Fault detection method for power grid side current transformer of inverter

Abstract

The invention discloses a fault detection method for a power grid side current transformer of an inverter, and the method comprises the steps: controlling the inverter to respond to reactive scheduling and output initial reactive power, and recording a power grid reactive power initial value or a load reactive power reference value; sequentially controlling the inverter to output reactive power disturbance with a preset amplitude in each disturbance stage, and respectively recording a power grid reactive power response value or a load reactive power response value corresponding to each disturbance stage; determining whether to accumulate abnormal signals based on the power grid reactive power initial value and the power grid reactive power response value corresponding to each disturbance stage; or determining whether to accumulate the 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 state of the power grid side current transformer according to the accumulated number of times of the abnormal signals. According to the invention, when no sensor is arranged at the load end, whether the power grid side CT has a fault or not can be detected during power-on self-test.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a method for detecting faults of a grid-side current transformer of an inverter. Background Art

[0002] When a photovoltaic energy storage inverter operates in the anti-islanding or self-consumption mode, the grid-side current transformer (CT) plays a very crucial role. Once the CT has abnormalities such as reverse connection, signal short circuit, signal open circuit, etc., it will lead to the loss of control of anti-islanding and the loss of control of self-consumption. Therefore, generally sensors are provided on the grid side, the load side, and the inverter side. By using the fact that the load reactive power = grid reactive power + inverter reactive power, when any abnormality occurs in the grid-side CT, the load reactive power ≠ grid reactive power + inverter reactive power, thereby detecting the abnormality of the grid-side CT. However, when there is no sensor at the load end, the above solution is not applicable and it is impossible to detect whether the grid-side CT is faulty during the power-on self-check. Summary of the Invention

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

[0004] An embodiment of the present invention provides a method for detecting faults of a grid-side current transformer of an inverter, including: controlling the inverter to respond to reactive power scheduling to output an initial reactive power, and recording the initial value of the reactive power on the grid side or the reference value of the load reactive power; sequentially controlling the inverter to output reactive power disturbances with a preset amplitude in each disturbance stage, and respectively recording the grid reactive power response values or the load reactive power response values corresponding to each disturbance stage; determining whether to accumulate abnormal signals based on the initial value of the grid reactive power and the grid reactive power response values corresponding to each disturbance stage, or determining whether to accumulate abnormal signals based on the reference value of the load reactive power and the load reactive power response values corresponding to each disturbance stage; determining the health state of the grid-side current transformer according to the accumulation times of the abnormal signals; wherein the health state includes a fault state, an uncertain state, and a normal operation state.

[0005] The fault detection method for the grid-side current transformer provided by the embodiment of the present invention controls the inverter to respond to reactive power scheduling and output the initial reactive power, and records the reactive power reference value of the load and the initial value of the grid reactive power, which can provide a comparison basis for the response in the subsequent disturbance stage. By actively injecting disturbances with different amplitudes (such as positive and negative alternation), scenarios of grid fluctuations or load mutations can be simulated, exposing potential faults of the current transformer under dynamic conditions. By comparing the difference between the reactive power response value in the adjacent stage and the reactive power reference value or the response value in the previous stage, if it exceeds the preset threshold, the abnormal signal is accumulated. Finally, the health status of the current transformer is judged according to the accumulated number of abnormal signals. That is to say, the fault detection method for the grid-side current transformer provided by the embodiment of the present invention can detect whether the grid-side CT is faulty during power-on self-check when there is no sensor at the load end.

[0006] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become easily 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 will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

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

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

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

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

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

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

[0014] Figure 7 It is a flowchart of another method for detecting faults in the grid - side current transformer of an inverter provided by an embodiment of the present invention;

[0015] Figure 8 It is a flowchart of another method for detecting faults in the grid - side current transformer of an inverter provided by an embodiment of the present invention;

[0016] Figure 9 It is a flowchart of another method for detecting faults in the grid - side current transformer of an inverter provided by an embodiment of the present invention. Detailed implementation manners

[0017] In order to enable those skilled in the art to better understand the solution 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 accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0018] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above - mentioned drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order different from those illustrated or described here. In addition, the terms "including" and "having" and any variations thereof are intended to cover non - exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0019] Figure 1 It is a flowchart of a method for detecting faults in the grid - side current transformer of an inverter provided by an embodiment of the present invention. The method of this embodiment can be executed by the control device of the inverter. The control device can be implemented in software and / or hardware and can be integrated on the energy storage and photovoltaic system.

