A multi-state water replenishment control method for steelmaking hybrid heat accumulator

Abstract

The present invention relates to a multi-state water replenishment control method for a steelmaking hybrid heat accumulator, and the method comprises the following steps: step 1: when the steam flow rate entering the hybrid heat accumulator is greater than the steam flow rate sent out of the hybrid heat accumulator and the RH steam consumption, the hybrid heat accumulator water replenishment valve is controlled by a first fuzzy control; step 2: when the steam flow rate entering the hybrid heat accumulator is less than the steam flow rate sent out of the hybrid heat accumulator and the RH steam consumption, the hybrid heat accumulator water replenishment valve is controlled by a second fuzzy control; step 3: when the steam flow rate entering the hybrid heat accumulator is substantially equal to the steam flow rate sent out of the heat accumulator and the RH steam consumption, the heat accumulator is substantially in a system stable state, and the control system automatically switches to proportional cascade PID control.

Description

Technical Field

[0001] The invention relates to a control method, in particular to a multi-state water replenishment control method for a steelmaking hybrid heat accumulator, and belongs to the technical field of steelmaking hybrid heat accumulator control. Background Art

[0002] Meishan Steel Plant No. 1 currently has 3 150-ton converter vaporization systems (sending steam to the accumulator), a 150-cubic-meter accumulator with 4 units in parallel, and No. 2 Steel Plant currently has 2 250-ton converter vaporization systems (sending steam to the accumulator), a 150-cubic-meter accumulator with 4 units in parallel. The medium-pressure steam of the power plant is used as security supplementary steam. At present, the No. 2 Steel Plant produces a large amount of steam but consumes less, while the No. 1 Steel Plant produces a small amount of steam but consumes more. The imbalanced state often requires external power plant steam balance. However, the No. 2 Steel Plant has a large surplus of steam. In order to more effectively improve the steam utilization rate and reduce the supplementary steam of the power plant, the steam main pipes of the steam accumulator stations of the No. 1 and No. 2 Steel Plants are connected to achieve steam balance in the steel plants. After the main pipes of the accumulators of the No. 1 and No. 2 Steel Plants are interconnected, the existing accumulators will form a series and parallel working mode of the accumulators. The water replenishment control of the original heat accumulator adopts single-loop PID control, that is, the water replenishment control is carried out according to the liquid level setting value of the heat accumulator. This single-loop heat accumulator liquid level replenishment control. It is convenient to use when the process application is not complicated, the disturbance is small, and the control accuracy requirement is not high. Its advantages are simple control system structure, good performance, and convenient system debugging. But its disadvantages are that when the process system is more complex, the system interference is large, and the system interference is more, it is difficult to make the control system reach a steady state using a single-loop control system. After the heat accumulators of the first and second steelmaking plants are connected in series and parallel, the operation mode of the steam inlet and outlet of the heat accumulator has changed (the eight heat accumulators are interconnected with each other), and the steam inlet and outlet of each heat accumulator will affect other heat accumulators. After the heat accumulators are connected in series and parallel, there are 5 converters that can generate steam and 3 RHs that can consume steam. Under the condition of variable steelmaking production and RH production, the disturbance points of the entire heat accumulator system are greatly increased, making the types of disturbances in the system more variable. The water replenishment control of the production mode of the hybrid heat accumulator in multiple states has the uncertainty of water replenishment control, the frequent changes of the heat accumulator liquid level, the low stability of the drainage control of the heat accumulator drain valve, the low stability of the system, and the weak anti-interference ability. The traditional heat accumulator water replenishment control method adopts a single-loop PID control scheme. The disadvantage of its control is that it is difficult to coordinate the contradiction between the rapidity and stability of the change of the steam volume of the heat accumulator, and its robustness is not good enough when the relevant parameters of the heat accumulator change and interference occur. Therefore, a new solution is urgently needed to solve the above technical problems. Summary of the invention

[0003] The present invention is aimed at the problems existing in the prior art, and provides a multi-state water replenishment control method for a steelmaking hybrid heat accumulator. The scheme is to establish a corresponding database based on various states such as the steam inlet flow of the hybrid heat accumulator, the flow of the external steam pipeline network of the hybrid heat accumulator, the steam consumption of different RH, and the liquid level of the heat accumulator itself. According to the relevant parameters of the heat accumulator under each state, a heat accumulator liquid level control model is established. When controlling the water replenishment of the heat accumulator, different heat accumulator water replenishment control methods are adopted by looking up the table of relevant heat accumulator parameters. The dynamic data regression technology is used to automatically enter the relevant heat accumulator parameters into the database each time, and the data in the database is optimized, and the water replenishment setting value is automatically corrected in the fuzzy control. In the process of water replenishment control of the heat accumulator, not only traditional control technology is used, but also multivariable dynamic control technology is used. A steady-state water replenishment control technology for the heat accumulator is realized.

