides connected to ac lines, the positive electrode and the negative electrode of each VSC are connected through two series-connected capacitor devices, wherein the negative electrode of the dc side of the VSC5-1 and the positive electrode of the dc side of the VSC5-2 are both grounded. The original four conductors in the low-voltage distribution network are randomly combined, any two conductors are connected with the positive electrode of the direct-current side of the VSC5-1 to serve as the positive electrode of a direct-current line, and the other two conductors are connected with the negative electrode of the direct-current side of the VSC5-2 to serve as the negative electrode of the direct-current line. The load may be connected between any of the positive and negative leads. This high impedance dc grounded bipolar configuration has no neutral, and the bipolar is disabled if one pole fails. Therefore, the reliability of this structure is lower than the bipolar system with the circuit shown in fig. 7. The economic investment is moderate due to the need of two VSCs.

Fig. 6 is a schematic diagram of a bipolar structure with a loop according to the present invention, as shown in fig. 6, the bipolar structure with a loop includes two VSCs having ac sides both connected to an ac line, and a positive electrode and a negative electrode of each VSC are connected to each other through two series-connected capacitor devices, wherein a negative electrode of the dc side of the VSC6-1 and a positive electrode of the dc side of the VSC6-2 are both grounded. Any three of the four original leads in the low-voltage distribution network are respectively used as the anode, the cathode and the zero line of the direct-current line, and the remaining lead can be used as a standby lead. The positive pole of direct current circuit links to each other with the positive pole of VSC6-1 direct current side, and the negative pole of direct current circuit links to each other with the negative pole of VSC6-2 direct current side, and the zero line ground connection is handled. The load can be connected between the positive pole and the zero line and also can be connected between the negative pole and the zero line. The zero line has no current if the currents of the positive and negative poles are balanced. One pole of the three-phase alternating current transformer is failed, normal operation of the other pole of the three-phase alternating current transformer cannot be influenced, and reliability is high. The economic investment is moderate due to the need of two VSCs.

Fig. 7 is an improved loop bipolar structure provided by the present invention, and as shown in fig. 7, in order to fully utilize the existing four wires, one wire may be added to the positive electrode or the negative electrode of the dc line in fig. 6, so as to obtain an improved loop bipolar structure. Fig. 7 illustrates an example in which a single lead is added to the positive electrode of the dc line, and is not intended to limit the scope of the present invention. The structure is similar to the bipolar structure with the loop shown in fig. 6, and the reliability is high. With this configuration, the load current difference between the positive and negative electrodes cannot exceed the maximum current capacity of the zero line. For example, when all the loads are connected to two conductors of the positive pole, and the positive pole is operating at full load, the neutral line may be overloaded by unbalanced current. This configuration also requires two VSCs with a capacity of half the maximum transmission capacity of the original ac line. The economic investment is moderate due to the need of two VSCs.

Further, no quantitative evaluation method exists for the improvement degree of the power supply capacity and the voltage drop of the direct current transformation in the prior art. The embodiment provides a quantitative analysis method for each scheme of the modified structure.

For the transformed line, compared with an alternating current line, the power supply capacity, the voltage drop and the line loss of the transformed line are all changed, and a resistance relation formula (1) after direct current transformation is as follows:

r_DC＝0.98r_AC；

in the formula, r_DCIs the resistance of the DC line, r_ACResistance of the AC line;

the current relation formula (2) after direct current transformation is as follows:

I_DC＝1.01I_AC；

I_DCis the maximum current of the DC line, I_ACIs the maximum current of the ac line.

In this embodiment, the voltage selected for use in the low-voltage dc distribution network is ± 375V, which is convenient for connection with a 380V low-voltage ac system. Based on this, the specific calculations of the supply capacity and the voltage drop of the different dc-modified structures are as follows.

In a first aspect, the maximum power supply capacity of the low-voltage distribution network refers to the maximum load of the energy band in a three-phase balanced state, and the maximum power supply capacity P of the alternating-current line before transformation_max-ACThe calculation formula (3) is as follows:

wherein, U_NIs the phase voltage of an AC line, I_ACFor maximum current of AC line, U_ACIs the line voltage of the AC line,

Is the power factor of the ac line.

The calculation formula (4) of the power supply capacity of the transformed direct current network is as follows:

P_max-DC＝U_DCI_DC(ii) a Wherein, P_max-DCFor maximum power supply capacity of the DC line, U_DCIs the voltage of the DC line, I_DCIs the maximum current of the dc line.

