CN110061645B - High-voltage flexible direct-current device with reduced capacitance - Google Patents

High-voltage flexible direct-current device with reduced capacitance Download PDF

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Publication number
CN110061645B
CN110061645B CN201910253065.XA CN201910253065A CN110061645B CN 110061645 B CN110061645 B CN 110061645B CN 201910253065 A CN201910253065 A CN 201910253065A CN 110061645 B CN110061645 B CN 110061645B
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bridge
bridge arm
voltage
sub
current
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CN110061645A (en
Inventor
刘万勋
田春筝
张凯
黄鑫
邵红博
孙思培
张丽华
贾鹏
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Huazhong University of Science and Technology
State Grid Corp of China SGCC
Economic and Technological Research Institute of State Grid Henan Electric Power Co Ltd
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Huazhong University of Science and Technology
State Grid Corp of China SGCC
Economic and Technological Research Institute of State Grid Henan Electric Power Co Ltd
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    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS 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
    • H02M7/00Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48Conversion 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
    • H02M7/483Converters with outputs that each can have more than two voltages levels
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS 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
    • H02M7/00Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48Conversion 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
    • H02M7/53Conversion 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
    • H02M7/537Conversion 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
    • H02M7/5387Conversion 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

Abstract

The invention provides a high-voltage flexible direct current device with reduced capacitance, which comprises three bridge arms A, B and C which have the same structure and are mutually connected in parallel, wherein the bridge arm A is formed by connecting an upper bridge arm and a lower bridge arm in series, the upper bridge arm is formed by sequentially connecting a plurality of half-bridge sub-modules in series end to end, the lower bridge arm and the upper bridge arm have the same structure, and two buffer inductors L are connected between the upper bridge arm and the lower bridge arm in seriesmTwo said buffer inductors LmThe series connection point between the bridge arms is an alternating current output end, and two parallel connection of the bridge arm A, the bridge arm B and the bridge arm C are direct current output ends; a bridge arm and an energy storage inductor are added to a half-bridge submodule of the device, so that fundamental frequency pulse power is transferred to the energy storage inductor, and capacitor voltage pulse is effectively reduced; the modularized design reduces the design and installation cost, reduces the capacitance value, reduces the volume of a large number of capacitors, directly reduces the volume of a system device, and improves the efficiency of the device.

