Single-phase photovoltaic energy storage inverter parallel operation system relay fault detection method

Abstract

The invention discloses a single-phase photovoltaic energy storage inverter parallel operation system relay fault detection method. The method comprises the following steps of determining a relay detection sequence according to configuration of a master machine and a slave machine; obtaining an absolute value of a difference value between the grid-connected port voltage effective value and the load port voltage effective value, comparing the absolute value with a preset first threshold value, and selecting a corresponding relay detection logic; the photovoltaic energy storage inverter unit is controlled to output open-loop voltage, the turn-on and turn-off sequence of the corresponding relays is controlled, and whether each relay has a sticking fault or a non-closing fault or not is detected in combination with a voltage judgment result. According to the method, all-working-condition adaptation of all-unit detection before grid connection of the parallel operation system, independent detection of a new machine and a reconnected slave machine in operation and all-unit re-detection after failure recovery of a host is met, and the detection problem in a dynamic adjustment scene of the parallel operation system is solved. Through the combinational logic of voltage threshold judgment and relay action time sequence control, the faults that the relay is stuck and cannot be closed can be accurately recognized, and missing detection and false detection are avoided.

Description

TECHNICAL FIELD

[0001] The application relates to a single-phase photovoltaic energy storage inverter parallel system relay fault detection method, and belongs to the technical field of inverter system relay fault detection methods. BACKGROUND

[0002] In the field of photovoltaic energy storage, a relay is a core component for realizing system on-grid and off-grid state switching and fault unit physical isolation: when the power supply is abnormal, the relay needs to be quickly switched to the off-grid mode to ensure power supply to the load; when the inverter fails, the relay needs to be disconnected to avoid the spread of faults to other equipment and loads.

[0003] For a parallel system composed of multiple inverters, the working condition is more complex than that of a single machine system: on the one hand, multiple inverters need to be cooperatively connected to the grid, and the fault state of the relay may directly affect the overall on-grid stability of the system; on the other hand, the number of inverters needs to be dynamically adjusted during system operation, and the online and offline situations of the inverters may frequently occur.

[0004] The existing relay detection method for a single machine system does not consider the master-slave machine cooperative control logic and the dynamic adjustment working condition of the machine group, cannot adapt to the complex scenarios of the parallel system, is prone to fault detection omission and false detection, or needs to stop the entire system operation to complete the detection, thereby seriously affecting the system operation efficiency and reliability. SUMMARY

[0005] The application aims to solve the problems of the prior art, and proposes a single-phase photovoltaic energy storage inverter parallel system relay fault detection method to solve the problem that the relay cannot be detected in the single machine mode due to the state difference of the inverter.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows: A single-phase photovoltaic energy storage inverter parallel system relay fault detection method, the single-phase photovoltaic energy storage inverter parallel system comprising a power grid, a load, and a plurality of photovoltaic energy storage inverter units, any photovoltaic energy storage inverter unit comprising a grid-connected port and a load port; the grid-connected ports of the plurality of photovoltaic energy storage inverter units are interconnected through L lines and N lines, and the load ports of the plurality of photovoltaic energy storage inverter units are respectively connected to the same load; Any photovoltaic energy storage inverter unit has a grid connection path connected to the power grid, a load connection path connected to the load port, and a communication connection path connected to the power grid and the load port, and at least one group of relays is respectively connected in series on the grid connection path, the load connection path, and the communication connection path. The fault detection method comprises the following steps: S1 determines the relay detection sequence of each photovoltaic energy storage inverter unit based on the master-slave configuration of several photovoltaic energy storage inverter units in the parallel system; S2 acquires the effective value of the grid-connected port voltage and the effective value of the load port voltage of each photovoltaic energy storage inverter unit to be tested, calculates the absolute value of the difference between the two, and selects the corresponding relay detection logic based on the comparison result of the absolute value and the preset first threshold. Based on the selected relay detection logic, S3 controls the open-loop voltage output of the photovoltaic energy storage inverter unit, controls the closing and closing sequence of the corresponding relays, and combines the voltage judgment results to detect whether each relay has a stuck fault or a failure to close fault.

[0007] Preferably, the single-phase photovoltaic energy storage inverter parallel system includes a photovoltaic energy storage inverter master and at least one photovoltaic energy storage inverter slave arranged in the grid connection sequence; In step S1, before the parallel system is normally connected to the grid, the photovoltaic energy storage inverter master is tested first, and then the photovoltaic energy storage inverter slave is tested in the order arranged according to the grid connection sequence. When the parallel system is in operation, only the newly added photovoltaic energy storage inverter slave and the photovoltaic energy storage inverter slave that has been reconnected due to a fault are tested separately. The newly added photovoltaic energy storage inverter slaves are arranged in sequence, and the photovoltaic energy storage inverter slaves that have been reconnected due to a fault are canceled from the original arrangement and rearranged in sequence. When the photovoltaic energy storage inverter host fails, the parallel system jumps to the fault state; after the fault is cleared, the test is re-executed according to the test sequence before normal grid connection of the parallel system.

