CN113991727B - Control method and device of hybrid MMC direct-current transmission system - Google Patents
Control method and device of hybrid MMC direct-current transmission system Download PDFInfo
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- CN113991727B CN113991727B CN202111381055.8A CN202111381055A CN113991727B CN 113991727 B CN113991727 B CN 113991727B CN 202111381055 A CN202111381055 A CN 202111381055A CN 113991727 B CN113991727 B CN 113991727B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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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
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
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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
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
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Abstract
The application relates to a control method, a control device, computer equipment and a computer readable storage medium of a hybrid MMC direct current transmission system. The mixed MMC direct current transmission system comprises a plurality of mixed MMC converter stations, and the control method comprises the following steps: acquiring a modulation signal; the modulation signal is determined according to a direct current modulation signal, an alternating current modulation signal and a double frequency modulation signal, wherein the direct current modulation signal is determined according to the voltage of the direct current side of the hybrid MMC direct current transmission system and the rated voltage of the direct current side of the hybrid MMC direct current transmission system; and determining a target submodule in a plurality of submodules of the hybrid MMC converter station according to the modulation signal, and controlling the input of the target submodule and the cutting of other submodules except the target submodule. The method inherits the modulation mode in the traditional half-bridge MMC direct-current transmission system, simplifies the control scheme, gives consideration to compatibility, avoids the defect of relatively complicated original direct-current modulation, and improves the direct-current modulation efficiency.
Description
Technical Field
The application relates to the technical field of flexible direct-current transmission, in particular to a control method, a control device, computer equipment and a computer readable storage medium of a hybrid MMC direct-current transmission system.
Background
In recent years, flexible direct current transmission technology is rapidly developed, and a control system is crucial to the realization of the functions of the flexible direct current transmission system, so that the research on the control system becomes a research hot spot. The conventional voltage source converter in flexible direct current transmission is a half-bridge modularized multi-level converter, has the advantages of low manufacturing difficulty, reduced loss in multiple, reduced step voltage, high waveform quality, high fault handling capability and the like, and is widely applied to a flexible direct current transmission system, and has relatively mature research results. The hybrid modular multilevel converter has the advantages of the half-bridge MMC and can utilize the negative level output capability of the full-bridge submodule, so that the hybrid MMC direct-current power transmission system based on the hybrid MMC converter station has direct-current fault processing capability, and meanwhile, the working condition that the voltage modulation ratio is larger than 1 can be realized under the steady state, and further, the direct-current voltage reduction operation or the alternating-current voltage boosting operation can be realized.
Based on the added advantages of the hybrid MMC direct current transmission system relative to the half bridge, new requirements are put forward for the control system, and as the full-bridge submodule capable of outputting negative level is introduced into the hybrid MMC converter station, the degree of freedom of direct current component control is increased in the modulation signal, and the problems of low modulation speed and excessively complex structure of the modulation module exist in the direct current modulation of the hybrid MMC converter station in the prior art.
Disclosure of Invention
In view of the foregoing, it is desirable to provide a control method, apparatus, computer device, and computer readable storage medium for a hybrid MMC dc power transmission system with a simple modulation structure, and capable of rapidly completing dc modulation.
In one aspect, an embodiment of the present application provides a control method for a hybrid MMC direct current power transmission system, where the hybrid MMC direct current power transmission system includes a plurality of hybrid MMC converter stations, and the control method includes: acquiring a modulation signal; the modulation signal is determined according to a direct current modulation signal, an alternating current modulation signal and a double frequency modulation signal, wherein the direct current modulation signal is determined according to the voltage of the direct current side of the hybrid MMC direct current transmission system and the rated voltage of the direct current side of the hybrid MMC direct current transmission system; determining a target sub-module in a plurality of sub-modules of the hybrid MMC converter station according to the modulation signal; obtaining a sub-module control signal according to the modulation signal; and controlling the input and the removal of the target submodule according to the submodule control signal, and controlling the input of the target submodule and the removal of the submodule except the target submodule.
In one embodiment, the modulated signals include an upper leg modulated signal and a lower leg modulated signal, the modulated signals being determined by:
wherein M is P For modulating the signal of the upper bridge arm M N For modulating the signal of the lower bridge arm M dc Is a direct current modulation signal, M is an alternating current modulation signal, M cir Is a frequency-doubled modulated signal.
