Control method and system for controlling fluid flow based on distributed control system (DCS)

Abstract

The invention discloses a control method for controlling fluid flow based on a DCS (Distributed Control System). The control method comprises the following steps: acquiring a valve control signal sent by the DCS; the valve control signal is obtained by the DCS according to the actual detection flow of the pipeline and the set flow of the pipeline, and the valve control signal comprises a valve action signal, a valve adjusting speed signal and a valve adjusting direction signal; the valve action signal and the valve adjusting speed signal are determined according to the error between the actual detection flow of the pipeline and the set flow of the pipeline; the valve adjusting direction signal is obtained by comparing the actual detection flow of the pipeline with the set flow of the pipeline; the stepping motor is adjusted according to the valve control signal, and the stepping motor adjusts opening and closing of the valve so as to control the flow of fluid in the pipeline. The opening and closing speed of the valve is adaptively controlled through the error between the actual flow and the set flow, and the accuracy of the valve pipeline conveying flow is improved.

Description

Technical Field

[0001] The present invention relates to flow control technology, and in particular to a control system and method for controlling fluid flow based on a distributed control system (DCS). Background Art

[0002] The traditional flow control system consists of a control valve body, a valve controller, and a flow meter. The valve controller is a product used in conjunction with the valve electric device to control the opening and closing of the electric valve, and can achieve remote control of the electric valve in the control room. The operator inputs the action command through the electronic control system, and the control system then drives the mechanical device, which drives the valve stem to rotate through the transmission shaft to achieve the opening and closing operation of the valve. In the process of pipeline transportation, valves are key components for controlling the safe transportation of pipelines, and their role in the entire pipeline transportation process is particularly important. The control of the valve opening of the valve is the core of the entire valve control system, and the implementation of necessary valve position opening control is an urgent problem to be solved in the pipeline transportation industry.

[0003] Since the flow rate of the valve pipeline changes at every moment, the requirements for the change of valve opening during the transportation process are different. When using a fixed valve opening control speed to regulate different delivery flow rates, if the valve opening change speed is too large, the flow in the pipeline changes too much, resulting in a large gap between the actual flow and the target flow, and the accuracy of the valve pipeline delivery flow is low; if the valve opening change speed is too small, the time for the actual flow in the pipeline to reach the target flow is too long, which also makes the accuracy of the valve pipeline delivery flow low. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method and system for controlling fluid flow based on a distributed control system (DCS) to improve the accuracy of pipeline transportation flow.

[0005] Technical solution: The present invention adopts a control method for controlling fluid flow based on a distributed control system DCS to obtain a valve control signal sent by the DCS control system; the valve control signal is obtained by the DCS control system according to the actual pipeline detection flow and the pipeline set flow, and the valve control signal includes a valve action signal, a valve adjustment speed signal and a valve adjustment direction signal;

[0006] The valve action signal and the valve adjustment speed signal are determined according to the error between the actual detected flow rate of the pipeline and the set flow rate of the pipeline;

[0007] The valve adjustment direction signal is obtained by comparing the actual detected flow rate of the pipeline with the set flow rate of the pipeline;

[0008] The stepper motor is adjusted according to the valve control signal, and the stepper motor adjusts the opening and closing of the valve to control the flow rate of the fluid in the pipeline.

[0009] Furthermore, the valve control signal also includes a switch limit signal, which is obtained by a DCS control system according to the valve opening, and the valve action signal is cut off according to the switch limit signal.

[0010] Further, the valve action signal is determined according to the error between the actual detected flow rate of the pipeline and the set flow rate of the pipeline, specifically including:

[0011] Calculate the difference between the actual detected flow rate of the pipeline and the set flow rate of the pipeline;

[0012] The calculated difference is converted into an absolute value as an adjustment error;

[0013] The adjustment error is compared with the set accuracy, and a valve action signal is output when the adjustment error is greater than the set accuracy.

