CN111697853B - Hybrid modulation method of modular multilevel converter - Google Patents

Hybrid modulation method of modular multilevel converter Download PDF

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Publication number
CN111697853B
CN111697853B CN202010492094.4A CN202010492094A CN111697853B CN 111697853 B CN111697853 B CN 111697853B CN 202010492094 A CN202010492094 A CN 202010492094A CN 111697853 B CN111697853 B CN 111697853B
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bridge arm
modulation
sub
modular multilevel
modules
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CN111697853A (en
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马柯
贺斌
蔡旭
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Shanghai Jiaotong University
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Shanghai Jiaotong University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
    • 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
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0038—Circuits or arrangements for suppressing, e.g. by masking incorrect turn-on or turn-off signals, e.g. due to current spikes in current mode control

Abstract

The invention provides a hybrid modulation method of a modular multilevel converter, which divides a modulation wave of each bridge arm of the modular multilevel converter into two parts according to alternating current output voltage and circulating current suppression control voltage, and carries out nearest level approximation modulation on the alternating current output voltage part of the modulation wave; pulse width modulation is carried out on the modulation wave circulation current suppression control voltage part; acquiring the capacitance voltage and the bridge arm current of a submodule in each bridge arm of the converter, and sequencing the capacitance voltage of submodules of the modular multilevel converter; and redistributing the trigger pulses of the sub-modules of the modular multilevel converter according to the nearest level approximation modulation of the first part of the modulation wave, the pulse width modulation of the second part of the modulation wave and the sequencing result of the capacitance and the voltage of the sub-modules. The invention can more finely modulate the circulating current suppression voltage under the condition of not increasing the switching frequency obviously, and eliminates the influence of the circulating current suppression voltage on the direct current side of the MMC under the traditional recent level approximation modulation.

Description

Hybrid modulation method of modular multilevel converter
Technical Field
The invention relates to the technical field of power electronics, in particular to a hybrid modulation method of a modular multilevel converter.
Background
The Modular Multilevel Converter (MMC) has the characteristics of high modular design, low harmonic content of output voltage and easiness in expanding voltage and power grade, and is widely applied to various medium-voltage and high-power electric energy conversion scenes, such as flexible direct-current transmission, new energy collection, intelligent transformers, motor driving and the like.
At present, the mainstream Modulation technology of the MMC includes two types, namely Carrier Phase Shift Pulse-width Modulation (CPS-PWM) and Nearest Level Control (NLC). CPS-PWM has good harmonic characteristics, but the switching frequency is high, and when the number of MMC sub-modules is large, a large amount of computing resources are needed, so that the CPS-PWM is mainly applied to the MMC with only a few sub-modules. NLC modulation respectively calculates the number of the switching-on sub-modules of the upper bridge arm and the lower bridge arm according to the modulation wave and switches on the sub-modules with corresponding number, and step waves are formed at MMC alternating current output. The method has the characteristics of low switching frequency of the sub-modules and small calculation burden, and is widely applied to MMC scenes with dozens of hundreds of sub-modules.
Negative-sequence double-frequency circulation exists on a bridge arm of the MMC, the circulation can increase the fluctuation of capacitance on the submodule and can also increase the loss on the submodule, and the circulation is also an important control target of the MMC. There are many methods for restraining the circulation current, including a proportional-integral controller in a rotating coordinate system, a proportional-resonant controller in a stationary coordinate system, etc., and these methods are all essentially that a circulation current restraining voltage with a frequency doubling negative sequence is superimposed on a modulation wave of a bridge arm to restrain the circulation current.
However, when the MMC is applied in a medium-voltage scenario, each bridge arm only has dozens of sub-modules, and the circulating current suppression voltage is smaller than the voltage of one sub-module capacitor. The NLC modulation can accurately modulate the alternating current output voltage, and the circulating current restraining voltage is difficult to accurately modulate, so that the direct current side current and power fluctuation of the MMC is caused.
At present, no explanation or report of the similar technology of the invention is found, and similar data at home and abroad are not collected.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a hybrid modulation method of a modular multilevel converter capable of inhibiting direct current fluctuation, which eliminates direct current side current fluctuation caused by circulation current inhibition in an MMC modulated by NLC in a medium-voltage scene.
The invention is realized by the following technical scheme.
A hybrid modulation method of a modular multilevel converter comprises the following steps:
dividing a modulation wave of each bridge arm of the modular multilevel converter into two parts according to alternating current output voltage and circulating current suppression control voltage;
carrying out nearest level approximation modulation on an alternating current output voltage part of the modulation wave of the modular multilevel converter;
dividing the ring current suppression control voltage part of the modulation waves of the upper bridge arm and the lower bridge arm of the modular multilevel converter into two parts according to positive and negative half cycles, and respectively carrying out pulse width modulation;
sampling the capacitor voltages of all sub-modules on each bridge arm of the modular multilevel converter and corresponding bridge arm currents, and sequencing the capacitor voltages of the sub-modules according to the direction of the bridge arm currents;
and dividing the sub-modules in the bridge arms into n operation modes according to the sequencing result of the sub-module capacitor voltage in the bridge arms of the modular multilevel converter, and redistributing the trigger pulse of the sub-modules on each bridge arm.
