CN114448220A - Method, device and equipment for eliminating primary current harmonic of modular multilevel DC converter and storage medium - Google Patents
Method, device and equipment for eliminating primary current harmonic of modular multilevel DC converter and storage medium Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
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Abstract
The invention discloses a method, a device, equipment and a storage medium for eliminating primary current harmonic waves of a modular multilevel DC converter. The method comprises the steps of constructing a primary current harmonic function with phase shift angles of submodules as variables based on transmission power of the submodules, direct current side voltage of a low-voltage side and direct current side voltage of a high-voltage side, calculating the phase shift angle of each submodule which enables the primary current harmonic of the primary current harmonic function to be minimum as a target phase shift angle, setting the submodules to operate according to the corresponding target phase shift angle in the next control period, and selecting the optimal phase shift angle combination by changing the phase shift angle combination of each submodule and carrying out continuous iterative calculation and comparing the primary current harmonic sizes of converters with different phase shift angles, so that the purpose of reducing the primary current harmonic is achieved, the size of a filter reactor can be reduced, and the cost of a power grid system is reduced.
Description
Technical Field
The present invention relates to harmonic cancellation technologies, and in particular, to a method, an apparatus, a device, and a storage medium for cancelling primary current harmonics of a modular multilevel dc converter.
Background
The Modular Multilevel Converter (MMC) is formed by cascading a plurality of Sub-modules (SM) with the same structure. Compared with the traditional multi-level converter, the MMC has the characteristics of small switching loss, high output waveform quality, strong fault processing capacity, easiness in capacity expansion, capability of running in four quadrants and the like, so that the MMC becomes a research focus of a direct-current power grid.
In each control cycle, a modular multilevel DC-DC converter (i.e., an MMC-type DC-DC converter) needs to calculate a phase shift angle of each sub-module of the control cycle, and then inputs a corresponding control signal based on the phase shift angle of each sub-module to control each sub-module to work. The existing method for calculating the phase shift angle is not accurate enough, so that the primary current harmonic wave of the high-voltage side of the modular multilevel DC converter is larger, a large filter reactor needs to be additionally arranged on the high-voltage side to filter the primary current harmonic wave, and the cost of a power grid system is undoubtedly increased.
Disclosure of Invention
The invention provides a method, a device, equipment and a storage medium for eliminating primary current harmonic of a modular multilevel DC converter, which are used for achieving the purpose of reducing the primary current harmonic, so that the size of a filter reactor can be reduced, and the cost of a power grid system can be reduced.
In a first aspect, the present invention provides a method for eliminating a primary current harmonic in a modular multilevel dc converter, the modular multilevel dc converter including a plurality of sub-modules, the method comprising:
acquiring the transmission power of the submodule, the direct current side voltage of a low-voltage side and the direct current side voltage of a high-voltage side in the control period;
constructing a primary current harmonic function with a phase shift angle of each submodule as a variable on the basis of the transmission power of the submodules, the direct current side voltage of a low-voltage side and the direct current side voltage of a high-voltage side;
calculating a phase shift angle of each sub-module which minimizes a primary current harmonic of the primary current harmonic function as a target phase shift angle;
and setting the submodule to operate according to the corresponding target phase shifting angle in the next control period.
Optionally, constructing a first current harmonic function with a phase shift angle of each sub-module as a variable based on the transmission power of the sub-modules, the dc-side voltage at the low-voltage side, and the dc-side voltage at the high-voltage side, includes:
calculating the duty ratio of the submodule based on the transmission power of the submodule, the direct current side voltage of the low-voltage side and the direct current side voltage of the high-voltage side;
calculating a first current harmonic coefficient of the sub-module based on the duty cycle of the sub-module;
and taking the phase shift angle of the sub-modules as a variable, calculating the product of the primary current harmonic coefficient of the sub-modules and the phase shift angle of the sub-modules, and taking the sum of the products of the primary current harmonic coefficient of each sub-module and the phase shift angle of the sub-modules as a primary current harmonic function taking the phase shift angle of each sub-module as the variable.
Optionally, a calculation formula for calculating the duty ratio 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:
wherein D iskIs the duty cycle of the kth sub-module, VGIs the DC side voltage of the high side, VdckIs a DC side voltage of the low side, PkIs the transmission power of the kth sub-module, PiAnd N is the total number of the submodules.
