Bridge arm multiplexing type modular multilevel converter circuit, control method and medium

Abstract

The application relates to the technical field of electric power, in particular to a bridge arm multiplexing type modular multilevel converter circuit, a control method and a medium. The converter circuit comprises a plurality of phase units, the input end of the phase unit is connected to a bipolar DC side, and the output end of the phase unit is connected to one phase of an AC side; the phase unit is provided with a fault ride-through module, the input end of the fault ride-through module is connected to a positive pole of the DC side, and the output end of the fault ride-through module is connected to a negative pole of the DC side; the fault ride-through module is provided with a plurality of half-bridge sub-modules in cascade, wherein, when the DC side is normally operated, the fault ride-through module functions as a bypass to suppress harmonics; when the DC side is short-circuited, the fault ride-through module dynamically adjusts the number of half-bridge sub-modules to be connected to clear the fault current of the DC side. The fault ride-through module can clear the fault current of the DC side when the DC side of the converter is short-circuited, so that the time for the control system to start the fault ride-through strategy is obtained, and the DC fault ride-through without locking is realized.

Description

Technical Field

[0001] This application relates to the field of power technology, and in particular to bridge arm multiplexed modular multilevel converter circuits, control methods and media. Background Technology

[0002] Modular multilevel converters are used for rectification and inversion on both the DC and AC sides of the power grid. The bridge-arm multiplexing type modular multilevel converter is a circuit topology type of modular multilevel converter. It features an upper bridge arm, a multiplexed bridge arm, and a lower bridge arm. The multiplexed bridge arm is time-division multiplexed to either the upper or lower bridge arm via a switching switch. Without sacrificing the number of output levels or waveform quality, the number of submodules per phase is reduced from 2N to 3N / 2, saving 25% of the submodule usage and effectively reducing hardware costs.

[0003] The DC side of the bridge arm multiplexed modular multilevel converter has a 6nth harmonic, which needs to be suppressed by a DC support capacitor. However, when a short circuit fault occurs on the DC side of the converter, the DC support capacitor will discharge at the short circuit point, and the fault current will reach its peak value in a very short time. The response time of the control system is too short to activate the fault ride-through strategy. Summary of the Invention

[0004] In view of this, the main objective of the embodiments of this application is to propose a bridge arm multiplexed modular multilevel converter circuit, control method and medium, which can clear the fault current on the DC side when the DC side of the converter is short-circuited, so as to buy time for the control system to start the fault ride-through strategy and realize the DC fault ride-through without blocking.

[0005] To achieve the above objectives, one aspect of this application provides a bridge arm multiplexing type modular multilevel converter circuit, the converter circuit including a plurality of phase units, the input terminal of the phase unit being connected to the bipolar DC side, and the output terminal of the phase unit being connected to one phase of the AC side; The phase unit is equipped with a fault ride-through module. The input terminal of the fault ride-through module is connected to the positive terminal of the DC side, and the output terminal of the fault ride-through module is connected to the negative terminal of the DC side. The fault ride-through module is equipped with several cascaded half-bridge sub-modules. Specifically, during normal operation on the DC side, the fault ride-through module is used to suppress DC side harmonics; during a short-circuit fault on the DC side, the fault ride-through module dynamically adjusts the number of half-bridge sub-modules in operation to reduce the fault current on the DC side.

[0006] In some embodiments, the half-bridge submodule is provided with a DC support capacitor, the voltage rating of which is determined based on the DC rated voltage and the total number of submodules of the half-bridge submodule.

[0007] In some embodiments, when the DC side is short-circuited, the number of modules connected to the half-bridge submodule is determined based on the degree of sag between the current DC voltage and the rated DC voltage.

[0008] In some embodiments, when the DC side is operating normally, the DC support capacitors of all the half-bridge submodules are connected between the positive and negative terminals of the DC side.

[0009] In some embodiments, the phase unit is provided with a multiplexed bridge arm, a first selection switch, a second selection switch, a first direction switch, and a second direction switch; Both ends of the multiplexed bridge arm are connected to the input terminal of the AC side via the first selection switch and the second selection switch, the lower bridge arm is connected via the first direction switch, and the upper bridge arm is connected via the second direction switch.

