1. A capacitive DC blocking device configuration optimization method based on a genetic algorithm is characterized by comprising the following steps:

step A: defining an evaluation function of the transformer neutral point direct current, reflecting the invasion degree of each grounding transformer by the subway stray current, and participating in the optimized configuration calculation of the DC blocking device;

and B: and numbering the substations in sequence according to the number of the substations, and carrying out binary coding on the installation scheme of the DC blocking device. Randomly generating 49 initial configuration schemes, and adding all schemes for installing the capacitance blocking devices into an initial generation matrix to finally form 50 initial configuration schemes;

and C: establishing an objective function, and quantizing the objective function into a superposition form of direct current treatment effect and blocking quantity, wherein the treatment effect is expressed by an exponential function, the blocking quantity is defined as a linear function, and the objective function represents that the installation quantity of blocking devices is minimum under the condition that the direct current magnetic bias treatment effect is satisfied;

step D: selecting a measured value of the direct current of the neutral point of the grounding transformer in a departure interval period during the peak running period of the train, calculating an initial value of a direct current evaluation value of the neutral point according to an evaluation function, and substituting the initial value of the direct current evaluation value of the neutral point into a target function for iterative calculation;

step E: defining the distribution probability of the stray current of the subway after the capacitive DC blocking device is put into the iterative calculation process;

step E1: defining the probability of the stray current of the subway flowing out of the urban power grid when the DC blocking device is put into operation; after the DC blocking device is set to be put into use, the proportion of the subway stray current flowing out of the power system is 50% -70%, and the rest 30% -50% of direct current continuously enters the power system through a neutral point of a grounding transformer without the capacitive DC blocking device;

step E2: defining a subway stray current propagation path and distribution proportion thereof in an urban district power grid; after the DC blocking device is put into use, 30% -50% of direct current entering the urban power grid is set to be 60% -80% of direct current flowing in the power transmission line, values are randomly taken in the range in the iteration process, and the rest 20% -40% of stray current flows through the overhead ground wire and the ground;

step E3: when the DC blocking device is put into use, distributing neutral points of 500kV and 220kV transformers according to the ratio of 6:4 by stray current transmitted by a power transmission line or a lightning conductor, and performing superposition calculation of direct current of the neutral points; the stray current circulating in the earth equivalent passage and the overhead ground wire above the earth equivalent passage is averagely distributed to the neutral point of each grounding transformer, and the direct current superposition calculation of the neutral points is carried out;

step F: optimizing the installation scheme of the blocking device under the specified distribution probability according to a genetic algorithm;

step F1: calculating the objective function value corresponding to each scheme according to the initial blocking scheme;

step F2: selecting, crossing and mutating according to the objective function value corresponding to the blocking scheme; the objective function value gradually tends to be minimum;

step F3: when the installation scheme of the blocking device is within the range of the distribution proportion and the objective function value reaches the minimum value, stopping the iterative computation process and outputting the optimal scheme;

step G: checking whether the direct current evaluation index of the neutral point of each grounding transformer meets the requirement; if the neutral point direct current of the 500kV transformer without the DC blocking device is within 8A, and the neutral point direct current of the 220kV transformer without the DC blocking device is within 5A, the optimization scheme meets the treatment requirement.

2. The method for optimizing the configuration of the capacitive DC blocking device based on the genetic algorithm as claimed in claim 1, wherein the evaluation function calculation formula in the step A is as follows:

in the formula I_dcThe direct current evaluation value is a neutral point direct current evaluation value; i.e. i_mThe current value of a sampling point of the DC data of the neutral point is obtained; n sampling points; f is the sampling frequency; t is the sampling time.

3. The method for optimizing the configuration of the capacitive DC blocking device based on the genetic algorithm according to claim 1, wherein the objective function of the step C is as follows:

in the formula, t is the number of a grounding transformer in an urban district power grid; s is the number of grounding transformers of the urban area power grid; i is_dctThe evaluation value is the neutral point direct current evaluation value of the grounding transformer with the number of t; i is_dct0The number is t, and the direct current limit value of the neutral point of the grounding transformer is the number t; and P is the installation number of the capacitance blocking devices.

