An ac-dc converter and control method

Abstract

The application provides an AC / DC converter and a control method, and relates to the technical field of electronic power. N The application realizes reliable series connection and voltage balance of switching devices in a medium-high voltage scene, solves the problem of difficult voltage and capacity expansion of a traditional two-level voltage source converter, and through the mode of setting module step length, shutting down the first switching device in batches and opening part of the second switching device in batches when the target bridge arm is turned off, makes the output voltage change in steps, reduces the output voltage change rate from the bus voltage level to the module voltage level, reaches the voltage change rate level of the multi-level topology, solves the problem that the traditional two-level voltage source converter is difficult to be applied to the medium-high voltage scene due to high voltage change rate, and meanwhile, compared with the multi-level topology, the AC / DC converter also has the advantages of fewer devices and simple topology, which is beneficial to reducing the equipment volume and cost.

Description

Technical Field

[0001] This application belongs to the field of electronic power technology, and in particular relates to an AC / DC converter and its control method. Background Technology

[0002] With the establishment of my country's dual-carbon goals, large-scale new energy power generation is rapidly becoming widespread, and high-voltage power systems are being built at an accelerated pace, leading to an ever-increasing demand for medium- and high-voltage AC / DC converters.

[0003] In medium- and high-voltage applications, the high output voltage change rate (expressed as dv / dt) generated by the AC port of the power electronic converter means that the voltage that the AC load can withstand changes by several kilovolts in an extremely short time of several μs. The high dv / dt generated by the power electronic converter has become a key technical bottleneck restricting further improvements in system reliability, safety, and performance. Summary of the Invention

[0004] This application provides an AC / DC converter and control method that reduces the output voltage change rate from the bus voltage level to the module voltage level, solving the problem that the high voltage change rate of traditional two-level voltage source converters makes them difficult to apply in medium and high voltage scenarios.

[0005] In a first aspect, embodiments of this application provide a control method for an AC / DC converter, the AC / DC converter including at least one bridge arm, each bridge arm including an upper bridge arm and a lower bridge arm connected in series, both the upper bridge arm and the lower bridge arm including N A series of switch modules; each switch module includes a first switch branch and a buffer branch connected in parallel. The first switch branch includes a first switch device and a protection unit connected in parallel. The buffer branch includes a second switch device, a clamping unit and an energy storage unit. The second switch device is connected in series with the energy storage unit and in parallel with the clamping unit. The control method includes: Acquire the switching signal of the target bridge arm, which includes either the upper or lower bridge arm of each bridge arm; Upon detecting a switch signal transitioning from an on state to an off state, within the first time period, the target bridge arm is turned off each time at a predetermined interval. N 2 The first switching device of the switching module, until the target bridge arm is turned off. N 1 The first switching device of a switching module; During the second time period, the remaining sections on the target bridge arm were shut down. N 3 The first switching device of a switching module; During the third time period, the target bridge arm is opened each time according to the second set interval. N2 The second switching device of the switching module, until the target bridge arm is turned on. N 1 The second switching device of the switching module is turned off when the on-time reaches a first time threshold. N 1 The second switching device of a switching module; in, N , N 1 , N 2 and N 3 All are integers greater than or equal to 1. N 2 Less than N 1 , N 1 Less than N , N 1 and N 3 The sum of equals N .

[0006] In some embodiments, during a first time period, the target bridge arm is shut down each time at a first predetermined interval. N 2 The first switching device of the switching module, until the target bridge arm is turned off. N 1 The first switching device of the switching module includes: Apply voltage to the target bridge arm in ascending order. N The switch modules are sorted in the first order; Within the first time period, according to the first sorting order, the first set interval time, and the target bridge arm being shut down each time. N 2 The first switching device of the switching module, until the target bridge arm is turned off. N 1 The first switching device of a switching module.

[0007] In some embodiments, during the third time period, the target bridge arm is opened each time according to the second predetermined interval. N 2 The second switching device of the switching module, until the target bridge arm is turned on. N 1 The second switching device of the switching module includes: Apply voltage to the target bridge arm in descending order. N Each switch module is sorted in the second order; During the third time period, according to the second sorting, the second set interval time, and the target bridge arm opened each time. N 2 The second switching device of the switching module, until the target bridge arm is turned on. N 1 The second switching device of a switching module.

[0008] In some embodiments, during the third time period, the target bridge arm is opened each time according to the second predetermined interval. N 2 The second switching device of the switching module, until the target bridge arm is turned on. N 1 Before the second switching device of the switching module, the control method further includes: Starting from the end of the second time period, the time corresponding to the delay of the second time threshold is determined as the start time of the third time period; The second time threshold is determined based on the dead time of the switching module.

[0009] In some embodiments, acquiring the switching signal of the target bridge arm includes: Acquire the modulation signals of the upper and lower bridge arms; When the modulation signal of one of the upper and lower bridge arms is detected to switch from the on state to the off state, the modulation signal of the other of the upper and lower bridge arms is switched from the off state to the on state, starting from the switching time and delayed by a preset bridge arm dead time, so as to obtain the switching signal of the target bridge arm.

[0010] In some embodiments, acquiring the modulation signals of the upper and lower bridge arms includes: Acquire the raw modulation signals of the upper and lower bridge arms; A minimum narrow pulse time constraint is applied to the original modulation signal to generate modulation signals for the upper and lower bridge arms; The minimum narrow pulse time constraint includes the duration of the modulated signal being greater than or equal to a third time threshold.

[0011] In some embodiments, the control method further includes: Upon detecting a switch signal changing from an off signal to an on signal, the target bridge arm is simultaneously activated. N The first switching device of a switching module.

[0012] Secondly, this application also provides an AC / DC converter, comprising: At least one bridge arm, each bridge arm comprising an upper bridge arm and a lower bridge arm connected in series, both the upper and lower bridge arms including NA series of switch modules; each switch module includes a first switch branch and a buffer branch connected in parallel. The first switch branch includes a first switch device and a protection unit connected in parallel. The buffer branch includes a second switch device, a clamping unit and an energy storage unit. The second switch device is connected in series with the energy storage unit and in parallel with the clamping unit. The controller is configured to: acquire the switching signal of a target bridge arm, the target bridge arm including either the upper or lower bridge arm of each bridge arm; and, upon detecting a switch signal switching from an on to an off state, shut down the upper arm of the target bridge arm at predetermined intervals within a first time period. N 2 The first switching device of the switching module, until the target bridge arm is turned off. N 1 The first switching device of the switching module; during the second time period, turning off the remaining switches on the target bridge arm. N 3 The first switching device of the switching module; during the third time period, according to the second set interval, the target bridge arm is turned on each time. N 2 The second switching device of the switching module, until the target bridge arm is turned on. N 1 The second switching device of the switching module is turned off when the on-time reaches a first time threshold. N 1 The second switching device of a switching module; in, N , N 1 , N 2 and N 3 All are integers greater than or equal to 1. N 2 Less than N 1 , N 1 Less than N , N 1 and N 3 The sum of equals N .

[0013] In some embodiments, the protection unit includes a first diode, the conduction direction of the first diode being opposite to that of the first switching device, and the reverse recovery time of the first diode being less than or equal to a fourth time threshold.

[0014] In some embodiments, the energy storage unit includes a buffer capacitor; And / or, the clamping unit includes a second diode, the conduction direction of the second diode being opposite to the conduction direction of the second switching device, and the reverse recovery time of the second diode being less than or equal to a fifth time threshold.