Preferably, dividing the modulation wave of each bridge arm of the modular multilevel converter into two parts according to the alternating current output voltage and the circulating current suppression control voltage, comprises:
each bridge arm of the modular multilevel converter is provided with N sub-modules, and the direct-current side voltage of the modular multilevel converter is VdcThen the average value of the sub-module voltage is Uc＝Vdc/N；
Modulation wave of upper bridge arm in each phase of the modular multilevel converter
Figure BDA0002521449740000021
Expressed as:
Figure BDA0002521449740000022
lower bridge arm modulated wave
Figure BDA0002521449740000023
Expressed as:
Figure BDA0002521449740000024
in the formula (I), the compound is shown in the specification,
Figure BDA0002521449740000025
is the j-th ac output voltage reference of the modular multilevel converter,
Figure BDA0002521449740000026
is the j-th phase circulating current suppression control voltage reference value;
dividing the modulation wave of the upper bridge arm of the j phase into two parts according to the alternating current output voltage and the circulating current suppression control voltage, wherein the alternating current output voltage part of the modulation wave of the upper bridge arm
Figure BDA0002521449740000027
Comprises the following steps:
Figure BDA0002521449740000031
the circulating current suppression control voltage part of the upper bridge arm modulation wave is
Figure BDA0002521449740000032
Dividing the modulation wave of the j-th phase lower bridge arm into two parts according to the alternating current output voltage and the circulating current suppression control voltage, wherein the alternating current output voltage part of the modulation wave of the lower bridge arm
Figure BDA0002521449740000033
Comprises the following steps:
Figure BDA0002521449740000034
the circulating current suppression control voltage part of the lower bridge arm modulation wave is
Figure BDA0002521449740000035
Preferably, the nearest level approach modulation is performed on the alternating current output voltage part of the modulation wave of the modular multilevel converter, and the method comprises the following steps:
the number of submodules for calculating the nearest level approximation modulation switching-on of the upper bridge arm is as follows:
Figure BDA0002521449740000036
in the formula, m is the number of sub-modules of the upper bridge arm which are closest to the modulation and are switched on, round (x) represents that the rounding operation is carried out on x, N is the number of the sub-modules on each bridge arm,
Figure BDA0002521449740000037
jth intersection for modular multilevel converterReference value of current output voltage, UcIs the average value of the sub-module voltages,
Figure BDA0002521449740000038
is the AC output voltage part of the upper bridge arm modulation wave,
Figure BDA0002521449740000039
an AC output voltage part for the modulation wave of the lower bridge arm;
the number of the submodules which are turned on by the nearest level approximation modulation in the lower bridge arm is as follows:
Figure BDA00025214497400000310
preferably, the step of dividing the ring current suppression control voltage part of the modulation wave of the upper and lower bridge arms of the modular multilevel converter into two parts according to the positive and negative half cycles, and performing pulse width modulation respectively comprises:
the circulation current of the modulation waves of the upper and lower bridge arms of the j-th phase is restrained and controlled by the voltage part
Figure BDA00025214497400000311
The device is divided into the following two parts according to positive and negative half cycles:
Figure BDA00025214497400000312
Figure BDA00025214497400000313
in the formula (I), the compound is shown in the specification,
Figure BDA00025214497400000314
representation modulation generation
Figure BDA00025214497400000315
The positive half-cycle portion of (a),
Figure BDA00025214497400000316
representation modulation generation
Figure BDA00025214497400000317
Negative half-cycle part of (U)cThe submodule voltage average value is taken;
the modulated wave of the upper and lower bridge arms is circularly suppressed to control the voltage part
Figure BDA0002521449740000041
Positive and negative half cycle parts of
Figure BDA0002521449740000042
And
Figure BDA0002521449740000043
a comparison is made with the same triangular carrier, wherein,
Figure BDA0002521449740000044
PWM trigger pulse S for generation1j，
Figure BDA0002521449740000045
For generating PWM trigger pulses S2j。
Preferably, the pulse width modulation is performed on positive and negative half cycle portions of the circulating current suppression control voltage portion of the upper and lower bridge arm modulation waves of the modular multilevel converter, so as to obtain the PWM trigger pulse, and the pulse width modulation includes:
when in use
Figure BDA0002521449740000046
When smaller than the triangular carrier, S1jOutput 1, submodule is put into; when in use
Figure BDA0002521449740000047
When the triangular carrier is larger than or equal to S1jOutputting 0, cutting off the submodule;
when in use
Figure BDA0002521449740000048
Is greater than or equal toWhen a triangular carrier wave is used, S2jOutput 1, submodule is put into; when in use
Figure BDA0002521449740000049
When smaller than the triangular carrier, S2jOutputting 0, cutting off the submodule;
the j-phase upper and lower bridge arms use the same carrier wave to perform pulse width modulation and have the same PWM trigger pulse.
