CN111178589A - Iterative guidance method and system based on gray prediction - Google Patents
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Abstract
The invention discloses an iterative guidance method and system based on gray prediction, wherein the method comprises the following steps: for known engine thrust vectorSampling to obtain a sampling sequence: performing primary accumulation on the sampling sequence to obtain a primary accumulation sequence: performing sequence reduction on the sampling sequence according to the primary accumulation sequence; determining a whitening equation set: solving by a least square method to obtain parameter values in the whitening equation set; predicting to obtain an engine thrust vector at the next moment according to the solved parameter value; and predicting to obtain a speed vector and a position vector at the next moment according to the predicted engine thrust vector at the next moment. The invention fully utilizes the existing information, predicts the required thrust vector direction of the engine on line in real time, can simplify the calculation process of iterative guidance, and is easy to realize。
Description
Technical Field
The invention belongs to the technical field of guidance, and particularly relates to an iterative guidance method and system based on gray prediction.
Background
With the continuous development of the related technology in the aerospace field, the requirement on the launch task of the launch vehicle is higher and higher, the guidance precision is an important index, and the traditional perturbation guidance cannot meet the requirements at the present stage.
Disclosure of Invention
The technical problem of the invention is solved: the iterative guidance method and the iterative guidance system based on gray prediction overcome the defects of the prior art, fully utilize the existing information, predict the required thrust vector direction of the engine on line in real time, simplify the calculation process of iterative guidance and are easy to realize.
In order to solve the technical problem, the invention discloses an iterative guidance method based on gray prediction, which comprises the following steps:
wherein n represents the length of the sampling sequence, n is 1, 2, 3, T, and T represents the iteration period;
performing primary accumulation on the sampling sequence to obtain a primary accumulation sequence:
sequence reduction according to formula (1) and formula (2) gives:
wherein k is more than or equal to 1 and less than or equal to n;
obtaining a whitening equation set according to the formula (3):
wherein, a represents a development coefficient, and b represents a gray effect amount;
solving by a least square method to obtain values of a and b;
according to the values of a and b obtained by solving, the engine thrust vector at the next moment is predicted and obtained by combining the formula (3)
The predicted engine thrust vector at the next momentSubstituting the speed and position solution formula (5) to predict the speed vector at the next momentAnd position vector
Wherein the content of the first and second substances,ω represents the angular velocity of the earth motion.
In the iterative guidance method based on gray prediction, the values of a and b are obtained by solving through a least square method, and the iterative guidance method comprises the following steps:
a and b satisfy:
wherein:
equations (7) to (9) are substituted for equation (6), and the values of a and b are obtained by solving.
In the iterative guidance method based on gray prediction, the engine thrust vector at the next moment is predicted according to the values of a and b obtained by solving and combining the formula (3)The method comprises the following steps:
solving the differential equation yields:
will be provided withAs an initial value for solving the differential equation (10), formula (10) is substituted for formula (3) to obtain formula (11):
wherein j represents the j prediction, and the values of j are n +1, n +2 and … …;
substituting the values of a and b obtained by solving into an equation (11), and obtaining the thrust vector of the engine at the next moment by solving
In the above iterative guidance method based on gray prediction, equation (5) is determined by the following steps:
determining a mass center motion equation outside the atmosphere of the active section of the rocket:
wherein:
wherein, W represents the apparent acceleration,which represents the gravitational force of the earth,the velocity vector is represented by a vector of velocities,the position vector is represented by a vector of positions,representing the nozzle swing angle in the pitching direction of the engine, and psi representing the nozzle swing angle in the yawing direction of the engine;
the centroid radial size of any point of the active segment can be expressed as:
r=rc+Δr····(14)
wherein Δ r represents a high-order term;
will accelerate the gravitational forceIn thatUnfolding and omitting high-level items to obtain an average gravitational acceleration as follows:
and (3) carrying the simplified gravitation item into formula (12), and obtaining a simplified motion equation as follows:
equation (16) is written as an expression of the equation of state:
discretization of formula (17) yields formula (5).
In the above iterative guidance method based on gray prediction, the method further includes:
determining a velocity vector at a next timeAnd position vectorWhether a terminal condition is satisfied;
if yes, ending; if not, returning iteration until the predicted speed vector and the predicted position vector meet the terminal condition.
In the above iterative guidance method based on gray prediction,
when in useOrDetermining that the predicted speed vector and the predicted position vector meet the terminal condition;
wherein the content of the first and second substances,a vector representing the desired speed of shutdown is shown,indicating a desired shutdown position vector.
In the above iterative guidance method based on gray prediction, the method further includes:
if the predicted speed vector and the predicted position vector do not meet the terminal condition after iteration for p times, then the pairCorrecting the initial value by small step length of 0.01 times until the requirement is met;
wherein pT > TThreshold value,TThreshold valueIndicating setting an iteration threshold time.
