CN114221301B - AC microgrid protection method and device considering photovoltaic low voltage ride-through characteristics - Google Patents

Abstract

The present disclosure relates to an AC microgrid protection method, device, electronic equipment and storage medium that consider photovoltaic low voltage ride-through characteristics. Among them, the method includes: analyzing and judging the phase angle relationship between the current fault component of the photovoltaic output and the voltage before the fault under different amplitudes of voltage drop of the independent distributed power supply when the fault occurs; analyzing the current fault on all branch feeders when the fault occurs The phase angle relationship between the components is used to determine the fault status of each branch feeder; when the microgrid bus voltage drops greater than the preset amplitude, the fault line is determined based on the fault status of each branch feeder, and fault line protection is initiated. This disclosure analyzes the photovoltaic low voltage ride-through characteristics of the microgrid, determines the phase angle relationship between the current fault components on all branch feeders on the independent distributed power bus when a fault occurs, and establishes a microgrid line protection method that only uses current information. , reducing the construction cost of the microgrid protection system.

Description

AC microgrid protection method and device considering photovoltaic low voltage ride-through characteristics

Technical field

The present disclosure relates to the field of new energy, and specifically to an AC microgrid protection method, device, electronic equipment, and computer-readable storage medium that consider photovoltaic low-voltage ride-through characteristics.

Background technique

Microgrids have many advantages, but their protection issues still restrict their further promotion and application. There is a bidirectional short-circuit current inside the AC microgrid, and protection needs to be able to determine the direction of the fault. In addition, the difference in short-circuit current in the microgrid between grid-connected and off-grid modes is obvious, and protection needs to be able to adaptively determine the fault state. In addition, the topology of the microgrid will change as the operation mode changes, and protection needs to be applicable to different topologies.

When a fault occurs in the microgrid, constant power controlled photovoltaics will enter a low voltage ride-through state, requiring photovoltaic output reactive power to support the voltage. The increase in reactive current will cause the size and phase of the photovoltaic output current to change, causing the current of the microgrid line to change, which can easily cause the directional components of the microgrid to misjudge the fault direction. Therefore, it is necessary to analyze the microgrid under the photovoltaic low voltage ride-through state. According to the fault characteristics, fault direction identification methods are studied. However, existing microgrid protection methods during photovoltaic low voltage ride-through generally require voltage transformers, which will increase the cost of the protection system.

Therefore, one or more methods are needed to solve the above problems.

It should be noted that the information disclosed in the above background section is only used to enhance understanding of the background of the present disclosure, and therefore may include information that does not constitute prior art known to those of ordinary skill in the art.

Contents of the invention

The purpose of the present disclosure is to provide an AC microgrid protection method, device, electronic equipment and computer-readable storage medium that considers photovoltaic low voltage ride-through characteristics, thereby overcoming, at least to a certain extent, a problem caused by limitations and defects of related technologies. or multiple questions.

According to one aspect of the present disclosure, an AC microgrid protection method considering photovoltaic low voltage ride-through characteristics is provided, including:

Based on a single independent distributed power supply in the microgrid model, analyze the photovoltaic low voltage ride-through characteristics of the independent distributed power supply when a fault occurs, and determine the phase between the current fault component of the photovoltaic output and the pre-fault voltage under different amplitudes of voltage drop. Angular relationship;

According to the phase angle relationship between the current fault component of the photovoltaic output and the voltage before the fault, analyze the phase angle relationship between the current fault components on all branch feeders on the independent distributed power bus when a fault occurs, and determine the fault status of each branch feeder. ;

When the microgrid bus voltage drops greater than the preset amplitude, the fault line determination is started. Based on the fault status judgment of each branch feeder, the fault line is determined and the fault line protection is started.

In an exemplary embodiment of the present disclosure, the method further includes:

According to the phase angle relationship between the current fault component of the photovoltaic output and the pre-fault voltage, the current fault components on all branch feeders on the independent distributed power supply bus are compared in pairs when the fault occurs, and the current fault components on the independent distributed power supply bus are generated. The phase angle relationship between the current fault components on all branch feeders is used to determine the fault status of each branch feeder through the phase angle interval where the current fault components on the branch feeders are located.

In an exemplary embodiment of the present disclosure, based on the formula

Analyze the phase angle relationship between the current fault components on all branch feeders on the independent distributed power bus when a fault occurs;

Among them, ΔI _A1 , ΔI _A2 , and ΔI _A3 are the current fault components of the three branch feeders on a single independent distributed power bus A in the microgrid model.

4. The method of claim 1, further comprising:

When the microgrid bus voltage drops by 10% greater than the original voltage value, the fault line determination is started. Based on the fault status judgment of each branch feeder, the fault line is determined and the fault line protection is started.

In an exemplary embodiment of the present disclosure, the method further includes:

When the microgrid bus voltage drops greater than the preset amplitude, the fault line determination is started, based on the fault status of each branch feeder, and a trip signal is sent to the line determined to be a fault line.

In an exemplary embodiment of the present disclosure, the method further includes:

While sending a trip signal to the line determined to be a faulty line, a trip signal is sent to the line on the opposite side of the faulty line, and the trip signal sent by the opposite side line is received. When the trip signal sent by the opposite side line is received, the execution Trip action.