In one embodiment, the step of determining a target sub-module of the plurality of sub-modules of the hybrid MMC converter station from the modulation signal comprises: carrying out carrier phase shift modulation on the modulation signal after taking an absolute value of the modulation signal, and summing the results of the carrier phase shift modulation to obtain the number of target submodules required to be input; under the condition that the modulation signal is larger than zero, selecting the submodules with the number of target submodules from all the submodules according to the sequence from small to large of the submodule voltage as target submodules if the bridge arm current is positive, and selecting the submodules with the number of target submodules from all the submodules according to the sequence from large to small of the submodule voltage as target submodules if the bridge arm current is negative; and under the condition that the modulation signal is smaller than zero, if the bridge arm current is positive, selecting the full-bridge submodules with the number of target submodules from all the full-bridge submodules according to the sequence from the large submodule voltage to the small submodule voltage as target submodules, and if the bridge arm current is negative, selecting the full-bridge submodules with the number of target submodules from all the full-bridge submodules according to the sequence from the small submodule voltage to the large submodule voltage as target submodules.
In one embodiment, the DC modulated signal is determined by:
wherein M is dc For DC modulated signals, U dc U is the voltage of the direct current side of the mixed MMC direct current transmission system dcn The voltage is the rated voltage of the direct current side of the mixed MMC direct current transmission system.
In one embodiment, the ac modulated signal is obtained by: inputting the active reference value and the active power of the mixed MMC converter station into an active outer loop control model to obtain an alternating current d-axis component reference value; inputting the reactive reference value and reactive power of the mixed MMC converter station into a reactive outer loop control model to obtain an alternating current q-axis component reference value; and inputting the alternating current d-axis component reference value, the alternating current d-axis component of the hybrid MMC converter station, the alternating current q-axis component reference value and the alternating current q-axis component of the hybrid MMC converter station into an inner ring current control model to obtain an alternating current modulation signal.
On the other hand, an embodiment of the present application provides a control device of a hybrid MMC direct-current power transmission system, including: the modulating signal acquisition module is used for acquiring a modulating signal; the modulation signal is determined according to a direct current modulation signal, an alternating current modulation signal and a double frequency modulation signal, wherein the direct current modulation signal is determined according to the voltage of the direct current side of the hybrid MMC direct current transmission system and the rated voltage of the direct current side of the hybrid MMC direct current transmission system; the target submodule determining module is used for determining a target submodule in a plurality of submodules of the hybrid MMC converter station according to the modulation signal; and the target sub-module switching module is used for determining a target sub-module in a plurality of sub-modules of the hybrid MMC converter station according to the modulation signal and controlling the input of the target sub-module and the cutting of the sub-modules except the target sub-module.
In one embodiment, the target submodule switching module includes a submodule number acquisition unit and a target submodule determination unit; the sub-module quantity acquisition unit is used for carrying out carrier phase shift modulation on the modulated signal after taking the absolute value of the modulated signal, and summing the results of the carrier phase shift modulation to obtain the quantity of target sub-modules to be input; the target submodule determining unit is used for selecting the submodules with the number of target submodules from all the submodules according to the sequence from small submodules to large submodules when the bridge arm current is positive and selecting the submodules with the number of target submodules from all the submodules according to the sequence from large submodules to small submodules when the bridge arm current is negative under the condition that the modulation signal is greater than zero; and under the condition that the modulation signal is smaller than zero, if the bridge arm current is positive, selecting the full-bridge submodules with the number of target submodules from all the full-bridge submodules according to the sequence from the large submodule voltage to the small submodule voltage as target submodules, and if the bridge arm current is negative, selecting the full-bridge submodules with the number of target submodules from all the full-bridge submodules according to the sequence from the small submodule voltage to the large submodule voltage as target submodules.
In one embodiment, the modulation signal acquisition module is further configured to input the active reference value and the active power of the hybrid MMC converter station into an active outer loop control model to obtain an ac current d-axis component reference value; inputting the reactive reference value and reactive power of the mixed MMC converter station into a reactive outer loop control model to obtain an alternating current q-axis component reference value; and inputting the alternating current d-axis component reference value, the alternating current d-axis component of the hybrid MMC converter station, the alternating current q-axis component reference value and the alternating current q-axis component of the hybrid MMC converter station into the inner ring current control model to obtain an alternating current modulation signal.
In still another aspect, an embodiment of the present application provides a computer device, including a memory and a processor, where the memory stores a computer program, and the processor implements the steps of the control method of the hybrid MMC dc power transmission system when executing the computer program.
In yet another aspect, an embodiment of the present application provides a computer readable storage medium having a computer program stored thereon, which when executed by a processor, implements the steps of the dc fault ride-through method of the flexible multi-terminal dc power transmission system described above.
