The significance of PID control
The current level of industrial automation industries to measure the level of modernization has become an important symbol. Meanwhile, the control also experienced the development of the theory of classical control theory, modern control theory and intelligent control theory of three stages. Intelligent control is a typical example of fuzzy automatic washing machine. Open-loop control system can be divided into control systems and closed-loop control system. A control system including controller, sensors, transmitters, actuators, input and output interfaces. Controller's output through the output interface, the implementing agency, added to the charged system; control system, the amount charged, through sensors, transmitters, sent to the controller through the input interface. Different control systems, sensors, transmitters, actuators are not the same. Such as pressure control system pressure sensor to be used. Electric heating control system sensor is a temperature sensor. At present, PID control and controller or intelligent PID controller (instrument) has a lot of products have been in the engineering practice has been widely applied, there is a wide range of PID controllers, the major companies have developed PID parameter self-tuning capabilities of intelligent controller (intelligent regulator), which automatically adjusts the PID controller parameters are adjusted through the intelligent or self-correction, adaptive algorithms to achieve. PID control are achieved using pressure, temperature, flow, liquid level controller, PID control can achieve programmable controller (PLC), also allows PID control of PC systems, etc.. Programmable Logic Controller (PLC) is to use the closed-loop PID control module to achieve control, programmable logic controller (PLC) can be connected directly with ControlNet, such as Rockwell's PLC-5 and so on. PID control function also allows the controller, such as Rockwell's Logix product line, which can be connected directly with ControlNet, use the network to achieve its remote control functions.
1, the open-loop control system
Open-loop control system (open-loop control system) is charged with the object output (controlled variables) on the controller (controller) did not affect the
output. In this control system, not dependent on the amount will be charged against sending it back to form any closed loops.
2, closed loop control system
Closed loop control system (closed-loop control system) is characterized by the system control object output (controlled variables) will affect the controller against the output sent back to form one or more closed loop. Closed-loop control system has positive feedback and negative feedback, if the feedback signal and system for a given value of signal contrast, is known as negative feedback (Negative Feedback), if the same polarity is called positive feedback, the general closed-loop negative feedback control systems are used , also known as negative feedback control system. Many examples of closed loop control system. Such person is a negative feedback loop control system, the eye is the sensor, as feedback, the human system through constant correction to all the right moves last. If there are no eyes, no feedback loop, will become an open-loop control system. Other cases, when a truly automatic washing machines have to continuously check whether clothes washed, and cut off the power automatically after cleaning, it is a closed loop control system.
3, step response
Step response is a step input (step function) added to the system, the system outputs. Steady-state error is the response of the system into steady state, the system's expected output and actual output of the difference. Control system performance can be stable, accurate, fast and three words to describe. Stability is the stability of the system (stability), a system to work properly, first of all must be stable, from the step response appears to be that convergence; quasi-control system refers to the accuracy, control precision, usually stable state error to (Steady-state error) description, it said the system output and the expected steady-state value of the difference; faster control system response is fast, usually the rise time to quantify.
4, PID control principles and characteristics
In engineering practice, the most widely used regulator control law is
proportional, integral, differential control, referred to as PID control, also known as PID regulator. PID controller has been developed for nearly 70 years, it is its simple structure, stable, reliable, easy to adjust and become one of the main techniques of industrial control. When the structure and parameters of the object and can not fully grasp, or lack of accurate mathematical models, control theory is difficult to use other technologies, the system controller structure and parameters must rely on experience and on-site commissioning to determine, when applied PID control technique is more convenient. That is, when we do not fully understand a system and the controlled object, or can not be an effective means of measurement to obtain system parameters, the most suitable PID control technology. PID control, in practice there are PI and PD control. PID controller is the error according to the system, using proportional, integral, differential calculation of the volume control to control.
Proportion (P) control
Proportional control is the most simple control method. The controller's output and the input error signal proportional. When only a proportional control system output when there is steady-state error (Steady-state error).