Preferably, sampling capacitor voltages of all sub-modules and corresponding bridge arm currents on each bridge arm of the modular multilevel converter, and sorting the capacitor voltages of the sub-modules according to the direction of the bridge arm currents, includes:
collecting the capacitance voltages of all sub-modules on the bridge arm and the currents flowing through the bridge arm, and when the currents flowing through the bridge arm are larger than zero, arranging the capacitance voltages of the sub-modules in an ascending order; and when the current flowing through the bridge arm is less than zero, the capacitance and voltage of the sub-modules are arranged in a descending order.
Preferably, according to the sequencing result of the sub-module capacitor voltages in the bridge arm of the modular multilevel converter, the sub-modules in the bridge arm are divided into n operation modes, and the redistribution of the trigger pulse of the sub-modules on each bridge arm includes:
setting n to 4, namely dividing the neutron modules of the bridge arms into 4 operation modes with different trigger pulses;
according to the sequencing result of the capacitor voltage of the sub-modules in the bridge arm, the 1 st to mth sub-modules operate in a mode 1 after sequencing; the (m + 1) th submodule after sequencing runs in a mode 2; the (m + 2) th submodule after sequencing runs in a mode 3; and (4) operating the m +3 th to N th sub-modules in the mode 4 after the sorting.
Preferably, the sub-modules in the bridge arm are divided into 4 operation modes with different trigger pulses, including:
the mode 1 is as follows: the submodule is in a recent level approaching modulation state, and the submodule is put into use;
the mode 2 is as follows: the submodule is in PWM modulation state, and the trigger pulse is PWM switching signal S1j；
The mode 3 is as follows: at the submoduleIn the PWM modulation state, the trigger pulse is a PWM switching signal S2j；
The mode 4 is as follows: the sub-module is in the most recent level-approaching modulation state and the sub-module is cut off.
Preferably, the submodules on each bridge arm of the modular multilevel converter adopt a half-bridge submodule structure.
Preferably, a digital signal processor, an FPGA chip and/or an arithmetic circuit are adopted to realize alternating current output voltage control, circulation suppression control, calculation of the number of recent level approaching modulation and opening submodules, division of positive and negative half cycles of a modulation wave circulation suppression control voltage part and generation of PWM trigger pulses.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a hybrid modulation method of a modular multilevel converter, which is a modulation strategy capable of inhibiting direct current fluctuation, and the method divides a modulation wave of the modular multilevel converter into two parts according to alternating current output voltage and circulating current inhibition control voltage, and carries out nearest level approximation modulation on the alternating current output voltage part of the modulation wave; pulse width modulation is carried out on the modulation wave circulation current suppression control voltage part to obtain a PWM switching signal; collecting the capacitance voltage of the sub-modules on each bridge arm and the current flowing through the bridge arms, and sequencing the capacitance voltages of the sub-modules of the modular multilevel converter; and redistributing the trigger pulses of the sub-modules of the modular multilevel converter according to the nearest level approximation modulation of the first part of the modulation wave, the pulse width modulation of the second part of the modulation wave and the sequencing result of the capacitance and the voltage of the sub-modules. The invention can more finely modulate the circulating current suppression voltage under the condition of not increasing the switching frequency, and eliminates the influence of the circulating current suppression voltage on the direct current side of the MMC under the traditional recent level approximation modulation.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
fig. 1 is a schematic structural diagram of a modular multilevel cascaded converter (MMC) using half-bridge sub-modules according to a preferred embodiment of the present invention;
fig. 2 is a flowchart of a hybrid modulation method of a modular multilevel converter according to a preferred embodiment of the present invention (taking the above bridge arm as an example);
fig. 3 is a schematic diagram of an operating structure and an operating process of a hybrid modulation method of a modular multilevel converter according to a preferred embodiment of the present invention (taking the above bridge arm as an example);
fig. 4 is a schematic diagram of modulation waveforms and PWM switching signals of a PWM part of a hybrid modulation method of a modular multilevel converter according to a preferred embodiment of the present invention;
FIG. 5 is a schematic diagram of the sub-module operation mode and trigger pulse allocation provided in a preferred embodiment of the present invention;
FIG. 6 is a graph showing simulation results of AC side voltage when the hybrid modulation method according to the preferred embodiment of the present invention is used;
fig. 7 is a diagram showing simulation results of the circulating current suppression voltage when the conventional NLC modulation method and the hybrid modulation method provided by a preferred embodiment of the present invention are used; wherein, (a) is a traditional NLC modulation method, and (b) is a mixed modulation method;
fig. 8 is a comparison graph of the circulation simulation results when the conventional NLC modulation method and the hybrid modulation method provided by a preferred embodiment of the present invention are used;
fig. 9 is a diagram showing simulation results of dc side current when the conventional NLC modulation method and the hybrid modulation method provided by a preferred embodiment of the present invention are used;
fig. 10 is a diagram illustrating simulation results of sub-module capacitor voltages when the hybrid modulation method provided by the embodiment of the present invention is used.
