WO2016149926A1

WO2016149926A1 - Anti-islanding method and device for distributed power source of direct-current electric distribution network

Info

Publication number: WO2016149926A1
Application number: PCT/CN2015/075086
Authority: WO
Inventors: 胡文平; 郭捷; 王磊; 段晓波
Original assignee: 国网河北省电力公司电力科学研究院; 河北省电力建设调整试验所
Priority date: 2015-03-26
Filing date: 2015-03-26
Publication date: 2016-09-29

Abstract

An anti-islanding method and device for a distributed power source of a direct-current electric distribution network. The method comprises: inject an alternating voltage component to an output end of an AC/DC interface converter, the frequency of the alternating voltage component being less than a working frequency; sample first voltage signals of the output end of the AC/DC converter; extract a first effective value of an alternating-current signal in the first voltage signals; compare the first effective value with a first preset voltage value; and an islanding phenomenon occurs on the distributed power source when it is determined that the first effective value is less than the first preset voltage value, and control the distributed power source to stop working. By determining whether the alternating voltage component exists on the output end of the AC/DC converter, whether the distributed power source needs to stop operation is determined. If the alternating voltage component does not exist on the output end of the AC/DC converter, the distributed power source is controlled to stop operation, and whether the islanding phenomenon exists can be determined accurately in a timely manner.

Description

Anti-islanding method and device for distributed power supply of DC distribution network

Technical field

The invention relates to the technical field of a DC distribution network, and particularly relates to an anti-islanding method and device for a distributed power supply of a DC distribution network.

Background technique

With the depletion of traditional fossil energy, global climate change and environmental pollution problems are becoming more and more serious. In order to meet the growing energy needs of human society and reduce the environmental burden, it is urgent to develop clean, low-carbon and sustainable green energy. Therefore, distributed photovoltaic power generation in distributed power sources is an effective form of solar energy utilization, and the conversion efficiency is high, which is beneficial to the full utilization of resources and improve the reliability of energy supply.

DC distribution network is one of the new development directions of distribution network in the future. In recent years, it has received extensive attention from academic circles, and demonstration projects have been put into use. One of the advantages of the DC distribution network is that it is flexible and open, eliminating the inverter link of DC power supply such as photovoltaic power generation, greatly reducing the cost of distributed power generation, and being able to adapt to the large-scale access of distributed power.

However, similar to AC access, distributed photovoltaic power generation has a technical problem of anti-islanding effect in the DC distribution network. For details, refer to the schematic diagram of the distributed power supply DC distribution network shown in Figure 1.

Figure 1 shows a DC distribution network with power distribution at both ends. The power supply systems at both ends are the AC system 1 and the AC system 2, respectively. The AC system 1 is connected to the DC distribution network via the first AC/DC interface converter 100a. The AC system 2 is connected to the DC distribution network via the second AC/DC interface converter 100b, and the distributed power source 300 is connected to the DC distribution network via the grid-connected DC/DC converter 200 and the circuit breaker 400; The local load 500 of the grid connection, other loads 600 and other power sources 700.

To prevent the distributed power source 300 from being out of operation when the grid is out of service, the power supply 300 cannot be discharged as scheduled, but the power supply to the local load 500 is continued, and an unplanned power supply island is formed in the shutdown power grid. In particular, when the distributed power supply 500 emits power substantially equal to the local load 500, an island of relatively stable power supply is formed, resulting in a detection dead zone.

The hazards brought by the islanding effect include: the stability of power supply and the quality of power in the island cannot be guaranteed, and the islanded electrification affects the low-voltage reclosing. During the overhaul, the islands are electrically charged to threaten the human body, the equipment is safe, and the power supply and responsibility are easy to dispute. Unlike the isolated islands of the AC distribution network, the anti-islanding of the DC distribution network cannot detect the frequency anomaly, and it is also impossible to implement the active frequency shift to avoid the blind zone, making it more difficult to prevent islands.

Therefore, those skilled in the art need to provide an anti-islanding method and device for a distributed power supply of a DC distribution network, which can detect whether an isolated island has an islanding phenomenon in time and accurately, and timely control the distributed power supply when an islanding phenomenon occurs. run.

