A kind of air supply automatic control system and method for inhibiting the disturbance of powder feeding machine to unit

Abstract

The application discloses a kind of inhibiting to send air automatic control system and method of unit disturbance of powder feeder lower powder not smooth, including total air volume reference instruction formation loop, RB air volume reference instruction formation loop, total air volume reference instruction disturbanceless switching loop, oxygen amount correction loop, corrected total air volume instruction formation loop, modified variable load feedforward formation loop, limit before total air volume instruction formation loop and total air volume instruction formation loop.The application can reduce the fluctuation of furnace pressure, main steam temperature, reheater temperature and other parameters;Air supply control can be fully invested in automatic operation mode, greatly reducing the amount of operation personnel operation;When unit RB acts, it can quickly switch to the small value of RB target air volume instruction S6 and total air volume reference instruction S1, meet the air volume demand of RB process, while ensuring that air volume has no possibility of up-regulation;Avoid total air volume instruction to cause total air volume instruction to decrease too slowly due to RB process actual load drop too slowly, unstable combustion and other serious threats to safe operation of unit phenomenon.

Description

Technical Field

[0001] This invention relates to the field of automatic control technology for coal-fired power units equipped with intermediate storage pulverizing systems, and specifically to an automatic air supply control system and method for suppressing disturbances to the unit caused by poor pulverizing by the pulverizer. Background Technology

[0002] In order to adapt to changes in the domestic coal and electricity markets, the operation mode of boilers in thermal power generating units has undergone significant changes: changes in the type of coal used in boilers and frequent participation of units in peak shaving have had a significant impact on the operation of power plant boilers and their pulverizing systems, bringing about a series of problems.

[0003] The existing air supply control is a cascade control system with oxygen content correction. The main steam flow rate, after passing through a function generator, provides a basic setpoint for the flue gas oxygen content under that load. Operators can manually adjust this basic setpoint based on the actual operating conditions of the unit. The average of the selected A and B side flue gas oxygen content signals is used as the flue gas oxygen content signal for the automatic adjustment system. The output of the oxygen correction station corrects the total air volume reference value given by the boiler main control command via a function converter. The corrected signal and the minimum air volume signal are selected together as the total air volume setpoint. Under RB operating conditions, the air supply control uses closed-loop regulation to control the decrease in total air volume. By controlling the rate of decrease, a reasonable air-fuel ratio is maintained to ensure combustion safety, while simultaneously improving furnace negative pressure changes.