Description

High-voltage flexible direct-current device with reduced capacitance
Technical Field
The invention relates to the technical field of high-voltage flexible direct current transmission, in particular to a high-voltage flexible direct current device with reduced capacitance.
Background
The China territorial breadth is wide, and the energy resource distribution is uneven: renewable energy sources (such as wind energy, solar energy and water energy) suitable for large-scale development are mostly concentrated in the southwest and northeast, wherein water resources are mainly concentrated in the southwest and northwest regions, accounting for about 15.5% of the total amount of the whole country, the southwest region occupies 67.8% of the whole country, and the northeast and northeast regions are relatively few and only account for about 6% of the whole country; the wind power resources are mainly distributed in northern Xinjiang, inner Mongolia, northern Gansu, Heilongjiang, eastern Jilin, northern Hebei and Liaodong peninsula, and are suitable for large-scale development and utilization of wind power; coal power is still the main supporting energy in China, and the coal resources which are proved to be suitable for power generation at present are mainly distributed in Mongolian, Sinkiang eastern, Shanxi province and Long Bin. Compared with the energy which is mostly distributed in the northeast and the southwest and the electric energy consumption is mainly concentrated in the middle east and the coastal, the energy and electric energy consumption are reversely distributed, the development of the long-distance power transmission in China is promoted, and compared with the alternating current, the high-voltage direct current is more suitable for the long-distance power transmission along with the accelerated research and development of the high-voltage direct current breaker and the completion of the engineering compared with the alternating current shown in figure 1.
Compared with the traditional high-voltage direct-current transmission, the flexible direct-current transmission has various advantages, is considered as the transmission mode with the most application value, and mainly shows that: 1) the problem of commutation failure of traditional high-voltage direct current is solved, 2) flexible direct current transmission can control reactive power and active power respectively, and the problem of reactive power compensation is solved, 3) higher equivalent switching frequency is adopted, harmonic frequency is reduced remarkably, and 4) the flexible direct current transmission system is suitable for forming a multi-terminal direct current transmission system.
According to the basic principle of the modular multilevel converter, the converter will bear reactive power which is generated by the high-voltage alternating-current side and has the same magnitude as active power, and the part of the reactive power is borne by each sub-module capacitor which forms the converter, and the part of the reactive power is represented as fundamental frequency (same frequency as the alternating-current side) voltage pulsation of the capacitor on the capacitor. The fundamental frequency ripple of the capacitor is the main component of the voltage ripple of the capacitor, the fundamental frequency ripple of the capacitor increases the voltage stress of the power switch device, increases the volume and the cost of the capacitor, causes the volume and the cost of the whole device to increase, reduces the utilization rate of the voltage of the capacitor, and increases the harmonic content of the output voltage. In view of the influence of low frequency ripple, in industrial applications, it is generally required to limit the ripple of the capacitor voltage to 5% or less in order to maintain the stability and waveform quality of the system.
The capacitor voltage ripple suppression method based on the modular multilevel converter has received extensive attention from researchers. A structure for eliminating voltage fundamental frequency pulsation is disclosed in application number CN201710150668, but the pulsation power is transmitted through upper and lower bridge arms, so that the modulation ratio is reduced, and the current stress of a power device is increased; documents (MMC capacitor voltage fluctuation suppression under low-frequency working conditions, Pengkun and the like) adopt a high-frequency injection method to convert low-frequency pulsation of capacitor voltage into pulsation with higher frequency, so that fundamental frequency voltage pulsation is reduced, but current stress of a power device is increased, and control is complex; the document (New modular converter with power channels between upper and lower arms for MV drivers' he.l etc.) studies a topology that the upper and lower arms of the arms exchange power through a coupling channel, but the coupling channel needs to bear the voltage of a common direct current bus stage, which increases the insulation cost, and is not suitable for high-voltage-level application.
Disclosure of Invention
In view of this, the invention provides a high-voltage flexible direct current device with reduced capacitance, in which a bridge arm and an energy storage inductor are added to a half-bridge submodule of the device, so that fundamental frequency ripple power is transferred to the energy storage inductor, thereby effectively reducing capacitance voltage ripple; the modularized design reduces the design and installation cost, reduces the capacitance value, reduces the volume of a large number of capacitors, directly reduces the volume of a system device, and improves the efficiency of the device.
In order to solve the problems, the invention provides a high-voltage flexible direct current device with reduced capacitance, which comprises three bridge arms A, B and C which have the same structure and are connected in parallel, wherein the bridge arm A is formed by connecting an upper bridge arm and a lower bridge arm in series, the upper bridge arm is formed by sequentially connecting a plurality of half-bridge sub-modules in series end to end, the lower bridge arm and the upper bridge arm have the same structure, and two buffering circuits are connected between the upper bridge arm and the lower bridge arm in seriesInductor LmTwo said buffer inductors LmThe series connection point between the bridge arms is an alternating current output end, and the two parallel connection points of the bridge arm A, the bridge arm B and the bridge arm C are direct current output ends;
the alternating current output end and the direct current output end are respectively connected with a direct current end and an alternating current end of the high-voltage flexible direct current transmission.
The upper bridge arm and the lower bridge arm are formed by connecting half-bridge submodules with the same number end to end in series.
The half-bridge submodule comprises three sub-bridge arms, wherein power switches S1 and S2 are connected in series to form a first sub-bridge arm, and a power switch u3And u4And the energy storage inductor L is arranged between the middle point of the second sub bridge arm and the middle point of the third sub bridge arm.
