CN113991727A - Control method and device of hybrid MMC direct-current power transmission system - Google Patents

Control method and device of hybrid MMC direct-current power transmission system Download PDF

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CN113991727A
CN113991727A CN202111381055.8A CN202111381055A CN113991727A CN 113991727 A CN113991727 A CN 113991727A CN 202111381055 A CN202111381055 A CN 202111381055A CN 113991727 A CN113991727 A CN 113991727A
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modulation signal
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direct current
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CN113991727B (en
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严喜林
梁宁
吴健颖
国建宝
张楠
黄炟超
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Maintenance and Test Center of Extra High Voltage Power Transmission Co
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Maintenance and Test Center of Extra High Voltage Power Transmission Co
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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
    • 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
    • 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
    • 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
    • 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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  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The application relates to a control method and device of a hybrid MMC direct-current power transmission system, computer equipment and a computer readable storage medium. The hybrid MMC direct current transmission system comprises a plurality of hybrid 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, and the direct current modulation signal is determined according to the voltage of the direct current side of the hybrid MMC direct current power transmission system and the rated voltage of the direct current side of the hybrid MMC direct current power transmission system; and 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 cutting off other sub-modules except the target sub-module. The method inherits the modulation mode in the traditional half-bridge MMC direct-current power transmission system, simplifies the control scheme, considers compatibility, avoids the defect of complex original direct-current modulation, and improves the direct-current modulation efficiency.

Description

Control method and device of hybrid MMC direct-current power transmission system
Technical Field
The present application relates to the field of flexible dc power transmission technologies, and in particular, to a method and an apparatus for controlling a hybrid MMC dc power transmission system, a computer device, and a computer-readable storage medium.
Background
In recent years, flexible direct current transmission technology is rapidly developed, and a control system is crucial to the realization of functions of the flexible direct current transmission system, so research on the control system becomes a research hotspot. The voltage source converter commonly used in flexible direct current transmission at present is a half-bridge type modular multilevel converter, and has the advantages of low manufacturing difficulty, loss doubling reduction, step voltage reduction, high waveform quality, strong fault handling capacity and the like, so the voltage source converter is widely applied to a flexible direct current transmission system and has relatively mature research results. And the mixed type modularization multi-level converter can utilize the negative level output capability of the full-bridge submodule while having the advantages of a half-bridge MMC, so that the mixed type MMC direct-current power transmission system based on the mixed type MMC converter station has direct-current fault processing capability, and meanwhile, the working condition that the voltage modulation ratio is greater than 1 can be realized under a 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 a half bridge, the hybrid MMC direct current transmission system has new requirements for a control system, and due to the fact that a full bridge submodule capable of outputting a negative level is introduced into the hybrid MMC converter station, the direct current component control freedom degree is increased in a modulation signal, and the problems of low modulation speed and excessively complex structure of a modulation module exist in direct current modulation of the hybrid MMC converter station in the traditional technology.
Disclosure of Invention
In view of the foregoing, there is a need to provide a control method, an apparatus, a computer device and a computer readable storage medium for a hybrid MMC direct-direct current power transmission system, which has a simple modulation structure and can rapidly complete direct current modulation.
In one aspect, an embodiment of the present invention provides a control method for a hybrid MMC direct-current transmission system, where the hybrid MMC direct-current 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, and the direct current modulation signal is determined according to the voltage of the direct current side of the hybrid MMC direct current power transmission system and the rated voltage of the direct current side of the hybrid MMC direct current power transmission system; determining a target submodule in a plurality of submodules of the hybrid MMC converter station according to the modulation signal; obtaining a submodule control signal according to the modulation signal; and controlling the input and the removal of the target sub-module according to the sub-module control signal, and controlling the input of the target sub-module and the removal of sub-modules except the target sub-module.
