Protection circuit, flying capacitor three-level BUCK circuit and photovoltaic hydrogen production power supply

Abstract

The utility model discloses a protection circuit, a flying capacitor three-level BUCK circuit and a photovoltaic hydrogen production power supply, relates to the technical field of photovoltaic hydrogen production power supply products, is used for realizing breakdown protection of an IGBT (Insulated Gate Bipolar Translator) in the flying capacitor three-level BUCK circuit, and provides the protection circuit aiming at the problem of bus voltage oscillation caused by a traditional scheme. The voltage oscillation generated when an IGBT device in the flying capacitor three-level BUCK circuit is turned off and turned on can be restrained, the high-frequency switching circuit is suitable for being applied to a high-frequency switch, the loss of the absorption circuit is small, and bus voltage oscillation is not prone to being caused. The IGBT device can be prevented from being broken down by the turn-off peak voltage, the quality of the output voltage of the flying capacitor three-level BUCK circuit can be optimized, the IGBT withstand voltage grade selection is reduced, and the product material cost is saved.

Description

Technical Field

[0001] The utility model relates to the field of photovoltaic hydrogen production power supply products, in particular to a protection circuit, a flying capacitor three-level BUCK circuit and a photovoltaic hydrogen production power supply. Background Art

[0002] In photovoltaic hydrogen production power products, in order to improve the performance and efficiency of the power system, a common solution is to apply the flying capacitor three-level BUCK circuit (Buck circuit is also called step-down conversion circuit) to photovoltaic hydrogen production power products. Insulated Gate Bipolar Transistor (IGBT) plays the key role of switch in the flying capacitor three-level BUCK circuit, responsible for controlling the direction and size of the current. Its fast switching characteristics enable the circuit to efficiently realize voltage conversion and control. At the same time, the voltage and current resistance capabilities of IGBT also ensure the stable operation of the circuit in high-voltage and high-current environments.

[0003] When the IGBT is turned off, if there is an inductor component in the circuit, a spike voltage will be generated at the moment of turn-off. If this spike voltage exceeds the highest peak voltage of the IGBT device, the IGBT may be broken down and damaged.

[0004] At present, a common protection scheme is to connect an absorption capacitor in parallel at both ends of the IGBT device to absorb the peak voltage generated when the IGBT device is turned off to prevent the IGBT from being broken down. However, although this scheme is easy to implement, the bus voltage is prone to oscillation due to the LC resonance formed by the parasitic inductance of the main circuit and the absorption capacitor, which brings additional problems.

[0005] Therefore, technicians in this field are in urgent need of a protection circuit for achieving breakdown protection of the IGBT in a flying capacitor three-level BUCK circuit without causing additional problems such as bus voltage oscillation. Utility Model Content

[0006] The utility model aims to provide a protection circuit, a flying capacitor three-level BUCK circuit and a photovoltaic hydrogen production power supply, so as to realize the breakdown protection of the IGBT in the flying capacitor three-level BUCK circuit without generating additional problems such as bus voltage oscillation.

[0007] In order to solve the above technical problems, the utility model provides a protection circuit, including: a first absorption capacitor, a second absorption capacitor, a first discharge resistor, a second discharge resistor, a first buffer diode and a second buffer diode;

[0008] Wherein, the first end of the first absorption capacitor is connected to the collector of the first switch tube in the flying capacitor three-level BUCK circuit, the second end of the first absorption capacitor is connected to the positive electrode of the first buffer diode and the first end of the first discharge resistor; the cathode of the first buffer diode is connected to the emitter of the first switch tube; the second end of the first discharge resistor is connected to the emitter of the second switch tube in the flying capacitor three-level BUCK circuit;

[0009] The first end of the second discharge resistor is connected to the collector of the first switch tube, and the second end of the second discharge resistor is connected to the cathode of the second buffer diode and the first end of the second absorption capacitor; the anode of the second buffer diode is connected to the collector of the second switch tube; and the second end of the second absorption capacitor is connected to the emitter of the second switch tube.

[0010] In a possible embodiment, the first buffer diode and the second buffer diode are fast recovery diodes.

[0011] In a possible embodiment, the internal inductance of the first absorption capacitor and the second absorption capacitor is less than 45 nH.

