A multi-inverter grid-connected control system and a working method thereof

Abstract

The application discloses a kind of multi-inverter grid-connected control system and its working method, system includes multiple and is not set with grid-connected switch inverter, also includes installation in grid-connected switch cabinet detection network, switch network and controller;Each inverter is connected with power grid by switch network, and detection network is used to collect the state data of inverter and power grid;Controller and inverter and detection network communication connection, controller and switch network control connection;Controller according to the feedback data of inverter and detection network, when the output voltage of inverter and power grid voltage is same frequency and same phase, control switch network connects the inverter with normal communication with power grid and is connected with grid.The beneficial effects of the application: the technical scheme of the application can remove the built-in grid-connected switch of inverter to reduce the cost of system under the condition of guaranteeing that system can normally and safely operate.

Description

Technical Field

[0001] This application relates to the field of new energy power generation technology, and in particular to a multi-inverter grid-connected control system and its operating method. Background Technology

[0002] For a single inverter, it connects to the downstream system via a built-in grid-connection switch, achieving grid connection by closing the switch. For multiple inverters, the conventional approach is to connect the parallel system to the downstream system via a grid-connection switch cabinet, which may be responsible for current sharing and system energy dispatching. In parallel systems with multiple inverters, since each inverter has its own internal grid-connection switch, which functions identically to the switch in the grid-connection switch cabinet, this results in grid redundancy in the inverter system, increases the complexity of grid control, and also increases costs. Summary of the Invention

[0003] One objective of this application is to provide a multi-inverter grid-connected control system that can solve at least one of the defects in the above-mentioned background art.

[0004] Another objective of this application is to provide a method for operating a multi-inverter grid-connected control system that can solve at least one of the defects in the above-mentioned background art.

[0005] To achieve at least one of the above objectives, the technical solution adopted in this application is as follows: a multi-inverter grid-connected control system, comprising multiple inverters without grid-connection switches, and further comprising a detection network, a switch network, and a controller installed in a grid-connection switch cabinet; each inverter is connected to the power grid through the switch network, and the detection network is used to collect status data of the inverters and the power grid; the controller is communicatively connected to the inverters and the detection network, and the controller is controllably connected to the switch network; based on the feedback data from the inverters and the detection network, when the output voltage of the inverter is in phase and frequency with the grid voltage, the controller controls the switch network to connect the normally communicating inverter to the grid.

[0006] Preferably, the switch network includes a first switch group and a second switch group; the first switch group is disposed on the output side of the inverter, and the second switch group is disposed on the grid side and connected to the first switch group; the first switch group is adapted to perform independent grid-connected connection of each inverter, and the second switch group is adapted to perform grid-connected connection of the grid with all inverters; the controller is adapted to control the second switch group to close before the first switch group during grid connection.

[0007] Preferably, the first switch group includes a plurality of individual first switches corresponding to the number of inverters, and each first switch is respectively disposed on the output side of the corresponding inverter and connected in series with the second switch group.

[0008] Preferably, the detection network includes a grid detection device and multiple inverter detection devices; the number of inverter detection devices corresponds to the number of inverters, the inverter detection devices are used to collect voltage, current and frequency data of the corresponding inverters, and the grid detection devices are used to collect voltage and frequency data of the grid; when the inverters are connected to the grid, the controller controls the inverters to perform phase-locking based on the feedback from the grid detection devices.

[0009] Preferably, the controller includes a communication module, a sampling module, a grid-connected control module, and a switch drive circuit. The communication module is connected to the inverter to identify the communication status of all inverters and to send adjustment signals for phase adjustment to the inverters. The sampling module is connected to the detection network to identify the voltage and frequency information of the power grid and all inverters. The grid-connected control module is connected to the sampling module and the communication module, and is adapted to output adjustment signals to the communication module when there is a phase difference between the power grid and the inverters, and to generate grid-connected control signals when the power grid and the inverters are in phase and at the same frequency. The switch drive circuit is connected to the grid-connected control module and the communication module, and controls the switch network to perform corresponding closing actions based on the feedback results of the communication module and the received grid-connected control signals.

