CN110098753B - Multi-output transformer-free symmetric hybrid converter and modulation method thereof - Google Patents

Multi-output transformer-free symmetric hybrid converter and modulation method thereof Download PDF

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CN110098753B
CN110098753B CN201910356992.4A CN201910356992A CN110098753B CN 110098753 B CN110098753 B CN 110098753B CN 201910356992 A CN201910356992 A CN 201910356992A CN 110098753 B CN110098753 B CN 110098753B
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vsi
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CN110098753A (en
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粟梅
唐忠廷
韩华
王辉
郭斌
万江湖
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Central South University
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    • H02J3/383—
    • 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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S40/00—Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
    • H02S40/30—Electrical components
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S40/00—Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
    • H02S40/30—Electrical components
    • H02S40/32—Electrical components comprising DC/AC inverter means associated with the PV module itself, e.g. AC modules
    • 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
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/008—Plural converter units for generating at two or more independent and non-parallel outputs, e.g. systems with plural point of load switching regulators
    • 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
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B10/00—Integration of renewable energy sources in buildings
    • Y02B10/10—Photovoltaic [PV]
    • 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
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Abstract

The invention provides a multi-output transformer-free symmetrical hybrid converter and a modulation method thereof, wherein symmetrical transformer-free VSI in the hybrid converter is time-division multiplexed in the hybrid converter, and can be used as a power switch in a DC-DC boost converter and a topology of a transformer-free voltage source grid-connected inverter. The invention adopts the design of a symmetrical hybrid converter, can simultaneously output direct current voltage and alternating current voltage, effectively inhibits leakage current, eliminates the short circuit phenomenon of a bridge arm switch in the conventional VSI, and can be widely applied to medium and low power commercial and household photovoltaic grid-connected power generation systems.

Description

Multi-output transformer-free symmetric hybrid converter and modulation method thereof
Technical Field
The invention relates to the technical field of power conversion, in particular to a multi-output transformer-free symmetrical hybrid converter and a modulation method thereof
Background
The photovoltaic power generation system is an intelligent power generation system which consists of a photovoltaic panel array, a power electronic converter, a power grid and a load and can work in two modes of grid connection and off-grid connection. The power electronic converter capable of converting photovoltaic electric energy into standard power for a power grid is a key hub. Generally, a transformer-less single-phase inverter is used for a medium-low power photovoltaic converter, which has the advantages of high power density, high efficiency and low cost, and accordingly, it is important to suppress leakage current in the transformer-less converter.
As one of the main new energy sources, the proportion of photovoltaic energy in a hybrid power grid is higher and higher, and due to the defects of intermittency and different regions of the photovoltaic energy, a huge challenge is brought to the stability of the whole power grid. Therefore, in order to obtain a friendly and supporting photovoltaic power generation system, in recent decades, various international standards (such as IEEE Standard 1547 and VDE-AR-N4105) have required reactive power regulation capability for a photovoltaic grid-connected system. And the requirements on the quality of the electric energy merged into the power grid are only increased but not reduced, and the corresponding harmonic distortion has strict requirements.
With increasing consumer demand and considering the versatility of converters, power plants with a variety of different voltage outputs (AC and DC voltages) will have greater applications. The traditional multi-output power generation system generally adopts a mode of connecting a DC-DC converter and a DC-AC converter in parallel, and has lower power density and higher cost. For this purpose, another multi-output power generation apparatus integrates a DC-DC converter and a DC-AC converter into a single-stage multi-purpose hybrid converter. The DC-DC modulation ratio and the DC-AC modulation ratio of the single-stage hybrid converter are limited to a certain extent, but the reliability of the device is greatly improved because the problem of short-circuit protection of a bridge arm power switch does not exist. However, the existing hybrid converter of the type is applied to medium and small power photovoltaic power generation systems, and the important problem of leakage current suppression also needs to be solved.
Disclosure of Invention
Technical problem to be solved
Aiming at the defects in the prior art, the invention provides a multi-output transformer-free symmetrical hybrid converter and a modulation method thereof, and the VSI (voltage source inverter) in the time-sharing multiplexing hybrid converter can be used as a power switch in a DC-DC converter and a topology of a transformer-free grid-connected inverter, so that the hybrid converter is ensured to have the characteristics of low leakage current, high efficiency, high electric energy quality, reactive power injection, simultaneous output of AC and DC voltages and the like in a photovoltaic power generation system, and the leakage current can be effectively inhibited.
(II) technical scheme
The present invention has been made to overcome the above problems or at least partially solve the above problems, and provides a multi-output transformer-less symmetric hybrid converter and a modulation method thereof. The invention adopts the main technical scheme that:
according to an aspect of the present invention, there is provided a multi-output transformer-less symmetric hybrid converter, including: comprising symmetrical boost filter inductors Lb1And Lb2Symmetrical transformerless VSI, power diode D and output capacitor CDCThe DC-DC boost converter comprises a DC-DC boost converter and a transformerless voltage source grid-connected inverter consisting of symmetrical transformerless VSI and symmetrical differential mode filter inductors; the VSI is subjected to time division multiplexing in the hybrid converter, and can be used as a power switch in a DC-DC boost converter and a topology of a transformerless voltage source grid-connected inverter;
said Lb1Is connected with the positive pole P of the input of the photovoltaic cell; l isb2The first pole of the photovoltaic cell is connected with the negative pole N of the photovoltaic cell input; l isb1Is connected with the anode of a power diode D, the cathode of which is connected with an output capacitor CDCIs connected to the positive electrode of Lb2Second pole and output capacitor CDCIs connected with the negative electrode of the capacitor, and the voltage of the output capacitor is the DC output voltage VdcoutThe VSI is regarded as a power switch, the positive and negative poles of the input end of the VSI are respectively a first pole S and a second pole T, and the first pole S and the second pole T are respectively connected with the Lb1Second pole sum L ofb2The second poles of the first and second electrodes are connected;
the output end of the VSI is connected with the symmetrical differential mode filter inductor and used for converting the boosted direct-current voltage into alternating-current voltage in an inverse mode, and grid connection or off-grid load work is achieved.