[0012] In order to solve the above technical problems, the utility model also provides a flying capacitor three-level BUCK circuit, comprising: a DC voltage source, a main circuit switch, a pre-charge circuit switch, a pre-charge current limiting resistor, an input filter capacitor, a flying capacitor, a first switch tube, a second switch tube, a freewheeling diode, an inductor and a load resistor; and also comprising: the protection circuit as described above;

[0013] Wherein, the protection circuit is connected in parallel at two ends of an IGBT half-bridge module consisting of the first switch tube and the second switch tube connected in series.

[0014] In a possible embodiment, it further includes: an output filter capacitor;

[0015] The output filter capacitor is connected in parallel across the load resistor for output filtering.

[0016] In order to solve the above technical problems, the utility model also provides a photovoltaic hydrogen production power supply, including: the flying capacitor three-level BUCK circuit as described above.

[0017] In a possible embodiment, it further includes: a first water cooling plate;

[0018] A protection circuit is disposed on the first water cooling plate, and the first water cooling plate is used to cool the protection circuit.

[0019] In a possible embodiment, it further includes: a second water cooling plate;

[0020] The second water cooling plate is provided with a power device in a flying capacitor three-level BUCK circuit, and the second water cooling plate is used to cool the power device;

[0021] Wherein, the power device includes a first switching tube and a second switching tube.

[0022] In a possible embodiment, the invention further includes: a copper busbar;

[0023] The copper busbar is used to realize the protection circuit deployed on the first water-cooling plate, and is connected to the circuit between the first switch tube and the second switch tube deployed on the second water-cooling plate.

[0024] In a possible embodiment, the first water-cooling plate and the second water-cooling plate are arranged relative to each other;

[0025] The first parallel end of the protection circuit disposed on the first water-cooling plate is arranged opposite to the collector of the first switch tube disposed on the second water-cooling plate;

[0026] The second parallel end of the protection circuit disposed on the first water-cooling plate is arranged opposite to the emitter of the second switch tube disposed on the second water-cooling plate;

[0027] Among them, the first parallel end is the first end of the first absorption capacitor and the first end of the second discharge resistor connected in the protection circuit; the second parallel end is the second end of the second absorption capacitor and the second end of the first discharge resistor connected in the protection circuit.

[0028] The utility model provides a protection circuit. When the switch tube IGBT in the flying capacitor three-level BUCK circuit is turned off, the load current will charge the absorption capacitor through the buffer diode; so that the voltage at both ends of the absorption capacitor rises slowly from 0 during the charging period; thereby slowing down the voltage change rate (du / dt); based on this, voltage mutations can be suppressed, that is, the generation of overvoltage can be suppressed; in addition, slowing down the voltage change rate can also reduce the switching loss of the switch tube and increase the life of the IGBT device. Similarly, when the switch tube IGBT is turned on, the energy of the absorption capacitor will be discharged to the switch tube through the discharge resistor; at this time, the role of the discharge resistor is to limit the size of the discharge current, avoid and suppress the oscillation of the buffer circuit, and prevent the IGBT device from being broken down.

[0029] This circuit can suppress the voltage oscillation generated by the IGBT device in the flying capacitor three-level BUCK circuit when it is turned off and on. It is suitable for high-frequency switching applications, has low loss in the absorption circuit, and is not easy to cause bus voltage oscillation. It can prevent the IGBT device from being broken down by the turn-off spike voltage, optimize the output voltage quality of the flying capacitor three-level BUCK circuit, reduce the IGBT withstand voltage level selection, and save product material costs.

[0030] The flying capacitor three-level BUCK circuit and photovoltaic hydrogen production power supply provided by the utility model correspond to the above protection circuit and have the same effect as above. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present utility model, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 This is a structural diagram of a common transcapacitor three-level BUCK circuit;

[0033] Figure 2 A structural diagram of a protection circuit and a flying capacitor three-level BUCK circuit provided by the utility model;

[0034] Figure 3 An exploded diagram of a flying capacitor three-level BUCK circuit portion in a photovoltaic hydrogen production power supply provided by the utility model;

[0035] Among them, 1 is a protection circuit, 2 is an IGBT half-bridge module, 3 is a first water-cooled plate, 4 is a freewheeling diode, 5 is an IGBT driver board, 6 is a second water-cooled plate, 7 is an absorption capacitor, 8 is a buffer diode, 9 is a discharge diode, and 10 is a copper busbar. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of them. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the utility model.

[0037] The core of the utility model is to provide a protection circuit, a flying capacitor three-level BUCK circuit and a photovoltaic hydrogen production power supply.