Optionally, a calculation formula for calculating the first current harmonic coefficient of the sub-module based on the duty ratio of the sub-module is as follows:
wherein,
is the first current harmonic coefficient of the kth sub-module.
Optionally, taking the phase shift angle of the sub-modules as a variable, calculating a product of a primary current harmonic coefficient of the sub-modules and the phase shift angle of the sub-modules, and taking a sum of the products of the primary current harmonic coefficient of each sub-module and the phase shift angle of the sub-module as a primary current harmonic function taking the phase shift angle of each sub-module as the variable, as follows:
wherein, Vc 1(φ1，…，φN) Is a first harmonic function of current, phi, with the phase shift angle of each of the sub-modules as a variablekIs the phase shift angle of the kth sub-module.
Optionally, calculating a phase shift angle of each sub-module that minimizes a primary current harmonic of the primary current harmonic function as a target phase shift angle includes:
initializing a phase shift angle of each sub-module;
aiming at each sub-module, changing the phase angle according to two iteration directions of increasing and decreasing by a preset stepping phase angle, and calculating function values of the primary current harmonic function corresponding to the two iteration directions in each iteration;
taking the iteration direction corresponding to the smaller value of the function values of the primary current harmonic function corresponding to the two iteration directions as the target iteration direction in the current iteration;
judging whether the difference value between the function value of the primary current harmonic function corresponding to the target iteration direction and the function value of the primary current harmonic function of the previous iteration is smaller than the maximum iteration difference value or not;
if not, returning to execute the preset stepping phase angle, changing the phase angle according to two iteration directions of increasing and decreasing, and calculating the function value of the primary current harmonic function corresponding to the two iteration directions during each iteration;
if so, stopping iteration, and taking the phase shift angle of each sub-module of the iteration as a target phase shift angle.
Optionally, the maximum iteration difference is a maximum value of a difference of function values of the first current harmonic function of two adjacent iterations, and the method further includes:
and continuously updating the maximum iteration difference value in the iteration process.
In a second aspect, the present invention also provides a primary current harmonic elimination apparatus for a modular multilevel dc converter, including:
the data acquisition module is used for acquiring the transmission power of the submodule, the direct current side voltage of the low-voltage side and the direct current side voltage of the high-voltage side in the control period;
the function building module is used for building a primary current harmonic function with the phase shift angle of each submodule as a variable on the basis of the transmission power of the submodules, the direct-current side voltage of the low-voltage side and the direct-current side voltage of the high-voltage side;
a target phase shift angle calculation module for calculating the phase shift angle of each sub-module which minimizes the primary current harmonic of the primary current harmonic function as a target phase shift angle;
and the operation module is used for setting the sub-modules to operate according to the corresponding target phase shift angle in the next control period.
Optionally, the function building module includes:
a duty ratio calculation unit for calculating a duty ratio 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;
the harmonic coefficient calculation unit is used for calculating a primary current harmonic coefficient of the submodule based on the duty ratio of the submodule;
and the function construction unit is used for calculating the product of the primary current harmonic coefficient of the submodule and the phase shift angle of the submodule by taking the phase shift angle of the submodule as a variable, and taking the sum of the product of the primary current harmonic coefficient of each submodule and the phase shift angle of the submodule as a primary current harmonic function by taking the phase shift angle of each submodule as a variable.
Optionally, the duty ratio calculating unit has the following calculation formula:
wherein D iskIs the duty cycle of the kth sub-module, VGIs the DC side voltage of the high side, VdckIs a DC side voltage of the low side, PkIs the transmission power of the kth sub-module, PiAnd N is the total number of the submodules.
Optionally, the calculation formula of the harmonic coefficient calculation unit is as follows:
wherein,
is the first current harmonic coefficient of the kth sub-module.
Optionally, the first current harmonic function constructed by the function construction unit is as follows:
wherein, Vc 1(φ1，…，φN) Is a first harmonic function of current, phi, with the phase shift angle of each of the sub-modules as a variablekIs the phase shift angle of the k-th sub-module.
