CN109412192B - Self-energy-storage multi-end back-to-back flexible straight device operation method - Google Patents

Self-energy-storage multi-end back-to-back flexible straight device operation method Download PDF

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CN109412192B
CN109412192B CN201811497997.0A CN201811497997A CN109412192B CN 109412192 B CN109412192 B CN 109412192B CN 201811497997 A CN201811497997 A CN 201811497997A CN 109412192 B CN109412192 B CN 109412192B
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energy
storage unit
energy storage
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power
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CN109412192A (en
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葛乐
陆怀谷
钱波
李绮
阮涛
孙蓉
袁晓冬
陈继忠
张伟
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State Grid Corp of China SGCC
State Grid Jiangsu Electric Power Co Ltd
Changzhou Power Supply Co of State Grid Jiangsu Electric Power Co Ltd
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State Grid Corp of China SGCC
State Grid Jiangsu Electric Power Co Ltd
Changzhou Power Supply Co of State Grid Jiangsu Electric Power Co Ltd
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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
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • 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
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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]

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Abstract

The invention relates to an operation method of a self-energy-storage multi-end back-to-back flexible-straight device, which comprises the steps of calculating whether the comprehensive power supply cost of a power distribution network has a lowest value when the self-energy-storage multi-end back-to-back flexible-straight device executes power regulation; reading the charge state of an energy storage unit in the self-energy-storage multi-end back-to-back flexible-straight device; switching the operation mode of the self-energy-storage multi-end back-to-back flexible-straight device according to the values of the two steps; the mode of operation from energy storage multiple-end back-to-back gentle straight device includes: when the energy storage unit does not operate, the self-energy-storage multi-end back-to-back flexible straight device executes power regulation; the energy storage unit operates, and the self-energy-storage multi-end back-to-back flexible straight device executes power energy time sequence adjustment; the energy storage unit executes charge state recovery, and the energy storage multi-end back-to-back flexible-straight device independently executes power regulation. The configuration capacity of the stored energy can be effectively reduced, the service life of the stored energy is prolonged, the high-permeability clean energy consumption capacity is effectively improved, the power supply reliability is improved, the power supply quality is improved, and the operation economy is improved.

Description

Self-energy-storage multi-end back-to-back flexible straight device operation method
Technical Field
The invention relates to the field of optimized operation of active power distribution networks, in particular to an operation method and device of a self-energy-storage multi-end back-to-back flexible-straight device.
Background
High-reliability power supply and full and friendly consumption of high-permeability clean energy put higher requirements on the construction and operation of the power distribution network in China in a new period. The operation of a power distribution network looped network is an important way for further improving the power supply reliability, but the safe operation of a power grid is damaged by larger impact/loop closing current due to the fact that potential and short-circuit impedance difference exists on two sides of a feeder line in an alternating current loop closing mode. The problems of short-time peak power generation load of clean energy and high voltage caused by the short-time peak power generation load are increasingly prominent, the construction/capacity increase of a power grid is increased, more reactive power compensation devices such as Static Var Generators (SVG) are put into use, the construction and operation cost of the power distribution network is greatly increased, the problem of voltage out-of-limit can be well solved by limiting active power output and adjusting reactive power output of an inverter, and the fact that wind and light are abandoned in the power distribution network is caused.
To solve the above problems, a new technical approach needs to be applied. Multi-terminal back-to-back flexible direct current (VSC-HVDC, VSC-MTDC) is a newly developed power grid flexible control technology, which performs AC-DC-AC decoupling interconnection on an alternating current system based on a voltage source converter sharing a DC bus, and can realize long-term safe loop closing operation of any feeder line; PQ four-quadrant control can accurately regulate and control power flow distribution of a power grid; the direct current circuit link is omitted, the cost and the complexity of a control system are reduced, and the method is more suitable for the practical distribution network in China.
The flexible power flow control technology represented by back-to-back flexibility and straightness is still the regulation and control of a power level in essence, and the energy level is embodied in that an energy container is provided on a spatial axis by a power grid, but when the adjustable capacity of an interconnection feeder line is low, the optimized operation effect of the interconnection power distribution network can be reduced, and even the situation that the system safety and the power supply quality constraint cannot be met can still occur. Energy Storage System (ESS) technology essentially improves the simultaneity of power production, transmission and consumption as a "energy container" of the timeline. Although a power grid can guide the energy storage equipment invested by a user or a clean energy power station to provide support for the operation of the power grid through incentive measures such as demand response, auxiliary service pricing and the like, the incentive cost/effect is not fully controllable, and the demand of energy storage configuration on the side of the power distribution grid is promoted.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a self-energy-storage multi-end back-to-back flexible and straight device operation method and device aiming at the defects of the prior art, so that the defects that clean energy cannot be fully and friendly consumed, power supply reliability and economy are poor, and operation requirements cannot be met only by power adjustment when the total adjustment margin of each feeder line of a system is insufficient are overcome.
The technical scheme adopted by the invention for solving the technical problems is as follows: the operation method of the self-energy-storage multi-end back-to-back flexible straight device is provided, and comprises the following steps: s1: calculating whether the comprehensive power supply cost of the power distribution network has a lowest value when the self-energy-storage multi-end back-to-back flexible-straight device executes power regulation; s2: reading the charge state of an energy storage unit in the self-energy-storage multi-end back-to-back flexible-straight device; s3: switching the operation mode of the self-energy-storage multi-end back-to-back flexible-and-straight device according to the condition that whether the comprehensive power supply cost of the power distribution network has the lowest value or not when the self-energy-storage multi-end back-to-back flexible-and-straight device performs power regulation and the charge state of an energy storage unit in the self-energy-storage multi-end back-to-back flexible-and-straight device; the operation mode of the self-energy-storage multi-end back-to-back flexible straight device comprises: the energy storage unit does not operate, and the self-energy-storage multi-end back-to-back flexible straight device performs power regulation; the energy storage unit operates, and the self-energy-storage multi-end back-to-back flexible straight device executes power energy time sequence adjustment; the energy storage unit executes charge state recovery, and the self-energy-storage multi-end back-to-back flexible-straight device independently executes power regulation.
The state of charge of the energy storage unit comprises: in a standby state, the energy storage unit is in a moderate charge state and can meet the requirement of optimal operation of the distribution network in the next time period at any time; in a normal non-standby state, the energy storage unit is in a wider charge state, and the adjustable capacity is smaller; and in an abnormal state, the energy storage unit is in an emergency charge state.
The standby state is that the charge value range of the energy storage unit is more than or equal to 0.4 and less than or equal to 0.6; the normal non-standby state is that the charge value range of the energy storage unit is more than or equal to 0.15 and less than or equal to 0.85; the abnormal state is that the charge value range of the energy storage unit is more than or equal to 0 and less than 0.15 or more than 0.85 and less than or equal to 1.
According to whether the self-energy-storage multi-end back-to-back flexible-to-straight device has the lowest value of the comprehensive power supply cost during power adjustment and the charge state of the energy storage unit, the operation mode of the self-energy-storage multi-end back-to-back flexible-to-straight device is switched to include: when the self-energy-storage multi-end back-to-back flexible-straight device performs power regulation, the comprehensive power supply cost has the lowest value, and when the energy storage unit is in a standby state, the energy storage unit does not operate, and the self-energy-storage multi-end back-to-back flexible-straight device performs power regulation; when the self-energy-storage multi-end back-to-back flexible-straight device is in a power regulation mode, the comprehensive power supply cost has the lowest value, and the energy storage unit is in a normal non-standby state or a non-normal state, the energy storage unit executes charge state recovery, and the self-energy-storage multi-end back-to-back flexible-straight device independently executes power regulation; when the self-energy-storage multi-end back-to-back flexible-straight device is in a power regulation mode, the comprehensive power supply cost has no lowest value, and the energy storage unit is in a standby state or a normal non-standby state, the energy storage unit is put into operation, and the self-energy-storage multi-end back-to-back flexible-straight device executes power energy time sequence regulation; when the self-energy-storage multi-end back-to-back flexible-straight device is in a power regulation mode, the comprehensive power supply cost has no lowest value, and when the energy storage unit is in an abnormal state, the energy storage unit executes charge state recovery, and the self-energy-storage multi-end back-to-back flexible-straight device independently executes power regulation.
The energy storage unit performing state of charge recovery comprises: and restoring the current charge value of the energy storage unit to be the minimum difference value with the intermediate value of the energy storage charge.
The objective function of the energy storage unit when the current charge value is restored to the minimum difference value with the energy storage charge intermediate value is as follows:
Figure BDA0001897379660000041
SOC (t) is the state of charge of the energy storage unit at time t;
PESS(t) the output power of the energy storage unit in a period t;
Δ t is the duration of each time segment;
SESSthe rated electric quantity of the energy storage unit is set;
SOCmidthe charge intermediate value of the energy storage unit is obtained;
the charging and discharging power of the energy storage unit is calculated according to the residual electric quantity of the energy storage unit;
and the nuclear power state of the energy storage unit in the next period is calculated according to the stored energy charge value in the current period and the stored energy power released in the current period.
