AC short - circuit fault detection method, device and electrical equipment

Abstract

The present invention discloses an AC short - circuit fault detection method, device and electrical equipment. The method includes: establishing a DC bus voltage, when it is determined that there is no voltage on the AC side of the equipment, controlling the equipment to enter the AC wiring self - inspection preparation state; controlling the equipment to output an AC voltage based on preset modulation parameters; obtaining the output voltage parameters of the equipment, and determining the absolute value of voltage and the relative value of voltage according to the output voltage parameters; determining whether the equipment has a short - circuit fault according to the absolute value of voltage and the relative value of voltage, and determining the type of short - circuit fault. The present invention controls the equipment to perform an inversion process on the DC bus voltage through an internal software program of the equipment, and detects short - circuit faults according to the output AC voltage, realizes fault detection before grid connection, without increasing the hardware cost, reduces the risk of shutdown of the equipment caused by AC short - circuit faults, and is beneficial to improving the safety and reliability of grid connection.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical equipment fault detection, and particularly to an AC short - circuit fault detection method, device and electrical equipment. Background Art

[0002] The grid - connected power generation system converts solar energy or wind energy into electrical energy and transports the electrical energy to the power grid through a grid - connected inverter. If the grid - connected inverter fails, the normal operation of the grid - connected power generation system will be affected. Therefore, it is necessary to detect open - circuit faults and short - circuit faults of the grid - connected inverter.

[0003] In the existing grid - connected power generation system, the AC output side of the grid - connected inverter is generally directly connected to the AC power grid through an AC switch. When detecting a short - circuit fault of the inverter, it is required that the AC side wiring of the inverter is normal and the power grid is energized. During the operation of the equipment, it is judged whether a phase - to - phase short - circuit or a phase - to - ground short - circuit fault occurs based on the detection of the AC side voltage.

[0004] However, the fault detection in the existing technology is to detect the short - circuit fault during the operation of the equipment after the inverter is connected to the grid. It has the following problems: If there is a short - circuit fault in the inverter before grid connection, closing the AC switch between the inverter and the grid - side box transformer may cause arcing of the switch. In severe cases, it will damage the switch or even the box transformer, resulting in low system safety and reliability. Summary of the Invention

[0005] The present invention provides an AC short - circuit fault detection method, device and electrical equipment to solve the problem that the existing inverter equipment cannot identify short - circuit faults before grid connection and improve the system safety and reliability.

[0006] According to one aspect of the present invention, an AC short - circuit fault detection method is provided. The outgoing line on the AC side of the device under test adopts a multi - wire parallel structure. The method includes the following steps: establishing a DC bus voltage; when it is judged that there is no voltage on the AC side of the device, controlling the device to enter the AC wiring self - inspection preparation state; controlling the device to output an AC voltage based on a preset modulation parameter; obtaining the output voltage parameters of the device and determining the absolute value of the voltage and the relative value of the voltage according to the output voltage parameters; determining whether the device has a short - circuit fault according to the absolute value of the voltage and the relative value of the voltage, and determining the type of the short - circuit fault.

[0007] According to another aspect of the present invention, there is provided an AC short - circuit fault detection device for performing the above - mentioned AC short - circuit fault detection method. The device includes: a DC power supply module for establishing a DC bus voltage; a logic judgment module for controlling the device to enter the AC wiring self - inspection preparation state when it is judged that there is no voltage on the AC side of the device; a modulation drive module for controlling the device to output an AC voltage according to preset modulation parameters; a voltage detection module for obtaining the output voltage parameters of the device and determining the absolute value and relative value of the voltage according to the output voltage parameters; a fault analysis module for determining whether the device has a short - circuit fault according to the absolute value and relative value of the voltage and determining the type of the short - circuit fault.

[0008] According to another aspect of the present invention, there is provided an electrical device including the above - mentioned AC short - circuit fault detection device.

[0009] The technical solution of the embodiment of the present invention, before the device is connected to the grid and operated, establishes the DC bus voltage of the device, and when it is judged that there is no voltage on the AC side of the device, controls the device to enter the AC wiring self - inspection preparation state, then controls the device to output an AC voltage based on preset modulation parameters. After the device starts and operates for a certain period of time, obtains the output voltage parameters of the device, determines the absolute value and relative value of the voltage according to the output voltage parameters, determines whether the inverter has a short - circuit fault according to the absolute value and relative value of the voltage, and determines the type of the short - circuit fault. This solves the problem that the existing inverters cannot identify short - circuit faults before grid connection, realizes the AC short - circuit fault detection before grid connection through a software program, without increasing the hardware cost, reduces the shutdown risk of devices such as inverters and box transformers caused by short - circuit faults, and is beneficial to improving the safety and reliability of grid connection.

[0010] 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 understandable through the following description. Brief Description of the Drawings

[0011] 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, without creative efforts, other drawings can also be obtained based on these drawings.

