CN113809945A - 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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CN113809945A
CN113809945A CN202111134314.7A CN202111134314A CN113809945A CN 113809945 A CN113809945 A CN 113809945A CN 202111134314 A CN202111134314 A CN 202111134314A CN 113809945 A CN113809945 A CN 113809945A
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bridge arm
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CN113809945B (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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Abstract

The invention discloses an MMC control method and a device based on integral modulation, wherein the method comprises the steps of adopting a double closed-loop control structure for sub-modules in an upper bridge arm and a lower bridge arm of a single-phase modular multilevel converter to obtain reference voltages of the upper bridge arm and the lower bridge arm; correcting the obtained reference voltages of the upper and lower bridge arms by adopting integral modulation; and comprehensively considering the voltage balance of the capacitor, and selecting the conducted sub-modules based on the corrected bridge arm reference voltage to obtain control signals of switches in the sub-modules. The invention can keep the balance between capacitor voltages and greatly reduce the average switching loss of the device.

Description

MMC control method and device based on integral modulation
Technical Field
The invention 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 (MMC) are widely used in high power scenarios, such as offshore wind farm systems and in the field of high voltage direct current transmission (HVDC). Compared with other types of multi-level converters, the modular multi-level converter has the following advantages: the method has the advantages of low manufacturing difficulty, low loss cost, low step voltage, high utilization rate, high redundancy, good output waveform quality and strong fault processing capability.
The traditional MMC modulation techniques mainly have three types: based on the carrier phase shift modulation technology, the carrier cascade modulation technology and the nearest level approximation modulation technology. The modulation technology based on the carrier wave is not easy to realize the standby of the redundant module, and has the problems of difficult equalization of capacitance and voltage, poor loss consistency of sub-modules and the like. Recently, although the level approximation modulation method is simple to implement, the quality of the generated voltage/current waveform is poor when the level number is low.
Disclosure of Invention
The invention aims to provide an MMC control method and device based on integral modulation, wherein a double closed-loop control structure is used, an outer ring controls the average capacitance voltage of each bridge arm, an inner ring controls load current and circulating current, the reference voltage of each bridge arm is modulated by an integral modulation technology, and then a conducted sub-module is selected to control the on-off of a switch, and simultaneously the balance between the voltage of capacitors is kept, so that the average switching loss of devices is greatly reduced.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the invention provides an MMC control method based on integral modulation, which comprises the following steps:
obtaining reference voltages of an upper bridge arm and a lower bridge arm by adopting a double closed-loop control structure for sub-modules in the upper bridge arm and the lower bridge arm of the single-phase modular multilevel converter;
correcting the obtained reference voltages of the upper and lower bridge arms by adopting integral modulation;
and comprehensively considering the voltage balance of the capacitor, and selecting the conducted sub-modules based on the corrected bridge arm reference voltage to obtain control signals of switches in the sub-modules.
Further, a double closed-loop control structure is adopted for sub-modules in upper and lower bridge arms of the single-phase modular multilevel converter, and the double closed-loop control structure comprises the following steps:
the capacitor voltage of the submodule is controlled by the outer loop and the load and circulating current are controlled by the inner loop.
Further, in the above-mentioned case,
in the outer ring control, an error signal is obtained by comparing a capacitor voltage reference value with the average capacitor voltage of a bridge arm
Figure BDA0003281477730000011
The capacitor voltage is made to track the capacitor voltage reference by the outer loop PI controller,
Figure BDA0003281477730000012
wherein the content of the first and second substances,
Figure BDA0003281477730000021
for the capacitor voltage reference, N is the number of half-bridge sub-modules,
Figure BDA0003281477730000022
and
Figure BDA0003281477730000023
the capacitor voltages of the jth sub-module on the upper bridge arm and the lower bridge arm are respectively.
