CN114019797B - Sewage treatment equipment ozone concentration sliding mode anti-interference control method under non-time-lag nominal model - Google Patents

Abstract

The invention belongs to the field of automatic control. What is disclosed is a sliding mode anti-disturbance control method for ozone concentration in sewage treatment equipment under a nominal model without time lag. In the entire sewage treatment system, the ozone used as the remaining liquid in the sewage treatment is passed through a self-made PTFE hollow The membrane contact component made of fiber hydrophobic membrane is coupled with UV to form a new membrane contact ozone oxidation-UV process. Using membranes to transmit ozone can improve efficiency. The original system mathematical model is a first-order large inertia and large time delay system. In order to simplify the sliding mode The design of the controller reduces the adverse impact of time delays on the system. The sliding mode controller is designed based on the nominal model of the system without time delays. The disturbance observer is used to predict the system disturbance, which greatly improves the robustness of the system and effectively It improves the system control efficiency and performance, and reduces the impact of interference on the ozone concentration control system.

Description

Sliding mode anti-disturbance control method of ozone concentration in sewage treatment equipment under no time delay nominal model

Technical field

The invention belongs to the field of automatic control technology. Based on the ozone concentration control of garbage residual liquid sewage treatment equipment, a control method for a large inertia and large time delay system is proposed. A sliding mode controller is designed based on the constructed nominal model without time delay and its feedback. , input the sliding mode control rate of the controller into the actual ozone concentration control system to improve system performance and reduce the adverse impact of the time delay in the original system on the system. A disturbance observer is designed based on the original large inertia and large time delay system, and the observation System disturbances are extracted and fed back to the forward channel for compensation, reducing system overshoot and improving system response speed, anti-interference ability and robustness.

Background technique

For now, environmental pollution has become a problem that requires strong attention in all countries and regions around the world. For developing countries, with the rapid development of industry in the past few decades, many industries have emerged in the process of rapid industrial development. pollution, and China has a large population, so how to deal with residual liquid sewage is necessary for the development of the country. It can not only reduce the discharge of water pollution, but also promote the renewable development of water sources.

Ozone oxidation treatment of sewage is currently widely used in sewage treatment systems

(1) Effectively remove COD, anionic detergents and ammonia nitrogen from sewage, and at room temperature, ozone can be reduced to oxygen in about 30 minutes, so there is no residue or secondary pollution.

(2) Ozone can be produced at the production site. Compared with liquid chlorine and sodium hypochlorite, there is no need for storage and transportation, which reduces operational risks.

(3) Ozone has strong oxidation effect and fast reaction speed. Ozone has good inactivation and lethal effects on microorganisms, bacteria, and viruses. Its effect in inactivating microorganisms is better than that of chlorine, chloramine, chlorine dioxide and other disinfectants. It can also oxidize and degrade other pollutants in the water.

(4) The remaining ozone in the water can quickly and naturally decompose into oxygen. The effluent contains high dissolved oxygen. It does not increase the burden on the water body after being discharged to the receiving water body, and can improve the water quality of the water body. It is the cleanest disinfectant.

However, in the sewage treatment process, the concentration of ozone also affects the sewage treatment efficiency and energy consumption. Increasing the ozone concentration will help promote ozone mass transfer, and the decolorization rate and COD removal rate will increase, but the mineralization efficiency (ΔCOD/ΔO ₃ ) and ozone utilization rate will decrease. Excessive ozone dosing does not lead to a proportional increase in the ozone concentration on the liquid side, and will result in residual ozone.

At present, in the actual control process of ozone concentration, it mainly focuses on switch control, PID control and fuzzy control. Switch control is the simplest control method, but the control accuracy is extremely low, the fluctuation is large, and the energy consumption is high; while fuzzy control requires a lot of practical on-site experience and does not have the ability to self-study. It cannot reflect the actual characteristics of the process very well and is not very good. To maintain the stability of ozone concentration.

In response to the problems raised above, this application proposes a sliding mode anti-disturbance control method to reduce the system output overshoot and improve the system's response speed, anti-interference ability and robustness.

Contents of the invention

The present invention mainly solves the technical problems existing in the prior art; and provides a sliding mode anti-disturbance control method for ozone concentration of sewage treatment equipment under a time-delay nominal model.

A sliding mode anti-disturbance control method for ozone concentration in sewage treatment equipment under a time-delay nominal model, which is characterized by including:

Step 1. The sliding mode controller takes the difference between the actual ozone concentration and the design value as the input quantity, and outputs the time-delay nominal model after removing the error to the disturbance observer;

Step 2. The disturbance observer uses the controlled variables and system output to estimate the system disturbance, and feeds the observed system disturbance to the forward channel to suppress the interference;

Step 3. The low-pass filter effectively filters out high-frequency noise, compensates for low-frequency interference, and converts the inverse model of g(s) into a true fraction.