[0012] Figure 1 is a flowchart of an AC short - circuit fault detection method provided by Embodiment 1 of the present invention;

[0013] Figure 2 is a schematic structural diagram of a DC power supply system provided by Embodiment 1 of the present invention;

[0014] Figure 3 Schematic diagram of another DC power supply system provided by Embodiment 1 of the present invention;

[0015] Figure 4 Flow chart of another AC short - circuit fault detection method provided by Embodiment 1 of the present invention;

[0016] Figure 5 Flow chart of yet another AC short - circuit fault detection method provided by Embodiment 1 of the present invention;

[0017] Figure 6 Flow chart of an AC short - circuit fault detection method provided by Embodiment 2 of the present invention;

[0018] Figure 7 Flow chart of an AC short - circuit fault detection method provided by Embodiment 3 of the present invention;

[0019] Figure 8 Flow chart of an AC short - circuit fault detection method provided by Embodiment 4 of the present invention;

[0020] Figure 9 Schematic diagram of the structure of an AC short - circuit fault detection device provided by Embodiment 5 of the present invention;

[0021] Figure 10 Schematic diagram of the structure of an electrical device provided by Embodiment 6 of the present invention. Detailed implementation manners

[0022] 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 with reference to 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. [[ID=3?]]

[0023] It should be noted that the terms "including" and "having" in the specification and claims of the present invention 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.

[0024] Embodiment 1

[0025] Figure 1FIG. 0 is a flowchart of a method for detecting AC short - circuit faults provided in the first embodiment of the present invention. This embodiment is applicable to the application scenario of detecting AC short - circuit faults in a device before grid connection. This method can be executed by a short - circuit fault detection device, which can be implemented in the form of hardware and / or software, and the short - circuit fault detection device can be integrally arranged in the device under test.

[0026] In this embodiment, the AC side outgoing line of the device under test adopts a multi - wire parallel structure for each phase. For example, the device under test can be an inverter, and the AC side of the inverter can output three - phase AC voltages of a, b, and c. The outgoing lines of phases a, b, and c all adopt a multi - wire parallel structure, that is, two parallel - connected cables are provided for each of phases a, b, and c. The first ends of the multi - wire parallel cables are electrically connected to the AC output terminals of the device, and the second ends of the multi - wire parallel cables are connected to the AC power grid through an external AC switch and a box - type transformer.

[0027] In the multi - wire parallel structure, the risk of short - circuit between the lines of each phase increases, and the types of short - circuit faults between the wires are complex. Identifying the types of AC - side short - circuit faults before the device is connected to the grid is beneficial to timely troubleshooting and improving grid - connection safety.

[0028] Among them, the device being connected to the grid and operating means that the device is connected to the AC power grid through AC outgoing cables, an external AC switch, and a box - type transformer, and performs inversion processing on the DC voltage according to the grid frequency and grid voltage, and provides an output voltage to the grid. If the AC switch between the device and the box - type transformer of the AC power grid is in the off state, or the AC power grid side is powered off, the device is in a non - grid - connected operating state.

[0029] As Figure 1 shown, the method for detecting AC short - circuit faults specifically includes the following steps:

[0030] Step S1: Establish a DC bus voltage.

[0031] Among them, the DC bus voltage is the DC voltage provided by the DC power supply to the DC side of the device. Typically, the DC power supply can be an energy storage unit or a photovoltaic module.

[0032] In one embodiment, a DC bus capacitor can be set on the DC side inside the device, and the charging voltage of the DC bus capacitor is used as the DC bus voltage.

[0033] It should be noted that for different types of DC power supplies, the DC power supply system structure and the connection method between the DC power supply and the device are different. The specific method for establishing the DC bus voltage can be adaptively adjusted according to the type of DC power supply, and this is not limited herein.

[0034] Step S2: When it is determined that there is no voltage on the AC side of the device, control the device under test to enter the AC wiring self - inspection preparation state.

[0035] Among them, the AC wiring self-check preparation state refers to the circuit state in which the AC side wiring of the device can be detected by executing a detection program when the device is in a non-grid-connected operation state.

[0036] Optionally, in the AC wiring self-check preparation state, the internal DC side switch of the device is closed, and the internal AC side switch of the device is open.

[0037] In this embodiment, the internal DC side switch and the internal AC side switch are integrally arranged with the inverter bridge arm of the device. The internal DC side switch is arranged between the DC power supply and the DC input side of the inverter bridge arm, and the internal AC side switch is arranged between the AC output side of the inverter bridge arm and the multi-wire parallel cable on the AC side. By controlling the on / off of the internal DC side switch and the internal AC side switch, the DC side of the device can receive the DC bus voltage, and there is no output voltage on the AC side of the device. At this time, the wiring condition of the AC side of the device can be detected without relying on the grid-connected operation condition.

[0038] Step S3: Control the device under test to output an AC voltage based on preset modulation parameters.

[0039] Among them, modulation refers to a control method in which, when the device is in a non-grid-connected operation state, the on / off of the inverter bridge arm of the device is controlled by a modulation signal given by an open-loop detection program, so that the device realizes the inversion function. During the modulation process, the device is in a stand-alone operation mode, and the on / off of the inverter bridge arm of the device is controlled by a modulation signal given by the detection program, so that the device realizes the inversion function without using a closed-loop control method with an energized AC grid side. Therefore, the AC switch between the AC output end of the device under test and the AC grid side (such as an AC power grid or a box transformer connected to the AC power grid) can be maintained in an open state.

[0040] In this embodiment, the preset modulation parameters are the parameters of the modulation signal output by the software program. During the modulation process, the software program outputs a modulation signal according to the preset modulation parameters. The modulation signal can be a PWM modulation signal. The device under test inverses the DC bus voltage into an AC voltage under the drive of the PWM modulation signal. Taking the device under test as a three-phase inverter as an example, after modulation, the AC side of the three-phase inverter can output three-phase AC voltages of a, b, and c.

