CN117439199A - Method and system for supporting high-proportion distributed photovoltaic frequency and voltage combination - Google Patents
Method and system for supporting high-proportion distributed photovoltaic frequency and voltage combination Download PDFInfo
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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
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/48—Controlling the sharing of the in-phase component
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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
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
- H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
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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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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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
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/50—Controlling the sharing of the out-of-phase component
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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
- 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]
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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- 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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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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Abstract
The invention discloses a method and a system for high-proportion distributed photovoltaic frequency and voltage combined support, wherein the method constructs a power output model of a distributed photovoltaic grid-connected converter through the active and reactive output characteristics of the converter; analyzing and modeling the distributed photovoltaic frequency support through the relation between active frequency and active frequency of the system power frequency characteristic analysis; analyzing the relation among the system active power, reactive power and voltage by using a DistFlow method, and constructing a voltage support model; determining corresponding constraint conditions according to actual topological conditions and actual capacity of the converter; and optimizing and solving the minimum net loss objective function by a second order cone method. The invention fully utilizes the distributed photovoltaic standby capacity to perform power compensation on the basis of photovoltaic load shedding operation, and can perform system optimization on the basis of qualified frequency and voltage, so that the system network loss is minimized, the stability and the economy of the system are improved, and the invention has important significance for guaranteeing the safe and stable operation of the new energy grid-connected system.
Description
Technical Field
The invention relates to a renewable energy grid-connected stability analysis technology, in particular to a method and a system for high-proportion distributed photovoltaic frequency and voltage combined support.
Background
In order to cope with the increasing power demand and environmental pressure, power systems are developing a high proportion of new energy and a high proportion of power electronics. As the permeability of new energy and power electronics increases, there is a trend of reduced inertia and weakened system strength in the power system, and stability problems become more serious. However, the converter is used as a main device for connecting the distributed photovoltaic into the power grid, so that the converter is already an important component of the power system, and therefore, the converter is controlled, the distributed photovoltaic is used as a flexible adjusting resource, the fluctuation can be stabilized, and the system frequency-voltage is supported, so that the system strength is enhanced, and the power quality is improved.
The students at home and abroad also develop related researches including the application of energy storage, the application of a traditional pressure regulating device, the primary frequency modulation by droop control and virtual synchronous machine control and the like.
However, the research in the related art is mainly a single research on frequency support or voltage support by a new energy unit, and the research on a frequency-voltage common support method for distributed new energy represented by distributed photovoltaic is not related, but the potential of the distributed photovoltaic for participating in power quality support at multiple angles is not fully exploited. Meanwhile, the existing frequency or voltage supporting method is mainly used for carrying out primary adjustment by using a traditional device or energy storage, so that the corresponding cost is increased, primary frequency modulation also belongs to differential frequency modulation, and sometimes the adjustment method can not meet the frequency modulation requirement, and certain difference exists.
Disclosure of Invention
The invention aims to: the invention aims to provide a method and a system for supporting a high-proportion distributed photovoltaic frequency and voltage combination, so that the stability and the economy of the system are improved on the basis of fully excavating the multi-angle supporting potential of the distributed photovoltaic.
The technical scheme is as follows: the invention discloses a high-proportion distributed photovoltaic frequency and voltage combined support method, which comprises the following steps of:
(1) And analyzing the active and reactive output coupling characteristic of the converter based on the output characteristic of the distributed photovoltaic grid-connected converter, and establishing an active and reactive output power model of the converter.
Determining the actual capacity of the distributed photovoltaic grid-connected converter;
determining the coupling relation of active and reactive outputs of the grid-connected converter and the power factor; the calculation formula of the coupling relation of the active and reactive outputs is as follows:
in which Q DG The reactive output capacity of the converter; p (P) DG Active power output by the converter; s is S DG Is the capacity of the current transformer;representing a power factor angle; it should be noted that the remaining reactive capacity of the converter may emit or absorb reactive power, thereby acting as a voltage active support for the grid.
And determining an active and reactive output power model of the grid-connected converter based on the coupling relation between the actual capacity and the active and reactive output of the converter and the power factor.
(2) And analyzing the relation between the output power of the converter and the frequency coupling based on the system frequency characteristic, and establishing a distributed photovoltaic frequency support model.
Determining the coupling relation between the system frequency and the power, wherein the formula is as follows:
ΔP L0 -ΔP G0 ＝-K G Δf”-K D Δf”＝-K S Δf” (49)
wherein DeltaP L0 Delta P is the system load delta G0 For secondary adjustment of the power of the distributed photovoltaic enhancement, Δf "is the system frequency variation, K G 、K D 、K S The unit regulating power of new energy, the unit regulating power of load and the unit regulating power of system are respectively MW/HZ;
based on the coupling relation between the system frequency and the power, adding secondary frequency modulation on the basis of a speed regulator model, wherein the model is as follows:
the model is a speed regulator model added with secondary frequency modulation, wherein, P m For mechanical power, P e Is electromagnetic power, deltaP G0 Active power, K, for distributed photovoltaic augmentation s Regulating power, ω, for system units ref For the rated angular velocity, Δω is the angular velocity variation value, J is the virtual inertia, and D is the damping coefficient.
(3) And analyzing the coupling relation between the output power and the voltage of the converter based on the system voltage characteristics, and establishing a distributed photovoltaic voltage support model.
Determining a coupling relationship between voltage and power; the coupling relationship between voltage and power is expressed as:
wherein V is i Representing the voltage amplitude at node i, V j Representing the voltage amplitude of node j, r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the amplitude, P, of the current flowing on branch ij ij And Q ij Active power reactive power flowing from node i to node j;
based on the system voltage and power coupling relationship, the voltage support is modeled, which is expressed as:
wherein P is i Expressed as net active value of node i, Q i Expressed as net reactive value of node i, P L,i Active load denoted as node i, Q L,i Reactive load, denoted node i, P GD,i Grid-connected active power of converter denoted as node i, Q DG,i Grid-connected reactive power of the converter denoted as node i; u (U) i Represented as voltage at arbitrary node i, R i Represented as the resistance between node i-1 and node i, X i Represented as reactance between node i-1 and node i, px inei And Q Linei The active power and the reactive power of the injection node i in the line between the node i-1 and the node i are respectively shown in the formula, wherein P Lossk And Q Lossk Is the active and reactive loss of the line between node k-1 and node k.
(4) Based on the actual topology condition of the network, the capacity of the converter and the condition of the reactive compensation device, and simultaneously combining active and reactive output power of the converter, the distributed photovoltaic frequency and voltage support model, a system power balance, adjustable resource constraint, network voltage and current constraint and a minimum network loss objective function are established.
