CN111064378B - Five-level hybrid neutral point clamped converter - Google Patents

Five-level hybrid neutral point clamped converter Download PDF

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Publication number
CN111064378B
CN111064378B CN202010024235.XA CN202010024235A CN111064378B CN 111064378 B CN111064378 B CN 111064378B CN 202010024235 A CN202010024235 A CN 202010024235A CN 111064378 B CN111064378 B CN 111064378B
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current
switching tube
converter
diode
tube
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CN111064378A (en
Inventor
孙丽敬
吴鸣
宋振浩
吕志鹏
刘国宇
李彬彬
蔺圣杰
于辉
季宇
刘晓娟
原熙博
魏琛
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China Online Shanghai Energy Internet Research Institute Co ltd
State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
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China Online Shanghai Energy Internet Research Institute Co ltd
State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
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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
    • H02M7/487—Neutral point clamped inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • 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

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The invention provides a five-level hybrid midpoint clamping converter, which comprises three bridge arm units connected in parallel between an anode direct-current bus and a cathode direct-current bus, wherein each bridge arm unit comprises eight switching tubes, three flying capacitors and six clamping diodes, and is small in size and high in reliability; the invention has the advantages of fewer required devices, simple topological structure and easy control; the MOSFET is used as a switching tube, so that the switching loss is small, the switching frequency is high, and the converter has high power density and high working efficiency; and the voltage born by each device is equal, namely one fourth of the voltage of the direct-current side bus, and the high-voltage device is not needed, so that the high-voltage device can be applied to medium-high voltage large-capacity industrial occasions.

Description

Five-level hybrid neutral point clamped converter
Technical Field
The invention relates to the technical field of power electronics, in particular to a five-level hybrid neutral point clamped converter.
Background
With the rapid development of modern socioeconomic, energy and environmental issues have become urgent issues facing mankind today. In 2017, BP world energy statistics yearbook shows that fossil energy such as petroleum, coal, natural gas and the like are still main sources in world primary energy consumption. However, with the gradual exhaustion of fossil energy and the increasing serious problem of environmental pollution in the process of consumption, the health development of human society has been significantly influenced. Renewable energy is an important option expected to replace traditional fossil energy, improve energy structure and realize sustainable development. In the process of new energy conversion and electric energy utilization, technical support of the power electronic converter cannot be removed.
The important equipment of the new energy of the power electronic converter accessed to the power grid is widely applied to various industrial occasions due to the fact that the important equipment has higher voltage output capacity, lower harmonic characteristics, voltage stress and electromagnetic interference, and becomes a core component and a key technology in a modern energy system. The multi-level converter has the obvious advantages in the aspects of switching frequency, output voltage grade, power grade, voltage change rate, filter volume and the like, and is widely concerned and researched in the fields of medium-high voltage and high power, such as a high-capacity alternating-current transmission system, electric energy quality control, flexible power transmission, new energy power generation and the like. Therefore, the multilevel converter has a wide application prospect and becomes one of the research hotspots in the field of electrical engineering.
However, the multi-level converter has the problems of multiple switching devices, complex topological structure, difficult control and the like, so that the popularization and the application of the multi-level converter are limited. Each bridge arm of the neutral point clamped converter in the prior art needs 18 clamping diodes, and the voltage stress of all the switching devices is equal, so that the neutral point clamped converter is suitable for medium-high voltage high-power occasions.
Disclosure of Invention
In order to overcome the defects of large volume and low reliability in the prior art, the invention provides a five-level hybrid midpoint clamping converter, which comprises three bridge arm units connected in parallel between an anode direct-current bus and a cathode direct-current bus, wherein each bridge arm unit comprises eight switching tubes, three flying capacitors and six clamping diodes, and the eight switching tubes are sequentially connected in series in the forward direction to form a switching tube branch; the three flying capacitors are sequentially connected in series in the forward direction to form a capacitor branch circuit, and the capacitor branch circuit is connected with the switch tube branch circuit; the three clamping diodes are sequentially connected in series in the forward direction to form a first diode branch, the first diode branch is connected with the switch tube branch, the other three clamping diodes are sequentially connected in series in the forward direction to form a second diode branch, and the second diode branches are all connected with the switch tube branch.