[0041] Optionally, the preset modulation parameters include at least one of the following: modulation duty cycle, modulation frequency, modulation amplitude, and modulation phase.

[0042] Among them, the modulation duty cycle is the duty cycle of the PWM modulation signal provided by the software program. The modulation duty cycle is used to define the ratio between the on-time of the inverter bridge arm and the modulation period. The magnitude of the duty cycle determines the magnitude of the output voltage. The modulation frequency is the modulation frequency of the modulation signal provided by the software program. The setting of the modulation frequency needs to meet the inverter performance requirements. Exemplarily, the value of the modulation frequency can be set to 50HZ. The modulation amplitude is the amplitude of the inverter output voltage after modulation. The modulation phase is the initial phase angle of the inverter output voltage after modulation.

[0043] It should be noted that those skilled in the art can set the modulation duty cycle, modulation frequency, modulation amplitude and modulation phase according to actual needs, and there is no limitation on their specific values.

[0044] Step S4: Obtain the output voltage parameters of the device under test, and determine the absolute voltage U and the relative voltage ΔU according to the output voltage parameters.

[0045] Among them, the output voltage parameter is the voltage parameter with a stable amplitude output on the AC output side of the device after the device starts to run for a period of time under the drive of the modulation signal. The absolute voltage U can be used to characterize the magnitude of the output voltage of each phase on the AC side of the device under test. The relative voltage ΔU is the difference between any two absolute voltages U. The relative voltage ΔU can be used to characterize the degree of imbalance between the output voltages of each phase on the AC side of the device under test.

[0046] In this embodiment, the output voltage parameters of the device can be detected by the voltage detection module integrated inside the device. After obtaining the output voltage parameters, the absolute voltage and the relative voltage can be obtained through comparison and calculation, and then it can be judged whether the output voltages of each phase on the AC side of the device under test are normal through the absolute voltage U and the relative voltage ΔU.

[0047] Step S5: Determine whether the device under test has an AC short circuit fault according to the absolute voltage U and the relative voltage ΔU, and determine the short circuit fault type.

[0048] Among them, the short circuit fault types include: ground short circuit fault, two-phase short circuit fault and three-phase short circuit fault.

[0049] Specifically, before the device is connected to the grid and operates, the AC switch between the outgoing line on the AC side of the device and the AC grid side is disconnected, that is, the device is in a non-grid-connected operating state. In the non-grid-connected operating state, the device executes an AC wiring self-check program. During the execution of the AC wiring self-check program, first, the DC bus voltage of the device is established. After the DC bus voltage is input into the device, the AC side voltage of the device is detected to determine whether the value of the AC side voltage of the device is equal to zero. If the DC bus voltage is greater than zero and the AC side voltage is equal to zero, the device is controlled to enter the AC wiring self-check preparation state. After the device enters the AC wiring self-check preparation state, the device internally executes a detection program, outputs a PWM modulation signal according to the preset modulation parameters, drives the inverter bridge arm of the device to conduct or cut off, so that the device operates in a single-machine operation mode, and the DC bus voltage is inverted into an AC output voltage. After the device is modulated and operates for a period of time, the AC output voltage reaches a stable state. The voltage detection module integrated inside the device collects the output voltage parameters of the device, and calculates the absolute value U of the voltage of each phase and the relative value ΔU of the voltage between each phase according to the output voltage parameters of the device. Furthermore, according to the absolute value U of the voltage and the relative value ΔU of the voltage, the unbalance degree between the output voltages of each phase on the AC side of the device under test is judged. If the unbalance degree between the output voltages of each phase is relatively high, it is determined that a short-circuit fault occurs in the AC cable on the AC side of the device under test; otherwise, it is determined that no short-circuit fault occurs in the AC cable on the AC side of the device under test. If a short-circuit fault occurs in the AC cable on the AC side of the device under test, the AC short-circuit fault type is determined according to one or more parameters in the absolute value U of the voltage and the relative value ΔU of the voltage. For example, a ground short-circuit fault, a two-phase short-circuit fault, and a three-phase short-circuit fault.

[0050] Thus, the present invention controls the device to perform an inversion process on the DC bus voltage through the internal software program of the device, and detects the short-circuit fault according to the output AC voltage, realizes the AC short-circuit fault detection before grid connection, does not need to increase the hardware cost, solves the problem that the existing inverter cannot identify the short-circuit fault before grid connection, effectively reduces the shutdown risk of devices such as inverters and box transformers caused by short-circuit faults, and is beneficial to improving the safety and reliability of grid connection.

[0051] Optionally, Figure 2 FIG. is a schematic structural diagram of a DC power supply system provided in Embodiment 1 of the present invention. In Figure 2 the illustrated embodiment, the DC power supply connected to the DC side of the device is a photovoltaic power generation module PV.

[0052] As Figure 2As shown in the figure, establishing the DC bus voltage includes: closing the DC side switch K1 of the control device; establishing the DC bus voltage based on the output voltage of the DC side switch K1; wherein, the input side of the DC side switch K1 is electrically connected to the photovoltaic power generation module PV, and the output side of the DC side switch K1 is electrically connected to the DC bus capacitor C0 of the device; or, controlling the start of the photovoltaic power generation module PV and establishing the DC bus voltage based on the output voltage of the photovoltaic power generation module PV.