The power switches S1, S2, u3And u4All the power switches are power switches with uniform models, and each power switch consists of a full-control device and an anti-parallel diode.
The working principle of the half-bridge submodule is as follows, and the control target is as follows:
Vsmis a set value of the DC voltage of the half-bridge submodule ucIs the traffic, omega0Is the fundamental angular frequency, i.e., the grid frequency,is the initial phase angle of the capacitor voltage;
according to the formula (1), the DC side voltage of the half-bridge submodule is VsmI.e. no voltage fluctuations, which is determined by the following relationship:
ic1=ic2+iL(2)
ic1,ic2currents of upper and lower two capacitors, iLIs the energy storage inductive current;
the power of the half-bridge sub-modules is then:
let PsmThe actual pulse power of the half-bridge submodule is equal to that of the submodule, and the direct-current side voltage of the submodule is VsmThereby suppressing low frequency voltage ripple;
actual ripple power of half-bridge sub-modules:
wherein, UdSetting voltage for the DC bus of the device, U is the amplitude of AC side phase voltage, I is the amplitude of AC output side phase current, Iz2Amplitude of secondary quantity of circulating current, α0Is the initial phase angle of the AC voltage, α2Is the initial phase angle of the secondary quantity of the circulating current,is the ac load power factor;
let P be PsmObtaining u in the formula (1)cThe amplitude and the initial phase angle of u can be controlled3And u4Output the desired voltage uc1And uc2
Aiming at the phenomenon that in the prior art, a coupling channel needs to bear the voltage of a common direct-current bus level, the insulation cost is increased, and the high-voltage level application is not suitable because of the phenomenon that the coupling channel in voltage source type high-voltage flexible direct-current transmission, a bridge arm and an energy storage inductor are added in a half-bridge submodule, so that fundamental frequency pulsating power is transferred to the energy storage inductor, and the capacitive voltage pulsation is effectively reduced; in addition, the modularized design is adopted, so that the design and installation cost is reduced, the capacitance value is reduced, the volume of a large number of capacitors is reduced, the volume of a system device is directly reduced, and the device efficiency is improved.
In addition, the invention improves the half-bridge submodule, has the modularization characteristic of modularization and multilevel, and is convenient to design, manufacture, install and maintain; in addition, a third bridge arm added in the half-bridge submodule adopts a power device with the same voltage grade as the original half-bridge module, and the high-insulation design is not required to be independently carried out; according to engineering practical experience, a large number of capacitors in the modularized multi-level device occupy huge space of the device, and the single cost of the modularized multi-level device is higher than that of a corresponding half-bridge sub-module.
Drawings
FIG. 1 is a schematic diagram of the comparison of AC/DC power transmission distance-cost in the background of the invention, which is derived from Zhao wan man (HVDC transmission engineering);
FIG. 2 is a schematic structural view of the present invention as a whole;
FIG. 3 is a schematic diagram of a half bridge sub-module of the present invention;
fig. 4 is a diagram of a flexible direct current transmission system.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to fig. 2 to 4 of the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention, are within the scope of the invention.
Example one
As shown in fig. 2-4: a high-voltage flexible direct-current device with reduced capacitance comprises three bridge arms A, B and C which are identical in structure and are connected in parallel, wherein the bridge arm A is formed by connecting an upper bridge arm and a lower bridge arm in series, the upper bridge arm is formed by sequentially connecting a plurality of half-bridge submodules end to end in series, the lower bridge arm is identical in structure with the upper bridge arm, two buffer inductors Lm are connected between the upper bridge arm and the lower bridge arm in series, a series connection point between the two buffer inductors Lm is an alternating-current output end, and two parallel connection points of the bridge arm A, the bridge arm B and the bridge arm C are direct-current output ends;
the alternating current output end and the direct current output end are respectively connected with a direct current end and an alternating current end of the high-voltage flexible direct current transmission.
The upper bridge arm and the lower bridge arm are formed by connecting half-bridge submodules with the same number end to end in series.
The half-bridge submodule comprises three sub-bridge arms, wherein power switches S1 and S2 are connected in series to form a first sub-bridge arm, and a power switch u3And u4And the energy storage inductor L is arranged between the middle point of the second sub bridge arm and the middle point of the third sub bridge arm.
The power switches S1, S2, u3And u4All the power switches are power switches with uniform models, and each power switch consists of a full-control device and an anti-parallel diode.
The working principle of the half-bridge submodule is as follows, and the control target is as follows:
Vsmis a set value of the DC voltage of the half-bridge submodule ucIs the traffic, omega0Is the fundamental angular frequency, i.e., the grid frequency,is the initial phase angle of the capacitor voltage;
according to the formula (1), the DC side voltage of the half-bridge submodule is VsmI.e. no voltage fluctuations, which is determined by the following relationship:
ic1=ic2+iL(2)
ic1,ic2currents of upper and lower two capacitors, iLIs the energy storage inductive current;
the power of the half-bridge sub-modules is then:
let PsmThe actual pulse power of the half-bridge submodule is equal to that of the submodule, and the direct-current side voltage of the submodule is VsmThereby suppressing low frequency voltage ripple;
actual ripple power of half-bridge sub-modules:
wherein, UdSetting voltage for the DC bus of the device, U is the amplitude of AC side phase voltage, I is the amplitude of AC output side phase current, Iz2Amplitude of secondary quantity of circulating current, α0Is the initial phase angle of the AC voltage, α2Is the initial phase angle of the secondary quantity of the circulating current,is the ac load power factor;
let P be PsmObtaining u in the formula (1)cThe amplitude and the initial phase angle of u can be controlled3And u4Output the desired voltage uc1And uc2
Wherein the instruction calculation method of the device has no substantial difference from the prior art (u in the divisor module)3And u4Control of (c).
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (1)