[0004] For units equipped with intermediate storage pulverizing systems, unstable pulverized coal feeding is a common problem during high-load periods. Poor pulverized coal feeding by the feeder has a severely adverse impact on combustion within the furnace, primarily manifested in large fluctuations in the air-coal mixture concentration and a deflected flame center in the furnace. Under coordinated control, feeder commands change frequently. When the air supply is in automatic control mode, the total air volume command fluctuates frequently in response to fuel volume fluctuations, leading to frequent fluctuations in total air volume, furnace negative pressure, steam temperature, and steam pressure. This significantly reduces the control quality of the coordinated control system and seriously affects the safe and economical operation of the unit. To reduce the disturbances caused by poor pulverized coal feeding during high-load periods, operators manually adjust the air supply to meet combustion demands, greatly increasing the workload of operators and the safety risks to unit operation. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned problems by providing an automatic air supply control system and method to suppress the disturbance of the unit caused by poor powder feeding from the pulverizer. By adaptively adjusting the weight coefficients of the boiler main control command and the unit load command, the variable load feedforward is self-corrected according to the load increase, decrease and different load segments. The total air volume reference command for RB operating condition and normal operating condition is distinguished to achieve automatic air supply control under wide load, thereby achieving the purpose of rapid response to grid load, stable unit parameters and safety assurance under abnormal operating conditions.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] An automatic air supply control system for suppressing unit disturbance caused by poor powder feeding from the powder feeder includes a unit load command input 3. The unit load command input 3 is connected to the inputs of a second function converter 10, a third function converter 12, a fourth function converter 14, and a fifth function converter 15. The output of the third function converter 12 is connected to input 1 of a second multiplier 24. Input 2 of the second multiplier 24 is connected to the output of a subtractor 18. Input 1 (minuend) of the subtractor 18 is connected to a constant module (constant 1) 11, and input 2 (subtrahend) of the subtractor 18 is connected to the output of the second function converter 10. The output of multiplier 24 is connected to input 1 of the first adder 26. Input 2 of the first adder 26 is connected to the output of the first multiplier 17. Input 1 of the first multiplier 17 is connected to the output of the second function converter 10. Input 2 of the first multiplier 17 is connected to the output of the first function converter 9. The input of the first function converter 9 is connected to the boiler main control command input 2. The output of adder 26 is connected to input 1 of small selection module 25 and input 1 of bumpless switching module 30. Input 2 of small selection module 25 is connected to the output of the sixth function converter 16. The input of the sixth function converter 16 is connected to the RB target fuel quantity input 1.Input 2 of the bumpless switching module 30 is connected to the output of the small selection module 25. Input 3 (selection signal) of the bumpless switching module 30 is connected to the output of the delay interrupt module 19. RB action input 5 is connected to the input of the delay interrupt module 19 and the input of the non-module 13, respectively. The output of the bumpless switching module 30 is connected to input 1 of the third multiplier 31. Input 2 of the third multiplier 31 is connected to the output of the PID controller 29. The input of the PID controller 29 is connected to the oxygen deviation input 6. The input of the PID controller 29 (tracking switch TS) is connected to the output of the pulse module 20. The input of the pulse module 20 is connected to the output of the non-module 13. The input of the PID controller 29 (tracking point TR) is connected to the output of the divider 27. Input 1 (divisor) of the divider 27 is connected to the total air volume input 4. Input 2 (dividend) of the divider 27 is connected to the output of the second multiplier 24. The output of the third multiplier 31 is connected to the third multiplier 25. The input 1 of the first adder 32 is connected to the input 2 of the third adder 32, which is connected to the output of the second adder 28. The input 1 of the second adder 28 is connected to the output of the first multiplier 21, and the input 2 of the second adder 28 is connected to the output of the second multiplier 22. The input 1 of the first multiplier 21 is connected to the output of the fourth function converter 14, and the input 1 of the second multiplier 22 is connected to the output of the fifth function converter 15. The variable load feedforward input 7 is connected to the input 2 of the first multiplier 21 and the input 2 of the second multiplier 22. The output of the third adder 32 is connected to the input 1 of the general election module 34. The input 2 of the general election module 34 is connected to the constant module 33 (minimum air volume). The input 3 of the general election module 34 is connected to the output of the seventh function converter 23. The input of the seventh function converter 23 is connected to the total fuel quantity input 8 after calorific value correction. The output of the general election module 34 is connected to the total air volume command output 35.

[0008] The aforementioned automatic air supply control system and method for suppressing disturbances to the unit caused by poor powder feeding from the powder feeder includes the following steps:

[0009] Step 1: Based on the boiler main control command input 2 and the unit load command input 3, obtain the total air volume reference command S1;

[0010] S1=f1(x1)*f2(x2)+f3(x2)*(1-f2(x2))

[0011] Where x1 is the boiler main control command input 2, x2 is the unit load command input 3, f1(x) is the output of the first function converter 9, f2(x) is the output of the second function converter 10, and f3(x) is the output of the third function converter 12;

[0012] The total air volume reference command S1 automatically adjusts the weighting coefficients of the total air volume reference commands corresponding to the boiler main control command input 2 and the unit load command input 3 according to the unit load command. As the load command increases, the weighting coefficient of the total air volume reference command corresponding to the boiler main control command gradually decreases to 0, and the weighting coefficient of the total air volume reference command corresponding to the unit load command gradually increases to 1.

[0013] Step 2: Based on the RB target fuel quantity input 1 and the total air volume reference command S1, obtain the RB target total air volume command S2;

[0014] S2 = min(f6(x3), S1)

[0015] Where x3 is the RB target fuel quantity input 1, f6(x) is the output of the sixth function converter 16; min() is the minimum value module, which performs a minimum operation on the two inputs so that the output is equal to the smaller of the two inputs.