In the sliding mode anti-disturbance control method of ozone concentration of sewage treatment equipment under the above-mentioned nominal model without time delay, the specific method of step 1 is that the sliding mode controller is designed according to the nominal model without time delay of the system and the feedback of the model. Specifically, yes:

Step 1.1: To control the ozone concentration in the garbage residual liquid sewage treatment system, introduce the integral design sliding mode function, that is

Among them, c is the sliding mode surface coefficient, and the tracking error is y _d is the ozone concentration setting value;

Step 1.2: Define the Lyapunov function as

but

In the control principle, the Lyapunov function is used to judge the stability of the system. The system equation

It can be seen that for the equilibrium point s, if there is a continuous function V that satisfies

with/>

Then the system will be in equilibrium at the equilibrium point s=0, that is

Step 1.3: Order Then the first condition and the second condition in Lyapunov's second law are satisfied/> When the conditions of Lyapunov's second law are met, s=0, s will eventually stabilize the sliding mode surface;

Step 1.4: Generally speaking, there are three options for sliding mode control law:

Select the second sliding mode control law to get

Among them, k and δ are design parameters, and sgn s is the switching function of s;

then

Step 1.5: Thus

inequality equation The solution is

It can be seen that V(t) exponentially converges to 0, so The exponential convergence speed of and e(t) depends on k; the exponential term -ks can ensure that when s is larger, the system state can approach the sliding mode at a larger speed.

In the sliding mode anti-disturbance control method of ozone concentration in sewage treatment equipment under the above-mentioned nominal model without time delay, the disturbance observer estimates the system disturbance through the controlled variable and the system output, and feeds the observed system disturbance to the forward direction. channel to suppress interference and reduce the adverse impact of interference on the controlled process; as shown in the dotted box 1 of the system block diagram of the control method of this application, r (s) is the system setting value, and u ₀ (s) is the sliding mode control device output, y(s) is the actual system output, G _p (s) is the actual controlled process, is the inverse of the minimum phase part model of the system, e ^-τ is the time delay link of the actual system; the dotted line box 1 is the disturbance observer, d(s) is the actual interference in the system,/> is the disturbance estimate of the disturbance observer.

Under the above-mentioned nominal model without time delay, the sliding mode anti-disturbance control method of ozone concentration in sewage treatment equipment, the low-pass filter in the disturbance observer is specifically implemented:

Step 3.1: Since the phase lag of an order that is too high will have an adverse effect on the system due to under-damping, the order k of the low-pass filter is generally the relative order of G _p (s); the system changes with the time of the low-pass filter As the constant η increases, it becomes more stable, but the anti-disturbance ability of the system will decrease accordingly. Therefore, the design of the disturbance observer should comprehensively consider the anti-interference performance and robustness of the system;

Step 3.2: Q(s) is usually a low-pass filter. Adding a low-pass filter can filter the external noise interference caused by the actual system operation, and can convert the minimum phase inverse model of the control object into a true fraction;

Among them, eta is the time constant of the filter, and k is the order of the filter;

Step 3.3: When the Q(s) static gain is 1, the disturbance estimate of the disturbance observer can be calculated

Description of the drawings

Figure 1 is a system block diagram of the sliding mode anti-disturbance control of ozone concentration in garbage residual liquid sewage under the no-time-delay model of the present invention.

Figure 2 is a simulation output diagram of the control method of this application and traditional PID control.

Figure 3 is a sewage treatment device for residual garbage liquid.

Detailed ways

The technical solution of the present invention will be further described in detail below through examples and in conjunction with the accompanying drawings.

Example:

The present invention proposes a sliding mode anti-disturbance control of ozone concentration in sewage treatment equipment under a time-delay nominal model. As shown in the system control block diagram in Figure 1, a time-delay nominal model system is constructed. The time-delay nominal model can simplify the sliding mode. The design of the model controller uses a sliding mode controller designed with no time-delay nominal model to control the original system, which can reduce the adverse impact of time-delay on the system, reduce system overshoot, and improve response speed and control accuracy; in practice When a disturbance is added to the system, the disturbance observer is designed to estimate and compensate for the disturbance and improve the anti-interference ability and robustness of the ozone concentration system. Specifically:

(1) The premise is that the membrane contact component made of a self-made PTFE hollow fiber hydrophobic membrane is coupled with UV to form a new membrane contact ozone oxidation-UV process. The transmission of ozone through the membrane can greatly improve the efficiency, which is commonly used in the printing and dyeing industry but is difficult to The degraded azo dye reactive brilliant red X-3B is used as the target pollutant for sewage treatment:

(2) The original system mathematical model is a first-order system with large inertia and large time delay. In order to simplify the design of the sliding mode controller and reduce the adverse impact of time delay on the system, the sliding mode controller is designed based on the nominal model of the system without time delay and its feedback. module controller. include:

Sliding mode controller: Sliding mode control, also called variable structure control, is a nonlinear controller. The sliding mode controller can ensure that the system can continuously change according to the state of the system, respond more quickly, and solve parameters. Problems such as changes and disturbances are not obvious, and the sliding mode, that is, the stable state, is reached faster.

