A minimum value taking control method and control system

Abstract

The application discloses a small value control method, a plurality of PID function blocks are arranged to receive a plurality of controlled variables respectively and output control instructions to a minimum value selection function block; after the minimum value selection function block receives the plurality of control instructions, comparison is carried out and a final minimum value control instruction output is output; the output of the minimum value selection function block is simultaneously sent to the PID function block as an external integration signal; the PID function block is internally provided with a switching switch for switching internal integration or external integration, the external integration signal is received into an integration module by selecting the external integration signal, and then the controlled variable of the PID function block is controlled. The application further discloses a small value control system; the PID function block of the application can select to receive the external integration signal, so that the output of the PID function block is not affected by the controlled variable and no longer changes, and the stability of the outputs of all the PID function blocks is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of automatic control technology for thermal power generating units, specifically to a method and control system for taking the smallest value. Background Technology

[0002] In the field of automatic control of thermal power generating units, the "minimum value" control loop is widely used.

[0003] The working principle of the existing control loop is as follows: In some process production processes, there are multiple control loops that control one actuator. For example, in the steam turbine DEH system, there are load control loops and pressure control loops that work together to control the steam turbine regulating valve. In the gas turbine control system, there are power control loops, load limiting control loops, exhaust temperature control loops, etc. that work together to control the fuel regulating valve stroke.

[0004] Since an actuator can only receive one control command at a time, and to ensure the safe operation of the actuator, the smaller value method is used to obtain the final control command output. However, the PID output of the unselected control loops is uncontrolled, resulting in drastic switching disturbances. If one control loop reaches its minimum value, it can stably maintain the setpoint, but the controlled variables of other control loops will constantly deviate from the setpoint. Due to the integral element of the PID function block, the output of the PID controller will continuously change, thus reducing the stability of the control loop output.

[0005] Patent application CN113110631A discloses a method for controlling the main steam pressure in a thermal power plant. This application uses a PID controller based on pure integral action to stabilize the coal quantity at a new equilibrium point based on the main steam pressure deviation, playing a decisive role in reducing frequent fluctuations in main steam pressure. For thermal power units during the heating season, maintaining the main steam pressure when the load is stable has a good effect, improving the unit's AGC and primary frequency regulation performance. However, the stability of all PID controllers when multiple PID controllers are used is not disclosed. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a method and system for taking the minimum value to improve the stability of the output of all PID function blocks.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] A method for controlling the minimum value includes the following steps:

[0009] S1. Set up multiple PID function blocks to receive multiple controlled variables and output control commands to the minimum value selection function block;

[0010] S2, the minimum value selection function block receives multiple control commands, compares them, and outputs the final minimum value control command output;

[0011] S3. The output of the minimum value selection function block is simultaneously sent to the PID function block as an external integration signal.

[0012] S4, the PID function block has an internal switch for switching between internal integral and external integral. By selecting the external integral signal, the external integral signal is received and enters the integral module, thereby controlling the controlled variable of the PID function block.

[0013] Advantages: The multiple PID function blocks of this invention can each receive multiple different controlled variables, and obtain a minimum control command output through the minimum value selection function block. Therefore, the controlled variable received by the minimum value PID function block can be controlled within the set value. Subsequently, the PID function block selects to receive an external integral signal, so that the output of other PID function blocks is not affected by the controlled variable and no longer changes, greatly improving the stability of the output of all PID function blocks.

[0014] Preferably, in step S1:

[0015] S11. Set a switch inside the PID function block to select internal integration or external integration, and switch the switch to internal integration.

[0016] S12. The controlled variable received by the PID function block is compared with the set value to obtain the deviation value;

[0017] S13. After the deviation value passes through the proportional module and the integral module, the feedforward signal is superimposed, and finally the control command is output.

[0018] Preferably, in step S4:

[0019] S41, the PID function block switch is switched to connect to the external integral, so that the external integral signal is connected to the integral module;

[0020] S42. The controlled variable received by the PID function block is compared with the set value to obtain the deviation value;

[0021] S43. After the deviation value passes through the proportional module and the integral module, the feedforward signal is superimposed, and finally the control command is output.