The charging and discharging power of the energy storage unit is calculated according to the remaining electric quantity of the energy storage unit by the following formula:
PESS(t)＝uPcd(t),u∈{-1,0,1}；
Figure BDA0001897379660000042
the next-period nuclear power state of the energy storage unit is calculated according to the stored energy charge value and the stored energy power released in the current period by the following formula:
Figure BDA0001897379660000043
SOC(0)＝SOC(T)；
t is the number of time periods divided by the complete scheduling cycle;
Δ t is the duration of each time period;
PESS(t) of the energy storage unit for a period of tOutputting power;
Pcd(t) the charging and discharging power of the energy storage unit is constant positive in a period t;
u is a charging and discharging mark of the energy storage unit;
Pch,max、Pdis,maxthe maximum charge and discharge power of the energy storage unit;
SESSthe rated electric quantity of the energy storage unit is set;
SOC (t) is the state of charge of the energy storage unit at time t;
SOCmax、SOCminrespectively representing the safe upper and lower limits of the state of charge of the energy storage unit;
ηch、ηdisrespectively the charge and discharge efficiency of the energy storage unit.
The invention also provides a self-energy-storage multi-end back-to-back flexible direct current device which comprises at least two AC/DC converters and at least one energy storage unit, wherein the direct current sides of the AC/DC converters are connected in parallel with the direct current bus, and the alternating current sides of the AC/DC converters are connected with a feeder line of a power distribution network; one side of the energy storage unit is connected with a DC/DC converter, and the other side of the DC/DC converter is connected with the direct current bus in parallel; the self-energy-storage multi-end back-to-back flexible-straight device further comprises an operation mode adjusting module, and the operation mode adjusting module switches the operation mode of the self-energy-storage multi-end back-to-back flexible-straight device according to the condition that whether the comprehensive power supply cost of the power distribution network has the lowest value or not and the charge state of the energy storage unit when the self-energy-storage multi-end back-to-back flexible-straight device performs power adjustment; the operation mode of the self-energy back-to-back gentle and straight device comprises: the energy storage unit does not operate, and the self-energy-storage multi-end back-to-back flexible straight device performs power regulation; the energy storage unit operates, and the self-energy-storage multi-end back-to-back flexible straight device executes power energy time sequence adjustment; the energy storage unit executes charge state recovery, and the self-energy-storage multi-end back-to-back flexible straight device independently executes power regulation; when the energy storage unit operates or performs state of charge recovery, the DC/DC converter controls charging and discharging of the energy storage unit.
The state of charge of the energy storage unit comprises: in a standby state, the energy storage unit is in a moderate charge state and can meet the requirement of optimal operation of the distribution network in the next time period at any time; in a normal non-standby state, the energy storage unit is in a wider charge state, and the adjustable capacity is smaller; and in an abnormal state, the energy storage unit is in an emergency charge state.
The standby state is that the charge value range of the energy storage unit is more than or equal to 0.4 and less than or equal to 0.6; the normal non-standby state is that the charge value range of the energy storage unit is more than or equal to 0.15 and less than or equal to 0.85; the abnormal state is that the charge value range of the energy storage unit is more than or equal to 0 and less than 0.15 or more than 0.85 and less than or equal to 1.
The operation mode adjusting module comprises a processor, and the processor switches the operation mode of the self-energy-storage multi-end back-to-back flexible-straight device according to the condition that whether the comprehensive power supply cost of the self-energy-storage multi-end back-to-back flexible-straight device has the lowest value or not when power adjustment is performed and the charge state of the energy storage unit.
The operation mode adjusting module is used for adjusting the operation mode of the self-energy-storage multi-end back-to-back flexible-to-straight device according to the condition that whether the comprehensive power supply cost has the lowest value or not when the self-energy-storage multi-end back-to-back flexible-to-straight device is used for executing power adjustment and the charge state of the energy storage unit, and the operation mode of the self-energy-storage multi-end back-to: when the self-energy-storage multi-end back-to-back flexible-straight device performs power regulation, the comprehensive power supply cost has the lowest value, and when the energy storage unit is in a standby state, the operation mode regulation module controls the energy storage unit not to operate and controls the self-energy-storage multi-end back-to-back flexible-straight device to perform power regulation; when the self-energy-storage multi-end back-to-back flexible-straight device executes a power regulation mode, the comprehensive power supply cost has the lowest value, and when the energy storage unit is in a normal non-standby state or a non-normal state, the operation mode regulation module controls the energy storage unit to execute charge state recovery and controls the self-energy-storage multi-end back-to-back flexible-straight device to independently execute power regulation; when the self-energy-storage multi-end back-to-back flexible straight device executes power adjustment, the comprehensive power supply cost has no lowest value, and the energy storage unit is in a standby state or a normal non-standby state, the operation mode adjustment module controls the energy storage unit to be operated and controls the self-energy-storage multi-end back-to-back flexible straight device to execute power energy time sequence adjustment; when the self-energy-storage multi-end back-to-back flexible and straight device executes a power regulation mode, the comprehensive power supply cost has no lowest value, and when the energy storage unit is in an abnormal state, the operation mode regulation module controls the energy storage unit to execute charge state recovery and controls the self-energy-storage multi-end back-to-back flexible and straight device to independently execute power regulation.
The energy storage unit performing state of charge recovery comprises: and restoring the current charge value of the energy storage unit to be the minimum difference value with the intermediate value of the energy storage charge.
The objective function of the energy storage unit when the current charge value is restored to the minimum difference value with the energy storage charge intermediate value is as follows:
Figure BDA0001897379660000071
SOC (t) is the state of charge of the energy storage unit at time t;
PESS(t) the output power of the energy storage unit in a period t;
Δ t is the duration of each time segment;
SESSthe rated electric quantity of the energy storage unit is set;
SOCmidthe charge intermediate value of the energy storage unit is obtained;
the charging and discharging power of the energy storage unit is calculated according to the residual electric quantity of the energy storage unit;
and the nuclear power state of the energy storage unit in the next period is calculated according to the stored energy charge value in the current period and the stored energy power released in the current period.
The charging and discharging power of the energy storage unit is calculated according to the remaining electric quantity of the energy storage unit by the following formula:
PESS(t)＝uPcd(t),u∈{-1,0,1}；
Figure BDA0001897379660000072
the next-period nuclear power state of the energy storage unit is calculated according to the stored energy charge value and the stored energy power released in the current period by the following formula:
Figure BDA0001897379660000081
SOC(0)＝SOC(T)；
t is the number of time periods divided by the complete scheduling cycle;
Δ t is the duration of each time period;
PESS(t) the output power of the energy storage unit in a period t;
Pcd(t) the charging and discharging power of the energy storage unit is constant positive in a period t;
u is a charging and discharging mark of the energy storage unit;
Pch,max、Pdis,maxthe maximum charge and discharge power of the energy storage unit;
SESSthe rated electric quantity of the energy storage unit is set;
SOC (t) is the state of charge of the energy storage unit at time t;
SOCmax、SOCminrespectively representing the safe upper and lower limits of the state of charge of the energy storage unit;
ηch、ηdisrespectively the charge and discharge efficiency of the energy storage unit.
The invention also provides a flexible interconnected power distribution network, which adopts the self-energy-storage multi-end back-to-back flexible-straight device, and the self-energy-storage multi-end back-to-back flexible-straight device switches the operation mode of the self-energy-storage back-to-back flexible-straight device according to the condition that whether the comprehensive power supply cost of the power distribution network has the lowest value or not in the power regulation mode and the charge state of the energy storage unit in the self-energy-storage back-to-back flexible-straight device.
The invention provides a composite control method of a self-energy-storage multi-end back-to-back flexible-straight device, which aims at the self-energy-storage multi-end back-to-back flexible-straight device, and aims to improve the clean energy consumption capability and the power supply reliability of a flexible interconnected power distribution network, effectively reduce the configuration capacity of an energy storage unit and prolong the service life of the energy storage unit.
The self-energy-storage multi-end back-to-back flexible and straight device enables the energy storage unit to be in a reasonable charge state in each time period in one operation cycle, participates in necessary energy time sequence optimization adjustment, can avoid overshoot or over discharge of the energy storage unit, and ensures that the energy storage unit has the adjustment capability in the next time period. Compared with a multi-end back-to-back flexible-direct device (VSC-MTDC) without an energy storage unit, the self-energy-storage multi-end back-to-back flexible-direct device (SES-VSC-MTDC) operation method provided by the invention can adapt to more complex high-permeability clean energy grid-connected operation scenes and control requirements.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a flow chart of a method for operating a self-storing multi-terminal back-to-back soft-straightening device (SES-VSC-MTDC) according to an embodiment of the present invention;
FIG. 2 is a control flow diagram of step 30 of the method of operating the self-storing multi-port back-to-back soft-straight device of FIG. 1;
FIG. 3 is a schematic block diagram of a self-storing multi-terminal back-to-back soft-direct device (SES-VSC-MTDC) according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a 33-node exemplary system in accordance with an embodiment of the present invention;
FIG. 5 is a graph of A feeder load versus DG for the graph of FIG. 4;
fig. 6 is a graph of B feeder load versus DG in fig. 4;
FIG. 7 is a graph of C feeder load versus DG for the graph of FIG. 4;
FIG. 8 is a graph of D feeder load versus DG for the graph of FIG. 4;
FIG. 9 is a graph of the feed line output for the system of FIG. 4 in open loop operation;
FIG. 10 is a graph of the individual feeder output curves for the system of FIG. 4 under power regulation;
FIG. 11 is a graph of the individual feeder output curves for the system of FIG. 4 under power-energy timing adjustment;
FIG. 12 is a graph of the integrated power cost versus time period for the system of FIG. 4 in open loop operation, power regulation, and power-energy timing regulation;
fig. 13 is a graph of the converter output curves of fig. 4;
FIG. 14 is a graph of the change in ESS charge during the energy storage operating period of FIG. 4;
FIG. 15 is the ESS charge-discharge power curve of the energy storage operating period of FIG. 4;
FIG. 16 is a graph of the change in charge level of the ESS of FIG. 4 over the entire operating cycle;
fig. 17 is a plot of charge and discharge power for the entire operating cycle of the ESS of fig. 4.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be described in further detail with reference to the accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. Hereinafter, exemplary embodiments are described to explain the present invention by referring to the figures.
