Bridge arm multiplexing type direct current transformer and sub-module quantity and type design method thereof
Patent Information
- Application Number
- CN202610860674.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-15
- Publication Date
- 2026-10-20
AI Technical Summary
[0004]本发明提供了一种桥臂复用型直流变压器及其子模块数量与类型设计方法，以解决现有技术中存在的子模块数量设计未充分考虑多维运行需求、导致成本过高或可靠性不足的问题
[0015]本申请针对高压、公共、低压三桥臂混合级联全桥与半桥子模块的拓扑，构建了多维度、分层级的子模块配置体系。首先获取端口电压、稳态运行工作点等关键参数，综合稳态运行、端口调压、桥臂能量平衡及子模块冗余多重约束，分步迭代确定各桥臂子模块总数与全桥、半桥配比，有效解决传统设计仅满足基础电压需求、工况适配性差、冗余不足的问题，保障稳态下功率传输稳定、调压灵活、能量均衡。在此基础上，通过引入源侧盈余功率阻断、感性元件故障续流吸收、端口故障穿越三项故障约束，在不增子模块总数前提下优化配比，通过多约束取最大值保证故障裕量。本申请兼顾稳态性能与故障保护，在控制成本与体积的同时，显著提升变压器运行可靠性与电网适配能力，工程应用价值突出。
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Abstract
Description
Technical Field
[0001] This invention relates to the field of high-voltage direct current transmission technology, specifically to a bridge arm multiplexed DC transformer and its sub-module quantity and type design method. Background Technology
[0002] With energy transition and green, low-carbon development becoming a global consensus, renewable energy sources, represented by wind power and photovoltaics, are being developed and utilized on a large scale. Flexible DC transmission technology is a key means to achieve stable transmission of large-scale clean energy. As a key piece of equipment in DC transmission systems, DC transformers can realize DC voltage transformation, power flow control, and fault isolation, and have significant technical and economic advantages in all-DC collection, grid connection, and utilization scenarios.
[0003] Bridge-arm reusable DC transformers are constructed based on modular multilevel converter (MMC) submodules, offering advantages such as adjustable port voltage, bidirectional power transmission, fewer conversion stages, and flexible control, resulting in high engineering feasibility. However, current research lacks systematic consideration of the number of submodules required for this topology. This leads to situations where the number of submodules is excessively high, increasing costs, or insufficient, failing to meet steady-state and transient operation requirements, thus affecting system reliability and safety. Summary of the Invention
[0004] This invention provides a bridge arm reuse type DC transformer and its sub-module quantity and type design method to solve the problems in the prior art where the sub-module quantity design does not fully consider multi-dimensional operation requirements, resulting in excessive cost or insufficient reliability.
[0005] This invention provides a design method for the number and type of submodules in a bridge-arm multiplexed DC transformer. The DC transformer includes a high-voltage bridge arm, a common bridge arm, and a low-voltage bridge arm. Each bridge arm is composed of cascaded full-bridge submodules and half-bridge submodules. The method includes: Obtain the design parameters, including port voltage parameters and the transformer steady-state operating point; Based on the steady-state operating point, port voltage regulation requirements, bridge arm energy balance requirements, and submodule redundancy requirements, determine the total number of submodules for each bridge arm and the total number of submodules for the entire bridge. The number of full-bridge sub-modules in the high-voltage bridge arm is adjusted according to the fault protection requirements, which include source-side surplus power blocking requirements, inductive component fault freewheeling absorption requirements, and port fault ride-through requirements.
[0006] In one optional implementation, the total number of submodules for each bridge arm and the total number of submodules for the entire bridge are determined based on the steady-state operating point, port voltage regulation requirements, bridge arm energy balance requirements, and submodule redundancy requirements, including: Based on the AC and DC components of the output voltage of each bridge arm, the maximum value of the output voltage of each bridge arm is calculated, and the total number of sub-modules of each bridge arm is determined by rounding. Based on the minimum output voltage of each bridge arm, the negative voltage capability that each bridge arm needs to be provided by the full-bridge submodule is determined, and the number of full-bridge submodules in each bridge arm is determined by rounding. The number of half-bridge submodules in each bridge arm is obtained by subtracting the total number of submodules in each bridge arm from the total number of full-bridge submodules in each bridge arm.
