A hybrid method and system for island detection of a photovoltaic grid-connected system

Abstract

This invention relates to the field of islanding detection technology, and provides a hybrid islanding detection method and system for photovoltaic grid-connected systems. The method includes: if the system is outside the blind zone, islanding detection is performed using a voltage-phase angle variation method: acquiring the voltage amplitude and power factor angle at the common coupling point; when the criterion composed of the voltage amplitude and power factor angle exceeds a set threshold, the photovoltaic grid-connected system is determined to be in an islanded state. If the system is within the blind zone, islanding detection is performed using an improved sliding film frequency shift method: monitoring the frequency of the common coupling point and calculating the frequency deviation; when the frequency deviation is less than a set frequency threshold, applying a low-gain phase perturbation; when the frequency deviation is greater than or equal to the set frequency threshold, applying a high-gain phase perturbation; when the detected frequency of the common coupling point exceeds the detection threshold, the photovoltaic grid-connected system is determined to be in an islanded state. This method improves the coverage of islanding detection and reduces the impact on power grid quality.

Description

Technical Field

[0001] This invention belongs to the field of islanding detection technology, and particularly relates to a hybrid islanding detection method and system for photovoltaic grid-connected systems. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With the high penetration rate of distributed power sources, the operating characteristics of power distribution networks are becoming increasingly complex, which places more stringent requirements on the grid connection performance and safety protection standards of grid-connected inverters.

[0004] When the grid experiences a power outage due to a fault or planned maintenance, if the grid-connected inverter fails to detect the grid disconnection in time and continues to supply power to the local load, an uncontrolled independent power supply island will be formed. This operating state not only endangers the personal safety of on-site maintenance personnel but may also damage electrical equipment due to the uncontrolled voltage and frequency of the islanded system. Furthermore, it will cause asynchronous closing shocks when the grid restores power, resulting in a secondary impact on the photovoltaic grid-connected system.

[0005] Islanding detection is a crucial technology for ensuring the safe operation of grid-connected photovoltaic (PV) systems. It prevents PV inverters from continuing to supply power during grid failures, thus avoiding equipment damage or safety accidents. As a core line of defense against unplanned islanding operation and ensuring the safety of equipment and personnel, the importance of islanding detection technology is becoming increasingly prominent.

[0006] Currently, the main island detection methods can be divided into two categories: passive detection and active detection. Passive detection determines islanding status by monitoring changes in electrical quantities such as voltage and frequency at the point of common coupling. Although it is simple to implement and does not affect power quality, it has a detection blind spot when the output of distributed power sources is basically balanced with the power of local loads. Active detection improves detection reliability by injecting specific disturbance signals into the power grid and observing the system response. Although it can effectively eliminate detection blind spots, the simultaneous injection of disturbances by multiple distributed power sources may cause mutual interference and have a potential impact on the power quality of the power grid. Summary of the Invention

[0007] To address the technical problems mentioned above, this invention provides a hybrid islanding detection method and system for photovoltaic grid-connected systems. By detecting the blind zone of passive methods, it switches in real time between the voltage-phase angle change method and the improved sliding film frequency shift method, thereby improving the coverage of islanding detection, solving the blind zone problem in traditional passive detection methods, and reducing the impact on power grid quality.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of the present invention provides a hybrid islanding detection method for a photovoltaic grid-connected system, comprising: Obtain local load parameter information, calculate the power imbalance, determine the blind zone range based on the power imbalance, and determine whether the photovoltaic grid-connected system is within the blind zone range: If the system is outside the blind zone, the voltage-phase angle change method is used for islanding detection: the voltage amplitude and power factor angle at the common coupling point are obtained. When the criterion composed of the voltage amplitude and power factor angle exceeds the set criterion threshold, the photovoltaic grid-connected system is determined to be in an islanding state. If the system is within the blind zone, the improved sliding plate frequency shift method is used for islanding detection: monitor the frequency of the common coupling point and calculate the frequency deviation; when the frequency deviation is less than the set frequency threshold, apply a phase perturbation with a low gain coefficient; when the frequency deviation is greater than or equal to the set frequency threshold, apply a phase perturbation with a high gain coefficient; when the frequency of the common coupling point is detected to exceed the detection threshold, the photovoltaic grid-connected system is determined to be in an islanded state.

