Hybrid island detection method with state switching and related device

Abstract

The invention belongs to the technical field of micro-grids, and provides a hybrid island detection method with state switching and a related device. The method comprises the following steps: calculating active power and reactive power of inversion output according to collected inversion output current, inversion output voltage and common point voltage; calculating active power and reactive power consumed by the load according to the collected load current and load voltage; when the micro-grid central controller detects that the active power output by the inverter is matched with the active power consumed by the load and the reactive power output by the inverter is matched with the reactive power consumed by the load, carrying out island detection on the micro-grid by adopting an active frequency deviation method; otherwise, the micro-grid central controller performs island detection on the micro-grid by adopting an over / under-frequency detection method in a passive method. Under the condition that the detection speed is considered, the calculation amount is effectively reduced, and more stable and reliable island detection is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrids, and in particular to a hybrid island detection method with state switching and a related device. Background Art

[0002] Microgrids play an increasingly important role in today's energy sector. With the widespread use of renewable energy such as solar and wind energy and the diversification of energy distribution, microgrids have become an important tool for achieving the reliability and sustainability of energy supply. Microgrids can not only provide the integration of renewable energy, but also improve the resilience of the power system, increase the stability of power supply, reduce dependence on traditional power grids, and reduce carbon emissions. Therefore, microgrids are expected to play a key role in future energy systems and promote the clean and sustainable development of energy.

[0003] Among them, island detection is an important part of microgrid management. It helps to identify and cut off the connection between the microgrid and the main grid in time to avoid potential safety risks. This is crucial to the life safety of power maintenance personnel, because during power failures or maintenance, the microgrid must be able to be isolated from the main grid to prevent power from feeding back to the maintenance area. In addition, island detection also affects the operation of distribution system protection switches. It ensures that these critical devices can respond quickly when necessary to isolate the microgrid or reconnect to the main grid to protect the entire power system from failures. In summary, island detection in microgrids not only helps to ensure the safety and stability of the power system, but also improves the reliability of microgrids and ensures that users always have a reliable power supply. This is crucial to promote the key role of microgrids in the integration of renewable energy and distributed energy and promote the development of a sustainable energy future.

[0004] Potential islanding effects in microgrids can endanger the lives of power maintenance personnel, cause voltage fluctuation hazards in islanded areas, and affect the operation of protection switches in distribution systems.

[0005] The traditional method has an obvious disadvantage, that is, it uses the active frequency offset method throughout the process, which leads to a huge amount of calculation. Therefore, how to provide an island detection method that combines detection speed and computational complexity is an urgent problem to be solved. Summary of the invention

[0006] In view of the defects in the prior art, the present invention provides a hybrid island detection method with state switching and a related device, so as to achieve both detection speed and computational complexity, and provide more stable and reliable island detection.

[0007] A hybrid island detection method with state switching, comprising:

[0008] According to the collected inverter output current, inverter output voltage and common point voltage, the active power and reactive power of the inverter output are calculated;

[0009] According to the collected load current and load voltage, the active power and reactive power consumed by the load are calculated;

[0010] When the microgrid central controller detects that the active power output by the inverter matches the active power consumed by the load, and the reactive power output by the inverter matches the reactive power consumed by the load, the active frequency shift method is used to perform island detection on the microgrid;

[0011] Otherwise, the microgrid central controller uses the over / under frequency detection method in the passive method to perform island detection on the microgrid.

[0012] Furthermore, the active power output by the inverter matches the active power consumed by the load, and the reactive power output by the inverter matches the reactive power consumed by the load, including:

[0013] P load =P inv ,

[0014] Q load =Q inv ,

[0015] Among them, P load and P inv Indicates the active power consumed by the load and the active power output by the inverter, Q load and Q inv Indicates the reactive power consumed by the load and the reactive power output by the inverter.

[0016] Furthermore, it also includes:

[0017] The active power and reactive power of the inverter output are calculated using the following formula:

[0018] P inv =V inv ×I inv ×cosΦ inv ,

[0019] Q inv =V inv ×I inv ×sinΦ inv ,

[0020] Where V inv is the inverter output voltage, I inv is the inverter output current, cosΦ inv is the power factor of the inverter output, where sinΦ inv It is the sine value of the inverter output power factor.