[0008] Preferably, the grid connection path is provided with a first relay group, a second relay group, and a third relay group in sequence from the photovoltaic energy storage inverter unit to the grid. A fourth relay group is provided on the load connection line; The connecting path includes a connecting path that connects the load connecting path and the power grid connecting path. A fifth relay group is provided on the connecting path. The connecting path passes through the third relay group, the second relay group, and the fifth relay group in sequence from the power grid to the load. The first relay group includes relay S1 and relay S2, the second relay group includes relay S3 and relay S4, the third relay group includes relay S5 and relay S6, the fourth relay group includes relay S7 and relay S8, and the fifth relay group includes relay S9 and relay S10.

[0009] Preferably, in step S2, the value of the preset first threshold is 30V, and the relay detection logic includes M1 detection logic and M2 detection logic; If the absolute value of the difference is ≤30V, the photovoltaic energy storage inverter unit to be tested executes the M1 detection logic; If the absolute value of the difference is greater than 30V, the photovoltaic energy storage inverter unit to be tested executes the M2 detection logic.

[0010] Preferably, when executing the M1 detection logic, the second threshold is preset to 60V, and the judgment is based on the effective values ​​of the inverter port voltage, grid-connected port voltage, and load port voltage of the photovoltaic energy storage inverter unit to be detected. The M1 detection logic includes the following steps: M11: Disconnect all the relay groups and control the photovoltaic energy storage inverter unit to not output open-loop voltage, and determine whether the effective value of the inverter port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the second and third relay groups has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M12: Controls the open-loop voltage output of the photovoltaic energy storage inverter unit, and simultaneously determines whether the effective value of the inverter port voltage is >60V and whether the effective value of the load port voltage is >60V; If the effective value of the inverter port voltage is >60V, at least one relay in the first relay group has a stuck fault and is removed from the test. If the effective value of the load port voltage is >60V, at least one relay in the fourth relay group has a stuck fault, and the detection is terminated. If neither is true, proceed to the next step; M13: Maintain the open-loop output voltage of the photovoltaic energy storage inverter unit, close the first relay group, and simultaneously determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the grid-connected port voltage is >30V and whether the effective value of the load port voltage is >60V. If the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the grid-connected port voltage is >30V, at least one relay in the first relay group has a failure to close, and the detection is terminated. If the effective value of the load port voltage is >60V, at least one relay in the fifth relay group has a stuck fault, and the test is terminated. If neither is true, proceed to the next step; M14: Keep the open-loop voltage output of the photovoltaic energy storage inverter unit, the first relay group and the fifth relay group closed, and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the load port voltage is >30V; If the judgment result is yes, at least one relay in the fifth relay group has a failure to close, and the test is terminated. If the result is negative, proceed to the next step; M15: Maintain the open-loop output voltage of the photovoltaic energy storage inverter unit, disconnect the first and fifth relay groups, close the fourth relay group, and determine whether the absolute value of the difference between the effective value of the load port voltage and the effective value of the grid-connected port voltage is >30V; If the judgment result is yes, at least one relay in the fourth relay group has a failure to close, and the test is terminated. If the result is negative, proceed to the next step; M16: Control the photovoltaic energy storage inverter unit to stop outputting open-loop voltage, disconnect the fourth relay group, close the second relay group, and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one relay in the third relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M17: Keep the second relay group closed, close the third relay group, and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the grid connection port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the second and third relay groups has a failure to close, and the detection is terminated. If the result is negative, proceed to the next step; M18: Disconnect the second relay group and determine whether the effective value of the inverter port voltage is >30V; If the judgment result is yes, at least one relay in the second relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M19: Controls the photovoltaic energy storage inverter unit to stop outputting open-loop voltage, disconnects all relay groups, and ends the detection.

