A method for controlling the molten salt temperature of the receiver in a tower-type solar thermal power plant

Abstract

This invention provides a method for controlling the molten salt temperature of the receiver in a tower-type solar thermal power plant. Specifically, it includes the following steps: S1, collecting relevant operating conditions affecting the molten salt temperature; S2, collecting information on factors related to the molten salt temperature, obtaining a predicted molten salt temperature value and an evaluation result of the accuracy of the predicted value; S3, regulating the temperature and flow rate through a temperature and flow rate regulation loop constructed by a cascaded PID control loop, wherein the parameters of the temperature PID controller are dynamically adjusted based on the operating condition judgment result and the evaluation result of the predicted molten salt temperature value. This invention's molten salt temperature control method can dynamically adapt to changes in external influencing factors while ensuring the reliability of its molten salt temperature control.

Description

Technical Field

[0001] This invention relates to the field of solar thermal power plants, and more particularly to a method for controlling the molten salt temperature of the receiver in a tower-type solar thermal power plant. Background Technology

[0002] Tower solar thermal power plants equipped with sufficient energy storage capacity feature decoupling of the steam generation system and its power generation unit from the solar energy collection system, resulting in extremely high system reliability. Furthermore, the power generation island of a tower solar thermal power plant offers exceptional operational flexibility: rapid start-up and shutdown, high load ramp-up and ramp-up rates, and its solar energy utilization attributes make it a rare and high-quality regulating resource for clean energy bases in desert and Gobi areas. The molten salt temperature of the receiver in a tower solar thermal power plant is a core equipment indicator for solar resource utilization, signifying the effectiveness and efficiency of solar concentrating and heat collection. Therefore, high-quality control of the receiver molten salt temperature is of paramount importance.

[0003] Controlling the molten salt temperature at the outlet of the absorber tower in a tower-type solar thermal power plant presents many challenges, and existing single-loop parameter control methods cannot solve the following main problems: 1. The inherent hysteresis of temperature parameters, the long-term flow and heat exchange of molten salt medium, the long physical distance between the temperature detection point and the regulating mechanism, and the need for the regulating valve to reflect temperature changes result in obvious problems such as control overshoot and oscillation, and the control quality cannot be guaranteed.

[0004] 2. Northwest my country has a wide terrain, a large pressure gradient, dry surface, frequent and strong winds, frequent sandstorms, blowing dust, and floating dust, large temperature differences, and frequent seasonal convective clouds (cumulonimbus clouds) in summer. In some areas, the mountain ranges near the capital cause a large number of cotton-like and scale-like cirrus clouds. These meteorological characteristics, such as wind, clouds, and temperature, make it difficult to stably control the molten salt temperature at the receiver outlet.

[0005] 3. Thin heat exchange tubes, numerous flow inflection points in the heat exchange tubes, and insufficient fluidity are the main inducing factors for molten salt solidification and tube blockage, affecting the safe and stable operation of the absorber.

[0006] 4. High molten salt medium temperature, long-term or frequent high-frequency temperature change rate of the absorber, and excessive temperature change will lead to changes in thermal stress of the material, which will endanger the life of the absorber.

[0007] Therefore, the current method for controlling the outlet temperature of the receiver in a tower solar thermal power plant mostly adopts a single temperature parameter feedback control loop. This involves setting a setpoint for the receiver outlet temperature control loop, calculating the deviation between the setpoint and the detected feedback value, and then using this deviation to drive the molten salt flow regulating valve actuator to perform negative feedback correction, thereby achieving the goal of controlling the outlet temperature. However, the current method lacks flexibility in setting the control value and has poor control performance.

[0008] Therefore, there is a need in the art for a method for controlling the temperature of molten salt. Summary of the Invention

[0009] The purpose of this invention is to provide a parameter-adaptive method for controlling the outlet temperature of the receiver in a solar thermal power plant, in order to solve the problems of reliability and flexibility in controlling the outlet temperature of the receiver in a solar thermal power plant.

