Control system and control method based on main steam pressure correction fluidizing air volume

Abstract

The present invention belongs to the field of automatic control, and specifically relates to a control system and a control method based on main steam pressure correction of fluidizing air volume; the control system specifically comprises the following steps: obtaining data preprocessing through a transmitter setting value unit PT1 and a transmitter measuring unit PT2 to obtain a deviation value O1; inputting the deviation value O1 into M2 for data processing to obtain a reference feedforward value O2 of a primary fluidizing air volume; a dynamic feedforward value I8 and a constant value 0 output by a setting value M7 enter a switching unit M6, and the switching unit M6 acts according to a pressure deviation change rate over-limit condition to select a dynamic feedforward value I8 or a constant value 0; the output value of the switching unit M6 passes through a rate generator M8 to obtain a rate smoothing value O8; an inertia post-value O3 and a rate smoothing value O8 are input into an adder unit M9 for data processing to obtain a final feedforward constant O9; the output value of PT3 and the final feedforward constant O9 together obtain a final primary fluidizing air volume instruction.

Description

Technical Field

[0001] The invention belongs to the field of automatic control, and in particular relates to a control system and a control method for correcting fluidizing air volume based on main steam pressure. Background Art

[0002] Since supercritical circulating fluidized bed units have the characteristics of large inertia, large delay and strong coupling of adjustment parameters, designing a complete air volume control strategy is the top priority for supercritical circulating fluidized bed units. With the continuous development of the power grid AGC (a system that adjusts the active output of multiple generators in different power plants to respond to changes in load) automatic power generation control system, when the power command on the grid side changes, the unit's turbine valve fluctuates rapidly to quickly respond to the grid load. At the same time, the boiler generates more steam flow by strengthening combustion to meet the main steam pressure in front of the turbine door, ensuring higher economic benefits of the unit.

[0003] The air volume control of conventional units is to achieve primary fluidization air volume control based on the air-coal ratio strategy. However, due to the wide adaptability of circulating fluidized bed boilers to burn coal types and large changes in coal quality, the control strategy that relies entirely on the air-coal ratio cannot meet the coordination of the regulation quality of the main parameters of the variable load boiler, which will cause the main steam pressure to be over-pressure or under-pressure during the unit's load change process. When the unit is in steady-state operation, the main steam pressure still has a large static deviation, which not only affects the economic benefits of the unit, but also reduces the regulation quality of the unit's important parameters. Summary of the invention

[0004] The present invention provides a control system and a control method for correcting the fluidizing air volume based on main steam pressure, improves and optimizes the control strategy and overcomes the shortcomings of the prior art.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a control system for correcting fluidizing air volume based on main steam pressure, comprising a transmitter setting value unit PT1, a transmitter measuring unit PT2, a transmitter setting value unit PT3 and a subtractor unit M1, wherein the output ends of the transmitter setting value unit PT1 and the transmitter measuring unit PT2 are connected to the input end of the subtractor unit M1, and the output end of the subtractor unit M1 is connected to two branch lines;

[0006] The branch line includes a first branch line and a second branch line, the first branch line is connected with a first function generator M2 and an inertia lag unit M3 in sequence, the second branch line is connected with a differential unit M4, a second function generator M5, a switching unit M6 and a rate generator M8 in sequence, the output ends of the inertia lag unit M3 and the rate generator M8 are both connected with the input ends of the first adder M9, the output end of the first adder M9 is connected with the input end i13 of the second adder M10, the output end of the transmitter setting value unit PT3 is connected with the input end i12 of the second adder M10, and the output end of the second adder M10 is connected with a primary fluidization air volume setting instruction.

[0007] The input terminal i9 of the switching unit M6 is connected to a setting value module M7, and the setting value module M7 is used to input a set value R=0 into the switching unit M6.

[0008] The selection end of the switching unit M6 is connected to a pressure deviation change rate over-limit condition action.