[0022] Preferably, the transfer function of the integration module is:

[0023]

[0024] In the formula, K I G(s) is the integral action coefficient, and G(s) is the output of the integral module.

[0025] This invention also discloses a minimum value control system, including...

[0026] Multiple PID function blocks are used to receive multiple controlled variables and output control commands to the minimum value selection function block;

[0027] The minimum value selection function block is used to compare multiple control commands received and output the final minimum value control command output; the output of the minimum value selection function block is also sent to the PID function block as an external integral signal.

[0028] The PID function block switch is used to select an external integral signal, so that the PID function block receives the external integral signal and enters the integral module. By selecting the external integral signal, the controlled variable of the PID function block can be controlled.

[0029] Preferably, when the PID function block selects internal integral:

[0030] The PID function block has a switch inside for selecting internal integration or external integration, and the switch is switched to internal integration.

[0031] The controlled variable received by the PID function block is compared with its internal setpoint to obtain the deviation value;

[0032] The deviation value is processed by the proportional module and the integral module, then superimposed with the feedforward signal, and finally the control command is output.

[0033] Preferably, when the PID function block selects external integral:

[0034] The PID function block switch is switched to connect to the external integral, so that the external integral signal is connected to the integral module;

[0035] The controlled variable received by the PID function block is compared with the set value to obtain the deviation value;

[0036] The deviation value is processed by the proportional module and the integral module, then superimposed with the feedforward signal, and finally the control command is output.

[0037] Preferably, the transfer function of the integration module is:

[0038]

[0039] In the formula, K I G(s) is the integral action coefficient, and G(s) is the output of the integral module.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows: the multiple PID function blocks of the present invention can each receive multiple different controlled variables, and obtain the minimum value control command output through the minimum value selection function block. Therefore, the controlled variable received by the minimum value PID function block can be controlled within the set value. Subsequently, the PID function block selects to receive an external integral signal, so that the output of other PID function blocks is not affected by the controlled variable and no longer changes, greatly improving the stability of the output of all PID function blocks. Attached Figure Description

[0041] Figure 1 This is a control loop logic block diagram of Embodiment 1 of the present invention;

[0042] Figure 2 This is an internal logic diagram of the PID function block in Embodiment 1 of the present invention. Detailed Implementation

[0043] To facilitate understanding of the technical solution of the present invention by those skilled in the art, the technical solution of the present invention will now be further described in conjunction with the accompanying drawings.

[0044] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0045] Example 1

[0046] See Figure 1 This embodiment discloses a method for controlling the minimum value, which includes the following steps:

[0047] S1. Set multiple PID function blocks 1 to receive multiple controlled variables respectively and output control commands to the minimum value selection function block 2.

[0048] S2, after receiving multiple control commands, the minimum value selection function block 2 compares them and outputs the final minimum value control command output;

[0049] S3. The output of the minimum value selection function block 2 is simultaneously sent to the PID function block 1 as an external integration signal;

[0050] S4. PID function block 1 receives external integral signals and enters the integral module. By selecting the external integral signal, it controls the controlled variable of PID function block 1.

[0051] In this embodiment, to ensure a clearer explanation, we will take setting up three PID function blocks 1 as an example.

[0052] First, let the three PID function blocks be designated as PID1, PID2, and PID3 respectively. The input of PID1 is used to receive the controlled variable 1, and after calculation, the output of PID2 is used to output the control command A. The input of PID2 is used to receive the controlled variable 2, and after calculation, the output of PID3 is used to output the control command C.

[0053] Since an actuator can only receive one control command at a time, and to ensure its safe operation, control command outputs A, B, and C are all input to the minimum value selection function block 2. The minimum value selection function block 2 compares and determines the minimum value among the current control command outputs A, B, and C, and outputs the minimum value is then used as the control command for the actuator. This embodiment uses control command output A as the minimum value for explanation.

[0054] Since the control loop A containing controlled variable 1 is at its minimum value, control loop A is selected. At this time, controlled variables 2 and 3 consistently deviate from their set values. Therefore, due to the action of the integral element of PID function block 1, the outputs of PID function blocks 2 and PID function blocks continuously change.

[0055] Therefore, refer to Figure 2 In this embodiment, a switching switch 11 for receiving external integrals is added to the PID function block 1.