[0004] In order to achieve the above object, the technical solution of the present invention is as follows: a multi-state water replenishment control method for a steelmaking hybrid heat accumulator, characterized in that the control method comprises the following steps:

[0005] Step 1: When the steam flow rate entering the hybrid heat accumulator is greater than the steam flow rate sent out of the hybrid heat accumulator and the RH steam consumption, the first fuzzy control is used to control the hybrid heat accumulator water supply valve;

[0006] Step 2: When the steam flow rate entering the hybrid heat accumulator is less than the steam flow rate sent out of the hybrid heat accumulator and the RH steam consumption, the second fuzzy control is used to control the water supply valve of the hybrid heat accumulator;

[0007] Step 3: When the steam flow entering the hybrid heat accumulator is basically equal to the steam flow sent out of the heat accumulator and the RH steam consumption, the heat accumulator is basically in a stable system state, and the control system automatically switches to proportional cascade PID control.

[0008] As an improvement of the present invention, the first fuzzy control is specifically as follows: the control of the hybrid heat accumulator water replenishment valve adopts fuzzy control, and according to the difference between the hybrid heat accumulator inlet steam flow, the external low-pressure steam volume and the RH steam consumption, the hybrid heat accumulator water replenishment control method adopts a method combining the water replenishment flow and the liquid level control to perform water replenishment control;

[0009] When the difference between the steam inlet flow rate of the hybrid heat accumulator and the external low-pressure steam volume and RH steam consumption is greater than 20t / h, the flow setting value of the heat accumulator water supply valve is set to 15t / h (this value can be dynamically adjusted according to the value in the database); when the difference between the steam inlet flow rate of the hybrid heat accumulator and the external low-pressure steam volume and RH steam consumption is greater than 10t / h, the flow setting value of the heat accumulator water supply valve is set to 25t / h (this value can be dynamically adjusted according to the value in the database), when the liquid level value of the heat accumulator reaches +350mm, the flow setting value of the heat accumulator water supply valve is set to 20t / h; when the liquid level value of the steam drum reaches +450mm, the flow setting value of the steam drum water supply valve is set to 15t / h; when the liquid level value of the steam drum reaches +500mm, the water supply valve is closed; under normal circumstances, the liquid level of the hybrid heat accumulator is between +350mm and +500mm. If the liquid level of the hybrid heat accumulator is lower than -300mm, the flow setting value of the water supply valve is set to 25t / h.

[0010] As an improvement of the present invention, the second fuzzy control is specifically as follows: the control of the hybrid heat accumulator water replenishment valve adopts fuzzy control, and according to the difference between the hybrid heat accumulator inlet steam flow, the external low-pressure steam volume and the RH steam consumption, the hybrid heat accumulator water replenishment control method adopts a method combining the water replenishment flow and the liquid level control to perform water replenishment control;

[0011] When the steam inlet flow rate of the hybrid heat accumulator is less than the low-pressure steam delivered and the RH steam consumption, and the difference is greater than 20t / h, the flow setting value of the hybrid heat accumulator water supply valve is set to 80t / h (this value can be dynamically adjusted according to the value in the database); when the steam inlet flow rate of the hybrid heat accumulator is less than the low-pressure steam delivered and the RH steam consumption, and the difference is greater than 10t / h, the flow setting value of the hybrid heat accumulator water supply valve is set to 60t / h (this value can be dynamically adjusted according to the value in the database). When the liquid level value of the hybrid heat accumulator reaches +350mm, the flow setting value of the hybrid heat accumulator water supply valve is set to 60t / h; when the liquid level value of the drum reaches +450mm, the flow setting value of the drum water supply valve is set to 40t / h; when the liquid level value of the drum reaches +500mm, the water supply valve is closed. If the water level of the hybrid heat accumulator is between -500mm and +500mm, the drain valve is opened with timing control. When the liquid level is between -100mm and 100mm, water is added at a flow rate of 70t / h for 30 seconds (this value can be dynamically adjusted according to the value in the database).