In one embodiment, the modulation signal includes an upper arm modulation signal and a lower arm modulation signal, and the modulation signal is determined by the following equation:
Figure BDA0003365551320000021
Figure BDA0003365551320000022
in the formula, MPFor modulating the signal for the upper arm, MNFor modulating the signal for the lower arm, MdcIs a DC modulated signal, M is an AC modulated signal, McirA signal is modulated at double frequency.
In one embodiment, the step of determining a target sub-module of a plurality of sub-modules of the hybrid MMC converter station from the modulated signal comprises: after the absolute value of the modulation signal is obtained, carrying out carrier phase shift modulation on the modulation signal, and summing the results of the carrier phase shift modulation to obtain the quantity of target sub-modules needing to be input; under the condition that the modulation signal is larger than zero, if the bridge arm current is positive, selecting the submodules with the target submodule quantity from all the submodules according to the sequence of the submodule voltages from small to large as target submodules, and if the bridge arm current is negative, selecting the submodules with the target submodule quantity from all the submodules according to the sequence of the submodule voltages from large to small as target submodules; and under the condition that the modulation signal is less than zero, if the bridge arm current is positive, selecting the full-bridge sub-modules with the target sub-module number as the target sub-modules from all the full-bridge sub-modules according to the sequence of the sub-module voltages from large to small, and if the bridge arm current is negative, selecting the full-bridge sub-modules with the target sub-module number as the target sub-modules from all the full-bridge sub-modules according to the sequence of the sub-module voltages from small to large.
In one embodiment, the dc modulated signal is determined by:
Figure BDA0003365551320000031
in the formula, MdcFor modulating signals by direct current, UdcIs the voltage, U, of the DC side of the mixed MMC DC power transmission systemdcnThe rated voltage of the DC side of the hybrid MMC DC power transmission system is obtained.
In one embodiment, the ac modulation signal is obtained by: inputting the active reference value and the active power of the hybrid MMC converter station into an active outer ring control model to obtain an alternating current d-axis component reference value; inputting the reactive reference value and the reactive power of the hybrid MMC converter station into a reactive outer ring control model to obtain an alternating current q-axis component reference value; and inputting the reference value of the alternating current d-axis component, the reference value of the alternating current d-axis component of the hybrid MMC converter station, the reference value of the alternating current q-axis component 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 another aspect, an embodiment of the present invention provides a control device for a hybrid MMC direct-current power transmission system, including: the modulation signal acquisition module is used for 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, and the direct current modulation signal is determined according to the voltage of the direct current side of the hybrid MMC direct current power transmission system and the rated voltage of the direct current side of the hybrid MMC direct current power transmission system; the target sub-module determining module is used for determining a target sub-module in a plurality of sub-modules of the mixed type 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 mixed MMC convertor station according to the modulation signal and controlling the input of the target sub-module and the cutting of sub-modules except the target sub-module.
In one embodiment, the target submodule switching module comprises a submodule quantity obtaining unit and a target submodule determining unit; the submodule quantity obtaining unit is used for carrying out carrier phase shift modulation on the modulation signal after the absolute value of the modulation signal is obtained, and summing the results of the carrier phase shift modulation to obtain the quantity of target submodules needing to be input; the target sub-module determining unit is used for selecting sub-modules with the target sub-module number from all the sub-modules according to the sequence of the sub-module voltages from small to large as target sub-modules if the bridge arm current is positive under the condition that the modulation signal is larger than zero, and selecting the sub-modules with the target sub-module number from all the sub-modules according to the sequence of the sub-module voltages from large to small as target sub-modules if the bridge arm current is negative; and under the condition that the modulation signal is less than zero, if the bridge arm current is positive, selecting the full-bridge sub-modules with the target sub-module number as the target sub-modules from all the full-bridge sub-modules according to the sequence of the sub-module voltages from large to small, and if the bridge arm current is negative, selecting the full-bridge sub-modules with the target sub-module number as the target sub-modules from all the full-bridge sub-modules according to the sequence of the sub-module voltages from small to large.
