Grid-connected and off-grid switching device and energy storage system

Abstract

The utility model discloses a grid-connected and off-grid switching device and an energy storage system, and belongs to the technical field of power electronics. The device comprises a bidirectional conversion module, a relay module and a control module, the first end of the bidirectional conversion module is connected with the power supply, and the second end is connected with the first end of the relay module. A second end and a third end of the relay module are respectively connected with a load and a power grid, the relay module comprises a bypass relay, two ends of the bypass relay are respectively connected with the load and the power grid, and the relay module is used for selectively connecting the power supply and the load, or connecting the power supply and the power grid, or connecting the load and the power grid; the control module is connected with the controlled end of the bidirectional conversion module and the controlled end of the relay module and used for controlling the bypass relay to be closed in the process that the working mode of the grid-connected and off-grid switching device is switched from the grid-connected mode to the off-grid mode and switching PI control of a current inner ring in constant power control of the bidirectional conversion module into PD control. The method can ensure stable operation of the load.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to an on-grid and off-grid switching device and an energy storage system. Background Art

[0002] At present, energy storage systems can work in different control modes in grid-connected and off-grid states. For example, PQ control (constant power control) is used in grid-connected state, and VF control (voltage-frequency conversion control) is used in off-grid state. When grid-connected / off-grid switching is required, due to the different control modes of the two states, it will cause temporary output loss or even distortion during the switching process, affecting the smooth operation of the load. Utility Model Content

[0003] The main purpose of this application is to provide an on-grid / off-grid switching device and an energy storage system, aiming to achieve fast and smooth on-grid / off-grid switching, avoid current overshoot and distortion during the switching process, and ensure that the load can operate smoothly.

[0004] To achieve the above-mentioned purpose, the present application provides an on-grid and off-grid switching device, the on-grid and off-grid switching device comprising: a bidirectional conversion module, a relay module and a control module;

[0005] The first end of the bidirectional conversion module is connected to a power source, and the second end of the bidirectional conversion module is connected to the first end of the relay module;

[0006] The second end and the third end of the relay module are connected to the load and the grid respectively, the relay module includes a bypass relay, the two ends of the bypass relay are connected to the load and the grid respectively, and the relay module is used to selectively connect the power supply and the load, or connect the power supply and the grid, or connect the load and the grid;

[0007] The control module is connected to the controlled ends of the bidirectional conversion module and the relay module respectively. The control module is used to control the bypass relay to close during the process of switching the working mode of the grid-connected and off-grid switching device from the grid-connected mode to the off-grid mode, and to switch the PI control of the current inner loop in the constant power control of the bidirectional conversion module to PD control.

[0008] In one embodiment, the on-grid and off-grid switching device further includes:

[0009] A current detection module, wherein the current detection module is connected to the bidirectional conversion module and the control module respectively, and the current detection module is used to detect the current flowing through the bidirectional conversion module during the process of switching the working mode of the grid-connected and off-grid switching device from the grid-connected mode to the off-grid mode, and output an overcurrent signal to the control module when the current is greater than a preset value, so that the control module controls the bypass relay to close, and switches the PI control of the current inner loop in the constant power control of the bidirectional conversion module to PD control.

[0010] In one embodiment, the relay module further comprises: a load-side relay and a grid-side relay;

[0011] The first end of the load-side relay is connected to the output end of the bidirectional conversion module, and the second end of the load-side relay is connected to the load;

[0012] A first end of the grid-side relay is connected to an output end of the bidirectional conversion module, and a second end of the grid-side relay is connected to the power grid.

[0013] In one embodiment, when the working mode of the on-grid and off-grid switching device is the off-grid mode, the load-side relay is closed, the bypass relay is disconnected, the grid-side relay is disconnected, and the bidirectional conversion module adopts voltage-frequency conversion control;

[0014] When the working mode of the grid-connected and off-grid switching device is the grid-connected mode, the grid-side relay is closed, the bypass relay is disconnected, the load-side relay is disconnected, and the bidirectional conversion module adopts constant power control.

[0015] In one embodiment, during the process of switching the working mode of the on-grid and off-grid switching device from the off-grid mode to the on-grid mode, the bypass relay is closed and the output power of the bidirectional conversion module gradually decreases to zero.