[0012] As an improvement of the present invention, in step 3, the control system automatically switches to proportional cascade PID control, as follows: Cascade PID control has two control loops, main and auxiliary, and uses two PID function blocks. At this time, the liquid level value of the heat accumulator itself is used as the main PID function block (controlling the steam liquid level) and the auxiliary PID function block (controlling the steam flow difference in and out of the heat accumulator). However, the PID control performance depends on the self-tuning of the parameters, and there is a contradiction between rapidity and overshoot. For a nonlinear, time-varying, uncertain and large-interference system such as the heat accumulator, the use of PID control cannot achieve a satisfactory dynamic control effect. In order to improve the adaptability of the PID controller, the nonlinear function is directly used for correction. Based on the pure lag and nonlinear characteristics of the heat accumulator flow regulation system, the Smith predictor is used for compensation. The design idea of ​​the Smith predictor is: pre-estimate the dynamic response of the control process, and then compensate it by the predictor, trying to make the controlled variable delayed by τ advance to the regulator, so that the regulator acts in advance, thereby reducing the overshoot and accelerating the regulation process.

[0013] Compared with the prior art, the present invention has the following advantages. The technical solution is to establish a corresponding database based on various states such as the steam inlet flow of the hybrid heat accumulator, the flow of the external steam pipeline of the hybrid heat accumulator, the steam consumption at different RH, the liquid level of the heat accumulator itself, etc. A heat accumulator liquid level control model is established according to the relevant parameters of the heat accumulator under each state. When controlling the water replenishment of the heat accumulator, different heat accumulator water replenishment control methods are adopted by looking up the table of relevant heat accumulator parameters. The dynamic data regression technology is used to automatically enter the relevant heat accumulator parameters into the database each time, and the data in the database is optimized, and the water replenishment setting value is automatically corrected in the fuzzy control. In the process of water replenishment control of the heat accumulator, not only the traditional control technology is used, but also the multivariable dynamic control technology is adopted to realize the steady-state water replenishment control technology of the heat accumulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the control principle of the present invention;

[0015] Figure 2 It is the first fuzzy control schematic diagram;

[0016] Figure 3 It is the second fuzzy control schematic diagram;

[0017] Figure 4 It is a nonlinear PID control system frame with Smith predictive compensation;

[0018] Figure 5 This is the changing curve of kp, kd, and ki. DETAILED DESCRIPTION

[0019] In order to deepen the understanding of the present invention, the present embodiment is described in detail below with reference to the accompanying drawings.

[0020] Example 1: See Figure 1 , a multi-state water replenishment control method for a steelmaking hybrid heat accumulator, the control method comprising the following steps:

[0021] Step 1: When the steam flow rate entering the hybrid heat accumulator is greater than the steam flow rate sent out of the hybrid heat accumulator and the RH steam consumption, the first fuzzy control is used to control the hybrid heat accumulator water supply valve;

[0022] Step 2: When the steam flow rate entering the hybrid heat accumulator is less than the steam flow rate sent out of the hybrid heat accumulator and the RH steam consumption, the second fuzzy control is used to control the water supply valve of the hybrid heat accumulator;

[0023] Step 3: When the steam flow entering the hybrid heat accumulator is basically equal to the steam flow sent out of the heat accumulator and the RH steam consumption, the heat accumulator is basically in a stable system state, and the control system automatically switches to proportional cascade PID control.

[0024] The first fuzzy control is specifically as follows: the control of the hybrid heat accumulator water supply valve adopts fuzzy control, and the hybrid heat accumulator water supply control method adopts a method combining water supply flow and liquid level control to control water supply according to the difference between the hybrid heat accumulator inlet steam flow, the external low-pressure steam volume and the RH steam consumption;

[0025] When the difference between the steam inlet flow rate of the hybrid heat accumulator and the external low-pressure steam volume and RH steam consumption is greater than 20t / h, the flow setting value of the heat accumulator water supply valve is set to 15t / h (this value can be dynamically adjusted according to the value in the database); when the difference between the steam inlet flow rate of the hybrid heat accumulator and the external low-pressure steam volume and RH steam consumption is greater than 10t / h, the flow setting value of the heat accumulator water supply valve is set to 25t / h (this value can be dynamically adjusted according to the value in the database), when the liquid level value of the heat accumulator reaches +350mm, the flow setting value of the heat accumulator water supply valve is set to 20t / h; when the liquid level value of the steam drum reaches +450mm, the flow setting value of the steam drum water supply valve is set to 15t / h; when the liquid level value of the steam drum reaches +500mm, the water supply valve is closed; under normal circumstances, the liquid level of the hybrid heat accumulator is between +350mm and +500mm. If the liquid level of the hybrid heat accumulator is lower than -300mm, the flow setting value of the water supply valve is set to 25t / h.

