CN115021541B - Method for suppressing pulsating power of non-isolated UPQC circuit in off-grid operation state - Google Patents

Method for suppressing pulsating power of non-isolated UPQC circuit in off-grid operation state Download PDF

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Publication number
CN115021541B
CN115021541B CN202210946726.9A CN202210946726A CN115021541B CN 115021541 B CN115021541 B CN 115021541B CN 202210946726 A CN202210946726 A CN 202210946726A CN 115021541 B CN115021541 B CN 115021541B
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capacitor
power
side converter
power tube
voltage
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CN115021541A (en
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马兰
向诗彪
伏瑞
曹晓琦
孟令辉
舒泽亮
何晓琼
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Southwest Jiaotong University
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Southwest 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1807—Arrangements for adjusting, eliminating or compensating reactive power in networks using series compensators
    • H02J3/1814—Arrangements for adjusting, eliminating or compensating reactive power in networks using series compensators wherein al least one reactive element is actively controlled by a bridge converter, e.g. unified power flow controllers [UPFC]
    • 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
    • H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • 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
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics

Abstract

The invention discloses a method for inhibiting pulsating power of a non-isolated UPQC circuit in an off-grid running state, wherein the non-isolated UPQC circuit comprises the following steps: single phase ac power supply
Figure 100004_DEST_PATH_IMAGE001
Solid state switch
Figure 100004_DEST_PATH_IMAGE002
Non-linear load
Figure 100004_DEST_PATH_IMAGE003
Series side converter MOSFET power tube
Figure 100004_DEST_PATH_IMAGE004
Series side converter MOSFET power tube
Figure 100004_DEST_PATH_IMAGE005
Filter inductor
Figure 100004_DEST_PATH_IMAGE006
Filter capacitor
Figure 100004_DEST_PATH_IMAGE007
Bypass switch
Figure 100004_DEST_PATH_IMAGE008
Energy storage unit and direct current capacitor
Figure 100004_DEST_PATH_IMAGE009
DC capacitor
Figure 100004_DEST_PATH_IMAGE010
MOSFET power tube of parallel side converter
Figure 100004_DEST_PATH_IMAGE011
MOSFET power tube of parallel side converter
Figure 100004_DEST_PATH_IMAGE012
Filter inductor
Figure 100004_DEST_PATH_IMAGE013
And a filter capacitor
Figure 100004_DEST_PATH_IMAGE014
. According to the invention, active power decoupling can be realized by directly utilizing the UPQC series side converter without adding an additional circuit, and direct-current voltage ripples are reduced.

Description

Method for suppressing pulse power of non-isolated UPQC circuit in off-network operation state
Technical Field
The invention relates to the technical field of electric energy quality, in particular to a method for inhibiting pulsating power of a non-isolated UPQC circuit in an off-grid operation state.
Background
The unified power quality regulator (UPQC) is used as a compensator with comprehensive performance and has the capability of processing two types of power quality problems of voltage and current, wherein a series side converter is used for compensating the power quality problems of network side voltage, such as undervoltage, overvoltage, voltage sag, sag and the like; the parallel side converter is used for compensating the current quality problems of harmonic current and reactive current caused by user load. The direct current side of the UPQC is connected with an energy storage device, and uninterrupted power supply to a load can be ensured under the special condition that the power supply voltage drops to zero (namely, the off-grid running state). When the UPQC works in an off-grid running state, the parallel side converter is used as a voltage source inverter, the output power is in pulsation twice the fundamental frequency, and a direct current side capacitor can generate voltage ripple twice the power frequency, so that the service life of the direct current side energy storage device is influenced.
The method commonly used for reducing the secondary ripple voltage is to increase the dc side capacitance, which increases the system size, increases the cost, and reduces the power density.
Disclosure of Invention
The invention aims to provide a method for inhibiting the pulsating power of a non-isolated UPQC circuit in an off-grid running state.
The technical scheme for solving the technical problems is as follows:
the invention provides a method for inhibiting pulsating power of a non-isolated UPQC circuit in an off-network running state, wherein the non-isolated UPQC circuit comprises the following steps:
single-phase AC power supply
Figure DEST_PATH_IMAGE001
Solid state switch
Figure DEST_PATH_IMAGE002
Non-linear load
Figure DEST_PATH_IMAGE003
Series side converter MOSFET power tube
Figure DEST_PATH_IMAGE004
Series side converter MOSFET power tube
Figure DEST_PATH_IMAGE005
Filter inductor
Figure DEST_PATH_IMAGE006
Filter capacitor
Figure DEST_PATH_IMAGE007
Bypass switch
Figure DEST_PATH_IMAGE008
Energy storage unit and direct current capacitor
Figure DEST_PATH_IMAGE009
DC capacitor
Figure DEST_PATH_IMAGE010
MOSFET power tube of parallel side converter
Figure DEST_PATH_IMAGE011
MOSFET power tube of parallel side converter
Figure DEST_PATH_IMAGE012
Filter inductor
Figure DEST_PATH_IMAGE013
And a filter capacitor
Figure DEST_PATH_IMAGE014
；
The solid state switch
Figure 322448DEST_PATH_IMAGE002
One end of the first power supply is connected with the single-phase alternating current power supply
Figure DEST_PATH_IMAGE015
And the other end of the non-linear load is connected with the non-linear load
Figure DEST_PATH_IMAGE016
Is connected with the positive terminal; the series side converter MOSFET power tube
Figure DEST_PATH_IMAGE017
The drain electrode of the capacitor is simultaneously connected with the anode of the energy storage unit and the direct current capacitor
Figure DEST_PATH_IMAGE018
And the parallel side converter MOSFET power tube
Figure DEST_PATH_IMAGE019
The drain electrodes of the two transistors are connected; the series side converter MOSFET power tube