[0056] When internal integration is selected, the BD connector of switch 11 is connected. At this time, in each PID function block 1, after the controlled variable enters the PID function block 1, it is compared with the set value in the PID function block 1. The deviation value after comparison is passed through the proportional module and the integral module, and then the feedforward signal is superimposed. Finally, the control command is output.

[0057] When the external integral is selected, the BC connector of the switch 11 is connected. At this time, the switch 11 of each PID function block 1 is switched to be connected to the external integral, so that the external integral signal is connected to the integral module; the controlled variable received by the PID function block 1 is compared with the set value to obtain the deviation value; the deviation value passes through the proportional module and the integral module, and then the feedforward signal is superimposed, and finally the control command is output.

[0058] The transfer function of the integration module is:

[0059]

[0060] In the formula, K IG(s) is the integral action coefficient, and G(s) is the output of the integral module.

[0061] The transfer function in this embodiment is based on the complex field, where s is the independent variable of the function, and K... I This is the integral action coefficient; the specific value needs to be adjusted and modified during actual application.

[0062] This embodiment effectively avoids the aforementioned problems through the above operations. Specifically, since the output of PID1 is the minimum value, the controlled variable 1 is stably controlled at the set value. The outputs of PID2 and PID3 are related to the deviations of controlled variables 2 and 3, respectively. Since controlled variables 2 and 3 consistently deviate from the set values, the outputs of PID2 and PID3 continuously change due to the action of the integral module in PID1. This embodiment, after obtaining the minimum value, introduces an external integral signal connected to the integral module in each PID1 function block, thereby controlling the outputs of PID2 and PID3. The analysis process is as follows:

[0063]

[0064]

[0065] Continuing to iterate over out(n-3), the value of out(n) is as follows: ...

[0066]

[0067] Kp is the proportional coefficient of the proportional module, T is the integral coefficient of the integral action, and en is the deviation at time n. s is the independent variable in the function.

[0068] The above analysis shows that by selecting an external integral signal, the control output of the PID2 function block is only related to the deviation of the controlled variable. Therefore, when the controlled variable 1 is stably controlled at the setpoint, the output of the PID2 function block will not change. Similarly, the output of the PID3 function block will also remain unchanged, thus greatly improving the stability of the PID outputs of all control loops.

[0069] This embodiment uses three PID function blocks 1, with PID1 function block outputting the minimum value as an example to illustrate the workflow:

[0070] First, connect the BD connectors of the switch 11 in the three PID function blocks 1, all connecting to the internal integral; the external integral is disconnected and not working. At this time, the three controlled variables are respectively sent to the input terminals of the three PID function blocks 1. The controlled variables are first compared with the setpoint, and the resulting deviation values ​​are passed through the proportional module and integral module, then superimposed with a feedforward signal, and finally output as control commands. Specifically, the three PID function blocks 1 are PID1, PID2, and PID3. PID1 outputs control command A, PID2 outputs control command B, and PID3 outputs control command C.

[0071] Subsequently, the minimum value selection function block 2 compares and obtains the minimum value among the control command output A, control command output B and control command output C at the current moment. In this embodiment, the minimum value selection function block 2 outputs control command output A as the control command of the actuator.

[0072] Then, the BC connectors of the switching switches 11 in the three PID function blocks 1 are connected, so that the external integral signal is connected to the integral module, and thus the external integral signal can enter the integral module. At this time, the output of the minimum value selection function block 2 is used as the external integral signal and connected to the integral modules of the three PID modules respectively. The controlled variable received by PID function block 1 is compared with the set value to obtain the deviation value. After the deviation value passes through the proportional module and the integral module, the feedforward signal is superimposed, and finally the control command is output.

[0073] In PID1, the controlled variable 1 is stably controlled at the setpoint and therefore remains unchanged. The output control of PID2 and PID3 is also only related to the deviation of the controlled variable 1. Therefore, when the controlled variable 1 is stably controlled at the setpoint, the outputs of PID2 and PID3 will no longer change, thus greatly improving the stability of the outputs of all PID1 function blocks.

[0074] Example 2

[0075] This invention also discloses a minimum value control system, including...