[0010] To achieve the above objectives, another aspect of this application proposes a control method for a bridge arm multiplexed modular multilevel converter circuit, the control method comprising: After detecting a short-circuit fault on the DC side, the current DC voltage on the DC side is obtained; The number of modules connected to the half-bridge sub-module is determined based on the current DC voltage; The number of half-bridge sub-modules connected to the control module is used to clear the fault current on the DC side.

[0011] In some embodiments, several of the half-bridge submodules are provided with the same DC support capacitor; The step of determining the number of modules connected to the half-bridge submodule based on the current DC voltage includes: The voltage sag is determined based on the ratio between the current DC voltage and the rated DC voltage, and the voltage sag is used to characterize the degree of descent between the current DC voltage and the rated DC voltage. The number of modules connected is determined based on the voltage drop magnitude and the total number of sub-modules of the half-bridge sub-module.

[0012] In some embodiments, several of the half-bridge submodules are provided with different DC support capacitors; The step of determining the number of modules connected to the half-bridge submodule based on the current DC voltage includes: The voltage sag is determined based on the ratio between the current DC voltage and the rated DC voltage, and the voltage sag is used to characterize the degree of descent between the current DC voltage and the rated DC voltage. A mapping table is determined for the voltage drop amplitude and a number of the half-bridge sub-modules. The number of half-bridge sub-modules connected is determined based on the voltage drop amplitude and the mapping table. The mapping table is used to represent the number of half-bridge sub-modules connected corresponding to the voltage drop amplitude. The sum of the voltage values ​​of the connected half-bridge sub-modules matches the degree of sag of the current DC voltage.

[0013] In some embodiments, the control method further includes: After the current DC voltage is restored to the rated DC voltage, the number of modules connected is determined to be the total number of sub-modules.

[0014] To achieve the above objectives, another aspect of this application provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the methods described above.

[0015] To achieve the above objectives, another aspect of the embodiments of this application proposes a computer-readable storage medium storing a computer program that, when executed by a processor, implements the methods described above.

[0016] To achieve the above objectives, another aspect of the embodiments of this application proposes a computer program product, including a computer program that, when executed by a processor, implements the methods described above.

[0017] The embodiments of this application include at least the following beneficial effects: This application provides a bridge arm multiplexing type modular multilevel converter circuit, control method, and medium. The converter circuit includes several phase units. The input terminal of each phase unit is connected to the DC side, and the output terminal of each phase unit is connected to one phase of the AC side, converting the DC input of the DC side into the AC output of the AC side. Each phase unit is equipped with a fault ride-through module. The input terminal of the fault ride-through module is connected to the positive terminal of the DC side, and the output terminal of the fault ride-through module is connected to the negative terminal of the DC side. The fault ride-through module is equipped with several cascaded half-bridge sub-modules. When the DC side is operating normally, the half-bridge sub-modules of the fault ride-through module can filter the 6nth harmonic of the DC side. When a short-circuit fault occurs on the DC side, the voltage on the DC side drops. The half-bridge sub-modules can be shut down according to the degree of voltage drop to reduce the fault current leaked by the half-bridge sub-modules, thus buying time for the control system to start the fault ride-through strategy and achieving unblocked DC fault ride-through. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the circuit structure of the bridge arm multiplexed modular multilevel converter circuit provided in the embodiments of this application; Figure 2 This is a schematic diagram of the circuit structure of the multiplexed bridge arm provided in the embodiments of this application; Figure 3 This is a circuit diagram of the first and second selection switches provided in the embodiments of this application; Figure 4 This is a circuit diagram of the first direction switch and the second direction switch provided in the embodiments of this application; Figure 5 This is a schematic diagram of the circuit structure of the fault ride-through module provided in the embodiments of this application; Figure 6 is a schematic diagram of the switching of the half-bridge sub-module provided in an embodiment of this application; Figure 7 This is an equivalent circuit diagram of the DC fault device after it is put into operation, as provided in the embodiments of this application; Figure 8 This is a flowchart of the control method for the bridge arm multiplexed modular multilevel converter circuit provided in the embodiments of this application; Figures 9(a) to 9(d) This is a schematic diagram simulating the current and voltage changes when the DC voltage drops to 50% of its rated value. Figures 10(a) to 10(d) This is a schematic diagram simulating the current and voltage changes when the DC voltage drops to its rated value of 0. Figure 11 This is a schematic diagram of the hardware structure of the electronic device provided in the embodiments of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit it. In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this application; they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0020] It is understood that the terms “first,” “second,” etc., used in this application may be used herein to describe various concepts, but unless otherwise stated, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the words “if,” “when,” or “in response to a determination” as used herein may be interpreted as “when…” or “when…” or “in response to a determination.”

