Anpc type three-level circuit and control method thereof

Abstract

The application discloses an ANPC type three-level circuit and a control method thereof, and belongs to the technical field of power electronics. The ANPC type three-level circuit comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube which are connected in series; an absorption capacitor module; two clamping tubes connected in series; and a controller connected with the first switch tube and the fourth switch tube, used for acquiring a current bus voltage of the DC bus, and controlling the first switch tube or the fourth switch tube to act based on the current bus voltage, so as to charge the absorption capacitor module. The circuit can safely and efficiently charge the absorption capacitor module, reduce the voltage difference between the absorption capacitor module and the DC bus, and be beneficial to balancing the device stress distribution and reducing the safety hidden danger.

Description

Technical Field

[0001] This application belongs to the field of power electronics technology, and in particular relates to an ANPC type three-level circuit and its control method. Background Technology

[0002] Active Neutral Point Clamped (ANPC) three-level topologies are widely used in photovoltaic inverters, energy storage converters, and other fields due to their advantages such as uniform loss distribution and high conversion efficiency. In practical applications, this type of topology typically uses a snubber capacitor connected in parallel across the inner tube to prevent damage from excessive voltage stress. However, if the voltage difference between the snubber capacitor and the DC bus is too large, it may cause uneven stress distribution in the device, leading to safety hazards. Summary of the Invention

[0003] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes an ANPC-type three-level circuit and its control method, which can safely and efficiently charge the absorption capacitor module, reduce the voltage difference between the absorption capacitor module and the DC bus, facilitate the equalization of device stress distribution, and reduce safety hazards.

[0004] In a first aspect, this application provides an ANPC-type three-level circuit, comprising: A first switch, a second switch, a third switch, and a fourth switch are connected in series. One end of the first switch is connected to the positive terminal of the DC bus, and one end of the fourth switch is connected to the negative terminal of the DC bus. An absorption capacitor module is connected in parallel between the common terminal of the first and second switching transistors and the common terminal of the third and fourth switching transistors. Two clamping transistors connected in series are connected in parallel between the common terminal of the first and second switching transistors and the common terminal of the third and fourth switching transistors. The common terminal of the two clamping transistors is connected to the neutral point of the DC bus. The controller, connected to the first switch and the fourth switch, is used to obtain the current bus voltage of the DC bus and, based on the current bus voltage, control the first switch or the fourth switch to operate to charge the absorption capacitor module.

[0005] According to the ANPC-type three-level circuit of this application, by obtaining the current bus voltage of the DC bus, the first or fourth switch is controlled to operate, thus constructing a circuit for charging the absorption capacitor module. This safely and efficiently charges the absorption capacitor module, reduces the voltage difference between the absorption capacitor module and the DC bus, helps to balance the stress distribution of the devices, and reduces safety hazards.

[0006] According to one embodiment of this application, when the current bus voltage is less than or equal to a first voltage threshold, the controller is used to first control the first switch or the fourth switch to remain on, and then start the pre-charging circuit of the DC bus so that the voltage of the absorption capacitor module changes with the voltage of the DC bus.

[0007] According to one embodiment of this application, when the current bus voltage is greater than a first voltage threshold and less than or equal to a second voltage threshold, the controller is configured to control the switching on and off of the first switch or the fourth switch according to a first switching frequency and a first duty cycle to increase the voltage of the absorption capacitor module; in response to the voltage of the absorption capacitor module reaching half the bus voltage, the controller first controls the first switch or the fourth switch to remain on, and then starts the pre-charging circuit of the DC bus so that the voltage of the absorption capacitor module changes with the voltage of the DC bus; Wherein, the first voltage threshold is less than the second voltage threshold, and the second voltage threshold is determined based on the grid-connected voltage of the ANPC type three-level circuit.

[0008] According to one embodiment of this application, when the current bus voltage is greater than a second voltage threshold, the controller is used to control the switching on and off of the first switch or the fourth switch according to a second switching frequency and a second duty cycle until the voltage of the absorption capacitor module reaches half the bus voltage. The second voltage threshold is determined based on the grid-connected voltage of the ANPC-type three-level circuit.

[0009] According to one embodiment of this application, the absorption capacitor module includes a first absorption capacitor, one end of which is connected to the common terminal of the first switch and the second switch, and the other end of which is connected to the common terminal of the third switch and the fourth switch.