Based on any embodiment, the alternating current modulation signal and the double frequency modulation signal inherit the modulation mode in the traditional half-bridge MMC direct current transmission system, the direct current modulation signal is simplified, a PI controller required by the traditional direct current modulation mode is omitted, the direct current side voltage of the hybrid MMC direct current transmission system obtained in real time and the set direct current side rated voltage of the hybrid MMC direct current transmission system are directly utilized to determine the direct current modulation signal, the control scheme is simplified, compatibility is considered, the defect that original direct current modulation is complicated is avoided, the direct current modulation efficiency is improved, the control system is clearer, and the method has stronger practicability.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments or the conventional techniques of the present application, the drawings required for the descriptions of the embodiments or the conventional techniques will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present application, and other drawings may be obtained according to the drawings without inventive effort for those skilled in the art.
Fig. 1 is a schematic structural diagram of a hybrid MMC dc power transmission system according to an embodiment;
fig. 2 is a flow chart of a control method of the hybrid MMC dc power transmission system according to an embodiment;
FIG. 3 is a flow chart of an embodiment for obtaining an AC modulated signal;
FIG. 4 is a flow chart of determining a target sub-module according to another embodiment;
fig. 5 is a block diagram of a control device of a hybrid MMC dc power transmission system according to an embodiment.
Detailed Description
In order that the application may be readily understood, a more complete description of the application will be rendered by reference to the appended drawings. Embodiments of the application are illustrated in the accompanying drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.
It will be understood that the terms first, second, etc. as used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another element.
Spatially relative terms, such as "under", "below", "beneath", "under", "above", "over" and the like, may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use and operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements or features described as "under" or "beneath" other elements would then be oriented "on" the other elements or features. Thus, the exemplary terms "below" and "under" may include both an upper and a lower orientation. Furthermore, the device may also include an additional orientation (e.g., rotated 90 degrees or other orientations) and the spatial descriptors used herein interpreted accordingly.
It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or be connected to the other element through intervening elements. Further, "connection" in the following embodiments should be understood as "electrical connection", "communication connection", and the like if there is transmission of electrical signals or data between objects to be connected.
As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," and/or the like, specify the presence of stated features, integers, steps, operations, elements, components, or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof. Also, the term "and/or" as used in this specification includes any and all combinations of the associated listed items.
Regarding the problems of slow modulation speed and excessively complex structure of the modulation module in the conventional technology in the background technology, the inventor researches and discovers that the problems are caused by the fact that the direct current modulation in the prior art needs to obtain an average value by measuring the capacitance voltage of the submodule, and then the PI controller is used for tracking the average value to obtain a direct current modulation signal. The PI controller requires a long time for tracking, and the processing module is complex, resulting in the above problem. In order to simplify the modulation process of the direct current modulation signal, the inventor firstly analyzes based on an average value model of the hybrid MMC converter station and researches a control method of the hybrid MMC converter station. The average value model ignores the high-frequency switching effect of the triggering link, so that the MMC is converted into a continuous system with the system state continuously transformed along with time, and the time domain and frequency domain characteristics of the fundamental frequency are easy to study. Deducing a mixed MMC state space model under a synchronous rotation dq coordinate system according to an average value model of the mixed MMC, thereby obtaining a differential equation of the mixed bridge MMC body:
wherein M is DC For DC modulated signals, M d For the d-axis component of the AC modulated signal M q For the q-axis component of the AC modulated signal M d2 For frequency-doubled modulation signal M cir D-axis component, M q2 For frequency-doubled modulation signal M cir Is the q-axis component of L is the equivalent inductance, L a Is bridge arm inductance, R a Is equivalent bridge arm resistance C eq Is equivalent capacitance of bridge arm series submodule, I dif0 As a direct current component, I difd2 Is the double frequency d-axis component of the alternating current, I difq2 Is the frequency doubling q-axis component of alternating current, I vd Is the fundamental d-axis component of the alternating phase current, I vq Is the fundamental frequency q-axis component of alternating phase current, V CP0 Is the direct-current voltage component of the upper bridge arm series submodule, V CPd Fundamental frequency d-axis component of alternating voltage of upper bridge arm serial submodule CPq Fundamental frequency q-axis component of alternating voltage of upper bridge arm serial submodule CPd2 Is the frequency doubling d-axis component of the alternating voltage of the upper bridge arm serial submodule, V CPq2 The upper bridge arm is connected in series with the frequency doubling q-axis component of the sub-module alternating voltage. From the above equations (6) to (10), 5 differential equations related to the lower arm voltage can be derived, and will not be described here.
The 10 differential equations of the above formulas (1) to (10) constitute the 10-step state space equation of the hybrid MMC converter station. From the above, it can be seen that the modulation signal M is based on DC DC And for the alternating current modulation signal M and the frequency doubling modulation signal M cir The dq decomposition is carried out and then the direct current, the direct voltage, the alternating current, the alternating voltage and other outputs of the converter station can be controlled by inputting the model, so that the converter station is controlled according to the power transmission requirement of a power grid.
