CN108306306B - Method for controlling reactive voltage of power distribution network by using distributed photovoltaic - Google Patents

Method for controlling reactive voltage of power distribution network by using distributed photovoltaic Download PDF

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CN108306306B
CN108306306B CN201810168854.9A CN201810168854A CN108306306B CN 108306306 B CN108306306 B CN 108306306B CN 201810168854 A CN201810168854 A CN 201810168854A CN 108306306 B CN108306306 B CN 108306306B
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CN108306306A (en
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程军照
钱纹
黄梅
刘宝林
冯磊
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Yunnan Power Grid 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
    • H02J3/12—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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

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Abstract

The invention provides a method for controlling reactive voltage of a power distribution network by using distributed photovoltaic, which comprises the following steps: determining a plurality of key nodes on a feeder line; calculating to obtain a quantitative relation between reactive power changes of the distributed photovoltaic DPVs and the voltage of the key node; establishing a reactive voltage optimization control objective function and constraint conditions which are easy to calculate; controlling the reactive voltage of the distribution network. The invention provides a concept of 'natural voltage', the minimum network loss is converted into an objective function based on 'natural voltage', a quantitative relation between node voltage and DPV reactive power regulation is established by utilizing constant sensitivity, the objective function is easy to calculate, constraint conditions are converted into simple linear constraint, the constraint does not include a power flow equation any more, and the information quantity required by optimization operation is greatly reduced through the processing. The method has the advantages of less required information, simple control and strong practicability.

Description

Method for controlling reactive voltage of power distribution network by using distributed photovoltaic
Technical Field
The disclosure relates to the technical field of power distribution networks, in particular to a method for controlling reactive voltage of a power distribution network by using distributed photovoltaic.
Background
The traditional reactive voltage control mode of the medium-voltage distribution network can only adjust the voltage of a 10kV bus of a transformer substation through a voltage regulating switch and a capacitor of the transformer, so that the voltage of each node on a 10kV feeder line can be indirectly adjusted. If the 10kV feeder line is short, the node voltage variation range on the feeder line is limited, and the reactive voltage regulation mode can basically ensure that the node voltage on the feeder line is within the range specified by the standard; if the feeder line is long and the fluctuation range of the node voltage on the feeder line is large, the problems that the voltage of a 10kV bus of a high-voltage distribution station is difficult to adjust and the voltage of the 10kV feeder line is easy to exceed the limit can occur. The distributed photovoltaic DPV (photovoltaic PV) can realize reactive stepless regulation and is used as a voltage regulation means, so that the problem can be solved. When the voltage is low, the DPV is used for reactive compensation, so that the voltage can be increased; when the voltage is higher, the DPV is used for absorbing the idle work, so that the voltage can be reduced. Therefore, a large number of distributed photovoltaic DPVs may be connected in a future power distribution network, but a large number of connected DPVs may cause a serious voltage out-of-limit problem, especially for rural areas with relatively long feeders, and when the photovoltaic is large and the load is light, a large number of node voltages are out-of-limit.
There are currently many ways in which DPVs participate in the regulation of the voltage of a distribution network. Such as an in-situ control method, comprising: the reduction of active power output realizes voltage regulation, cos (P) control, Q (V) control and Q (P) voltage regulation. The method is based only on DPV-based local volumes and is easy to implement. However, lack of coordination between DPV inverters using the in-situ control method sometimes results in contradiction between each other, causes oscillation, and makes optimization impossible. Except for the in-place control method, other methods are over theoretical, complete distribution network state information is usually needed, and the method is difficult to be practical, for example, an optimization algorithm is utilized to carry out global optimization calculation; the method comprises a DPV online regulation and control method based on voltage sensitivity and a two-stage coordination control mode. The above methods all require tidal current equation information, namely: the method needs the running state information of the distribution network on the same time section, and most state information of the distribution network is not measured, so that the method is like a black box for an operator, and the characteristic determines that the method is lack of practicability; even if the state information is obtained and the optimization result is calculated, it is difficult to implement, because the coordinated control of a plurality of control devices cannot be realized in the power distribution network.
