Voltage reduction charging method and system of modular multilevel hybrid bridge arm converter, storage medium, electronic device and computer program product

Abstract

The application discloses a step-down charging method and system of a modular multi-level hybrid bridge arm converter, a storage medium, an electronic device and a computer program product. The step-down charging method comprises: executing a first alternating charging step within a first preset time; and executing a second alternating charging step within a second preset time. The first alternating charging step comprises: sending a first voltage equalization instruction set to the converter to make the upper bridge arm in a voltage equalization state; and sending a first balance instruction set to the converter to make the lower bridge arm in a balance state. The second alternating charging step comprises: sending a second balance instruction set to the converter to make the upper bridge arm in a balance state; and sending a second voltage equalization instruction set to the converter to make the lower bridge arm in a voltage equalization state. The first preset time and the second preset time are within a preset period, and the first preset time and the second preset time are both half of the preset period.

Description

Technical Field

[0001] This application relates to the field of converter charging technology, and more specifically, to a step-down charging method, system, storage medium, electronic device, and computer program product for a modular multilevel hybrid bridge arm converter. Background Technology

[0002] Modular multilevel hybrid bridge arm converters typically employ synchronous charging of the upper and lower bridge arms. For example, this can be achieved by activating the full-bridge module switch T4 in all six bridge arms, or by deactivating some full-bridge or half-bridge modules, thus boosting and balancing the voltages of the full-bridge and half-bridge modules. Under this charging method, the positive bus voltage is the positive peak value of the phase voltage, and the negative bus voltage is the negative peak value of the phase voltage. Therefore, the voltage across the DC side of the converter is approximately twice the peak value of the phase voltage on the valve side.

[0003] However, the inventors of this application have discovered that this charging method is suitable for charging and equalization control of full-bridge and half-bridge modules under full-voltage charging of the hybrid bridge arm DC bus. For modular multilevel hybrid bridge arm converters operating at step-down voltage, such as those with energy storage converters connected to the DC side, if the energy storage converter's operating voltage is designed according to step-down DC voltage, the DC side needs to operate in step-down charging mode, meaning the opposite-end converter also charges the energy storage converter on this side in step-down mode. The charging method of synchronous charging of the upper and lower bridge arms is not suitable for modular multilevel hybrid bridge arm converters operating at step-down voltage.

[0004] The content of the background section is merely technology known to the public and does not necessarily represent existing technology in the field. Summary of the Invention

[0005] According to one aspect of this application, a step-down charging method for a modular multilevel hybrid bridge arm converter is provided. The step-down charging method includes: performing a first alternating charging step within a first preset time period; and performing a second alternating charging step within a second preset time period. The first alternating charging step includes: sending a first voltage equalization command set to the converter to bring the upper bridge arm into a voltage equalization state; and sending a first balancing command set to the converter to bring the lower bridge arm into a balancing state. The second alternating charging step includes: sending a second balancing command set to the converter to bring the upper bridge arm into a balancing state; and sending a second voltage equalization command set to the converter to bring the lower bridge arm into a voltage equalization state. The first preset time and the second preset time are within one preset period, and both the first preset time and the second preset time are half a preset period.

[0006] According to one aspect of this application, a buck charging system for a modular multilevel hybrid arm converter is provided. The buck charging system may include a converter and a valve control system. The converter includes an upper arm and a lower arm; the valve control system performs a first alternating charging step within a first preset time period, including: the valve control system sending a first voltage equalization command set to the converter to bring the upper arm into a voltage equalization state; and the valve control system sending a first balancing command set to the converter to bring the lower arm into a balanced state. Within a second preset time period, the valve control system performs a second alternating charging step, including: the valve control system sending a second balancing command set to the converter to bring the upper arm into a balanced state; and the valve control system sending a second voltage equalization command set to the converter to bring the lower arm into a voltage equalization state. The first preset time and the second preset time are within one preset period, and both the first preset time and the second preset time are half a preset period.

[0007] According to another aspect of this application, this application also provides a non-volatile computer-readable storage medium storing a computer program thereon, which, when executed by a processor, is capable of implementing the buck charging method for a modular multilevel hybrid bridge arm converter as described above.

[0008] According to another aspect of this application, this application also provides an electronic device, including: one or more processors; and a storage device for storing one or more programs, which, when executed by the one or more processors, enable the one or more processors to implement the buck charging method for the modular multilevel hybrid bridge arm converter as described above.

[0009] According to another aspect of this application, this application also provides a computer program product, comprising: a computer program stored on a computer-readable storage medium; the computer program includes program instructions that, when executed by a computer, cause the computer to perform the buck charging method for a modular multilevel hybrid bridge arm converter as described above.

[0010] This application reduces the DC bus voltage during the converter charging process by controlling the alternating step-down charging of the upper and lower bridge arms. This application can simultaneously boost the voltage of the upper and lower bridge arms to a preset boost voltage while reducing the DC-side inter-terminal voltage. The step-down charging method provided in this application is applicable to charging applications of hybrid bridge arm converters operating with step-down unlocking. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 A schematic diagram of the converter according to an embodiment of this application is shown;

[0013] Figure 2 A schematic flowchart of a buck charging method 1000 according to an embodiment of this application is shown;

[0014] Figure 3 A flowchart illustrating step S100 according to an embodiment of this application is shown;

[0015] Figure 4 A flowchart illustrating step S200 according to an embodiment of this application is shown;

[0016] Figure 5 A flowchart illustrating step S110 according to an embodiment of this application is shown;

[0017] Figure 6 A flowchart illustrating step S112 according to an embodiment of this application is shown;

[0018] Figure 7 A flowchart illustrating step S114 according to an embodiment of this application is shown;

[0019] Figure 8 A flowchart illustrating step S210 according to an embodiment of this application is shown;

[0020] Figure 9 A flowchart illustrating step S120 according to an embodiment of this application is shown;

[0021] Figure 10 A flowchart illustrating step S220 according to an embodiment of this application is shown;

[0022] Figure 11 A flowchart illustrating step S222 according to an embodiment of this application is shown;

[0023] Figure 12 A flowchart illustrating step S224 according to an embodiment of this application is shown;

[0024] Figure 13 A schematic diagram of the structure of a buck charging system according to an embodiment of this application is shown;

[0025] Figure 14 This paper shows another structural schematic diagram of a buck charging system according to an embodiment of the present application.

[0026] Figure label:

[0027] 300 step-down charging system;

[0028] Converter 310; Valve control system 320; Measurement unit 330; Converter control and protection system 340. Detailed Implementation

[0029] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this application will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0030] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of these specific details, or other methods, components, materials, devices, etc. In these cases, well-known structures, methods, devices, implementations, materials, or operations will not be shown or described in detail.

[0031] 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 includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0032] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order.

[0033] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0034] According to one aspect of this application, a buck charging method 1000 for a modular multilevel hybrid bridge arm converter is provided. This buck charging method 1000 can be executed by a buck charging system with computing capabilities.

[0035] This modular multilevel hybrid bridge arm converter (hereinafter referred to as the converter) consists of an upper bridge arm and a lower bridge arm. See also Figure 1The converter consists of three upper arms and three lower arms. The converter can also be connected to a start-up circuit. The start-up circuit controls the connection method between the converter and the AC bus.

[0036] See Figure 2 The step-down charging method 1000 may include steps S100 and S200.

[0037] In step S100, the buck charging system performs a first alternating charging step within a first preset time period. In step S200, the buck charging system performs a second alternating charging step within a second preset time period.

[0038] According to the example embodiment, after step S200, the buck charging system executes step S100 again, so that the upper and lower arms of the converter can be continuously charged alternately.

[0039] According to the example embodiment, the first preset time and the second preset time are within a preset period, and both the first preset time and the second preset time are half a preset period.

[0040] The preset period can be the preset charging period of the modular multilevel hybrid bridge arm converter. For example, the preset period can be T, where T ranges from 1ms to M seconds, and M ranges from 1 to 10.

[0041] The first preset time can be the charging time of the upper arm of the modular multilevel hybrid bridge arm converter. The second preset time can be the charging time of the lower arm of the modular multilevel hybrid bridge arm converter. Both the first and second preset times can be set to T / 2.

