A relay failure detection method and system

Abstract

The application discloses a relay failure detection method and system, wherein the method comprises the following steps: in response to a shutdown signal of a three-phase inverter module, selecting a group of relay control units as target detection units and disconnecting the target detection units; acquiring first voltage values of output ends of the three-phase inverter module of each phase line branch relative to a reference line within a preset time; acquiring second voltage values of an alternating current power grid of each phase line branch relative to the reference line within the preset time; selecting one phase line branch; judging whether a difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than or equal to a first preset threshold value; if the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than or equal to the first preset threshold value, marking a relay in the target detection unit corresponding to the phase line branch; otherwise, returning until all phase line branches are selected. The application can accurately reflect whether sticking failure occurs and avoid sending false alarm signals.

Description

Technical Field

[0001] This invention belongs to the field of relay protection technology, specifically relating to a relay failure detection method and system. Background Technology

[0002] For electrical safety reasons, electrical isolation is required between the output of the three-phase inverter and the AC power grid. In one isolation method, relays are installed on each phase branch between the three phases (L1, L2, L3) of the power grid and the output of the three-phase inverter. When the three-phase inverter is not operating, the relays must be disconnected to ensure complete disconnection between the inverter and the power grid. If a relay fails due to sticking, it will pose a safety hazard. Therefore, a sticking failure test must be performed on the relays before starting the inverter.

[0003] In traditional testing methods, the presence of a stuck relay is determined by checking whether the voltage at the output of the three-phase inverter is equal to the voltage of the grid phases. Under normal circumstances, since the potential at the DC bus neutral point and the neutral line are equal, the three-phase inverter output voltage is measured by detecting the voltage between the three-phase output terminals of the inverter and the DC bus neutral point, while the grid phase voltage is measured by detecting the voltage between the three phases of the grid and the neutral line.

[0004] However, in actual operation, the DC bus midpoint potential may be unequal to the neutral potential, or there may be residual charge in the inverter output capacitor. This means that the difference between the three-phase inverter output voltage and the grid phase voltage cannot accurately reflect whether a sticking failure has occurred, leading to the issuance of incorrect alarm signals. Consequently, the three-phase inverter cannot start up and operate normally, affecting normal power generation. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a relay failure detection method and system to accurately reflect whether adhesion failure has occurred, and to avoid issuing false alarm signals that would affect the normal start-up and operation of the three-phase inverter.

[0006] To solve the above technical problems, the present invention provides a relay failure detection method, comprising:

[0007] Step S100: In response to the shutdown signal of the three-phase inverter module, select a set of relay control units as the target detection unit and disconnect the target detection unit;

[0008] Step S200: Obtain the first voltage value of the output terminal of the three-phase inverter module of each phase line branch relative to the reference line within a preset time.

[0009] Step S300: Obtain the second voltage value of the AC power grid relative to the reference line for each phase branch within a preset time period;

[0010] Step S400: Select a phase line branch;

[0011] Step S500: Determine whether the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than or equal to a first preset threshold.

[0012] In step S600, if the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than or equal to the first preset threshold, then mark the relay in the target detection unit corresponding to the phase line branch; otherwise, return to step S400 until all phase line branches are selected.

[0013] Preferably, before step S100, the method further includes:

[0014] Step S101: Obtain the current three-phase voltage and current frequency of the AC power grid, respectively;

[0015] Step S102: Determine whether the current three-phase voltage is within the preset voltage range;

[0016] Step S103: If the current three-phase voltage is within the preset voltage range, then further determine whether the current frequency is within the preset frequency range.

[0017] Step S104: If the current frequency is within the preset frequency range, then execute step S100.

[0018] Preferably, after step S600, the method further includes:

[0019] Step S611, further determine whether the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than a second preset threshold; wherein, the second preset threshold is less than the first preset threshold;

[0020] Step S612: If the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than the second preset threshold, then the marked relay is confirmed to be faulty.

[0021] Step S613: If the difference between the first voltage value and the second voltage value corresponding to the candidate failure relay is greater than or equal to the second preset threshold, then return to the step of obtaining the first voltage value of the output terminal of the three-phase inverter module of each phase branch relative to the reference line within a preset time.

