Three-level DC / DC circuit and power supply system

Abstract

The present application discloses a three-level DC / DC circuit, comprising: an anti-backflow device, an input capacitor, a first switch transistor, a second switch transistor, a third switch transistor, a fourth switch transistor, a floating capacitor, an inductor, and an output capacitor. The positive terminal of a load of the DC / DC circuit is not connected to ground. The anti-backflow device is connected to a current path between the output positive terminal and the input positive terminal, and the anti-backflow device cuts off conduction when the current direction is from the output positive terminal to the input positive terminal. When the input positive terminal is connected to ground, the anti-backflow device cuts off conduction when the current direction is from the output positive terminal to the input positive terminal. During normal operation of the three-level DC / DC circuit, the anti-backflow device conducts normally, thereby avoiding the risk of short-circuiting from the output positive terminal to the input positive terminal of the DC / DC circuit and protecting the components within the three-level DC / DC circuit.

Description

A three-level DC / DC circuit and power supply system

[0001] This application claims priority to the Chinese patent application with application number 202311258244.5 and application name “A three-level DC / DC circuit and power supply system” filed with the State Intellectual Property Office of China on September 26, 2023, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of new energy technology, and in particular to a three-level DC / DC circuit and a power supply system. Background Art

[0003] At present, with the continuous development of new energy, DC / DC circuits are increasingly used as the last stage of the power supply system to provide DC voltage. For example, in the application scenario of electrolyzers, the electrolyzers are powered by DC power, and DC / DC circuits provide DC working voltage for the electrolyzers.

[0004] The electrolytic cell is generally grounded at the negative pole or midpoint as a load. For this type of DC / DC circuit with positive grounding as a non-load, if the DC / DC circuit is grounded due to broken skin or foreign objects on the copper busbar during operation, the positive input of the DC / DC circuit may be grounded.

[0005] Because the negative pole of the load of the DC / DC circuit is grounded or the midpoint of the load is grounded, the positive input pole of the DC / DC circuit is grounded when an abnormality occurs. There is a risk of short circuit from the output positive pole to the input positive pole of the DC / DC circuit, which may damage the components in the DC / DC circuit.

[0006] Summary of the Invention

[0007] In view of this, the present application provides a three-level DC / DC circuit and power supply system, which can ground the positive input pole of the DC / DC circuit to avoid the risk of short circuit from the output positive pole to the input positive pole of the DC / DC circuit.

[0008] The present application provides a three-level DC / DC circuit, comprising: a backflow prevention device, an input capacitor, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a floating capacitor, an inductor, and an output capacitor; the non-positive electrode of the load of the DC / DC circuit is grounded;

[0009] The first end and the second end of the input capacitor are connected to the first node and the input cathode, respectively; the input anode of the DC / DC circuit is connected to the first node; the first end and the second end of the output capacitor are connected to the fourth node and the output cathode of the DC / DC circuit, respectively; the output anode of the DC / DC circuit is connected to the fourth node;

[0010] The first end and the second end of the first switching tube are connected to the first node and the second node respectively, the first end and the second end of the second switching tube are connected to the second node and the third node respectively, the first end and the second end of the inductor are connected to the third node and the fourth node respectively, the first end and the second end of the third switching tube are connected to the third node and the first end of the fourth switching tube respectively, and the second end of the fourth switching tube is connected to the input negative electrode; the first end and the second end of the floating capacitor are connected to the second node and the second end of the third switching tube respectively.

[0011] The backflow prevention device is connected to the current path between the output positive electrode and the input positive electrode, and the backflow prevention device is cut off when the current direction is from the output positive electrode to the input positive electrode.

[0012] Preferably, the backflow prevention device is at least one of the following:

[0013] Diodes, half-controlled semiconductor devices or fully-controlled semiconductor devices;

[0014] When the backflow prevention device is a semi-controlled semiconductor device or a fully controlled semiconductor device, the DC / DC circuit further includes: a controller;

[0015] The controller is electrically connected to the semi-controlled semiconductor device or the fully controlled semiconductor device;

[0016] A controller is used to control the switching state of a semi-controlled semiconductor device or a fully controlled semiconductor device.

