CN113809945B - MMC control method and device based on integral modulation - Google Patents

MMC control method and device based on integral modulation Download PDF

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CN113809945B
CN113809945B CN202111134314.7A CN202111134314A CN113809945B CN 113809945 B CN113809945 B CN 113809945B CN 202111134314 A CN202111134314 A CN 202111134314A CN 113809945 B CN113809945 B CN 113809945B
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bridge arm
voltage
capacitor
current
reference voltage
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CN113809945A (en
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林金娇
孔祥平
郑俊超
周琦
李鹏
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State Grid Jiangsu Electric Power Co Ltd
Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
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State Grid Jiangsu Electric Power Co Ltd
Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
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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
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • 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)
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Abstract

The application discloses an MMC control method and device based on integral modulation, wherein the method comprises the steps of adopting a double closed-loop control structure for submodules in an upper bridge arm and a lower bridge arm of a single-phase modularized multi-level converter to obtain reference voltages of the upper bridge arm and the lower bridge arm; correcting the obtained upper bridge arm reference voltage by adopting integral modulation; and comprehensively considering the voltage balance of the capacitor, and selecting a conducting submodule based on the corrected bridge arm reference voltage to obtain a control signal of a switch in the submodule. The application can keep balance between the voltages of the capacitors and greatly reduce the average switching loss of the device.

Description

MMC control method and device based on integral modulation
Technical Field
The application relates to an MMC control method and device based on integral modulation, and belongs to the technical field of power electronics.
Background
In recent years, modular Multilevel Converters (MMCs) have been widely used in high power scenarios, such as offshore wind farm systems and the field of high voltage direct current transmission (HVDC). Compared with other types of multilevel converters, the modular multilevel converter has the following advantages: the manufacturing difficulty is reduced, the loss cost is reduced, the step voltage is reduced, the utilization rate is high, the redundancy is high, the output waveform quality is good, and the fault processing capability is high.
The traditional MMC modulation technology mainly comprises three types: based on carrier phase shift modulation technique, carrier stacked modulation technique and recent level approximation modulation technique. The carrier-based modulation technology is not easy to realize redundancy module standby, and has the problems of difficult equalization of capacitance voltage, poor consistency of submodule loss and the like. The recent level approximation modulation method is simple to implement, but when the number of levels is low, the quality of the generated voltage/current waveform is poor.
Disclosure of Invention
The application aims to provide an MMC control method and device based on integral modulation, which uses a double closed-loop control structure, wherein an outer loop controls the average capacitance voltage of each bridge arm, an inner loop controls load current and circulating current, and an integral modulation technology is used for modulating the reference voltage of each bridge arm so as to select a conducting submodule to control the on-off of a switch, and meanwhile, the balance between the capacitor voltages is maintained, so that the average switching loss of a device is greatly reduced.
In order to achieve the above purpose, the application adopts the following technical scheme:
the application provides an MMC control method based on integral modulation, which comprises the following steps:
the sub-modules in the upper bridge arm and the lower bridge arm of the single-phase modularized multi-level converter adopt a double closed-loop control structure to obtain the reference voltages of the upper bridge arm and the lower bridge arm;
correcting the obtained upper bridge arm reference voltage by adopting integral modulation;
and comprehensively considering the voltage balance of the capacitor, and selecting a conducting submodule based on the corrected bridge arm reference voltage to obtain a control signal of a switch in the submodule.
Further, a double closed-loop control structure is adopted for the submodules in the upper bridge arm and the lower bridge arm of the single-phase modularized multi-level converter, and the method comprises the following steps:
the voltage of the capacitor of the submodule is controlled through the outer loop, and the load and the circulating current are controlled through the inner loop.
Further, the method comprises the steps of,
in the outer loop control, an error signal is obtained by comparing a capacitor voltage reference value with a bridge arm average capacitor voltageThe capacitor voltage is made to track the capacitor voltage reference value by the outer loop PI controller,
wherein,for the capacitor voltage reference value, N is the number of half-bridge submodules, +.>And->The capacitor voltages of the jth sub-module on the upper bridge arm and the lower bridge arm respectively.