[0009] Furthermore, the power imbalance: ; ; ; ; ; in, R , L , C These are the equivalent resistance, inductance, and capacitance of the local load, respectively. U g The rated operating voltage of the power grid; P load and Q load These are the active and reactive power delivered by the DG to the local load, respectively. Represents the angular frequency of the power grid, Δ Q This represents the difference between the reactive power required by the local load and the reactive power output by the inverter, Δ. P This represents the difference between the active power required by the local load and the active power output of the inverter. Q inv This indicates the reactive power output of the photovoltaic inverter. P inv This indicates the active power output of the photovoltaic inverter.

[0010] Furthermore, the range of the blind zone is: ; ; Among them, Tset_high and T set_low These are the upper and lower boundary thresholds of the blind zone range, where U0 represents the rated voltage during normal grid operation, and Δ Q This represents the difference between the reactive power required by the local load and the reactive power output by the inverter, Δ. P This represents the difference between the active power required by the local load and the active power output of the inverter. P load and Q load These represent the active and reactive power delivered by the DG to the local load, respectively.

[0011] Furthermore, the criterion composed of the voltage amplitude and the power factor angle is: ; Among them, △ u The voltage amplitude at the common coupling point. The power factor angle, u This is the voltage at the common coupling point.

[0012] Furthermore, the phase perturbation of the low gain coefficient is: ;in, f g The rated frequency of the power grid. f For the common coupling point frequency, β The hyperbolic tangent shape factor is... K low The first gain coefficient is determined when the contribution of the total harmonic distortion rate of the grid-connected current is lower than the requirement.

[0013] Furthermore, the phase perturbation of the high gain coefficient is: ;in, f g The rated frequency of the power grid. f For the common coupling point frequency, β The hyperbolic tangent shape factor is... K high The second gain coefficient is determined when the slope of the SMS curve is greater than the slope of the load impedance phase.

[0014] Furthermore, it also includes: after determining that the photovoltaic grid-connected system is in an islanded state, triggering an islanding alarm and performing corresponding protection actions, such as disconnecting the circuit breaker at the common coupling point or switching to islanded mode operation.

[0015] A second aspect of the present invention provides a hybrid islanding detection system for a photovoltaic grid-connected system, comprising: The blind zone identification module is configured to: acquire local load parameter information, calculate the power imbalance, determine the blind zone range based on the power imbalance, and determine whether the photovoltaic grid-connected system is within the blind zone range. The first islanding detection module is configured to: if it is outside the blind zone, use the voltage-phase angle change method to detect islanding: obtain the voltage amplitude and power factor angle at the common coupling point; when the criterion composed of voltage amplitude and power factor angle exceeds the set criterion threshold, determine that the photovoltaic grid-connected system is in an islanding state. The second islanding detection module is configured to: if the system is within the blind zone, use the improved sliding plate frequency shift method for islanding detection: monitor the frequency of the common coupling point and calculate the frequency deviation; when the frequency deviation is less than the set frequency threshold, apply a phase perturbation with a low gain coefficient; when the frequency deviation is greater than or equal to the set frequency threshold, apply a phase perturbation with a high gain coefficient; when the frequency of the common coupling point is detected to exceed the detection threshold, the photovoltaic grid-connected system is determined to be in an islanded state.

[0016] A third aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the hybrid islanding detection method for a photovoltaic grid-connected system as described above.

[0017] A fourth aspect of the present invention provides a computer device including a computer-readable storage medium, a processor, and a computer program stored on the computer-readable storage medium and executable on the processor, wherein the processor executes the program to implement the steps of the hybrid islanding detection method for a photovoltaic grid-connected system as described above.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This invention improves the coverage of island detection by detecting the blind zone of passive methods and switching in real time between voltage-phase angle change method and improved sliding film frequency shift method, thus solving the blind zone problem in traditional passive detection methods and reducing the impact on power grid power quality.

