CN112615551A - MMC type medium voltage power supply quality comprehensive improving system - Google Patents
MMC type medium voltage power supply quality comprehensive improving system Download PDFInfo
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- CN112615551A CN112615551A CN202011448579.XA CN202011448579A CN112615551A CN 112615551 A CN112615551 A CN 112615551A CN 202011448579 A CN202011448579 A CN 202011448579A CN 112615551 A CN112615551 A CN 112615551A
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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
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
- H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
- H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
- H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
- H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/007—Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources
- H02J3/0073—Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources for providing alternative feeding paths between load and source when the main path fails, e.g. transformers, busbars
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/01—Arrangements for reducing harmonics or ripples
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/10—Flexible AC transmission systems [FACTS]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/40—Arrangements for reducing harmonics
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Abstract
The invention provides an MMC type medium-voltage power supply quality comprehensive improvement system which comprises an alternating current power grid access end, a load access end, an input switch, an output switch, a bypass switch, a phase-shifting transformer, m three-phase rectifiers, m energy storage devices and an MMC current converter. The input switch is connected between the AC power grid access end and the primary three-phase winding of the high-voltage side of the phase-shifting transformer, and the m secondary three-phase winding output ends of the low-voltage side of the phase-shifting transformer are respectively connected with the AC input ends of the m three-phase rectifiers in a one-to-one correspondence manner; the direct current output ends of the m three-phase rectifiers are connected in a cascading mode and are connected to the positive pole and the negative pole of the direct current end of the MMC converter, and the direct current ends of the m three-phase rectifiers are further connected with the ports of the m energy storage devices in parallel correspondingly. The invention can ensure high-capacity user high-reliability power supply, greatly reduce the number of secondary windings, three-phase rectifiers and energy storage devices of the phase-shifting transformer, and save the system volume and the cost.
Description
Technical Field
The invention relates to the technical field of power transmission and distribution of a power system, in particular to an MMC type medium-voltage power supply quality comprehensive improvement system.
Background
Under the great trend of global industrial automation production, the rapid development of a high-power supply quality comprehensive improvement system is promoted by the increasing load of a power system and the requirement of high power quality for operation of the power system. The traditional high-power supply quality comprehensive improvement system usually adopts a six-pulse wave rectification mode at the input end of a power grid, so that the problem of power harmonic pollution is brought to the power grid side, and the multiple-pulse wave rectification of a phase-shifting transformer can effectively solve the problem, wherein the cascaded H-bridge type medium-voltage UPS system containing the phase-shifting transformer is widely concerned with the advantages of small grid side harmonic, high modularization degree, large system capacity, good redundancy characteristic and the like.
The cascaded H-bridge type medium-voltage UPS topology with the phase-shifting transformer mainly comprises an input/output switch, a bypass switch, the phase-shifting transformer, a three-phase rectifier, an energy storage device and a three-phase cascaded H bridge, wherein each secondary winding of the phase-shifting transformer forms direct-current voltage input of each submodule of the cascaded H bridge after three-phase rectification, and a phase unit is formed by cascading each submodule to output three-phase load voltage. The medium-voltage UPS can increase the voltage grade to the medium voltage without a step-up transformer for each phase alternating current output, effectively increases the capacity of a single module, avoids the problem of current and voltage sharing caused by parallel connection of multiple units, and is suitable for application scenes with medium-voltage and large capacity. However, the direct-current voltage input of each sub-module in the three-phase cascade H-bridge needs a secondary winding of the phase-shifting transformer, a three-phase rectifier and an energy storage device, which not only causes the secondary winding of the phase-shifting transformer, the three-phase rectifier and the energy storage device to be numerous, but also causes the large volume, the high cost and the complex system control. In addition, in order to minimize the output voltage harmonic at the load end, the number of cascaded H-bridge submodules needs to be significantly increased, that is, the number of secondary windings, three-phase rectifiers and energy storage devices of the phase-shifting transformer is correspondingly significantly increased, so that the above disadvantages are increasingly highlighted. In particular, the requirements on the manufacturing process of the secondary winding of the phase-shifting transformer are increased, and the use of important users with high requirements on the quality of electric energy is increasingly limited.
The existing medium-voltage UPS system has certain contradiction problems in the aspects of system voltage output characteristics, module utilization efficiency, economy and the like, and along with the increasing of the load capacity of important users and the increasing of the requirement of electric energy quality, the production cost of the cascaded H-bridge type medium-voltage UPS containing the phase-shifting transformer is remarkably increased, and meanwhile, the performance improvement effect is not obvious. The power supply system aims to solve the problem of safe and reliable power supply of large-capacity important users and simultaneously give consideration to economic benefits, and provides higher and higher challenges for the power supply quality comprehensive improvement system.
