Fault detection circuit and method for AC grid-connected relay of energy storage converter

Abstract

The invention relates to the technical field of energy storage converter fault detection, in particular to a fault detection circuit and method for an AC grid-connected relay of an energy storage converter. A primary relay is removed, a group of detection relay loop is added on the side of an alternating current grid-connected relay and a converter, and the detection relay loop is composed of a detection relay and a detection loop resistor. In the fault detection link of the alternating-current grid-connected relay, the voltage of the detection relay loop is judged by sequentially closing the detection relays of the detection relay loop, so that the short-circuit detection of the alternating-current grid-connected relay is realized. And then the detection relay loop is disconnected, the AC grid-connected relays are sequentially closed, and the voltage of the detection relay loop is judged, so that open circuit detection of the AC grid-connected relays is realized. The added detection relay loop is simple in structure and small in occupied space, the design cost of the alternating current grid-connected relay can be effectively reduced, and the overall structure utilization rate and the power density of the energy storage converter are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage converter fault detection, in particular to an energy storage converter AC grid-connected relay fault detection circuit and method. Background Art

[0002] The application of energy storage systems can effectively make up for the inherent intermittent and instability deficiencies of renewable energy power generation, making it possible for large-scale renewable energy to be connected to the grid for a long time. With the rapid development and widespread application of energy storage systems, energy storage converters have been widely used in power systems. When the relay is on-load, arcing will occur between the contacts. Arc erosion will cause oxidation of the contact surface. Multiple erosions and contact heating will cause the relay contacts to stick together, making it impossible to open normally, resulting in failure of the relay product. At present, the grid-connected side of the string-type energy storage converter still uses power relays as grid-connected switching devices. In actual use, there are often application conditions such as frequent on-load disconnection and large current impact disconnection, which greatly increases the risk of relay contact adhesion. While affecting the service life of the relay and energy storage converter, it also affects the safe and stable operation of the energy storage system. The current mainstream energy storage converter solution is to configure a relay as a grid-connected switch on the grid side (load side) and the converter output side. When the converter is shut down or fails, the two relays are disconnected through the command issued by the control system, forming an electrical disconnection point on the grid side (load side) and the converter output side, and quickly cutting off the converter from the grid or load. This design solution not only increases hardware costs, but also wastes resources of digital processing chips.

[0003] In the field of energy storage converters, the current mainstream AC grid-connected relay detection method is to connect two main circuit power relays in series, control the main circuit power relays to open and close alternately through the control system, and judge the difference between the sampled voltage on the grid side and the sampled voltage on the converter side to perform relay fault logic judgment. The traditional solution uses two-stage main circuit power relays for segmented judgment, which has the following disadvantages: (1) High material cost, the material cost of a single power relay ranges from tens to hundreds of yuan; (2) During the detection process of the traditional detection method, the power relay is closed and disconnected at least twice with load (the AC side grid is energized), which affects the service life of the relay and reduces the life and reliability of the device and the entire equipment; (3) The different patented methods and software calculation methods in the detection process are relatively complex, and the judgment and execution time is long, resulting in high software resource consumption. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a fault detection circuit and method for an AC grid-connected relay of an energy storage converter. By optimizing the bipolar series scheme of the traditional AC grid-connected relay, removing the primary relay, and adding a set of detection relay circuits on the output side of the AC grid-connected relay and the converter, the detection relay circuit is composed of a detection relay and a detection circuit resistor. In the AC grid-connected relay fault detection link, firstly, by closing the detection relays of the detection relay circuit in sequence, the voltage of the detection relay circuit is judged to realize the short circuit detection of the AC grid-connected relay. Then, the detection relay circuit is disconnected, the AC grid-connected relay is closed in sequence, the voltage of the detection relay circuit is judged, and the open circuit detection of the AC grid-connected relay is realized.

[0005] In order to solve the technical problem, the technical solution adopted by the present invention is: an energy storage inverter AC grid-connected relay fault detection circuit, including an energy storage inverter and an AC grid-connected relay located on the grid side, the AC grid-connected relay serves as a grid-connected switch on the grid side of the energy storage inverter, and a group of detection relay circuits are added between the output end of the energy storage inverter and the AC grid-connected relay. The detection relay circuit includes a three-phase circuit, and each phase detection relay circuit includes a detection relay, one end of the detection relay is connected between the output end of the energy storage inverter and the AC grid-connected relay, and the other end of the detection relay is connected to the inverter AC neutral point N'.

