Method, device and equipment for eliminating primary current harmonics of modular multilevel dc converter and storage medium

Abstract

The application discloses a primary current harmonic elimination method, device and equipment of a modular multilevel direct current converter and a storage medium. A primary current harmonic function with a phase shift angle of each sub-module as a variable is constructed based on transmission power of the sub-module, a direct current side voltage of a low-voltage side and a direct current side voltage of a high-voltage side, a phase shift angle of each sub-module that makes a primary current harmonic of the primary current harmonic function minimum is calculated as a target phase shift angle, and the sub-modules are set to operate according to the corresponding target phase shift angle in a next control period. Through changing a phase shift angle combination of each sub-module and continuously iteratively calculating, a primary current harmonic size of the converter under different phase shift angles is compared to select an optimal phase shift angle combination, so that the purpose of reducing the primary current harmonic is achieved, and then the volume of a filter reactor can be reduced, and the cost of a power grid system is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to harmonic elimination technology, in particular to a primary current harmonic elimination method, device, equipment and storage medium of a modular multilevel DC converter. BACKGROUND

[0002] The modular multilevel converter (MMC) is composed of a plurality of sub-modules (SMs) with the same structure in cascade. Compared with the traditional multilevel converter, the MMC has the characteristics of small switching loss, high output waveform quality, strong fault handling capability, easy expansion, four-quadrant operation, etc., and thus becomes the research focus of the DC power grid.

[0003] The modular multilevel DC converter (i.e., MMC type DC-DC converter) needs to calculate the phase shift angle of each sub-module in each control period, and then input the corresponding control signal based on the phase shift angle of each sub-module to control the operation of each sub-module. The existing method for calculating the phase shift angle is not accurate enough, resulting in a large primary current harmonic on the high-voltage side of the modular multilevel DC converter, which requires the additional installation of a large filter reactor on the high-voltage side to filter out the primary current harmonic, which undoubtedly increases the cost of the power grid system. SUMMARY

[0004] The present application provides a primary current harmonic elimination method, device, equipment and storage medium of a modular multilevel DC converter to achieve the purpose of reducing the primary current harmonic, thereby reducing the size of the filter reactor and the cost of the power grid system.

[0005] In a first aspect, the present application provides a primary current harmonic elimination method of a modular multilevel DC converter, the modular multilevel DC converter comprising a plurality of sub-modules, the method comprising:

[0006] obtaining the transmission power of the sub-modules, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side in the current control period;

[0007] constructing a primary current harmonic function with the phase shift angle of each sub-module as a variable based on the transmission power of the sub-modules, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side;

[0008] calculating the phase shift angle of each sub-module that minimizes the primary current harmonic of the primary current harmonic function as the target phase shift angle;

[0009] setting the sub-modules to operate according to the corresponding target phase shift angle in the next control period.

[0010] Optionally, based on the transmission power of the sub-modules, the DC side voltage of the low voltage side and the DC side voltage of the high voltage side, a first current harmonic function with the phase shift angle of each sub-module as a variable is constructed, comprising:

[0011] The duty cycle of the sub-module is calculated based on the transmission power of the sub-module, the DC side voltage of the low voltage side and the DC side voltage of the high voltage side;

[0012] The first current harmonic coefficient of the sub-module is calculated based on the duty cycle of the sub-module;

[0013] The product of the first current harmonic coefficient of the sub-module and the phase shift angle of the sub-module is calculated with the phase shift angle of the sub-module as a variable, and the sum of the product of the first current harmonic coefficient of each sub-module and the phase shift angle of the sub-module is taken as the first current harmonic function with the phase shift angle of each sub-module as a variable.

[0014] Optionally, the calculation formula of the duty cycle of the sub-module based on the transmission power of the sub-module, the DC side voltage of the low voltage side and the DC side voltage of the high voltage side is as follows:

[0015]

[0016] Wherein, D k is the duty cycle of the kth sub-module, V G is the DC side voltage of the high voltage side, V dck is the DC side voltage of the low voltage side, P k is the transmission power of the kth sub-module, P i is the transmission power of the ith sub-module, and N is the total number of sub-modules.

[0017] Optionally, the calculation formula of the first current harmonic coefficient of the sub-module based on the duty cycle of the sub-module is as follows:

[0018]

[0019] Wherein, is the first current harmonic coefficient of the kth sub-module.

[0020] Optionally, the product of the first current harmonic coefficient of the sub-module and the phase shift angle of the sub-module is calculated with the phase shift angle of the sub-module as a variable, and the sum of the product of the first current harmonic coefficient of each sub-module and the phase shift angle of the sub-module is taken as the first current harmonic function with the phase shift angle of each sub-module as a variable, as follows:

[0021]

[0022] Wherein, V c 1(φ1,..., φ N ) is a first current harmonic function with the phase shift angle of each of the sub-modules as a variable, φ k is the phase shift angle of the kth sub-module.

