Grid-connected and off-grid switching cabinet and grid-connected and off-grid switching control method

Abstract

The invention discloses a grid-connected and off-grid switching cabinet and a grid-connected and off-grid switching control method, and relates to the technical field of grid-connected and off-grid switching. In order to solve a series of problems caused by the fact that a power grid N line and a local N line are not isolated when grid-connected and off-grid switching is carried out at present, the grid-connected and off-grid switching cabinet is provided, and connection control between a power grid and a local alternating current bus of the grid-connected and off-grid switching cabinet is achieved through a four-pole frame circuit breaker. Therefore, the connection control between the N line of the power grid and the N line of the local AC bus is realized, and the isolation between the N line and the N line can be realized, so that a series of safety problems caused by non-isolation of the neutral line are avoided. In addition, connection between the ground wire and the neutral wire of the local alternating current bus is added. When the protection switch arranged on the ground wire is closed, the local N wire can be directly grounded through the ground wire, zero-ground connection is achieved, and an independent TN system can be guaranteed while the N wire of the power grid is isolated.

Description

Technical Field

[0001] This application relates to the technical field of on-grid and off-grid switching, and particularly to an on-grid and off-grid switching cabinet and an on-grid and off-grid switching control method. Background Art

[0002] In a power system, to ensure the continuity and stability of power supply, an on-grid and off-grid switching cabinet is generally used. The on-grid and off-grid switching cabinet can switch the load from the main power grid to a backup power supply (usually an energy storage system) when a fault occurs in the main power grid or during maintenance, so as to ensure the uninterrupted operation of the load. Among them, powering the load through the main power grid is called on-grid, and powering the load through a backup power supply such as an energy storage system is called off-grid.

[0003] Currently, the on-grid and off-grid switching cabinet realizes the switching control of on-grid and off-grid by setting a frame circuit breaker with mutually exclusive switch states between the power grid and the energy storage cabinet (an important part of the energy storage system). However, this switching control is only limited to the three live wires (i.e., L1, L2, and L3) in the three-phase four-wire system. For the neutral wire (i.e., the N wire), the local N wire is directly connected to the N wire of the power grid and the N wire of the energy storage cabinet to achieve common grounding. This results in the direct connection of the neutral wire of the off-grid system to the power grid, thus bringing a series of safety risks such as neutral wire circulating current, voltage offset and abnormal neutral point potential, power grid reverse power transmission, and grounding system conflict.

[0004] Therefore, those skilled in the art now urgently need an on-grid and off-grid switching cabinet to avoid a series of problems caused by the non-isolation of the off-grid system from the power grid neutral wire when operating in the off-grid mode. Summary of the Invention

[0005] The purpose of this application is to provide an on-grid and off-grid switching cabinet and an on-grid and off-grid switching control method to avoid the safety risks caused by the non-isolation of the off-grid system from the power grid neutral wire.

[0006] To solve the above technical problems, this application provides an on-grid and off-grid switching cabinet, including: a four-pole frame circuit breaker, a ground wire, and a protection switch;

[0007] Wherein, the four-pole frame circuit breaker is arranged between the power grid and the AC bus of the local on-grid and off-grid switching cabinet, and is used to control whether the three-phase input line and the neutral wire of the power grid are conducted with the AC bus;

[0008] One end of the ground wire is connected to the neutral wire in the AC bus, and the other end is grounded;

[0009] The protection switch is arranged on the ground wire and is used to control whether the neutral wire in the AC bus is grounded.

[0010] In a possible embodiment, the protection switch is interlocked with the four-pole frame circuit breaker.

[0011] In a possible embodiment, it further includes: a parallel operation control board, a power supply board, a frame circuit breaker controller, a first switch, and a second switch;

[0012] Wherein, the AC end of the power supply board is connected to one end of the four-pole frame circuit breaker close to the power grid side, and the DC end of the power supply board is connected to the opening control end, closing control end, and under-voltage release end of the frame circuit breaker controller;

[0013] The first switch is arranged between the opening control end and the power supply board, and the second switch is arranged between the closing control end and the power supply board; the parallel operation control board is connected to the controlled ends of the first switch and the second switch;

[0014] The frame circuit breaker controller is configured to: control the four-pole frame circuit breaker to open when the opening control end accesses the DC power supply signal output by the power supply board, control the four-pole frame circuit breaker to close when the closing control end accesses the DC power supply signal output by the power supply board, and control the four-pole frame circuit breaker to open when the under-voltage release end does not access the DC power supply signal output by the power supply board.

[0015] In a possible embodiment, it further includes: a first relay; the first relay includes: a normally open contact and a coil;

[0016] Wherein, the normally open contact of the first relay is arranged at the DC end of the power supply board;

[0017] Both ends of the coil of the first relay are connected to the parallel operation control board; the parallel operation control board continuously supplies power to both ends of the coil of the first relay after power-on.

