Tower type heliostat defocus path determination method

Abstract

This invention discloses a method for determining the defocusing path of a tower-type solar thermal heliostat, belonging to the field of solar thermal power generation technology. The invention establishes a coordinate system to calculate the intersection point of the reflected light from the heliostat and the receiver plane, as well as the radial distance of the light spot. The defocusing process is discretized into multiple time steps, and a multi-objective optimization model is constructed using the mirror normal of each heliostat at each time step as the optimization variable. Constraints are set for the final light spot leaving the receiver and for the reflected light to avoid the tower throughout the process. The optimal mirror normal sequence is obtained by solving the model and then converted into pitch and azimuth angles to drive the heliostat to perform defocusing. This invention enables safe, accurate, and rapid defocusing of the heliostat, ensuring that the receiver tower is not illuminated throughout the defocusing process. Heat flow distribution is controllable, and movement is smooth. It is applicable to various operating conditions such as receiver overheating, cloud transients, load fluctuations, and start-up / shutdown, significantly improving the operational safety and intelligence level of tower-type solar thermal power plants.

Description

Technical Field

[0001] This invention belongs to the field of solar thermal power generation technology, and specifically relates to a method for determining the defocusing path of a tower-type solar thermal heliostat. Background Technology

[0002] In tower-type concentrated solar power (CSP) systems, heliostats arranged in a specific geometric shape typically employ dual-axis solar tracking control. The control system calculates the pitch and azimuth angles of each heliostat at a given moment based on the real-time solar altitude and azimuth angles and the current attitude of the heliostats. It then drives the azimuth and pitch axes to rotate synchronously, adjusting the mirror attitude in real time. Through precise reflection angle control, sunlight is directionally reflected and focused onto the receiver at the top of the tower, continuously stabilizing the position of the light spot and achieving precise focusing throughout the day. This ensures continuous solar and thermal input, thereby enabling efficient solar-thermal and photovoltaic conversion.

[0003] In the operation of tower solar thermal power plants, when the receiver faces risks such as overheating, transient cloud disturbances, insufficient molten salt flow, sudden load drops, or is in the process of startup / shutdown, it is necessary to coordinate the defocusing of thousands of heliostats. This involves controlling the heliostats to deviate from their ideal focusing posture, ensuring that the reflected light spot completely leaves the effective area of ​​the receiver and does not illuminate prohibited areas such as the tower, supports, and cable trays. Simultaneously, it is crucial to ensure smooth and continuous mirror movement, not exceeding actuator capacity, controllable heat flux distribution across the entire field, and the absence of localized hot or cold spots. The defocusing process requires reasonable timing, low energy consumption, and repeatability, ultimately causing the light spot to leave or partially leave the receiver, rapidly and smoothly reducing heat flux density and preventing damage to the receiver.

[0004] Current commercial tower solar thermal power plants generally employ a heuristic defocusing strategy of radially proportional outward offset, where all heliostats are uniformly offset radially by the same proportion to achieve light spot diffusion. This method does not fully consider the differences in the spatial position, distance, and arrangement of the mirrors, easily leading to problems such as uneven heat flow distribution and overshoot of adjustment. Specifically, the light spot is easily projected onto the receiver tower body; multi-mirror coordinated defocusing induces local hot spots in the receiver; sudden changes in mirror attitude exacerbate wear on the drive mechanism; and it is difficult to achieve coordinated optimization of heat flow across the entire field. Furthermore, existing methods typically only ensure that the light spot is far away from the receiver at the final moment, failing to guarantee that reflected light does not illuminate the receiver tower throughout the defocusing process, posing a safety hazard.