[0038] In order to enable those skilled in the art to better understand the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0039] At present, in order to further improve the performance and efficiency of photovoltaic hydrogen production power products, flying capacitor three-level BUCK circuit (Buck circuit is also called step-down conversion circuit) is usually applied to photovoltaic hydrogen production power products. The flying capacitor three-level BUCK circuit can more effectively realize voltage conversion and control, improve the quality of output voltage, and reduce harmonic distortion, thereby optimizing the operation effect of the entire power system. At the same time, combined with the technical characteristics of photovoltaic hydrogen production power, it can better utilize solar energy, a renewable energy source, to achieve efficient and clean power supply and hydrogen production.

[0040] like Figure 1 A common flying capacitor three-level BUCK circuit is as follows Figure 1 As shown, it includes: a DC voltage source Udc, a main circuit switch K1, a pre-charge circuit switch K2, a pre-charge current limiting resistor R1, an input filter capacitor C1, a flying capacitor Cfly, a first switch tube S1, a second switch tube S2, freewheeling diodes VD1 and VD2, an inductor L1 and a load resistor R.

[0041] Among them, the switch tubes S1 and S2 are insulated gate bipolar transistors (IGBT), which play a key switching role in the flying capacitor three-level BUCK circuit. IGBT is responsible for controlling the direction and size of the current, and its fast switching characteristics enable the circuit to efficiently achieve voltage conversion and control. At the same time, the voltage and current resistance capabilities of IGBT also ensure the stable operation of the circuit in a high-voltage and high-current environment.

[0042] However, when the IGBT is turned off, if there is an inductor component in the circuit, a spike voltage will be generated at the moment of turn-off. If this spike voltage exceeds the highest peak voltage of the IGBT device, the IGBT may be broken down and damaged. This overvoltage damage can be subdivided into collector-gate overvoltage, gate-emitter overvoltage, high voltage change rate (du / dt) overvoltage and other types. In order to avoid the harm of IGBT spike voltage, it is usually necessary to take some measures in the design to suppress or eliminate the spike voltage, such as optimizing the drive circuit design, adding a suitable protection circuit, etc.

[0043] In the related art, a common protection circuit is Figure 1As shown, it includes an absorption capacitor Cs. The absorption capacitor Cs is connected in parallel at both ends of the IGBT half-bridge module composed of the first switch tube S1 and the second switch tube S2 connected in series, and is used to absorb the IGBT turn-off peak voltage. This protection circuit is simple to implement, but the parasitic inductance of the main circuit and the absorption capacitor will form an inductor-capacitor (LC) resonance, at which time the bus voltage is prone to oscillation, which in turn brings additional problems.

[0044] In order to solve the above problems, the present application provides a protection circuit 1, such as Figure 2 As shown, it includes: a first absorption capacitor Cs1, a second absorption capacitor Cs2, a first discharge resistor Rs1, a second discharge resistor Rs2, a first buffer diode VDs1 and a second buffer diode VDs2;

[0045] Wherein, the first end of the first absorption capacitor Cs1 is connected to the collector of the first switch tube S1 in the flying capacitor three-level BUCK circuit, the second end of the first absorption capacitor Cs1 is connected to the positive electrode of the first buffer diode VDs1 and the first end of the first discharge resistor Rs1; the cathode of the first buffer diode VDs1 is connected to the emitter of the first switch tube S1; the second end of the first discharge resistor Rs1 is connected to the emitter of the second switch tube S2 in the flying capacitor three-level BUCK circuit;

[0046] A first end of the second discharge resistor Rs2 is connected to the collector of the first switch tube S1, and a second end of the second discharge resistor Rs2 is connected to the cathode of the second buffer diode VDs2 and the first end of the second absorption capacitor Cs2; an anode of the second buffer diode VDs2 is connected to the collector of the second switch tube S2; and a second end of the second absorption capacitor Cs2 is connected to the emitter of the second switch tube S2.

[0047] It should be noted that when the circuit is applied to a flying capacitor three-level BUCK circuit, in order to further improve the performance, the inductance value in the loop should be minimized.

[0048] Specifically, this embodiment provides a possible implementation scheme for reducing the loop inductance value:

[0049] The first snubber diode VDs1 and the second snubber diode VDs2 are fast recovery diodes.

[0050] Fast recovery diode (FRD) is a semiconductor diode with good switching characteristics and short reverse recovery time. Because its base region is very thin and the reverse recovery charge is very small, the fast recovery diode has a short reverse recovery time, a low forward voltage drop, a high reverse breakdown voltage (withstand voltage), and a lower internal inductance.