[0011] Preferably, when executing the M2 detection logic, the second threshold is preset to 60V, and the judgment is based on the effective values ​​of the inverter port voltage, grid-connected port voltage, and load port voltage of the photovoltaic energy storage inverter unit to be detected. The M2 detection logic includes the following steps: M21: Disconnect all the relays and control the photovoltaic energy storage inverter unit to not output open-loop voltage, and determine whether the effective value of the inverter port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the second and third relay groups, the combination of the first and fourth relay groups, or the fifth relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M22: Close the fifth relay group and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the load port voltage is >30V; If the judgment result is yes, at least one relay in the fifth relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M23: Disconnect the fifth relay group, close the fourth relay group, and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one relay in the first relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M24: Close the first relay group and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the load port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the first relay group and the second relay group has a failure to close, and the detection is terminated. If the result is negative, proceed to the next step; M25: Disconnect the fourth relay group and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one relay in the fourth relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M26: Disconnect the first relay group, close the second relay group, and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one of the relays in the third relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M27: Close the third relay group and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the grid connection port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the second and third relay groups has a failure to close, and the detection is terminated. If the result is negative, proceed to the next step; M28: Disconnect the second relay group and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one relay in the second relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M29: Control the photovoltaic energy storage inverter unit to stop outputting open-loop voltage, disconnect all the relays, and end the detection.

[0012] Preferably, the "sticky failure" refers to the relay remaining in a closed state after receiving a disconnect command; the "failure to close failure" refers to the relay remaining in an open state after receiving a close command.

[0013] The beneficial effects of this invention are mainly reflected in: 1. It meets the full-condition adaptation requirements of the parallel system, including full unit testing before grid connection, individual testing of new units and reconnected slave units during operation, and full unit retesting after master unit failure recovery, thus solving the testing challenges in dynamic adjustment scenarios of the parallel system.

[0014] 2. By combining voltage threshold judgment and relay action timing control logic, relay sticking and failure to close faults can be accurately identified, avoiding missed detections and false detections.

[0015] 3. During operation, only newly added and reconnected slave devices are detected separately, without stopping the operation of the master and other slave devices, ensuring continuous power supply to the system and improving operating efficiency.

[0016] 4. Clarify the master-slave architecture of the parallel system, the correspondence between relay groups and lines, provide a clear hardware foundation for the implementation of detection logic, and reduce the difficulty of engineering implementation. Attached Figure Description

[0017] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a flowchart illustrating a relay fault detection method for a single-phase photovoltaic energy storage inverter parallel system according to the present invention.

[0018] Figure 2 This is a circuit diagram of the single-phase photovoltaic energy storage inverter parallel system in this invention.

[0019] Figure 3 This is a timing diagram of the M1 detection logic in this invention.

[0020] Figure 4 This is a timing diagram of the M2 detection logic in this invention. Detailed Implementation

[0021] 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. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in the present application can be combined with each other.

[0023] This invention provides a method for detecting relay faults in a single-phase photovoltaic energy storage inverter parallel system, wherein the single-phase photovoltaic energy storage inverter parallel system is as follows: Figure 2 As shown, the system includes a power grid, a load, and several photovoltaic energy storage inverter units. Each photovoltaic energy storage inverter unit includes a grid connection port and a load port. The grid connection ports of several photovoltaic energy storage inverter units are interconnected through L-line and N-line, and the load ports of several photovoltaic energy storage inverter units are respectively connected to the same load.

[0024] Any photovoltaic energy storage inverter unit has a grid connection path for connecting to the power grid, a load connection path for connecting to the load port, and a connection path for connecting the power grid and the load port. At least one set of relays is connected in series on each of the grid connection path, the load connection path, and the connection path.

[0025] Reference Figure 2 As shown, the grid is connected to any photovoltaic energy storage inverter unit via a grid connection path, the load is connected to any load port, and the load port is connected to the photovoltaic energy storage inverter unit INV via a load connection path. The grid-connected ports of each photovoltaic energy storage inverter unit are interconnected via L and N lines. (Refer to...) Figure 2 As shown, the L line and N line can be laid independently or connected based on the power grid connection.

[0026] like Figure 1 As shown, the fault detection method includes the following steps: S1 determines the relay detection sequence of each photovoltaic energy storage inverter unit based on the master-slave configuration of several photovoltaic energy storage inverter units in the parallel system; S2 acquires the effective value of the grid-connected port voltage and the effective value of the load port voltage of each photovoltaic energy storage inverter unit to be tested, calculates the absolute value of the difference between the two, and selects the corresponding relay detection logic based on the comparison result of the absolute value and the preset first threshold. Based on the selected relay detection logic, S3 controls the open-loop voltage output of the photovoltaic energy storage inverter unit, controls the closing and closing sequence of the corresponding relays, and combines the voltage judgment results to detect whether each relay has a stuck fault or a failure to close fault.

