Inverter relay contact adhesion detection circuit and method
By using pull-up resistor strings and pull-down resistor strings in the inverter, the blind zone problem of inverter relay contact sticking detection is solved, realizing reliable detection and cost control of four-phase relays, and ensuring the balance between equipment safety and economy.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GOODWE TECHNOLOGIES CO LTD
- Filing Date
- 2025-12-30
- Publication Date
- 2026-04-24
AI Technical Summary
Existing methods for detecting inverter relay contact adhesion are difficult to balance equipment safety and cost control. Ordinary single-relay solutions have blind spots in N-phase adhesion detection, while high-priced solutions with contact status feedback are expensive.
By adopting an innovative configuration of pull-up resistor strings and pull-down resistor strings, and by detecting the voltage difference between the contacts of the parallel-to-grid switching relays of each phase, a contactless status feedback function that is compatible with phases A, B, C, and N is achieved, thereby reducing costs.
It enables reliable testing of four-phase relays (A, B, C, N), reduces relay procurement costs and overall hardware costs, and ensures a balance between equipment safety and economy.
Smart Images
Figure CN121917829A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of power conversion technology, specifically to a detection circuit and method for inverter relay contact adhesion. Background Technology
[0002] In grid maintenance scenarios, inverters must ensure that there is no high-voltage electricity on the external power lines connected to the grid to prevent electric shock to maintenance personnel. Furthermore, safety regulations require that this safety condition be met even when the inverter experiences a single fault. To achieve these requirements, the industry has developed two types of inverter grid-side on / off-grid switching and contact adhesion detection solutions, as detailed below: Option 1 involves connecting two sets of relays (each set containing four relays: R, S, T, and N, for a total of eight) in series in the inverter's grid-side on-grid switching circuit. During grid maintenance, both sets of relays are disconnected, ensuring that the grid-side power lines are still disconnected from the inverter's high-voltage section even if a single relay contact becomes stuck. However, this option has drawbacks: a large number of relays, large size, significant PCB footprint, high heat generation, and high design cost.
[0003] Option 2 involves using a single relay group (containing four channels: R, S, T, and N) with contact status feedback. During maintenance, this single relay group is disconnected, and the contact status is monitored in real time. If sticking is detected, the inverter output switch and diesel generator switch are disconnected. However, relays with contact status feedback are expensive, increasing the overall cost of the equipment.
[0004] In summary, existing technologies cannot effectively detect the sticking of all relay contacts when using ordinary relays throughout the entire circuit, and cannot simultaneously meet the dual requirements of equipment operation safety and overall cost control. Summary of the Invention
[0005] This invention provides a detection circuit and method for inverter relay contact adhesion, in order to solve the problem that existing inverter relay contact adhesion detection methods cannot simultaneously meet the requirements of equipment safety and cost control.
[0006] In a first aspect, the present invention provides a detection circuit for inverter relay contact sticking, applied to the grid-side parallel-to-grid switching circuit of an inverter. The detection circuit includes: a pull-up resistor string, a pull-down resistor string, and an A\B\C\N parallel-to-grid switching relay. One end of the pull-up resistor string is connected to the grid-side contact of the N-phase grid-connected / off-grid switching relay, and the other end of the pull-up resistor string is connected to the inverter-side contact of any one of the corresponding grid-connected / off-grid switching relays in phases A, B, and C. One end of the pull-down resistor string is connected to the grid-side contact of the N-phase parallel-to-grid switching relay, and the other end of the pull-down resistor string is connected to the PE line. The inverter detects the voltage difference between the contacts of the grid-connected and grid-connected switching relays of each phase in real time, and determines whether the contacts of the corresponding A, B, C, and N phase grid-connected and grid-connected switching relays are stuck together based on the voltage difference.
[0007] This invention provides a detection circuit for inverter relay contact sticking. Through an innovative configuration of pull-up and pull-down resistor strings, it utilizes mature voltage difference detection logic for phases A, B, and C to ensure detection stability and reliability. Furthermore, by employing a voltage divider structure design, it provides precisely distinguishable voltage difference characteristics for the N phases, resolving the blind spot in the sticking detection of the N-phase grid-connected / off-grid switching relays in existing conventional single-relay solutions. This enables all four phases (A, B, C, and N) to be compatible with ordinary single-relay relays without contact status feedback, eliminating the need for expensive relays with contact status feedback. This significantly reduces the relay procurement cost and overall hardware cost of the inverter, achieving a highly efficient balance between economy and practicality.