[0010] In a first aspect of the present invention, a method for controlling the molten salt temperature of a receiver in a tower solar thermal power plant is provided, comprising the following steps: S1. Collect relevant operating conditions that affect the temperature of molten salt, and use the operating condition identification device to judge the operating conditions and obtain the operating condition judgment results. The judgment results include clear and steady state, sudden drop or rapid drop in temperature, sudden change in wind, sudden change in cloud image, and sudden change in temperature field. S2. Collect information on factors related to molten salt temperature, predict molten salt temperature using a molten salt temperature prediction device, and evaluate the accuracy of the prediction value using a prediction evaluation device to obtain the predicted molten salt temperature value and the evaluation result of the prediction accuracy. The prediction mechanism of the molten salt temperature prediction module at the absorber outlet is constructed using a Long Short-Term Memory Network (LSTM) and a Recurrent Neural Network (RNN). The evaluation mechanism of the prediction evaluation module is to measure the average deviation between the predicted value and the actual value detected in historical time periods. S3. The temperature and flow rate are regulated by a temperature and flow rate regulation loop composed of a cascade PID control loop, which includes an outer loop temperature PID controller and an inner loop flow rate PID controller. The temperature PID controller takes the difference between the set value of the molten salt temperature at the absorber outlet and the value detected by the molten salt temperature transmitter as input to obtain the temperature control value. The flow rate PID controller takes the set value of the molten salt flow rate and the value detected by the molten salt flow rate transmitter as input and outputs the flow rate control value. The temperature control value is accumulated with the initial value of the molten salt flow rate setting to obtain the molten salt flow rate set value. The temperature PID controller dynamically adjusts its parameters based on the operating condition determination result obtained in step S1 and the molten salt temperature prediction evaluation result obtained in step S2. This dynamic adjustment includes the following steps: Y1. Detect the evaluation result of the predicted value of molten salt temperature. When the evaluation accuracy is high, proceed to step Y2. When the evaluation accuracy is not high, the temperature PID controller does not perform parameter adjustment operation. Y2. Query the working condition judgment result: When the working condition is a clear and stable state, the temperature PID controller does not perform parameter adjustment operation; when the working condition is any of the following working conditions: sudden drop in temperature or rapid drop, sudden change in wind, sudden change in cloud appearance, or sudden change in temperature field, proceed to step Y3. Y3: Determine whether the change direction of the molten salt temperature is a temperature-decreasing direction, if yes, execute step Y3.1; if it is a temperature-increasing direction, execute step Y3.2; Y3.1: When the change direction of the molten salt temperature is the temperature-decreasing direction, determine whether the temperature state meets the following conditions at the same time: n1) T-T set <X5; n2) T k+20 -T set <X6; Wherein, T is the current detected value of the molten salt temperature; T set is the set value of the molten salt temperature; T k+20 is the predicted value of the molten salt temperature at 20 seconds after the current moment; X5 and X6 are preset first thresholds; If the above conditions are satisfied, the parameter adjustment operation is not performed; if the above conditions are not satisfied, proceed to step Y4; Y3.2: When the change direction of the molten salt temperature is the temperature-increasing direction, determine whether the temperature state meets any of the following conditions: m1) T k+20 - T set <X1; or m2) ΔT k+2 , ΔT k+4 ...ΔT k+20 the decreasing rate of the trend <X2; Wherein, T set is the set value of the molten salt temperature; T k+20 is the predicted value of the molten salt temperature at 20 seconds after the current moment; ΔT k+2 is the calculated change rate at the 2nd second after the current moment of the molten salt temperature, ΔT k+4 is the change rate of the previous 2-second interval calculated at the 4th second after the current moment of the molten salt temperature, and so on; X1 and X2 are preset second thresholds, wherein X2 is the average value of change rates at 2-second intervals within a 20-second interval; If any of the above conditions is satisfied, the parameter adjustment operation is not performed; if not, proceed to step Y4; Y4: Adjust the parameters according to the following formula: Wherein, is the initial value of the proportional coefficient of the controller, is the initial value of the integral coefficient of the controller; n is the counting sequence for re-adjustment after interval parameter correction, and N is a positive integer; is the adjustment coefficient; wherein, the adjustment coefficient is adjusted and optimized by performing the following steps : Z1) Under the same triggering factors, the computational controller performs different... The adjustment time parameter and accuracy parameter are set at the specified values, and each is determined based on the adjustment time parameter and accuracy parameter. The value controls the quality of the numerical value; Z2) Record each The values ​​and their corresponding control quality values ​​are used to calculate the mean of all control quality values, and the mean is used as the reward and punishment line. Z3) will each The control quality value corresponding to the value is compared with the reward / penalty line, and the value is higher than the reward / penalty line. Values ​​are rewarded, and those below the reward / penalty threshold are punished. The value is subject to a penalty; Z4) Adjust according to the results of rewards and punishments The value of the coefficient is such that... Iterative learning optimization; S4. Based on the flow control value obtained in step S4, adjust the molten salt flow rate through the molten salt regulating valve, thereby controlling the molten salt temperature at the absorber outlet.

[0011] In another preferred embodiment, X5 is an integer between 3 and 7, and X6 is an integer between 4 and 12.

[0012] In another preferred embodiment, the specific values ​​of X5 and X6 are adjusted according to the on-site operation and debugging conditions of the project.

[0013] In another preferred embodiment, X6 is an integer between 4 and 12.

[0014] In another preferred embodiment, the specific value of X1 is adjusted according to the on-site operation and debugging situation of the project.

[0015] In another preferred embodiment, the determination of the direction of change of the molten salt temperature is based on a logical judgment made according to the execution status of step Y2.

[0016] In another preferred embodiment, the adjustment parameter employs an interval parameter correction and readjustment strategy, wherein the interval parameter correction and readjustment strategy includes the following steps: X1) A preset time interval is defined, divided into a pre-interval and a post-interval. Calculations are performed during the pre-interval. The value is then calculated over 3 seconds. The numerical values, and so on, are described in the following... The value of the controller proportional coefficient after the first adjustment, the This is the value of the controller proportional coefficient after the second adjustment; X2) Stop adjusting when the following conditions are met: T k+10 -Tset < X10 T k+20 T is the predicted value of the molten salt temperature 10 seconds after the current moment. set X10 is the preset third threshold value for molten salt temperature.

[0017] In another preferred embodiment, the interval parameter correction and readjustment strategy results in a large adjustment force in the early stage, and the adjustment force gradually weakens as time goes by.

[0018] In another preferred embodiment, the initial value of X10 is set to 3 to 5.

[0019] In another preferred embodiment, the value of X10 is adjusted according to the on-site operation and debugging situation.

[0020] In another preferred embodiment, the adjustment coefficient The initial value is set to 0.5~0.8.

[0021] In another preferred embodiment, the operation condition determination in step S1 via the operation condition identification device includes performing the following steps: S1-1. Select relevant operating conditions that affect the temperature of molten salt, including: air temperature, wind speed, cloud cover, and temperature. S1-2. Collect external driving data and internal driving data, wherein the external driving parameters include air temperature data, wind speed data and cloud data, and the internal driving parameters include absorber wall temperature field data. S1-3. Determine the operating condition through the following steps: (i) A state is considered to be in a good steady state when the following conditions are met: (1) The temperature data model for the current season's sunny weather has a downward deviation of no more than a set threshold in at least two of the three consecutive time periods; (2) The wind speed value is lower than the average value of at least two of the three consecutive time periods during the sunny weather of the season; (3) Cloud map data shows that there are basically no clouds or the impact of clouds is negligible. (4) The temperature field of the absorber wall is in a stable state; (ii) When the conditions for determining the favorable steady-state condition are not met, the corresponding operating condition shall be determined according to the relevant conditions: (1) When the temperature deviates from the temperature data model of the sunny weather of the current season in at least two of the three consecutive time periods, it is judged as a sudden drop or rapid drop in temperature. (2) When the wind speed value is higher than the average value of at least two of the three consecutive time periods during the sunny weather of the season, it is judged as a sudden wind change condition; (3) When the cloud impact cannot be ignored, it is judged as a sudden change in cloud imagery. (4) When the temperature field of the absorber wall changes drastically, it is determined to be a sudden temperature field change condition.