Optionally, the target phase shift angle calculating module includes:
the initialization unit is used for initializing the phase shifting angle of each sub-module;
the calculation unit is used for changing the phase angle according to two iteration directions of increasing and decreasing by a preset stepping phase angle for each sub-module, and calculating function values of the primary current harmonic function corresponding to the two iteration directions during each iteration;
the iteration direction determining unit is used for taking the iteration direction corresponding to the smaller value of the function values of the primary current harmonic function corresponding to the two iteration directions as the target iteration direction in the current iteration;
a judging unit, configured to judge whether a difference between a function value of the primary current harmonic function corresponding to the target iteration direction and a function value of the primary current harmonic function of a previous iteration is smaller than a maximum iteration difference;
a return execution unit, configured to, when a difference between the function value of the primary current harmonic function corresponding to the target iteration direction and the function value of the primary current harmonic function of the previous iteration is greater than or equal to a maximum iteration difference, return to execution to change the phase angle by a preset step phase angle according to two iteration directions of increasing and decreasing, and calculate the function values of the primary current harmonic function corresponding to the two iteration directions at each iteration;
and the iteration termination unit is used for stopping iteration when the difference value between the function value of the primary current harmonic function corresponding to the target iteration direction and the function value of the primary current harmonic function of the previous iteration is smaller than the maximum iteration difference value, and taking the phase shift angle of each submodule of the current iteration as a target phase shift angle.
Optionally, the maximum iteration difference is a maximum value of a difference between function values of the first current harmonic function of two adjacent iterations, and the apparatus further includes:
and the maximum iteration difference value updating module is used for continuously updating the maximum iteration difference value in the iteration process.
In a third aspect, the present invention also provides a computer device, comprising:
one or more processors;
storage means for storing one or more programs;
when the one or more programs are executed by the one or more processors, the one or more processors implement the method for first harmonic cancellation of current in a modular multilevel dc converter as provided by the first aspect of the present invention.
In a fourth aspect, the present invention also provides a computer readable storage medium having stored thereon a computer program which, when executed by a processor, implements the first order harmonic cancellation method of a modular multilevel dc converter as provided in the first aspect of the present invention.
The invention provides a method for eliminating primary current harmonic waves of a modular multilevel DC converter, which comprises the following steps: the method comprises the steps of obtaining transmission power of submodules, direct current side voltage of a low-voltage side and direct current side voltage of a high-voltage side in a control period, constructing a primary current harmonic function with a phase shift angle of each submodule as a variable based on the transmission power of the submodules, 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 submodule which enables primary current harmonic of the primary current harmonic function to be minimum as a target phase shift angle, setting the submodules to operate according to the corresponding target phase shift angle in the next control period, and comparing the primary current harmonic of converters at different phase shift angles through changing the phase shift angle combination of each submodule and carrying out continuous iterative calculation so as to select the optimal phase shift angle combination, thereby achieving the purpose of reducing the primary current harmonic, further reducing the size of a filter reactor and reducing the cost of a power grid system.
Drawings
Fig. 1A is a flowchart of a first current harmonic cancellation method of a modular multilevel dc converter according to an embodiment of the present invention;
fig. 1B is a schematic structural diagram of a modular multilevel dc converter according to an embodiment of the present invention;
fig. 1C is a schematic structural diagram of a sub-module according to an embodiment of the present invention;
fig. 1D is a waveform diagram of primary current harmonics of a prior art modular multi-level-dc converter;
FIG. 1E is a waveform diagram of the first harmonic of the modular multilevel DC converter of the present invention;
fig. 2 is a schematic structural diagram of a primary current harmonic elimination apparatus of a modular multilevel dc converter according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a computer device according to a third embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Example one
Fig. 1A is a flowchart of a method for eliminating a primary current harmonic in a modular multilevel dc converter according to an embodiment of the present invention, where the present embodiment is applicable to a situation of eliminating a primary current harmonic in a modular multilevel dc converter, and the method may be performed by an apparatus for eliminating a primary current harmonic in a modular multilevel dc converter according to an embodiment of the present invention, where the apparatus may be implemented by software and/or hardware, and is generally configured in a computer device, as shown in fig. 1A, where the method specifically includes the following steps:
s101, acquiring transmission power of a submodule, direct current side voltage of a low-voltage side and direct current side voltage of a high-voltage side in the control period.
Fig. 1B is a schematic structural diagram of a modular multilevel dc converter according to an embodiment of the present invention, and exemplarily, as shown in fig. 1B, the modular multilevel dc converter includes an input side, an output side, and a unidirectional ac transformer T, and the input side and the output side are connected through the unidirectional ac transformer T. The input side comprises two bridge arms, and likewise, the output side comprises two bridge arms. Each bridge arm is composed of a plurality of sub-modules (SM) which are connected with each other and have the same structure. The unidirectional alternating current transformer T is used for providing a conversion reactance, improving the transformation ratio of the converter and playing a role of 'electrical isolation'.