[0026] The second fuzzy control is specifically as follows: the control of the hybrid heat accumulator water supply valve adopts fuzzy control, and according to the difference between the hybrid heat accumulator inlet steam flow, the external low-pressure steam volume and the RH steam consumption, the hybrid heat accumulator water supply control method adopts a method combining water supply flow and liquid level control to perform water supply control;

[0027] When the steam inlet flow rate of the hybrid heat accumulator is less than the low-pressure steam delivered and the RH steam consumption, and the difference is greater than 20t / h, the flow setting value of the hybrid heat accumulator water supply valve is set to 80t / h (this value can be dynamically adjusted according to the value in the database); when the steam inlet flow rate of the hybrid heat accumulator is less than the low-pressure steam delivered and the RH steam consumption, and the difference is greater than 10t / h, the flow setting value of the hybrid heat accumulator water supply valve is set to 60t / h (this value can be dynamically adjusted according to the value in the database). When the liquid level value of the hybrid heat accumulator reaches +350mm, the flow setting value of the hybrid heat accumulator water supply valve is set to 60t / h; when the liquid level value of the drum reaches +450mm, the flow setting value of the drum water supply valve is set to 40t / h; when the liquid level value of the drum reaches +500mm, the water supply valve is closed. If the water level of the hybrid heat accumulator is between -500mm and +500mm, the drain valve is opened with timing control. When the liquid level is between -100mm and 100mm, water is added at a flow rate of 70t / h for 30 seconds (this value can be dynamically adjusted according to the value in the database).

[0028] In step 3, the control system automatically switches to proportional cascade PID control, as follows: Cascade PID control has two control loops, the main and auxiliary, and uses two PID function blocks. At this time, the liquid level value of the heat accumulator itself is used as the main PID function block (controlling the steam liquid level) and the auxiliary PID function block (controlling the steam flow difference in and out of the heat accumulator). However, the PID control performance depends on the self-tuning of the parameters, and there is a contradiction between rapidity and overshoot. For nonlinear, time-varying, uncertain and large-interference systems such as heat accumulators, PID control cannot achieve satisfactory dynamic control effects. In order to improve the adaptability of the PID controller, the nonlinear function is directly used for correction. Based on the pure lag and nonlinear characteristics of the heat accumulator flow regulation system, the Smith predictor is used for compensation. The design idea of ​​the Smith predictor is: pre-estimate the dynamic response of the control process, and then compensate it by the predictor, trying to make the controlled variable delayed by τ advance to the regulator, so that the regulator can act in advance, thereby reducing the overshoot and accelerating the regulation process.