In one embodiment, the modulation signal obtaining module is further configured to input an active reference value and active power of the hybrid MMC converter station into an active outer-loop control model to obtain a reference value of a d-axis component of the alternating current; inputting the reactive reference value and the reactive power of the hybrid MMC converter station into a reactive outer ring control model to obtain an alternating current q-axis component reference value; and inputting the reference value of the alternating current d-axis component, the reference value of the alternating current d-axis component of the hybrid MMC converter station, the reference value of the alternating current q-axis component 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 another aspect, an embodiment of the present invention provides a computer device, which includes a memory and a processor, where the memory stores a computer program, and the processor implements the steps of the control method for the hybrid MMC direct-current power transmission system when executing the computer program.
In another aspect, an embodiment of the present invention provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps of the dc fault ride-through method for a flexible multi-terminal dc power transmission system described above.
Based on any of the above embodiments, the ac modulation signal and the double frequency modulation signal inherit the modulation mode in the conventional half-bridge type MMC dc power transmission system, the dc modulation signal is simplified, a PI controller required by the conventional dc modulation mode is omitted, the dc side voltage of the hybrid type MMC dc power transmission system obtained in real time and the set dc side rated voltage of the hybrid type MMC dc power transmission system are directly utilized to determine the dc modulation signal, the control scheme is simplified and compatibility is considered, the defect that the original dc modulation is complex is avoided, the dc modulation efficiency is improved, the control system is clearer, and the method has stronger implementability.
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In order to more clearly illustrate the technical solutions in the embodiments or the conventional technologies of the present application, the drawings used in the descriptions of the embodiments or the conventional technologies will be briefly introduced below, it is obvious that the drawings in the following descriptions are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of a hybrid MMC DC power transmission system in one embodiment;
FIG. 2 is a flow chart illustrating a method for controlling a hybrid MMC DC power transmission system according to an exemplary embodiment;
FIG. 3 is a schematic flow chart of an embodiment for acquiring an AC modulated signal;
FIG. 4 is a flow diagram of a determine target sub-module in another embodiment;
fig. 5 is a block diagram of a control apparatus of a hybrid MMC dc power transmission system according to an embodiment.
Detailed Description
To facilitate an understanding of the present application, the present application will now be described more fully with reference to the accompanying drawings. Embodiments of the present application are set forth 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 present 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, as used herein, the terms "first," "second," and the like may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another.
Spatial relational terms, such as "under," "below," "under," "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 or 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 "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary terms "under" and "under" can encompass both an orientation of above and below. In addition, the device may also include additional orientations (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 is understood to mean "electrical connection", "communication connection", or the like, if there is a transfer of electrical signals or data between the connected objects.
As used herein, the singular forms "a", "an" and "the" may include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises/comprising," "includes" or "including," etc., specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof. Also, as used in this specification, the term "and/or" includes any and all combinations of the associated listed items.
