Dual stable control method for cavity temperature of radiometer absorption cavity based on adaptive smith predictor

Abstract

The present application relates to the technical field of irradiance measurement, and more particularly to a radiation meter absorption cavity temperature bistable control method based on adaptive Smith predictor, which combines feedforward control, PI control and adaptive Smith predictor: feedforward control is performed on the absorption cavity temperature interference source in the measurement process, an adaptive Smith predictor is used to predict the behavior of the radiation meter absorption cavity, PI control is used to complete the electric heating output of the radiation meter absorption cavity, the output of the temperature controller and the controlled cavity temperature are quickly adjusted, and the stable state is simultaneously entered, and high-precision radiation meter absorption cavity temperature and stable electric heating output meeting the measurement accuracy requirement are obtained.

Description

Technical Field

[0001] This invention belongs to the field of irradiance measurement technology, and particularly relates to a bistable control method for the absorption cavity temperature of a radiometer based on adaptive Smith prediction. Background Technology

[0002] Long-term, accurate monitoring of total solar irradiance (TSI) in space provides a scientific basis for climate change prediction and environmental policy formulation, and offers more accurate climate and meteorological forecasts for my country's military and civilian industries. The sun is Earth's only external energy source and a driving force for the formation, development, and change of ecosystems; therefore, TSI is one of the key parameters in Earth's climate models. The solar radiometer, as the core measuring device of a solar radiation monitoring instrument, is responsible for completing the TSI measurement and monitoring task. The radiometer mainly consists of a radiation absorption cavity, a heat sink, an absorption cavity heating circuit, and an absorption cavity temperature measuring circuit. Precise measurement and control of the absorption cavity temperature is a key technology for achieving accurate TSI measurements.

[0003] The temperature control model of the radiometer absorption cavity is a typical first-order inertial model with a delay. Therefore, many existing control techniques can be used in the temperature control algorithm of the absorption cavity. In classical control theory, the cavity temperature control model can be obtained quickly and accurately through methods such as the ascent curve method. A temperature control PID algorithm (proportional-integral-derivative control algorithm) with good control performance can be obtained through parameter tuning methods commonly used in engineering practice. However, due to the influence of the pure delay element in the cavity temperature control transfer function, traditional PID control usually requires 1 to 3 time constants to achieve bistable temperature control and controller output. In modern control theory, the thermal state of the system can be described through state space, enabling the control of multi-input multi-output nonlinear time-varying systems. However, while modern control theory is powerful, its design and analysis processes are complex, and its practical applications may be limited by inaccurate mathematical models and the difficulty in expressing performance indicators mathematically. In radiometer measurement systems, the physical principle of the measurement process is an equivalent process of electrothermal substitution. The heat transfer process is affected by objective factors such as structural design and material selection, making it difficult to obtain an accurate heat transfer model, especially during the absorption cavity fabrication process, where the heat transfer link model is difficult to control and detect. Therefore, it is difficult to achieve the measurement objective of rapidly synchronizing the radiometer detector cavity temperature and the controller output to a steady state using only classical and modern control theories. Summary of the Invention

[0004] In view of this, the present invention aims to provide a bistable control method for the absorption cavity temperature of a radiometer based on adaptive Smith predictor. The method uses an adaptive Smith predictor to predict the output of a PI controller with feedforward to achieve detector cavity temperature control. This allows both the target cavity temperature and the controller output to be rapidly adjusted on-orbit and synchronously enter a steady state during the cavity temperature control process, thereby achieving high-precision rapid measurement of total solar irradiance.

[0005] To achieve the above objectives, the technical solution created by this invention is implemented as follows:

[0006] A bistable control method for the cavity temperature of a radiometer absorption cavity based on adaptive Smith prediction includes:

[0007] S1: Open the radiometer shutter, and the radiometer absorption cavity begins photometry. Adjust the thermal power of the absorption cavity motor through feedforward control to stabilize the cavity temperature. After the cavity temperature stabilizes, close the radiometer shutter, and adjust the electric heating power of the absorption cavity through feedforward control to stabilize the cavity temperature. After the cavity temperature stabilizes, one measurement is completed.