Further, the transformerless voltage source grid-connected inverter comprises a symmetrical transformerless VSI topology and a symmetrical differential mode filter inductor L1And L2,When the VSI is used as an inverter, the VSI is a topology of a transformerless voltage source grid-connected inverter; the VSI output terminals are port A and port B, and port A and port L1Is connected to the first pole, ports B and L2Is connected to the first pole of L1Second pole and L of2Second pole and single-phase mains voltage vgAre connected.
Further, the structure of the transformerless voltage source grid-connected inverter is symmetrical, and the symmetrical transformerless VSI is a hybrid converter based on a full-bridge VSI or a hybrid converter based on a HERIC type VSI.
Furthermore, the hybrid converter based on the full-bridge VSI adopts a single-phase full-bridge topology VSI and comprises 2 switching tubes Sv1、Sv3Upper arm and S of the structurev2、Sv4A lower bridge arm; wherein, the switch tube Sv1、Sv3Is connected with the first pole S, and the second pole is connected with the switch tube S in turnv2、Sv4Is connected to the port A, B; the switch tube Sv2、Sv4Is connected to the second pole T.
Further, the HERIC-type VSI-based hybrid converter adopts a HERIC-type topology VSI and comprises 2 switching tubes Sh1、Sh3Upper arm of the structure, Sh2、Sh4Constituted lower arm and Sh5、Sh6The alternating bypass current is formed; wherein, the switch tube Sh1、Sh3Is connected with the first pole S, and the second pole is connected with the switch tube S in turnh2、Sh4Is connected to the port A, B; the switch tube Sh2、Sh4Is connected with the second pole T; the switch tube Sh5Is connected with the port A, and the second pole is connected with the switch tube Sh6Is connected to the second pole, and Sh6To (1) aOne pole is connected with the port B to form an alternating current bypass channel.
In another aspect, the modulation method is implemented using the hybrid converter described above, which guarantees a common-mode voltage V of the converter in each of the operating modes ST, P and NCMIs a constant value, wherein the common mode voltage VCMIs expressed as
Figure GDA0002708689010000041
Wherein, VANAnd VBNThe voltages from the VSI output port a and B to the input cathode N of the photovoltaic cell are respectively, and the working modes ST, P and N are specifically as follows:
mode ST: all switch tubes of the VSI are closed, and the photovoltaic cell gives the inductor Lb1And Lb2Charging, the power diode D is in reverse cut-off state, and the output capacitor CDCDischarge, common mode voltage V of the converterCMCan be expressed as
Figure GDA0002708689010000042
Wherein, VLb1And VLb2Are respectively Lb1And Lb2Voltage of the inductor, VLb1＝VLb2＝Vdcin/2；
And (3) mode P: switch tube Sv1、Sv4Closed, switch tube Sv2、Sv3Turn-off, inductance Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCCharging, in this mode, VANIs equal to Vdcin+VLb1，VBNIs equal to-VLb2，VLb1＝VLb2＝Vdcin/2, common mode voltage V of the converterCMCan be expressed as
Figure GDA0002708689010000043
And a mode N: switch tube Sv1、Sv4Turn-off, switch tube Sv2、Sv3Closed, inductor Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCCharging, in this mode, VANIs equal to-VLb1，VBNIs equal to Vdcin+VLb1，VLb1＝VLb2＝Vdcin/2, common mode voltage V of the converterCMCan be expressed as
Figure GDA0002708689010000044
Further, the modulation method specifically includes a short-circuit boosting mode and an alternating current inversion mode:
short circuit boosting mode: corresponding to mode ST, switch tube Sv1、Sv2、Sv3、Sv4All closed for d unit times, wherein one unit time is a switching cycle time TswThe step-up ratio M (d) of the DC-DC converter, the expression of which can be written as
Figure GDA0002708689010000051
An alternating current inversion mode: corresponding to the mode P and the mode N, the full-bridge VSI adopts a bipolar pulse width modulation method, and a switching tube Sv1、Sv4And Sv2、Sv3High-frequency complementary switching, no dead zone in the switching process and modulation ratio m of full-bridge VSIBCan be written as
Figure GDA0002708689010000052
The bipolar pulse width modulation works in a mode P and the switch tube Sv1、Sv4Closed, switch tube Sv2、Sv3OFF, FULL-BRIDGE VSI OUTPUT DIFFERENTIAL MODE VOLTAGE VABIs + vSTThe mode continues to beThe time is (1+ m)B-d)/2 units of time, wherein vSTIs the boosted DC bus voltage; operating in mode N, switching tube Sv1、Sv4Turn-off, switch tube Sv2、Sv3Closed, full bridge VSI output differential mode voltage vABIs-vSTThe pattern duration is (1-m)BD)/2 unit times, the reference voltage can be written as
Figure GDA0002708689010000053
Wherein the content of the first and second substances,
mB+d≤1
the DC-DC boost ratio d based on the full-bridge VSI hybrid converter and the modulation m of the inverterBWith the constraints described by the above equations.