Based on the state equation and the problems existing in the conventional technology, the embodiment of the application provides a control method of a hybrid MMC direct current transmission system, which can be applied to the hybrid MMC direct current transmission system shown in fig. 1, wherein HBSM is a half-bridge sub-module, and FBSM is a full-bridge sub-module. Each bridge arm is formed by connecting N full-bridge submodules and N-N half-bridge submodules in series. Because the full-bridge submodule has negative level output capability, the hybrid MMC converter station can additionally introduce control over direct current, and has higher control freedom compared with the traditional half-bridge MMC converter station. As shown in fig. 2, the control method of the hybrid MMC dc power transmission system includes steps S202 to S208.
S202, obtaining a modulation signal.
The modulation signal is determined according to a direct current modulation signal, an alternating current modulation signal and a frequency doubling modulation signal, and the direct current modulation signal is determined according to the voltage of the direct current side of the hybrid MMC direct current transmission system and the rated voltage of the direct current side of the hybrid MMC direct current transmission system. It can be understood that the input and output of the converter station are controlled by the input and the removal of each sub-module, and the modulation signal is used for generating a trigger signal for each sub-module through maximum level modulation, carrier phase shift modulation and the like, so as to control the input and the removal of the sub-module. The conventional half-bridge type MMC converter station has an alternating current modulation signal for controlling alternating current of the converter station and a frequency doubling modulation signal for inhibiting circulation in the converter station, and the alternating current modulation signal and the frequency doubling modulation signal in the embodiment follow the modulation mode of the alternating current modulation signal and the frequency doubling modulation signal which are relatively mature in research of the conventional half-bridge type MMC converter station, so that the method is beneficial to using similar general modeling with the conventional half-bridge type MMC converter station, and the applicability of the method is enhanced. According to the research of the state space equation, the inventor finds that the direct current modulation signal can be determined through the obtained relationship between the voltage of the direct current side of the hybrid MMC direct current transmission system and the rated voltage of the direct current side of the hybrid MMC direct current transmission system, a PI controller is omitted, the influence of parameter selection in the PI controller on the system is reduced, and the modulation structure is simplified.
S204, determining a target submodule in a plurality of submodules of the hybrid MMC converter station according to the modulation signal, and controlling the input of the target submodule and the excision of the submodules except the target submodule.
It can be appreciated that, since the hybrid MMC converter station includes both a half-bridge sub-module and a full-bridge sub-module, the half-bridge sub-module can only output a positive level and the full-bridge sub-module can output a positive level and a negative level, and the modulation signal is related to the output of the hybrid MMC converter station, the output of the hybrid MMC converter station can be matched with the actual need only by selecting an appropriate sub-module as a target sub-module according to the modulation signal. The submodule generally comprises a plurality of switching tubes, the input and the cutting of the submodule are determined by the switching on and off of each switching tube, and after the target submodule is determined, the switching tubes corresponding to the target submodule can be controlled to be switched on, so that the target submodule is input, the switching tubes corresponding to other submodules except the target submodule are switched off, the other submodules except the target submodule are cut off, and the output control of the mixed MMC converter station is realized.
Based on the control method of the hybrid MMC direct current transmission system in the embodiment, the alternating current modulation signal and the double frequency modulation signal inherit the modulation mode in the traditional half-bridge MMC direct current transmission system, the direct current modulation signal is simplified, a PI controller required by the traditional direct current modulation mode is omitted, the direct current side voltage of the hybrid MMC direct current transmission system obtained in real time and the set direct current side rated voltage of the hybrid MMC direct current transmission system are directly utilized to determine the direct current modulation signal, the control scheme is simplified, compatibility is considered, the defect that original direct current modulation is complicated is avoided, the direct current modulation efficiency is improved, the control system is clearer, and the method has stronger practicability.
In one embodiment, the DC modulated signal is determined by:
wherein M is dc For DC modulated signals, U dc U is the voltage of the direct current side of the mixed MMC direct current transmission system dcn The voltage is the rated voltage of the direct current side of the mixed MMC direct current transmission system. Specifically, the voltage on the direct current side of the hybrid MMC direct current transmission system is collected through the voltage collection device, and the voltage collected by the voltage collection device is input into the proportional processing device for signal processing, so that the output value of the proportional processing device meets the above formula, and the acquisition of the direct current modulation signal is realized.
In one embodiment, as shown in fig. 3, the ac modulation signal is obtained from steps S302 to S306.
S302, inputting the active reference value and the active power of the hybrid MMC converter station into an active outer loop control model to obtain an alternating current d-axis component reference value.
S304, inputting the reactive reference value and reactive power of the mixed MMC converter station into a reactive outer loop control model to obtain an alternating current q-axis component reference value.