[0029] Specific embodiment: refer to Figure 1 — Figure 5The present invention discloses a multi-state water replenishment control method for a steelmaking hybrid heat accumulator, which solves the water replenishment control method in the multi-state production mode of the existing steelmaking hybrid heat accumulator. The method is to establish a corresponding database based on various states such as the steam inlet flow of the hybrid heat accumulator, the flow of the external steam pipeline network of the hybrid heat accumulator, the steam consumption of different RHs, and the liquid level of the heat accumulator itself. When the heat accumulators of two steelmaking plants are connected in series and parallel, a total of 8 heat accumulators are running in the same network. The main user points consuming steam are: 1# and 2#RH in the first steelmaking plant, with a steam consumption of 15t per furnace and a daily processing capacity of 1#RH: 16 furnaces; 2#RH has a daily processing capacity of 20 furnaces, and the steam requirement is not less than 1.3MPa saturated steam before the pressure regulating valve of the heat storage station. The steam consumption of 3#RH in the second steelmaking plant is 20t / furnace, and the steam requirement is: not less than 1.3MPa saturated steam before the pressure regulating valve, and the daily processing capacity is 20 furnaces. The steam consumption of the single furnace of the three RHs and the production status of each RH are calculated. The main parameters of the 8 series-parallel accumulators are: the superheat of the steam temperature of the sub-cylinder is 5-10℃, the average pressure of the accumulator is higher than 1.5MPa, and the steam is delivered according to the set pressure of 1.27MPa after the valve; if the pressure of the accumulator is lower than 1.5MPa, the valve is closed. The highest water level of the accumulator cannot be higher than +800mm, and the lowest water level cannot be lower than -800mm. The normal water level of the accumulator is controlled at ±500mm. The cut-off valve of the two-way steam release pipeline at the outlet of the sub-cylinder is opened when it is greater than 3.3MPa and closed when it is less than 2.9MPa. The pressure before the RH steam pressure regulating valve is 2.0-3.2MPa, and 1.5MPa after the valve. The above parameters are used to establish corresponding static data tables (corresponding control tables are established according to different RH production states and process parameters of the heat accumulator, and static control models are established according to the instantaneous steam consumption of the heat accumulator and the relevant parameters of the heat accumulator. When controlling the water replenishment of the heat accumulator liquid level, the various process parameters of the heat accumulator and the production states of the three RHs are detected, and different control strategies are adopted according to the results of the table lookup by using the method of successive table lookup. The static model control table of the heat accumulator liquid level control established based on the production state of RH, the steam consumption of the heat accumulator and the various process parameters of the heat accumulator is limited, and the eight heat accumulators are in series-parallel state, and the system is disturbed by multiple factors. If only static table lookup control is used, it is difficult to adapt to the state changes of the heat accumulator. Therefore, the model based on static table lookup is calibrated according to the changes in the heat accumulator parameters every 10 batches during operation. The correction method is to collect the heat accumulator parameter values ​​of 10 furnaces each time (specifically the pressure of the heat accumulator, the liquid level of the heat accumulator, the RH steam consumption, and the water replenishment of the heat accumulator) and calculate the changes in the parameters of the heat accumulator for 10 batches by weighted average. Ten batches of data are collected continuously as the basis for the control parameters of the heat accumulator. After 10 batches of data, the program automatically removes the first set of data for each batch of data collected. The program is made to perform self-learning to form a dynamic table lookup basis.That is, the relevant heat accumulator parameters are automatically entered into the database each time, and the data in the database is optimized, and the water replenishment setting value is automatically corrected in the fuzzy control. In the process of heat accumulator water replenishment control, not only the traditional control technology is used, but also the multivariable dynamic control method is adopted. The steady-state water replenishment control technology of the heat accumulator is realized. The water replenishment control of the hybrid heat accumulator will be affected by multiple factors, which increases the difficulty of the water replenishment control of the hybrid heat accumulator. After analysis, it can be seen that the factors affecting the water replenishment of the hybrid heat accumulator are mainly divided into several parts: the steam inlet volume of the heat accumulator; the low-pressure steam volume of the heat accumulator sent to the external company; the steam consumption of the heat accumulator to send RH; the liquid level height of the heat accumulator itself; the water discharge volume of the heat accumulator. The steam entering the hybrid heat accumulator may be generated continuously or intermittently. The steam consumption of the hybrid heat accumulator to send RH and the amount of low-pressure steam sent to the external company may be continuous or intermittent. After the steam of the hybrid heat accumulator changes, the increase, decrease and pressure change of the steam volume will cause the liquid level fluctuation of the heat accumulator. If a fixed value is set for the water replenishment of the hybrid heat accumulator, it cannot adapt to the changes caused by the fluctuation of the liquid level of the hybrid heat accumulator. Meigang's hybrid heat accumulator system uses a dynamic table lookup to select different water replenishment control methods to keep the liquid level of the hybrid heat accumulator within the range required by the process. It can control the false liquid level and liquid level fluctuation of the hybrid heat accumulator, shorten the system control time, enhance the control response speed, and make the liquid level control of the hybrid heat accumulator safer and more reliable. The control principle is as follows. Figure 1 ,The specific method of water replenishment control of hybrid heat storage device is as follows.

[0030] Step 1: When the steam flow rate entering the hybrid heat accumulator is greater than the steam flow rate sent out of the hybrid heat accumulator and the RH steam consumption, the hybrid heat accumulator itself is in a hybrid state, and there are multiple disturbances. If the traditional single-loop or cascade control is used, it is difficult to keep the hybrid heat accumulator system in a steady state. Based on this, a fuzzy control is used. The control method is as follows: See Figure 2 Fuzzy control is used to control the water supply valve of the hybrid heat accumulator. According to the difference between the steam inlet flow rate, the amount of low-pressure steam delivered and the RH steam consumption of the hybrid heat accumulator, the water supply control method of the hybrid heat accumulator adopts a method combining water supply flow rate and liquid level control to control water supply.