The present invention is described below with reference to a flowchart of a method according to an exemplary embodiment of the present invention. It will be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a suitable computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, implement the functions specified in the flowchart block or blocks. These computer program instructions may also be stored in a computer usable or computer-readable memory that may direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer usable or computer-readable memory produce an article of manufacture including instruction means that implement the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks.
In addition, each block of the flowchart illustrations may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the blocks may occur out of order. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.
As shown in fig. 1, which is a method for operating a self-energy-storage multi-terminal back-to-back flexible-direct device (SES-VSC-MTDC) according to an embodiment of the present invention, step 10 is to calculate whether the comprehensive power supply cost of a power distribution network has a minimum value when the self-energy-storage multi-terminal back-to-back flexible-direct device is in a power regulation mode; step 20, reading the charge state of an energy storage unit (ESS) in the self-energy-storage multi-end back-to-back flexible and straight device, and step 30, switching the operation mode of the self-energy-storage multi-end back-to-back flexible and straight device according to the condition that whether the comprehensive power supply cost of the power distribution network has the lowest value when the self-energy-storage multi-end back-to-back flexible and straight device is in a power regulation mode and the charge state of the energy storage unit (ESS) in the self-energy-storage multi-end back-to-; the mode of operation from energy storage multiple-end back-to-back gentle straight device includes: mode I: the energy storage unit does not operate, and from the gentle straight device execution power regulation of energy storage multiterminal back-to-back, mode II: the energy storage unit operates, and the self-energy-storage multi-end back-to-back flexible straight device executes power energy time sequence adjustment, mode III: the energy storage unit executes the charge state recovery, and the self-energy-storage multi-end back-to-back flexible-straight device executes the independent execution power regulation mode.
The power energy time sequence regulation is not only the power regulation of the multi-end back-to-back flexible straight device, but also the energy time sequence regulation participated by the energy storage unit, namely, the energy storage unit also participates in the charge and discharge control of the power distribution network. The mode of operation from energy storage multiple-end back-to-back gentle straight device includes: the control method comprises a power regulation mode, a power energy time sequence regulation mode and a charge state recovery mode, wherein a corresponding control mode is selected according to the condition that whether the comprehensive power supply cost of the power distribution network has the lowest value in the pure power regulation mode and the charge state of the energy storage unit.
Considering the requirements of the cost and the service life of the energy storage unit, the configuration capacity and the charging and discharging times of the ESS are reduced as much as possible, so that the ESS is required to be switched into operation seamlessly according to a control strategy only when the adjustable capacity of the interconnection feeder line is not enough to meet the system power supply reliability and the full consumption of high-permeability clean energy. The general idea of the SES-VSC-MTDC composite control strategy is mainly power regulation, and energy storage is put into operation only when the SES-VSC-MTDC composite control strategy cannot meet the system safety and power supply quality constraints. The overshoot or over discharge of the energy storage unit can be avoided, and the energy storage unit is ensured to have the adjusting capability in the next time period. Compared with a multi-end back-to-back flexible-direct device (VSC-MTDC) without an energy storage unit, the self-energy-storage multi-end back-to-back flexible-direct device (SES-VSC-MTDC) operation method provided by the invention can adapt to more complex high-permeability clean energy grid-connected operation scenes and control requirements.
Aiming at the self-energy-storage multi-end back-to-back flexible and straight device, from the viewpoints of improving the clean energy consumption capability and the power supply reliability of a flexible interconnected power distribution network, effectively reducing the configuration capacity of an energy storage unit and prolonging the service life of the energy storage unit, the invention provides the composite control method of the self-energy-storage multi-end back-to-back flexible and straight device.
In one embodiment, the self-energy-storage multi-terminal back-to-back flexible-straight device is in powerWhen the operation mode is adjusted, the SES-VSC-MTDC main converter can adopt a fixed U under the normal working condition of a distribution networkdcQ control, slave inverter can adopt fixed PQ control. The main converter balances the system active power to maintain the dc bus voltage. Under the condition of distribution network fault, when a feeder (and an upper-level power grid) connected with the slave converter fails, the SES-VSC-MTDC master converter can still adopt a fixed UdcQ control, the fault end can be switched from the current converter to the fixed Uacf, other slave converters can still be controlled by the fixed PQ. When the feeder line (and the upper-level power grid) connected with the main converter fails, any slave converter can be switched to a fixed UdcQ control becomes a new main converter, and the original main converter becomes a slave converter and is switched to a fixed Uacf, other slave converters can still adopt fixed PQ control.
Under the condition of normal operation of the power distribution network, each port realizes active flexible exchange and reactive independent control among feeders according to an optimal operation scheduling instruction; when a certain feeder line (including a superior power grid) breaks down, the control modes of a plurality of groups of converters can be quickly switched, the real-time transfer of loads in a non-fault area is ensured, and the power supply reliability is improved.
When the self-energy-storage multi-end back-to-back flexible direct-current device is in a power energy time sequence regulation operation mode and under the normal working condition of a distribution network, the SES-VSC-MTDC main converter can adopt a fixed UdcThe Q control, ESS converter and other slave converters can adopt fixed PQ control. Under the distribution network fault working condition, the control mode of each current converter in the power regulation operation mode can be the same, and the details are not repeated.
And (4) considering power balance constraint, active output constraint, converter capacity constraint, direct-current bus voltage constraint and the like of each port of the SES-VSC-MTDC, and establishing mathematical models of two operation modes of SES-VSC-MTDC power regulation and power energy time sequence regulation under the condition of normal/fault operation of the distribution network.
And establishing a mathematical model of a power regulation operation mode and a power energy time sequence regulation mode of the self-energy-storage multi-end back-to-back flexible-straight device aiming at the normal/fault working condition of the power distribution network.
Power regulation mode: under the normal working condition of a distribution network, the SES-VSC-MTDC main converter adopts a fixed UdcQ controlAnd other slave converters adopt fixed PQ control. The main converter balances the system active power to maintain the dc bus voltage. In order to realize active/reactive power decoupling control, the d-axis voltage of a current converter is positioned in the grid voltage vector direction through a phase-locked loop under a d-q synchronous rotating coordinate system, so that Usq＝0，Usd＝UsThe converter active power and reactive power can be expressed as:
Figure BDA0001897379660000141
Figure BDA0001897379660000142
in the formula: id, iqThe components of the current vectors at the side of the current distribution network of the converter, i.e. the d-axis and the q-axis, UsdIs the d-axis component of the converter grid side voltage vector.
As can be seen from equations (1) and (2), the active power and the reactive power can be independently controlled by controlling the dq-axis component of the converter current. The power at the AC end and the DC end of the converter is equal, and the following results can be obtained:
Figure BDA0001897379660000143
in the formula: n is a radical ofVSCThe total number of the converters of the SES-VSC-MTDC is; c is a DC side capacitor, UdcIs a DC bus voltage, PlossIs converter losses.
Due to the isolation of the direct current link, the reactive power output by the converters does not influence each other, so that only the capacity constraint of each converter needs to be met. Thus, the mathematical model is as follows:
Figure BDA0001897379660000144
in the formula: pk(t)、Qk(t) the active and reactive power of the kth converter at time t, respectively, are fed in as powerThe direct current bus is positive; a. thekThe loss coefficient of the kth converter;
Figure BDA0001897379660000145
the active power upper limit of the kth converter; skRated capacity of the kth converter; u shapedcIs a dc bus voltage; u shapedc,refThe direct current bus command voltage.
Under the condition of distribution network fault, when a feeder (and a superior power grid) connected with the slave converter fails, the SES-VSC-MTDC master converter still adopts a fixed UdcQ control, the fault end is switched from the current converter to the fixed Uacf, and the other slave converters are still controlled by the fixed PQ. When the feeder line (and the upper-level power grid) connected with the main converter fails, any slave converter can be switched to a fixed UdcQ control becomes a new main converter, and the original main converter becomes a slave converter and is switched to a fixed Uacf, controlling other slave converters by adopting fixed PQ. When a power grid fails, the control requirement of the main converter is unchanged, at the moment, the fault side slave converter equivalently supplies power to the passive network, the control objects are alternating voltage amplitude and frequency, the alternating voltage amplitude control can be directly controlled through d-q decoupling, and the frequency can be realized by modifying a period register in the controller. The control variables of the SES-VSC-MTDC are the reactive power of the main converter and the active and reactive power of the converter at the fault-free end. The mathematical model is added with the following formula on the basis of the formula (4):
Figure BDA0001897379660000151
in the formula: u shapeacIs the fault end converter alternating voltage; u shapeac,reAnd f is the rated voltage of the power grid.
The following discussion will focus on the mathematical model in the power energy timing adjustment mode.