[0016] In one embodiment, after the working mode of the grid-connected and off-grid switching device is switched from the off-grid mode to the grid-connected mode, the load-side relay is disconnected, the bypass relay is disconnected, the grid-side relay is closed, and the bidirectional conversion module adopts constant power control.

[0017] In one embodiment, after the working mode of the grid-connected and off-grid switching device is switched from the grid-connected mode to the off-grid mode, the grid-side relay is disconnected, the bypass relay is disconnected, the load-side relay is closed, and the bidirectional conversion module adopts voltage-frequency conversion control.

[0018] In one embodiment, the on-grid and off-grid switching device further includes:

[0019] A comparison circuit, the comparison circuit comprising a first input terminal, a first comparison reference terminal, a second comparison reference terminal and an output terminal, the first input terminal is connected to any phase current of the bidirectional conversion module, the first comparison reference terminal is connected to a first comparison reference current, the second comparison reference terminal is connected to a second comparison reference current, and the comparison circuit outputs a comparison result signal from the output terminal according to the magnitude of the current of the first input terminal, the current of the first comparison reference terminal and the current of the second comparison reference terminal;

[0020] The control module is connected to the output end of the comparison circuit, and controls whether the bidirectional conversion module works according to the comparison result signal received from the output end of the comparison circuit.

[0021] In one embodiment, the on-grid and off-grid switching device further includes:

[0022] A filter module, wherein a first input end of the filter module is connected to a second end of the relay module, a first output end of the filter module is connected to the load, a second input end of the filter module is connected to a third end of the relay module, and a second output end of the filter module is connected to the power grid.

[0023] In one embodiment, the filtering module includes: a load-side filtering unit and a grid-side filtering unit;

[0024] The input end of the load-side filter unit serves as the first input end of the filter module, and the output end of the load-side filter unit serves as the first output end of the filter module;

[0025] The input end of the network-side filter unit serves as the second input end of the filter module, and the output end of the network-side filter unit serves as the second output end of the filter module.

[0026] In addition, to achieve the above-mentioned purpose, the present application also provides an energy storage system, which includes the on-grid and off-grid switching device as described above.

[0027] The present application proposes a grid-connected and off-grid switching device and energy storage system, which overcomes the problem in the prior art that short-term output loss or even distortion will occur during the grid-connected / off-grid switching process, affecting the smooth operation of the load. The grid-connected and off-grid switching device includes: a bidirectional conversion module, a relay module and a control module; the first end of the bidirectional conversion module is connected to the power supply, and the second end of the bidirectional conversion module is connected to the first end of the relay module; the second end and the third end of the relay module are respectively connected to the load and the power grid, and the relay module includes a bypass relay, and the two ends of the bypass relay are respectively connected to the load and the power grid, and the relay module is used to select the connection between the power supply and the load, or the connection between the power supply and the power grid, or the connection between the load and the power grid; the control module is respectively connected to the controlled ends of the bidirectional conversion module and the relay module, and the control module is used to control the bypass relay to close during the process of switching the working mode of the grid-connected and off-grid switching device from the grid-connected mode to the off-grid mode, and switch the PI control of the current inner loop in the constant power control of the bidirectional conversion module to the PD control. The on-grid and off-grid switching device proposed in the present application achieves the purpose of current limiting control by switching the PI control of the current inner loop in the constant power control of the bidirectional conversion module to PD control during the switching process from on-grid to off-grid, thereby avoiding current overshoot and distortion during the switching process. At the same time, by adding a bypass relay and closing the bypass relay during the switching process, the load can be guaranteed to run smoothly. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0029] Figure 1 A schematic diagram of the structure of an on-grid and off-grid switching device provided in an embodiment of the present application;

[0030] Figure 2 A schematic diagram of off-grid control logic involved in an on-grid and off-grid switching device provided in an embodiment of the present application;

[0031] Figure 3 A schematic diagram of grid-connected control logic involved in a grid-connected and off-grid switching device provided in an embodiment of the present application;

[0032] Figure 4 A schematic diagram of on-grid / off-grid switching control logic involved in an on-grid / off-grid switching device provided in an embodiment of the present application;

[0033] Figure 5 A schematic diagram of the structure of another on-grid and off-grid switching device provided in an embodiment of the present application;

[0034] Figure 6 A detailed structural diagram of a relay module in an on-grid and off-grid switching device provided in an embodiment of the present application;

[0035] Figure 7 A schematic diagram of the structure of another on-grid and off-grid switching device provided in an embodiment of the present application;

[0036] Figure 8 A detailed structural diagram of a filter module in another on-grid and off-grid switching device provided in an embodiment of the present application;

[0037] Fig. 9 A schematic diagram of the structure of another on-grid and off-grid switching device provided in an embodiment of the present application;

[0038] Fig.10 A schematic diagram of the structure of an on-grid and off-grid switching device with a comparison circuit provided in an embodiment of the present application;

[0039] Fig.11 A schematic diagram of the structure of a comparison circuit provided in an embodiment of the present application.

