A fault detection method for a current transformer on the grid side of an inverter

Abstract

The present invention discloses a fault detection method for a grid-side current transformer of an inverter, comprising: controlling the inverter to output an initial reactive power in response to reactive power scheduling, recording the initial grid reactive power value or the load reactive power reference value; sequentially controlling the inverter to output a reactive power disturbance of a preset amplitude at each disturbance stage, and recording the grid reactive power response value or the load reactive power response value corresponding to each disturbance stage; determining whether to accumulate an abnormal signal based on the initial grid reactive power value and the grid reactive power response value corresponding to each disturbance stage; or determining whether to accumulate an abnormal signal based on the load reactive power reference value and the load reactive power response value corresponding to each disturbance stage; and determining the health status of the grid-side current transformer based on the number of accumulated abnormal signals. The present invention can detect whether a grid-side CT is faulty during power-on self-test when no sensor is present at the load end.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a fault detection method for a current transformer on the grid side of an inverter. Background Art

[0002] When the PV-storage inverter operates in reverse flow prevention or self-consumption mode, the grid-side current transformer (CT) plays a crucial role. Any CT anomaly, such as reverse connection, signal short circuit, or signal break, can cause loss of control in reverse flow prevention or loss of control in self-consumption. Therefore, sensors are typically installed on the grid, load, and inverter sides. Using the equation load reactive power = grid reactive power + inverter reactive power, any grid-side CT anomaly will cause the load reactive power to equal grid reactive power + inverter reactive power, thus detecting grid-side CT anomalies. However, if there are no sensors on the load side, this solution is not applicable, and a grid-side CT failure cannot be detected during the power-on self-test. Summary of the Invention

[0003] The present invention provides a fault detection method for a current transformer on the grid side of an inverter, which can detect whether the grid side CT is faulty during power-on self-test when there is no sensor at the load end or the sensor is damaged.

[0004] An embodiment of the present invention provides a fault detection method for a grid-side current transformer of an inverter, comprising: controlling the inverter to output an initial reactive power in response to reactive scheduling, and recording the initial reactive power value or the load reactive power reference value on the grid side; sequentially controlling the inverter to output reactive power disturbances of preset amplitudes in each disturbance stage, and respectively recording the grid reactive power response value or the load reactive power response value corresponding to each disturbance stage; determining whether to accumulate an abnormal signal based on the grid reactive power initial value and the grid reactive power response value corresponding to each disturbance stage, or determining whether to accumulate an abnormal signal based on the load reactive power reference value and the load reactive power response value corresponding to each disturbance stage; and determining the health status of the grid-side current transformer according to the number of accumulations of the abnormal signal; wherein the health status includes a fault state, an uncertain state, and a normal operating state.

[0005] The grid-side current transformer fault detection method provided in an embodiment of the present invention controls the inverter to output initial reactive power in response to reactive scheduling, records the load's reactive power reference value and the grid's initial reactive power value, and can provide a comparison basis for responses in subsequent disturbance phases. By actively injecting disturbances of different amplitudes (such as alternating positive and negative), grid fluctuations or load mutation scenarios can be simulated, exposing potential faults of the current transformer under dynamic operating conditions. By comparing the reactive power response values ​​of adjacent phases with the reactive power reference value or the response value of the previous phase, if the difference exceeds a preset threshold, an abnormal signal is accumulated. Finally, the health status of the current transformer is determined based on the number of accumulated abnormal signals. In other words, the grid-side current transformer fault detection method provided in an embodiment of the present invention can detect whether the grid-side CT is faulty during power-on self-test when there is no sensor at the load end.

[0006] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present invention, nor is it intended to limit the scope of the present invention. Other features of the present invention will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0008] Figure 1 This is a flow chart of a fault detection method for a grid-side current transformer of an inverter provided by an embodiment of the present invention;

[0009] Figure 2 This is a schematic diagram of a grid-side CT abnormality detection principle provided by an embodiment of the present invention;

[0010] Figure 3 This is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention;

[0011] Figure 4 This is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention;

[0012] Figure 5 This is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention;

[0013] Figure 6 This is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention;

[0014] Figure 7 This is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention;

[0015] Figure 8 This is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention;

[0016] Figure 9 This is a flowchart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0018] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0019] Figure 1 This is a flow chart of a method for detecting a fault in a grid-side current transformer of an inverter, provided by an embodiment of the present invention. The method of this embodiment can be executed by a control device of the inverter, which can be implemented in software and / or hardware and integrated into a photovoltaic storage system.

[0020] like Figure 1 As shown, the fault detection method of the grid-side current transformer includes:

[0021] S101 , controlling the inverter to output initial reactive power in response to reactive power scheduling, and recording the initial value of grid reactive power or the reference value of load reactive power.

[0022] An inverter is a power electronic device that converts direct current (such as the electricity generated by solar panels) into alternating current and can adjust the output active power and reactive power as needed.

[0023] Inverter response reactive power dispatch means that the inverter dynamically adjusts the output reactive power according to the reactive power demand instructions of the power grid or energy management system to maintain grid voltage stability or meet power factor requirements.

[0024] Initial reactive power refers to the reactive power output by the inverter at the beginning according to the load demand. It is understood that the initial reactive power can be 0 or not.

[0025] The load reactive power reference value refers to the load reactive power reference value recorded in the undisturbed state, which is used for abnormal signal judgment in the subsequent disturbance stage.

[0026] The initial value of the grid reactive power refers to the grid reactive power reference value recorded in the undisturbed state, which is used for abnormal signal judgment in the subsequent disturbance stage.

[0027] Figure 2 This is a schematic diagram of a grid-side CT abnormality detection principle provided by an embodiment of the present invention. Figure 2 As shown, by measuring the inverter output current and voltage, we can calculate the inverter's reactive power, Q_inv. By measuring the grid-side current and voltage, we can calculate the grid's reactive power, Q_grid. Using the power balance formula Q_load = Q_grid + Q_inv, we can obtain the load's reactive power, Q_load.

[0028] The reactive power baseline provides a basis for comparison of responses during subsequent disturbance phases. Without a reactive power baseline, it is impossible to quantify the reactive power change caused by the disturbance, making it difficult to determine whether it is caused by a current transformer fault.

[0029] S102 , sequentially controlling the inverter to output reactive power disturbances of preset amplitudes at each disturbance stage, and respectively recording the grid reactive power response value or the load reactive power response value corresponding to each disturbance stage.

[0030] Specifically, the disturbance phase refers to dividing the detection process into multiple time periods, and actively injecting a specific amplitude of reactive power change (disturbance) into the system in each time period to simulate different working conditions and observe the system response.

[0031] The reactive power disturbance of the preset amplitude is a preset value of the rated power of a single phase of the inverter, wherein the preset amplitudes of the reactive power disturbances in different disturbance stages are different or the same.