The inventor researches and finds that the above problem occurs because the dc modulation in the prior art needs to obtain an average value by measuring the capacitor voltage of the sub-module, and then the PI controller tracks the average value to obtain a dc modulation signal. The PI controller pair requires a long time in the tracking process and the processing module is complex, resulting in the above problems. In order to simplify the modulation process of the dc modulated signal, the inventor first conducted an analysis based on an average model of the hybrid MMC converter station and studied the control method of the hybrid MMC converter station. The average value model ignores the high-frequency switching effect of a trigger link, so that the MMC is converted into a continuous system with the system state continuously changed along with time, and the time domain and frequency domain characteristics of the fundamental frequency of the MMC are easy to study. Deducing a mixed MMC state space model under a synchronous rotation dq coordinate system according to the average value model of the mixed MMC, thereby obtaining a differential equation of a mixed bridge MMC body:
Figure BDA0003365551320000071
Figure BDA0003365551320000072
Figure BDA0003365551320000073
Figure BDA0003365551320000074
Figure BDA0003365551320000075
Figure BDA0003365551320000076
Figure BDA0003365551320000077
Figure BDA0003365551320000078
Figure BDA0003365551320000079
Figure BDA00033655513200000710
in the formula, MDCFor DC modulated signals, MdBeing d-axis component of AC modulated signal M, MqFor the q-axis component of the AC modulated signal M, Md2Modulating the signal M for two frequenciescirD-axis component of (1), Mq2For modulation at double frequencySignal McirQ-axis component of (1), L is equivalent inductance, LaIs bridge arm inductance, RaIs equivalent bridge arm resistance CeqEquivalent capacitance of bridge arm series sub-module, Idif0Is a direct current component, Idifd2Is a frequency-doubled d-axis component of the alternating current, Idifq2Is a double frequency q-axis component of the alternating current, IvdIs the fundamental d-axis component of the AC phase current, IvqThe fundamental q-axis component of the AC phase current, VCP0Is a DC voltage component, V, of an upper bridge arm series submoduleCPdIs the fundamental frequency d-axis component, V, of the AC voltage of the upper bridge arm series sub-moduleCPqFor the fundamental frequency q-axis component, V, of the AC voltage of the upper bridge arm series sub-moduleCPd2Is a double frequency d-axis component, V, of the AC voltage of the upper bridge arm series sub-moduleCPq2Is a double frequency q-axis component of the alternating voltage of the upper bridge arm series submodule. From the above equations (6) to (10), 5 differential equations relating to the lower arm voltages can be derived, which are not described in detail herein.
The 10-order state space equations of the hybrid type MMC converter station are formed by 10 differential equations from the above equations (1) to (10). According to the above formula, it can be seen that the signal M is modulated according to the DCDCAnd for AC modulated signal M and double frequency modulated signal McirThe direct current, direct voltage, alternating current, alternating voltage and other outputs of the converter station can be controlled by inputting the model after dq decomposition, so that the converter station is controlled according to the power transmission requirement of a power grid.
Based on the above equation of state and the problems existing in the conventional technology, an embodiment of the present invention provides a control method for a hybrid MMC direct-current power transmission system, which can be applied to the hybrid MMC direct-current power transmission system shown in fig. 1, where 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 compared with the traditional half-bridge MMC converter station, the hybrid MMC converter station has higher control freedom degree. As shown in fig. 2, the control method of the hybrid MMC direct-current power transmission system includes steps S202 to S208.
S202, 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, and the direct current modulation signal is determined according to the voltage of the direct current side of the hybrid MMC direct current power transmission system and the rated voltage of the direct current side of the hybrid MMC direct current power transmission system. It can be understood that the input and output of the commutation station are controlled by switching in and switching out 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 switching in and switching out of the sub-modules. The alternating current modulation signal used for controlling the alternating current of the converter station and the double-frequency modulation signal used for inhibiting the circular current in the converter station exist in the traditional half-bridge type MMC converter station, the alternating current modulation signal and the double-frequency modulation signal in the embodiment follow the modulation mode of the alternating current modulation signal and the double-frequency modulation signal which are well researched in the traditional half-bridge type MMC converter station, the use of a similar general modeling with the traditional half-bridge type MMC converter station is facilitated, 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 according to the obtained relation between the voltage at the direct current side of the hybrid MMC direct current power transmission system and the rated voltage at the direct current side of the hybrid MMC direct current power 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.
And S204, 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 sub-modules except the target sub-module.
It can be understood that, because the hybrid MMC converter station includes both the half-bridge submodule and the full-bridge submodule, the half-bridge submodule can only output a positive level and the full-bridge submodule can both output a positive level and a negative level, and the modulation signal is related to the output of the hybrid MMC converter station, it is necessary to select a suitable submodule as a target submodule according to the modulation signal so as to match the output of the hybrid MMC converter station with the actual requirement. The submodule generally comprises a plurality of switch tubes, the switching-in and the switching-out of the submodule are determined by the switching-on and the switching-off of each switch tube, the switch tube corresponding to the target submodule can be controlled to be switched on after the target submodule is determined, so that the target submodule is switched in, the switch tubes corresponding to other submodules except the target submodule are switched off, and the output of the hybrid MMC converter station is controlled.