In one aspect of the present disclosure, an AC microgrid protection device considering photovoltaic low voltage ride-through characteristics is provided, including:

The phase angle relationship analysis module is based on a single independent distributed power supply in the microgrid model, analyzes the photovoltaic low voltage ride-through characteristics of the independent distributed power supply when a fault occurs, and determines the current fault component of the photovoltaic output under different amplitudes of voltage drop. Phase angle relationship with pre-fault voltage;

The fault state determination module, based on the phase angle relationship between the current fault component of the photovoltaic output and the voltage before the fault, analyzes the phase angle relationship between the current fault components on all branch feeders on the independent distributed power bus when a fault occurs, and determines each Fault status of branch feeders;

The fault protection module starts fault line determination when the microgrid bus voltage drops greater than the preset amplitude. Based on the fault status judgment of each branch feeder, the fault line is determined and fault line protection is started.

In one aspect of the present disclosure, an electronic device is provided, including:

processor; and

A memory, computer-readable instructions are stored on the memory, and when the computer-readable instructions are executed by the processor, the method according to any one of the above is implemented.

In one aspect of the present disclosure, a computer-readable storage medium is provided, a computer program is stored thereon, and when the computer program is executed by a processor, the method according to any one of the above is implemented.

In an exemplary embodiment of the present disclosure, an AC microgrid protection method considering photovoltaic low voltage ride-through characteristics includes: analyzing and determining the current fault component of the photovoltaic output under different amplitudes of voltage drops of independent distributed power sources when a fault occurs. The phase angle relationship with the pre-fault voltage; analyze the phase angle relationship between the current fault components on all branch feeders when a fault occurs, and determine the fault status of each branch feeder; when the microgrid bus voltage drops greater than the preset amplitude, based on the The fault status of each branch feeder is determined to determine the fault line, and fault line protection is initiated. This disclosure analyzes the photovoltaic low voltage ride-through characteristics of the microgrid, determines the phase angle relationship between the current fault components on all branch feeders on the independent distributed power bus when a fault occurs, and establishes a microgrid line protection method that only uses current information. , reducing the construction cost of the microgrid protection system.

It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and do not limit the present disclosure.

Description of the drawings

The above and other features and advantages of the present disclosure will become more apparent by describing in detail example embodiments thereof with reference to the accompanying drawings.

Figure 1 shows a flow chart of an AC microgrid protection method considering photovoltaic low voltage ride through characteristics according to an exemplary embodiment of the present disclosure;

2A-2B illustrate a schematic diagram of a photovoltaic microgrid fault component of an AC microgrid protection method considering photovoltaic low voltage ride through characteristics according to an exemplary embodiment of the present disclosure;

3A-3B show schematic diagrams of the voltage and current of photovoltaic output before and after a fault according to an AC microgrid protection method that considers photovoltaic low voltage ride-through characteristics according to an exemplary embodiment of the present disclosure;

4A-4B illustrate a schematic diagram of a simple microgrid and a positive sequence fault additional network of an AC microgrid protection method that considers photovoltaic low voltage ride-through characteristics according to an exemplary embodiment of the present disclosure;

5A-5C show schematic diagrams of each fault voltage component and fault current component when a fault occurs at point F according to an AC microgrid protection method that considers photovoltaic low voltage ride-through characteristics according to an exemplary embodiment of the present disclosure;

6A-6B show a simplified model of the microgrid and a schematic diagram of the positive sequence fault additional network of the AC microgrid protection method considering the photovoltaic low voltage ride-through characteristics according to an exemplary embodiment of the present disclosure;

Figure 7 shows a schematic diagram of the phase relationship of fault components on bus G during F2 fault according to an AC microgrid protection method that considers photovoltaic low voltage ride-through characteristics according to an exemplary embodiment of the present disclosure;

Figure 8 shows a schematic diagram of the phase relationship of fault components on bus F during F2 fault according to an AC microgrid protection method that considers photovoltaic low voltage ride-through characteristics according to an exemplary embodiment of the present disclosure;

Figure 9 shows a schematic diagram of the phase relationship of the fault components on the bus F during the F3 fault of the AC microgrid protection method considering the photovoltaic low voltage ride-through characteristics according to an exemplary embodiment of the present disclosure;

Figure 10 shows a schematic diagram of the phase relationship of fault components on bus G during F4 fault according to an AC microgrid protection method that considers photovoltaic low voltage ride-through characteristics according to an exemplary embodiment of the present disclosure;

Figure 11 shows a microgrid protection system configuration diagram of an AC microgrid protection method considering photovoltaic low voltage ride-through characteristics according to an exemplary embodiment of the present disclosure;

Figure 12 shows a schematic diagram of the trip signal triggering module of the AC microgrid protection method considering photovoltaic low voltage ride-through characteristics according to an exemplary embodiment of the present disclosure;

Figure 13 shows a fault determination flow chart of the AC microgrid protection method considering photovoltaic low voltage ride-through characteristics according to an exemplary embodiment of the present disclosure;

Figure 14 shows a schematic block diagram of an AC microgrid protection device considering photovoltaic low voltage ride-through characteristics according to an exemplary embodiment of the present disclosure;

Figure 15 schematically illustrates a block diagram of an electronic device according to an exemplary embodiment of the present disclosure; and

FIG. 16 schematically illustrates a computer-readable storage medium according to an exemplary embodiment of the present disclosure.