[0032] The load reactive power response value refers to the actual calculated value of reactive power at the load after each disturbance phase. The load reactive power response value is equal to the reactive power output by the inverter plus the reactive power response value on the grid side. The reactive power output by the inverter is a known quantity, while the reactive power on the grid side is calculated from the voltage and current measured by the grid-side CT. Therefore, by monitoring the load reactive power response value or the grid reactive power response value, it is possible to determine whether the grid-side CT is faulty.

[0033] In some embodiments, a reactive disturbance of +15Var can be output in the first disturbance stage, and the first load reactive power response value Q1 or the first grid reactive power response value Qe1 of the first disturbance stage can be recorded; a reactive disturbance of 0Var (restore to the initial state) can be output in the second disturbance stage, and the second load reactive power response value Q2 or the second grid reactive power response value Qe2 of the second disturbance stage can be recorded; a reactive disturbance of -15Var can be output in the third disturbance stage, and the third load reactive power response value Q3 or the third grid reactive power response value Qe3 of the third disturbance stage can be recorded; a reactive disturbance of 0Var can be output in the fourth disturbance stage, and the fourth load reactive power response value Q4 or the fourth grid reactive power response value Qe4 of the fourth disturbance stage can be recorded.

[0034] By actively injecting disturbances of varying amplitudes (e.g., alternating positive and negative), grid fluctuations or sudden load changes can be simulated, exposing potential current transformer faults (e.g., response delays and signal distortion) under dynamic operating conditions. Multiple disturbances in stages can reduce the probability of misjudgment due to sporadic interference (e.g., transient grid harmonics). For example, a fault condition is only identified when abnormal signals are present in multiple stages.

[0035] S103. Determine whether to accumulate abnormal signals based on the grid reactive power initial value and the grid reactive power response value corresponding to each disturbance stage, or determine whether to accumulate abnormal signals based on the load reactive power reference value and the load reactive power response value corresponding to each disturbance stage.

[0036] In some embodiments, the difference between the load reactive power response value at each stage and the load reactive power reference value or the response value at the adjacent stage is compared step by step, or the difference between the grid reactive power response value at each stage and the grid reactive power initial value or the response value at the adjacent stage is compared step by step, and whether to accumulate abnormal signals can be determined based on a preset threshold.

[0037] Specifically, when the grid reactive power response value follows the reactive power output by the inverter, the grid-side CT operates normally. For example, when the inverter outputs +300Var reactive power to the load, the grid should output -300Var reactive power to the load, and the grid-side CT operates normally. If a grid-side CT fails (e.g., short-circuit or open), the grid reactive power response value equals the initial grid reactive power value. In other words, when the absolute value of the difference between the grid reactive power response value and the initial grid reactive power value corresponding to each disturbance phase is less than a preset value, an abnormal signal is accumulated.

[0038] When the difference between the load reactive power response value and the load reactive power reference value Q0 is equal to 0, the grid-side CT operates normally. That is, under normal circumstances, when a reactive disturbance is applied to the load, the load reactive power response value does not change.

[0039] Exemplarily, when the absolute value of the difference between the first load reactive power response value Q1 and the load reactive power reference value Q0 is greater than a preset threshold, an abnormal signal is accumulated once. When the absolute value of the difference between the second load reactive power response value Q2 and the first load reactive power response value Q1 is greater than a preset threshold, an abnormal signal is accumulated once. When the absolute value of the difference between the third load reactive power response value Q3 and the second load reactive power response value Q2 is greater than a preset threshold, an abnormal signal is accumulated once. When the absolute value of the difference between the fourth load reactive power response value Q4 and the third load reactive power response value Q3 is greater than a preset threshold, an abnormal signal is accumulated once.

[0040] S104: Determine the health status of the grid-side current transformer according to the accumulated number of abnormal signals.

[0041] The health status includes fault status, uncertain status and normal operation status.

[0042] In some embodiments, when the number of accumulated abnormal signal occurrences is greater than or equal to a first set value (e.g., 3), the health status of the grid-side current transformer is determined to be a faulty state. When the number of accumulated abnormal signal occurrences is greater than or equal to a second set value and less than or equal to a third set value (e.g., 1 ≤ accumulated occurrences ≤ 2), the health status of the grid-side current transformer is determined to be an uncertain state. When the number of accumulated abnormal signal occurrences is equal to 0, the health status of the grid-side current transformer is determined to be a normal operating state.

[0043] The Fault state indicates frequent anomalies during multi-stage disturbances, suggesting a persistent problem with the grid-side current transformer (such as reverse connection, open circuit, or signal distortion). The Uncertain state indicates that sporadic anomalies may be caused by transient interference (such as grid harmonics) and require further verification. The Normal Operation state indicates that the response during all disturbance stages is as expected, indicating that the grid-side current transformer is functioning normally.

[0044] The grid-side current transformer fault detection method provided in an embodiment of the present invention controls the inverter to output initial reactive power in response to reactive scheduling, records the load's reactive power reference value and the grid's initial reactive power value, and can provide a comparison basis for responses in subsequent disturbance phases. By actively injecting disturbances of different amplitudes (such as alternating positive and negative), grid fluctuations or load mutation scenarios can be simulated, exposing potential faults of the current transformer under dynamic operating conditions. By comparing the reactive power response values ​​of adjacent phases with the reactive power reference value or the response value of the previous phase, if the difference exceeds a preset threshold, an abnormal signal is accumulated. Finally, the health status of the current transformer is determined based on the number of accumulated abnormal signals. In other words, the grid-side current transformer fault detection method provided in an embodiment of the present invention can detect whether the grid-side CT is faulty during power-on self-test when there is no sensor at the load end.

[0045] Figure 3 FIG. 1 is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention. Figure 3 As shown, the fault detection method includes:

[0046] S201 : Control the inverter to respond to reactive power scheduling to output initial reactive power, and record a load reactive power reference value.

[0047] S202. Control the inverter in sequence to output a reactive power disturbance of a first preset amplitude in a first disturbance stage, output a zero reactive power disturbance in a second disturbance stage, output a reactive power disturbance of a second preset amplitude in a third disturbance stage, and output a zero reactive power disturbance in a fourth disturbance stage, and record the grid reactive power response value or the load reactive power response value corresponding to each disturbance stage respectively.

[0048] Specifically, the first preset amplitude is greater than 0, the second preset amplitude is less than 0, and the first preset amplitude and the second preset amplitude are opposite to each other. For example, the first preset amplitude is +10Var, and the second preset amplitude is -10Var.

[0049] The load reactive power response value corresponding to the first disturbance stage is the first load reactive power response value Q1, the load reactive power response value corresponding to the second disturbance stage is the second load reactive power response value Q2, the load reactive power response value corresponding to the third disturbance stage is the third load reactive power response value Q3, and the load reactive power response value corresponding to the fourth disturbance stage is the fourth load reactive power response value Q4.

[0050] S203: When the difference between the load reactive power reference value and the first load reactive power response value is less than a first set threshold, accumulate an abnormal signal once.

[0051] Specifically, the first set threshold is a preset critical value used to determine whether the difference in responses between adjacent stages is abnormal. The first set threshold is less than 0, such as -300Var.

