CN116488491A - Multi-index comprehensive optimized hybrid multi-level converter and regulation and control method thereof - Google Patents

Multi-index comprehensive optimized hybrid multi-level converter and regulation and control method thereof Download PDF

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CN116488491A
CN116488491A CN202310689033.0A CN202310689033A CN116488491A CN 116488491 A CN116488491 A CN 116488491A CN 202310689033 A CN202310689033 A CN 202310689033A CN 116488491 A CN116488491 A CN 116488491A
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frequency
close
bridge arm
module
voltage
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CN116488491B (en
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侯玉超
郭祺
涂春鸣
王鑫
肖凡
黄泽钧
任鹏
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Hunan University
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Hunan University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
    • 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
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • 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
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

The invention provides a multi-index comprehensive optimized hybrid multi-level converter and a regulating and controlling method thereof. The hybrid multi-level converter is of a three-phase structure, each phase is provided with an upper bridge arm and a lower bridge arm connected below the upper bridge arm, and each of the upper bridge arm and the lower bridge arm comprises a high-frequency sub-module, a plurality of cascaded low-frequency sub-modules and a bridge arm inductor which are sequentially connectedAnd an output port of the hybrid multi-level converter is led out between the upper bridge arm and the lower bridge arm of each phase. The low-frequency submodule in the hybrid multi-level converter adopts the nearest level to approximate the modulation and output power frequency step wave, and the high-frequency submodule adopts the unipolar pulse width modulation and outputs high-frequency shaping wave. The mixed multi-level converter and the regulating and controlling method thereof can reduce the overall cost of the device and ensure the deviceAnd the quality and the efficiency of the output waveform are improved, and the comprehensive optimization of multiple indexes is realized.

Description

Multi-index comprehensive optimized hybrid multi-level converter and regulation and control method thereof
Technical Field
The invention relates to the technical field of power electronics, in particular to a multi-index comprehensive optimized hybrid multi-level converter and a regulating and controlling method thereof.
Background
The multi-level converter is widely applied to various scenes such as electric transmission, electric traction, new energy power generation and the like by virtue of the advantages of more output level numbers, less harmonic content, small voltage stress of a switching device and the like. The multilevel converter may be classified into a neutral point clamped type, a flying capacitor type, a cascaded H-bridge type, and a modularized multilevel converter (Modular Multilevel Converter, MMC) according to a circuit configuration. The MMC is widely applied to alternating current and direct current power grids and flexible and direct current power transmission by virtue of the advantages of strong expandability, good redundancy and the like.
The traditional MMC is mainly based on a single type device, and the traditional MMC device based on an Si-based Insulated Gate Bipolar Transistor (IGBT) device is low in cost, but high in loss and low in efficiency; whereas MMC efficiency and power density based on SiC-based Metal Oxide Semiconductor Field Effect Transistor (MOSFET) devices are higher, but cost prohibitive. Therefore, indexes such as efficiency, cost and the like of MMC devices based on single-type devices are difficult to comprehensively optimize, and for this reason, MMCs based on heterogeneous device mixing are receiving attention of students. Such as: MMC based on Si IGBT device and SiC MOSFET device mixes, see fig. 1 (a), and this MMC's Si IGBT device is at low frequency, and the SiC MOSFET device is at high frequency, and it has fully played the advantage that Si device on-state loss is low, siC device switching loss is low. But compared with the traditional carrier phase shift modulation method, the MMC topological structure and the modulation method can only outputA level. Another modified mixed MMC is shown in fig. 1 (b), which can output +.>Level, but the number of SiC devices needs to be doubled, and the cost is higher. Therefore, how to further reduce the number of SiC devices and the overall cost of the MMC converter while maintaining the waveform quality has become one of the key issues to be solved in the industry.
Disclosure of Invention
In order to solve the problem that the traditional MMC cannot comprehensively optimize the output waveform quality, efficiency and cost of the device, the invention provides a multi-index comprehensive optimized hybrid multi-level converter and a regulating and controlling method thereof.
