Pre-charging circuit for two-phase interleaved flying capacitor three-level converter and the converter

Abstract

The present invention provides a pre-charging circuit for a two-phase interleaved flying capacitor three-level converter, including: a first switch, a second switch, a third switch, a fourth switch, and a buffer resistor. One end of the first switch is connected to the positive bus, the other end of the first switch is connected to one end of the buffer resistor, and the other end of the buffer resistor is used to connect to the positive electrode of the first flying capacitor. One end of the second switch is used to connect to the negative electrode of the first flying capacitor, and the other end of the second switch is used to connect to the first capacitor unit. The third switch is used to connect to the negative electrode of the second flying capacitor. One end of the fourth switch is connected to the third switch, and the other end of the fourth switch is connected to the negative bus. Closing the first switch to the fourth switch forms a charging loop for pre-charging the first flying capacitor and the second flying capacitor. The pre-charging circuit of the present invention charges the first flying capacitor and the second flying capacitor by closing the first switch to the fourth switch to form a charging loop, and has a simple structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and particularly relates to a pre-charging circuit and a converter for a two-phase interleaved flying capacitor three-level converter. Background Art

[0002] The two-phase interleaved flying capacitor three-level converter is often used in energy storage systems to achieve bidirectional conversion of energy between energy storage devices and DC power grids. Generally, before the system of the converter operates, it is necessary to pre-charge the flying capacitors in the converter to half of the input voltage value to complete soft start operation and avoid overvoltage damage to the power semiconductor devices in the circuit topology when they are turned on instantaneously.

[0003] In related technologies, the commonly used soft start methods include two categories. The first is to add an external charging power supply to charge the flying capacitors separately with the external power supply. When the voltage value of the flying capacitors reaches half of the input side voltage, stop charging the flying capacitors and remove the externally added pre-charging circuit from the main circuit of the converter to complete the soft start of the converter system. The second is to directly use the energy of the power grid or energy storage device to pre-charge the flying capacitors, which requires improving the circuit topology and adding a soft start switch. Usually, a switch or power semiconductor device needs to be added in the connection line between the flying capacitor and the main circuit. The first method is simple to implement but requires adding an additional pre-charging circuit, resulting in the complication of the design and structure of the converter system. The switches or power semiconductor devices added in the second method become a part of the circuit topology after the soft start is completed. Therefore, there are requirements for the power rating of the added switches or power semiconductor devices, which will affect the service life of the converter system in the long run. Summary of the Invention

[0004] The present invention provides a pre-charging circuit for a two-phase interleaved flying capacitor three-level converter, which can pre-charge all flying capacitors simultaneously without changing the structure of the converter itself and has a simple structure.

[0005] The present invention is implemented as follows. A pre-charging circuit for a two-phase interleaved flying capacitor three-level converter includes:

[0006] A first switch, a second switch, a third switch, a fourth switch, and a buffer resistor. One end of the first switch is connected to the positive bus, the other end of the first switch is connected to one end of the buffer resistor, and the other end of the buffer resistor is respectively used to connect to the positive poles of all the first flying capacitors of the two-phase interleaved flying capacitor three-level converter. One end of the second switch is respectively used to connect to the negative poles of all the first flying capacitors, and the other end of the second switch is used to connect to the first capacitor unit of the two-phase interleaved flying capacitor three-level converter. The third switch is respectively used to connect to the negative poles of all the second flying capacitors of the two-phase interleaved flying capacitor three-level converter. One end of the fourth switch is connected to the third switch, and the other end of the fourth switch is connected to the negative bus. The first switch, the second switch, the third switch, and the fourth switch are closed to form a charging circuit for pre-charging all the first flying capacitors and the second flying capacitors.

[0007] Furthermore, the pre-charging circuit of the two-phase interleaved flying capacitor three-level converter further includes a first clamping diode. The first clamping diodes are arranged in one-to-one correspondence with the first flying capacitors. The positive pole of the first clamping diode is used to connect to the negative pole of the first flying capacitor, and the negative pole of the first clamping diode is connected to one end of the second switch. The other end of the second switch is used to connect to the mid-potential point of the first capacitor unit.

[0008] Furthermore, the pre-charging circuit of the two-phase interleaved flying capacitor three-level converter further includes a first diode. The first diodes are arranged in one-to-one correspondence with the first flying capacitors. The positive pole of the first diode is connected to one end of the buffer resistor, and the negative pole of the first diode is used to connect to the positive pole of the first flying capacitor.

[0009] Furthermore, the pre-charging circuit of the two-phase interleaved flying capacitor three-level converter further includes a fifth switch and a second clamping diode. One end of the fifth switch is used to connect to the mid-potential point of the second capacitor unit, the other end of the fifth switch is connected to the negative pole of the second clamping diode, and the positive pole of the second clamping diode is connected between the third switch and the fourth switch.

[0010] The present invention also provides a converter, including:

[0011] A first switch tube module, including at least two groups of first switch tube units and first flying capacitors. The first flying capacitors are arranged in one-to-one correspondence with the first switch tube units. The first switch tube units are respectively connected to the positive bus and the negative bus, and the first flying capacitors are connected in parallel with the corresponding first switch tube units;

[0012] The second switch tube module includes at least two groups of second switch tube units and second flying capacitors. The second flying capacitors are arranged in one-to-one correspondence with the second switch tube units. The second switch tube units are respectively connected to the positive bus and the negative bus. The second flying capacitors are connected in parallel with the corresponding second switch tube units. The first switch tube unit and the second switch tube unit are connected by an inductor;

[0013] A first capacitor unit, with both ends of the first capacitor unit respectively connected to the positive bus and the negative bus;

[0014] A second capacitor unit, with both ends of the second capacitor unit respectively connected to the positive bus and the negative bus. The first switch tube module and the second switch tube module are located between the first capacitor unit and the second capacitor unit;

[0015] The pre-charging circuit of the two-phase interleaved flying capacitor three-level converter as described above includes a first switch, a second switch, a third switch, a fourth switch, and a buffer resistor. One end of the first switch is connected to the positive bus, the other end of the first switch is connected to one end of the buffer resistor, and the other end of the buffer resistor is respectively connected to the positive electrodes of all the first flying capacitors. One end of the second switch is respectively connected to the negative electrodes of all the first flying capacitors, the other end of the second switch is connected to the first capacitor unit, the third switch is respectively connected to the negative electrodes of all the second flying capacitors, one end of the fourth switch is connected to the third switch, and the other end of the fourth switch is connected to the negative bus. The first switch, the second switch, the third switch, and the fourth switch are closed to form a charging loop for pre-charging all the first flying capacitors and the second flying capacitors.