[0053] As Figure 2 shown in the figure, the photovoltaic power generation module PV is connected to the DC input terminal of the device under test through the DC side switch K1. When detecting the AC short-circuit fault of the device under test, control the DC side switch K1 to close. The DC voltage generated by the photovoltaic power generation module PV is input into the device under test through the DC side switch K1, and the DC bus capacitor C0 of the device under test is charged until the charging voltage reaches the DC bus voltage required for the single-unit operation of the device.

[0054] Optionally, Figure 3 is a schematic structural diagram of another DC power supply system provided by Embodiment 1 of the present invention. In the Figure 3 embodiment shown, the DC power supply connected to the DC side of the device is the energy storage component BA. The energy storage component can be a battery component.

[0055] As Figure 3 shown in the figure, establishing the DC bus voltage includes: controlling the start of the energy storage component; establishing the DC bus voltage based on the output voltage of the energy storage component; wherein, the energy storage component is electrically connected to the DC bus capacitor of the device.

[0056] As Figure 3 shown in the figure, the energy storage component BA is directly electrically connected to the DC input terminal of the device under test. When detecting the AC short-circuit fault of the device under test, control the energy storage component BA to start. The electric energy stored in the energy storage component BA is directly input into the device under test, and the DC bus capacitor C0 of the device under test is charged until the charging voltage reaches the DC bus voltage required for the single-unit operation of the device.

[0057] Optionally, Figure 4 is a flowchart of another AC short-circuit fault detection method provided by Embodiment 1 of the present invention. On the basis of Figure 1 , Figure 4 the embodiment in shows a specific implementation manner of short-circuit fault analysis, rather than a limitation to the above method.

[0058] As Figure 4 shown in the figure, the short-circuit fault detection method includes:

[0059] Step S1: Establish the DC bus voltage.

[0060] Step S2: When it is determined that there is no voltage on the AC side of the device, control the device to enter the self-check preparation state for AC wiring.

[0061] Step S3: Control the device under test to output an AC voltage based on preset modulation parameters.

[0062] Step S4: Obtain the output voltage parameters of the device under test, and determine the absolute voltage value and the relative voltage value according to the output voltage parameters.

[0063] Step S501: Obtain the preset differential pressure safety threshold and the preset voltage lower limit threshold.

[0064] Among them, the preset differential pressure safety threshold is the critical voltage value for maintaining the three-phase voltage balance; the preset voltage lower limit threshold is

[0065] Step S502: Determine whether the relative voltage value is greater than the preset differential pressure safety threshold.

[0066] If the relative voltage value ΔU is less than or equal to the preset differential pressure safety threshold ΔU th , then execute Step S503; if the relative voltage value ΔU is greater than the preset differential pressure safety threshold ΔU th , then execute Step S504.

[0067] Step S503: Determine whether the absolute voltage value U is less than the preset voltage lower limit threshold U L .

[0068] If the absolute voltage value U is less than the preset voltage lower limit threshold U L , then execute Step S504; otherwise, execute Step S505.

[0069] Step S504: An AC short circuit fault occurs in the device under test, and continue to execute Step S506.

[0070] Step S505: No AC short circuit fault occurs in the device under test, and end the self-check program.

[0071] Step S506: Determine the short circuit fault type according to the absolute voltage value U and the relative voltage value ΔU.

[0072] Specifically, the above Steps S501 to S505 describe a specific method for analyzing short circuit faults according to the absolute voltage value and the relative voltage value. If the relative voltage value ΔU is greater than the preset differential pressure safety threshold ΔU th , or, the absolute voltage value U is less than the preset voltage lower limit threshold U L, it is determined that the degree of imbalance between the output voltages of each phase is relatively high, and it can be determined that a short - circuit fault has occurred in the AC cable on the AC side of the device under test; otherwise, it is determined that no short - circuit fault has occurred in the AC cable on the AC side of the device under test. Performing short - circuit fault analysis by setting multiple parameters such as the absolute value of voltage and the relative value of voltage is conducive to avoiding missed detection of faults and improving the safety and reliability of grid connection.

[0073] Optionally, Figure 5 is a flowchart of another AC short - circuit fault detection method provided in Embodiment 1 of the present invention. Based on Figure 4 , Figure 5 an exemplary specific implementation manner for determining the short - circuit fault type is shown.

[0074] As Figure 5 shown, the above - mentioned step S506: determining the short - circuit fault type according to the absolute value of voltage U and the relative value of voltage ΔU includes:

[0075] Step S5061: determining whether the short - circuit fault type is a two - phase short - circuit fault according to the relative value of voltage between any two phases on the AC side and the preset differential voltage safety threshold.

[0076] Step S5062: determining whether the short - circuit fault type is a three - phase short - circuit fault according to the absolute value of the phase voltage of each phase on the AC side.

[0077] Step S5063: determining whether the short - circuit fault type is a ground - short - circuit fault according to the absolute value of the voltage to ground of each phase on the AC side.

[0078] Specifically, if the numerical values of the absolute values of each phase voltage are approximately equal, and the numerical values of the absolute values of each phase voltage are greater than 0, and the relative value of voltage between any two phases is less than the preset differential voltage safety threshold, it is determined that no short - circuit fault has occurred in the grid - connection loop of the device under test; if the relative value of voltage between two phases is greater than the preset differential voltage safety threshold, it is determined that the short - circuit fault type is a two - phase short - circuit fault; if the relative values of voltage between each phase are less than the preset differential voltage safety threshold, and the absolute value of voltage U of each phase is approximately zero, it is determined that the short - circuit fault type is a three - phase short - circuit fault.