Disclosure of Invention
In order to solve the technical problems of the existing power supply quality comprehensive lifting system, the invention provides an MMC type medium-voltage power supply quality comprehensive lifting system, which adopts the steps that after the direct-current ends of three-phase rectifiers connected with each secondary winding of a phase-shifting transformer are connected in a cascading mode to lift the voltage level of the direct-current ends, the voltage of the direct-current ends is output to stable three-phase alternating-current voltage of a load end through an MMC converter; by the design of the topological structure, the number of secondary windings, three-phase rectifiers and energy storage devices of the phase-shifting transformer can be greatly reduced while high-reliability power supply of a high-capacity user is ensured, the system volume and cost are saved, the modularization degree is higher, the system reliability is improved, the MMC current converter can be independently designed according to the electric energy quality requirement of an important user, and the expandability is high.
The technical scheme for realizing the functions is as follows:
an MMC type medium-voltage power supply quality comprehensive improvement system comprises an alternating current power grid access end, a load access end, an input switch, an output switch, a bypass switch, a phase-shifting transformer, m three-phase rectifiers, m energy storage devices and an MMC current converter, wherein,
the first port of the input switch is connected to the alternating current power grid access end, and the second port of the input switch is connected to a primary three-phase winding on the high-voltage side of the phase-shifting transformer;
the low-voltage side of the phase-shifting transformer comprises m secondary three-phase windings, and the output ends of the m secondary three-phase windings on the low-voltage side of the phase-shifting transformer are respectively connected with the alternating current input ends of the m three-phase rectifiers in a one-to-one correspondence manner;
the direct current output ends of the m three-phase rectifiers are connected in a cascading mode to improve the voltage level of the direct current end and are connected to the positive pole and the negative pole of the direct current end of the MMC current converter;
the anodes of the direct current output ends of the m three-phase rectifiers are respectively connected with the anodes of the m energy storage devices in a one-to-one correspondence manner, and the cathodes of the direct current output ends of the m three-phase rectifiers are respectively connected with the cathodes of the m energy storage devices in a one-to-one correspondence manner;
the alternating current end of the MMC converter is connected to a first port of an output switch, and a second port of the output switch is connected to a load access end;
the first port of the bypass switch is connected to the alternating current power grid access end, and the second port of the bypass switch is connected to the load access end.
Further, m direct current output ends of the three-phase rectifier are connected in a cascading mode to improve the voltage level of the direct current end and are connected to the positive pole and the negative pole of the direct current end of the MMC current converter, and the method specifically comprises the following steps:
the positive pole of the direct current output end of the three-phase rectifier is connected with the positive pole of the direct current end of the MMC converter, the negative pole of the direct current output end of the three-phase rectifier is connected with the positive pole of the direct current output end of the three-phase rectifier, other three-phase rectifiers are sequentially connected according to the connection method, the negative pole of the direct current output end of the three-phase rectifier m-1 is connected with the positive pole of the direct current output end of the three-phase rectifier m, and the negative pole of the direct current output end of the three-phase rectifier m is connected with the negative pole.
Furthermore, a primary three-phase winding on the high-voltage side of the phase-shifting transformer is in star connection or delta connection; the low-voltage side of the phase-shifting transformer comprises m secondary three-phase windings, the m secondary three-phase windings adopt an extended connection mode of extending triangular phase shifting, the extended connection mode comprises a forward connection mode and a backward connection mode, the voltage of a secondary winding wire can lead or lag the voltage of a primary winding wire by any angle within a range of 0-30 degrees, and the number of the secondary three-phase windings is selected according to the voltage grade of the direct-current end of the MMC current converter, the phase-shifting pulse wave number requirement of the phase-shifting transformer and the manufacturing process feasibility of the secondary three-phase windings of the phase-shifting transformer.
Furthermore, the topology of the three-phase rectifier is a bridge circuit structure or a zero-type circuit structure, and according to the formed semiconductor switch device, the m three-phase rectifiers are one or a combination of a three-phase uncontrolled rectifier, a three-phase half-controlled rectifier and a three-phase fully-controlled rectifier.
Furthermore, the energy storage device is composed of a DC-DC converter and an energy storage battery, a port of the energy storage device includes an output end anode of the energy storage device and an output end cathode of the energy storage device, the output end anode of the energy storage device is a high-voltage end anode of the DC-DC converter, the output end cathode of the energy storage device is a high-voltage end cathode of the DC-DC converter, the low-voltage end anode of the DC-DC converter is connected with the anode of the energy storage battery, and the low-voltage end cathode of the DC-DC converter is connected with the cathode of the energy storage battery.