[0020] As Figure 1 shown, the method for detecting faults in the grid - side current transformer includes:

[0021] S101. Control the inverter to respond to the reactive power dispatch and output the initial reactive power, and record the initial value of the grid reactive power or the reference value of the load reactive power.

[0022] An inverter is a power electronic device used to convert direct current (such as the electrical energy generated by solar panels) into alternating current and can adjust the active power and reactive power of the output as needed.

[0023] Inverter reactive power scheduling refers to the inverter dynamically adjusting the output reactive power according to the reactive power demand instructions of the power grid or the energy management system to maintain the stability of the power grid voltage or meet the power factor requirements.

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

[0025] The load reactive power reference value is the reference value of the load reactive power recorded under the non-disturbed state and is used for the judgment of abnormal signals in the subsequent disturbance stage.

[0026] The initial value of the grid reactive power is the reference value of the grid reactive power recorded under the non-disturbed state and is used for the judgment of abnormal signals in the subsequent disturbance stage.

[0027] Figure 2 It is a schematic diagram of grid-side CT abnormal detection provided by an embodiment of the present invention. As Figure 2 shown, by measuring the current and voltage output by the inverter, the reactive power Q_inv provided by the inverter can be calculated. By measuring the current and voltage on the grid side, the grid reactive power value Q_grid can be calculated. According to the power balance formula Q_load = Q_grid + Q_inv, the load reactive power value Q_load can be obtained.

[0028] The reactive power reference value provides a comparison basis for the response in the subsequent disturbance stage. Without the reactive power reference value, it is impossible to quantify the change in reactive power caused by the disturbance and it is difficult to judge whether it is caused by a current transformer failure.

[0029] S102. Control the inverter to output reactive power disturbances with a preset amplitude in each disturbance stage in sequence, and record the corresponding grid reactive power response value or load reactive power response value in each disturbance stage respectively.

[0030] Specifically, the disturbance stage 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 with a preset amplitude is a preset value of the rated power of a single phase of the inverter. Among them, the preset amplitudes in the reactive power disturbances in different disturbance stages are different or the same.

[0032] The reactive power response value of the load refers to the actual calculated value of the reactive power at the load end after each disturbance stage. The reactive power response value of the load is equal to the reactive power output by the inverter plus the reactive power response value on the grid side. Among them, the reactive power output by the inverter is a known quantity, and the reactive power on the grid side is calculated from the voltage and current measured by the CT on the grid side. Therefore, whether the CT on the grid side fails can be determined by detecting the reactive power response value of the load or detecting the reactive power response value of the grid.

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

[0034] By actively injecting disturbances of different amplitudes (such as positive and negative alternation), scenarios of grid fluctuations or load mutations can be simulated, exposing potential faults (such as response delay, signal distortion) of the current transformer under dynamic operating conditions. Multiple disturbances in stages can reduce the misjudgment probability of occasional interference (such as instantaneous grid harmonics). For example, a fault state is determined only when abnormal signals appear in multiple stages.

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

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

[0037] Specifically, when the reactive power response value of the power grid follows the change of the reactive power output on the inverter side, the CT on the power grid side operates normally. Exemplarily, when the inverter outputs +300 Var reactive power to the load, the power grid side should output -300 Var reactive power to the load, and the CT on the power grid side operates normally. When the CT on the power grid side fails (such as short circuit or open circuit), the reactive power response value of the power grid is equal to the initial value of the reactive power of the power grid. That is, when the absolute value of the difference between the reactive power response value of the power grid corresponding to each disturbance stage and the initial value of the reactive power of the power grid is less than a preset value, an abnormal signal is accumulated once.