[0005] Therefore, there is an urgent need for a method to determine the defocusing path of heliostats that can comprehensively consider the differences in the mirror field space, the safety constraints of tower avoidance throughout the entire process, and the smoothness of motion, so as to improve the operational safety and intelligent control level of tower solar thermal power plants. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for determining the defocusing path of a tower-type photothermal heliostat, achieving safe, accurate, and rapid defocusing while avoiding the tower throughout the entire process.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A method for determining the defocusing path of a tower-type photothermal heliostat includes the following steps: Step 1: Establish a coordinate system, including a geodetic coordinate system and a local coordinate system for the receiver; Step 2: According to the law of reflection, calculate the intersection point of the reflected light from the heliostat and the plane of the absorber to obtain the radial distance of the center of the light spot on the tangential plane of the absorber. This radial distance is determined by the normal vector of the heliostat's mirror surface. Step 3: Discretize the defocusing process into multiple time steps, and construct a multi-objective optimization model using the mirror normal of each heliostat at each time step as the optimization variable. The optimization objective of the model is to minimize the weighted sum of the thermal contribution index and the motion smoothness index. The thermal contribution index refers to the sum of the thermal contribution values ​​at each time step when the radial distance is less than the equivalent radius of the receiver, weighted by time. The motion smoothness index refers to the sum of the squares of the changes in the mirror normal at adjacent time steps. The constraints of the model include: the radial distance of each heliostat at the final time step is not less than the sum of the equivalent radius of the receiver and the safety margin, and the distance from the horizontal projection of the reflected light from each heliostat at all time steps to the center of the tower is greater than the radius of the receiver tower. Step 4: Solve the optimization model to obtain the optimal mirror normal sequence for each heliostat at each time step, which serves as the defocusing path; Step 5: Convert the optimal mirror normal sequence into the pitch and azimuth angles of each heliostat at each time step, which are used to drive the heliostat to perform defocusing.

[0008] In the above scheme, the thermal contribution value is specifically defined as: ; in, The radial distance from the center of the light spot to the tangential plane of the absorber. Let be the equivalent radius of the heat absorber. Thermal contribution value.

[0009] In the above scheme, the time weights are an increasing sequence, which gives higher weight to the time steps in the later stages of defocusing.

[0010] In the above scheme, the weighting coefficients of the weighted sum are adjusted according to the operating conditions: under emergency shutdown or over-temperature conditions, the weight of the thermal contribution index is much greater than the weight of the motion smoothness index.

[0011] In the above scheme, the safety margin is between 0.5 meters and 1.0 meters.

[0012] In the above scheme, the intersection point of the reflected ray and the heat absorber plane is calculated as follows: ; ; in, Let these be the coordinates of the intersection point. The center position of the heliostat. Let be the distance parameter along the reflected ray. The vector of the reflected ray. The center position of the heat absorber is the normal vector of the absorber plane.

[0013] In the above scheme, the radial distance is calculated as follows: the difference vector between the intersection point and the center of the absorber is projected onto two orthogonal directions of the tangential plane of the absorber, and then the square root of the sum of the squares of the two projected components is calculated: ; ; ; in, Let be the intersection point of the reflected ray from the i-th heliostat and the plane of the absorber. Relative to the center of the absorber The projection component of the offset in the X-axis direction of the local coordinate system of the receiver. The projection component along the Y-axis is... Let be the coordinates of the intersection point of the reflected ray and the plane of the absorber. The coordinates of the receiver center are: and Let be two orthogonal unit direction vectors on the tangential plane of the receiver. It is the radial distance of the center of the light spot on the tangential plane of the absorber.

[0014] In the above scheme, the optimization model is solved using the interior point method or the IPOPT solver.

[0015] In the above scheme, the specific method for converting the mirror normal into pitch and azimuth angles is as follows: ; ; in, and Heliostats exist The corresponding pitch and azimuth angles at each moment These are the mirror normal directions. The X, Y, and Z components.

