Three-level DC / DC circuit and power supply system

Abstract

The present application discloses a three-level DC / DC circuit and a power supply system. The three-level DC / DC circuit comprises: a reverse current protection device, a first input capacitor, a second input capacitor, a first switch transistor, a second switch transistor, a third switch transistor, a fourth switch transistor, a first inductor, a second inductor, a first output capacitor, and a second output capacitor. The reverse current protection device is connected onto a current path between an output positive electrode and an input positive electrode. When the current flows in a direction from the output positive electrode to the input positive electrode, the reverse current protection device is turned off. When the input positive electrode is grounded, and when the current flows in a direction from the output positive electrode to the input positive electrode, the reverse current protection device is turned off. During normal operation of the three-level DC / DC circuit, the reverse current protection device is normally turned on. Thus, the risk of short-circuiting occurring from the output positive electrode to the input positive electrode of the DC / DC circuit can be avoided, and devices in the three-level DC / DC circuit can be protected.

Description

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

[0001] This application claims priority to the Chinese patent application with application number 202311258223.3 filed with the State Intellectual Property Office of China on September 26, 2023, and application name “A three-level DC / DC circuit and power supply system”, 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, a first input capacitor, a second input capacitor, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a first inductor, a second inductor, a first output capacitor, and a second output capacitor;

[0009] The first end and the second end of the first input capacitor are connected to the first node and the midpoint respectively, the positive input electrode of the DC / DC circuit is connected to the first node, and the first end and the second end of the second input capacitor are connected to the midpoint and the sixth node respectively;

[0010] 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 midpoint respectively, the first end and the second end of the third switch tube are connected to the midpoint and the fifth node respectively, and the first end and the second end of the fourth switch tube are connected to the fifth node and the sixth node respectively.

[0011] The first end and the second end of the first inductor are connected to the second node and the third node, respectively; the first end and the second end of the first output capacitor are connected to the third node and the midpoint, respectively; the first end and the second end of the second output capacitor are connected to the midpoint and the fourth node, respectively; the first end and the second end of the second inductor are connected to the fifth node and the fourth node, respectively; the output positive electrode and the output negative electrode of the DC / DC circuit are connected to the third node and the fourth node, respectively;

[0012] 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.

[0013] Preferably, the backflow prevention device is at least one of the following:

[0014] Diodes, half-controlled semiconductor devices or fully-controlled semiconductor devices;

[0015] 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;

[0016] The controller is electrically connected to the semi-controlled semiconductor device or the fully controlled semiconductor device;

[0017] A controller is used to control the switching state of a semi-controlled semiconductor device or a fully controlled semiconductor device.

[0018] Preferably, the DC / DC circuit further includes: an overvoltage protection device connected to the current path between the output negative electrode and the input negative electrode of the DC / DC circuit, the overvoltage protection device including a fully controlled semiconductor device, the overvoltage protection device being controlled to be turned on when the current direction is from the output negative electrode to the input negative electrode during normal operation; the fully controlled semiconductor device is disconnected when the input positive electrode is short-circuited to the ground.

[0019] 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;

[0020] A detection device, used for detecting the voltage between the positive electrode of the input and the ground, and sending the voltage between the positive electrode of the input and the ground to the controller;

[0021] The controller is used to determine the ground fault of the positive input terminal based on the voltage between the positive input terminal and the ground and report the fault; the controller is used to control the disconnection of the fully controlled semiconductor device that allows the current to flow in both directions;

[0022] When a ground fault occurs at 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;

[0023] 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.

[0024] Preferably, the detection device is further used to detect the voltage of the first input capacitor and the voltage of the second input capacitor to determine whether a voltage imbalance occurs, the current of the first inductor and the current of the second inductor to determine whether a voltage imbalance occurs, or the current of the output positive pole and the current of the output negative pole to determine whether a voltage imbalance occurs.

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

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

[0027] Preferably, the backflow prevention device is connected between the second node and the third node.

[0028] Preferably, the backflow prevention device is connected between the third node and the output positive electrode.

[0029] Preferably, the overvoltage protection device is connected between the input negative electrode and the sixth node.

[0030] Preferably, the overvoltage protection device is connected between the sixth node and the midpoint.

[0031] Preferably, the overvoltage protection device is connected between the midpoint and the fifth node.

[0032] Preferably, the overvoltage protection device is connected between the fifth node and the fourth node.

[0033] Preferably, the overvoltage protection device is connected between the fourth node and the output negative electrode.