[0018] In a possible embodiment, it further includes: a second relay, an auxiliary contact, and a third switch;

[0019] The second relay includes: a first normally open contact, a second normally open contact, and a coil; wherein, the protection switch is the first normally open contact of the second relay; the second normally open contact of the second relay is arranged between the opening control end and the DC power supply;

[0020] The auxiliary contact is a normally closed contact, and the auxiliary contact opens when the closing control end of the frame circuit breaker controller receives the DC power supply signal output by the power supply board;

[0021] The coil of the second relay, the auxiliary contact, and the third switch are connected in series between the three-phase live wires and the neutral wire of the AC bus;

[0022] The controlled end of the third switch is connected to the parallel operation control board.

[0023] In a possible embodiment, the controlled end of the protection switch is connected to the parallel operation control board;

[0024] Wherein, the parallel operation control board is used to control the switch state of the four-pole frame circuit breaker, and the switch states of the first switch and the protection switch are always opposite at the same moment.

[0025] In a possible embodiment, there are multiple four-pole frame circuit breakers; and the multiple four-pole frame circuit breakers are connected in parallel, and at most only one of the four-pole frame circuit breakers is in the closed state at the same moment.

[0026] To solve the above technical problems, the present application also provides a grid-connected and off-grid switching control method, which is applied to the grid-connected and off-grid switching cabinet as described above. The method includes:

[0027] When it is necessary to switch to the grid-connected mode, control the first switch and the protection switch to disconnect and the second switch to close;

[0028] When it is necessary to switch to the off-grid mode, control the second switch to disconnect and the first switch and the protection switch to close.

[0029] In a possible embodiment, the grid-connected and off-grid switching cabinet further includes: a first relay; the first relay includes: a normally open contact and a coil; wherein, the normally open contact of the first relay is arranged at the DC end of the power supply board; both ends of the coil of the first relay are connected to the parallel operation control board;

[0030] The method further includes:

[0031] After power-on, continuously supply power to both ends of the coil of the first relay.

[0032] In a possible embodiment, the grid-connected and off-grid switching cabinet further includes: a second relay, an auxiliary contact and a third switch; the second relay includes: a first normally open contact, a second normally open contact and a coil; wherein, the protection switch is the first normally open contact of the second relay; the second normally open contact of the second relay is arranged between the opening control end and the DC power supply; the auxiliary contact is a normally closed contact, and the auxiliary contact opens when the closing control end of the frame circuit breaker controller receives the DC power supply signal output by the power supply board; the coil of the second relay, the auxiliary contact and the third switch are connected in series between the three-phase live wire and the neutral wire of the AC bus; the controlled end of the third switch is connected to the parallel operation control board;

[0033] The method further includes:

[0034] When it is necessary to switch to the grid-connected mode, control the third switch to disconnect;

[0035] When it is necessary to switch to the off-grid mode, control the third switch to close.

[0036] A grid-connected / off-grid switching cabinet provided by the present application realizes the connection control between the power grid and the local AC bus of the grid-connected / off-grid switching cabinet by using a four-pole frame circuit breaker, so as to also realize the connection control between the neutral line (N line) of the power grid and the N line of the local AC bus. When operating in the grid-connected mode, the four-pole frame circuit breaker closes, and the N line of the power grid can be connected to the N line of the AC bus in the same way as the three-phase input of the power grid is connected to the three-phase live wires L1, L2, and L3 of the local AC bus, ensuring the normal operation of the grid-connected mode. When operating in the off-grid mode, the four-pole frame circuit breaker opens, and at this time, the N line of the power grid is disconnected from the N line of the local AC bus, realizing the isolation of the neutral line, so as to avoid a series of safety problems caused by the non-isolation of the neutral line. In addition, to ensure that the off-grid system meets an independent TN (protective earthing) system, a connection between the ground wire and the neutral line of the local AC bus is additionally added in the grid-connected / off-grid switching cabinet provided by the present application. When the protection switch provided on the ground wire closes, the neutral line of the AC bus is directly grounded through the ground wire, realizing zero-ground connection and ensuring an independent TN system. When it is necessary to switch back to the grid-connected mode, the protection switch can be controlled to open to avoid the direct grounding of the neutral line of the power grid.

[0037] In summary, the grid-connected / off-grid switching cabinet provided by the present application can realize the isolation between the neutral line of the off-grid system and the neutral line of the power grid, and at the same time, can ensure the zero-ground connection of the off-grid system and meet an independent TN system. Compared with the traditional grid-connected / off-grid switching control scheme, it can better ensure the safe, stable and reliable operation of the off-grid system.

[0038] The grid-connected / off-grid switching control method provided by the present application corresponds to the above grid-connected / off-grid switching cabinet, and the effect is the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0040] Figure 1 It is a structural diagram of a grid-connected / off-grid switching cabinet provided by the present invention;

[0041] Figure 2 It is a structural diagram of a closing and opening control scheme provided by the present invention;

[0042] Figure 3 It is a structural diagram of an interlock mechanism implemented in a hardware form provided by the present invention;

[0043] Figure 4 This is a flowchart of a grid-connected and off-grid switching control method provided by the present invention. Detailed implementation manners

[0044] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present application.