[0016] Through the above technical solution, the defocusing path determination method for a tower-type photothermal heliostat provided by the present invention has the following beneficial effects: 1. High safety, with tower avoidance throughout the entire process. This invention introduces a full-process tower avoidance constraint into the optimization model, requiring that the horizontal projection of reflected light from each heliostat at all discrete moments during the defocusing process be outside the radius of the heat absorber tower. Compared with existing technologies that only ensure the final light spot leaves the heat absorber but cannot guarantee that the intermediate process does not irradiate the tower body, this invention fundamentally eliminates the safety hazard of the light spot irradiating the heat absorber tower body, support frame, and cable tray during the defocusing process.

[0017] 2. Controllable heat flow distribution, avoiding localized hot spots. This invention minimizes the thermal contribution index and quantitatively controls the radial distance of the light spot of each heliostat at different times, so that the process of the light spot leaving the receiver is smooth and orderly. This avoids the problem of uneven heat flow distribution or local hot spots caused by the uniform radial offset ratio when multiple mirrors defocus together. The overall heat flow density can be predicted and adjusted.

[0018] 3. Smooth movement, reducing mechanical wear. This invention incorporates the sum of squares of the changes in the mirror normal in adjacent time steps as a smoothness index into the optimization objective. This effectively suppresses abrupt changes in mirror attitude, ensuring that the azimuth and pitch axes of the heliostat move continuously and smoothly, without exceeding the actuator's capability range. This reduces wear on the drive mechanism and extends the equipment's lifespan.

[0019] 4. Fast response, adaptable to various working conditions This invention discretizes the defocusing process into a finite-time optimal control problem and solves it using an efficient nonlinear programming solver (such as the interior-point method or IPOPT). This allows for the acquisition of time-optimal or near-time-optimal defocusing paths while satisfying constraints. Furthermore, the weighting coefficients of the thermal contribution index and the smoothness index can be dynamically adjusted according to different operating conditions such as emergency shutdown, overheating, sudden load drops, and start-up / shutdown, enabling customized strategies and strong applicability.

[0020] 5. Global optimization enhances the intelligence level of the mirror field. This invention is based on a mathematical optimization model, which takes into account global information such as the spatial position of all heliostats in the mirror field, the trajectory of reflected light rays, the geometry of the receiver, and the size of the tower. It outputs a differentiated defocus path for each heliostat, which overcomes the blindness and overshoot problem of the traditional unified radial offset method. It provides core algorithm support for the intelligent operation and maintenance and intelligent control of tower solar thermal power plants. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0022] Figure 1 This is a schematic flowchart of a method for determining the defocusing path of a tower-type photothermal heliostat disclosed in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of a heliostat focusing (working). Figure 3 This is a schematic diagram of a heliostat in defocus.

[0024] In the diagram, 1 is the heat absorption tower; 2 is the heat absorber; and 3 is the heliostat. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0026] This invention provides a method for determining the defocusing path of a tower-type photothermal heliostat, such as... Figure 1 As shown, it includes the following steps: I. Establishment of Coordinate System This embodiment uses a tower-type solar thermal power plant as an example. The heliostat field is arranged on the north side of the absorber tower 1, including M heliostats 3 (M≥1000). Normally, when the heliostats 3 are focusing, as shown... Figure 2 As shown, firstly, a geodetic coordinate system and a local coordinate system for receiver 2 are established.

[0027] The origin of the geodetic coordinate system is set at the center of the base of the heat absorber tower 1: the X-axis points due east, the Y-axis points due north, and the Z-axis points to the zenith. The center positions of all heliostats 3, the center positions of receivers 2, and the solar direction vector are represented in this coordinate system. For example, the center position of a certain heliostat i is denoted as... The center position of heat absorber 2 is denoted as (The center of the tower base is X=0, Y=0, Z=0).

[0028] The origin of the local coordinate system of receiver 2 is located at the geometric center of the receiver. Its Z-axis is along the normal of receiver 2 Pointing towards the centroid of the mirror field (in this embodiment) (i.e., due north). The X-axis is horizontal (east-west direction), obtained by normalizing the cross product of the zenith vector and the normal vector: ,in The Y-axis is the vertical direction, from... Sure( This coordinate system is used to describe the offset of the light spot on the tangential plane of the absorber.