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

[0039] Exemplarily, when the absolute value of the difference between the first load reactive power response value Q1 and the reference load reactive power 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 current transformer on the power grid side according to the accumulated number of abnormal signals.

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

[0042] In some embodiments, when the accumulated number of abnormal signals is greater than or equal to a first set value (such as 3 times), determine that the health status of the current transformer on the power grid side is a fault status. When the accumulated number of abnormal signals is greater than or equal to a second set value and less than or equal to a third set value (such as 1 ≤ accumulated number ≤ 2), determine that the health status of the current transformer on the power grid side is an uncertain status. When the accumulated number of abnormal signals is equal to 0, determine that the health status of the current transformer on the power grid side is a normal operation status.

[0043] Among them, the fault status indicates that abnormal conditions are frequently triggered during multi-stage disturbances, indicating that there are persistent problems with the current transformer on the power grid side (such as reverse connection, open circuit, or signal distortion). The uncertain status indicates that occasional abnormalities may be caused by instantaneous interference (such as power grid harmonics) and further verification is required. The normal operation status indicates that the responses in all disturbance stages meet expectations and the current transformer on the power grid side operates normally.

[0044] The fault detection method for the grid-side current transformer provided by the embodiment of the present invention controls the inverter to respond to reactive power scheduling to output the initial reactive power, and records the reactive power reference value of the load and the initial value of the grid reactive power, which can provide a comparison basis for the response in the subsequent disturbance stage. By actively injecting disturbances with different amplitudes (such as positive and negative alternation), scenarios of grid fluctuations or load mutations can be simulated, exposing potential faults of the current transformer under dynamic working conditions. By comparing the difference between the reactive power response value in the adjacent stage and the reactive power reference value or the response value in the previous stage, if it exceeds the preset threshold, the abnormal signal is accumulated. Finally, the health status of the current transformer is judged according to the accumulated number of abnormal signals. That is to say, the fault detection method for the grid-side current transformer provided by the embodiment of the present invention can detect whether the grid-side CT is faulty during power-on self-check when there is no sensor at the load end.

[0045] Figure 3 It is a flowchart of another fault detection method for the grid-side current transformer of the inverter provided by the embodiment of the present invention. As Figure 3 shown, the fault detection method includes:

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

[0047] S202. Control the inverter to output reactive power disturbances with a first preset amplitude in the first disturbance stage, zero reactive power disturbances in the second disturbance stage, reactive power disturbances with a second preset amplitude in the third disturbance stage, and zero reactive power disturbances in the fourth disturbance stage in sequence, and record the corresponding grid reactive power response values or load reactive power response values in 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. Exemplarily, the first preset amplitude is +10 Var, and the second preset amplitude is -10 Var.

[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 reactive power reference value of the load and the first load reactive power response value is less than the first set threshold, accumulate an abnormal signal once.

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

[0052] When the inverter superimposes positive reactive power (such as reactive power of 5% of the rated power), theoretically, the reactive power of the load should be equal to the original load reactive power (i.e., the load reactive power reference value). However, a fault in the CT on the grid side will cause the measured value to remain unchanged, and the reactive power of the load will change following the change in the reactive power output by the inverter.

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

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

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

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

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

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

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

[0060] S205. 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, accumulate an abnormal signal once.

[0061] 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 (i.e., the third load reactive power response value) should be equal to 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 = QV1 + Qe0; the inverter superimposes negative reactive power of -400 Var.

[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 there is a fault in the grid-side CT, the reactive power response value of the grid-side CT remains unchanged, that is, equal to the initial grid reactive power Qe0. At this time, the reactive power output by the inverter-side CT is QV1 - 400 Var. Then, according to the measurement and calculation of the inverter-side CT and the grid-side CT, the third load reactive power response value Q3 = QV1 - 400 + Qe0 = Q0 - 400 Var. At this time, Q2 - Q3 = Q0 - (Q0 - 400) = 400 Var > 300 Var, and an abnormal signal is accumulated once at this time.

