A primary air pressure automatic control system and control method

Abstract

The present invention discloses a primary air pressure automatic control system and method. Based on the study of the primary air pressure response characteristics, the dynamic feedforward prediction technology is adopted to make the primary air fan output respond in advance during the load change process, thereby accelerating the boiler response speed. At the same time, the fuzzy control theory is adopted to correct the primary air pressure by adopting different main steam pressure deviation functions according to the different load changes, so as to reduce the variation amplitude of the main parameters of the unit in the load change process to a certain extent, which is conducive to the rapid stabilization of the unit; a correction loop for the main steam pressure deviation to the primary air pressure setting value is added to ensure the rapid response of the main steam pressure and reduce the disturbance of the main parameters of the unit; the primary air pressure setting reference value is given by the average coal amount of the running coal feeder through a function converter, and at the same time, the correction of the primary air pressure setting value by the unit load instruction is added to ensure the rationality of the primary air pressure in the full load section, realize the automatic control of the primary air pressure in all working conditions, and meet the requirements of the unit for rapid load change and energy saving and consumption reduction.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic control of thermal power plants, and in particular to a primary wind pressure automatic control system and method. Background Art

[0002] The air and smoke system accounts for a significant portion of plant electricity consumption in coal-fired units. The primary air fan (PAF) consumes relatively high power due to throttling of the hot and cold air dampers in the pulverizers. The primary air supply primarily dries and conveys pulverized coal. Excessive PAF pressure can delay ignition, increase exhaust temperatures, and reduce unit efficiency. Furthermore, excessive PAF output increases PAF energy consumption, hindering energy conservation. However, excessively low PAF pressure can easily clog the pulverized coal pipe and even damage the burner. Therefore, an appropriate PAF pressure must ensure safe unit operation and AGC speed requirements while also balancing energy conservation.

[0003] Currently, there are several ways to determine the primary air pressure setpoint: 1. Determined by the unit load command after passing through a function converter; 2. Determined by the total coal quantity command after passing through a function converter; 3. Determined by the number of operating pulverizers; 4. Determined by the maximum coal quantity of the operating feeder after passing through a function converter; 5. Determined by the average coal quantity of the operating feeder after passing through a function converter. Existing methods for determining the primary air pressure setpoint have various problems: Methods 1 and 2 fail to consider the impact of the pulverizing system's start-up and shutdown; Method 3 maintains the primary air pressure setpoint constant for a fixed number of operating pulverizers, ignoring changes in the resistance that the pulverizers must overcome; in Method 4, when the output of one feeder increases and the output of another decreases, the pulverizer resistance remains virtually unchanged, yet the increase in the primary air pressure setpoint causes unit disturbances; and Method 5 fails to fully account for changes in load. At the same time, the design of the loop forming the primary air pressure setting value is not perfect, and it does not fully consider the correction of the primary air pressure setting value during the start-up and shutdown and load change process of the powder making system. As a result, the operating personnel need to manually modify the primary air pressure setting value offset during the start-up and shutdown and load change process of the powder making system, which increases the operating intensity of the operating personnel. Due to the inconsistent operating levels of the operating personnel, the operating parameters of the unit fluctuate greatly, and even endanger the safe and stable operation of the unit. Summary of the Invention