[0022] In another preferred embodiment, the set threshold is 1-5℃, preferably 2-4℃, for example 3℃.

[0023] In another preferred embodiment, the set threshold is adjusted according to the on-site conditions.

[0024] In another preferred embodiment, the factors related to the molten salt temperature in step S2 include, but are not limited to, direct solar radiation (DNI), clouds, wind, molten salt flow rate, and receiver inlet molten salt temperature; In another preferred embodiment, evaluating the accuracy of the predicted value using the prediction evaluation device in step S2 includes performing the following steps: S2-1) Set the evaluation threshold and select a time period, then obtain the predicted values ​​of the evaluation device within the historical time segment of 1 to 8 minutes prior to the selected time. and the actual detection value corresponding to the selected time. ; S2-2) Calculate the accuracy of the assessment using the following formula: in, For predicted values, For the corresponding detection value, To predict the mean of the actual detection values ​​within the predicted time interval, N To set the calculation time for the prediction and evaluation; S2-3) Compare the calculated prediction accuracy A with the evaluation threshold to obtain the evaluation result of the accuracy of the prediction value; S2-4) Output the evaluation results via the output terminal.

[0025] In another preferred embodiment, the method further includes correcting the initial value of the molten salt flow rate setting in step S3, wherein correcting the initial value of the flow rate setting includes performing the following steps: W1) Obtain wind speed and wind direction detection information and combine them with factors related to the configuration and installation location of the heat absorber of the heat absorption tower to set wind speed threshold and wind direction combination, and set key ranges that affect wind direction and wind speed in order to formulate trigger conditions for dynamic correction of molten salt flow rate setpoint. W2) Compare the real-time detected actual wind speed and direction with the triggering conditions. When the influence relationship between the actual wind speed and direction falls into the triggering conditions for dynamic correction of the molten salt flow rate setpoint, the molten salt flow rate setpoint is revised.

[0026] In another preferred embodiment, the factors related to the configuration and installation location of the heat absorber of the heat tower include, but are not limited to, the configuration of the heat absorber tube panel (single or double row), the flow direction of the tube panel (north-in, south-out, etc.), and the overall structural setting of the tube panel (crossing, parallel, etc.).

[0027] In another preferred embodiment, the correction amount for the molten salt flow rate is determined by combining the simulated numerical range with the on-site operational effect to determine the set value of the molten salt flow rate.

[0028] In another preferred embodiment, the molten salt flow rate setpoint is dynamically adjusted based on the correction amount of the molten salt flow rate to ensure a rapid response in the control of the molten salt temperature at the absorber outlet under wind speed conditions.

[0029] In another preferred embodiment, step S4 further includes a sub-step: Step S4-1) Provide a temperature rise controller, a temperature drop controller, and a minimum flow controller; Step S4-2) The temperature rise controller inputs a temperature rise setpoint and outputs a temperature rise limit value; the temperature drop controller inputs a temperature drop setpoint and outputs a temperature drop limit value; the minimum flow controller inputs a minimum flow setpoint and outputs a minimum flow limit value. Step S4-3) Compare the flow control value, temperature rise limit value, and temperature drop limit value obtained in step S4-2, and select the smaller value; Step S4-4) Compare the minimum flow limit value obtained in step S4-2 with the smaller value obtained in step S4-3, and select the larger value; (Step S4-5) Based on the larger value obtained in step S4-4, adjust the molten salt flow rate through the molten salt regulating valve, thereby controlling the molten salt temperature at the absorber outlet.

[0030] In another preferred embodiment, the flow controller, temperature rise controller, and temperature drop controller are all PID controllers.

[0031] In another preferred embodiment, the parameters of the PID controller are fixed.

[0032] In another preferred embodiment, the parameters are determined based on on-site debugging.

[0033] In another preferred embodiment, the method further includes setting a display window, wherein the display window displays a temperature rise limit value, a temperature drop limit value, a minimum flow rate limit value, and a normal temperature control value.

[0034] A second aspect of the present invention provides a molten salt temperature control device for an absorber outlet, the molten salt temperature control device being configured between a pipeline connecting the absorber inlet buffer tank and the absorber heat-receiving tube panel, comprising: The working condition identification module is used to determine the working condition. The input terminal of the working condition identification module receives signals that affect the relevant working conditions that affect the molten salt temperature, and the output terminal outputs the working condition determination result. The molten salt temperature prediction module at the absorber outlet is used to predict the molten salt temperature. The input terminal of the molten salt temperature prediction module receives the signal of factors related to the molten salt temperature. The output terminal is equipped with a prediction evaluation module to evaluate the accuracy of the prediction value and output the predicted molten salt temperature value and the evaluation result of the accuracy of the prediction value. The molten salt flow rate setpoint dynamic correction module is used to correct the initial value of the molten salt flow rate setting. The input of the correction module receives wind speed and wind direction signals, and the output outputs the molten salt flow rate correction signal. The temperature and flow rate regulation loop consists of a cascaded PID control loop. The outer loop of the control loop is equipped with a temperature controller, and the inner loop is equipped with a flow controller. The input terminal of the temperature controller is connected to the output terminals of the molten salt temperature prediction module and the operating condition identification module. The PID controller parameters of the temperature controller are dynamically adjusted based on the operating condition judgment result and the evaluation result. The input terminal is also configured to receive the difference between the setpoint of the molten salt temperature at the absorber outlet and the detected value of the molten salt temperature transmitter, and the output terminal outputs the temperature control value. The input terminal of the flow controller is connected to the output terminals of the temperature controller and the molten salt flow transmitter, and is used to receive the temperature control value, the setpoint of the molten salt flow rate, and the detected value of the molten salt flow transmitter. The output terminal outputs the flow control value, wherein the temperature control value and the corrected initial setpoint of the molten salt flow rate are accumulated to form the setpoint. A molten salt regulating valve is used to regulate the flow rate of molten salt. The control end of the regulating valve is connected to the output end of the flow controller, and the output end is connected to the heat receiving tube panel of the absorber through a pipeline.