In another aspect, the modulation method is implemented using the hybrid converter described above, which guarantees a common-mode voltage V of the converter in each of the operating modes ST, P, N and ZCMIs a constant value, wherein the common mode voltage is expressed by
Figure GDA0002708689010000054
Wherein, VANAnd VBNThe voltages from the VSI output port A and the VSI output port B to the input cathode N of the photovoltaic cell are respectively, and the working modes ST, P, N and Z are specifically as follows:
mode ST: all switch tubes of the VSI are closed, and the photovoltaic cell gives the inductor Lb1And Lb2Charging, the power diode D is in reverse cut-off state, and the output capacitor CDCDischarge, common mode voltage V of the converterCMCan be expressed as
Figure GDA0002708689010000061
Wherein, VLb1And VLb2Are respectively an inductance Lb1And an inductance Lb2Voltage of the inductor, VLb1＝VLb2＝Vdcin/2；
And (3) mode P: switch tube Sh1、Sh4And Sh6Closed, switch tube Sh2、Sh3And Sh5Turn-off, inductance Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCCharging, in this mode, VANIs equal to Vdcin+VLb1，VBNIs equal to-VLb2，VLb1＝VLb2＝Vdcin/2, common mode voltage V of the converterCMCan be expressed as
Figure GDA0002708689010000062
And a mode N: switch tube Sh1、Sh4And Sh6Cut off and switch tube Sh2、Sh3And Sh5Closed, inductor Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCCharging, in this mode, VANIs equal to-VLb1，VBNIs equal to Vdcin+VLb1，VLb1＝VLb2＝Vdcin/2, common mode voltage V of the converterCMCan be expressed as
Figure GDA0002708689010000063
Mode Z: switch tube Sh5And Sh6Closed, switch tube Sh1、Sh2、Sh3And Sh4Open, inductance Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCCharging, in which mode the switching tube Sh1、Sh2、Sh3And Sh4Are all in an off state, and have parasitic capacitance C of C-E poleg1、Cg2、Cg3And Cg4Voltage V ofcg1＝Vcg2＝Vcg3＝Vcg4＝(Vdcin+VLb1+VLb2) /2, in this mode, VANIs equal to Vcg2-VLb1，VBNIs equal to Vcg4-VLb1Common mode voltage V of the converterCMCan be expressed as
Figure GDA0002708689010000064
Further, the modulation method specifically includes a short-circuit boosting mode and an alternating current inversion mode:
short circuit boosting mode: corresponding to mode ST, switch tube Sh1、Sh2、Sh3、Sh4、Sh5、Sh6All closed for d unit times, wherein one unit time is a switching cycle time TswThe step-up ratio M (d) of the DC-DC converter, the expression of which can be written as
Figure GDA0002708689010000065
An alternating current inversion mode: high-efficiency pulse width modulation with reactive injection capability is adopted for the HERIC type VSI corresponding to the mode P, the mode N and the mode Z, and a switching tube Sh1、Sh2、Sh3、Sh4High frequency switching, AC bypass switch tube Sh5、Sh6Power frequency switching, no dead zone in the switching process, and HERIC type VSI modulation ratio mUCan be written as
Figure GDA0002708689010000071
The high-efficiency pulse width modulation with the reactive injection capability works in a mode P and a switching tube Sh1、Sh4And Sh6Closed, switch tube Sh2、Sh3And Sh5Shut down, HERIC type VSI output differential mode voltage vABIs + vSTThe pattern duration is mUPer unit time, same vSTIs the boosted DC bus voltage; operating in mode N, switching tube Sh1、Sh4And Sh6Turn-off, switch tube Sh2、Sh3And Sh5Closed, output differential mode voltage vABIs-vSTThe pattern duration is mUA unit time; when reference voltage vrefNot less than 0, working in mode Z, switching tube Sh5And Sh6Closed, switch tube Sh1、Sh2、Sh3And Sh4Shut down, HERIC type VSI output differential mode voltage vABIs 0, the pattern duration is 1-mUD unit times, the reference voltage can be written
vref＝mU×Vdcout+1-mU-d×(0)＝mUVdcout
Wherein the content of the first and second substances,
mU+d≤1
the DC-DC boost ratio d based on the HERIC VSI hybrid converter and the modulation m of the inverterUWith the constraints described by the above equations.
(III) advantageous effects
As can be seen from the above technical solutions, the converter and the modulation method thereof of the present invention have the following advantages: two hybrid converters with DC output and AC output are constructed by arranging symmetrical input filter inductors, symmetrical VSI topological structures (for example, based on a full-bridge VSI topology and based on a HERIC type VSI topology) and symmetrical differential mode inductors and combining traditional power diodes and output capacitors. In addition, the invention also designs a corresponding modulation method, and the converters have the capability of reactive power injection, and are particularly suitable for the application occasions of the photovoltaic grid-connected power generation device.
Drawings
The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are illustrative and not to be construed as limiting the invention in any way, and in which:
FIG. 1 is a schematic diagram of a multiple output, transformerless, symmetric hybrid converter of the present invention;
FIG. 2 is a schematic diagram of a hybrid converter based on a full-bridge VSI;
FIG. 3 is a schematic diagram of a modulation method for the full-bridge VSI based hybrid converter of FIG. 2;
fig. 4 shows diagrams (a), (b) and (c) respectively illustrating three operation modes of the full-bridge VSI-based hybrid converter;
fig. 5 is a schematic diagram of the structure of a hybrid converter based on a horic VSI;
fig. 6 is a schematic diagram of a modulation method of the hybrid converter based on the HERIC type VSI in fig. 5;
graphs (a), (b), (c) and (d) in fig. 7 are schematic diagrams of four operation modes of the hybrid converter based on the hiric VSI, respectively;
FIG. 8 is a schematic diagram of system parameters for a full bridge VSI-based hybrid converter and a HERIC-based hybrid converter;
FIGS. 9(a), (b) and (c) are schematic diagrams of simulated waveforms for a full-bridge VSI based hybrid converter at different power factors;
graphs ((a), (b) and (c) in fig. 10 are schematic graphs of simulated waveforms of a hybrid converter based on a horic-type VSI at different power factors;
fig. 11 is a schematic diagram of a method of constructing a hybrid converter of the present invention.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
A technical embodiment of the present invention provides a multi-output transformer-less symmetric hybrid converter, as shown in fig. 1, including: the voltage source grid-connected inverter comprises a DC-DC boost converter consisting of symmetrical boost filter inductors, VSI equivalent power switches, power diodes and an output capacitor, and a transformer-free voltage source grid-connected inverter consisting of symmetrical transformer-free VSI (voltage source inverter) topology and symmetrical differential mode filter inductors;
symmetrical boosting filter inductor Lb1And Lb2The VSI is taken as a power switch, forms a DC-DC boost converter with a power diode and an output capacitor and outputs direct-current voltage; the transformer-free voltage source grid-connected inverter is used for inverting the boosted direct-current voltage into alternating-current voltage and realizing grid-connected or off-grid load work.