Figure DEST_PATH_IMAGE020
Source electrode of the series side converter MOSFET power tube
Figure DEST_PATH_IMAGE021
And said filter inductance
Figure DEST_PATH_IMAGE022
Is connected to the filter inductor
Figure 875045DEST_PATH_IMAGE022
The other end of the same is connected with the single-phase alternating current power supply
Figure DEST_PATH_IMAGE023
And said filter capacitor
Figure DEST_PATH_IMAGE024
The positive electrodes of the two electrodes are connected; the series side converter MOSFET power tube
Figure DEST_PATH_IMAGE025
The source electrode of the capacitor is simultaneously connected with the negative end of the energy storage unit and the direct current capacitor
Figure DEST_PATH_IMAGE026
And the parallel side converter MOSFET power tube
Figure DEST_PATH_IMAGE027
A source electrode of (a); the DC capacitor
Figure DEST_PATH_IMAGE028
And the DC capacitor
Figure DEST_PATH_IMAGE029
Are connected in series; the parallel side converter MOSFET power tube
Figure DEST_PATH_IMAGE030
Source electrodes of the parallel side converter are connected with the MOSFET power tubes of the parallel side converter at the same time
Figure DEST_PATH_IMAGE031
Drain electrode of and said filter inductor
Figure DEST_PATH_IMAGE032
One end of (a); the filter inductor
Figure DEST_PATH_IMAGE033
While the other end of the non-linear load is connected to the non-linear load
Figure DEST_PATH_IMAGE034
And said filter capacitor
Figure DEST_PATH_IMAGE035
One end of (a); the filter capacitor
Figure 580702DEST_PATH_IMAGE035
The other end of (2), the nonlinear load
Figure DEST_PATH_IMAGE036
And the negative terminal of the filter capacitor
Figure DEST_PATH_IMAGE037
Is connected to the DC capacitor
Figure DEST_PATH_IMAGE038
And said DC capacitor
Figure DEST_PATH_IMAGE039
To (c) to (d); the bypass switch
Figure 842226DEST_PATH_IMAGE008
Connected in parallel to the filter capacitor
Figure 372564DEST_PATH_IMAGE037
Two ends.
Optionally, the non-isolated UPQC circuit may have a grid-connected operating state in which the solid-state switch is in the on-line operating state
Figure 843866DEST_PATH_IMAGE002
Closed, the bypass switch
Figure 725234DEST_PATH_IMAGE008
Off, said series side converter MOSFET power tube
Figure DEST_PATH_IMAGE040
The series side converter MOSFET power tube
Figure DEST_PATH_IMAGE041
The filter inductor
Figure DEST_PATH_IMAGE042
The filter capacitor
Figure DEST_PATH_IMAGE043
The DC capacitor
Figure DEST_PATH_IMAGE044
And said DC capacitor
Figure DEST_PATH_IMAGE045
The dynamic voltage restorer is formed together and used for compensating the power quality problem caused by the alternating voltage on the network side; the parallel side converter MOSFET power tube
Figure DEST_PATH_IMAGE046
The parallel side converter MOSFET power tube
Figure DEST_PATH_IMAGE047
The filter inductor
Figure DEST_PATH_IMAGE048
The filter capacitor
Figure DEST_PATH_IMAGE049
The DC capacitor
Figure 926802DEST_PATH_IMAGE044
And said DC capacitor
Figure 780488DEST_PATH_IMAGE045
Together forming an active power filter for compensating for current quality problems caused by the load.
Optionally, the non-isolated UPQC circuit may have an off-grid operating state in which the solid state switch is in operation
Figure 439003DEST_PATH_IMAGE002
Off, the bypass switch
Figure 56935DEST_PATH_IMAGE008
When the power supply is closed, the energy storage unit is rapidly discharged to form stable direct current voltage, and the MOSFET power tube of the parallel side converter
Figure DEST_PATH_IMAGE050
The parallel side converter MOSFET power tube
Figure 560729DEST_PATH_IMAGE047
The filter inductor
Figure DEST_PATH_IMAGE051
And said filter capacitor
Figure DEST_PATH_IMAGE052
Simultaneously working in an inverter voltage source mode to supply the nonlinear load
Figure DEST_PATH_IMAGE053
Uninterrupted power supply; the series side converter MOSFET power tube
Figure DEST_PATH_IMAGE054
The series side converter MOSFET power tube
Figure DEST_PATH_IMAGE055
The filter inductor
Figure 442490DEST_PATH_IMAGE042
The DC capacitor
Figure 271906DEST_PATH_IMAGE044
And said DC capacitor
Figure DEST_PATH_IMAGE056
And forming a half-bridge power decoupling circuit for inhibiting secondary pulsating power on the direct current side.
Optionally, the power of the half-bridge power decoupling circuit satisfies:
Figure DEST_PATH_IMAGE057
wherein the content of the first and second substances,
Figure DEST_PATH_IMAGE058
is the power sent out by the energy storage unit,
Figure DEST_PATH_IMAGE059
in order to decouple the power of the circuit,
Figure DEST_PATH_IMAGE060
is the average dc power required by the load,
Figure DEST_PATH_IMAGE061
the low-frequency ripple power needs to be buffered for the direct current side.
Optionally, the DC capacitor
Figure DEST_PATH_IMAGE062
And the DC capacitor
Figure 377134DEST_PATH_IMAGE045
Are equal.
Optionally, the method for suppressing the pulsating power in the off-grid operating state includes:
s1: collecting the DC capacitor
Figure 215777DEST_PATH_IMAGE062
And said DC capacitor
Figure 824482DEST_PATH_IMAGE045
Voltages on two sides are used for obtaining the total direct current bus voltage;
s2: obtaining a direct-current side secondary ripple voltage according to the direct-current bus voltage and the direct-current voltage reference value;
s3: performing frequency reduction processing on the secondary ripple voltage on the direct current side to obtain fundamental frequency ripple voltage;
s4: processing the fundamental frequency ripple voltage by using voltage outer loop DQ decoupling control to obtain the direct current capacitor
Figure DEST_PATH_IMAGE063
And the DC capacitor
Figure 762482DEST_PATH_IMAGE062
The difference in current between;
s5: obtaining a modulation wave through current inner loop proportion control according to the current difference;
s6: obtaining the MOSFET power tube of the series side converter by utilizing SPWM modulation according to the modulation wave
Figure DEST_PATH_IMAGE064
And the series side converter MOSFET power tube
Figure DEST_PATH_IMAGE065
The switching signal of (1);
s7: controlling the series side converter MOSFET power tube according to the switching signal
Figure 764461DEST_PATH_IMAGE064
And said series side converter MOSFET power transistor
Figure 656062DEST_PATH_IMAGE065
And switching on or off to realize the suppression of the pulsating power in the off-grid running state.