Fig. 1C is a schematic structural diagram of a sub-module according to an embodiment of the present invention, and exemplarily, as shown in fig. 1C, each sub-module includes a half-bridge circuit composed of two IGBTs as switching units and an LC filter circuit. U shapeSMFor outputting voltage, U, to ports of submodulesINFor the port input voltage, U, of the submoduleCIs the capacitor voltage of the submodule. Each submodule is a two-terminal element, and the submodule outputs a voltage U by controlling the turn-on and turn-off of VT1 and VT2SMCan alternately output the capacitor voltage U under the condition of 2 current directionsCAnd 0. Taking the upper bridge arm on the high-voltage side of the converter as an example, the total number of the N sub-modules is N, and the total voltage output by the N sub-modules can be equivalent to a controllable voltage source. If the number of the submodules of the bridge arm is enough, the input and the output of each submodule are controlled in each control period, and the voltages with various waveforms can be output.
It should be noted that the specific structure of the above modular multilevel dc converter and sub-module is an exemplary illustration of an embodiment of the present invention, and in other embodiments of the present invention, different structures may be adopted, and the embodiment of the present invention is not limited herein.
In the embodiment of the invention, the transmission power of the submodule, the direct current side voltage of the low-voltage side and the direct current side voltage of the high-voltage side in the control period are obtained. Wherein, the transmission power of the sub-module refers to the ratio of the output power of the sub-module to the input power. The direct current side voltage of the low-voltage side refers to the direct current voltage of the output end of the submodule, and the direct current side voltage of the high-voltage side refers to the direct current voltage of the input end of the submodule.
S102, constructing a primary current harmonic function with the phase shift angle of each submodule as a variable based on the transmission power of the submodules, the direct current side voltage of the low-voltage side and the direct current side voltage of the high-voltage side.
In the embodiment of the invention, after 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 are obtained, the primary current harmonic function with the phase shift angle of each sub-module as a variable is constructed on the basis of 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.
Illustratively, in some embodiments of the present invention, the step S102 includes:
1. and calculating the duty ratio of the submodule based on the transmission power of the submodule, the direct current side voltage of the low-voltage side and the direct current side voltage of the high-voltage side.
For example, the calculation formula for calculating the duty ratio 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:
wherein D iskIs the duty cycle of the kth sub-module, VGIs the DC side voltage of the high side, VdckIs a DC side voltage of the low side, PkIs the transmission power of the kth sub-module, PiN is the total number of submodules.
2. And calculating the primary current harmonic coefficient of the submodule based on the duty ratio of the submodule.
For example, the calculation formula for calculating the harmonic coefficient of the primary current of the submodule based on the duty ratio of the submodule is as follows:
wherein,
is the first current harmonic coefficient of the kth sub-module.
3. And taking the phase shift angle of the submodule as a variable, calculating the product of the primary current harmonic coefficient of the submodule and the phase shift angle of the submodule, and taking the sum of the products of the primary current harmonic coefficient of each submodule and the phase shift angle of the submodule as a primary current harmonic function taking the phase shift angle of each submodule as the variable.
For example, the first order current harmonic function may be expressed as:
wherein, Vc 1(φ1，…，φN) Is a first harmonic function of current with the phase shift angle of each submodule as a variablekIs the phase shift angle of the kth sub-module.
S103, calculating phase shift angles of all sub-modules which enable the primary current harmonic of the primary current harmonic function to be minimum as target phase shift angles.
In order to effectively reduce or even eliminate the primary current harmonic and reduce the size and weight of the filter reactor, in the embodiment of the invention, the phase shift angle of each submodule, which minimizes the primary current harmonic of the primary current harmonic function, is used as a target phase angle by taking the phase shift angle of each submodule as a variable. I.e. setting the objective function to g (phi)1,…,φN)：
The objective function means that the phase shift angle of the first sub-module is set as the reference phase shift angle and then the appropriate phase shift angle combination (phi) is selected1,…,φN) So as to minimize the amplitude of the first harmonic of the current of the DC-DC converter, and the above-mentioned selection process is performed by iterative calculations.
