CN115189341B - Full direct current power system - Google Patents
Full direct current power system Download PDFInfo
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- CN115189341B CN115189341B CN202211099210.1A CN202211099210A CN115189341B CN 115189341 B CN115189341 B CN 115189341B CN 202211099210 A CN202211099210 A CN 202211099210A CN 115189341 B CN115189341 B CN 115189341B
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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
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/10—Parallel operation of dc sources
- H02J1/102—Parallel operation of dc sources being switching converters
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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
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/10—Parallel operation of dc sources
- H02J1/106—Parallel operation of dc sources for load balancing, symmetrisation, or sharing
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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
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/14—Balancing the load in a network
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/40—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation wherein a plurality of decentralised, dispersed or local energy generation technologies are operated simultaneously
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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
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
Abstract
The invention discloses a full direct current power system. The system comprises at least one full-direct-current power subsystem, wherein the full-direct-current power subsystem comprises a first direct-current power subsystem for grid connection of a new energy or energy storage system, a second direct-current power subsystem for grid connection of the new energy system, a third direct-current power subsystem for grid connection of the new energy system, a fourth direct-current power subsystem for grid connection of the new energy or energy storage system, a fifth direct-current power subsystem for grid connection of the new energy or energy storage system, a high-voltage direct-current power transmission network and at least one direct-current power transmission subsystem. According to the invention, the source load and the storage are interconnected in a direct current network form, and the fluctuation and the intermittence of the new energy power generation can be stabilized in a large range at the source side and the storage side, so that the impact of the new energy power generation on a power grid is reduced to the maximum extent; on the network side, large-scale new energy large-scale tide regulation and control are completed, and the safety and stability of the power grid are improved; on the load side, the high-efficiency access and flexible management of a distributed direct-current power supply and a load can be realized.
Description
Technical Field
The invention belongs to the field of direct current power systems, and particularly relates to a full direct current power system.
Background
The development and utilization of new energy such as wind and light are accelerated, and the power utilization efficiency of a power grid is improved. The traditional alternating current energy hook frequency is less and less, the power grid inertia is reduced, large-capacity electric energy changes to easily form frequency oscillation, and large-scale and high-proportion new energy access brings huge challenges to the stable operation of an alternating current power grid. Meanwhile, with the rapid increase of direct current loads of an electric vehicle charging station, a large-scale data center, communication equipment and the like, and the access of direct current power supplies such as a direct current fan and a photovoltaic power supply and energy storage large capacity, the source load and storage direct current characteristics of a novel power system become increasingly significant, if the source load and storage are still connected through an alternating current power grid, the conversion link and the grid-connected difficulty are increased, the overall efficiency of the system can be reduced, and the electric energy quality and the power supply reliability are reduced.
The direct current technology in China is researched as follows:
on the source side, the new energy is mainly accessed in an alternating current collection-alternating current sending mode and an alternating current collection-direct current sending mode at present, but when large-scale new energy is accessed to a weak alternating current power grid in the two modes, the bearing capacity and the stability of the power grid are seriously challenged. According to the operation experience of the commissioning engineering, the problem that the new energy is affected by a long cable and harmonic amplification and even system oscillation occurs if an alternating current collection-alternating current sending technology is adopted. If the new energy adopts an alternating current collection-direct current sending technology, the problems of broadband and oscillation are easy to occur, although the broadband oscillation is avoided by adopting an open-close loop conversion strategy at present, the oscillation risk still exists in the flexible direct-current closed-loop control when an alternating current system fails or is in an overload working condition.
On the network side, the main grid structures in the direct current transmission project which is put into operation at home and abroad at present have three structures of an end-to-end structure, a multi-end structure and a direct current power grid.
On the load side, the series of direct current distribution network engineering built in China at present realizes the access of direct current loads such as electric vehicle charging stations, large data centers and communication equipment, and the development of a full direct current power system is further promoted along with the development of the direct current loads in the future.
On the storage side, the current centralized energy storage mainly adopts an alternating current access mode, and a direct current access case exists in the application scenes of a distribution network and a microgrid.
Generally, the direct current technology penetrates into each side of the source network load storage, but the development degree is in the demonstration exploration stage, and the connection and inheritance among projects are less.
Disclosure of Invention
The invention aims to solve the technical problem of providing a full direct current power system integrating source network load and storage, which interconnects source load and storage in a direct current network form and constructs a system architecture of the full direct current power system.
Therefore, the invention adopts the following technical scheme: a full direct current power system comprises at least one full direct current power subsystem, wherein the full direct current power subsystem comprises a first direct current power subsystem for grid connection of a new energy or energy storage system, a second direct current power subsystem for grid connection of the new energy system, a third direct current power subsystem for grid connection of the new energy system, a fourth direct current power subsystem for grid connection of the new energy or energy storage system, a fifth direct current power subsystem for grid connection of the new energy or energy storage system, a high-voltage direct current power transmission network and at least one direct current power transmission subsystem;
the first to fifth direct-current power supply subsystems respectively adopt a power frequency alternating current collection-VSC rectification output mode, a power frequency alternating current collection-diode rectification output mode, a medium frequency alternating current collection-diode rectification output mode, a series boosting type direct current collection-direct current output mode and a parallel boosting type direct current collection-direct current output mode; the first to fifth direct current power supply subsystems are respectively connected with one side of a high-voltage direct current transmission network, and the other side of the high-voltage direct current transmission network is connected with the direct current transmission subsystem.