[0040] Description of Figure Numbers:

[0041]

[0042]

[0043] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0045] It should be noted that all directional indications in the embodiments of the present application (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0046] In addition, the descriptions of "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In addition, the meaning of "and / or" appearing in the full text is to include three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B.

[0047] In this application, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0048] It should also be understood that the references to "one embodiment" or "some embodiments" described in the specification of the embodiments of the present application mean that one or more embodiments of the embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0049] Energy is the basis for people's survival and development. In the era of rapid social and economic development, as people's demand for energy continues to increase, renewable energy such as wind energy, solar energy, hydropower, tidal energy, etc. are gradually being discovered and used. However, the development of renewable energy also has certain limitations. For example, renewable energy such as solar energy and wind energy are seriously affected by factors such as weather, season, geographical location and time, and power generation is unstable and volatile.

[0050] Based on this, energy storage systems came into being. By adopting appropriate control strategies, energy storage systems can smooth the output power of renewable energy sources such as wind and light, adjust the voltage and frequency of the grid, suppress harmonic pollution, and improve power supply reliability.

[0051] At present, energy storage systems can work in different control modes in grid-connected and off-grid states. For example, PQ control (constant power control) is used in grid-connected state, and VF control (voltage-frequency conversion control) is used in off-grid state. When grid-connected / off-grid switching is required, due to the different control modes of the two states, it will cause temporary output loss or even distortion during the switching process, affecting the smooth operation of the load.

[0052] Based on this, the embodiment of the present application proposes a grid-connected and off-grid switching device and energy storage system, which overcomes the problem in the prior art that there will be a short-term output loss or even distortion during the grid-connected / off-grid switching process, which affects the smooth operation of the load. The grid-connected and off-grid switching device proposed in the embodiment of the present application achieves the purpose of current limiting control by switching the PI control of the current inner loop in the constant power control (i.e., PQ control) of the bidirectional conversion module to PD control during the grid-connected / off-grid switching process, thereby avoiding current overshoot and distortion during the switching process. At the same time, by adding a bypass relay and closing the bypass relay during the switching process, the load can be guaranteed to run smoothly.

[0053] In this embodiment, PI control and PD control are both existing technologies. The control module 300 in this embodiment does not involve improvements to the control algorithms of PI control and PD control themselves, but only selects one of the two control methods, or switches between the two control modes at an appropriate time.

[0054] In some embodiments, the control module 300 may be ARM, FPGA, CPLD, etc., such as ARM's MIMXRT1061CVL5B model, CPLD's EG4X20BG256, etc.

[0055] The on-grid and off-grid switching device and energy storage system provided in the embodiments of the present application are specifically described through the following embodiments, and the on-grid and off-grid switching device is first described.

[0056] The present application embodiment provides a grid-connected and off-grid switching device, referring to Figure 1 , Figure 1 A schematic diagram of the structure of an on-grid and off-grid switching device provided in an embodiment of the present application, wherein the on-grid and off-grid switching device comprises: a bidirectional conversion module 100, a relay module 200 and a control module 300;

[0057] The first end of the bidirectional conversion module 100 is connected to a power source, and the second end of the bidirectional conversion module 100 is connected to the first end of the relay module 200;

[0058] The second end and the third end of the relay module 200 are connected to the load and the grid respectively. The relay module 200 includes a bypass relay T2. The two ends of the bypass relay T2 are connected to the load and the grid respectively. The relay module 200 is used to selectively connect the power supply and the load, or connect the power supply and the grid, or connect the load and the grid;

[0059] The control module 300 is respectively connected to the controlled ends of the bidirectional conversion module 100 and the relay module 200. The control module 300 is used to control the bypass relay T2 to close during the process of switching the working mode of the grid-connected and off-grid switching device from the grid-connected mode to the off-grid mode, and to switch the PI control of the current inner loop in the constant power control of the bidirectional conversion module 100 to PD control.