[0010] Preferably, the inverter detection device can also collect the current data of the inverter; the controller further includes a fault protection module, which is communicatively connected to the sampling module and the switch drive circuit; the fault protection module judges the overcurrent fault of the inverter based on the voltage and current data fed back by the sampling module; the fault protection module is adapted to send an isolation signal to the switch drive circuit when the inverter experiences an overcurrent fault, and then the switch drive circuit controls the switch network to perform a corresponding disconnection action.

[0011] Preferably, the inverter detection device can also collect the current data of the inverter; the multi-inverter grid-connected control system also includes a protection device installed in the grid-connected switch cabinet, the protection device is communicatively connected to the detection network, and the protection device is hardware-controlled connected to the switch network; when the protection device identifies a fault in the inverter based on the information fed back by the detection network, the hardware controls the switch network to perform a corresponding disconnection action.

[0012] A method for operating the aforementioned multi-inverter grid-connected control system includes the following steps: under normal grid conditions, the controller detects the communication and output status of the inverters; isolates inverters with abnormal communication and / or output and proceeds to the next step; the controller detects the output voltage waveform of the inverters in normal condition and the voltage waveform of the grid, and communicates with each inverter to adjust the voltage phase as needed based on the detection results; after the output voltage of the inverters is in phase and frequency with the grid voltage, the controller controls the switching network to connect the inverters in normal condition to the grid to achieve grid connection.

[0013] Preferably, when the grid is in normal condition, the controller controls the second switch group on the grid side of the switch network to close, while the first switch on the output side of each inverter in the switch network remains open; when the controller performs grid connection of the inverter, it controls the first switch on the output side of the inverter in normal condition to close.

[0014] Preferably, when an overcurrent fault occurs during inverter grid connection, the specific process for controlling the faulty inverter is as follows: After each inverter communicates with the controller, it sends its own power level and overcurrent shutdown protection point information to the controller; when the controller detects that the output current of the inverter reaches the corresponding overcurrent shutdown protection point, the controller controls the switching network to disconnect the inverter from the grid, and at the same time sets the fault flag bit of the inverter so that the controller will not perform corresponding control on the inverter with the fault flag bit set; when the fault of the faulty inverter is cleared, it notifies the controller through communication; after receiving the fault clearance information, the controller resets the fault flag bit of the inverter and controls the switching network to reconnect the inverter to the grid.

[0015] Compared with the prior art, the beneficial effects of this application are as follows:

[0016] Compared to traditional methods, the technical solution of this application can reduce system costs by eliminating the grid-connection switch built into the inverter while ensuring the normal and safe operation of the system. Furthermore, removing the grid-connection switch can effectively improve the inverter's grid-connection response speed. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the basic structure of this application.

[0018] Figure 2 This is a schematic diagram of the specific structure of this application.

[0019] Figure 3 This is a schematic diagram of the specific structure of the controller in this application.

[0020] Figure 4 This is a schematic diagram of the grid connection control waveform during grid connection in this application.

[0021] Figure 5 This is a schematic diagram of the overcurrent circuit when a DC-side ground fault occurs in this application.

[0022] Figure 6 This is a schematic diagram of the protection waveform when the fault protection is performed in this application.

[0023] In the diagram: Inverter 100, grid-connected switchgear 200, inverter detection device 210, first switch group 220, second switch group 230, grid detection device 240, controller 250, communication module 251, grid voltage and frequency sampling module 252, inverter voltage and frequency sampling module 253, inverter current sampling module 254, grid-connected control module 255, fault protection module 256, switch drive circuit 257, protection device 260, grid 300. Detailed Implementation

[0024] The present application will now be further described in conjunction with specific embodiments. It should be noted that, in the description of this specification, the use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicates that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0025] In the description of this application, it should be noted that the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., which indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and should not be construed as limiting the specific protection scope of this application.