Furthermore, the direct current transmission subsystem comprises a first direct current transmission electronic system for extra-high voltage direct current transmission;
the first direct current transmission subsystem comprises a power grid commutation converter, a high-voltage direct current transformer and a direct current switch, the second alternating current power grid rectifies alternating current into direct current through the power grid commutation converter, then the direct current voltage at the outlet of the power grid commutation converter is reduced to the direct current voltage of the high-voltage direct current transmission network through the high-voltage direct current transformer, and finally the direct current voltage is connected to the high-voltage direct current transmission network through the direct current switch.
Further, the direct current transmission subsystem further comprises a second direct current transmission subsystem for flexible direct current transmission;
the second dc power transmission sub-system comprises a voltage source converter and a dc switch, through which the first ac power grid rectifies ac to dc and then connects to the high voltage dc power transmission network.
Further, the direct current transmission subsystem further comprises a third direct current transmission subsystem for direct current distribution;
and the third direct-current transmission subsystem comprises a direct-current switch, a high-voltage direct-current transformer and a direct-current distribution and utilization system, absorbs energy from the high-voltage direct-current transmission network, reduces the high-voltage direct current to medium-voltage direct current through the direct-current switch and the high-voltage direct-current transformer, and then is connected to the direct-current distribution and utilization system.
Further, the first dc power subsystem includes a first new energy source or energy storage system, a photovoltaic inverter, an ac transformer, a voltage source converter, and a dc switch;
when the first new energy system is photovoltaic, the photovoltaic cell panel group string is collected and connected to an alternating current transformer after passing through a photovoltaic inverter, alternating current is rectified into direct current through a voltage source converter, and the direct current is connected to a high-voltage direct current power transmission network through a direct current switch; when the first new energy system is wind power, the alternating current fan is connected with an alternating current transformer in a gathering mode on the offshore platform, alternating current is rectified into direct current through a voltage source converter, and the direct current is connected into a high-voltage direct current power transmission network through a direct current switch.
Furthermore, the second direct-current power supply subsystem comprises a second new energy system, a photovoltaic inverter, a power-frequency alternating-current transformer, a diode rectifier valve and a direct-current switch;
when the second new energy system is photovoltaic, the photovoltaic cell panel group string is converged and connected to a power frequency alternating current transformer after passing through a photovoltaic inverter, and is boosted by the power frequency alternating current transformer to form a high-voltage alternating current bus, on one hand, the high-voltage alternating current bus is directly connected to an alternating current power grid to realize photovoltaic alternating current convergence-alternating current sending, on the other hand, the high-voltage alternating current bus is also subjected to alternating current rectification through a diode rectifier valve to form direct current, and is connected to a high-voltage direct current power transmission network through a direct current switch;
when the second new energy system is wind power, the alternating current fan is connected with a power frequency alternating current transformer in a converging mode on the offshore platform, a high-voltage alternating current bus is formed after the voltage of the power frequency alternating current transformer is boosted, on one hand, the high-voltage alternating current bus is directly connected to an alternating current power grid to achieve wind power alternating current collection-alternating current sending, on the other hand, the high-voltage alternating current bus rectifies alternating current into direct current through a diode rectifier valve, and the direct current is connected to a high-voltage direct current power transmission network through a direct current switch.
Furthermore, the third direct-current power supply subsystem comprises a third new energy system, a photovoltaic inverter, an intermediate-frequency alternating-current transformer, a diode rectifier valve and a direct-current switch;
when the third new energy system is photovoltaic, the photovoltaic cell panel string is collected and connected to the intermediate-frequency alternating current transformer after forming intermediate-frequency alternating current through the photovoltaic inverter, is boosted by the intermediate-frequency alternating current transformer to form a high-voltage intermediate-frequency alternating current bus, rectifies the alternating current into direct current through the diode rectifier valve, and is connected to the high-voltage direct current power transmission network through the direct current switch;
when the third new energy system is wind power, the alternating current fan is converged and connected to the intermediate frequency alternating current transformer on the offshore platform, a high-voltage intermediate frequency alternating current bus is formed after the alternating current is boosted by the intermediate frequency alternating current transformer, alternating current is rectified into direct current through the diode rectifier valve, and the direct current is connected to the high-voltage direct current power transmission network through the direct current switch.
