A cascade proportional double auxiliary loop PID control system

Abstract

The present invention relates to a cascade proportional dual auxiliary loop PID control system, which belongs to the field of coal gas automation. The system includes a mixer, a sensor, an actuator, an intelligent control system and a pipeline; the mixer is connected to the sensor and the actuator in sequence through a pipeline; and then connected to the gas-using equipment; the sensor and the actuator are connected to the intelligent control system signal; the high-concentration gas A is mixed with the low-concentration gas B in the mixer through a pipeline, and a flow sensor, a concentration sensor and a regulating valve are respectively arranged on the air intake pipelines of the two gases. The mixed gas is transported to the rear-end gas-using equipment through the pipeline, and the function of the cut-off valve is that when the concentration after mixing exceeds the limit, the cut-off valve is quickly closed to prevent the mixed gas from entering the rear-end gas-using equipment; the present invention can solve the sudden change of concentration or flow in the adjustment process in the traditional adjustment scheme, realize accurate adjustment, and realize simultaneous adjustment and control of flow and concentration.

Description

Technical Field

[0001] The invention belongs to the field of gas automation and relates to a cascade proportional double auxiliary loop PID control system. Background Art

[0002] In gas utilization and chemical synthesis and other related fields, it is often necessary to fully mix two gases of different concentrations to obtain a mixed gas with a stable concentration that meets the process requirements.

[0003] Most of the existing mixing technology solutions remain at the manual control stage, and some automatic controls only use simple PID control algorithms to control only one loop of flow or concentration.

[0004] Although simple PID regulation has a simple structure, due to the full output, each output is related to the past state, and the calculation must be accumulated, which is a lot of work; and because the computer output corresponds to the actual position of the actuator, if the computer fails, the output will change drastically, causing a drastic change in the actuator, which may cause serious production accidents.

[0005] Traditional single-loop regulation can generally only adjust one parameter, namely, the concentration or flow rate of the gas. If the concentration is given priority, the flow rate cannot be regulated.

[0006] The present invention can solve the sudden change of concentration or flow rate during the regulation process in the traditional regulation scheme, realize accurate regulation, and realize simultaneous regulation and control of flow rate and concentration. Summary of the invention

[0007] In view of this, an object of the present invention is to provide a cascade proportional dual auxiliary loop PID control system.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] A cascade proportional dual auxiliary loop PID control system, the system comprising a mixer, a sensor, an actuator, an intelligent control system and a pipeline;

[0010] The mixer is connected to the sensor and the actuator in sequence through pipelines;

[0011] Then connect it to the gas-using equipment;

[0012] The sensors and actuators are connected to the intelligent control system signals;

[0013] High-concentration gas A is mixed with low-concentration gas B in the mixer through the pipeline. Flow sensors, concentration sensors and regulating valves are respectively installed on the intake pipelines of the two gases. The evenly mixed gas is transported to the gas-using equipment at the back end through the pipeline. The function of the cut-off valve is to quickly close the cut-off valve when the concentration after mixing exceeds the limit to prevent the mixed gas from entering the gas-using equipment at the back end.

[0014] The mixer is used to provide a space for mixing two gases, and spiral blades are installed inside the mixer to achieve turbulence and sufficient mixing of the gases;

[0015] The sensor measures the parameters of gas composition, flow rate and pressure, and inputs the measured parameters into the intelligent control system through electrical signals;

[0016] The intelligent control system can read, store and analyze the measured parameters, and output control signals to drive the actuator to control the flow rate and concentration.

[0017] The actuator is a moving part that receives signals from the intelligent control system and performs regulating and cutting actions.

[0018] Optionally, the sensor includes a flow sensor and a concentration sensor;

[0019] The actuator includes a regulating valve and a cut-off valve.