Further, the DC-DC converter adopts a non-isolated DC-DC converter or an isolated DC-DC converter, wherein the non-isolated DC-DC converter is a Buck/Boost, Cuk or Zeta topology; the converters at two ends of the isolation transformer in the isolation type DC-DC converter are in a half-bridge type, full-bridge type or mixed topology.
Furthermore, the energy storage battery adopts a combination conversion form of series connection, parallel connection or series connection and parallel connection of a plurality of energy storage battery units, the capacity of the energy storage battery is selected according to the capacity of the piezoelectric energy quality comprehensive improvement system and the number of the energy storage devices, and a certain margin is reserved.
Further, the MMC transverter comprises six bridge arms, and the bridge arm port contains the crossing stream port of MMC transverter direct current end positive pole, MMC transverter direct current end negative pole, MMC transverter A, the crossing stream port of MMC transverter B and the crossing stream port of MMC transverter C, six bridge arms of MMC transverter are constituteed by a N cascaded submodule pieces and a series reactance, the submodule piece is the half-bridge submodule piece, perhaps is the self-resistance submodule piece, perhaps is the full-bridge submodule piece, perhaps for the clamp gemini module, perhaps is the mixed form of above-mentioned multiple type submodule piece.
Further, the input switch, the output switch and the bypass switch are three-phase switches, the three-phase switches are three-phase linkage switches or split-phase operation switches, and the three-phase switches are circuit breakers or contactors.
Further, a first port of the bypass switch is connected to the first ac grid incoming end or to the second ac grid incoming end, and a second port of the bypass switch is connected to the load incoming end, where the first ac grid incoming end is the ac grid incoming end to which the first port of the input switch is connected, and the second ac grid incoming end is another three-phase power supply.
In general, compared with the prior art, the above contents of the present invention can achieve the following beneficial effects:
1. the MMC type medium-voltage power supply quality comprehensive improving system is designed through a topological structure, namely, after the direct-current end of a three-phase rectifier connected with each secondary winding in a phase-shifting transformer improves the direct-current voltage grade in a cascading mode, the direct-current end of each three-phase rectifier is connected to the positive pole and the negative pole of a direct-current end of an MMC current converter, the direct-current end of each three-phase rectifier is correspondingly connected with an energy storage device in parallel, and the MMC current converter is adopted to output the cascaded direct-current voltage into stable and reliable load three-phase alternating-current voltage. Compared with the cascaded H-bridge type medium-voltage UPS containing the phase-shifting transformer in the prior art, under the condition that the phase-shifting transformer realizes the same pulse wave multiplexing rectification mode, the number of the secondary winding, the three-phase rectifier and the energy storage device of the phase-shifting transformer is reduced by two times, the system volume and the production cost are greatly saved, the modularization degree is higher, and the system reliability is improved;
2. the MMC type medium-voltage power supply quality comprehensive improving system does not have the strong association phenomenon that the number of cascaded H bridge submodules is equal to the number of secondary windings of the phase-shifting transformer in the prior art through the improvement of the topological structure 1), and solves the problem that the step number of the voltage waveform of the cascaded output load is limited by the number of the secondary windings of the phase-shifting transformer, which is caused by the phenomenon. In order to ensure the realization of the DC end voltage of the MMC converter required by the invention, the output voltage of a single three-phase rectifier can be independently designed according to the number of secondary windings, and in order to meet the special requirements of important users on the electric energy quality, the number of each bridge arm submodule in the MMC converter can be independently designed, so that the output voltage harmonic wave of a load end of the user is effectively reduced, and the load voltage with higher electric energy quality requirements can be output;
3. the number of the energy storage devices required by the MMC type medium-voltage power supply quality comprehensive improving system is equal to that of the secondary windings of the phase-shifting transformer, the number of the energy storage devices is small, the management of the energy storage devices is optimized, the system loss is small, and the energy storage control strategy simplification effect is obvious;
4. the single-machine capacity and voltage grade requirements of the MMC type medium-voltage power supply quality comprehensive improvement system can be independently designed according to the capacities of the MMC converter and the three-phase rectifier and the voltage sum of the direct current end of the cascaded MMC converter, the system has strong expandability, and the topological limitation conditions of the system on single-machine capacity increase and load end output voltage electric energy quality improvement are less through the advantages of the 1), the 2) and the 3).