Further, in the above-mentioned case,
controlling a load current by adopting a first PI controller, wherein the input of the first PI controller is a load current reference value irefThe error between the current and the actual load current is U, and the output of the first PI controller is UL-UU；
The load current is determined by:
Figure BDA0003281477730000024
i＝iU-iL；
wherein i is the load current, UUAnd ULUpper and lower bridge arm voltages, iUAnd iLRespectively an upper bridge arm current and a lower bridge arm current, RloadAnd LloadRespectively a load resistor and a load inductor, and L is a half-bridge series inductor;
controlling the circulating current by adopting a second PI controller, wherein the input of the second PI controller is circulating reference current
Figure BDA0003281477730000025
And the actual circulating current iSThe output of the second PI controller is UL+UUThe cyclic reference current
Figure BDA0003281477730000026
Is the output of the outer loop control;
the circulating current is determined by:
iS＝iU+iL；
Figure BDA0003281477730000027
wherein, UDCIs the dc side voltage.
Further, by applying a pair of outputs UL-UUAnd UL+UUDecoupling to obtain reference voltages of upper and lower bridge arms
Figure BDA0003281477730000028
And
Figure BDA0003281477730000029
Figure BDA00032814777300000210
further, the correcting the obtained reference voltages of the upper and lower bridge arms by using integral modulation includes:
U′ref(K)＝Uref(K)+int U(K-1)；
int U(K)＝int U(K-1)+Uref(K)-Usum(K)；
wherein the content of the first and second substances,
Figure BDA0003281477730000031
U′Uref(K) is a reference voltage U 'corrected by an upper bridge arm at a sampling time K'Lref(K) For sampling the reference voltage corrected by the lower bridge arm at the moment K,
Figure BDA0003281477730000032
UUref(K) upper bridge arm reference voltage, U, obtained by double closed-loop control for sampling time KLref(K) The lower bridge arm reference voltage is obtained by double closed-loop control at the sampling time K,
Figure BDA0003281477730000033
UUsum(K) is the sum of the capacitor voltages of all the conducting submodules of the bridge arm at the sampling moment K, ULsum(K) The sum of the capacitor voltages of all conducted submodules of the lower bridge arm at the sampling moment K.
Further, the selecting the conducting sub-module based on the corrected bridge arm reference voltage to obtain a control signal of a switch in the sub-module includes:
respectively sequencing the sub-modules on the upper bridge arm and the lower bridge arm of the single-phase modular multilevel converter according to the capacitor voltage;
and respectively conducting the upper bridge arm selection submodule and the lower bridge arm selection submodule according to the sorted submodules in the following modes:
the conduction number a is calculated according to the following formula:
Figure BDA0003281477730000034
Usum,a-1(K)≤U'ref(K)≤Usum,a(K)，
wherein the content of the first and second substances,
Figure BDA0003281477730000035
representing the capacitor voltage, U ', of the sequenced jth sub-module'ref(K) Dividing the corrected bridge arm reference voltage into an upper bridge arm reference voltage and a lower bridge arm reference voltage; u shapesum,a-1(K) Is the sum of the capacitor voltages of the first a-1 sub-modules, Usum,a(K) Is the sum of the capacitor voltages of the first a sub-modules,
if (| U'ref(K)-Usum,a(K)|＞|U'ref(K)-Usum,a-1(K) I), selecting submodules with the sequence from 1 to a-1 to conduct, and determining control signals of switches in the submodules;
if (| U'ref(K)-Usum,a(K)|＜|U'ref(K)-Usum,a-1(K) And |), selecting the submodules with the sequence from 1 to a to conduct, and determining the control signals of the switches in the submodules.
Further, in the above-mentioned case,
if the bridge arm current is positive, the sub-modules sort according to the capacitor voltage from the lowest to the highest;
if the bridge arm current is negative, the sub-modules are sorted from the highest capacitor voltage to the lowest capacitor voltage.
The invention also provides an MMC control device based on integral modulation, which comprises:
the control module is used for obtaining the reference voltages of the upper bridge arm and the lower bridge arm by adopting a double closed-loop control structure for the sub-modules in the upper bridge arm and the lower bridge arm of the single-phase modular multilevel converter;
the correction module is used for correcting the obtained reference voltages of the upper bridge arm and the lower bridge arm by adopting integral modulation;
and the number of the first and second groups,
and the selection module is used for comprehensively considering the voltage balance of the capacitor, selecting the conducted sub-module based on the corrected bridge arm reference voltage and obtaining a control signal of a switch in the sub-module.