The invention also discloses an iterative guidance system based on gray prediction, which comprises the following components:
wherein n represents the length of the sampling sequence, n is 1, 2, 3, T, and T represents the iteration period;
the accumulation module is used for carrying out primary accumulation on the sampling sequence to obtain a primary accumulation sequence:
a sequence reduction module for performing sequence reduction according to formula (1) and formula (2) to obtain:
wherein k is more than or equal to 1 and less than or equal to n;
a whitening equation set determination module for obtaining a whitening equation set according to equation (3):
wherein, a represents a development coefficient, and b represents a gray effect amount;
the parameter solving module is used for solving by a least square method to obtain values of a and b;
a thrust vector predicting module for predicting the engine thrust vector at the next moment according to the values of a and b obtained by solving and the combination formula (3)
A speed position prediction module for predicting the engine thrust vector at the next momentSubstituting the speed and position solution formula (5) to predict the speed vector at the next momentAnd position vector
Wherein the content of the first and second substances,ω represents the angular velocity of the earth motion.
The invention has the following advantages:
the invention discloses an iterative guidance method and an iterative guidance system based on gray prediction, which adopt a gray prediction theory to predict the future change trend of an obtained engine thrust vector direction data by mining the relationship between the obtained engine thrust vector direction data, so that the terminal constraint condition can be quickly achieved, the calculation process of iterative guidance is simplified, the iterative guidance is easy to realize, and an optimization scheme is provided for iterative guidance.
Drawings
FIG. 1 is a flowchart illustrating steps of an iterative guidance method based on gray prediction according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Example 1
As shown in fig. 1, in this embodiment, the iterative guidance method based on gray prediction includes:
where n denotes the length of the sample sequence, n ═ 1, 2, 3, ·, T, and T denotes the iteration period.
wherein k is more than or equal to 1 and less than or equal to n.
And 104, obtaining a whitening equation set according to the formula (3):
wherein a represents a coefficient of progression and b represents an amount of action of gray.
And step 105, solving the values of a and b by a least square method.
And step 106, predicting and obtaining the engine thrust vector at the next moment according to the values of a and b obtained by solving and the combination formula (3)
Wherein the content of the first and second substances,ω represents the angular velocity of the earth motion.
In a preferred embodiment of the present invention, the solving process for a and b is as follows:
a and b satisfy:
wherein:
equations (7) to (9) are substituted for equation (6), and the values of a and b are obtained by solving.
In a preferred embodiment of the present invention, the engine thrust vector at the next time is predicted according to the solved values of a and b, in combination with equation (3)The method specifically comprises the following steps:
solving the differential equation yields:
will be provided withAs an initial value for solving the differential equation (10), formula (10) is substituted for formula (3) to obtain formula (11):
wherein j represents the j prediction, and the values of j are n +1, n +2 and … ….
Substituting the values of a and b obtained by solving into an equation (11), and obtaining the thrust vector of the engine at the next moment by solving
In a preferred embodiment of the present invention, formula (5) can be determined by:
determining a mass center motion equation outside the atmosphere of the active section of the rocket:
wherein:
wherein, W represents the apparent acceleration,which represents the gravitational force of the earth,the velocity vector is represented by a vector of velocities,the position vector is represented by a vector of positions,representing the nozzle yaw angle in the engine pitch direction and psi representing the nozzle yaw angle in the engine yaw direction.
In equation (12), the engine thrust direction is the control variable, the starting condition is given by the navigation system, and the terminal condition is determined according to the specific task. Because the gravity item has serious nonlinearity and is not beneficial to development in the process of solving iterative guidance, the gravity item needs to be simplified.
the centroid radial size of any point of the active segment can be expressed as:
r=rc+Δr····(14)
where Δ r represents a high-order term.
Will accelerate the gravitational forceIn thatUnfolding and omitting high-level items to obtain an average gravitational acceleration as follows:
and (3) carrying the simplified gravitation item into formula (12), and obtaining a simplified motion equation as follows:
in equation (16), the average gravity is used to replace the true gravity, which brings a certain error term, but since the iterative guidance method will eliminate the accumulated error of the previous cycle in each iteration cycle, the final iteration result will not cause large deviation.
Equation (16) is written as an expression of the equation of state:
discretization of formula (17) yields formula (5).
As can be seen from the formula (5), the speed and the position at the next moment can be predicted only by knowing the value of the thrust vector of the engine and combining the current speed and position, and the ideal predicted value can be obtained by sufficiently taking the value of the thrust vector of the engine.
In a preferred embodiment of the present invention, the iterative guidance method based on gray prediction may further include: determining a velocity vector at a next timeAnd position vectorWhether a terminal condition is satisfied; if yes, ending; if not, returning iteration until the predicted speed vector and the predicted position vector meet the terminal condition.
Preferably, whenOrAnd then, determining that the predicted speed vector and the predicted position vector meet the terminal condition. Wherein the content of the first and second substances,a vector representing the desired speed of shutdown is shown,indicating a desired shutdown position vector.
