A cascade control method for emission value of smoke concentration of coal-fired unit

Abstract

The present invention discloses a cascade control method for smoke concentration emission values ​​of coal-fired units. The method comprises: establishing a dust removal dynamic characteristic model for a dry electrostatic precipitator and a wet desulfurization tower based on a step test; constructing a cascade control framework in which an inner loop controller directly controls the dry electrostatic precipitator, and an outer loop controller generates an inner loop setpoint based on the deviation between the system output and the setpoint; using a compensation method to simultaneously tune the inner and outer loop controllers, and considering the dynamic coupling of the inner and outer loops, by designing the outer loop controller parameters to improve the dynamic characteristics of the equivalent controlled object, and then designing the inner loop controller parameters based on the dynamic characteristics of the equivalent controlled object; and developing a controller to implement the control method in actual industrial processes. The proposed method can achieve dynamic dust removal control of the dry electrostatic precipitator while fully utilizing the auxiliary dust removal capacity of the desulfurization tower.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of thermal power generator set control, and more particularly relates to a cascade control method for smoke dust concentration emission value. BACKGROUND

[0002] The flue gas treatment device in the coal-fired unit can remove pollutants before the flue gas is discharged into the atmosphere. Realizing automatic, efficient and energy-saving control of the pollutant treatment device of the coal-fired unit is of great significance to realizing clean use of coal, ensuring energy security and meeting the requirements of energy saving and emission reduction.

[0003] The pollutant treatment device of part of the coal-fired unit adopts the process flow of "dry-type electric precipitator-wet desulfurization tower". The flue gas discharged from the boiler is sequentially treated by the dry-type electric precipitator and the wet desulfurization tower, and then discharged into the atmosphere through the chimney. In this process flow, the operation goals of the two devices are to ensure that the smoke dust concentration and the sulfur dioxide concentration at the discharge port are lower than the dischargeable concentration. In this process, the main control equipment for the smoke dust concentration is the dry-type electric precipitator, and the main control equipment for the sulfur dioxide concentration is the wet desulfurization tower. However, the desulfurization tower has an auxiliary dust removal capacity that cannot be ignored, and when its operating state changes with the desulfurization demand, the auxiliary dust removal capacity will fluctuate, which is not conducive to the stability of the smoke dust concentration at the discharge port.

[0004] Directly controlling the smoke dust concentration at the discharge port by the dry-type electric precipitator has the problems of long process flow and large lag. At the same time, when the desulfurization tower changes its operating condition with the desulfurization demand, it will cause large fluctuations in the smoke dust concentration at the discharge port, and direct control cannot suppress this disturbance. At present, manual control or single-loop closed-loop control of the dry-type electric precipitator is usually used in such process flow. Such control method often uses a conservative strategy to make the dry-type electric precipitator run at high power, causing energy waste; or the dry-type electric precipitator fails to adjust in time, and the auxiliary dust removal capacity of the desulfurization tower is urgently increased, causing the quality of gypsum to decrease. SUMMARY

[0005] Technical problem: The purpose of the present application is to provide a cascade control method for smoke dust concentration emission value of a coal-fired unit, which is aimed at the process of "dry-type electric precipitator-wet desulfurization tower", considers the auxiliary dust removal capacity of the desulfurization tower, constructs a cascade control framework, and realizes dynamic control of the smoke dust concentration of the dry-type electric precipitator considering the auxiliary dust removal capacity of the desulfurization tower.

[0006] Technical solution: In order to achieve the above purpose, a cascade control method for smoke dust concentration emission value of a coal-fired unit according to the present application includes the following steps:

[0007] Step 1, establish the dust removal dynamic characteristic model of dry-type electric dust removal and establish the dust removal dynamic characteristic model of wet desulfurization tower, based on the step experiment data of the running parameters of the dust removal and desulfurization system, identify and calculate the dust removal dynamic characteristic model parameters of the inner and outer loops, and clarify the dust removal characteristics of the controlled object of the control system;

[0008] Step 2, based on the dust removal dynamic characteristic model of the inner and outer loops in step 1, construct a cascade control framework, wherein the inner loop controller directly controls the dry-type electric dust removal, and the outer loop controller generates the inner loop set value according to the deviation between the dust concentration output of the dust removal and desulfurization system and the dust concentration set value;