[0079] When the output voltage parameter is the three - phase voltage to ground, if one phase voltage to ground is close to zero, it is determined that the short - circuit fault type is a single - phase ground - short - circuit fault; if multiple phase voltages to ground are close to zero, it is determined that the short - circuit fault type is a multi - phase ground - short - circuit fault.

[0080] It should be noted that when performing fault - type analysis, only any one step or a combination of multiple steps among the above steps S5061 to S5063 can be executed, and the short - circuit fault type is determined according to the comparison result of the absolute value of each phase voltage with zero. The specific comparison strategy can be determined according to the actual situation and the selected voltage parameters.

[0081] Therefore, the present invention analyzes the short - circuit fault type by setting multiple parameters such as the absolute value of voltage and the relative value of voltage, which is beneficial to accurately locate the fault position and improve the efficiency of later maintenance and fault troubleshooting.

[0082] In one embodiment, the output voltage parameters of the device under test include at least one of the following: the phase voltage parameters of each phase on the AC side, the voltage parameters of each phase to the ground, or the line voltage parameters between each phase. The absolute value of voltage may include: the maximum voltage value and the minimum voltage value among the same voltage parameters of each phase; the relative value of voltage may be the voltage difference between the same voltage parameters of each phase.

[0083] Exemplarily, taking the device under test as a three - phase inverter (phase a, phase b, and phase c) as an example, the phase voltage parameters include: the phase - a voltage U a , the phase - b voltage U b , and the phase - c voltage U c . The voltage parameters to the ground include: the voltage of phase a to the ground U a0 , the voltage of phase b to the ground U b0 , and the voltage of phase c to the ground U c0 . The line voltage parameters include: the line voltage U ab between phase a and phase b, the line voltage U ac between phase a and phase c, and the line voltage U bc between phase b and phase c. In this embodiment, the absolute value of voltage and the relative value of voltage can be calculated according to any one of the phase voltage, the voltage to the ground, or the line voltage, and the short - circuit fault can be analyzed according to the calculated parameters.

[0084] Specifically, the absolute value of voltage U may include: the maximum phase voltage value U max and the minimum phase voltage value U min in the phase voltage parameters, the maximum voltage value U0 max and the minimum voltage value U0 min to the ground in the voltage parameters to the ground, or the maximum line voltage value U max ' and the minimum line voltage value U min ' in the line voltage parameters; the relative value of voltage includes at least one of the following: the voltage difference between any two values in the phase voltage parameters, the voltage difference between any two values in the voltage parameters to the ground, or the voltage difference between any two values in the line voltage parameters.

[0085] When analyzing the short - circuit fault of the device under test, one or a combination of the phase voltage parameters, the voltage parameters to the ground, or the line voltage parameters can be used, and there is no limitation on this.

[0086] Next, taking the device under test as a three-phase inverter and using the phase voltage parameters of three phases a, b, and c for short-circuit fault analysis as an example, the specific implementation manner of the present invention will be described in detail.

[0087] After obtaining the phase voltage parameters (U a , U b , U c ) of three phases a, b, and c, compare the magnitudes of the three-phase voltages to determine the maximum phase voltage value U max and the minimum phase voltage value U min , and calculate the voltage difference ΔU between the maximum phase voltage value U max and the minimum phase voltage value U min . If the relative voltage value ΔU is greater than the preset differential voltage safety threshold ΔU th , or the minimum phase voltage value U min is less than the preset voltage lower limit threshold U L , it is determined that the degree of imbalance between the output voltages of each phase is relatively high, and it can be determined that a short-circuit fault has occurred in the AC cable on the AC side of the device under test; otherwise, it is determined that no short-circuit fault has occurred in the AC cable on the AC side of the device under test. By setting the minimum voltage value and the difference between the maximum voltage value and the minimum voltage value to perform short-circuit fault analysis, it is beneficial to reduce the amount of data and improve the self-checking efficiency.

[0088] Embodiment 2

[0089] Optionally, Figure 6 is a flowchart of an AC short-circuit fault detection method provided in Embodiment 2 of the present invention. On the basis of the above embodiment, the specific implementation manner of self-checking state detection is added in this embodiment.

[0090] As Figure 6 shown, the AC short-circuit fault detection method specifically includes the following steps:

[0091] Step S1: Establish the DC bus voltage.

[0092] Step S2: When it is determined that there is no voltage on the AC side of the device, control the device to enter the AC wiring self-checking preparation state.

[0093] Step S101: Obtain the initial DC-side voltage and the initial AC-side voltage of the device under test.

[0094] Step S102: Determine whether to terminate the fault detection according to the initial DC-side voltage and the initial AC-side voltage.

[0095] If the fault detection is not terminated, continue to execute the subsequent step S3.

[0096] Step S3: Control the device under test to output an AC voltage based on the preset modulation parameters.

[0097] Step S4: Obtain the output voltage parameter of the device under test, and determine the absolute voltage value and the relative voltage value according to the output voltage parameter.