[0060] In this embodiment, the on-grid and off-grid switching device includes multiple working modes such as off-grid mode, on-grid mode, on-grid and off-grid sharing, and grid direct supply load.

[0061] As an example, the bidirectional conversion module 100 in this embodiment can realize DC to AC or AC to DC, and the power supply connected to its first end can be a DC power supply such as a battery, a dry cell, a solar cell, etc. When the grid-connected and off-grid switching device operates in the off-grid mode, the VF control method (i.e., voltage-frequency conversion control) is used to control the bidirectional conversion module 100. When the grid-connected and off-grid switching device operates in the grid-connected mode, the PQ control method (i.e., constant power control) is used to control the bidirectional conversion module 100.

[0062] In this embodiment, corresponding to the above-mentioned different working modes, the relay module 200 is respectively used to connect the bidirectional conversion module 100 and the load, connect the bidirectional conversion module 100 and the power grid, connect the bidirectional conversion module 100 and the load and the bidirectional conversion module 100 and the power grid, and connect the power grid and the load.

[0063] Compared with the related art, the relay module 200 in the present application includes a bypass relay T2. During the on-grid and off-grid switching process of the on-grid and off-grid switching device, the load can be ensured to operate stably without power failure by closing the bypass relay T2. At the same time, during this process, the PI control of the current inner loop in the PQ control of the bidirectional conversion module 100 will be switched to PD control, thereby achieving the purpose of current limiting control and avoiding current overshoot and distortion during the on-grid and off-grid switching process.

[0064] As an example, the off-grid control logic, grid-connected control logic, and grid-connected / off-grid switching control logic involved in this embodiment can be combined with Figures 2 to 4 To understand, by Figures 2 to 4It can be seen that in the process of switching from grid-connected to off-grid, the PI control of the current inner loop in the PQ control will switch to PD control. After the switching is completed, VF control will be used normally.

[0065] The present embodiment provides an on-grid and off-grid switching device, which switches the PI control of the current inner loop in the constant power control of the bidirectional conversion module to PD control through the control module during the process of switching the on-grid and off-grid switching device from on-grid to off-grid, thereby achieving the purpose of current limiting control and avoiding current overshoot and distortion during the switching process. At the same time, by adding a bypass relay and closing the bypass relay during the switching process, the load can be guaranteed to run smoothly.

[0066] Reference Figure 5 In some feasible embodiments, the above-mentioned on-grid and off-grid switching device further includes:

[0067] A current detection module 400, wherein the current detection module 400 is connected to the bidirectional conversion module 100 and the control module 300 respectively, and the current detection module 400 is used to detect the current flowing through the bidirectional conversion module 100 when the working mode of the grid-connected and off-grid switching device is switched from the grid-connected mode to the off-grid mode, and output an overcurrent signal to the control module 300 when the current is greater than a preset value, so that the control module 300 controls the bypass relay T2 to close, and switches the PI control of the current inner loop in the constant power control of the bidirectional conversion module 100 to PD control.

[0068] It should be noted that, in the present embodiment, when the working mode of the on-grid / off-grid switching device is switched from the on-grid mode to the off-grid mode, the bypass relay T2 is closed first, that is, the power grid supplies power to the load during the transition period to ensure the smooth operation of the load. When the relay is energized, the current surges instantly. The current at the output end of the bidirectional conversion module 100 can be detected by a comparator or other device with a current detection function (i.e., the current detection module 400). If the current is greater than the set value (i.e., overcurrent), in order to limit the system from responding too quickly, the current inner loop PI control in the constant power control needs to be switched to PD control (the outer loop is still PI control).

[0069] Reference Figure 6 , in some feasible embodiments, the relay module 200 further includes: a load-side relay T1 and a grid-side relay T3;

[0070] The first end of the load-side relay T1 is connected to the output end of the bidirectional conversion module, and the second end of the load-side relay T1 is connected to the load;

[0071] A first end of the grid-side relay T3 is connected to the output end of the bidirectional conversion module, and a second end of the grid-side relay T3 is connected to the power grid.

[0072] It can be understood that, in this embodiment, when the load-side relay T1 is closed, the bidirectional conversion module 100 and the load are connected, and when the grid-side relay T3 is closed, the bidirectional conversion module 100 and the grid are connected.