[0009] A control method of a control system based on main steam pressure correction of fluidizing air volume specifically comprises the following steps:

[0010] S1: Obtain data through the transmitter setting value unit PT1 and the transmitter measurement unit PT2 and pre-process it to obtain the deviation value O1;

[0011] S2: The subtraction unit M1 inputs the deviation value O1 to the first function generator M2 for data processing to obtain a reference feedforward value O2 of the primary fluidizing air volume;

[0012] S3: The subtraction unit M1 simultaneously inputs the deviation value O1 to the differential unit M4 for data processing, and then inputs it to the second function generator M5 to obtain the dynamic feedforward value I8 of the primary fluidizing air volume. Step S3 and step S2 are performed simultaneously;

[0013] S4: The reference feedforward value O2 enters the hysteresis unit M3, which makes the reference feedforward value O2 change slowly, reduces the disturbance to the system, and then outputs the inertia post value O3;

[0014] S5: The dynamic feedforward value I8 and the fixed value 0 output by the set value M7 enter the switching unit M6, and the switching unit M6 determines according to the pressure deviation change rate exceeding the limit condition, and specifically selects the dynamic feedforward value I8 or the fixed value 0 to work;

[0015] S6: the output value of the switching unit M6 passes through the rate generator M8, so that the output value of the switching unit M6 is smoothly transitioned at a certain rate during the switching process to obtain a rate smoothing value O8;

[0016] S7: the inertia post-value O3 in step S3 and the rate smoothing value O8 in step S5 are input to the adder unit M9 for data processing to obtain the final feedforward constant O9;

[0017] S8: The output value of the primary fluidization air volume setting curve transmitter PT3 and the final feedforward constant O9 work together to obtain the final primary fluidization air volume instruction.

[0018] In step S2, the deviation value O1 is used as the value of the horizontal coordinate x of the piecewise function fx, and the reference feedforward value O2 is used to output the corresponding vertical coordinate y value; in the first function generator M2, the functional relationship between the horizontal coordinate x and the vertical coordinate y is shown in Table 1:

[0019] Table 1 Changes in the functional relationship of the first function generator M2

[0020]

[0021] In step S3, the deviation value O1 is converted into the differential action of the automatic control principle for data processing, and is used as the value of the horizontal coordinate x of the piecewise function fx. The dynamic feedforward value I8 is used to output the corresponding vertical coordinate y value. In the second function generator M5, the functional relationship between the horizontal coordinate x and the vertical coordinate y is shown in Table 2:

[0022] Table 2 Changes in the functional relationship of the second function generator M5

[0023] Pressure deviation change rate (Mpa / min) -0.3 -0.2 -0.15 0.15 0.2 0.3 <![CDATA[Dynamic feedforward value I8 (KNm3·h-1)]]> -20 -10 0 0 10 20

[0024] The output value of the switching unit M6 in step S5 is determined by the pressure deviation change rate over-limit condition action; when the pressure deviation change rate over-limit condition action is 1, the switching unit M6 selects the dynamic feedforward value I8 as the output value, otherwise it selects the fixed value 0 as the output value.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention solves the technical problems of poor adjustment quality of important parameters of the unit, large deviation between the main steam pressure and the pressure setting value, and large fluctuation of superheat at the intermediate point during the coordinated load change process. The control principle is a control idea that the primary fluidizing air volume increases or decreases proportionally with the main steam pressure deviation synchronously; on the basis of the air volume curve corresponding to the load instruction, a primary fluidizing air volume curve fitted by the pressure deviation is superimposed, and a primary fluidizing air volume curve fitted by the pressure deviation change rate is introduced. In the process of load increase and decrease, the heat storage of the circulating fluidized bed boiler is used more quickly and intelligently, so as to improve the ability of the unit to respond to load, and at the same time effectively ensure that the important parameters of the unit are kept within a safe and stable range, so that the unit can operate safely and stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below in conjunction with the accompanying drawings.

[0028] Figure 1 is a circuit diagram of the control system of the present invention;

[0029] Figure 2 Flow chart of the control method of the present invention. DETAILED DESCRIPTION

[0030] like Figure 1-Figure 2 As shown, the control system based on the main steam pressure correction fluidizing air volume includes a transmitter setting value unit PT1, a transmitter measuring unit PT2, a transmitter setting value unit PT3 and a subtractor unit M1, the output ends of the transmitter setting value unit PT1 and the transmitter measuring unit PT2 are connected to the input end of the subtractor unit M1, and the output end of the subtractor unit M1 is connected to two branch lines;

[0031] The branch line includes a first branch line and a second branch line, the first branch line is connected with a first function generator M2 and an inertia lag unit M3 in sequence, the second branch line is connected with a differential unit M4, a second function generator M5, a switching unit M6 and a rate generator M8 in sequence, the output ends of the inertia lag unit M3 and the rate generator M8 are both connected with the input ends of the first adder M9, the output end of the first adder M9 is connected with the input end i13 of the second adder M10, the output end of the transmitter setting value unit PT3 is connected with the input end i12 of the second adder M10, and the output end of the second adder M10 is connected with a primary fluidization air volume setting instruction.

