Proportional Integral (PI) Controller

Proportional Integral (PI) Controller

 At present, the PI controller is most widely adopted in industrial application due to its simple structure, easy to design and low cost. Despite these advantages, the PI controller fails when the controlled object is highly nonlinear and uncertain. PI controller will eliminate forced oscillations and steady state error resulting in operation of on-off controller and P controller respectively.

However, introducing integral mode has a negative effect on speed of the response and overall stability of the system. Thus, PI controller will not increase the speed of response. It can be expected since PI controller does not have means to predict what will happen with the error in near future.

 This problem can be solved by introducing derivative mode which has ability to predict what will happen with the error in near future and thus to decrease a reaction time of the controller. PI controllers are very often used in industry, especially when speed of the response is not an issue. A control without D mode is used when

1. Fast response of the system is not required

2. Large disturbances and noise are present during operation of the process

3. There is only one energy storage in process (capacitive or inductive)

 4. There are large transport delays in the system.

Therefore, we would like to keep the advantages of the PI controller. This leads to propose a PI controller shown in Fig. 6. This controller uses of the proportional term while the integral term is kept, unchanged.

The controller output in this case is

 u (t) = K p . e (t) + K i∫ e (t ) dt

Fig. 6.block diagram PI controller an integral error compensation scheme, the output response depends in some manner upon the integral of the actuating signal. This type of compensation is introduced by a using a controller which produces an output signal consisting of two terms, one proportional to the actuating signal and the other proportional to its integral. Such a controller is called proportional plus integral controller or PI controller