[0042] See Figure 3 Step S100 may include steps S110 and S120. Steps S110 and S120 may be executed simultaneously.

[0043] In step S110, the buck charging system sends a first voltage equalization command set to the converter so that the upper bridge arm is in a voltage equalization state.

[0044] According to the example embodiment, the first voltage equalization instruction set can be a set of instructions preset according to a preset period and the voltage information of the upper bridge arm.

[0045] The voltage equalization state can be considered as the upper arm of the converter being in a charging state. The voltage equalization state can include a boost phase and a voltage equalization phase. In the boost phase, the voltage of the full-bridge or half-bridge module of the upper arm of the converter is boosted to a preset boost voltage. The buck charging system can increase the voltage of the upper arm by turning on the first switch of the upper arm. The preset boost voltage can be the peak operating voltage of the upper arm. The preset boost voltage can be adjusted according to actual conditions, and this application does not impose any limitations on it.

[0046] During the voltage equalization phase, the voltage of the upper arm of the converter operates from a preset boost voltage to a preset average voltage. The preset average voltage can be the rated operating voltage of the upper arm. The buck charging system can reduce the voltage of the full-bridge or half-bridge modules of the upper arm to the preset average voltage by disconnecting some of them.

[0047] In step S120, the buck charging system sends a first balancing command set to the converter so that the lower bridge arm is in a balanced state.

[0048] According to an example embodiment, the first balancing instruction set can be a set of instructions preset according to a preset period and the voltage information of the lower bridge arm.

[0049] The balanced state can be defined as the lower bridge arm not being charged. The buck charging system can reduce the voltage of the negative DC bus connected to the lower bridge arm to close to 0 by activating some full-bridge or half-bridge modules of the lower bridge arm, thereby reducing the inter-terminal voltage on the DC side of the converter.

[0050] Within the first preset time period, the inter-terminal voltage on the DC side of the converter is the difference between the positive bus voltage and the negative bus voltage on the DC side of the converter.

[0051] See Figure 4 Step S200 may include steps S210 and S220. Steps S210 and S220 may be executed simultaneously.

[0052] In step S210, the buck charging system sends a second balancing command set to the converter to bring the upper bridge arm into a balanced state.

[0053] According to an example embodiment, the second balancing instruction set can be a set of instructions preset according to a preset period and the voltage information of the upper bridge arm.

[0054] The balanced state can also be defined as the upper bridge arm not being charged. The buck charging system can reduce the voltage between terminals on the DC side of the converter by turning on some full-bridge or half-bridge modules of the upper bridge arm, thereby bringing the voltage of the positive DC bus connected to the upper bridge arm close to 0.

[0055] In step S220, the buck charging system sends a second voltage equalization command set to the converter so that the lower bridge arm is in a voltage equalization state.

[0056] According to an example embodiment, the second voltage equalization instruction set can be a set of instructions preset according to a preset period and the voltage information of the lower bridge arm.

[0057] The voltage equalization state can also refer to the lower arm of the converter being in a charging state. The voltage equalization state can include a boost phase and a voltage equalization phase. In the boost phase, the voltage of the full-bridge module or half-bridge module of the lower arm of the converter is boosted to a preset boost voltage. The preset boost voltage can also be the peak operating voltage of the lower arm. The preset boost voltage can be adjusted according to actual conditions, and this application does not impose any limitations. The buck charging system can increase the voltage of the upper arm by opening the third switch of the lower arm.

[0058] During the voltage equalization phase, the voltage of the lower arm of the converter operates from a preset boost voltage to a preset average voltage. The preset average voltage can also be the rated operating voltage of the lower arm. The buck charging system can reduce the voltage of the lower arm's full-bridge or half-bridge modules to the preset average voltage by disconnecting some of the full-bridge or half-bridge modules.

[0059] During the second preset time period, the inter-terminal voltage on the DC side of the converter is the difference between the positive bus voltage and the negative bus voltage on the DC side of the converter.

[0060] Through the above embodiments, the buck charging method provided in this application can send a first voltage equalization command set to the converter within a first preset time period to ensure that the upper bridge arm is in a voltage equalization state, and send a first balancing command set to the converter to ensure that the lower bridge arm is in a balancing state. This application can also send a second balancing command set to the converter within a second preset time period to ensure that the upper bridge arm is in a balancing state, and send a second voltage equalization command set to the converter to ensure that the lower bridge arm is in a voltage equalization state.

[0061] This application reduces the DC bus voltage during the converter charging process by controlling the alternating step-down charging of the upper and lower bridge arms. This application can simultaneously boost the voltage of the upper and lower bridge arms to a preset boost voltage while reducing the DC-side inter-terminal voltage. The step-down charging method provided in this application is applicable to charging applications of hybrid bridge arm converters operating with step-down unlocking.

[0062] Optionally, the upper bridge arm includes an upper full-bridge module and an upper half-bridge module. See also Figure 1 The upper bridge arm may include multiple upper bridge sub-modules (upper bridge sub-module 1 to upper bridge sub-module N). Among them, the multiple upper bridge sub-modules can be upper full bridge modules or upper half bridge modules, and the multiple upper bridge sub-modules include at least one upper full bridge module and at least one upper half bridge module.

[0063] For example, such as Figure 1 As shown, the upper full-bridge module may include four switching transistors (switching transistor T1, switching transistor T2, switching transistor T3, and switching transistor T4). The upper half-bridge module may include two switching transistors (switching transistor T5 and switching transistor T6).

[0064] According to an example embodiment, the first voltage equalization instruction set includes a first boost instruction and a first voltage equalization instruction.

[0065] The first boost command can be an instruction message that raises the voltage of the upper full-bridge module and the upper half-bridge module to a preset boost voltage. The preset boost voltage can be the peak voltage at which the upper bridge arm operates. The preset boost voltage can be adjusted according to actual conditions, and this application does not impose any restrictions.

[0066] The first voltage equalization command can be a command message that causes the voltage of the upper full-bridge module and the upper half-bridge module to operate at a preset average voltage. The preset average voltage can be the rated voltage for the upper bridge arm to operate at.

[0067] See Figure 5 Step S110 may include steps S111-S114.

[0068] In step S111, the buck charging system generates a first boost command based on the collected voltage information of the upper bridge arm.

[0069] According to the example embodiment, the buck charging system can acquire the voltage information of the upper bridge arm in real time through a measurement unit. The voltage information of the upper bridge arm may include the voltage of the upper full-bridge module, the voltage of the upper half-bridge module, and the average voltage of the upper bridge arm.

[0070] For example, the measurement unit can be a capacitor voltage sampling device or a bridge arm current measuring device for a full-bridge module or a half-bridge module.

[0071] In step S112, the buck charging system sends a first boost command to the converter to boost the upper full-bridge module and the upper half-bridge module to a preset boost voltage.

[0072] According to the example embodiment, the buck charging system can boost the voltage of the upper full-bridge module and the upper half-bridge module to a preset boost voltage by turning on the first switch of the upper bridge arm.

[0073] Optionally, see Figure 6 Step S112 may include step S112a.

[0074] In step S112a, the buck charging system sends a first boost command to the converter, causing the upper full-bridge module to turn on the first switch at a first preset rate until the upper full-bridge module and the upper half-bridge module boost to the preset boost voltage.

[0075] According to the example embodiment, the first switch can be the switching transistor T4 of the upper full-bridge module.

[0076] The first preset rate can be the rate at which the first switch is turned on. The first preset rate can be 1 switch / t1, where t1 is the first preset period. t1 can be set to 1tic to 1s. tic is the program execution period (e.g., 50ms). For example, if t1 can be 1s, then the first preset rate can be 1 switch / 1s, and the buck charging system can turn on one switch T4 of the upper full-bridge module per second.

[0077] For example, the buck charging system sends a first boost command to the converter. The buck charging system can turn on the switching transistor T4 of each upper full-bridge module one by one according to a first preset rate. After all the switching transistors T4 of the upper full-bridge modules are turned on, the upper full-bridge module and the upper half-bridge module boost the voltage to the preset boost voltage.

[0078] In step S113, the buck charging system generates a first voltage equalization command based on the collected voltage information of the boosted upper bridge arm.

[0079] According to the example embodiment, after the upper full-bridge module and the upper half-bridge module boost the voltage to the preset boost voltage, the buck charging system can collect the voltage information of the boosted upper bridge arm through the measurement unit.