[0022] Preferably, before step S611, the method further includes:

[0023] Step S601: Determine whether the number of comparisons between the difference between the first voltage value and the second voltage value corresponding to the phase line branch and the second preset threshold is greater than the preset number threshold.

[0024] Step S602: If the number of comparisons between the difference between the first voltage value and the second voltage value corresponding to the phase line branch and the second preset threshold is greater than the preset threshold, then the marked relay is confirmed to be faulty.

[0025] Step S603: If the number of comparisons between the difference between the first voltage value and the second voltage value corresponding to the phase line branch and the second preset threshold is less than or equal to the preset threshold, then step S611 is executed.

[0026] Preferably, step S100 specifically includes:

[0027] Step S111: Determine whether the number of relay control units is equal to 1;

[0028] Step S112: If the number of relay control units is equal to 1, then the relay control unit is used as the target detection unit, and the relay in the target detection unit is controlled to disconnect.

[0029] Preferably, step S100 further includes:

[0030] Step S113: If the number of relay control units is greater than 1, then one group of relay control units is used as the target detection unit, the relay in the target detection unit is controlled to open, and the relays in other relay control units are controlled to close.

[0031] Preferably, step S200 specifically includes:

[0032] Step S210: Obtain the sampling voltage Va of the first preset number of sampling points within one power grid cycle;

[0033] Step S220: Calculate the effective voltage value V within one power grid cycle using the following formula. e :

[0034]

[0035] Where N represents the first preset number of sampling points within a power grid cycle;

[0036] Step S230: Calculate the average value of the effective voltage over a second preset number of power grid cycles within a preset time period as the first voltage value.

[0037] The present invention also provides a relay failure detection system, comprising:

[0038] The first voltage detection circuit is used to detect the first voltage value of the output terminal of the three-phase inverter module of each phase line branch relative to the reference line within a preset time.

[0039] The second voltage detection circuit is used to detect the second voltage value of the AC power grid of each phase branch relative to the reference line within a preset time.

[0040] A controller for performing the relay failure detection method as described in any one of claims 1 to 7;

[0041] The drive module is used to output drive signals to control the on / off state of the relay control unit according to the control commands issued by the controller;

[0042] The first voltage detection circuit, the second voltage detection circuit, and the drive module are respectively connected to the controller.

[0043] Preferably, the first voltage detection circuit includes three first voltmeters, each phase branch is provided with a first voltage detection point, and the first voltage detection point is located between the three-phase inverter module and at least one relay control unit; the first voltmeters are electrically connected between the first voltage detection point and the reference line.

[0044] Preferably, the second voltage detection circuit includes three second voltmeters, each phase branch is provided with a second voltage detection point, and the second voltage detection point is located between the AC power grid and at least one relay control unit; the second voltmeters are electrically connected between the second voltage detection point and the reference line.

[0045] The present invention has the following beneficial effects: By acquiring the first voltage value of the output terminal of the three-phase inverter module of the phase branch relative to the reference line and the second voltage value of the AC grid relative to the reference line within a preset time, if the difference between the first voltage value and the second voltage value of a certain phase branch is within a first preset threshold, it indicates that the relay connected to that phase branch may be stuck and failed. Since the first voltage value and the second voltage value are both voltages relative to the reference line, the first voltage value and the second voltage value will not be affected if the DC bus midpoint potential is not equal to the reference line potential or if the first capacitor has residual charge. This accurately reflects whether a sticking failure has occurred, avoids issuing false alarm signals that would affect the normal start-up and operation of the three-phase inverter, and ensures normal power generation. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a flowchart illustrating a relay failure detection method according to an embodiment of the present invention.

[0048] Figure 2This is a schematic diagram of the structure of a three-phase grid-connected inverter system applying a relay failure detection method according to an embodiment of the present invention.

[0049] Figure 3 This is another structural schematic diagram of a three-phase grid-connected inverter system applying a relay failure detection method according to an embodiment of the present invention.

[0050] Figure 4 This is a schematic diagram of a relay failure detection system according to Embodiment 2 of the present invention.

[0051] Figure 5 This is another structural schematic diagram of a relay failure detection system according to Embodiment 2 of the present invention.

[0052] Figure 6 This is another structural schematic diagram of a relay failure detection system according to Embodiment 2 of the present invention.