In practical application, as shown in fig. 1, the filter inductor L is symmetrical in boostingb1And Lb2(Lb1＝Lb2) Power diode D and output capacitor CDCAnd a VSI circuit used as a power switch constitute a DC-DC boost converter. Filter inductance Lb1Is connected with the positive pole P of the input of the photovoltaic cell; filter inductance Lb2The first pole of the photovoltaic cell is connected with the negative pole N of the photovoltaic cell input; l isb1Is connected to the anode of a power diode D, the cathode of which is connected to an output capacitor CDCIs connected to the positive electrode of Lb2Second pole and output capacitor CDCIs connected with the negative electrode of the capacitor, and the voltage of the output capacitor is the DC output voltage Vdcout. VSI is regarded as a switch, the first pole (S) and the second pole (T) of which are connected to Lb1Second pole sum L ofb2Is connected to the second pole.
In fig. 1, a transformerless voltage source grid-connected inverter includes a symmetrical transformerless VSI topology and symmetrical differential mode filter inductors L1And L2(L1＝L2) It should be noted that the VSI is time-division multiplexed in the hybrid converter, and can be used as a power switch in the DC-DC converter or a topology of a transformer-less grid-connected inverter. Input anode S and differential mode filter inductor L of symmetrical transformerless VSIb1Is connected with the second pole, the input cathode T of the VSI and the differential mode filter inductor Lb2The second poles of the first and second electrodes are connected; two output ends of the VSI are a port A and a port B, and the port A and a differential mode filter inductor L1Is connected to the first pole of the first electrode,port B and differential mode filter inductor L2Is connected to the first pole of L1Second pole and L of2Second pole and single-phase mains voltage vgAre connected.
Fig. 2 shows a hybrid converter based on a full-bridge VSI proposed by the hybrid converter according to the present invention, which includes 2 switching tubes Sv1、Sv3Upper arm and S of the structurev2、Sv4A lower bridge arm; wherein, the switch tube Sv1、Sv3The first pole of the switch is connected with a boosting voltage anode S, a port A, B is a midpoint between two groups of upper and lower bridge arms, and the second pole of the switch is sequentially connected with the switching tube Sv2、Sv4Is connected to the port A, B; the switch tube Sv2、Sv4Is connected to the boost voltage negative pole T.
Fig. 3 shows a modulation method based on a full-bridge VSI hybrid converter, which is described in detail as follows:
short boost mode (ST): switch tube Sv1、Sv2、Sv3、Sv4All closed for d unit times, wherein one unit time is a switching cycle time TswThe step-up ratio M (d) of the DC-DC converter, the expression of which can be written as
Figure GDA0002708689010000101
Ac inversion mode (mode P and mode N): the full-bridge VSI adopts a bipolar pulse width modulation method and a switching tube Sv1、Sv4And Sv2、Sv3High-frequency complementary switching is carried out, and no dead zone exists in the switching process. Modulation ratio m of full-bridge VSIBCan be written as
Figure GDA0002708689010000102
The bipolar pulse width modulation works in a mode P and the switch tube Sv1、Sv4Closed, switch tube Sv2、Sv3OFF, FULL-BRIDGE VSI OUTPUT DIFFERENTIAL MODE VOLTAGE VABIs + vSTThe pattern duration is (1+ m)B-d)/2 units of time, wherein vSTIs the boosted DC bus voltage; operating in mode N, switching tube Sv1、Sv4Turn-off, switch tube Sv2、Sv3Closed, full bridge VSI output differential mode voltage vABIs-vSTThe pattern duration is (1-m)B-d)/2 units of time. Reference voltages can be written as
Figure GDA0002708689010000103
Wherein the content of the first and second substances,
mB+d≤1
the DC-DC boost ratio d based on the full-bridge VSI hybrid converter and the modulation m of the inverterBWith the constraints described by the above equations.
Fig. 4 shows three modes of operation of a full bridge VSI based hybrid converter. The common mode voltage is expressed as
Figure GDA0002708689010000111
Wherein, VANAnd VBNThe voltages from the VSI output ports a and B to the negative input N of the photovoltaic cell, respectively.
As shown in fig. 4 (a), mode ST: all switch tubes of the VSI are closed, and the photovoltaic cell gives the inductor Lb1And Lb2Charging, the power diode D is in reverse cut-off state, and the output capacitor CDCAnd (4) discharging. Common mode voltage V of converterCMCan be expressed as
Figure GDA0002708689010000112
Wherein, VLb1And VLb2Respectively symmetrical boosting filter inductance Lb1And Lb2Voltage of the inductor, VLb1＝VLb2＝Vdcin/2。
As shown in fig. 4 (b), pattern P: switch tube Sv1、Sv4Closed, switch tube Sv2、Sv3Turn-off, inductance Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCAnd (6) charging. In this mode, VANIs equal to Vdcin+VLb1，VBNIs equal to-VLb2，VLb1＝VLb2＝Vdcin/2, common mode voltage V of the converterCMCan be expressed as
Figure GDA0002708689010000113
As shown in (c) in fig. 4, mode N: switch tube Sv1、Sv4Turn-off, switch tube Sv2、Sv3Closed, inductor Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCAnd (6) charging. In this mode, VANIs equal to-VLb1，VBNIs equal to Vdcin+VLb1，VLb1＝VLb2＝Vdcin/2, common mode voltage V of the converterCMCan be expressed as
Figure GDA0002708689010000114
The above analysis shows that the common-mode voltage of the modulation method based on the full-bridge VSI hybrid converter is constant V no matter what mode the modulation method works indcinAnd/2, thereby having good leakage current suppression capability. And the bipolar modulation adopted by the full-bridge VSI has the capability of reactive power regulation.