[0029] II. Calculation of the radial distance between the reflected ray and the center of the light spot For any heliostat i, at time t, the solar direction vector is known. (From the mirror surface towards the sun) and the current mirror normal vector (Variables to be optimized) According to the law of vector reflection, the vector of the reflected ray is: ;

[0030] This formula represents the incident ray (- The direction of emission after reflection by the mirror.

[0031] The receiver is modeled as a plane (actually a prism, but approximated as a plane in the calculation of the light spot center), and its plane equation is: The intersection of the reflected light rays and the plane of the absorber. We obtain the following by finding the intersection of the line and the plane: ; ; in, This is the distance parameter along the reflected ray. The intersection point is the position of the center of the light spot on the absorber (assuming the heliostat is an ideal point reflector).

[0032] Project the difference vector between the intersection point and the center of the receiver onto two orthogonal bases of the receiver's tangent plane. Above, we obtain the two-dimensional offset: ; ; in, Let be the intersection point of the reflected ray from the i-th heliostat and the plane of the absorber. Relative to the center of the absorber The projection component of the offset in the X-axis direction of the local coordinate system of the receiver. The projection component along the Y-axis is... Let be the coordinates of the intersection point of the reflected ray and the plane of the absorber. The coordinates of the receiver center are: and These are two orthogonal unit direction vectors on the tangential plane of the absorber.

[0033] The radial distance of the light spot center on the tangential plane of the absorber for: ; This radial distance directly reflects whether the light spot falls within the effective area of ​​the absorber: if (Equivalent radius of the absorber, such as the radius of its circumscribed circle), then the light spot may partially or completely illuminate the absorber; if Then the light spot has completely left the absorber.

[0034] III. Optimization Modeling of Defocus Path The entire defocusing process is considered as a finite-time optimal control problem. Let the upper limit of the total defocusing time be T (e.g., 5 seconds), and divide T evenly into N time steps (e.g., N=10), with a step size of... Discrete time is denoted as ,in This is the moment when defocusing begins (when the heliostat is in its normal focusing position). This is the moment when defocusing ends.

[0035] Define optimization variables: For each heliostat i (i=1,2,…,M) and each discrete time k (k=0,1,2,…,N), introduce the mirror normal vector. .Notice The initial focusing normal is known (given by the sun-tracking algorithm) and requires no optimization; the actual optimization variable is... .

[0036] Construct the following multi-objective optimization model: The optimization objective is to minimize the weighted sum: , in: This is a thermal contribution index, measuring the cumulative thermal contribution of all heliostats to the receiver during defocusing. Its calculation method is as follows: ; ; in, As a time weight, it is set as an increasing sequence in this embodiment: This results in a higher penalty for the heat contribution during the later stages of defocusing (when k is larger), thus forcing the light spot to leave the receiver as quickly as possible. (Function) Approaching 0 when D is close to 0 , in D= When D equals 1, and D is slightly greater than 1. The heat contribution drops rapidly to 0, reflecting the physical fact that the heat contribution tends to zero when the light spot just leaves the absorber.

[0037] This is a motion smoothness index that penalizes drastic changes in the mirror normal to prevent excessive impact on the heliostat drive mechanism. The calculation formula is: ; This expression represents the square of the Euclidean norm of the difference between the normal vectors of adjacent time steps. By minimizing... This makes the defocus path smooth and continuous.

[0038] Weighting coefficient and It is a positive number and can be adjusted according to specific operating conditions. For example, it can be set to [value] during an emergency shutdown due to receiver overheating. It emphasizes rapidly reducing heat contribution; under normal load regulation and with high requirements for mechanical life, it can be set to... This ensures smooth movement.

[0039] Constraints: Finally, the light spot leaves the receiver constraint: for each heliostat i, at the last discrete time... The radial distance from the center of the light spot must be greater than the equivalent radius of the receiver plus a safety margin to ensure that the light spot completely leaves the receiver with sufficient margin. ;

[0040] In this embodiment (Equivalent radius of the heat absorber). This requires a final radial distance of at least 4.8 meters.

