Superheated steam temperature control method and system of secondary reheating unit

Abstract

The invention provides a superheated steam temperature control method and system for a secondary reheating unit, and belongs to the field of thermotechnical automation, and the method comprises the following steps: obtaining a leading zone superheated steam temperature and an inert zone superheated steam temperature of a three-stage superheater of the secondary reheating unit; the cascade control system of the secondary reheating unit comprising a main loop and an auxiliary loop is designed, a stepped predictive controller SGPC is adopted as a main loop controller of the cascade control system, the stepped predictive controller SGPC is adopted as the main loop controller of the cascade control system, control parameters of the main loop are adjusted through the main loop controller, and the control parameters of the auxiliary loop are adjusted through the auxiliary loop controller. The problems of large delay and large inertia of the system can be solved; by adopting the ADRC as the auxiliary loop controller of the cascade control system and adjusting the control parameters of the auxiliary loop, the secondary disturbance in the auxiliary loop can be inhibited, and the influence of the secondary disturbance on the control of the superheated steam temperature is reduced, so that the superheated steam temperature is controlled within a set range.

Description

Technical Field

[0001] The present invention belongs to the field of thermal automation, and in particular relates to a superheated steam temperature control method and system for a secondary reheat unit. Background Art

[0002] Compared with traditional thermal power generating units, the layout of the superheater and the distribution of the furnace temperature field in the ultra-supercritical secondary reheat unit are different. When the load changes, the superheated steam temperature of the superheater often exceeds the allowable range of the unit, resulting in the water spray regulating valve being unable to adjust the valve opening in real time with the change of steam temperature, causing the superheated steam temperature of the superheater to have large inertia and large lag during the control process.

[0003] Currently, conventional PID control is used to control superheated steam temperature. This involves coarsely adjusting the superheated steam temperature by adjusting the water-coal ratio and fine-tuning it through staged water spraying. However, during fine-tuning, the PID controller uses an integral action to eliminate errors. This integral action has a 90° phase lag, which can easily lead to integral saturation and reduce system stability. Consequently, the superheater's superheated steam temperature experiences significant inertia and lag during control, failing to achieve the desired control effect. Summary of the Invention

[0004] In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides a method for controlling the superheated steam temperature of a double reheat unit, comprising the following steps: Obtain the superheated steam temperature in the inert zone and the superheated steam temperature in the third-stage superheater of the double reheat unit; The superheated steam temperature in the leading zone and the superheated steam temperature in the inert zone of the three-stage superheater are input into a cascade control system, wherein the cascade control system is a cascade control system of a secondary reheat unit including a main loop and a sub-loop, a step-type predictive controller SGPC is used as the main loop controller of the cascade control system, and an active disturbance rejection controller ADRC is used as the sub-loop controller of the cascade control system; the main loop controller and the sub-loop controller are used to adjust the control parameters of the main loop and the control parameters of the sub-loop respectively, to obtain the control action of the desuperheating water of the cascade control system, and the superheated steam temperature is controlled according to the control action.

[0005] Preferably, adjusting the control parameters of the main loop includes the following steps: Obtain reference values of optimization performance indicators of the main loop; determining an objective function of a main loop controller according to the reference value and adding a soft constraint to a control increment; Obtaining an optimal analytical solution equation for the control action of the main loop controller at a certain moment through the objective function; A step factor is introduced into the main loop controller, and the optimal analytical solution equation of the control action is simplified by the step factor. The optimal analytical solution of the control action of the main loop controller is obtained according to the simplified equation.

[0006] Preferably, the process of adjusting the control parameters of the secondary loop includes the following steps: The optimal analytical solution of the control action of the main loop controller is used as the setting value of the sub-loop controller; The state estimation variables, controller gains and system parameters of the secondary loop are obtained, and the control action of the secondary loop controller is determined in combination with the setting value of the secondary loop controller.

[0007] Preferably, the method further includes evaluating the system tracking performance of the cascade control system of the secondary reheat unit, specifically evaluating the performance index values of the adjustment time, overshoot and ITAE.

[0008] Preferably, the objective function is: ; Where, j is a moment in the time domain, N represents the prediction time domain, Indicates the reference value, M Represents the control time domain λ represents the control weight, Indicates the future k+j The optimal output prediction value at time Δ u ( k + j -1) k + j -1 moment of control increment.