Integral (I) control
In integral control, the controller's output and the input error signal proportional to the integral. An automatic control system into the steady state if there is steady-state error, claimed that this control system is called a steady-state error or poor system (System with Steady-state Error). In order to eliminate steady state error, the controller must introduce the \error depends on the time integral, as time increases, integral term will increase. Thus, even if the error is very small, integral term will increase over time to increase its promotion of the controller output increases to further reduce the steady-state error, until zero. Therefore, the ratio of + integral (PI) controller allows the system to enter steady state of no steady state error.
Differential (D) control
In the differential control, the controller output and differential input error
signal (ie, rate of change of error) is proportional to. Automatic control system to overcome the errors in the adjustment process of oscillation or even instability may occur. The reason is because of greater inertia components (links), or a lag (delay) component, can inhibit the role of error, the changes always lag behind changes in the error. The solution is to change the role of inhibition of error, \close to zero in the error and suppress the role of error should be zero. This means that the controller only the introduction of the \proportion of item only to enlarge the role of the magnitude of the error, but now need to increase the \In this way, with the proportion of + differential controller, it can advance to the role of inhibition of the control error is zero, even negative, thus avoiding the charged amount of serious overshoot. Therefore have greater inertia or lag the controlled object, proportional + derivative (PD) controller
5, PID controller tuning
Tuning PID controller is the core of the control system design. It is based on the characteristics of controlled process to determine the proportion of PID controller coefficients, integral time and derivative time, the size of the. PID controller tuning are many ways to sum up, there are two categories: First, tuning the theoretical calculation. It is mainly based on the mathematical model, through theoretical calculations to determine the controller parameters. This method the calculated data may not be directly used, it must adjust and revise engineering. Second, the tuning method works, it mainly relies on engineering experience, directly in the control experiments carried out, and the method is simple, easy to master, in engineering practice is widely used. PID controller parameter tuning method works, mainly the critical ratio, reaction curve and attenuation. Three methods have their own characteristics, their common points are the experiment, and then follow the empirical formula works on the controller parameter tuning. But no matter which method used by the controller parameters are needed in the actual operation of the final adjustment and improvement. Now commonly used is the critical ratio method. PID controller using the method parameter setting of the following steps:
(1) first pre-select a short enough sampling period of the system to work; (2) by adding proportional control only part until the system appears critical step response input oscillation Note the amplification factor and the proportion of time critical oscillation period; (3) a certain degree of control in the formula be adopted under the PID controller parameters
PID控制的意义
目前工业自动化水平已成为衡量各行各业现代化水平的一个重要标志。同时，控制理论的发展也经历了古典控制理论、现代控制理论和理论三个阶段。智能控制的典型实例是模糊全自动洗衣机等。自动控制系统可分为开环控制系统和闭环控制系统。一个控制系统包括控制器、传感器、变送器、、输入输出接口。控制器的输出经过输出接口、执行机构，加到被控系统上；控制系统的被控量，经过传感器，变送器，通过输入接口送到控制器。不同的控制系统，其传感器、变送器、执行机构是不一样的。比如压力控制系统要采用压力传感器。电加热控制系统的传感器是温度传感器。目前，PID控制及其控制器或智能PID控制器（仪表）已经很多，产品已在工程实际中得到了广泛的应用，有各种各样的PID控制器产品，各大公司均开发了具有PID参数自整定功能的智能调节器，其中PID控制器参数的自动调整是通过智能化调整或自校正、自适应算法来实现。有利用PID控制实现的压力、温度、流量、液位控制器，能实现PID控制功能的可编程控制器(PLC)，还有可实现PID控制的PC系统等等。 可编程控制器(PLC) 是利用其闭环控制模块来实现PID控制，而可编程控制器可以直接与ControlNet相连，如Rockwell的PLC-5等。还有可以实现 PID控制功能的控制器，如Rockwell 的Logix产品系列，它可以直接与ControlNet相连，利用网络来实现其远程控制功能。
1、开环控制系统
开环控制系统是指被控对象的输出(被控制量)对控制器的输出没有影响。在这种控制系统中，不依赖将被控量反送回来以形成任何闭环回路。
PID控制的意义中英文翻译资料