[0004] The purpose of the present invention is to provide a primary air pressure automatic control system and method in order to overcome the above problems, and to improve the response speed of the pulverizing system in the variable load process through dynamic feedforward prediction technology; to increase the start-stop mill to correct the primary air pressure set value logic, to ensure the precise control of the primary air pressure in the start-stop process of the pulverizing system, thereby reducing the disturbance of the pulverizing system to the system caused by the start-stop; to increase the correction loop of the main steam pressure deviation to the primary air pressure set value, to ensure the rapid response of the main steam pressure, and reduce the disturbance of the main parameters of the unit; the primary air pressure setting reference value is given by the average coal amount of the running coal feeder through a function converter, and at the same time, the correction of the primary air pressure set value by the unit load instruction is increased to ensure the rationality of the primary air pressure full load section, and realize the automatic control of the primary air pressure in all working conditions, without the need for manual intervention by the operating personnel, greatly reducing the operating intensity of the operating personnel, and at the same time ensuring the stability of the boiler combustion during the start-stop and load change of the pulverizing system, greatly reducing the disturbance of the main parameters of the unit under the start-stop and load change conditions of the pulverizing system, and meeting the requirements of the unit for rapid load change and energy saving and consumption reduction.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A primary wind pressure automatic control system includes a primary wind pressure input, the signal of which is connected to the input PV of a first PID controller, the input SP of a first PID controller is connected to the output of a first high and low limit link, the input of the first high and low limit link is connected to the output of an adder, the input of the adder is connected to the output of a second high and low limit link, the input of the second high and low limit link is connected to the output of a first lead-lag link, the input of the first lead-lag link is connected to the output of a first function converter, the main steam pressure deviation input is respectively connected to the input of the first function converter, the input of the second function converter, the input of a first differentiator and the input of a seventh function converter, the input of the adder is connected to the output of a third high and low limit link, the input of the third high and low limit link is connected to the output of the second lead-lag link, and the output of the second lead-lag link is connected to the output of the second lead-lag link. The input of the adder is connected to the output of the multiplier. The input of the multiplier is connected to the output of the second function converter. The input of the multiplier is connected to the output of the third function converter. The input of the third function converter is connected to the output of the first differentiator. The unit load command input is connected to the input of the first differentiator, the input of the fourth function converter, and the input of the eighth function converter, respectively. The input of the adder is connected to the output of the multiplier. The input of the multiplier is connected to the output of the third function converter. The input of the multiplier is connected to the output of the seventh function converter. The input of the adder is connected to the output of the adder. The input of the adder is connected to the output of the first inertia link. The input of the first inertia link is connected to the output of the first rate limiter. The positive rate limit input PL of the first rate limiter is a constant 0.5. The negative rate limit input NL of the first rate limiter is a constant 100. The input of the first rate limiter is connected to the output of the multiplier. The input of the multiplier is connected to the output of the fourth function converter. The input of the multiplier is connected to the output of the fifth function converter. The input of the fifth function converter is connected to the output of the subtractor. The minimum instruction input of the coal feeder is connected to the subtrahend input of the subtractor. The average instruction input of the coal feeder is connected to the minuend input of the subtractor and the input of the sixth function converter respectively. The input of the adder is connected to the output of the second inertia link. The input of the second inertia link is connected to the output of the multiplier. The input of the multiplier is connected to the output of the sixth function converter, the input of the multiplier is connected to the output of the eighth function converter, the output of the first PID controller is connected to the input of the first two-output balancing link, the output of the first two-output balancing link is connected to the input of the adder and the minuend input of the subtractor, the bias input is connected to the input of the adder and the subtrahend input of the subtrahend, the output of the adder is connected to the input of the first manual operation station, the output of the first manual operation station is connected to the damper adjustment command output of primary fan A, the output of the subtractor is connected to the input of the second manual operation station, and the output of the second manual operation station is connected to the damper adjustment command output of primary fan B.

[0007] The primary air pressure automatic control system and method include the following steps:

[0008] Step 1: Obtain the primary air pressure setting reference value S1 according to the average command input of the coal feeder and the unit load command input;

[0009] S1=LAG2[f6(x1)*f8(x2)]

[0010] Among them, x1 is the average command input of the coal feeder, x2 is the unit load command input, f6(x1) is the output of the sixth function converter, and f8(x2) is the output of the eighth function converter;

[0011] LAG2() is the inertia link, and its transfer function is:

[0012]

[0013] Where T2 is the inertia time and S is the Laplace operator.

[0014] Step 2: Obtain the primary air pressure setting correction value C1 according to the main steam pressure deviation input;

[0015] C1=LIM2(LEADLAG1(f1(x3)))

[0016] Among them, x3 is the main steam pressure deviation input, f1(x3) is the output of the first function converter;

[0017] LIM2() is a limiting link that limits the input so that the output is limited between the upper and lower limits;

[0018] LEADLAG1() is a lead-lag link, and its transfer function is:

[0019]

[0020] Where, T 11 is the lead time, T 12 is the lag time, and S is the Laplace operator.