[0023] Optionally, the method further comprises:

[0024] initializing the phase shift angle of each of the sub-modules;

[0025] for each of the sub-modules, changing the phase shift angle according to two iteration directions of increment and decrement with a preset step phase angle, and calculating the function value of the first current harmonic function corresponding to the two iteration directions at each iteration;

[0026] taking the iteration direction corresponding to the smaller one of the function values of the first current harmonic function corresponding to the two iteration directions as the target iteration direction at this iteration;

[0027] judging whether the difference between the function value of the first current harmonic function corresponding to the target iteration direction and the function value of the first current harmonic function at the previous iteration is less than a maximum iteration difference value;

[0028] if not, returning to the step of changing the phase shift angle according to two iteration directions of increment and decrement with a preset step phase angle, and calculating the function value of the first current harmonic function corresponding to the two iteration directions at each iteration;

[0029] if yes, stopping the iteration and taking the phase shift angle of each of the sub-modules at this iteration as the target phase shift angle.

[0030] Optionally, the maximum iteration difference value is the maximum value of the difference between the function values of the first current harmonic function at adjacent two iterations, and the method further comprises:

[0031] continuously updating the maximum iteration difference value during the iteration.

[0032] In a second aspect, the present application further provides a first current harmonic elimination device for a modular multilevel DC converter, comprising:

[0033] a data acquisition module, configured to acquire the transmission power of the sub-modules, the DC side voltage of the low voltage side and the DC side voltage of the high voltage side in the current control period;

[0034] a function construction module, configured to construct a first current harmonic function with the phase shift angle of each of the sub-modules as a variable based on the transmission power of the sub-modules, the DC side voltage of the low voltage side and the DC side voltage of the high voltage side;

[0035] A target phase-shifting angle calculation module is configured to calculate a phase-shifting angle of each of the sub-modules that minimizes a first current harmonic of the first current harmonic function as a target phase-shifting angle.

[0036] A running module is configured to set the sub-modules to run according to the corresponding target phase-shifting angles in a next control period.

[0037] Optionally, the function construction module comprises:

[0038] A duty cycle calculation unit is configured to calculate a duty cycle of the sub-module based on a transmission power of the sub-module, a DC side voltage of the low-voltage side and a DC side voltage of the high-voltage side.

[0039] A harmonic coefficient calculation unit is configured to calculate a first current harmonic coefficient of the sub-module based on the duty cycle of the sub-module.

[0040] A function construction unit is configured to calculate a product of the first current harmonic coefficient of the sub-module and the phase-shifting angle of the sub-module with the phase-shifting angle of the sub-module as a variable, and take a sum of the product of the first current harmonic coefficient of each of the sub-modules and the phase-shifting angle of the sub-module as a first current harmonic function with the phase-shifting angle of each of the sub-modules as a variable.

[0041] Optionally, the calculation formula of the duty cycle calculation unit is as follows:

[0042]

[0043] wherein, D k is the duty cycle of the kth sub-module, V G is the DC side voltage of the high-voltage side, V dck is the DC side voltage of the low-voltage side, P k is the transmission power of the kth sub-module, P i is the transmission power of the ith sub-module, and N is the total number of the sub-modules.

[0044] Optionally, the calculation formula of the harmonic coefficient calculation unit is as follows:

[0045]

[0046] wherein, is the first current harmonic coefficient of the kth sub-module.

[0047] Optionally, the first current harmonic function constructed by the function construction unit is as follows:

[0048]

[0049] wherein, V c 1 (φ1, …, φ N) is a first-order current harmonic function with the phase-shifting angle of each of the sub-modules as a variable, φ k is the phase-shifting angle of the kth sub-module.

