Converter system based on BUCK-BOOST circuit

Abstract

The utility model discloses a current transformer system based on a BUCK-BOOST circuit. The converter system comprises a DAB circuit, the low-voltage side of the DAB circuit is connected to a battery through a low-voltage direct-current bus, the high-voltage side and the low-voltage side are isolated, the safety of a photovoltaic module and the safety of the battery side are improved, and the converter system further comprises one or more BUCK-BOOST circuits. And the BUCK-BOOST circuit is provided with a direct current input end connected with a photovoltaic module and a direct current output end connected with the low-voltage direct current bus, so that electric energy accessed by the photovoltaic module is boosted or reduced and then merged into the low-voltage direct current bus. The converter system adopts a BUCK-BOOST circuit, and solves the problem that PV voltage tracking of a maximum power point cannot be realized when the voltage corresponding to the maximum power point of a photovoltaic module adopted by the PV side of the converter system is greater than or close to that of a battery. The low-voltage bus is directly connected with the battery, and the PV charges the battery through the first-stage BUCK-BOOST circuit, so that the charging efficiency of the PV side to the battery is improved.

Description

Technical Field

[0001] The utility model belongs to the field of photovoltaic energy storage and relates to an inverter system based on a BUCK - BOOST circuit. Background Art

[0002] In inverter systems such as balcony photovoltaic or outdoor portable mobile power supplies, most adopt an architecture mode of DC energy storage and AC output. Among them, DC energy storage is further divided into low - voltage energy storage and high - voltage energy storage according to the level of battery voltage. As Figure 1 shown, high - voltage energy storage usually adopts a non - isolated scheme, that is, PV goes through a first - stage BOOST circuit to the high - voltage bus BAR, the battery BAT goes through a first - stage DC / DC bidirectional buck - boost circuit to the high - voltage bus BAR, and then outputs alternating current AC through DC / AC. While low - voltage energy storage needs to adopt an isolation scheme. Among them, PV goes through a first - stage BOOST circuit to the low - voltage bus, the battery is directly connected to the low - voltage bus, then goes through a DAB circuit to the high - voltage bus, and finally outputs alternating current AC through DC / AC. Currently, common isolation schemes include DAB (bidirectional DC - DC conversion circuit) and LLC resonant circuit, etc.; however, in the existing low - voltage energy storage scheme, when the voltage corresponding to the maximum power point of the photovoltaic module adopted on the PV side is greater than or close to the battery, the problem of being unable to achieve maximum power point PV voltage tracking occurs.

[0003] The above information disclosed in the background art section is only used to enhance the understanding of the background of the present application. Therefore, it may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Utility Model

[0004] In view of this, the utility model provides an inverter system based on a BUCK - BOOST circuit, which adopts a DAB isolation circuit to isolate the high - voltage side and the low - voltage side, improves the safety of the photovoltaic module and the battery side, and directly charges the battery from the PV side, improving the charging efficiency from the photovoltaic module to the battery side.

[0005] The utility model adopts the following technical solutions:

[0006] An inverter system includes a DAB circuit. The low - voltage side of the DAB circuit is connected to a battery through a low - voltage DC bus. The inverter system further includes one or more BUCK - BOOST circuits, and each BUCK - BOOST circuit has a DC input terminal for connecting to a photovoltaic module and a DC output terminal for connecting to the low - voltage DC bus, so as to step up or step down the electric energy accessed by the photovoltaic module and then incorporate it into the low - voltage DC bus.

[0007] In a preferred embodiment, the inverter system includes a plurality of the BUCK - BOOST circuits, and the DC input terminal of each BUCK - BOOST circuit is connected to at least one path of photovoltaic modules.

[0008] In a more preferred embodiment, the DC output terminals of the plurality of BUCK-BOOST circuits are all connected to the low-voltage DC bus.