[0080] In step S114, the buck charging system sends a first voltage equalization command to the converter so that the upper full-bridge module and the upper half-bridge module operate at a preset average voltage.

[0081] According to an example embodiment, the buck charging system can reduce the voltage of the upper full-bridge module and the upper half-bridge module by cutting off part of the upper full-bridge module and / or the upper half-bridge module of the upper bridge arm, so that the upper full-bridge module and the upper half-bridge module operate at a preset average voltage.

[0082] Optionally, see Figure 7 Step S114 may include step S114a.

[0083] In step S114a, the buck charging system sends a first voltage equalization command to the converter, causing the upper bridge arm to cut off a first preset number of upper full-bridge modules and / or upper half-bridge modules according to the first voltage equalization command and the first preset rule, until the upper full-bridge modules and upper half-bridge modules operate at a preset average voltage.

[0084] According to the example embodiment, the first preset rule can be to sort all the voltages of the upper full-bridge modules and the upper half-bridge modules from highest to lowest, and then disconnect the upper full-bridge modules and / or upper half-bridge modules with higher voltages. The first preset number can be the number of upper full-bridge modules and / or upper half-bridge modules to be disconnected. The first preset number can be set according to the primary voltage of the converter, the number of upper full-bridge modules, and the number of upper half-bridge modules.

[0085] For example, the buck charging system can send a first voltage equalization command to the converter. The buck charging system sorts the voltages of all the upper full-bridge modules and upper half-bridge modules from high to low according to their voltage magnitude. Based on the sorting result, it disconnects the upper full-bridge modules and / or upper half-bridge modules with higher voltages, thereby balancing the voltages of the upper full-bridge modules and upper half-bridge modules and ensuring that the voltages of the upper full-bridge modules and upper half-bridge modules operate at a preset average voltage.

[0086] Optionally, the second balancing instruction set may include a first off instruction and a first on instruction.

[0087] See Figure 8 Step S210 may include steps S211-S212.

[0088] In step S211, the buck charging system generates a first shutdown command based on the voltage information of the upper bridge arm after it has been working to a preset average voltage, so that the upper full-bridge module shuts down the first switch at a second preset rate.

[0089] According to the example embodiment, after the upper full-bridge module and the upper half-bridge module operate to a preset average voltage, the buck charging system can collect the voltage information of the upper bridge arm through the measurement unit.

[0090] According to the example embodiment, the first shutdown command can be an instruction to shut down the first switch. The second preset rate can be the rate at which the first switch is shut down. The second preset rate can be 1 unit / t2, where t2 can be a second preset period. t2 can be set to 1 tic ~ 1 s.

[0091] For example, the buck charging system sends a first shutdown command to the converter. The buck charging system can then sequentially shut down the switching transistor T4 of each upper full-bridge module at a second preset rate. After all the switching transistors T4 of the upper full-bridge modules are shut down, the upper full-bridge modules become locked, and the upper half-bridge modules also become locked.

[0092] In step S212, the buck charging system generates a first start command based on the collected voltage information of the upper bridge arm after the first switch is turned off, so that the upper full-bridge module turns on the second switch at a third preset rate.

[0093] According to the example embodiment, after the first switch is turned off, the buck charging system collects the voltage information of the upper bridge arm through the measurement unit.

[0094] According to the example embodiment, the second switch can be either switch T2 or switch T3 of the upper full-bridge module. The first activation command can be an instruction to activate the second switch. The third preset rate can be 1 / t3, where t3 is a third preset period. t3 can be set to 1tic to 1s. The number of times the second switch is activated is greater than or equal to the number of upper half-bridge modules. For example, if the number of upper full-bridge modules is NFS and the number of upper half-bridge modules is NHS, then the number of times the second switch is activated is greater than or equal to NHS.

[0095] For example, the buck charging system sends a first start command to the converter. The buck charging system can turn on each switch T2 (or switch T3) of the upper full-bridge module one by one at a third preset rate, until at least the number of switches T2 (or switches T3) of the upper full-bridge modules of NHS are turned on.

[0096] After switching transistor T2 (or T3) of the NHS upper full-bridge module is turned on, the upper full-bridge module and the upper half-bridge module of the upper bridge arm are in a balanced state. With switching transistor T2 (or T3) of the NHS upper full-bridge module turned on, the DC bus voltage connected to the three upper bridge arms is approximately 0, thereby reducing the DC side inter-terminal voltage, and the upper half-bridge module remains in a locked state.

[0097] When the number of switching transistors T2 (or T3) of the full-bridge module is greater than that of NHS, for example, when the number of switching transistors T2 (or T3) of NHS+1, NHS+2, or NHS+3 is turned on, the upper full-bridge module and the upper half-bridge module of the upper bridge arm are in a balanced state, and the DC side inter-terminal voltage can be further reduced.

[0098] Optionally, see Figure 8 Step S210 may also include step S213.

[0099] In step S213, the buck charging system generates a second shutdown command based on the collected voltage information of the upper bridge arm after the second switch is turned on, so that the upper full-bridge module shuts down the second switch at a fourth preset rate.

[0100] According to the example embodiment, after the second switch is turned on, the buck charging system collects the voltage information of the upper bridge arm through the measurement unit.

[0101] According to the example embodiment, the second shutdown command can be an instruction to shut down the second switch. The fourth preset rate can be 1 unit / t4, where t4 is a fourth preset period. t4 can be set to 1 tic ~ 1 s.

[0102] For example, the buck charging system sends a second shutdown command to the converter. The buck charging system can sequentially shut down the switching transistor T2 (or switching transistor T3) of each open upper full-bridge module at a fourth preset rate. After shutting down all the open upper full-bridge modules' switching transistors T2 (or switching transistor T3), the upper half-bridge module remains in a locked state.

[0103] Optionally, the lower bridge arm includes a lower full-bridge module and a lower half-bridge module. See also Figure 1 The lower bridge arm may include multiple lower bridge sub-modules (lower bridge sub-module 1 to lower bridge sub-module N). These multiple lower bridge sub-modules can be lower full-bridge modules or lower half-bridge modules, and at least one lower full-bridge module and at least one lower half-bridge module are included among them. The lower full-bridge module may have the same structure as the upper full-bridge module. The lower half-bridge module may have the same structure as the upper half-bridge module. For example, the lower full-bridge module may include four switching transistors (switching transistor T1, switching transistor T2, switching transistor T3, and switching transistor T4). The lower half-bridge module may include two switching transistors (switching transistor T5 and switching transistor T6).

[0104] According to an example embodiment, the first balancing instruction set may include a third shut-off instruction and a second turn-on instruction.

[0105] See Figure 9 Step S120 may include steps S121 and S122.

[0106] In step S121, the buck charging system generates a third shutdown command based on the collected voltage information of the lower bridge arm, so that the lower full-bridge module shuts down the third switch at a fifth preset rate.

[0107] According to the example embodiment, the buck charging system can acquire the voltage information of the lower bridge arm in real time through a measurement unit. The voltage information of the lower bridge arm may include the voltage of the lower full-bridge module, the voltage of the lower half-bridge module, and the average voltage of the lower bridge arm.

[0108] According to the example embodiment, the third switch can be the switching transistor T4 of the lower full-bridge module. The third shutdown command can be the command information to shut down the third switch. The fifth preset rate can be the rate at which the third switch is shut down. The fifth preset rate can be 1 cycle / t5, where t5 can be the fifth preset period. t5 can be set to 1 tic ~ 1 s.

[0109] For example, the buck charging system sends a third shutdown command to the converter. The buck charging system can then sequentially shut down the switching transistor T4 of each lower full-bridge module according to a fifth preset rate. After shutting down the switching transistor T4 of the lower full-bridge module, the lower full-bridge module becomes locked, and the lower half-bridge module also becomes locked.

[0110] In step S122, the buck charging system generates a second start command based on the voltage information of the lower bridge arm after the third switch is turned off, so that the lower full bridge module turns on the fourth switch at a sixth preset rate.

[0111] According to the example embodiment, after the third switch is turned off, the buck charging system collects the voltage information of the lower bridge arm through the measurement unit.

