CN111682547B - 10kV active power distribution network based on power flow control nodes and control method thereof - Google Patents

10kV active power distribution network based on power flow control nodes and control method thereof Download PDF

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CN111682547B
CN111682547B CN202010645293.4A CN202010645293A CN111682547B CN 111682547 B CN111682547 B CN 111682547B CN 202010645293 A CN202010645293 A CN 202010645293A CN 111682547 B CN111682547 B CN 111682547B
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converter
power
power flow
node
flow control
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CN111682547A (en
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梁一桥
梁家诚
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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
    • H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
    • H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
    • 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
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00001—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by the display of information or by user interaction, e.g. supervisory control and data acquisition systems [SCADA] or graphical user interfaces [GUI]
    • 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
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00002—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by monitoring
    • 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
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00032—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for
    • H02J13/00036—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for the elements or equipment being or involving switches, relays or circuit breakers
    • H02J13/0004—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for the elements or equipment being or involving switches, relays or circuit breakers involved in a protection system
    • 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
    • Y02E40/70—Smart grids as climate change mitigation technology in the energy generation sector
    • 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
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications

Abstract

The invention discloses a 10kV active power distribution network based on power flow control nodes and a control method thereof. A plurality of power flow control nodes are configured in a 10kV power distribution network, the power flow control nodes connect two or more 10kV distribution lines, and active control over power flow of the connected 10kV distribution lines is achieved through series-connection type AC/DC converter devices in the power flow control nodes. The direct current sides of all series type AC/DC converter devices and the direct current sides of all parallel type AC/DC converter devices are connected to the same direct current bus. The invention can continuously and smoothly control the power flow of each 10kV line connected to the power flow control node, can reduce the construction cost of a 10kV distribution network or an upper-level power transmission network, reduces the line loss, and improves the utilization rate and the power supply reliability of the line.

Description

10kV active power distribution network based on power flow control nodes and control method thereof
Technical Field
The invention relates to the field of optimized construction and operation of a 10kV power distribution network, in particular to a power distribution network power flow control node which is introduced into the 10kV power distribution network and is used for actively controlling the power flow of the 10kV power distribution network.
Background
The power consumer is connected to the upper power transmission bearing network of the 10kV power distribution network in the power system, and plays an important role in transmitting and distributing electric energy in the power network. With the access of a large number of electric vehicle charging stations and distributed photovoltaic power supplies, the change of the size and direction of the power flow of a 10kV power distribution network is aggravated, the conditions of light load of partial circuits and overload of partial circuits are often caused, the line loss rate can be greatly increased when the circuits are in overload operation for a long time, and the aging of the circuits and equipment is accelerated to cause faults.
Along with the increasingly prominent environmental problems and the improvement of battery technologies, the public acceptance of electric vehicles is higher and higher, and in the future, electric vehicles are bound to develop along the trend of large battery capacity, strong cruising ability and gradually improved matching services. In order to meet the quick charging requirement of the electric automobile, the power of a charger and a charging station is increased, and the maximum power of a single set of direct-current quick charging equipment reaches 500 kW. With the increase of the number of electric automobiles, the electric automobiles are used as important loads of a power distribution network in the future, the randomness of charging time and high-power loads during charging can bring great challenges to the construction and safe operation of a 10kV power distribution network, and even the reliability and safety of power supply of the 10kV power distribution network can be deteriorated under extreme conditions.
In recent years, distributed photovoltaic power generation has been rapidly developed. Governments have introduced various policies to actively support photovoltaic grid-connected projects and have focused on promoting distributed photovoltaic power generation, encouraging organizations, communities, and homes to install and use photovoltaic power generation systems. However, after a large amount of distributed photovoltaic power generation is connected to the grid, due to the characteristics of the power generation, numerous uncertain factors and problems are brought to the tide, voltage, protection, electric energy quality, planning design, reliability and the like of the power distribution network.