[0016] Step 3: Differentiate between the total air volume reference commands for RB operating conditions and normal operating conditions. The undisturbed switching module 30 selects between the total air volume commands for RB operating conditions and normal operating conditions. When RB is activated, the total air volume reference value S3 switches from the total air volume reference command S1 to the RB target total air volume command S2 at a certain rate to ensure a suitable air-coal ratio during the RB process, achieving stable combustion. Within 1 second after the RB operation ends, the oxygen correction regulator output tracks the actual total air volume / total air volume reference value S1. After 1 second, the total air volume reference value S3 switches from the RB target total air volume command S2 back to the total air volume reference command S1, ensuring undisturbed total air volume command switching.

[0017] Step 4: Based on the output S9 of the oxygen content correction PID controller and the total air volume reference value S3, obtain the total air volume correction command S4;

[0018] S4 = S9 * S3

[0019] Step 5: Obtain the total air volume setpoint S5 based on the total air volume correction command S4, variable load feedforward input 7, and unit load command input 3;

[0020] S5=S4+(max(f4(x2)*x4,0)+(min(f5(x2)*x4,0)

[0021] Where x2 is the unit load command input 3, x4 is the variable load feedforward input 7, f4(x) is the output of the fourth function converter 14, and f5(x) is the output of the fifth function converter 15.

[0022] The variable load feedforward dynamically corrects the load according to the unit's load command and uses different parameters for increasing and decreasing the load to ensure that the total air volume meets the combustion requirements during the load increase, decrease, and different load segments.

[0023] Step 5: Obtain the total air volume command SP based on the total air volume setting value S5, the corrected total fuel quantity input 8, and the minimum air volume S8;

[0024] SP = max(S5, S8, f7(x4))

[0025] Where x4 is the corrected total fuel input 8, f7(x) is the output of the seventh function converter 23; max() is the maximum value module, which performs the maximum operation on the three inputs so that the output is equal to the maximum value of the three inputs; x4 is the corrected total fuel input 6.

[0026] The design incorporates cross-limits between the total air volume command and the total fuel quantity signal, as well as minimum air volume limits, to ensure oxygen-enriched combustion and safe operation of the boiler.

[0027] The beneficial effects of this invention are:

[0028] The automatic air supply control system and method of this invention for suppressing unit disturbance caused by poor pulverizer feeding in the pulverizer, in specific operation, can automatically change the weighting coefficient of the boiler main control command and the total air volume command corresponding to the unit load command according to the unit load command during normal operation. As the load increases, the total air volume command is gradually given by the unit load command through the function converter, reducing the fluctuation of the total air volume command in the high load section, thereby reducing the fluctuation of parameters such as furnace pressure, main steam temperature, and reheater temperature. The air supply control can be put into automatic operation throughout the process, greatly reducing the amount of operation required by the operators. When the unit RB is activated, it can quickly switch to the smaller value between the RB target air volume command S6 and the total air volume reference command S1 to meet the air volume requirements of the RB process, while ensuring that there is no possibility of air volume increase. It avoids the phenomenon that the total air volume command decreases too slowly due to the actual load decrease in the RB process, resulting in unstable combustion and other serious threats to the safe operation of the unit.

[0029] This control method is applicable to the automatic control logic design and optimization of the air supply control in the pulverizing system of coal-fired power units. It can effectively suppress the fluctuation of the main parameters of the unit caused by the poor powder feeding of the pulverizer and meet the requirements of rapid response AGC. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the present invention.