[0021] Furthermore, it also includes:

[0022] The active power and reactive power consumed by the load are calculated using the following formula:

[0023] P load =V load ×I load ×cosΦ load ,

[0024] Q load =V load ×I load ×sinΦ load ,

[0025] Where V load is the load voltage, I load is the load current, cosΦ load is the power factor of the load, sinΦ load is the sine value of the load power factor.

[0026] Furthermore, it also includes:

[0027] The active frequency shift method is improved by using a positive feedback mechanism.

[0028] The positive feedback mechanism is characterized by the method shown in the following formula:

[0029] cf n =cf0+F(Δω n )

[0030] In the formula, cf n is the cutoff coefficient of the "n"th cycle, cf0 is the cutoff coefficient of the initial cycle, F(Δω n ) is the angular frequency difference Δω n The positive feedback expression, F(Δω n ) is a linear function, F(Δω n )=kΔω n .

[0031] A hybrid island detection device with state switching includes a first calculation unit, a second calculation unit, an active detection unit and a passive detection unit, wherein:

[0032] The first calculation unit is used to calculate the active power and reactive power of the inverter output according to the collected inverter output current, inverter output voltage and common point voltage;

[0033] The second calculation unit is used to calculate the active power and reactive power consumed by the load according to the collected load current and load voltage;

[0034] An active detection unit, used to perform island detection on the microgrid using an active frequency shift method when the microgrid central controller detects that the active power output by the inverter matches the active power consumed by the load, and the reactive power output by the inverter matches the reactive power consumed by the load;

[0035] The passive detection unit is used to detect the islanding of the microgrid by the over / under frequency detection method in the passive method.

[0036] A terminal, characterized in that it includes a processor, an input device, an output device and a memory, wherein the processor, the input device, the output device and the memory are interconnected, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is configured to call the program instructions to execute any of the above-mentioned hybrid island detection methods with state switching.

[0037] A computer-readable storage medium, characterized in that the computer-readable storage medium stores a computer program, the computer program includes program instructions, and when the program instructions are executed by a processor, the processor executes any one of the above-mentioned hybrid island detection methods with state switching. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the specific embodiments of the present invention, the following will briefly introduce the drawings required for the specific embodiments or the prior art description. In all the drawings, each element or part is not necessarily drawn according to the actual scale.

[0039] Figure 1 A flow chart of a hybrid island detection method with state switching provided by an embodiment of the present invention;

[0040] Figure 2 A schematic structural diagram of a hybrid island detection device with state switching provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The following embodiments of the technical solution of the present invention are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.

[0042] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0043] In one embodiment, if Figure 1 As shown, a hybrid island detection method with state switching is provided, characterized in that it includes:

[0044] 1. Calculate the active power and reactive power of the inverter output according to the collected inverter output current, inverter output voltage and common point voltage;

[0045] Preferably, the active power and reactive power output by the inverter are calculated using the method shown in the following formula:

[0046] P inv =V inv ×I inv ×cosΦ inv ,

[0047] Q inv =V inv ×I inv ×sinΦ inv ,

[0048] Where V inv is the inverter output voltage, I inv is the inverter output current, cosΦ inv is the power factor of the inverter output, where sinΦ inv It is the sine value of the inverter output power factor.

[0049] Specifically, the voltage (inverter output voltage) or the current (inverter output current) at the output end of the grid-connected inverter can be directly measured by a voltmeter or a digital multimeter (DMM), or the inverter output voltage and inverter output current can be obtained using a monitoring system or a communication interface.

[0050] The power factor of the inverter output can be obtained through a power factor meter or a power analyzer.

[0051] 2. Calculate the active power and reactive power consumed by the load based on the collected load current and load voltage;

[0052] Preferably, the active power and reactive power consumed by the load are calculated using the method shown in the following formula:

[0053] P load =V load ×I load ×cosΦ load ,

[0054] Q load =V load ×I load ×sinΦ load ,

[0055] Where V load is the load voltage, I load is the load current, cosΦ load is the power factor of the load, sinΦ loadis the sine value of the load power factor.