[0019] This invention uses an improved sliding membrane frequency shift method after the passive method fails, reducing the power quality problems that the improved sliding membrane frequency shift method may cause, avoiding additional disturbances to the power grid, and solving the contradiction between the traditional SMS method and the mutual constraints between the detection blind zone (NDZ) and the power quality (THD).

[0020] The voltage-phase angle change method of the present invention can effectively amplify the islanding characteristics and significantly reduce the detection blind zone under power matching conditions by coupling voltage and phase angle change characteristics. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0022] Figure 1 This is a flowchart of a hybrid islanding detection method for a photovoltaic grid-connected system according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of a distributed photovoltaic system simulation model according to Embodiment 1 of the present invention; Figure 3 This is a simplified circuit diagram of a distributed photovoltaic system according to Embodiment 1 of the present invention; Figure 4 This is a comparison diagram of the blind zone range of the passive detection method based on voltage-phase angle change and the overvoltage method in Embodiment 1 of the present invention; Figure 5 This is a waveform diagram of the voltage-phase angle criterion in scenario 1 of embodiment 1 of the present invention; Figure 6 This is a waveform diagram of the voltage-phase angle criterion in scenario 2 of embodiment 1 of the present invention; Figure 7 This is a waveform diagram of the frequency in scenario 2 of embodiment 1 of the present invention; Figure 8 This is a schematic diagram of the structure of a computer device according to Embodiment 4 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0024] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] Example 1 This embodiment provides a hybrid islanding detection method for photovoltaic grid-connected systems.

[0026] This embodiment provides a hybrid islanding detection method for photovoltaic grid-connected systems, aiming to achieve more efficient and accurate islanding detection.

[0027] This embodiment provides a hybrid islanding detection method for photovoltaic grid-connected systems. Its innovations lie in the following aspects: the detection method based on voltage-phase angle change amplifies voltage fluctuations through phase angle change, thereby improving the sensitivity of passive detection; and it proposes a sliding film frequency shift method based on segmented perturbation to reduce actively injected harmonic interference; by using two algorithms to switch the blind zone of the passive detection method in real time, the blind zone problem existing in the traditional passive detection method is solved, and the impact on the power quality of the power grid is reduced.

[0028] This embodiment provides a hybrid islanding detection method for a photovoltaic grid-connected system. First, a passive method is used to calculate the blind zone. Outside the blind zone, a passive detection method based on voltage-phase angle change is adopted to ensure timely detection and processing of the islanding effect without affecting power quality, thereby improving the safety and stability of system operation. Inside the blind zone, an improved sliding film frequency shift method is adopted, which has higher reliability and stronger adaptability.

[0029] This embodiment provides a hybrid islanding detection method for photovoltaic grid-connected systems. By combining multiple detection technologies and monitoring from multiple dimensions, it can more accurately distinguish between normal operation and islanding states, while minimizing the impact on power quality.

[0030] This embodiment provides a hybrid islanding detection method for photovoltaic grid-connected systems, such as... Figure 1 As shown, it includes the following steps: Step 1: Calculate the applicable range of the passive detection method for voltage-phase angle changes. Within the applicable range, the passive detection method for voltage-phase angle changes is used; outside the applicable range, the improved sliding plate frequency shift method is used. The specific applicable range, i.e., the calculation process for the dead zone of voltage-phase angle changes, is as follows: Step 101: Collect local load parameter information and the inverter's output current, output voltage, and common coupling point voltage, and calculate the power imbalance using the following formula: ; ; ; ; ; in, R , L , C These are the equivalent resistance, inductance, and capacitance of the local load, respectively. U g The rated operating voltage of the power grid; P load and Q load These are the active and reactive power delivered by the DG to the local load, respectively. Represents the angular frequency of the power grid, Δ Q This represents the difference between the reactive power required by the local load and the reactive power output by the inverter, Δ. P This represents the difference between the active power required by the local load and the active power output of the inverter. Q inv This indicates the reactive power output of the photovoltaic inverter. P inv This indicates the active power output of the photovoltaic inverter.