[0009] In a preferred embodiment, the BUCK-BOOST circuit includes a first switch module, a second switch module, a first capacitor, a second capacitor, an inductor, a first diode, and a second diode. The first end of the first switch module and the positive electrode of the first capacitor are connected to the positive electrode of the DC input terminal. The inductor and the negative electrode of the first diode are connected to the second end of the first switch module. The positive electrode of the second diode and the first end of the second switch module are connected to the other end of the inductor. The negative electrode of the second diode and the positive electrode of the second capacitor are connected to the positive electrode of the low-voltage DC bus. The negative electrode of the second capacitor, the positive electrode of the first diode, the second end of the second switch module, and the negative electrode of the second capacitor are connected between the negative electrode of the DC input terminal and the negative electrode of the low-voltage DC bus.

[0010] In a more preferred embodiment, the first switch module includes a first MOS transistor. The drain of the first MOS transistor is connected to the positive electrode of the DC input terminal. The source of the first MOS transistor is connected to the inductor. The gate of the first MOS transistor is connected to the control module of the converter system. A diode is reversely connected in parallel between the source and the drain of the first MOS transistor.

[0011] In a further preferred embodiment, the second switch module includes a second MOS transistor. The drain of the second MOS transistor is connected to the inductor. The source of the second MOS transistor is connected to the negative electrode of the DC input terminal. The gate of the second MOS transistor is connected to the control module of the converter system. A diode is reversely connected in parallel between the source and the drain of the second MOS transistor.

[0012] In a preferred embodiment, the BUCK-BOOST circuit includes a first switch module, a second switch module, a third switch module, a fourth switch module, a first capacitor, a second capacitor, and an inductor. The first end of the first switch module and the positive electrode of the first capacitor are connected to the positive electrode of the DC input terminal. The inductor and the first end of the second switch module are connected to the second end of the first switch module. The first end of the third switch module and the first end of the fourth switch module are connected to the other end of the inductor. The second end of the fourth switch module and the positive electrode of the second capacitor are connected to the positive electrode of the low-voltage DC bus. The negative electrode of the second capacitor, the second end of the second switch module, the second end of the third switch module, and the negative electrode of the second capacitor are connected between the negative electrode of the DC input terminal and the negative electrode of the low-voltage DC bus.

[0013] In a more preferred embodiment, the first switching module includes a first MOS transistor. The drain of the first MOS transistor is connected to the positive pole of the DC input terminal. The source of the first MOS transistor is connected to the inductor. The gate of the first MOS transistor is connected to the control module of the converter system. Further, a diode is reversely connected in parallel between the source and the drain of the first MOS transistor.

[0014] In a preferred embodiment, the second switching module includes a second MOS transistor. The drain of the second MOS transistor is connected to the inductor. The source of the second MOS transistor is connected to the negative pole of the low-voltage DC bus. The gate of the second MOS transistor is connected to the control module of the converter system. Further, a diode is reversely connected in parallel between the source and the drain of the second MOS transistor.

[0015] In a preferred embodiment, the third switching module includes a third MOS transistor. The drain of the third MOS transistor is connected to the inductor. The source of the third MOS transistor is connected to the negative pole of the DC input terminal. The gate of the third MOS transistor is connected to the control module of the converter system. Further, a diode is reversely connected in parallel between the source and the drain of the third MOS transistor.

[0016] In a preferred embodiment, the fourth switching module includes a fourth MOS transistor. The source of the fourth MOS transistor is connected to the inductor. The drain of the fourth MOS transistor is connected to the positive pole of the DC output terminal. The gate of the fourth MOS transistor is connected to the control module of the converter system. Further, a diode is reversely connected in parallel between the source and the drain of the fourth MOS transistor.

[0017] In a preferred embodiment, the DAB circuit is connected to the DC / AC conversion module through the high-voltage DC bus on its output side. The DC / AC conversion module is respectively connected to the power grid and the load through the grid-connected and off-grid relay modules after passing through the filter circuit, so as to convert the direct current output by the DAB circuit into alternating current and supply it to the power grid or the load.