Further, the modification module is specifically configured to,
correcting the obtained upper and lower bridge arm reference voltages by adopting the following method:
U′ref(K)＝Uref(K)+int U(K-1)；
int U(K)＝int U(K-1)+Uref(K)-Usum(K)；
wherein the content of the first and second substances,
Figure BDA0003281477730000041
U′Uref(K) is a reference voltage U 'corrected by an upper bridge arm at a sampling time K'Lref(K) For sampling the reference voltage corrected by the lower bridge arm at the moment K,
Figure BDA0003281477730000042
UUref(K) upper bridge arm reference voltage, U, obtained by double closed-loop control for sampling time KLref(K) The lower bridge arm reference voltage is obtained by double closed-loop control at the sampling time K,
Figure BDA0003281477730000043
UUsum(K) is the sum of the capacitor voltages of all the conducting submodules of the bridge arm at the sampling moment K, ULsum(K) The sum of the capacitor voltages of all conducted submodules of the lower bridge arm at the sampling moment K.
Further, the selection module is specifically configured to,
respectively sequencing the sub-modules on the upper bridge arm and the lower bridge arm of the single-phase modular multilevel converter according to the capacitor voltage;
and respectively conducting the upper bridge arm selection submodule and the lower bridge arm selection submodule according to the sorted submodules in the following modes:
the conduction number a is calculated according to the following formula:
Figure BDA0003281477730000044
Usum,a-1(K)≤U'ref(K)≤Usum,a(K)，
wherein the content of the first and second substances,
Figure BDA0003281477730000045
representing the capacitor voltage, U ', of the sequenced jth sub-module'ref(K) Dividing the corrected bridge arm reference voltage into an upper bridge arm reference voltage and a lower bridge arm reference voltage; u shapesum,a-1(K) Is the sum of the capacitor voltages of the first a-1 sub-modules, Usum,a(K) Is the sum of the capacitor voltages of the first a sub-modules,
if (| U'ref(K)-Usum,a(K)|＞|U'ref(K)-Usum,a-1(K) I), selecting submodules with the sequence from 1 to a-1 to conduct, and determining control signals of switches in the submodules;
if (| U'ref(K)-Usum,a(K)|＜|U'ref(K)-Usum,a-1(K) And |), selecting the submodules with the sequence from 1 to a to conduct, and determining the control signals of the switches in the submodules.
The invention achieves the following beneficial effects:
the invention provides an MMC control method based on integral modulation, which uses a double closed-loop control structure, an outer ring controls the average capacitance voltage of each bridge arm, an inner ring controls load current and circulating current, the reference voltage of each bridge arm is corrected through the integral modulation technology, and then a conducted sub-module is selected to control the on-off of a switch, so that the balance among capacitor voltages can be kept, and the average switching loss of a device is greatly reduced.
Drawings
Fig. 1 is a single-phase modular multilevel converter topology.
Fig. 2 is a schematic diagram of modulation and voltage balancing in the present invention.
Fig. 3 is a schematic diagram of the dual closed loop control of the present invention.
FIG. 4 is a graph comparing the number of commutations in the example of the present invention.
Detailed Description
The invention is further described below. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
The embodiment of the invention provides an MMC control method based on integral modulation, which comprises the following steps:
step 1: and establishing a dynamic equation of the single-phase modular multilevel converter based on the topological structure of the single-phase modular multilevel converter.
Step 2: and determining conducting sub-modules by comprehensively considering capacitance-voltage balance based on the established dynamic equation of the single-phase modular multilevel converter, wherein the conducting sub-modules comprise three stages of sequencing, selecting and integrating.
And step 3: and a double closed-loop control structure is adopted for the sub-modules which are determined to be conducted, the capacitance voltage of the sub-modules is controlled through an outer ring, the load and the output current are controlled through an inner ring, 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 keep the balance between the capacitor voltages.