Disclosure of Invention
The embodiment of the invention provides a method for controlling reactive voltage of a power distribution network by using distributed photovoltaic, which aims to solve the problems of poor harmony and lack of practicability in the prior art.
The invention provides a method for controlling reactive voltage of a power distribution network by using distributed photovoltaic, which comprises the following steps:
determining a plurality of key nodes on each feeder line by taking each feeder line as an independent control area;
calculating to obtain a quantitative relation between reactive power change of a plurality of any distributed photovoltaic DPVs in the feeder line and the voltage of a key node i through the impedance parameter of the feeder line;
establishing an objective function and a constraint condition of reactive voltage optimization control easy for engineering calculation according to the quantitative relation between the reactive power change of the distributed photovoltaic DPVs and the voltage of the key node i;
and performing optimization calculation according to the optimization regulation model to obtain the reactive power regulation quantity of the DPV, and issuing the reactive power regulation quantity to the DPV for execution to realize the reactive power voltage optimization control of the power distribution network.
Preferably, the determining a plurality of key nodes on the feeder line includes:
judging whether a plurality of distributed photovoltaic DPVs exist in the feeder line;
if there are multiple distributed photovoltaic DPVs in the feeder, the multiple distributed photovoltaic DPVs may be identified as corresponding critical nodes.
Preferably, the quantitative relation between the reactive change of any distributed photovoltaic DPV in the feeder line and the voltage of the key node i is as follows:
Figure GDA0002855994990000021
wherein, VnVoltage of node numbered n, XhkRespectively representing the resistance and reactance of the line hk, and CM (i, j) represents a part where two paths are overlapped when tracing back to a root node (a substation bus) from a point i and a point j, and is called as a common path; h and k are any two adjacent nodes on the common path.
Preferably, the obtaining of the quantitative relation between the reactive change of the plurality of distributed photovoltaic DPVs and the voltage of the key node i is as follows:
Figure GDA0002855994990000022
wherein, Vi 0，Vi'minute' toThe voltage of a node i before and after the reactive power regulation of the DPV, M is the set of the adjustable DPV nodes in the feeder line, and Delta QpvjIs the reactive adjustment of the DPV numbered j;
Figure GDA0002855994990000023
is a relatively fixed quantity, ViVoltage of node numbered i, XhkThe resistance and the reactance of the line hk are represented, and CM (i, j) represents a part where two paths are overlapped when tracing back to a root node from a point i and a point j respectively and is called a common path; Δ ViThe voltage variation at node i caused after reactive regulation for the DPV.
Preferably, the optimization objective function for establishing the reactive voltage of the power distribution network is as follows:
Figure GDA0002855994990000024
where C is the set of key nodes, VkIs the key node voltage, Vset-kIs the target voltage value of the key node.
Preferably, when the node voltage does not exceed the limit or exceed the lower limit, the optimization objective function of the reactive voltage of the power distribution network can be obtained according to the natural voltage, and the optimization objective function comprises the following steps:
setting the reactive power of all nodes to zero, and obtaining natural voltage through load flow calculation, wherein the natural voltage of a node i is Vp-iThe natural voltages of other nodes are marked according to the same mode;
the voltage is not out-of-limit or the voltage is out-of-limit but the natural voltage of all key nodes is higher than VminThen, the target voltage of the key node i is the natural voltage Vset-i＝Vp-iIf there is a voltage below VminThe target voltage of the key control point is:
let Δ V be Vmin-Vp-lAnd the number of the key node with the lowest voltage is l, if a key point i exists and is positioned at the upstream of the key point l with the lowest voltage, the key node with the lowest voltage passes through a formula
Figure GDA0002855994990000025
Calculating a target voltage of the key point i, wherein XiAnd XlRespectively tracing the reactance of a bus of the transformer substation for the key points i and l;
if there is a keypoint i downstream of the keypoint l with the lowest voltage, then pass through formula Vset-i＝Vp-i+ Δ V, calculating a target voltage of the key point i;
by the formula
Figure GDA0002855994990000031
Calculating an objective function when the voltage is not out of limit or out of lower limit, wherein C is a set of key nodes, VkIs the key node voltage, Vset-kIs the target voltage value of the key node.