[0008] S2: Using a PI controller, combined with the set target cavity temperature, the electric heating power of the absorption cavity is dynamically adjusted in real time to maintain a stable cavity temperature;

[0009] S3: Add a Smith prediction feedback loop to the original Smith predictor to obtain an adaptive Smith predictor; input the cavity electric heating power output by the PI controller obtained in step S2 into the adaptive Smith predictor to obtain the predicted cavity temperature of the absorption cavity.

[0010] S4: The predicted cavity temperature obtained in step S3 is integrated with the actual cavity temperature of the absorption cavity and used as the cavity temperature feedback of the PI controller closed-loop control loop. The PI controller adjusts the electric heating power of the absorption cavity in real time to make the cavity temperature of the absorption cavity consistent with the set cavity temperature.

[0011] Furthermore, step S1 includes:

[0012] The electric heating power of the absorption cavity is set based on historical optical power measurements.

[0013] Metering phase: At the same time the shutter opens, the initial electric heating power of the absorption cavity is set to the difference between the calibration power and the light power obtained during the previous metering.

[0014] Calibration phase: At the same time as the shutter is closed, the initial electric heating power of the absorption cavity is set to the calibration power, and the calibration power is greater than the measured light power of the radiometer.

[0015] Furthermore, in step S2, the parameters of the PI controller are set using the Cohen-Coon method.

[0016] Furthermore, in step S3, the Smith estimate of the feedback loop gain in the feedback loop is:

[0017] ;

[0018] Where Ks represents the feedback loop gain, Kp represents the proportional coefficient in the PI controller, Ki represents the integral coefficient in the PI controller, θ represents the delay time of the pure delay element in the transfer function of the absorption cavity temperature, τ represents the time constant, and K represents the gain of the delayed first-order inertial joint transfer function in the radiometer absorption cavity model. This indicates the difference between the set cavity temperature and the current cavity temperature.

[0019] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0020] The present invention describes a bistable control method for the absorption cavity temperature of a radiometer based on adaptive Smith predictor. Firstly, by introducing a feedforward mechanism, it suppresses the heating shock interference of the absorption cavity at the initial moment during the measurement and calibration phases, effectively reducing the amplitude of temperature instability in the radiometer absorption cavity and decreasing the thermal shock to the heat sink. This makes it possible to design a small and lightweight heat sink, effectively reducing the size and structural complexity of the equipment. The adaptive Smith predictor is the core of this invention. It allows the PI control to ignore the pure delay element in the transfer function of the controlled object (radiometer absorption cavity temperature). After entering the steady state, the controlled object is equivalent to the Smith predictor model, almost independent of the radiometer absorption cavity model. This characteristic greatly improves the output stability of the controller during the steady state of temperature control, eliminating the influence of sampling system noise. The adaptive Smith predictor dynamically adjusts the PI controller input, improving the dynamic adjustment capability of the cavity temperature, reducing the difficulty of PI controller parameter tuning, and enhancing the adaptability of the PI controller parameters. By reasonably adapting the proportional and integral coefficients, highly stable and accurate cavity temperature control results can be obtained. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0022] Figure 1 A schematic flowchart of the bistable control method for the absorption cavity temperature of a radiometer based on adaptive Smith prediction, as described in an embodiment of the present invention;

[0023] Figure 2 A flowchart illustrating the bistable control method for the absorption cavity temperature of a radiometer based on adaptive Smith prediction, as described in an embodiment of the present invention.