[0021] As used in this application, the terms "at least one", "multiple", "each", "any", etc., "at least one" includes one, two or more, "multiple" includes two or more, "each" refers to each of the corresponding multiples, and "any" refers to any one of the multiples.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0023] Before providing a detailed description of the embodiments of this application, some of the nouns and terms involved in the embodiments of this application will be explained first. The nouns and terms involved in the embodiments of this application are subject to the following interpretations.

[0024] 1) Modular multilevel converter: Each phase consists of an upper arm and a lower arm. Each arm is composed of a large number of identical sub-modules connected in series. Through the cascading and superposition of a large number of sub-modules, the DC input is synthesized into a sinusoidal AC output.

[0025] 2) Bridge arm multiplexing type modular multilevel converter: Each phase consists of an upper bridge arm, a lower bridge arm, and a multiplexing bridge arm. The number of sub-modules is reduced by having the three bridge arms work in turn.

[0026] 3) Half-bridge submodule: It consists of two IGBTs, two anti-parallel diodes and a capacitor. It is a widely used submodule topology in power systems. By controlling the conduction or shutdown of the two IGBTs, the capacitor can be charged, discharged or maintained.

[0027] Modular multilevel converters are used for rectification and inversion on the DC and AC sides of the power grid. The bridge-arm multiplexing type modular multilevel converter is a circuit topology type of modular multilevel converter. It has an upper bridge arm, a multiplexing bridge arm, and a lower bridge arm. The multiplexing bridge arm is time-division multiplexed to the upper or lower bridge arm via a switching switch. Without sacrificing the number of output levels and waveform quality, the number of submodules per phase is reduced from 2N to 3N / 2, saving 25% of the submodule usage and effectively reducing hardware costs.

[0028] The DC side of the bridge arm multiplexed modular multilevel converter has a 6nth harmonic, which needs to be suppressed by a DC support capacitor. However, when a short circuit fault occurs on the DC side of the converter, the DC support capacitor will discharge at the short circuit point, and the fault current will reach its peak value in a very short time. The response time of the control system is too short to activate the fault ride-through strategy.

[0029] In view of this, this application provides a bridge arm multiplexing type modular multilevel converter circuit, control method and medium. The converter circuit includes several phase units. The input terminal of each phase unit is connected to the DC side, and the output terminal of each phase unit is connected to one phase of the AC side, converting the DC input of the DC side into the AC output of the AC side. Each phase unit is equipped with a fault ride-through module. The input terminal of the fault ride-through module is connected to the positive terminal of the DC side, and the output terminal of the fault ride-through module is connected to the negative terminal of the DC side. The fault ride-through module is equipped with several cascaded half-bridge sub-modules. When the DC side is operating normally, the half-bridge sub-modules of the fault ride-through module can filter the 6nth harmonic of the DC side. When the DC side is short-circuited, the DC side voltage drops. According to the degree of voltage drop, some half-bridge sub-modules can be shut down to reduce the fault current leaked by the half-bridge sub-modules, thus giving the control system time to start the fault ride-through strategy and realizing unblocked DC fault ride-through.

[0030] Figure 1 This is a schematic diagram of the structure of the bridge arm multiplexed modular multilevel converter circuit provided in the embodiments of this application.