Detailed Description
The following examples illustrate the invention in detail: the embodiment is implemented on the premise of the technical scheme of the invention, and a detailed implementation mode and a specific operation process are given. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.
The embodiment of the invention provides a hybrid modulation method of a modular multilevel converter capable of inhibiting direct current fluctuation, which comprises the following steps:
s1, dividing the modulation wave of each bridge arm of the modular multilevel converter into two parts according to the alternating current output voltage and the circulating current suppression control voltage;
s2, carrying out nearest level approximation modulation on the alternating current output voltage part of the modulation wave of the modular multilevel converter;
s3, dividing the ring current suppression control voltage part of the modulation wave of the upper bridge arm of the modular multilevel converter into two parts according to positive and negative half cycles for pulse width modulation respectively, and dividing the lower bridge arm according to the same method;
s4, sampling the capacitance voltages of all sub-modules on each bridge arm of the modular multilevel converter and corresponding bridge arm currents, and sequencing the capacitance voltages of the sub-modules according to the direction of the bridge arm currents;
and S5, dividing the sub-modules in the bridge arms into n operation modes according to the sequencing result of the sub-module capacitor voltage in the bridge arms of the modular multilevel converter, and redistributing the trigger pulse of the sub-modules on each bridge arm.
As a preferred embodiment, S1, includes:
assuming that each bridge arm of the modular multilevel converter has N sub-modules, the direct-current side voltage of the modular multilevel converter is VdcThen the average value of the sub-module voltage is Uc＝Vdc/N；
Modulation wave of upper bridge arm in each phase of modular multilevel converter
Figure BDA0002521449740000061
Expressed as:
Figure BDA0002521449740000062
lower bridge arm modulated wave
Figure BDA0002521449740000063
Expressed as:
Figure BDA0002521449740000064
in the formula (I), the compound is shown in the specification,
Figure BDA0002521449740000071
is the j-th ac output voltage reference of the modular multilevel converter,
Figure BDA0002521449740000072
is the j-th phase circulating current suppression control voltage reference value;
dividing the modulation wave of the upper bridge arm of the j phase into two parts according to the alternating current output voltage and the circulating current suppression control voltage, wherein the alternating current output voltage part of the modulation wave of the upper bridge arm
Figure BDA0002521449740000073
Comprises the following steps:
Figure BDA0002521449740000074
the circulating current suppression control voltage part of the upper bridge arm modulation wave is
Figure BDA0002521449740000075
Dividing the modulation wave of the j-th phase lower bridge arm into two parts according to the alternating current output voltage and the circulating current suppression control voltage, wherein the alternating current output voltage part of the modulation wave of the lower bridge arm
Figure BDA0002521449740000076
Comprises the following steps:
Figure BDA0002521449740000077
the circulating current suppression control voltage part of the lower bridge arm modulation wave is
Figure BDA0002521449740000078
As a preferred embodiment, S2, includes:
the number of submodules for calculating the nearest level approximation modulation switching-on of the upper bridge arm is as follows:
Figure BDA0002521449740000079
wherein m is the number of submodules for the upper bridge arm to be turned on by the nearest level approximation modulation, round (x) represents that the integer operation is carried out on x, the result is an integer obtained by rounding x, N is the number of submodules on each bridge arm,
Figure BDA00025214497400000710
reference value of j-th AC output voltage, U, for modular multilevel convertercIs the average value of the sub-module voltages,
Figure BDA00025214497400000711
is the AC output voltage part of the upper bridge arm modulation wave,
Figure BDA00025214497400000712
an AC output voltage part for the modulation wave of the lower bridge arm;
the number of the submodules which are turned on by the nearest level approximation modulation in the lower bridge arm is as follows:
Figure BDA00025214497400000713
as a preferred embodiment, S3, includes:
the circulation current of the modulation wave of the upper bridge arm of the j phase is restrained and controlled by the voltage part
Figure BDA00025214497400000714
The device is divided into the following two parts according to positive and negative half cycles:
Figure BDA00025214497400000715
Figure BDA00025214497400000716
