Laminar mass flow control system based on feedforward compensation and cascade control

Abstract

This utility model belongs to the field of flow measurement and control technology, and discloses a laminar flow mass flow control system based on feedforward compensation and cascade control. In the system: the laminar flow element is equipped with low-pressure and high-pressure side detection ports; the low-pressure side detection port is connected to the low-pressure end of a pressure sensor and a differential pressure sensor, and the high-pressure side detection port is connected to the high-pressure end of the differential pressure sensor; the laminar flow element is connected to a regulating valve; the output end of the pressure sensor is connected to the input end of a feedforward compensation module; the output end of an A / D converter is connected to the input ends of the main controller and the secondary controller; the output end of the main controller is connected to the input end of the secondary controller; the output end of the feedforward compensation module is connected to the control end of the regulating valve; the output end of the secondary controller is connected to the control end of the regulating valve via a D / A converter. This utility model adopts feedforward compensation and cascade control technology, adding a pressure feedforward compensation module and a differential pressure secondary control loop, avoiding the problem of inaccurate flow accuracy in the control system caused by sudden changes in fluid pressure.

Description

Technical Field

[0001] This utility model belongs to the field of flow measurement and control technology, and specifically relates to a laminar flow quality flow control system based on feedforward compensation and cascade control. Background Technology

[0002] Laminar flow mass flow controllers or control systems are crucial components in many industrial control fields, significantly impacting the quality of numerous industrial products. For example, they are essential components of etching machines in chip manufacturing. However, in actual operation, sudden changes in fluid pressure, particularly gas pressure, within the pipeline (e.g., a malfunction or damage to a pressure reducing valve at the gas path) can lead to inaccurate flow control accuracy. In applications requiring high gas flow control precision, such as etching machines in chip manufacturing, inaccurate flow control can severely impact chip manufacturing quality, rendering the laminar flow mass flow controller or control system unusable. Therefore, it is necessary to minimize and avoid inaccuracies in flow control system accuracy caused by sudden changes in fluid pressure, especially gas pressure, to improve the accuracy, reliability, stability, and anti-interference capabilities of laminar flow mass flow controllers or control systems. Utility Model Content

[0003] The purpose of this invention is to provide a laminar mass flow control system based on feedforward compensation and cascade control. By adopting feedforward compensation and cascade control technology, a pressure feedforward compensation module and a differential pressure control loop are added to the laminar mass flow control system, which avoids the problem of inaccurate flow accuracy of the control system caused by sudden changes in fluid pressure, especially gas pressure.

[0004] To achieve the above objectives, this utility model provides the following technical solution: The laminar flow mass flow control system based on feedforward compensation and cascade control includes: a main controller, a feedforward compensation module, an A / D converter, a D / A converter, a secondary controller, a differential pressure sensor, a pressure sensor, laminar flow elements, and a regulating valve; The laminar flow element is equipped with a low-pressure side detection port and a high-pressure side detection port; the low-pressure side detection port is connected to the low-pressure end of the pressure sensor and the differential pressure sensor, and the high-pressure side detection port is connected to the high-pressure end of the differential pressure sensor; the laminar flow element is connected to a regulating valve; The output of the pressure sensor is connected to the input of the feedforward compensation module and the input of the A / D converter; the output of the differential pressure sensor is connected to the input of the A / D converter; the output of the A / D converter is connected to the input of the main controller and the input of the secondary controller; the output of the main controller is connected to the input of the secondary controller. The output of the feedforward compensation module is connected to the control terminal of the regulating valve; the output of the secondary controller is connected to the control terminal of the regulating valve via a D / A converter.

[0005] A further improvement of this invention is that it also includes a temperature sensor; the temperature sensor is used to measure the temperature of the fluid flowing through the laminar flow element; the output terminal of the temperature sensor is connected to the input terminal of the main controller.

[0006] A further improvement of this utility model is that it also includes a secondary controlled object; the secondary controller, D / A converter, regulating valve, secondary controlled object, differential pressure sensor and A / D converter constitute a secondary control loop.

[0007] A further improvement of this utility model is that it also includes a main controlled object; the main controller, the secondary control loop, the main controlled object, and the flow detector constitute the main control loop.