[0112] According to the example embodiment, the fourth switch can be either switch T2 or switch T3 of the lower full-bridge module. The second activation command can be an instruction to activate the fourth switch. The sixth preset rate can be 1 / t6, where t6 is the sixth preset period. t6 can be set to 1tic to 1s. The number of times the fourth switch is activated is greater than or equal to the number of lower half-bridge modules. For example, if the number of lower full-bridge modules is NFX and the number of lower half-bridge modules is NHX, then the number of times the second switch is activated is greater than or equal to NHX.

[0113] For example, the buck charging system sends a second start command to the converter. The buck charging system can turn on each switch T2 (or switch T3) of each lower full-bridge module one by one at a sixth preset rate, until at least NHX number of switches T2 (or switch T3) of the lower full-bridge modules are turned on.

[0114] After switching transistor T2 (or T3) of each of the NHX lower full-bridge modules is turned on, the lower full-bridge module and the lower half-bridge module of the lower bridge arm are in a balanced state. With switching transistor T2 (or T3) of each of the NHX lower full-bridge modules turned on, the DC bus voltage connected to the three lower bridge arms is approximately 0, thereby reducing the DC side inter-terminal voltage, and the lower half-bridge module remains in a locked state.

[0115] When the number of switching transistors T2 (or T3) of the full-bridge module is greater than NHX, for example, when the number of switching transistors T2 (or T3) is NHX+1, NHX+2, or NHX+3, the lower full-bridge module and the lower half-bridge module of the lower bridge arm are in a balanced state, and the DC-side inter-terminal voltage can be further reduced.

[0116] Optionally, see Figure 9 Step S120 may also include step S123.

[0117] In step S123, the buck charging system generates a fourth shutdown command based on the voltage information of the lower bridge arm after the fourth switch is turned on, so that the lower full-bridge module shuts down the fourth switch at a seventh preset rate.

[0118] According to the example embodiment, after the fourth switch is turned on, the buck charging system collects the voltage information of the lower bridge arm through the measurement unit.

[0119] According to the example embodiment, the fourth shutdown command can be an instruction to shut down the fourth switch. The seventh preset rate can be 1 unit / t7, where t7 can be the seventh preset period. t7 can be set to 1 tic ~ 1 s.

[0120] For example, the buck charging system sends a fourth shutdown command to the converter. The buck charging system can sequentially shut down each open lower full-bridge module's switch T2 (or switch T3) at a fourth preset rate. After shutting down all open lower full-bridge module switches T2 (or switch T3), the lower half-bridge module remains in a locked state.

[0121] Optionally, according to an example embodiment, the second voltage equalization instruction set includes a second boost instruction and a second voltage equalization instruction.

[0122] The second boost command can be an instruction message that causes the voltage of the lower full-bridge module and the lower half-bridge module to rise to a preset boost voltage. The preset boost voltage of the lower bridge arm can be the same as the preset boost voltage of the upper bridge arm.

[0123] The second voltage equalization command can be a command message that causes the voltage of the lower full-bridge module and the lower half-bridge module to operate at a preset average voltage. The preset average voltage can also be the rated voltage of the lower bridge arm. The preset average voltage of the lower bridge arm can be the same as the preset average voltage of the upper bridge arm.

[0124] See Figure 10 Step S220 may also include steps S221-S224.

[0125] In step S221, the buck charging system generates a second boost command based on the voltage information of the lower bridge arm after the fourth switch is turned off.

[0126] According to the example embodiment, the buck charging system can acquire the voltage information of the lower bridge arm after the fourth switch is turned off through the measurement unit.

[0127] In step S222, the buck charging system sends a second boost command to the converter to boost the lower full-bridge module and the lower half-bridge module to a preset boost voltage.

[0128] According to the example embodiment, the buck charging system can boost the voltage of the lower full-bridge module and the lower half-bridge module to a preset boost voltage by opening the third switch of the lower bridge arm.

[0129] Optionally, see Figure 11 Step S222 may include step S222a.

[0130] In step S222a, the buck charging system sends a second boost command to the converter, causing the lower full-bridge module to open the third switch at an eighth preset rate until the lower full-bridge module and the lower half-bridge module boost to the preset boost voltage.

[0131] According to the example embodiment, the eighth preset rate can be the rate at which the third switch is opened. The eighth preset rate can be 1 unit / t8, and t8 can be the eighth preset period. t8 can be set to 1 tic ~ 1 s.

[0132] For example, the buck charging system sends a second boost command to the converter. The buck charging system can turn on the switching transistor T4 of each lower full-bridge module one by one according to the eighth preset rate. After all the switching transistors T4 of the lower full-bridge modules are turned on, the lower full-bridge modules and the lower half-bridge modules boost the voltage to the preset boost voltage.

[0133] In step S223, the buck charging system generates a second voltage equalization command based on the collected voltage information of the boosted lower bridge arm.

[0134] According to the example embodiment, after the lower full-bridge module and the lower half-bridge module are boosted to the preset boost voltage, the buck charging system can collect the voltage information of the boosted lower bridge arm through the measurement unit.

[0135] In step S224, the buck charging system sends a second voltage equalization command to the converter so that the lower full-bridge module and the lower half-bridge module operate at a preset average voltage.

[0136] According to an example embodiment, the buck charging system can reduce the voltage of the lower full-bridge module and the lower half-bridge module by cutting off part of the lower full-bridge module and / or the lower half-bridge module of the lower bridge arm, so that the lower full-bridge module and the lower half-bridge module operate at a preset average voltage.

[0137] Optionally, see Figure 12 Step S224 may include step S224a.

[0138] In step S224a, the buck charging system sends a second voltage equalization command to the converter, causing the lower bridge arm to cut off a second preset number of lower full-bridge modules and / or lower half-bridge modules according to the second voltage equalization command and the second preset rule, until the lower full-bridge modules and lower half-bridge modules operate at a preset average voltage.

[0139] According to the example embodiment, the second preset rule can be to sort all the voltages of the lower full-bridge modules and the lower half-bridge modules from highest to lowest, and then disconnect the lower full-bridge modules and / or lower half-bridge modules with higher voltages. The second preset quantity can be the number of lower full-bridge modules and / or lower half-bridge modules to be disconnected. The second preset quantity can be set based on the primary voltage of the converter, the number of lower full-bridge modules, and the number of lower half-bridge modules.

[0140] For example, the buck charging system can send a second voltage equalization command to the converter. The buck charging system sorts the voltages of all lower full-bridge modules and lower half-bridge modules from high to low according to their voltage magnitude. Based on the sorting result, it disconnects the lower full-bridge modules and / or lower half-bridge modules with higher voltages, thereby balancing the voltages of the lower full-bridge modules and lower half-bridge modules and ensuring that the voltages of the lower full-bridge modules and lower half-bridge modules operate at a preset average voltage.

[0141] It is understandable that for modular multilevel hybrid bridge arm converters operating at reduced voltage, devices such as surge arresters on the DC bus are configured with overvoltage parameters according to the unlocked reduced voltage mode. If the opposite converter operates under normal full-voltage charging mode, it will cause the surge arresters and other devices to malfunction due to overvoltage. Therefore, the opposite converter needs to be charged using the reduced voltage mode.

[0142] Through the above embodiments, the step-down charging method 1000 provided in this application is simple in steps and clear in principle. It can prevent the DC-side surge arrester equipment from being triggered due to excessive bus voltage, thus preventing abnormal operation of the DC-side equipment. This application can reduce the DC-side inter-terminal voltage during converter charging. When the DC side of the converter is connected to another converter, it can avoid the problem of charging harmonic current on the AC side connected to the modular multilevel hybrid bridge arm converter due to frequent DC-side charging current.

[0143] According to one aspect of this application, a buck charging system 300 for a modular multilevel hybrid bridge arm converter is provided. See also... Figure 13 The step-down charging system 300 may include a converter 310 and a valve control system 320.

[0144] According to an example embodiment, converter 310 can be a modular multilevel hybrid arm converter. Converter 310 includes an upper arm and a lower arm. See also... Figure 1 The converter 310 includes three upper bridge arms and three lower bridge arms.

[0145] The valve control system 320 performs a first alternating charging step within a first preset time period. The valve control system 320 performs a second alternating charging step within a second preset time period.