[0016] Furthermore, the converter further includes a soft-start unit. The soft-start unit includes a sixth switch and a second resistor. Both ends of the sixth switch are connected to the positive bus, and the second resistor is connected in series with the sixth switch.

[0017] Furthermore, the converter further includes a seventh switch. The seventh switch is arranged in one-to-one correspondence with the soft-start unit, and the seventh switch is connected in parallel with the soft-start unit.

[0018] Furthermore, the converter further includes two discharge modules. The discharge modules are used to release the electric energy stored in the first capacitor unit and the second capacitor unit. Both ends of the discharge modules are respectively connected to the positive bus and the negative bus.

[0019] Furthermore, the discharge module includes an eighth switch and a third resistor. The eighth switch is connected in series with the third resistor.

[0020] Further, the first switch tube unit and the second switch tube unit each include two groups. Each group of the first switch tube unit includes four first switch tubes, and each of the first switch tubes is connected in series. One end of the first first switch tube is connected to the positive bus, and one end of the fourth first switch tube is connected to the negative bus. The positive electrode of the first flying capacitor is connected between the first first switch tube and the second first switch tube, and the negative electrode of the first flying capacitor is connected between the third first switch tube and the fourth first switch tube. Each group of the second switch tube unit includes four second switch tubes, and each of the second switch tubes is connected in series. One end of the first second switch tube is connected to the positive bus, and one end of the fourth second switch tube is connected to the negative bus. The positive electrode of the second flying capacitor is connected between the first second switch tube and the second second switch tube, and the negative electrode of the second flying capacitor is connected between the third second switch tube and the fourth second switch tube.

[0021] The pre-charge circuit of the two-phase interleaved flying capacitor three-level converter provided by the present invention includes a first capacitor unit, a first switch, a second switch, a third switch, a fourth switch, and a buffer resistor. The first capacitor unit is connected to the positive and negative buses. The first switch is connected to the buffer resistor, the buffer resistor is connected to the positive electrode of the first flying capacitor, the second switch is connected to the negative electrode of the first flying capacitor, the third switch is connected to the negative electrode of the second flying capacitor, and the fourth switch is respectively connected to the third switch and the negative bus. After the switch is closed, a charging circuit is formed. After the charging circuit is formed, all the first flying capacitors and the second flying capacitors can be pre-charged to complete soft start. There is no need to add a switch or a power semiconductor device in the connection line between the flying capacitor and the main circuit. After the soft start is completed, the corresponding switch is disconnected, so that the pre-charge circuit will not become a part of the circuit topology and will not affect the original circuit composition of the converter, and there is no need to change the composition of the converter itself. Moreover, all the first flying capacitors and the second flying capacitors are charged simultaneously, which can simplify the structure of the pre-charge circuit, and the structure of the pre-charge circuit is simple. Description of the Drawings

[0022] Figure 1 is a schematic circuit structure diagram of the converter according to an embodiment of the present invention.

[0023] Figure 2 is a schematic diagram of the charging process of the pre-charge circuit of the two-phase interleaved flying capacitor three-level converter according to an embodiment of the present invention.

[0024] Figure 3 is a schematic circuit structure diagram of the converter according to another embodiment of the present invention.

[0025] Reference Numerals:

[0026] The first switch tube unit 100, the first switch tube Sa1, and the first flying capacitor C1; the second switch tube unit 200, the second switch tube Sb1, and the second flying capacitor C2; the first capacitor C3, the second capacitor C4, the first switch K1, the second switch K2, the third switch K3, the fourth switch K4, the fifth switch K5, the buffer resistor R1, the first resistor R2, the first clamping diode D1, the second clamping diode D2, the first diode D3, the third capacitor C5, the fourth capacitor C6, the soft start unit 300, the sixth switch K6, the second resistor R3; the first inductor L1, the second inductor L2; the seventh switch K7; the discharge module 400, the eighth switch K8, and the third resistor R4. Detailed implementation manners

[0027] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] The present invention provides a pre-charging circuit and a converter for a two-phase interleaved flying capacitor three-level converter. The pre-charging circuit for the two-phase interleaved flying capacitor three-level converter can be applied to the converter to pre-charge capacitors such as flying capacitors, so that the voltage value of the flying capacitor is half of the input voltage value, which can effectively avoid overvoltage damage to the power semiconductor devices in the circuit topology of the converter when they are turned on instantaneously.

[0029] Example 1

[0030] Please refer to Figure 1 , the present invention provides a pre-charging circuit for a two-phase interleaved flying capacitor three-level converter, including a first switch K1, a second switch K2, a third switch K3, a fourth switch K4, and a buffer resistor R1. One end of the first switch K1 is connected to the positive bus, the other end of the first switch K1 is connected to one end of the buffer resistor R1, and the other end of the buffer resistor R1 is respectively used to connect to the positive poles of all the first flying capacitors C1 of the two-phase interleaved flying capacitor three-level converter. One end of the second switch K2 is respectively used to connect to the negative poles of all the first flying capacitors C1, and the other end of the second switch K2 is used to connect to the first capacitor unit of the two-phase interleaved flying capacitor three-level converter. The third switch K3 is respectively used to connect to the negative poles of all the second flying capacitors C2 of the two-phase interleaved flying capacitor three-level converter. One end of the fourth switch K4 is connected to the third switch K3, and the other end of the fourth switch K4 is connected to the negative bus. The first switch K1, the second switch K2, the third switch K3, and the fourth switch K4 are closed to form a charging loop for pre-charging all the first flying capacitors C1 and the second flying capacitors C2.