Detailed ways

Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments may, however, be embodied in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concepts of the example embodiments. To those skilled in the art. The same reference numerals in the drawings represent the same or similar parts, and thus their repeated description will be omitted.

Furthermore, the described features, structures or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to provide a thorough understanding of embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of the specific details described, or other methods, components, materials, devices, steps, etc. may be employed. In other instances, well-known structures, methods, devices, implementations, materials, or operations have not been shown or described in detail to avoid obscuring aspects of the present disclosure.

The block diagrams shown in the figures are functional entities only and do not necessarily correspond to physically separate entities. That is, these functional entities may be implemented in the form of software, or implemented in one or more software-hardened modules, or part of the functional entities, or in different networks and/or processor devices and/or microcontroller devices. implement these functional entities.

In this example embodiment, an AC microgrid protection method that considers photovoltaic low voltage ride through characteristics is first provided; with reference to Figure 1, the AC microgrid protection method that considers photovoltaic low voltage ride through characteristics may include the following steps:

Step S110: Based on a single independent distributed power supply in the microgrid model, analyze the photovoltaic low voltage ride-through characteristics of the independent distributed power supply when a fault occurs, and determine whether the current fault component of the photovoltaic output is the same as before the fault under different amplitudes of voltage drop. Phase angle relationship of voltage;

Step S120: Based on the phase angle relationship between the current fault component of the photovoltaic output and the pre-fault voltage, analyze the phase angle relationship between the current fault components on all branch feeders on the independent distributed power bus when a fault occurs, and determine each branch feeder. fault status;

Step S130: When the voltage drop of the microgrid busbar is greater than the preset amplitude, fault line determination is started. Based on the fault status judgment of each branch feeder, the fault line is determined and fault line protection is started.

In an exemplary embodiment of the present disclosure, an AC microgrid protection method considering photovoltaic low voltage ride-through characteristics includes: analyzing and determining the current fault component of the photovoltaic output under different amplitudes of voltage drops of independent distributed power sources when a fault occurs. The phase angle relationship with the pre-fault voltage; analyze the phase angle relationship between the current fault components on all branch feeders when a fault occurs, and determine the fault status of each branch feeder; when the microgrid bus voltage drops greater than the preset amplitude, based on the The fault status of each branch feeder is determined to determine the fault line, and fault line protection is initiated. This disclosure analyzes the photovoltaic low voltage ride-through characteristics of the microgrid, determines the phase angle relationship between the current fault components on all branch feeders on the independent distributed power bus when a fault occurs, and establishes a microgrid line protection method that only uses current information. , reducing the construction cost of the microgrid protection system.

Next, the AC microgrid protection method considering photovoltaic low voltage ride-through characteristics in this exemplary embodiment will be further described.

In step S110, based on a single independent distributed power supply in the microgrid model, the photovoltaic low voltage ride-through characteristics of the independent distributed power supply when a fault occurs can be analyzed to determine the current fault component of the photovoltaic output under different amplitudes of voltage drop. Phase angle relationship with pre-fault voltage.

In the embodiment of this example, when the microgrid is connected to the grid, the photovoltaic works under PQ control and has a low voltage ride-through function. When the microgrid fails, the photovoltaic will reduce the active power and increase the output reactive power to provide power for the microgrid. The power grid performs voltage regulation, and its AC side output current only has a positive sequence component. In fault-added networks, PQ-controlled photovoltaics can be directly equivalent to positive sequence current sources. According to the equivalent mathematical model of IIDG controlled by PQ, the fault current output by IIDG can be expressed as:

In the formula: I _qf and I _df are the reactive current and active current generated by the PV during fault respectively; U _d.0 is the d-axis component of the PV grid connection point voltage during normal operation; is the positive sequence component of the PV grid connection point voltage during a fault; I _max is the maximum fault current of the PV output during a fault; I _amp.f is the fault current amplitude; α is the fault current phase angle; k is the reactive power compensation coefficient.

According to the analysis of formula (1), when the photovoltaic microgrid fails, the photovoltaic microgrid can be analyzed by the equivalent model shown in Figure 2A-2B below. The content represented by some variables in the figure has been explained in formula (1). The unexplained new variables are explained below: Z _L is the equivalent impedance of the line, Z _S is the equivalent positive sequence impedance of the system, ΔI is the current Fault component.

When a fault occurs, photovoltaics need to emit reactive power to suppress voltage drops, so you can first analyze the changes in output voltage and current before and after the photovoltaic fault. Then the changes in bus voltage and current are analyzed based on the photovoltaic output. The photovoltaic output voltage vector and current vector before and after the fault are shown in Figure 3.