The results of the power supply capacity calculations for the different retrofit configurations are shown in table 1.

TABLE 1 comparison of Power supply Capacity for different retrofit situations

Second, the active power P for a given load_lAnd reactive power Q_lVoltage drop delta U of low-voltage three-phase four-wire system low-voltage distribution network_ACThe calculation formula (5) is as follows:

wherein Z is_ACIs a line impedance matrix;

for the phase current of the line, it is,

is the neutral current. The calculation formula (6) of the phase current is as follows:

wherein,

is composed of

The phase current of the phase(s),

is composed of

The active power of the phase load is obtained,

is composed of

The reactive power of the phase load is calculated,

is composed of

Phase voltages.

Supposing that the DC transformed load active power P_lAre evenly distributed on each direct current line. For the structures of FIGS. 2-5, the DC voltage drop Δ U_DCThe calculation formula (7) is:

ΔU_DC＝P_l/4U_DC·r_DC；

wherein, P_lFor transforming the active power, U, of the afterload by DC_DCIs the voltage of the DC line, r_DCIs the resistance of the dc line.

For the configuration shown in FIG. 6, the DC voltage drop Δ U_DCThe calculation formula (8) is:

ΔU_DC＝P_l/2U_DC·r_DC；

For the configuration shown in FIG. 7, the DC voltage drop Δ U_DCThe calculation formula (9) is:

ΔU_DC＝P_l/3U_DC·r_DC；

The following low-voltage distribution network parameters are taken as an example in the embodiment, wherein the line is4-core cable, impedance matrix Z_ACComprises the following steps:

the three-phase load is respectively 4kW, 2kW and 0kW, and the power factors are all 0.9. For example, in fig. 2, the resistance of the newly-built wire is 0.1384 Ω, which is 1/4 of the original ac line resistance. The supply capacity and voltage drop of the ac-dc line were calculated from the above analysis and the reliability and investment costs of these dc retrofit configurations were compared as shown in table 2:

TABLE 2 comparison of different modification situations

Fig. 8 is a schematic structural diagram of the urban low-voltage distribution network before dc modification, as shown in fig. 8, for the urban low-voltage distribution network, because the power line corridor space of the city is limited, the urban low-voltage distribution network widely uses four-core cables, and the current-carrying capacities of the zero line and the phase line of the four-core cables are the same. Due to the fact that the transformer and the line are overloaded due to the rapid increase of the load of the urban low-voltage distribution network, and due to the increase of direct-current loads of electric automobiles and the like, the voltage out-of-limit and three-phase imbalance can be further increased. Therefore, the dc transformation scheme of the urban low voltage distribution network needs to meet the increasing load demand and the requirement of high reliability and power quality. When the four-core cable is used in urban areas, a first preset transformation scheme is adopted, and a low-voltage distribution network is transformed into an alternating-current and direct-current mixed line as shown in fig. 9 according to a parallel monopole structure shown in fig. 4. After the alternating current circuit is converted into direct current to run, direct current loads such as an electric automobile can be connected to a direct current circuit, and the interconnection of the alternating current circuit and the direct current circuit is achieved through VSC.

For the low-voltage distribution network in cities and towns, as shown in fig. 10, the low-voltage distribution network in the cities and towns usually adopts a three-phase four-wire overhead line, wherein the zero line is a bare copper conductor and is thinner than other phase lines. The increase of the number of photovoltaic grid-connected users in urban areas may cause voltage out-of-limit and voltage fluctuation. Therefore, the photovoltaic digestion is promoted to solve the problem that the low-voltage distribution network in the cities and towns needs to be solved urgently. In a direct current system, the zero line cannot be used for power transmission because the current-carrying capacity is smaller than that of other phase lines. Therefore, the existing three ac lines are fully utilized, a second preset transformation scheme is adopted, and the low-voltage distribution network is transformed into an ac-dc hybrid line shown in fig. 11 according to the looped bipolar structure shown in fig. 6, wherein two lines are connected through the VSC.