[0053] The attached figures are labeled as follows:

[0054] 100 - Three-phase grid-connected inverter system; LS - DC bus; C01, C02 - Bus capacitors; D1 - Bus midpoint; 110 - Three-phase inverter module; 300 - AC grid; S1 - Relay control unit; S11, S12, S13 - Relays; S2 - Relay control unit; S21, S22, S23 - Relays; C11, C12, C13 - First capacitor; C21, C22, C23 - Second capacitor; L1, L2, L3 - Phase line branch; B1 - First voltage detection point; B2 - Second voltage detection point; 200 - Relay failure detection system; 210 - First voltage detection circuit; V11, V12, V13 - First voltmeter; 220 - Second voltage detection circuit; V21, V22, V23 - Second voltmeter; 230 - Controller; 240 - Drive module. Detailed Implementation

[0055] The following description of the embodiments is taken with reference to the accompanying drawings, which illustrate specific embodiments in which the invention can be implemented.

[0056] Please refer to Figure 1 As shown, Embodiment 1 of the present invention provides a relay failure detection method, including:

[0057] Step S100: In response to the shutdown signal of the three-phase inverter module, select a set of relay control units as the target detection unit and disconnect the target detection unit;

[0058] Step S200: Obtain the first voltage value of the output terminal of the three-phase inverter module of each phase line branch relative to the reference line within a preset time.

[0059] Step S300: Obtain the second voltage value of the AC power grid relative to the reference line for each phase branch within a preset time period;

[0060] Step S400: Select a phase line branch;

[0061] Step S500: Determine whether the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than or equal to a first preset threshold.

[0062] In step S600, if the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than or equal to the first preset threshold, then mark the relay in the target detection unit corresponding to the phase line branch; otherwise, return to step S400 until all phase line branches are selected.

[0063] As can be seen from the above steps, this embodiment of the invention obtains the first voltage value of the output terminal of the three-phase inverter module of the phase branch relative to the reference line and the second voltage value of the AC grid relative to the reference line within a preset time. If the difference between the first voltage value and the second voltage value of a certain phase branch is within a first preset threshold, it indicates that the relay connected to that phase branch may have failed due to adhesion. Since both the first voltage value and the second voltage value are relative to the reference line, the difference between the DC bus midpoint potential and the reference line potential or the presence of residual charge in the first capacitor will not affect the first voltage value and the second voltage value. This accurately reflects whether adhesion failure has occurred, avoids issuing false alarm signals that would affect the normal start-up and operation of the three-phase inverter, and ensures normal power generation.

[0064] It should be noted that the relay failure detection method of this invention is applied to, for example, Figure 2 and Figure 3 The three-phase grid-connected inverter system 100 is shown. For example... Figure 2 and 3 As shown, the three-phase grid-connected inverter system 100 includes a DC bus LS, bus capacitors C01 and C02, a three-phase inverter module 110, at least one set of relay control units, first capacitors C11, C12, and C13, and second capacitors C21, C22, and C23.

[0065] Specifically, the output of the three-phase inverter module 110 is electrically connected to the AC power grid 300 through three phase line branches L1, L2, and L3. More specifically, the three-phase inverter module 110 includes at least a three-phase inverter.

[0066] The two bus capacitors C01 and C02 are connected by a bus midpoint D1. The first capacitors C11, C12, and C13 are electrically connected between the output terminal of the three-phase inverter module 110 and the bus midpoint D1, respectively. The second capacitors C21, C22, and C23 are electrically connected between the AC power grid 300 and the reference line N, respectively.

[0067] The relay control unit is provided with at least one set, connected in series to the phase line branch, for achieving electrical isolation between the three-phase inverter module 110 and the AC power grid 300. The relay control unit includes three relays, each connected in series to a phase line branch, and the relays in the same set of relay control units are of the same specification.

[0068] Figure 2 The schematic diagram of a three-phase grid-connected inverter system 100 containing only one set of relay control unit S1 is shown. The relay control unit S1 includes relays S11, S12, and S13. Among them, relay S11 is connected in series in phase branch L1, relay S12 is connected in series in phase branch L2, and relay S13 is connected in series in phase branch L3.