[0009] Step 3, based on the cascade control framework established in step 2, the inner and outer loop controllers are simultaneously tuned by using compensation method, while considering the mutual influence of the dynamic characteristics of the inner and outer loops, first, the dynamic characteristics of the equivalent controlled object are improved by designing the parameters of the outer loop controller, and then the parameters of the inner loop controller are designed according to the dynamic characteristics of the equivalent controlled object;

[0010] Step 4, based on the parameter design results of the inner and outer loop controllers in step 3, develop a dust concentration cascade controller, and apply the controller to the actual production process.

[0011] Among them:

[0012] In step 1, the dust removal dynamic characteristic model of dry-type electric dust removal and the dust removal dynamic characteristic model of wet desulfurization tower are established, including,

[0013] Step 11, step test is conducted on the dry-type electric dust removal, and the dry-type electric dust removal step parameters, dry-type electric dust removal outlet dust concentration parameters and desulfurization tower outlet dust concentration parameters data are collected;

[0014] Step 12, based on the dry-type electric dust removal running parameters and dry-type electric dust removal outlet dust concentration parameters in the step test data, the dry-type electric dust removal dust removal dynamic characteristic model is established,

[0015] ,

[0016] Among them, is the dry-type electric dust removal outlet dust concentration, is the dry-type electric dust removal running parameter, , , , are the gain parameter, time constant, time delay constant and model order of the dry-type electric dust removal dynamic characteristic model respectively, is the natural logarithm base Euler number, indicates the time delay link of the dry-type electric dust removal dust removal dynamic characteristic model, is the Laplace operator, For the dynamic characteristic model of dry-type electric precipitator;

[0017] Step 13, based on the dry-type electric precipitator operating parameters in the step test data and the outlet flue dust concentration parameters of the wet desulfurization tower, an overall dust removal dynamic characteristic model containing the dust removal dynamic characteristics of the dry-type electric precipitator and the dust removal dynamic characteristics of the desulfurization tower is established, ,

[0018] Wherein, is the outlet flue dust concentration of the wet desulfurization tower, is the dry-type electric precipitator operating parameter, , , , are the gain parameters, time constants, time delay constants and model orders of the overall dust removal dynamic characteristic model respectively, is the base of natural logarithm (Euler number), represents the time delay link of the overall dust removal dynamic characteristic model, is the Laplace operator, is the overall dynamic characteristic model of the dust removal and desulfurization system;

[0019] Step 14, based on the dry-type electric precipitator dust removal dynamic characteristic model and the overall dust removal dynamic characteristic model of the system established in steps 12 and 13, the dust removal dynamic characteristic model of the wet desulfurization tower is calculated,

[0020] When , ,

[0021] When , the dry-type electric precipitator dust removal dynamic characteristic model established in step 12 is reduced to a first-order equivalent model, wherein the equivalent model order , the equivalent model time constant ; and the is calculated to obtain , ,

[0022] Wherein, , , , are the gain parameters, time constants, time delay constants and model orders of the wet desulfurization tower dust removal dynamic characteristic model respectively, is the base of natural logarithm (Euler number), represents the time delay link of the wet desulfurization tower dust removal dynamic characteristic model, is the Laplace operator, is the dynamic characteristic model of the wet desulfurization tower, is the dry-type electric precipitator dust removal dynamic characteristic model The first-order equivalent model.

[0023] In step 2, a cascade control framework is constructed, including:

[0024] The inner loop controller is , the inner loop adjusts the current or voltage operating parameters of the dry electrostatic precipitator by giving a control action, so that the smoke concentration at the outlet of the dry electrostatic precipitator tracks the set value of the inner loop;

[0025] The outer loop controller is The outer loop passes through the deviation of the smoke concentration at the discharge port and the emission set value, combined with the dynamic characteristics of the dust removal of the desulfurization tower, to give the inner loop set value, that is, the output of the outer loop controller is the inner loop set value, which is the expected smoke concentration at the dry electrostatic precipitator outlet.