The control variable of the SES-VSC-MTDC in the self-energy-storage multi-end back-to-back flexible-direct device operation modes II and III increases energy storage power output on the basis of the mode I, and corresponding ESS charge and discharge power constraint and SOC constraint are increased under constraint conditions. SES-VSC-MTDCCalculating the active power P output by the ESS according to the SES-VSC-MTDC operation mode after passing through the current SOC value of the ESSESSAnd (t) taking the output range as a constraint condition to enter a power distribution network optimized operation or energy storage SOC recovery model. The SOC value of the ESS is then calculated again to provide constraints for the next period decision.
In one embodiment, when the self-energy-storage multi-terminal back-to-back flexible-and-straight device performs power energy timing adjustment, the input power and the output power of the self-energy-storage multi-terminal back-to-back flexible-and-straight device are equal to each other when the power distribution network is in a fault-free condition. And under the working condition of distribution network fault, the power-energy time sequence regulation model is the same as the power regulation model.
In one embodiment, the input power and the output power of the self-energy-storage multi-terminal back-to-back soft-and-straight device may be equal to the sum of the output power of all inverters in the self-energy-storage multi-terminal back-to-back soft-and-straight device, the loss power of all inverters in the self-energy-storage multi-terminal back-to-back soft-and-straight device, and the output power of all energy storage units in the self-energy-storage multi-terminal back-to-back soft-and-straight device.
As a preferred embodiment, when the self-energy-storage multi-end back-to-back flexible direct-current device performs power energy time sequence adjustment, under the normal working condition of a distribution network, the SES-VSC-MTDC main converter adopts a fixed UdcAnd the Q control, the ESS converter and other flexible direct-current slave converters adopt fixed PQ control. The power balance equation may be equation (6):
Figure BDA0001897379660000161
NVSCthe total number of the current converters of the self-energy-storage multi-end back-to-back flexible-straight device is shown;
Pk(t) the output power of the kth converter at time t respectively;
Akthe loss coefficient of the kth converter;
PESS(t) is the output power of the energy storage unit in a period of t;
the charging and discharging power of the energy storage unit is calculated according to the residual electric quantity of the energy storage unit; and the nuclear power state of the energy storage unit in the next period is calculated according to the stored energy charge value in the current period and the stored energy power released in the current period.
As a preferred embodiment, the charge and discharge power of the energy storage unit may be calculated according to the remaining capacity of the energy storage unit by the following formula:
PESS(t)＝uPcd(t),u∈{-1,0,1} (7)
Figure BDA0001897379660000162
the calculation formula of the nuclear power state of the energy storage unit in the next period according to the stored energy charge value in the current period and the stored energy power released in the current period can be as follows:
Figure BDA0001897379660000163
SOC(0)＝SOC(T) (10)
NVSCthe total number of the current converters of the self-energy-storage multi-end back-to-back flexible-straight device is the total number;
Pk(t) the output power of the kth converter at time t respectively;
Akis the loss factor of the kth converter;
t is the number of time periods divided by the complete scheduling cycle;
Δ t is the duration of each time period;
PESS(t) the output power of the energy storage unit in a period t;
Pcd(t) the charging and discharging power of the energy storage unit is constant positive in a period t;
u is a charging and discharging mark of the energy storage unit, and values of-1, 0 and 1 respectively represent three states of charging, non-working and discharging;
Pch,max、Pdis,maxthe maximum charge and discharge power of the energy storage unit;
SESSthe rated electric quantity of the energy storage unit is set;
SOC (t) is the state of charge of the energy storage unit at time t;
SOCmax、SOCminrespectively representing the safe upper and lower limits of the state of charge of the energy storage unit;
ηch、ηdisrespectively the charge and discharge efficiency of the energy storage unit.
The method is based on the comprehensive power supply cost of the power selling enterprises, and establishes the objective function with the minimum cost, wherein the comprehensive power supply cost can comprise two parts of electricity purchasing cost and distribution network loss cost, the electricity purchasing cost can be related to unit internet surfing electricity price and high-voltage transmission cost amortization, and the electricity purchasing cost is embodied as node electricity price of a substation bus connected with a feeder line. For a distribution ring network, the bus bar node electricity prices of different feeders are usually different.
As a preferred embodiment, the integrated power supply cost minimum objective function may be as follows:
Figure BDA0001897379660000171
Figure BDA0001897379660000172
Figure BDA0001897379660000181
in the formula: n is the number of system nodes; f. of1(t)、f2(t) the electricity purchasing cost and the network loss cost in the period t; ci(t)、PSTi(t)、PDGi(t)、PDi(t) the electricity price of the bus node at the node i in the period t, the outlet power of the transformer substation, the active output of the distributed power supply and the active power of the load; cw(t) the electricity price of the grid loss cost in the period t, CiAnd (t) is the general electricity purchasing price.
On the basis of the constraint that the distribution network operates in the mode, the outlet power P of the transformer substation needs to be addedSTi(t)、QSTi(t) distributed power supply output PDGi(t)、QDGi(t) and converter output power of SES-VSC-MTDC
Figure BDA0001897379660000183
The constraints considered mainly include: the system power flow equation, the outlet power constraint of the transformer substation, the voltage constraint and the line capacity constraint.
Figure BDA0001897379660000182
In the formula: u shapei(t)、Uj(t) is the voltage amplitude of the node i and the node j at the moment t; gij、BijRespectively are mutual conductance and mutual susceptance between a node i and a node j;ij(t) is the phase difference between node i and node j at time t; qDiAnd (t) is the reactive power of the load at the node i at the time t. Sij(t) is the line power between node i and node j at time t; the superscript "-" and subscript "_" of a variable denote the upper and lower limits of the variable.
In the formula (14), the first two formulas are a system power flow equation, the 3 rd and 4 th formulas are substation outlet power constraints, the 5 th formula is a voltage constraint of each node in the power distribution network, and the 6 th formula is a line capacity constraint.
For mode III of operation of the self-storing multi-terminal back-to-back soft-straight device, the ESS in the SES-VSC-MTDC performs state-of-charge (SOC) state recovery.
In one embodiment, the configured capacity and the number of charging and discharging of the ESS should be minimized in view of the cost of energy storage and operational lifetime requirements. The energy storage state of charge (SOC) is divided into three categories: a standby state, a normal non-standby state, and an abnormal state. The standby state mark ESS is in a moderate SOC interval, and the optimal operation requirement of the distribution network in the next time interval can be met at any time; the normal non-standby state mark ESS is in a relatively wider SOC interval, and the adjustable capacity is relatively smaller as the safety margin is required to be met; the abnormal state identifies that the ESS is in an emergency SOC interval. When the ESS is in an abnormal state, SOC recovery should be performed immediately. The configuration capacity and the charging and discharging times of the ESS are reduced, and when the adjustable capacity of the interconnected feeder line is not enough to meet the system power supply reliability and the full consumption of high-permeability clean energy, the ESS seamlessly switches in operation according to a control strategy, so that overshoot/overdischarge is avoided, and the energy storage has the adjusting capacity in the next time period.
As a preferred embodiment, the standby state may be that the charge value range of the energy storage unit is greater than or equal to 0.4 and less than or equal to 0.6; the normal non-standby state can be that the charge value range of the energy storage unit is more than or equal to 0.15 and less than or equal to 0.85; the abnormal state can be that the charge value range of the energy storage unit is more than or equal to 0 and less than 0.15 or more than 0.85 and less than or equal to 1. The implementation mode ensures that the energy storage charge quantity has strict continuity in time sequence, avoids overshoot/overdischarge, ensures that the energy storage has the regulation capacity of the next time period, reasonably divides the energy storage running state, controls the charging/discharging of the energy storage running state, and reduces the configuration capacity and the charging/discharging times of the energy storage unit.
Based on the above analysis, the operation method of the self-energy-storage multi-terminal back-to-back flexible-straight device first performs preprocessing, that is, determines whether the comprehensive power supply cost of the self-energy-storage multi-terminal back-to-back flexible-straight device is the lowest in the operation mode I (ESS is not operated, and power adjustment is only performed), and then executes the corresponding operation mode in combination with the SOC value of the energy storage unit, as shown in table 1.
TABLE 1
Figure BDA0001897379660000201
In one embodiment, the control flow of step 30 of the operation method of the self-energy-storage multi-terminal back-to-back flexible-direct device in fig. 1 is as shown in fig. 2, and step 301 determines whether the ESS is not operated in the SES-VSC-MTDC, and the objective function of the integrated power supply cost of the distribution network has a solution when only power is regulated? When the comprehensive power supply cost objective function has a solution, executing step 303, judging whether the SOC value in the energy storage unit is in a standby state, and when the SOC value in the energy storage unit is in the standby state, executing step 307, wherein the ESS is not put into operation, and the SES-VSC-MTDC executes power regulation; when the SOC value in the energy storage unit is not in a standby state, step 309 is executed, the ESS is put into operation, SOC state recovery is executed, and SES-VSC-MTDC independently executes power regulation; when the integrated power supply cost objective function is not solved, executing step 305, judging whether the SOC value in the energy storage unit is in a standby state or a normal non-standby state, and when the SOC value in the energy storage unit is in the standby state or the normal non-standby state, executing step 311, the ESS is put into operation, and the SES-VSC-MTDC executes power energy time sequence regulation; when the SOC value in the energy storage unit is not in the standby state or the normal non-standby state, step 309 is executed, the ESS is put into operation, SOC state recovery is executed, and the SES-VSC-MTDC independently executes power regulation.