[0008] A further improvement of this invention is that the flow detector is composed of a temperature sensor, a pressure sensor, and a differential pressure sensor.

[0009] A further improvement of this utility model is that the input end of the feedforward compensation module is connected to the output end of the pressure sensor; the output end of the feedforward compensation module is connected to the control end of the regulating valve.

[0010] A further improvement of this utility model is that the output terminal of the feedforward compensation module and the output terminal of the D / A converter are both connected to the control terminal of the regulating valve.

[0011] A further improvement of this utility model is that it also includes a communication module; the main controller is connected to the communication module.

[0012] A further improvement of this invention is that it also includes a memory; the main controller is connected to the memory.

[0013] A further improvement of this utility model is that the temperature sensor is located at the inlet of the laminar flow element, and the regulating valve is located at the outlet of the laminar flow element. Alternatively, the temperature sensor may be located at the outlet of the laminar flow element, and the regulating valve may be located at the inlet of the laminar flow element; Alternatively, both the temperature sensor and the regulating valve may be located at the inlet of the laminar flow element; Alternatively, both the temperature sensor and the regulating valve may be located at the outlet of the laminar flow element.

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a laminar flow mass flow control system based on feedforward compensation and cascade control, comprising: a main controller, a feedforward compensation module, an A / D converter, a D / A converter, a secondary controller, a differential pressure sensor, a pressure sensor, a laminar flow element, and a regulating valve; the laminar flow element is provided with a low-pressure side detection port and a high-pressure side detection port; the low-pressure side detection port is connected to the low-pressure end of the pressure sensor and the differential pressure sensor, and the high-pressure side detection port is connected to the high-pressure end of the differential pressure sensor; the laminar flow element is connected to the regulating valve; the output end of the pressure sensor is connected to the input end of the feedforward compensation module and the input end of the A / D converter; the output end of the differential pressure sensor is connected to the input end of the A / D converter; the output end of the A / D converter is connected to the input end of the main controller and the input end of the secondary controller; the output end of the main controller is connected to the input end of the secondary controller; the output end of the feedforward compensation module is connected to the control end of the regulating valve; the output end of the secondary controller is connected to the control end of the regulating valve through the D / A converter. This invention employs feedforward compensation and cascade control technology to add a pressure feedforward compensation module and a differential pressure control loop to the laminar flow mass flow control system, thereby avoiding the inaccuracy of the control system's flow rate accuracy caused by sudden changes in fluid pressure, especially gas pressure.

[0015] Furthermore, this invention specifically incorporates feedforward compensation of the pressure signal and a secondary control loop with differential pressure as the controlled variable into the laminar flow mass flow control system through feedforward compensation and cascade control techniques. The feedforward compensation module of the pressure signal can quickly compensate for strong interference caused by sudden pressure changes, and the secondary control loop with differential pressure as the controlled variable can quickly compensate for the impact of sudden pressure changes on the differential pressure signal. By combining feedforward compensation and cascade control techniques, the inaccuracy of the flow rate accuracy of the control system caused by sudden changes in fluid pressure, especially gas pressure, is avoided, thus maintaining the high-precision operation of the laminar flow mass flow control system. This invention features strong anti-interference capability, high control accuracy, high reliability, and good stability in the laminar flow mass flow control system. Attached Figure Description

[0016] The accompanying drawings, which form part of this specification, are used to provide a further understanding of this utility model. The illustrative embodiments and descriptions of this utility model are used to explain this utility model and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the structure of a laminar mass flow control system based on feedforward compensation and cascade control, according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the flow detector according to an embodiment of the present invention; Figure 3 This is a block diagram illustrating the operational structure of a laminar mass flow control system based on feedforward compensation and cascade control, according to an embodiment of this utility model. In the attached diagram: 1 Main controller, 2 Communication module, 3 Memory, 4 Feedforward compensation module, 5 A / D converter, 6 D / A converter, 7 Sub-controller, 8 Differential pressure sensor, 9 Pressure sensor, 10 Temperature sensor, 11 First connecting pipe, 12 Second connecting pipe, 13 High-pressure side detection port, 14 Laminar flow element, 15 Low-pressure side detection port, 16 Regulating valve. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0018] The following detailed description is exemplary and intended to provide further detailed explanation of the present invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this invention is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this invention.