[0010] According to one embodiment of this application, the absorption capacitor module includes a second absorption capacitor and a third absorption capacitor connected in series, the second absorption capacitor being connected in parallel across the second switching transistor, and the third absorption capacitor being connected in parallel across the third switching transistor.

[0011] Secondly, this application provides a control method for an ANPC-type three-level circuit, the ANPC-type three-level circuit comprising: A first switch, a second switch, a third switch, and a fourth switch are connected in series. One end of the first switch is connected to the positive terminal of the DC bus, and one end of the fourth switch is connected to the negative terminal of the DC bus. An absorption capacitor module is connected in parallel between the common terminal of the first and second switching transistors and the common terminal of the third and fourth switching transistors. Two clamping transistors connected in series are connected in parallel between the common terminal of the first and second switching transistors and the common terminal of the third and fourth switching transistors. The common terminal of the two clamping transistors is connected to the neutral point of the DC bus. The control method includes: Obtain the current bus voltage of the DC bus; Based on the current bus voltage, control the first switch or the fourth switch to operate in order to charge the absorption capacitor module.

[0012] According to one embodiment of this application, controlling the operation of the first switch or the fourth switch based on the current bus voltage includes: When the current bus voltage is less than or equal to the first voltage threshold, the first switch or the fourth switch is first kept on, and then the pre-charging circuit of the DC bus is started so that the voltage of the absorption capacitor module changes with the voltage of the DC bus.

[0013] According to one embodiment of this application, controlling the operation of the first switch or the fourth switch based on the current bus voltage includes: When the current bus voltage is greater than the first voltage threshold and less than or equal to the second voltage threshold, the first switch or the fourth switch is switched on and off according to the first switching frequency and the first duty cycle to increase the voltage of the absorption capacitor module. In response to the voltage of the absorption capacitor module reaching half bus voltage, the first switch or the fourth switch is first controlled to remain on, and then the pre-charging circuit of the DC bus is started so that the voltage of the absorption capacitor module changes with the voltage of the DC bus. Wherein, the first voltage threshold is less than the second voltage threshold, and the second voltage threshold is determined based on the grid-connected voltage of the ANPC type three-level circuit.

[0014] According to one embodiment of this application, controlling the operation of the first switch or the fourth switch based on the current bus voltage includes: When the current bus voltage is greater than the second voltage threshold, the first switch or the fourth switch is controlled to switch on and off according to the second switching frequency and the second duty cycle until the voltage of the absorption capacitor module reaches half the bus voltage. The second voltage threshold is determined based on the grid-connected voltage of the ANPC-type three-level circuit.

[0015] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0016] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is one of the structural schematic diagrams of the ANPC type three-level circuit provided in the embodiments of this application; Figure 2 This is the second schematic diagram of the structure of the ANPC type three-level circuit provided in the embodiments of this application; Figure 3 This is the third schematic diagram of the structure of the ANPC type three-level circuit provided in the embodiments of this application; Figure 4 This is the fourth schematic diagram of the structure of the ANPC type three-level circuit provided in the embodiments of this application; Figure 5 This is the fifth schematic diagram of the structure of the ANPC type three-level circuit provided in the embodiments of this application; Figure 6 This is a flowchart illustrating the control method for the ANPC-type three-level circuit provided in the embodiments of this application. Detailed Implementation

[0017] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0018] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0019] The ANPC-type three-level circuit and its control method provided in this application will be described in detail below with reference to the accompanying drawings, through specific embodiments and application scenarios.

[0020] The ANPC-type three-level circuit of this application embodiment can be used in power conversion equipment such as photovoltaic inverters and energy storage converters to optimize loss distribution and improve system efficiency.

[0021] The ANPC type three-level circuit includes: a first switch, a second switch, a third switch, and a fourth switch connected in series, an absorption capacitor module, two clamping transistors connected in series, and a controller.

[0022] One end of the first switching transistor is connected to the positive terminal of the DC bus, and one end of the fourth switching transistor is connected to the negative terminal of the DC bus. The absorption capacitor module is connected in parallel between the common terminal of the first and second switching transistors and the common terminal of the third and fourth switching transistors. Two clamping transistors are connected in parallel between the common terminal of the first and second switching transistors and the common terminal of the third and fourth switching transistors. The common terminal of the two clamping transistors is connected to the neutral point of the DC bus.