[0098] Step S5: Determine whether a short - circuit fault occurs in the device under test according to the absolute voltage value U and the relative voltage value ΔU, and determine the type of short - circuit fault.

[0099] Specifically, before controlling the device under test to output an AC voltage, the voltage detection module inside the device under test respectively collects the initial DC - side voltage and the initial AC - side voltage of the device under test. If the initial DC - side voltage is equal to the DC power supply voltage and the initial AC - side voltage is equal to zero, it is determined that the device under test is in the AC wiring self - inspection preparation state, and the subsequent detection program can be executed; if the initial AC - side voltage is greater than zero, it is determined that the device under test is in the grid - connected state, and the fault detection is terminated. By setting the self - inspection state detection step, it is beneficial to improve the reliability of the fault self - inspection program operation.

[0100] Embodiment III

[0101] Optionally, Figure 7 is a flowchart of an AC short - circuit fault detection method provided by Embodiment III of the present invention. On the basis of Figure 1 it adds the internal switch control strategy of the device under test.

[0102] As Figure 7 shown, the AC short - circuit fault detection method specifically includes the following steps:

[0103] Step S1: Establish the DC bus voltage.

[0104] Step S2: When it is determined that there is no voltage on the AC side of the device, control the device to enter the AC wiring self - inspection preparation state.

[0105] Step S3: Control the device under test to output an AC voltage based on the preset modulation parameters.

[0106] Step S201: Control the internal AC - side switch of the device under test to close.

[0107] Step S4: Obtain the output voltage parameter of the device under test, and determine the absolute voltage value and the relative voltage value according to the output voltage parameter.

[0108] Step S5: Determine whether a short - circuit fault occurs in the inverter according to the absolute voltage value U and the relative voltage value ΔU, and determine the type of short - circuit fault.

[0109] Specifically, after controlling the inspected device to output an AC voltage for a preset time, a stable AC output voltage is output on the AC side of the inspected device. At this time, the internal AC side switch is controlled to close, so that the AC output side of the bridge arm of the inspected device is electrically connected to the multi-line parallel cable on the AC side. Through fault detection, the detection of internal short-circuit faults and external AC cable short-circuit faults of the inspected device can be realized, effectively reducing the shutdown risk of devices such as inverters and box transformers caused by AC short-circuit faults, and being beneficial to improving the safety and reliability of grid connection.

[0110] Embodiment 4

[0111] Optionally, Figure 8 is a flowchart of an AC short-circuit fault detection method provided by Embodiment 4 of the present invention.

[0112] As Figure 8 shown, the AC short-circuit fault detection method specifically includes the following steps:

[0113] Step S1: Establish a DC bus voltage.

[0114] Step S2: When it is determined that there is no voltage on the AC side of the device, control the device to enter the AC wiring self-check preparation state.

[0115] Step S3: Control the inspected device to output an AC voltage based on preset modulation parameters.

[0116] Step S4: Obtain the output voltage parameters of the inspected device, and determine the absolute voltage value and the relative voltage value according to the output voltage parameters.

[0117] Step S5: Determine whether a short-circuit fault occurs in the inverter according to the absolute voltage value U and the relative voltage value ΔU, and determine the short-circuit fault type.

[0118] Step S6: Send corresponding fault warning information according to the short-circuit fault type.

[0119] Among them, the fault warning information includes: ground short-circuit fault warning information, two-phase short-circuit fault warning information, and three-phase short-circuit fault warning information.

[0120] In one embodiment, an alarm module can be set on the surface of the inspected device, and the fault warning information is displayed through the alarm module. Alternatively, a wireless communication module can also be integrated inside the inspected device, and the fault warning information is sent to the dispatching terminal through network communication technology to realize the short-circuit fault risk prompt.

[0121] Embodiment 5

[0122] According to another aspect of the present invention, an AC short-circuit fault detection device is provided. The device is used to execute the short-circuit fault detection method provided in any embodiment of the present invention, and has the corresponding functional modules and beneficial effects for executing the method.

[0123] Figure 9 It is a schematic structural diagram of an AC short - circuit fault detection device provided in Embodiment 5 of the present invention.

[0124] As Figure 9 shown, the AC short - circuit fault detection device 00 includes:

[0125] A DC power supply module 101 for establishing a DC bus voltage;

[0126] A logic judgment module 102 for controlling the device to enter the AC wiring self - inspection preparation state when it is judged that there is no voltage on the AC side of the device;

[0127] A modulation and drive module 103 for controlling the device under test to output an AC voltage according to preset modulation parameters;

[0128] A voltage detection module 104 for obtaining the output voltage parameters of the device under test and determining the absolute value and relative value of the voltage according to the output voltage parameters;

[0129] A fault analysis module 105 for determining whether a short - circuit fault occurs in the device and determining the type of short - circuit fault according to the absolute value and relative value of the voltage.

[0130] In this embodiment, the AC short - circuit fault detection device can be integrally arranged in the device under test, and the AC - side outgoing line of the device under test adopts a multi - wire parallel structure for each phase.

[0131] In one embodiment, referring to Figure 2 shown, the DC power supply module 101 includes a DC - side switch K1 and a DC bus capacitor C0. The input side of the DC - side switch K1 is electrically connected to the photovoltaic power generation module PV, and the output side of the DC - side switch K1 is electrically connected to the DC bus capacitor C0 of the device. When establishing the DC bus voltage, the AC short - circuit fault detection device 00 can control the DC - side switch K1 to close, and the DC voltage generated by the photovoltaic power generation module PV is input into the device under test through the DC - side switch K1 to charge the DC bus capacitor C0 of the device under test until the charging voltage reaches the DC bus voltage required for the single - machine operation of the device.

