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# Cold water machine PID control: proportional, integral, differential circuit

2020/10/14
Ratio ( P) Control: proportional control is one of the most simple control method. The controller output to the input error signal is proportional to the relationship. When only proportional control system output steady-state error. Integral (

I） Control: in integral control, the controller output is proportional to the input of the error signal integral relationship. Of an automatic control system, if exist steady-state error on entering the steady state, according to the control system is a steady-state error or there system ( 系统稳定, 状态误差) 。 In order to eliminate the steady-state error, in the controller must introduce & other; Integral item & throughout; 。 Integral item depends on the time integral of error, with the increase of time, integral will increase. In this way, even if the error is very small, integral item will also be increased with the increase of time, it drive controller increases the output of the reduce steady-state error further, until is equal to zero. Therefore, the proportional plus integral ( PI) Controller, can make the system in the steady state after no steady-state error. Differential (

D） Control: in the differential control, the controller output to the input error signal differential ( The error rate) Is proportional to the relationship. Automatic control system in the process of overcoming the error adjustment oscillation even instability may occur. The reason is because there are large inertia components ( Link) Or have a lag ( 延迟) Components, have to inhibit the action of the error, the change is always behind the change of the error. The solution is to make to inhibit the action of the error change & other; Advance & throughout; In which the error close to zero, to inhibit the action of the error should be zero. That is to say, in the controller only introduce & other; Scale & throughout; Item is often not enough, the role of proportional is only amplified amplitude error, and the need to increase & other Differential item & throughout; , it can predict error change trend, so has the proportion + differential controller, can advance to suppress error control function is equal to zero, even negative, so as to avoid the serious overshoot of the amount of the accused. So for controlled object with large inertia or lag, proportion + differential ( PD) Controller can improve the system dynamic characteristics in the process of adjustment.
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