PID控制器毕业设计外文翻译

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1、 附录 一、英文原文 PID controller A proportionalintegralderivative controller (PID controller) is a generic control loopfeedback mechanism(controller) widely used in industrial control systems a PID is the most commonly used feedback controller. A PID controller calculates an error value as the difference b

2、etween a measuredprocess variable and a desired setp oint. The controller attempts to minimize the error by adjusting the process control inputs. In the absence of knowledge of the underlying process, PID controllers are the best controllers.1 However, for best performance, the PID parameters used i

3、n the calculation must be tuned according to the nature of the system while the design is generic, the parameters depend on the specific system. The PID controller calculation (algorithm) involves three separate parameters, and is accordingly sometimes calledthree-term control: the proportional, the

4、 integral and derivative values, denoted P, I, and D. The proportionalvalue determines the reaction to the current error, the integral value determines the reaction based on the sum of recent errors, and the derivative value determines the reaction based on the rate at which the error has been chang

5、ing. The weighted sum of these three actions is used to adjust the process via a control element such as the position of a control valve or the power supply of a heating element. Heuristically, these values can be interpreted in terms of time: P depends on the present error, I on the accumulation of

6、 past errors, and D is a prediction offuture errors, based on current rate of change. By tuning the three constants in the PID controller algorithm, the controller can provide control action designed for specific process requirements. The response of the controller can be described in terms of the r

7、esponsiveness of the controller to an error, the degree to which the controller overshoots the setpoint and the degree of system oscillation. Note that the use of the PID algorithm for control does not guarantee optimal control of the system or system stability. Some applications may require using o

8、nly one or two modes to provide the appropriate system control. This is achieved by setting the gain of undesired control outputs to zero. A PID controller will be called a PI, PD, P or I controller in the absence of the respective control actions. PI controllers are fairly common, since derivative

9、action is sensitive to measurement noise, whereas the absence of an integral value may prevent the system from reaching its target value due to the control action. Note: Due to the diversity of the field of control theory and application, many naming conventions for the relevant variables are in com

10、mon use. Control loop basics A familiar example of a control loop is the action taken when adjusting hot and cold faucet valves to maintain the faucet water at the desired temperature. This typically involves the mixing of two process streams, the hot and cold water. The person touches the water to

11、sense or measure its temperature. Based on this feedback they perform a control action to adjust the hot and cold water valves until the process temperature stabilizes at the desired value. Sensing water temperature is analogous to taking a measurement of the process value or process variable (PV).

12、The desired temperature is called the setpoint (SP). The input to the process (the water valve position) is called the manipulated variable (MV). The difference between the temperature measurement and the setpoint is the error (e), that quantifies whether the water is too hot or too cold and by how

13、much. After measuring the temperature (PV), and then calculating the error, the controller decides when to change the tap position (MV) and by how much. When the controller first turns the valve on, they may turn the hot valve only slightly if warm water is desired, or they may open the valve all th

14、e way if very hot water is desired. This is an example of a simple proportional control. In the event that hot water does not arrive quickly, the controller may try to speed-up the process by opening up the hot water valve more-and-more as time goes by. This is an example of an integral control. By

15、using only the proportional and integral control methods, it is possible that in some systems the water temperature may oscillate between hot and cold, because the controller is adjusting the valves too quickly and over-compensating or overshooting the set point. In the interest of achieving a gradu

16、al convergence at the desired temperature (SP), the controller may wish to dampthe anticipated future oscillations. So in order to compensate for this effect, the controller may elect to temper their adjustments. This can be thought of as a derivative control method. Making a change that is too larg

17、e when the error is small is equivalent to a high gain controller and will lead to overshoot. If the controller were to repeatedly make changes that were too large and repeatedly overshoot the target, the output would oscillate around the setpoint in either a constant, growing, or decaying sinusoid.

18、 If the oscillations increase with time then the system is unstable, whereas if they decrease the system is stable. If the oscillations remain at a constant magnitude the system is marginally stable. A human would not do this because we are adaptive controllers, learning from the process history； ho

19、wever, simple PID controllers do not have the ability to learn and must be set up correctly. Selecting the correct gains for effective control is known as tuning the controller. If a controller starts from a stable state at zero error (PV = SP), then further changes by the controller will be in resp

20、onse to changes in other measured or unmeasured inputs to the process that impact on the process, and hence on the PV. Variables that impact on the process other than the MV are known as disturbances. Generally controllers are used to reject disturbances and/or implement setpoint changes. Changes in

21、 feed water temperature constitute a disturbance to the faucet temperature control process. In theory, a controller can be used to control any process which has a measurable output (PV), a known ideal value for that output (SP) and an input to the process (MV) that will affect the relevant PV. Controllers are used in industry to regulate temperature, pressure, flow rate, chemical composition, speed and