[0021] Step 3: Obtain the primary air pressure setting correction value C2 according to the main steam pressure deviation input and the unit load command input;

[0022] C2=LIM3(LEADLAG2(f2(x3)*f3(DIFF(x2))+f7(x3)*f3(DIFF(x2))))

[0023] Among them, x3 is the main steam pressure deviation input; x2 is the unit load command input, f2(x3) is the output of the second function converter, f7(x3) is the output of the seventh function converter, and f3(DIFF(x2)) is the output of the third function converter;

[0024] LIM3() is a limiting link that limits the input so that the output is limited between the upper and lower limits.

[0025] LEADLAG2() is the lead-lag link, and its transfer function is:

[0026]

[0027] Where, T 21 is the lead time, T 22 is the lag time, and S is the Laplace operator.

[0028] DIFF() is the differential link, and its transfer function is:

[0029]

[0030] Where T is the differential time, KG is the differential gain, and S is the Laplace operator.

[0031] Step 4: Obtain a primary air pressure setting correction value C3 based on the unit load command input, the minimum command input for the coal feeder, and the average command input for the coal feeder;

[0032] C3=LAG1(RATE1(f4(x2)*f5(x1-x4)))

[0033] Among them, x1 is the average command input of the coal feeder, x2 is the unit load command input, x4 is the minimum command input of the coal feeder, f4(x2) is the output of the fourth function converter, and f5(x1-x4) is the output of the fifth function converter;

[0034] RATE1() is the rate limit link, which limits the input change rate so that the output change is within the set range; the rate limit link includes the positive rate limit PL and the negative rate limit NL functions;

[0035] LAG1() is the inertia link, and its transfer function is:

[0036]

[0037] Where T1 is the inertia time and S is the Laplace operator.

[0038] Step 5: The primary wind pressure setting reference value S1, the primary wind pressure setting correction value C1, the primary wind pressure setting correction value C2, and the primary wind pressure setting correction value C3 are summed to form the primary wind pressure setting value SP;

[0039] SP=LIM1(S1+C1+C2+C3)

[0040] Among them, LIM1() is a limiting link, which limits the input so that the output is limited between the upper limit and the lower limit;

[0041] Step 6: The primary air pressure control PID regulator controls the primary fans A and B according to the primary air pressure set value SP and the primary air pressure actual value PV to make the primary air pressure meet the actual demand.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] 1) The present invention discloses an automatic primary air pressure control system and method. Based on research on the response characteristics of primary air pressure, it uses dynamic feedforward prediction technology to enable the primary fan output to respond in advance during load changes, thereby accelerating the boiler's response speed. Fuzzy control theory is also used to correct the primary air pressure using different main steam pressure deviation functions according to the load changes. This reduces the amplitude of changes in the unit's main parameters during load changes to a certain extent, thereby facilitating rapid stabilization of the unit.

[0044] 2) The primary air pressure setting value adopts the function of the average command of the coal feeder, and the primary air pressure setting function is corrected by the unit load command, which is conducive to low-load energy saving and fast response of high-load boilers;

[0045] 3) Add a start-stop mill correction circuit for the primary air pressure set value. The primary air pressure set value is self-corrected based on the deviation between the average coal amount of the running coal feeder and the minimum coal amount of the running coal feeder. This circuit can quickly reduce the primary air pressure set value during the start-up and shutdown phases of the pulverizing system. As the deviation decreases, the primary air pressure correction value slowly returns to zero, which can greatly suppress the fluctuation of the main parameters of the unit (main steam pressure, intermediate point temperature, main steam temperature, etc.);

[0046] Taking the startup of a pulverizing system as an example, when the pulverizing system is started, the instructions of other running coal feeders will be rapidly reduced to maintain the current coal quantity instruction. At this time, the primary air pressure setting baseline value will be rapidly reduced as the average instruction of the running coal feeder decreases. However, the reduction in primary air pressure is often insufficient, which can easily cause the main steam pressure, intermediate point temperature, and main steam temperature to rise. In this case, adding a start-stop mill to correct the primary air set value loop can quickly reduce the primary air pressure set value during the mill startup phase, which can effectively suppress the changes in the main parameters of the unit.

