Three-level conversion circuit

Abstract

The invention discloses a three-level conversion circuit. The three-level conversion circuit comprises a main circuit and a frequency control module, the main circuit comprises a direct current output end and an alternating current input end, and a first inner tube device, a second inner tube device, a first outer tube device, a second outer tube device, a first clamping tube and a second clamping tube are arranged between the direct current output end and the alternating current input end; the frequency control module is connected with the control end of the first inner tube device and the control end of the second inner tube device and used for limiting the working frequency of the first inner tube device and the working frequency of the second inner tube device in the zero-crossing switching process of the three-level conversion circuit so as to restrain voltage overshoot. By means of the mode, the frequency control module of the three-level conversion circuit can effectively restrain voltage overshoot, it is guaranteed that a power device works in a safe area of the power device, overvoltage breakdown does not occur, and therefore the operation reliability of the three-level conversion circuit is improved.

Description

Technical Field

[0001] This application relates to the technical field of three-level active neutral-point-clamped inverters, and particularly to a three-level conversion circuit. Background Art

[0002] In the fields of frequency converters or energy storage, etc., the circuit topology usually consists of a three-level topology. Compared with the two-level topology, the three-level topology can effectively reduce the voltage stress of power devices, reduce the difficulty of power device selection, and reduce the switching loss of each power transistor. Its characteristics such as lower voltage change rate and better noise performance are favored by medium and high power applications. Among the three-level topologies, the three-level active neutral-point-clamped (ANPC) circuit is favored due to its advantages in balanced loss and diverse neutral-point balancing means. However, in three-level circuits such as ANPC, the application of the ANPC circuit with hybrid devices can not only greatly reduce the product cost while ensuring performance, but in the ANPC circuit with hybrid devices, the voltage spikes caused by the combined action of the forward recovery of the switching devices and the line parasitic inductance often easily cause overvoltage breakdown of its power devices, resulting in damage to the switching devices. Summary of the Invention

[0003] This application proposes a three-level conversion circuit to solve the above problems.

[0004] To solve the above technical problems, a technical solution adopted by this application is: to provide a three-level conversion circuit, which includes a main circuit and a frequency control module. Among them, the main circuit includes a DC output terminal and an AC input terminal, and a first internal tube device, a second internal tube device, a first external tube device, a second external tube device, a first clamping tube, and a second clamping tube are arranged between the DC output terminal and the AC input terminal; the frequency control module is connected to the control ends of the first internal tube device and the second internal tube device, and is used to limit the operating frequencies of the first internal tube device and the second internal tube device during the zero-crossing switching process of the three-level conversion circuit to suppress voltage overshoot.

[0005] Among them, the frequency control module is also used to obtain the voltage peak value of the three-level conversion circuit and adjust the operating frequencies of the first internal tube device and the second internal tube device based on the voltage peak value.

[0006] Among them, when the voltage peak value is greater than the preset peak threshold value, the frequency control module reduces the operating frequencies of the first internal tube device and the second internal tube device.

[0007] Among them, the frequency control module is also used to restore the operating frequencies of the first internal tube device and the second internal tube device after the zero-crossing switching process of the three-level conversion circuit ends.

[0008] Wherein, a first outer device, a first inner device, a second inner device and a second outer device are connected in series between the DC output terminal and the AC input terminal. A first clamping tube is connected in parallel between the connection point of the first outer device and the first inner device and the midpoint of the DC bus. A second clamping tube is connected in parallel between the connection point of the second inner device and the second outer device and the midpoint of the DC bus. The connection point of the first inner device and the second inner device serves as the AC input terminal.

[0009] Wherein, the three-level conversion circuit further includes a first capacitor assembly and a second capacitor assembly. The DC output terminal is connected in parallel with the first capacitor assembly and the second capacitor assembly. The first capacitor assembly and the second capacitor assembly are connected in series, and the connection point of the first capacitor assembly and the second capacitor assembly serves as the midpoint of the DC bus.