[0017] Preferably, when the backflow prevention device is a semi-controlled semiconductor device or a fully controlled semiconductor device, the DC / DC circuit further comprises: a detection device;

[0018] a detection device for detecting at least one of the voltage of the input positive electrode to ground, the voltage of the input capacitor, the voltage change rate of the input capacitor, the current change rate of the inductor, the voltage of the floating capacitor, or the voltage change rate of the floating capacitor, and sending the above detection results to the controller;

[0019] A controller is used to report a fault when a ground fault occurs at the positive input terminal according to the detection result, and to disconnect the fully controlled semiconductor device that controls the bidirectional flow of current;

[0020] When a ground fault occurs on the positive input terminal, the half-controlled semiconductor device with unidirectional current flow or the fully controlled semiconductor device with unidirectional current flow will be automatically cut off;

[0021] The controller is also used to control the conduction of the half-controlled semiconductor device or the fully-controlled semiconductor device when no ground fault occurs to the positive input terminal.

[0022] Preferably, the backflow prevention device is connected between the input positive electrode and the first node.

[0023] Preferably, the backflow prevention device is connected between the first node and the second node.

[0024] Preferably, the backflow prevention device is connected between the third node and the fourth node.

[0025] Preferably, the backflow prevention device is connected between the fourth node and the output positive electrode.

[0026] Preferably, the backflow prevention device is connected between the second node and the third node.

[0027] Preferably, the input capacitor includes a first input capacitor and a second input capacitor;

[0028] The first end and the second end of the second input capacitor are connected to the fifth node and the input negative electrode respectively; the input positive electrode is connected to the fifth node, and the backflow prevention device is connected between the first node and the fifth node.

[0029] Preferably, the output capacitor includes a first output capacitor and a second output capacitor;

[0030] The first end and the second end of the second output capacitor are connected to the sixth node and the output negative electrode respectively, and the output positive electrode is connected to the sixth node; the backflow prevention device is connected between the fourth node and the sixth node.

[0031] The present application also provides a power supply system, characterized in that it includes the three-level DC / DC circuit described above, and further includes: an electrolytic cell;

[0032] The positive output electrode of the three-level DC / DC circuit is connected to the positive electrode of the electrolytic cell, and the negative output electrode of the three-level DC / DC circuit is connected to the negative electrode of the electrolytic cell. The negative electrode or the midpoint of the electrolytic cell is grounded.

[0033] It can be seen that this application has the following beneficial effects:

[0034] The three-level DC / DC circuit provided in the embodiments of the present application includes a backflow prevention device. The backflow prevention device is connected to the current path between the output positive electrode and the input positive electrode. When the input positive electrode is grounded, the backflow prevention device is cut off and turned on when the current flows from the output positive electrode to the input positive electrode. When the three-level DC / DC circuit is operating normally, the backflow prevention device is turned on normally, thereby preventing the risk of a short circuit from the DC / DC circuit's output positive electrode to the input positive electrode and protecting the components in the three-level DC / DC circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a diagram illustrating an application scenario of a three-level DC / DC circuit provided in an embodiment of the present application;

[0036] FIG2 is a schematic diagram of a three-level DC / DC circuit with a floating capacitor provided in an embodiment of the present application;

[0037] FIG3 is a schematic diagram of short-circuit current when the positive input electrode is grounded according to an embodiment of the present application;

[0038] FIG4 is a schematic diagram of another three-level DC / DC circuit provided in an embodiment of the present application;

[0039] FIG5 is a schematic diagram of another three-level DC / DC circuit provided in an embodiment of the present application;

[0040] FIG6 is a schematic diagram of a diode as a backflow prevention device provided in an embodiment of the present application;

[0041] FIG7 is a schematic diagram of a backflow prevention device connected at position P1 in a three-level DC / DC circuit provided by an embodiment of the present application;