[0132] In one embodiment, referring to Figure 3 shown, the DC power supply module 101 includes a DC bus capacitor C0. Among them, the DC bus capacitor C0 is directly electrically connected to the energy storage module BA. When establishing the DC bus voltage, the AC short - circuit fault detection device 00 can control the energy storage module BA to start, and the electric energy stored in the energy storage module BA is directly input into the device under test to charge the DC bus capacitor C0 of the device under test until the charging voltage reaches the DC bus voltage required for the single - machine operation of the device.

[0133] In one embodiment, the preset modulation parameters include modulation duty cycle, modulation frequency, modulation amplitude, and modulation phase.

[0134] In one embodiment, the output voltage parameters include at least one of the following: phase voltage parameters of each phase on the AC side, voltage parameters of each phase to ground, or line voltage parameters between each phase; the voltage absolute value includes: the maximum voltage value and the minimum voltage value in the same voltage parameter of each phase; the voltage relative value includes: the voltage difference between the same voltage parameters of each phase.

[0135] In one embodiment, the fault analysis module 105 is configured to obtain a preset differential pressure safety threshold and a preset voltage lower limit threshold; determine whether the device has an AC short - circuit fault according to the voltage relative value and the preset differential pressure safety threshold; and / or determine whether the device has an AC short - circuit fault according to the voltage absolute value and the preset voltage lower limit threshold.

[0136] In one embodiment, the short - circuit fault types include any one of the following: ground short - circuit fault, two - phase short - circuit fault, and three - phase short - circuit fault.

[0137] In one embodiment, the fault analysis module 105 is further configured to determine whether the short - circuit fault type is a two - phase short - circuit fault according to the voltage relative value between any two phases on the AC side and the preset differential pressure safety threshold; determine whether the short - circuit fault type is a three - phase short - circuit fault according to the voltage absolute value of the phase voltage of each phase on the AC side; determine whether the short - circuit fault type is a ground short - circuit fault according to the voltage absolute value of the voltage of each phase to ground on the AC side.

[0138] Optionally, before controlling the device under test to output an AC voltage, the voltage detection module 104 is further configured to obtain the initial DC - side voltage and the initial AC - side voltage of the device under test; the fault analysis module 105 is further configured to determine whether to terminate the fault detection according to the initial DC - side voltage and the initial AC - side voltage.

[0139] Optionally, after a preset time when the device under test outputs an AC voltage, the voltage detection module 104 is further configured to control the internal AC - side switch to close to obtain the output voltage parameters of the device under test.

[0140] Optionally, the AC short - circuit fault detection device 00 includes an alarm module, and the alarm module is configured to send corresponding fault warning information according to the short - circuit fault type; wherein, the fault warning information includes: single - phase short - circuit fault warning information, two - phase short - circuit fault warning information, and three - phase short - circuit fault warning information.

[0141] Embodiment Six

[0142] According to another aspect of the present invention, there is provided an electrical device, including: the above - mentioned AC short - circuit fault detection device 00.

[0143] Figure 10It is a schematic structural diagram of an electrical device provided in Embodiment 6 of the present invention.

[0144] Typically, the electrical device 1 can be an inverter.

[0145] As Figure 10 shown, the DC side of the electrical device 1 is electrically connected to the DC power supply 2, and the AC side of the electrical device 1 is connected to the AC grid through the three-phase AC cable 3, the external AC switch 4, and the box transformer 5 in sequence. The above AC short-circuit fault detection device 00 is integrally provided inside the electrical device 1.

[0146] Referring Figure 10 shown, each phase outgoing line on the AC side of the electrical device 1 adopts a multi-line parallel structure. For example, the a-phase outgoing line includes the first a-phase outgoing line a1 and the second a-phase outgoing line a2 connected in parallel, the b-phase outgoing line includes the first b-phase outgoing line b1 and the second b-phase outgoing line b2 connected in parallel, and the c-phase outgoing line includes the first c-phase outgoing line c1 and the second c-phase outgoing line c2 connected in parallel. The first ends of the multi-line parallel cables are electrically connected to the AC output terminals of the electrical device 1, and the second ends of the multi-line parallel cables are connected to the AC grid through the three-phase AC cable 3, the external AC switch 4, and the box transformer 5. In the multi-line parallel structure, the risk of short circuit between the lines of each phase increases, and the types of short-circuit faults between the lines are complex. Identifying the AC side short-circuit fault type before the device is connected to the grid is beneficial to timely troubleshooting and improving the grid connection safety.

[0147] The electrical device of the embodiment of the present invention is provided with an AC short-circuit fault detection device. The device is provided with a DC power supply module, a logic judgment module, a modulation drive module, a voltage detection module, and a fault analysis module. The DC power supply module establishes the DC bus voltage of the device before the device is connected to the grid. The logic judgment module controls the device under test to enter the AC wiring self-check preparation state when it judges that there is no voltage on the AC side of the device. The modulation drive module controls the device under test to output an AC voltage according to the preset modulation parameters. After the device under test starts and runs for a certain period of time, the voltage detection module acquires the output voltage parameters of the device under test and determines the absolute value and relative value of the voltage according to the output voltage parameters. The fault analysis module determines whether the inverter has a short-circuit fault according to the absolute value and relative value of the voltage and determines the short-circuit fault type, solving the problem that the existing inverter cannot identify the short-circuit fault before grid connection, realizing the fault detection before grid connection through a software program, without increasing the hardware cost, reducing the shutdown risk of the inverter and the box transformer caused by the short-circuit fault, and being beneficial to improving the safety and reliability of grid connection.