Due to the addition of the energy storage unit, the SES-VSC-MTDC enables the flexible interconnected power distribution network to have tide transfer capability in two dimensions of space and time, can be dynamically adjusted according to the change of the running state of the power distribution network, quickly responds to DG and load fluctuation, achieves full consumption of clean energy, improves power supply reliability, improves power supply quality, reduces comprehensive power supply cost, and ensures safe, economic and efficient running of the power grid.
In one embodiment, the energy storage unit performs the state of charge recovery including recovering the current charge value of the energy storage unit to a state with a minimum difference from the intermediate value of the energy storage charge, so as to ensure that the ESS can be recovered to a moderate state as soon as possible, so as to deal with the adjustment problem of energy storage in a future period.
In a preferred embodiment, the objective function of the energy storage unit to restore the current charge value to the minimum difference from the intermediate value of the energy storage charge may be
Figure BDA0001897379660000211
SOC (t) is the state of charge of the energy storage unit at time t;
PESS(t) is the output power of the energy storage unit in a period of t;
Δ t is the duration of each time segment;
SESSthe rated electric quantity is the rated electric quantity of the energy storage unit;
SOCmidthe charge intermediate value of the energy storage unit;
in the formula: SOCmidGenerally, the value is about 0.5, and the preferred value is 0.5. Charging and discharging power of energy storage unitCalculating according to the residual electric quantity of the energy storage unit; and the nuclear power state of the energy storage unit in the next period is calculated according to the stored energy charge value in the current period and the stored energy power released in the current period.
As a preferred embodiment, the charge and discharge power of the energy storage unit may be calculated according to the remaining capacity of the energy storage unit by the following formula:
PESS(t)＝uPcd(t),u∈{-1,0,1}；
Figure BDA0001897379660000212
the calculation formula of the nuclear power state of the energy storage unit in the next period according to the stored energy charge value in the current period and the stored energy power released in the current period can be as follows:
Figure BDA0001897379660000221
SOC(0)＝SOC(T)；
t is the number of time periods divided by the complete scheduling cycle;
Δ t is the duration of each time period;
PESS(t) the output power of the energy storage unit in a period t;
Pcd(t) the charging and discharging power of the energy storage unit is constant positive in a period t;
u is a charging and discharging mark of the energy storage unit, and values of-1, 0 and 1 respectively represent charging, non-working and discharging;
Pch,max、Pdis,maxthe maximum charge and discharge power of the energy storage unit;
SESSthe rated electric quantity of the energy storage unit is set;
SOC (t) is the state of charge of the energy storage unit at time t;
SOCmax、SOCminrespectively representing the safe upper and lower limits of the state of charge of the energy storage unit;
ηch、ηdisrespectively the charge-discharge efficiency of the energy storage unit。
In the specific implementation mode, the total working time length and the standby time period requirement of the stored energy are comprehensively considered, and when the SOC (t) is recovered to 0.9SOCmid≤SOC(t)≤1.1SOCmidWithin the range, the energy storage SOC state recovery operating mode is terminated.
According to the SES-VSC-MTDC composite control method provided by the invention, three models need to be solved, namely power regulation, power energy time sequence regulation and SOC state recovery. Power energy timing adjustment and SOC State recovery P determined by SOC valueESSAnd (t) after the output range, the equality constraint of the active power balance is changed into inequality constraint, and the problem of nonlinear optimization is essentially the same as that of power regulation optimization, and both the problem and the problem can be solved by adopting a primal-dual interior point method.
Fig. 3 is a schematic diagram of a self-energy-storage multi-terminal back-to-back flexible direct current device (SES-VSC-MTDC) according to an embodiment of the present invention, which includes at least two AC/DC converters and at least one energy storage unit (ESS), wherein the DC sides of the AC/DC converters are connected in parallel to a common DC bus, and the AC sides of the AC/DC converters are connected to feeder lines of a power distribution network, so as to implement flexible interconnection (AC-DC-AC decoupling) between multiple feeder lines; one side of an energy storage unit (ESS) is connected with a DC/DC converter, the other side of the DC/DC converter is connected in parallel with a common direct current bus, and the DC/DC converter realizes the charge and discharge control of the energy storage unit, so that the SES-VSC-MTDC system has the energy sequential adjustment capability and becomes a highly integrated comprehensive device. The self-energy-storage multi-end back-to-back flexible straight device also comprises an operation mode adjusting module, and the operation mode adjusting module switches the operation mode of the self-energy-storage multi-end back-to-back flexible straight device according to the condition that whether the comprehensive power supply cost of the power distribution network has the lowest value or not and the charge state of the energy storage unit when the self-energy-storage multi-end back-to-back flexible straight device is in the power adjusting mode; the operational mode from storing from gentle straight device of ability back to back includes: mode I: the energy storage unit does not operate and the self-storage self-energy-storage multi-end back-to-back flexible and straight device executes a power regulation mode; mode II: the energy storage unit operates and executes a power energy time sequence adjusting mode from the energy storage multi-end back-to-back flexible straight device; mode III: the energy storage unit executes the state of charge recovery and the self-storage self-energy storage multi-end back-to-back flexible-straight device independently executes the power regulation mode.
Under the condition of normal operation, each port realizes active flexible exchange and reactive independent control among feeders according to an optimal operation scheduling instruction; when a certain feeder line (including a superior power grid) breaks down, the control modes of a plurality of groups of converters can be quickly switched, the real-time transfer of loads in a non-fault area is ensured, and the power supply reliability is improved.
The self-energy-storage multi-end back-to-back flexible and straight device enables the energy storage unit to be in a reasonable charge state in each time period in one operation cycle, participates in necessary energy time sequence optimization adjustment, can avoid overshoot or over discharge of the energy storage unit, and ensures that the energy storage unit has the adjustment capability in the next time period. Compared with a multi-end back-to-back flexible-direct device (VSC-MTDC) without an energy storage unit, the self-energy-storage multi-end back-to-back flexible-direct device (SES-VSC-MTDC) operation method provided by the invention can adapt to more complex high-permeability clean energy grid-connected operation scenes and control requirements.
The invention provides a self-energy-storage multi-end back-to-back flexible-straight device aiming at a self-energy-storage multi-end back-to-back flexible-straight device, aiming at improving the clean energy consumption capability and the power supply reliability of a flexible interconnected power distribution network, effectively reducing the configuration capacity of an energy storage unit and prolonging the service life of the energy storage unit, and the self-energy-storage multi-end back-to-back flexible-straight device can effectively reduce the configuration capacity of energy storage, prolong the service life of energy storage, effectively improve the high-permeability clean energy consumption capability, improve the power supply reliability, improve the power supply quality and improve the.
In one embodiment, when the power distribution network is fault-free and the self-energy-storage multi-terminal back-to-back flexible-to-straight device performs power regulation, the main converter of the self-energy-storage multi-terminal back-to-back flexible-to-straight device may adopt a fixed UdcQ control, the slave converter can adopt fixed PQ control; when the power distribution network has no fault and the self-energy-storage multi-end back-to-back flexible-to-straight device executes power energy time sequence adjustment, the main converter of the self-energy-storage multi-end back-to-back flexible-to-straight device can adopt a fixed UdcQ control, wherein a converter of the energy storage unit and a slave converter of the self-energy-storage multi-end back-to-back flexible-straight device can adopt fixed PQ control; when the self-energy-storage multi-end back-to-back flexible-straight device is in fault with the feeder line connected with the slave converter, the master converter still can adopt the fixed UdcQ controlThe fault end can be switched to a fixed U from the current converteracf, controlling other slave converters to still use fixed PQ control; when a feeder line connected with the main converter of the self-energy-storage multi-end back-to-back flexible-to-straight device fails, any slave converter of the self-energy-storage multi-end back-to-back flexible-to-straight device can be switched to be fixed UdcQ control, the original main converter can be switched to fixed Uacf, other slave converters can still adopt fixed PQ control.
In one embodiment, when the power distribution network is fault-free and the self-energy-storage multi-terminal back-to-back flexible-straight device performs power energy timing adjustment, the normal operation of the whole power distribution network is ensured, so that the input power and the output power of the self-energy-storage multi-terminal back-to-back flexible-straight device are equal.
In a specific embodiment, the equalizing the input power and the output power of the self-energy-storage multi-terminal back-to-back soft-straight device may include: in fig. 3, the sum of the output power of all the AC/DC converters, the loss power of all the AC/DC converters, and the output power of all the energy storage units is 0, and at this time, it is ensured that the power entering the SES-VSC-MTDC is balanced with the output power, and the balance of the power distribution network is ensured.
In a preferred embodiment, the power balance equation of the self-energy-storage multi-terminal back-to-back flexible-straight device with equal input power and output power is
Figure BDA0001897379660000251
NVSCThe total number of the AC/DC converters of the self-energy-storage multi-end back-to-back flexible-straight device is;
Pk(t) output power of kth AC/DC converter at time t, respectively;
Akthe loss coefficient of the kth AC/DC converter;
PESS(t) is the output power of the energy storage unit in a period of t;
the charging and discharging power of the energy storage unit is calculated according to the residual electric quantity of the energy storage unit; and the nuclear power state of the energy storage unit in the next period is calculated according to the stored energy charge value in the current period and the stored energy power released in the current period.
