Background
The economic dispatching takes the lowest power supply cost or energy consumption of the whole network as an objective function, carries out dispatching according to an equal micro-increment rate method and a coordination equation, is an important tool for realizing the economic operation of a power system, is a scientific method in an operation link, and is a dispatching principle generally adopted by various countries in the world so far. At present, the problems mainly encountered in the online economic dispatching research of a large power grid are that the data volume is large, the time period of acquisition and operation is long, and the running condition of the power grid is difficult to reflect in real time, so that the economic dispatching is difficult to realize. The economic dispatching of the power system is a high-dimensional, non-convex and non-linear constrained optimization problem, so that the solution of the problem, particularly the treatment of the mutual coupling constraint condition is very difficult. China power system insists on centralized dispatching for a long time. The centralized scheduling makes the solution of the economic scheduling of the power system more difficult, and an effective method for solving the economic scheduling of the large power grid needs to be found urgently. Therefore, the method has important significance for the research on the problem solving of the large power grid economic dispatching.
Disclosure of Invention
The invention aims to provide a particle computing method for solving the large-scale economic scheduling problem of a power grid, which adopts a layering method to decompose the economic scheduling problem into multiple layers so as to reduce the computational complexity, shorten the computation time and improve the accuracy and efficiency of load flow computation.
In order to realize the purpose, the following technical scheme is adopted: the method comprises the following steps:
step 1, establishing an economic dispatching model, including a target function and constraint conditions thereof;
step 2, layering and granulating the power grid;
step 3, equivalence of parameters;
step 4, dividing the granularity;
step 5, processing constraint conditions;
and 6, optimizing the network load flow by adopting a particle calculation method.
Further, in step 1, the specific process of establishing the economic dispatch model is as follows:
step 1-1, establishing an objective function
Under the condition that constraint conditions are met, the lowest total power generation cost of the generator is taken as an objective function, and the mathematical expression is as follows:
in the formula PG,iIs the output power of the ith generator; a isi,bi,ciIs the cost factor of the generator set i; n is the number of total generators;
step 1-2, setting constraint conditions of the model, wherein the constraint conditions comprise system power balance constraint and conventional unit output upper and lower limit constraint;
the specific constraint conditions are as follows:
1) system power balance constraints
In the formula PDTotal load demand; pLossIs the line loss.
Neglecting line losses, equation (2) is modified to:
2) upper and lower limits of output of conventional unit
In the formula Pi min,Pi maxIs the minimum and maximum output power of the generator i.
Further, the specific process of step 2 is as follows:
according to a layered quotient space method, granulating a power network, collecting a plurality of fine particles with similar properties to form coarse particles as an equivalent unit, or collecting some coarse particles to form coarse particles as an equivalent unit; all coarse particles are divided into a plurality of layers to form a hierarchical quotient space; the coarse particles are refined into fine particles from the upper layer by layer, the output power of each layer can be obtained after calculation of each layer is completed, the output power is respectively transmitted to the corresponding fine particles to serve as the load requirement of the next layer, and the result of the fine particles of the last layer is the result of economic dispatching.