[0031] Step 102: Based on the power imbalance calculated in Step 101, calculate the blind zone of the passive detection method based on voltage-phase angle, as shown in the following formula: ; ; Among them, T set_high and T set_low These are the upper and lower boundary thresholds of the criteria for the passive detection method of voltage-phase angle change, respectively, and U0 represents the rated voltage value when the power grid is operating normally.

[0032] Step 2: When the blind zone formula calculated above is not met, i.e., when outside the blind zone range, islanding detection is performed using the voltage-phase angle change method (i.e., a passive detection method based on voltage and phase angle changes): Obtain the voltage amplitude Δ at the common coupling point. u and power factor angle When the criterion T, composed of voltage amplitude and power factor angle, exceeds the set criterion threshold, the photovoltaic grid-connected system is determined to be in an islanded state.

[0033] When islanding occurs, the grid voltage at the point of common coupling of the photovoltaic grid-connected system u As a photovoltaic grid-connected system transitions from grid-connected to off-grid mode, without the support of a large power grid, voltage fluctuations occur. Simultaneously, upon entering islanded mode, the power factor angle shifts from its original zero. It will break away from its original value of 0 and become a value less than 1, resulting in a combined voltage. u and The mathematical relationship can be used to set criteria: ; When the criterion condition is met, that is, when When T>T is detected set_high This proves that they are in an isolated state; when When T was detected <T set_low This proves that the island is in a state of isolation.

[0034] In addition, considering that voltage disturbances may cause false triggering, a 1-second delay is set. If the above conditions continue for 1 second, the system is determined to be in an islanded state.

[0035] Compared to the traditional overvoltage method, the passive detection method of voltage-phase angle change can amplify voltage changes, speed up detection, and reduce the blind zone.

[0036] Step 3: When the blind zone formula calculated above is satisfied, that is, when it is within the blind zone range, the improved sliding membrane frequency shift method is activated.

[0037] The specific implementation principle of the improved sliding plate frequency shift method is as follows: a piecewise variable gain controller is used. When the power grid is operating normally, the frequency deviation is within a safe range. The controller automatically adopts a minimum gain to minimize the impact on system harmonics and ensure stable power quality. Once the frequency deviation is detected to exceed the preset trigger threshold, indicating that islanding may occur, the controller immediately switches to a high gain and rapidly amplifies the frequency offset through strong feedback, thereby quickly confirming the islanding.

[0038] The improved sliding film frequency shift method perturbs the phase of the inverter output current. Specifically, it involves real-time monitoring of the common coupling point frequency and calculating the frequency deviation; when the frequency deviation | ff g | Less than the set frequency threshold When applying a phase perturbation with a low gain coefficient; when the frequency deviation | ff g | Greater than or equal to the set frequency threshold At that time, a phase perturbation with a high gain coefficient is applied; after the perturbation is injected, the frequency of the common coupling point is detected. When the frequency after the perturbation exceeds the detection threshold, i.e., greater than f... max or less than f min This indicates that the area is currently in an isolated state.

[0039] Disturbing the output current phase of the photovoltaic inverter creates a phase difference between it and the grid voltage. This disturbance causes a change in the frequency of the PCC point. The presence of the disturbance phase leads to a continuous shift in the grid frequency, making it an effective means of islanding detection.