[0027] Detailed implementation process and principle explanation: Grid-connected systems such as Figure 2 As shown, it realizes the electrical connection of several INV grid-connected ports through L line and N line. This grid connection is existing technology. In this case, the detection method is mainly used to detect the relay group connected in series on the power grid connection circuit, load connection circuit and connection circuit to determine the relay sticking fault or inability to close fault.

[0028] During testing, a master-slave testing sequence is configured, primarily for offline sequential testing. During testing, the absolute value of the difference between the effective values ​​of the grid-connected port voltage and the load port voltage is calculated to select the appropriate relay detection logic. After the relay detection logic is selected, the open-loop output voltage and the sequence of control closing and closing, combined with voltage performance analysis, are used to determine the results, identifying stuck-on and non-closing faults in each relay group.

[0029] Among them, the "sticky" fault refers to the relay being in a closed state after receiving a disconnect command; the "unable to close" fault refers to the relay being in an open state after receiving a close command.

[0030] In one specific embodiment, the parallel system is as follows: Figure 2 As shown, a single-phase photovoltaic energy storage inverter parallel system includes a photovoltaic energy storage inverter master unit and at least one photovoltaic energy storage inverter slave unit arranged in the grid connection sequence.

[0031] Generally, the master unit is recorded with a unique number, while the slave unit is numbered according to the normal network connection sequence. When a new network connection occurs or a fault is repaired and the network is connected, the slave unit is renumbered in sequence according to the deletion and addition logic of the original sequence.

[0032] Before the parallel system is normally connected to the grid, the photovoltaic energy storage inverter master is tested first, and then the photovoltaic energy storage inverter slave is tested in the order of grid connection sequence. When the parallel system is in operation, only the newly added photovoltaic energy storage inverter slave and the photovoltaic energy storage inverter slave that has been reconnected due to a fault are tested separately. The newly added photovoltaic energy storage inverter slaves are arranged in sequence, and the photovoltaic energy storage inverter slaves that have been reconnected due to a fault are canceled from the original arrangement and rearranged in sequence. When the photovoltaic energy storage inverter main unit fails, the parallel system jumps to the fault state; after the fault is cleared, the test is re-executed according to the test sequence before normal grid connection of the parallel system.

[0033] In one specific embodiment, such as Figure 2 As shown, the grid connection path is provided with a first relay group, a second relay group, and a third relay group in sequence from the photovoltaic energy storage inverter unit to the grid; the load connection path is provided with a fourth relay group; the connecting connection path has a connecting path connecting the load connection path and the grid connection path, and a fifth relay group is provided on the connecting path. The connecting connection path passes through the third relay group, the second relay group, and the fifth relay group in sequence from the grid to the load.

[0034] The first relay group includes relays S1 and S2; the second relay group includes relays S3 and S4; the third relay group includes relays S5 and S6; the fourth relay group includes relays S7 and S8; and the fifth relay group includes relays S9 and S10.

[0035] Combination Figure 2 To elaborate further, each inverter unit contains five sets of relays. The inverter unit INV is connected to the grid, the grid to the load port, and the inverter unit INV to the load port via separate lines. Specifically, three relay sets (S1 & S2, S3 & S4, and S5 & S6) are connected in series on the line between the inverter unit INV and the grid; three relay sets (S5 & S6, S3 & S4, and S9 & S10) are connected in series on the line between the grid and the load port; and one relay set (S7 & S8) is connected in series on the line between the INV and the load. The L and N lines of the grid connection ports of each inverter unit are connected; the load ports are connected to the same load system.

[0036] In one specific embodiment, the preset first threshold value is 30V, and the relay detection logic includes M1 detection logic and M2 detection logic; if the absolute value of the difference is ≤30V, the photovoltaic energy storage inverter unit to be tested executes the M1 detection logic; if the absolute value of the difference is >30V, the photovoltaic energy storage inverter unit to be tested executes the M2 detection logic.

[0037] Specifically, the effective value of the grid-connected port voltage of each inverter is obtained through sampling and calculation. and the effective value of the load port voltage Before the parallel system is connected to the grid normally, the voltage difference between the two does not exceed 30V, and the inverter unit executes the M1 relay detection logic; when the system is running normally, the voltage difference between the two exceeds 30V, and the newly added or reconnected inverter unit executes the M2 relay detection logic.

[0038] like Figure 3 As shown, when executing the M1 detection logic, the second threshold is preset to 60V, and the judgment is based on the effective values ​​of the inverter port voltage, grid-connected port voltage, and load port voltage of the photovoltaic energy storage inverter unit to be detected. The M1 detection logic includes the following steps: M11: Disconnect all relay groups and control the photovoltaic energy storage inverter unit to not output open-loop voltage, and determine whether the effective value of the inverter port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the second and third relay groups has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step.