[0019] Please see Figures 1 to 3 As shown, this utility model embodiment provides a laminar flow mass flow control system based on feedforward compensation and cascade control, including a main controller 1, a communication module 2, a memory 3, a feedforward compensation module 4, an A / D converter 5, a D / A converter 6, a secondary controller 7, a temperature sensor 10, a first connecting pipe 11, a second connecting pipe 12, a laminar flow element 14, and a regulating valve 16. The input end of the feedforward compensation module 4 is connected to the output end of the pressure sensor 9, and the output end of the feedforward compensation module 4 is connected to the control end of the regulating valve 16. The input terminal of the secondary controller 7 is connected to the output terminal of the main controller 1 and the output terminal of the A / D converter 5; the output terminal of the secondary controller 7 is connected to the control terminal of the regulating valve 16 through the D / A converter 6. The flow detector consists of a temperature sensor 10, a pressure sensor 9, and a differential pressure sensor 8. The laminar flow element 14 is provided with a low-pressure side detection port 15 and a high-pressure side detection port 13; the high-pressure side detection port 13 is close to the inlet of the laminar flow element 14; the low-pressure side detection port 15 is close to the outlet of the laminar flow element 14. The low-pressure side detection port 15 is connected to the low-pressure end of the pressure sensor 9 and the differential pressure sensor 8, and the high-pressure side detection port 13 is connected to the high-pressure end of the differential pressure sensor 8; the inlet and outlet of the laminar flow element 14 are respectively connected to the second connecting pipe 12 and the regulating valve 16; the inlet of the second connecting pipe 12 is connected to the first connecting pipe 11; a temperature sensor 10 is provided on the first connecting pipe 11. The main controller 1 is connected to the communication module 2, the memory 3, the A / D converter 5, the secondary controller 7, and the temperature sensor 10; the input end of the A / D converter 5 is connected to the output end of the differential pressure sensor 8 and the output end of the pressure sensor 9; the output end of the A / D converter 5 is connected to the input end of the main controller 1 and the input end of the secondary controller 7.

[0020] The fluid flows sequentially through the first connecting pipe 11, the second connecting pipe 12, the laminar flow element 14, and the regulating valve 16. A temperature sensor 10 is installed on the first connecting pipe 11, and the signal from the temperature sensor 10 is sent to the main controller 1. The output signal of the secondary controller 7 is sent to the regulating valve 16 after passing through the D / A converter 6 to adjust the opening of the regulating valve 16.

[0021] The positions of temperature sensor 10 and regulating valve 16 can be interchanged.

[0022] In one specific embodiment, the first connecting pipe 11 and the temperature sensor 10 are located in front of the second connecting pipe 12, or between the laminar flow element 14 and the regulating valve 16.

[0023] In order to reduce and avoid the inaccuracy of the laminar flow mass flow control system caused by sudden changes in fluid pressure, especially gas pressure (e.g., failure or damage to the pressure reducing valve located at the front end of the gas path), and to improve the accuracy, stability, reliability and anti-interference capability of the laminar flow mass flow control system, this utility model adds a feedforward compensation module 4 and a differential pressure control loop to the laminar flow mass flow control system.

[0024] Please see Figure 3 As shown in the figure, the operating structure of a laminar flow mass flow control system based on feedforward compensation and cascade control according to an embodiment of the present invention includes: a main controller 1, a secondary controller 7, a D / A converter 6, a regulating valve 16, a secondary controlled object controller, a main controlled object controller, an A / D converter 5, a differential pressure sensor 8, a flow detector, a pressure sudden change interference channel, and a feedforward compensation module 4.

[0025] The secondary control loop consists of the secondary controller 7, D / A converter 6, regulating valve 16, secondary controlled object controller, differential pressure sensor 8, and A / D converter 5.

[0026] The main control loop consists of the main controller 1, the secondary control loop, the main controlled object controller, and the flow detector.