Disturbance observer: The difference between the actual model and the ideal model output caused by external interference and changes in model parameters can be equated to equivalent input, that is, equivalent interference can be observed, and the observed interference can be introduced into equal compensation to achieve Complete suppression of interference

Low-pass filter: Since the disturbance observer is not obvious to the measurement noise, but it can effectively filter out the high-frequency noise, adding a low-pass filter can effectively compensate for the low-frequency interference and effectively filter out the high-frequency noise, and The inverse model of g(s) can be converted into a true fraction, which simplifies the control design.

A sliding mode anti-disturbance control of ozone concentration in sewage treatment equipment under a time-delay nominal model, including:

Step 1. The sliding mode controller takes the difference between the actual ozone concentration and the design value as the input quantity, and outputs the time-delay nominal model after removing the error to the disturbance observer.

Step 2. The disturbance observer uses the controlled variables and system output to estimate the system disturbance, and feeds the observed system disturbance to the forward channel to suppress the interference and reduce the adverse impact of the interference on the controlled process.

Step 3. The low-pass filter can effectively filter out high-frequency noise. Adding a low-pass filter can effectively compensate for low-frequency interference and effectively filter out high-frequency noise. It can also convert the inverse of g(s). The model is converted to a true fraction, and the first-order low-pass filter can reduce costs and simplify control design without reducing the effect.

Among them, the specific method of step 1 is to design the sliding mode controller based on the system's time-delay-free nominal model and its feedback, specifically:

Step 1.1: To control the ozone concentration in the garbage residual liquid sewage treatment system, introduce the integral design sliding mode function, that is

Among them, c is the sliding mode surface coefficient, and the tracking error is y _d is the ozone concentration setting value.

Step 1.2: Define the Lyapunov function as

but

In the control principle, the Lyapunov function is used to judge the stability of the system. The system equation

It can be seen that for the equilibrium point s, if there is a continuous function V that satisfies

with/>

Then the system will be in equilibrium at the equilibrium point s=0, that is

Step 1.3: Order Then the first condition and the second condition in Lyapunov's second law are satisfied/> When the conditions of Lyapunov's second law are satisfied, s=0, s will eventually stabilize the sliding mode surface.

Step 1.4: Generally speaking, there are three options for sliding mode control law:

Select the second sliding mode control law to get

Among them, k and δ are design parameters, and sgn s is the switching function of s.

then

Step 1.4: Thus

inequality equation The solution is

It can be seen that V(t) exponentially converges to 0, so The exponential convergence rate of and e(t) depends on k. The exponential term -ks can ensure that when s is larger, the system state can approach the sliding mode at a larger speed.

Step 2: Design the disturbance observer.

The disturbance observer estimates the system disturbance through the controlled variables and system output, and feeds the observed system disturbance to the forward channel to suppress the interference and reduce the adverse impact of the interference on the controlled process. As shown in the dotted box 1 of the system block diagram of the control method of this application, r(s) is the system setting value, u ₀ (s) is the output of the sliding mode controller, y(s) is the actual system output, G _p (s) is the actual controlled process, is the inverse of the minimum phase part model of the system, and e ^-τ is the time delay link of the actual system. The dotted box 1 is the disturbance observer, d(s) is the actual interference in the system,/> is the disturbance estimate of the disturbance observer,

Step 3: Design the low-pass filter in the disturbance observer.

Step 3.1: In the design of the disturbance observer, the design of the low-pass filter has an important impact on the dynamic characteristics of the observer and the robustness of the system. The response speed and ability to suppress disturbances of the disturbance observer will change with the order of the low-pass filter. The higher the order of the low-pass filter, the faster the response speed of the disturbance observer, and the robustness of the system will decrease. stronger,

Step 3.2: Since an order that is too high and a large phase lag will have an adverse effect on the system due to under-damping, the order k of the low-pass filter is generally the relative order of G _p (s). The system becomes more stable as the time constant of the low-pass filter increases, but the anti-disturbance capability of the system will decrease accordingly. Therefore, the design of the disturbance observer should comprehensively consider the anti-interference performance and robustness of the system.

