A dc-dc converter and power transmission system

Abstract

The application provides a DC-DC converter and a power transmission system. The DC-DC converter can include a DC / DC conversion module and a neutral grounding module. The first end of the neutral grounding module is connected with the neutral point of the DC / DC conversion module, and the second end of the neutral grounding module is grounded. The neutral grounding module can clamp the midpoint potential, can greatly reduce the transient overvoltage peak value and inhibit voltage oscillation when a single-pole grounding fault occurs in the power transmission system, can reduce the design cost of the insulation withstand voltage of the equipment, can slow down the voltage impact stress, can facilitate accurate detection of the grounding fault, can block the diffusion of the fault voltage to multiple ports, can reduce the risk of electric shock and insulation breakdown, and can improve the operation reliability of the DC-DC converter.

Description

Technical Field

[0001] This application relates to the field of DC power transmission technology, specifically to a DC-DC converter and a power transmission system. Background Technology

[0002] A power transmission system is composed of multiple interconnected power electronic devices that transmit electrical energy in direct current (DC). It not only possesses technical advantages such as convenient and rapid power flow reversal and flexible operation modes, but also maximizes the integration of various new energy sources and load distribution characteristics for multi-source complementarity, thus becoming a research hotspot in power systems. Similar to AC transformers, DC... DC-DC converters enable interconnection of modules with different voltage levels and are core equipment in large-scale new energy all-DC collection and transmission technology. Because large photovoltaic power plants and offshore wind farms have low internal DC collection voltage levels, while the DC transmission voltage levels are high, DC... DC-DC converters need to meet technical requirements such as high voltage and large voltage ratio.

[0003] If DC The neutral point of the DC-DC converter is not grounded; once the DC-DC converter... When a single-pole ground fault occurs on the high-voltage side of a DC-DC converter, the overvoltage level of its low-voltage side components and low-voltage port equipment will rise, causing insulation breakdown. How to reduce the overvoltage of DC-DC converters? The overvoltage level of DC converters under unipolar ground faults is an urgent problem to be solved. Summary of the Invention

[0004] This application provides a DC-DC converter, which may include a DC / DC conversion module and a neutral point grounding module. The first terminal of the neutral point grounding module is connected to the neutral point of the DC / DC conversion module, and the second terminal of the neutral point grounding module is grounded.

[0005] In some possible implementations, the neutral point grounding module includes any of the following: switch.

[0006] Resistor.

[0007] Reactor.

[0008] A resistor and a reactor connected in series.

[0009] Optionally, the reactor can be an air-core reactor or an iron-core reactor, etc.

[0010] In some other possible implementations, the DC / DC converter module includes a first low-voltage bridge arm, a second low-voltage bridge arm, a first common bridge arm, a second common bridge arm, a first high-voltage bridge arm, and a second high-voltage bridge arm.

[0011] The first end of the first low-voltage bridge arm is connected to the first low-voltage positive bus, and the first end of the second low-voltage bridge arm is connected to the first low-voltage negative bus. The first low-voltage bridge arm and the second low-voltage bridge arm constitute the first low-voltage port of the DC-DC converter.

[0012] The second end of the first low-voltage bridge arm, the first end of the first high-voltage bridge arm, and the first end of the first common bridge arm are connected through a first common point. The second end of the second low-voltage bridge arm, the first end of the second high-voltage bridge arm, and the first end of the second common bridge arm are connected through a second common point. The second end of the first common bridge arm and the second end of the second common bridge arm are connected through a neutral point. The second end of the first high-voltage bridge arm is connected to the high-voltage positive bus, and the second end of the second high-voltage bridge arm is connected to the high-voltage negative bus. The first high-voltage bridge arm and the second high-voltage bridge arm constitute the high-voltage port of the DC-DC converter.

[0013] Furthermore, the DC / DC converter module also includes a third low-voltage bridge arm and a fourth low-voltage bridge arm.

[0014] The first end of the third low-voltage bridge arm is connected to the second low-voltage positive bus, and the second end of the third low-voltage bridge arm is connected to the first common point. The first end of the fourth low-voltage bridge arm is connected to the second low-voltage negative bus, and the second end of the fourth low-voltage bridge arm is connected to the second common point. The third and fourth low-voltage bridge arms constitute the second low-voltage port of the DC-DC converter.