[0010] Wherein, the zero-crossing switching process includes a zero-level operating state. When the three-level conversion circuit operates in the positive-level state, the first outer device and the second clamping tube are turned on, and the second outer device and the first clamping tube are turned off. The frequency control module controls the first inner device and the second inner device to operate in a first frequency modulation mode. When the three-level conversion circuit operates in the zero-level operating state, the first outer device and the second outer device are turned off, and the first clamping tube and the second clamping tube are turned on. The frequency control module controls the first inner device and the second inner device to operate in a second frequency modulation mode. In response to the three-level conversion circuit operating in the negative-level state, the first outer device and the second clamping tube are turned off, and the second outer device and the first clamping tube are turned on. The frequency control module controls the first inner device and the second inner device to operate in the first frequency modulation mode. Wherein, the frequency of the second frequency modulation mode is lower than the frequency of the first frequency modulation mode.

[0011] Wherein, the zero-crossing switching process further includes a positive zero-level transition state and a negative zero-level transition state. When the three-level conversion circuit operates in the positive zero-level transition state, the first outer device, the second outer device and the first clamping tube are turned off, and the second clamping tube is turned on. The frequency control module controls the first inner device and the second inner device to operate in the second frequency modulation mode. When the three-level conversion circuit operates in the negative zero-level transition state, the first outer device, the second outer device and the second clamping tube are turned off, and the first clamping tube is turned on. The frequency control module controls the first inner device and the second inner device to operate in the second frequency modulation mode.

[0012] Wherein, the first inner device includes a first inner tube and a first diode, and the second inner device includes a second inner tube and a second diode. The first inner tube is connected in parallel with the first diode, and the second inner tube is connected in parallel with the second diode. The first inner tube and the second inner tube are MOS tubes. The first outer device includes a first outer tube and a third diode, and the second outer device includes a second outer tube and a fourth diode. The first outer tube is connected in parallel with the third diode, and the second outer tube is connected in parallel with the fourth diode. The first outer tube and the second outer tube are IGBT tubes.

[0013] Among them, the first clamping tube includes a first switching tube and a fifth diode, and the second clamping tube includes a second switching tube and a sixth diode; the first switching tube is connected in parallel with the fifth diode, the second switching tube is connected in parallel with the sixth diode, and the first switching tube and the second switching tube are IGBT tubes; among them, the positive electrode of the fifth diode is connected to the negative electrode of the sixth diode, the negative electrode of the fifth diode is connected to the connection point of the first inner tube device and the first outer tube device; the positive electrode of the sixth diode is connected to the connection point of the second inner tube device and the second outer tube device.

[0014] The beneficial effects of this application are as follows: Different from the prior art, the three-level conversion circuit of this application includes a main circuit and a frequency control module. Among them, the main circuit includes a DC output terminal and an AC input terminal, and a first inner tube device, a second inner tube device, a first outer tube device, a second outer tube device, a first clamping tube, and a second clamping tube are arranged between the DC output terminal and the AC input terminal; the frequency control module is connected to the control terminals of the first inner tube device and the second inner tube device, and is used to limit the operating frequencies of the first inner tube device and the second inner tube device during the zero-crossing switching process of the three-level conversion circuit to suppress voltage overshoot. Through the above method, the frequency control module of this application can limit the operating frequencies of the first inner tube device and the second inner tube device during the zero-crossing switching process of the three-level conversion circuit, can effectively reduce the voltage superposition caused by the forward recovery superposition of the switching tubes, that is, can effectively suppress voltage overshoot, ensure that the power devices work within their safe areas, do not occur overvoltage breakdown, thereby improving the reliability of the operation of the three-level conversion circuit. In addition, limiting the operating frequency can also reduce the turn-off loss of the switching tubes, improve the efficiency of the three-level conversion circuit, extend the service life and reduce the heat dissipation cost. Description of the Drawings

[0015] The drawings here are incorporated into the specification and constitute a part of this specification. These drawings show embodiments consistent with this application and are used together with the specification to illustrate the technical solutions of this application.

