CN112769160B - Microgrid cluster self-optimization-seeking control method considering grid-connected and island operation modes - Google Patents

Microgrid cluster self-optimization-seeking control method considering grid-connected and island operation modes Download PDF

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CN112769160B
CN112769160B CN202110007028.8A CN202110007028A CN112769160B CN 112769160 B CN112769160 B CN 112769160B CN 202110007028 A CN202110007028 A CN 202110007028A CN 112769160 B CN112769160 B CN 112769160B
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CN112769160A (en
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杨梓锋
郭创新
陈晓刚
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Zhejiang University ZJU
State Grid Zhejiang Electric Power Co Ltd
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State Grid Zhejiang 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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • 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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • 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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • 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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/48—Controlling the sharing of the in-phase component
    • 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]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • 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
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

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Abstract

The invention discloses a micro-grid group self-optimization-seeking control method considering grid-connected and island operation modes, which comprises the steps of firstly, carrying out communication based on a discrete consistency algorithm and constructing a micro-grid hierarchical control framework based on droop control; then, aiming at a microgrid island operation mode, a self-optimization-approaching control model of each microgrid in the microgrid group system in the island mode is constructed; then, considering coordination control among all micro-grids of the micro-grid group, and constructing a self-optimization-approaching control model of each micro-grid in the micro-grid group system in a grid-connected mode; and finally, realizing the stable and economic operation of the micro-grid group system and each micro-grid in grid-connected and isolated island operation modes through a micro-grid group coordination control algorithm. The invention ensures that the micro-grid can maintain the voltage stability and the frequency stability of the micro-grid by means of a simple communication network in a grid-connected mode or an island mode, and realizes the self-optimization operation of distributed output of each distributed power supply in the micro-grid according to the principle of equal micro-increment rate and the coordination control of each micro-grid in a micro-grid group.

Description

Microgrid cluster self-optimization-seeking control method considering grid-connected and island operation modes
Technical Field
The invention belongs to the field of micro-grid group operation control, and provides a micro-grid group self-optimization-approaching control method considering grid-connected and island operation modes.
Background
The traditional microgrid control method mainly comprises a centralized control mode, a distributed control mode and a decentralized control mode. Among them, distributed control can realize hierarchical control while simplifying a communication network, and thus is widely used. With the development of an autonomous microgrid structure, each microgrid can be coordinated with one another to form a microgrid group system, so that the aims of improving the consumption rate of renewable energy sources and the like are fulfilled. In order to improve the reliability, stability and economy of the micro-grid group operation, the micro-grid system not only needs to ensure the safety and stability of a single micro-grid in modes such as grid connection and island, but also needs to realize the coordination control among the micro-grid groups by self-optimization control to reduce the system operation cost.
At present, a distributed hierarchical control method for a single microgrid has been proposed, but research on applying distributed control to a microgrid group system has not been in depth. In addition, in order to improve the reliability and the economy of the system, the relationship between a single microgrid and a microgrid group system must be coordinated, and the self-optimization control of the microgrid and the operation control of the microgrid group system must be coordinated. Therefore, how to realize the self-optimization-seeking control method of the micro-grid group considering the grid-connected and island operation modes becomes a problem which needs to be solved urgently.
Disclosure of Invention
The invention aims to provide a self-optimization-seeking control method of a micro-grid group in consideration of grid-connected and island operation modes. The invention can realize the distributed hierarchical control of the micro-grid group system, coordinate the relationship between the self-optimization-seeking control of a single micro-grid and the operation control of the micro-grid group system, and ensure the reliability and the economy of the operation of the micro-grid group system.
The purpose of the invention is realized by the following technical scheme: a self-optimization-seeking control method of a micro-grid group considering grid-connected and island operation modes comprises the following steps:
step 1, establishing a microgrid distributed layered control model: the model mainly comprises a primary control layer based on droop control, a secondary control layer for ensuring the frequency stability and the voltage stability of the microgrid and a tertiary control layer for ensuring that the output of each distributed power supply is consistent with a set value. In order to realize distributed control, each distributed power supply of the microgrid iterates based on a discrete consistency algorithm to carry out communication;
step 2, establishing a self-optimization-approaching control model of each microgrid in the microgrid group system under an island mode: in an island operation mode, self-optimization-seeking control of the distributed power supply operating according to the principle of equal micro-increment rate is realized, and the light storage system and the distributed power supply with the output reaching the upper limit do not participate in the self-optimization-seeking control;
step 3, establishing a self-optimization-approaching control model of each micro-grid in the micro-grid group system under a grid-connected mode: under a grid-connected operation mode, source load balance inside the micro-grid is achieved through a power ring in a tertiary control layer, and micro-grid group coordination control is achieved by controlling power exchanged between each micro-grid and a connecting line:
and 4, realizing stable and economic operation of the micro-grid group system and each micro-grid in a grid-connected and isolated island operation mode by the micro-grid group coordination control method.
Further, the self-optimization-approaching control model of each microgrid in the microgrid group system in the step 2 under the island mode is specifically realized as follows:
2.1 Secondary control
In island mode, to return the output frequency of each distributed power supply to the nominal value ωnFrequency correction must be introduced in the quadratic control. Firstly, obtaining the frequency omega of the microgrid through iteration according to a discrete consistency algorithmaveI.e. by
Figure BDA0002883898580000021
Wherein n isg1The number of distributed power supplies using droop control. On the basis, the frequency omega of the micro-grid is adjustedaveWith rated frequency omeganThe difference is input into a PI link to obtain a frequency correction quantity delta omega1I.e. by
Figure BDA0002883898580000022
Wherein k isp,ωAnd ki,ωThe PI controller parameters are corrected for frequency.
In addition, as a basis for the cubic control, in order to adjust the output active power, a power loop control needs to be introduced. Using active power reference value PrefInputting the difference value of the actual output power P and the actual output power P into a PI link to obtain a frequency correction quantity delta omega2I.e. by
Figure BDA0002883898580000023
Wherein k isp,PAnd ki,PThe PI controller parameters are corrected for power.
Similarly, for reference voltage correction, firstly, the phase voltage amplitude U of the microgrid is obtained through iteration according to a discrete consistency algorithmaveAnd connecting it with rated voltage UnThe difference value is input into a PI link to obtain a voltage correction quantity delta U, namely
Figure BDA0002883898580000024
Wherein k isp,UAnd ki,UThe PI controller parameters are corrected for voltage.
By combining the primary control and the secondary control, the following formula can be obtained
ωref *＝ωref+Δω1+Δω2
Uref *＝Uref+ΔU
Wherein, ω isref *And Uref *And controlling the frequency reference value and the voltage reference value for the droop corrected by the secondary control.
2.2 triple control
The goal of tertiary control is to achieve power distribution among the distributed power sources. Firstly, according to different operation modes, the reference power of each distributed power supply inverter can be obtained through an optimization algorithm or an equal micro-increment rate mode.