[0007] In one optional implementation, based on the steady-state operating point, port voltage regulation requirements, bridge arm energy balance requirements, and submodule redundancy requirements, the total number of submodules for each bridge arm and the total number of submodules for the entire bridge are determined, further including: When only the high-voltage port needs to have voltage regulation capability, the DC component of the output voltage of the high-voltage bridge arm and the common bridge arm is corrected according to the preset voltage regulation range, the maximum and minimum values of the bridge arm output voltage are recalculated, the total number of sub-modules of the high-voltage bridge arm and the common bridge arm is increased according to the updated voltage extreme values, and the number of full-bridge sub-modules and half-bridge sub-modules in the bridge arm is re-determined. When only the low-voltage port needs to have voltage regulation capability, the DC component of the output voltage of the low-voltage bridge arm and the common bridge arm is corrected according to the preset voltage regulation range, the maximum and minimum values of the bridge arm output voltage are recalculated, the total number of sub-modules of the low-voltage bridge arm and the common bridge arm is increased according to the updated voltage extreme values, and the number of full-bridge sub-modules and half-bridge sub-modules in the bridge arm is re-determined. When both the high-voltage and low-voltage ports need to have voltage regulation capabilities, the DC component of the output voltage of all bridge arms is corrected according to the preset voltage regulation range, the maximum and minimum values of the output voltage of each bridge arm are recalculated, the total number of sub-modules of all bridge arms is increased according to the updated voltage extreme values, and the number of full-bridge sub-modules and half-bridge sub-modules in each bridge arm is re-determined.
[0008] In one optional implementation, based on the steady-state operating point, port voltage regulation requirements, bridge arm energy balance requirements, and submodule redundancy requirements, the total number of submodules for each bridge arm and the total number of submodules for the entire bridge are determined, further including: Calculate the voltage between the reactance terminals of each bridge arm based on the AC current of the bridge arm and the reactance inductance of the bridge arm; The voltage between the reactant terminals is superimposed on the AC component of the output voltage of each bridge arm to correct the maximum and minimum values of the output voltage of each bridge arm. Based on the corrected output voltage extreme values, the number of submodules for each bridge arm is redetermined.
[0009] In one optional implementation, based on the steady-state operating point, port voltage regulation requirements, bridge arm energy balance requirements, and submodule redundancy requirements, the total number of submodules for each bridge arm and the total number of submodules for the entire bridge are determined, further including: The total number of sub-modules in each bridge arm and the total number of sub-modules in the entire bridge are increased proportionally according to the preset redundancy coefficient. The corrected number of half-bridge submodules is obtained by subtracting the corrected total number of submodules from the total number of full-bridge submodules.
[0010] In one alternative implementation, the constraint condition for the source-side surplus power blocking requirement is: The sum of the rated voltages of the full-bridge submodules of the low-voltage bridge arm and the high-voltage bridge arm is higher than the rated voltage of the low-voltage side.
[0011] In one alternative implementation, the constraint condition for the inductive element fault freewheeling absorption requirement is: The energy absorbed by the full-bridge submodules of the low-voltage and high-voltage bridge arms is higher than the fault follow current energy stored in the inductive elements of the DC transformer.
[0012] In one alternative implementation, the constraint condition for the port fault traversal requirement is: The absolute value of the negative voltage generated by the full-bridge submodule in the high-voltage bridge arm is not less than the sum of the positive DC voltage component of the common bridge arm and the AC voltage component required for energy balance between the bridge arms.
[0013] In one alternative implementation, when there are multiple fault protection requirements, the number of full-bridge submodules of the high-voltage bridge arm is taken as the maximum value that satisfies all fault protection requirement constraints.
[0014] Secondly, the present invention provides a bridge arm reuse type DC transformer, comprising: at least one phase unit, each phase unit including one or two sets of bridge arm units; the bridge arm unit includes: a high-voltage bridge arm, a common bridge arm and a low-voltage bridge arm; In each phase unit, one end of the high-voltage bridge arm, the common bridge arm, and the low-voltage bridge arm are connected to each other to form a common connection point; the other end of the high-voltage bridge arm is used to connect to the high-voltage port, and the other end of the low-voltage bridge arm is used to connect to the low-voltage port. Each bridge arm is composed of a hybrid cascade of full-bridge submodules and half-bridge submodules, and the total number of submodules in each bridge arm and the number of full-bridge submodules are determined by the design method of the number and type of submodules of the bridge arm multiplexing DC transformer described in the first aspect or any of its corresponding embodiments.