[0027] The main function of the secondary control loop is to make the differential pressure reach the set value, while the main function of the primary control loop is to make the flow rate reach the set value.

[0028] The input signal of the feedforward compensation module 4 is the pressure change signal from the pressure sensor 9, and the output is a compensation signal. This compensation signal is sent to the regulating valve 16. Its main function is to reduce or offset the influence of sudden changes in fluid pressure, especially gas pressure signal, on the flow rate. Under the strong interference of sudden changes in fluid pressure, especially gas pressure signal, the flow output value of the laminar flow mass flow control system can maintain good control accuracy to meet the usage requirements.

[0029] When the transfer function of the pressure change disturbance channel is The transfer function of regulating valve 16 is The transfer function of the secondary controlled object controller is Then the transfer function of feedforward compensation module 4 for: .

[0030] The pressure change interference channel is a "two-way input" circuit. Its input signal is the pressure change detection value of pressure sensor 9, and its output signal is the change in pressure difference caused by the pressure change.

[0031] Since the transfer functions of the pressure surge interference channel, the control valve 16, and the secondary controlled object controller are objectively known, the transfer function of the feedforward compensation module 4 can be calculated using the above formula. .

[0032] Once the transfer function of feedforward compensation module 4 is determined Then, based on the input signal, namely the pressure change signal from the pressure sensor 9, the output compensation signal of the feedforward compensation module 4 can be calculated.

[0033] The transfer function of the feedforward compensation module 4 reflects the characteristics of the feedforward compensation module 4. Its input signal is the pressure change signal. After passing through the transfer function, the output signal is generated, which is the compensation signal. The compensation signal is superimposed with the output signal of the D / A converter and acts on the valve together.

[0034] This utility model provides a control method for a laminar flow mass flow control system based on feedforward compensation and cascade control, comprising the following steps: When a sudden change in fluid pressure, especially gas pressure, causes a deviation between the flow rate setpoint and the actual flow rate detected, this flow rate deviation is sent to the main controller 1. The main controller 1 calculates and outputs a differential pressure setpoint. This setpoint is compared with the differential pressure detected by the differential pressure sensor 8 in the secondary control loop. The resulting differential pressure deviation is sent to the secondary controller 7. The secondary controller 7 calculates and outputs a control signal to the D / A converter 6. The D / A converter 6 converts the digital signal to an analog signal, which is then superimposed on the analog signal output by the feedforward compensation module 4 and sent to the regulating valve 16. Upon receiving this signal, the regulating valve 16 changes its valve opening and, via the secondary controlled object... The controller adjusts the differential pressure value. The differential pressure is superimposed on the output signal of the pressure sudden change interference channel. The superimposed differential pressure is detected by the differential pressure sensor 8 in the secondary control loop and converted into a digital value by the A / D converter 5 to obtain the differential pressure detection value. The differential pressure setpoint output by the main controller 1 is compared with the differential pressure detection value of the secondary control loop. The deviation is then sent to the secondary controller 7. The secondary controller 7 calculates and sends its output control signal to the D / A converter 6. The D / A converter 6 converts the digital value into an analog value, which is superimposed on the analog signal output by the feedforward compensation module 4 and sent to the regulating valve 16 to further adjust the differential pressure. This process is repeated until the differential pressure reaches the set value. When the differential pressure reaches the set value, the flow rate is further adjusted by the main controlled object controller, and the flow rate is detected to obtain the actual flow rate value. The flow rate setpoint is compared with the flow rate detection value, and the flow rate deviation is sent to the main controller 1. Through the secondary control loop and the main controlled object controller, the flow rate is further adjusted. This process is repeated until the flow rate reaches the set value. This effectively reduces or avoids the impact of strong pressure fluctuations on flow accuracy when fluid pressure, especially gas pressure, changes abruptly.