[0016] Figure 1 is a schematic diagram of the circuit structure of an embodiment of the three-level conversion circuit of this application;

[0017] Figure 2 is Figure 1 a flowchart of an embodiment in which the ANPC three-level inverter circuit in [reference] switches from the positive half-cycle to the negative half-cycle for operation;

[0018] Figure 3 is a schematic diagram of an embodiment of the voltage spike of a three-phase ANPC hybrid three-level circuit without a frequency control module;

[0019] Figure 4It is a schematic diagram of an embodiment of a voltage spike of a three-phase ANPC hybrid three-level circuit provided with a frequency control module.

[0020] Marking description: Three-level conversion circuit 100, main circuit 10, frequency control module 20, first internal tube device S2, second internal tube device S3, first external tube device S1, second external tube device S4, first clamping tube Sp, second clamping tube Sn, first capacitor assembly C1, second capacitor assembly C2, first external tube Q1, third diode D1, first internal tube Q2, first diode D2, second internal tube Q3, second diode D3, second external tube Q4, fourth diode D4, first switching tube Q5, fifth diode D5, second switching tube Q6, sixth diode D6, DC bus midpoint N, AC input terminal M. Specific implementation mode

[0021] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solutions of the present application more clearly, so they are only examples and cannot be used to limit the protection scope of the present application.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion.

[0023] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "a plurality" is more than two, unless otherwise specifically defined.

[0024] Referring to "embodiment" herein means that a specific feature, structure or characteristic described in connection with the embodiment can be included in at least one embodiment of this application. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0025] In the description of the embodiments of the present application, unless otherwise clearly specified and defined, technical terms such as "installation", "connection", "connection", "fixation" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific situations.

[0026] In fields such as frequency converters or energy storage, the circuit topology usually consists of a three-level topology. Compared with the two-level topology, the three-level topology can effectively reduce the voltage stress of power devices, reduce the difficulty of power device selection, and reduce the switching loss of each power transistor. Its characteristics such as lower voltage change rate and better noise performance are favored by medium and high power application scenarios. Among the three-level topologies, the three-level active neutral-point-clamped (ANPC) circuit is highly regarded due to its advantages in terms of balanced losses and diverse means of neutral point balance. However, in three-level circuits such as ANPC, the application of the ANPC circuit with hybrid devices can not only greatly reduce the product cost while ensuring performance, but in the ANPC circuit with hybrid devices, the voltage spikes caused by the combined action of the forward recovery of the switching device and the line parasitic inductance often easily cause overvoltage breakdown of its power devices, resulting in damage to the switching devices.

[0027] In the ANPC circuit with hybrid devices, there are two commutation architectures. One is the architecture with 2 low-frequency switching tubes and 4 high-frequency switching tubes, and the other is the architecture with 2 high-frequency switching tubes and 4 low-frequency switching tubes. However, in the prior art, in order to reduce the leakage inductance turn-off spikes caused by the parasitic inductance in the circuit, the method of adjusting the turn-off speed of the high-frequency switching tubes by increasing the resistance value of the drive resistor or adjusting the gate capacitance and other drive parameters is adopted. However, the voltage spikes caused by the superposition of the forward recovery of the Insulated Gate Bipolar Transistor (IGBT) switching tubes are often ignored. Reducing the switching speed of the high-frequency switching tubes can only suppress the voltage spikes caused by the line leakage inductance, and will not effectively compensate for the influence brought by the forward recovery of the IGBT switching tubes. In addition, excessive addition of passive components such as resistors and capacitors to meet the working requirements reduces the working performance of the switching tubes themselves; and under heavy load working conditions, the superposition of the forward recovery of the IGBT switching tubes and the leakage inductance spikes caused by the turn-off current very easily causes overvoltage breakdown of the power devices, resulting in damage to the switching devices.