[0015] This application addresses the topology of a hybrid cascaded full-bridge and half-bridge submodule system with high-voltage, common, and low-voltage arms, constructing a multi-dimensional, hierarchical submodule configuration system. First, key parameters such as port voltage and steady-state operating point are obtained. By comprehensively considering multiple constraints including steady-state operation, port voltage regulation, arm energy balance, and submodule redundancy, the total number of submodules for each arm and the full-bridge / half-bridge ratio are determined iteratively step-by-step. This effectively solves the problems of traditional designs that only meet basic voltage requirements, have poor adaptability to operating conditions, and insufficient redundancy, ensuring stable power transmission, flexible voltage regulation, and balanced energy under steady-state conditions. Based on this, by introducing three fault constraints—source-side surplus power blocking, inductive element fault freewheeling absorption, and port fault ride-through—the ratio is optimized without increasing the total number of submodules. The maximum value of multiple constraints ensures fault margin. This application balances steady-state performance and fault protection, significantly improving transformer operational reliability and grid adaptability while controlling cost and size, demonstrating significant engineering application value. Attached Figure Description
[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0017] Figure 1 This is a schematic diagram of a bridge arm multiplexed DC transformer topology according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the submodule topology according to an embodiment of the present invention; Figure 3 This is a flowchart illustrating the design method for the number and type of sub-modules of a bridge arm multiplexed DC transformer according to an embodiment of the present invention. Figure 4 This is a schematic diagram illustrating the complete design flow of the number of submodules according to an embodiment of the present invention. Detailed Implementation
[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0019] It is understood that before using the technical solutions disclosed in the various embodiments of the present invention, users should be informed of the types, scope of use, and usage scenarios of the personal information involved in the present invention and their authorization should be obtained in accordance with relevant laws and regulations through appropriate means.
[0020] This invention provides a bridge arm multiplexing type DC transformer, which is a non-isolated DC transformer, and its topology is as follows: Figure 1 As shown, it includes at least one phase unit; each phase unit includes one or two sets of bridge arm units; each bridge arm unit includes: a high-voltage bridge arm, a common bridge arm, and a low-voltage bridge arm.
[0021] In each phase unit, one end of the high-voltage bridge arm, the common bridge arm, and the low-voltage bridge arm are interconnected to form a common connection point; the other end of the high-voltage bridge arm is used to connect to the high-voltage port, and the other end of the low-voltage bridge arm is used to connect to the low-voltage port. The positive high-voltage bridge arm and the negative high-voltage bridge arm together constitute the high-voltage port, and the positive low-voltage bridge arm and the negative low-voltage bridge arm together constitute the low-voltage port, which can realize the conversion of DC voltage between the high-voltage side and the low-voltage side and bidirectional power transmission.
[0022] Furthermore, the high-voltage arm, common arm, and low-voltage arm are all composed of a hybrid cascade of full-bridge and half-bridge submodules, connected in series with the arm reactors. Specifically, the low-voltage arm, high-voltage arm, and common arm all employ a hybrid cascade topology of full-bridge and half-bridge submodules. The submodule topology is as follows: Figure 2 As shown, the full-bridge submodule has both positive and negative voltage output capabilities, while the half-bridge submodule only has positive voltage output capability. The mixed configuration of the two can balance the advantages of operating performance and cost.
[0023] When a bridge arm reuse type DC transformer is in operation, the voltage modulated by the low-voltage bridge arm, common bridge arm, and high-voltage bridge arm is a mixed AC and DC voltage; the current in the low-voltage bridge arm, common bridge arm, and high-voltage bridge arm is a mixed AC and DC current.
[0024] Based on this, in order to ensure that the bridge arm reuse type DC transformer meets the design requirements in terms of steady-state operation, port voltage regulation, energy balance, fault redundancy and fault protection, in this embodiment, the total number of sub-modules of each of the high-voltage bridge arm, the common bridge arm and the low-voltage bridge arm, as well as the total number of sub-modules of the whole bridge, are determined by the design method of the number and type of sub-modules of the bridge arm reuse type DC transformer proposed in this embodiment.
[0025] based on Figure 1 This invention provides a design method for the number and type of submodules in a bridge-arm multiplexed DC transformer topology, the process of which is as follows: Figure 3 As shown, the specific steps include the following: Step S1: Obtain design parameters, including port voltage parameters and the transformer steady-state operating point.
[0026] Specifically, the port voltage parameters include: high-voltage side DC voltage. U dc1 Low-voltage side DC voltage U dc2 The steady-state operating point includes the DC component of the output voltage of the high-voltage bridge arm, the common bridge arm, and the low-voltage bridge arm. U dcH , U dcW , U dcL DC components of current in the high-voltage arm, common arm, and low-voltage arm I dcH , I dcW , I dcL AC current components of the high-voltage arm, common arm, and low-voltage arm. I acH , I acW , I acL AC voltage inside the transformer U ac These key operating parameters provide the basic input conditions for the subsequent design of the number of submodules. In addition, the required design parameters also include: the rated power delivered by the converter. P N ;Phase number M ; Rated voltage of transformer submodule capacitor u capN Bridge arm reactance inductance value L ; Transformer high-voltage port reactance L H The reactance L at the low-voltage port of the transformer L The capacitance value C of the transformer submodule. These parameters together constitute the basic input conditions for designing the number of submodules.