[0015] The AC / DC converter and control method provided in this application embodiment include, for each bridge arm, both the upper and lower bridge arms. N The series-connected switching modules achieve reliable series connection and voltage balancing of switching devices in medium and high voltage scenarios, solving the problem of difficult voltage and capacity expansion of traditional two-level voltage source converters (VSCs). By using a step-wise method of setting the number of modules when turning off the target bridge arm, and turning off the first switching device in batches and turning on some of the second switching devices in batches, the output voltage changes in a stepped manner, reducing the output voltage change rate from the bus voltage level to the module voltage level, achieving the voltage change rate level of multi-level topologies. This solves the problem that traditional two-level VSCs are difficult to apply to medium and high voltage scenarios due to their high voltage change rate. At the same time, compared with multi-level topologies, this AC / DC converter also has the advantages of fewer devices and a simpler topology, which helps to reduce equipment size and cost. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of a single-phase AC / DC converter provided in one embodiment of this application; Figure 2 This is a schematic diagram of the structure of a three-phase AC / DC converter provided in one embodiment of this application; Figure 3 This is a schematic diagram of the structure of a bridge arm provided in one embodiment of this application; Figure 4 This is a schematic diagram of the structure of a switch module provided in one embodiment of this application; Figure 5 A flowchart illustrating a control method for an AC / DC converter provided in one embodiment of this application; Figure 6 A schematic diagram of the module trigger pulse control timing of the upper and lower bridge arms provided in one embodiment of this application; Figure 7 A flowchart illustrating a control method for an AC / DC converter provided in another embodiment of this application; Figure 8 A flowchart illustrating a control method for an AC / DC converter provided in yet another embodiment of this application; Figure 9 This is a schematic diagram of the structure of a bridge arm provided in another embodiment of this application; Figure 10 This application provides a schematic diagram of the series bridge arm waveform of a single-phase switching module when the load current is DC, as shown in one embodiment. Figure 11 A waveform diagram illustrating the active shutdown process of the upper arm as provided in one embodiment of this application; Figures 12-17 An equivalent circuit for the active shutdown process of the upper arm provided in one embodiment of this application; Figure 18 A waveform diagram illustrating the active opening process of the upper bridge arm according to an embodiment of this application; Figures 19-23 An equivalent loop for the active opening process of the upper arm provided in one embodiment of this application; Figure 24 The load current provided in one embodiment of this application is the waveform of a single-phase switch module connected in series when it is AC. Detailed Implementation

[0018] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0019] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, 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..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0020] In the field of medium- and high-voltage high-power power conversion, the AC / DC interconnection of medium-voltage distribution networks requires a large number of low-cost medium-voltage AC / DC conversion devices, and the large-scale construction of flexible high-voltage DC transmission requires new low-cost converter topology solutions. In the field of medium- and high-voltage high-power frequency conversion, there is a large demand not only in traditional industrial drives, mining machinery, and ship propulsion, but also in the growing demand from clean energy power generation and pumped storage grid connection scenarios.

[0021] However, in these medium- and high-voltage application scenarios, the high output voltage change rate (dv / dt) generated at the AC port of the power electronic converter means that the voltage withstand capability of the AC load changes by several kilovolts in an extremely short time of several μs. This dv / dt poses a severe test to the insulation withstand capability of the AC port loads of the converter, such as filter reactors, transformers, and motor windings, and presents a great challenge to insulation design. For example, it can affect the uneven distribution of the electric field, causing electrical stress breakdown of the inter-turn insulation of the windings, causing partial discharge and insulation aging of the insulation material, and increasing the dielectric loss of the insulation material, resulting in thermal aging.

[0022] In the field of medium and high voltage variable frequency drives, the inverter and the AC motor (load) are usually connected by a cable of tens to hundreds of meters in length. The extremely high dv / dt pulse will cause significant wave reflection in the distributed inductance and distributed capacitance of the cable, resulting in overvoltage at the motor end and threatening the insulation safety of the load.

[0023] In addition, high dv / dt can lead to strong electromagnetic interference and radiation, which can interfere with the normal operation of sensitive electronic equipment in the system and make it difficult to meet electromagnetic compatibility standards.

[0024] In summary, the high dv / dt generated by power electronic converters has become a key technical bottleneck restricting further improvements in system reliability, safety, and performance.

[0025] To address the aforementioned technical issues, the applicant, through in-depth research, discovered that the dv / dt level generated at the AC port of a power electronic converter mainly depends on the voltage change during the output level change process caused by the converter's primary switching behavior, and is primarily determined by the converter's topology and control.

[0026] In related technologies, medium-voltage frequency converters / converters below 10kV DC often employ neutral point clamped (NPC) multilevel topologies and capacitor-skimmed multilevel topologies. However, these topologies face a significant increase in complexity in topology and control as the number of levels increases. In engineering applications, three-level systems are more common, with five-level or higher applications being rare, making it difficult to increase the voltage and capacity of the equipment. Moreover, in addition to the increased complexity in topology and control, they still require more clamping diodes or floating capacitors than traditional two-level VSCs, increasing the cost and size of the equipment.

[0027] Modular multilevel converters (MMCs) are commonly used in DC converters above 10kV and medium-high voltage. In the field of DC frequency conversion above 10kV and medium-high voltage, cascaded H-bridge (CHB) or modular matrix multilevel converters are more commonly used. These topologies based on half-bridge or full-bridge submodules require twice or more of the number of power electronic devices compared to traditional two-level VSCs. Furthermore, the submodules require a large number of module support capacitors to smooth low-frequency energy pulsations in the bridge arms. The volume and weight of the module support capacitors exceed 70% of the submodules, significantly increasing the size and cost of the equipment.

[0028] Two-level VSC is the most basic AC / DC conversion unit, requiring only the fewest components and bridge arms. It is the most common AC / DC conversion and frequency conversion topology in low-voltage scenarios. However, if two-level VSC is applied to medium- and high-voltage scenarios, not only will a large number of power electronic components be connected in series, but without special design, the synchronous turn-off of the entire high-voltage series bridge arm will cause a dv / dt of more than 10 kV / us, which the load cannot withstand.

[0029] Based on this, embodiments of this application provide an AC / DC converter and a control method, wherein each bridge arm includes an upper bridge arm and a lower bridge arm. N The series-connected switching modules achieve reliable series connection and voltage balancing of switching devices in medium and high voltage scenarios, solving the problem of difficult voltage and capacity expansion in traditional two-level VSCs. By using a step-wise method of setting the number of modules when turning off the target bridge arm, and turning off the first switching device in batches and turning on some of the second switching devices in batches, the output voltage changes in a stepped manner, reducing the output voltage change rate from the bus voltage level to the module voltage level, achieving the voltage change rate level of multi-level topologies. This solves the problem that traditional two-level VSCs are difficult to apply in medium and high voltage scenarios due to their high voltage change rate. At the same time, compared with multi-level topologies, this AC / DC converter also has the advantages of fewer devices and a simpler topology, which helps to reduce equipment size and cost.

[0030] The AC / DC converter provided in the embodiments of this application will be described below.

[0031] In one embodiment, such as Figure 1 or Figure 2 As shown, the AC / DC converter may include at least one bridge arm 10 and a controller (not shown in the figure).

[0032] Among them, such as Figure 3 As shown, the bridge arm 10 includes an upper bridge arm 11 and a lower bridge arm 12 connected in series. Both the upper bridge arm 11 and the lower bridge arm 12 include... N 13 series-connected switch modules. Among them, NIt is an integer greater than or equal to 1. N The voltage capacity of the AC / DC converter and the withstand voltage capability of the switching module 13 can be determined.