[0026] In step 3, the compensation method is used to adjust the inner and outer loop controllers, including the following steps:

[0027] Step 31, use the compensation method to perform equivalent transformation on the cascade control system.

[0028] The equivalent control object after equivalent transformation is: ,

[0029] The equivalent controller after equivalent transformation is: ,

[0030] Step 32: Design an outer loop controller based on the dynamic characteristics of the equivalent control object. parameters to improve the dynamic characteristics of the equivalent control object,

[0031] Step 33, in step 32 The design parameters have been designed based on Parameters,

[0032] In step 34, the controller parameters designed in steps 32 and 33 are put into a closed-loop control system for simulation experiment. If the control performance of the cascade control system does not meet the expected performance, the process returns to step 32; if the control performance meets the expected performance, the set of controller parameters that meet the control performance is determined as the controller parameters of the control system.

[0033] In step 4, a smoke concentration cascade controller is developed, including:

[0034] The designed controller is put into field application, and the hardware connection with the power plant DCS system and electrostatic precipitator equipment is realized based on the industrial PLC. The smoke concentration and electric field parameters are collected in real time through high-precision sensors. The controller realizes rapid closed-loop control of smoke concentration through data reading, program operation and instruction issuance.

[0035] Beneficial effects: the cascade control method of coal-fired unit flue dust concentration emission value can construct the cascade controller of the dry-type electric dust collector, the controller can consider the auxiliary dust removal capacity of the wet desulfurization tower; meanwhile, the cascade control framework can improve the long process and large lag problems of the single loop control, has a faster response to the interference of the wet desulfurization tower operation state on the flue dust concentration, and has good application value. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is the system structure schematic diagram in the application;

[0037] Figure 2 is the cascade control system structure block diagram in the application;

[0038] Figure 3 is the compensation method equivalent transformation block diagram of the cascade control system in the application;

[0039] Figure 4 is the compensation method parameter setting flow chart in the application;

[0040] Figure 5 is the control performance curve of example 1 in the application;

[0041] Figure 6 is the control performance curve of example 2 in the application. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages of the application more clear, the application will be described in detail below with the help of the drawings and specific examples.

[0043] The application provides a cascade control method of coal-fired unit flue dust concentration emission value, which is used for processing the flue dust concentration control problem when multiple devices (for example, dry-type electric dust collector, wet desulfurization tower) in the coal-fired unit have dust removal capacity, and only one device (for example, dry-type electric dust collector) can be used as the main dust removal device.

[0044] The following takes the process flow of "dry-type electric dust collector-wet desulfurization tower" as an example to describe the cascade control system considering the auxiliary dust removal capacity of the wet desulfurization tower. The "dry-type electric dust collector-wet desulfurization tower" process flow of the example and the corresponding cascade control system structure are as follows: Figure 1The process flow is shown. In the process flow, the dry electric dust collector and the wet desulfurization tower have dust removal capacity, but the dry electric dust collector is the only device for controlling the smoke dust concentration. The control target of the dry electric dust collector is to realize accurate control of the smoke dust concentration at the chimney outlet, so that the smoke dust concentration at the chimney outlet is not higher than the limited value. In view of the problems of long control process, large lag and interference of the running state of the wet desulfurization tower on the smoke dust concentration at the chimney outlet existing in the control process, the cascade control method proposed in the application can realize accurate control of the smoke dust concentration at the chimney outlet.

[0045] It should be noted that the application requires arranging smoke dust concentration measuring points among multiple dust removal devices. For example, in the process flow of the dry electric dust collector-wet desulfurization tower, smoke dust concentration measuring points need to be arranged at the outlet of the dry electric dust collector and the outlet of the wet desulfurization tower, which are used to test the smoke dust concentration at the outlet of the device and serve as feedback data of the control system to build a cascade control system.

