英语资料及译文About PID controlRecently automation technology is based on the concept of feedback. Elements of feedback theory consist of three parts: measurement, comparison and implementation. Measurement variables of concern, compared with expectations, with the control system to correct the error response.The theory and application of automatic control, the key is to make the correct measurement and comparison of how best to rectify the system.PID (proportional - integral - differential) controller as the first practical use of the controller more than 50 years of history, is still the most widely used industrial controller. Simple PID controller, the use of the system does not accurately model a prerequisite that they have become the most widely used controller.PID controller is the proportion of cells (P), integral unit (I) and the differential unit (D) component.Because of its wide range of uses, the use of flexible, has been serialized products, the use of only three parameters setting (Kp, Ti and Td) can be. In many cases, does not necessarily need all three modules, which can take 1-2 unit, but the proportion of the control unit is essential.First of all, PID broad range of applications. Although many industrial processes or time-varying non-linear, but can be simplified through their basic non-linear and dynamic characteristics of the system over time, so that you can control the PID.Secondly, PID parameter can tune easier. That is, PID parameters Kp, Ti and Td can be based on the dynamic characteristics of the process of setting a timely manner. If the dynamic characteristics of the process ofchange, for example, changes may be caused by the load dynamic characteristics of the system changes, PID parameters can be re-tuning.Third, PID controller in practice is to be improved continuously, the following are two examples of improvements.In factories, we always see a lot of loops are in manual, and because of the difficulty of the course so that the "automatic" mode, a smooth working. As a result of these deficiencies, the use of the industrial control system PID is always subject to product quality, safety, waste production and energy problems. PID parameter self-tuning PID parameters in order to deal with this problem setting generated. Now, the auto-tuning or self-tuning of PID controller is a business single-loop controllers and distributed control system of a standard.In some cases the system-specific design of PID controller to control very well, but they are there are still some problems to be solved: If self-tuning should be based on the model, in order to re-PID tuning parameters online to find and maintain a good process model is more difficult. When closed-loop works, the requirements in the process of inserting must have a test signal. This method will cause disturbance, so model-based PID parameter self-tuning is not too good in the industrial applications.If self-tuning control law based on the often difficult to load disturbance caused by the impact and dynamic characteristics of the process of the impact of changes in the distinction between the effects of so disturbed overshoot controller will have to create a self-adaptive unnecessary conversion. In addition, since the control law based on the maturity of the system is not the stability of analytical methods, the reliability of parameter tuning, there are many problems.Therefore, many self-tuning PID controller parameters work in the auto-tuning mode and not in the self-tuning mode. Auto-tuning is oftenused to describe the state of open-loop based on a simple process model to determine automatic calculation of PID parameters.PID in controlling nonlinear, time-varying, coupling and parameter uncertainty and structural complexity of the process, the work is not very good. The most important thing is, if the PID controller can not control the complexity of the process, regardless of how not to use transfer parameters.Despite these shortcomings, PID controller is sometimes the most simple is the best controller.At present, the level of industrial automation has become a measure of the level of modernization in all walks of life an important sign. At the same time, the development of control theory has also experienced a classical control theory, modern control theory and intelligent control theory of three stages. Classic example of intelligent control is ambiguous, such as full-automatic washing machine. Automatic control system can be divided into open-loop control systems and closed-loop control system.A control system, including controllers, sensors, transmitters, implementing agencies, input and output interfaces. Controller's output after the output interface, the implementing agencies, added to the system was charged with; control system charged with the amount, after the sensor, transmitter, through the input interface to the controller. Different control system, the sensor, transmitter, the executing agency is not the same. For example pressure sensors need to be used in pressure control system. Electric heating control system is the sensor temperature sensor. At present, PID control and PID controller or a smart controller (instrument) has a lot of products have been in practice in engineering is widely used, there are a wide range of PID controller products, major companies have developed with PID parameter self-tuning regulator function smart (intelligent regulator), which the PID controller parameters are automatically adjusted through the intelligent or self-tuning, adaptivealgorithms to achieve. PID control are achieved using pressure, temperature, flow, liquid level controller, PID control functions to achieve the programmable logic controller (PLC), also enables the PC system, PID control and so on. Programmable Logic Controller (PLC) is the use of its closed-loop control module to achieve PID control, and programmable logic controller (PLC) can be connected directly with the