For a rural low-voltage distribution network, in a part of rural areas, three-phase lines of the low-voltage distribution network are independently used for supplying power, as shown in fig. 12. The three-circuit power supply lines A-N, B-N and C-N are separated from the outlet of the distribution transformer, and the structure can cause serious three-phase unbalance problems. In the structure, the current-carrying capacity of the zero line and other phase lines after three-phase separation is the same. The dc retrofit solution for this configuration requires three circuits to be guaranteed. Therefore, the rural low-voltage distribution network adopts a third preset scheme, and the low-voltage distribution network is transformed into an alternating-current and direct-current hybrid line as shown in fig. 13 according to the improved loop bipolar structure shown in fig. 7, so that the existing alternating-current line can be fully utilized.

The direct current transformation control method of the power distribution network quantifies and analyzes the transmission capability, voltage drop, reliability and investment cost of direct current transformation structures of different low-voltage power distribution networks, provides a direct current transformation scheme suitable for alternating current low-voltage power distribution networks in cities, towns and rural areas aiming at the structures and requirements of three typical alternating current low-voltage power distribution networks and the characteristics of various direct current transformation structures, and can provide guidance for the direct current transformation of a three-phase four-wire low-voltage power distribution network in practice.

For the condition that multiple power quality problems of distribution transformer overload, three-phase imbalance and voltage out-of-limit simultaneously occur, the mutual influence among the multiple power quality problems is considered, and the transformed AC/DC hybrid power distribution network needs to be controlled. Fig. 14 is a schematic flow chart of a dc control method for a power distribution network according to the present invention, and as shown in fig. 14, in an operation process of an ac/dc hybrid low-voltage power distribution network, operation parameters of the ac/dc hybrid low-voltage power distribution network are obtained to determine an abnormal operation state of the ac/dc hybrid low-voltage power distribution network; adjusting the output state of the voltage source converter according to the abnormal running state of the AC/DC hybrid low-voltage power distribution network; the method comprises the following steps:

under the condition of communication, acquiring the three-phase unbalance of each preset node in the alternating current-direct current hybrid low-voltage power distribution network based on the communication network, and under the condition that the three-phase unbalance of any preset node is determined not to be in a threshold interval, acquiring the reactive capacity of the VSC;

under the condition that the reactive capacity is determined to be sufficient, adjusting the reactive power of the voltage source converter until the three-phase unbalance degree is within the threshold interval, and after the preset time interval, re-executing the step 1;

and under the condition that the reactive capacity is determined to be insufficient, adjusting the active power and the reactive power of the voltage source converter until the three-phase unbalance degree is in the threshold interval, and after the preset time interval, re-executing the step 1.

In this embodiment, through adjusting VSC three-phase active and reactive power among the second transformation structure, thereby can realize that the power of interconnection circuit changes the confession and alleviates and joins in marriage and become transshipping, can improve three-phase unbalance degree and voltage off-limit problem simultaneously.

The line reconstruction structure is that two transformers shown in fig. 9 are operated in parallel in urban and urban areas and a single transformer is independently supplied in rural areas according to different regions, and the following description uses an example of parallel operation of two transformers shown in fig. 15, which is not to be considered as a limitation to the protection range.

Aiming at the communication condition of the low-voltage distribution network, the control strategy is divided into a communication strategy and a non-communication strategy. The non-communication means that the VSC can only measure local voltage and adjust the active and reactive power of the VSC according to the local voltage value.

When there is communication in the distribution network, the VSC can communicate with important nodes and distribution transformer in distribution transformer and the circuit, and the VSC adjusts according to distribution transformer power and the voltage of the node that can communicate this moment.

The invention firstly provides a multi-mode control strategy based on three-phase four-wire sensitivity, and the multi-mode control strategy is respectively used for relieving the problems of distribution transformer overload, voltage out-of-limit and three-phase imbalance. Based on the control strategy, a self-adaptive multi-mode control strategy is provided for various power quality problems occurring simultaneously in the alternating current and direct current hybrid low-voltage power distribution network.

Fig. 15 is a schematic structural diagram of a typical ac/dc hybrid low-voltage distribution network provided by the invention, wherein a first modified structure adopts V_dcThe control mode of Q stabilizes the voltage at the direct current side, and the second transformation structure adopts the control mode of P-Q to control the active and reactive power between the alternating current and direct current lines. First transformation structure is used for stabilizing direct current side voltage, and the control to the mixed low voltage distribution network of alternating current-direct current is realized mainly through adjusting the VSC in the second transformation structure below.