Based on the control method of the hybrid-type MMC direct-current power 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-type MMC direct-current power 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 modulation signal is determined by directly utilizing the direct-current side voltage of the hybrid-type MMC direct-current power transmission system obtained in real time and the set direct-current side rated voltage of the hybrid-type MMC direct-current power transmission system, the control scheme is simplified, compatibility is considered, the defect that original direct-current modulation is complex is overcome, 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:
Figure BDA0003365551320000101
in the formula, MdcFor modulating signals by direct current, UdcIs the voltage, U, of the DC side of the mixed MMC DC power transmission systemdcnThe rated voltage of the DC side of the hybrid MMC DC power transmission system is obtained. Specifically, the voltage acquisition device is used for acquiring the voltage on the direct current side of the mixed MMC direct current transmission system, and the voltage acquired by the voltage acquisition device is input into the proportion processing device for signal processing, so that the output value of the proportion processing device meets the formula, and the direct current modulation signal is acquired.
In one embodiment, as shown in fig. 3, the ac modulation signal is obtained from step S302 to step S306.
And S302, inputting the active reference value and the active power of the hybrid MMC converter station into an active outer ring control model to obtain an alternating current d-axis component reference value.
And S304, inputting the reactive reference value and the reactive power of the hybrid MMC converter station into a reactive outer ring control model to obtain a reference value of the q-axis component of the alternating current.
It can be understood that the present embodiment continues to use the ac modulation mode of the conventional half-bridge type MMC converter station, i.e., the internal and external dual-ring control. The outer loop is controlled by outer loop power, the outer loop comprises an active outer loop control loop and a reactive outer loop control loop, 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 the 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 real-time active power of the hybrid MMC converter station with an active reference value. Similarly, the reactive outer loop control model is based on a PI controller to output 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.
And S306, inputting the reference value of the alternating current d-axis component, the reference value of the alternating current d-axis component of the hybrid MMC converter station, the reference value of the alternating current q-axis component 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.
An inner ring in the inner and outer double-ring control is controlled by inner ring alternating current, and the inner ring 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 the alternating current d-axis component reference value and the alternating current d-axis component of the hybrid MMC converter station into a d-axis alternating current control loop, inputting the alternating current q-axis component reference value and the alternating current q-axis component of the hybrid MMC converter station into a q-axis alternating current control loop, and finally carrying out dq inverse transformation on output values of the two control loops to obtain an alternating current modulation signal.
For the double frequency modulation signal, the common mode voltage can be obtained by double-loop control similar to the alternating current modulation signal, and the common mode voltage is converted into a current value i in a rotating coordinate system from a three-phase static coordinate system through park transformationcirdAnd icirqConstructing a negative feedback control systemSo that the output variable tracks its instruction value icird0 and icirq0. The inner loop current controller output can obtain a double frequency circulation modulation signal through the transformation from a rotating coordinate system to a 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 the upper bridge arm and the lower bridge arm by taking connection points va, vb, and vc of each phase power supply on the ac side and each submodule as boundary points, the upper bridge arm modulation signal is a modulation signal corresponding to a submodule in the upper bridge arm, and the lower bridge arm modulation signal is a modulation signal corresponding to a submodule in the lower bridge arm. The modulation signal is determined by:
Figure BDA0003365551320000121
Figure BDA0003365551320000122
in the formula, MPFor modulating the signal for the upper arm, MNFor modulating the signal for the lower arm, MDCIs a DC modulated signal, M is an AC modulated signal, McirA signal is modulated at double frequency. After the direct current modulation signal, the alternating current modulation signal and the double frequency modulation signal are obtained, the three modulation signals are mixed to respectively obtain an upper bridge arm modulation signal and a lower bridge arm modulation signal.