[0023] Among them, the first and fourth switching transistors are the external transistors of the ANPC type three-level circuit, which are connected to the positive and negative terminals of the DC bus, respectively; the second and third switching transistors are the internal transistors of the ANPC type three-level circuit, and the common terminal between the second and third switching transistors is the AC output terminal of the ANPC type three-level circuit.

[0024] The two clamping transistors connected in series can be the fifth and sixth switching transistors. One end of the fifth switching transistor is connected to the common terminal between the first and second switching transistors, and one end of the sixth switching transistor is connected to the common terminal between the third and fourth switching transistors. The common terminal between the fifth and sixth switching transistors is connected to the neutral point of the DC bus.

[0025] The first, fourth, fifth, and sixth switching transistors can be insulated gate bipolar transistors (IGBTs) or other switching devices suitable for low- to medium-frequency operating conditions, while the second and third switching transistors can be silicon carbide metal-oxide-semiconductor field-effect transistors (SiC MOSFETs) or other switching devices suitable for high-frequency operating conditions.

[0026] It should be noted that the second and third switching transistors perform switching actions rapidly at high frequency, which can easily generate large voltage spikes in the circuit. The absorption capacitor module is connected in parallel across the two inner transistors. When the inner transistors are turned off or when a voltage spike is generated, the absorption capacitor module can absorb the excess energy, suppress the amplitude of the voltage spike, make the voltage change more gradual, and reduce the voltage stress impact on the switching transistors.

[0027] In practice, the absorption capacitor module can adopt structures such as single capacitor (C) absorption circuit, resistor-capacitor (RC) absorption circuit, and inductor-capacitor (LC) absorption circuit, and the selection can be made according to the actual application requirements.

[0028] In some embodiments, the absorption capacitor module includes a first absorption capacitor, one end of which is connected to the common terminal of the first and second switching transistors, and the other end of which is connected to the common terminal of the third and fourth switching transistors.

[0029] In this embodiment, the second and third switching transistors share the first absorption capacitor, and the ANPC type three-level circuit has a simple structure and occupies little space.

[0030] For example, such as Figure 1 As shown, the first switch Q1, the second switch M2, the third switch M3, and the fourth switch Q4 are connected in series. One end of Q1 is connected to the positive terminal BUS+ of the DC bus, and P_BUS is the positive bus capacitor. One end of Q4 is connected to the negative terminal BUS- of the DC bus, and N_BUS is the negative bus capacitor. One end of the fifth switch Q5 is connected to the common terminal between Q1 and M2. One end of the sixth switch Q6 is connected to the common terminal between M3 and Q4. The common terminal between Q5 and Q6 is connected to the neutral point BUSN of the DC bus.

[0031] Among them, Q1 is connected in parallel with freewheeling diode D1, M2 is connected in parallel with freewheeling diode D2, M3 is connected in parallel with freewheeling diode D3, Q4 is connected in parallel with freewheeling diode D4, and Q5 is connected in parallel with freewheeling diode D5.

[0032] One end of the first absorption capacitor C1 is connected to the common terminal of Q1 and M2, and the other end of the first absorption capacitor is connected to the common terminal of M3 and Q4. M2 and M3 share C1.

[0033] In actual implementation, C1 can also be connected in series with the first resistor R1 to form an RC absorption circuit structure.

[0034] For example, such as Figure 3 As shown, the first resistor R1 is connected between BUS+ and the common terminal of Q1 and M2, forming a loop BUSN→Q6→C1→R1→BUS+, which charges C1; Figure 4 As shown, the first resistor R1 is connected between the common terminal of M3 and Q4 and BUS-, forming a loop BUSN→D5→C1→R1→BUS-, which charges C1.

[0035] In some embodiments, the absorption capacitor module includes a second absorption capacitor and a third absorption capacitor connected in series, the second absorption capacitor being connected in parallel across the two ends of the second switching transistor, and the third absorption capacitor being connected in parallel across the two ends of the third switching transistor.

[0036] In this embodiment, the second and third switching transistors are each equipped with an absorption capacitor, which can effectively balance the voltage stress distribution between the second and third switching transistors. When one of the absorption capacitors fails, the inner transistor connected in parallel with the other absorption capacitor can still be protected, which helps to improve the safety redundancy of the circuit.

