Three-phase photovoltaic inverter islanding detection method and equipment, photovoltaic system

Abstract

The present invention provides a three-phase photovoltaic inverter islanding detection method and device, as well as a photovoltaic system. The method comprises: obtaining a reactive voltage component of a target grid's raw components, extracting an AC component of a preset frequency from the reactive voltage component, generating an islanding disturbance value based on the AC component of the preset frequency, and superimposing the islanding disturbance value on a current setpoint in a target control loop; wherein the target grid's raw components are the grid's raw components corresponding to a target three-phase photovoltaic inverter, and the target control loop is the control loop corresponding to the target three-phase photovoltaic inverter; in response to an internal / external islanding detection trigger signal, obtaining a reactive voltage component of the current target grid's raw components, and determining whether an islanding effect exists based on the cumulative amount of the AC component of the preset frequency contained in the current reactive voltage component. The present invention can minimize the impact on system power quality while ensuring islanding detection capabilities.

Description

Technical Field

[0001] The present invention belongs to the technical field of island detection, and more specifically, relates to a three-phase photovoltaic inverter island detection method and device, and a photovoltaic system. Background Art

[0002] In the field of photovoltaic grid-connected systems, the islanding effect occurs when the photovoltaic system fails to detect the outage and is unable to disconnect from the utility grid due to a power outage, such as a fault or maintenance outage. This creates a self-sufficient power supply island, where the photovoltaic system supplies power to surrounding loads. Generally speaking, the islanding effect can adversely affect the entire distribution system and user-side equipment. Therefore, timely detection of the islanding effect is crucial.

[0003] Existing islanding detection methods primarily include passive and active detection. Passive detection methods do not require additional hardware circuitry, but they lose their ability to detect islanding when the PV system's output power is balanced with the local load power. Active detection methods avoid these drawbacks, offering high detection accuracy and a small non-detection zone. However, they are more complex to control and can potentially degrade the quality of the PV system's output power.

[0004] Therefore, how to ensure the islanding detection capability while minimizing the impact on the system power quality has become an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] The object of the present invention is to provide a three-phase photovoltaic inverter islanding detection method and device, and a photovoltaic system, so as to minimize the impact on the system power quality while ensuring the islanding detection capability.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is to provide a three-phase photovoltaic inverter islanding detection method, comprising:

[0007] Obtaining a reactive voltage component of the original component of the target power grid, extracting an AC component of a preset frequency from the reactive voltage component, generating an islanding disturbance amount based on the AC component of the preset frequency, and superimposing the islanding disturbance amount on a current set value in a target control loop;

[0008] The target grid original component is the grid original component corresponding to the target three-phase photovoltaic inverter, and the target control loop is the control loop corresponding to the target three-phase photovoltaic inverter;

[0009] In response to an internal / external islanding detection trigger signal, the reactive voltage component of the current target grid original component is obtained, and whether an islanding effect exists is determined based on the cumulative amount of the AC component of the preset frequency contained in the current reactive voltage component.

[0010] In a possible implementation, extracting the AC component of a preset frequency from the reactive voltage component includes:

[0011] The reactive voltage component is filtered based on a filter of a preset frequency to obtain an AC component of a preset frequency.

[0012] In a possible implementation, the filter based on the preset frequency performs filtering processing on the reactive voltage component, including:

[0013] Through U xhz =BPF(u q ) calculating an AC component of a preset frequency;

[0014] Among them, U xhz is the AC component with a preset frequency of x, u q is the reactive voltage component, and BPF represents a band-pass filter.

[0015] In a possible implementation, generating the islanding disturbance amount based on the AC component of the preset frequency includes:

[0016] By I island =K*i ref *U xhz Get the island disturbance amount;

[0017] Among them, U xhz is the AC component of the preset frequency, K is the preset disturbance coefficient, i ref is the current given value corresponding to the target three-phase photovoltaic inverter, I island is the island disturbance.

[0018] In a possible implementation, the preset disturbance coefficient is calculated as follows:

[0019] K=a*U rate 2 / P

[0020] Wherein, K is the preset disturbance coefficient, a is the preset proportional coefficient, and U rate is the rated voltage of the target three-phase photovoltaic inverter, and P is the rated power of the target three-phase photovoltaic inverter.

[0021] In a possible implementation, before superimposing the islanding disturbance amount onto the current set value in the target control loop, the three-phase photovoltaic inverter islanding detection method further includes:

[0022] performing a limiting process on the islanding disturbance amount;

[0023] The amplitude limiting value corresponding to the amplitude limiting process is positively correlated with the maximum value of the current given value corresponding to the target three-phase photovoltaic inverter.