[0050] Optionally, the target phase-shifting angle calculation module comprises:

[0051] an initialization unit configured to initialize the phase-shifting angle of each of the sub-modules;

[0052] a calculation unit configured to, for each of the sub-modules, change the phase angle in two iteration directions of increment and decrement with a preset step phase angle, and calculate the function value of the first-order current harmonic function corresponding to the two iteration directions at each iteration;

[0053] an iteration direction determination unit configured to take the iteration direction corresponding to the smaller one of the function values of the first-order current harmonic function corresponding to the two iteration directions as the target iteration direction at this iteration;

[0054] a judgment unit configured to judge whether the difference between the function value of the first-order current harmonic function corresponding to the target iteration direction and the function value of the first-order current harmonic function at the previous iteration is less than a maximum iteration difference value;

[0055] a return execution unit configured to, when the difference between the function value of the first-order current harmonic function corresponding to the target iteration direction and the function value of the first-order current harmonic function at the previous iteration is greater than or equal to the maximum iteration difference value, return to execute the step of changing the phase angle in two iteration directions of increment and decrement with a preset step phase angle, and calculating the function value of the first-order current harmonic function corresponding to the two iteration directions at each iteration;

[0056] an iteration termination unit configured to, when the difference between the function value of the first-order current harmonic function corresponding to the target iteration direction and the function value of the first-order current harmonic function at the previous iteration is less than the maximum iteration difference value, stop the iteration, and take the phase-shifting angle of each of the sub-modules at this iteration as the target phase-shifting angle.

[0057] Optionally, the maximum iteration difference value is the maximum value of the difference between the function values of the first-order current harmonic function at adjacent two iterations, and the device further comprises:

[0058] a maximum iteration difference value updating module configured to constantly update the maximum iteration difference value during the iteration.

[0059] In a third aspect, the present application further provides a computer device comprising:

[0060] one or more processors;

[0061] a storage device configured to store one or more programs;

[0062] When the one or more programs are executed by the one or more processors, the one or more processors implement the primary current harmonic elimination method of the modular multilevel DC converter as provided in the first aspect of the present application.

[0063] In a fourth aspect, the present application further provides a computer readable storage medium having stored thereon a computer program, which, when executed by a processor, implements the primary current harmonic elimination method of the modular multilevel DC converter as provided in the first aspect of the present application.

[0064] The primary current harmonic elimination method of the modular multilevel DC converter provided by the present application comprises: obtaining the transmission power of a sub-module, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side in the current control period, constructing a primary current harmonic function with the phase-shifting angle of each sub-module as a variable based on the transmission power of the sub-module, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side, calculating the phase-shifting angle of each sub-module that makes the primary current harmonic of the primary current harmonic function minimum as a target phase-shifting angle, setting the sub-modules to operate according to the corresponding target phase-shifting angle in the next control period, and selecting the optimal phase-shifting angle combination by changing the phase-shifting angle combination of each sub-module and iteratively calculating, comparing the primary current harmonic size of the converter under different phase-shifting angles to select the optimal phase-shifting angle combination, thereby achieving the purpose of reducing the primary current harmonic, and further reducing the size of the filter reactor and the cost of the power grid system. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1A A flowchart of a primary current harmonic elimination method of a modular multilevel DC converter provided by an embodiment of the present application;

[0066] Figure 1B A structural schematic diagram of a modular multilevel DC converter provided by the present application;

[0067] Figure 1C A structural schematic diagram of a sub-module provided by the present application;

[0068] Figure 1D A waveform diagram of the primary current harmonic of the existing modular multilevel DC converter;

[0069] Figure 1E A waveform diagram of the primary current harmonic of the modular multilevel DC converter of the present application;

[0070] Figure 2 A structural schematic diagram of a primary current harmonic elimination device of a modular multilevel DC converter provided by an embodiment of the present application;

[0071] Figure 3This is a schematic diagram of the structure of a computer device provided in Embodiment 3 of the present invention. Detailed Implementation

[0072] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0073] Example 1

[0074] Figure 1A This is a flowchart illustrating a primary current harmonic elimination method for a modular multilevel DC-DC converter according to Embodiment 1 of the present invention. This embodiment is applicable to the primary current harmonic elimination of modular multilevel DC-DC converters. The method can be executed by the primary current harmonic elimination device for the modular multilevel DC-DC converter provided in this embodiment. This device can be implemented in software and / or hardware, and is typically configured in a computer device, such as... Figure 1A As shown, the method specifically includes the following steps:

[0075] S101. Obtain the transmission power, DC side voltage of the low-voltage side and DC side voltage of the high-voltage side of the submodule during the current control cycle.

[0076] Figure 1B This is a schematic diagram of a modular multilevel DC-DC converter provided in an embodiment of the present invention, exemplarily, as shown below. Figure 1B As shown, the modular multilevel DC-DC converter includes an input side, an output side, and a unidirectional AC transformer T. The input and output sides are connected via the unidirectional AC transformer T. The input side includes two bridge arms, and similarly, the output side also includes two bridge arms. Each bridge arm consists of several interconnected and structurally identical sub-modules (SMs). The unidirectional AC transformer T provides commutation reactance, improves the converter's turns ratio, and also serves as electrical isolation.