Illustratively, the above iterative process is as follows:
1. initializing the phase shift angle of each submodule, and setting the change value of each phase shift angle, namely the stepping phase shift angle delta phi, the interval time of two adjacent iterations, and the maximum iteration difference value Emax。
2. And aiming at each sub-module, changing the phase angle according to two iteration directions of increasing and decreasing by a preset stepping phase angle, and calculating a function value of a primary current harmonic function corresponding to the two iteration directions during each iteration.
In the above iterative calculation, two iteration directions may be (phi)1,…,φk+Δφ,…,φN) May also be (phi)1,…,φk-Δφ,…,φN). When choosing the iteration direction, the first current harmonics Ep (corresponding to an increase Δ Φ) and En (corresponding to a decrease Δ Φ) in both iteration directions should first be determined and calculated, which can be expressed in particular as:
3. and taking the iteration direction corresponding to the smaller value of the function values of the primary current harmonic functions corresponding to the two iteration directions as the target iteration direction in the current iteration.
Illustratively, if the first current harmonics of both satisfy Ep<En, the reference phase shift angle calculated in this iteration should be selected as (phi)1,…,φk+Δφ,…,φN) (ii) a On the contrary, the reference phase shift angle calculated in the current iteration should be selected as (phi)1,…,φk-Δφ,…,φN)。
4. And judging whether the difference value between the function value of the primary current harmonic function corresponding to the target iteration direction and the function value of the primary current harmonic function of the previous iteration is smaller than the maximum iteration difference value.
After the target iteration direction is determined, calculating a function value of a primary current harmonic function obtained by iteration according to the target iteration direction, calculating a difference value between the function value of the primary current harmonic function obtained by iteration and the function value of the primary current harmonic function obtained by previous iteration, and judging whether the difference value is smaller than a maximum iteration difference value E or notmax。
Illustratively, in some embodiments of the invention, the maximum iteration difference EmaxThe maximum value of the first current harmonic in the iterative process can be selected and updated continuously, which can be expressed as:
Emax＝||Vc 1(φ1，…，φN)||max
5. if not, returning to execute the preset stepping phase angle, changing the phase angle according to the two iteration directions of increasing and decreasing, and calculating the function value of the primary current harmonic function corresponding to the two iteration directions in each iteration.
6. If so, stopping iteration, and taking the phase shift angle of each submodule of the iteration as a target phase shift angle.
And S104, setting the submodule to operate according to the corresponding target phase shifting angle in the next control period.
And setting the sub-modules to operate according to the corresponding target phase shift angle in the next control period, so that the primary current harmonic minimization of the modular multilevel DC converter can be realized.
Fig. 1D is a waveform diagram of a primary current harmonic of a conventional modular multilevel dc converter, and fig. 1E is a waveform diagram of a primary current harmonic of a modular multilevel dc converter according to the present invention, and as can be seen from fig. 1D and fig. 1E, after the method for eliminating a primary current harmonic of a modular multilevel dc converter according to an embodiment of the present invention is adopted, an amplitude of a primary current harmonic in a power grid is significantly reduced.
The method for eliminating the primary current harmonic of the modular multilevel DC converter provided by the embodiment of the invention comprises the following steps: the method comprises the steps of obtaining transmission power of submodules, direct current side voltage of a low-voltage side and direct current side voltage of a high-voltage side in a control period, constructing a primary current harmonic function with a phase shift angle of each submodule as a variable based on the transmission power of the submodules, 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 submodule which enables primary current harmonic of the primary current harmonic function to be minimum as a target phase shift angle, setting the submodules to operate according to the corresponding target phase shift angle in the next control period, and comparing the primary current harmonic of converters at different phase shift angles through changing the phase shift angle combination of each submodule and carrying out continuous iterative calculation so as to select the optimal phase shift angle combination, thereby achieving the purpose of reducing the primary current harmonic, further reducing the size of a filter reactor and reducing the cost of a power grid system.
Example two
An embodiment of the present invention provides a primary current harmonic cancellation device for a modular multilevel dc converter, and fig. 2 is a schematic structural diagram of the primary current harmonic cancellation device for the modular multilevel dc converter according to the embodiment of the present invention, as shown in fig. 2, the device includes:
a data obtaining module 201, configured to obtain transmission power of the sub-module, a dc side voltage at a low voltage side, and a dc side voltage at a high voltage side in the current control period;
a function constructing module 202, configured to construct a first-order current harmonic function with a 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 at the low-voltage side, and the dc-side voltage at the high-voltage side;
a target phase shift angle calculation module 203, configured to calculate a phase shift angle of each sub-module that minimizes a primary current harmonic of the primary current harmonic function as a target phase shift angle;
and the operation module 204 is configured to set the sub-modules to operate according to the corresponding target phase shift angle in the next control period.
