Disturbance Rejection

Apart from tracking the set point, the system should also be able to reject disturbances. There may be several factors influencing the controlled variable and not all of them can be manipulated. Therefore, it becomes necessary for the controller to not let the changes in the non-manipulated variables to affect the controlled variable. This is called Disturbance Rejection.
In this system, the disturbance variable is the fan input. Therefore, the controller has to work in such a way that changes in the fan input does not affect the temperature in the SBHS.
In this project, several experiments were conducted with the self tuning and conventional PI/PID Controllers. Table 9.4 shows the fan input changes given during the various experiments that were conducted with conventional and self tuning controllers designed using several methods.

Table 9.4: Fan input changes in experiments conducted for Disturbance Rejection

	Conventional Controller	Self Tuning Controller
Direct Synthesis PI	50 to 100	50 to 100
	100 to 50	100 to 50
Ziegler Nichols PI	50 to 100	50 to 100
	100 to 50	100 to 50
Ziegler Nichols PID	50 to 100	50 to 100
	100 to 50	100 to 50