Further, the specific process of step 3 is as follows:
step 3-1, calculating equivalent parameters
In the economic dispatch model, the cost coefficient a
i、b
i、c
iMinimum output power
Maximum output power
Calculations are required, in which they are replaced by equivalent parameters;
in the jth particle, the unit number is assumed to be m, and the equivalent principle is as follows:
(5) in the formula (I), the compound is shown in the specification,
is the equivalent cost coefficient for the jth particle; (6) in the formula P
G,jIs the output power of the jth particle;
the equivalent parameters can be calculated as follows:
in the formula, Pj eqmin,Pj eqmaxIs the equivalent minimum and equivalent maximum output power of the jth particle;
however, before the economic scheduling problem is solved, PG,iIs unknown. But equivalent parameters must be prepared prior to particle computation. An approximate method is therefore proposed to initialize PG,i。
Step 3-2, initialization procedure
P
G,iThe initialization of (2) is critical to the granularity calculation method, as it determines the equivalent parameters; the closer the initial output power is
The closer to the optimal value, the better the result will be shown; there are three steps to P
G,iAnd (3) initializing:
first, initializing the output power of each unit
P′G,i=Pi min+(Pi max-Pi min)/2 (12)
P″G,i=σP′G,i (14)
P′G,iIs the average output power of unit i; σ is the load level coefficient; p ″)G,iIs the output power of unit i;
the process enables the output power of each unit to be close to the average power, and the power balance constraint is met;
second, forward migration
λ′i=2aiP″G,i+bi (15)
PD′=αPD (16)
λ′iIs the micro-increment rate of the ith unit; α is a positive number; pD' is load compensation; p'G,iIs the output power after the migration of the ith unit;
the process makes the unit have smaller lambda'iObtaining a relatively large positive deviation value;
third, negative migration
(18) In the formula (I), the compound is shown in the specification,
is the initialized output power of the ith unit;
this process gives the unit a greater lambda'iAnd obtaining a relatively large negative deviation amount; according to the increment principle, the second step and the third step can ensure that the output power is close to the optimal solution;
fourthly, balancing the constraints
The offset adjustment may result in unequal power constraints, so a constraint process is necessary to correct
The correction process is in
step 5.
Step 3-3, granularity calculation model
After equivalence, the cost function formula of the granularity calculation is as follows:
(19) wherein M is the number of subparticles of the host particle;
the power balance constraint of the particle calculation is modified as follows:
(20) in the formula, PGDThe output power of the main particle is the load requirement of the next layer of sub-particles;
the power constraints of the particles are as follows:
Pj eqmin≤PG,j≤Pj eqmax (21)
in the particle size calculation method, one particle is considered as an equivalent unit; particles with one unit (M ═ 1) are called fine particles; the equivalent parameters of the fine particles are equal to the parameters of the unit contained in the fine particles; particles with more than one set of units (M > 1) are called coarse particles.
Further, the step 4 is as follows:
particle size is an average measurement of particle size; when describing information, granularity is mainly used for measuring the abstraction degree of data information and knowledge; the particle size is determined by the number of units contained in the particles;
the obvious fluctuation point of the micro-increment rate divides the unit into particles, and the calculation formula of the micro-increment rate is as follows:
(22) in the formula, λiIs the micro-increment rate of the ith unit;
after calculation, sorting the micro-increment rates of all the units according to the sequence; separating the unit according to the obvious fluctuation point;
(23) in the formula, theta
sIs the point of fluctuation of the micro-increment rate,
is the rank order fractional increase; s is a sequence number with increasing rate;
θ
sreact to
And
the difference in (a); if theta is greater than theta
sIs significantly greater than the other values, then θ
sIs the point of significant fluctuation.
Further, the specific process of step 5 is as follows:
step 5-1, examining each
All elements are adjusted to satisfy the inequality constraint as follows:
(24) in the formula, if
Or
Then the transition variable T
jSet to 0, otherwise
k is the current number of iterations;
step 5-2, by
Calculating P
RIf | P
RIf | is greater than ε, go to step 5-3, if | P
RIf | ≦ epsilon, go to
step 4, epsilon is the precision requirement;
step 5-3, modification
To satisfy the following equation constraint:
step 5-4, checking all
If the inequality constraint is violated, returning to the step 5-1; if the inequality constraint is not violated, entering step 5-5;
5-5, stopping the constraint processing process;
calculating according to the steps, wherein the initial output power of the equivalent parameter is close to the actual power level, so that the equivalent parameter is more accurate; then hold
Put into equations (7) and (8), substitute for P
G,jTo calculate
And
further, the step 6 specifically includes:
and 6-1, parameter preparation. The basic parameters of all units need to be input, namely a
i、b
i、c
i、
And
calculating initial output power
Step 6-2, determining the hierarchical structure of the coarse particles and calculating parameters; determining a proper number of layers according to the scale of the power system; although the hierarchical method can improve the search efficiency and reduce the calculation time, the equivalent process causes deviation; accuracy is reduced if there is too much delamination; first layer M1Number of particles and maximum number of units n of second layermaxSetting is needed before calculation so as to guide the division process of the unit; when the unit division is completed, calculating equivalent parameters in the next part;
6-3, calculating the output power of the particles; the results are transferred accordingly to their sub-particles as the loading requirements for the next layer;
when the bottom layer particle calculation is completed, a final optimized solution is obtained.