It can be appreciated that the present embodiment uses the ac modulation scheme of the conventional half-bridge MMC converter station, i.e. the internal and external double loop control. The outer loop is outer loop power control, and comprises an active outer loop control loop and a reactive outer loop control loop, wherein the active outer loop control loop and the reactive outer loop control loop are respectively realized through an active outer loop control model and a reactive outer loop control model, and control targets are active power and reactive power. The active outer loop control model is based on a PI controller and outputs an alternating current d-axis component reference value for matching the real-time active power and the active reference value of the hybrid MMC converter station. Similarly, the reactive outer loop control model outputs an ac current q-axis component reference value for matching the real-time reactive power and reactive reference value of the hybrid MMC converter station based on the PI controller.
S306, inputting the alternating current d-axis component reference value, the alternating current d-axis component of the hybrid MMC converter station, the alternating current q-axis component reference value and the alternating current q-axis component of the hybrid MMC converter station into the inner ring current control model to obtain an alternating current modulation signal.
The inner loop in the inner loop and outer loop control is an inner loop alternating current control, the pair is realized through an inner loop current control model, and the inner loop current control model is a typical dq decoupling control model and comprises two control loops of d-axis alternating current control and q-axis alternating current control. Inputting an alternating current d-axis component reference value and an alternating current d-axis component of the mixed MMC converter station into a d-axis alternating current control loop, inputting an alternating current q-axis component reference value and an alternating current q-axis component of the mixed MMC converter station into a q-axis alternating current control loop, and finally performing dq inverse transformation on output values of the two control loops to obtain an alternating current modulation signal.
For the frequency doubling modulation signal, the common mode voltage can be converted from the three-phase stationary coordinate system to the current value i in the rotating coordinate system through park transformation by double-loop control similar to the alternating current modulation signal cird And i cirq A negative feedback control system is constructed such that the output variable tracks its command value i cird =0 and i cirq =0. The output of the inner loop current controller can obtain the double frequency circulation modulation signal through the transformation from the rotating coordinate system to the three-phase coordinate system.
In one embodiment, the modulation signals include an upper bridge arm modulation signal and a lower bridge arm modulation signal, and it can be seen from fig. 1 that the converter station can be divided into an upper bridge arm and a lower bridge arm by taking connection points va, vb and vc of each phase power supply and each sub-module on the ac side as boundary points, where the upper bridge arm modulation signal is a modulation signal corresponding to a sub-module in the upper bridge arm, and the lower bridge arm modulation signal is a modulation signal corresponding to a sub-module in the lower bridge arm. The modulation signal is determined by:
wherein M is P For modulating the signal of the upper bridge arm M N For modulating the signal of the lower bridge arm M DC Is a direct current modulation signal, M is an alternating current modulation signal, M cir Is a frequency-doubled modulated signal. And mixing the three modulation signals after obtaining the direct current modulation signal, the alternating current modulation signal and the double frequency modulation signal to obtain an upper bridge arm modulation signal and a lower bridge arm modulation signal respectively.
In one embodiment, as shown in fig. 4, the step of determining a target sub-module of a plurality of sub-modules of the hybrid MMC converter station according to the modulation signal includes steps S402 to S406.
S402, carrying out carrier phase shift modulation on the modulated signal after taking an absolute value of the modulated signal, and summing the results of the carrier phase shift modulation to obtain the number of target submodules required to be input.
In the traditional technology, the nearest level approximation modulation is often adopted, but the requirement on the number of sub-modules is higher, and the effect is poor when the number of the sub-modules is smaller. In the embodiment, the submodules of the converter station are controlled based on an improved carrier phase-shift modulation mode, so that the modulation structure is simpler, and the method has better performance when the bridge arm outputs negative level and the number of the submodules is small.
S404, if the modulation signal is greater than zero, selecting the sub-modules with the number of target sub-modules from all sub-modules according to the sequence from small to large of the sub-module voltage as the target sub-module if the bridge arm current is positive, and selecting the sub-modules with the number of target sub-modules from all sub-modules according to the sequence from large to small of the sub-module voltage as the target sub-module if the bridge arm current is negative.
