WO2021056896A1

WO2021056896A1 - Direct current microgrid branch linkage control system and method

Info

Publication number: WO2021056896A1
Application number: PCT/CN2019/128721
Authority: WO
Inventors: 张广洁; 宋万广; 马小虎; 岳圣鹏
Original assignee: 北京天诚同创电气有限公司
Priority date: 2019-09-29
Filing date: 2019-12-26
Publication date: 2021-04-01
Also published as: CN112582992A; CN112582992B

Abstract

Provided in the present invention are a direct current microgrid branch linkage control system and method. The direct current microgrid branch linkage control system comprises: a detection unit, which detects in real time the voltage and current of each branch connected to a direct current microgrid bus; a controller, which performs frequency analysis and threshold analysis on the detected voltage and current, determines on the basis of the frequency analysis and threshold analysis a fault that had occurred in a direct current microgrid, and performs linkage control on a plurality of branches on the basis of the fault; and a branch linkage mechanism, which executes linkage protection on the branches in the system under the control of the controller.

Description

DC microgrid branch linkage control system and method

Technical field

The present invention relates to the technical field of power electronics. Specifically, the present invention relates to a DC microgrid branch linkage protection control system and method.

Background technique

With the increase of photovoltaic power generation projects, the large number of applications of electric vehicle charging stations, and the large number of applications of lithium battery backup power stations, the applications of DC systems and DC microgrids are also increasing. However, DC protection requires faster speed and reliable protection than AC protection. Its realization is difficult. The DC microgrid has also just emerged in recent years, and its protection theory and protection methods are not as complete and mature as the AC protection system.

DC microgrid has just emerged in recent years, so there are many shortcomings from control theory to specific implementation methods and equipment. For example, in the DC protection method, most of the prior art uses voltage and current threshold protection methods, which cannot accurately distinguish between different working conditions and are prone to malfunction; in addition, the prior art also uses the current and voltage slope method, which Compared with the threshold method, this method improves the situation and reduces the misjudgment situation, but it is also prone to misjudgment for some high-speed load changes. In addition, these methods only deal with specific fault situations and do not consider the linkage control of the overall microgrid.

Summary of the invention

Aiming at the deficiencies of the prior art, the present invention proposes a new fault identification method, implementation mode, and specific control system. According to the characteristics of DC microgrid application, a method of fault identification based on frequency characteristics is proposed. According to the characteristics of DC microgrid application, a control strategy of simultaneous linkage of multiple branches in DC microgrid is proposed, and specific control is proposed based on the above. system.

A DC microgrid branch linkage control system, including: a detection unit, which performs real-time voltage detection and current detection on each branch connected to the DC microgrid bus; a controller, which performs frequency analysis and threshold value for the detected voltage and current Analysis, based on the frequency analysis and threshold analysis to determine the faults in the DC microgrid, and based on the faults to perform linkage control of multiple branches; and a branch linkage mechanism, which controls the system under the control of the controller The branch implements linkage protection.

The frequency analysis performed by the controller can obtain the DC component and the high frequency component by performing real-time fast Fourier transform analysis on the voltage signal and current signal of each branch collected in real time.

The frequency analysis performed by the controller may prejudge the high frequency component and then judge the direct current component.

When the frequency analysis performed by the controller determines that the high-frequency component has a sudden change and the threshold analysis performed by the controller determines that the amplitude of the direct current component exceeds a predetermined threshold, it can be confirmed that a fault has occurred.

The controller can control the branch linkage mechanism to cut off the faulty branch and adjust the load distribution and bus voltage of the remaining branches according to the current operating conditions of each branch.

A DC microgrid branch linkage control method includes: performing real-time voltage detection and current detection on each branch connected to the DC microgrid bus; performing frequency analysis and threshold analysis for the detected voltage and current; based on the frequency Analysis and threshold analysis to determine the faults in the DC microgrid; when the fault is judged to occur, the linkage protection of the branches in the system is performed.

In the method, the frequency analysis can obtain the DC component and the high frequency component by performing real-time fast Fourier transform analysis on the voltage and current signals of each branch collected in real time.

In the method, the frequency analysis may make a pre-judgment on the high-frequency component, and then make a judgment on the DC component.

