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

Abstract

The invention discloses a cascade control method for a smoke concentration emission value of a coal-fired unit. The method comprises the following steps: establishing a dust removal dynamic characteristic model of a dry electric dust remover and a wet desulfurization tower based on a step test; a cascade control framework is constructed, an inner loop controller directly controls the dry-type electric precipitator, and an outer loop controller generates an inner loop set value according to the deviation between system output and the set value; an inner loop controller and an outer loop controller are set at the same time through a compensation method, on the basis of considering dynamic coupling of the inner loop and the outer loop, parameters of the outer loop controller are designed, the dynamic characteristics of an equivalent controlled object are improved, and then parameters of the inner loop controller are designed according to the dynamic characteristics of the equivalent controlled object; the controller is developed, and the control method is applied in the actual industrial process. According to the method, on the basis that the auxiliary dust removal capacity of the desulfurization tower is fully utilized, dynamic dust removal control over the dry-type electric dust remover is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal power generation set control, and more specifically, relates to a cascade control method for smoke concentration emission values. Background Art

[0002] Flue gas treatment devices in coal-fired units remove pollutants before the flue gas is released into the atmosphere. Automatic, efficient, and energy-saving control of pollutant treatment devices in coal-fired units is crucial for achieving clean coal utilization and ensuring energy security, meeting energy conservation and emission reduction requirements.

[0003] The pollutant treatment devices of some coal-fired units use a "dry electrostatic precipitator-wet desulfurization tower" process. The flue gas discharged from the boiler is treated in turn by a dry electrostatic precipitator and a wet desulfurization tower before being discharged into the atmosphere through a chimney. In this process, the operating objectives of the two devices are to ensure that the smoke concentration and sulfur dioxide concentration at the discharge port are lower than the dischargeable concentration. During this process, the main control device for smoke concentration is the dry electrostatic precipitator, and the main control device for sulfur dioxide concentration is the wet desulfurization tower. However, the desulfurization tower has a significant auxiliary dust removal capacity, and its operating status fluctuates as the desulfurization demand changes, which is not conducive to the stability of the smoke concentration at the discharge port.

[0004] Directly controlling the dust concentration at the exhaust port through dry ESPs presents problems with long processes and significant lags. Furthermore, as the desulfurization tower's operating conditions change in response to desulfurization demand, the dust concentration at the exhaust port fluctuates significantly, making it difficult to suppress these disturbances through direct control. Currently, such processes typically employ manual control or single-circuit closed-loop control of the dry ESP. These control methods often employ conservative strategies, causing the dry ESP to operate at high power, resulting in energy waste. Alternatively, if the dry ESP is not adjusted promptly, the desulfurization tower's auxiliary dust removal capacity may be urgently increased, leading to reduced gypsum quality. Summary of the Invention

[0005] Technical problem: The purpose of the present invention is to provide a cascade control method for the smoke concentration emission value of a coal-fired unit. For the "dry electrostatic precipitator-wet desulfurization tower" process, the auxiliary dust removal capacity of the desulfurization tower is taken into consideration, a cascade control framework is constructed, and dynamic control of the smoke concentration of the dry electrostatic precipitator considering the auxiliary dust removal capacity of the desulfurization tower is realized.

[0006] Technical Solution: To achieve the above-mentioned purpose, the present invention provides a cascade control method for smoke concentration emission values ​​of coal-fired units, comprising 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 used in the actual production process.

[0007] in: 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] Beneficial effect: After adopting the above scheme, the cascade control method of the smoke concentration emission value of the coal-fired unit of the present invention can construct a cascade controller of the dry electrostatic precipitator, which can take into account the auxiliary dust removal capability of the wet desulfurization tower; at the same time, the cascade control framework can improve the problems of long process and large lag in single-loop control, and also has a faster response to the interference of the operating state of the wet desulfurization tower on the smoke concentration, and has good application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the system structure of the present invention; Figure 2 It is a structural block diagram of the cascade control system in the present invention; Figure 3 This is the equivalent transformation block diagram of the cascade control system compensation method in the present invention; Figure 4 This is a flow chart of parameter setting of the compensation method in the present invention; Figure 5 is the control performance curve of Example 1 of the present invention; Figure 6 It is the control performance curve of Example 2 in the present invention. DETAILED DESCRIPTION

[0013] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] The present invention provides a cascade control method for the smoke concentration emission value of a coal-fired unit. The control method is used to address the smoke concentration control problem when there are multiple devices (such as dry electrostatic precipitators and wet desulfurization towers) with dust removal capabilities in the coal-fired unit, but only one device (such as the dry electrostatic precipitator) can serve as the main dust removal control device.