Determining power balance constraint, voltage safety constraint, current safety constraint and controllable resource output constraint;
power balance constraint:
where u (j) represents the head end node set of the branch having the j point as the end point, and set v (j) represents the tail end node set of the branch having the j point as the end point, P j And Q j The active and reactive injection powers of the j nodes are respectively expressed as r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the amplitude, P, of the current flowing on branch ij ij And Q ij Active power and reactive power flowing from node i to node j, respectively;
voltage safety constraints:
in the method, in the process of the invention,representing the lower voltage limit at node j of the distribution network, < >>Representing an upper voltage limit at a power distribution network node j;
current safety constraints:
in the method, in the process of the invention,current limit for branch ij;
adjustable resource output constraint:
(P DG,i ) 2 +(Q DG,i ) 2 ≤(S DG,i ) 2 (59)
wherein P is DG,i Active output, Q, of new energy converter expressed as node i access DG,i Reactive output of new energy converter indicated as node i access, S DG,i The capacity of the new energy converter accessed by the node i is represented;
the distributed photovoltaic is utilized to support the frequency-voltage of the power distribution system, and the distribution of power is involved, so that the optimal distribution of power is selected by taking the minimum net loss as an objective function on the basis of qualified supporting frequency-voltage, and the optimal distribution is expressed as:
Wherein, the set v (i) represents a tail end node set of a branch taking an i node as a head end point; n is the total number of nodes of the power distribution network; r is (r) ij The branch resistance, denoted as branch ij, I ij The current amplitude flowing on the branch ij is represented by the expression:
wherein P is ij And Q ij Active power and reactive power respectively flowing from node i to node j, V i Representing the voltage amplitude of node I, I ij Representing the magnitude of the current flowing on branch ij.
(5) Based on the equation form, the non-convex problem is subjected to convex optimization by utilizing a second order cone, an objective function is solved, and a reactive power compensation device in the system and optimal distribution of active power and reactive power of each distributed photovoltaic are determined.
(5.1) determining a second order cone form according to a second order cone method;
the standard second order cone is expressed as:
the rotating second order cone is expressed as:
wherein K is a second order cone constraint condition; variable x i ∈R n The method comprises the steps of carrying out a first treatment on the surface of the y is an objective function under a standard second order cone; yz is the objective function under a rotating second order cone.
(5.2) convex optimization is carried out on the non-convex problem by using a second order cone method, and then solving is carried out. In the optimization solving process, a non-convex optimization solving problem exists, so that an optimal solution is difficult to obtain, although some nonlinear solvers can be used for solving, the optimal solution is often trapped in a local optimal solution, and a global optimal solution cannot be obtained.
The second order cone principle can be expressed as:
where f (x) is an objective function, ax=b is a linear constraint, and K is a second order cone constraint.
The standard second order cone can be expressed as:
as a preferred scheme of the method for supporting the high-proportion distributed photovoltaic frequency and voltage combination, the invention comprises the following steps: the rotating second order cone can be expressed as:
the second-order cone programming method is a method popularized by linear programming, has higher solving efficiency and has wide research and application scenes, so the problem can be well solved by applying the second-order cone method, and the globally optimal solution can be obtained, thereby reasonably distributing the output of each distributed photovoltaic.
Voltage current amplitude:
in the formula, v is i And i ij Replacing the square of the voltage amplitude and the square of the branch current amplitude;
objective function:
wherein, the set v (i) represents a tail end node set of a branch taking an i node as a head end point; n is the total number of nodes of the power distribution network; r is (r) ij The branch resistance, i, denoted as branch ij ij Representing the square of the amplitude of the current flowing on branch ij;
branch current constraint function:
wherein P is ij And Q ij Active power and reactive power, v, respectively, flowing from node i to node j i Representing the square of the voltage amplitude at node i, i ij Representing the square of the amplitude of the current flowing on branch ij. From the above equation, it can be found that this equation is a rotational second order cone constraint, which is further equivalently deformed;
standard second order cone form of branch current constraint function:
the power balance constraint is:
where u (j) represents the head end node set of the branch having the point j as the end point, v (j) represents the end node set of the branch having the point j as the end point, and P j And Q j The active and reactive injection powers, P, of the j nodes are respectively shown ij And Q ij Active power and reactive power respectively flowing from node i to node j, V i Representing the voltage amplitude at node i, V j Representing the voltage amplitude of node j, r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the magnitude of the current flowing on branch ij.
A system for high-proportion distributed photovoltaic frequency-voltage combination support, comprising the following modules:
the active and reactive output power model building module of the converter: analyzing active and reactive output coupling characteristics of the converter based on the output characteristics of the distributed photovoltaic grid-connected converter, and establishing an active and reactive output power model of the converter;
the distributed photovoltaic frequency support model building module comprises: analyzing the relation between the output power of the converter and frequency coupling based on the system frequency characteristic, and establishing a distributed photovoltaic frequency support model;
The distributed photovoltaic voltage support model building module comprises: analyzing the coupling relation between the output power of the converter and the voltage based on the system voltage characteristics, and establishing a distributed photovoltaic voltage support model;
and a multifunctional building module: based on the actual topology condition of the network, the capacity of the converter and the condition of the reactive compensation device, simultaneously combining active and reactive output power of the converter, the distributed photovoltaic frequency and the voltage support model, and establishing a system power balance, adjustable resource constraint, network voltage and current constraint and a minimum network loss objective function;
and (3) an optimization solving module: based on the equation form, the non-convex problem is subjected to convex optimization by utilizing a second order cone, an objective function is solved, and a reactive power compensation device in the system and optimal distribution of active power and reactive power of each distributed photovoltaic are determined.
The operation steps of the active and reactive output power model building module of the converter are as follows:
determining the actual capacity of the distributed photovoltaic grid-connected converter;
determining the coupling relation of active and reactive outputs of the grid-connected converter and the power factor; the calculation formula of the coupling relation of the active and reactive outputs is as follows:
in which Q DG The reactive output capacity of the converter; p (P) DG Active power output by the converter; s is S DG Is the capacity of the current transformer;representing a power factor angle;
and determining an active and reactive output power model of the grid-connected converter based on the coupling relation between the actual capacity and the active and reactive output of the converter and the power factor.