[0073] As an example, the relay control and on-grid disconnection logic involved in this embodiment can refer to the following Table 1, wherein the on-off state "1" represents closed, and the on-off state "0" represents open.

[0074] Table 1 Relay control on-grid and off-grid logic

[0075]

[0076] As an example, this embodiment provides a circuit connection state at each stage of switching of an on-grid and off-grid switching device from an off-grid mode to a on-grid mode, which is specifically as follows:

[0077] When the working mode of the on-grid and off-grid switching device is the off-grid mode, the load-side relay T1 is closed, the bypass relay T2 is disconnected, the grid-side relay T3 is disconnected, and the bidirectional conversion module 100 adopts voltage-frequency conversion control;

[0078] During the process of the working mode of the on-grid and off-grid switching device switching from the off-grid mode to the on-grid mode, the bypass relay T2 is closed, and the output power of the bidirectional conversion module 100 gradually decreases to zero;

[0079] After the working mode of the grid-connected and off-grid switching device is switched from the off-grid mode to the grid-connected mode, the load-side relay T1 is disconnected, the bypass relay T2 is disconnected, the grid-side relay T3 is closed, and the bidirectional conversion module 100 adopts constant power control.

[0080] In this embodiment, since the working mode of the on-grid and off-grid switching device is the off-grid mode, only the load-side relay T1 is closed. When the working mode of the on-grid and off-grid switching device is switched from the off-grid mode to the on-grid mode, the bypass relay T2 is closed first, that is, the power grid supplies power to the load during the transition period to ensure the smooth operation of the load. Then the output power of the bidirectional conversion module 100 is gradually reduced to zero, and then the load-side relay T1 is disconnected. At the same time, the voltage and angular velocity of the grid can also be obtained in this process to perform VF control, and the output voltage and angular velocity of the bidirectional conversion module 100 are adjusted to the same frequency and amplitude as the grid. At this time, the grid-side relay T3 can be closed, the bypass relay T2 can be disconnected, and the off-grid switching device completes the switching from the off-grid mode to the on-grid mode.

[0081] As an example, this embodiment provides a circuit connection state of an on-grid and off-grid switching device at each stage of switching from the on-grid mode to the off-grid mode, which is as follows:

[0082] When the working mode of the on-grid and off-grid switching device is the on-grid mode, the grid-side relay T3 is closed, the bypass relay T2 is disconnected, the load-side relay T1 is disconnected, and the bidirectional conversion module 100 adopts constant power control;

[0083] During the process of switching the working mode of the grid-connected and off-grid switching device from the grid-connected mode to the off-grid mode, the bypass relay T2 is closed, and the PI control of the current inner loop in the constant power control of the bidirectional conversion module 100 is switched to PD control;

[0084] After the working mode of the grid-connected and off-grid switching device is switched from the grid-connected mode to the off-grid mode, the grid-side relay T3 is disconnected, the bypass relay T2 is disconnected, the load-side relay T1 is closed, and the bidirectional conversion module 100 adopts voltage-frequency conversion control.

[0085] In this embodiment, since the working mode of the grid-connected and off-grid switching device is the grid-connected mode, only the grid-side relay T3 is closed. When the working mode of the grid-connected and off-grid switching device is switched from the grid-connected mode to the off-grid mode, the bypass relay T2 is closed first, that is, the grid supplies power to the load during the transition period to ensure the smooth operation of the load. When the relay is energized, the current surges instantly. The current at the output end of the bidirectional conversion module 100 can be detected by a comparator or other device with a current detection function. If the current is greater than the set value (i.e., overcurrent), in order to limit the system from responding too quickly, the current inner loop PI control in the constant power control needs to be switched to PD control (the outer loop is still PI control), and then the output power of the bidirectional conversion module 100 is gradually reduced until it is zero. At this time, the grid-side relay T3 can be disconnected, the load-side relay T1 can be closed, and the output power of the bidirectional conversion module 100 can be gradually increased until the load requirement is met. Then the bypass relay T2 is disconnected, and the off-grid switching device completes the switching from the grid-connected mode to the off-grid mode.

[0086] It should be noted that in the basic control law, differential control can have an effect on the change of the input signal, and then generate a correction signal to reduce overshoot, increase the damping of the system, and improve the dynamic performance of the system. Because the differential control has no effect on the steady-state process, but it is very sensitive to system noise, the differential control is combined with proportional control or integral control to form a PD or PID controller, which can meet different control requirements.