In the method, when it is determined through the frequency analysis that the high-frequency component has a sudden change and the threshold value analysis determines that the amplitude of the direct current component exceeds a predetermined threshold, it is confirmed that a fault has occurred.

In the method, the faulty branch can be removed and the load distribution and bus voltage of the remaining branches can be adjusted according to the current operating conditions of each branch.

The DC microgrid branch linkage protection control system provided by the present invention can provide the following advantages: a new DC fault detection method is proposed, which can be used in conjunction with other protection methods to achieve fault judgment more quickly and accurately; and a linkage is proposed The DC microgrid branch control structure is applied to the DC microgrid to make the DC microgrid control more efficient and reliable.

Description of the drawings

Figure 1 is a diagram of a DC microgrid branch linkage protection control system according to the present invention;

Figure 2 is a schematic diagram of a three-branch small-capacity microgrid according to the present invention;

Figure 3 is a voltage and current waveform diagram of the three-branch small-capacity microgrid according to the present invention;

Fig. 4 is an enlarged view at time T1 of the voltage and current waveforms of the three-branch small-capacity microgrid according to the present invention;

5A and 5B are respectively a hardware structure diagram and a software flow chart of the frequency measurement method according to the present invention;

Figure 6 is a control flow chart of the DC microgrid branch linkage protection control system according to the present invention;

Fig. 7 is a flowchart of a DC microgrid branch linkage protection control method according to the present invention.

detailed description

In order to enable those skilled in the art to better understand the present invention, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The embodiments of the present invention propose a new DC fault detection method, control method and corresponding control system based on the actual application of the DC microgrid.

The advantages of the embodiments of the present invention are that the frequency measurement method plus the threshold method is used for a single fault point, thereby speeding up the fault identification speed and preparation rate, and at the same time, the central control system is used to perform multi-branch intelligent control of the microgrid, so as to maintain The purpose of system stability.

In the DC microgrid branch linkage protection control system provided by the embodiment of the present invention, a branch linkage protection control system is set on the basis of the DC microgrid architecture.

Fig. 1 is a diagram of a DC microgrid branch linkage protection control system according to the present invention. As shown in Figure 1, the DC microgrid includes a DC bus and multiple DC branches connected to the DC bus. The DC branch includes a DC/DC converter, one end of the DC/DC converter is connected to a DC bus, and the other end is respectively connected to a distributed DC power supply or an energy storage system. For example, the distributed DC power source may be photovoltaic cells, and the energy storage system may be lithium batteries, lead-carbon batteries or super capacitors. The DC/DC converter can also be connected to an electric vehicle charging system. In addition, the DC branch also includes a load connected to the DC bus. The DC bus is connected to the AC power grid through an AC/DC converter and an AC transformer.

The branch linkage protection control system includes a detection unit 100, a controller (for example, an intelligent control device) 200, and a branch linkage mechanism 300.

The DC bus in the DC microgrid is connected to a distributed DC power supply, an energy storage system or a load through the branch linkage mechanism 300 and the detection unit 100.

The detection unit 100 performs real-time voltage and current detection on each branch connected to the DC microgrid bus. The detection unit 100 can be implemented in various forms, including but not limited to a sensor, a transformer, and the like.

The branch linkage mechanism 300 is an executive mechanism of the branch linkage protection system, which implements linkage protection for branches in the system through the control of the intelligent control device 200. The branch linkage mechanism 300 can be implemented in a variety of ways, including but not limited to a circuit breaker with a communication function, a solid-state protection switch with a communication function, and the like.

The intelligent control device 200 is a core component of the branch linkage protection control system. The intelligent control device 200 communicates with the detection unit 100 and the branch linkage mechanism 300, collects the voltage and current in the DC branch in real time through the detection unit 100, and controls the circuit breaker or protection switch in the branch linkage mechanism 300 to conduct or Shut down. The intelligent control device 200 quickly recognizes faults in accordance with preset linkage control strategies and protection algorithms, and uses the algorithms to classify and classify the fault types of each branch, and then send fault information in real time through the communication module to perform communication between multiple branches. Linkage control. The intelligent control device 200 can be implemented in a variety of ways, including but not limited to industrial computers, industrial computers, and so on.