[0031] See Figure 1 The converter circuit includes several phase units. The input terminal of each phase unit is connected to the DC side, and the output terminal of each phase unit is connected to one phase of the AC side. Each phase unit is equipped with a fault ride-through module. The input terminal of the fault ride-through module is connected to the positive terminal of the DC side, and the output terminal of the fault ride-through module is connected to the negative terminal of the DC side. The fault ride-through module is equipped with several cascaded half-bridge sub-modules. During normal operation of the DC side, the fault ride-through module is used to suppress DC side harmonics. During a short-circuit fault on the DC side, the fault ride-through module dynamically adjusts the number of half-bridge sub-modules in operation to reduce the fault current on the DC side.

[0032] In the three-phase AC output, the bridge arm multiplexing modular multilevel converter circuit includes three symmetrical phase units. Each phase unit includes a multiplexing bridge arm (MSC), an upper bridge arm, and a lower bridge arm. The AC side is connected to the output terminals of the upper bridge arm and the lower bridge arm. The input terminal of the upper bridge arm is connected to the positive terminal of the DC side, and the input terminal of the lower bridge arm is connected to the negative terminal of the DC side. The multiplexing bridge arm is connected between the output terminals of the upper bridge arm and the lower bridge arm. The multiplexing bridge arm is switched by a switch to achieve multiplexing.

[0033] Understandably, when the multiplexed bridge arms of a multiplexed alternating converter alternately switch current, harmonics appear in the DC-side current. After Fourier decomposition, the harmonics exhibit a six-pulse characteristic of the 6nth order, and a capacitor is usually set on the DC side for filtering.

[0034] In this embodiment, when the DC side is operating normally, the half-bridge sub-module of the fault ride-through module can filter the 6nth harmonic of the DC side. When the DC side is short-circuited, the DC side voltage drops. The half-bridge sub-module can be shut down according to the degree of voltage drop to reduce the fault current leaked by the half-bridge sub-module, thus giving the control system time to start the fault ride-through strategy and realizing unblocked DC fault ride-through.

[0035] See Figures 2 to 4 The phase unit is also provided with a multiplexing bridge arm and a first selection switch. Second selection switch First direction switch Second direction switch , The reused bridge arm is composed of It consists of cascaded half-bridge modules. The value is a positive integer. The rated voltage of the capacitor in the half-bridge submodule is U. smN First selection switch Second selection switch First direction switch and the second direction switch All by An IGBT with an anti-parallel diode and The multiplexed bridge arm consists of IGBTs connected in reverse series with anti-parallel diodes, and the two ends of the multiplexed bridge arm are connected by a first selection switch. Second selection switch Connect to the AC side port via the first direction switch Second direction switch Connect to the DC side port.

[0036] In this embodiment, the multiplexed bridge arm is used to provide some reactive power support to the AC side during DC faults. When a DC side short circuit occurs, the DC side fault-crossing module clears the fault current. At this time, the DC side does not output power, but stabilizes the AC side voltage through the multiplexed bridge arm.

[0037] like Figure 5 As shown, the fault-crossing module consists of It consists of cascaded half-bridge modules.

[0038] In some embodiments, the half-bridge submodule is provided with a DC support capacitor, the voltage rating of which is determined based on the DC rated voltage and the total number of submodules of the half-bridge submodule.

[0039] The voltage rating of the DC support capacitor of the half-bridge submodule is , must meet ,in, This refers to the rated voltage of the DC support capacitor. DC rated voltage, This represents the total number of modules.

[0040] In this embodiment, the AC side can still output a three-phase sinusoidal current without interrupting the power supply from the DC side to the AC side. For the AM-AAC converter topology, its operating characteristics dictate that a DC support capacitor needs to be installed on the DC side to filter out the 6nth harmonic coupled from the AC side to the DC side. The fault ride-through module adopts a cascaded half-bridge sub-module configuration to ensure the filtering capability of the 6nth harmonic, while taking into account both fault current suppression and continuous power supply capability after DC voltage dips, thus achieving fault ride-through after DC voltage dips.

[0041] In some embodiments, when the DC side is short-circuited, the number of modules connected to the half-bridge submodule is determined based on the degree of sag between the current DC voltage and the rated DC voltage.

[0042] In this embodiment, after a short-circuit fault occurs on the DC side, the DC side voltage is assumed to drop to... , This indicates the degree of sag of the current DC voltage compared to the rated DC voltage. The number of submodules activated by the DC fault ride-through module at this time is... , This represents the floor function.