in the formula (I), the compound is shown in the specification,
Figure BDA0002521449740000081
representation modulation generation
Figure BDA0002521449740000082
The positive half-cycle portion of (a),
Figure BDA0002521449740000083
representation modulation generation
Figure BDA0002521449740000084
Negative half-cycle part of (U)cThe submodule voltage average value is taken;
the j-phase lower bridge arm divides the circulating current suppression control voltage part into parts according to the same method as the j-phase upper bridge arm
Figure BDA0002521449740000085
And
Figure BDA0002521449740000086
two parts;
the j-phase upper and lower bridge arms have the same
Figure BDA0002521449740000087
And
Figure BDA0002521449740000088
the modulated wave of the upper and lower bridge arms is circularly suppressed to control the voltage part
Figure BDA0002521449740000089
Positive and negative half cycle parts of
Figure BDA00025214497400000810
And
Figure BDA00025214497400000811
a comparison is made with the same triangular carrier, wherein,
Figure BDA00025214497400000812
PWM trigger pulse S for generation1j，
Figure BDA00025214497400000813
For generating PWM trigger pulses S2j；
In particular, the amount of the solvent to be used,
when in use
Figure BDA00025214497400000814
When smaller than the triangular carrier, S1jOutput 1, submodule is put into; when in use
Figure BDA00025214497400000815
When the triangular carrier is larger than or equal to S1jOutputting 0, cutting off the submodule;
when in use
Figure BDA00025214497400000816
When the triangular carrier is larger than or equal to S2jOutput 1, submodule is put into; when in use
Figure BDA00025214497400000817
When smaller than the triangular carrier, S2jOutputting 0, cutting off the submodule;
the j-phase upper and lower bridge arms use the same carrier wave to perform pulse width modulation and have the same PWM trigger pulse. .
As a preferred embodiment, S4, includes:
collecting the capacitance voltages of all sub-modules on the bridge arm and the currents flowing through the bridge arm, and when the currents flowing through the bridge arm are larger than zero, arranging the capacitance voltages of the sub-modules in an ascending order; and when the current flowing through the bridge arm is less than zero, the capacitance and voltage of the sub-modules are arranged in a descending order.
As a preferred embodiment, S5, includes:
setting n to 4, namely dividing the neutron modules of the bridge arms into 4 operation modes with different trigger pulses;
according to the sequencing result of the capacitor voltage of the sub-modules in the bridge arm, the 1 st to mth sub-modules operate in a mode 1 after sequencing; the (m + 1) th submodule after sequencing runs in a mode 2; the (m + 2) th submodule after sequencing runs in a mode 3; and (4) operating the m +3 th to N th sub-modules in the mode 4 after the sorting.
In particular, the amount of the solvent to be used,
the mode 1 is as follows: the submodule is in a recent level approaching modulation state, and the submodule is put into use;
the mode 2 is as follows: the submodule is in PWM modulation state, and the trigger pulse is PWM switching signal S1j；
The mode 3 is as follows: the submodule is in PWM modulation state, and the trigger pulse is PWM switching signal S2j；
Mode 4 is: the sub-module is in the most recent level-approaching modulation state and the sub-module is cut off.
As a preferred embodiment, the sub-modules on each bridge arm of the modular multilevel converter adopt a half-bridge sub-module structure.
As a preferred embodiment, a chip (such as a digital signal processor, an FPGA chip, etc.), an arithmetic circuit and/or software are used to implement ac output voltage control, circulation suppression control, calculation of the number of sub-modules for nearest level approaching modulation turn-on, division of positive and negative half cycles of a modulated wave circulation suppression control voltage part, and generation of PWM trigger pulses.
The hybrid modulation method of the modular multilevel converter provided by the embodiment of the invention is further described in detail with reference to the accompanying drawings.
Fig. 1 is a schematic structural diagram of a Modular Multilevel Converter (MMC) using half-bridge sub-modules according to an embodiment of the present invention. The modular multilevel converter in fig. 1 includes six three-phase arms, each arm is formed by connecting 16 half-bridge submodules in series, the rated power of the modular multilevel converter is 20MW, and the total direct-current bus voltage is Vdc20kV per dayThe voltage average value of the sub-module capacitor is Uc＝VdcThe method is mainly suitable for MMC medium-voltage application scenes with dozens of sub-modules on each bridge arm.
The hybrid modulation method provided by the embodiment of the present invention is specifically described below, as shown in fig. 2 and fig. 3.