For different types of distributed power supplies, after factors such as fuel oil cost, maintenance cost and the like are comprehensively considered, the cost function can be uniformly simplified into a quadratic function form, namely
Figure BDA0002883898580000031
Wherein, ai，biAnd ciThe cost coefficients of the distributed power supply are positive numbers, Ci(Pi) When the output active power of the distributed power supply is PiThe cost of electricity generation. The total operation cost of the distributed power supply participating in the tertiary control in the micro-grid system is
Figure BDA0002883898580000032
The marginal power generation cost of each distributed power supply can be obtained by the following formula
Figure BDA0002883898580000037
Wherein, MCi(Pi) When the output active power of the distributed power supply is PiMarginal power generation cost. According to the principle of equal micro-increment rate, when the marginal cost of each distributed power supply is equal, the total operation cost of the system is minimum, namely
Figure BDA0002883898580000033
The above equation can be implemented by a consistency algorithm, with marginal cost MCiAs a state variable, the final iteration yields the MCaveI.e. by
Figure BDA0002883898580000034
Therefore, the active power reference value of each distributed power supply can be obtained
Figure BDA0002883898580000035
And then, the actual output power of each distributed power supply inverter reaches the set power by modifying the droop coefficient of the droop control curve.
In droop control, in order to distribute the output power of each distributed power supply according to the droop coefficient, the no-load angular frequency ω of the droop curve is generally set0Equality, i.e. by adjusting the sag factor
Figure BDA0002883898580000036
Wherein m isiIs the droop coefficient, P, of the active-frequency droop curve of the ith distributed power supplyrefiReference value of active power, n, for the output of the ith distributed power supplyg2Is the number of distributed power supplies participating in the tertiary control. The above equation can be implemented by a consistency algorithm, which multiplies the droop coefficient by the active power (mP)ref)iAs state variables, the final iteration yields (mP)ref)ave
Figure BDA0002883898580000041
From this, the droop control coefficient of each distributed power supply can be obtained as
Figure BDA0002883898580000042
Furthermore, the output limits of each distributed power source need to be taken into account, i.e.
0≤Pi≤Pi,max i＝1,2,...,ng2
In the formula, Pi,maxAnd the output upper limit of the ith distributed power supply is shown. When the distributed power supply outputs active power PiReaches the upper limit of output Pi,maxWhen the temperature of the water is higher than the set temperature,quitting the self-optimization-seeking control, wherein the number n of the distributed power supplies participating in the third control layerg2And the state transition matrix a of the coherency algorithm will change accordingly. And the rest distributed power supplies are iterated according to a consistency algorithm based on the principle of equal micro-increment rate again and reach a new stable operation state.
Meanwhile, in order to improve the new energy consumption rate, a light storage system consisting of the photovoltaic unit and the energy storage unit does not participate in self-optimization-approaching control, but maximizes the energy conversion efficiency through a maximum power tracking control algorithm.
Further, the self-optimization-seeking control of each microgrid in the microgrid group system in the step 3 in the grid-connected mode is specifically realized as follows:
3.1 droop control
Under the grid-connected mode, the primary control layer of each microgrid in the microgrid group still adopts droop control in the following form
Figure BDA0002883898580000043
Meanwhile, the frequency and the voltage of each microgrid are ensured by the power grid due to the fact that the microgrid is directly connected with the power grid, and the frequency and the voltage do not need to be compensated.
3.2 Secondary control
Under the grid-connected mode, the frequency stability and the voltage stability of the micro-grid are guaranteed by the main grid, and the active power output by the distributed power supply inverter can reach an active power reference value only by starting a power loop in the secondary control layer. Reference value P of active powerrefInputting the difference value of the actual output power P and the actual output power P into a PI link to obtain a frequency correction quantity delta omega2：
Figure BDA0002883898580000044
By combining the primary control and the secondary control, the following formula can be obtained:
ωref *＝ωref+Δω2
wherein, ω isref *The droop control frequency reference value is corrected through secondary control.
3.3 triple control
Compared with an island mode, the three-time control in the grid-connected mode needs to consider that the marginal cost of each distributed power supply is equal, and needs to realize the source-load balance inside the micro-grid. In particular, the total load of the microgrid is of the magnitude
Figure BDA0002883898580000051
In the formula, PLThe total load size of the micro-grid is,
Figure BDA0002883898580000052
is the ith of a microgrid3Size of individual load, nLIs the load number of the microgrid. The output of the distributed power supply without the participation of the micro-grid in the self-optimization-approaching control is as follows
Figure BDA0002883898580000053
In the formula, ng3Number of distributed power supplies, P, not participating in self-optimizing controlG2The output of the distributed power supply is not participated in self-optimization control of the micro-grid.
Considering the power balance, the output of each distributed power source in the self-optimization-seeking control should be equal to
Figure BDA0002883898580000054
In the formula, PG1The output of the distributed power supply participating in self-optimization control of the micro-grid is large. Considering the principle of equal micro-increment rate to optimize the output of each distributed power supply, the method includes
Figure BDA0002883898580000055
Figure BDA0002883898580000056
The method is consistent with an island mode, based on a consistency algorithm, and performs output distribution on the distributed power supply according to the principle of equal micro-increment rate, namely
Figure BDA0002883898580000057
Therefore, the active power reference value of each distributed power supply can be obtained
Figure BDA0002883898580000058
In addition, in order to realize source-load balance, a power ring is added in three times of control, and the average output of the distributed power supply participating in self-optimization control is obtained according to a consistency algorithm, namely the average output is obtained
Figure BDA0002883898580000059
The average output is obtained by iterationaveWhereby the active power reference of the distributed power supply can be modified to ensure source-to-charge balance within the microgrid, i.e.
Figure BDA0002883898580000061
In the formula, kp,P1And ki,P1And the parameters are respectively the power PI controller parameters of the tertiary control layer in the grid-connected mode.
Under the grid-connected mode, the power distribution can be realized by directly modifying the active power reference value in droop control without modifying the droop coefficient, namely
Figure BDA0002883898580000062
In the formula, ωrefiAnd UrefiRespectively is a frequency reference value and a phase voltage amplitude reference value of the ith distributed power supply. Therefore, a micro-grid hierarchical control model under a micro-grid group grid-connected mode is established, and self-optimization control considering micro-grid internal source load balance is realized.
3.3 microgrid group coordination control
On the basis of establishing a self-optimization-approaching control model of the micro-grid under the grid-connected operation mode of the micro-grid group, the coordination control among the micro-grids in the micro-grid group system is further considered.
Under the normal operation condition, the source charge balance is kept inside each microgrid, and power exchange is not carried out between the microgrids. When a certain micro-grid has distributed power supply faults and the like, the power sent to the public connecting line by other micro-grids can be increased through coordination control, and the source-load balance of a micro-grid group system is ensured; when a certain micro-grid is subjected to conditions that new energy such as photovoltaic energy cannot be consumed and the like, the power absorbed by other micro-grids from a public tie line can be increased through coordination control, and the new energy consumption level of a micro-grid group system is guaranteed.
Suppose the power sent by the microgrid to the tie line is PPCC，PPCC< 0 indicates that the microgrid is drawing power from the tie line. Considering the power balance, the output of each distributed power source in the self-optimization-seeking control should be equal to
Figure BDA0002883898580000063
Suppose that a microgrid group includes n in totalmgA micro-grid, wherein the i5If one micro-grid distributed power supply fails, the rest nmg-1 sum of the total amount of power to be sent to the junctor is
Figure BDA0002883898580000064
In the formula,
Figure BDA0002883898580000067
is the ith5The power shortage of the individual micro-grids,
Figure BDA0002883898580000066
is jth5The amount of power delivered by the individual microgrid to the tie line.
