Elimination of loop oscillation caused by viscous fault of pneumatic control valve

Elimination of loop oscillation caused by viscous fault of pneumatic control valve

Circuit oscillation caused by viscosity of pneumatic control valve

Pneumatic control valve is the most frequently used executive component in the operating system, so the normal operation of its circuit is the key to ensure the scientific operation. However, according to the data of the national industrial survey, in China, only 30% of the industrial control circuit performance is within the standard range, while in the unqualified control circuit, 30% of the circuit oscillation is caused by the viscosity of the regulating valve. In general, the viscosity of the valve leads to the limit cycle of the circuit, so the amount of control is also in the fluctuation and transformation of the set value. Therefore, eliminating the influence of viscosity on the circuit can not only improve the quality of production, but also reduce operation waste and improve economic value, which also plays a role in promoting the daily operation of pneumatic control valve.

Valve stickiness refers to the nonlinear fault caused by the large static friction between the valve stem and the packing after the valve operates for a period of time. In today's system operation, the calculation method of most control loops still adopts the traditional PID control calculation method. In the PID control loop, the controller needs to spend more time on repeated adjustment to make it reach a certain set state. In this process, the controller will constantly change the direction. When there is a sticking fault on the circuit of a pneumatic control valve, the controller will change the direction, and the valve will further stick. This situation will continue until the output of the controller is greater than a certain value (s), and then the valve rod will produce a jump of a certain size (J) (refer to the figure below). In this process of reckless, deviation can hardly be avoided. In order to eliminate this deviation, the controller will change again, and the viscous fault will occur again, resulting in the dynamic oscillation of the control variable up and down at the set value. Therefore, PID is the main cause of numerical oscillation.

Elimination of circuit oscillation caused by viscosity of pneumatic control valve

In the traditional PI controller, when the controller develops and changes, the reason for the viscosity of the valve is that the output of the controller is too small. This shows that when the valve is viscous, the function of integral can be further changed to control and plan the input, so as to eliminate the influence of viscosity on the control loop. The value of the input rate of the controller has a great impact on the operation of the valve stem of the pneumatic control valve. When the valve stem is viscous, the large output rate of the controller can further help the valve stem run quickly, so as to get rid of the influence of viscosity. On the contrary, it can reduce a certain amount of output rate to ensure the normal operation of the pneumatic control valve. At the same time, the values of E (k) and EC (k) that affect the output rate will also have a different impact on the viscosity phenomenon. According to a number of experimental data, when the two are not equal to 0, it indicates that the control variable has not reached the specific set value and is still changing. Therefore, at this time, the valve stem does not have the viscosity phenomenon. When e (k) is not equal to 0 and EC (k) is equal to 0, its control amount has not changed while it has not reached the set value, so viscosity has occurred. When e (k) is equal to 0 and EC (k) is not equal to 0, the control quantity is still changing, so there is no viscosity. Finally, when the two are equal to 0 at the same time, the control amount reaches the set value, and there is no other change, so there is no viscosity.

To sum up, using the new model to fuzzy control the controller, so as to eliminate the loop oscillation phenomenon, we should first obtain the specific parameters through the traditional PI controller, then give the same parameters to the fuzzy controller, and finally rest the sticky loop through reasonable parameters, so as to finally achieve the goal of improving the working quality of the pneumatic control valve.