1 Proportional adjustment function:
It is the deviation of proportional reaction system. Once the system has deviation, proportional adjustment will immediately produce adjustment function to reduce the deviation. A large proportion can speed up the adjustment and reduce the error, but a large proportion will reduce the stability of the system and even cause instability of the system.
2 Integral adjustment function:
Is to make the system eliminate steady-state errors and improve inertia. Because there is an error, the integral adjustment is carried out until there is no difference, the integral adjustment stops, and the integral adjustment outputs a constant value. The strength of integration depends on the integration time constant ti, and the smaller ti is, the stronger the integration is.
On the other hand, if Ti is large, the integral effect is weak, and adding integral adjustment will reduce the stability of the system and slow down the dynamic response. Integration is usually combined with the other two regulation laws to form a PI regulator or a PID regulator.
3 differential adjustment:
Differential action reflects the rate of change of system deviation signal, which is predictive and can predict the trend of deviation change, so it can produce advanced control effect, which has been eliminated by differential adjustment before the deviation is formed. Therefore, the dynamic performance of the system can be improved. When the appropriate differential time is selected, the overshoot and adjustment time can be reduced.
Differential will amplify noise interference, so too strong differential regulation is unfavorable to the anti-interference of the system. In addition, the differential reaction is the rate of change. When the input is constant, the output of differential action is zero. Differential action can not be used alone, it needs to be combined with other two regulation laws to form a PD or PID controller.
Extended data:
Parameter tuning of PID controller is the core content of control system design. According to the characteristics of the controlled process, the proportional coefficient, integral time and differential time of PID controller are determined. There are many methods for tuning PID controller parameters, which can be summarized into two categories:
The first is the theoretical calculation setting method.
It mainly determines the controller parameters through theoretical calculation according to the mathematical model of the system. The calculated data obtained by this method cannot be used directly, and must be adjusted and corrected through engineering practice.
The second is the engineering setting method.
Mainly rely on engineering experience, directly in the test of control system. This 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.
Their similarities are all through experiments, and then the controller parameters are adjusted according to the engineering experience formula.
But no matter which method is adopted, the parameters of the controller need to be finally adjusted and improved in actual operation. At present, the critical proportion method is generally used. Use this method.
In the process of adjusting to overcome the error, the automatic control system may oscillate or even become unstable. The reason is that there are components (links) with large inertia or delayed components, which can suppress errors, and their changes always lag behind the changes of errors. The solution is to introduce the change of error suppression effect, that is, when the error is close to zero, the error suppression effect should be zero.
In other words, it is often not enough to introduce only the "proportion" item into the controller. The function 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 the error.
This proportional+differential controller can make the control effect of restraining error equal to zero or even negative value in advance, thus avoiding the serious overshoot of the controlled quantity. Therefore, for the controlled object with large inertia or time delay, the Proportional+Differential (PD) controller can improve the dynamic characteristics of the system during the adjustment process.
Different control systems have different sensors, transmitters and actuators. For example, a pressure control system should use a pressure sensor. The sensor of the electric heating control system is a temperature sensor.
There are many PID controllers and their controllers or intelligent PID controllers (instruments), and their products have been widely used in engineering practice. There are many kinds of PID controller products, and all major companies have developed intelligent regulators with PID parameter self-tuning function, in which the automatic adjustment of PID controller parameters is realized by intelligent adjustment or self-tuning and adaptive algorithm.
Pressure, temperature, flow and liquid level controllers with PID control, programmable controller (PLC) with PID control function, PC system with PID control, etc.
Programmable controller (PLC) uses its closed-loop control module to realize PID control. Programmable controller (PLC) can be directly connected with ControlNet, such as Rockwell PLC-5. There are also controllers that can realize PID control function, such as Rockwell's Logix product series, which can be directly connected with ControlNet and realize its remote control function through the network.
References:
Baidu encyclopedia -PID regulator