[0077] Figure 1C This is a schematic diagram of the structure of a submodule provided in an embodiment of the present invention, exemplarily, as shown below. Figure 1C As shown, each submodule includes a half-bridge circuit consisting of two IGBTs acting as switching units and an LC filter circuit. SM U is the port output voltage of the submodule. IN U is the input voltage at the port of the submodule. C This refers to the capacitor voltage of the submodule. Each submodule is a two-terminal component; by controlling the on and off states of VT1 and VT2, the submodule output voltage U... SM It can alternately output capacitor voltage U under two current directions simultaneously.C Taking the bridge arm on the high-voltage side of the converter as an example, there are N sub-modules, and the total voltage output by the N sub-modules can be equivalent to a controllable voltage source. If the number of sub-modules of the bridge arm is sufficient, a variety of waveforms of voltage can be output by controlling the input and cut-off of each sub-module in each control period.

[0078] It should be noted that the specific structure of the modular multilevel DC converter and the sub-module is an exemplary description of the embodiments of the present application, and different structures can also be used in other embodiments of the present application, which are not limited herein.

[0079] In the embodiments of the present application, the transmission power of the sub-module in the current control period, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side are obtained. The transmission power of the sub-module refers to the ratio of the power output by the sub-module to the power input. The DC side voltage of the low-voltage side refers to the DC voltage at the output end of the sub-module, and the DC side voltage of the high-voltage side refers to the DC voltage at the input end of the sub-module.

[0080] S102, based on the transmission power of the sub-module, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side, a first current harmonic function with the phase shift angle of each sub-module as a variable is constructed.

[0081] In the embodiments of the present application, after obtaining the transmission power of the sub-module, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side, a first current harmonic function with the phase shift angle of each sub-module as a variable is constructed based on the transmission power of the sub-module, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side.

[0082] For example, in some embodiments of the present application, the above step S102 includes:

[0083] 1. Calculate the duty cycle of the sub-module based on the transmission power of the sub-module, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side.

[0084] For example, the calculation formula for calculating the duty cycle of the sub-module based on the transmission power of the sub-module, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side is as follows:

[0085]

[0086] Where Dk is the duty cycle of the kth sub-module, Vpk is the DC side voltage of the high-voltage side, Vpl is the DC side voltage of the low-voltage side, Pk is the transmission power of the kth sub-module, Pi is the transmission power of the ith sub-module, and N is the total number of sub-modules. k G dck k i ​​​​​

[0087] 2. Calculate the first current harmonic coefficient of each sub-module based on the duty ratio of the sub-module.

[0088] For example, the calculation formula of the first current harmonic coefficient of each sub-module based on the duty ratio of the sub-module is as follows:

[0089]

[0090] wherein, is the first current harmonic coefficient of the kth sub-module.

[0091] 3. Take the phase shift angle of each sub-module as a variable, calculate the product of the first current harmonic coefficient of each sub-module and the phase shift angle of the sub-module, and take the sum of the product of the first current harmonic coefficient of each sub-module and the phase shift angle of the sub-module as the first current harmonic function with the phase shift angle of each sub-module as a variable.

[0092] For example, the first current harmonic function can be expressed as:

[0093]

[0094] wherein, V c 1 (φ1, …, φ N ) is the first current harmonic function with the phase shift angle of each sub-module as a variable, and φ k is the phase shift angle of the kth sub-module.

[0095] S103. Calculate the phase shift angle of each sub-module that makes the first current harmonic of the first current harmonic function minimum as the target phase shift angle.

[0096] In order to effectively reduce or even eliminate the first current harmonic, and reduce the volume and weight of the filter reactor, in the embodiment of the present application, the phase shift angle of each sub-module is taken as a variable, and the phase shift angle of each sub-module that makes the first current harmonic of the first current harmonic function minimum is taken as the target phase angle. That is, the target function is set as g(φ1, …, φ N ):

[0097]

[0098] The target function means that the phase shift angle of the first sub-module is set as the reference phase shift angle, and then a suitable phase shift angle combination (φ1, …, φ N ) is selected to make the first current harmonic amplitude of the DC-DC converter minimum, and the above selection process is realized by iterative calculation.

[0099] For example, the above iterative process is as follows:

[0100] 1. Initialize the phase shift angles of each sub-module, and set the change value of each phase shift angle, i.e. the step phase shift angle Δφ, the interval time of adjacent two iterations, and the maximum iteration difference E. max .

[0101] 2. For each sub-module, change the phase angle according to the preset step phase angle in the increasing and decreasing iteration directions, and calculate the function value of the first current harmonic function corresponding to the two iteration directions at each iteration.