After the direct current transformation of the three-phase four-wire system low-voltage power distribution network is completed, the control of the alternating current and direct current hybrid low-voltage power distribution network is performed in the operation of the power grid, in the step 1, the three-phase four-wire system low-voltage power distribution network comprises a communication power grid and a non-communication power grid, and under the condition that the alternating current and direct current hybrid low-voltage power distribution network has communication, the VSC in the transformation structure can obtain the active power of the distribution transformer at a low-voltage outlet through a communication function and execute the step 2.

Further, in step 2, in case it is determined that all distribution transformers are not overloaded, step 3 is performed.

The step 2 further comprises: and under the condition that the distribution transformer is determined to be overloaded, adjusting the active power of the voltage source converter until all the distribution transformers are not overloaded, and executing the step 3.

To the low voltage distribution network that has the communication, VSC can obtain the measurement value of joining in marriage and become export three-phase active power through communication network, alleviates to join in marriage and becomes overload problem through the active power who adjusts VSC in the second transformation structure. Of VSC in the second modified configuration

Amount of phase active power regulation

The calculation formula (10) is:

wherein,

active power at the outlet of the distribution transformer;

the maximum active power allowed for the distribution transformer,

the minimum active power allowed for the distribution transformer.

The capacities of the two transformers interconnected in fig. 15 can be complemented, and in the case of overload of any transformer, as long as the distribution transformer on the other side has redundant capacity, the treatment of the overload problem of the distribution transformer can be realized by adjusting the power of the VSC.

And (3) under the condition that the alternating current-direct current hybrid low-voltage distribution network is not in communication, executing step 3.

According to the direct current transformation control method for the power distribution network, the problem of overload of the electric transformer is solved by controlling the power output of the VSC in the transformation structure under the condition of communication, the service life of the distribution transformer is prolonged, the safe operation of the low-voltage power distribution network is guaranteed, and the power supply reliability is improved. In addition, the situation of no communication is considered, and the application range is wider.

Further, in step 3, acquiring a direct-current voltage of a direct-current line in the alternating-current and direct-current hybrid low-voltage power distribution network; if the direct-current voltage is determined to be in the preset direct-current voltage interval, executing the step 4;

step 3 also includes: under the condition that the direct-current voltage is determined to exceed the preset direct-current voltage interval, acquiring the active power regulating quantity of the voltage source converter;

in the case that it is determined that the active power adjustment amount does not exceed the voltage source converter capacity constraint, adjusting the active power of the voltage source converter until the direct-current voltage is in the preset direct-current voltage interval, and executing the step 4;

and under the condition that the active power adjustment quantity is determined to exceed the capacity constraint of the voltage source converter, adjusting the active power and the reactive power of the voltage source converter until the direct-current voltage is in the preset direct-current voltage interval, and executing the step 4.

The voltage regulation equation (11) on the dc side in the second modified structure is as follows:

wherein, is Δ V^DCMeasuring the deviation between the voltage and the upper limit or the lower limit of the voltage on the alternating current side of the VSC in the second modified structure;

is a second modificationActive power regulating quantity, S, of VSC direct current side in structure^V-QTo measure the voltage-reactive sensitivity between the node and the second modified structure.

VSC exchanges side active power regulating variable in structure is reformed transform to second

And DC side active power regulating quantity

Equation (12) should be satisfied as follows:

when the voltage of the alternating current line is out of limit, firstly, the reactive power of the VSC in the second transformation structure is adjusted, and the reactive power of the alternating current side of the VSC in the second transformation structure is adjusted to not influence the voltage of the direct current line.

Three-phase reactive power regulating quantity of VSC in second modified structure

The calculation formula (13) of (a) is as follows:

wherein,

is an i node

Deviation between phase voltage and upper limit or lower limit of voltage, upper and lower limits of voltage at AC side are 1.07 and 0.90 respectively;

and the three-phase voltage-reactive sensitivity between the node i and the second improved structure is obtained.

Since the capacity of the VSC is fixed, the adjustable amount of reactive power is also determined in case the active power of the VSC is determined, thus forming a capacity constraint.

If the second modified structure is used for the three-phase reactive power regulation of the VSC

Exceeding the capacity constraint of the VSC in the second modified configuration requires active power supplementary regulation of the VSC, and the regulation formula (14) is as follows:

wherein,

for the three-phase voltage-reactive sensitivity between the node i and the second modified structure,

for three-phase active power regulation of the VSC in the second modified configuration,

is the three-phase voltage-active sensitivity between the node i and the second modified structure,

for three-phase reactive regulation of the VSC in the second modified configuration,

for the active power injected by the VSC to the ac side in the second modified configuration,

for regulating the three-phase active power on the alternating current side of the VSC in the second modified structure,

for the reactive power injected by the VSC to the ac side in the second modified configuration,

for regulating the three-phase reactive power on the alternating current side of the VSC in the second modified structure,

the rated capacity of the VSC in the second modified configuration.