Summary of the invention

The technical problem to be solved by the present invention is to provide an anti-islanding method and device for a distributed power supply of a DC distribution network, which can timely and accurately detect whether an islanding phenomenon occurs in a distributed power source, and timely control a distributed power source when an islanding phenomenon occurs. Stop running.

An embodiment of the present invention provides an anti-islanding method for a distributed power supply of a DC distribution network, which is applied to a DC distribution network, where the distributed power source is connected to an input end of a DC/DC converter, and the DC/DC commutation is performed. The output end of the device is connected to the DC distribution network through a grid-connected DC circuit breaker; the AC system is connected to the input end of the AC/DC interface converter, and the output end of the AC/DC interface converter is connected to the DC power distribution Net; the method includes:

Transmitting an AC voltage component to an output of the AC/DC interface converter, the frequency of the AC voltage component being less than a power frequency;

Sampling a first voltage signal at an output of the DC/DC converter;

Extracting a first effective value of the alternating current signal in the first voltage signal;

Comparing the first effective value with a first preset voltage value;

When it is determined that the first effective value is less than the first preset voltage value, the distributed power source generates an islanding phenomenon, and the distributed power supply is controlled to stop running.

Preferably, the DC distribution network is a single-ended distribution network or a distribution network at both ends.

Preferably, when the DC distribution network is a two-terminal distribution network, the two AC/DC interface converters are respectively replaced by a first AC/DC interface converter and a second AC/DC interface. a first AC system connected to the DC distribution network through the first AC/DC interface converter, and a second AC system connected to the DC distribution network through the second AC/DC interface converter; The output of the AC/DC interface converter is injected with an AC voltage component, which specifically includes:

Determining that the two AC/DC interface converters are working normally, and injecting an AC voltage component into an output of any one of the AC/DC interface converters;

When it is judged that one of the two AC/DC interface converters has failed, an AC voltage component is injected to the output of one of the normally operating AC/DC interface converters.

Preferably, determining that the AC/DC interface converter is faulty includes:

Sampling a second voltage signal at an output of the AC/DC interface converter;

Extracting a second effective value of the alternating current signal in the second voltage signal;

Comparing the second effective value with a second predetermined voltage value;

When it is determined that the second effective value is less than the second preset voltage value, it is determined that the AC/DC interface converter is faulty.

Preferably, the alternating voltage component

The expression is as follows:

Where U _dc is the rated DC voltage of the DC distribution network; k is the percentage of the injected AC voltage component; f _ac is the frequency of the AC voltage component; k is in the range of 2 to 5 %;

f _ac is 10% - 60% of the power frequency.

Preferably, the first preset voltage value and the second preset voltage value are the same, both being U _set ;

The value of the U _set ranges from 5 to 20% of kU _dc .

The invention provides an anti-islanding device for a distributed power supply of a DC distribution network, which is applied to a DC distribution network, wherein the distributed power source is connected to an input end of a DC/DC converter, and the DC/DC converter is The output end is connected to the DC distribution network through a grid-connected DC circuit breaker; the AC system is connected to the input end of the AC/DC interface converter, and the output end of the AC/DC interface converter is connected to the DC distribution network; The device includes:

An AC voltage dividing injection unit is configured to inject an AC voltage component to an output end of the AC/DC interface converter, wherein a frequency of the AC voltage component is less than a power frequency;

a first voltage signal sampling unit, configured to sample a first voltage signal at an output of the DC/DC converter;

a first effective value extracting unit, configured to extract a first valid value of the alternating current signal in the first voltage signal;

The first comparing unit compares the first effective value with the first preset voltage value;

And the control unit is configured to: when the first effective value is less than the first preset voltage value, the distributed power source generates an islanding phenomenon, and the distributed power supply is controlled to stop running.

Preferably, the DC distribution network is a single-ended distribution network or a distribution network at both ends;

When the DC distribution network is a power distribution network at both ends, the two AC/DC interface converters are included, The first AC/DC interface converter and the second AC/DC interface converter are respectively; the first AC system is connected to the DC distribution network through the first AC/DC interface converter, and the second AC system passes through the The second AC/DC interface converter is connected to the DC distribution network; and further includes: a fault judging unit;

The fault judging unit is configured to: when the two AC/DC interface converters are working normally, the AC voltage component injection unit injects an AC voltage component into an output end of any one of the AC/DC interface converters ;

The fault judging unit is configured to determine, when one of the two AC/DC interface converters fails, an output of the AC/DC interface converter that the AC voltage component injection unit operates normally The terminal injects an alternating voltage component.

