Design method, system and equipment of modular multilevel converter and medium
By optimizing the design method of modular multilevel converters and combining active overload current and capacitive reactive power constraints, the number of bridge arm sub-modules was increased, which solved the problem of insufficient overload operation of modular multilevel converters in high-proportion renewable energy transmission scenarios, improved their overload operation capability and reactive power support capability, and enhanced the system's operational stability and flexibility.
Patent Information
- Application Number
- CN202511522574.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-23
- Publication Date
- 2026-02-13
AI Technical Summary
Existing modular multilevel converters cannot provide emergency overload adjustment of redundant power in renewable energy power plants in scenarios with a high proportion of renewable energy transmission, and their overload operation capability is insufficient, affecting the system's operational stability and flexibility.
By obtaining the reference active overload current and combining it with the preset active overload-commutator ratio relationship algorithm, the target commutator ratio is determined. Based on the capacitive reactive power constraint, the number of new bridge arm sub-modules is calculated, and the modular multilevel converter design is updated to improve its overload operation capability and reactive power support capability.
It realizes the overload operation adaptability of modular multilevel converters in high-proportion new energy scenarios, ensures a balance between active power overload capacity and reactive power support capacity, and improves the system's operational flexibility and stability.
Smart Images
Figure CN121530188A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of converter design, and more particularly to a design method, system, device, and medium for a modular multilevel converter. Background Technology
[0002] With the advancement of new power system construction, the high proportion of new energy transmission scenarios places higher demands on the operational flexibility and regulation capabilities of flexible DC transmission systems. As the core equipment of flexible DC transmission systems, modular multilevel converters (MMCs) undertake the key functions of AC / DC voltage conversion and active and reactive power transmission. Their overload capacity and reactive power support capacity directly affect the system's regulation effect on the redundant power of new energy power plants and the level of grid stability.
[0003] Currently, flexible DC-DC converter units based on modular multilevel converters (MMCs) lack overload operation capabilities, primarily due to limitations in the current-carrying capacity of the IGBTs in the bridge arm submodules. When applied to scenarios with a high proportion of renewable energy transmission, they lack the ability to provide emergency overload regulation of redundant power in renewable energy power plants, thus limiting their application. Summary of the Invention
[0004] This invention provides a design method, system, device, and medium for a modular multilevel converter, which can improve the adaptability of the modular multilevel converter to overload operation.
[0005] This invention discloses a design method for a modular multilevel converter, comprising: Obtain the reference active overload current and the reference modular multilevel converter, and determine the reference lower arm modulation voltage, DC voltage and the rated voltage of the arm submodule of the reference modular multilevel converter; Based on the preset active overload-commutator ratio relationship algorithm and the reference active overload current, the target commutator ratio is obtained; Based on the preset capacitive reactive power constraint and the target converter ratio, the target converter modulation voltage is obtained; Based on the reference lower arm modulation voltage, the DC voltage, the target converter modulation voltage, and the rated voltage of the arm submodule, the number of new arm submodules is obtained. The reference modular multilevel converter is updated based on the number of newly added bridge arm sub-modules and the target converter ratio to obtain the target modular multilevel converter.
[0006] In the above scheme, the target converter ratio is obtained by acquiring the reference active overload current and combining it with the preset active overload-converter ratio relationship algorithm. This effectively solves the problem that the existing technology cannot output a converter ratio that is suitable for active overload scenarios. Furthermore, the target converter modulation voltage is determined based on the capacitive reactive power constraint condition. The number of new bridge arm sub-modules is calculated by combining the reference lower arm modulation voltage, DC voltage and rated voltage of the bridge arm sub-module. Finally, the target modular level converter is updated. This ensures that the converter has the preset active overload capacity to cope with the redundant power regulation needs of new energy power plants. At the same time, the capacitive reactive power output loss caused by the change of converter ratio is compensated by adjusting the number of sub-modules. This avoids the deviation between the design result and the actual situation and improves the adaptability of the modular multilevel converter's overload operation capability.
[0007] Further, the step of acquiring the reference active overload current and the reference modular multilevel converter, and determining the reference lower arm modulation voltage, DC voltage, and rated voltage of the arm submodule of the reference modular multilevel converter, includes: When all the lower bridge arm sub-modules of the reference modular multilevel converter are engaged, the reference lower bridge arm modulation voltage is obtained based on the DC voltage.
[0008] In the above scheme, the reference bridge arm modulation voltage is determined based on the DC voltage when all bridge arm sub-modules are in operation, providing a data basis for subsequent calculation of the number of new sub-modules.