[0047] When the pulverizing system is started, as the output of the pulverizing system increases, the commands of other running coal feeders will be reduced accordingly to maintain the current coal quantity command. At this time, the primary air pressure setting reference value will decrease as the average command of the running coal feeders decreases, causing the main steam pressure to drop. At this time, the start-stop mill correction circuit for the primary air setting value increases the primary air pressure setting value at a certain rate, which is beneficial to the stability of the main steam pressure and, in turn, the stability of the main parameters of the unit.

[0048] 4) The pulverizing system start-up and shutdown correction of the primary air pressure set value loop is designed with the unit load instruction correction logic, which can effectively suppress the disturbance of the unit's main parameters caused by the start-up and shutdown of the pulverizing system in different load sections;

[0049] 5) The primary air set value has been enhanced with a main steam pressure deviation correction logic. When the main steam pressure deviation changes, the primary air pressure set value can be quickly corrected, which is beneficial to the stability of the main steam pressure to a certain extent, thereby reducing the fluctuation of the main parameters of the unit;

[0050] 6) Wide range of applications: This control method is applicable to the automatic control logic design of primary air pressure in the direct-blowing pulverizing system of coal-fired power plants. It can effectively suppress the disturbance of the unit operating parameters caused by starting and stopping the mill and quickly respond to the requirements of AGC. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a control logic diagram of a primary wind pressure automatic control system and method of the present invention.

[0052] In the picture:

[0053] PID——PID controller; F(x)——function converter; ADD——adder;

[0054] LEADLAG——lead-lag link; ≯≮——high and low limit links;

[0055] DIFF——differentiator; LAG——inertia link; BALANCER——two-output balancing link;

[0056] MUL——Multiplier; RATE——Rate limiter; T——Analog switch;

[0057] M / A——manual operator; A——bias setting station; SUB——subtractor; DETAILED DESCRIPTION

[0058] A primary air pressure automatic control system includes: a primary air pressure input 1, a main steam pressure deviation input 2, a unit load instruction input 3, a minimum instruction input 4 for running a coal feeder, an average instruction input 5 for running a coal feeder, a first differentiator 6, a subtractor 7, a first function converter 8, a second function converter 9, a third function converter 10, a seventh function converter 11, a fourth function converter 12, a fifth function converter 13, a sixth function converter 14, an eighth function converter 38, a multiplier 15, a multiplier 17, a multiplier 16, an adder 19, a first rate Limiter 18, multiplier 37, first lead-lag link 20, second lead-lag link 21, first inertia link 22, second inertia link 39, second high and low limit link 23, third high and low limit link 24, adder 25, adder 26, first high and low limit link 27, first PID controller 28, first two-output balancing link 29, adder 31, bias station 30, subtractor 32, first manual operation station 33, second manual operation station 34, primary fan A damper adjustment command output 35 and primary fan B damper adjustment command output 36.