Optionally, the step S3 includes:
secondary ripple voltage on DC side
Figure DEST_PATH_IMAGE066
And through
Figure DEST_PATH_IMAGE067
The delayed orthogonal components are respectively connected with
Figure DEST_PATH_IMAGE068
And
Figure DEST_PATH_IMAGE069
multiplying, and adding the multiplication results to obtain fundamental frequency ripple voltage
Figure DEST_PATH_IMAGE070
In which
Figure DEST_PATH_IMAGE071
，
Figure DEST_PATH_IMAGE072
In order to be able to sample the frequency,
Figure DEST_PATH_IMAGE073
is the frequency of the power grid line,
Figure DEST_PATH_IMAGE074
in order to obtain the angular frequency of the power grid,
Figure DEST_PATH_IMAGE075
as a matter of time, the time is,
Figure DEST_PATH_IMAGE076
is a complex variable.
Optionally, the step S4 includes:
will fundamental frequency ripple voltage
Figure DEST_PATH_IMAGE077
And
Figure DEST_PATH_IMAGE078
and
Figure DEST_PATH_IMAGE079
after being multiplied respectively, the signals are transmitted to a low-pass filter with cut-off frequency lower than 50Hz, then multiplied by 2, processed by a PI controller, multiplied by corresponding trigonometric functions respectively and then added to obtain a direct current capacitor
Figure 383189DEST_PATH_IMAGE045
And a DC capacitor
Figure 819987DEST_PATH_IMAGE062
Current difference of
Figure DEST_PATH_IMAGE080
。
Optionally, the step S5 includes:
comparing the difference of the capacitance current and the load current
Figure DEST_PATH_IMAGE081
Subtracting to obtain a series side filter inductor
Figure DEST_PATH_IMAGE082
Current reference value of
Figure DEST_PATH_IMAGE083
Obtaining a modulation wave by using a proportional controller according to the reference value and the actual current value of the inductance current
Figure DEST_PATH_IMAGE084
。
Optionally, in step S7, the suppressing the pulsating power in the off-grid operating state includes:
controlling the DC capacitor
Figure 696545DEST_PATH_IMAGE062
And the DC capacitor
Figure 876991DEST_PATH_IMAGE045
Absorbing secondary pulse power at a direct current side;
controlling the DC capacitor
Figure 211020DEST_PATH_IMAGE062
And said DC capacitor
Figure 70916DEST_PATH_IMAGE045
Are equal and are half of the total voltage on the direct current side, and the direct current capacitor is controlled
Figure 123186DEST_PATH_IMAGE062
And said DC capacitor
Figure 107322DEST_PATH_IMAGE045
Respectively, comprise the pulse quantities of the fundamental frequencies which are 180 DEG out of phase.
The invention has the following beneficial effects:
according to the invention, an additional circuit is not required to be added, and the idle series side bridge arm switching tube in the non-isolated UPQC off-grid operation state is utilized to realize half-bridge active power decoupling, so that the direct current side pulse power suppression effect of the inverter is achieved, and the direct current voltage ripple is reduced under the condition of smaller direct current capacitance.
Drawings
FIG. 1 is a schematic diagram of a non-isolated UPQC circuit according to the present invention;
FIG. 2 is a schematic structural diagram of a non-isolated UPQC off-grid operation state circuit structure;
FIG. 3 is a flow chart of the ripple power suppression method in the off-line operation state of the non-isolated UPQC circuit according to the present invention;
FIG. 4 is a schematic diagram of a power decoupling control system;
fig. 5 is a comparison graph of dc voltage when ripple power is not suppressed in the non-isolated UPQC off-grid operating state and dc voltage after ripple power is suppressed.
Detailed Description
The principles and features of this invention are described below in conjunction with the following drawings, which are set forth to illustrate, but are not to be construed to limit the scope of the invention.