As a preferred embodiment, the charge and discharge power of the energy storage unit is calculated according to the formula of the remaining capacity of the energy storage unit:
PESS(t)＝uPcd(t),u∈{-1,0,1}；
Figure BDA0001897379660000252
the next-period nuclear power state of the energy storage unit is calculated according to the stored energy charge value and the stored energy power released in the current period by the following formula:
Figure BDA0001897379660000253
SOC(0)＝SOC(T)；
NVSCthe total number of the AC/DC converters of the self-energy-storage multi-end back-to-back flexible-straight device is;
Pk(t) output power of kth AC/DC converter at time t, respectively;
Akthe loss coefficient of the kth AC/DC converter;
t is the number of time periods divided by the complete scheduling cycle;
Δ t is the duration of each time period;
PESS(t) is the output power of the energy storage unit in a period of t;
Pcd(t) is the charge-discharge power of the energy storage unit in the period of t, and is always positive;
u is a charging and discharging mark of the energy storage unit, and values of-1, 0 and 1 respectively represent three states of charging, non-working and discharging;
Pch,max、Pdis,maxthe maximum charge and discharge power of the energy storage unit;
SESSthe rated electric quantity is the rated electric quantity of the energy storage unit;
SOC (t) is the state of charge of the energy storage unit at time t;
SOCmax、SOCminrespectively representing the safe upper and lower limits of the state of charge of the energy storage unit;
ηch、ηdisrespectively the charge and discharge efficiency of the energy storage unit.
In one embodiment, the state of charge of the energy storage unit of the self-energy-storage back-to-back soft-and-straight device may include a standby state, a normal non-standby state, and a non-normal state. The standby state marks that the energy storage unit is in a moderate charge state, and can meet the requirement of optimal operation of the distribution network in the next time interval at any time; the normal non-standby state marks that the energy storage unit is in a relatively wider charge state, and the adjustable capacity is relatively smaller; the abnormal state identifies that the energy storage unit is in an emergency state of charge. When the ESS is in an abnormal state, SOC recovery should be performed immediately. The energy storage operation state is reasonably divided and the charging/discharging of the energy storage operation state is controlled, so that overshoot/overdischarge can be avoided, and the energy storage has the regulation capability in the next time period.
As a preferred embodiment, the standby state may be that the charge value range of the energy storage unit is greater than or equal to 0.4 and less than or equal to 0.6; the normal non-standby state may be a state in which the charge value range of the energy storage unit is greater than or equal to 0.15 and less than or equal to 0.85; the abnormal state can be that the charge value range of the energy storage unit is more than or equal to 0 and less than 0.15 or more than 0.85 and less than or equal to 1, and the configuration capacity and the charging and discharging times of the ESS can be reduced.
In an embodiment, the operation mode adjustment module of the self-energy-storage multi-end back-to-back flexible-straight device may include a processor, and the processor switches the operation mode of the self-energy-storage multi-end back-to-back flexible-straight device according to a condition that whether the comprehensive power supply cost of the self-energy-storage multi-end back-to-back flexible-straight device has a minimum value or not when performing power adjustment and a state of charge of the energy storage unit. The clean energy consumption capability and the power supply reliability of the flexible interconnected power distribution network are improved, the configuration capacity of the stored energy is effectively reduced, and the service life of the stored energy is prolonged.
As a preferred embodiment, the switching, by the operation mode adjustment module, the operation mode of the self-energy-storage multi-terminal back-to-back soft-and-straight device according to whether the integrated power supply cost has the lowest value when the self-energy-storage multi-terminal back-to-back soft-and-straight device performs power adjustment and the charge state of the energy storage unit may include: when the self-energy-storage multi-end back-to-back flexible-straight device executes power adjustment, the comprehensive power supply cost has the lowest value, and when the energy storage unit is in a standby state, the operation mode adjusting module controls the energy storage unit not to operate and controls the self-energy-storage multi-end back-to-back flexible-straight device to execute power adjustment; when the self-energy-storage multi-end back-to-back flexible-straight device executes a power regulation mode, the comprehensive power supply cost has the lowest value, and the energy storage unit is in a normal non-standby state or a non-normal state, the operation mode regulation module controls the energy storage unit to execute charge state recovery and controls the self-energy-storage multi-end back-to-back flexible-straight device to independently execute power regulation; when the self-energy-storage multi-end back-to-back flexible-straight device executes power adjustment, the comprehensive power supply cost has no lowest value, and the energy storage unit is in a standby state or a normal non-standby state, the operation mode adjusting module controls the energy storage unit to be operated and controls the self-energy-storage multi-end back-to-back flexible-straight device to execute power energy time sequence adjustment; when the self-energy-storage multi-end back-to-back flexible-straight device executes the power regulation mode, the comprehensive power supply cost has no lowest value, and when the energy storage unit is in an abnormal state, the operation mode regulation module controls the energy storage unit to execute charge state recovery and controls the self-energy-storage multi-end back-to-back flexible-straight device to independently execute power regulation.
The SES-VSC-MTDC composite control strategy can effectively reduce the configuration capacity of energy storage and prolong the service life of the energy storage, and the self-energy-storage flexible interconnected power distribution network optimized operation strategy can effectively improve the high-permeability clean energy consumption capability, improve the power supply reliability, improve the power supply quality and improve the operation economy.
In one embodiment, the energy storage unit performs the state of charge recovery including recovering the current charge value of the energy storage unit to a state with a minimum difference from the intermediate value of the energy storage charge, so as to ensure that the ESS can be recovered to a moderate state as soon as possible, so as to deal with the adjustment problem of energy storage in a future period.
In a preferred embodiment, the objective function of the energy storage unit to restore the current charge value to the minimum difference from the intermediate value of the energy storage charge may be
Figure BDA0001897379660000281
SOC (t) is the state of charge of the energy storage unit at time t;
PESS(t) is the output power of the energy storage unit in a period of t;
Δ t is the duration of each time segment;
SESSthe rated electric quantity is the rated electric quantity of the energy storage unit;
SOCmidthe charge intermediate value of the energy storage unit;
in the formula: SOCmidGenerally, the value is about 0.5, and the preferred value is 0.5. The charging and discharging power of the energy storage unit is calculated according to the residual electric quantity of the energy storage unit; and the nuclear power state of the energy storage unit in the next period is calculated according to the stored energy charge value in the current period and the stored energy power released in the current period.
As a preferred embodiment, the charge and discharge power of the energy storage unit may be calculated according to the remaining capacity of the energy storage unit by the following formula:
PESS(t)＝uPcd(t),u∈{-1,0,1}；
Figure BDA0001897379660000282
the calculation formula of the nuclear power state of the energy storage unit in the next period according to the stored energy charge value in the current period and the stored energy power released in the current period can be as follows:
Figure BDA0001897379660000291
SOC(0)＝SOC(T)；
t is the number of time periods divided by the complete scheduling cycle;
Δ t is the duration of each time period;
PESS(t) the output power of the energy storage unit in a period t;
Pcd(t) the charging and discharging power of the energy storage unit is constant positive in a period t;
u is a charging and discharging mark of the energy storage unit, and values of-1, 0 and 1 respectively represent charging, non-working and discharging;
Pch,max、Pdis,maxthe maximum charge and discharge power of the energy storage unit;
SESSthe rated electric quantity of the energy storage unit is set;
SOC (t) is the state of charge of the energy storage unit at time t;
SOCmax、SOCminrespectively representing the safe upper and lower limits of the state of charge of the energy storage unit;
ηch、ηdisrespectively the charge and discharge efficiency of the energy storage unit.
In the specific implementation mode, the total working time length and the standby time period requirement of the stored energy are comprehensively considered, and when the SOC (t) is recovered to 0.9SOCmid≤SOC(t)≤1.1SOCmidWithin the range, the energy storage SOC state recovery operating mode is terminated.
The invention also provides a flexible interconnected power distribution network, which adopts the self-energy-storage multi-end back-to-back flexible-straight device, and the self-energy-storage multi-end back-to-back flexible-straight device switches the operation mode of the self-energy-storage multi-end back-to-back flexible-straight device according to the condition that whether the comprehensive power supply cost of the power distribution network has the lowest value or not in the power regulation mode and the charge state of the energy storage unit in the self-energy-storage multi-end back-to-back flexible-straight device. The self-energy-storage flexible interconnected power distribution network optimization operation strategy can effectively improve the high-permeability clean energy consumption capability, improve the power supply reliability, improve the power supply quality and improve the operation economy.
In order to verify the feasibility and effectiveness of the optimized operation strategy provided by the invention, simulation and verification are carried out on a 33-node calculation example system shown in fig. 4, wherein the system is a flexible interconnected power distribution network formed by connecting feeders of 4 different substations through SES-VSC-MTDC. The rated voltage of the system is 10kV, the YJV 22-3X 400 type cable used in the main stream of urban distribution networks in China is selected as the line, and the parameters of the cable and the topological parameters of the system are shown in tables 2 and 3. 5 groups of photovoltaic and 4 groups of wind power are connected into the system, and the configuration parameters are shown in a table 4. The peak time electricity rates (07: 00-19: 00) and the valley time electricity rates (19: 00-07: 00) of each bus are shown in table 5. The rated capacity of the SES-VSC-MTDC converter is 4.5MVA, and the loss coefficient is 0.02. The configured ESS is 0.5MW/1MW & h, the initial SOC value is 50%, the upper and lower SOC safety limits are 100% and 10% respectively, and the charge-discharge efficiency is 90%. The power interval of the substation outlet is 0 MW-8 MW (power is not allowed to be sent backwards), the line capacity is 8MVA, and the value range of each node voltage is [0.93,1.07 ]. And performing comparative analysis on three scenes, namely system open-loop operation, power regulation flexible interconnection operation and power-energy time sequence regulation flexible interconnection operation. Setting a complete operation cycle to be 24h, dividing a time period every 15min, and counting 96 time periods, wherein the DG output and the load are considered to be kept unchanged within 15min, and the DG output and load curves of the feeder lines are shown in FIGS. 5-8. Assuming a fault occurs between nodes 20 and 21 on the 14: 30C feeder, the two-sided switch is open and the 16:00 line fault clears.