[0039] M12: Controls the open-loop voltage output of the photovoltaic energy storage inverter unit, and simultaneously determines whether the effective value of the inverter port voltage is >60V and whether the effective value of the load port voltage is >60V; If the effective value of the inverter port voltage is >60V, at least one relay in the first relay group has a stuck fault and is removed from the test. If the effective value of the load port voltage is >60V, at least one relay in the fourth relay group has a stuck fault, and the test is terminated. If neither is true, proceed to the next step.

[0040] M13: Maintain the open-loop output voltage of the photovoltaic energy storage inverter unit, close the first relay group, and at the same time determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the grid-connected port voltage is >30V and whether the effective value of the load port voltage is >60V. If the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the grid-connected port voltage is >30V, at least one relay in the first relay group has a failure to close, and the detection is terminated. If the effective value of the load port voltage is >60V, at least one relay in the fifth relay group has a stuck fault, and the test is terminated. If neither is true, proceed to the next step.

[0041] M14: Keep the open-loop voltage of the photovoltaic energy storage inverter unit output, the first relay group and the fifth relay group closed, and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the load port voltage is >30V; If the judgment result is yes, at least one relay in the fifth relay group has a failure to close, and the test is terminated. If the result is negative, proceed to the next step.

[0042] M15: Maintain the open-loop output voltage of the photovoltaic energy storage inverter unit, disconnect the first and fifth relay groups, close the fourth relay group, and determine whether the absolute value of the difference between the effective value of the load port voltage and the effective value of the grid-connected port voltage is >30V; If the judgment result is yes, at least one relay in the fourth relay group has a failure to close, and the test is terminated. If the result is negative, proceed to the next step.

[0043] M16: Control the photovoltaic energy storage inverter unit to stop outputting open-loop voltage, disconnect the fourth relay group, close the second relay group, and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one relay in the third relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step.

[0044] M17: Keep the second relay group closed, close the third relay group, and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the grid connection port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the second and third relay groups has a failure to close, and the detection is terminated. If the result is negative, proceed to the next step.

[0045] M18: Disconnect the second relay group and determine whether the effective value of the inverter port voltage is >30V; If the judgment result is yes, at least one relay in the second relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step.

[0046] M19: Controls the photovoltaic energy storage inverter unit to stop outputting open-loop voltage, disconnects all relay groups, and ends the detection.

[0047] Combination Figure 2 and Figure 3 Explanation: Disconnect all relays, and the inverter does not output open-loop voltage; determine the inverter port voltage. If the effective value is greater than 30V; if yes, then at least one of S3&S5 or S4&S6 has a stuck fault, and the relay detection is terminated; if no.

[0048] Based on the previous step, control the inverter output open-loop voltage, condition 1: determine the inverter port voltage. Condition 2: Determine if the effective value is greater than 60V; Condition 3: Determine the voltage at the load port. Is the effective value greater than 60V? If condition 1 is true, then at least one relay in S1 & S2 has a stuck fault, and the relay detection is terminated. If condition 2 is true, then at least one relay in S7 & S8 has a stuck fault, and the relay detection is terminated. If both condition 1 and condition 2 are false, then continue.

[0049] Based on the previous step, close relays S1 & S2; Condition 1: Determine the effective value of the inverter port voltage. and the effective value of the grid port voltage Condition 2: Determine the effective value of the load port voltage. (Is the absolute value of the difference greater than 30V?) Is it greater than 60V? If condition 1 is true, then at least one relay in S1 & S2 has a failure to close, and the relay detection is terminated. If condition 2 is true, then at least one relay in S9 & S10 has a stuck fault, and the relay detection is terminated. If both condition 1 and condition 2 are false, then continue.

[0050] Based on the previous step, close relays S9 and S10; determine the effective value of the inverter port voltage. and the effective value of the load port voltage Check if the absolute value of the difference is greater than 30V; if yes, then at least one relay in S9 & S10 has a failure to close, and the relay detection is terminated; if no, continue.

[0051] Based on the previous step, disconnect relays S1 & S2, S9 & S10, and close S7 & S8; determine the effective value of the inverter load port voltage. and the effective value of the grid port voltage Check if the absolute value of the difference is greater than 30V; if yes, then at least one of S7 & S8 has a failure to close, and the relay detection is terminated; if no, continue.

[0052] Based on the previous step, control the inverter to stop outputting open-loop voltage, disconnect relays S7 & S8, and close relays S3 & S4; determine the inverter port voltage. Check if the effective value is greater than 60V; if yes, then at least one relay in S5 & S6 has a stuck fault, and exit relay detection; if no, continue.