[0024] Figure 3This is a schematic diagram illustrating the measurement process of the solar absolute radiometer electro-thermal equivalent measurement method described in the embodiments of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0027] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0028] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] like Figures 1 to 3 As shown in the embodiment of the present invention, the bistable control method for the absorption cavity temperature of a radiometer based on adaptive Smith prediction includes:

[0031] S1: Open the radiometer shutter, and the radiometer absorption cavity begins photometry. Adjust the thermal power of the absorption cavity motor through feedforward control to stabilize the cavity temperature. After the cavity temperature stabilizes, close the radiometer shutter, and adjust the electric heating power of the absorption cavity through feedforward control to stabilize the cavity temperature. After the cavity temperature stabilizes, one measurement is completed.

[0032] The radiometer measurement process includes two phases: a photometric phase with the shutter open (measurement phase) and an electric heating calibration phase with the shutter closed (calibration phase). Before the photometric phase begins, the electric heating power Pe of the radiometer's absorption cavity is configured to a stable heating power value, which is greater than the measured optical power of the radiometer; in this embodiment, it is 75mW. However, after superimposing the optical power, the absorption cavity temperature will significantly deviate from the operating point temperature. The calibration phase suffers from the same problem. Therefore, this invention introduces feedforward control to ensure the stability of the absorption cavity temperature. Specifically, in some embodiments, step S1 includes:

[0033] The electric heating power of the absorption cavity is set based on historical optical power measurements.

[0034] Metering phase: At the same time the shutter opens, the initial electric heating power of the absorption cavity is set to the difference between the calibration power and the light power obtained during the previous metering.

[0035] Calibration phase: At the same time as the shutter is closed, the initial electric heating power of the absorption cavity is set to the calibration power, and the calibration power is greater than the measured light power of the radiometer.

[0036] It is understood that, in this embodiment of the invention, step S1 specifically includes:

[0037] Metering Phase: At the start, the shutter is opened, and the initial electric heating power Pe1 of the absorption cavity is set to the difference between the calibration power of 75mW and the light heating power obtained during the previous photometry. The process continues until the temperature of the radiometer absorption cavity stabilizes, at which point the temperature is T1. In this invention, the feedforward control output value during the measurement phase is determined by the previous light power measurement result. The absorption ratio of the radiometer absorption cavity to the light power is not considered here. Therefore, other variables such as absorption ratio compensation can be added to the feedforward control during the measurement phase to jointly calculate a more accurate feedforward output value.

[0038] Calibration phase: At the beginning, close the shutter, adjust the calibration power Pe2 to 75mW, and wait for the temperature of the radiometer absorption cavity to stabilize. At this time, the temperature of the radiometer absorption cavity is T2.

[0039] Due to factors such as changes in the ambient temperature of the radiometer absorption cavity, differences in the thermal characteristics of optical heating and electric heating, and light absorptivity, the cavity temperatures T1 and T2 at different stages are usually not equal. Therefore, power measurement correction is required using the radiometer absorption cavity responsivity parameter, denoted by α, with units of ℃ / mW. The measured optical power Po is then:

[0040] Po = Pe2 - Pe1 - (T2 - T1) / α.

[0041] S2: Using a PI controller and considering the target cavity temperature, the output electric heating power of the absorption cavity is dynamically adjusted in real time. In some embodiments, the Cohen-Kuhn method is employed, and an incremental digital PI controller is designed using parameters such as transfer function gain, time constant, and delay time. Figure 2 G in c (s) represents the transfer function of the PI controller. Specifically, using the PI controller G... c (s), combined with the set target cavity temperature X(s) of the absorption cavity, the output electric heating power of the absorption cavity is dynamically adjusted in real time to maintain the cavity temperature of the absorption cavity stable. At the same time, the dynamic adjustment time can be controlled within a time constant, and the PI controller can better resist external disturbances F(s).