In order to realize coordinated control between the micro grids, power distribution between the micro grids needs to be considered. Firstly, iteration is carried out through a consistency algorithm to obtain the active output adjustable quantity of the whole micro-grid group system, namely
Figure BDA0002883898580000065
Obtaining the average value P of the active power output adjustable quantity of the micro-grid group system through iterationadj,aveThen there is
Padj＝nmgPadj,ave
In the formula, PadjThe active output of the whole micro-grid group system can be regulated. Further, defining the response ratio of the microgrid as
Figure BDA0002883898580000071
In the formula,
Figure BDA0002883898580000074
is the ith5The active power output response ratio of each micro-grid. In order to ensure the safe and stable operation of each micro-grid and the whole micro-grid group, the distribution can be carried out according to the principle of response ratio of each micro-grid and the like, and the distribution is realized through a consistency algorithm, namely
Figure BDA0002883898580000072
After iterative convergence, the average response ratio of the microgrid group is raveThen there is
Figure BDA0002883898580000073
And each micro-grid can adjust the output according to the adjustable amount of the active power of the micro-grid, so that the micro-grid can still operate in a safe and stable state. Each microgrid obtains active power output required to be born
Figure BDA0002883898580000075
And then, the coordination control between the micro-grids can be realized only by correcting the power loop of the third control layer.
When a certain micro-grid is under the condition that new energy such as photovoltaic energy cannot be consumed, other micro-grids need to increase active power absorbed from a connecting line to ensure the consumption level of the new energy of the micro-grid group, and the coordination control process is similar to the process.
Further, the stable and economic operation of the microgrid group system and each microgrid in grid-connected and island operation modes is realized through the microgrid group coordination control algorithm in the step 4, which is specifically realized as follows:
in the primary control layer, each distributed power inverter in the microgrid operates in a droop control mode;
in the secondary control layer, if the micro-grid is in an island mode, starting a power loop, a frequency regulation link and a voltage regulation link, and calculating the voltage amplitude and the frequency of the micro-grid through a frequency consistency iterative algorithm and a voltage consistency iterative algorithm; if the grid-connected mode is adopted, only the power loop is started;
in the third control layer, if the microgrid is in an island mode, a power ring is not started, each distributed power supply calculates a distributed power supply output reference value through a marginal cost consistency iterative algorithm, and the distributed power supply output is controlled to reach the reference value by modifying parameters such as a power reference value and a droop coefficient of droop control, so that self-optimization-trend operation of the microgrid is realized. And when the output of the distributed power supply reaches the upper limit, quitting the self-optimization-trending operation, modifying the state transition matrix A by the rest distributed power supplies, and performing output distribution again through a marginal cost consistency iterative algorithm. If the micro-grid is in a grid-connected mode, a power ring needs to be started, if each micro-grid in the micro-grid group normally operates, each micro-grid and a public connecting line are controlled to exchange power to be zero, and the algorithm flow is consistent with the island mode; when power shortage occurs in a certain microgrid or new energy cannot be consumed and the like, the other microgrids calculate the power transmitted to the public connecting line by the microgrids through an active response ratio consistency iterative algorithm.
The invention has the beneficial effects that: the self-optimization-seeking control of the micro-grid suitable for the micro-grid group system is realized through a layered control algorithm based on distributed control, so that the self-optimization-seeking operation of distributed power of each distributed power supply according to the principle of equal micro-increment rate can be realized only by depending on a simple communication network in a grid-connected operation mode or an isolated island operation mode of the micro-grid, and the voltage stability and the frequency stability of the micro-grid are maintained. When the micro-grid group is in a grid-connected operation mode, the active output response ratio consistency iterative algorithm is adopted, so that the micro-grid group can respond to the output of the power shortage of a certain micro-grid or the situation that new energy cannot be absorbed under the condition of ensuring safe and stable operation, and the coordinated control of a micro-grid group system is realized.
Drawings
FIG. 1 is a self-optimization-seeking control flow chart of a micro-grid island mode;
FIG. 2 is a self-optimization-seeking control flow chart of a microgrid grid-connected mode;
FIG. 3 is a flow chart of a microgrid group coordination control algorithm;
FIG. 4 is a diagram of a microgrid group system topology;
FIG. 5 is a diagram of simulation results of island-mode self-optimization-trending operation of a microgrid; the system comprises a micro-grid, a micro-grid voltage curve, a micro-grid frequency curve, a micro-grid voltage curve and a micro-grid voltage curve, wherein (a) is a micro-grid frequency curve in an island mode, (b) is a micro-grid voltage curve in the island mode, and (c) is a micro-grid distributed power marginal cost curve in the island mode;
FIG. 6 is a diagram of simulation results of grid-connected mode self-optimization-approaching operation of a microgrid group; the microgrid grid-connected mode switching method comprises the following steps of (a) a microgrid grid frequency curve chart in a grid-connected mode, (b) a microgrid grid voltage curve chart in the grid-connected mode, and (c) marginal cost curve charts of distributed power supplies of the microgrid grid.
Detailed Description
The invention is further illustrated by the following figures and examples.
As shown in fig. 1 to 3, the self-optimization-seeking control method for a microgrid cluster considering grid-connected and island operation modes of the invention comprises the following steps:
step 1, establishing a microgrid distributed layered control model: the model mainly comprises a primary control layer based on droop control, a secondary control layer for ensuring the frequency stability and the voltage stability of the microgrid and a tertiary control layer for ensuring that the output of each distributed power supply is consistent with a set value. In order to achieve distributed control, each distributed power source of the micro-grid iterates based on a discrete consistency algorithm to communicate.
Step 1.1, consistency algorithm for distributed control of micro-grid
In distributed control, information transmission is required between adjacent micro-grids or adjacent distributed power supplies, and a consistency algorithm is introduced to ensure that the states of all nodes converge to a uniform value so as to ensure the stable operation of the whole system.
The communication network topology of the distributed system may be represented by the graph G ═ (V, E), V ═ V1,v2,...,vsDenotes the set of nodes, ns is the total number of nodes,
Figure BDA0002883898580000081
represents a set of edges, wherein (i)1,j1) E denotes that there is a slave in graph G
Figure BDA0002883898580000084
To
Figure BDA0002883898580000085
Is provided with a directional edge of the frame,
Figure BDA0002883898580000082
to represent
Figure BDA0002883898580000083
Of the neighboring node.