At present, measures for solving the problems of the 10kV power distribution network mainly solve the problems of load increase, large line loss, low tail end voltage and the like by means of technical measures such as accurate load prediction and strengthening of 10kV distribution line construction, compensation device addition, optimal scheduling, real-time network reconstruction and the like in a planning stage. Such as: the method comprises the following steps of patent application 201410630097.4 (an active power distribution network planning method with distributed photovoltaic grid connection), patent application 201410662732.7 (an active power distribution network optimization configuration structure and a configuration method thereof), patent application 201310755765.1 (a power distribution network active reconstruction strategy and a prevention control method thereof), patent application 201410643725.2 (a multi-target network reconstruction method suitable for an active power distribution network) and the like. The technical measures have a series of problems, such as: large investment, long construction period, incapability of greatly improving the power distribution reliability and lack of the flexibility of tidal current regulation. A recent patent (power switching node and medium voltage distribution network active power flow control network and control method CN 104934972A) better solves the above problems, but also has the problem that the capacity of the AC/DC converter in the proposed "power switching node" is large, and thus the volume and cost of the whole device are high.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a technical scheme of a 10kV active power distribution network based on a power flow control node and a control method thereof.
The 10kV active power distribution network based on the power flow control node is characterized in that: a plurality of power flow control nodes are configured in a 10kV power distribution network, the power flow control nodes connect two or more than two 10kV power distribution lines, and active adjustment of power flow of the connected 10kV power distribution lines is achieved through series-connection type AC/DC converter devices in the power flow control nodes.
The 10kV active power distribution network based on the power flow control node is characterized in that the power flow control node comprises at least one or more than one 10kV distribution line series type AC/DC converter device, a parallel type AC/DC converter device, a direct current bus, a common connection point of the converter devices and a node control protection system.
The 10kV active power distribution network based on the power flow control nodes is characterized in that the 10kV power distribution lines are from the same or different 10kV buses of the same upper-level transformer substation or from 10kV buses of different upper-level transformer substations.
The 10kV active power distribution network based on the power flow control nodes is characterized in that the initial end of each 10kV power distribution line is connected with a 10kV bus of a transformer substation corresponding to the 10kV power distribution line, the tail end of each 10kV power distribution line is connected with the incoming line end of a series AC/DC converter corresponding to the 10kV power distribution line through a node incoming line switch, and the outgoing line end of the series AC/DC converter is connected with a common connection point of the converters; the alternating current end of the parallel AC/DC converter is also connected with the common connection point of the converter; the direct current sides of the series AC/DC converter device and the parallel AC/DC converter device are connected with the same direct current bus; the common connection point of the converter devices can be connected with a three-phase load or a power supply, or no load or power supply exists; the node control protection system monitors the operation conditions of all devices in the power flow control node in real time, is in two-way communication with a distribution network regulation and control center, and obtains a scheduling instruction to control the operation of the power flow control node by sending node state information; when the interior of the power flow control node or a power grid system has a fault, the node control protection system outputs a protection signal to protect devices in the node and a 10kV distribution line connected with the node.
The 10kV active power distribution network based on the power flow control node is characterized in that the series AC/DC converter device comprises an AC/DC converter main circuit consisting of power electronic switching devices, a series transformer, a bypass switch and a corresponding control protection circuit; the topology of the main circuit of the AC/DC converter is a three-phase two-level converter, a diode clamping type multi-level converter, a flying capacitor type multi-level converter or an MMC type converter; the main circuit of the AC/DC converter adopts a full-control power electronic device and/or a half-control power electronic switching device; the bypass switch can be arranged on the 10kV side and also can be arranged on the low-voltage side of the series transformer; the AC side of the AC/DC converter main circuit is connected with the low-voltage side of the series transformer, and the DC side of the AC/DC converter main circuit is connected with the DC bus; the high-voltage side of the series transformer is connected in series with a corresponding 10kV distribution line; and all 10kV distribution lines connected to the power flow control node, wherein at most one distribution line is directly connected to the common connection point of the current transformers without passing through the series AC/DC current transformers.
The 10kV active power distribution network based on the power flow control node is characterized in that the parallel AC/DC converter device comprises an AC/DC converter main circuit consisting of power electronic switching devices, a booster transformer and a corresponding control protection circuit; the topology of the main circuit of the AC/DC converter is a three-phase two-level converter, a diode clamping type multi-level converter, a flying capacitor type multi-level converter or an MMC type converter; the main circuit adopts a full-control power electronic device and/or a half-control power electronic switching device; the AC side of the AC/DC converter main circuit is connected with the low-voltage side of the step-up transformer, and the DC side of the AC/DC converter main circuit is connected with the DC bus; the high-voltage side of the boosting transformer is connected with the common connection point of the converter device.