Furthermore, the fourth direct-current power supply subsystem comprises a fourth new energy or energy storage system, a high-voltage direct-current transformer, a direct-current power distribution and utilization system and a direct-current switch;
when the direct-current transformer adopts a bidirectional topological structure, the tide of the fourth direct-current power supply subsystem realizes bidirectional circulation and is suitable for the access of new energy and an energy storage system, otherwise, the tide is only suitable for the access of the new energy; when the fourth new energy system adopts a system architecture of 'series boosting + high-voltage direct-current transformer', the new energy subunits form medium-voltage direct-current voltage through series connection, then are boosted to high-voltage direct current through the high-voltage direct-current transformer, and are connected to a high-voltage direct-current power transmission network through a direct-current switch; in addition, the medium-voltage direct-current voltage can be introduced into a direct-current power distribution system to form a new situation of new energy direct-current collection, direct-current sending and direct-current consumption.
Furthermore, the fifth dc power subsystem includes a fifth new energy or energy storage system, a medium-voltage dc transformer, a high-voltage dc transformer, a dc distribution system, and a dc switch;
when the direct-current transformer adopts a bidirectional topological structure, the tide of the fifth direct-current power supply subsystem realizes bidirectional circulation and is suitable for the access of new energy and an energy storage system, otherwise, the fifth direct-current power supply subsystem is only suitable for the access of the new energy; when the fifth new energy system adopts a system architecture of 'medium-voltage direct-current transformer + high-voltage direct-current transformer', the voltage is boosted to medium-voltage direct-current voltage through the medium-voltage direct-current transformer, the multiple branch circuits are parallelly collected at a medium-voltage direct-current bus, then are boosted to high-voltage direct current through a high-voltage direct-current transformer, and are connected to a high-voltage direct-current power transmission network through a direct-current switch; in addition, the medium-voltage direct-current voltage grade can also be introduced into a direct-current power distribution system to form a new situation of new energy direct-current collection, direct-current sending and direct-current consumption.
Furthermore, the full-direct-current power system comprises a plurality of full-direct-current power subsystems, and the two full-direct-current power subsystems are connected through a high-voltage direct-current transformer or a direct-current line, so that mutual power flow assistance between the subsystems is realized.
The direct-current voltage grades of the full direct-current power subsystems cannot be completely equal, so that the full direct-current power subsystems with the same direct-current voltage can be directly connected through a direct-current line, and the mutual aid of power flows among the subsystems is realized; for full-direct-current power subsystems with unequal direct-current voltages, the two subsystems need to be interconnected through a high-voltage direct-current transformer, and mutual power flow assistance between the subsystems is achieved.
The invention has the following beneficial effects: according to the invention, the source load and the storage are interconnected in a direct current network form, and the fluctuation and intermittence of new energy power generation can be stabilized in a large range and the impact of the new energy power generation on a power grid can be reduced to the maximum extent by combining the multiform power supply, energy storage complementation and the flexible and rapid adjustment capability of a direct current power grid on the source side and the storage side; on the network side, large-scale new energy large-scale tide regulation and control are completed through multi-receiving-end power supply and multi-drop point power utilization of a direct current network, wide-area optimal configuration of clean energy is realized, and the safety and stability of a power grid are improved; on the load side, the high-efficiency access and flexible management of a distributed direct-current power supply and a load can be realized.
The invention integrates source network load storage into a whole, and the full direct current power system is an indispensable technical means for constructing a novel power system, and has wide development prospect and popularization value.
Drawings
FIG. 1 is a block diagram of an all DC power system according to the present invention;
FIG. 2 is a schematic structural diagram of the interior of the AC direct drive fan of the present invention;
FIG. 3 is a schematic structural diagram of the interior of the direct-current direct-drive fan according to the invention;
FIG. 4 is a schematic diagram of a photovoltaic power frequency AC sink-VSC rectification output mode of a first DC power supply subsystem according to the present invention;
FIG. 5 is a schematic diagram of a wind power frequency AC sink-VSC rectification output mode of a first DC power supply subsystem according to the present invention;
FIG. 6 is a schematic diagram of a photovoltaic power frequency AC collection-diode rectification output mode of a second DC power supply subsystem according to the present invention;
FIG. 7 is a schematic diagram of a wind power frequency AC collection-diode rectification output mode of a second DC power supply subsystem according to the present invention;
fig. 8 is a schematic structural diagram of a hybrid flexible power transformer according to the present invention;
FIG. 9 is a schematic diagram of a photovoltaic medium frequency AC collection-diode rectification output mode of a third DC power subsystem in accordance with the present invention;
FIG. 10 is a schematic diagram of a wind power intermediate frequency AC collection-diode rectification output mode of a third DC power supply subsystem according to the present invention;
fig. 11 is a schematic diagram of a new energy series boost dc sink-dc send mode of a fourth dc power subsystem according to the present invention;
fig. 12 is a schematic diagram of a fifth dc power subsystem according to the present invention in a new energy parallel boost dc sink-dc send mode;
fig. 13 is a schematic structural diagram of a diode switch according to the present invention.
Detailed Description
The present invention will now be described in more detail with reference to the accompanying drawings, in which the description of the invention is given by way of illustration and not limitation. The various embodiments may be combined with each other to form other embodiments not shown in the following description.