[0026] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0027] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0029] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0030] One aspect of this application provides a multi-inverter grid-connected control system, such as Figure 1 and Figure 2 As shown, one preferred embodiment includes multiple inverters 100 without grid-connected switches, and a detection network, a switch network, and a controller 250 installed within a grid-connected switch cabinet 200. Each inverter 100 is connected to the power grid 300 via the switch network. The detection network collects status data from the inverters 100 and the power grid 300. The controller 250 communicates with both the inverters 100 and the detection network, allowing each inverter 100 to send its status information to the controller 250. Simultaneously, the detection network sends power parameters and other information from the inverters 100 and the power grid 300 to the controller 250. The controller 250 can control the switch network, enabling it to connect the normally communicating inverters 100 to the power grid 300 based on feedback data from the inverters 100 and the detection network, ensuring that the output voltage of the inverters 100 is in phase and frequency with the voltage of the power grid 300.

[0031] Understandably, compared to traditional methods, the technical solution of this application eliminates the traditionally built-in grid-connection switch of the inverter 100, thereby reducing system costs. Simultaneously, with the grid-connection switch of the inverter 100 removed, this application uses the controller 250 in conjunction with a switch network to achieve grid-connection control of the inverter 100. This is equivalent to placing the grid-connection switch of the inverter 100 externally within the grid-connection switch cabinet 200 and centrally controlling it through the controller 250, thereby reducing the communication frequency between the inverter 100 and the controller 250 and improving the grid-connection response efficiency of the inverter 100. There are various communication methods between the controller 250 and the inverter 100; in this embodiment, the RS-485 communication protocol is preferred.

[0032] It should be noted that the control logic of the controller 250 for the switching network is based on the identification and judgment of the status data of the inverter 100. If the controller 250 is directly informed of the required switching action by each inverter 100 through communication, the communication delay may cause the switch to fail to act in time, resulting in problems such as load power failure and device damage.

[0033] It is important to understand that, to ensure the safe operation of the grid-connected system, the switching network needs to possess both device-level and system-level shutdown capabilities. Specifically, when a single inverter 100 fails, the switching network can individually shut down that faulty inverter 100 and the grid 300; alternatively, when a fault occurs that could affect all inverters 100, the switching network can simultaneously shut down all inverters 100 and the grid 300. Based on these requirements, there are various specific structural types of switching networks. For ease of understanding, one specific structure will be described in detail below.

[0034] Specifically, such as Figure 2 As shown, the switch network includes a first switch group 220 and a second switch group 230. The first switch group 220 is located on the output side of the inverter 100, and can perform independent grid-connected connection of each inverter 100; that is, the first switch group 220 performs individual shutdown and turn-on control on each inverter 100 and the grid 300. The second switch group 230 is located on the grid side and connected to the first switch group 220, and can perform grid-connected connection between the grid 300 and all inverters 100; that is, the second switch group 230 performs simultaneous shutdown and turn-on control on all inverters 100 and the grid 300.

[0035] It is important to understand that the first switch group 220 is used to implement the device-level shutdown function, while the second switch group 230 is used to implement the system-level shutdown power. Generally, during grid-connected control of the inverter 100, the controller 250 can control the second switch group 230 to close before the first switch group 220; that is, the controller 250 can detect the power and status data of the power grid 300 through the detection network after the second switch group 230 is closed.

[0036] It should be understood that the second switch group 230 can be a single switch or a parallel redundant arrangement of multiple switches. For a second switch group 230 with multiple switches, during normal operation, the controller 250 only controls one switch to open or close, while the other switches remain open. The first switch group 220 can be a multi-contact switch or multiple independent switches. For ease of understanding, the following detailed explanation will use an example where the second switch group 230 uses a single switch and the first switch group 220 uses multiple independent switches.

[0037] Specifically, such as Figure 2 As shown, the first switch group 220 includes multiple individual first switches corresponding to the number of inverters 100. Assuming there are N inverters 100, each inverter 100 can be labeled as inverter #1 to #N; then the first switches corresponding to inverters #1 to #N can be labeled as first switches S221 to S22N. First switches S221 to S22N are respectively located on the output side of the corresponding inverter 100 and connected in series with the second switch group 230, while each first switch is independent of the others. The individual switches corresponding to the second switch group 230, and the first switches S221 to S22N, can be controllable devices or devices with current breaking capability, such as relays or switching transistors, or their series-parallel connections.