In order to achieve the purpose of the invention, the invention adopts the following technical scheme:
the invention provides a five-level hybrid neutral point clamped converter which comprises three bridge arm units connected in parallel between a positive direct current bus and a negative direct current bus, wherein each bridge arm unit comprises eight switching tubes, three flying capacitors and six clamping diodes;
the eight switching tubes are sequentially connected in series in the forward direction to form a switching tube branch; the three flying capacitors are sequentially connected in series in the forward direction to form a capacitor branch circuit, and the capacitor branch circuit is connected with the switch tube branch circuit; the three clamping diodes are sequentially connected in series in a forward direction to form a first diode branch, the first diode branch is connected with the switch tube branch, the other three clamping diodes are sequentially connected in series in the forward direction to form a second diode branch, and the second diode branches are all connected with the switch tube branch.
The drain electrode of the first switching tube S1 is connected with the positive electrode direct current bus, and the source electrode of the eighth switching tube S8 is connected with the negative electrode direct current bus;
the anode of the first flying capacitor C1 is connected with the midpoint between the source of the first switching tube S1 and the drain of the second switching tube S2, and the cathode of the third flying capacitor C3 is connected with the midpoint between the source of the seventh switching tube S7 and the drain of the eighth switching tube S8;
the cathode of a first clamping diode D1 in the first diode branch is connected with the midpoint of the source of a second switching tube S2 and the drain of a third switching tube S3, and the anode of a third clamping diode D3 in the first diode branch is connected with the midpoint of the source of a fifth switching tube S5 and the drain of a sixth switching tube S6; the cathode of the first clamping diode D4 in the second diode branch is connected with the midpoint of the source of the third switching tube S3 and the drain of the fourth switching tube S4, and the anode of the third clamping diode D6 in the second diode branch is connected with the midpoint of the source of the sixth switching tube S6 and the drain of the seventh switching tube S7;
the midpoint of the first and second flying capacitors C1 and C2 is connected to the midpoint of the first and second clamping diodes D1 and D2 in the first diode branch, and the midpoint of the second and third flying capacitors C2 and C3 is connected to the midpoint of the second and third clamping diodes D5 and D6 in the second diode branch.
Each bridge arm unit further comprises eight body diodes, and the body diodes are connected with the switching tubes in an anti-parallel mode.
The switch tube is MOSFET or IGBT.
8. An output end connected with a load is arranged between the source electrode of the fourth switching tube S4 and the drain electrode of the fifth switching tube S5.
The converter comprises the following operating modes:
the first mode of operation: the first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 are all turned on, the other switch tubes are all turned off, the output level number of the converter is 4, and the output voltage of the converter is direct-current bus voltage;
the second working mode is as follows: the first switch tube S1, the third switch tube S3, the fourth switch tube S4 and the fifth switch tube S5 are all turned on, the other switch tubes are all turned off, the output level number of the converter is 3, and the output voltage of the converter is 75% of the direct-current bus voltage;
the third mode of operation: the second switch tube S2, the third switch tube S3, the fourth switch tube S4 and the eighth switch tube S8 are all turned on, the rest switch tubes are all turned off, the output level number of the converter is 3, and the output voltage of the converter is 75% of the voltage of the direct-current bus;
a fourth mode of operation: the first switch tube S1, the fourth switch tube S4, the fifth switch tube S5 and the sixth switch tube S6 are all turned on, the rest switch tubes are all turned off, the output level number of the converter is 2, and the output voltage of the converter is 50% of the direct-current bus voltage;
the fifth working mode: the third switch tube S3, the fourth switch tube S4, the fifth switch tube S5 and the eighth switch tube S8 are all turned on, the rest switch tubes are all turned off, the output level number of the converter is 2, and the output voltage of the converter is 50% of the direct-current bus voltage;
sixth mode of operation: the first switch tube S1, the fifth switch tube S5, the sixth switch tube S6 and the seventh switch tube S7 are all turned on, the rest switch tubes are all turned off, the output level number of the converter is 1, and the output voltage of the converter is 25% of the direct-current bus voltage;
seventh mode of operation: the fourth switch tube S4, the fifth switch tube S5, the sixth switch tube S6 and the eighth switch tube S8 are all turned on, the rest switch tubes are all turned off, the output level number of the converter is 1, and the output voltage of the converter is 25% of the direct-current bus voltage;
the eighth mode of operation: the fifth switch tube S5, the sixth switch tube S6, the seventh switch tube S7 and the eighth switch tube S8 are all turned on, the rest of the switch tubes are all turned off, the number of output levels of the converter is 0, and the output voltage of the converter is 0 of the direct current bus voltage.