Preferably, the fault determining unit comprises:

a second voltage signal sampling subunit for sampling a second voltage signal at an output of the AC/DC interface converter;

a second effective value extraction subunit, configured to extract a second effective value of the alternating current signal in the second voltage signal;

Comparing a subunit for comparing the second effective value with a second preset voltage value;

And determining, by the determining subunit, that the second valid value is less than the second preset voltage value, determining that the AC/DC interface converter is faulty.

Preferably,

The alternating voltage component

The expression is as follows:

f _ac is 10%-60% of the power frequency;

The first preset voltage value and the second preset voltage value are the same, both being U _set ;

The value of the U _set ranges from 5 to 20% of kU _dc .

Compared with the prior art, the present invention has the following advantages:

The anti-islanding method provided in this embodiment detects whether the distributed power supply needs to be stopped by injecting an AC voltage component at an output end of the AC/DC interface converter to detect whether the AC voltage component exists at the output end of the DC/DC converter. run. If the DC/DC converter output does not exist, the AC voltage is divided. Quantity, it is necessary to control the distributed power supply to stop running, so as to avoid the island power supply between the distributed power supply and the local load. The method provided in this embodiment is simple to implement, and can accurately and timely determine whether there is an island phenomenon.

DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below. Obviously, the drawings in the following description are only It is a certain embodiment of the present invention, and other drawings can be obtained from those skilled in the art without any creative work.

1 is a schematic diagram of a distributed power supply DC distribution network in the prior art;

2 is a flow chart of Embodiment 1 of an anti-islanding method for a distributed power supply of a DC distribution network provided by the present invention;

3 is a flow chart of Embodiment 2 of an anti-islanding method for a distributed power supply of a DC distribution network provided by the present invention;

4 is a waveform diagram of a positive voltage U _dc at the output end of a distributed photovoltaic power generation grid-connected DC/DC converter according to the present invention;

5 is a schematic diagram of Embodiment 1 of an anti-islanding device for a DC power distribution network distributed power supply provided by the present invention;

6 is a schematic diagram of Embodiment 2 of an anti-islanding device for a DC power distribution network distributed power supply provided by the present invention;

FIG. 7 is a schematic structural diagram of a fault judging unit provided by the present invention.

detailed description

The technical solutions in the embodiments of the present invention are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

The above described objects, features and advantages of the present invention will become more apparent from the aspects of the appended claims.

Method embodiment one:

Referring to FIG. 2, the figure shows an implementation of an anti-islanding method for a distributed power supply of a DC distribution network provided by the present invention. Example 1 flow chart.

The anti-islanding method for the distributed power supply of the DC distribution network provided in this embodiment is applied to a DC distribution network, where the distributed power source is connected to an input end of the DC/DC converter, and the DC/DC converter is The output end is connected to the DC distribution network through a grid-connected DC circuit breaker; the AC system is connected to the input end of the AC/DC interface converter, and the output end of the AC/DC interface converter is connected to the DC distribution network; The method includes:

S201: inject an AC voltage component to an output end of the AC/DC interface converter, where a frequency of the AC voltage component is less than a power frequency;

For example, if the AC frequency of the AC system connected to the DC distribution network is 50 Hz, then the frequency of the AC voltage component is lower than 50 Hz, for example, 10 Hz.

The reason why the frequency of the AC voltage component is set lower than the power frequency is:

The AC voltage component is not easy to be generated by other reasons in the DC distribution network, the propagation distance is long, the external interference is small, and the DC/DC converter is connected to the distributed photovoltaic power generation side voltage regulation control, but the AC voltage component When the frequency is too low, the first effective value delay time is too long. Therefore, the frequency of the AC voltage component can be selected from 10% to 60% of the power frequency.

On the other hand, it also prevents crosstalk of interference signals in the AC system to the DC distribution network, which affects the accuracy of signal detection.

S202: sampling a first voltage signal at an output end of the DC/DC converter;

It can be understood that if the DC distribution network does not stop running, it is normal operation, and the grid-connected DC circuit breaker is not disconnected, the AC voltage component is included in the first voltage signal.