Examples
The technical scheme for solving the technical problems is as follows:
the invention provides a method for suppressing the pulsating power of a non-isolated UPQC circuit in an off-network operation state, which is shown in a reference figure 1 and comprises the following steps:
single phase ac power supply
Figure 561437DEST_PATH_IMAGE001
Solid state switch
Figure 589305DEST_PATH_IMAGE002
Non-linear load
Figure 128871DEST_PATH_IMAGE003
Series side converter MOSFET power tube
Figure 651119DEST_PATH_IMAGE004
Series side converter MOSFET power tube
Figure 412270DEST_PATH_IMAGE005
Filter inductor
Figure 361772DEST_PATH_IMAGE006
Filter capacitor
Figure 123055DEST_PATH_IMAGE007
Bypass switch
Figure 448994DEST_PATH_IMAGE008
Energy storage unit and direct current capacitor
Figure 861389DEST_PATH_IMAGE009
DC capacitor
Figure 247371DEST_PATH_IMAGE010
MOSFET power tube of parallel side converter
Figure 761529DEST_PATH_IMAGE011
MOSFET power tube of parallel side converter
Figure 625580DEST_PATH_IMAGE012
Filter inductor
Figure 895412DEST_PATH_IMAGE013
And a filter capacitor
Figure 655558DEST_PATH_IMAGE014
；
The solid state switch
Figure 391432DEST_PATH_IMAGE002
One end of which is connected with the single-phase alternating current power supply
Figure 308442DEST_PATH_IMAGE015
The other end of the non-linear load is connected with the non-linear load
Figure 180583DEST_PATH_IMAGE016
Is connected with the positive terminal; the series side converter MOSFET power tube
Figure 908367DEST_PATH_IMAGE017
The drain electrode of the capacitor is simultaneously connected with the anode of the energy storage unit and the direct current capacitor
Figure 131538DEST_PATH_IMAGE018
And the parallel side converter MOSFET power tube
Figure 852238DEST_PATH_IMAGE019
The drain electrodes of the two transistors are connected; the series side converter MOSFET power tube
Figure 844465DEST_PATH_IMAGE020
Source electrode of the series side converter MOSFET power tube
Figure 743151DEST_PATH_IMAGE021
And said filter inductance
Figure 188039DEST_PATH_IMAGE022
Is connected to one end of the filter inductor
Figure 650113DEST_PATH_IMAGE022
The other end of the same is connected with the single-phase alternating current power supply
Figure 762426DEST_PATH_IMAGE023
And the negative terminal of the filter capacitor
Figure 566434DEST_PATH_IMAGE024
The positive electrodes of the two electrodes are connected; the series side converter MOSFET power tube
Figure 16394DEST_PATH_IMAGE025
The source electrode of the capacitor is simultaneously connected with the negative end of the energy storage unit and the direct current capacitor
Figure 564050DEST_PATH_IMAGE026
And the parallel side converter MOSFET power tube
Figure 530869DEST_PATH_IMAGE027
A source electrode of (a); the DC capacitor
Figure 505778DEST_PATH_IMAGE028
And the DC capacitor
Figure 705684DEST_PATH_IMAGE029
Are connected in series; the MOSFET power tube of the parallel side converter
Figure 57031DEST_PATH_IMAGE030
Source electrodes of are simultaneously connectedThe MOSFET power tube of the parallel side converter is connected
Figure 878357DEST_PATH_IMAGE031
Drain electrode of and said filter inductor
Figure 289746DEST_PATH_IMAGE032
One end of (a); the filter inductor
Figure 649052DEST_PATH_IMAGE033
While the other end of the non-linear load is connected with the non-linear load
Figure 538511DEST_PATH_IMAGE034
And said filter capacitor
Figure 479922DEST_PATH_IMAGE035
One end of (a); the filter capacitor
Figure 45902DEST_PATH_IMAGE035
The other end of (2), the nonlinear load
Figure 439974DEST_PATH_IMAGE036
And said filter capacitor
Figure 398703DEST_PATH_IMAGE037
Is connected to the DC capacitor
Figure 194620DEST_PATH_IMAGE038
And the DC capacitor
Figure 391554DEST_PATH_IMAGE039
To (c) to (d); the bypass switch
Figure 272922DEST_PATH_IMAGE008
Connected in parallel to the filter capacitor
Figure 504183DEST_PATH_IMAGE037
Two ends.
Alternatively, the above is notThe isolated UPQC circuit has a grid-connected operating state in which the solid state switch is engaged
Figure 403875DEST_PATH_IMAGE002
Closed, the bypass switch
Figure 593548DEST_PATH_IMAGE008
Off, said series side converter MOSFET power tube
Figure 962212DEST_PATH_IMAGE040
The series side converter MOSFET power tube
Figure 997164DEST_PATH_IMAGE041
The filter inductor
Figure 751363DEST_PATH_IMAGE042
The filter capacitor
Figure 846357DEST_PATH_IMAGE043
The DC capacitor
Figure 905580DEST_PATH_IMAGE044
And said DC capacitor
Figure 727912DEST_PATH_IMAGE045
The dynamic voltage restorer is formed together and used for compensating the power quality problem caused by the alternating voltage on the network side; the MOSFET power tube of the parallel side converter
Figure 352928DEST_PATH_IMAGE046
The parallel side converter MOSFET power tube
Figure 884404DEST_PATH_IMAGE047
The filter inductor
Figure 962081DEST_PATH_IMAGE048
The filter capacitor
Figure 856612DEST_PATH_IMAGE049
The DC capacitor
Figure 336135DEST_PATH_IMAGE044
And said DC capacitor
Figure 772933DEST_PATH_IMAGE045
Together forming an active power filter for compensating current quality problems caused by the load.
Optionally, the non-isolated UPQC circuit may have an off-grid operating state in which the solid state switches of fig. 1 are open
Figure 790436DEST_PATH_IMAGE002
Off, the bypass switch
Figure 705302DEST_PATH_IMAGE008
And (5) closing. I.e., a circuit configuration that enables the obtaining of an off-grid operating state of the non-isolated UPQC, as shown with reference to fig. 2. The energy storage unit is rapidly discharged to form stable direct current voltage, and the MOSFET power tube of the parallel side converter
Figure 570490DEST_PATH_IMAGE050
The parallel side converter MOSFET power tube
Figure 178189DEST_PATH_IMAGE047
The filter inductor
Figure 479726DEST_PATH_IMAGE051
And said filter capacitor
Figure 198284DEST_PATH_IMAGE052
Simultaneously operating in an inverter voltage source mode to supply the nonlinear load
Figure 652399DEST_PATH_IMAGE053
Uninterrupted power supply; the series side converter MOSFET power tube
Figure 430999DEST_PATH_IMAGE054
The series side converter MOSFET power tube
Figure 219832DEST_PATH_IMAGE055
The filter inductor
Figure 742080DEST_PATH_IMAGE042
The DC capacitor
Figure 50702DEST_PATH_IMAGE044
And said DC capacitor
Figure 455663DEST_PATH_IMAGE056
And forming a half-bridge power decoupling circuit for inhibiting secondary pulsating power on the direct current side.
In order to realize suppression of secondary pulsating power on the direct current side, optionally, the power of the half-bridge power decoupling circuit satisfies:
Figure 216946DEST_PATH_IMAGE057
wherein the content of the first and second substances,
Figure 542885DEST_PATH_IMAGE058
is the power sent out by the energy storage unit,
Figure 706013DEST_PATH_IMAGE059
in order to decouple the power of the circuit,
Figure 75683DEST_PATH_IMAGE060
is the average dc power required by the load,
Figure 589841DEST_PATH_IMAGE061
the low-frequency ripple power needs to be buffered for the direct current side.