[0059] The primary wind pressure input 1 is connected to the input PV of the first PID controller 28, the input SP of the first PID controller 28 is connected to the output of the first high and low limit link 27, the input of the first high and low limit link 27 is connected to the output of the adder 26, the input 1 of the adder 26 is connected to the output of the second high and low limit link 23, the input of the second high and low limit link 23 is connected to the output of the first lead-lag link 20, the input of the first lead-lag link 20 is connected to the output of the first function converter 8, the main steam pressure deviation input 2 is connected to the input of the first function converter 8, the input of the second function converter 9, the input of the first differentiator 6 and the input of the seventh function converter 11 respectively, the input 2 of the adder 26 is connected to the output of the third high and low limit link 24, the input of the third high and low limit link 24 is connected to the output of the second lead-lag link 21, the input of the second lead-lag link 21 is connected to the output of the adder 19, and the adder Input 1 of multiplier 19 is connected to the output of multiplier 15, input 1 of multiplier 15 is connected to the output of second function converter 9, input 2 of multiplier 17 is connected to the output of third function converter 10, the input of third function converter 10 is connected to the output of first differentiator 6, unit load command input 3 is connected to the input of first differentiator 6, the input of fourth function converter 12, and the input of eighth function converter 38, respectively. Input 2 of adder 19 is connected to the output of multiplier 17, input 1 of multiplier 17 is connected to the output of third function converter 10, and input 2 of multiplier 17 is connected to the output of seventh function converter 11. Input 3 of adder 26 is connected to the output of adder 25, input 1 of adder 25 is connected to the output of first inertia link 22, the input of first inertia link 22 is connected to the output of first rate limiter 18, and the positive rate limit input PL of first rate limiter 18 is a constant 0.5, the negative rate limit input NL of the first rate limiter 18 is a constant 100, the input of the first rate limiter 18 is connected to the output of the multiplier 16, the input 1 of the multiplier 16 is connected to the output of the fourth function converter 12, the input 2 of the multiplier 16 is connected to the output of the fifth function converter 13, the input of the fifth function converter 13 is connected to the output of the subtractor 7, the minimum instruction input 4 of the coal feeder operation is connected to the subtrahend input of the subtractor 7, the average instruction input 5 of the coal feeder operation is respectively connected to the minuend input of the subtractor 7 and the input of the sixth function converter 14, the input 2 of the adder 25 is connected to the output of the second inertia link 39, the input of the second inertia link 39 is connected to the output of the multiplier 37, the input of the multiplier 37 is connected to the output of the multiplier 37. Input 1 is connected to the output of the sixth function converter 14, input 2 of multiplier 37 is connected to the output of the eighth function converter 38, the output of the first PID controller 28 is connected to the input of the first two-output balancing link 29, the output of the first two-output balancing link 29 is connected to input 1 of adder 31 and the minuend input of subtractor 32, the bias input 30 is connected to input 2 of adder 31 and the subtrahend input of subtractor 32, the output of adder 31 is connected to the input of a first manual operation station 33, the output of the first manual operation station 33 is connected to the primary fan A damper adjustment command output 35, the output of subtractor 32 is connected to the input of a second manual operation station 34, and the output of the second manual operation station 34 is connected to the primary fan B damper adjustment command output 36.

[0060] A control method based on the above-mentioned primary air pressure automatic control system includes obtaining a primary air pressure setting reference value through a function converter according to the average command of the running coal feeder, and then correcting the reference value according to the unit load command to ensure the rationality of the primary air pressure in the full load section; using the deviation signal between the average command of the running coal feeder and the minimum command input of the running coal feeder and the main steam pressure deviation signal to correct the primary air pressure setting value to ensure the stability of the main parameters of the unit under start-up and shutdown and abnormal conditions; adding a primary air pressure variable load feedforward in the variable load process, and at the same time, using different fuzzy control rules according to the different load increases and decreases, which is conducive to the main steam pressure deviation signal to correct the variable load feedforward amount, thereby accelerating the unit response speed in the variable load process and reducing the fluctuation of the main parameters of the unit.

[0061] Example Demonstration

[0062] The boiler of a certain coal-fired unit adopts an ultra-supercritical pressure, variable pressure operation, single furnace, single intermediate reheat, balanced ventilation, tight sealing, solid slag discharge, all-steel frame, full suspension structure, and Π-shaped layout coal-fired direct current furnace manufactured by Shanghai Boiler Factory; the pulverizing system adopts a medium-speed coal mill positive pressure direct blowing cold primary air fan system, with 6 medium-speed coal mills per boiler, five in operation and one in standby.

[0063] The specific control method of the primary air pressure automatic control system includes the following steps:

[0064] Step (1), obtaining a primary wind pressure setting reference value according to the average command input 4 of the coal feeder operation and the sixth function converter 14;

[0065] The sixth function converter parameter settings are as follows:

[0066]

[0067] Step (2): the primary wind pressure setting reference value is corrected by the unit load instruction input 3 through the eighth function converter 38, and then the primary wind pressure basic setting value S1 is obtained after the landscape inertia link processing;

[0068] The eighth function converter parameter settings are as follows:

[0069]

[0070] Step (3), the main steam pressure deviation input 2 (actual value - set value) passes through the first function converter 8 to obtain the primary wind pressure correction value C1;

[0071] The first function transformer parameter settings are as follows:

[0072]

[0073] Step (4), under variable load conditions, according to the differential signal of the unit load command input 3 (the output of the first differentiator 6), the primary wind pressure variable load feedforward amount is set through the third function converter 10;

[0074] The third function converter parameter settings are as follows:

[0075]

