A closed-loop control method for a point-focusing solar furnace

Abstract

The present invention provides a closed-loop control method for a point-focus solar furnace. A CCD camera is placed at the principal optical axis of the reflective surface of a secondary concentrator. A computer controls the CCD camera to capture an image of the light spot reflected by the secondary concentrator onto a heat absorber. Image processing calculates the horizontal deviation ΔX and vertical deviation ΔY between the center position O' of the light spot and the center position O of the heat absorber. The computer then transmits the light spot deviation to an on-site controller of the heliostat, which controls the heliostat to adjust the center position O' back to the center position O of the heat absorber until the horizontal and vertical deviations fall below set thresholds, indicating the completion of the light spot deviation correction process and completing closed-loop control. This method does not affect the normal operation of the solar furnace, can automatically detect and correct solar furnace tracking errors, and significantly improves solar furnace tracking accuracy compared to open-loop control. This provides a real-time, efficient closed-loop control method for solar furnaces.

Description

Technical Field

[0001] The present invention belongs to the field of solar high-temperature heat utilization, and in particular relates to a closed-loop control method for a point-focusing solar furnace. Background Art

[0002] Point-focus solar furnaces are an important form of medium- and high-temperature solar thermal utilization. They can precisely reflect and concentrate low-density solar radiation onto a smaller area, achieving ultra-high temperatures (>2000°C) and extremely high energy flux. They are widely used in basic and applied research in fields such as materials, chemicals, fuel production, and power generation. Due to the high parameter requirements of point-focus solar furnaces, they place higher demands on tracking accuracy. Therefore, high-precision tracking control is a crucial means of achieving efficient operation.

[0003] The solar furnace tracking control system uses a dual-axis azimuth / elevation drive system to control the heliostats. Based on the sun's trajectory and incorporating optical reflection principles, the system calculates the required azimuth and elevation angles for operation, thereby achieving automatic sun tracking. A review of relevant patents (CN106766240B and CN107368101B) reveals that currently used methods for solar furnace control include: installing photoelectric encoders, inclinometers, and other measurement sensors on the heliostat's structural components to measure the heliostat's attitude, creating a semi-closed-loop tracking control method. However, this method can only reduce the heliostat's own errors; it cannot measure the overall system error consisting of the heliostat and secondary reflectors, nor can it accurately determine the specific location of the reflected light spot on the heat sink. Another method uses a four-quadrant light sensor to detect direct sunlight. A rotary control device adjusts the angle of the concentrator based on the light sensor's determination. This method is suitable for dish-type solar furnaces but not for point-focus solar furnaces with secondary reflectors. Current point-focus solar furnaces use an open-loop control system. When the center of the light spot deviates from the center of the receiver, operators must rely on their experience to modify the initial azimuth / elevation angle parameters of the heliostats and send these parameters to a local controller to control the heliostats and eliminate this tracking error. This method is inefficient in practice and cannot eliminate tracking errors in real time, requiring a high level of operator experience. Furthermore, due to the open-loop control method, if the solar furnace is left unattended for extended periods, significant light spot offset errors and cumulative errors can occur, compromising the efficient operation of the receiver. Therefore, a real-time, efficient closed-loop control method for solar furnaces that does not rely on experience is needed. Summary of the Invention

[0004] In order to overcome the shortcomings of the existing open-loop control method of the solar furnace, the present invention provides a closed-loop control method of the point-focusing solar furnace, which is real-time, efficient, does not rely on human intervention, and is automatically completed.

[0005] The unit reflectors used in secondary concentrators of solar furnaces are generally rectangular or orthogonal, and their surface shape can be approximated as a sphere. Utilizing the geometric optical properties of spherical reflectors, whereby parallel light beams converge to a focal point after reflection, a CCD camera is placed on the principal optical axis of the secondary concentrator's reflective surface to capture the reflected light spot on a heat absorber placed at the focal point of the secondary concentrator's focal plane. Image processing is used to calculate the deviation between the center of the light spot and the center of the heat absorber. This information is fed back to the on-site controller of the heliostat, which corrects the light spot position until the deviation between the center of the light spot and the center of the heat absorber falls below a designed threshold.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides a closed-loop control method for a point-focusing solar furnace, comprising the following steps:

[0008] Step 1: Determine the geographical location for the point-focus solar furnace. Arrange the heliostat and secondary concentrator in a south-north orientation, with the heliostat placed north of the secondary concentrator and the heat absorber between them. Install the secondary concentrator vertically so that its principal optical axis is parallel to the ground.

[0009] Step 2: Install the center of the heat absorber at the focus of the secondary concentrator so that the heat absorber plane coincides with the focal plane of the secondary concentrator;

[0010] Step 3: Install an image acquisition device at the center of the secondary concentrator, with the image acquisition device facing the heat absorber and the camera lens plane perpendicular to the horizontal plane; ultimately, the center of the heat absorber and the lens center of the image acquisition device are both located on the principal optical axis of the secondary concentrator;

[0011] Step 4: Connect the computer to the image acquisition device, and set the parameters of the image acquisition device through the computer: aperture, focal length, exposure, so that the image acquisition device captures the spot image reflected by the secondary concentrator to the heat absorber and transmits it to the computer;

[0012] Step 5: The computer sends an automatic tracking instruction to the on-site controller of the heliostat to control the heliostat to automatically track the sun. The solar radiation is reflected by the heliostat to the secondary concentrator and then concentrated and reflected to the heat absorber. The computer controls the image acquisition device to collect the spot image of the heat absorber in real time.