[0027] Step S2: Based on the steady-state operating point, port voltage regulation requirements, bridge arm energy balance requirements, and submodule redundancy requirements, determine the total number of submodules for each bridge arm, the number of full-bridge submodules, and the number of half-bridge submodules.
[0028] Specifically, based on the AC / DC voltage components of the bridge arms at the steady-state operating point, the maximum and minimum values of the bridge arm output voltage are calculated to initially determine the total number of submodules required for each bridge arm, the number of full-bridge submodules, and the number of half-bridge submodules. Based on this, and considering the port voltage regulation range, the DC component of the bridge arm voltage is corrected, and the total number of submodules for each bridge arm, as well as the configuration of full-bridge and half-bridge submodules, are updated. Then, based on the bridge arm energy balance requirements and considering the AC voltage drop across the bridge arm reactance, the AC voltage components of the bridge arms are further corrected, and the number of the three types of submodules is optimized again. Finally, considering the submodule fault bypass redundancy requirements, the total number of submodules for each bridge arm is increased according to a preset redundancy ratio, and the number of full-bridge submodules is adjusted accordingly. The number of half-bridge submodules is determined based on the difference between the total number and the number of full-bridge submodules, thus obtaining the total number of submodules for each bridge arm, the number of full-bridge submodules, and the number of half-bridge submodules that meet the requirements of steady-state operation, voltage regulation, energy balance, and redundancy.
[0029] Step S3: Adjust the ratio of full-bridge submodules to half-bridge submodules in the high-voltage bridge arm according to the fault protection requirements. The fault protection requirements include source-side surplus power blocking requirements, inductive component fault freewheeling absorption requirements, and port fault ride-through requirements.
[0030] Specifically, while keeping the total number of high-voltage bridge arm sub-modules unchanged, constraints are established based on three fault protection requirements to determine the lower limit of the number of full-bridge sub-modules in the high-voltage bridge arm; by combining all constraints, the number of full-bridge sub-modules that meet all requirements is selected to complete the final correction of the number of full-bridge sub-modules in the high-voltage bridge arm, and then the corresponding number of half-bridge sub-modules is determined.
[0031] This application addresses the topology of a hybrid cascaded full-bridge and half-bridge submodule system with high-voltage, common, and low-voltage arms, constructing a multi-dimensional, hierarchical submodule configuration system. First, key parameters such as port voltage and steady-state operating point are obtained. By comprehensively considering multiple constraints including steady-state operation, port voltage regulation, arm energy balance, and submodule redundancy, the total number of submodules for each arm and the full-bridge / half-bridge ratio are determined iteratively step-by-step. This effectively solves the problems of traditional designs that only meet basic voltage requirements, have poor adaptability to operating conditions, and insufficient redundancy, ensuring stable power transmission, flexible voltage regulation, and balanced energy under steady-state conditions. Based on this, by introducing three fault constraints—source-side surplus power blocking, inductive element fault freewheeling absorption, and port fault ride-through—the ratio is optimized without increasing the total number of submodules. The maximum value of multiple constraints ensures fault margin. This application balances steady-state performance and fault protection, significantly improving transformer operational reliability and grid adaptability while controlling cost and size, demonstrating significant engineering application value.
[0032] In one optional implementation, step S2 specifically includes the following steps: Step S211: Based on the AC and DC components of the output voltage of each bridge arm, calculate the maximum value of the output voltage of each bridge arm, and determine the total number of sub-modules of each bridge arm by rounding.
[0033] Step S212: Based on the minimum output voltage of each bridge arm, determine the negative voltage capability that each bridge arm needs to be provided by the full-bridge submodule, and determine the number of full-bridge submodules for each bridge arm by rounding.
[0034] Step S213: Subtract the total number of submodules in each bridge arm from the total number of full-bridge submodules in each bridge arm to obtain the number of half-bridge submodules in each bridge arm.
