PID control rules

Reply to 1# The pillars are very domineering. Proportional (P) control. Proportional control is the simplest control method. The output of its controller is proportional to the input error signal. When there is only proportional control, there is a steady-state error integral (I) control in the system output. 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 entering the steady state, the control system is said to have a steady-state error or simply a system with a difference (System with Steady-state Error). In order to eliminate the steady-state error, an "integral term" must be introduced in the controller. However, the error of the integral term depends on the integration of time. As time increases, the integral term will increase. In this way, even if the error is small, the integral term will increase as time increases, which promotes the controller's output to increase and further reduce the steady-state error until it is equal to zero. Therefore, in order to make the system have no steady-state error after entering the steady state, a proportional + integral (PI) controller is usually used. 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 oscillate or even become unstable during the adjustment process to overcome errors. The reason is that there are large inertia components (links) or delay components, which have the effect of suppressing errors, and their changes always lag behind the changes in errors. The solution is to make the change in the effect of suppressing errors "ahead", that is, when the error is close to zero, the effect of suppressing errors should be zero. That is to say, it is often not enough to only introduce the "proportional" term in the controller. The role of the proportional term is only to amplify the amplitude of the error. What needs to be added now is the "differential term", which can predict the trend of error changes. In this way, a controller with proportion + differential can make the control effect of suppressing the error equal to zero or even negative in advance, thus avoiding serious overshoot of the controlled variable. Therefore, for controlled objects with large inertia or hysteresis, the proportional + derivative (PD) controller can improve the dynamic characteristics of the system during the adjustment process.

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Sir, your two or three questions have raised issues in several disciplines. It is best to analyze them in detail with specific cases.