[0028] To solve the above problems, the present application first proposes a three-level conversion circuit. Please refer toFigure 1 , Figure 1 is a schematic circuit diagram of an embodiment of the three-level conversion circuit of the present application. As Figure 1 shown, in this embodiment, the three-level conversion circuit 100 includes a main circuit 10 and a frequency control module 20. Among them, the main circuit 10 includes a DC output terminal and an AC input terminal. A first internal tube device S2, a second internal tube device S3, a first external tube device S1, a second external tube device S4, a first clamping tube Sp, and a second clamping tube Sn are arranged between the DC output terminal and the AC input terminal; the frequency control module 20 is connected to the control ends of the first internal tube device S2 and the second internal tube device S3, and is used to limit the operating frequencies of the first internal tube device S2 and the second internal tube device S3 during the zero-crossing switching process of the three-level conversion circuit 100 to suppress voltage overshoot.

[0029] In this embodiment, the three-level conversion circuit 100 takes the Figure 1 shown ANPC three-level inverter circuit as an example. In the ANPC three-level inverter circuit, during the working cycle of each phase voltage, there are a positive half-cycle for supplying positive voltage and a negative half-cycle for supplying negative voltage. Please refer to Figure 2 , Figure 2 is Figure 1 a flowchart of an embodiment in which the ANPC three-level inverter circuit in Figure 1 switches from the positive half-cycle to the negative half-cycle for operation. In the ANPC three-level inverter circuit as shown in Figure 1 , in order to prevent overvoltage breakdown of the first internal tube device S2 and the second internal tube device S3 in the middle caused by positive and negative switching, a positive and negative cycle switching method is designed. The purpose is to release the voltage energy on the capacitors of the first internal tube device S2 and the second internal tube device S3 operating at high frequency, thereby preventing overvoltage from occurring under the condition that current flows into the inverter.

[0030] Before the end of each commutation process and before the other half starts to work, the PN junctions in the switching tubes of the first internal tube device S2 and the second internal tube device S3 in the ANPC three-level inverter circuit will experience a process from being reverse-biased and cut off to being forward-conducted. Among them, the deeper the PN junction is cut off, the greater the forward recovery effect caused during the forward turn-on process, and thus the greater the voltage spike superimposed on the switching tubes of the first internal tube device S2 and the second internal tube device S3. When the voltage spike exceeds the tolerance value of the power device, device damage will occur.

[0031] As Figure 2 shown, this embodiment takes the switching process from the positive half-cycle to the negative half-cycle of the ANPC three-level inverter circuit as an example to illustrate the overvoltage mechanism of the positive and negative cycle switching process, which is specifically as follows:

[0032] The working state of the ANPC three-level inverter circuit in the positive half-cycle is as Figure 2As shown in Fig. a, the first outer tube device S1 and the second clamping tube Sn are in the closed state, the first clamping tube Sp and the second outer tube device S4 are in the open state, the first inner tube device S2 and the second inner tube device S3 are in the state of high-frequency modulation, and the input current of the ANPC three-level inverter circuit charges the first capacitor assembly C1 of the positive half bus through the first inner tube device S2 and the first outer tube device S1; at the beginning state of the positive-negative switching, as Figure 2 shown in Fig. b, first disconnect the first outer tube device S1. Under this condition, the current path of the ANPC three-level inverter circuit remains unchanged temporarily; as Figure 2 shown in Fig. c, close the first clamping tube Sp. Due to the closing of the first clamping tube Sp, the voltage across the two ends of the first outer tube device S1 is clamped by the first capacitor assembly C1, and the current path changes to flow through the second inner tube device S3 and the second clamping tube Sn. The second clamping tube Sn generates a forward recovery effect due to the sudden increase in current, and then generates a voltage fluctuation across the second clamping tube Sn; as Figure 2 shown in Fig. d, in the second half cycle of the zero-crossing switching, the second clamping tube Sn is disconnected; as Figure 2 shown in Fig. e, the second outer tube device S4 is closed. At this time, the second clamping tube Sn is clamped by the second capacitor assembly C2, and the current flow direction conversion generates a forward recovery at both ends of the first clamping tube Sp, as Figure 2 shown in Fig. f, this voltage will be superimposed on both ends of the first inner tube device S2 and the second inner tube device S3 of the high-frequency switching together with the voltage across the second capacitor assembly C2 and the loop leakage inductance spike during the negative half cycle. When the voltage exceeds the withstand voltage threshold conditions of the electronic devices of the first inner tube device S2 and the second inner tube device S3, the first inner tube device S2 and the second inner tube device S3 will be damaged.