[0037] For example, such as Figure 5 As shown, the first switch Q1, the second switch M2, the third switch M3, and the fourth switch Q4 are connected in series. One end of Q1 is connected to the positive terminal BUS+ of the DC bus, and P_BUS is the positive bus capacitor. One end of Q4 is connected to the negative terminal BUS- of the DC bus, and N_BUS is the negative bus capacitor. One end of the fifth switch Q5 is connected to the common terminal between Q1 and M2. One end of the sixth switch Q6 is connected to the common terminal between M3 and Q4. The common terminal between Q5 and Q6 is connected to the neutral point BUSN of the DC bus.

[0038] Among them, Q1 is connected in parallel with freewheeling diode D1, M2 is connected in parallel with freewheeling diode D2, M3 is connected in parallel with freewheeling diode D3, Q4 is connected in parallel with freewheeling diode D4, and Q5 is connected in parallel with freewheeling diode D5.

[0039] The second absorption capacitor C2 is connected in parallel across M2, and the third absorption capacitor C3 is connected in parallel across M3. M2 and M3 are each configured with a separate absorption capacitor.

[0040] In this embodiment, C2 is connected in series with the second resistor R2 to form an RC absorption circuit structure; C3 is connected in series with the second resistor R2 to form an RC absorption circuit structure.

[0041] The ANPC-type three-level circuit also includes a controller, which is connected to the first and fourth switching transistors to obtain the current bus voltage of the DC bus and, based on the current bus voltage, control the first or fourth switching transistor to charge the absorption capacitor module.

[0042] It should be noted that controlling the operation of the first or fourth switching transistor creates a charging loop for the absorption capacitor module in the ANPC-type three-level circuit. By using the switching transistors of the ANPC-type three-level circuit itself to charge the absorption capacitor module, the use of hardware circuits can be reduced, and circuit protection can also be achieved.

[0043] For example, such as Figure 1 As shown, the controller controls Q1 to turn on, and a circuit for charging C1 is constructed through Q1, C1, and D6 connected in parallel with Q6; or, the controller controls Q4 to turn on, and a circuit for charging C1 is constructed through Q4, C1, and D5 connected in parallel with Q5.

[0044] In actual operation, the controller controls the operation of the first or fourth switching transistor based on the current bus voltage of the DC bus, including controlling the switching state, switching frequency or duty cycle of the switching transistor.

[0045] It should be noted that the first and fourth switching transistors do not operate simultaneously. For example, after the first switching transistor is turned on, the fourth switching transistor does not operate until the charging of the absorption capacitor module is completed, and then the first switching transistor is turned off. Subsequently, the switching transistors of the ANPC type three-level circuit can be controlled to operate according to normal logic.

[0046] According to the ANPC-type three-level circuit provided in the embodiments of this application, by obtaining the current bus voltage of the DC bus, the first or fourth switch is controlled to operate, thereby constructing a circuit for charging the absorption capacitor module. This safely and efficiently charges the absorption capacitor module, reduces the voltage difference between the absorption capacitor module and the DC bus, helps to balance the stress distribution of the devices, and reduces safety hazards.

[0047] The embodiments of this application will be described in detail below from three different implementation perspectives.

[0048] In some embodiments, when the current bus voltage is less than or equal to a first voltage threshold, the controller is used to first control the first switch or the fourth switch to remain on, and then start the pre-charging circuit of the DC bus so that the voltage of the absorption capacitor module changes with the voltage of the DC bus.

[0049] Among them, the pre-charging circuit of the DC bus can slowly charge the DC bus during the power-on process, balance the positive and negative bus voltages, and realize the safe start-up of the circuit.

[0050] In practice, the pre-charging circuit can use either a DC power supply or an AC power supply as its input power source.

[0051] In this embodiment, when the current bus voltage is less than or equal to a preset first voltage threshold, the first or fourth switch is kept on, and the pre-charging circuit of the DC bus is started. Through the pre-charging circuit, the charging circuit composed of the first or fourth switch charges the absorption capacitor module, so that the voltage of the absorption capacitor module rises with the voltage of the DC bus.

[0052] In actual implementation, starting the pre-charging circuit of the DC bus can be used as a switch to close the pre-charging circuit of the DC bus, and the absorption capacitor module can be charged through the pre-charging circuit and the charging circuit.

[0053] For example, such as Figure 2As shown, when the current bus voltage is less than or equal to the first voltage threshold, the controller controls Q1 to turn on and controls S3 of the pre-charging circuit to close, so that C1 is charged through the charging circuit constructed by the pre-charging circuit through Q1, C1 and D6 connected in parallel with Q6.