4. The method as claimed in claim 1, wherein the selection mode in step F2 is roulette selection mode, the crossing rate is set to 0.8, and the variation mode is basic bit variation mode.

Background

At present, a direct current traction power supply system is mostly adopted for subways, and due to the fact that complete insulation between a steel rail and the ground cannot be achieved, in the process that traction current flows back through the steel rail, partial current leaks to the ground to form subway stray current. Because there are a large amount of grounding transformers in the urban power grid, when the stray current of the subway circulates in the ground, the stray current flows into the grounding grid connected with the transformers through the ground, and then invades the urban power grid. The phenomenon of direct current magnetic biasing of the transformer can be caused by the fact that stray current of a subway invades an urban power grid, so that the vibration of the transformer is aggravated, the noise is increased, the local temperature rise is increased, and the service life of the transformer is greatly influenced when the transformer is serious; meanwhile, the invasion of the stray current of the subway can cause the phenomena of harmonic wave increase of a power grid reactor, accelerated corrosion of a grounding grid and the like, and brings serious hidden danger to the normal operation of the power grid.

Aiming at the suppression of the direct current magnetic bias of the transformer caused by the stray current of the subway, the method is mainly characterized in that a capacitive DC blocking device is additionally arranged at a neutral point of the transformer with the excessive direct current, but the method can cause the direct current of the neutral point of the nearby transformer to exceed the standard so as to further aggravate the direct current magnetic bias phenomenon, and if the mode that all the transformers of the urban area power grid are additionally provided with the DC blocking devices is adopted, the treatment cost is too high. According to the existing research, the existing optimization and treatment research aiming at the direct current magnetic biasing of the transformer caused by the stray current of the subway is less and not deep enough, and the optimization and inhibition are mostly carried out only aiming at the direct current magnetic biasing phenomenon of the transformer caused by the grounding current of a direct current grounding electrode and the geomagnetic induction current. The method is not completely suitable for direct-current magnetic bias control with subway stray current as a source. A capacitor blocking device configuration optimization method based on a genetic algorithm is researched, a scientific and effective blocking device deployment scheme can be provided for suppression of direct-current magnetic bias of a transformer, and treatment cost is saved.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a method for optimizing configuration of a capacitive dc blocking device based on a genetic algorithm, which can realize research on suppression of dc magnetic biasing of an urban power grid grounding transformer caused by stray current in a subway, and as a result, can provide instructive suggestions for optimizing configuration of a field dc blocking device.

The invention discloses a capacitive blocking device configuration optimization method based on a genetic algorithm, which comprises the following steps of:

step A: and defining an evaluation function of the transformer neutral point direct current, reflecting the invasion degree of each grounding transformer by the subway stray current, and participating in the optimal configuration calculation of the DC blocking device.

And B: and numbering the substations in sequence according to the number of the substations, and carrying out binary coding on the installation scheme of the DC blocking device. 49 initial configuration schemes (such as [1,0,0,1,1,0,1,0,0, 0,1]) are randomly generated, and all the schemes of installing the capacitance blocking devices are added into the initial generation matrix, and finally 50 initial configuration schemes are formed.

And C: establishing an objective function, and quantizing the objective function into a superposition form of direct current treatment effect and blocking quantity, wherein the treatment effect is expressed by an exponential function, the blocking quantity is defined as a linear function, and the objective function expresses that the installation quantity of the blocking devices is minimum under the condition that the direct current magnetic bias treatment effect is satisfied.

Step D: selecting a measured value of the direct current of the neutral point of the grounding transformer in about one departure interval period during the peak running period of the train, calculating an initial value of the direct current evaluation value of the neutral point according to an evaluation function, and substituting the initial value of the direct current evaluation value of the neutral point into a target function for iterative calculation.