Compared with the prior art, the invention has the following advantages:
1. the factors are considered comprehensively, and the calculation precision is improved;
2. providing a layered quotient space, applying an analytic hierarchy process, and solving the problem in a layered granulation manner, so that the solving time can be reduced, and the solving efficiency can be improved;
3. for a large-scale power network, if a reasonable hierarchical particle calculation method is adopted, the problem of difficult convergence can be solved, and the calculation speed can be increased.
Detailed Description
The invention is further described below with reference to the accompanying drawings:
as shown in fig. 4, the method of the present invention includes the following steps:
step 1, establishing an economic dispatching model, including a target function and constraint conditions thereof;
step 1-1, the specific process of establishing the economic dispatching model is as follows:
under the condition that constraint conditions are met, the lowest total power generation cost of the generator is taken as an objective function, and the mathematical expression is as follows:
in the formula PG,iIs the output power of the ith generator; a isi,bi,ciIs the cost factor of the generator set i; n is the number of total generators;
step 1-2, setting constraint conditions of the model, wherein the constraint conditions comprise system power balance constraint and conventional unit output upper and lower limit constraint;
the specific constraint conditions are as follows:
1) system power balance constraints
In the formula PDTotal load demand; pLossIs the line loss;
neglecting line losses, equation (2) is modified to:
2) upper and lower limits of output of conventional unit
In the formula
Is the minimum and maximum output power of the generator i.
Step 2, layering and granulating the power grid;
the specific process of layering and granulating the power grid is as follows:
according to an analytic hierarchy process, a method for establishing a hierarchical quotient space is provided for an economic scheduling problem. To clarify the layered structure, a 10-unit power system is taken as an example. The numbers are #1- # 10. Assuming that the system can be divided into three layers, as shown in fig. 1, the respective characteristics of each layer are as follows:
1) a first layer: there are three coarse particles V11,V12,V13In this layer. V11Comprising four units (#1, #3, #6, #7), as shown in FIG. 1, V12(#2, #9) and V13(#4, #5, #8, #10) and V11As such. V11,V12,V13Are three equivalent units. Thus reducing the warpThe dimensionality of the scheduling problem is saved, and the optimization efficiency is improved. After this layer is calculated, V11,V12,V13Their output power can be derived and delivered to their sub-particles separately as the load demand of the next layer.
2) A second layer: the layer has six particles V21,V22,V23,V24,V25,V26。V21And V22Is V11Are considered to be equivalent sets, and V21And V22From V11A load demand is obtained. Host particle V11Is responsible for calculating V21And V22The power output of (1). Calculation of the other two particles and V11The transformation is similar. As shown in fig. 1, at V23,V24,V26There is only one set, so the results for these three particles are exactly the final power outputs of #9, #2, and #5, respectively. However, V21、V22、V25Can still be divided into several sub-particles in the third layer.
3) And a third layer: this layer is the bottom layer, which comprises seven particles, each V31,V32,V33,V34,V35,V36,V37. There is only one unit per particle. The calculation process is similar to the method of the second layer, including V21Is equivalent to V31And V32,V22Is equivalent to V33And V34,V25Is equivalent to V35、V36And V37. When all the calculation processes are completed, V31,V32,V33,V34,V35,V36,V37And V23,V24,V26The result is the final unit output result of 10 units.
In the design of the hierarchical model, a method for finding a reasonable equivalent parameter of the computer set is critical and has a remarkable influence on a final result.