[0031] In the picture:

[0032] MUL – Multiplier f(x) – Function Converter ADD – Adder SFT – No-Bumper Switching Module

[0033] MIN – Retrieves the smaller module; MAX – Retrieves the larger module; SUB – Subtractor constant module

[0034] DIV – Divider; PID – PID Controller; NOT – Not Module; PLS – Pulse Module

[0035] TOF - Delay Module Detailed Implementation

[0036] An automatic air supply control system for suppressing the disturbance of unit parameters caused by poor pulverizer feed includes: RB target fuel quantity input 1, boiler main control command input 2, unit load command input 3, total air volume input 4, RB action input 5, oxygen deviation input 6, variable load feedforward input 7, total fuel quantity input after calorific value correction 8, first function converter 9, second function converter 10, constant module 11, third function converter 12, non-module 13, fourth function converter 14, and fifth function converter 15. 5. Sixth function converter; 16. First multiplier; 17. Subtractor; 18. Delay interrupt module; 19. Pulse module; 20. First multiplier; 21. Second multiplier; 22. Seventh function converter; 23. Second multiplier; 24. Small selection module; 25. First adder; 26. Divider; 27. Second multiplier; 28. PID controller; 29. ​​Bumper-free switching module; 30. Third multiplier; 31. Third adder; 32. Constant module; 33. Large selection module; 34. Total air volume command output; 35.

[0037] The unit load command input 3 is connected to the inputs of the second function converter 10, the third function converter 12, the fourth function converter 14, and the fifth function converter 15, respectively. The output of the third function converter 12 is connected to input 1 of the second multiplier 24. Input 2 of the second multiplier 24 is connected to the output of the subtractor 18. Input 1 (minuend) of the subtractor 18 is connected to the constant module (constant 1) 11. Input 2 (subtrahend) of the subtractor 18 is connected to the output of the second function converter 10. The output of the second multiplier 24 is connected to the first adder 26. The input 1 of the first adder 26 is connected to the output of the first multiplier 17. The input 1 of the first multiplier 17 is connected to the output of the second function converter 10. The input 2 of the first multiplier 17 is connected to the output of the first function converter 9. The input of the first function converter 9 is connected to the boiler main control command input 2. The output of the adder 26 is connected to the input 1 of the small selection module 25 and the input 1 of the bumpless switching module 30. The input 2 of the small selection module 25 is connected to the output of the sixth function converter 16. The input of the sixth function converter 16 is connected to the RB target fuel quantity input 1.Input 2 of the bumpless switching module 30 is connected to the output of the small selection module 25. Input 3 (selection signal) of the bumpless switching module 30 is connected to the output of the delay interrupt module 19. RB action input 5 is connected to the input of the delay interrupt module 19 and the input of the non-module 13, respectively. The output of the bumpless switching module 30 is connected to input 1 of the third multiplier 31. Input 2 of the third multiplier 31 is connected to the output of the PID controller 29. The input of the PID controller 29 is connected to the oxygen deviation input 6. The input of the PID controller 29 (tracking switch TS) is connected to the output of the pulse module 20. The input of the pulse module 20 is connected to the output of the non-module 13. The input of the PID controller 29 (tracking point TR) is connected to the output of the divider 27. Input 1 (divisor) of the divider 27 is connected to the total air volume input 4. Input 2 (dividend) of the divider 27 is connected to the output of the second multiplier 24. The output of the third multiplier 31 is connected to the third multiplier 25. The input 1 of the first adder 32 is connected to the input 2 of the third adder 32, which is connected to the output of the second adder 28. The input 1 of the second adder 28 is connected to the output of the first multiplier 21, and the input 2 of the second adder 28 is connected to the output of the second multiplier 22. The input 1 of the first multiplier 21 is connected to the output of the fourth function converter 14, and the input 1 of the second multiplier 22 is connected to the output of the fifth function converter 15. The variable load feedforward input 7 is connected to the input 2 of the first multiplier 21 and the input 2 of the second multiplier 22. The output of the third adder 32 is connected to the input 1 of the general election module 34. The input 2 of the general election module 34 is connected to the constant module 33 (minimum air volume). The input 3 of the general election module 34 is connected to the output of the seventh function converter 23. The input of the seventh function converter 23 is connected to the total fuel quantity input 8 after calorific value correction. The output of the general election module 34 is connected to the total air volume command output 35.