[0038] In this embodiment, the detection network may consist of only one detection device but has multiple acquisition terminals to collect data from each inverter 100 and the power grid 300 respectively; it may also include a power grid detection device 240 for collecting data from the power grid 300 and inverter detection devices 210 for collecting data from all inverters 100; or it may include a power grid detection device 240 for collecting data from the power grid 300 and multiple inverter detection devices 210 for collecting data from each inverter 100, i.e., the number of inverter detection devices 210 corresponds to the number of inverters 100. Considering the data interference between the power grid 300 and the inverters 100, as well as the data interference between the inverters 100, this embodiment preferably uses a detection network including a power grid detection device 240 and multiple inverter detection devices 210.

[0039] Specifically, such as Figure 2As shown, multiple inverter detection devices 210 can be labeled as detection devices #1 to #N. The inverter detection devices 210 are used to collect voltage, current, and frequency data of the corresponding inverter 100, while the grid detection device 240 is used to collect voltage and frequency data of the grid 300. When the inverter 100 is connected to the grid, the controller 250 controls the inverter 100 to perform phase-locked loop (PLL) based on feedback from the grid detection device 240. PLL means that after the controller 250 detects a phase difference between the output voltage waveform of the inverter 100 and the voltage waveform of the grid 300, it can communicate with each inverter 100 to adjust the required voltage phase based on the detection result; then each inverter 100 can adjust its own voltage waveform based on the received data. After the output voltage waveform of the inverter 100 is in phase and frequency with the voltage waveform of the grid 300, the controller 250 can control the switching network to perform the corresponding grid connection closing action.

[0040] In this embodiment, the controller 250 has various specific structures. For ease of understanding, one of these structures will be described in detail below. For example... Figure 3 As shown, the controller 250 includes a communication module 251, a sampling module, a grid-connected control module 255, and a switch drive circuit 257. The communication module 251 communicates with the inverter 100 to identify the communication status of all inverters 100, and then records any abnormal communication statuses of the inverters 100 based on the identification results. Simultaneously, the communication module 251 can also send adjustment signals to the inverters 100 for phase adjustment, facilitating phase-locked looping (PLL). The sampling module communicates with the detection network to identify the voltage and frequency information of the power grid 300 and all inverters 100. The grid-connected control module 255 communicates with the sampling module and the communication module 251. The grid-connected control module 255 receives the identification results from the sampling module and then judges the phase difference between the voltage of the grid 300 and the output voltage of the inverter 100. When the voltage of the grid 300 and the output voltage of the inverter 100 are in phase and frequency, a grid-connected control signal is generated. When there is a phase difference between the voltage of the grid 300 and the output voltage of the inverter 100, an adjustment signal can be sent to the communication module 251. The switch drive circuit 257 communicates with the grid-connected control module 255 and the communication module 251. Based on the feedback results from the communication module 251 and the received grid-connected control signal, the switch drive circuit 257 controls the switch network to perform corresponding closing actions.

[0041] Specifically, as described above, the detection network includes a grid detection device 240 and an inverter detection device 210. To avoid interference between the detection data of the grid detection device 240 and the inverter detection device 210, the sampling module includes a grid voltage and frequency sampling module 252 and an inverter voltage and frequency sampling module 253. The grid voltage and frequency sampling module 252 is communicatively connected to the grid detection device 240, and the inverter voltage and frequency sampling module 253 is communicatively connected to the inverter detection device 210. Simultaneously, the grid-connected control module 255 is communicatively connected to both the grid voltage and frequency sampling module 252 and the inverter voltage and frequency sampling module 253. Thus, the grid voltage and frequency sampling module 252 can send the voltage and frequency information of the grid 300 to the grid-connected control module 255 based on the feedback results of the grid detection device 240. Similarly, the inverter voltage and frequency sampling module 253 can also send the voltage and frequency information of the inverter 100 to the grid-connected control module 255 based on the feedback results of the inverter detection device 210. The grid-connected control module 255 can then analyze the phase difference between the voltage of the grid 300 and the output voltage waveform of the inverter 100. If there is a phase difference between the voltage of the grid 300 and the output voltage of the inverter 100, the communication module 251 can inform the inverter 100 of the phase difference that needs to be adjusted, thereby enabling the inverter 100 to adjust the waveform of the output voltage until the voltage of the grid 300 and the output voltage of the inverter 100 are in phase and frequency. Then, the grid-connected control signal is output to the switch drive circuit 257, thereby controlling the first switch group 220 and the second switch group 230 to perform corresponding closing actions.