[0035] In another preferred embodiment, the molten salt temperature control device further includes: The temperature rise controller receives the temperature rise setpoint at its input terminal and outputs the temperature rise limit value at its output terminal. A temperature drop controller receives a temperature drop setpoint at its input and outputs a temperature drop limit value at its output. A minimum flow controller, whose input terminal receives the minimum flow set value and whose output terminal outputs the minimum flow limit value; Take a small module, connect the input end to the output end of the flow controller, temperature rise controller, and temperature drop controller, and use it to compare the smaller value of the input value. The output end outputs the smaller value command. The input terminal of the larger value module is connected to the output terminal of the smaller value module and the minimum flow controller. It is used to input a larger value instruction for comparison and selection, and the output terminal outputs the larger value instruction.

[0036] In another preferred embodiment, the control terminal of the molten salt regulating valve is connected to the output terminal of the large-capacity module, and the output terminal is connected to the heat absorption tube panel of the absorber through a pipeline.

[0037] In another preferred embodiment, the molten salt temperature control device further includes a display indicator module, wherein the display indicator module displays the temperature rise limit value, the temperature drop limit value, the minimum flow rate limit value, and the normal temperature control value.

[0038] In another preferred embodiment, the operations of determining the operating conditions, predicting the molten salt temperature, evaluating the accuracy of the predicted value, dynamically adjusting the temperature PID controller parameters, and correcting the initial value of the molten salt flow rate setting are the same as those described in the first aspect of the present invention.

[0039] In a third aspect, the present invention provides a tower-type solar thermal power plant receiver, comprising: The receiver inlet buffer tank, the receiver heating tube screen, and the molten salt temperature control device are provided, wherein the outlet of the receiver inlet buffer tank is connected to the receiver heating tube screen via a pipeline, and the molten salt temperature control device is disposed between the pipeline connecting the receiver inlet buffer tank and the receiver heating tube screen, and the molten salt temperature control device is configured to control the temperature of the molten salt at the receiver outlet of the heat collection tower according to the method of the first aspect of the present invention.

[0040] It should be understood that, within the scope of this invention, the above-described technical features of this invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, they will not be described in detail here. Attached Figure Description

[0041] Figure 1 A schematic flowchart of the heat absorber is shown.

[0042] Figure 2 A schematic diagram of the molten salt process in the absorber is shown.

[0043] Figure 3 A principle flow chart of a single-loop receiver is shown.

[0044] Figure 4 A diagram showing the method for controlling the molten salt temperature at the absorber outlet is displayed.

[0045] Figure 5 The setup scheme for the operating condition identification device is shown.

[0046] Figure 6 The block diagram of the variable parameter method for PID controller is shown. Detailed Implementation

[0047] Through extensive and in-depth research, the inventors have discovered for the first time a method for controlling the molten salt temperature of a tower-type solar thermal power plant receiver. This method includes a molten salt temperature control device configured between the receiver inlet buffer tank and the receiver's heat-receiving tube panel. The molten salt temperature control device comprises: an operating condition identification module; a receiver outlet molten salt temperature prediction module; a molten salt flow rate setpoint dynamic correction module; a temperature and flow rate regulation loop composed of a cascaded PID control loop, wherein the outer loop of the control loop is equipped with a temperature controller, and the inner loop is equipped with a flow controller; a temperature rise controller; a temperature drop controller; a minimum flow rate controller; a minimum flow rate selection module; a maximum flow rate selection module; and a molten salt regulating valve. This invention employs a cascade control structure consisting of a PID molten salt temperature controller with variable external loop parameters and a PID molten salt flow controller with fixed internal loop parameters. This dynamically adapts to changes in external influencing factors while ensuring internal loop reliability. A condition identification module is also included. A receiver outlet molten salt temperature prediction module enables timely response to changes in relevant factors, and a dynamic correction function for molten salt flow rate setpoints based on wind speed and direction effectively adjusts the flow regulation internal loop to enhance the reliability of molten salt temperature control. Based on these principles, this invention was completed.

[0048] the term Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0049] As used herein, the terms “comprising,” “including,” and “containing” are used interchangeably and include not only closed definitions but also semi-closed and open definitions. In other words, the terms include “consisting of” and “substantially consisting of”.

[0050] As used herein, when referring to a specific enumerated value, the term “about” means that the value can vary by no more than 1% from the enumerated values. For example, as used herein, the expression “about 100” includes all values ​​between 99 and 101 (e.g., 99.1, 99.2, 99.3, 99.4, etc.).

[0051] As used in this article, the term "seasonal clear weather temperature data model" refers to the seasonal clear weather temperature data model constructed by the project by comprehensively determining factors such as temperature, wind speed, cloud cover, and date of the location.

[0052] Tower solar thermal power plant receiver The tower-type solar thermal power plant's receiver employs a dual-loop configuration. Under the action of a cryogenic molten salt pump, molten salt at approximately 297°C is fed into the receiver's inlet buffer tank via a riser pipe. Under pressure within the tank, the molten salt working fluid is fed into the receiver's heat exchange tube panels from the north side via connecting pipes in two separate streams. Each stream consists of eight tube panels connected in series. The two streams of molten salt flow sequentially through the four tube panels on the north side in clockwise / counterclockwise directions, respectively. After cross-heat exchange via connecting pipes, they are then fed into the corresponding four tube panels on the south side for further flow and heating. The two streams of molten salt flow continuously within the tube panels, absorbing heat and reaching the design temperature of approximately 560°C. Finally, they flow out from the south side and converge into the outlet buffer tank. (Receiver principle flow diagram) Figure 1 As shown, the molten salt process of the receiver is as follows: Figure 2 As shown.

[0053] It is worth noting that the above system diagram only illustrates a general system principle and does not emphasize specific quantities. The number of devices can be configured according to system requirements. For example, redundancy design can be implemented based on device reliability, and triple redundancy can be set for molten salt flow and temperature detection elements. Such settings will increase the stability and reliability of the system, but are not the focus of this article.