In order to solve the technical problems, the invention adopts the following technical methods: a multi-index comprehensive optimized hybrid multi-level converter is of a three-phase structure, each phase is provided with an upper bridge arm and a lower bridge arm connected below the upper bridge arm, and the upper bridge arm and the lower bridge arm respectively comprise a high-frequency submodule and a bridge arm inductorAnd a plurality of cascaded low frequency sub-modules;
the high frequency sub-module comprises four SiC MOSFET devices、/>、/>、/>And two Si IGBT devices->、/>And two capacitances->、/>The method comprises the steps of carrying out a first treatment on the surface of the By->、/>To form a half-bridge converter, ">、/>Forming another half-bridge converter; />Emitter and +.>A first port leading out from the connection point to form a high frequency sub-module; />Emitter and +.>A second port leading out from the connection point to form a high-frequency sub-module; />Positive electrode of (2) and->Is connected to the collector of (1), the negative electrode is connected to->Is connected with the emitter of the (C); />Positive electrode of (2) and->Is used for collecting currentThe poles are connected, the negative pole is connected with->Is connected with the emitter of the (C); />Collector and->Is connected with the positive electrode of->Emitter and->Is connected with the negative electrode of the battery; />Collector and->Is connected with the positive electrode of->Emitter and->Is connected with the negative electrode of the battery;
the low frequency sub-module comprises two Si IGBT devices、/>And a capacitor->The method comprises the steps of carrying out a first treatment on the surface of the By->、/>Forming a half-bridge converter; />Emitter and->A first port which is a low frequency sub-module is led out from the connection point; from->The emitter of (a) is led out to serve as a second port of the low-frequency sub-module; capacitance->Positive electrode of (2) and->Is connected to the collector of (1), the negative electrode is connected to->Is connected with the emitter of the (C);
in each phase of upper bridge arm, the first port of the high-frequency sub-module is connected with the first port of the first low-frequency sub-module, the first port and the second port of the middle low-frequency sub-module are respectively connected with the upper low-frequency sub-module and the lower low-frequency sub-module, and the second port of the last low-frequency sub-module is connected with the bridge arm inductorConnecting; the lower bridge arm of each phase is symmetrical to the upper bridge arm structure of the same phase, and the output port of the hybrid multi-level converter is formed by leading out the upper bridge arm and the lower bridge arm of each phase.
As another aspect of the invention, a regulation and control method of a multi-index comprehensive optimized hybrid multi-level converter is provided, the low-frequency submodule adopts the nearest level to approach and modulate and output power frequency step waves, and the high-frequency submodule adopts the unipolar pulse width modulation and outputs high-frequency shaping waves.
Further, when the low-frequency submodule adopts the nearest level to approximate and modulate and output power frequency step waves:
the output voltage of the hybrid multi-level converter is defined firstThe method comprises the following steps:
(1)
wherein ,three phases representing a hybrid multilevel converter; />Is the output voltage amplitude; />Is angular frequency;
then according to kirchhoff voltage law, determining the modulation wave of the upper bridge arm or the lower bridge armExpressed as:
(2)
wherein ,the high-voltage direct-current side voltage is the high-voltage direct-current side voltage of the hybrid multi-level converter;
then obtaining the quantity of the upper bridge arm or the lower bridge arm low-frequency submodule needed to be input from the (2)The method comprises the following steps:
(3)
wherein ,for the DC side capacitor voltage of the low frequency submodule, < >>To take downA whole function;
finally, determining the ladder wave voltage output by all low-frequency submodules of the upper bridge arm or the lower bridge arm togetherThe method comprises the following steps:
(4)。
still further, when the high-frequency submodule adopts unipolar pulse width modulation to output high-frequency shaping waves:
firstly, determining a modulation wave of an upper bridge arm or a lower bridge arm high-frequency submoduleWhich is a modulated wave of the same bridge arm +.>And step wave voltage->Is the following formula:
(5)
then based on the obtained modulated waveDetermining a high-frequency shaping wave output by the high-frequency submodule, namely:
1) If it isOne half-bridge converter in the high-frequency sub-module bypasses and the other half-bridge converter outputs 0 to +.>Is a high-frequency shaping wave of (2);
2) If it isA half-bridge converter in the high frequency sub-module is normally connectedGo out->The other half-bridge converter outputs 0 to +.>Is equivalent to the high-frequency shaping wave of (2), the high-frequency submodule outputs +.>To->Is a high-frequency shaping wave of (2);
3) If it isOne half-bridge converter in the high-frequency sub-module bypasses and the other half-bridge converter outputs +.>High frequency shaping wave to 0;
4) If it isThen a half-bridge converter in the high-frequency sub-module is normally on output +.>The other half-bridge converter outputs +.>High-frequency shaping wave to 0, high-frequency submodule equivalent output +.>To->Is a high frequency shaping wave of (a).
Further, the high frequency sub-module includes two modes of operation whenDisconnect, & gt>When the high-frequency submodule is turned on, the high-frequency submodule outputs a positive-polarity high-frequency shaping wave, which is defined as a mode +.>The method comprises the steps of carrying out a first treatment on the surface of the When->Conduction and/or->When the switch is turned off, the high-frequency submodule outputs a high-frequency shaping wave with negative polarity, which is defined as a mode +.>The method comprises the steps of carrying out a first treatment on the surface of the Use->Represents the high frequency shaping voltage of the high frequency sub-module output, < +.>Representing the bridge arm current of the high frequency sub-module, if the current flows in from the first port and out from the second port of the high frequency sub-module, +.>If the current flows in from the second port and out from the first port of the high-frequency sub-module, +.>The method comprises the steps of carrying out a first treatment on the surface of the Mode of the high-frequency submodule +.>Mode->The device comprises the following 8 working states:
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>、/>Charging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Charging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Charging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>、/>A bypass;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>、/>Discharging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Discharging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>Bypass, & lt>Discharging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>、/>A bypass;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>、/>Discharging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Discharging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Discharging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>、/>A bypass;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>、/>Charging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Charging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>Bypass, & lt>Charging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>、/>And (5) bypassing.
