1. A reliability assessment method for an area autonomous power grid considering a random fault scene is characterized by comprising the following steps:

1) inputting time sequence load demand data, time sequence electricity price data and time sequence distributed power output prediction data of each node in a power grid;

2) considering the influence of an extreme scene on the operation reliability of a power grid, respectively establishing a typhoon wind speed random model and a path random model;

3) establishing a line fault random model caused by typhoon;

4) load, photovoltaic and uncertainty of fault scenes are calculated, and a typical scene set is generated;

5) determining fault positions according to the reduced typical scenes to form a power grid structure under each typical scene;

6) constructing a regional autonomous power grid reliability index;

7) and determining the automatic operation of the power grid according to a random optimization model formed by the reliability index and the operation constraint condition.

2. The regional autonomous power grid reliability assessment method considering stochastic fault scenarios according to claim 1, wherein the wind speed stochastic model and the path stochastic model of the typhoon in step 2) consider two scenarios of occurrence of the typhoon and after landing, and respectively establish wind speed and intensity attenuation formulas of the typhoon;

the time sequence characteristics of the typhoon path can be represented by three characteristic quantities which are respectively an angle of attack to the wind, a landing position and a translation speed, uncertainty of the three characteristic quantities is analyzed, corresponding probability density functions are respectively established, a power distribution network topology is mapped on a two-dimensional plane to establish a coordinate system according to the characteristic quantities, the time sequence position of the typhoon and the distance from a typhoon central point to a certain component of a distribution network are calculated by taking an expected landing position of the typhoon as an origin of the coordinate system, and the wind speed of each point of the distribution network is calculated according to the distance from the central point.

3. The method for evaluating the reliability of the regional autonomous power grid considering the stochastic fault scenario according to claim 2, wherein a stochastic model of the line fault caused by the typhoon is established in step 3), and the stochastic fault model of each time period is obtained by combining a vulnerability curve and a wind speed curve of components in the power distribution network, as follows:

in the formula (I), the compound is shown in the specification,the fault probability of the line l at the time t;andrespectively representing a critical wind speed with a fault and a critical wind speed without the fault; by generating random numbers n following a U (0,1) distribution_i,sDetermining the fault scene of the power distribution network line, if soThe line i fails, the lineAnd (5) disconnecting the path i, and dividing the power distribution network into a plurality of sub-areas.

4. The method for evaluating the reliability of the regional autonomous power grid considering the stochastic fault scenario according to claim 1, wherein in step 4), considering that the load in each time period obeys normal distribution, the photovoltaic unit output in each time period obeys Beta distribution, m groups of load samples, m groups of photovoltaic output samples, and m groups of line state samples in each time period are generated by a latin hypercube sampling method, and in order to reduce the calculated amount, a k-mediads clustering method is adopted to perform scene reduction on the original samples, so as to obtain n groups of load samples and corresponding probabilities thereof, n groups of photovoltaic output samples and corresponding probabilities thereof, and n groups of line state samples and corresponding probabilities thereof.

5. The method for evaluating the reliability of the regional autonomous power grid considering the stochastic fault scenarios according to claim 1, wherein in the step 5), according to the generated typical scenarios, the regional division result of the power distribution network under each fault scenario at each time period is determined, wherein a part connected with a main network can continue to operate normally; the part separated from the main network forms an area autonomous power grid, if the power supply and the energy storage device are contained, the autonomous operation can be realized by implementing corresponding optimized scheduling measures, and if the power supply and the energy storage device are not contained, the power supply and the energy storage device are a passive island and cannot normally operate, and all loads are lost.

6. The method according to claim 5, wherein in step 6), the reliability indexes include an unexpected cost and an unexpected power, and the reliability indexes of the regional autonomous power grid are calculated according to the form of the power grid after the occurrence of the fault.

7. The method according to claim 6, wherein in the step 7), a second-order cone relaxation stochastic optimization model is established by using the load loss expected cost minimization as one of objective functions, and the method for evaluating the reliability of the regional autonomous power grid in the stochastic fault scenario specifically includes the following steps:

calculating the loss load cost reliability index, and constructing a multi-objective optimization objective function of the operation scheduling of the power distribution network;

considering the operation constraint conditions of the power distribution network, constructing a random optimization model of the power distribution network under the influence of extreme weather, wherein the random optimization model mainly comprises power balance constraint, power flow interruption model second-order cone constraint and distributed power supply operation constraint;

and synthesizing the objective function and the constraint condition to obtain a mixed integer second-order cone optimization model, and realizing optimal scheduling in an extreme scene.