[0056] 3. When the microgrid central controller detects that the active power output by the inverter matches the active power consumed by the load, and the reactive power output by the inverter matches the reactive power consumed by the load, the active frequency offset method is used to perform island detection on the microgrid;

[0057] When the power of the main grid is not zero, disconnecting the main grid may cause frequency and voltage changes at the point of common connection (PCC). If the power supplied by the grid-connected inverter matches the power consumed by the local load (including active and reactive power), the frequency and voltage changes at the PCC will remain within the grid-permitted range before and after the circuit breaker is disconnected. The grid-connected inverter adjusts its output to synchronize with the load, and the island detection mechanism will not be triggered at this time, so the grid-connected inverter will continue to supply power to the local load, forming a power supply island.

[0058] From the above analysis, it can be concluded that in order for the island effect to occur, the microgrid system usually needs to meet the following conditions:

[0059] (1) The active power required by the local load matches the active power obtained from the grid-connected inverter (the active power output by the inverter matches the active power consumed by the load).

[0060] (2) The reactive power required by the local load matches the reactive power obtained from the grid-connected inverter (the reactive power output by the inverter matches the reactive power consumed by the load).

[0061] Preferably, the active power output by the inverter matches the active power consumed by the load, and the reactive power output by the inverter matches the reactive power consumed by the load, including:

[0062] P load =P inv ,

[0063] Q load =Q inv ,

[0064] Among them, P load and P inv Indicates the active power consumed by the load and the active power output by the inverter, Q load and Q inv Indicates the reactive power consumed by the load and the reactive power output by the inverter.

[0065] Real-time monitoring of the active power (P inv ) and reactive power (Q inv ), and the active power consumed by the load (P load ) and reactive power (Q load). These data will be transmitted to the microcontroller to check whether they approximately meet P load =P inv , Q load =Q inv If the above equation is satisfied, the active frequency offset method is immediately switched on to detect islands in real time; if not, only passive island detection is switched on, that is, only whether the frequency exceeds the normal frequency range is detected.

[0066] In one embodiment, the active power output by the inverter matches the active power consumed by the load, and the reactive power output by the inverter matches the reactive power consumed by the load, further comprising: load With P inv The ratio is greater than 99.5%, and Q load With Q inv The difference value is greater than a threshold (the threshold can be a fixed value, such as 0.1 kvar, 0.01 kvar, etc.), which is a situation of approximate equality.

[0067] For example, if the inverter output active power is 1000W and the load consumes 995W, the difference is 5W, which is only 0.5% of the inverter output active power. In this case, we can consider the inverter output active power and the load consumption active power to be "approximately equal" because the difference is very small and can be ignored.

[0068] It should be noted that since reactive power is mainly used to compensate for inductive or capacitive loads in the power grid, the accuracy of its value is not as important as that of active power. In some cases, even if the difference in reactive power is slightly larger, it can be considered acceptable as long as it does not significantly affect the stable operation of the system.

[0069] Active Frequency Drift (AFD) is a commonly used method for island detection in microgrids. The island effect refers to the situation when the main grid is interrupted due to electrical failure, misoperation, etc., the microgrid system fails to detect the power outage and disconnects from the main grid, and continues to supply power to the main grid, making the microgrid and the surrounding loads form a self-sufficient power supply island that the power company cannot control. This situation may pose a threat to equipment and personal safety, so it needs to be detected in a timely manner.

[0070] The principle of the active frequency offset method is to detect the island by applying a disturbance signal to the output current of the grid-connected inverter. When an island occurs, the frequency will be offset to a certain extent. When the main grid and the microgrid are connected to the grid, the inclusiveness of the main grid keeps the voltage of the point of common coupling (PCC) stable, and the current has no effect on the voltage. As long as the current disturbance is applied appropriately, the frequency offset of the point of common coupling will not exceed the normal range and will generally not affect the normal operation of the system. However, when the main grid is powered off for some reason and an island occurs, the inclusive effect disappears and the island effect occurs. The current offset will cause the frequency of the PCC point voltage to change. At the same time, due to the existence of the output current offset time tz of the grid-connected inverter, a certain positive feedback is generated, thereby increasing the frequency offset of the PCC point voltage. When the frequency offset exceeds the threshold set by the system, the system will detect the formation of an island.