[0069] Figure 3 The schematic diagram of a three-phase grid-connected inverter system 100 includes two sets of relay control units S1 and S2. Relay control unit S1 includes relays S11, S12, and S13. Relay control unit S2 includes relays S21, S12, and S23. Relays S11 and S21 are connected in series in phase branch L1, relays S12 and S22 are connected in series in phase branch L2, and relays S13 and S23 are connected in series in phase branch L3.

[0070] In step S100, in response to the shutdown signal of the three-phase inverter module 110, a set of relay control units is selected as the target detection unit, and the target detection unit is disconnected. Specifically, the relay failure detection of the present invention can be performed from the current shutdown point of the three-phase inverter module 110 to before the next startup of the three-phase inverter module 110.

[0071] Step S200 involves acquiring the first voltage value of the output terminal of the three-phase inverter module 110 of each phase branch relative to the reference line N within a preset time period. The preset time period includes at least one power grid cycle.

[0072] Step S300: Obtain the second voltage value of the AC power grid 300 of each phase branch relative to the reference line N within a preset time period, wherein the preset time period includes at least one power grid cycle.

[0073] Step S500 determines whether the difference between the first voltage value and the second voltage value corresponding to the selected phase line branch is less than or equal to a first preset threshold. Considering that the magnitudes of the first voltage value and the second voltage value may change in actual testing, this embodiment takes the absolute value of the difference between the first voltage value and the second voltage value as the difference between the two.

[0074] In this embodiment, by acquiring the first voltage value of the output terminal of the three-phase inverter module 110 of a phase branch relative to the reference line and the second voltage value of the AC grid 300 relative to the reference line within a preset time period, if the difference between the first voltage value and the second voltage value of a certain phase branch is within a first preset threshold, it indicates that the relay connected to that phase branch may have failed due to adhesion. Since both the first voltage value and the second voltage value are relative to the reference line, the difference between the potential at the midpoint of the DC bus LS and the potential at the reference line N, or the presence of residual charge in the first capacitor, will not affect the first voltage value and the second voltage value. This accurately reflects whether adhesion failure has occurred, avoids issuing false alarm signals that could affect the normal start-up and operation of the three-phase inverter, and ensures normal power generation.

[0075] As a further improvement to this embodiment, before step S100, the following is also included:

[0076] Step S101: Obtain the current three-phase voltage and current frequency of AC power grid 300.

[0077] Step S102: Determine whether the current three-phase voltage is within the preset voltage range.

[0078] Specifically, the preset voltage range can be taken as the range near the nominal voltage. For example, if the nominal voltage is 220V, the preset voltage range is greater than or equal to 187V and less than or equal to 253V. Of course, the actual preset voltage range can be determined according to the actual grid connection regulations.

[0079] Step S103: If the current three-phase voltage is within the preset voltage range, then further determine whether the current frequency is within the preset frequency range.

[0080] Specifically, the preset frequency range can be greater than or equal to 48.5Hz to less than or equal to 50.2Hz. Of course, the actual preset frequency range can be determined according to the actual grid connection regulations.

[0081] Step S104: If the current frequency is within the preset frequency range, then execute step S100.

[0082] In this embodiment, by detecting the current three-phase voltage and current frequency of the AC power grid 300, the influence of power grid anomalies on the detection of the second voltage value is eliminated, thereby improving the accuracy of subsequent adhesion failure detection results.

[0083] Due to uncontrollable factors such as fluctuations in grid voltage or voltage sampling errors, there may be situations where the difference between the first voltage value and the second voltage value is within a certain range below a first preset threshold, and the relay operates normally. If only the first preset threshold is used to judge the difference, misjudgment is likely to occur.

[0084] In one embodiment of the present invention, after step S600, the method further includes:

[0085] Step S611: Further determine whether the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than the second preset threshold.

[0086] Specifically, the second preset threshold is less than the first preset threshold.

[0087] Step S612: If the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than the second preset threshold, then the marked relay is confirmed to be faulty.

[0088] Step S613: If the difference between the first voltage value and the second voltage value corresponding to the candidate failure relay is greater than or equal to the second preset threshold, then return to the step of obtaining the first voltage value of the output terminal of the three-phase inverter module 110 of each phase branch relative to the reference line within a preset time.