Preferably, the voltage equalizing method of the high-frequency sub-module is as follows:
1) Calculating the quantity of low-frequency submodules required to be input in the same bridge arm as the high-frequency submodules by the aid of the step (3)；
2) Calculating the current time and the last timeComparing, if the change does not occur, recalculating; if the frequency is changed, the overall voltage equalizing and internal voltage equalizing judging modes of the high-frequency submodule are sequentially entered;
3) Overall pressure equalizing:
if it isAnd->The high frequency sub-module is then operated in mode +.>；
If it isAnd->Judging-> and />Relation of (1)/(2 ]>The high frequency sub-module is then operated in mode +.>If->The high frequency sub-module is then operated in mode +.>；
If it isAnd->The high frequency sub-module is then operated in mode +.>；
If it isAnd->Judging-> and />Relation of (1)/(2 ]>The high frequency sub-module is then operated in mode +.>The method comprises the steps of carrying out a first treatment on the surface of the If->The high frequency sub-module is then operated in mode +.>；
4) Internal pressure equalizing:
if it isIs->To->High-frequency shaping wave of>The high-frequency submodule is charged as a whole and />The medium voltage is normally on, and the high voltage is used as high-frequency shaping wave;
if it isIs->To->High-frequency shaping wave of>The high-frequency submodule is in a discharge state as a whole, then and />The medium voltage is normally on, and the low voltage is used for shaping the wave at high frequency;
if it isIs 0 to->High-frequency shaping wave of>The high-frequency submodule is charged as a whole, and is +.> and />Bypass with large medium voltage and high frequency shaping wave with small voltage;
if it isIs 0 to->High-frequency shaping wave of>The high-frequency submodule is in a discharge state as a whole, then and />Bypass with small medium voltage and high voltage is used for shaping wave with high frequency;
if it isIs->To->High-frequency shaping wave of>The high-frequency submodule is in a discharge state as a whole, then and />The medium voltage is normally on, and the low voltage is used for shaping the wave at high frequency;
if it isIs->To->High-frequency shaping wave of>The high-frequency submodule is charged as a whole, and is +.> and />The medium voltage is normally on, and the high voltage is used as high-frequency shaping wave;
if it isIs 0 to->High-frequency shaping wave of>The high-frequency submodule is in a discharge state as a whole, and is +.> and />Bypass with small medium voltage and high voltage is used for shaping wave with high frequency;
if it isIs 0 to->High-frequency shaping wave of>The high-frequency submodule is charged as a whole, and is +.> and />Bypass with large medium voltage and high frequency shaping wave with small voltage;
wherein ：representing the sum of the numbers of high-frequency sub-modules and low-frequency sub-modules of the same bridge arm, < ->The total number of the low-frequency sub-modules of the same bridge arm is obtained; />Representing the sum of the capacitor voltages at the DC side of the high-frequency submodule; />A reference value representing the sum of the capacitor voltages at the DC side of the high frequency submodule.
Preferably, the low-frequency sub-modules all adopt a sequencing voltage equalizing method to realize voltage stabilization.
Compared with the existing MMC topology, the mixed multi-level converter and the regulation and control method thereof can reduce the overall cost of the device, ensure the output waveform quality and efficiency of the device, and realize the comprehensive optimization of multiple indexes. Specifically, the mixed multi-level converter provided by the invention improves the high-frequency submodule into a structure formed by the cross connection of the bridge arms of the two half-bridge converters after reversing on the basis of the existing MMC topology, so that only one high-frequency submodule is required to be arranged on each phase of upper bridge arm and lower bridge arm, namely the whole device can be matched with each phase of upper bridge arm and lower bridge arm only by 24 SiC MOSFET devicesThe individual low-frequency submodules realize an output +.>A level. In addition, the regulation and control method of the hybrid multilevel converter can fix the high-frequency switching action to the SiC MOSFET device, the Si IGBT device works in a low-frequency state, and the advantages of low switching loss of the SiC device and low on-state loss of the Si device are fully exerted.