In the embodiment of the invention, the dynamic equation of the single-phase modular multilevel converter is established as follows:
referring to fig. 1, a typical single-phase modular multilevel topology is composed of an upper bridge arm and a lower bridge arm, wherein each bridge arm comprises N identical half-bridge sub-modules (SM) and an inductor L connected in series. Voltage U of upper and lower bridge armsUAnd ULCan be expressed as:
Figure BDA0003281477730000051
wherein the content of the first and second substances,
Figure BDA0003281477730000061
the capacitive voltage of the jth sub-module of the upper bridge arm is referred to;
Figure BDA0003281477730000062
refers to the capacitive voltage of the jth sub-module of the lower bridge arm.
SjCan be expressed as:
Figure BDA0003281477730000063
each SM has two states, as shown in table 1.
TABLE 1
Figure BDA0003281477730000064
When the upper switch D1On and off of the lower switch D2When closed, USM＝UC(ii) a When the lower switch D2On and upper switch D1When closed, USM＝0。USMRepresenting the sub-module voltage.
In the on-state, the SM output voltage variation depends on the actual bridge arm current iarmFlow direction: when bridge arm current iarmTo be positive, the capacitor is in charge mode and the voltage across the sub-module will increase. When i isarmNegative, the capacitor is in discharge mode and the voltage across the sub-module will decrease. When SM is in OFF state, no matter iarmHow the flow direction is, the corresponding capacitive voltage U in SMCUnchanged, the voltage and current equations are:
Figure BDA0003281477730000065
i＝iU-iL (4)
in the formula, RloadAnd LloadRespectively, load resistance and load inductance, i is load current, iUFor upper arm current, iLFor lower bridge arm current, U is load voltage, UDCIs the dc side voltage.
Based on equation (3), the dynamic equation of a single-phase MMC can be expressed as:
Figure BDA0003281477730000071
in the formula, L is an inductor connected in series in the submodule;
α, β, γ are positive numbers:
Figure BDA0003281477730000072
in the embodiment of the invention, the conducting sub-modules are determined by comprehensively considering the voltage balance of the capacitors, and the conducting sub-modules comprise three stages of sorting, selecting and integrating. See FIG. 2, where UarmThe bridge arm voltage is represented by the voltage of the bridge arm,
Figure BDA0003281477730000073
representing the capacitor voltage of the first 1 st sub-module to the nth sub-module in the sequence. The method comprises the following specific steps:
(1) sorting phase
Firstly, sequencing all the sub-module capacitor voltages on one bridge arm according to a sequencing principle in the traditional balance algorithm. If the leg currents are positive (capacitor charging), the ranking will be from the lowest capacitor voltage to the highest voltage,
Figure BDA0003281477730000074
if the leg currents are negative (capacitor discharge), the ranking will be from the highest capacitor voltage to the lowest,
Figure BDA0003281477730000075
(2) selection phase
Based on the first stage sequencing and the bridge arm reference voltage selection submodule, the number of capacitors selected in one sampling period is denoted by a, as shown in equation (7).
Figure BDA0003281477730000076
When a is more than or equal to 1 and less than or equal to N (7)
Wherein the content of the first and second substances,
Figure BDA0003281477730000077
representing the capacitor voltage of the j-th sub-module after sorting, UrefIs the bridge arm reference voltage.