[0052] When the inverter adds forward reactive power (for example, 5% of rated power), the load's reactive power should theoretically equal the original load reactive power (i.e., the load's reactive power baseline value). However, a grid-side CT fault will cause the measured value to remain unchanged, and the load's reactive power will change in tandem with the inverter's output reactive power.

[0053] Assume that the load reactive power reference value Q0 = the initial reactive power output by the inverter + the initial value of the grid reactive power = QV1 + Qe0; the inverter superimposed forward reactive power is 400Var, and the first set threshold is -300Var.

[0054] When there is no fault in the grid-side CT, the first load reactive power response value Q1 should be Q0.

[0055] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial grid reactive power value Qe0. At this time, the reactive power output by the inverter-side CT is QV1+400Var. Then, based on the measurement and calculation of the inverter-side CT and the grid-side CT, the first load reactive power response value Q1=QV1+400+Qe0=Q0+400Var is obtained. At this time, Q0-Q1=Q0-(Q0+400)=-400Var<-300Var, and an abnormal signal is accumulated once.

[0056] S204: When the difference between the first load reactive power response value and the second load reactive power response value is greater than a second set threshold, accumulate an abnormal signal once.

[0057] Assume that the load reactive power reference value Q0 = the initial reactive power output by the inverter + the initial value of the grid reactive power = QV1 + Qe0, and the second set threshold is greater than 0, such as 300Var.

[0058] When there is no fault in the grid-side CT, the second load reactive power response value Q2 should be Q0.

[0059] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial grid reactive power value Qe0. At this time, the reactive power output by the inverter-side CT is QV1. Then, based on the measurement and calculation of the inverter-side CT and the grid-side CT, the second load reactive power response value Q2=QV1+Qe0=Q0 is obtained. At this time, Q1-Q2=Q0+400-Q0=400Var>300Var, and an abnormal signal is accumulated once.

[0060] S205: When the difference between the second load reactive power response value and the third load reactive power response value is greater than a second set threshold, accumulate an abnormal signal once.

[0061] When the inverter actively adds negative reactive power (e.g., -5% of rated power), the load's reactive power (i.e., the third load reactive power response value) should theoretically equal the load reactive power reference value. Assume that the load reactive power reference value Q0 = the initial reactive power output by the inverter + the initial reactive power value of the grid (QV1 + Qe0). The inverter's added negative reactive power is -400Var.

[0062] When there is no fault in the grid-side CT, the third load reactive power response value Q3 should be Q0.

[0063] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial grid reactive power value Qe0. At this time, the reactive power output by the inverter-side CT is QV1-400Var. Then, based on the measurements of the inverter-side CT and the grid-side CT, the third load reactive power response value Q3 = QV1-400 + Qe0 = Q0-400Var is obtained. At this time, Q2-Q3 = Q0-(Q0-400) = 400Var>300Var, and an abnormal signal is accumulated once.

[0064] S206: When the difference between the third load reactive power response value and the fourth load reactive power response value is less than a first set threshold, accumulate an abnormal signal once.

[0065] When there is no fault in the grid-side CT, the fourth load reactive power response value Q4 should be Q0.

[0066] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial grid reactive power value Qe0. At this time, the reactive power output by the inverter-side CT is equal to the initial reactive power QV1. Then, based on the measurement and calculation of the inverter-side CT and the grid-side CT, the fourth load reactive power response value Q4=QV1+Qe0=Q0 is obtained. At this time, Q3-Q4=Q0-400-Q0=-400Var<-300Var, and an abnormal signal is accumulated once.

[0067] S207: Determine the health status of the grid-side current transformer according to the accumulated number of abnormal signals.

[0068] Figure 4 FIG. 1 is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention. Figure 4 As shown, the fault detection method includes:

[0069] S301 : Control the inverter to respond to reactive power scheduling to output initial reactive power, and record a load reactive power reference value.

[0070] S302. Control the inverter in sequence to output a reactive power disturbance of a first preset amplitude in the first disturbance stage, output a zero reactive power disturbance in the second disturbance stage, output a reactive power disturbance of a second preset amplitude in the third disturbance stage, and output a zero reactive power disturbance in the fourth disturbance stage, and record the grid reactive power response value or the load reactive power response value corresponding to each disturbance stage respectively.

[0071] Specifically, the first preset amplitude is less than 0, the second preset amplitude is greater than 0, and the first preset amplitude and the second preset amplitude are opposite numbers.

[0072] The load reactive power response value corresponding to the first disturbance stage is the first load reactive power response value, the load reactive power response value corresponding to the second disturbance stage is the second load reactive power response value, the load reactive power response value corresponding to the third disturbance stage is the third load reactive power response value, and the load reactive power response value corresponding to the fourth disturbance stage is the fourth load reactive power response value.

[0073] S303: When the difference between the load reactive power reference value and the first load reactive power response value is greater than a second set threshold, accumulate an abnormal signal once.

[0074] When the inverter superimposes negative reactive power (e.g., reactive power of -5% of rated power), the load reactive power should theoretically equal the original load reactive power (i.e., the load reactive power baseline value). However, a grid-side CT fault will cause the grid reactive power response value to remain unchanged.

[0075] Assume that the load reactive power reference value Q0 = the initial reactive power output by the inverter + the initial value of the grid reactive power = QV1 + Qe0; the inverter superimposed negative reactive power is -400Var, and the second set threshold is 300Var.

[0076] When there is no fault in the grid-side CT, the first load reactive power response value Q1 should be Q0.

[0077] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial grid reactive power value Qe0. At this time, the reactive power output by the inverter-side CT is QV1-400Var. Then, based on the measurement and calculation of the inverter-side CT and the grid-side CT, the first load reactive power response value Q1=QV1-400+Qe0=Q0-400Var is obtained. At this time, Q0-Q1=Q0-(Q0-400)=400Var>300Var, and an abnormal signal is accumulated once.

[0078] S304: When the difference between the first load reactive power response value and the second load reactive power response value is less than a first set threshold, accumulate an abnormal signal once.

[0079] When the inverter stops adding reactive power, it is assumed that the load reactive power reference value Q0 = the initial reactive power output by the inverter + the initial value of the grid reactive power = QV1 + Qe0, and the first set threshold is -300Var.

[0080] When there is no fault in the grid-side CT, the second load reactive power response value Q2 should be Q0.

[0081] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial grid reactive power value Qe0. At this time, the reactive power output by the inverter-side CT is equal to the initial reactive power QV1. Then, based on the measurement and calculation of the inverter-side CT and the grid-side CT, the second load reactive power response value Q2=QV1+Qe0=Q0 is obtained. At this time, Q1-Q2=Q0-400-Q0=-400Var<-300Var, and an abnormal signal is accumulated once.

[0082] S305: When the difference between the second load reactive power response value and the third load reactive power response value is less than a first set threshold, accumulate an abnormal signal once.