Drawings
FIG. 1 is a diagram of a conventional hybrid MMC topology (wherein (a) is the output)Level hybrid MMC topology structure diagram; (b) For outputting->Level hybrid MMC topology structure diagram);
FIG. 2 is a topological structure diagram of a hybrid multilevel converter with multi-index comprehensive optimization according to the invention;
FIG. 3 is a schematic view of the present inventionA modulation principle waveform diagram of the phase upper bridge arm low-frequency submodule;
FIG. 4 is a schematic view of the present inventionA modulation principle waveform diagram of the upper bridge arm high-frequency submodule;
FIG. 5 shows a high frequency sub-module mode according to the present invention8 working state diagrams of (a);
FIG. 6 shows a high frequency sub-module mode according to the present invention8 working state diagrams of (a);
FIG. 7 is a flow chart of the equalizing voltage of the high frequency submodule in the regulating method provided by the invention;
FIG. 8 is a waveform diagram of HMMC a phase output voltage in an embodiment of the invention;
fig. 9 is a waveform diagram of a high-frequency shaping voltage output by the HMMC a phase upper bridge arm high-frequency submodule in the embodiment of the present invention;
fig. 10 is a waveform diagram of a low-frequency sub-module output step wave voltage of an HMMC a phase upper bridge arm in the embodiment of the invention;
fig. 11 is a waveform diagram of HMMC capacitor voltage in an embodiment of the present invention (a) is a waveform diagram of capacitor voltage on a dc side of 7 low frequency sub-modules of an a-phase upper bridge arm, and (b) is a waveform diagram of capacitor voltage on a dc side of a high frequency sub-module of an a-phase upper bridge arm.
Detailed Description
The invention will be further described with reference to examples and drawings, to which reference is made, but which are not intended to limit the scope of the invention.
1. Hybrid MMC (HMMC) Hybrid multilevel converter with multi-index comprehensive optimization
As shown in FIG. 2, the HMMC provided by the invention has a three-phase structure, each phase is provided with an upper bridge arm and a lower bridge arm connected below the upper bridge arm, and the upper bridge arm and the lower bridge arm respectively comprise a High-frequency sub-module (HSM) and a bridge arm inductorAnd cascade->Low-frequency sub-modules (LSMs).
The high frequency sub-module includes four SiC MOSFET devices、/>、/>、/>And two Si IGBT devices->、/>And two capacitances->、/>The method comprises the steps of carrying out a first treatment on the surface of the By->、/>To form a half-bridge converter, ">、/>Forming another half-bridge converter; />Emitter and +.>A first port leading out from the connection point to form a high frequency sub-module; />Emitter and +.>A second port leading out from the connection point to form a high-frequency sub-module; />Positive electrode of (2) and->Is connected with the collector of the cathode and the anodeIs connected with the emitter of the (C); />Positive electrode of (2) and->Is connected to the collector of (1), the negative electrode is connected to->Is connected with the emitter of the (C); />Collector and->Is connected with the positive electrode of->Emitter and->Is connected with the negative electrode of the battery; />Collector and->Is connected with the positive electrode of->Emitter and emitter of (2)Is connected to the negative electrode of the battery.
The low frequency sub-module includes two Si IGBT devices、/>And a capacitor->The method comprises the steps of carrying out a first treatment on the surface of the By->、/>Forming a half-bridge converter; />Emitter and->A first port which is a low frequency sub-module is led out from the connection point; from->The emitter of (a) is led out to serve as a second port of the low-frequency sub-module; capacitance->Positive electrode of (2) and->Is connected to the collector of (1), the negative electrode is connected to->Is connected to the emitter of (c).
In each phase upper bridge arm, a first port of a high-frequency sub-module is connected with a first port of a first low-frequency sub-module, a first port and a second port of a low-frequency sub-module positioned in the middle are respectively connected with a low-frequency sub-module above and a low-frequency sub-module below, and a second port of the last low-frequency sub-module is connected with a bridge arm inductorConnecting; the lower bridge arm of each phase is symmetrical to the upper bridge arm structure of the same phase, and the output ports of the mixed multi-level converter are led out from between the upper bridge arm and the lower bridge arm of each phase, as shown in figure 2 +.>、/>、/>Output voltages of HMMC a phase, b phase and c phase respectively, HMMC high-voltage direct-current side voltage value +.>。
2. Regulating and controlling method for multi-index comprehensive optimized hybrid multi-level converter
The invention relates to an improvement of a regulating and controlling method of a multi-index comprehensive optimized hybrid multi-level converter, which mainly comprises two aspects of a regulating strategy and a voltage equalizing method, and other aspects refer to the traditional regulating and controlling technology, wherein the contents of the two aspects are as follows.
2.1 modulation strategy
The modulation strategy of the HMMC is divided into a low-frequency submodule modulation part and a high-frequency submodule modulation part. The low-frequency submodule adopts the nearest level to approximate and modulate and output the power frequency step wave, and the high-frequency submodule adopts the unipolar pulse width modulation and outputs the high-frequency shaping wave.
1. Low frequency sub-module modulation principle
The output voltage of the hybrid multi-level converter is defined firstThe method comprises the following steps:
(1)
wherein ,three phases representing a hybrid multilevel converter; />Is the output voltage amplitude; />Is the angular frequency.
Then according to kirchhoff's voltage law, determining the upper bridge arm orModulated wave of lower bridge armExpressed as:
(2)
wherein ,is the high-voltage direct-current side voltage of the hybrid multi-level converter.