Further, the method comprises the steps of,
controlling the load current by using a first PI controller, wherein the input of the first PI controller is a load current reference value i ref Error with actual load current, the output of the first PI controller is U L -U U ；
The load current is determined by:
i＝i U -i L ；
where i is the load current, U U And U L Respectively an upper bridge arm voltage and a lower bridge arm voltage, i U And i L Respectively an upper bridge arm current and a lower bridge arm current, R load And L load The load resistor and the load inductor are respectively, and L is a half-bridge series inductor;
the circulating current is controlled by a second PI controller, and the input of the second PI controller is a circulating reference currentAnd the actual circulating current i S Error between the first and second PI controllers, the output of the second PI controller is U L +U U The cyclic reference current +.>The output of the outer loop control;
the circulating current is determined by:
i S ＝i U +i L ；
wherein U is DC Is a direct current side voltage.
Further, by outputting U L -U U And U L +U U Decoupling to obtain upper and lower bridge arm reference voltagesAnd
further, the correcting the obtained upper and lower bridge arm reference voltages by adopting integral modulation includes:
U′ ref (K)＝U ref (K)+int U(K-1)；
int U(K)＝int U(K-1)+U ref (K)-U sum (K)；
wherein,U′ Uref (K) For the reference voltage after the bridge arm correction at the sampling time K, U' Lref (K) For the reference voltage after correction of the bridge arm at sampling instant K, < >>U Uref (K) Upper bridge arm reference voltage U obtained by double closed loop control for sampling time K Lref (K) For sampling time K, the lower bridge arm reference voltage obtained by double closed loop control, < >>U Usum (K) For the sum of the capacitor voltages of all the conducting submodules of the bridge arm at the sampling instant K, U Lsum (K) The sum of the capacitor voltages of all the conducting submodules of the bridge arm at the sampling moment K.
Further, the selecting the conducting sub-module based on the corrected bridge arm reference voltage to obtain the control signal of the switch in the sub-module includes:
sequencing submodules on an upper bridge arm and a lower bridge arm of the single-phase modularized multi-level converter according to capacitor voltages;
according to the ordered submodules, the upper bridge arm selection submodule and the lower bridge arm selection submodule are respectively conducted in the following mode:
the number of turns on a is calculated according to the following equation:
U sum,a-1 (K)≤U' ref (K)≤U sum,a (K)，
wherein,representing capacitor voltage of the j-th submodule after sequencing, U' ref (K) The corrected bridge arm reference voltage is divided into an upper bridge arm reference voltage and a lower bridge arm reference voltage; u (U) sum,a-1 (K) Is the sum of the capacitor voltages of the previous a-1 sub-modules, U sum,a (K) Is the sum of the capacitor voltages of the first a sub-modules,
if (|U ')' ref (K)-U sum,a (K)|＞|U' ref (K)-U sum,a-1 (K) I), the submodules sequenced from 1 to a-1 are selected to be conducted, and a control signal of a switch in the submodule is determined;
if (|U ')' ref (K)-U sum,a (K)|＜|U' ref (K)-U sum,a-1 (K) I), the submodules ordered from 1 to a are selected to be conducted, and the control signals of the switches in the submodules are determined.
Further, the method comprises the steps of,
if the bridge arm current is positive, the submodules are sequenced from the lowest capacitor voltage to the highest capacitor voltage;
if the bridge arm current is negative, the submodules order from the highest capacitor voltage to the lowest capacitor voltage.
The application also provides an MMC control device based on integral modulation, which comprises:
the control module is used for adopting a double closed-loop control structure for the submodules in the upper bridge arm and the lower bridge arm of the single-phase modularized multi-level converter to obtain the reference voltages of the upper bridge arm and the lower bridge arm;
the correction module is used for correcting the obtained upper and lower bridge arm reference voltages by adopting integral modulation;
the method comprises the steps of,
and the selection module is used for comprehensively considering the voltage balance of the capacitor, selecting a conducting submodule based on the corrected bridge arm reference voltage, and obtaining a control signal of a switch in the submodule.