[0040] The phase perturbation formula is as follows: ; in, f g The rated frequency of the power grid. f The measured common point frequency, To determine the boundary between low-gain and high-gain disturbances, the meaning of the remaining parameters and the tuning principles will be explained below: First, regarding the hyperbolic tangent shape factor The value of 2.5 is set to ensure that the frequency shift curve has significant linearity and maximized first derivative in the early stage of the fault (i.e., within the deviation range of 0~0.5Hz), thereby providing sufficient positive feedback starting torque at the moment of islanding. In the low-gain stage, the introduced phase disturbance is minimal. Under the condition that the contribution of the total harmonic distortion (THD) of the grid-connected current is far less than the national standard requirement of 5%, the steady-state gain (first gain coefficient) can be calculated. K low It is 0.052 rad, used to maintain low harmonic distortion in steady state; During the high-gain phase K high The core theory behind the value of Q is that to eliminate the detection dead zone (NDZ), the slope of the SMS curve must be greater than the slope of the load impedance phase; for high-quality factor loads (assuming Q...), f =2.5), and its phase change slope near the resonant frequency can be approximated as: ; in, f 0 represents the resonant frequency of the load.

[0041] The SMS curve is near the incision point. Therefore, the slope of the SMS curve can be approximated as: ; To meet ; At the same time, due to K high It intervenes at 0.1Hz. To ensure "absolute suppression," a margin of 2-3 times the load slope is typically taken, hence the setting of a second gain coefficient. K high =0.314rad, used to eliminate detection blind spots in the transient phase after islanding is determined.

[0042] Step 4: After determining that the photovoltaic grid-connected system is in islanded state, trigger the islanding alarm and perform corresponding protection actions, such as disconnecting the circuit breaker at the common coupling point or switching to islanded mode operation.

[0043] This embodiment, based on voltage-phase angle variation and an improved sliding film frequency shift method, first calculates the power imbalance by collecting electrical parameters at the common coupling point, thus defining the blind zone range of passive detection. Then, a regional detection strategy is adopted: outside the blind zone, the voltage-phase angle variation passive detection method is used, amplifying voltage fluctuation characteristics by establishing a coupling relationship between voltage amplitude and power factor angle, thereby achieving rapid islanding detection; within the blind zone, an improved active sliding film frequency shift method is activated, applying phase perturbation to the inverter based on the hyperbolic tangent function. Simultaneously, this active method introduces piecewise variable gain control, maintaining low gain under normal grid-connected steady state to ensure extremely low current harmonic distortion; upon determining a possible islanding state, the gain instantly jumps to high, using strong perturbation to force a rapid frequency shift to ensure islanding detection. While reducing the impact on grid-connected power quality, this eliminates the detection blind zone of the proposed passive method under source-load matching conditions, significantly improving the speed and accuracy of islanding detection.

[0044] This embodiment, by using voltage-phase angle variation and an improved sliding plate frequency shift method, can switch algorithms in real time, improving the speed and accuracy of island detection. The improved sliding plate frequency shift method can effectively eliminate the blind zone problem of the passive method and improve the coverage of island detection. After the passive method fails, the improved sliding plate frequency shift method is used to reduce the power quality problems that the improved sliding plate frequency shift method may cause and avoid causing additional disturbances to the power grid.

[0045] Compared with the traditional passive islanding detection method, the voltage-phase angle change method in this embodiment can effectively amplify the islanding characteristics under power matching conditions by coupling voltage and phase angle change characteristics, and significantly reduce the detection blind zone.

[0046] The improved sliding film frequency shift method in this embodiment solves the contradiction between the "detection blind zone (NDZ)" and "power quality (THD)" in the traditional SMS method.

[0047] This embodiment takes the distribution network of a distributed photovoltaic (PV) grid as the research object. Figure 2 The diagram shows a schematic of the distribution network for the target system of distributed photovoltaic power.

[0048] Building on the PSCAD / EMTDC platform, such as Figure 2 The simulation model of the distributed photovoltaic system shown is set to switch from grid-connected to islanded state when the simulation time is 0.5 seconds.

[0049] Specific parameter settings are shown in Tables 1 and 2. Switch K is disconnected during the simulation period of 0.5 seconds to form an island. The blind zone ranges calculated based on the voltage imbalance, using the conventional overvoltage method and the passive detection method for voltage and phase changes, are as follows: Figure 3 As shown, the waveforms of the frequency, voltage, and phase angle changes at the time of islanding occurrence in two different scenarios are respectively as follows: Figure 4 , Figure 5 and Figure 6 As shown.