[0043] For example, if the rated DC voltage is 300kV and the current DC voltage is 200kV, then... , Two and a half bridge modules, that is, two-thirds of the total number of half bridge modules are invested.

[0044] When the half-bridge submodule is engaged, the upper switch is turned on and the lower switch is turned off, as shown in Figure 6(a); when the half-bridge submodule is not engaged, the upper switch is turned off and the lower switch is turned on, as shown in Figure 6(b).

[0045] like Figure 7 As shown, after the fault ride-through module's submodule is engaged, the half-bridge submodule capacitor and the DC-side equivalent resistance R... dc Inductor L dc DC side voltage source kU dc Forming an RLC circuit. The output voltage U of the DC fault ride-through module. sm_out = round(kU dcN / U sm_dcN )*U sm_dcN At this point, the voltage difference between the DC fault ride-through module and the voltage source is close to 0, which is much smaller than the voltage difference U when the DC support capacitor is directly used. dcN -kU dcNThis ensures that the peak current after the DC voltage dip is much smaller than the fault current when the DC support capacitor is directly used, thus clearing the fault current.

[0046] In some embodiments, when the DC side is operating normally, the DC support capacitors of all the half-bridge submodules are connected between the positive and negative terminals of the DC side.

[0047] In this embodiment, during normal operation of the DC side, the DC side voltage of the converter remains at the rated value. At this time, the number of sub-modules activated by the DC fault ride-through module is: The DC side voltage is at its rated value. This equals the total number of modules. All half-bridge sub-modules are then engaged to suppress harmonics on the DC side.

[0048] See Figure 8 Another aspect of this application provides a control method for a bridge arm multiplexed modular multilevel converter circuit, the control method including steps 801 to 803.

[0049] Step 801: After detecting a short circuit fault on the DC side, obtain the current DC voltage on the DC side; Step 802: Determine the number of modules connected to the half-bridge submodule based on the current DC voltage; Step 803: Control the number of half-bridge sub-modules connected to the module to clear the fault current on the DC side.

[0050] In one embodiment of step 802, several half-bridge submodules are provided with the same DC support capacitor; determining the number of modules connected to the half-bridge submodule based on the current DC voltage includes: Step 8021: Determine the voltage sag amplitude based on the ratio between the current DC voltage and the rated DC voltage, wherein the voltage sag amplitude is used to characterize the degree of descent between the current DC voltage and the rated DC voltage; Step 8022: Determine the number of modules to be connected based on the voltage drop amplitude and the total number of sub-modules of the half-bridge sub-module.

[0051] When the DC support capacitors selected for the half-bridge sub-modules are of the same specification, the appropriate number of half-bridge sub-modules are connected to the DC side according to the voltage drop amplitude.

[0052] In another embodiment of step 802, several half-bridge submodules are provided with different DC support capacitors; determining the number of modules connected to the half-bridge submodule based on the current DC voltage includes: Step 8023: Determine the voltage sag amplitude based on the ratio between the current DC voltage and the rated DC voltage, wherein the voltage sag amplitude is used to characterize the degree of descent between the current DC voltage and the rated DC voltage; Step 8024: Determine the voltage drop amplitude and the mapping table of several half-bridge sub-modules, and determine the number of modules connected to the half-bridge sub-modules based on the voltage drop amplitude and the mapping table.

[0053] It is understood that the mapping table is used to represent the voltage drop magnitude corresponding to a number of the input half-bridge sub-modules, and the sum of the voltage values ​​of the input half-bridge sub-modules matches the degree of sag of the current DC voltage.

[0054] If different voltage ratings are selected for the DC support capacitors between the half-bridge sub-modules, a mapping table is pre-configured so that each voltage drop corresponds to several half-bridge sub-modules indicated by the mapping table. This ensures that the sum of the voltage values ​​of the several half-bridge sub-modules is matched with the degree of sag of the current DC voltage, thereby clearing the fault current.

[0055] In some embodiments, the control method further includes: after the current DC voltage recovers to the rated DC voltage, determining the number of modules connected to be the total number of sub-modules.