The operation steps of the distributed photovoltaic frequency support model building module are as follows:
determining the coupling relation between the system frequency and the power, wherein the formula is as follows:
ΔP L0 -ΔP G0 ＝-K G Δf”-K D Δf”＝-K S Δf” (76)
wherein DeltaP L0 Delta P is the system load delta G0 For secondary adjustment of the power of the distributed photovoltaic enhancement, Δf "is the system frequency variation, K G 、K D 、K S The unit regulating power of new energy, the unit regulating power of load and the unit regulating power of system are respectively MW/HZ;
based on the coupling relation between the system frequency and the power, adding secondary frequency modulation on the basis of a speed regulator model, wherein the model is as follows:
the model is a speed regulator model added with secondary frequency modulation, wherein, P m For mechanical power, P e Is electromagnetic power, deltaP G0 Active power, K, for distributed photovoltaic augmentation s Regulating power, ω, for system units ref For the rated angular velocity, Δω is the angular velocity variation value, J is the virtual inertia, and D is the damping coefficient.
The operation steps of the distributed photovoltaic voltage support model building module are as follows:
determining a coupling relationship between voltage and power; the coupling relationship between voltage and power is expressed as:
Wherein V is i Representing the voltage amplitude at node i, V j Representing the voltage amplitude of node j, r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the amplitude, P, of the current flowing on branch ij ij And Q ij Active power reactive power flowing from node i to node j;
based on the system voltage and power coupling relationship, the voltage support is modeled, which is expressed as:
wherein P is i Expressed as net active value of node i, Q i Expressed as net reactive value of node i, P L,i Active load denoted as node i, Q L,i Reactive load, denoted node i, P DG,i Grid-connected active power of converter denoted as node i, Q DG,i Grid-connected reactive power of the converter denoted as node i; u (U) i Represented as voltage at arbitrary node i, R i Represented as the resistance between node i-1 and node i, X i Represented as reactance between node i-1 and node i, P Linei And Q Linei The active power and the reactive power of the injection node i in the line between the node i-1 and the node i are respectively shown in the formula, wherein P Lossk And Q Lossk Is the active and reactive loss of the line between node k-1 and node k.
The operation steps of the multifunctional building module are as follows: determining power balance constraint, voltage safety constraint, current safety constraint and controllable resource output constraint;
Power balance constraint:
where u (j) represents the head end node set of the branch having the j point as the end point, and set v (j) represents the tail end node set of the branch having the j point as the end point, P j And Q j The active and reactive injection powers of the j nodes are respectively expressed as r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the amplitude, P, of the current flowing on branch ij ij And Q ij Active power and reactive power flowing from node i to node j, respectively;
voltage safety constraints:
in the method, in the process of the invention,representing the lower voltage limit at node j of the distribution network, < >>Representing an upper voltage limit at a power distribution network node j;
current safety constraints:
in the method, in the process of the invention,current limit for branch ij;
adjustable resource output constraint:
(P DG,i ) 2 +(Q DG,i ) 2 ≤(S DG,i ) 2 (86)
wherein P is DG,i Active output, Q, of new energy converter expressed as node i access DG,i Reactive output of new energy converter indicated as node i access, S DG,i The capacity of the new energy converter accessed by the node i is represented;
an objective function is determined targeting the minimum net loss, which is expressed as:
wherein, the set v (i) represents a tail end node set of a branch taking an i node as a head end point; n is the total number of nodes of the power distribution network; r is (r) ij The branch resistance, denoted as branch ij, I ij Representing the magnitude of the current flowing on branch ij.
The operation steps of the optimization solving module are as follows:
(1) Determining a second-order cone form according to a second-order cone method;
the standard second order cone is expressed as:
the rotating second order cone is expressed as:
wherein K is a second order cone constraint condition; variable x i ∈R n The method comprises the steps of carrying out a first treatment on the surface of the y is an objective function under a standard second order cone; yz is the objective function under a rotating second order cone.
(2) The non-convex problem is subjected to convex optimization by a second order cone method, and then is solved, specifically:
voltage current amplitude:
in the formula, v is i And i ij Replacing the square of the voltage amplitude and the square of the branch current amplitude;
objective function:
wherein, the set v (i) represents a tail end node set of a branch taking an i node as a head end point; n is the total number of nodes of the power distribution network; r is (r) ij The branch resistance, i, denoted as branch ij ij Representing the square of the amplitude of the current flowing on branch ij;
branch current constraint function:
wherein P is ij And Q ij Active power and reactive power, v, respectively, flowing from node i to node j i Representing the square of the voltage amplitude at node i, i ij Representing the square of the amplitude of the current flowing on branch ij. From the above equation, it can be found that this equation is a rotational second order cone constraint, which is further equivalently deformed;
Standard second order cone form of branch current constraint function:
the power balance constraint is:
where u (j) represents the head end node set of the branch having the point j as the end point, v (j) represents the end node set of the branch having the point j as the end point, and P j And Q j The active and reactive injection powers, P, of the j nodes are respectively shown ij And Q ij Active power and reactive power respectively flowing from node i to node j, V i Representing the voltage amplitude at node i, V j Representing the voltage amplitude of node j, r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the magnitude of the current flowing on branch ij.
A computer storage medium having stored thereon a computer program which when executed by a processor implements a method of high-proportion distributed photovoltaic frequency-voltage combination support as described above.
A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing a method of high-proportion distributed photovoltaic frequency-voltage combination support as described above when the computer program is executed.
The beneficial effects are that: compared with the prior art, the invention has the following advantages: the invention comprehensively considers the active and reactive output characteristics of the converter and the coupling relation between the frequency voltage and the power of the system, and improves the stability and the economy of the system on the basis of fully excavating the multi-angle supporting potential of the distributed photovoltaic.
Drawings
FIG. 1 is a schematic flow diagram of a distributed photovoltaic participation frequency-voltage combination support method;
FIG. 2 is a schematic diagram of a distributed photovoltaic participation frequency-voltage support;
FIG. 3 is a topology of the governor after adding secondary frequency modulation;
fig. 4 is a graph of frequency-voltage characteristics after distributed photovoltaic engagement with a frequency-voltage support.
Fig. 5 is an optimal distribution of active and reactive power output of each distributed photovoltaic after model solving.
FIG. 6 is an optimal distribution of reactive compensation devices in a system after model solving
Detailed Description
The technical scheme of the invention is further described below with reference to the accompanying drawings.
As shown in fig. 1, the invention provides a method for supporting a high-proportion distributed photovoltaic frequency and voltage combination, which comprises the following steps:
and step 1, analyzing active and reactive output coupling characteristics of the converter based on the output characteristics of the distributed photovoltaic grid-connected converter, and establishing an active and reactive output power model of the converter.