[0035] During the control process, the flow rate detection value is calculated from the detection values ​​of differential pressure sensor 8, pressure sensor 9, and temperature sensor 10 in the secondary control loop. Specifically: Volumetric flow rate under standard conditions It is calculated using the following formula (1): (1) In the above formula, Volumetric flow rate under standard conditions; Temperature, in degrees Celsius; The pressure at the low-pressure side detection port 15 detected by pressure sensor 9, in units of ; A coefficient related to temperature; , The coefficients are related to the laminar flow channel structure, and the units are... ; The dynamic viscosity of the gas is determined by... Confirmed, unit is ; A coefficient related to pressure;

[0036] The pressure difference between the low-pressure side detection port 15 and the high-pressure side detection port 13 detected by the differential pressure sensor 8; The beneficial effects of this invention are that it enables the laminar flow mass flow control system to have strong anti-interference ability, high control accuracy, high reliability and good stability.

[0037] This utility model embodiment provides a laminar flow mass flow control system based on feedforward compensation and cascade control. During operation, the specific details are as follows: When the flow rate setpoint is 20 liters / minute, and the fluid is nitrogen, the steady-state flow rate is 19.9999 liters / minute. The deviation between the steady-state flow rate and the setpoint is -0.0001 liters / minute, which is extremely small. At this time, the fluid temperature... t The temperature was 25.3℃, and the pressure detected by pressure sensor 9 was [missing information]. p The actual measured differential pressure value is 301 kPa, detected by differential pressure sensor 8. The pressure is 1.0002 kPa, and the system is operating normally. When the pressure reducing valve located at the front end of the gas path malfunctions or is damaged, the pressure... pWithin one second, the pressure changes abruptly from 301 kPa to 350.12 kPa. Without the feedforward compensation and cascade control technology described in this invention, the actual flow rate would abruptly change to 18.5521 liters / minute, far below the set flow rate of 20 liters / minute. When the feedforward compensation and cascade control technology of this invention is used, when pressure sensor 9 detects a pressure signal abruptly changing to 350.12 kPa, the main controller 1 calculates and outputs a differential pressure setpoint of 0.8616 kPa. At this time, the differential pressure detected by differential pressure sensor 8 in the secondary control loop, at 0.7992 kPa, is compared with the set differential pressure value. The deviation of -0.0624 kPa is sent to the secondary controller 7. The secondary controller 7 calculates and outputs a control signal value. The D / A converter converts the digital quantity into an analog voltage signal of 11.393V. This value is superimposed with the analog compensation value of 0.652V from the feedforward compensation module 4, resulting in an analog voltage signal of 12.045V. The signal V is sent to the regulating valve 16. After receiving the signal, the regulating valve 16 adjusts the differential pressure value by changing the valve opening and controlling the secondary controlled object controller. The differential pressure is superimposed on the output signal of the pressure change interference channel. The superimposed differential pressure is detected by the differential pressure sensor 8 in the secondary control loop and converted into a digital value by the A / D converter 5, resulting in a differential pressure value of 0.8608 kPa. The differential pressure detection value of 0.8608 kPa in the secondary control loop is compared with the differential pressure set value of 0.8616 kPa output by the main controller. The deviation of -0.0008 kPa is sent to the secondary controller 7. After calculation, the secondary controller 7 outputs a control signal value. The digital value is converted into an analog voltage signal of 11.405V by the D / A converter 6. This value is superimposed on the analog compensation value of 0.652V from the feedforward compensation module 4, resulting in an analog voltage signal of 12.057V, which is sent to the regulating valve 16 to further adjust the differential pressure. This process is repeated until the differential pressure reaches the set value of 0.8616 kPa. When the differential pressure reaches the set value, the flow rate is further adjusted by the main controlled object controller, and the flow rate is measured, resulting in a flow rate of 19.9999 liters / minute. The deviation between this flow rate of 19.9999 liters / minute and the set flow rate of 20 liters / minute is very small, with a deviation of -0.0001 liters / minute. This flow rate of 19.9999 liters / minute is the same as the stable output flow rate of 19.9999 liters / minute before the pressure jump, indicating that the flow rate was not affected by the pressure change. This demonstrates the strong anti-interference capability, high control accuracy, high reliability, and good stability of the flow control system.

[0038] The above-mentioned flow rate refers to the flow rate under standard conditions.