In the first operating mode: if the current is greater than 0, the current sequentially passes through the first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 to flow out of the inverter to realize the conversion from direct current to alternating current, and if the current is less than 0, the current sequentially passes through the body diodes which are respectively connected in anti-parallel with the first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 to flow into the inverter to realize the conversion from alternating current to direct current;
in the second operating mode: if the current is greater than 0, the current sequentially passes through a first switching tube S1, a first flying capacitor C1, a first clamping diode D1 of a first diode branch, a third switching tube S3 and a fourth switching tube S4 to flow out of the converter, so that the conversion from direct current to alternating current is realized, and if the current is less than 0, the current sequentially passes through a fifth switching tube S5, a third clamping diode D3 of the first diode branch, a second clamping diode D2 of the first diode branch, a first flying capacitor C1 and a body diode which is reversely connected with the first switching tube S1 in parallel, so that the conversion from alternating current to direct current is realized;
in the third operating mode: if the current is greater than 0, the current sequentially passes through an eighth switching tube S8 anti-parallel body diode, a third flying capacitor C3, a second flying capacitor C2, a first flying capacitor C1, a second switching tube S2, a third switching tube S3 and a fourth switching tube S4 to flow out of the converter to realize conversion from direct current to alternating current, and if the current is less than 0, the current sequentially passes through a fourth switching tube S4 anti-parallel body diode, a third switching tube S3 anti-parallel body diode, a second switching tube S2 anti-parallel body diode, a first flying capacitor C1, a second flying capacitor C2, a third flying capacitor C3 and an eighth switching tube S8 to flow into the converter to realize conversion from alternating current to direct current;
in the fourth operating mode: if the current is greater than 0, the current sequentially passes through a first switching tube S1, a first flying capacitor C1, a second flying capacitor C2, a second clamping diode D5 of a second diode branch, a first clamping diode D4 of the second diode branch and a fourth switching tube S4 to flow out of the converter, so that the conversion from direct current to alternating current is realized, and if the current is less than 0, the current sequentially passes through a fifth switching tube S5, a sixth switching tube S6, a third clamping diode D6 of the second diode branch, a second flying capacitor C2, a first flying capacitor C1 and a body diode which is in anti-parallel connection with the first switching tube S1 to flow into the converter, so that the conversion from alternating current to direct current is realized;
in the fifth operating mode: if the current is greater than 0, the current sequentially passes through an eighth switching tube S8 anti-parallel body diode, a third flying capacitor C3, a second flying capacitor C2, a first clamping diode D1 of a first diode branch, a third switching tube S3 and a fourth switching tube S4 to flow out of the converter to realize the conversion from direct current to alternating current, and if the current is less than 0, the current sequentially passes through a fifth switching tube S5, a third clamping diode D3 of the first diode branch, a second clamping diode D2 of the first diode branch, a second flying capacitor C2, a third flying capacitor C3 and an eighth switching tube S8 to flow into the converter to realize the conversion from alternating current to direct current;
in the sixth operating mode: if the current is greater than 0, the current sequentially passes through a first switch tube S1, a first flying capacitor C1, a second flying capacitor C2, a third flying capacitor C3, a body diode in inverse parallel with a seventh switch tube S7, a body diode in inverse parallel with a sixth switch tube S6 and a body diode in inverse parallel with a fifth switch tube S5 to flow out of the converter to realize the conversion from the direct current to the alternating current, and if the current is less than 0, the current sequentially passes through a body diode in inverse parallel with a fifth switch tube S5, a sixth switch tube S6, a seventh switch tube S7, a third flying capacitor C3, a second flying capacitor C2, a first flying capacitor C1 and a first switch tube S1 to flow into the converter to realize the conversion from the alternating current to the direct current;
in the seventh operating mode: if the current is greater than 0, the current sequentially passes through an eighth switching tube S8 anti-parallel body diode, a third flying capacitor C3, a second clamping diode D5 of a second diode branch, a first clamping diode D4 of the second diode branch and a fourth switching tube S4 to flow out of the converter, so that the conversion from direct current to alternating current is realized, and if the current is less than 0, the current sequentially passes through a fifth switching tube S5, a sixth switching tube S6, a third clamping diode D6 of the second diode branch, a third flying capacitor C3 and an eighth switching tube S8 to flow into the converter, so that the conversion from alternating current to direct current is realized;
in the eighth operating mode: if the current is greater than 0, the current sequentially passes through the body diodes which are respectively connected in inverse parallel with the eighth switching tube S8, the seventh switching tube S7, the sixth switching tube S6 and the fifth switching tube S5 and flows out of the converter to realize the conversion from the direct current to the alternating current, and if the current is less than 0, the current sequentially passes through the fifth switching tube S5, the sixth switching tube S6, the seventh switching tube S7 and the eighth switching tube S8 and flows into the converter to realize the conversion from the alternating current to the direct current.