[0018] The present utility model adopts the above scheme and has the following advantages:

[0019] In the converter system of the utility model, the battery and the DAB circuit are connected through a low-voltage DC bus, the power of the photovoltaic module is boosted and stepped up by the BUC-BOOST circuit and then merged into the low-voltage DC bus, the power of the low-voltage DC bus is converted by the DAB circuit and then transmitted to the rear-end power grid or load through the high-voltage DC bus, thereby isolating the photovoltaic module and the battery from the high-voltage side of the converter system, and improving the safety of the photovoltaic module side and the battery side; in addition, the power of the photovoltaic module can charge the battery after passing through the primary BUCK-BOOST circuit, thereby improving the charging efficiency of the photovoltaic module to the battery, and photovoltaic modules of various specifications can be flexibly selected.

[0020] In a further preferred solution, the BUCK-BOOST circuit has a high degree of control freedom, can realize multiple control modes, and improve the power density of buck-boost conversion. The BUCK conversion module and the BOOST conversion module are cascaded, which has the advantages of input and output polarity and buck-boost, lower stress on the switch tube and diode, and fewer passive components compared to other non-isolated bidirectional DC-DC converter topologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 A block diagram of a converter system using a high-voltage energy storage solution.

[0023] Figure 2 It is a module diagram of a converter system according to an embodiment of the utility model.

[0024] Figure 3 The topological diagram of a BUCK-BOOST circuit according to an embodiment of the utility model.

[0025] Figure 4 FIG. 4 is a topological diagram of another BUCK-BOOST circuit according to an embodiment of the utility model.

[0026] Figure 5 It is a module diagram of another converter system according to an embodiment of the utility model. DETAILED DESCRIPTION

[0027] The following will elaborate on the preferred embodiments of the present invention in conjunction with the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art. It should be noted here that the description of these embodiments is for helping to understand the present invention, but does not constitute a limitation to the present invention.

[0028] This embodiment provides a converter system, particularly a converter system based on a balcony photovoltaic or outdoor portable mobile power supply system. Referring to Figure 2 as shown, the converter system includes a DAB circuit 5. The low-voltage side of the DAB circuit 5 is connected to a battery 4 through a low-voltage DC bus 3. A photovoltaic module 1 is connected to the low-voltage DC bus 3 through a BUCK-BOOST circuit 2. The BUCK-BOOST circuit 2 has a DC input terminal for connecting to the photovoltaic module 1 and a DC output terminal for connecting to the low-voltage DC bus 3, so as to boost or buck the electric energy accessed by the photovoltaic module 1 and then incorporate it into the low-voltage DC bus 3. The DAB circuit 5 is connected to a DC / AC conversion module 7 through a high-voltage DC bus 6 on its output side. The DC / AC conversion module 7 is respectively connected to a power grid and a load through a filter circuit and a grid-connected and off-grid relay module, so as to convert the high-voltage direct current output by the DAB circuit 5 into alternating current and supply it to the power grid or the load.

[0029] This system uses the low-voltage battery 4 as the low-voltage DC bus 3. Considering that the voltage of the battery 4 may be less than the DC input voltage, the photovoltaic module 1 is directly incorporated into the low-voltage DC bus 3 after being stepped up or down by the BUCK-BOOST circuit 2. The low-voltage DC bus 3 is incorporated into the high-voltage DC bus 6 through the DAB circuit 5, and the high-voltage DC bus 6 is then converted into alternating current by the DC / AC conversion module 7 and output to the power grid or the load. This topological structure realizes the purpose of isolating the photovoltaic module 1 and the battery 4 from the high-voltage side of the system, greatly improving the safety of the photovoltaic module 1 side and the battery 4 side. At the same time, since the battery 4 directly serves as the bus on the low-voltage side, the photovoltaic module 1 only needs to pass through one-level BUCK-BOOST circuit 2 to charge the battery 4, improving the charging efficiency from the photovoltaic to the battery 4 and enabling the selection of more specifications of photovoltaic panels.