As shown in fig. 1, the present embodiment provides an all-dc power system, which is composed of N +1 all-dc power subsystems, and is divided into a first all-dc power subsystem, a second all-dc power subsystem, a third all-dc power subsystem, an nth all-dc power subsystem, and an N +1 th all-dc power subsystem.
From the perspective of a full-direct-current power system, the direct-current voltage grades of a plurality of full-direct-current power subsystems cannot be completely equal, so that for the full-direct-current power subsystems with equal direct-current voltages, the full-direct-current power subsystems can be directly connected through direct-current lines to realize power flow mutual assistance among the systems, for example, the first full-direct-current power subsystem, the third full-direct-current power subsystem and the Nth full-direct-current power subsystem are connected through the direct-current lines; for the full direct current power subsystems with unequal direct current voltages, the two systems need to be interconnected through a high-voltage direct current transformer to realize the mutual compensation of power flows between the systems, for example, the second full direct current power subsystem is connected with the (N + 1) th full direct current power subsystem through the high-voltage direct current transformer.
From the full dc power subsystem level, the first full dc power subsystem is taken as an example for description.
The first full-direct-current power subsystem is composed of a first direct-current power subsystem for grid connection of a new energy or energy storage system, a second direct-current power subsystem for grid connection of the new energy system, a third direct-current power subsystem for grid connection of the new energy system, a fourth direct-current power subsystem for grid connection of the new energy or energy storage system, a fifth direct-current power subsystem for grid connection of the new energy or energy storage system, a high-voltage direct-current power transmission network, and a first direct-current power transmission subsystem, a second direct-current power transmission subsystem and a third direct-current power transmission subsystem.
The first to fifth direct-current power supply subsystems respectively adopt a power frequency alternating current collection-VSC rectification output mode, a power frequency alternating current collection-diode rectification output mode, a medium frequency alternating current collection-diode rectification output mode, a series boosting type direct current collection-direct current output mode and a parallel boosting type direct current collection-direct current output mode; the first to fifth direct current power supply subsystems are respectively connected with one side of a high-voltage direct current transmission network, and the other side of the high-voltage direct current transmission network is connected with the three direct current transmission subsystems.
1. DC power supply subsystem
The direct-current power supply subsystem mainly comprises new energy sources such as wind power and photovoltaic and an energy storage system, and the energy storage system is mainly a battery energy storage system.
The output of the double-fed and direct-driven fans which are commonly used at present is alternating current, and the photovoltaic and energy storage outputs are direct current. FIG. 2 shows a structure of a direct-drive fan, which is rectified by an AC/DC converter, inverted by a DC/AC converter, and boosted by an AC transformer to convert wind energy into 50Hz AC power for output. By modifying the direct-drive wind turbine, the original inversion link is modified into a direct-current boosting link (i.e., the DC/AC converter and the alternating-current transformer are replaced by the DC/DC converter), so that direct current collection of wind power is realized, as shown in fig. 3. By adopting the scheme of alternating current collection, if the new energy is in the alternating current output characteristic, the new energy is only required to be output and collected through the boosting of an alternating current transformer; if the new energy is in the DC output characteristic, the new energy is also required to be converted into AC by DC inversion and is boosted and collected by an AC transformer. By adopting a direct current collection scheme, if the new energy is in a direct current output characteristic, the new energy is only required to be output and collected through a direct current transformer in a boosting way; if the new energy is in an alternating current output characteristic, the new energy is rectified from alternating current into direct current and is boosted and collected through a direct current transformer.
Since the energy storage flow needs to flow in two directions, the corresponding power electronic device needs to have a function of flowing in two directions. For photovoltaic, the tide flows in a one-way mode, when illumination reaches a certain intensity, the power consumption requirement of an auxiliary system can be met through self-energy taking, reverse electricity taking from a high-voltage side is not needed, and therefore the corresponding power electronic equipment adopts a one-way topological structure to obtain better economy. For wind power, the tidal current of the wind power flows in a one-way mode, but when the wind power is started in a black mode, the fan needs to start the control system first to adjust the blade state, and at the moment, the auxiliary system cannot get electricity through the fan, so that the electricity needs to be obtained reversely from the high-voltage side, and therefore the corresponding power electronic equipment usually adopts a two-way topological structure. The second and third dc power supply subsystems comprise diode rectifier valves, and the power flow can only flow in one direction, so that the second and third dc power supply subsystems in fig. 1 are not suitable for energy storage, and for a fan, an auxiliary system of the fan needs to be externally introduced with a new ac power supply.
The first, second and third DC power supply subsystems all adopt an AC collection mode.
The first dc power subsystem comprises a first new energy source/storage system, a photovoltaic inverter (when the new energy source is photovoltaic), an ac transformer, a Voltage Source Converter (VSC) and a dc switch. The system can circulate in two directions, so that the system is suitable for new energy or energy storage systems. As shown in fig. 4, when the new energy is photovoltaic, the photovoltaic cell panel string is inverted into ac by the MPPT converter and the photovoltaic inverter, and then boosted by the first-stage ac transformer and collected in the medium-voltage ac bus, and then boosted by the first-stage ac transformer and collected in the high-voltage ac bus, and then the ac is rectified into dc by the Voltage Source Converter (VSC), and then the dc is connected to the high-voltage dc power transmission network via the dc switch. As shown in fig. 5, when the new energy is wind power, the ac fan is collected to a medium-voltage ac bus on the offshore platform, and is boosted by the ac transformer and collected to a high-voltage ac bus, and the ac is rectified into dc by a Voltage Source Converter (VSC), and is connected to the high-voltage dc power transmission network through a dc switch.