Fig. 5 shows a hybrid converter based on a HERIC VSI proposed by the hybrid converter according to the present invention, comprising 2 switching tubes Sh1、Sh3Upper arm of the structure, Sh2、Sh4Constituted lower arm and Sh5、Sh6Is composed ofAn alternating bypass current; wherein, the switch tube Sh1、Sh3The first pole of the switch is connected with the boosting voltage anode S, and the second pole of the switch is connected with the switching tube S in turnh2、Sh4Is connected to port A, B, port A, B is the midpoint between the two sets of upper and lower legs; switch tube Sh2、Sh4Is connected with the boost voltage cathode T; switch tube Sh5Is connected with the port A, and the second pole is connected with the switch tube Sh6Is connected to the second pole, and Sh6The first pole of (a) is connected with port B to form an ac bypass channel.
Fig. 6 shows a modulation method based on a hiric VSI hybrid converter, described in detail below,
short boost mode (ST): switch tube Sh1、Sh2、Sh3、Sh4、Sh5、Sh6All closed for d unit times, wherein one unit time is a switching cycle time TswThe step-up ratio M (d) of the DC-DC converter, the expression of which can be written as
Figure GDA0002708689010000121
Alternating current inversion mode (mode P, mode N, and mode Z): HERIC type VSI adopts high-efficiency pulse width modulation with reactive injection capability, and a switching tube Sh1、Sh2、Sh3、Sh4High frequency switching, AC bypass switch tube Sh5、Sh6And power frequency switching is carried out, and no dead zone exists in the switching process. Modulation ratio m of HERIC type VSIUCan be written as
Figure GDA0002708689010000122
The high-efficiency pulse width modulation with the reactive injection capability works in a mode P and a switching tube Sh1、Sh4And Sh6Closed, switch tube Sh2、Sh3And Sh5Shut down, HERIC type VSI output differential mode voltage vABIs + vSTThe pattern duration is mUPer unit time, same vSTIs the boosted DC bus voltage; operating in mode N, switching tube Sh1、Sh4And Sh6Turn-off, switch tube Sh2、Sh3And Sh5Closed, output differential mode voltage vABIs-vSTThe pattern duration is mUA unit time; when reference voltage vrefNot less than 0, working in mode Z, switching tube Sh5And Sh6Closed, switch tube Sh1、Sh2、Sh3And Sh4Shut down, HERIC type VSI output differential mode voltage vABIs 0, the pattern duration is 1-mU-d units of time. Reference voltages can be written as
vref＝mU×Vdcout+1-mU-d×(0)＝mUVdcout
Wherein the content of the first and second substances,
mU+d≤1
the DC-DC boost ratio d based on the HERIC VSI hybrid converter and the modulation m of the inverterUWith the constraints described by the above equations.
As shown in fig. 7, the four operating modes (modes ST, P, N and Z) of the hiric VSI hybrid converter are based on the common mode voltage expressed as
Figure GDA0002708689010000131
Wherein, VANAnd VBNThe voltages from the VSI output ports a and B to the negative input N of the photovoltaic cell, respectively.
As shown in sub-diagram (a) in fig. 7, pattern ST: all switch tubes of the VSI are closed, and the photovoltaic cell gives the inductor Lb1And Lb2Charging, the power diode D is in reverse cut-off state, and the output capacitor CDCAnd (4) discharging. Common mode voltage V of converterCMCan be expressed as
Figure GDA0002708689010000132
Wherein, VLb1And VLb2Are respectively an inductance Lb1And an inductance Lb2Voltage of the inductor, VLb1＝VLb2＝Vdcin/2。
As shown in (b) of fig. 7, pattern P: switch tube Sh1、Sh4And Sh6Closed, switch tube Sh2、Sh3And Sh5Turn-off, inductance Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCAnd (6) charging. In this mode, VANIs equal to Vdcin+VLb1，VBNIs equal to-VLb2，VLb1＝VLb2＝Vdcin/2, common mode voltage V of the converterCMCan be expressed as
Figure GDA0002708689010000133
As shown in (c) in fig. 7, mode N: switch tube Sh1、Sh4And Sh6Cut off and switch tube Sh2、Sh3And Sh5Closed, inductor Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCAnd (6) charging. In this mode, VANIs equal to-VLb1，VBNIs equal to Vdcin+VLb1，VLb1＝VLb2＝Vdcin/2, common mode voltage V of the converterCMCan be expressed as
Figure GDA0002708689010000134
As shown in (d) in fig. 7, the pattern Z: switch tube Sh5And Sh6Closed, switch tube Sh1、Sh2、Sh3And Sh4Open, inductance Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCAnd (6) charging. In this mode, the switch tube Sh1、Sh2、Sh3And Sh4Are all in an off state, and have parasitic capacitance C of C-E poleg1、Cg2、Cg3And Cg4Voltage V ofcg1＝Vcg2＝Vcg3＝Vcg4＝(Vdcin+VLb1+VLb2)/2. In this mode, VANIs equal to Vcg2-VLb1，VBNIs equal to Vcg4-VLb1Common mode voltage V of the converterCMCan be expressed as
Figure GDA0002708689010000141
The above analysis shows that the common-mode voltage of the modulation method based on the HERIC VSI hybrid converter is constant V in all the working modesdcinAnd/2, the leakage current suppression capability is good. The modulation method has the function of bidirectional current circulation in the Z mode, has the capability of reactive power regulation and ensures low switching loss.