Since the actual communication process is a discrete process, the distributed control is based on a discrete consistency algorithm. Node in distributed system
Figure BDA0002883898580000091
The information wanted to be transferred is a state variable
Figure BDA0002883898580000092
The discrete consistency algorithm can be expressed as:
Figure BDA0002883898580000093
wherein k is the iteration step number of the consistency algorithm,
Figure BDA0002883898580000098
for the elements of the state transition matrix a, the matrix a can be constructed by the Metropolis method as:
Figure BDA0002883898580000094
wherein,
Figure BDA0002883898580000095
representing nodes
Figure BDA0002883898580000096
The number of neighbor nodes. The discrete consistency algorithm can thus be written in matrix form:
Xk+1＝AXk
where k represents the number of iteration steps of the consistency algorithm, XkRepresenting state variables of nodes of the system at the k-th step
Figure BDA0002883898580000099
Constructed column vectors, i.e. Xk＝[x1 x2 ... xns]T。
Step 1.2, droop control
In order to realize distributed control of the microgrid, each distributed power inverter adopts a droop control mode, each distributed power does not have a master-slave relationship in the control mode, but is in the same position, and each distributed power distributes output power according to a droop curve.
Specifically, when the line impedance is mainly inductive, the active power transmitted on the line mainly depends on the power angle difference between the two ends, the reactive power mainly depends on the voltage amplitude difference between the two ends, and the frequency replaces the power angle as the feedback signal, so that the active and reactive power control of the distributed power supply, that is, droop control, can be realized by changing the frequency and voltage amplitude reference values of the distributed power supply inverter:
Figure BDA0002883898580000097
wherein, ω isrefAnd UrefFrequency reference and phase voltage amplitude reference, omega, respectively, output by the inverternAnd UnRated frequency and rated phase voltage amplitude respectively, P and Q are active power and reactive power respectively output by the inverter, PrefAnd QrefThe active power reference value and the reactive power reference value which are respectively output by the inverter, m and n are respectively coefficients of active-frequency and reactive-voltage droop curves, and the above formula can be in the following form:
Figure BDA0002883898580000101
wherein, ω is0＝ωn+mPrefAnd U0＝Un+nQrefRespectively, the frequency and phase voltage amplitude at idle. Under the droop control mode, each distributed power supply inverter can distribute power according to the proportion of the droop coefficient.
Step 2, establishing a self-optimization-approaching control model of each microgrid in the microgrid group system under an island mode: in an island operation mode, self-optimization-seeking control of the distributed power supply operating according to the principle of equal micro-increment rate is realized, and the light storage system and the distributed power supply with the output reaching the upper limit do not participate in the self-optimization-seeking control, as shown in fig. 1.
Aiming at the isolated island operation mode of each microgrid of a microgrid group system, a microgrid self-optimization-approaching control model is provided.
And 2.1, in the primary control layer, each distributed power supply in the microgrid adopts droop control in the step 1.2. Although droop control allows each distributed power supply to distribute active power, it also causes deviations in the microgrid frequency and voltage that must be corrected in the secondary control layer.
Step 2.2, secondary control
In island mode, to return the output frequency of each distributed power supply to the nominal value ωnFrequency correction must be introduced in the quadratic control. Firstly, obtaining the frequency omega of the microgrid through iteration according to a discrete consistency algorithmave：
Figure BDA0002883898580000102
Wherein n isg1For the number of distributed power supplies using droop control, k represents the number of iteration steps of the coherency algorithm,
Figure BDA0002883898580000103
denotes the ith2The frequency of the output of each distributed power inverter,
Figure BDA0002883898580000104
expressed as elements of the state transition matrix A, ωaveRepresents ng1Average frequency of the distributed power inverter outputs. On the basis, the frequency omega of the micro-grid is adjustedaveWith rated frequency omeganThe difference is input into a proportional integral PI link to obtain a frequency correction quantity delta omega1：
Figure BDA0002883898580000105
Wherein k isp,ωAnd ki,ωThe PI controller parameters are corrected for frequency.
In addition, as a basis for the cubic control, in order to adjust the output active power, a power loop control needs to be introduced. Using active power reference value PrefInputting the difference value of the actual output power P and the actual output power P into a PI link to obtain a frequency correction quantity delta omega2：
Figure BDA0002883898580000106
Wherein k isp,PAnd ki,PThe PI controller parameters are corrected for power.
Similarly, for reference voltage correction, firstly, the phase voltage amplitude U of the microgrid is obtained through iteration according to a discrete consistency algorithmave：
Figure BDA0002883898580000111
Wherein k represents the number of iteration steps of the consistency algorithm,
Figure BDA0002883898580000112
denotes the ith2Voltage, U, output from distributed power invertersaveRepresents ng1Average value of voltage output by each distributed power inverter. On the basis, the phase voltage amplitude U of the micro-grid is measuredaveTo rated voltage UnThe difference is input into a proportional integral PI link to obtain a voltage correction quantity delta U:
Figure BDA0002883898580000113
wherein k isp,UAnd ki,UThe PI controller parameters are corrected for voltage.
By combining the primary control and the secondary control, the following formula can be obtained:
ωref *＝ωref+Δω1+Δω2
Uref *＝Uref+ΔU
wherein, ω isref *And Uref *And controlling the frequency reference value and the voltage reference value for the droop corrected by the secondary control.
Step 2.3, control three times
The goal of tertiary control is to achieve power distribution among the distributed power sources. Firstly, according to different operation modes, the reference power of each distributed power supply inverter can be obtained through an optimization algorithm or an equal micro-increment rate mode.
For different types of distributed power supplies, after factors such as fuel oil cost, maintenance cost and the like are comprehensively considered, the cost function can be uniformly simplified into a quadratic function form:
Figure BDA0002883898580000114
wherein, Ci(Pi) When the output active power of the distributed power supply is PiCost of electricity generation of time, ai、bi、ciThe cost coefficients of the distributed power supply are positive numbers; n isg2Is the number of distributed power supplies participating in the tertiary control. The total operation cost C of the distributed power supply participating in the third control in the micro-grid system is as follows:
Figure BDA0002883898580000115
the marginal power generation cost of each distributed power supply can be obtained by the following formula:
Figure BDA0002883898580000121
wherein, MCi(Pi) When the output active power of the distributed power supply is PiMarginal power generation cost. According to the principle of equal micro-increment rate, when the marginal cost of each distributed power supply is equal, the systemThe total operating cost is minimal:
Figure BDA0002883898580000122
the above equation can be implemented by a consistency algorithm, with marginal cost MCiAs state variables, n is finally obtained by iterationg2Marginal cost average value MC of distributed power suppliesave：
Figure BDA0002883898580000123
Where k denotes the number of iteration steps of the consistency algorithm, aijDenoted as elements of the state transition matrix a.
Therefore, the active power reference value of each distributed power supply can be obtained:
Figure BDA0002883898580000124
and then, the actual output power of each distributed power supply inverter reaches the set power by modifying the droop coefficient of the droop control curve.
In droop control, in order to distribute the output power of each distributed power supply according to the droop coefficient, the no-load angular frequency ω of the droop curve is generally set0Equality, i.e. by adjusting the droop coefficient such that:
Figure BDA0002883898580000125
wherein m isiIs the droop coefficient, P, of the active-frequency droop curve of the ith distributed power supplyref,iReference value of active power, n, for the output of the ith distributed power supplyg2Is the number of distributed power supplies participating in the tertiary control. The above formula can be realized by a consistency algorithm, and the droop coefficient m is obtainediAnd active power Pref,iProduct of (mP)ref)iAs state variablesFinally, iterate to obtain ng2Each (mP)ref)iAverage value of (mP)ref)ave：
Figure BDA0002883898580000126
Where k represents the number of iteration steps of the coherency algorithm.