[0024] In a possible implementation, the preset frequency range is 5-10 Hz.

[0025] In a possible implementation, determining whether an islanding effect exists based on the cumulative amount of an AC component of a preset frequency included in the current reactive voltage component includes:

[0026] If the cumulative amount of the AC component of the preset frequency contained in the current reactive voltage component is greater than the preset threshold, it is determined that an islanding effect exists;

[0027] If the cumulative amount of the AC component of the preset frequency included in the current reactive voltage component is not greater than the preset threshold, it is determined that no islanding effect exists.

[0028] In another aspect of the present invention, a three-phase photovoltaic inverter islanding detection device is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the three-phase photovoltaic inverter islanding detection method described above are implemented.

[0029] In another aspect of the present invention, a photovoltaic system is provided, comprising:

[0030] The above-mentioned three-phase photovoltaic inverter islanding detection equipment.

[0031] The three-phase photovoltaic inverter islanding detection method and device, and the photovoltaic system provided by the present invention have the following beneficial effects:

[0032] First, the present invention performs islanding detection based on an active detection method of reactive disturbance, which can effectively ensure the islanding detection capability. The reactive disturbance method can also minimize the impact on the electrical parameters of the three-phase photovoltaic inverter itself.

[0033] Secondly, the present invention extracts the AC component from the reactive component of the three-phase photovoltaic inverter itself (the original component of the power grid) and generates a reactive disturbance quantity based on the AC component. The method of "generating reactive disturbance quantity based on the voltage parameters of the three-phase photovoltaic inverter itself" can better reduce the impact of the disturbance process on the electrical parameters of the three-phase photovoltaic inverter because there is no artificially introduced disturbance, thereby ensuring the power quality of the three-phase photovoltaic inverter. Compared with the method of "generating disturbance quantity based on frequency" commonly used in the prior art, "generating reactive disturbance quantity based on AC component" can also effectively reduce the degree of dependence of island detection on the grid frequency resolution, making the present invention more reliable than the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 A schematic flow chart of a method for detecting islanding in a three-phase photovoltaic inverter according to an embodiment of the present invention;

[0036] Figure 2 A schematic diagram of the structure of a three-phase photovoltaic inverter islanding detection device provided by an embodiment of the present invention;

[0037] Figure 3 A calculation loop diagram of the islanding disturbance amount provided by one embodiment of the present invention;

[0038] Figure 4 A partial control loop diagram of a three-phase photovoltaic inverter provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Please refer to Figure 1 , Figure 1 A schematic flow chart of a method for detecting islanding of a three-phase photovoltaic inverter according to an embodiment of the present invention is provided. The method comprises:

[0042] S101: Obtain the reactive voltage component of the original component of the target power grid, extract the AC component of a preset frequency from the reactive voltage component, generate an islanding disturbance amount based on the AC component of the preset frequency, and superimpose the islanding disturbance amount on the current set value in the target control loop.

[0043] In this embodiment, the target grid raw components are the grid raw components corresponding to the target three-phase photovoltaic inverter, and the target control loop is the control loop corresponding to the target three-phase photovoltaic inverter. The target control loop is used to control the active and reactive power of the target three-phase photovoltaic inverter by controlling the active and reactive power of the grid current. The target control loop can be an existing control loop, and its detailed structure is not further described here.

[0044] In this embodiment, step S101 is essentially a disturbance step before performing islanding detection, that is, a corresponding islanding disturbance amount is generated based on the AC component of a preset frequency extracted from the reactive voltage component, and reactive disturbance is achieved by superimposing the islanding disturbance amount on the current set value in the target control loop.

[0045] S102: In response to an internal / external islanding detection trigger signal, obtain the reactive voltage component of the current target grid original component, and determine whether there is an islanding effect based on the cumulative amount of the AC component of the preset frequency contained in the current reactive voltage component.

[0046] In this embodiment, when islanding detection is required (i.e., when an internally transmitted or externally input islanding detection signal is received), the reactive voltage component of the current target power grid original component can be obtained. It is known that a reactive disturbance has occurred in step S101. When the power grid is operating normally, due to the presence of the power grid, the AC component disturbance of the preset frequency cannot be detected, and the AC component of the preset frequency will not accumulate. Once a power grid fault occurs, the islanding disturbance continues, and the AC component of the preset frequency will rapidly accumulate. At this time, detecting the accumulated amount of the AC component of the preset frequency contained in the current reactive voltage component can determine whether an islanding effect exists.