Drawings
FIG. 1 is a schematic diagram of a prior art cascaded H-bridge type medium voltage UPS topology with phase shifting transformers;
FIG. 2 is a schematic diagram of a power unit in a cascaded medium-voltage UPS topology based on a phase-shifting transformer in the prior art;
fig. 3 is a schematic structural diagram of an MMC medium-voltage power supply quality integrated improvement system according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a primary winding of a phase-shifting transformer in an MMC type medium-voltage power supply quality integrated lifting system according to an embodiment of the present invention in a star connection manner;
fig. 5 is a schematic diagram of an MMC medium-voltage power supply quality comprehensive improvement system according to an embodiment of the present invention, in which a three-phase rectifier is an uncontrolled rectification mode;
fig. 6 is a schematic structural diagram of an energy storage device in an MMC medium-voltage power supply quality integrated lifting system according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a half-bridge sub-module topology;
FIG. 8 is a schematic topology diagram of a full bridge sub-module with fault self-clearing and negative level output capability;
FIG. 9 is a schematic diagram of a self-blocking sub-module topology with fault self-clearing capability;
FIG. 10 is a topology of a clamped dual submodule with fault self clearing capability;
fig. 11 is a schematic diagram of a first port of a bypass switch in an MMC medium-type medium-voltage power supply quality integrated lifting system according to another embodiment of the present invention being connected to a second ac power grid.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
Fig. 1 is a schematic diagram of a cascaded H-bridge type medium voltage UPS topology including a phase-shifting transformer in the prior art, and fig. 2 is a schematic diagram of a power unit structure of the medium voltage UPS, where the medium voltage UPS topology mainly includes an ac grid connection terminal 11, a load connection terminal 12, an input switch 13, an output switch 14, a bypass switch 15, a phase-shifting transformer 16, an a-phase power unit combination 17, a B-phase power unit combination 18, and a C-phase power unit combination 19, the three-phase power unit combinations 17, 18, and 19 are all composed of n power units 2, and the power unit 2 is composed of a three-phase rectifier 21, an energy storage device 22, and an H-bridge submodule 23 (as shown in fig. 2).
The input switch 13 is connected between the three-phase ac power grid access end 11 and a primary three-phase winding at the high-voltage side of the phase-shifting transformer 16, and a plurality of secondary three-phase windings at the low-voltage side of the phase-shifting transformer 16 are respectively connected with the input ends of 3n power units 2 in the three-phase power unit combinations 17, 18 and 19 in a one-to-one correspondence manner; the input end of the power unit 2 is the alternating current input end of the three-phase rectifier 21, the direct current output end of the three-phase rectifier 21 is sequentially connected with the direct current end of the H-bridge submodule 23 and the direct current end of the energy storage device 22, and the output end of the H-bridge submodule 23 is the output end of the power unit 2; the n power units 2 form a first output end and a second output end of the three-phase power unit combination 17, 18 and 19 through the output end cascade connection of the H bridge submodule 23; first output terminals of the three-phase power cell combinations 17, 18 and 19 are connected together, second output terminals of the three-phase power cell combinations 17, 18 and 19 are connected to the load access terminal 12 through the output switch 13, and the bypass switch 15 is connected between the ac grid access terminal 11 and the load access terminal 12.
It can be seen that each secondary winding of the phase-shifting transformer 16 forms a dc voltage input of each H-bridge submodule 23 after three-phase rectification, and forms a phase unit by cascading n H-bridge submodules 23 in each phase power unit combination, thereby outputting a three-phase load voltage. According to the medium-voltage UPS, the voltage grade can be increased to the medium voltage by the cascade mode of the n H-bridge submodules 23 without a step-up transformer in the output of each phase alternating current, the capacity of a single machine is effectively increased, and the problems of current equalization and voltage equalization caused by parallel connection of multiple machines are solved. However, the direct-current voltage input of each H-bridge sub-module 23 of the three-phase cascade connection needs a secondary winding of the phase-shifting transformer 16, a three-phase rectifier 21 and an energy storage device 22, that is, the secondary windings of the 3n phase-shifting transformers 16, the three-phase rectifier 21 and the energy storage device 22 are needed, which not only results in a large number of modules, a large system volume, high cost and complex system control, but also results in the number of secondary windings, three-phase rectifiers 21 and energy storage devices 22 of the phase-shifting transformer 16 being further increased because the output voltage harmonics at the load end are as small as possible, and the number of the cascaded H-bridge sub-modules 23 needs to be significantly increased, which brings about the above disadvantages to be. In particular, the requirements on the manufacturing process of the secondary winding of the phase-shifting transformer 16 are increased, and the use of important users with high requirements on the quality of electric energy is limited.