[0045] The core of the present application is to provide a grid-connected and off-grid switching cabinet and a grid-connected and off-grid switching control method.

[0046] In order to enable those skilled in the art to better understand the solution of the present application, the present application will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0047] Currently, the grid-connected and off-grid switching cabinet realizes the switching control between grid connection and off-grid by setting a frame circuit breaker with mutually exclusive switch states between the power grid and the energy storage cabinet. However, this switching control is only limited to the three live wires (i.e., L1, L2, and L3) in the three-phase four-wire system. The neutral wire (N wire) of the local AC bus is directly connected to the grid N wire, which makes the N wire of the off-grid system directly connected to the grid N wire even when switched to the off-grid mode, thus leading to the following problems:

[0048] 1. Neutral wire circulating current: When the neutral wires of the off-grid system and the power grid are not isolated, a closed loop may be formed between the neutral points of the two due to the potential difference, resulting in current flowing between the two systems through the neutral wire.

[0049] At this time, the circulating current may exceed the rated capacity of the wire or equipment, causing equipment overload, problems such as heating, insulation aging, and even burnout. In addition, the circulating current will also cause reactive energy loss and reduce the system efficiency. Moreover, the circulating current may also cause the grounding protection device (such as the residual current device RCD) to misjudge as leakage and trip.

[0050] 2. Voltage deviation and abnormal neutral point potential: When the neutral wires of the off-grid system and the power grid are directly connected, the load fluctuation or fault (such as single-phase ground short circuit) on the grid side will directly affect the neutral point potential of the off-grid system.

[0051] At this time, the phase voltage of the off-grid system may deviate (for example, a certain phase voltage rises to 380V), resulting in overvoltage damage to the equipment (such as burning out single-phase loads). In addition, the voltage of the neutral wire to the ground may rise abnormally (such as in the case of a broken neutral fault), and touching the equipment shell or the neutral wire may cause electric shock, presenting a potential safety hazard to personnel.

[0052] 3. Grid reverse power transmission risk: If the off-grid system is not completely isolated from the grid (including the neutral line), the off-grid system may reverse power to the grid through the neutral line.

[0053] At this time, if the power grid is not completely de-energized during maintenance, the reverse power transmission of the grid may cause electric shock accidents to maintenance personnel. Also, when the voltage / frequency of the grid and the off-grid system are not synchronized, equipment oscillation or damage may occur.

[0054] 4. Grounding system conflict: The power grid and the off-grid system may adopt different grounding methods (such as TN-S, IT systems, etc.). If the neutral lines between them are not isolated, it may lead to a chaotic path of the grounding current.

[0055] At this time, the fault current may flow between the power grid and the off-grid system through the neutral line, resulting in an expansion of the fault range. Also, due to the existence of the fault current, the grounding protection device cannot correctly detect the fault location, which will delay the removal of the fault.

[0056] Therefore, to solve the above problems, the present application provides a grid-connected and off-grid switching cabinet, as Figure 1 shown, including: a four-pole frame circuit breaker, a ground wire, and a protection switch.

[0057] Among them, the four-pole frame circuit breaker is arranged between the power grid and the local AC bus of the grid-connected and off-grid switching cabinet, and is used to control whether the three-phase input line and the neutral line of the power grid are connected to the AC bus.

[0058] One end of the ground wire is connected to the neutral line in the AC bus, and the other end is grounded.

[0059] The protection switch is arranged on the ground wire and is used to control whether the neutral line in the AC bus is grounded.

[0060] It should be noted that the above structure and connection relationship of the grid-connected and off-grid switching cabinet only involve the improved part of the grid-connected and off-grid switching cabinet provided by the present application compared with the traditional grid-connected and off-grid switching cabinet, and do not limit that the grid-connected and off-grid switching cabinet provided by the present application only includes the above hardware structure part. It can Figure 1 be easily seen that the grid-connected and off-grid switching cabinet should also include: a three-pole (3P) frame circuit breaker arranged between the local AC bus and the energy storage cabinet, a three-pole frame circuit breaker arranged between the local AC bus and the load (LOAD1), and the corresponding connection relationship. Even further, a three-pole frame circuit breaker can be arranged between the four-pole frame circuit breaker and the power grid in the grid-connected and off-grid switching cabinet for realizing the circuit protection of the grid-connected system.

[0061] After that, for the function of the above-mentioned four-pole (4P) frame circuit breaker, it should cover the three-pole (3P) frame circuit breaker that is traditionally used to control whether the three-phase input of the power grid is connected to the local AC bus, and it also needs to play the role of controlling whether the N line of the power grid (hereinafter simply referred to as the grid N line) is connected to the N line of the local AC bus (hereinafter simply referred to as the local N line). It is not difficult to understand that the four contacts of the four-pole frame circuit breaker open and close simultaneously. That is, when the three-phase input of the power grid is connected to the live wires L1, L2, and L3 of the local AC bus (i.e., when operating in the grid-connected mode), the grid N line is also connected to the local N line. And when the three-phase input of the power grid is disconnected from the live wires L1, L2, and L3 of the local AC bus (i.e., when operating in the off-grid mode), the grid N line is also disconnected from the local N line to achieve isolation.

