Flying capacitor converter circuit and flying capacitor converter

Abstract

The invention discloses a flying capacitor converter circuit and a flying capacitor converter, and belongs to the field of power electronic power converters, the flying capacitor converter circuit comprises a direct current terminal, an alternating current terminal, a direct current bus capacitor, a flying capacitor, a power device and a charging unit, other power devices are connected in parallel with charging units; the flying capacitor can be automatically charged while the direct-current bus capacitor is pre-charged without additional control; an auxiliary power supply and a suspension direct-current power supply are not needed, the circuit is simpler and can also be suitable for high-voltage application, and the applicability of the technology is greatly improved.

Description

Technical Field

[0001] The present application belongs to the field of power electronic power converters, and specifically relates to a flying capacitor converter circuit and a flying capacitor converter. Background Art

[0002] The flying capacitor converter has the advantages of simple structure and large number of levels, and can be applied to various power conversion occasions such as DC-DC and DC-AC. One difficulty of the flying capacitor converter is that one or more flying capacitors need to be precharged at the same time as the DC bus is precharged, otherwise it will cause overvoltage breakdown of the power device.

[0003] At present, the flying capacitor pre-charging technology requires that the auxiliary power supply or external suspended DC power supply work in advance before the DC bus capacitor and the flying capacitor are pre-charged. However, for the converter system that draws power from the DC bus capacitor, when the DC bus capacitor is pre-charged, the auxiliary power supply has not yet worked, and the switching state of the power device and the switching state of the flying capacitor charging auxiliary switch cannot be controlled, so the pre-charging cannot be completed by the auxiliary power supply. In addition, for high-voltage applications, such as power electronic transformers with a module series structure, if multiple sets of mutually suspended DC power supplies with the same insulation and withstand voltage requirements as the main circuit are set up, the system will be too complicated and costly. Therefore, the applicability of the existing flying capacitor pre-charging technology is insufficient. Summary of the invention

[0004] Purpose of the invention: An embodiment of the present application provides a flying capacitor converter circuit, aiming to solve the technical problem of insufficient applicability of existing flying capacitor pre-charging technology; another purpose of an embodiment of the present application is to provide a flying capacitor converter.

[0005] Technical solution: A flying capacitor converter circuit described in an embodiment of the present application includes:

[0006] a first DC terminal, a second DC terminal and an AC terminal, and,

[0007] A first arm includes a plurality of first power devices and a first charging unit, wherein the plurality of first power devices are connected in series between the first DC terminal and the AC terminal; one of the first power devices is directly connected to the AC terminal, and the remaining first power devices are connected in parallel to the first charging unit one by one;

[0008] A second arm includes a plurality of second power devices and a second charging unit, wherein the plurality of second power devices are connected in series between the second DC terminal and the AC terminal and in series with the first power device, wherein one of the second power devices is directly connected to the AC terminal, and the remaining second power devices are connected in parallel with the second charging units one by one;

[0009] A DC bus capacitor, connected between the first DC terminal and the second DC terminal, and connected in parallel with the first arm and the second arm;

[0010] A flying capacitor has one end connected between two adjacent first power devices, and the other end connected between two adjacent second power devices.

[0011] In some embodiments, the first arm further comprises a first normally closed switch, the first normally closed switch being connected in series with the first charging unit in a one-to-one correspondence, and being connected in parallel with the remaining first power devices in a one-to-one correspondence;

[0012] The second arm further includes a second normally closed switch, which is connected in series with the second charging units in a one-to-one correspondence and connected in parallel with the remaining second power devices in a one-to-one correspondence.

[0013] In some embodiments, the positive polarity end of the first charging unit is connected to the collector of the first power device, and the negative polarity end is connected to the emitter of the first power device;

[0014] The positive polarity end of the second charging unit is connected to the collector of the second power device, and the negative polarity end is connected to the emitter of the second power device.

[0015] In some embodiments, the first charging unit is a voltage regulator or a transient suppression diode;

[0016] The second charging unit is a voltage regulator tube or a transient voltage suppressor diode.

[0017] In some embodiments, the first charging unit is a plurality of voltage regulator tubes connected in parallel or a plurality of transient suppression diodes connected in parallel;

[0018] The second charging unit is a plurality of voltage regulator tubes connected in parallel or a plurality of transient voltage suppression diodes connected in parallel.

[0019] In some embodiments, the first charging unit is a plurality of voltage regulator tubes connected in series or a plurality of transient suppression diodes connected in series;

[0020] The second charging unit is a plurality of voltage regulator tubes connected in series or a plurality of transient voltage suppressor diodes connected in series.