[0087] Reference Figure 7 In some feasible embodiments, the above-mentioned on-grid and off-grid switching device further includes:

[0088] A filter module 500, wherein a first input end of the filter module 500 is connected to a second end of the relay module 200, a first output end of the filter module 500 is connected to the load, a second input end of the filter module 500 is connected to a third end of the relay module 200, and a second output end of the filter module 500 is connected to the power grid.

[0089] It can be understood that, in this embodiment, the filter module 500 is used to filter out electromagnetic interference in the alternating current.

[0090] Reference Figure 8 , in some feasible embodiments, the filtering module 500 includes: a load-side filtering unit 501 and a grid-side filtering unit 502;

[0091] The input end of the load-side filter unit 501 serves as the first input end of the filter module 500, and the output end of the load-side filter unit 501 serves as the first output end of the filter module 500;

[0092] The input end of the network-side filter unit 302 serves as the second input end of the filter module 500 , and the output end of the network-side filter unit 502 serves as the second output end of the filter module 500 .

[0093] As an example, the load-side filter unit 501 and the grid-side filter unit 502 in this embodiment may be EMI (Electromagnetic Interference) filters.

[0094] Please refer to Fig. 9 , Fig. 9 This is a schematic diagram of the structure of a grid-connected and off-grid switching device provided in an embodiment of the present application. Fig. 9 As shown, the bidirectional conversion module 100 in this embodiment may include an inverter circuit, a rectifier circuit, etc. composed of IGBT devices to realize the function of bidirectional conversion; the relay module 200 includes a load-side relay T1, a bypass relay T2 and a grid-side relay T3, the first end of the load-side relay T1 is connected to the output end of the bidirectional conversion module 100, and the second end of the load-side relay T1 is connected to the load; the first end of the bypass relay T2 is connected to the grid, and the second end of the bypass relay T2 is connected to the load; the first end of the grid-side relay T3 is connected to the output end of the bidirectional conversion module 100, and the second end of the grid-side relay T3 is connected to the grid. Of course, the output end of the bidirectional conversion module 100 can also be connected to a filtering circuit, and then connected to the load-side relay T1 and the grid-side relay T3 after filtering.

[0095] Please refer to Fig.10 , Fig.10A schematic diagram of the structure of an on-grid and off-grid switching device with a comparison circuit provided in an embodiment of the present application. In this embodiment, the on-grid and off-grid switching device also includes a comparison circuit 600, which includes a first input terminal, a first comparison reference terminal, a second comparison reference terminal, and an output terminal. The first input terminal of the comparison circuit 600 is connected to the bidirectional conversion module 100 and is used to access any phase current of the bidirectional conversion module 100. The first comparison reference terminal is used to access the first comparison reference current, and the second comparison reference terminal is used to access the second comparison reference current. The comparison circuit 600 can output a comparison result signal from the output terminal according to the magnitude of the current at the first input terminal, the current at the first comparison reference terminal, and the current at the second comparison reference terminal; the comparison result signal can be a level signal. Exemplarily, when the current value of the first input terminal is between the current value of the first comparison reference terminal and the current value of the second comparison reference terminal, it indicates that the current of the bidirectional conversion module 100 is normal at this time, and a low-level signal can be output. When the current value of the first input terminal is greater than the current value of the first comparison reference terminal, or the current value of the first input terminal is less than the current value of the second comparison reference terminal, it indicates that the current of the bidirectional conversion module 100 is abnormal at this time, and a high-level signal can be output to distinguish it from the low-level signal under normal circumstances. Of course, the above-mentioned high and low-level signals can be interchangeable, and this embodiment does not limit it.

[0096] The control module 300 is connected to the output end of the comparison circuit 600, and the control module 300 controls whether the bidirectional conversion module 100 works according to the comparison result signal received from the output end of the comparison circuit 600. For example, when the current in the bidirectional conversion module 100 is abnormal, that is, when the control module 300 receives a high-level signal transmitted by the comparison circuit 600, the bidirectional conversion module 100 can be controlled to stop working to prevent excessive current from causing device damage and then causing equipment failure; when the current of the bidirectional conversion module 100 is within the normal range, that is, when the control module receives a low-level signal transmitted by the comparison circuit 600, the bidirectional conversion module 100 can be controlled to continue to work normally. Therefore, through the cooperation of the comparison circuit 600 and the control module 300, the current in the bidirectional conversion module 100 can be effectively controlled during the switching process from grid-connected to off-grid, avoiding device damage and then causing equipment failure.