Preferably, when the voltage exceeds the upper limit, the optimal regulation model of the reactive voltage of the power distribution network is as follows:
Figure GDA0002855994990000032
wherein Q isjRepresenting the initial reactive output, Δ Q, of the DPV numbered j per control cyclejAnd M is the set of adjustable DPVs, and is the reactive adjustment quantity of the DPV at the node j.
Preferably, the method further comprises establishing constraints of reactive voltage optimization control, including:
for all key nodes i ∈ C, the following requirements need to be met:
Figure GDA0002855994990000033
for all DPV nodes j ∈ M, the following requirements need to be met:
Qjmin≤ΔQj≤Qjmax
wherein Q isjminAnd QjmaxIs the reactive compensation limit value of the adjustable DPV and can be adjusted according to the current power P of the DPVj+jQjIs calculated to obtain
Figure GDA0002855994990000034
Wherein S isNjDenotes the rated capacity, P, of the DPV numbered jjRepresenting the initial active output, Q, of a DPV numbered j per control cyclejRepresenting the initial reactive output of the DPV numbered j for each control cycle.
The beneficial effect of this application is as follows:
in view of the above problems, the present invention proposes a novel voltage control method for practical use. The method comprises the following steps: determining a plurality of key nodes on a feeder line; calculating to obtain a quantitative relation between reactive power change of any distributed photovoltaic DPV in the feeder line and the voltage of the key node through the impedance parameter of the feeder line; according to the quantitative relation between the reactive power change of any distributed photovoltaic DPV in the feeder line and the voltage of the key node, calculating to obtain the quantitative relation between the reactive power change of a plurality of distributed photovoltaic DPVs and the voltage of the key node; establishing a reactive voltage optimization control objective function and constraint conditions which are easy to calculate according to the quantitative relation between the reactive power change of the distributed photovoltaic DPVs and the voltage of the key node; on the basis, the optimization calculation is realized, and the reactive voltage of the power distribution network is controlled. The method reduces the dimensionality of voltage control by a key node control method, and is favorable for practicality; obtaining a quantitative relation between node voltage and DPV reactive power determined only by feeder impedance through theoretical derivation and special processing; the concept of natural voltage is provided, and global optimization calculation to a certain degree can be realized under the condition of only needing a small amount of information through special processing of an objective function. The method has the advantages of less required information, simple control and strong practicability.
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The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive exercise.
Fig. 1 is a flowchart of a method for controlling reactive voltage of a power distribution network by using distributed photovoltaics according to an embodiment of the present disclosure;
FIG. 2 is a schematic diagram of an embodiment grid architecture;
fig. 3 is a comparison graph of voltage distribution of nodes before and after main line control of the feeder 1 when the voltage exceeds the upper limit, according to the embodiment of the present application;
fig. 4 is a comparison graph of voltage distribution of nodes before and after the main line control of the feeder 1 is performed when the voltage is not out-of-limit or the voltage is out-of-limit provided by the embodiment of the present application.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention mainly comprises three contents: (1) the key node control method comprises the following steps: the dimensionality of voltage control is reduced by a key node control method, and the method is favorable for practicality; (2) constant sensitivity between node voltage and DPV reactive: obtaining a quantitative relation between node voltage and DPV reactive power determined only by feeder impedance through theoretical derivation and special processing; (3) reactive voltage optimization model: a natural voltage concept is provided, and global optimization calculation to a certain degree can be realized on the basis of natural voltage through special processing of an objective function and a constraint condition under the condition of only needing a small amount of information.
Referring to fig. 1, a flowchart of a method for controlling reactive voltage of a power distribution network by using distributed photovoltaic according to an embodiment of the present application is shown. As can be seen from fig. 1, the method comprises:
step S100: and taking each feeder line as an independent control area, and determining a plurality of key nodes on the feeder line.
Specifically, step S100 further includes:
step S101: and judging whether a plurality of distributed photovoltaic DPVs exist in the feeder line, and if so, executing the step S102. A point may be selected at the back in the feeder as the key node. For very long feeders, several critical nodes may be added as appropriate.
Step S102: the plurality of distributed photovoltaic DPVs may be identified as corresponding key nodes.