[0035] Specifically, based on the AC and DC components of the output voltage of each bridge arm, the maximum value of the output voltage of each bridge arm is calculated, and the total number of sub-modules required for the bridge arm is obtained by rounding. Then, based on the minimum value of the output voltage of the bridge arm, the negative voltage capability that the bridge arm needs to be provided by the full-bridge sub-modules is determined, and the initial number of full-bridge sub-modules is calculated. Finally, the initial number of half-bridge sub-modules is determined by the difference between the total number of sub-modules and the number of full-bridge sub-modules.
[0036] One feasible calculation method is as follows: First, the AC and DC components of the output voltage of each bridge arm are superimposed to calculate the maximum value of the bridge arm output voltage. The total number of submodules of bridge arm X (X=H, W, L) is obtained by rounding.
[0037]
[0038] In the formula, N smX This represents the total number of submodules.
[0039] Secondly, calculate the minimum output voltage of the bridge arm. This minimum value is obtained by subtracting the AC component from the DC component of the bridge arm output voltage, and can be expressed as:
[0040] in, This represents the minimum output voltage of the bridge arm.
[0041] Considering that the negative voltage output of the bridge arm is provided by the full-bridge submodule, the number of full-bridge submodules in bridge arm X can be expressed as:
[0042] In the formula, This represents the total number of sub-modules in the bridge.
[0043] Finally, subtract the number of full-bridge submodules from the total number of submodules to obtain the number of half-bridge submodules.
[0044]
[0045] In the formula, This represents the number of half-bridge sub-modules.
[0046] In an optional implementation, step S2 further includes the following steps: Step S221: When only the high-voltage port needs to have voltage regulation capability, correct the DC component of the output voltage of the high-voltage bridge arm and the common bridge arm according to the preset voltage regulation range, recalculate the maximum and minimum values of the bridge arm output voltage, increase the total number of sub-modules of the high-voltage bridge arm and the common bridge arm according to the updated voltage extreme values, and redetermine the number of full-bridge sub-modules and half-bridge sub-modules in the bridge arm.
[0047] Step S222: When only the low-voltage port needs to have voltage regulation capability, correct the DC component of the output voltage of the low-voltage bridge arm and the common bridge arm according to the preset voltage regulation range, recalculate the maximum and minimum values of the bridge arm output voltage, increase the total number of sub-modules of the low-voltage bridge arm and the common bridge arm according to the updated voltage extreme values, and redetermine the number of full-bridge sub-modules and half-bridge sub-modules in the bridge arm.
[0048] Step S223: When both the high-voltage port and the low-voltage port need to have voltage regulation capability, correct the DC component of the output voltage of all bridge arms according to the preset voltage regulation range, recalculate the maximum and minimum values of the output voltage of each bridge arm, increase the total number of sub-modules of all bridge arms according to the updated voltage extreme values, and redetermine the number of full-bridge sub-modules and half-bridge sub-modules in each bridge arm.
[0049] Specifically, in actual operation, the external system voltage of a DC transformer is prone to dynamic fluctuations, requiring control of the transmitted power through port voltage regulation. To ensure that each port has a preset voltage regulation capability, the number of bridge arm sub-modules needs to be specifically modified.
[0050] Depending on the range of voltage regulation requirements, this embodiment adopts the following correction method: when only the high-voltage port needs to have voltage regulation capability, increase the number of sub-modules of the high-voltage bridge arm and the common bridge arm; when only the low-voltage port needs to have voltage regulation capability, increase the number of sub-modules of the low-voltage bridge arm and the common bridge arm; when both the high-voltage port and the low-voltage port need to have voltage regulation capability, simultaneously increase the number of sub-modules of all bridge arms.
[0051] Assume the maximum voltage regulation range of the high-voltage port is ±ε H The maximum voltage regulation range of the low-voltage port is ±ε. L Then, one feasible calculation method is: The DC component of the output voltage of each bridge arm is corrected as follows:
[0052] In the formula, This is the corrected DC component of the high-voltage bridge arm. The DC component after correction for the common arm. This is the DC component corrected for the low-voltage bridge arm.
[0053] Based on this, the maximum and minimum values of the bridge arm output voltage are further corrected, and then the total number of sub-modules of each bridge arm and the total number of sub-modules of the whole bridge are re-determined according to the corrected voltage extreme values. The specific calculation method is consistent with steps S211-S213.
[0054] In an optional implementation, step S2 further includes the following steps: Step S231: Calculate the voltage between the reactance terminals of each bridge arm based on the AC current of the bridge arm and the reactance inductance of the bridge arm.
[0055] Step S232: The voltage between the reactor terminals is superimposed on the AC component of the output voltage of each bridge arm to correct the maximum and minimum values of the output voltage of each bridge arm.
