Closed-loop control method for point focusing solar furnace

Abstract

The invention provides a closed-loop control method for a point focusing solar furnace, which comprises the following steps of: placing a CCD (Charge Coupled Device) camera at a main optical axis of a reflecting surface of a secondary condenser, and controlling the CCD camera by a computer to collect light spot images which are converged and reflected to a heat absorber by the secondary condenser; the horizontal direction deviation delta X and the vertical direction deviation delta Y of the light spot center position O'and the center position O of the heat absorber are calculated through image processing, and the computer sends the light spot deviation to the heliostat local controller to control the heliostat to adjust the light spot center position O 'to return to the center position O of the heat absorber; and when the deviation of the light spot in the horizontal direction and the deviation of the light spot in the vertical direction are smaller than a set threshold value, the light spot deviation correction process is finished, and closed-loop control is completed. Normal work of the solar furnace is not affected, tracking errors of the solar furnace can be automatically detected and corrected, the tracking precision of the solar furnace can be remarkably improved compared with open-loop control, and the solar furnace closed-loop control method is real-time and efficient.

Description

Technical Field

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

[0002] Point-focusing solar furnace is one of the important forms of medium- and high-temperature heat utilization of solar energy. It can reflect and focus low-density solar radiation energy to a smaller area with high precision, achieving ultra-high temperature (>2000℃) and extremely strong energy flux density. It can be widely used in basic and applied research in many fields such as materials, chemical industry, fuel preparation and power generation. Due to the high parameter characteristics of point-focusing solar furnace, higher requirements are placed on the tracking accuracy of solar furnace. Therefore, high-precision solar furnace tracking control is an important means to achieve its efficient operation.

[0003] The solar furnace tracking control system uses an azimuth / pitch dual-axis drive method to control the heliostat based on the trajectory of the sun's motion, and combines the optical reflection principle to calculate the azimuth and altitude angle required for the heliostat to operate, thereby realizing automatic tracking of the sun. After consulting relevant patents such as (CN106766240B, CN107368101B), it is known that the methods currently used in solar furnace control are: one is to measure the heliostat's attitude information by installing photoelectric encoders, inclinometers and other measuring sensors on the heliostat structural components to form a semi-closed loop method for heliostat tracking control; but this method can only reduce the error of the heliostat body, and cannot measure the error of the entire system composed of the heliostat and the secondary reflector, and cannot accurately determine the specific position of the reflected light spot on the heat absorber. Another method is to use a four-quadrant light sensor to sense whether the sunlight is direct, and the rotation control device can adjust the angle of the focusing device according to the judgment of the light sensor. This method is applicable to dish-type solar furnaces but not to point-focusing solar furnaces with secondary reflections. At present, the point-focusing solar furnace adopts an open-loop control method. When the center of the light spot deviates from the center of the heat absorber, the operator needs to modify the initial azimuth / elevation angle parameters of the heliostat based on experience and send them to the local controller to control the heliostat to eliminate this tracking error. This method is inefficient in practice and cannot eliminate the tracking error in real time, and requires a high level of experience from the operator. In addition, due to the use of an open-loop control method, if the solar furnace is not intervened by humans for a long time, a large light spot offset error and cumulative error will occur, affecting the efficient operation of the heat absorber. Therefore, a real-time and 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 a point-focusing solar furnace, which is real-time, efficient, does not rely on human intervention, and can be completed automatically.

[0005] The unit reflector for the secondary concentrator of the solar furnace is generally rectangular or positive, and its surface shape can be approximately considered as a sphere. Using the geometric optical properties of the spherical reflector, that is, the parallel light beams converge to the focus after being reflected by the reflector: a CCD camera is placed at the main optical axis of the reflective surface of the secondary concentrator to shoot the reflected light spot on the absorber placed at the focus of the focal plane of the secondary concentrator, and the deviation between the center of the light spot and the center of the absorber is calculated through image processing, and the feedback is given to the local controller of the given heliostat to correct the light spot position until the deviation between the center of the light spot and the center of the absorber is less than the design 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 of the point-focusing solar furnace. The heliostat and the secondary concentrator are arranged due south and due north. The heliostat is placed on the north side of the secondary concentrator, and the absorber is located between the two. The secondary concentrator is installed and fixed vertically so that its main optical axis is parallel to the ground.