[0146] According to the example embodiment, after the valve control system 320 performs the second alternating charging step within a second preset time, the valve control system 320 performs the first alternating charging step again within a first preset time, so that the upper and lower bridge arms of the converter 310 can be continuously charged alternately.

[0147] According to the example embodiment, the first preset time and the second preset time are within a preset period, and both the first preset time and the second preset time are half a preset period.

[0148] The preset period can be the preset charging period of the modular multilevel hybrid bridge arm converter. For example, the preset period can be T, where T ranges from 1ms to M seconds, and M ranges from 1 to 10.

[0149] The first preset time can be the charging time of the upper arm of the modular multilevel hybrid bridge arm converter. The second preset time can be the charging time of the lower arm of the modular multilevel hybrid bridge arm converter. Both the first and second preset times can be set to T / 2.

[0150] According to the example embodiment, the valve control system 320 sends a first pressure equalization command set to the converter 310 so that the upper arm is in a pressure equalization state.

[0151] According to the example embodiment, the first voltage equalization command set can be a set of commands preset according to a preset period and the voltage information of the upper bridge arm. The power module of the converter 310 can receive the first voltage equalization command set.

[0152] The voltage equalization state can be described as the upper arm of converter 310 being in a charging state. The voltage equalization state can include a boost phase and a voltage equalization phase. In the boost phase, the voltage of the full-bridge module or half-bridge module of the upper arm of converter 310 is boosted to a preset boost voltage. Converter 310 can increase the voltage of the upper arm by opening the first switch of the upper arm. The preset boost voltage can be the peak operating voltage of the upper arm. The preset boost voltage can be adjusted according to actual conditions, and this application does not impose any limitations on it.

[0153] During the voltage equalization phase, the voltage of the upper arm of converter 310 operates from a preset boost voltage to a preset average voltage. The preset average voltage can be the rated operating voltage of the upper arm. Valve control system 320 can make the voltage of the full-bridge module or half-bridge module of the upper arm operate at the preset average voltage by disconnecting part of the full-bridge module or half-bridge module.

[0154] According to an example embodiment, the valve control system 320 sends a first balancing command set to the converter 310 to bring the lower bridge arm into a balanced state.

[0155] According to an example embodiment, the first balancing command set can be a set of commands preset based on a preset period and the voltage information of the lower bridge arm. The power module of the converter 310 can receive the first balancing command set.

[0156] The balanced state can be achieved when the lower bridge arm is not charging. The converter 310 can reduce the inter-terminal voltage on the DC side of the converter 310 by turning on some full-bridge modules or half-bridge modules of the lower bridge arm, thereby making the voltage of the negative DC bus connected to the lower bridge arm close to 0.

[0157] During the first preset time period, the inter-terminal voltage of the DC side of converter 310 is the difference between the positive bus voltage of the DC side of converter 310 and the negative bus voltage of the DC side of converter 310.

[0158] According to an example embodiment, the valve control system 320 sends a second set of balancing commands to the converter 310 to bring the upper arm into a balanced state.

[0159] According to the example embodiment, the second balancing command set can be a set of commands preset according to a preset period and the voltage information of the upper bridge arm. The power module of the converter 310 can receive the second balancing command set.

[0160] The balanced state can also be achieved when the upper bridge arm is not in a charging state. The valve control system 320 can reduce the inter-terminal voltage on the DC side of the converter 310 by turning on some full-bridge modules or half-bridge modules of the upper bridge arm, thereby making the voltage of the positive DC bus connected to the upper bridge arm close to 0.

[0161] According to the example embodiment, the valve control system 320 sends a second pressure equalization command set to the converter 310 so that the lower bridge arm is in a pressure equalization state.

[0162] According to the example embodiment, the second voltage equalization command set can be a set of commands preset according to a preset period and the voltage information of the lower bridge arm. The power module of the converter 310 can receive the second voltage equalization command set.

[0163] The voltage equalization state can also refer to the lower bridge arm of converter 310 being in a charging state. The voltage equalization state can include a boost phase and a voltage equalization phase. In the boost phase, the voltage of the full-bridge module or half-bridge module of the lower bridge arm of converter 310 is boosted to a preset boost voltage. The preset boost voltage can also be the peak operating voltage of the lower bridge arm. The preset boost voltage can be adjusted according to actual conditions, and this application does not impose any limitations. Converter 310 can increase the voltage of the upper bridge arm by opening the third switch of the lower bridge arm.

[0164] During the voltage equalization phase, the voltage of the lower bridge arm of converter 310 operates from a preset boost voltage to a preset average voltage. The preset average voltage can also be the rated operating voltage of the lower bridge arm. Converter 310 can make the voltage of the full-bridge module or half-bridge module of the lower bridge arm operate at the preset average voltage by disconnecting part of the full-bridge module or half-bridge module of the lower bridge arm.

[0165] During the second preset time period, the inter-terminal voltage on the DC side of converter 310 is the difference between the positive bus voltage and the negative bus voltage on the DC side of converter 310.

[0166] Through the above embodiments, this application can send a first pressure equalization command set to the converter within a first preset time period via the valve control system to ensure the upper bridge arm is in a pressure equalization state, and send a first balancing command set to the converter to ensure the lower bridge arm is in a balancing state. This application can also send a second balancing command set to the converter within a second preset time period to ensure the upper bridge arm is in a balancing state, and send the second pressure equalization command set to the converter to ensure the lower bridge arm is in a pressure equalization state.

[0167] This application reduces the DC bus voltage during the converter charging process by controlling the alternating step-down charging of the upper and lower bridge arms. This application can simultaneously boost the voltage of the upper and lower bridge arms to a preset boost voltage while reducing the DC-side inter-terminal voltage. This application is applicable to applications involving hybrid bridge arm converters with step-down unlocking operation during charging.

[0168] Optionally, the upper bridge arm includes an upper full-bridge module and an upper half-bridge module. See also Figure 1 The upper bridge arm may include multiple upper bridge sub-modules (upper bridge sub-module 1 to upper bridge sub-module N). These multiple upper bridge sub-modules can be either full-bridge modules or half-bridge modules, and at least one of the multiple upper bridge sub-modules must include a full-bridge module and at least one half-bridge module. For example, a full-bridge module may include four switches (switches T1, T2, T3, and T4). An upper half-bridge module may include two switches (switches T5 and T6).

[0169] According to an example embodiment, the first voltage equalization instruction set includes a first boost instruction and a first voltage equalization instruction.

[0170] The first boost command can be an instruction message that raises the voltage of the upper full-bridge module and the upper half-bridge module to a preset boost voltage. The preset boost voltage can be the peak voltage at which the upper bridge arm operates. The preset boost voltage can be adjusted according to actual conditions, and this application does not impose any restrictions.

[0171] The first voltage equalization command can be a command message that causes the voltage of the upper full-bridge module and the upper half-bridge module to operate at a preset average voltage. The preset average voltage can be the rated voltage for the upper bridge arm to operate at.

[0172] See Figure 14 The step-down charging system 300 may also include a measurement unit 330.

[0173] According to the example embodiment, the measurement unit 330 acquires the voltage information of the upper bridge arm in real time. The voltage information of the upper bridge arm may include the voltage of the upper full-bridge module, the voltage of the upper half-bridge module, and the average voltage of the upper bridge arm. For example, the measurement unit 330 can be a capacitor voltage sampling device for the full-bridge module or the half-bridge module, or a bridge arm current measuring device.

[0174] According to an example embodiment, the valve control system 320 generates a first boost command based on the collected voltage information of the upper bridge arm.

[0175] The valve control system 320 sends a first boost command to the converter 310, causing the upper full-bridge module and the upper half-bridge module to boost to a preset boost voltage. The power module of the converter 310 receives the first boost command.

[0176] According to the example embodiment, the valve control system 320 can boost the voltage of the upper full-bridge module and the upper half-bridge module to a preset boost voltage by opening the first switch of the upper bridge arm.

[0177] According to the example embodiment, the valve control system 320 sends a first boost command to the converter 310, causing the upper full-bridge module to open the first switch at a first preset rate until the upper full-bridge module and the upper half-bridge module boost to the preset boost voltage.