[0008] In one alternative implementation, the pull-up resistor string includes at least two resistors connected in series.
[0009] In one alternative implementation, the pull-down resistor string includes at least two resistors connected in series.
[0010] In one optional implementation, the pull-up resistor string and the output phase voltage of the inverter to which it is connected satisfy the following relationship: UX0 / Rx≤Isf Where UX0 is the inverter output phase voltage connected to the pull-up resistor string, X is A, B, and C, Rx is the total resistance of the pull-up resistor string, and Isf is the human safety current.
[0011] In one optional implementation, the pull-up resistor string, the pull-down resistor string, and the inverter output phase voltage connected to the pull-up resistor string satisfy the following relationship: UX0*Rx / ( Rx+ Ry)≤Us Where UX0 is the inverter output phase voltage connected to the pull-up resistor string, X is A, B, and C, Rx is the total resistance of the pull-up resistor string, Ry is the total resistance of the pull-down resistor string, and Us is the preset safety voltage.
[0012] In one optional implementation, the pull-down resistor string satisfies the following relationship with the maximum voltage difference between the N-phase and the PE line under the maximum grid imbalance: Unpe_max / Ry≤30mA Where Unpe_max is the maximum voltage difference between the N-phase and the PE line under the maximum imbalance of the power grid, and Ry is the total resistance of the pull-down resistor string.
[0013] Secondly, the present invention provides a method for detecting inverter relay contact adhesion, based on the inverter relay contact adhesion detection circuit of the first aspect or any corresponding embodiment thereof, the detection method comprising: Real-time detection of the voltage difference between the contacts of the grid-side A\B\C\N phase parallel-to-grid switching relays of the inverter; Based on the voltage difference, determine whether the contacts of the corresponding A\B\C\N phase parallel-to-offline switching relays are stuck together.
[0014] This invention provides a method for detecting relay contact sticking in inverters. Through an innovative configuration of pull-up and pull-down resistor strings, it utilizes mature voltage difference detection logic for phases A, B, and C to ensure detection stability and reliability. Furthermore, by employing a voltage divider structure design, it provides precisely distinguishable voltage difference characteristics for the N phases, resolving the blind spot in the sticking detection of the N-phase grid-connected / off-grid switching relays in existing conventional single-relay solutions. This enables all four phases (A, B, C, and N) to be compatible with ordinary single-relay relays without contact status feedback, eliminating the need for expensive relays with contact status feedback. This significantly reduces the relay procurement cost and overall hardware cost of the inverter, achieving a highly efficient balance between economy and practicality.
[0015] In one optional implementation, determining whether the corresponding A\B\C\N phase parallel-to-off-grid switching relay contacts are stuck together based on the voltage difference includes: If the voltage difference of the A-phase grid-connected / off-grid switching relay remains at zero, it is determined that the contacts of the A-phase grid-connected / off-grid switching relay are stuck together. If the voltage difference of the A-phase grid-connected / off-grid switching relay is not at zero, it is determined that the contacts of the A-phase grid-connected / off-grid switching relay are not stuck together. The zero state means that the voltage difference is zero, or the voltage difference fluctuates near zero and its fluctuation amplitude does not exceed a preset threshold. If the voltage difference of the B-phase grid connection / disconnection switching relay remains at zero, it is determined that the contacts of the B-phase grid connection / disconnection switching relay are stuck together. If the voltage difference of the B-phase grid connection / disconnection switching relay is not at zero, it is determined that the contacts of the B-phase grid connection / disconnection switching relay are not stuck together. If the voltage difference of the C-phase parallel-to-off-grid switching relay remains at zero, it is determined that the contacts of the C-phase parallel-to-off-grid switching relay are stuck together. If the voltage difference of the C-phase parallel-to-off-grid switching relay is not zero, it is determined that the contacts of the C-phase parallel-to-off-grid switching relay are not stuck together.
[0016] In one optional implementation, determining whether the corresponding A\B\C\N phase parallel-to-off-grid switching relay contacts are stuck together based on the voltage difference further includes: If the voltage difference of the N-phase parallel-to-off-grid switching relay remains at zero, it is determined that the contacts of the N-phase parallel-to-off-grid switching relay are stuck together. The zero state means that the voltage difference is zero, or the voltage difference fluctuates near zero and its fluctuation amplitude does not exceed a preset threshold. If the voltage difference of the N-phase grid-connected switching relay is proportional to the output phase voltage of the inverter connected to the pull-up resistor series, then it is determined that the contacts of the N-phase grid-connected switching relay have not stuck together.
