we have expertly designed the contr

we have expertly designed the controller so that the closed-loop feedback system is stable,wecan further quantify the degree of stability, often referred to as relative stability. So, a closedsystem with a different controller design. This all relates to the concept of a robust feedbacf neloop feedback system can be more (or less stable)with a given controller design than the sarcontrol system. That is, a robust feedback control system is one that maintains acceptableperformance in the presence of plant uncertainty, external disturbances, and measurementnoise.From the point of view of relative stability, a robust controller typically displays a greaterrelative stability than a controller with less ability to retain closed-loop stability inthe presenceof plant uncertainty,external disturbances, and measurement noise. Consider the PD controllerfor the self-balancing robot that allows the robot to remain stable even when a large load(such as a book)is placed on the top thereby significantly changing the plant or when anexternal gentlepush is applied. A well-designed PID controller can be very robust and explwhy they are utilized in industry to such a large extent. Note that the PD controller is a plsinscontroller with the integral gain set to zero.