In reactive voltage control, if all node voltages are monitored and then optimized calculation and control are performed, a large amount of state information is needed, and the reactive voltage control is difficult to use practically. Therefore, several key nodes on the feeder line are selected, and the voltage of the key nodes is optimally controlled, so that the control flow can be greatly simplified, and the method is more practical. In general, the key node control method can achieve the purpose of voltage control and achieve a certain degree of optimization because: (1) the key nodes divide the feeder line into a plurality of sections with smaller lengths, and because the length of each section of line section is smaller, the voltage variation range in the line section is smaller, the voltage of each key node is controlled in a reasonable range, the voltage of the line section can be basically in the reasonable range, and the voltage of the feeder line is also reasonably controlled; (2) the reactive distribution in the feeder line can influence the network loss, the node voltage represents the reactive distribution, and if the key node voltage is controlled at a reasonable value, the optimization can be realized to a certain degree, and the problem can be further analyzed later.
The selection of the key nodes does not apply sensitivity analysis, so that the method cannot be used practically and is unnecessary; in the embodiment, a simpler selection method is adopted, namely a fixed key node is adopted, and the feeder line is divided into a plurality of shorter sections. For example: several critical nodes may be added slightly for longer lines, at each of the feed line length 2/3 and the tail end. If a plurality of DPVs exist in the feeder line, the DPVs are likely to divide the feeder line into a plurality of line segments with short enough lengths, and the DPVs are used as key points, so that the key points do not need to be additionally increased, and the selection and the division of the key nodes are further simplified.
Step S200: and calculating to obtain the quantitative relation between the reactive power change of a plurality of any distributed photovoltaic DPVs in the feeder line and the voltage of the key node i through the impedance parameters of the feeder line.
To determine the DPV reactive power regulation quantity, the quantitative relation between the DPV reactive power and the node voltage must be clear, and in order to improve the practicability, the quantitative relation must be calculated through a small amount of information.
Aiming at the problem, the invention combines the characteristics of the medium-voltage distribution network to carry out certain approximate processing to obtain the quantitative relation, which is only calculated by the impedance of the feeder line, and the specific introduction is as follows:
the 10kV feeder line head end bus is number 0 node and the voltage is V0And the voltage at the node marked with i is ViAnd then:
Figure GDA0002855994990000051
v in formula (1)0iRepresenting the voltage difference, V, between node 0 and node i(i-1)iRepresenting the voltage drop from node (i-1) to node i, BRiRepresenting the path taken from node i to root node 0, VhkRepresenting the voltage drop between adjacent nodes h and k.
According to circuit theory, VhkCan be expressed as follows:
Figure GDA0002855994990000052
in the formula (2), PskRepresenting the sum, Q, of node k and its downstream total active load and downstream total line active lossskRepresenting node k and its downstream total reactive load and downstream total line reactive loss, RhkAnd XhkRepresenting the resistance and reactance of line hk, respectively. Wherein, PskAnd QskThe expression of (a) is as follows:
Figure GDA0002855994990000053
Figure GDA0002855994990000054
in the formulae (3) and (4), DSkA set of nodes downstream of node k, rs represents a line segment between two nodes r and s downstream of node k, Ploss-rsRepresenting active loss, Q, in the line rsloss-rsRepresenting reactive losses, P, in the line rsmRepresenting the active load of node m, QmRepresenting the reactive load of node m.
Line loss and Ploss-rsAnd Qloss-rsNegligible compared to the load, therefore:
Figure GDA0002855994990000055
Figure GDA0002855994990000056
in sum, the voltage at node i can be expressed as:
Figure GDA0002855994990000057
Figure GDA0002855994990000058
obviously, formula (9) is derived from formula (8):
Figure GDA0002855994990000059
obviously:
Figure GDA00028559949900000510
equation (9) becomes:
Figure GDA0002855994990000061
in the above formula, CM (i, j) represents a portion where two paths overlap when tracing back to a root node (substation bus) from the point i and the point j, respectively, and is referred to as a common path.
It can be seen from equation (11) that after the approximation processing, the quantitative influence of the reactive change of any DPV in the feeder on the voltage of the node i can be calculated only through the impedance parameter of the feeder.