[0009] Furthermore, the active power overload-converter transformer ratio relationship algorithm includes the safe value of the total current of the bridge arm, the transmission capacity of the three-phase converter transformer, and the effective value of the line voltage on the converter transformer network side. The step of obtaining the target converter transformer ratio based on the preset active power overload-converter transformer ratio relationship algorithm and the reference active power overload current includes: Based on the safety value of the total current of the bridge arm, the reference active overload current is subjected to a safety assessment to obtain the fundamental component of the AC current on the converter transformer valve side. Based on the transmission capacity of the three-phase converter transformer and the effective value of the line voltage on the converter transformer network side, the fundamental component of the AC current on the valve side of the converter transformer is processed to obtain the converter transformer ratio, thus obtaining the target converter transformer ratio.
[0010] In the above scheme, by combining parameters such as the safety value of the total current of the bridge arm and the transmission capacity of the converter transformer, the fundamental component of the AC current on the valve side of the converter transformer is first obtained through a safety assessment, and then the target converter transformer ratio is further calculated. This ensures that the reference active overload current is within the safe range and that the converter transformer ratio adapted to the overload operation requirements can be accurately obtained.
[0011] Further, the safety assessment of the reference active overload current based on the total current safety value of the bridge arm to obtain the fundamental component of the AC current on the converter transformer valve side includes: The safe value of the total current of the bridge arm is squared to obtain the squared safe value of the total current of the bridge arm. The reference active overload current and the preset first constant are squared to obtain the squared reference active overload current; Based on the total current safety value of the square bridge arm and the square reference active overload current, the fundamental component of the AC current on the converter transformer valve side is obtained.
[0012] In the above scheme, by squaring the safe value of the total current of the bridge arm and the reference active overload current respectively, and then deriving the fundamental component of the AC current on the valve side of the converter transformer, the fundamental component of the AC current on the valve side of the converter transformer is obtained, which provides a data basis for the subsequent calculation of a more accurate target converter transformer ratio.
[0013] Further, the process of calculating the converter transformer ratio based on the fundamental component of the AC current on the valve side of the converter transformer according to the transmission capacity of the three-phase converter transformer and the effective value of the line voltage on the converter transformer network side, to obtain the target converter transformer ratio, includes: The fundamental component of the AC current on the converter transformer valve side, the effective value of the line voltage on the converter transformer grid side, and a preset second constant are multiplied to obtain the target product value. The target converter transformer ratio is obtained by dividing the transmission capacity of the three-phase converter transformer by the target product value.
[0014] In the above scheme, the target transformer ratio is obtained by dividing the product of parameters such as the fundamental component of the AC current on the valve side of the converter transformer and the line voltage on the grid side by the transmission capacity of the converter transformer, thus obtaining the target converter transformer ratio that is suitable for overload operation.
[0015] Further, the step of determining the number of new bridge arm submodules based on the reference lower bridge arm modulation voltage, the DC voltage, the target converter modulation voltage, and the rated voltage of the bridge arm submodule includes: Based on the DC voltage and the target converter modulation voltage, the target lower arm modulation voltage is obtained; The number of new bridge arm submodules is obtained based on the reference lower bridge arm modulation voltage, the target lower bridge arm modulation voltage, and the rated voltage of the bridge arm submodule.
[0016] In the above scheme, the target lower arm modulation voltage is first determined by combining the DC voltage and the target modulation voltage. Then, the number of new bridge arm sub-modules is calculated, and the modulation voltage requirement, i.e. the target lower arm modulation voltage, is converted into a specific bridge arm sub-module number adjustment scheme, thereby making up for the reactive power loss caused by the adjustment of the converter transformer ratio.
[0017] Further, the step of obtaining the number of newly added bridge arm submodules based on the reference lower bridge arm modulation voltage, the target lower bridge arm modulation voltage, and the rated voltage of the bridge arm submodule includes: The difference between the reference lower bridge arm modulation voltage and the target lower bridge arm modulation voltage is obtained as the target difference. The ratio of the target difference to the rated voltage of the bridge arm submodule is obtained to determine the number of newly added bridge arm submodules.
[0018] In the above scheme, the difference between the reference lower arm modulation voltage and the target lower arm modulation voltage is calculated, and then compared with the rated voltage of the arm submodule to obtain the number of new submodules. This quantifies the adjustment requirements of the arm submodules, ensuring that the new submodules can accurately and effectively compensate for reactive power loss and guarantee the reactive power support capability of the converter.