[0015] For example, each bridge arm includes a bridge arm reactor and a controllable power supply unit connected in series.

[0016] The controllable power supply unit includes a controllable voltage source or a power unit.

[0017] In one example, where the neutral point grounding module includes a resistor, the resistor's resistance value satisfies:

[0018] in, R enu Indicates the resistance value of the resistor. I SH This indicates the maximum current that the controllable voltage source unit is allowed to pass through. U dc1 This indicates the voltage to ground of the high-voltage fault electrode. U dc3 This indicates the voltage to ground of the low-voltage fault electrode. △t This indicates the latch-up time of the controllable voltage source unit. ε This represents the reliability coefficient of the controllable voltage source unit. N p Indicates the number of phases in the DC / DC converter module. L 1 represents the inductance value of the bridge arm reactance of the first, second, third, or fourth low-voltage bridge arm.L 2 represents the inductance value of the arm reactance of the first or second common bridge arm. L 3 represents the inductance value of the arm reactance of the first or second high-voltage bridge arm. I 1 indicates the peak current of the first low-voltage bridge arm, the second low-voltage bridge arm, the third low-voltage bridge arm, or the fourth low-voltage bridge arm. I 2 indicates the peak current of the first or second common bridge arm. I 3 indicates the peak current of the first or second high-voltage bridge arm.

[0019] In another example, where the neutral point grounding module includes a reactor, the inductance value of the reactor satisfies:

[0020] in, L enu This indicates the inductance value of the reactor. I SH This indicates the maximum current that the controllable voltage source unit is allowed to pass through. U dc1 This indicates the voltage to ground of the high-voltage fault electrode. U dc3 This indicates the voltage to ground of the low-voltage fault electrode. △t This indicates the latch-up time of the controllable voltage source unit. ε This represents the reliability coefficient of the controllable voltage source unit. N p Indicates the number of phases in the DC / DC converter module. L 1 represents the inductance value of the bridge arm reactance of the first, second, third, or fourth low-voltage bridge arm. L 2 represents the inductance value of the arm reactance of the first or second common bridge arm. L 3 represents the inductance value of the arm reactance of the first or second high-voltage bridge arm. I 1 indicates the peak current of the first low-voltage bridge arm, the second low-voltage bridge arm, the third low-voltage bridge arm, or the fourth low-voltage bridge arm. I 2 indicates the peak current of the first or second common bridge arm. I 3 indicates the peak current of the first or second high-voltage bridge arm.

[0021] In yet another example, where the neutral point grounding module includes a resistor and a reactor connected in series, the resistance value of the resistor and the inductance value of the reactor satisfy the following:

[0022] in, R enu Indicates the resistance value of the resistor. Lenu This indicates the inductance value of the reactor. I SH This indicates the maximum current that the controllable voltage source unit is allowed to pass through. U dc1 This indicates the voltage to ground of the high-voltage fault electrode. U dc3 This indicates the voltage to ground of the low-voltage fault electrode. △t This indicates the latch-up time of the controllable voltage source unit. ε This represents the reliability coefficient of the controllable voltage source unit. N p Indicates the number of phases in the DC / DC converter module. L 1 represents the inductance value of the bridge arm reactance of the first, second, third, or fourth low-voltage bridge arm. L 2 represents the inductance value of the arm reactance of the first or second common bridge arm. L 3 represents the inductance value of the arm reactance of the first or second high-voltage bridge arm. I 1 indicates the peak current of the first low-voltage bridge arm, the second low-voltage bridge arm, the third low-voltage bridge arm, or the fourth low-voltage bridge arm. I 2 indicates the peak current of the first or second common bridge arm. I 3 indicates the peak current of the first or second high-voltage bridge arm.

[0023] Furthermore, this application also provides a power transmission system that may include the aforementioned DC-DC converter.

[0024] Optionally, the power transmission system may also include other components, which are not limited in this application.