Compared with the closest prior art, the technical scheme provided by the invention has the following beneficial effects:
the five-level hybrid neutral point clamped converter comprises three bridge arm units connected in parallel between a positive direct current bus and a negative direct current bus, wherein each bridge arm unit comprises eight switching tubes, three flying capacitors and six clamping diodes, and the eight switching tubes are sequentially connected in series in a forward direction to form a switching tube branch; the three flying capacitors are sequentially connected in series in the forward direction to form a capacitor branch circuit, and the capacitor branch circuit is connected with the switch tube branch circuit; the three clamping diodes are sequentially connected in series in the forward direction to form a first diode branch, the first diode branch is connected with the switch tube branch, the other three clamping diodes are sequentially connected in series in the forward direction to form a second diode branch, and the second diode branches are all connected with the switch tube branch, so that the circuit is small in size and high in reliability;
the five-level hybrid neutral point clamping converter provided by the invention has the advantages of fewer required devices, simple topological structure and easiness in control;
the five-level hybrid neutral point clamping converter provided by the invention adopts the MOSFET as the switching tube, the switching loss is small, the switching frequency is high, and the converter has high power density and high working efficiency;
the voltage born by each device in the five-level hybrid neutral point clamped converter provided by the invention is equal, namely one fourth of the voltage of a direct-current side bus, and the five-level hybrid neutral point clamped converter can be applied to medium-high voltage large-capacity industrial occasions without high-voltage devices.
Drawings
FIG. 1 is a topology structure diagram of a five-level hybrid neutral point clamped converter in an embodiment of the present invention;
FIG. 2 is a current loop diagram for a first mode of operation in accordance with an embodiment of the present invention;
FIG. 3 is a current loop diagram for a second mode of operation in accordance with an embodiment of the present invention;
FIG. 4 is a current loop diagram for a third mode of operation in accordance with an embodiment of the present invention;
FIG. 5 is a current loop diagram for a fourth mode of operation of an embodiment of the present invention;
FIG. 6 is a current loop diagram for a fifth mode of operation of an embodiment of the present invention;
FIG. 7 is a current loop diagram for a sixth mode of operation of an embodiment of the present invention;
FIG. 8 is a current loop diagram for a seventh mode of operation of an embodiment of the present invention;
fig. 9 is a current loop diagram in an eighth operating mode according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The invention provides a five-level hybrid midpoint clamping converter, which comprises three bridge arm units connected in parallel between a positive direct-current bus and a negative direct-current bus as shown in figure 1, wherein the three bridge arm units are an a-phase bridge arm unit, a b-phase bridge arm unit and a C-phase bridge arm unit respectively, subscripts a, b and C in figure 1 represent three phases a, b and C respectively, each bridge arm unit comprises eight switching tubes (S1 to S8), three flying capacitors (C1 to C3) and six clamping diodes (D1 to D6);
the eight switching tubes are sequentially connected in series in the forward direction to form a switching tube branch; the three flying capacitors are sequentially connected in series in the forward direction to form a capacitor branch circuit, and the capacitor branch circuit is connected with the switch tube branch circuit; the three clamping diodes are sequentially connected in series in a forward direction to form a first diode branch, the first diode branch is connected with the switch tube branch, the other three clamping diodes are sequentially connected in series in the forward direction to form a second diode branch, and the second diode branches are all connected with the switch tube branch.
The drain electrode of the first switching tube S1 is connected with the positive electrode direct current bus, and the source electrode of the eighth switching tube S8 is connected with the negative electrode direct current bus;
the anode of the first flying capacitor C1 is connected with the midpoint between the source of the first switching tube S1 and the drain of the second switching tube S2, and the cathode of the third flying capacitor C3 is connected with the midpoint between the source of the seventh switching tube S7 and the drain of the eighth switching tube S8;
the cathode of the first clamping diode D1 in the first diode branch is connected with the midpoint of the source of the second switching tube S2 and the drain of the third switching tube S3, and the anode of the third clamping diode D3 in the first diode branch is connected with the midpoint of the source of the fifth switching tube S5 and the drain of the sixth switching tube S6; the cathode of the first clamping diode D4 in the second diode branch is connected with the midpoint of the source of the third switching tube S3 and the drain of the fourth switching tube S4, and the anode of the third clamping diode D6 in the second diode branch is connected with the midpoint of the source of the sixth switching tube S6 and the drain of the seventh switching tube S7;
the midpoint of the first and second flying capacitors C1 and C2 is connected to the midpoint of the first and second clamping diodes D1 and D2 in the first diode branch, and the midpoint of the second and third flying capacitors C2 and C3 is connected to the midpoint of the second and third clamping diodes D5 and D6 in the second diode branch.