[0031] When the difference between the steam inlet flow rate of the hybrid heat accumulator and the external low-pressure steam volume and RH steam consumption is greater than 20t / h, the flow setting value of the heat accumulator water supply valve is set to 15t / h (this value can be dynamically adjusted according to the value in the database); when the difference between the steam inlet flow rate of the hybrid heat accumulator and the external low-pressure steam volume and RH steam consumption is greater than 10t / h, the flow setting value of the heat accumulator water supply valve is set to 25t / h (this value can be dynamically adjusted according to the value in the database), when the liquid level value of the heat accumulator reaches +350mm, the flow setting value of the heat accumulator water supply valve is set to 20t / h; when the liquid level value of the steam drum reaches +450mm, the flow setting value of the steam drum water supply valve is set to 15t / h; when the liquid level value of the steam drum reaches +500mm, the water supply valve is closed; under normal circumstances, the liquid level of the hybrid heat accumulator is between +350mm and +500mm. If the liquid level of the hybrid heat accumulator is lower than -300mm, the flow setting value of the water supply valve is set to 25t / h.

[0032] Step 2: When the steam flow rate entering the hybrid heat accumulator is less than the steam flow rate sent out of the hybrid heat accumulator and the RH steam consumption, the hybrid heat accumulator itself is in a hybrid state, and there are multiple disturbances. If the traditional single-loop or cascade control is used, it is difficult to keep the hybrid heat accumulator system in a steady state. Based on this, a fuzzy control is used. The control method is as follows: See Figure 3 Fuzzy control is used to control the water supply valve of the hybrid heat accumulator. According to the difference between the steam inlet flow rate, the amount of low-pressure steam delivered and the RH steam consumption of the hybrid heat accumulator, the water supply control method of the hybrid heat accumulator adopts a method combining water supply flow rate and liquid level control to control water supply. When the steam inlet flow rate of the hybrid heat accumulator is less than the low-pressure steam delivered and the RH steam consumption, and the difference is greater than 20t / h, the flow setting value of the hybrid heat accumulator water supply valve is set to 80t / h (this value can be dynamically adjusted according to the value in the database); when the steam inlet flow rate of the hybrid heat accumulator is less than the low-pressure steam delivered and the RH steam consumption, and the difference is greater than 10t / h, the flow setting value of the hybrid heat accumulator water supply valve is set to 60t / h (this value can be dynamically adjusted according to the value in the database). When the liquid level value of the hybrid heat accumulator reaches +350mm, the flow setting value of the hybrid heat accumulator water supply valve is set to 60t / h; when the liquid level value of the drum reaches +450mm, the flow setting value of the drum water supply valve is set to 40t / h; when the liquid level value of the drum reaches +500mm, the water supply valve is closed. If the water level of the hybrid heat accumulator is between -500mm and +500mm, the drain valve is opened with timing control. When the liquid level is between -100mm and 100mm, water is added at a flow rate of 70t / h for 30 seconds (this value can be dynamically adjusted according to the value in the database).