Frequency measurement method to judge the fault

DC faults are mostly divided into DC short-circuit faults, arcing faults between poles, and overvoltage faults. The overvoltage type of fault can be effectively detected and protected by the ordinary threshold method, and the related description will be omitted here. It is more difficult to detect DC short-circuit faults and inter-pole arcing faults. The present invention proposes a frequency measurement method (frequency analysis) for fault judgment for these two types of faults.

The following describes the frequency measurement method with three branches as an example. Figure 2 is a schematic diagram of a three-branch small-capacity microgrid according to the present invention.

The principle of the frequency measurement method to determine the fault will be described with reference to FIG. 2. In FIG. 2, the schematic diagram of the three-branch small-capacity micro-grid only shows the structure of the small-capacity micro-grid with three branches. However, the embodiment of the present invention does not Limited to this, and can be applied to systems with more than 3 branches. The bus voltage of the DC microgrid shown in Figure 2 is 800V, and the branch impedance is equivalent to inductance and resistance. In branch 2, the normal load and short-circuit fault are respectively connected to indicate that the normal load is switched on and the short-circuit fault occurs.

At the same time, monitor the bus voltage and branch current, and perform fast Fourier transform (FFT) analysis on the monitored bus voltage Etest and branch current Itest, that is, perform frequency analysis on the measured signal to obtain Umeg, Udc, 4 components such as Imeg and Idc are used to judge the fault. The specific waveform data is shown in Figure 3.

Fig. 3 is a voltage and current waveform diagram of the three-branch small-capacity microgrid according to the present invention.

Figure 3 shows that the normal load is put into operation at T0 time (ie around 0.2s), and the voltage and current fluctuate. It can be seen from A in Figure 3 that the voltage and current fluctuate when the load is put on, but the voltage The fluctuation range is small, and the current rise rate is small. At time T1 (ie around 0.4S), a branch short-circuit fault occurred. It can be seen from B in Figure 3 that both the current and voltage have changed greatly. When the branch is short-circuited, the voltage drops significantly, and the current rise slope Larger. In Figure 3, the voltage waveform Udc indicates the change of the bus voltage; the current waveform Idc indicates the current change of branch 2; Umeg is the voltage spectrum change of the voltage waveform Udc after FFT frequency analysis; Imeg is the branch 2 The current spectrum changes of the current waveform Idc after FFT frequency analysis.

Fig. 4 is an enlarged view at time T1 of the voltage and current waveforms of the three-branch small-capacity microgrid according to the present invention. With reference to Figures 3 and 4, it can be seen that when the load is turned on, the voltage and current of the branch where it is located change and the corresponding Umeg and Imeg also change simultaneously. In addition, when a normal load is put into operation at T0, the branch current and voltage have small changes and the Umeg and Imeg changes are also small; and when a short-circuit fault occurs at T1, the branch current and voltage change greatly, and its voltage Both the rate of decrease and the rate of increase of the current are large (compared to the normal load input), and the Umeg and Imeg changes are also large.

Based on the above characteristics, an effective DC branch fault judgment can be made.

The specific embodiments of the present invention are used to illustrate the frequency measurement method for monitoring DC short-circuit faults. However, the method can be applied not only in the DC microgrid, but also in the fault monitoring of other DC circuits.

There are multiple judgment methods for DC faults, including: threshold method, which sets the protection threshold of voltage or current in advance. When the voltage or current reaches or exceeds the preset threshold, it is judged as a fault; slope method is used for voltage Or the rate of change of current is judged. When the rate of change of voltage or current has a large change, it is judged as a fault; the frequency measurement method is to perform spectrum analysis on the voltage or current monitored in real time, and follow the normal load operation. The frequency spectrum is different from the frequency spectrum when the fault occurs, and different frequency spectrum characteristics are used to judge the fault. In the frequency measurement method, when a fault occurs, the high-frequency component of the voltage and current changes greatly, so as to identify the fault and carry out effective protection. The fault identification method adopted by the present invention is based on the frequency measurement method combined with the threshold method to monitor and analyze the faults in the system.

5A and 5B are respectively a hardware structure diagram and a software flow chart of the frequency measurement method according to the present invention.