[0014] Further, the valve adjustment speed signal is determined according to the error between the actual detected flow rate of the pipeline and the set flow rate of the pipeline, specifically including:

[0015] Calculate the difference between the actual detected flow rate of the pipeline and the set flow rate of the pipeline;

[0016] The calculated difference is converted into an absolute value as an adjustment error;

[0017] Calculate the ratio between the regulation error and the pipeline set flow rate;

[0018] The ratio is compared with the set proportion. When the ratio is greater than or equal to the set proportion, a valve fast adjustment signal is output; when the ratio is less than the set proportion, a valve slow adjustment signal is output.

[0019] Furthermore, the valve adjustment direction signal obtained by comparing the actual pipeline detection flow rate with the pipeline set flow rate specifically includes:

[0020] The actual detected flow rate of the pipeline is compared with the set flow rate of the pipeline. When the actual detected flow rate of the pipeline is greater than the set flow rate of the pipeline, a signal to close the valve is output; when the actual detected flow rate of the pipeline is less than the set flow rate of the pipeline, a signal to open the valve is output.

[0021] The present invention also adopts a control system for controlling fluid flow based on a distributed control system DCS, including a DCS control system, a flow meter, a valve control box, and a stepper motor driven control valve; the stepper motor driven control valve includes a stepper motor and a valve adjusted by the stepper motor;

[0022] The DCS control system is connected to the valve control box, the DCS control system obtains data collected in real time by the valve control box, and sends a valve control signal to the valve control box;

[0023] The valve control box is used to obtain the actual detection flow of the pipeline collected by the flow meter, and is also used to adjust the stepper motor according to the received valve control signal. The stepper motor adjusts the opening and closing of the valve to control the fluid flow in the pipeline.

[0024] Furthermore, the valve control box is also used to obtain the valve opening and feed the valve opening back to the DCS control system. The DCS control system obtains a switch limit signal according to the valve opening and cuts off the valve action signal according to the switch limit signal.

[0025] Furthermore, the valve control box includes an input and output module, an intermediate relay K1, an intermediate relay K2, a stepper motor control module, a stepper motor driver, and a valve motor. The input and output module includes a first DCS start control port and a second DCS start control port. The input end of the intermediate relay K1 is electrically connected to the first DCS start control port, the output end of the intermediate relay K1 is electrically connected to the stepper motor control module, the input end of the intermediate relay K2 is electrically connected to the second DCS start control port, the output end of the intermediate relay K2 is electrically connected to the stepper motor control module, the stepper motor control module is electrically connected to the stepper motor driver, and the stepper motor driver is electrically connected to the valve motor. The DCS control system sends control signals to the intermediate relay K1 and the intermediate relay K2 through the first DCS start control port and the second DCS start control port. The intermediate relays K1 and the intermediate relays K2 output control signals to the stepper motor control module, and the motor control module controls the stepper motor driver to operate the valve motor.

[0026] Furthermore, the valve control box also includes an intermediate relay K3, an intermediate relay K4, and a valve body limit switch, and the input-output module also includes a DCS closing limit port and a DCS opening limit port. The input end of the intermediate relay K3 is electrically connected to the valve body limit switch and the stepper motor control module, and the output end of the intermediate relay K3 is connected to the DCS opening limit port; the input end of the intermediate relay K4 is electrically connected to the valve body limit switch and the stepper motor control module, and the output end of the intermediate relay K4 is connected to the DCS closing limit port; the valve body limit switch is used to detect the extreme position signal of the valve, and feed the signal back to the DCS control system through the intermediate relay K3 and the intermediate relay K4 from the DCS opening limit port and the DCS closing limit port.

[0027] Furthermore, the valve control box also includes a valve body opening feedback signal module, and the input-output module also includes a DCS valve opening collection port. The valve body opening feedback signal module is electrically connected to the DCS valve opening collection port of the input-output module. The valve body opening feedback signal module is used to collect the valve opening and feed back the valve opening from the DCS valve opening collection port to the DCS control system.