And 2, analyzing the relation between the output power of the converter and the frequency coupling based on the system frequency characteristic, and establishing a distributed photovoltaic frequency support model.
And 3, analyzing the coupling relation between the output power of the converter and the voltage based on the system voltage characteristics, and establishing a distributed photovoltaic voltage support model.
And 4, based on the actual topology condition of the network, the capacity of the converter and the condition of the reactive compensation device, simultaneously combining active and reactive output power of the converter, the distributed photovoltaic frequency and the voltage support model, and establishing a system power balance, an adjustable resource constraint, a network voltage and current constraint and a minimum network loss objective function.
And 5, based on an equation form, performing convex optimization on the non-convex problem by utilizing a second order cone, solving an objective function, and determining a reactive compensation device in the system and optimal distribution of active power and reactive power of each distributed photovoltaic.
In the implementation of the step 1, an active and reactive output power model of the converter is built according to the output characteristics of the distributed photovoltaic grid-connected converter.
1) The power output of the grid-connected converter is expressed as:
(P DG,i ) 2 +(Q DG,i ) 2 ≤(S DG,i ) 2 (97)
wherein P is DG,i Active output, Q, of new energy converter expressed as node i access DG,i Reactive output of new energy converter indicated as node i access, S DG,i The capacity of the new energy converter accessed by the node i is shown.Representing the power factor angle.
In the implementation of the step 2, according to the frequency characteristic of the system, the relation between power and frequency coupling is analyzed, and a distributed photovoltaic frequency support model is established.
1) The power versus frequency coupling relationship is expressed as:
wherein DeltaP L0 Delta P is the system load delta G0 For secondary adjustment of the power of the distributed photovoltaic enhancement, Δf "is the system frequency variation, K G 、K D 、K S The unit regulating power of the new energy, the unit regulating power of the load and the unit regulating power of the system are respectively MW/HZ.
2) The distributed photovoltaic frequency support model is expressed as:
wherein P is m For mechanical power, P e Is electromagnetic power, deltaP G0 Active power, K, for distributed photovoltaic augmentation s Regulating power, ω, for system units ref For the rated angular velocity, Δω is the angular velocity variation value, J is the virtual inertia, and D is the damping coefficient.
In the implementation of the step 3, according to the system voltage characteristics, the power-voltage coupling relation is analyzed, and a distributed photovoltaic voltage support model is established.
1) The power-voltage coupling relationship is expressed as:
wherein V is i Representing the voltage amplitude at node i, V j Representing the voltage amplitude of node j, r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the amplitude, P, of the current flowing on branch ij ij And Q ij Active power reactive power flowing from node i to node j, respectively.
2) The distributed photovoltaic voltage support model is expressed as:
Wherein P is i Expressed as net active value of node i, Q i Expressed as net reactive value of node i, P L,i Active load denoted as node i, Q L,i Reactive load, denoted node i, P DG,i Grid-connected active power of converter denoted as node i, Q DG,i The converter, denoted node i, is grid connected with reactive power. U (U) i Represented as voltage at arbitrary node i, R i Represented as the resistance between node i-1 and node i, X i Represented as reactance between node i-1 and node i, P Linei And Q Linei The active power and the reactive power of the injection node i in the line between the node i-1 and the node i are respectively shown in the formula, wherein P Lossk And Q Lossk Is the active and reactive loss of the line between node k-1 and node k.
In the implementation of step 4, constraints such as power balance and a minimum network loss objective function are established according to the actual topology condition of the network, the capacity of the converter and the like.
1) Objective function:
wherein, the set v (i) represents a tail end node set of a branch taking an i node as a head end point; and n is the total number of nodes of the power distribution network. r is (r) ij The branch resistance, denoted as branch ij, I ij The current amplitude flowing on the branch ij is expressed as:
wherein P is ij And Q ij Active power and reactive power respectively flowing from node i to node j, V i Representing the voltage amplitude of node I, I ij Representing the magnitude of the current flowing on branch ij.
2) Power balance constraint:
where u (j) represents the head end node set of the branch having the j point as the end point, and set v (j) represents the tail end node set of the branch having the j point as the end point, P j And Q j The active and reactive injection powers of the j nodes are respectively expressed as r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the amplitude, P, of the current flowing on branch ij ij And Q ij Active power and reactive power flowing from node i to node j, respectively.
3) Voltage safety constraints:
in the method, in the process of the invention,representing the lower voltage limit at node j of the distribution network, < >>Representing the upper voltage limit at the distribution network node j.
4) Current safety constraints:
in the method, in the process of the invention,for the current limit of branch ij.
5) Adjustable resource output constraint:
the adjustable resources comprise active output of the converter and reactive output of the converter, and the functions are as follows:
(P DG,i ) 2 +(Q DG,i ) 2 ≤(S DG,i ) 2 (111)
wherein P is DG,i Active output, Q, of new energy converter expressed as node i access DG,i Reactive output of new energy converter indicated as node i access, S DG,i The capacity of the new energy converter accessed by the node i is shown.
In the implementation of step 5, since the equation contains a non-convex problem, the non-convex problem is convex optimized by using a second order cone, and finally solved. Because the model has non-convexity, which leads to a model containing mixed integer non-convexity optimization problem, the optimal solution is difficult to directly obtain, therefore, the model is considered to be firstly processed and converted and then solved, the non-convexity constraint in the original problem is firstly subjected to convexity relaxation, the non-convexity constraint is converted into the mixed integer convexity optimization problem which is convenient to solve, and then the second order cone programming method is used for solving.
1) Standard second order cone principle:
where f (x) is an objective function, ax=b is a linear constraint, and K is a second order cone constraint.
2) The standard second order cone is expressed as:
3) The rotating second order cone is expressed as:
thus, the non-convex problem in the present invention after convex optimization can be expressed as:
in the formula, v i And i ij Instead of the square of the voltage amplitude and the square of the branch current amplitude.
4) The objective function becomes:
wherein, the set v (i) represents a tail end node set of a branch taking an i node as a head end point; and n is the total number of nodes of the power distribution network. r is (r) ij The branch resistance, i, denoted as branch ij ij Representing the square of the amplitude of the current flowing on branch ij.
5) The branch current constraint function becomes:
wherein P is ij And Q ij Active power and reactive power, v, respectively, flowing from node i to node j i Representing the square of the voltage amplitude at node i, i ij Representing the square of the amplitude of the current flowing on branch ij. From the above equation, it can be found that this equation is a rotating second order cone constraint, which is further equivalently deformed.