The 10kV active power distribution network based on the power flow control node is characterized in that each series type AC/DC converter device and each parallel type AC/DC converter device are provided with a controller corresponding to the series type AC/DC converter device, and the total control strategy is as follows: 1) the node control protection system cooperatively adjusts the power flow of the corresponding 10kV distribution line according to the instruction of the power grid regulation center and the operation condition of the 10kV distribution line and the controllers of all the series AC/DC converter devices; the control method is that the load flow of the 10kV line is adjusted by changing the voltage amplitude and the phase of the series AC/DC converter device injected into the 10kV line; 2) the parallel AC/DC converter device adopts a constant direct current voltage control method to control the voltage of the direct current bus and controls the reactive power injected into the common connection point of the converter device according to the instruction of the power grid regulation center.
The 10kV active power distribution network based on the power flow control node and the control method thereof are characterized in that the node control protection system comprises: 1) monitoring the states of an AC/DC converter, a series transformer, a parallel transformer, a bypass switch of a converter device and a node incoming line switch in the power flow control node in real time; collecting the load and the power output of the common connection point of the converter in real time; 2) carrying out information interaction with an EMS or SCADA system of a distribution network regulation and control center; 3) after calculating according to a power flow instruction issued by a distribution network control center and detected load and power output, sending a corresponding adjusting instruction to a controller of each AC/DC converter; 4) when the interior of the power flow control node or the power grid system has a fault, the control protection system outputs a protection signal to a bypass switch and a node incoming line switch of the converter device to realize the protection of the device in the node.
The power flow control node is characterized in that: the system comprises one or more series AC/DC converter devices, a parallel AC/DC converter device, a direct current bus, a common connection point of the converter devices and a node control protection system; the incoming line end of the series AC/DC converter device is connected with the tail end of the corresponding 10kV distribution line through a 10kV incoming line switch, the outgoing line end of the series AC/DC converter device is connected with the common connection point of the converter devices, and the direct current end of the series AC/DC converter device is connected to the direct current bus; the AC end of the parallel AC/DC converter is connected with the common connection point of the converter, and the DC end of the parallel AC/DC converter is connected to the DC bus; the common connection point of the converter devices can be connected with a three-phase load or a power supply, or no load or power supply exists; the node control protection system monitors the operation condition of each device in the power flow control node in real time, is in two-way communication with a distribution network regulation and control center, and controls the operation of the power flow control node by sending node state information, obtaining a scheduling instruction and the operation condition of a 10kV distribution line.
The control method of the power distribution network is characterized in that:
under normal conditions, the control strategy of the power flow control node is as follows: the node control protection system calculates the amplitude and the phase of the voltage which needs to be injected into the corresponding 10kV distribution line of each series AC/DC converter device according to the electrical parameters of all 10kV distribution lines connected to the power flow control node, the real-time operation working condition and the power flow target value issued by the distribution network control center, and then sends the voltage amplitude and phase instructions to the controller of each series AC/DC converter device to realize the real-time control of the power flow of all 10kV distribution lines connected to the power flow control node; the parallel AC/DC converter device controls the voltage of the direct current bus according to the set value of the direct current bus voltage;
when a 10kV bus of a transformer substation of one 10kV distribution line connected to the power flow control node loses power, the control strategy of the power flow control node is as follows: adjusting the power flow of the rest 10kV distribution lines connected to the power flow control node so that the rest 10kV distribution lines can transfer power to the load of the 10kV distribution lines on the premise of no overload; and the parallel AC/DC converter device controls the voltage of the direct current bus according to the set value of the direct current bus voltage.
The invention has the beneficial effects that:
1) the power flow control node provided by the invention can continuously and smoothly control the power flow of each 10kV distribution line connected to the power flow control node, so that the utilization rate of equipment is increased, the service life of the equipment is prolonged, and the power supply reliability is improved. The basic working principle is that the current of a distribution line is adjusted by adjusting the voltage injected into the 10kV distribution line by a series AC/DC converter, so as to adjust the power flow.