S203: Extract a first valid value of the alternating current signal in the first voltage signal;

The first voltage signal may include both a direct current component and an alternating current component. Therefore, by determining whether or not the alternating voltage component is included to determine whether or not an island is generated, the alternating voltage component needs to be extracted. Specifically, the AC voltage component can be extracted by a band pass filter.

S204: compare the first effective value with a first preset voltage value;

S205: When it is determined that the first effective value is less than the first preset voltage value, the distributed power source generates an islanding phenomenon, and the distributed power supply is controlled to stop running.

It should be noted that, when it is generally determined that the first effective value is less than the first preset voltage value for a longer period of time than the first preset time period T _set1 , it is considered that the true first effective value is smaller than the first preset voltage value because The instantaneous less than may be caused by the jitter of the grid.

If it is determined that the first effective value is greater than the first preset voltage value, it indicates that there is an injected AC voltage component at the output end of the DC/DC converter, thereby indicating that the DC distribution network is in normal operation and the grid-connected DC circuit breaker is closed. If the first effective value is less than the first preset voltage value,

If the DC distribution network is stopped or the grid-connected DC breaker is disconnected, or the DC distribution network is stopped and the grid-connected DC breaker is disconnected, there is no injected AC voltage component at the DC/DC converter output. When it is determined that the first effective value is less than the first preset voltage value, it indicates that the distributed power source needs to stop working, otherwise the island power supply phenomenon may be formed with the local load.

The anti-islanding method provided in this embodiment detects whether the distributed power supply needs to be stopped by injecting an AC voltage component at an output end of the AC/DC interface converter to detect whether the AC voltage component exists at the output end of the DC/DC converter. run. If the AC voltage component does not exist at the DC/DC converter output, it is necessary to control the distributed power supply to stop running, thus avoiding the island power supply between the distributed power source and the local load. The method provided in this embodiment is simple to implement, and can accurately and timely determine whether there is an island phenomenon.

Method Embodiment 2:

Referring to FIG. 3, which is a flowchart of Embodiment 2 of an anti-islanding method for a distributed power supply of a DC distribution network according to the present invention.

It should be noted that the DC distribution network is a single-ended distribution network or a distribution network at both ends. The method provided by the invention is applicable to the DC distribution network as a single-ended distribution network, and also to the case where the DC distribution network is a distribution network at both ends.

The following describes the situation when the DC distribution network is the power distribution network at both ends, including two AC/DC interface converters, which are the first AC/DC interface converter and the second AC/DC interface, respectively. Inverter; the specific system structure diagram can be seen in Figure 1. The first AC system is connected to the DC distribution network through the first AC/DC interface converter, and the second AC system is connected to the DC distribution network through the second AC/DC interface converter;

It should be noted that one AC/DC interface converter that is injected with an AC voltage component is in the master mode, and the other AC/DC interface converter is in the slave mode.

The reason for setting the master/slave mode of the AC/DC interface converter is to prevent the formation of converters between the two interfaces. Circulating current, only one AC/DC interface converter is injected into the AC voltage component during normal operation. If the main mode converter is stopped for any reason, the mode converter is used to inject the AC voltage component.

The difference between the embodiment and the method embodiment 1 is that the AC voltage component is injected into the output end of the AC/DC interface converter, which specifically includes:

Determining that the AC/DC interface converter is faulty, specifically includes:

S301: sampling a second voltage signal at an output end of the AC/DC interface converter;

S302: Extract a second effective value of the alternating current signal in the second voltage signal;

S303: Compare the second effective value with a second preset voltage value;

S304: Determine that the second valid value is less than the second preset voltage value, and determine that the AC/DC interface converter is faulty.

It should be noted that, when it is generally determined that the second effective value is less than the second preset voltage value for a longer period of time than the second preset time period T _set2 , the true second effective value is considered to be smaller than the second preset voltage value because The instantaneous less than may be caused by the jitter of the grid.

It should be noted that T _set1 should be less than 2 seconds, and T _set1 > T _{set2 is} guaranteed to be injected in the AC/DC interface converter due to master-slave mode switching.

When the island is not blocked, it will not malfunction.

It should be noted that the first preset voltage value and the second preset voltage value are the same, both being U _set ;

Considering the partial pressure of the DC distribution line, the value range of the U _set can be selected to be 5-20% of kU _dc .

For example, for a typical ±200V DC distribution network with both ends, U _set can be selected to be 0.5V.