[0021] In some embodiments, the first charging unit includes a first subunit, and the first subunit is a voltage regulator and a bipolar transistor connected in parallel;

[0022] The second charging unit includes a second subunit, and the second subunit is a voltage regulator tube and a bipolar transistor connected in parallel.

[0023] In some embodiments, the first charging unit includes a plurality of first sub-units, and the plurality of first sub-units are connected in series;

[0024] The second charging unit includes a plurality of second sub-units, and the plurality of second sub-units are connected in series.

[0025] In some embodiments, the number of the first power devices and the number of the second power devices are both N, N≥2; the number of the flying capacitors, the first charging units, and the second charging units are all M, M=N-1.

[0026] In some embodiments, the first power device and the second power device are selected from one or more of a power diode, a power transistor, and a power module.

[0027] In some embodiments, an operating voltage of the first charging unit and the second charging unit is higher than a voltage of the first power device and the second power device in an off state, and is lower than a rated voltage of the first power device and the second power device.

[0028] Accordingly, a flying capacitor converter described in an embodiment of the present application includes the flying capacitor converter circuit described in any of the above embodiments.

[0029] Beneficial effects: Compared with the prior art, the flying capacitor converter circuit of the embodiment of the present application includes: a first DC terminal, a second DC terminal and an AC terminal, and a first arm, including a plurality of first power devices and a first charging unit, wherein the plurality of first power devices are connected in series between the first DC terminal and the AC terminal; wherein one first power device is directly connected to the AC terminal, and the remaining first power devices are connected in parallel with the first charging unit in a one-to-one correspondence; a second arm, including a plurality of second power devices and a second charging unit, wherein the plurality of second power devices are connected in series between the second DC terminal and the AC terminal, and in series with the first power device, wherein one second power device is directly connected to the AC terminal, and the remaining second power devices are connected in parallel with the second charging unit in a one-to-one correspondence; a DC bus capacitor, connected between the first DC terminal and the second DC terminal, and connected in parallel with the first arm and the second arm; a flying capacitor, one end of which is connected between two adjacent first power devices, and the other end of which is connected between two adjacent second power devices. In the flying capacitor converter circuit, except for the power device directly connected to the AC terminal, the charging unit is set in parallel with the other power devices. Without additional control, the flying capacitor can be automatically charged while the DC bus capacitor is pre-charged. No auxiliary power supply and floating DC power supply are required. The circuit is simpler and can also be applied to high-voltage applications, which greatly improves the applicability of the technology.

[0030] Compared with the prior art, the flying capacitor converter can have all the technical features and beneficial effects of the above-mentioned flying capacitor converter circuit, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 A schematic diagram of the structure of a flying capacitor converter circuit provided in the first embodiment of the present application;

[0033] Figure 2 A schematic diagram of a first structure of a first charging power source and a second charging unit;

[0034] Figure 3 A second structural schematic diagram of the first charging power source and the second charging unit;

[0035] Figure 4 A third structural schematic diagram of the first charging power source and the second charging unit;

[0036] Figure 5 A fourth structural schematic diagram of the first charging power source and the second charging unit;

[0037] Figure 6 is a fifth structural schematic diagram of the first charging power source and the second charging unit;

[0038] Figure 7 A pre-charge waveform of a flying capacitor converter circuit according to some embodiments of the present application;

[0039] Figure 8 This is a schematic diagram of the structure of a flying capacitor converter circuit in the second embodiment of the present application;

[0040] Figure numerals: 100 - first DC terminal; 200 - second DC terminal; 300 - AC terminal; 400 - first arm; 410 - first power device; 420 - first charging unit; 430 - first normally closed switch; 500 - second arm; 510 - second power device; 520 - second charging unit; 530 - second normally closed switch; 600 - DC bus capacitor; 700 - flying capacitor. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0042] In the description of the present application, it should be understood that the terms "upper", "lower", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In the description of the present application, "multiple" means two or more, and at least one means one, two, or more than two, unless otherwise clearly and specifically defined.

[0043] The applicant found that there are two main types of flying capacitor pre-charging technologies. One type is to set up an auxiliary power supply, which works first. During the pre-charging process of the DC bus capacitor, the flying capacitor is charged by controlling the on-off state of each power device. However, this method is not suitable for converter systems that take points from the DC bus capacitor. The other type is to set up an auxiliary power supply and multiple groups of suspended DC power supplies, which work first and are sorted from low to high according to the normal voltage. The suspended DC power supply charges each flying capacitor in turn. However, for high-voltage applications, it will cause the circuit to be too complicated and costly, and therefore it is not applicable.