The second direct-current power supply subsystem comprises a second new energy system, a photovoltaic inverter (contained when new energy is photovoltaic), a power frequency alternating-current transformer, a diode rectifier valve (DRU) and a direct-current switch. Because the rectifier valve of the diode is included, the tide of the system can only flow in a single direction, and therefore, the rectifier valve is only suitable for the access of a new energy system. As shown in fig. 6, when the new energy is photovoltaic, the photovoltaic cell panel string is inverted into ac by the MPPT converter and the photovoltaic inverter, and then is boosted by the first-stage power frequency ac transformer and collected to the medium-voltage power frequency ac bus, and then is boosted by the first-stage power frequency ac transformer and collected to the high-voltage power frequency ac bus. As shown in fig. 7, when the new energy is wind power, the ac fan is collected at the medium-voltage power-frequency ac bus on the offshore platform, and is connected to the power-frequency ac transformer, and is boosted by the power-frequency ac transformer to form a high-voltage power-frequency ac bus, on one hand, the high-voltage power-frequency ac bus is directly connected to the ac grid to realize photovoltaic ac collection-ac sending, and on the other hand, the high-voltage power-frequency ac bus can also rectify ac into dc through a diode rectifier valve (DRU), and is connected to the high-voltage dc power transmission network through a dc switch.
In the system, new energy can be sent out by adopting an alternating current mode and a direct current mode, and the new energy is redundant and standby mutually, so that the reliability of sending out the new energy is improved. When the alternating current sending branch is disconnected, new energy is sent out in a direct current mode after passing through the DRU, and at the moment, an inverter or a photovoltaic inverter in a front-stage fan needs to adopt a network construction type control strategy to stabilize the frequency and amplitude of the voltage of the alternating current side of the DRU. When the direct current sending branch is disconnected, the new energy is connected to an alternating current power grid through a high-voltage alternating current bus, and at the moment, an inverter or a photovoltaic inverter in a front-stage fan needs to adopt a network following type control strategy to track the voltage and the phase of the alternating current power grid. When the alternating current-direct current sending branches are in a connection state, the high-voltage alternating current bus is connected to the alternating current power grid, the voltage of the high-voltage alternating current bus is clamped by the voltage of the alternating current power grid, the DRU is adopted at the rear stage, the tide cannot be controlled, and a voltage regulating transformer needs to be added in front of the DRU in order to achieve controllable sending of new energy. In consideration of the fluctuation and randomness of new energy, high requirements are put on the adjusting frequency, the adjusting speed and the adjusting capacity of the voltage-regulating transformer, and therefore the hybrid flexible power transformer in fig. 8 is adopted. The hybrid flexible power transformer topology is composed of a main transformer and a back-to-back AC-DC converter, wherein W1 in the main transformer is a primary winding, W2 and W3 are secondary windings, voltages at two ends of the three windings are u1, u2 and u3 respectively, W1 is connected with a power grid, W2 is connected with a Load and is responsible for supplying power to the Load, W3 is connected with an AC/DC converter to realize the control of line current, the DC side of the AC/DC converter is connected with a DC/AC converter, the voltages u1 at two ends of the primary winding of the transformer can be adjusted by adjusting the output voltage u4 of the DC/AC converter, and the voltage u2 induced to the secondary winding from the primary winding is also synchronously changed.
The third direct current power supply subsystem comprises a third new energy system, a photovoltaic inverter (when the new energy is photovoltaic), a medium-frequency alternating current transformer, a diode rectifier valve (DRU) and a direct current switch. Because the rectifier valve of the diode is included, the tide of the system can only flow in a single direction, and therefore, the rectifier valve is only suitable for the access of a new energy system. As shown in fig. 9, when the new energy is photovoltaic, the photovoltaic cell panel string passes through the MPPT converter and the photovoltaic inverter to form intermediate frequency ac, and then is collected into the first-stage intermediate frequency ac transformer, and is collected into the intermediate voltage power frequency ac bus after being boosted, and is collected into the high voltage intermediate frequency ac bus after being boosted by the first-stage intermediate frequency ac transformer, and the ac is rectified into dc by the diode rectifier valve (DRU), and is connected into the high voltage dc power transmission network by the dc switch. As shown in fig. 10, when the new energy is wind power, the ac fan is collected in a medium-voltage and medium-frequency ac bus on the offshore platform, and is connected to a medium-frequency ac transformer, and is boosted by the transformer to form a high-voltage and medium-frequency ac bus, and the ac is rectified into dc by a diode rectifier valve (DRU), and is connected to the high-voltage dc transmission network through a dc switch. The medium frequency is adopted in the alternating current link in the system, compared with the power frequency, the size and cost of magnetic elements such as a transformer and the like can be greatly reduced, the fault current can be cut off more quickly, and in addition, the DRU also reduces the cost of power electronic equipment and the uncertainty introduced by a control system. In the system, an inverter or a photovoltaic inverter in a fan needs to adopt a network type control strategy to stabilize the frequency and amplitude of the voltage at the alternating current side of the DRU.