[0033] Therefore, in order to effectively reduce the voltage superposition caused by the forward recovery superposition of the switching tube, that is, to effectively suppress the voltage overshoot and ensure that the power device operates in its safe area without overvoltage breakdown, a frequency control module 20 is added to the three-level conversion circuit 100 in this embodiment. In this embodiment, the frequency control module 20 is used to limit the operating frequencies of the first inner tube device S2 and the second inner tube device S3 during the zero-crossing switching process of the three-level conversion circuit 100. During the zero-crossing switching process of the three-level conversion circuit, that is, during the above Figure 2 processes from Fig. b to Fig. e, the operating frequencies of the first inner tube device S2 and the second inner tube device S3 are limited, so that the voltage superposition caused by the forward recovery superposition of the switching tube can be effectively reduced. This method can effectively suppress the influence of the voltage spike caused by the forward recovery of the PN junction, quantitatively control the forward recovery of the switching tube fundamentally, and reduce the voltage spike during its turn-off process.

[0034] Different from the prior art, the three-level conversion circuit 100 of the present application includes a main circuit 10 and a frequency control module 20. Among them, the main circuit 10 includes a DC output terminal and an AC input terminal. Between the DC output terminal and the AC input terminal, a first internal transistor device S2, a second internal transistor device S3, a first external transistor device S1, a second external transistor device S4, a first clamping transistor Sp, and a second clamping transistor Sn are provided; the frequency control module 20 is connected to the control terminals of the first internal transistor device S2 and the second internal transistor device S3, and is used to limit the operating frequencies of the first internal transistor device S2 and the second internal transistor device S3 during the zero-crossing switching process of the three-level conversion circuit 100 to suppress voltage overshoot. In the above manner, the frequency control module 20 of the present application can limit the operating frequencies of the first internal transistor device S2 and the second internal transistor device S3 during the zero-crossing switching process of the three-level conversion circuit 100, can effectively reduce the voltage superposition caused by the forward recovery superposition of the switching transistors, that is, can effectively suppress voltage overshoot, ensure that the power devices operate within their safe regions, and do not undergo overvoltage breakdown, thereby improving the reliability of the operation of the three-level conversion circuit 100. In addition, limiting the operating frequency can also reduce the turn-off loss of the switching transistors, improve the efficiency of the three-level conversion circuit 100, extend the service life, and reduce the heat dissipation cost.

[0035] Optionally, based on the above embodiment, in this embodiment, the frequency control module 20 is further used to obtain the voltage peak value of the three-level conversion circuit 100, and adjust the operating frequencies of the first internal transistor device S2 and the second internal transistor device S3 based on the voltage peak value.

[0036] That is, in this embodiment, the frequency control module 20 can also add a closed-loop working mode, detect the value of the voltage spike in real time, and adjust the operating frequencies of the first internal transistor device S2 and the second internal transistor device S3 in real time according to the degree of the voltage spike, so as to finely control the starting working state. In the above manner, the frequency control module 20 of this embodiment can further reduce the overvoltage risk and increase the reliability of the operation of the three-level conversion circuit 100.

[0037] Optionally, as Figure 1 shown, between the DC output terminal and the AC input terminal of the three-level conversion circuit 100 in this embodiment, a first internal transistor device S2, a second internal transistor device S3, a first external transistor device S1, a second external transistor device S4 are connected in series. A first clamping transistor Sp is connected in parallel between the connection point of the first external transistor device S1 and the first internal transistor device S2 and the midpoint of the DC bus. A second clamping transistor Sn is connected in parallel between the connection point of the second internal transistor device S3 and the second external transistor device S4 and the midpoint N of the DC bus. The connection point of the first internal transistor device S2 and the second internal transistor device S3 serves as the AC input terminal M.