Further, the correction module is specifically used for,
the obtained upper and lower bridge arm reference voltages are corrected by adopting the following modes:
U′ ref (K)＝U ref (K)+int U(K-1)；
int U(K)＝int U(K-1)+U ref (K)-U sum (K)；
wherein,U′ Uref (K) U is the reference voltage after the bridge arm correction at the sampling moment K′ Lref (K) For the reference voltage after correction of the bridge arm at sampling instant K, < >>U Uref (K) Upper bridge arm reference voltage U obtained by double closed loop control for sampling time K Lref (K) For sampling time K, the lower bridge arm reference voltage obtained by double closed loop control, < >>U Usum (K) For the sum of the capacitor voltages of all the conducting submodules of the bridge arm at the sampling instant K, U Lsum (K) The sum of the capacitor voltages of all the conducting submodules of the bridge arm at the sampling moment K.
Further, the selection module is specifically configured to,
sequencing submodules on an upper bridge arm and a lower bridge arm of the single-phase modularized multi-level converter according to capacitor voltages;
according to the ordered submodules, the upper bridge arm selection submodule and the lower bridge arm selection submodule are respectively conducted in the following mode:
the number of turns on a is calculated according to the following equation:
U sum,a-1 (K)≤U' ref (K)≤U sum,a (K)，
wherein,representing capacitor voltage of the j-th submodule after sequencing, U' ref (K) The corrected bridge arm reference voltage is divided into an upper bridge arm reference voltage and a lower bridge arm reference voltage; u (U) sum,a-1 (K) Is the sum of the capacitor voltages of the previous a-1 sub-modules, U sum,a (K) Is the sum of the capacitor voltages of the first a sub-modules,
if (|U ')' ref (K)-U sum,a (K)|＞|U' ref (K)-U sum,a-1 (K) I), the submodules sequenced from 1 to a-1 are selected to be conducted, and a control signal of a switch in the submodule is determined;
if (|U ')' ref (K)-U sum,a (K)|＜|U' ref (K)-U sum,a-1 (K) I), the submodules ordered from 1 to a are selected to be conducted, and the control signals of the switches in the submodules are determined.
The beneficial effects achieved by the application are as follows:
the application provides an MMC control method based on integral modulation, which uses a double closed-loop control structure, wherein an outer loop controls the average capacitance voltage of each bridge arm, an inner loop controls load current and circulating current, and the reference voltage of each bridge arm is corrected through an integral modulation technology, so that a conducting submodule is selected to control the on-off of a switch, the balance between capacitor voltages can be maintained, and meanwhile, the average switching loss of a device is greatly reduced.
Drawings
Fig. 1 is a topology diagram of a single-phase modular multilevel converter.
Fig. 2 is a schematic diagram of modulation and voltage balancing in the present application.
Fig. 3 is a schematic diagram of a dual closed loop control in accordance with the present application.
Fig. 4 is a graph showing the comparison of the commutation times in the embodiment of the present application.
Detailed Description
The application is further described below. The following examples are only for more clearly illustrating the technical aspects of the present application, and are not intended to limit the scope of the present application.
The embodiment of the application provides an MMC control method based on integral modulation, which comprises the following steps:
step 1: based on the topological structure of the single-phase modularized multi-level converter, a dynamic equation of the single-phase modularized multi-level converter is established.
Step 2: based on the established dynamic equation of the single-phase modularized multi-level converter, the capacitor voltage balance is comprehensively considered to determine the conducted submodule, and the method comprises three stages of sequencing, selecting and integrating.
Step 3: the determined conduction submodule adopts a double closed-loop control structure, the capacitance voltage of the submodule is controlled through an outer loop, the load and the output current are controlled through an inner loop, and the voltage applied by each bridge arm is modulated through an integral modulation technology so as to control the on-off of the switch and simultaneously maintain the balance between the capacitor voltages.
In the embodiment of the application, the dynamic equation for establishing the single-phase modularized multi-level converter is specifically as follows:
referring to fig. 1, a typical single-phase modular multilevel topology is composed of an upper and a lower bridge arm, each of which contains N identical half-bridge sub-modules (SM) and one inductance L connected in series. Voltage U of upper and lower bridge arm U And U L Can be expressed as:
wherein,the capacitor voltage of the j sub-module of the upper bridge arm; />Refers to the capacitance voltage of the j-th sub-module of the lower bridge arm.
S j Can be expressed as:
each SM has two states as shown in table 1.
TABLE 1
When the upper switch D 1 On and lower switch D 2 When closed, U SM ＝U C The method comprises the steps of carrying out a first treatment on the surface of the Lower switch D 2 On and upper switch D 1 When closed, U SM ＝0。U SM Representing the sub-module voltage.