[0042] To facilitate understanding, the phase modulation process of inverters #1 and #2 will be described in detail below, taking the output phase A of inverters #1 and #2 as examples.

[0043] like Figure 4 As shown, at time t0, the controller 250 controls the control signal S0 of the second switch group 230 to output a high level to close the second switch group 230.

[0044] After time t0, controller 250 detects the waveform Vout1A of phase A output from inverter #1, the waveform Vout2A of phase A output from inverter #2, and the waveform VgridA of phase A voltage from the grid 300. Based on the phase difference, it communicates with inverter #1 and inverter #2 to inform them of the output phase that needs adjustment.

[0045] At time t1, the output voltage waveform of inverter #1 completes phase-locking with the voltage waveform of grid 300, and the controller 250 controls the control signal S1 of the first switch S221 to output a high level to close the first switch S221.

[0046] At time t2, the voltage waveform output by inverter #2 completes phase-locking with the voltage waveform of grid 300, and controller 250 controls the control signal S2 of the first switch S222 to output a high level to close the first switch S222.

[0047] For ease of understanding, the following will take the example of inverter #1 experiencing a communication failure while the other inverters 100 are all functioning normally, to provide a detailed description of the grid connection control process for inverters #2 to #N.

[0048] Initially, the controller 250 can control the second switch group 230 to close via the grid-connected control module 255.

[0049] At this time, inverters #1 to #N communicate with the communication module 251 of controller 250. If inverter #1 experiences a communication failure, while the other inverters #2 to #N communicate normally, controller 250 records the failure of inverter #1 and controls the first switch S221 to remain open, while not recognizing the feedback result from detection device #1.

[0050] Simultaneously, detection devices #2 to #N feed back the output voltage waveforms of inverters #2 to #N to inverter voltage and frequency sampling modules 253, while grid detection device 240 feeds back the voltage waveforms of grid 300 to grid voltage and frequency sampling modules 252. Inverter voltage and frequency sampling modules 253 send the output voltage phase information of inverters #2 to #N to grid connection control modules 255 based on the received data, and grid voltage and frequency sampling modules 252 send the voltage phase information of grid 300 to grid connection control modules 255 based on the received data. The grid-connected control module 255 analyzes the voltage waveform phase of inverters #2 to #N and the grid 300, and sends a first control signal to the switch drive circuit 257 based on the analysis results. The first control signal is used to close the first switch corresponding to the inverter 100 in inverters #2 to #N that is already in phase and frequency with the grid 300. At the same time, the controller 250 communicates with the remaining inverters 100 in inverters #2 to #N through the communication module 251 to adjust the waveform until the remaining inverters 100 are in phase and frequency with the grid 300. Then, the grid-connected control module 255 sends a second control signal to the switch drive circuit 257. The second control signal is used to close the first switch corresponding to the remaining inverters 100 in inverters #2 to #N, thereby realizing the grid connection between inverters #2 to #N and the grid 300.

[0051] It's important to know that inverter 100 can experience not only communication failures but also overcurrent faults, such as DC-side grounding faults and short circuits in the DC / AC circuit switching transistors. Taking a DC-side grounding fault as an example, even if inverter 100 blocks the DC / AC circuit, an overcurrent loop will still form through the body diode of the DC / AC circuit's switching device. For example... Figure 5 As shown, when the DC-side negative terminal of inverter #N is shorted to ground, even if the DC / AC circuit is blocked, an overcurrent loop will still be formed through the body diode of the lower transistor during the negative half-cycle of the 300V grid. Figure 5 The loop is shown by the red line in the middle. Therefore, the multi-inverter grid-connected control system in this embodiment also needs to design overcurrent protection for inverter 100 in case of overcurrent fault. There are multiple ways to implement overcurrent protection for inverter 100, including hardware protection and software protection. For ease of understanding, hardware protection and software protection will be described in detail below.

[0052] I. Software protection for overcurrent faults in inverter 100.