[0062] In addition, as can be seen from the above, the four-pole frame circuit breaker in this embodiment plays the role of originally controlling whether the power grid is connected to the AC bus in the grid-connected and off-grid switching cabinet. Therefore, the four-pole frame circuit breaker should be interlocked with the three-pole frame circuit breaker on the energy storage cabinet side, that is, the opening and closing states of each other are always opposite. This belongs to the conventional grid-connected and off-grid switching control requirements, and this embodiment will not elaborate on this.

[0063] Regarding the ground wire and the protection switch added in the grid-connected and off-grid switching cabinet in this embodiment. Among them, the ground wire is used to ground the local N line, and the protection switch provided on the ground wire is used to control whether the ground wire is conducting, that is, whether the local N line can be directly grounded.

[0064] It is easy to understand that the desired effect of the grid-connected and off-grid switching cabinet provided by this application is to isolate the local N line of the off-grid system from the grid N line. However, there is no requirement for isolation between the local N line and the grid N line in the grid-connected system (i.e., when operating in the grid-connected mode), and even the local N line of the grid-connected system should be directly connected to the grid N line. This connection relationship is controlled by the above-mentioned four-pole frame circuit breaker. When operating in the grid-connected mode, the local N line must be directly connected to the grid N line.

[0065] At this time, if the local N line is grounded, it will cause the grid N line to be grounded at two different points, and then a series of serious safety problems such as circulating current or electromagnetic interference will be caused by multi-point grounding. Therefore, this application sets a protection switch on the ground wire to control whether the local N line is grounded, so as to meet the TN system in the off-grid mode and avoid multi-point grounding of the grid N line in the grid-connected mode.

[0066] Furthermore, based on the above safety requirements, this embodiment also provides a possible control scheme for the switch state of the protection switch:

[0067] The protection switch is interlocked with the four-pole frame circuit breaker.

[0068] As can be easily seen from the above description, the four-pole frame circuit breaker should be in the closed state (i.e., the on state) in the grid-connected mode and in the open state (i.e., the off state) in the off-grid mode, which is exactly mutually exclusive with the switch state of the protection switch. Therefore, by interlocking the protection switch and the four-pole frame circuit breaker, the above-mentioned mutually exclusive switch states can be ensured, thus ensuring system safety.

[0069] It should be noted that this embodiment does not limit how the above interlock is implemented. It can be a mechanical interlock or an electrical interlock, and this interlock can be implemented through a hardware circuit or a software method. Further, this embodiment does not limit specifically what the control device for controlling the switch state of the protection switch is.

[0070] However, as can be easily seen from the above, the switch state of the protection switch is strongly related to the grid-connected / off-grid mode in which the grid-connected / off-grid switching cabinet operates. The protection switch should be open in the grid-connected mode and closed in the off-grid mode. Based on this control logic, the control device of the protection switch can reuse the control device for controlling whether the grid-connected / off-grid switching cabinet operates in the grid-connected mode or the off-grid mode, such as the parallel operation control board. The parallel operation control board can be implemented by a Digital Signal Processor (DSP) and is used to control the opening and closing states of all frame circuit breakers, including the four-pole frame circuit breaker on the grid side and the three-pole frame circuit breaker on the energy storage cabinet side and the load side.

[0071] As can be known from the above, a grid-connected / off-grid switching cabinet provided by the present application realizes the conduction control between the grid N line and the local N line by changing the three-pole frame circuit breaker originally set on the grid side to a four-pole one. When the grid-connected / off-grid switching cabinet operates in the off-grid mode, the four-pole frame circuit breaker on the grid side will open, disconnecting the grid N line from the local N line to achieve isolation. Thus, a series of safety problems caused by the direct connection between the N line of the off-grid system and the grid N line are avoided. And, since the local N line of the off-grid system is no longer connected to the grid N line, the original independent TN system is damaged. Therefore, the present application also directly grounds the local N line through the ground wire to ensure the zero-ground connection, thereby meeting the requirements of the TN system and effectively ensuring system safety.

[0072] On the other hand, for how to control the opening and closing states of the above-mentioned four-pole frame circuit breaker, this embodiment also provides a possible implementation scheme. As Figure 2 shown, the above-mentioned grid-connected / off-grid switching cabinet further includes: a parallel operation control board, a power supply board, a frame circuit breaker controller, a first switch (J3), and a second switch (J4).

[0073] Among them, the AC end of the power supply board is connected to one end of the four-pole frame circuit breaker close to the grid side, and the DC end of the power supply board is connected to the opening control end, closing control end, and under-voltage tripping end of the frame circuit breaker controller.

[0074] The first switch is arranged between the opening control terminal and the power supply board, and the second switch is arranged between the closing control terminal and the power supply board; the parallel operation control board is connected to the controlled terminals of the first switch and the second switch.