Optionally, the DC capacitor
Figure 719471DEST_PATH_IMAGE062
And said DC capacitor
Figure 737106DEST_PATH_IMAGE045
Are equal.
Based on the above technical solution, the present invention further provides a method for suppressing ripple power of a non-isolated UPQC circuit in an off-network operating state, which is shown in fig. 3 and includes:
s1: collecting the DC capacitor
Figure 543257DEST_PATH_IMAGE062
And said DC capacitor
Figure 279131DEST_PATH_IMAGE045
Obtaining the total direct current bus voltage by the voltage at the two sides;
s2: obtaining a secondary ripple voltage at the direct current side according to the direct current bus voltage and the direct current voltage reference value;
specifically, the dc bus voltage and the dc voltage reference value are subtracted, so that the dc-side secondary ripple voltage can be obtained.
S3: performing frequency reduction processing on the secondary ripple voltage on the direct current side to obtain fundamental frequency ripple voltage;
here, the DC-side secondary ripple voltage is set
Figure 681294DEST_PATH_IMAGE066
And pass through
Figure 819014DEST_PATH_IMAGE067
The delayed orthogonal components are respectively connected with
Figure 999329DEST_PATH_IMAGE068
And
Figure 956920DEST_PATH_IMAGE069
multiplying, adding the multiplied results to obtain the fundamental frequency ripple voltage
Figure 428353DEST_PATH_IMAGE070
In which
Figure 672777DEST_PATH_IMAGE071
，
Figure 305884DEST_PATH_IMAGE072
In order to be able to sample the frequency,
Figure 16351DEST_PATH_IMAGE073
is the frequency of the power grid line,
Figure 291474DEST_PATH_IMAGE074
in order to obtain the angular frequency of the power grid,
Figure DEST_PATH_IMAGE085
in the form of a time, the time,
Figure 59579DEST_PATH_IMAGE076
is a complex variable.
S4: processing the fundamental frequency ripple voltage by using voltage outer loop DQ decoupling control to obtain the direct current capacitor
Figure 129166DEST_PATH_IMAGE063
And the DC capacitor
Figure 310618DEST_PATH_IMAGE062
The difference in current between;
here, referring to fig. 4, the fundamental frequency ripple voltage is set
Figure 123853DEST_PATH_IMAGE077
And
Figure 90672DEST_PATH_IMAGE078
and
Figure 331160DEST_PATH_IMAGE079
after multiplying respectively, transmitting to a low-pass filter with cut-off frequency lower than 50Hz, then multiplying by 2, processing by a PI controller, multiplying by corresponding trigonometric functions respectively, and adding to obtain a direct current capacitor
Figure 265487DEST_PATH_IMAGE045
And a DC capacitor
Figure 616834DEST_PATH_IMAGE062
Current difference of
Figure 438160DEST_PATH_IMAGE080
。
S5: obtaining a modulation wave through current inner loop proportion control according to the current difference;
optionally, the step S5 includes:
comparing the difference of the capacitance current and the load current
Figure 583970DEST_PATH_IMAGE081
Subtracting to obtain a series side filter inductor
Figure 754662DEST_PATH_IMAGE082
Current reference value of
Figure 909700DEST_PATH_IMAGE083
Obtaining a modulation wave by using a proportional controller according to the reference value and the actual current value of the inductance current
Figure 585532DEST_PATH_IMAGE084
。
S6: according to the modulation wave, SPWM modulation is utilized to obtain the MOSFET power tube of the series side converter
Figure 167823DEST_PATH_IMAGE064
And said series side converter MOSFET power transistor
Figure 811163DEST_PATH_IMAGE065
The switching signal of (1);
s7: controlling the series side converter MOSFET power tube according to the switching signal
Figure 504313DEST_PATH_IMAGE064
And the series side converter MOSFET power tube
Figure 300230DEST_PATH_IMAGE065
And switching on or off to realize the suppression of the pulsating power in the off-grid running state.
Optionally, in step S7, the suppressing the pulsating power in the off-grid operating state includes:
controlling the DC capacitor
Figure 53423DEST_PATH_IMAGE062
And said DC capacitor
Figure 918479DEST_PATH_IMAGE045
Absorbing secondary pulse power at a direct current side;
controlling the DC capacitor
Figure 618582DEST_PATH_IMAGE062
And said DC capacitor
Figure 269006DEST_PATH_IMAGE045
Are equal and are each half of the total voltage on the dc side, and the dc capacitors are controlled
Figure 442367DEST_PATH_IMAGE062
And said DC capacitor
Figure 811032DEST_PATH_IMAGE045
Respectively, comprise the pulse quantities of the fundamental frequencies which are 180 DEG out of phase.
Specifically, the idea of suppressing the pulsating power in the non-isolated UPQC off-grid running state is to use a direct current capacitor
Figure 845984DEST_PATH_IMAGE062
And a DC capacitor
Figure 350915DEST_PATH_IMAGE045
And secondary pulse power on the direct current side is absorbed. The active power decoupling circuit not only needs to eliminate direct currentSide pulse power, also needs to stabilize the dc side bus voltage. DC capacitance selected here
Figure 698107DEST_PATH_IMAGE062
And direct current
Figure 288488DEST_PATH_IMAGE045
The capacitance values of the capacitors are equal, so that the average voltage of the capacitors is equal and is half of the total voltage of the direct current side, and simultaneously, the capacitors also respectively contain a fundamental frequency pulsating quantity with a phase difference of 180 degrees.
