Voltage equalization modulation method and device, voltage equalization modulation method and system for MMC bridge arm

Abstract

The application discloses a voltage equalization modulation method and device of mixed connection of different voltage level submodules in a bridge arm, a voltage equalization modulation method and system of an MMC bridge arm. The method comprises the following steps: firstly, obtaining voltage information of the mixed connection of different voltage level submodules in the bridge arm; then, according to the voltage information, converting all running submodules into equivalent total submodules under the same reference voltage, converting all submodules into equivalent input / output submodules under the same reference voltage, and ensuring that all submodules are sorted in the same reference system for voltage equalization control; then, according to the difference between the equivalent total submodule quantity under the reference voltage in the current period and the last period, and in combination with a compensation coefficient, adjusting the input / output of the submodules to realize voltage equalization modulation. Through the steps, voltage equalization modulation under the mixed condition of different voltage level submodules can be effectively realized, so that all submodules in the bridge arm have the characteristic that the voltage fluctuation proportion is consistent.

Description

Technical Field

[0001] This invention belongs to the field of power transmission and transformation technology, and particularly relates to a voltage equalization modulation method, device, and MMC bridge arm voltage equalization modulation method and system for mixed connection of sub-modules of different voltage levels in a bridge arm. Background Technology

[0002] In the current field of flexible DC transmission engineering, full-bridge and half-bridge sub-modules in modular multilevel converters (MMCs) are widely used due to their significant advantages. These advantages include simple structure, fewer components, easy implementation of control algorithms, low energy consumption, and high system operating efficiency.

[0003] However, most mainstream modular multilevel converter projects on the market currently use power devices at the 4.5kV voltage level. This means that the number of flexible DC transmission (Flexible DC) submodules in the converter valve cannot be reduced, and their size and weight remain large, thus posing a significant challenge to the economic development of Flexible DC projects.

[0004] It is worth noting that some device manufacturers have successfully developed power devices with voltage levels of 6.5kV and higher. The introduction of these high-voltage power devices has quickly attracted widespread attention in the industry due to their significant advantages in reducing the number of submodules and shrinking the size of converter valves.

[0005] However, the idea of ​​mixing submodules of different voltage levels has not yet been realized in the existing technology because 6.5kV power modules and 4.5kV power modules cannot be mixed and used within the same flexible DC converter valve. The main reason for this limitation is that existing control methods, including the Nearest Level Approximation (NLM) sequencing method, cannot effectively achieve voltage equalization modulation when submodules of different voltage levels are mixed within the bridge arm, thus failing to ensure that all submodules within the bridge arm have a consistent voltage fluctuation ratio. This technical obstacle severely affects the collaborative operation of submodules of different voltage levels, and a solution to overcome this limitation is urgently needed. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the above-mentioned shortcomings of the prior art by proposing a voltage equalization modulation method, device, MMC bridge arm voltage equalization modulation method and system for mixed connection of submodules of different voltage levels in a bridge arm. This method can effectively realize voltage equalization modulation under mixed conditions of submodules of different voltage levels, thereby ensuring that all submodules in the bridge arm have the characteristic of consistent voltage fluctuation ratio.

[0007] In a first aspect, the present invention provides a voltage equalization modulation method for mixing submodules of different voltage levels within a bridge arm, the method comprising the following steps:

[0008] Obtain the voltage of sub-modules of different voltage levels that are connected in parallel within the bridge arm;

[0009] Based on the voltage of the sub-modules at different voltage levels, all sub-modules are converted to the equivalent total sub-modules under the same reference voltage;

[0010] Based on the difference between the equivalent total number of submodules engaged in the current cycle and the previous cycle at the reference voltage, the switching of submodules is controlled to achieve voltage equalization modulation of submodules of different voltage levels in the bridge arm.

[0011] Furthermore, the step of converting all submodules to the equivalent total submodule under the same reference voltage specifically includes the following steps:

[0012] Step A1: Calculate the voltage reference coefficient k_Usm of the i-th submodule. i Its calculation

[0013] The formula is as follows:

[0014]

[0015] Among them, k_Usm i This is the ratio of the voltage of the i-th submodule to the reference voltage;

[0016] C i C is the capacitance value of the i-th submodule; ref The maximum capacitance value among all submodules;

[0017] i∈n, where n is the total number of sub-modules within the bridge arm, and n is a natural number greater than 1;

[0018] Step A2: Based on different voltage ratio values, calculate the equivalent submodule voltage converted to the reference voltage, and calculate the equivalent total submodule under the same reference voltage;

[0019] The equivalent total input submodule N under the same reference voltage eq-total Calculation formula

[0020] The formula is as follows:

[0021]

[0022] in,

[0023] N eq-i =Fgt i *k_Usm i ;

[0024] In the formula, Fgt i For the switching state of the i-th submodule, when Fgt i =1 indicates input, Fgt i =0 indicates excision; Neq-i N represents the equivalent number of engaged submodules for the i-th submodule at the reference voltage. eq-total This refers to the equivalent input submodule under the same reference voltage.

[0025] Furthermore, the step of controlling the switching of sub-modules based on the difference between the equivalent total number of sub-modules in operation under the reference voltage in the current cycle and the previous cycle specifically includes the following steps:

[0026] Step B1: Establish a data structure; the data structure includes the submodule device number index_i, and the actual submodule voltage feedback value U of the i-th submodule. i The voltage reference coefficient k_Usm of the i-th submodule i The equivalent voltage U of the i-th submodule eq-i The previous cycle switching state F gti A data structure for five sets of data (k-1); 0 ≤ i ≤ n;

[0027] Step B2: Based on the data structure, convert all sub-modules of the previous cycle to the equivalent total sub-module under the same reference voltage to obtain the first total sub-module; and convert all sub-modules of the current cycle to the equivalent total sub-module under the same reference voltage to obtain the second total sub-module;

[0028] First submodule N on-ref The formula for calculating (K-1) is as follows:

[0029]

[0030] Second submodule N on-ref The formula for calculating (K) is as follows:

[0031] N on-ref (K) = round(Uarm) ref / Uref);

[0032] U armref For the current control cycle, the named value of the corresponding bridge arm voltage modulation wave of the control output;

[0033] U ref This is the rated reference operating voltage of the submodule;

[0034] N on-ref (K-1) represents the number of the first total sub-modules, which is the equivalent total number of sub-modules in the previous cycle;

[0035] N on-ref (K) represents the number of the second total sub-modules, which is the equivalent total number of sub-modules in the current control cycle;

[0036] Step B3: Calculate the difference between the first sub-module and the second sub-module to obtain the module difference value;

[0037] The module difference value N diff The calculation formula is as follows:

[0038] N diff =N on-ref (K)-round(N on-ref (K-1));

[0039] Step B4: Control the switching of sub-modules based on the module difference value and the switching compensation coefficient.

[0040] Furthermore, the switching compensation coefficient in step B4 is determined based on the order of the sub-modules;

[0041] The sorting of the sub-modules specifically includes: sorting the sub-modules in the previous cycle's input state based on the data structure; and sorting the sub-modules in the previous cycle's cut-off state.

[0042] The process of sorting the sub-modules in the previous cycle's operational state includes the following steps:

[0043] Based on the submodule device number index_i and the operational status index array Construct the first dual-index exchange mechanism;

[0044] Based on the first dual-index exchange mechanism, several sub-modules that were in the input state in the previous cycle are based on their corresponding equivalent voltage U. eq-i Arrange them in ascending order or descending order to obtain the sorting of sub-modules in the previous cycle's input state;

[0045] The sub-modules in the previous cycle cut-off state are sorted, specifically including the following steps:

[0046] Based on the submodule device number index_i and the cut-off status index array Construct a second dual-index exchange mechanism;

[0047] Based on the second dual-index exchange mechanism, several sub-modules that were in the cut-off state in the previous cycle are processed based on their corresponding equivalent voltage U. eq-i Arrange them in ascending order or descending order to obtain the sorting of sub-modules in the previous cycle's input state;

[0048] Among them, the equivalent submodule voltage U eq-i The calculation formula is as follows:

[0049] U eq-i =U i / k_Usmi ;

[0050] Among them, U i This represents the actual submodule voltage feedback value of the i-th submodule.

[0051] Further, step B4 specifically includes:

[0052] If N diff If the value is greater than 0, then the sub-modules that have been cut off in the previous cycle are selected for input based on the module difference value and the input / output compensation coefficient.