[0076] Multiple PID function blocks 1 are used to receive multiple controlled variables and output control commands to the minimum value selection function block 2;

[0077] Minimum value selection function block 2 is used to compare multiple control commands received and output the final minimum value control command output; the output of minimum value selection function block 2 is also sent to PID function block 1 as an external integral signal.

[0078] The switch 11 of PID function block 1 is used to select an external integral signal, so that PID function block 1 receives the external integral signal and enters the integral module. By selecting the external integral signal, the controlled variable of PID function block 1 can be controlled.

[0079] When PID function block 1 selects internal integration:

[0080] Switch 11 to internal integration so that the integration module receives internal signals;

[0081] The controlled variable received by PID function block 1 is compared with its internal setpoint to obtain the deviation value;

[0082] The deviation value is processed by the proportional module and the integral module, then superimposed with the feedforward signal, and finally the control command is output.

[0083] When PID function block 1 selects external integral:

[0084] The switch 11 of PID function block 1 is switched to be connected to the external integral, so that the external integral signal is connected to the integral module;

[0085] The controlled variable received by PID function block 1 is compared with the set value to obtain the deviation value;

[0086] The deviation value is processed by the proportional module and the integral module, then superimposed with the feedforward signal, and finally the control command is output.

[0087] The transfer function of the integral module is:

[0088]

[0089] In the formula, K I G(s) is the integral action coefficient, and G(s) is the output of the integral module.

[0090] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0091] The above embodiments are merely examples of implementation methods of the invention. The scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for controlling the minimum value, characterized in that: Includes the following steps: S1. Set up multiple PID function blocks (1) to receive multiple controlled variables respectively and output control commands to the minimum value selection function block (2); in step S1: S11. Switch the switch (11) to the internal integration module so that the integration module receives the internal signal; S12, the PID function block (1) compares the received controlled variable with the set value to obtain the deviation value; S13. After the deviation value passes through the proportional module and the integral module, the feedforward signal is superimposed, and finally the control command is output. S2, Minimum value selection function block (2) receives multiple control commands, compares them, and outputs the final minimum value control command output; S3, The output of the minimum value selection function block (2) is simultaneously sent as an external integration signal to each PID function block (1); S4. The PID function block (1) is internally equipped with a switch (11) for switching between internal integral and external integral. By selecting the external integral signal, the external integral signal is received and enters the integral module, thereby controlling the controlled variable of the PID function block (1); in step S4: S41, the switch (11) of the PID function block (1) is switched to be connected to the external integral, so that the external integral signal is connected to the integral module; S42, PID function block (1) compares the received controlled variable with the set value to obtain the deviation value; S43. After the deviation value passes through the proportional module and the integral module, the feedforward signal is superimposed, and finally the control command is output.

2. The method for controlling the minimum value according to claim 1, characterized in that: The transfer function of the integral module is: In the formula, K I G(s) is the integral action coefficient, and G(s) is the output of the integral module.

3. A minimum value control system, characterized in that: include Multiple PID function blocks (1) are used to receive multiple controlled variables respectively and output control commands to the minimum value selection function block (2); when the PID function block (1) selects the internal integral: Switch the switch (11) to internal integration so that the integration module receives internal signals; The PID function block (1) compares the received controlled variable with its internal setpoint to obtain the deviation value; The deviation value is passed through the proportional module and the integral module, then the feedforward signal is added, and finally the control command is output. The minimum value selection function block (2) is used to compare and output the final minimum value control command output after receiving multiple control commands; the output of the minimum value selection function block (2) is also sent as an external integration signal to each PID function block (1); The switch (11) of the PID function block (1) is used to select an external integral signal, so that the PID function block (1) receives the external integral signal and enters the integral module. By selecting the external integral signal, the controlled variable of the PID function block (1) is controlled. When the PID function block (1) selects the external integral signal: The switch (11) of the PID function block (1) is switched to be connected to the external integral, so that the external integral signal is connected to the integral module; The PID function block (1) compares the received controlled variable with the set value to obtain the deviation value; The deviation value is processed by the proportional module and the integral module, then superimposed with the feedforward signal, and finally the control command is output.

4. The minimum value control system according to claim 3, characterized in that: The transfer function of the integral module is: In the formula, K I G(s) is the integral action coefficient, and G(s) is the output of the integral module.

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