FIG. 8 is a schematic diagram of simulation parameters for a full-bridge VSI-based hybrid converter and a HERIC-type VSI-based hybrid converter according to embodiments of the present invention, including DC output power, AC output power, DC output voltage, grid-connected voltage, and BOOST inductor (i.e., symmetrical BOOST filter inductor L)b1And an inductance Lb2) The photovoltaic power generation system comprises a DC-DC output capacitor, a DC load, a differential mode filter inductor, a switching frequency and a photovoltaic cell grounding parasitic capacitor.
Fig. 9(a), (b) and (c) show waveform diagrams of a full-bridge VSI-based hybrid converter. The method comprises the following steps: DC input voltage VdcinD.c. output voltage VdcoutV. grid-connected voltage vgGrid-connected current igLeakage current ileakCommon mode voltage VCMOutput port voltage V of inverterANAnd VBN. FIGS. 9(a), (b), and (c) illustrate the operation of a grid-connected inverter based on a full-bridge VSI hybrid converter at unity power factor and power factor+0.8 and-0.8 power factor, the simulation results show that a full-bridge VSI based hybrid converter can output both DC and AC voltages with the common mode voltage held at a constant VdcinAnd 2, the leakage current suppression condition is good, the reactive power regulation capability is realized, no dead zone needs to be inserted during the modulation mode switching period, and the quality of the output grid-connected current electric energy is good.
Fig. 9(a), (b) and (c) show waveform diagrams of the hybrid converter based on the full-bridge VSI, including fig. 10 with the same parameters as fig. 9, wherein fig. 10 (a), (b) and (c) are waveform diagrams of the hybrid converter based on the HERIC VSI, respectively, in which the grid-connected inverter operates at the unity power factor, the power factor is +0.8 and the power factor is-0.8, and the simulation result shows that the hybrid converter based on the HERIC VSI can output the DC voltage and the AC voltage at the same time, and the common mode voltage is maintained at the constant VdcinAnd 2, the leakage current suppression condition is good, the reactive power regulation capability is realized, no dead zone needs to be inserted during the modulation mode switching period, and the quality of the output grid-connected current electric energy is good.
As can be seen by comparing FIG. 9 with FIG. 10, V in FIG. 9ANAnd VBNAlways varies at high frequencies of 0V and 200V, whereas V of FIG. 10ANAnd VBNAnd high-frequency switching is respectively carried out between 0V-100V and 100V-200V in each half power frequency period. The results show that the switching losses of the full-bridge VSI-based hybrid converter shown in fig. 9 are almost twice the switching losses of the HERIC-type VSI-based hybrid converter shown in fig. 10.
Fig. 11 is a schematic diagram of a method for constructing a hybrid converter according to the present invention, in which the circuit structures and modulation methods of the hybrid converter based on a full-bridge VSI and the hybrid converter based on a HERIC type VSI are based on the same inventive concept (i.e., fig. 1), and although the specific modulation methods and switching losses of the two converters are different, it will be appreciated by those skilled in the art that the specific structure design of the transformer-less VSI is different.
The converter and the modulation method thereof have the following advantages: two hybrid converters with DC output and AC output are constructed by arranging symmetrical input filter inductors, symmetrical VSI topological structures (for example, based on a full-bridge VSI topology and based on a HERIC type VSI topology) and symmetrical differential mode inductors and combining traditional power diodes and output capacitors. In addition, the invention also designs a corresponding modulation method, and the converters have the capability of reactive power injection, and are particularly suitable for the application occasions of the photovoltaic grid-connected power generation device. Furthermore, the switching losses of a hybrid converter based on a full-bridge VSI are almost twice those of a hybrid converter based on a hiric type VSI.
Finally, the method of the present application is only a preferred embodiment and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (2)

1. A modulation method for a multi-output transformer-less symmetrical hybrid converter including symmetrical boost filter inductors Lb1And Lb2Symmetrical transformerless VSI, power diode D and output capacitor CDCThe DC-DC boost converter comprises a DC-DC boost converter and a transformerless voltage source grid-connected inverter consisting of symmetrical transformerless VSI and symmetrical differential mode filter inductors; the VSI is subjected to time division multiplexing in the hybrid converter, and can be used as a power switch in a DC-DC boost converter and a topology of a transformerless voltage source grid-connected inverter;