Active power regulation of VSC to reduce the effect on DC side

As small as possible, the specific implementation of equation (14) is: gradually reducing the absolute value of the VSC active power in the second modified structure, while

Taking the maximum value that satisfies the capacity constraint until the voltage satisfies

According to the direct current transformation control method for the power distribution network, the problem that direct current voltage is out of limit is solved by controlling the power output of the VSC in the transformation structure, the operation modes of communication and non-communication are further designed, the application range is wide, meanwhile, the safe operation of the low-voltage power distribution network is guaranteed, and the power supply reliability is improved.

the step 4 further comprises: under the condition that the alternating voltage is determined to exceed the preset alternating voltage interval, acquiring reactive power regulating quantity of the voltage source converter;

under the condition that the reactive power regulation amount is determined not to exceed the capacity constraint of the voltage source converter, regulating the reactive power of the voltage source converter until the alternating voltage is in the preset alternating voltage interval, and executing the step 5;

and under the condition that the reactive power regulation amount is determined to exceed the capacity constraint of the voltage source converter, regulating the active power and the reactive power of the voltage source converter until the alternating voltage is in the preset alternating voltage interval, and executing the step 5.

Because the R/X of the low-voltage line is high, both active power and reactive power can have a relatively remarkable influence on the voltage, the voltage control method based on the active and reactive power regulation of the inverter is provided. Considering that the calculation capacity of the low-voltage distribution network is limited, the voltage sensitivity method can be adopted to realize the rapid voltage regulation of the low-voltage distribution network. The second improved structure decouples the alternating-current and direct-current hybrid low-voltage distribution network into an alternating-current part and a direct-current part, and the direct-current part and the alternating-current part can be respectively controlled by adopting a sensitivity method.

The alternating current side adopts three-phase four-wire voltage sensitivity, and a voltage regulation equation (15) of the alternating current side of the second transformation structure is as follows:

wherein Δ V^ACFor the deviation between the AC-side measured voltage and the upper or lower voltage limit, S^V-PIn order to measure the voltage-active sensitivity between the node and the second modified structure,

for the active power regulating quantity, S, of the VSC AC side in the second modified structure^V-QIn order to measure the voltage-reactive sensitivity between the node and the second modified structure,

and the reactive power regulating quantity of the VSC alternating current side in the second modified structure is obtained.

When the voltage of the direct current line is out of limit, firstly calculating the active power regulating quantity of the VSC in the second modified structure

The calculation formula (16) is as follows:

wherein,

for the active power regulation on the dc side of the VSC in the second modified configuration,

is the deviation between the voltage of the j node on the direct current side and the upper limit or the lower limit of the voltage,

node j is the voltage-real sensitivity before VSC in the second modified configuration.

If the active capacity is insufficient, releasing the active capacity by reducing the absolute value of the reactive power, and adjusting the active and reactive powers of the VSC in the second modified structure according to the following formula (17):

wherein,

for the regulation of the active power on the ac side of the VSC in the second modified configuration,

adjusting the active power on the direct current side of the VSC in the second modified structure;

the upper and lower limits of the direct-current side voltage are respectively 1.07 and 0.93 for the three-phase active power regulating quantity of the VSC in the second modified structure;

and adjusting the three-phase reactive power of the VSC in the second improved structure. Equation (17) has two solutions, taken to reduce the effect on the AC side

The smaller solution.

For a low-voltage distribution network without communication, Δ V in formulas (13) to (17) is the out-of-limit deviation of the voltage of the node connected to the ac side and the dc side of the VSC in the second modified structure;

for a communications network, Δ V in equations (13) - (17) is the maximum voltage out-of-limit deviation that the VSC can measure in the second modified architecture.

According to the direct current transformation control method for the power distribution network, the problem that the alternating current voltage is out of limit is solved by controlling the power output of the VSC in the transformation structure, the operation modes of communication and non-communication are further designed, the application range is wide, the safe operation of the low-voltage power distribution network is guaranteed, and the power supply reliability is improved.