[0009] Preferably, the control parameters of the main loop include a softening factor α , optimize the time domain starting value N 1. Optimize the final value of the time domain N p , control time domain M and step factors β .

[0010] Preferably, the control parameters of the secondary loop include controller gain k p and k d , observer gain β 1. β 2 and β 3. System parameters b 0, controller bandwidth ω c and observer bandwidth .

[0011] The present invention also provides a superheated steam temperature control system for a double reheat unit, comprising: The parameter acquisition module is used to obtain the superheated steam temperature in the leading zone and the superheated steam temperature in the inert zone of the three-stage superheater of the double reheat unit; a superheated steam temperature control module, configured to input the superheated steam temperature in the leading zone and the superheated steam temperature in the inert zone of the three-stage superheater into a cascade control system, wherein the cascade control system is a cascade control system of a secondary reheat unit including a main loop and a sub-loop, adopting a step-type predictive controller SGPC as the main loop controller of the cascade control system, and adopting an active disturbance rejection controller ADRC as the sub-loop controller of the cascade control system; using the main loop controller and the sub-loop controller to adjust the control parameters of the main loop and the control parameters of the sub-loop respectively, to obtain a control action of the desuperheating water of the cascade control system, and controlling the superheated steam temperature according to the control action.

[0012] The superheated steam temperature control method of the double reheat unit provided by the present invention has the following beneficial effects: The present invention inputs the superheated steam temperature of the leading zone and the superheated steam temperature of the inert zone of the three-stage superheater into the cascade control system, adopts a step-by-step predictive controller SGPC as the main loop controller of the cascade control system, and adjusts the control parameters of the main loop through the main loop controller, thereby handling the problems of large delay and large inertia of the system; adopts an active disturbance rejection controller ADRC as the secondary loop controller of the cascade control system, and adjusts the control parameters of the secondary loop, thereby suppressing secondary disturbances in the secondary loop and reducing the influence of secondary disturbances on superheated steam temperature control, thereby controlling the superheated steam temperature within a set range. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] To more clearly illustrate the embodiments of the present invention and its design, the following briefly introduces the drawings required for this embodiment. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0014] Figure 1 This is a flow chart of a method for controlling the superheated steam temperature of a double reheat unit according to an embodiment of the present invention; Figure 2 This is the schematic diagram of superheated steam temperature generation for the double reheat unit; Figure 3 This is a cascade control system diagram according to an embodiment of the present invention; Figure 4 This is the response curve of the controlled object in the three-stage superheated steam temperature pilot area under 750MW steady-state load; Figure 5This is the response curve of the controlled object in the three-stage superheated steam temperature inert zone under 750MW steady-state load; Figure 6 This is the response curve of the controlled object in the three-stage superheated steam temperature pilot zone under 1000MW steady-state load; Figure 7 This is the response curve of the controlled object in the three-stage superheated steam temperature inert zone under 1000MW steady-state load; Figure 8 This is the superheated steam temperature tracking curve of the double reheat unit under 750MW steady-state load; Figure 9 This is the control curve of the three-stage superheated steam temperature desuperheating water valve of the double reheat unit under 750MW steady-state load; Figure 10 This is the change curve of the steam temperature increment before the third-stage superheater of the double reheat unit under 750MW steady-state load; Figure 11 This is the superheated steam temperature tracking curve of the double reheat unit under 1000MW steady-state load; Figure 12 This is the control curve of the desuperheating water valve of the third-stage superheater of the double reheat unit under 1000MW steady-state load; Figure 13 This is the change curve of the steam temperature increment before the third-stage superheater of the double reheat unit under 1000MW steady-state load. DETAILED DESCRIPTION

[0015] In order to enable those skilled in the art to better understand the technical solution of the present invention and to be able to implement it, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are not intended to limit the scope of protection of the present invention.

[0016] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the technical solutions of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0017] In addition, the terms "first", "second", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance. In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meaning of the above terms in the present invention can be understood according to the specific circumstances. In the description of the present invention, unless otherwise specified, "plurality" means two or more, which will not be described in detail here.

[0018] Example The present invention provides a method for controlling the superheated steam temperature of a secondary reheat unit, the method comprising the following steps: Figure 1 As shown: Step 1: Obtain the superheated steam temperature in the inert zone and the superheated steam temperature in the guide zone of the third-stage superheater of the double reheat unit.