[0053] If N diff =0, then the switching state of the sub-module in the current cycle remains unchanged from the switching state of the sub-module in the previous cycle;

[0054] If N diff If the value is less than 0, then the sub-modules that have been deployed in the previous cycle are selected for removal based on the module difference value and the deployment compensation coefficient.

[0055] Furthermore, the so-called N diff If the value is greater than 0, then based on the module difference value and the switching compensation coefficient, the sub-modules that were already cut off in the previous cycle are selected for deployment, specifically including:

[0056] When N diff >0, and when the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the lowest voltage (N) from the submodules that have been removed in the previous cycle. diff -

[0057] N iff_offset ) Sub-modules are deployed; or,

[0058] When N diff >0, and when the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the largest voltage (N) from the submodules that have been disconnected in the previous cycle. diff -

[0059] N off_offset ) Sub-modules were deployed;

[0060] Where, N off_offset This is a compensation coefficient for the number of modules to be cut.

[0061] When selecting the voltage with the lowest value (N) diff -N off_offset When a submodule is deployed, the compensation coefficient N for the number of modules to be cut is calculated. off_offset The process of obtaining it includes:

[0062] when When using ascending sorting conditions

[0063] or,

[0064] when When using a descending sort condition,

[0065]

[0066] When selecting the voltage with the largest (N) diff -N off_offset When a submodule is deployed, the process of obtaining the compensation coefficient for the number of modules to be cut includes:

[0067] when When using a descending sort condition,

[0068] or,

[0069] when When using ascending sorting conditions

[0070]

[0071] In the formula: round() is the rounding function; mod() is the modulo operation; n1 is the number of submodules in the cut-off state in the bridge arm in the previous cycle; For submodule index parameters; In the index of the removed submodules, the k_Usm value corresponding to the i-th submodule is found in the submodule voltage sorting sequence based on the removed state.

[0072] Furthermore, the so-called N diff If the value is less than 0, then based on the module difference value and the switching compensation coefficient, the sub-modules that were already deployed in the previous cycle are selected for removal, specifically including:

[0073] When N diff When the voltage is <0 and the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the highest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -

[0074] N in_iffset ) submodules are removed; or,

[0075] When N diff When the voltage is less than 0 and the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the lowest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -

[0076] N on_offser ) submodules were removed;

[0077] Where, N on_offset The compensation coefficient is the number of modules to be invested.

[0078] When selecting the voltage with the largest (N) diff -N on_offset When a submodule is removed, the compensation coefficient N for the number of modules deployed is calculated. on_offset The process of obtaining it includes:

[0079] when When using a descending sort condition,

[0080]

[0081] or,

[0082] when When using ascending sorting conditions

[0083]

[0084] When selecting the voltage with the lowest value (N) diff -N on_offset When a submodule is removed, the compensation coefficient N for the number of modules deployed is calculated. on_offset The process of obtaining it includes:

[0085] when When using ascending sorting conditions

[0086]

[0087] or,

[0088] when When using a descending sort condition,

[0089]

[0090] In the formula: round() is the rounding function; mod() is the modulo operation; n2 is the number of submodules in the cut-off state in the bridge arm in the previous cycle; For submodule index parameters; In the submodule index to be removed, the K_usm value corresponding to the i-th submodule in the submodule voltage sorting sequence based on the input status is given.

[0091] Secondly, the present invention provides a voltage equalization modulation method for an MMC bridge arm, wherein the MMC bridge arm is a full-bridge power module and / or a half-bridge power module;

[0092] The method includes the following steps:

[0093] Real-time monitoring of voltage and current values ​​of each submodule in the MMC bridge arm;

[0094] Based on the voltage and current values ​​of each submodule, the voltage equalization modulation method of mixing submodules of different voltage levels in the bridge arm as described in the first aspect is used to perform voltage equalization modulation on the MMC bridge arm.

[0095] Thirdly, the present invention provides a voltage equalization modulation device for mixing submodules of different voltage levels within a bridge arm, the device comprising:

[0096] The acquisition unit is used to acquire the voltage of sub-modules of different voltage levels that are mixed in the bridge arm;

[0097] The calculation unit, connected to the acquisition unit, is used to convert all sub-modules to the equivalent total input sub-modules under the same reference voltage based on the voltage of the sub-modules of different voltage levels.

[0098] The control unit, connected to the computing unit, is used to control the switching of sub-modules based on the difference between the equivalent total number of sub-modules in operation under the reference voltage in the current cycle and the previous cycle, so as to achieve voltage equalization modulation of sub-modules of different voltage levels in the bridge arm.

[0099] Furthermore, the computing unit includes:

[0100] The first calculation module is used to calculate the voltage reference coefficient k_Usm of the i-th submodule. i ;

[0101] The first calculation module stores the following calculation formulas:

[0102]

[0103] Among them, k_Usm i This is the ratio of the voltage of the i-th submodule to the reference voltage;

[0104] C i C is the capacitance value of the i-th submodule; ref The maximum capacitance value among all submodules;

[0105] i∈n, where n is the number of submodules and n is a natural number greater than 1;

[0106] The second calculation module, connected to the first calculation module, is used to calculate the equivalent submodule voltage of the submodule converted to the reference voltage according to the different voltage ratio values, and to calculate the equivalent total input submodule under the same reference voltage.

[0107] The second calculation module stores the following calculation formulas:

[0108]

[0109] in,

[0110] N eq-i =Fgt i *k_Usm i ;

[0111] In the formula, Fgt i For the switching state of the i-th submodule, when Fgt i =1 indicates input, Fgt i =0 indicates excision; N eq-i N represents the equivalent number of engaged submodules for the i-th submodule at the reference voltage. eq-total This refers to the equivalent input submodule under the same reference voltage.

[0112] Furthermore, the control unit includes:

[0113] A construction module is used to establish a data structure; the data structure is based on the submodule device number index_i, and the actual submodule voltage feedback value U of the i-th submodule. i The voltage reference coefficient k_Usmi of the i-th submodule, and the equivalent voltage U of the i-th submodule. eq-i The previous cycle switching state F gti A data structure for five sets of data (k-1); 0 ≤ i ≤ n;

[0114] The conversion module, connected to the construction module, is used to convert all sub-modules of the previous cycle to the equivalent total sub-module under the same reference voltage based on the data structure to obtain a first total sub-module; and to convert all sub-modules of the current cycle to the equivalent total sub-module under the same reference voltage to obtain a second total sub-module.

[0115] First submodule N on-ref The formula for calculating (K-1) is as follows:

[0116]

[0117] Second submodule N on-ref The formula for calculating (K) is as follows:

[0118] N on-ref (K) = round(Uarm) ref / Uref);

[0119] U armref For the current control cycle, the named value of the corresponding bridge arm voltage modulation wave of the control output;

[0120] U ref This is the rated reference operating voltage of the submodule;

[0121] N on-ref (K-1) represents the number of the first total sub-modules, which is the equivalent total number of sub-modules in the previous cycle;

[0122] N on-ref (K) represents the number of the second total sub-modules, which is the equivalent total number of sub-modules in the current control cycle;

[0123] A calculation module, connected to the conversion module, is used to calculate the difference between the first total submodule and the second total submodule to obtain the module difference value;

[0124] The calculation module stores module difference values ​​N. diff The calculation formula is as follows:

[0125] N diff =N on-ref (K)-round(N on-ref (K-1));

[0126] A control module, connected to the calculation module, is used to determine a switching strategy based on the module difference value and the switching compensation coefficient; and to control the switching of sub-modules based on the switching strategy.

[0127] Furthermore, the control unit also includes a sorting module, which is connected to the control module and is used to sort the sub-modules so that the control module can perform switching control according to the sorting of the sub-modules;

[0128] The sorting submodule includes a first sorting submodule and a second sorting submodule; the first sorting submodule is used to sort the submodules in the input state of the previous cycle based on the data structure; the second sorting submodule is used to sort the submodules in the cut-off state of the previous cycle based on the data structure.