[0042] FIG8 is a schematic diagram of a three-level DC / DC circuit provided by an embodiment of the present application in which a backflow prevention device is connected at position P2;

[0043] FIG9 is a schematic diagram of a backflow prevention device connected at position P3 in a three-level DC / DC circuit provided by an embodiment of the present application;

[0044] FIG10 is a schematic diagram of a backflow prevention device connected at position P4 in a three-level DC / DC circuit provided by an embodiment of the present application;

[0045] FIG11 is a schematic diagram of a three-level DC / DC circuit provided by an embodiment of the present application in which a backflow prevention device is connected at position P5;

[0046] FIG12 is a schematic diagram of a three-level DC / DC circuit with two input capacitors provided in an embodiment of the present application;

[0047] FIG13 is a schematic diagram of a three-level DC / DC circuit with two output capacitors provided in an embodiment of the present application;

[0048] FIG14 is a schematic diagram of a power supply system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0049] In order to enable those skilled in the art to better understand and implement the technical solutions provided by the embodiments of the present application, the application scenarios are first introduced below.

[0050] Refer to FIG1 , which is an application scenario diagram of a three-level DC / DC circuit provided in an embodiment of the present application.

[0051] The three-level DC / DC circuit 100 provided in the embodiment of the present application is not limited to a specific load and can be any load that is directly powered but not positively grounded, for example, an alkaline electrolytic cell with its negative electrode or midpoint grounded.

[0052] For ease of understanding, the load is described by taking the electrolytic cell 200 as an example, and the negative electrode of the electrolytic cell 200 is grounded as an example.

[0053] The three-level DC / DC circuit 100 includes an input positive electrode IN+ and an input negative electrode IN−, and also includes an output positive electrode OUT+ and an output negative electrode OUT−. The output positive electrode OUT+ and the output negative electrode OUT− are connected to the positive electrode and the negative electrode of the electrolytic cell 200 respectively.

[0054] The following describes a three-level DC / DC circuit as a three-level DC / DC circuit with a floating capacitor.

[0055] Refer to FIG2 , which is a schematic diagram of a three-level DC / DC circuit with floating capacitors provided in an embodiment of the present application.

[0056] The three-level DC / DC circuit provided in the embodiment of the present application includes: an input capacitor Ci, a first switching transistor Sa1, a second switching transistor Sa2, a third switching transistor Sa3, a fourth switching transistor Sa4, a floating capacitor Cf, an inductor L, and an output capacitor Co; the load Load of the DC / DC circuit is grounded;

[0057] The first end and the second end of the input capacitor Ci are connected to the input positive electrode IN+ and the input negative electrode IN- of the DC / DC circuit respectively; the first end and the second end of the output capacitor Co are connected to the output positive electrode OUT+ and the output negative electrode OUT- of the DC / DC circuit respectively;

[0058] The first end and the second end of the first switching tube Sa1 are respectively connected to the first end of the input capacitor Ci and the first end of the second switching tube Sa2, the first end and the second end of the third switching tube Sa3 are respectively connected to the second end of the second switching tube Sa2 and the first end of the fourth switching tube Sa4, and the second end of the fourth switching tube Sa4 is connected to the input negative electrode IN-; the first end and the second end of the floating capacitor Cf are respectively connected to the first end of the second switching tube Sa2 and the second end of the third switching tube Sa3.

[0059] A first end and a second end of the inductor L are connected to a first end of the third switch tube Sa3 and a first end of the output capacitor Co respectively.

[0060] As shown in FIG3 , when the positive input electrode IN+ of the DC / DC circuit is grounded, a current path will exist from the positive output electrode OUT+ to the positive input electrode IN+, as shown by the dotted line with an arrow in the figure. There is a risk that the output capacitor Co and the load Load will be short-circuited through the inductor L, the anti-parallel diode of the first switch tube Sa1 and the anti-parallel diode of the second switch tube Sa2, the positive input electrode, and the negative output electrode.