[0019] like Figure 2 As shown in the figure, the double reheat unit has an additional ultra-high pressure cylinder compared to the single reheat unit, resulting in two types of steam: cold primary reheat steam and cold secondary reheat steam. Specifically, after the superheated steam performs work in the ultra-high pressure cylinder, cold primary reheat steam is generated. The cold primary reheat steam is heated by the high-pressure low-temperature reheater and the high-pressure high-temperature reheater, and then sent back to the high-pressure cylinder to perform work, generating cold secondary reheat steam. After being heated by the low-pressure low-temperature reheater and the low-pressure high-temperature reheater, the cold secondary reheat steam enters the medium and low-pressure cylinders again to perform work.

[0020] Superheated steam temperature (superheated steam temperature) is primarily affected by flue gas heat, steam flow, and attemperating water flow. The real-time power generation load determines flue gas heat and steam flow, which are external disturbances of superheated steam temperature. Attemperating water flow, on the other hand, allows for rapid adjustment of the inlet temperature, providing direct control of superheated steam temperature.

[0021] For the higher level three superheater, it is necessary to obtain the superheated steam temperature of the leading zone of the three-stage superheater and the superheated steam temperature of the inert zone of the three-stage superheater, as shown in the following example: Figure 2 of T 1 and T As shown in Figure 2, by taking these two parameters as the input of the superheated steam temperature and processing and adjusting them through the controller, the superheated steam temperature can be controlled.

[0022] Step 2: Input the superheated steam temperature in the leading zone and the superheated steam temperature in the inert zone of the three-stage superheater into the cascade control system, wherein the cascade control system is a cascade control system of a secondary reheat unit including a main loop and a sub-loop, adopts a step-type predictive controller SGPC as the main loop controller of the cascade control system, and adopts an active disturbance rejection controller ADRC as the sub-loop controller of the cascade control system; use the main loop controller and the sub-loop controller to adjust the control parameters of the main loop and the control parameters of the sub-loop respectively, obtain the control action of the desuperheating water of the cascade control system, and control the superheated steam temperature according to the control action.

[0023] The definition of a cascade control system is a control system that uses two controllers to work in series. The set value of the latter controller is the output value of the former controller. This system is mainly used in situations where the object has lag, large time constant, frequent and strong interference, large load changes, and high control quality requirements.

[0024] The cascade control system consists of two controllers and two detection transmitters, where the set value of the second controller is the output value of the first controller, and the output of the second controller is then adjusted by a regulating valve. The function of the two detection transmitters is to respectively detect the superheated steam temperature in the pilot zone and the inert zone of the three-stage superheater, and to subtract the measured values from the set values of the superheated steam temperature in the pilot zone and the inert zone of the three-stage superheater, and send them to the main loop controller and the sub-loop controller respectively for calculating the control action. Usually, the former controller is called the main controller, and the variables it detects and controls are called the main controlled parameters or main variables; the latter controller is called the sub-controller, and the variables it detects and controls are called the sub-controlled parameters or sub-variables. The introduction of sub-variables is to stabilize the main variables.

[0025] The cascade control system consists of a main control loop and two sub-control loops: the main loop includes the main controller, the controlled object in the inert zone, and the main variable detection transmitter; the sub-loop includes the sub-controller, the sub-variable detection transmitter, and the controlled object in the leading zone.

[0026] The disturbance that acts on the main loop but is not included in the secondary loop is called a primary disturbance, and the disturbance that acts on the secondary loop is called a secondary disturbance.

[0027] In the present invention, to address the problem of superheated steam temperature control in an ultra-supercritical double reheat unit, an Active Disturbance Rejection Controller (ADRC) is first applied to the secondary loop to improve the dynamic characteristics of the generalized controlled object. Then, a Stair-like Generalized Predictive Control (SGPC) is applied to the primary loop to ensure that both the dynamic and steady-state performance indicators of the entire closed-loop system meet the requirements. For ease of description, the control method of the present invention is named the SGPC-ADRC control method.

[0028] Specific as Figure 3 As shown, Figure 3 middle, R is the superheated steam temperature in the inert zone of the three-stage superheater T The setting value of 2, r is the secondary loop set value, u 1 is the cooling water control amount, d 1 is the secondary perturbation, d 2 is a single disturbance, SGPC is a step-wise predictive controller, ADRC is an active disturbance rejection controller, G 1(s) is the transfer function of the controlled object of superheated steam temperature in the leading zone, G 2(s) is the transfer function of the controlled object of superheated steam temperature in the inert zone, T 1 is the superheated steam temperature in the pilot zone of the three-stage superheater, T 2 is the superheated steam temperature in the inert zone of the three-stage superheater.