Suppose that the ac side voltage and current of the inverter are respectively:
Figure DEST_PATH_IMAGE086
wherein, the first and the second end of the pipe are connected with each other,
Figure DEST_PATH_IMAGE087
、
Figure DEST_PATH_IMAGE088
respectively, alternating side voltage and current;
Figure DEST_PATH_IMAGE089
，
Figure DEST_PATH_IMAGE090
the amplitudes of the alternating voltage and the alternating current respectively;
Figure DEST_PATH_IMAGE091
is the grid frequency;
Figure DEST_PATH_IMAGE092
is the phase difference between the ac voltage and the ac current.
The ac side output power can be expressed as:
Figure DEST_PATH_IMAGE093
it is obvious that the output power of the alternating current side is a constant power plus a secondary pulsating power.
The voltage of the upper and lower capacitors on the direct current side is set as follows:
Figure DEST_PATH_IMAGE094
Figure DEST_PATH_IMAGE095
，
Figure DEST_PATH_IMAGE096
are respectively DC capacitors
Figure 501033DEST_PATH_IMAGE062
And a DC capacitor
Figure 126049DEST_PATH_IMAGE045
The instantaneous voltage of (d);
Figure DEST_PATH_IMAGE097
is a direct current side bus voltage;
Figure DEST_PATH_IMAGE098
the amplitude of the capacitance voltage alternating current is obtained;
Figure DEST_PATH_IMAGE099
is the phase angle of the alternating current of the capacitor voltage.
The upper and lower capacitance currents can be obtained by differentiating the above two equations:
Figure DEST_PATH_IMAGE100
wherein
Figure DEST_PATH_IMAGE101
And
Figure DEST_PATH_IMAGE102
are respectively DC capacitors
Figure 706459DEST_PATH_IMAGE062
And a DC capacitor
Figure 784137DEST_PATH_IMAGE045
The instantaneous current of the current source is measured,
Figure DEST_PATH_IMAGE103
is a DC capacitor
Figure 879001DEST_PATH_IMAGE062
Or DC capacitor
Figure 358524DEST_PATH_IMAGE045
The capacity value of (c).
Neglecting filter inductance
Figure DEST_PATH_IMAGE104
The instantaneous power of the half-bridge power decoupling circuit is easily obtained as follows:
Figure DEST_PATH_IMAGE105
the instantaneous power of the decoupling circuit is equal to the pulse power on the alternating current side through control, namely:
Figure DEST_PATH_IMAGE106
the control target of the power decoupling circuit is divided into upper and lower capacitance instantaneous voltage and inductive current, and the specific control method comprises the following steps:
sampling DC bus voltage
Figure DEST_PATH_IMAGE107
And a DC voltage reference value
Figure DEST_PATH_IMAGE108
Making difference to obtain secondary ripple voltage on DC side
Figure DEST_PATH_IMAGE109
Obtained by frequency reduction
Figure DEST_PATH_IMAGE110
，
Figure 578677DEST_PATH_IMAGE110
Are respectively connected with
Figure DEST_PATH_IMAGE111
And
Figure DEST_PATH_IMAGE112
multiplying, sending into a low-pass filter with cut-off frequency lower than 50Hz, multiplying by 2, respectively multiplying by corresponding trigonometric functions after passing through a PI controller, and adding to obtain a direct current capacitor
Figure 596180DEST_PATH_IMAGE045
And a DC capacitor
Figure 776626DEST_PATH_IMAGE062
Current difference of
Figure DEST_PATH_IMAGE113
Then subtract the load current
Figure DEST_PATH_IMAGE114
To obtain an inductor
Figure DEST_PATH_IMAGE115
Current reference value of
Figure DEST_PATH_IMAGE116
Reference value of inductor current
Figure 500868DEST_PATH_IMAGE116
And the actual value
Figure DEST_PATH_IMAGE117
Making difference, and obtaining modulated wave after passing through proportional controller P
Figure DEST_PATH_IMAGE118
Finally, the MOSFET power tube is controlled by Sinusoidal Pulse Width Modulation (SPWM)
Figure DEST_PATH_IMAGE119
And MOSFET power tube
Figure DEST_PATH_IMAGE120
On and off.
In the present invention, the DC voltage
Figure DEST_PATH_IMAGE121
=300V, dc capacitor
Figure DEST_PATH_IMAGE122
=
Figure DEST_PATH_IMAGE123
=90 μ F, inductance
Figure DEST_PATH_IMAGE124
=4mH, inductance
Figure DEST_PATH_IMAGE125
Filter capacity of =4mH
Figure DEST_PATH_IMAGE126
And the output alternating voltage has an effective value of 80V, the frequency of the alternating voltage is 50Hz and the switching frequency is 20kHz, and the used nonlinear load is a resistor and a capacitor which are connected with a 25 omega resistor and then connected with a 20 omega +2200 muF uncontrolled rectifier bridge.
Fig. 5 shows the dc voltage when ripple power is not suppressed and the dc voltage after ripple power suppression in the non-isolated UPQC off-grid operating state. When the ripple power is not suppressed, the total voltage fluctuation of the direct current side is 33V; after the ripple power is suppressed, the total voltage fluctuation of the direct current side is 3.6V, which is reduced by 89% compared with the direct current voltage fluctuation when the ripple power is not suppressed.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the scope of the present invention, which is intended to cover any modifications, equivalents, improvements, etc. within the spirit and scope of the present invention.