[0042] In this embodiment of the invention, due to the constraint of the pure delay element in the transfer function of the controlled object (radiometer absorption cavity temperature), the control cycle of the PI controller must be strictly less than or equal to half the delay time in the pure delay element. Furthermore, the control method of the PI controller in this embodiment can be a traditional PI control method, or it can be piecewise PI control, fuzzy PI control, or neural network PI control. Specifically, in piecewise PI control, different parameters of the PI controller are configured at different control stages through time segmentation or error segmentation, including the proportional coefficient Kp and integral coefficient Ki, or an additional output gain Kpe. For example, for time segmentation, the proportional coefficient Kp is increased by 10% during the time period from 0 to τ / 2 to quickly reduce the cavity temperature error; after τ / 2, the proportional coefficient Kp is restored to achieve a low-noise steady-state control effect. For error segmentation, when the error is greater than or equal to 0.1℃, the proportional coefficient Kp is increased by 10% to quickly reduce the cavity temperature error; when the error is less than 0.1℃, the proportional coefficient Kp is restored to achieve a ground-regenerative steady-state control effect. Piecewise PI control can be incorporated into an adaptive Smith predictor PI controller to improve its dynamic response performance at shutter opening / closing times. Based on piecewise PI control, two or more membership functions are established according to fuzzy control theory. Different proportional coefficients Kp and integral coefficients Ki are configured for the PI controller for different time periods / error segments, or an additional output gain Kpe is added, thus achieving fuzzy PI control. Fuzzy control allows parameters to transition linearly or semi-linearly between different control stages through membership functions. It can also integrate time-based piecewise PI control and error-based piecewise PI control by integrating membership intervals, achieving a better trade-off between real-time performance and control accuracy through flexible rules and parameter tuning methods. Neural network PI control reconstructs the PI controller through a neuron structure and dynamically optimizes the PI controller parameters, including the proportional coefficient Kp and integral coefficient Ki, through neural network feedback iterative learning. The neural network learning algorithm can dynamically adjust the PI controller parameters in real time by monitoring the cavity temperature to achieve ideal real-time performance and control accuracy. By controlling its learning rules, the PI controller parameters can be intelligently learned and tuned online. Neural network PI control methods differ significantly from traditional PI controllers in their theoretical foundation, making it impossible to integrate them with piecewise PI control and fuzzy PI control in terms of control theory. However, the experience gained from debugging examples of both can be used to set parameter adjustment strategies that meet engineering needs.

[0043] S3: Add a Smith prediction feedback loop to the original Smith predictor to obtain an adaptive Smith predictor; input the output electric heating power obtained in step S2 into the Smith predictor to obtain the predicted output cavity temperature of the absorption cavity.

[0044] In some embodiments, the adaptive Mies predictor is as follows: Figure 2The dashed box in the figure represents the transfer function of the adaptive Smith predictor. An adaptive Smith predictor is obtained by adding a Smith predictor feedback loop to the traditional Smith predictor. This loop adjusts the Smith predictor input in real time, enabling rapid and accurate dynamic adjustment of the Smith predictor output to better reflect the cavity temperature output (G0(s)e). -τs The estimation is performed, where G0(s) is the first-order inertial transfer function of the delayed first-order inertial joint in the radiometer absorption cavity model, and τ represents the time constant of the first-order inertial transfer function G0(s). Specifically, Smith predicts the feedback loop, including the feedback loop gain; the feedback loop gain is:

[0045] ;

[0046] Where Ks represents the feedback loop gain, Kp represents the proportional coefficient in the PI controller, Ki represents the integral coefficient in the PI controller, θ represents the delay time of the pure delay element in the transfer function of the absorption cavity temperature, and K represents the gain of the first-order inertial transfer function G0(s). This indicates the difference between the set cavity temperature and the current cavity temperature.

[0047] S4: The predicted output cavity temperature obtained in step S3 is integrated with the actual output cavity temperature of the absorption cavity. Then, the PI controller is controlled to dynamically adjust the output electric heating power in real time based on the target cavity temperature and the integrated cavity temperature to ensure the stability of the cavity temperature of the absorption cavity. After the cavity temperature stabilizes, it is equivalent to the PI controller dynamically adjusting a delay-free inertial element, namely G0(s).

