Instrumentation: [Weekly Question] Week 21 of 2011: How cascade control systems compensate for nonlinear characteristics
Thread Content
This post was last edited by narshi on 2012-12-1 17:57. Explain how a cascade control system compensates for nonlinear characteristics Answer: Industrial processes are generally nonlinear; changes in load can cause the operating point to shift, resulting in variations in the static gain. Such variations can be compensated for by adjusting the characteristics of the control valve, but this approach has significant limitations. The cascade control system possesses a certain degree of adaptability: when load changes cause the operating point to shift, the output of the main controller adjusts the set value for the secondary controller, and it is the secondary controller that adjusts the position of the control valve. The nonlinear characteristics present in the secondary loop may affect its gain when the operating point changes, which could lead to a decline in its control quality. However, once the secondary loop is closed, it functions as a proportional element whose gain is determined by the feedback mechanism and remains constant regardless of load changes, thereby improving the performance of the cascade system.
This post was last edited by denghl on 2012-12-21 at 21:04. Since cascade control systems possess a certain degree of adaptability, when changes in load cause the operating point of the controlled process to change, the output of the main controller adjusts the setpoint for the secondary controller; the secondary controller then adjusts the opening degree of the control valve. As a result, although the attenuation rate of the secondary loop changes, the overall attenuation rate of the system remains essentially unchanged.
This post was last edited by denghl on 2012-12-21 at 21:06. Reply to 1#: Industrial systems in Baghdad generally exhibit non-linearity; changes in load can cause the operating point to shift, resulting in variations in the static gain. Such variations can be compensated for by adjusting the characteristics of the control valves, but this approach has significant limitations. The cascade control system possesses a certain degree of adaptability: when load changes cause the operating point to shift, the output of the main controller adjusts the setpoint of the secondary controller, and it is the secondary controller that adjusts the position of the control valve. The nonlinear characteristics present in the secondary loop may affect its gain when the operating point changes, which could lead to a decline in its control quality. However, once the secondary loop is closed, it functions as a proportional element whose gain is determined by the feedback mechanism and remains unchanged regardless of load variations; as a result, the performance of the cascade system improves.
This post was last edited by denghl on 2012-12-21 at 21:07. Reply 1# Baghdad: In a cascade control system, the main regulator and the secondary regulator have different functions. The main regulator operates in fixed-value control, while the secondary regulator operates in follow-up control. The system has different requirements for the two circuits. The main circuit is generally required to have no error, and the control law for the main regulator should be PI or PID control ； The secondary loop requires rapid control, and a margin of error is acceptable; generally, a P-control law is used without introducing I or D control. If I control is introduced, it will prolong the control process and weaken the rapid control effect of the secondary loop ； There is also no need to introduce D-control, as the P-control used in the secondary loop already provides rapid control; introducing D-control would cause the control valve to move excessively, which is not conducive to the control of the entire system.
The linear requirement is met through multiple stages of parameter correction
This post was last edited by denghl on 2012-12-21 at 21:08. Reply to 1# Baghdad: Since the cascade control system has a certain degree of adaptability, when changes in load cause the operating point of the controlled process to change, the output of the main controller adjusts the set value for the secondary controller; the secondary controller then adjusts the opening degree of the control valve. As a result, although the attenuation rate of the secondary loop changes, the overall attenuation rate of the system remains essentially unchanged.
This post was last edited by denghl on 2012-12-21 at 21:09. Industrial systems are generally nonlinear; changes in load can cause the operating point to shift, resulting in variations in the static gain. Such variations can be compensated for by adjusting the characteristics of the control valves, but this approach has significant limitations. The cascade control system possesses a certain degree of adaptability: when load changes cause the operating point to shift, the output of the main controller adjusts the setpoint of the secondary controller, and it is the secondary controller that adjusts the position of the control valve. The nonlinear characteristics present in the secondary loop may affect its gain when the operating point changes, which could lead to a decline in its control quality. However, once the secondary loop is closed, it functions as a proportional element whose gain is determined by the feedback mechanism and remains unchanged regardless of load variations; as a result, the performance of the cascade system improves.
This post was last edited by denghl on 2012-12-21 at 21:10. Industrial systems generally exhibit non-linearity; changes in load can cause the operating point to shift, resulting in variations in the static gain. Such variations can be compensated for by adjusting the characteristics of the control valves, but this approach has significant limitations. The cascade control system possesses a certain degree of adaptability: when load changes cause the operating point to shift, the output of the main controller adjusts the setpoint of the secondary controller, and it is the secondary controller that adjusts the position of the control valve. The nonlinear characteristics present in the secondary loop may affect its gain when the operating point changes, which could lead to a decline in its control quality. However, once the secondary loop is closed, it functions as a proportional element whose gain is determined by the feedback mechanism and remains unchanged regardless of load variations; as a result, the performance of the cascade system improves.
This post was last edited by denghl on 2012-12-21 at 21:12. Industrial systems generally exhibit non-linearity; changes in load can cause the operating point to shift, resulting in variations in the static gain. Such variations can be compensated for by adjusting the characteristics of the control valves, but this approach has significant limitations. The cascade control system possesses a certain degree of adaptability: when load changes cause the operating point to shift, the output of the main controller adjusts the setpoint of the secondary controller, and it is the secondary controller that adjusts the position of the control valve. The nonlinear characteristics present in the secondary loop may affect its gain when the operating point changes, which could lead to a decline in its control quality. However, once the secondary loop is closed, it functions as a proportional element whose gain is determined by the feedback mechanism and remains unchanged regardless of load variations; as a result, the performance of the cascade system improves.
This post was last edited by denghl on 2012-12-21 at 21:14. Industrial systems generally exhibit non-linearity; changes in load can cause the operating point to shift, resulting in variations in the static gain. Such variations can be compensated for by adjusting the characteristics of the control valves, but this approach has significant limitations. The cascade control system possesses a certain degree of adaptability: when load changes cause the operating point to shift, the output of the main controller adjusts the setpoint of the secondary controller, and it is the secondary controller that controls the position of the control valve. The nonlinear characteristics present in the secondary loop may affect its gain when the operating point changes, which could lead to a decline in its control quality. However, once the secondary loop is closed, it functions as a proportional element whose gain is determined by the feedback mechanism and remains unchanged regardless of load variations; as a result, the performance of the cascade system improves
The characteristics of control valves include linear, equal percentage, parabolic, and cascade control; is there also a linear type?