[0148] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in the present invention can be executed in parallel, sequentially, or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and no limitation is imposed herein.

[0149] The above specific embodiments 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 method for detecting AC short - circuit faults, characterized in that, The AC side outgoing line of the device under test adopts a multi-line parallel structure, and the method includes the following steps: Establish a DC bus voltage; wherein, establishing the DC bus voltage includes: controlling a DC power supply to provide a DC voltage to the DC side of the device under test; When it is determined that there is no voltage on the AC side of the device, control the device to enter the AC wiring self-check preparation state; in the AC wiring self-check preparation state, the internal DC side switch of the device is closed, and the internal AC side switch of the device is open; Control the device to output an AC voltage based on preset modulation parameters; Obtain the output voltage parameters of the device, and determine the absolute voltage value and the relative voltage value according to the output voltage parameters; Determine whether the device has a short-circuit fault according to the absolute voltage value and the relative voltage value, and determine the short-circuit fault type.

2. The method according to claim 1, characterized in that The preset modulation parameters include at least one of the following: modulation duty cycle, modulation frequency, modulation amplitude, and modulation phase.

3. The method according to claim 1, wherein The output voltage parameters include at least one of the following: phase voltage parameters of each phase on the AC side, voltage parameters of each phase to ground, and line voltage parameters between each phase; The absolute voltage value includes: the maximum voltage value and the minimum voltage value in the same voltage parameter of each phase; The relative voltage value includes: the voltage difference between the same voltage parameters of each phase.

4. The method according to claim 1, wherein Establishing the DC bus voltage includes: Controlling the DC side switch of the device to close; Establish a DC bus voltage based on the output voltage of the DC side switch; Wherein, the input side of the DC side switch is electrically connected to a photovoltaic power generation component, and the output side of the DC side switch is electrically connected to the DC bus capacitor of the device.

5. The method according to claim 1, wherein Establishing the DC bus voltage includes: Controlling the energy storage component to start; Establish a DC bus voltage based on the output voltage of the energy storage component; Wherein, the energy storage component is electrically connected to the DC bus capacitor of the device.

6. The method according to claim 1, characterized in that, Determining whether the device has a short-circuit fault according to the absolute voltage value and the relative voltage value includes: Obtain a preset differential pressure safety threshold and a preset voltage lower limit threshold; Determine whether the device has an AC short-circuit fault according to the relative voltage value and the preset differential pressure safety threshold; and / or, Determine whether the device has an AC short-circuit fault according to the absolute voltage value and the preset voltage lower limit threshold.

7. The method according to claim 1, characterized in that Determining the short-circuit fault type according to the absolute voltage value and the relative voltage value includes: Determine whether the short-circuit fault type is a two-phase short-circuit fault according to the relative voltage value between any two phases on the AC side and the preset differential pressure safety threshold; Determine whether the short-circuit fault type is a three-phase short-circuit fault according to the absolute voltage value of the phase voltage of each phase on the AC side; Determine whether the short-circuit fault type is a ground short-circuit fault according to the absolute voltage value of the voltage to ground of each phase on the AC side.

8. The method according to any one of claims 1-7, characterized in that, Before controlling the device to output an AC voltage, the method further includes the following steps: Obtain the initial DC side voltage and the initial AC side voltage of the device; Determine whether to terminate the fault detection according to the initial DC side voltage and the initial AC side voltage.

9. The method according to any one of claims 1 to 7, characterized in that After controlling the device to output an AC voltage for a preset time, the method further includes: Control the internal AC side switch of the device to close to obtain the output voltage parameters of the device.

10. The method according to any one of claims 1-7, characterized in that, It further includes the following steps: Sending corresponding fault warning information according to the short-circuit fault type; Wherein, the fault warning information includes: ground short-circuit fault warning information, two-phase short-circuit fault warning information, and three-phase short-circuit fault warning information.

11. An AC short - circuit fault detection device, characterized in that, For implementing the AC short-circuit fault detection method according to any one of claims 1-10, the device includes: A DC power supply module for establishing a DC bus voltage; wherein, establishing the DC bus voltage includes: controlling a DC power supply to provide a DC voltage to the device under test; A logic judgment module for controlling the device to enter the AC wiring self-check preparation state when it is judged that there is no voltage on the AC side of the device; in the AC wiring self-check preparation state, the internal DC side switch of the device is closed, and the internal AC side switch of the device is opened; A modulation driving module for controlling the device to output an AC voltage according to preset modulation parameters; A voltage detection module for obtaining the output voltage parameters of the device and determining the absolute voltage value and the relative voltage value according to the output voltage parameters; A fault analysis module for determining whether a short-circuit fault occurs in the device and determining the short-circuit fault type according to the absolute voltage value and the relative voltage value; 12. An electrical device, characterized in that, Including: The AC short-circuit fault detection device according to claim 11.

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