[0056] Understandably, when the DC side is short-circuited, the DC side fault-crossing module clears the fault current. At this time, the DC side does not output power, but stabilizes the AC side voltage by using the multiplexed bridge arm.

[0057] To illustrate the effectiveness of the converter and control method described above, a simulation model of the bridge arm multiplexed modular multilevel converter circuit shown in the above embodiments will be constructed for verification.

[0058] (1) The simulation parameters are set as shown in Table 1.

[0059] Table 1: System Parameters

[0060] (2) Simulation results description Simulation results for DC voltage dropping to 50% of rated value are as follows: Figures 9(a)-9(d)The diagram shows the current and voltage changes. As shown in Figure 9(a), when a DC short-circuit fault occurs at t=1.0s, the DC voltage Udc drops to 50% of its rated value, i.e., Udc=0.5UdcN. At this time, the number of sub-modules activated by the DC fault-crossing module is adjusted to round(0.5UdcN / Usm_dcN). The simulation results of the DC side current are shown in Figure 9(b), which remain basically stable during the fault. The simulation results of the AC side current are shown in Figure 9(c), indicating that the converter can provide some reactive power support to the AC side during the DC fault. The total capacitor voltage of the sub-modules of the three-phase multiplexed bridge arm are shown in Figure 9(d), which basically remain near the rated value, indicating that the converter can maintain stable operation before and after the fault.

[0061] Simulation results of DC voltage dropping to 0 are as follows Figures 10(a) to 10(d) The diagram shows the current and voltage changes. A DC short-circuit fault occurs at t=1.0s, causing the DC voltage Udc to drop to 0, i.e., Udc=0. At this time, the number of sub-modules activated by the DC fault-crossing module is adjusted to 0. The simulation results of the DC side current are shown in Figure 10(b), which remains basically stable during the fault. The simulation results of the AC side current are shown in Figure 10(c), which can provide some reactive power support to the AC side during the DC fault. The total capacitor voltage of the sub-modules of the three-phase MSC is shown in Figure 10(d), which basically remains near the rated value, indicating that the converter can maintain stable operation before and after the fault.

[0062] It is understood that the specific functions implemented in this method embodiment are the same as those in the circuit embodiment described above, and the beneficial effects achieved are also the same as those achieved in the circuit embodiment described above.

[0063] This application also provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the method described above. This electronic device can be any intelligent terminal, including edge devices and computers.

[0064] It is understood that the content of the above method embodiments is applicable to this device embodiment. The specific functions implemented by this device embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0065] Please see Figure 11 , Figure 11 The hardware structure of an electronic device according to another embodiment is illustrated. The electronic device includes: The processor 1101 can be implemented using a general-purpose CPU (Central Processing Unit), microprocessor, application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of this application. The memory 1102 can be implemented as a read-only memory (ROM), a static storage device, a dynamic storage device, or a random access memory (RAM). The memory 1102 can store the operating system and other applications. When the technical solutions provided in the embodiments of this specification are implemented through software or firmware, the relevant program code is stored in the memory 1102 and is called and executed by the processor 1101 using the methods described in the embodiments of this application. Input / output interface 1103 is used to implement information input and output; The communication interface 1104 is used to enable communication and interaction between this device and other devices. Communication can be achieved through wired means (such as USB, network cable, etc.) or wireless means (such as mobile network, WIFI, Bluetooth, etc.). Bus 1105 transmits information between various components of the device (e.g., processor 1101, memory 1102, input / output interface 1103, and communication interface 1104); The processor 1101, memory 1102, input / output interface 1103 and communication interface 1104 are connected to each other within the device via bus 1105.

[0066] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method.

[0067] It is understood that the content of the above method embodiments is applicable to this storage medium embodiment. The specific functions implemented in this storage medium embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0068] This application also provides a computer program product, including a computer program that, when executed by a processor, implements the above-described method.

[0069] It is understood that the content of the above method embodiments is applicable to the embodiments of this program product. The specific functions implemented by the embodiments of this program product are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0070] Memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs. Furthermore, memory may include high-speed random access memory, and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device.