[0083] When the inverter actively adds forward reactive power (e.g., 5% of rated power), the load's reactive power (i.e., the third load reactive power response value) should theoretically equal the load reactive power reference value. Assume that the load reactive power reference value Q0 = the initial reactive power output by the inverter + the initial grid reactive power value = QV1 + Qe0; and the inverter's added forward reactive power is +400Var.

[0084] When there is no fault in the grid-side CT, the third load reactive power response value Q3 should be Q0.

[0085] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial grid reactive power value Qe0. At this time, the reactive power output by the inverter-side CT is QV1-400Var. Then, based on the measurements of the inverter-side CT and the grid-side CT, the third load reactive power response value Q3=QV1+400+Qe0=Q0+400Var is obtained. At this time, Q2-Q3=Q0-(Q0+400)=-400Var<-300Var, and an abnormal signal is accumulated once.

[0086] S306: When the difference between the third load reactive power response value and the fourth load reactive power response value is greater than a second set threshold, accumulate an abnormal signal once.

[0087] When the inverter stops adding reactive power, theoretically the reactive power of the load (ie, the fourth load reactive power response value Q4) should be restored to the load reactive power reference value Q0.

[0088] When there is no fault in the grid-side CT, the fourth load reactive power response value Q4 should be Q0.

[0089] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial grid reactive power value Qe0. At this time, the reactive power output by the inverter-side CT is equal to the initial reactive power QV1. Then, based on the measurement and calculation of the inverter-side CT and the grid-side CT, the fourth load reactive power response value Q4 = QV1 + Qe0 = Q0. At this time, Q3-Q4 = Q0 + 400-Q0 = 400Var>300Var, and an abnormal signal is accumulated once.

[0090] S307: Determine the health status of the grid-side current transformer according to the accumulated number of abnormal signals.

[0091] Figure 5 FIG. 1 is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention. Figure 5 As shown, the fault detection method includes:

[0092] S401 : Control the inverter to respond to reactive power scheduling to output initial reactive power, and record a load reactive power reference value.

[0093] S402. Control the inverter in sequence to output a reactive power disturbance of a first preset amplitude in a first disturbance stage, output a zero reactive power disturbance in a second disturbance stage, output a reactive power disturbance of a second preset amplitude in a third disturbance stage, and output a zero reactive power disturbance in a fourth disturbance stage, and record the grid reactive power response value or the load reactive power response value corresponding to each disturbance stage respectively.

[0094] S403: When the absolute value of the difference between the load reactive power reference value and the first load reactive power response value is greater than a third set threshold, accumulate an abnormal signal once.

[0095] Specifically, when the inverter superimposes forward reactive power (for example, 5% of rated power), the load's reactive power should theoretically equal the original load reactive power (i.e., the load reactive power baseline value). However, a grid-side CT fault can cause the measured value to remain unchanged, and the load's reactive power will change in tandem with the inverter's output reactive power.

[0096] The third set threshold is greater than 0. Exemplarily, the third set threshold may be 300Var.

[0097] When there is no fault in the grid-side CT, the first load reactive power response value Q1 should be Q0.

[0098] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial grid reactive power value Qe0. At this time, the reactive power output by the inverter-side CT is QV1+400Var. Then, based on the measurement and calculation of the inverter-side CT and the grid-side CT, the first load reactive power response value Q1=QV1+400+Qe0=Q0+400Var is obtained. At this time, |Q0-Q1|=|Q0-(Q0+400)|=400Var, which is greater than 300Var. At this time, an abnormal signal is accumulated.

[0099] S404: When the absolute value of the difference between the first load reactive power response value and the second load reactive power response value is greater than a third set threshold, accumulate an abnormal signal once.

[0100] Specifically, after the inverter stops adding reactive power, when there is no fault in the grid-side CT, the second load reactive power response value Q2 should be Q0.

[0101] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial grid reactive power value Qe0. At this time, the reactive power output by the inverter-side CT is equal to the initial reactive power QV1. Then, the second load reactive power response value Q2 = QV1 + Qe0 = Q0 obtained based on the measurements of the inverter-side CT and the grid-side CT. At this time, |Q1-Q2| = |Q0+400-Q0| = 400Var>300Var, and an abnormal signal is accumulated once.

[0102] S405: When the absolute value of the difference between the second load reactive power response value and the third load reactive power response value is greater than a third set threshold, accumulate an abnormal signal once.

[0103] Specifically, when the inverter actively superimposes negative reactive power (such as reactive power of -5% of the rated power), theoretically the reactive power of the load (ie, the third load reactive power response value) should be equal to the load reactive power reference value.

[0104] When there is no fault in the grid-side CT, the third load reactive power response value Q3 should be Q0.

[0105] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial grid reactive power value Qe0. At this time, the reactive power output by the inverter-side CT is QV1-400Var. Then, based on the measurements of the inverter-side CT and the grid-side CT, the third load reactive power response value Q3 = QV1-400 + Qe0 = Q0-400Var is obtained. At this time, |Q2-Q3| = |Q0-(Q0-400)| = 400Var>300Var, and an abnormal signal is accumulated once.

[0106] S406: When the absolute value of the difference between the third load reactive power response value and the fourth load reactive power response value is greater than a third set threshold, accumulate an abnormal signal once.

[0107] Specifically, after the inverter stops adding reactive power, when there is no fault in the grid-side CT, the fourth load reactive power response value Q4 should be Q0.

[0108] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial grid reactive power value Qe0. At this time, the reactive power output by the inverter-side CT is equal to the initial reactive power QV1. Then, the fourth load reactive power response value Q4 calculated based on the measurements of the inverter-side CT and the grid-side CT is Q4=QV1+Qe0=Q0. At this time, |Q3-Q4|=|Q0+400-Q0|=400Var>300Var, and an abnormal signal is accumulated once.

[0109] S407: Determine the health status of the grid-side current transformer according to the accumulated number of abnormal signals.

[0110] Figure 6 FIG. 1 is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention. Figure 6 As shown, the fault detection method includes:

[0111] S501 : Control the inverter to respond to reactive power scheduling to output initial reactive power, and record the initial value of the grid reactive power.

[0112] S502. Control the inverter in sequence to output a reactive power disturbance of a first preset amplitude in the first disturbance stage, output a zero reactive power disturbance in the second disturbance stage, output a reactive power disturbance of a second preset amplitude in the third disturbance stage, and output zero reactive power disturbance in the fourth disturbance stage, and record the grid reactive power response value or the load reactive power reference value corresponding to each disturbance stage.

[0113] Specifically, the first preset amplitude is greater than 0, the second preset amplitude is less than 0, and the first preset amplitude and the second preset amplitude are opposite numbers.

[0114] The grid reactive power response value corresponding to the first disturbance stage is the first grid reactive power response value Qe1, the grid reactive power response value corresponding to the second disturbance stage is the second grid reactive power response value Qe2, the grid reactive power response value corresponding to the third disturbance stage is the third grid reactive power response value Qe3, and the grid reactive power response value corresponding to the fourth disturbance stage is the fourth grid reactive power response value Qe4.

[0115] S503: When the difference between the first grid reactive power response value and the grid reactive power initial value is greater than a fourth set threshold, accumulate an abnormal signal once.