In the on state, the SM output voltage varies depending on the actual bridge arm current i arm Flow direction: when the bridge arm current i arm In order to be positive, the capacitor is in charge mode and the voltage across the submodule will increase. When i arm When negative, the capacitor is in discharge mode and the voltage across the submodule will decrease. SM is in off state, no matter i arm How to flow, the corresponding capacitance voltage U in SM C The voltage and current equations are unchanged:
i＝i U -i L (4)
wherein R is load And L load Respectively a load resistor and a load inductor, i is a load current, i U For upper arm current, i L Is the current of the lower bridge arm, U is the load voltage, U DC Is a direct current side voltage.
Based on equation (3), the dynamic equation for a single phase MMC can be expressed as:
wherein L is an inductance connected in series in the submodule;
alpha, beta, gamma are positive numbers:
in the embodiment of the application, the submodule for determining conduction by comprehensively considering the capacitance-voltage balance comprises three stages of sequencing, selecting and integrating. See FIG. 2, wherein U arm Representing the voltage of the bridge arm,capacitor electricity representing 1 st to nth sub-modules before sequencingPressing. The method comprises the following steps:
(1) Sequencing stage
All sub-module capacitor voltages on one leg need to be ordered according to the ordering principle in the traditional balancing algorithm. If the bridge arm current is positive (capacitor charged), the sequencing will go from the lowest capacitor voltage to the highest voltage,if the bridge arm current is negative (capacitor discharge), the sequencing will go from highest capacitor voltage to lowest voltage, +.>
(2) Selection phase
The sub-module is selected based on the ordering of the first stage and the bridge arm reference voltage, and the number of capacitors selected in one sampling period is denoted by a as shown in equation (7).
When a is 1.ltoreq.a.ltoreq.N (7)
Wherein,represents the capacitor voltage of the j sub-module after sequencing, U ref Is the bridge arm reference voltage.
Selecting and conducting the ordered submodules:
in the above, SM' 1 →SM′ a The submodules representing 1 to a are on, SM' a+1 →SM′ N The sub-modules representing a+1 to N are turned off.
In each sampling period, a positive error 'epsilon' is generated between the bridge arm voltage and the reference voltage, and the positive error 'epsilon' is shown as the following formula:
in order to reduce the error between the bridge arm voltage and the reference voltage. The definition formula (10) is as follows:
wherein,
U sum,a-1 ≤U ref ≤U sum,a (11)
if (|U) ref -U sum,a |＞|U ref -U sum,a-1 I), then let U sum ＝U sum,a-1 ；
If (|U) ref -U sum,a |＜|U ref -U sum,a-1 I), then let U sum ＝U sum,a 。
Thus, the error ε is shown in the following equation:
ε＝U sum -U ref (12)
(3) Integration phase
Introducing an integration phase reduces the error epsilon to 0. The reference voltage U is modified by ref The following is shown:
U′ ref (K)＝U ref (K)+int U(K-1) (13)
wherein,
int U(K)＝int U(K-1)+U ref (K)-U sum (K) (14)
defining int U (0) as zero, adding the accumulated error int U (K-1) calculated at K-1 to the reference voltage U at K by the method described above ref (K) And (3) upper part. The accumulated error at the previous moment is added to the voltage reference value at the current moment, so that the error at the current moment is greatly reduced, and the error gradually converges to 0 along with continuous operation of the system. Therefore, in the actual working process, the voltage reference value U is obtained by the outer ring control ref (K) A new reference value U 'is obtained by the integration phase' ref (K) In U' ref (K) For the purpose, the selection stage is used for selecting the conduction submodule, so that the error epsilon is reduced, and the ideal control effect is obtained.
In the embodiment of the application, the submodule adopts a double closed-loop control structure, the capacitor voltage of the submodule is controlled through the outer loop, the load and the circulating current are controlled through the inner loop, the voltage applied by each bridge arm is modulated through an integral modulation technology, so that the on-off of the switch is controlled, and meanwhile, the balance between the capacitor voltages is kept, and the implementation process is as follows:
(1) Outer loop control
Referring to fig. 3, in the outer loop control, the error signal shown in equation (15) is derived by comparing the capacitor voltage reference value with the average capacitor voltageCapacitor voltage is made +_ by outer loop control>Tracking reference value->
The output of the outer loop PI controller is used as a reference for the inner loop circulating current.