And (3) conducting selection on the sequenced submodules:
Figure BDA0003281477730000078
in the above formula, SM'1→SM′aSub-module conduction, SM 'representing 1 to a'a+1→SM′NThe submodules 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, as shown in the following formula:
Figure BDA0003281477730000079
in order to reduce the error between the bridge arm voltage and the reference voltage. Equation (10) is defined as follows:
Figure BDA0003281477730000081
wherein the content of the first and second substances,
Usum,a-1≤Uref≤Usum,a (11)
if (| U)ref-Usum,a|＞|Uref-Usum,a-1| then order Usum＝Usum,a-1；
If (| U)ref-Usum,a|＜|Uref-Usum,a-1| then order Usum＝Usum,a。
Therefore, the error ε is represented by the following equation:
ε＝Usum-Uref (12)
(3) integration phase
The integration stage is introduced to reduce the error e to 0. The reference voltage U is modified byrefAs follows:
U′ref(K)＝Uref(K)+int U(K-1) (13)
wherein the content of the first and second substances,
int U(K)＝int U(K-1)+Uref(K)-Usum(K) (14)
defining int U (0) as zero, the accumulated error int U (K-1) calculated at K-1 is added to the reference voltage U at K by the method described aboveref(K) The above. And adding the accumulated error of the previous moment into the voltage reference value of the current moment, so that the error of the current moment is greatly reduced, and the error can be gradually converged to 0 along with the continuous operation of the system. Therefore, in the actual working process, the voltage reference value U obtained by the outer ring controlref(K) The new reference value U 'is obtained through the integration stage'ref(K) Is of U'ref(K) For the purpose, the conducting sub-modules are selected by the selection stage, so that the error epsilon is reduced, and an ideal control effect is obtained.
In the embodiment of the invention, a double closed-loop control structure is adopted for the sub-modules, the capacitance voltage of the sub-modules is controlled through an outer ring, the load and the circulating current are controlled through an inner ring, the voltage applied by each bridge arm is modulated through an integral modulation technology to control the on-off of a switch, and the balance between the voltages of capacitors is kept at the same time, and the specific implementation process is as follows:
(1) outer loop control
Referring to fig. 3, in the outer loop control, an error signal shown in equation (15) is derived by comparing a capacitor voltage reference value with an average capacitor voltage
Figure BDA0003281477730000082
Capacitor voltage controlled by outer loop
Figure BDA0003281477730000083
Tracking reference values
Figure BDA0003281477730000084
Figure BDA0003281477730000085
And taking the output of the outer ring PI controller as a reference of the inner ring circulating current.
(2) Inner loop control
(1) Load current control
The load current is controlled using a PI controller, which directly affects the capacitor voltage ripple. Load current i ═ iU-iLCan be determined by equation (3) and equation (4):
Figure BDA0003281477730000091
the input of the PI controller is a load current reference value irefThe error between the current and the actual load current is the difference value U of the output of the PI controllerL-UU。
(2) Circulating current control
Controlling internal circulating current by adopting a PI controller, wherein the input of the PI controller is circulating reference current
Figure BDA0003281477730000092
And the actual circulating current iSThe reference value is obtained by the outer loop control. Circulating current iS＝iU+iLIs determined by equations (3) and (4) as follows:
Figure BDA0003281477730000093
the output of the PI controller is a difference value UL+UU。
Then, for UL-UUAnd UL+UUDecoupling to obtain bridge arm reference voltage
Figure BDA0003281477730000094
And
Figure BDA0003281477730000095
as shown in fig. 3, the decoupling process is:
Figure BDA0003281477730000096
Figure BDA0003281477730000097
in the context of figure 3, it is shown,
Figure BDA0003281477730000098
Figure BDA0003281477730000099
the average value of the upper arm and lower arm capacitance voltages is shown.
Finally, the modulation technology pair proposed in step 2 is used
Figure BDA00032814777300000910
And
Figure BDA00032814777300000911
modulating to obtain an upper switch D in the upper bridge arm and the lower bridge arm sub-module1And a lower switch D2The control signal of (2).
Finally, a single-phase MMC model is built by adopting MATLAB/Simulink based on the method provided by the invention, and specific parameters are shown in Table 2. For comparison, the simulation includes two modulation methods, the integral modulation method and the PWM method, and the modulation scheme provided by the present invention significantly reduces the average commutation times of the device compared to the PWM method, as shown in fig. 4. Thereby reducing the overall switching losses of the converter.