[0061] In order to solve the above technical problems, the following describes the solutions provided by the embodiments of the present application in conjunction with the accompanying drawings. Referring to Figure 4, this figure is a schematic diagram of another three-level DC / DC circuit provided by the embodiments of the present application.

[0062] The three-level DC / DC circuit provided in the embodiment of the present application includes: a backflow prevention device, an input capacitor Ci, a first switch tube Sa1, a second switch tube Sa2, a third switch tube Sa3, a fourth switch tube Sa4, a floating capacitor Cf, an inductor L, and an output capacitor Co; the load Load of the DC / DC circuit is grounded;

[0063] The first and second ends of the input capacitor Ci are connected to the first node A and the input negative electrode IN-, respectively; the input positive electrode IN+ of the DC / DC circuit is connected to the first node A; the first and second ends of the output capacitor Co are connected to the fourth node D and the output negative electrode OUT- of the DC / DC circuit, respectively; the output positive electrode OUT+ of the DC / DC circuit is connected to the fourth node D;

[0064] The first end and the second end of the first switching transistor Sa1 are connected to the first node A and the second node B, respectively. The first end and the second end of the second switching transistor Sa2 are connected to the second node B and the third node C, respectively. The first end and the second end of the inductor L are connected to the third node C and the fourth node D, respectively. The first end and the second end of the third switching transistor Sa3 are connected to the third node C and the first end of the fourth switching transistor Sa4, respectively. The second end of the fourth switching transistor Sa4 is connected to the input negative electrode IN-. The first end and the second end of the floating capacitor Cf are connected to the second node B and the second end of the third switching transistor Sa3, respectively.

[0065] The backflow prevention device is connected to the current path between the output positive electrode and the input positive electrode, and the backflow prevention device is cut off when the current direction is from the output positive electrode to the input positive electrode.

[0066] For example, the backflow prevention device can be connected to at least one of P1, P2, P3, P4, and P5 in FIG4 . When the backflow prevention device is connected to the P3 position, it can be connected to the P3 position in FIG4 , and it can also be connected to the P3 position in FIG5 , that is, the upper and lower positions of Sa2 and the backflow prevention device are not limited, and the backflow prevention device and Sa2 are connected in series and then connected between the second end of Sa1 and the first end of Sa3. Similarly, the present application does not limit the backflow prevention device to be connected to the P4 position in FIG4 or FIG5 , that is, the backflow prevention device and L are connected in series and then connected between the first end of Sa3 and the first end of Co.

[0067] When the three-level DC / DC circuit is operating normally, the backflow prevention device is forward-conducting. When a ground fault occurs at the positive input of the three-level DC / DC circuit, the backflow prevention device is reverse-conducting.

[0068] The three-level DC / DC circuit provided in the embodiments of the present application does not specifically limit the specific type of the backflow prevention device, and can be configured according to actual needs, as long as it can block the current path from the output positive electrode to the input positive electrode. For example, the backflow prevention device can be at least one of the following:

[0069] Diodes, half-controlled semiconductor devices or fully-controlled semiconductor devices;

[0070] When the backflow prevention device is a semi-controlled semiconductor device or a fully controlled semiconductor device, the DC / DC circuit further includes: a controller (not shown in the figure); for example, the controller can be implemented using a single-chip microcomputer or MCU, or other control chips.

[0071] The controller is electrically connected to the semi-controlled semiconductor device or the fully controlled semiconductor device;

[0072] A controller is used to control the switching state of a semi-controlled semiconductor device or a fully controlled semiconductor device.

[0073] Fully controlled semiconductor devices can be, for example, any of the following: insulated-gate bipolar transistors (IGBTs), integrated gate-commutated thyristors (IGCTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), or silicon carbide (SiC) devices. Semi-controlled semiconductor devices can be silicon controlled rectifiers (SCRs), also known as thyristors.