[0017] In one optional implementation, when the contacts of the N-phase grid-connected switching relay do not stick together, the voltage difference of the N-phase grid-connected switching relay and the preset proportional relationship between the output phase voltage of the inverter connected to the pull-up resistor series are as follows: UN=UX0*Rx / Ry Where UN is the voltage difference of the N-phase grid-connected / off-grid switching relay, UX0 is the inverter output phase voltage connected to the pull-up resistor string, X is A, B, and C, Rx is the total resistance of the pull-up resistor string, and Ry is the total resistance of the pull-down resistor string.
[0018] In one optional implementation, the detection method further includes: When it is detected that the contacts of any phase off-grid switching relay are stuck together, disconnect the inverter output switch and / or the diesel generator input switch. Attached Figure Description
[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0020] Figure 1 This is a schematic diagram of the first type of inverter commonly used in parallel-to-off-grid switching schemes; Figure 2 This is a schematic diagram of the second type of inverter commonly used in parallel and off-grid switching schemes; Figure 3 This is a schematic diagram of a detection circuit for inverter relay contact adhesion according to an embodiment of the present invention; Figure 4 This is a flowchart illustrating a method for detecting inverter relay contact adhesion according to an embodiment of the present invention. Detailed Implementation
[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0022] It is understood that before using the technical solutions disclosed in the various embodiments of the present invention, users should be informed of the types, scope of use, and usage scenarios of the personal information involved in the present invention and their authorization should be obtained in accordance with relevant laws and regulations through appropriate means.
[0023] According to safety regulations, during grid maintenance, inverters must ensure that there is no high-voltage electricity on the grid-side external power lines to eliminate the risk of electric shock for grid maintenance personnel. Because this scenario directly relates to personal safety, the safety requirements are extremely high. Relevant regulations clearly stipulate that even if the inverter experiences a single fault, it is still necessary to ensure that the grid-side power lines do not carry dangerous high-voltage electricity.
[0024] To meet this stringent safety requirement, the grid-side on-grid switching stage of the inverter often employs a dual-relay series scheme to reliably disconnect the inverter from the grid in the event of a single fault. As shown in Figure 1, when the grid enters maintenance mode, the grid switch KM is disconnected; after the inverter detects the grid power failure, it will simultaneously disconnect the internally connected on-grid relay groups KB and KC (KB and KC are relay groups containing four independent relays A, B, C, and N, for a total of 8 relays). At this time, the power supply to the load port can continue to be provided by the photovoltaic modules or batteries through the inverter unit, or the diesel generator switch KE can be closed to supply power through the generator connected to the diesel generator port. Under this condition, the A, B, C, and N lines connected to the inverter's grid-side port are neither connected to the grid nor to the high-voltage part of the inverter operating off-grid, and are in a non-energized floating state to ensure the personal safety of maintenance personnel when touching them. The core advantage of this dual-relay series design is that even if any one of the relays KB or KC experiences a contact sticking fault, it can still ensure that the grid-side A, B, C, and N lines remain disconnected from the high-voltage section inside the inverter. This meets the safety requirements that ensure that when a single fault occurs in the inverter, the wires that may be touched during maintenance are not carrying dangerous high-voltage electricity.
[0025] However, this solution has significant drawbacks. Both sets of relays KB and KC are connected in series in the inverter power circuit, and their contact current carrying capacity must be no less than the maximum current of the inverter grid-side port, resulting in the selected relays being too large. At the same time, the configuration of 8 relays not only occupies a lot of printed circuit board (PCB) space, but also generates a lot of heat, ultimately increasing the design and manufacturing cost of the equipment.
[0026] To overcome the aforementioned shortcomings of the dual-relay series scheme, the inverter-to-grid switching scheme employs a single-relay scheme with contact status feedback. As shown in Figure 2, this scheme uses a single set of relays KB (containing four independent relays A, B, C, and N with contact status feedback function), connected in series in the grid-side output line. During grid maintenance, after KM is disconnected, the inverter disconnects KB and switches to off-grid operation mode, while simultaneously monitoring the contact status of each relay in KB in real time. Once contact sticking is detected in any relay, the inverter will immediately disconnect the inverter output switch KA and / or the diesel generator switch KE, cutting off the high-voltage conduction path at the source and preventing the grid-side A, B, C, and N lines from carrying high voltage due to relay sticking, thereby ensuring the safety of maintenance personnel. However, relays with contact status feedback function are usually more expensive to purchase.