[0025] Compared with the prior art, the beneficial effects of this application are as follows: The DC-DC converter provided in this application may include a DC / DC conversion module and a neutral point grounding module. The first terminal of the neutral point grounding module is connected to the neutral point of the DC / DC conversion module, and the second terminal of the neutral point grounding module is grounded. The neutral point grounding module can clamp the neutral point potential, significantly reducing transient overvoltage peaks and suppressing voltage oscillations when a single-pole ground fault occurs in the power transmission system; reducing the cost of equipment insulation withstand voltage design and mitigating voltage surge stress; facilitating accurate detection of ground faults; preventing fault voltage from spreading to multiple ports; reducing the risk of electric shock and insulation breakdown; and improving the operational reliability of the DC-DC converter.

[0026] The technical solution provided in this application can reduce transient overvoltage levels when a single-pole ground fault occurs in a power transmission system, thus protecting the insulation of equipment such as cables and power units from damage as much as possible. Furthermore, it reduces the likelihood of contact voltage on the DC-DC converter casing, significantly lowering the risk of electric shock. Simultaneously, the protection device also avoids malfunctions or failures to operate. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic structural diagram of a DC-DC converter in an embodiment of this application; Figure 2 This is a schematic structural diagram of a DC-DC converter in an embodiment of this application; Figure 3 This is a schematic structural diagram of a DC-DC converter in an embodiment of this application; Figure 4 This is a schematic structural diagram of a DC-DC converter in an embodiment of this application; Figure 5 This is a schematic structural diagram of a DC-DC converter in an embodiment of this application; Figure 6 This is a schematic structural diagram of a DC-DC converter in an embodiment of this application. Detailed Implementation

[0029] The technical solutions in this application will now be described with reference to the accompanying drawings.

[0030] The terms "first," "second," etc., used in the specification, embodiments, claims, and drawings of this application are for distinguishing purposes only and should not be construed as indicating or implying relative importance or order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, such as including a series of steps or units. A method, system, product, or apparatus is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses.

[0031] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0032] This application provides a DC-DC converter, such as Figures 1-5 As shown. The DC-DC converter 100 includes a DC / DC conversion module 10 and a neutral point grounding module 20. The first terminal of the neutral point grounding module 20 is connected to the neutral point of the DC / DC conversion module 10, and the second terminal of the neutral point grounding module 20 is grounded.

[0033] Among some possible implementations, refer to Figures 1-5 The DC / DC conversion module 10 may include a first low-voltage bridge arm 11, a second low-voltage bridge arm 12, a first common bridge arm 13, a second common bridge arm 14, a first high-voltage bridge arm 15, and a second high-voltage bridge arm 16.

[0034] The first end of the first low-voltage bridge arm 11 is connected to the first low-voltage positive bus BUS1+, and the first end of the second low-voltage bridge arm 12 is connected to the first low-voltage negative bus BUS1-. The first low-voltage bridge arm 11 and the second low-voltage bridge arm 12 constitute the first low-voltage port of the DC-DC converter 100.

[0035] The second end of the first low-voltage bridge arm 11, the first end of the first high-voltage bridge arm 15, and the first end of the first common bridge arm 13 are connected through a first common point (including common points T11, T12, and T13). The second end of the second low-voltage bridge arm 12, the first end of the second high-voltage bridge arm 16, and the first end of the second common bridge arm 14 are connected through a second common point (including common points T21, T22, and T213). The second end of the first common bridge arm 13 and the second end of the second common bridge arm 14 are connected through a neutral point N. The second end of the first high-voltage bridge arm 15 is connected to the high-voltage positive bus BUS2+, and the second end of the second high-voltage bridge arm 16 is connected to the high-voltage negative bus BUS2-. The first high-voltage bridge arm 15 and the second high-voltage bridge arm 16 constitute the high-voltage port of the DC-DC converter 100.

[0036] For example, refer to Figures 1-5 Each bridge arm includes a bridge arm reactance L connected in series with a controllable power supply unit (CPSU).

[0037] The controllable power supply unit (CPSU) includes a controllable voltage source or power unit, etc., which are not limited in the embodiments of this application.

[0038] like Figure 2 As shown, the neutral point grounding module 20 can be a switch K. One end of the switch K is connected to the neutral point N, and the other end is grounded.

[0039] like Figure 3 As shown, the neutral point grounding module 20 can be a resistor Rneu. One end of the resistor R is connected to the neutral point N, and the other end is grounded.