[0048] In embodiments of the present invention, such as Figure 2 As shown, the predicted output cavity temperature is added to the actual output cavity temperature Y(s) of the absorption cavity and integrated. Then, the PI controller dynamically adjusts the output electric heating power in real time based on the target cavity temperature X(s) and the integrated cavity temperature to ensure the stability of the cavity temperature of the absorption cavity.

[0049] The bistable control method for the absorption cavity temperature of a radiometer based on adaptive Smith predictor provided by this invention can achieve consistent absorption cavity temperature with an error of less than 0.05%, and data repeatability of the measurement results of absorption cavity temperature and absorption cavity electric heating power of less than 0.005%. Furthermore, the duration of the dynamic adjustment process of cavity temperature and absorption cavity electric heating power during the photometry and electrical calibration stages is essentially consistent, less than or equal to one time constant. Existing single PI controllers without a Smith predictor cannot complete the dynamic adjustment process of cavity temperature within one time constant. The method provided by this invention is also applicable to temperature control systems with transfer functions exhibiting significant delay characteristics and known external disturbances. That is, the method provided by this invention can be applied to temperature control scenarios described by first-order delayed inertial elements, and to temperature control objects with significant delays.

[0050] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0051] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for dual stable control of a radiometer absorption cavity temperature based on adaptive Smith predictor, characterized in that, Comprise: S1: open the shutter of the radiometer, the radiometer absorption cavity starts to measure light, adjust the electric heating power of the absorption cavity by feedforward control to stabilize the cavity temperature of the absorption cavity; After the cavity temperature is stabilized, the shutter of the radiometer is closed, and the electric heating power of the absorption cavity is adjusted by feedforward control to stabilize the cavity temperature of the absorption cavity; After the cavity temperature is stabilized, the measurement is completed; Step S1 includes: setting the electric heating power of the absorption cavity according to the historical light power measurement value; In the light measurement stage, the initial electric heating power of the absorption cavity is set as the difference between the calibration power and the light power obtained in the last light measurement while the shutter is opened; in the calibration stage, the initial electric heating power of the absorption cavity is set as the calibration power while the shutter is closed, and the calibration power is greater than the measured light power of the radiometer; S2: use the PI controller to dynamically adjust the electric heating power of the absorption cavity in real time combined with the set target cavity temperature of the absorption cavity to maintain the cavity temperature stable; S3: add a Smith prediction feedback loop based on the original Smith predictor to obtain an adaptive Smith predictor; input the cavity electric heating power output by the PI controller in step S2 into the adaptive Smith predictor to obtain the predicted cavity temperature of the absorption cavity; S4: integrate the predicted cavity temperature obtained in step S3 and the actual cavity temperature of the absorption cavity as the cavity temperature feedback of the closed loop control loop of the PI controller, and adjust the electric heating power of the absorption cavity by the PI controller in real time to realize that the cavity temperature of the absorption cavity is consistent with the set cavity temperature.

2. The method of claim 1, wherein the method is a method of adaptive Smith predictor based radiometer absorption cavity temperature bistable control. In step S2, the parameters of the PI controller are set by Cohen-Coon method.

3. The method of claim 1, wherein the method is a method of adaptive Smith predictor based radiometer absorption cavity temperature bistable control. The feedback loop gain in the Smith prediction feedback loop in step S3 is: ； where Ks represents a feedback loop gain, Kp represents a proportional coefficient in a PI controller, Ki represents an integral coefficient in the PI controller, θ represents a delay time of a pure delay link in a transfer function of the absorption cavity cavity temperature, τ represents a time constant, K represents a gain of a delay first-order inertia link transfer function in a model of the radiometer absorption cavity, represents a difference between the set cavity temperature and the current cavity temperature.

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