[0027] To address the aforementioned problems, this application provides a detection circuit for inverter relay contact sticking, applied to the grid-side and off-grid switching circuit of the inverter. For example... Figure 3 As shown, the detection circuit includes: a pull-up resistor string, a pull-down resistor string, and an A / B / C / N grid-connected switching relay. One end of the pull-up resistor string is connected to the grid-side contact of the N-phase grid-connected switching relay, and the other end is connected to the inverter-side contact of any corresponding A / B / C phase grid-connected switching relay. One end of the pull-down resistor string is connected to the grid-side contact of the N-phase grid-connected switching relay, and the other end is connected to the PE line. The inverter monitors the voltage difference between the contacts of each phase grid-connected switching relay in real time and determines whether the contacts of the corresponding A / B / C / N phase grid-connected switching relays are stuck together based on the voltage difference.
[0028] Specifically, in Figure 3 In the detection circuit shown, the grid-side contact of the inverter grid-side N-phase parallel-to-grid switching relay is connected to any one of the inverter output phase voltages A0, B0, and C0 through a pull-up resistor string consisting of at least two high-resistance resistors connected in series (taking pull-up to A0 as an example in this application); at the same time, it is connected to the PE line (protective ground) through a pull-down resistor string consisting of at least two high-resistance resistors connected in series.
[0029] When the power grid enters maintenance mode, the grid switch KM is open. Upon detecting the power outage, the inverter simultaneously performs two actions: first, it disconnects the four-phase (A, B, C, N) off-grid switching relays within the KB group; second, it closes switch KD, connecting the inverter output N line to the PE line, thus establishing a grounded microgrid system to ensure a continuous and stable power supply to the load ports. Under this condition, the inverter will collect the voltage difference across the relay contacts of each phase within the KB group in real time. Based on the numerical characteristics of the voltage difference, it determines whether the contacts are stuck together. The specific detection logic is as follows: 1) Detection logic for relay sticking in phases A, B, and C: In the KB group, the left contacts of the A, B, and C phase relays are connected to the A0, B0, and C0 terminals of the inverter output, respectively. Since the inverter output N line is connected to the PE line after KD is closed, the voltages of the A0, B0, and C0 terminals relative to the N and PE lines are the inverter output AC phase voltages. The right contacts of the A, B, and C phase relays are connected to the grid-side floating power line, and their voltage relative to the PE line is 0V. If the contacts of the A, B, and C phase relays are not stuck together, the voltage differences UA, UB, and UC between the contacts are equal to the corresponding inverter output AC phase voltages (i.e., UA=UA0, UB=UB0, UC=UC0). If any one of the A, B, or C phase relay contacts becomes stuck, the voltage difference between the contacts of that phase will remain zero, and the inverter can directly determine that the phase relay has an output contact sticking fault. In this embodiment of the invention, a zero state refers to a voltage difference of zero, or a voltage difference fluctuating around zero with the fluctuation amplitude not exceeding a preset threshold. The preset threshold is set based on the inverter model power and relay contact impedance. For example, the preset threshold is 0.5V, which means that [-0.5V-0.5V] all belong to the zero state referred to in this application.
[0030] 2) N-phase relay sticking detection logic: The left contact of the N-phase relay is connected to the inverter output N-line, and the right contact is connected to the grid-side floating N-line. Regardless of whether the contacts are stuck together, the potentials at both ends are always the same, and the voltage difference remains zero, making it impossible to detect sticking by voltage difference. Therefore, this problem is solved by adding pull-up resistors and pull-down resistors in series. For example, the pull-up resistor series uses R1 and R2 connected in series, and the pull-down resistor series uses R3 and R4 connected in series (R1, R2, R3, and R4 are all high-resistance resistors), and they are pulled up to the inverter output phase voltage A0 (corresponding to voltage value UA0). When the power grid is under maintenance and the N-phase relay is disconnected, the potential of its right-hand contact is determined by the voltage division of the pull-up resistor series (R1+R2) and the pull-down resistor series (R3+R4) connected in series. At this time, the voltage difference UN between the two contacts of the N-phase relay is UN=UA0*(R1+R2) / (R1+R2+R3+R4), which has a fixed proportional relationship with the inverter output phase voltage UA0. If the N-phase relay contacts stick together, the two contacts are directly electrically connected, and the voltage difference will remain at zero. The inverter can accurately determine whether sticking has occurred by identifying whether the voltage difference between the N-phase relay contacts is a fixed proportional value or remains at zero.