In Figure 3A, U _d is the voltage before the fault, and the output active current at this time is I _d ; U' _d is the voltage after the fault, and the voltage phase lag angle is θ; I' ₁ and I' ₂ are the fault currents, and the fault current range is I _max is the sector-shaped area surrounded by arcs of radius; ΔI _f1 and ΔI _f2 are current fault components. It can be seen from the voltage and current phasor diagram output before and after the photovoltaic fault in Figure 3A that when the distribution network fails, if the voltage drop is large, that is, U' _d is small, the current fault component ΔI and the pre-fault voltage U _d are two vectors The phase difference is greater than 90°; if the voltage drop is small, that is, U' _d is large, the phase difference between the two vectors of the current fault component ΔI and the pre-fault voltage U _d is less than 90°. Therefore, it can be found that the degree of voltage drop will affect the phase difference between the fault component ΔI of the output current and the pre-fault voltage U _d . Moreover, the post-fault voltage has a critical value, as shown in Figure 3B. In the figure, I' _d and I' _q are the active and reactive current values corresponding to the post-fault current I' respectively. At this time, the pre-fault voltage U _d and the fault current The angle between the components ΔI is 90°.

From Figure 3B, the following relationships can be summarized:

Since |I'|=I _max , so:

According to regulations, when the voltage drop exceeds 10%, for every 1% voltage drop, 2% of reactive current needs to be provided correspondingly. The mathematical meaning is:

In the formula, k'≥2. Put formula (4) into (3) to get the relationship between voltage and critical voltage value during normal operation:

According to the analysis results, when the post-fault voltage is smaller than the critical voltage value, the phase angle difference between the current fault component ΔI of the photovoltaic output and the pre-fault voltage U _d is greater than 90°. When the post-fault voltage is greater than the critical voltage value, the phase angle difference between the current fault component ΔI of the photovoltaic output and the pre-fault voltage U _d is less than 90°. Analysis of photovoltaic output current fault characteristics can provide a basis for microgrid fault analysis.

In step S120, based on the phase angle relationship between the current fault component of the photovoltaic output and the pre-fault voltage, the phase angle relationship between the current fault components on all branch feeders on the independent distributed power bus when the fault occurs can be analyzed to determine Fault status of each branch feeder.

In this example embodiment, the method further includes:

According to the phase angle relationship between the current fault component of the photovoltaic output and the pre-fault voltage, the current fault components on all branch feeders on the independent distributed power supply bus are compared in pairs when the fault occurs, and the current fault components on the independent distributed power supply bus are generated. The phase angle relationship between the current fault components on all branch feeders is used to determine the fault status of each branch feeder through the phase angle interval where the current fault components on the branch feeders are located.

In this example embodiment, the method further includes, based on the formula

Analyze the phase angle relationship between the current fault components on all branch feeders on the independent distributed power bus when a fault occurs;

Among them, ΔI _A1 , ΔI _A2 , and ΔI _A3 are the current fault components of the three branch feeders on a single independent distributed power bus A in the microgrid model.

In this exemplary embodiment, fault characteristics are analyzed by building a simple microgrid model. Figure 4A is a microgrid with four busbars as well as feeders and photovoltaic grid-connected operation. Bus E is connected to three feeders E1, E2 and E3. Bus F is connected to three feeders F1, F2 and F3. Bus G connects three feeders G1, G2 and G3. Bus M is connected to three feeders M1, M2 and M3. LD1, LD2 and LD3 are loads. IIDG1 and IIDG2 are independent distributed power supplies.

When a fault occurs at point F, the positive sequence fault additional network of the microgrid is shown in Figure 4B. In the figure, Z _S is the equivalent positive sequence impedance of the system; ΔI _E1 — ΔI _E3 , ΔI _F1 — ΔI _F3 , ΔI _M1 — ΔI _M3 , ΔI _G1 — ΔI _G3 are the fault currents on each feeder at different busbars after a fault occurs. Z ₁ , Z ₂ , and Z ₃ are the positive sequence impedances of the load. ΔU _F is the positive sequence additional voltage source at the fault point; Z _F is the transition impedance at the fault point. Z _AF , Z _BF , Z _EM , and Z _FG are the equivalent positive sequence impedances of the lines between different busbars. ΔI ₁ and ΔI ₂ are the current fault components output by IIDG1 and IIDG2 respectively.

When a fault occurs at point F, since the microgrid and the distribution grid operate in parallel, the large grid can provide voltage support, so the voltage drops of bus E and bus M are small. However, if the fault point is very close to bus E, there may also be a large voltage drop between bus E and bus M. If the voltage drops at bus E and bus M are relatively large, the analysis results at bus E are similar to those at bus G. Therefore, this article mainly analyzes the situation where the voltage drops at bus E and bus M are small.

From the above analysis, it can be seen that when a fault occurs at point F, the angle between the current fault component ΔI ₂ output by IIDG2 at bus M and the bus voltage U _M before the fault is less than 90°. It can be seen from Figure 4B that ΔI _M2 =-ΔI ₂ , ΔI _M3 = _-ΔUM /Z ₂ , ΔI _M1 =-(ΔI _M2 +ΔI _M3 ), where _ΔUM is the positive sequence voltage fault component at bus M, Z ₂ is the positive sequence impedance of the load and is inductive, so the angle between ΔI _M3 and ΔU _M is less than 90° and is in the third quadrant. Through analysis, the phase relationship between the voltage component and the current component when a fault occurs at bus M can be obtained, as shown in Figure 5A.