[0071] The embodiments described in this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0072] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of this application, and may include more or fewer steps than shown, or combine certain steps, or different steps.

[0073] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0074] Those skilled in the art will understand that all or some of the steps in the methods disclosed above, as well as the functional modules / units in the systems and devices, can be implemented as software, firmware, hardware, or suitable combinations thereof.

[0075] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0076] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0077] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of the units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0078] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0079] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0080] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes multiple instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application. The aforementioned storage medium includes various media capable of storing programs, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0081] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. A bridge arm multiplexing type modular multilevel converter circuit, characterized in that, The converter circuit includes several phase units, the input terminal of which is connected to the DC side, and the output terminal of which is connected to one phase of the AC side. The phase unit is equipped with a fault ride-through module. The input terminal of the fault ride-through module is connected to the positive terminal of the DC side, and the output terminal of the fault ride-through module is connected to the negative terminal of the DC side. The fault ride-through module is equipped with several cascaded half-bridge sub-modules. Specifically, during normal operation on the DC side, the fault ride-through module is used to suppress DC side harmonics; during a short-circuit fault on the DC side, the fault ride-through module dynamically adjusts the number of half-bridge sub-modules in operation to reduce the fault current on the DC side.

2. The circuit as described in claim 1, characterized in that, The half-bridge submodule is equipped with a DC support capacitor, and the rated voltage of the DC support capacitor is determined based on the rated DC voltage and the total number of submodules of the half-bridge submodule.

3. The circuit as described in claim 2, characterized in that, When the DC side is short-circuited, the number of modules connected to the half-bridge submodule is determined based on the degree of sag between the current DC voltage and the rated DC voltage.

4. The circuit as described in claim 2, characterized in that, During normal operation on the DC side, the DC support capacitors of all the half-bridge submodules are connected between the positive and negative terminals of the DC side.

5. The circuit as described in claim 1, characterized in that, The phase unit is provided with a multiplexed bridge arm, a first selection switch, a second selection switch, a first direction switch, and a second direction switch; Both ends of the multiplexed bridge arm are connected to the input terminal of the AC side via the first selection switch and the second selection switch, the lower bridge arm is connected via the first direction switch, and the upper bridge arm is connected via the second direction switch.

6. A control method for a bridge arm multiplexed modular multilevel converter circuit, characterized in that, The control method, applied to the bridge arm multiplexing modular multilevel converter circuit according to any one of claims 1 to 5, comprises: After detecting a short-circuit fault on the DC side, the current DC voltage on the DC side is obtained; The number of modules connected to the half-bridge sub-module is determined based on the current DC voltage; The number of half-bridge sub-modules connected to the control module is used to clear the fault current on the DC side.

7. The control method as described in claim 6, characterized in that, Several of the aforementioned half-bridge submodules are equipped with the same DC support capacitor; The step of determining the number of modules connected to the half-bridge submodule based on the current DC voltage includes: The voltage sag is determined based on the ratio between the current DC voltage and the rated DC voltage, and the voltage sag is used to characterize the degree of descent between the current DC voltage and the rated DC voltage. The number of modules connected is determined based on the voltage drop magnitude and the total number of sub-modules of the half-bridge sub-module.

8. The control method as described in claim 6, characterized in that, Several of the aforementioned half-bridge submodules are equipped with different DC support capacitors; The step of determining the number of modules connected to the half-bridge submodule based on the current DC voltage includes: The voltage sag is determined based on the ratio between the current DC voltage and the rated DC voltage, and the voltage sag is used to characterize the degree of descent between the current DC voltage and the rated DC voltage. A mapping table is determined for the voltage drop amplitude and a number of the half-bridge sub-modules. The number of half-bridge sub-modules connected is determined based on the voltage drop amplitude and the mapping table. The mapping table is used to represent the number of half-bridge sub-modules connected corresponding to the voltage drop amplitude. The sum of the voltage values ​​of the connected half-bridge sub-modules matches the degree of sag of the current DC voltage.

9. The control method as described in claim 6, characterized in that, The control method further includes: After the current DC voltage is restored to the rated DC voltage, the number of modules connected is determined to be the total number of sub-modules.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the method of any one of claims 6 to 9.

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