[0053] Based on the previous step, close relays S5 and S6; determine the effective value of the inverter port voltage. and the effective value of the grid port voltage Check if the absolute value of the difference is greater than 30V; if yes, then at least one of S3&S4 and S5&S6 has a failure to close, and exit relay detection; if no, continue.

[0054] Based on the previous step, disconnect relays S3 and S4; determine the inverter port voltage of the inverter. Check if the effective value is greater than 30V; if yes, then at least one relay in S3 & S4 has a stuck fault, and exit relay detection; if no, continue.

[0055] Based on the previous step, control the inverter to stop outputting open-loop voltage, disconnect all relays, and end relay detection.

[0056] like Figure 4 As shown, when executing the M2 detection logic, the preset second threshold is 60V, and the judgment is based on the effective values ​​of the inverter port voltage, grid connection port voltage, and load port voltage of the photovoltaic energy storage inverter unit to be detected. The M2 detection logic includes the following steps: M21: Disconnect all the relays and control the photovoltaic energy storage inverter unit to not output open-loop voltage, and determine whether the effective value of the inverter port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the second and third relay groups, the combination of the first and fourth relay groups, or the fifth relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step.

[0057] M22: Close the fifth relay group and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the load port voltage is >30V; If the judgment result is yes, at least one relay in the fifth relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step.

[0058] M23: Disconnect the fifth relay group, close the fourth relay group, and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one relay in the first relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step.

[0059] M24: Close the first relay group and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the load port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the first relay group and the second relay group has a failure to close, and the detection is terminated. If the result is negative, proceed to the next step.

[0060] M25: Disconnect the fourth relay group and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one relay in the fourth relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step.

[0061] M26: Disconnect the first relay group, close the second relay group, and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one of the relays in the third relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step.

[0062] M27: Close the third relay group and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the grid connection port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the second and third relay groups has a failure to close, and the detection is terminated. If the result is negative, proceed to the next step.

[0063] M28: Disconnect the second relay group and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one relay in the second relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step.

[0064] M29: Control the photovoltaic energy storage inverter unit to stop outputting open-loop voltage, disconnect all the relays, and end the detection.

[0065] Combination Figure 2 and Figure 4 Detailed explanation: Disconnect all relays, and the inverter does not output open-loop voltage; determine the inverter port voltage. Check if the effective value is greater than 30V; if yes, at least one of the relays in S3&S4, S5&S6 or S1&S2, S7&S8 or S9&S10 has a stuck fault, and exit relay detection; if no, continue.

[0066] Based on the previous step, close relays S9 and S10 to determine the effective value of the inverter port voltage. and the effective value of the load port voltage Check if the absolute value of the difference is greater than 30V; if yes, then at least one relay in S9 & S10 has a stuck fault, and exit relay detection; if no, continue.

[0067] Based on the previous step, disconnect relays S9 and S10, and close relays S7 and S8 to determine the inverter port voltage. Check if the effective value is greater than 60V; if yes, then at least one relay in S1 & S2 has a stuck fault, and exit relay detection; if no, continue.

[0068] Based on the previous step, close relays S1 and S2 to determine the effective value of the inverter port voltage. and the effective value of the load port voltage Check if the absolute value of the difference is greater than 30V; if yes, then at least one of S1&S2 or S7&S8 has a failure to close, and exit relay detection; if no, continue.

[0069] Based on the previous step, disconnect relays S7 and S8 to determine the inverter port voltage. Check if the effective value is greater than 60V; if yes, then at least one relay in S7 & S8 has a stuck fault, and exit relay detection; if no, continue.

[0070] Based on the previous step, disconnect relays S1 & S2 and close relays S3 & S4 to determine the inverter port voltage. Check if the effective value is greater than 60V; if yes, then at least one relay in S5 & S6 has a stuck fault, and exit relay detection; if no, continue.

[0071] Based on the previous step, close relays S5 and S6 to determine the effective value of the inverter port voltage. and the effective value of the grid port voltage Check if the absolute value of the difference is greater than 30V; if yes, then at least one of S3&S4 and S5&S6 has a failure to close, and exit relay detection; if no, continue.

[0072] Based on the previous step, disconnect relays S3 and S4 to determine the inverter port voltage. Check if the effective value is greater than 60V; if yes, then at least one relay in S3 & S4 has a stuck fault, and exit relay detection; if no, continue.

[0073] Based on the previous step, control the inverter to stop outputting open-loop voltage, disconnect all relays, and end relay detection.