Step 3, equivalence of parameters;
step 3-1, calculating equivalent parameters
In the economic dispatch model, the cost coefficient a
i、b
i、c
iMinimum output power
Maximum output power
Calculations are required, in which they are replaced by equivalent parameters;
in the jth particle, the unit number is assumed to be m, and the equivalent principle is as follows:
(5) in the formula (I), the compound is shown in the specification,
is the equivalent cost coefficient for the jth particle; (6) in the formula P
G,jIs the output power of the jth particle;
the equivalent parameters can be calculated as follows:
in the formula, Pj eqmin,Pj eqmaxIs the equivalent minimum and equivalent maximum output power of the jth particle;
step 3-2, initialization procedure
P
G,iThe initialization of (2) is critical to the granularity calculation method, as it determines the equivalent parameters; the closer the initial output power is
The closer to the optimal value, the better the result will be shown; there are three steps to P
G,iAnd (3) initializing:
first, initializing the output power of each unit
P′G,i=Pi min+(Pi max-Pi min)/2 (12)
P″G,i=σP′G,i (14)
P′G,iIs the average output power of unit i; σ is the load level coefficient; p ″)G,iIs the output power of unit i;
the process enables the output power of each unit to be close to the average power, and the power balance constraint is met;
second, forward migration
λ′i=2aiP″G,i+bi (15)
PD′=αPD (16)
λ′iIs the micro-increment rate of the ith unit; α is a positive number; pD' is load compensation; p'G,iIs the output power after the migration of the ith unit;
the process makes the unit have smaller lambda'iObtaining a relatively large positive deviation value;
third, negative migration
(18) In the formula (I), the compound is shown in the specification,
is the initialized output power of the ith unit;
this process gives the unit a greater lambda'iAnd obtaining a relatively large negative deviation amount; according to the increment principle, the second step and the third step can ensure that the output power is close to the optimal solution;
fourthly, balancing the constraints
The offset adjustment may result in unequal power constraints, so a constraint process is necessary to correct
Step 3-3, granularity calculation model
After equivalence, the cost function formula of the granularity calculation is as follows:
(19) wherein M is the number of subparticles of the host particle;
the power balance constraint of the particle calculation is modified as follows:
(20) in the formula, PGDThe output power of the main particle is the load requirement of the next layer of sub-particles;
the power constraints of the particles are as follows:
Pj eqmin≤PG,j≤Pj eqmax (21)
in the particle size calculation method, one particle is considered as an equivalent unit; particles with one unit (M ═ 1) are called fine particles; the equivalent parameters of the fine particles are equal to the parameters of the unit contained in the fine particles; particles with more than one set of units (M > 1) are called coarse particles.
Step 4, dividing the granularity;
particle size is an average measurement of particle size. When describing information, granularity is mainly used to measure the abstraction degree of data information and knowledge. In this context, the particle size is determined by the number of units the particle contains.
The obvious fluctuation point of the micro-increment rate divides the unit into particles, and the calculation formula of the micro-increment rate is as follows:
(22) in the formula, λiIs the micro-increment rate of the ith unit.
After the calculation is finished, the micro-increment rates of all the units need to be sorted to be small to large. And separating the unit according to the obvious fluctuation point.
(23) In the formula, theta
sIs the point of fluctuation of the micro-increment rate,
is the rank order fractional increase; s is the sequence number of the increasing rate ascending order.
θ
sReact to
And
the difference in (a). If theta is greater than theta
sIs significantly greater than the other values, then θ
sIs the point of significant fluctuation.
The granularity division of a 10-unit system is listed in table 1, the power system division scheme of the 10 units is listed, and the fluctuation graph of the ordered growth rate is shown in fig. 2, which shows how the significant fluctuation point fluctuates.
TABLE 1
1) Dividing a first layer:
in FIG. 2, we observe θ5And theta7Significantly greater than the average, which means that the growth rates of #9 and #4 are significantly different from the units before them, and then these units are divided into three groups to form (V)11,V12,V13) Three particles.