[0075] The frame circuit breaker controller is used to: control the four-pole frame circuit breaker to open when a DC power supply signal output by the power supply board is connected to the opening control terminal, control the four-pole frame circuit breaker to close when a DC power supply signal output by the power supply board is connected to the closing control terminal, and control the four-pole frame circuit breaker to open when no DC power supply signal output by the power supply board is connected to the under-voltage release terminal.

[0076] Specifically, the frame circuit breaker controller is directly used to control the opening and closing states of the four-pole frame circuit breaker. How it controls the opening and closing of the four-pole frame circuit breaker is related to whether the opening control terminal, the closing control terminal, and the under-voltage release terminal can receive the DC power supply signal (220VDC) output by the power supply board. When the opening control terminal receives the DC power supply signal (at this time, the under-voltage release terminal also receives the DC power supply signal), the four-pole frame circuit breaker opens; when the closing control terminal receives the DC power supply signal (at this time, the under-voltage release terminal also receives the DC power supply signal), the four-pole frame circuit breaker closes; when the under-voltage release terminal does not receive the DC power supply signal, the four-pole frame circuit breaker opens.

[0077] The parallel operation control board controls the opening and closing states of the first switch (J3) and the second switch (J4), so as to control whether the opening control terminal or the closing control terminal of the frame circuit breaker controller receives the DC power supply signal output by the power supply board, thereby realizing the control of the opening and closing states of the four-pole frame circuit breaker. Moreover, when the power supply board loses power due to an abnormality or a fault, the under-voltage release terminal fails to receive the DC power supply signal, which will also cause the four-pole frame circuit breaker to trip due to under-voltage release.

[0078] It should be noted that this opening and closing control scheme in this embodiment can also be analogously extended to other frame circuit breakers in the on-grid / off-grid switching cabinet. For example, the three-pole frame circuit breaker on the energy storage cabinet side can also achieve opening and closing control through the corresponding frame circuit breaker controller and the parallel operation control board. The difference is only that the ports connected to the parallel operation control board are different. The opening signal of the four-pole frame circuit breaker is the closing signal for the three-pole frame circuit breaker on the energy storage cabinet side. Similarly, the closing signal of the four-pole frame circuit breaker is the opening signal for the three-pole frame circuit breaker on the energy storage cabinet side.

[0079] In addition, it should also be noted that this embodiment does not limit the specific implementation forms of the first switch and the second switch. Considering the control requirements of the parallel operation control board, common electronic switches can be used as the above-mentioned first switch and second switch. In a possible embodiment, such as Figure 2As shown, both the first switch and the second switch are relays. The parallel operation control board controls the on / off of the circuit where the relay contact is located by controlling whether the relay coil is energized.

[0080] The switching control scheme provided by this embodiment is simple and reliable. At the same time, it realizes voltage domain separation, avoiding the direct access of the parallel operation control board with a lower voltage level to the main circuit with a higher voltage level for control, ensuring the safety of the circuit. At the same time, on the basis of providing switching control, an under-voltage release protection mechanism is also introduced to ensure that when abnormal conditions such as power failure or under-voltage occur on the power supply board, the four-pole frame circuit breaker trips to avoid the safety risks brought by the mis-triggering of the grid access to the local AC bus.

[0081] Furthermore, as can be seen from the above embodiment, the parallel operation control board can be used to control the switching of the four-pole frame circuit breaker. Therefore, this embodiment provides a software-based implementation scheme for the interlock between the protection switch and the four-pole frame circuit breaker:

[0082] The controlled end of the protection switch is connected to the parallel operation control board.

[0083] Among them, the parallel operation control board is used to control the switch state of the four-pole frame circuit breaker, and the switch states of the first switch and the protection switch are always opposite at the same time.

[0084] After this embodiment takes the parallel operation control board that controls the switching state of the four-pole frame circuit breaker as the control party of its own switch state, the software-based interlock can be realized through the parallel operation control board without adding any additional hardware circuits. And because the parallel operation control board is originally used to control the switching of all frame circuit breakers in the parallel / grid-connected switching cabinet, the frame circuit breaker on the grid side and the frame circuit breaker on the energy storage side are also in an interlock relationship. Therefore, adding the interlock control between the four-pole frame circuit breaker and the protection switch can be achieved by making simple modifications to the original control logic of the parallel operation control board, greatly reducing the implementation difficulty.

[0085] Furthermore, although the switching control scheme provided by the previous embodiment adds an under-voltage release protection mechanism, which can protect the system when the power supply board is under-voltage or loses power. However, it still has deficiencies. For example, the switching control overly relies on the parallel operation control board. When the parallel operation control board crashes, it is impossible to control the switching state of the four-pole frame circuit breaker. If it is necessary to switch from the grid-connected mode back to the off-grid mode at this time, the failure of the four-pole frame circuit breaker to trip in time will bring serious safety risks.

[0086] Based on this, this embodiment further provides an implementation scheme on the basis of the above embodiment, as Figure 2 shown, the parallel / grid-connected switching cabinet further includes: a first relay (J1); the first relay includes: a normally open contact and a coil.