Background

In recent years, natural disasters frequently occur in partial areas, a power grid is affected by the frequent natural disasters and is subjected to serious power failure events, safe and stable operation in a normal state is threatened, and under the background, the characteristics of extreme events are analyzed, and the capability of the power distribution network for resisting the natural disasters is improved.

Taking typhoon as an example, because the development process of typhoon has strong randomness, the influence of the typhoon on the power distribution network has certain uncertainty, and a fine modeling scheme of typhoon needs to be introduced into the operation safety analysis of the power distribution network to analyze the influence of a fault scene on the power distribution network. In addition, in order to effectively resist the influence of natural disasters, the method has very important significance for realizing the autonomous operation of the post-disaster regional power grid by implementing a corresponding strategy. Therefore, the invention provides a regional autonomous power grid reliability assessment method considering a stochastic fault scene.

Disclosure of Invention

In view of the defects in the prior art, the present invention provides a method for evaluating reliability of an area autonomous power grid in consideration of a random fault scenario, so as to solve the problems in the background art.

The purpose of the invention can be realized by the following technical scheme: a reliability evaluation method for an area autonomous power grid considering a random fault scene comprises the following steps:

step 1: inputting load demand data, electricity price data and distributed power output prediction data;

step 2: establishing a typhoon wind speed random model and a path random model;

and step 3: establishing a line fault random model caused by typhoon;

and 4, step 4: load, photovoltaic and uncertainty of fault scenes are calculated, and a typical scene set is generated;

and 5: determining fault positions according to the reduced typical scenes to form a power grid structure under each typical scene;

step 6: constructing a regional autonomous power grid reliability index;

and 7: and determining the automatic operation of the power grid according to a random optimization model formed by the reliability index and the operation constraint condition.

As a further scheme of the invention, the wind speed stochastic model and the path stochastic model of the typhoon in the step 2) consider two scenes of occurrence of the typhoon and after landing, and respectively establish an initial wind speed and an intensity attenuation formula of the typhoon;

the time sequence characteristics of the typhoon path can be represented by three characteristic quantities which are respectively an angle of attack to the wind, a landing position and a translation speed, uncertainty of the three characteristic quantities is analyzed, corresponding probability density functions are respectively established, a power distribution network topology is mapped on a two-dimensional plane to establish a coordinate system according to the characteristic quantities, the time sequence position of the typhoon and the distance from a typhoon central point to a certain component of a distribution network are calculated by taking an expected landing position of the typhoon as an origin of the coordinate system, and the wind speed of each point of the distribution network is calculated according to the distance from the central point.

As a further scheme of the present invention, a line fault random model caused by typhoon is established in step 3), and a vulnerability curve and a wind speed curve of components in the power distribution network are combined to obtain a random fault model at each time interval, as follows:

in the formula (I), the compound is shown in the specification,the fault probability of the line l at the time t;andrespectively representing a critical wind speed with a fault and a critical wind speed without the fault; by generating random numbers n following a U (0,1) distribution_i,sDetermining the fault scene of the power distribution network line, if soAnd if the line i fails, the line i is disconnected, and the power distribution network is divided into a plurality of sub-areas.

As a further scheme of the present invention, in step 4), considering that the load of each time period obeys normal distribution, and the photovoltaic unit output of each time period obeys Beta distribution, a latin hypercube sampling method is adopted to generate m groups of load samples, m groups of photovoltaic output samples, and m groups of line state samples in each time period, and in order to reduce the calculated amount, a k-mediads clustering method is adopted to perform scene reduction on the original samples, so as to obtain n groups of load samples and their corresponding probabilities, n groups of photovoltaic output samples and their corresponding probabilities, and n groups of line state samples and their corresponding probabilities.

As a further scheme of the present invention, in the step 5), according to the generated typical scene, determining a result of area division of the power distribution network under each fault scene at each time interval, wherein a part connected with the main network can continue to operate normally; the part separated from the main network forms an area autonomous power grid, if the power supply and the energy storage device are contained, the autonomous operation can be realized by implementing corresponding optimized scheduling measures, and if the power supply and the energy storage device are not contained, the power supply and the energy storage device are a passive island and cannot normally operate, and all loads are lost.

As a further scheme of the present invention, in step 6), the reliability index includes an expected cost of load loss and an expected power of load loss, and the reliability index of the regional autonomous power grid is calculated according to the form of the power grid after the fault occurs.

