Abstract—In this paper, a relatively optimal controller (ROC) is designed for stabilisation of ball and beam module. It is a nonlinear, underactuated bench mark system with two degrees of freedom. The controller has a dynamic structure and is designed by solving a convex optimisation problem. All the constraints associated with the system are incorporated for controller design. The performance analysis of closed-loop system under the effects of parametric uncertainties, external disturbances and perturbations in initial conditions are incorporated.