[0087] Among them, the normally open contact of the first relay is arranged at the DC end of the power supply board; both ends of the coil of the first relay are connected to the parallel machine control board; after the parallel machine control board is powered on, it continuously supplies power to both ends of the coil of the first relay.

[0088] Based on the setting of the first relay in this embodiment, whether the DC power supply signal output by the DC end of the power supply board can be accessed by the three ports of the frame circuit breaker controller is directly controlled by whether the parallel machine control board can continuously supply power to the coil of the first relay. When the parallel machine control board is working normally, the parallel machine control board will continuously supply power to the coil of the first relay as soon as it is powered on. At this time, the contact of the first relay is closed, and the contact of the first relay can be ignored on the path. The frame circuit breaker controller can control the opening and closing of the four-pole frame circuit breaker based on whether the three ports receive the DC power supply signal output by the power supply board as described in the above embodiment. When the parallel machine control board breaks down and cannot guarantee its normal control function, the broken-down parallel machine control board also cannot guarantee continuous power supply to the coil of the first relay, so the contact of the first relay is disconnected. At this time, even if the power supply board is in normal working condition, it will cause the under-voltage release terminal of the frame circuit breaker controller not to receive the DC power supply signal output by the power supply board, thereby triggering the under-voltage release protection of the frame circuit breaker controller and tripping the four-pole frame circuit breaker to ensure that the power grid is disconnected from the system, thus ensuring the safety of the entire system.

[0089] Furthermore, the above embodiment provides an interlock scheme between the four-pole frame circuit breaker and the protection switch implemented in software form. This embodiment also provides an interlock scheme implemented in hardware form, as Figure 3 shown, the off-grid switching cabinet further includes: a second relay, an auxiliary contact and a third switch.

[0090] The second relay includes: a first normally open contact, a second normally open contact and a coil; among them, the protection switch is the first normally open contact of the second relay; the second normally open contact of the second relay is arranged between the opening control end and the DC power supply.

[0091] The auxiliary contact is a normally closed contact, and the auxiliary contact opens when the closing control end of the frame circuit breaker controller receives the DC power supply signal output by the power supply board.

[0092] The coil of the second relay, the auxiliary contact and the third switch are connected in series between the three-phase live wire and the neutral wire of the AC bus. The controlled end of the third switch is connected to the parallel machine control board.

[0093] Specifically, in the grid-connected mode, the four-pole frame circuit breaker is in the closed state. At this time, the closing control terminal of the frame circuit breaker controller should receive the DC power supply signal output by the power supply board. Based on the above settings, the auxiliary contact will disconnect, which will cause the series branch of the coil, auxiliary contact of the second relay and the third switch (hereinafter referred to as the series branch) to disconnect, so that the coil of the second relay cannot be energized. Also, since the protection switch in this embodiment is a normally open contact of the second relay, when the coil of the second relay cannot be energized, this normally open contact cannot be closed and always remains open. An interlock in one switching direction is achieved, which can prevent the grid N line from grounding through the ground wire.

[0094] For the interlock in the other switching direction, in the off-grid mode, the closing control terminal of the frame circuit breaker controller fails to receive the DC power supply signal output by the power supply board, and at this time the auxiliary contact is closed. If the third switch is closed (that is, the parallel machine control board can control the protection switch to close by controlling the third switch), the series branch is turned on, the coil of the second relay is energized, and the protection switch, which is a normally open contact of the second relay, is closed to ensure that the local N line grounding meets the requirements of an independent TN system. Also, because the coil of the second relay is energized, the second normally open contact of the second relay is closed, and the DC power supply is directly connected to the tripping control terminal of the frame circuit breaker controller, which is equivalent to giving a tripping signal to the frame circuit breaker controller. At this time, the four-pole frame circuit breaker trips, avoiding the direct connection between the grid N line and the local N line, and thus the problem of multi-point grounding through the ground wire.

[0095] As can be seen from the above, this embodiment provides an interlock mechanism between a four-pole frame circuit breaker and a protection switch implemented in a hardware form. It is more reliable and stable than the software-based interlock mechanism, and can still ensure the interlock between the four-pole frame circuit breaker and the protection switch when the parallel machine control board works abnormally, better ensuring system safety.

[0096] On the other hand, this embodiment also provides another possible implementation scheme, as Figure 1 shown:

[0097] There are multiple four-pole frame circuit breakers. And the multiple four-pole frame circuit breakers are connected in parallel, and at most only one four-pole frame circuit breaker is in the closed state at the same time.

[0098] That is to say, this embodiment provides a redundancy protection scheme to ensure the reliability of the grid access to the local AC bus through multiple redundantly set four-pole frame circuit breakers. However, it should be noted that only one of the multiple redundantly set four-pole frame circuit breakers works at the same time, that is, the closing and tripping states are controlled by the parallel machine control board, and the other four-pole frame circuit breakers do not work, that is, they are defaulted to the tripping state.