Table 2 YJV22-3 x 400 cable data
Figure BDA0001897379660000301
TABLE 3 System parameter data
Figure BDA0001897379660000302
Figure BDA0001897379660000311
TABLE 4 DG configuration parameters
Figure BDA0001897379660000312
TABLE 5 Electricity price parameter
Figure BDA0001897379660000313
When the open loop operates, the DG output of each feeder line in a plurality of time periods is larger than the load requirement, the distributed electric energy cannot be fully consumed, and the wind and light abandon is required to be 12.25MW & h; in a plurality of time periods, because the output of clean energy is large, the voltages of a plurality of nodes are out of limit, the power supply quality is poor, the safe operation of the system is influenced, and the wind and light are abandoned by 3.23MW & h, as shown in tables 6 and 7. And in the 14: 30-16: 00 fault period, all loads in non-fault areas at the downstream of the node 21 on the C feeder lose power supply. In addition, because of the natural distribution of the power flow, the network loss and the electricity purchasing cost cannot be optimized, and the comprehensive power supply cost is high (see table 7). In summary, the open-loop operation cannot satisfy the full-scale and friendly consumption of clean energy, and the power supply reliability and the economical efficiency are poor.
TABLE 6 System flow non-feasible solution time period and reason
Figure BDA0001897379660000321
Table 7 comparison of distribution network operation results under three scenarios
Figure BDA0001897379660000322
When the power regulation is in flexible interconnection operation, the system load flow is optimally distributed, and the comprehensive power supply cost in the operation period is obviously reduced (see table 7). In open-loop operation, the problems of power reverse feeding, voltage out-of-limit and the like caused by high output of clean energy in a plurality of time periods can be effectively solved by adjusting the power of the interconnected feeder lines. However, there are few time periods (01: 45-02: 45, 11: 30-12: 30, 13: 00-13: 15) and there is no problem due to restriction, as shown in Table 6. Through analysis, in the time periods of 01: 45-02: 45 and 11: 30-12: 30, the total distributed energy output in the system is greater than the total load, and the constraint that the power cannot be sent backwards cannot be met; in the period of 13: 00-13: 15, the DG output on the A feeder is larger than the load, the DG output on the C, D feeder is basically equivalent to the load, and the feed power can be small, so that the unreserved DG on the A feeder needs to be transferred to the B feeder, and the voltage of partial nodes on the B feeder is out of limit. Therefore, in the three periods, the wind and the light still need to be abandoned.
And in a 14: 30-16: 00 fault period, the C feeder line flexible-straight port changes the control mode to supply power to the passive network, and the power supply from the node 21 to all the downstream power-off loads is guaranteed. But partial time periods (14: 45-15: 00, 15: 15-15: 30) exist, and no solution occurs due to constraint limitation. Analysis shows that the A, B, D feeder line has heavier load in the period of 14: 45-15: 00, the adjustable power of the feeder line is smaller due to the line capacity, and the requirement of power loss load on the C feeder line cannot be met; in the period of 15: 15-15: 30, because the C feeder is a passive network and has no regulation capacity, the DG output of the D feeder is basically equivalent to the load, and the excess DG output on the A feeder needs to be transferred to the B feeder, so that the voltage of partial nodes of the A feeder is out of limit. Therefore, the above-mentioned period still needs to abandon wind and light.
In conclusion, in a power regulation flexible interconnection operation scene, when the adjustability of the feeder line is relatively sufficient, the power flow distribution can be effectively optimized, and the constraint requirements of the system, such as the failure of power to be sent backwards, the node voltage, the line capacity and the like, are met. However, in a few periods, when the total adjustment margin of each feeder line of the system is insufficient, the operation requirement cannot be met only by power adjustment, and energy storage needs to be introduced for energy adjustment and control of a time axis.
In the power-energy time sequence regulation flexible interconnection operation scene, in the non-solution time period, the energy storage participates in optimization, the system has solutions, wind and light abandoning is not needed, and the comprehensive power supply cost is further reduced as shown in table 7. Under the three scenes, the power curve of each feeder outlet is shown in fig. 9-11, and the comprehensive power supply cost comparison curve at each time interval is shown in fig. 12.
The output of each port of the SES-VSC-MTDC is shown in fig. 13, and reflects that the SES-VSC-MTDC has power flow transfer capability in two dimensions of space and time due to the addition of energy storage, can be dynamically adjusted according to the change of the running state of the distribution network, quickly responds to DG and load fluctuation, realizes full consumption of clean energy, improves power supply reliability, improves power supply quality, reduces comprehensive power supply cost, and ensures safe, economic and efficient running of a power grid.
The electric quantity variation curve and the charge-discharge power curve of the stored energy are respectively shown in fig. 14 and fig. 15 (only the energy storage working period is selected, and the whole operation cycle of the stored energy is shown in fig. 16 and fig. 17), the initial time, the SOC is 0.5, and the state of standby is achieved. In the period of 01: 45-02: 45, no solution is calculated through preprocessing (whether the comprehensive power supply cost is the lowest when the self-energy-storage multi-end back-to-back flexible-straight device is in the operation mode I (ESS is not operated and pure power adjustment is carried out or not)) and the energy storage is put into operation to provide energy time sequence optimization adjustment, so that the surplus clean energy is absorbed. And at the time point 02:45, the SOC is in an abnormal state, and in order to cope with the situation that no solution exists in the next pretreatment, the SOC recovery mode is operated in the energy storage mode and is recovered to the standby state in the time period 02: 45-03: 30. In the 11: 30-12: 30 time period, no solution exists in preprocessing calculation, energy storage is put into operation, and surplus clean energy is absorbed. If the SOC recovery mode does not exist, the energy storage has no regulation capacity in the time period of 11: 30-12: 30. In the period of 12: 30-13: 00, operating an energy storage SOC recovery mode; at the moment of 13:00, no solution appears in the pretreatment again, the stored energy is in a normal non-standby state, and the energy timing sequence optimization adjustment is provided for ensuring the system to run and stopping the SOC recovery of the stored energy. And in the period of 13: 15-13: 45, the stored energy continues to run, the SOC recovers, and the stored energy recovers to a moderate standby state. And in the period of 14: 45-15: 00, the stored energy feeds electric energy into the system, so that the power shortage of the power-losing load of the C feeder line is compensated. At the moment of 15:00, the SOC is in a non-standby state, and the running SOC is recovered. The operation mode is the same in the 15: 15-15: 30 time period and the 13: 00-13: 15 time period.
From the above analysis, the SES-VSC-MTDC composite control strategy provided herein enables the energy storage unit to be in a reasonable state of charge at each time interval in one operation cycle, and participate in the necessary energy timing optimization adjustment. Through calculation, if the composite control strategy provided by the text is not adopted, the energy storage configuration capacity needs to be increased to 2.3MW & h to achieve the optimal operation target of the distribution network, and the charging and discharging times of energy storage in one operation period are increased by 6 times, so that the energy storage configuration capacity can be effectively reduced and the energy storage operation life can be prolonged by adopting the composite control strategy provided by the text.
The invention provides an SES-VSC-MTDC composite control method from the viewpoints of improving the clean energy consumption capability and the power supply reliability of a flexible interconnected power distribution network, effectively reducing the configuration capacity of stored energy and prolonging the service life of the stored energy, and the SES-VSC-MTDC composite control method effectively combines energy transfer in two dimensions of time and space and integrally complements and coordinates the energy transfer, so that on one hand, the high-permeability clean energy consumption level can be improved, the power supply reliability is improved, the operation economy of the power distribution network is optimized, and meanwhile, the configuration capacity of the stored energy can also be effectively reduced. Modeling and analyzing two operation modes of SES-VSC-MTDC power regulation and power-energy time sequence regulation, establishing a flexible interconnected power distribution network optimization operation model based on SES-VSC-MTDC, and verifying the effectiveness of the SES-VSC-MTDC technology and the operation control strategy thereof by a simulation example.
It should be understood that the above embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same, and those skilled in the art can modify the technical solutions described in the above embodiments, or make equivalent substitutions for some technical features; and all such modifications and alterations are intended to fall within the scope of the appended claims.