said Lb1Is connected with the positive pole P of the input of the photovoltaic cell; l isb2The first pole of the photovoltaic cell is connected with the negative pole N of the photovoltaic cell input; l isb1Is connected with the anode of a power diode D, the cathode of which is connected with an output capacitor CDCThe positive electrodes of the anode and the cathode are connected,Lb2second pole and output capacitor CDCIs connected with the negative electrode of the capacitor, and the voltage of the output capacitor is the DC output voltage VdcoutThe VSI is regarded as a power switch, the positive and negative poles of the input end of the VSI are respectively a first pole S and a second pole T, and the first pole S and the second pole T are respectively connected with the Lb1Second pole sum L ofb2The second poles of the first and second electrodes are connected;
the output end of the VSI is connected with a symmetrical differential mode filter inductor and is used for inverting the boosted direct-current voltage into alternating-current voltage so as to realize grid-connected or off-grid load work,
the transformer-free voltage source grid-connected inverter comprises a symmetrical transformer-free VSI topology and a symmetrical differential mode filter inductor L1And L2When the VSI is used as an inverter, the VSI is a topology of a transformerless voltage source grid-connected inverter; the VSI output terminals are port A and port B, and port A and port L1Is connected to the first pole, ports B and L2Is connected to the first pole of L1Second pole and L of2Second pole and single-phase mains voltage vgConnecting; the structure of the transformer-free voltage source grid-connected inverter is symmetrical, and the symmetrical transformer-free VSI is a hybrid converter based on a full-bridge VSI; the hybrid converter based on the full-bridge VSI adopts a single-phase full-bridge topology VSI and comprises 2 switching tubes Sv1、Sv3Upper arm and S of the structurev2、Sv4A lower bridge arm; wherein, the switch tube Sv1、Sv3Is connected with the first pole S, and the second pole is connected with the switch tube S in turnv2、Sv4Is connected to the port A, B; the switch tube Sv2、Sv4Is connected with the second pole T;
the hybrid converter is characterized in that the hybrid converter can ensure the common-mode voltage V of the converter under the working modes ST, P and NCMIs a constant value, wherein the common mode voltage VCMIs expressed as
Figure FDA0002708687000000021
Wherein, VANAnd VBNThe voltages from the VSI output port a and B to the input cathode N of the photovoltaic cell are respectively, and the working modes ST, P and N are specifically as follows:
mode ST: all switch tubes of the VSI are closed, and the photovoltaic cell gives the inductor Lb1And Lb2Charging, the power diode D is in reverse cut-off state, and the output capacitor CDCDischarge, common mode voltage V of the converterCMCan be expressed as
Figure FDA0002708687000000022
Wherein, VLb1And VLb2Are respectively Lb1And Lb2Voltage of the inductor, VLb1＝VLb2＝Vdcin/2；
And (3) mode P: switch tube Sv1、Sv4Closed, switch tube Sv2、Sv3Turn-off, inductance Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCCharging, in this mode, VANIs equal to Vdcin+VLb1，VBNIs equal to-VLb2，VLb1＝VLb2＝Vdcin/2, common mode voltage V of the converterCMCan be expressed as
Figure FDA0002708687000000023
And a mode N: switch tube Sv1、Sv4Turn-off, switch tube Sv2、Sv3Closed, inductor Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCCharging, in this mode, VANIs equal to-VLb1，VBNIs equal to Vdcin+VLb1，VLb1＝VLb2＝Vdcin/2, common mode voltage V of the converterCMCan be expressed as
Figure FDA0002708687000000024
The modulation method specifically comprises a short-circuit boosting mode and an alternating current inversion mode:
short circuit boosting mode: corresponding to mode ST, switch tube Sv1、Sv2、Sv3、Sv4All closed for d unit times, wherein one unit time is a switching cycle time TswThe step-up ratio M (d) of the DC-DC converter, the expression of which can be written as
Figure FDA0002708687000000025
An alternating current inversion mode: corresponding to the mode P and the mode N, the full-bridge VSI adopts a bipolar pulse width modulation method, and a switching tube Sv1、Sv4And Sv2、Sv3High-frequency complementary switching, no dead zone in the switching process and modulation ratio m of full-bridge VSIBCan be written as
Figure FDA0002708687000000031
The bipolar pulse width modulation works in a mode P and the switch tube Sv1、Sv4Closed, switch tube Sv2、Sv3OFF, FULL-BRIDGE VSI OUTPUT DIFFERENTIAL MODE VOLTAGE VABIs + vSTThe pattern duration is (1+ m)B-d)/2 units of time, wherein vSTIs the boosted DC bus voltage; operating in mode N, switching tube Sv1、Sv4Turn-off, switch tube Sv2、Sv3Closed, full bridge VSI output differential mode voltage vABIs-vSTThe duration of the pattern is (1-m)BD)/2 unit times, the reference voltage can be written as
Figure FDA0002708687000000032
Wherein the content of the first and second substances,
mB+d≤1
the DC-DC boost ratio d based on the full-bridge VSI hybrid converter and the modulation m of the inverterBWith the constraint described by the above formula, at a reference voltage vrefWhen the voltage is more than or equal to 0, the control is carried out according to the modes P, N, ST, N and P in sequence in one switching period, and the reference voltage v isrefAnd when the voltage is less than 0, sequentially carrying out switching control according to the modes N, P, ST, P and N in one switching period.