[0006] Furthermore, only one level of grid-connected relay is provided between the output side and the grid side of the energy storage converter.

[0007] Furthermore, the detection relay of each phase detection relay circuit is connected in series with a sampling resistor, one end of the sampling resistor is connected to the detection relay, and the other end of the sampling resistor is connected to the AC neutral point N' of the converter.

[0008] The present invention also discloses a method for detecting faults of an AC grid-connected relay of an energy storage converter. The method is implemented based on the above-mentioned fault detection circuit. In the AC grid-connected relay fault detection link, the detection relays of the three-phase detection relay circuit are first closed in sequence to determine the voltage of the detection relay circuit to achieve short-circuit detection of the AC grid-connected relay; then the detection relay circuit is disconnected, the AC grid-connected relays are closed in sequence to determine the voltage of the detection relay circuit to achieve open-circuit detection of the AC grid-connected relay.

[0009] Furthermore, the implementation process of this method is: S01), the three-phase AC grid-connected relays remain disconnected; S02), first close the detection relay of the single-phase detection relay circuit; S03), collecting the voltage of the circuit where the closed detection relay is located, and comparing it with the set voltage threshold Uset1; S04), if the collected voltage in step S03) is greater than the set voltage threshold Uset1, it is determined that the AC grid-connected relay in the same phase as the closed detection relay has a short circuit fault, the fault information is latched, and the fault processing is performed; S05), if the collected voltage in step S03) is less than the set voltage threshold Uset1, the phase detection relay is disconnected and the other phase detection relay is closed; S06), repeating step S03) to step S05), until all operations of the three-phase detection relay are completed; S07) disconnect the three-phase detection relay and close the single-phase AC grid-connected relay; S08), collecting the voltage of the detection relay circuit in phase with the closed AC grid-connected relay, and comparing it with the set voltage threshold Uset2; S09), if the voltage collected in step S08) is less than the set voltage threshold Uset2, it is determined that the closed AC grid-connected relay has an open circuit fault, the fault information is latched, and the fault processing is performed; S10), if the voltage collected in step S08) is greater than the set voltage threshold Uset2, the AC grid-connected relay Sa of the phase is disconnected, and the AC grid-connected relay of the other phase is closed; S11), repeat step S08) to step S10), until all operations of the three-phase AC grid-connected relay are completed.

[0010] Furthermore, the value range of the voltage threshold Uset1 is set to (0.2~0.4)*Ugrid, where Ugrid is the grid phase voltage.

[0011] Furthermore, the value range of the voltage threshold Uset2 is set to (0.6~0.7)*Ugrid, where Ugrid is the grid phase voltage.

[0012] Furthermore, in step S04) and step S09), the fault information is latched in the following manner: the fault information is stored in a set storage area, and the set storage area is queried during the power-on operation of the detection relay circuit to determine whether there is a fault information mark, and this is used as a basis for determining whether the grid-connected relay is operating normally.

[0013] Furthermore, in step S01) to step S06), detection is performed in the order of phase A, phase B, and phase C.

[0014] Furthermore, in step S07) to step S11), detection is performed in the order of phase A, phase B, and phase C.

[0015] Beneficial effects of the present invention: The energy storage converter AC grid-connected relay fault detection circuit and method proposed by the present invention are easy to operate and implement, safe and reliable in design, and have high detection accuracy. The added detection relay circuit has a simple structure, occupies a small space, and is highly economical. It can effectively reduce the design cost of the AC grid-connected relay, save the design circuit space, and improve the overall structural utilization and power density of the energy storage converter. The detection method proposed by the present invention reduces the primary main circuit grid-connected relay through the action coordination of the main relay and the detection relay during the detection process, and reduces the one-time action process of the main relay during the relay detection process, thereby improving the service life of the main relay. The detection circuit relay has a sampling resistor in series, and a low-power soft-start relay can be used to ensure that the service life is greater than the main relay, which improves the detection accuracy as a whole, reduces the detection cost, and also improves the service life and reliability of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of the fault detection circuit described in Example 1; Figure 2 is a schematic diagram of the fault detection circuit described in Example 2; Figure 3 This is a flow chart of the fault detection method described in Example 3. DETAILED DESCRIPTION

[0017] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0018] Example 1 The present embodiment discloses an AC grid-connected relay fault detection circuit for an energy storage converter. By optimizing the bipolar series scheme of a traditional AC grid-connected relay, a primary relay is removed, and a set of detection relay circuits is added to the output side of the AC grid-connected relay and the energy storage converter. The detection relay circuit is composed of a detection relay and a detection circuit resistor.