[0029] The design process of the main loop of the cascade control system of the present invention is as follows: (1) Design of set value of main circuit.

[0030] In the optimization performance index of the control system, a reference value with a "soft" transition can be used to replace the expected value of the system output instead of directly using the set value. The reference value can be obtained by the following equation: w ( k + j )= α j y ( k )+(1- α j ) y r , j =1,..., N p (1); Where, y ris the reference setting value, k For the current moment, α is the softening factor, N p is the final value of the optimized time domain, w is the softened system setting value, j is a moment in the time domain; α j is the softening factor at a certain moment in the time domain; y ( k )yes k The output of the main loop controller at this moment.

[0031] (2) Calculation of control action.

[0032] The controlled object formula of the inert zone of superheated steam temperature is: A (z -1 ) y ( k )= B ( z -1 ) u ( k- 1)+ C ( z -1 ) ξ ( k ) / Δ (2); Where, z is a complex variable, A (z -1 ), and C ( z -1 ) are n a , n b , n c Level z -1 The polynomial of z -1 is the backshift operator, y ( k )and u ( k ) are k The output and input of the cascade control system at each moment, u ( k- 1) Yes k- The input quantity of the main loop controller at time 1, ξ ( k ) is the value of the white noise sequence with zero mean, and Δ=1- z-1 , is called the difference operator, the present invention makes C (z -1 )=1.

[0033] By using the Diophantine Equation, we can get j The predicted output after step 1 is: 1= E j ( z -1 ) A ( z -1 )Δ+ z -j F j ( z -1 ), j =1, 2, ..., N p (3); Where, E j ( z -1 )and F j ( z -1 )yes A ( z -1 ) and the predicted length j When performing recursive calculations on the determined polynomial, let: E 1= e 1,0 =1, F 1= z (1- A ( z -1 )Δ) (4); E j ( z -1 )= e j,0 + e j,1 z -1 +...+ e j,j-1 z -(j-1) (5); F j ( z -1)= f j,0 + f j ,1 z -1 +...+ f j , nb z -nb (6); Where, E 1 and F 1 are all Diophantine polynomials with a predicted length of 1; e j,i are the polynomial coefficients of the Diophantine equation, i =0, ..., j -1; f j,i are the polynomial coefficients of the Diophantine equation, i =0,..., nb .

[0034] Multiply both ends of formula (1) by E j ( z -j )Δ z -j , then combined with formula (2), we can get k + j The predicted output value at time: y ( k + j) = E j ( z -1 ) B ( z -1 )Δ u ( k + j -1)+ F j ( z -1 ) y ( k )+ ξ ( k + j ) (7); Where, Δ u ( k + j -1) k + j -1 moment of control increment.

[0035] becausek The noise in the future is unknown, so in the future k+j The optimal output prediction value at the moment should be: y ( k + j) = E j ( z -1 ) B ( z -1 )Δ u ( k + j -1)+ F j ( z -1 ) y ( k ) (8); The present invention enhances the robustness of the system by adding soft constraints to the control increment and error amount in the optimization performance index, and adopts the following objective function: (9); Where, j is a moment in the time domain, N represents the prediction time domain, Indicates the reference value, M Represents the control time domain λ represents the control weight, Indicates the future k+j The optimal output prediction value at time Δ u ( k + j -1) k + j -1 moment of control increment.

[0036] make: G j ( z -1 )= E j ( z -1 ) B ( z -1 )= B ( z -1 )[1- z -j F j ( z -1)] / ( A ( z -1 )Δ)= g j,0 + g j,1 z -1 +...+ g j , nb+j- 1 z -(nb+j-1) (10); Where, g j,i for j At the prediction moment, the system unit step response coefficient is: i =0, 1, 2, ..., nb + j -1.

[0037] From this we can get, G j ( z -1 ) j The term is the first term in the unit step response of the time-delay system. j The sampling value of the item, that is g j,i = g i+1 , i =1,2,..., j -1.