[0030] Figure 3 One of the BUCK-BOOST circuits 2 is shown. As Figure 3As shown, the BUCK-BOOST circuit 2 includes a first switch module 211, a second switch module 212, a first capacitor C1, a second capacitor C2, an inductor L, a first diode D1, and a second diode D2. The first end of the first switch module 211 and the positive electrode of the first capacitor C1 are connected to the positive electrode of the DC input terminal (the positive electrode of the photovoltaic module 1). The inductor L and the negative electrode of the first diode D1 are connected to the second end of the first switch module 211. The positive electrode of the second diode D2 and the first end of the second switch module 212 are connected to the other end of the inductor L. The negative electrode of the second diode D2 and the positive electrode of the second capacitor C2 are connected to the positive electrode of the low-voltage DC bus 3. The negative electrode of the second capacitor C2, the positive electrode of the first diode D1, the second end of the second switch module 212, and the negative electrode of the second capacitor C2 are connected between the negative electrode of the DC input terminal (the negative electrode of the photovoltaic module 1) and the negative electrode of the low-voltage DC bus 3.

[0031] The first switch module 211 includes a first MOS transistor Tbuck. The drain of the first MOS transistor Tbuck is connected to the positive electrode of the DC input terminal (the positive electrode of the photovoltaic module 1). The source of the first MOS transistor Tbuck is connected to the inductor L. The gate of the first MOS transistor Tbuck is connected to the control module of the converter system. A diode is reversely connected in parallel between the source and the drain of the first MOS transistor Tbuck.

[0032] The second switch module 212 includes a second MOS transistor Tbst. The drain of the second MOS transistor Tbst is connected to the inductor L. The source of the second MOS transistor Tbst is connected to the negative electrode of the DC input terminal (the negative electrode of the photovoltaic module 1). The gate of the second MOS transistor Tbst is connected to the control module of the converter system. A diode is reversely connected in parallel between the source and the drain of the second MOS transistor Tbst.

[0033] This topology cascades a BUCK converter and a BOOST converter. Compared with other non-isolated bidirectional DC-DC converter topologies, it has the advantages of the same polarity of input and output, the ability to step up and down voltage, lower stress on the switching tubes and diodes, and fewer passive components.

[0034] Figure 4 Another BUCK-BOOST circuit 2 is shown. Refer to Figure 4As shown, the BUCK - BOOST circuit 2 includes a first switch module 221, a second switch module 222, a third switch module 223, a fourth switch module 224, a first capacitor C1, a second capacitor C2, and an inductor L. The first terminal of the first switch module 221 and the positive electrode of the first capacitor C1 are connected to the positive electrode of the DC input terminal (the positive electrode of the photovoltaic module 1). The inductor L and the first terminal of the second switch module 222 are connected to the second terminal of the first switch module 221. The first terminal of the third switch module 223 and the first terminal of the fourth switch module 224 are connected to the other end of the inductor L. The second terminal of the fourth switch module 224 and the positive electrode of the second capacitor C2 are connected to the positive electrode of the low - voltage DC bus 3. The negative electrode of the second capacitor C2, the second terminal of the second switch module 222, the second terminal of the third switch module 223 are connected between the negative electrode of the DC input terminal (the negative electrode of the photovoltaic module 1) and the negative electrode of the low - voltage DC bus 3.

[0035] The first switch module 221 includes a first MOS transistor T1. The drain of the first MOS transistor T1 is connected to the positive electrode of the DC input terminal (the positive electrode of the photovoltaic module 1). The source of the first MOS transistor T1 is connected to the inductor L. The gate of the first MOS transistor T1 is connected to the control module of the converter system. Further, a diode is reversely connected in parallel between the source and the drain of the first MOS transistor T1.

[0036] The second switch module 222 includes a second MOS transistor T2. The drain of the second MOS transistor T2 is connected to the inductor L. The source of the second MOS transistor T2 is connected to the negative electrode of the low - voltage DC bus 3. The gate of the second MOS transistor T2 is connected to the control module of the converter system. Further, a diode is reversely connected in parallel between the source and the drain of the second MOS transistor T2.