[0071] Preferably, the method further includes improving the active frequency shift method by using a positive feedback mechanism.

[0072] The positive feedback mechanism is characterized by the method shown in the following formula:

[0073] cf n =cf0+F(Δω n )

[0074] In the formula, cf n is the cutoff coefficient of the "n"th cycle, cf0 is the cutoff coefficient of the initial cycle, F(Δω n ) is the angular frequency difference Δω n The positive feedback expression, F(Δω n ) is a linear function, F(Δω n )=kΔω n .

[0075] Positive feedback is applied to the frequency of the output voltage at the grid-connected inverter end, causing its frequency to deviate from the normal value faster. During grid-connected operation, the frequency remains normal due to the phase-locked effect. When the grid is disconnected, the positive feedback mechanism will accelerate the accumulation of frequency changes at the output of the grid-connected inverter. Therefore, after the active frequency deviation method is improved, the area where the islanding effect cannot be detected (i.e., the non-detection area) has been significantly reduced compared to before the improvement.

[0076] 4. Otherwise, the microgrid central controller uses the over / under frequency detection method in the passive method to perform island detection on the microgrid.

[0077] The passive method is a commonly used islanding detection method. It does not require the injection of additional disturbance signals into the microgrid, but instead determines whether an islanding phenomenon occurs by analyzing the changes in the electrical quantities of the microgrid itself. Among them, the over / under frequency detection method is a commonly used method in the passive method.

[0078] Overfrequency detection: When the microgrid is disconnected from the main grid, if the output power of the distributed power source is greater than the load power, the frequency in the microgrid will increase. When the frequency exceeds the preset threshold, it can be judged that an overfrequency island phenomenon has occurred.

[0079] Underfrequency detection: On the contrary, if the output power of the distributed generation is less than the load power, it will cause the frequency in the microgrid to decrease. When the frequency is lower than the preset threshold, it can be judged that underfrequency islanding has occurred.

[0080] The present invention proposes a hybrid island detection method with state switching, which successfully distinguishes two different working states by detecting the matching of the grid-connected inverter power and the load consumption power. This improved method can not only effectively reduce the amount of calculation, but also more accurately identify the state of the microgrid during the island detection process. By paying attention to the matching between the power generated by the grid-connected inverter and the load consumption, it is possible to more accurately judge whether the microgrid is in an island state or connected to the main grid without sacrificing the detection speed. This efficient state discrimination helps to take appropriate measures in a timely manner to ensure the stability and safety of the power system.

[0081] A hybrid island detection method with state switching proposed in the present invention effectively reduces the amount of calculation while taking into account the detection speed, and is expected to provide a more stable and reliable island detection in the microgrid system, thereby ensuring that the power system can be quickly isolated or reconnected when needed, thereby ensuring the continuity of power supply.

[0082] In one embodiment, if Figure 2 As shown, a hybrid island detection device with state switching is provided, comprising a first computing unit, a second computing unit, an active detection unit and a passive detection unit, wherein:

[0083] The first calculation unit is used to calculate the active power and reactive power of the inverter output according to the collected inverter output current, inverter output voltage and common point voltage;

[0084] The second calculation unit is used to calculate the active power and reactive power consumed by the load according to the collected load current and load voltage;

[0085] An active detection unit, used to perform island detection on the microgrid using an active frequency shift method when the microgrid central controller detects that the active power output by the inverter matches the active power consumed by the load, and the reactive power output by the inverter matches the reactive power consumed by the load;

[0086] The passive detection unit is used for the microgrid central controller to perform island detection on the microgrid by adopting the over / under frequency detection method in the passive method.