[0015] The following takes the process flow of "dry electrostatic precipitator-wet desulfurization tower" as an example to explain the cascade control system considering the auxiliary dust removal capacity of the wet desulfurization tower. The process flow of "dry electrostatic precipitator-wet desulfurization tower" in the embodiment and its corresponding cascade control system structure are as follows: Figure 1 As shown. In this process flow, both the dry electrostatic precipitator and the wet flue gas desulfurization tower have dust removal capabilities, but only the dry electrostatic precipitator is used to control the smoke concentration. The control objective of the dry electrostatic precipitator is to achieve precise control of the smoke concentration at the chimney outlet, so that the smoke concentration at the chimney outlet does not exceed the specified value. To address the problems existing in this control process, such as long control flow, large hysteresis, and interference of the wet flue gas desulfurization tower operating status on the smoke concentration at the chimney outlet, the cascade control method proposed in this invention can achieve precise control of the smoke concentration at the chimney outlet.

[0016] It should be noted that the present invention requires the placement of dust concentration measurement points between multiple dust removal devices. For example, in a "dry electrostatic precipitator - wet desulfurization tower" process, dust concentration measurement points are required at the dry electrostatic precipitator outlet and the wet desulfurization tower outlet. These measurement points are used to measure the dust concentration at the equipment outlet and serve as feedback data for the control system to build a cascade control system.

[0017] The establishment of the control system includes the following steps: S1, establish the dust removal dynamic characteristic model of dry electrostatic precipitator and wet desulfurization tower, including, First, perform a step test on the operating parameters of the dry electrostatic precipitator (such as the voltage or current of the dry electrostatic precipitator). Record the operating parameters of the dust removal main control equipment during the test, such as the voltage / current of the dry electrostatic precipitator in this example. Record the smoke concentration values ​​at each measuring point during the test, such as the smoke concentration at the dry electrostatic precipitator outlet and the smoke concentration at the desulfurization tower outlet in this example. Secondly, based on the step test data, the dynamic characteristic model parameters of the dry electrostatic precipitator are identified. 、 、 、 , establish the dynamic characteristic model of dry electrostatic precipitator dust removal, , 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; Then, based on the step test data, the dynamic characteristic model parameters of the cascade system overall dust removal are identified. 、 、 、 , establish an overall dust removal dynamic characteristics model including the dynamic characteristics of dry electrostatic precipitator dust removal and desulfurization tower dust removal, , 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, It 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; Finally, 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, the wet desulfurization tower dust removal dynamic characteristic model parameters are calculated. 、 、 、 , and establish the dynamic characteristic model of wet desulfurization tower dust removal, when hour, , , , , The established dynamic characteristic model of wet desulfurization tower dust removal is: ; 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 , Recalculate , , , , Then the dynamic characteristic model of wet desulfurization tower dust removal is established as follows: , 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 Euler number of the natural logarithm, 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.

[0018] Taking the step test data of a dust removal and desulfurization system as an example, the immune genetic algorithm is used to identify the model parameters, and the dynamic characteristic model of the dry electrostatic precipitator dust removal is obtained as follows: , The obtained overall dust removal dynamic characteristic model of the dust removal and desulfurization system is: , Then calculate the dust removal dynamic characteristic model of the wet desulfurization tower: First, determine the order relationship between the dynamic characteristic model of the dry electrostatic precipitator and the overall dynamic characteristic model of the dust removal and desulfurization system. , , ; Secondly, calculate the various model parameters of the dynamic characteristics of the wet desulfurization tower. , , , ; Finally, the dynamic characteristic model of dust removal of wet desulfurization tower is obtained as follows: .

[0019] It should be noted that in this implementation, a dust removal dynamic characteristics model for the dry ESP is first established, followed by a comprehensive dust removal dynamic characteristics model for the dust removal and desulfurization system. Finally, the comprehensive dust removal dynamic characteristics model and the dry ESP dust removal dynamic characteristics model are used together to calculate the dust removal dynamic characteristics model for the wet desulfurization tower. This is done because, in actual dry ESP operating parameter step tests, it is easy to perform operating parameter step tests on the dry ESP, thereby obtaining the dust concentration at the dry ESP outlet and the dust concentration at the output of the dust removal and desulfurization system (i.e., the dust concentration at the wet desulfurization tower outlet), and then establish the dry ESP dust removal dynamic characteristics model and the comprehensive dust removal dynamic characteristics model for the dust removal and desulfurization system, respectively. However, it is not easy to directly obtain dust concentration step data at the wet desulfurization tower inlet for directly establishing the dust removal dynamic characteristics model for the wet desulfurization tower.