TABLE 2 Single-phase MMC model parameters
Figure BDA00032814777300000912
Figure BDA0003281477730000101
Compared with the traditional PWM method, the integral modulation technology provided by the invention reduces the commutation times. With the control method proposed by the present invention, 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 invention provides an MMC control apparatus based on integral modulation, including:
the control module is used for obtaining the reference voltages of the upper bridge arm and the lower bridge arm by adopting a double closed-loop control structure for the sub-modules in the upper bridge arm and the lower bridge arm of the single-phase modular multilevel converter;
the correction module is used for correcting the obtained reference voltages of the upper bridge arm and the lower bridge arm by adopting integral modulation;
and the number of the first and second groups,
and the selection module is used for comprehensively considering the voltage balance of the capacitor, selecting the conducted sub-module based on the corrected bridge arm reference voltage and obtaining a control signal of a switch in the sub-module.
In the embodiment of the present invention, the modification module is specifically configured to,
correcting the obtained upper and lower bridge arm reference voltages by adopting the following method:
U′ref(K)＝Uref(K)+int U(K-1)；
int U(K)＝int U(K-1)+Uref(K)-Usum(K)；
wherein the content of the first and second substances,
Figure BDA0003281477730000102
U′Uref(K) is a reference voltage U 'corrected by an upper bridge arm at a sampling time K'Lref(K) For sampling the reference voltage corrected by the lower bridge arm at the moment K,
Figure BDA0003281477730000103
UUref(K) upper bridge arm reference voltage, U, obtained by double closed-loop control for sampling time KLref(K) The lower bridge arm reference voltage is obtained by double closed-loop control at the sampling time K,
Figure BDA0003281477730000104
UUsum(K) is the sum of the capacitor voltages of all the conducting submodules of the bridge arm at the sampling moment K, ULsum(K) The sum of the capacitor voltages of all conducted submodules of the lower bridge arm at the sampling moment K.
In the embodiment of the present invention, the selection module is specifically configured to,
respectively sequencing the sub-modules on the upper bridge arm and the lower bridge arm of the single-phase modular multilevel converter according to the capacitor voltage;
and respectively conducting the upper bridge arm selection submodule and the lower bridge arm selection submodule according to the sorted submodules in the following modes:
the conduction number a is calculated according to the following formula:
Figure BDA0003281477730000111
Usum,a-1(K)≤U'ref(K)≤Usum,a(K)，
wherein the content of the first and second substances,
Figure BDA0003281477730000112
representing the capacitor voltage, U ', of the sequenced jth sub-module'ref(K) Dividing the corrected bridge arm reference voltage into an upper bridge arm reference voltage and a lower bridge arm reference voltage; u shapesum,a-1(K) Is the sum of the capacitor voltages of the first a-1 sub-modules, Usum,a(K) Is the sum of the capacitor voltages of the first a sub-modules,
if (| U'ref(K)-Usum,a(K)|＞|U'ref(K)-Usum,a-1(K) I), selecting submodules with the sequence from 1 to a-1 to conduct, and determining control signals of switches in the submodules;
if (| U'ref(K)-Usum,a(K)|＜|U'ref(K)-Usum,a-1(K) And |), selecting the submodules with the sequence from 1 to a to conduct, and determining the control signals of the switches in the submodules.
It is to be noted that the apparatus embodiment corresponds to the method embodiment, and the implementation manners of the method embodiment are all applicable to the apparatus embodiment and can achieve the same or similar technical effects, so that the details are not described herein.
As will be appreciated by one skilled in the art, 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 flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams 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 solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.

Claims (11)

1. An MMC control method based on integral modulation is characterized by comprising the following steps:
obtaining reference voltages of an upper bridge arm and a lower bridge arm by adopting a double closed-loop control structure for sub-modules in the upper bridge arm and the lower bridge arm of the single-phase modular multilevel converter;
correcting the obtained reference voltages of the upper and lower bridge arms by adopting integral modulation;
and comprehensively considering the voltage balance of the capacitor, and selecting the conducted sub-modules based on the corrected bridge arm reference voltage to obtain control signals of switches in the sub-modules.