[0038] Optionally, as Figure 1As shown, the three-level conversion circuit 100 further includes a first capacitor component C1 and a second capacitor component C2. The DC output terminal is connected in parallel with the first capacitor component C1 and the second capacitor component C2. The first capacitor component C1 and the second capacitor component C2 are connected in series, and the connection point of the first capacitor component C1 and the second capacitor component C2 serves as the midpoint N of the DC bus.

[0039] Wherein, in this embodiment, the first capacitor component C1 and the second capacitor component C2 are the same capacitor components.

[0040] Optionally, as Figure 1 shown, the first inner tube device S2 includes a first inner tube Q2 and a first diode D2, and the second inner tube device S3 includes a second inner tube Q3 and a second diode D3; the first inner tube Q2 is connected in parallel with the first diode D2, and the second inner tube Q3 is connected in parallel with the second diode D3.

[0041] The first outer tube device S1 includes a first outer tube Q1 and a third diode D1, and the second outer tube device S4 includes a second outer tube Q4 and a fourth diode D4; the first outer tube Q1 is connected in parallel with the third diode D1, and the second outer tube Q4 is connected in parallel with the fourth diode D4.

[0042] In this embodiment, the first inner tube Q2 and the second inner tube Q3 can be set as MOS tubes; the first outer tube Q1 and the second outer tube Q4 are IGBT tubes. In other embodiments, the first inner tube Q2 and the second inner tube Q3 can also be set as IGBT tubes, which is not limited herein.

[0043] Optionally, as Figure 1 shown, the first clamping tube Sp includes a first switching tube Q5 and a fifth diode D5, and the second clamping tube Sn includes a second switching tube Q6 and a sixth diode D6; the first switching tube Q5 is connected in parallel with the fifth diode D5, the second switching tube Q6 is connected in parallel with the sixth diode D6, and the first switching tube Q5 and the second switching tube Q6 are IGBT tubes.

[0044] Wherein, the positive electrode of the fifth diode D5 is connected to the negative electrode of the sixth diode D6, the negative electrode of the fifth diode D5 is connected to the connection point of the first inner tube device S2 and the first outer tube device S1; the positive electrode of the sixth diode D6 is connected to the connection point of the second inner tube device S3 and the second outer tube device S4.

[0045] In this embodiment, the first clamping tube Sp and the second clamping tube Sn are also the same clamping tubes.

[0046] Optionally, in this embodiment, the frequency control module 20 can be set to reduce the operating frequencies of the first inner tube device S2 and the second inner tube device S3 in response to the voltage peak being greater than a preset peak threshold.

[0047] That is, in this embodiment, if the monitored voltage peak value is greater than the preset peak threshold value, the operating frequencies of the first inner tube device S2 and the second inner tube device S3 are further reduced.

[0048] Optionally, in this embodiment, the frequency control module 20 is further configured to restore the operating frequencies of the first inner tube device S2 and the second inner tube device S3 after the zero-crossing switching process of the three-level conversion circuit 100 ends.

[0049] That is, after the zero-crossing ends, the frequency control module 20 stops restricting the operating frequencies of the first inner tube device S2 and the second inner tube device S3, and the first inner tube device S2 and the second inner tube device S3 resume their original designed operating frequencies to work.

[0050] Optionally, based on the above embodiment, this embodiment will further illustrate the operating states of the switching tubes during the zero-crossing switching process after adding the frequency control module 20. In this embodiment, the zero-crossing switching process includes a zero-level operating state. When the three-level conversion circuit 100 operates in the positive-level state, the first outer tube device S1 and the second clamping tube Sn are turned on, and the second outer tube device S4 and the first clamping tube Sp are turned off. The frequency control module 20 controls the first inner tube device S2 and the second inner tube device S3 to operate in the first frequency modulation mode.