[0129] The first sorting submodule includes:

[0130] Construct the first grandchild module, which is used to construct the submodule based on the device number index_i and the array of input / output status indices. Construct the first dual-index exchange mechanism;

[0131] The first sorting sub-module, connected to the first construction sub-module, is used to sort several sub-modules that were in the input state in the previous cycle based on their corresponding equivalent voltage U, according to the first dual-index exchange mechanism. eq-i Arrange them in ascending order or descending order to obtain the sorting of sub-modules in the previous cycle's input state;

[0132] The second sorting submodule includes:

[0133] Construct a second grandchild module for use with the submodule device number index_i and the cut-off state index array. Construct a second dual-index exchange mechanism;

[0134] The second sorting sub-module, connected to the second sub-module construction module, is used to sort several sub-modules that were in the cut-off state in the previous cycle based on their corresponding equivalent voltage U, according to the second dual-index exchange mechanism. eq-i Arrange them in ascending order or descending order to obtain the sorting of sub-modules in the previous cycle's input state;

[0135] The sorting submodule stores the equivalent submodule voltage U. eq-i The calculation formula is as follows:

[0136] U eq-i =U i / k_U smi ;

[0137] Among them, U i This represents the actual submodule voltage feedback value of the i-th submodule.

[0138] Furthermore, the control module includes:

[0139] The first control submodule is used when N diff >0, and when the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the lowest voltage (N) from the submodules that have been removed in the previous cycle. diff -N off_offset ) Sub-modules were deployed;

[0140] The second control submodule is used when N diff >0, and when the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the largest voltage (N) from the submodules that have been disconnected in the previous cycle. diff -N off_offset ) Sub-modules were deployed;

[0141] Both the first control submodule and the second control submodule store a compensation coefficient N for the number of modules to be cut. off_offset ;

[0142] When selecting the voltage with the lowest value (N) diff -N off_offset When a submodule is deployed, the compensation coefficient N for the number of modules to be cut is calculated. off_offset The process of obtaining it includes:

[0143] when When using ascending sorting conditions

[0144] or,

[0145] when When using a descending sort condition,

[0146]

[0147] When selecting the voltage with the largest (N) diff -N off_offset When a submodule is deployed, the process of obtaining the compensation coefficient for the number of modules to be cut includes:

[0148] when When using a descending sort condition,

[0149] or,

[0150] when When using ascending sorting conditions

[0151]

[0152] In the formula: round() is the rounding function; mod() is the modulo operation; n1 is the number of submodules in the cut-off state in the bridge arm in the previous cycle; For submodule index parameters; In the index of the removed submodules, the k_Usm value corresponding to the i-th submodule in the submodule voltage sorting sequence based on the removed state;

[0153] The third control submodule is used when N diff When the voltage is <0 and the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the highest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -N on_offset ) submodules were removed;

[0154] The fourth control submodule is used when N diff When the voltage is less than 0 and the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the lowest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -N on_offset ) submodules were removed;

[0155] Both the third and fourth control submodules store a compensation coefficient N for the number of modules to be cut. on_offset ;

[0156] When selecting the voltage with the largest (N) diff -N on_offsetWhen a submodule is removed, the compensation coefficient N for the number of modules deployed is calculated. on_offset The process of obtaining it includes:

[0157] when When using a descending sort condition,

[0158]

[0159] or,

[0160] when When using ascending sorting conditions

[0161]

[0162] When selecting the voltage with the lowest value (N) diff -N on_offset When a submodule is removed, the compensation coefficient N for the number of modules deployed is calculated. on_offset The process of obtaining it includes:

[0163] when When using ascending sorting conditions

[0164]

[0165] or,

[0166] when When using a descending sort condition,

[0167]

[0168] In the formula: round() is the rounding function; mod() is the modulo operation; n2 is the number of submodules in the cut-off state in the bridge arm in the previous cycle; For submodule index parameters; In the submodule index to be removed, the K_usm value corresponding to the i-th submodule in the submodule voltage sorting sequence based on the input status is given.

[0169] Fourthly, the present invention provides a voltage equalization modulation system for an MMC bridge arm, wherein the MMC bridge arm is a full-bridge power module and / or a half-bridge power module;

[0170] The system includes:

[0171] Monitoring devices;

[0172] The third aspect describes a voltage equalization modulation device for mixing submodules of different voltage levels within a bridge arm. The voltage equalization modulation device is connected to the monitoring device and is used to perform voltage equalization modulation on the MMC bridge arm based on the voltage and current values ​​of each submodule monitored by the monitoring device.

[0173] This invention effectively achieves voltage equalization modulation under mixed conditions of submodules with different voltage levels by converting them to a unified reference voltage and precisely controlling the connection and disconnection of submodules through compensation coefficients. This ensures that all submodules within the bridge arm have a consistent voltage fluctuation ratio. Specific beneficial effects are as follows:

[0174] 1. Improved modulation method:

[0175] This invention improves upon the conventional Nearest Level Approximation (NLM) method by introducing an equivalent submodule voltage coefficient, enabling modules of different voltage levels to be ordered under the same reference. This improvement ensures that power modules of both voltage levels within the bridge arm operate at the design average voltage, thereby enhancing the stability of the hybrid system.

[0176] Meanwhile, this invention introduces a switching compensation coefficient, effectively reducing the voltage difference impact caused by the switching process of modules with different voltage levels. This measure avoids high-frequency switching of modules within the bridge arm, achieving equal switching frequencies and equal voltage fluctuation ratios for modules of both voltage levels, thereby improving system efficiency and reliability.

[0177] 2. Compatibility and flexibility:

[0178] The modulation method of this invention uses an input / output interface consistent with conventional nearest-level approximation methods, enabling voltage equalization, sorting, and switching control of modules at two voltage levels with arbitrary voltage ratios within one or more bridge arms. This compatibility and flexibility allow this invention to be widely applied to different system configurations and meet the batch grid connection requirements of new high-voltage devices at different stability stages.

[0179] 3. Economy and scalability:

[0180] By introducing high-voltage power devices (such as those with voltage levels of 6.5kV and above), this invention significantly reduces the number of required submodules, thereby reducing the size and weight of the converter valve. This not only lowers the cost of system manufacturing but also improves overall economic efficiency.

[0181] Furthermore, the modulation method of the present invention has good scalability and can adapt to the application requirements of future higher voltage level power devices, laying a solid technical foundation for the further development of flexible DC transmission systems.

[0182] 4. System stability and reliability:

[0183] By precisely controlling the differences in the deployment and disconnection of sub-modules, this invention effectively avoids system instability caused by inconsistencies in the characteristics of modules at different voltage levels. This significantly improves the operational stability and reliability of the system, and reduces maintenance costs and failure rates.

[0184] 5. Broad application prospects:

[0185] The modulation method of this invention is not only applicable to existing flexible DC transmission projects, but can also be widely applied to other fields requiring multi-level converter technology, such as new energy power generation, low-frequency power transmission, and power electronic transformers. This broad application prospect further enhances its technical and economic value. Attached Figure Description

[0186] Figure 1 This is a schematic diagram of a voltage equalization modulation method for mixing sub-modules of different voltage levels within a bridge arm in an embodiment of the present invention;

[0187] Figure 2 This is a schematic diagram of the voltage equalization modulation process of different voltage level sub-modules being connected in the bridge arm in an embodiment of the present invention.

[0188] Figure 3 This is a schematic diagram of the input / output interface of the NLM algorithm in an embodiment of the present invention;

[0189] Figure 4 This is a schematic diagram of a voltage equalization modulation device in which sub-modules of different voltage levels are connected in a bridge arm in an embodiment of the present invention.

[0190] Reference numerals: 10, acquisition unit; 20, calculation unit; 30, control unit. Detailed Implementation

[0191] To enable those skilled in the art to better understand the technical solution of the present invention, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0192] It is understood that the specific embodiments and accompanying drawings described herein are merely for explaining the invention and are not intended to limit the invention.

[0193] It is understood that, without conflict, the various embodiments and features in the embodiments of the present invention can be combined with each other.

[0194] It is understood that, for ease of description, only the parts related to the present invention are shown in the accompanying drawings, while the parts unrelated to the present invention are not shown in the drawings.

[0195] It is understood that each unit or module involved in the embodiments of the present invention may correspond to only one entity structure, or may be composed of multiple entity structures, or multiple units or modules may be integrated into one entity structure.

[0196] It is understood that, without conflict, the functions and steps marked in the flowcharts and block diagrams of this invention may occur in a different order than that marked in the accompanying drawings.