In a practical example, θsNeed to be listed in descending order. Then, according to the number M of particles arranged in the first layer1M before picking1-a point of 1. If there are too many particles, the efficiency of the calculation is reduced. Thus M1The range of (1) is 2 to 9.
2) And second layer division:
at V11In, theta3Is a significant point of fluctuation, and V11Is divided into V21And V22. Likewise, V12And V13Are also divided into V23,V24,V25,V26Which constitute the second layer shown in figure 1.
In practical applications, the division of the layer is implemented independently in each host particle. In the jth main particle of the layer, the number of sub-particles
Is set by setting the maximum number n of units
maxDetermined, the formula is as follows:
in the formula, mjIs the total unit number of the jth main particle.
Then according to the previous
The fluctuation point of (a) divides the jth particle into
And (4) sub-particles. If the total unit number ratio n of one main particle
maxSmall, this host particle cannot be divided into sub-particles. Such as n
maxIf it is too small, this will have too many sub-particles, which will increase the dimensionality of the GrC method and will reduce the computational efficiency. If n is
maxToo large, this will not reduce the time-efficient sub-particles of the GrC process. Thus n is
maxThe range of (1) is 10 to 30.
In the first-layer and second-layer division, if only one unique unit set exists in the particles, the particles are combined with the previous particles to improve the global search capability of the GrC method.
3) Bottom layer partitioning:
in this layer, all coarse particles must be broken down into fine particles to obtain the final power output of each unit.
Step 5, processing constraint conditions;
step 5-1, examining each
Adjust all elementsThe elements satisfy the inequality constraint as follows:
(24) in the formula, if
Or
Then the transition variable T
jSet to 0, otherwise
k is the current number of iterations;
step 5-2, by
Calculating P
RIf | P
RIf | is greater than ε, go to step 5-3, if | P
RIf | ≦ epsilon, go to
step 4, epsilon is the precision requirement;
step 5-3, modification
To satisfy the following equation constraint:
step 5-4, checking all
If the inequality constraint is violated, returning to the step 5-1; if the inequality constraint is not violated, entering step 5-5;
5-5, stopping the constraint processing process;
calculating according to the steps, wherein the initial output power of the equivalent parameter is close to the actual power level, so that the equivalent parameter is more accurate; then hold
Put into equations (7) and (8), substitute for P
G,jTo calculate
And
and 6, optimizing the network load flow by adopting a particle calculation method, wherein a flow chart of a particle calculation process is shown in fig. 3.
And 6-1, parameter preparation. The basic parameters of all units need to be input, namely a
i、b
i、c
i、
And
calculating initial output power
And 6-2, determining the hierarchical structure of the coarse particles and calculating parameters. The appropriate number of tiers is determined based on the size of the power system. Although the hierarchical approach can improve search efficiency and reduce computation time, the equivalent process can cause bias. Accuracy is reduced if there is too much delamination. First layer M1Number of particles and maximum number of units n of second layermaxBefore calculation, setting is needed to guide the division process of the unit. When the crew division is complete, the next part is to calculate the equivalent parameters.
And 6-3, calculating the output power of the particles. A new intelligent optimization algorithm can be applied to the output power of the optimized particles and the results are transferred to their sub-particles accordingly as the load demand of the next layer.
When the bottom layer particle calculation is completed, a final optimized solution is obtained.
In order to verify the effectiveness of the invention more completely, the comparison between the particle swarm algorithm and the mean variance mapping method shows that the invention can provide a satisfactory global optimal solution and has better time benefit. The two results are compared as follows:
TABLE 2 comparison of Power Generation cost versus time results for two algorithms
Obviously, the advantages of the power generation cost of the invention are not obvious, but the efficiency is greatly improved for the calculation time, and the superiority of the particle calculation is more obvious as the scale of the power grid is enlarged. The above results demonstrate the superiority of the present invention.
The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solution of the present invention by those skilled in the art should fall within the protection scope defined by the claims of the present invention without departing from the spirit of the present invention.