(2) Inner loop control
(1) Load current control
The PI controller is used to control the load current, which directly affects the capacitor voltage ripple. Load current i=i U -i L Can be determined by equation (3) and equation (4):
the PI controller inputs as the load current reference i ref And actual loadError between currents, output of PI controller is difference U L -U U 。
(2) Circulating current control
The PI controller is adopted to control internal circulating current, and the input of the PI controller is a circulating reference currentAnd the actual circulating current i S The error between the two is obtained by the outer ring control. Circulating current i S ＝i U +i L The dynamic characteristics of (2) are determined by equations (3) and (4), as follows:
the output of the PI controller is the difference U L +U U 。
Then, to U L -U U And U L +U U Decoupling to obtain bridge arm reference voltageAnd->As shown in fig. 3, the decoupling process is:
in the view of figure 3 of the drawings, representing the upper bridge arm and the lower bridge armAverage value of capacitance voltage.
Finally, the modulation technique proposed in the step 2 is used forAnd->Modulating to obtain upper switches D in the upper bridge arm and lower bridge arm submodules 1 And a lower switch D 2 Is controlled by a control signal of (a).
Finally, a single-phase MMC model is built by adopting MATLAB/Simulink based on the method provided by the application, and specific parameters are shown in Table 2. For comparison, the simulation includes two modulation methods, namely an integral modulation method and a PWM method, and compared with the PWM method, the modulation scheme provided by the application remarkably reduces the average commutation times of the device, as shown in fig. 4. Thereby reducing the overall switching losses of the converter.
Table 2 parameters of single phase MMC model
Compared with the traditional PWM method, the integral modulation technology provided by the application reduces the commutation times. By using the control method proposed by the present application, the capacitor voltage can be made to follow any desired value and maintain a good balance between them by modifying the balancing algorithm to reduce the switching losses.
Another embodiment of the present application provides an MMC control device based on integral modulation, including:
the control module is used for adopting a double closed-loop control structure for the submodules in the upper bridge arm and the lower bridge arm of the single-phase modularized multi-level converter to obtain the reference voltages of the upper bridge arm and the lower bridge arm;
the correction module is used for correcting the obtained upper and lower bridge arm reference voltages by adopting integral modulation;
the method comprises the steps of,
and the selection module is used for comprehensively considering the voltage balance of the capacitor, selecting a conducting submodule based on the corrected bridge arm reference voltage, and obtaining a control signal of a switch in the submodule.
In the embodiment of the application, the correction module is specifically used for,
the obtained upper and lower bridge arm reference voltages are corrected by adopting the following modes:
U′ ref (K)＝U ref (K)+int U(K-1)；
int U(K)＝int U(K-1)+U ref (K)-U sum (K)；
wherein,U′ Uref (K) For the reference voltage after the bridge arm correction at the sampling time K, U' Lref (K) For the reference voltage after correction of the bridge arm at sampling instant K, < >>U Uref (K) Upper bridge arm reference voltage U obtained by double closed loop control for sampling time K Lref (K) For sampling time K, the lower bridge arm reference voltage obtained by double closed loop control, < >>U Usum (K) For the sum of the capacitor voltages of all the conducting submodules of the bridge arm at the sampling instant K, U Lsum (K) The sum of the capacitor voltages of all the conducting submodules of the bridge arm at the sampling moment K.
In the embodiment of the application, the selection module is specifically used for,
sequencing submodules on an upper bridge arm and a lower bridge arm of the single-phase modularized multi-level converter according to capacitor voltages;
according to the ordered submodules, the upper bridge arm selection submodule and the lower bridge arm selection submodule are respectively conducted in the following mode:
the number of turns on a is calculated according to the following equation:
U sum,a-1 (K)≤U' ref (K)≤U sum,a (K)，
wherein,representing capacitor voltage of the j-th submodule after sequencing, U' ref (K) The corrected bridge arm reference voltage is divided into an upper bridge arm reference voltage and a lower bridge arm reference voltage; u (U) sum,a-1 (K) Is the sum of the capacitor voltages of the previous a-1 sub-modules, U sum,a (K) Is the sum of the capacitor voltages of the first a sub-modules,
if (|U ')' ref (K)-U sum,a (K)|＞|U' ref (K)-U sum,a-1 (K) I), the submodules sequenced from 1 to a-1 are selected to be conducted, and a control signal of a switch in the submodule is determined;
if (|U ')' ref (K)-U sum,a (K)|＜|U' ref (K)-U sum,a-1 (K) I), the submodules ordered from 1 to a are selected to be conducted, and the control signals of the switches in the submodules are determined.