[0033] This application extends a single power device into a modular switch. For example... Figure 4 As shown, each switch module 13 includes a first switch branch 131 and a buffer branch 132 connected in parallel. The first switch branch 131 includes a first switch device connected in parallel. S The protection unit 1311 and the buffer branch 132 include a second switching device. S a Clamping unit 1321 and energy storage unit 1322, second switching device S a The second switching device is connected in series with the energy storage unit 1322. S a Connected in parallel with clamping unit 1321. Combined Figure 3 Multiple switching modules 13 are connected in series to form an upper bridge arm 11 or a lower bridge arm 12. The upper bridge arm 11 and the lower bridge arm 12 are connected in series to form a complete bridge arm 10. By controlling the voltage balance of the series modules, the voltage withstand limit of the power devices can be overcome to construct a high-voltage switching bridge arm.

[0034] The controller is configured to: acquire the switching signal of a target bridge arm, the target bridge arm including any one of the upper bridge arm 11 and the lower bridge arm 12 of each bridge arm 10; and, upon detecting that the switching signal of the target bridge arm has switched from an on state to an off state, within a first time period, shut down the upper bridge arm of the target bridge arm at first predetermined intervals. N 2 The first switching device of the switching module 13 S Until the target bridge arm is shut down N 1 The first switching device of the switching module 13 S During the second time period, the remaining [functions] on the target bridge arm were shut down. N 3 The first switching device of the switching module 13 S During the third time period, the target bridge arm is opened each time according to the second set interval. N 2 The second switching device of the switching module 13 S a Until the target bridge arm is opened N 1 The second switching device of the switching module 13 S a and in the second switching device S a Shut down if the activation time reaches the first time threshold. N1 The second switching device of the switching module 13 S a .

[0035] N 1 , N 2 and N 3 All are integers greater than or equal to 1. N 2 Less than N 1 , N 1 Less than N , N 1 and N 3 The sum of equals N .

[0036] As an example, N 3 Greater than or equal to N 2 ,and N 3 Less than or equal to 2 times N 2 .

[0037] As an example, Figure 1 The AC / DC converter shown is a single-phase AC / DC converter, which includes two parallel bridge arms 10. Each bridge arm includes an upper bridge arm 11 and a lower bridge arm 12 connected in series. Both the upper bridge arm 11 and the lower bridge arm 12 include N series-connected switching modules 13.

[0038] As an example, Figure 2 The AC / DC converter shown is a three-phase AC / DC converter, which includes three parallel bridge arms 10. Each bridge arm includes an upper bridge arm 11 and a lower bridge arm 12 connected in series. Both the upper bridge arm 11 and the lower bridge arm 12 include N series-connected switching modules 13.

[0039] It should be noted that, Figure 1 and Figure 2 The AC / DC converter shown is merely an example and may include single-phase AC / DC converters and three-phase AC / DC converters, and may also include all types of AC / DC converters known to those skilled in the art, without limitation herein.

[0040] First switching device S Its function is to turn the load on and off, perform pulse width adjustment, and modulate the required sinusoidal voltage on the AC side of the AC-DC converter.

[0041] Protection unit 1311 is used in the first switching deviceS When turned off, a low-impedance freewheeling path is provided for the inductive current generated by the load or line. The inductive current continues to flow through the protection unit 1311 and feeds energy back to the DC bus or load, thereby turning off the first switching device. S The voltage at both ends is clamped at a safe bus voltage level, thus protecting the first switching device. S Its function.

[0042] Second switching device S a It is used for transient current flowing through the bridge arm during the commutation process and has the characteristic of zero current turn-off.

[0043] Energy storage unit 1322 is used to buffer and absorb transient charging energy caused by stray inductance in the circuit during the transient process after the bridge arm is turned off. When the second switching device S a When turned off, the voltage of the energy storage unit 1322 can be maintained at a stable DC bias voltage by utilizing the clamping effect of the clamping unit 1321, and the second switching device... S a Discharge occurs during active activation.

[0044] In the bridge arms (upper bridge arm 11 and lower bridge arm 13) of the series connection of the switching module 13, the second switching device S a The flexible control allows for balanced voltage control of each switching module 13 in the series bridge arm. This ensures series voltage balance of the switching devices, requiring only a bandwidth of the bridge arm's kHz-level switching frequency for voltage balancing. This reduces the controller's bandwidth, is feasible in engineering, offers high reliability, and avoids the problems associated with high-bandwidth control, such as electromagnetic interference and electromagnetic compatibility issues.

[0045] The duration of the first time period can be determined based on the first preset interval time and... N 1 The first switching device S The number of shutdowns is determined. As an example, the duration of the first time period is greater than or equal to the first set interval time. N 1 The first switching device S The product of the number of times it is turned off, i.e. T 1 ≥t s1 ·N 1 / N 2 , T 1 Indicates the duration of the first period. t s1 This indicates the first set interval time.

[0046] The duration of the second time period is greater than or equal to the first preset interval. The first preset interval and the second preset interval may be equal or unequal, and are not limited here.

[0047] Second switching device S a The turn-on time refers to the time from the first second switching device. S a The countdown begins at the moment of activation. N 1 A second switching device S a The timer continues until the time exceeds or equals the first time threshold, at which point it stops and is turned off. N 1 A second switching device S a .

[0048] N 1 A second switching device S a After activation, N 1 The energy storage unit 1322 of the switching module 13 begins to discharge. The output voltage of the target bridge arm is close to the bus voltage, and the effect on the voltage change rate is negligible. The half-wave discharge process ends. N 1 A second switching device S a Under the action of clamping unit 1321, natural clamping and blocking occur. N 1 The second switching device is turned on. S a Zero-current turn-off, the target bridge arm remains off. From the first second switching device... S a From the time of its opening, until N 1 The second switching device is turned on. S a The time up to the turn-off moment is the period of time for the second switching device. S a The opening time is greater than or equal to the first time threshold.

[0049] For example, taking the shutdown of the upper bridge arm 11 as an example, when the switch signal of the upper bridge arm is detected to switch from the on state to the off state, for example, the switch signal switches from 1 to 0, the upper bridge arm 11 is shut down sequentially in batches during the first time period. N 1 The first switching device of the switching module 13S The number of shutdowns set for each batch (e.g.) N 2 The first switching device S The first set interval time is between adjacent batches; during the second time period, the remaining equipment on the upper bridge arm is shut off. N 3 The first switching device S All first switching devices on the upper bridge arm 11 S After all are shut down, the upper bridge arm 11 will be opened sequentially in batches during the third time period. N 1 The second switching device of the switching module 13 S a Each batch activates a set number (e.g., N2) of the second switching devices. S a The interval between adjacent batches is a second predetermined interval time; in the second switching device S a When the activation time reaches the first time threshold, N1 second switching devices in the activated state will be activated. S a The upper bridge arm 11 is turned off, and only then can the lower bridge arm 11 be turned on, i.e., the first switching device of the N switching modules 13 controlling the lower bridge arm. S It is now open.

[0050] The AC / DC converter provided in this application embodiment includes at least one bridge arm 10, and each bridge arm has an upper bridge arm 11 and a lower bridge arm 12, both of which include... N The series-connected switching modules 13 achieve reliable series connection and voltage balancing of switching devices in medium and high voltage scenarios, solving the problem of difficult voltage and capacity expansion of traditional two-level VSCs. By setting the step size of the number of modules when turning off the target bridge arm, the first switching device is turned off in batches and some of the second switching devices are turned on in batches, so that the output voltage changes in a step manner, reducing the output voltage change rate from the bus voltage level to the module voltage level, achieving the voltage change rate level of multi-level topologies. This solves the problem that traditional two-level VSCs are difficult to apply to medium and high voltage scenarios due to their high voltage change rate. At the same time, compared with multi-level topologies, this AC / DC converter also has the advantages of fewer devices and simpler topology, which helps to reduce equipment size and cost.