1. The utility model provides a flexible DC device of high pressure of electric capacity reduction which characterized in that: the bridge arm A is formed by serially connecting an upper bridge arm and a lower bridge arm, the upper bridge arm is formed by serially connecting a plurality of half-bridge sub-modules end to end in sequence, the lower bridge arm is identical to the upper bridge arm in structure, and two buffer inductors L are serially connected between the upper bridge arm and the lower bridge armmTwo said buffer inductors LmA point of concatenation betweenThe bridge arm A, the bridge arm B and the bridge arm C are connected in parallel to form a bridge arm A;
the alternating current output end and the direct current output end are respectively connected with a direct current end and an alternating current end of high-voltage flexible direct current transmission;
the upper bridge arm and the lower bridge arm are formed by connecting half-bridge sub-modules in series end to end, wherein the half-bridge sub-modules are the same in number;
the half-bridge submodule comprises three sub-bridge arms, wherein power switches S1 and S2 are connected in series to form a first sub-bridge arm, and a power switch u3And u4The energy storage capacitor bridge comprises a first sub bridge arm, a second sub bridge arm, two identical capacitors and an energy storage inductor, wherein the first sub bridge arm and the second sub bridge arm are connected in series to form the first sub bridge arm;
the power switches S1, S2, u3And u4All the power switches are power switches with uniform models, and each power switch consists of a full-control device and an anti-parallel diode;
the working principle of the half-bridge submodule is as follows, and the control target is as follows:
Vsmis a set value of the DC voltage of the half-bridge submodule ucIs the traffic, omega0Is the fundamental angular frequency, i.e., the grid frequency,is the initial phase angle of the capacitor voltage;
according to the formula (1), the DC side voltage of the half-bridge submodule is VsmI.e. no voltage fluctuations, which is determined by the following relationship:
ic1=ic2+iL(2)
ic1,ic2currents of upper and lower two capacitors, iLIs the energy storage inductive current;
the power of the half-bridge sub-modules is then:
let PsmThe actual pulse power of the half-bridge submodule is equal to that of the submodule, and the direct-current side voltage of the submodule is VsmThereby suppressing low frequency voltage ripple;
actual ripple power of half-bridge sub-modules:
wherein, UdSetting voltage for the DC bus of the device, U is the amplitude of AC side phase voltage, I is the amplitude of AC output side phase current, Iz2Amplitude of secondary quantity of circulating current, α0Is the initial phase angle of the AC voltage, α2Is the initial phase angle of the secondary quantity of the circulating current,is the ac load power factor;
let P equal to Psm, find u in formula (1)cThe amplitude and the initial phase angle of u can be controlled3And u4Output the desired voltage uc1And uc2
CN201910253065.XA 2019-03-29 2019-03-29 High-voltage flexible direct-current device with reduced capacitance Active CN110061645B (en)

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CN111682575B (en) * 2020-06-22 2021-11-30 哈尔滨工业大学(深圳)(哈尔滨工业大学深圳科技创新研究院) Three-phase series CA-MMC (capacitor-multilevel converter) with voltage-stabilizing capacitor bridge arm in flexible direct current transmission system and system
CN111682576B (en) * 2020-06-22 2022-02-15 哈尔滨工业大学(深圳)(哈尔滨工业大学深圳科技创新研究院) Three-phase series CA-MMC (CA-Modular multilevel converter) with direct-current fault ride-through capability in flexible direct-current power transmission system and system

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