Effects of the Proportional, Integral, and Derivative Components of the PID Algorithm on the System Response.Primary Software: LabVIEW Toolkits>>PID Control ToolkitPrimary Software Version: 6.0 Primary Software Fixed Version: N/A Secondary Software: N/A
Problem: I want to use the PID VI in my closed-loop control application and I need to know the effect of each component on the system response. Solution: The Proportional-Integral-Derivative (PID) Algorithm is the most common control algorithm used in industry. In PID control, the algorithm computes the desired Actuator Output by calculating proportional, integral, and derivative responses and summing those three components to compute the Output. Therefore, understanding the effect of each PID component is very important in tuning PID controllers. Proportional Effect : The proportional component depends only on the Error, which is the difference between the Set Point and the Process Variable. The Proportional gain (Kc) determines the ratio of Output response to the Error. For instance, if the Error signal has a magnitude of 10, a Proportional Gain of 5 would produce a proportional response of 50. In general, increasing the Proportional Gain will increase the speed of the control system response and also decrease the steady-state error which is the final difference between Process variable and Set Point. However, if the Proportional Gain is too large the Process Variable will begin to oscillate. If Kc is increased further, the oscillations will become larger and the system will become unstable. Integral Effect : The Integral components integrates the Error over time to overcome the steady-state error. Therefore, the integral response will continually increase over time unless the Error is zero. However, the integral action may cause overshoot, oscillation, and/or instability problems if the selected integral gain (Ti) is too small. Note that smaller values of Ti will have a stronger integral effect on the system response. Derivative Effect : The derivative part of the PID algorithm anticipates future behavior of the Error because the response of the derivative component is proportional to the rate of change of the Error. Therefore, in general the derivative action prevents overshoot and eliminates oscillations. On the other hand, most practical control systems use very small derivative gain (Td) because the derivative response is highly sensitive to noise in the Process Variable signal. If the sensor feedback signal which represents the Process Variable is noisy, the derivative component can make the control system unstable. Please refer to the PID Control Toolset User Manual linked below for more information. Related Links: LabVIEW PID Control Toolset for Windows PID Control of Continuous Processes. Closed-Loop Control System FieldPoint PID Interactive Tutorial. Advanced Features in PID Tuning Attachments:
Report Date: 03/25/2003 Last Updated: 08/24/2007 Document ID: 2VO9SEVS |
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