[0038] An automatic air supply control method based on the above-mentioned method for suppressing the disturbance of unit parameters caused by poor powder feeding from the pulverizer includes obtaining the total air volume set reference value through a function converter based on the boiler main control command, obtaining the total air volume set reference value through a function converter based on the unit load command, then automatically distributing the two total air volume reference commands according to the unit load command, correcting the load shift feedforward based on load increase / decrease and different load segments, distinguishing the total air volume set value between RB operating condition and normal operating condition, ensuring that the total air volume meets the actual needs under stable operating condition, variable load operating condition and RB condition within a wide load range, and ensuring seamless switching of total air volume commands between normal operating condition and RB condition.

[0039] Example Demonstration

[0040] The boiler of a certain coal-fired unit adopts a subcritical, single-stage reheat, forced circulation, double-arch furnace, solid ash discharge, and coal-fired steam drum manufactured by STEIN. The pulverizing system is a steel ball mill with an intermediate storage system. The drying medium is hot flue gas, and the temperature control medium is hot secondary air and cold air. The exhaust gas from the pulverizer outlet is partially recirculated into the pulverizer outlet, and the other part is sent into the furnace for combustion via the exhaust gas fan.

[0041] A control method for an automatic air supply control system that suppresses disturbances to unit parameters caused by poor powder feeding from the powder feeder includes the following steps:

[0042] Step (1): Obtain the total air volume setting reference value S11 according to the boiler main control instruction input 2 and the first function converter 9;

[0043] The parameters for the first function converter are set as follows:

[0044] Boiler main control commands (%) 0 34 43.2 54.4 65.9 73.5 100 Total air volume command (%) 30 30 36.6 44.5 52.6 58 75

[0045] Step (2): The total air volume setting reference value S12 is obtained by inputting the unit load command 3 through the third function converter 12;

[0046] The parameters for the second function converter are set as follows:

[0047] Unit load command (%) 0 40 50 61 77.8 80.6 100 Total air volume command (%) 30 35 35.76 37.61 47.6 50 63

[0048] Step (3): The total air volume setpoint allocation coefficient S13 is obtained by inputting the unit load command 3 through the second function converter 10;

[0049] The parameters for the third function converter are set as follows:

[0050] Unit load command (%) 0 40 60 90 100 Allocation coefficient 1 1 0.8 0 0

[0051] Step (4): Total air volume reference command S1 = S11*S13 + S12*(1-S13)

[0052] Step (5): Input the total fuel quantity after calorific value correction to 8, and obtain the total air volume limit value S7 through the seventh function converter 23;

[0053] The parameters for the seventh function converter are set as follows:

[0054] Fuel quantity (%) 0 20 40 60 80 100 Total air volume limit (%) 0 20 28 38 50 62

[0055] Step (6): Under normal operating conditions, the total air volume positive command S5 = S9 * S1 + S10;

[0056] The parameters for the fourth function converter are set as follows:

[0057] Unit load command (%) 0 20 40 60 80 100 coefficient 1 1 1 0.95 0.8 0.7

[0058] The parameters for the fifth function converter are set as follows:

[0059] Unit load command (%) 0 20 40 60 80 100 coefficient 0.25 0.25 0.2 0.18 0.15 0.12

[0060] Step (7): Under RB operating conditions, the RB target fuel quantity input 1 is used to obtain the RB target air volume command S6 through the sixth function converter 16;

[0061] The parameters for the sixth function converter are set as follows:

[0062] RB target fuel quantity (%) 40 43 48 RB airflow command (%) 36 38.2 42

[0063] Under RB operating conditions, the total air volume correction command S5 = S9 * S2; (Note: Under RB operating conditions, the unit is in TF control mode, and the variable load feedforward is always 0)

[0064] When the RB operation is activated, the total air volume reference command S3 switches from the total air volume reference command S1 to the RB target total air volume command S2, and the rate is set to 25% / min to ensure that the air volume during the RB process meets the combustion requirements.

[0065] When the RB action ends, the oxygen correction regulator output tracks the actual total air volume / total air volume reference value S1. After 1 second, the total air volume reference value S3 is switched from the RB target total air volume command S2 to the total air volume reference command S1 to ensure that the total air volume command is not disturbed during the switching process.