And the fourth and fifth direct-current power supply subsystems are connected in a direct-current collecting-direct-current sending mode.
The fourth direct-current power supply subsystem comprises a fourth new energy source/energy storage system, a high-voltage direct-current transformer, a direct-current power distribution and utilization system and a direct-current switch. When the direct-current transformer adopts a bidirectional topological structure, the tide of the system can realize bidirectional circulation, so that the system is suitable for accessing new energy and an energy storage system, and otherwise, the system is only suitable for accessing the new energy. The fourth direct-current power supply subsystem adopts a system architecture of 'series boosting + high-voltage direct-current transformer', the new energy subunit forms medium-voltage direct-current voltage through series connection, then the medium-voltage direct-current voltage is boosted to high-voltage direct current through the high-voltage direct-current transformer, and the high-voltage direct-current voltage is connected to a high-voltage direct-current power transmission network through a direct-current switch. In addition, the medium-voltage direct-current voltage level can be introduced into a direct-current power distribution system to form a new situation of new energy direct-current collection, direct-current sending and direct-current consumption. The system architecture has the advantages that power electronic conversion links are reduced, the overall cost is reduced, the efficiency is high, when direct-current single-pole ground faults occur, the problem that the insulation level of new energy close to polar lines at two ends is high can occur, the system architecture is limited by series operation, and the new energy cannot operate in an optimal state. As shown in fig. 11, when the new energy is a wind turbine, the direct current output side of the direct current wind turbine is directly connected in series to form a medium voltage direct current voltage, and when the new energy is a photovoltaic, the photovoltaic strings are directly connected in series to form a medium voltage direct current voltage after passing through an MPPT (maximum power point tracking) link, and are connected to the high voltage direct current power transmission network after being boosted to a high voltage direct current by the high voltage direct current transformer.
The fifth direct-current power supply subsystem comprises a fifth new energy source/energy storage system, a medium-voltage direct-current transformer, a high-voltage direct-current transformer, a direct-current power distribution and utilization system and a direct-current switch. When the direct-current transformer adopts a bidirectional topological structure, the tidal current of the system can realize bidirectional circulation, so that the system is suitable for the access of new energy and an energy storage system, and otherwise, the system is only suitable for the access of the new energy. As shown in fig. 12, the fifth dc power subsystem adopts a system architecture of "medium voltage dc transformer + high voltage dc transformer", the new energy subunit is boosted to medium voltage dc voltage by the medium voltage dc transformer, the multiple branches are collected in parallel at the medium voltage dc bus, and then boosted to high voltage dc by the high voltage dc transformer, and connected to the high voltage dc power transmission network via the dc switch. In addition, the medium-voltage direct-current voltage grade can also be introduced into a direct-current power distribution system to form a new situation of new energy direct-current collection, direct-current sending and direct-current consumption. The system architecture needs two-stage boosting, the overall efficiency is not as good as that of the second direct-current power supply subsystem, and the problems that the new energy is high in insulation and cannot operate in the optimal state do not exist.
2. DC power transmission subsystem
The first direct current transmission electronic system comprises a power grid commutation converter (LCC), a high-voltage direct current transformer and a direct current switch, mainly aims at the application scene of ultra-high voltage direct current transmission, a second alternating current power grid rectifies alternating current into direct current through the power grid commutation converter, and the direct current voltage at the outlet of the power grid commutation converter is required to be reduced to the direct current voltage of a direct current transmission network through the high-voltage direct current transformer because the outlet direct current voltage level of the power grid commutation converter is higher than the outlet voltage of a voltage source converter, and then the direct current voltage at the outlet of the power grid commutation converter is connected to the direct current transmission network through the direct current switch. And under the influence of the characteristics of the power grid commutation converter, the power flow direction of the first direct-current power transmission system is fixed into the second alternating-current power grid and transmitted to the direct-current power transmission network.
The second direct-current power transmission subsystem comprises a voltage source converter and a direct-current switch and mainly aims at the application scene of flexible direct-current power transmission. The first ac grid rectifies the ac to dc via a voltage source converter and then connects to the high voltage dc transmission network via a dc switch. Since the voltage source converter may enable bidirectional control of the power flow, the first ac electrical network may both output energy to the dc transmission network and absorb energy from the dc transmission network.
The third direct-current transmission subsystem comprises a direct-current switch, a high-voltage direct-current transformer and a direct-current power distribution system, and is mainly directed at the application scene of direct-current power distribution. Energy is absorbed from the direct current transmission network, and after the direct current is reduced to medium voltage direct current through the direct current switch and the high voltage direct current transformer, the direct current transmission network is connected to a direct current distribution and utilization system, and when the direct current distribution and utilization system further comprises a new energy source besides a load, the new energy source can be fed into the direct current transmission network through the high voltage direct current transformer when more surplus exists. The third dc power transmission subsystem may also enable bidirectional flow of power flow.