6) The standard second order cone form of the branch current constraint function is as follows:
7) The power balance constraint is:
where u (j) represents the head end node set of the branch having the point j as the end point, v (j) represents the end node set of the branch having the point j as the end point, and P j And Q j The active and reactive injection powers, P, of the j nodes are respectively shown ij And Q ij Active power and reactive power respectively flowing from node i to node j, V i Representing the voltage amplitude at node i, V j Representing the voltage amplitude of node j, r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the magnitude of the current flowing on branch ij.
According to the above, the solving steps are as follows:
1) And determining the capacity of the distributed photovoltaic grid-connected converter, prescribing a power factor, enabling the distributed photovoltaic to operate under load, and reserving spare capacity.
2) And solving a frequency-voltage support model according to the coupling relation of the power, the frequency and the voltage.
3) And determining an objective function, and solving constraint conditions according to the actual topology and other conditions.
4) And (3) performing convex optimization on the problem by using a second-order cone, and finally performing optimization solution.
Fig. 2 is a schematic diagram of distributed photovoltaic participation frequency-voltage support, as shown in fig. 2, distributed photovoltaic distributed at different positions has different capacities and parameter settings, so that each distributed photovoltaic has different support capacities, when disturbance occurs, power compensation is distributed to each distributed photovoltaic according to the actual condition and the topological condition of the distributed photovoltaic and the scheme of minimum network loss, so as to support the frequency and the voltage of the power distribution network, but the distributed photovoltaic output at different positions can influence the conditions of node voltage, tide and the like, so that the distributed photovoltaic at different positions is distributed by taking the minimum network loss as an objective function, and economy can be realized on the basis of qualified voltage frequency.
FIG. 3 is a topology of the governor after adding the secondary frequency modulation, as shown in FIG. 3, the governor model without adding the secondary frequency modulation is:
because the primary frequency modulation is poor in frequency modulation, the frequency may not meet the requirement after only the primary frequency modulation, as shown in the frequency characteristic diagram in fig. 4, and therefore, the secondary frequency modulation is added on the basis of the primary frequency modulation, and the mode of the speed regulator is changed into:
wherein P is m For mechanical power, P e Is electromagnetic power, deltaP G0 Active power, K, for distributed photovoltaic augmentation s Regulating power, ω, for system units ref For the rated angular velocity, Δω is the angular velocity variation value, J is the virtual inertia, and D is the damping coefficient.
Fig. 4 is a frequency-voltage characteristic diagram after the distributed photovoltaic is subjected to frequency-voltage support, as shown in fig. 4, after the distributed photovoltaic is subjected to frequency-voltage support, the frequency quality is improved, the voltage is also within a specified range, and it is noted that if only the distributed photovoltaic is applied to perform frequency support, the voltage quality may be disqualified due to the change of power.
Fig. 5 is an optimal distribution of active and reactive power output of each distributed photovoltaic after model solving, as shown in fig. 5, after the distributed photovoltaic frequency voltage is supported, when the frequency voltage reaches the standard, the optimal conditions of active and reactive power output of the distributed photovoltaic at different positions are obtained by taking the minimum net loss as a target.
Fig. 6 is an optimal distribution of reactive power compensation devices in the system after model solving, as shown in fig. 6, when the frequency voltage reaches the standard through the frequency voltage support of the reactive power compensation devices in the system, the optimal distribution of reactive power compensation devices in different positions or different types is obtained by taking the minimum network loss as the target.
A system for high-proportion distributed photovoltaic frequency-voltage combination support, comprising the following modules:
the active and reactive output power model building module of the converter: analyzing active and reactive output coupling characteristics of the converter based on the output characteristics of the distributed photovoltaic grid-connected converter, and establishing an active and reactive output power model of the converter;
the distributed photovoltaic frequency support model building module comprises: analyzing the relation between the output power of the converter and frequency coupling based on the system frequency characteristic, and establishing a distributed photovoltaic frequency support model;
the distributed photovoltaic voltage support model building module comprises: analyzing the coupling relation between the output power of the converter and the voltage based on the system voltage characteristics, and establishing a distributed photovoltaic voltage support model;
and a multifunctional building module: based on the actual topology condition of the network, the capacity of the converter and the condition of the reactive compensation device, simultaneously combining active and reactive output power of the converter, the distributed photovoltaic frequency and the voltage support model, and establishing a system power balance, adjustable resource constraint, network voltage and current constraint and a minimum network loss objective function;
And (3) an optimization solving module: based on the equation form, the non-convex problem is subjected to convex optimization by utilizing a second order cone, an objective function is solved, and a reactive power compensation device in the system and optimal distribution of active power and reactive power of each distributed photovoltaic are determined.
The operation steps of the active and reactive output power model building module of the converter are as follows:
determining the actual capacity of the distributed photovoltaic grid-connected converter;
determining the coupling relation of active and reactive outputs of the grid-connected converter and the power factor; the calculation formula of the coupling relation of the active and reactive outputs is as follows:
in which Q DG The reactive output capacity of the converter; p (P) DG Active power output by the converter; s is S DG Is the capacity of the current transformer;representing a power factor angle;
and determining an active and reactive output power model of the grid-connected converter based on the coupling relation between the actual capacity and the active and reactive output of the converter and the power factor.
The operation steps of the distributed photovoltaic frequency support model building module are as follows:
determining the coupling relation between the system frequency and the power, wherein the formula is as follows:
ΔP L0 -ΔP G0 ＝-K G Δf”-K D Δf”＝-K S Δf” (126)
wherein DeltaP L0 Delta P is the system load delta G0 For secondary adjustment of the power of the distributed photovoltaic enhancement, Δf "is the system frequency variation, K G 、K D 、K S The unit regulating power of new energy, the unit regulating power of load and the unit regulating power of system are respectively MW/HZ;
based on the coupling relation between the system frequency and the power, adding secondary frequency modulation on the basis of a speed regulator model, wherein the model is as follows:
the model is a speed regulator model added with secondary frequency modulation, wherein, P m For mechanical power, P e Is electromagnetic power, deltaP G0 Active power, K, for distributed photovoltaic augmentation s Regulating power, ω, for system units ref For the rated angular velocity, Δω is the angular velocity variation value, J is the virtual inertia, and D is the damping coefficient.