It will be appreciated that when the modulation signal is greater than zero, it represents that the converter station should output a positive level, i.e. the sub-modules put into should all output a positive level, and all the sub-modules of the hybrid MMC converter station have the capability of outputting a positive level, so the range of the selected target sub-module is all the sub-modules of all the hybrid MMC converter station. In order to ensure the voltage balance of the energy storage elements in the sub-modules, when the bridge arm current is positive and the converter station needs to output positive voltage, the energy storage elements in the input sub-modules are charged, so that the sub-modules with the lowest voltage of the energy storage elements are sequentially selected from small to large to be the target sub-modules, the target sub-modules are charged, the voltages of the energy storage elements of the sub-modules with lower voltages are increased, and the voltage balance of the energy storage elements of all the sub-modules is gradually realized. For the same purpose, when the bridge arm current is negative and the converter station needs to output positive voltage, the energy storage elements in the input submodules are discharged outwards, so that the number of the submodules of the target submodules is sequentially selected from the highest submodule of the energy storage element voltage to be the target submodule from the highest to the lowest, the target submodule is discharged, the voltage of the energy storage elements of the submodules with higher voltage is reduced, and the voltage balance of the energy storage elements of all the submodules is gradually realized.
S406, if the modulation signal is smaller than zero, selecting the full-bridge submodules with the number of target submodules from all the full-bridge submodules according to the sequence from the large submodule voltage to the small submodule voltage as target submodules if the bridge arm current is smaller than zero, and selecting the full-bridge submodules with the number of target submodules from all the full-bridge submodules according to the sequence from the small submodule voltage to the large submodule voltage as target submodules if the bridge arm current is negative.
It will be appreciated that when the modulation signal is greater than zero, it represents that the sub-modules to which the converter station should output a negative level, i.e. the sub-modules to which it is put should all output a negative level, and that only the full-bridge sub-modules of all sub-modules of the hybrid MMC converter station have the capability of outputting a negative level, so that the range of the selected target sub-module is all the full-bridge sub-modules of all the hybrid MMC converter station. In order to ensure the voltage balance of the energy storage elements in the sub-modules, when the bridge arm current is positive and the converter station needs to output negative level, the energy storage elements in the input full-bridge sub-modules are discharged, so that the full-bridge sub-modules with the highest voltage of the energy storage elements are sequentially selected from the large to the small to be the target sub-modules, the target sub-modules are discharged, the voltage of the energy storage elements of the full-bridge sub-modules with higher voltage is reduced, and the voltage balance of the energy storage elements of all the sub-modules is gradually realized. For the same purpose, when the bridge arm current is negative and the converter station needs to output negative power, the energy storage elements in the input full-bridge submodules are discharged outwards, so that the number of full-bridge submodules of the target submodules is sequentially selected from the lowest voltage submodule of the energy storage element to be the target submodule from small to large, the target submodule is charged, the voltage of the energy storage elements of the full-bridge submodules with lower voltage is increased, and the voltage balance of the energy storage elements of all the submodules is gradually realized.
It should be understood that, although the steps in the flowcharts of fig. 2-4 are shown in order as indicated by the arrows, these steps are not necessarily performed in order as indicated by the arrows. The steps are not strictly limited to the order of execution unless explicitly recited herein, and the steps may be executed in other orders. Moreover, at least a portion of the steps of fig. 2-4 may include multiple steps or stages that are not necessarily performed at the same time, but may be performed at different times, nor does the order in which the steps or stages are performed necessarily occur sequentially, but may be performed alternately or alternately with at least a portion of the steps or stages in other steps or other steps.
Referring to fig. 5, the control device of the hybrid MMC dc power transmission system includes a modulation signal acquisition module 110 and a target submodule switching module 130. The modulated signal acquisition module 110 is configured to acquire a modulated signal. The modulation signal is determined according to a direct current modulation signal, an alternating current modulation signal and a frequency doubling modulation signal, and the direct current modulation signal is determined according to the voltage of the direct current side of the hybrid MMC direct current transmission system and the rated voltage of the direct current side of the hybrid MMC direct current transmission system. The target submodule switching module 130 is configured to determine a target submodule of the plurality of submodules of the hybrid MMC converter station according to the modulation signal, and control input of the target submodule and excision of submodules other than the target submodule.
In one embodiment, the target submodule switching module 130 includes a submodule number acquisition unit and a target submodule determination unit. The submodule quantity acquisition unit is used for carrying out carrier phase shift modulation on the modulated signal after the absolute value of the modulated signal is taken, and summing the results of the carrier phase shift modulation to obtain the target submodule quantity required to be input. The target submodule determining unit is used for selecting the submodules with the number of target submodules from all the submodules according to the sequence from small submodules to large submodules when the bridge arm current is positive and selecting the submodules with the number of target submodules from all the submodules according to the sequence from large submodules to small submodules when the bridge arm current is negative under the condition that the modulation signal is greater than zero; and under the condition that the modulation signal is smaller than zero, if the bridge arm current is positive, selecting the full-bridge submodules with the number of target submodules from all the full-bridge submodules according to the sequence from the large submodule voltage to the small submodule voltage as target submodules, and if the bridge arm current is negative, selecting the full-bridge submodules with the number of target submodules from all the full-bridge submodules according to the sequence from the small submodule voltage to the large submodule voltage as target submodules.