2) Because the current of distribution lines can be adjusted at will (through adjusting the injection voltage of tandem type AC/DC converter), consequently can accomplish the load of balanced each interconnecting link, shift some load on the heavy load circuit to the light load circuit, improve the utilization ratio of distribution network line resource, reduce the construction input of 10kV distribution network, reduce the loss that falls of distribution network.
3) Compared with the capacity of the AC/DC converter in patent CN104934972A (the capacity of the AC/DC converter in patent CN104934972A is equal to the power supply capacity of the distribution line), the capacity of the series AC/DC converter in the present invention is very small. The reason is that most 10kV distribution lines are short in length and low in impedance, and the series type AC/DC converter device can greatly change the power flow of the distribution lines only by injecting low voltage, so that the capacity of the series type AC/DC converter device can be configured to be small.
Drawings
Figure 1 is a schematic partial view of a medium voltage distribution network including power flow control nodes;
fig. 2 is a schematic diagram of an internal structure of a power flow control node;
FIG. 3 is a schematic diagram of an embodiment of the present invention.
Detailed Description
The invention will be further described with reference to the accompanying drawings in which:
as shown in fig. 1, a plurality of power flow control nodes are configured in a 10kV power distribution network, and the "power flow control nodes" connect two or more 10kV power distribution lines in the 10kV power distribution network, and actively adjust the power flow of the connected 10kV power distribution lines through series-type AC/DC converters in the power flow control nodes. The 10kV distribution lines are the same or different 10kV buses from the same upper-level transformer substation or the 10kV buses from different upper-level transformer substations.
The power flow control node comprises at least one or more than one 10kV distribution line series type AC/DC converter device, a parallel type AC/DC converter device, a direct current bus, a common connection point of the converter devices and a node control protection system.
The starting end of each 10kV distribution line is connected with a 10kV bus of a corresponding transformer substation, the tail end of each 10kV distribution line is connected with the wire inlet end of the corresponding series AC/DC converter device through a node wire inlet switch, and the wire outlet end of the series AC/DC converter device is connected with the common connection point of the converter devices; the alternating current end of the parallel AC/DC converter is also connected with the common connection point of the converter; the direct current sides of the series AC/DC converter and the parallel AC/DC converter are connected with the same direct current bus; the common connection point of the current transformers can be connected with a three-phase load or a power supply, or no load or power supply is arranged; the node control protection system monitors the operation condition of each device in the power flow control node in real time, bidirectionally communicates with a distribution network regulation and control center, and obtains a scheduling instruction to control the operation of the power flow control node by sending node state information; when the interior of the power flow control node or a power grid system has a fault, the node control protection system outputs a protection signal to protect devices in the node and a 10kV distribution line connected with the node.
The series AC/DC converter comprises an AC/DC converter main circuit consisting of power electronic switching devices, a series transformer, a bypass switch and a corresponding control protection circuit; the topology of the main circuit of the AC/DC converter is a three-phase two-level converter, a diode clamping type multi-level converter, a flying capacitor type multi-level converter or an MMC type converter; the main circuit of the AC/DC converter adopts a full-control power electronic device and/or a half-control power electronic switching device; the bypass switch can be arranged at the 10kV side and also can be arranged at the low-voltage side of the series transformer; the AC side of the AC/DC converter main circuit is connected with the low-voltage side of the series transformer, and the DC side of the AC/DC converter main circuit is connected with the DC bus; the high-voltage side of the series transformer is connected in series with a corresponding 10kV distribution line; and all 10kV distribution lines connected to the power flow control node, wherein at most one distribution line is directly connected to the common connection point of the current transformers without passing through the series AC/DC current transformers.
The parallel AC/DC converter comprises an AC/DC converter main circuit consisting of power electronic switching devices, a step-up transformer and a corresponding control protection circuit; the topology of the main circuit of the AC/DC converter is a three-phase two-level converter, a diode clamping type multi-level converter, a flying capacitor type multi-level converter or an MMC type converter; the main circuit adopts a full-control power electronic device and/or a half-control power electronic switching device; the AC side of the AC/DC converter main circuit is connected with the low-voltage side of the step-up transformer, and the DC side of the AC/DC converter main circuit is connected with the DC bus; the high-voltage side of the step-up transformer is connected with the common connection point of the converter devices.