[0020] Optionally, the intelligent control system adopts variable speed integral PID control, specifically:

[0021] Change the accumulated speed of the integral term to make it correspond to the deviation size: the larger the deviation, the slower the integration, and vice versa. To this end, set the coefficient f(e(k)), which is a function of e(k). When the absolute value of e(k) increases, f decreases, and vice versa. The PID integral term expression of variable speed integral is:

[0022]

[0023] Coefficient f and current value of deviation | e(k) | The relationship is linear or nonlinear, set as:

[0024]

[0025] The f value varies in the interval [0, l]. | When the difference of e(k) is greater than the given separation interval A+B, f=0, and the current value e(k) is no longer accumulated; when the deviation | When e(k) is less than B, add the current value e(k), that is, the integral term becomes The integral action reaches the highest speed; when the deviation |e(k) | When it is between B and A+B, part of the current value is added, and its value is between 0 and | e(k) | Between | e(k) | The size of the integral varies with the and Between; variable speed integral PID algorithm is:

[0026]

[0027] Optionally, the control system includes three PID function blocks, namely: a main PID function block, a gas A auxiliary PID function block and a gas B auxiliary PID function block;

[0028] The feedback signal of the main PID function block is the concentration after mixing, and the given value is selected according to the process requirements; the output of the main PID function block is "given gas A flow rate"; it is used as the given value of the two auxiliary control loops;

[0029] The feedback signal of the auxiliary PID function block of gas A is the flow rate of gas A, and its control output is loaded to the gas A pipeline regulating valve to control the flow rate of gas A entering the mixer;

[0030] The feedback signal of the auxiliary PID function block of gas B is the flow rate of gas B pipeline. Its control output is loaded to the gas B pipeline regulating valve to control the flow rate of gas B entering the mixer. The given value of the gas B control loop always changes with the set value of the gas loop according to the ratio specified by the "A / B ratio" to keep the gas A and gas B entering the mixer in a suitable ratio to ensure that the concentration after mixing has a high accuracy and stability.

[0031] When the concentration after mixing is lower than the given value, the control output of the main PID function block will increase; that is, the given gas A flow rate of the gas A control PID function block will increase, so that the gas A flow rate deviation will increase. After adjustment by the gas A auxiliary PID function block, the control output of the gas A regulating valve will be increased, so that the gas A valve will increase its opening and increase the gas A flow rate; at the same time, the given gas B flow rate of the gas B control auxiliary PID function block will be reduced according to the gas B ratio, so that the gas B flow rate deviation will decrease. After adjustment by the gas B auxiliary PID function block, the control output of the gas B regulating valve will be reduced, so that the gas B valve will decrease its opening and reduce the gas B flow rate;

[0032] The calculation order of the cascade proportional dual auxiliary loop is the main loop PID1 first, then the auxiliary loop PID2; the control method adopts asynchronous sampling control, that is, the sampling control period T1 of the main loop is not an integer multiple of the sampling control period T2 of the auxiliary loop.

[0033] The beneficial effects of the present invention are:

[0034] Traditional single-loop regulation can generally only adjust one parameter, namely, the concentration or flow rate of the gas. If the concentration is given priority, the flow rate cannot be regulated.

[0035] The present invention can solve the sudden change of concentration or flow rate during the regulation process in the traditional regulation scheme, realize accurate regulation, and realize simultaneous regulation and control of flow rate and concentration.

[0036] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0038] Figure 1 It is the principle diagram of the system of the present invention;

[0039] Figure 2 This is the PID control principle diagram of the cascade proportional dual auxiliary loop in the present invention. DETAILED DESCRIPTION

[0040] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0041] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0042] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0043] See also Figure 1-2 , which is a cascade proportional dual auxiliary loop PID control system. The system includes: mixer, sensors (flow sensor, concentration sensor, etc.), actuators (regulating valve, shut-off valve), intelligent control system, pipeline, etc. High-concentration gas A is mixed with low-concentration gas B in the mixer through a pipeline. Flow sensors, concentration sensors and regulating valves are respectively set on the intake pipelines of the two gases. The evenly mixed gas is transported to the gas-using equipment at the back end through a pipeline. A flow sensor, concentration sensor and shut-off valve are set on the pipeline. The function of the shut-off valve is to quickly close the shut-off valve when the concentration after mixing exceeds the limit to prevent the mixed gas from entering the gas-using equipment at the back end. Figure 1 shown.

[0044] The mixer is the main equipment of the device system. It provides a space for the two gases to mix. It is equipped with spiral blades inside to achieve turbulence and sufficient mixing of the gases. The sensor measures gas components, flow, pressure and other parameters, and inputs the measured parameters into the intelligent control system through electrical signals. The intelligent control system is the core equipment of this device system. It reads, stores and analyzes the measured parameters, and outputs control signals to drive the actuator to achieve control of flow and concentration. The actuator is a moving part that receives signals from the intelligent control system and performs adjustment and cutting actions.