[0019] Another embodiment of the present invention also provides a design system for a modular multilevel converter, comprising: The acquisition module is used to acquire the reference active overload current and the reference modular multilevel converter, and to determine the reference lower arm modulation voltage, DC voltage and the rated voltage of the arm submodule of the reference modular multilevel converter. The target commutator ratio module is used to obtain the target commutator ratio based on a preset active overload-commutator ratio relationship algorithm and the reference active overload current; The target converter modulation voltage module is used to obtain the target converter modulation voltage based on the preset capacitive reactive power constraint and the target converter ratio. The module for increasing the number of new bridge arm sub-modules is used to determine the number of new bridge arm sub-modules based on the reference bridge arm modulation voltage, the DC voltage, the target converter modulation voltage, and the rated voltage of the bridge arm sub-module. The target modular multilevel converter module is used to update the reference modular multilevel converter based on the number of newly added bridge arm sub-modules and the target converter ratio, so as to obtain the target modular multilevel converter.
[0020] Another embodiment of the present invention provides a terminal device, including: a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, it implements the steps of the design method of a modular multilevel converter as described in the present invention.
[0021] Another embodiment of the present invention also provides a computer-readable storage medium item, including: a stored computer program, which, when the computer program is running, controls the device where the computer-readable storage medium is located to perform the steps of the design method of a modular multilevel converter of the present invention. Attached Figure Description
[0022] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0023] Figure 1 This is a flowchart illustrating a design method for a modular multilevel converter provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the design system for a modular multilevel converter provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of a modular multilevel converter provided in an embodiment of the present invention; Figure 4 This is an analysis diagram of the impact of adjusting the converter transformer ratio on the reactive power of a modular multilevel converter, provided in an embodiment of the present invention. Figure 5 This is an analysis diagram of the impact of increasing the number of bridge arm sub-modules on the reactive power of a modular multilevel converter, provided by an embodiment of the present invention. Figure label: 1. AC power supply; 2. Converter transformer; 3. Bridge arm submodule. Detailed Implementation
[0024] To make the objectives, technical solutions, and advantages of this application clearer, 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 embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.
[0026] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.
[0027] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.
[0028] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.
[0029] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).
[0030] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.
[0031] See Figure 1 To improve the overload adaptability of modular multilevel converters, an embodiment of the present invention provides a design method for a modular multilevel converter, comprising: Step S1: Obtain the reference active overload current and the reference modular multilevel converter, and determine the reference lower arm modulation voltage, DC voltage and rated voltage of the arm submodule of the reference modular multilevel converter; Step S2: Based on the preset active overload-commutator ratio relationship algorithm and the reference active overload current, obtain the target commutator ratio; Step S3: Based on the preset capacitive reactive power constraint and the target converter ratio, obtain the target converter modulation voltage; Step S4: Based on the reference lower arm modulation voltage, DC voltage, target converter modulation voltage, and rated voltage of the arm submodule, obtain the number of new arm submodules; Step S5: Update the reference modular multilevel converter based on the number of newly added bridge arm sub-modules and the target converter ratio to obtain the target modular multilevel converter.
[0032] In the above scheme, the target converter ratio is obtained by acquiring the reference active overload current and combining it with the preset active overload-converter ratio relationship algorithm. This effectively solves the problem that the existing technology cannot output a converter ratio that is suitable for active overload scenarios. Furthermore, the target converter modulation voltage is determined based on the capacitive reactive power constraint condition. The number of new bridge arm sub-modules is calculated by combining the reference lower arm modulation voltage, DC voltage and rated voltage of the bridge arm sub-module. Finally, the target modular level converter is updated. This ensures that the converter has the preset active overload capacity to cope with the redundant power regulation needs of new energy power plants. At the same time, the capacitive reactive power output loss caused by the change of converter ratio is compensated by adjusting the number of sub-modules. This avoids the deviation between the design result and the actual situation and improves the adaptability of the modular multilevel converter's overload operation capability.
[0033] It is understandable that the reference modular multilevel converter is the existing standard modular multilevel converter.
[0034] To improve the overload adaptability of modular multilevel converters (MMCs), the converter transformer valve-side voltage can be increased by reducing the converter transformer ratio, thereby reducing the converter transformer valve-side current and thus lowering the proportion of AC component in the converter valve arm current. This further provides an overload margin for DC current, enabling the converter valve to operate under overload conditions. While reducing the converter transformer ratio improves the converter's overload capacity, it also reduces its reactive power support capability. Therefore, this invention proposes increasing the number of arm submodules to increase the modulation voltage and compensate for the reduced reactive power support capability of the converter, enabling the MMC to possess both higher active power overload capacity and reactive power support capability. The determination of the target converter transformer ratio and the number of additional arm submodules is described in detail through the following embodiments: In another embodiment, the step of acquiring the reference active overload current and the reference modular multilevel converter, and determining the reference lower arm modulation voltage, DC voltage, and rated voltage of the arm submodule of the reference modular multilevel converter, includes: When all the lower bridge arm sub-modules of the reference modular multilevel converter are engaged, the reference lower bridge arm modulation voltage is obtained based on the DC voltage.