[0087] A terminal, characterized in that it includes a processor, an input device, an output device and a memory, wherein the processor, the input device, the output device and the memory are interconnected, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is configured to call the program instructions to execute part or all of the steps of any one of the hybrid island detection methods with state switching recorded in the above method embodiments.

[0088] A computer-readable storage medium, characterized in that the computer-readable storage medium stores a computer program, the computer program includes program instructions, and when the program instructions are executed by a processor, the processor executes part or all of the steps of any hybrid island detection method with state switching recorded in the above method embodiments.

[0089] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0090] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A hybrid island detection method with state switching, characterized in that: include: According to the collected inverter output current, inverter output voltage and common point voltage, the active power and reactive power of the inverter output are calculated; According to the collected load current and load voltage, the active power and reactive power consumed by the load are calculated; When the microgrid central controller detects that the active power output by the inverter matches the active power consumed by the load, and the reactive power output by the inverter matches the reactive power consumed by the load, the active frequency shift method is used to perform island detection on the microgrid; Otherwise, the microgrid central controller uses the over / under frequency detection method in the passive method to perform island detection on the microgrid.

2. A hybrid island detection method with state switching as claimed in claim 1, characterized in that: The active power output by the inverter matches the active power consumed by the load, and the reactive power output by the inverter matches the reactive power consumed by the load, including: P load =P inv , Q load =Q inv , Among them, P load and P inv Indicates the active power consumed by the load and the active power output by the inverter, Q load and Q inv Indicates the reactive power consumed by the load and the reactive power output by the inverter.

3. A hybrid island detection method with state switching as claimed in claim 1, characterized in that: Also includes: The active power and reactive power of the inverter output are calculated using the following formula: P inv =V inv ×I inv ×cosΦ inv , Q inv =V inv ×I inv ×sinΦ inv , Where V inv is the inverter output voltage, I inv is the inverter output current, cosΦ inv is the power factor of the inverter output, where sinΦ inv It is the sine value of the inverter output power factor.

4. A hybrid island detection method with state switching as claimed in claim 1, characterized in that: Also includes: The active power and reactive power consumed by the load are calculated using the following formula: P load =V load ×I load ×cosΦ load , Q load =V load ×I load ×sinΦ load , Where V load is the load voltage, I load is the load current, cosΦ load is the power factor of the load, sinΦ load is the sine value of the load power factor.

5. A hybrid island detection method with state switching as claimed in claim 1, characterized in that: Also includes: The active frequency shift method is improved by using a positive feedback mechanism. The positive feedback mechanism is characterized by the method shown in the following formula: cf n =cf0+F(Dω n ) In the formula, cf n is the cutoff coefficient of the "n"th cycle, cf0 is the cutoff coefficient of the initial cycle, F(Δω n ) is the angular frequency difference Δω n The positive feedback expression, F(Δω n ) is a linear function, F(Δω n )=kΔω n .

6. A hybrid island detection device with state switching, characterized in that: It includes a first computing unit, a second computing unit, an active detection unit and a passive detection unit, wherein: The first calculation unit is used to calculate the active power and reactive power of the inverter output according to the collected inverter output current, inverter output voltage and common point voltage; The second calculation unit is used to calculate the active power and reactive power consumed by the load according to the collected load current and load voltage; The active detection unit is used to perform island detection on the microgrid using an active frequency offset method when the microgrid central controller detects that the active power output by the inverter matches the active power consumed by the load, and the reactive power output by the inverter matches the reactive power consumed by the load; The passive detection unit is used for otherwise, the microgrid central controller adopts the over / under frequency detection method in the passive method to perform island detection on the microgrid.

7. A terminal, characterized in that: The method comprises a processor, an input device, an output device and a memory, wherein the processor, the input device, the output device and the memory are interconnected, wherein the memory is used to store a computer program, the computer program comprises program instructions, and the processor is configured to call the program instructions to execute the method according to any one of claims 1 to 5.

8. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, wherein the computer program includes program instructions, and when the program instructions are executed by a processor, the processor is caused to perform the method according to any one of claims 1 to 5.

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