[0116] Specifically, when the inverter superimposes forward reactive power (such as a reactive power of 5% of the rated power), theoretically the reactive power of the grid should be equal to the original grid reactive power (i.e., the initial value of the grid reactive power Qe0) plus the opposite of the superimposed reactive power (such as a reactive power of -5% of the rated power).

[0117] The fourth threshold is less than 0, and its absolute value is generally half of the inverter's superimposed reactive power. Assuming the grid's initial reactive power is Qe0 and the inverter's superimposed forward reactive power is 300Var, the fourth threshold is -150Var.

[0118] When there is no fault in the grid-side CT, the first grid reactive power response value Qe1=Qe0-300, and at this time Qe1-Qe0=(Qe0-300)-Qe0=-300Var<-150Var.

[0119] However, when the grid-side CT fails, the first grid reactive power response value Qe1=Qe0. At this time, the first grid reactive power response value Qe1 minus the grid reactive power initial value Qe0 is zero, which is greater than -150Var. At this time, an abnormal signal is accumulated.

[0120] S504: When the difference between the reactive power response value of the second power grid and the reactive power response value of the first power grid is less than a fifth set threshold, accumulate an abnormal signal once.

[0121] Specifically, the fifth set threshold is greater than 0. Exemplarily, the fifth set threshold is 150Var.

[0122] After the inverter stops adding reactive power, if the grid-side CT is not faulty, the second grid reactive power response value Qe2 should be the initial grid reactive power value Qe0. However, if the grid-side CT fails, the grid-side CT's reactive power response value remains unchanged, i.e., it is equal to the first grid reactive power response value Qe1 = Qe0. At this time, Qe2 - Qe1 = 0 < 150Var, and an abnormal signal is accumulated.

[0123] S505: When the difference between the reactive power response value of the third power grid and the reactive power response value of the second power grid is less than a fifth set threshold, accumulate an abnormal signal once.

[0124] Specifically, when the inverter superimposes negative reactive power (such as reactive power of -5% of the rated power), theoretically the reactive power of the grid (i.e., the third grid reactive power response value) should be equal to the initial value of the grid reactive power plus the inverse of the superimposed reactive power (such as reactive power of 5% of the rated power).

[0125] The negative reactive power added by the inverter is -300Var, and the fifth set threshold is 150Var.

[0126] When the grid-side CT is not faulty, the third grid reactive power response value Qe3 should be Qe2 + 300Var. However, when the grid-side CT is faulty, the grid-side CT reactive power response value remains unchanged, that is, it is equal to the second grid reactive power response value. At this time, Qe3 - Qe2 = 0 < 150Var, and an abnormal signal is accumulated.

[0127] S506: When the difference between the reactive power response value of the fourth power grid and the reactive power response value of the third power grid is greater than a fourth set threshold, accumulate an abnormal signal once.

[0128] Specifically, after the inverter stops adding reactive power, theoretically the reactive power of the grid (ie, the fourth grid reactive power response value Qe4) should be restored to the initial grid reactive power value Qe0.

[0129] When the grid-side CT is not faulty, the fourth grid reactive power response value Qe4 should be the initial grid reactive power value Qe0. However, when the grid-side CT fails, the grid-side CT's reactive power response value remains unchanged, i.e., it is equal to the third grid reactive power response value. In this case, Qe4 - Qe3 = 0 > -150Var, and an abnormal signal is accumulated.

[0130] S507: Determine the health status of the grid-side current transformer according to the accumulated number of abnormal signals.

[0131] Figure 7 FIG. 1 is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention. Figure 7 As shown, the fault detection method includes:

[0132] S601 : Control the inverter to respond to reactive power scheduling to output initial reactive power, and record the initial value of the grid reactive power.

[0133] S602. Control the inverter in sequence to output a reactive power disturbance of a first preset amplitude in a first disturbance stage, output a zero reactive power disturbance in a second disturbance stage, output a reactive power disturbance of a second preset amplitude in a third disturbance stage, and output a zero reactive power disturbance in a fourth disturbance stage, and record the grid reactive power response value or the load reactive power reference value corresponding to each disturbance stage.

[0134] Specifically, the first preset amplitude is less than 0, the second preset amplitude is greater than 0, and the first preset amplitude and the second preset amplitude are reciprocal of each other; the grid reactive power response value corresponding to the first disturbance stage is the first grid reactive power response value, the grid reactive power response value corresponding to the second disturbance stage is the second grid reactive power response value, the grid reactive power response value corresponding to the third disturbance stage is the third grid reactive power response value, and the grid reactive power response value corresponding to the fourth disturbance stage is the fourth grid reactive power response value.

[0135] S603: When the difference between the first grid reactive power response value and the grid reactive power initial value is less than a fifth set threshold, accumulate an abnormal signal once.

[0136] Specifically, when the inverter superimposes negative reactive power (such as reactive power of -5% of the rated power), theoretically the reactive power of the grid should be equal to the original grid reactive power (that is, the initial value of the grid reactive power Qe0) plus the opposite of the superimposed reactive power (such as reactive power of +5% of the rated power).

[0137] The fifth threshold is greater than 0. The absolute value of the fifth threshold is generally half of the inverter's superimposed reactive power. Assuming the grid's initial reactive power is Qe0 and the inverter's superimposed forward reactive power is 300Var, the fifth threshold is 150Var.

[0138] When there is no fault in the grid-side CT, the first grid reactive power response value Qe1=Qe0+300, and at this time Qe1-Qe0=(Qe0+300)-Qe0=+300Var>150Var.

[0139] However, when the grid-side CT fails, the first grid reactive power response value Qe1=Qe0. At this time, the first grid reactive power response value Qe1 minus the grid reactive power initial value Qe0 is zero, which is less than 150Var. At this time, an abnormal signal is accumulated.

[0140] S604: When the difference between the reactive power response value of the second power grid and the reactive power response value of the first power grid is greater than a fourth set threshold, accumulate an abnormal signal once.

[0141] Specifically, the fourth set threshold is less than 0. Exemplarily, the fourth set threshold is -150Var.

[0142] After the inverter stops adding reactive power, if the grid-side CT is not faulty, the second grid reactive power response value Qe2 should be equal to the initial grid reactive power value Qe0. However, if the grid-side CT fails, the grid-side CT's reactive power response value remains unchanged, i.e., equal to the first grid reactive power response value Qe1 = Qe0. At this point, Qe2 - Qe1 = 0 > -150Var, and an abnormal signal is accumulated.

[0143] S605: When the difference between the reactive power response value of the third power grid and the reactive power response value of the second power grid is greater than a fourth set threshold, accumulate an abnormal signal once.

[0144] Specifically, when the inverter superimposes negative reactive power (such as reactive power of -5% of the rated power), theoretically the reactive power of the grid (i.e., the third grid reactive power response value) should be equal to the initial value of the grid reactive power plus the inverse of the superimposed reactive power (such as reactive power of 5% of the rated power).