[0035] It should be noted that a modular multilevel converter (MMC), or simply an MMC converter, refers to a converter where, when all the lower bridge arm submodules are engaged, U... n =U dc =NU CN Among them, Un To reference the lower bridge arm modulation voltage, U dc U is a DC voltage. CN The reference lower bridge arm modulation voltage is obtained based on the DC voltage, given the rated voltage of the bridge arm submodule. Simultaneously, the number of reference lower bridge arm submodules, N=U, can also be obtained. dc / U CN .
[0036] In another embodiment, the active power overload-converter transformer ratio relationship algorithm includes the safe value of the total current of the bridge arm, the transmission capacity of the three-phase converter transformer, and the effective value of the line voltage on the converter transformer network side. The step of obtaining the target converter transformer ratio based on the preset active power overload-converter transformer ratio relationship algorithm and the reference active power overload current includes: Based on the safety value of the total current of the bridge arm, the reference active overload current is subjected to a safety assessment to obtain the fundamental component of the AC current on the converter transformer valve side. Based on the transmission capacity of the three-phase converter transformer and the effective value of the line voltage on the converter transformer network side, the fundamental component of the AC current on the valve side of the converter transformer is processed to obtain the converter transformer ratio, thus obtaining the target converter transformer ratio.
[0037] It should be noted that this is based on the total current safety value of the bridge arm. For the reference active overload current A safety assessment was performed to obtain the fundamental component of the AC current on the converter transformer valve side. Based on the transmission capacity S of the three-phase converter transformer N and the effective value of the converter transformer side line voltage U s The fundamental component of the AC current on the converter valve side The target converter transformer ratio is obtained by performing converter transformer ratio calculation. .
[0038] In another embodiment, the step of performing a safety assessment on the reference active overload current based on the total current safety value of the bridge arm to obtain the fundamental component of the AC current on the converter transformer valve side includes: The safe value of the total current of the bridge arm is squared to obtain the squared safe value of the total current of the bridge arm. The reference active overload current and the preset first constant are squared to obtain the squared reference active overload current; Based on the total current safety value of the square bridge arm and the square reference active overload current, the fundamental component of the AC current on the converter transformer valve side is obtained.
[0039] It should be noted that the total current of the MMC bridge arms satisfies: ; Among them, I IGBT The total current of the bridge arm, Reference current; I ac_50Hz The fundamental component of the AC current on the converter transformer valve side is used as a reference. During overload operation (taking a 1.1 pu overload as an example, i.e., assuming the reference current of the modular multilevel converter is...),... Currently, the desired overload capacity is 1.1 pu, meaning the DC current should be able to decrease from I... dc Increased to 1.1I dc Thus, the reference active overload current is obtained. At this point, it is necessary to reduce the fundamental component (i.e., the fundamental component of the AC current on the converter transformer valve side) in the bridge arm component. ac_50Hz To ensure that the total arm current does not exceed the limit (typically ≤3.65kA; the overload operating capacity of the MMC converter is mainly limited by the current-carrying capacity of the IGBTs in the arm submodules; taking the commonly used 4.5kV / 5kA IGBT devices in UHV flexible DC transmission as an example, due to the limitation of the operating junction temperature, the arm current should not exceed the operating limit of 3.65kA when the converter valve is overloaded), the maximum value of the total arm current is taken as the safe value of the total arm current. Based on the total current safety value of the bridge arm For the reference active overload current A safety assessment was performed to obtain the fundamental component of the AC current on the converter transformer valve side. : Safety value of total current of the bridge arm By squaring, we obtain the safe total current value for the squared bridge arm: 2 ; for the reference active overload current Squaring the result with the preset first constant, we get the squared reference active overload current = Based on the total current safety value of the square bridge arm 2 and the squared reference active overload current The fundamental component of the AC current on the converter transformer valve side is obtained. .
[0040] In another embodiment, the process of calculating the converter transformer ratio based on the fundamental component of the AC current on the valve side of the converter transformer according to the transmission capacity of the three-phase converter transformer and the effective value of the line voltage on the converter transformer network side, to obtain the target converter transformer ratio, includes: The fundamental component of the AC current on the converter transformer valve side, the effective value of the line voltage on the converter transformer grid side, and a preset second constant are multiplied to obtain the target product value. The target converter transformer ratio is obtained by dividing the transmission capacity of the three-phase converter transformer by the target product value.