2. The MMC control method based on integral modulation of claim 1, wherein a double closed-loop control structure is adopted for the sub-modules in the upper and lower bridge arms of the single-phase modular multilevel converter, and comprises:
the capacitor voltage of the submodule is controlled by the outer loop and the load and circulating current are controlled by the inner loop.
3. The MMC control method based on integral modulation of claim 2,
in the outer ring control, an error signal is obtained by comparing a capacitor voltage reference value with the average capacitor voltage of a bridge arm
Figure FDA0003281477720000011
Tracking capacitor voltage by outer loop PI controllerThe reference value of the voltage of the capacitor,
Figure FDA0003281477720000012
wherein the content of the first and second substances,
Figure FDA0003281477720000013
for the capacitor voltage reference, N is the number of half-bridge sub-modules,
Figure FDA0003281477720000014
and
Figure FDA0003281477720000015
the capacitor voltages of the jth sub-module on the upper bridge arm and the lower bridge arm are respectively.
4. The MMC control method based on integral modulation of claim 2, wherein, in the inner loop control,
controlling a load current by adopting a first PI controller, wherein the input of the first PI controller is a load current reference value irefThe error between the current and the actual load current is U, and the output of the first PI controller is UL-UU；
The load current is determined by:
Figure FDA0003281477720000016
i＝iU-iL；
wherein i is the load current, UUAnd ULUpper and lower bridge arm voltages, iUAnd iLRespectively an upper bridge arm current and a lower bridge arm current, RloadAnd LloadRespectively a load resistor and a load inductor, and L is a half-bridge series inductor;
controlling the circulating current with a second PI controllerInput is a cyclic reference current
Figure FDA0003281477720000017
And the actual circulating current iSThe output of the second PI controller is UL+UUThe cyclic reference current
Figure FDA0003281477720000018
Is the output of the outer loop control;
the circulating current is determined by:
iS＝iU+iL；
Figure FDA0003281477720000021
wherein, UDCIs the dc side voltage.
5. The MMC control method based on integral modulation of claim 4, wherein the output U is output byL-UUAnd UL+UUDecoupling to obtain reference voltages of upper and lower bridge arms
Figure FDA0003281477720000022
And
Figure FDA0003281477720000023
Figure FDA0003281477720000024
6. the MMC control method based on integral modulation of claim 5, wherein the correcting the obtained upper and lower bridge arm reference voltages by integral modulation comprises:
U′ref(K)＝Uref(K)+intU(K-1)；
intU(K)＝intU(K-1)+Uref(K)-Usum(K)；
wherein the content of the first and second substances,
Figure FDA0003281477720000025
U′Uref(K) is a reference voltage U 'corrected by an upper bridge arm at a sampling time K'Lref(K) For sampling the reference voltage corrected by the lower bridge arm at the moment K,
Figure FDA0003281477720000026
UUref(K) upper bridge arm reference voltage, U, obtained by double closed-loop control for sampling time KLref(K) The lower bridge arm reference voltage is obtained by double closed-loop control at the sampling time K,
Figure FDA0003281477720000027
UUsum(K) is the sum of the capacitor voltages of all the conducting submodules of the bridge arm at the sampling moment K, ULsum(K) The sum of the capacitor voltages of all conducted submodules of the lower bridge arm at the sampling moment K.
7. The MMC control method based on integral modulation of claim 6, wherein the selecting the sub-module that is turned on based on the corrected bridge arm reference voltage to obtain the control signal of the switch in the sub-module comprises:
respectively sequencing the sub-modules on the upper bridge arm and the lower bridge arm of the single-phase modular multilevel converter according to the capacitor voltage;
and respectively conducting the upper bridge arm selection submodule and the lower bridge arm selection submodule according to the sorted submodules in the following modes:
the conduction number a is calculated according to the following formula:
Figure FDA0003281477720000031
Usum,a-1(K)≤U′ref(K)Usum,a(K)，
wherein the content of the first and second substances,
Figure FDA0003281477720000032
representing the capacitor voltage, U ', of the sequenced jth sub-module'ref(K) Dividing the corrected bridge arm reference voltage into an upper bridge arm reference voltage and a lower bridge arm reference voltage; u shapesum,a-1(K) Is the sum of the capacitor voltages of the first a-1 sub-modules, Usum,a(K) Is the sum of the capacitor voltages of the first a sub-modules,
if (| U'ref(K)-Usum,a(K)|＞|U′ref(K)-Usum,a-1(K) I), selecting submodules with the sequence from 1 to a-1 to conduct, and determining control signals of switches in the submodules;
if (| U'ref(K)-Usum,a(K)|＜|U′ref(K)-Usum,a-1(K) And |), selecting the submodules with the sequence from 1 to a to conduct, and determining the control signals of the switches in the submodules.