ControlNet, such as Rockwell's PLC-5 and so on. There can be the controller PID control functions, such as Rockwell's Logix product line, it can be connected directly with the ControlNet, using the Internet to achieve its long-range control functions.1, Open-loop control systemOpen-loop control system is the object of the output (volume control) on the controller does not affect the output. In this control system, do not rely on volume will be charged back to the formation of anti-any closed-loop circuit.2, Closed-loop control systemClosed-loop control system is characterized by the output of the system object (volume control) will be sent back to the impact of anti-output controller to form one or more of the closed-loop. Closed-loop control system has positive feedback and negative feedback, if the feedback signal and the system to set the value of the signal the other hand, is referred to as negative feedback, if the same polarity is called positive feedback, the general closed-loop control system using negative feedback, also known as negative feedback control system. Closed-loop control system has many examples. For example, people with negative feedback is a closed-loop control system, the eye is the sensor to act as a feedback, the human body system through the constant variety of the right to make amendments to the final action. If there are no eyes, there is no feedback loops, it became an open-loop control system. Another example, when a full-automatic washing machine with a realcontinuously check whether the washed clothing, and wash off automatically after the power supply, it is a closed-loop control system.3, Step responseStep response refers to a step input (step function) when added to the system, the system output. Steady-state error is the system response into the steady-state, the system's desired output and actual output of the difference. The performance of control system can be stable, accurate and fast three words to describe. Stability is the stability of the system, a system must be able to work, first of all must be stable, from the step response should be a convergence point of view; quasi-control system refers to the accuracy, control precision, stability is usually state error description, it said the system output steady-state value and the difference between expectations; fast control system refers to the rapid response, and usually to a quantitative description of the rise time.4, Theory and the characteristics of PID controlIn engineering practice, the most widely used control laws regulate the proportional, integral, differential control, referred to as PID control, also known as PID regulator. PID controller has been available for nearly 70 years of history, which in its simple structure, stable, reliable, easy to adjust and become the main industrial control technologies. When charged with the structure and parameters of the object can not completely grasp, or lack of accurate mathematical model, control theory it is difficult using other techniques, the system controller structure and parameters have to rely on experience and on-site testing to determine when the application PID control of the most convenient technology. That is, when we do not fully understand the system and charged with an object, or can not be an effective means of measuring system parameters to obtain the most suitable PID control technology. PID control, in practice there are PI and PD control. PID controller is the error of the system, using proportional, integral, differential calculationfor the control of the volume control.The ratio of (P) controlProportional control is one of the most simple control methods. The controller's output and input error signal proportional to the relationship. The output has the existence of steady-state error when there is only a proportional control system.Integral (I) controlIn integral control, the controller's output and input error signal is proportional to the integral relationship. For an automatic control system, if steady-state error exists after entering the steady-state, the control system is referred to as steady-state error or having a poor system. In order to eliminate steady-state error, the controller must be the introduction of the "key points." Points of error depend on the time of the points of the increase over time, will increase the integral term. In this way, even if the error is very small, integral term will increase as time increases, it increased to promote the output of the controller so that steady-state error further reduced until zero. Therefore, the proportional + integral (PI) controller, you can make the system after entering the steady-state non-steady-state error.Differential (D) controlIn the differential control, the controller's output and input of the differential error signal (the rate of change of error) is directly proportional to the relationship. Automatic control system to overcome the errors in the adjustment process may be unstable or even oscillation. The reason is because of greater inertial components (links) or there is lag components, can inhibit the role of error, the changes always lag behind changes in error. The solution is to inhibit the changes in the role of error "in advance", that is 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 often is not enough, the proportion of the role isonly to enlarge the amplitude error, the current need to increase the "differential item" that can change the trend of prediction error, In this way, with the proportion of + differential controller, will be able to advance so that the role of inhibitory control error equal to zero or even negative, thus avoiding the amount charged with a serious overshoot. Therefore, greater inertia of the charged object or lag, the proportion of + differential (PD) controller to improve the system in the regulation of the dynamic characteristics of the process.PID控制简介当今的自动控制技术都是基于反馈的概念。