As a further scheme of the present invention, in step 7), a second-order cone relaxation stochastic optimization model is established with the load-shedding expected cost minimization as one of objective functions, and a power grid dispatching operation under a stochastic fault scenario is solved, specifically including the following steps:

firstly, considering the loss load cost reliability index, and constructing a multi-objective optimization objective function of the operation scheduling of the power distribution network;

then, considering the operation constraint conditions of the power distribution network, constructing a random optimization model of the power distribution network under the influence of extreme weather, wherein the random optimization model mainly comprises power balance constraint, power flow interruption model second-order cone constraint and distributed power supply operation constraint;

and synthesizing the objective function and the constraint condition to obtain a mixed integer second-order cone optimization model, and realizing optimal scheduling in an extreme scene.

The invention has the beneficial effects that: compared with the prior art, the invention has the following advantages:

1. the invention establishes a power grid dispatching model considering the fault scene, the model considers the randomness of the extreme scene of typhoon, gives consideration to the operating characteristics of the regional autonomous power grid and the power distribution network connected with the main network, and realizes the safe and economic operation of the power grid in the extreme fault scene;

2. in consideration of the random characteristic of an extreme scene of typhoon and the randomness of load and photovoltaic output, a random wind speed model and a random path model of the typhoon are established, a corresponding power distribution network fault scene is obtained through a space-time influence analysis model of the typhoon on the power distribution network, a corresponding regional autonomous power grid form is divided, and the situation perception of the power distribution network is realized;

3. and considering the reliability indexes of the regional autonomous power grid under the condition of random interruption, namely the load loss expected cost and the load loss expected power, establishing a second-order cone relaxation random optimization model by taking the load loss expected cost minimization as one of objective functions, and solving the power grid dispatching operation under the extreme scene of randomness.

Drawings

In order to more clearly illustrate the embodiments or technical solutions in the prior art of the present invention, the drawings used in the description of the embodiments or prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.

FIG. 1 is a flow chart of a method for evaluating reliability of an area autonomous power grid in consideration of a stochastic fault scenario according to the present invention;

FIG. 2 is a diagram of a modified IEEE33 node structure employed by the present invention and a grid partition diagram under a fault scenario 10;

fig. 3 is a time sequence scheduling curve of distributed power sources and stored energy of nodes 25 in the regional autonomous power grid 1, which is obtained by using the method provided by the invention;

FIG. 4 shows the load recovery of the first, second and third loads in the regional autonomous grid 1 using the scheduling scheme obtained in the present invention;

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.

Fig. 1 is a flowchart of an overall method of the present invention, and the present invention provides a method for evaluating reliability of an area autonomous power grid considering a stochastic fault scenario, where the method includes the following steps:

step 1: as shown in fig. 1, load demand data, electricity price data, and distributed power output prediction data are input first;

step 2: considering the influence of an extreme scene of typhoon natural disasters on the operation reliability of the power grid, and respectively establishing a wind speed random model and a path random model of the typhoon;

during typhoon, influenced by gust wind speed, distribution lines may suffer physical damage and thus break down, and the wind speed at a distance from typhoon eye l can be expressed as:

a, B are shape parameters of typhoon wind speed respectively; r is_lThe radius from the center point of the typhoon to a certain component of the distribution network; ρ is the air density; delta p is a typhoon eye pressure prediction error; omega is the earth angular velocity; phi is typhoon latitude.

After typhoon landing, the intensity of the typhoon will decay in the following way:

in the formula, V_l,tIs typhoon intensity after landing;is the gust intensity; beta is a decay constant; v^bThe continuous wind speed after the typhoon event occurs; r is a wind speed reduction factor; t is^lfThe landing time for typhoon; sigma_vTo predict the error, obey the normal distribution;

the time sequence characteristic of the typhoon path can be represented by three characteristic quantities, namely an angle phi of the windward_sLanding position Δ x_sAnd translation speed c_sAnd analyzing the uncertainty of the three characteristic quantities to establish a probability density function as follows:

in the formula, σ_φ、σ_x、σ_lncRespectively is the standard deviation of the windward angle, landing position and translation speed logarithm; m is_φ、m_x、m_lncRespectively the windward angle, landing position and the expectation of the logarithm of the translation speed.

According to the random variables, the power distribution network topology is mapped on a two-dimensional plane to establish a coordinate system, and the time sequence position of the typhoon and the distance from the typhoon central point to a certain component of the power distribution network are calculated by taking the expected typhoon landing position as the origin of the coordinate system:

in the formula, Y_s,tIs the typhoon position at the time t;the total distance traveled by the typhoon; NT is the time period when typhoon exists; x is the number of_iThe abscissa represents the position of the distribution network component corresponding to the position; y is_iA vertical coordinate corresponding to the position of the power distribution network component is represented;the distance of component i from the center of the typhoon at time t.