[0047] From the above description, it can be seen that, first, the embodiment of the present invention performs island detection based on an active detection method of reactive disturbance, which can effectively ensure the island detection capability. The reactive disturbance method can also minimize the impact on the electrical parameters of the three-phase photovoltaic inverter itself. Secondly, the embodiment of the present invention extracts the AC component from the reactive component of the three-phase photovoltaic inverter itself (the original component of the power grid) and generates the reactive disturbance quantity based on the AC component. The method of "generating the reactive disturbance quantity based on the voltage parameter of the three-phase photovoltaic inverter itself" can better reduce the impact of the disturbance process on the electrical parameters of the three-phase photovoltaic inverter because there is no artificially introduced disturbance, thereby ensuring the power quality of the three-phase photovoltaic inverter. The "generating the reactive disturbance quantity based on the AC component" can also effectively reduce the dependence of the island detection on the power grid frequency resolution compared to the "generating the disturbance quantity based on the frequency" method commonly used in the prior art, making the embodiment of the present invention more reliable than the prior art.

[0048] In one possible implementation, before obtaining the reactive voltage component of the original component of the target power grid, the three-phase photovoltaic inverter islanding detection method further includes:

[0049] Get the original components of the target power grid.

[0050] The original components of the target power grid are subjected to double-quadruple generalized integral phase-locked processing and Park transformation in sequence to obtain the reactive voltage components of the original components of the target power grid.

[0051] In this embodiment, before obtaining the reactive voltage component of the original component of the target power grid, the three-phase photovoltaic inverter islanding detection method may further include: determining the reactive voltage component of the original component of the target power grid.

[0052] Among them, the step of determining the reactive voltage component of the original component of the target power grid is: performing double second-order generalized integral phase-locked processing and Park transformation (that is, converting from the αβ coordinate system to the dq coordinate system) on the original component of the target power grid in sequence, and the reactive voltage component of the original component of the target power grid can be obtained.

[0053] In one possible implementation, extracting an AC component of a preset frequency from a reactive voltage component includes:

[0054] The filter based on the preset frequency performs filtering processing on the reactive voltage component to obtain an AC component of the preset frequency.

[0055] In this embodiment, the reactive voltage component can be directly filtered using a filter of a preset frequency to obtain an AC component of a preset frequency. For example, if a 5 Hz AC component is extracted, the reactive voltage component can be filtered using a 5 Hz filter to obtain a 5 Hz AC component. Specifically, filtering the reactive voltage component using a filter of a preset frequency can be described in detail as follows:

[0056] Through U xhz =BPF(u q ) calculates the AC component of a preset frequency.

[0057] Among them, U xhz is the AC component with a preset frequency of x, u q is the reactive voltage component, and BPF represents a bandpass filter. Optionally, filtering of the reactive voltage component can also be implemented using a second-order generalized integrator.

[0058] In this embodiment, the extraction of the AC component of the preset frequency from the reactive voltage component can also be achieved by using a notch filter. For example: the reactive voltage component can be processed based on the notch filter of the preset frequency, and then the AC component of the preset frequency can be obtained based on the processed reactive voltage component. Specifically, the reactive voltage component can be directly processed by the notch filter of the preset frequency to obtain the reactive voltage component after the notch filter processing, and then the AC component of the preset frequency can be obtained by subtracting the reactive voltage component processed by the notch filter by 1. For example, if the 5Hz AC component is extracted, the reactive voltage component can be processed by the 5Hz notch filter, and then the 5Hz AC component can be obtained by subtracting the reactive voltage component processed by the notch filter by 1. That is, the AC component of the preset frequency is obtained based on the reactive voltage component processed by the notch filter, which can be described in detail as follows: by U xhz =1-U' xhzCalculate the AC component of the preset frequency. xhz is the AC component of the preset frequency, U' xhz is the reactive voltage component after notch filter processing.

[0059] In a possible implementation, generating an islanding disturbance amount based on an AC component of a preset frequency includes:

[0060] By I island =K*i ref *U xhz Get the island disturbance amount.

[0061] Among them, U xhz is the AC component of the preset frequency, K is the preset disturbance coefficient, i ref is the current given value corresponding to the target three-phase photovoltaic inverter, I island is the island disturbance.

[0062] In this embodiment, the islanding disturbance amount is associated with the current set value corresponding to the target three-phase photovoltaic inverter, which can better limit the size of the islanding disturbance amount within a certain range, and is conducive to reducing the impact of the islanding disturbance amount on the power quality of the photovoltaic system (where the target three-phase photovoltaic inverter is located).