[0046] The establishment of the control system includes the following steps,

[0047] S1, a dust removal dynamic characteristic model of the dry electric dust collector and a dust removal dynamic characteristic model of the wet desulfurization tower are established, including,

[0048] Firstly, step test is performed on the operating parameters of the dry electric dust collector (such as the operating parameters of the dry electric dust collector such as voltage or current), and the operating parameters of the dust main control device in the test process are recorded, such as the dry electric dust collector voltage / current in this example; the smoke dust concentration values of each measuring point in the test process are recorded, such as the smoke dust concentration at the outlet of the dry electric dust collector and the smoke dust concentration at the outlet of the desulfurization tower in this example;

[0049] Secondly, based on the step test data, the parameters of the dry electric dust collector dust removal dynamic characteristic model are identified 、 、 、 , the dry electric dust collector dust removal dynamic characteristic model is established, ,

[0050] Among them, is the smoke dust concentration at the outlet of the dry electric dust collector, is the operating parameter of the dry electric dust collector, 、 、 、 are the gain parameter, time constant, time delay constant and model order of the dry electric dust collector dynamic characteristic model respectively, is the base Euler number of natural logarithm, indicates the time delay link of the dry electric dust collector dust removal dynamic characteristic model, is the Laplace operator, A dry-type electric dust collector dynamic characteristic model;

[0051] Then, based on the step test data, the overall dust removal dynamic characteristic model parameters of the cascade system are identified 、 、 、 An overall dust removal dynamic characteristic model containing the dust removal dynamic characteristic of the dry-type electric dust collector and the dust removal dynamic characteristic of the desulfurization tower is established ,

[0052] Wherein, is the outlet flue dust concentration of the wet desulfurization tower, is the dry-type electric dust collector operation parameter, 、 、 、 are the gain parameter, time constant, time delay constant and model order of the overall dust removal dynamic characteristic model respectively, is the natural logarithm base Euler number, represents the time delay link of the overall dust removal dynamic characteristic model time delay link, is the Laplace operator, is the overall dynamic characteristic model of the dust removal and desulfurization system;

[0053] Finally, based on the dry-type electric dust collector dust removal dynamic characteristic model and the system overall dust removal dynamic characteristic model constructed in steps 12 and 13, the wet desulfurization tower dust removal dynamic characteristic model parameter 、 、 、 is calculated, and the wet desulfurization tower dust removal dynamic characteristic model is established

[0054] When , , , , ,

[0055] The established wet desulfurization tower dust removal dynamic characteristic model is:

[0056] ;

[0057] When , the dry-type electric dust collector dust removal dynamic characteristic model established in step 12 is reduced to a first-order equivalent model, wherein the equivalent model order , the equivalent model time constant ,

[0058] Then , , , ,

[0059] The dust removal dynamic characteristic model of the wet desulfurization tower is further established as follows:

[0060] ,

[0061] wherein, , , , are gain parameters, time constants, time delay constants and model orders of the dust removal dynamic characteristic model of the wet desulfurization tower respectively, is Euler number of the base of natural logarithm, represents a time delay link of the dust removal dynamic characteristic model of the wet desulfurization tower, is a Laplace operator, is a dynamic characteristic model of the wet desulfurization tower, is a first-order equivalent model of a dust removal dynamic characteristic model of the dry-type electric dust collector.

[0062] Taking step test data of a certain dust removal and desulfurization system as an example, the model parameters are identified by using an immune genetic algorithm, and the dust removal dynamic characteristic model of the dry-type electric dust collector obtained is as follows:

[0063] ,

[0064] The overall dust removal dynamic characteristic model of the dust removal and desulfurization system obtained is as follows:

[0065] ,

[0066] The dust removal dynamic characteristic model of the wet desulfurization tower is further calculated as follows:

[0067] Firstly, the order relationship between the dust removal dynamic characteristic model of the dry-type electric dust collector and the overall dynamic characteristic model of the dust removal and desulfurization system is judged, , , ;

[0068] Secondly, the model parameters of the dust removal dynamic characteristic of the wet desulfurization tower are calculated,

[0069] ,

[0070] ,

[0071] ,

[0072] ;

[0073] ​Finally, the dust removal dynamic characteristic model of the wet desulfurization tower is obtained,

[0074] .