Then obtaining the quantity of the upper bridge arm or the lower bridge arm low-frequency submodule needed to be input from the (2)The method comprises the following steps:
(3)
wherein ,for the DC side capacitor voltage of the low frequency submodule, < >>Is a round down function.
Finally, determining the ladder wave voltage output by all low-frequency submodules of the upper bridge arm or the lower bridge arm togetherThe method comprises the following steps:
(4)
taking an a-phase upper bridge arm as an example, a modulation principle waveform diagram of the low-frequency sub-module is shown in fig. 3, and modulation principle waveform diagrams of the low-frequency sub-modules of other bridge arms are shown in fig. 3.
2. High frequency submodule modulation principle
Firstly, determining a modulation wave of an upper bridge arm or a lower bridge arm high-frequency submoduleWhich is a modulated wave of the same bridge arm +.>And step wave voltage->Is the following formula:
(5)
then based on the obtained modulated waveDetermining a high-frequency shaping wave output by the high-frequency submodule, namely:
1) If it isOne half-bridge converter in the high-frequency sub-module bypasses and the other half-bridge converter outputs 0 to +.>Is a high-frequency shaping wave of (2);
2) If it isThen a half-bridge converter in the high-frequency sub-module is normally on output +.>The other half-bridge converter outputs 0 to +.>Is equivalent to the high-frequency shaping wave of (2), the high-frequency submodule outputs +.>To->Is a high-frequency shaping wave of (2);
3) If it isOne half-bridge converter in the high-frequency sub-module bypasses and the other half-bridge converter outputs +.>High frequency shaping wave to 0;
4) If it isThen a half-bridge converter in the high-frequency sub-module is normally on output +.>The other half-bridge converter outputs +.>High-frequency shaping wave to 0, high-frequency submodule equivalent output +.>To->Is a high frequency shaping wave of (a).
To be used forFor example, the modulation principle waveform diagram of the high-frequency sub-module is shown in fig. 4, and the modulation principle waveform diagrams of the high-frequency sub-modules of other bridge arms are shown in fig. 4.
The high frequency sub-module can output、/>、0、/>、/>Five levels, whose switching patterns are shown in Table 1, in which a "1" represents device closure"0" represents device off.
The high frequency sub-module includes two modes of operation whenDisconnect, & gt>When the high-frequency submodule is turned on, the high-frequency submodule outputs a positive-polarity high-frequency shaping wave, which is defined as a mode +.>The method comprises the steps of carrying out a first treatment on the surface of the When->Conduction and/or->When the switch is turned off, the high-frequency submodule outputs a high-frequency shaping wave with negative polarity, which is defined as a mode +.>The method comprises the steps of carrying out a first treatment on the surface of the Use->Represents the high frequency shaping voltage of the high frequency sub-module output, < +.>Representing the bridge arm current of the high frequency sub-module, if the current flows in from the first port and out from the second port of the high frequency sub-module, +.>If the current flows in from the second port and out from the first port of the high-frequency sub-module, +.>The method comprises the steps of carrying out a first treatment on the surface of the Mode of high-frequency submodule->Mode->The capacitor comprises 8 working states, 8 working states corresponding to two working modes are shown in fig. 5 and 6, and the operation states of the capacitor corresponding to the high-frequency sub-module in each working mode are specifically analyzed as follows:
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>、/>Charging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Charging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Charging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>、/>A bypass;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>、/>Discharging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>Bypass, & lt>Discharging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>Bypass, & lt>Discharging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>、/>A bypass;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>、/>Discharging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Discharging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Discharging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>、/>A bypass;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>、/>Charging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Charging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>Bypass, & lt>Charging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>、/>And (5) bypassing.
In summary, by controlling the high frequency sub-module to flexibly switch between 16 operating states, two capacitors in the high frequency sub-module can be changed、/>To realize the stable capacitor voltage.