Analyzing bus E from Figure 4B, ΔI _E3 =-ΔI _M1 , ΔI _E1 = _ΔUE /Z _S , ΔI _E2 =-(ΔI _E1 + ΔI _E3 ), where _ΔUE is the positive sequence voltage fault component at bus E , the equivalent positive sequence impedance Z _S of the system is inductive, so the angle between ΔI _E1 and ΔU _E is less than 90°, which is located in the third quadrant. From the above analysis, we can get the fault voltage component and current component on the bus E when the fault point F fails. The phase relationship is shown in Figure 5B.

Analyzing bus F, it can be seen from the fault network diagram that ΔI _F3 =-ΔI _G1 , so the phase relationship between the fault voltage component and the fault current component on bus G is first analyzed. It can be seen from the figure that ΔI _G2 =-ΔI ₁ , ΔI _G3 = ΔU _G /Z ₁ , ΔI _G1 =-(ΔI _G2 +ΔI _G3 ), where ΔU _G is the positive sequence voltage fault component at bus G, and the positive sequence impedance of the load Z ₁ is inductive, so the angle between ΔI _G3 and ΔU _G is less than 90°, which is in the third quadrant. When a fault occurs at point F, bus G is not supported by a large power grid, so the voltage drop is relatively large. Therefore, the angle between the post-fault current ΔI ₁ and the pre-fault bus voltage U _G is greater than 90°, so ΔI _G3 is located in the third quadrant. From the fault component diagram, it can be seen that the relationship between the fault components of each feeder of bus F after a fault occurs: ΔI _F3 =-ΔI _G1 , ΔI _F2 = ΔU _F /Z ₃ , ΔI _F1 =-(ΔI _F2 + ΔI _F3 ). The fault vector direction of ΔI _G1 is known through the above analysis. From the above analysis, the phasor diagram of each fault component at bus F can be obtained, as shown in Figure 5C below.

When point F fails, it can be known from the positive sequence current fault components at bus E and bus F that the fault point appears between feeder E2 on bus E and feeder F1 on bus F.

A fault is set up in the microgrid model shown in Figure 4A. Four fault points F1, F2, F3, and F4 are set up, as shown in Figure 6A. Figure 6B shows the positive sequence fault additional network when the microgrid model shown in Figure 6A fails at point F4. In Figure 6B, ΔU _F is the positive sequence additional voltage source at the fault point; Z _F is the transition impedance at the fault point; Z _S is the equivalent positive sequence impedance of the system; Z ₁₁ and Z ₁₂ are the equivalent positive sequence impedance of the line; Z _EF , Z _BF and Z _FG are the equivalent positive sequence impedances of the lines between different buses. The remaining variables in Figure 6B are the same as those existing in the positive sequence fault additional network of the microgrid shown in Figure 4B when a fault occurs at point F above.

The following analyzes the fault components on bus E, bus F, bus G and bus M when each fault point fails: The situation when point F1 fails has been analyzed in Figure 4 and will not be described again.

When a fault occurs at point F2, the analysis process of the positive sequence fault additional network of the microgrid is similar to that when a fault occurs at point F1. The current phasor diagrams at bus E and bus M are similar to the phasor diagrams at point F, which are not discussed here. Repeat. Analyze bus G in the fault-added network. When the voltage drop of bus G is relatively small, the angle between the post-fault current ΔI ₁ and the pre-fault bus voltage U _G is less than 90°, so ΔI ₁ is located in the fourth quadrant. It can be seen from the fault additional network as shown in Figure 7.

Analyzing bus F, it is known from the fault additional network that ΔI _F1 =-ΔI _E2 , ΔI _F3 =-ΔI _G1 , ΔI _F2 =-(ΔI _F1 + ΔI _F3 ), then the fault current component at bus F is shown in Figure 8.

When a fault occurs at point F3, the relationship between the positive sequence fault phasors at bus E and bus M is similar to Figure 5B and Figure 5A and will not be repeated here.

Since bus F has a large power grid to provide voltage, the voltage drop is relatively small. From the positive sequence current fault component diagram, we can get: ΔI _F1 =-ΔI _E2 , ΔI _F2 = ΔU _F /Z ₃ , ΔI _F3 =-(ΔI _F1 + ΔI _F2 ), where the phasor of ΔI _E3 is similar to Figure 8 and will not be described again here. Among them, ΔU _F is the positive sequence voltage fault component at bus F, and the positive sequence impedance Z ₃ of the load is inductive, so the angle between ΔI _F2 and ΔU _F is less than 90°, which is in the third quadrant. From the above relationship, the phase relationship between the fault voltage component and the fault current component at bus F during fault can be obtained, as shown in Figure 8.

When a fault occurs at point F4, the positive sequence fault additional network is shown in Figure 6B. When a fault occurs, the phasor relationship of each fault component at bus E, bus M, and bus F is similar to Figure 5B, Figure 5A, and Figure 9 analyzed previously, and will not be shown again.