[0064] S206. 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, 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 there is a fault in the grid-side CT, the reactive power response value of the grid-side CT remains unchanged, that is, equal to the initial grid reactive power Qe0. At this time, the reactive power output by the inverter-side CT is equal to the initial reactive power QV1. Then, according to 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 = -400 Var < -300 Var, and an abnormal signal is accumulated once at this time.

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

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

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

[0070] S302. Sequentially control the inverter to output reactive power disturbances with a first preset amplitude in the first disturbance stage, zero reactive power disturbances in the second disturbance stage, reactive power disturbances with a second preset amplitude in the third disturbance stage, and zero reactive power disturbances in the fourth disturbance stage, and record the corresponding grid reactive power response values or load reactive power response values in 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 to each other.

[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 reference value of the load reactive power and the first load reactive power response value is greater than the second set threshold, accumulate an abnormal signal once.

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

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

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

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

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

[0079] After the inverter stops superimposing reactive power, assume that the load reactive power reference value Q0 = the initial reactive power output by the inverter + the initial grid reactive power = QV1 + Qe0, and the first set threshold is -300 Var.

[0080] When the grid-side CT has no fault, 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, equal to the initial grid reactive power Qe0. At this time, the reactive power output by the inverter-side CT is equal to the initial reactive power QV1. Then, according to 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. At this time, Q1 - Q2 = Q0 - 400 - Q0 = -400 Var < -300 Var, and an abnormal signal is accumulated once at this time.

[0082] S305. 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, accumulate the abnormal signal once.

[0083] When the inverter actively superimposes positive reactive power (such as reactive power of 5% of the rated power), theoretically the reactive power of the load (that is, the third load reactive power response value) should be equal to 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 = QV1 + Qe0; the inverter superimposes positive reactive power of +400 Var.

[0084] When the grid-side CT has no fault, 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, equal to the initial grid reactive power Qe0. At this time, the reactive power output by the inverter-side CT is QV1 - 400 Var. Then, according to the measurement and calculation of the inverter-side CT and the grid-side CT, the third load reactive power response value Q3 = QV1 + 400 + Qe0 = Q0 + 400 Var. At this time, Q2 - Q3 = Q0 - (Q0 + 400) = -400 Var < -300 Var, and an abnormal signal is accumulated once at this time.

[0086] S306. 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, accumulate the abnormal signal once.

[0087] When the inverter stops superimposing reactive power, theoretically, the reactive power of the load (i.e., the fourth load reactive power response value Q4) should recover to the load reactive power reference value Q0.

[0088] When the grid-side CT is not faulty, 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, 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, according to 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 = 400 Var > 300 Var, 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 It is a flowchart of another method for detecting faults in the grid-side current transformer of an inverter provided by an embodiment of the present invention. As Figure 5 shown, the fault detection method includes:

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

[0093] S402. Sequentially control the inverter to output a reactive power disturbance with a first preset amplitude in the first disturbance stage, output zero reactive power disturbance in the second disturbance stage, output a reactive power disturbance with a second preset amplitude in the third disturbance stage, and output zero reactive power disturbance in the fourth disturbance stage, and record the corresponding grid reactive power response value or load reactive power response value in 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 positive reactive power (such as reactive power of 5% of the rated power), theoretically, the reactive power of the load should be equal to the original load reactive power (i.e., the load reactive power reference value). However, a fault in the grid-side CT will cause the measured value to remain unchanged, and the reactive power of the load will change with the change of the reactive power output by the inverter.

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

[0097] When the grid-side CT is not faulty, 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, i.e., 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 + 400 Var. Then, according to 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 + 400 Var. At this time, |Q0 - Q1| = |Q0 - (Q0 + 400)| = 400 Var, which is greater than 300 Var. At this time, an abnormal signal is accumulated once.

[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 the third set threshold, an abnormal signal is accumulated once.

[0100] Specifically, when the inverter stops superimposing reactive power and the grid-side CT has no fault, 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, i.e., 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, according to 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. At this time, |Q1 - Q2| = |Q0 + 400 - Q0| = 400 Var > 300 Var. At this time, 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 the third set threshold, an abnormal signal is accumulated 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 (i.e., the third load reactive power response value) should be equal to the load reactive power reference value.