[0054] The main control mechanism of the method of this invention To comprehensively address the issue of molten salt temperature control in the receiver as described above, this invention proposes a molten salt temperature control method with operating condition identification capabilities and adaptability to changes in relevant factors, such as... Figure 4 As shown. The main control mechanism of this control method includes: 1. To overcome the control lag and overshoot caused by the large inertia of temperature parameters, a molten salt flow controller is installed. A molten salt temperature controller is installed outside the molten salt flow controller. The molten salt temperature controller uses variable parameter PID control to adapt to the dynamic changes of external influencing factors.

[0055] 2. Set up an outlet molten salt temperature prediction device to predict the molten salt temperature. The input of the prediction device includes relevant factors such as DNI, cloud, wind, and molten salt. A prediction evaluation device is set up at the outlet of the prediction device to dynamically evaluate the prediction effect of the prediction device. Based on the evaluation results, a decision is made on whether to introduce the prediction effect into the control loop to reduce the strong hysteresis effect of temperature.

[0056] 3. To avoid the impact of frequent fluctuations on the control loop, a condition identification device is set up to determine the condition. The condition identification result serves as another constraint for the entry and exit of predictive data into the control loop.

[0057] 4. Set a dynamic correction function for the molten salt flow rate setpoint based on wind speed and direction factors to reduce the lag of wind influence.

[0058] 5. The high temperature of the molten salt medium and the rapid temperature change will cause changes in the thermal stress of the material, affecting the service life of the material. Therefore, a temperature change rate limiting control function should be set.

[0059] 6. To prevent damage to system equipment caused by the low-temperature solidification of molten salt, a minimum flow control function is set.

[0060] Key points of this invention (1) Set up a cascade control structure of an outer layer variable parameter PID molten salt temperature controller and an inner layer fixed parameter PID molten salt flow controller to dynamically adapt to changes in external influencing factors and ensure the reliability of the internal loop.

[0061] (2) A molten salt temperature prediction device is set up at the receiver outlet to predict the molten salt temperature. The input of the prediction device includes relevant factors such as DNI, cloud, wind, and molten salt. The prediction mechanism is constructed using Long Short-Term Memory Network (LSTM) and Recurrent Neural Network (RNN). A prediction evaluation device is set up inside the prediction device to dynamically evaluate the prediction effect of the prediction device. Based on the evaluation results, a decision is made on whether to introduce the prediction effect into the control loop to reduce the strong hysteresis effect of temperature.

[0062] (3) Set up a working condition identification device to judge the working condition. The working condition identification result serves as another constraint for the prediction data to enter and exit the control loop. The working condition identification device sets the working conditions based on the correlation with the molten salt temperature at the receiver outlet, including: clear and steady state, sudden / rapid temperature drop, sudden wind change, sudden cloud appearance change, and sudden temperature field change.

[0063] (4) The variable parameter method of the PID molten salt temperature controller with variable parameters takes into account the evaluation results of the working condition identification device and the prediction device, and is carried out in accordance with the steps described above.

[0064] (5) Set up a molten salt temperature rise controller, temperature drop controller and minimum flow controller and integrate them into the control loop for variable working condition identification and correction to increase the performance guarantee of the control loop.

[0065] (6) The method for dynamic correction of the molten salt flow rate setpoint by wind speed and direction is as follows: Obtain the wind speed and direction detection information at the top of the heat absorption tower, and consider factors such as the configuration and installation location of the heat absorption tower absorber. Set wind speed thresholds and wind direction combinations respectively, and set key influencing wind directions and wind speed ranges. When the actual wind speed and direction influence relationship falls into the dynamic correction condition of the molten salt flow rate setpoint, the molten salt flow rate setpoint revision is initiated. The magnitude of the correction can be achieved by using a combination of simulation numerical range and on-site operational effect correction to ensure rapid response of the absorber outlet molten salt temperature control under wind speed influence conditions.

[0066] The main advantages of this invention include: (1) The method of the present invention can dynamically adapt to changes in external influencing factors.

[0067] (2) The method of the present invention can effectively adjust the inner loop of the flow regulation to enhance the reliability of molten salt temperature control.

[0068] (3) The method of the present invention enables the absorber outlet temperature control to respond promptly to changes in factors related to the molten salt temperature.

[0069] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, percentages and parts are weight percentages and parts by weight.

[0070] Example 1: A molten salt temperature control device is installed at the inlet of each unit circuit. A temperature detection element is installed at the outlet of each tube panel.

[0071] The difference between the setpoint of the molten salt temperature at the absorber outlet and the value detected by the molten salt temperature transmitter is input to the temperature controller. The temperature controller is a PID controller, which employs a dynamic parameter adjustment strategy. See details... Figure 6 The temperature controller output is accumulated with the molten salt flow rate setpoint driven by wind speed and direction parameters, serving as the setpoint for the flow controller. The flow controller's detected value comes from the molten salt flow transmitter, and the flow controller employs a PID controller. The flow controller output, along with the set outputs of the molten salt temperature rise controller and temperature drop controller, are sent to the minimum flow rate control module for instruction comparison. The minimum flow rate control module output instruction, along with the minimum flow rate controller set for the molten salt flow rate, enters the maximum flow rate control module. The maximum flow rate control module output instruction is then sent to the molten salt regulating valve for adjustment. The temperature rise controller, temperature drop controller, and minimum flow rate controller all use fixed-parameter PID controllers, with parameters determined through on-site commissioning. To promptly and accurately understand the system's operating status, a mode display window is set on the molten salt regulating valve's operating interface, displaying mode information including: temperature rise limit, temperature drop limit, minimum flow rate limit, and normal temperature control.

[0072] The method for dynamically correcting the molten salt flow rate setpoint based on wind speed and direction is as follows: Obtain wind speed and direction detection information at the top of the heat exchanger tower. Considering factors such as the configuration and installation location of the heat exchanger tower receiver, set wind speed thresholds and wind direction combinations, and define key influencing wind directions and speed ranges. When the actual wind speed and direction influence falls within the conditions for dynamic correction of the molten salt flow rate setpoint, the molten salt flow rate setpoint revision is initiated. The magnitude of the correction can be achieved by combining simulation numerical ranges with on-site operational effect corrections to ensure rapid response of the receiver outlet molten salt temperature control under wind speed influence conditions.