In one embodiment, as shown in fig. 4, the step of determining a target sub-module of the plurality of sub-modules of the hybrid MMC converter station from the modulated signal includes steps S402 to S406.
S402, carrier phase shift modulation is carried out on the modulation signals after the absolute value of the modulation signals is obtained, and the results of the carrier phase shift modulation are summed to obtain the quantity of target sub-modules needing to be input.
The traditional technology usually adopts the nearest level approximation modulation, but the requirement on the number of sub-modules is higher, and the effect is not good when the number of sub-modules is less. In the embodiment, the sub-modules of the converter station are controlled based on an improved carrier phase shift modulation mode, so that the modulation structure is simpler, and the performance is better when the bridge arm outputs a negative level and the number of the sub-modules is less.
S404, under the condition that the modulation signal is larger than zero, if the bridge arm current is positive, selecting the submodules with the target submodule quantity from all the submodules according to the sequence of the submodule voltages from small to large as target submodules, and if the bridge arm current is negative, selecting the submodules with the target submodule quantity from all the submodules according to the sequence of the submodule voltages from large to small as target submodules.
It is understood that when the modulation signal is greater than zero, this indicates that the converter station should output a positive level, i.e. the sub-modules that are put in should all output a positive level, and all 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 sub-modules of all hybrid MMC converter stations. 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 a positive voltage, the energy storage elements in the input sub-modules are charged, so that the sub-modules with the target number of the sub-modules are sequentially selected from the sub-module with the lowest voltage of the energy storage elements from small to large as the target sub-module to charge the target sub-module, so that the voltage of the energy storage elements of the sub-modules with the lower voltage is increased, and the voltage balance of the energy storage elements of each sub-module is gradually realized. For the same purpose, when the bridge arm current is negative and the converter station needs to output a positive voltage, the energy storage elements in the inputted sub-modules are discharged outwards, so that the sub-modules with the target number of the sub-modules are sequentially selected from the sub-module with the highest voltage of the energy storage elements from large to small as the target sub-module, the target sub-modules are discharged, the voltage of the energy storage elements of the sub-modules with higher voltage is reduced, and the voltage balance of the energy storage elements of each sub-module is gradually realized.
And S406, under the condition that the modulation signal is less than zero, if the bridge arm current is positive, selecting the full-bridge sub-modules with the target sub-module number as the target sub-modules from all the full-bridge sub-modules according to the sequence of the sub-module voltages from large to small, and if the bridge arm current is negative, selecting the full-bridge sub-modules with the target sub-module number as the target sub-modules from all the full-bridge sub-modules according to the sequence of the sub-module voltages from small to large.
It can be understood that when the modulation signal is greater than zero, it represents that the converter station should output a negative level, that is, the put-in sub-modules should all output a negative level, and only the full-bridge sub-module of all the sub-modules of the hybrid MMC converter station has 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 stations. 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 voltage, the energy storage elements in the input full-bridge sub-modules are discharged, so that the full-bridge sub-modules with the target number of the sub-modules are sequentially selected from the full-bridge sub-module with the highest voltage of the energy storage elements from large to small as 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 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 voltage, the energy storage elements in the full-bridge sub-modules are charged to discharge outwards, so that the full-bridge sub-modules with the target number of the sub-modules are sequentially selected from the sub-module with the lowest voltage of the energy storage elements from small to large as the target sub-module to charge the target sub-module, and the voltage of the energy storage elements of the full-bridge sub-modules with the lower voltage is increased to gradually realize the voltage balance of the energy storage elements of the sub-modules.
It should be understood that although the various steps in the flowcharts of fig. 2-4 are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least some of the steps in fig. 2-4 may include multiple steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, which are not necessarily performed in sequence, but may be performed in turn or alternately with other steps or at least some of the other steps or stages.
