PID controller is a feedback loop component has been common in industrial automation and control applications, PID control, its programming is not difficult, but for its parameter settings. First take a look at the meaning and role of the three parameters of PID control.
P: proportional (Proportional)
I: Integral (integral)
D：微分（differential）
P: proportional action
A proportional controller is actually adjustable magnification of the amplifier, i.e., △ P = Kp × e, where Kp is proportional gain, i.e., Kp may be greater than 1, may be less than 1; E is input to the controller, which is measured value given to the difference value, also known as the deviation.
It is noted that, for most analog controller, the proportional gain Kp is not employed as a scale, but proportional to the degree of scale, i.e. δ = 1 / Kc × 100%. That is the reciprocal of the magnification ratio is proportional controller; the smaller the proportion of the controller, the greater its magnification, the larger the deviation larger capacity, and vice versa.
See above relationships can know: the larger the ratio, the smaller the magnification controller, the controlled smooth curve parameters; smaller proportion, the greater the magnification controller, the fluctuation of the controlled parameter curve .
Proportional control has a drawback that will produce more than poor, to overcome the residuals must introduce the integral action.
I: integral action
Integral action of the controller is to eliminate the residual error automatic control system and settings. The so-called integration, is performed with time accumulation means, i.e., when there exists a deviation input e, the integral controller must continue to accumulate with time variation, which is proportional to the integral of the cumulative size and integrating the speed deviation e and the speed. As long as there is a deviation e, the output of the integral controller will change, that is integral always work, and only when there is no deviation, integration will stop.
For a constant deviation, integral action to adjust the rate of change of the substance is to change the controller output, the period of time required rate Q output proportional action by the output of the integrator is equal to the measured effect. Integration time is small, the speed of integration represents a large, integral action is strong; the other hand, the integration time is large, the integral action is weak. If the integration time is infinite, that there is no integral action, the controller becomes a pure proportional controller.
Indeed integral action rarely used alone, often used in conjunction with proportional action, it only has the effect of a deviation of the ratio of enlarged (or reduced), but also has accumulated over time deviation integral action, and it is the same direction of action. In this case the output of the controller is: △ P = Ke + △ Pi, where △ P is the change in the controller output values; Ke output due to the proportional action; △ Pi is output due to the integral action.
D: derivative action
Derivative action primarily designed to overcome the controlled object hysteresis commonly used in the temperature control system. In addition to using differential effect, when using the control system to be noted that the transmission lag measurements, such as selecting and mounting position of the temperature measuring element and the like.
In the conventional PID controller, and the output variation of the derivative action time and the speed differential is proportional to the deviation change, regardless of the size of the deviation, the greater the change in the speed deviation, the longer the time differential, the greater the change in output of the derivative action . However, if differentiating action is too strong, it may be too fast due to changes in the oscillation caused by itself, so the controller output significant of "spikes" or "jumps." To avoid this disturbance, the PID controller can be used in DCS and differential first PID operation rules, i.e. only the measurement value PV is differentiated, when the artificial change controller setpoint the SP, the controller output will not cause mutations to avoid the change control system SP moment to bring disturbance. The TDC-3000, a soft switch is increased in a conventional PID algorithm, the user selection controller for the deviation, or differentiating the measured values during configuration.
When the input step signal, the ratio of change in the output after a maximum change value and differential effect differentiator start output disappears is the differential magnification Kd of, i.e. differential gain, differential enlargement of beneficial unit time, set the derivative time (or derivative gain ) function will be canceled zero differential.
PID parameter adjustment method
When setting the parameters of the PID controller, according to the qualitative relationship between the control parameters and the dynamic performance and steady state performance of the system, the controller adjusting the experimental parameters. Experienced debugger can debug usually get more satisfactory results faster. The most important in debugging problems when the system performance is unsatisfactory, know which parameter adjustment, this parameter should be increased or decreased.
To reduce the required tuning parameters, may be employed first PI controller. To ensure the safety of the system, more conservative set of parameters should start commissioning, such as scaling factor not too big, not too small integration time, in order to avoid system instability or abnormal conditions of excessive overshoot occurs. Gives a signal given step, the amount charged in accordance with the output waveform of the system performance information can be obtained, for example, overshoot and settling time. PID parameters should be based on the relationship between the system performance, iteratively adjusting the PID parameters.
If the amount is too large overshoot step response, after several oscillation to stabilize or simply unstable, the scale factor should be reduced, increasing the integration time. If you do not overshoot step response, but the amount charged rises too slowly, the transition process is too long, it should be in the opposite direction to adjust the parameters.
If slower to eliminate the error, the integration time can be suitably reduced, to enhance the integral action.
Iteratively adjusting proportional coefficient and integration time, if the overshoot is still large, may be added to the differential control, differential time is gradually increased from 0, the controller repeatedly adjusting proportional, integral and derivative parameters portions.
In summary, the commissioning of PID parameters is an integrated, process the parameters influence each other, several attempts actual debugging process is very important and necessary.
Reproduced in: https: //www.jianshu.com/p/be4528f9e598