[0075] It should be noted that in the present embodiment, firstly, the dust removal dynamic characteristic model of the dry-type electric dust collector is established, secondly, the overall dust removal dynamic characteristic model of the dust removal and desulfurization system is established, and finally, the dust removal dynamic characteristic model of the wet desulfurization tower is calculated from the overall dust removal dynamic characteristic model and the dust removal dynamic characteristic model of the dry-type electric dust collector. This is because in the actual dry-type electric dust collector operation parameter step test, it is easy to make the operation parameter step test of the dry-type electric dust collector, and then the dry-type electric dust collector outlet dust concentration and the output dust concentration of the dust removal and desulfurization system (i.e. the dust concentration at the outlet of the wet desulfurization tower) are obtained, and the dust removal dynamic characteristic model of the dry-type electric dust collector and the overall dust removal dynamic characteristic model of the dust removal and desulfurization system are respectively established; but it is not easy to directly obtain the dust concentration step data at the inlet of the wet desulfurization tower for directly establishing the dust removal dynamic characteristic model of the wet desulfurization tower.

[0076] S2, a cascade control framework is constructed, as shown in Figure 2 The cascade control framework is used to solve the problem of long process and large lag caused by the fact that multiple devices have dust removal capability at the same time, but only one master device exists.

[0077] In the cascade control framework, the inner loop is the master control loop, and the controlled object of the inner loop is the dry-type electric dust collector; the controlled object of the outer loop is the wet desulfurization tower. The inner loop controller is , and the inner loop adjusts the operating parameters (current or voltage) of the dry-type electric dust collector by giving a control action so that the dry-type electric dust collector outlet dust concentration tracks the inner loop set value ; the outer loop controller is , and the outer loop gives the inner loop set value by combining the deviation of the discharge dust concentration from the discharge set value and the dust removal dynamic characteristic of the desulfurization tower, that is, the output of the outer loop controller is the inner loop set value (the expected dry-type electric dust collector outlet dust concentration); the possible disturbances in the system include the inner loop disturbance mainly including the flue gas flow, the dry-type electric dust collector inlet dust concentration and other disturbances that may cause the dry-type electric dust collector outlet dust concentration to fluctuate; the outer loop disturbance mainly includes the number of desulfurization tower slurry variable frequency pump stations, the frequency change and other disturbances that may cause the desulfurization tower outlet dust concentration to fluctuate.

[0078] S3, the inner and outer loop controller is set by compensation method, compensation method equivalent transformation as shown in Figure 3 The setting process of compensation method is shown in Figure 4

[0079] First, the controller to be set parameters, for example, when using PID controller,

[0080]

[0081]

[0082] The to-be-set parameters are the proportional gain , integral time , derivative time of the inner loop and the proportional gain , integral time , derivative time of the outer loop;

[0083] Next, the compensation method is used for equivalent transformation of the cascade control system,

[0084] The equivalent control object after equivalent transformation is

[0085] The equivalent controller after equivalent transformation is:

[0086] Secondly, according to the dynamic characteristics of the equivalent control object , the parameters of the outer loop controller are designed , , to improve the dynamic characteristics of the equivalent control object;

[0087] Then, on the basis of the parameters , that have been designed, the parameters of , are designed;

[0088] Finally, the designed controller parameters are put into the closed-loop control system for simulation experiment, if the control performance of the cascade control system does not meet the expected performance, the parameters of are returned to be redesigned; if the control performance meets the expected performance, the set of controller parameters that meet the control performance is determined as the controller parameters of the control system.

[0089] ​​​​​​​​​​According to the dust removal dynamic characteristic model obtained from the aforementioned step test,

[0090] ,

[0091] ,

[0092] The following two embodiments illustrate the process of adjusting controller parameters using the compensation method of the present invention.

[0093] Example 1: In this example, both the inner and outer loop controllers of the control system adopt PID controllers.

[0094] ,

[0095] ,

[0096] The parameters to be tuned are , , and , , ;

[0097] First design The parameters are,

[0098] , , ,

[0099] ,

[0100] Then the equivalent control object is obtained as: , equivalent control object All the parameters of the controller are known; get the equivalent controller ,in The parameters of are currently unknown and are designed using a multi-objective immune genetic algorithm. The parameters are obtained,

[0101] , , ,

[0102] The tracking and anti-disturbance effects of this example are as follows Figure 5 shown.