Referring to fig. 5, the control device includes a modulation signal obtaining module 110 and a target sub-module switching module 130. The modulation signal obtaining module 110 is used for obtaining 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, and the direct current modulation signal is determined according to the voltage of the direct current side of the hybrid MMC direct current power transmission system and the rated voltage of the direct current side of the hybrid MMC direct current power transmission system. The target sub-module switching module 130 is configured to determine a target sub-module of a plurality of sub-modules of the hybrid MMC converter station according to the modulation signal, and control the switching of the target sub-module and the cutting of sub-modules other than the target sub-module.
In one embodiment, the target sub-module switching module 130 includes a sub-module number obtaining unit and a target sub-module determining unit. The submodule quantity obtaining unit is used for carrying out carrier phase shift modulation on the modulation signal after the absolute value of the modulation signal is obtained, and summing the results of the carrier phase shift modulation to obtain the quantity of target submodules needing to be input. The target sub-module determining unit is used for selecting sub-modules with the target sub-module number from all the sub-modules according to the sequence of the sub-module voltages from small to large as target sub-modules if the bridge arm current is positive under the condition that the modulation signal is larger than zero, and selecting the sub-modules with the target sub-module number from all the sub-modules according to the sequence of the sub-module voltages from large to small as target sub-modules if the bridge arm current is negative; and under the condition that the modulation signal is less than zero, if the bridge arm current is positive, selecting the full-bridge sub-modules with the target sub-module number as the target sub-modules from all the full-bridge sub-modules according to the sequence of the sub-module voltages from large to small, and if the bridge arm current is negative, selecting the full-bridge sub-modules with the target sub-module number as the target sub-modules from all the full-bridge sub-modules according to the sequence of the sub-module voltages from small to large.
In one embodiment, the modulation signal obtaining module 110 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 a reference value of an ac current d-axis component; inputting the reactive reference value and the reactive power of the hybrid MMC converter station into a reactive outer ring control model to obtain an alternating current q-axis component reference value; and inputting the reference value of the alternating current d-axis component, the reference value of the alternating current d-axis component of the hybrid MMC converter station, the reference value of the alternating current q-axis component 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 apparatus of the hybrid MMC direct-current power transmission system, reference may be made to the above limitations of the control method of the hybrid MMC direct-current power transmission system, and details are not repeated here. All or part of each module in the control device of the hybrid MMC direct current power transmission system can be realized by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules. It should be noted that, in the embodiment of the present application, the division of the module is schematic, and is only one logic function division, and there may be another division manner in actual implementation.
In another aspect, an embodiment of the present invention 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 for the hybrid MMC direct-current power transmission system in any of the above embodiments when executing the computer program.
In a further aspect, an embodiment of the present invention provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps of the dc fault ride-through method for a flexible multi-terminal dc power transmission system in any of the above embodiments.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database or other medium used in the embodiments provided herein can include at least one of non-volatile and volatile memory. Non-volatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical storage, or the like. Volatile Memory can include Random Access Memory (RAM) or external cache Memory. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM), among others.
In the description herein, references to the description of "some embodiments," "other embodiments," "desired embodiments," 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, a schematic description of the above terminology may not necessarily refer to the same embodiment or example.
The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above examples only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (10)

1. A control method of a hybrid MMC direct current transmission system, the hybrid MMC direct current transmission system comprising a plurality of hybrid MMC converter stations, characterized in that the control method comprises:
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 power transmission system and the rated voltage of the direct current side of the hybrid MMC direct current power transmission system;
and 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 other sub-modules except the target sub-module to be cut off.
2. The method of controlling a hybrid MMC direct current power transmission system of claim 1, wherein the modulated signals comprise an upper arm modulated signal and a lower arm modulated signal, the modulated signals determined by:
Figure FDA0003365551310000011
Figure FDA0003365551310000012
in the formula, MPModulating signals for said upper bridge arm, MNModulating signals for said lower bridge arm, MdcFor said DC modulated signal, M for said AC modulated signal, McirThe signal is modulated at double frequency.