[0178] The first switch can be the switching transistor T4 of the upper full-bridge module. The first preset rate can be the rate at which the first switch is turned on. The first preset rate can be 1 switch / t1, where t1 is the first preset period. t1 can be set to 1tic to 1s. tic is the program execution period (e.g., 50ms). For example, if t1 can be 1s, then the first preset rate can be 1 switch / 1s, and the converter 310 can turn on one switching transistor T4 of the upper full-bridge module per second.

[0179] For example, the valve control system 320 sends a first boost command to the converter 310. The converter 310 can turn on the switching transistor T4 of each upper full-bridge module one by one at a first preset rate. After all the switching transistors T4 of the upper full-bridge modules are turned on, the upper full-bridge modules and the upper half-bridge modules boost the voltage to the preset boost voltage.

[0180] According to the example embodiment, after the upper full-bridge module and the upper half-bridge module boost the voltage to a preset boost voltage, the measurement unit 330 collects the voltage information of the boosted upper bridge arm. The valve control system 320 generates a first voltage equalization command based on the collected voltage information of the boosted upper bridge arm.

[0181] The valve control system 320 sends a first voltage equalization command to the converter 310, causing the upper full-bridge module and the upper half-bridge module to operate at a preset average voltage. The power module of the converter 310 receives the first voltage equalization command.

[0182] According to the example embodiment, the converter 310 can reduce the voltage of the upper full-bridge module and the upper half-bridge module by cutting off part of the upper full-bridge module and / or the upper half-bridge module of the upper bridge arm, so that the upper full-bridge module and the upper half-bridge module operate at a preset average voltage.

[0183] Optionally, the valve control system 320 sends a first equalization command to the converter 310, causing the upper bridge arm to cut off a first preset number of upper full-bridge modules and / or upper half-bridge modules according to the first equalization command and the first preset rule, until the upper full-bridge modules and upper half-bridge modules operate at a preset average voltage.

[0184] According to the example embodiment, the first preset rule can be to sort all the voltages of the upper full-bridge modules and the upper half-bridge modules from highest to lowest, and then disconnect the upper full-bridge modules and / or upper half-bridge modules with higher voltages. The first preset number can be the number of upper full-bridge modules and / or upper half-bridge modules to be disconnected. The first preset number can be set according to the primary voltage of the converter, the number of upper full-bridge modules, and the number of upper half-bridge modules.

[0185] For example, the valve control system 320 can send a first voltage equalization command to the converter 310. The converter 310 sorts the voltages of all the upper full-bridge modules and the upper half-bridge modules from high to low according to the voltage magnitude. Based on the sorting result, it disconnects the upper full-bridge modules and / or the upper half-bridge modules with higher voltages, thereby balancing the voltages of the upper full-bridge modules and the upper half-bridge modules, and ensuring that the voltages of the upper full-bridge modules and the upper half-bridge modules operate at a preset average voltage.

[0186] Optionally, the second balancing instruction set may include a first off instruction and a first on instruction.

[0187] According to the example embodiment, after the upper full-bridge module and the upper half-bridge module operate to a preset average voltage, the measurement unit 330 collects the voltage information of the upper bridge arm.

[0188] The valve control system 320 generates a first shutdown command based on the voltage information of the upper bridge arm after it has been working to a preset average voltage, so that the upper full-bridge module shuts down the first switch at a second preset rate.

[0189] According to the example embodiment, the first shutdown command can be an instruction to shut down the first switch. The second preset rate can be the rate at which the first switch is shut down. The second preset rate can be 1 unit / t2, where t2 can be a second preset period. t2 can be set to 1 tic ~ 1 s.

[0190] For example, the valve control system 320 sends a first shutdown command to the converter 310. The power module of the converter 310 can receive the first shutdown command. The converter 310 can sequentially shut down the switching transistor T4 of each upper full-bridge module at a second preset rate. After all the switching transistors T4 of the upper full-bridge modules are shut down, the upper full-bridge modules become locked, and the upper half-bridge modules also become locked.

[0191] According to the example embodiment, after the first switch is turned off, the measurement unit 330 collects the voltage information of the upper bridge arm. The valve control system 320 generates a first opening command based on the collected voltage information of the upper bridge arm after the first switch is turned off, so that the upper full-bridge module opens the second switch at a third preset rate.

[0192] According to the example embodiment, the second switch can be either switch T2 or switch T3 of the upper full-bridge module. The first activation command can be an instruction to activate the second switch. The third preset rate can be 1 / t3, where t3 is a third preset period. t3 can be set to 1tic to 1s. The number of times the second switch is activated is greater than or equal to the number of upper half-bridge modules. For example, if the number of upper full-bridge modules is NFS and the number of upper half-bridge modules is NHS, then the number of times the second switch is activated is greater than or equal to NHS.

[0193] For example, the valve control system 320 sends a first start command to the converter 310. The power module of the converter 310 receives the first start command. The converter 310 can turn on each of the upper full-bridge modules' switching transistors T2 (or T3) one by one at a third preset rate, until at least the number of upper full-bridge modules NHS's switching transistors T2 (or T3) are turned on.

[0194] After switching transistor T2 (or T3) of the NHS upper full-bridge module is turned on, the upper full-bridge module and the upper half-bridge module of the upper bridge arm are in a balanced state. With switching transistor T2 (or T3) of the NHS upper full-bridge module turned on, the DC bus voltage connected to the three upper bridge arms is approximately 0, thereby reducing the DC side inter-terminal voltage, and the upper half-bridge module remains in a locked state.

[0195] When the number of switching transistors T2 (or T3) of the full-bridge module is greater than that of NHS, for example, when the number of switching transistors T2 (or T3) of NHS+1, NHS+2, or NHS+3 is turned on, the upper full-bridge module and the upper half-bridge module of the upper bridge arm are in a balanced state, and the DC side inter-terminal voltage can be further reduced.

[0196] Optionally, after the second switch is turned on, the measurement unit 330 collects the voltage information of the upper bridge arm. The valve control system 320 generates a second shutdown command based on the collected voltage information of the upper bridge arm after the second switch is turned on, so that the upper full-bridge module shuts off the second switch at a fourth preset rate.

[0197] According to the example embodiment, the second shutdown command can be an instruction to shut down the second switch. The fourth preset rate can be 1 unit / t4, where t4 is a fourth preset period. t4 can be set to 1 tic ~ 1 s.

[0198] For example, the valve control system 320 sends a second shutdown command to the converter 310. The power module of the converter 310 receives the second shutdown command. The converter 310 can sequentially shut down the switching transistors T2 (or T3) of each open upper full-bridge module at a fourth preset rate. After shutting down all the open switching transistors T2 (or T3) of the upper full-bridge modules, the upper half-bridge module remains in a locked state.

[0199] Optionally, the lower bridge arm includes a lower full-bridge module and a lower half-bridge module. The lower bridge arm may include multiple lower bridge sub-modules (lower bridge sub-module 1 - lower bridge sub-module N). These multiple lower bridge sub-modules can be either lower full-bridge modules or lower half-bridge modules, and at least one lower full-bridge module and at least one lower half-bridge module are included among them. The lower full-bridge module may have the same structure as the upper full-bridge module. The lower half-bridge module may have the same structure as the upper half-bridge module. For example, the lower full-bridge module may include four switching transistors (switching transistor T1, switching transistor T2, switching transistor T3, and switching transistor T4). The lower half-bridge module may include two switching transistors (switching transistor T5 and switching transistor T6).

[0200] According to an example embodiment, the first balancing instruction set may include a third shut-off instruction and a second turn-on instruction.

[0201] According to the example embodiment, the buck charging system 300 can acquire the voltage information of the lower bridge arm in real time through the measurement unit 330. The voltage information of the lower bridge arm may include the voltage of the lower full-bridge module, the voltage of the lower half-bridge module, and the average voltage of the lower bridge arm.

[0202] The valve control system 320 generates a third shutdown command based on the collected voltage information of the lower bridge arm, so that the lower full bridge module shuts down the third switch at a fifth preset rate.

[0203] According to the example embodiment, the third switch can be the switching transistor T4 of the lower full-bridge module. The third shutdown command can be the command information to shut down the third switch. The fifth preset rate can be the rate at which the third switch is shut down. The fifth preset rate can be 1 cycle / t5, where t5 can be the fifth preset period. t5 can be set to 1 tic ~ 1 s.