[0019] In this embodiment, the added detection relay circuit is located between the output side of the energy storage converter and the AC grid-connected relay. The detection relay circuit includes a three-phase circuit. Each phase detection relay circuit includes a detection relay. One end of the detection relay is connected between the output side of the energy storage converter and the AC grid-connected relay, and the other end of the detection relay is connected to the converter AC neutral point N'. And only one level of grid-connected relay is set between the output side of the energy storage converter and the grid side. The energy storage converter is U1 in the figure, which includes auxiliary circuits, such as Figure 1 As shown, specifically: The DC bus capacitor module includes two DC bus capacitors C1 and C2. C1 and C2 evenly divide the DC bus side voltage and are connected in parallel with the DC input side of the converter module to achieve the DC bus side voltage access to the converter module.

[0020] The AC output side of the converter module U1 is connected to the input sides of the filter inductors L1, L2, and L3 respectively, so as to realize the function of converting DC power into AC power.

[0021] The filter inductor module includes three-phase filter inductors L1, L2 and L3, and the output side is respectively connected to the filter capacitor module, the detection relay loop module and the AC grid-connected relay module to realize the AC filtering function.

[0022] The filter capacitor module includes three-phase filter capacitors C3, C4 and C5, and the input side is connected to the output side of the filter inductors L1, L2 and L3 respectively; after the output side is short-circuited at point N', it is connected to the DC side of the converter module and the detection relay loop module to realize the AC filtering function.

[0023] The detection relay circuit module includes a three-phase circuit, and each phase detection relay circuit is composed of a detection relay, that is, Figure 1 The detection relays Sa', Sb', and Sc' in the circuit have their input sides connected to the output sides of the filter inductors L1, L2, and L3, the input sides of the filter capacitors C3, C4, and C5, and the grid-connected relay module respectively; the output sides of the detection relays Sa', Sb', and Sc' are short-circuited at the point N', connected to the midpoint of the DC side of the converter module, and short-circuited to the output sides of the filter capacitors C3, C4, and C5 at the point N', thereby realizing the detection of the short-circuit or open-circuit state of the grid-connected relay module.

[0024] The grid-connected relay module includes three-phase grid-connected relays Sa, Sb, and Sc, and the input side is respectively connected to the output side of the filter inductors L1, L2, and L3, the input side of the filter capacitors C3, C4, and C5, and the input side of the detection relays Sa', Sb', and Sc'; the output side is respectively connected to the grid-side filter capacitor module and the power terminal module to realize the grid-connected function of the energy storage converter.

[0025] The grid-side filter capacitor module includes C6, C7, and C8, and the input side is connected to the output side of the grid-connected relays Sa, Sb, Sc and the power terminal module respectively; the output side is short-circuited and connected to the earth PE to realize the power-mode interference filtering function of the grid.

[0026] The power terminal module includes three-phase terminals A, B, and C. The input side is respectively connected to the output side of grid-connected relays Sa, Sb, and Sc and the input side of grid-side filter capacitors C6, C7, and C8; the output side is short-circuited and connected to the neutral point N of the grid to achieve reliable access to the grid power supply.

[0027] In this embodiment, the removed primary relay is a power relay, which is used to disconnect the high voltage and high current grid-connected relay of the main circuit, and the added detection relay is only used to detect the open circuit and short circuit status of the main circuit grid-connected relay. The breaking current is very small, and the volume and cost are greatly reduced compared with the power relay. Therefore, the relay material cost can be effectively reduced, and then the hardware design cost can be reduced. The detection relay added in this embodiment is used to detect the operating status of the grid-connected relay, which can timely detect whether the grid-connected relay has a fault, and detect potential fault risks such as adhesion of the grid-connected relay, thereby ensuring the safe and stable operation of the system. Compared with various relay state detection methods under the double relay series working condition, while improving the detectable accuracy, the detection judgment time and judgment complexity are reduced.