8. The MMC control method based on integral modulation of claim 7,
if the bridge arm current is positive, the sub-modules sort according to the capacitor voltage from the lowest to the highest;
if the bridge arm current is negative, the sub-modules are sorted from the highest capacitor voltage to the lowest capacitor voltage.
9. An MMC control device based on integral modulation, characterized by comprising:
the control module is used for obtaining the reference voltages of the upper bridge arm and the lower bridge arm by adopting a double closed-loop control structure for the sub-modules in the upper bridge arm and the lower bridge arm of the single-phase modular multilevel converter;
the correction module is used for correcting the obtained reference voltages of the upper bridge arm and the lower bridge arm by adopting integral modulation;
and the number of the first and second groups,
and the selection module is used for comprehensively considering the voltage balance of the capacitor, selecting the conducted sub-module based on the corrected bridge arm reference voltage and obtaining a control signal of a switch in the sub-module.
10. The MMC control device based on integral modulation of claim 9, wherein the correction module is specifically configured to,
correcting the obtained upper and lower bridge arm reference voltages by adopting the following method:
U′ref(K)＝Uref(K)+intU(K-1)；
intU(K)＝intU(K-1)+Uref(K)-Usum(K)；
wherein the content of the first and second substances,
Figure FDA0003281477720000041
U′Uref(K) is a reference voltage U 'corrected by an upper bridge arm at a sampling time K'Lref(K) For sampling the reference voltage corrected by the lower bridge arm at the moment K,
Figure FDA0003281477720000042
UUref(K) upper bridge arm reference voltage, U, obtained by double closed-loop control for sampling time KLref(K) The lower bridge arm reference voltage is obtained by double closed-loop control at the sampling time K,
Figure FDA0003281477720000043
UUsum(K) is the sum of the capacitor voltages of all the conducting submodules of the bridge arm at the sampling moment K, ULsum(K) The sum of the capacitor voltages of all conducted submodules of the lower bridge arm at the sampling moment K.
11. The MMC control device based on integral modulation of claim 10, wherein the selection module is specifically configured to,
respectively sequencing the sub-modules on the upper bridge arm and the lower bridge arm of the single-phase modular multilevel converter according to the capacitor voltage;
and respectively conducting the upper bridge arm selection submodule and the lower bridge arm selection submodule according to the sorted submodules in the following modes:
the conduction number a is calculated according to the following formula:
Figure FDA0003281477720000044
Usum,a-1(K)≤U′ref(K)≤Usum,a(K)，
wherein the content of the first and second substances,
Figure FDA0003281477720000045
representing the capacitor voltage, U ', of the sequenced jth sub-module'ref(K) Dividing the corrected bridge arm reference voltage into an upper bridge arm reference voltage and a lower bridge arm reference voltage; u shapesum,a-1(K) Is the sum of the capacitor voltages of the first a-1 sub-modules, Usum,a(K) Is the sum of the capacitor voltages of the first a sub-modules,
if (| U'ref(K)-Usum,a(K)|＞|U′ref(K)-Usum,a-1(K) I), selecting submodules with the sequence from 1 to a-1 to conduct, and determining control signals of switches in the submodules;
if (| U'ref(K)-Usum,a(K)|＜|U′ref(K)-Usum,a-1(K) And |), selecting the submodules with the sequence from 1 to a to conduct, and determining the control signals of the switches in the submodules.
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