[0056] Step S233: Based on the corrected output voltage extreme values, redetermine the number of submodules for each bridge arm.
[0057] Specifically, during the steady-state operation of a DC transformer, an AC component exists in the current of each bridge arm to maintain energy balance. To meet the energy balance requirements, the necessary AC voltage needs to be generated between the reactance terminals of each bridge arm; therefore, a certain number of sub-modules need to be added to each bridge arm.
[0058] The specific method is as follows: Based on the design results obtained in steps S221-S223, the voltage between the reactance terminals of each bridge arm is calculated according to the AC current and reactance inductance of the bridge arm. The AC component of the output voltage of the bridge arm is corrected accordingly. The maximum and minimum values of the output voltage are further corrected, and then the number of full-bridge submodules and half-bridge submodules in each bridge arm is re-determined.
[0059] In an optional implementation, step S2 further includes the following steps: Step S241: Increase the total number of sub-modules for each bridge arm and the total number of sub-modules for the entire bridge in proportion to the preset redundancy coefficient.
[0060] Step S242: Subtract the total number of submodules after correction from the total number of full-bridge submodules to obtain the corrected number of half-bridge submodules.
[0061] Specifically, during the operation of a DC transformer, submodules may fail, requiring the faulty submodules to be bypassed. To ensure the transformer can still operate normally even with a given number of submodule failures, each bridge arm needs to have a certain number of additional submodules, with the redundancy factor selected based on project requirements.
[0062] A feasible redundancy factor in engineering is 5%. In this case, the number of submodules can be calculated as follows:
[0063] In the formula, N smX0 The number of bridge arm X sub-modules determined according to steps S231-S233.
[0064] The method for calculating the number of full-bridge submodules is as follows:
[0065] In the formula, N smX0,FB The number of bridge arm X full bridge sub-modules determined according to steps S231-S233.
[0066] The number of half-bridge submodules for each bridge arm can be obtained by subtracting the number of submodules from the number of full-bridge submodules. The specific calculation method is consistent with steps S211-S213.
[0067] In one optional implementation, based on the design results of steps S241-S242, the number of full-bridge submodules in the high-voltage bridge arm is further modified. The modification principle is: without changing the total number of submodules, adjust the ratio of full-bridge submodules to half-bridge submodules in the high-voltage bridge arm to meet the fault protection requirements.
[0068] To address the three requirements for fault protection, this embodiment presents a feasible method for calculating the number of full-bridge submodules in a high-voltage bridge arm, as detailed below: 1) Source-side surplus power blocking requirement To reliably block surplus power on the source side under fault conditions, the corresponding constraint is that the sum of the rated voltages of the full-bridge submodules of the low-voltage and high-voltage bridge arms must be higher than the rated voltage of the low-voltage side. Based on this, a lower limit constraint of 1 is determined for the number of full-bridge submodules in the high-voltage bridge arm, specifically calculated as follows:
[0069] In the formula, The rated voltage of the full-bridge submodule for the low-voltage bridge arm. This is the rated voltage of the full-bridge submodule of the high-voltage bridge arm.
[0070] 2) Inductive component fault freewheeling absorption requirements To absorb the fault follow current energy stored in the inductive elements of the DC transformer, the corresponding constraint is that the energy absorbed by the full-bridge submodules of both the low-voltage and high-voltage arms must be higher than the fault follow current energy stored in the inductive elements of the DC transformer. Based on this, a lower limit constraint 2 is determined for the number of full-bridge submodules in the high-voltage arm, specifically calculated as follows:
[0071] In the formula, u maxThis is the maximum inter-terminal voltage that the submodule can withstand after being locked out. i faultLa For the peak value of the low-voltage bridge arm fault current, i faultHa For the peak value of the fault current of the high-voltage bridge arm, i faultWa This represents the peak value of the fault current in the common bridge arm.
[0072] 3) Port fault traversal requirements To achieve fault current clearance and low-voltage port voltage stabilization, the full-bridge submodules in the high-voltage arm must be able to generate a specific negative voltage. This voltage consists of two parts: first, a negative DC voltage component whose absolute value is not less than the positive DC voltage component retained in the common arm; and second, an AC voltage component that satisfies the energy balance between the arms during fault ride-through. Summing the DC and AC voltage components and taking the absolute value, then rounding it down to the submodule's rated voltage, yields the lower limit constraint 3 for the number of full-bridge submodules in the high-voltage arm. The corresponding constraint for port fault ride-through requirements is: the absolute value of the negative voltage generated by the full-bridge submodules in the high-voltage arm is not less than the sum of the positive DC voltage component of the common arm and the AC voltage component required for energy balance between the arms.