[0076] Step (5), under the load-raising condition, according to the main steam pressure deviation input 3, the primary wind pressure variable load feedforward is corrected by the second function converter 9 to obtain the primary wind pressure load-raising feedforward;

[0077] Under load reduction conditions, according to the main steam pressure deviation input 3, the primary air pressure variable load feedforward is corrected by the seventh function converter 11 to obtain the primary air pressure load reduction feedforward;

[0078] The primary wind pressure load increase feedforward quantity and the primary wind pressure load decrease feedforward quantity together constitute the primary wind pressure correction value C2;

[0079] The second function transformer parameter settings are as follows:

[0080]

[0081] The seventh function converter parameter settings are as follows:

[0082]

[0083] Step (6): Based on the deviation between the average command of the coal feeder and the minimum command input of the coal feeder, the primary air pressure set value is corrected by the fifth function converter 13; at the same time, based on the unit load command, the correction value is corrected by the fourth function converter 12 to obtain the primary air pressure correction value C3;

[0084] The fifth function converter parameter settings are as follows:

[0085]

[0086] The fourth function converter parameter settings are as follows:

[0087]

[0088] Step (7), the primary wind pressure setting value SP = S1 + C1 + C2 + C3, and at the same time, the limit processing is performed according to the setting value to ensure the safety of the primary wind pressure operation;

[0089] Step (7), the primary air pressure controller performs PID operation according to the primary air pressure set value and the primary air pressure measured value, and achieves the purpose of the primary air pressure reaching the set value by controlling the primary fan to adjust the damper instruction.

Claims

1. A primary air pressure automatic control system, characterized in that: The invention comprises a primary wind pressure input (1), wherein the primary wind pressure input (1) signal is connected to the input primary wind pressure actual value PV of the first PID controller (28), the input primary wind pressure set value SP of the first PID controller (28) is connected to the output of the first high and low amplitude limiting link (27), the input of the first high and low amplitude limiting link (27) is connected to the output of the first adder (26), the first input end of the first adder (26) is connected to the output of the second high and low amplitude limiting link (23), the input of the second high and low amplitude limiting link (23) is connected to the output of the first lead-lag link (20), and the first The input of the leading-lag link (20) is connected to the output of the first function converter (8), and the main steam pressure deviation input (2) is connected to the input of the first function converter (8), the input of the second function converter (9), and the input of the seventh function converter (11). The second input end of the first adder (26) is connected to the output of the third high and low limit link (24), the input of the third high and low limit link (24) is connected to the output of the second leading-lag link (21), the input of the second leading-lag link (21) is connected to the output of the second adder (19), and the second adder (19) is connected to the output of the second leading-lag link (21). The first input end of the first adder (19) is connected to the output of the first multiplier (15), the first input end of the first multiplier (15) is connected to the output of the second function converter (9), the second input end of the first multiplier (15) is connected to the output of the third function converter (10), the input of the third function converter (10) is connected to the output of the first differentiator (6), the unit load instruction input (3) is connected to the input of the first differentiator (6), the input of the fourth function converter (12), and the input of the eighth function converter (38), respectively. The second input end of the second adder (19) is connected to the third multiplier (10). The output of the third function converter (17) is connected to the first input of the third multiplier (17), the output of the third function converter (10), the second input of the third multiplier (17) is connected to the output of the seventh function converter (11), the third input of the first adder (26) is connected to the output of the third adder (25), the first input of the third adder (25) is connected to the output of the first inertia link (22), the input of the first inertia link (22) is connected to the output of the first rate limiter (18), and the forward rate limit input PL of the first rate limiter (18) is a constant 0.5, the negative rate limit input NL of the first rate limiter (18) is a constant 100, the input of the first rate limiter (18) is connected to the output of the second multiplier (16), the first input end of the second multiplier (16) is connected to the output of the fourth function converter (12), the second input end of the second multiplier (16) is connected to the output of the fifth function converter (13), the input of the fifth function converter (13) is connected to the output of the first subtracter (7), the minimum instruction input (4) of the coal feeder is connected to the subtrahend input of the first subtracter (7), the average instruction input (5) of the coal feeder is respectively connected to the minuend input of the first subtracter (7) and the input of the sixth function converter (14), the second input end of the third adder (25) is connected to the output of the second inertia link (39), the input of the second inertia link (39) is connected to the output of the fourth multiplier (37), the output of the fourth multiplier (37) is connected to the output of the fourth multiplier (37). The first input end is connected to the output of the sixth function converter (14), the second input end of the fourth multiplier (37) is connected to the output of the eighth function converter (38), the output of the first PID controller (28) is connected to the input of the first two-output balancing link (29), the output of the first two-output balancing link (29) is connected to the first input end of the fourth adder (31) and the minuend input of the second subtractor (32), the bias input (30) is connected to the second input end of the fourth adder (31) and the subtrahend input of the second subtractor (32), the output of the fourth adder (31) is connected to the input of the first manual operation station (33), the output of the first manual operation station (33) is connected to the primary fan A damper adjustment command output (35), the output of the second subtractor (32) is connected to the input of the second manual operation station (34), and the output of the second manual operation station (34) is connected to the primary fan B damper adjustment command output (36).