[0197] It is understood that the flowcharts and block diagrams of this invention illustrate the possible architecture, functions, and operations of systems, apparatuses, devices, and methods according to various embodiments of this invention. Each block in the flowchart or block diagram may represent a unit, module, program segment, or code, containing executable instructions for implementing the specified function. Furthermore, each block or combination of blocks in the block diagram and flowchart can be implemented using a hardware-based system to achieve the specified function, or using a combination of hardware and computer instructions.

[0198] It is understood that the units and modules involved in the embodiments of the present invention can be implemented by software or by hardware. For example, the units and modules can be located in a processor.

[0199] Example 1:

[0200] like Figure 1 and Figure 2 As shown, this embodiment provides a voltage equalization modulation method for mixing submodules of different voltage levels within a bridge arm. This method, primarily applied to modular multilevel converters (MMCs), is particularly suitable for flexible direct current transmission (VSC-HVDC) projects. By converting submodules of different voltage levels to a unified reference voltage and introducing equivalent submodule voltage coefficients and switching compensation coefficients, this method achieves voltage equalization sequencing and precise control switching of submodules of various voltage levels within the bridge arm. This modulation method effectively reduces the number of submodules, decreases the size and weight of converter valves, improves system economy and operating efficiency, while ensuring system stability and reliability. Its application scenarios cover high-voltage direct current transmission, new energy access, power electronic transformers, and other fields, laying a technical foundation for the future application of higher voltage level power devices.

[0201] The voltage equalization modulation method includes the following steps:

[0202] 1. Obtain the voltage of sub-modules of different voltage levels that are mixed in the bridge arm, and based on the voltage of the sub-modules of different voltage levels, convert all sub-modules to the equivalent total sub-modules under the same reference voltage.

[0203] Based on the voltages of the submodules at different voltage levels, all submodules are converted to an equivalent total submodule under the same reference voltage. The reference voltage is determined according to actual conditions and can be greater than, less than, or equal to the voltage in the submodules. For convenience, in the following embodiments, there are two sets of voltages, 4.5kV and 6.5kV, which represent the 4.5kV value converted from the reference voltage to the submodule voltage; that is, the minimum of these two sets of voltages. Converting all submodules to an equivalent total submodule under the same reference voltage can be done using the rated voltage or the capacitance value of the submodules, and specifically includes the following steps:

[0204] Step A1: Calculate the voltage reference coefficient k_Usm of the i-th submodule. i The calculation formula is as follows:

[0205]

[0206] Among them, k_Usm i This is the ratio of the voltage of the i-th submodule to the reference voltage;

[0207] C i C is the capacitance value of the i-th submodule; ref The maximum capacitance value among all submodules;

[0208] i∈n, where n is the total number of sub-modules within the bridge arm, and n is a natural number greater than 1;

[0209] Step A2: Based on the different voltage ratio values, calculate the equivalent submodule voltage of the submodule converted to the reference voltage, and calculate the equivalent total submodule under the same reference voltage;

[0210] The equivalent total input submodule N under the same reference voltage eq-total The calculation formula is as follows:

[0211]

[0212] in,

[0213] N eq-i =Fgt i *k_Usm i ;

[0214] In the formula, Fgt i For the switching state of the i-th submodule, when Fgt i =1 indicates input, Fgt i =0 indicates excision; N eq-i N represents the equivalent number of engaged submodules for the i-th submodule at the reference voltage. eq-total This refers to the equivalent input submodule under the same reference voltage.

[0215] 2. Based on the difference between the equivalent total number of sub-modules in operation under the reference voltage in the current cycle and the previous cycle, control the switching of sub-modules to achieve equal voltage modulation of sub-modules of different voltage levels in the bridge arm.

[0216] Specifically, based on the difference between the equivalent total number of sub-modules in operation under the reference voltage in the current cycle and the previous cycle, the switching of sub-modules is controlled, which includes the following steps:

[0217] Step B1: Establish a data structure; the data structure is a data structure consisting of five sets of data: submodule device number index_i, actual submodule voltage feedback value Ui of the i-th submodule, voltage reference coefficient kUsmi of the i-th submodule, equivalent voltage Ueq-i of the i-th submodule, and switching state Fgti(k-1) of the previous cycle; 0≤i≤n;

[0218] Step B2: Based on the data structure, convert all sub-modules of the previous cycle to the equivalent total sub-module under the same reference voltage to obtain the first total sub-module; and convert all sub-modules of the current cycle to the equivalent total sub-module under the same reference voltage to obtain the second total sub-module;

[0219] First submodule N on-ref The formula for calculating (K-1) is as follows:

[0220]

[0221] Second submodule N on-ref The formula for calculating (K) is as follows:

[0222] N on-ref (K) = round(Uarm) ref / Uref);

[0223] U armref For the current control cycle, the named value of the corresponding bridge arm voltage modulation wave of the control output;

[0224] U ref This is the rated reference operating voltage of the submodule;

[0225] N on-ref (K-1) represents the number of the first total sub-modules, which is the equivalent total number of sub-modules in the previous cycle;

[0226] N on-ref (K) represents the number of the second total sub-modules, which is the equivalent total number of sub-modules in the current control cycle;

[0227] The second total number of submodules is usually one of the external input parameters of the sorting algorithm.

[0228] Step B3: Calculate the difference between the first sub-module and the second sub-module to obtain the module difference value;

[0229] The module difference value N diff The calculation formula is as follows:

[0230] N diff =N on-ref (K)-round(N on-ref (K-1));

[0231] Step B4: Control the switching of sub-modules based on the module difference value and the switching compensation coefficient.

[0232] In one specific implementation, the switching compensation coefficient in step B4 is determined according to the order of the sub-modules;

[0233] The sorting of the sub-modules specifically includes: sorting the sub-modules in the previous cycle's input state based on the data structure; and sorting the sub-modules in the previous cycle's cut-off state.

[0234] The process of sorting the sub-modules in the previous cycle's operational state includes the following steps:

[0235] Based on the submodule device number index_i and the operational status index array Construct the first dual-index exchange mechanism;

[0236] The equivalent submodule voltage is represented by U. eq-i The submodule switching state of the previous cycle is represented by F. gti (k-1), the input state index array is represented as follows:

[0237] Based on the first dual-index exchange mechanism, several sub-modules that were in the input state in the previous cycle are based on their corresponding equivalent voltage U. eq-i Arrange them in ascending order or descending order to obtain the sorting of sub-modules in the previous cycle's input state;

[0238] The sub-modules in the previous cycle cut-off state are sorted, specifically including the following steps:

[0239] Based on the submodule device number index_i and the cut-off status index array Construct a second dual-index exchange mechanism;

[0240] The equivalent submodule voltage is represented by U. eq-i The submodule switching state of the previous cycle is represented by F. gti (k-1), the input state index array is represented as follows: The excision state index array is represented as

[0241] Based on the second dual-index exchange mechanism, several sub-modules that were in the cut-off state in the previous cycle are processed based on their corresponding equivalent voltage U. eq-i Arrange them in ascending order or descending order to obtain the sorting of sub-modules in the previous cycle's input state;

[0242] Among them, the equivalent submodule voltage U eq-i The calculation formula is as follows:

[0243] U eq-i =U i / k_U smi ;

[0244] Among them, U i This represents the actual submodule voltage feedback value of the i-th submodule.

[0245] As one specific implementation, step B4 specifically includes:

[0246] If N diff If the value is greater than 0, then the sub-modules that have been cut off in the previous cycle are selected for input based on the module difference value and the input / output compensation coefficient.

[0247] If N diff =0, then the switching state of the sub-module in the current cycle remains unchanged from the switching state of the sub-module in the previous cycle;

[0248] If N diff If the value is less than 0, then the sub-modules that have been deployed in the previous cycle are selected for removal based on the module difference value and the deployment compensation coefficient.

[0249] As one specific implementation method, if N diff If the value is greater than 0, then based on the module difference value and the switching compensation coefficient, the sub-modules that were already cut off in the previous cycle are selected for deployment, specifically including:

[0250] When N diff >0, and when the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the lowest voltage (N) from the submodules that have been removed in the previous cycle. diff -

[0251] N off_offset ) Sub-modules are deployed; or,

[0252] When N diff >0, and when the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the largest voltage (N) from the submodules that have been disconnected in the previous cycle. diff -

[0253] N off_offset ) Sub-modules were deployed;

[0254] Where, N off_offset This is a compensation coefficient for the number of modules to be cut.