[0040] like Figure 4 As shown, the neutral point grounding module 20 can be a reactor Lneu. One end of the reactor Lneu is connected to the neutral point N, and the other end is grounded.

[0041] like Figure 5 As shown, the neutral point grounding module 20 may include a resistor Rneu and a reactor Lneu connected in series.

[0042] In other words, the neutral point grounding module 20 includes any one of the following: a switch, a resistor, a reactor, a series resistor and a reactor, etc. Optionally, the reactor may be an air-core reactor or an iron-core reactor, etc., and this application embodiment does not limit the specific type of reactor.

[0043] Optional, such as Figure 6 As shown, the DC / DC converter module 10 also includes a third low-voltage bridge arm 17 and a fourth low-voltage bridge arm 18.

[0044] The first end of the third low-voltage bridge arm 17 is connected to the second low-voltage positive bus BUS3+, and the second end of the third low-voltage bridge arm 17 is connected to the first common point (including common points T11, T12, and T13). The first end of the fourth low-voltage bridge arm 18 is connected to the second low-voltage negative bus BUS3-, and the second end of the fourth low-voltage bridge arm 18 is connected to the second common point (including common points T21, T22, and T213). The third low-voltage bridge arm 17 and the fourth low-voltage bridge arm 18 constitute the second low-voltage port of the DC-DC converter 100.

[0045] Of course, this application may also include a fourth low-voltage bridge arm and a fifth low-voltage bridge arm, etc. Other connection methods for low-voltage bridge arms can be found in [reference needed]. Figure 6 The embodiments in this application will not be described in detail.

[0046] In this embodiment, the inductance values ​​and peak current values ​​of the bridge arm reactances of all low-voltage bridge arms can be equal. Similarly, the inductance values ​​and peak current values ​​of the bridge arm reactances of all high-voltage bridge arms can be equal. The inductance values ​​and peak current values ​​of the bridge arm reactances of all common bridge arms can also be equal.

[0047] In one example, where the neutral point grounding module includes a resistor, the resistor's resistance value satisfies:

[0048] in, R enu This indicates the resistance value of the resistor. I SH This indicates the maximum current that the controllable voltage source unit is allowed to pass through. U dc1 This indicates the voltage to ground of the high-voltage fault electrode. U dc3 This indicates the voltage to ground of the low-voltage fault electrode. △t This indicates the latch-up time of the controllable voltage source unit. ε This represents the reliability coefficient of the controllable voltage source unit. N p This indicates the number of phases in the DC / DC converter module (which can be greater than or equal to 2). L 1 represents the inductance value of the bridge arm reactance of the first, second, third, or fourth low-voltage bridge arm. L 2 represents the inductance value of the arm reactance of the first or second common bridge arm. L 3 represents the inductance value of the arm reactance of the first or second high-voltage bridge arm. I 1 indicates the peak current of the first low-voltage bridge arm, the second low-voltage bridge arm, the third low-voltage bridge arm, or the fourth low-voltage bridge arm. I 2 indicates the peak current of the first or second common bridge arm. I 3 indicates the peak current of the first or second high-voltage bridge arm.

[0049] In another example, where the neutral point grounding module includes a reactor, the inductance value of the reactor satisfies:

[0050] in, L enu This indicates the inductance value of the reactor. I SH This indicates the maximum current that the controllable voltage source unit is allowed to pass through. U dc1 This indicates the voltage to ground of the high-voltage fault electrode. U dc3This indicates the voltage to ground of the low-voltage fault electrode. △t This indicates the latch-up time of the controllable voltage source unit. ε This represents the reliability coefficient of the controllable voltage source unit. N p Indicates the number of phases in the DC / DC converter module. L 1 represents the inductance value of the bridge arm reactance of the first, second, third, or fourth low-voltage bridge arm. L 2 represents the inductance value of the arm reactance of the first or second common bridge arm. L 3 represents the inductance value of the arm reactance of the first or second high-voltage bridge arm. I 1 indicates the peak current of the first low-voltage bridge arm, the second low-voltage bridge arm, the third low-voltage bridge arm, or the fourth low-voltage bridge arm. I 2 indicates the peak current of the first or second common bridge arm. I 3 indicates the peak current of the first or second high-voltage bridge arm.