[0031] When the inverter detects that the relay contacts of any one of the A, B, C, and N phases are stuck, it will immediately trigger a safety protection action: disconnect the inverter output switch KA and / or the diesel generator switch KE, cut off the high-voltage conduction path from the source, ensure that the grid-side A, B, C, and N lines are not carrying high-voltage electricity, and fully protect the personal safety of maintenance personnel.
[0032] In this embodiment of the invention, the four-phase parallel-to-off-grid switching relays A, B, C, and N in the KB group are all ordinary single relays with no contact status feedback function. They are all connected in series in the inverter grid-side output line, which not only undertakes the core function of parallel-to-off-grid switching, but also greatly reduces the hardware procurement cost, taking into account both safety and economy.
[0033] This invention provides a detection circuit for inverter relay contact sticking. Through an innovative configuration of pull-up and pull-down resistor strings, it utilizes mature voltage difference detection logic for phases A, B, and C to ensure detection stability and reliability. Furthermore, by employing a voltage divider structure design, it provides precisely distinguishable voltage difference characteristics for the N phases, resolving the blind spot in the sticking detection of the N-phase grid-connected / off-grid switching relays in existing conventional single-relay solutions. This enables all four phases (A, B, C, and N) to be compatible with ordinary single-relay relays without contact status feedback, eliminating the need for expensive relays with contact status feedback. This significantly reduces the relay procurement cost and overall hardware cost of the inverter, achieving a highly efficient balance between economy and practicality.
[0034] In one alternative implementation, the pull-up resistor string and the output phase voltage of the inverter to which it is connected satisfy the following relationship: UX0 / Rx≤Isf Where UX0 is the inverter output phase voltage connected to the pull-up resistor string, X is A, B, and C, Rx is the total resistance of the pull-up resistor string, and Isf is the human safety current.
[0035] Specifically, to ensure the personal safety of maintenance personnel, the pull-up and pull-down resistors used in this application must meet the safety protection requirements under a single fault scenario. The pull-up resistors must consist of two or more high-resistance resistors connected in series. Their resistance values must strictly adhere to the following current safety constraints: when a maintenance personnel accidentally touch the neutral (N) line on the grid side, the current flowing through their body must not exceed the human safety current Isf. Taking the pull-up resistor series pulling up to A0 as an example, this satisfies UA0 / (R1+R2)<Isf, where R1+R2 is the total resistance of the pull-up resistor series.
[0036] In one optional implementation, the pull-up resistor string, the pull-down resistor string, and the inverter output phase voltage connected to the pull-up resistor string satisfy the following relationship: UX0*Rx / ( Rx+ Ry)≤Us Where UX0 is the inverter output phase voltage connected to the pull-up resistor string, X is A, B, and C, Rx is the total resistance of the pull-up resistor string, Ry is the total resistance of the pull-down resistor string, and Us is the preset safety voltage.
[0037] Specifically, the voltage difference between the grid-side N line and PE line (protective ground) must be strictly controlled within the safe voltage Us range. Taking the pull-up resistor string pulling up to A0 as an example, this means satisfying UA0*(R1+R2) / (R1+R2+R3+R4)<Us, where R3+R4 is the total resistance of the pull-down resistor string. According to the provisions of the decisive voltage level A in GB / T 37408-2019 "Technical Requirements for Photovoltaic Power Generation Grid-Connected Relays", the effective value of this safe voltage AC voltage Us≤25V.
[0038] In one alternative implementation, the pull-down resistor string satisfies the following relationship with the maximum voltage difference between the N-phase and the PE line under the maximum grid imbalance: Unpe_max / Ry<30mA Where Unpe_max is the maximum voltage difference between the N-phase and the PE line under the maximum imbalance of the power grid, and Ry is the total resistance of the pull-down resistor string.
[0039] Specifically, under the maximum grid imbalance condition allowed by the inverter (where the maximum voltage difference between the N phase and the PE line is Unpe_max), the selection of the pull-down resistor string must meet the leakage current safety constraint: ensure that the leakage current of the inverter does not exceed the leakage current protection threshold of 30mA, that is, satisfy Unpe_max / (R3+R4)<30mA.