Modulation wave of upper bridge arm in each phase of modular multilevel converter
Figure BDA0002521449740000091
Expressed as:
Figure BDA0002521449740000092
lower bridge arm modulated wave
Figure BDA0002521449740000093
Expressed as:
Figure BDA0002521449740000094
in the formula (I), the compound is shown in the specification,
Figure BDA0002521449740000095
is the j-th ac output voltage reference of the modular multilevel converter,
Figure BDA0002521449740000096
is the j-th phase circulating current suppression control voltage reference value;
dividing the modulation wave of the upper bridge arm of the j phase into two parts according to the alternating current output voltage and the circulating current suppression control voltage, wherein the alternating current output voltage part of the modulation wave of the upper bridge arm
Figure BDA0002521449740000097
Comprises the following steps:
Figure BDA0002521449740000098
the circulating current suppression control voltage part of the upper bridge arm modulation wave is
Figure BDA0002521449740000099
Dividing the modulation wave of the j-th phase lower bridge arm into two parts according to the alternating current output voltage and the circulating current suppression control voltage, wherein the alternating current output voltage part of the modulation wave of the lower bridge arm
Figure BDA00025214497400000910
Comprises the following steps:
Figure BDA00025214497400000911
the circulating current suppression control voltage part of the lower bridge arm modulation wave is
Figure BDA00025214497400000912
The number of submodules for calculating the nearest level approximation modulation switching-on of the upper bridge arm is as follows:
Figure BDA0002521449740000101
wherein m is the number of submodules for the upper bridge arm to be turned on by the nearest level approximation modulation, round (x) represents that the integer operation is carried out on x, the result is an integer obtained by rounding x, N is the number of submodules on each bridge arm,
Figure BDA0002521449740000102
reference value of j-th AC output voltage, U, for modular multilevel convertercIs the average value of the sub-module voltages,
Figure BDA0002521449740000103
is the AC output voltage part of the upper bridge arm modulation wave,
Figure BDA0002521449740000104
an AC output voltage part for the modulation wave of the lower bridge arm;
the number of the submodules which are turned on by the nearest level approximation modulation in the lower bridge arm is as follows:
Figure BDA0002521449740000105
the circulation current of the modulation wave of the upper bridge arm of the j phase is restrained and controlled by the voltage part
Figure BDA0002521449740000106
The device is divided into the following two parts according to positive and negative half cycles:
Figure BDA0002521449740000107
Figure BDA0002521449740000108
in the formula (I), the compound is shown in the specification,
Figure BDA0002521449740000109
representation modulation generation
Figure BDA00025214497400001010
The positive half-cycle portion of (a),
Figure BDA00025214497400001011
representation modulation generation
Figure BDA00025214497400001012
Negative half-cycle part of (U)cThe submodule voltage average value is taken;
the j-phase lower bridge arm divides the circulating current suppression control voltage part into parts according to the same method as the j-phase upper bridge arm
Figure BDA00025214497400001013
And
Figure BDA00025214497400001014
two parts;
the j-phase upper and lower bridge arms have the same
Figure BDA00025214497400001015
And
Figure BDA00025214497400001016
the modulated wave of the upper and lower bridge arms is circularly suppressed to control the voltage part
Figure BDA00025214497400001017
Positive and negative half cycle parts of
Figure BDA00025214497400001018
And
Figure BDA00025214497400001019
a comparison is made with the same triangular carrier, wherein,
Figure BDA00025214497400001020
PWM trigger pulse S for generation1j，
Figure BDA00025214497400001021
For generating PWM trigger pulses S2j；
When in use
Figure BDA00025214497400001022
When smaller than the triangular carrier, S1jOutput 1, submodule is put into; when in use
Figure BDA00025214497400001023
When the triangular carrier is larger than or equal to S1jOutputting 0, cutting off the submodule;
when in use
Figure BDA00025214497400001024
When the triangular carrier is larger than or equal to S2jOutput 1, submodule is put into; when in use
Figure BDA00025214497400001025
When smaller than the triangular carrier, S2jOutputting 0, cutting off the submodule;
the j-phase upper and lower bridge arms use the same carrier wave to perform pulse width modulation and have the same PWM trigger pulse. As shown in fig. 4.
Collecting the capacitance voltages of all sub-modules on the bridge arm and the currents flowing through the bridge arm, and when the currents flowing through the bridge arm are larger than zero, arranging the capacitance voltages of the sub-modules in an ascending order; and when the current flowing through the bridge arm is less than zero, the capacitance and voltage of the sub-modules are arranged in a descending order.
Dividing the neutron modules of the bridge arm into 4 operation modes with different trigger pulses;
according to the sequencing result of the capacitor voltage of the sub-modules in the bridge arm, the 1 st to mth sub-modules operate in a mode 1 after sequencing; the (m + 1) th submodule after sequencing runs in a mode 2; the (m + 2) th submodule after sequencing runs in a mode 3; and (4) operating the m +3 th to N th sub-modules in the mode 4 after the sorting.
In particular, the amount of the solvent to be used,
the mode 1 is as follows: the submodule is in a recent level approaching modulation state, and the submodule is put into use;
the mode 2 is as follows: the submodule is in PWM modulation state, and the trigger pulse is PWM switching signal S1j；
The mode 3 is as follows: the submodule is in PWM modulation state, and the trigger pulse is PWM switching signal S2j；
Mode 4 is: the sub-module is in the most recent level-approaching modulation state and the sub-module is cut off.
The operating mode of the sub-modules and the trigger pulse allocation are shown in fig. 5.