[0013] Step 6: The computer processes the light spot image captured by the image acquisition device and calculates the horizontal and vertical deviations ΔX and ΔY between the center position O' of the light spot and the center position O of the heat absorber. The computer then sends the horizontal and vertical deviations to the heliostat on-site controller to control the heliostat to adjust the center position O' of the light spot back to the center position O of the heat absorber.

[0014] Step 7: The deviation image of the center of the light spot 7 and the center of the heat sink obtained in step 6 is processed and calculated by a computer to obtain new deviations ΔX' and ΔY', and then compared with the designed threshold value. If the deviation is greater than the threshold value, it indicates that the tracking error is large, and the process continues to step 6 based on the newly calculated deviation value.

[0015] Repeat steps 6 and 7 until the horizontal and vertical deviations of the light spot are less than the set thresholds, indicating that the tracking error meets the requirements and the closed-loop control is completed.

[0016] Furthermore, the image acquisition device is installed at the main optical axis of the secondary concentrator so that its lens faces the heat absorber, and the optical axis of the image acquisition device is parallel to the ground; and the optical axis of the image acquisition device coincides with the main optical axis of the secondary concentrator; the heat absorber is installed at the focus of the focal plane of the secondary concentrator, and the heat absorber plane is perpendicular to the ground; the main optical axis of the secondary concentrator, the center of the heat absorber, and the center of the image acquisition device are on the same line and at the same height.

[0017] Furthermore, the reflective surface of the secondary concentrator is spherical or a rotating parabola; and the heat absorber is square, rectangular or circular.

[0018] Furthermore, the image acquisition device is a CCD camera or a digital camera.

[0019] Beneficial effects:

[0020] 1. The closed-loop control method of the solar furnace in the present invention does not rely on manual intervention and is completed automatically;

[0021] 2. The present invention does not affect the normal operation of the point-focusing solar furnace;

[0022] 3. The present invention realizes real-time and efficient closed-loop control of the solar furnace based on image processing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the closed-loop control method of the midpoint focusing solar furnace of the present invention;

[0024] Figure 2 This is a front view of the position deviation between the center of the light spot and the center of the heat absorber in the present invention;

[0025] Figure 3 This is a logic diagram of the closed-loop control method of the solar furnace in the present invention.

[0026] The reference numerals in the drawings are: computer 1 , CCD camera 2 , secondary concentrator 3 , heat absorber 4 , heliostat 5 , heliostat on-site controller 6 , and light spot 7 . DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] like Figure 1 As shown, the components used in the closed-loop control method of the point-focusing solar furnace of the present invention include a computer 1, a CCD camera 2, a secondary concentrator 3, a heat absorber 4, a heliostat 5, and a heliostat on-site controller 6. The center of the heat absorber 4 and the center of the CCD camera 2 are located on the main optical axis of the secondary concentrator 3, and the plane of the heat absorber 4 coincides with the focal plane of the secondary concentrator 3. The lens of the CCD camera 2 faces the heat absorber 4, and the center of the lens of the CCD camera 2 coincides with the center of the secondary concentrator 3, and is perpendicular to the main optical axis of the secondary concentrator 3; the computer 1 controls the CCD camera 2 to collect an image of the light spot 7 reflected by the secondary concentrator 3 on the surface of the heat absorber 4. Figure 2 As shown, it is a front view of the deviation between the center of the heat absorber 4 and the center of the light spot 7 reflected by the secondary concentrator 3 in the present invention, ΔX and ΔY represent the deviation in the horizontal and vertical directions, O' represents the center of the light spot 7, and O represents the center of the heat absorber 4.

[0029] like Figure 3 As shown, the closed-loop control method of the point-focusing solar furnace of the present invention comprises the following steps:

[0030] Step 1: Determine the geographic location for the point-focus solar furnace. Arrange the heliostat 5 and secondary concentrator 3 in a south-north orientation, with the heliostat 5 positioned north of the secondary concentrator 3 and the absorber 4 positioned between them. Install the secondary concentrator 3 vertically, with its principal optical axis parallel to the ground.

[0031] Step 2: Install the center of the heat absorber 4 at the focus of the secondary concentrator 3 so that the plane of the heat absorber 4 coincides with the focal plane of the secondary concentrator 3.

[0032] Step 3: Install the CCD camera 2 at the center of the secondary concentrator 3, with the CCD camera 2 facing the heat absorber 4 and the camera lens plane perpendicular to the horizontal plane. Ultimately, the center of the heat absorber 4 and the center of the CCD camera 2 lens are both located on the principal optical axis of the secondary concentrator 3.