From this, the droop control coefficients for each distributed power supply can be found as:
Figure BDA0002883898580000131
furthermore, the output limits of each distributed power supply need to be considered:
0≤Pi≤Pi,max i＝1,2,...,ng2
in the formula, Pi,maxFor the ith station distributed power supply PiUpper limit of the output. When the distributed power supply outputs active power PiReaches the upper limit of output Pi,maxThen the self-optimization-seeking control is exited, and the number n of distributed power supplies participating in the third control layer at the momentg2And the state transition matrix a of the coherency algorithm will change accordingly. And the rest distributed power supplies are iterated according to a consistency algorithm based on the principle of equal micro-increment rate again and reach a new stable operation state.
Meanwhile, in order to improve the new energy consumption rate, a light storage system consisting of the photovoltaic unit and the energy storage unit does not participate in self-optimization-approaching control, but maximizes the energy conversion efficiency through a maximum power tracking control algorithm.
Step 3, establishing a self-optimization-approaching control model of each micro-grid in the micro-grid group system under a grid-connected mode: in the grid-connected operation mode, the source-load balance inside the microgrid is realized through the power loop in the tertiary control layer, and the microgrid group coordination control is realized by controlling the power exchanged between each microgrid and the connecting line, as shown in fig. 2.
Step 3.1, droop control
Under the grid-connected mode, the primary control layer of each microgrid in the microgrid group still adopts droop control, and the form is as follows:
Figure BDA0002883898580000132
meanwhile, the frequency and the voltage of each microgrid are ensured by the power grid due to the fact that the microgrid is directly connected with the power grid, and the frequency and the voltage do not need to be compensated.
Step 3.2, secondary control
Under the grid-connected mode, the frequency stability and the voltage stability of the micro-grid are guaranteed by the main grid, and the active power output by the distributed power supply inverter can reach an active power reference value only by starting a power loop in the secondary control layer. Reference value P of active powerrefInputting the difference value of the actual output power P and the actual output power P into a PI link to obtain a frequency correction quantity delta omega2：
Figure BDA0002883898580000133
By combining the primary control and the secondary control, the following formula can be obtained:
ωref *＝ωref+Δω2
wherein, ω isref *The droop control frequency reference value is corrected through secondary control.
Step 3.3, control three times
Compared with an island mode, the three-time control in the grid-connected mode needs to consider that the marginal cost of each distributed power supply is equal, and needs to realize the source-load balance inside the micro-grid. Specifically, the total load of the microgrid is:
Figure BDA0002883898580000141
in the formula, PLThe total load size of the micro-grid is,
Figure BDA0002883898580000142
is the ith of a microgrid3Size of individual load, nLIs the load number of the microgrid. The micro-grid does not participate in the self-optimization-approaching control distributed power supply, for example, the output of the optical storage system is as follows:
Figure BDA0002883898580000143
in the formula, ng3Number of distributed power supplies, P, not participating in self-optimizing controlG2The output of the distributed power supply is not participated in self-optimization control of the micro-grid.
Considering the power balance, the magnitude of the output of each distributed power source in the self-optimization-seeking control should be:
Figure BDA0002883898580000144
in the formula, PG1The output of a distributed power supply participating in self-optimization-approaching control of the micro-grid is large; pPCCThe amount of power sent by the microgrid to the tie line. Considering that the output of each distributed power supply is optimized based on the principle of equal micro-increment rate, the following steps are performed:
Figure BDA0002883898580000145
Figure BDA0002883898580000146
wherein, CiIs the operating cost of the ith distributed power supply.
And (4) performing output distribution on the distributed power supply according to the principle of equal micro-increment rate based on a consistency algorithm and consistent with the island mode, and finally iterating to obtain MCave：
Figure BDA0002883898580000147
Where k represents the number of iteration steps of the coherency algorithm.
Therefore, the active power reference value of each distributed power supply can be obtained:
Figure BDA0002883898580000151
in addition, in order to realize source-load balance, a power ring is required to be added in three times of control, and the output P of the distributed power supply participating in self-optimization control is obtained according to a consistency algorithmi：
Figure BDA0002883898580000152
The average output is obtained by iterationaveTherefore, the active power output reference value of the distributed power supply can be corrected to ensure the source-load balance inside the microgrid:
Figure BDA0002883898580000153
in the formula, kp,P1And ki,P1And the parameters are respectively the power PI controller parameters of the tertiary control layer in the grid-connected mode.
Under the grid-connected mode, power distribution can be realized by directly modifying an active power reference value in droop control without modifying a droop coefficient:
Figure BDA0002883898580000154
in the formula, ωref,iAnd Uref,iRespectively is a frequency reference value and a phase voltage amplitude reference value of the ith distributed power supply. Therefore, a micro-grid hierarchical control model under a micro-grid group grid-connected mode is established, and self-optimization control considering micro-grid internal source load balance is realized.
Step 3.3, coordination control of the microgrid group
On the basis of establishing a self-optimization-approaching control model of the micro-grid under the grid-connected operation mode of the micro-grid group, the coordination control among the micro-grids in the micro-grid group system is further considered.
Under the normal operation condition, the source charge balance is kept inside each microgrid, and power exchange is not carried out between the microgrids. When a certain micro-grid has distributed power supply faults and the like, the power sent to the public connecting line by other micro-grids can be increased through coordination control, and the source-load balance of a micro-grid group system is ensured; when a certain micro-grid is subjected to conditions that new energy such as photovoltaic energy cannot be consumed and the like, the power absorbed by other micro-grids from a public tie line can be increased through coordination control, and the new energy consumption level of a micro-grid group system is guaranteed.
Suppose the power sent by the microgrid to the tie line is PPCC，PPCC< 0 indicates that the microgrid is drawing power from the tie line. Considering the power balance, the magnitude of the output of each distributed power source in the self-optimization-seeking control should be:
Figure BDA0002883898580000161
suppose that a microgrid group includes n in totalmgA microgrid i5＝1～nmg(ii) a Wherein the ith5When the distributed power supply of the micro-grid fails, the rest nmg-1 the sum of the total amount of power that needs to be sent out to the junctor is:
Figure BDA00028838985800001610
in the formula,
Figure BDA0002883898580000162
is the ith5The power deficit when a single microgrid distributed power supply fails,
Figure BDA0002883898580000163
is jth5The amount of power delivered by the individual microgrid to the tie line.
In order to realize coordinated control between the micro grids, power distribution between the micro grids needs to be considered. Firstly, obtaining the active power output adjustable quantity of the whole microgrid group system through iteration of a consistency algorithm:
Figure BDA0002883898580000164
wherein k represents the number of iteration steps of the consistency algorithm,
Figure BDA0002883898580000165
denotes the ith5The active power output of the micro-grid can be adjusted,
Figure BDA0002883898580000166
denoted as elements of the state transition matrix a.