[0028] Beneficial effects: Compared with the prior art, the advantages of the present invention are: the speed of valve opening and closing is adaptively controlled by the size of the error between the actual flow rate and the set flow rate, thereby improving the accuracy of the flow rate delivered by the valve pipeline. By combining the control unit, the detection unit, and the execution unit together, a complete PID closed-loop control model is formed, which meets the accuracy of equipment control of 0.1 and meets the process requirements of the paper machine; the program is simplified, the failure rate is lower, and a limit protection interlock is provided, which provides good protection for the operation of the equipment; in addition, it is easy to maintain, the accessories are universal and modular, and the replacement is convenient, and spare parts can be shared with the high-pressure spray system; the cost of the entire equipment is reduced to 6,000. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the flow control system in the present invention;

[0030] Figure 2 It is a flow chart of the control method in the present invention;

[0031] Figure 3 It is a control logic schematic diagram of the DCS control system in the present invention;

[0032] Figure 4 It is a schematic diagram of the principle of the control system in the present invention;

[0033] Figure 5 This is a circuit wiring diagram inside the valve control box of the present invention. DETAILED DESCRIPTION

[0034] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] like Figure 1 As shown, in this embodiment, a control system based on a distributed control system DCS controls fluid flow, including a stepper motor driven control valve, a valve control box, a flow meter, and a DCS control system. The stepper motor driven control valve includes a stepper motor and a valve regulated by the stepper motor, such as Figure 2As shown in the figure, the distributed control system (DCS) sets the required fluid flow rate, and transmits the control signal to the valve control box through the control program programming operation comparison. The valve control box converts the received control signal into a control signal that can be received by the control valve. The valve performs corresponding opening or closing actions, thereby affecting the flow rate of the flow in the pipeline. The flow change is detected by the flow meter, and the real-time flow is transmitted to the valve control box, and then converted into a signal that can be received by the DCS control system. The DCS compares the received flow signal with the set value, adjusts the control signal, and sends it to the valve control box. This cycle repeats to form a perfect closed-loop control system until the fluid flow in the pipeline reaches the set value of the DCS control system and the valve stops.

[0036] like Figure 3 As shown, the control logic of the distributed control system DCS is:

[0037] Step 1: First, set the set flow rate of the pipeline. The DCS control system obtains the actual detection flow rate of the pipeline, and calculates the difference between the actual detection flow rate of the pipeline and the set flow rate of the pipeline. After calculating the difference, it is converted into an absolute value as the adjustment error. The adjustment error e is compared with the set accuracy. The smaller the set accuracy is, the higher the accuracy is. It is evaluated according to the actual flow meter range. For example, if the flow meter range is 0-5000, then when the error is set to 5, the control accuracy is 5 / 5000=0.001, that is, the accuracy is 1‰, and the accuracy is set to 1% based on the existing equipment. When the adjustment error e> set accuracy, the flow rate in the pipeline needs to be adjusted, and the DCS control system outputs a valve action signal, otherwise the DCS control system does not output a control signal.

[0038] Step 2: After outputting the valve action signal, the valve action speed is determined. The DCS control system calculates the ratio between the adjustment error and the pipeline set flow rate, and compares the ratio with the set proportion. In this embodiment, the set proportion is set to 1%. When the ratio is greater than or equal to the set proportion of 1%, it means that when the adjustment error exceeds 1% of the pipeline set flow rate, a fast adjustment signal is output. When the ratio is less than or equal to the set proportion of 1%, it switches to a slow adjustment signal, that is, the fine-tuning mode.

[0039] Step 3: After determining the valve action and speed, compare the actual flow rate of the pipeline with the set flow rate of the pipeline. When the actual flow rate of the pipeline is greater than the set flow rate of the pipeline, output a signal to close the valve; when the actual flow rate of the pipeline is less than the set flow rate of the pipeline, output a signal to open the valve. In addition, the valve opening and closing limit switch signals are introduced to prevent damage to the valve control mechanism. When the valve is opened to 100%, the valve opening direction signal output is cut off by the module. When the valve is closed to 0%, the valve closing direction signal output is cut off by the module.