[0031] Specifically, in this embodiment, one end of the fourth switch K4 is connected to the third switch K3, the other end of the fourth switch K4 is connected to one end of the first resistor R2, and the other end of the first resistor R2 is connected to the negative bus. By setting the first resistor R2, the device can be protected from damage due to excessive current.

[0032] The embodiment of the present invention provides a pre-charge circuit for a two-phase interleaved flying capacitor three-level converter, which includes a first switch K1, a second switch K2, a third switch K3, a fourth switch K4, and a buffer resistor R1. The first capacitor unit is connected to the positive and negative buses. The first switch K1 is connected to the buffer resistor R1, the buffer resistor R1 is connected to the positive electrode of the first flying capacitor C1, the second switch K2 is connected to the negative electrode of the first flying capacitor C1, the third switch K3 is connected to the negative electrode of the second flying capacitor C2, and the fourth switch K4 is respectively connected to the third switch K3 and the negative bus. After the switch is closed, a charging loop is formed. After the charging loop is formed, all the first flying capacitors C1 and the second flying capacitors C2 can be pre-charged to complete soft start. There is no need to add switches or power semiconductor devices in the connection line between the flying capacitor and the main circuit. After the soft start is completed, the corresponding switch is disconnected, so that the pre-charge circuit will not become a part of the circuit topology and will not affect the original circuit composition of the converter, and there is no need to change the composition of the converter itself. Moreover, all the first flying capacitors C1 and the second flying capacitors C2 are charged simultaneously. There is no need to design a pre-charge circuit corresponding to the flying capacitor on the output side or the flying capacitor on the input side, which can simplify the structure of the pre-charge circuit, and the structure of the pre-charge circuit is simple.

[0033] More specifically, the pre-charge circuit of the two-phase interleaved flying capacitor three-level converter of the present invention can be applied to a converter, which includes a first switch tube module, a second switch tube module, a first capacitor unit, and a second capacitor unit. The first switch tube module includes at least two groups of first switch tube units 100 and first flying capacitors C1. The first flying capacitors C1 are arranged in one-to-one correspondence with the first switch tube units 100. The first switch tube units 100 are respectively connected to the positive bus and the negative bus, and the first flying capacitors C1 are connected in parallel with the corresponding first switch tube units 100. The second switch tube module includes at least two groups of second switch tube units 200 and second flying capacitors C2. The second flying capacitors C2 are arranged in one-to-one correspondence with the second switch tube units 200. The second switch tube units 200 are respectively connected to the positive bus and the negative bus, and the second flying capacitors C2 are connected in parallel with the corresponding second switch tube units 200. The first switch tube units 100 and the second switch tube units 200 are connected by an inductor. The two ends of the first capacitor unit are respectively connected to the positive bus and the negative bus. The two ends of the second capacitor unit are respectively connected to the positive bus and the negative bus. The first switch tube module and the second switch tube module are located between the first capacitor unit and the second capacitor unit.

[0034] Among them, a converter according to an embodiment of the present invention is a bidirectional converter. More specifically, in this embodiment, the converter is a two-phase interleaved flying capacitor three-level converter. When the converter is in use, one side of the positive bus and one side of the negative bus can be used as the input terminal or the output terminal, and the other sides of the positive bus and the negative bus correspond to the output terminal or the input terminal respectively. The input terminal and the output terminal are not limited to a certain side, but can be adjusted according to the usage situation.

[0035] In this embodiment, by connecting a battery or a power grid to the left side of the positive and negative buses as the input to charge all the capacitors of the entire converter (including the pre-charging of the first flying capacitor C1 and the second flying capacitor C2, and the charging of the first capacitor unit and the second capacitor unit).

[0036] Example 2

[0037] Please refer to Figure 1 , the pre-charging circuit of the two-phase interleaved flying capacitor three-level converter further includes a first clamping diode D1. The first clamping diode D1 is arranged corresponding to the first flying capacitor C1. The positive electrode of the first clamping diode D1 is used to connect to the negative electrode of the first flying capacitor C1, and the negative electrode of the first clamping diode D1 is connected to one end of the second switch K2. The other end of the second switch K2 is used to connect to the intermediate potential point of the first capacitor unit.

[0038] Example 3

[0039] Please refer to Figure 1 , the pre-charging circuit of the two-phase interleaved flying capacitor three-level converter further includes a first diode D3. The first diode D3 is arranged corresponding to the first flying capacitor C1. The positive electrode of the first diode D3 is connected to one end of the buffer resistor R1, and the negative electrode of the first diode D3 is connected to the positive electrode of the first flying capacitor C1. By utilizing the unidirectional conduction characteristic of the diode, by setting the first diode D3, the current flow direction can be restricted, so that the current flows into the first flying capacitor C1 from the positive electrode and charges the first flying capacitor C1.

[0040] Example 4

[0041] Please refer to Figure 3 , the pre-charging circuit of the two-phase interleaved flying capacitor three-level converter further includes a fifth switch K5 and a second clamping diode D2. One end of the fifth switch K5 is used to connect to the intermediate potential point of the second capacitor unit. The other end of the fifth switch K5 is connected to the negative electrode of the second clamping diode D2. The positive electrode of the second clamping diode D2 is connected between the third switch K3 and the fourth switch K4.

[0042] It can be understood that the first switch K1 to the fifth switch K5 can adopt low-power switches, which can effectively reduce costs. It can be understood that the first switch K1 and the fifth switch K5 can also adopt common switch devices such as relays, contactors, circuit breakers, or power semiconductor devices.

[0043] After setting the fifth switch K5 and the second clamping diode D2, the right side of the positive and negative busbars can be used as the input side to connect to a battery or the grid, and the second flying capacitor C2 and the first flying capacitor C1 are charged from right to left. It can be understood that the left side of the positive and negative busbars can also be used as the input side to connect to a battery or the grid, and the first flying capacitor C1 and the second flying capacitor C2 are charged from left to right.