[0104] When the grid-side CT has no fault, 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, i.e., 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 - 400 Var. Then, according to the measurement and calculation of the inverter-side CT and the grid-side CT, the third load reactive power response value Q3 = QV1 - 400 + Qe0 = Q0 - 400 Var. At this time, |Q2 - Q3| = |Q0 - (Q0 - 400)| = 400 Var > 300 Var. At this time, an abnormal signal is accumulated once.

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

[0107] Specifically, when the inverter stops superimposing reactive power and the grid-side CT has no fault, the reactive power response value Q4 of the fourth load 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, 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, according to the measurement and calculation of the inverter-side CT and the grid-side CT, the reactive power response value Q4 of the fourth load = QV1 + Qe0 = Q0. At this time, |Q3 - Q4| = |Q0 + 400 - Q0| = 400 Var > 300 Var, and an abnormal signal is accumulated once at this time.

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

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

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

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

[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 reactive power response value of the first power grid and the initial reactive power value of the power grid is greater than the fourth set threshold, accumulate an abnormal signal once.

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

[0117] The fourth set threshold is less than 0, and its absolute value is generally taken as half of the reactive power superimposed by the inverter. Assume that the initial reactive power value of the power grid is Qe0; if the inverter superimposes positive reactive power of 300 Var, then the fourth set threshold is -150 Var.

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

[0119] However, when there is a fault in the CT on the power grid side, the reactive power response value Qe1 of the first power grid = Qe0. At this time, the difference between the reactive power response value Qe1 of the first power grid and the initial reactive power value Qe0 of the power grid is zero, which is greater than -150 Var. At this time, accumulate an abnormal signal once.

[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 the fifth set threshold, accumulate an abnormal signal once.

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

[0122] When the inverter stops superimposing reactive power, when there is no fault in the CT on the power grid side, the reactive power response value Qe2 of the second power grid should be the initial reactive power value Qe0 of the power grid. However, when there is a fault in the CT on the power grid side, the reactive power response value of the CT on the power grid side remains unchanged, that is, it is equal to the reactive power response value Qe1 of the first power grid = Qe0. At this time, Qe2 - Qe1 = 0 < 150 Var. At this time, accumulate an abnormal signal once.

[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 the 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 power grid (i.e., the reactive power response value of the third power grid) should be equal to the initial reactive power value of the power grid plus the opposite of the superimposed reactive power (such as reactive power of 5% of the rated power).

[0125] If the inverter superimposes a negative reactive power of -300 Var, the fifth set threshold is 150 Var.

[0126] When the grid-side CT has no fault, the third grid reactive power response value Qe3 should be Qe2 + 300 Var. 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 second grid reactive power response value. At this time, Qe3 - Qe2 = 0 < 150 Var, and an abnormal signal is accumulated once.

[0127] S506: 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, accumulate an abnormal signal once.

[0128] Specifically, when the inverter stops superimposing reactive power, theoretically the reactive power of the grid (i.e., the fourth grid reactive power response value Qe4) should return to the initial grid reactive power value Qe0.

[0129] When the grid-side CT has no fault, 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 reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the third grid reactive power response value. At this time, Qe4 - Qe3 = 0 > -150 Var, and an abnormal signal is accumulated once.

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

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

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

[0133] S602: Sequentially control the inverter to output a reactive power disturbance with a first preset amplitude in the first disturbance stage, output zero reactive power disturbance in the second disturbance stage, output a reactive power disturbance with 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.

[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 opposite to 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 initial grid reactive power value is less than the fifth set threshold, an abnormal signal is accumulated once.

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

[0137] The fifth set threshold is greater than 0, and the absolute value of the fifth set threshold generally takes half of the reactive power superimposed by the inverter. Assume that the initial grid reactive power value is Qe0; when the inverter superimposes positive reactive power of 300 Var, the fifth set threshold is 150 Var.

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

[0139] However, when there is a fault in the grid-side CT, the first grid reactive power response value Qe1 = Qe0. At this time, the difference between the first grid reactive power response value Qe1 and the initial grid reactive power value Qe0 is zero, which is less than 150 Var. At this time, an abnormal signal is accumulated once.