Fig. 6 to 10 are graphs of simulation results obtained when the hybrid modulation method according to the embodiment of the present invention is used.
According to the hybrid modulation method of the modular multilevel converter provided by the embodiment of the invention, the modulation wave of the modular multilevel converter is divided into two parts according to the alternating current output voltage and the circulating current suppression control voltage, and the alternating current output voltage part of the modulation wave is subjected to nearest level approximation modulation; pulse width modulation is carried out on the modulation wave circulation current suppression control voltage part to obtain a PWM switching signal; collecting the capacitance voltage of the sub-modules on each bridge arm and the current flowing through the bridge arms, and sequencing the capacitance voltages of the sub-modules of the modular multilevel converter; and redistributing the trigger pulses of the sub-modules of the modular multilevel converter according to the nearest level approximation modulation of the first part of the modulation wave, the pulse width modulation of the second part of the modulation wave and the sequencing result of the capacitance and the voltage of the sub-modules. The hybrid modulation method for the modular multilevel converter provided by the embodiment of the invention can more finely modulate the circulating current suppression voltage under the condition of not increasing the switching frequency, and eliminates the influence of the circulating current suppression voltage on the direct current side of the MMC under the traditional recent level approximation modulation.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims (9)

1. A hybrid modulation method for a modular multilevel converter is characterized by comprising the following steps:
dividing a modulation wave of each bridge arm of the modular multilevel converter into two parts according to alternating current output voltage and circulating current suppression control voltage;
carrying out nearest level approximation modulation on an alternating current output voltage part of the modulation wave of the modular multilevel converter;
dividing the ring current suppression control voltage part of the modulation waves of the upper bridge arm and the lower bridge arm of the modular multilevel converter into two parts according to positive and negative half cycles, and respectively carrying out pulse width modulation;
sampling the capacitor voltages of all sub-modules on each bridge arm of the modular multilevel converter and corresponding bridge arm currents, and sequencing the capacitor voltages of the sub-modules according to the direction of the bridge arm currents;
according to the sequencing result of the capacitor voltage of the sub-modules in the bridge arm of the modular multilevel converter, dividing the sub-modules in the bridge arm into n operation modes, and redistributing the trigger pulse of the sub-modules on each bridge arm;
according to the sequencing result of the sub-module capacitor voltage in the bridge arm of the modular multilevel converter, the sub-modules in the bridge arm are divided into n operation modes, and the trigger pulse of the sub-modules on each bridge arm is redistributed, which comprises the following steps:
setting n to 4, namely dividing the neutron modules of the bridge arms into 4 operation modes with different trigger pulses;
according to the sequencing result of the capacitor voltage of the sub-modules in the bridge arm, the 1 st to mth sub-modules operate in a mode 1 after sequencing; the (m + 1) th submodule after sequencing runs in a mode 2; the (m + 2) th submodule after sequencing runs in a mode 3; and (4) operating the m +3 th to N th sub-modules in the mode 4 after the sorting.
2. The hybrid modulation method of the modular multilevel converter according to claim 1, wherein the dividing of the modulation wave of each leg of the modular multilevel converter into two parts according to the ac output voltage and the ringing suppression control voltage comprises:
each bridge arm of the modular multilevel converter is provided with N sub-modules, and the direct-current side voltage of the modular multilevel converter is VdcThen the average value of the sub-module voltage is Uc＝Vdc/N；
Modulation wave of upper bridge arm in each phase of the modular multilevel converter
Figure FDA0003206809860000011
Expressed as:
Figure FDA0003206809860000012
lower bridge arm modulated wave
Figure FDA0003206809860000013
Expressed as:
Figure FDA0003206809860000014
in the formula (I), the compound is shown in the specification,
Figure FDA0003206809860000015
is the j-th ac output voltage reference of the modular multilevel converter,
Figure FDA0003206809860000016
is the j-th phase circulating current suppression control voltage reference value;
dividing the modulation wave of the upper bridge arm of the j phase into two parts according to the alternating current output voltage and the circulating current suppression control voltage, wherein the alternating current output voltage part of the modulation wave of the upper bridge arm
Figure FDA0003206809860000021
Comprises the following steps:
Figure FDA0003206809860000022
the circulating current suppression control voltage part of the upper bridge arm modulation wave is
Figure FDA0003206809860000023
Dividing the modulation wave of the j-th phase lower bridge arm into two parts according to the alternating current output voltage and the circulating current suppression control voltage, wherein the alternating current output voltage part of the modulation wave of the lower bridge arm
Figure FDA0003206809860000024
Comprises the following steps:
Figure FDA0003206809860000025
the circulating current suppression control voltage part of the lower bridge arm modulation wave is
Figure FDA0003206809860000026