[0041] Full-process tower avoidance constraint: For each heliostat i and each discrete time k, the reflected ray vector The horizontal projection (i.e., the XY components) must satisfy: ; in, for The X and Y components, The radius of the heat absorption tower (in this embodiment) This constraint ensures that reflected light does not point towards the tower, thus preventing light spots from illuminating prohibited areas such as the tower body and cable trays.

[0042] Furthermore, the mirror normal vector must be a unit vector, i.e. This is an implicit constraint, and the unit vector parameterization should be used directly in the optimization variable representation (e.g., represented by pitch and azimuth angles, or using spherical coordinates).

[0043] IV. Model Solving The above optimization model belongs to nonlinear programming (NLP), with a variable size of . (Each normal has three components). For a typical scale of a thousand-faceted heliostat with N=10, the number of variables is approximately 30,000, and the number of constraints is approximately... This is a medium-sized NLP problem and can be solved using the interior point method or the open-source solver IPOPT.

[0044] The specific solution steps are as follows: Initialization: Set the initial values ​​of the mirror normals of each heliostat at each discrete time as the initial focusing normals. A simple linear extrapolation (e.g., keeping it unchanged) or a radial offset method can be used to generate an initial solution.

[0045] Call the IPOPT solver and set an appropriate tolerance (e.g., 1e-6) and maximum number of iterations (e.g., 5000).

[0046] The solver outputs the optimal solution, which is the optimal mirror normal vector for each heliostat i at each discrete time k. .

[0047] If the solution time is too long or convergence is difficult, the value of N can be reduced (e.g., N=5), or a decomposition strategy can be adopted (solve the time direction first, then the spatial direction), or distributed optimization can be used.

[0048] 5. Convert to pitch and azimuth angles After obtaining the optimal mirror normal sequence, it needs to be converted into elevation and azimuth angles that the heliostat control system can directly execute. The conversion formula is: ; ; in, and Heliostats exist The corresponding pitch and azimuth angles at each moment These are the mirror normal directions. The X, Y, and Z components. Note: When When approaching 0, the pitch angle approaches 0°, and the mirror surface approaches horizontal; when When the angle approaches 1, the pitch angle approaches 90°, and the mirror faces upwards.

[0049] VI. Perform defocusing The calculated pitch angle sequence and azimuth sequence According to time step The commands are sequentially sent to the heliostat drive controller. The controller drives the azimuth and pitch motors in either position or velocity mode, ensuring the heliostat smoothly moves to the target attitude within each time step, such as... Figure 3 As shown, since the optimization objective already includes a smoothness penalty, the attitude changes between adjacent time steps are small, and the motor acceleration and velocity are both within the allowable range, avoiding overshoot and oscillation.

[0050] VII. Examples of Working Condition Adaptation The parameters in the optimization model can be dynamically adjusted based on the power plant's operating status. Emergency Over-Temperature Shutdown: Setting Time weight Using exponential increment (e.g.) The forced light spot leaves the absorber within 1-2 seconds.

[0051] Cloud transient disturbance: settings The thermal contribution weight should be appropriately relaxed to maintain a certain smoothness and avoid frequent and large-scale movements of the heliostat.

[0052] Low load adjustment: setting Prioritizing smooth motion and mechanical lifespan allows for slower defocusing speeds.

[0053] Startup / Shutdown Process: Settings To balance safety and efficiency.

[0054] VIII. Verification of Implementation Results This method was used to simulate a 100MW tower-type solar thermal mirror field containing 25,600 heliostats, with a total defocusing time of T=10 seconds and N=20. Comparison with the traditional radial proportional offset method: In traditional methods, approximately 12% of heliostats experience scattering of reflected light during defocusing, and the peak local heat flux density of the receiver exceeds the safety threshold (>300kW / m²). 2 ).