[0038] After simplifying formula (8), we can get: y ( k + j )= G j ( z -1 )Δ u ( k + j- 1)+ F j (z -1 ) y ( k ) (11); According to formula (11), the measured value of the future output that can satisfy formula (8) is obtained as follows: y ( k +1)= g 1,0 Δ u ( k )+...+ g1,nb Δ u ( kn b )+ F 1 y ( k ) (12); ... y ( k + N )= g N,N-M Δ u ( k+N- 1)+..+ g N,N-1 Δ u ( k )+ g N,N Δ u ( k- 1)+.+ g N,N+nb-1 Δ u ( kn b )+ F N y ( k )(13); Where, g N,0 =...= g N,N-M-1 =0, g N , i is the system unit step response coefficient at the prediction moment, i = N - M ,..., N + nb -1; Δ u ( kn b )for kn b The control increment at the moment.

[0039] Written in matrix form: (14); In formula (14), let: (15); (16); (17); (18); (19); (20); (twenty one); Without considering the input and output constraints, the optimal analytical solution of formula (9) is: (twenty two); Where, .

[0040] From formula (22), we can see that in the process of solving the optimal analytical solution, it is also necessary to solve the matrix ( The inverse matrix of the matrix is computationally intensive and its inverse matrix may not exist. In addition, there is the possibility of a singular matrix, which makes the calculation inconvenient.

[0041] To simplify the above algorithm, this paper introduces a stair-like generalized predictive control (SGPC) to address the issues of large time lag and high inertia. Compared with traditional PID control, the SGPC offers greater robustness, better handling of high-inertia objects, and can further reduce the system's phase lag.

[0042] The step predictive controller introduces the step factor β To avoid the process of solving the inverse matrix in the process of solving the optimal control law, the step factor β The calculation formula is as follows: (twenty three); Then in formula (22) It can be expressed as: Δ U= [Δ u ( k ),...,Δ u ( k+M- 1)] T =[1, β,...,β M-1 ] T Δ u ( k ) (twenty four); G Δ U=G [1, β,...,β M-1 ] T Δ u ( k )= G 1Δ u ( k ) (25); Therefore, the optimal control action is: (26); Then we can conclude that the control action acting on the current control process is: u ( k )= u ( k -1)+Δ u ( k ) (27); In formula (25), once β The value of is determined, and the future control increment Δ u ( k ) can also be determined, however, in the actual control process, the degree of change of the control increment at adjacent moments is uncertain and needs to be dynamically adjusted according to the specific situation. Therefore, the present invention designs a sub-loop.

[0043] The design process of the secondary loop of the present invention is as follows: (1) Design of secondary circuit set value.

[0044] The setting value of the secondary loop control system is the control action in formula (27), that is, r = u ( k ).

[0045] (2) Calculation of control action.

[0046] The superheated steam temperature secondary loop is designed using a linear active disturbance rejection controller. The control action of the secondary loop controller is: u 1=[ k p ( r - Z (1))- k d Z (2)-Z(3)] / b 0(28); Where, u 1 is the control action of the secondary loop controller, Z is the state estimation variable, r is the secondary loop set value, k p , k d is the controller gain, b 0 is the system parameter.

[0047] Among them, the linear expansion observer is: (29); (30); Where, AE =[0 1 0; 0 0 1; 0 0 0]; BE =[0 b 00]; L =[ β 1, β 2, β 3] T ; CC =[1 0 0].

[0048] Therefore, the control action of the secondary loop can be calculated as u 1.

[0049] In summary, the present invention can more effectively reduce the impact of secondary disturbances through ADRC in the secondary loop of the cascade control system. In the main loop, it takes advantage of the advantages of SGPC and adopts the idea of predictive control to solve the problems of large time lag and large inertia, thereby improving both the dynamic performance and steady-state performance of the system.

[0050] The present invention also provides a superheated steam temperature control system for a double reheat unit, comprising: The parameter acquisition module is used to obtain the superheated steam temperature in the leading zone and the superheated steam temperature in the inert zone of the three-stage superheater of the double reheat unit; The superheated steam temperature control module is used to input the superheated steam temperature in the leading zone and the inert zone of the three-stage superheater into the cascade control system, wherein the cascade control system is a cascade control system of a secondary reheat unit including a main loop and a sub-loop, adopts a step-type predictive controller SGPC as the main loop controller of the cascade control system, and adopts an active disturbance rejection controller ADRC as the sub-loop controller of the cascade control system; the main loop controller and the sub-loop controller are used to adjust the control parameters of the main loop and the control parameters of the sub-loop respectively, obtain the control action of the desuperheating water of the cascade control system, and control the superheated steam temperature according to the control action.