[0040] This invention provides a method for detecting inverter relay contact adhesion, based on Figure 3 The circuit shown is for detecting stuck inverter relay contacts. Figure 4 As shown, the detection methods include: Step S1: Real-time detection of the voltage difference between the contacts of the inverter grid-side A\B\C\N phase parallel-to-grid switching relays.
[0041] Specifically, when the power grid enters maintenance mode, the grid switch KM is opened. After the inverter detects the power outage, it will simultaneously perform two actions: first, disconnect the four-phase off-grid switching relays (A, B, C, and N) within the KB group; second, close switch KD to connect the inverter output N line to the PE line, constructing a grounded microgrid system to ensure continuous and stable power supply to the load ports. Under this condition, the inverter will collect the voltage difference across the relay contacts of each phase within the KB group in real time, and determine whether the contacts are stuck based on the numerical characteristics of the voltage difference.
[0042] Step S2: Determine whether the contacts of the corresponding A\B\C\N phase parallel-to-offline switching relays are stuck together based on the voltage difference.
[0043] Specifically, step S2 above includes: Step S21: If the voltage difference of the A-phase parallel-to-off-grid switching relay remains at zero, it is determined that the contacts of the A-phase parallel-to-off-grid switching relay are stuck together. If the voltage difference of the A-phase parallel-to-off-grid switching relay is not zero, it is determined that the contacts of the A-phase parallel-to-off-grid switching relay are not stuck together.
[0044] Step S22: If the voltage difference of the phase B grid connection / disconnection switching relay remains at zero, it is determined that the contacts of the phase A grid connection / disconnection switching relay are stuck together. If the voltage difference of the phase B grid connection / disconnection switching relay is not zero, it is determined that the contacts of the phase B grid connection / disconnection switching relay are not stuck together.
[0045] Step S23: If the voltage difference of the C-phase grid-connected / off-grid switching relay remains at zero, it is determined that the contacts of the A-phase grid-connected / off-grid switching relay are stuck together. If the voltage difference of the C-phase grid-connected / off-grid switching relay is not zero, it is determined that the contacts of the C-phase grid-connected / off-grid switching relay are not stuck together.
[0046] Step S24: If the voltage difference of the N-phase parallel-to-off-grid switching relay remains at zero, it is determined that the contacts of the N-phase parallel-to-off-grid switching relay are stuck. Zero state means that the voltage difference is zero, or the voltage difference fluctuates near zero and its fluctuation amplitude does not exceed the preset threshold.
[0047] Step S25: If the voltage difference between the N-phase grid-connected and off-grid switching relays is proportional to the output phase voltage of the inverter connected to the pull-up resistor series, then it is determined that the contacts of the N-phase grid-connected and off-grid switching relays have not stuck together.
[0048] Specifically, in the KB group, the left contacts of the A, B, and C phase relays are connected to the A0, B0, and C0 terminals of the inverter output, respectively. Since the inverter output N line is connected to the PE line after KD is closed, the voltages of the A0, B0, and C0 terminals relative to the N and PE lines are the inverter output AC phase voltages. The right contacts of the A, B, and C phase relays are connected to the grid-side floating power line, and their voltage relative to the PE line is 0V. If the contacts of the A, B, and C phase relays are not stuck together, the voltage differences UA, UB, and UC between the contacts are equal to the corresponding inverter output AC phase voltages (i.e., UA=UA0, UB=UB0, UC=UC0). If any one of the A, B, or C phase relay contacts becomes stuck, the voltage difference between the contacts of that phase will remain at zero, and the inverter can directly determine that the phase relay has an output contact sticking fault. In this embodiment of the invention, a zero state refers to a voltage difference of zero, or a voltage difference fluctuating around zero with the fluctuation amplitude not exceeding a preset threshold. The preset threshold is set based on the inverter model power and relay contact impedance. For example, the preset threshold is 0.5V, which means that [-0.5V-0.5V] all belong to the zero state referred to in this application.