Further, in step 5, under the condition that the alternating current-direct current hybrid low-voltage distribution network is not in communication, after a preset time interval, the step 1 is executed again;

The step 5 further comprises:

and under the condition that the three-phase unbalance degrees of all the preset nodes do not exceed the threshold value, after the preset time interval, re-executing the step 1.

The three-phase unbalance of the low-voltage distribution network is defined by the following formula (18):

therein, VUF_iRepresenting the voltage three-phase unbalance degree of the node i;

is the phase voltage at the node i and,

is the average voltage of node i, V_i,a、V_i,b、V_i,cThe line voltage at node i.

When three-phase unbalance VUF_iAnd when the upper limit is exceeded, the three-phase voltage is regulated to the average voltage by regulating the power of the VSC2 so as to realize voltage balance. And (3) controlling by adopting a voltage sensitivity method, firstly adjusting reactive power according to a formula (13) in order to reduce the influence on the direct current side, and when the reactive capacity is insufficient, realizing VSC active and reactive coordination control by adopting a formula (14). It is to be noted that, in the control for improving the three-phase imbalance, in equations (13) to (14)

Is an i node

Phase voltage

And the average voltage of the node

A difference of (i.e.

For a low-voltage distribution network without communication,

voltage unbalance deviation of nodes connected to the alternating current side and the direct current side of the VSC 2; with respect to the presence of a communication network,

the maximum voltage imbalance deviation that is measured for the VSC 2.

The direct current transformation control method for the power distribution network, provided by the invention, is based on three-phase four-wire sensitivity, and can be used for relieving multiple power quality problems of overload, voltage out-of-limit, three-phase imbalance and the like of a distribution transformer, which are simultaneously generated in an alternating current and direct current mixed low-voltage power distribution network, realizing comprehensive treatment of the three-phase imbalance, the overload and the voltage out-of-limit problems, providing a new means for treating the power quality problems of the low-voltage power distribution network, further designing an operation mode with communication and without communication, and having wide application range.

Fig. 16 is a schematic structural diagram of a dc modification control system of a power distribution network according to the present invention, and as shown in fig. 16, the system includes:

the transformation unit 1 is used for carrying out direct current transformation on a three-phase four-wire system low-voltage power distribution network by using a voltage source converter to obtain an alternating current-direct current hybrid low-voltage power distribution network;

the control unit 2 is used for acquiring the operation parameters of the AC/DC hybrid low-voltage distribution network in the operation process of the AC/DC hybrid low-voltage distribution network so as to determine the abnormal operation state of the AC/DC hybrid low-voltage distribution network; adjusting the output state of the voltage source converter according to the abnormal running state of the AC/DC hybrid low-voltage power distribution network; abnormal operating conditions include distribution transformer overload, voltage violations, and three-phase imbalances.

In practical application, the transformation unit 1 utilizes a voltage source converter to perform direct current transformation on a three-phase four-wire system low-voltage power distribution network to obtain an alternating current-direct current hybrid low-voltage power distribution network; the control unit 2 acquires operation parameters of the AC/DC hybrid low-voltage distribution network in the operation process of the AC/DC hybrid low-voltage distribution network so as to determine the abnormal operation state of the AC/DC hybrid low-voltage distribution network; adjusting the output state of the voltage source converter according to the abnormal running state of the AC/DC hybrid low-voltage power distribution network; abnormal operating conditions include distribution transformer overload, voltage violations, and three-phase imbalances.

In the three-phase four-wire system low voltage distribution network in original electric wire netting, reform transform unit 1 utilizes VSC to reform transform a part alternating current circuit into direct current circuit, acquires the mixed low voltage distribution network of alternating current-direct current.

Further, in the running process of the alternating current-direct current hybrid low-voltage distribution network, the control unit 2 acquires running parameters of the alternating current-direct current hybrid low-voltage distribution network so as to determine the running abnormal state of the alternating current-direct current hybrid low-voltage distribution network; according to the abnormal operation state of the AC-DC hybrid low-voltage power distribution network, the DC active power injected to the DC side by the voltage source converter, and the AC active power and the AC reactive power injected to the AC side are adjusted; abnormal operating conditions include distribution transformer overload, voltage violations, and three-phase imbalances.