Claims (9)

1. A method for suppressing ripple power of a non-isolated UPQC circuit in an off-grid operation state, wherein the non-isolated UPQC circuit comprises:
single-phase AC power supply
Figure 322012DEST_PATH_IMAGE001
Solid state switch
Figure 338510DEST_PATH_IMAGE002
Non-linear load
Figure 771241DEST_PATH_IMAGE003
Series side converter MOSFET power tube
Figure 214991DEST_PATH_IMAGE004
Series side converter MOSFET power tube
Figure 368892DEST_PATH_IMAGE005
Filter inductor
Figure 189081DEST_PATH_IMAGE006
Filter capacitor
Figure 479248DEST_PATH_IMAGE007
Bypass switch
Figure 359479DEST_PATH_IMAGE008
Energy storage unit and direct current capacitor
Figure 735097DEST_PATH_IMAGE009
DC capacitor
Figure 296659DEST_PATH_IMAGE010
MOSFET power tube of parallel side converter
Figure 506579DEST_PATH_IMAGE011
MOSFET power tube of parallel side converter
Figure 495395DEST_PATH_IMAGE012
Filter inductor
Figure 358309DEST_PATH_IMAGE013
And a filter capacitor
Figure 317038DEST_PATH_IMAGE014
；
The solid state switch
Figure 581797DEST_PATH_IMAGE002
One end of the first power supply is connected with the single-phase alternating current power supply
Figure 803831DEST_PATH_IMAGE015
The other end of the non-linear load is connected with the non-linear load
Figure 154041DEST_PATH_IMAGE016
Is connected with the positive terminal; the series side converter MOSFET power tube
Figure 854143DEST_PATH_IMAGE017
The drain electrode of the capacitor is simultaneously connected with the anode of the energy storage unit and the direct current capacitor
Figure 970479DEST_PATH_IMAGE018
And the parallel side converter MOSFET power tube
Figure 363415DEST_PATH_IMAGE019
The drain electrodes of the two electrodes are connected; the series side converter MOSFET power tube
Figure 200921DEST_PATH_IMAGE020
Source electrode of the series side converter MOSFET power tube
Figure 704714DEST_PATH_IMAGE021
Drain electrode of and said filter inductor
Figure 678487DEST_PATH_IMAGE022
Is connected to the filter inductor
Figure 445585DEST_PATH_IMAGE023
The other end of the same phase AC power supply
Figure 770387DEST_PATH_IMAGE024
And the negative terminal of the filter capacitor
Figure 812293DEST_PATH_IMAGE025
The positive electrodes of the two electrodes are connected; the series side converter MOSFET power tube
Figure 897362DEST_PATH_IMAGE026
The source electrode of the capacitor is simultaneously connected with the negative end of the energy storage unit and the direct current capacitor
Figure 897679DEST_PATH_IMAGE027
And the parallel side converter MOSFET power tube
Figure 444198DEST_PATH_IMAGE028
A source electrode of (a); the DC capacitor
Figure 555373DEST_PATH_IMAGE029
And the DC capacitor
Figure 503738DEST_PATH_IMAGE030
Are connected in series; the parallel side converter MOSFET power tube
Figure 409377DEST_PATH_IMAGE031
Source electrodes of the same are connected toMOSFET power tube of parallel side converter
Figure 443192DEST_PATH_IMAGE032
And said filter inductance
Figure 826900DEST_PATH_IMAGE033
One end of (a); the filter inductor
Figure 892420DEST_PATH_IMAGE034
While the other end of the non-linear load is connected to the non-linear load
Figure 296857DEST_PATH_IMAGE035
And said filter capacitor
Figure 817968DEST_PATH_IMAGE036
One end of (a); the filter capacitor
Figure 5367DEST_PATH_IMAGE037
The other end of (1), the nonlinear load
Figure 928323DEST_PATH_IMAGE038
And the negative terminal of the filter capacitor
Figure 175765DEST_PATH_IMAGE039
Is connected to the DC capacitor
Figure 856276DEST_PATH_IMAGE040
And said DC capacitor
Figure 847366DEST_PATH_IMAGE041
To (c) to (d); the bypass switch
Figure 627759DEST_PATH_IMAGE008
Connected in parallel to the filter capacitor
Figure 46102DEST_PATH_IMAGE039
Two ends;
the non-isolated UPQC circuit has an off-grid operating state in which the solid state switch is in
Figure 276226DEST_PATH_IMAGE042
Off, the bypass switch
Figure 71007DEST_PATH_IMAGE008
When the power supply is closed, the energy storage unit is rapidly discharged to form stable direct current voltage, and the MOSFET power tube of the parallel side converter
Figure 702976DEST_PATH_IMAGE043
The parallel side converter MOSFET power tube
Figure 292221DEST_PATH_IMAGE044
The filter inductor
Figure 603116DEST_PATH_IMAGE045
And said filter capacitor
Figure 936009DEST_PATH_IMAGE046
Simultaneously operating in an inverter voltage source mode to supply the nonlinear load
Figure 422485DEST_PATH_IMAGE047
Uninterrupted power supply; the series side converter MOSFET power tube
Figure 445280DEST_PATH_IMAGE048
The series side converter MOSFET power tube
Figure 649996DEST_PATH_IMAGE049
The filter inductor
Figure 521000DEST_PATH_IMAGE050
The DC capacitor
Figure 393141DEST_PATH_IMAGE051
And the DC capacitor
Figure 996292DEST_PATH_IMAGE052
And forming a half-bridge power decoupling circuit for inhibiting secondary pulsating power on the direct current side.
2. The method for suppressing pulsating power during off-grid operation of a non-isolated UPQC circuit of claim 1, wherein the non-isolated UPQC circuit has a grid-tied operation state in which the solid state switch is on
Figure 422725DEST_PATH_IMAGE042
Closed, the bypass switch
Figure 363000DEST_PATH_IMAGE008
Off, said series side converter MOSFET power tube
Figure 838716DEST_PATH_IMAGE053
The series side converter MOSFET power tube
Figure 940665DEST_PATH_IMAGE054
The filter inductor
Figure 119973DEST_PATH_IMAGE050
The filter capacitor
Figure 598359DEST_PATH_IMAGE055
The DC capacitor
Figure 913934DEST_PATH_IMAGE051
And said DC capacitor
Figure 452363DEST_PATH_IMAGE056
The dynamic voltage restorer is formed together and used for compensating the power quality problem generated by the alternating voltage at the network side; the parallel side converter MOSFET power tube
Figure 853388DEST_PATH_IMAGE057
The parallel side converter MOSFET power tube
Figure 135465DEST_PATH_IMAGE044
The filter inductor
Figure 899022DEST_PATH_IMAGE058
The filter capacitor
Figure 339843DEST_PATH_IMAGE059
The DC capacitor
Figure 493743DEST_PATH_IMAGE051
And said DC capacitor
Figure 313932DEST_PATH_IMAGE056
Together forming an active power filter for compensating for current quality problems caused by the load.