[0063] In a possible implementation, the preset disturbance coefficient is calculated as follows:

[0064] K=a*U rate 2 / P

[0065] Among them, K is the preset disturbance coefficient, a is the preset proportional coefficient, U rate is the rated voltage of the target three-phase photovoltaic inverter, and P is the rated power of the target three-phase photovoltaic inverter.

[0066] In this embodiment, compared with the method of directly limiting the value of K based on experience, setting K to be related to the rated voltage and rated power of the target three-phase photovoltaic inverter can better take into account the disturbance tolerance of the system itself where the target three-phase photovoltaic inverter is located, thereby helping to reduce the impact on the system power quality during the disturbance.

[0067] In one possible implementation, before superimposing the islanding disturbance value onto the current set value in the target control loop, the three-phase photovoltaic inverter islanding detection method further includes:

[0068] The island disturbance is limited.

[0069] The amplitude limiting value corresponding to the amplitude limiting process is positively correlated with the maximum value of the current given value corresponding to the target three-phase photovoltaic inverter.

[0070] To minimize the increase in the AC component of the output current corresponding to the target three-phase photovoltaic inverter, this embodiment may further perform a limit operation on the islanding disturbance before adding it to the current setpoint in the target control loop. The limit value corresponding to the limit operation may be positively correlated with the maximum value of the current setpoint corresponding to the target three-phase photovoltaic inverter.

[0071] In a possible implementation, the preset frequency range is 5-10 Hz.

[0072] In this embodiment, in order to prevent the AC component from oscillating, the range of the preset frequency needs to be much smaller than the fundamental wave 50Hz. On this basis, in order to further meet the period of islanding protection (2s is taken as an example in this embodiment), the value of a single cycle of the AC component is more appropriately between 0.5Hz and 5Hz. However, the value of 0.5Hz can only cover one cycle, which is too short. It is more appropriate to take 5-10 cycles. Therefore, this embodiment sets the preset frequency range between 5-10Hz, thereby ensuring the effect of islanding detection while avoiding AC component oscillation.

[0073] In one possible implementation, determining whether an islanding effect exists based on the cumulative amount of an AC component of a preset frequency included in a current reactive voltage component includes:

[0074] If the cumulative amount of the AC component of the preset frequency contained in the current reactive voltage component is greater than a preset threshold, it is determined that an islanding effect exists.

[0075] If the cumulative amount of the AC component of the preset frequency included in the current reactive voltage component is not greater than the preset threshold, it is determined that no islanding effect exists.

[0076] In this embodiment, if a power grid failure occurs, the presence of an islanding disturbance will cause the AC component of a preset frequency to continue to accumulate and exceed a certain threshold. Therefore, this embodiment can determine whether there is an islanding effect by detecting whether the cumulative amount of the AC component of a preset frequency contained in the current reactive voltage component is greater than the preset threshold.

[0077] In this embodiment, the method for extracting the cumulative amount of the AC component of the preset frequency contained in the current reactive voltage component can be: extracting the absolute value of the AC component of the preset frequency contained in the current reactive voltage component and integrating it, and low-pass filtering the absolute value of the integrated AC component to obtain the cumulative amount of the AC component of the preset frequency contained in the current reactive voltage component.

[0078] In this embodiment, the preset threshold may be associated with the aforementioned islanding disturbance amount to improve the accuracy of islanding detection.

[0079] In a possible implementation, the loop diagram for calculating the islanding disturbance amount can be as follows: Figure 3 As shown ( Figure 3 Take the preset frequency as 5Hz as an example), where u q is the reactive voltage component of the original component of the target grid, K is the preset disturbance coefficient, i ref is the current given value corresponding to the target three-phase photovoltaic inverter, I island is the island disturbance. Figure 3 The 5Hz notch filter is used to filter u q After processing, the u after processing with 1 minus notch filter q You can get the 5Hz AC component (which can be recorded as U 5hz ), on this basis, according to I island =K*i ref *U 5hz The island disturbance I can be obtained island .

[0080] Based on the above embodiments, you can refer to Figure 4 ( Figure 4 in,i ref is the current given value corresponding to the target three-phase photovoltaic inverter, i Lfb is the output current of the target three-phase photovoltaic inverter, U grid is the original component of the target power grid), and the island disturbance quantity I is obtained island Afterwards, I island Superimposed on the current given value i ref Then, reactive disturbance is realized. q The accumulated amount of the 5Hz AC component in the PWM is used to determine whether there is an islanding effect and whether to trigger the islanding protection action.