[0049] The left contact of the N-phase relay is connected to the inverter output N-line, and the right contact is connected to the grid-side floating N-line. Regardless of whether the contacts are stuck together, the potentials at both ends are always the same, and the voltage difference remains zero, making it impossible to detect sticking by voltage difference. Therefore, this problem is solved by adding pull-up resistors and pull-down resistors in series. For example, the pull-up resistors are R1 and R2 connected in series, and the pull-down resistors are R3 and R4 connected in series (R1, R2, R3, and R4 are all high-resistance resistors), and they are pulled up to the inverter output phase voltage A0 (corresponding to voltage value UA0). When the grid is under maintenance and the N-phase relay is disconnected, the potential of its right contact is determined by the voltage division of the pull-up resistor series (R1+R2) and the pull-down resistor series (R3+R4). At this time, the voltage difference between the N-phase grid-connected and disconnected relays and the preset proportional relationship of the inverter output phase voltage connected to the pull-up resistor series is as follows: UN = UX0 * Rx / (Rx + Ry) Where UN is the voltage difference of the N-phase grid-connected / off-grid switching relay, UX0 is the inverter output phase voltage connected to the pull-up resistor string, X is A, B, and C, Rx is the total resistance of the pull-up resistor string, and Ry is the total resistance of the pull-down resistor string.
[0050] Taking the pull-up resistor series pulled up to A0 as an example, the voltage difference UN between the contacts of the N-phase relay is UN = UA0 * (R1 + R2) / (R1 + R2 + R3 + R4), which is proportional to the inverter output phase voltage UA0. If the contacts of the N-phase relay stick together, the two contacts are directly electrically connected, and the voltage difference will remain at zero. The inverter can accurately determine whether sticking has occurred by identifying whether the voltage difference between the contacts of the N-phase relay is a fixed proportional value or 0V.
[0051] This invention provides a method for detecting relay contact sticking in inverters. Through an innovative configuration of pull-up and pull-down resistor strings, it utilizes mature voltage difference detection logic for phases A, B, and C to ensure detection stability and reliability. Furthermore, by employing a voltage divider structure design, it provides precisely distinguishable voltage difference characteristics for the N phases, resolving the blind spot in the sticking detection of the N-phase grid-connected / off-grid switching relays in existing conventional single-relay solutions. This enables all four phases (A, B, C, and N) to be compatible with ordinary single-relay relays without contact status feedback, eliminating the need for expensive relays with contact status feedback. This significantly reduces the relay procurement cost and overall hardware cost of the inverter, achieving a highly efficient balance between economy and practicality.
[0052] In one optional implementation, the detection method further includes: Step S3: When it is detected that the contacts of any phase off-grid switching relay are stuck together, disconnect the inverter output switch and / or the diesel generator input switch.
[0053] Specifically, when the inverter detects that the relay contacts of any one of the A, B, C, and N phases are stuck together, it will immediately trigger a safety protection action: disconnect the inverter output switch KA and / or the diesel generator input switch KE, cut off the high-voltage conduction path from the source, ensure that the grid-side A, B, C, and N lines are not carrying high-voltage electricity, and fully protect the personal safety of maintenance personnel.
[0054] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.
Claims
1. A detection circuit for inverter relay contact adhesion, characterized in that, The detection circuit, applied to the grid-side grid-to-grid switching circuit of an inverter, includes: a pull-up resistor string, a pull-down resistor string, and an A\B\C\N grid-to-grid switching relay. One end of the pull-up resistor string is connected to the grid-side contact of the N-phase grid-connected / off-grid switching relay, and the other end of the pull-up resistor string is connected to the inverter-side contact of any one of the corresponding grid-connected / off-grid switching relays in phases A, B, and C. One end of the pull-down resistor string is connected to the grid-side contact of the N-phase parallel-to-grid switching relay, and the other end of the pull-down resistor string is connected to the PE line. The inverter detects the voltage difference between the contacts of the grid-connected and grid-connected switching relays of each phase in real time, and determines whether the contacts of the corresponding A, B, C, and N phase grid-connected and grid-connected switching relays are stuck together based on the voltage difference.
2. The detection circuit for inverter relay contact adhesion according to claim 1, characterized in that, The A, B, C, and N phase parallel-to-off-grid switching relays are all single relays without contact status feedback.
3. The detection circuit for inverter relay contact adhesion according to claim 1, characterized in that, The pull-up resistor string includes at least two resistors connected in series.
4. The detection circuit for inverter relay contact adhesion according to claim 1, characterized in that, The pull-down resistor string includes at least two resistors connected in series.
5. The detection circuit for inverter relay contact adhesion according to claim 1, characterized in that, The pull-up resistor string and the output phase voltage of the inverter it is connected to satisfy the following relationship: UX0 / Rx ≤Isf Where UX0 is the inverter output phase voltage connected to the pull-up resistor string, X is A, B, and C, Rx is the total resistance of the pull-up resistor string, and Isf is the human safety current.