[0041] It should be noted that the fundamental component of the MMC arm current is equal to the fundamental component I of the AC current on the valve side of the reference converter transformer. ac_50Hz Half of, I ac_50Hz satisfy: ; Among them, I ac_50Hz For reference, the fundamental component of the AC current on the valve side of the converter transformer, S N For the transmission capacity of the three-phase converter transformer, U s Here, I represents the effective value of the line voltage on the converter substation side, and K represents the reference converter transformer ratio of the reference modular multilevel converter. Therefore, during overload operation, the above I can be relied upon. ac_50Hz The required equations must be satisfied to determine the target converter transformer ratio: based on the transmission capacity S of the three-phase converter transformer. N and the effective value of the converter transformer side line voltage U s The fundamental component of the AC current on the converter valve side The target converter transformer ratio is obtained by performing converter transformer ratio calculation. Specifically: for the fundamental component I of the AC current on the converter transformer valve side ac_50Hz The effective value of the line voltage U on the converter transformer side s Multiply by the preset second constant to obtain the target product value. U s Based on the target product value, the transmission capacity S of the three-phase converter transformer N The target converter transformer ratio is obtained by performing a phase division process. = .
[0042] Combining the above formulas, we can obtain: ; in, In practical operation, it is also necessary to comply with the safety value of the total current of the bridge arm. The value is ≤3.65kA. Therefore, the reference active overload current is... Target commutator ratio Inversely proportional, by reducing the converter transformer ratio It can increase This improves the overload capacity of the flexible DC converter valve.
[0043] Furthermore, regarding step S3: based on the preset capacitive reactive power constraint and the target converter transformer ratio, the target converter modulation voltage is obtained, specifically: The capacitive reactive power constraint condition, namely the capacitive reactive power Q injected into the AC grid through the converter transformer from the flexible DC converter valve. s Satisfying the capacitive reactive power constraint conditions: ; Among them, Q s To reference the reference capacitive reactive power of the modular multilevel converter, U s X is the effective value of the line voltage on the converter transformer side; K is the reference converter transformer ratio; X T The sum of the converter transformer and the bridge arm reactor is a fixed constant; U v P is the reference converter modulation voltage; s This refers to the active power injected into the AC grid via the converter transformer. As can be seen above, increasing the converter transformer's turns ratio K will reduce the capacitive reactive power Q. s Increase the modulation voltage U of the converter v It can improve capacitive reactive power Q s .
[0044] Therefore, the target modular multilevel converter also needs to comply with the above-mentioned capacitive reactive power constraints, that is, to ensure sufficient reactive power support capacity, a preset minimum capacitive reactive power value (i.e., That is, under the preset minimum capacitive reactive power limit, based on the above capacitive reactive power constraint, substituting the target converter transformer ratio, the target converter modulation voltage is obtained. ,Right now ; In another embodiment, determining the number of new bridge arm submodules based on the reference lower bridge arm modulation voltage, the DC voltage, the target converter modulation voltage, and the rated voltage of the bridge arm submodule includes: Based on the DC voltage and the target converter modulation voltage, the target lower arm modulation voltage is obtained; The number of new bridge arm submodules is obtained based on the reference lower bridge arm modulation voltage, the target lower bridge arm modulation voltage, and the rated voltage of the bridge arm submodule.
[0045] It should be noted that the reference converter modulation voltage of the standard, existing reference modular multilevel converter , among which, U n = , To reference the lower bridge arm modulation voltage, U p = , For reference upper bridge arm modulation voltage; U dc It is a DC voltage. Therefore, based on the DC voltage U... dc and the target converter modulation voltage The target lower bridge arm modulation voltage is obtained. Based on the reference lower bridge arm modulation voltage U n The target lower bridge arm modulation voltage and the rated voltage U of the bridge arm submodule CNThe number of newly added bridge arm sub-modules, ΔN, is obtained.
[0046] In another embodiment, determining the number of new bridge arm submodules based on the reference lower bridge arm modulation voltage, the target lower bridge arm modulation voltage, and the rated voltage of the bridge arm submodule includes: The difference between the reference lower bridge arm modulation voltage and the target lower bridge arm modulation voltage is obtained as the target difference. The ratio of the target difference to the rated voltage of the bridge arm submodule is obtained to determine the number of newly added bridge arm submodules.
[0047] It should be noted that the difference between the reference lower arm modulation voltage and the target lower arm modulation voltage is obtained as the target difference = U. n - ; Obtain the ratio of the target difference to the rated voltage of the bridge arm submodule, and obtain the number of newly added bridge arm submodules ΔN = (U n - ) / U CN .