Analyze bus G. Since bus G is supported by a large power grid, the voltage drop is relatively small, so the angle between the post-fault current ΔI ₁ and the pre-fault bus voltage U _G is less than 90°, so ΔI ₁ is located in the fourth quadrant. As can be seen from FIG. 6B , ΔI _G2 =-ΔI ₁ , ΔI _G1 =-ΔI _F3 , and ΔI _G3 =-(ΔI _G1 + ΔI _G2 ). Based on the above analysis of ΔI _G1 , ΔI _G2 and ΔI _G3 , the phase relationship of the fault voltage component and fault current component on bus G can be obtained as shown in Figure 10.

Through the above analysis, when faults occur at different locations, based on the phase relationship between each fault component, the phase angle relationship between the positive sequence fault current components on all branch feeders on a bus can be obtained. When the microgrid is operating normally, the phase angle difference of the current components on any two feeders is between 0° and 90°. When a fault occurs in the microgrid, the difference between the phase angle of the fault current and the phase angle of the normal current is between 90° and 180°. Assume that bus A has three branch feeders, namely ΔI _A1 , ΔI _A2 , and ΔI _A3 . When a fault occurs on the A3 bus, the fault current component phase angles on the three feeders are first extracted and simplified to between -180° and 180°. Take the difference between the phase angle of the fault current component on one branch feeder and the phase angle of the fault current component on the other two feeders and then get the absolute value. The phasor angle difference of different feeders can be determined according to equation (6).

In step S130, when the microgrid bus voltage drops greater than a preset amplitude, fault line determination can be started. Based on the fault status judgment of each branch feeder, the fault line can be determined and fault line protection can be started.

In this example embodiment, the method further includes:

When the microgrid bus voltage drops by 10% greater than the original voltage value, the fault line determination is started. Based on the fault status judgment of each branch feeder, the fault line is determined and the fault line protection is started.

In this example embodiment, the method further includes:

When the microgrid bus voltage drops greater than the preset amplitude, the fault line determination is started, based on the fault status of each branch feeder, and a trip signal is sent to the line determined to be a fault line.

In this example embodiment, the method further includes:

While sending a trip signal to the line determined to be a faulty line, a trip signal is sent to the line on the opposite side of the faulty line, and the trip signal sent by the opposite side line is received. When the trip signal sent by the opposite side line is received, the execution Trip action.

In the embodiment of this example, as shown in Figure 11, which is a microgrid protection system configuration diagram, the microgrid protection system proposed in this disclosure adopts a centralized-distributed protection scheme, and unit protection modules (unit protection) are distributed at bus nodes. , measure the current information on each feeder. Compared with the traditional unit protection module that requires a measuring device to be installed on each feeder line, the new protection method proposed in this disclosure only needs to install a voltage transformer at the grid-connected bus and does not need to be installed at each node. Voltage transformers can reduce certain costs. As shown in Figure 12, it is a schematic diagram of the trip signal trigger module. In the unit protection module, the current information is obtained from the grid-connected bus and the positive sequence fault current component is extracted. Once a voltage drop occurs at the microgrid's grid-connected bus, information will be transmitted to the unit protection module to initiate fault line judgment and locate the faulty feeder. Protection information can be transmitted between two adjacent unit protection modules through communication tie lines.

In the embodiment of this example, the fault line is determined based on the following: the voltage on the bus drops and the drop value exceeds the original voltage value by 10%. When the criteria for determining the fault line are met, the fault determination is started. The fault diagnosis process is shown in Figure 13.

First, extract the phase angle of the fault current component on the corresponding feeder of the bus and convert it to between -180° and 180°. Take the difference between the phase angle of the fault current component on one feeder and the phase angle of the fault current component on other feeders and then get the absolute value. Expressed according to the following formula:

|α|＝|arg(ΔI _Y )-arg(ΔI _Yn )| (7)

Among them, α is the phase angle difference, ΔI _Y is the detected line, and ΔI _Yn is the other lines on the bus X except the detected line. If the calculation results of the above formula are all between 90° and 180°, the branch feeder is a fault line, and the fault status criterion output is -1. On the contrary, the branch feeder is a healthy line, and the fault status criterion output is 1. After starting the criterion, it starts to simultaneously detect whether there is a fault in the outlet direction of all branch feeders on the bus. If it is a faulty line, a trip signal will be sent. At the same time, it sends a trip signal to the opposite side. If it receives a trip signal from the opposite side while sending the signal, it will trip directly, otherwise it will not trip.

It should be noted that although the various steps of the method in the present disclosure are described in a specific order in the drawings, this does not require or imply that these steps must be performed in this specific order, or that all of the steps shown must be performed. Achieve desired results. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step for execution, and/or one step may be decomposed into multiple steps for execution, etc.