Each bridge arm unit further comprises eight body diodes, and the body diodes are connected with the switching tubes in an anti-parallel mode.
The switch tube is a MOSFET or an IGBT, and a silicon carbide MOSFET is adopted in the embodiment of the invention.
An output end connected with a load is arranged between the source electrode of the fourth switching tube S4 and the drain electrode of the fifth switching tube S5.
The converter comprises the following operating modes:
the first mode of operation: the first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 are all turned on, the other switch tubes are all turned off, the output level number of the converter is 4, and the output voltage of the converter is direct-current bus voltage;
the second working mode is as follows: the first switch tube S1, the third switch tube S3, the fourth switch tube S4 and the fifth switch tube S5 are all switched on, the other switch tubes are all switched off, the output level number of the converter is 3, and the output voltage of the converter is 75% of the voltage of the direct-current bus;
the third mode of operation: the second switch tube S2, the third switch tube S3, the fourth switch tube S4 and the eighth switch tube S8 are all switched on, the other switch tubes are all switched off, the output level number of the converter is 3, and the output voltage of the converter is 75% of the voltage of the direct-current bus;
a fourth mode of operation: the first switch tube S1, the fourth switch tube S4, the fifth switch tube S5 and the sixth switch tube S6 are all switched on, the other switch tubes are all switched off, the output level number of the converter is 2, and the output voltage of the converter is 50% of the direct-current bus voltage;
the fifth working mode: the third switch tube S3, the fourth switch tube S4, the fifth switch tube S5 and the eighth switch tube S8 are all switched on, the rest switch tubes are all switched off, the output level number of the converter is 2, and the output voltage of the converter is 50% of the voltage of the direct-current bus;
sixth mode of operation: the first switch tube S1, the fifth switch tube S5, the sixth switch tube S6 and the seventh switch tube S7 are all switched on, the other switch tubes are all switched off, the output level number of the converter is 1, and the output voltage of the converter is 25% of the direct-current bus voltage;
seventh mode of operation: the fourth switch tube S4, the fifth switch tube S5, the sixth switch tube S6 and the eighth switch tube S8 are all switched on, the rest switch tubes are all switched off, the output level number of the converter is 1, and the output voltage of the converter is 25% of the direct-current bus voltage;
the eighth mode of operation: the fifth switch tube S5, the sixth switch tube S6, the seventh switch tube S7 and the eighth switch tube S8 are all turned on, the rest of the switch tubes are all turned off, the number of output levels of the converter is 0, and the output voltage of the converter is 0 of the voltage of the direct current bus.
The conversion process of the five-level hybrid midpoint clamping converter provided by the embodiment of the invention is as follows:
in a first mode of operation: if the current is greater than 0, the current flows out of the inverter through the first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 in sequence to realize the conversion from direct current to alternating current, and if the current is less than 0, the current flows into the inverter through the body diodes which are connected in inverse parallel respectively and are connected in the first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 in sequence to realize the conversion from alternating current to direct current, as shown in fig. 2;
in a second mode of operation: if the current is greater than 0, the current sequentially passes through the first switching tube S1, the first flying capacitor C1, the first clamping diode D1 of the first diode branch, the third switching tube S3 and the fourth switching tube S4 to flow out of the converter, so that the conversion from the direct current to the alternating current is realized, and if the current is less than 0, the current sequentially passes through the fifth switching tube S5, the third clamping diode D3 of the first diode branch, the second clamping diode D2 of the first diode branch, the first flying capacitor C1 and the body diode which is reversely connected with the first switching tube S1 in parallel, so that the conversion from the alternating current to the direct current is realized, as shown in fig. 3;
in a third mode of operation: if the current is greater than 0, the current flows out of the converter through the body diode, the third flying capacitor C3, the second flying capacitor C2, the first flying capacitor C1, the second switching tube S2, the third switching tube S3 and the fourth switching tube S4 which are connected in inverse parallel through the eighth switching tube S8, the converter is used for converting the direct current into the alternating current, and if the current is less than 0, the current flows into the converter through the body diode connected in inverse parallel through the fourth switching tube S4, the body diode connected in inverse parallel through the third switching tube S3, the body diode connected in inverse parallel through the second switching tube S2, the first flying capacitor C1, the second flying capacitor C2, the third flying capacitor C3 and the eighth switching tube S8 in order for converting the alternating current into the direct current, as shown in fig. 4;