And step 3: establishing a line fault random model caused by typhoon;

combining the vulnerability curve and the wind speed curve of the components in the power distribution network to obtain a random fault model of each time period as follows:

in the formula (I), the compound is shown in the specification,the fault probability of the line l at the time t;andrespectively a critical wind speed with a fault and a critical wind speed without a fault.

By generating random numbers n following a U (0,1) distribution_i,sDetermining the fault scene of the power distribution network line, if soAnd if the line i fails, the line i is disconnected, and the power distribution network is divided into a plurality of sub-areas.

And 4, step 4: load, photovoltaic and uncertainty of fault scenes are calculated, and a typical scene set is generated;

considering that the load of each time period obeys normal distribution, considering that the output of the photovoltaic unit of each time period obeys Beta distribution, generating m groups of load samples, m groups of photovoltaic output samples and m groups of line state samples in each time period by adopting a Latin hypercube sampling method, and in order to reduce calculated amount, carrying out scene reduction on original samples by adopting a k-media clustering method to obtain n groups of load samples and corresponding probabilities thereof, n groups of photovoltaic output samples and corresponding probabilities thereof, and n groups of line state samples and corresponding probabilities thereof.

And 5: determining fault positions according to the reduced typical scenes to form a power grid structure under each typical scene;

determining the region division result of the power distribution network under each fault scene at each time interval according to the generated typical scene, wherein the part connected with the main network can continue to normally operate; the part separated from the main network forms an area autonomous power grid, if the power supply and the energy storage device are contained, the autonomous operation can be realized by implementing corresponding optimized scheduling measures, and if the power supply and the energy storage device are not contained, the power supply and the energy storage device are a passive island and cannot normally operate, and all loads are lost.

Step 6: constructing a regional autonomous power grid reliability index;

the reliability indexes comprise load loss expected cost and load loss expected power, the regional autonomous power grid reliability indexes are calculated according to the form of the power grid after the fault occurs, and the expression modes are respectively as follows:

in the formula, ECOST is a load loss cost reliability index; EENS is the loss load power reliability index; CIC_i,c,t,sLoad interruption cost of a user c of the node i in a scene s at the moment t; LC (liquid Crystal)_i,c,t,sLoad reduction amount of a user c of a node i in a scene s at the time t; pi_sIs the probability of occurrence of scene s; tau is the duration of the load interruption in the scene s at the time period t; t is_endIs the fault end time;a load interruption cost reference value of unit time;the time when the fault occurs under the scene s; gamma ray_i,c,t,sIs a binary variable, if user c is clipped, the value is 0, otherwise the value is 1; p_i,c,t,sAnd the load active power of the user c of the node i in the scene s at the moment t.

And 7: and determining the automatic operation of the power grid according to a random optimization model formed by the reliability index and the operation constraint condition.

Firstly, considering the loss load cost reliability index, and constructing a target function f of the multi-objective optimization of the operation scheduling of the power distribution network:

in the formula, T_eventThe time when the fault caused by the typhoon starts under the scene s; SG is a node set connected with a distributed power supply;the unit electricity purchasing price of purchasing electricity from the power distribution network to the superior power grid at the time t;the power purchasing quantity of the power distribution network to a superior power grid under the scene s at the moment t is obtained;the price of selling electricity for the power supply of the node i;active power generated by a power supply of a node i under a scene s at the moment t; pi_sIs the probability of occurrence of scene s; tau is₁、τ₂Respectively the duration of no fault in the period t and the duration of fault in the period t; α, β, and γ represent weight coefficients, respectively.

Then, considering the operation constraint conditions of the power distribution network, constructing a random optimization model of the power distribution network under the influence of extreme weather, wherein the random optimization model mainly comprises power balance constraint, power flow interruption model second-order cone constraint of the power distribution network and distributed power supply operation constraint. Wherein the power balance constraint is as follows:

in the formula (I), the compound is shown in the specification,respectively the active power and the reactive power generated by the distributed power supply of the node i under the scene s at the moment t; d_i,t,s、C_i,t,sRespectively representing the energy storage discharge power and the charging power of a node i under a scene s at the moment t;reactive power distributed by the stored energy; q_i,c,t,sLoad reactive power of a user c of a node i in a scene s at the moment t;respectively the active power and the reactive power flowing through the line ij under the scene s at the moment t; n (i) is another end node set of lines with node i as one end node.