The direct-current power supply subsystem and the direct-current power transmission subsystem are connected through the high-voltage direct-current power transmission network, the direct-current power supply subsystem and the direct-current power transmission subsystem can be in a radial shape or a mesh shape, direct-current switches of all branches can be combined into a multi-port direct-current switch according to the condition that multiple paths of direct currents are collected at a direct-current bus, and the economy of direct-current on-off equipment is improved. Aiming at the complex mesh-shaped direct current transmission network, a direct current power flow controller needs to be installed on a line to realize the control of the power flow of the direct current transmission line. And aiming at the line with the fault current exceeding the standard, a fault current suppressor is required to be installed to prevent the fault current from damaging equipment.
3. Selection principle of direct-current transformer
The direct current transformer in the full direct current power system can select a proper topology according to the requirement of the transformation ratio, and a non-isolated direct current transformer is generally selected for an application scene with the transformation ratio less than 5 to obtain higher economy; for an application scenario with a transformation ratio greater than 5, an isolated direct current transformer is generally selected, and a larger transformation ratio is realized through the transformer. For occasions requiring bidirectional flow of tide, the direct-current transformer needs to select a bidirectional topological structure; for the occasions only needing unidirectional transmission of power flow, the DC transformer selects a unidirectional topological structure.
4. Configuration principle of DC switch
The dc switch in the full dc power system may be selected from a dc breaker capable of breaking a fault current, a dc load switch capable of breaking a rated current, a diode switch capable of blocking a high-voltage side fault current, and the like, and the diode switch mainly includes a diode module, an ac breaker, and a current limiting reactor, as shown in fig. 13. For branch faults, the diodes D1 and D2 are used for blocking fault current fed in from the +/-20 kV direct-current bus side; after the fault current of the alternating current circuit breakers KM1 and KM2 is reduced to 0, isolating a fault line; for the fault of the +/-20 kV direct current bus side, the current limiting reactors L1 and L2 are used for limiting the fault current and protecting the diode. Selecting a direct current breaker for a scene needing to rapidly cut off short-circuit current; selecting a direct current load switch for a scene needing to quickly cut off rated current; for the branch with a single current direction, a diode switch can be selected to block the short-circuit current fed in from the high-voltage side.
Various other modifications and changes may occur to those skilled in the art based on the foregoing teachings and concepts, and all such modifications and changes are intended to be included within the scope of the appended claims.
Claims (6)
1. A full direct current power system comprises a plurality of full direct current power subsystems and is characterized in that the full direct current power subsystems comprise a first direct current power subsystem for grid connection of a new energy or energy storage system, a second direct current power subsystem for grid connection of the new energy system, a third direct current power subsystem for grid connection of the new energy system, a fourth direct current power subsystem for grid connection of the new energy or energy storage system, a fifth direct current power subsystem for grid connection of the new energy or energy storage system, a high-voltage direct current power transmission network and at least one direct current power transmission subsystem;
the first direct-current power supply subsystem is sent out by adopting power-frequency alternating-current collection-VSC rectification, the second direct-current power supply subsystem is sent out by adopting power-frequency alternating-current collection-diode rectification, the third direct-current power supply subsystem is sent out by adopting intermediate-frequency alternating-current collection-diode rectification, the fourth direct-current power supply subsystem is sent out by adopting series boosting type direct-current collection-direct-current, and the fifth direct-current power supply subsystem adopts a parallel boosting type direct-current collection-direct-current sending mode;
the first direct-current power supply subsystem, the second direct-current power supply subsystem, the third direct-current power supply subsystem and the fourth direct-current power supply subsystem are connected with one side of a high-voltage direct-current power transmission network respectively;
the direct-current transmission subsystem comprises a first direct-current transmission electronic system for extra-high voltage direct-current transmission; the first direct-current transmission subsystem comprises a power grid commutation converter, a high-voltage direct-current transformer and a direct-current switch, the second alternating-current power grid rectifies alternating current into direct current through the power grid commutation converter, then reduces direct-current voltage at an outlet of the power grid commutation converter to direct-current voltage of the high-voltage direct-current transmission network through the high-voltage direct-current transformer, and finally is connected to the high-voltage direct-current transmission network through the direct-current switch;
the direct current transmission subsystem further comprises a second direct current transmission subsystem for flexible direct current transmission; the second direct-current power transmission subsystem comprises a voltage source converter and a direct-current switch, and the first alternating-current power grid rectifies alternating current into direct current through the voltage source converter and then is connected to the high-voltage direct-current power transmission network through the direct-current switch;
the direct-current transmission subsystem further comprises a third direct-current transmission subsystem for direct-current distribution and utilization; the third direct-current transmission subsystem comprises a direct-current switch, a high-voltage direct-current transformer and a direct-current distribution and utilization system, absorbs energy from the high-voltage direct-current transmission network, reduces the high-voltage direct current to medium-voltage direct current through the direct-current switch and the high-voltage direct-current transformer, and then is connected to the direct-current distribution and utilization system;
the two full-direct-current power subsystems are connected through a high-voltage direct-current transformer or a direct-current line, and mutual power flow assistance between the subsystems is achieved.