[0255] When selecting the voltage with the lowest value (N) diff -N off_offset When a submodule is deployed, the compensation coefficient N for the number of modules to be cut is calculated. off_offset The process of obtaining it includes:

[0256] when When using ascending sorting conditions

[0257] or,

[0258] when When using a descending sort condition,

[0259]

[0260] When selecting the voltage with the largest (N) diff -N off_offset When a submodule is deployed, the process of obtaining the compensation coefficient for the number of modules to be cut includes:

[0261] when When using a descending sort condition,

[0262] or,

[0263] when When using ascending sorting conditions

[0264]

[0265] In the formula: round() is the rounding function; mod() is the modulo operation; n1 is the number of submodules in the cut-off state in the bridge arm in the previous cycle; For submodule index parameters; In the submodule removal index, the k_Usm value corresponding to the i-th position of the submodule in the submodule voltage sorting sequence based on the removal state is used. As a specific implementation, if N diff If the value is less than 0, then based on the module difference value and the switching compensation coefficient, the sub-modules that were already deployed in the previous cycle are selected for removal, specifically including:

[0266] When N diffWhen the voltage is <0 and the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the highest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -

[0267] N on_offser ) submodules are removed; or,

[0268] When N diff When the voltage is less than 0 and the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the lowest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -

[0269] N on_offser ) submodules were removed;

[0270] Where, N on_offset The compensation coefficient is the number of modules to be invested.

[0271] When selecting the voltage with the largest (N) diff -N on_offset When a submodule is removed, the compensation coefficient N for the number of modules deployed is calculated. ob_offset The process of obtaining it includes:

[0272] when When using a descending sort condition,

[0273]

[0274] or,

[0275] when When using ascending sorting conditions

[0276]

[0277] When selecting the voltage with the lowest value (N) diff -N on_offset When a submodule is removed, the compensation coefficient N for the number of modules deployed is calculated. on_offset The process of obtaining it includes:

[0278] when When using ascending sorting conditions

[0279]

[0280] or,

[0281] when When using a descending sort condition,

[0282]

[0283] In the formula: round() is the rounding function; mod() is the modulo operation; n2 is the number of submodules in the cut-off state in the bridge arm in the previous cycle; For submodule index parameters; In the submodule index to be removed, the K_usm value corresponding to the i-th submodule in the submodule voltage sorting sequence based on the input status is given.

[0284] This embodiment involves multiple voltage levels, including but not limited to two. However, for convenience, a detailed description will be provided using two voltage levels (4.5kV and 6.5kV connected in the same bridge arm) as an example.

[0285] Consider the MMC converter valves of a 2GW, ±500kV flexible DC power transmission project. In this system, the rated operating voltage of the 4.5kV power modules is 2.1kV, the module capacitance is 10mF, and there are 476 modules per bridge arm. The plan is to replace a certain proportion of the power modules with 6.5kV, 2kA IGBT devices. It is expected that the 6.5kV, 2kA IGBTs will operate at 3kV, and the replacement ratio is set at 1 / 2 of the single-bridge arm voltage. To achieve mixed-connection voltage equalization modulation of submodules of different voltage levels within the bridge arm, the target value U of the rated operating voltage of the two voltage levels of power devices must be predetermined. cL and U cH Calculate the capacitor value C of the high-voltage power module using the following formula and conditions. smH .

[0286]

[0287] Different voltage submodules I within the same bridge arm arm Under the condition that the resection time dt is equal, we have the following formula 2:

[0288]

[0289] In this embodiment, the capacitance of the 4.5kV submodule is 10mF, corresponding to a steady-state voltage of 2.1kV. The design steady-state voltage of the 6.5kV submodule is 3kV, so the capacitance of the 6.5kV VGBT module is 7mF.

[0290] The number of corresponding bridge arm modules can be obtained from the following formula 3:

[0291] U dc =U CL *N L +U CH *N H ------Formula 3

[0292] In this embodiment, U is calculated. dc =1000kV, U CL=2.1kV,U cH =3kV, the replacement ratio is 1 / 2 of the single-bridge arm voltage, then 0.5*Udc = U CL *N L =U CH *N H .

[0293] Corresponding to N L =238,N H =167.

[0294] Based on the parameters determined for the hybrid system described above, the hybrid sorting algorithm is as follows: Figure 2 As shown, the specific method includes the following steps (the formula is the same as the previous formula in this embodiment, and will not be repeated):

[0295] Step 1: Obtain the steady-state operating voltage ratio values ​​of the two sub-modules; and obtain the sorting definition of sub-modules with different voltage levels within the bridge arm.

[0296] Step 2: Obtain the number of conducting modules required by the low-voltage module in the bridge arm for this control cycle; and obtain the actual number of conducting modules fed back in the previous control cycle (which can be referred to as the previous cycle or the previous period).

[0297] Step 3: Obtain the real-time voltage value of each module and calculate the voltage conversion value of the sub-module.

[0298] Step 4: Assuming that m sub-modules were put into operation in the previous cycle, sort the m sub-modules in ascending order (or descending order) based on their equivalent sub-modules under the reference voltage, and count the number of equivalent sub-modules put into operation in the previous cycle.

[0299] Step 5: Assuming that n sub-modules were removed in the previous cycle, sort the equivalent input sub-modules of the n sub-modules under the reference voltage from smallest to largest (or from largest to smallest).

[0300] Step 6: Calculate the difference N in the number of equivalent input sub-modules. diff .

[0301] Step 7: Based on N diff Different switching compensation coefficients are calculated based on the different values.

[0302] Step 8: Based on N diff The switching of the switching compensation coefficient control submodule.

[0303] This step specifically includes:

[0304] (1) If N diff =0, then the switching state of the submodule in the current cycle remains unchanged from the switching state of the submodule in the previous cycle.

[0305] (2) When N diff >0, and when the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the lowest voltage (N) from the submodules that have been removed in the previous cycle. diff -N off_offset ) Sub-modules were put into operation.

[0306] (3) When N diff >0, and when the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the largest voltage (N) from the submodules that have been disconnected in the previous cycle. diff -N off_offset ) Sub-modules were put into operation.

[0307] (4) When N diff When the voltage is <0 and the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the highest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -N on_offset () Submodules were removed.

[0308] (5) When N diff When the voltage is less than 0 and the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the lowest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -N on_offset () Submodules were removed.

[0309] like Figure 3 As shown, the voltage equalization modulation method for mixing sub-modules of different voltage levels in the bridge arm in this embodiment is based on the traditional NLM algorithm applicable to the same voltage level. Therefore, the external interface remains consistent with the traditional NLM interface. The input is the voltage of the sub-module, the bridge arm current, and the number of modules with the standard voltage to be turned on in the current cycle. The output is the switching status of N modules in the bridge arm in the current cycle. It can be applied to the algorithm implementation of the mixed modulation strategy for MMC1-6 bridge arms.

[0310] After implementing this modulation, the voltage of the 6.5kV module in the same bridge arm exhibits periodic fluctuations around 3.2kV, and the voltage of the 4.5kV module exhibits periodic fluctuations around 2.1kV. The two voltage fluctuation ratios are basically the same, and the average switching frequency of the two sub-modules can be kept consistent.

[0311] Example 2:

[0312] This embodiment provides a voltage equalization modulation method for an MMC bridge arm, wherein the MMC bridge arm is a full-bridge power module and / or a half-bridge power module;

[0313] The method includes the following steps:

[0314] Real-time monitoring of voltage and current values ​​of each submodule in the MMC bridge arm;

[0315] Based on the voltage and current values ​​of each submodule, the voltage equalization modulation method of mixing submodules of different voltage levels in the bridge arm as described in the first aspect is used to perform voltage equalization modulation on the MMC bridge arm.

[0316] Example 3:

[0317] like Figure 4 As shown, this embodiment provides a voltage equalization modulation device for mixing submodules of different voltage levels within a bridge arm. The device includes:

[0318] Acquisition unit 10 is used to acquire the voltage of sub-modules of different voltage levels that are mixed in the bridge arm;

[0319] The calculation unit 20, connected to the acquisition unit 10, is used to convert all sub-modules to the equivalent total sub-modules under the same reference voltage based on the voltage of the sub-modules of different voltage levels.

[0320] The control unit 30, connected to the computing unit 20, is used to control the switching of sub-modules based on the difference between the equivalent total number of sub-modules engaged under the reference voltage in the current cycle and the previous cycle, so as to achieve voltage equalization modulation of sub-modules of different voltage levels in the bridge arm.