The alternating voltage component

The expression is as follows:

Where U _dc is the rated DC voltage of the DC distribution network; k is the percentage of the injected AC voltage component; f _ac is the frequency of the AC voltage component; k ranges from 2% to 5%;

f _ac is 10% - 60% of the power frequency.

The value of k should be under the premise of ensuring that the low-frequency components can be reliably detected at each grid-connected point of the all-DC distribution network. Take small values to minimize the effects of low frequency voltage injection, typically 2% to 5%.

To enable those skilled in the art to better understand and implement the present invention, the following description is presented in conjunction with a specific simulation.

Referring to FIG. 4, the figure is a waveform diagram of a positive voltage U _dc at the output end of the distributed photovoltaic power generation grid-connected DC/DC converter provided by the present invention.

Referring to Figure 1, the first AC/DC interface converter 100a is set to operate in the master mode and the second AC/DC interface converter 100b is operated in the slave mode. K takes 2%, f _ac takes 10Hz, U _set takes 0.5V, T _set2 takes 0.2 seconds, and T _set1 takes 0.5 seconds.

It can be seen from the waveform that after the start of the simulation, the first AC/DC interface converter 100a first injects a 10 Hz low frequency voltage component, the second second stops the trip, and the second AC/DC interface converter 100b takes over after 0.3 seconds. Injection of 10Hz AC voltage component, since the 10Hz low-frequency voltage component recovers within 0.5 seconds, the anti-island does not malfunction during the switching process; at the 5th second, the grid-connected DC breaker trips to form an island, at this time the DC/DC converter and The DC distribution network loses contact. Because the local load and the distributed photovoltaic power generation are equal, the DC component remains unchanged, resulting in a dead zone. However, since there is no 10Hz AC voltage component injection in the island, the photovoltaic power generation device stops after 0.7 seconds of tripping.

The simulation results show that the method provided by the embodiment of the invention can quickly and effectively prevent the photovoltaic distribution island from generating a photovoltaic island, can overcome the detection dead zone, and ensure that no malfunction occurs when the AC/DC interface converter is switched.

Based on the anti-islanding method of the distributed power supply of the DC distribution network provided by the above embodiments, the present invention also provides an anti-islanding device for the distributed power supply of the DC distribution network, which will be described in detail below with reference to the accompanying drawings.

Equipment embodiment 1:

Referring to FIG. 5, it is a schematic diagram of Embodiment 1 of an anti-islanding device for a distributed power supply of a DC distribution network according to the present invention.

The anti-islanding device of the DC power distribution network distributed power supply provided in this embodiment is applied to a DC distribution network, and the distributed power source is connected to an input end of the DC/DC converter, and the DC/DC converter is The output end is connected to the DC distribution network through a grid-connected DC circuit breaker; the AC system is connected to the input end of the AC/DC interface converter, and the output end of the AC/DC interface converter is connected to the DC distribution network; The device include:

The AC voltage dividing injection unit 500 is configured to inject an AC voltage component to an output end of the AC/DC interface converter, where a frequency of the AC voltage component is less than the power frequency;

For example, if the power frequency is 50 Hz, then the frequency of the AC voltage component is below 50 Hz, for example 10 Hz.

a first voltage signal sampling unit 600, configured to sample a first voltage signal of the output end of the DC/DC converter;

The first effective value extracting unit 700 is configured to extract a first valid value of the alternating current signal in the first voltage signal;

The first comparison unit 800 compares the first effective value with a first preset voltage value;

The control unit 900 is configured to: when the first effective value is less than the first preset voltage value, the distributed power source generates an islanding phenomenon, and the distributed power supply is controlled to stop running.

If it is determined that the first effective value is greater than the first preset voltage value, it indicates that there is an injected AC voltage component at the output end of the DC/DC converter, thereby indicating that the DC distribution network is in normal operation and the grid-connected DC circuit breaker is closed. Hehe. If the first effective value is less than the first preset voltage value,

The anti-islanding device provided in this embodiment detects whether the distributed power supply needs to be stopped by injecting an AC voltage component at the output end of the AC/DC interface converter to detect whether the AC voltage component exists at the output end of the DC/DC converter. run. If the AC voltage component does not exist at the DC/DC converter output, it is necessary to control the distributed power supply to stop running, thus avoiding the island power supply between the distributed power source and the local load. The method provided in this embodiment is simple to implement, and can accurately and timely determine whether there is an island phenomenon.