2.2 Voltage sharing strategy
For the low-frequency submodule, voltage stabilization can be realized by adopting a traditional ordering voltage-equalizing algorithm, and the description is omitted here. The high-frequency sub-module voltage equalizing mainly comprises an integral voltage equalizing part and an internal voltage equalizing part, and referring to fig. 7, the voltage equalizing method of the high-frequency sub-module is specifically as follows:
1) Calculating the quantity of low-frequency submodules required to be input in the same bridge arm as the high-frequency submodules by the aid of the step (3)；
2) Calculating the current time and the last timeComparing, if the change does not occur, recalculating; if the frequency is changed, the frequency is sequentially subjected to overall voltage equalizing and internal voltage equalizing judgment of the high-frequency submoduleA cut-off mode;
3) Overall pressure equalizing:
if it isAnd->The high frequency sub-module is then operated in mode +.>；
If it isAnd->Judging-> and />Relation of (1)/(2 ]>The high frequency sub-module is then operated in mode +.>If->The high frequency sub-module is then operated in mode +.>；
If it isAnd->The high frequency sub-module is then operated in mode +.>；
If it isAnd->Judging-> and />Relation of (1)/(2 ]>The high frequency sub-module is then operated in mode +.>The method comprises the steps of carrying out a first treatment on the surface of the If->The high frequency sub-module is then operated in mode +.>；
4) Internal pressure equalizing:
if it isIs->To->High-frequency shaping wave of>The high-frequency submodule is charged as a whole and />Medium voltage small normally-on high-frequency shaping wave；
If it isIs->To->High-frequency shaping wave of>The high-frequency submodule is in a discharge state as a whole, then and />The medium voltage is normally on, and the low voltage is used for shaping the wave at high frequency;
if it isIs 0 to->High-frequency shaping wave of>The high-frequency submodule is charged as a whole, and is +.> and />Bypass with large medium voltage and high frequency shaping wave with small voltage;
if it isIs 0 to->High-frequency shaping wave of>The high-frequency submodule is in a discharge state as a whole, then and />Bypass with small medium voltage and high voltage is used for shaping wave with high frequency;
if it isIs->To->High-frequency shaping wave of>The high-frequency submodule is in a discharge state as a whole, then and />The medium voltage is normally on, and the low voltage is used for shaping the wave at high frequency;
if it isIs->To->High-frequency shaping wave of>The high-frequency submodule is charged as a whole, and is +.> and />The medium voltage is normally on, and the high voltage is used as high-frequency shaping wave; />
If it isIs 0 to->High-frequency shaping wave of>The high-frequency submodule is in a discharge state as a whole, and is +.> and />Bypass with small medium voltage and high voltage is used for shaping wave with high frequency;
if it isIs 0 to->High-frequency shaping wave of>The high-frequency submodule is charged as a whole, and is +.> and />Bypass with large medium voltage and high frequency shaping wave with small voltage;
wherein ：representing the sum of the numbers of high-frequency sub-modules and low-frequency sub-modules of the same bridge arm, < ->I.e. the total number of low-frequency sub-modules of the same bridge arm；/>Representing the sum of the capacitor voltages at the DC side of the high-frequency submodule; />A reference value representing the sum of the capacitor voltages at the DC side of the high frequency submodule.
3. Simulation analysis
In order to better prove the effectiveness of the topological structure and the regulation method provided by the invention, the following verification is carried out by combining a simulation example. According to the HMMC topology shown in FIG. 2, a simulation platform is built in MATLAB/Simulink, and simulation parameters are shown in Table 2.
FIG. 8 is a phase a output voltage of HMMCWaveform of the output voltage +>The output result is similar to the output result after the traditional carrier phase shift modulation, is a high-frequency step wave, and the output level is 17 level.
As shown in fig. 9 and 10, the a-phase upper arm high-frequency sub-module outputs a high-frequency shaped wave with a voltage of 5 level, and the a-phase upper arm low-frequency sub-module outputs a power frequency step wave with a voltage of 2 level. Therefore, the modulation strategy provided by the invention can control the SiC MOSFET device to work in a high-frequency state and the Si IGBT device to work in a low-frequency state on the premise of ensuring the waveform quality of the HMMC output voltage, so that the switching loss of the device is reduced.
FIG. 11 shows a DC side capacitor voltage waveform of 7 low frequency sub-modules and 1 high frequency sub-module of an a-phase upper bridge arm; fig. 11 (a) shows waveforms of capacitor voltage on dc side of 7 low frequency submodules of the a-phase upper bridge arm, wherein,、/>……/>respectively representing the direct-current side capacitor voltages of 7 low-frequency submodules; FIG. 11 (b) shows a waveform of a DC side capacitor voltage of the high-frequency sub-module of the upper arm of the a-phase, wherein +.>Represents the direct-current side capacitance of the high-frequency submodule>Is a voltage waveform of (a); the fluctuation range of all the capacitor voltages can be seen to be less than 5%, the capacitor voltage of the high-frequency submodule is half of the capacitor voltage of the low-frequency submodule, and the provided voltage-equalizing strategy well achieves the voltage-equalizing purpose.
The foregoing embodiments are preferred embodiments of the present invention, and in addition, the present invention may be implemented in other ways, and any obvious substitution is within the scope of the present invention without departing from the concept of the present invention.
In order to facilitate understanding of the improvements of the present invention over the prior art, some of the figures and descriptions of the present invention have been simplified, and some other elements have been omitted from this document for clarity, as will be appreciated by those of ordinary skill in the art.