[0033] Step 3: When the steam flow entering the hybrid heat accumulator is basically equal to the steam flow sent out of the heat accumulator and the RH steam consumption, the heat accumulator is basically in a stable system state. In this state, the heat accumulator itself is less affected by external disturbances. The control system automatically switches to proportional cascade PID control. Cascade PID control has two control loops, main and auxiliary, and it uses two PID function blocks. At this time, the liquid level value of the heat accumulator itself is used as the main PID function block (controlling the steam liquid level) and the auxiliary PID function block (controlling the steam flow difference in and out of the heat accumulator). However, the PID control performance depends on the self-tuning of the parameters, and there is a contradiction between rapidity and overshoot. For nonlinear, time-varying, uncertain and large-interference systems such as heat accumulators, PID control cannot achieve satisfactory dynamic control effects. In order to improve the adaptability of the PID controller, the nonlinear function is directly used for correction. Based on the pure lag and nonlinear characteristics of the heat accumulator flow regulation system, the Smith predictor is used for compensation. The design idea of ​​the Smith predictor is to estimate the dynamic response of the control process in advance, and then the predictor will compensate for it, trying to make the controlled variable with a delay of τ reflected in advance to the regulator, so that the regulator can act in advance, thereby reducing the overshoot and accelerating the regulation process. The specific control function principle is as follows: Based on the pure lag and nonlinear characteristics of the hybrid heat accumulator itself in a hybrid state and the existence of multiple disturbances, the Smith predictor is used for compensation. The design idea of ​​the Smith predictor is to estimate the dynamic response of the control process in advance, and then the predictor will compensate for it, trying to make the controlled variable with a delay of τ reflected in advance to the regulator, so that the regulator can act in advance, thereby reducing the overshoot and accelerating the regulation process. The following figure shows the block diagram of a nonlinear PID control system using Smith predictor compensation:, see for details. Figure 4 ,exist Figure 4 In, G C (S) is the transfer function of the nonlinear PID controller. If the model is accurate, that is, G O (S) = G M (S), and there is no load disturbance (D = 0), then Y = Y M ,E M =YY M =0,X=X M Then XM can be used instead of X as the first feedback loop to move the pure delay link outside the control loop. If the model is inaccurate or there is a load disturbance, X will not be equal to XM, Em=Y-Ym≠0, and the control accuracy will not be satisfactory. For this reason, Em is used to implement the second feedback loop. This is the control strategy of the Smith predictor.

[0034] Design of nonlinear PID controller Gc(s):

[0035] (1) Proportional gain parameter:

[0036] Construct nonlinear function kp:

[0037] k p (e p (t)) = a p +b p (1-sech(c p e p (t))) (3)

[0038] Where: ap, bp, cp are positive constants. When the error ep→±∞, kp takes the maximum value ap+bp; when ep=0, kp takes the minimum value ap; bp is the range of kp change, and adjusting the size of cp can adjust the rate of kp change. Where sech is the hyperbolic secant function.

[0039]

[0040] The variation curve of kp function is as follows Figure 4 As shown in the first figure. Analyzing the kp change curve, when ep>0, kp increases with the increase of ep and decreases with the decrease of ep. This is to ensure that the system has a faster response speed and a smaller overshoot. When ep<0, when the absolute value of ep(t) increases, in order to increase the reverse control effect and reduce the overshoot, kp also increases accordingly; when the absolute value of ep(t) decreases, in order to make the system return to stability as soon as possible, the kp point also decreases.

[0041] (2) Differential gain parameter kd:

[0042] Construct a nonlinear function:

[0043] k d (e p (t)) = a d +b d / (1+c d exp(d d e p (t))) (5)

[0044] Where: ad, bd, cd, dd are positive real constants, ad is the minimum value of kd, ad+bd is the maximum value of kd, when ep(t)=0,

[0045] kd(ep(t))=ad+bd / (1+cd). Adjusting the size of dd can adjust the kd change rate.

[0046] The variation curve of the kd function in this paper is as follows Figure 5 As shown in the second figure of . It can be seen from the figure that when the overshoot of the system increases, kd increases rapidly, thereby increasing the reverse control effect and effectively suppressing the generation of overshoot.

[0047] (3) Integral gain parameter ki:

[0048] Construct a nonlinear function:

[0049] k i (e p (t)) = a i sech(c i e p (t)) (6)

[0050] Where: the range of ki is (0, ai), and ki takes the maximum value when ep(t) = 0. The value of ci determines the speed of ki's change.

[0051] The change curve of Ki function is as follows Figure 5 As shown in the third figure of . It can be seen from the figure that when the error signal is large, the integral gain should not be too large to prevent the response from oscillating, which is beneficial to reduce overshoot; when the error is small, the integral gain is increased to eliminate the steady-state error of the system.

[0052] The control output of the nonlinear PID regulator is:

[0053]

[0054] If the parameters in the nonlinear gain function are properly selected, the control system can achieve the goal of fast response and small overshoot. In addition, the gain parameters in the nonlinear PID regulator can change with the control error, so its anti-interference ability is stronger than that of the conventional linear PID controller. For the change curve of kp, kd, ki, see Figure 5 .

[0055] The control system selects the control mode by cyclic table lookup according to the sampled RH production status and various process parameters of the heat accumulator during control. During the dynamic control process, dynamic control is performed by cyclic table lookup until the control meets the process control requirements.

[0056] It should be noted that the above embodiments are not intended to limit the protection scope of the present invention, and equivalent changes or substitutions made on the basis of the above technical solutions all fall within the protection scope of the claims of the present invention.