[0097] In some embodiments, optionally, the control module 300 can also determine whether to continue to execute the strategy of switching from the grid-connected mode to the off-grid mode according to the number of high-level signals in the comparison result signal received within a preset period. In other words, the number of times the high-level signal appears indicates the number of times the excessively high inrush current appears. The more times, the more heat accumulation in the device, which is more likely to cause damage to the device. Therefore, by setting a certain number of times, within the preset number of times, the heat accumulation will not be too high, and the switching strategy can be completed. After exceeding the preset number of times, the heat accumulation is too high, and the switching strategy is still not completed, then it is necessary to stop switching, report a fault, and ensure the safety of the device.

[0098] In some embodiments, the current value of the first comparison reference terminal and the current value of the second comparison reference terminal are adjustable. For example, the current value of the first comparison reference terminal and the current value of the second comparison reference terminal can be adjusted according to the bus voltage of the bidirectional switching module to achieve flexible adjustment, ensure the safety of the device, and smoothly complete the switching strategy.

[0099] Please refer to Fig.11 , Fig.11 This is a schematic diagram of the structure of the comparison circuit provided in the embodiment of the present application. Fig.11 As shown, in some embodiments of the present application, the comparison circuit 600 includes a first comparator U1 and a second comparator U2, the positive terminal of the first comparator U1 can be connected to the first comparison reference terminal to access the first comparison reference current, and the negative terminal of the first comparator U1 can be connected to the first access terminal, which is used to connect the bidirectional conversion module 100 to access a certain phase current of the bidirectional conversion module 100. The negative terminal of the second comparator U2 can be connected to the second comparison reference terminal to access the second comparison reference current, and the positive terminal of the second comparator U2 is also connected to the first access terminal, which is used to connect the bidirectional conversion module 100 to access a certain phase current of the bidirectional conversion module 100. The output terminal of the first comparator U1 is connected to the output terminal of the second comparator to serve as the output terminal of the comparison circuit 600, and output the comparison result signal.

[0100] In some embodiments, a first resistor R1 and a second resistor R2 are connected in series between the negative terminal of the first comparator U1 and the first access terminal, and a third resistor R3 is connected in series between the positive terminal of the first comparator U1 and the first comparison reference terminal.

[0101] In some embodiments, a sixth resistor R6 is connected in series between the negative terminal of the second comparator U2 and the second comparison reference terminal, the positive terminal of the second comparator U2 is connected to the first terminal of the seventh resistor R7, and the second terminal of the seventh resistor R7 is connected to the negative terminal of the first comparator U1. The first terminal of the seventh resistor R7 is also connected to the first terminal of the eighth resistor R8, and the second terminal of the eighth resistor R8 is connected to the output terminal of the first comparator U1 and the output terminal of the second comparator U2.

[0102] In some embodiments, a fourth resistor R4 is connected in series between the positive terminal of the first comparator U1 and the output terminal of the first comparator U1. The output terminal of the first comparator U1 is also connected to the working power supply through a fifth resistor R5. The working power supply can be set to 3.3V.

[0103] In some embodiments, the connection point between the first resistor R1 and the second resistor R2 is also grounded through the first capacitor C1. The output end of the first comparator U1 is also grounded through an RC series circuit formed by a ninth resistor R9 and a second capacitor C2, and the connection point between the ninth resistor R9 and the second capacitor C2 serves as the output end of the comparison circuit 600.

[0104] In addition, an embodiment of the present application further provides an energy storage system, which includes the on-grid and off-grid switching device provided in the above embodiment.

[0105] Since the energy storage system proposed in this embodiment includes the grid-connected and off-grid switching device proposed in the above embodiments, it has the beneficial effects of the above embodiments. For details of the specific working process and principle of the grid-connected and off-grid switching device, please refer to the grid-connected and off-grid switching devices provided in the above embodiments, which will not be described one by one here, and they are all within the protection scope of this embodiment.