[0089] In this embodiment, by setting a second preset threshold, the difference between the first voltage value and the second voltage value is further judged. When the difference is between the first preset threshold and the second preset threshold, the first voltage value and the second voltage value are reacquired for further judgment on the first preset threshold and the second preset threshold. This two-stage threshold judgment avoids the influence of uncontrollable factors on the first or second voltage value, improves the reliability of adhesion failure detection, and reduces the possibility of misjudgment.

[0090] Since the difference between the first voltage value and the second voltage value may be detected whether the relay is malfunctioning or normal, and the difference is within the range between the first preset threshold and the second preset threshold, repeating the above steps may not be able to achieve rapid division.

[0091] In one embodiment of the present invention, prior to step S611, the relay failure detection method further includes:

[0092] Step S601: Determine whether the number of comparisons between the difference between the first voltage value and the second voltage value corresponding to the phase line branch and the second preset threshold is greater than the preset number threshold.

[0093] Step S602: If the number of comparisons between the difference between the first voltage value and the second voltage value corresponding to the phase line branch and the second preset threshold is greater than the preset threshold, then the marked relay is confirmed to be faulty.

[0094] Step S603: If the number of comparisons between the difference between the first voltage value and the second voltage value corresponding to the phase line branch and the second preset threshold is less than or equal to the preset threshold, then step S611 is executed.

[0095] In this embodiment, by adding a determination of the number of times step S611 is run before step S611, if the number of times step S611 is run is greater than a preset threshold, it is not possible to effectively determine whether the relay is faulty, and manual inspection and confirmation are required.

[0096] In one embodiment of the present invention, step S100 specifically includes:

[0097] Step S111: Determine whether the number of relay control units is equal to 1.

[0098] Step S112: If the number of relay control units is equal to 1, then the relay control unit is used as the target detection unit, and the relay in the target detection unit is controlled to disconnect.

[0099] like Figure 4 As shown, only the relay control unit S1 is included. At this time, all the relays of the relay control unit S1 are disconnected.

[0100] Step S113: If the number of relay control units is greater than 1, then one group of relay control units is used as the target detection unit, the relay in the target detection unit is controlled to open, and the relays in other relay control units are controlled to close.

[0101] like Figure 5 As shown, relay control units S1 and S2 are provided. When selecting to disconnect all relays in relay control unit S1 and close all relays in relay control unit S2, a sticking failure detection is performed on the relays in relay control unit S1. Alternatively, when selecting to disconnect all relays in relay control unit S2 and close all relays in relay control unit S1, a sticking failure detection is performed on the relays in relay control unit S2.

[0102] Specifically, when multiple relay control units are connected in series, failure detection needs to be performed on each group of relay control units separately. When testing a relay in one group of relay control units, it is sufficient to test the relays in other groups of relay control units while they are in the energized state. By performing this process sequentially, all relays sharing the same drive signal can be tested.

[0103] In this embodiment, the method of the present invention can be applied to a group of relay control units or multiple groups of relay control units simultaneously.

[0104] In one embodiment of the present invention, step S200 specifically includes:

[0105] Step S210: Obtain the sampling voltage Va of the first preset number of sampling points within one power grid cycle.

[0106] Specifically, the grid cycle is 50Hz, 20ms, and the first preset quantity can be in the range of 300 to 400.

[0107] Step S220: Calculate the effective voltage value V within one power grid cycle using the following formula 1. e :

[0108]

[0109] Where N represents the first preset number of sampling points within a power grid cycle.

[0110] Step S230: Calculate the average value of the effective voltage over a second preset number of power grid cycles within a preset time period as the first voltage value.

[0111] Specifically, the value of the second preset quantity can be determined according to actual needs. In one possible embodiment, the second preset quantity is 60.

[0112] In this embodiment, the accuracy of the first voltage value detection is improved by calculating the average value of the effective voltage of the second preset number of power grid cycles within a preset time as the first voltage value.

[0113] Of course, the same steps S210 to S230 can be used to calculate the second voltage value.

[0114] In one embodiment of the present invention, the reference line N is a zero line or a floating potential.

[0115] For example, such as Figure 4 and 5 As shown, baseline N is the zero line. Figure 6 As shown, the baseline N represents the floating potential.

[0116] In this embodiment, the present invention only needs to ensure that the reference lines are at the same potential, without considering whether there is a neutral line connected. It is applicable not only to three-phase grid-connected inverters with reference line connection, but also to three-phase grid-connected inverters without reference line connection.