[0073] The following steps are performed to determine the operating condition using an operating condition identification device: I. Select relevant operating conditions that affect the temperature of molten salt, including: air temperature, wind speed, cloud cover, and temperature. II. Collect external driving data and internal driving data, wherein the external driving parameters include air temperature data, wind speed data and cloud data, and the internal driving parameters include absorber wall temperature field data; III. Determine the operating condition through the following steps: (i) A state is considered to be in a good steady state when the following conditions are met: (1) The temperature deviation of the temperature data model during three consecutive time periods in the same season does not exceed the set threshold in at least two of the three consecutive time periods in the same season; (2) The wind speed value is lower than the average value of the wind speed data model during three consecutive time periods in the same season; (3) The cloud map data shows that there are basically no clouds or the influence of clouds is basically ignored; (4) The temperature field of the absorber wall is in a stable state; wherein, the set threshold is about 3°C ​​and is adjusted according to the on-site conditions.

[0074] (ii) When the conditions for determining the favorable steady-state condition are not met, the corresponding operating condition shall be determined according to the relevant conditions: (1) When the temperature deviates from the temperature data model of the current season's sunny weather in at least two out of three consecutive time periods, it is determined to be a sudden drop or rapid drop in temperature. (2) When the wind speed value is higher than the average value of the current season's sunny weather in at least two out of three consecutive time periods, it is determined to be a sudden wind change. (3) When the cloud influence cannot be ignored, it is determined to be a sudden cloud phenomenon. (4) When the temperature field of the absorber wall changes drastically, it is determined to be a sudden temperature field change. The setting scheme of the condition identification device is as follows: Figure 5 As shown.

[0075] The absorber outlet molten salt temperature prediction device predicts the outlet molten salt temperature. The input to the prediction device includes relevant factors such as DNI (Darkness Intake), cloud cover, wind, and molten salt. The prediction mechanism is constructed using Long Short-Term Memory (LSTM) networks and Recurrent Neural Networks (RNNs). The prediction device embeds a prediction evaluation device to dynamically evaluate the prediction effect. The evaluation mechanism uses the average deviation between the predicted value and the actual detected value over a historical time period as a measure. For example, the accuracy of the predicted value compared to the actual detected value within 3-5 minutes after the actual time point is expressed by the following formula: Where P is the predicted value, M is the corresponding detected value, and N is the set prediction and evaluation calculation time.

[0076] The calculated accuracy data is compared with the set evaluation threshold, and the judgment result is output to the control loop for use.

[0077] Wherein, the PID controller parameter varying method comprehensively considers the evaluation results of the working condition identification device and the prediction device, and specifically proceeds according to the following steps: 1. A prediction accuracy evaluation mechanism is provided in the molten salt temperature prediction device at the outlet of the heat absorber. When the evaluation accuracy of the prediction device is high, proceed to step 2. When the evaluation accuracy of the prediction device is not high, the prediction device operates in a follow-up mode, and the PID controller does not perform the parameter varying operation.

[0078] 2. Query the identification result of the working condition identification device. When the working condition is a stable sunny working condition, the PID controller does not perform the parameter varying operation. When the working condition is any one of sudden / rapid temperature drop, sudden wind change, sudden cloud image change, and sudden temperature field change, proceed to step 3.

[0079] 3. Is it determined that the direction of changing the molten salt temperature is decreasing? If yes, proceed to step 3.1. If no, proceed to step 3.2.

[0080] 3.1 Determine whether the temperature state meets the following conditions T-T set <X5 and T k+20 -T set <X6 Wherein, T is the detected value of molten salt temperature at the current moment; T set is the set value of molten salt temperature; T k+20 is the predicted value of molten salt temperature 20s after the current moment; X5 and X6 are set thresholds, the initial values can be selected as X5=5 and X6=8, and the specific values are adjusted according to the operation and commissioning conditions of the project site.

[0081] If the conditions are met, the system state remains unchanged and no change is performed. If the conditions are not met, proceed to step 4.

[0082] 3.2 Determine whether the temperature state meets 1)T k+20 - T set <X1 or 2)ΔT k+2 , ΔT k+4 ...ΔT k+20 the trend is decreasing, and the speed < X2 Wherein, T set is the set value of molten salt temperature; T k+20 is the predicted value of molten salt temperature 20s after the current moment; ΔT k+2 is the change rate calculated at the 2nd second after the current moment of molten salt temperature, ΔTk+4 calculate the change rate of the molten salt temperature in the 2s interval before the 4th second after the current moment, and so on.

[0083] X1 and X2 are set thresholds, the initial value of X1 can be selected as X1=8, and the specific value is adjusted according to the operation and commissioning conditions of the project site. X2 is the average value of the change rate at 2s intervals within a 20s interval.

[0084] If the condition is satisfied, the system state remains unchanged and no adjustment is performed. If the condition is not satisfied, the process proceeds to step 4.

[0085] 4. Adjust the parameters of the PID controller, specifically as follows: Wherein, , are the original values of the proportional coefficient and integral coefficient of the controller respectively; N=1, 2, 3... is a counting sequence for re-adjusting interval parameter correction; is an adjustment coefficient, the initial value is selected from 0.5 to 0.8, and an optimization strategy for the adjustment coefficient k is set.

[0086] The parameter adjustment of the PID controller adopts a dynamic adjustment strategy, which specifically includes a strategy of performing interval parameter correction and readjustment (such as 3s or setting unequal intervals). For example, the value of KP1 is calculated in the first 3 seconds, and the value of KP2 is calculated in the subsequent 3s, and so on. Until T k+10 - T set <X10, that is, the deviation between the predicted value at 10s and the set value is less than a set threshold. The initial value of X10 can be set to 3~5, and can be adjusted according to the on-site operation and commissioning conditions. The interval parameter correction and readjustment strategy makes the parameter adjustment have a greater impact in the early stage, and as time goes by, the adjustment intensity gradually weakens, so that the control loop can achieve the effect of steady recovery. The optimization strategy for the adjustment coefficient k includes: calculating the actual adjustment time and accuracy parameters of the control loop for a certain k value, and setting rules: under the same triggering condition, recording the k value and the above control quality values, taking the average quality as the reward and punishment line, rewarding those higher than the average value, and punishing those lower than the average value, so that the coefficient k can be optimized through iterative learning. The variable parameter method of the PID controller is as Figure 6 shown.