[0051] In order to verify the control effect of the cascade control system of the present invention, the superheated steam temperature of the third stage superheater of a 750MW and 1000MW ultra-supercritical double reheat unit under steady-state load is taken as an example. G 1(s) and inert zone G The transfer function of 2(s) is shown in Table 1.

[0052] Table 1 Superheated steam temperature object transfer function under typical operating conditions In order to simplify the calculation process, the present invention uses Taylor's formula to convert 、 、 、 Approximately 、 、 、 , and conducted simulation comparisons. Their corresponding evaluation indicators are mean absolute error MAE (Mean Absolute Error), mean squared error MSE (Mean Squared Error) and root mean square error RMSE (Root Mean Squared Error). The results are as follows: Leading area: 750MW: MAE=0.6914; MSE=22.2784; RMSE=4.

[0053] 1000MW: MAE=0.213; MSE=2.0168; RMSE=1.4201.

[0054] Inert zone: 750MW: MAE=8.2202e -05 ;MSE=2.3357e -07 ;RMSE=4.8329e -04 .

[0055] 1000MW: MAE=1.8661e -04 ;MSE=8.1237e -07 ;RMSE=9.0132e -04 .

[0056] According to the simulation results Figure 4-Figure 7 It can be seen that the mean absolute error MAE between the transfer function simplified by Taylor's formula and the original transfer function is less than 0.25, so the two functions fit well. Therefore, the present invention uses the transfer function in Table 2 for simulation based on it.

[0057] Table 2 Simplified superheated steam temperature transfer function Two sets of simulations were performed using three control methods: SIMC, MIGO, and SGPC-ADRC. Performance analysis was performed. The three control methods are shown in Table 3. The controller parameters of SGPC-ADRC are selected as follows: The parameters of SGPC-ADRC are set as follows: Main circuit: Simulation time: T= 400 s ;Superheated steam temperature in the inert zone of the third-stage superheater T Setting value of 2: R= 1.

[0058] Sampling time:t= 1s; softening factor: α= 0.1; control weight: λ= 1; Optimize the time domain starting value: N 1 = 12; Optimize the final value of the time domain: N p = 22; Control time domain: M= 2; Step factor: β= 0.8.

[0059] Secondary circuit: Sampling time: t= 0.01 s ; Controller bandwidth: .

[0060] Observer bandwidth: ;Observer gain: ; ; .

[0061] Controller gain: ; ;System parameters: .

[0062] The test results are Figures 8-13 It can be seen that the response characteristics of the SGPC-ADRC control method are optimal, the control speed of the control action is the fastest, the adjustment time is the shortest, the overshoot is the smallest, and the performance index value of the integrated time and absolute error (ITAE) is the smallest, which shows that the SGPC-ADRC control method has better set point tracking performance.

[0063] It's important to note that while setpoint tracking performance is a key control system metric, other metrics may need to be prioritized in different application scenarios. For example, in some scenarios, higher requirements may be placed on the system's anti-vibration and anti-interference capabilities, so the controller's anti-interference performance should be prioritized.

[0064] Therefore, in actual control applications, it is very important to select the control method that best suits the application scenario. At the same time, in order to more comprehensively evaluate the performance of the control method, it is necessary to combine the actual application scenario and control objectives, and comprehensively consider multiple indicators to select the most appropriate control method.

[0065] Table 3 Comparison of system dynamic performance indicators under three control schemes (750MW) In order to verify the accuracy of the simulation experiment and eliminate the influence of accidental factors, the present invention also conducted another set of simulation experiments under 1000MW working conditions, as shown in Table 4. The experimental results are as follows: Table 4 Comparison of system dynamic performance indicators under three control schemes (1000MW) As shown in Table 4, the simulation experimental results under 1000MW conditions and 750MW conditions show that compared with the SIMC and MIGO methods, the SGPC-ADRC method has the smallest overshoot, adjustment time, comprehensive time and absolute error, so the influence of accidental factors can be eliminated. The simulation results show that this method can suppress the set value and secondary disturbances, and effectively improve the control quality of the superheated steam temperature of the secondary reheat unit.

[0066] Furthermore, compared to the external optimization control station connected to the DCS system currently used by most thermal power plants, the Stepwise Predictive Controller algorithm and Active Disturbance Rejection Control algorithm are more conveniently programmed in C language on an embedded system platform, which offers significant advantages for practical engineering implementation and promotion. Furthermore, because ADRC controllers avoid the integral saturation problem caused by the integral action of PID controllers and do not require the controller's positive and negative actions, they can simplify system design and enhance system stability.