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

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

[0142] When the inverter stops superimposing reactive power, when there is no fault in the grid-side CT, the second grid reactive power response value Qe2 should be the initial grid reactive power value Qe0. However, when there is a fault in the grid-side CT, the reactive power response value of the grid-side CT remains unchanged, that is, it is equal to the first grid reactive power response value Qe1 = Qe0. At this time, Qe2 - Qe1 = 0 > -150 Var. At this time, an abnormal signal is accumulated once.

[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 the 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 power grid (i.e., the reactive power response value of the third power grid) should be equal to the initial reactive power value of the power grid plus the opposite of the superimposed reactive power (such as reactive power of 5% of the rated power).

[0145] If the inverter superimposes positive reactive power of +300 Var, the fourth set threshold is -150 Var.

[0146] When there is no fault in the CT on the power grid side, the reactive power response value Qe3 of the third power grid should be Qe2 - 300 Var. However, when there is a fault in the CT on the power grid side, the reactive power response value of the CT on the power grid side remains unchanged, that is, it is equal to the reactive power response value of the second power grid. At this time, Qe3 - Qe2 = 0 > -150 Var, and an abnormal signal is accumulated once at this time.

[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 the fifth set threshold, accumulate an abnormal signal once.

[0148] Specifically, when the inverter stops superimposing reactive power, theoretically the reactive power of the power grid (i.e., the reactive power response value Qe4 of the fourth power grid) should return to the initial reactive power value Qe0 of the power grid.

[0149] When there is no fault in the CT on the power grid side, the reactive power response value Qe4 of the fourth power grid should be the initial reactive power value Qe0 of the power grid. However, when there is a fault in the CT on the power grid side, the reactive power response value of the CT on the power grid side remains unchanged, that is, it is equal to the reactive power response value of the third power grid. At this time, Qe4 - Qe3 = 0 < 150 Var, and an abnormal signal is accumulated once at this time.

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

[0151] Figure 8 It is a flowchart of another method for detecting faults in the current transformer on the power grid side of an inverter provided by an embodiment of the present invention. As Figure 8 shown, the fault detection method includes:

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

[0153] S702. Control the inverter to output reactive power disturbances with a first preset amplitude in the first disturbance stage, zero reactive power disturbances in the second disturbance stage, reactive power disturbances with a second preset amplitude in the third disturbance stage, and zero reactive power disturbances in the fourth disturbance stage in sequence, and record the grid reactive power response values or load reactive power reference values 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 the sixth set threshold, accumulate an abnormal signal once.

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

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

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

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

[0159] S704. 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, accumulate an abnormal signal once.

[0160] Specifically, when the inverter stops superimposing reactive power, when there is no fault in the grid-side CT, the second grid reactive power response value Qe2 should be the initial grid reactive power value Qe0. But when there is a fault in the grid-side CT, the reactive power response value of the grid-side CT remains unchanged, that is, equal to the first grid reactive power response value Qe1 = Qe0. At this time, |Qe2 - Qe1| = 0 < 150 Var, and an abnormal signal is accumulated once at this time.

[0161] S705. 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, accumulate an abnormal signal once.

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

[0163] When there is no fault in the CT on the power grid side, the reactive power response value Qe3 of the third power grid should be Qe2 + 300Var. However, when there is a fault in the CT on the power grid side, the reactive power response value of the CT on the power grid side remains unchanged, that is, it is equal to the reactive power response value of the second power grid. At this time, |Qe3 - Qe2| = 0 < 150Var, and an abnormal signal is accumulated once at this time.

[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 the sixth set threshold, an abnormal signal is accumulated once.

[0165] Specifically, when the inverter stops superimposing reactive power, theoretically, the reactive power of the power grid (i.e., the reactive power response value Qe4 of the fourth power grid) should return to the initial reactive power Qe0 of the power grid.