2. A full dc power system according to claim 1, wherein the first dc power subsystem comprises a first new energy source or storage system, a photovoltaic inverter, an ac transformer, a voltage source converter and a dc switch;
when the first new energy system is photovoltaic, the photovoltaic cell panel string is collected and connected to an alternating current transformer after passing through a photovoltaic inverter, alternating current is rectified into direct current through a voltage source converter, and the direct current is connected to a high-voltage direct current power transmission network through a direct current switch; when the first new energy system is wind power, the alternating current fan is connected with an alternating current transformer in a gathering mode on the offshore platform, alternating current is rectified into direct current through a voltage source converter, and the direct current is connected with a high-voltage direct current power transmission network through a direct current switch.
3. The full direct current power system according to claim 1, wherein the second direct current power subsystem comprises a second new energy system, a photovoltaic inverter, a power frequency alternating current transformer, a diode rectifier valve and a direct current switch;
when the second new energy system is photovoltaic, the photovoltaic cell panel string is converged and connected to a power frequency alternating current transformer after passing through a photovoltaic inverter, and is boosted by the power frequency alternating current transformer to form a high-voltage alternating current bus, on one hand, the high-voltage alternating current bus is directly connected to an alternating current power grid to realize photovoltaic alternating current convergence-alternating current sending, on the other hand, the high-voltage alternating current bus is also subjected to alternating current rectification into direct current through a diode rectifier valve and is connected to a high-voltage direct current power transmission network through a direct current switch;
when the second new energy system is wind power, the alternating current fan is connected with a power frequency alternating current transformer in a converging mode on the offshore platform, a high-voltage alternating current bus is formed after the voltage of the power frequency alternating current transformer is boosted, on one hand, the high-voltage alternating current bus is directly connected to an alternating current power grid to achieve wind power alternating current collection-alternating current sending, on the other hand, the high-voltage alternating current bus rectifies alternating current into direct current through a diode rectifier valve, and the direct current is connected to a high-voltage direct current power transmission network through a direct current switch.
4. The full dc power system of claim 1, wherein the third dc power subsystem comprises a third new energy system, a photovoltaic inverter, an intermediate frequency ac transformer, a diode rectifier valve, and a dc switch;
when the third new energy system is photovoltaic, the photovoltaic cell panel string is collected and connected to the intermediate-frequency alternating current transformer after forming intermediate-frequency alternating current through the photovoltaic inverter, is boosted by the intermediate-frequency alternating current transformer to form a high-voltage intermediate-frequency alternating current bus, rectifies the alternating current into direct current through the diode rectifier valve, and is connected to the high-voltage direct current power transmission network through the direct current switch;
when the third new energy system is wind power, the alternating current fan is converged and connected to the intermediate frequency alternating current transformer on the offshore platform, a high-voltage intermediate frequency alternating current bus is formed after the alternating current is boosted by the intermediate frequency alternating current transformer, alternating current is rectified into direct current through the diode rectifier valve, and the direct current is connected to the high-voltage direct current power transmission network through the direct current switch.
5. The full dc power system of claim 1, wherein the fourth dc power subsystem comprises a fourth new energy or energy storage system, a high voltage dc transformer, a dc distribution system, and a dc switch;
when the direct-current transformer adopts a bidirectional topological structure, the tide of the fourth direct-current power supply subsystem realizes bidirectional circulation and is suitable for new energy and energy storage system access, otherwise, the fourth direct-current power supply subsystem is only suitable for new energy access; when the fourth new energy system adopts a system architecture of 'series boosting + high-voltage direct-current transformer', the new energy subunits are connected in series to form medium-voltage direct-current voltage, then boosted to high-voltage direct current through the high-voltage direct-current transformer, and connected to the high-voltage direct-current power transmission network through the direct-current switch.
6. The full dc power system of claim 1, wherein the fifth dc power subsystem comprises a fifth new energy source or energy storage system, a medium voltage dc transformer, a high voltage dc transformer, a dc distribution system, a dc switch;
when the direct-current transformer adopts a bidirectional topological structure, the tide of the fifth direct-current power supply subsystem realizes bidirectional circulation and is suitable for the access of new energy and an energy storage system, otherwise, the fifth direct-current power supply subsystem is only suitable for the access of the new energy; when the fifth new energy system adopts a system architecture of 'medium-voltage direct-current transformer + high-voltage direct-current transformer', the voltage is boosted to medium-voltage direct-current voltage through the medium-voltage direct-current transformer, and the multiple branch circuits are connected in parallel and converged at a medium-voltage direct-current bus, then are boosted to high-voltage direct current through a high-voltage direct-current transformer and are connected to a high-voltage direct-current power transmission network through a direct-current switch.
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