in a fourth mode of operation: if the current is greater than 0, the current sequentially flows out of the converter through a first switching tube S1, a first flying capacitor C1, a second flying capacitor C2, a second clamping diode D5 of the second diode branch, a first clamping diode D4 of the second diode branch and a fourth switching tube S4, so that the conversion from direct current to alternating current is realized, and if the current is less than 0, the current sequentially flows into the converter through a fifth switching tube S5, a sixth switching tube S6, a third clamping diode D6 of the second diode branch, a second flying capacitor C2, a first flying capacitor C1 and a body diode of the first switching tube S1 which are connected in anti-parallel, so that the conversion from alternating current to direct current is realized, as shown in fig. 5;
in a fifth mode of operation: if the current is greater than 0, the current flows out of the converter through the body diode, the third flying capacitor C3, the second flying capacitor C2, the first clamping diode D1, the third switching tube S3 and the fourth switching tube S4 which are connected in parallel in reverse through the eighth switching tube S8, so that the conversion from the direct current to the alternating current is realized, and if the current is less than 0, the current flows into the converter through the fifth switching tube S5, the third clamping diode D3, the second clamping diode D2, the second flying capacitor C2, the third flying capacitor C3 and the eighth switching tube S8 in sequence, so that the conversion from the alternating current to the direct current is realized, as shown in fig. 6;
in a sixth mode of operation: if the current is greater than 0, the current sequentially passes through a body diode formed by antiparallel connection of a first switching tube S1, a first flying capacitor C1, a second flying capacitor C2, a third flying capacitor C3 and a seventh switching tube S7, a body diode formed by antiparallel connection of a sixth switching tube S6 and a body diode formed by antiparallel connection of a fifth switching tube S5, and flows out of the converter to realize conversion from direct current to alternating current, and if the current is less than 0, the current sequentially passes through a body diode formed by antiparallel connection of a fifth switching tube S5, a sixth switching tube S6, a seventh switching tube S7, a third flying capacitor C3, a second flying capacitor C2, a first flying capacitor C1 and a first switching tube S1 and flows into the converter to realize conversion from alternating current to direct current, as shown in fig. 7;
in a seventh mode of operation: if the current is greater than 0, the current flows out of the converter through the body diode, the third flying capacitor C3, the second clamping diode D5 of the second diode branch, the first clamping diode D4 of the second diode branch and the fourth switching tube S4 which are connected in parallel in an anti-parallel mode through the eighth switching tube S8, so that the conversion from direct current to alternating current is realized, and if the current is less than 0, the current flows into the converter through the fifth switching tube S5, the sixth switching tube S6, the third clamping diode D6 of the second diode branch, the third flying capacitor C3 and the eighth switching tube S8 in sequence, so that the conversion from alternating current to direct current is realized, as shown in fig. 8;
in the eighth mode of operation: if the current is greater than 0, the current flows out of the inverter through the body diodes connected in anti-parallel with the eighth switching tube S8, the seventh switching tube S7, the sixth switching tube S6 and the fifth switching tube S5 in sequence, so that the conversion from the direct current to the alternating current is realized, and if the current is less than 0, the current flows into the inverter through the fifth switching tube S5, the sixth switching tube S6, the seventh switching tube S7 and the eighth switching tube S8 in sequence, so that the conversion from the alternating current to the direct current is realized, as shown in fig. 9.
Finally, it should be noted that: the above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and a person of ordinary skill in the art can make modifications or equivalents to the specific embodiments of the present invention with reference to the above embodiments, and such modifications or equivalents without departing from the spirit and scope of the present invention are within the scope of the claims of the present invention as set forth in the claims.