[0020] S2, build a cascade control framework, such as Figure 2 As shown, the cascade control framework is used to solve the problem of long processes and large lags caused by the existence of only one master control device when multiple devices have dust removal capabilities at the same time.

[0021] In the cascade control framework, the inner loop is the main control loop, and the controlled object of the inner loop is It is a dry electrostatic precipitator; the controlled object of the external circuit is It is a wet desulfurization tower. The inner loop controller is , the inner loop gives the control action Adjust the operating parameters (current or voltage) of the dry electrostatic precipitator so that the dust concentration at the outlet of the dry electrostatic precipitator is Tracking inner loop set value ; The outer loop controller is , the dust concentration of the outer circuit passing through the exhaust port and emission setpoints Deviation, combined with the dynamic characteristics of dust removal of the desulfurization tower, gives the inner loop setting value , that is, the output of the outer loop controller is the inner loop set value (the desired dust concentration at the outlet of the dry electrostatic precipitator); the possible disturbances contained in this system are: the disturbance of the inner loop Mainly includes flue gas flow, dust concentration at the inlet of dry electrostatic precipitator and other disturbances that may cause fluctuation of dust concentration at the outlet of dry electrostatic precipitator; disturbance of external circuit It mainly includes the number of variable frequency pumps for slurry in the desulfurization tower, frequency changes, and other disturbances that may cause fluctuations in the dust concentration at the desulfurization tower outlet; S3, use the compensation method to adjust the internal and external loop controllers, the compensation method is equivalent to the transformation Figure 3 As shown in the figure, the tuning process using the compensation method is as follows Figure 4 As shown, First, clarify the controller parameters to be tuned. For example, when using a PID controller, , , The parameters to be tuned are the proportional gain of the inner loop , integration time , differential time and the proportional gain of the outer loop , integration time , differential time ; Then, the cascade control system is transformed into an equivalent system using the compensation method. The equivalent control object after equivalent transformation is: , The equivalent controller after equivalent transformation is: ; Secondly, for equivalent control objects Dynamic characteristics of the outer loop controller Parameters , , , to improve the dynamic characteristics of the equivalent control object; Then, in parameter , , Based on the already designed Parameters , , ; 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, it is returned to redesign. and If the control performance reaches the expected performance, the set of controller parameters that meet the control performance is determined as the controller parameters of the control system.

[0022] According to the dust removal dynamic characteristic model obtained from the aforementioned step test, , , The following two embodiments illustrate the process of adjusting controller parameters using the compensation method of the present invention. Example 1: In this example, both the inner and outer loop controllers of the control system adopt PID controllers. , , The parameters to be tuned are , , and , , ; First design The parameters are, , , , , 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, , , , The tracking and anti-disturbance effects of this example are as follows Figure 5 shown.

[0023] Example 2: In this example, the control system uses an ADRC controller for the inner loop and a PID controller for the outer loop. In the cascade control method for a dry-type electrostatic precipitator designed in this invention, the primary control loop is the inner loop, corresponding to the controlled object being the dry-type electrostatic precipitator. The outer loop primarily generates the setpoint for the inner loop. Therefore, when designing the controller, it is preferred to use an ADRC controller for the inner loop, as it offers better performance.

[0024] The inner loop uses an ADRC controller, and the control law output by the controller is, , in is the control rate, is the feedback gain, is the set value of the controller loop, in this case the inner loop set value, is the output response of the controller loop, in this case the inner loop output response, is the observer’s estimate of the disturbance, is the controller channel gain.

[0025] The ADRC controller uses an observer to obtain the disturbance estimate required in the above control law , the observer is, , in is the state of the control system, is the controller’s estimate of the state, are model parameters, is the controller channel gain, is the controller output control law, is the delay constant of the inner loop, is the observation gain of the observer; The outer loop uses a PID controller, , In this embodiment, the inner loop adopts an ADRC controller and the outer loop adopts a PID controller. The parameters to be tuned for the inner and outer loops are: Inner circuit: , , ; External circuit: , , .

[0026] First design The parameters are, , , , , 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, , , , The tracking and anti-disturbance effects of this example are as follows Figure 6 shown.

[0027] S4, develop a smoke concentration cascade controller, including, The designed controller was put into field use, using an industrial PLC to establish hardware connections with the power plant's DCS system and electrostatic precipitator equipment. High-precision sensors collected real-time data on smoke concentration and electric field parameters. The system achieved rapid closed-loop control of smoke concentration through data reading, program calculations, and command issuance.

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 used in the actual production process.

2. The cascade control method for smoke concentration emission values ​​of a coal-fired unit according to claim 1, characterized in that: 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.

3. 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.

4. 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.

5. 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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