[0028] Example 2 In this embodiment, Figure 2 As shown, the detection relay circuit module includes a three-phase circuit, which is composed of detection relays Sa', Sb', Sc' and detection circuit resistors R1, R2, R3 connected in series. The input sides of the detection relays Sa', Sb', Sc' are respectively connected to the outputs of the filter inductors L1, L2, L3, the input sides of the filter capacitors C3, C4, C5, and the grid-connected relay module; the output sides of the detection circuit resistors R1, R2, R3 are short-circuited at the N' point, and are short-circuited to the midpoint of the DC side of the converter module and the output sides of the filter capacitors C3, C4, C5 at the N' point, so as to detect the short-circuit or open-circuit state of the grid-connected relay module.

[0029] In this embodiment, the detection circuit relay is connected in series with a sampling resistor, and a low-power soft-start relay is used to ensure that the service life is greater than that of the main relay, which improves the detection accuracy as a whole, reduces the detection cost, and also improves the service life and reliability of the equipment.

[0030] The other parts of this embodiment are the same as those of Embodiment 1 and will not be described again here.

[0031] Example 3 This embodiment discloses a method for detecting faults of AC grid-connected relays of energy storage converters. This method first detects short circuits of AC grid-connected relays by closing the detection relay circuits in sequence and judging the voltage of the detection relay circuits. Then, the detection relay circuits are disconnected and the AC grid-connected relays are closed in sequence to judge the voltage of the detection relay circuits and detect open circuits of the AC grid-connected relays. Figure 3 As shown, the method comprises the following steps: S01), the three-phase AC grid-connected relays Sa, Sb, and Sc are all kept in the disconnected state; S02), first close the detection relay Sa' of the A phase detection relay circuit module; S03), collect the voltage Ua' of the A phase detection relay circuit module, and compare it with the set voltage threshold Uset1; S04), if the detection voltage Ua'>Uset1, it is determined that there is a short circuit fault in the A-phase AC grid-connected relay, the fault information is latched, and the fault processing is performed, wherein the value range of Uset1 is (0.2~0.4)*Ugrid, and Ugrid is the grid phase voltage; S05) If the detection voltage Ua'<Uset1, the A phase detection relay is disconnected and the B phase detection relay Sb' is closed; S06), repeat the above operation until all operations of the three-phase detection relay are completed; S07), disconnect the three-phase detection relays Sa', Sb', Sc', and close the A-phase AC grid-connected relay Sa; S08), collect the voltage Ua' of the A phase detection relay circuit module, and compare it with the set voltage threshold Uset2; S09), if the detection voltage Ua'<Uset2, it is determined that the A-phase AC grid-connected relay Sa has an open circuit fault, the fault information is latched, and the fault processing is performed, wherein the value range of Uset2 is (0.6~0.8)*Ugrid; S10) If the detected voltage Ua'>Uset2, the A-phase AC grid-connected relay Sa is disconnected, and the B-phase AC grid-connected relay Sb is closed; S11), repeat the above operation until all operations of the three-phase AC grid-connected relays Sa, Sb, and Sc are completed; S12) and finally give the detection result of the three-phase AC grid-connected relay.

[0032] In this embodiment, in step S04) and step S09), the method of latching the fault information is: storing the fault information in a set storage area, querying the set storage area during the power-on operation of the detection relay circuit, and determining whether there is a fault information mark, which is used as a basis for determining whether the grid-connected relay is operating normally.

[0033] In this embodiment, in step S01) to step S06), short circuit fault detection is performed in the order of phase A, phase B, and phase C. In other embodiments, detection may also be performed in other orders, such as phase B-phase A-phase C, phase C-phase B-phase A, etc. The order described in this embodiment is only a specific implementation method and is not a limitation.

[0034] In this embodiment, in step S07) to step S11), open circuit fault detection is performed in the order of phase A, phase B, and phase C. In other embodiments, detection may also be performed in other orders, such as phase B-phase A-phase C, phase C-phase B-phase A, etc. The order described in this embodiment is only a specific implementation method and is not a limitation.

[0035] The improvements and innovations of the method proposed in this patent are as follows: (1) Compared with the traditional method, it saves a first-level power relay and adds a first-level detection circuit (relay). The cost of the detection relay is about a few yuan, and the cost of the sampling resistor is about a few cents, which greatly reduces the equipment cost; (2) The number of power relay actions in the detection method of this patent is halved, the corresponding relay service life is increased, and the service life and reliability of the equipment are improved. (3) The judgment logic is simple and the software resources are less occupied.

[0036] What is shown above is only a preferred embodiment of the present invention, and is not intended to limit the scope of implementation of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of this patent, and these improvements and substitutions should also be regarded as the scope of protection of this patent.