The operation steps of the distributed photovoltaic voltage support model building module are as follows:
determining a coupling relationship between voltage and power; the coupling relationship between voltage and power is expressed as:
wherein V is i Representing the voltage amplitude at node i, V j Representing the voltage amplitude of node j, r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the amplitude, P, of the current flowing on branch ij ij And Q ij Active power reactive power flowing from node i to node j;
based on the system voltage and power coupling relationship, the voltage support is modeled, which is expressed as:
wherein P is i Expressed as net active value of node i, Q i Expressed as net reactive value of node i, P L,i Active load denoted as node i, Q L,i Reactive load, denoted node i, P DG,i Grid-connected active power of converter denoted as node i, Q DG,i Grid-connected reactive power of the converter denoted as node i; u (U) i Represented as voltage at arbitrary node i, R i Represented as the resistance between node i-1 and node i, X i Represented as reactance between node i-1 and node i, P Linei And Q Linei The active power and the reactive power of the injection node i in the line between the node i-1 and the node i are respectively shown in the formula, wherein P Lossk And Q Lossk Is the active and reactive loss of the line between node k-1 and node k.
The operation steps of the multifunctional building module are as follows: determining power balance constraint, voltage safety constraint, current safety constraint and controllable resource output constraint;
power balance constraint:
where u (j) represents the head end node set of the branch having the j point as the end point, and set v (j) represents the tail end node set of the branch having the j point as the end point, P j And Q j The active and reactive injection powers of the j nodes are respectively expressed as r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the amplitude, P, of the current flowing on branch ij ij And Q ij Active power and reactive power flowing from node i to node j, respectively;
Voltage safety constraints:
in the method, in the process of the invention,representing the lower voltage limit at node j of the distribution network, < >>Representing an upper voltage limit at a power distribution network node j;
current safety constraints:
in the method, in the process of the invention,current limit for branch ij;
adjustable resource output constraint:
(P DG,i ) 2 +(Q DG,i ) 2 ≤(S DG,i ) 2 (136)
wherein P is DG,i Active output, Q, of new energy converter expressed as node i access DG,i Reactive output of new energy converter indicated as node i access, S DG,i The capacity of the new energy converter accessed by the node i is represented;
an objective function is determined targeting the minimum net loss, which is expressed as:
wherein, the set v (i) represents a tail end node set of a branch taking an i node as a head end point; n is the total number of nodes of the power distribution network; r is (r) ij The branch resistance, denoted as branch ij, I ij Representing the magnitude of the current flowing on branch ij.
The operation steps of the optimization solving module are as follows:
(1) Determining a second-order cone form according to a second-order cone method;
the standard second order cone is expressed as:
the rotating second order cone is expressed as:
wherein K is a second order cone constraint condition; variable x i ∈R n The method comprises the steps of carrying out a first treatment on the surface of the y is an objective function under a standard second order cone; yz is the objective function under a rotating second order cone.
(2) The non-convex problem is subjected to convex optimization by a second order cone method, and then is solved, specifically:
voltage current amplitude:
In the formula, v is i And i ij Replacing the square of the voltage amplitude and the square of the branch current amplitude;
objective function:
wherein, the set v (i) represents a tail end node set of a branch taking an i node as a head end point; n is the total number of nodes of the power distribution network; r is (r) ij The branch resistance, i, denoted as branch ij ij Representing the square of the amplitude of the current flowing on branch ij;
branch current constraint function:
wherein P is ij And Q ij Active power and reactive power, v, respectively, flowing from node i to node j i Representing the square of the voltage amplitude at node i, i ij Representing the square of the amplitude of the current flowing on branch ij. From the above equation, it can be found that this equation is a rotational second order cone constraint, which is further equivalently deformed;
standard second order cone form of branch current constraint function:
the power balance constraint is:
where u (j) represents the head end node set of the branch having the point j as the end point, v (j) represents the end node set of the branch having the point j as the end point, and P j And Q j The active and reactive injection powers, P, of the j nodes are respectively shown ij And Q ij Active power and reactive power respectively flowing from node i to node j, V i Representing the voltage amplitude at node i, V j Representing the voltage amplitude of node j, r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the magnitude of the current flowing on branch ij.
A computer storage medium having stored thereon a computer program which when executed by a processor implements a method of high-proportion distributed photovoltaic frequency-voltage combination support as described above.
A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing a method of high-proportion distributed photovoltaic frequency-voltage combination support as described above when the computer program is executed.
It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein. The scheme in the embodiment of the invention can be realized by adopting various computer languages, such as object-oriented programming language Java, an transliteration script language JavaScript and the like.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, 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, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These 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 flow or flows and/or block diagram block or blocks.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (14)
1. A method for high-proportion distributed photovoltaic frequency and voltage combination support, comprising the following steps:
Based on the output characteristics of the distributed photovoltaic grid-connected converter, analyzing the active and reactive output coupling relation of the converter, and establishing an active and reactive output power model of the converter;
establishing a distributed photovoltaic frequency support model; analyzing the coupling relation between the output power of the converter and the voltage based on the system voltage characteristics, and establishing a distributed photovoltaic voltage support model;
based on the actual topology condition of the network, the capacity of the converter and the condition of the reactive compensation device, simultaneously combining an active and reactive output power model of the converter and a distributed photovoltaic frequency and voltage support model, establishing a system power balance, an adjustable resource constraint, a network voltage and current constraint and a minimum network loss objective function;
based on an equation form, the non-convex problem is subjected to convex optimization by utilizing a second order cone, a minimum net loss objective function is solved, and an active power compensation device in the system and active power output and reactive power output optimal distribution of each distributed photovoltaic are determined.
2. The method for high-proportion distributed photovoltaic frequency and voltage combined support according to claim 1, wherein analyzing the active and reactive output coupling relation of the converter based on the output characteristics of the distributed photovoltaic grid-connected converter and establishing a converter active and reactive output power model comprises the following steps:
Determining the actual capacity of the distributed photovoltaic grid-connected converter;
determining the coupling relation of active and reactive outputs of the grid-connected converter and the power factor; the calculation formula of the coupling relation of the active and reactive outputs is as follows:
in which Q DG The reactive output capacity of the converter; p (P) DG Active power output by the converter; s is S DG Is the capacity of the current transformer;representing a power factor angle;
and determining an active and reactive output power model of the grid-connected converter based on the coupling relation between the actual capacity and the active and reactive output of the converter and the power factor.