[0032] Preferably, the input terminal i9 of the switching unit M6 is connected to a setting value module M7, and the setting value module M7 is used to input a fixed value R=0 into the switching unit M6.

[0033] Preferably, the selection end of the switching unit M6 is connected to a pressure deviation change rate over-limit condition action.

[0034] A control method of a control system based on main steam pressure correction of fluidizing air volume specifically comprises the following steps:

[0035] S1: Obtain data through the transmitter setting value unit PT1 and the transmitter measurement unit PT2 and pre-process it to obtain the deviation value O1;

[0036] S2: The subtraction unit M1 inputs the deviation value O1 to the first function generator M2 (piecewise function) for data processing as the value of the abscissa x of the piecewise function fx, and the reference feedforward value O2 is output as the corresponding ordinate y value; in the first function generator M2, the functional relationship between the abscissa x and the ordinate y is shown in Table 1:

[0037] Table 1 Changes in the functional relationship of the first function generator M2

[0038]

[0039] S3: The subtraction unit M1 simultaneously inputs the deviation value O1 to the differential unit M4, converts it into the differential action of the automatic control principle for data processing, and then enters the second function generator M5 as the value of the horizontal coordinate x of the piecewise function fx, and outputs the corresponding vertical coordinate y value as the dynamic feedforward value I8; step S3 and step S2 work simultaneously;

[0040] In the second function generator M5, the functional relationship between the abscissa x and the ordinate y is shown in Table 2:

[0041] Table 2 Changes in the functional relationship of the second function generator M5

[0042] Pressure deviation change rate (Mpa / min) -0.3 -0.2 -0.15 0.15 0.2 0.3 <![CDATA[Dynamic feedforward value I8 (KNm3·h-1)]]> -20 -10 0 0 10 20

[0043] S4: The reference feedforward value O2 enters the hysteresis unit M3, which makes the reference feedforward value O2 change slowly, reduces the disturbance to the system, and then outputs the inertia post value O3;

[0044] S5: The constant value 0 output by the dynamic feedforward value I8 and the set value M7 enters the switching unit M6, and the switching unit M6 determines its output value according to the pressure deviation change rate over-limit condition action. When the pressure deviation change rate over-limit condition action is 1, the switching unit M6 selects the dynamic feedforward value I8 as the output value, otherwise it selects the constant value 0 as the output value.

[0045] S6: the output value of the switching unit M6 passes through the rate generator M8, so that the output value of the switching unit M6 is smoothly transitioned at a certain rate during the switching process to obtain a rate smoothing value O8;

[0046] S7: the inertia post-value O3 in step S3 and the rate smoothing value O8 in step S5 are input to the adder unit M9 for data processing to obtain the final feedforward constant O9;

[0047] S8: The output value of the primary fluidization air volume setting curve transmitter PT3 and the final feedforward constant O9 work together to obtain the final primary fluidization air volume instruction.

[0048] Based on the load-air volume control strategy, the present invention directly connects the main steam pressure and pressure setting value deviation into the primary fluidization air volume control loop by introducing the main steam pressure deviation control and the main steam pressure deviation change rate control, and uses the size of the feedforward pressure deviation to instantly increase or decrease the supply of the primary fluidization air volume according to a certain proportion, so that the primary fluidization air volume matches the boiler load, ensuring that the boiler material is in a high-speed fluidization state. The change rate of the pressure deviation in the steady-state process can timely increase or decrease the primary fluidization air volume, better stabilize the main parameters of the unit such as the main steam pressure, superheat, and main steam temperature, and better solve the problems of insufficient main steam pressure or excessive response and large static deviation in the load response process, thereby enhancing the unit's ability to coordinate variable loads. Reliably ensure the safe and stable operation of the unit.