[0102] In the iteration calculation described above, the iteration direction has two, i.e. (φ1,…,φ k +Δφ,…,φ N ) or (φ1,…,φ k -Δφ,…,φ N ). When selecting the iteration direction, the first judgment and calculation should be made on the first current harmonics Ep(corresponding to increasing Δφ) and En(corresponding to decreasing Δφ) in the two iteration directions, which can be specifically represented as:

[0103]

[0104] 3. The iteration direction corresponding to the smaller value of the function value of the first current harmonic function in the two iteration directions is taken as the target iteration direction in this iteration.

[0105] For example, if the first current harmonics of the two satisfy Ep<En, the reference phase shift angle of the present iteration calculation should be selected as (φ1,…,φ k +Δφ,…,φ N ); otherwise, the reference phase shift angle of the present iteration calculation should be selected as (φ1,…,φ k -Δφ,…,φ N ).

[0106] 4. Judge whether the difference between the function value of the first current harmonic function corresponding to the target iteration direction and the function value of the first current harmonic function of the previous iteration is less than the maximum iteration difference.

[0107] After determining the target iteration direction, the function value of the first current harmonic function obtained by iteration according to the target iteration direction is calculated, and the difference between the function value and the function value of the first current harmonic function of the previous iteration is calculated, and it is judged whether the difference is less than the maximum iteration difference E max .

[0108] For example, in some embodiments of the present application, the maximum iteration difference E max can be selected as the maximum value of the first current harmonic in the iteration process and constantly updated, which can be represented as:

[0109] Emax =||V c 1 (φ1,..., φ N )| max

[0110] 5, if no, return to execute with preset step phase angle, change phase angle in two iteration directions of increment and decrement, and calculate function value of primary current harmonic function corresponding to two iteration directions in each iteration.

[0111] 6, if yes, stop iteration, and take phase shift angle of each sub-module in this iteration as target phase shift angle.

[0112] S104, set sub-module to run according to corresponding target phase shift angle in next control period.

[0113] Set sub-module to run according to corresponding target phase shift angle in next control period, so that primary current harmonic minimization of modular multilevel DC converter can be realized.

[0114] Figure 1D Fig. 1 is a waveform diagram of primary current harmonic of existing modular multilevel DC converter, Figure 1E Fig. 2 is a waveform diagram of primary current harmonic of modular multilevel DC converter provided by the embodiment of the present application, which is obtained by Figure 1D and Figure 1E It can be seen that, after the primary current harmonic elimination method of modular multilevel DC converter provided by the embodiment of the present application is adopted, the amplitude of primary current harmonic in power grid is obviously reduced.

[0115] The primary current harmonic elimination method of modular multilevel DC converter provided by the embodiment of the present application comprises: obtaining transmission power of sub-module, DC side voltage of low voltage side and DC side voltage of high voltage side in this control period, constructing primary current harmonic function with phase shift angle of each sub-module as variable based on transmission power of sub-module, DC side voltage of low voltage side and DC side voltage of high voltage side, calculating phase shift angle of each sub-module that makes primary current harmonic of primary current harmonic function minimum as target phase shift angle, setting sub-module to run according to corresponding target phase shift angle in next control period, changing phase shift angle combination of each sub-module and continuously iterating and calculating, comparing primary current harmonic of converter under different phase shift angles to select optimal phase shift angle combination, so that the purpose of reducing primary current harmonic is realized, and then the volume of filter reactor can be reduced and the cost of power grid system can be reduced.

[0116] Embodiment two

[0117] The embodiment two of the present application provides a primary current harmonic elimination device of modular multilevel DC converter, Figure 2A structure diagram of a primary current harmonic elimination device of a modular multilevel direct current converter provided by an embodiment of the present application is shown in the figure, and the device comprises: Figure 2

[0118] A data acquisition module 201 is configured to acquire transmission power of the sub-modules, DC side voltage of the low-voltage side and DC side voltage of the high-voltage side in the current control period;

[0119] A function construction module 202 is configured to construct a primary current harmonic function with the phase shift angle of each sub-module as a variable based on the transmission power of the sub-modules, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side;

[0120] A target phase shift angle calculation module 203 is configured to calculate the phase shift angle of each sub-module that makes the primary current harmonic of the primary current harmonic function minimum as a target phase shift angle;

[0121] A running module 204 is configured to set the sub-modules to run according to the corresponding target phase shift angle in the next control period.