Each of the series type AC/DC converter device and the parallel type AC/DC converter device is provided with a controller corresponding thereto, and the total control strategy is as follows: 1) the node control protection system cooperatively adjusts the power flow of the corresponding 10kV distribution line according to the instruction of the power grid regulation center and the operation condition of the 10kV distribution line and the controllers of all the series AC/DC converter devices; the control method is that the load flow of the 10kV line is adjusted by changing the voltage amplitude and the phase of the 10kV line injected by the series AC/DC converter device; 2) the parallel AC/DC converter device adopts a constant direct current voltage control method to control the voltage of the direct current bus and controls the reactive power injected into the common connection point of the converter device according to the instruction of the power grid regulation center.
The node control protection system comprises: 1) monitoring the states of an AC/DC converter, a series transformer, a parallel transformer, a bypass switch of a converter device and a node incoming line switch in the power flow control node in real time; collecting the load and the power output of the common connection point of the converter in real time; 2) carrying out information interaction with an EMS or SCADA system of a distribution network regulation and control center; 3) after calculating according to a power flow instruction issued by a distribution network control center and detected load and power output, sending a corresponding adjusting instruction to a controller of each AC/DC converter; 4) when the interior of the power flow control node or the power grid system has a fault, the control protection system outputs a protection signal to a bypass switch and a node incoming line switch of the converter device to realize the protection of the device in the node.
A power flow control node comprises one or more series-connection type AC/DC converter devices, a parallel-connection type AC/DC converter device, a direct current bus, a common connection point of the converter devices and a node control protection system; the incoming line end of the series AC/DC converter device is connected with the tail end of the corresponding 10kV distribution line through a 10kV incoming line switch, the outgoing line end of the series AC/DC converter device is connected with the common connection point of the converter devices, and the direct current end of the series AC/DC converter device is connected to the direct current bus; the AC end of the parallel AC/DC converter is connected with the common connection point of the converters, and the DC end of the parallel AC/DC converter is connected to the DC bus; the common connection point of the current transformers can be connected with a three-phase load or a power supply, or no load or power supply is arranged; the node control protection system monitors the operation condition of each device in the power flow control node in real time, is in two-way communication with the distribution network regulation and control center, and controls the operation of the power flow control node by sending node state information, obtaining a scheduling instruction and the operation condition of a 10kV distribution line.
A control method of a 10kV active power distribution network based on a power flow control node is characterized in that under a normal condition, the control strategy of the power flow control node is as follows: the node control protection system calculates the amplitude and the phase of the voltage which needs to be injected into the corresponding 10kV distribution line of each series AC/DC converter device according to the electrical parameters of all 10kV distribution lines connected to the power flow control node, the real-time operation working condition and the power flow target value issued by the distribution network control center, and then sends the voltage amplitude and phase instructions to the controller of each series AC/DC converter device to realize the real-time control of the power flow of all 10kV distribution lines connected to the power flow control node; the parallel AC/DC converter device controls the voltage of the direct current bus according to the set value of the direct current bus voltage; when a 10kV bus of a transformer substation of one 10kV distribution line connected to the power flow control node loses power, the control strategy of the power flow control node is as follows: adjusting the power flow of the rest 10kV distribution lines connected to the power flow control node so that the rest 10kV distribution lines can transfer power to the load of the 10kV distribution lines on the premise of no overload; and the parallel AC/DC converter device controls the voltage of the direct current bus according to the set value of the direct current bus voltage.