[0051] In one embodiment, such as Figure 4 As shown, the first switching device S It may include fully controllable power switching devices and second switching devices. S a It can include fully controlled power switching devices or semi-controlled power switching devices.

[0052] Among them, the first switching deviceS It may include all fully controllable power switching devices known to those skilled in the art, such as insulated gate bipolar transistors (IGBTs), integrated gate commutated thyristors (IGCTs), and metal-oxide-semiconductor field-effect transistors (MOSFETs), etc., without limitation.

[0053] As an example, the first switching device S By employing a reverse-conduction type fully controlled power switching device, the first switching device can be... S Integrating it with the protection unit 1311 on the same chip has the advantage of high integration, which helps to reduce package size, reduce cost and increase power density.

[0054] As an example, the first switching device S The asymmetric fully controlled power switching device is used in conjunction with an independent protection unit 1311. Compared with the symmetric device, it has a lower on-state voltage drop, which helps to reduce conduction loss.

[0055] Second switching device S a This may include fully controlled power switching devices such as IGBTs, IGCTs, and MOSFETs, or thyristors of the semi-controlled power switching device type (i.e., semi-controlled thyristors), which are not limited here.

[0056] As an example, the second switching device S a By employing a reverse-conduction type fully controlled power switching device, the second switching device S can be... a Integrating with the clamping unit 1321 on the same chip has the advantage of high integration, which helps to reduce package size, reduce cost and increase power density.

[0057] As an example, the second switching device S a The asymmetric fully controlled power switching device is used in conjunction with an independent clamping unit 1321. Compared with the symmetric device, it has a lower on-state voltage drop, which helps to reduce conduction loss.

[0058] As an example, the second switching device S aThe semi-controlled power switching device needs to be used in conjunction with the independent clamping unit 1321. Compared with the fully controlled power switching device, it has the advantages of simple structure, robustness and durability, high voltage resistance and low cost.

[0059] In one embodiment, such as Figure 4 As shown, the protection unit 1311 includes a first diode. D First diode D The conduction direction is the same as that of the first switching device. S The conduction is opposite, and the first diode D The reverse recovery time is less than or equal to the fourth time threshold.

[0060] In this embodiment, the protection unit 1311 is connected to the first switching device. S The first diode in reverse parallel D In the first switching device S After being turned off, the inductor current flows through the first diode. D The flow continues, feeding energy back to the DC bus or load, thereby switching the first switching device. S The voltage at both ends is clamped at a safe bus voltage level, protecting the first switching device. S .

[0061] In addition, the first diode D It is also used to provide a reverse current path, enabling bidirectional flow of reactive power. For example, in the first switching device of the upper bridge arm. S The first switching device of the lower bridge arm is turned off. S When not yet conducting, reverse current in the load can flow from the first diode of the lower bridge arm. D It flows back to the negative terminal of the DC bus.

[0062] In this embodiment, the first diode has a short reverse recovery time, which can be shortened to tens or hundreds of nanoseconds. Correspondingly, it has a high operating frequency, which can reach tens to hundreds of kHz, to meet the high frequency and high power requirements of the converter.

[0063] In one embodiment, such as Figure 4 As shown, the clamping unit 1321 may include a second diode. D a The second diode D a The conduction direction is the same as that of the second switching device. S a The conduction directions are opposite, and the second diode D a The reverse recovery time is less than or equal to the fifth time threshold.

[0064] In one embodiment, such as Figure 4As shown, the energy storage unit 1322 includes a buffer capacitor. C .

[0065] In one embodiment, such as Figure 4 As shown, the energy storage unit 1322 includes a buffer capacitor. C The clamping unit 1321 includes a second diode. D a Second diode D a The conduction direction is the same as that of the second switching device. S a The conduction directions are opposite, and the second diode D a The reverse recovery time is less than or equal to the fifth time threshold.

[0066] In this embodiment, in the first switching device S During the phased shutdown process, the first switching device S The energy generated during turn-off needs to be absorbed by the buffer branch. When the second switching device... S a When turned on, energy storage unit 1322 (or buffer capacitor) C (Through the second switching device) S a Release energy and absorb the first switching device. S It can shut off peaks or participate in voltage balancing.

[0067] When the second switching device S a When shut down, if the energy storage unit 1322 (or buffer capacitor) C A forward voltage has been established across the two ends of the first diode, and a second diode connected in reverse parallel... D a When reverse biased, it exhibits high impedance, and the energy storage unit 1322 (or buffer capacitor) is in a high impedance state. C Unable to pass through the second diode D a Discharge, energy storage unit 1322 (or buffer capacitor) C The voltage was maintained stably.

[0068] Buffer capacitor C Used to buffer and absorb transient charging energy caused by stray inductance in the circuit during the transient process after the target bridge arm is turned off, its capacitance is relatively small, typically in the range of tens to hundreds of μF. In the second switching device... S a When in the off state, clamping unit 1321 (or the second diode) D a Under the clamping action of the buffer capacitor, CMaintaining a stable DC bias voltage only at the second switching device S a Discharge occurs when the circuit is in the ON state.

[0069] Based on the AC / DC converter provided in the above embodiments, this application also provides a specific implementation of a control method for the AC / DC converter, which is executed by the controller of the AC / DC converter. Please refer to the following embodiments.

[0070] In one embodiment, such as Figure 5 As shown, the control method of the AC / DC converter may include the following steps: S110~S140.

[0071] S110, Obtain the switching signal of the target bridge arm.

[0072] The target bridge arm includes either the upper or lower bridge arm of each bridge arm. The switching signals may include on and off state signals. For example, the switching signals of the upper and lower bridge arms are represented by binary values ​​of 0 and 1, where 0 represents the off state and 1 represents the on state.

[0073] S120. Upon detecting that the switch signal has switched from the on state to the off state, within the first time period, the target bridge arm is turned off each time according to the first preset interval. N 2 The first switching device of the switching module, until the target bridge arm is turned off. N 1 The first switching device of a switching module.

[0074] in, N , N 1 and N 2 All are integers greater than or equal to 1. N 2 Less than N 1 , N 1 Less than N .

[0075] The first set interval time can be determined based on the maximum turn-off delay of the first switching device.

[0076] In this step, when the switch signal state of the target bridge arm is detected to switch from the on state to the off state, i.e., the target bridge arm is the bridge arm to be turned off, then... N 2 As the module number step size, the interval between each step size period is the first set interval time t. s1The first switching device of the switch module on the target bridge arm is turned off sequentially until the number of first switching devices turned off reaches a certain threshold. N 1 Up to this point, during this process, the output voltage of the target bridge arm decreases in a stepwise manner (refer to...). Figure 6 In g p The voltage change is related to the voltage of the switching module and the number of first switching devices turned off each time (i.e., N 2 (The value of ) is related to the reduction of the output voltage change rate from the bus voltage level to the module voltage level.

[0077] S130, During the second time period, shut down the remaining [functions / equipment] on the target bridge arm. N 3 The first switching device of a switching module.

[0078] in, N 1 and N 3 The sum of equals N .

[0079] In this step, the first switching device of the non-off switch module on the target bridge arm is turned off together.

[0080] As an example, N 3 Greater than or equal to N 2 ,and N 3 Less than or equal to 2 times N 2 .

[0081] For example, the upper or lower bridge arm may include eight switch modules, and the first switch device of one switch module is turned off at a time. After six first switch devices are turned off, the first switch devices of the remaining two switch modules are turned off simultaneously.

[0082] For example, the upper or lower bridge arm may include eight switch modules, which turn off the first switching devices of two switch modules at a time, and after turning off six first switching devices, turn off the first switching devices of the remaining two switch modules simultaneously.