Step E: and defining the distribution probability of the stray current of the subway after the capacitive DC blocking device is put into the iterative calculation process.

Step E1: and defining the probability of the stray current of the subway flowing out of the urban power grid when the DC blocking device is put into operation. After the DC blocking device is set to be put into use, the proportion of the subway stray current flowing out of the power system is 50% -70%, and the rest 30% -50% of direct current continuously enters the power system through the neutral point of the grounding transformer without the capacitor DC blocking device.

Step E2: and defining the subway stray current propagation path and the distribution proportion thereof in the urban district power grid. After the DC blocking device is put into use, 30% -50% of direct current entering the urban power grid is set to be 60% -80% of direct current flowing in the power transmission line, values are randomly taken in the range in the iteration process, and the rest 20% -40% of stray current flows through the overhead ground wire and the ground.

Step E3: when the DC blocking device is put into use, the neutral points of the 500kV and 220kV transformers are respectively distributed by stray currents transmitted through the power transmission line or the lightning conductor according to the ratio of 6:4, and the direct current superposition calculation of the neutral points is carried out. And averagely distributing stray current circulating in the earth equivalent path and the overhead ground wire above the earth equivalent path to the neutral point of each grounding transformer, and performing superposition calculation of direct current of the neutral point.

Step F: and optimizing the installation scheme of the blocking device under the specified distribution probability according to a genetic algorithm.

Step F1: and calculating the objective function value corresponding to each scheme according to the initial blocking scheme.

Step F2: and carrying out operations such as selection, intersection, variation and the like according to the objective function values corresponding to the blocking schemes. The value of the objective function gradually tends to be minimal.

Step F3: and when the installation scheme of the blocking device is within the distribution proportion range and the target function value reaches the minimum value, stopping the iterative computation process and outputting the optimal scheme.

Step G: and checking whether the direct current evaluation index of the neutral point of each grounding transformer meets the requirement. If the neutral point direct current of the 500kV transformer without the DC blocking device is within 8A, and the neutral point direct current of the 220kV transformer without the DC blocking device is within 5A, the optimization scheme meets the treatment requirement.

Further, the evaluation function calculation formula in the step a is as follows:

in the formula I_dcThe direct current evaluation value is a neutral point direct current evaluation value; i.e. i_mThe current value of a sampling point of the DC data of the neutral point is obtained; n sampling points; f is the sampling frequency; t isThe sampling time.

Further, the objective function of step C is:

in the formula, t is the number of a grounding transformer in an urban district power grid; s is the number of grounding transformers of the urban area power grid; i is_dctThe evaluation value is the neutral point direct current evaluation value of the grounding transformer with the number of t; i is_dct0The number is t, and the direct current limit value of the neutral point of the grounding transformer is the number t; and P is the installation number of the capacitance blocking devices.

Further, in step F2, the selection mode is roulette selection mode, the crossing rate is set to 0.8, and the variation mode is base bit variation mode.

The beneficial technical effects of the invention are as follows:

firstly, in the optimizing process of the genetic algorithm, the range of an initial forming scheme is expanded through the intervention of an initial generating matrix, and the problems of local convergence and the like in advance in the optimizing process are avoided.

And secondly, by reasonably setting a target function and evaluation indexes, the severity of the invasion of the subway stray current into the grounding transformer is effectively evaluated.

And based on a genetic algorithm, the optimization of the number and the installation positions of the capacitive DC blocking devices is realized, a scientific and effective deployment scheme is provided, and the treatment cost of enterprises is saved.

Drawings

Fig. 1 is a flow chart of a method for optimizing the configuration of a capacitive dc blocking device based on a genetic algorithm according to the present invention.

Detailed Description

The invention is described in further detail below with reference to the figures and the detailed description.

The flow of the method for optimizing the configuration of the capacitive blocking device based on the genetic algorithm is shown in figure 1, and specifically comprises the following steps:

step A: and defining an evaluation function of the transformer neutral point direct current, reflecting the invasion degree of each grounding transformer by the subway stray current, and participating in the optimal configuration calculation of the DC blocking device.