The working principle of the invention is as follows: the power flow control node connects two or more 10kV distribution lines, and the power flow of each line is adjusted by controlling the amplitude and the phase of the output voltage of the series AC/DC converter device in the power flow control node, so that the active control of the power flow of each 10kV distribution line is realized. And a control protection system in the power flow control node receives an instruction of a dispatching center through rapid communication and reasonably adjusts the power flow of each 10kV distribution line. The common connection point of the converter devices in the power flow control node can be connected with a large load, and when large emerging loads such as an electric vehicle rapid charging station, a large data center and the like are responded, a multi-circuit 10kV voltage distribution line simultaneous power supply mode can be adopted, and load balanced distribution of all lines is realized. When the power output and the consumption of a distributed photovoltaic power station with larger capacity (1-10 MW) are dealt with, a power flow control node can be configured at the position of the power station to transmit the generated photovoltaic power to 10kV distribution lines connected with the power flow control node, and the generated photovoltaic power is directly consumed by loads on the lines. A plurality of power flow control nodes are configured in a 10kV power distribution network, a power distribution network regulation and control center comprehensively controls all the power flow control nodes in the network, and a scheduling instruction is sent to a control protection system of each power flow control node, so that the overall multi-target optimized operation of the 10kV power distribution network is realized.
As shown in fig. 2, the "power flow control node" includes two or more series AC/DC converters, a parallel AC/DC converter, a DC bus, a common connection point of the converters, and a node control protection system. The inlet end of the series AC/DC converter is connected with the tail end of a corresponding 10kV distribution line through an inlet switch, the outlet end of the series AC/DC converter is connected with the common connection point of the converter, and the direct current end of the series AC/DC converter is connected to the direct current bus; the AC end of the parallel AC/DC converter is connected with the common connection point of the converters, and the DC end is connected to the DC bus. The common connection point of the current transformers can be connected with a three-phase load or a power supply, or no load or power supply is arranged; the node control protection system monitors the operation condition of each device in the power flow control node in real time, is in two-way communication with the distribution network regulation and control center, and controls the operation of the power flow control node by sending node state information and obtaining a scheduling instruction. The control strategy of the power flow control node is as follows: all the series AC/DC converter devices control the active power flow and the reactive power flow of corresponding 10kV distribution lines according to the instruction of the power grid dispatching control system; and the parallel AC/DC converter device controls the voltage of the direct-current bus and controls the reactive power injected into the common connection point of the converter device according to the instruction of the power grid dispatching control system. The node control protection system can monitor the power flow condition of each line in the power flow control node in real time, is in two-way communication with the distribution network regulation and control center, and controls the operation of the power flow control node by sending node state information and obtaining a scheduling instruction. The power distribution network regulation and control center comprehensively controls all 'power flow control nodes' in the network, and sends scheduling instructions to the monitoring systems of all the power flow control nodes, so that the overall multi-target optimized operation of the 10kV power distribution network is realized.
Examples
And one power flow control node is connected with two 10kV distribution lines with the same parameters. The parameters of the distribution line are as follows: 10kV three-core cross-linked armored cable, aluminum core and 240mm cross-sectional area2(ii) a R =0.162 ohm/km; x =0.0881 ohm/km. The line length is 5 km. The single-phase equivalent circuit of the system is shown in fig. 3. In fig. 3, U1 and U2 are phase voltages of 10kV bus bars of outgoing substations of distribution line 1 and distribution line 2, respectively; r1, X1 and R2, X2 are the resistance and reactance values of the distribution line 1 and the distribution line 2, respectively; according to the parameters, the following parameters are obtained: r1= R2=0.162x5=0.81 ohm; x1= X2=0.881X5=0.4405 ohms; its impedance is then:
Figure DEST_PATH_IMAGE002
ohm; u shape1 string ofAnd U2 bunchThe injection voltages of the series-type AC/DC converter devices corresponding to the distribution line 1 and the distribution line 2 are arbitrarily adjustable in magnitude and phase, and I is the current flowing through the distribution line 1 and the distribution line 2.
We know that the bus voltage of a substation is controlled around its rated voltage and their phases are also very close, i.e.: u1= U2= U =10kV/1.732=5.77 kV. Then, as can be seen from fig. 3:
I=(U1-U2+U1 string of- U2 bunch)/(2Z) =(U1 string of- U2 bunch)/(2Z)= UStringZ in the formula, UString= U1 string of= - U2 bunch(ii) a From this equation it can be seen that: as long as series type AC/DC converter is regulatedThe injection voltage of the current means can regulate the current I and thus the power flow of the distribution lines 1, 2. If it is desired to adjust the current of the distribution line 1 and the distribution line 2 to the full load current (cross-sectional area of 240 mm)2The full load current of the aluminum core cable of (a) is about: 435A) injection voltages of the two series AC/DC converters:
Ustring= IZ =435 × 0.992=432V =0.432 kV. The capacities of the two series AC/DC converters are:
Sstring=3UStringI =3 × 0.432x435=563 kVA. And the transmission capacity of the two 10kV distribution lines at the moment is as follows:
s =3UI =3 × 5.77x435=7530 kVA. It can be seen that the capacity of the series AC/DC converter is only 7.5% (563/7530=0.075) of the transmission capacity of a 10kV distribution line.