[0037] The third switch module 223 includes a third MOS transistor T3. The drain of the third MOS transistor T3 is connected to the inductor L. The source of the third MOS transistor T3 is connected to the negative electrode of the DC input terminal (the negative electrode of the photovoltaic module 1). The gate of the third MOS transistor T3 is connected to the control module of the converter system. Further, a diode is reversely connected in parallel between the source and the drain of the third MOS transistor T3.

[0038] The fourth switch module 224 includes a fourth MOS transistor T4. The source of the fourth MOS transistor T4 is connected to the inductor L. The drain of the fourth MOS transistor T4 is connected to the positive electrode of the DC output terminal. The gate of the fourth MOS transistor T4 is connected to the control module of the converter system. Further, a diode is reversely connected in parallel between the source and the drain of the fourth MOS transistor T4.

[0039] The BUCK - BOOST circuit 2 includes four MOS transistors. Compared with Figure 3The proposed solution has a higher degree of freedom, so it can achieve multiple control methods and improve the power density of the BUCK-BOOST circuit 2. This topology cascades a BUCK converter and a BOOST converter. Compared with other non-isolated bidirectional DC-DC converter topologies, it has the advantages of the same polarity of input and output and the ability to step up and down voltage, lower stress on switching tubes and diodes, and fewer passive components.

[0040] Referring to Figure 5 As shown, the converter system may include multiple BUCK-BOOST circuits 2. The DC input terminals of each BUCK-BOOST circuit 2 are connected to at least one path of photovoltaic modules 11, such as Figure 5 PV1 and PV2 shown. The DC output terminals of multiple BUCK-BOOST circuits 2 are all connected to the same low-voltage DC bus 3, and the battery 4 is charged through this low-voltage DC bus 3. The DAB circuit 5 is connected to the DC / AC conversion module 7 through the high-voltage DC bus 6 on its output side. The DC / AC conversion module 7 is connected to the power grid 8 and the load 9 through the grid-connected and off-grid relay module 10 after passing through the filter circuit, so as to convert the high-voltage direct current output by the DAB circuit 5 into alternating current and supply it to the power grid 8 or the load 9.

[0041] In this converter system, two paths of photovoltaic modules 1, namely PV1 and PV2, after input, pass through EMI filtering and BUCK-BOOST, and the circuits are aggregated to the low-voltage DC bus 3. The battery 4 is directly connected to the low-voltage DC bus 3. The system can adjust whether the PV side is in the BUCK mode or the BOOST mode according to the voltages of the photovoltaic modules 1 and the battery 4, and adjust the duty cycle of the BUCK-BOOST circuit 2 according to the voltage difference to make the output voltage consistent with the voltage of the battery 4; when the battery 4 or the photovoltaic modules 1 transmit energy to the grid side, control the phase-shift angle of the two unit bridges on both sides of the DAB circuit 5 (bidirectional active bridge circuit), so that the low-voltage side unit bridge leads the high-voltage side unit bridge, and the power flows from the low-voltage DC bus 3 to the high-voltage DC bus 6. The high-voltage DC bus 6 then outputs industrial-frequency alternating current through the inverter circuit (DC / AC conversion module 7) to be grid-connected to 8 or supply power to the load 9; when it is necessary to charge the battery 4 from the grid, the grid voltage is rectified to the high-voltage DC bus 6 through the inverter bridge, and control the phase-shift angle of the two unit bridges on both sides of the DAB circuit 5 (bidirectional active bridge circuit), so that the high-voltage side unit bridge leads the low-voltage side unit bridge, and the power flows from the high-voltage DC bus 6 to the low-voltage DC bus 3 to realize the function of charging the battery 4 from the grid 8. When the grid power fails, use the relays RLY1 and RLY2 to realize the grid-connected and off-grid switching, and the photovoltaic modules 1 and the battery 4 continue to supply power to the load 9.