[0040] like Figure 4 As shown in the figure, the control principle of the valve control box is as follows: the stepper motor control module receives the control command of the distributed control system (DCS), including three control signals HV, F / L, and DIR, which are valve action signal, valve adjustment speed signal, and valve adjustment direction signal. After the three signals are analyzed by the stepper motor control module, the control signal is transmitted to the stepper motor driver. The stepper motor driver performs the corresponding action of the valve according to the control command of the stepper motor control module. The two limit signal feedbacks of 0% and 100% of the opening are directly fed back to the distributed control system (DCS) to determine whether the valve is opened to the maximum or closed to the minimum. Then, the distributed control system (DCS) makes a logical judgment to disconnect the valve action signal and stop the valve from moving, so as to avoid overheating and damage of the drive unit caused by excessive operation of the valve.

[0041] like Figure 5 As shown, the valve control box includes an input and output module, an intermediate relay module, a stepper motor control module, a stepper motor driver, a valve motor, a valve body limit switch, a valve body opening feedback signal module and a power supply module.

[0042] The input and output module is used to receive external input signals and output control signals, including a first DCS start control port, a second DCS start control port, a DCS valve opening acquisition port, a DCS close limit port and a DCS open limit port. In this embodiment, the input module uses an external wiring terminal.

[0043] The intermediate relay module includes a first intermediate relay K1, a second intermediate relay K2, a third intermediate relay K3 and a fourth intermediate relay K4.

[0044] The input end of the intermediate relay K1 is electrically connected to the first DCS start control port, the output end of the intermediate relay K1 is electrically connected to the stepper motor control module, the input end of the intermediate relay K2 is electrically connected to the second DCS start control port, the output end of the intermediate relay K2 is electrically connected to the stepper motor control module, the stepper motor control module is electrically connected to the stepper motor driver, the stepper motor driver is electrically connected to the valve motor, the DCS control system sends control signals to the intermediate relay K1 and the intermediate relay K2 through the first DCS start control port and the second DCS start control port, the intermediate relay K1 and the intermediate relay K2 output control signals to the stepper motor control module, and the motor control module controls the stepper motor driver to operate the valve motor.

[0045] The input end of the intermediate relay K3 is electrically connected to the valve body limit switch and the stepper motor control module, and the output end of the intermediate relay K3 is connected to the DCS open limit port; the input end of the intermediate relay K4 is electrically connected to the valve body limit switch and the stepper motor control module, and the output end of the intermediate relay K4 is connected to the DCS closed limit port; the valve body limit switch is used to detect the extreme position signal of the valve, and feed the signal back to the DCS control system through the intermediate relay K3 and the intermediate relay K4 from the DCS open limit port and the DCS closed limit port.

[0046] The valve body opening feedback signal module is electrically connected to the DCS valve opening acquisition port of the input and output module. The valve body opening feedback signal module is used to collect the valve opening and feed back the valve opening from the DCS valve opening acquisition port to the DCS control system.

[0047] The power supply module includes a 24V switching power supply that mainly provides power to the stepper motor control module and a 220V transformer that mainly provides power to the stepper motor driver.

Claims

1. A method for controlling fluid flow based on a distributed control system DCS, characterized in that: Obtaining a valve control signal sent by a DCS control system; the valve control signal is obtained by the DCS control system according to the actual detected flow rate of the pipeline and the set flow rate of the pipeline, and the valve control signal includes a valve action signal, a valve adjustment speed signal and a valve adjustment direction signal; The valve action signal and the valve adjustment speed signal are determined according to the error between the actual detected flow rate of the pipeline and the set flow rate of the pipeline; The valve adjustment direction signal is obtained by comparing the actual detected flow rate of the pipeline with the set flow rate of the pipeline; The stepper motor is adjusted according to the valve control signal, and the stepper motor adjusts the opening and closing of the valve to control the flow rate of the fluid in the pipeline.

2. The control method according to claim 1, characterized in that: The valve control signal also includes a switch limit signal, which is obtained by the DCS control system according to the valve opening, and the valve action signal is cut off according to the switch limit signal.

3. The control method according to claim 1, characterized in that: The valve action signal obtained according to the error between the actual pipeline detection flow and the pipeline set flow includes: Calculate the difference between the actual detected flow rate of the pipeline and the set flow rate of the pipeline; The calculated difference is converted into an absolute value as an adjustment error; The adjustment error is compared with the set accuracy, and a valve action signal is output when the adjustment error is greater than the set accuracy.