[0166] When there is no fault in the CT on the power grid side, the reactive power response value Qe4 of the fourth power grid should be the initial reactive power Qe0 of the power grid. However, when there is a fault in the CT on the power grid side, the reactive power response value of the CT on the power grid side remains unchanged, that is, it is equal to the reactive power response value of the third power grid. At this time, |Qe4 - Qe3| = 0 < 150Var, and an abnormal signal is accumulated once at this time.

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

[0168] Figure 9 It is a flowchart of another method for detecting faults in the current transformer on the power grid side of an inverter provided by an embodiment of the present invention. As Figure 9 shown, the fault detection method includes:

[0169] S801. Control the inverter to respond to reactive power scheduling and output the initial reactive power, and record the reactive power reference value of the load and the initial reactive power of the power grid.

[0170] S802. Control the inverter to output reactive power disturbances with a preset amplitude in each disturbance stage in sequence, and record the reactive power response value of the power grid or the reactive power response value of the load corresponding to each disturbance stage respectively.

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

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

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

[0176] Among them, the first set time is greater than the second set time, and the third set time is greater than the first set time. Exemplarily, the first set time can be 5 minutes, the second set time can be 1 minute, and the third set time can be 24 hours.

[0177] Specifically, when the system determines that the current transformer is in a fault state, the protection mechanism may have been triggered (such as disconnecting the grid connection or derating operation). At this time, it is necessary to wait for the system to stabilize to ensure that the fault will not expand due to immediate re - detection (such as the arc has not been completely extinguished); the maintenance personnel may need to be on - site for troubleshooting. The longer the delay, the wider the response window; if the fault persists, frequent re - detection will waste resources and cannot be restored. Therefore, the first set time is set appropriately.

[0178] The uncertain state may be caused by instantaneous interference (such as grid harmonics, sensor noise), and it is necessary to confirm whether it is a real fault through re - detection. A shorter delay can quickly verify whether the anomaly has disappeared (such as the interference only lasts for a few seconds). Therefore, the second set time is the shortest.

[0179] When the system is normal, it is necessary to monitor regularly to prevent potential faults, but the frequency should not be too high. Therefore, the third set time is the longest.

[0180] In the specific implementation process, the detection conditions are the single - machine grid - connection mode and the inverter is in the running state, the grid sampling uses CT, the anti - reverse power flow is enabled or the self - consumption mode. Taking a single - phase 6KW photovoltaic - energy - storage inverter as an example, the steps of using the fault - detection method of the present invention are described as follows:

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

[0182] S2: The inverter outputs reactive power with 5% of the rated power superimposed. After a 1-second delay, the reactive power response value of the first load is Q1. Calculate the first reactive power difference ΔQ1 = Q0 - Q1. If ΔQ1 is less than -300 Var, increment the cumulative count of abnormal grid-side CT signals by 1; record the reactive power response value Q1 of the first load.

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

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

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

[0186] S6: If the cumulative count of abnormal grid-side CT signals is greater than or equal to 4, determine that the health status of the grid-side CT is a fault state, trigger an alarm, prohibit the output of inverter power, and re-detect after 5 minutes. If the cumulative count of abnormal grid-side CT signals is greater than or equal to 1 and less than or equal to 3, determine that the health status of the grid-side CT is an uncertain state, and re-detect after 1 minute. If the cumulative count of abnormal grid-side CT signals is equal to 0, it indicates that the grid-side CT sampling is normal, and re-detect after 24 hours.

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

[0188] For example, the reactive power superposition process described in the text can be: no superposition → superposition of reactive power → no superposition → superposition of reactive power → no superposition, no superposition → superposition of reactive power → superposition of reactive power... → no superposition → superposition of reactive power → superposition of reactive power... → no superposition, no superposition → superposition of reactive power →... → superposition of reactive power → no superposition and other transformation forms and their corresponding reactive power difference calculation methods.

[0189] Fault judgment mechanism (There are different fault judgment values according to different reactive power superposition methods. For example, if the reactive power superposition changes n times and i represents the cumulative number of abnormal signals, then when i≥n, it is judged that the CT on the grid side has a fault; when 1≤i≤n, the CT on the grid side is in an uncertain state; when i<1, the CT on the grid side is in a normal operating state).