[0074] The controller is electrically connected to the half-controlled semiconductor device or the fully-controlled semiconductor device to control the switching state of the half-controlled semiconductor device or the fully-controlled semiconductor device. That is, when the three-level DC / DC circuit is operating normally, the controller controls the half-controlled semiconductor device or the fully-controlled semiconductor device to be forward-conducted. When the positive input electrode is grounded, the controller controls the half-controlled semiconductor device or the fully-controlled semiconductor device to be disconnected.

[0075] For example, as shown in Figure 6, a diode is used as a backflow protection device. The diode can be connected to at least one of P1-P5 in Figure 4. For example, when a diode is connected to P1, the anode of the diode is connected to the positive input terminal, and the cathode of the diode is connected to the first terminal of the input capacitor. When the positive input terminal is grounded, even if current flows from the positive output terminal to the positive input terminal, the reverse-blocking characteristic of the diode blocks the current path, thereby protecting the components in the three-level DC / DC circuit.

[0076] The advantage of using a diode as a backflow prevention device is that no control is required. The diode can automatically achieve reverse cutoff. When a ground fault occurs at the positive input, it can respond quickly and provide protection.

[0077] In a possible implementation, the three-level DC / DC circuit provided in the embodiment of the present application, when the backflow prevention device is a semi-controlled semiconductor device or a fully-controlled semiconductor device, the DC / DC circuit further includes: a detection device (not shown in the figure); the detection device is electrically connected to the input positive electrode and the controller, the detection device is used to detect a ground fault at the input positive electrode, the controller is used to report the fault, and is also used to control the disconnection of the fully-controlled semiconductor device with bidirectional current flow. It should be understood that when a ground fault occurs at the input positive electrode, the semi-controlled semiconductor device or the fully-controlled semiconductor device with unidirectional current flow is automatically cut off; for example, the fully-controlled semiconductor device with unidirectional current flow can be an IGBT. The fully-controlled semiconductor device with bidirectional current flow can be a MOS.

[0078] Among them, the detection device is used to detect at least one of the input positive pole voltage to ground, the input capacitor voltage, the input capacitor voltage change rate, the inductor current change rate, the suspended capacitor voltage or the suspended capacitor voltage change rate, and send the above detection results to the controller; for example, the detection device can detect the input positive pole voltage. When the input positive pole is grounded, the voltage will drop significantly and even be equal to 0V.

[0079] The controller is also used to control the conduction of the half-controlled semiconductor device or the fully-controlled semiconductor device when there is no ground fault at the input positive pole, that is, during normal operation.

[0080] The following examples illustrate several specific implementations of connecting the backflow prevention device at different locations.

[0081] 7 , in the three-level DC / DC circuit provided by an embodiment of the present application, the backflow prevention device is connected between the input positive electrode IN+ and the first node A, that is, at the position of P1.

[0082] Referring to Figure 8 , an embodiment of the present invention provides a three-level DC / DC circuit in which a backflow prevention device is connected between a first node A and a second node B, i.e., at the location of P2. It should be understood that P2 and Sa1 can be connected in series between the first node A and the second node B, and Figure 8 is merely illustrative.

[0083] Referring to Figure 9 , an embodiment of the present application provides a three-level DC / DC circuit in which the backflow prevention device is connected between the second node B and the third node C, i.e., at the location of P3. It should be understood that P3 and Sa2 can be connected in series between the second node B and the third node C, and Figure 9 is merely illustrative.

[0084] Referring to Figure 10 , in the three-level DC / DC circuit provided in an embodiment of the present application, the backflow prevention device is connected between the third node C and the fourth node D, i.e., at the position of P4. It should be understood that P4 and L can be connected in series between the third node C and the fourth node D. Figure 10 is merely illustrative.

[0085] 11 , in the three-level DC / DC circuit provided by the embodiment of the present application, the backflow prevention device is connected between the fourth node D and the output positive electrode OUT+, that is, at the position of P5 .