In some embodiments of the present invention, function building module 202 comprises:
a duty ratio calculation unit for calculating a duty ratio 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;
the harmonic coefficient calculation unit is used for calculating a primary current harmonic coefficient of the submodule based on the duty ratio of the submodule;
and the function construction unit is used for calculating the product of the primary current harmonic coefficient of the sub-modules and the phase shift angle of the sub-modules by taking the phase shift angle of the sub-modules as a variable, and taking the sum of the products of the primary current harmonic coefficient of each sub-module and the phase shift angle of the sub-modules as a primary current harmonic function taking the phase shift angle of each sub-module as a variable.
In some embodiments of the present invention, the calculation formula of the duty ratio calculation unit is as follows:
wherein D iskIs the duty cycle of the kth sub-module, VGIs the DC side voltage of the high side, VdckIs a DC side voltage of the low side, PkIs the transmission power of the kth sub-module, PiAnd N is the total number of the submodules.
In some embodiments of the present invention, the calculation formula of the harmonic coefficient calculation unit is as follows:
wherein,
is the first current harmonic coefficient of the kth sub-module.
In some embodiments of the invention, the first current harmonic function constructed by the function construction unit is as follows:
wherein, Vc 1(φ1，…，φN) Is a first harmonic function of current, phi, with the phase shift angle of each of the sub-modules as a variablekIs the phase shift angle of the kth sub-module.
In some embodiments of the present invention, target phase shift angle calculation module 303 comprises:
the initialization unit is used for initializing the phase shifting angle of each submodule;
the calculation unit is used for changing the phase angle according to two iteration directions of increasing and decreasing by a preset stepping phase angle for each sub-module, and calculating function values of the primary current harmonic function corresponding to the two iteration directions during each iteration;
the iteration direction determining unit is used for taking the iteration direction corresponding to the smaller value of the function values of the primary current harmonic function corresponding to the two iteration directions as the target iteration direction in the current iteration;
a judging unit, configured to judge whether a difference between a function value of the primary current harmonic function corresponding to the target iteration direction and a function value of the primary current harmonic function of a previous iteration is smaller than a maximum iteration difference;
a return execution unit, configured to, when a difference between the function value of the primary current harmonic function corresponding to the target iteration direction and the function value of the primary current harmonic function of the previous iteration is greater than or equal to a maximum iteration difference, return to execution to change the phase angle by a preset step phase angle according to two iteration directions of increasing and decreasing, and calculate the function values of the primary current harmonic function corresponding to the two iteration directions at each iteration;
and the iteration termination unit is used for stopping iteration when the difference value between the function value of the primary current harmonic function corresponding to the target iteration direction and the function value of the primary current harmonic function of the previous iteration is smaller than the maximum iteration difference value, and taking the phase shift angle of each submodule of the current iteration as a target phase shift angle.
In some embodiments of the invention, the maximum iteration difference is a maximum of a difference of function values of the first current harmonic function of two adjacent iterations, the apparatus further comprises:
and the maximum iteration difference value updating module is used for continuously updating the maximum iteration difference value in the iteration process.
The primary current harmonic elimination device of the modular multilevel DC converter can execute the primary current harmonic elimination method of the modular multilevel DC converter provided by any embodiment of the invention, and has the corresponding functional modules and beneficial effects of executing the primary current harmonic elimination method of the modular multilevel DC converter.
EXAMPLE III
A third embodiment of the present invention provides a computer device, and fig. 3 is a schematic structural diagram of a computer device provided in the third embodiment of the present invention, as shown in fig. 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 may be one or more, and one processor 301 is taken as an example in fig. 3; the processor 301, the memory 302, the communication module 303, the input device 304 and the output device 305 in the computer apparatus may be connected by a bus or other means, and fig. 3 illustrates an example of connection by a bus. The processor 301, the memory 302, the communication module 303, the input device 304 and the output device 305 may be integrated on a control motherboard of the computer apparatus.