Claims (10)

1. A self-energy-storage multi-end back-to-back flexible straight device operation method is characterized by comprising the following steps:
s1: calculating whether the comprehensive power supply cost of the power distribution network has a lowest value when the self-energy-storage multi-end back-to-back flexible-straight device executes a power regulation mode;
s2: reading the charge state of an energy storage unit in the self-energy-storage multi-end back-to-back flexible-straight device;
s3: switching the operation mode of the self-energy-storage multi-end back-to-back flexible-and-straight device according to the condition that whether the comprehensive power supply cost of the power distribution network has the lowest value or not when the self-energy-storage multi-end back-to-back flexible-and-straight device executes the power regulation mode and the charge state of an energy storage unit in the self-energy-storage multi-end back-to-back flexible-and-straight device;
when the self-energy-storage multi-end back-to-back flexible-straight device executes a power regulation mode, the comprehensive power supply cost has the lowest value, and when the energy storage unit is in a standby state, the energy storage unit does not run, and the self-energy-storage multi-end back-to-back flexible-straight device executes power regulation;
when the self-energy-storage multi-end back-to-back flexible-straight device is in a power regulation mode, the comprehensive power supply cost has the lowest value, and the energy storage unit is in a normal non-standby state or a non-normal state, the energy storage unit executes charge state recovery, and the self-energy-storage multi-end back-to-back flexible-straight device independently executes power regulation;
when the self-energy-storage multi-end back-to-back flexible-straight device is in a power regulation mode, the comprehensive power supply cost has no lowest value, and the energy storage unit is in a standby state or a normal non-standby state, the energy storage unit is put into operation, and the self-energy-storage multi-end back-to-back flexible-straight device executes power energy time sequence regulation;
when the self-energy-storage multi-end back-to-back flexible-straight device is in a power regulation mode, the comprehensive power supply cost has no lowest value, and when the energy storage unit is in an abnormal state, the energy storage unit executes charge state recovery, and the self-energy-storage multi-end back-to-back flexible-straight device independently executes power regulation;
the standby state is that the charge value range of the energy storage unit is more than or equal to 0.4 and less than or equal to 0.6; the normal non-standby state is that the charge value range of the energy storage unit is more than or equal to 0.15 and less than 0.4 or more than 0.6 and less than or equal to 0.85; the abnormal state is that the charge value range of the energy storage unit is more than or equal to 0 and less than 0.15 or more than 0.85 and less than or equal to 1.
2. The method of claim 1, wherein performing state-of-charge recovery on the energy storage unit comprises: and recovering the current charge value of the energy storage unit to the minimum difference value with the intermediate value of the stored energy charge.
3. The method of claim 2, wherein the objective function of the energy storage unit to restore the current charge value to the minimum difference from the intermediate value of the energy storage charge is:
Figure FDA0002580673230000021
PESS(t)＝uPcd(t),u∈{-1,0,1}
SOC (t) is the state of charge of the energy storage unit at time t;
PESS(t) is the period of tThe output power of the energy unit;
Δ t is the duration of each time segment;
SESSthe rated electric quantity of the energy storage unit is set;
SOCmidthe charge intermediate value of the energy storage unit is obtained;
Pcd(t) the charging and discharging power of the energy storage unit is constant positive in a period t;
u is a charging and discharging mark of the energy storage unit, wherein-1 is a charging state, 0 is an inoperative state, and 1 is a discharging state;
the charging and discharging power of the energy storage unit is calculated according to the residual electric quantity of the energy storage unit;
and the charge state of the energy storage unit in the next period is calculated according to the stored energy charge value in the current period and the stored energy power released in the current period.
4. The method according to claim 3, wherein the charge/discharge power of the energy storage unit is calculated according to the remaining capacity of the energy storage unit by the following formula:
Figure FDA0002580673230000031
the charge state of the energy storage unit in the next period is calculated according to the stored energy charge value in the current period and the stored energy power released in the current period by the following formula:
Figure FDA0002580673230000032
SOC(0)＝SOC(T)；
t is the number of time periods divided by the complete scheduling cycle;
Δ t is the duration of each time period;
PESS(t) the output power of the energy storage unit in a period t;
Pch,max、Pdis,maxis the most important of the energy storage unitLarge charging and discharging power;
SESSthe rated electric quantity of the energy storage unit is set;
SOC (t) is the state of charge of the energy storage unit at time t;
SOCmax、SOCminthe safe upper limit and the safe lower limit of the charge state of the energy storage unit are respectively set;
ηch、ηdisand respectively charging and discharging efficiencies of the energy storage unit.
5. A self-energy-storage multi-terminal back-to-back flexible direct current device comprises at least two AC/DC converters and at least one energy storage unit, wherein the direct current sides of the AC/DC converters are connected in parallel with a direct current bus, the alternating current sides of the AC/DC converters are connected with a feeder line of a power distribution network, one side of the energy storage unit is connected with a DC/DC converter, the other side of the DC/DC converter is connected in parallel with the direct current bus,
the self-energy-storage multi-end back-to-back flexible-straight device further comprises an operation mode adjusting module, and the operation mode adjusting module switches the operation mode of the self-energy-storage multi-end back-to-back flexible-straight device according to the condition that whether the comprehensive power supply cost of the power distribution network has the lowest value or not and the charge state of the energy storage unit when the self-energy-storage multi-end back-to-back flexible-straight device executes the power adjusting mode;
when the self-energy-storage multi-end back-to-back flexible-straight device executes a power regulation mode, the comprehensive power supply cost has the lowest value, and when the energy storage unit is in a standby state, the operation mode regulation module controls the energy storage unit not to operate and controls the self-energy-storage multi-end back-to-back flexible-straight device to execute power regulation;
when the self-energy-storage multi-end back-to-back flexible-straight device executes a power regulation mode, the comprehensive power supply cost has the lowest value, and when the energy storage unit is in a normal non-standby state or a non-normal state, the operation mode regulation module controls the energy storage unit to execute charge state recovery and controls the self-energy-storage multi-end back-to-back flexible-straight device to independently execute power regulation;
when the self-energy-storage multi-end back-to-back flexible straight device executes a power adjusting mode, the comprehensive power supply cost has no lowest value, and when the energy storage unit is in a standby state or a normal non-standby state, the operation mode adjusting module controls the energy storage unit to be operated and controls the self-energy-storage multi-end back-to-back flexible straight device to execute power energy time sequence adjustment;
when the self-energy-storage multi-end back-to-back flexible and straight device executes a power regulation mode, the comprehensive power supply cost has no lowest value, and when the energy storage unit is in an abnormal state, the operation mode regulation module controls the energy storage unit to execute charge state recovery and controls the self-energy-storage multi-end back-to-back flexible and straight device to independently execute power regulation;
the standby state is that the charge value range of the energy storage unit is more than or equal to 0.4 and less than or equal to 0.6; the normal non-standby state is that the charge value range of the energy storage unit is more than or equal to 0.15 and less than 0.4 or more than 0.6 and less than or equal to 0.85; the abnormal state is that the charge value range of the energy storage unit is more than or equal to 0 and less than 0.15 or more than 0.85 and less than or equal to 1.
6. The self-storing multi-ended back-to-back soft-straight device of claim 5, wherein the operation mode adjustment module comprises a processor,
and the processor switches the operation mode of the self-energy-storage multi-end back-to-back flexible-straight device according to the condition that whether the comprehensive power supply cost has the lowest value or not when the self-energy-storage multi-end back-to-back flexible-straight device executes a power regulation mode and the charge state of the energy storage unit.
7. The self-storing multi-ended back-to-back soft-straight device of claim 5, wherein the energy storage unit performing state-of-charge recovery comprises: and recovering the current charge value of the energy storage unit to the minimum difference value with the intermediate value of the stored energy charge.
8. The self-energy-storing multi-end back-to-back soft and straight device according to claim 7, wherein the objective function of the energy-storing unit for recovering the current charge value to the minimum difference value with the intermediate value of the energy-storing charge is as follows:
Figure FDA0002580673230000061
PESS(t)＝uPcd(t),u∈{-1,0,1}
SOC (t) is the state of charge of the energy storage unit at time t;
PESS(t) the output power of the energy storage unit in a period t;
Δ t is the duration of each time segment;
SESSthe rated electric quantity of the energy storage unit is set;
SOCmidthe charge intermediate value of the energy storage unit is obtained;
Pcd(t) the charging and discharging power of the energy storage unit is constant positive in a period t;
u is a charging and discharging mark of the energy storage unit, wherein-1 is a charging state, 0 is an inoperative state, and 1 is a discharging state;
the charging and discharging power of the energy storage unit is calculated according to the residual electric quantity of the energy storage unit;
and the charge state of the energy storage unit in the next period is calculated according to the stored energy charge value in the current period and the stored energy power released in the current period.
9. The self-energy-storage multi-terminal back-to-back flexible-straight device as claimed in claim 8, wherein the charge and discharge power of the energy storage unit is calculated according to the remaining capacity of the energy storage unit by the following formula:
Figure FDA0002580673230000062
the charge state of the energy storage unit in the next period is calculated according to the stored energy charge value in the current period and the stored energy power released in the current period by the following formula:
Figure FDA0002580673230000071
SOC(0)＝SOC(T)；
t is the number of time periods divided by the complete scheduling cycle;
Δ t is the duration of each time period;
PESS(t) the output power of the energy storage unit in a period t;
Pch,max、Pdis,maxthe maximum charging and discharging power of the energy storage unit is obtained;
SESSthe rated electric quantity of the energy storage unit is set;
SOC (t) is the state of charge of the energy storage unit at time t;
SOCmax、SOCminthe safe upper limit and the safe lower limit of the charge state of the energy storage unit are respectively set;
ηch、ηdisand respectively charging and discharging efficiencies of the energy storage unit.
10. A flexible interconnected power distribution network comprising the self-energy-storing multi-terminal back-to-back flexible-straight device as claimed in any one of claims 5 to 9,
the self-energy-storage multi-end back-to-back flexible-straight device switches the operation mode of the self-energy-storage back-to-back flexible-straight device according to the condition that whether the comprehensive power supply cost of the power distribution network has the lowest value or not in the power regulation mode and the charge state of the energy storage unit in the self-energy-storage back-to-back flexible-straight device.
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Inventor after: Lu Huaigu

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