[0044] Example 5

[0045] The present invention also provides a converter, which includes a first switch tube module, a second switch tube module, a first capacitor unit, and a second capacitor unit. The first switch tube module includes a first switch tube unit 100 and a first flying capacitor C1, and the second switch tube module includes a second switch tube unit 200 and a second flying capacitor C2.

[0046] Specifically, please refer to Figure 1 , the first switch tube unit 100 and the second switch tube unit 200 each include two groups. Each group of the first switch tube unit 100 includes four first switch tubes Sa1, and each first switch tube Sa1 is connected in series. One end of the first first switch tube Sa1 is connected to the positive busbar, and one end of the fourth first switch tube Sa1 is connected to the negative busbar. Each group of the second switch tube unit 200 includes four second switch tubes Sb1, and each second switch tube Sb1 is connected in series. One end of the first second switch tube Sb1 is connected to the positive busbar, and one end of the fourth second switch tube Sb1 is connected to the negative busbar.

[0047] Specifically, there are four first switch tubes Sa1. In the direction from the positive busbar to the negative busbar, they are the first first switch tube Sa1, the second first switch tube Sa1, the third first switch tube Sa1, and the fourth first switch tube Sa1 in sequence. The collector of the first first switch tube Sa1 is connected to the positive busbar, the emitter of the first first switch tube Sa1 is connected to the collector of the second first switch tube Sa1, the emitter of the second first switch tube Sa1 is connected to the collector of the third first switch tube Sa1, the emitter of the third first switch tube Sa1 is connected to the collector of the fourth first switch tube Sa1, and the emitter of the fourth first switch tube Sa1 is connected to the negative busbar. Both groups of the first switch tube units 100 are connected in the above form. A diode is connected to the collector and emitter of each first switch tube Sa1, and this diode can prevent device damage caused by overvoltage due to the absence of a path in the first switch tube Sa1 when the current reverses.

[0048] There are four second switching transistors Sb1, which are the first second switching transistor Sb1, the second second switching transistor Sb1, the third second switching transistor Sb1, and the fourth second switching transistor Sb1 in sequence from the positive bus to the negative bus. The collector of the first second switching transistor Sb1 is connected to the positive bus, the emitter of the first second switching transistor Sb1 is connected to the collector of the second second switching transistor Sb1, the emitter of the second second switching transistor Sb1 is connected to the collector of the third second switching transistor Sb1, the emitter of the third second switching transistor Sb1 is connected to the collector of the fourth second switching transistor Sb1, and the emitter of the fourth second switching transistor Sb1 is connected to the negative bus. Both groups of second switching transistor units 200 are connected in the above form. A diode is connected to the collector and emitter of each second switching transistor Sb1, and this diode can prevent device damage caused by overvoltage due to the absence of a path in the second switching transistor Sb1 when the current reverses.

[0049] Among them, in this embodiment, both the first switching transistor Sa1 and the second switching transistor Sb1 are IGBTs (Insulated Gate Bipolar Transistors), that is, insulated gate bipolar transistors.

[0050] More specifically, the first switching transistor unit 100 and the second switching transistor unit 200 are connected by inductors. The inductors include a first inductor L1 and a second inductor L2. One end of the first inductor L1 is connected between the second first switching transistor Sa1 and the third first switching transistor Sa1 of one group of the first switching transistor units 100 (that is, between the emitter of the second first switching transistor Sa1 and the collector of the third first switching transistor Sa1), and the other end of the first inductor L1 is connected between the second second switching transistor Sb1 and the third second switching transistor Sb1 of one group of the second switching transistor units 200 (that is, between the emitter of the second second switching transistor Sb1 and the collector of the third second switching transistor Sb1). One end of the second inductor L2 is connected between the second first switching transistor Sa1 and the third first switching transistor Sa1 of the other group of the first switching transistor units 100 (that is, between the emitter of the second first switching transistor Sa1 and the collector of the third first switching transistor Sa1), and the other end of the second inductor L2 is connected between the second second switching transistor Sb1 and the third second switching transistor Sb1 of the other group of the second switching transistor units 200 (that is, between the emitter of the second second switching transistor Sb1 and the collector of the third second switching transistor Sb1). The first inductor L1 and the second inductor L2 play a role in filtering and current limiting.

[0051] Please refer to Figure 1, the positive electrode of the first flying capacitor C1 is connected between the first first switching transistor Sa1 and the second first switching transistor Sa1, and the negative electrode of the first flying capacitor C1 is connected between the third first switching transistor Sa1 and the fourth first switching transistor Sa1. The positive electrode of the second flying capacitor C2 is connected between the first second switching transistor Sb1 and the second second switching transistor Sb1, and the negative electrode of the second flying capacitor C2 is connected between the third second switching transistor Sb1 and the fourth second switching transistor Sb1.

[0052] Among them, the first switching transistor unit 100 includes two groups. Correspondingly, the number of the first flying capacitors C1 is also two. The second switching transistor unit 200 includes two groups. Correspondingly, the number of the second flying capacitors C2 is also two. In this embodiment, the pre-charging circuit of the two-phase interleaved flying-capacitor three-level converter pre-charges the two first flying capacitors C1 and the two second flying capacitors C2. It can be understood that when the number of the first switching transistor unit 100 and the second switching transistor unit 200 is three groups each, the pre-charging circuit of the two-phase interleaved flying-capacitor three-level converter charges three first flying capacitors C1 and three second flying capacitors C2. The pre-charging circuit of the two-phase interleaved flying-capacitor three-level converter charging the flying capacitors is not limited to two groups of the first switching transistor unit 100 and two groups of the second switching transistor unit 200.