[0122] In some embodiments of the present application, the function construction module 202 comprises:

[0123] A duty cycle calculation unit is configured to calculate the duty cycle of the sub-modules based on the transmission power of the sub-modules, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side;

[0124] A harmonic coefficient calculation unit is configured to calculate the primary current harmonic coefficient of the sub-modules based on the duty cycle of the sub-modules;

[0125] A function construction unit is configured to calculate the product of the primary current harmonic coefficient of the sub-modules and the phase shift angle of the sub-modules with the phase shift angle of the sub-modules as a variable, and take the sum of the product of the primary current harmonic coefficient of each sub-module and the phase shift angle of the sub-module as the primary current harmonic function with the phase shift angle of each sub-module as a variable.

[0126] In some embodiments of the present application, the calculation formula of the duty cycle calculation unit is as follows:

[0127]

[0128] Wherein, D k is the duty cycle of the kth sub-module, V G is the DC side voltage of the high-voltage side, V dck is the DC side voltage of the low-voltage side, P k is the transmission power of the kth sub-module, P i is the transmission power of the ith sub-module, and N is the total number of sub-modules.

[0129] ​In some embodiments of the present application, the calculation formula of the harmonic coefficient calculation unit is as follows:

[0130]

[0131] wherein, is the first current harmonic coefficient of the kth sub-module.

[0132] In some embodiments of the present application, the first current harmonic function constructed by the function construction unit is as follows:

[0133]

[0134] wherein, V c 1 (φ1, …, φ N ) is the first current harmonic function with the phase shift angle of each sub-module as the variable, and φ k is the phase shift angle of the kth sub-module.

[0135] In some embodiments of the present application, the target phase shift angle calculation module 303 comprises:

[0136] An initialization unit, configured to initialize the phase shift angle of each sub-module;

[0137] A calculation unit, configured to change the phase angle in two iteration directions of increment and decrement with a preset step phase angle for each sub-module, and calculate the function value of the first current harmonic function corresponding to the two iteration directions at each iteration;

[0138] An iteration direction determination unit, configured to take the iteration direction corresponding to the smaller one of the function values of the first current harmonic function corresponding to the two iteration directions as the target iteration direction at this iteration;

[0139] A judgment unit, configured to judge whether the difference between the function value of the first current harmonic function corresponding to the target iteration direction and the function value of the first current harmonic function at the previous iteration is less than a maximum iteration difference;

[0140] A return execution unit, configured to return to execute the changing of the phase angle in two iteration directions of increment and decrement with a preset step phase angle and the calculation of the function value of the first current harmonic function corresponding to the two iteration directions at each iteration when the difference between the function value of the first current harmonic function corresponding to the target iteration direction and the function value of the first current harmonic function at the previous iteration is greater than or equal to the maximum iteration difference;

[0141] The iteration termination unit is configured to stop the iteration when a difference between the function value of the first-order current harmonic function corresponding to the target iteration direction and a function value of the first-order current harmonic function of a previous iteration is less than a maximum iteration difference, and the phase-shifting angle of each of the sub-modules in the current iteration is taken as a target phase-shifting angle.

[0142] In some embodiments of the present application, the maximum iteration difference is a maximum value of a difference between the function values of the first-order current harmonic function in two adjacent iterations, and the device further comprises:

[0143] The maximum iteration difference updating module is configured to update the maximum iteration difference continuously during the iteration.

[0144] The first-order current harmonic elimination device of the modular multilevel DC converter can execute the first-order current harmonic elimination method of the modular multilevel DC converter provided by any of the embodiments of the present application, and has the corresponding functional modules and beneficial effects of executing the first-order current harmonic elimination method of the modular multilevel DC converter.

[0145] Embodiment three

[0146] The embodiment three of the present application provides a computer device, Figure 3 A structural schematic diagram of the computer device provided by the embodiment three of the present application is shown in the figure, Figure 3 The computer device includes a processor 301, a memory 302, a communication module 303, an input device 304 and an output device 305; the number of the processors 301 in the computer device can be one or more, Figure 3 and the processor 301 in the computer device is taken as an example; the processor 301, the memory 302, the communication module 303, the input device 304 and the output device 305 in the computer device can be connected through a bus or other ways, Figure 3 and the connection through the bus is taken as an example. The processor 301, the memory 302, the communication module 303, the input device 304 and the output device 305 can be integrated on a control mainboard of the computer device.

[0147] The memory 302 is a computer readable storage medium, which can be used to store software programs, computer executable programs and modules, such as the module corresponding to the first-order current harmonic elimination method of the modular multilevel DC converter in the embodiment. The processor 301 executes the software programs, instructions and modules stored in the memory 302, thereby executing various functional applications and data processing of the computer device, that is, implementing the first-order current harmonic elimination method of the modular multilevel DC converter provided by the above-mentioned embodiments.