Obtaining the average value P of the active power output adjustable quantity of the micro-grid group system through iterationadj,aveThen, there are:
Padj＝nmgPadj,ave
in the formula, PadjThe active output of the whole micro-grid group system can be regulated. Further, defining the response ratio of the microgrid as:
Figure BDA0002883898580000167
in the formula,
Figure BDA0002883898580000168
is the ith5The active power output response ratio of each micro-grid. In order to ensure the safe and stable operation of each micro-grid and the whole micro-grid group, the distribution can be carried out according to the principle of response ratio of each micro-grid and the like, and the consistency algorithm is adopted to realize that:
Figure BDA0002883898580000169
where k represents the number of iteration steps of the coherency algorithm.
After iterative convergence, the average response ratio of the microgrid group is raveThen, there are:
Figure BDA0002883898580000171
wherein, PlossThe power shortage when any one micro-grid distributed power supply fails.
And each micro-grid can adjust the output according to the adjustable amount of the active power of the micro-grid, so that the micro-grid can still operate in a safe and stable state. Each microgrid obtains active power output required to be born
Figure BDA0002883898580000172
And then, the coordination control between the micro-grids can be realized only by correcting the power loop of the third control layer.
When a certain micro-grid is under the condition that new energy such as photovoltaic energy cannot be consumed, other micro-grids need to increase active power absorbed from a connecting line to ensure the consumption level of the new energy of the micro-grid group, and the coordination control process is similar to the process.
And 4, realizing stable and economic operation of the micro-grid group system and each micro-grid in a grid-connected and isolated island operation mode by a micro-grid group coordination control method, wherein the overall implementation flow of the control algorithm is shown in fig. 3.
(4.1) primary control layer: each distributed power inverter in the microgrid operates in a droop control mode; and judging whether the micro-grid is in an island mode or a grid-connected state.
(4.1.1) if the microgrid is in an island mode.
(4.1.1.1) secondary control layer: and starting a power loop, a frequency regulation link and a voltage regulation link, and calculating the voltage amplitude and the frequency of the microgrid through a frequency consistency iterative algorithm and a voltage consistency iterative algorithm.
(4.1.1.2) three control layers: and (4) not starting the power ring, calculating the output reference value of the distributed power supply by each distributed power supply through a marginal cost consistency iterative algorithm, and modifying the droop coefficient of droop control.
(4.1.1.3) determining whether the distributed power supply output reaches an upper limit.
(4.1.1.3.1) if the output of the distributed power supply reaches the upper limit, the distributed power supply exits from the optimization-oriented control, and after the remaining distributed power supplies modify the distributed control state transition matrix A, the operation jumps to the step (4.1.1.2) to perform output distribution again through a marginal cost consistency iterative algorithm.
(4.1.1.3.2) if the output of the distributed power supply does not reach the upper limit, after the output reference value of the droop controller is modified, the output of the distributed power supply is controlled to reach the reference value, the self-optimization-approaching operation of the micro-grid is realized, and the step (4.1) is skipped to enter the next control cycle.
And (4.1.2) if the micro-grid is in a grid-connected state.
(4.1.2.1) secondary control layer: only the power loop is started, and the links of frequency regulation and voltage regulation are not started.
(4.1.2.2) control layer three times: starting a power loop; judging whether the power shortage of the micro-grid or the new energy cannot be absorbed or not: if the micro-grid normally operates, setting the exchange power P between the micro-grid and the public connecting linePCCIs 0; if the power shortage of a microgrid or the new energy cannot be consumed and the like, setting the power P for exchanging with the public connecting linePCCThe corresponding power value calculated for the following equation:
PPCC＝ravePadj
(4.1.2.3) the microgrid calculates a power reference value for the microgrid to deliver to the public tie line by an active response ratio consistency iterative algorithm according to the following formula:
Figure BDA0002883898580000181
(4.1.2.4) starting marginal cost consistency iteration by the microgrid, calculating the output reference value of each distributed power supply, modifying the output reference value of the droop controller, and then entering the next control cycle by the control algorithm.
And (4.1.2.4) judging whether the output of the distributed power supply reaches an upper limit.
(4.1.2.4.1) if the output of the distributed power supply reaches the upper limit, the distributed power supply exits from the optimization-oriented control, and after the remaining distributed power supplies modify the distributed control state transition matrix A, the distributed control state transition matrix A jumps to the step (4.1.2.4) to perform output distribution again through the marginal cost consistency iterative algorithm.
(4.1.2.4.2) if the output of the distributed power supply does not reach the upper limit, after the output reference value of the droop controller is modified, the output of the distributed power supply is controlled to reach the reference value, the self-optimization-approaching operation of the micro-grid is realized, and the step (4.1) is skipped to enter the next control cycle.
And (4.2) exiting the control loop until the micro-grid stops running.
Therefore, the control algorithm ensures safe, stable and economic operation of each micro-grid in the micro-grid group, and has higher new energy consumption level.
Examples
Taking a certain microgrid group as an example, the following demonstration of coordination control is carried out:
the topological structure of the microgrid group system is shown in fig. 4 and is composed of 3 microgrids, each microgrid is composed of 3 distributed power supplies, 1 optical storage system and 3 loads, the parameters of the microgrid group system are shown in table 1 below, and the cost coefficients of the distributed power supplies are shown in table 2 below.
Table 1: parameters of microgrid group system
Figure BDA0002883898580000182
Figure BDA0002883898580000191
Table 2: cost factor of each distributed power supply
DG a/[$/(kW·h)2] b/[$/(kW·h)] c/($/h)
DG1 0.020 0.20 0.0400
DG2 0.013 0.16 0.0140
DG3 0.010 0.10 0.0015
DG5 0.020 0.20 0.0400
DG6 0.013 0.16 0.0140
DG7 0.010 0.10 0.0015
DG9 0.020 0.20 0.0400
DG10 0.013 0.16 0.0140
DG11 0.010 0.10 0.0015
Scene 1: self-optimization-seeking control of the micro-grid in an island mode;
by taking an example of the operation of the microgrid 1 in the island mode, the self-optimization control of the microgrid in the island mode is explained, and the loads Load2 and Load3 are switched out when t is 3s and are switched in again when t is 5s, and the simulation result is shown in fig. 5.
As can be seen from fig. 5(a) and (b), the voltage of the microgrid is maintained at 220V in the island mode, the frequency is maintained near 50Hz, the fluctuation range does not exceed ± 0.1Hz, and as can be seen from fig. 5(c), the distributed power supplies distribute the output according to the principle that the marginal cost is equal, so that the self-optimization-seeking control of the microgrid in the island mode is realized.
Scene 2: self-optimization-approaching control of each microgrid in a microgrid group grid-connected operation mode;
to explain the self-optimization control of each microgrid in the microgrid group grid-connection mode, loads Load2 and Load3 are switched out when t is 3s and are switched in again when t is 5s, and the simulation result is shown in fig. 6.
As can be seen from fig. 6(a) and (b), the voltage and the frequency of each microgrid are kept stable in the grid-connected operation mode, and as can be seen from fig. 6(c), the distributed power supplies of each microgrid perform output distribution according to the principle that the marginal cost is equal, so that self-optimization-seeking control of each microgrid in the microgrid group grid-connected mode is realized.

