【正文】 arying KpA high proportional gain results in a large change in the output for a given change in the error. If the proportional gain is too high, the system can bee unstable (See the section on Loop Tuning). In contrast, a small gain results in a small output response to a large input error, and a less responsive (or sensitive) controller. If the proportional gain is too low, the control action may be too small when responding to system disturbances. In the absence of disturbances, pure proportional control will not settle at its target value, but will retain a steady state error that is a function of the proportional gain and the process gain. Despite the steadystate offset, both tuning theory and industrial practice indicate that it is the proportional term that should contribute the bulk of the output change. term The contribution from the integral term is proportional to both the magnitude of the error and the duration of the error. Summing the instantaneous error over time (integrating the error) gives the accumulated offset that should have been corrected previously. The accumulated error is then multiplied by the integral gain and added to the controller output. The magnitude of the contribution of the integral term to the overall control action is determined by the integral gain, Ki. The integral term is given by: Iout: Integral output Ki: Integral Gain, a tuning parameter e: Error = SP ? PV τ: Time in the past contributing to the integral response The integral term (when added to the proportional term) accelerates the movement of the process towards set point and eliminates the residual steadystate error that occurs with a proportional only controller. However, since the integral term is responding to accumulated errors from the past, it can cause the present value to overshoot the set point value (cross over the set point and then create a deviation in the other direction). For further notes regarding integral gain tuning and controller stability, see the section on loop tuning. Derivative term The rate of change of the process error is calculated by determining the slope of the error over time (. its first derivative with respect to time) and multiplying this rate of change by the derivative gain Kd. The magnitude of the contribution of the derivative term to the overall control action is termed the derivative gain, Kd. The derivative term is given by: Dout: Derivative output Kd: Derivative Gain, a tuning parameter e: Error = SP ? PV t: Time or instantaneous time (the present) The derivative term slows the rate of change of the controller output and this effect is most noticeable close to the controller setpoint. Hence, derivative control is used to reduce the magnitude of the overshoot produced by the integral ponent and improve the bined controllerprocess stability. However, differentiation of a signal amplifies noise and thus this term in the controller is highly sensitive to noise in the error term, and can cause a process to bee unstable if the noise and the derivative gain are sufficiently large. Summary The output from the three terms, the proportional, the integral and the derivative terms are summed to calculate the output of the PID controller. Defining u(t) as the controller output, the final form of the PID algorithm is: and the tuning parameters are Kp: Proportional Gain Larger Kp typically means faster response since the larger the error, the larger the Proportional term pensation. An excessively large proportional gain will lead to process instability and oscillation. Ki: Integral Gain Larger Ki implies steady state errors are eliminated quicker. The tradeoff is larger overshoot: any negative error integrated during transient response must be integrated away by positive error before we reach steady state. Kd: Derivative Gain Larger Kd decreases overshoot, but slows down transient response and may lead to instability due to signal noise amplification in the differentiation of the error. 二 Matlab Introduction The MATLAB174。t call senior strategy. In addition to tier 3 most can have 127 strategy outside, other three grades maximum respectively are 255 strategy. Control strategy of by some basic function blocks, a function blocks represent an operation, algorithm or variables. Function blocks basic execution element is strategy, similar to an integrated circuit blocks, have several input and output, each input and output tube feet all have the only name. Force control control strategy is in control strategy, edited generated generators in automatic control strategy for strategies when inventory piled, and check grammar mistakes, pile can also manually. Control strategy, and you can also call between if A strategy was B strategy calls, says A is B son strategy. 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