The branch obtains the DC component and high frequency component through real-time acquisition of voltage and current and real-time FFT analysis. FFT analysis can be realized by hardware circuit, and can also be realized by software. Through FFT analysis, fault judgment is made based on the size of the DC component and the size of the high-frequency component. It can be seen in the software flow chart of Fig. 5B that the frequency measurement method to judge the fault is to pre-judge the high-frequency component, and then judge the DC component. This is because as shown in Figure 4, a short-circuit fault occurs at T1, and high-frequency components begin to appear at T2 (see Umeg and Imeg curves), during which the current amplitude gradually increases, and then reaches the branch at T3 The protection reference threshold of the current amplitude (see IDC graph), or the protection reference threshold of the DC bus voltage amplitude. It can be seen that when a short-circuit fault occurs, high-frequency components will appear in advance. This feature can be used to predict the fault in advance to shorten the time required for fault judgment; and then use threshold analysis to determine the amplitude of the DC component. The second confirmation makes the fault judgment more accurate to prevent misjudgment.

Linkage Control Strategy of DC Microgrid Branch

Fig. 6 is a control flow chart of the DC microgrid branch linkage protection control system according to the present invention.

1 and 6, the detection unit 100 is arranged in each DC branch of the DC microgrid to perform real-time detection of the voltage and current of each branch. The voltage and current signals detected by the detection unit 100 during the monitoring period may include fault abnormalities. Signals, detected voltage and current signals including fault abnormal signals are sent to the intelligent control device 200 by means of communication. The intelligent control device 200 can use an intelligent algorithm to analyze whether the branch has a fault. The intelligent algorithm includes, but is not limited to, a frequency measurement method in which the aforementioned FFT analysis is performed on the voltage and current signals, and then a threshold value analysis is performed. The branch fault is determined by judging the characteristics of the DC component and the high-frequency component obtained by the FFT analysis. Because the high-frequency components usually appear in advance when the fault occurs in the branch, the fault can be judged in advance by detecting the change of the high-frequency component obtained by the FFT analysis, and then the branch fault can be determined by judging whether the DC component exceeds the threshold. Prevent misjudgments. Through the combination of frequency analysis and threshold analysis to determine the occurrence of a fault, the intelligent control device 200 performs comprehensive control according to the current operating conditions of each branch, uses the branch linkage mechanism 300 to remove the faulty branch, and adjusts the load distribution of other circuits (for example, adjusting the load). Lower the load of other branches), and adjust the DC bus voltage (for example, increase the voltage adjustment parameter in the power branch) to ensure the stable and normal operation of the DC bus and avoid the expansion of faults. The intelligent branch linkage protection control system of the DC microgrid according to the present invention realizes fault judgment and protection of the microgrid system, thereby realizing the stable operation of the voltage and current of the DC bus.

Referring to FIG. 7, in step 710, the DC microgrid branch linkage control method performs real-time voltage detection and current detection on each branch connected to the DC microgrid bus. The voltage and current signals detected during the monitoring period may contain abnormal signals. The detected voltage and current signals are sent to the intelligent control device 200 through communication.

In step 720, an intelligent algorithm can be used to analyze whether the branch has a fault. The intelligent algorithm includes but is not limited to the frequency measurement method. In the frequency measurement method, the aforementioned FFT analysis is performed on the voltage and current signals, and then the DC bus is analyzed. Threshold analysis of voltage amplitude or branch current amplitude.

In step 730, since the high-frequency components usually appear in advance when the branch fails, the change in the high-frequency components obtained by the FFT analysis can be detected to determine the fault in advance, and then the branch failure can be determined by judging whether the DC component exceeds the threshold. , Which can prevent misjudgments.

In step 740, comprehensive control is performed according to the current operating conditions of each branch, and the branch linkage mechanism 300 is used to remove the faulty branch, while adjusting the load distribution of other circuits, and adjusting the bus voltage to ensure that the bus works normally. The branch circuit implements linkage protection to avoid the enlargement of the fault.

The DC microgrid branch linkage protection control system and method provided by the present invention can provide the following advantages: a new DC fault detection method is proposed, which can be used in conjunction with other protection methods to realize fault judgment more quickly and accurately; The linked DC microgrid branch control structure is applied to the DC microgrid to make the DC microgrid control more efficient and reliable.