Claims

1. An AC grid-connected relay fault detection circuit for an energy storage converter, comprising an energy storage converter and an AC grid-connected relay located on the grid side, wherein the AC grid-connected relay serves as a grid-connected switch on the grid side of the energy storage converter, and is characterized in that: A set of detection relay circuits is added between the output end of the energy storage converter and the AC grid-connected relay. The detection relay circuit includes a three-phase circuit. Each phase detection relay circuit includes a detection relay. One end of the detection relay is connected between the output end of the energy storage converter and the AC grid-connected relay, and the other end of the detection relay is connected to the converter AC neutral point N'.

2. The energy storage converter AC grid-connected relay fault detection circuit according to claim 1, characterized in that: Only one-stage grid-connected relay is provided between the output side and the grid side of the energy storage converter.

3. The energy storage converter AC grid-connected relay fault detection circuit according to claim 1, characterized in that: The detection relay of each phase detection relay circuit is connected in series with a sampling resistor, one end of the sampling resistor is connected to the detection relay, and the other end of the sampling resistor is connected to the AC neutral point N' of the converter.

4. A method for detecting faults of AC grid-connected relays of energy storage converters, characterized in that: This method is implemented based on the fault detection circuit described in any one of claims 1 to 3. In the AC grid-connected relay fault detection link, the detection relays of the three-phase detection relay circuit are first closed in sequence to determine the voltage of the detection relay circuit to achieve short-circuit detection of the AC grid-connected relay; then the detection relay circuit is disconnected, the AC grid-connected relays are closed in sequence to determine the voltage of the detection relay circuit to achieve open-circuit detection of the AC grid-connected relay.

5. The method for detecting faults of AC grid-connected relays of energy storage converters according to claim 4, characterized in that: The implementation process of this method is: S01), the three-phase AC grid-connected relays remain disconnected; S02), first close the detection relay of the single-phase detection relay circuit; S03), collecting the voltage of the circuit where the closed detection relay is located, and comparing it with the set voltage threshold Uset1; S04), if the collected voltage in step S03) is greater than the set voltage threshold Uset1, it is determined that the AC grid-connected relay in the same phase as the closed detection relay has a short circuit fault, the fault information is latched, and the fault processing is performed; S05), if the collected voltage in step S03) is less than the set voltage threshold Uset1, the phase detection relay is disconnected and the other phase detection relay is closed; S06), repeating step S03) to step S05), until all operations of the three-phase detection relay are completed; S07) disconnect the three-phase detection relay and close the single-phase AC grid-connected relay; S08), collecting the voltage of the detection relay circuit in phase with the closed AC grid-connected relay, and comparing it with the set voltage threshold Uset2; S09), if the voltage collected in step S08) is less than the set voltage threshold Uset2, it is determined that the closed AC grid-connected relay has an open circuit fault, the fault information is latched, and the fault processing is performed; S10), if the voltage collected in step S08) is greater than the set voltage threshold Uset2, the AC grid-connected relay Sa of the phase is disconnected, and the AC grid-connected relay of the other phase is closed; S11), repeat step S08) to step S10), until all operations of the three-phase AC grid-connected relay are completed.

6. The method for detecting faults of AC grid-connected relays of energy storage converters according to claim 5, characterized in that: The value range of the voltage threshold Uset1 is set to (0.2~0.4)*Ugrid, where Ugrid is the grid phase voltage.

7. The method for detecting faults of AC grid-connected relays of energy storage converters according to claim 5, characterized in that: The voltage threshold Uset2 is set in the range of (0.6~0.7)*Ugrid, where Ugrid is the grid phase voltage.

8. The method for detecting faults of AC grid-connected relays of energy storage converters according to claim 5, characterized in that: In step S04) and step S09), the method of latching the fault information is: storing the fault information in a set storage area, querying the set storage area during the power-on operation of the detection relay circuit, and determining whether there is a fault information mark, which is used as a basis for determining whether the grid-connected relay is operating normally.

9. The method for detecting faults of AC grid-connected relays of energy storage converters according to claim 5, characterized in that: In step S01) to step S06), detection is performed in the order of phase A, phase B, and phase C.

10. The method for detecting faults of AC grid-connected relays of energy storage converters according to claim 5, characterized in that: In step S07) to step S11), detection is performed in the order of phase A, phase B, and phase C.

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