2. The control method of the primary air pressure automatic control system according to claim 1, characterized in that: The following steps are involved: Step 1: Obtain the primary air pressure setting reference value S1 according to the average command input (5) of the coal feeder and the unit load command input (3); S1=LAG2[f6(x1)*f8(x2)] Wherein, x1 is the average command input of the coal feeder (5), x2 is the unit load command input (3), f6(x1) is the output of the sixth function converter (14), and f8(x2) is the output of the eighth function converter (38); LAG2( ) is the second inertia link, and its transfer function is: Where, is the inertia time, S is the Laplace operator; Step 2: Obtain the primary air pressure setting correction value C1 according to the main steam pressure deviation input (2); C1=LIM2(LEADLAG1(f1(x3))) Where x3 is the main steam pressure deviation input (2), f1(x3) is the output of the first function converter (8); LIM2 ( ) is the second high and low limit link, which limits the input so that the output is limited between the upper and lower limits; LEADLAG1( ) is the first lead-lag link, and its transfer function is: Where, To advance time, is the lag time, S is the Laplace operator; Step 3: Obtain the primary air pressure setting correction value C2 according to the main steam pressure deviation input (2) and the unit load command input (3); C2=LIM3(LEADLAG2(f2(x3)*f3(DIFF(x2))+ f7(x3)*f3(DIFF(x2)))) Where x3 is the main steam pressure deviation input (2); x2 is the unit load command input (3); f2(x3) is the output of the second function converter (9); f7(x3) is the output of the seventh function converter (11); and f3(DIFF(x2)) is the output of the third function converter (10). LIM3 ( ) is the third high and low limit link, which limits the input so that the output is limited between the upper and lower limits; LEADLAG2( ) is the second lead-lag link, and its transfer function is: Where, To advance time, is the lag time, S is the Laplace operator; DIFF( ) is the differential link, and its transfer function is: Where T is the differential time, KG is the differential gain, and S is the Laplace operator; Step 4, obtaining the primary air pressure setting correction value C3 according to the unit load command input (3), the minimum command input of the coal feeder (4), and the average command input of the coal feeder (5); C3=LAG1(RATE1(f4(x2)*f5(x1-x4))) Wherein, x1 is the average command input of the coal feeder (5), x2 is the unit load command input (3), x4 is the minimum command input of the coal feeder (4), f4(x2) is the output of the fourth function converter (12), and f5(x1-x4) is the output of the fifth function converter (13); RATE1 ( ) is the first rate limiter, which limits the input change rate to keep the output change within the set range. The rate limit link includes the positive rate limit PL and the negative rate limit NL functions. LAG1( ) is the first inertia link, and its transfer function is: Where, is the inertia time, S is the Laplace operator; Step 5: The primary wind pressure setting reference value S1, the primary wind pressure setting correction value C1, the primary wind pressure setting correction value C2, and the primary wind pressure setting correction value C3 are summed to form the primary wind pressure setting value SP; SP=LIM1(S1+C1+C2+C3) Among them, LIM1 () is the first high and low limit link, which limits the input so that the output is limited between the upper and lower limits; Step 6: The primary air pressure control PID regulator controls the primary fans A and B according to the primary air pressure set value SP and the primary air pressure actual value PV to make the primary air pressure meet the actual demand.

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