Methods for PID controller parameter tuning

There are many methods for PID controller parameter tuning, which can be summarized into two categories:

The first is the theoretical calculation tuning method. It is mainly based on the mathematical model of the system and determines the controller parameters through theoretical calculation. The calculated data obtained by this method may not be directly used, and must be adjusted and modified through actual engineering.

The second is the engineering setting method, which mainly relies on engineering experience and is carried out directly in the control system test. The method is simple and easy to master, and is widely used in engineering practice.

The engineering tuning methods for PID controller parameters mainly include critical proportion method, response curve method and attenuation method.

The critical ratio method is generally used now.

The steps for tuning the PID controller parameters using this method are as follows:

(1) First, preselect a sampling period that is short enough for the system to work;

(2) Only add proportional control until the system shows critical oscillation in response to the input step, and record the proportional gain and critical oscillation period at this time;

(3) Under a certain control degree, the parameters of the PID controller are calculated by the formula.

PID parameter setting: It depends on experience and familiarity with the process, referring to the measured value tracking and set value curve to adjust the size of PID.

Engineering tuning of PID controller parameters. The empirical data of PID parameters in various adjustment 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 rate L: P=40~100%, T=6~60s.

Commonly used formulas:

Parameter tuning to find the best, check from small to large

First the proportion, then the integration, and finally the differential

The curve oscillates frequently, the scale should be enlarged

The curve floats around the bay, and the scale dial moves down

The curve deviates and recovers slowly, and the integral time decreases

The curve fluctuation period is long, and the integration time is further extended

The curve oscillates quickly, so lower the differential first.

The larger the difference, the slower the fluctuation. The differential time should be longer.

The ideal curve has two waves, with a high at the front and a low at the back, a ratio of 4 to 1

One look, two adjustments, and more analysis will ensure high quality of adjustment.