3. The method of claim 1, wherein the creating the distributed photovoltaic frequency support model comprises:
determining the coupling relation between the system frequency and the power, wherein the formula is as follows:
ΔP L0 -ΔP G0 ＝-K G Δf”-K D Δf”＝-K S Δf” (3)
wherein DeltaP L0 Delta P is the system load delta G0 For secondary adjustment of the power of the distributed photovoltaic enhancement, Δf "is the system frequency variation, K G 、K D 、K S The unit regulating power of new energy, the unit regulating power of load and the unit regulating power of system are respectively MW/HZ;
based on the coupling relation between the system frequency and the power, adding secondary frequency modulation on the basis of a speed regulator model, wherein the model is as follows:
The model is a speed regulator model added with secondary frequency modulation, wherein, P m For mechanical power, P e Is electromagnetic power, deltaP G0 Active power, K, for distributed photovoltaic augmentation s Regulating power, ω, for system units ref For the rated angular velocity, Δω is the angular velocity variation value, J is the virtual inertia, and D is the damping coefficient.
4. The method for supporting high-proportion distributed photovoltaic frequency and voltage combination according to claim 1, wherein the step of establishing a distributed photovoltaic voltage supporting model based on the system voltage characteristic analysis of the relation between the output power of the converter and the voltage coupling comprises the steps of:
determining a coupling relationship between voltage and power; the coupling relationship between voltage and power is expressed as:
wherein V is i Representing the voltage amplitude at node i, V j Representing the voltage amplitude of node j, r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the amplitude, P, of the current flowing on branch ij ij And Q ij Active power reactive power flowing from node i to node j;
based on the system voltage and power coupling relationship, the voltage support is modeled, which is expressed as:
wherein P is i Expressed as net active value of node i, Q i Expressed as net reactive value of node i, P L,i Active load denoted as node i, Q L,i Reactive load, denoted node i, P DG,i Grid-connected active power of converter denoted as node i, Q DG,i Grid-connected reactive power of the converter denoted as node i; u (U) i Represented as voltage at arbitrary node i, R i Represented as the resistance between node i-1 and node i, X i Represented as reactance between node i-1 and node i, P Linei And Q Linei The active power and the reactive power of the injection node i in the line between the node i-1 and the node i are respectively shown in the formula, wherein P Lossk And Q Lossk Is the active and reactive loss of the line between node k-1 and node k.
5. The method for building a high-ratio distributed photovoltaic frequency-voltage combination support according to claim 1, wherein the power balance, the adjustable resource constraint, the network voltage-current constraint and the minimum network loss objective function are specifically as follows:
determining power balance constraint, voltage safety constraint, current safety constraint and controllable resource output constraint;
power balance constraint:
where u (j) represents the head end node set of the branch having the j point as the end point, and set v (j) represents the tail end node set of the branch having the j point as the end point, P j And Q j The active and reactive injection powers of the j nodes are respectively expressed as r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the amplitude, P, of the current flowing on branch ij ij And Q ij Active power and reactive power flowing from node i to node j, respectively;
voltage safety constraints:
in the method, in the process of the invention,representing the lower voltage limit at node j of the distribution network, < >>Representing an upper voltage limit at a power distribution network node j;
current safety constraints:
in the method, in the process of the invention,current limit for branch ij;
adjustable resource output constraint:
wherein P is DG,i Active output, Q, of new energy converter expressed as node i access DG,i Reactive output of new energy converter indicated as node i access, S DG,i The capacity of the new energy converter accessed by the node i is represented;
an objective function is determined targeting the minimum net loss, which is expressed as:
wherein, the set v (i) represents a tail end node set of a branch taking an i node as a head end point; n is the total number of nodes of the power distribution network; r is (r) ij The branch resistance, denoted as branch ij, I ij Representing the magnitude of the current flowing on branch ij.
6. The method for supporting high-proportion distributed photovoltaic frequency and voltage combination according to claim 1, wherein the method is characterized in that a second order cone is utilized to perform convex optimization on a non-convex problem, then solution is performed, and the distribution of distributed photovoltaic output is determined as follows:
Determining a second-order cone form according to a second-order cone method;
the standard second order cone is expressed as:
the rotating second order cone is expressed as:
in the method, in the process of the invention,k is a second order cone constraint condition; variable x i ∈R n The method comprises the steps of carrying out a first treatment on the surface of the y is an objective function under a standard second order cone; yz is the objective function under a rotating second order cone.
The non-convex problem is subjected to convex optimization by a second order cone method, and then is solved, specifically:
voltage current amplitude:
in the formula, v is i And i ij Replacing the square of the voltage amplitude and the square of the branch current amplitude;
objective function:
wherein, the set v (i) represents a tail end node set of a branch taking an i node as a head end point; n is the total number of nodes of the power distribution network; r is (r) ij The branch resistance, i, denoted as branch ij ij Representing the square of the amplitude of the current flowing on branch ij;
branch current constraint function:
wherein P is ij And Q ij Active power and reactive power, v, respectively, flowing from node i to node j i Representing the square of the voltage amplitude at node i, i ij Representing the square of the amplitude of the current flowing on branch ij. From the above equation, it can be found that this equation is a rotational second order cone constraint, which is further equivalently deformed;
standard second order cone form of branch current constraint function:
the power balance constraint is:
where u (j) represents the head end node set of the branch having the point j as the end point, v (j) represents the end node set of the branch having the point j as the end point, and P j And Q j The active and reactive injection powers, P, of the j nodes are respectively shown ij And Q ij Active power and reactive power respectively flowing from node i to node j, V i Representing the voltage amplitude at node i, V j Representing the voltage amplitude of node j, r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the magnitude of the current flowing on branch ij.
7. A system for high-proportion distributed photovoltaic frequency-voltage combination support, comprising the following modules:
the active and reactive output power model building module of the converter: analyzing active and reactive output coupling characteristics of the converter based on the output characteristics of the distributed photovoltaic grid-connected converter, and establishing an active and reactive output power model of the converter;
the distributed photovoltaic frequency support model building module comprises: analyzing the relation between the output power of the converter and frequency coupling based on the system frequency characteristic, and establishing a distributed photovoltaic frequency support model;
the distributed photovoltaic voltage support model building module comprises: analyzing the coupling relation between the output power of the converter and the voltage based on the system voltage characteristics, and establishing a distributed photovoltaic voltage support model;
and a multifunctional building module: based on the actual topology condition of the network, the capacity of the converter and the condition of the reactive compensation device, simultaneously combining active and reactive output power of the converter, the distributed photovoltaic frequency and the voltage support model, and establishing a system power balance, adjustable resource constraint, network voltage and current constraint and a minimum network loss objective function;
And (3) an optimization solving module: based on the equation form, the non-convex problem is subjected to convex optimization by utilizing a second order cone, an objective function is solved, and a reactive power compensation device in the system and optimal distribution of active power and reactive power of each distributed photovoltaic are determined.