[0204] For example, the valve control system 320 sends a third shutdown command to the converter 310. The power module of the converter 310 receives the third shutdown command. The converter 310 can then sequentially shut down the switching transistor T4 of each lower full-bridge module at a fifth preset rate. After shutting down the switching transistor T4 of the lower full-bridge module, the lower full-bridge module becomes locked, and the lower half-bridge module also becomes locked.

[0205] According to the example embodiment, after the third switch is closed, the measurement unit 330 collects the voltage information of the lower bridge arm. The valve control system 320 generates a second opening command based on the collected voltage information of the lower bridge arm after the third switch is closed, so that the lower full-bridge module opens the fourth switch at a sixth preset rate.

[0206] According to the example embodiment, the fourth switch can be either switch T2 or switch T3 of the lower full-bridge module. The second activation command can be an instruction to activate the fourth switch. The sixth preset rate can be 1 / t6, where t6 is the sixth preset period. t6 can be set to 1tic to 1s. The number of times the fourth switch is activated is greater than or equal to the number of lower half-bridge modules. For example, if the number of lower full-bridge modules is NFX and the number of lower half-bridge modules is NHX, then the number of times the second switch is activated is greater than or equal to NHX.

[0207] For example, the valve control system 320 sends a second start command to the converter 310. The power module of the converter 310 receives the second start command. The converter 310 can turn on each of the switches T2 (or switches T3) of the lower full-bridge module one by one at a sixth preset rate, until at least NHX of the switches T2 (or switches T3) of the lower full-bridge modules are turned on.

[0208] After switching transistor T2 (or T3) of each of the NHX lower full-bridge modules is turned on, the lower full-bridge module and the lower half-bridge module of the lower bridge arm are in a balanced state. With switching transistor T2 (or T3) of each of the NHX lower full-bridge modules turned on, the DC bus voltage connected to the three lower bridge arms is approximately 0, thereby reducing the DC side inter-terminal voltage, and the lower half-bridge module remains in a locked state.

[0209] When the number of switching transistors T2 (or T3) of the full-bridge module is greater than NHX, for example, when the number of switching transistors T2 (or T3) is NHX+1, NHX+2, or NHX+3, the lower full-bridge module and the lower half-bridge module of the lower bridge arm are in a balanced state, and the DC-side inter-terminal voltage can be further reduced.

[0210] According to the example embodiment, after the fourth switch is turned on, the buck charging system 300 collects the voltage information of the lower bridge arm through the measurement unit 330. The valve control system 320 generates a fourth shutdown command based on the collected voltage information of the lower bridge arm after the fourth switch is turned on, so that the lower full-bridge module shuts off the fourth switch at a seventh preset rate.

[0211] According to the example embodiment, the fourth shutdown command can be an instruction to shut down the fourth switch. The seventh preset rate can be 1 unit / t7, where t7 can be the seventh preset period. t7 can be set to 1 tic ~ 1 s.

[0212] For example, the valve control system 320 sends a fourth shutdown command to the converter 310. The power module of the converter 310 receives the fourth shutdown command. The converter 310 can sequentially shut down the switching transistors T2 (or T3) of each open lower full-bridge module at a fourth preset rate. After shutting down all the open switching transistors T2 (or T3) of the lower full-bridge modules, the lower half-bridge module remains in a locked state.

[0213] Optionally, according to an example embodiment, the second voltage equalization instruction set includes a second boost instruction and a second voltage equalization instruction.

[0214] The second boost command can be an instruction to raise the voltage of the lower full-bridge module and the lower half-bridge module to a preset boost voltage. The preset boost voltage can also be the peak operating voltage of the lower bridge arm. The preset boost voltage can be adjusted according to actual conditions, and this application does not impose any restrictions. The preset boost voltage of the lower bridge arm can be the same as the preset boost voltage of the upper bridge arm.

[0215] The second voltage equalization command can be a command message that causes the voltage of the lower full-bridge module and the lower half-bridge module to operate at a preset average voltage. The preset average voltage can also be the rated voltage of the lower bridge arm. The preset average voltage of the lower bridge arm can be the same as the preset average voltage of the upper bridge arm.

[0216] According to the example embodiment, after the fourth switch is turned off, the measurement unit 330 acquires the voltage information of the lower bridge arm. The valve control system 320 generates a second boost command based on the acquired voltage information of the lower bridge arm after the fourth switch is turned off.

[0217] The valve control system 320 sends a second boost command to the converter 310, causing the lower full-bridge module and the lower half-bridge module to boost to a preset boost voltage. The power module of the converter 310 receives the second boost command.

[0218] According to the example embodiment, the converter 310 can boost the voltage of the lower full-bridge module and the lower half-bridge module to a preset boost voltage by opening the third switch of the lower bridge arm.

[0219] The valve control system 320 sends a second boost command to the converter 310, causing the lower full-bridge module to open the third switch at the eighth preset rate until the lower full-bridge module and the lower half-bridge module boost to the preset boost voltage.

[0220] According to the example embodiment, the eighth preset rate can be the rate at which the third switch is opened. The eighth preset rate can be 1 unit / t8, and t8 can be the eighth preset period. t8 can be set to 1 tic ~ 1 s.

[0221] For example, the valve control system 320 sends a second boost command to the converter 310. The converter 310 can then sequentially turn on the switching transistor T4 of each lower full-bridge module at an eighth preset rate. After all the switching transistors T4 of the lower full-bridge modules are turned on, the lower full-bridge modules and the lower half-bridge modules boost to the preset boost voltage.

[0222] According to the example embodiment, after the lower full-bridge module and the lower half-bridge module boost the voltage to a preset boost voltage, the measurement unit 330 collects the voltage information of the boosted lower bridge arm. The valve control system 320 generates a second voltage equalization command based on the collected voltage information of the boosted lower bridge arm.

[0223] According to an example embodiment, the valve control system 320 sends a second voltage equalization command to the converter 310, causing the lower full-bridge module and the lower half-bridge module to operate at a preset average voltage. The power module of the converter 310 receives the second voltage equalization command.

[0224] According to the example embodiment, the converter 310 can reduce the voltage of the lower full-bridge module and the lower half-bridge module by cutting off part of the lower full-bridge module and / or the lower half-bridge module of the lower bridge arm, so that the lower full-bridge module and the lower half-bridge module operate at a preset average voltage.

[0225] The valve control system 320 sends a second equalization command to the converter 310, causing the lower bridge arm to cut off a second preset number of lower full-bridge modules and / or lower half-bridge modules according to the second equalization command and the second preset rule, until the lower full-bridge modules and lower half-bridge modules operate at a preset average voltage.

[0226] According to the example embodiment, the second preset rule can be to sort all the voltages of the lower full-bridge modules and the lower half-bridge modules from highest to lowest, and then disconnect the lower full-bridge modules and / or lower half-bridge modules with higher voltages. The second preset quantity can be the number of lower full-bridge modules and / or lower half-bridge modules to be disconnected. The second preset quantity can be set based on the primary voltage of the converter, the number of lower full-bridge modules, and the number of lower half-bridge modules.

[0227] For example, a voltage equalization command can send a second voltage equalization command to converter 310. Converter 310 sorts the voltages of all lower full-bridge modules and lower half-bridge modules from high to low according to their voltage magnitude. Based on the sorting result, it disconnects the lower full-bridge modules and / or lower half-bridge modules with higher voltages, thereby balancing the voltages of the lower full-bridge modules and lower half-bridge modules and ensuring that the voltages of the lower full-bridge modules and lower half-bridge modules operate at a preset average voltage.

[0228] Through the above embodiments, the steps of this application are simple and the principle is clear. It can prevent the DC-side surge arrester equipment from being triggered due to excessive bus voltage, thus preventing abnormal operation of the DC-side equipment. This application can reduce the DC-side inter-terminal voltage during converter charging. When the DC side of the converter is connected to another converter, it can avoid the problem of charging harmonic current on the AC side connected to the modular multilevel hybrid bridge arm converter due to frequent DC-side charging current.

[0229] Optionally, see Figure 14 The step-down charging system 300 may also include a converter control and protection system 340.