[0074] The above description demonstrates full-condition adaptability, satisfying pre-grid-connection testing of all units in parallel systems, individual testing of newly added and reconnected slave units during operation, and full-unit retesting after master unit failure recovery, thus solving the testing challenges in dynamic adjustment scenarios of parallel systems. Through a combination of voltage threshold judgment and relay action timing control logic, it can accurately identify relay sticking and inability to close faults, avoiding missed or false detections. During operation, only newly added and reconnected slave units are tested individually, without stopping the master unit and other slave units, ensuring continuous power supply and improving operational efficiency. Clearly defining the master-slave architecture of the parallel system and the correspondence between relay groups and lines provides a clear hardware foundation for the implementation of the testing logic, reducing the difficulty of engineering implementation.

[0075] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent in such process, method, article, or apparatus / device.

[0076] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for detecting relay faults in a single-phase photovoltaic energy storage inverter parallel system, characterized in that: The single-phase photovoltaic energy storage inverter parallel system includes a power grid, a load, and several photovoltaic energy storage inverter units. Each photovoltaic energy storage inverter unit includes a grid connection port and a load port. The grid connection ports of several photovoltaic energy storage inverter units are interconnected through L-line and N-line, and the load ports of several photovoltaic energy storage inverter units are respectively connected to the same load. Any of the photovoltaic energy storage inverter units has a grid connection path connected to the power grid, a load connection path connected to the load port, and a connection path connecting the power grid and the load port. At least one set of relays is connected in series on each of the grid connection path, the load connection path, and the connection path. The fault detection method includes the following steps: S1 determines the relay detection sequence of each photovoltaic energy storage inverter unit based on the master-slave configuration of several photovoltaic energy storage inverter units in the parallel system; S2 acquires the effective value of the grid-connected port voltage and the effective value of the load port voltage of each photovoltaic energy storage inverter unit to be tested, calculates the absolute value of the difference between the two, and selects the corresponding relay detection logic based on the comparison result of the absolute value and the preset first threshold. Based on the selected relay detection logic, S3 controls the open-loop voltage output of the photovoltaic energy storage inverter unit, controls the closing and closing sequence of the corresponding relays, and combines the voltage judgment results to detect whether each relay has a stuck fault or a failure to close fault.

2. The method for detecting relay faults in a single-phase photovoltaic energy storage inverter parallel system according to claim 1, characterized in that: The single-phase photovoltaic energy storage inverter parallel system includes a photovoltaic energy storage inverter master and at least one photovoltaic energy storage inverter slave arranged in the grid connection sequence; In step S1, before the parallel system is normally connected to the grid, the photovoltaic energy storage inverter master is tested first, and then the photovoltaic energy storage inverter slave is tested in the order arranged according to the grid connection sequence. When the parallel system is in operation, only the newly added photovoltaic energy storage inverter slave and the photovoltaic energy storage inverter slave that has been reconnected due to a fault are tested separately. The newly added photovoltaic energy storage inverter slaves are arranged in sequence, and the photovoltaic energy storage inverter slaves that have been reconnected due to a fault are canceled from the original arrangement and rearranged in sequence. When the photovoltaic energy storage inverter host fails, the parallel system jumps to the fault state; after the fault is cleared, the test is re-executed according to the test sequence before normal grid connection of the parallel system.

3. The method for detecting relay faults in a single-phase photovoltaic energy storage inverter parallel system according to claim 1, characterized in that: The grid connection path is provided with a first relay group, a second relay group, and a third relay group in sequence from the photovoltaic energy storage inverter unit to the grid. A fourth relay group is provided on the load connection line; The connecting path includes a connecting path that connects the load connecting path and the power grid connecting path. A fifth relay group is provided on the connecting path. The connecting path passes through the third relay group, the second relay group, and the fifth relay group in sequence from the power grid to the load. The first relay group includes relay S1 and relay S2, the second relay group includes relay S3 and relay S4, the third relay group includes relay S5 and relay S6, the fourth relay group includes relay S7 and relay S8, and the fifth relay group includes relay S9 and relay S10.

4. The relay fault detection method for a single-phase photovoltaic energy storage inverter parallel system according to claim 3, characterized in that: In step S2, the value of the preset first threshold is 30V, and the relay detection logic includes M1 detection logic and M2 detection logic. If the absolute value of the difference is ≤30V, the photovoltaic energy storage inverter unit to be tested executes the M1 detection logic; If the absolute value of the difference is greater than 30V, the photovoltaic energy storage inverter unit to be tested executes the M2 detection logic.