[0086] In addition, the three-level DC / DC circuit provided in the embodiment of the present application does not specifically limit the types of the first switch tube and the second switch tube. They can be fully controlled switch devices that can be controlled to be turned on and off, and include anti-parallel diodes.

[0087] In addition, the three-level DC / DC circuit provided in the embodiment of the present application does not specifically limit the number of input capacitors and output capacitors. For example, the input capacitor can be one or more, and the output capacitor can be one or more.

[0088] The following description will be made by taking two input capacitors as an example. Referring to FIG12 , this figure is a schematic diagram of a three-level DC / DC circuit with two input capacitors provided in an embodiment of the present application.

[0089] In the three-level DC / DC circuit provided in the embodiment of the present application, the input capacitor includes a first input capacitor Ci1 and a second input capacitor Ci2.

[0090] The first and second ends of the second input capacitor Ci2 are respectively connected to the fifth node E and the input negative electrode IN-; the input positive electrode IN+ is connected to the fifth node E, and the backflow prevention device (taking diode D1 as an example) is connected between the first node A and the fifth node E.

[0091] As can be seen from FIG12 , when the positive input electrode IN+ is grounded, the circuit from the positive output electrode OUT+ to the positive input electrode IN+ is cut off by the diode D1 .

[0092] The following description will be made by taking two output capacitors as an example. Referring to FIG13 , this figure is a schematic diagram of a three-level DC / DC circuit with two output capacitors provided in an embodiment of the present application.

[0093] The three-level DC / DC circuit provided in the embodiment of the present application has an output capacitor including a first output capacitor Co1 and a second output capacitor Co2.

[0094] Preferably, the output capacitor includes a first output capacitor Co1 and a second output capacitor Co2;

[0095] The first and second ends of the second output capacitor Co2 are respectively connected to the sixth node F and the output negative electrode OUT-, and the output positive electrode OUT- is connected to the sixth node F; the backflow prevention device (taking the diode D1 as an example) is connected between the fourth node D and the sixth node F.

[0096] As can be seen from FIG13 , when the positive input electrode IN+ is grounded, the circuit from the positive output electrode OUT+ to the positive input electrode IN+ is cut off by the diode D1 .

[0097] Based on the three-level DC / DC circuit provided in the above embodiment, an embodiment of the present application further provides a power supply system, which is described in detail below with reference to the accompanying drawings.

[0098] See Figure 14, which is a schematic diagram of a power supply system provided in an embodiment of the present application.

[0099] The power supply system provided in the embodiment of the present application includes the three-level DC / DC circuit described in the above embodiment, and further includes: an electrolytic cell 200;

[0100] The positive output of the three-level DC / DC circuit is connected to the positive electrode of the electrolytic cell 200 , and the negative output of the three-level DC / DC circuit is connected to the negative electrode of the electrolytic cell 200 . The negative electrode of the electrolytic cell 200 is grounded.

[0101] The electrolytic cell 200 may be an alkaline electrolytic cell. The negative electrode of the electrolytic cell 200 is grounded as an example for description. Alternatively, the midpoint of the electrolytic cell 200 may be grounded.

[0102] Since the three-level DC / DC circuit is equipped with a backflow prevention device at at least one position P1-P5, when the positive input terminal IN+ is grounded, the current path from the positive electrode of the electrolytic cell to the positive input terminal IN+ of the three-level DC / DC circuit is cut off, thereby protecting the components in the three-level DC / DC circuit.