Exemplary embodiments according to the present invention also provide a computer-readable storage medium storing a computer program. The computer-readable storage medium stores a computer program that, when executed by a processor, causes the processor to execute the method for controlling a DC brushless motor according to the present invention. The computer-readable recording medium is any data storage device that can store data read by a computer system. Examples of computer-readable recording media include read-only memory, random access memory, read-only optical disks, magnetic tapes, floppy disks, optical data storage devices, and carrier waves (such as data transmission through the Internet via a wired or wireless transmission path).

According to an exemplary embodiment of the present invention, a computer device is also provided. The computer device includes a processor and a memory. The memory is used to store computer programs. The computer program is executed by the processor to cause the processor to execute the computer program of the DC microgrid branch linkage control method according to the present invention.

The specific embodiments of the present invention are described in detail above. Although some embodiments have been shown and described, those skilled in the art should understand that without departing from the principle and spirit of the present invention whose scope is defined by the claims and their equivalents Under the circumstances, these embodiments can be modified and modified, and these modifications and modifications should also fall within the protection scope of the claims of the present invention.

Claims

A direct current microgrid branch linkage control system, the direct current microgrid comprising a direct current bus and a plurality of direct current branches connected to the direct current bus, characterized in that it comprises:

The detection unit performs real-time voltage detection and current detection on each branch connected to the DC microgrid bus;

The controller performs frequency analysis and threshold value analysis for the detected voltage and current, determines a fault in the DC microgrid based on the frequency analysis and threshold value analysis, and performs linkage control of multiple branches based on the fault; and

Branch linkage mechanism, under the control of the controller, performs linkage protection on the branches in the system.
The DC microgrid branch linkage control system according to claim 1, characterized in that:

The frequency analysis performed by the controller obtains the DC component and the high frequency component by performing real-time fast Fourier transform analysis on the voltage signal and current signal of each branch collected in real time.
The DC microgrid branch linkage control system according to claim 2, wherein the frequency analysis performed by the controller prejudges the high frequency component, and then judges the direct current component.
The DC microgrid branch linkage control system according to claim 2, wherein when the frequency analysis performed by the controller determines that the high-frequency component has a sudden change and the threshold analysis performed by the controller determines that the DC When the magnitude of the component exceeds a predetermined threshold, a fault is confirmed.
The DC microgrid branch linkage control system according to claim 1, wherein the controller controls the branch linkage mechanism to remove the faulty branch and adjust the control of the remaining branches according to the current operating conditions of each branch. Load sharing and bus voltage.
A DC microgrid branch linkage control method, the DC microgrid comprising a DC bus and a plurality of DC branches connected to the DC bus, characterized in that it comprises:

Real-time voltage detection and current detection for each branch connected to the DC microgrid bus;

Perform frequency analysis and threshold analysis for the detected voltage and current;

Based on the frequency analysis and threshold analysis to determine the faults in the DC microgrid;

When it is judged that there is a fault, it will perform linkage protection for the branches in the system.
The DC microgrid branch linkage control method according to claim 6, characterized in that:

The frequency analysis obtains the DC component and the high frequency component by performing real-time fast Fourier transform analysis on the voltage and current signals of each branch collected in real time.
The DC microgrid branch linkage control method according to claim 7, wherein the frequency analysis prejudges the high frequency component, and then judges the direct current component.
The DC microgrid branch linkage control method according to claim 7, wherein when the frequency analysis determines that the high frequency component has a sudden change and the threshold analysis determines that the amplitude of the DC component exceeds a predetermined value A fault is confirmed when the threshold is reached.
The DC microgrid branch linkage control method according to claim 6, characterized in that, according to the current operating conditions of each branch, the faulty branch is removed and the load distribution and bus voltage of the remaining branches are adjusted.
A computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the DC microgrid branch linkage control method according to any one of claims 6 to 10 is realized .
A computer device, characterized in that, the computer device includes:

processor;

The memory stores a computer program, and when the computer program is executed by the processor, the DC microgrid branch linkage control method according to any one of claims 6 to 10 is realized.