[0042] The converter system adopts a low-voltage energy storage mode, using the low-voltage battery 4 as the system's low-voltage bus. The photovoltaic module 1 is stepped up or down through a first-stage BUCK-BOOST circuit 2 and then incorporated into the low-voltage DC bus 3. The low-voltage DC bus 3 is boosted to the high-voltage DC bus 6 through a DAB circuit 5, and then converted into alternating current through a first-stage DC / AC conversion module 7 and incorporated into the power grid or output to the load. Moreover, relays RLY1 and RLY2 of the grid-connected and off-grid relay module are used at the inverter output end to achieve automatic grid-connected and off-grid switching.

[0043] The converter system of the above embodiment has the following advantages: 1. The photovoltaic module 1 is stepped up or down through a dual-switch or four-switch BUCK-BOOST circuit 2 and incorporated into the low-voltage DC bus 3. The battery 4 is directly connected to the low-voltage DC bus 3. The mode of the BUCK-BOOST circuit 2 can be adjusted according to the magnitudes of the input and output voltages on the photovoltaic module 1 side, and the working mode can be automatically adjusted when the input and output voltages change. It can ensure normal operation of the photovoltaic module 1 side even when the input voltage is high, and more photovoltaic panel specifications can be selected. 2. Due to the presence of the grid-connected and off-grid relay, automatic grid-connected and off-grid switching can be achieved. When the power grid is powered off, it can automatically switch to the off-grid mode to supply power to the load, improving the reliability of the machine. In the prior art, when the maximum power point corresponding voltage of the photovoltaic module adopted on the PV side of the converter system is greater than or similar to that of the battery, maximum power point PV voltage tracking cannot be achieved. However, the solution of this embodiment replaces the BOOST circuit with a BUCK-BOOST circuit, which can solve the above problem and improve the efficiency of the PV side. The converter system adopts a DAB isolation circuit to isolate the high-voltage side and the low-voltage side, improving the safety of the PV side and the battery side.

[0044] As shown in this specification and the claims, the terms "comprising" and "including" only indicate the inclusion of the clearly identified steps and elements, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements. The term "and / or" used herein includes any combination of one or more of the related listed items.

[0045] It can be further understood that in this disclosure, "a plurality of" means two or more, and other quantifiers are similar.

[0046] It should be noted that unless otherwise specified, when a feature is referred to as "connected" to another feature, it can be directly connected to the other feature or indirectly connected to the other feature.

[0047] The above embodiments are only for illustrating the technical concept and features of the present utility model, and are a preferred embodiment. The purpose is to enable those skilled in the art to understand the content of the present utility model and implement it accordingly, and it is not intended to limit the protection scope of the present utility model. Any equivalent transformation or modification made according to the principle of the present utility model should be covered within the protection scope of the present utility model.

Claims

1. A converter system based on a BUCK-BOOST circuit, including a DAB circuit, wherein the low-voltage side of the DAB circuit is connected to a battery through a low-voltage DC bus, and is characterized in that, The converter system further includes one or more BUCK - BOOST circuits. The BUCK - BOOST circuit has a DC input terminal for connecting to a photovoltaic module and a DC output terminal for connecting to the low - voltage DC bus, so as to step up or step down the electrical energy accessed by the photovoltaic module and then incorporate it into the low - voltage DC bus.

2. The converter system based on the BUCK - BOOST circuit according to claim 1, characterized in that, The converter system includes a plurality of the BUCK - BOOST circuits, and the DC input terminal of each BUCK - BOOST circuit is connected to at least one path of photovoltaic modules.

3. The converter system based on the BUCK-BOOST circuit according to claim 2, wherein The DC output terminals of the plurality of BUCK - BOOST circuits are all connected to the low - voltage DC bus.