[0055] Using the method of this invention, no heliostat reflected light hits the tower throughout the entire process, and the radial distance of all light spots is ultimately greater than [missing information]. The thermal contribution index is reduced by 95%, the motion smoothness index is improved by 60%, and the peak torque of the drive motor is reduced by 40%.

[0056] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for determining the defocusing path of a tower-type photothermal heliostat, characterized in that, Includes the following steps: Step 1: Establish a coordinate system, including a geodetic coordinate system and a local coordinate system for the receiver; Step 2: According to the law of reflection, calculate the intersection point of the reflected light from the heliostat and the plane of the absorber to obtain the radial distance of the center of the light spot on the tangential plane of the absorber. This radial distance is determined by the normal vector of the heliostat's mirror surface. Step 3: Discretize the defocusing process into multiple time steps, and construct a multi-objective optimization model using the mirror normal of each heliostat at each time step as the optimization variable. The optimization objective of the model is to minimize the weighted sum of the thermal contribution index and the motion smoothness index. The thermal contribution index refers to the sum of the thermal contribution values ​​at each time step when the radial distance is less than the equivalent radius of the receiver, weighted by time. The motion smoothness index refers to the sum of the squares of the changes in the mirror normal at adjacent time steps. The constraints of the model include: the radial distance of each heliostat at the final time step is not less than the sum of the equivalent radius of the receiver and the safety margin, and the distance from the horizontal projection of the reflected light from each heliostat at all time steps to the center of the tower is greater than the radius of the receiver tower. Step 4: Solve the optimization model to obtain the optimal mirror normal sequence for each heliostat at each time step, which serves as the defocusing path; Step 5: Convert the optimal mirror normal sequence into the pitch and azimuth angles of each heliostat at each time step, which are used to drive the heliostat to perform defocusing.

2. The method according to claim 1, characterized in that, The heat contribution value is specifically defined as: ； in, The radial distance from the center of the light spot to the tangential plane of the absorber. Let be the equivalent radius of the heat absorber. Thermal contribution value.

3. The method according to claim 1, characterized in that, The time weights are an increasing sequence, which gives higher weight to the time steps in the later stages of defocusing.

4. The method according to claim 1, characterized in that, The weighting coefficients of the weighted sum are adjusted according to the operating conditions: under emergency shutdown or over-temperature conditions, the weight of the thermal contribution index is much greater than the weight of the motion smoothness index.

5. The method according to claim 1, characterized in that, The safety margin is between 0.5 meters and 1.0 meter.

6. The method according to claim 1, characterized in that, The intersection point of the reflected ray and the absorber plane is calculated as follows: ； ； in, Let these be the coordinates of the intersection point. The center position of the heliostat. Let be the distance parameter along the reflected ray. The vector of the reflected ray. The center position of the heat absorber is the normal vector of the absorber plane.

7. The method according to claim 1, characterized in that, The radial distance is calculated as follows: the difference vector between the intersection point and the center of the absorber is projected onto two orthogonal directions of the tangential plane of the absorber, and then the square root of the sum of the squares of the two projected components is calculated. ； ； ； in, Let be the intersection point of the reflected ray from the i-th heliostat and the plane of the absorber. Relative to the center of the absorber The projection component of the offset in the X-axis direction of the local coordinate system of the receiver. The projection component along the Y-axis is... Let be the coordinates of the intersection point of the reflected ray and the plane of the absorber. The coordinates of the receiver center are: and Let be two orthogonal unit direction vectors on the tangential plane of the receiver. It is the radial distance of the center of the light spot on the tangential plane of the absorber.

8. The method according to claim 1, characterized in that, The optimization model is solved using the interior point method or the IPOPT solver.

9. The method according to claim 1, characterized in that, The specific method for converting the mirror normal into pitch and azimuth angles is as follows: ； ； in, and Heliostats exist The corresponding pitch and azimuth angles at each moment These are the mirror normal directions. The X, Y, and Z components.

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