According to the direct current transformation control system for the power distribution network, the existing resources of the low-voltage alternating current power distribution network are fully utilized, the direct current transformation is carried out on the alternating current power grid, the transformed power grid is controlled by adjusting the active power and the reactive power of the VSC, the coordination control and the comprehensive treatment of various power quality problems of three-phase imbalance, overload and voltage out-of-limit are realized, and the power quality and the power supply reliability of the power grid are improved.

It should be noted that, when specifically executed, the dc modification control system for a power distribution network provided by the present invention may be implemented based on the dc modification control method for a power distribution network described in any of the above embodiments, and details of this embodiment are not described herein.

Fig. 17 is a schematic structural diagram of an electronic device provided in the present invention, and as shown in fig. 17, the electronic device may include: a processor (processor)1710, a communication Interface 1720, a memory (memory)1730, and a communication bus 1740, wherein the processor 1710, the communication Interface 1720, and the memory 1730 communicate with each other via the communication bus 1740. The processor 1710 may call logic instructions in the memory 1730 to perform a dc retrofit control method for a power distribution network, the method comprising: acquiring terminal network flow in the operation process of the power wireless private network; based on the attribute information of the terminal network flow, under the condition that the terminal network flow is determined to contain abnormal flow, acquiring a blocking point of the abnormal flow, and analyzing the abnormal flow to acquire an abnormal service terminal generating the abnormal flow; and blocking the abnormal flow at the blocking point, and performing access blocking processing on the abnormal service terminal.

In addition, the logic instructions in the memory 1730 may be implemented in software functional units and stored in a computer readable storage medium when the logic instructions are sold or used as a stand-alone product. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: various media capable of storing program codes, such as a usb disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk.

In another aspect, the present invention also provides a computer program product, the computer program product including a computer program stored on a non-transitory computer readable storage medium, the computer program including program instructions, when the program instructions are executed by a computer, the computer being capable of executing the dc reconstruction control method for a power distribution network provided by the above methods, the method including: performing direct current transformation on the three-phase four-wire system low-voltage power distribution network by using a voltage source converter to obtain an alternating current-direct current hybrid low-voltage power distribution network; in the running process of the AC/DC hybrid low-voltage distribution network, obtaining running parameters of the AC/DC hybrid low-voltage distribution network so as to determine the running abnormal state of the AC/DC hybrid low-voltage distribution network; adjusting the output state of the voltage source converter according to the abnormal running state of the AC/DC hybrid low-voltage power distribution network; abnormal operating conditions include distribution transformer overload, voltage violations, and three-phase imbalances.

In another aspect, the present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored, where the computer program is implemented by a processor to execute the method for controlling dc transformation of a power distribution network provided in the foregoing embodiments, and the method includes: performing direct current transformation on the three-phase four-wire system low-voltage power distribution network by using a voltage source converter to obtain an alternating current-direct current hybrid low-voltage power distribution network; in the running process of the AC/DC hybrid low-voltage distribution network, obtaining running parameters of the AC/DC hybrid low-voltage distribution network so as to determine the running abnormal state of the AC/DC hybrid low-voltage distribution network; adjusting the output state of the voltage source converter according to the abnormal running state of the AC/DC hybrid low-voltage power distribution network; abnormal operating conditions include distribution transformer overload, voltage violations, and three-phase imbalances.

The above-described embodiments of the apparatus are merely illustrative, and the units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

Through the above description of the embodiments, those skilled in the art will clearly understand that each embodiment can be implemented by software plus a necessary general hardware platform, and certainly can also be implemented by hardware. With this understanding in mind, the above-described technical solutions may be embodied in the form of a software product, which can be stored in a computer-readable storage medium such as ROM/RAM, magnetic disk, optical disk, etc., and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute various embodiments or some portions of embodiments described above.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. A direct current transformation control method of a power distribution network is characterized by at least comprising the following steps:

performing direct current transformation on the three-phase four-wire system low-voltage power distribution network by using a voltage source converter to obtain an alternating current-direct current hybrid low-voltage power distribution network;

in the running process of the AC/DC hybrid low-voltage distribution network, obtaining running parameters of the AC/DC hybrid low-voltage distribution network so as to determine the running abnormal state of the AC/DC hybrid low-voltage distribution network; adjusting the output state of the voltage source converter according to the abnormal operation state of the alternating current-direct current hybrid low-voltage power distribution network; the abnormal operating conditions include distribution transformer overload, voltage out-of-limit, and three-phase imbalance.