[0148] The memory 302 can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system and application programs required by at least one function; and the data storage area can store data created according to the use of the computer device, etc. In addition, the memory 302 can include a high-speed random access memory, and can also include a non-volatile memory, such as at least one magnetic disk storage device, a flash memory device, or other non-volatile solid-state memory device. In some examples, the memory 302 can further include a memory remotely arranged with respect to the processor 301, which can be connected to the computer device through a network. Examples of the above network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and a combination thereof.

[0149] The communication module 303 is configured to establish a connection with an external device (for example, a smart terminal) and to realize data interaction with the external device. The input device 304 can be configured to receive input digital or character information, and to generate key signal input related to user settings and function control of the computer device.

[0150] The computer device provided in the embodiment can execute the primary current harmonic elimination method of the modular multilevel DC converter provided in any of the above embodiments of the application, and specific corresponding functions and advantages.

[0151] Embodiment four

[0152] The embodiment four of the application provides a storage medium containing computer executable instructions, and the computer program is stored on the storage medium. When the program is executed by a processor, the primary current harmonic elimination method of the modular multilevel DC converter provided in any of the above embodiments of the application is realized. The method comprises the following steps:

[0153] obtaining the transmission power of the sub-modules, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side in the current control period;

[0154] constructing a primary current harmonic function with the phase shift angle of each sub-module as a variable based on the transmission power of the sub-modules, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side;

[0155] calculating the phase shift angle of each sub-module that makes the primary current harmonic of the primary current harmonic function as a target phase shift angle;

[0156] setting the sub-modules to operate according to the corresponding target phase shift angle in the next control period.

[0157] Of course, the computer executable instructions of the storage medium provided in the embodiment of the application are not limited to the method operations described above, but can also perform related operations in the primary current harmonic elimination method of the modular multilevel DC converter provided in the embodiment of the application.

[0158] It should be noted that the apparatus, device and storage medium embodiments are basically similar to the method embodiments, and thus are described simply, and the relevant parts are described in the method embodiment.

[0159] From the above description of the embodiments, those skilled in the art can clearly understand that the present application can be implemented by means of software and necessary universal hardware, and of course can also be implemented by hardware, but in many cases the former is a better embodiment. Based on this understanding, the technical solutions of the present application can be embodied in the form of a software product, which can be stored in a computer readable storage medium, such as a floppy disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a FLASH, a hard disk, or an optical disc, etc., and includes a number of instructions to make a computer device (which can be a robot, a personal computer, a server, or a network device, etc.) execute the current harmonic elimination method of the modular multilevel direct current converter described in any embodiment of the present application.

[0160] It should be noted that the above apparatus includes various modules and units, which are only divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be realized; in addition, the specific names of the functional units are only for easy distinction, and do not limit the protection scope of the present application.

[0161] It should be understood that the parts of the present application can be realized by hardware, software, firmware or their combination. In the above embodiments, the plurality of steps or methods can be realized by software or firmware stored in the memory and executed by the appropriate instruction execution device. For example, if realized by hardware, and as in another embodiment, it can be realized by any one or their combination of the following technologies known in the art: discrete logic circuit with logic gate circuit for implementing logic function on data signal, application specific integrated circuit with appropriate combination logic gate circuit, programmable gate array (PGA), field programmable gate array (FPGA), etc.

[0162] In the description of the present application, reference can be made to terms such as "one embodiment", "some embodiments", "an example", "a specific example" or "some examples" etc. It is to be understood that such terms are merely used to describe a particular feature, structure, material or characteristic under discussion. Therefore, in no way do these terms limit the scope of the present application to the particular embodiment describing these terms. Further, the use of these terms does not imply that any feature, structure, material or characteristic is essential to the present application.

[0163] Note that the above merely describes preferred embodiments of the present application and the applied technical principles. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and that various obvious changes, modifications and substitutions can be made thereto without departing from the scope of the present application. Therefore, although the present application has been described in detail through the above embodiments, the present application is not limited to the above embodiments, and can include more other equivalent embodiments without departing from the concept of the present application, and the scope of the present application is determined by the scope of the claims.

Claims

1. A method for eliminating primary current harmonics of a modular multilevel DC converter, characterized in that, The modular multi-level direct current converter comprises a plurality of sub-modules, and the method comprises: obtaining transmission power of the sub-modules, direct current side voltage of the low voltage side and direct current side voltage of the high voltage side in the current control period; constructing a first current harmonic function with the phase shift angle of each sub-module as a variable based on the transmission power of the sub-modules, the direct current side voltage of the low voltage side and the direct current side voltage of the high voltage side; calculating the phase shift angle of each sub-module that makes the first current harmonic of the first current harmonic function minimum as a target phase shift angle; setting the sub-modules to operate according to the corresponding target phase shift angle in the next control period.