Fig. 3 is a schematic structural diagram of an MMC medium-voltage power supply quality comprehensive improvement system according to an embodiment of the present invention, where a system topology mainly includes an ac power grid access end 31, a load access end 32, an input switch 33, an output switch 34, a bypass switch 35, a phase-shifting transformer 36, m three-phase rectifiers 37, m energy storage devices 38, and an MMC converter 39, where:
a first port of the input switch 33 is connected to the ac power grid access terminal 31, and a second port of the input switch 33 is connected to a primary three-phase winding on the high-voltage side of the phase-shifting transformer 36; the low-voltage side of the phase-shifting transformer 36 comprises m secondary three-phase windings, and the output ends of the m secondary three-phase windings on the low-voltage side of the phase-shifting transformer 36 are respectively connected with the alternating-current input ends of the m three-phase rectifiers 37 in a one-to-one correspondence manner; the m dc output terminals of the three-phase rectifiers 37 are connected in a cascade manner to increase the dc voltage level, and are connected to the positive and negative terminals of the dc terminal of the MMC converter 39, that is, the positive terminal of the dc output terminal of the three-phase rectifier 1 is connected to the positive terminal of the dc terminal of the MMC converter 39, the negative terminal of the dc output terminal of the three-phase rectifier 1 is connected to the positive terminal of the dc output terminal of the three-phase rectifier 2, and according to the above connection method, the other three-phase rectifiers are connected in sequence, the negative terminal of the dc output terminal of the dc-to-three-phase rectifier m-1 is connected to the positive terminal of the dc output terminal of the three-phase rectifier m, and the negative terminal of the dc output terminal of the three.
The phase-shifting angles of the m secondary three-phase windings on the low-voltage side of the phase-shifting transformer 36 can be different, and the phase-shifting angle intervals are designed at equal intervals according to the number of the secondary three-phase windings in the range of the total phase-shifting angle; the phase shift angles of the m secondary three-phase windings can also be partially the same, and in the range of the total phase shift angle, the phase shift angle interval is designed at equal intervals according to the number of the secondary three-phase windings with different phase shift angles.
The anodes of the direct current output ends of the m three-phase rectifiers 37 are respectively connected with the anodes of the m energy storage devices 38 in a one-to-one correspondence manner, and the cathodes of the direct current output ends of the m three-phase rectifiers 37 are respectively connected with the cathodes of the m energy storage devices 38 in a one-to-one correspondence manner; the ac terminal of the MMC inverter 39 is connected to a first port of the output switch 34, and a second port of the output switch 34 is connected to the load access terminal 32; a first port of the bypass switch 35 is connected to the ac grid input 31 and a second port of the bypass switch 35 is connected to the load input 32.
The MMC current converter 39 is composed of six bridge arms, and includes an MMC current converter dc end positive electrode 391, an MMC current converter dc end negative electrode 392, an MMC current converter a cross current port 393, an MMC current converter B cross current port 394 and an MMC current converter C alternating current port 395, each two of the bridge arms are respectively connected through a bridge arm port to form a phase unit, for example, the bridge arm 396 and the bridge arm 397 in fig. 3 are connected to form a phase unit, the six bridge arms form three phase units, and through the connection, the three phase units each include a first port and a second port; the three phase units are connected through first ports to form an MMC converter direct-current end anode 391, the three phase units are connected through second ports to form an MMC converter direct-current end cathode 392, the MMC converter direct-current end anode 391 and the MMC converter direct-current end cathode 392 are respectively connected with a direct-current end anode and a direct-current end cathode formed by direct-current ends of m cascaded three-phase rectifiers 37, and bridge arm port connection points of the three phase units are MMC converter three-phase alternating-current output ports 393, 394 and 395.