The memory 302 is a computer-readable storage medium, and can be used for storing software programs, computer-executable programs, and modules, such as the modules corresponding to the first harmonic elimination method of the modular multilevel dc converter in the present embodiment. The processor 301 executes various functional applications and data processing of the computer device by executing the software programs, instructions and modules stored in the memory 302, namely, implements the first-order current harmonic elimination method of the modular multilevel dc converter provided by the above-described embodiments.
The memory 302 may mainly include a program storage area and a data storage area, wherein the program storage area may store an operating system, an application program required for at least one function; the storage data area may store data created according to use of the computer device, and the like. Further, the memory 302 may include high speed random access memory, and may also include non-volatile memory, such as at least one magnetic disk storage device, flash memory device, or other non-volatile solid state storage device. In some examples, the memory 302 may further include memory located remotely from the processor 301, which may be connected to a computer device through a network. Examples of such networks include, but are not limited to, the internet, intranets, local area networks, mobile communication networks, and combinations thereof.
The communication module 303 is configured to establish a connection with an external device (e.g., an intelligent terminal), and implement data interaction with the external device. The input means 304 may be used to receive input numeric or character information and to generate key signal inputs relating to user settings and function controls of the computer device.
The present embodiment provides a computer device, which can perform the method for eliminating a primary current harmonic of a modular multilevel dc converter according to any of the above embodiments of the present invention, and its corresponding functions and advantages.
Example four
A fourth embodiment of the present invention provides a storage medium containing computer-executable instructions, where the storage medium stores a computer program, and the computer program, when executed by a processor, implements a first-order current harmonic cancellation method for a modular multilevel dc converter according to any of the above embodiments of the present invention, where the method includes:
acquiring the transmission power of the submodule, the direct current side voltage of a low-voltage side and the direct current side voltage of a high-voltage side in the control period;
constructing a primary current harmonic function with a phase shift angle of each submodule as a variable on the basis of the transmission power of the submodules, the direct current side voltage of a low-voltage side and the direct current side voltage of a high-voltage side;
calculating a phase shift angle of each sub-module which minimizes a primary current harmonic of the primary current harmonic function as a target phase shift angle;
and setting the sub-module to operate according to the corresponding target phase shifting angle in the next control period.
Of course, the storage medium containing the computer-executable instructions provided by the embodiments of the present invention is not limited to the method operations described above, and may also perform related operations in the primary current harmonic cancellation method of the modular multilevel dc converter provided by the embodiments of the present invention.
It should be noted that, as for the apparatus, the device and the storage medium embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and in relevant places, reference may be made to the partial description of the method embodiments.
From the above description of the embodiments, it is obvious for those skilled in the art that the present invention can be implemented by software and necessary general hardware, and certainly, can also be implemented by hardware, but the former is a better embodiment in many cases. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which may 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 Memory (FLASH), a hard disk or an optical disk of a computer, and includes instructions for enabling a computer device (which may be a robot, a personal computer, a server, or a network device) to execute the method for eliminating a first harmonic wave of a modular multilevel dc converter according to any embodiment of the present invention.
It should be noted that, in the above apparatus, each module and unit included in the apparatus is only divided according to functional logic, but is not limited to the above division as long as the corresponding function can be realized; in addition, specific names of the functional units are only for convenience of distinguishing from each other, and are not used for limiting the protection scope of the present invention.
It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the various steps or methods may be implemented in software or firmware stored in memory and executed by suitable instruction execution devices. For example, if implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
It is to be noted that the foregoing description is only exemplary of the invention and that the principles of the technology may be employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (10)
1. A method of primary current harmonic cancellation in a modular multilevel dc converter, the modular multilevel dc converter comprising a plurality of sub-modules, the method comprising:
acquiring the transmission power of the submodule, the direct current side voltage of a low-voltage side and the direct current side voltage of a high-voltage side in the control period;
constructing a primary current harmonic function with a phase shift angle of each submodule as a variable on the basis of the transmission power of the submodules, the direct current side voltage of a low-voltage side and the direct current side voltage of a high-voltage side;
calculating a phase shift angle of each sub-module which minimizes a primary current harmonic of the primary current harmonic function as a target phase shift angle;
and setting the sub-module to operate according to the corresponding target phase shifting angle in the next control period.