[0321] As one specific implementation, the computing unit 20 includes:

[0322] The first calculation module is used to calculate the voltage reference coefficient k_Usm of the i-th submodule. i

[0323] The first calculation module stores the following calculation formulas:

[0324]

[0325] Among them, k_Usm i This is the ratio of the voltage of the i-th submodule to the reference voltage;

[0326] C i C is the capacitance value of the i-th submodule; ref The maximum capacitance value among all submodules;

[0327] i∈n, where n is the number of submodules and n is a natural number greater than 1;

[0328] The second calculation module, connected to the first calculation module, is used to calculate the equivalent submodule voltage of the submodule converted to the reference voltage according to the different voltage ratio values, and to calculate the equivalent total input submodule under the same reference voltage.

[0329] The second calculation module stores the following calculation formulas:

[0330]

[0331] in,

[0332] N eq-i =Fgt i *k_Usm i ;

[0333] In the formula, Fgt i For the switching state of the i-th submodule, when Fgt i =1 indicates input, Fgt i =0 indicates excision; N eq-i N represents the equivalent number of engaged submodules for the i-th submodule at the reference voltage. eq-total This refers to the equivalent input submodule under the same reference voltage.

[0334] In one specific implementation, the control unit 30 includes:

[0335] A construction module is used to establish a data structure; the data structure is based on the submodule device number index_i, and the actual submodule voltage feedback value U of the i-th submodule. i The voltage reference coefficient k_Usmi of the i-th submodule, the equivalent voltage Ueq-i of the i-th submodule, and the switching state F of the previous cycle. gti A data structure for five sets of data (k-1); 0 ≤ i ≤ n;

[0336] The conversion module, connected to the construction module, is used to convert all sub-modules of the previous cycle to the equivalent total sub-module under the same reference voltage based on the data structure to obtain a first total sub-module; and to convert all sub-modules of the current cycle to the equivalent total sub-module under the same reference voltage to obtain a second total sub-module.

[0337] First submodule N on-ref The formula for calculating (K-1) is as follows:

[0338]

[0339] Second submodule N on-ref The formula for calculating (K) is as follows:

[0340] N on-ref (K) = round(Uarm) ref / Uref);

[0341] U armref For the current control cycle, the named value of the corresponding bridge arm voltage modulation wave of the control output;

[0342] U ref This is the rated reference operating voltage of the submodule;

[0343] N on-ref (K-1) represents the number of the first total sub-modules, which is the equivalent total number of sub-modules in the previous cycle;

[0344] N on-ref (K) represents the number of the second total sub-modules, which is the equivalent total number of sub-modules in the current control cycle;

[0345] A calculation module, connected to the conversion module, is used to calculate the difference between the first total submodule and the second total submodule to obtain the module difference value;

[0346] The calculation module stores module difference values ​​N. diff The calculation formula is as follows:

[0347] N diff =N on-ref (K)-round(N on-ref (K-1));

[0348] A control module, connected to the calculation module, is used to determine a switching strategy based on the module difference value and the switching compensation coefficient; and to control the switching of sub-modules based on the switching strategy.

[0349] In one specific implementation, the control unit further includes a sorting module, which is connected to the control module and is used to sort the sub-modules so that the control module can perform switching control according to the sorting of the sub-modules.

[0350] The sorting submodule includes a first sorting submodule and a second sorting submodule; the first sorting submodule is used to sort the submodules in the input state of the previous cycle based on the data structure; the second sorting submodule is used to sort the submodules in the cut-off state of the previous cycle based on the data structure.

[0351] The first sorting submodule includes:

[0352] Construct the first grandchild module, which is used to construct the submodule based on the device number index_i and the array of input / output status indices. Construct the first dual-index exchange mechanism;

[0353] The first sorting sub-module, connected to the first construction sub-module, is used to sort several sub-modules that were in the input state in the previous cycle based on their corresponding equivalent voltage U, according to the first dual-index exchange mechanism. eq-i Arrange them in ascending order or descending order to obtain the sorting of sub-modules in the previous cycle's input state;

[0354] The second sorting submodule includes:

[0355] Construct a second grandchild module to use the submodule device number index_i and the cut-off state index array. Construct a second dual-index exchange mechanism;

[0356] The second sorting sub-module, connected to the second sub-module construction module, is used to sort several sub-modules that were in the cut-off state in the previous cycle based on their corresponding equivalent voltage U, according to the second dual-index exchange mechanism. eq-i Arrange them in ascending order or descending order to obtain the sorting of sub-modules in the previous cycle's input state;

[0357] The sorting submodule stores the equivalent submodule voltage U. eq-i The calculation formula is as follows:

[0358] U eq-i =U i / k_U smi ;

[0359] Among them, U i This represents the actual submodule voltage feedback value of the i-th submodule.

[0360] As one specific implementation method, the control module includes:

[0361] The first control submodule is used when N diff >0, and when the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the lowest voltage (N) from the submodules that have been removed in the previous cycle. diff -N off_offset ) Sub-modules were deployed;

[0362] The second control submodule is used when N diff >0, and when the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the largest voltage (N) from the submodules that have been disconnected in the previous cycle. diff -N off_offset ) Sub-modules were deployed;

[0363] Both the first control submodule and the second control submodule store a compensation coefficient N for the number of modules to be cut. off_offset ;

[0364] When selecting the voltage with the lowest value (N) diff -N off_offset When a submodule is deployed, the compensation coefficient N for the number of modules to be cut is calculated. off_offset The process of obtaining it includes:

[0365] when When using ascending sorting conditions

[0366] or,

[0367] when When using a descending sort condition,

[0368]

[0369] When selecting the voltage with the largest (N) diff -N off_offset When a submodule is deployed, the process of obtaining the compensation coefficient for the number of modules to be cut includes:

[0370] when When using a descending sort condition,

[0371] or,

[0372] when When using ascending sorting conditions

[0373]

[0374] In the formula: round() is the rounding function; mod() is the modulo operation; n1 is the number of submodules in the cut-off state in the bridge arm in the previous cycle; For submodule index parameters; In the index of the removed submodules, the k_Usm value corresponding to the i-th submodule in the submodule voltage sorting sequence based on the removed state;

[0375] The third control submodule is used when N diff When the voltage is <0 and the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the highest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -N on_offset ) submodules were removed;

[0376] The fourth control submodule is used when N diff When the voltage is less than 0 and the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the lowest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -N on_offset ) submodules were removed;

[0377] Both the third and fourth control submodules store a compensation coefficient N for the number of modules to be cut. on_offset ;

[0378] When selecting the voltage with the largest (N) diff -N on_offset When a submodule is removed, the compensation coefficient N for the number of modules deployed is calculated. on_offset The process of obtaining it includes:

[0379] when When using a descending sort condition,

[0380]

[0381] or,

[0382] when When using ascending sorting conditions

[0383]

[0384] When selecting the voltage with the lowest value (N) diff -N on_offset When a submodule is removed, the compensation coefficient N for the number of modules deployed is calculated. on_offset The process of obtaining it includes:

[0385] when When using ascending sorting conditions

[0386]

[0387] or,

[0388] when When using a descending sort condition,

[0389]

[0390] In the formula: round() is the rounding function; mod() is the modulo operation; n2 is the number of submodules in the cut-off state in the bridge arm in the previous cycle; For submodule index parameters; In the submodule index to be removed, the K_usm value corresponding to the i-th submodule in the submodule voltage sorting sequence based on the input status is given.

[0391] The apparatus in this embodiment is capable of performing the method in Embodiment 1.

[0392] Example 4:

[0393] This embodiment provides a voltage equalization modulation system for an MMC bridge arm, wherein the MMC bridge arm is a full-bridge power module and / or a half-bridge power module;

[0394] The system includes:

[0395] Monitoring devices;

[0396] The voltage equalization modulation device for mixing submodules of different voltage levels in the bridge arm as described in Example 3 is connected to the monitoring device. It is used to perform voltage equalization modulation on the MMC bridge arm based on the voltage and current values ​​of each submodule monitored by the monitoring device.