[0034] 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;

[0035] 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 of the electrolytic cell is grounded or the midpoint of the electrolytic cell is grounded.

[0036] It can be seen that this application has the following beneficial effects:

[0037] 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

[0038] FIG1 is a diagram illustrating an application scenario of a three-level DC / DC circuit provided in an embodiment of the present application;

[0039] FIG2 is a schematic diagram of a three-level Buck TL circuit provided in an embodiment of the present application;

[0040] FIG3 is a schematic diagram of short-circuit current when the positive input electrode is grounded according to an embodiment of the present application;

[0041] FIG4 is a schematic diagram of another three-level DC / DC circuit provided in an embodiment of the present application;

[0042] FIG5 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;

[0043] FIG6 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;

[0044] FIG7 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;

[0045] 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 P4;

[0046] FIG9 is a schematic diagram of another three-level DC / DC circuit provided in an embodiment of the present application;

[0047] FIG10 is a schematic diagram of an overvoltage protection device provided in an embodiment of the present application located at P5;

[0048] FIG11 is a schematic diagram of an overvoltage protection device provided in an embodiment of the present application located at P6;

[0049] FIG12 is a schematic diagram of an overvoltage protection device provided in an embodiment of the present application located at P7;

[0050] FIG13 is a schematic diagram of an overvoltage protection device provided in an embodiment of the present application located at P8;

[0051] FIG14 is a schematic diagram of an overvoltage protection device provided in an embodiment of the present application located at P9;

[0052] FIG15 is a schematic diagram of a fully-controlled semiconductor device provided in an embodiment of the present application located at P9;

[0053] FIG16 is a schematic diagram of a power supply system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0054] 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.

[0055] Refer to FIG1 , which is an application scenario diagram of a three-level DC / DC circuit provided in an embodiment of the present application.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] The following takes a three-level DC / DC circuit as a three-level Buck TL circuit as an example for introduction.

[0060] See FIG2 , which is a schematic diagram of a three-level Buck TL circuit provided in an embodiment of the present application.

[0061] The three-level DC / DC circuit provided in the embodiment of the present application includes: a first input capacitor Ci1, a second input capacitor Ci2, a first switch tube Sa1, a second switch tube Sa2, a third switch tube Sa3, a fourth switch tube Sa4, a first inductor L1, a second inductor L2, a first output capacitor Co1, and a second output capacitor Co2;

[0062] A first end and a second end of the first input capacitor Ci1 are connected to the first node A and the midpoint O respectively, an input positive electrode IN+ of the DC / DC circuit is connected to the first node A, and a first end and a second end of the second input capacitor Ci2 are connected to the midpoint O and the sixth node F respectively;

[0063] The first end and the second end of the first switch 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 switch transistor Sa2 are connected to the second node B and the midpoint O, respectively. The first end and the second end of the third switch transistor Sa3 are connected to the midpoint O and the fifth node E, respectively. The first end and the second end of the fourth switch transistor Sa4 are connected to the fifth node E and the sixth node F, respectively.

[0064] The first end and the second end of the first inductor L1 are connected to the second node B and the third node C, respectively. The first end and the second end of the first output capacitor Co1 are connected to the third node C and the midpoint O, respectively. The first end and the second end of the second output capacitor Co2 are connected to the midpoint O and the fourth node D, respectively. The first end and the second end of the second inductor L2 are connected to the fifth node E and the fourth node D, respectively. The output positive electrode OUT+ and the output negative electrode OUT- of the DC / DC circuit are connected to the third node C and the fourth node D, respectively.

[0065] The control strategy of a traditional three-level Buck TL circuit is to alternately turn on Sa1 and Sa2, and then Sa3 and Sa4. This ensures that at least two of the four switches Sa1-Sa4 are simultaneously exposed to the total input voltage, the sum of the voltages Ci1 and Ci2. By alternating the conduction of Sa1 and Sa2, the circuit controls the output voltage of the upper half of the busbar (Ci1). By alternating the conduction of Sa3 and Sa4, the circuit controls the output voltage of the lower half of the busbar (Ci2). The sum of the voltages Co1 and Co2 is the total output voltage of the circuit.

[0066] This application takes the grounding of the negative pole of the load as an example for description. In addition, it is also applicable to the midpoint grounding of the load. The midpoint of the three-level DC / DC circuit in Figure 2 is the O of the output terminal.