[0048] Based on the number of newly added bridge arm sub-modules and the target converter ratio, the number of bridge arm sub-modules and the reference converter ratio in the reference modular multilevel converter are updated to obtain the target modular multilevel converter. Specifically, by adjusting the converter ratio and appropriately increasing the number of bridge arm sub-modules to improve overload capacity, once the desired overload capacity (i.e., reference active overload current) in practical applications is determined, the specific design of the target modular multilevel converter can be immediately determined. This improves the adaptability of overload capacity during the design of the modular multilevel converter, endowing the flexible DC converter valve with overload operating capability while simultaneously meeting the reactive power support requirements of the system, thus improving the operational flexibility of the flexible DC converter.
[0049] The following are specific examples: Taking the UHV flexible DC converter as a reference and the modular multilevel converter as an example, the overload capacity improvement calculation is carried out. Figure 3 This is a structural diagram of a standard modular level converter, which includes an AC power supply 1, a converter transformer 2, and a bridge arm submodule 3. The AC power supply 1 provides AC power input to the entire converter system, and its output three-phase voltage U a U b and U c It serves as the energy source for the subsequent converter process. The converter transformer 2 has a turns ratio of K:1 and is used to convert the AC power supply voltage to a voltage U suitable for the converter's operation. ta U tb and U tcBridge arm submodule 3 is the basic building block of the converter. Through the switching and other control of bridge arm submodule 3, AC / DC power conversion can be achieved. Each bridge arm submodule 3 consists of an IGBT (Insulated Gate Bipolar Transistor) and a capacitor, and is the basic unit of the MMC (Modular Multilevel Converter). Among them, U... pa It is the modulation voltage of the upper bridge arm of phase A of the converter, U na It is the modulation voltage of the lower arm of phase A of the converter. Together, these two voltages determine the output voltage of the phase A arm, achieving precise control of the converter output. va U vb and U vc These are the three-phase voltages output from the AC side of the converter, which are the voltages interacting with the load after AC-DC conversion by the converter. dc It is the DC voltage of the converter, the voltage formed on the DC side after the AC-DC conversion of the converter, and the positive voltage is +U. dc / 2, negative terminal voltage is -U dc / 2. The upgraded target modular multilevel converter is required to have an overload capacity of 1.1 pu (pu is a per-unit value, using a relative unit system based on the baseline), and a reactive power support capacity of 30% under 1.0 pu conditions (i.e., the preset minimum capacitive reactive power limit). In other words, under 1.0 pu conditions, U... dc I dc =2000MVA, of which reactive power support capacity is required, i.e., minimum capacitive reactive power value. (30%, or 600 Mvar).
[0050] Converter technical parameters: Three-phase converter transmission capacity S N =2250MVA; DC voltage U dc =400kV; Reference DC current I dc =5kA; the voltage operating range of the converter transformer side is 750kV-800kV. It is assumed that the flexible DC converter needs to have an overload capacity of 1.1 times, i.e., the maximum DC current (reference active overload current). =I dcmax =5 x 1.1 = 5.5 kA. When the AC power grid operates at its minimum voltage (effective value of the converter transformer side line voltage) U s When the voltage is 750kV, the maximum arm current of the IGBT (i.e., the safe value of the total arm current) is taken as 3.65kA.
[0051] The target commutator ratio K = 3.65 can be obtained based on the following formula.
[0052] ; refer to Figure 4 , Figure 4The power operating range of the converter is given under the condition of target converter ratio K=3.65. The positive direction is defined as the flow of power into the converter from the AC bus. The horizontal axis represents active power, and the vertical axis represents reactive power. Where: In the first quadrant, both active and reactive power are positive, indicating that the converter is operating in rectification mode and injecting inductive reactive power into the AC grid.
[0053] In the second quadrant, active power is negative and reactive power is positive, indicating that the converter is operating in inverter mode and injecting inductive reactive power into the AC grid.
[0054] In the third quadrant, both active and reactive power are negative, indicating that the converter is operating in inverter mode and injecting capacitive reactive power into the AC grid.
[0055] The fourth quadrant has positive active power and negative reactive power, indicating that the converter is operating in rectification mode and injecting capacitive reactive power into the AC grid.
[0056] Under normal circumstances, converters should not inject inductive reactive power into the AC grid, therefore they need to operate in the third or fourth quadrant. However, due to... Figure 4 It can be seen that when the converter operates under a 1.1 pu overload condition, it will absorb 38 Mvar of capacitive reactive power from the AC grid. Figure 4 The vertical axis value corresponding to the maximum value of the horizontal axis); when the converter operates at full active power (2000MW), it can only generate 500Mvar of capacitive reactive power, which does not meet the requirement of 30% reactive power support capacity.