[0073] One feasible way to calculate this negative voltage is as follows:
[0074] In the formula, The negative voltage generated by the full-bridge submodule in the high-voltage bridge arm, the proportional coefficient k dc One feasible value for the project is 0.75.
[0075] In one alternative implementation, when there are multiple fault protection requirements, the number of full-bridge submodules of the high-voltage bridge arm is taken as the maximum value that satisfies all fault protection requirement constraints.
[0076] Specifically, to ensure reliable protection and stable operation of the DC transformer under various fault conditions and to avoid insufficient fault protection capabilities due to a single constraint value, in this embodiment, the number of high-voltage bridge arm full-bridge submodules must simultaneously meet the above-mentioned multiple lower limit constraints for fault protection, and the maximum value among all constraint conditions is ultimately selected. This configuration allows the high-voltage bridge arm full-bridge submodule configuration to fully cover the performance requirements of all fault conditions, effectively improving the fault tolerance and operational reliability of the DC transformer, and ensuring that the equipment stably completes functions such as fault blocking, freewheeling absorption, and fault ride-through under complex fault scenarios.
[0077] Furthermore, by combining the steady-state redundancy configuration results from steps S241 to S242 with various fault protection constraints, the final sub-module configuration scheme for each bridge arm that balances steady-state operation, voltage regulation adaptation, energy balance, fault redundancy, and fault protection performance can be determined. The complete design process for the number of sub-modules is as follows: Figure 4 As shown.
[0078] The specific configuration rules are as follows: The total number of submodules, full-bridge submodules, and half-bridge submodules of the low-voltage bridge arm and common bridge arm are all directly adopted from the optimization design results of step S241-S242; the total number of submodules of the high-voltage bridge arm also follows the design values of step S241-S242; the number of full-bridge submodules of the high-voltage bridge arm needs to be comprehensively verified by combining the aforementioned steady-state redundancy design results and multiple fault protection lower limit constraints, and the maximum value corresponding to all constraints is selected to meet the operating requirements of all fault conditions; the number of half-bridge submodules of the high-voltage bridge arm is finally calculated by subtracting the total number of high-voltage bridge arm submodules from the optimized number of full-bridge submodules.
[0079] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.
Claims
1. A method for designing the number and type of submodules in a bridge arm multiplexed DC transformer, characterized in that, The DC transformer includes a high-voltage bridge arm, a common bridge arm, and a low-voltage bridge arm. Each bridge arm is composed of cascaded full-bridge submodules and half-bridge submodules. The method includes: Obtain the design parameters, including port voltage parameters and the transformer steady-state operating point; Based on the steady-state operating point, port voltage regulation requirements, bridge arm energy balance requirements, and submodule redundancy requirements, determine the total number of submodules for each bridge arm, the number of full-bridge submodules, and the number of half-bridge submodules. Adjust the ratio of full-bridge submodules to half-bridge submodules in the high-voltage bridge arm according to fault protection requirements. The fault protection requirements include source-side surplus power blocking requirements, inductive component fault freewheeling absorption requirements, and port fault ride-through requirements.
2. The design method for the number and type of submodules of the bridge arm multiplexed DC transformer according to claim 1, characterized in that, Based on the steady-state operating point, port voltage regulation requirements, bridge arm energy balance requirements, and submodule redundancy requirements, the total number of submodules for each bridge arm, the number of full-bridge submodules, and the number of half-bridge submodules are determined, including: Based on the AC and DC components of the output voltage of each bridge arm, the maximum value of the output voltage of each bridge arm is calculated, and the total number of sub-modules of each bridge arm is determined by rounding. Based on the minimum output voltage of each bridge arm, the negative voltage capability that each bridge arm needs to be provided by the full-bridge submodule is determined, and the number of full-bridge submodules in each bridge arm is determined by rounding. The number of half-bridge submodules in each bridge arm is obtained by subtracting the total number of submodules in each bridge arm from the total number of full-bridge submodules in each bridge arm.