5. The relay fault detection method for a single-phase photovoltaic energy storage inverter parallel system according to claim 4, characterized in that: When executing the M1 detection logic, the second threshold is preset to 60V, and the judgment is based on the effective values ​​of the inverter port voltage, grid-connected port voltage, and load port voltage of the photovoltaic energy storage inverter unit to be detected. The M1 detection logic includes the following steps: M11: Disconnect all the relay groups and control the photovoltaic energy storage inverter unit to not output open-loop voltage, and determine whether the effective value of the inverter port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the second and third relay groups has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M12: Controls the open-loop voltage output of the photovoltaic energy storage inverter unit, and simultaneously determines whether the effective value of the inverter port voltage is >60V and whether the effective value of the load port voltage is >60V; If the effective value of the inverter port voltage is >60V, at least one relay in the first relay group has a stuck fault and is removed from the test. If the effective value of the load port voltage is >60V, at least one relay in the fourth relay group has a stuck fault, and the detection is terminated. If neither is true, proceed to the next step; M13: Maintain the open-loop output voltage of the photovoltaic energy storage inverter unit, close the first relay group, and simultaneously determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the grid-connected port voltage is >30V and whether the effective value of the load port voltage is >60V. If the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the grid-connected port voltage is >30V, at least one relay in the first relay group has a failure to close, and the detection is terminated. If the effective value of the load port voltage is >60V, at least one relay in the fifth relay group has a stuck fault, and the test is terminated. If neither is true, proceed to the next step; M14: Keep the open-loop voltage output of the photovoltaic energy storage inverter unit, the first relay group and the fifth relay group closed, and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the load port voltage is >30V; If the judgment result is yes, at least one relay in the fifth relay group has a failure to close, and the test is terminated. If the result is negative, proceed to the next step; M15: Maintain the open-loop output voltage of the photovoltaic energy storage inverter unit, disconnect the first and fifth relay groups, close the fourth relay group, and determine whether the absolute value of the difference between the effective value of the load port voltage and the effective value of the grid-connected port voltage is >30V; If the judgment result is yes, at least one relay in the fourth relay group has a failure to close, and the test is terminated. If the result is negative, proceed to the next step; M16: Control the photovoltaic energy storage inverter unit to stop outputting open-loop voltage, disconnect the fourth relay group, close the second relay group, and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one relay in the third relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M17: Keep the second relay group closed, close the third relay group, and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the grid connection port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the second and third relay groups has a failure to close, and the detection is terminated. If the result is negative, proceed to the next step; M18: Disconnect the second relay group and determine whether the effective value of the inverter port voltage is >30V; If the judgment result is yes, at least one relay in the second relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M19: Controls the photovoltaic energy storage inverter unit to stop outputting open-loop voltage, disconnects all relay groups, and ends the detection.

6. The method for detecting relay faults in a single-phase photovoltaic energy storage inverter parallel system according to claim 4, characterized in that: When executing the M2 detection logic, the second threshold is preset to 60V, and the judgment is based on the effective values ​​of the inverter port voltage, grid-connected port voltage, and load port voltage of the photovoltaic energy storage inverter unit to be detected. The M2 detection logic includes the following steps: M21: Disconnect all the relays and control the photovoltaic energy storage inverter unit to not output open-loop voltage, and determine whether the effective value of the inverter port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the second and third relay groups, the combination of the first and fourth relay groups, or the fifth relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M22: Close the fifth relay group and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the load port voltage is >30V; If the judgment result is yes, at least one relay in the fifth relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M23: Disconnect the fifth relay group, close the fourth relay group, and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one relay in the first relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M24: Close the first relay group and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the load port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the first relay group and the second relay group has a failure to close, and the detection is terminated. If the result is negative, proceed to the next step; M25: Disconnect the fourth relay group and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one relay in the fourth relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M26: Disconnect the first relay group, close the second relay group, and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one of the relays in the third relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M27: Close the third relay group and determine whether the absolute value of the difference between the effective value of the inverter port voltage and the effective value of the grid connection port voltage is >30V; If the judgment result is yes, at least one relay in the combination of the second and third relay groups has a failure to close, and the detection is terminated. If the result is negative, proceed to the next step; M28: Disconnect the second relay group and determine whether the effective value of the inverter port voltage is >60V; If the judgment result is yes, at least one relay in the second relay group has a stuck fault, and the test is terminated. If the result is negative, proceed to the next step; M29: Control the photovoltaic energy storage inverter unit to stop outputting open-loop voltage, disconnect all the relays, and end the detection.

7. A method for detecting relay faults in a single-phase photovoltaic energy storage inverter parallel system according to any one of claims 1 to 6, characterized in that: The term "sticky fault" refers to a relay that remains in a closed state after receiving a disconnect command; the term "failure to close fault" refers to a relay that remains in an open state after receiving a close command.

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