[0083] For example, the upper or lower bridge arm may include nine switch modules, and the first switching devices of two switch modules are turned off at a time. After six first switching devices are turned off, the first switching devices of the remaining three switch modules are turned off simultaneously.

[0084] S140. During the third time period, the target bridge arm is opened each time according to the second set interval. N2 The second switching device of the switching module, until the target bridge arm is turned on. N 1 The second switching device of the switching module is turned off when the on-time reaches a first time threshold. N 1 The second switching device of a switching module.

[0085] Among them, the second set interval time t s2 The first set interval time can be determined based on the maximum turn-on delay of the second switching device. t s1 With the second set interval time t s2 They can be equal or unequal; there is no limitation here.

[0086] Combination Figure 6 The duration of the third period is as follows t b This indicates that the third time period begins when the first second switching device on the target bridge arm is turned on, and ends when... N 1 The turn-off time of the second switching device. The duration of the third time period is greater than or equal to the first time threshold.

[0087] In this step, on the target bridge arm N After the first switching device of each switching module is turned off, N 2 As the module step size, the interval between each step period is the second preset interval time. t s2 The second switching device on the target bridge arm is sequentially activated until the number of activated second switching devices reaches N1. During this process, the output voltage of the target bridge arm increases in a stepwise manner (refer to...). Figure 6 In g pa The voltage change is related to the voltage of the switching module and the number of second switching devices turned on each time (i.e., N 2 (The value of the value is related to the output voltage change rate, which is reduced from the bus voltage level to the module voltage level.) After the second switching device is turned on, the buffer capacitor of its switching module discharges. When the discharge time of the target bridge arm reaches the first time threshold, it is turned off. N 1 The second switching device of the switching module, the target bridge arm completes the turn-off.

[0088] In this embodiment, when the target bridge arm's switch signal is detected to switch from an on state (e.g., 1) to an off state (e.g., 0), after a first predetermined interval time...t s1 Turn off N 2 In a switching module, as the number of first switching devices turned off increases, the output voltage of the target bridge arm decreases in a stepwise manner. V out =V dc –kV sm (k≤N) 1 ） , V dc Indicates bus voltage. V sm This indicates the voltage of each switching module at this time. V sm =V dc / N 1 Until shut down N 1 The first switching device of the switching module, at this time the remaining N 3 The first switching device of each switching module is still in the ON state, at which time the output voltage is drawn from the bus voltage. V dc The load current is reduced to 0, and the shutdown switch module is charged with a constant current. The remaining... N 3 The first switching device of each switching module is simultaneously turned off, at which point the target bridge arm's... N When the first switching device of each switching module is completely turned off, the output voltage remains approximately constant. V out =（V dc –kV sm ) / 2 (k=N) At this time, the voltage of the target bridge arm is higher than the bus voltage. V dc The commutator circuit noise is in N 3 Under the influence of the module voltage, constant-voltage controllable commutation occurs, with the current decreasing approximately linearly from the first switching device of the target bridge arm to the first diode of the main circuit of another bridge arm. During this process, the decaying current continues to charge all the N switched modules that are turned off. In the target bridge arm... N After the first switching device of each switching module is turned off, the commutation is complete, and the target bridge arm maintains a brief off-state steady state. Entering the third time period, after each second predetermined interval... t s2 , then open N 2The second switching device of each switching module, as the number of second switching devices turned on increases, the output voltage of the target bridge arm increases in a stepwise manner, until the target bridge arm is turned on. N 1 The second switching device of the switching module outputs voltage at this time. V out =(V dc –kV sm ) / 2 (k=N 1 ） The output voltage is close to the bus voltage. V dc The effect on dv / dt is negligible until the corresponding discharge process ends. The second diode on the target bridge arm is naturally clamped and blocked, all the turned-on second switching devices are turned off with zero current, the discharge transient process ends, and the target bridge arm remains in a turn-off steady state. Only then is the turn-off of the target bridge arm completed.

[0089] The AC / DC converter control method provided in this application embodiment includes an AC / DC converter comprising at least one bridge arm, wherein each bridge arm includes an upper bridge arm and a lower bridge arm. N The series-connected switching modules achieve reliable series connection and voltage balancing of switching devices in medium and high voltage scenarios, solving the problem of difficult voltage and capacity expansion in traditional two-level VSCs. By setting the module number step size and turning off the first switching device in batches and turning on some of the second switching devices in batches when turning off the target bridge arm, the output voltage changes in a step manner, reducing the output voltage change rate from the bus voltage level to the module voltage level, achieving the voltage change rate level of multi-level topologies. This solves the problem that traditional two-level VSCs are difficult to apply in medium and high voltage scenarios due to their high voltage change rate. At the same time, compared with multi-level topologies, this AC / DC converter also has the advantages of fewer devices and a simpler topology, which helps to reduce equipment size and cost.

[0090] In one embodiment, such as Figure 7 As shown, the control method further includes the following step: S150.

[0091] S150, Upon detecting that the switch signal has switched from an off signal to an on signal, simultaneously turn on the target bridge arm. N The first switching device of a switching module.

[0092] In this embodiment, when the switching signal of the target bridge arm is detected to switch from 0 to 1, the target bridge arm is the bridge arm to be activated. Whether it is the upper or lower bridge arm, the activation process of the first switching device is synchronized with the switching signal of the bridge arm, that is, upon receiving the corresponding bridge arm's switching signal (… T p or Tn When switching from 0 to 1, N All the first switching devices of each switching module are turned on (e.g., ... Figure 6 middle g n (as shown) N The second switching device of each switching module remains off (e.g., Figure 6 middle g na (As shown).

[0093] In one embodiment, "during a first time period, the first switching devices of N2 switching modules on the target bridge arm are turned off at first predetermined intervals until the target bridge arm is completely turned off." N 1 The "first switching device of a switching module" may include the following steps: Apply voltage to the target bridge arm in ascending order. N The switch modules are sorted in the first order; Within the first time period, according to the first sorting order, the first set interval time, and the target bridge arm being shut down each time. N 2 The first switching device of the switching module, until the target bridge arm is turned off. N 1 The first switching device of a switching module.

[0094] In this embodiment, before turning off the first switching device of the target bridge arm, the target bridge arm is... N The voltages of the switching modules are sorted in ascending order. Switches with lower voltages have a higher turn-off priority than those with higher voltages; that is, the first switching device of the lower-voltage module is turned off first. This voltage sorting is performed at predetermined intervals. t s1 The target bridge arm was shut down. N 2 The first switching device of the switching module, until the target bridge arm is turned off. N 1 The first switching device of each switching module. By turning off the first switching device in order of voltage from low to high, the current is actively guided to charge the lower voltage switching modules, thereby increasing their voltage and effectively maintaining the voltage balance of all switching modules, which is beneficial to improving the stable operation of the AC-DC converter.

[0095] In one embodiment, "during the third time period, according to the second predetermined interval, the target bridge arm is opened each time." N 2 The second switching device of the switching module, until the target bridge arm is turned on. N 1The second switching device of a switching module may include the following steps: Apply voltage to the target bridge arm in descending order. N Each switch module is sorted in the second order; During the third time period, according to the second sorting, the second set interval time, and the target bridge arm opened each time. N 2 The second switching device of the switching module, until the target bridge arm is turned on. N 1 The second switching device of a switching module.