2. A modulation method for multi-output transformer-free symmetrical hybrid converter includes symmetrical boosting filter inductance Lb1And Lb2Symmetrical transformerless VSI, power diode D and output capacitor CDCThe DC-DC boost converter comprises a DC-DC boost converter and a transformerless voltage source grid-connected inverter consisting of symmetrical transformerless VSI and symmetrical differential mode filter inductors; the VSI is subjected to time division multiplexing in the hybrid converter, and can be used as a power switch in a DC-DC boost converter and a topology of a transformerless voltage source grid-connected inverter;
said Lb1Is connected with the positive pole P of the input of the photovoltaic cell; l isb2The first pole of the photovoltaic cell is connected with the negative pole N of the photovoltaic cell input; l isb1Is connected with the anode of a power diode D, the cathode of which is connected with an output capacitor CDCIs connected to the positive electrode of Lb2Second pole and output capacitor CDCIs connected with the negative electrode of the capacitor, and the voltage of the output capacitor is the DC output voltage VdcoutThe VSI is regarded as a power switch, the positive and negative poles of the input end of the VSI are respectively a first pole S and a second pole T, and the first pole S and the second pole T are respectively connected with the Lb1Second pole sum L ofb2The second poles of the first and second electrodes are connected;
the output end of the VSI is connected with a symmetrical differential mode filter inductor and is used for inverting the boosted direct-current voltage into alternating-current voltage so as to realize grid-connected or off-grid load work;
the transformer-free voltage source grid-connected inverter comprises a symmetrical transformer-free VSI topology and a symmetrical differential mode filter inductor L1And L2When the VSI is used as an inverter, the VSI is a topology of a transformerless voltage source grid-connected inverter; the VSI output terminals are port A and port B, and port A and port L1Is connected to the first pole, ports B and L2Is connected to the first pole of L1Second pole and L of2Second pole and single-phase mains voltage vgConnecting; the symmetrical transformerless VSI is a hybrid converter based on a HERIC type VSI;
the HERIC-type VSI-based hybrid converter adopts HERIC-type topology VSI and comprises 2 switching tubes Sh1、Sh3Upper arm of the structure, Sh2、Sh4Constituted lower arm and Sh5、Sh6The alternating bypass current is formed; wherein, the switch tube Sh1、Sh3Is connected with the first pole S, and the second pole is connected with the switch tube S in turnh2、Sh4Is connected to the port A, B; the switch tube Sh2、Sh4Is connected with the second pole T; the switch tube Sh5Is connected with the port A, and the second pole is connected with the switch tube Sh6Is connected to the second pole, and Sh6The first pole of the second switch is connected with the port B to form an alternating current bypass channel;
the hybrid converter is characterized in that the hybrid converter can ensure the common-mode voltage V of the converter under the working modes ST, P, N and ZCMIs a constant value, wherein the common mode voltage is expressed by
Figure FDA0002708687000000041
Wherein, VANAnd VBNThe voltages from the VSI output port A and the VSI output port B to the input cathode N of the photovoltaic cell are respectively, and the working modes ST, P, N and Z are specifically as follows:
mode ST: all switch tubes of the VSI are closed, and the photovoltaic cell gives the inductor Lb1And Lb2Charging, power diodeThe tube D is in reverse cut-off state and outputs a capacitor CDCDischarge, common mode voltage V of the converterCMCan be expressed as
Figure FDA0002708687000000042
Wherein, VLb1And VLb2Are respectively an inductance Lb1And an inductance Lb2Voltage of the inductor, VLb1＝VLb2＝Vdcin/2；
And (3) mode P: switch tube Sh1、Sh4And Sh6Closed, switch tube Sh2、Sh3And Sh5Turn-off, inductance Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCCharging, in this mode, VANIs equal to Vdcin+VLb1，VBNIs equal to-VLb2，VLb1＝VLb2＝Vdcin/2, common mode voltage V of the converterCMCan be expressed as
Figure FDA0002708687000000051
And a mode N: switch tube Sh1、Sh4And Sh6Cut off and switch tube Sh2、Sh3And Sh5Closed, inductor Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCCharging, in this mode, VANIs equal to-VLb1，VBNIs equal to Vdcin+VLb1，VLb1＝VLb2＝Vdcin/2, common mode voltage V of the converterCMCan be expressed as
Figure FDA0002708687000000052
Mode Z: switch tube Sh5And Sh6Closed, switch tube Sh1、Sh2、Sh3And Sh4Open, inductance Lb1And Lb2Discharging, the power diode D is in forward conduction state, and the output capacitor CDCCharging, in which mode the switching tube Sh1、Sh2、Sh3And Sh4Are all in an off state, and have parasitic capacitance C of C-E poleg1、Cg2、Cg3And Cg4Voltage V ofcg1＝Vcg2＝Vcg3＝Vcg4＝(Vdcin+VLb1+VLb2) /2, in this mode, VANIs equal to Vcg2-VLb1，VBNIs equal to Vcg4-VLb1Common mode voltage V of the converterCMCan be expressed as
Figure FDA0002708687000000053
The modulation method specifically comprises a short-circuit boosting mode and an alternating current inversion mode:
short circuit boosting mode: corresponding to mode ST, switch tube Sh1、Sh2、Sh3、Sh4、Sh5、Sh6All closed for d unit times, wherein one unit time is a switching cycle time TswThe step-up ratio M (d) of the DC-DC converter, the expression of which can be written as
Figure FDA0002708687000000054
An alternating current inversion mode: high-efficiency pulse width modulation with reactive injection capability is adopted for the HERIC type VSI corresponding to the mode P, the mode N and the mode Z, and a switching tube Sh1、Sh2、Sh3、Sh4High frequency switching, AC bypass switch tube Sh5、Sh6Power frequency switching, no dead zone in the switching process, and HERIC type VSI modulation ratio mUCan be written as
Figure FDA0002708687000000061
The high-efficiency pulse width modulation with the reactive injection capability works in a mode P and a switching tube Sh1、Sh4And Sh6Closed, switch tube Sh2、Sh3And Sh5Shut down, HERIC type VSI output differential mode voltage vABIs + vSTThe pattern duration is mUPer unit time, same vSTIs the boosted DC bus voltage; operating in mode N, switching tube Sh1、Sh4And Sh6Turn-off, switch tube Sh2、Sh3And Sh5Closed, output differential mode voltage vABIs-vSTThe pattern duration is mUA unit time; when reference voltage vrefNot less than 0, working in mode Z, switching tube Sh5And Sh6Closed, switch tube Sh1、Sh2、Sh3And Sh4Shut down, HERIC type VSI output differential mode voltage vABIs 0, the pattern duration is 1-mUD unit times, the reference voltage can be written
vref＝mU×Vdcout+1-mU-d×(0)＝mUVdcout
Wherein the content of the first and second substances,
mU+d≤1
the DC-DC boost ratio d based on the HERIC VSI hybrid converter and the modulation m of the inverterUWith the constraint described by the above formula, at a reference voltage vrefWhen the voltage is greater than or equal to 0, the control is carried out according to the patterns P, Z, ST, Z and P in sequence in one switching period, and the reference voltage v isrefAnd when the switching frequency is less than 0, sequentially carrying out switching control according to the modes N, Z, ST, Z and N in one switching period.
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