[0066] Step (8): Total air volume command = max(S5, S7, S8).

Claims

1. An automatic air supply control system for suppressing disturbances to the unit caused by poor powder feeding from the powder feeder, characterized in that, The circuit includes a total air volume reference command formation loop, an RB air volume reference command formation loop, a total air volume reference command disturbance-free switching loop, an oxygen correction loop, a corrected total air volume command formation loop, a corrected variable load feedforward formation loop, a pre-limit total air volume command formation loop, and a total air volume command formation loop. The total air volume reference command formation loop includes a unit load command input, which is connected to the input of the second function converter (10) and the input of the third function converter (12). The output of the third function converter (12) is connected to the second multiplier. The input of the second multiplier (24) is connected to the output of the subtractor (18), the input of the subtractor (18) is connected to the constant module (11), the input of the subtractor (18) is connected to the output of the second function converter (10), the output of the second multiplier (24) is connected to the input of the first adder (26), the input of the first adder (26) is connected to the output of the first multiplier (17), the input of the first multiplier (17) is connected to the output of the second function converter (10), and the second multiplier (24) is connected to the input of the first adder (26). The input of multiplier 1 (17) is connected to the output of the first function converter (9), and the input of the first function converter (9) is connected to the boiler main control command input; the output of the first adder (26) is the total air volume reference command, the RB air volume reference command forming loop includes the RB target fuel quantity input, the RB target fuel quantity input is connected to the input of the sixth function converter (16), the output of the sixth function converter (16) is connected to the input of the small selection module (25), and the input of the small selection module (25) is connected to the output of the first adder (26). Next, the output of the small selection module (25) is the RB air volume reference command. The total air volume reference command disturbance-free switching loop includes the output of the small selection module (25). The output of the small selection module (25) is connected to the input of the disturbance-free switching module (30). The input of the disturbance-free switching module (30) is connected to the output of the first adder (26). The input of the disturbance-free switching module (30) is connected to the output of the delay interrupt module (19). The RB action input is connected to the input of the delay interrupt module (19). The output of the disturbance-free switching module (30) is the total air volume reference command disturbance-free switching value.

2. The automatic air supply control system for suppressing unit disturbance caused by poor powder feeding from the powder feeder according to claim 1, characterized in that, The oxygen correction loop includes an oxygen deviation input, which is connected to the input of the PID controller (29). The input of the PID controller (29) is connected to the output of the pulse module (20). The input of the pulse module (20) is connected to the output of the non-module (13). The input of the non-module (13) is connected to the RB action input. The input of the PID controller (29) is connected to the output of the divider (27). The input of the divider (27) is connected to the total air volume input. The input of the divider (27) is connected to the output of the second multiplier (24). The output of the PID controller (29) is the oxygen correction value.

3. The automatic air supply control system for suppressing unit disturbance caused by poor powder feeding from the powder feeder according to claim 1, characterized in that, The corrected total air volume command formation loop includes the output of the bumpless switching module (30), the output of the bumpless switching module (30) is connected to the input of the third multiplier (31), the output of the PID regulator (29) is connected to the input of the third multiplier (31), and the output of the third multiplier (31) is the corrected total air volume command.

4. The automatic air supply control system for suppressing unit disturbance caused by poor powder feeding from the powder feeder according to claim 1, characterized in that, The modified variable load feedforward circuit includes a variable load feedforward input, which is connected to the input of the first multiplier 2 (21) and the input of the second multiplier 1 (22). The input of the first multiplier 2 (21) is connected to the output of the fourth function converter (14), and the input of the second multiplier 1 (22) is connected to the output of the fifth function converter (15). The unit load command input is connected to the input of the fourth function converter (14) and the input of the fifth function converter (15). The output of the first multiplier 2 (21) is connected to the input of the second adder (28), and the output of the second multiplier 1 (22) is connected to the input of the second adder (28). The output of the second adder (28) is the modified variable load feedforward value.