3. The method for suppressing the ripple power of the non-isolated UPQC circuit in the off-grid operation state according to claim 1, wherein the power of the half-bridge power decoupling circuit satisfies the following conditions:
Figure 604099DEST_PATH_IMAGE060
wherein the content of the first and second substances,
Figure 218751DEST_PATH_IMAGE061
is the power sent out by the energy storage unit,
Figure 594369DEST_PATH_IMAGE062
in order to decouple the power of the circuit,
Figure 218248DEST_PATH_IMAGE063
is the average dc power required by the load,
Figure 362922DEST_PATH_IMAGE064
the low-frequency ripple power needs to be buffered for the direct current side.
4. The method for suppressing the ripple power of a non-isolated UPQC circuit in the off-grid operation state according to claim 1, wherein the DC capacitors
Figure 416984DEST_PATH_IMAGE065
And the DC capacitor
Figure 279898DEST_PATH_IMAGE056
Are equal.
5. The method for suppressing the ripple power of the non-isolated UPQC circuit in the off-grid operation state according to any one of claims 1 to 4, wherein the method for suppressing the ripple power in the off-grid operation state comprises:
s1: collecting the DC capacitor
Figure 441889DEST_PATH_IMAGE065
And said DC capacitor
Figure 706648DEST_PATH_IMAGE056
Obtaining the total direct current bus voltage by the voltage at the two sides;
s2: obtaining a secondary ripple voltage at the direct current side according to the direct current bus voltage and the direct current voltage reference value;
s3: performing frequency reduction processing on the secondary ripple voltage on the direct current side to obtain fundamental frequency ripple voltage;
s4: processing the fundamental frequency ripple voltage by using voltage outer ring DQ decoupling control to obtain the direct current capacitor
Figure 928682DEST_PATH_IMAGE066
And the DC capacitor
Figure 13313DEST_PATH_IMAGE065
The difference in current between;
s5: obtaining a modulation wave through current inner loop proportion control according to the current difference;
s6: according to the modulation wave, SPWM modulation is utilized to obtain the MOSFET power tube of the series side converter
Figure 978995DEST_PATH_IMAGE067
And the series side converter MOSFET power tube
Figure 98260DEST_PATH_IMAGE068
The switching signal of (a);
s7: controlling the series side converter MOSFET power tube according to the switching signal
Figure 488266DEST_PATH_IMAGE067
And said series side converter MOSFET power transistor
Figure 325772DEST_PATH_IMAGE068
And switching on or off to realize the suppression of the pulsating power in the off-grid running state.
6. The method for suppressing the ripple power of the non-isolated UPQC circuit in the off-grid operation state according to claim 5, wherein the step S3 comprises:
secondary ripple voltage at DC side
Figure 829566DEST_PATH_IMAGE069
And pass through
Figure 803338DEST_PATH_IMAGE070
Delayed orthogonal components are respectively connected with
Figure 367174DEST_PATH_IMAGE071
And
Figure 426397DEST_PATH_IMAGE072
multiplying, and adding the multiplication results to obtain fundamental frequency ripple voltage
Figure 405986DEST_PATH_IMAGE073
In which
Figure 22213DEST_PATH_IMAGE074
，
Figure 756951DEST_PATH_IMAGE075
In order to be able to sample the frequency,
Figure 303470DEST_PATH_IMAGE076
is the frequency of the power grid line,
Figure 883487DEST_PATH_IMAGE077
in order to obtain the angular frequency of the power grid,
Figure 503955DEST_PATH_IMAGE078
as a matter of time, the time is,
Figure 144015DEST_PATH_IMAGE079
is a complex variable.
7. The method for suppressing the ripple power of the non-isolated UPQC circuit in the off-grid operation state according to claim 5, wherein the step S4 comprises:
will fundamental frequency ripple voltage
Figure 974568DEST_PATH_IMAGE080
And
Figure 355346DEST_PATH_IMAGE081
and
Figure 423796DEST_PATH_IMAGE082
after being multiplied respectively, the signals are transmitted to a low-pass filter with cut-off frequency lower than 50Hz, then multiplied by 2, processed by a PI controller, multiplied by corresponding trigonometric functions respectively and then added to obtain a direct current capacitor
Figure 500337DEST_PATH_IMAGE056
And a DC capacitor
Figure 755868DEST_PATH_IMAGE065
Current difference of
Figure 208847DEST_PATH_IMAGE083
。
8. The method for suppressing the ripple power of the non-isolated UPQC circuit in the off-grid operation state according to claim 5, wherein step S5 comprises:
comparing the difference of the capacitance current and the load current
Figure 131803DEST_PATH_IMAGE084
Subtracting to obtain a series side filter inductor
Figure 379245DEST_PATH_IMAGE085
Current reference value of
Figure 387652DEST_PATH_IMAGE086
Obtaining a modulation wave by using a proportional controller according to the reference value and the actual current value of the inductance current
Figure 381672DEST_PATH_IMAGE087
。
9. The method for suppressing the ripple power of the non-isolated UPQC circuit in the off-grid operation state according to claim 5, wherein in step S7, the suppression of the ripple power in the off-grid operation state comprises:
controlling the DC capacitor
Figure 159135DEST_PATH_IMAGE065
And said DC capacitor
Figure 577478DEST_PATH_IMAGE056
Absorbing secondary pulse power at the direct current side;
controlling the DC capacitor
Figure 807602DEST_PATH_IMAGE065
And said DC capacitor
Figure 336803DEST_PATH_IMAGE056
Are equal and are half of the total voltage on the direct current side, and the direct current capacitor is controlled
Figure 234352DEST_PATH_IMAGE065
And the DC capacitor
Figure 89176DEST_PATH_IMAGE056
Respectively, comprise the pulse quantities of the fundamental frequencies which are 180 DEG out of phase.
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