[0096] In this embodiment, before activating the second switching device of the target bridge arm, the target bridge arm is... N The voltages of the switching modules are sorted in descending order, with higher voltage switching modules having a higher turn-on priority than lower voltage switching modules. Specifically, the second switching device of the higher voltage switching module is turned on first. This voltage sorting is performed at predetermined intervals. t s2 The target bridge arm will be opened. N 2 The second switching device of the switching module, until the target bridge arm is turned on. N 1 The second switching device of each switching module. By turning on the second switching device in order of voltage from high to low, the higher voltage switching module is bypassed first. After the switching module is bypassed, the charging of the buffer capacitor stops, and its voltage no longer rises. Meanwhile, the lower voltage switching module remains in the working state, continues to charge and its voltage rises. The rise and fall between the high and low voltages reduces the difference between them, which helps to speed up the voltage equalization process.

[0097] In one embodiment, "during the third time period, according to the second predetermined interval, the target bridge arm is opened each time." N 2 The second switching device of the switching module, until the target bridge arm is turned on. N 1 Before the second switching device of the switching module, the control method may further include the following steps: Starting from the end of the second time period, the time corresponding to the delay of the second time threshold is determined as the start time of the third time period; The second time threshold can be determined based on the dead time of the switching module. As an example, the second time threshold is greater than or equal to the dead time of the switching module. The dead time of the switching module can be determined based on the maximum turn-off delay of the first switching device, where the dead time of the switching module is greater than or equal to the turn-off delay of the first switching device. Combined with... Figure 6 The dead time of the switching module is td express.

[0098] The end time of the second period is the [missing information]. N The moment the first switching device turns off is taken as the starting point for timing. After the dead time of the switching module, the corresponding moment is the start time of the third time period, at which point the target bridge arm can be turned on. N 2 The second switching device of each switching module waits for a second set interval before turning on the target bridge arm. N 2 The second switching device of each switching module, until the number of second switching devices on the target bridge arm is reached. N 1 .

[0099] In this embodiment, the target bridge arm is shut down in batches. N After the first switching device of the switching module is turned off, a safety buffer is added between the first switching device being turned off and the second switching device being turned on through a delay operation. This provides a time window for the residual current to decay naturally, so that the current of the target bridge arm has been reduced to a safe level before the operation of turning on the second switching device in batches is performed, thereby reducing the risk of short circuit and shoot-through between the upper and lower bridge arms.

[0100] In one embodiment, S110 may include the following steps: Acquire the modulation signals of the upper and lower bridge arms; When it is detected that the modulation signal of one of the upper and lower bridge arms has switched from the on modulation signal to the off modulation signal, the modulation signal of the other of the upper and lower bridge arms is switched from the off modulation signal to the on modulation signal after a preset dead time, starting from the switching time, so as to obtain the switching signal of the target bridge arm.

[0101] In this embodiment, the switching signals of the upper and lower bridge arms are obtained by adding a bridge arm turn-on delay (i.e., bridge arm dead time) to the modulated signals. The bridge arm dead time is determined based on the maximum turn-off delay of the upper and lower bridge arms, and the bridge arm dead time is greater than or equal to the maximum turn-off delay. As an example, the value range of the bridge arm dead time is 1.2 to 1.5 times the maximum turn-off delay.

[0102] Modulation signal of upper arm S p Modulation signal with lower bridge arm S n Complementary. For example, such as Figure 6 As shown, the modulation signals of the upper and lower bridge arms are represented by binary values ​​of 0 and 1, where 0 represents the off state and 1 represents the on state; when the modulation signal of the upper bridge arm... S pThe signal changes from the ON state to the OFF state (i.e., the signal value changes from 1 to 0), and simultaneously the modulation signal of the lower arm... S n Switching from the off state to the on state (i.e., the signal value changes from 0 to 1); the modulation signal of the upper arm. S p The signal value switches from 1 to 0 as the starting point, followed by a delay of the bridge arm dead time. t d0 Then, the modulation signal of the lower bridge arm S n The signal value only switches from 0 to 1, indicating that the modulation signal of the lower bridge arm is about to change. S n The signal value switching time is delayed, which delays the dead time t of the bridge arm. d0 This allows us to obtain the switching signal for the lower bridge arm. T n Similarly, the modulation signal of the following bridge arm... S n The signal value switches from 1 to 0 as the starting point, followed by a delay of the bridge arm dead time. t d0 Then, the modulation signal of the upper bridge arm S p The signal value only switches from 0 to 1, indicating that the modulation signal of the upper bridge arm is about to change. S p The signal value switching time was delayed, which increased the dead time of the bridge arm. t d0 Thus, the switching signal of the upper bridge arm is obtained. T p .

[0103] In this embodiment, by adding dead time to the modulation signals of the upper and lower bridge arms, the switching signals of the upper and lower bridge arms are obtained, so that the other bridge arm is turned on only after one of the upper and lower bridge arms (located in the same bridge arm) is turned off, which reduces the risk of direct short circuit between the upper and lower bridge arms and is beneficial to protecting power devices and improving the safety of the converter.

[0104] In one embodiment, "acquiring the modulation signals of the upper and lower bridge arms" may include the following steps: Acquire the raw modulation signals of the upper and lower bridge arms; A minimum narrow pulse time constraint is applied to the original modulation signal to generate modulation signals for the upper and lower bridge arms; The minimum narrow pulse time constraint includes ensuring that the duration of the modulated signal is greater than or equal to a third time threshold. The third time threshold can be determined based on the turn-off delay of the upper or lower bridge arm. The turn-off delay of the upper or lower bridge arm can be determined based on the maximum turn-off delay of the first switching device, the maximum turn-on delay of the second switching device, and the maximum turn-off delay of the second switching device.

[0105] This embodiment does not limit the pulse width modulation method and can use all pulse modulation methods known to those skilled in the art, such as pulse width modulation (PWM), sinusoidal pulse width modulation (SPWM), and space vector pulse width modulation (SVPWM).

[0106] For example, such as Figure 6 As shown, the modulation signal of the upper bridge arm S p Modulation signal of lower bridge arm S n The duration after the state value switch is greater than t z That is, it satisfies the minimum narrow pulse time constraint.

[0107] In this embodiment, the minimum narrow pulse time is applied to the modulation signals of the upper and lower bridge arms, such that the duration of the modulation signals of the upper and lower bridge arms is greater than or equal to the third time threshold. By maintaining the signal for a sufficiently long time, the bridge arms to be turned off are turned off in batches within this duration. N The first switching device of each switching module is activated in batches. N 1 The second switching device of the switching module and the turn-off N 1 The second switching device of the switching module ensures that the other bridge arm is turned on only after the bridge arm to be turned off is completely turned off, reducing the risk of short circuit between the upper and lower bridge arms.

[0108] For example, such as Figure 8 As shown, the control method of the AC / DC converter may include the following steps: S801~S812.

[0109] S801, Level step conversion reduces dv / dt control starts.

[0110] S802, after carrier comparison and equal pulse width modulation, outputs a minimum narrow pulse. t z Constrained binary modulation signal S p andS n .

[0111] S803, to S p , S n Add activation delay t d0 Obtain binary bridge arm switch signal T p and T p .

[0112] S804, T p / T n Has the instruction changed?

[0113] In this step, if the determination result is yes, T p / T n The instructions have changed, including T p / T n From 1 to 0 and T p / T n There are two possibilities: 0 and 1. This determines whether a demerit is recorded. T p / T n It remains unchanged.

[0114] S805, T p / T n From 1 to 0.

[0115] S806, Corresponding bridge arm first switching device turns off: Immediately with N 2 represents the module number step size, and the time interval for each step period is... t s Based on the module voltage sorting results from low to high, the common circuits are turned off sequentially. N The first switching device of a switching module directly turns off the remaining devices in the last cycle. N The first switching device of the three switching modules; the corresponding second switching device of the bridge arm is turned on / off: delay. t a Later N 2 represents the module number step size, and the time interval for each step period is... t s Based on the module voltage sorting results from high to low, the modules are activated sequentially.N The second switching device of a switching module; delay t a + t b Then shut this off N The second switching device of a switching module.