[0230] According to the example embodiment, the converter control and protection system 340 can send a high-frequency modulated signal or other level signal to the valve control system 320. The converter control and protection system 340 can also send voltage reference waves of the upper and lower arms of the converter 310 to the valve control system 320. The measurement unit 330 can also acquire the current values ​​of the upper and lower arms of the converter 310, the voltage values ​​of the capacitors in the upper full-bridge module, the upper half-bridge module, the lower full-bridge module, and the lower half-bridge module. After acquiring the current and voltage values, the measurement unit 330 can send them to the valve control system 320.

[0231] According to another aspect of this application, this application also provides a non-volatile computer-readable storage medium storing a computer program thereon, which, when executed by a processor, is capable of implementing the buck charging method for a modular multilevel hybrid bridge arm converter as described above.

[0232] According to another aspect of this application, this application also provides an electronic device, including: one or more processors; and a storage device for storing one or more programs, which, when executed by the one or more processors, enable the one or more processors to implement the buck charging method for the modular multilevel hybrid bridge arm converter as described above.

[0233] According to another aspect of this application, this application also provides a computer program product, comprising: a computer program stored on a computer-readable storage medium; the computer program includes program instructions that, when executed by a computer, cause the computer to perform the buck charging method for a modular multilevel hybrid bridge arm converter as described above.

[0234] Finally, it should be noted that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions of the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A step-down charging method for a modular multilevel hybrid bridge arm converter, characterized in that, The converter includes an upper bridge arm and a lower bridge arm, and the buck charging method includes: Within a first preset time period, a first alternating charging step is performed, including: Send a first set of equalization commands to the converter so that the upper arm is in an equalization state; Send a first balancing command set to the converter so that the lower bridge arm is in a balanced state; During a second preset time period, a second alternating charging step is performed, including: Send a second balancing command set to the converter to bring the upper bridge arm into a balanced state; Send a second set of equalization commands to the converter so that the lower bridge arm is in an equalization state; The first preset time and the second preset time are within a preset period, and both the first preset time and the second preset time are half of the preset period.

2. The step-down charging method according to claim 1, characterized in that, The upper bridge arm includes an upper full-bridge module and an upper half-bridge module, and the first voltage equalization command set includes a first boost command and a first voltage equalization command. Sending a first voltage equalization command set to the converter to put the upper bridge arm in a voltage equalization state includes: The first boost command is generated based on the collected voltage information of the upper bridge arm; Send the first boost command to the converter so that the upper full-bridge module and the upper half-bridge module boost the voltage to a preset boost voltage; The first voltage equalization command is generated based on the collected voltage information of the upper bridge arm after voltage boosting. A first voltage equalization command is sent to the converter so that the upper full-bridge module and the upper half-bridge module operate at a preset average voltage.

3. The step-down charging method according to claim 2, characterized in that, Sending the first boost command to the converter to cause the upper full-bridge module and the upper half-bridge module to boost to a preset boost voltage includes: Send the first boost command to the converter, causing the upper full-bridge module to turn on the first switch at a first preset rate until the upper full-bridge module and the upper half-bridge module boost the voltage to the preset boost voltage; Sending a first voltage equalization command to the converter to cause the upper full-bridge module and the upper half-bridge module to operate at a preset average voltage includes: A first voltage equalization command is sent to the converter, causing the upper bridge arm to cut off a first preset number of the upper full-bridge modules and / or the upper half-bridge modules according to the first voltage equalization command and a first preset rule, until the upper full-bridge modules and the upper half-bridge modules operate at the preset average voltage.

4. The step-down charging method according to claim 3, characterized in that, The upper bridge arm includes an upper full bridge module and an upper half bridge module; Sending a second balancing command set to the converter to bring the upper bridge arm into a balanced state includes: A first shutdown command is generated based on the voltage information of the upper bridge arm after the collected working voltage reaches the preset average voltage, so that the upper full-bridge module shuts down the first switch at a second preset rate; A first start command is generated based on the voltage information of the upper bridge arm after the first switch is turned off, so that the upper full-bridge module turns on the second switch at a third preset rate.

5. The step-down charging method according to claim 4, characterized in that, After generating a first start command based on the collected voltage information of the upper bridge arm after the first switch is turned off, so that the upper full-bridge module turns on the second switch at a third preset rate, the buck charging method further includes: A second shutdown command is generated based on the voltage information of the upper bridge arm after the second switch is turned on, so that the upper full-bridge module shuts down the second switch at a fourth preset rate.

6. The step-down charging method according to claim 1, characterized in that, The lower bridge arm includes a lower full-bridge module and a lower half-bridge module; Sending a first balancing command set to the converter to bring the lower bridge arm into a balanced state includes: A third shutdown command is generated based on the collected voltage information of the lower bridge arm, so that the lower full-bridge module shuts down the third switch at a fifth preset rate; A second start command is generated based on the voltage information of the lower bridge arm after the third switch is turned off, so that the lower full-bridge module turns on the fourth switch at a sixth preset rate.

7. The step-down charging method according to claim 6, characterized in that, After generating a second start command based on the voltage information of the lower bridge arm after the third switch is turned off, so that the lower full-bridge module turns on the fourth switch at a sixth preset rate, the buck charging method further includes: A fourth shutdown command is generated based on the voltage information of the lower bridge arm after the fourth switch is turned on, so that the lower full-bridge module turns off the fourth switch at a seventh preset rate.

8. The step-down charging method according to claim 7, characterized in that, The lower bridge arm includes a lower full-bridge module and a lower half-bridge module, and the second voltage equalization command set includes a second boost command and a second voltage equalization command. Sending a second voltage equalization command set to the converter to put the lower bridge arm into a voltage equalization state includes: The second boost command is generated based on the voltage information of the lower bridge arm after the fourth switch is turned off. Send the second boost command to the converter so that the lower full-bridge module and the lower half-bridge module boost the voltage to the preset boost voltage; The second voltage equalization command is generated based on the collected voltage information of the lower bridge arm after the voltage boost. Send the second voltage equalization command to the converter so that the lower full-bridge module and the lower half-bridge module operate at the preset average voltage.

9. The step-down charging method according to claim 8, characterized in that, Sending the second boost command to the converter to cause the lower full-bridge module and the lower half-bridge module to boost to the preset boost voltage includes: Send the second boost command to the converter, causing the lower full-bridge module to open the third switch at an eighth preset rate until the lower full-bridge module and the lower half-bridge module boost the voltage to the preset boost voltage; Sending the second voltage equalization command to the converter so that the lower full-bridge module and the lower half-bridge module operate at the preset average voltage includes: The second voltage equalization command is sent to the converter, causing the lower bridge arm to disconnect a second preset number of the lower full-bridge modules and / or the lower half-bridge modules according to the second voltage equalization command and the second preset rule, until the lower full-bridge modules and the lower half-bridge modules operate at the preset average voltage.

10. A step-down charging system for a modular multilevel hybrid bridge arm converter, characterized in that, The buck charging system executes the buck charging method for the modular multilevel hybrid bridge arm converter as described in any one of claims 1-9, and the buck charging system includes: A converter, the converter comprising an upper bridge arm and a lower bridge arm; The valve-controlled system executes a first alternating charging step within a first preset time period, including: The valve control system sends a first pressure equalization command set to the converter so that the upper arm is in a pressure equalization state. The valve control system sends a first set of balancing commands to the converter so that the lower bridge arm is in a balanced state. The valve control system executes a second alternating charging step within a second preset time period, including: The valve control system sends a second set of balancing commands to the converter so that the upper bridge arm is in a balanced state. The valve control system sends a second pressure equalization command set to the converter so that the lower bridge arm is in a pressure equalization state; The first preset time and the second preset time are within a preset period, and both the first preset time and the second preset time are half of the preset period.

11. A non-volatile computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the buck charging method for the modular multilevel hybrid bridge arm converter as described in any one of claims 1-9.

12. An electronic device, characterized in that, include: One or more processors; Storage device for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the buck charging method for the modular multilevel hybrid bridge arm converter as described in any one of claims 1-9.

13. A computer program product, characterized in that, The method includes a computer program stored on a computer-readable storage medium, the computer program including program instructions that, when executed by a computer, cause the computer to perform a buck charging method for a modular multilevel hybrid bridge arm converter as described in any one of claims 1-9.

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