PID regulation is one of the most commonly used functions in the field of industrial control, but for novices, there is no way to start in the face of a lot of parameters.

PID parameter setting: the size of P \ ind can be adjusted by experience and process familiarity, referring to the measured value tracking and set value curve.

For the engineering setting of PID controller parameters, the empirical data of p.i.d parameters in various regulation systems can be referred to as follows:

Temperature T: P = 20 ~ 60%, t = 180 ~ 600s, d = 3-180s

Pressure P: P = 30 ~ 70%, t = 24 ~ 180s,

Liquid level L: P = 20 ~ 80%, t = 60 ~ 300s,

Flow L: P = 40 ~ 100%, t = 6 ~ 60s.

No control algorithm is more effective and convenient than PID regulation law. Now some fashionable regulators are basically derived from PID. It can even be said: is the PID regulator the of other control and regulation algorithms.

Why is PID used so widely and for a long time?

Because PID solves the most basic problem to be solved by automatic control theory, that is, the stability, rapidity and accuracy of the system. Adjusting the parameters of PID can realize the load carrying capacity and anti-interference capacity of the system on the premise of system stability. At the same time, the integral term is introduced into the PID regulator, and the system adds a zero product point to make it a system of one order or more, so that the steady-state error of the system step response is zero.

Because the controlled objects of the automatic control system are very different, the parameters of PID must also change to meet the performance requirements of the system. This brings considerable trouble to users, especially for beginners. The following is a brief introduction to the general steps of debugging PID parameters:

1. Negative feedback

Automatic control theory is also called negative feedback control theory. First, check the system wiring to determine that the feedback of the system is negative feedback. For example, in the motor speed regulation system, the input signal is positive. When the motor is required to rotate forward, the feedback signal is also positive (error = input feedback in PID algorithm). At the same time, the higher the motor speed, the greater the feedback signal. Other systems are the same as this method.

2. General principles of PID commissioning

a. When the output does not oscillate, increase the proportional gain P.

b. When the output does not oscillate, the integral time constant ti is reduced.

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 PID, generally make Ti = 0 and td = 0 (see the parameter setting description of PID for details), so as to make PID pure proportional adjustment. The input is set to 60% ~ 70% of the maximum allowable value of the system, and the proportional gain P is gradually increased from 0 until the system oscillates; In turn, the proportional gain P decreases gradually from this time until the system oscillation disappears, record the proportional gain P at this time, and set the proportional gain P of PID to 60% ~ 70% of the current value. The proportional gain P commissioning is completed.

b. Determine the integration time constant ti

After the proportional gain P is determined, set a large initial value of the integral time constant Ti, then gradually reduce Ti until the system oscillates, and then gradually increase Ti until the system oscillation disappears. Record Ti at this time and set the integral time constant Ti of PID to 150% ~ 180% of the current value. 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 to 0. To set, it is the same as the method for determining P and Ti, taking 30% without oscillation.

d. No load and on load joint commissioning of the system, and then fine tune the PID parameters until they meet the requirements.

Electrician learning network, baidu experience, comprehensive arrangement of industrial control automation exchange network

Responsible editor: LQ