[0044] In view of this, an embodiment of the present application provides a flying capacitor converter circuit to improve the applicability of the solution.

[0045] See also Figure 1 The flying capacitor converter circuit of the first embodiment of the present application mainly includes: a first DC terminal 100, a second DC terminal 200, an AC terminal 300, a first arm 400, a second arm 500, a DC bus capacitor 600 and a flying capacitor 700.

[0046] The first DC terminal 100 and the second DC terminal 200 are used to connect to a DC power grid, and the AC terminal 300 is used to connect to an AC power grid.

[0047] The first arm 400 is connected between the first DC terminal 100 and the AC terminal 300. The first arm 400 includes a plurality of first power devices 410 and a first charging unit 420. The plurality of first power devices 410 are connected in series between the first DC terminal 100 and the AC terminal 300. Moreover, among the plurality of first power devices 410, one first power device 410 is directly connected to the AC terminal 300, and the remaining first power devices 410 are connected in parallel with the first charging unit 420 in a one-to-one correspondence. That is, except for the first power device 410 directly connected to the AC terminal 300, the other first power devices 410 are connected in parallel with the corresponding first charging unit 420.

[0048] The second arm 500 includes a plurality of second power devices 510 and a second charging unit 520, wherein the plurality of second power devices 510 are connected in series between the second DC terminal 200 and the AC terminal 300, and are connected in series with the first power device 410. Furthermore, among the plurality of second power devices 510, one second power device 510 is directly connected to the AC terminal 300, and the remaining second power devices 510 are connected in parallel with the second charging unit 520 in a one-to-one correspondence. That is, except for the second power device 510 directly connected to the AC terminal 300, the other second power devices 510 are connected in parallel with the corresponding second charging unit 520.

[0049] The DC bus capacitor 600 is connected between the first DC terminal 100 and the second DC terminal 200 , and is connected in parallel with the first arm 400 and the second arm 500 .

[0050] One end of the flying capacitor 700 is connected between two adjacent first power devices 410 , and the other end of the flying capacitor 700 is connected between two adjacent second power devices 510 .

[0051] Therefore, it can be understood that in the flying capacitor converter circuit, except for the power device directly connected to the AC terminal 300 (including a first power device 410 and a second power device 510 directly connected to the AC terminal 300), other power devices are connected in parallel with the corresponding charging unit. Without additional control, the flying capacitor 700 can be automatically charged while the DC bus capacitor 600 is pre-charged, without auxiliary power supply and suspended DC power supply, the whole circuit is simpler, and can also be applied to high voltage applications, which greatly improves the applicability of the technical solution.

[0052] Specifically, in some embodiments, the number of the first power device 410 and the second power device 510 is N, N≥2; the number of the flying capacitor 700, the first charging unit 420, and the second charging unit 520 is M, M=N-1. That is, in the flying capacitor converter circuit, the total number of power devices is 2N, the number of flying capacitors 700 is N-1, and the total number of charging units is 2N-2.

[0053] Please refer again Figure 1 In some embodiments, the number of the first power device 410 and the second power device 510 are both 3, that is, the number of power devices is 6, namely T1, T2, T3, T4, T5, T6, the number of flying capacitors 700 is 2, namely C1 and C2, the number of the first charging unit 420 and the number of the second charging unit 520 are both 2, that is, the total number of charging units is 4. Except for the power devices directly connected to both sides of the AC terminal 300, the other 4 power devices are respectively connected in parallel with the corresponding charging units.

[0054] The first power device 410 and the second power device 510 may be the same electrical component. Specifically, the first power device 410 and the second power device 510 are selected from one or more of a power diode, a power transistor, and a power module. For example, the first power device 410 and the second power device 510 may both be insulated gate transistors (IGBTs).

[0055] In some embodiments, the positive polarity end of the first charging unit 420 is connected to the collector of the first power device 410, and the negative polarity end is connected to the emitter of the first power device 410; the positive polarity end of the second charging unit 520 is connected to the collector of the second power device 510, and the negative polarity end is connected to the emitter of the second power device 510. In other words, the charging unit has positive and negative polarities. Taking an insulated gate transistor (IGBT) as an example, the positive polarity end of the charging unit is connected to the collector of the IGBT, and the negative polarity end of the charging unit is connected to the emitter of the IGBT.