[0067] The proposed cascade control system can effectively solve the superheated steam temperature control problem of ultra-supercritical double reheat units, as verified in system simulations. The structure can also be applied to control problems in other fields.

[0068] The above embodiments are only preferred specific implementation methods of the present invention, and the protection scope of the present invention is not limited thereto. Any simple changes or equivalent replacements of the technical solutions that can be obviously obtained by any technician familiar with the field within the technical scope disclosed in the present invention fall within the protection scope of the present invention.

Claims

1. A method for controlling superheated steam temperature of a double reheat unit, characterized in that: The steps include: Obtain the superheated steam temperature in the inert zone and the superheated steam temperature in the third-stage superheater of the double reheat unit; The superheated steam temperature in the leading zone and the superheated steam temperature in the inert zone of the three-stage superheater are input into a cascade control system, wherein the cascade control system is a cascade control system of a secondary reheat unit including a main loop and a sub-loop, a step-type predictive controller SGPC is used as the main loop controller of the cascade control system, and an active disturbance rejection controller ADRC is used as the sub-loop controller of the cascade control system; the main loop controller and the sub-loop controller are used to adjust the control parameters of the main loop and the control parameters of the sub-loop respectively, to obtain the control action of the desuperheating water of the cascade control system, and the superheated steam temperature is controlled according to the control action.

2. The superheated steam temperature control method of a double reheat unit according to claim 1, characterized in that: The step of adjusting the control parameters of the main loop comprises the following steps: Obtain reference values of optimization performance indicators of the main loop; determining an objective function of a main loop controller according to the reference value and adding a soft constraint to a control increment; Obtaining an optimal analytical solution equation for the control action of the main loop controller at a certain moment through the objective function; A step factor is introduced into the main loop controller, and the optimal analytical solution equation of the control action is simplified by the step factor. The optimal analytical solution of the control action of the main loop controller is obtained according to the simplified equation.

3. The superheated steam temperature control method of a double reheat unit according to claim 2, characterized in that: The process of adjusting the control parameters of the secondary loop includes the following steps: The optimal analytical solution of the control action of the main loop controller is used as the set value of the sub-loop controller; The state estimation variables, controller gains and system parameters of the secondary loop are obtained, and the control action of the secondary loop controller is determined in combination with the secondary loop controller setting value.

4. The superheated steam temperature control method of a double reheat unit according to claim 1, characterized in that: It also includes the evaluation of the system tracking performance of the cascade control system of the double reheat unit, specifically through the performance index values of adjustment time, overshoot and ITAE.

5. The superheated steam temperature control method of a double reheat unit according to claim 1, characterized in that: The objective function is: ； Where, j is a moment in the time domain, N represents the prediction time domain, Indicates the reference value, M represents the control time domain, λ represents the control weight, Indicates the future k+j The optimal output prediction value at time Δ u ( k + j -1) k + j -1 moment of control increment.

6. The superheated steam temperature control method of a double reheat unit according to claim 1, characterized in that: The control parameters of the main loop include the softening factor α , optimize the time domain starting value N 1. Optimize the final value of the time domain N p , control time domain M and step factors β .

7. The superheated steam temperature control method of a double reheat unit according to claim 1, characterized in that: The control parameters of the secondary loop include the controller gain k p and k d , observer gain β 1. β 2 and β 3. System parameters b 0, controller bandwidth ω c and observer bandwidth .

8. A superheated steam temperature control system for a secondary reheat unit, characterized in that: include: The parameter acquisition module is used to obtain the superheated steam temperature in the leading zone and the superheated steam temperature in the inert zone of the three-stage superheater of the double reheat unit; a superheated steam temperature control module, configured to input the superheated steam temperature in the leading zone and the superheated steam temperature in the inert zone of the three-stage superheater into a cascade control system, wherein the cascade control system is a cascade control system of a secondary reheat unit including a main loop and a sub-loop, adopting a step-type predictive controller SGPC as the main loop controller of the cascade control system, and adopting an active disturbance rejection controller ADRC as the sub-loop controller of the cascade control system; using the main loop controller and the sub-loop controller to adjust the control parameters of the main loop and the control parameters of the sub-loop respectively, to obtain a control action of the desuperheating water of the cascade control system, and controlling the superheated steam temperature according to the control action.

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