By the same derivation method, the voltage of the node i after the multiple DPVs are reactive-load regulated is:
Figure GDA0002855994990000062
in the formula (12), Vi 0，Vi' is the voltage of node i before and after reactive adjustment of DPV, M is the set of adjustable DPV nodes in the feeder, and Delta QpvjIs the reactive power regulation of DPV numbered j, aiIs a relatively fixed quantity calculated according to equation (11).
In practical applications, the reactive voltage control is not regulated in real time, but rather is periodic, optimized and regulated only once per period. Because the voltage of the key node is only needed to be monitored, the voltage of the key node after reactive power regulation can be easily calculated by the formula (12) according to the voltage of the key node before reactive power regulation and the reactive power regulation quantity of the adjustable DPV.
Step S300: and establishing an objective function and a constraint condition of reactive voltage optimization control easy for engineering calculation according to the quantitative relation between the reactive power change of the distributed photovoltaic DPVs and the voltage of the key node i.
In order to realize the optimal regulation of voltage reactive power, optimal calculation must be carried out according to a certain optimization model, and the invention constructs a corresponding optimization model for practical purposes.
Assuming that the set of key nodes is C and the set of adjustable DPVs is M, for any key node, the following optimization model can be established:
(1) objective function
When the DPV does not perform reactive compensation, reactive power consumed by the load is provided by a transformer substation, and the reactive power needs to flow over a longer distance, so that the loss is relatively large; when the DPV performs reactive compensation, the voltage is increased, part of reactive power consumed by the load is provided by the DPV, and the reactive power consumed by the load is compensated nearby and the loss is reduced because the DPV is closer to the load; when the DPV further increases the reactive compensation amount, the voltage rises higher, but the reactive power provided by the DPV exceeds the load requirement, reactive power feedback occurs, and the network loss is increased. In summary, the reactive compensation of the DPV cannot be too low or too high, and needs to reach a reasonable value. In the most ideal case, the DPV provides reactive power exactly equal to a few loads in its vicinity, with the lowest grid loss, i.e. the natural voltage at the node, which reflects the reactive flow situation. Therefore, the reactive power of all the nodes can be set to zero, and the natural voltage can be obtained through load flow calculation. In practical engineering, only the total active power P of each feeder line is generally measuredΣThe active power of each node can be estimated approximately according to the loading capacity of the distribution transformer on the feeder line.
Because the voltage reflects the reactive flow on the feeder line, theoretically, the reactive flow is closest to the ideal condition when the voltage of the key node is equal to the natural voltage of the key node, and the optimization effect is the best, but the key node voltage not only needs to consider the optimization effect but also needs to consider the constraint of the upper limit and the lower limit of the voltage. Therefore, the target voltage of the key node needs to be obtained by further processing on the basis of natural voltage, and the following is discussed in two cases of 'no voltage overrun or no voltage photovoltaic backflow', and 'voltage overrun'.
Target function when voltage is not over limit or voltage is over lower limit
The voltage is not out-of-limit or the voltage is out-of-limit but the natural voltage of all key nodes is higher than Vmin(this is mostly the case) the target voltage of the key control point i is its natural voltage, i.e. Vset-i＝Vp-iIf there is a voltage below VminThe target voltage of the key control point is:
the key node with the lowest voltage is numbered as l, and the number is delta Vmin-Vp-lIf the key point i is located upstream of the key point l with the lowest voltage, the target voltage is as shown in equation (13):
Figure GDA0002855994990000071
in formula (13), XiAnd XlRespectively tracing the reactance of a substation bus for key points i and l, wherein if the key point i is positioned at the downstream of the key point l with the lowest voltage, the target voltage is as shown in a formula (14):
Vset-i＝Vp-i+ΔV (14)
after the target voltage of the key node is obtained, the target function when the voltage is not out of limit or the voltage is out of lower limit is set as an equation (15):
Figure GDA0002855994990000072
in the formula, VkIs the key node voltage, Vset-kIs the target voltage value of the key node.