It should be noted that the embodiment of the apparatus corresponds to the embodiment of the method, and the implementation manner of the embodiment of the method is applicable to the embodiment of the apparatus and can achieve the same or similar technical effects, so that the description thereof is omitted herein.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical aspects of the present application and not for limiting the same, and although the present application has been described in detail with reference to the above embodiments, it should be understood by those of ordinary skill in the art that: modifications and equivalents may be made to the specific embodiments of the application without departing from the spirit and scope of the application, which is intended to be covered by the claims.

Claims (7)

1. An MMC control method based on integral modulation is characterized by comprising the following steps:
the sub-modules in the upper bridge arm and the lower bridge arm of the single-phase modularized multi-level converter adopt a double closed-loop control structure to obtain the reference voltages of the upper bridge arm and the lower bridge arm; in the inner loop control of the double closed loop control,
controlling the load current by using a first PI controller, wherein the input of the first PI controller is a load current reference valueError from actual load current, the output of the first PI controller is +.>；
The load current is determined by:
；
；
wherein,for load current +.>And->Upper bridge arm voltage and lower bridge arm voltage respectively, +.>And->Upper bridge arm current and lower bridge arm current respectively, +.>And->Load resistance and load inductance, respectively, +.>The inductor is connected in series with the half bridge;
the circulating current is controlled by a second PI controller, and the input of the second PI controller is a circulating reference currentIs +.>Error between the first and second PI controller, the output of the second PI controller is +.>The cyclic reference current +.>The output of the outer loop control;
the circulating current is determined by:
；
；
wherein,is a direct current side voltage;
by outputtingAnd->Decoupling to obtain upper and lower bridge arm reference voltages +.>And->：
；
Correcting the obtained upper and lower bridge arm reference voltages by adopting integral modulation, including:
；
；
wherein,，/>for sampling timeKReference voltage after correction of upper bridge arm, +.>For sampling timeKReference voltage after correction of lower bridge arm, +.>，/>For sampling timeKThe upper bridge arm reference voltage obtained through double closed loop control,/>for sampling timeKLower bridge arm reference voltage obtained through double closed loop control, < ->，/>For sampling timeKThe sum of the capacitor voltages of all the conducting submodules of the upper bridge arm,/->For sampling timeKThe sum of the capacitor voltages of all the conducting submodules of the lower leg,/->Is thatK-cumulative error calculated at-1, +.>Is thatKAccumulated errors calculated at that time;
and comprehensively considering the voltage balance of the capacitor, and selecting a conducting submodule based on the corrected bridge arm reference voltage to obtain a control signal of a switch in the submodule.
2. The MMC control method based on integral modulation of claim 1, wherein a double closed-loop control structure is adopted for sub-modules in upper and lower bridge arms of a single-phase modular multilevel converter, comprising:
the voltage of the capacitor of the submodule is controlled through the outer loop, and the load and the circulating current are controlled through the inner loop.
3. The MMC control method based on integral modulation of claim 2,
in the outer loop control, an error signal is obtained by comparing a capacitor voltage reference value with a bridge arm average capacitor voltageThe capacitor voltage is made to track the capacitor voltage reference value by the outer loop PI controller,
；
wherein,for the capacitor voltage reference value, ">For half-bridge submodule number,/-, for example>And->The upper bridge arm and the lower bridge arm are respectively the +.>Capacitor voltage of the sub-module.