Equipment Embodiment 2:

Referring to FIG. 6, which is a schematic diagram of Embodiment 2 of an anti-islanding device for a distributed power supply of a DC distribution network according to the present invention.

It should be noted that the DC distribution network is a single-ended distribution network or a distribution network at both ends. The device provided by the invention is applicable to the DC distribution network as a single-ended distribution network, and also to the case where the DC distribution network is a distribution network at both ends.

The following describes the situation when the DC distribution network is the power distribution network at both ends, including two AC/DC interface converters, which are the first AC/DC interface converter and the second AC/DC interface, respectively. An inverter; the first AC system is connected to the DC distribution network through the first AC/DC interface converter, and the second AC system is connected to the DC distribution network through the second AC/DC interface converter;

The reason for setting the master/slave mode of the AC/DC interface converter is to prevent the loop between the two interface converters. In normal operation, only one AC/DC interface converter injects the AC voltage component, if the main mode converter If it is out of service for a reason, it is injected from the mode converter to inject the AC voltage component.

The device further includes: a fault judging unit 1000;

The fault judging unit 1000 is configured to determine that the two AC/DC interface converters are all working normally. In the process, the AC voltage component injection unit 500 injects an AC voltage component to an output of any one of the AC/DC interface converters;

The fault judging unit 1000 is configured to determine that one of the two AC/DC interface converters is faulty, and the AC voltage component injection unit 500 is configured to operate one of the AC/DC interface converters. The output is injected with an AC voltage component.

Equipment Embodiment 3:

Referring to FIG. 7, the figure is a schematic structural diagram of a fault judging unit provided by the present invention.

The fault judging unit includes:

a second voltage signal sampling subunit 1001, configured to sample a second voltage signal of an output end of the AC/DC interface converter;

a second effective value extraction subunit 1002, configured to extract a second effective value of the alternating current signal in the second voltage signal;

a comparison subunit 1003, configured to compare the second effective value with a second preset voltage value;

The determining subunit 1004 is configured to determine that the AC/DC interface converter is faulty when the second effective value is less than the second preset voltage value.

When the island is not blocked, it will not malfunction.

The alternating voltage component

The expression is as follows:

f _ac is 10% - 60% of the power frequency.

The value of k should be as small as possible under the premise of ensuring that the AC voltage components of all DC distribution networks can reliably detect the AC voltage component, so as to minimize the impact of AC voltage component injection, generally 2% to 5%. .

The above description is only a preferred embodiment of the invention and is not intended to limit the invention in any way. While the invention has been described above in the preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention by using the methods and technical contents disclosed above, or modify the equivalents of equivalent changes without departing from the scope of the technical solutions of the present invention. Example. Therefore, any simple modifications, equivalent changes, and modifications of the above embodiments may be made without departing from the spirit and scope of the invention.

Claims

An anti-islanding method for distributed power supply of a DC distribution network, characterized in that, in a DC distribution network, the distributed power source is connected to an input end of a DC/DC converter, and the DC/DC converter is The output end is connected to the DC distribution network through a grid-connected DC circuit breaker; the AC system is connected to the input end of the AC/DC interface converter, and the output end of the AC/DC interface converter is connected to the DC distribution network ; the method includes:

Transmitting an AC voltage component to an output of the AC/DC interface converter, the frequency of the AC voltage component being less than a power frequency;

Sampling a first voltage signal at an output of the DC/DC converter;

Extracting a first effective value of the alternating current signal in the first voltage signal;

Comparing the first effective value with a first preset voltage value;

When it is determined that the first effective value is less than the first preset voltage value, the distributed power source generates an islanding phenomenon, and the distributed power supply is controlled to stop running.
The anti-islanding method for a distributed power supply of a DC distribution network according to claim 1, wherein the DC distribution network is a single-ended distribution network or a distribution network at both ends.
The anti-islanding method for a distributed power supply of a DC distribution network according to claim 2, wherein when the DC distribution network is a distribution network at both ends, the two AC/DC interface converters are included a first AC/DC interface converter and a second AC/DC interface converter; the first AC system is connected to the DC distribution network through the first AC/DC interface converter, and the second AC system passes The second AC/DC interface converter is connected to the DC distribution network; and the AC voltage component is injected into the output end of the AC/DC interface converter, which specifically includes:

Determining that the two AC/DC interface converters are working normally, and injecting an AC voltage component into an output of any one of the AC/DC interface converters;

When it is judged that one of the two AC/DC interface converters has failed, an AC voltage component is injected to the output of one of the normally operating AC/DC interface converters.
The anti-islanding method of the distributed power supply of the DC distribution network according to claim 3, wherein determining that the AC/DC interface converter is faulty comprises:

Sampling a second voltage signal at an output of the AC/DC interface converter;

Extracting a second effective value of the alternating current signal in the second voltage signal;

Comparing the second effective value with a second predetermined voltage value;

When it is determined that the second effective value is less than the second preset voltage value, it is determined that the AC/DC interface converter is faulty.
The anti-islanding method for a distributed power supply of a DC distribution network according to any one of claims 1 to 4, characterized in that the AC voltage component
The expression is as follows:

Where U dc is the rated DC voltage of the DC distribution network; k is the percentage of the injected AC voltage component; f ac is the frequency of the AC voltage component; k is in the range of 2 to 5 %;

f ac is 10% - 60% of the power frequency.
The anti-islanding method for a distributed power supply of a DC distribution network according to claim 4, wherein the first preset voltage value and the second preset voltage value are the same, both being U set ;

The value of the U set ranges from 5 to 20% of kU dc .
An anti-islanding device for distributed power supply of a DC distribution network, characterized in that it is applied to a DC distribution network, the distributed power source is connected to an input end of a DC/DC converter, and the DC/DC converter is The output end is connected to the DC distribution network through a grid-connected DC circuit breaker; the AC system is connected to the input end of the AC/DC interface converter, and the output end of the AC/DC interface converter is connected to the DC distribution network The device includes:

An AC voltage dividing injection unit is configured to inject an AC voltage component to an output end of the AC/DC interface converter, wherein a frequency of the AC voltage component is less than a power frequency;

a first voltage signal sampling unit, configured to sample a first voltage signal at an output of the DC/DC converter;

a first effective value extracting unit, configured to extract a first valid value of the alternating current signal in the first voltage signal;

The first comparing unit compares the first effective value with the first preset voltage value;

And the control unit is configured to: when the first effective value is less than the first preset voltage value, the distributed power source generates an islanding phenomenon, and the distributed power supply is controlled to stop running.
The anti-islanding device of the distributed power supply of a DC distribution network according to claim 7, wherein the DC distribution network is a single-ended distribution network or a distribution network at both ends;

When the DC distribution network is a power distribution network at both ends, the two AC/DC interface converters are included, The first AC/DC interface converter and the second AC/DC interface converter are respectively; the first AC system is connected to the DC distribution network through the first AC/DC interface converter, and the second AC system passes through the The second AC/DC interface converter is connected to the DC distribution network; and further includes: a fault judging unit;

The fault judging unit is configured to: when the two AC/DC interface converters are working normally, the AC voltage component injection unit injects an AC voltage component into an output end of any one of the AC/DC interface converters ;

The fault judging unit is configured to determine, when one of the two AC/DC interface converters fails, an output of the AC/DC interface converter that the AC voltage component injection unit operates normally The terminal injects an alternating voltage component.
The anti-islanding device of the distributed power supply of the DC distribution network according to claim 8, wherein the fault determining unit comprises:

a second voltage signal sampling subunit for sampling a second voltage signal at an output of the AC/DC interface converter;

a second effective value extraction subunit, configured to extract a second effective value of the alternating current signal in the second voltage signal;

Comparing a subunit for comparing the second effective value with a second preset voltage value;

And determining, by the determining subunit, that the second valid value is less than the second preset voltage value, determining that the AC/DC interface converter is faulty.
The anti-islanding device for distributed power supply of a DC distribution network according to claim 9, wherein

The alternating voltage component
The expression is as follows:

Where U dc is the rated DC voltage of the DC distribution network; k is the percentage of the injected AC voltage component; f ac is the frequency of the AC voltage component; k is in the range of 2 to 5 %;

f ac is 10%-60% of the power frequency;

The first preset voltage value and the second preset voltage value are the same, both being U set ;

The value of the U set ranges from 5 to 20% of kU dc .