The MMC type medium voltage power supply quality comprehensive improvement system provided by the embodiment of the invention adopts the steps that after the direct current ends of the three-phase rectifier 37 connected with each secondary winding of the phase-shifting transformer 36 are connected in a cascading mode to improve the voltage level of the direct current ends, the voltage of the direct current ends is output to stable load-end three-phase alternating current voltage through the MMC current converter 39. The topology can guarantee that high-capacity users can supply power with high reliability, and the numbers of the secondary winding of the phase-shifting transformer 36, the three-phase rectifier 37 and the energy storage device 38 are m, compared with a cascaded H-bridge type medium-voltage UPS containing the phase-shifting transformer in the prior art, under the condition that the phase-shifting transformer 36 realizes the same pulse wave multiplexing rectification mode, the numbers of the secondary winding of the phase-shifting transformer 36, the three-phase rectifier 37 and the energy storage device 38 are reduced by two times, the system volume and the cost are greatly saved, the modularization degree is higher, and the system reliability is improved. On the other hand, the invention does not have the strong association phenomenon that the number of the cascaded H bridge submodules of the power unit 2 is equal to the number of the secondary windings of the phase-shifting transformer 36 in the prior art, and solves the problem that the number of the cascade output load voltage waveform steps is limited by the number of the secondary windings of the phase-shifting transformer 36 caused by the phenomenon. Further, in the invention, the direct-current terminal voltage of the MMC converter 39 can be independently designed for the output voltage of a single three-phase rectifier 37 according to the number of secondary windings, and the number of each bridge arm submodule in the MMC converter 39 can be independently designed for meeting the special requirements of important users on the electric energy quality, thereby effectively reducing the output voltage harmonic waves of a user load terminal.
Fig. 4 is a schematic diagram illustrating a primary winding of a phase-shifting transformer in an MMC medium-voltage power supply quality integrated lifting system according to an embodiment of the present invention in a star connection manner, wherein a high-voltage side of the phase-shifting transformer 4 is a primary three-phase winding 40, and the primary three-phase winding 40 is selectively connected in a star connection manner; the low-voltage side of the phase-shifting transformer 4 comprises m secondary three-phase windings (41, 42, … … and 4m), the m secondary three-phase windings adopt an extended connection mode of extended triangular phase shifting, the extended connection mode comprises a forward connection mode and a backward connection mode, and the voltage of the secondary winding wire can lead or lag the voltage of the primary winding wire by any angle within a range of 0-30 degrees; the number of the secondary three-phase windings can be selected according to the voltage level of the direct-current end of the MMC current converter, the requirement of the phase-shifted pulse wave number and the feasibility of the manufacturing process of the phase-shifted transformer 4.
Fig. 5 is a schematic diagram of an uncontrolled rectification mode of a three-phase rectifier in an MMC medium-voltage power supply quality comprehensive improvement system according to an embodiment of the present invention, where the three-phase uncontrolled rectifier 5 includes a three-phase uncontrolled rectifier bridge 51, a voltage stabilizing capacitor 52, and a discharge resistor 53, and includes an ac input terminal of the three-phase uncontrolled rectifier, a positive terminal of a dc output terminal of the three-phase uncontrolled rectifier, and a negative terminal of the dc output terminal of the three-phase uncontrolled rectifier, and the voltage stabilizing capacitor 52 and the discharge resistor 53 are both connected in parallel to the dc output terminal of the three-phase uncontrolled rectifier.
Fig. 6 is a schematic diagram of an energy storage device in an MMC type medium-voltage power supply quality comprehensive improvement system provided by the present invention, where the energy storage device 6 is composed of an energy storage battery 61 and a DC-DC converter 62, a port of the energy storage device 6 includes an output-end positive electrode of the energy storage device and an output-end negative electrode of the energy storage device, a low-voltage-end positive electrode of the DC-DC converter 62 is connected to a positive electrode of the energy storage battery 61, a low-voltage-end negative electrode of the DC-DC converter 62 is connected to a negative electrode of the energy storage battery 61, a high-voltage-end positive electrode of the DC-DC converter 62 is an output-end positive electrode of the energy storage device 6, and a high-voltage-end negative electrode of the DC-DC converter 62 is an. The DC-DC converter 62 may be selected based on the ratio of the voltage of the energy storage battery 61 to the voltage of the three-phase rectifier, and system requirements.
Six bridge arms of the MMC current converter 39 are composed of N Sub-modules (SM) and a series reactor, the N Sub-modules of the six bridge arms may all be half-bridge Sub-modules, or all be self-resistance Sub-modules, or all be full-bridge Sub-modules, or all be clamping Sub-modules, or be a mixture of the above types of Sub-modules, and the Sub-modules may be formed by connecting a plurality of Sub-modules in parallel according to the requirement of the invention for comprehensively improving the system capacity by piezoelectric energy quality, so as to improve the rated working current of the system.
Fig. 7, 8, 9, and 10 show topologies of a half-bridge sub-module, a full-bridge sub-module with self-clearing and negative level output capabilities, a self-resistance sub-module with self-clearing and self-clearing capabilities, and a clamping sub-module with self-clearing capabilities, which can be used as sub-modules of six arms of the MMC current converter, further, a sub-module of each arm of the six arms of the MMC current converter 39 can be a mixed form of the above sub-modules, and the sub-modules can be formed by connecting a plurality of sub-modules in parallel according to the requirement of the system capacity of the present invention, so as to increase the rated operating current of the system.