[0051] When the three-level conversion circuit 100 operates in the zero-level operating state, the first outer tube device S1 and the second outer tube device S4 are turned off, and the first clamping tube Sp and the second clamping tube Sn are turned on. The frequency control module 20 controls the first inner tube device S2 and the second inner tube device S3 to operate in the second frequency modulation mode; in response to the three-level conversion circuit 100 operating in the negative-level state, the first outer tube device S1 and the second clamping tube Sn are turned off, and the second outer tube device S|4 and the first clamping tube Sp are turned on. The frequency control module 20 controls the first inner tube device S2 and the second inner tube device S3 to operate in the first frequency modulation mode; where the frequency of the second frequency modulation mode is lower than the frequency of the first frequency modulation mode.

[0052] Optionally, the zero-crossing switching process further includes a positive zero-level transition state and a negative zero-level transition state; when the three-level conversion circuit 100 operates in the positive zero-level transition state, the first outer tube device S1, the second outer tube device S4, and the first clamping tube Sp are turned off, and the second clamping tube Sn is turned on. The frequency control module 20 controls the first inner tube device S2 and the second inner tube device S3 to operate in the second frequency modulation mode; when the three-level conversion circuit 100 operates in the negative zero-level transition state, the first outer tube device S1, the second outer tube device S4, and the second clamping tube Sn are turned off, and the first clamping tube Sp is turned on. The frequency control module 20 controls the first inner tube device S2 and the second inner tube device S3 to operate in the second frequency modulation mode.

[0053] Among them, the second frequency modulation mode is the mode that limits the operating frequencies of the first inner tube device S2 and the second inner tube device S3, and the first frequency modulation mode is the mode of the operating frequency in the original design described above.

[0054] In an application scenario, the frequency control module 20 of the present application is applied to a three-phase ANPC three-level inverter circuit. Please refer to Figure 3 , Figure 3 which is a schematic diagram of an embodiment of the voltage spike of a three-phase ANPC hybrid three-level circuit without a frequency control module; please refer to Figure 4 , Figure 4 which is a schematic diagram of an embodiment of the voltage spike of a three-phase ANPC hybrid three-level circuit provided with a frequency control module. Comparing Figure 3 and Figure 4 for the voltage spikes, it can be found that under the condition that the load power is 10 kW, as Figure 3 shows, the maximum value of the voltage spike without the frequency control module 20 is 40 V. When the frequency control module 20 is provided, under the same load power condition, the maximum value of the voltage spike is 30 V. It can be seen that setting the frequency control module 20 can reduce the voltage spike by 25%.

[0055] In other embodiments, the frequency control module 20 of this embodiment can also be applied to other types of three-level inverter circuits, which is not limited herein.

[0056] The above are only the embodiments of the present application, and do not limit the patent scope of the present application accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present application, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present application.

Claims

1. A three-level conversion circuit, characterized in that, It includes a main circuit and a frequency control module. Among them, the main circuit includes a DC output terminal and an AC input terminal, and a first inner tube device, a second inner tube device, a first outer tube device, a second outer tube device, a first clamping tube, and a second clamping tube are arranged between the DC output terminal and the AC input terminal. The frequency control module is connected to the control terminals of the first inner tube device and the second inner tube device, and is used to limit the operating frequencies of the first inner tube device and the second inner tube device during the zero-crossing switching process of the three-level conversion circuit to suppress voltage overshoot.

2. The three-level conversion circuit according to claim 1, wherein The frequency control module is also used to obtain the voltage peak value of the three-level conversion circuit and adjust the operating frequencies of the first inner tube device and the second inner tube device based on the voltage peak value.

3. The three-level conversion circuit according to claim 2, wherein, When the voltage peak value is greater than the preset peak threshold value, the frequency control module reduces the operating frequencies of the first inner tube device and the second inner tube device.