[0050] Table 1. Parameter Settings

[0051] Table 2. Parameter Settings

[0052] Scenario 1: Based on the blind zone calculated by the power imbalance, outside the blind zone, a passive detection method based on voltage and phase angle changes is adopted. Figure 5 As shown, a threshold setting with a criterion greater than 1.1 can detect isolated islands.

[0053] Scenario 2: Based on the blind zone calculated from the power imbalance, within this blind zone, the improved sliding film frequency shift method is used for detection. Figure 6 and Figure 7 As shown, the hybrid criterion does not have a trigger threshold setting, while the improved sliding plate frequency shift method can detect islands by injecting phase angle perturbations and exceeding the frequency limit (greater than 50.5Hz).

[0054] Example 2 This embodiment provides a hybrid islanding detection system for a photovoltaic grid-connected system, comprising: The blind zone identification module is configured to: acquire local load parameter information, calculate the power imbalance, determine the blind zone range based on the power imbalance, and determine whether the photovoltaic grid-connected system is within the blind zone range. The first islanding detection module is configured to: if it is outside the blind zone, use the voltage-phase angle change method to detect islanding: obtain the voltage amplitude and power factor angle at the common coupling point; when the criterion composed of voltage amplitude and power factor angle exceeds the set criterion threshold, determine that the photovoltaic grid-connected system is in an islanding state. The second islanding detection module is configured to: if the system is within the blind zone, use the improved sliding plate frequency shift method for islanding detection: monitor the frequency of the common coupling point and calculate the frequency deviation; when the frequency deviation is less than the set frequency threshold, apply a phase perturbation with a low gain coefficient; when the frequency deviation is greater than or equal to the set frequency threshold, apply a phase perturbation with a high gain coefficient; when the frequency of the common coupling point is detected to exceed the detection threshold, the photovoltaic grid-connected system is determined to be in an islanded state.

[0055] It should be noted that each module in this embodiment corresponds one-to-one with each step in Embodiment 1, and their specific implementation processes are the same, so they will not be repeated here.

[0056] Example 3 This embodiment provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps in the hybrid islanding detection method for a photovoltaic grid-connected system as described in Embodiment 1 above.

[0057] Example 4 This embodiment provides a computer device, such as... Figure 8 As shown, the system includes a computer-readable storage medium 1003, a processor 1001, a communication interface 1002, and a computer program stored on the computer-readable storage medium 1003 and executable on the processor 1001. The processor 1001, communication interface 1002, and computer-readable storage medium 1003 can be connected via a bus or other means. The communication interface 1002 is used to receive and transmit data. When the processor 1001 executes the program, it implements the steps in the hybrid islanding detection method for a photovoltaic grid-connected system as described in Embodiment 1 above.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hybrid islanding detection method for a photovoltaic grid-connected system, characterized in that, include: Obtain local load parameter information, calculate the power imbalance, determine the blind zone range based on the power imbalance, and determine whether the photovoltaic grid-connected system is within the blind zone range: If the system is outside the blind zone, the voltage-phase angle change method is used for islanding detection: the voltage amplitude and power factor angle at the common coupling point are obtained. When the criterion composed of the voltage amplitude and power factor angle exceeds the set criterion threshold, the photovoltaic grid-connected system is determined to be in an islanding state. If the system is within the blind zone, the improved sliding plate frequency shift method is used for islanding detection: monitor the frequency of the common coupling point and calculate the frequency deviation; when the frequency deviation is less than the set frequency threshold, apply a phase perturbation with a low gain coefficient; when the frequency deviation is greater than or equal to the set frequency threshold, apply a phase perturbation with a high gain coefficient; when the frequency of the common coupling point is detected to exceed the detection threshold, the photovoltaic grid-connected system is determined to be in an islanded state.