[0067] In applications where the load's negative terminal or midpoint is grounded, when the DC / DC circuit's input positive terminal (IN+) is grounded, as shown in Figure 3, a current path will flow from the output positive terminal (OUT+) to the input positive terminal (IN+). As shown by the dotted arrow in Figure 3, the DC input capacitor Ci1 is shorted through the grounding of the input positive terminal (IN+), the grounding of the output negative terminal (OUT-), and the anti-parallel diodes of L2 and Sa3. Furthermore, Co1, Co2, and the load are connected through the anti-parallel diodes of L1 and Sa1, the input positive terminal (IN+), and the output negative terminal (OUT-) to ground. Because Ci1 is shorted, Ci2 and Sa4 are both exposed to the DC input voltage, making these two components susceptible to overvoltage damage. Furthermore, in electrolytic cell applications, the output capacitor and load are discharged through an abnormal circuit, causing instantaneous reverse discharge in the electrolytic cell, which can cause irreversible damage to the cell's diaphragm and other materials.

[0068] 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.

[0069] An embodiment of the present application provides a three-level DC / DC circuit, including: a backflow prevention device, a first input capacitor Ci1, a second input capacitor Ci2, a first switch tube Sa1, a second switch tube Sa2, a third switch tube Sa3, a fourth switch tube Sa4, a first inductor L1, a second inductor L2, a first output capacitor Co1, and a second output capacitor Co2.

[0070] Except for the anti-backflow device, the connection relationship of other devices has been introduced in Figure 3 and will not be repeated here.

[0071] The backflow prevention device is connected to the current path between the output positive electrode OUT+ and the input positive electrode IN+. The backflow prevention device is cut off and turned on when the current direction is from the output positive electrode OUT+ to the input positive electrode IN+.

[0072] As shown in FIG4 , the backflow prevention device may be connected to at least one of P1 , P2 , P3 and P4 .

[0073] FIG4 is merely a schematic representation. For example, if the backflow prevention device is connected at position P2, the backflow prevention device is between the first end of Ci1 and the first end of Sa1. It should be understood that the position of P2 can also be between the second end of Sa1 and the first end of L1. Similarly, if the backflow prevention device is connected at position P3, the backflow prevention device is between the second end of L1 and the first end of Co1. It should be understood that the position of P3 can also be between the first end of Sa2 and the first end of L1.

[0074] 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.

[0075] 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:

[0076] Diodes, half-controlled semiconductor devices or fully-controlled semiconductor devices;

[0077] 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.

[0078] The controller is electrically connected to the semi-controlled semiconductor device or the fully controlled semiconductor device;

[0079] A controller is used to control the switching state of a semi-controlled semiconductor device or a fully controlled semiconductor device.

[0080] 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.

[0081] The controller is electrically connected to the semi-controlled semiconductor device or the fully-controlled semiconductor device to control the switching state of the semi-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 semi-controlled semiconductor device or the fully-controlled semiconductor device to be forward-conducted. When the positive input terminal is grounded, the semi-controlled semiconductor device or the fully-controlled semiconductor device is automatically disconnected.

[0082] For example, the backflow prevention device can be a diode, which can be connected to at least one of P1-P4 in Figure 4. For example, when a diode is connected to P1, the anode of the diode is connected to the positive input terminal IN+, and the cathode of the diode is connected to the first terminal of the first input capacitor Ci1. When the positive input terminal IN+ is grounded, even if current flows from the positive output terminal OUT+ to the positive input terminal IN+, the reverse-blocking characteristic of the diode blocks the current path, thereby protecting the components in the three-level DC / DC circuit.

[0083] 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.

[0084] In one possible implementation, in the three-level DC / DC circuit provided in an 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); the detection device is electrically connected to the input positive electrode and the controller, and the detection device is used to detect a ground fault at the input positive electrode, and the controller reports the fault; the controller is used to control the fully-controlled semiconductor device with bidirectional current flow to disconnect; 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.

[0085] When a ground fault occurs at the positive input terminal, the half-controlled semiconductor device or the fully-controlled semiconductor device in which current flows in one direction is automatically cut off.

[0086] The controller is further configured to control the semi-controlled semiconductor device or the fully-controlled semiconductor device to conduct when the positive input terminal is not grounded. For example, a detection device may detect the voltage of the positive input terminal and transmit the voltage relative to ground to the controller. When the positive input terminal is grounded, the voltage will drop significantly, even reaching 0V. The controller is configured to control the semi-controlled semiconductor device or the fully-controlled semiconductor device to disconnect when a ground fault is detected at the positive input terminal based on the voltage relative to ground.