[0190] The above specific implementation manners do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub - combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A fault detection method for 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 an initial value of grid reactive power or a reference value of load reactive power; The inverter is sequentially controlled to output reactive power disturbances of preset amplitudes at each disturbance stage, and the reactive power response values ​​of the power grid or the reactive power response values ​​of the load corresponding to each disturbance stage are recorded respectively; wherein the preset amplitudes in 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; The health state of the grid-side current transformer is determined according to the accumulated number of abnormal signals; wherein the health state includes a fault state, an uncertain state and a normal operating state.

2. The fault detection method of the grid-side current transformer of the inverter according to claim 1, characterized in that: The steps of sequentially controlling the inverter to output reactive power disturbances of preset amplitudes at each disturbance stage, and respectively recording the reactive power response value of the power grid or the reactive power response value of the load 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 reactive power response value of the grid or the reactive power response value of the load corresponding to each disturbance stage is recorded respectively.

3. The fault detection method of the current transformer on the grid side of the inverter according to claim 2, characterized in that: 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 comprises: 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.

4. The fault detection method of the current transformer on the grid side of the inverter according to claim 2, characterized in that: 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 comprises: 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.

5. The fault detection method of the current transformer on the grid side of the inverter according to claim 2, characterized in that: 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 comprises: 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.

6. The fault detection method for the grid-side current transformer of the inverter according to claim 2, 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 reactive power response value of the power grid corresponding to the first disturbance stage is a first reactive power response value of the power grid, the reactive power response value of the power grid corresponding to the second disturbance stage is a second reactive power response value of the power grid, the reactive power response value of the power grid corresponding to the third disturbance stage is a third reactive power response value of the power grid, and the reactive power response value of the power grid corresponding to the fourth disturbance stage is a fourth reactive power response value of the power grid; The step of 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 comprises: When the difference between the reactive power response value of the first power grid and the initial reactive power value of the power grid 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 reactive power response value of the third power grid and the reactive power response value of the second power grid is less than the fifth set threshold, accumulating the abnormal signal once; When the difference between the fourth power grid reactive power response value and the third power 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.

7. The fault detection method for the grid-side current transformer of the inverter according to claim 2, 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 reactive power response value of the power grid corresponding to the first disturbance stage is a first reactive power response value of the power grid, the reactive power response value of the power grid corresponding to the second disturbance stage is a second reactive power response value of the power grid, the reactive power response value of the power grid corresponding to the third disturbance stage is a third reactive power response value of the power grid, and the reactive power response value of the power grid corresponding to the fourth disturbance stage is a fourth reactive power response value of the power grid; The step of 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 comprises: When the difference between the reactive power response value of the first power grid and the initial reactive power value of the power grid 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 reactive power response value of the third power grid and the reactive power response value of the second power grid is greater than the fourth set threshold, accumulating the abnormal signal once; When the difference between the fourth power grid reactive power response value and the third power 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.

8. The fault detection method of the current transformer on the grid side of the inverter according to claim 2, characterized in that: The reactive power response value of the power grid corresponding to the first disturbance stage is a first reactive power response value of the power grid, the reactive power response value of the power grid corresponding to the second disturbance stage is a second reactive power response value of the power grid, the reactive power response value of the power grid corresponding to the third disturbance stage is a third reactive power response value of the power grid, and the reactive power response value of the power grid corresponding to the fourth disturbance stage is a fourth reactive power response value of the power grid; 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 comprises: When the absolute value of the difference between the initial value of the grid reactive power 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 reactive power response value of the first power grid and the reactive power response value of the second power grid is less than the sixth set threshold, accumulating the abnormal signal once; 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 the sixth set threshold, accumulating the abnormal signal once; 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 the sixth set threshold, the abnormal signal is accumulated once.

9. The fault detection method of the current transformer on the grid side of the inverter according to claim 1, characterized in that: The step of determining the health status of the grid-side current transformer according to the accumulated number of abnormal signals comprises: When the accumulated number of times 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 is greater than or equal to the second set value and less than or equal to the 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.

10. The fault detection method of the current transformer on the grid side of the inverter according to claim 1, characterized in that: 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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