Claims (7)

1. The utility model provides a mixed type multilevel converter of multi-index comprehensive optimization, is three-phase structure, has an upper bridge arm and the lower bridge arm of connecting the upper bridge arm below on each phase, upper bridge arm and lower bridge arm all include high frequency submodule, bridge arm inductance and a plurality of low frequency submodules of cascade, its characterized in that:
the high frequency sub-module comprises four SiC MOSFET devices、/>、/>、/>And two Si IGBT devices->、/>And two capacitances->、/>The method comprises the steps of carrying out a first treatment on the surface of the By->、/>To form a half-bridge converter, ">、/>Forming another half-bridge converter; />Emitter and +.>A first port leading out from the connection point to form a high frequency sub-module; />Emitter and +.>A second port leading out from the connection point to form a high-frequency sub-module; />Positive electrode of (2) and->Is connected with the collector of the cathode and the anodeIs connected with the emitter of the (C); />Positive electrode of (2) and->Is connected to the collector of (1), the negative electrode is connected to->Is connected with the emitter of the (C); />Collector and->Is connected with the positive electrode of->Emitter and->Is connected with the negative electrode of the battery; />Collector and->Is connected with the positive electrode of->Emitter and emitter of (2)Is connected with the negative electrode of the battery;
the low frequency sub-module comprises two Si IGBT devices、/>And a capacitor->The method comprises the steps of carrying out a first treatment on the surface of the By->、/>Forming a half-bridge converter; />Emitter and->A first port which is a low frequency sub-module is led out from the connection point; from the slaveThe emitter of (a) is led out to serve as a second port of the low-frequency sub-module; capacitance->Positive electrode of (2) and->Is connected with the collector of the cathode and the anodeIs connected with the emitter of the (C);
in each phase upper bridge arm, a first port of the high-frequency sub-module is connected with a first port of a first low-frequency sub-module, a first port and a second port of the middle low-frequency sub-module are respectively connected with a low-frequency sub-module above the high-frequency sub-module and a low-frequency sub-module below the high-frequency sub-module, and a second port of the last low-frequency sub-module is connected with a bridge arm inductor; the lower bridge arm of each phase is symmetrical to the upper bridge arm structure of the same phase, and the output port of the hybrid multi-level converter is formed by leading out the upper bridge arm and the lower bridge arm of each phase.
2. The method for regulating and controlling the multi-index comprehensive optimized hybrid multi-level converter according to claim 1, wherein the method comprises the following steps: the low-frequency submodule adopts the nearest level to approximate and modulate and output the power frequency step wave, and the high-frequency submodule adopts the unipolar pulse width modulation and outputs the high-frequency shaping wave.
3. The method for regulating and controlling the multi-index comprehensive optimized hybrid multi-level converter according to claim 2, wherein the method comprises the following steps: when the low-frequency submodule adopts the nearest level to approximate and modulate and output power frequency step waves:
the output voltage of the hybrid multi-level converter is defined firstThe method comprises the following steps:
(1)
wherein ,three phases representing a hybrid multilevel converter; />To output voltage amplitudeA value; />Is angular frequency;
then according to kirchhoff voltage law, determining the modulation wave of the upper bridge arm or the lower bridge armExpressed as:
(2)
wherein ,the high-voltage direct-current side voltage is the high-voltage direct-current side voltage of the hybrid multi-level converter;
then obtaining the quantity of the upper bridge arm or the lower bridge arm low-frequency submodule needed to be input from the (2)The method comprises the following steps:
(3)
wherein ,for the DC side capacitor voltage of the low frequency submodule, < >>Is a downward rounding function;
finally, determining the ladder wave voltage output by all low-frequency submodules of the upper bridge arm or the lower bridge arm togetherThe method comprises the following steps:
(4)。
4. the method for regulating and controlling a multi-index comprehensive optimized hybrid multi-level converter according to claim 3, wherein the method comprises the following steps: when the high-frequency submodule adopts unipolar pulse width modulation to output high-frequency shaping waves:
firstly, determining a modulation wave of an upper bridge arm or a lower bridge arm high-frequency submoduleWhich is a modulated wave of the same bridge arm +.>And step wave voltage->Is the following formula:
(5)
then based on the obtained modulated waveDetermining a high-frequency shaping wave output by the high-frequency submodule, namely:
1) If it isOne half-bridge converter in the high-frequency sub-module bypasses and the other half-bridge converter outputs 0 to +.>Is a high-frequency shaping wave of (2);
2) If it isThen a half-bridge converter in the high-frequency sub-module is normally on output +.>The other half-bridge converter outputs 0 to +.>Is equivalent to the high-frequency shaping wave of (2), the high-frequency submodule outputs +.>To->Is a high-frequency shaping wave of (2);
3) If it isOne half-bridge converter in the high frequency sub-module bypasses and the other half-bridge converter outputsHigh frequency shaping wave to 0;
4) If it isThen a half-bridge converter in the high-frequency sub-module is normally on output +.>The other half-bridge converter outputs +.>High-frequency shaping wave to 0, high-frequency submodule equivalent output +.>To->Is a high frequency shaping wave of (a).
