The PID Controller (Algorithm)

Chapter # 4


As we have mentioned earlier, that different types of accountants are used to command the place of an aerial. One among them as antecedently mentioned is PID accountant.


The PID accountant ( algorithm ) is the most popular feedback accountant used within the procedure industries. It has been successfully used for over 50 old ages. It is robust easy understood algorithm that can supply first-class control public presentation despite the varied dynamic features of procedure works. In planing the PID accountant, tuning of the accountant is the chief point of focal point, so that the coveted transient and steady-state responses could be obtained. The procedure of choosing the accountant parametric quantities to run into given public presentation specifications is known as accountant tuning.

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Tuning OF Pelvic inflammatory disease:

Ziegler & A ; Nichols suggested regulations for tuning PID accountants, i.e: to put values of Kp, Ti and Td based on experimental measure responses. In fact, Ziegler & A ; Nichols tuning regulations give an educated conjecture for the parametric quantity values and supply a starting point for the tuning instead than giving the concluding scenes for Kp, Ti and Td in a individual shooting.

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Ziegler and Nichols proposed regulations for finding the value of relative addition Kp, built-in clip Ti and derivative clip Td based on the transient response features of a given works. Such finding of the parametric quantities of PID accountants or tuning of the PID accountants can be made by the applied scientists on-site by experiments on the works. Many other methods have besides been proposed to make so.

There are two methods called Ziegler-Nichols tuning regulations: the first method and the 2nd method.

First Method:

In the first method, we obtain by experimentation the response of the works to a unit measure input as shown in the figure below. If the works involves neither planimeter ( s ) nor dominant complex conjugate poles, so such a measure response curve may look S-shaped curve as shown below. This method applies if the response to a measure input exhibits an S-shaped curve. Such measure response curves may be generated by experimentation or from a dynamic simulation of a works.

The S-shaped curve may be characterized by two invariables, hold clip L and clip changeless T.The hold clip and the clip changeless are determined by pulling a tangent line at the inflexion point of the S-shaped curve and finding the intersections of the tangent line with the clip axis and line degree Celsius ( T ) =K.

Second METHOD:

In the 2nd method, we foremost set Ti=8 Td=0.Using the relative control action merely, increase Kp from 0 to the critical value Kcr at which the end product exhibits sustained oscillations.

The figure is given on following page ; figure 2.1 shows closed-loop system with a relative accountant and figure 2.2 is demoing the sustained oscillations.

If the end product does non exhibit sustained oscillations for whatever value Kp may take, so this method does non use. Thus the critical addition Kcr and the corresponding period Pcr are by experimentation determined. Ziegler and Nichols suggested that we set the values of the parametric quantities Kp, Ti and Td harmonizing to the tabular array shown below:

As we know that in planing 3 major aims are really of import to be taken attention of:

  1. Transient response
  2. Steady-state mistake
  3. Achieving stableness

The above curve response of PID shows satisfactory consequences, the transient response has an wave-off and so goes down and remains changeless.

Following, we train the web by utilizing nervous web ‘s preparation algorithm TRAINLM. The inputs taken are the relative, built-in and derivative of the mistake signal. The concealed bed of the MLP architecture has 8 nerve cells and there is one nerve cell at its end product. The diagram on the following page is the simulation of the system.

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