[0145] The inverter superimposed forward reactive power is +300Var, and the fourth set threshold is -150Var.

[0146] When the grid-side CT is not faulty, the third grid reactive power response value Qe3 should be Qe2-300Var. However, when the grid-side CT is faulty, the grid-side CT reactive power response value remains unchanged, that is, it is equal to the second grid reactive power response value. At this time, Qe3-Qe2=0>-150Var, and an abnormal signal is accumulated.

[0147] S606: When the difference between the reactive power response value of the fourth power grid and the reactive power response value of the third power grid is less than a fifth set threshold, accumulate an abnormal signal once.

[0148] Specifically, after the inverter stops adding reactive power, theoretically the reactive power of the grid (ie, the fourth grid reactive power response value Qe4) should be restored to the initial grid reactive power value Qe0.

[0149] When the grid-side CT is not faulty, the fourth grid reactive power response value Qe4 should be the initial grid reactive power value Qe0. However, when the grid-side CT fails, the grid-side CT reactive power response value remains unchanged, that is, it is equal to the third grid reactive power response value. In this case, Qe4-Qe3=0<150Var, and an abnormal signal is accumulated.

[0150] S607: Determine the health status of the grid-side current transformer according to the accumulated number of abnormal signals.

[0151] Figure 8 FIG. 1 is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention. Figure 8 As shown, the fault detection method includes:

[0152] S701 , controlling the inverter to respond to reactive power scheduling to output initial reactive power, and recording the initial value of the grid reactive power.

[0153] S702. Control the inverter in sequence to output a reactive power disturbance of a first preset amplitude in the first disturbance stage, output a zero reactive power disturbance in the second disturbance stage, output a reactive power disturbance of a second preset amplitude in the third disturbance stage, and output zero reactive power disturbance in the fourth disturbance stage, and record the grid reactive power response value or the load reactive power reference value corresponding to each disturbance stage.

[0154] S703: When the absolute value of the difference between the initial grid reactive power value and the first grid reactive power response value is less than a sixth set threshold, accumulate an abnormal signal once.

[0155] Specifically, when the inverter superimposes forward reactive power (such as a reactive power of 5% of the rated power), theoretically the reactive power of the grid should be equal to the original grid reactive power (i.e., the initial value of the grid reactive power Qe0) plus the opposite of the superimposed reactive power (such as a reactive power of -5% of the rated power).

[0156] The sixth set threshold is greater than 0. Exemplarily, the sixth set threshold may be 150Var.

[0157] When there is no fault in the grid-side CT, the first grid reactive power response value Qe1 should be Qe0-300.

[0158] However, when the grid-side CT fails, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the initial value of the grid reactive power Qe0. At this time, |Qe0-Qe1|=|Qe0-Qe0|=0Var is less than 150Var, and an abnormal signal is accumulated once.

[0159] S704: When the absolute value of the difference between the reactive power response value of the first power grid and the reactive power response value of the second power grid is less than a sixth set threshold, accumulate an abnormal signal once.

[0160] Specifically, after the inverter stops adding reactive power, if the grid-side CT is not faulty, the second grid reactive power response value Qe2 should be equal to the initial grid reactive power value Qe0. However, if the grid-side CT fails, the grid-side CT's reactive power response value remains unchanged, i.e., equal to the first grid reactive power response value Qe1 = Qe0. At this point, |Qe2 - Qe1| = 0 < 150Var, and an abnormal signal is accumulated.

[0161] S705: When the absolute value of the difference between the reactive power response value of the second power grid and the reactive power response value of the third power grid is less than a sixth set threshold, accumulate an abnormal signal once.

[0162] Specifically, when the inverter superimposes negative reactive power (such as reactive power of -5% of the rated power), theoretically the reactive power of the grid (i.e., the third grid reactive power response value) should be equal to the initial value of the grid reactive power plus the inverse of the superimposed reactive power (such as reactive power of 5% of the rated power).

[0163] When the grid-side CT is not faulty, the third grid reactive power response value, Qe3, should be Qe2 + 300Var. However, when the grid-side CT fails, the grid-side CT's reactive power response value remains unchanged, equal to the second grid reactive power response value. In this case, |Qe3 - Qe2| = 0 < 150Var, and an abnormal signal is accumulated.

[0164] S706: When the absolute value of the difference between the reactive power response value of the third power grid and the reactive power response value of the fourth power grid is less than a sixth set threshold, accumulate an abnormal signal once.

[0165] Specifically, after the inverter stops adding reactive power, theoretically the reactive power of the grid (ie, the fourth grid reactive power response value Qe4) should be restored to the initial grid reactive power value Qe0.

[0166] When the grid-side CT is not faulty, the fourth grid reactive power response value Qe4 should be the initial grid reactive power value Qe0. However, when the grid-side CT fails, the grid-side CT's reactive power response value remains unchanged, i.e., it is equal to the third grid reactive power response value. In this case, |Qe4-Qe3|=0<150Var, and an abnormal signal is accumulated.

[0167] S707: Determine the health status of the grid-side current transformer according to the accumulated number of abnormal signals.

[0168] Figure 9 FIG. 1 is a flow chart of another method for detecting a fault of a grid-side current transformer of an inverter provided by an embodiment of the present invention. Figure 9 As shown, the fault detection method includes:

[0169] S801 , controlling the inverter to output initial reactive power in response to reactive power scheduling, and recording the reactive power reference value of the load and the initial reactive power value of the grid.

[0170] S802 , sequentially controlling the inverter to output reactive power disturbances of preset amplitudes at each disturbance stage, and respectively recording the grid reactive power response value or the load reactive power response value corresponding to each disturbance stage.

[0171] S803. Determine whether to accumulate abnormal signals based on the grid reactive power initial value and the grid reactive power response value corresponding to each disturbance stage, or determine whether to accumulate abnormal signals based on the load reactive power reference value and the load reactive power response value corresponding to each disturbance stage.

[0172] S804: Determine the health status of the grid-side current transformer according to the accumulated number of abnormal signals.

[0173] S805: When it is determined that the health status of the grid-side current transformer is a fault state, re-detect the health status after a first set time delay.

[0174] S806: When it is determined that the health status of the grid-side current transformer is in an uncertain state, re-detect the health status after a second set time delay.

[0175] S807: When it is determined that the health status of the grid-side current transformer is a normal operating status, re-detect the health status after a third set time delay.

[0176] The first set time is greater than the second set time, and the third set time is greater than the first set time. For example, the first set time may be 5 minutes, the second set time may be 1 minute, and the third set time may be 24 hours.

[0177] Specifically, when the system determines that the current transformer is faulty, protection mechanisms (such as disconnection from the grid or derating) may have already been triggered. Waiting for the system to stabilize is necessary to ensure that the fault does not escalate if rechecked immediately (for example, if the arc is not completely extinguished). Maintenance personnel may need to be present for on-site inspection. A longer delay increases the response window. If the fault persists, frequent rechecks waste resources and may prevent recovery. Therefore, a moderate initial set time is recommended.