[0081] Please refer to Figure 2In another aspect, the present invention further provides a three-phase photovoltaic inverter islanding detection device 200, comprising: one or more processors 201, one or more input devices 202, one or more output devices 203, and one or more memories 204. The processors 201, input devices 202, output devices 203, and memories 204 communicate with each other via a communication bus 205. The memory 204 is used to store computer programs, which include program instructions. The processor 201 is used to execute the program instructions stored in the memory 204. The processor 201 is configured to invoke the program instructions to execute the steps of the above-described method embodiments. It should be understood that in the embodiments of the present invention, the processor 201 may be a central processing unit (CPU). The processor may also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may be any conventional processor, etc. The input device 202 may include a touchpad, a fingerprint sensor (for collecting the user's fingerprint information and fingerprint direction information), a microphone, etc., and the output device 203 may include a display (LCD, etc.), a speaker, etc. The memory 204 may include a read-only memory and a random access memory, and provide instructions and data to the processor 201. A portion of the memory 204 may also include a non-volatile random access memory. For example, the memory 204 may also store information about the device type. In a specific implementation, the processor 201, the input device 202, and the output device 203 described in the embodiment of the present invention may execute the implementation method described in the first embodiment and the second embodiment of the three-phase photovoltaic inverter island detection method provided in the embodiment of the present invention.

[0082] In another aspect of the present invention, a photovoltaic system is provided, comprising:

[0083] The three-phase photovoltaic inverter islanding detection equipment described above.

[0084] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A three-phase photovoltaic inverter islanding detection method, characterized in that: include: Obtaining a reactive voltage component of the original component of the target power grid, extracting an AC component of a preset frequency from the reactive voltage component, generating an islanding disturbance amount based on the AC component of the preset frequency, and superimposing the islanding disturbance amount on a current set value in a target control loop; The target grid original component is the grid original component corresponding to the target three-phase photovoltaic inverter, and the target control loop is the control loop corresponding to the target three-phase photovoltaic inverter; In response to an internal / external islanding detection trigger signal, the reactive voltage component of the current target grid original component is obtained, and whether an islanding effect exists is determined based on the cumulative amount of the AC component of a preset frequency contained in the current reactive voltage component; wherein the preset frequency range is 1 / 10 to 1 / 5 of the fundamental frequency; Generating an islanding disturbance amount based on the AC component of the preset frequency includes: pass Get the island disturbance amount; in, is the AC component of the preset frequency, is the preset disturbance coefficient, is the current given value corresponding to the target three-phase photovoltaic inverter, is the island disturbance.

2. The three-phase photovoltaic inverter islanding detection method according to claim 1, wherein: The step of extracting the AC component of a preset frequency from the reactive voltage component comprises: The reactive voltage component is filtered based on a filter of a preset frequency to obtain an AC component of a preset frequency.

3. The three-phase photovoltaic inverter islanding detection method according to claim 2, wherein: The filter based on the preset frequency performs filtering processing on the reactive voltage component, comprising: pass Calculate the AC component of the preset frequency; in, The preset frequency is The AC component, is the reactive voltage component, Represents a bandpass filter.

4. The three-phase photovoltaic inverter islanding detection method according to claim 1, wherein: The calculation method of the preset disturbance coefficient is: in, is the preset disturbance coefficient, is the preset scale factor, is the rated voltage of the target three-phase photovoltaic inverter, is the rated power of the target three-phase photovoltaic inverter.

5. The three-phase photovoltaic inverter islanding detection method according to claim 1, wherein: Before superimposing the islanding disturbance amount onto the current set value in the target control loop, the three-phase photovoltaic inverter islanding detection method further includes: performing a limiting process on the islanding disturbance amount; The amplitude limiting value corresponding to the amplitude limiting process is positively correlated with the maximum value of the current given value corresponding to the target three-phase photovoltaic inverter.

6. The three-phase photovoltaic inverter islanding detection method according to any one of claims 1 to 5, characterized in that: The preset frequency range is 5-10 Hz.

7. The three-phase photovoltaic inverter islanding detection method according to any one of claims 1 to 5, characterized in that: The determining whether an islanding effect exists based on the cumulative amount of the AC component of the preset frequency contained in the current reactive voltage component includes: If the cumulative amount of the AC component of the preset frequency contained in the current reactive voltage component is greater than the preset threshold, it is determined that an islanding effect exists; If the cumulative amount of the AC component of the preset frequency included in the current reactive voltage component is not greater than the preset threshold, it is determined that no islanding effect exists.

8. A three-phase photovoltaic inverter islanding detection device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

9. A photovoltaic system, characterized in that: It includes the three-phase photovoltaic inverter islanding detection device as described in claim 8.

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