Claims

1. A multi-state water replenishment control method for a steelmaking hybrid heat accumulator, characterized in that: The control method comprises the following steps: Step 1: When the steam flow rate entering the hybrid heat accumulator is greater than the steam flow rate sent out of the hybrid heat accumulator and the RH steam consumption, the first fuzzy control is used to control the hybrid heat accumulator water supply valve; Step 2: When the steam flow rate entering the hybrid heat accumulator is less than the steam flow rate sent out of the hybrid heat accumulator and the RH steam consumption, the second fuzzy control is used to control the water supply valve of the hybrid heat accumulator; Step 3: When the steam flow entering the hybrid heat accumulator is basically equal to the steam flow sent out of the heat accumulator and the RH steam consumption, the heat accumulator is basically in a stable system state, and the control system automatically switches to proportional cascade PID control.

2. The multi-state water replenishment control method for steelmaking hybrid heat accumulator according to claim 1 is characterized in that: In the step 1, the first fuzzy control is specifically as follows: the control of the hybrid heat accumulator water supply valve adopts fuzzy control, and the hybrid heat accumulator water supply control method adopts a method combining water supply flow and liquid level control to perform water supply control according to the difference between the hybrid heat accumulator steam inlet flow rate, the external low-pressure steam amount and the RH steam consumption; when the difference between the hybrid heat accumulator steam inlet flow rate and the external low-pressure steam amount and the RH steam consumption is greater than 20t / h, the flow setting value of the heat accumulator water supply valve is set to 15t / h; when the difference between the heat accumulator steam inlet flow rate and the external low-pressure steam amount and the RH steam consumption is greater than 1 When the liquid level of the heat accumulator reaches +350mm, the flow setting value of the heat accumulator water supply valve is set to 20t / h; when the liquid level of the drum reaches +450mm, the flow setting value of the drum water supply valve is set to 15t / h; when the liquid level of the drum reaches +500mm, the water supply valve is closed; under normal circumstances, the liquid level of the hybrid heat accumulator is between +350mm and +500mm; if the liquid level of the hybrid heat accumulator is lower than -300mm, the flow setting value of the water supply valve is set to 25t / h.

3. The multi-state water replenishment control method for steelmaking hybrid heat accumulator according to claim 2 is characterized in that: In step 2, the second fuzzy control is specifically as follows: fuzzy control is used to control the water replenishment valve of the hybrid heat accumulator. According to the difference between the inlet steam flow rate of the hybrid heat accumulator, the amount of low-pressure steam delivered and the RH steam consumption, the water replenishment control method of the hybrid heat accumulator adopts a method combining water replenishment flow rate and liquid level control to perform water replenishment control; when the inlet steam flow rate of the hybrid heat accumulator is less than the amount of low-pressure steam delivered and the RH steam consumption, and the difference is greater than 20t / h, the flow setting value of the water replenishment valve of the hybrid heat accumulator is set to 80t / h; when the inlet steam flow rate of the hybrid heat accumulator is less than the amount of low-pressure steam delivered and the RH steam consumption, and the difference is greater than 10t / h / h, set the flow setting value of the hybrid heat accumulator water supply valve to 60t / h; when the liquid level value of the hybrid heat accumulator reaches +350mm, set the flow setting value of the hybrid heat accumulator water supply valve to 60t / h; when the liquid level value of the steam drum reaches +450mm, set the flow setting value of the steam drum water supply valve to 40t / h; when the liquid level value of the steam drum reaches +500mm, close the water supply valve; if the water level of the hybrid heat accumulator is between -500mm and +500mm, the drain valve is opened with timing control; when the liquid level is lower than between -100mm and 100mm, water is supplied at a flow rate of 70t / h for 30 seconds.

4. The multi-state water replenishment control method for steelmaking hybrid heat accumulator according to claim 3 is characterized in that: In step 3, the control system automatically switches to proportional cascade PID control, as follows: The cascade PID control has two control loops, the main and auxiliary. It uses two PID function blocks. At this time, the liquid level value of the heat accumulator itself is used as the main PID function block and the auxiliary PID function block, and the Smith predictor is used for compensation. The design idea of ​​the Smith predictor is: pre-estimate the dynamic response of the control process, and then the predictor is used for compensation, trying to make the controlled variable delayed by τ be reflected to the regulator in advance, so that the regulator can act in advance, thereby reducing the overshoot and accelerating the regulation process.

Images