8. The system for high-proportion distributed photovoltaic frequency and voltage combination support according to claim 7, wherein the operation steps of the active and reactive output power model building module of the converter are as follows:
determining the actual capacity of the distributed photovoltaic grid-connected converter;
determining the coupling relation of active and reactive outputs of the grid-connected converter and the power factor; the calculation formula of the coupling relation of the active and reactive outputs is as follows:
in which Q DG The reactive output capacity of the converter; p (P) DG Active power output by the converter; s is S DG Is the capacity of the current transformer;representing a power factor angle;
and determining an active and reactive output power model of the grid-connected converter based on the coupling relation between the actual capacity and the active and reactive output of the converter and the power factor.
9. The system for high-proportion distributed photovoltaic frequency-voltage combination support according to claim 7, wherein the distributed photovoltaic frequency support model building module comprises the following operation steps:
Determining the coupling relation between the system frequency and the power, wherein the formula is as follows:
ΔP L0 -ΔP G0 ＝-K G Δf”-K D Δf”＝-K S Δf” (26)
wherein DeltaP L0 Delta P is the system load delta G0 For secondary adjustment of the power of the distributed photovoltaic enhancement, Δf "is the system frequency variation, K G 、K D 、K S The unit regulating power of new energy, the unit regulating power of load and the unit regulating power of system are respectively MW/HZ;
based on the coupling relation between the system frequency and the power, adding secondary frequency modulation on the basis of a speed regulator model, wherein the model is as follows:
the model is a speed regulator model added with secondary frequency modulation, wherein, P m For mechanical power, P e Is electromagnetic power, deltaP G0 Active power, K, for distributed photovoltaic augmentation s Regulating power, ω, for system units ref For the rated angular velocity, Δω is the angular velocity variation value, J is the virtual inertia, and D is the damping coefficient.
10. The system for high-proportion distributed photovoltaic frequency-voltage combination support according to claim 7, wherein the distributed photovoltaic voltage support model building module comprises the following operation steps:
determining a coupling relationship between voltage and power; the coupling relationship between voltage and power is expressed as:
wherein V is i Representing the voltage amplitude at node i, V j Representing the voltage amplitude of node j, r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the amplitude, P, of the current flowing on branch ij ij And Q ij Active power reactive power flowing from node i to node j;
based on the system voltage and power coupling relationship, the voltage support is modeled, which is expressed as:
wherein P is i Expressed as net active value of node i, Q i Expressed as net reactive value of node i, P L,i Active load denoted as node i, Q L,i Reactive load, denoted node i, P DG,i Grid-connected active power of converter denoted as node i, Q DG,i Grid-connected reactive power of the converter denoted as node i; u (U) i Represented as voltage at arbitrary node i, R i Represented as the resistance between node i-1 and node i, X i Represented as reactance between node i-1 and node i, P Linei And Q Linei The active power and the reactive power of the injection node i in the line between the node i-1 and the node i are respectively shown in the formula, wherein P Lossk And Q Lossk Is the line between the node k-1 and the node kRoad active and reactive losses.
11. The high-ratio distributed photovoltaic frequency-voltage combination support system of claim 7, wherein the multi-function building block operates as follows:
determining power balance constraint, voltage safety constraint, current safety constraint and controllable resource output constraint;
Power balance constraint:
where u (j) represents the head end node set of the branch having the j point as the end point, and set v (j) represents the tail end node set of the branch having the j point as the end point, P j And Q j The active and reactive injection powers of the j nodes are respectively expressed as r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the amplitude, P, of the current flowing on branch ij ij And Q ij Active power and reactive power flowing from node i to node j, respectively;
voltage safety constraints:
in the method, in the process of the invention,representing the lower voltage limit at node j of the distribution network, < >>Representing an upper voltage limit at a power distribution network node j;
current safety constraints:
in the method, in the process of the invention,current limit for branch ij;
adjustable resource output constraint:
wherein P is DG,i Active output, Q, of new energy converter expressed as node i access DG,i Reactive output of new energy converter indicated as node i access, S DG,i The capacity of the new energy converter accessed by the node i is represented;
an objective function is determined targeting the minimum net loss, which is expressed as:
wherein, the set v (i) represents a tail end node set of a branch taking an i node as a head end point; n is the total number of nodes of the power distribution network; r is (r) ij The branch resistance, denoted as branch ij, I ij Representing the magnitude of the current flowing on branch ij.
12. The high-ratio distributed photovoltaic frequency-voltage combination support system of claim 7, wherein the optimization solution module operates as follows:
(1) Determining a second-order cone form according to a second-order cone method;
the standard second order cone is expressed as:
the rotating second order cone is expressed as:
wherein K is a second order cone constraint condition; variable x i ∈R n The method comprises the steps of carrying out a first treatment on the surface of the y is an objective function under a standard second order cone; yz is the objective function under a rotating second order cone. (2) The non-convex problem is subjected to convex optimization by a second order cone method, and then is solved, specifically:
voltage current amplitude:
in the formula, v is i And i ij Replacing the square of the voltage amplitude and the square of the branch current amplitude;
objective function:
wherein, the set v (i) represents a tail end node set of a branch taking an i node as a head end point; n is the total number of nodes of the power distribution network; r is (r) ij The branch resistance, i, denoted as branch ij ij Representing the square of the amplitude of the current flowing on branch ij;
branch current constraint function:
wherein P is ij And Q ij Active power and reactive power, v, respectively, flowing from node i to node j i Representing the square of the voltage amplitude at node i, i ij Representing the square of the amplitude of the current flowing on branch ij. From the above equation, it can be found that this equation is a rotational second order cone constraint, which is further equivalently deformed;
Standard second order cone form of branch current constraint function:
the power balance constraint is:
where u (j) represents the head end node set of the branch having the point j as the end point, v (j) represents the end node set of the branch having the point j as the end point, and P j And Q j The active and reactive injection powers, P, of the j nodes are respectively shown ij And Q ij Active power and reactive power respectively flowing from node i to node j, V i Representing the voltage amplitude at node i, V j Representing the voltage amplitude of node j, r ij The branch resistance, x, denoted as branch ij ij The branch reactance, denoted as branch ij, I ij Representing the magnitude of the current flowing on branch ij.
13. A computer storage medium having stored thereon a computer program which, when executed by a processor, implements a method of high-proportion distributed photovoltaic frequency-voltage combination support according to any of claims 1-6.
14. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the processor implements a method of high-proportion distributed photovoltaic frequency-voltage combination support according to any one of claims 1-6 when executing the computer program.
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