[0045] (1) Use fast-response concentration sensors and high-precision ultrasonic gas flow meters to provide timely and reliable data for high-precision intelligent control.

[0046] (2) Use variable speed integral PID control instead of traditional PID control to improve control accuracy. The specific process is as follows:

[0047] In the common PID control algorithm, since the integral coefficient is a constant, the integral increment remains unchanged during the entire control process. However, the system's requirement for the integral term is that the integral effect should be weakened or even eliminated when the system deviation is large, and should be strengthened when the deviation is small. If the integral coefficient is too large, overshoot or even integral saturation will occur, while if it is too small, static error cannot be eliminated. Therefore, how to change the speed of integration according to the size of the system deviation is very important for improving the quality of the system. Variable speed integral PID can solve this problem well.

[0048] Change the accumulated speed of the integral term to make it correspond to the deviation size: the larger the deviation, the slower the integration, and vice versa. To this end, set the coefficient f(e(k)), which is a function of e(k). When the absolute value of e(k) increases, f decreases, and vice versa. The PID integral term expression of variable speed integral is:

[0049]

[0050] Coefficient f and current value of deviation | e(k) | The relationship is linear or nonlinear, set as:

[0051]

[0052] The f value varies in the interval [0, l]. | When the difference of e(k) is greater than the given separation interval A+B, f=0, and the current value e(k) is no longer accumulated; when the deviation | When e(k) is less than B, add the current value e(k), that is, the integral term becomes The integral action reaches the highest speed; when the deviation | e(k) | When it is between B and A+B, part of the current value is added, and its value is between 0 and | e(k) | Between | e(k) | The size of the integral varies with the and Between; variable speed integral PID algorithm is:

[0053]

[0054] (3) Adopt cascade proportional dual auxiliary loop PID control method to achieve precise control of flow and concentration, such as Figure 2 shown.

[0055] The system uses three PID function blocks, namely: main PID function block, gas A auxiliary PID function block, gas B auxiliary PID function block.

[0056] The feedback signal of the main PID function block is the concentration after mixing, and the given value is selected according to the process requirements. The output of the main PID function block is "given gas A flow rate". It is used as the given value of the two auxiliary control loops.

[0057] The feedback signal of the Gas A auxiliary PID function block is the flow rate of Gas A, and its control output is loaded to the Gas A pipeline regulating valve to control the flow rate of Gas A entering the mixer.

[0058] The feedback signal of the Gas B auxiliary PID function block is the flow rate of the Gas B pipeline, and its control output is loaded to the Gas B pipeline regulating valve to control the flow rate of Gas B entering the mixer. The set value of the Gas B control loop always changes with the set value of the gas loop according to the ratio specified by the "A / B ratio" to keep the appropriate ratio of Gas A and Gas B entering the mixer to ensure that the concentration after mixing has high accuracy and stability.

[0059] From the PID function control principle, when the concentration after mixing is lower than the given value, the control output of the main PID function block will increase. That is, the given gas A flow rate of the gas A control PID function block increases, which increases the gas A flow rate deviation. After adjustment by the gas A auxiliary PID function block, the control output of the gas A regulating valve will increase, so that the gas A valve will increase its opening and increase the gas A flow rate. At the same time, the given gas B flow rate of the gas B control auxiliary PID function block will decrease according to the gas B ratio, so that the gas B flow rate deviation will decrease. After adjustment by the gas B auxiliary PID function block, the control output of the gas B regulating valve will decrease, so that the gas B valve will decrease its opening and reduce the gas B flow rate.

[0060] The calculation order of the cascade proportional dual auxiliary loop is the main loop (PID1) first, then the auxiliary loop (PID2). The control method adopts asynchronous sampling control, that is, the sampling control period T1 of the main loop is not an integer multiple of the sampling control period T2 of the auxiliary loop. This is because the response speed of the main control object in the general cascade intelligent control system is slow, and the response speed of the auxiliary control object is fast.

