Seeking help with methods for tuning PID parameters!

For temperature-controlled, pressure-controlled, and fluid-controlled valves, there are no standard values for the PID parameters; instead, a deviation is given and its changes are observed, with the parameter values determined based on experience. But those that use DCS seem to come with a small software program that can automatically tune the PID parameters. I’m not an expert in self-control; I don’t understand it very well.

This post was last edited by Linlang08 on 2009-11-30 at 21:45. As long as one has a clear understanding of the functions of a PID, it becomes possible to develop strategies for tuning the PID specifically. Additionally, tuning is divided into theoretical calculation-based methods and engineering-based tuning methods. The approach used by experienced practitioners in reality is generally the engineering-based tuning method, which is quite practical based on experience. Proportional (P) control: Proportional control is the simplest form of control. The output of its controller is proportional to the input error signal. When only proportional control is used, there is a steady-state error in the system output. Integral (I) control: In integral control, the output of the controller is proportional to the integral of the input error signal. For an automatic control system, if there is a steady-state error after it reaches steady state, then such a system is said to have a steady-state error, or simply to be a system with error. To eliminate this steady-state error, an \"integral term\" is introduced into the controller. The integral term represents the time-dependent integration of the error, and as time increases, this integral term grows. In this way, even if the error is small, the integral term increases over time; it drives the output of the controller to increase, thereby further reducing the steady-state error until it becomes zero. Therefore, a proportional-plus-integral (PI) controller enables the system to have no steady-state error after reaching steady state. Differential (D) control: In differential control, the output of the controller is proportional to the derivative of the input error signal (i.e., the rate of change of the error). Automatic control systems may experience oscillations or even instability during the process of correcting errors. The reason is that the effect of error suppression always lags behind the changes in the error. The solution is to make the change in the error-suppression effect \"lead,\" that is, when the error approaches zero, the error-suppression effect should be zero. In other words, it is often not sufficient to include only the \"proportional\" term in the controller; the function of this term is merely to amplify the magnitude of the error. What is needed now is the addition of a \"derivative\" term, which can predict the trend of error changes. Thus, a controller with both proportional and derivative elements can bring the control action to zero, or even to a negative value, in advance, thereby preventing severe overshoot of the controlled variable. Therefore, for controlled objects with high inertia or lag, a proportional-plus-differential (PD) controller can improve the dynamic characteristics of the system during the regulation process. ------------------------------------------- PID is an abbreviation for Proportional, Integral, and Derivative. The proportional control mechanism responds in proportion to the system’s deviation; as soon as a deviation occurs, proportional control takes action to reduce that deviation. A large proportional gain can accelerate regulation and reduce errors, but an excessive proportionality value reduces the stability of the system, and may even lead to its instability. Integral control function: It enables the system to eliminate steady-state error and improve accuracy. Due to errors, integral regulation is carried out until no error remains, at which point it stops; the output of integral regulation becomes a constant value. The strength of the integration effect depends on the integration time constant Ti; the smaller Ti is, the stronger the integration effect. Conversely, a larger Ti value results in a weaker integral effect; the addition of integral control can reduce system stability and slow down the dynamic response. Integral action is often combined with the other two control laws to form a PI controller or a PID controller. Differential control action: The differential effect reflects the rate of change of the system’s error signal; it has predictive capabilities, allowing it to anticipate the trend in error changes. As a result, it enables proactive control, eliminating the error before it even arises. Therefore, the dynamic performance of the system can be improved. By selecting an appropriate differential time, overshoot can be reduced, as well as the settling time. Differential action amplifies noise interference; therefore, excessive differential adjustment is detrimental to the system’s resistance to interference. Furthermore, a differential reaction is the rate of change, and when there is no change in the input, the output of the differential operation is zero. Differential action cannot be used alone; it needs to be combined with the other two control mechanisms to form PD or PID controllers. ◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎◎ The methods used in practice are generally known as engineering tuning methods. They rely primarily on engineering experience, are applied directly during the testing of control systems, and are simple and easy to master, which is why they are widely used in practical engineering applications. The engineering tuning methods for PID controller parameters mainly include the critical ratio method, the response curve method, and the attenuation method. The three methods each have their own characteristics, and what they all have in common is that experiments are conducted first, followed by the tuning of controller parameters using engineering experience formulas. However, the controller parameters obtained using either method require final adjustment and refinement during actual operation. The critical ratio method is generally used nowadays. The steps for tuning the PID controller parameters using this method are as follows: (1) First, pre-select a sufficiently short sampling period for the system to operate ； (2) Only a proportional control element is added, until the system exhibits critical oscillation in its step response to the input; at that point, the proportional gain and the critical oscillation period are recorded ； (3) The parameters of the PID controller are calculated using formulas under a certain degree of control. In actual debugging, one can only first set a rough empirical value and then adjust it based on the results. For temperature systems: P (%): 20–60, I (minutes): 3–10, D (minutes): 0.5–3. For flow rate systems: P (%): 40–100, I (minutes): 0.1–1. For pressure systems: P (%): 30–70, I (minutes): 0.4–3. For level systems: P (%): 20–80, I (minutes): 1–5

What is gain? Proportionality coefficient?

Adjust the parameters to find the optimal setting, checking in ascending order. Start with the proportional element, then add the integral element, and finally add the derivative element. If the curve oscillates frequently, increase the value of the proportional gain; if the curve wanders around in large loops, decrease the proportional gain. If the curve takes a long time to return to its normal position, reduce the integral time; if the curve has long fluctuation cycles, extend the integral time further. If the oscillation frequency of the curve is high, first reduce the derivative value. Large errors lead to slow fluctuations. The differential time should be increased; the two waves of the ideal curve are high at the beginning and low at the end, in a 4:1 ratio (expansion response curve method). Observe, adjust, and analyze thoroughly – adjusting the quality will not result in a decline

How to set and adjust PID parameters http://bbs.hcbbs.com/thread-545397-1-1.html