6. The detection circuit for inverter relay contact adhesion according to claim 1, characterized in that, The pull-up resistor string, the pull-down resistor string, and the inverter output phase voltage connected to the pull-up resistor string satisfy the following relationship: UX0*Rx / ( Rx+ Ry) ≤ Us Where UX0 is the inverter output phase voltage connected to the pull-up resistor string, X is A, B, and C, Rx is the total resistance of the pull-up resistor string, Ry is the total resistance of the pull-down resistor string, and Us is the preset safety voltage.
7. The detection circuit for inverter relay contact adhesion according to claim 1, characterized in that, The pull-down resistor string satisfies the following relationship with the maximum voltage difference between phase N and the PE line under the maximum grid imbalance: Unpe_max / Ry≤30mA Where Unpe_max is the maximum voltage difference between the N-phase and the PE line under the maximum imbalance of the power grid, and Ry is the total resistance of the pull-down resistor string.
8. A method for detecting contact adhesion of inverter relays, characterized in that, Based on the detection circuit for inverter relay contact adhesion according to any one of claims 1-7, the detection method includes: Real-time detection of the voltage difference between the contacts of the inverter grid-side A\B\C\N phase parallel-to-grid switching relays; Based on the voltage difference, determine whether the contacts of the corresponding A\B\C\N phase parallel-to-offline switching relays are stuck together.
9. The method for detecting inverter relay contact adhesion according to claim 8, characterized in that, Based on the voltage difference, determine whether the contacts of the corresponding A\B\C\N phase parallel-to-off-grid switching relays are stuck together, including: If the voltage difference of the A-phase grid-connected / off-grid switching relay remains at zero, it is determined that the contacts of the A-phase grid-connected / off-grid switching relay are stuck together. If the voltage difference of the A-phase grid-connected / off-grid switching relay is not at zero, it is determined that the contacts of the A-phase grid-connected / off-grid switching relay are not stuck together. The zero state means that the voltage difference is zero, or the voltage difference fluctuates near zero and its fluctuation amplitude does not exceed a preset threshold. If the voltage difference of the B-phase grid connection / disconnection switching relay remains at zero, it is determined that the contacts of the B-phase grid connection / disconnection switching relay are stuck together. If the voltage difference of the B-phase grid connection / disconnection switching relay is not at zero, it is determined that the contacts of the B-phase grid connection / disconnection switching relay are not stuck together. If the voltage difference of the C-phase parallel-to-off-grid switching relay remains at zero, it is determined that the contacts of the C-phase parallel-to-off-grid switching relay are stuck together. If the voltage difference of the C-phase parallel-to-off-grid switching relay is not zero, it is determined that the contacts of the C-phase parallel-to-off-grid switching relay are not stuck together.
10. The method for detecting inverter relay contact adhesion according to claim 8, characterized in that, Based on the voltage difference, determining whether the corresponding A\B\C\N phase parallel-to-off-grid switching relay contacts are stuck together also includes: If the voltage difference of the N-phase parallel-to-off-grid switching relay remains at zero, it is determined that the contacts of the N-phase parallel-to-off-grid switching relay are stuck together. The zero state means that the voltage difference is zero, or the voltage difference fluctuates near zero and its fluctuation amplitude does not exceed a preset threshold. If the voltage difference of the N-phase grid-connected switching relay is proportional to the output phase voltage of the inverter connected to the pull-up resistor series, then it is determined that the contacts of the N-phase grid-connected switching relay have not stuck together.
11. The method for detecting inverter relay contact adhesion according to claim 10, characterized in that, When the contacts of the N-phase grid-connected / off-grid switching relay are not stuck, the preset proportional relationship between the voltage difference of the N-phase grid-connected / off-grid switching relay and the output phase voltage of the inverter connected in the pull-up resistor series is as follows: UN = UX0 * Rx / (Rx + Ry) Where UN is the voltage difference of the N-phase grid-connected switching relay, UX0 is the inverter output phase voltage connected to the pull-up resistor string, X is A, B, and C, Rx is the total resistance of the pull-up resistor string, and Ry is the total resistance of the pull-down resistor string.
12. The method for detecting inverter relay contact adhesion according to any one of claims 8-10, characterized in that, The detection method further includes: When it is detected that the contacts of any phase off-grid switching relay are stuck together, disconnect the inverter output switch and / or the diesel generator input switch.