[0051] In addition, this embodiment also provides another possible implementation scheme for reducing the loop inductance value:

[0052] The internal inductance of the first absorption capacitor Cs1 and the second absorption capacitor Cs2 is less than 45 nH.

[0053] This embodiment reduces the loop inductance by limiting the internal inductance of the selected first absorption capacitor Cs1 and the second absorption capacitor Cs2. However, it should be noted that the capacitance of the absorption capacitor should not be too small to ensure the effect of suppressing overvoltage through charging and discharging.

[0054] When the protection circuit 1 provided in the present application is applied to the flying capacitor three-level BUCK circuit, when the IGBT is turned off, the load current will charge the absorption capacitors Cs1 and Cs2 through the buffer diodes VDs1 and VDs2; so that the voltage at both ends of the absorption capacitors Cs1 and Cs2 slowly rises from 0 during the charging period; thereby slowing down the voltage change rate (du / dt); based on this, the voltage mutation can be suppressed, that is, the generation of overvoltage can be suppressed; in addition, slowing down the voltage change rate can also reduce the switching loss of the switch tubes S1 and S2 and improve the life of the IGBT device. Similarly, when the IGBT is turned on, the energy of the absorption capacitors Cs1 and Cs2 will be discharged to the switch tubes S1 and S2 through the discharge resistors Rs1 and Rs2; at this time, the role of the discharge resistors Rs1 and Rs2 is to limit the size of the discharge current, avoid and suppress the oscillation of the buffer circuit, and prevent the IGBT device from being broken down.

[0055] Compared to Figure 1 The protection circuit 1 shown in the figure can suppress the voltage oscillation generated by the IGBT device in the flying capacitor three-level BUCK circuit when it is turned off and on, and is suitable for high-frequency switching applications, with low loss in the absorption circuit and not easy to cause bus voltage oscillation. It can prevent the IGBT device from being broken down by the turn-off spike voltage, and can also optimize the output voltage quality of the flying capacitor three-level BUCK circuit, reduce the selection of IGBT withstand voltage level, and save product material costs.

[0056] In the above embodiment, a protection circuit 1 is described in detail. The present application also provides an embodiment corresponding to a novel flying capacitor three-level BUCK circuit. Figure 2 As shown, this embodiment provides a flying capacitor three-level BUCK circuit, including: Udc, a main circuit switch K1, a pre-charge circuit switch K2, a pre-charge current limiting resistor R1, an input filter capacitor C1, a flying capacitor Cfly, a first switch tube S1, a second switch tube S2, freewheeling diodes VD1 and VD2, an inductor L1 and a load resistor R, and also includes: a protection circuit 1 as in any of the above embodiments;

[0057] The protection circuit 1 is connected in parallel to two ends of an IGBT half-bridge module 2 which is composed of a first switch tube S1 and a second switch tube S2 connected in series.

[0058] Since the embodiments of the flying capacitor three-level BUCK circuit part correspond to the embodiments of the protection circuit 1 part, the embodiments of the flying capacitor three-level BUCK circuit part refer to the description of the embodiments of the protection circuit 1 part, which will not be repeated here.

[0059] However, it should be noted that this embodiment also provides a preferred embodiment of a flying capacitor three-level BUCK circuit, such as Figure 2 As shown, the above-mentioned flying capacitor three-level BUCK circuit further includes: an output filter capacitor C2;

[0060] The output filter capacitor C2 is connected in parallel across the load resistor R for output filtering.

[0061] In this embodiment, an output filter capacitor C2 is arranged at both ends of the load resistor R to filter the output, thereby improving the output waveform and enhancing the performance of the flying capacitor three-level BUCK circuit and the photovoltaic hydrogen production power supply to which it is applied.

[0062] Finally, the present application also provides an embodiment corresponding to a photovoltaic hydrogen production power supply, a photovoltaic hydrogen production power supply including: a flying capacitor three-level BUCK circuit as provided in the above embodiment.

[0063] Since there are corresponding parts between the embodiments of the photovoltaic hydrogen production power supply part and the embodiments of the above-mentioned protection circuit and the flying capacitor three-level BUCK circuit part, the embodiments of the photovoltaic hydrogen production power supply part can refer to the description of the embodiments of the above-mentioned protection circuit and the flying capacitor three-level BUCK circuit part, which will not be repeated here.

[0064] On the other hand, this embodiment also provides a preferred implementation scheme of a photovoltaic hydrogen production power source, such as Figure 3 As shown, the photovoltaic hydrogen production power source further includes: a first water cooling plate 3;

[0065] The protection circuit 1 is disposed on the first water cooling plate 3 , and the first water cooling plate 3 is used to achieve temperature reduction of the protection circuit.