Claims (3)

1. A self-optimization-seeking control method of a micro-grid group considering grid-connected and island operation modes is characterized by comprising the following steps:
step 1, establishing a microgrid distributed layered control model: the model mainly comprises a primary control layer based on droop control, a secondary control layer for ensuring the frequency stability and the voltage stability of the microgrid and a tertiary control layer for ensuring the output of each distributed power supply to be consistent with a set value; in order to realize distributed control, each distributed power supply of the microgrid iterates based on a discrete consistency algorithm to carry out communication;
step 2, establishing a self-optimization-approaching control model of each microgrid in the microgrid group system under an island mode: in an island operation mode, self-optimization-seeking control of the distributed power supply operating according to the principle of equal micro-increment rate is realized, and the light storage system and the distributed power supply with the output reaching the upper limit do not participate in the self-optimization-seeking control;
step 3, establishing a self-optimization-approaching control model of each micro-grid in the micro-grid group system under a grid-connected mode: under a grid-connected operation mode, source load balance inside the micro-grid is achieved through a power ring in a tertiary control layer, and micro-grid group coordination control is achieved by controlling power exchanged between each micro-grid and a connecting line:
and 4, realizing stable and economic operation of the micro-grid group system and each micro-grid in grid-connected and isolated island operation modes by using the micro-grid group coordination control method, which is specifically realized as follows:
in the primary control layer, each distributed power inverter in the microgrid operates in a droop control mode;
in the secondary control layer, if the micro-grid is in an island mode, starting a power loop, a frequency regulation link and a voltage regulation link of secondary control, and calculating the voltage amplitude and the frequency of the micro-grid through a frequency consistency iterative algorithm and a voltage consistency iterative algorithm; if the grid-connected mode is adopted, only the power loop of the secondary control is started;
in the third control layer, if the microgrid is in an island mode, a power loop of the third control is not started, each distributed power supply calculates a distributed power supply output reference value through a marginal cost consistency iterative algorithm, and the distributed power supply output is controlled to reach the reference value by modifying a power reference value and a droop coefficient of droop control, so that self-optimization-approaching operation of the microgrid is realized; when the output of the distributed power supply reaches the upper limit, the self-optimization-approaching operation is quitted, the remaining distributed power supply modifies the state transition matrix A, and the output distribution is carried out through the marginal cost consistency iterative algorithm again; if the micro-grid is in a grid-connected mode, a power loop for controlling for three times needs to be started, if each micro-grid in the micro-grid group normally operates, the exchange power of each micro-grid and a public connecting line is controlled to be zero, and the algorithm flow is consistent with the island mode; when power shortage occurs in a certain microgrid or new energy cannot be consumed, the other microgrids calculate the power transmitted to the public connecting line by the microgrids through an active response ratio consistency iterative algorithm.
2. The microgrid cluster self-optimization-seeking control method considering grid-connected and island operation modes according to claim 1, characterized in that the self-optimization-seeking control model of each microgrid in the microgrid cluster system in the island mode in step 2 is specifically realized as follows:
2.1 Secondary control
In island mode, to return the output frequency of each distributed power supply to the nominal value ωnFrequency correction must be introduced in the secondary control; firstly, obtaining the frequency omega of the microgrid through iteration according to a discrete consistency algorithmaveI.e. by
Figure FDA0003537037690000021
Wherein,
Figure FDA0003537037690000022
being an element of the state transition matrix A, ng1The number of distributed power sources for which droop control is used; on the basis, the frequency omega of the micro-grid is adjustedaveWith rated frequency omeganThe difference is input into a PI link to obtain a frequency correction quantity delta omega1I.e. by
Figure FDA0003537037690000023
Wherein k isp,ωAnd ki,ωCorrecting the PI controller parameters for the frequency;
in addition, as the basis of the three-time control, in order to adjust the output active power, a power loop control needs to be introduced; using active power reference value PrefInputting the difference value of the actual output power P and the actual output power P into a PI link to obtain a frequency correction quantity delta omega2I.e. by
Figure FDA0003537037690000024
Wherein k isp,PAnd ki,PCorrecting the PI controller parameters for power;
similarly, for reference voltage correction, firstly, the phase voltage amplitude U of the microgrid is obtained through iteration according to a discrete consistency algorithmaveAnd connecting it with rated voltage UnThe difference value is input into a PI link to obtain a voltage correction quantity delta U, namely
Figure FDA0003537037690000025
Wherein k isp,UAnd ki,UCorrecting the PI controller parameters for the voltage;
by combining the primary control and the secondary control, the following formula can be obtained
ωref *＝ωref+Δω1+Δω2
Uref *＝Uref+ΔU
Wherein, ω isref *And Uref *The droop control frequency reference value and the voltage reference value are corrected through secondary control;
2.2 triple control
The purpose of the tertiary control is to realize power distribution among the distributed power supplies; firstly, according to different operation modes, the reference power of each distributed power supply inverter can be obtained through an optimization algorithm or an equal micro-increment rate mode;
for different types of distributed power supplies, after factors of fuel oil cost and maintenance cost are comprehensively considered, cost functions can be uniformly simplified into a quadratic function form, namely
Ci(Pi)＝aiPi 2+biPi+cii＝1,2,...,ng2
Wherein, ai，biAnd ciThe cost coefficients of the distributed power supply are positive numbers, Ci(Pi) When the output active power of the distributed power supply is PiThe cost of electricity generation; the total operation cost of the distributed power supply participating in the tertiary control in the micro-grid system is
Figure FDA0003537037690000031
The marginal power generation cost of each distributed power supply can be obtained by the following formula
Figure FDA0003537037690000032
Wherein, MCi(Pi) When the output active power of the distributed power supply is PiMarginal power generation cost; according to the principle of equal micro-increment rate, when the marginal cost of each distributed power supply is equal, the total operation cost of the system is minimum, namely
Figure FDA0003537037690000033
The above equation can be implemented by a consistency algorithm, with marginal cost MCiAs state variables, ultimatelyIterating to obtain MCaveI.e. by
Figure FDA0003537037690000034
Wherein, aijIs an element of the state transition matrix a;
therefore, the active power reference value of each distributed power supply can be obtained
Figure FDA0003537037690000035
Then, the actual output power of each distributed power inverter reaches the set power by modifying the droop coefficient of the droop control curve;
in droop control, in order to distribute the output power of each distributed power supply according to the droop coefficient, the no-load angular frequency ω of the droop curve is generally set0Equality, i.e. by adjusting the sag factor
Figure FDA0003537037690000036
Wherein m isiIs the droop coefficient, P, of the active-frequency droop curve of the ith distributed power supplyrefiReference value of active power, n, for the output of the ith distributed power supplyg2The number of distributed power supplies participating in the tertiary control;
the above equation can be implemented by a consistency algorithm, which multiplies the droop coefficient by the active power (mP)ref)iAs state variables, the final iteration yields (mP)ref)ave
Figure FDA0003537037690000037
Wherein, aijIs an element of the state transition matrix a;
from this, the droop control coefficient of each distributed power supply can be obtained as
Figure FDA0003537037690000038
Furthermore, the output limits of each distributed power source need to be taken into account, i.e.