Aim function when voltage exceeds upper limit
When the load is light, the voltage is easy to be higher when the DPV is large. Since the upper limit of the voltage of a plurality of nodes is higher, the natural voltage is the voltage obtained by the load reactive power after the close compensation, obviously, the natural voltage is higher, and the upper limit of the natural voltage of more nodes is higher, so the natural voltage cannot be used as the target voltage of the key node.
Since the optimization goal is to reduce the network loss, which can be processed in a simplified way, the reduction of the network loss can be processed approximately to minimize the sum of the reactive compensation capacities of the DPVs, that is:
Figure GDA0002855994990000073
(2) constraint conditions
For all key nodes, the following requirements are to be met:
Figure GDA0002855994990000074
wherein, VminAnd VmaxRespectively, a lower limit value and an upper limit value of the voltage.
For all photovoltaics, the following requirements need to be met:
Qjmin≤ΔQj≤Qjmax (18)
in the formula (18), QjminAnd QjmaxThe reactive compensation limit value of the DPV can be adjusted according to the current power P of the DPVj+jQjIs calculated to obtain
Figure GDA0002855994990000075
Wherein S isNjDenotes the rated capacity, P, of the DPV numbered jjRepresenting the initial active output, Q, of a DPV numbered j per control cyclejRepresenting the initial reactive output of the DPV numbered j for each control cycle.
Step S400: and performing optimization calculation according to the optimization regulation model to obtain the reactive power regulation quantity of the DPV, and issuing the reactive power regulation quantity to the DPV for execution to realize the reactive power voltage optimization control of the power distribution network.
The control mode provided by the application has small investment and good economical efficiency. The DPV participates in reactive compensation without large-scale hardware transformation, and only a control algorithm needs to be changed. The control scheme needs to add a main station at the dispatching (or local dispatching) and a control terminal (sub-station) at each DPV participating in control. The investment is mainly concentrated on a main station, the main station can be shared, and if the distribution (local) station has a plurality of 10kV feeders with voltage problems, the construction cost of the main station which is shared by each feeder is very low.
A plurality of key nodes are selected to divide the feeder into a plurality of sections (generally 2-3 sections), and if the proper DPV is arranged on the feeder, the DPV can be directly used as the key nodes. Calculating the sensitivity coefficient a of the adjustable DPV to the node voltage according to the equation (12) according to the impedance parameter of the feeder linei. The reactive voltage control method does not need to be adjusted in real time, but is divided into a plurality of periods (such as one period every 15 minutes), each period is optimally controlled once, and the calculation is carried out in the following mode in each control period.
(1) Measuring the voltage of each key node and the voltage, active and reactive information of each adjustable DPV, and uploading the information to a distribution (or ground) master station;
(2) determining inequality constraints by the main distribution and dispatching station (or the local dispatching station) according to the key node voltage and the voltage, active power and reactive power information of each adjustable DPV according to an equation (17) and an equation (18);
(3) the main station of the distribution and dispatching (or the local dispatching) adopts a formula (15) or a formula (16) as an objective function according to the situation to carry out optimization calculation to obtain the reactive power adjustment quantity of the DPV;
(4) and the distribution and dispatching (or local dispatching) master station transmits the calculated DPV reactive power regulation amount to a corresponding DPV to execute.
This is further described below in conjunction with a specific example.
A35 kV transformer substation in a certain province in the southwest and a 10kV feeder line are taken as an example, and the structure of a power grid is shown in figure 2. And simulating a longer feeder line, wherein the length of the main line of the feeder line is 13.6km, the photovoltaic is connected into the feeder line 1 in a scattered manner, the photovoltaics 1, 2, 3 and 4 are respectively connected into the nodes 10, 19, 44 and 49, and the capacities are all 0.06p.u. (the reference capacity is 10 MVA). Since the four photovoltaics have already separated the feeder 1 into segments short enough, 4 photovoltaics are selected as key control points, and no other key control points are added. The active output of the photovoltaic 1, 2, 3 and 4 is set to be 0.048p.u., the upper voltage limit is set to be 1.07p.u., and the lower voltage limit is set to be 0.93 p.u.. The power flow algorithm adopts a forward-backward substitution method, the optimization algorithm adopts a Particle Swarm Optimization (PSO) algorithm, and the parameters are set as follows: the particle group size N is 80, the maximum number of iterations is 300, the particle dimension d is 4, the inertial weight w is 0.729, and the learning factor is 1.49445.