In addition, in this example embodiment, an AC microgrid protection device that considers photovoltaic low voltage ride-through characteristics is also provided. Referring to FIG. 14 , the AC microgrid protection device 400 that considers photovoltaic low voltage ride-through characteristics may include: a phase angle relationship analysis module 410 , a fault state determination module 420 and a fault protection module 430 . in:

The phase angle relationship analysis module 410 is based on a single independent distributed power supply in the microgrid model, analyzes the photovoltaic low voltage ride-through characteristics of the independent distributed power supply when a fault occurs, and determines the current fault of the photovoltaic output under different amplitudes of voltage drop. The phase angle relationship between the component and the voltage before the fault;

The fault state determination module 420 analyzes the phase angle relationship between the current fault components on all branch feeders on the independent distributed power supply bus when a fault occurs, based on the phase angle relationship between the current fault component of the photovoltaic output and the voltage before the fault, and determines The fault status of each branch feeder;

The fault protection module 430 starts fault line determination when the microgrid bus voltage drops greater than the preset amplitude, determines the fault line based on the fault status of each branch feeder, and starts fault line protection.

The specific details of each of the above AC microgrid protection device modules that consider photovoltaic low voltage ride through characteristics have been described in detail in the corresponding AC microgrid protection method that considers photovoltaic low voltage ride through characteristics, so they will not be described again here.

It should be noted that although several modules or units of the AC microgrid protection device 400 considering photovoltaic low voltage ride-through characteristics are mentioned in the above detailed description, this division is not mandatory. In fact, according to embodiments of the present disclosure, the features and functions of two or more modules or units described above may be embodied in one module or unit. Conversely, the features and functions of one module or unit described above may be further divided into being embodied by multiple modules or units.

Furthermore, in an exemplary embodiment of the present disclosure, an electronic device capable of implementing the above method is also provided.

Those skilled in the art will understand that various aspects of the present invention may be implemented as systems, methods or program products. Therefore, various aspects of the present invention may be embodied in the following forms, namely: complete hardware embodiments, complete software embodiments (including firmware, microcode, etc.), or embodiments combining hardware and software aspects, which may be collectively referred to herein as "Circuit", "Module" or "System".

An electronic device 500 according to such an embodiment of the present invention is described below with reference to FIG. 15 . The electronic device 500 shown in FIG. 15 is only an example and should not impose any limitations on the functions and usage scope of the embodiments of the present invention.

As shown in Figure 15, electronic device 500 is embodied in the form of a general computing device. The components of the electronic device 500 may include, but are not limited to: the above-mentioned at least one processing unit 510, the above-mentioned at least one storage unit 520, a bus 530 connecting different system components (including the storage unit 520 and the processing unit 510), and the display unit 540.

Wherein, the storage unit stores program code, and the program code can be executed by the processing unit 510, so that the processing unit 510 performs various exemplary methods according to the present invention described in the above-mentioned "Example Method" section of this specification. Example steps. For example, the processing unit 510 may perform steps S110 to S130 as shown in FIG. 1 .

The storage unit 520 may include a readable medium in the form of a volatile storage unit, such as a random access storage unit (RAM) 5201 and/or a cache storage unit 5202, and may further include a read-only storage unit (ROM) 5203.

Storage unit 520 may also include a program/utility 5204 having a set of (at least one) program modules 5203, such program modules 5205 including, but not limited to: an operating system, one or more application programs, other program modules, and program data, Each of these examples, or some combination, may include the implementation of a network environment.

Bus 550 may be a local area representing one or more of several types of bus structures, including a memory unit bus or memory unit controller, a peripheral bus, a graphics acceleration port, a processing unit, or using any of a variety of bus structures. bus.

Electronic device 500 may also communicate with one or more external devices 570 (e.g., keyboard, pointing device, Bluetooth device, etc.), may also communicate with one or more devices that enable a user to interact with electronic device 500, and/or with Any device that enables the electronic device 500 to communicate with one or more other computing devices (eg, router, modem, etc.). This communication may occur through input/output (I/O) interface 550. Furthermore, the electronic device 500 may also communicate with one or more networks (eg, a local area network (LAN), a wide area network (WAN), and/or a public network, such as the Internet) through the network adapter 560. As shown, network adapter 560 communicates with other modules of electronic device 500 via bus 550 . It should be understood that, although not shown in the figures, other hardware and/or software modules may be used in conjunction with electronic device 500, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives And data backup storage system, etc.

Through the description of the above embodiments, those skilled in the art can easily understand that the example embodiments described here can be implemented by software, or can be implemented by software combined with necessary hardware. Therefore, the technical solution according to the embodiment of the present disclosure can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (which can be a CD-ROM, U disk, mobile hard disk, etc.) or on the network , including several instructions to cause a computing device (which may be a personal computer, a server, a terminal device, a network device, etc.) to execute a method according to an embodiment of the present disclosure.

In an exemplary embodiment of the present disclosure, a computer-readable storage medium is also provided, on which a program product capable of implementing the method described above in this specification is stored. In some possible embodiments, various aspects of the present invention can also be implemented in the form of a program product, which includes program code. When the program product is run on a terminal device, the program code is used to cause the The terminal device performs the steps according to various exemplary embodiments of the present invention described in the "Exemplary Method" section above in this specification.

Referring to Figure 16, a program product 600 for implementing the above method according to an embodiment of the present invention is described, which can adopt a portable compact disk read-only memory (CD-ROM) and include program code, and can be used on a terminal device, For example, run on a personal computer. However, the program product of the present invention is not limited thereto. In this document, a readable storage medium may be any tangible medium containing or storing a program that may be used by or in combination with an instruction execution system, apparatus or device.

