A control method for dual target points of heliostats in a tower solar thermal mirror field

Abstract

The present invention relates to the field of heliostat control, and discloses a control method for dual target points of heliostats in a tower-type solar thermal mirror field, including the following steps: determining the coordinates of two target points of each heliostat; under the condition of meeting the limiting conditions, establishing a 0-1 integer linear programming model with the goal of achieving the maximum power by selecting the target points of each heliostat; using the implicit enumeration algorithm to solve the above model to obtain the optimal solution of the target point selection of each heliostat at this moment; calculating the target points of the heliostats at all moments by the above method, and then performing real-time control on the heliostats through the mirror field control system. The control method disclosed by the present invention can adjust the target points of the heliostats in real time, so that the power of the heat absorber reaches the maximum, with simple calculation, flexible control and high efficiency.

Description

Technical Field

[0001] The present invention relates to the field of heliostat control, and particularly to a control method for dual target points of heliostats in a tower-type solar thermal mirror field. Background Art

[0002] Tower-type solar thermal power generation not only has the advantage of low power generation cost. Compared with photovoltaic power generation, tower-type solar thermal power generation can achieve continuous 24-hour power generation. As Figure 1 shown, the principle of tower-type solar thermal power generation is that first, thousands of heliostats 1 are arranged around the absorber tower 3 in different geometric shapes, and a large amount of low-density solar energy 4 is reflected onto the absorber 2 at the top of the absorber tower 3 to become high-density solar energy, and then converted into working medium heat energy. At the same time, tower-type solar thermal technology can be used for oil extraction, hydrogen production, etc. Therefore, tower-type solar thermal technology is becoming more and more popular.

[0003] The tower-type solar thermal system mainly consists of a concentrating system, a heat collection system, a calibration system, and a control system. Among them, the control system is the most complex and also the most critical part, which connects the concentrating system and the heat collection system in series. The control system is further divided into modules such as preheating, production, salt filling, and salt drainage. Among them, the most critical is the production module, which calculates which heliostats should track the sun through which target points of the heliostats, so as to most effectively reflect sunlight onto the absorber.

[0004] In the tower-type solar thermal system, the target points of the heliostats are not unique. There can be multiple target points for the heliostats. The advantage of multiple target points is that they are more flexible and can achieve maximum efficiency. The target points selected by the heliostats can be different at different times. Therefore, for each heliostat, how to set different target points and which target point to select at a certain moment becomes particularly important.

[0005] The existing selection of the target points of the heliostats is through a method based on the arrangement of large and small light spots. The target point of the large light spot is specified at the center of the absorber, and the small light spots are randomly distributed on the upper and lower sides of the absorber. If some areas are overheated, the corresponding heliostats are removed and placed in the non-overheated area corresponding to the symmetric target point. This method has disadvantages such as only satisfying local optimality but not achieving global optimality and being difficult to control. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a control method for dual target points of heliostats in a tower-type solar thermal mirror field, so as to achieve the purpose of being able to adjust the target points of the heliostats in real time and maximize the power of the absorber.

[0007] To achieve the above purpose, the technical solution of the present invention is as follows:

[0008] A control method for dual target points of heliostats in a tower-type solar thermal mirror field, comprising the following steps:

[0009] Step 1: Determine the coordinates of two target points for each heliostat.

[0010] Step 2: Establish a 0-1 integer linear programming model:

[0011] Let x i be whether the first target point is used by heliostat i at a certain moment. If x i = 0, it means that heliostat i uses the second target point at this moment; if x i = 1, it means that heliostat i uses the first target point at this moment. Combining the power values reflected by heliostat i onto the heat absorption panel through the first or second target point at this moment, establish the following 0-1 integer linear programming model:

[0012]

[0013] s.t. x i = 0 or 1

[0014] where M represents the total number of heliostats in the mirror field, and the objective function f refers to achieving the maximum power by selecting the target points of each heliostat under the satisfaction of the constraint conditions; p i1 is the power value when heliostat i reflects sunlight onto the heat absorption panel through the first target point at a certain moment, and p i2 is the power value when heliostat i reflects sunlight onto the heat absorption panel through the second target point at a certain moment.

[0015] Step 3: Use the implicit enumeration algorithm to solve the above model to obtain the optimal solution (x1, x2,..., x M ) of the target point selection for each heliostat at this moment, where x M represents the target point selection result of the Mth heliostat at this moment.

[0016] Step 4: Calculate the target points of the heliostats at all moments using the methods in Step 2 to Step 3, and then perform real-time control on the heliostats through the mirror field control system.