[0087] All documents mentioned in the present invention are incorporated by reference in this application, just as if each document was individually incorporated by reference. In addition, it should be understood that after reading the above teaching content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims appended to this application.

Claims

1. A method for controlling the molten salt temperature of the receiver in a tower-type solar thermal power plant, characterized in that, Includes the following steps: S1. Collect relevant operating conditions that affect the temperature of molten salt, and use the operating condition identification device to judge the operating conditions and obtain the operating condition judgment results. The judgment results include clear and steady state, sudden drop or rapid drop in temperature, sudden change in wind, sudden change in cloud image, and sudden change in temperature field. S2. Collect information on factors related to molten salt temperature, predict molten salt temperature using a molten salt temperature prediction device, and evaluate the accuracy of the prediction value using a prediction evaluation device to obtain the predicted molten salt temperature value and the evaluation result of the prediction accuracy. The prediction mechanism of the molten salt temperature prediction module at the absorber outlet is constructed using a Long Short-Term Memory Network (LSTM) and a Recurrent Neural Network (RNN). The evaluation mechanism of the prediction evaluation module is to measure the average deviation between the predicted value and the actual value detected in historical time periods. S3. The temperature and flow rate are regulated by a temperature and flow rate regulation loop composed of a cascade PID control loop, which includes an outer loop temperature PID controller and an inner loop flow rate PID controller. The temperature PID controller takes the difference between the set value of the molten salt temperature at the absorber outlet and the value detected by the molten salt temperature transmitter as input to obtain the temperature control value. The flow rate PID controller takes the set value of the molten salt flow rate and the value detected by the molten salt flow rate transmitter as input and outputs the flow rate control value. The temperature control value is accumulated with the initial value of the molten salt flow rate setting to obtain the molten salt flow rate set value. The temperature PID controller dynamically adjusts its parameters based on the operating condition determination result obtained in step S1 and the molten salt temperature prediction evaluation result obtained in step S2. This dynamic adjustment includes the following steps: Y1. Detect the evaluation result of the predicted value of molten salt temperature. When the evaluation accuracy is high, proceed to step Y2. When the evaluation accuracy is not high, the temperature PID controller does not perform parameter adjustment operation. Y2. Query the working condition judgment result: When the working condition is a clear and stable state, the temperature PID controller does not perform parameter adjustment operation; when the working condition is any of the following working conditions: sudden drop in temperature or rapid drop, sudden change in wind, sudden change in cloud appearance, or sudden change in temperature field, proceed to step Y3. Y3. Determine whether the direction of change in the molten salt temperature is downward. If it is downward, proceed to step Y3.1; if it is upward, proceed to step Y3.

2. Y3.1 When the direction of change of the molten salt temperature is the cooling direction, determine whether the temperature state simultaneously meets the following conditions: n1) T-T set <X5; n2) T k+20 -T set <X6; Where T is the current measured value of the molten salt temperature; T set Set value for molten salt temperature; T k+20 X5 and X6 are the predicted values ​​of the molten salt temperature 20 seconds after the current moment; X5 and X6 are the preset first threshold values. If the above conditions are met, the parameter adjustment operation will not be performed; if the above conditions are not met, proceed to step Y4. Y3.2 When the direction of change of the molten salt temperature is the heating direction, determine whether the temperature state meets any of the following conditions: m1) T k+20 - T set <X1; or m2) ΔT k+2 ΔT k+4 ...ΔT k+20 The rate at which the trend decreases <X2; Among them, T set Set value for molten salt temperature; T k+20 This is the predicted value of the molten salt temperature 20 seconds after the current moment; ΔT k+2 Calculate the rate of change of molten salt temperature 2 seconds after the current moment, ΔT. k+4 The rate of change of the molten salt temperature in the first 2 seconds is calculated 4 seconds after the current time, and so on; X1 and X2 are preset second thresholds, where X2 is the average rate of change of the 2-second interval within the 20-second interval; If any of the above conditions are met, the parameter adjustment operation will not be performed; otherwise, proceed to step Y4. Y4. Adjust the parameters according to the following formula: in, This is the initial value of the controller proportional coefficient. is the initial value of the controller integral coefficient; n is the counting sequence for interval parameter correction and readjustment, where N is a positive integer; The adjustment coefficient is determined by performing the following steps. Adjustments and optimizations were made: Z1) Under the same triggering factors, the computational controller performs different... The adjustment time parameter and accuracy parameter are set at the specified values, and each is determined based on the adjustment time parameter and accuracy parameter. The value controls the quality of the numerical value; Z2) Record each The values ​​and their corresponding control quality values ​​are used to calculate the mean of all control quality values, and the mean is used as the reward and punishment line. Z3) will each The control quality value corresponding to the value is compared with the reward / penalty line, and the value is higher than the reward / penalty line. Values ​​are rewarded, and those below the reward / penalty threshold are punished. The value is subject to a penalty; Z4) Adjust according to the results of rewards and punishments The value of the coefficient is such that... Iterative learning optimization; S4. Based on the flow control value obtained in step S4, adjust the molten salt flow rate through the molten salt regulating valve, thereby controlling the molten salt temperature at the absorber outlet.

2. The method as described in claim 1, characterized in that, The step S1, which involves determining the operating condition using the operating condition identification device, includes the following steps: S1-1. Select relevant operating conditions that affect the temperature of molten salt, including: air temperature, wind speed, cloud cover, and temperature. S1-2. Collect external driving data and internal driving data, wherein the external driving parameters include air temperature data, wind speed data and cloud data, and the internal driving parameters include absorber wall temperature field data. S1-3. Determine the operating condition through the following steps: (i) A state is considered to be in a good steady state when the following conditions are met: (1) The temperature data model for the current season's sunny weather has a downward deviation of no more than a set threshold in at least two of the three consecutive time periods; (2) The wind speed value is lower than the average value of at least two of the three consecutive time periods during the sunny weather of the season; (3) Cloud map data shows that there are basically no clouds or the impact of clouds is negligible. (4) The temperature field of the absorber wall is in a stable state; (ii) When the conditions for determining the favorable steady-state condition are not met, the corresponding operating condition shall be determined according to the relevant conditions: (1) When the temperature deviates from the temperature data model of the sunny weather of the current season in at least two of the three consecutive time periods, it is judged as a sudden drop or rapid drop in temperature. (2) When the wind speed value is higher than the average value of at least two of the three consecutive time periods during the sunny weather of the season, it is judged as a sudden wind change condition; (3) When the cloud impact cannot be ignored, it is judged as a sudden change in cloud imagery. (4) When the temperature field of the absorber wall changes drastically, it is determined to be a sudden temperature field change condition.