[0051] In yet another example, where the neutral point grounding module includes a resistor and a reactor connected in series, the resistance value of the resistor and the inductance value of the reactor satisfy the following:

[0052] in, R enu This indicates the resistance value of the resistor. L enu This indicates the inductance value of the reactor. I SH This indicates the maximum current that the controllable voltage source unit is allowed to pass through. U dc1 This indicates the voltage to ground of the high-voltage fault electrode. U dc3 This indicates the voltage to ground of the low-voltage fault electrode. △t This indicates the latch-up time of the controllable voltage source unit. ε This represents the reliability coefficient of the controllable voltage source unit. N p Indicates the number of phases in the DC / DC converter module. L 1 represents the inductance value of the bridge arm reactance of the first, second, third, or fourth low-voltage bridge arm. L 2 represents the inductance value of the arm reactance of the first or second common bridge arm. L 3 represents the inductance value of the arm reactance of the first or second high-voltage bridge arm. I 1 indicates the peak current of the first low-voltage bridge arm, the second low-voltage bridge arm, the third low-voltage bridge arm, or the fourth low-voltage bridge arm. I 2 indicates the peak current of the first or second common bridge arm.I 3 indicates the peak current of the first or second high-voltage bridge arm.

[0053] In this embodiment, the specific parameters of the DC-DC converter are shown in Table 1: Table 1

[0054] Substitute the parameters from Table 1 into It can be obtained through calculation. R enu ≥14.26Ω. In the embodiments of this application, R enu 200Ω can be used.

[0055] This application also provides a power transmission system that may include the aforementioned DC-DC converter.

[0056] Optionally, the power transmission system may also include other components, which are not limited in this application.

[0057] The above are merely embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application shall be included within the scope of the claims of this application pending approval.

Claims

1. A DC-DC converter, characterized in that, It includes a DC / DC conversion module and a neutral point grounding module; the first end of the neutral point grounding module is connected to the neutral point of the DC / DC conversion module, and the second end of the neutral point grounding module is grounded.

2. The DC-DC converter according to claim 1, characterized in that, The neutral point grounding module includes any one of the following: switch; Resistor; Reactor; A resistor and a reactor connected in series.

3. The DC-DC converter according to claim 2, characterized in that, The reactor is either an air-core reactor or an iron-core reactor.

4. The DC-DC converter according to claim 1, characterized in that, The DC / DC conversion module includes a first low-voltage bridge arm, a second low-voltage bridge arm, a first common bridge arm, a second common bridge arm, a first high-voltage bridge arm, and a second high-voltage bridge arm. The first end of the first low-voltage bridge arm is connected to the first low-voltage positive bus, and the first end of the second low-voltage bridge arm is connected to the first low-voltage negative bus. The first low-voltage bridge arm and the second low-voltage bridge arm constitute the first low-voltage port of the DC-DC converter. The second end of the first low-voltage bridge arm, the first end of the first high-voltage bridge arm, and the first end of the first common bridge arm are connected through a first common point. The second end of the second low-voltage bridge arm, the first end of the second high-voltage bridge arm, and the first end of the second common bridge arm are connected through a second common point. The second end of the first common bridge arm and the second end of the second common bridge arm are connected through a neutral point. The second end of the first high-voltage bridge arm is connected to the high-voltage positive bus, and the second end of the second high-voltage bridge arm is connected to the high-voltage negative bus. The first high-voltage bridge arm and the second high-voltage bridge arm constitute the high-voltage port of the DC-DC converter.

5. The DC-DC converter according to claim 4, characterized in that, The DC / DC converter module also includes a third low-voltage bridge arm and a fourth low-voltage bridge arm; The first end of the third low-voltage bridge arm is connected to the second low-voltage positive bus, the second end of the third low-voltage bridge arm is connected to the first common point, the first end of the fourth low-voltage bridge arm is connected to the second low-voltage negative bus, and the second end of the fourth low-voltage bridge arm is connected to the second common point; the third low-voltage bridge arm and the fourth low-voltage bridge arm constitute the second low-voltage port of the DC-DC converter.

6. The DC-DC converter according to claim 5, characterized in that, Each bridge arm includes a bridge arm reactor and a controllable power supply unit connected in series; The controllable power supply unit includes a controllable voltage source or a power unit.