2. The method of harmonic cancellation of primary current of a modular multilevel dc converter according to claim 1, wherein constructing a primary current harmonic function with a phase shift angle of each of the submodules as a variable based on the transmission power of the submodules, the dc side voltage of the low voltage side and the dc side voltage of the high voltage side comprises:
calculating the duty ratio of the submodule based on the transmission power of the submodule, the direct current side voltage of the low-voltage side and the direct current side voltage of the high-voltage side;
calculating a first current harmonic coefficient of the sub-module based on the duty cycle of the sub-module;
and taking the phase shift angle of the sub-modules as a variable, calculating the product of the primary current harmonic coefficient of the sub-modules and the phase shift angle of the sub-modules, and taking the sum of the products of the primary current harmonic coefficient of each sub-module and the phase shift angle of the sub-modules as a primary current harmonic function taking the phase shift angle of each sub-module as the variable.
3. The method for eliminating the first harmonic of the modular multilevel converter according to claim 2, wherein the calculation formula for calculating the duty ratio of the submodule based on the transmission power of the submodule, the dc side voltage of the low voltage side and the dc side voltage of the high voltage side is as follows:
wherein D iskIs the duty cycle of the kth sub-module, VGIs a DC side voltage of the high side, VdckIs a DC side voltage of the low side, PkIs the transmission power of the kth sub-module, PiN is the total number of submodules.
4. The method for eliminating the primary current harmonic of the modular multilevel DC converter according to claim 3, wherein the calculation formula for calculating the primary current harmonic coefficient of the sub-module based on the duty ratio of the sub-module is as follows:
wherein,
is the first current harmonic coefficient of the kth sub-module.
5. The method of claim 4, wherein the product of the harmonic coefficient of the primary current of the sub-modules and the phase shift angle of the sub-modules is calculated with the phase shift angle of the sub-modules as a variable, and the sum of the product of the harmonic coefficient of the primary current of each sub-module and the phase shift angle of the sub-module is used as a harmonic function of the primary current with the phase shift angle of each sub-module as a variable, as follows:
wherein,
is a first harmonic function of current, phi, with the phase shift angle of each of the sub-modules as a variablekIs the phase shift angle of the k-th sub-module.
6. The method for primary current harmonic cancellation in a modular multilevel dc converter according to any of claims 1-5 wherein calculating the phase shift angle of each of the submodules that minimizes the primary current harmonic of the primary current harmonic function as a target phase shift angle comprises:
initializing a phase shift angle of each sub-module;
aiming at each sub-module, changing the phase angle according to two iteration directions of increasing and decreasing by a preset stepping phase angle, and calculating function values of the primary current harmonic function corresponding to the two iteration directions in each iteration;
taking the iteration direction corresponding to the smaller value of the function values of the primary current harmonic function corresponding to the two iteration directions as the target iteration direction in the current iteration;
judging whether the difference value between the function value of the primary current harmonic function corresponding to the target iteration direction and the function value of the primary current harmonic function of the previous iteration is smaller than the maximum iteration difference value or not;
if not, returning to execute the preset stepping phase angle, changing the phase angle according to two iteration directions of increasing and decreasing, and calculating the function value of the primary current harmonic function corresponding to the two iteration directions during each iteration;
if yes, stopping iteration, and taking the phase shift angle of each submodule of the iteration as a target phase shift angle.
7. The method of modular multilevel dc converter according to claim 6, wherein a maximum iteration difference is a maximum value of a difference of function values of the primary current harmonic function of two adjacent iterations, the method further comprising:
and continuously updating the maximum iteration difference value in the iteration process.
8. A primary current harmonic cancellation arrangement for a modular multilevel dc converter, comprising:
the data acquisition module is used for acquiring the transmission power of the submodule, the direct current side voltage of the low-voltage side and the direct current side voltage of the high-voltage side in the control period;
the function building module is used for building a primary current harmonic function with the phase shift angle of each submodule as a variable on the basis of the transmission power of the submodules, the direct-current side voltage of the low-voltage side and the direct-current side voltage of the high-voltage side;
a target phase shift angle calculation module for calculating the phase shift angle of each sub-module which minimizes the primary current harmonic of the primary current harmonic function as a target phase shift angle;
and the operation module is used for setting the sub-modules to operate according to the corresponding target phase shift angle in the next control period.
9. A computer device, comprising:
one or more processors;
storage means for storing one or more programs;
when executed by the one or more processors, cause the one or more processors to implement a method of primary current harmonic cancellation for a modular multilevel dc converter according to any of claims 1-7.
10. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out a method of primary current harmonic cancellation for a modular multilevel dc converter according to any of claims 1 to 7.
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