When the voltage is beyond the upper limit, with the formula (16) as an objective, in order to prevent the optimized key node voltage from being too close to the upper and lower voltage limits (0.93p.u. and 1.07p.u.), the key node voltage is set to be optimized to be within the range of 0.935p.u. to 1.065p.u., the adjustable DPV reactive output before optimization is 0, the reactive power regulation range of the DPV is shown in table 1, and the corresponding optimization simulation result is shown in table 2.
Table 1: control range of reactive power control variables
Reactive power regulating equipment Access node Reactive range
Photovoltaic 1 10 -0.036p.u.～0.036p.u.
Photovoltaic 2 19 -0.036p.u.～0.036p.u.
Photovoltaic 3 44 -0.036p.u.～0.036p.u.
Photovoltaic 4 49 -0.036p.u.～0.036p.u.
Table 2: optimizing simulation results
Optimization/control quantity Before optimization After optimization
Number of out-of-limit nodes 20 0
Active network loss/p.u. 0.0040 0.0051
Photovoltaic 1 reactive output/p.u. 0 0
Photovoltaic 2 reactive output/p.u. 0 0
Photovoltaic 3 reactive output/p.u. 0 -0.0360
Photovoltaic 4 reactive output/p.u. 0 -0.0037
When the voltage goes beyond the upper limit, the feeder 1 main line controls the front and rear node voltage distribution pairs as shown in fig. 3. Comparing results before and after control, eliminating node voltage out-of-limit after optimization, and showing that the control method can effectively solve the problem of voltage out-of-limit; but the active network loss increases after optimization because the higher the voltage, the more the upper limit, the more the photovoltaic 3 and 4 need to absorb inductive reactive power to reduce the node voltage, resulting in increased active network loss.
When the voltage is not out of limit or the voltage is out of lower limit, the formula (15) is adopted as an objective function, reactive power regulation control variables and target voltage calculation values of all key nodes are shown in the table 3, and corresponding optimization simulation results are shown in the table 4.
Table 3: reactive power regulation control variable and target voltage
Figure GDA0002855994990000081
Figure GDA0002855994990000091
Table 4: optimizing simulation results
Optimization/control quantity Before optimization After optimization
Number of out-of-limit nodes 20 0
Active network loss/p.u. 0.0302 0.0268
Photovoltaic 1 reactive output/p.u. 0 0.0550
Photovoltaic 2 reactive output/p.u. 0 0.0550
Photovoltaic 3 reactive output/p.u. 0 0.0550
Photovoltaic 4 reactive output/p.u. 0 0.0104
When the voltage is not beyond the limit or the voltage is beyond the lower limit, the main line of the feeder line 1 controls the front and rear node voltage distribution pairs as shown in fig. 4. Comparing results before and after control, the node voltage out-of-limit is eliminated after optimization, which shows that the control method can effectively solve the problem of voltage out-of-limit, and the active network loss is reduced after optimization.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for apparatus or system embodiments, since they are substantially similar to method embodiments, they are described in relative terms, as long as they are described in partial descriptions of method embodiments. The above-described embodiments of the apparatus and system are merely illustrative, and the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
The foregoing is merely a detailed description of the invention, and it should be noted that modifications and adaptations by those skilled in the art may be made without departing from the principles of the invention, and should be considered as within the scope of the invention.