[0397] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements to reduce the switching frequency based on this strategy can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A voltage equalization modulation method for mixing submodules of different voltage levels in a bridge arm, characterized in that, The method includes the following steps: Obtain the voltage of sub-modules of different voltage levels that are connected in parallel within the bridge arm; Based on the voltage of the sub-modules at different voltage levels, all sub-modules are converted to the equivalent total sub-modules under the same reference voltage; Based on the difference between the equivalent total number of submodules engaged in the current cycle and the previous cycle at the reference voltage, the switching of submodules is controlled to achieve voltage equalization modulation of submodules of different voltage levels in the bridge arm.

2. The voltage equalization modulation method for mixing submodules of different voltage levels within a bridge arm according to claim 1, characterized in that, The step of converting all submodules to the equivalent total submodule under the same reference voltage specifically includes the following steps: Step A1: Calculate the voltage reference coefficient k_Usm of the i-th submodule. i The calculation formula is as follows: Among them, k_Usm i This is the ratio of the voltage of the i-th submodule to the reference voltage; C i C is the capacitance value of the i-th submodule; ref The maximum capacitance value among all submodules; i∈n, where n is the total number of sub-modules within the bridge arm, and n is a natural number greater than 1; Step A2: Based on different voltage ratio values, calculate the equivalent submodule voltage converted to the reference voltage, and calculate the equivalent total submodule under the same reference voltage; The equivalent total input submodule N under the same reference voltage eq-total The calculation formula is as follows: in, N eq-i =Fgt i *k_Usm i ; In the formula, Fgt i For the switching state of the i-th submodule, when Fgt i =1 indicates input, Fgt i =0 indicates excision; N eq-i N represents the equivalent number of engaged submodules for the i-th submodule at the reference voltage. eq-total This refers to the equivalent input submodule under the same reference voltage.

3. The voltage equalization modulation method for mixing submodules of different voltage levels in a bridge arm according to claim 2, characterized in that, The step of controlling the switching of sub-modules based on the difference between the equivalent total number of sub-modules in operation under the reference voltage in the current cycle and the previous cycle specifically includes the following steps: Step B1: Establish a data structure; the data structure includes the submodule device number index_i, and the actual submodule voltage feedback value U of the i-th submodule. i The voltage reference coefficient k_Usm of the i-th submodule i The equivalent voltage U of the i-th submodule eq-i The previous cycle switching state F gti A data structure for five sets of data (k-1); 0 ≤ i ≤ n; Step B2: Based on the data structure, convert all sub-modules of the previous cycle to the equivalent total sub-module under the same reference voltage to obtain the first total sub-module; And by converting all sub-modules in the current cycle to the equivalent total sub-module under the same reference voltage, a second total sub-module is obtained; First submodule N on-ref The formula for calculating (K-1) is as follows: Second submodule N on-ref The formula for calculating (K) is as follows: N on-ref (K)=round(Uarm ref / Uref); U armref For the current control cycle, the named value of the corresponding bridge arm voltage modulation wave of the control output; U ref This is the rated reference operating voltage of the submodule; N on-ref (K-1) represents the number of the first total sub-modules, which is the equivalent total number of sub-modules in the previous cycle; N on-ref (K) represents the number of the second total sub-modules, which is the equivalent total number of sub-modules in the current control cycle; Step B3: Calculate the difference between the first sub-module and the second sub-module to obtain the module difference value; The module difference value N diff The calculation formula is as follows: N diff =N on-ref (K)-round(N on-ref (K-1)); Step B4: Control the switching of sub-modules based on the module difference value and the switching compensation coefficient.

4. The voltage equalization modulation method for mixing submodules of different voltage levels in a bridge arm according to claim 3, characterized in that, The switching compensation coefficient in step B4 is determined based on the order of the sub-modules; The sorting of the sub-modules specifically includes: sorting the sub-modules in the previous cycle's input state based on the data structure; and sorting the sub-modules in the previous cycle's cut-off state. The process of sorting the sub-modules in the previous cycle's operational state includes the following steps: Based on the submodule device number index_i and the operational status index array Construct the first dual-index exchange mechanism; Based on the first dual-index exchange mechanism, several sub-modules that were in the active state in the previous cycle are processed based on their corresponding equivalent voltage U. eq-i Arrange them in ascending order or descending order to obtain the sorting of sub-modules in the previous cycle's input state; The sub-modules in the previous cycle cut-off state are sorted, specifically including the following steps: Based on the submodule device number index_i and the cut-off status index array Construct a second dual-index exchange mechanism; Based on the second dual-index exchange mechanism, several sub-modules that were in the cut-off state in the previous cycle are processed based on their corresponding equivalent voltage U. eq-i Arrange them in ascending order or descending order to obtain the sorting of sub-modules in the previous cycle's input state; Among them, the equivalent submodule voltage U eq-i The calculation formula is as follows: IN eq-i =U i / k_U smi ; Among them, U i This represents the actual submodule voltage feedback value of the i-th submodule.

5. The voltage equalization modulation method for mixing submodules of different voltage levels in a bridge arm according to claim 3, characterized in that, Step B4 specifically includes: If N diff If the value is greater than 0, then the sub-modules that have been cut off in the previous cycle are selected for input based on the module difference value and the input / output compensation coefficient. If N diff =0, then the switching state of the sub-module in the current cycle remains unchanged from the switching state of the sub-module in the previous cycle; If N diff If the value is less than 0, then the sub-modules that have been deployed in the previous cycle are selected for removal based on the module difference value and the deployment compensation coefficient.

6. The voltage equalization modulation method for mixing submodules of different voltage levels in a bridge arm according to claim 5, characterized in that, If N diff If the value is greater than 0, then based on the module difference value and the switching compensation coefficient, the sub-modules that were already cut off in the previous cycle are selected for deployment, specifically including: When N diff >0, and when the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the lowest voltage (N) from the submodules that have been removed in the previous cycle. diff -N off_offset ) Sub-modules are deployed; or, When N diff >0, and when the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the largest voltage (N) from the submodules that have been disconnected in the previous cycle. diff -N off_offset ) Sub-modules were deployed; Where, N off_offset This is a compensation coefficient for the number of modules to be cut. When selecting the voltage with the lowest value (N) diff -N off_offset When a submodule is deployed, the compensation coefficient N for the number of modules to be cut is calculated. off_offset The process of obtaining it includes: when When using ascending sorting conditions or, when When using a descending sort condition, When selecting the voltage with the largest (N) diff -N off_offset When a submodule is deployed, the process of obtaining the compensation coefficient for the number of modules to be cut includes: when When using a descending sort condition, or, when When using ascending sorting conditions In the formula: round() is the rounding function; mod() is the modulo operation; n1 is the number of submodules in the cut-off state in the bridge arm in the previous cycle; For submodule index parameters; In the index of the removed submodules, the k_Usm value corresponding to the i-th submodule is found in the submodule voltage sorting sequence based on the removed state.

7. The voltage equalization modulation method for mixing submodules of different voltage levels in a bridge arm according to claim 5, characterized in that, If N diff If the value is less than 0, then based on the module difference value and the switching compensation coefficient, the sub-modules that were already deployed in the previous cycle are selected for removal, specifically including: When N diff When the voltage is <0 and the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the highest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -N on_offset ) submodules are removed; or, When N diff When the voltage is less than 0 and the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the lowest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -N on_offset ) submodules were removed; Where, N on_offset The compensation coefficient is the number of modules involved. When selecting the voltage with the largest (N) diff -N on_offset When a submodule is removed, the compensation coefficient N for the number of modules deployed is calculated. on_offset The process of obtaining it includes: when When using a descending sort condition, or, when When using ascending sorting conditions When selecting the voltage with the lowest value (N) diff -N on_offset When a submodule is removed, the compensation coefficient N for the number of modules deployed is calculated. on_offset The process of obtaining it includes: when When using ascending sorting conditions or, when When using a descending sort condition, In the formula: round() is the rounding function; mod() is the modulo operation; n2 is the number of submodules in the cut-off state in the bridge arm in the previous cycle; For submodule index parameters; In the submodule index to be removed, the K_usm value corresponding to the i-th submodule in the submodule voltage sorting sequence based on the input status is given.

8. A voltage equalization modulation method for an MMC bridge arm, characterized in that, The MMC bridge arm is a full-bridge power module and / or a half-bridge power module; The method includes the following steps: Real-time monitoring of voltage and current values ​​of each submodule in the MMC bridge arm; Based on the voltage and current values ​​of each submodule, the voltage equalization modulation method of mixing submodules of different voltage levels in the bridge arm as described in any one of claims 1 to 7 is used to perform voltage equalization modulation on the MMC bridge arm.