[0103] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the systems or devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0104] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A three-level DC / DC circuit, characterized in that: include: A backflow prevention device, an input capacitor, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a floating capacitor, an inductor and an output capacitor; the load of the DC / DC circuit is non-positively grounded; The first end and the second end of the input capacitor are connected to the first node and the input negative electrode respectively; the input positive electrode of the DC / DC circuit is connected to the first node; the first end and the second end of the output capacitor are connected to the fourth node and the output negative electrode of the DC / DC circuit respectively; the output positive electrode of the DC / DC circuit is connected to the fourth node; The first end and the second end of the first switch tube are connected to the first node and the second node respectively, the first end and the second end of the second switch tube are connected to the second node and the third node respectively, the first end and the second end of the inductor are connected to the third node and the fourth node respectively, the first end and the second end of the third switch tube are connected to the third node and the first end of the fourth switch tube respectively, and the second end of the fourth switch tube is connected to the input negative electrode; the first end and the second end of the floating capacitor are connected to the second node and the second end of the third switch tube respectively; The backflow prevention device is connected to the current path between the output positive electrode and the input positive electrode, and the backflow prevention device is cut off when the current direction is from the output positive electrode to the input positive electrode.

2. The three-level DC / DC circuit according to claim 1, characterized in that: The anti-backflow device is at least one of the following: Diodes, semi-controlled semiconductor devices or fully controlled semiconductor devices; When the backflow prevention device is the semi-controlled semiconductor device or the fully-controlled semiconductor device, the DC / DC circuit further includes: a controller; The controller is electrically connected to the half-controlled semiconductor device or the fully-controlled semiconductor device; The controller is used to control the switching state of the half-controlled semiconductor device or the fully-controlled semiconductor device.

3. The three-level DC / DC circuit according to claim 2, characterized in that: When the backflow prevention device is the half-controlled semiconductor device or the fully-controlled semiconductor device, the DC / DC circuit further includes: a detection device; The detection device is used to detect the voltage of the input positive electrode to ground, the voltage of the input capacitor, the voltage change rate of the input capacitor, the current change rate of the inductor, the voltage of the floating capacitor or at least one of the voltage change rates of the suspension capacitor, and sending the above detection results to the controller; The controller is used to report a fault when it is determined according to the detection result that a ground fault occurs at the positive input electrode, and to disconnect the fully controlled semiconductor device that controls the current to flow in both directions; When a ground fault occurs to the positive input electrode, the half-controlled semiconductor device with unidirectional current flow or the fully-controlled semiconductor device with unidirectional current flow is automatically cut off; The controller is also used to control the half-controlled semiconductor device or the fully-controlled semiconductor device to be turned on when no ground fault occurs to the input positive pole.

4. The three-level DC / DC circuit according to any one of claims 1 to 3, characterized in that: The backflow prevention device is connected between the input positive electrode and the first node.

5. The three-level DC / DC circuit according to any one of claims 1 to 3, characterized in that: The backflow prevention device is connected between the first node and the second node.

6. The three-level DC / DC circuit according to any one of claims 1 to 3, characterized in that: The backflow prevention device is connected between the third node and the fourth node.

7. The three-level DC / DC circuit according to any one of claims 1 to 3, characterized in that: The backflow prevention device is connected between the fourth node and the output positive electrode.

8. The three-level DC / DC circuit according to any one of claims 1 to 3, characterized in that: The backflow prevention device is connected between the second node and the third node.

9. The three-level DC / DC circuit according to any one of claims 1 to 3, characterized in that: The input capacitor includes a first input capacitor and a second input capacitor; The first end and the second end of the second input capacitor are connected to the fifth node and the input negative electrode respectively; the input positive electrode is connected to the fifth node, and the anti-reverse current device is connected between the first node and the fifth node.

10. The three-level DC / DC circuit according to any one of claims 1 to 3, characterized in that: The output capacitor includes a first output capacitor and a second output capacitor; The first end and the second end of the second output capacitor are connected to the sixth node and the output negative electrode respectively, and the output positive electrode is connected to the sixth node; the backflow prevention device is connected between the fourth node and the sixth node.

11. A power supply system, characterized in that: The three-level DC / DC circuit comprising any one of claims 1 to 10, further comprising: an electrolytic cell; The positive output electrode of the three-level DC / DC circuit is connected to the positive electrode of the electrolytic cell, the negative output electrode of the three-level DC / DC circuit is connected to the negative electrode of the electrolytic cell, and the negative electrode or the midpoint of the electrolytic cell is grounded.

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