2. The method of claim 1, wherein, The step of constructing the first current harmonic function with the phase shift angle of each sub-module as a variable based on the transmission power of the sub-modules, the direct current side voltage of the low voltage side and the direct current side voltage of the high voltage side comprises: calculating the duty ratio of the sub-modules based on the transmission power of the sub-modules, the direct current side voltage of the low voltage side and the direct current side voltage of the high voltage side; calculating the first current harmonic coefficient of the sub-modules based on the duty ratio of the sub-modules; calculating the product of the first current harmonic coefficient of the sub-modules and the phase shift angle of the sub-modules with the phase shift angle of the sub-modules as a variable, and taking the sum of the product of the first current harmonic coefficient of each sub-module and the phase shift angle of the sub-module as the first current harmonic function with the phase shift angle of each sub-module as a variable.

3. The method of claim 2, wherein the method is implemented in a modular multilevel DC converter. The calculation formula of the step of calculating the duty ratio of the sub-modules based on the transmission power of the sub-modules, the direct current side voltage of the low voltage side and the direct current side voltage of the high voltage side is as follows: where D k is the duty ratio of the kth submodule, V G is the DC side voltage of the high voltage side, V dck is the DC side voltage of the low voltage side, P k is the transmission power of the kth submodule, P i is the transmission power of the ith submodule, and N is the total number of submodules.

4. The method of claim 3, wherein the method is applied to a modular multilevel DC converter. The calculation formula of the step of calculating the first current harmonic coefficient of the sub-modules based on the duty ratio of the sub-modules is as follows: wherein, is the kth sub-module of a current harmonic coefficient.

5. The method of claim 4, wherein the one-cycle current harmonic elimination method is a method of a modular multilevel DC converter, characterized by, The step of calculating the product of the first current harmonic coefficient of the sub-modules and the phase shift angle of the sub-modules with the phase shift angle of the sub-modules as a variable, and taking the sum of the product of the first current harmonic coefficient of each sub-module and the phase shift angle of the sub-module as the first current harmonic function with the phase shift angle of each sub-module as a variable is as follows: wherein, is a first order current harmonic function of the phase shift angle of each of the submodules, φ k is the phase shift angle of the kth submodule.

6. The method of claim 1-5, wherein, The step of calculating the phase shift angle of each sub-module that makes the first current harmonic of the first current harmonic function minimum as a target phase shift angle comprises: initializing the phase shift angle of each sub-module; for each sub-module, changing the phase angle according to two iteration directions of increment and decrement with a preset step phase angle, and calculating the function value of the first current harmonic function corresponding to the two iteration directions at each iteration; taking the iteration direction corresponding to the smaller one of the function values of the first current harmonic function in the two iteration directions as the target iteration direction at this iteration; judging whether the difference between the function value of the first current harmonic function corresponding to the target iteration direction and the function value of the first current harmonic function at the previous iteration is less than a maximum iteration difference; if not, returning to perform the step of changing the phase angle according to two iteration directions of increment and decrement with a preset step phase angle, and calculating the function value of the first current harmonic function corresponding to the two iteration directions at each iteration; if yes, stopping iteration and taking the phase shift angle of each sub-module at this iteration as the target phase shift angle.

7. The method of claim 6, wherein the one-cycle current harmonic elimination method is a method of a modular multilevel DC converter, characterized in that, a maximum iteration difference is a maximum value of differences between function values of the first current harmonic function in two adjacent iterations, and the method further comprises: updating the maximum iteration difference in the iteration process.

8. A device for eliminating primary current harmonics of a modular multilevel DC converter, characterized in that comprise: a data acquisition module, configured to acquire transmission power of a sub-module, DC side voltage of a low-voltage side and DC side voltage of a high-voltage side in a current control period; a function construction module, configured to construct a first current harmonic function with phase-shifting angles of each sub-module as variables based on the transmission power of the sub-module, the DC side voltage of the low-voltage side and the DC side voltage of the high-voltage side; a target phase-shifting angle calculation module, configured to calculate the phase-shifting angle of each sub-module that makes a first current harmonic of the first current harmonic function minimum as a target phase-shifting angle; a running module, configured to set the sub-modules to run according to corresponding target phase-shifting angles in a next control period.

9. A computer device, comprising: comprise: one or more processors; a storage device configured to store one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors are caused to implement the first current harmonic elimination method of the modular multilevel DC converter as claimed in any one of claims 1-7.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The program is executed by the processor to implement the first current harmonic elimination method of the modular multilevel DC converter as claimed in any one of claims 1-7.

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