[0117] The present invention also discloses a relay failure detection system 200.

[0118] like Figures 4 to 6 As shown, in one embodiment of the present invention, the relay failure detection system 200 of the present invention includes a first voltage detection circuit 210, a second voltage detection circuit 220, a controller 230 and a drive module 240.

[0119] Specifically, the first voltage detection circuit 210 is used to detect the first voltage value of the output terminal of the three-phase inverter module 110 of each phase branch relative to the reference line within a preset time. The second voltage detection circuit 220 is used to detect the second voltage value of the AC power grid 300 of each phase branch relative to the reference line within a preset time.

[0120] The controller 230 is used to execute the relay failure detection method described above. Specifically, the controller 230 of this invention can be a DSP chip or an MCU. The drive module 240 is used to output drive signals to control the on / off state of the relay control unit according to the control commands issued by the controller 230. The first voltage detection circuit 210, the second voltage detection circuit 220, and the drive module 240 are respectively signal-connected to the controller 230.

[0121] In this embodiment, voltage data is collected by the first voltage detection circuit 210 and the second voltage detection circuit 220 within a preset time period. The controller 230 processes the voltage data acquired by the first voltage detection circuit 210 and the second voltage detection circuit 220 to obtain a first voltage value and a second voltage value. If the difference between the first voltage value and the second voltage value of a certain phase branch is within a first preset threshold, it indicates that the relay connected to that phase branch may have failed due to sticking. Since both the first voltage value and the second voltage value are voltages relative to a reference line, they can accurately reflect whether sticking failure has occurred, avoiding the issuance of false alarm signals that would affect the normal start-up and operation of the three-phase inverter, and ensuring normal power generation.

[0122] like Figures 4 to 6 As shown, in one embodiment of the present invention, the first voltage detection circuit 210 includes three first voltmeters V11, V12, and V13. Each phase branch is provided with a first voltage detection point B1, and the first voltage detection point B1 is located between the three-phase inverter module 110 and at least one set of relay control units. The first voltmeters are electrically connected between the first voltage detection point B1 and the reference line N.

[0123] In this embodiment, the voltage of the first voltage detection point relative to the reference line can be detected by using a first voltmeter, without the need for additional design or modification costs of the three-phase inverter, and without affecting the existing functions of the three-phase inverter.

[0124] like Figures 4 to 6 As shown, in one embodiment of the present invention, the second voltage detection circuit 220 includes three second voltmeters V21, V22, and V23. Each phase branch is provided with a second voltage detection point B2, and the second voltage detection point B2 is located between the AC power grid 300 and at least one set of relay control units. The second voltmeter 221 is electrically connected between the second voltage detection point B2 and the reference line N.

[0125] In this embodiment, the voltage of the second voltage detection point relative to the reference line can be detected by using a second voltmeter, without the need for additional design or modification costs of the three-phase inverter, and without affecting the existing functions of the three-phase inverter.

[0126] For the working principle and process of this embodiment, please refer to the description of Embodiment 1 of the present invention, which will not be repeated here.

[0127] As can be seen from the above description, compared with the prior art, the beneficial effects of the present invention are as follows: The present invention obtains the first voltage value of the output terminal of the three-phase inverter module of the phase branch relative to the reference line and the second voltage value of the AC grid relative to the reference line within a preset time. If the difference between the first voltage value and the second voltage value of a certain phase branch is within a first preset threshold, it indicates that the relay connected to the phase branch may be stuck and failed. Since the first voltage value and the second voltage value are both voltages relative to the reference line, the first voltage value and the second voltage value will not be affected if the DC bus midpoint potential is not equal to the reference line potential or if the first capacitor has residual charge. This accurately reflects whether a sticking failure has occurred, avoids issuing false alarm signals that would affect the normal start-up and operation of the three-phase inverter, and ensures normal power generation.

[0128] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for detecting relay failure, characterized in that, include: Step S100: In response to the shutdown signal of the three-phase inverter module, select a set of relay control units as the target detection unit and disconnect the target detection unit; Step S200: Obtain the first voltage value of the output terminal of the three-phase inverter module of each phase line branch relative to the reference line within a preset time period; the reference line is the zero line or a floating potential. Step S300: Obtain the second voltage value of the AC power grid relative to the reference line for each phase branch within a preset time period; Step S400: Select a phase line branch; Step S500: Determine whether the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than or equal to a first preset threshold. In step S600, if the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than or equal to the first preset threshold, then mark the relay in the target detection unit corresponding to the phase line branch; otherwise, return to step S400 until all phase line branches are selected.