[0103] In this embodiment, the inner loop of the control system uses an ADRC controller, and the outer loop uses a PID controller. In the cascade control method of the dry-type electric dust collector designed by the present application, the main control loop is the inner loop, and the corresponding controlled object is the dry-type electric dust collector. The main function of the outer loop is to generate the set value of the inner loop. Therefore, when designing the controller, the ADRC controller with better performance is used in the inner loop.

[0104] The inner loop uses an ADRC controller, and the control law output by the controller is

[0105] ,

[0106] wherein is the control rate, is the feedback gain, is the set value of the loop in which the controller is located, which is the inner loop set value in this example, is the output response of the loop in which the controller is located, which is the inner loop output response in this example, is the disturbance estimate of the observer, is the controller channel gain.

[0107] The ADRC controller uses an observer to obtain the disturbance estimate required in the above control law , and the observer is

[0108] ,

[0109] wherein is the state of the control system, is the state estimate of the controller, is the model parameter, is the controller channel gain, is the controller output control law, is the time delay constant of the inner loop, is the observation gain of the observer;

[0110] The outer loop uses a PID controller,

[0111] ,

[0112] For the case where the ADRC controller is used in the inner loop and the PID controller is used in the outer loop in this embodiment, the parameters to be tuned in the inner and outer loops are as follows:

[0113] Inner loop: , , ;

[0114] Outer loop: , , .

[0115] Firstly, design The parameters of

[0116] , , ,

[0117] ,

[0118] Secondly, obtain the equivalent control object The parameters of the equivalent control object are all known; obtain the equivalent controller wherein The parameters of the equivalent controller are currently unknown, design the parameters of the equivalent controller

[0119] , , ,

[0120] The tracking and anti-interference effects of this example are shown in Figure 6 .

[0121] S4, develop a flue dust concentration cascade controller, including

[0122] Put the designed controller into field application, realize hardware connection with the power plant DCS system and the electric dust removal equipment based on industrial PLC, and collect flue dust concentration and electric field parameters in real time through high-precision sensors. The system realizes rapid closed-loop control of flue dust concentration through data reading, program operation and instruction issuing.​