The program product may take the form of any combination of one or more readable media. The readable medium may be a readable signal medium or a readable storage medium. The readable storage medium may be, for example, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device or device, or any combination thereof. More specific examples (non-exhaustive list) of readable storage media include: electrical connection with one or more conductors, portable disk, hard disk, random access memory (RAM), read only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination of the above.

A computer-readable signal medium may include a data signal propagated in baseband or as part of a carrier wave carrying readable program code therein. Such propagated data signals may take many forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. A readable signal medium may also be any readable medium other than a readable storage medium that can send, propagate, or transport the program for use by or in connection with an instruction execution system, apparatus, or device.

Program code embodied on a readable medium may be transmitted using any suitable medium, including but not limited to wireless, wireline, optical cable, RF, etc., or any suitable combination of the foregoing.

Program code for performing the operations of the present invention may be written in any combination of one or more programming languages, including object-oriented programming languages such as Java, C++, etc., as well as conventional procedural Programming language—such as "C" or a similar programming language. The program code may execute entirely on the user's computing device, partly on the user's device, as a stand-alone software package, partly on the user's computing device and partly on a remote computing device, or entirely on the remote computing device or server execute on. In situations involving remote computing devices, the remote computing device may be connected to the user computing device through any kind of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computing device, such as provided by an Internet service. (business comes via Internet connection).

Furthermore, the above-mentioned drawings are only schematic illustrations of processes included in methods according to exemplary embodiments of the present invention, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal sequence of these processes. In addition, it is also easy to understand that these processes may be executed synchronously or asynchronously in multiple modules, for example.

Other embodiments of the disclosure will be readily apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the disclosure that follow the general principles of the disclosure and include common knowledge or customary technical means in the technical field that are not disclosed in the disclosure. . It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.

It is to be understood that the present disclosure is not limited to the precise structures described above and illustrated in the accompanying drawings, and various modifications and changes may be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims (6)

1. An ac microgrid protection method taking photovoltaic low voltage ride through characteristics into consideration, the method comprising:

based on a single independent distributed power supply in a micro-grid model, analyzing the photovoltaic low-voltage ride through characteristics of the independent distributed power supply when faults occur, and judging the phase angle relation between the current fault component of photovoltaic output and the voltage before faults under different amplitudes of voltage drop;

analyzing the phase angle relation between the current fault components on all branch feeder lines on the independent distributed power bus when faults occur according to the phase angle relation between the current fault components of the photovoltaic output and the voltage before faults, and judging the fault state of each branch feeder line; based on the formula

Analyzing phase angle relations among current fault components on all branch feeder lines on the independent distributed power bus when faults occur; wherein DeltaI _A1 、ΔI _A2 、ΔI _A3 The current fault components of three branch feeder lines on a single independent distributed power bus A in the micro-grid model are respectively;

when the voltage drop of the busbar of the micro-grid is larger than a preset amplitude, starting fault line judgment, judging a fault line according to the fault state judgment of each branch feeder line, and starting fault line protection.

2. The method of claim 1, wherein the method further comprises:

and comparing the current fault components on all branch feeder lines on the independent distributed power bus when faults occur in pairs according to the phase angle relation between the current fault components of the photovoltaic output and the voltage before faults, generating the phase angle relation between the current fault components on all branch feeder lines on the independent distributed power bus, and judging the fault state of each branch feeder line through the phase angle section where the current fault components on the branch feeder lines are located.

3. The method of claim 1, wherein the method further comprises:

and sending a tripping signal to the line judged to be the fault line, sending a tripping signal to the opposite side line of the fault line, receiving the tripping signal sent by the opposite side line, and executing tripping action when the tripping signal sent by the opposite side line is received.

4. An ac microgrid protection device that takes into account photovoltaic low voltage ride through characteristics, the device comprising:

the phase angle relation analysis module is used for analyzing the photovoltaic low-voltage ride through characteristics of the independent distributed power supplies when faults occur based on the single independent distributed power supplies in the micro-grid model, and judging the phase angle relation between the current fault components of the photovoltaic output and the voltage before the faults under different amplitudes of voltage drop;

the fault state judging module is used for analyzing the phase angle relation between the current fault components on all branch feeder lines on the independent distributed power bus when faults occur according to the phase angle relation between the current fault components of the photovoltaic output and the voltage before faults and judging the fault state of each branch feeder line; based on the formula

Analyzing phase angle relations among current fault components on all branch feeder lines on the independent distributed power bus when faults occur; wherein DeltaI _A1 、ΔI _A2 、ΔI _A3 The current fault components of three branch feeder lines on a single independent distributed power bus A in the micro-grid model are respectively;

and the fault protection module is used for starting fault line judgment when the voltage drop of the busbar of the micro-grid is larger than a preset amplitude, judging a fault line according to the fault state judgment of each branch feeder line, and starting fault line protection.

5. An electronic device, comprising

A processor; and

a memory having stored thereon computer readable instructions which, when executed by the processor, implement the method according to any of claims 1 to 3.

6. A computer readable storage medium having stored thereon a computer program which, when executed by a processor, implements a method according to any of claims 1 to 3.