[0056] The first charging unit 420 and the second charging unit 520 may be the same electrical components. For details, please refer to Figure 2 In some embodiments, the first charging unit 420 may be a voltage regulator or a transient suppression diode; and the second charging unit 520 may be a voltage regulator or a transient suppression diode. In particular, for a low-voltage and low-power flying capacitor converter, a single voltage regulator or a transient suppression diode may be used to form a charging unit to meet the low-voltage and low-power working condition requirements.

[0057] See also Figure 3In some embodiments, if the flying capacitor 700 has a large capacity, in order to increase the charging current, multiple voltage regulators or transient suppression diodes may be connected in parallel to form a charging unit. That is, the first charging unit 420 may be multiple voltage regulators connected in parallel or multiple transient suppression diodes connected in parallel; and the second charging unit 520 may be multiple voltage regulators connected in parallel or multiple transient suppression diodes connected in parallel.

[0058] See also Figure 4 In some embodiments, if the rated operating voltage of the power device is relatively high, greater than the operating voltage of a single Zener diode or a transient suppression diode, multiple Zener diodes or transient suppression diodes may be connected in series to form a charging unit. In other words, the first charging unit 420 is a plurality of Zener diodes or a plurality of transient suppression diodes connected in series; the second charging unit 520 is a plurality of Zener diodes or a plurality of transient suppression diodes connected in series.

[0059] See also Figure 5 In some embodiments, another implementation circuit of a high current charging unit is provided, wherein the first charging unit 420 includes a first subunit, which is a voltage regulator and a bipolar transistor connected in parallel; the second charging unit 520 includes a second subunit, which is a voltage regulator and a bipolar transistor connected in parallel. That is, by connecting the voltage regulator in parallel between the collector and the base of the bipolar transistor, the current amplification function of the bipolar transistor is used to increase the overall current capacity.

[0060] For further information, see Figure 6 In some embodiments, for applications where the flying capacitor 700 has a large capacity and a high operating voltage of the power device, the first charging unit 420 may include multiple first sub-units, which are connected in series; the second charging unit 520 may include multiple second sub-units, which are connected in series.

[0061] In some embodiments, the operating voltage of the first charging unit 420 and the second charging unit 520 is higher than the voltage of the first power device 410 and the second power device 510 in the off state, and lower than the rated voltage of the first power device 410 and the second power device 510. This can prevent the flying capacitor converter circuit from overvoltage breakdown during the pre-charging process, and prevent current from flowing through the charging unit during the normal working stage. In addition, the charging unit has an automatic voltage limiting function without external control.

[0062] For details, please refer to Figure 7, the power devices (including the first power device 410 and the second power device 510) use IGBTs with a rated voltage of 1.7kV, the DC bus operating voltage is 3000V (that is, the operating voltage between the first DC terminal 100 and the second DC terminal 200 is 3000V), and the voltage of each power device in the off state during the normal working stage of the flying capacitor converter circuit is 1000V. In order to prevent the overvoltage breakdown of the power device during the pre-charging process of the flying capacitor converter circuit, and to prevent current from flowing through the charging unit during the normal working stage, the charging unit operating voltage must be higher than the off-state voltage of the power device and lower than the rated voltage of the power device. In this embodiment, the maximum voltage of each charging unit is set to 1200V. When the DC bus capacitor C3 is charged from zero voltage to 3000V, the voltage waveforms of the flying capacitor C1 and the flying capacitor C2 are as follows: Figure 7 As shown, automatic charging of the flying capacitor is achieved.

[0063] See also Figure 8 In the second embodiment of the present application, the first arm 400 also includes a first normally closed switch 430, which is connected in series with the first charging unit 420 in a one-to-one correspondence, and is connected in parallel with the remaining first power devices 410 in a one-to-one correspondence; the second arm 500 also includes a second normally closed switch 530, which is connected in series with the second charging unit 520 in a one-to-one correspondence, and is connected in parallel with the remaining second power devices 510 in a one-to-one correspondence. By adding a normally closed switch, each charging unit is connected in series with the normally closed switch and then in parallel with the power device. When the flying capacitor converter completes pre-charging, the normally closed switch is disconnected. At this time, the maximum voltage of the power device in the off state is no longer limited by the charging unit. Thereby, it is possible to avoid limiting the operating range of the converter as a whole.

[0064] Accordingly, the present application also provides a flying capacitor converter, including the flying capacitor converter circuit of any of the above embodiments. The flying capacitor converter may have all the technical features and beneficial effects of the above flying capacitor converter circuit, which will not be described in detail here.

[0065] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0066] The flying capacitor converter circuit and the flying capacitor converter provided in the embodiments of the present application are introduced in detail above, and the principles and implementation methods of the present application are explained by using specific examples. The description of the above embodiments is only used to help understand the technical solution and its core idea of ​​the present application; ordinary technicians in this field should understand that: they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the present application.