3. The hybrid modulation method of claim 1, wherein the performing nearest level approximation modulation on the ac output voltage portion of the modulated wave of the modular multilevel converter comprises:
the number of submodules for calculating the nearest level approximation modulation switching-on of the upper bridge arm is as follows:
Figure FDA0003206809860000027
in the formula, m is the number of sub-modules of the upper bridge arm which are closest to the modulation and are switched on, round (x) represents that the rounding operation is carried out on x, N is the number of the sub-modules on each bridge arm,
Figure FDA0003206809860000028
reference value of j-th AC output voltage, U, for modular multilevel convertercIs the average value of the sub-module voltages,
Figure FDA0003206809860000029
is the AC output voltage part of the upper bridge arm modulation wave,
Figure FDA00032068098600000210
an AC output voltage part for the modulation wave of the lower bridge arm;
the number of the submodules which are turned on by the nearest level approximation modulation in the lower bridge arm is as follows:
Figure FDA00032068098600000211
4. the hybrid modulation method of claim 1, wherein the step of dividing the ringing suppression control voltage part of the upper and lower arm modulated waves of the modular multilevel converter into two parts according to the positive and negative half cycles, and performing pulse width modulation respectively comprises:
the circulation current of the modulation waves of the upper and lower bridge arms of the j-th phase is restrained and controlled by the voltage part
Figure FDA00032068098600000212
The device is divided into the following two parts according to positive and negative half cycles:
Figure FDA00032068098600000213
Figure FDA0003206809860000031
in the formula (I), the compound is shown in the specification,
Figure FDA0003206809860000032
representation modulation generation
Figure FDA0003206809860000033
The positive half-cycle portion of (a),
Figure FDA0003206809860000034
representation modulation generation
Figure FDA0003206809860000035
Negative half-cycle part of (U)cThe submodule voltage average value is taken;
the modulated wave of the upper and lower bridge arms is circularly suppressed to control the voltage part
Figure FDA0003206809860000036
Positive and negative half cycle parts of
Figure FDA0003206809860000037
And
Figure FDA0003206809860000038
a comparison is made with the same triangular carrier, wherein,
Figure FDA0003206809860000039
PWM trigger pulse S for generation1j，
Figure FDA00032068098600000310
For generating PWM trigger pulses S2j。
5. The hybrid modulation method of the modular multilevel converter according to claim 4, wherein the pulse width modulation is performed on the positive and negative half cycle parts of the ringing suppression control voltage part of the upper and lower bridge arm modulation waves of the modular multilevel converter to obtain the PWM trigger pulse, and the method comprises:
when in use
Figure FDA00032068098600000311
When smaller than the triangular carrier, S1jOutput 1, submodule is put into; when in use
Figure FDA00032068098600000312
When the triangular carrier is larger than or equal to S1jOutputting 0, cutting off the submodule;
when in use
Figure FDA00032068098600000313
When the triangular carrier is larger than or equal to S2jOutput 1, submodule is put into; when in use
Figure FDA00032068098600000314
When smaller than the triangular carrier, S2jOutput 0, sonThe module is cut off;
the j-phase upper and lower bridge arms use the same carrier wave to perform pulse width modulation and have the same PWM trigger pulse.
6. The hybrid modulation method of claim 1, wherein sampling capacitor voltages of all sub-modules and corresponding bridge arm currents of each bridge arm of the modular multilevel converter, and sorting the capacitor voltages of the sub-modules according to the direction of the bridge arm currents comprises:
collecting the capacitance voltages of all sub-modules on the bridge arm and the currents flowing through the bridge arm, and when the currents flowing through the bridge arm are larger than zero, arranging the capacitance voltages of the sub-modules in an ascending order; and when the current flowing through the bridge arm is less than zero, the capacitance and voltage of the sub-modules are arranged in a descending order.
7. The hybrid modulation method of the modular multilevel converter according to claim 1, wherein the dividing of the sub-modules in the bridge arm into 4 operation modes with different trigger pulses comprises:
the mode 1 is as follows: the submodule is in a recent level approaching modulation state, and the submodule is put into use;
the mode 2 is as follows: the submodule is in PWM modulation state, and the trigger pulse is PWM switching signal S1j；
The mode 3 is as follows: the submodule is in PWM modulation state, and the trigger pulse is PWM switching signal S2j；
The mode 4 is as follows: the sub-module is in the most recent level-approaching modulation state and the sub-module is cut off.
8. The hybrid modulation method of the modular multilevel converter according to claim 1, wherein the sub-modules on each leg of the modular multilevel converter adopt a half-bridge sub-module structure.
9. The hybrid modulation method of the modular multilevel converter according to any one of claims 1 to 8, wherein a digital signal processor, an FPGA chip and/or an arithmetic circuit are adopted to realize alternating current output voltage control, circulation suppression control, calculation of the number of submodules of which the latest level approaches to modulation and switching on, division of positive and negative half cycles of a modulation wave circulation suppression control voltage part and generation of PWM trigger pulses.
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