3. The design method for the number and type of submodules of the bridge arm multiplexed DC transformer according to claim 2, characterized in that, Based on the steady-state operating point, port voltage regulation requirements, bridge arm energy balance requirements, and submodule redundancy requirements, the total number of submodules for each bridge arm, the number of full-bridge submodules, and the number of half-bridge submodules are determined, including: When only the high-voltage port needs to have voltage regulation capability, the DC component of the output voltage of the high-voltage bridge arm and the common bridge arm is corrected according to the preset voltage regulation range, the maximum and minimum values of the bridge arm output voltage are recalculated, the total number of sub-modules of the high-voltage bridge arm and the common bridge arm is increased according to the updated voltage extreme values, and the number of full-bridge sub-modules and half-bridge sub-modules in the bridge arm is re-determined. When only the low-voltage port needs to have voltage regulation capability, the DC component of the output voltage of the low-voltage bridge arm and the common bridge arm is corrected according to the preset voltage regulation range, the maximum and minimum values of the bridge arm output voltage are recalculated, the total number of sub-modules of the low-voltage bridge arm and the common bridge arm is increased according to the updated voltage extreme values, and the number of full-bridge sub-modules and half-bridge sub-modules in the bridge arm is re-determined. When both the high-voltage and low-voltage ports need to have voltage regulation capabilities, the DC component of the output voltage of all bridge arms is corrected according to the preset voltage regulation range, the maximum and minimum values of the output voltage of each bridge arm are recalculated, the total number of sub-modules of all bridge arms is increased according to the updated voltage extreme values, and the number of full-bridge sub-modules and half-bridge sub-modules in each bridge arm is re-determined.
4. The design method for the number and type of submodules of the bridge arm multiplexed DC transformer according to claim 3, characterized in that, Based on the steady-state operating point, port voltage regulation requirements, bridge arm energy balance requirements, and submodule redundancy requirements, the total number of submodules for each bridge arm, the number of full-bridge submodules, and the number of half-bridge submodules are determined, including: Calculate the voltage between the reactance terminals of each bridge arm based on the AC current of the bridge arm and the reactance inductance of the bridge arm; The voltage between the reactant terminals is superimposed on the AC component of the output voltage of each bridge arm to correct the maximum and minimum values of the output voltage of each bridge arm. Based on the corrected output voltage extreme values, the number of submodules for each bridge arm is redetermined.
5. The design method for the number and type of submodules of the bridge arm multiplexed DC transformer according to claim 4, characterized in that, Based on the steady-state operating point, port voltage regulation requirements, bridge arm energy balance requirements, and submodule redundancy requirements, the total number of submodules for each bridge arm, the number of full-bridge submodules, and the number of half-bridge submodules are determined, including: The total number of sub-modules in each bridge arm and the total number of sub-modules in the entire bridge are increased proportionally according to the preset redundancy coefficient. The corrected number of half-bridge submodules is obtained by subtracting the corrected total number of submodules from the total number of full-bridge submodules.
6. The design method for the number and type of submodules of the bridge arm multiplexed DC transformer according to claim 1, characterized in that, The constraint condition for the source-side surplus power blocking requirement is: The sum of the rated voltages of the full-bridge submodules of the low-voltage bridge arm and the high-voltage bridge arm is higher than the rated voltage of the low-voltage side.
7. The design method for the number and type of submodules of the bridge arm multiplexed DC transformer according to claim 1, characterized in that, The constraint condition for the fault freewheeling absorption requirement of the inductive element is: The energy absorbed by the full-bridge submodules of the low-voltage and high-voltage bridge arms is higher than the fault follow current energy stored in the inductive elements of the DC transformer.
8. The design method for the number and type of submodules of the bridge arm multiplexed DC transformer according to claim 1, characterized in that, The constraints for the port fault traversal requirement are as follows: The absolute value of the negative voltage generated by the full-bridge submodule in the high-voltage bridge arm is not less than the sum of the positive DC voltage component of the common bridge arm and the AC voltage component required for energy balance between the bridge arms.
9. The design method for the number and type of submodules of the bridge arm multiplexed DC transformer according to claim 1, characterized in that, When there are multiple fault protection requirements, the number of full-bridge submodules of the high-voltage bridge arm is taken as the maximum value that satisfies the constraints of all fault protection requirements.
10. A bridge-arm multiplexed DC transformer, characterized in that, include: At least one phase unit, each phase unit including one or two sets of bridge arm units; the bridge arm units include: high-voltage bridge arm, common bridge arm and low-voltage bridge arm; In each phase unit, one end of the high-voltage bridge arm, the common bridge arm, and the low-voltage bridge arm are connected to each other to form a common connection point; the other end of the high-voltage bridge arm is used to connect to the high-voltage port, and the other end of the low-voltage bridge arm is used to connect to the low-voltage port. Each bridge arm is composed of a hybrid cascade of full-bridge submodules and half-bridge submodules, and the total number of submodules in each bridge arm and the number of full-bridge submodules are determined by the design method for the number and type of submodules of the bridge arm multiplexing DC transformer as described in any one of claims 1 to 9.