[0053] like Figure 3 As shown, the inverter detection device 210 can also collect the current data of the inverter 100; the controller 250 also includes a fault protection module 256, and the sampling module includes an inverter current sampling module 254. The inverter current sampling module 254 can communicate with the inverter detection device 210, thereby identifying the current data of all inverters 100 based on the feedback results of the inverter detection device 210. The fault protection module 256 communicates with the grid voltage and frequency sampling module 252, the inverter voltage and frequency sampling module 253, the inverter current sampling module 254, and the switch drive circuit 257; thus, the fault protection module 256 can analyze the overcurrent fault of each inverter 100 based on the received grid voltage 300 and the output voltage and current of each inverter 100. When the fault protection module 256 determines that one or more inverters 100 have an overcurrent fault, it can send an isolation signal to the switch drive circuit 257, thereby controlling the switch network to perform the corresponding disconnection action.

[0054] Understandably, with Figure 5 Taking the overcurrent fault of inverter #N as an example, the fault protection module 256 can determine that the inverter #N has an overcurrent fault based on the received voltage and current output. At this time, the fault protection module 256 can send an isolation signal to the switch drive circuit 257 to control the inverter #N to disconnect from the grid. Then the switch drive circuit 257 can control the first switch S22N to disconnect.

[0055] II. Hardware protection against overcurrent faults in inverter 100.

[0056] like Figure 2 As shown, the inverter detection device 210 can also collect current data from the inverter 100. The multi-inverter grid-connected control system also includes a protection device 260 installed in the grid-connected switchgear 200. The protection device 260 is communicatively connected to the inverter detection device 210 in the detection network, and also has a hardware control connection to the first switch group 220 in the switch network. The protection device 260 can receive the output voltage and current of the inverter 100 collected by the inverter detection device 210, and then determine the overcurrent fault of the inverter 100. When the protection device 260 determines that an overcurrent fault has occurred in the inverter 100, it can control the switch network to perform a corresponding disconnection action through hardware control.

[0057] Understandably, with Figure 5 Taking the overcurrent fault of inverter #N as an example, when the protection device 260 identifies an overcurrent fault in inverter #N based on the feedback result of the detection device #N, it can disconnect the first switch S22N through hardware control. There are several ways for the protection device 260 to control the first switch group 220 in hardware. It can be that the drive signal of the first switch is directly controlled to a low level (high level for closing, low level for opening) via a local electrical signal; or it can be connected in series with a fuse, so that when an overcurrent fault occurs in the corresponding inverter 100, the fuse is directly heated and melted, etc.

[0058] It should be understood that, based on the detection results of the detection network, the controller 250 or the protection device 260 can also identify other faults of the inverter 100; when other types of faults occur in the inverter 100, the first switch group 220 can also be disconnected through the above control method, so as to ensure that the fault of the inverter 100 will not affect the overall system, and to ensure the safe and normal operation of the system.

[0059] Another aspect of this application provides a method for operating the aforementioned multi-inverter grid-connected control system, comprising the following steps: The controller 250 can first detect the status of the grid 300. If the grid 300 is abnormal, grid connection is directly stopped. If the grid 300 is normal, the controller 250 detects the communication and output status of the inverter 100. Based on the detection results, the controller 250 isolates inverters 100 with communication and / or output abnormalities and proceeds to the next step. The controller 250 detects the output voltage waveform of the normal inverter 100 and the voltage waveform of the grid 300, and communicates with each inverter 100 to adjust the voltage phase as needed based on the detection results. After the output voltage of the inverter 100 is synchronized with the voltage of the grid 300, the controller 250 controls the switching network to connect the normal inverter 100 to the grid 300 to achieve grid connection.

[0060] It should be noted that when the grid 300 is in normal condition, the controller 250 controls the second switch group 230 located on the grid 300 side of the switch network to close. At this time, the first switches S221 to S22N located on the output side of each inverter 100 in the switch network remain open. When the controller 250 performs grid connection of the inverter 100, it controls the first switch on the output side of the inverter 100 in normal condition to close.