[0053] Example 6

[0054] Please refer to Figure 1 , in this embodiment, the first capacitor unit includes a first capacitor C3 and a second capacitor C4. One end of the first capacitor C3 is connected to the positive bus, the other end of the first capacitor C3 is connected to one end of the second capacitor C4, and the other end of the second capacitor C4 is connected to the negative bus. The other end of the second switch K2 is connected between the first capacitor C3 and the second capacitor C4 (that is, the other end of the second switch K2 is connected to the middle potential point of the first capacitor unit). In this embodiment, the first capacitor C3 and the second capacitor C4 are connected in series for voltage division. The number of the first flying capacitors C1 is two. Correspondingly, the number of the first clamping diodes D1 of the pre-charging circuit of the two-phase interleaved flying-capacitor three-level converter is also two. By setting the first clamping diode D1, when the second switch K2 is closed, the voltage of the fourth first switching transistor Sa1 in the two groups of the first switching transistor units 100 can be clamped to be the same as the voltage of the second capacitor C4 (the voltage of the fourth first switching transistor Sa1 is equivalent to half of the input voltage), which can protect the fourth first switching transistor Sa1 and reduce the switching voltage stress of the first switching transistor Sa1.

[0055] Please refer to Figure 1, in this embodiment, the second capacitor unit includes a capacitor, and both ends of the capacitor are respectively connected to the positive bus and the negative bus. The first switch tube module and the second switch tube module are located between the first capacitor unit and the second capacitor unit.

[0056] Please refer to Figure 3 , in this embodiment, the second capacitor unit includes a third capacitor C5 and a fourth capacitor C6. One end of the third capacitor C5 is connected to the positive bus, the other end of the third capacitor C5 is connected to one end of the fourth capacitor C6, and the other end of the fourth capacitor C6 is connected to the negative bus. The first switch tube module and the second switch tube module are located between the first capacitor unit and the second capacitor unit. Specifically, after both ends of the third switch K3 are respectively connected to the negative electrodes of two second flying capacitors C2, the fourth switch K4 is connected to one end of the third switch K3, and the positive electrode of the second clamping diode D2 is connected between the fourth switch K4 and the third switch K3. The negative electrode of the second clamping diode D2 is connected to one end of the fifth switch K5, and the other end of the fifth switch K5 is connected between the third capacitor C5 and the fourth capacitor C6 (that is, the other end of the fifth switch K5 is connected to the intermediate potential point of the second capacitor unit). In this embodiment, the third capacitor C5 and the fourth capacitor C6 are connected in series for voltage division. By setting the second clamping diode D2, when the fifth switch K5 is closed, the voltage of the fourth second switch Sb1 in the two groups of second switch tube units 200 can be clamped to be the same as the voltage of the fourth capacitor C6, which can protect the fourth second switch Sb1 and reduce the switching voltage stress of the second switch Sb1.

[0057] Example 7

[0058] Please refer to Figure 1 , the converter further includes a soft start unit 300. The soft start unit 300 includes a sixth switch K6 and a second resistor R3. Both ends of the sixth switch K6 are connected to the positive bus, and the second resistor R3 is connected in series with the sixth switch K6. In this embodiment, soft start units 300 are provided on both the left and right sides of the positive bus, and the structures of the soft start units 300 on both sides are the same.

[0059] When pre-charging the first flying capacitor C1 and the second flying capacitor C2, after connecting a battery or a power grid to the left side of the positive and negative buses, closing the sixth switch K6, the first switch K1, the second switch K2, the third switch K3, and the fourth switch K4 forms a charging circuit, which can charge the first flying capacitor C1, the second flying capacitor C2, the first capacitor unit, and the second capacitor unit.

[0060] Please refer to Figure 1, the converter further includes a seventh switch K7, which is arranged in one-to-one correspondence with the soft start unit 300, and the seventh switch K7 is connected in parallel with the soft start unit 300. In this embodiment, both ends of the seventh switch K7 are respectively connected to the positive busbar, and by closing the seventh switch K7, the second resistor R3 can be cut off after charging is completed.

[0061] Example 8

[0062] Please refer to Figure 1 , the converter further includes two sets of discharge modules 400, and the discharge modules 400 are used to release the electric energy stored in the first capacitor unit and the second capacitor unit. Both ends of the discharge module 400 are respectively connected to the positive busbar and the negative busbar. After the converter is used up, it is necessary to discharge the first capacitor unit and the second capacitor unit. By setting the discharge module 400, the first capacitor unit and the second capacitor unit can be discharged to avoid damage to the converter.

[0063] In this embodiment, the discharge module 400 includes an eighth switch K8 and a third resistor R4, and the eighth switch K8 is connected in series with the third resistor R4. Specifically, one end of the eighth switch K8 is connected to the positive busbar, the other end of the eighth switch K8 is connected to one end of the third resistor R4, and the other end of the third resistor R4 is connected to the negative busbar.

[0064] In this embodiment, the sixth switch K6 to the eighth switch K8 can be relays, contactors, circuit breakers or power semiconductor devices. The second resistor R3 and the third resistor R4 are power resistors.

[0065] After the converter is used up, after closing the seventh switch K7 and the eighth switch K8, the first capacitor unit and the second capacitor unit can be discharged through the third resistor R4.

[0066] Example 9

[0067] Please refer to Figure 1 , an embodiment of the present invention provides a pre-charge circuit and a converter for a two-phase interleaved flying capacitor three-level converter.