[0061] The advantages of cascade control are:

[0062] (a) The interference is added to the secondary loop, and the secondary loop control suppresses it;

[0063] (b) The change of parameters in the secondary loop is controlled by the secondary loop, and the influence on the controlled quantity GC1 is greatly reduced;

[0064] (c) The inertia of the secondary loop is adjusted by the secondary loop, thereby improving the response speed of the entire system.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A cascade proportional dual auxiliary loop PID control system, characterized in that: The system includes mixers, sensors, actuators, intelligent control systems and pipelines; The mixer is connected to the sensor and the actuator in sequence through pipelines; Then connect it to the gas-using equipment; The sensors and actuators are connected to the intelligent control system signals; High-concentration gas A is mixed with low-concentration gas B in the mixer through the pipeline. Flow sensors, concentration sensors and regulating valves are respectively installed on the intake pipelines of the two gases. The evenly mixed gas is transported to the gas-using equipment at the back end through the pipeline. The function of the cut-off valve is to quickly close the cut-off valve when the concentration after mixing exceeds the limit to prevent the mixed gas from entering the gas-using equipment at the back end. The mixer is used to provide a space for mixing two gases, and spiral blades are installed inside the mixer to achieve turbulence and sufficient mixing of the gases; The sensor measures the parameters of gas composition, flow rate and pressure, and inputs the measured parameters into the intelligent control system through electrical signals; The intelligent control system can read, store and analyze the measured parameters, and output control signals to drive the actuator to control the flow rate and concentration. The actuator is a moving part that receives signals from the intelligent control system and performs regulation and cutting actions; The sensors include a flow sensor and a concentration sensor; The actuator includes a regulating valve and a cut-off valve; The intelligent control system adopts variable speed integral PID control, specifically: Change the accumulated speed of the integral term to make it correspond to the deviation size: the larger the deviation, the slower the integration, and vice versa. To this end, set the coefficient f(e(k)), which is a function of e(k). When the absolute value of e(k) increases, f decreases, and vice versa. The PID integral term expression of variable speed integral is: The relationship between the coefficient f and the current value of the deviation |e(k)| is linear or nonlinear, and is set as: The f value changes in the interval [0, l]. When the |e(k) difference is greater than the given separation interval A+B, f = 0, and the current value e(k) is no longer accumulated; when the deviation |e(k) is less than B, the current value e(k) is added, that is, the integral term becomes The integral action reaches the highest speed; when the deviation |e(k)| is between B and A+B, part of the current value is accumulated, and its value varies between 0 and |e(k)| with the size of |e(k)|, and its integral speed is and Between; variable speed integral PID algorithm is: The control system includes three PID function blocks, namely: a main PID function block, a gas A auxiliary PID function block and a gas B auxiliary PID function block; The feedback signal of the main PID function block is the concentration after mixing, and the given value is selected according to the process requirements; the output of the main PID function block is "given gas A flow rate", which is used as the given value of the two auxiliary control loops; The feedback signal of the auxiliary PID function block of gas A is the flow rate of gas A, and its control output is loaded to the gas A pipeline regulating valve to control the flow rate of gas A entering the mixer; The feedback signal of the auxiliary PID function block of gas B is the flow rate of gas B pipeline. Its control output is loaded to the gas B pipeline regulating valve to control the flow rate of gas B entering the mixer. The given value of the gas B control loop always changes with the set value of the gas loop according to the ratio specified by the "A / B ratio" to keep the appropriate ratio of gas A and gas B entering the mixer, so as to ensure that the concentration after mixing has high accuracy and stability. When the concentration after mixing is lower than the given value, the control output of the main PID function block will increase; that is, the given gas A flow rate of the gas A control PID function block will increase, so that the gas A flow rate deviation will increase. After adjustment by the gas A auxiliary PID function block, the control output of the gas A regulating valve will increase, so that the gas A valve will increase its opening and increase the gas A flow rate; at the same time, the given gas B flow rate of the gas B control auxiliary PID function block will decrease according to the gas B ratio, so that the gas B flow rate deviation will decrease. After adjustment by the gas B auxiliary PID function block, the control output of the gas B regulating valve will decrease, so that the gas B valve will decrease its opening and reduce the gas B flow rate. The calculation order of the cascade proportional dual auxiliary loop is the main loop PID1 first, then the auxiliary loop PID2; the control method adopts asynchronous sampling control, that is, the sampling control period T1 of the main loop is not an integer multiple of the sampling control period T2 of the auxiliary loop.

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