Proportional Integral Derivative (PID) Controller.

Proportional Integral Derivative (PID) Controller. 

Many industrial controllers employ a proportional, integral plus differential PID regulator arrangement that can be tailored to optimize a particular control system. PID controller is most commonly used algorithm for controller design and it is most widely used controller in industry. The controllers used in industry are either PID controller or its improved version. The basic types of PID controller are parallel controller, serial controller, and mixed controller.

The PID controller algorithm utilized for is design velocity algorithm, it is also called incremental algorithm. In the industry, PID controllers are the most common control methodology to use in real applications. PID controller has all the necessary dynamics: fast reaction on change of the controller input (D mode), increase in control signal to lead error towards zero (I mode) and suitable action inside control error area to eliminate oscillations (P mode).

Derivative mode improves stability of the system and enables increase in gain K and decrease in integral time constant Ti, which increases speed of the controller response.PID controllers are the most often used controllers in the process industry. The majority of control systems in the world are operated PID controllers.

 It has been reported that 98% of the control loops in the pulp and paper industries are controlled by single-input single output PI controllers and that in process control applications, more than 95% of the controllers are of the PID type controller. PID controller combines the advantage of proportional, derivative and integral control action.

The control signal is proportional to the error signal and the proportional gain Kp. A proportional controller will have the effect of reducing the rise time and will reduce, but never eliminate. If an integrator is added, the control signal is proportional to the integral of error and the integral gain Ki . Integral control will have the effect of reduced the error, in principle, to zero value. The in principle must be added, because there are always limits on accuracy in any system. Derivative control is used to anticipate the future behavior of the error signal by using corrective actions based on the rate of change in the error signal.

The control signal is proportional to the derivative of the error and Kd is the derivative gain. Derivative control will have the effect of increasing the stability of the system, reducing the overshoot, and improving the transient response. Derivative control action can never be used alone because this control action is effective only during transient.