[0068] The first switching transistor units 100 in the converter are connected in series in sequence by the respective first switching transistors Sa1. One end of the first switching transistor Sa1 of the first one is connected to the positive bus, and one end of the first switching transistor Sa1 of the fourth one is connected to the negative bus. The positive electrode of the first flying capacitor C1 is connected between the first switching transistor Sa1 of the first one and the second switching transistor Sa1 of the second one, and the negative electrode of the first flying capacitor C1 is connected between the third switching transistor Sa1 and the fourth switching transistor Sa1. The connection modes of the two groups of first switching transistor units 100 and the two first flying capacitors C1 are the same, and the two groups of first switching transistor units 100 are located on the left side of the positive and negative buses. The respective second switching transistors Sb1 in the second switching transistor unit 200 are connected in series in sequence. One end of the first switching transistor Sb1 of the first one is connected to the positive bus, and one end of the first switching transistor Sb1 of the fourth one is connected to the negative bus. The positive electrode of the second flying capacitor C2 is connected between the first switching transistor Sb1 of the first one and the second switching transistor Sb1 of the second one, and the negative electrode of the second flying capacitor C2 is connected between the third switching transistor Sb1 and the fourth switching transistor Sb1. The connection modes of the two groups of second switching transistor units 200 and the two second flying capacitors C2 are the same, and the two groups of second switching transistor units 200 are located on the right side of the positive and negative buses. One end of the first inductor L1 is connected between the second switching transistor Sa1 and the third switching transistor Sa1 of the same group, and the other end of the first inductor L1 is connected between the second switching transistor Sb1 and the third switching transistor Sb1 of the same group. One end of the second inductor L2 is connected between the second switching transistor Sa1 and the third switching transistor Sa1 of the other group, and the other end of the second inductor L2 is connected between the second switching transistor Sb1 and the third switching transistor Sb1 of the other group. When using the two-phase interleaved flying capacitor three-level converter pre-charging circuit, the left side of the positive and negative buses can be used as the input end or the output end. Correspondingly, the right side of the positive and negative buses can be used as the output end or the input end. The two-phase interleaved flying capacitor three-level converter pre-charging circuit has the ability of bidirectional energy flow, and the positions of the input end and the output end can be swapped. When the left side of the positive and negative buses is used as the input end and the right side of the positive and negative buses is used as the output end, the first flying capacitor C1 is the flying capacitor of the input end, and the second flying capacitor C2 is the flying capacitor of the output end. The charging circuit of the present invention can charge the flying capacitor of the input end and the flying capacitor of the output end simultaneously, without separately designing pre-charging circuits for the flying capacitor of the input end and the flying capacitor of the output end, which can simplify the structure of the entire pre-charging circuit and also simplify the structure of the entire two-phase interleaved flying capacitor three-level converter pre-charging circuit.A first capacitor unit is provided on the left side of the positive and negative busbars. The first capacitor C3 and the second capacitor C4 are connected in series. A discharge module 400 is provided on the left side of the positive and negative busbars. The eighth switch K8 and the third resistor R4 in the discharge module 400 are connected in series. The first capacitor unit is located between the discharge module 400 and the first switch tube unit 100. A second capacitor unit is provided on the right side of the positive and negative busbars. The third capacitor C5 and the fourth capacitor C6 are connected in series. A discharge module 400 is provided on the right side of the positive and negative busbars. The eighth switch K8 and the third resistor R4 in the discharge module 400 are connected in series. The second capacitor unit is located between the discharge module 400 and the second switch tube unit 200. The two ends of one seventh switch K7 are connected to the left side of the positive busbar, and the two ends of the other seventh switch K7 are connected to the right side of the positive busbar. Correspondingly, a group of soft start units 300 is connected in parallel with the seventh switch K7 on the left side, and another group of soft start units 300 is connected in parallel with the seventh switch K7 on the right side. More specifically, the sixth switch K6 in the soft start unit 300 is connected in series with the second resistor R3 and then connected in parallel with the seventh switch K7.

[0069] One end of the first switch K1 of the pre-charging circuit of the two-phase interleaved flying capacitor three-level converter is connected to the positive busbar. The first switch K1 is located between the first capacitor unit and the first switch tube unit 100. The other end of the first switch K1 is connected to the buffer resistor R1. The other end of the buffer resistor R1 is respectively connected to the positive electrodes of two first diodes D3. The negative electrodes of the two first diodes D3 are correspondingly connected to the positive electrode of the first flying capacitor C1. The negative electrode of the first flying capacitor C1 is respectively connected to the positive electrodes of two first clamping diodes D1. The negative electrodes of the two first clamping diodes D1 are both connected to one end of the second switch K2. The other end of the second switch K2 is connected between the first capacitor C3 and the second capacitor C4. The third switch K3 is respectively connected to the negative electrodes of all the second flying capacitors C2. One end of the fourth switch K4 is connected to the third switch K3. The other end of the fourth switch K4 is connected to one end of the first resistor R2. The other end of the first resistor R2 is connected to the negative busbar.

[0070] During pre-charging, the first switching transistors Sa1 of the two groups of first switching transistor units 100 and the second switching transistors Sb1 of the two groups of second switching transistor units 200 are both in the off state. The third switch K3 and the fourth switch K4 are closed. After the third switch K3 and the fourth switch K4 are closed, the second flying capacitor C2 is connected to the negative bus, which can provide a loop for the charging current. Then the second switch K2 is closed. After the second switch K2 is closed, due to the function of the first clamping diode D1, the positive electrode potentials of the two second flying capacitors C2 will be the same as that of the second capacitor C4 at this time. When the first switch K1 is closed, a charging loop is formed, and the sixth switch K6 of the soft start unit 300 is closed. Then a battery or a power grid is connected to the left side of the positive and negative buses. The buffer resistor R1 charges the first flying capacitor C1 and the second flying capacitor C2, and also charges all the capacitors in the first capacitor unit and the second capacitor unit. The current flows in from the left side and flows into the first flying capacitor C1 and the second flying capacitor C2 through each switch, some diodes connected to the first switching transistor Sa1 or the second switching transistor Sb1, and the inductor. When the sum of the voltages of the two first flying capacitors C1 is the same as the bus voltage, that is, when the voltage of the first flying capacitor C1 reaches half of the bus voltage, the soft start is completed. At this time, the first switch K1 is opened to cut off the charging loop, and then the second switch K2, the third switch K3, and the fourth switch K4 are sequentially opened to complete the pre-charging. After the pre-charging is completed, the converter can operate normally by closing the seventh switch K7. After use, the eighth switch K8 is closed to discharge the capacitors in the first capacitor unit and the second capacitor unit.