Claims (5)

1. The five-level hybrid neutral point clamped converter is characterized by comprising three bridge arm units connected in parallel between a positive direct current bus and a negative direct current bus, wherein each bridge arm unit comprises eight switching tubes, three flying capacitors and six clamping diodes;
the eight switching tubes are sequentially connected in series in the forward direction to form a switching tube branch; the three flying capacitors are sequentially connected in series in the forward direction to form a capacitor branch circuit, and the capacitor branch circuit is connected with the switch tube branch circuit; the three clamping diodes are sequentially connected in series in a forward direction to form a first diode branch, the first diode branch is connected with the switch tube branch, the other three clamping diodes are sequentially connected in series in the forward direction to form a second diode branch, and the second diode branches are all connected with the switch tube branch;
the converter comprises the following operating modes:
the first mode of operation: the first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 are all turned on, the other switch tubes are all turned off, the output level number of the converter is 4, and the output voltage of the converter is direct-current bus voltage;
the second working mode is as follows: the first switch tube S1, the third switch tube S3, the fourth switch tube S4 and the fifth switch tube S5 are all turned on, the other switch tubes are all turned off, the output level number of the converter is 3, and the output voltage of the converter is 75% of the direct-current bus voltage;
the third mode of operation: the second switch tube S2, the third switch tube S3, the fourth switch tube S4 and the eighth switch tube S8 are all turned on, the rest switch tubes are all turned off, the output level number of the converter is 3, and the output voltage of the converter is 75% of the voltage of the direct-current bus;
a fourth mode of operation: the first switch tube S1, the fourth switch tube S4, the fifth switch tube S5 and the sixth switch tube S6 are all turned on, the rest switch tubes are all turned off, the output level number of the converter is 2, and the output voltage of the converter is 50% of the direct-current bus voltage;
the fifth working mode: the third switch tube S3, the fourth switch tube S4, the fifth switch tube S5 and the eighth switch tube S8 are all turned on, the rest switch tubes are all turned off, the output level number of the converter is 2, and the output voltage of the converter is 50% of the direct-current bus voltage;
sixth mode of operation: the first switch tube S1, the fifth switch tube S5, the sixth switch tube S6 and the seventh switch tube S7 are all turned on, the rest switch tubes are all turned off, the output level number of the converter is 1, and the output voltage of the converter is 25% of the direct-current bus voltage;
seventh mode of operation: the fourth switch tube S4, the fifth switch tube S5, the sixth switch tube S6 and the eighth switch tube S8 are all turned on, the rest switch tubes are all turned off, the output level number of the converter is 1, and the output voltage of the converter is 25% of the direct-current bus voltage;
the eighth mode of operation: the fifth switch tube S5, the sixth switch tube S6, the seventh switch tube S7 and the eighth switch tube S8 are all turned on, the rest of the switch tubes are all turned off, the number of output levels of the converter is 0, and the output voltage of the converter is 0 of the voltage of the direct-current bus;
the drain electrode of the first switching tube S1 is connected with the positive electrode direct current bus, and the source electrode of the eighth switching tube S8 is connected with the negative electrode direct current bus;
the anode of the first flying capacitor C1 is connected with the midpoint between the source of the first switching tube S1 and the drain of the second switching tube S2, and the cathode of the third flying capacitor C3 is connected with the midpoint between the source of the seventh switching tube S7 and the drain of the eighth switching tube S8;
the cathode of a first clamping diode D1 in the first diode branch is connected with the midpoint of the source of a second switching tube S2 and the drain of a third switching tube S3, and the anode of a third clamping diode D3 in the first diode branch is connected with the midpoint of the source of a fifth switching tube S5 and the drain of a sixth switching tube S6; the cathode of the first clamping diode D4 in the second diode branch is connected with the midpoint of the source of the third switching tube S3 and the drain of the fourth switching tube S4, and the anode of the third clamping diode D6 in the second diode branch is connected with the midpoint of the source of the sixth switching tube S6 and the drain of the seventh switching tube S7;
the midpoint of the first and second flying capacitors C1 and C2 is connected to the midpoint of the first and second clamping diodes D1 and D2 in the first diode branch, and the midpoint of the second and third flying capacitors C2 and C3 is connected to the midpoint of the second and third clamping diodes D5 and D6 in the second diode branch.
2. The five-level hybrid midpoint clamp converter according to claim 1, wherein each leg unit further comprises eight body diodes, the body diodes being connected in anti-parallel with a switching tube.
3. The five-level hybrid midpoint clamp converter according to claim 1, wherein the switching tubes are MOSFETs or IGBTs.
4. The five-level hybrid midpoint clamp converter according to claim 1, wherein an output terminal connected to a load is provided between the source of the fourth switching tube S4 and the drain of the fifth switching tube S5.