[0066] In this embodiment, the protection circuit is deployed on a water cooling plate, so that the circulating water in the water cooling plate cools down the various electrical components in the protection circuit, thereby ensuring the stable operation of the buffer circuit.

[0067] Furthermore, this embodiment also provides a preferred implementation scheme of a photovoltaic hydrogen production power source, such as Figure 3 As shown, the photovoltaic hydrogen production power source further includes: a second water cooling plate 6;

[0068] The power devices in the flying capacitor three-level BUCK circuit are arranged on the second water cooling plate 6, and the second water cooling plate 6 is used to cool the power devices;

[0069] The power device includes a first switch tube S1 and a second switch tube S2.

[0070] Similar to the above embodiment, in this embodiment, the power devices in the flying capacitor three-level BUCK circuit are deployed on a water cooling plate, so that the power devices in the flying capacitor three-level BUCK circuit are cooled by circulating water in the water cooling plate. Among them, the above power devices at least include: a first switch tube S1 and a second switch tube S2 in the flying capacitor three-level BUCK circuit. As the electrical component that is most likely to heat up in the flying capacitor three-level BUCK circuit, cooling the power device is conducive to ensuring the stable operation of the flying capacitor three-level BUCK circuit.

[0071] Furthermore, based on the configuration of the first water-cooling plate 3 and the second water-cooling plate 6 in the above embodiment, this embodiment also provides a preferred implementation scheme, such as Figure 3 As shown, the photovoltaic hydrogen production power source further includes: a copper bus 10;

[0072] The copper busbar 10 is used to realize the protection circuit disposed on the first water-cooling plate 3 and connect the circuit between the first switch tube S1 and the second switch tube S2 disposed on the second water-cooling plate 6 .

[0073] It can be seen from the embodiments of the above-mentioned protection circuit and the flying capacitor three-level BUCK circuit part that there is a circuit connection between the protection circuit and the flying capacitor three-level BUCK circuit. In the above-mentioned embodiment, the power devices in the protection circuit and the flying capacitor three-level BUCK circuit are respectively deployed in the first water-cooled plate 3 and the second water-cooled plate 6, so in order to ensure the function of the protection circuit, the present embodiment realizes the circuit connection between the two through the copper bar 10. The electrical conductivity of the copper bar 10 is excellent, and it is not easy to generate electric sparks during the electrical conduction of the copper bar 10, which is conducive to avoiding the occurrence of fire. In addition, the mechanical properties of the copper bar 10 are good, and it is well suitable for the circuit connection between the circuits respectively deployed on the two water-cooled plates targeted by the present embodiment.

[0074] Based on this embodiment, Figure 3 The devices shown in the figure include: an IGBT half-bridge module 2, a first water-cooling plate 3, a freewheeling diode 4, an IGBT driving plate 5, a second water-cooling plate 6, an absorption capacitor 7, a buffer diode 8, a discharge diode 9 and a copper bus 10.

[0075] Further, based on the implementation scheme provided in the above embodiment, this embodiment also provides a preferred implementation scheme, such as Figure 3 As shown:

[0076] The first water cooling plate 3 and the second water cooling plate 6 are arranged relative to each other;

[0077] The first parallel end of the protection circuit disposed on the first water-cooling plate 3 is arranged opposite to the collector of the first switch tube S1 disposed on the second water-cooling plate 6;

[0078] The second parallel end of the protection circuit disposed on the first water-cooling plate 3 is arranged opposite to the emitter of the second switch tube S2 disposed on the second water-cooling plate 6;

[0079] Among them, the first parallel end is the first end of the first absorption capacitor Cs1 and the first end of the second discharge resistor Rs2 connected in the protection circuit; the second parallel end is the second end of the second absorption capacitor Cs2 and the second end of the first discharge resistor Rs1 connected in the protection circuit.

[0080] It should be noted that the above relative arrangement is for the first water-cooling plate 3 and the second water-cooling plate 6. In a possible embodiment, the first water-cooling plate 3 and the second water-cooling plate 6 have the same shape and specification. Then the relative arrangement of the first water-cooling plate 3 and the second water-cooling plate 6 should satisfy that when the two are observed from at least one angle, one water-cooling plate can completely cover the other water-cooling plate.