[0099] In the above embodiments, a grid-connected and off-grid switching cabinet has been described in detail. In some embodiments, the switching between the grid-connected mode and the off-grid mode of the grid-connected and off-grid switching cabinet is mainly achieved by the parallel operation control board. For this, this embodiment also provides a grid-connected and off-grid switching control method applied to the parallel operation control board, as Figure 4 shown, the method includes:

[0100] S11: When it is necessary to switch to the grid-connected mode, control the first switch and the protection switch to open, and the second switch to close.

[0101] S12: When it is necessary to switch to the off-grid mode, control the second switch to open, and the first switch and the protection switch to close.

[0102] Based on the above embodiments of the grid-connected and off-grid switching cabinet part and Figure 2 it is not difficult to see that when the first switch is open and the second switch is closed, the closing control terminal of the frame circuit breaker controller receives the DC power signal output by the power board, while the opening control terminal does not receive it. Therefore, the frame circuit breaker controller controls the four-pole frame circuit breaker to close, and the local AC bus is connected to the power grid, entering the grid-connected mode. In addition, since the switch states of the protection switch and the four-pole frame circuit breaker (the first switch) are mutually exclusive, the protection switch is open, and the local N line will not be grounded, thus avoiding multi-point grounding of the power grid N line.

[0103] Similarly, when the second switch is open and the first switch is closed, the opening control terminal of the frame circuit breaker controller receives the DC power signal output by the power board, while the closing control terminal does not receive it. Therefore, the frame circuit breaker controller controls the four-pole frame circuit breaker to open, the local AC bus is disconnected from the power grid, and the energy storage cabinet is connected to the local AC bus, entering the off-grid mode. In addition, since the switch states of the protection switch and the four-pole frame circuit breaker (the first switch) are mutually exclusive, the protection switch is closed, and the local N line is grounded, ensuring that the local N line can still achieve zero-ground connection after being isolated from the power grid N line, meeting the independent TN system.

[0104] The grid-connected and off-grid switching control method provided in this embodiment is applied to the grid-connected and off-grid switching cabinet provided in the above embodiment, so it can bring the same technical effects as the above grid-connected and off-grid switching cabinet. For details, please refer to the embodiments of the above grid-connected and off-grid switching cabinet part, and this embodiment will not be elaborated here.

[0105] Furthermore, the above embodiments of the grid-connected and off-grid switching cabinet part provide a parallel operation control board downtime protection mechanism realized by the first relay. For details, please refer to the embodiments of the above grid-connected and off-grid switching cabinet part and Figure 2 . This embodiment then provides a corresponding control method for this, as Figure 4 shown, the above method further includes:

[0106] S0: After power-on, continuously supply power to both ends of the coil of the first relay.

[0107] That is, in this embodiment, by controlling the parallel control board to continuously supply power to both ends of the coil of the first relay after power-on, the influence of the addition of the first relay on the normal parallel / grid-isolation switching control is avoided. Moreover, when the parallel control board crashes, step S0 cannot be guaranteed to be executed normally, causing the coil of the first relay to lose power. At this time, the DC power signal output by the power board cannot be output to the under-voltage release terminal of the frame circuit breaker controller, which will trigger its under-voltage release protection mechanism and cause the four-pole frame circuit breaker to trip, disconnecting the power grid from the local AC bus and avoiding the safety risks brought by the crash of the parallel control board.

[0108] On the other hand, the above embodiments of the parallel / grid-isolation switching cabinet part also provide an interlock mechanism between the four-pole frame circuit breaker and the protection switch in the form of software implemented based on the parallel control board. This embodiment provides a specific method for the interlock mechanism implemented in this software form. The above method further includes:

[0109] S21: When it is necessary to switch to the grid-connected mode, control the third switch to open.

[0110] S22: When it is necessary to switch to the off-grid mode, control the third switch to close.

[0111] It is not difficult to see that the triggering conditions of step S21 are the same as those of the above step S11, and the triggering conditions of step S22 are the same as those of the above step S12. And there is no conflict between step S21 and step S11, and they can be implemented together. The same is true for step S22 and step S12. Therefore, after combining step S21 and step S11, and combining step S22 and step S12, we can get:

[0112] S1: When it is necessary to switch to the grid-connected mode, control the first switch, the protection switch, and the third switch to open, and the second switch to close.

[0113] S2: When it is necessary to switch to the off-grid mode, control the second switch to open, and the first switch, the protection switch, and the third switch to close.

[0114] Thus, it can be seen that in this embodiment, by modifying the control logic of the parallel control board, an interlock mechanism between the protection switch and the four-pole frame circuit breaker is implemented in the form of software. Thereby ensuring that the grid N line is not grounded at multiple points, and also ensuring that the off-grid system can still meet the requirements of the TN system after isolating the grid N line.

[0115] The above has provided a detailed introduction to a grid-connected and off-grid switching cabinet and a grid-connected and off-grid switching control method provided in this application. Each embodiment in the specification is described in a progressive manner. The key point of each embodiment is the difference from other embodiments. For the same or similar parts between the embodiments, reference can be made to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple. For the relevant parts, reference can be made to the description in the method part. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle of this application, several improvements and modifications can be made to this application, and these improvements and modifications also fall within the protection scope of this application.