9. A voltage equalization modulation device for mixing submodules of different voltage levels in a bridge arm, characterized in that, include: The acquisition unit is used to acquire the voltage of sub-modules of different voltage levels that are mixed in the bridge arm; The calculation unit, connected to the acquisition unit, is used to convert all sub-modules to the equivalent total input sub-modules under the same reference voltage based on the voltage of the sub-modules of different voltage levels. The control unit, connected to the computing unit, is used to control the switching of sub-modules based on the difference between the equivalent total number of sub-modules in operation under the reference voltage in the current cycle and the previous cycle, so as to achieve voltage equalization modulation of sub-modules of different voltage levels in the bridge arm.

10. The voltage equalization modulation device for mixing submodules of different voltage levels in a bridge arm according to claim 9, characterized in that, The computing unit includes: The first calculation module is used to calculate the voltage reference coefficient k_Usm of the i-th submodule. i ; The first calculation module stores the following calculation formulas: Among them, k_Usm i This is the ratio of the voltage of the i-th submodule to the reference voltage; C i C is the capacitance value of the i-th submodule; ref The maximum capacitance value among all submodules; i∈n, where n is the number of submodules and n is a natural number greater than 1; The second calculation module, connected to the first calculation module, is used to calculate the equivalent submodule voltage of the submodule converted to the reference voltage according to the different voltage ratio values, and to calculate the equivalent total submodule input under the same reference voltage. The second calculation module stores the following calculation formulas: in, N eq-i =Fgt i *k_Usm i ; In the formula, Fgt i For the switching state of the i-th submodule, when Fgt i =1 indicates input, Fgt i =0 indicates excision; N eq-i N represents the equivalent number of engaged submodules for the i-th submodule at the reference voltage. eq-total This refers to the equivalent input submodule under the same reference voltage.

11. The voltage equalization modulation device for mixing submodules of different voltage levels in a bridge arm according to claim 10, characterized in that, The control unit includes: A construction module is used to establish a data structure; the data structure is based on the submodule device number index_i, and the actual submodule voltage feedback value U of the i-th submodule. i The voltage reference coefficient k_Usmi of the i-th submodule, and the equivalent voltage U of the i-th submodule. eq-i The previous cycle switching state F gti A data structure for five sets of data (k-1); 0 ≤ i ≤ n; The conversion module, connected to the construction module, is used to convert all sub-modules of the previous cycle to the equivalent total sub-module under the same reference voltage to obtain the first total sub-module; and to convert all sub-modules of the current cycle to the equivalent total sub-module under the same reference voltage to obtain the second total sub-module. First submodule N on-ref The formula for calculating (K-1) is as follows: Second submodule N on-ref The formula for calculating (K) is as follows: N on-ref (K)=round(Uarm ref / Uref); U armref For the current control cycle, the named value of the corresponding bridge arm voltage modulation wave of the control output; U ref This is the rated reference operating voltage of the submodule; N on-ref (K-1) represents the number of the first total sub-modules, which is the equivalent total number of sub-modules in the previous cycle; N on-ref (K) represents the number of the second total sub-modules, which is the equivalent total number of sub-modules in the current control cycle; A calculation module, connected to the conversion module, is used to calculate the difference between the first total submodule and the second total submodule to obtain the module difference value; The calculation module stores module difference values ​​N. diff The calculation formula is as follows: N diff =N on-ref (K)-round(N on-ref (K-1)); A control module, connected to the calculation module, is used to determine a switching strategy based on the module difference value and the switching compensation coefficient; and to control the switching of sub-modules based on the switching strategy.

12. The voltage equalization modulation device for mixing submodules of different voltage levels in a bridge arm according to claim 11, characterized in that, The control unit also includes a sorting module, which is connected to the control module and is used to sort the sub-modules so that the control module can perform switching control according to the sorting of the sub-modules. The sorting submodule includes a first sorting submodule and a second sorting submodule; the first sorting submodule is used to sort the submodules in the previous cycle input state based on the data structure. The second sorting submodule is used to sort the submodules in the previous cycle cut-off state based on the data structure; The first sorting submodule includes: Construct the first grandchild module, which is used to construct the submodule based on the device number index_i and the array of input / output status indices. Construct the first dual-index exchange mechanism; The first sorting sub-module, connected to the first construction sub-module, is used to sort several sub-modules that were in the input state in the previous cycle based on their corresponding equivalent voltage U, according to the first dual-index exchange mechanism. eq-i Arrange them in ascending order or descending order to obtain the sorting of sub-modules in the previous cycle's input state; The second sorting submodule includes: Construct a second grandchild module to use the submodule device number index_i and the cut-off state index array. Construct a second dual-index exchange mechanism; The second sorting sub-module, connected to the second sub-module construction module, is used to sort several sub-modules that were in the cut-off state in the previous cycle based on their corresponding equivalent voltage U, according to the second dual-index exchange mechanism. eq-i Arrange them in ascending order or descending order to obtain the sorting of sub-modules in the previous cycle's input state; The sorting submodule stores the equivalent submodule voltage U. eq-i The calculation formula is as follows: IN eq-i =U i / k_U smi ; Among them, U i This represents the actual submodule voltage feedback value of the i-th submodule.

13. The voltage equalization modulation device for mixing submodules of different voltage levels in a bridge arm according to claim 11, characterized in that, The control module includes: The first control submodule is used when N diff >0, and when the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the lowest voltage (N) from the submodules that have been removed in the previous cycle. diff -N off_offset ) Sub-modules were deployed; The second control submodule is used when N diff >0, and when the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the largest voltage (N) from the submodules that have been disconnected in the previous cycle. diff -N off_offset ) Sub-modules were deployed; Both the first control submodule and the second control submodule store a compensation coefficient N for the number of modules to be cut. off_offset ; When selecting the voltage with the lowest value (N) diff -N off_offset When a submodule is deployed, the compensation coefficient N for the number of modules to be cut is calculated. off_offset The process of obtaining it includes: when When using ascending sorting conditions or, when When using a descending sort condition, When selecting the voltage with the largest (N) diff -N off_offset When a submodule is deployed, the process of obtaining the compensation coefficient for the number of modules to be cut includes: when When using a descending sort condition, or, when When using ascending sorting conditions In the formula: round() is the rounding function; mod() is the modulo operation; n1 is the number of submodules in the cut-off state in the bridge arm in the previous cycle; For submodule index parameters; In the index of the removed submodules, the k_Usm value corresponding to the i-th submodule in the submodule voltage sorting sequence based on the removed state; The third control submodule is used when N diff When the voltage is <0 and the bridge arm current is greater than zero, i.e., when the bridge arm is in a charging state, select the submodule with the highest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -N on_offset ) submodules were removed; The fourth control submodule is used when N diff When the voltage is less than 0 and the bridge arm current is less than zero, i.e., when the bridge arm is in a discharging state, select the submodule with the lowest voltage (N) from the submodules that have been put into operation in the previous cycle. diff -N on_offset ) submodules were removed; Both the third and fourth control submodules store a compensation coefficient N for the number of modules to be cut. on_offset ; When selecting the voltage with the largest (N) diff -N on_offset When a submodule is removed, the compensation coefficient N for the number of modules deployed is calculated. on_offset The process of obtaining it includes: when When using a descending sort condition, or, when When using ascending sorting conditions When selecting the voltage with the lowest value (N) diff -N on_offset When a submodule is removed, the compensation coefficient N for the number of modules deployed is calculated. on_offset The process of obtaining it includes: when When using ascending sorting conditions or, when When using a descending sort condition, In the formula: round() is the rounding function; mod() is the modulo operation; n2 is the number of submodules in the cut-off state in the bridge arm in the previous cycle; For submodule index parameters; In the submodule index to be removed, the K_usm value corresponding to the i-th submodule in the submodule voltage sorting sequence based on the input status is given.

14. A voltage equalization modulation system for an MMC bridge arm, characterized in that, The MMC bridge arm is a full-bridge power module and / or a half-bridge power module; The system includes: Monitoring devices; The voltage equalization modulation device for mixing submodules of different voltage levels in a bridge arm as described in any one of claims 9 to 13, wherein the voltage equalization modulation device is connected to the monitoring device and is used to perform voltage equalization modulation on the MMC bridge arm based on the voltage and current values ​​of each submodule monitored by the monitoring device.

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