[0178] An indeterminate state may be caused by a transient disturbance (such as grid harmonics or sensor noise), requiring retesting to confirm whether it is a true fault. A shorter delay allows for quick verification of the anomaly (e.g., if the disturbance lasts only a few seconds), thus minimizing the second set time.

[0179] When the system is operating normally, regular monitoring is required to prevent potential failures, but the frequency should not be too high, so the third setting time is set to the longest.

[0180] In the specific implementation process, the detection conditions are single-machine grid-connected mode and the inverter is in operation, grid sampling uses CT, anti-backflow is enabled or self-generation and self-use mode. Taking a single-phase 6KW photovoltaic storage inverter as an example, the steps of using the fault detection method of the present invention are explained:

[0181] S1: Under initial conditions, the inverter outputs reactive power superimposed with 0% rated power, allowing the inverter to output reactive power in response to reactive power scheduling, and the load reactive power reference value is recorded as Q0.

[0182] S2: The inverter outputs a reactive power superimposed with 5% of the rated power. After a 1s delay, the reactive power response value of the first load is Q1. The first reactive difference ΔQ1 is calculated as Q0-Q1. If ΔQ1 is less than -300Var, the cumulative number of grid-side CT abnormal signals is increased by 1; the first load reactive power response value Q1 is recorded.

[0183] S3: The inverter outputs reactive power superimposed with 0% rated power. After a 1s delay, the reactive power response value of the second load is Q2. The second reactive difference ΔQ2 is calculated as Q1-Q2. If ΔQ2 is greater than 300Var, the cumulative number of grid-side CT abnormal signals is increased by 1; the reactive power response value of the second load is Q2.

[0184] S4: The inverter outputs a reactive power superimposed with -5% of the rated power. After a 1s delay, the reactive power response value of the third load is Q3. The third reactive difference ΔQ3 = Q2-Q3 is calculated. If ΔQ3 is greater than 300Var, the cumulative number of grid-side CT abnormal signals is increased by 1; the reactive power response value of the third load is recorded as Q3.

[0185] S5: The inverter outputs reactive power superimposed with 0% rated power. After a 1s delay, the reactive power response value of the fourth load is Q4. The fourth reactive difference ΔQ4 is calculated as Q3-Q4. If ΔQ4 is less than 300Var, the cumulative number of abnormal CT signals on the grid side is increased by 1.

[0186] S6: If the cumulative number of grid-side CT abnormal signals is greater than or equal to 4, the grid-side CT health status is determined to be faulty, an alarm is triggered, inverter power output is disabled, and retest is performed after 5 minutes. If the cumulative number of grid-side CT abnormal signals is greater than or equal to 1 and less than or equal to 3, the grid-side CT health status is determined to be uncertain, and retest is performed after 1 minute. If the cumulative number of grid-side CT abnormal signals is equal to 0, the grid-side CT sampling is normal, and retest is performed after 24 hours.

[0187] The above description only illustrates the technical solution of the present invention and does not limit the present invention in any form. Once those skilled in the art know the basic creative concept, they can use the methods and technical contents disclosed above to make many possible changes and modifications to the solution of the present invention without departing from the scope of the solution of the present invention, or modify it into an equivalent embodiment with equivalent changes.

[0188] For example, the reactive power superposition process described in the article can be: no superposition → reactive power superposition → no superposition → reactive power superposition → no superposition, no superposition → reactive power superposition → reactive power superposition… → no superposition → reactive power superposition → reactive power superposition… → no superposition, no superposition → reactive power superposition →… → reactive power superposition → no superposition, etc., and the corresponding reactive power difference calculation methods.

[0189] Fault judgment mechanism (different fault judgment values ​​are used according to different reactive power superposition modes. For example, if the reactive power superposition changes n times, i represents the cumulative number of abnormal signals. If i≥n, the grid-side CT is judged to be faulty. If 1≤i≤n, the grid-side CT is judged to be in an uncertain state. If i<1, the grid-side CT is judged to be in normal operating state).

[0190] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for detecting a fault of a current transformer on the grid side of an inverter, characterized in that: include: Controlling the inverter to output initial reactive power in response to reactive power scheduling, and recording the initial value of grid reactive power or the reference value of load reactive power; The inverter is sequentially controlled to output a reactive power disturbance of a preset amplitude at each disturbance stage, and the grid reactive power response value or the load reactive power response value corresponding to each disturbance stage is recorded respectively; wherein the preset amplitudes of the reactive power disturbances at different disturbance stages are different or the same; Determining whether to accumulate abnormal signals based on the grid reactive power initial value and the grid reactive power response value corresponding to each disturbance stage, or determining whether to accumulate abnormal signals based on the load reactive power reference value and the load reactive power response value corresponding to each disturbance stage; Determining the health state of the grid-side current transformer according to the accumulated number of abnormal signals; wherein the health state includes a fault state, an uncertain state and a normal operating state; The steps of sequentially controlling the inverter to output reactive power disturbances of preset amplitudes at each disturbance stage, and respectively recording grid reactive power response values ​​or load reactive power response values ​​corresponding to each disturbance stage include: The inverter is sequentially controlled to output a reactive power disturbance of a first preset amplitude in a first disturbance stage, to output a zero reactive power disturbance in a second disturbance stage, to output a reactive power disturbance of a second preset amplitude in a third disturbance stage, and to output a zero reactive power disturbance in a fourth disturbance stage, and the grid reactive power response value or the load reactive power response value corresponding to each disturbance stage is recorded respectively.

2. The method for detecting a fault of a current transformer on the grid side of an inverter according to claim 1, wherein: The first preset amplitude is greater than 0, the second preset amplitude is less than 0, and the first preset amplitude and the second preset amplitude are opposite numbers of each other; The load reactive power response value corresponding to the first disturbance stage is a first load reactive power response value, the load reactive power response value corresponding to the second disturbance stage is a second load reactive power response value, the load reactive power response value corresponding to the third disturbance stage is a third load reactive power response value, and the load reactive power response value corresponding to the fourth disturbance stage is a fourth load reactive power response value; The step of determining whether to accumulate abnormal signals based on the load reactive power reference value and the load reactive power response value corresponding to each disturbance stage includes: When the difference between the load reactive power reference value and the first load reactive power response value is less than a first set threshold, accumulating the abnormal signal once; When the difference between the first load reactive power response value and the second load reactive power response value is greater than a second set threshold, accumulating the abnormal signal once; When the difference between the second load reactive power response value and the third load reactive power response value is greater than the second set threshold, accumulating the abnormal signal once; When the difference between the third load reactive power response value and the fourth load reactive power response value is less than the first set threshold, the abnormal signal is accumulated once; wherein the first set threshold is less than 0 and the second set threshold is greater than 0.