[0009] Step 2, install the center of the absorber at the focus of the secondary concentrator so that the 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, so that the image acquisition device faces the direction of the absorber and the camera lens plane is perpendicular to the horizontal plane; finally, the center of the absorber and the lens center of the image acquisition device are both located on the main optical axis of the secondary concentrator;

[0011] Step 4, the computer is connected to the image acquisition device, and the parameters of the image acquisition device are set by the computer: aperture, focal length, exposure, so that the image acquisition device collects 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 local 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 acquired by the image acquisition device and calculates the horizontal deviation and vertical deviation ΔX and ΔY between the center position O' of the light spot and the center position O of the heat absorber. The computer sends the horizontal deviation and vertical deviation of the light spot to the on-site controller of the heliostat 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 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', ΔY' and compare them with the designed thresholds; if the deviation is greater than the threshold, it means that the tracking error is large, and then continue to enter step 6 based on the newly calculated deviation;

[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; the shape of 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 It 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 It 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 , light spot 7 . DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with 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 clearer, the present invention is further described in detail below in conjunction with 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, an absorber 4, a heliostat 5, and a heliostat on-site controller 6. The center of the absorber 4 and the center of the CCD camera 2 are located on the principal optical axis of the secondary concentrator 3, and the plane of the absorber 4 coincides with the focal plane of the secondary concentrator 3. The lens of the CCD camera 2 faces the absorber 4, and the center of the lens of the CCD camera 2 coincides with the center of the secondary concentrator 3, perpendicular to the principal optical axis of the secondary concentrator 3; the computer 1 controls the CCD camera 2 to collect an image of a light spot 7 reflected by the secondary concentrator 3 on the surface of the 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, ΔY represent the deviation in the horizontal direction and the vertical direction, 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 geographical location of the point-focusing solar furnace. The heliostat 5 and the secondary concentrator 3 are arranged due south and due north. The heliostat 5 is placed on the north side of the secondary concentrator 3, and the absorber 4 is located between the two. The secondary concentrator 3 is installed and fixed vertically so that its main optical axis is 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 condenser 3, so that the CCD camera 2 faces the heat absorber 4 and the camera lens plane is perpendicular to the horizontal plane. Finally, the center of the heat absorber 4 and the lens center of the CCD camera 2 are both located on the main optical axis of the secondary condenser 3.

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

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

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

[0036] Step 7. After step 6, the deviation image of the center of the new 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', ΔY' are obtained and compared with the designed threshold values; if the deviation is greater than the threshold value, it means that the tracking error is large, and then continue to enter step 6 based on the newly calculated deviation amount.

[0037] Repeat steps 6 and 7 until the horizontal deviation and vertical deviation of the light spot 7 are less than the set threshold, 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 only 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 protection scope 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 of the point-focusing solar furnace. The heliostat and the secondary concentrator are arranged due south and due north. The heliostat is placed on the north side of the secondary concentrator, and the absorber is located between the two. The secondary concentrator is installed and fixed vertically so that its main optical axis is parallel to the ground. Step 2, install the center of the absorber at the focus of the secondary concentrator so that the 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, so that the image acquisition device faces the direction of the absorber and the plane of the image acquisition device is perpendicular to the horizontal plane; finally, the center of the absorber and the center of the image acquisition device are both located on the main optical axis of the secondary concentrator; Step 4, the computer is connected to the image acquisition device, and the parameters of the image acquisition device are set by the computer: aperture, focal length, exposure, so that the image acquisition device collects 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 local 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 absorber. The computer controls the image acquisition device to collect the spot image on the surface of the absorber in real time. Step 6: The computer processes the light spot image acquired by the image acquisition device and calculates the horizontal deviation and vertical deviation ΔX and ΔY between the center position O' of the light spot and the center position O of the heat absorber. The computer sends the horizontal deviation and vertical deviation of the light spot to the on-site controller of the heliostat 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', ΔY' and compared with the designed thresholds; If the deviation is greater than the threshold, it means that the tracking error is large, and then 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 principal 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 parabola.

7. The closed-loop control method of 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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