In one embodiment, the modulation signal acquisition module 110 is further configured to input the active reference value and the active power of the hybrid MMC converter station into the active outer loop control model to obtain an ac d-axis component reference value; inputting the reactive reference value and reactive power of the mixed MMC converter station into a reactive outer loop control model to obtain an alternating current q-axis component reference value; and inputting the alternating current d-axis component reference value, the alternating current d-axis component of the hybrid MMC converter station, the alternating current q-axis component reference value and the alternating current q-axis component of the hybrid MMC converter station into the inner ring current control model to obtain an alternating current modulation signal.
For specific limitations of the control device of the hybrid MMC dc power transmission system, reference may be made to the above limitation of the control method of the hybrid MMC dc power transmission system, which is not repeated here. All or part of each module in the control device of the hybrid MMC direct current transmission system can be realized by software, hardware and a combination thereof. The above modules may be embedded in hardware or may be independent of a processor in the computer device, or may be stored in software in a memory in the computer device, so that the processor may call and execute operations corresponding to the above modules. It should be noted that, in the embodiment of the present application, the division of the modules is schematic, which is merely a logic function division, and other division manners may be implemented in actual implementation.
In still another aspect, an embodiment of the present application provides a computer device, including a memory and a processor, where the memory stores a computer program, and the processor implements the steps of the control method of the hybrid MMC dc power transmission system in any of the foregoing embodiments when executing the computer program.
In yet another aspect, an embodiment of the present application provides a computer readable storage medium having a computer program stored thereon, which when executed by a processor, implements the steps of the dc fault ride-through method of the flexible multi-terminal dc power transmission system of any of the embodiments described above.
Those skilled in the art will appreciate that implementing all or part of the above described methods may be accomplished by way of a computer program stored on a non-transitory computer readable storage medium, which when executed, may comprise the steps of the embodiments of the methods described above. Any reference to memory, storage, database, or other medium used in embodiments provided herein may include at least one of non-volatile and volatile memory. The nonvolatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical Memory, or the like. Volatile memory can include random access memory (Random Access Memory, RAM) or external cache memory. By way of illustration, and not limitation, RAM can be in the form of a variety of forms, such as static random access memory (Static Random Access Memory, SRAM) or dynamic random access memory (Dynamic Random Access Memory, DRAM), and the like.
In the description of the present specification, reference to the terms "some embodiments," "other embodiments," "desired embodiments," and the like, means 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 application. In this specification, schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The foregoing examples illustrate only a few embodiments of the application, which are described in detail and are not to be construed as limiting the scope of the application. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of protection of the present application is to be determined by the appended claims.
Claims (7)
1. A control method of a hybrid MMC direct current transmission system including a plurality of hybrid MMC converter stations, the control method comprising:
acquiring a modulation signal; the modulation signal is determined according to a direct current modulation signal, an alternating current modulation signal and a frequency doubling modulation signal, wherein the direct current modulation signal is determined according to the voltage of the direct current side of the hybrid MMC direct current transmission system and the rated voltage of the direct current side of the hybrid MMC direct current transmission system;
the modulation signals comprise an upper bridge arm modulation signal and a lower bridge arm modulation signal, and the modulation signals are determined by the following formula:
in the method, in the process of the application,M P for modulating the signal of the upper bridge arm, M N For modulating the signal of the lower bridge arm, M dc For the DC modulation signal, M is the AC modulation signal, M cir For the frequency-doubled modulated signal;
determining a target submodule in a plurality of submodules of the hybrid MMC converter station according to the modulation signal, and controlling the input of the target submodule and the cutting of other submodules except the target submodule;
the step of determining a target sub-module of a plurality of sub-modules of the hybrid MMC converter station from the modulation signal comprises:
carrying out carrier phase shift modulation on the modulation signal after taking an absolute value of the modulation signal, and summing the results of the carrier phase shift modulation to obtain the number of target submodules required to be input;
if the bridge arm current is greater than zero, selecting the submodules with the target submodule number from all the submodules according to the order of the submodule voltages from small to large as the target submodule, and if the bridge arm current is negative, selecting the submodules with the target submodule number from all the submodules according to the order of the submodule voltages from large to small as the target submodule;
and if the bridge arm current is negative, selecting the full-bridge submodules with the target submodule number from all the full-bridge submodules according to the order of the submodule voltages from high to low as the target submodule.
2. The method of controlling a hybrid MMC dc power transmission system of claim 1, wherein the dc modulation signal is determined by:
wherein M is dc For the direct current modulation signal, U dc U is the voltage of the direct current side of the mixed MMC direct current transmission system dcn And the rated voltage of the direct current side of the hybrid MMC direct current transmission system is obtained.