[0106] It should be noted that the technical solutions of the various embodiments of the present application can be combined with each other, but it must be based on the fact that they can be implemented by technical personnel in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0107] The above are only optional embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A grid-connected and off-grid switching device, characterized in that: The on-grid and off-grid switching device comprises: a bidirectional conversion module, a relay module and a control module; The first end of the bidirectional conversion module is connected to a power source, and the second end of the bidirectional conversion module is connected to the first end of the relay module; The second end and the third end of the relay module are connected to the load and the grid respectively, the relay module includes a bypass relay, the two ends of the bypass relay are connected to the load and the grid respectively, and the relay module is used to selectively connect the power supply and the load, or connect the power supply and the grid, or connect the load and the grid; The control module is connected to the controlled ends of the bidirectional conversion module and the relay module respectively. The control module is used to control the bypass relay to close during the process of switching the working mode of the grid-connected and off-grid switching device from the grid-connected mode to the off-grid mode, and to switch the PI control of the current inner loop in the constant power control of the bidirectional conversion module to PD control.

2. The on-grid and off-grid switching device according to claim 1, characterized in that: The on-grid and off-grid switching device further comprises: A current detection module, wherein the current detection module is connected to the bidirectional conversion module and the control module respectively, and the current detection module is used to detect the current flowing through the bidirectional conversion module during the process of switching the working mode of the grid-connected and off-grid switching device from the grid-connected mode to the off-grid mode, and output an overcurrent signal to the control module when the current is greater than a preset value, so that the control module controls the bypass relay to close, and switches the PI control of the current inner loop in the constant power control of the bidirectional conversion module to PD control.

3. The on-grid and off-grid switching device according to claim 1, characterized in that: The relay module also includes: a load-side relay and a grid-side relay; The first end of the load-side relay is connected to the output end of the bidirectional conversion module, and the second end of the load-side relay is connected to the load; A first end of the grid-side relay is connected to an output end of the bidirectional conversion module, and a second end of the grid-side relay is connected to the power grid.

4. The on-grid and off-grid switching device according to claim 3, characterized in that: When the working mode of the on-grid and off-grid switching device is the off-grid mode, the load-side relay is closed, the bypass relay is disconnected, the grid-side relay is disconnected, and the bidirectional conversion module adopts voltage-frequency conversion control; When the working mode of the grid-connected and off-grid switching device is the grid-connected mode, the grid-side relay is closed, the bypass relay is disconnected, the load-side relay is disconnected, and the bidirectional conversion module adopts constant power control.

5. The on-grid and off-grid switching device according to claim 3, characterized in that: During the process of the working mode of the on-grid and off-grid switching device switching from the off-grid mode to the on-grid mode, the bypass relay is closed, and the output power of the bidirectional conversion module gradually decreases to zero.

6. The on-grid and off-grid switching device according to claim 3, characterized in that: After the working mode of the grid-connected and off-grid switching device is switched from the off-grid mode to the grid-connected mode, the load-side relay is disconnected, the bypass relay is disconnected, the grid-side relay is closed, and the bidirectional conversion module adopts constant power control.

7. The on-grid and off-grid switching device according to claim 3, characterized in that: After the working mode of the grid-connected and off-grid switching device is switched from the grid-connected mode to the off-grid mode, the grid-side relay is disconnected, the bypass relay is disconnected, the load-side relay is closed, and the bidirectional conversion module adopts voltage-frequency conversion control.

8. The on-grid and off-grid switching device according to claim 1, characterized in that: The on-grid and off-grid switching device further comprises: A comparison circuit, the comparison circuit comprising a first input terminal, a first comparison reference terminal, a second comparison reference terminal and an output terminal, the first input terminal is connected to any phase current of the bidirectional conversion module, the first comparison reference terminal is connected to a first comparison reference current, the second comparison reference terminal is connected to a second comparison reference current, and the comparison circuit outputs a comparison result signal from the output terminal according to the magnitude of the current of the first input terminal, the current of the first comparison reference terminal and the current of the second comparison reference terminal; The control module is connected to the output end of the comparison circuit, and controls whether the bidirectional conversion module works according to the comparison result signal received from the output end of the comparison circuit.

9. The on-grid and off-grid switching device according to claim 1, characterized in that: The on-grid and off-grid switching device further comprises: A filter module, wherein a first input end of the filter module is connected to a second end of the relay module, a first output end of the filter module is connected to the load, a second input end of the filter module is connected to a third end of the relay module, and a second output end of the filter module is connected to the power grid.

10. An energy storage system, characterized in that: The energy storage system comprises the on-grid and off-grid switching device according to any one of claims 1 to 9.

Images