[0057] Therefore, to improve the reactive power support capability of the converter, the number of bridge arm sub-modules needs to be further increased. At this point, the active power output P of the converter... s =2000MW; =600Mvar; U s Take the maximum value of 800kV; X T The series value of the converter transformer leakage reactance and bridge reactance is taken as 8.36Ω; based on the following formula: ; The target converter modulation voltage can be obtained. Compared to the reference converter modulation voltage U V An additional 20kV is needed. In ultra-high voltage flexible DC transmission projects, the rated voltage U of a single bridge arm submodule... CN =2.105kV, and thus the number of new bridge arm sub-modules needed is approximately ΔN=10.
[0058] refer to Figure 5 , Figure 5This describes the power operating range of the converter under conditions of increasing the number of added bridge arm submodules. Again, assuming the positive direction of flow from the AC bus to the converter, the horizontal axis represents active power and the vertical axis represents reactive power. It can be seen that when the converter operates at full active power (2000MW), the corresponding reactive power reaches 600Mvar. In other words, with an increase in the number of bridge arm submodules: [The text abruptly ends here, likely due to an incomplete sentence or missing information.] Figure 4 Compared to adjusting only the converter transformer ratio, after adding the bridge arm submodule, the capacitive reactive power output of the converter during full active power operation increased from 500Mvar to 600Mvar, meeting the requirement of 30% reactive power support capability. This shows that increasing the number of bridge arm submodules effectively improved the reactive power support capability of the converter.
[0059] like Figure 2 As shown, based on the above method embodiments, corresponding system embodiments are provided; One embodiment of the present invention provides a design system for a modular multilevel converter, comprising: The acquisition module is used to acquire the reference active overload current and the reference modular multilevel converter, and to determine the reference lower arm modulation voltage, DC voltage and the rated voltage of the arm submodule of the reference modular multilevel converter. The target commutator ratio module is used to obtain the target commutator ratio based on a preset active overload-commutator ratio relationship algorithm and the reference active overload current; The target converter modulation voltage module is used to obtain the target converter modulation voltage based on the preset capacitive reactive power constraint and the target converter ratio. The module for increasing the number of new bridge arm sub-modules is used to determine the number of new bridge arm sub-modules based on the reference bridge arm modulation voltage, the DC voltage, the target converter modulation voltage, and the rated voltage of the bridge arm sub-module. The target modular multilevel converter module is used to update the reference modular multilevel converter based on the number of newly added bridge arm sub-modules and the target converter ratio, so as to obtain the target modular multilevel converter.
[0060] It is understood that the above system embodiments correspond to the method embodiments of the present invention, and can implement the design method of a modular multilevel converter provided by any of the above method embodiments of the present invention.
[0061] It should be noted that the system embodiments described above are merely illustrative, and some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Furthermore, in the accompanying drawings of the system embodiments provided by this invention, the connection relationships between modules indicate that they have communication connections, which can be specifically implemented as one or more communication buses or signal lines. Those skilled in the art can understand and implement this without any creative effort.
[0062] Based on the above-described embodiment of a modular multilevel converter design method, another embodiment of the present invention provides a terminal device, which includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements a modular multilevel converter design method according to any embodiment of the present invention.
[0063] For example, in this embodiment, the computer program can be divided into one or more modules, which are stored in the memory and executed by the processor to complete the present invention. The one or more modules may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program in the terminal device.
[0064] The terminal device may be a desktop computer, laptop, handheld computer, or cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.
[0065] The processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor. The processor is the control center of the terminal device, connecting all parts of the terminal device via various interfaces and lines.
[0066] Based on the above-described method embodiments, another embodiment of the present invention provides a computer-readable storage medium including a stored computer program, wherein, when the computer program is executed, it controls the device where the computer-readable storage medium is located to execute the design method of a modular multilevel converter described in any of the above-described method embodiments of the present invention.
[0067] The modules / units integrated in the device / terminal equipment, if implemented as software functional units and sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.
[0068] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.
Claims
1. A design method for a modular multilevel converter, characterized in that, include: Obtain the reference active overload current and the reference modular multilevel converter, and determine the reference lower arm modulation voltage, DC voltage and the rated voltage of the arm submodule of the reference modular multilevel converter; Based on the preset active overload-commutator ratio relationship algorithm and the reference active overload current, the target commutator ratio is obtained; Based on the preset capacitive reactive power constraint and the target converter ratio, the target converter modulation voltage is obtained; Based on the reference lower arm modulation voltage, the DC voltage, the target converter modulation voltage, and the rated voltage of the arm submodule, the number of new arm submodules is obtained. The reference modular multilevel converter is updated based on the number of newly added bridge arm sub-modules and the target converter ratio to obtain the target modular multilevel converter.