[0054] Alternatively, if the current bus voltage is less than or equal to the first voltage threshold, the controller controls Q4 to turn on and controls S3 of the pre-charging circuit to close, so that C1 is charged through the charging circuit constructed by the pre-charging circuit through Q4, C1 and D5 connected in parallel with Q5.

[0055] The sampling circuit is connected in parallel across C1. The voltage of C1 can be collected in real time through the sampling circuit to monitor whether the voltage of the absorption capacitor module changes with the voltage of the DC bus. The data collected by the sampling circuit can also be used to monitor the voltage spikes generated by the inner tube and realize overvoltage protection.

[0056] In some embodiments, when the current bus voltage is greater than a first voltage threshold and less than or equal to a second voltage threshold, the controller is used to control the switching of a first switch or a fourth switch according to a first switching frequency and a first duty cycle to increase the voltage of the absorption capacitor module; in response to the voltage of the absorption capacitor module reaching half the bus voltage, the controller first controls the first switch or the fourth switch to remain on, and then starts the pre-charging circuit of the DC bus so that the voltage of the absorption capacitor module changes with the voltage of the DC bus.

[0057] Among them, half bus voltage refers to the voltage from the positive (or negative) pole of the DC bus to the neutral point, which accounts for half of the total DC bus voltage.

[0058] For example, the half-bus voltage can be the voltage from BUS+ to BUSN, that is, the voltage across P_BUS; or, the half-bus voltage can be the voltage from BUSN to BUS-, that is, the voltage across N_BUS.

[0059] In this embodiment, when the current bus voltage is greater than the first voltage threshold and less than or equal to the second voltage threshold, the controller first controls the first or fourth switch to operate according to the first switching frequency and the first duty cycle to increase the voltage of the absorption capacitor module; when the voltage of the absorption capacitor module is increased to half the bus voltage, the controller then controls the first or fourth switch to remain on, and finally starts the pre-charging circuit of the DC bus. Through the pre-charging circuit, the absorption capacitor module is charged through the charging circuit composed of the first or fourth switch, so that the voltage of the absorption capacitor module rises with the voltage of the DC bus.

[0060] If the controller first controls the switching of the first switching transistor according to the first switching frequency and the first duty cycle, when the voltage of the absorption capacitor module rises to half bus voltage, the controller controls the first switching transistor to remain on.

[0061] If the controller first controls the switching of the fourth switch according to the first switching frequency and the first duty cycle, when the voltage of the absorption capacitor module rises to half bus voltage, the controller will control the fourth switch to remain on.

[0062] The first switching frequency and the first duty cycle are preset control parameters.

[0063] In actual implementation, the first switching frequency can be set to a high-frequency value close to the rated frequency of the switching transistor, and the first duty cycle can be set to a small duty cycle. By controlling the external transistor to switch on and off in a high-frequency, low-duty-cycle manner, the amplitude of the charging current is effectively suppressed, preventing instantaneous large current from impacting the switching transistor and capacitor. At the same time, the energy transfer ratio within each switching cycle is controllable, making the charging process smoother and enabling the absorption capacitor module to be charged safely and stably to half bus voltage.

[0064] For example, the first switching frequency can be 95%-98% of the rated frequency, and the first duty cycle can be 1%-10%.

[0065] The first voltage threshold is less than the second voltage threshold, and the second voltage threshold is determined based on the grid-connected voltage of the ANPC type three-level circuit.

[0066] In practice, the second voltage threshold can be 95%-100% of the grid-connected voltage, and the first voltage threshold can be determined based on the second voltage threshold. The first voltage threshold is 5%-15% of the second voltage threshold.

[0067] For example, the grid connection voltage is 1000V, the second voltage threshold can be set to 950V, and the first voltage threshold can be set to 100V.

[0068] In some embodiments, when the current bus voltage is greater than the second voltage threshold, the controller is used to control the switching of the first or fourth switch according to the second switching frequency and the second duty cycle until the voltage of the absorption capacitor module reaches half the bus voltage.

[0069] In this embodiment, when the current bus voltage is greater than the second voltage threshold, the controller controls the first or fourth switch to operate according to the second switching frequency and the second duty cycle to increase the voltage of the absorption capacitor module. When the voltage of the absorption capacitor module is increased to half the bus voltage, charging ends and the first or fourth switch is turned off.

[0070] The second switching frequency and the second duty cycle are preset control parameters.