[0081] As for the protection circuit and the power device, the relative setting should satisfy: the copper bar 10 required to connect the first parallel end of the protection circuit with the collector of the first switch tube S1 is the shortest, and the copper bar 10 required to connect the second parallel end of the protection circuit with the emitter of the second switch tube S2 is the shortest.

[0082] In summary, this embodiment can ensure that the copper busbar 10 connecting the protection circuit and the power device deployed on two different water-cooled plates is as short as possible through the relative arrangement of the deployment positions, that is, the length of the main circuit is as short as possible. This ensures that the inductance brought by the copper busbar 10 is minimized, minimizes the stray inductance in the main circuit, and avoids increasing the working pressure of the protection circuit.

[0083] The above is a detailed introduction to a protection circuit, a flying capacitor three-level BUCK circuit and a photovoltaic hydrogen production power supply provided by the utility model. The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the embodiments can refer 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, and the relevant parts can refer to the method part description. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the utility model, the utility model can also be improved and modified, and these improvements and modifications also fall within the scope of protection of the utility model.

[0084] It should also be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

Claims

1. A protection circuit, characterized in that: include: A first absorption capacitor, a second absorption capacitor, a first discharge resistor, a second discharge resistor, a first buffer diode and a second buffer diode; Wherein, the first end of the first absorption capacitor is connected to the collector of the first switch tube in the flying capacitor three-level BUCK circuit, the second end of the first absorption capacitor is connected to the positive electrode of the first buffer diode and the first end of the first discharge resistor; the cathode of the first buffer diode is connected to the emitter of the first switch tube; the second end of the first discharge resistor is connected to the emitter of the second switch tube in the flying capacitor three-level BUCK circuit; The first end of the second discharge resistor is connected to the collector of the first switch tube, and the second end of the second discharge resistor is connected to the cathode of the second buffer diode and the first end of the second absorption capacitor; the anode of the second buffer diode is connected to the collector of the second switch tube; and the second end of the second absorption capacitor is connected to the emitter of the second switch tube.

2. The protection circuit according to claim 1, characterized in that: The first buffer diode and the second buffer diode are fast recovery diodes.

3. The protection circuit according to claim 1, characterized in that: The internal inductance of the first absorption capacitor and the second absorption capacitor is less than 45nH.

4. A flying capacitor three-level BUCK circuit, comprising: A DC voltage source, a main circuit switch, a pre-charge circuit switch, a pre-charge current limiting resistor, an input filter capacitor, a flying capacitor, a first switch tube, a second switch tube, a freewheeling diode, an inductor and a load resistor; characterized in that it also includes: a protection circuit as described in any one of claims 1 to 3; Wherein, the protection circuit is connected in parallel at two ends of an IGBT half-bridge module consisting of the first switch tube and the second switch tube connected in series.

5. The flying capacitor three-level BUCK circuit according to claim 4, characterized in that: Also includes: Output filter capacitor; The output filter capacitor is connected in parallel across the load resistor for output filtering.

6. A photovoltaic hydrogen production power source, characterized in that: include: A flying capacitor three-level BUCK circuit as claimed in claim 4 or 5.

7. The photovoltaic hydrogen production power source according to claim 6, characterized in that: Also includes: First water cooling plate; A protection circuit is disposed on the first water cooling plate, and the first water cooling plate is used to cool the protection circuit.

8. The photovoltaic hydrogen production power source according to claim 7, characterized in that: Also includes: Second water cooling plate; The second water cooling plate is provided with a power device in a flying capacitor three-level BUCK circuit, and the second water cooling plate is used to cool the power device; Wherein, the power device includes a first switching tube and a second switching tube.

9. The photovoltaic hydrogen production power source according to claim 8, characterized in that: Also includes: Copper busbar; The copper busbar is used to realize the protection circuit deployed on the first water-cooling plate, and is connected to the circuit between the first switch tube and the second switch tube deployed on the second water-cooling plate.

10. The photovoltaic hydrogen production power source according to claim 9, characterized in that: The first water-cooling plate and the second water-cooling plate are arranged relative to each other; The first parallel end of the protection circuit disposed on the first water-cooling plate is arranged opposite to the collector of the first switch tube disposed on the second water-cooling plate; The second parallel end of the protection circuit disposed on the first water-cooling plate is arranged opposite to the emitter of the second switch tube disposed on the second water-cooling plate; Among them, the first parallel end is the first end of the first absorption capacitor and the first end of the second discharge resistor connected in the protection circuit; the second parallel end is the second end of the second absorption capacitor and the second end of the first discharge resistor connected in the protection circuit.

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