5. The five-level hybrid midpoint clamp converter of claim 1,
in a first mode of operation: if the current is greater than 0, the current sequentially passes through the first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 to flow out of the inverter to realize the conversion from direct current to alternating current, and if the current is less than 0, the current sequentially passes through the body diodes which are respectively connected in anti-parallel with the first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 to flow into the inverter to realize the conversion from alternating current to direct current;
in the second operating mode: if the current is greater than 0, the current sequentially passes through a first switching tube S1, a first flying capacitor C1, a first clamping diode D1 of a first diode branch, a third switching tube S3 and a fourth switching tube S4 to flow out of the converter, so that the conversion from direct current to alternating current is realized, and if the current is less than 0, the current sequentially passes through a fifth switching tube S5, a third clamping diode D3 of the first diode branch, a second clamping diode D2 of the first diode branch, a first flying capacitor C1 and a body diode which is reversely connected with the first switching tube S1 in parallel, so that the conversion from alternating current to direct current is realized;
in the third operating mode: if the current is greater than 0, the current sequentially passes through an eighth switching tube S8 anti-parallel body diode, a third flying capacitor C3, a second flying capacitor C2, a first flying capacitor C1, a second switching tube S2, a third switching tube S3 and a fourth switching tube S4 to flow out of the converter to realize conversion from direct current to alternating current, and if the current is less than 0, the current sequentially passes through a fourth switching tube S4 anti-parallel body diode, a third switching tube S3 anti-parallel body diode, a second switching tube S2 anti-parallel body diode, a first flying capacitor C1, a second flying capacitor C2, a third flying capacitor C3 and an eighth switching tube S8 to flow into the converter to realize conversion from alternating current to direct current;
in the fourth operating mode: if the current is greater than 0, the current sequentially passes through a first switching tube S1, a first flying capacitor C1, a second flying capacitor C2, a second clamping diode D5 of a second diode branch, a first clamping diode D4 of the second diode branch and a fourth switching tube S4 to flow out of the converter, so that the conversion from direct current to alternating current is realized, and if the current is less than 0, the current sequentially passes through a fifth switching tube S5, a sixth switching tube S6, a third clamping diode D6 of the second diode branch, a second flying capacitor C2, a first flying capacitor C1 and a body diode which is in anti-parallel connection with the first switching tube S1 to flow into the converter, so that the conversion from alternating current to direct current is realized;
in the fifth operating mode: if the current is greater than 0, the current sequentially passes through an eighth switching tube S8 anti-parallel body diode, a third flying capacitor C3, a second flying capacitor C2, a first clamping diode D1 of a first diode branch, a third switching tube S3 and a fourth switching tube S4 to flow out of the converter to realize the conversion from direct current to alternating current, and if the current is less than 0, the current sequentially passes through a fifth switching tube S5, a third clamping diode D3 of the first diode branch, a second clamping diode D2 of the first diode branch, a second flying capacitor C2, a third flying capacitor C3 and an eighth switching tube S8 to flow into the converter to realize the conversion from alternating current to direct current;
in the sixth operating mode: if the current is greater than 0, the current sequentially passes through a first switch tube S1, a first flying capacitor C1, a second flying capacitor C2, a third flying capacitor C3, a body diode in inverse parallel with a seventh switch tube S7, a body diode in inverse parallel with a sixth switch tube S6 and a body diode in inverse parallel with a fifth switch tube S5 to flow out of the converter to realize the conversion from the direct current to the alternating current, and if the current is less than 0, the current sequentially passes through a body diode in inverse parallel with a fifth switch tube S5, a sixth switch tube S6, a seventh switch tube S7, a third flying capacitor C3, a second flying capacitor C2, a first flying capacitor C1 and a first switch tube S1 to flow into the converter to realize the conversion from the alternating current to the direct current;
in the seventh operating mode: if the current is greater than 0, the current sequentially passes through an eighth switching tube S8 anti-parallel body diode, a third flying capacitor C3, a second clamping diode D5 of a second diode branch, a first clamping diode D4 of the second diode branch and a fourth switching tube S4 to flow out of the converter, so that the conversion from direct current to alternating current is realized, and if the current is less than 0, the current sequentially passes through a fifth switching tube S5, a sixth switching tube S6, a third clamping diode D6 of the second diode branch, a third flying capacitor C3 and an eighth switching tube S8 to flow into the converter, so that the conversion from alternating current to direct current is realized;
in the eighth operating mode: if the current is greater than 0, the current sequentially passes through the body diodes which are respectively connected in inverse parallel with the eighth switching tube S8, the seventh switching tube S7, the sixth switching tube S6 and the fifth switching tube S5 and flows out of the converter to realize the conversion from the direct current to the alternating current, and if the current is less than 0, the current sequentially passes through the fifth switching tube S5, the sixth switching tube S6, the seventh switching tube S7 and the eighth switching tube S8 and flows into the converter to realize the conversion from the alternating current to the direct current.
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