[0116] In this embodiment, the first preset interval time and the second preset interval time are equal, both being... t s . t a The corresponding time periods include the first time period and the second time period. t b The corresponding time period is the third period.

[0117] S807 T p / T n From 0 to 1.

[0118] S808, corresponding bridge arm first switching device turned on: all N The first switching device of a series switch module is turned on.

[0119] S809, T p / T n It remains unchanged.

[0120] S810, corresponding bridge arm first and second switching devices according to T p / T n When the instruction changes, the trigger pulse is modified; otherwise, the existing switch state is maintained.

[0121] S811, the obtained bridge arm N The trigger pulses of the first and second switching devices of the switching module are sent to the devices of the opposite bridge arm.

[0122] S812, series module voltage maintains balanced output level with step changes.

[0123] The control method of this two-level AC / DC converter can reduce the dv / dt of the AC port and achieve voltage balancing of the switching modules. The specific analysis process is as follows: Under the two-level control sequence, the level change process of the bridge arm and the commutation process are decoupled. The output level is changed by the constant current freewheeling ladder of the load current in different loops. Then, a constant voltage difference is constructed to perform commutation of the upper / lower bridge arm. During the process, the transient process after each turn-off will keep the total energy of the bridge arm constant, and the switching is performed by relying on the voltage sorting of the switching modules to achieve voltage balancing of the switching modules.

[0124] Considering the symmetry of the three phases in VSC, Figure 9 Taking the example of a single-phase switch module connected in series in a bridge arm, we will analyze the number of switch modules connected in series in each bridge arm. N It is 8, of which N 1 It is 6. N 2 =1, N 3 The value is 2.

[0125] like Figure 10 As shown, the load current is DC (i.e., i load =DC When the current direction is outflow, the active turn-off process of the upper bridge arm and the active turn-on process of the upper bridge arm (corresponding to the bridge arm turn-off process when the first diode connected in anti-parallel to the first switching device on the lower bridge arm is in operation) can represent two typical commutation conditions in VSC. In addition, the load current being DC is also equivalent to the inverter limit condition where the frequency of the load current is 0. At this time, both the upper and lower bridge arms continuously turn off the maximum load current, which is the most stringent scenario for module voltage balance control.

[0126] Taking the active shutdown of the upper bridge arm as an example, combined with Figure 11 Waveform of the active turn-off process of the upper and middle bridge arms Figures 12-17 In the equivalent circuit, the upper bridge arm that is actively turned off experiences energy fluctuations, and the dominant change in the output voltage is shown below: (1) t 1 Before, as Figure 12 As shown, the upper bridge arm remains in a steady-state state of operation.

[0127] (2) t 1 ~ t 2 :like Figure 13 As shown, t 1 At that moment, the upper bridge arm received a shutdown command. Subsequently... N 2 Step-by-step shutdown for unit step size N 1 The first switching device (module voltage sorted from low to high) outputs the voltage at this time. V out = V dc – kV sm ( k ≤ N 1 From bus voltage Vdc When the step decreases to 0, the load current charges the shutdown module with a constant current.

[0128] (3) t 2 ~ t 3 :like Figure 14 As shown, t 2 At that moment, directly shut off the remaining... N 3 A switching module initiates commutation in the circuit. Output voltage. V out To be approximately invariant, V out =( V dc – kV sm ) / 2 ( k = N At this time, the bridge arm voltage is higher than the bus voltage, and the random inductance in the converter circuit is... N 3 Under the influence of the module voltage, constant-voltage controllable commutation occurs, with the current decreasing approximately linearly from the first switching device in the upper bridge arm to the first diode in the lower bridge arm. During this process, the decaying current continues to supply power to the upper bridge arm that is turned off. N The buffer capacitor of each switching module is charged.

[0129] (4) t 3 ~ t 4 :like Figure 15 As shown, t 3 The commutation is complete. The upper arm maintains a brief off steady state.

[0130] (5) t 4 ~ t 5 :like Figure 16 As shown, t 4 time N 1 All the second switching devices are turned on. N 1 The buffer capacitor of each switching module begins to discharge, at which point the output voltage... V out =( V dc – kV sm ) / 2 ( k = N 1(), close to bus voltage V dc The effect on dv / dt is negligible compared to the previous effect, until the sinusoidal half-wave discharge process ends, after which the second diode of the upper bridge arm naturally clamps and blocks. t 5 At any given time, all the second switching devices that are turned on are turned off with zero current.

[0131] (6) t 5 After that, as Figure 17 As shown, the charging-discharging transient process ends after the upper bridge arm is turned off, and the upper bridge arm maintains a steady state of being turned off.

[0132] In the above process, the upper bridge arm is first charged during the level change and commutation processes, and then discharged by turning on the second switching device. At the end of a complete active turn-off process, the energy of the bridge arm remains unchanged. Furthermore, during charging, the switching module with the lower voltage is turned off first, and during discharging, the module with the highest voltage is selected. N 1 Each switching module, through voltage sequencing, can maintain a balanced voltage across its modules, and stabilize the voltage of each module at a certain level. V sm0 = V dc / N 1 .

[0133] Taking the active opening of the upper bridge arm as an example, combined with Figure 18 Waveform of the active opening process of the upper and middle bridge arms and Figures 19-23 Analyzing the equivalent circuit, we find that the lower bridge arm, which is actively turned on by the opposite bridge arm, experiences energy fluctuations, and the dominant output voltage change is shown below: (1) t 1 ’ Before, as Figure 19 As shown, the first switching device of the lower bridge arm has been completely turned off, but the load current freewheels in the first diode (connected in antiparallel to the first switching device).

[0134] (2) t 1 ’ ~ t 2 ’ As shown in 20, t 1 ’ At this moment, the second switching device of the bridge arm begins to... N 2 Step-by-step conduction to unit step size N 1 (Module voltage sorting results from high to low). Output voltage at this time.V out =kV sm (k≤N 1 ) Ascending from step 0 to V dc ·N 1 / N The load current provides a constant current discharge to the switching modules turned on by these second switching devices.

[0135] (3) t 2 ’ ~ t 3 ’ ,like Figure 21 As shown, t 2 ’ At any given moment, all the first switching devices on the upper bridge arm are turned on, and commutation begins in the circuit. The output voltage remains approximately constant. V out =( V dc + kV sm ) / 2 ( k = N 1 At this time, the second switching device of the lower bridge arm is turned on. N 1 The voltage of each switching module is lower than the bus voltage. Under the influence of the voltage difference, the commutation circuit inductance exhibits approximately constant-voltage controllable commutation. The current decreases approximately linearly from the lower bridge arm, commutating to the first switching device of the upper bridge arm. During this process, the decaying current continues to supply power to all the switches connected to the lower bridge arms. N 1 Each module discharges.

[0136] (4) t 3 ’ ~ t 4 ’ ,like Figure 22 As shown, t 3 ’ When the commutation is complete, the lower bridge arm's switching module discharges during the preceding transient process, causing the lower bridge arm's... N The sum of the voltages of each module is less than the bus voltage. V dc Therefore, the bus voltage begins to charge and replenish all the switching modules of the lower bridge arm, at which point the output voltage... V out =(V dc + kV sm ) / 2 ( k = N (), close to bus voltage V dc The impact on dv / dt is negligible until the sinusoidal half-wave charging process ends, after which the second diode of the lower bridge arm naturally clamps and blocks. During this process, the transient charging current of the lower bridge arm passes through the second diode (connected in anti-parallel with the second switching device), making... N 1 The second switching device of the switching module is turned off with zero current.