5. The method for regulating and controlling the multi-index comprehensive optimized hybrid multi-level converter according to claim 4, wherein the method comprises the following steps: the high-frequency submodule comprises two submodulesMode of operation whenDisconnect, & gt>When the high-frequency submodule is turned on, the high-frequency submodule outputs a positive-polarity high-frequency shaping wave, which is defined as a mode +.>The method comprises the steps of carrying out a first treatment on the surface of the When->Conduction and/or->When the switch is turned off, the high-frequency submodule outputs a high-frequency shaping wave with negative polarity, which is defined as a mode +.>The method comprises the steps of carrying out a first treatment on the surface of the Use->Represents the high frequency shaping voltage of the high frequency sub-module output, < +.>Representing the bridge arm current of the high frequency sub-module, if the current flows in from the first port and out from the second port of the high frequency sub-module, +.>If the current flows in from the second port and out from the first port of the high-frequency sub-module, +.>The method comprises the steps of carrying out a first treatment on the surface of the Mode of the high-frequency submodule +.>Mode->The device comprises the following 8 working states:
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>、/>Charging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Charging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Charging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>、/>A bypass;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>、/>Discharging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>Bypass, & lt>Discharging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>Bypass, & lt>Discharging;
: bridge arm current->；/>Open and/or close>Closing; />、/>Close, close (I)>、/>Opening; />；/>、/>A bypass;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>、/>Discharging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Discharging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Discharging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>、/>A bypass;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>、/>Charging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Charging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>A bypass path,Charging;
: bridge arm current->；/>Close, close (I)>Opening; />、/>Close, close (I)>、/>Opening; />；/>、/>And (5) bypassing.
6. The method for regulating and controlling the multi-index comprehensive optimized hybrid multi-level converter according to claim 5, wherein the method comprises the following steps: the voltage equalizing method of the high-frequency submodule comprises the following steps:
1) Calculating the quantity of low-frequency submodules required to be input in the same bridge arm as the high-frequency submodules by the aid of the step (3)；
2) Calculating the current time and the last timeComparing, if the change does not occur, recalculating; if the frequency is changed, the overall voltage equalizing and internal voltage equalizing judging modes of the high-frequency submodule are sequentially entered;
3) Overall pressure equalizing:
if it isAnd->The high frequency sub-module is then operated in mode +.>；
If it isAnd->Judging-> and />Relation of (1)/(2 ]>The high frequency sub-module is then operated in mode +.>If->The high frequency sub-module is then operated in mode +.>；
If it isAnd->High-frequency sub-dieThe block works in mode->；
If it isAnd->Judging-> and />Relation of (1)/(2 ]>The high frequency sub-module is then operated in mode +.>The method comprises the steps of carrying out a first treatment on the surface of the If->The high frequency sub-module is then operated in mode +.>；
4) Internal pressure equalizing:
if it isIs->To->High-frequency shaping wave of>The high-frequency submodule is charged as a whole, and is +.>Andthe medium voltage is normally on, and the high voltage is used as high-frequency shaping wave;
if it isIs->To->High-frequency shaping wave of>The high-frequency submodule is in a discharge state as a whole, and is +.>Andthe medium voltage is normally on, and the low voltage is used for shaping the wave at high frequency;
if it isIs 0 to->High-frequency shaping wave of>The high-frequency submodule is charged as a whole, and is +.>Andbypass with large medium voltage and high frequency shaping wave with small voltage;
if it isIs 0 to->High-frequency shaping wave of>The high-frequency submodule is in a discharge state as a whole, and is +.>Andbypass with small medium voltage and high voltage is used for shaping wave with high frequency;
if it isIs->To->High-frequency shaping wave of>The high-frequency submodule is in a discharge state as a whole, and is +.> and />The medium voltage is normally on, and the low voltage is used for shaping the wave at high frequency;
if it isIs->To->High-frequency shaping wave of>The high-frequency submodule is charged as a whole and />The medium voltage is normally on, and the high voltage is used as high-frequency shaping wave;
if it isIs 0 to->High-frequency shaping wave of>The high-frequency submodule is in a discharge state as a whole, and is +.>Andbypass with small medium voltage and high voltage is used for shaping wave with high frequency;
if it isIs 0 to->High-frequency shaping wave of>The high-frequency submodule is charged as a whole, and is +.>Andbypass with large medium voltage and high frequency shaping wave with small voltage;
wherein ：representing the sum of the numbers of high-frequency sub-modules and low-frequency sub-modules of the same bridge arm, < ->The total number of the low-frequency sub-modules of the same bridge arm is obtained; />Representing the sum of the capacitor voltages at the DC side of the high-frequency submodule; />A reference value representing the sum of the capacitor voltages at the DC side of the high frequency submodule.
7. The method for regulating and controlling the multi-index comprehensive optimized hybrid multi-level converter according to claim 6, wherein the method comprises the following steps: and the low-frequency submodule realizes voltage stabilization by adopting a sequencing voltage equalizing method.
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