2. The design method of a modular multilevel converter according to claim 1, characterized in that, The process of acquiring the reference active overload current and the reference modular multilevel converter, and determining the reference lower arm modulation voltage, DC voltage, and rated voltage of the arm submodule of the reference modular multilevel converter, includes: When all the lower bridge arm sub-modules of the reference modular multilevel converter are engaged, the reference lower bridge arm modulation voltage is obtained based on the DC voltage.
3. The design method of a modular multilevel converter according to claim 1, characterized in that, The active power overload-commutator transformer ratio relationship algorithm includes the safe value of the total current of the bridge arm, the transmission capacity of the three-phase converter transformer, and the effective value of the line voltage on the converter transformer network side. The target converter transformer ratio is obtained based on the preset active power overload-commutator transformer ratio relationship algorithm and the reference active power overload current, including: Based on the safety value of the total current of the bridge arm, the reference active overload current is subjected to a safety assessment to obtain the fundamental component of the AC current on the converter transformer valve side. Based on the transmission capacity of the three-phase converter transformer and the effective value of the line voltage on the converter transformer network side, the fundamental component of the AC current on the valve side of the converter transformer is processed to obtain the converter transformer ratio, thus obtaining the target converter transformer ratio.
4. The design method of a modular multilevel converter according to claim 3, characterized in that, The safety assessment of the reference active overload current based on the total current safety value of the bridge arm, to obtain the fundamental component of the AC current on the converter transformer valve side, includes: The safe value of the total current of the bridge arm is squared to obtain the squared safe value of the total current of the bridge arm. The reference active overload current and the preset first constant are squared to obtain the squared reference active overload current; Based on the safe value of the total current of the square bridge arm and the square reference active overload current, the fundamental component of the AC current on the converter transformer valve side is obtained.
5. The design method of a modular multilevel converter according to claim 3, characterized in that, The process of calculating the converter transformer ratio based on the fundamental component of the AC current on the valve side of the converter transformer according to the transmission capacity of the three-phase converter transformer and the effective value of the line voltage on the converter transformer network side, to obtain the target converter transformer ratio, includes: The fundamental component of the AC current on the converter transformer valve side, the effective value of the line voltage on the converter transformer grid side, and a preset second constant are multiplied to obtain the target product value. The target converter transformer ratio is obtained by dividing the transmission capacity of the three-phase converter transformer by the target product value.
6. The design method of a modular multilevel converter according to claim 1, characterized in that, The method of determining the number of new bridge arm submodules based on the reference lower bridge arm modulation voltage, the DC voltage, the target converter modulation voltage, and the rated voltage of the bridge arm submodule includes: Based on the DC voltage and the target converter modulation voltage, the target lower arm modulation voltage is obtained; The number of new bridge arm submodules is obtained based on the reference lower bridge arm modulation voltage, the target lower bridge arm modulation voltage, and the rated voltage of the bridge arm submodule.
7. The design method of a modular multilevel converter according to claim 6, characterized in that, The method of determining the number of new bridge arm submodules based on the reference lower bridge arm modulation voltage, the target lower bridge arm modulation voltage, and the rated voltage of the bridge arm submodule includes: The difference between the reference lower bridge arm modulation voltage and the target lower bridge arm modulation voltage is obtained as the target difference. The ratio of the target difference to the rated voltage of the bridge arm submodule is obtained to determine the number of newly added bridge arm submodules.
8. A design system for a modular multilevel converter, characterized in that, include: The acquisition module is used to acquire the reference active overload current and the reference modular multilevel converter, and to determine the reference lower arm modulation voltage, DC voltage and the rated voltage of the arm submodule of the reference modular multilevel converter. The target commutator ratio module is used to obtain the target commutator ratio based on a preset active overload-commutator ratio relationship algorithm and the reference active overload current; The target converter modulation voltage module is used to obtain the target converter modulation voltage based on the preset capacitive reactive power constraint and the target converter ratio. The module for increasing the number of new bridge arm sub-modules is used to determine the number of new bridge arm sub-modules based on the reference bridge arm modulation voltage, the DC voltage, the target converter modulation voltage, and the rated voltage of the bridge arm sub-module. The target modular multilevel converter module is used to update the reference modular multilevel converter based on the number of newly added bridge arm sub-modules and the target converter ratio, so as to obtain the target modular multilevel converter.
9. A terminal device, characterized in that, The device includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, it implements a design method for a modular multilevel converter as described in any one of claims 1-7.
10. A computer-readable storage medium, characterized in that, include: A stored computer program, wherein, when the computer program is executed, it controls the device containing the computer-readable storage medium to perform a design method for a modular multilevel converter as described in any one of claims 1-7.