Claims

1. A flying capacitor converter circuit, It is characterized in that include: a first DC terminal (100), a second DC terminal (200) and an AC terminal (300), and The first arm (400) comprises a plurality of first power devices (410) and a first charging unit (420), wherein the plurality of first power devices (410) are connected in series between the first DC terminal (100) and the AC terminal (300); one of the first power devices (410) is directly connected to the AC terminal (300), and the remaining first power devices (410) are connected in parallel to the first charging unit (420) in a one-to-one correspondence; The second arm (500) comprises a plurality of second power devices (510) and a second charging unit (520), wherein the plurality of second power devices (510) are connected in series between the second DC terminal (200) and the AC terminal (300), and are connected in series with the first power device (410), wherein one of the second power devices (510) is directly connected to the AC terminal (300), and the remaining second power devices (510) are connected in parallel with the second charging unit (520) in a one-to-one correspondence; A DC bus capacitor (600) connected between the first DC terminal (100) and the second DC terminal (200), and connected in parallel with the first arm (400) and the second arm (500); A flying capacitor (700) has one end connected between two adjacent first power devices (410) and the other end connected between two adjacent second power devices (510).

2. The flying capacitor converter circuit according to claim 1, It is characterized in that The first arm (400) further comprises a first normally closed switch (430), the first normally closed switch (430) being connected in series with the first charging unit (420) in a one-to-one correspondence, and being connected in parallel with the remaining first power devices (410) in a one-to-one correspondence; The second arm (500) further comprises a second normally closed switch (530), wherein the second normally closed switch (530) is connected in series with the second charging unit (520) in a one-to-one correspondence, and is connected in parallel with the remaining second power devices (510) in a one-to-one correspondence.

3. The flying capacitor converter circuit according to claim 1, It is characterized in that The positive polarity end of the first charging unit (420) is connected to the collector of the first power device (410), and the negative polarity end is connected to the emitter of the first power device (410); The positive polarity end of the second charging unit (520) is connected to the collector of the second power device (510), and the negative polarity end is connected to the emitter of the second power device (510).

4. The flying capacitor converter circuit according to any one of claims 1 to 3, It is characterized in that The first charging unit (420) is a voltage regulator tube or a transient voltage suppressor diode; The second charging unit (520) is a voltage regulator tube or a transient voltage suppressor diode.

5. The flying capacitor converter circuit according to claim 4, It is characterized in that The first charging unit (420) is a plurality of voltage regulator tubes connected in parallel or a plurality of transient voltage suppression diodes connected in parallel; The second charging unit (520) is a plurality of voltage regulator tubes connected in parallel or a plurality of transient voltage suppression diodes connected in parallel.

6. The flying capacitor converter circuit according to claim 4, It is characterized in that The first charging unit (420) is a plurality of voltage regulator tubes connected in series or a plurality of transient suppression diodes connected in series; The second charging unit (520) is a plurality of voltage regulator tubes connected in series or a plurality of transient voltage suppression diodes connected in series.

7. The flying capacitor converter circuit according to any one of claims 1 to 3, It is characterized in that The first charging unit (420) comprises a first subunit, wherein the first subunit is a voltage regulator tube and a bipolar transistor connected in parallel with each other; The second charging unit (520) comprises a second subunit, which is a voltage regulator tube and a bipolar transistor connected in parallel.

8. The flying capacitor converter circuit according to claim 7, It is characterized in that The first charging unit (420) comprises a plurality of first subunits, and the plurality of first subunits are connected in series; The second charging unit (520) includes a plurality of second sub-units, and the plurality of second sub-units are connected in series.

9. The flying capacitor converter circuit according to claim 1, It is characterized in that The number of the first power devices (410) and the number of the second power devices (510) are both N, where N≥2; the number of the flying capacitors (700), the first charging units (420), and the second charging units (520) are both M, where M=N-1.

10. The flying capacitor converter circuit according to claim 1, It is characterized in that The first power device (410) and the second power device (510) are selected from one or more of a power diode, a power transistor, and a power module.

11. The flying capacitor converter circuit according to claim 1, It is characterized in that The operating voltage of the first charging unit (420) and the second charging unit (520) is higher than the voltage of the first power device (410) and the second power device (510) in the off state, and lower than the rated voltage of the first power device (410) and the second power device (510).

12. A flying capacitor converter, It is characterized in that It comprises the flying capacitor converter circuit as claimed in any one of claims 1 to 11.

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