From this example, it is known that the power flow is adjusted by adjusting the voltage injected into the 10kV distribution line by the series AC/DC converter to adjust the current of the distribution line. Compared with the capacity of the AC/DC converter in patent CN104934972A (the capacity of the AC/DC converter in patent CN104934972A is equal to the power supply capacity of the distribution line), the capacity of the series AC/DC converter in the present invention is very small. The reason is that most 10kV distribution lines are short in length and low in impedance, and the series type AC/DC converter device can greatly change the power flow of the distribution lines only by injecting low voltage, so that the capacity of the series type AC/DC converter device can be configured to be small.

Claims (8)

1. The utility model provides a 10kV initiative distribution network based on trend control node which characterized in that: configuring a plurality of power flow control nodes in a 10kV power distribution network, connecting two or more than two 10kV distribution lines by the power flow control nodes, and actively adjusting the power flow of the connected 10kV distribution lines through a series AC/DC converter device in the power flow control nodes;
the power flow control node comprises more than one 10kV distribution line series type AC/DC converter device, a parallel type AC/DC converter device, a direct current bus, a common connection point of the converter devices and a node control protection system;
the starting end of each 10kV distribution line is connected with a 10kV bus of a corresponding transformer substation, the tail end of each 10kV distribution line is connected with the incoming line end of the corresponding series AC/DC converter device through a node incoming line switch, and the outgoing line end of the series AC/DC converter device is connected with the common connection point of the converter devices; the alternating current end of the parallel AC/DC converter is also connected with the common connection point of the converter; the direct current sides of the series AC/DC converter device and the parallel AC/DC converter device are connected with the same direct current bus; the common connection point of the converter devices can be connected with a three-phase load or a power supply, or no load or power supply exists; the node control protection system monitors the operation conditions of all devices in the power flow control node in real time, is in two-way communication with a distribution network regulation and control center, and obtains a scheduling instruction to control the operation of the power flow control node by sending node state information; when the interior of the power flow control node or a power grid system has a fault, the node control protection system outputs a protection signal to protect devices in the node and a 10kV distribution line connected with the node.
2. The 10kV active power distribution network based on the power flow control nodes as claimed in claim 1, wherein the 10kV distribution lines are the same or different 10kV buses from the same upper-level substation or the 10kV buses from different upper-level substations.
3. The 10kV active power distribution network based on the power flow control nodes as claimed in claim 1, wherein the series type AC/DC converter device comprises an AC/DC converter main circuit composed of power electronic switching devices, a series transformer, a bypass switch and a corresponding control protection circuit; the topology of the main circuit of the AC/DC converter is a three-phase two-level converter, a diode clamping type multi-level converter, a flying capacitor type multi-level converter or an MMC type converter; the main circuit of the AC/DC converter adopts a full-control power electronic device and/or a half-control power electronic switching device; the bypass switch can be arranged on the 10kV side and also can be arranged on the low-voltage side of the series transformer; the AC side of the AC/DC converter main circuit is connected with the low-voltage side of the series transformer, and the DC side of the AC/DC converter main circuit is connected with the DC bus; the high-voltage side of the series transformer is connected in series with a corresponding 10kV distribution line; and all 10kV distribution lines connected to the power flow control node, wherein at most one distribution line is directly connected to the common connection point of the current transformers without passing through the series AC/DC current transformers.