3. The method for detecting a fault of a current transformer on the grid side of an inverter according to claim 1, wherein: The first preset amplitude is less than 0, the second preset amplitude is greater than 0, and the first preset amplitude and the second preset amplitude are opposite numbers of each other; The load reactive power response value corresponding to the first disturbance stage is a first load reactive power response value, the load reactive power response value corresponding to the second disturbance stage is a second load reactive power response value, the load reactive power response value corresponding to the third disturbance stage is a third load reactive power response value, and the load reactive power response value corresponding to the fourth disturbance stage is a fourth load reactive power response value; The step of determining whether to accumulate abnormal signals based on the load reactive power reference value and the load reactive power response value corresponding to each disturbance stage includes: When the difference between the load reactive power reference value and the first load reactive power response value is greater than a second set threshold, accumulating the abnormal signal once; When the difference between the first load reactive power response value and the second load reactive power response value is less than a first set threshold, accumulating the abnormal signal once; When the difference between the second load reactive power response value and the third load reactive power response value is less than the first set threshold, accumulating the abnormal signal once; When the difference between the third load reactive power response value and the fourth load reactive power response value is greater than the second set threshold, the abnormal signal is accumulated once; wherein the first set threshold is less than 0 and the second set threshold is greater than 0.

4. The method for detecting a fault of a current transformer on the grid side of an inverter according to claim 1, wherein: The load reactive power response value corresponding to the first disturbance stage is a first load reactive power response value, the load reactive power response value corresponding to the second disturbance stage is a second load reactive power response value, the load reactive power response value corresponding to the third disturbance stage is a third load reactive power response value, and the load reactive power response value corresponding to the fourth disturbance stage is a fourth load reactive power response value; The step of determining whether to accumulate abnormal signals based on the load reactive power reference value and the load reactive power response values ​​corresponding to each disturbance stage includes: When the absolute value of the difference between the load reactive power reference value and the first load reactive power response value is greater than a third set threshold, accumulating the abnormal signal once; When the absolute value of the difference between the first load reactive power response value and the second load reactive power response value is greater than the third set threshold, accumulating the abnormal signal once; When the absolute value of the difference between the second load reactive power response value and the third load reactive power response value is greater than the third set threshold, accumulating the abnormal signal once; When the absolute value of the difference between the third load reactive power response value and the fourth load reactive power response value is greater than the third set threshold, the abnormal signal is accumulated once.

5. The method for detecting a fault of a grid-side current transformer of an inverter according to claim 1, wherein the first preset amplitude is greater than 0, the second preset amplitude is less than 0, and the first preset amplitude and the second preset amplitude are inverse numbers of each other; The grid reactive power response value corresponding to the first disturbance stage is a first grid reactive power response value, the grid reactive power response value corresponding to the second disturbance stage is a second grid reactive power response value, the grid reactive power response value corresponding to the third disturbance stage is a third grid reactive power response value, and the grid reactive power response value corresponding to the fourth disturbance stage is a fourth grid reactive power response value; The step of determining whether to accumulate abnormal signals based on the grid reactive power initial value and the grid reactive power response values ​​corresponding to each disturbance stage includes: When the difference between the first grid reactive power response value and the grid reactive power initial value is greater than a fourth set threshold, accumulating the abnormal signal once; When the difference between the reactive power response value of the second power grid and the reactive power response value of the first power grid is less than a fifth set threshold, accumulating the abnormal signal once; When the difference between the third grid reactive power response value and the second grid reactive power response value is less than the fifth set threshold, accumulating the abnormal signal once; When the difference between the fourth grid reactive power response value and the third grid reactive power response value is greater than the fourth set threshold, the abnormal signal is accumulated once; wherein the fourth set threshold is less than 0 and the fifth set threshold is greater than 0.

6. The method for detecting a fault of a grid-side current transformer of an inverter according to claim 1, wherein the first preset amplitude is less than 0, the second preset amplitude is greater than 0, and the first preset amplitude and the second preset amplitude are inverse numbers of each other; The grid reactive power response value corresponding to the first disturbance stage is a first grid reactive power response value, the grid reactive power response value corresponding to the second disturbance stage is a second grid reactive power response value, the grid reactive power response value corresponding to the third disturbance stage is a third grid reactive power response value, and the grid reactive power response value corresponding to the fourth disturbance stage is a fourth grid reactive power response value; The step of determining whether to accumulate abnormal signals based on the grid reactive power initial value and the grid reactive power response values ​​corresponding to each disturbance stage includes: When the difference between the first grid reactive power response value and the grid reactive power initial value is less than a fifth set threshold, accumulating the abnormal signal once; When the difference between the reactive power response value of the second power grid and the reactive power response value of the first power grid is greater than a fourth set threshold, accumulating the abnormal signal once; When the difference between the third grid reactive power response value and the second grid reactive power response value is greater than the fourth set threshold, accumulating the abnormal signal once; When the difference between the fourth grid reactive power response value and the third grid reactive power response value is less than the fifth set threshold, the abnormal signal is accumulated once; wherein the fourth set threshold is less than 0 and the fifth set threshold is greater than 0.

7. The method for detecting a fault of a current transformer on the grid side of an inverter according to claim 1, wherein: The grid reactive power response value corresponding to the first disturbance stage is a first grid reactive power response value, the grid reactive power response value corresponding to the second disturbance stage is a second grid reactive power response value, the grid reactive power response value corresponding to the third disturbance stage is a third grid reactive power response value, and the grid reactive power response value corresponding to the fourth disturbance stage is a fourth grid reactive power response value; The step of determining whether to accumulate abnormal signals based on the grid reactive power initial value and the grid reactive power response values ​​corresponding to each disturbance stage includes: When the absolute value of the difference between the initial grid reactive power value and the first grid reactive power response value is less than a sixth set threshold, accumulating the abnormal signal once; When the absolute value of the difference between the first grid reactive power response value and the second grid reactive power response value is less than the sixth set threshold, accumulating the abnormal signal once; When the absolute value of the difference between the second grid reactive power response value and the third grid reactive power response value is less than the sixth set threshold, accumulating the abnormal signal once; When the absolute value of the difference between the third power grid reactive power response value and the fourth power grid reactive power response value is smaller than the sixth set threshold, the abnormal signal is accumulated once.

8. The method for detecting a fault of a current transformer on the grid side of an inverter according to claim 1, wherein: The step of determining the health status of the grid-side current transformer according to the accumulated number of abnormal signals includes: When the accumulated number is greater than or equal to a first set value, determining that the health state of the grid-side current transformer is the fault state; When the accumulated number of times is greater than or equal to a second set value and less than or equal to a third set value, determining that the health state of the grid-side current transformer is the uncertain state; When the accumulated number is equal to 0, it is determined that the health state of the grid-side current transformer is the normal operating state; wherein the first set value is greater than the third set value.

9. The method for detecting a fault of a current transformer on the grid side of an inverter according to claim 1, wherein: Also includes: When it is determined that the health state of the grid-side current transformer is the fault state, re-detecting the health state after a first set time delay; When it is determined that the health state of the grid-side current transformer is the uncertain state, re-detecting the health state after a second set time delay; When it is determined that the health state of the grid-side current transformer is the normal operating state, the health state is re-detected after a delay of a third set time; wherein the first set time is greater than the second set time, and the third set time is greater than the first set time.

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