Claims (2)

1. A method for controlling reactive voltage of a power distribution network by using distributed photovoltaic is characterized by comprising the following steps:
determining a plurality of key nodes on each feeder line by taking each feeder line as an independent control area;
calculating to obtain a quantitative relation between reactive power change of a plurality of any distributed photovoltaic DPVs in the feeder line and the voltage of a key node i through the impedance parameter of the feeder line;
establishing an objective function and a constraint condition of reactive voltage optimization control easy for engineering calculation according to the quantitative relation between the reactive power change of the plurality of random distributed photovoltaic DPVs and the voltage of the key node i;
performing optimization calculation according to the optimization regulation model to obtain the reactive regulation quantity of the DPV, and issuing the reactive regulation quantity to the DPV for execution to realize the reactive voltage optimization control of the power distribution network;
the quantitative relation between the reactive power change of a plurality of random distributed photovoltaic DPVs and the voltage of the key node i is as follows:
Figure FDA0002855994980000011
wherein, Vi 0，Vi' the voltage of a key node i before and after the reactive power regulation of the DPV is respectively, and M is a set of adjustable DPV nodes in a feeder line; delta QpvjIs the reactive adjustment of the DPV numbered j;
Figure FDA0002855994980000012
is a relatively fixed quantity, ViVoltage of key node numbered i, XhkRepresenting the reactance of line hk, CM (i)J) represents a part where two paths are overlapped when the key node i and the DPV node j are traced back to a root node respectively, and the part is called as a common path; Δ ViThe voltage variation of the key node i caused by DPV reactive power regulation is obtained;
the objective function for establishing reactive voltage optimization control easy for engineering calculation is as follows:
Figure FDA0002855994980000013
where C is the set of key nodes, VkIs the key node voltage, Vset-kA target voltage value for a key node;
when the node voltage is not out of limit or out of limit, the objective function of reactive voltage optimization control which is easy for engineering calculation can be obtained according to the natural voltage, and the objective function comprises the following steps:
setting the reactive power of all nodes to zero, estimating the active power of each node according to the active power of the head end of the feeder line and the proportion of the distribution and transformation capacity of each node on the feeder line, and obtaining the natural voltage of each node through load flow calculation, wherein the natural voltage of the node i is Vp-iThe natural voltages of other nodes are marked according to the same mode;
the voltage is not out of limit or the voltage is out of limit but the natural voltage of all key nodes is higher than VminWhen, VminThe lower limit value of the voltage is represented, and the target voltage of the key node i is the natural voltage V of the key node iset-i＝Vp-iIf there is a voltage below VminThe target voltage of the key node is:
let Δ V be Vmin-Vp-lAnd the number of the key node with the lowest voltage is l, and if the key node i is positioned at the upstream of the key node with the lowest voltage, the key node is obtained through a formula
Figure FDA0002855994980000014
Calculating a target voltage of the key node i, wherein XiAnd XlRespectively tracing the reactance of a bus of the transformer substation for the key nodes i and l;
if there is a critical node i downstream of the lowest voltage critical node l, then pass through equation Vset-i＝Vp-i+ Δ V, calculating a target voltage of the key node i;
by the formula
Figure FDA0002855994980000015
Calculating an objective function when the voltage is not out of limit or out of lower limit, wherein C is a set of key nodes, VkIs the key node voltage, Vset-kA target voltage value for a key node;
when the voltage exceeds the upper limit, the optimal regulation model of the reactive voltage is as follows:
Figure FDA0002855994980000021
wherein Q isjRepresenting the initial reactive output, Δ Q, of the DPV numbered j per control cyclejThe reactive power adjustment quantity of the DPV at the DPV node j is M, and M is a set of adjustable DPV nodes in the feeder line;
establishing a constraint condition for reactive voltage optimization control, comprising the following steps:
for all key nodes i ∈ C, the following requirements need to be met:
Figure FDA0002855994980000022
for all DPV nodes j ∈ M, where M is a set of adjustable DPV nodes in a feeder, the following requirements need to be satisfied:
Qjmin≤ΔQj≤Qjmax
wherein Q isjminAnd QjmaxIs the reactive compensation limit value of the adjustable DPV and can be adjusted according to the current power P of the DPVj+jQjIs calculated to obtain
Figure FDA0002855994980000023
Wherein S isNjNumber of the displayRated capacity of DPV of j, PjRepresenting the initial active output, Q, of a DPV numbered j per control cyclejRepresenting the initial reactive output, V, of a DPV numbered j per control cyclemaxRepresents the upper limit value of the voltage.
2. The method of claim 1, wherein determining a number of key nodes on a feeder line using each feeder line as an independent control area comprises:
judging whether a plurality of distributed photovoltaic DPVs exist in the feeder line;
if there are multiple distributed photovoltaic DPVs in the feeder, the multiple distributed photovoltaic DPVs may be identified as corresponding critical nodes.
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