2. The relay failure detection method according to claim 1, characterized in that, Before step S100, the method further includes: Step S101: Obtain the current three-phase voltage and current frequency of the AC power grid, respectively; Step S102: Determine whether the current three-phase voltage is within the preset voltage range; Step S103: If the current three-phase voltage is within the preset voltage range, then further determine whether the current frequency is within the preset frequency range. Step S104: If the current frequency is within the preset frequency range, then execute step S100.

3. The relay failure detection method according to claim 1, characterized in that, Following step S600, the method further includes: Step S611, further determine whether the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than a second preset threshold; wherein, the second preset threshold is less than the first preset threshold; Step S612: If the difference between the first voltage value and the second voltage value corresponding to the phase line branch is less than the second preset threshold, then the marked relay is confirmed to be faulty. Step S613: If the difference between the first voltage value and the second voltage value corresponding to the candidate failure relay is greater than or equal to the second preset threshold, then return to the step of obtaining the first voltage value of the output terminal of the three-phase inverter module of each phase branch relative to the reference line within a preset time.

4. The relay failure detection method according to claim 3, characterized in that, Before step S611, the method further includes: Step S601: Determine whether the number of comparisons between the difference between the first voltage value and the second voltage value corresponding to the phase line branch and the second preset threshold is greater than the preset number threshold. Step S602: If the number of comparisons between the difference between the first voltage value and the second voltage value corresponding to the phase line branch and the second preset threshold is greater than the preset threshold, then the marked relay is confirmed to be faulty. Step S603: If the number of comparisons between the difference between the first voltage value and the second voltage value corresponding to the phase line branch and the second preset threshold is less than or equal to the preset threshold, then step S611 is executed.

5. The relay failure detection method according to claim 1, characterized in that, Step S100 specifically includes: Step S111: Determine whether the number of relay control units is equal to 1; Step S112: If the number of relay control units is equal to 1, then the relay control unit is used as the target detection unit, and the relay in the target detection unit is controlled to disconnect.

6. The relay failure detection method according to claim 5, characterized in that, Step S100 further includes: Step S113: If the number of relay control units is greater than 1, then one group of relay control units is used as the target detection unit, the relay in the target detection unit is controlled to open, and the relays in other relay control units are controlled to close.

7. The relay failure detection method according to claim 6, characterized in that, Step S200 specifically includes: Step S210: Obtain the sampling voltage of the first preset number of sampling points within one power grid cycle. ; Step S220: Calculate the effective voltage value within one power grid cycle using the following formula. V e : Where N represents the first preset number of sampling points within a power grid cycle; Step S230: Calculate the average value of the effective voltage over a second preset number of power grid cycles within a preset time period as the first voltage value.

8. A relay failure detection system, characterized in that, include: The first voltage detection circuit is used to detect the first voltage value of the output terminal of the three-phase inverter module of each phase line branch relative to the reference line within a preset time. The baseline is either a zero line or a floating potential; The second voltage detection circuit is used to detect the second voltage value of the AC power grid of each phase branch relative to the reference line within a preset time. A controller for performing the relay failure detection method as described in any one of claims 1 to 7; The drive module is used to output drive signals to control the on / off state of the relay control unit according to the control commands issued by the controller; The first voltage detection circuit, the second voltage detection circuit, and the drive module are respectively connected to the controller.

9. The relay failure detection system according to claim 8, characterized in that, The first voltage detection circuit includes three first voltmeters, each phase branch is provided with a first voltage detection point, and the first voltage detection point is located between the three-phase inverter module and at least one relay control unit; the first voltmeters are electrically connected between the first voltage detection point and the reference line.

10. The relay failure detection system according to claim 8, characterized in that, The second voltage detection circuit includes three second voltmeters, with one second voltage detection point set for each phase branch, and the second voltage detection point is located between the AC power grid and at least one relay control unit; the second voltmeters are electrically connected between the second voltage detection point and the reference line.

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