[0039] In one specific implementation, the primary controlled object controller and the secondary controlled object controller can each be regarded as a control system component with input and output; the input signal of the secondary controlled object controller is the valve opening degree, and the output signal is the differential pressure; the input signal of the primary controlled object controller is the differential pressure, and the output is the flow rate.

[0040] In one specific embodiment, in the laminar flow mass flow control system based on feedforward compensation and cascade control of this utility model, the main controller 1 and the auxiliary controller 7 can be PLC-type controllers or processors, and the feedforward compensation module 4 can be implemented using PLC-type controllers or analog signal circuits.

[0041] As is known from common technical knowledge, this utility model can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this utility model or its equivalents are included in this utility model.

Claims

1. A laminar mass flow control system based on feedforward compensation and cascade control, characterized in that, include: The main controller (1), feedforward compensation module (4), A / D converter (5), D / A converter (6), secondary controller (7), differential pressure sensor (8), pressure sensor (9), laminar flow element (14) and regulating valve (16). The laminar flow element (14) is provided with a low-pressure side detection port (15) and a high-pressure side detection port (13); the low-pressure side detection port (15) is connected to the low-pressure end of the pressure sensor (9) and the differential pressure sensor (8), and the high-pressure side detection port (13) is connected to the high-pressure end of the differential pressure sensor (8); the laminar flow element (14) is connected to the regulating valve (16). The output of the pressure sensor (9) is connected to the input of the feedforward compensation module (4) and the input of the A / D converter (5); the output of the differential pressure sensor (8) is connected to the input of the A / D converter (5); the output of the A / D converter (5) is connected to the input of the main controller (1) and the input of the secondary controller (7); the output of the main controller (1) is connected to the input of the secondary controller (7); The output of the feedforward compensation module (4) is connected to the control terminal of the regulating valve; the output of the secondary controller (7) is connected to the control terminal of the regulating valve through the D / A converter (6).

2. The laminar flow mass flow control system based on feedforward compensation and cascade control according to claim 1, characterized in that, It also includes a temperature sensor (10); the temperature sensor (10) is used to measure the temperature of the fluid flowing through the laminar flow element (14); the output of the temperature sensor (10) is connected to the input of the main controller (1).

3. The laminar flow mass flow control system based on feedforward compensation and cascade control according to claim 1, characterized in that, It also includes a secondary controlled object; the secondary controller (7), D / A converter (6), regulating valve (16), secondary controlled object, differential pressure sensor (8) and A / D converter (5) form a secondary control loop.

4. The laminar flow mass flow control system based on feedforward compensation and cascade control according to claim 3, characterized in that, It also includes the main controlled object; the main controller (1), the secondary control loop, the main controlled object, and the flow detector constitute the main control loop.

5. The laminar flow mass flow control system based on feedforward compensation and cascade control according to claim 4, characterized in that, The flow detector consists of a temperature sensor (10), a pressure sensor (9), and a differential pressure sensor (8).

6. The laminar flow mass flow control system based on feedforward compensation and cascade control according to claim 1, characterized in that, The output of the feedforward compensation module (4) and the output of the D / A converter (6) are connected together to the control terminal of the regulating valve (16).

7. The laminar flow mass flow control system based on feedforward compensation and cascade control according to claim 1, characterized in that, It also includes a communication module (2); the main controller (1) is connected to the communication module (2).

8. The laminar flow mass flow control system based on feedforward compensation and cascade control according to claim 1, characterized in that, It also includes a memory (3); the main controller (1) is connected to the memory (3).

9. The laminar flow mass flow control system based on feedforward compensation and cascade control according to claim 2, characterized in that, The temperature sensor (10) is located at the inlet of the laminar flow element (14), and the regulating valve is located at the outlet of the laminar flow element (14).

10. The laminar flow mass flow control system based on feedforward compensation and cascade control according to claim 2, characterized in that, The temperature sensor (10) is located at the outlet of the laminar flow element (14), and the regulating valve is located at the inlet of the laminar flow element (14). Alternatively, the temperature sensor (10) and the regulating valve are both located at the inlet of the laminar flow element (14); Alternatively, the temperature sensor (10) and the regulating valve are both located at the outlet of the laminar flow element (14).

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