How to debug PID parameters?

I searched on the forum, but there are only some simple methods without clear examples, which is very difficult for newbies. Please give me some advice! Thanks! ! :handshake

It determines the proportional coefficient, integral time and differential time of the PID controller based on the characteristics of the controlled process. There are many methods for tuning PID controller parameters, which can be summarized into two categories:: The first is the theoretical calculation and setting method. It is mainly based on the mathematical model of the system and determines the controller parameters through theoretical calculations. The calculation data obtained by this method may not be directly used, and must be adjusted and modified through actual engineering. The second is the engineering tuning method, which mainly relies on engineering experience and is carried out directly in the test of the control system. The method is simple and easy to master, and is widely used in engineering practice. The engineering tuning methods of PID controller parameters mainly include critical proportion method, response curve method and attenuation method. Each of the three methods has its own characteristics, but what they have in common is that the controller parameters are adjusted through experiments and then according to engineering experience formulas. However, no matter which method is used, the controller parameters obtained need to be finally adjusted and improved in actual operation. Nowadays, the critical proportion method is generally used. The steps to use this method to tune the parameters of the PID controller are as follows:: (1) First, pre-select a sampling period that is short enough for the system to work. ； (2) Only add proportional control links until critical oscillation occurs in the system's step response to the input. Record the proportional amplification coefficient and critical oscillation period at this time. ； (3) Under a certain degree of control, the parameters of the PID controller are calculated through formulas. In actual debugging, one can only roughly set an experience value first, and then modify it according to the adjustment effect. For temperature system: P (%) 20--60, I (min) 3--10, D (min) 0.5--3 for flow system: P (%) 40--100, I (minutes) 0.1--1 for pressure systems: P (%) 30--70, I (min) 0.4--3 for liquid level system: P (%) 20--80, I (minutes) 1--5. Find the best parameter setting. Check the proportion first and then the integral in order from small to large. Finally, add the differential to the curve. The oscillation is very frequent. The proportional dial should be enlarged and the curve will float around the bay. When the proportional dial is small, the curve deviates and the recovery is slow. When the integration time goes downward, the wave fluctuation period of the curve is long. If the integration time is extended, the frequency of the curve oscillation is fast. Lower the differential first and the dynamic difference will be large to slow down the wave. The differential time should be lengthened for the two waves of the ideal curve, with the front high and the back low 4 to 1. If you look at the second tone and analyze it more, the quality of the adjustment will not be low.

Nowadays, each DCS has its own self-tuning function. As long as the self-tuning function block is required when purchasing the DCS, the PID self-tuning function can generally be realized quickly.

There are mainly three types of DCS used. The meaning of their proportion P and the PID parameter setting operation authority are slightly different.: 1. Yokogawa Electric’s DCS models mainly include: CENTUM-XL ； μXL ； CUNTUM ； CS-3000, etc., for their PID parameter setting, just press the adjustment screen professional button to bring up the PID parameter setting screen, and the operating authority belongs to the operator. 2. The DCS models of Foxboro Company are mainly I/A series. Their PID parameter setting operation authority is generally configured at the squad leader level. It is necessary to set the "key key" to the middle squad leader position to change the PID parameters. You can also ask the instrument personnel to configure the PID parameter setting operation authority at the operator level, so that the operator can easily modify the PID parameters. 3. Honeywell’s DCS models mainly include: TDC-3000 ； TPS etc. Their PID parameter setting operation permissions are generally configured at the squad leader level, and the "key key" needs to be set to the middle squad leader position to change the PID parameters. You can also ask the instrument personnel to configure the PID parameter setting operation authority at the operator level, so that the operator can easily modify the PID parameters. Another thing to note is that for Honeywell's DCS system, their proportional action parameters do not use the concept of proportion P, but the concept of amplification K. Please note that the value setting is not a percentage, but a decimal place. :)

1. PID debugging steps There is no control algorithm that is more effective and convenient than the PID adjustment rule. Some of the more fashionable regulators nowadays are basically derived from PID. It can even be said that: Is the PID regulator based on other control and regulation algorithms? 　　Why is PID used so widely and enduring for a long time? Because PID solves the most basic problems that automatic control theory needs to solve, namely the stability, rapidity and accuracy of the system. By adjusting the parameters of the PID, the load capacity and interference immunity of the system can be taken into account under the premise of system stability. At the same time, by introducing an integral term in the PID regulator, the system adds a zero integral point, making it a first-order or higher-order system, so that the steady-state error of the system's step response is zero. 　　Since the controlled objects of the automatic control system vary widely, the parameters of the PID must also change accordingly to meet the performance requirements of the system. This brings considerable trouble to users, especially beginners. The following is a brief introduction to the general steps for debugging PID parameters.: 　　1． Negative feedback automatic control theory is also called negative feedback control theory. First check the system wiring to confirm that the feedback of the system is negative feedback. For example, in a motor speed control system, the input signal is positive. When the motor is required to rotate forward, the feedback signal is also positive (in PID algorithm, error = input - feedback). At the same time, the higher the motor speed, the greater the feedback signal. The same method applies to other systems. 　　2． General principles of PID debugging a. When the output does not oscillate, increase the proportional gain P. 　　b. When the output does not oscillate, reduce the integration time constant Ti. 　　c. When the output does not oscillate, increase the differential time constant Td. 　　3． General steps a. Determine the proportional gain P. When determining the proportional gain P, first remove the integral term and differential term of the PID. Generally, Ti=0, Td=0 (see the PID parameter setting instructions for details), so that the PID is a purely proportional adjustment. The input is set to 60%~70% of the maximum value allowed by the system, and the proportional gain P is gradually increased from 0 until the system oscillates. ； In turn, the proportional gain P at this time gradually decreases until the system oscillation disappears. Record the proportional gain P at this time and set the PID proportional gain P to 60% to 70% of the current value. The proportional gain P debugging is completed. 　　b. Determine the integration time constant Ti. After the proportional gain P is determined, set a larger initial value of the integration time constant Ti, then gradually decrease Ti until the system oscillates, and then in turn, gradually increase Ti until the system oscillation disappears. Record the Ti at this time and set the PID integration time constant Ti to 150%~180% of the current value. The integration time constant Ti debugging is completed. 　　c. Determine the integration time constant Td. Generally, the integration time constant Td does not need to be set, and it can be set to 0. To set, use the same method as determining P and Ti, take 30% of the value without oscillation. 　　d. The system is jointly debugged with no load and with load, and then the PID parameters are fine-tuned until the requirements are met. 2. Introduction to PID control

When normal operation is started, you can only look at the curve adjustment, and estimate each step response so that the operator will not let you do it. It is best to adjust when their workmanship is stable, otherwise the adjustment will not have much effect. With the following formulas, look at the curve changes and adjust a few to find the best parameter setting. Check the proportion first and then the integral in order from small to large, and finally add the differential to the curve. The oscillation is very frequent. The proportional dial should be enlarged and the curve will float around the bay. When the proportional dial is turned small, the deviation of the curve will slow down. When the integration time goes downward, the curve will have a long fluctuation period. If the integration time is longer, the curve will oscillate at a faster frequency. First, lower the differential and the dynamic difference will be large to make the fluctuation slow. Differentiation time should be lengthened