Claims

1. A cascade control method for smoke dust concentration emission values ​​of a coal-fired unit, characterized by: The control method comprises the following steps: Step 1: Establish a dynamic dust removal characteristic model for the dry electrostatic precipitator and a dynamic dust removal characteristic model for the wet desulfurization tower. Based on the step experimental data of the operating parameters of the dry electrostatic precipitator in the dust removal and desulfurization system, identify and calculate the dynamic dust removal characteristic model parameters of the internal and external circuits, and clarify the dust removal characteristics of the controlled object of the control system. Step 2: Based on the dynamic characteristic model of the inner and outer loop dust removal in step 1, a cascade control framework is constructed, wherein the inner loop controller directly controls the dry electrostatic precipitator, and the outer loop controller generates an inner loop set value based on the deviation between the dust concentration output of the dust removal and desulfurization system and the dust concentration set value; Step 3: Based on the cascade control framework established in Step 2, the inner and outer loop controllers are tuned simultaneously using a compensation method. While considering the mutual influence of the inner and outer loop dynamic characteristics, the outer loop controller parameters are first designed to improve the dynamic characteristics of the equivalent controlled object. Then, the inner loop controller parameters are designed based on the dynamic characteristics of the equivalent controlled object. Step 4: Based on the parameter design results of the inner and outer loop controllers in step 3, a smoke concentration cascade controller is developed and applied to the actual production process; In the step 1, a dynamic characteristic model of dust removal for a dry electrostatic precipitator and a dynamic characteristic model of dust removal for a wet desulfurization tower are established, including: Step 11: Perform a step test on the dry electrostatic precipitator to collect data on the dry electrostatic precipitator step parameters, dry electrostatic precipitator outlet dust concentration parameters, and desulfurization tower outlet dust concentration parameter data; Step 12: Based on the dry electrostatic precipitator operating parameters and dry electrostatic precipitator outlet dust concentration parameters in the step test data, a dry electrostatic precipitator dust removal dynamic characteristic model is established. ， in, is the dust concentration at the outlet of dry electrostatic precipitator, is the operating parameter of dry electrostatic precipitator, 、 、 、 are the gain parameter, time constant, time delay constant and model order of the dynamic characteristic model of dry electrostatic precipitator, is the base Euler number of the natural logarithm, represents the time delay link of the dynamic characteristic model of dry electrostatic precipitator dust removal, is the Laplace operator, It is the dynamic characteristic model of dry electrostatic precipitator; Step 13: Based on the dry electrostatic precipitator operating parameters and the wet desulfurization tower outlet dust concentration parameters in the step test data, an overall dust removal dynamic characteristics model including the dry electrostatic precipitator dust removal dynamic characteristics and the desulfurization tower dust removal dynamic characteristics is established. ， in, is the dust concentration at the outlet of the wet desulfurization tower, is the operating parameter of dry electrostatic precipitator, 、 、 、 are the gain parameter, time constant, delay constant and model order of the overall dust removal dynamic characteristic model respectively, is the base Euler number of the natural logarithm, Represents the time delay link of the overall dust removal dynamic characteristic model, is the Laplace operator, It is the overall dynamic characteristic model of the dust removal and desulfurization system; Step 14, based on the dry electrostatic precipitator dust removal dynamic characteristic model and the system overall dust removal dynamic characteristic model constructed in steps 12 and 13, calculate the wet desulfurization tower dust removal dynamic characteristic model, when hour, , when When the dynamic characteristic model of dry electrostatic precipitator established in step 12 is Reduced to a first-order equivalent model, , where the equivalent model order is , the equivalent model time constant ; then calculate to obtain , ， in, 、 、 、 are the gain parameter, time constant, delay constant and model order of the dynamic characteristic model of wet desulfurization tower dust removal, is the base of natural logarithms (Euler's number), It represents the time delay link of the dynamic characteristic model of wet desulfurization tower dust removal, is the Laplace operator, is the dynamic characteristic model of the wet desulfurization tower, Dynamic characteristic model of dry electrostatic precipitator dust removal The first-order equivalent model.

2. The cascade control method for smoke concentration emission values ​​of a coal-fired unit according to claim 1, characterized in that: In step 2, a cascade control framework is constructed, including: The inner loop controller is , the inner loop adjusts the current or voltage operating parameters of the dry electrostatic precipitator by giving a control action, so that the smoke concentration at the outlet of the dry electrostatic precipitator tracks the set value of the inner loop; The outer loop controller is The outer loop passes through the deviation of the smoke concentration at the discharge port and the emission set value, combined with the dynamic characteristics of the dust removal of the desulfurization tower, to give the inner loop set value, that is, the output of the outer loop controller is the inner loop set value, which is the expected smoke concentration at the dry electrostatic precipitator outlet.

3. The cascade control method for smoke concentration emission values ​​of a coal-fired unit according to claim 1, characterized in that: In step 3, the compensation method is used to adjust the inner and outer loop controllers, including the following steps: Step 31, use the compensation method to perform equivalent transformation on the cascade control system. The equivalent control object after equivalent transformation is: , The equivalent controller after equivalent transformation is: , Step 32: Design an outer loop controller based on the dynamic characteristics of the equivalent control object. parameters to improve the dynamic characteristics of the equivalent control object, Step 33, in step 32 The design parameters have been designed based on Parameters, In step 34, the controller parameters designed in steps 32 and 33 are put into a closed-loop control system for simulation experiment. If the control performance of the cascade control system does not meet the expected performance, the process returns to step 32; if the control performance meets the expected performance, the set of controller parameters that meet the control performance is determined as the controller parameters of the control system.

4. The cascade control method for smoke concentration emission values ​​of a coal-fired unit according to claim 1, characterized in that: In step 4, a smoke concentration cascade controller is developed, including: The designed controller is put into field application, and the hardware connection with the power plant DCS system and electrostatic precipitator equipment is realized based on the industrial PLC. The smoke concentration and electric field parameters are collected in real time through high-precision sensors. The controller realizes rapid closed-loop control of smoke concentration through data reading, program operation and instruction issuance.

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