5. The automatic air supply control system for suppressing unit disturbance caused by poor powder feeding from the powder feeder according to claim 1, characterized in that, The total air volume limit command forming loop includes the output of the third multiplier (31), the output of the third multiplier (31) is connected to the input of the third adder (32), the input of the third adder (32) is connected to the output of the second adder (28), and the output of the third adder (32) is the total air volume limit command.

6. The automatic air supply control system for suppressing unit disturbance caused by poor powder feeding from the powder feeder according to claim 1, characterized in that, The total air volume command forming loop includes a total fuel quantity input after calorific value correction (8), which is connected to the input of the seventh function converter (23). The output of the seventh function converter (23) is connected to the input of the election module (34). The constant module 2 (33) is connected to the input of the election module (34). The output of the third adder (32) is connected to the input of the election module (34). The output of the election module (34) is the total air volume command output (35).

7. A method for using an automatic air supply control system as described in claim 1 to suppress disturbances to the unit caused by poor powder feeding from the powder feeder, comprising the following steps: Step 1: Based on the boiler main control command input and the unit load command input, obtain the total air volume reference command S1; S1=f1(x1)*f2(x2)+f3(x2) *(1-f2(x2)) Where x1 is the boiler main control command input, x2 is the unit load command input, f1(x) is the output of the first function converter (9), f2(x) is the output of the second function converter (10), and f3(x) is the output of the third function converter (12); The total air volume reference command S1 automatically adjusts the weighting coefficient of the total air volume reference command corresponding to the boiler main control command input and the unit load command input according to the unit load command; as the load command increases, the weighting coefficient of the total air volume reference command corresponding to the boiler main control command gradually decreases to 0, and the weighting coefficient of the total air volume reference command corresponding to the unit load command gradually increases to 1. Step 2: Based on the RB target fuel quantity input and the total air volume reference command S1, obtain the RB target total air volume command S2; S2 = min(f6(x3), S1) Where x3 is the RB target fuel quantity input, f6(x) is the output of the sixth function converter (16); min() is the minimum value module, which performs a minimum operation on the two inputs to make the output equal to the smaller value of the two inputs; Step 3: Distinguish between the total air volume reference command for RB operating condition and normal operating condition, and select the total air volume command for RB operating condition and normal operating condition through the non-disruptive switching module (30); when RB is activated, the total air volume reference value S3 is switched from the total air volume reference command S1 to the RB target total air volume command S2 at a certain rate to ensure a suitable air-coal ratio in the RB process and achieve stable combustion. Within 1 second after the RB is activated, the oxygen correction regulator output tracks the actual total air volume / total air volume reference value S1. After 1 second, the total air volume reference value S3 is switched from the RB target total air volume command S2 to the total air volume reference command S1 to ensure that the total air volume command is non-disruptive during the switching process. Step 4: Based on the output S9 of the oxygen content correction PID controller and the total air volume reference value S3, obtain the total air volume correction command S4; S4 = S9 * S3 Step 5: Obtain the total air volume setpoint S5 based on the total air volume correction command S4, the variable load feedforward input, and the unit load command input; S5= S4+(max(f4(x2)*x4,0) + min(f5(x2)*x4,0 )) Where x2 is the unit load command input, x4 is the variable load feedforward input, f4(x) is the output of the fourth function converter (14), and f5(x) is the output of the fifth function converter (15); The variable load feedforward dynamically corrects the load according to the unit load command and uses different parameters for increasing and decreasing load to ensure that the total air volume meets the combustion requirements during the load increase, decrease and different load segments. Step 6: Obtain the total air volume command SP based on the total air volume setting value S5, the corrected total fuel quantity input, and the minimum air volume S8; SP = max(S5, S8, f7(x5)) Where x5 is the corrected total fuel input, f7(x) is the output of the seventh function converter (23); max() is the maximum value module, which performs the maximum operation on the three inputs so that the output is equal to the maximum value of the three inputs; The design incorporates cross-limits between the total air volume command and the total fuel quantity signal, as well as minimum air volume limits, to ensure oxygen-enriched combustion and safe operation of the boiler.

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