[0049] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Those familiar with the technology may modify or improve the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A control system based on main steam pressure correction of fluidizing air volume, characterized in that: It includes a transmitter setting value unit PT1, a transmitter measuring unit PT2, a transmitter setting value unit PT3 and a subtractor unit M1, wherein the output ends of the transmitter setting value unit PT1 and the transmitter measuring unit PT2 are connected to the input end of the subtractor unit M1, and the output end of the subtractor unit M1 is connected to two branch lines; The branch line includes a first branch line and a second branch line, the first branch line is connected with a first function generator M2 and an inertia lag unit M3 in sequence, the second branch line is connected with a differential unit M4, a second function generator M5, a switching unit M6 and a rate generator M8 in sequence, the output ends of the inertia lag unit M3 and the rate generator M8 are both connected with the input ends of the first adder M9, the output end of the first adder M9 is connected with the input end i13 of the second adder M10, the output end of the transmitter setting value unit PT3 is connected with the input end i12 of the second adder M10, and the output end of the second adder M10 is connected with a primary fluidization air volume setting instruction.

2. The control system based on main steam pressure correction fluidizing air volume according to claim 1, characterized in that: The input terminal i9 of the switching unit M6 is connected to a setting value module M7, and the setting value module M7 is used to input a set value R=0 into the switching unit M6.

3. The control system based on main steam pressure correction fluidizing air volume according to claim 2, characterized in that: The selection end of the switching unit M6 is connected to a pressure deviation change rate over-limit condition action.

4. A control method for a control system based on main steam pressure correction fluidizing air volume according to claim 1, characterized in that: The specific steps include: S1: Obtain data through the transmitter setting value unit PT1 and the transmitter measurement unit PT2 and pre-process it to obtain the deviation value O1; S2: The subtraction unit M1 inputs the deviation value O1 to the first function generator M2 for data processing to obtain a reference feedforward value O2 of the primary fluidizing air volume; S3: The subtraction unit M1 simultaneously inputs the deviation value O1 to the differential unit M4 for data processing, and then inputs it to the second function generator M5 to obtain the dynamic feedforward value I8 of the primary fluidizing air volume. Step S3 and step S2 are performed simultaneously; S4: The reference feedforward value O2 enters the hysteresis unit M3, which makes the reference feedforward value O2 change slowly, reduces the disturbance to the system, and then outputs the inertia post value O3; S5: The dynamic feedforward value I8 and the fixed value 0 output by the set value M7 enter the switching unit M6, and the switching unit M6 acts according to the pressure deviation change rate exceeding the limit condition, specifically selecting the dynamic feedforward value I8 to work or the fixed value 0 to work; S6: the output value of the switching unit M6 passes through the rate generator M8, so that the output value of the switching unit M6 is smoothly transitioned at a certain rate during the switching process to obtain a rate smoothing value O8; S7: the inertia post-value O3 in step S3 and the rate smoothing value O8 in step S5 are input to the adder unit M9 for data processing to obtain the final feedforward constant O9; S8: The output value of the primary fluidization air volume setting curve transmitter PT3 and the final feedforward constant O9 work together to obtain the final primary fluidization air volume instruction.

5. The control method of the control system based on main steam pressure correction fluidizing air volume according to claim 4, characterized in that: In step S2, the deviation value O1 is used as the value of the horizontal coordinate x of the piecewise function fx, and the reference feedforward value O2 is used as the output corresponding vertical coordinate y value.

6. The control method of the control system based on main steam pressure correction fluidizing air volume according to claim 4, characterized in that: In step S3, the deviation value O1 is converted into the differential action of the automatic control principle for data processing, and then used as the value of the horizontal coordinate x of the piecewise function fx, and the dynamic feedforward value I8 is the output of the corresponding vertical coordinate y value.

7. The control method of the control system based on main steam pressure correction fluidizing air volume according to claim 4, characterized in that: The output value of the switching unit M6 in step S5 is determined by the pressure deviation change rate over-limit condition action; when the pressure deviation change rate over-limit condition action is 1, the switching unit M6 selects the dynamic feedforward value I8 as the output value, otherwise it selects the fixed value 0 as the output value.

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