4. The MMC control method based on integral modulation of claim 3, wherein the selecting the conductive sub-module based on the corrected bridge arm reference voltage, to obtain the control signal of the switch in the sub-module, includes:
sequencing submodules on an upper bridge arm and a lower bridge arm of the single-phase modularized multi-level converter according to capacitor voltages;
according to the ordered submodules, the upper bridge arm selection submodule and the lower bridge arm selection submodule are respectively conducted in the following mode:
calculating the number of turns on according to：
；
；
Wherein,representing post-ordering->Capacitor voltage of submodule->The corrected bridge arm reference voltage is respectively an upper bridge arm reference voltage and a lower bridge arm reference voltage; />For front->Sum of capacitor voltages of sub-modules +.>For front->The sum of the capacitor voltages of the sub-modules,
if it isThen select the order to be 1 to +.>The sub-module of the power supply is conducted, and a control signal of a switch in the sub-module is determined;
if it isThen select the order to be 1 to +.>Is turned on to determine a control signal for a switch in the sub-module.
5. The MMC control method based on integral modulation of claim 4,
if the bridge arm current is positive, the submodules are sequenced from the lowest capacitor voltage to the highest capacitor voltage;
if the bridge arm current is negative, the submodules order from the highest capacitor voltage to the lowest capacitor voltage.
6. An MMC control device based on integral modulation, characterized by comprising:
the control module is used for adopting a double closed-loop control structure for the submodules in the upper bridge arm and the lower bridge arm of the single-phase modularized multi-level converter to obtain the reference voltages of the upper bridge arm and the lower bridge arm; in particular, in the inner loop control of the double closed loop control,
controlling the load current by using a first PI controller, wherein the input of the first PI controller is a load current reference valueError from actual load current, the output of the first PI controller is +.>；
The load current is determined by:
；
；
wherein,for load current +.>And->Upper bridge arm voltage and lower bridge arm voltage respectively, +.>And->Upper bridge arm current and lower bridge arm current respectively, +.>And->Load resistance and load inductance, respectively, +.>The inductor is connected in series with the half bridge;
the circulating current is controlled by a second PI controller, and the input of the second PI controller is a circulating reference currentIs +.>Error between the first and second PI controller, the output of the second PI controller is +.>The cyclic reference current +.>The output of the outer loop control;
the circulating current is determined by:
；
；
wherein,is a direct current side voltage;
by outputtingAnd->Decoupling to obtain upper and lower bridge arm reference voltages +.>And->：
；
The correction module is used for correcting the obtained upper bridge arm reference voltage and the lower bridge arm reference voltage by adopting integral modulation, in particular,
the obtained upper and lower bridge arm reference voltages are corrected by adopting the following modes:
；
；
wherein,，/>for sampling timeKReference voltage after correction of upper bridge arm, +.>For sampling timeKReference voltage after correction of lower bridge arm, +.>，/>For sampling timeKUpper bridge arm reference voltage obtained through double closed loop control, < >>For sampling timeKThe lower bridge arm reference voltage obtained through double closed loop control,，/>for sampling timeKThe sum of the capacitor voltages of all the conducting submodules of the upper bridge arm,for sampling timeKThe sum of the capacitor voltages of all the conducting submodules of the lower leg,/->Is thatK-cumulative error calculated at-1, +.>Is thatKAccumulated errors calculated at that time;
the method comprises the steps of,
and the selection module is used for comprehensively considering the voltage balance of the capacitor, selecting a conducting submodule based on the corrected bridge arm reference voltage, and obtaining a control signal of a switch in the submodule.
7. An MMC control device based on integral modulation as claimed in claim 6, characterized in that the selection module is specifically adapted to,
sequencing submodules on an upper bridge arm and a lower bridge arm of the single-phase modularized multi-level converter according to capacitor voltages;
according to the ordered submodules, the upper bridge arm selection submodule and the lower bridge arm selection submodule are respectively conducted in the following mode:
calculating the number of turns on according to：
；
；
Wherein,representing post-ordering->Capacitor voltage of submodule->The corrected bridge arm reference voltage is respectively an upper bridge arm reference voltage and a lower bridge arm reference voltage; />For front->Sum of capacitor voltages of sub-modules +.>For front->The sum of the capacitor voltages of the sub-modules,
if it isThen select the order to be 1 to +.>The sub-module of the power supply is conducted, and a control signal of a switch in the sub-module is determined;
if it isThen select the order to be 1 to +.>Is turned on to determine a control signal for a switch in the sub-module.
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