English: PidRegulator
Different control systems, their sensors, transmitters, and actuators are different. For example, a pressure control system needs to use a pressure sensor. The sensor of the electric heating control system is a temperature sensor. PID control and its controller or intelligent PID controller (instrument) have been widely used in the actual engineering actual, there are a variety of PID controller products, and major companies have developed PID parameters. IntelligentRegulator, tuning function, automatic adjustment of PID controller parameters is achieved by intelligent adjustment or self-correction, adaptive algorithm. There is a pressure, temperature, flow, and liquid level controller implemented by PID control, and can implement PID control functions, and a PC system that implements PID control, etc. Programmable Controller (PLC) is a PID control using its closed-loop control module, while programmable controller (PLC) can be connected directly to ControlNet, such as Rockwell's PLC-5, etc. There is also a controller that enables PID control functions, such as Rockwell's Logix product line, which can be connected directly to Controlnet, using a network to implement its remote control.
PID principle
open loop control system
open loop control system (Open-loopControlsystem) refers to the output (controlled amount) control of the controlled object The output of Controller has no effect. In this control system, it is not dependent on which the controlled amount is reversed back to form any closed loop circuit.
principle and characteristics
In the actual engineering actual, the most widely used regulator control law is proportional, integral, differential control, referred to as PID control, also known as PID adjustment. The PID controller has been in the past 70 years of history, which has become one of the main technologies of industrial control with simple structure, good stability, reliable work, and convenient adjustment. When the structure and parameters of the controlled object cannot be fully grasped, or if there is no precise mathematical model, other techniques of control theory are difficult to adopt, the structure and parameters of the system controller must be determined by empirical and field debugging. PID control technology is most convenient. That is, when we do not fully understand a system and a controlled object, or cannot obtain the system parameters by valid measurement means, it is best to use PID control technology. PID control, there is also PI and PD control. The PID controller is controlled by the system's error, the use ratio, integral, and differential calculation.
step response
step response means the output of the system when a step input is added to the system. Steadless error is the difference between the system's desired output and the actual output of the system's response to the system. The performance of the control system can be described steady, accurate, and three words. Stability refers to the stability of the system (STABILITY), a system must work properly, first must be stable, see the step response should be convergent; the quasi-the accuracy of the control system, control accuracy, usually stable STEADY-STATEERROR) Description, it indicates the difference between the system output steady state value and the expected value; it refers to the rapidity of the control system response, usually uses a rise time to quantify.
Closed loop control system
The characteristic of the closed-loop control system is that the output of the system's controlled object (controlled) will be reversed back to affect the output of the controller. One or more closed loops. The closed-loop control system has posit feedback and negative feedback. If the feedback signal is opposite to the system given the value signal, it is called negative feedbackback, and if the polarity is the same, it is called positive feedback, and the general closed loop control system is negative feedback, A negative feedback control system is also known. There are many examples of closed-loop control systems. For example, people are a closed-loop control system with negative feedback, the eyes are sensors, which act as feedback, and the human body system can make a variety of correct actions through constant corrections. If there is no eye, there is no feedback loop, and it will become an open-loop control system. Also, when a real automatic washing machine has a continuous examination of whether the clothing is washed and the power is automatically cut off after washing, it is a closed-loop control system.
(1) Proportional (P) Controls
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 (Steady-StateError).
(2) Integral (i) Control
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 steady state, this control system is called a steady-state error or a short-stated systemwithsteady-stateerror. In order to eliminate steady state errors, "integration item" must be introduced in the controller. The integral item is dependent on time, and the integral item will increase over time. In this way, even if the error is small, the integration item will increase over time, and it drives the output of the controller to further decrease the steady state error until it is equal to zero. Therefore, the proportional + integral (PI) controller can make the system have no steady state errors after entering steady state.
(3) Differential (D) Control
In different sorting control, the output of the controller is proportional to the differentiation of the input error signal (ie, the change rate of the error).
The automatic control system may have oscillation or even instability during the adjustment of the error. The reason is due to the presence of a large inertial component (link) or a delay component, which has the effect of suppressing the error, and its change is always lagging behind the error. The solution is to make the effect of suppressing the effect of "super", that is, when the error is close to zero, the effect of suppressing the error should be zero. That is to say, only "proportional" items in the controller are often insufficient, the proportional role is only the amplitude of the amplification error, but it needs to be increased "Differential", which predicts the trend of error change, so However, the controller with proportional + differential can make the control of suppression errors in advance are equal to zero, even negative values, thereby avoiding the serious overshoot of the controlled amount. Therefore, there is a controlled object with greater inertia or lag, the proportional + differential (PD) controller can improve the dynamic characteristics of the system in the adjustment process.
parameter setting
PID controller parameter setting is the core content of the control system design. It is based on the characteristics of the control process to determine the proportional factor, integration time, and differential time of the PID controller. The PID controller parameters are made a lot, and there are two categories: one is the theoretical calculation. It is mainly based on the system's mathematical model, and the controller parameters are determined by the theory. The calculation data obtained by this method may not be used directly, and it must also be adjusted and modified by the actual progress. Second, the engineering tunition, it mainly depends on engineering experience, directly in the test of the control system, and is simple, easy to master, and is widely used in the actual engineering. The engineering tunition of PID controller parameters, mainly a critical proportional method, reaction curve method and attenuation method. The three methods have its characteristics, and their common points are tested, and then tested according to the engineering experience formula. However, no matter which method obtained, the controller parameters obtained are needed, but the final adjustment and improvement is performed in the actual operation. Generally adopted a critical ratio. Using this method
tuning step
(1) first pre-selected a sufficiently short sampling cycle to work;
(2) only add proportional control The link until the system's critical oscillation should appear to the input step response, and note that the proportional amplification coefficient and the critical oscillator cycle;
(3) Calculate the PID controller by formula under certain control Parameters.
The scales of the integral differential regulator. Using the leading role of the proportional differentiation to increase the current, improve the accuracy, and accelerate the dynamic response speed.