Preferably, if the predicted speed vector and the predicted position vector do not satisfy the terminal condition after p iterations, the pairThe initial value is corrected in small steps of 0.01 times until the requirement is met. Wherein pT > TThreshold value,TThreshold valueIndicating setting an iteration threshold time.
Example 2
On the basis of the above embodiment, the present invention also discloses an iterative guidance system based on gray prediction, which includes:
the accumulation module is used for carrying out primary accumulation on the sampling sequence to obtain a primary accumulation sequence:
a sequence reduction module for performing sequence reduction according to formula (1) and formula (2) to obtain:
a whitening equation set determination module for obtaining a whitening equation set according to equation (3):
and the parameter solving module is used for solving by a least square method to obtain the values of a and b.
A thrust vector predicting module for predicting the engine thrust vector at the next moment according to the values of a and b obtained by solving and the combination formula (3)
A speed position prediction module for predicting the engine thrust vector at the next momentSubstituting the speed and position solution formula (5) to predict the speed vector at the next momentAnd position vector
For the system embodiment, since it corresponds to the method embodiment, the description is relatively simple, and for the relevant points, refer to the description of the method embodiment section.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.
Those skilled in the art will appreciate that the invention may be practiced without these specific details.
Claims (8)
1. An iterative guidance method based on gray prediction is characterized by comprising the following steps:
wherein n represents the length of the sampling sequence, n is 1, 2, 3, …, T, and T represents the iteration period;
performing primary accumulation on the sampling sequence to obtain a primary accumulation sequence:
sequence reduction according to formula (1) and formula (2) gives:
wherein k is more than or equal to 1 and less than or equal to n;
obtaining a whitening equation set according to the formula (3):
wherein, a represents a development coefficient, and b represents a gray effect amount;
solving by a least square method to obtain values of a and b;
according to a and obtained by solvingb value, in conjunction with equation (3), the engine thrust vector at the next time is predicted
The predicted engine thrust vector at the next momentSubstituting the speed and position solution formula (5) to predict the speed vector at the next momentAnd position vector
3. Iterative guidance method based on grey prediction according to claim 2, characterized in that the engine thrust vector at the next moment is predicted according to the values of a and b obtained by solving, in combination with equation (3)The method comprises the following steps:
solving the differential equation yields:
will be provided withAs an initial value for solving the differential equation (10), formula (10) is substituted for formula (3) to obtain formula (11):
wherein j represents the j prediction, and the values of j are n +1, n +2 and … …;
4. The iterative guidance method based on gray prediction of claim 1, wherein equation (5) is determined by:
determining a mass center motion equation outside the atmosphere of the active section of the rocket:
wherein:
wherein, W represents the apparent acceleration,which represents the gravitational force of the earth,the velocity vector is represented by a vector of velocities,the position vector is represented by a vector of positions,representing the nozzle swing angle in the pitching direction of the engine, and psi representing the nozzle swing angle in the yawing direction of the engine;
the centroid radial size of any point of the active segment can be expressed as:
r=rc+Δr…·(14)
wherein Δ r represents a high-order term;
will accelerate the gravitational forceIn thatUnfolding and omitting high-level items to obtain an average gravitational acceleration as follows:
and (3) carrying the simplified gravitation item into formula (12), and obtaining a simplified motion equation as follows:
equation (16) is written as an expression of the equation of state:
discretization of formula (17) yields formula (5).
5. The iterative guidance method based on gray prediction of claim 1, further comprising:
determining a velocity vector at a next timeAnd position vectorWhether a terminal condition is satisfied;
if yes, ending; if not, returning iteration until the predicted speed vector and the predicted position vector meet the terminal condition.
6. The iterative guidance method based on gray prediction of claim 5,
when in useOrDetermining that the predicted speed vector and the predicted position vector meet the terminal condition;
7. The iterative guidance method based on gray prediction of claim 5, further comprising:
if the predicted speed vector and the predicted position vector do not meet the terminal condition after iteration for p times, then the pairCorrecting the initial value by small step length of 0.01 times until the requirement is met;
wherein pT > TThreshold value,TThreshold valueIndicating setting an iteration threshold time.
8. An iterative guidance system based on gray prediction, comprising:
wherein n represents the length of the sampling sequence, n is 1, 2, 3, …, T, and T represents the iteration period;
the accumulation module is used for carrying out primary accumulation on the sampling sequence to obtain a primary accumulation sequence:
a sequence reduction module for performing sequence reduction according to formula (1) and formula (2) to obtain:
wherein k is more than or equal to 1 and less than or equal to n;
a whitening equation set determination module for obtaining a whitening equation set according to equation (3):
wherein, a represents a development coefficient, and b represents a gray effect amount;
the parameter solving module is used for solving by a least square method to obtain values of a and b;
a thrust vector predicting module for predicting the engine thrust vector at the next moment according to the values of a and b obtained by solving and the combination formula (3)
A speed position prediction module for predicting the engine thrust vector at the next momentSubstituting the speed and position solving formula (5) to predict the next timeVelocity vector of the momentAnd position vector
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