[0071] More specifically, please refer to Figure 2, taking the connection of the battery or the power grid to the left side of the positive and negative busbars as an example, after the connection, the sixth switch K6 of the soft start unit 300 on the left side is closed, and the current flow direction is as follows: a part of the current flows into the first capacitor C3 and the second capacitor C4 to the negative busbar (i.e., charging the first capacitor C3 and the second capacitor C4 in the first capacitor unit), and another part of the current flows through the first switch K1, the buffer resistor R1, and the first diode D3 and then flows into two first flying capacitors C1 respectively (i.e., charging all the first flying capacitors C1). The current flowing through the first flying capacitor C1 close to the first capacitor unit flows from the positive pole to the negative pole of the first flying capacitor C1, and then a part of it flows through the first clamping diode D1 and then into the second switch K2 and then through the second capacitor C4 to the negative busbar, and another part of it flows through the first switch tube unit 100 in parallel with it, and after passing through the diode anti-parallel to the third first switch tube Sa1, it flows into the first inductor L1, and after passing through the first inductor L1, it flows into the second switch tube unit 200 connected to the first inductor L1 (actually flowing into the diode anti-parallel to the second second switch tube Sb1). A part of the current flows into the positive pole of the second flying capacitor C2 from this diode, flows out from the negative pole of the second flying capacitor C2, passes through the fourth switch K4 to the first resistor R2 and then to the negative busbar, and another part of the current flows into the diode anti-parallel to the first second switch tube Sb1 from this diode, and then flows into the second capacitor unit (charging the capacitors in the second capacitor unit) to the negative busbar. The current flowing through the first flying capacitor C1 far from the first capacitor unit flows from the positive pole to the negative pole of the first flying capacitor C1, and then a part of it flows through the first clamping diode D1 and then into the second switch K2 and then through the second capacitor C4 to the negative busbar, and another part of it flows through the first switch tube unit 100 in parallel with it, and after passing through the diode anti-parallel to the third first switch tube Sa1, it flows into the second inductor L2, and after passing through the second inductor L2, it flows into the second switch tube unit 200 connected to the second inductor L2 (actually flowing into the diode anti-parallel to the second second switch tube Sb1). A part of the current flows into the positive pole of the second flying capacitor C2 from this diode, flows out from the negative pole of the second flying capacitor C2, passes through the third switch K3, the fourth switch K4, and the first resistor R2 in sequence and then to the negative busbar, and another part of the current flows into the diode anti-parallel to the first second switch tube Sb1 from this diode, and then flows into the second capacitor unit (charging the capacitors in the second capacitor unit) to the negative busbar.

[0072] The above-mentioned pre-charging circuit of the two-phase interleaved flying capacitor three-level converter can form a charging loop after closing the corresponding switches by setting the pre-charging circuit, and can realize the simultaneous pre-charging of all the first flying capacitors C1 and the second flying capacitors C2 at the input end and the output end. There is no need to set corresponding charging loops for the flying capacitors at the input end or the output end, which can effectively reduce the number of components in the pre-charging circuit. Moreover, after the corresponding switches are opened, the pre-charging circuit can be cut off from the main circuit of the converter, which can effectively avoid the influence on the load operation of the converter during later use and improve the reliability of the entire converter system.

[0073] Please refer to Figure 3 , another embodiment of the present invention provides a pre-charging circuit for a two-phase interleaved flying capacitor three-level converter, which is different from Figure 1 that a second clamping diode D2 and a fifth switch K5 are added to the right side of the positive and negative busbars, and one capacitor in the second capacitor unit becomes two capacitors, namely a third capacitor C5 and a fourth capacitor C6. The third capacitor C5 and the fourth capacitor C6 are connected in series and then connected to the positive and negative busbars respectively. The second capacitor unit is located between the discharge module 400 on the right side and the second flying capacitor C2. The positive electrode of the second clamping diode D2 is connected between the third switch K3 and the fourth switch K4, the negative electrode of the second clamping diode D2 is connected to one end of the fifth switch K5, and the other end of the fifth switch K5 is connected between the third capacitor C5 and the fourth capacitor C6. It can be understood that by moving the first switch K1, the buffer resistor R1, and the first diode D3 to the right side of the positive and negative busbars and connecting them corresponding to the second flying capacitor C2, the capacitors in the converter can be charged by connecting a battery to the right side of the positive and negative busbars.

[0074] The operation mode of the pre-charging circuit of the two-phase interleaved flying capacitor three-level converter in this embodiment is similar to that in Figure 1 the embodiment, and will not be elaborated here.

[0075] The above-mentioned pre-charging circuit of the two-phase interleaved flying capacitor three-level converter can form a charging loop after closing the corresponding switches (i.e., the first switch K1 to the fifth switch K5), and can realize the simultaneous pre-charging of all the first flying capacitors C1 and the second flying capacitors C2 at the input end and the output end. There is no need to set corresponding charging loops for the flying capacitors at the input end or the output end, which can effectively reduce the number of components in the pre-charging circuit. Moreover, after the corresponding switches are opened, the pre-charging circuit can be cut off from the main circuit of the converter, which can effectively avoid the influence on the load operation of the converter during later use and improve the reliability of the entire converter system.