4. The 10kV active power distribution network based on the power flow control nodes as claimed in claim 1, wherein the parallel type AC/DC converter device comprises an AC/DC converter main circuit consisting of power electronic switching devices, a step-up transformer and a corresponding control protection circuit; the topology of the main circuit of the AC/DC converter is a three-phase two-level converter, a diode clamping type multi-level converter, a flying capacitor type multi-level converter or an MMC type converter; the main circuit adopts a full-control power electronic device and/or a half-control power electronic switching device; the AC side of the AC/DC converter main circuit is connected with the low-voltage side of the step-up transformer, and the DC side of the AC/DC converter main circuit is connected with the DC bus; the high-voltage side of the boosting transformer is connected with the common connection point of the converter device.
5. The 10kV active power distribution network based on the power flow control nodes as claimed in claim 1, wherein each of the series type AC/DC converter devices and the parallel type AC/DC converter devices is provided with a controller corresponding thereto, and the total control strategy is as follows: 1) the node control protection system cooperatively adjusts the power flow of the corresponding 10kV distribution line according to the instruction of the power grid regulation center and the operation condition of the 10kV distribution line and the controllers of all the series AC/DC converter devices; the control method is that the load flow of the 10kV line is adjusted by changing the voltage amplitude and the phase of the series AC/DC converter device injected into the 10kV line; 2) the parallel AC/DC converter device adopts a constant direct current voltage control method to control the voltage of the direct current bus and controls the reactive power injected into the common connection point of the converter device according to the instruction of the power grid regulation center.
6. The 10kV active power distribution network based on the power flow control nodes and the control method thereof as claimed in claim 1, wherein the node control protection system: 1) monitoring the states of an AC/DC converter, a series transformer, a parallel transformer, a bypass switch of a converter device and a node incoming line switch in the power flow control node in real time; collecting the load and the power output of the common connection point of the converter in real time; 2) carrying out information interaction with an EMS or SCADA system of a distribution network regulation and control center; 3) after calculating according to a power flow instruction issued by a distribution network control center and detected load and power output, sending a corresponding adjusting instruction to a controller of each AC/DC converter; 4) when the interior of the power flow control node or the power grid system has a fault, the control protection system outputs a protection signal to a bypass switch and a node incoming line switch of the converter device to realize the protection of the device in the node.
7. A power flow control node, characterized by: the system comprises more than one series-connection type AC/DC converter device, a parallel-connection type AC/DC converter device, a direct-current bus, a common connection point of the converter devices and a node control protection system; the incoming line end of the series AC/DC converter device is connected with the tail end of the corresponding 10kV distribution line through a 10kV incoming line switch, the outgoing line end of the series AC/DC converter device is connected with the common connection point of the converter devices, and the direct current end of the series AC/DC converter device is connected to the direct current bus; the AC end of the parallel AC/DC converter is connected with the common connection point of the converter, and the DC end of the parallel AC/DC converter is connected to the DC bus; the common connection point of the converter devices can be connected with a three-phase load or a power supply, or no load or power supply exists; the node control protection system monitors the operation condition of each device in the power flow control node in real time, is in two-way communication with a distribution network regulation and control center, and controls the operation of the power flow control node by sending node state information, obtaining a scheduling instruction and the operation condition of a 10kV distribution line.
8. A method of controlling a power distribution network according to claim 1, characterized by:
under normal conditions, the control strategy of the power flow control node is as follows: the node control protection system calculates the amplitude and the phase of the voltage which needs to be injected into the corresponding 10kV distribution line of each series AC/DC converter device according to the electrical parameters of all 10kV distribution lines connected to the power flow control node, the real-time operation working condition and the power flow target value issued by the distribution network control center, and then sends the voltage amplitude and phase instructions to the controller of each series AC/DC converter device to realize the real-time control of the power flow of all 10kV distribution lines connected to the power flow control node; the parallel AC/DC converter device controls the voltage of the direct current bus according to the set value of the direct current bus voltage;
when a 10kV bus of a transformer substation of one 10kV distribution line connected to the power flow control node loses power, the control strategy of the power flow control node is as follows: adjusting the power flow of the rest 10kV distribution lines connected to the power flow control node so that the rest 10kV distribution lines can transfer power to the load of the 10kV distribution lines on the premise of no overload; and the parallel AC/DC converter device controls the voltage of the direct current bus according to the set value of the direct current bus voltage.
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