The evaluation function calculation formula is as follows:

in the formula I_dcThe direct current evaluation value is a neutral point direct current evaluation value; i.e. i_mThe current value of a sampling point of the DC data of the neutral point is obtained; n sampling points; f is the sampling frequency; t is the sampling time.

And B: and numbering the substations in sequence according to the number of the substations, and carrying out binary coding on the installation scheme of the DC blocking device. 49 initial configuration schemes (such as [1,0,0,1,1,0,1,0,0, 0,1]) are randomly generated, and all the schemes of installing the capacitance blocking devices are added into the initial generation matrix, and finally 50 initial configuration schemes are formed.

And C: establishing an objective function, and quantizing the objective function into a superposition form of direct current treatment effect and blocking quantity, wherein the treatment effect is expressed by an exponential function, the blocking quantity is defined as a linear function, and the objective function expresses that the installation quantity of the blocking devices is minimum under the condition that the direct current magnetic bias treatment effect is satisfied.

The objective function is:

in the formula, t is the number of a grounding transformer in an urban district power grid; s is the number of grounding transformers of the urban area power grid; i is_dctThe evaluation value is the neutral point direct current evaluation value of the grounding transformer with the number of t; i is_dct0The number is t, and the direct current limit value of the neutral point of the grounding transformer is the number t; and P is the installation number of the capacitance blocking devices.

Step D: selecting a measured value of the direct current of the neutral point of the grounding transformer in about one departure interval period during the peak running period of the train, calculating an initial value of the direct current evaluation value of the neutral point according to an evaluation function, and substituting the initial value of the direct current evaluation value of the neutral point into a target function for iterative calculation.

Step E: and defining the distribution probability of the stray current of the subway after the capacitive DC blocking device is put into the iterative calculation process.

Step E1: and defining the probability of the stray current of the subway flowing out of the urban power grid when the DC blocking device is put into operation. After the DC blocking device is set to be put into use, the proportion of the subway stray current flowing out of the power system is 50% -70%, and the rest 30% -50% of direct current continuously enters the power system through the neutral point of the grounding transformer without the capacitor DC blocking device.

Step E2: and defining the subway stray current propagation path and the distribution proportion thereof in the urban district power grid. After the DC blocking device is put into use, 30% -50% of direct current entering the urban power grid is set to be 60% -80% of direct current flowing in the power transmission line, values are randomly taken in the range in the iteration process, and the rest 20% -40% of stray current flows through the overhead ground wire and the ground.

Step E3: when the DC blocking device is put into use, the neutral points of the 500kV and 220kV transformers are respectively distributed by stray currents transmitted through the power transmission line or the lightning conductor according to the ratio of 6:4, and the direct current superposition calculation of the neutral points is carried out. And averagely distributing stray current circulating in the earth equivalent path and the overhead ground wire above the earth equivalent path to the neutral point of each grounding transformer, and performing superposition calculation of direct current of the neutral point.

Step F: and optimizing the installation scheme of the blocking device under the specified distribution probability according to a genetic algorithm.

Step F1: and calculating the objective function value corresponding to each scheme according to the initial blocking scheme.

Step F2: and carrying out operations such as selection, intersection, variation and the like according to the objective function values corresponding to the blocking schemes. The value of the objective function gradually tends to be minimal. The selection mode adopts a roulette selection mode, the crossing rate is set to be 0.8, and the variation mode adopts a basic bit variation mode.

Step F3: and when the installation scheme of the blocking device is within the distribution proportion range and the target function value reaches the minimum value, stopping the iterative computation process and outputting the optimal scheme.

Step G: and checking whether the direct current evaluation index of the neutral point of each grounding transformer meets the requirement. If the neutral point direct current of the 500kV transformer without the DC blocking device is within 8A, and the neutral point direct current of the 220kV transformer without the DC blocking device is within 5A, the optimization scheme meets the treatment requirement.