2. The direct-current transformation control method for the power distribution network according to claim 1, wherein the direct-current transformation is performed on the three-phase four-wire low-voltage power distribution network by using the voltage source converter to obtain an alternating-current and direct-current hybrid low-voltage power distribution network, and the method comprises the following steps:

aiming at an urban low-voltage distribution network, acquiring the alternating current-direct current hybrid low-voltage distribution network by adopting a first preset transformation scheme;

aiming at the town low-voltage power distribution network, acquiring the alternating current-direct current hybrid low-voltage power distribution network by adopting a second preset transformation scheme;

aiming at a rural low-voltage power distribution network, a third preset transformation scheme is adopted to obtain the alternating current-direct current hybrid low-voltage power distribution network;

the first preset reconstruction scheme comprises: transforming the three-phase four-wire system low-voltage distribution network into an alternating current-direct current hybrid line with a parallel monopole structure;

the second preset reconstruction scheme comprises: transforming the three-phase four-wire system low-voltage distribution network into an alternating current-direct current hybrid line with a loop and a bipolar structure;

the third preset reconstruction scheme comprises: and transforming the three-phase four-wire system low-voltage distribution network into an improved alternating-current and direct-current hybrid line with a loop bipolar structure.

3. The direct-current transformation control method for the power distribution network according to claim 1, wherein in the running process of the alternating-current and direct-current hybrid low-voltage power distribution network, running parameters of the alternating-current and direct-current hybrid low-voltage power distribution network are obtained to determine the running abnormal state of the alternating-current and direct-current hybrid low-voltage power distribution network; adjusting the output state of the voltage source converter according to the abnormal operation state of the alternating current-direct current hybrid low-voltage power distribution network; the method comprises the following steps:

step 1, in the running process of the alternating current-direct current hybrid low-voltage power distribution network, under the condition that the alternating current-direct current hybrid low-voltage power distribution network is in communication, active power of all distribution transformers in the alternating current-direct current hybrid low-voltage power distribution network is obtained based on a communication network, and step 2 is executed; under the condition that the alternating current-direct current hybrid low-voltage power distribution network is not in communication, executing a step 3;

step 2, under the condition that all distribution transformers are determined not to be overloaded, executing the step 3;

step 3, acquiring the direct-current voltage of a direct-current line in the alternating-current and direct-current hybrid low-voltage power distribution network; if the direct-current voltage is determined to be in the preset direct-current voltage interval, executing the step 4;

step 4, acquiring the alternating-current voltage of an alternating-current line in the alternating-current and direct-current hybrid low-voltage power distribution network, and executing step 5 under the condition that the alternating-current voltage is determined to be in a preset alternating-current voltage interval;

4. The direct current transformation control method for the power distribution network according to claim 3, wherein the step 2 further comprises:

and under the condition that the distribution transformer is determined to be overloaded, adjusting the active power of the voltage source converter until all the distribution transformers are not overloaded, and executing the step 3.

5. The direct current transformation control method for the power distribution network according to claim 2, wherein the step 3 further comprises:

under the condition that the direct-current voltage is determined to exceed the preset direct-current voltage interval, acquiring the active power regulating quantity of the voltage source converter;

6. The direct current transformation control method for the power distribution network according to claim 3, wherein the step 4 further comprises:

under the condition that the alternating voltage is determined to exceed the preset alternating voltage interval, acquiring reactive power regulating quantity of the voltage source converter;

7. The direct current transformation control method for the power distribution network according to claim 3, wherein the step 5 further comprises:

8. The utility model provides a direct current of distribution network reforms transform control system which characterized in that includes at least:

the control unit is used for acquiring the operation parameters of the AC/DC hybrid low-voltage distribution network in the operation process of the AC/DC hybrid low-voltage distribution network so as to determine the abnormal operation state of the AC/DC hybrid low-voltage distribution network; adjusting the output state of the voltage source converter according to the abnormal operation state of the alternating current-direct current hybrid low-voltage power distribution network; the abnormal operating conditions include distribution transformer overload, voltage out-of-limit, and three-phase imbalance.

9. An electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements the steps of the dc modification control method for the power distribution network according to any one of claims 1 to 7 when executing the computer program.

10. A non-transitory computer readable storage medium having stored thereon a computer program, wherein the computer program when executed by a processor implements the dc retrofit control method steps of the power distribution network according to any of claims 1 to 7.