[0137] (5) t 4 ’ Afterwards, the discharge-charge transient process after the lower bridge arm is turned off ends, and the lower bridge arm maintains a steady state of being turned off.

[0138] In the above process, the lower bridge arm first discharges during the level change and commutation processes, and then the bus voltage charges and replenishes the lower bridge arm. At the end of a complete active switching process of the opposite bridge arm, the bridge arm energy remains unchanged. Furthermore, during discharge, the second switching device of the higher-voltage switching module is turned on first. During charging and replenishment, all modules charge at the same rate. Voltage sequencing ensures that the module voltages remain balanced and stable. V sm1 = V dc / N (Average module voltage under bridge arm shutdown condition) V dc / N 1 Small).

[0139] For example, when the load current is alternating current (i.e., i load =AC When ), the waveform of the single-phase switch module in series bridge arm is as follows: Figure 24 As shown, under AC load current conditions, the single-side bridge arm is actively turned off during the positive half-cycle of current outflow, and the opposite side bridge arm is actively turned on during the negative half-cycle. Therefore, the voltage of the switching module will... V sm0 = V dc / N 1 and V sm1 = V dc / NThe system alternates between two stable voltage points, while maintaining strict voltage balance between the series modules throughout the process.

[0140] It should also be noted that the exemplary embodiments mentioned in this application describe methods or systems based on a series of steps or apparatus. However, this application is not limited to the order of the above steps; that is, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0141] The above are merely specific embodiments of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific operation processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A control method for an AC / DC converter, characterized in that, The AC / DC converter includes at least one bridge arm, each bridge arm including an upper bridge arm and a lower bridge arm connected in series, both the upper bridge arm and the lower bridge arm including N A series of switch modules; each of the switch modules includes a first switch branch and a buffer branch connected in parallel. The first switch branch includes a first switch device and a protection unit connected in parallel. The buffer branch includes a second switch device, a clamping unit and an energy storage unit. The second switch device is connected in series with the energy storage unit and in parallel with the clamping unit. The control method includes: Acquire the switching signal of the target bridge arm, wherein the target bridge arm includes any one of the upper and lower bridge arms of each bridge arm; Upon detecting that the switch signal has switched from the on state to the off state, the target bridge arm is turned off at each set interval during a first time period. N 2 The first switching device of the switching module, until the target bridge arm is turned off. N 1 The first switching device of the aforementioned switching module; During the second time period, the remaining [unclear] on the target bridge arm were shut down. N 3 The first switching device of the aforementioned switching module; During the third time period, the target bridge arm is activated each time according to the second predetermined interval. N 2 The second switching device of the aforementioned switching module, until the target bridge arm is turned on. N 1 The second switching device of the switching module is turned off when the on-time reaches a first time threshold. N 1 The second switching device of the aforementioned switching module; in, N , N 1 , N 2 and N 3 All are integers greater than or equal to 1. N 2 Less than N 1 , N 1 Less than N , N 1 and N 3 The sum of equals N .

2. The control method according to claim 1, characterized in that, During the first time period, the target bridge arm is shut down at each predetermined interval. N 2 The first switching device of the switching module, until the target bridge arm is turned off. N 1 The first switching device of the switching module includes: Apply voltage to the target bridge arm in ascending order. N The switch modules are sorted in the first order; During the first time period, the target bridge arm is shut down each time according to the first sorting, the first set interval time, and the first set interval time. N 2 The first switching device of the switching module, until the target bridge arm is turned off. N 1 The first switching device of the switching module.

3. The control method according to claim 1, characterized in that, During the third time period, the target bridge arm is activated at each of the second predetermined intervals. N 2 The second switching device of the aforementioned switching module, until the target bridge arm is turned on. N 1 The second switching device of the switching module includes: Apply voltage to the target bridge arm in descending order. N The switch modules are then sorted in a second order. During the third time period, the target bridge arm is opened each time according to the second sorting, the second set interval time. N 2 The second switching device of the aforementioned switching module, until the target bridge arm is turned on. N 1 The second switching device of the aforementioned switching module.

4. The control method according to claim 1, characterized in that, During the third time period, the target bridge arm is activated at each of the second predetermined intervals. N 2 The second switching device of the aforementioned switching module, until the target bridge arm is turned on. N 1 Before the second switching device of the switching module, the control method further includes: Starting from the end of the second time period, the time corresponding to the delay of the second time threshold is determined as the start time of the third time period; The second time threshold is determined based on the dead time of the switching module.

5. The control method according to claim 1, characterized in that, The acquisition of the target bridge arm's switching signal includes: Acquire the modulation signals of the upper bridge arm and the lower bridge arm; When the modulation signal of one of the upper bridge arm and the lower bridge arm is detected to switch from the on state to the off state, the modulation signal of the other of the upper bridge arm and the lower bridge arm is switched from the off state to the on state, starting from the switching time and delayed by a preset bridge arm dead time, so as to obtain the switching signal of the target bridge arm.

6. The control method according to claim 5, characterized in that, The acquisition of the modulation signals of the upper bridge arm and the lower bridge arm includes Obtain the original modulation signals of the upper bridge arm and the lower bridge arm; A minimum narrow pulse time constraint is applied to the original modulation signal to generate the modulation signals for the upper bridge arm and the lower bridge arm; The minimum narrow pulse time constraint includes the duration of the modulated signal being greater than or equal to a third time threshold.

7. The control method according to any one of claims 1-6, characterized in that, Also includes: Upon detecting that the switch signal has switched from an off signal to an on signal, the target bridge arm is simultaneously turned on. N The first switching device of the switching module.

8. An AC / DC converter, characterized in that, The AC / DC converter includes: At least one bridge arm, each of the bridge arms comprising an upper bridge arm and a lower bridge arm connected in series, wherein both the upper bridge arm and the lower bridge arm include N A series of switch modules; each of the switch modules includes a first switch branch and a buffer branch connected in parallel. The first switch branch includes a first switch device and a protection unit connected in parallel. The buffer branch includes a second switch device, a clamping unit and an energy storage unit. The second switch device is connected in series with the energy storage unit and in parallel with the clamping unit. The controller is configured to: acquire a switch signal of a target bridge arm, wherein the target bridge arm includes either the upper or lower bridge arm of each bridge arm; and, upon detecting that the switch signal has switched from an on state to an off state,, within a first time period, shut down the upper arm of the target bridge arm at first predetermined intervals. N 2 The first switching device of the switching module, until the target bridge arm is turned off. N 1 The first switching device of the aforementioned switching module; during the second time period, turning off the remaining switches on the target bridge arm. N 3 The first switching device of the aforementioned switching module; during the third time period, according to the second preset interval time, the target bridge arm is turned on each time. N 2 The second switching device of the aforementioned switching module, until the target bridge arm is turned on. N 1 The second switching device of the switching module is turned off when the on-time reaches a first time threshold. N 1 The second switching device of the aforementioned switching module; in, N , N 1 , N 2 and N 3 All are integers greater than or equal to 1. N 2 Less than N 1 , N 1 Less than N , N 1 and N 3 The sum of equals N .

9. The AC / DC converter according to claim 8, characterized in that, The protection unit includes a first diode, the conduction direction of the first diode is opposite to that of the first switching device, and the reverse recovery time of the first diode is less than or equal to a fourth time threshold.

10. The AC / DC converter according to claim 8, characterized in that, The energy storage unit includes a buffer capacitor; And / or, the clamping unit includes a second diode, the conduction direction of the second diode being opposite to the conduction direction of the second switching device, and the reverse recovery time of the second diode being less than or equal to a fifth time threshold.

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