3. The control method of a hybrid MMC dc power transmission system according to claim 1, characterized in that the ac modulation signal is obtained by:
inputting the active reference value and the active power of the mixed MMC converter station into an active outer loop control model to obtain an alternating current d-axis component reference value;
inputting the reactive reference value and reactive power of the mixed MMC converter station into a reactive outer loop control model to obtain an alternating current q-axis component reference value;
and inputting the alternating current d-axis component reference value, the alternating current d-axis component of the hybrid MMC converter station, the alternating current q-axis component reference value and the alternating current q-axis component of the hybrid MMC converter station into an inner ring current control model to obtain the alternating current modulation signal.
4. A control device of a hybrid MMC direct current transmission system, the hybrid MMC direct current transmission system including a plurality of hybrid MMC converter stations, characterized in that the control device includes:
the modulating signal acquisition module is used for acquiring a modulating signal; the modulation signal is determined according to a direct current modulation signal, an alternating current modulation signal and a frequency doubling modulation signal, wherein the direct current modulation signal is determined according to the voltage of the direct current side of the hybrid MMC direct current transmission system and the rated voltage of the direct current side of the hybrid MMC direct current transmission system;
the modulation signals comprise an upper bridge arm modulation signal and a lower bridge arm modulation signal, and the modulation signals are determined by the following formula:
wherein M is P For modulating the signal of the upper bridge arm, M N For modulating the signal of the lower bridge arm, M dc For the DC modulation signal, M is the AC modulation signal, M cir For the frequency-doubled modulated signal;
the target submodule switching module is used for determining a target submodule in a plurality of submodules of the hybrid MMC converter station according to the modulation signal and controlling the input of the target submodule and the cutting of other submodules except the target submodule;
the target sub-module switching module comprises a sub-module quantity acquisition unit and a target sub-module determination unit;
the submodule quantity obtaining unit is used for carrying out carrier phase shift modulation on the modulation signal after taking an absolute value of the modulation signal, and summing the results of the carrier phase shift modulation to obtain the target submodule quantity required to be input;
the target submodule determining unit is configured to select, when the modulation signal is greater than zero, the number of submodules of the target submodule from all the submodules according to the order of the submodule voltages from small to large if the bridge arm current is positive, and select, from all the submodules according to the order of the submodule voltages from large to small if the bridge arm current is negative, the number of submodules of the target submodule as the target submodule; and if the bridge arm current is negative, selecting the full-bridge submodules with the target submodule number from all the full-bridge submodules according to the order of the submodule voltages from high to low as the target submodule.
5. The control device of the hybrid MMC dc power transmission system as recited in claim 4, characterized in that the modulation signal acquisition module is further configured to input an active reference value and an active power of the hybrid MMC converter station into an active outer loop control model to obtain an ac d-axis component reference value; inputting the reactive reference value and reactive power of the mixed MMC converter station into a reactive outer loop control model to obtain an alternating current q-axis component reference value; and inputting the alternating current d-axis component reference value, the alternating current d-axis component of the hybrid MMC converter station, the alternating current q-axis component reference value and the alternating current q-axis component of the hybrid MMC converter station into the inner ring current control model to obtain an alternating current modulation signal.
6. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor, when executing the computer program, carries out the steps of the control method of the hybrid MMC direct-current power-transmission system of any one of claims 1 to 3.
7. A computer-readable storage medium, on which a computer program is stored, characterized in that the computer program, when being executed by a processor, implements the steps of the control method of the hybrid MMC direct-current power transmission system of any one of claims 1 to 3.
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| CN104269838A (en) * | 2013-09-24 | 2015-01-07 | 许继集团有限公司 | Valve level control method for flexible DC power transmission system |
| CN105024574A (en) * | 2015-07-22 | 2015-11-04 | 上海交通大学 | MMC slave module capacitance voltage balance control method suitable for carrier phase shifting modulation |
| CN112103983A (en) * | 2020-09-10 | 2020-12-18 | 中国南方电网有限责任公司超高压输电公司检修试验中心 | Control method based on mixed MMC-HVDC |
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| CN104269838A (en) * | 2013-09-24 | 2015-01-07 | 许继集团有限公司 | Valve level control method for flexible DC power transmission system |
| CN105024574A (en) * | 2015-07-22 | 2015-11-04 | 上海交通大学 | MMC slave module capacitance voltage balance control method suitable for carrier phase shifting modulation |
| CN112103983A (en) * | 2020-09-10 | 2020-12-18 | 中国南方电网有限责任公司超高压输电公司检修试验中心 | Control method based on mixed MMC-HVDC |
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