3. The method of controlling a hybrid MMC direct current transmission system according to claim 1, wherein 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:
after the absolute value of the modulation signal is obtained, carrying out carrier phase shift modulation on the modulation signal, and summing the results of the carrier phase shift modulation to obtain the quantity of target sub-modules needing to be input;
under the condition that the modulation signal is larger than zero, if the bridge arm current is positive, selecting the submodules with the target submodule quantity as the target submodules from all the submodules according to the sequence of the submodule voltages from small to large, and if the bridge arm current is negative, selecting the submodules with the target submodule quantity as the target submodules from all the submodules according to the sequence of the submodule voltages from large to small;
and under the condition that the modulation signal is smaller than zero, if the bridge arm current is positive, selecting the full-bridge sub-modules with the target sub-module number as the target sub-modules from all the full-bridge sub-modules according to the sequence of the sub-module voltages from large to small, and if the bridge arm current is negative, selecting the full-bridge sub-modules with the target sub-module number as the target sub-modules from all the full-bridge sub-modules according to the sequence of the sub-module voltages from small to large.
4. The method of controlling a hybrid MMC direct current power transmission system of claim 1, wherein the direct current modulation signal is determined by:
Figure FDA0003365551310000021
in the formula, MdcFor said DC modulated signal, UdcIs the voltage, U, of the DC side of the hybrid MMC DC transmission systemdcnAnd the rated voltage is the rated voltage of the DC side of the hybrid MMC DC power transmission system.
5. The method of controlling a hybrid MMC direct current power transmission system according to claim 1, wherein the ac modulated signal is obtained by:
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;
inputting a reactive reference value and the reactive power of the hybrid MMC converter station into a reactive outer ring 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.
6. The utility model provides a controlling means of mixed type MMC direct current transmission system, mixed type MMC direct current transmission system includes a plurality of mixed type MMC converter stations, its characterized in that, controlling means includes:
the modulation signal acquisition module is used for 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 power transmission system and the rated voltage of the direct current side of the hybrid MMC direct current power transmission system;
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 other sub-modules except the target sub-module.
7. The control device of the hybrid MMC direct current transmission system of claim 6, wherein the target sub-module switching module comprises a sub-module quantity obtaining unit and a target sub-module determining unit;
the sub-module quantity obtaining unit is used for carrying out carrier phase shift modulation on the modulation signal after the absolute value of the modulation signal is obtained, and summing the results of the carrier phase shift modulation to obtain the quantity of target sub-modules needing to be input;
the target sub-module determining unit is used for selecting sub-modules with the number of target sub-modules from all sub-modules as the target sub-modules according to the sequence of sub-module voltages from small to large if the bridge arm current is positive under the condition that the modulation signal is larger than zero, and selecting the sub-modules with the number of target sub-modules from all sub-modules as the target sub-modules according to the sequence of sub-module voltages from large to small 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 sub-modules with the target sub-module number as the target sub-modules from all the full-bridge sub-modules according to the sequence of the sub-module voltages from large to small, and if the bridge arm current is negative, selecting the full-bridge sub-modules with the target sub-module number as the target sub-modules from all the full-bridge sub-modules according to the sequence of the sub-module voltages from small to large.
8. A control apparatus for a hybrid MMC direct current transmission system according to claim 6, wherein said modulation signal obtaining module is further configured to obtain an AC current d-axis component reference value from an active reference value and an active power input active outer loop control model of the hybrid MMC converter station; inputting the reactive reference value and the reactive power of the hybrid MMC converter station into a reactive outer ring control model to obtain an alternating current q-axis component reference value; and inputting the reference value of the alternating current d-axis component, the reference value of the alternating current d-axis component of the hybrid MMC converter station, the reference value of the alternating current q-axis component 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.
9. A computer device comprising a memory and a processor, said memory storing a computer program, characterized in that said processor when executing said computer program realizes the steps of the control method of a hybrid MMC direct current power transmission system as claimed in any one of claims 1 to 5.
10. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the dc fault ride-through method of the flexible multi-terminal dc power transmission system of any one of claims 1 to 5.
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