Fig. 11 is a schematic diagram of a MMC medium-voltage power supply quality integrated boost system according to another embodiment of the present invention, in which a first port of a bypass switch is connected to a second ac power grid, a system topology mainly includes a first ac power grid access terminal 31, a load access terminal 32, an input switch 33, an output switch 34, a bypass switch 35, a phase-shifting transformer 36, m three-phase rectifiers 37, m energy storage devices 38, an MMC converter 39, a second ac power grid access terminal 111,
a first port of the input switch 33 is connected to the first ac grid inlet 31, and a second port of the input switch 33 is connected to a primary three-phase winding on the high-voltage side of the phase-shifting transformer 36; the low-voltage side of the phase-shifting transformer 36 comprises m secondary three-phase windings, and the output ends of the m secondary three-phase windings on the low-voltage side of the phase-shifting transformer 36 are respectively connected with the alternating-current input ends of the m three-phase rectifiers 37 in a one-to-one correspondence manner; the direct current output ends of the m three-phase rectifiers 37 are connected in a cascading manner to improve the direct current end voltage level and are connected to the positive pole and the negative pole of the direct current end of the MMC converter 39, namely, the positive pole of the direct current output end of the three-phase rectifier 1 is connected with the positive pole of the direct current end of the MMC converter 39, the negative pole of the direct current output end of the three-phase rectifier 1 is connected with the positive pole of the direct current output end of the three-phase rectifier 2, the other three-phase rectifiers are sequentially connected according to the connection method, the negative pole of the direct current output end of the direct current-to-three-phase rectifier m-1 is connected with the positive pole of the direct current output end of the three-phase rectifier m, and the negative pole of; the anodes of the direct current output ends of the m three-phase rectifiers 37 are respectively connected with the anodes of the m energy storage devices 38 in a one-to-one correspondence manner, and the cathodes of the direct current output ends of the m three-phase rectifiers 37 are respectively connected with the cathodes of the m energy storage devices 38 in a one-to-one correspondence manner; the alternating current end of the MMC inverter 39 is connected to a first port of the output switch, and a second port of the output switch 34 is connected to the load access end 32;
a first port of the bypass switch 35 is connected to the second ac grid input 111 and a second port of the bypass switch 35 is connected to the load input 32. When the system is in a fault or is periodically maintained, in order to ensure uninterrupted power supply of an important load, the system is switched to supply power from the first port of the bypass switch 35 to the second alternating current grid access end 111, namely, the electric energy of the second alternating current grid directly supplies power to the load through the bypass switch 35, the second alternating current grid access end 111 serves as another power supply source of the important load and can be a power supply source with higher power supply quality, when the piezoelectric energy quality comprehensive lifting system is in a fault or is periodically maintained, the important load is switched to the another three-phase power supply source through the bypass switch 35 to supply power, more stable and reliable power is provided for the important load, and safe and stable operation of the load is ensured.
The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. An MMC type medium-voltage power supply quality comprehensive improvement system is characterized by comprising an alternating current power grid access end, a load access end, an input switch, an output switch, a bypass switch, a phase-shifting transformer, m three-phase rectifiers, m energy storage devices and an MMC current converter, wherein,
the first port of the input switch is connected to the alternating current power grid access end, and the second port of the input switch is connected to a primary three-phase winding on the high-voltage side of the phase-shifting transformer;
the low-voltage side of the phase-shifting transformer comprises m secondary three-phase windings, and the output ends of the m secondary three-phase windings on the low-voltage side of the phase-shifting transformer are respectively connected with the alternating current input ends of the m three-phase rectifiers in a one-to-one correspondence manner;
the direct current output ends of the m three-phase rectifiers are connected in a cascading mode to improve the voltage level of the direct current end and are connected to the positive pole and the negative pole of the direct current end of the MMC current converter;
the anodes of the direct current output ends of the m three-phase rectifiers are respectively connected with the anodes of the m energy storage devices in a one-to-one correspondence manner, and the cathodes of the direct current output ends of the m three-phase rectifiers are respectively connected with the cathodes of the m energy storage devices in a one-to-one correspondence manner;
the alternating current end of the MMC converter is connected to a first port of an output switch, and a second port of the output switch is connected to a load access end;
the first port of the bypass switch is connected to the alternating current power grid access end, and the second port of the bypass switch is connected to the load access end.