[0087] The following examples illustrate several specific implementations of connecting the backflow prevention device at different locations.

[0088] 5 , in the three-level DC / DC circuit provided in an embodiment of the present application, the backflow prevention device is connected between the input positive electrode IN+ and the first node A.

[0089] 6 , in the three-level DC / DC circuit provided by an embodiment of the present application, the backflow prevention device is connected between the first node A and the second node B.

[0090] 7 , in the three-level DC / DC circuit provided by an embodiment of the present application, the backflow prevention device is connected between the second node B and the third node C.

[0091] 8 , in the three-level DC / DC circuit provided by an embodiment of the present application, the backflow prevention device is connected between the third node C and the output positive electrode OUT+.

[0092] In addition, the three-level DC / DC circuit provided in the embodiments of the present application does not specifically limit the types of the first to fourth switching transistors. They can be fully controlled semiconductor devices that can be controlled to turn on and off and include anti-parallel diodes. The specific types of fully controlled semiconductor devices can be found in the description above.

[0093] In addition, in the three-level Buck TL circuit provided in the embodiment of the present application, when the voltage of the first input capacitor and the voltage of the second input capacitor are severely uneven, under normal circumstances, the voltage of the first input capacitor and the voltage of the second input capacitor are equal, and the voltage borne by the second input capacitor and the third switch tube and the fourth switch tube will be greater than half of the DC input voltage, which may exceed their tolerance range and cause damage to them.

[0094] Therefore, in order to solve the technical problem of unbalanced voltage between the first input capacitor and the second input capacitor, the three-level DC / DC circuit provided in the embodiments of the present application further includes: an overvoltage protection device connected in the current path between the negative output electrode and the negative input electrode of the DC / DC circuit, the overvoltage protection device including a fully controlled semiconductor device. The specific type of fully controlled semiconductor device can be found in the description above. The fully controlled semiconductor device is disconnected when the voltage between the first input capacitor and the second input capacitor is unbalanced, as described in detail below with reference to the accompanying drawings.

[0095] Refer to FIG9 , which is a schematic diagram of another three-level DC / DC circuit provided in an embodiment of the present application.

[0096] The detection device in the three-level DC / DC circuit provided in the embodiment of the present application is further used to detect the voltage of the first input capacitor and the voltage of the second input capacitor to determine whether a voltage imbalance occurs, the current of the first inductor and the current of the second inductor to determine whether a voltage imbalance occurs, or the current of the output positive electrode and the current of the output negative electrode to determine whether a voltage imbalance occurs.

[0097] The overvoltage protection device can be connected to at least one of P5-P9 in Figure 9. When the voltages of the two input capacitors are balanced, the overvoltage protection device is turned on. When the voltages of the two input capacitors are unbalanced, the overvoltage protection device needs to be controlled to be disconnected to block the overvoltage path.

[0098] The specific locations of several overvoltage protection components are introduced below with reference to the accompanying drawings.

[0099] Refer to FIG10 , which is a schematic diagram of an overvoltage protection device provided in an embodiment of the present application located at P5 .

[0100] In the three-level DC / DC circuit provided in the embodiment of the present application, the overvoltage protection device is connected between the negative input electrode IN- and the sixth node F, that is, the position of P5.

[0101] Refer to FIG11 , which is a schematic diagram of an overvoltage protection device provided in an embodiment of the present application located at P6.

[0102] In the three-level DC / DC circuit provided in the embodiment of the present application, the overvoltage protection device is connected between the sixth node F and the midpoint O, that is, the position of P6; it should be understood that P6 is above Ci2 in Figure 11, and P6 can also be below Ci2.

[0103] Refer to Figure 12, which is a schematic diagram of the overvoltage protection device provided in an embodiment of the present application located at P7.

[0104] In the three-level DC / DC circuit provided in the embodiment of the present application, the overvoltage protection device is connected between the midpoint O and the fifth node E, that is, the position of P7; it should be understood that P7 is above Sa3 in Figure 12, and P7 can also be below Sa3.

[0105] Refer to Figure 13, which is a schematic diagram of the overvoltage protection device provided in an embodiment of the present application located at P8.

[0106] In the three-level DC / DC circuit provided in the embodiment of the present application, the overvoltage protection device is connected between the fifth node E and the fourth node D, i.e., at the position of P8. It should be understood that in Figure 13, P8 is to the right of L2. Alternatively, P8 can also be to the left of L2.

[0107] Refer to Figure 14, which is a schematic diagram of the overvoltage protection device provided in an embodiment of the present application located at P9.