Establishing a second-order cone constraint of a power distribution network power flow interruption model under extreme weather, and firstly introducing the following intermediate variables:

in the formula (I), the compound is shown in the specification,indicating the state of the line, if the value is 1, the line ij has no fault, and if the value is 0, the line ij is disconnected in fault; v_i,t,sThe voltage amplitude of node i under scene s at time t.

The power distribution network flow interruption second-order cone constraint model is as follows:

of the above equations, equation (13) equation (14) is an intermediate variable constraint that accounts for random faults of the line, wherein,is the upper voltage limit of node i; equations (15) and (16) are power flow constraints, where g_ij、b_ij、Respectively the conductance of the line ij and the susceptance of the line ij as the grounding susceptance of the line ij; the formula (17) is a second-order cone constraint after the power flow equation is relaxed; equations (18) and (19) are branch current and node voltage safety constraints, where S^ij,maxIs the maximum apparent power that line ij can pass through.

The distributed power operation constraints are as follows:

in the above equations, equation (20) is the upper and lower limit constraint of the active and reactive power output of the distributed power supply, wherein,respectively outputting an active upper limit value and an output reactive upper limit value for the distributed power supply of the node i; equation (21) is the distributed power fuel constraint, wherein,fuel reserve for the distributed power supply population of node i; equation (22) is an upper and lower energy limit constraint for energy storage, wherein,lower and upper energy limits, E, respectively, stored at time t_i,t,sEnergy stored for the energy storage of the node i under the scene s at the moment t; the equations (23) and (24) are energy storage charge and discharge power constraints, wherein,respectively the charging efficiency of stored energy and the discharging efficiency of stored energy,rated power for stored energy; equation (25) is the reactive power constraint distributed by the stored energy, wherein,is the reactive power upper limit value.

And synthesizing the objective function and the constraint condition to obtain a mixed integer second-order cone optimization model, and realizing optimal scheduling in an extreme scene.

In the embodiment of the invention, an embodiment based on an IEEE33 node power distribution system is adopted, as shown in fig. 2. The system comprises nodes 14, 21 and 25, a distributed power supply, an energy storage device, a distributed photovoltaic device and an energy storage device, wherein the nodes 14, 21 and 25 are respectively connected with the distributed power supply and the energy storage device, the node 33 is connected with the distributed photovoltaic device and the energy storage device, the system comprises 32 lines and 33 nodes in total, the reference active power is 3.715MW, and the reference reactive power is 2.3 Mvar. The load of each node is divided into a first-level load, a second-level load and a third-level load, and the 24-hour scheduling range is divided into 96 equal time intervals, namely tau is 15 minutes. 1000 fault scenes are generated by utilizing Latin hypercube sampling, and 10 typical fault scenes are obtained by utilizing scene reduction. Next, the simulation results of the embodiment of the present invention will be explained.

Fig. 2 is a structural diagram of a system in a scene 10 after a scene is cut, in this scene, a simulated typhoon causes a line in a dotted line part to be interrupted in a time period t of 40, a dotted line block diagram part in the figure is separated from an original grid frame, and dotted line areas all contain energy storage and distributed power sources, so in this scene, an area autonomous power grid in the dotted line part can be subjected to autonomous operation by performing optimal scheduling on the area autonomous power grid. As can be seen from fig. 3, after the fault occurs in the period t-40, both the distributed power supply and the energy storage device in the regional autonomous power grid 1 implement corresponding scheduling measures immediately, the output of the distributed power supply increases, and the energy storage discharge power increases. As can be seen from fig. 4, under the scheduling scheme of the present invention, the primary load is fully recovered, and the reliable operation of the regional autonomous power grid is ensured to a certain extent. Table 1 lists the reliability analysis results for three cases, respectively:

TABLE 1

Respectively as follows: 1) only the stored energy is considered; 2) energy storage and distributed power sources are considered simultaneously; 3) while taking into account energy storage and distributed power but not distributed power fuel limitations. It can be seen that the reliability of the regional autonomous grid in case 3 is the best, and the reliability of the regional autonomous grid in case 1 is the worst. Therefore, the reliability evaluation method for the power grid with uncertain fault scenes provided by the invention can well analyze the influence of the fault scenes and source load uncertainty on the power grid, and has practical application value.

The foregoing describes specific embodiments of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the embodiments and descriptions described above are merely illustrative of the method of the present invention, and that various changes and modifications may be made without departing from the spirit and scope of the invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.