2. The MMC type medium voltage power supply quality comprehensive improvement system of claim 1, wherein the direct current output ends of the m three-phase rectifiers are connected in a cascading manner to improve the voltage level of the direct current end and are connected to the positive pole and the negative pole of the direct current end of the MMC current converter, specifically:
the positive pole of the direct current output end of the three-phase rectifier is connected with the positive pole of the direct current end of the MMC converter, the negative pole of the direct current output end of the three-phase rectifier is connected with the positive pole of the direct current output end of the three-phase rectifier, other three-phase rectifiers are sequentially connected according to the connection method, the negative pole of the direct current output end of the three-phase rectifier m-1 is connected with the positive pole of the direct current output end of the three-phase rectifier m, and the negative pole of the direct current output end of the three-phase rectifier m is connected with the negative pole.
3. The MMC type medium voltage power supply quality comprehensive improvement system of claim 1, wherein a primary three-phase winding of a high voltage side of the phase-shifting transformer is star-connected or delta-connected; the low-voltage side of the phase-shifting transformer comprises m secondary three-phase windings, the m secondary three-phase windings adopt an extended connection mode of extending triangular phase shifting, the extended connection mode comprises a forward connection mode and a backward connection mode, the voltage of a secondary winding wire can lead or lag the voltage of a primary winding wire by any angle within a range of 0-30 degrees, and the number of the secondary three-phase windings is selected according to the voltage grade of the direct-current end of the MMC current converter, the phase-shifting pulse wave number requirement of the phase-shifting transformer and the manufacturing process feasibility of the secondary three-phase windings of the phase-shifting transformer.
4. The MMC medium voltage power supply quality comprehensive improvement system of claim 1 or 2, wherein the topology of the three-phase rectifiers is a bridge circuit structure or a zero circuit structure, and according to the composed semiconductor switch devices, the m three-phase rectifiers are one or a combination of a three-phase uncontrolled rectifier, a three-phase half-controlled rectifier and a three-phase full-controlled rectifier.
5. The MMC type medium voltage power supply quality comprehensive improvement system of claim 1 or 2, wherein the energy storage device is composed of a DC-DC converter and an energy storage battery, the port of the energy storage device comprises an output end anode of the energy storage device and an output end cathode of the energy storage device, the output end anode of the energy storage device is a high voltage end anode of the DC-DC converter, the output end cathode of the energy storage device is a high voltage end cathode of the DC-DC converter, the low voltage end anode of the DC-DC converter is connected with the anode of the energy storage battery, and the low voltage end cathode of the DC-DC converter is connected with the cathode of the energy storage battery.
6. The MMC type medium voltage power supply quality comprehensive improvement system of claim 5, wherein the DC-DC converter is a non-isolated DC-DC converter or an isolated DC-DC converter, wherein the non-isolated DC-DC converter is a Buck/Boost, Cuk or Zeta topology; the converters at two ends of the isolation transformer in the isolation type DC-DC converter are in a half-bridge type, full-bridge type or mixed topology.
7. The MMC type medium voltage power supply quality comprehensive improvement system of claim 5, wherein the energy storage battery adopts a plurality of energy storage battery units in series connection, or in parallel connection, or in a combination transformation form of series connection and parallel connection, the capacity of the energy storage battery is selected according to the capacity of the piezoelectric energy quality comprehensive improvement system and the number of energy storage devices, and a certain margin is left.
8. The MMC type medium voltage power supply quality comprehensive improvement system of claim 1, characterized in that, the MMC transverter comprises six bridge arms, the bridge arm port contains the positive pole of the direct current end of the MMC transverter, the negative pole of the direct current end of the MMC transverter, the cross current port of the MMC transverter A, the cross current port of the MMC transverter B and the cross current port of the MMC transverter C, the six bridge arms of the MMC transverter are composed of N cascaded submodules and a series reactance, the submodules are half-bridge submodules, self-resistance submodules, full-bridge submodules or clamping bimodules, or a mixed form of the above-mentioned various submodul.
9. A medium voltage power supply quality integrated boosting system according to the MMC type of claim 1, characterized in that the input, output and bypass switches are three-phase switches, which are either three-phase ganged switches or phase-split operating switches, which are either circuit breakers or contactors.
10. The MMC type medium voltage power supply quality integrated lifting system of claim 1, wherein a first port of the bypass switch is connected to a first AC grid access terminal or a second AC grid access terminal, and a second port of the bypass switch is connected to a load access terminal, wherein the first AC grid access terminal is an AC grid access terminal to which the first port of the input switch is connected, and the second AC grid access terminal is another three-phase power supply.
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| Publication number | Priority date | Publication date | Assignee | Title |
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