[0061] In this embodiment, when an overcurrent fault occurs during the grid connection of inverter 100, the specific process for isolating the faulty inverter 100 is as follows: After each inverter 100 communicates with the controller 250, it sends its own power level and overcurrent shutdown protection point information to the controller 250. When the controller 250 detects that the output current of inverter 100 reaches the corresponding overcurrent shutdown protection point, the controller 250 controls the switching network to disconnect inverter 100 from the grid 300, and simultaneously sets the fault flag bit of inverter 100, so that the controller 250 will not subsequently perform corresponding control on inverter 100 with the fault flag bit set. When the fault of inverter 100 is cleared, it notifies the controller 250 through communication. After receiving the fault clearance information, the controller 250 resets the fault flag bit of inverter 100 and controls the switching network to reconnect inverter 100 to the grid.

[0062] It is understandable that, through the above-described overcurrent protection control method for inverter 100, different overcurrent shutdown protection points can be set for inverters 100 of different power levels connected to the grid-connected switchgear 200; thereby, when an output overcurrent occurs in inverter 100, the corresponding first switch is shut off, the overcurrent short-circuit loop is cut off, and the safety of inverter 100 and the first switch group 220 is protected. For ease of understanding, the output A phase of inverters #1 and #2 will be described in detail below.

[0063] Specifically, such as Figure 6 As shown, before time t0, under the control of controller 250, the control signal S0 of the second switch group 230, the control signal S1 of the first switch S221, and the control signal S2 of the first switch S222 are output at high level, so that the second switch group 230, the first switch S221, and the first switch S222 are all in the closed state.

[0064] At time t1, the output current Iout2A of inverter #2 reaches the set overcurrent protection cutoff point Imax, triggering overcurrent protection. At this time, the controller 250 controls the control signal S2 of the first switch S222 to output a low level. The time period t1-t2 is the cutoff delay of the first switch S222. At time t2, the first switch S222 opens, and the overcurrent of inverter #2 is eliminated. During this process, the second switch group 230 remains closed. At the same time, the output current Iout1A of inverter #1 never reaches the set overcurrent protection cutoff point Imax, so the first switch S221 also remains closed.

[0065] In this embodiment, overcurrent faults in inverter 100 can also be addressed by installing a protection device 260 in the grid-connected switchgear 200 to achieve hardware overcurrent protection; specific implementation methods can be found in the foregoing description. Similar to the software control scheme, protection devices 260 with different hardware parameters can be set for each inverter 100 connected to the grid-connected switchgear 200 according to its power level, enabling separate shutdown overcurrent protection point settings for inverters 100 with different power levels. Alternatively, a digital potentiometer can be used in the protection device 260. After receiving the shutdown overcurrent protection point information from each inverter 100, the controller 250 adjusts the hardware parameters of the protection device 260 through communication with the protection device 260 by adjusting the digital potentiometer.

[0066] Understandably, overcurrent fault protection for inverter 100 can be implemented using either software or hardware methods. Software protection eliminates the need for additional protection circuitry, resulting in lower costs and more flexible parameter settings for different protection points. However, its shutdown time is longer than hardware protection, increasing the risk of damage to inverter 100 and the first switch. While hardware protection using digital potentiometers allows for setting the overcurrent protection shutdown point based on the actual power rating of the inverter 100, its adjustable range is limited, and it is more expensive. Therefore, those skilled in the art can choose the appropriate solution based on the specific operating conditions.