[0108] In the three-level DC / DC circuit provided in the embodiment of the present application, the overvoltage protection device is connected between the fourth node D and the output negative electrode OUT-, that is, the position of P9.

[0109] 15 is a schematic diagram of a fully controlled semiconductor device located at P9 according to an embodiment of the present application. FIG15 shows that the overvoltage protection device is included at P9, and the fully controlled semiconductor device Sa5 is used as an example for description.

[0110] 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.

[0111] See Figure 16, which is a schematic diagram of a power supply system provided in an embodiment of the present application.

[0112] 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;

[0113] 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 or the midpoint of the electrolytic cell 200 is grounded.

[0114] 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.

[0115] Since the three-level DC / DC circuit is equipped with a backflow prevention device at at least one position P1-P4, 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.

[0116] Continuing with FIG16 , the three-level DC / DC circuit provided in an embodiment of the present application may further include an overvoltage protection device at at least one position P5-P9. When the voltages of the first input capacitor and the second input capacitor are unbalanced, the overvoltage protection device is controlled to disconnect, thereby blocking the overvoltage path and protecting the devices in the three-level DC / DC circuit.

[0117] 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.

[0118] 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, a first input capacitor, a second input capacitor, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a first inductor, a second inductor, a first output capacitor, and a second output capacitor; The first end and the second end of the first input capacitor are connected to the first node and the midpoint respectively, the input positive electrode of the DC / DC circuit is connected to the first node, and the first end and the second end of the second input capacitor are connected to the midpoint and the sixth node respectively; 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 midpoint respectively, the first end and the second end of the third switch tube are connected to the midpoint and the fifth node respectively, and the first end and the second end of the fourth switch tube are connected to the fifth node and the sixth node respectively; The first end and the second end of the first inductor are connected to the second node and the third node respectively, the first end and the second end of the first output capacitor are connected to the third node and the midpoint respectively, the first end and the second end of the second output capacitor are connected to the midpoint and the fourth node respectively; the first end and the second end of the second inductor are connected to the fifth node and the fourth node respectively; the output positive electrode and the output negative electrode of the DC / DC circuit are connected to the third node and the fourth node 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: The DC / DC circuit further includes: an overvoltage protection device connected to the current path between the output negative electrode and the input negative electrode of the DC / DC circuit, the overvoltage protection device including a fully controlled semiconductor device, the overvoltage protection device being controlled to be turned on when the current direction is from the output negative electrode to the input negative electrode during normal operation; the fully controlled semiconductor device being disconnected when the input positive electrode is short-circuited to the ground.

4. The three-level DC / DC circuit according to claim 2 or 3, 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 input positive electrode voltage to ground and send the input positive electrode voltage to ground to the controller; The controller is used to report a fault when a ground fault occurs at the input positive electrode according to the voltage between the input positive electrode and the ground; the controller is used to control the fully controlled semiconductor device through which current flows in both directions to be disconnected; 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 electrode.

5. The three-level DC / DC circuit according to claim 4, characterized in that: The detection device is also used to detect the voltage of the first input capacitor and the voltage of the second input capacitor to determine whether the voltage imbalance occurs, the current of the first inductor and the current of the second inductor to determine whether the voltage imbalance occurs, or the current of the output positive electrode and the current of the output negative electrode to determine whether the voltage imbalance occurs.

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

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

8. The three-level DC / DC circuit according to any one of claims 1 to 5, 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 5, characterized in that: The backflow prevention device is connected between the third node and the output positive electrode.

10. The three-level DC / DC circuit according to any one of claims 3 to 5, characterized in that: The overvoltage protection device is connected between the input cathode and the sixth node.

11. The three-level DC / DC circuit according to any one of claims 3 to 5, characterized in that: The overvoltage protection device is connected between the sixth node and the midpoint.

12. The three-level DC / DC circuit according to any one of claims 3 to 5, characterized in that: The overvoltage protection device is connected between the midpoint and the fifth node.

13. The three-level DC / DC circuit according to any one of claims 3 to 5, characterized in that: The overvoltage protection device is connected between the fifth node and the fourth node.

14. The three-level DC / DC circuit according to any one of claims 3 to 5, characterized in that: The overvoltage protection device is connected between the fourth node and the output cathode.

15. A power supply system, characterized in that: The three-level DC / DC circuit comprising any one of claims 1 to 14, 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, 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 of the electrolytic cell is grounded or the midpoint of the electrolytic cell is grounded.

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