7. The DC-DC converter according to claim 6, characterized in that, When the neutral point grounding module includes a resistor, the resistance value of the resistor satisfies: in, R enu This indicates the resistance value of the resistor. I SH This indicates the maximum current that the controllable voltage source unit is allowed to pass through. U dc1 This indicates the voltage to ground of the high-voltage fault electrode. U dc3 This indicates the voltage to ground of the low-voltage fault electrode. △t This indicates the latch-up time of the controllable voltage source unit. ε This represents the reliability coefficient of the controllable voltage source unit. N p This indicates the number of phases in the DC / DC converter module. L 1 represents the inductance value of the bridge arm reactance of the first low-voltage bridge arm, the second low-voltage bridge arm, the third low-voltage bridge arm, or the fourth low-voltage bridge arm. L 2 represents the inductance value of the arm reactance of the first common arm or the second common arm. L 3 represents the inductance value of the arm reactance of the first high-voltage bridge arm or the second high-voltage bridge arm. I 1 represents the peak current of the first low-voltage bridge arm, the second low-voltage bridge arm, the third low-voltage bridge arm, or the fourth low-voltage bridge arm. I 2 represents the peak current of the first common bridge arm or the second common bridge arm. I 3 indicates the peak current of the first high-voltage bridge arm or the second high-voltage bridge arm.

8. The DC-DC converter according to claim 5, characterized in that, When the neutral point grounding module includes a reactor, the inductance value of the reactor satisfies: in, L enu This indicates the inductance value of the reactor. I SH This indicates the maximum current that the controllable voltage source unit is allowed to pass through. U dc1 This indicates the voltage to ground of the high-voltage fault electrode. U dc3 This indicates the voltage to ground of the low-voltage fault electrode. △t This indicates the latch-up time of the controllable voltage source unit. ε This represents the reliability coefficient of the controllable voltage source unit. N p This indicates the number of phases in the DC / DC converter module. L 1 represents the inductance value of the bridge arm reactance of the first low-voltage bridge arm, the second low-voltage bridge arm, the third low-voltage bridge arm, or the fourth low-voltage bridge arm. L 2 represents the inductance value of the arm reactance of the first common arm or the second common arm. L 3 represents the inductance value of the arm reactance of the first high-voltage bridge arm or the second high-voltage bridge arm. I 1 represents the peak current of the first low-voltage bridge arm, the second low-voltage bridge arm, the third low-voltage bridge arm, or the fourth low-voltage bridge arm. I 2 represents the peak current of the first common bridge arm or the second common bridge arm. I 3 indicates the peak current of the first high-voltage bridge arm or the second high-voltage bridge arm.

9. The DC-DC converter according to claim 5, characterized in that, When the neutral point grounding module includes a resistor and a reactor connected in series, the resistance value of the resistor and the inductance value of the reactor satisfy the following: in, R enu This indicates the resistance value of the resistor. L enu This indicates the inductance value of the reactor. I SH This indicates the maximum current that the controllable voltage source unit is allowed to pass through. U dc1 This indicates the voltage to ground of the high-voltage fault electrode. U dc3 This indicates the voltage to ground of the low-voltage fault electrode. △t This indicates the latch-up time of the controllable voltage source unit. ε This represents the reliability coefficient of the controllable voltage source unit. N p This indicates the number of phases in the DC / DC converter module. L 1 represents the inductance value of the bridge arm reactance of the first low-voltage bridge arm, the second low-voltage bridge arm, the third low-voltage bridge arm, or the fourth low-voltage bridge arm. L 2 represents the inductance value of the arm reactance of the first common arm or the second common arm. L 3 represents the inductance value of the arm reactance of the first high-voltage bridge arm or the second high-voltage bridge arm. I 1 represents the peak current of the first low-voltage bridge arm, the second low-voltage bridge arm, the third low-voltage bridge arm, or the fourth low-voltage bridge arm. I 2 represents the peak current of the first common bridge arm or the second common bridge arm. I 3 indicates the peak current of the first high-voltage bridge arm or the second high-voltage bridge arm.

10. A power transmission system, characterized in that, Includes the DC-DC converter as described in any one of claims 1 to 9.

Images