2. The hybrid islanding detection method for a photovoltaic grid-connected system as described in claim 1, characterized in that, The power imbalance: ； ； ； ； ； in, R , L , C These are the equivalent resistance, inductance, and capacitance of the local load, respectively. U g The rated operating voltage of the power grid; P load and Q load These are the active and reactive power delivered by the DG to the local load, respectively. Represents the angular frequency of the power grid, Δ Q This represents the difference between the reactive power required by the local load and the reactive power output by the inverter, Δ. P This represents the difference between the active power required by the local load and the active power output of the inverter. Q inv This indicates the reactive power output of the photovoltaic inverter. P inv This indicates the active power output of the photovoltaic inverter.

3. The hybrid islanding detection method for a photovoltaic grid-connected system as described in claim 1, characterized in that, The blind zone range is: ； ； Among them, T set_high and T set_low These are the upper and lower boundary thresholds of the blind zone range, where U0 represents the rated voltage during normal grid operation, and Δ Q This represents the difference between the reactive power required by the local load and the reactive power output by the inverter, Δ. P This represents the difference between the active power required by the local load and the active power output of the inverter. P load and Q load These represent the active and reactive power delivered by the DG to the local load, respectively.

4. The hybrid islanding detection method for a photovoltaic grid-connected system as described in claim 1, characterized in that, The criterion composed of the voltage amplitude and the power factor angle is: Among them, △ u The voltage amplitude at the common coupling point. The power factor angle, u This is the voltage at the common coupling point.

5. The hybrid islanding detection method for a photovoltaic grid-connected system as described in claim 1, characterized in that, The phase perturbation of the low gain coefficient is: ;in, f g The rated frequency of the power grid. f For the common coupling point frequency, β The hyperbolic tangent shape factor is... K low The first gain coefficient is determined when the contribution of the total harmonic distortion rate of the grid-connected current is lower than the requirement.

6. The hybrid islanding detection method for a photovoltaic grid-connected system as described in claim 1, characterized in that, The phase perturbation of the high gain coefficient is: ;in, f g The rated frequency of the power grid. f For the common coupling point frequency, β The hyperbolic tangent shape factor is... K high The second gain coefficient is determined when the slope of the SMS curve is greater than the slope of the load impedance phase.

7. The hybrid islanding detection method for a photovoltaic grid-connected system as described in claim 1, characterized in that, Also includes: Once the photovoltaic grid-connected system is determined to be in an islanded state, an islanding alarm is triggered, and corresponding protective actions are taken, such as disconnecting the circuit breaker at the common coupling point or switching to islanded mode operation.

8. A hybrid islanding detection system for a photovoltaic grid-connected system, characterized in that, include: The blind zone identification module is configured to: acquire local load parameter information, calculate the power imbalance, determine the blind zone range based on the power imbalance, and determine whether the photovoltaic grid-connected system is within the blind zone range. The first islanding detection module is configured to: if it is outside the blind zone, use the voltage-phase angle change method to detect islanding: obtain the voltage amplitude and power factor angle at the common coupling point; when the criterion composed of voltage amplitude and power factor angle exceeds the set criterion threshold, determine that the photovoltaic grid-connected system is in an islanding state. The second islanding detection module is configured to: if the system is within the blind zone, use the improved sliding plate frequency shift method for islanding detection: monitor the frequency of the common coupling point and calculate the frequency deviation; when the frequency deviation is less than the set frequency threshold, apply a phase perturbation with a low gain coefficient; when the frequency deviation is greater than or equal to the set frequency threshold, apply a phase perturbation with a high gain coefficient; when the frequency of the common coupling point is detected to exceed the detection threshold, the photovoltaic grid-connected system is determined to be in an islanded state.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps in the hybrid islanding detection method for a photovoltaic grid-connected system as described in any one of claims 1-7.

10. A computer device comprising a computer-readable storage medium, a processor, and a computer program stored on the computer-readable storage medium and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the hybrid islanding detection method for a photovoltaic grid-connected system as described in any one of claims 1-7.

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