4. The control method according to claim 1, characterized in that: The valve adjustment speed signal is determined based on the error between the actual pipeline detection flow and the pipeline set flow, including: Calculate the difference between the actual detected flow rate of the pipeline and the set flow rate of the pipeline; The calculated difference is converted into an absolute value as an adjustment error; Calculate the ratio between the regulation error and the pipeline set flow rate; The ratio is compared with the set proportion. When the ratio is greater than or equal to the set proportion, a valve fast adjustment signal is output; when the ratio is less than the set proportion, a valve slow adjustment signal is output.

5. The control method according to claim 1, characterized in that: The valve adjustment direction signal obtained by comparing the actual pipeline detection flow rate with the pipeline set flow rate includes: The actual detected flow rate of the pipeline is compared with the set flow rate of the pipeline. When the actual detected flow rate of the pipeline is greater than the set flow rate of the pipeline, a signal to close the valve is output; when the actual detected flow rate of the pipeline is less than the set flow rate of the pipeline, a signal to open the valve is output.

6. A control system using the control method according to any one of claims 1 to 5, characterized in that: It includes a DCS control system, a flow meter, a valve control box, and a stepper motor driven control valve; the stepper motor driven control valve includes a stepper motor and a valve adjusted by the stepper motor; The DCS control system is connected to the valve control box, the DCS control system obtains data collected in real time by the valve control box, and sends a valve control signal to the valve control box; The valve control box is used to obtain the actual detection flow of the pipeline collected by the flow meter, and is also used to adjust the stepper motor according to the received valve control signal. The stepper motor adjusts the opening and closing of the valve to control the fluid flow in the pipeline.

7. The control system according to claim 6, characterized in that: The valve control box is also used to obtain the valve opening and feed the valve opening back to the DCS control system. The DCS control system obtains a switch limit signal according to the valve opening and cuts off the valve action signal according to the switch limit signal.

8. The control system according to claim 7, characterized in that: The valve control box includes an input-output module, an intermediate relay K1, an intermediate relay K2, a stepper motor control module, a stepper motor driver, and a valve motor. The input-output module includes a first DCS startup control port and a second DCS startup control port. The input end of the intermediate relay K1 is electrically connected to the first DCS startup control port, the output end of the intermediate relay K1 is electrically connected to the stepper motor control module, the input end of the intermediate relay K2 is electrically connected to the second DCS startup control port, the output end of the intermediate relay K2 is electrically connected to the stepper motor control module, the stepper motor control module is electrically connected to the stepper motor driver, and the stepper motor driver is electrically connected to the valve motor. The DCS control system sends control signals to the intermediate relay K1 and the intermediate relay K2 through the first DCS startup control port and the second DCS startup control port. The intermediate relays K1 and the intermediate relays K2 output control signals to the stepper motor control module, and the motor control module controls the stepper motor driver to operate the valve motor.

9. The control system according to claim 8, characterized in that: The valve control box also includes an intermediate relay K3, an intermediate relay K4, and a valve body limit switch. The input and output module also includes a DCS closing limit port and a DCS opening limit port. The input end of the intermediate relay K3 is electrically connected to the valve body limit switch and the stepper motor control module, and the output end of the intermediate relay K3 is connected to the DCS opening limit port; the input end of the intermediate relay K4 is electrically connected to the valve body limit switch and the stepper motor control module, and the output end of the intermediate relay K4 is connected to the DCS closing limit port; the valve body limit switch is used to detect the extreme position signal of the valve, and feed the signal back to the DCS control system through the intermediate relay K3 and the intermediate relay K4 from the DCS opening limit port and the DCS closing limit port.

10. The control system according to claim 9, characterized in that: The valve control box also includes a valve body opening feedback signal module, and the input-output module also includes a DCS valve opening acquisition port. The valve body opening feedback signal module is electrically connected to the DCS valve opening acquisition port of the input-output module. The valve body opening feedback signal module is used to collect the valve opening and feed back the valve opening from the DCS valve opening acquisition port to the DCS control system.

Images