[0067] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A multi-inverter grid-connected control system, characterized in that, This includes multiple inverters that are not equipped with grid-connected switches, as well as those installed in grid-connected switch cabinets: A switching network; each of the inverters is connected to the power grid through the switching network; A detection network; the detection network is used to collect status data of the inverter and the power grid; and The controller is communicatively connected to the inverter and the detection network, and is also controllably connected to the switching network. Based on feedback data from the inverter and the detection network, when the output voltage of the inverter is in phase and frequency with the voltage of the power grid, the controller controls the switching network to connect the normally communicating inverter to the power grid. The switching network includes a first switch group and a second switch group; the first switch group is located on the output side of the inverter, and the second switch group is located on the grid side and connected to the first switch group; The first switch group is adapted to perform independent grid-connected connection of each inverter, and the second switch group is adapted to perform grid-connected connection of the power grid with all the inverters; The first switch group includes a plurality of individual first switches corresponding to the number of inverters, and each first switch is respectively disposed on the output side of the corresponding inverter and connected in series with the second switch group; The controller is adapted to control the second switch group to close before the first switch group during grid connection; The controller includes: A communication module; the communication module is connected to the inverter to identify the communication status of all the inverters and to send adjustment signals for phase adjustment to the inverters; A sampling module; the sampling module is communicatively connected to the detection network to identify the voltage and frequency information of the power grid and all the inverters; Grid-connected control module; the grid-connected control module is communicatively connected to the sampling module and the communication module, and the grid-connected control module is adapted to output an adjustment signal to the communication module when there is a phase difference between the grid and the inverter, and to generate a grid-connected control signal when the grid and the inverter are in phase and at the same frequency; and A switch driving circuit is provided; the switch driving circuit is connected to the grid-connected control module and the communication module for communication. The switch driving circuit controls the switch network to perform corresponding closing actions based on the feedback results of the communication module and the received grid-connected control signals.

2. The multi-inverter grid-connected control system as described in claim 1, characterized in that, The detection network includes: A power grid detection device; the power grid detection device is used to collect voltage and frequency data of the power grid; and Multiple inverter detection devices; the number of inverter detection devices corresponds to the number of inverters, and the inverter detection devices are used to collect voltage, current and frequency data of the corresponding inverters; When the inverter is connected to the grid, the controller controls the inverter to perform phase-locking based on the feedback data from the grid detection device.

3. The multi-inverter grid-connected control system as described in claim 2, characterized in that, The inverter detection device can also collect the inverter's current data; the controller also includes a fault protection module, which is communicatively connected to the sampling module and the switch drive circuit. The fault protection module determines the overcurrent fault of the inverter based on the voltage and current data fed back by the sampling module; The fault protection module is adapted to send an isolation signal to the switch drive circuit when an overcurrent fault occurs in the inverter, and then the switch drive circuit controls the switch network to perform a corresponding disconnection action.

4. The multi-inverter grid-connected control system as described in claim 2, characterized in that, The inverter detection device can also collect the inverter's current data; The multi-inverter grid-connected control system also includes a protection device installed in the grid-connected switch cabinet. The protection device is communicatively connected to the detection network and is hardware-controlled connected to the switch network. When the protection device identifies a fault in the inverter based on information fed back from the detection network, it controls the switching network to perform a corresponding disconnection action.

5. A method for operating a multi-inverter grid-connected control system as described in any one of claims 1-4, characterized in that, Includes the following steps: Under normal grid conditions, the controller monitors the inverter's communication and output status. Isolate the inverter with communication and / or output abnormalities and proceed to the next step; The controller detects the output voltage waveform of the inverters in normal condition and the voltage waveform of the power grid, and communicates with each inverter to adjust the voltage phase as needed based on the detection results. Once the inverter's output voltage is in phase and frequency with the grid voltage, the controller connects the normally functioning inverter to the grid via the control switching network to achieve grid connection.

6. The operating method of the multi-inverter grid-connected control system as described in claim 5, characterized in that, When the power grid is in normal condition, the controller controls the second switch group located on the grid side of the switch network to close, while the first switch located on the output side of each inverter in the switch network remains open. When the controller performs grid connection of the inverter, the first switch on the output side of the inverter, which is in normal control state, is closed.

7. The operating method of the multi-inverter grid-connected control system as described in claim 5, characterized in that, When an overcurrent fault occurs during inverter grid connection, the specific process for controlling the faulty inverter is as follows: After each inverter communicates with the controller, it sends its own power rating and overcurrent shutdown protection point information to the controller. When the controller detects that the output current of the inverter reaches the corresponding overcurrent shutdown protection point, the controller controls the switching network to disconnect the inverter from the grid and sets the fault flag of the inverter so that the controller will not perform corresponding control on the inverter with the fault flag set in the future. Once the fault in the inverter is cleared, it will notify the controller via communication. Upon receiving the fault clearance information, the controller will reset the fault flag of the inverter and control the switching network to reconnect the inverter to the grid.

Images