[0071] In actual implementation, the second switching frequency can be set to a high-frequency value close to the rated frequency of the switching transistor, and the second duty cycle can be set to a smaller duty cycle. By controlling the external transistor to switch on and off in a high-frequency, low-duty-cycle manner, the amplitude of the charging current is effectively suppressed, preventing instantaneous large current from impacting the switching transistor and capacitor. At the same time, the energy transfer ratio within each switching cycle is controllable, making the charging process smoother and enabling the absorption capacitor module to be charged safely and stably to half bus voltage.

[0072] For example, the second switching frequency can be 95%-98% of the rated frequency, and the second duty cycle can be 1%-10%.

[0073] This application also provides a control method for an ANPC-type three-level circuit.

[0074] The ANPC type three-level circuit includes: The first switch, the second switch, the third switch, and the fourth switch are connected in series. One end of the first switch is connected to the positive terminal of the DC bus, and one end of the fourth switch is connected to the negative terminal of the DC bus. An absorption capacitor module is connected in parallel between the common terminal of the first and second switching transistors and the common terminal of the third and fourth switching transistors. Two clamping transistors connected in series are connected in parallel between the common terminal of the first and second switching transistors and the common terminal of the third and fourth switching transistors. The common terminal of the two clamping transistors is connected to the neutral point of the DC bus.

[0075] like Figure 6 As shown, the control method for the ANPC type three-level circuit includes steps 610 and 620.

[0076] Step 610: Obtain the current bus voltage of the DC bus.

[0077] Step 620: Based on the current bus voltage, control the first or fourth switch to operate in order to charge the absorption capacitor module.

[0078] According to the control method of the ANPC type three-level circuit provided in the embodiments of this application, by obtaining the current bus voltage of the DC bus, the first or fourth switch is controlled to operate, thereby constructing a circuit for charging the absorption capacitor module. This safely and efficiently charges the absorption capacitor module, reduces the voltage difference between the absorption capacitor module and the DC bus, helps to balance the stress distribution of the devices, and reduces safety hazards.

[0079] In some embodiments, controlling the operation of a first switch or a fourth switch based on the current bus voltage includes: When the current bus voltage is less than or equal to the first voltage threshold, first control the first or fourth switch to remain on, and then start the pre-charging circuit of the DC bus so that the voltage of the absorption capacitor module changes with the voltage of the DC bus.

[0080] In some embodiments, controlling the operation of a first switch or a fourth switch based on the current bus voltage includes: When the current bus voltage is greater than the first voltage threshold and less than or equal to the second voltage threshold, the first or fourth switching transistor is switched on and off according to the first switching frequency and the first duty cycle to increase the voltage of the absorption capacitor module. In response to the voltage of the absorption capacitor module reaching half bus voltage, first control the first or fourth switch to remain on, and then start the pre-charging circuit of the DC bus so that the voltage of the absorption capacitor module changes with the voltage of the DC bus. The first voltage threshold is less than the second voltage threshold, and the second voltage threshold is determined based on the grid-connected voltage of the ANPC type three-level circuit.

[0081] In some embodiments, controlling the operation of a first switch or a fourth switch based on the current bus voltage includes: When the current bus voltage is greater than the second voltage threshold, the first or fourth switch is switched on or off according to the second switching frequency and the second duty cycle until the voltage of the absorption capacitor module reaches half the bus voltage. The second voltage threshold is determined based on the grid-connected voltage of the ANPC-type three-level circuit.

[0082] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0083] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the related technology, can be embodied in the form of a computer software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a terminal (which may be a mobile phone, computer, server, or network device, etc.) to execute the methods described in the various embodiments of this application.

[0084] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

[0085] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0086] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. An ANPC-type three-level circuit, characterized in that, include: A first switch, a second switch, a third switch, and a fourth switch are connected in series. One end of the first switch is connected to the positive terminal of the DC bus, and one end of the fourth switch is connected to the negative terminal of the DC bus. An absorption capacitor module is connected in parallel between the common terminal of the first and second switching transistors and the common terminal of the third and fourth switching transistors. Two clamping transistors connected in series are connected in parallel between the common terminal of the first and second switching transistors and the common terminal of the third and fourth switching transistors. The common terminal of the two clamping transistors is connected to the neutral point of the DC bus. The controller, connected to the first switch and the fourth switch, is used to obtain the current bus voltage of the DC bus and, based on the current bus voltage, control the first switch or the fourth switch to operate in order to charge the absorption capacitor module.