3. The method as described in claim 1, characterized in that, The factors related to molten salt temperature in step S2 include, but are not limited to, direct solar radiation (DNI), clouds, wind, molten salt flow rate, and molten salt temperature at the absorber inlet.

4. The method as described in claim 1, characterized in that, The step S2, which evaluates the accuracy of the predicted value using a prediction evaluation device, includes the following steps: S2-1) Set the evaluation threshold and select a time period, then obtain the predicted values ​​of the evaluation device within the historical time segment of 1 to 8 minutes prior to the selected time. and the actual detection value corresponding to the selected time. ; S2-2) Calculate the accuracy of the assessment using the following formula: in, For predicted values, For the corresponding detection value, To predict the mean of the actual detection values ​​within the predicted time interval, N To set the calculation time for the prediction and evaluation; S2-3) Compare the calculated prediction accuracy A with the evaluation threshold to obtain the evaluation result of the accuracy of the prediction value; S2-4) Output the evaluation results via the output terminal.

5. The method as described in claim 1, characterized in that, The method further includes correcting the initial value of the molten salt flow rate setting in step S3, wherein correcting the initial value of the flow rate setting includes performing the following steps: W1) Obtain wind speed and wind direction detection information and combine them with factors related to the configuration and installation location of the heat absorber of the heat absorption tower to set wind speed threshold and wind direction combination, and set key ranges that affect wind direction and wind speed in order to formulate trigger conditions for dynamic correction of molten salt flow rate setpoint. W2) Compare the real-time detected actual wind speed and direction with the triggering conditions. When the influence relationship between the actual wind speed and direction falls into the triggering conditions for dynamic correction of the molten salt flow rate setpoint, the molten salt flow rate setpoint is revised.

6. The method as described in claim 1, characterized in that, Step S4 further includes a sub-step: Step S4-1) Provide a temperature rise controller, a temperature drop controller, and a minimum flow controller; Step S4-2) The temperature rise controller inputs a temperature rise setpoint and outputs a temperature rise limit value; the temperature drop controller inputs a temperature drop setpoint and outputs a temperature drop limit value; the minimum flow controller inputs a minimum flow setpoint and outputs a minimum flow limit value. Step S4-3) Compare the flow control value, temperature rise limit value, and temperature drop limit value obtained in step S4-2, and select the smaller value; Step S4-4) Compare the minimum flow limit value obtained in step S4-2 with the smaller value obtained in step S4-3, and select the larger value; (Step S4-5) Based on the larger value obtained in step S4-4, adjust the molten salt flow rate through the molten salt regulating valve, thereby controlling the molten salt temperature at the absorber outlet.

7. The method as described in claim 6, characterized in that, The flow controller, temperature rise controller, and temperature drop controller are all PID controllers.

8. The method as described in claim 1, characterized in that, The method also includes setting a display window, wherein the display window displays the temperature rise limit value, temperature drop limit value, minimum flow limit value, and normal temperature control value.

9. A device for controlling the temperature of molten salt at the outlet of a heat absorber, characterized in that, The molten salt temperature control device is configured between the absorber inlet buffer tank and the absorber heating tube panel, including: The working condition identification module is used to determine the working condition. The input terminal of the working condition identification module receives signals that affect the relevant working conditions that affect the molten salt temperature, and the output terminal outputs the working condition determination result. The molten salt temperature prediction module at the absorber outlet is used to predict the molten salt temperature. The input terminal of the molten salt temperature prediction module receives the signal of factors related to the molten salt temperature. The output terminal is equipped with a prediction evaluation module to evaluate the accuracy of the prediction value and output the predicted molten salt temperature value and the evaluation result of the accuracy of the prediction value. The molten salt flow rate setpoint dynamic correction module is used to correct the initial value of the molten salt flow rate setting. The input of the correction module receives wind speed and wind direction signals, and the output outputs the molten salt flow rate correction signal. The temperature and flow rate regulation loop consists of a cascaded PID control loop. The outer loop of the control loop is equipped with a temperature controller, and the inner loop is equipped with a flow controller. The input terminal of the temperature controller is connected to the output terminals of the molten salt temperature prediction module and the operating condition identification module. The PID controller parameters of the temperature controller are dynamically adjusted based on the operating condition judgment result and the evaluation result. The input terminal is also configured to receive the difference between the setpoint of the molten salt temperature at the absorber outlet and the detected value of the molten salt temperature transmitter, and the output terminal outputs the temperature control value. The input terminal of the flow controller is connected to the output terminals of the temperature controller and the molten salt flow transmitter, and is used to receive the temperature control value, the setpoint of the molten salt flow rate, and the detected value of the molten salt flow transmitter. The output terminal outputs the flow control value, wherein the temperature control value and the corrected initial setpoint of the molten salt flow rate are accumulated to form the setpoint. A molten salt regulating valve is used to regulate the flow rate of molten salt. The control end of the regulating valve is connected to the output end of the flow controller, and the output end is connected to the heat receiving tube panel of the absorber through a pipeline.

10. A tower-type solar thermal power plant receiver, characterized in that, include: The receiver inlet buffer tank, the receiver heating tube screen, and the molten salt temperature control device are provided, wherein the outlet of the receiver inlet buffer tank is connected to the receiver heating tube screen via a pipeline, and the molten salt temperature control device is configured to control the temperature of the molten salt at the receiver outlet of the heat collection tower as described in any one of claims 1-7.

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