4. The three-level conversion circuit according to claim 1, wherein The frequency control module is also used to restore the operating frequencies of the first inner tube device and the second inner tube device after the zero-crossing switching process of the three-level conversion circuit ends.

5. The three-level conversion circuit according to claim 1, wherein the first outer tube device, the first inner tube device, the second inner tube device, and the second outer tube device are connected in series between the DC output terminal and the AC input terminal, the first clamping tube is connected in parallel between the connection point of the first outer tube device and the first inner tube device and the midpoint of the DC bus, the second clamping tube is connected in parallel between the connection point of the second inner tube device and the second outer tube device and the midpoint of the DC bus, and the connection point of the first inner tube device and the second inner tube device serves as the AC input terminal.

6. The three-level conversion circuit according to claim 5, wherein The three-level conversion circuit further includes a first capacitor assembly and a second capacitor assembly. The DC output terminal is connected in parallel with the first capacitor assembly and the second capacitor assembly. The first capacitor assembly and the second capacitor assembly are connected in series, and the connection point of the first capacitor assembly and the second capacitor assembly serves as the midpoint of the DC bus.

7. The three-level conversion circuit according to claim 6, wherein The zero-crossing switching process includes a zero-level operating state. When the three-level conversion circuit operates in the positive-level state, the first outer tube device and the second clamping tube are turned on, the second outer tube device and the first clamping tube are turned off, and the frequency control module controls the first inner tube device and the second inner tube device to operate in a first frequency modulation mode. When the three-level conversion circuit operates in the zero-level operating state, the first outer tube device and the second outer tube device are turned off, the first clamping tube and the second clamping tube are turned on, and the frequency control module controls the first inner tube device and the second inner tube device to operate in a second frequency modulation mode. In response to the three-level conversion circuit operating in the negative-level state, the first outer tube device and the second clamping tube are turned off, the second outer tube device and the first clamping tube are turned on, and the frequency control module controls the first inner tube device and the second inner tube device to operate in a first frequency modulation mode. Among them, the frequency of the second frequency modulation mode is lower than the frequency of the first frequency modulation mode.

8. The three-level conversion circuit according to claim 7, wherein, The zero-crossing switching process further includes a positive zero-level transition state and a negative zero-level transition state; When the three-level conversion circuit operates in the positive zero-level transition state, the first external transistor device, the second external transistor device, and the first clamping transistor are turned off, the second clamping transistor is turned on, and the frequency control module controls the first internal transistor device and the second internal transistor device to operate in the second frequency modulation mode; When the three-level conversion circuit operates in the negative zero-level transition state, the first external transistor device, the second external transistor device, and the second clamping transistor are turned off, the first clamping transistor is turned on, and the frequency control module controls the first internal transistor device and the second internal transistor device to operate in the second frequency modulation mode.

9. The three-level conversion circuit according to claim 5, characterized in that, The first internal transistor device includes a first internal transistor and a first diode; the second internal transistor device includes a second internal transistor and a second diode; the first internal transistor is connected in parallel with the first diode, the second internal transistor is connected in parallel with the second diode, and the first internal transistor and the second internal transistor are MOS transistors; The first external transistor device includes a first external transistor and a third diode; the second external transistor device includes a second external transistor and a fourth diode; the first external transistor is connected in parallel with the third diode, the second external transistor is connected in parallel with the fourth diode, and the first external transistor and the second external transistor are IGBT transistors; 10. The three-level conversion circuit according to claim 5, characterized in that, The first clamping transistor includes a first switching transistor and a fifth diode; the second clamping transistor includes a second switching transistor and a sixth diode; the first switching transistor is connected in parallel with the fifth diode, the second switching transistor is connected in parallel with the sixth diode, and the first switching transistor and the second switching transistor are IGBT transistors; Wherein, the positive electrode of the fifth diode is connected to the negative electrode of the sixth diode, and the negative electrode of the fifth diode is connected to the connection point of the first internal transistor device and the first external transistor device; the positive electrode of the sixth diode is connected to the connection point of the second internal transistor device and the second external transistor device.

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