[0033] Step 4: Connect computer 1 to CCD camera 2 and set the parameters of CCD camera 2: aperture, focal length, exposure, so that CCD camera 2 can clearly and comprehensively capture the image of light spot 7 reflected from secondary concentrator 3 to heat absorber 4 and transmit it to computer 1.

[0034] Step 5: Computer 1 sends an automatic tracking instruction to the heliostat on-site controller 6 to control heliostat 5 to automatically track the sun. The solar radiation is reflected by heliostat 5 to the secondary concentrator 3 and then concentrated and reflected to the heat absorber 4. Computer 1 controls CCD camera 2 to capture an image of the light spot 7 on the heat absorber 4 in real time.

[0035] Step 6: Computer 1 processes the image of light spot 7 captured by CCD camera 2 and calculates the horizontal and vertical deviations ΔX and ΔY between the center position O' of light spot 7 and the center position O of heat absorber 4. Computer 1 then sends the horizontal and vertical deviations of light spot 7 to heliostat controller 6 to control heliostat 5 to adjust the center position O' of light spot 7 back to the center position O of heat absorber 4.

[0036] Step 7: After step 6, a new deviation image of the center of the light spot 7 and the center of the heat absorber 4 is obtained. After image processing and calculation by computer 1, new deviation amounts ΔX' and ΔY' are obtained and compared with the designed threshold value; if the deviation is greater than the threshold value, it means that the tracking error is large, and then continue to step 6 based on the newly calculated deviation amount.

[0037] Repeat steps 6 and 7 until the horizontal and vertical deviations of the spot 7 are less than the set thresholds, indicating that the tracking error meets the requirements and the closed-loop control is completed.

[0038] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A closed-loop control method for a point-focusing solar furnace, characterized in that: The steps include: Step 1: Determine the geographical location for the point-focus solar furnace. Arrange the heliostat and secondary concentrator in a south-north orientation, with the heliostat placed north of the secondary concentrator and the heat absorber between them. Install the secondary concentrator vertically so that its principal optical axis is parallel to the ground. Step 2: Install the center of the heat absorber at the focus of the secondary concentrator so that the heat absorber plane coincides with the focal plane of the secondary concentrator; Step 3: Install an image acquisition device at the center of the secondary concentrator, with the image acquisition device facing the direction of the heat absorber and the plane of the image acquisition device perpendicular to the horizontal plane; ultimately, the center of the heat absorber and the center of the image acquisition device are both located on the principal optical axis of the secondary concentrator; Step 4: Connect the computer to the image acquisition device, and set the parameters of the image acquisition device through the computer: aperture, focal length, exposure, so that the image acquisition device captures the image of the light spot reflected by the secondary concentrator to the surface of the heat absorber, and transmits it to the computer; Step 5: The computer sends an automatic tracking instruction to the on-site controller of the heliostat to control the heliostat to automatically track the sun. The solar radiation is reflected by the heliostat to the secondary concentrator and then concentrated and reflected to the heat absorber. The computer controls the image acquisition device to collect the spot image on the surface of the heat absorber in real time. Step 6: The computer processes the light spot image captured by the image acquisition device and calculates the horizontal and vertical deviations ΔX and ΔY between the center position O' of the light spot and the center position O of the heat absorber. The computer then sends the horizontal and vertical deviations to the heliostat on-site controller to control the heliostat to adjust the center position O' of the light spot back to the center position O of the heat absorber. Step 7: The deviation image between the center of the light spot 7 and the center of the heat absorber obtained in step 6 is processed and calculated by a computer to obtain new deviations ΔX' and ΔY' and compare them with the designed thresholds; If the deviation is greater than the threshold, it indicates that the tracking error is large, and the process proceeds to step 6 based on the newly calculated deviation. Repeat steps 6 and 7 until the horizontal and vertical deviations of the light spot are less than the set thresholds, indicating that the tracking error meets the requirements and the closed-loop control is completed.

2. A closed-loop control method for a point-focusing solar furnace according to claim 1, characterized in that: The image acquisition device is installed on the main optical axis of the secondary concentrator so that its lens faces the heat absorber and the optical axis of the image acquisition device is parallel to the ground.

3. A closed-loop control method for a point-focusing solar furnace according to claim 2, characterized in that: The optical axis of the image acquisition device coincides with the main optical axis of the secondary condenser.

4. A closed-loop control method for a point-focusing solar furnace according to claim 1, characterized in that: The absorber is installed at the focal plane of the secondary concentrator, and the absorber plane is perpendicular to the ground.

5. A closed-loop control method for a point-focusing solar furnace according to claim 4, characterized in that: The main optical axis of the secondary concentrator, the center of the heat absorber, and the center of the image acquisition device are on the same line and at the same height.

6. The closed-loop control method for a point-focusing solar furnace according to claim 1, characterized in that: The reflective surface of the secondary concentrator is in the shape of a sphere or a rotational paraboloid.

7. The closed-loop control method for a point-focusing solar furnace according to any one of claims 1 to 6, characterized in that: The image acquisition device is a CCD camera or a digital camera.

8. The closed-loop control method for a point-focusing solar furnace according to claim 1, characterized in that: The shape of the heat absorber is square, rectangular or circular.

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