[0017] In the above solution, the specific method of Step 1 is as follows:

[0018] (1) Determine the X coordinate and Y coordinate of each heliostat target point:

[0019] Establish a plane rectangular coordinate system with the center of the heat absorber as the coordinate origin. Assume that the heat absorber is a regular N-prism with a prism side length of L and a height of S; first, find the circumscribed circle corresponding to the projection of the target point (x, y) on the heat absorber in the horizontal plane, and establish the following equation:

[0020]

[0021] For the i-th heliostat (hx i , hy i , hz i ), the equation of the line connecting the heliostat and the center of the receiver tower is as follows:

[0022]

[0023] Solve the following system of equations simultaneously:

[0024]

[0025] The X and Y coordinates of the target point of the i-th heliostat are obtained by solving:

[0026]

[0027]

[0028] (2) Determine the Z coordinate of each heliostat target point:

[0029] According to the principle of maximum overflow efficiency, determine the Z coordinates of the two target points of the i-th heliostat:

[0030]

[0031] where h is the height of the receiver tower center, and fs i is the diameter of the light spot formed by the i-th heliostat on the receiver panel in the vertical direction;

[0032]

[0033] where r i is the horizontal distance from the center of the heliostat to the center of the receiver tower, and θ i is the angle formed by the line connecting the center of the heliostat to the center of the light spot and the horizontal plane;

[0034]

[0035]

[0036] Through the above technical solution, a control method for double target points of heliostats in a tower-type solar thermal mirror field provided by the present invention has the following beneficial effects:

[0037] 1. The double target point control strategy of the invention, due to the adoption of 0-1 integer linear programming, has the characteristics of simple calculation and fast response, and is particularly suitable for the control of tower-type solar thermal mirror fields, enabling the heliostat to perform feedback in a very short time (the optimal solution can be obtained within a few seconds, and it only takes 1 to 2 minutes for the final response of the heliostat to be completed), and ensuring that the global optimum is achieved at each moment.

[0038] 2. The two - target - point control method of the heliostat of the present invention adopts a setting method that separates the horizontal (XY coordinates) and vertical (Z coordinates). The advantage is that the control method is simple and the horizontal and vertical directions do not affect each other.

[0039] 3. Based on the integer - linear - programming mathematical model, the present invention can more scientifically and rigorously perform the multi - target - point control strategy of the heliostat, so as to achieve the global - optimal effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art.

[0041] Figure 1 It is a schematic diagram of a tower - type solar thermal mirror field;

[0042] Figure 2 It is a flowchart of a control method for the two - target - points of the heliostat in a tower - type solar thermal mirror field disclosed by the present invention;

[0043] Figure 3 It is a schematic diagram of the plane rectangular coordinate system established between the heliostat and the heat absorber;

[0044] Figure 4 It is a schematic diagram of the spot diameter formed by the heliostat;

[0045] Figure 5 It is a schematic diagram of the positions of the two target points of the heliostat.

[0046] In the figure, 1. Heliostat; 2. Heat absorber; 3. Heat - absorption tower; 4. Sun; 5. Heat - absorption panel. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention.

[0048] The present invention provides a control method for the two - target - points of the heliostat in a tower - type solar thermal mirror field, as Figure 2 shown, including the following steps:

[0049] Step 1: Determine the coordinates of the two target points of each heliostat;

[0050] (1) Determine the X - coordinate and Y - coordinate of the target point of each heliostat 1:

[0051] According to the principle of the shortest distance, the horizontal distance from each heliostat to the target point is the shortest distance from each heliostat to the heat - absorption tower.

[0052] As Figure 3As shown, a plane rectangular coordinate system is established with the center of the absorber 2 as the origin. Assume that the absorber 2 is a regular N-shaped prism with a side length of L and a height of S. First, the circumscribed circle corresponding to the projection of the target point (x, y) on the absorber on the horizontal plane is obtained, and the following equation is established:

[0053]

[0054] For the i-th heliostat (hx i ,hy i ,hz i ), the line equation between the heliostat and the center of the heat absorption tower (0,0) is as follows:

[0055]

[0056] Solve the following system of equations:

[0057]

[0058] Solve to obtain the X and Y coordinates of the target point of the i-th heliostat:

[0059]

[0060]

[0061] (2) Determine the Z coordinate of each heliostat target point:

[0062] According to the maximum spillover efficiency principle (i.e., the larger the spot formed by the heliostat on the absorber, the closer the target point is to the center of the absorber panel 5), the Z coordinates of the two target points of the i-th heliostat are determined:

[0063]

[0064] Where, h is the center tower height of the absorber, fs i is the diameter of the light spot formed by the i-th heliostat on the heat absorption panel 5 in the vertical direction;

[0065] like Figure 4 As shown in the figure, through simulation experiment (assuming that the center of the heat absorption tower is at the center origin of the mirror field), the heliostat coordinates (hx i ,hy i ,hz i ), the diameter of the light spot in the vertical direction is fs i , the central tower height h of the heat absorber, and other data, and the diameter fs of the light spot formed by the heliostat i reflecting the sun's light onto the heat absorber in the vertical direction is obtained by nonlinear regression method. i and the heliostat position (hx i ,hy i ,hz i) Relationship with the height h of the heat absorption tower 3:

[0066]

[0067] Among them, r i is the horizontal distance from the center of the heliostat to the center of the heat absorption tower, and θ i is the angle formed by the straight line from the center of the heliostat to the center of the light spot and the horizontal plane;

[0068]

[0069]

[0070] Therefore, as Figure 5 shown, the two target points of each heliostat are respectively:

[0071] The 1st target point A:

[0072]

[0073] The 2nd target point B:

[0074]

[0075] Step 2, establish a 0-1 integer linear programming model:

[0076] Let x i be whether the 1st target point is used by the heliostat i at a certain moment. If x i = 0, it indicates that the heliostat i uses the 2nd target point at this moment; if x i = 1, it indicates that the heliostat i uses the 1st target point at this moment; combined with the power value reflected by the heliostat i to the heat absorption panel 5 through the 1st or 2nd target point at this moment, the following 0-1 integer linear programming model is established:

[0077]

[0078] s.t. x i = 0 or 1

[0079] Among them, M represents the total number of heliostats in the mirror field, and the objective function f refers to achieving the maximum power by selecting the target points of each heliostat under the condition of meeting the constraints; p i1 is the power value when the heliostat i reflects the sunlight to the heat absorption panel 5 through the 1st target point at a certain moment, and p i2 is the power value when the heliostat i reflects the sunlight to the heat absorption panel 5 through the 2nd target point at a certain moment; the power value can be calculated according to the light path tracing method, which is the prior art and will not be elaborated here.

[0080] Step 3: Use the implicit enumeration algorithm to solve the above model to obtain the optimal solution (x1, x2, …, x M ) of the target point selection of each heliostat at this moment, where x M represents the target point selection result of the Mth heliostat at this moment;

[0081] The implicit enumeration algorithm is the most common and efficient algorithm for solving the 0-1 integer linear programming model. It performs pruning by comparing branches and upper and lower bounds, and does not require listing all solutions for calculation, greatly reducing the computational amount.

[0082] Step 4: Use the methods in Step 2 to Step 3 to calculate the target points of the heliostats at all moments, and then perform real-time control on the heliostats through the mirror field control system.

[0083] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for dual target points of heliostats in a tower-type solar thermal mirror field, characterized in that, It includes the following steps: Step 1: Determine the coordinates of two target points of each heliostat. Step 2: Establish a 0-1 integer linear programming model: Let be whether the heliostat \(i\) uses the first target point at a certain moment. If , it indicates that the heliostat \(i\) uses the second target point at this moment; if , it indicates that the heliostat \(i\) uses the first target point at this moment. Combining the power value reflected by the heliostat \(i\) to the heat absorption panel through the first or second target point at this moment, the following 0-1 integer linear programming model is established: ； s.t. ; Among them, represents the total number of heliostats in the mirror field, and the objective function means that, under the satisfaction of the limiting conditions, the maximum power is achieved by selecting the target points of each heliostat. is the power value when the sunlight is reflected by the i-th heliostat through the first target point onto the heat absorption panel at a certain moment, is the power value when the sunlight is reflected by the i-th heliostat through the second target point onto the heat absorption panel at a certain moment; Step 3: Use the implicit enumeration algorithm to solve the above model to obtain the optimal solution for the target point selection of each heliostat at this moment , represents the target point selection result of the Mth heliostat at this moment; Step 4: Calculate the target points of the heliostats at all times by using the methods in Step 2 to Step 3, and then perform real-time control on the heliostats through the mirror field control system. The specific method of Step 1 is as follows: (1) Determine the X coordinate and Y coordinate of each heliostat target point: Establish a plane rectangular coordinate system with the center of the receiver as the coordinate origin. Assume that the receiver is a regular N-prism with a prism side length of L and a height of S; first, find the circumcircle corresponding to the projection of the target point (x, y) on the receiver in the horizontal plane, and establish the following equation: ； For the i-th heliostat , the equation of the line connecting the heliostat and the center of the receiver tower is as follows: ； Simultaneously solve the following system of equations: ； Solve to obtain the X coordinate and Y coordinate of the target point of the i-th heliostat: ； ； (2) Determine the Z coordinate of each heliostat target point: According to the principle of maximum overflow efficiency, determine the Z coordinates of the two target points of the i-th heliostat: ； Among them, is the height of the central tower of the receiver, is the diameter in the vertical direction of the light spot formed by the i-th heliostat on the heat absorption panel; ； Among them, is the horizontal distance from the center of the heliostat to the center of the receiver tower, is the angle formed by the straight line from the center of the heliostat to the center of the light spot and the horizontal plane; ； 。

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