0≤Pi≤Pi,max i＝1,2,...,ng2
In the formula, Pi,maxThe output upper limit of the ith distributed power supply is set; when the distributed power supply outputs active power PiReaches the upper limit of output Pi,maxThen the self-optimization-seeking control is exited, and the number n of distributed power supplies participating in the third control layer at the momentg2The state transition matrix A of the consistency algorithm will be changed correspondingly; the rest distributed power supplies are iterated according to a consistency algorithm based on the principle of equal micro-increment rate again and reach a new stable operation state;
meanwhile, in order to improve the new energy consumption rate, a light storage system consisting of the photovoltaic unit and the energy storage unit does not participate in self-optimization-approaching control, but maximizes the energy conversion efficiency through a maximum power tracking control algorithm.
3. The microgrid cluster self-optimization control method considering grid-connected and island operation modes according to claim 2, characterized in that self-optimization control of each microgrid in the microgrid cluster system in the step 3 in the grid-connected mode is specifically realized as follows:
3.1 droop control
Under the grid-connected mode, the primary control layer of each microgrid in the microgrid group still adopts droop control in the following form
Figure FDA0003537037690000041
Meanwhile, because the micro-grid is directly connected with a power grid, the frequency and voltage stability of each micro-grid are ensured by the power grid, and the frequency and voltage do not need to be compensated;
3.2 Secondary control
Under a grid-connected mode, the frequency stability and the voltage stability of the micro-grid are ensured by the main grid, and the active power output by the distributed power supply inverter is ensured to reach an active power reference value only by starting a power loop in the secondary control layer; reference value P of active powerrefInputting the difference value of the actual output power P and the actual output power P into a PI link to obtain a frequency correction quantity delta omega2：
Figure FDA0003537037690000042
By combining the primary control and the secondary control, the following formula can be obtained:
ωref *＝ωref+Δω2
wherein, ω isref *The droop control frequency reference value is corrected through secondary control;
3.3 triple control
Compared with an island mode, the three-time control in the grid-connected mode needs to consider that the marginal cost of each distributed power supply is equal, and needs to realize the source-load balance inside the micro-grid; in particular, the total load of the microgrid is of the magnitude
Figure FDA0003537037690000043
In the formula, PLThe total load size of the micro-grid is,
Figure FDA0003537037690000051
is the ith of a microgrid3Size of individual load, nLThe load quantity of the micro-grid; the output of the distributed power supply without the participation of the micro-grid in the self-optimization-approaching control is as follows
Figure FDA0003537037690000052
In the formula, ng3To do not participate inNumber of distributed power supplies, P, of optimal controlG2The output of the distributed power supply which does not participate in self-optimization-approaching control for the micro-grid is large;
considering the power balance, the output of each distributed power source in the self-optimization-seeking control should be equal to
Figure FDA0003537037690000053
In the formula, PG1The output of a distributed power supply participating in self-optimization-approaching control of the micro-grid is large; considering the principle of equal micro-increment rate to optimize the output of each distributed power supply, the method includes
Figure FDA0003537037690000054
Figure FDA0003537037690000055
The method is consistent with an island mode, based on a consistency algorithm, and performs output distribution on the distributed power supply according to the principle of equal micro-increment rate, namely
Figure FDA0003537037690000056
Therefore, the active power reference value of each distributed power supply can be obtained
Figure FDA0003537037690000057
In addition, in order to realize source-load balance, a power ring is added in three times of control, and the average output of the distributed power supply participating in self-optimization control is obtained according to a consistency algorithm, namely the average output is obtained
Figure FDA0003537037690000058
The average output is obtained by iterationaveWhereby the active power reference of the distributed power supply can be modified to ensure source-to-charge balance within the microgrid, i.e.
Figure FDA0003537037690000059
In the formula, kp,P1And ki,P1Respectively setting power PI controller parameters of a tertiary control layer in a grid-connected mode;
under the grid-connected mode, the power distribution can be realized by directly modifying the active power reference value in droop control without modifying the droop coefficient, namely
Figure FDA0003537037690000061
In the formula, ωrefiAnd UrefiRespectively a frequency reference value and a phase voltage amplitude reference value of the ith distributed power supply; therefore, a micro-grid hierarchical control model under a micro-grid group grid-connected mode is established, and self-optimization control considering micro-grid internal source load balance is realized;
3.4 microgrid group coordination control
On the basis of establishing a self-optimization-approaching control model of the micro-grid under the grid-connected operation mode of the micro-grid group, further considering coordination control among the micro-grids in the micro-grid group system;
under the normal operation condition, the source charge balance is kept inside each micro-grid, and power exchange is not carried out between the micro-grids; when a distributed power supply fault occurs in a certain micro-grid, the power sent to the public connecting line by other micro-grids can be increased through coordination control, and the source-load balance of a micro-grid group system is ensured; when a certain micro-grid generates a situation that new energy cannot be consumed, the power absorbed by other micro-grids from a public connecting line can be increased through coordination control, and the new energy consumption level of a micro-grid group system is ensured;
suppose the power sent by the microgrid to the tie line is PPCC，PPCC< 0 indicates that the microgrid is absorbing power from the tie line; considering the power balance, the output of each distributed power source in the self-optimization-seeking control should be equal to
Figure FDA0003537037690000062
Suppose that a microgrid group includes n in totalmgA micro-grid, wherein the i5If one micro-grid distributed power supply fails, the rest nmg-1 sum of the total amount of power to be sent to the junctor is
Figure FDA0003537037690000063
In the formula,
Figure FDA0003537037690000064
is the ith5The power shortage of the individual micro-grids,
Figure FDA0003537037690000065
is jth5The power sent by the micro-grid to the connecting line is large or small;
in order to realize the coordination control among the micro-grids, the power distribution among the micro-grids needs to be considered; firstly, iteration is carried out through a consistency algorithm to obtain the active output adjustable quantity of the whole micro-grid group system, namely
Figure FDA0003537037690000066
Obtaining the average value P of the active power output adjustable quantity of the micro-grid group system through iterationadj,aveThen there is
Padj＝nmgPadj,ave
In the formula, PadjTo be integratedThe active output of each micro-grid group system can be adjusted; further, defining the response ratio of the microgrid as
Figure FDA0003537037690000067
In the formula,
Figure FDA0003537037690000071
is the ith5The active power output response ratio of each micro-grid; in order to ensure the safe and stable operation of each micro-grid and the whole micro-grid group, the distribution can be carried out according to the principle of response ratio of each micro-grid and the like, and the distribution is realized through a consistency algorithm, namely
Figure FDA0003537037690000072
After iterative convergence, the average response ratio of the microgrid group is raveThen there is
Figure FDA0003537037690000073
Each micro-grid adjusts the output according to the adjustable quantity of the active power of the micro-grid, and the micro-grid is ensured to still operate in a safe and stable state; each microgrid obtains active power output required to be born
Figure FDA0003537037690000074
Then, the coordination control between the micro-grids can be realized only by correcting the power loop of the third control layer;
when a certain micro-grid generates a situation that new energy cannot be consumed, other micro-grids need to increase active power absorbed from a connecting line to ensure the consumption level of the new energy of the micro-grid group, and the coordination control process is similar to the process.
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