2. The ANPC-type three-level circuit according to claim 1, characterized in that, When the current bus voltage is less than or equal to a first voltage threshold, the controller is used to first control the first switch or the fourth switch to remain on, and then start the pre-charging circuit of the DC bus so that the voltage of the absorption capacitor module changes with the voltage of the DC bus.

3. The ANPC-type three-level circuit according to claim 1, characterized in that, When the current bus voltage is greater than a first voltage threshold and less than or equal to a second voltage threshold, the controller controls the switching of the first switch or the fourth switch according to a first switching frequency and a first duty cycle to increase the voltage of the absorption capacitor module; in response to the voltage of the absorption capacitor module reaching half the bus voltage, the controller first controls the first switch or the fourth switch to remain on, and then starts the pre-charging circuit of the DC bus so that the voltage of the absorption capacitor module changes with the voltage of the DC bus. Wherein, the first voltage threshold is less than the second voltage threshold, and the second voltage threshold is determined based on the grid-connected voltage of the ANPC type three-level circuit.

4. The ANPC-type three-level circuit according to claim 1, characterized in that, When the current bus voltage is greater than the second voltage threshold, the controller is used to control the switching on and off of the first switch or the fourth switch according to the second switching frequency and the second duty cycle until the voltage of the absorption capacitor module reaches half the bus voltage. The second voltage threshold is determined based on the grid-connected voltage of the ANPC-type three-level circuit.

5. The ANPC-type three-level circuit according to any one of claims 1-4, characterized in that, The absorption capacitor module includes a first absorption capacitor, one end of which is connected to the common terminal of the first switch and the second switch, and the other end of which is connected to the common terminal of the third switch and the fourth switch.

6. The ANPC-type three-level circuit according to any one of claims 1-4, characterized in that, The absorption capacitor module includes a second absorption capacitor and a third absorption capacitor connected in series. The second absorption capacitor is connected in parallel across the two ends of the second switching transistor, and the third absorption capacitor is connected in parallel across the two ends of the third switching transistor.

7. A control method for an ANPC-type three-level circuit, characterized in that, The ANPC-type three-level circuit includes: A first switch, a second switch, a third switch, and a fourth switch are connected in series. One end of the first switch is connected to the positive terminal of the DC bus, and one end of the fourth switch is connected to the negative terminal of the DC bus. An absorption capacitor module is connected in parallel between the common terminal of the first and second switching transistors and the common terminal of the third and fourth switching transistors. Two clamping transistors connected in series are connected in parallel between the common terminal of the first and second switching transistors and the common terminal of the third and fourth switching transistors. The common terminal of the two clamping transistors is connected to the neutral point of the DC bus. The control method includes: Obtain the current bus voltage of the DC bus; Based on the current bus voltage, control the first switch or the fourth switch to operate in order to charge the absorption capacitor module.

8. The control method for the ANPC type three-level circuit according to claim 7, characterized in that, The step of controlling the operation of the first switch or the fourth switch based on the current bus voltage includes: When the current bus voltage is less than or equal to the first voltage threshold, the first switch or the fourth switch is first kept on, and then the pre-charging circuit of the DC bus is started so that the voltage of the absorption capacitor module changes with the voltage of the DC bus.

9. The control method for the ANPC type three-level circuit according to claim 7, characterized in that, The step of controlling the operation of the first switch or the fourth switch based on the current bus voltage includes: When the current bus voltage is greater than the first voltage threshold and less than or equal to the second voltage threshold, the first switch or the fourth switch is switched on and off according to the first switching frequency and the first duty cycle to increase the voltage of the absorption capacitor module. In response to the voltage of the absorption capacitor module reaching half bus voltage, the first switch or the fourth switch is first controlled to remain on, and then the pre-charging circuit of the DC bus is started so that the voltage of the absorption capacitor module changes with the voltage of the DC bus. Wherein, the first voltage threshold is less than the second voltage threshold, and the second voltage threshold is determined based on the grid-connected voltage of the ANPC type three-level circuit.

10. The control method for the ANPC type three-level circuit according to claim 7, characterized in that, The step of controlling the operation of the first switch or the fourth switch based on the current bus voltage includes: When the current bus voltage is greater than the second voltage threshold, the first switch or the fourth switch is controlled to switch on and off according to the second switching frequency and the second duty cycle until the voltage of the absorption capacitor module reaches half the bus voltage. The second voltage threshold is determined based on the grid-connected voltage of the ANPC-type three-level circuit.

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