Step 3.3: Q(s) is usually a low-pass filter. Adding a low-pass filter can filter the external noise interference caused by the actual system operation, and can convert the minimum phase inverse model of the control object into a true fraction.

Among them, eta is the time constant of the filter, and k is the order of the filter.

Step 3.3: When the Q(s) static gain is 1, the disturbance estimate of the disturbance observer can be calculated

The ozone concentration control method for garbage residual sewage treatment as described in claim 1, the sliding mode controller is a sliding mode surface designed according to the desired dynamic characteristics of the system, and the system state sliding mode surface is controlled by the sliding mode controller. The outward sliding mode surface converges. Once the system reaches the sliding mode control effect, it will ensure that the system reaches the system origin along the sliding mode surface, thereby achieving precise control of the mathematical model, improving accuracy, anti-interference ability, and reducing overshoot and adjustment. time.

3. The ozone concentration control method for garbage residual sewage treatment as described in claim 1, the described disturbance observer estimates the system disturbance through the controlled variable and the system output, and feeds it back to the forward channel for compensation, improving the system anti-interference ability and robustness.

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

(1) Strong anti-interference ability, high control accuracy and good control effect. Compared with traditional PID control, the system controller uses a sliding mode controller and a disturbance observer to improve the system control accuracy, response speed and anti-interference ability.

(2) Using a time-delay-free nominal model and its output feedback to construct a sliding mode controller simplifies the design of the sliding mode controller and eliminates the adverse impact of time delays on the system.

(4) The entire control method is simple and has high working reliability. The use of sliding mode as the controller can improve the control accuracy and response speed of ozone, and a disturbance observer is added to meet the control needs of the system under different working conditions. .

The specific embodiments described in this application are merely illustrative of the spirit of the invention. Those skilled in the art to which the present invention belongs can make various modifications or additions to the described specific embodiments or substitute them in similar ways, but this will not deviate from the spirit of the present invention or exceed the definition of the appended claims. range.

Claims (3)

1. A sliding mode anti-disturbance control method for ozone concentration in garbage residual liquid sewage treatment equipment based on a time-delay nominal model, which is characterized by including: Step 1. The sliding mode controller takes the difference between the actual ozone concentration and the design value as the input quantity, and outputs the time-delay nominal model after removing the error to the disturbance observer; Step 2. The disturbance observer uses the controlled variables and system output to estimate the system disturbance, and feeds the observed system disturbance to the forward channel to suppress the interference; Step 3. The low-pass filter effectively filters out high-frequency noise, compensates for low-frequency interference, and converts the inverse model of g(s) into a true fraction; The specific method of step 1 is to design the sliding mode controller based on the system's time-delay-free nominal model and its feedback, specifically: Step 1.1: To control the ozone concentration in the garbage residual liquid sewage treatment system, introduce the integral design sliding mode function, that is Among them, c is the sliding mode surface coefficient, and the tracking error is y _d is the ozone concentration setting value; Step 1.2: Define the Lyapunov function as but In the control principle, the Lyapunov function is used to judge the stability of the system. The system equation It can be seen that for the equilibrium point s, if there is a continuous function V that satisfies with/> Then the system will be in equilibrium at the equilibrium point s=0, that is Step 1.3: Order Step 1.4: Sliding mode control law: Available Among them, k and δ are design parameters, and sgn s is the switching function of s; then Step 1.5: Thus inequality equation The solution is It can be seen that V(t) exponentially converges to 0, so The exponential convergence speed of and e(t) depends on k; the exponential term -ks can ensure that when s is larger, the system state can approach the sliding mode at a larger speed. 2. A sliding mode anti-disturbance control method for ozone concentration in garbage residual liquid sewage treatment equipment based on a time-delay nominal model according to claim 1, characterized in that the disturbance observer controls the system through controlled variables and system output. The disturbance is estimated, and the observed system disturbance is fed forward to the forward channel to suppress the interference and reduce the adverse impact of the interference on the controlled process. 3. A sliding mode anti-disturbance control method for ozone concentration in garbage residual liquid sewage treatment equipment based on a time-delay nominal model according to claim 1, characterized in that the low-pass filter in the disturbance observer is specifically implemented: Step 3.1: Since a phase lag that is too high in order will have an adverse effect on the system due to under-damping, the order κ of the low-pass filter is generally the relative order of G _p (s); Step 3.2: Q(s) is usually a low-pass filter. Adding a low-pass filter can filter the external noise interference caused by the actual system operation, and can convert the minimum phase inverse model of the control object into a true fraction; Among them, eta is the time constant of the filter, and κ is the order of the filter; Step 3.3: When the Q(s) static gain is 1, the disturbance estimate of the disturbance observer can be calculated