4. The converter system based on the BUCK-BOOST circuit according to claim 1, wherein The BUCK - BOOST circuit includes a first switch module, a second switch module, a first capacitor, a second capacitor, an inductor, a first diode, and a second diode. The first end of the first switch module and the positive electrode of the first capacitor are connected to the positive electrode of the DC input terminal. The inductor and the negative electrode of the first diode are connected to the second end of the first switch module. The positive electrode of the second diode and the first end of the second switch module are connected to the other end of the inductor. The negative electrode of the second diode and the positive electrode of the second capacitor are connected to the positive electrode of the low - voltage DC bus. The negative electrode of the second capacitor, the positive electrode of the first diode, the second end of the second switch module, and the negative electrode of the second capacitor are connected between the negative electrode of the DC input terminal and the negative electrode of the low - voltage DC bus.

5. The converter system based on the BUCK-BOOST circuit according to claim 4, wherein The first switch module includes a first MOS transistor. The drain of the first MOS transistor is connected to the positive electrode of the DC input terminal. The source of the first MOS transistor is connected to the inductor. The gate of the first MOS transistor is connected to the control module of the converter system. A diode is reversely connected in parallel between the source and the drain of the first MOS transistor.

6. The converter system based on the BUCK-BOOST circuit according to claim 4 or 5, characterized in that, The second switch module includes a second MOS transistor. The drain of the second MOS transistor is connected to the inductor. The source of the second MOS transistor is connected to the negative electrode of the DC input terminal. The gate of the second MOS transistor is connected to the control module of the converter system. A diode is reversely connected in parallel between the source and the drain of the second MOS transistor.

7. The converter system based on the BUCK-BOOST circuit according to claim 1, wherein The BUCK - BOOST circuit includes a first switch module, a second switch module, a third switch module, a fourth switch module, a first capacitor, a second capacitor, and an inductor. The first end of the first switch module and the positive electrode of the first capacitor are connected to the positive electrode of the DC input terminal. The inductor and the first end of the second switch module are connected to the second end of the first switch module. The first end of the third switch module and the first end of the fourth switch module are connected to the other end of the inductor. The second end of the fourth switch module and the positive electrode of the second capacitor are connected to the positive electrode of the low - voltage DC bus. The negative electrode of the second capacitor, the second end of the second switch module, the second end of the third switch module, and the negative electrode of the second capacitor are connected between the negative electrode of the DC input terminal and the negative electrode of the low - voltage DC bus.

8. The converter system based on the BUCK - BOOST circuit according to claim 7, wherein, The first switching module includes a first MOS transistor. The drain of the first MOS transistor is connected to the positive pole of the DC input terminal. The source of the first MOS transistor is connected to the inductor. The gate of the first MOS transistor is connected to the control module of the converter system. A diode is reversely connected in parallel between the source and the drain of the first MOS transistor. The second switching module includes a second MOS transistor. The drain of the second MOS transistor is connected to the inductor. The source of the second MOS transistor is connected to the negative pole of the low-voltage DC bus. The gate of the second MOS transistor is connected to the control module of the converter system. A diode is reversely connected in parallel between the source and the drain of the second MOS transistor.

9. The converter system based on the BUCK-BOOST circuit according to claim 7, characterized in that, The third switching module includes a third MOS transistor. The drain of the third MOS transistor is connected to the inductor. The source of the third MOS transistor is connected to the negative pole of the DC input terminal. The gate of the third MOS transistor is connected to the control module of the converter system. A diode is reversely connected in parallel between the source and the drain of the third MOS transistor. The fourth switching module includes a fourth MOS transistor. The source of the fourth MOS transistor is connected to the inductor. The drain of the fourth MOS transistor is connected to the positive pole of the DC output terminal. The gate of the fourth MOS transistor is connected to the control module of the converter system. A diode is reversely connected in parallel between the source and the drain of the fourth MOS transistor.

10. The converter system based on the BUCK - BOOST circuit according to claim 1, characterized in that, The DAB circuit is connected to the DC / AC conversion module through the high-voltage DC bus on its output side. The DC / AC conversion module is connected to the power grid and the load through the grid-connected and off-grid relay modules after passing through the filter circuit, so as to convert the direct current output by the DAB circuit into alternating current and supply it to the power grid or the load.

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