[0076] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A pre-charging circuit for a two-phase interleaved flying capacitor three-level converter, characterized in that Comprising: A first switch, a second switch, a third switch, a fourth switch, and a buffer resistor. One end of the first switch is connected to the positive busbar, the other end of the first switch is connected to one end of the buffer resistor, and the other end of the buffer resistor is respectively used to connect to the positive electrodes of all the first flying capacitors of the two-phase interleaved flying capacitor three-level converter. One end of the second switch is respectively used to connect to the negative electrodes of all the first flying capacitors, and the other end of the second switch is used to connect to the mid-potential point of the first capacitor unit of the two-phase interleaved flying capacitor three-level converter. Both ends of the third switch are respectively used to connect to the negative electrodes of the two second flying capacitors of the two-phase interleaved flying capacitor three-level converter. One end of the fourth switch is connected to the third switch, and the other end of the fourth switch is connected to the negative busbar. The first switch, the second switch, the third switch, and the fourth switch are closed to form a charging circuit for pre-charging all the first flying capacitors and the second flying capacitors. The two-phase interleaved flying capacitor three-level converter includes: A first switch tube module, including two groups of first switch tube units and first flying capacitors. The first flying capacitors are arranged in one-to-one correspondence with the first switch tube units, and the first switch tube units are respectively connected to the positive busbar and the negative busbar. Each group of the first switch tube units includes two sets. Each set of the first switch tube units includes four first switch tubes, and each first switch tube is connected in series. The other end of the first first switch tube is connected to the positive busbar, and the other end of the fourth first switch tube is connected to the negative busbar. The positive electrode of the first flying capacitor is connected between the first first switch tube and the second first switch tube, and the negative electrode of the first flying capacitor is connected between the third first switch tube and the fourth first switch tube. Wherein, a diode is connected to the collector and emitter of each first switch tube. A second switch tube module, including two groups of second switch tube units and second flying capacitors. The second flying capacitors are arranged in one-to-one correspondence with the second switch tube units, and the second switch tube units are respectively connected to the positive busbar and the negative busbar. The second first switch tube and the third first switch tube between one group of the first switch tube units are connected to one end of a first inductor, and the second second switch tube and the third second switch tube between one group of the second switch tube units are connected to the other end of the first inductor. The second first switch tube and the third first switch tube between the other group of the first switch tube units are connected to one end of a second inductor, and the second second switch tube and the third second switch tube between the other group of the second switch tube units are connected to the other end of the second inductor. The second switch tube unit includes two groups. Each group of the second switch tube unit includes four second switch tubes. Each of the second switch tubes is connected in series. One end of the first second switch tube is connected to the positive bus, and one end of the fourth second switch tube is connected to the negative bus. The positive electrode of the second flying capacitor is connected between the first second switch tube and the second second switch tube, and the negative electrode of the second flying capacitor is connected between the third second switch tube and the fourth second switch tube. Wherein, a diode is connected to the collector and emitter of each of the second switch tubes; A first capacitor unit, both ends of the first capacitor unit are respectively connected to the positive bus and the negative bus, and the first capacitor unit includes two capacitors connected in series; A second capacitor unit, both ends of the second capacitor unit are respectively connected to the positive bus and the negative bus, and the first switch tube module and the second switch tube module are located between the first capacitor unit and the second capacitor unit.

2. The pre-charging circuit of the two-phase interleaved flying capacitor three-level converter according to claim 1, wherein It further includes a first clamping diode. The first clamping diode is arranged corresponding to the first flying capacitor. The positive electrode of the first clamping diode is used to be connected to the negative electrode of the first flying capacitor, and the negative electrode of the first clamping diode is connected to one end of the second switch. The other end of the second switch is used to be connected to the intermediate potential point of the first capacitor unit.

3. The pre-charging circuit of the two-phase interleaved flying-capacitor three-level converter according to claim 1, wherein, It further includes a first diode. The first diode is arranged corresponding to the first flying capacitor. The positive electrode of the first diode is connected to one end of the buffer resistor, and the negative electrode of the first diode is used to be connected to the positive electrode of the first flying capacitor.

4. The pre-charging circuit of the two-phase interleaved flying-capacitor three-level converter according to claim 1, wherein It further includes a fifth switch and a second clamping diode. One end of the fifth switch is used to be connected to the intermediate potential point of the second capacitor unit, the other end of the fifth switch is connected to the negative electrode of the second clamping diode, and the positive electrode of the second clamping diode is connected between the third switch and the fourth switch. The second capacitor unit includes two capacitors connected in series.

5. A converter, characterized in that, It includes: A first switch tube module, including two groups of first switch tube units and a first flying capacitor. The first flying capacitor is arranged corresponding to the first switch tube unit. The first switch tube units are respectively connected to the positive bus and the negative bus; Each group of the first switch tube units includes four first switch tubes. Each of the first switch tubes is connected in series. The other end of the first first switch tube is connected to the positive bus, and the other end of the fourth first switch tube is connected to the negative bus. The positive electrode of the first flying capacitor is connected between the first first switch tube and the second first switch tube, and the negative electrode of the first flying capacitor is connected between the third first switch tube and the fourth first switch tube. Wherein, a diode is connected to the collector and emitter of each of the first switch tubes; The second switch tube module includes two groups of second switch tube units and a second flying capacitor. The second flying capacitor is arranged corresponding to the second switch tube units one by one. The second switch tube units are respectively connected to the positive bus and the negative bus. One end of a first inductor is connected between the second and the third first switch tubes of one group of the first switch tube units, and the other end of the first inductor is connected between the second and the third second switch tubes of one group of the second switch tube units. One end of a second inductor is connected between the second and the third first switch tubes of the other group of the first switch tube units, and the other end of the second inductor is connected between the second and the third second switch tubes of the other group of the second switch tube units. The second switch tube unit includes two groups. Each group of the second switch tube units includes four second switch tubes. Each of the second switch tubes is connected in series. One end of the first second switch tube is connected to the positive bus, and one end of the fourth second switch tube is connected to the negative bus. The positive pole of the second flying capacitor is connected between the first and the second second switch tubes, and the negative pole of the second flying capacitor is connected between the third and the fourth second switch tubes. Wherein, a diode is connected to the collector and the emitter of each second switch tube. A first capacitor unit, both ends of the first capacitor unit are respectively connected to the positive bus and the negative bus. A second capacitor unit, both ends of the second capacitor unit are respectively connected to the positive bus and the negative bus. The first switch tube module and the second switch tube module are located between the first capacitor unit and the second capacitor unit. The pre-charging circuit of a two-phase interleaved flying capacitor three-level converter according to any one of claims 1-4.

6. The converter according to claim 5, characterized in that, It further includes a soft start unit. The soft start unit includes a sixth switch and a second resistor. Both ends of the sixth switch are connected to the positive bus, and the second resistor is connected in series with the sixth switch.

7. The converter according to claim 6, characterized in that, It further includes a seventh switch. The seventh switch is arranged corresponding to the soft start unit one by one. The seventh switch is connected in parallel with the soft start unit, and the seventh switch is connected in series in the positive bus.

8. The converter according to claim 5, characterized in that, It further includes two groups of discharge modules. The discharge modules are used to release the electric energy stored in the first capacitor unit and the second capacitor unit. Both ends of the discharge modules are respectively connected to the positive bus and the negative bus.

9. The converter according to claim 8, characterized in that, The discharge module includes an eighth switch and a third resistor. The eighth switch is connected in series with the third resistor.

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