[0116] It should also be noted that in this specification, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the element.

Claims

1. A grid-connected and off-grid switching cabinet, characterized in that, Including: A four-pole frame circuit breaker, a ground wire, and a protection switch; Among them, the four-pole frame circuit breaker is arranged between the power grid and the AC bus of the local grid-connected and off-grid switching cabinet, and is used to control whether the three-phase input line and the neutral line of the power grid are connected to the AC bus; One end of the ground wire is connected to the neutral line in the AC bus, and the other end is grounded; The protection switch is arranged on the ground wire and is used to control whether the neutral line in the AC bus is grounded.

2. The off-grid and grid-connected switching cabinet according to claim 1, characterized in that The protection switch is interlocked with the four-pole frame circuit breaker.

3. The grid-connected and off-grid switching cabinet according to claim 2, characterized in that, Also including: A parallel operation control board, a power supply board, a frame circuit breaker controller, a first switch, and a second switch; Among them, the AC end of the power supply board is connected to one end of the four-pole frame circuit breaker close to the power grid side, and the DC end of the power supply board is connected to the opening control end, closing control end, and under-voltage tripping end of the frame circuit breaker controller; The first switch is arranged between the opening control end and the power supply board, and the second switch is arranged between the closing control end and the power supply board; the parallel operation control board is connected to the controlled ends of the first switch and the second switch; The frame circuit breaker controller is used to: control the four-pole frame circuit breaker to trip when the opening control end receives the DC power supply signal output by the power supply board, control the four-pole frame circuit breaker to close when the closing control end receives the DC power supply signal output by the power supply board, and control the four-pole frame circuit breaker to trip when the under-voltage tripping end does not receive the DC power supply signal output by the power supply board.

4. The grid-connected and off-grid switching cabinet according to claim 3, wherein Also including: A first relay; the first relay includes: a normally open contact and a coil; Among them, the normally open contact of the first relay is arranged at the DC end of the power supply board; Both ends of the coil of the first relay are connected to the parallel operation control board; the parallel operation control board continuously supplies power to both ends of the coil of the first relay after power-on.

5. The grid-connected and off-grid switching cabinet according to claim 3, characterized in that, Also including: A second relay, an auxiliary contact, and a third switch; The second relay includes: a first normally open contact, a second normally open contact, and a coil; among them, the protection switch is the first normally open contact of the second relay; the second normally open contact of the second relay is arranged between the opening control end and the DC power supply; The auxiliary contact is a normally closed contact, and the auxiliary contact opens when the closing control end of the frame circuit breaker controller receives the DC power supply signal output by the power supply board; The coil of the second relay, the auxiliary contact, and the third switch are connected in series between the three-phase live wire and the neutral line of the AC bus; The controlled end of the third switch is connected to the parallel operation control board.

6. The off-grid and grid-connected switching cabinet according to claim 3, characterized in that, The controlled end of the protection switch is connected to the parallel operation control board; Among them, the parallel operation control board is used to control the switch state of the four-pole frame circuit breaker, and at the same time, the switch states of the first switch and the protection switch are always opposite.

7. The off-grid and grid-connected switching cabinet according to claim 1, wherein There are multiple four-pole frame circuit breakers; and multiple four-pole frame circuit breakers are connected in parallel, and at most only one four-pole frame circuit breaker is in the closed state at the same time.

8. A grid-connected and off-grid switching control method, characterized in that Applied to the grid-connected and off-grid switching cabinet as described in claim 3, the method includes: When it is necessary to switch to the grid-connected mode, control the first switch and the protection switch to open and the second switch to close; When it is necessary to switch to the off-grid mode, control the second switch to open and the first switch and the protection switch to close.

9. The grid-connected and off-grid switching control method according to claim 8, wherein The grid-connected / off-grid switching cabinet further includes: a first relay; the first relay includes: a normally open contact and a coil; wherein, the normally open contact of the first relay is disposed at the DC end of the power supply board; both ends of the coil of the first relay are connected to the parallel machine control board; The method further includes: After power-on, continuously supply power to both ends of the coil of the first relay.

10. The grid-connected and off-grid switching control method according to claim 8, characterized in that, The grid-connected / off-grid switching cabinet further includes: a second relay, an auxiliary contact and a third switch; the second relay includes: a first normally open contact, a second normally open contact and a coil; wherein, the protection switch is the first normally open contact of the second relay; the second normally open contact of the second relay is disposed between the opening control end and the DC power supply; the auxiliary contact is a normally closed contact, and the auxiliary contact opens when the closing control end of the frame circuit breaker controller receives the DC power supply signal output by the power supply board; the coil of the second relay, the auxiliary contact and the third switch are connected in series between the three-phase live wire and the neutral wire of the AC bus; the controlled end of the third switch is connected to the parallel machine control board; The method further includes: When it is necessary to switch to the grid-connected mode, control the third switch to open; When it is necessary to switch to the off-grid mode, control the third switch to close.

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